JPH10308352A - Plasma treatment and manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make hard to exfolitate a reaction product from vacuum containers by a method wherein after the reaction product adhered to the inner wants or the vacuum containers is removed by a plasma treatment, a prescribed intermediate layer is formed on the inner walls of the containers immediately before the following plasma treatment. SOLUTION: An etching of one lot of silicon wafers 10 ends and after the wafers 10 are carried out from a device, wafers for cleaning use are set on a sampling board 32 instead of the wafers 10. An SiO2 reaction product adhered to the inner walls of a plasma producing chamber 12 and a reaction chamber 14 is removed with an F gas plasma in the chambers 12 and 14. Then, the interior of each of the chambers 12 and 14 is exhausted and after the wafers for cleaning use are replaced for new base silicon wafers, an intermediate layer is formed on the inner wall of each of the chambers 12 and 14 with a Cl2 +O2 reaction gas plasma and immediately after the formation, a process treatment of the following lot of wafers 10 is started. Thereby, at the time of the following plasma treatment, the stress between the material for the intermediate layer and the reaction product adhered to the inner walls of the chambers is reduced and exfolitation of the product adhered to the inner wall of each chamber can be inhibited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing technique for performing processes such as etching and thin film formation in a process of manufacturing electronic parts and semiconductor elements by using plasma.

[0002]

2. Description of the Related Art In a plasma processing apparatus, a microwave is introduced into a vacuum vessel containing a trace amount of a reaction gas, and a gas discharge is generated in the vacuum vessel to generate plasma.
By irradiating the surface of the sample substrate with the plasma, processes such as etching and thin film formation are performed. Such a plasma processing apparatus is being studied as being indispensable for manufacturing a highly integrated semiconductor device. In particular, an ECR plasma processing apparatus using electron cyclotron resonance (ECR) for exciting plasma is regarded as promising as an apparatus capable of generating highly active plasma under a low gas pressure region.

Incidentally, etching of a semiconductor substrate and CV
When a plasma treatment such as D (chemical vapor deposition) is performed, a reaction product adheres to the inner wall of the vacuum vessel where the treatment is performed. Since such reaction products cause particles, they need to be removed periodically. Therefore, conventionally, the deposits on the inner wall of the vacuum vessel have been removed by dry etching or wet cleaning.

[0004]

However, even if the reaction product adhered to the inner wall of the vacuum vessel is removed by the cleaning process, the reaction product adheres again when the plasma process is started. The reaction product adhering to the inner wall of the vacuum vessel in a thin film form is separated by stress caused by a difference in physical properties from the material of the inner wall of the vacuum vessel, and generates particles. As a result, the particles adhere to a sample to be processed such as a wafer, thereby deteriorating the quality of the plasma processing, and lowering the yield of the finally manufactured semiconductor device. On the other hand, if the frequency of cleaning is increased so as not to deposit the reaction products attached to the inner wall of the vacuum vessel, the operation rate of the plasma processing apparatus is reduced, and the working efficiency of the entire semiconductor manufacturing process is reduced.

The present invention has been made in view of the above situation, and has as its first object to provide a plasma processing method capable of improving the plasma processing quality.

It is a second object of the present invention to provide a method of manufacturing a semiconductor device which contributes to the improvement of the quality of a semiconductor device to be manufactured by improving the plasma processing quality.

[0007]

In order to solve the above-mentioned problems, after removing a reaction product attached to the inner wall of the vacuum vessel (12, 14) by plasma treatment, the vacuum vessel (1) is removed.
A predetermined intermediate layer (buffer layer) is formed on the inner wall of (2, 14). Preferably, the intermediate layer is formed immediately before the next plasma treatment.

For example, when the present invention is applied to an etching process of etching a Si-based film formed on a sample (10) by plasma using Cl ₂ + O ₂ -based gas, a vacuum is applied by the etching process. Container (12, 1
4) SiO ₂ -based reaction products attached to the inner wall are removed using an F-based gas. Thereafter, an intermediate layer is formed on the inner wall of the vacuum vessel (12, 14) using a Cl ₂ + O ₂ gas.

