JP2011171414A - Heat treatment method of silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat treatment method of a silicon wafer capable of extinguishing a crystal defect such as a COP on the surface of a wafer as a device active region, capable of forming a BMD with a high density in a bulk, and capable of suppressing a slip generated in an RTP. <P>SOLUTION: The heat treatment method thermally treats the silicon wafer obtained by slicing a silicon single-crystal ingot manufactured by a Czochralski method. In the heat treatment method of the silicon wafer, the front and rear surface of the wafer are supplied with an oxygen-containing gas, a maximum reaching temperature T1 is set at a value from 1,300°C to the melting point of silicon and a temperature-drop speed from the maximum reaching temperature is set at the value from 75°C/sec to 120°C/sec, and rapid-heating/rapid-cooling heat treatment is conducted. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a heat treatment method applied to apply a silicon wafer obtained by slicing a silicon single crystal ingot manufactured by the Czochralski method to a semiconductor device.

  Silicon wafers used as semiconductor device forming substrates (hereinafter also simply referred to as wafers) have crystal defects such as COP (Crystal Originated Particles) in the vicinity of the surface (hereinafter referred to as the surface portion) of the wafer serving as a device active region. It is required not to exist.

  Such a silicon wafer is obtained by growing a silicon single crystal ingot having a defect-free region free from crystal defects and slicing from the defect-free region when growing a silicon single crystal by the Czochralski method (CZ method). The wafer can be manufactured by a method of forming a defect-free layer on the surface portion of the wafer by heat-treating the wafer at a high temperature.

  Among these methods, the method of heat-treating the wafer at a high temperature is to carry out the heat treatment at a high temperature of 1250 ° C. or higher for 1 hour or more in an inert gas or reducing gas atmosphere to remove the solid solution oxygen on the surface of the wafer outward. A technique for diffusing and eliminating COP, BMD (Balk Micro Defect) and the like is known (for example, Patent Document 1).

However, since the heat treatment method as shown in Patent Document 1 performs heat treatment for a long time, the productivity is lowered and the manufacturing cost in the heat treatment is increased. Moreover, since the concentration of dissolved oxygen in silicon decreases due to the outward diffusion of oxygen at the surface portion of the wafer that has been heat-treated for a long time, when such a wafer is used in a device process, Dislocations generated by the application of strain tend to extend in the subsequent heat treatment, causing a reduction in device yield.
Further, since the heat treatment takes a long time, there is also a problem that the wafer is likely to slip even during the heat treatment.

  Therefore, in recent years, a silicon wafer is subjected to a rapid heating / cooling heat treatment (hereinafter also simply referred to as RTP (Rapid Thermal Process)) at a high temperature of 1150 ° C. or more in seconds, thereby becoming a device active region. A technique for forming a defect-free layer on the surface of a wafer has been used (for example, Patent Document 2).

However, a silicon wafer manufactured using a technique as described in Patent Document 2 has a BMD density formed inside the wafer (hereinafter referred to as a bulk portion) of 5.0 × 10 ⁹ cm ⁻ at the maximum. It is about ³ , and there is a limit in improving the BMD density in the bulk part.
Further, Patent Document 2 does not describe that slip generated on the wafer in the heat treatment can be suppressed.

On the other hand, in Patent Document 3, a silicon substrate manufactured by the CZ method has a maximum holding temperature of 1125 ° C. or higher and a melting point of silicon or lower in a mixed atmosphere of 100% nitrogen or 100% oxygen, or oxygen and nitrogen, After performing heat treatment with a holding time of 5 seconds or more, a silicon substrate having desired oxygen precipitation characteristics can be obtained without controlling the oxygen concentration by rapid cooling from the maximum holding temperature at a cooling rate of 8 ° C./second or more. Techniques that can be obtained are disclosed.
By using this technique, it is possible to form a BMD having a high internal defect density (BMD density in the bulk portion) of about 1.0 × 10 ¹⁰ cm ^{−3 at the} maximum.

JP 2006-261632 A JP-T-2001-509319 JP 2000-31150 A

  However, Patent Document 3 does not describe that a defect-free layer is formed on the surface portion of the wafer or that slip generated on the wafer during the heat treatment can be suppressed.

