JPH04176868A - Surface protecting method - Google Patents

Abstract

PURPOSE:To prevent the surfaces of various materials after dry etching from being oxidized by dry-etching these surfaces by the plasma of reactive gas and thereafter treating them by the plasma of gaseous carbon compd. and forming a polymer film on these surfaces. CONSTITUTION:When dry etching treatment is performed on the surface of material such as single crystalline Si, polycrystalline Si, Si3N4, Al, Mo, WSi2, MoSi2, TiSi2, W and TaSi2 and thereafter this material is allowed to stand, an oxidative film is naturally formed on the etched surface. Therefor in order to prevent it, a polymer film is formed by the plasma of gaseous carbon-based compd. In this case, a high frequency discharge parallel plane type plasma etching device, etc., are used. As a gaseous raw material, CF4, CHF3, CClF3, CCl4, CHClF2, and gas contg. the other carbon are used. Plasma treatment of the gas is performed at <=-60 deg.C and a polymer film is formed on the etched surface. Thereby an oxidative film is prevented from being naturally formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface protection method for preventing oxidation of the surface of a material after dry etching.

[Conventional technology]

Conventionally, there has been no means to proactively prevent the formation of a natural oxide film on the surface of a material after dry etching, and the oxide film has been removed by cleaning at important points in the manufacturing process of semiconductor highly integrated circuits.

[Problem to be solved by the invention]

In the above-mentioned prior art, a natural oxide film of about 10 to 30 layers was formed on the surface of the material after dry etching in the atmosphere.

One object of the present invention is to prevent the formation of a natural oxide film on the surface of a material after dry etching.

Another object of the present invention is to accomplish the above objects without contaminating the etching chamber with a gas plasma of carbon-containing molecules.

[Means to solve the problem]

The above object is achieved by covering the surface of the material after dry etching with a film of a carbon-containing polymer. A polymer film is formed on the material surface by irradiating the material surface with a gas plasma of carbon-containing molecules without moving the wafer from the etching chamber after tri-etching. At that time, the wafer was cooled to below room temperature, and a polymer film was deposited on the room temperature surface, but no polymer film was deposited on the low temperature surface.If the material surface was irradiated with a gas plasma of carbon-containing molecules, the material surface could be cooled to a low temperature. A polymer film is formed only on the surface of the material, and it is possible to prevent polymer from depositing and contaminating other parts of the etching chamber. Furthermore, irradiation with the gas plasma of the carbon-containing molecules described above is coupled to the etching chamber, which is isolated from the etching chamber by a vacuum valve, and carried out in a separate processing chamber in which the wafer can be transferred from the etching chamber in an evacuated atmosphere. The method can prevent contamination of the etching chamber.

To remove the polymer film, use NH3,
This is done using N2 or H2 gas plasma. Thereby, oxidation of the material surface can be prevented.

[Effect]

The operation of the present invention will be explained using as an example a method of preventing surface oxidation by irradiating the wafer surface with CF4, CHF, and gas plasma to deposit a polymer film after dry etching single crystal Si.

After dry etching, single crystal Si has a concentration of 10 to 3 in the atmosphere.
A natural oxide film of approximately 0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000 type type type type type type type type type type type type form, type has been removed has been removed. Oxidation of the Si surface can be prevented. The fact that the Si surface on which the polymer film is deposited is difficult to oxidize even in the atmosphere is due to the fact that
photoelectron spectroscopy
) As a result of the analysis, it was found that the Si surface on which the polymer was deposited had extremely fewer electrons from oxygen atoms than the Si surface on which no polymer was deposited.

The deposition rate of a polymer film by carbon-based gas plasma depends on the surface temperature. For example, in the case of CF4 and CHF3 gas plasma using a high-frequency discharge parallel plate plasma etching apparatus, it was found from experiments that the deposition rate on low-temperature surfaces increases as shown in FIG. CHF3
For gas plasma, RF power is 400W and gas pressure is 100W.
Under mTorr conditions, the deposition rate is about 30 nm/min at 20°C, but increases to about 140 nm/min at -10.0°C. In addition, in the case of CF and gas plasma, deposition does not occur at 20°C under the same discharge conditions, but when the wafer temperature decreases to -80°C or less, deposition occurs, and at -100°C.
The deposition rate is about 10 nm/min.

From this result, when using a gas plasma that causes deposition even at room temperature, such as CHF3 gas plasma, if the wafer is cooled to a low temperature, the same deposition rate can be obtained with a lower discharge gas pressure, and the polymer film thickness sufficient to prevent oxide film can be obtained. Therefore, contamination caused by polymer deposition in other parts of the etching chamber can be reduced. Furthermore, when using a gas plasma such as CF4 gas plasma that does not deposit a polymer film on the surface at room temperature, if the wafer is cooled to a temperature at which deposition occurs, the polymer film will be deposited only on the wafer surface and will not be deposited on other parts of the etching chamber. It is possible to prevent contamination caused by polymer build-up on the surface.

