JPH0831443B2 - Plasma processing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus for performing plasma processing on a substrate, and more particularly to a plasma apparatus suitable for high-speed plasma etching processing that does not damage the substrate.

[Conventional technology]

As a conventional plasma processing apparatus, for example, a sputter etching apparatus, an etching electrode on which a substrate is placed is provided in a vacuum chamber, high-frequency power is applied to the electrode, and high-frequency power is applied to the plasma generated on the substrate. Ion,
It is known that the electric field of the electric power applied to the electrode collides with the substrate to etch the substrate. However, in such an apparatus, the density of plasma generated on the substrate is not high, and therefore the rate of sputter etching is high. Is slow and again
It is known that when the high frequency power applied to the etching electrode is increased and the sputter etching rate is increased, the voltage of the electrode increases and the energy of the ions that collide with the substrate increases, causing damage to the substrate. . JP-A-60-74436 is known as a method for reducing damage to the substrate by reducing the energy of ions incident on the substrate due to the high speed of this sputter etching. In this method, the plasma generated by the high-frequency power applied to the etching electrode is confined on the substrate by using the floating electrode and the magnet, the plasma density is increased by preventing the diffusion of the plasma on the substrate, and the number of ions is increased. This prevents the voltage of the electrode from increasing with respect to the electric power applied to the etching electrode. However, since the density of this plasma is not directly proportional to the electric power applied to the electrode in a one-to-one manner, the voltage generated at the electrode also increases as the applied high-frequency power is increased in order to further increase the etching rate. It becomes large and damages the substrate.

[Problems to be solved by the invention]

The above-mentioned conventional technique obtains the plasma required for plasma processing and the voltage for accelerating the ions in the plasma to collide with the substrate from the high frequency power applied to the etching electrode. No consideration was given to the point of individually controlling the energy of the ions. When the high frequency power applied to the electrodes was increased, the density of the plasma increased, but the energy of the ions colliding with the substrate also increased. There was a problem that the substrate was damaged by more than the power.

An object of the present invention is to independently control the voltage for generating plasma and the voltage for causing ions in the plasma to collide with the substrate by using different power supplies, and to generate plasma, a high density plasma can be uniformly obtained. It is to obtain a plasma processing apparatus that has a high etching rate and does not damage the substrate by using a simple and highly reliable mechanism.

[Means for solving problems]

The purpose of the above is to provide a plasma generating means facing the plasma processing electrode on which the substrate is placed in the vacuum chamber, and use microwaves (for example, frequency 2.45 GHz) to generate high plasma on the substrate. This is achieved by generating a high density plasma, preventing the plasma from diffusing to the surroundings by the magnetic field generating means, and causing the ions in the plasma to collide with the substrate by the voltage generated by the electric power applied to the plasma processing electrode. .

The microwave plasma generating means includes a microwave generation source, a cavity, and a microwave introduction window. The cavity may be provided with a matching means so that the cavity serves as a microwave cavity resonator. Also,
It is needless to say that the cavity has a coaxial structure, and the cavity can be dimensioned so that the microwave mode is axially symmetric. The cavity resonator may be of a well-known circular shape, coaxial or rectangular shape, but is preferably a coaxial shape of a circular cavity resonator, and the plasma has a uniform density distribution on the electrodes. Is easy to obtain.

 The specific configuration of the present invention will be described in detail below.

A feature of the plasma processing apparatus of the present invention is that a plasma processing electrode having a substrate placed therein is provided in a vacuum chamber having a gas supply means and a vacuum exhaust means, and a plasma generating means by microwaves is provided facing the substrate. A microwave applying window is provided in the vacuum chamber, and a voltage applying unit for causing ions in the plasma generated by the plasma generating unit to collide with the substrate is provided at the plasma processing electrode to generate a plasma. In a device in which a microwave power source and a power source for applying a voltage to the plasma processing electrode are independently provided, plasma generated in a space between the substrate and the microwave introduction window is surrounded by magnetic lines of force from its periphery. The magnetic field generating means for forming a magnetic field is provided on the substrate. The characteristic points of the magnetism generating means will be listed below.