[0009]

In the present invention as described above, the vacuum vessel (1)
Since the intermediate layer (buffer layer) is formed on the inner wall of the vacuum vessel (12, 14) after removing the deposits on the inner wall of (2, 14), the reaction products adhered in the next plasma treatment The stress applied to the film is reduced. That is,
Since the material of the intermediate layer formed on the inner wall of the vacuum vessel and the physical properties of the reaction product in the form of a thin film adhered thereto are close to each other, the stress applied to the film of the reaction product is reduced due to the difference in the physical properties of the two. As a result, the reaction products adhered to the inner walls of the vacuum vessels (12, 14) are less likely to be peeled off, the generation of particles can be suppressed, and the plasma processing quality can be improved.

Further, if an intermediate layer is formed on the inner wall of the vacuum vessel (12, 14) immediately before the next plasma processing, there is an advantage that the temperature state in the next plasma processing is stabilized. That is, when forming the intermediate layer, the vacuum vessel (1
2, 14) is warmed to some extent, and immediately after that, when the processing of the sample (10) is started, the vacuum container (1) is heated.
The temperature in 2,14) does not rise sharply. As a result, it is possible to further reduce the stress applied to the reaction product film attached to the inner wall of the vacuum vessel (12, 14).

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to examples. In the present embodiment, the technical idea of the present invention is applied to plasma processing of a silicon wafer which forms a part of a semiconductor device manufacturing process.

[0012]

FIG. 1 shows a configuration of a plasma processing apparatus according to an embodiment of the present invention. The plasma processing apparatus of the present embodiment includes:
A predetermined plasma process such as etching is performed on the silicon wafer 10 having a diameter of 300 mm. The apparatus includes a hollow cylindrical plasma generation chamber 12 for generating plasma, and a reaction chamber 14 communicating with the plasma generation chamber 12. The sample processed by this device has a diameter of 3
In addition to the silicon wafer 10 of 00 mm,
Various kinds of samples, such as a wafer of m and a glass substrate for LCD, can be targeted. In the present embodiment, the silicon wafer 10 is processed in units of, for example, 25 lots.

A circular waveguide 16 connected to a microwave oscillator (not shown) such as a magnetron is connected to the upper part of the plasma generation chamber 12. The microwave (2.45 GHz) generated by the microwave oscillator is guided to the plasma generation chamber 12 via the circular waveguide 16. Note that the inner walls of the plasma generation chamber 12 and the reaction chamber 14 are covered with a deposition-preventing plate made of quartz.

A microwave introducing window 20 made of a microwave transmitting material such as quartz glass is arranged between the circular waveguide 16 and the plasma generation chamber 12. The microwave introduction window 20 is designed to hermetically seal the plasma generation chamber 12. Outside the plasma generation chamber 12,
Three-stage main coils 22, 24, and 26, which include a connection portion of the circular waveguide 16 and surround them concentrically, are arranged. Also, below the main coils 22, 24, 26,
One-stage sub-coil 28 is arranged. The main coils 22, 24, 26 and the sub-coils 28 receive a necessary current from the current supply unit 40, apply an axial magnetic field having a magnetic flux density of 875 gauss to the plasma generation chamber 12, and cause an ECR phenomenon. It has become.

A reaction chamber 14 communicating with the plasma generation chamber 12
Inside, a sample stage 32 for holding the silicon wafer 10 by fixing means such as electrostatic attraction is provided. In addition, the plasma generation chamber 12 and the reaction chamber 1
An exhaust pipe 34 for exhausting the fourth gas is provided, and the plasma generation chamber 12 and the reaction chamber 14 can be maintained in a high vacuum state by evacuation from the exhaust pipe 34. The reaction chamber 14 is provided with a gas supply pipe 36 for supplying a reaction gas required for plasma generation. Although not shown, a coolant path is formed around the plasma generation chamber 12, and the plasma generation chamber 12 is cooled by cooling water (coolant) circulating through the coolant path.

