JP2002367920A - Silicon wafer, pretreatment method and heat treatment method therefor and silicon wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform heat treatment favorably for a long period by removing an oxide film on the surface of a silicon wafer, thereby making a quartz tube less easily blurred even if heat treatment is repeated. SOLUTION: The oxide film on the surface of the silicon wafer before heat treatment is removed by washing the surface of the silicon wafer with H (hydrofluoric acid) thereby replacing oxygen combined with Si on the surface of the silicon wafer by H(hydrogen).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pretreatment method and a heat treatment method for a silicon wafer for favorably performing a heat treatment such as an RTA treatment on the silicon wafer, and a silicon wafer manufactured by the method.

[0002]

2. Description of the Related Art A silicon wafer manufactured by processing a silicon single crystal grown by the CZ (Czochralski) method contains a large amount of oxygen impurities, which generate dislocations and defects. Oxygen precipitate (BMD: Bulk M
icro Defect). When this oxygen precipitate is present on the surface on which the device is formed, it causes an increase in leak current and a decrease in oxide film breakdown voltage, which greatly affects the characteristics of the semiconductor device.

For this reason, conventionally, a heat treatment (RTA) of rapid heating and quenching at a high temperature of 1250 ° C. or more for a short time is performed on a silicon wafer surface in a predetermined atmosphere gas, and an excess vacancy (Vacancy) is internally formed. While burying
A method of uniformly forming a DZ layer (a defect-free layer) by outwardly diffusing vacancies on the surface by a subsequent heat treatment is used (for example, a technique described in International Publication WO 98/38675). After the formation of the DZ layer, a step of forming and stabilizing an oxygen precipitation nucleus as an internal defect layer by performing a heat treatment at a temperature lower than the above temperature to form a BMD layer having a gettering effect is adopted. As another conventional technique (for example, a technique described in International Publication WO98 / 45507), a heat treatment is first performed in an oxygen atmosphere, and then a heat treatment is performed in a non-oxidizing atmosphere to thereby obtain a DZ on the surface layer. And BMD formation inside.

Conventionally, as an apparatus for performing the heat treatment for forming the DZ layer, a silicon wafer is placed in a quartz tube and externally heated by a lamp using an infrared lamp or the like while supplying an atmospheric gas into the quartz tube. Irradiation of infrared rays (light rays) is performed. Further, in such a heat treatment apparatus, N ₂ (nitrogen) is used as the atmosphere gas.
Is mainly used. That, N ₂ is decomposed at a high temperature, by the surface of the silicon wafer Si _x N _y (nitride film) is formed, it is possible to inject Vacancy, it is possible to increase moderately internal BMD density It is. In this heat treatment apparatus, the temperature of the silicon wafer installed in the quartz tube is measured from outside the quartz tube using an optical thermometer such as an optical pyrometer, and the heat treatment of the silicon wafer is performed using the thermometer of this thermometer. The heating temperature is controlled based on the measured value. Here, if the light emitted from the silicon wafer is absorbed by the quartz tube, the thermometer cannot measure the temperature of the silicon wafer accurately. Is made of anhydrous quartz with low light absorption.

[0005]

As shown in FIG. 4, the silicon wafer before the heat treatment has O (Si) on the surface.
A natural oxide film (SiO _x ) formed by bonding (oxygen) by dangling bonds is formed. When this silicon wafer W is subjected to a heat treatment, the SiO _X formed on the surface of the silicon wafer W sublimates and adheres to the inner surface of the quartz tube to form a film, and particularly adheres much to the inner surface near the silicon wafer W. As the heat treatment was repeated, uneven fogging gradually occurred in the quartz tube. In this case, the transparency and non-uniformity of the transparency of the quartz tube are reduced, the transmittance of infrared rays is reduced by lamp heating, the temperature on the wafer surface is reduced, the temperature distribution is non-uniform, the heat treatment is insufficient, and the slip is insufficient. In some cases, inconveniences such as generation of odor occurred. In addition, for this reason, maintenance for cleaning the inner surface of the quartz tube in a short cycle and replacement of the quartz tube are required, and the throughput is reduced.

