JP2008166517A - Manufacturing method of semiconductor substrate - Google Patents

Abstract

A method of manufacturing a semiconductor substrate that realizes a high yield of semiconductor devices by reducing COP in the surface layer of the semiconductor substrate while suppressing a decrease in oxygen concentration in the surface layer of the semiconductor substrate.
A method of slicing a semiconductor single crystal ingot and a semiconductor wafer obtained by the slicing step under a normal pressure under a reducing gas, an inert gas, or a mixed gas of a reducing gas and an inert gas. Manufacturing of a semiconductor substrate comprising a step of heat-treating in an atmosphere at a temperature rising / falling rate of 100 ° C./second to 1000 ° C./second, a temperature of 1200 ° C. to 1400 ° C., and a time of 5 seconds to 5 minutes. Method.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a semiconductor substrate, and more particularly, to a method for manufacturing a semiconductor substrate that reduces COP in the surface layer of a semiconductor substrate while suppressing a decrease in oxygen concentration in the surface layer of the semiconductor substrate.

  In order to improve the electrical characteristics such as oxide breakdown voltage of the semiconductor substrate, it is desirable that the surface layer of the semiconductor substrate on which the semiconductor device is formed be a defect-free layer without crystal defects. For example, a crystal defect of an octahedral structure called COP (Crystal Originated Particle) introduced as a Grown-in defect during the growth of a silicon single crystal exists on the surface layer of a silicon wafer. This COP is a crystal defect (Void defect) formed by aggregation of vacancies. If such a COP is present on the surface layer of the silicon wafer, for example, the initial oxide breakdown voltage (Time Zero Dielectric Break Down: TZDB) and the time-dependent dielectric breakdown down (TDDB) of the silicon wafer oxide film are deteriorated, It is known that it causes a decrease in yield in a semiconductor device manufacturing process.

In order to improve the initial oxide film breakdown voltage and the breakdown characteristics of the insulating film over time, high-temperature heat treatment is performed in an atmosphere such as a reducing gas to form silicon vacancies and interstitial silicon (interstitial silicon). There has been reported a method of moving and consequently reducing COP (for example, Patent Document 1).
JP-A-6-295912

  However, in such a conventional manufacturing method, the COP on the surface layer of the silicon wafer is reduced, and the oxygen concentration on the surface layer of the silicon wafer is also reduced by outward diffusion. For this reason, the problem that the yield fell by generation | occurrence | production of the crystal defect etc. in the silicon wafer surface layer has arisen. That is, when a silicon single crystal is produced by the CZ (Czochralski) method, oxygen is taken into interstitial positions in the silicon single crystal from a quartz crucible that stores a silicon melt. This oxygen later contributes to the formation of BMD (Bulk Micro Defect), which is an oxygen precipitate inside the wafer, and is used for gettering of metal impurities and crystal defects, as well as improving the mechanical strength of the wafer. Has contributed. However, due to the heat treatment for reducing COP, the oxygen concentration in the surface layer portion of the silicon wafer is reduced, and lattice mismatch occurs between the silicon wafer and the inside of the silicon wafer having a high oxygen concentration. When the mechanical strength and oxygen concentration of the silicon wafer have a positive correlation, when a device structure such as STI (Shallow Trench Isolation) is formed on the wafer due to the generated lattice strain, Crystal defects such as dislocations occur in the surface layer of the silicon wafer having a low oxygen concentration, thereby reducing the yield of semiconductor devices.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to reduce the COP of the semiconductor substrate surface layer while reducing the oxygen concentration of the semiconductor substrate surface layer, thereby reducing the high yield of semiconductor devices. It is an object of the present invention to provide a method of manufacturing a semiconductor substrate that realizes the above.

The method for producing a semiconductor substrate of the present invention comprises:
Slicing a semiconductor single crystal ingot;
The semiconductor wafer obtained by the slicing step is heated and lowered at a rate of 100 ° C./second to 1000 ° C./second in a reducing gas, an inert gas, or a mixed gas atmosphere of a reducing gas and an inert gas. It has the process of heat-processing at the temperature of 1200 degreeC or more and 1400 degrees C or less, and the time for 5 seconds or more and 5 minutes or less.

