JPH11149997A - Plasma processing equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-quality treatment which has good power efficiency of plasma formation, can be treated with plasma having high uniformity, and has little contamination of a substrate. SOLUTION: A side wall electrode 8 provided so as to constitute a side wall portion of a processing chamber 1 in which a substrate 9 is disposed.
1 is supplied with high-frequency power having a frequency such that the pressure dependence of plasma uniformity is eliminated by an electron trapping effect of 20 MHz or more, and the uniformity in a plane parallel to the substrate 9 is increased by the pressure rise. Plasma that is suppressed to 7% or less. The inner surface of the side wall electrode 81 is covered with a shield 83 made of a material that does not stain the surface of the substrate 9, and a magnet 84 is provided inside the side wall electrode 81 for setting a magnetic line 85 bulging toward the central axis of the processing chamber 1. I have.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an apparatus for performing various processes using plasma, for example, dry etching of a thin film formed on the surface of a substrate by plasma,
The present invention relates to a plasma CVD (chemical vapor deposition) apparatus for forming a thin film on a surface of a substrate by utilizing a gas phase reaction by plasma.

[0002]

2. Description of the Related Art Processing using plasma is actively performed in manufacturing processes of various semiconductor devices and liquid crystal displays. For example, in etching a silicon oxide film formed on a silicon semiconductor, as one of dry etching techniques, etching is performed using the action of active species or ions generated in plasma. In a process of forming an amorphous silicon thin film on a liquid crystal substrate, a plasma CVD method of depositing an amorphous silicon thin film on a liquid crystal substrate using a decomposition reaction in a plasma of a silane-based gas is used.

FIG. 7 shows an example of a conventional plasma processing apparatus used for such processing.
1 is a diagram illustrating a schematic configuration of a plasma processing apparatus disclosed in Japanese Patent Application Laid-Open No. 79025/1990. The apparatus shown in FIG. 7 is an example of a plasma processing apparatus using a flat plate type inductively coupled plasma source, and includes a cylindrical processing chamber 1 and a processing chamber 1.
A substrate holder 2 provided to dispose a substrate 9 to be processed at a predetermined position in the inside thereof, and a plate-type inductively coupled plasma source 3 for forming plasma in the processing chamber 1 and enabling plasma processing on the substrate 9 It is mainly composed.

[0004] The flat plate type inductively coupled plasma source 3 is in contact with or in contact with a dielectric window 31 which is airtightly filled in the vessel wall (upper vessel wall) of the processing chamber 1 facing the substrate 9. A high-frequency antenna 32 provided in close proximity thereto, and a high-frequency power supply 33 for supplying high-frequency power to the high-frequency antenna 32
It is mainly composed of In the high frequency antenna 32,
An annular antenna in which a plurality of annular members having different diameters are concentrically arranged and connected, or a spiral antenna including a single spiral member is used. When high-frequency power is supplied from the high-frequency power supply 33 to the high-frequency antenna 32, a high-frequency electric field is set in the processing chamber 1 through the dielectric window 31.

[0005] The processing chamber 1 is provided with an exhaust system 4 and a gas introduction system 5. The gas introduced into the processing chamber 1 is turned into a plasma by receiving energy from the high-frequency electric field, and a plasma is formed. At this time, a high-frequency current flows in the plasma due to the induced electric field, and the plasma and the high-frequency antenna are inductively coupled. For this reason,
This type of plasma is called an inductively coupled plasma.
Furthermore, since high frequency is applied through the flat dielectric window 31, it is called flat inductively coupled plasma.

In the device shown in FIG. 7, a high frequency of several tens of MHz is applied to the high frequency antenna 32 so that 10 ^-3 is applied.
It is possible to form a high-density plasma of 10 ¹¹ / cm ^{−3 on} the Torr level. Then, when this plasma is formed by introducing a fluorine-based gas, dry etching of the silicon oxide film or the like on the surface of the substrate 9 placed on the substrate holder 2 is possible. Note that “「 / cm ⁻³ ”is a unit of the plasma density and means the number of electrons per unit volume.

In the device shown in FIG. 7, a high frequency antenna 32 for applying a high frequency is arranged on a plane parallel to the substrate 9. The dielectric window 3 provided in parallel with the substrate 9
High frequency is applied from the parallel high frequency antenna 32 through 1. Therefore, the uniformity of the plasma in a plane parallel to the substrate 9 is relatively good, and a relatively uniform process can be performed on the surface of the substrate 9.

However, the device shown in FIG. 7 has the following problems. First, quartz glass is often used for the material of the dielectric window 31, but quartz glass is sputter-etched by plasma to release oxygen gas. Oxygen gas affects the characteristics of the plasma processing. For example, when performing dry etching, the activated oxygen gas may unnecessarily etch the surface of the substrate 9. In addition, when plasma CVD is performed, a large amount of oxygen is taken into the deposited thin film, and the electrical characteristics of the thin film such as specific resistance may be impaired.

For this reason, it has been attempted to use a material other than quartz glass such as alumina for the dielectric window 31, but there is a drawback that the thermal shock resistance is poor. That is, 2 kW
In a high-power process in which a large amount of power or more is applied to the high-frequency antenna 32 to speed up the processing, the temperature gradient formed in the dielectric window 31 becomes large, and the processing is rapidly and locally heated. . As a result, materials such as alumina cannot withstand thermal shock and are destroyed by thermal stress.

Further, in recent plasma processing, the substrate 9 to be processed tends to be large. This is to increase productivity by increasing the number of devices produced from one wafer in the case of a semiconductor wafer, and to respond to the increase in the area of the liquid crystal display to be manufactured in the case of a liquid crystal substrate. It is. In any case, in the apparatus shown in FIG. 7, when the size of the substrate 9 is increased, the plasma forming space must be increased, and therefore, the dielectric window 31 must be enlarged.