  The present invention has been made to solve the above technical problem, and can eliminate crystal defects such as COP in the surface portion of the wafer serving as a device active region, and BMD at a high density in the bulk portion. It is an object of the present invention to provide a method for heat-treating a silicon wafer that can be formed and that can suppress slip generated in RTP.

  The silicon wafer heat treatment method according to the present invention is a method of heat treating a silicon wafer obtained by slicing a silicon single crystal ingot produced by the Czochralski method, supplying an oxygen-containing gas to the front and back surfaces of the wafer, Rapid heating / cooling heat treatment is performed by setting the maximum temperature to 1300 ° C. or more and the melting point of silicon or less, and the temperature decreasing rate from the maximum temperature to 75 ° C./second or more and 120 ° C./second or less.

  The supply amount of the oxygen-containing gas supplied to the front surface of the wafer is preferably larger than the supply amount of the oxygen-containing gas supplied to the back surface of the wafer.

According to the heat treatment method of a silicon wafer according to the present invention, crystal defects such as COP can be eliminated in the surface portion of the wafer to be a device active region, and BMD can be formed at a high density in the bulk portion, Furthermore, a silicon wafer heat treatment method capable of suppressing slips generated in RTP is provided.
Therefore, the silicon wafer subjected to the heat treatment by the method according to the present invention greatly contributes to the improvement of the yield in the semiconductor device process.

It is sectional drawing which shows the outline | summary of the chamber part of the RTP apparatus used for the heat processing method of the silicon wafer which concerns on this invention. It is a conceptual diagram for demonstrating an example of the heat processing sequence in RTP applied to the heat processing method of the silicon wafer which concerns on this embodiment. It is the figure which showed typically the relationship between V / G and the generation | occurrence | production position of a crystal defect at the time of silicon single crystal ingot manufacture. It is a graph which shows the relationship between the temperature-fall rate in Test 1, BMD density, and slip total length. It is a graph which shows the relationship between the temperature-fall rate in Test 2, BMD density, and slip total length.

Hereinafter, the present invention will be described in more detail with reference to the drawings. The silicon wafer heat treatment method according to the present invention is such that RTP is applied to a silicon wafer obtained by slicing a silicon single crystal ingot produced by the Czochralski method, and oxygen-containing gas is supplied to the front and back surfaces of the wafer. RTP is performed by setting the maximum temperature to 1300 ° C. or higher and the melting point of silicon or lower and the rate of temperature decrease from the maximum temperature to be 75 ° C./second or higher and 120 ° C./second or lower.
By performing such a heat treatment, crystal defects such as COP can be eliminated in the surface portion of the wafer serving as a device active region, and BMD has a high density of 1.0 × 10 ¹⁰ cm ⁻³ level in the bulk portion. Further, slip generated on the wafer in RTP can be suppressed.

  As described above, an oxygen-containing gas is supplied to the front and back surfaces of the wafer to perform RTP, thereby forming a silicon oxide film on the wafer surface. At this time, a large amount of interstitial silicon is generated at the silicon oxide film and the silicon interface. If the RTP temperature is high, these interstitial silicon diffuses into the wafer, and in particular fills the COP present on the surface of the wafer, so that crystal defects on the surface of the wafer can be eliminated. Further, since oxygen is injected into the wafer, the concentration of dissolved oxygen in the surface portion of the wafer can be increased. For this reason, when the wafer subjected to the heat treatment as described above is used in the device process, it is possible to suppress the elongation of dislocations generated by the application of stress or strain generated in the device process.

In addition, by increasing the temperature-decreasing rate from the highest temperature achieved in RTP and controlling it within the above range, the interstitial silicon having a high diffusion rate is outwardly diffused while suppressing the occurrence of slip, so that BMD grows. In this way, a depth region can be formed in which the holes necessary for the remaining are left.
As a result, it is possible to prevent vacancies existing in the bulk portion of the wafer from being buried and extinguished by the interstitial silicon, and to increase the concentration of vacancies remaining in the bulk portion. BMD density can be improved.

Further, by setting the maximum temperature reached in RTP to 1300 ° C. or higher and the melting point of silicon or lower, the inner wall oxide film of COP existing in the wafer can be efficiently dissolved.
For this reason, the COP extinction force due to the interstitial silicon filling can be increased in the surface portion of the wafer, while many vacancies can be formed in the bulk portion of the wafer. Can be formed.

