JPH0748482B2 - Method for cleaning substrate surface after removal of oxide film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to, for example, the surface of a silicon wafer, the surface of a polysilicon film, the surface of an alumophus silicon film (these surfaces are collectively referred to as “silinco layer” hereinafter). The native oxide film formed on the surface) is removed from the wafer surface by using a halide such as hydrogen fluoride (HF), and various silicon insulating films formed on the surface of the silicon layer are converted to a halide. The present invention relates to a method of cleaning a substrate surface for removing a halide remaining on the substrate surface after etching or the like.

[Conventional technology]

In the process of manufacturing a semiconductor device, for example, when cleaning or etching an oxide film on the surface of a substrate such as a silicon wafer, or when etching a metal film such as an aluminum film on a substrate, HF, NF ₃ , SF ₆ , ClF ₃ , Cl _{2 and} other halides are often used.

Since all of these halides are used in an active state such as ions and radicals, ionic contamination of halogens such as fluorine and chlorine on the substrate surface at the stage when the etching or cleaning treatment process is completed. Will remain. If the device is formed while leaving the ionic contamination on the substrate surface, it may cause various device defects such as film formation defects and electrical operation defects. Therefore,
The ionic contamination remaining on the substrate surface after the etching or cleaning process needs to be cleaned and removed from the substrate surface.

As a method for removing ionic contamination from the surface of the substrate, a method of cleaning the surface of the substrate with pure water (ultra pure water) has been generally used. Further, for example, in JP-A-62-173720, after the vapor of hydrofluoric acid (hydrofluoric acid) is supplied into the container containing the wafer to wash and remove the natural oxide film on the wafer surface, the same container is used. A method is disclosed in which high-purity water vapor is supplied into the interior of the wafer to wash out the hydrofluoric acid from the surface of the wafer. In addition, UV light (ultraviolet light) irradiation and Ar
A method of removing ionic contamination from the surface of the substrate by a treatment such as (argon) ion sputtering is performed in some cases.

[Problems to be Solved by the Invention]

However, in the above-mentioned conventional method, the Si
If the metal such as (silicon) or aluminum is exposed, there is a problem that an oxide film is secondarily formed easily in the process of removing ionic contamination.

Further, in the case of UV light irradiation or Ar ion sputtering, damage to the silicon wafer is unavoidable, such as device defects.

This invention, compared with the above-mentioned conventional method that was performed to remove the ionic contamination of halogen such as fluorine from the substrate surface after etching or cleaning treatment in the manufacturing process of semiconductor devices, the formation of a secondary oxide film. It is a technical object to provide a cleaning method capable of significantly reducing the amount of ionic contamination from the surface of a substrate to an extremely low level.

[Means for Solving the Problems]

As a means for achieving the above object, the present invention supplies a halide such as hydrogen fluoride to a substrate to etch or clean the surface of the substrate, and then to a surface of the substrate, which is anhydrous and low-valent. The gist of the configuration is that the halide remaining on the substrate surface is removed by supplying alcohol.

In the above structure, anhydrous lower and monohydric alcohol can be supplied to the substrate surface in a vapor state.

[Action]

When alcohol is supplied to the surface of the substrate on which a halide such as hydrogen fluoride remains, hydrogen fluoride is dissolved in the alcohol and solvated by alcohol molecules, and is removed from the surface of the substrate together with the alcohol.

Here, it is known that the presence of both oxygen and water is necessary for the growth of a native oxide film on the surface of a substrate, for example, a silicon wafer (for example, `` Science Technical Report Vol.
89No.111; IEICE technical report P11-12 "Control of Si native oxide film formation", The Institute of Electronics, Information and Communication Engineers 1989.6.26
However, in the method according to the present invention, since anhydrous alcohol is supplied to the substrate and the water content of the system is suppressed to a low level, the conventional method of cleaning the substrate with pure water or steam may be used. In comparison, the occurrence of a secondary oxide film on the substrate surface is significantly reduced.

