JP7078496B2 - Manufacturing method of silicon wafer - Google Patents

Description

The present invention relates to a method for manufacturing a silicon wafer, and particularly to a method for manufacturing a silicon wafer that can prevent warpage when the thickness is reduced.

Silicon wafers (also simply called wafers) used as substrates for semiconductor devices require not only defect-free surface layers but also wafer strength and metal impurity gettering performance in recent years in order to improve device quality. Has been done.
In response to such demands, measures have been taken such as forming oxygen precipitates called BMD (Bulk Micro Defects) inside the wafer. For example, in Patent Document 1, a wafer is subjected to rapid elevating heat treatment (RTP: Rapid Thermal Process) of 1300 ° C. or higher to leave a large amount of atomic pores, which are point defects, inside the wafer, and then precipitation heat treatment. Sometimes a method of forming BMD at high density has been proposed.

By the way, it is known that the density distribution in the depth direction of the BMD formed during the precipitation heat treatment of the RTP-treated silicon wafer becomes a convex or M-shaped distribution having a low density toward the front and back surfaces of the wafer. .. It is known that the distribution is symmetrical between the front surface side and the back surface side with the center in the wafer depth direction as a boundary unless there is a large difference in the RTP conditions to which the front and back surfaces of the wafer are exposed (see Patent Document 2). ..

On the other hand, in recent years, in a device having a three-dimensional laminated structure or the like, it is necessary to reduce the thickness of the wafer in the manufacturing process. Generally, the back surface of the wafer is back grinded to perform the thinning work, but this causes the above-mentioned symmetry of the density distribution of the BMD in the wafer depth direction to be lost.

The basic composition formula of BMD is SiO ₂ , but since the coefficient of thermal expansion is different from that of Si (silicon), stress is generated inside the wafer when the temperature rises, which causes a problem that the wafer warps. Therefore, there is a demand for a method capable of suppressing warpage caused by BMD precipitation even when the wafer is thinned.
Further, when the silicon wafer is thinned, it is difficult to control the BMD density in the depth direction. Therefore, Patent Document 3 describes a method of forming a gettering sink on the back surface of the wafer by polishing.

Japanese Patent Application Laid-Open No. 2015-204326 WO2009 / 151707A Japanese Unexamined Patent Publication No. 2017-45990

However, in the method of polishing the back surface of the wafer to form a gettering sink as described in Patent Document 3, the mechanical strength of the wafer is weakened, and there is a high risk of brittle fracture when the wafer is thinned. There was a problem of becoming.

Under such circumstances, the inventor of the present application has focused on the fact that the BMD density distribution in the wafer depth direction changes due to the influence of temperature and oxygen partial pressure in RTP, and has arrived at the present invention.
An object of the present invention is to provide a method for manufacturing a silicon wafer, which can prevent warpage of the wafer when oxygen precipitates (BMD) are formed inside the silicon wafer and the wafer is thinned. ..

In the method for manufacturing a silicon wafer according to the present invention, which has been made to solve the above-mentioned problems, oxygen precipitates are formed inside the silicon wafer after rapid elevating and heating heat treatment of the silicon wafer, and the silicon wafer is thinned. In the method for manufacturing a silicon wafer, the maximum holding temperature is set in the range of 1300 ° C. or higher and 1350 ° C. or lower in the rapid elevating temperature heat treatment, and the oxygen partial pressure is divided with respect to the target thickness t [μm] of the thinning process. Is heat-treated under the condition that the critical oxygen partial pressure PO _2cr calculated by the following formula (1) is within ± 5%, and the density of oxygen precipitates becomes the highest on the wafer surface side than in the center in the wafer depth direction. In the thinning process, the peak position of the oxygen precipitate density is set at the center of the silicon wafer thinned to the target thickness t by back grind from the back surface side of the wafer in the depth direction . Have.
[Number 1]
Critical oxygen partial pressure PO _2cr [%] = 1.5 × 10 ^-6 t ^ (5.4 × 10 ^-3 T-4.21)… (1)

In the rapid elevating and lowering heat treatment, it is desirable that the temperature lowering rate from the maximum holding temperature is 50 ° C. to 150 ° C./s.
Further, it is desirable that the oxygen precipitation heat treatment is carried out after the rapid elevating temperature heat treatment, and the density of the oxygen precipitate after the oxygen precipitation heat treatment is 1 × 10 ⁹ / cm ³ or more.