When the size of the dielectric window 31 increases, the thickness of the dielectric window 31 must be increased in order to withstand the pressure difference in the processing chamber 1. However, the dielectric window 31
When the thickness is increased, the loss of high frequency in the portion of the dielectric window 31 is increased, and there is a problem that the power efficiency of plasma formation is deteriorated. The bigger problem is that the dielectric window 3
If the thickness of the dielectric window 31 is large, the heat capacity increases, so that the temperature control of the dielectric window 31 becomes difficult.

That is, as the heat capacity of the dielectric window 31 increases, the time required for the dielectric window 31 to be heated to a predetermined temperature and reach thermal equilibrium becomes longer. In this case, if the process is started after waiting for thermal equilibrium to be reached, the time required until the start of the process becomes longer and the productivity is reduced. Further, if the processing is started before the thermal equilibrium, the temperature of the dielectric window 31 is not constant, so the radiant heat received by the substrate 9 from the dielectric window 31 changes, and the temperature condition changes during the processing. If the temperature of the dielectric window 31 is not constant, the staying time of the active species generated by the plasma on the surface of the dielectric window 31 changes, and as a result, the active species composition ratio in the plasma changes. .

Further, when the heat capacity of the dielectric window 31 is increased, the time required for heat dissipation after the processing is extended, and the processing of the next substrate 9 may be started in a state where the temperature does not decrease to about room temperature. In this case, the thermal equilibrium temperature of the dielectric window 31 changes, and the temperature condition changes every time processing is performed. Then, if the next process is started after the temperature is lowered to about room temperature, the processing interval becomes longer, which causes a decrease in productivity. As described above, the apparatus shown in FIG. 7 is relatively good in terms of processing uniformity, but is not suitable for processing a large-sized substrate 9.

On the other hand, an apparatus as shown in FIG. 8 has been known as an apparatus which has solved the drawbacks of the flat plate type inductively coupled plasma source 3. FIG. 8 shows an example of a conventional plasma processing apparatus, and is a view showing a schematic configuration of a plasma processing apparatus using a cylindrical inductively coupled plasma source. The apparatus shown in FIG. 8 forms a cylindrical processing chamber 1, a substrate holder 2 provided to dispose a substrate 9 to be processed at a predetermined position in the processing chamber 1, and forms plasma in the processing chamber 1. And a cylindrical inductively coupled plasma source 6 that enables plasma processing of the substrate 9.

The cylindrical inductively coupled plasma source 6 includes a dielectric window 61 provided to constitute a side wall of the cylindrical processing chamber 1, and a coiled high-frequency antenna wound around the dielectric window 61. The high frequency power supply 63 mainly supplies a high frequency power to the high frequency antenna 62. In the device shown in FIG. 8, since the dielectric window 61 is cylindrical, the mechanical strength of the dielectric window 61 is greater than that of the device shown in FIG. Therefore, even if the processing chamber 1 becomes large for processing a large-sized substrate 9, the thickness of the dielectric window 61 does not need to be so large. For this reason, there is no problem that the power efficiency of plasma formation is reduced, and the temperature control of the dielectric window 61 is difficult and the reproducibility of the processing temperature condition is reduced.

However, in the apparatus shown in FIG. 8, the region where the plasma is initially formed is limited to the vicinity of the inner surface of the dielectric window 61 distant from the central axis of the processing chamber 1, so that the uniformity of the plasma is controlled. There is a problem that it is difficult. That is, when the pressure in the processing chamber 1 is high to some extent, plasma is actively generated near the inner surface of the dielectric window 61, and a dense plasma is formed in this portion.
When the pressure is reduced, the collision with the gas molecules is reduced, so that the diffusion of the plasma is promoted, and the plasma is diffused toward the center of the processing chamber 1.

When the pressure is lowered, a large amount of plasma diffuses toward the dielectric window 61, and as a result, the dielectric window 6
Also, the plasma loss on the surface of No. 1 increases. For this reason,
When the pressure decreases, the density decreases near the inner surface of the dielectric window 61 due to the loss in the dielectric window 61 and increases in the center of the processing chamber 1. Further, the problem that the dielectric window 61 is sputter-etched has not been solved by the apparatus shown in FIG.

A cylindrical inductively coupled plasma source 6 as described above
An apparatus shown in FIG. 9 has been proposed as a solution to the above disadvantage. FIG. 9 shows an example of a conventional plasma processing apparatus.
It is a figure which shows the schematic structure of the plasma processing apparatus disclosed by the 5th volume, page 241.

The apparatus shown in FIG.
Is used as a side wall electrode 71. That is, the side wall portion of the processing chamber 1 includes a cylindrical side wall electrode 71 having a low height and a pair of annular insulators 14 and 15 sandwiching the side wall electrode 71 from above and below. And sandwich the side wall part,
An upper plate 11 and a lower plate 12 are provided. A high frequency power supply 72 is connected to the side wall electrode 71 via a transformer coupler 73.
Is connected. One end on the secondary side of the transformer coupler 72 is grounded. Therefore, the side wall electrode 71 is at the DC ground potential. That is, the high frequency is a waveform that swings positively and negatively around the ground potential.

The lower plate 12 constituting the processing chamber 1 is grounded via a tuning circuit 121 composed of a coil and a capacitor. When the impedance of the tuning circuit 121 is set to an appropriate value, a large self-bias voltage is applied to the lower plate 12. By the self-bias voltage, ions are efficiently extracted from the plasma, and plasma processing such as etching can be performed efficiently.

Further, outside the side wall electrode 71, two ring-shaped magnets 74 are provided above and below. The inner surfaces of the two ring-shaped magnets 74 have different magnetic poles. As a result, an arch-shaped magnetic force line 75 as shown in FIG. 9 is set so as to protrude inside the side wall electrode 71. The magnetic lines of force 75 are circumferentially set inside the side wall electrode 71 and act to confine electrons between the magnetic lines of force 75 and the side wall electrode 71. Therefore, plasma is efficiently formed near the inner side surface of the side wall electrode 71,
The power efficiency of plasma formation is increased.