  Further, since the oxygen-containing gas is also supplied to the back surface of the wafer, the concentration of dissolved oxygen on the back surface side of the wafer can be increased. Thereby, since the intensity | strength on the back surface side of a wafer improves, the slip which generate | occur | produces in the said RTP can further be suppressed.

The silicon wafer heat treatment method according to the present invention as described above can be suitably performed by, for example, an RTP apparatus as shown in FIG.
FIG. 1 is a cross-sectional view showing an outline of a chamber portion of an RTP apparatus used in a silicon wafer heat treatment method according to the present invention.
A chamber unit 10 of the RTP apparatus shown in FIG. 1 includes a reaction tube 20 that accommodates a wafer W, a wafer support unit 30 that is disposed in the reaction tube 20 and on which the wafer W is placed, and the wafer W. And a plurality of lamps 40 that are heated by light irradiation.

The reaction tube 20 includes a gas supply port 22 for supplying a first atmospheric gas F _A (solid arrow in the figure) to the first space 20a on the surface W1 side where the semiconductor device of the wafer W is formed, and the first A gas discharge port 26 for discharging gas from the first space 20a, a gas supply port 24 for supplying a second atmospheric gas F _B (dotted arrow in the figure) to the second space 20b on the back surface W2 side of the wafer W, And a gas discharge port 28 for discharging gas from the second space 20b.
The first atmospheric gas F _A and the second atmospheric gas F _B are used as atmospheric gases during heat treatment in the RTP of the wafer W. The second atmosphere gas F _B is also used as a cooling gas in the RTP if necessary.
In the present invention, in the RTP, an oxygen-containing gas is used for both the first atmospheric gas F _A and the second atmospheric gas F _B.

  Hereinafter, an example of a heat treatment method for a silicon wafer according to the present invention using the RTP apparatus shown in FIG. 1 will be described. FIG. 2 is a conceptual diagram for explaining an example of a heat treatment sequence in RTP applied to the silicon wafer heat treatment method according to the present embodiment.

In the heat treatment sequence shown in FIG. 2, first, the outer peripheral portion of the back surface W2 of the wafer W is placed on the susceptor 32 of the wafer support portion 30 in the reaction tube 20 maintained at a temperature T0 (for example, 600 ° C.). To support. Then, while supplying the first atmospheric gas F _A from the gas supply port 22, the gas discharge port 26 is discharged first atmospheric gas F _A, and a second atmosphere gas F _B from the gas supply port 24 while supplying, to the gas discharge port 28 discharging the second ambient gas F _B. Then, while rotating the susceptor 32 by the susceptor rotating unit 34, the wafer W is rapidly heated to a maximum temperature T1 (° C.) at a predetermined temperature increase rate ΔTu (° C./second) by light irradiation from the lamp 40.
Next, the maximum temperature T1 is maintained for a predetermined time t (seconds).
Then, if necessary, from the gas supply port 24 by increasing the supply amount of the second ambient gas F _B, rapidly cooling the wafer W at a predetermined temperature lowering rate .DELTA.Td (° C. / sec).

Note that the temperature measurement of the wafer W in the heat treatment sequence is performed by, for example, a radiation thermometer (not shown) disposed below the wafer W. The temperature increase rate and the temperature decrease rate are controlled by a control means (not shown) based on the temperature measured as described above, or by individual output control of the lamp 40 or the first atmospheric gas F _A or performed by controlling the flow rate or the like of the second ambient gas F _B.

The wafer subjected to RTP in the present invention is a wafer obtained by slicing a silicon single crystal ingot manufactured by the CZ method.
Production of a silicon single crystal ingot by the CZ method can be performed by a known method. Specifically, the polycrystalline silicon filled in the quartz crucible is heated to form a silicon melt, the seed crystal is brought into contact with the liquid surface of the silicon melt, and the seed crystal is pulled up while rotating the seed crystal and the quartz crucible. The silicon single crystal ingot is grown by expanding to a desired diameter to form a straight body portion and then separating from the silicon melt.
Next, the silicon single crystal ingot thus obtained is processed into a silicon wafer by a known method. Specifically, after slicing a silicon single crystal ingot into a wafer shape with an inner peripheral blade or a wire saw, processing such as chamfering, lapping, etching, and mirror polishing of the outer peripheral portion is performed.