In the apparatus shown in FIG. 1, a high-frequency power supply 48 having one end grounded is connected to the sample table 32,
By applying RF power to the sample stage 32, a chemical reaction occurring near the surface of the silicon wafer 10 can be promoted. This makes it possible to improve the efficiency of plasma processing, such as improving the film formation rate of a thin film.

Next, the overall operation of this embodiment will be described.
The polysilicon formed on the silicon wafer 10 (Poly-
An example of etching of a Si) film will be described with reference to FIG. First, the silicon wafer 10 to be processed is set on the sample stage 32. Thereafter, the internal pressures of the plasma generation chamber 12 and the reaction chamber 14 are reduced to a predetermined pressure by evacuation from the exhaust pipe 34. Next, a reaction gas (Cl ₂ + O ₂ ) is supplied from the gas supply pipe 36 into the plasma generation chamber 12 and the reaction chamber 14.
To maintain the internal pressure of the plasma generation chamber 12 and the reaction chamber 14 at about 1 × 10 ⁻³ Torr.

Thereafter, a magnetic field is formed inside the plasma generation chamber 12 by energizing the main coils 22, 24, 26 and the sub-coil 28, and at the same time, a microwave is introduced into the plasma generation chamber 12 through the microwave introduction window 20. .
This microwave has a frequency f = 2.45 GHz (wavelength λ =
(About 12.2 cm) and the power is set to 1000 W. When microwaves are introduced into the plasma generation chamber 12, EC
The reaction gas is resonantly excited on the R surface 100 to generate plasma. The magnetic field formed by the main coils 22, 24, 26 and the sub-coil 28 is a divergent magnetic field in which the magnetic flux density decreases toward the reaction chamber 14 side. As a result, the surface of the silicon wafer 10 on the sample stage 32 is irradiated to the surface of the silicon wafer 10 to etch the polysilicon film. Such processing is performed for one lot (25
S) during the operation on the silicon wafer 10
The iO ₂ -based reaction products adhere to the inner walls of the plasma generation chamber 12 and the reaction chamber 14.

When etching of all the silicon wafers 10 in one lot (25) is completed, the plasma generation chamber 12
Then, the cleaning operation of the reaction chamber 14 is started. The cleaning operation includes a cleaning step (STEP 1) for removing a reaction product attached to the inner walls of the plasma generation chamber 12 and the reaction chamber 14.
A seasoning step (STEP 2) of forming an intermediate layer (buffer layer) on the inner wall. First, the last silicon wafer 10 of the processed lot is unloaded from the apparatus, and a bare silicon cleaning wafer is set on the sample table 32 instead. Next, an F-based gas (SF ₆ , CF ₄ , NF _3, etc.) is introduced as a reaction gas into the plasma generation chamber 12 and the reaction chamber 14 from the gas supply pipe 36 at a flow rate of about 120 sccm. Is maintained at about 3.0 × 10 ⁻³ Torr.

Next, at the same time when the main coils 22, 24 and 26 are energized, about 18
A microwave having a power of 00 W is introduced into the plasma generation chamber 12. Further, an RF bias is applied to the sample stage 32 to prevent the reaction products from re-adhering to the cleaning wafer.

Under the above-described conditions, for example, an etching process is performed for about 13 minutes, so that the S
The iO ₂ -based reaction product is removed. If the time for such a cleaning operation is not set to a fixed time, the end of the cleaning is detected using a predetermined end point detector. For example, the plasma generation chamber 1
The completion of the removal of the reaction product is detected by observing the light emission state of F (fluorine) in the reaction chamber 2 and the reaction chamber 14. That is, while the reactive product remains in the vacuum vessel, the F, which is an etching species, is absorbed by the etching of the reaction product, so that the luminescence intensity of F decreases. On the other hand, when the reaction product disappears and cleaning is completed, the luminescence intensity of F in the vacuum vessel increases. Alternatively, by changing the pressure in the plasma generation chamber 12 and the reaction chamber 14,
The completion of removal of the reaction product is detected.