In this way, the critical oxygen partial pressure according to the target thickness after thinning the wafer is obtained from the relational expression (1), and RTP is performed under the condition using the oxygen partial pressure based on the critical oxygen partial pressure to reduce the thickness. The peak of the BMD density can be positioned at the center in the depth direction of the subsequent wafer, and the occurrence of warpage can be suppressed.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method for manufacturing a silicon wafer, which can prevent warpage of the wafer when oxygen precipitates are formed inside the silicon wafer and the wafer is thinned.

FIG. 1 is a flow showing a flow of a silicon wafer manufacturing method according to the present invention. FIG. 2 is a graph showing a curve of the critical oxygen partial pressure obtained by the embodiment according to the present invention.

Hereinafter, a method for manufacturing a silicon wafer according to the present invention will be described. FIG. 1 is a flow showing a flow of a silicon wafer manufacturing method according to the present invention.
As shown in FIG. 1, in step S1, a plurality of silicon wafers having a predetermined thickness of 775 μm and a diameter of 300 mm are prepared from a nitrogen-doped silicon single crystal that has been pulled up by, for example, the Czochralski method and is doped with nitrogen of 1 × 10 ¹⁴ / cm ³ or more. .. When a silicon wafer doped with nitrogen of 1 × 10 ¹⁴ / cm ³ or more is used, nitrogen is combined with the pores generated in the RTP to form a nitrogen-vacancy complex by RTP in the step described later. However, the overall pore density can be increased. As a result, the BMD precipitation density is higher than that of the non-nitrogen-doped wafer.

As other characteristics of the silicon wafer, for example, a P type (boron dope), a substrate resistance of, for example, 13 Ω · cm, and an oxygen concentration of, for example, 1.2 × 10 ¹⁸ / cm ³ can be used.

Further, the critical oxygen content for obtaining the oxygen partial pressure in the RTP based on the target thickness t when the silicon wafer is finally thinned, the maximum holding temperature T in the RTP, and the following relational expression (1). The pressure is determined (step S2 in FIG. 1). In the formula (1), t is the target thickness (μm) and T is the maximum holding temperature (° C.).

[Number 1]
Critical oxygen partial pressure PO _2cr [%] = 1.5 × 10 ^-6 t ^ (5.4 × 10 ^-3 T-4.21)… (1)

The oxygen partial pressure set by RTP is set to a value within ± 5% of the critical oxygen partial pressure PO _2cr obtained by the above equation (1). Within that range, warpage of the wafer can be prevented. If the value exceeds ± 5% of the critical oxygen partial pressure PO _2cr , the wafer may warp, which is not preferable.

Here, the temperature range of RTP (range of maximum holding temperature) is within the range of 1300 ° C to 1350 ° C. By setting the maximum holding temperature T of RTP to 1300 ° C. or higher, a large number of pores can be generated inside the wafer. If it is less than 1300 ° C., the pore concentration is low and BMD precipitation is not promoted. Further, if the temperature exceeds 1350 ° C., slip occurs on the wafer, which is not preferable.

Further, the temperature lowering rate from the maximum holding temperature of RTP is set to 50 ° C. to 150 ° C./s. This is a temperature lowering rate condition necessary for increasing the residual pore concentration as much as possible. If the temperature is less than 50 ° C./s, the pore concentration is low and BMD precipitation is not promoted. Further, if the temperature exceeds 150 ° C., slip occurs on the wafer, which is not preferable.

Next, RTP is carried out based on the above-mentioned conditions (step S3 in FIG. 1). That is, based on the conditions such as the oxygen partial pressure and the maximum holding temperature (1300 ° C. to 1350 ° C.) determined in step S2, the silicon wafer is held for a predetermined time (for example, 30 s), heated at the maximum holding temperature, and then lowered to a predetermined temperature. A rapid elevating temperature heat treatment (RTP) for cooling at (50 ° C. to 150 ° C./s) is performed.

When RTP is completed, for example, a heat treatment at 780 ° C. is carried out for 3 hours in a 100% argon atmosphere, and then a heat treatment at 1000 ° C. is carried out for 16 hours to perform BMD precipitation (step S4 in FIG. 1).