  Here, in the step of performing the heat treatment, it is desirable to perform the heat treatment at a temperature increase / decrease rate of 400 ° C./second to 800 ° C./second and a temperature of 1250 ° C. to 1350 ° C.

Here, it is preferable that the interstitial oxygen concentration of the semiconductor wafer is 1.2 × 10 ¹⁸ atoms / cm ³ or more and 1.8 × 10 ¹⁸ atoms / cm ³ or less.

  Further, in the heat treatment step, it is desirable to perform the heat treatment in an argon gas or nitrogen gas atmosphere.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the manufacturing method of the semiconductor substrate which implement | achieves the high yield of a semiconductor device by reducing COP of a semiconductor substrate surface layer, suppressing the oxygen concentration fall of a semiconductor substrate surface layer. .

In the prior art, as described above, it has been unavoidable that the oxygen concentration in the surface layer of the semiconductor substrate is also reduced in the heat treatment for reducing the COP.
The inventors have found that the COP can be reduced while suppressing the reduction of the oxygen concentration in the surface layer of the semiconductor substrate by performing the heat treatment for reducing the COP at a high temperature rise and fall.

Embodiments of a method for manufacturing a semiconductor substrate according to the present invention will be described below with reference to the accompanying drawings.
In the embodiment, a case where a silicon wafer is used as a semiconductor wafer will be described as an example. However, the present invention is not necessarily limited to a method for manufacturing a semiconductor substrate using a silicon wafer.
Further, in the present embodiment, the normal pressure means a so-called atmospheric pressure, that is, approximately 101325 Pa (1 atm). The high pressure means a pressure higher than the normal pressure.

Embodiment
The method of manufacturing a semiconductor substrate according to the present embodiment includes a step of slicing a silicon single crystal ingot and a silicon wafer obtained by the slicing step using a reducing gas, an inert gas, or a reducing gas and an inert gas. It has the process of heat-processing in the mixed gas atmosphere with gas at the temperature increase / decrease rate of 100 to 1000 degree-C / sec, and the temperature of 1200 to 1400 degreeC.

  Hereinafter, the manufacturing method of the semiconductor substrate of the present embodiment will be described more specifically.

For example, a silicon single crystal ingot with a crystal orientation (100) pulled by the Czochralski method (CZ method) is sliced with respect to the (100) plane at an inclination angle (off angle) of, for example, 0 ° to 5 ° To do.
Next, mirror polishing is performed on the silicon wafer obtained by this slicing while maintaining the above plane orientation.
Then, after performing pretreatment such as RCA cleaning, the temperature rise / fall is 100 ° C./second or more and 1000 ° C./second or less in a reducing gas, an inert gas, or a mixed gas atmosphere of a reducing gas and an inert gas. The heat treatment is performed at a speed in a temperature range of 1200 ° C. to 1400 ° C. and a time of 5 seconds to 5 minutes to reduce the COP of the silicon wafer surface layer.

Thus, the heat treatment for reducing the COP of the silicon wafer surface layer, which has been conventionally performed at a temperature increase / decrease rate of about 2 to 10 ° C./min, is performed at a temperature increase / decrease rate of 100 ° C./second to 1000 ° C./second That is, by performing high-speed heating / cooling heat treatment, it is possible to suppress a decrease in oxygen concentration on the silicon wafer surface layer while maintaining the COP reduction effect on the silicon wafer surface layer.
Here, the silicon wafer surface layer refers to a region contributing to the characteristics of the semiconductor device, that is, a region having a depth of about 15 μm from the surface of the silicon wafer.
In addition, according to the present embodiment, by suppressing the decrease in the oxygen concentration on the surface layer of the silicon wafer, it is possible to obtain the operation and effect that the decrease in yield due to the occurrence of crystal defects or the like on the surface layer of the silicon wafer can be suppressed.

