JP2000195868A - Silicon wafer and heat treatment thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for heat treating a wafer which can reduce crystal defects on the surface layer part of the wafer with less quantity of hydrogen, while avoiding deterioration of micro-roughness of the wafer. SOLUTION: In this method for thermally treating a silicon wafer, the silicon wafer is heat treated in an inert gas atmosphere at a temperature not lower than 1,000 deg.C and not higher than a silicon melting point and, at lowering the temperature of the heat treatment, it is carried out in an atmosphere containing 1-60 volume % of hydrogen. In the silicon wafer which is heat treated by this method, the crystal defect density of a wafer bulk part is 1.0×104 defects or more per cm3, a crystal defect density of a wafer surface part down to the depth of 0.5 μm from its surface is 1.0×104 defects or less per cm3, the crystal defect density of a wafer surface is 0.15 defects or less per cm2, and a surface roughness is 1.0 nm less in P-V value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heat-treating a silicon wafer, and more particularly to a method for heat-treating a silicon wafer which is excellent in safety and can obtain a high-quality silicon wafer.

[0002]

2. Description of the Related Art As a wafer for manufacturing a semiconductor device such as a semiconductor integrated circuit, a silicon wafer is mainly used. In this semiconductor device manufacturing,
One of the factors that lower the yield is COP (Crystal
Originated Particles) and other crystal defects existing in the wafer surface layer. If such crystal defects exist in the wafer surface layer, for example, in a MOS transistor, when a high voltage is applied to a thermal oxide film such as a gate oxide film formed on the wafer surface, dielectric breakdown of the oxide film occurs. Cause it to occur.

Further, as a factor that deteriorates the yield of semiconductor device production, there is micro roughness on a wafer surface. It is known that the micro-roughness existing on the wafer surface has an adverse effect on the carrier mobility just below the gate oxide film (Shinya Yamakawa, Hirai Uen
o, Kenji Taniguchi, Chihiro Hamaguchi, Kazuo Miyat
suji, Umbert Ravaioli, J. Appl. Phys. 79 911.1995). In a semiconductor device, as the degree of integration increases, it is necessary to correspondingly improve the carrier mobility. In recent years, the driving frequency of CPUs has become increasingly higher, and accordingly, the writing and reading speeds of memories have also been required to be higher. Therefore, it is more important to reduce the micro roughness to improve carrier mobility. Have been.

As a method of reducing crystal defects in the surface layer of a silicon wafer, the defects have been eliminated by annealing heat treatment or the like. A typical example is a high-temperature hydrogen anneal. In this method, crystal defects are eliminated by performing annealing heat treatment in a high-temperature hydrogen atmosphere (see Japanese Patent Application Laid-Open No. 6-349839).

[0005] However, heat treatment in a hydrogen atmosphere can reduce crystal defects in the surface layer portion of the wafer, but has the disadvantage that the surface of the wafer is etched by the heat treatment. For example, when a heat treatment is performed at 1200 ° C. for 60 minutes, about 0.5 μm of silicon in the wafer surface layer is etched. For this reason, the portion of the wafer surface layer having few crystal defects (the defect-free layer) has a small thickness. Furthermore, it is very dangerous to handle high-concentration hydrogen gas in such a high temperature state for a long time, and it cannot be put to practical use unless safety issues are solved.

Therefore, a method of removing crystal defects in the wafer surface layer by performing a heat treatment using an inert gas such as argon in the atmosphere has been considered. However, in this method, although crystal defects can be removed without etching the wafer surface layer, there is a drawback that the micro-roughness of the wafer surface becomes worse than before the heat treatment. In addition, local etching is likely to occur under the influence of a small amount of oxygen in the atmosphere, and there is also a problem that haze occurs.

As another method for avoiding the danger of hydrogen gas, a method in which a heat treatment in a hydrogen atmosphere and a heat treatment in an atmosphere of an inert gas such as argon have been considered. According to this method, first, a step of heat-treating a wafer in an inert gas atmosphere is performed, and then a heat treatment is performed in an atmosphere containing hydrogen (see Japanese Patent Application Laid-Open No. 4-167433). However, if the heat treatment is performed in an atmosphere containing hydrogen at the same temperature after the heat treatment in an inert gas atmosphere, the wafer surface is eventually etched, and the thickness of the defect-free layer is small. Will be.