Further, since alcohol easily creates a reducing atmosphere and has an extremely low oxidizing ability, the surface of the substrate is covered with alcohol to be protected in a layered manner, so that even in a region where silicon or metal is exposed on the surface of the substrate, Secondary oxidation will be prevented more effectively, and contamination by organic substances will be extremely unlikely.

On the other hand, the dissolution of a halide such as hydrogen fluoride HF in water H ₂ O and alcohol ROH is carried out in the following process (J.H. Simmons; Fluorine Chemistry), 1 ,twenty two
5 (1950)).

nH ₂ O + 2HF → (H ₂ O) _n H ⁺ + HF ₂ ⁻ ROH + 2HF → (ROH) H ⁺ + HF ₂ ⁻ Thus, in forming HF ₂ ⁻ , 1 mol of alcohol corresponds to n mol of water. Further, hydrogen fluoride is more easily dissolved in alcohol than water, as can be seen from the fact that the equivalent conductivity of hydrogen fluoride solution such as methanol and ethanol is higher than that of water. For this reason,
According to the cleaning method of the present invention using alcohol,
Ionic contaminants such as fluorine and chlorine are well solvated by alcohol, and the ionic contaminants are removed from the substrate surface with higher efficiency as compared with the conventional cleaning method using pure water or water vapor.

Since a low-grade and monovalent alcohol is used as the alcohol, the alcohol layer formed so as to cover the substrate surface is easily separated from the substrate surface by evacuation or heating at a relatively low temperature. Therefore, there is no need for a special drying step as in the case of using pure water or steam.

Further, when supplying anhydrous lower and monohydric alcohol to the substrate surface in a vapor state, after removing a film such as an oxide film from the substrate surface with a halide,
Anhydrous alcohol may be supplied to the substrate while keeping the substrate in that state. Then, the alcohol vapor supplied to the substrate is promptly discharged from the substrate surface after removing the residual halide on the substrate surface.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an example of a silicon wafer cleaning apparatus for carrying out the method of the present invention. In the figure, a container 12 containing a silicon wafer 10 to be cleaned is formed by using Teflon, and the inside thereof is airtightly isolated from the outside air. The container 12 is provided with a supply port 14 and an exhaust port 16 which are connected to a gas / steam supply pipeline 20 and an exhaust pipeline 22, respectively, and a bypass pipeline 18 is also provided. Although not shown in FIG. 1, a door for loading and unloading the silicon wafer is provided on the side surface of the container 12, but a load lock chamber is provided adjacent to the door, or another door. It is also possible to connect the process device and the transfer line to be in-line.

A supply pipe 20 communicating with the supply port 14 of the container 12 is joined with three pipe lines 24, 26, 28, and anhydrous fluorinated is provided at the end of each pipe line 24, 26, 28. A hydrogen source 30, an alcohol source 32, and a carrier gas, a nitrogen gas source 34, are provided. A branch line 36 of a carrier gas line 28 communicates with the anhydrous hydrogen fluoride gas supply line 24.

Further, the anhydrous hydrogen fluoride gas supply line 24 and the nitrogen gas supply line 28 are respectively connected to the mass flow controllers 38, 40.
Has been inserted. On the other hand, a nitrogen gas supply source 44 is connected via a mass flow controller 46 to a pipeline 42 that is connected to communicate with the alcohol storage tank of the alcohol supply source 32. Can be supplied to the container 12 at different times. Further, temperature controllers 48 and 50 are respectively provided in the supply sources 30 and 32 of anhydrous hydrogen fluoride and alcohol. Then, the supply amounts of the anhydrous hydrogen fluoride gas and the carrier gas (nitrogen) are adjusted by the respective supply pipelines 24,
This is performed by mass flow controllers 38 and 40 provided in 28. Also, the adjustment of the supply amount of alcohol vapor is
The mass flow controller 46 controls the flow rate of nitrogen gas and the temperature of alcohol (liquid) (thus the vapor pressure of alcohol). Also, in order to prevent dew condensation in each supply system of anhydrous hydrogen fluoride gas and alcohol vapor, each supply pipeline 2
4, 26 are kept warm by heat insulating materials 52, 54 as shown by the broken lines.