  For the mirror-polished silicon wafer obtained as described above, an oxygen-containing gas is supplied to the front and back surfaces of the wafer using an RTP apparatus as shown in FIG. RTP is performed at a temperature lower than the melting point of silicon and a rate of temperature decrease from the highest temperature reached not lower than 75 ° C./second and not higher than 120 ° C./second.

When the gas supplied to the front and back surfaces of the wafer is a non-oxidizing gas (for example, 100% inert gas or 100% hydrogen gas), a silicon oxide film is not formed on the wafer surface, and a large amount of lattice Silicon is not produced. For this reason, it is not preferable because the crystal defects in the wafer surface layer cannot be efficiently eliminated.
Further, in this case, oxygen is not injected into the wafer, but conversely diffuses outward, so that the concentration of dissolved oxygen in the surface layer portion of the wafer decreases. Therefore, when a wafer subjected to the heat treatment as described above is used in a device process, it is difficult to suppress the elongation of dislocations generated by application of stress or strain generated in the device process.
Further, since the concentration of dissolved oxygen on the back surface side of the wafer cannot be increased, the strength on the back surface side of the wafer is not improved, and it is difficult to suppress slip generated in the RTP.

In the oxygen-containing gas, the oxygen partial pressure is preferably 20% or more and 100% or less.
If the oxygen partial pressure is less than 20%, the concentration of interstitial silicon that fills the COP decreases, and the COP extinction power at the surface of the wafer decreases, which is not preferable.

The gas other than oxygen gas in the oxygen-containing gas is preferably an inert gas.
When nitrogen gas is used as a gas other than the oxygen gas, a nitride film is formed on the wafer surface in the RTP, and an additional etching process or the like must be added to remove the nitride film, which increases the number of processes. Therefore, it is not preferable. Also, it is not preferable to use hydrogen gas because a mixed gas of oxygen and hydrogen has a risk of explosion. In addition, an ammonia-based gas is not preferable because the extinction power of crystal defects such as COP is reduced.
Argon gas is preferably used as the inert gas. By using argon gas, RTP can be performed without forming other films such as a nitride film, chemical reaction, or the like.

When the maximum temperature reached is less than 1300 ° C., it is difficult to increase the extinction power of crystal defects such as COP in the surface portion of the wafer that becomes the device active region.
On the other hand, when the highest temperature exceeds the silicon melting point, the silicon wafer to be heat-treated is melted, which is not preferable.
The upper limit of the maximum temperature reached is more preferably 1380 ° C. or less from the viewpoint of the device life as an RTP device.

Further, when the temperature lowering rate is less than 75 ° C./second, it is difficult to increase the BMD density in the bulk portion of the wafer to a level of 1.0 × 10 ¹⁰ cm ⁻³ .
On the other hand, when the temperature decreasing rate exceeds 120 ° C./second, the BMD density inside the wafer can be further increased, but it is difficult to suppress slip generated on the wafer in RTP, which is not preferable.

The rate of temperature increase in the RTP heat treatment sequence is preferably 10 ° C./second or more and 150 ° C./second or less.
When the rate of temperature increase is less than 10 ° C./second, productivity is lowered, which is not preferable.
On the other hand, if the rate of temperature rise exceeds 150 ° C./second, it cannot withstand a rapid temperature change, and the wafer may slip.

The holding time t for holding the maximum temperature T1 is preferably 1 second or more and 60 seconds or less.
When the holding time t is less than 1 second, it is difficult to achieve reduction of crystal defects and improvement of BMD density, which are the original purposes of RTP.
On the other hand, when the holding time t exceeds 60 seconds, productivity is lowered, which is not preferable.

In the present invention, the wafer subjected to RTP is obtained by slicing a silicon single crystal ingot manufactured by the CZ method as described above, but the void type point defect is dominant in the silicon single crystal ingot. It is preferable that it is obtained by slicing from an existing region.
Hereinafter, the defect region in the silicon single crystal ingot will be described with reference to FIG.