On the other hand, Japanese Patent Application Laid-Open No. 7-235507 discloses a method in which heat treatment is performed in an inert atmosphere, and hydrogen is introduced into the atmosphere when the temperature of the heat treatment is raised or lowered. However, this method is performed for the purpose of preventing the occurrence of slip dislocation in the wafer by introducing hydrogen having a higher thermal conductivity than the inert gas at the time of raising or lowering the temperature. It does not remove the crystal defects existing in the portions or improve the micro roughness of the wafer surface.

That is, this method simply introduces 1 liter of hydrogen per minute at the time of temperature rise and fall, and the composition of the optimal heat treatment atmosphere at the time of temperature rise and fall is unknown. The amount of etching on the wafer surface may increase, or the micro roughness may deteriorate,
The crystal defect density and the surface roughness of the wafer could not be simultaneously improved.

[0010]

As described above, according to the conventional heat treatment method, the crystal defects in the wafer surface layer portion can be obtained without etching the wafer surface layer portion and deteriorating the micro-roughness of the wafer with a small amount of hydrogen used. There has been no method for reducing this, and the development of an effective method has been desired.

[0011] The present invention has been made in view of such problems, and without etching the wafer surface layer,
It is another object of the present invention to provide a heat treatment method capable of reducing crystal defects in the surface layer of a wafer with a small amount of hydrogen used without deteriorating the micro roughness of the wafer.

[0012]

According to a first aspect of the present invention, there is provided a method for heat-treating a silicon wafer, comprising the steps of: providing a silicon wafer with a silicon wafer having a temperature of 1000 ° C. or more in an inert gas atmosphere; Heat treatment at a temperature equal to or lower than the melting point of
A heat treatment method for a silicon wafer, wherein the temperature is lowered in an atmosphere containing hydrogen by volume.

As described above, by subjecting a silicon wafer to a heat treatment in an inert gas atmosphere at a temperature not lower than 1000 ° C. and not higher than the melting point of silicon, crystal defects in the surface layer of the wafer are first removed. 60
By lowering the temperature in an atmosphere containing hydrogen by volume, microroughness can be improved by migration of silicon atoms on the wafer surface. In this case, a small amount of the hydrogen gas is used, so that the safety of the heat treatment step can be improved.

In this case, it is preferable that the inert gas atmosphere be an argon atmosphere or an argon atmosphere containing 30% by volume or less of hydrogen. Argon is easy to handle,
Even if it contains hydrogen, if the concentration is 30% by volume or less, etching by hydrogen in the atmosphere hardly occurs, and conversely, the effect of improving the micro roughness on the wafer surface becomes high. is there.

Further, as described in claim 3, claim 1
Alternatively, the silicon wafer heat-treated by the method described in claim 2 is, for example, a silicon wafer having a crystal defect density of 1.0 × 10 ⁴ pieces / cm ^{3 in} a wafer bulk portion as described in claim 4. As described above, the crystal defect density of the surface layer portion of the wafer from the surface to a depth of 0.5 μm is 1.
The silicon wafer has a crystal defect density of 0 × 10 ⁴ pieces / cm ³ or less, a crystal defect density of 0.15 pieces / cm ² or less, and a surface roughness of 1.0 nm or less in PV value. Here, the wafer bulk portion is defined as 0. 0 from the wafer surface.
A region having a depth exceeding 5 μm.

As described above, the silicon wafer of the present invention has a high crystal defect density at the time of growing a silicon single crystal, and the silicon surface layer portion extends from the surface to a depth of 0.5 μm. Crystal defect density of 1.0
Low defect density of × 10 ⁴ / cm ³ or less and surface roughness of P
This is a silicon wafer having a micro-roughness of less than 1.0 nm in -V value. In addition, since the bulk has crystal defects necessary for gettering impurities such as heavy metals, if a semiconductor device is manufactured using the silicon wafer of the present invention, an oxide film having excellent withstand voltage characteristics and carrier mobility can be obtained. And the yield of device fabrication can be improved.