In this device, as described above, the anhydrous hydrogen fluoride gas and the methanol vapor can be supplied into the container 12 at different times. For example, as shown in (1) of FIG. As shown in the chart, the supply of anhydrous hydrogen fluoride gas and the supply of methanol vapor are started simultaneously, and after cleaning to remove the native oxide film from the substrate surface, the supply of anhydrous hydrogen fluoride gas is stopped. Then, only the methanol vapor is supplied for a predetermined time (for example, 10 to 30 seconds), and then the supply is stopped. As a result, hydrogen fluoride remaining on the surface of the substrate when the cleaning process is completed can be cleaned and removed from the surface of the substrate. In addition, as shown in FIG.
Is stored in the container 12, and after purging with N ₂ gas, first, methanol vapor is introduced into the container 12 for a predetermined time (for example, 10 to
After the lapse of 60 seconds), the anhydrous hydrogen fluoride gas is started to be supplied, and the anhydrous hydrogen fluoride gas and the methanol vapor are simultaneously supplied for a predetermined time to perform the cleaning treatment, and after removing the natural oxide film and the like from the substrate surface, Similarly to the above, it is also possible to stop the supply of anhydrous hydrogen fluoride gas, supply only methanol vapor for a predetermined time (for example, 10 to 30 seconds), and then stop the supply.

Next, using the above cleaning apparatus, the native oxide film on the surface of the silicon wafer is cleaned and removed using hydrogen fluoride, and then the hydrogen fluoride remaining on the wafer surface is further cleaned and removed, and the residual fluorine amount after the cleaning is removed. An example of an experiment in which the cleaning effect is investigated by measuring is described. In this experiment, a phosphorus-doped n-type silicon wafer having a resistivity of 2 to 8 Ω · cm was used, and the silicon wafer was immersed in a H ₂ SO ₄ —H ₂ O ₂ mixed solution for oxidation to be oxidized to a thickness of 13 Å. What formed the film was used as a sample. Also, in the experiment, as cleaning gas / reagent, ultra-high purity anhydrous hydrogen fluoride manufactured by Showa Denko KK, EL grade 50% hydrofluoric acid manufactured by Daikin Industries, Ltd., Nippon Oxygen Co., Ltd. Ultra-high purity nitrogen manufactured by Kanto Chemical Co., Inc. and EL grade methanol manufactured by Kanto Chemical Co., Inc. were used.

First, the cleaning removal of the natural oxide film on the surface of the silicon wafer is
The following two methods were used.

The silicon wafer 10 having an oxide film formed on its surface is loaded into the container 12 of the apparatus shown in FIG. 1 and installed, and the inside of the container 12 is completely sealed, and then the nitrogen gas supply source 34
Further, high-purity N ₂ gas was fed into the container 12 at a flow rate of 15 l / min through the supply pipes 28 and 20, and the inside of the container 12 was purged for 30 seconds. Then, each gas vapor has 100 to 1,000 cc / min (25 ° C) of anhydrous hydrogen fluoride gas and 500 to 5,000 cc / min (25 ° C) of N ₂ gas for buffling to generate methanol vapor.
C.) and nitrogen gas are supplied into the container 12 at respective flow rates of 0 to 5,000 cc / min (25.degree. C.). Under the above conditions, the cleaning treatment was performed for 30 seconds, and after the treatment was completed, the inside of the container 12 was purged with N ₂ gas for 30 seconds.

The silicon wafer 10 having an oxide film formed on its surface was immersed in 1% hydrofluoric acid for 30 seconds to perform a cleaning treatment, and after the treatment was completed, it was blown with N ₂ gas for 30 seconds.