Finally, backgrinding is performed on the silicon wafer to reduce the thickness to a predetermined target thickness t (step S5 in FIG. 1).
Here, in the RTP in step S3, since the density of the BMD is controlled to be the highest on the wafer front surface side rather than the center in the wafer depth direction, the back grind from the wafer back surface side makes the thickness as thin as the target thickness t. The center of the silicon wafer in the depth direction is the peak position of the BMD density. That is, the BMD densities on the front surface side and the back surface side of the wafer become symmetrical, and the occurrence of warpage after thinning the wafer is suppressed.

As described above, according to the embodiment of the present invention, the critical oxygen partial pressure according to the target thickness after the wafer thinning is obtained from the relational expression, and the condition using the oxygen partial pressure based on the critical oxygen partial pressure is obtained. By performing RTP in, the peak of BMD density can be positioned at the center in the depth direction of the wafer after thinning, and the occurrence of warpage can be suppressed.

In the above embodiment, the silicon wafer is manufactured from a silicon wafer cut out from a silicon single crystal pulled up by the Czochralski method, but the present invention is not limited thereto. For example, it may be produced by cutting out from a silicon single crystal obtained by the floating zone (FZ) method. Further, the diameter of the silicon wafer is not limited in the present invention.

The method for manufacturing a silicon wafer according to the present invention will be further described based on examples. In this example, the following experiments were performed based on the above-described embodiment.

(Experiment 1)
In Experiment 1, it was grown by the Czochralski method with P type (boron dope), substrate resistance 13 Ω · cm, oxygen concentration 1.2 × 10 ¹⁸ / cm ³ , nitrogen concentration 3.9 × 10 ¹⁴ / cm ³ , and diameter 300 mm. A plurality of silicon wafers cut out from a silicon single crystal were used.

RTP for the prepared silicon wafer by changing the holding temperature conditions (1300 ° C, 1325 ° C, 1350 ° C) and oxygen partial pressure conditions (0%, 5%, 25%, 50%, 100%: diluting gas is argon). Was given.
As other common RTP conditions, the holding time was 30 s, and the temperature lowering rate from the maximum holding temperature was 120 ° C./s.

Further, as the subsequent BMD precipitation heat treatment, a heat treatment at 780 ° C. was carried out for 3 hours under a 100% argon atmosphere, and then a heat treatment at 1000 ° C. was carried out for 16 hours.
After this BMD precipitation treatment, the BMD density distribution in the depth direction was measured for each silicon wafer by IR tomography (Ratic, MO441), and the peak depth of the BMD density from the wafer surface under each RTP condition was evaluated (). Table 1).

After that, it was determined whether or not the wafer was warped when the wafer was thinned to a predetermined thickness (for example, 200 μm, 300 μm, 400 μm) by backgrinding for all the wafers subjected to the BMD precipitation treatment. Warpage supports the outer peripheral part of the wafer, measures the amount of deflection (displacement amount) at the center of the wafer due to its own weight, and warps the wafer when the difference from the theoretical value estimated from the physical properties of silicon is 5% or more. It was determined that it was.
As a result, under the conditions shown in Table 1, when the target thickness was 200 μm, the oxygen partial pressure was 0% at 1300 ° C, the oxygen partial pressure was 0% and 5% at 1325 ° C, and the oxygen partial pressure was 25% at 1350 ° C. When the target thickness is 300 μm, no warp occurs, and when the target thickness is 400 μm, the oxygen partial pressure is 25% and the oxygen partial pressure is 100% at 1350 ° C. No warpage occurred at a partial pressure of 50% and an oxygen partial pressure of 100% at 1325 ° C. From this result, it was found that warpage does not occur under the condition that the peak position of the BMD density of the thinned wafer is in the range of ± 10% at the center in the depth direction.

