JPS6367332B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In the manufacture of various devices including semiconductor integrated circuits, the present invention introduces raw materials in a gaseous state and uses the action of plasma to adhere and deposit various materials on a sample substrate. It relates to a plasma deposition device for forming thin films, and in particular uses the action of a divergent magnetic field to draw out plasma generated by microwave discharge due to electron cyclotron resonance, and irradiates the sample surface with the plasma to deposit it at low temperatures. The present invention relates to a plasma low temperature deposition apparatus for efficiently forming high quality thin films.

Conventional equipment of this type is called a plasma CVD equipment, and consists of a sample chamber, a gas introduction system, and an exhaust system. Inside the sample chamber, a high-frequency electrode for plasma generation and a sample stage are arranged opposite to it. Ru. This sample stage has a heating mechanism. As an example, to describe the case of forming a silicon nitride film, silane gas (SiH ₄ ) and ammonia gas (NH ₃ ) are introduced as raw materials through a gas introduction system, and while being exhausted through an exhaust system, the gas pressure is increased from 0.1 to
The surface of the sample substrate on the sample stage is kept constant in the range of 10 Torr, generates plasma using high-frequency power, dissociates SiH ₄ and NH ₃ gas molecules, and is also affected by the incident ions and electrons. Deposit silicon nitride on. However, in this case,
It is necessary to heat the sample stage to 300-500℃ and also use a thermal reaction, which is not sufficient for the purpose of forming a film while keeping the sample substrate at a low temperature using plasma. Furthermore, since the decomposition of SiH ₄ and NH ₃ is insufficient, H is incorporated into the formed film, and the Si--N bond is insufficient, making it impossible to obtain a high-quality film. For this reason,
The drawback is that it is severely limited in its application to sample substrates with low heat resistance and semiconductor integrated circuits that require high-quality films.

On the other hand, another method using plasma, called plasma transport method, is known, and the formation and control of plasma flow for material transport is being studied. This method applies to both thin film formation and etching. This device consists of a plasma source using microwave discharge and a sample chamber with a parallel magnetic field.Using the effect of the magnetic pipe of the parallel magnetic field, the plasma flow is directed from the plasma source to the sample by thermal diffusion. The membrane is attached to the sample by transporting it to the surface. However, when this method is applied to film formation, the plasma flow is only transported by thermal diffusion, and the impact of incident or bombardment of ions and electrons on the film formation reaction on the sample surface is negligible. Not used. Therefore, even in the plasma transport method, it was necessary to heat the sample to a temperature of 300 to 500°C and to use a thermal reaction using thermal energy. Furthermore, since the plasma source used here utilizes microwave discharge using a discharge chamber with a coaxial structure or microwave discharge within a waveguide, the diameter of the plasma flow is as small as about 2 cm.
The drawback was that productivity was extremely low. Also,
It is necessary to lower the gas pressure inside the sample chamber so as not to attenuate the density of the plasma that reaches the sample surface, and it is also necessary to set the gas pressure inside the plasma source to an appropriate level for discharge. Therefore, it has been difficult to increase the diameter of the plasma flow.

On the other hand, attempts have been made to scan the plasma flow using a scanning magnetic coil in order to increase the area where a film can be formed, but this method reduces the film formation rate and does not improve productivity. Requires complex configuration. In addition, in order to avoid exhaustion of source gas or generation of harmful deposits inside the plasma source, for example, _N2 gas may be introduced into the plasma source and _SiH4 gas may be introduced into the sample chamber to form a silicon nitride film. In such cases, the diameter of the plasma flow is small and the SiH ₄ gas pressure in the sample chamber cannot be increased, so the interaction between the N ₂ plasma flow and the SiH ₄ gas is insufficient, and high quality and efficient The drawback was that it was not possible to form a film.