In the apparatus shown in FIG. 9, since the side wall electrode 71 is DC grounded, no self-bias voltage is generated on the side wall electrode 71. Therefore, ion impact on the side wall electrode 71 is small, and the problem of sputter etching of the side wall electrode 71 is suppressed. And the dielectric window 3
Since high frequency is introduced without using 1,61,
The problem of loss of high frequency in the portions of the dielectric windows 31 and 61, the problem of the temperature of the dielectric windows 31 and 61 affecting the processing characteristics, and the problem caused by sputter etching of the dielectric windows 31 and 61 also occur. Absent.

However, the apparatus shown in FIG. 9 has a problem that the plasma density becomes relatively uniform when the pressure in the processing chamber 1 is low, but the plasma density becomes non-uniform when the pressure is high. This will be described with reference to FIG. FIG. 10 is a diagram showing a problem of the device shown in FIG. FIG. 10 shows the result of actually manufacturing the device shown in FIG. 9 and measuring the ion current density of the plasma.
Note that the horizontal axis in FIG. 10 is a position in the processing chamber 1, more precisely, a position (radial position) in a plane perpendicular to the central axis of the processing chamber 1. The inner diameter of the processing chamber 1 is 450 mm in diameter, and 0 on the horizontal axis in FIG. 10 indicates a position on the central axis of the processing chamber 1.

As can be seen from FIG. 10, the pressure is 1 mTorr.
In the case of r, the ion current density is relatively uniform, and a highly uniform plasma is formed in the processing chamber 1. However, when the pressure is 10 mTorr, the ion current density increases at a large radial position, that is, near the inner surface of the side wall electrode 71, and the plasma uniformity deteriorates.
The deterioration of the plasma uniformity in the high pressure region is the same as in the case of FIG. 8 described above. That is, when the pressure is increased, gas molecules are increased, so that the diffusion of plasma is suppressed. As a result, the plasma density distribution becomes particularly dense near the inner side surface of the side wall electrode 71.

[0025]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. In other words, a high-performance plasma processing apparatus capable of performing high-uniformity plasma processing with high power efficiency of plasma formation and high uniformity by high-uniformity plasma, and capable of performing high-quality processing with less contamination of the substrate. The purpose is to provide.

[0026]

According to a first aspect of the present invention, there is provided a processing chamber in which a substrate as a processing object is disposed, and an exhaust system for exhausting the processing chamber. And a plasma introducing apparatus for introducing a predetermined gas into the processing chamber, and a plasma source for forming plasma in the processing chamber, wherein the plasma source constitutes a side wall portion of the processing chamber. And a high-frequency power supply for supplying high-frequency power to the side-wall electrode, the high-frequency power having a frequency at which the pressure dependence of plasma uniformity is eliminated by an electron trapping effect. Is supplied to the side wall electrode. According to a second aspect of the present invention, in order to solve the above-described problem, in the configuration of the first aspect, the high-frequency power supply is an ion current observed in a plane parallel to the substrate in a set plasma forming space. When the maximum value of the density is A and the minimum value of the ion current density observed in the plane is B, (A−
B) A high frequency power of a frequency that can suppress the plasma uniformity expressed by {(A + B) / 2} × 100 (%) to 7% or less regardless of the pressure increase of the processing chamber is supplied to the side wall electrode. It has a configuration that does.
According to a third aspect of the present invention, in order to solve the above-mentioned problem, in the configuration of the second aspect, the high-frequency power supply is
It has a configuration in which high-frequency power of a frequency of 20 MHz or more is supplied to the side wall electrode. According to a fourth aspect of the present invention, in order to solve the above-mentioned problem, in the configuration of the first, second or third aspect, the substrate is provided on a lower surface plate of the processing chamber or on a substrate holder fixed to the lower surface plate. The upper plate facing the lower plate is provided with a gas blowing unit for blowing gas into the processing chamber. According to a fifth aspect of the present invention, in order to solve the above problem, in the configuration of the fourth aspect, the gas blowing portion is provided below the upper surface plate so as to form a gas reservoir together with the upper surface plate. And a gas blowing plate having gas blowing holes evenly. According to a sixth aspect of the present invention, in order to solve the above-described problem, in the configuration of the first, second, third, fourth, or fifth aspect, the inside of the side wall electrode covers an inner side surface of the side wall electrode. And a shield that is formed of a material that does not stain the surface of the substrate.
According to a seventh aspect of the present invention, in order to solve the above problem, in the configuration of the sixth aspect, the shield is formed of any one of silicon, carbon, silicon carbide, silicon nitride, quartz, alumina, and aluminum nitride. It has a configuration that has been done. Further, in order to solve the above-mentioned problems, the invention according to claim 8 is directed to claim 1, 2, 3, 4, 5,
In the structure of 6 or 7, a magnet is provided inside the side wall electrode to set a magnetic line of force bulging toward a central axis of the processing chamber. According to a ninth aspect of the present invention, in the configuration of the eighth aspect, the magnet sets and arranges a plurality of arch-shaped magnetic force lines along a central axis direction of the processing chamber. .

[0027]

Embodiments of the present invention will be described below. FIG. 1 is a schematic front sectional view showing a configuration of a plasma processing apparatus according to an embodiment of the present invention. The apparatus shown in FIG. 1 includes a processing chamber 1 in which a substrate 9 as a processing target is disposed, an exhaust system 4 for exhausting the inside of the processing chamber 1, and a gas for introducing a predetermined gas into the processing chamber 1. The system includes an introduction system 5 and a plasma source 8 that forms plasma in the processing chamber 1.

First, the processing chamber 1 is a cylindrical container, and has an airtight structure in which the upper and lower plates 11 and 12 are closed vertically. The evacuation system 4 includes a vacuum pump such as a turbo molecular pump and the like.
It is configured to be able to exhaust up to about ^-5 Torr.
The upper plate 11 and the lower plate 12 are made of stainless steel,
It is electrically grounded.

The gas introduction system 5 is configured so that a gas corresponding to the plasma processing can be introduced into the processing chamber 1. For example, when dry etching is performed as a plasma treatment, a fluorine-based gas such as C ₄ F ₈ is mixed with a hydrogen gas as a carrier gas and introduced. The gas introduction system 5 includes a gas cylinder (not shown) storing these gases, and a flow controller 51 and a valve 52 provided on a pipe connecting the gas cylinder and the processing chamber 1.