Further, when the wafer thickness t (μm) after thinning is obtained based on the peak depth of the BMD density under each of the above RTP conditions, the critical oxygen partial pressure (1300 ° C., 1325 ° C., 1350 ° C.) at each maximum holding temperature (1300 ° C., 1325 ° C., 1350 ° C.) is obtained. %) Is as shown in the graph of FIG.
From this graph, the relational expression (1) between the critical oxygen partial pressure PO _2cr [%], the target thickness t (μm), and the maximum holding temperature T (° C.) was obtained.
[Number 1]
Critical oxygen partial pressure PO _2cr [%] = 1.5 × 10 ^-6 t ^ (5.4 × 10 ^-3 T-4.21)… (1)

(Experiment 2)
In Experiment 2, the effectiveness of the relational expression (1) obtained in Experiment 1 was verified.
In Example 1, when the maximum holding temperature is 1300 ° C. and the target thickness is 500 μm, the critical oxygen partial pressure is obtained from the relational expression (1) using them as parameters, and the oxygen partial pressure of + 5% is oxygen in RTP. It was set to partial pressure. The holding time in RTP was 30 s, and the temperature lowering rate from the maximum holding temperature was 120 ° C./s.

Then, after RTP and BMD precipitation treatment (heat treatment at 780 ° C. for 3 hours in a 100% argon atmosphere, followed by heat treatment at 1000 ° C. for 16 hours), thinning treatment is performed so that the target thickness is t, and the wafer depth direction is reached. The peak position of the BMD density was confirmed. Further, it was exposed to an environment of 1000 ° C., and it was determined whether or not the wafer was warped.

Further, in Example 2, when the maximum holding temperature is 1300 ° C. and the target thickness is 500 μm, the critical oxygen partial pressure is obtained from the equation (1) using them as parameters, and the oxygen partial pressure of -5% is obtained by RTP. The oxygen partial pressure was set. Other conditions are the same as in Example 1.

Further, in Example 3, when the maximum holding temperature is 1350 ° C. and the target thickness is 300 μm, the critical oxygen partial pressure is obtained from the equation (1) using them as parameters, and the oxygen partial pressure of + 5% is oxygen in RTP. It was set to partial pressure. Other conditions are the same as in Example 1.

Further, in Example 4, when the maximum holding temperature was 1350 ° C. and the target thickness was 300 μm, the critical oxygen partial pressure was obtained from the equation (1) using them as parameters, and the oxygen partial pressure of -5% was obtained by RTP. The oxygen partial pressure was set. Other conditions are the same as in Example 1.

Further, in Example 5, when the maximum holding temperature was 1350 ° C. and the target thickness was 300 μm, the critical oxygen partial pressure was obtained from the equation (1) using them as parameters, and the oxygen partial pressure of -3% was obtained by RTP. The oxygen partial pressure was set.
Further, the temperature lowering rate in RTP was set to 50 ° C./s. Other conditions are the same as in Example 1.

Further, in Example 6, when the maximum holding temperature is 1350 ° C. and the target thickness is 300 μm, the critical oxygen partial pressure is obtained from the equation (1) using them as parameters, and the oxygen partial pressure of -3% is obtained by RTP. The oxygen partial pressure was set.
Further, the temperature lowering rate in RTP was set to 150 ° C./s. Other conditions are the same as in Example 1.

Further, as Comparative Example 1, when the maximum holding temperature is 1300 ° C. and the target thickness is 500 μm, the critical oxygen partial pressure is obtained from the equation (1) using them as parameters, and the oxygen partial pressure of + 6% is obtained by RTP. The oxygen partial pressure was set. Other conditions are the same as in Example 1.

Further, as Comparative Example 2, when the maximum holding temperature is 1300 ° C. and the target thickness is 500 μm, the critical oxygen partial pressure is obtained from the equation (1) using them as parameters, and the oxygen partial pressure of -6% is obtained by RTP. It was set to the oxygen partial pressure of. Other conditions are the same as in Example 1.

Further, as Comparative Example 3, when the maximum holding temperature is 1350 ° C. and the target thickness is 300 μm, the critical oxygen partial pressure is obtained from the equation (1) using them as parameters, and the oxygen partial pressure of + 6% is oxygen in RTP. It was set to partial pressure. Other conditions are the same as in Example 1.

Further, as Comparative Example 4, when the maximum holding temperature is 1350 ° C. and the target thickness is 300 μm, the critical oxygen partial pressure is obtained from the equation (1) using them as parameters, and the oxygen partial pressure of -6% is obtained by RTP. The oxygen partial pressure was set. Other conditions are the same as in Example 1.

Further, as Comparative Example 5, RTP was performed with an oxygen partial pressure of 0% and a target thickness of 400 μm, followed by a BMD precipitation treatment and a thinning treatment to a desired thickness. Other conditions are the same as in Example 1.