Next, when the above cleaning operation is completed, so-called seasoning for forming an intermediate layer (buffer layer) on the inner wall of the reaction chamber 14 is performed. First, the plasma generation chamber 12 and the reaction chamber 14 are evacuated, and the bare silicon wafer used for cleaning is replaced with a new bare silicon wafer. 85sccm as reaction gas in
Of Cl ₂ + O ₂ gas is introduced in 15 sccm, maintaining the internal pressure of the plasma generation chamber 12 and reaction chamber 14 around 1 × 10 ^-3 Torr. Next, about 1400 through the microwave introduction window 20.
At the same time as introducing a microwave having a power of W into the plasma generation chamber 12, the main coils 22, 24 and 26 and the sub coil 28 are energized.

Under the conditions described above, etching is performed for about 2 minutes to form an intermediate layer (buffer layer) on the inner walls of the plasma generation chamber 12 and the reaction chamber 14. Then, immediately after that, the process processing of the silicon wafer 10 of the next lot is started. Since the intermediate layer is formed on the inner walls of the plasma generation chamber 12 and the reaction chamber 14, the stress applied to the film of the reaction product adhered in the next plasma processing is reduced. That is, the material of the intermediate layer formed on the inner walls of the plasma generation chamber 12 and the reaction chamber 14 and the physical properties of the thin film-like reaction product adhered thereto are close to each other, and the stress caused by the difference in the physical properties of the two is reduced. As a result, the reaction products adhering to the inner walls of the plasma generation chamber 12 and the reaction chamber 14 are less likely to be separated, and the generation of particles can be suppressed, and the plasma processing quality can be improved.

Further, immediately after the formation of the intermediate layer on the inner wall of the reaction chamber 14, by starting the next process, the temperature state of the plasma generation chamber 12 and the reaction chamber 14 is stabilized. That is, since the plasma generation chamber 12 and the reaction chamber 14 are heated to some extent when the intermediate layer is formed, the temperature in the plasma generation chamber 12 and the reaction chamber 14 rapidly increases when the process of the silicon wafer 10 is started immediately thereafter. It will not rise. Thereby, the stress applied to the film of the reaction product adhered to the inner walls of the plasma generation chamber 12 and the reaction chamber 14 can be kept even lower. As a result, generation of particles in the plasma generation chamber 12 and the reaction chamber 14 can be suppressed, plasma processing quality can be improved, and the quality of a semiconductor device as a final product can be stabilized. Become.

In the above embodiment, the SiO ₂ -based reaction product adhered to the inner wall of the reaction chamber 14 is removed in the etching process of the polysilicon film formed on the silicon wafer 10. Also, a-
It goes without saying that the present invention can be applied to the removal of reaction products generated in the etching process of Si, WSi-based, and TiSi-based films. Further, the frequency of the cleaning operation is not limited to the case where the cleaning operation is performed between the processing of lots of 25 sheets, and the interval can be changed as necessary.

Next, an experimental example for showing the operation and effect of the present invention will be described with reference to FIGS. As shown in FIG. 3, this experiment was performed in a format for comparing the case where the method according to the present invention was adopted (A) with the case where the conventional method was adopted (B). That is, in the method (A) of the present invention, cleaning for eight minutes (STEP 1) and seasoning for two minutes (STEP 2) are performed between lots of wafer processing. On the other hand, in the method of the comparative example (conventional), the cleaning (S
Only TEP1) is performed. In the process of this experiment, a 3000 ° polysilicon film formed on a 200 mm diameter silicon wafer was
% Overetch. FIGS. 3A and 3B
Each of the steps shown in (1) is defined as 1 RUN (cycle) and 3 RUNs
It was repeated every time.