Further, the processing chamber 1 is provided on the upper plate 11.
A gas blowing unit 13 for blowing gas is provided in the inside. Specifically, a gas inlet 110 is provided in a central portion of the upper surface plate 11 of the processing chamber 1, and the end of a pipe of the gas inlet system 5 is connected to the gas inlet 110 in an airtight manner. Further, a gas blowing plate 131 is provided below the upper surface plate 11 so as to form a gas reservoir together with the upper surface plate 11. Top plate 11 and gas blowing plate 131
Are parallel to each other, and the gas introduced from the gas introduction port 110 accumulates between them. The gas blowing plate 131 has gas blowing holes 132 evenly. The gas accumulated between the upper surface plate 11 and the gas blowing plate 131 is blown out uniformly from the gas blowing holes 132 and introduced into the lower plasma forming space.

The way of providing the gas blowing holes 132 requires some contrivance. As an example, all the small circular holes may be provided at equal intervals, but in this case, a large amount of gas tends to blow out from a portion directly below the gas inlet 110. Therefore, in the portion immediately below the gas inlet 110, the gas blowing holes 132
It is preferable to increase the interval (decrease the aperture ratio) and shorten the interval (increase the aperture ratio) in the peripheral portion. In any case, it is important to introduce the amount of gas blown out from each gas blowout hole 132 so as to be uniform on a plane parallel to the substrate 9. Specific examples of the configuration of the gas blowing holes 132 will be given with numerical values. For example, in a region having a radius of about 50 mm from the central axis of the processing chamber 1, the aperture ratio is about 0.01%, and the radius is from 50 mm to 150 mm.
It is preferable to set the aperture ratio to about 0.1% in a region of about 0.1%.

The plasma source 8, which is a major feature of the apparatus of this embodiment, includes a side wall electrode 81 provided so as to constitute a side wall portion of the processing chamber 1, and the side wall electrode 81.
And a high frequency power supply 82 for supplying high frequency power to the power supply. As shown in FIG. 1, the side wall portion of the processing chamber 1 includes a side wall electrode 81, a pair of insulators 14 and 15 provided vertically above and below the side wall electrode 81, and a lower plate 1.
2 and a chamber side wall 16 extending upward from the periphery of the chamber. The chamber side wall 16 is provided with a gate valve 17 that is opened and closed when the substrate 9 is taken in and out. The side wall electrode 81 has a cylindrical shape with a height of 100 mm, an inner diameter of 450 mm, and an outer diameter of 470 mm, for example. The side wall electrode 81 is made of aluminum.

Further, a shield 83 is provided inside the side wall electrode 81 so as to cover the inner side surface of the side wall electrode 81. The shield 83 has a cylindrical shape concentric with the side wall electrode 81, and is provided in contact with the inner side surface of the side wall electrode 81. The shield 83 is made of a material that does not stain the surface of the substrate 9, specifically, silicon. In the present embodiment, since a silicon semiconductor wafer is assumed as the substrate 9, the material of the shield 83 may be silicon carbide, silicon nitride, or the like, in addition to silicon. In addition, the substrate 9
Depending on the material, carbon, quartz, alumina, aluminum nitride, or the like may be used.

Also in the present embodiment, since the side wall electrode 81 is at the ground potential in terms of DC, flying of ions in the plasma toward the side wall electrode 81 is suppressed. However, it is sufficient for ions to move toward the side wall electrode 81 by free movement, and without the shield 83, the side wall electrode 81 may be sputtered. In this case, when the material of the sputtered side wall electrode 81 reaches the substrate 9, there is a problem that the substrate 9 is stained or the quality of the plasma processing is reduced. The shield 83 effectively solves such a problem.

In the present embodiment, a high-frequency power supply 82 having an oscillation frequency of 40 MHz and an output which can be adjusted in a range of about 0 to 3 kW is used. A matching device 86 is provided on a high-frequency line such as a coaxial cable connecting the high-frequency power supply 82 and the side wall electrode 81, and performs high-frequency impedance matching applied to the side wall electrode 81.

Unlike the device shown in FIG. 9, the side wall electrode 81 is not DC grounded but is grounded via a plasma potential control capacitor 87. This is for suppressing a positive shift of the plasma potential and preventing local abnormal discharge. That is, when the side wall electrode 81 is grounded in a DC manner as in the device shown in FIG. 9, the side wall electrode 81 has a potential change that swings positive and negative around the ground potential. In this case, a large amount of electrons that move extremely are incident on the side wall electrode 81 in the positive half cycle, whereas positive ions having low mobility are not incident on the side wall electrode 81 in the negative half cycle. As a result, electrons are relatively reduced in the plasma formation space, and the plasma potential shifts in the positive direction. However, when the plasma potential shifts in the positive direction, the reverse electric field increases for the electrons incident on the side wall electrode 81, so that the incidence of the electrons on the side wall electrode 81 is suppressed. Therefore, the shift of the plasma potential in the positive direction stops and the equilibrium is reached in a state where the amounts of the electrons and the positive ions incident on the side wall electrode 81 are balanced.

When the plasma potential shifts in the positive direction, the electric field between the upper surface plate 11 and the lower surface plate 12 and the plasma maintained at the ground potential increases. On the other hand, the top plate 11
There is a case where an insulator adheres to the inner side surface of the bottom plate 12 due to dirt or the like. This insulator is charged up by a high electric field between the plasma and the top plate 11 or the like. When the charge-up increases, dielectric breakdown sometimes occurs in the insulator, and abnormal discharge such as sparks may occur.

However, if the plasma potential controlling capacitor 87 is provided between the side wall electrode 81 and the ground portion as in the present embodiment, the above-mentioned positive shift of the plasma potential is suppressed, and Discharge can be prevented from occurring. That is, because of the presence of the plasma potential controlling capacitor 87, the electrons incident on the side wall electrode 81 do not flow to the ground portion as they are, but act to lower the potential of the side wall electrode 81. However, when the potential of the side wall electrode 81 decreases, an electric field in a direction opposite to that of electrons incident on the side wall electrode 81 becomes stronger, so that the incidence of electrons is suppressed. For this reason, the plasma potential is prevented from shifting in the positive direction in an attempt to balance the incident amounts of electrons and positive ions, and the plasma potential is maintained at a low value.

