JPH0521392A - Plasma processing device - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the processing speed while maintaining the processing accuracy of the plasma processing apparatus using electron cyclotron resonance. [Composition] A plasma chamber for ionizing a reactive gas for processing in plasma generated under electron cyclotron resonance,
A reaction chamber that processes the target with this reactive ion,
A magnetic field generating coil for accelerating ions disposed between the plasma chamber and the object to be processed, and means for pulsing the magnetic field generating coil are provided,
Ions are accelerated under a pulsed magnetic field generated by a magnetic field generating coil, and then a processing target is irradiated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention ionizes a reaction gas in plasma generated by electron cyclotron resonance (hereinafter referred to as ECR), and the reaction gas ions cause etching of a processing object such as a semiconductor wafer. The present invention relates to a plasma processing apparatus used for performing various kinds of processing.

[0002]

2. Description of the Related Art As is well known, a dry process using plasma instead of a chemical wet process has been more and more widely adopted for processing such as etching of a semiconductor wafer to be processed. Although various processing devices have been developed, the processing device using the above-mentioned ECR, which is the object of the present invention, has the advantage of high plasma generation efficiency and, therefore, high ionization efficiency of various reaction gases, and has potential for future development. Is what is being sought after. An outline of a conventional example of this ECR processing apparatus will be described below with reference to FIG.

A plasma processing apparatus shown in FIG. 4 is provided with a plasma chamber 10 for generating plasma and ions of a reaction gas, a semiconductor wafer 1 to be processed, etc., and is subjected to predetermined processing under reaction with reaction gas ions. And a reaction chamber 20 to be applied. The high-vacuum container 11 of the plasma chamber 10 is provided with a microwave MW waveguide 11a and a reaction gas RG introduction pipe 11b in the upper portion, and the lower portion is communicated with the reaction chamber 20, and the inside thereof is generally 10 ^-4.
A vacuum of about 10 ^-3 Torr is maintained. A normal 2450 MHz microwave MW is injected from the waveguide 11a into the inside of the container 11 of the plasma chamber 10 through the window 12 made of alumina or the like, which closes the lower end of the waveguide 11a in a vacuum-tight manner, and the magnetic field generating coil 14 disposed around it.
A plasma produced by ECR is usually generated in an up and down direct current magnetic field of 875 Gauss.

As is well known, this ECR plasma is generated under the cyclotron resonance condition for electrons rotating at high speed in the circumferential direction while interlinking the magnetic field in the container 11 and introduced into the container 11. The molecules of the reaction gas RG are ionized by the impact ionization with the fast electrons, and the ions I of the atoms and molecules are generated.

An upper portion of the high-vacuum container 21 on the side of the reaction chamber 20 communicates with the plasma chamber 10 as shown in the drawing, and an exhaust pipe 22 for drawing the inside thereof and the container 11 of the plasma chamber 10 to a high vacuum V in the lower portion. And a processing table 23 near its bottom. The wafer 1 to be processed by the above-mentioned ions I is loaded or mounted on the processing table 23 through an entrance / exit window 24 which is shown in a very simple manner in the figure.

Since the magnetic field generated by the magnetic field generating coil 14 spreads from the plasma chamber 10 toward the reaction chamber 20, the above-mentioned ions I generated in the plasma chamber 10 are moved downward in the figure by this divergent magnetic field. The wafer 1 on the processing table 23 is accelerated toward the wafer 1, and the wafer 1 is subjected to predetermined processing such as etching in accordance with conditions such as the type of the reaction gas RG and the form of its ions I or free radicals. .
The processing conditions are appropriately controlled by other conditions such as the pressure in the reaction chamber 20, the flow rate of the reaction gas RG introduced into the plasma chamber 10, the temperature of the wafer 1, and the like.

From the above, various kinds of processing can be performed in principle under various conditions, but in the actual processing, a high frequency electric field has been widely applied to the wafer 1 in order to improve accuracy. Therefore, as shown in FIG. 3, the processing table 23 on which the wafer 1 is placed is placed by being insulated from the container 21 by the insulating plate 25, and a high frequency voltage of 13.56 MHz is usually applied from the high frequency power source 26 thereto. This high-frequency electric field forms a sheath of ions so as to surround the processing table 23, and the in-plane distribution of the ions I irradiated on the surface of the wafer 1 is averaged by this, so that the in-plane variation in processing is reduced.
Further, since the ions I are accelerated by the electric field in the sheath, the processing speed is improved.