FIG. 4 shows the working conditions of cleaning (STEP 1) and seasoning (STEP 2) of the present invention and the comparative example. In the cleaning operation (STEP 1), SF ₆ of 120 sccm was used as a reaction gas, the pressure in the plasma chamber 12 and the reaction chamber 14 was set to 3 × 10 ⁻³ Torr, and microwaves of 1800 W were used for the sample stage 32. Applies a 70 W RF bias. Further, by using a bare silicon wafer as a cleaning wafer and controlling the current values of the coils 22, 24, 26, and 28, the distance (L) from the ECR surface 100 to the wafer is reduced to 28.
Set to 0 mm. On the other hand, seasoning work (STEP
In 2), 85 sccm of Cl ₂ and 1
The pressure in the plasma chamber 12 and the reaction chamber 14 is set to 1 × 10 ⁻³ Torr using O ₂ of 5 sccm, and a microwave bias of 1400 W is used, and an RF bias of 50 W is applied to the sample stage 32. Further, a bare silicon wafer is used as a cleaning wafer, and coils 22, 24, 26, 2 are used.
By controlling the current value of No. 8, the distance (L) from the ECR surface 100 to the wafer is set to 390 mm. In the cleaning operation (STEP 1), the wafer 1
The reason why the distance (L) to 0 is reduced is that the cleaning speed in the lower part of the reaction chamber 14 and in the vicinity of the sample table 32 is improved.

FIG. 5 shows the deposition rate of the reaction product deposited on each position of the inner walls of the plasma chamber 12 and the reaction chamber 14 in the seasoning step according to the method (A) of the present invention. The deposition rate of the reaction product is measured by changing the distance h from the wafer. In addition, since the inner walls of the plasma chamber 12 and the reaction chamber 14 are covered with a quartz deposition-preventing plate, the reaction products actually adhere to the deposition-preventing plate. The reaction product thus attached becomes an intermediate layer (buffer layer).

FIG. 6 shows the number of particles detected in the plasma chamber 12 and the reaction chamber 14 in the method (A) according to the present invention, and the number of particles detected in the method (B) in the comparative example. Is shown. The particles are 0.2μ
The measurement was performed for the second, ninth, eighteenth, and twenty-fifth wafers during the wafer processing for objects having a size of m or more. In addition, such particle detection is performed by three lot processing of wafers (RUN # 1, #RUN).
2, # 3). As can be seen from the figure, the number of particles is clearly smaller when the method (A) of the present invention is employed. In particular, the difference in effect from the method (B) of the comparative example is remarkable in the latter half when the number of processed wafers increases. That is, in the method (A) of the present invention, the change in the number of particles is small from the second to the 25th, but in the method (B) of the comparative example, the number of processed wafers increases. The number of particles has increased rapidly in the latter half of the year.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments and does not depart from the gist of the technical idea of the present invention shown in the claims. Various changes are possible within the scope.

[0031]

As described above, according to the present invention,
After removing the reaction products adhered to the inner walls of the vacuum vessels (12, 14), an intermediate layer (buffer layer) is formed on the inner walls of the vacuum vessels (12, 14). The stress applied to the reaction product film is reduced. For this reason, the reaction products adhered to the inner walls of the vacuum vessels (12, 14) are less likely to be peeled off, the generation of particles can be suppressed, and the plasma processing quality can be improved. As a result, it is possible to improve the quality of a semiconductor device manufactured through the above-described plasma processing process. Here, as a semiconductor device,
It includes a semiconductor element itself such as a transistor, and a completed semiconductor device (IC, LSI) such as a RAM.

[Brief description of the drawings]

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

FIG. 2 is a flowchart showing an operation of a cleaning operation in a vacuum vessel, which is a main part of the embodiment of the present invention.

FIG. 3 is a simplified flowchart showing the steps of an experimental example for explaining the effects of the present invention, wherein (A) shows the method of the present invention and (B) shows the method of the comparative example.

