JPH11224872A - Surface treatment method for silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely and efficiently form a clean surface of silicon. SOLUTION: A silicon clean surface is formed by vacuum heating a silicon substrate 5, where an oxidized film 4 provided with a film thickness of 1 nm or larger and 2 nm or smaller is present on the surface. Since the silicon clean surface is formed by vacuum heating the silicon substrate 5, where the oxidized film 4 provided with a film thickness of 1 nm or lager is present on the surface, the physical or chemical bonding to an active silicon surface and carbon in gas is restrained and carbon 3 is almost all removed. Also since the time required for reaction for sublimating the oxidized film 4 increases along with the increase of an oxidized film thickness, when the oxidized film 4 become thick, it takes more than the required time for oxidized film removal reaction in a vacuum and becomes inefficient. However, since the film thickness of the oxidized film 4 is set to be 1 nm or larger and 2 nm or smaller, the carbon is sufficiently removed and processing time is shortened. Thus, a clean silicon surface for not generating Si-C bonding is formed surely and efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a surface of silicon such as a silicon wafer used for forming all kinds of electronic devices.

[0002]

2. Description of the Related Art Conventionally, silicon surface treatment is performed by chemical cleaning called RCA cleaning and homoepitaxial silicon by MBE (molecular beam epitaxy).
Surface treatment by heat treatment at about 900 to 1100 ° C. has been performed in a high vacuum of 10 ⁻⁸ torr or more.

Conventionally, silicon surface treatment is disclosed in
Japanese Patent Application Laid-Open No. 3266 and JP-A-6-40798 are known. The silicon surface treatment (Japanese Patent Laid-Open No. 5-243266) of Conventional Example 1 shown in FIG. 7 will be described. As shown in FIG. 7A, the substrate 6 after the RCA cleaning is formed by the RCA cleaning. An oxide film 9 is formed on the surface of the silicon substrate 10, and a very small amount of carbon 11 adheres from the air. As shown in FIG. 7B, after the RCA cleaning wet oxidation, the substrate 7 is formed after dilute hydrofluoric acid cleaning after removing the oxide film by dilute HF. When the silicon surface is exposed, carbon 11 is more likely to adhere than in the atmosphere. As shown in FIG. 7C, when the silicon substrate 10 is set in an ultra-high vacuum chamber and a cleaned surface is obtained by an instantaneous heating method, the substrate 8 is formed after the ultra-high vacuum cleaning. The silicon carbide 12 is easily formed on the surface. By gradually cooling the silicon substrate 10 on the clean surface, silicon surface atoms are rearranged, and a step appears on the surface.

Another conventional example 2 shown in FIG.
-40798) will be described. Vacuum container 13
The silicon substrate 14 fixed by the holder 15 is introduced therein. 5 × 10 ⁻⁷ oxygen is ^supplied from the valve 16 to the silicon substrate 14 in the valve vacuum vessel 13 connected to the vacuum pump 21.
An oxide film is formed on the silicon surface at a substrate temperature of 600 ° C. with a vacuum of torr. Hydrogen is introduced from the valve 16, the silicon substrate 14 is kept at 600 ° C. at a degree of vacuum of 1 × 10 ⁻⁶ torr, ultraviolet rays 18 having a wavelength of 308 nm from the excimer laser 17 are condensed by the lens 19, and passed through the ultraviolet transmission window 20. The irradiation density on the surface of the silicon substrate 14 is 5
Irradiation is performed so as to be J / cm ² .