Further, as Comparative Example 6, when the maximum holding temperature is 1350 ° C. and the target thickness is 300 μm, the critical oxygen partial pressure is obtained from the equation (1) using them as parameters, and the oxygen partial pressure of -3% is obtained by RTP. The oxygen partial pressure was set.
Further, the temperature lowering rate in RTP was set to 45 ° C./s. Other conditions are the same as in Example 1.

Further, as Comparative Example 7, when the maximum holding temperature is 1350 ° C. and the target thickness is 300 μm, the critical oxygen partial pressure is obtained from the equation (1) using them as parameters, and the oxygen partial pressure of -3% is obtained by RTP. The oxygen partial pressure was set.
Further, the temperature lowering rate in RTP was set to 155 ° C./s. Other conditions are the same as in Example 1.

Further, as Comparative Example 8, when the maximum holding temperature is 1275 ° C. and the target thickness is 200 μm, the critical oxygen partial pressure is obtained from the equation (1) using them as parameters, and the oxygen partial pressure of -3% is obtained by RTP. The oxygen partial pressure was set. Other conditions are the same as in Example 1.

Further, as Comparative Example 9, when the maximum holding temperature was 1325 ° C. and the target thickness was 400 μm, the critical oxygen partial pressure was obtained from the equation (1) using them as parameters, and the oxygen partial pressure of -3% was obtained by RTP. The oxygen partial pressure was set.
Further, the temperature lowering rate in RTP was set to 155 ° C./s. Other conditions are the same as in Example 1.

The results of Experiment 2 are shown in Table 2. In the column of "Peak position of BMD density" in Table 2, ◯ indicates that the peak position is at the center position in the wafer depth direction after thinning, and × indicates that the peak position is not the center position in the wafer depth direction. Show the case. Further, when the BMD density is less than 1 × 10 ⁹ / cm ³ , it is indicated that the BMD density is low, and such a condition is not preferable because the gettering performance of metal impurities may be insufficient.

As shown in Table 2, as a result of Experiment 2, if the oxygen partial pressure in RTP is within ± 5% of the critical oxygen partial pressure (%) obtained by the relational expression (1), the peak of BMD after thinning is achieved. It was confirmed that the position can be centered in the depth direction of the wafer.
Further, the maximum holding temperature of RTP is in the range of 1300 ° C. to 1350 ° C. and the temperature lowering rate is in the range of 50 to 150 ° C., and the oxygen partial pressure set within ± 5% of the critical oxygen partial pressure obtained from the relational expression (1). It was confirmed that a good silicon wafer without warpage can be obtained.

As described above, according to the present invention, it has been confirmed that the occurrence of warpage can be suppressed even in a high temperature environment after thinning.

t Target thickness T Maximum holding temperature

Claims (3)

A method for manufacturing a silicon wafer, in which oxygen precipitates are formed inside the silicon wafer after rapid elevating and heating heat treatment of the silicon wafer, and the silicon wafer is thinned.
In the rapid elevating heat treatment,
The maximum holding temperature is set in the range of 1300 ° C. or higher and 1350 ° C. or lower, and the oxygen partial pressure is calculated with respect to the target thickness t [μm] of the thinning treatment, and the critical oxygen partial pressure PO calculated by the following formula (1). Heat treatment is performed under the condition of within ± 5% of _2cr , and the density of oxygen precipitates is controlled to be the highest on the surface side of the wafer rather than the center in the depth direction of the wafer.
In the thinning treatment
The peak position of the density of oxygen precipitates is set at the center in the depth direction of the silicon wafer thinned to the target thickness t by the back grind from the back surface side of the wafer.
A method for manufacturing a silicon wafer.
[Number 1]
Critical oxygen partial pressure PO _2cr [%] = 1.5 × 10 ^-6 t ^ (5.4 × 10 ^-3 T-4.21)… (1) In the rapid elevating heat treatment,
The method for manufacturing a silicon wafer according to claim 1, wherein the temperature lowering rate from the maximum holding temperature is 50 ° C. to 150 ° C./s. After the rapid elevating heat treatment, oxygen precipitation heat treatment was performed.
The method for manufacturing a silicon wafer according to claim 1 or 2, wherein the density of oxygen precipitates after the oxygen precipitation heat treatment is 1 × 10 ⁹ / cm ³ or more.

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