Hereinafter, the present invention will be described in more detail. The present invention is based on the results of various quantitative studies conducted by the inventors on the heat treatment conditions for silicon wafers, especially on the composition of the heat treatment atmosphere, and as a result, has been able to find the optimum conditions, and has completed the present invention based on the results. is there.

First, the present inventors conducted an experimental investigation on the influence of the atmospheric conditions at the time of raising and lowering the temperature of the heat treatment on the surface state of the wafer. First, a plurality of silicon wafers having the same specifications are prepared, inserted into a heat treatment furnace, and heated to 1200 ° C. at a rate of 10 ° C./min.
Then, a heat treatment experiment was conducted in which the temperature was kept at 60 ° C. for 60 minutes and then cooled at a cooling rate of 3 ° C./min. At the time of this temperature rise / fall, each wafer was subjected to a heat treatment while changing the atmosphere, and the micro-roughness of the wafer after the heat treatment was evaluated by measuring a PV value (the maximum difference between a peak and a valley). The measurement was performed using an AFM (atomic force microscope) to measure a 2 μm square. The measurement results are shown in FIG.

From FIG. 1, as is conventionally known,
The PV value when the heat treatment is performed only in the argon atmosphere is about 4 times that in the case where the heat treatment is performed only in the hydrogen atmosphere.
It turns out that it has worsened by a factor of two. It can also be seen that this tendency is not affected at all even if the atmosphere at the time of temperature rise is changed to another gas.

On the other hand, unlike the case where the atmosphere at the time of temperature change is changed, when the temperature is changed from the hydrogen atmosphere to the argon atmosphere and the temperature is lowered, P-
The V value has deteriorated, and when the temperature is changed from the argon atmosphere to the hydrogen atmosphere and the temperature is lowered, the PV value is almost the same as when the heat treatment is performed in the hydrogen atmosphere despite the heat treatment in the argon atmosphere. It turns out that it is the value of.

From this fact, it was found that the micro-roughness of the wafer was not affected at all by the atmosphere at the time of raising the temperature, and the micro-roughness of the wafer was determined by the atmosphere conditions at the time of lowering the temperature. That is, even if the heat treatment is performed in an argon atmosphere, a wafer surface equivalent to that in the case where the heat treatment is performed in a hydrogen atmosphere can be obtained by changing to a hydrogen atmosphere when the temperature is lowered.

However, if the hydrogen concentration in the atmosphere at the time of temperature decrease is too high, the amount of etching of the wafer is undesirably increased. Then, the present inventors conducted further experimental studies on the heat treatment atmosphere conditions. As in the above experiment, an experiment was conducted in which a plurality of silicon wafers were prepared, heated at a heating rate of 10 ° C./min, kept at 1200 ° C. for 60 minutes, and then cooled at a cooling rate of 3 ° C./min. Atmosphere at the time of raising the temperature and maintaining the temperature was 100% argon. At the time of cooling, hydrogen was mixed in an argon atmosphere in a range of 1 to 100% by volume for each wafer, and heat treatment was performed. The micro-roughness of the heat-treated wafer was evaluated by measuring the PV value of the wafer. The result is shown in FIG.

FIG. 2 shows that if the amount of hydrogen mixed in at the time of temperature decrease is 1% by volume or more, there is an effect of improving the surface roughness of the wafer. For this reason, if the heat treatment is performed in an inert atmosphere such as argon and the temperature is lowered by mixing 1% by volume or more of hydrogen when the temperature is lowered, the micro-roughness of the wafer can be improved with a minimum amount of hydrogen used. . Conversely, if the amount of hydrogen incorporation is less than 1% by volume, the effect of improving the surface roughness of the wafer is significantly reduced, so it has been found that it is important that the amount of hydrogen incorporation be 1% by volume or more.

Further, the present inventors also performed similar measurements on the haze of the wafer. The results are shown in FIG. FIG.
It can be seen from the above that the haze of the wafer is improved by introducing 1% by volume or more of hydrogen at the time of the temperature lowering as in the case of the micro-roughness.