  FIG. 3 is a cross-sectional view of the ingot schematically showing the relationship between v / G and the position of occurrence of crystal defects during the production of a silicon single crystal ingot. Here, v represents the pulling speed, and G represents the temperature gradient G in the pulling axis direction in the single crystal. [V] is a region where vacancy type point defects exist predominantly (hereinafter referred to as [V] region), and [I] is a region where interstitial silicon type point defects exist predominantly (hereinafter referred to as [I]. ], [N] is an area where no interstitial silicon type point defect aggregates and vacancy type point defect aggregates exist (hereinafter referred to as [N] area), and [OSF] is the [V] area. And a region where an OSF (Oxidation-induced Stacking Fault) occurs when a silicon single crystal ingot is thermally oxidized in the state of a silicon wafer (hereinafter referred to as an [OSF] region).

In FIG. 3, the wafer to be heat-treated in the present invention is from a region where vacancy-type point defects exist predominantly, that is, from a position including only the [V] region or only the [OSF] region and the [V] region. It is preferably sliced.
The wafer sliced from the [N] region does not have holes necessary for the growth of BMD nuclei in the bulk portion, so there is a limit to increasing the BMD density. Further, it is well known that a wafer sliced from the [I] region cannot be used as a semiconductor device forming substrate.

As described above, if the wafer is sliced from only the [V] region or from a position including only the [OSF] region and the [V] region, the v / G during the growth of the silicon single crystal ingot in the CZ method. , That is, the pulling speed v can be increased, so that productivity can be improved and ingot growing cost can be reduced. Furthermore, since many holes necessary for the growth of BMD nuclei can be formed in the bulk portion, BMD can be formed at a high density in later RTP.
More preferably, the whole wafer is sliced so as to be composed of only the [V] area not including the [OSF] area. If the wafer does not include the [OSF] region, the BMD density can be made uniform in the wafer surface in addition to the above effects.

The supply amount of the oxygen-containing gas supplied to the front surface of the wafer is preferably larger than the supply amount of the oxygen-containing gas supplied to the back surface of the wafer.
With such a configuration, since the pressure on the front surface W1 of the wafer W is larger than the pressure on the back surface W2, the movement of the wafer W on the susceptor 32 in the RTP is suppressed, so that slip generated in the RTP is generated. Can be further suppressed. Further, when the wafer W is rotated by the susceptor rotating unit 34, the flying wafer W can be prevented from flying.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not restrict | limited by the following Example.
(Test 1) Relationship 1 between temperature drop rate, BMD density and slip total length
A silicon single crystal ingot having a region in which vacancy-type point defects exist predominantly by controlling v / G by the CZ method, and a silicon wafer in which both surfaces obtained by slicing from the region are mirror-polished ( 100% oxygen (flow rate 15 slm) gas is supplied to the front and back sides of the silicon wafer for a diameter of 300 mm and a thickness of 775 μm), a temperature T0: 600 ° C., a heating rate of 70 ° C./second, a maximum attained temperature of 1350 ° C., RTP was performed while changing the cooling rate as shown in Table 1 during the holding time of 15 seconds.
When the temperature decreasing rate is 120 ° C./second or more (Example 3, Comparative Examples 2 and 3), the flow rate of 100% oxygen gas supplied to the back side of the silicon wafer is set to increase the wafer cooling rate. Increased.

The obtained annealed wafer was subjected to a BMD precipitation heat treatment (780 ° C. × 3 hours + 1000 ° C. × 16 hours), and then the BMD density in the bulk portion of the wafer from the surface to a depth of 180 μm was measured by IR tomography (Inc. Measured with MO-411) manufactured by Raytex.
Further, the total slip length of the annealed wafer obtained above was measured by X-ray topography (XRT300, manufactured by Rigaku Corporation).
Table 1 shows the measurement results of the BMD density and slip total length at each cooling rate. FIG. 4 is a graph showing the relationship between the cooling rate, the BMD density, and the slip total length based on the results of Table 1.

From the results shown in Table 1 and the graph of FIG. 4, it was recognized that the BMD density of the wafer increased and the slip length due to thermal stress increased as the temperature drop rate in RTP increased.
From the above results, if the rate of temperature decrease is in the range of 75 ° C./second or more and 120 ° C./second or less, the slip generated in RTP is suppressed to an allowable range, and the BMD density is 1.0 × 10 ¹⁰ in the bulk portion. It has been observed that it can be grown at a density higher than the cm ⁻³ level.