[0008]

However, in the conventional ECR plasma processing apparatus as described above, even if the high-frequency power supplied to the processing table 23 is increased in order to further increase the processing speed, the processing speed is still improved. However, there is a problem that the processing accuracy is lowered. FIG. 5 shows this state. The horizontal axis represents the radius r from the center of the wafer 1 to the peripheral edge, and the vertical axis represents the processing speed S which is etching in this example. Further, the characteristic A shown in the figure is when the high frequency power is 0,
Characteristics P and Q are for high frequency powers of 100 W and 300 W, respectively. As can be seen from this, when there is no high frequency power of the characteristic A, the in-plane variation of the processing speed S is very small,
The in-plane variation increases in the order of the characteristics P and Q where the high frequency power becomes higher, and the machining speed S is slightly improved in the characteristic P, but it is lower than the characteristic P in a certain range in the surface in the characteristic Q. There is a tendency to do.

Considering the results of this experiment, since the voltage or bias that the ion sheath can hold even when the high frequency power is raised to a certain level or more is limited by the pressure of the reaction chamber 20, etc., the acceleration voltage of the sheath for the ion I is increased. Is saturated and does not contribute much to the improvement of the processing speed, and the sheath tries to take in an amount of ions I commensurate with the high frequency power, so that the state of the thermal and electromagnetic flow of plasma in the plasma chamber 10 is increased. It is conceivable that the machining accuracy will be deteriorated due to the disturbance of machining. It should be noted that the characteristics P and Q in FIG.
It is considered that this is a result of amplification of a very slight error in the inclination and position of the wafer 1, and it is presumed from this that the plasma and the sheath are in an unstable state.

The present invention solves the above conventional problems,
An object of the present invention is to provide a plasma processing apparatus capable of further improving processing speed while maintaining high processing accuracy.

[0011]

According to the present invention, the above object is to provide a plasma chamber for ionizing a reaction gas in plasma generated by ECR under a predetermined magnetic field by receiving a microwave, and a reaction gas from the plasma chamber. A reaction chamber that receives ions and performs predetermined processing with ions on a processing target loaded inside, and a coil that is disposed between the processing target in the reaction chamber and the plasma chamber and that generates a magnetic field along the direction between them. And a means for pulsating the magnetic field generating coil with a pulse, a plasma processing apparatus is configured, and the pulse urging means repeatedly urges the magnetic field generating coil to accelerate the reaction gas ions under the pulse magnetic field generated thereby. It is achieved by irradiating the object to be processed.

Since the microwave is normally oscillated intermittently and applied to the plasma chamber, the energization of the magnetic field generating coil by the pulse energizing means described above is synchronized with the cycle of the intermittent oscillation of the microwave. It is advantageous to carry out such energizing at a timing almost matched to each stop of each oscillation of the microwaves intermittently oscillated.

The magnetic field strength generated by the magnetic field generating coil is 5 to 100% of the magnetic field generated due to ECR.
Particularly, it is preferable to set it in the range of 10 to 50%. Further, it is very advantageous to dispose a plurality of magnetic field generating coils along the direction from the plasma chamber toward the processing object and to sequentially energize the pulses with a time difference corresponding to the flight speed of the reaction gas ions. It is advantageous that the number of the magnetic field generating coils is 2 in order to obtain a substantial effect without complicating the device structure too much.

The magnetic field generating coil is preferably a simple circular loop coil, and it is advantageous to set the number of turns to one in order to reduce the inductance and make the pulse waveform of the current during the activation steep. . As the pulse energizing means for this, it is preferable to use a circuit structure in which the capacitor is charged and placed, and the capacitor is discharged for a short time by the trigger signal to energize the magnetic field generating coil.

[0015]

The present invention utilizes the property that charged particles such as ions show an adiabatic change while preserving their magnetic moment when the magnetic field changes temporally or spatially. It accelerates. That is,
By pulsing the above-mentioned magnetic field generating coil,
The charged particles are adiabatically changed by the temporal change of the generated magnetic field and are first accelerated in the circumferential direction, and then the divergent magnetic field of the pulse magnetic field or even after its disappearance is adiabatically changed by the divergent magnetic field of the ECR magnetic field, that is, the spatial change of the magnetic field. Then, the speed is converted from the circumferential direction to the axial direction.