As an improvement over the conventional technology, in Japanese Patent Application No. 55-57877, the applicant used a large plasma generation chamber configured with a microwave cavity resonator, thereby increasing the electric field strength, and further developed an electron cyclotron. By combining resonance conditions, gas pressure
It enables low gas pressure microwave discharge of less than 10 ^-4 Torr level and generates a large amount of plasma with high activity (degree of decomposition, degree of ionization).Moreover, it is possible to generate plasma using the action of a divergent magnetic field. We previously proposed a plasma deposition device that enables efficient formation of high-quality films over large areas at low temperatures by extracting plasma, accelerating it, and directing it onto the sample surface.

FIG. 1 shows the basic configuration of such a plasma deposition apparatus. Here, 1 is a plasma generation chamber, 2 is a sample chamber, and 3 is a microwave introduction window. As a microwave source, for example, a magnetron with a frequency of 2.45 GHz can be used.
It is connected to the outside through a rectangular waveguide 4, a matching box, a microwave power meter, and an isolator (not shown). The plasma generation chamber 1 is water-cooled via a water supply and water distribution port 5. The gas introduction system has two systems, the first gas introduction system 6 is for introducing gas into the plasma generation chamber 1, and the second gas introduction system 7 is for introducing gas into the sample chamber 2. be. In the plasma generation chamber 1, a plasma extraction window 9 for extracting a plasma flow 8 is provided at the other end opposite to the microwave introduction window 3. The sample stage 10 is installed in an electrically floating state with respect to the plasma generation chamber 1, so that it can supplementally heat the sample substrate 11.
It has a built-in heater (not shown). The sample chamber 1 is connected to an exhaust system 12.

The plasma generation chamber 1 is set as a microwave cavity resonator, and a circular cavity resonance mode TE ₁₁₃ is adopted as an example, and a cylindrical shape with an inner diameter of 20 cm and a height of 20 cm is used to increase the microwave electric field strength. and increased the efficiency of microwave discharge. The plasma extraction window 9 was a circular window with a diameter of 10 cm relative to the 20 cm inner diameter of the plasma generation chamber 1, and was used as a reflecting surface for microwaves.

A magnetic coil 13 is disposed around the outer periphery of the plasma generation chamber 1, and the intensity of the magnetic field generated thereby is determined so that the conditions for electron cyclotron resonance by microwaves are satisfied inside the plasma generation chamber 1. For example, for microwaves with a frequency of 2.45 GHz, this condition is a magnetic flux density of 875 G. The magnetic field inside the plasma generation chamber 1 adopts a diverging magnetic field whose intensity decreases in the direction of the plasma extraction window 9.
The plasma is efficiently moved in the direction of the plasma extraction window 9.

The magnetic field generated by the magnetic coil 13 is not only used for electron cyclotron resonance in the plasma generation chamber 1, but also extends to the sample chamber 2, and the intensity of the magnetic field within the sample chamber 2 is is used to form a diverging magnetic field that further decreases at an appropriate gradient from the plasma extraction window 9 toward the sample stage 10.

In a diverging magnetic field, charged particles generally move in a circular motion, and the energy of the circular motion is converted into kinetic energy in the direction of the diverging magnetic field while preserving angular momentum, and is accelerated along the direction of the magnetic field lines where the magnetic field strength decreases. . In plasma generated by microwave discharge of electron cyclotron resonance, electrons have high energy, so not only is the efficiency of decomposition and ionization of gas molecules, that is, the activation efficiency, high, but also the efficiency of the divergent magnetic field is high. It is vigorously accelerated in the direction and reaches the sample stage 5. Since the sample stage 5 is electrically floating, that is, in an insulated state, the sample stage 5 is negatively charged by the incidence of electrons, and as a result, the condition is such that the number of incident ions and the number of incident electrons match. reaches an equilibrium state. That is, an electrostatic field is induced within the plasma flow 8 by the effect of the diverging magnetic field, which increases the number of incident ions and decreases the number of incident electrons. In other words, the circular kinetic energy of the electrons is converted into the kinetic energy of the ions in the direction of the divergent magnetic field, and not only the electrons but also the ions are accelerated and enter the sample stage 10.