〔Example〕

Hereinafter, the present invention will be explained in detail using Examples.

Example 1 An example in which the present invention is implemented in a high-frequency discharge parallel plate type plasma etching apparatus will be described.

In the etching apparatus used in this example, a cooling water tank is connected to the lower part of the sample stage, and the temperature of the sample can be adjusted in a temperature range of 0° C. or higher using the cooling water and a heater built into the sample stage. 13.56MHz from the high frequency power supply to the sample stage
A high frequency wave is applied to generate plasma.

After etching polycrystalline Si masked with photoresist using this etching apparatus, the discharge gas was switched to CHF3 and discharge was performed for 1 minute at a pressure of 100 mTorr and RF power of 400 W to form a polymer film on the sample surface. Thereafter, the sample was taken out into the atmosphere and the polymer film thickness was measured. As a result, a 37 nm polymer film was formed on the sample surface. XPS 24 hours after taking the sample out into the atmosphere
The analysis showed that the amount of oxygen atoms on the surface of this sample was about 1720 when it was not protected by a polymer film.
A natural oxidation film prevention effect was observed.

Regarding the gas pressure dependence of the deposition rate of CHF and gas plasma, the results shown in FIG. 2 have been obtained from experiments. 20
In the case of .degree. C., the deposition rate increases in proportion to the gas pressure up to about 40 mTorr, but above 40 mTorr, even if the gas pressure increases, the deposition rate is saturated and does not increase much. 1 at gas pressure 40 m Torr, RF power 400W
When discharged for one minute, a polymer film with a thickness of 32 nm was formed. In this case as well, the effect of preventing natural oxide film was observed.

The discharge gas is CH2F2. C2F,, C,F,, C
, FIl.

C4F engineering. Instead, the surface after dry etching was treated with plasma, but the formation of a polymer film had the effect of preventing a natural oxide film.

If a plasma for forming a polymer is discharged in a water-cooled etching apparatus as in this embodiment, the polymer will be deposited in the etching chamber. Therefore, it is necessary to frequently remove the polymer with oxygen plasma so as not to interfere with etching.

Using this etching apparatus, polycrystalline Si was dry etched at a low temperature of -130° C., and then treated with CHF and gas plasma at an RF power of 400 W and a gas pressure of 10 mTorr.

Example 2 An example carried out using the low temperature reactive ion etching apparatus of the present invention will be described. This apparatus is an improved version of the sample stage of the high-frequency discharge parallel plate plasma etching apparatus used in Example 1 for low-temperature dry etching.
A liquid nitrogen tank is connected to the lower part of the sample stand, and the temperature on the back side of the sample is measured with a thermocouple, and the temperature of the sample can be adjusted to a low temperature below 0°C using liquid nitrogen and a heater built into the sample stand.

Using this etching apparatus, a single crystal Si masked with photoresist is cooled to -130°C to perform low-temperature tri-etching, and then the discharge gas is changed to C while keeping the sample temperature the same.
Switch to HF, pressure 20mTorr, RF power 400
A polymer film was formed on the sample surface by discharging with W for 1 minute. Thereafter, the sample was taken out into the atmosphere, and the polymer film thickness was measured. As a result, a 42 nm polymer film was formed on the sample surface. X 24 hours after the sample was taken out into the atmosphere
PS analysis was conducted and it was confirmed that the coating with the polymer film has a natural oxidation film prevention effect. As shown in Figure 1, CF
(The deposition rate of F3 gas plasma increases as the surface temperature decreases. Therefore, a 42 nm polymer film was deposited on the Si surface, but the amount deposited was small because the other parts of the etching chamber were at room temperature.) Contamination within the etching chamber can be reduced by cooling the sample temperature to a low temperature and depositing a polymer film by plasma polymerization.

After cooling the single-crystal Si masked with photoresist to -130°C and performing low-temperature dry etching, the discharge gas was changed to CF4 and the pressure was 100 m while keeping the sample temperature the same.
Torr, RF power of 400 W was applied for 1 minute to form a polymer film on the sample surface.

Thereafter, the sample was taken out into the atmosphere, and the polymer film thickness was measured. As a result, a 36 nm polymer film was formed on the sample surface. XP 24 hours after removing the sample to the atmosphere
S analysis was conducted and it was confirmed that the coating with the polymer film has a natural oxidation film prevention effect. As shown in Figure 1, CF4
Gas plasmas deposit polymers on low-temperature surfaces even under discharge conditions that do not deposit polymers on room-temperature surfaces.