Further, since the transparency of the quartz tube is reduced and the light transmittance is reduced, the thermometer measures the temperature of the silicon wafer W lower than the actual temperature. As described above, since the temperature of the silicon wafer W is measured lower, even if the silicon wafer W is heated to an appropriate temperature based on the temperature measured by the thermometer, the silicon wafer W is actually heated to an unnecessarily high temperature. Was sometimes done. Further, when the silicon wafer W is heated to an unnecessarily high temperature, sublimation of SiO _x is further promoted, and clouding of the quartz tube becomes severe. Conventionally, before the heat treatment, the surface of the silicon wafer was subjected to SC1 cleaning to remove the oxide film on the surface. However, this method only removes the oxide film on the surface. An oxide film is again formed on the surface of the silicon wafer before the application.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a silicon wafer pretreatment method capable of effectively performing a heat treatment over a long period of time without causing fogging of a quartz tube even when silicon wafer heat treatment is repeated. And a heat treatment method, and a silicon wafer manufactured by the pretreatment method and the heat treatment method.

[0008]

The present invention has the following features to attain the object mentioned above. That is, the pretreatment method for a silicon wafer of the present invention is a pretreatment method for a silicon wafer performed before irradiating the silicon wafer with a light beam and performing a heat treatment, wherein the surface of the silicon wafer before the heat treatment is cleaned with hydrofluoric acid. In this method, oxygen bonded to silicon on the surface is replaced with hydrogen. In this method for pretreating a silicon wafer, the surface of the silicon wafer is cleaned with hydrofluoric acid to replace oxygen bonded to silicon on the surface with hydrogen, so that an oxide film formed on the surface of the silicon wafer is removed. Furthermore, since hydrogen is bonded to silicon on the surface of the silicon wafer by this, an oxide film is less likely to be formed on the surface of the silicon wafer after performing the pretreatment and removing the oxide film.

In addition, by irradiating a light beam to the silicon wafer which has been subjected to the pre-treatment by the pre-treatment method of the silicon wafer and performing a heat treatment, sublimation of SiO _X from the surface of the silicon wafer during the heat treatment. Is difficult to form, so that a SiO _X film is not easily formed on the inner surface of the quartz tube, and the quartz tube is less likely to be fogged.

[0010] The silicon wafer of the present invention is a silicon wafer before being subjected to a heat treatment, characterized in that the surface is cleaned with hydrofluoric acid and oxygen bonded to silicon on the surface is replaced with hydrogen. I have. In the silicon wafer configured as described above, the surface is cleaned with hydrofluoric acid, oxygen bonded to silicon on the surface is replaced with hydrogen, and the oxide film formed on the surface is removed. Further, since hydrogen is bonded to silicon on the surface, an oxide film is not easily formed on the surface of the silicon wafer.

Further, the silicon wafer of the present invention is characterized in that the silicon wafer is subjected to a heat treatment.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 4, the surface of the silicon wafer before the heat treatment
O (oxygen) is bonded to (silicon) by a dangling bond to form an oxide film. In the pretreatment method for a silicon wafer according to the present embodiment, the surface of the silicon wafer before the heat treatment is cleaned with HF (hydrofluoric acid).

As described above, the surface of the silicon wafer is
By cleaning, the S on the surface of the silicon wafer
O bonded to i is replaced with H, and the oxide film on the surface of the silicon wafer is removed. In the silicon wafer W1 thus obtained, since the surface Si is bonded to H as shown in FIG. 1, O is hardly bonded to the surface Si for a while after the cleaning, and the silicon wafer W1 is oxidized. The formation of a film is suppressed.