In addition, the present inventors also measured the relationship between the hydrogen concentration in the atmosphere when the temperature was lowered and the etching amount of the wafer. The evaluation of the etching amount was performed by using an SOI (Silicon On Insulator) wafer having a film thickness of 1 μm, measuring the SOI film thickness before and after the heat treatment, and determining the difference. FIG. 4 shows the measurement results. The vertical axis in FIG. 4 indicates an arbitrary unit (Arbitrary Unit), and is based on the etching amount at a hydrogen concentration of 100%.

As shown in FIG. 4, when the hydrogen concentration in the atmosphere at the time of temperature decrease is 30% by volume or less, the etching of the wafer surface hardly occurs. However, when the hydrogen concentration is 30% by volume
It was found that the etching began to occur when the amount exceeded 60%, and that the amount of etching of the wafer rapidly increased when the amount exceeded 60% by volume.

To summarize the above, the surface condition of the wafer after the heat treatment can be improved by introducing hydrogen into the atmosphere at the time of the temperature decrease of the heat treatment. The effect of improving roughness and haze can be sufficiently provided. Further, it was found that when the hydrogen concentration was set to 60% by volume or less, the wafer etching amount could be within an allowable range.

On the other hand, the present inventors also examined the atmosphere composition at the time of maintaining the heat treatment temperature in the heat treatment. Since it has been found that the surface roughness of the wafer can be improved by introducing an appropriate amount of hydrogen into the atmosphere at the time of temperature decrease as described above, there is no problem even if argon is used as the heat treatment atmosphere at the time of maintaining the constant temperature. The present inventors conducted experiments and studies on the relationship between the amount of etching of a wafer and the composition of the atmosphere when the heat treatment temperature was maintained.

A plurality of SOI wafers each having a thickness of 1 μm were prepared, inserted into a heat treatment furnace, and heated at a rate of 10 ° C./min.
After heating to 200 ° C. and holding at 1200 ° C. for 60 minutes, a heat treatment experiment was performed in which the temperature was lowered at a rate of 3 ° C./min.
During the constant temperature holding, each wafer was subjected to a heat treatment while changing the amount of hydrogen mixed into the argon atmosphere, and the etching amount of the SOI wafer after the heat treatment was measured.
Note that an argon atmosphere was used when the temperature was raised and lowered. Figure 5 shows the measurement results.
Shown in

As shown in FIG. 5, when the hydrogen concentration in the heat treatment atmosphere at the time of maintaining the constant temperature is 30% by volume or less, almost no etching of the wafer surface occurs even after the heat treatment at 1200 ° C. for 60 minutes. It turns out that it does not happen. Therefore, by introducing 30% by volume or less of hydrogen into the atmosphere during the constant temperature holding, the surface roughness of the wafer can be improved even during the constant temperature holding without causing etching. On the other hand, if the amount of hydrogen introduced exceeds 30% by volume, the amount of etching on the wafer surface increases, so it was found that it is preferable not to exceed this value.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. FIG. 6 is a schematic diagram showing one example of a heat treatment apparatus for performing the heat treatment according to the present invention. As shown in FIG. 6, the heat treatment apparatus 10 has a chamber 1 in which heat treatment is performed, and a support table 2 on which a wafer W to be subjected to heat treatment is placed.

A heater 3 surrounding the periphery of the chamber 1 is provided outside the chamber 1. In addition, an argon supply source 7 is supplied through a mixer 6 to an intake port 4 of the chamber 1.
And a hydrogen supply source 8 are connected so that any one of the gases can be introduced into the chamber 1 alone or an atmosphere gas having a desired mixing ratio can be introduced. Further, the chamber 1 has an exhaust port 5 from which air is exhausted.

Next, a method of heat-treating the wafer W using the heat treatment apparatus 10 will be described. First support 2
A wafer W is placed on the wafer 1 and placed in the chamber 1. Next, argon is supplied from the argon supply source 7 into the chamber 1 through the air inlet 4. In this case, a mixed gas atmosphere in which hydrogen is mixed from the hydrogen supply source 8 through the mixer 6 may be used. In this case, as described above, the mixing ratio of hydrogen is preferably set to 30% by volume or less in order to prevent wafer etching.