A 36 nm polymer film was deposited on the Si surface cooled to a low temperature, but no deposition occurred in other parts of the etching chamber because the temperature was at room temperature. If the sample temperature is cooled to a low temperature in this way and the discharge gas and discharge conditions are selected so that no polymer is deposited on the surface at room temperature, a polymer film can be formed on the material surface without contaminating the etching chamber and natural oxidation can be prevented. be able to.

The discharge gas is CH2F2. C2F4. CCQF.

CH, F, C2F5. c3Fs, C4F engineering. .

CHClF2. CCQ,,C2CQ2F2゜C2CβF
,,C2CQ2F,C2HCΩ2F3゜CHCflF2
．． C2CQ, 3F3. C2CQ2F,.

C2HCΩF4. CCQ F3. I replaced it with CCQ2F2 and plasma treated the surface after dry etching, but
The formation of a polymer film had the effect of preventing a natural oxide film.

The material is Si3N4. AQ, W, Mo, WSi□.

Mo S izt T i S i2. T a Si
As a result of forming a polymer film on the surface using 02F4 gas plasma instead of Z, there was a natural oxidation prevention effect.

When performing dry etching, there is an appropriate temperature for anisotropic processing depending on the combination of the material to be etched and the etching gas. For example, when processing 81 with SF and gas, -113
SF again at around 0℃! -6 when processing W with gas
The wafer temperature may be set to about 0°C. When forming a polymer using carbon-based gas plasma after this low-temperature dry etching, time can be saved if the polymer is formed without changing the wafer temperature. Therefore, the discharge gas may be selected depending on the surface temperature so as to obtain an appropriate deposition rate. For example, -130
CF when forming a polymer after processing Si at ℃
When forming a polymer after processing W at -60° C. using gas plasma, it is desirable to use CHF gas plasma because the deposition rate is extremely low with CF4 gas plasma.

Example 3 In an apparatus in which a processing chamber for forming a polymer film is combined with a low temperature microwave plasma etching apparatus.

An example of implementing the present invention will be described.

FIG. 3 is a schematic diagram of the low temperature microwave plasma etching apparatus and surface protection apparatus according to the present invention, viewed from the side. First, an overview of the single-line etching apparatus will be explained. The apparatus of this embodiment is equipped with a load lock mechanism, and the etching chamber 2 and wafer exchange chamber 3 are separated by a gate valve 4, and each is independently evacuated through an exhaust port 5. In the etching chamber, a sample stage 6 and a liquid nitrogen tank 7 connected to the bottom surface of the sample stage 6 are installed in the etching chamber 2 with an insulator 8 in between, as shown in FIG.

The wafer 1 is transferred from the wafer exchange chamber 3 to the etching chamber 2 by a transfer system 9. The sample stage 6 and the liquid nitrogen tank 7 are raised and lowered by the specimen stage up and down mechanism 10, the wafer up and down pins 11 are raised and lowered by the wafer up and down pin up and down mechanism 12, and the wafer 1 is transferred. Fix it on the sample stage 6. The wafer 1 is cooled by liquid nitrogen 16 supplied from the liquid nitrogen capacity 14 to the liquid nitrogen tank 7 through the liquid nitrogen supply pipe 15 . Liquid nitrogen tank 7
A liquid nitrogen outlet 17 is attached to the.

Overflowing liquid nitrogen and evaporated nitrogen gas exit the tank from here. The temperature of the wafer 1 is measured by a temperature sensor 18 and a thermometer 19 installed on the sample stage 6. The wafer temperature is controlled by adjusting the output voltage of the power source 22 of the electric heater 21 using the temperature control system 20 and by adjusting the amount of liquid nitrogen in the liquid nitrogen tank 7 using the liquid nitrogen supply control system 23. To generate plasma, discharge gas is introduced into the etching chamber 2 through the discharge gas inlet 24, and microwaves excited by the magnetron 25 are guided into the etching chamber 8 through the waveguide 26 to generate plasma 2F. The magnet 28 functions to increase excitation efficiency through electron cyclotron resonance. R on the sample stage 6
A high frequency of 13.56 MHz is applied by the F power supply 29.

A processing chamber 30 is connected to the etching chamber 2 through a gate valve 4', and is evacuated through an exhaust port 5'. In the processing chamber 30, a sample stage 6' and a refrigerant tank 31 connected to the bottom surface thereof are connected to the processing chamber 30 via an insulator 8'.
It is installed in

The wafer 1 that has been dry etched in the etching chamber 2 is transported to a processing chamber 30 by a transport system 9.