Therefore, by arranging the magnetic field generating coil between the plasma chamber and the object to be processed in the reaction chamber as described in the preceding paragraph and energizing the pulse, the magnetic field for ECR is extracted from the plasma chamber by the divergent magnetic field. While accelerating the reactive gas ions in the axial direction, that is, in the direction toward the workpiece,
The ions can be given to the object to be processed in the same velocity direction as possible by stopping the axial acceleration to the tendency that the ions become isotropically thermodynamically isotropic.

As described above, according to the present invention, the processing speed can be increased by accelerating the ions of the reaction gas, and the above-described action of aligning the ion speed in the axial direction passes through the loop of the magnetic field generating coil to generate plasma. Of course, the ions moving from the chamber to the object to be processed act almost uniformly within the area, so that the in-plane processing speed of the object to be processed can be made uniform and the processing accuracy can be improved.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a plasma processing apparatus according to the present invention in the same manner as in FIG. 4, and the same parts as those in FIG. In the following description, the processing target is a semiconductor wafer and the processing content is dry etching, but of course the present invention can be applied to other objects and content.

2450M injected into the container 11 of the plasma chamber 10
The microwave MW of Hz is normally oscillated intermittently at a cycle T of the commercial frequency by an oscillator such as a magnetron 13 arranged above the waveguide 11a as shown in FIG. 2 (a). Ions I of the reaction gas RG ionized in the ECR plasma generated by the microwave MW under the magnetic field generated by the magnetic field generation coil 14 are extracted from the plasma chamber 10 under the divergent magnetic field as described above, and the reaction chamber 20 And goes toward the wafer, which is the processing target 1, placed on the processing table 23. In the present invention, it is not necessary to apply the high frequency power to the processing table 23 as shown in FIG. 4, but it may be used in combination unless the power is particularly high.

In the present invention, a magnetic field generating coil 30 is arranged so as to surround the passage from the plasma chamber 10 of the ions I to the processing object 1. Two magnetic field generating coils 30 are provided as shown by coils 31 and 32 in the illustrated embodiment. To be The coils 31 and 32 are preferably formed in a one-turn circular loop having a small inductance, and the diameter thereof is, for example, 2 of the processing object 1 so that the generated magnetic field is substantially uniform in the area corresponding to the processing object 1. It is about doubled. Further, it is preferable that the vertical distance between the two is set to about several cm.

The pulse energizing means 40 for supplying the pulse current to the magnetic field generating coil 30 has coils 31 and 32 in the example of FIG.
It consists of two pulse generation circuits 41 and 42 corresponding to, each of which includes a capacitor 43 and a switch 44, which are simply shown in the figure. After charging the capacitor 43 and placing it, the switch 44 is turned on. , Its discharge current is pulse current P1
And P2 are supplied to the corresponding coils 31 and 32, respectively. Since these currents require a peak of several thousand amperes, the capacitor 43 should be a high-voltage and large-capacity one capable of outputting a large discharge current, and a steep current waveform is desirable. Use possible semiconductor switches.

The operation timing of the pulse energizing means 40 will be described with reference to FIG. In the plasma chamber 10, almost exactly corresponding to the intermittent oscillation of the microwave of FIG.
As shown in (b), light emission L indicating the generation of plasma occurs,
It is considered that the charged particles containing the ions I are mainly generated during this light emission period, but as shown in FIG. 6 (c), the density D of charged particles in the plasma chamber 10 is equal to the plasma emission in FIG. 2 (b). L
Tends to last longer. From this, it is considered that the transfer of the ion I from the plasma chamber 10 to the reaction chamber 20 continues from the period when the emission L is from the certain period to the duration of the charged particle density D. Therefore, in the present invention, the pulse energizing means 40 is used. The operation timing is preferably within the period in which the charged particle density D in FIG. 2 (c) is decreasing.

However, according to the experimental result obtained by operating the pulse energizing means 40 by changing the timing within this matching period,
Figure 2 (a) Microwave MW oscillation interruption point or figure
FIG. 2 (d), which is the vicinity of the time when the plasma emission L of FIG.
The timing shown in (1) is optimal in terms of the effect of effectively accelerating the ions I and increasing the processing speed. Further, when the pulse energizing means 40 is composed of two pulse generating circuits 41 and 42 as in this embodiment, two pulse currents P1 as shown in FIG.
It is better to operate them sequentially so that there is a short time difference dt between P2 and P2. This desirable time difference dt obviously varies depending on the flight speed of the ions I and the mutual distance between the coils 31 and 32 on the side of the magnetic field generating coil 30, but is generally within the range of several to several tens μs.

The timing circuit 45 of FIG. 1 is a pulse energizing means.
This is an electronic circuit for controlling the above-mentioned timing for operating 40. In this embodiment, the timing signal S0 indicating the interruption of the oscillation of the microwave MW is received from the magnetron 13, and the timing signals S1 and S2 are pulse-energized accordingly. It outputs to the pulse generation circuits 41 and 42 of the means 40 as a trigger command for the switches 44, respectively. Note that the above-mentioned time difference dt
Changes depending on the type of reaction gas RG, operating conditions of the device, etc., the timing circuit 45
The time difference dt between S2 is adjustable.

The magnetic field generating coil 30 energized by the pulse energizing means 40 produces a pulse magnetic field for accelerating the ions I. To obtain this effective acceleration effect in the present invention, the peak intensity of the pulse magnetic field is required. Of the magnetic field for ECR
It is better to set it in the range of 100%, especially in the range of 10 to 50%, and at about 10%, a processing speed equivalent to the normal acceleration effect of about 0.2 eV when using conventional high frequency power is obtained. To be As is well known, this acceleration effect increases in proportion to the square of the magnetic field strength, so at 50%, a large acceleration effect of about 5 eV can be obtained. Also, the above-mentioned pulse current P1 required to obtain the pulse magnetic field strength in the optimum range of 10 to 50%
Or P2 is, for example, the diameter of the coils 31 and 32 of the magnetic field generation coil 30
It is about 1000 to 5000 A when it is about 12 cm.

In the plasma processing apparatus of the present invention constructed as described above, the magnetic field generating coil 30 is urged by the pulse urging means 40, and the processing target 1 is processed by etching or the like under the same processing conditions as the conventional one. It is good to give. In the present invention, the ions I ionized in the plasma chamber 10 and extracted into the reaction chamber 20 are accelerated in the circumferential direction by the adiabatic change in the pulse magnetic field that changes with time by the magnetic field generating coil 30 as described above, and the pulse magnetic field is further increased. Or, since it is irradiated to the machining target 1 after being accelerated in the axial direction by the adiabatic change in the divergent magnetic field that spatially changes the ECR magnetic field, a machining speed that is controllable by the intensity of the pulse magnetic field and higher than the conventional machining speed is obtained. Moreover, since the axial acceleration action on the ions I acts almost uniformly within the area of the loop of the magnetic field generating coil, the in-plane processing speed of the processing target 1 becomes uniform and the processing accuracy is improved as compared with the conventional case.

The results of a processing experiment using the plasma processing apparatus of the present invention according to FIG. 3 will be illustrated. In this experiment, a silicon wafer having a diameter of 4 inches was used as a processing target 1, and a narrow and deep trench groove was dug under the condition of a microwave MW of 450 W by anisotropic dry etching using a chlorine-based gas as a reaction gas RG. The etching rate S and the in-plane distribution at the time of insertion were measured. Similar to FIG. 5 above, the horizontal axis of FIG. 3 is the radius r from the center to the periphery of the wafer 1, and the vertical axis is the etching rate S. Characteristic A in the figure is the case where the magnetic field generating coil 30 is not energized, and characteristics B and C are 2000 A and 3000 respectively.
This is the case where the pulse current of A is applied. In this experiment, the coils 31 and 32 of the magnetic field generating coil 30 having a diameter of 12 cm were used.

As can be seen from FIG. 3, the machining speed S increases as the pulse current for energizing the magnetic field generating coil 30 increases, and the in-plane distribution of the machining speed S shows the characteristic P of FIG.
There is no left-right bias like Q and Q, and the variation is smaller than before. It is considered that this is because the pulsed magnetic field of the magnetic field generating coil 30 has a certain effect of accelerating the ions I, and the pulsed magnetic field has little effect on the plasma chamber 10, and the ECR plasma is stable. Incidentally, in the experimental result of FIG. 3, the processing speed S of the characteristic Q having a larger pulse current is slightly decreased at the peripheral portion of the wafer. 1
It is considered possible to improve by making the intensity of the pulsed magnetic field within the area corresponding to

[0029]

As described above, according to the present invention, the plasma chamber which receives the microwaves and ionizes the reaction gas in the plasma generated by the ECR under the magnetic field, and the processing object which is charged inside by receiving the ions are processed. A plasma processing apparatus is configured by a reaction chamber that performs processing by ions, a coil that is arranged between the plasma chamber and an object to be processed and that generates a magnetic field along the direction between the two, and a means for pulsing the magnetic field generating coil. The following effects can be obtained by repeatedly energizing the magnetic field generation coil by the pulse energizing means and accelerating the ions by the pulse magnetic field to irradiate the object to be processed.