The silicon wafer W1 is heat-treated by, for example, a heat treatment apparatus 1 shown in FIG. As a heat treatment condition at this time, for example, a treatment is performed at 1250 ° C. for 10 seconds.
The heat treatment apparatus 1 uses a support or the like in a quartz tube 2 to place the silicon wafer W1 in a state of being separated from the inner surface thereof, and supplies an atmospheric gas G into the quartz tube 2 while externally supplying an infrared lamp 3 Heat treatment is performed by performing infrared irradiation by lamp heating using a method such as the above. Since the silicon wafer W1 is heat-treated in a state where the oxide film on the surface is removed, the silicon wafer W1
Sublimation of SiO _X hardly occurs from the inner surface of the quartz tube 2 is coating of SiO _X is hardly formed, fogging is less likely to occur in the quartz tube 2 by repeating heat treatment.

As described above, according to the pretreatment method and heat treatment method for a silicon wafer and the silicon wafer W1 according to the present embodiment, the heat treatment can be performed with the oxide film on the surface of the silicon wafer removed. SiO _x from silicon wafer W1 even if
Is less likely to occur, so that uneven fogging of the quartz tube 2 can be suppressed. For this reason, it is possible to make it difficult to reduce the transparency of the quartz tube 2 and to make the transparency non-uniform. And a good heat treatment can be performed. In addition, since the decrease in the light transmittance of the quartz tube 2 is suppressed, the optical thermometer 4 is used.
Accordingly, the temperature of the silicon wafer W1 can be accurately measured, the temperature control during the heat treatment can be improved, and a silicon wafer that has been appropriately heat-treated can be obtained.

The technical scope of the present invention is not limited to the above embodiment, and various changes can be made without departing from the spirit of the present invention. For example, in the above embodiment, the silicon wafer W1 is heated by irradiating the silicon wafer W1 with infrared rays using the infrared lamp 3 when performing the heat treatment on the silicon wafer W1, but may be heated by another light beam (visible light or the like). Absent.

[0017]

EXAMPLE Next, a test was conducted to measure the effect of suppressing the formation of an oxide film on a silicon wafer W1 which has been subjected to a silicon wafer pretreatment according to the present invention. In this test, in the heat treatment apparatus 1, the silicon wafer W1 immediately after the cleaning with HF and the silicon wafer W1 with a time after the cleaning are each continuously heat-treated (RTA treatment) for 100 wafers, and then similarly to the monitoring silicon wafer. And a heat treatment is performed, and the thickness variation σ (%) of the oxide film formed on the surface of the monitor silicon wafer
Was examined. The variation σ (%) in the thickness of the oxide film formed on the surface of the monitoring silicon wafer indicates uneven heating of the monitoring silicon wafer during the heat treatment, which occurs in the quartz tube 2 of the heat treatment apparatus 1. Caused by uneven light transmittance. In this test, the state of the film formed on the inner surface of the quartz tube 2 by SiO _X sublimated from the silicon wafer W1 was determined from the magnitude of the variation σ (%). In addition,
In this RTA process for forming an oxide film, heating was performed at 1250 ° C. for 10 seconds in a dryO ₂ atmosphere. The results are shown in the graph of FIG.

FIG. 3 shows that 100 silicon wafers W1 immediately after the cleaning with HF and within one hour after the cleaning were subjected to RTA.
In the case of the treatment, the variation σ (%) of the thickness of the oxide film formed on the surface of the monitoring silicon wafer is 1.2%.
Since the thickness of the oxide film is not uneven, it can be understood that the light transmittance of the quartz tube 2 is not uneven. From this, the silicon wafer W1 immediately after the cleaning with the HF and within one hour after the cleaning is SiO
_It can be seen that sublimation of _X hardly occurs and the film hardly grows. In addition, after RTA processing of 100 silicon wafers W1 within 2 hours after the cleaning with HF, the variation σ in the thickness of the oxide film on the surface of the monitoring silicon wafer is obtained.
(%) Is 1.3%, indicating that the thickness of the oxide film is similarly small. However, when the RTA treatment is performed on the silicon wafer W1 which has been left for a long time after the cleaning,
The variation σ (%) in the thickness of the oxide film on the surface of the silicon wafer for monitoring indicates that the silicon wafer W1 immediately after the cleaning is RT.
The variation in thickness of the oxide film on the surface of the monitoring silicon wafer after RTA processing of 100 silicon wafers W1 three days after cleaning, which is larger than that in the case of processing A, σ
(%) Is as large as 2.0%, and it can be seen that the film formed on the inner surface of the quartz tube 2 is thick and unevenness is increased. As described above, according to the pretreatment method and heat treatment method for a silicon wafer and the silicon wafer according to the present invention, an oxide film is not easily formed on the surface of the silicon wafer for a while after the cleaning, and the oxide film is removed by the cleaning. In the silicon wafer within 24 hours after the cleaning, particularly the silicon wafer within 2 hours after the cleaning, the unevenness of the film thickness distribution of the SiO _X film formed on the inner surface of the quartz tube 2 during the RTA treatment is suppressed, and the RTA treatment S if
iO sublimation hardly occurs in _X, it can be seen that the film is less likely to grow.