The wafer up/down pin 1 is moved by the wafer up/down pin up/down mechanism 12'.
1' is moved up and down, and the wafer 1 is transferred and fixed to the sample stage 6'. The wafer 1 is transferred from the refrigerant circulator 32 to the refrigerant supply pipe 3
It is cooled by the refrigerant 34 supplied to the refrigerant tank 31 through the refrigerant 3 . The temperature of the wafer 1 is measured by a temperature sensor 18' and a thermometer 19' installed on the sample stage 6. The wafer temperature is controlled by adjusting the output voltage of the power source 22' of the electric heater 21' by the temperature control system 20', and by adjusting the amount of refrigerant in the refrigerant tank 31 by the refrigerant #i ring 32.

The sample stage 6' is equipped with 13.56M H by the RF power supply 29'.
A high frequency wave of z is applied. A discharge gas supply port 24' is attached to the center of the counter electrode 35, and a polymer film is formed on the surface of the wafer 1 by plasma 27' generated by high frequency discharge.

The wafer 1 is transported to the wafer exchange chamber 3 by the transport system 9,
After being heated to room temperature by the heating lamp 36.

taken out into the atmosphere.

The surface temperature of the material dry-etched in the etching chamber 2 is set at -100°C in the processing chamber 30, and CF4 is applied.
2 at gas pressure 100 mTorr, RF power 400W
A polymer film was formed by plasma treatment for minutes. As a result, a polymer film with a thickness of 20 nm was formed, which had an effect of preventing surface oxidation.

In this example apparatus, the etching chamber was not contaminated even when using CHF or gas plasma, which deposits polymer on the surface at room temperature.

A similar effect was obtained even when the refrigerant in the processing chamber 30 was changed to liquid nitrogen.

〔Effect of the invention〕

According to the present invention, oxidation of the material surface after dry etching could be prevented.

[Brief explanation of drawings]

Figure 1 shows the surface temperature dependence of the deposition rate of CF and CHF3 gas plasma on the Si surface, and Figure 2 shows the dependence of the deposition rate on the Si surface of CHF3 gas plasma.
FIG. 3 is a diagram showing the gas pressure dependence of the deposition rate of F3 gas plasma on the Si surface, and is a schematic diagram of an example apparatus according to the present invention. 1... Sample to be etched, 2... Etching chamber, 3
...Wafer exchange room, 4...Gate valve, 5...
Exhaust port, 6... Sample stand, 7... Liquid nitrogen tank, 8
... Insulator, 9 ... Transport system, 10 ... Sample table vertical mechanism, 11 ... Wafer top and bottom pin, 12 ... Wafer top and bottom pin vertical mechanism, 13 ... Wafer holder, 14 ...・Liquid nitrogen container, 15...Liquid nitrogen supply pipe, 16...Liquid nitrogen, 17...Liquid nitrogen outlet, 18...Sensor, 19...Thermometer, 2°...Temperature control Series, 21・
...Electric heater, 22...Heater power supply 23...
Liquid nitrogen supply control system, 24...discharge gas inlet, 25
... Magnetron, 26... Waveguide, 27... Plasma, 28... Magnet, 29... RF power supply,
30... Processing chamber 31... Refrigerant tank, 32... Refrigerant circulator, 33... Refrigerant supply pipe, 34... Refrigerant, 3
5Figure 1 Figure 2 Portion 3 ■

Claims (1)

[Claims] 1. The method is characterized by comprising the steps of: dry etching the surface of the material with reactive gas plasma; and forming a polymer film on the surface of the material by treating it with gas plasma of carbon-containing molecules. surface protection method. 2. The surface protection method according to claim 1, wherein the formation of the polymer film is performed by cooling the material to a temperature of -60°C or lower. 3. Dry etching the surface of the material using reactive gas plasma in a first chamber; transporting the material in vacuum from the first chamber to a second chamber;
A method for protecting a surface, comprising the step of forming a polymer film on the surface of the material by treating it with a gas plasma of molecules containing carbon in a chamber of the material. 4. In the surface protection method according to claims 1 and 3, the carbon-containing molecules include hydrogen, fluorine,
A surface protection method characterized by containing any one of bromine, chlorine, oxygen, and nitrogen. 5. In the surface protection method according to claims 1 and 3, the carbon-containing molecules are CF_4, CHF_3, CH
_2F_2, CH_3F, C_2F_4, C_2F_6
, C_3F_■, C_4F_1_0, CClF_3, C
HClF_2, CCl_4, C_2Cl_2F_2, C
_2ClF_5, CHCl_2F, C_2HCl_2F
_3, CHClF_2, C_2Cl_3F_3, C_2
A surface protection method characterized by being Cl_2F_4, C_2HClF_4, CClF_3 or CCl_2F_2. 6. In the surface protection method according to claims 1 and 3, the material is single crystal Si, single crystal Si, Si_3N_
4, Al, Mo, WSi_2, MoSi_2, TiSi
_2, W or TaSi_2.