Outside the side wall electrode 81, two annular magnets 84 are provided vertically. This magnet 84
Have magnetic poles whose inner surfaces are different from each other. As a result, an arcuate magnetic force line 85 bulging toward the central axis of the processing chamber 1 is set inside the side wall electrode 81.

Further, the pair of upper and lower insulators 14 and 15 has a cylindrical shape having the same diameter as the side wall electrode 81. These insulators 1
Reference numerals 4 and 15 are formed of an insulating material such as alumina.
A sealing member such as an O-ring is provided at a contact portion between the upper and lower insulators 14 and 15 and the side wall electrode 81 and at a contact portion between the lower insulator 15 and the chamber side wall 16.
The airtight structure is secured.

The apparatus of this embodiment has a substrate holder 2 for placing a substrate 9 at a predetermined position in the processing chamber 1. Specifically, the lower plate 1 of the processing chamber 1
A relatively large opening is provided at the center of 2, and a substrate holder 2 is provided so as to airtightly close this opening. The substrate holder 2 includes a holder main body 21 on which the substrate 9 is mounted, a cover 22 that covers an area on the upper surface of the holder main body 21 where the substrate 9 is not mounted, a processing chamber that covers the periphery of the holder main body 21 and 1 lower plate 1
2 mainly composed of an insulating block 23 in contact with 2.

The holder body 21 is made of metal such as stainless steel. The holder main body 21 is connected to a substrate bias power supply 24. Power supply for substrate bias 24
Is configured to supply a high frequency of 1.6 MHz to the holder body 21 with power of about 1 kW in this embodiment.

A high-frequency line connecting the substrate bias power supply 24 and the holder body 21 is provided with a substrate bias capacitor 25 and a matching device 26. The substrate bias capacitor 25 is for generating a self-bias voltage on the substrate 9 by the interaction between the high frequency and the plasma. The matching unit 26 is for performing impedance matching to reduce reflected waves.

When the plasma is formed by the above-described plasma source 8, the substrate bias power supply 24
When high-frequency power is supplied to the holder body 21 via the capacitor 6 and the substrate bias capacitor 25, positive ions and electrons in the plasma are periodically attracted to the substrate 9. In this case, many electrons having a high mobility are attracted to the substrate 9 in the positive half cycle to lower the potential of the substrate 9, but positive ions are not attracted much to the substrate 9 in the negative half cycle because the mobility is low. The potential of 9 does not rise much. Therefore, the potential of the substrate 9 changes as if a negative DC voltage is superimposed on a high-frequency potential change. The negative DC voltage is called a self-bias voltage. The self-bias voltage is used to efficiently extract positive ions from the plasma. Positive ions extracted from the plasma enter the substrate 9 and are used to enhance the effect of the plasma processing.

The cover 22 placed around the substrate 9
Is to prevent etching or thin film deposition on the region of the upper surface of the holder main body 21 where the substrate 9 is not placed. If the upper surface of the holder body 21 is unnecessarily etched or a thin film is unnecessarily deposited on the upper surface,
Particles are generated in the processing chamber 1 and the substrate 9
Is likely to cause staining. The cover 22 prevents this problem. When the cover 22 is etched, the cover 22 may be formed of a material that does not cause any problem even if it is etched, for example, the same material as the substrate 9, or may be subjected to a surface treatment such as an alumite treatment that is resistant to etching. Further, the cover 22 is provided easily when necessary, and is replaced with a new one when the cover 22 is etched and thinned or when a predetermined amount of thin film is deposited on the cover 22.

The insulating block 23 prevents unnecessary discharge from occurring due to the plasma flowing around the side surface of the substrate holder 2. Also, the insulating block 23
Is interposed between the grounded lower plate 12 and the holder main body 21 to electrically insulate them.

The substrate holder 2 is provided with a temperature adjusting mechanism for adjusting the temperature of the substrate 9 as required. For example, when the substrate 9 is heated to a predetermined temperature and the temperature is maintained, a heater for generating Joule heat is provided in the holder main body 21, and the temperature of the substrate 9 is measured with a thermocouple or the like to control the heater. Is done. When the substrate 9 is cooled and maintained at a predetermined temperature, a coolant flow passage is provided in the holder main body 21, and the substrate 9 is cooled through the coolant maintained at the predetermined temperature in the coolant flow passage.

Next, the operation of the plasma processing apparatus according to this embodiment having the above configuration will be described. First, the substrate 9 is placed in a load lock chamber (not shown) air-tightly adjacent to the processing chamber 1 via the gate valve 17, and the load lock chamber and the processing chamber 1 are evacuated to a predetermined pressure. The gate 9 is opened to carry the substrate 9 into the processing chamber 1 and placed on the substrate holder 2.

After the gate valve 17 is closed, the gas introduction system 5 is operated to introduce a predetermined gas into the processing chamber 1 at a predetermined flow rate. The plasma source 8 is operated while controlling the exhaust system 4 to maintain the pressure in the processing chamber 1 at a predetermined value. That is, the high-frequency power supply 82 is operated to supply high-frequency power to the side wall electrode 81 via the matching unit 84. At the same time, the substrate bias power supply 24 is operated to generate a self-bias voltage on the substrate 9.

A high-frequency electric field is set in the plasma forming space above the substrate 9 by the high-frequency power supplied to the side wall electrode 81, and high-frequency energy is given to the introduced gas to form a plasma. Then, a predetermined process is performed on the substrate 9 by the action of the plasma. At this time, positive ions are extracted from the plasma by the self-bias voltage generated on the substrate 9 and used for processing.

The lines of magnetic force 85 set by the pair of upper and lower magnets 84 are partially orthogonal to the direction of the electric field as described later. Therefore, a discharge in which the electromagnetic fields are orthogonal to each other, that is, a magnetron discharge is achieved. In a magnetron discharge, electrons fly circumferentially around a central axis while drifting, and the action of these electrons efficiently ionizes neutral electrons, contributing to the formation of high-density plasma.