When the air in the chamber 1 has been sufficiently replaced by a predetermined atmospheric gas, the power supplied to the heater 3 is increased, and the chamber 1 is heated to a desired temperature. This temperature is maintained for a predetermined time. Here, maintaining the temperature means maintaining the temperature within the heat treatment temperature range, and the temperature may be increased or decreased as needed during the heat treatment.

At the end of the heat treatment of the wafer W, the hydrogen concentration in the atmosphere is increased as necessary in order to reduce the micro roughness on the surface of the wafer W. In this case, the mixing ratio of hydrogen from the hydrogen supply source 8 is increased by the mixer 6, and the hydrogen concentration in the atmosphere is controlled so as to be 1 to 60% by volume. While feeding the mixed gas having the desired hydrogen concentration from the intake port 4, the power supplied to the heater 3 is stopped or reduced to lower the temperature at a predetermined temperature lowering rate. When the temperature is lowered to a sufficient temperature, the wafer W and the support 2 are taken out of the chamber 1.

By subjecting the silicon wafer to the heat treatment as described above, it is possible to obtain a silicon wafer in which the defect-free layer thickness of the wafer surface layer is large and the micro roughness and haze of the wafer surface are improved. further,
According to the method of the present invention, hydrogen is cooled during heat treatment,
Since only a very small amount may be used, the safety of the heat treatment step can be ensured.

[0037]

EXAMPLES The present invention will now be described specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these examples. (Examples and Comparative Examples) A plurality of silicon wafers having the same specifications were prepared, inserted into a heat treatment furnace, and heated at a rate of 10 ° C / m.
After heating to 1200 ° C. and holding at 1200 ° C. for 60 minutes, a heat treatment of cooling at a temperature lowering rate of 3 ° C./min was performed. For each wafer, heat treatment was performed while changing the atmosphere conditions during temperature rise / constant temperature maintenance and the temperature conditions during temperature decrease.
Then, for each wafer after the heat treatment, the PV value, haze, COP (Crystal Originated P
article) The density and the COP density at a depth of 0.5 μm from the wafer surface were measured to evaluate the effect of the heat treatment.

As the silicon wafer, a silicon ingot manufactured by the Czochralski method, sliced by a generally used method, mirror-finished, and having a diameter of 8 inches and a crystal orientation of <100> was used. .

The PV value is measured by an AFM (Atomic Force).
Microscope, atomic force microscope, NanoScope-II
/ Digital Instruments Co., Ltd.)
The area of μm square was defined as the measurement range. Haze measurement is KL
A The test was performed using SP-1 manufactured by Tencor.

The COP on the surface of the wafer was measured using a particle counter (LS-6030, manufactured by Hitachi Electronics Engineering Co., Ltd.) in the 700 V range.
It was determined by counting the number of OPs.

The measurement of the COP density at a depth of 0.5 μm from the wafer surface was performed by growing a thermal oxide film of about 1 μm on the wafer surface and measuring the oxide film on the particle counter. . That is, the increase in the measured value before and after the oxidation is the total number of COPs included from the original silicon surface to a depth of about 0.5 μm, and the COP density is determined from this. Table 1 shows the measurement results thus obtained.

[0042]

[Table 1]

From Table 1, it can be seen that the silicon wafer (Example) subjected to the heat treatment by the heat treatment method of the present invention has a P- as good as the wafer when heat treatment is carried out only in a hydrogen atmosphere (Comparative Example 2). It has a V value and a haze, indicating that the wafer surface has low microroughness and excellent flatness.

Further, this wafer has a surface COP density as good as that of the wafer when heat treatment is performed only in an argon atmosphere (Comparative Example 3), and a COP having a depth of 0.5 μm from the surface. As for the density, the same value as in the case of only the argon atmosphere is shown. That is,
This wafer has a thick defect-free layer despite the use of an atmosphere containing hydrogen as the temperature-falling atmosphere, and it is presumed that etching of the silicon wafer surface hardly occurs.

As described above, the wafer subjected to the heat treatment of the present invention did not deteriorate the micro roughness of the wafer surface as compared with the wafer before the heat treatment (Comparative Example 1).
It can be seen that the wafer is a high quality silicon wafer from which crystal defects on the wafer surface and surface layer have been removed.