Next, cleaning and removal of residual fluorine (ionic contamination) on the surface of the silicon wafer was performed by the following three methods of the method according to the present invention and two conventional methods for comparison.

i. Place a silicon wafer that has been cleaned with a natural oxide film in the container 12 of the apparatus shown in FIG. 1 and seal the inside of the container 12 with methanol vapor for buffing.
N ₂ gas flow rate of 4,000 to 5,000 cc / min (25 ° C)
It was supplied to the container 12 for 30 seconds. After the cleaning process was completed, N ₂ gas was sent into the container 12 at a flow rate of 15 l / min for 30 seconds to purge the container 12.

ii. The silicon wafer from which the natural oxide film had been cleaned and removed was dipped in running pure water for 30 seconds to perform cleaning, and blown with N ₂ gas for 30 seconds after completion of the cleaning treatment.

iii. Inside the aluminum vacuum container, a silicon wafer was installed after the natural oxide film had been cleaned and removed, and the interior of the vacuum container was evacuated to 10 ^-3 mmHg by a vacuum pump, while a 290 W low-pressure mercury lamp was drawn from above the wafer. Was irradiated with UV light for 10 minutes.

The above two natural oxide film cleaning methods and three residual fluorine cleaning methods i.ii.iii. Are combined to clean and remove the natural oxide film from the surface of the silicon wafer, and then the residual fluorine on the wafer surface is cleaned. The effect of removing fluorine from the wafer surface was evaluated for each removed one. The thickness of the fluorine and oxygen layers on the surface of the silicon wafer is measured by photoelectron spectroscopy (ESCA measurement),
ESCA850 manufactured by Shimadzu Corporation was used as a measuring device. The comparison of the residual amount of each element of fluorine or oxygen is made by dividing the peak area value of the spectrum of each element by the peak area value of the spectrum of Si _{2 P} (F _1S peak area / Si _2P
Peak area or O _1S peak area / Si _2P peak area) was used.

After removing the natural oxide film on the surface of the silicon wafer by exposing the surface of the silicon wafer to anhydrous hydrogen fluoride gas and methanol vapor (the above method), methanol vapor was supplied to the surface of the silicon wafer to wash and remove residual fluorine. When the residual amount of fluorine (ESCA peak area ratio F _1S / Si _2P ) in the case of (i. Above) is 1, the removal method of the natural oxide film on the surface of the silicon wafer is the same (above method), and pure water is used. When the silicon wafer is dipped in and washed (method ii. Above), the residual amount of fluorine is 1.9, and the silicon wafer is UV
The amount of residual fluorine when irradiated with light (method of iii. Above) is
2.3, the residual amount of fluorine when the residual fluorine was not washed was 2.4. Further, after removing the native oxide film on the surface of the wafer by immersing the silicon wafer in hydrofluoric acid (the above method), methanol vapor was supplied to the surface of the silicon wafer to wash and remove the residual fluorine (the above). In the case of i. method), the residual amount of fluorine is 1.7, and similarly, the silicon wafer is immersed in pure water for cleaning (above).
ii. method), the residual fluorine amount is 3.1, and similarly, the residual fluorine amount when the residual fluorine is not washed is 5.5.
Met.

From the above results, it is found that the efficiency of removing fluorine is high when the surface of the silicon wafer is cleaned with methanol vapor after the natural oxide film on the surface of the silicon wafer is cleaned and removed. When the surface of the silicon wafer was washed with methanol vapor after removing the natural oxide film on the surface of the silicon wafer using anhydrous hydrogen fluoride gas and methanol vapor, the residual amount of fluorine was the smallest.