For example, when the substrate 9 is a silicon semiconductor wafer and the plasma processing is etching of silicon oxide on the surface of the substrate 9, a carbon fluoride gas such as C ₄ H ₈ is used. Is done. In a plasma of a carbon fluoride-based gas, many active species and ions of fluorine and carbon fluoride are generated, and silicon oxide is etched by the action of the active species and ions. At this time, ions are efficiently incident on the substrate 9 by the self-bias voltage, and the etching efficiency is increased. In the case of performing plasma CVD, the energy of ions incident on the substrate 9 is used for depositing a thin film, and there is an effect that a film forming speed is improved and a film quality is improved.

After performing such plasma processing for a predetermined time, the operations of the substrate bias power supply 24, the plasma source 8, and the gas introduction system 5 are stopped, and the inside of the processing chamber 1 is evacuated again. Thereafter, the gate valve 17 is opened, and the substrate 9 is taken out to the atmosphere via the load lock chamber.

In the plasma processing apparatus according to the present embodiment having the above configuration and operation, the pressure dependence of the plasma uniformity is eliminated by the electron trapping effect, so that a highly uniform plasma can always be obtained regardless of the pressure. It has become. Hereinafter, this point will be described in detail.

FIG. 2 is a diagram showing the ion current density of the plasma observed when the apparatus of FIG. 1 was operated. In the operation example shown in FIG. 2, the high frequency power supplied to the side wall electrode 81 is 1 kW at 40 MHz. The horizontal axis in FIG. 2 is a position in the processing chamber 1, more precisely, a position (radial position) in a plane perpendicular to the central axis of the processing chamber 1. 0 on the horizontal axis in FIG. 10 indicates a position on the central axis of the processing chamber 1. As can be clearly understood from a comparison between FIG. 10 and FIG. 2, in the apparatus of this embodiment, 1
In both cases of mTorr and 10 mTorr, the ion current density shows extremely high uniformity in the radial direction in the processing chamber 1. That is, the pressure dependency of the uniformity of the ion current density distribution as shown in FIG. 10 is eliminated.

The cause of eliminating the pressure dependency of the plasma uniformity is considered as follows. That is, as described above, in the apparatus shown in FIG. 9, the plasma is initially formed near the inner surface of the dielectric window 61 away from the central axis of the processing chamber 1 and diffuses toward the central axis of the processing chamber 1. . In this case, when the pressure increases, a large number of gas molecules are present in the space, so that the plasma immediately collides with the gas molecules, loses energy, recombines and disappears. Therefore, the plasma is difficult to diffuse toward the central axis, and stays near the inner surface of the dielectric window 61. That is, whether or not the plasma is uniform depends on whether or not the plasma is diffused, and therefore, the uniformity of the plasma depends on the pressure. This is the non-uniformity of the ion current density at 10 mTorr shown in FIG.

However, when a high frequency of a high frequency is used as in this embodiment, the effect of trapping electrons in the plasma formation space is increased. Due to the electron trapping effect, plasma is actively formed even in a region away from the inner side surface of the side wall electrode 81. As a result,
As shown in FIG. 2, even if the pressure increases, the plasma is formed uniformly, and the pressure dependence of the plasma uniformity is eliminated.

The above point will be described in more detail with reference to FIGS. First, FIG. 3 is an explanatory diagram of an electric field in the device of FIG. In the apparatus shown in FIG. 1, when a high-frequency voltage is applied to the side wall electrode 81, a high-frequency electric field is set in the processing chamber 1 by the side wall electrode 81. FIG.
Shows the state of the instantaneous electric field in the processing chamber 1, and shows the state of the electric field when the potential of the side wall electrode 81 swings, for example, in the negative direction.

A side wall electrode 81 to which a high frequency voltage is applied;
An electric field represented by lines of electric force 80 as shown in FIG. 3 is set between the upper surface plate 11 and the lower surface plate 12 which are always kept at the ground potential. The direction of this electric field changes periodically according to the period of the high frequency applied to the side wall electrode 81. The electrons constituting the plasma are trapped by the periodically changing electric field and stay in the plasma forming space while moving back and forth widely in the plasma forming space.

This point will be described in more detail with reference to FIG. FIG. 4 is an explanatory diagram of the electron trapping effect. In FIG. 4, for simplicity of explanation, the side wall electrode 81 is shown.
The electric field between the upper surface plate 11 and the lower surface plate 12 (hereinafter referred to as the upper surface plate 11 and the like) is replaced with the case of a parallel plate electrode.

As shown in FIG. 4, when the potential of the side wall electrode 81 swings to the negative side, an electric field indicated by a solid line is set between the side wall electrode 81 and the top plate 11 and the like. The electrons e existing near the inner side surface of the side wall electrode 81 are accelerated by this electric field and fly toward the upper surface plate 11 and the like. In this case, if the high frequency is selected to an appropriate value, the potential of the side wall electrode 81 fluctuates positively before the electrons e reach the top plate 11, and an electric field is set as shown by a dotted line in FIG. The electrons e flying toward the upper surface plate 11 and the like are pulled back by the electric field in the opposite direction as shown by the dotted line, and fly toward the side wall electrode 81. When the electric field returns to the electric field as shown by the solid line after a further half period has elapsed, the electrons e traveling toward the side wall electrode 81 are again inverted and the upper surface plate 1
It comes to 1st mag. As described above, the magnet 8
The magnetic lines of force 85 and the electric field (lines of electric force 80) are partially orthogonal to each other. Therefore, some of the electrons fly as described above while performing magnetron motion. Specifically, while rotating around the central axis of the processing chamber 1 while drifting, the processing chamber 1 approaches the central axis or moves away from the central axis.