FIG. 9 shows the surface state of the silicon substrate at this time. As shown in FIG. 9A, first, the surface of the silicon substrate 22 is covered with an oxide film 23 to form an RC.
After A cleaning, the substrate 24 is used. Carbon 25 from the air adheres to the surface of oxide film 23. As shown in FIG. 9B, an oxygen-exposed substrate 28 having an oxide film thickened by oxygen exposure 27 is formed. As shown in FIG. 9C, by irradiating with hydrogen exposure 29 and ultraviolet light 30, the evaporation of impurities on the surface becomes remarkable, a cleaner surface is easily obtained, and the substrate 31 is formed after cleaning. . In particular, when carbon or the like is present on the silicon surface, a Si—C bond may be formed, and this bond is strong, so it is very difficult to obtain a clean surface. However, the silicon surface is previously covered with the oxide film 23. By using silicon, even when carbon or the like is present on the surface, the carbon can be oxidized to easily form a clean surface, which is preferable.

[0006]

However, in the conventional structure as described above, after removing the oxide film by HF treatment and exposing the silicon surface as in Conventional Example 1, short-time instantaneous heating causes the SiO ₂ to be removed. When sublimation and silicon surface rearrangement are performed, the reaction occurs in a short time, and the carbon remaining locally on the surface is not oxidized, and a Si—C bond is generated.
There was a problem that -C bonding occurs.

In the case of using silicon in which the silicon surface is previously coated with an oxide film as in Conventional Example 2, if the oxide film is too thick, the reaction hardly takes place and the treatment takes a long time. However, there is a problem that the carbon which is not oxidized and a Si—C bond is generated. Further, an ultraviolet light incidence device, an optical lens device thereof, an exposure device for oxygen and hydrogen, and the like are required in the reaction chamber, which has a problem that the entire device is complicated and the volume of the device is increased.

Accordingly, an object of the present invention is to provide a silicon surface treatment method capable of forming a clean silicon surface reliably and efficiently in view of the above problems.

[0009]

According to a first aspect of the present invention, there is provided a method for treating a surface of silicon, comprising the steps of: vacuuming a silicon substrate having an oxide film having a thickness of 1 nm or more on a surface thereof; It is characterized by forming a clean silicon surface by heating. As described above, the silicon substrate having an oxide film having a thickness of 1 nm or more forms a clean silicon surface by vacuum heating, so that the active silicon surface and the carbon in the gas are physically or chemically bonded. And carbon is almost completely removed. Therefore, it is possible to reliably form a clean silicon surface on which no Si—C bond is generated.

According to a second aspect of the present invention, in the first aspect, the thickness of the oxide film is set to 2 nm or less. Since the time required for the reaction for sublimating the oxide film increases with an increase in the oxide film thickness, when the oxide film becomes thicker, the oxide film removal reaction in vacuum takes more time than necessary and becomes inefficient, The thickness of the oxide film is 1 nm or more and 2 nm
With the following settings, carbon can be sufficiently removed and the processing time can be shortened. For this reason, Si
A clean silicon surface free from -C bonding can be reliably and efficiently formed.

According to a third aspect of the present invention, there is provided a method of treating a silicon surface, comprising the steps of increasing a sublimation temperature and lowering the silicon substrate to a predetermined temperature again when a silicon substrate is sublimated by vacuum heating to form an oxide film on the surface. The process is performed a plurality of times, and processing is performed with a temperature profile in which the maximum surface temperature at that time is gradually increased. As described above, the process of increasing the sublimation temperature and lowering it again to a certain temperature is performed a plurality of times, and the temperature profile in which the maximum surface temperature at that time is gradually increased is used. In order to happen little by little,
Exposure of the locally active silicon surface allows S
No iC bond is generated, and as a result, a clean surface with less carbon is easily formed.