(A) Utilizing the property that charged particles exhibit an adiabatic change while preserving the magnetic moment when the magnetic field changes temporally or spatially, the reaction gas ions generated in the ECR plasma in the plasma chamber are By accelerating by a magnetic field generating coil that generates a pulse magnetic field along the traveling direction and aligning the speed directions to efficiently irradiate the processing target in the reaction chamber, the processing speed by ECR plasma can be further increased. (b) When the machining speed is increased considerably by making the velocity of the ions in the irradiation direction that passes through the loop and heads to the machining target by the magnetic field generating coil almost uniform within the area near the center of the loop. Also, the in-plane distribution of the object to be processed can be made substantially uniform, and the processing accuracy can be significantly improved compared to the conventional case. (c) The pulsed magnetic field for accelerating ions created by the magnetic field generating coil is the same as the conventional high frequency power in the EC inside the plasma chamber.
Since there is no fear of making the R plasma state unstable, the reproducibility of the processing speed and the processing accuracy is excellent, and particularly the reproducibility during anisotropic etching processing becomes good.

As described above, the plasma processing apparatus of the present invention having the characteristics of excellent processing speed and processing accuracy and good reproducibility is particularly suitable for manufacturing a semiconductor device, and is applied to a process such as etching to improve the manufacturing efficiency. It is possible to achieve a remarkable effect of reducing damage.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a plasma processing apparatus according to the present invention.

2 shows matters related to the operation of the embodiment of FIG. 1, FIG. 2 (a) is a waveform diagram of intermittent oscillation of microwaves, and FIG. 2 (b) is E.
FIG. 3C is a waveform diagram of CR plasma emission, FIG. 3C is a waveform diagram of charged particle density in the plasma chamber, and FIG. 3D is a waveform diagram of energizing current pulses of the magnetic field generating coil.

FIG. 3 is a characteristic diagram of a processing speed and an in-plane distribution of a processing target showing an example of processing performance of the plasma processing apparatus of the present invention.

FIG. 4 is a configuration diagram of a conventional plasma processing apparatus.

FIG. 5 is a characteristic diagram of a processing speed showing the processing performance of a conventional plasma processing apparatus and an in-plane distribution of the processing target.

[Explanation of symbols]

1 Processing target or semiconductor wafer 10 Plasma chamber 14 Electron cyclotron resonance magnetic field generating coil 20 Reaction chamber 30 Magnetic field generating coil 31 One coil as magnetic field generating coil 32 The other coil as magnetic field generating coil 40 Pulse energizing means 41 With pulse One pulse generating circuit constituting the energizing means 42 The other pulse generating circuit constituting the pulse energizing means I Ions of the reaction gas D Density of charged particles in the plasma chamber dt Time difference between current pulses L Plasma emission MW at electron cyclotron resonance Microwave P1 One current pulse for energizing the magnetic field generation coil P2 Other current pulse for energizing the magnetic field generation coil RG Reaction gas T Microwave intermittent oscillation cycle t time

Claims (4)

[Claims] 1. A plasma chamber which receives a microwave and ionizes a reaction gas in plasma generated by electron cyclotron resonance under a predetermined magnetic field, and a machining which receives the reaction gas ion from the plasma chamber and is charged therein. A reaction chamber for subjecting a target to a predetermined processing with this ion, a coil arranged between the target to be processed in the reaction chamber and the plasma chamber for generating a magnetic field along the direction therebetween, and a pulse-energizing magnetic field generating coil. And a means for irradiating the object to be processed by accelerating reaction gas ions under a pulsed magnetic field generated by repeatedly energizing the magnetic field generating coil by the pulse energizing means. Plasma processing equipment. 2. The apparatus according to claim 1, wherein microwaves are intermittently applied to the plasma chamber, and the magnetic field generating coil is energized by the pulse energizing means in synchronization with the intermittent cycle. A plasma processing apparatus characterized by the above. 3. The plasma processing apparatus according to claim 1, wherein the intensity of the magnetic field generated by the magnetic field generating coil is set within the range of 5 to 100% of the magnetic field for electron cyclotron resonance. 4. The apparatus according to claim 1, wherein a plurality of magnetic field generating coils are provided along the direction from the plasma chamber toward the object to be processed, and the magnetic field generating coils are driven by a pulse energizing means to fly the reaction gas ions. The plasma processing apparatus is characterized in that the pulse is sequentially energized with a time difference according to.