In addition to the electrostatic field caused by such a divergent magnetic field, a certain amount of electric field is generated on the surface of the sample stage 10 due to the thermal movement of electrons, and this portion is called an ion sheath. The kinetic energy of ions incident on the sample surface is the sum of the kinetic energies generated by these electric fields, and this energy has an extremely large effect on the adhesion reaction in thin film formation.

In addition, since the plasma is extracted along the lines of magnetic force of the divergent magnetic field, the plasma flow 8 that was extracted with a diameter of 10 cm increases to a diameter of about 20 cm on the sample stage 10, which not only has an effect on the film formation reaction but also has an effect on the film formation reaction. It is possible to form a film over a large area.

As stated in Japanese Patent Application No. 57877-1987, a plasma deposition apparatus having such a configuration and operation has an extremely excellent effect in forming thin films of various materials.

However, subsequent studies revealed that even greater effects could be achieved if the following problems were resolved. That is, (1) Depending on the type of gas introduced into the plasma generation chamber 1, the gas pressure, or the microwave power introduced, the dimensions of the plasma generation chamber that satisfy the conditions of the microwave cavity resonator may vary slightly.

(2) Even when thermal energy is not used for the film-forming reaction, the temperature of the sample substrate rises to about 150℃ to 200℃ due to the heating effect of the plasma, and it cannot be applied to sample substrates with extremely low heat resistance. There are cases.

(3) In the configuration of the divergent magnetic field, it may be necessary to improve plasma generation efficiency, extraction efficiency, and uniformity of plasma flow, and to change the attachment area depending on the application.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a plasma low temperature deposition apparatus that can solve the above-mentioned problems.

To this end, in the present invention, highly active plasma is stably and efficiently generated by making the end plate with the plasma extraction window a movable structure and arranging a high magnetic permeability material around the magnetic coil. It is possible to form a high-quality thin film only by the action of plasma without the aid of thermal energy, and by installing a cooling mechanism on the sample stage, it can be used even for sample substrates with extremely low heat resistance. To efficiently form a high quality film.

The present invention will be described in detail below with reference to the drawings.

FIG. 2 shows an example of the configuration of a plasma low temperature deposition apparatus according to the present invention. Here, a portion corresponding to the upper half of the apparatus shown in the first figure is shown in detail. In FIG. 2, an end plate 14 having a plasma extraction window 9 is connected to a cylinder 15 constituting the plasma generation chamber 1.
It should be possible to move up and down in the figure while lightly touching the inner surface of the A screw (not shown) is attached to the lowermost end of the cylinder 15 constituting the plasma generation chamber 1, and the vertical dimensions of the cylinder 15 constituting the plasma generation chamber 1 can be adjusted by the screw.

Furthermore, abnormal discharge may occur at the contact portion between the end plate 14 and the inner surface of the cylinder 15 due to the electric field caused by the microwave, which may adversely affect plasma generation.
To avoid unnecessary consumption of microwave power,
A known chiyoke structure in microwave three-dimensional circuits is provided on the end plate 14. That is, a structure having folded grooves 16 having a length of λg/4 for the wavelength λg of the microwave excited in the plasma generation chamber 1 is formed in the end plate 14. In this way, the plasma generation chamber 1 can operate with optimum efficiency as a microwave cavity resonator under all various plasma generation conditions. In addition, it is necessary to efficiently convert the microwaves propagated through the rectangular waveguide 4 into a cavity resonance mode in the plasma generation chamber 1, but this is achieved by an iris structure in the microwave introduction window 3. 17 to match the impedance.