According to a fourth aspect of the present invention, there is provided a silicon surface treatment method comprising: cleaning a holder for holding a substrate sample to remove impurities on the surface; heating and cleaning the holder in a vacuum; It is characterized by forming a clean silicon surface by heating. If the amount of impurity contamination on the holder that is in close contact with the silicon substrate is high, carbon adheres to the cleaned silicon surface due to diffusion at a high temperature to form a Si-C bond, but the holder holding the substrate sample is cleaned and impurities on the surface are removed. After the removal, the holder is heated and cleaned in vacuum, and then the silicon substrate is set on the holder and vacuum-heated to form a clean silicon surface, so that impurity diffusion from the holder can be completely prevented, and silicon can be completely prevented. It is possible to form a clean surface in which no Si—C bond is generated without depositing carbon on the substrate surface.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic sectional view showing a processing procedure of a silicon surface treatment method according to a first embodiment of the present invention. 1 (a) and 1 (b), 1 is R
After the CA cleaning, the substrate is 1 nm thick on the surface of the silicon substrate 5.
The above oxide film 4 is formed. 3 is carbon attached to the surface. Reference numeral 2 denotes a vacuum-heated ultra-high vacuum-cleaned substrate having a silicon-cleaned surface formed thereon. By gradually cooling the silicon substrate 5 on the clean surface, silicon surface atoms are rearranged, and a step appears on the surface.

Next, a method for surface treatment of silicon will be described. First, as shown in FIG.
The substrate 1 is formed after RCA cleaning by removing particles, metals, and organic impurities on the silicon substrate by cleaning (cleaning with a mixed solution of ammonia water / hydrogen peroxide water / water). After the RCA cleaning, the substrate 1 has a thickness of 1 nm on the surface of the silicon substrate 5.
The above oxide film 4 exists. When the oxide film 4 is formed, a sample substrate is prepared using a chemical mixture ratio and a temperature at which an oxide film can be formed to a thickness of 1 nm or more on the silicon surface. Alternatively, an oxide film is formed in a thermal oxidation furnace, and then etched with dilute hydrofluoric acid to form an oxide film on the silicon surface with a thickness of 1 nm.
There is also a method for preparing a sample substrate that remains as described above. Also,
A small amount of carbon 3 adheres to the surface of the oxide film 4 in the air.

Thereafter, the substrate 1 is introduced into a vacuum,
At 900 ° C or higher, and the degree of vacuum at 1 × 10 ^-8To a high vacuum
The silicon substrate is processed as shown in FIG.
The oxide film 4 on the surface of the plate 5 is sufficiently removed, and ultra-high vacuum cleaning is performed.
The rear substrate 2 is formed. At this time, the initial oxide film thickness is 1 nm.
Or by removing the oxide film 4 with an HF solution or the like.
When the active silicon surface and the carbon in the gas are
Physically or chemically combined, followed by vacuum cleaning
Impurity on the silicon surface
4 has a thickness of 1 nm or more.

Thereafter, the temperature of the substrate is lowered and gradually cooled. FIG. 2 shows the results of the comparative experiment. When an oxide film having an oxide film having a thickness of 1 nm or more and 1 nm or less on the silicon surface was formed and then subjected to ultra-high vacuum cleaning treatment, the amount of carbon deposited after the cleaning was measured as a C1s spectrum by XPS (photoelectron spectroscopy). 32 is a C1s spectrum when an ultrahigh vacuum cleaning treatment is performed after forming an oxide film of 1 nm or more, and 33 is 1
9 is a C1s spectrum when an ultra-high vacuum cleaning process is performed after an oxide film having a thickness of not more than nm is formed. The horizontal axis represents the binding energy (B
Indicating Energy) (eV), vertical axis is XPS
Spectral intensity (cps (count per sec)
ond)). When ultra-high vacuum cleaning treatment is performed after forming an oxide film of 1 nm or more, carbon is almost completely removed. However, when ultra-high vacuum cleaning treatment is performed after forming an oxide film of 1 nm or less, carbon remains. It remains.