On the other hand, a wafer which was heated and maintained at a constant temperature in an argon atmosphere and cooled with 100% by volume of hydrogen (Comparative Example 4) and a wafer which was cooled with 80% by volume of hydrogen and 20% by volume of argon (Comparative Example 5) , PV value and haze are good, but the COP density at a depth of 0.5 μm from the wafer surface is a value worse than that of the wafer of the present invention. It is considered that this is because the wafer surface was etched due to the high hydrogen concentration in the atmosphere at the time of temperature decrease, and the thickness of the defect-free layer on the surface layer of the wafer was reduced to 0.5 μm or less.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.

For example, in the above-described embodiment, the description has been made mainly on the case where the silicon wafer containing many crystal defects such as COP is subjected to the heat treatment before the heat treatment is performed. The present invention can also be applied to a wafer for the purpose of improving the micro roughness of the wafer surface.

[0049]

As described above, according to the present invention, in a method of heat-treating a silicon wafer, by defining an optimum composition of a heat treatment atmosphere, the number of crystal defects on the wafer surface is small, and the defect-free layer thickness on the wafer surface layer is reduced. And a silicon wafer having a small thickness and a small micro roughness on the wafer surface can be obtained. Therefore, the yield of device manufacturing can be improved. In addition, the method of the present invention makes it possible to minimize the amount of hydrogen used, thereby ensuring the safety of the heat treatment operation.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between atmospheric conditions at the time of temperature increase and temperature decrease of a heat treatment and a PV value of a wafer after a heat treatment.

FIG. 2 shows the hydrogen concentration of the atmosphere when the temperature of the heat treatment is lowered,
FIG. 4 is a diagram showing a relationship between a wafer and a PV value after heat treatment.

FIG. 3 shows the hydrogen concentration of the atmosphere when the temperature of the heat treatment is lowered,
FIG. 3 is a diagram showing a relationship between the wafer and haze after heat treatment.

FIG. 4 is a diagram showing a relationship between a hydrogen concentration in an atmosphere at the time of temperature decrease and an etching amount of a wafer after heat treatment.

FIG. 5 is a diagram showing a relationship between an atmosphere composition at the time of maintaining a constant temperature in heat treatment and an etching amount of a wafer after heat treatment.

FIG. 6 is a schematic view showing an example of a heat treatment apparatus for performing a heat treatment according to the present invention.

[Explanation of symbols]

1 ... chamber, 2 ... support base, 3 ... heater, 4 ...
Inlet, 5: exhaust, 6: mixer, 7: argon supply, 8: hydrogen supply, 10: heat treatment apparatus, W: wafer.

[Procedure amendment]

[Submission date] December 17, 1999 (1999.12.
17)

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Fig. 5

[Correction method] Change

[Correction contents]

FIG. 5

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuichi Matsumoto 2-13-1, Isobe, Annaka-shi, Gunma Prefecture Shin-Etsu Semiconductor Semiconductor Isobe Laboratory (72) Inventor Masao Tamazuka 2 Isobe, Annaka-shi, Gunma Prefecture No. 13-1, Shin-Etsu Semiconductor Co., Ltd.

Claims (4)

[Claims] 1. A method for heat treating a silicon wafer, comprising the steps of:
A heat treatment method for a silicon wafer, comprising: performing a heat treatment at a temperature of 000 ° C. or more and a temperature equal to or lower than a melting point of silicon; 2. The method according to claim 1, wherein the inert gas atmosphere is an argon atmosphere or an argon atmosphere containing 30% by volume or less of hydrogen. 3. A silicon wafer heat-treated by the method according to claim 1. 4. A silicon wafer, wherein a crystal defect density of a wafer bulk portion is 1.0 × 10 ⁴ pieces / cm ³ or more,
In addition, the crystal defect density of the wafer surface layer portion is 1.0 × 10 ⁴ / cm ³ or less from the surface to a depth of 0.5 μm, the crystal defect density of the wafer surface is 0.15 / cm ² or less, and the surface roughness is A silicon wafer having a PV value of 1.0 nm or less.