In order to efficiently absorb the microwave electric field strengthened by cavity resonance into the plasma, the magnetic field distribution, which is important for electron cyclotron resonance conditions, is corrected to create a uniform magnetic field in the upper region of the plasma generation chamber 1. It is necessary. To that end, in this example,
An annular member 18 made of a high magnetic permeability material, for example soft iron, is placed above the microwave introduction window 3. Here, a circular plate 15 cm in diameter and 3 cm thick with a rectangular opening having the same cross-sectional shape as the rectangular waveguide 4 is used as the annular member 18, and this annular member 18 is inserted into the rectangular waveguide 4. let

Furthermore, in order to adjust the distribution of the divergent magnetic field, which is important from the point of view of efficient use of the magnetic coil 13 and plasma extraction, an outer casing 19 made of a high magnetic permeability material is placed around and over the magnetic coil 13.
Although the magnetic coil 13 shown in FIG. 1 is divided into two parts for convenience in manufacturing the device, it is also possible to use a single magnetic coil 13 as shown in FIG. 2. FIG. 3 shows the state of the magnetic lines of force when the outer case 19 made of a high magnetic permeability material is placed. By using such a configuration, it is possible not only to prevent unnecessary magnetic fields from leaking to the outside of the device, but also to reduce the DC power consumed by the magnetic coil 13.

In another example of the present invention shown in FIG. 4, an outer casing 19A made of a high magnetic permeability material is arranged extending from the periphery of the magnetic coil 13 to the periphery of the sample chamber 2, and its arrangement and shape are determined appropriately. By adjusting the distribution of the divergent magnetic field, a divergent magnetic field is constructed such that the end portions of the magnetic lines of force are oriented in a direction close to perpendicular to the central axis of the magnetic coil 13, and the concentric annular plasma extraction window 9A is used. , the sample 11 is placed on the cylindrical sample stage 20A.
Arranged on the inner surface of the cylinder. According to this, films can be formed on a large number of samples 11 at the same time. In such a case, since the sample surface is close to vertical, the occurrence of defects due to dust falling onto the sample surface can be reduced.

Incidentally, in order to prevent dust from falling onto the sample surface, it is also possible to use a configuration in which the apparatus configuration shown in FIG. 2 is turned upside down. However, in this case, the exhaust system 12 is connected to the side surface of the sample chamber 2, and the sample stage 10 needs to be changed into a sample holder capable of holding a sample.

The results of a film formation experiment conducted using the plasma deposition apparatus of the present invention with improved performance as shown in FIG. 2 or FIG. 4 will be described below. As an example,
_N2 gas is supplied to the first gas introduction system 6 at 10c.c./min, and the second
SiH ₄ gas was introduced into the gas introduction system 7 at 10 c.c./min, the gas pressure in the sample chamber 2 was set to 2×10 ^-4 Torr, and 200 W of microwave power was supplied to form a silicon nitride film. The sample substrate was not heated; on the contrary, a heat dissipation support was used to maintain the temperature at 100° C. or lower during film formation. As a result, the deposition rate was 300 Å/min,
The uniformity of adhesion is ±5% in an area of 20 cm in diameter,
Furthermore, a film with extremely good adhesion was obtained on a silicon substrate or a silicon oxide substrate. The refractive index of this film was measured using ellipsometry.
2.0, and the hydrofluoric acid resistance at this time is in buffered hydrofluoric acid solution.
It showed an extremely excellent value of less than 30 Å/min.

Thus, in the plasma deposition apparatus of the present invention,
The adhesion reaction (or film-forming reaction) does not require the aid of thermal energy as in the past, and extremely high-quality films can be efficiently formed over a large area.

As described above, according to the present invention, there is no need to heat the sample substrate for the film formation reaction, so by providing the sample stage 20 with a cooling mechanism instead of the conventional heating mechanism, the film formation reaction can be performed by the action of plasma. This makes it possible to prevent the resulting rise in temperature of the sample (100 to 200°C). Sample stage 20 equipped with a cooling mechanism
By using this method, a film can be stably formed over a long period of time while keeping the sample substrate at an extremely low temperature of 100°C or less. As a cooling mechanism for the sample stage 20, a normal water cooling or air cooling method can be used.