As described above, in this embodiment, the film thickness 1
In a simple method of removing the silicon substrate 5 having an oxide film 4 having a thickness of not less than nm on the surface by vacuum heating, Si-C
A clean silicon surface free of bonding can be reliably formed. A second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a graph showing a relationship between a carbon residual ratio (%) and a processing time (minute) in the silicon processing method according to the second embodiment of the present invention. This embodiment is similar to the first embodiment, except that the initial oxide film thickness is set to 1 nm or more and 2 nm or less. As the oxide film thickness of silicon increases, the time required for the reaction for sublimating the oxide film increases as the oxide film thickness increases. Si / S
When the thickness of the oxide film, which is the path from the SiO ₂ + Si → 2SiO generated at the interface of iO ₂ to the SiO ₂ diffused in the oxide film and goes out into the vacuum, is thick, the time required for the reaction increases, and the thickness is extremely large. In this case, the oxide film is very difficult to sublime.
When the oxide film on the silicon surface becomes thick as described above, the reaction for removing the oxide film in a vacuum takes an unnecessarily long time, resulting in inefficiency.

Specifically, as shown in FIG. 3, the surface oxide film thickness is 1 nm or more, the carbon residual ratio is 0%, and the processing time is 1
about 1 minute in nm and about 3 minutes in 2 nm. Therefore, 1
By vacuum heating a silicon substrate having an oxide film of nm to 2.0 nm on the surface, carbon can be sufficiently removed and the processing time can be shortened. In addition,
When an oxide film having a thickness of 2.0 nm or more is present on the surface, the treatment takes 3 minutes or more, which is inefficient.

As described above, in this embodiment, 1 nm
Since a silicon substrate having an oxide film having a thickness of ~ 2.0 nm is formed on the surface of the silicon substrate by vacuum heating, the Si-C
A clean silicon surface free of bonding can be formed reliably and efficiently. A third embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a graph showing a temperature profile in the silicon processing method according to the third embodiment of the present invention. The processing method is compared with a conventional example. Conventionally, when cleaning in vacuum, the degree of vacuum is 1 × 1
Temperature 8 while maintaining a high vacuum that does not fall below 0 ^-8 torr
Gradually raise the temperature to 00 ° C, then 900 ~
An oxide film on the surface is sublimated by instantaneous heating at 1100 ° C. to obtain a clean surface. At this time, when the instantaneous heating is performed only by one high-temperature treatment, local sublimation occurs on the substrate surface, and Si-C bonds remain from flying objects from other parts.

To prevent this, in this embodiment, in the ultra-high vacuum cleaning process after the RCA cleaning, when the silicon substrate is sublimated by vacuum heating to form an oxide film on the surface to form a silicon-cleaned surface, The process of increasing the sublimation temperature and lowering it again to a certain temperature is performed a plurality of times, and processing is performed with a temperature profile in which the maximum surface temperature at that time is gradually increased. Specifically, as shown in FIG.
The temperature is gradually increased to 800 ° C. while maintaining a high degree of vacuum that does not become 10 ⁻⁸ torr or less.
Lower to 0 ° C. Next, the temperature is raised at a maximum temperature of 900 ° C. for 10 seconds, and the temperature is again lowered to 800 ° C. Next, the maximum temperature 9
The temperature is increased at 50 ° C. for 10 seconds, and the temperature is decreased again to 800 ° C. Next, the temperature is increased at a maximum temperature of 1000 ° C. for several tens of seconds, and then lowered again to 800 ° C.

As described above, the step of increasing the sublimation temperature and lowering it again to a certain temperature is performed a plurality of times, and the temperature profile in which the maximum surface temperature at that time is stepwise increased allows sublimation of the oxide film on the silicon surface. Since it occurs gradually little by little on the surface, a locally active silicon surface is not exposed to form a Si—C bond, and as a result, a clean surface with less carbon is easily formed. In addition, the carbon remaining on the oxide film surface is gradually oxidized and sublimated on the oxide film without contacting the silicon substrate in a plurality of steps of increasing the sublimation temperature and lowering the temperature again to a certain temperature, and finally cleaning the silicon. It does not remain as Si-C bonds on the surface.