The oxygen concentration (the amount of O in the SiO _2, thus corresponding to the thickness of SiO ₂₎ of the silicon wafer surface after cleaning was measured. As a result, the silicon wafer surface using anhydrous hydrogen fluoride gas and methanol vapor After removing the natural oxide film of the above (the above method), methanol vapor was supplied to the surface of the silicon wafer to wash and remove the residual fluorine (the above method i.), And the amount of oxygen (ESCA peak area ratio O _1S / Si
_2P ), the amount of oxygen when the natural oxide film on the surface of the silicon wafer is removed by the same method (above method), and the silicon wafer is immersed in pure water and washed (method ii. Above). Is 1.9, the amount of oxygen is 1.4 when the silicon wafer is irradiated with UV light (method in iii. Above), and the amount of oxygen is just 0.2 when the N ₂ gas is purged without cleaning the residual fluorine.
It was 9. Further, after removing the native oxide film on the surface of the wafer by immersing the silicon wafer in hydrofluoric acid (the above method), methanol vapor was supplied to the surface of the silicon wafer to wash and remove the residual fluorine (the above). i.
The amount of oxygen in the case of (1) is 1.1, and the amount of oxygen in the case of cleaning by dipping a silicon wafer in pure water (the method of ii. Above) is 2.7, similarly, when the residual fluorine is not cleaned. The amount of oxygen was 1.5.

From the above results, when the surface of the silicon wafer is cleaned by using methanol vapor after cleaning and removing the natural oxide film on the surface of the silicon wafer, the silicon wafer is immersed in pure water or UV is applied to the silicon wafer. Compared with the conventional method of removing fluorine from the silicon wafer surface by irradiating light, the oxygen concentration on the wafer surface can be suppressed to a low level, that is, secondary regrowth of the natural oxide film can be suppressed.

Next, the effect of water present in methanol vapor for fluorine cleaning on the fluorine removal efficiency and the reoxidation of the silicon wafer surface after the cleaning treatment was examined.

Experiments using the apparatus shown in FIG. 1, anhydrous HF-CH ₃ OH
After removing the natural oxide film on the surface of the silicon wafer with the system vapor (the above method), methanol vapor is supplied to the surface of the silicon wafer to wash and remove the residual fluorine (the above method i.). Water was mixed as impurities in various concentrations in methanol for cleaning fluorine. The film thickness of the native oxide film by reoxidation of the silicon wafer surface was measured using an ellipsometer 1 hour and 20 minutes after each cleaning.

As a result, when the ratio of water (steam) to the total amount of methanol vapor and nitrogen gas was 5% or less, the efficiency of removing fluorine was almost unchanged. The natural oxide film thickness on the surface of the silicon wafer after 1 hour and 20 minutes from the cleaning treatment is 4.1Å under the condition that the water content in methanol vapor and nitrogen gas is 0.3% or less.
4.3 under the condition that the water content is 0.3% or more and less than 1.0%
〜4.6Å, 5.3〜5.8Å under the condition that the water content is 1.0% or more and 5.0% or less. From these experimental results, it can be seen that the presence of a small amount of water in the reaction system does not significantly affect the reoxidation of the silicon wafer surface after the cleaning process.

In the above embodiment, the natural oxide film on the surface of the silicon wafer was washed and removed, and then the surface of the silicon wafer was exposed to methanol vapor. It is also possible to carry out by spraying alcohol on the surface of the wafer in a sprayed state.

Further, in the above embodiment, after removing the silicon natural oxide film on the silicon wafer surface with anhydrous hydrogen fluoride gas and methanol vapor, by supplying methanol vapor, the fluoride remaining on the silicon wafer surface is removed. However, the present invention is not limited thereto as described below.

That is, instead of anhydrous hydrogen bromide gas, NF ₃ , SF ₆ , Cl
A halide gas such as F ₃ or Cl ₂ may be used. Further, instead of methanol vapor, other lower monovalent alcohol such as ethanol may be used. However, even in that case, the halide gas and alcohol are anhydrous as in the case of the above embodiment.

Further, the present invention is not limited to the case of removing the silicon natural oxide film on the surface of the silicon wafer, and may be applied to the removal of the silicon natural oxide film formed on the surface of the polysilicon film or the amorphous silicon film. Incidentally, such a polysilicon film or an amorphous silicon film is not limited to a film formed on a silicon wafer, and for example, on various semiconductor wafers such as gallium / arsenic wafers, glass substrates, ceramic substrates, etc. May be formed on various substrates.

Furthermore, the method is not limited to such removal of the silicon natural oxide film on the surface of the silicon layer, and it is not limited to the thermal silicon oxide film, a silicon oxide film formed by a method other than thermal oxidation (for example, CVD), or a silicon nitride film, It can also be applied to etching silicon insulating films such as phosphorus-doped glass film, boron-phosphorus-doped glass film, arsenic-doped glass film.

As described above, the "substrate surface" in the configuration of the present invention means not only the silicon wafer surface but also various semiconductor wafers such as gallium / arsenic wafers, and various substrates such as glass substrates and ceramic substrates. Including the surface of polysilicon film and amorphous silicon film. In addition, "after removing the coating film such as the oxide film deposited on the surface of the substrate" in the configuration of the present invention also includes after etching the silicon insulating film. Furthermore, "after removing the coating film such as the oxide film deposited on the surface of the substrate" in the configuration of the present invention is not limited to the removal treatment of the coating film using a halide gas and alcohol. Including the case of the film removal treatment using anhydrous halide gas alone.

〔The invention's effect〕

Since the present invention is configured and operates as described above, in a manufacturing process of a semiconductor device or the like, a natural oxide film, a silicon insulating film, or a metal film formed on a substrate surface is formed by using a halide such as hydrogen fluoride. When the halide according to the present invention is removed by cleaning after the etching or cleaning treatment, the formation of a secondary oxide film is significantly reduced as compared with the conventional method. In addition, it is possible to remove ionic contamination from the substrate surface with high efficiency, and there is no damage to the silicon wafer as in the case of UV light irradiation or Ar ion sputtering. High quality can be maintained without it.

When anhydrous low-grade monohydric alcohol is supplied to the substrate surface in a vapor state, a series of steps can be carried out in a gas phase in one container. The structure of the reaction container is simplified, the supply of alcohol to the substrate can be quantitatively controlled, and the alcohol is quickly discharged from the surface of the substrate, which improves efficiency.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a silicon wafer cleaning apparatus for carrying out the method of the present invention, and FIG. 2 is a gas for cleaning a silicon wafer by the apparatus shown in FIG. -It is a time chart for explaining a method of supplying steam. 10 …… Silicon wafer (substrate), 12 …… Container, 30 …… Supply source of anhydrous hydrogen fluoride, 32 …… Supply source of alcohol, 3
4, 44 ... Nitrogen gas supply source.

Front Page Continuation (72) Keiji Kirie Keiji Kirie 1 No. 1 Tenjin Kita-cho, 4-chome, Horikawa-dori Teranouchi, Kyokyo-ku, Kyoto Prefecture Dai-Nippon Screen Manufacturing Co., Ltd. (72) Inventor Shinatsu Watanabe Nagaokakyo, Kyoto Prefecture Uguisudai, Ichi, Japan (72) Inventor, Zheng Bao, 1 394, No. 394, 14 Sengendori, Senbon-dori, Kamigyo-ku, Kyoto, Kyoto Prefecture Nishijin Grand Heights 601 (56) Reference JP 62-272541 (JP, A) ) JP-A-63-56921 (JP, A)

Claims (2)

[Claims] 1. After removing a film such as an oxide film deposited on the substrate surface by supplying a halide to the substrate and exposing the substrate surface to the halide,
A method for cleaning a substrate surface after removing a coating film such as an oxide film, by removing a halide remaining on the substrate surface by supplying anhydrous lower and monohydric alcohol to the substrate surface. 2. The method for cleaning a substrate surface after removing a film such as an oxide film according to claim 1, wherein anhydrous low-grade monohydric alcohol is supplied to the substrate surface in a vapor state.