By using a sample stage equipped with such a cooling mechanism, it is possible to deposit a film onto a material with extremely low heat resistance, such as a semiconductor substrate with a resist pattern.
It has become possible to form high-quality films on various substrates such as various compound semiconductors with low heat resistance, superconducting materials, and even plastics. In particular, since the formation of a high-quality film on a resist pattern can be applied to a lift-off technique known in the field of semiconductor device manufacturing technology, the scope of its application is extremely wide and important.

As explained above, according to the present invention, the microwave cavity structure of the plasma generation chamber can be operated more efficiently, and the distribution structure of the diverging magnetic field, which is important for electron cyclotron resonance discharge and plasma extraction by microwaves, can be made more efficient. As a result, it is now possible to generate a large amount of highly active plasma and irradiate the sample over a large area with enhanced reaction effects.
High quality films can be formed solely by the action of plasma without the aid of thermal energy. Furthermore, in the present invention, by using a sample stage equipped with a cooling mechanism, a high-quality film can be formed with good productivity even on a sample substrate with extremely low heat resistance.

Note that although silicon nitride Si ₃ N ₄ has been mainly explained as the material for film formation, silicon Si, silicon oxide SiO ₂ , molybdenum silicide MoSi ₂ , molybdenum Mo, aluminum Al
It is clear that the present invention can also be applied to cases in which films are formed from various materials such as the following.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the basic configuration of a plasma deposition apparatus proposed earlier by the present inventor, FIG. 2 is a cross-sectional view showing an embodiment of the plasma deposition apparatus of the present invention, and FIG.
The figure is an explanatory diagram of the state of the lines of magnetic force, and FIG. 4 is a sectional view showing another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Plasma generation chamber, 2... Sample chamber, 3... Microwave introduction window, 4... Microwave rectangular waveguide, 5... Water supply and drainage port, 6... First gas introduction system, 7... Second gas introduction system, 8... Plasma flow, 9...Plasma drawer window, 1
0...sample stage, 11...sample substrate, 12...exhaust system, 1
3...Magnetic coil, 14...Movable end plate, 15...Cylinder, 16...Folding groove with chiyoke structure, 17...Aperture (iris), 18...Annular member made of high magnetic permeability material, 1
9... Outer box made of high magnetic permeability material, 20... Cooling sample stand.

Claims (1)

[Scope of Claims] 1. A plasma generating chamber comprising a plasma generation chamber and a sample chamber provided with a sample stage on which a sample is placed; plasma raw material and microwave power are introduced into the plasma generation chamber to generate plasma; The generation chamber is provided with an end plate having a plasma extraction window for drawing the plasma into the sample chamber as a plasma flow, and a magnetic circuit is disposed around the outer periphery of the plasma generation chamber, and the magnetic circuit allows the plasma to be drawn out into the sample chamber. In the generation chamber, a magnetic flux density of a strength necessary to increase plasma generation efficiency is formed, and in the sample chamber, the magnetic flux density intensity is maintained at an appropriate gradient from the plasma generation chamber to the sample stage in the sample chamber. In the plasma deposition apparatus configured to form a diverging magnetic field that becomes weaker, the plasma generation chamber has a cavity resonator structure for microwave power introduced for plasma generation, and has the plasma extraction window. A plasma low-temperature deposition apparatus characterized in that the end plate has a movable structure so as to adjust the microwave cavity resonance state. 2. The plasma low temperature deposition apparatus according to claim 1, wherein the sample stage has a cooling mechanism. 3. In the plasma low-temperature deposition apparatus according to claim 1 or 2, the magnetic circuit has a magnetic coil for forming a divergent magnetic field for plasma generation and plasma extraction, and the magnetic coil A low-temperature plasma deposition apparatus characterized in that a high magnetic permeability material is arranged around the plasma generating chamber and the sample chamber, and the magnetic field distribution in the plasma generation chamber and the sample chamber can be adjusted by the arrangement and shape of the high magnetic permeability material.