As described above, when the high frequency is selected to be an appropriate value in accordance with the distance between the side wall electrode 81 and the upper surface plate 11 or the like, electrons move between the side wall electrode 81 and the upper surface plate 11 or the like. While staying. In this specification, such a phenomenon is called an electron trapping effect.
When electrons are trapped in a wide area of the plasma formation space, ionization of neutral gas molecules occurs in a wide area of the plasma formation space, so that plasma is formed in a wide area of the plasma formation space. As a result, the plasma becomes uniform over a wide area of the plasma formation space. Since the plasma uniformity is not a result of plasma diffusion but a result of electrons being spread over a wide area of the plasma formation space, there is no dependency on pressure. The high plasma uniformity at both 1 mTorr and 10 mTorr shown in FIG. 2 is due to the electron trapping effect.

As described above, in the present embodiment, electrons are confined between the side wall electrode 81 and the arched line of magnetic force 85. Therefore, the electron trapping effect means that other electrons that have not been confined are trapped in a wide area of the plasma formation space.

The value of the high frequency selected to obtain a sufficient electron trapping effect is affected not only by the distance between the side wall electrode 81 and the top plate 11 and the like, but also by the electron moving speed. . The electron moving speed is related to the electron temperature, and the operating condition of the device is influenced by the magnitude of high frequency power to be supplied. However, the cycle or frequency of the alternating electric field has the greatest influence on the electron trapping effect.

FIG. 5 is a diagram showing the relationship between the high frequency and the pressure dependency of the plasma uniformity. The plasma uniformity on the vertical axis in FIG. 5 is calculated according to the following equation. That is, since the plasma uniformity is a problem of the uniformity of the plasma processing on the substrate 9, it is the plasma uniformity in a plane parallel to the substrate 9 in the set plasma forming space. More specifically, in the case shown in FIG. 2, the maximum value of the ion current density observed near the inner side surface of the side wall electrode 81 is A, and the ion current density observed at a position further from the central axis than that is A. , The plasma uniformity is (A−B) / {(A + B) / 2} × 100
(%). In addition, although it is a definition of "plasma formation space", it can be expressed as a space which is planned as a space region where plasma is formed. The plasma formation space is a space having at least a cross-sectional area equal to or larger than the size of the substrate 9.

As can be seen from FIG. 5, for the frequency of 13.56 MHz used in the device of FIG.
When the pressure exceeds orr, the plasma uniformity gradually deteriorates.
At 0 mTorr, it reaches 50%. However, when a frequency of 40 MHz is used as in the apparatus of the present embodiment, as shown in FIG.
Even if it exceeds orr, it can be suppressed to about ± 5% or less. According to experiments by the inventor, when a frequency of 20 MHz or more is used, the plasma uniformity is suppressed to ± 7% or less, which is a practically allowable range. The dimensions of the processing chamber 1 at this time are as follows. Side wall electrode 81: 450 mm in inner diameter, 100 mm in height Distance from side wall electrode 81 to top plate 11 (d in FIG. 1)
1): 20 mm Distance from the side wall electrode 81 to the lower plate 12 (d in FIG. 1)
2): 100 mm Height of chamber side wall 16 (d3 in FIG. 1): 220 mm

As described above, in the apparatus according to the present embodiment, since the pressure dependence of the plasma uniformity is eliminated by the electron trapping effect, uniform plasma can be obtained over a wide pressure range. Therefore, highly uniform plasma processing can be performed on the substrate 9 while freely selecting the processing pressure. In addition, since the plasma uniformity is improved without depending on the plasma diffusion, the plasma density is greatly improved as compared with the apparatus shown in FIG. Therefore, the processing efficiency is improved as compared with the conventional case.

The side wall electrode 81 has the same structure as the substrate 9,
A negative self-bias voltage occurs. However, when the plasma density increases, a large high-frequency current flows in the plasma, and when inductive coupling is achieved, a large high-frequency current is induced by this current and also flows through the side wall electrode 81. Therefore, under a constant power, the self-bias voltage generated on the side wall electrode 81 decreases. As a result, the problem of sputter etching of the shield 83 (the side wall electrode 81 when there is no shield 83) is also suppressed in the apparatus of the present embodiment.

Further, the apparatus of the present embodiment provides a practical structure for introducing gas into the processing chamber 1.
That is, the document that discloses the apparatus of FIG. 9 does not describe a configuration related to gas introduction. For high plasma uniformity, it is important to uniformly introduce gas into the plasma formation space, but the apparatus of the present embodiment provides a suitable configuration for achieving this.

Further, the configuration in which the shield 83 made of a material that does not stain the surface of the substrate 9 is provided so as to cover the inner surface of the side wall electrode 81 greatly contributes to improving the quality of the plasma processing. ing. For example, the substrate 9
It may be difficult to form the side wall electrode 81 itself from a “material that does not stain the surface of the substrate” depending on the type of the substrate and the content of the plasma treatment. A plasma treatment or the like for forming an insulating film is a typical example of this. In this case, by providing the shield 83, the contamination of the insulating film due to the contamination of the conductor can be suitably prevented while forming the side wall electrode 81 with the conductor.

Next, another embodiment of the present invention will be described. FIG. 6 is a schematic front sectional view showing a configuration of a main part of another embodiment of the present invention. The apparatus of the embodiment shown in FIG. 6 is configured such that two arch-shaped magnetic force lines 85 are set side by side in the central axis direction of the processing chamber 1. That is, three magnets 84 are provided outside the side wall electrode 81 as shown in FIG. Each magnet 84
Has an annular shape and is provided coaxially with the processing chamber 1. Among the three magnets 84, the magnetic poles on the inner surface of the middle magnet 84 and the magnetic poles on the inner surface of the upper and lower magnets 84 are different from each other. For this reason, as shown in FIG. 6, two arch-shaped lines of magnetic force 85 are arranged vertically. The two lines of magnetic force 85 are also set circumferentially around the central axis of the processing chamber 1.