(1) The magnetism generating means is magnetized in a radial direction,
A ring-shaped magnet in which the polarity of the magnetization is sequentially reversed in the radial direction.

(2) As the magnetism generating means, magnets are arranged on the microwave introduction window side and the etching electrode side to form a two-stage ring-shaped magnet.

(3) The two-stage ring-shaped magnet is composed of a coil.

(4) Applying reverse currents to the two-stage ring coils.

(5) Applying currents in the same direction to the two-stage ring-shaped coils.

(6) The two-stage ring-shaped magnet is a permanent magnet.

(7) The ring-shaped permanent magnets are magnetized in the circumferential direction and in the opposite directions.

(8) The ring-shaped permanent magnets are magnetized in the thickness direction and in the opposite directions.

(9) The ring-shaped permanent magnets are magnetized in the radial direction and in the opposite directions.

When forming a magnet with a coil as the magnetism generating means, a superconducting coil can be used instead of the normal conducting coil, and a permanent current is passed through the superconducting coil to provide a more stable and higher magnetic field. A magnetic field can be generated. Further, the cusp type is more preferable as the magnetic field for stably confining the plasma.

In addition, the power supply applied to the etching electrode is generally 10
A high frequency power of 0 kHz to 100 MHz is used, but a DC power supply may be used when the substrate to be processed is a conductor such as metal. When the substrate is an insulator, high frequency power is essential.

Furthermore, since the microwave introduction window functions as a partition wall that constitutes the vacuum chamber and as a window that radiates microwaves from the cavity into the vacuum chamber, the material is an insulating material that absorbs less microwaves. The material is selected from impermeable materials which are difficult to allow gas to permeate from the viewpoint of constituting the vacuum partition wall. For example, a quartz plate or a ceramic plate such as alumina is provided.

[Action]

The plasma generating means includes a microwave generating source, a cavity, a matching means for allowing the microwave to effectively enter the cavity, and an entrance window through which the microwave is introduced into the vacuum chamber. The microwave oscillated from is guided to the cavity by the waveguide, and the matching means makes the cavity a cavity resonator of the microwave, so that the microwave is effectively introduced into the cavity. The microwaves are guided through the entrance window into the vacuum chamber, where the microwaves ionize atmospheric gas (eg, Ar gas) in the vacuum chamber to generate plasma.
Here, since the microwave can propagate in the plasma and supply energy to the plasma, the density of the plasma can be as high as about 7.4 × 10 ¹⁰ / cm ² with the microwave of 2.45 GHz. Moreover, uniform plasma generation can be obtained by forming the cavity so that the microwave mode in the cavity is axially symmetric or in the shape of a coaxial tube.

Further, a magnetism generating means is disposed around the plasma, and the magnetic field generated by the magnetism generating means traps the plasma on the substrate and prevents the plasma from diffusing to the surroundings.
Therefore, the plasma has a stable and high density regardless of the pressure.

A plasma processing electrode on which a substrate is placed is provided under the high-density plasma generated by the plasma generating means, and a high frequency power source is connected to the plasma processing electrode to generate high frequency power (generally,
(100 kHz to 100 MHz) is applied, and the voltage generated on the substrate surface of the etching electrode by this power causes ions in the plasma to collide with the substrate, and as a result, the substrate is subjected to spasm treatment. In this way, the generation of plasma and the application of the voltage for causing ions to collide with the substrate serve as different power sources, and the density of the generated plasma and the energy with which the ino in the plasma collide with the substrate can be controlled individually, and the plasma Since the generation can be densified by microwaves, the etching rate is fast and plasma processing without damaging the substrate becomes possible. The high-frequency power source is indispensable when the material to be plasma-treated on the substrate is an insulator, but a DC power source may be used when it is a conductive material such as a metal, as described above.

Next, a sputter etching apparatus is used as an example of the plasma processing apparatus having the configuration shown in FIG. 1, and a silicon wafer having a thermal oxide film (SiO ₂ ) formed on its surface as a sample is subjected to sputter etching under the following conditions. As an example, it is shown in FIG. 8 in comparison with the result of the apparatus without the magnetic generation means.
The vertical axis of the figure shows the etching rate, and the horizontal axis shows the distance from the center of the wafer.