(Test 2) Relationship 2 between temperature drop rate, BMD density and slip total length 2
100% oxygen (flow rate 15 slm) gas was supplied to the front side of the silicon wafer, and 100% oxygen (flow rate 5 slm) gas was supplied to the back side of the silicon wafer.

The obtained annealed wafer was subjected to a BMD precipitation heat treatment (780 ° C. × 3 hours + 1000 ° C. × 16 hours), and then the BMD density in the bulk portion of the wafer from the surface to a depth of 180 μm was measured by IR tomography (Inc. Measured with MO-411) manufactured by Raytex.
Further, the total slip length of the annealed wafer obtained above was measured by X-ray topography (XRT300, manufactured by Rigaku Corporation).
Table 2 shows the measurement results of the BMD density and slip total length at each cooling rate. FIG. 5 is a graph showing the relationship between the cooling rate, the BMD density, and the total slip length based on the results shown in Table 2.

From the results shown in the graphs of Table 2 and FIG. 5, as in Test 1, the BMD density of the wafer tends to increase and the slip length due to thermal stress tends to increase as the temperature drop rate in RTP increases. It was.
Similarly to Test 1, when the temperature decrease rate is in the range of 75 ° C./second or more and 120 ° C./second or less, the slip generated in RTP is suppressed to an allowable range, and the BMD density is set to 1.0 in the bulk portion. It was confirmed that it can be grown at a high density of × 10 ¹⁰ cm ⁻³ level or higher.

  Further, when the obtained result is compared with Test 1, by reducing the supply amount of the oxygen-containing gas supplied to the back surface of the wafer from the supply amount of the oxygen-containing gas supplied to the front surface of the wafer, the slip of RTP is reduced. A reduction effect was observed.

(Test 3) Comparison of Atmosphere and Maximum Achievable Temperature A silicon single crystal ingot having a region in which vacancy-type point defects exist predominantly by controlling v / G by the CZ method is obtained by slicing from the region. The wafer (diameter 300 mm, thickness 775 μm) having both surfaces mirror-polished is set to a temperature T0: 600 ° C., a temperature rising rate 70 ° C./second, a holding time 30 seconds at the highest temperature, and a temperature falling rate 120 ° C./second. Then, RTP was performed by changing the oxygen partial pressure, the type of gas, and the maximum temperature reached in the heat treatment atmosphere.
The LSTD reduction rate before and after the RTP in the wafer surface portion from the surface on which the semiconductor device of each obtained annealed wafer was formed to a depth of 5 μm was evaluated with an LSTD scanner (MO-601 manufactured by Raytex Co., Ltd.). Table 3 shows the evaluation results.

As shown in Table 3, when the oxygen partial pressure was 50% or more and the maximum temperature reached was higher than 1300 ° C. (Examples 8 to 10), it was confirmed that LSTD could be extinguished by nearly 70%. . In addition, it was confirmed that LSTD could be eliminated by nearly 60% even when the oxygen partial pressure was 20% (Examples 11 and 12).
On the other hand, when the maximum temperature reached is less than 1300 ° C. (Comparative Examples 7 to 10), when the oxygen partial pressure is 5% (Comparative Examples 11 and 12) or in an ammonia atmosphere (Comparative Example 13), the extinction rate of LSTD Was found to be small.

10 Chamber part 20 Reaction tube 30 Wafer support part 40 Lamp

Claims (2)

In a method of heat treating a silicon wafer obtained by slicing a silicon single crystal ingot produced by the Czochralski method,
Oxygen-containing gas is supplied to the front and back surfaces of the wafer, the maximum temperature reached 1300 ° C. or higher and the melting point of silicon or lower, and the temperature lowering rate from the maximum temperature reached 75 ° C./second or higher and 120 ° C./second or lower. A method for heat treating a silicon wafer, comprising performing a cooling heat treatment.   The method for heat-treating a silicon wafer according to claim 1, wherein the supply amount of the oxygen-containing gas supplied to the front surface of the wafer is larger than the supply amount of the oxygen-containing gas supplied to the back surface of the wafer.

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