[0019]

According to the present invention, the following effects can be obtained.
According to the pretreatment method and heat treatment method for a silicon wafer and the silicon wafer according to the present invention, the surface of the silicon wafer is cleaned with hydrofluoric acid to replace oxygen bonded to silicon on the surface with hydrogen, so that the surface of the silicon wafer The oxide film formed on the substrate is removed. Furthermore, since hydrogen is bonded to silicon on the surface of the silicon wafer by this, an oxide film is less likely to be formed on the surface of the silicon wafer after performing the pretreatment and removing the oxide film. Since the silicon wafer can be subjected to the heat treatment in a state where the oxide film on the surface is removed in this manner, sublimation of SiO _X from the surface of the silicon wafer is less likely to occur, and the SiO _X film is formed on the inner surface of the quartz tube. It is difficult to be formed, and clouding is less likely to occur in the quartz tube. This makes it difficult for the quartz tube to have reduced transparency and non-uniformity in transparency, and maintains the transmittance of infrared light due to lamp heating of the quartz tube even after repeated heat treatments, thereby lowering the temperature and unevenness in the temperature distribution on the wafer surface. Good heat treatment can be performed without uniformity.
In addition, since the decrease in the light transmittance of the quartz tube is suppressed in this manner, the temperature of the silicon wafer can be accurately measured by an optical thermometer, and the temperature control during the heat treatment is improved and the It is possible to obtain a silicon wafer that has been subjected to an appropriate heat treatment.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a surface state of a silicon wafer subjected to a pretreatment of the silicon wafer according to one embodiment of the present invention.

FIG. 2 is a diagram schematically showing a configuration of a heat treatment apparatus for a silicon wafer.

FIG. 3 is a graph showing a variation in thickness of an oxide film formed on a monitor wafer that has been subjected to a heat treatment after heat-treating 100 cleaned silicon wafers according to the example of the present invention.

FIG. 4 is a view schematically showing a surface state of a conventional silicon wafer before heat treatment.

[Explanation of symbols]

 W1 Silicon wafer Si Silicon O Oxygen H Hydrogen

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hiroyuki Shiraki F-term (reference) 5F043 AA02 BB02 BB27 DD02 GG10 in 5-1-1, Otemachi, Chiyoda-ku, Tokyo

Claims (4)

[Claims] 1. A pretreatment method for a silicon wafer, which is performed before irradiating the silicon wafer with a light beam to perform a heat treatment, wherein the surface of the silicon wafer before the heat treatment is washed with hydrofluoric acid and bonded to silicon on the surface. A method for pretreating a silicon wafer, wherein oxygen is replaced with hydrogen. 2. A method for heat treating a silicon wafer, wherein the silicon wafer pretreated by the method for pretreating a silicon wafer according to claim 1 is irradiated with a light beam to perform a heat treatment. 3. A silicon wafer before being subjected to a heat treatment, wherein the surface of the silicon wafer is cleaned with hydrofluoric acid and oxygen bonded to silicon on the surface is replaced with hydrogen. 4. A silicon wafer obtained by subjecting the silicon wafer according to claim 3 to heat treatment.