Etching conditions: Specimen: Silicon wafer with thermal oxide film (SiO ₂ ) Etching gas: Argon (Ar) Pressure: 5 × 10 ^-3 Torr Microwave power: 400W High frequency power: 600W (applied to sputter etching electrode) Above As is clear from FIG. 8, the curve 81 in which the plasma is confined by the magnet, which is the embodiment of the present invention, has a flat etching rate with a relatively small variation from the center to the periphery of the wafer, and the uniformity is uniform. It shows that it has been improved. On the other hand, curve 82 showing a comparative example without a magnet
, The speed decreases as it goes to the peripheral portion of the wafer, and a large variation occurs from the central portion.

FIG. 9 shows the relationship between the etching rate and the high-frequency power applied to the sputter etching electrode for the same sample as in FIG. 8 above, in the case of a magnet with an embodiment of the present invention (curve 91). FIG. 9 is a characteristic curve diagram shown in comparison with the case where there is no (curve 92) and the case of a conventional parallel plate system (curve 93) that does not have plasma generation means by microwaves. From this figure, it can be seen that the curve 91, which is an example of the present invention, has a markedly improved etching rate as compared with the other comparative examples. The etching conditions are as follows.

Etching conditions: Specimen: Silicon wafer with thermal oxide film (SiO ₂ ) Etching gas: Argon (Ar) Pressure: 5 × 10 ^-3 Torr Microwave power: 400W (for curves 91 and 92) Above characteristic curves As is clear from the figure, in the present invention, the insertion of the magnet prevents the diffusion of the plasma, and in particular, the plasma density of the surroundings increases, so that the average sputter etching rate increases and the conventional problem is particularly encountered. Because the sputter etch rate around the substrate can be increased,
The uniformity is also improved at the same time. Comparing the variation showing the uniformity (central part and peripheral part), in the present data, it is ± 5% in the case of the present invention with a magnet, whereas it is ± 20% in the comparative example without a magnet. .

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

First, the first embodiment shown in FIG. 1 will be described. It comprises a vacuum chamber 1, a plasma generating means 2, a vacuum exhausting means 3 and a gas supplying means 4, and a substrate 5 is placed in the vacuum chamber 1. A plasma etching electrode (hereinafter abbreviated as an etching electrode) 6 is installed via a flange 7 having a function of electrically insulating and vacuum-sealing from the vacuum chamber 1, and a power source is provided at an end 9 of the etching electrode 6. 8 are connected. Further, the plasma generating means includes a microwave generation source 10, a waveguide 11, a cavity 12, a matching means 1, a conductor rod 14 and an introduction window 15 which serves as a microwave introduction portion. A magnet 16 is arranged around the space surrounded by the introduction window 15 and the etching electrode 6.

In the above structure, the microwave generation source 10 oscillates a microwave and sends the microwave to the cavity 12 through the waveguide 11. Now adjust the alignment means 13 to
By setting 12 as a microwave cavity resonance condition, the electric field of the microwave in the cavity 12 is increased, and the microwave introduced into the vacuum chamber 1 through the introduction window 15 causes the gas chamber 4 to supply the vacuum chamber 1 with the microwave. The atmospheric gas in the tank supplied into the chamber is ionized to generate plasma 17. FIG. 2 shows a sectional view of the magnet 16 installed around the plasma 17 as seen from the thickness direction. In this embodiment, a permanent magnet is shown as the magnet, but it goes without saying that it may be an electromagnet. The ring-shaped magnet 16 is divided into an even number in the circumferential direction, and the magnetic field lines 19
Has a convex shape inward (generally referred to as a multiple cusp magnetic field for confining the plasma), and the plasma 17 can be confined on the substrate 5, so that the plasma 17 can be stably generated in a low pressure region and the plasma 17 can be easily generated. It can be highly dense. The density of the plasma 17 is supplied up to a limit density at which the microwave propagates in the plasma 17 and can supply energy (for example, if the microwave frequency is 2.45 GHz, the plasma density is 7.4 × 10 ¹⁰ / cm ³ ). It can be controlled by wave power. Plasma 17 generated in this way
The ions inside are accelerated by a voltage generated on the substrate 5 through the etching electrode 6 by a power source 8 (in this example, high-frequency power is applied) connected to the etching electrode 6 to collide with the substrate to perform sputter etching. Here, by making the dimensions of the cavity 12 such that the microwave mode in the cavity 12 is axisymmetric, the density distribution of the plasma 17 on the substrate 5 becomes uniform. Further, the cavity 12 is a coaxial type having a shaft (conductor rod 14) in the center, but the same effect can be obtained in a hollow type without a shaft.

Although a quartz plate was used as the introduction window 15,
As described above, an insulating material that does not allow gas to pass therethrough (impermeable) and has a small microwave absorption, for example, ceramics such as alumina, since it also serves as a partition wall of the vacuum chamber.

FIG. 3 shows a second embodiment of the present invention, in which the structure of the vacuum chamber 1, the plasma generation means 2, the vacuum exhaust means 3, the gas supply means 4, etc. is the same as that of the first embodiment. The only difference is that the magnet 16 of the plasma generating means 2 is replaced by a ring coil 18. With such a configuration, the coils 18a and 18b are concentrically arranged in two stages, and currents are passed in opposite directions, respectively.
The lines of magnetic force 19 from the two coils are closed around the periphery of the substrate 5, the plasma is not diffused in the radial direction, and the plasma can be more stably confined, so that the plasma can be efficiently generated with high density.

4 and 5 both have a structure similar to that of the second embodiment, in which the two-stage coil 18 of the embodiment of FIG. 3 is replaced by a permanent magnet 16. FIG. 4 shows a pair of upper and lower permanent magnets magnetized in opposite directions in the circumferential direction of the ring.
16 so that the magnetic field lines 19 close around the plasma 17 and confine the plasma 17 on the substrate 5. In FIG. 5, the magnetization of the magnet 16 is taken in opposite directions in the thickness direction, and a magnetic field almost the same as in FIG. 4 is obtained, and the confinement effect of the plasma 17 is obtained.

FIG. 6 shows a third embodiment of the present invention. The structure is the same as that of the second embodiment shown in FIG. 3, and ring-shaped coils 18a and 18b are mounted as magnetic field generating means. But
By supplying currents in the same direction to the coils 18a and 18b, the magnetic force lines 19 formed by the coil 18 have a convex shape inward on the substrate 5 to prevent diffusion of the plasma 17 in the outer peripheral direction.

FIG. 7 shows a third embodiment of the present invention, which is similar to that of FIG. 6 except that the coil 18 of FIG. 6 is replaced by the magnet 16. Since the magnet 16 is magnetized in the radial direction and the polarities of the two magnets are reversed, the magnetic field line 19 is
The shape is similar to that in the figure, and has the effect of confining the plasma 17.

〔The invention's effect〕

According to the present invention, the plasma can be generated at a high density by the plasma generating means by the microwave, and the cavity size is made the cavity resonator of the axisymmetric mode of the microwave by the cavity matching means and the coaxial etc. By preventing diffusion around the plasma by the magnetic field,
It is possible to generate stable, high-density axisymmetric plasma at low pressure.
It has the effect of speeding up the etching and reducing damage to the substrate.

Further, since the plasma generation is microwave power and the energy of the ions colliding with the substrate can be separately controlled by the second power applied to the plasma processing electrode, for example, high frequency power,
Since the etching rate and the ion collision energy at that time can be individually controlled, optimum conditions can be selected according to the substrate, and the yield of plasma processing can be improved.