FIG. 5 shows the result of a comparative experiment with the conventional example. The amount of carbon deposited after the ultra-high vacuum cleaning treatment was measured as a C1s spectrum by XPS. 3
4 is a C1s spectrum having a temperature profile, and 35 is a C1s spectrum in a conventional case. Vacuum 1 × 10
^-8 torr or less while maintaining high vacuum
When the temperature is gradually increased to 0 ° C. and then gradually cooled to room temperature, the step of increasing the sublimation temperature shown in this embodiment and lowering it again to a certain temperature is performed a plurality of times, and the maximum surface temperature at that time is changed stepwise. A comparative experiment was performed with a case where the temperature was gradually increased to room temperature and then gradually cooled to room temperature. According to this, in the case of the embodiment (C1s spectrum 34), carbon is almost completely removed,
In the conventional case (C1s spectrum 35), carbon remains.

As described above, in this embodiment, when forming a clean silicon surface by vacuum heating a silicon substrate having an oxide film on the surface, a step of increasing the sublimation temperature and lowering the sublimation temperature to a predetermined temperature is performed a plurality of times. Since the temperature profile is such that the maximum surface temperature at that time is stepwise increased, a clean surface free of Si-C bonding can be formed without fail. Note that the third embodiment is applicable to the first and second embodiments.

A fourth embodiment of the present invention will be described with reference to FIG. In an apparatus for forming a clean silicon surface by heating a silicon substrate under vacuum, a sample holder for holding a substrate sample is cleaned to remove impurities from the surface. As a cleaning method, a mixed solution of sulfuric acid and hydrogen peroxide (mixing ratio 1: 5) was used, and the MO substrate holder was cleaned for 1 minute. After washing with water, dry with dry nitrogen blow,
Thereafter, the holder is heated and cleaned in a vacuum, the silicon substrate is placed on the holder, and the cleaned silicon surface is formed by vacuum heating. As in the first embodiment, the silicon clean surface is formed by RCA cleaning of the silicon substrate and then by ultra-high vacuum cleaning.

FIG. 6 is a comparison experiment result showing the difference between the C1s spectrum before and after the holder cleaning. 36 is a C1s spectrum when the holder before washing is used, and 37 is a C1s spectrum when the holder after washing is used. When the sample holder before cleaning is used, carbon is adhered when the silicon substrate is cleaned with a silicon substrate by vacuum heating and the surface is measured by XPS. In the C1s spectrum 36 before cleaning, carbon is considerably left. I have. On the other hand, when the cleaned sample holder is used, no carbon is attached, and the C1s spectrum 37 after the cleaning indicates that carbon on the MO substrate surface is completely removed. If the amount of impurity contamination on the holder that is in close contact with the silicon substrate as before the holder cleaning is high, carbon adheres to the cleaned silicon surface due to diffusion at a high temperature to form a Si—C bond. However, the impurity diffusion from the sample holder can be completely prevented by cleaning the sample holder.

As described above, in this embodiment, in the apparatus for forming a clean silicon surface by vacuum heating a silicon substrate, the holder for holding the substrate sample is cleaned and impurities on the surface are removed, and then the holder is heated in vacuum. Cleanse,
After that, the silicon substrate is placed on the holder and the silicon clean surface is formed by vacuum heating, so that the Si-
A clean surface free of C bonding can be formed.

Although heating in ultra-high vacuum to form a silicon clean surface has been described, all methods such as a method of forming a clean silicon surface by reduction in a hydrogen atmosphere and a method of cleaning by energizing heating of silicon are used. Including a clean surface forming process.

[0028]

According to the silicon surface treatment method according to the first aspect of the present invention, a silicon substrate having an oxide film having a thickness of 1 nm or more is formed on a silicon substrate by vacuum heating to form a clean silicon surface. Physical or chemical bonding between the active silicon surface and carbon in the gas is suppressed, and carbon is almost removed. For this reason,
A clean silicon surface free of Si-C bonds can be reliably formed.

According to the second aspect, the time required for the reaction for sublimating the oxide film increases as the oxide film thickness increases. Therefore, if the oxide film becomes thicker, the time required for the oxide film removal reaction in vacuum becomes longer than necessary. However, since the thickness of the oxide film is set to 1 nm or more and 2 nm or less, carbon can be sufficiently removed and the processing time can be shortened. Therefore, it is possible to reliably and efficiently form a clean silicon surface on which no Si—C bond is generated.