FIG. 4 is an explanatory view (table) showing operating conditions of a cleaning step and a seasoning step in the experimental example shown in FIG. 3;
It is.

FIG. 5 is an explanatory diagram (table) showing an attachment rate of a reaction product attached to an inner wall of the vacuum vessel in a seasoning step of the experimental example shown in FIG. 4;

FIG. 6 is a table showing the effects of the experimental examples shown in FIGS. 3 to 5, and shows the number of particles generated by the method (A) of the present invention and the method (B) of the comparative example.

[Explanation of symbols]

 10 silicon wafer (sample) 12 plasma generation chamber (vacuum vessel) 14 reaction chamber (vacuum vessel)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/31 H05H 1/46 C H05H 1/46 H01L 21/302 N

Claims (14)

[Claims] 1. A plasma processing method for performing a predetermined plasma processing on a sample placed in a vacuum vessel, a first step of removing a reaction product attached to an inner wall of the vacuum vessel by the plasma processing; Forming a predetermined intermediate layer on the inner wall of the vacuum vessel after the first step;
And a plasma processing method. Wherein said plasma treatment is an etching process for etching a film of Si-based formed on the sample by plasma using Cl ₂ + O ₂ base gas, the in the second step, Cl ₂ + O _2. The plasma processing method according to claim 1, wherein an intermediate layer is formed on an inner wall of the vacuum vessel by a process using a _two- system gas. 3. The method according to claim 1, wherein in the first step, SiO ₂ -based reaction products adhered to the inner wall of the vacuum vessel by the etching process are removed by a process using an F-based gas. 3. The plasma processing method according to 2. 4. The method according to claim 3, wherein in the first step, the completion of the removal of the SiO ₂ -based reaction product is detected based on the emission state of the F element in the vacuum vessel. The plasma processing method as described above. 5. The method according to claim 1, wherein in the first step, completion of removal of the SiO ₂ -based reaction product is detected based on a pressure change in the vacuum vessel.
4. The plasma processing method according to 2 or 3. 6. The plasma processing method according to claim 1, wherein at least the second step is performed immediately before the next plasma processing. 7. The method according to claim 1, wherein the processing of the sample is performed in units of a plurality of lots, and the first step and the second step are performed immediately before each lot processing. Plasma processing method. 8. A method for manufacturing a semiconductor device including a plasma processing step of performing a predetermined plasma processing on a semiconductor substrate disposed in a vacuum chamber, wherein a reaction product adhered to an inner wall of the vacuum chamber by the plasma processing. A second step of forming a predetermined intermediate layer on the inner wall of the vacuum vessel after the first step.
And a method of manufacturing a semiconductor device. Wherein said plasma treatment, said a etch process for etching by plasma using membrane Cl ₂ + O ₂ based gas Si system formed in a semiconductor substrate, in the second step, Cl ₂ 9. The method for manufacturing a semiconductor device according to claim 8, wherein an intermediate layer is formed on an inner wall of the vacuum vessel by a process using a + O ₂ -based gas. 10. In the first step, SiO ₂ adhered to the inner wall of the vacuum vessel by the etching process.
10. The method of manufacturing a semiconductor device according to claim 9, wherein a reaction product of the system is removed by a treatment using an F-based gas. 11. The method according to claim 10, wherein in the first step, completion of removal of the SiO ₂ -based reaction product is detected based on a light emission state of the F element in the vacuum vessel. The manufacturing method of the semiconductor device described in the above. 12. The method according to claim 8, wherein in the first step, completion of removal of the SiO ₂ -based reaction product is detected based on a change in pressure in the vacuum vessel. 13. The method for manufacturing a semiconductor device according to item 5. 13. The method according to claim 8, wherein at least the second step is performed immediately before the next plasma processing. 14. The method according to claim 8, wherein the processing of the semiconductor substrate is performed in units of a plurality of lots, and the first step and the second step are performed immediately before each lot processing. The manufacturing method of the semiconductor device described in the above.