[Brief description of drawings]

1 is a longitudinal sectional view of a sputter etching apparatus according to an embodiment of the present invention, FIG. 2 is a lateral sectional view of a magnet portion of FIG. 1, and FIG.
FIG. 4, FIG. 5, FIG. 5, FIG. 6 and FIG. 7 are vertical cross-sectional views of different sputter etching apparatuses of the present invention.
FIG. 8 and FIG. 9 are characteristic curve diagrams showing examples in which the SiO ₂ film was etched by the device of the present invention, in comparison with comparative examples. In the figure, 1 ... vacuum tank, 2 ... plasma generating means 3 ... vacuum exhausting means, 4 ... gas supply means 5 ... substrate, 6 ... etching electrode 7 ... flange, 8 ... power supply 9 ... End, 10 ... Microwave source 11 ... Waveguide, 12 ... Cavity 13 ... Matching means, 14 ... Conductor rod 15 ... Introduction window, 16 ... Magnet 17 ... Plasma, 18 ... Coil 19 ... Magnetic field lines

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazuhiro Nakajima 2326 Imai, Ome-shi, Tokyo Hitachi, Ltd. Computer Division Device Development Center

Claims (17)

[Claims] 1. A plasma processing electrode on which a substrate is mounted is provided in a vacuum chamber having a gas supply unit and a vacuum exhaust unit, and a plasma generating unit for generating microwaves is introduced into the vacuum chamber facing the substrate. The plasma processing electrode is provided through a window, and the plasma processing electrode is provided with voltage applying means for causing ions in the plasma generated by the plasma generating means to collide with the substrate, and a microwave power source for generating plasma and the plasma processing electrode. In a device comprising a power source for applying a voltage to the substrate and a power source for independently applying a voltage to the substrate, a magnetic field is formed on the substrate so that plasma generated in the space between the substrate and the microwave introduction window is surrounded by magnetic lines of force. A plasma processing apparatus, characterized in that it is provided with a magnetism generating means. 2. The plasma processing apparatus according to claim 1, wherein high frequency power is applied to the plasma processing electrode. 3. The plasma processing according to claim 1 or 2, wherein the plasma generation means by the microwave includes a microwave generation source, a cavity and a microwave introduction window. apparatus. 4. The method according to claim 1, wherein the cavity of the plasma generating means is provided with a matching means, and the cavity is a microwave cavity resonator. Plasma processing equipment. 5. The plasma processing apparatus according to claim 3 or 4, wherein the cavity of said plasma generating means has a coaxial structure. 6. The plasma processing apparatus according to claim 4, wherein the cavity of the plasma generating means is dimensioned such that the microwave mode is axially symmetric. 7. The microwave introduction window is made of an insulating material that absorbs microwaves from the partition walls and cavities that form the vacuum chamber into the vacuum chamber and that absorbs less microwaves. What is claimed is: Claim 1
The plasma processing apparatus according to item 2, item 3, item 3, item 4, item 5, or item 6. 8. The plasma processing apparatus according to claim 7, wherein the insulating material is made of either quartz or ceramics. 9. The plasma processing according to claim 1, wherein the magnetism generating means is a ring magnet magnetized in a radial direction and the polarity of the magnetization is sequentially reversed in the radial direction. apparatus. 10. The magnet as the magnetism generating means is a two-stage ring-shaped magnet in which magnets are arranged on the microwave introduction window side and the etching electrode side, respectively. Plasma processing equipment. 11. The plasma processing apparatus according to claim 10, wherein the two-stage ring-shaped magnet is composed of a coil. 12. The plasma processing apparatus according to claim 11, wherein currents of opposite directions are respectively supplied to the two-stage plasma coils. 13. The plasma processing apparatus according to claim 11, wherein currents in the same direction are applied to the two-stage ring-shaped coils. 14. The plasma processing apparatus according to claim 10, wherein the two-stage ring-shaped magnet is a permanent magnet. 15. The plasma processing apparatus according to claim 14, wherein the ring-shaped permanent magnets are magnetized in the circumferential direction and in mutually opposite directions. 16. The plasma processing apparatus according to claim 14, wherein the ring-shaped permanent magnets are magnetized in the thickness direction and in opposite directions to each other. 17. The plasma processing apparatus according to claim 14, wherein the ring-shaped permanent magnets are magnetized in radial directions and in opposite directions to each other.