In the device of this embodiment, three magnets 84
Is used, the magnetic flux density is higher than in the embodiment of FIG. 1, and the effect of confining the electrons is improved. In particular, when the height of the side wall electrode 81 increases,
It is preferable to use a large number of magnets 84 because a decrease in magnetic flux density can be prevented. Note that the number of magnetic forces 85 arranged along the central axis direction is not limited to two, and it is a matter of course that three, four or more magnetic force lines 85 may be arranged. In this case, the number of magnets 84 also increases according to the number of magnetic force lines 85. Also,
An arch-shaped magnetic field line may be set by two magnets adjacent in the circumferential direction. In this case, a rectangular parallelepiped magnet is arranged at predetermined intervals in the vertical and horizontal directions, and such a magnet group surrounds the side wall electrode 81.

[0073]

As described above, claims 1 and 2 of the present application are provided.
According to the third aspect of the invention, since the pressure dependence of the plasma uniformity is eliminated by the electron trapping effect, uniform plasma can be obtained over a wide pressure range. Therefore, a highly uniform plasma process can be performed on the substrate while freely selecting the process pressure. Further, according to the invention of claim 4 or 5, in addition to the above effects, a practical configuration for introducing gas into the processing chamber is provided. According to the sixth or seventh aspect of the present invention, in addition to the above effects, the shield is provided inside the side wall electrode, so that the side wall electrode is prevented from being sputtered, and the quality of the plasma processing can be further improved. it can. According to the invention of claim 8, in addition to the above-mentioned effects, electrons can be magnetron-moved by an orthogonal electromagnetic field.
It is possible to improve the plasma formation efficiency. According to the ninth aspect of the present invention, in the effect of the eighth aspect, by increasing the magnetic flux density to more efficiently perform the magnetron motion of the electrons, it is possible to further improve the plasma formation efficiency. .

[Brief description of the drawings]

FIG. 1 is a schematic front sectional view showing a configuration of a plasma processing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing the ion current density of plasma observed when the apparatus of FIG. 1 was operated.

FIG. 3 is an explanatory view of an electric field in the device of FIG.

FIG. 4 is an explanatory diagram of an electron trapping effect.

FIG. 5 is a diagram showing a relationship between a high frequency and a pressure dependency of plasma uniformity.

FIG. 6 is a schematic front sectional view showing a configuration of a main part of another embodiment of the present invention.

FIG. 7 is a diagram illustrating an example of a conventional plasma processing apparatus.

FIG. 8 is a diagram illustrating an example of a conventional plasma processing apparatus.

FIG. 9 is a diagram illustrating an example of a conventional plasma processing apparatus.

FIG. 10 is a view showing the result of measuring the ion current density of plasma in the apparatus shown in FIG. 9;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Processing chamber 11 Top plate 12 Lower plate 13 Gas blowout part 131 Gas blowout plate 132 Gas blowout hole 14 Insulator 15 Insulator 2 Substrate holder 21 Holder body 22 Cover 23 Insulation block 24 Power supply for substrate bias 4 Exhaust system 5 Gas introduction system Reference Signs List 8 Plasma source 81 Side wall electrode 82 High frequency power supply 83 Shield 84 Magnet 85 Line of magnetic force 9 Substrate

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tsutomu Tsukada 5-8-1, Yotsuya, Fuchu-shi, Tokyo Anelva Co., Ltd. (72) Inventor Sunir Wikuramanayaka 5-81-1, Yotsuya, Fuchu-shi, Tokyo Anelva Shares In-house (72) Inventor Noriyoshi Sato 4-17-113 Kadan, Aoba-ku, Sendai City, Miyagi Prefecture (72) Inventor Tetsu Iizuka 6-10-10-201, Koriyama, Taihaku-ku, Sendai City, Miyagi Prefecture (72) Inventor Lee Unryu Miyagi Grand Park 305, 11-2 Mizuhodai, Izumi-ku, Sendai

Claims (9)

[Claims] A processing chamber in which a substrate as a processing target is disposed; an exhaust system for exhausting the inside of the processing chamber; a gas introduction system for introducing a predetermined gas into the processing chamber; A plasma processing apparatus comprising a plasma source for forming plasma, wherein the plasma source includes a side wall electrode provided to constitute a side wall portion of the processing chamber, and a high frequency power supply for supplying high frequency power to the side wall electrode. Wherein the high frequency power supply supplies high frequency power to the side wall electrode at such a frequency that the pressure dependence of plasma uniformity is eliminated by an electron trapping effect. 2. The high-frequency power supply sets a maximum value of an ion current density observed in a plane parallel to the substrate in a set plasma formation space to A, and sets a minimum value of an ion current density observed in the plane to a minimum. When the value is B, (AB) /
A high-frequency power of a frequency that can suppress plasma uniformity expressed by {(A + B) / 2} × 100 (%) to 7% or less regardless of a pressure increase in the processing chamber is supplied to the side wall electrode. 2. The plasma processing apparatus according to claim 1, wherein: 3. The plasma processing apparatus according to claim 2, wherein the high-frequency power supply supplies high-frequency power having a frequency of 20 MHz or more to the side wall electrode. 4. The substrate is disposed on a lower plate of the processing chamber or on a substrate holder fixed to the lower plate, and a gas is introduced into the processing chamber on the upper plate facing the lower plate. 4. The plasma processing apparatus according to claim 1, further comprising a gas blowing section for blowing. 5. The gas blow-off portion is provided on a lower side of the upper surface plate so as to form a gas reservoir together with the upper surface plate, and comprises a gas blow-out plate having gas blow-out holes uniformly. The plasma processing apparatus according to claim 4, wherein 6. A shield is provided inside the side wall electrode so as to cover an inner side surface of the side wall electrode.
6. The plasma processing apparatus according to claim 1, wherein the shield is made of a material that does not stain the surface of the substrate. 7. The shield is made of silicon, carbon,
The plasma processing apparatus according to claim 6, wherein the plasma processing apparatus is formed of any one of silicon carbide, silicon nitride, quartz, alumina, and aluminum nitride. 8. The apparatus according to claim 1, further comprising: a magnet provided inside the side wall electrode to set a magnetic line of force bulging toward a central axis of the processing chamber. Plasma processing equipment. 9. The plasma processing apparatus according to claim 8, wherein the magnet sets a plurality of arch-shaped magnetic lines of force along the central axis direction of the processing chamber.