According to the silicon surface treatment method according to the third aspect of the present invention, the step of increasing the sublimation temperature and lowering it again to a certain temperature is performed a plurality of times, and the maximum surface temperature at that time is increased stepwise. By the profile, the sublimation of the oxide film on the silicon surface occurs uniformly little by little on the surface, so that the Si—C bond does not occur due to the exposure of the locally active silicon surface. To easily form a clean surface with less carbon.

According to the silicon surface treatment method of the present invention, if the amount of impurity contamination on the holder that is in close contact with the silicon substrate is high, carbon adheres to the cleaned silicon surface by diffusion at a high temperature, and -C bond is formed, but after cleaning the holder holding the substrate sample and removing impurities on the surface, the holder is heated and cleaned in vacuum, and then
Since the silicon substrate is placed on the holder and the clean surface of the silicon is formed by vacuum heating, the diffusion of impurities from the holder can be completely prevented. A clean surface free of cracks can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a processing procedure of a silicon surface treatment method according to a first embodiment of the present invention.

FIG. 2 is a C1s spectrum diagram in the silicon surface treatment method according to the first embodiment of the present invention.

FIG. 3 is a graph showing a relationship between a carbon residual ratio and a processing time in a silicon surface treatment method according to a second embodiment of the present invention.

FIG. 4 is a graph showing a temperature profile in a silicon surface treatment method according to a third embodiment of the present invention.

FIG. 5 is a C1s spectrum diagram in a silicon surface treatment method according to a third embodiment of the present invention.

FIG. 6 is a C1s spectrum diagram in a silicon surface treatment method according to a fourth embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view showing a processing procedure of a silicon surface treatment method of Conventional Example 1.

FIG. 8 is a schematic view of an apparatus in a silicon surface treatment method of Conventional Example 2.

FIG. 9 is a schematic cross-sectional view showing a processing procedure of a silicon surface treatment method of Conventional Example 2.

[Explanation of symbols]

1,6,24 Silicon substrate after RCA cleaning 2,8 Silicon substrate after ultra-vacuum cleaning 3,11,25 Carbon 4,9,23 Oxide film 5,10,14,22 Silicon substrate 7 Silicon after dilute hydrofluoric acid cleaning Substrate 12 Silicon carbide 13 Vacuum container 15 Holder 16 Valve 17 Excimer laser 18, 30 Ultraviolet light 19 Lens 20 Transmission window 21 Pump 27 Oxygen exposure 28 Substrate after oxygen exposure 29 Hydrogen exposure 31 Substrate after cleaning 32 In case of initial oxide film 1 nm or more 33 C1s spectrum when the initial oxide film is 1 nm or less 34 C1s spectrum at the time of the temperature profile experiment of FIG. 7 35 C1s spectrum at 800 ° C. holding 36 C1s spectrum before holder cleaning 37 C1s spectrum after holder cleaning

Claims (4)

[Claims] 1. A silicon surface treatment method comprising: forming a clean silicon surface by vacuum heating a silicon substrate having an oxide film having a thickness of 1 nm or more on its surface. 2. The silicon surface treatment method according to claim 1, wherein the thickness of the oxide film is set to 2 nm or less. 3. When sublimating an oxide film on the surface of a silicon substrate by vacuum heating to form a clean silicon surface, a step of increasing the sublimation temperature and lowering it again to a certain temperature is performed a plurality of times. A silicon surface treatment method, wherein the treatment is performed with a temperature profile that is gradually increased. 4. A method for cleaning a holder holding a substrate sample to remove impurities on the surface, heating and cleaning the holder in a vacuum, and then setting a silicon substrate on the holder to form a silicon-cleaned surface by vacuum heating. A surface treatment method for silicon, characterized in that: