JPH03129731A - Cleaning of substrate surface after removal treatment of oxide film and the like - Google Patents

Abstract

PURPOSE:To remove an ionic contamination from the surface of a substrate down to an extremely low level by a method wherein anhydrous alcohol is supplied to the surface of the substrate and a halogenide remaining on the surface of the substrate is removed. CONSTITUTION:A silicon wafer 10 where an oxide film has been formed on the surface is carried in and set up inside a container 12; the inside of the container 12 is hermetically sealed completely; high-purity N2 gas is fed into the container 12 through supply pipe routes 28, 20 from a supply source 34 of nitrogen gas; the inside of the container 12 is purged. Anhydrous hydrogen fluoride gas is fed into the container 12 through pipe routes 24, 20 from a supply source 30 of the anhydrous hydrogen fluoride gas; the oxide film on the surface of the wafer is removed. After that, N2 gas for buffing which is used to generate a methanol steam is fed into the container 12 through a gas route 20; a cleaning treatment is executed. After the treatment has been finished, the inside of the container 12 is purged by using the N2 gas.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to, for example, the surface of a silicon wafer, the surface of a polysilicon film, or the surface of an amorphous silicon film (hereinafter, these surfaces are collectively referred to as "silicon layer surface"). The natural oxide film formed on the wafer surface is removed from the wafer surface using a halide such as hydrogen fluoride (HF), and various silicon insulating films formed on the surface of the silicon layer are etched with a halide. The present invention relates to a method for cleaning a substrate surface for removing halides remaining on the substrate surface after cleaning.

[Conventional technology]

In the manufacturing process of semiconductor devices, for example, HF, NF3, SF C
Halides such as IF, C12, etc. are often used.

All of these halides are ions.

Since it is used in an active state such as a radical, ionic contamination from halogens such as fluorine and chlorine remains on the substrate surface after etching and cleaning processes are completed. If devices are formed with these ionic contaminants remaining on the substrate surface, it will cause various device defects such as film formation defects and electrical malfunctions. Therefore, any ionic contamination remaining on the substrate surface after etching or cleaning processes must be removed from the substrate surface by cleaning.

Conventionally, as a method for removing ionic contamination from a substrate surface, a method of cleaning the substrate surface with pure water (ultra-pure water) has been generally performed. Also, for example, JP-A-62-173
Publication No. 720 describes a method in which hydrofluoric acid (hydrofluoric acid) vapor is supplied into a container in which a wafer is housed to clean and remove a natural oxide film on the wafer surface, and then high-purity water vapor is supplied into the same container. A method is disclosed in which hydrofluoric acid is washed off from the wafer surface. In addition, some methods are used to remove ionic contamination from the substrate surface by treatments such as UV light irradiation and Ar (argon) ion sputtering.

[Problem to be solved by the invention]

However, in the conventional method described above, S
If metals such as i (silicon) or aluminum are exposed, there is a problem in that an oxide film is easily formed as a secondary oxide film during the treatment process for removing ionic contamination.

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

This invention reduces the formation of secondary oxide films compared to the conventional method described above, which is used to remove ionic contamination of halogens such as fluorine from the substrate surface after etching or cleaning treatment in the manufacturing process of semiconductor devices. It is an object of the present invention to provide a cleaning method that can significantly reduce ionic contamination and remove ionic contamination from a substrate surface to an extremely low level.

[Means to solve the problem]

As a means for achieving the above-mentioned object, this invention supplies a halide such as hydrogen fluoride to a substrate to perform etching or cleaning treatment on the surface of the substrate, and then supplies anhydrous alcohol to the surface of the substrate. The gist of the configuration is that halides remaining on the substrate surface are removed.

[For production]

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

It is known that the presence of both oxygen and moisture is necessary for a natural oxide film to grow on the surface of a substrate, such as a silicon wafer (for example, "IEICE Technical Report V
ol, 89 Na1ll; Institute of Electronics, Information and Communication Engineers technical report pH ~ 121rSi natural oxide film formation controlffl,
In the method according to this invention, anhydrous alcohol is supplied to the substrate, and since the water content of the system is kept low, pure water Compared to the conventional method of cleaning the substrate with water or water vapor, the occurrence of secondary oxide film formation on the substrate surface is significantly reduced.

In addition, since alcohol easily creates a reducing atmosphere and has extremely low oxidizing ability, the substrate surface is covered with a layer of alcohol to protect it, even in areas where silicon or metal is exposed on the substrate surface. Secondary oxidation is more effectively prevented, and contamination by organic matter becomes extremely difficult.

On the other hand, halides such as hydrogen fluoride HF, water H,
mM to O and alcohol ROH is carried out by the following process (J. H. Simons; Fluorine Chemistry (J. H. Simons;
lineChemistry), 1,225 (195
0)).

nH,O+2HF→(H,0)nH+HF2−ROH+
2HF→(ROH)H"+HF2- Therefore, when forming HF,-, 1 mole of alcohol corresponds to n moles of water. Also, the electrical conductivity of a hydrogen fluoride solution such as methanol or ethanol is: Hydrogen fluoride is more soluble in alcohol than in water, as can be seen from the fact that it is larger than the equivalent type conductivity of a hydrogen fluoride solution in water.Therefore, according to the cleaning method of the present invention using alcohol, fluorine, Ionic contaminants such as chlorine are well solvated by alcohol, and are removed from the substrate surface with higher efficiency than conventional cleaning methods using pure water or steam.

The alcohol layer formed to cover the substrate surface can be easily removed from the substrate surface by evacuation or heating at a relatively low temperature. There is no need for any special drying process.

〔Example〕

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

FIG. 1 is a schematic diagram showing an example of a silicon wafer cleaning apparatus for carrying out the method of the present invention. In FIG. The interior is hermetically isolated from the outside air. This container 12 is provided with a supply port 14 and an exhaust port 16 connected to a gas/steam supply pipe 20 and an exhaust pipe 22, respectively, and is also provided with a bypass pipe 18. still.

Although not shown in FIG. 1, a door is provided on the side of the container 12 for loading and unloading silicon wafers. It is also possible to configure an in-line configuration by connecting the device and a conveyance line.

Three pipes 24, 26, and 28 join the supply pipe 20 that communicates with the supply port 14 of the container 12, and the supply pipe 8
24. At the end of 26.28, source 3 of anhydrous hydrogen fluoride
0, an alcohol supply source 32, and a nitrogen gas supply source 34 as a carrier gas. Also,
A branch pipe 36 of the carrier gas pipe 28 is in communication with the anhydrous hydrogen fluoride gas supply pipe 24 .

Furthermore, mass flow controllers 38 and 40 are inserted into the anhydrous hydrogen fluoride gas supply line 24 and the nitrogen gas supply line 28, respectively. On the other hand, alcohol supply lol
Pipe line 42 connected to the alcohol storage tank of X32
A nitrogen gas supply g44 is connected via a mass flow controller 46, so that anhydrous hydrogen fluoride gas and methanol vapor can be supplied to a volume of 1 m 12 at different times. . Additionally, each of the anhydrous hydrogen fluoride and alcohol supply sources 30.32 is provided with a temperature controller 48.50, respectively.

And anhydrous hydrogen fluoride gas and carrier gas (nitrogen)
The adjustment of the supply amount is carried out by mass flow controllers 38.40 provided in the respective supply lines 24.28. Further, the supply amount of alcohol vapor is adjusted by controlling the flow rate of nitrogen gas and the temperature of alcohol (liquid) (therefore, the vapor pressure of alcohol) by the mass flow controller 46. In addition, in order to prevent dew condensation from occurring in each supply system of anhydrous hydrogen fluoride gas and alcohol vapor, each supply pipe line 2
4.26 is kept warm by the heat insulating material 52.54 as shown by the broken line.

In this device, as described above, anhydrous hydrogen fluoride gas and methanol vapor can be supplied into the container 12 at different times. As shown in the chart, the supply of anhydrous hydrogen fluoride gas and methanol vapor are started at the same time, and after cleaning is performed to remove natural oxide films from the substrate surface, the supply of anhydrous hydrogen fluoride gas is stopped. Then, only methanol vapor is supplied for a predetermined period of time (for example, 10 to 30 seconds), and then the supply is stopped.This removes the hydrogen fluoride remaining on the substrate surface when the cleaning process is completed. The silicon wafer 10 can be cleaned and removed from the substrate surface.Also, as shown in FIG.
First, methanol vapor is introduced into the container 12, and after a predetermined period of time (for example, 10 to 60 seconds) has passed, supply of anhydrous hydrogen fluoride gas is started, and anhydrous hydrogen fluoride gas and methanol vapor are simultaneously supplied for a predetermined period of time. After performing a cleaning process to remove natural oxide films etc. from the substrate surface, in the same way as above, after stopping the supply of non-hopped hydrogen gas, only methanol vapor is supplied for a predetermined period of time (for example, 10 to 30 seconds). After that, the supply can be stopped.

Next, using the above cleaning equipment, the natural 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 amount of residual fluorine after the cleaning is An example of an experiment in which the cleaning effect was investigated by measuring . In this experiment, a phosphorus-doped n-type silicon wafer with a resistivity of 2 to 8 Ω was used.
, oxidize by immersing it in a mixed solution.

A sample on which an oxide film with a thickness of 13 A was formed was used. In addition, as cleaning gases and reagents, ultra-high purity anhydrous hydrogen fluoride manufactured by Showa Denko ■, EL grade 50% hydrofluoric acid manufactured by Daikin Industries @, and ultra-high purity nitrogen manufactured by Nippon Sanso ■ were used for the experiment. , and EL grade methanol manufactured by Kanto Kagaku ■ were used.

First, the natural oxide film on the silicon wafer surface is cleaned and removed.
The following two methods were used.

■ The above-mentioned silicon wafer lO with an oxide film formed on its surface is carried into the container 12 of the apparatus shown in FIG. 34 through the supply pipes 28 and 20 into the container 12 at a flow rate of 15Q/min.
The inside of 2 was purged for 30 seconds. Each gas paper contains 100 to 1 liters of anhydrous hydrogen fluoride gas.

000cc/min (25℃), 500~5.0 cc/min of N2 gas for puffing to generate methanol vapor
00cc/min (25°C).

Nitrogen gas from O to 5.0OOcc/min (25℃)
The liquid was supplied into the container 12 at each flow rate. Under the above conditions, a cleaning process was performed for 30 seconds, and after the process was completed, the inside of the container 12 was purged with N2 gas for 30 seconds.

(2) Cleaning treatment was carried out by immersing the silicon wafer 10 with an oxide film formed on the surface in 1% hydrofluoric acid for 30 seconds, and after the treatment was completed, it was blown with N2 gas for 30 seconds.

Next, residual fluorine (ionic contamination) on the surface of the silicon wafer was cleaned and removed using the following three methods: the method according to the present invention and two conventional methods for comparison.

i. Place the silicon wafer whose natural oxide film has been cleaned and removed in the container 12 of the apparatus shown in FIG.
With the inside of 2 sealed.

Methanol vapor is used as N2 gas flow rate for puffing.
．． The water was supplied into the container 12 for 30 seconds at a flow rate of OOO to 5,000 cc/min (25° C.). After the cleaning process is completed, the inside of the container 12 is heated to 15 n/m of N2 gas.
Purge was performed by pumping in for 30 seconds at a flow rate of i.

(2) The silicon wafer from which the natural oxide film had been removed was immersed in running pure water for 30 seconds for cleaning, and after the cleaning process was completed, it was blown with N2 gas for 30 seconds.

m. A silicon wafer whose natural oxide film has been cleaned and removed is placed inside an aluminum vacuum container, and while the inside of the vacuum container is evacuated to 10-3+s+Hg using a vacuum pump, a 290W low-pressure mercury lamp is used from above the wafer for 10 UV light was irradiated for minutes.

As described above, the two natural oxide film cleaning methods ■■ and the three residual fluorine cleaning methods i, it, and ni are combined,
After cleaning and removing the native oxide film from the surface of the silicon wafer, the fluorine remaining on the wafer surface was cleaned and removed, and the effectiveness of removing fluorine from the wafer surface was evaluated. The thickness of the fluorine and oxygen layers on the silicon wafer surface is measured by photoelectron spectroscopy (ESCA measurement), and the measuring device used is ■ ESC manufactured by Shimadzu Corporation.
A850 was used. In addition, the residual amount of each element, fluorine or oxygen, can be compared by dividing the peak area value of the spectrum of each element by the peak area value of the spectrum of 5i2P (Fl
, peak area/S x 2P peak area, or 01s
The calculation was performed using the following formula: peak area/S i 2P peak area).

After removing the natural oxide film on the wafer surface by exposing the surface of the silicon wafer to anhydrous hydrogen fluoride gas and methanol vapor (method ① above), methanol vapor is supplied to the surface of the silicon wafer to clean and remove residual fluorine. I want to do the above i.

method)), the residual amount of fluorine (ESCA peak area ratio F
15/512p) is set to 1, the natural oxide film on the silicon wafer surface is removed using the same method (method ① above),
The silicon wafer was immersed in pure water and cleaned (see ■,
When the silicon wafer is irradiated with UV light (method 2), the residual amount of fluorine is 2.3. The residual amount of fluorine when cleaning of residual fluorine was not performed was 2.4.

In addition, after removing the native oxide film on the wafer surface by immersing the Hesilicon wafer in hydrofluoric acid (method ① above), methanol vapor was supplied to the surface of the silicon wafer to wash and remove residual fluorine ( Method i above)
The residual amount of fluorine in the case is 1.7, and the residual amount of fluorine in the case where the silicon wafer is washed by immersing it in pure water (method ① above) is 3.1, and similarly, the residual amount of fluorine is not cleaned. The residual amount of fluorine was 5.5.

From the above results, it can be seen that fluorine removal efficiency is high when the surface of the silicon wafer is cleaned using methanol vapor after cleaning and removing the natural oxide film on the surface of the silicon wafer. Note that after removing the natural oxide film on the surface of the silicon wafer using anhydrous hydrogen fluoride gas and methanol vapor.

When the surface of the silicon wafer was cleaned with methanol vapor, the amount of residual fluorine was the lowest.

In addition, the oxygen concentration on the surface of the silicon wafer after the cleaning process (the amount of O in S i 02, therefore, the amount of O in S i O2
(corresponding to the film thickness).

To remove the natural oxide film on the surface of a silicon wafer using anhydrous hydrogen fluoride gas and methanol vapor (method described in ■ above)
Afterwards, residual fluorine was washed and removed by supplying methanol vapor to the surface of the silicon wafer (method i). Oxygen amount (ESCA peak area ratio 015/S
p) is 1, then a is obtained by using the same method for removing the natural oxide film on the surface of the silicon wafer (method ① above) and cleaning the silicon wafer by immersing it in pure water (method ① above). The amount of oxygen is 1.9 when the silicon wafer is irradiated with UV light (the above method), and the amount of oxygen is 1.4 when the remaining fluorine is not cleaned and only N2 gas is purged.The amount of oxygen is 0. It was 9. In addition, after removing the natural oxide film on the wafer surface by immersing the silicon wafer in hydrofluoric acid (method ① above), methanol vapor was supplied to the surface of the silicon wafer to wash and remove residual fluorine ( The amount of oxygen in the case of method i) above is 1.1, and the amount of oxygen in the case of cleaning the silicon wafer by immersing it in pure water (method above) is 2.7. The oxygen amount when no washing was performed was 1.5.

Based on the above results, if the surface of the silicon wafer is cleaned using methanol vapor after cleaning and removing the natural oxide film on the surface of the silicon wafer, it is possible to immerse the silicon wafer in pure water or apply UV irradiation to the silicon wafer. Compared to conventional methods in which fluorine is removed from the silicon wafer surface by irradiating light, the oxygen concentration on the wafer surface can be kept low, which means that secondary regrowth of the native oxide film can be suppressed.

Next, we investigated the effect of moisture present in methanol vapor for fluorine cleaning on fluorine removal efficiency and reoxidation of the silicon wafer surface after cleaning.

The experiment was carried out using the apparatus shown in Figure 1, using anhydrous HF-CH.
After removing the natural oxide film on the surface of the silicon wafer with OH vapor (method ① above), methanol vapor is supplied to the surface of the silicon wafer to clean and remove residual fluorine (method i above). This was done by mixing water as an impurity in methanol for fluorine cleaning at various concentrations. The thickness of the natural oxide film caused by reoxidation on the surface of the silicon wafer was measured using an ellipsometer 1 hour and 20 minutes after each cleaning.

As a result, when the proportion of water (steam) to the total amount of methanol vapor and nitrogen gas was 5% or less, the fluorine removal efficiency remained almost unchanged. In addition, the thickness of the natural oxide film on the surface of the silicon wafer after 1 hour and 20 minutes after the cleaning process was determined by 4.1 people under the condition that the moisture content in methanol vapor and nitrogen gas was 0.3% or less. 4.3 to 4.6 people when the moisture content is 0.3% or more and less than 1.0%, and 5 when the moisture content is 1.0% or more and 5.0% or less. It was .3 to 5.8A. These experimental results show that the presence of a small amount of water in the reaction system does not have much effect on reoxidation of the silicon wafer surface after cleaning.

In the above embodiment, the surface of the silicon wafer was exposed to methanol vapor after washing and removing the natural oxide film on the surface of the silicon wafer. It is also possible to carry out by a method such as spraying alcohol in a spray state onto the surface of the wafer.

Further, in the above embodiment, after removing the silicon natural oxide film on the surface of the silicon wafer with non-hopped hydrogen gas and methanol vapor, methanol vapor is supplied to remove fluoride remaining on the surface of the silicon wafer. However, the present invention is not limited thereto, as explained below.

That is, instead of anhydrous hydrogen fluoride gas, NF,,S
A halide gas such as FCI F, 01□ may also be used. Furthermore, other alcohols such as ethanol may be used instead of methanol vapor. However, even in that case, the halide gas and alcohol are anhydrous as in the above embodiments.

Further, the present invention is not limited to the case where the present invention is applied to the removal of a silicon natural oxide film on the surface of a silicon wafer, but may be applied to the removal of a silicon natural oxide film formed on the surface of a polysilicon film or an amorphous silicon film. Note that such polysilicon films and amorphous silicon films are not limited to films formed on silicon wafers, for example, on various semiconductor wafers such as gallium arsenide wafers, glass substrates, ceramic substrates, etc. may be formed on various substrates.

Furthermore, the removal is not limited to such a natural silicon oxide film on the surface of a silicon layer, but also a silicon thermal oxide film or a silicon oxide film formed by a method other than thermal oxidation (for example, CVD, etc.).
Or silicon #l such as silicon nitride, phosphorus doped glass film, boron phosphorus doped glass film, arsenic doped glass film, etc! ! It can also be applied to etching the membrane.

As described above, the "substrate surface" in the configuration of this invention refers not only to the surface of a silicon wafer, but also to the surface formed on various semiconductor wafers such as gallium arsenide wafers, and various substrates such as glass substrates and ceramic substrates. It also includes the surface of polysilicon films and amorphous silicon films. Further, in the structure of the present invention, "after removing a film such as an oxide film deposited on the surface of the substrate" also includes after etching a silicon insulating film. Furthermore, in the structure of the present invention, "after removing a film such as an oxide film deposited on the substrate surface" is not limited to a film removal process using halide gas and alcohol. This also includes the case of coating removal treatment using anhydrous halide gas alone.

〔Effect of the invention〕

Since the present invention is configured and operates as described above, in the manufacturing process of semiconductor devices, etc., the natural oxide film, silicon insulating film, or metal film formed on the surface of the substrate is replaced with a halide such as hydrogen fluoride. When the method according to the present invention is used to wash and remove the halide remaining on the substrate surface after etching or cleaning using a substrate, the formation of a secondary oxide film is reduced compared to the conventional method. In addition to significantly reducing ionic contamination, it is possible to remove ionic contamination from the substrate surface with high efficiency.
There is no damage to the silicon wafer as would be caused by U-light irradiation or Ar ion sputtering, and high quality can be maintained by eliminating various causes of defects in semiconductor devices.

[Brief explanation of the drawing]

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. It is a time chart for explaining the method of supplying steam. 10... Silicon wafer (substrate), 12... Container. 30... Source of anhydrous hydrogen fluoride, 32... Source of alcohol, 34.44... Source of nitrogen gas. Figure - 11-cho

Claims (1)

[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, anhydrous alcohol is further applied to the substrate surface. A method for cleaning a substrate surface after a film removal process such as an oxide film, which removes halides remaining on the substrate surface by supplying the substrate.