FIG. 1 is a diagram for explaining the operation and effect of the present embodiment. FIG. 1A is a diagram showing the relationship between the depth from the silicon wafer surface and the oxygen concentration, and FIG. 1B is a diagram showing the relationship between the depth from the silicon wafer surface and the COP density.
As shown in FIG. 1 (b), in either case, the conventional technique for heat treatment at a temperature increase / decrease rate of about 2 to 10 ° C./minute, the present embodiment (the present invention) for heat treatment at a high temperature increase / decrease temperature, as shown in FIG. The COP density decreases in the surface layer, particularly in the vicinity of the surface, that is, in the region of about 1 μm from the surface of the silicon wafer. This is because the disappearance of COP occurs when oxygen in the inner wall oxide film of COP is decomposed and further, interstitial silicon diffuses into the internal voids. In other words, the disappearance of COP depends on the diffusion of vacancies and interstitial silicon in a silicon single crystal, and the diffusion rate thereof depends largely on the maximum temperature reached, in particular, on the pressure of the heat treatment atmosphere. .

Contrary to this, as shown in FIG. 1A, the oxygen concentration is reduced in the surface layer of the silicon wafer in the prior art, but in the present embodiment (the present invention), the oxygen concentration silicon is used. Reduction in the wafer surface layer is suppressed. This is because the reduction of the oxygen concentration on the surface layer of the silicon wafer largely depends on the oxygen concentration gradient generated by the outward diffusion of oxygen from the silicon wafer surface into the heat treatment atmosphere.
That is, when heat treatment is applied to a silicon wafer, interstitial oxygen in the silicon single crystal is diffused out of the silicon surface into the atmosphere. For this reason, the oxygen concentration on the silicon wafer surface decreases. Therefore, an oxygen concentration gradient is generated from the inside of the silicon wafer toward the surface. This oxygen concentration gradient causes diffusion from the inside of the interstitial oxygen toward the surface, and the oxygen concentration of the silicon surface layer decreases.
In the case of the heat treatment at a temperature increasing / decreasing rate of about 2 to 10 ° C./min in the prior art, it takes a long time to increase and decrease the temperature. For example, when a wafer is introduced into a processing furnace at 700 ° C. and the temperature is increased to 1300 ° C. in order to eliminate COP, even if the temperature is increased at 10 ° C./min, 50 minutes are required. For this reason, a large amount of interstitial oxygen in the silicon single crystal diffuses outward from the silicon surface into the atmosphere during a long period of temperature increase / decrease, particularly during a temperature increase in which the oxygen concentration in the wafer is still high. Therefore, the oxygen concentration on the surface layer of the silicon wafer is greatly reduced.
On the other hand, in the case of this embodiment, unlike the prior art, the heat treatment is performed at a high temperature rise / fall. For example, even if the temperature is increased from 700 ° C. to 1300 ° C. as described above, it takes only 5 seconds when the temperature is increased at 100 ° C./second. Therefore, the outward diffusion of interstitial oxygen from the silicon surface into the atmosphere is very limited. Therefore, a decrease in the oxygen concentration on the surface layer of the silicon wafer is suppressed as compared with the prior art.

  Note that the heat treatment apparatus used in the manufacturing method of the present embodiment is not particularly limited, and single-wafer RTP using a halogen lamp or the like as a heat source, for example, can be used as long as high-speed heating and cooling and atmospheric control are possible. It is possible to use a (Rapid Thermal Processing) apparatus, a FLA (Flash Lamp Annealing) apparatus using a xenon lamp or the like as a heat source, a laser annealing apparatus, or the like.

  In addition, the tilt angle (off angle) when slicing a silicon single crystal ingot is not particularly limited, but an extremely tilt is provided with respect to the silicon single crystal ingot in terms of manufacturing a circular silicon wafer. This is not preferable, and is desirably in the range of 0 ° to 5 °. Further, it is desirable to keep the tilt angle within the above range in order to realize flattening by reconfiguration of silicon atoms, which will be described later.

In addition, the temperature increase / decrease rate is set to 100 ° C./second or more and 1000 ° C./second or less because, when the speed is lower than this, the decrease in the oxygen concentration in the surface layer of the silicon wafer becomes remarkable. This is because the disappearance of COP is insufficient, the temperature variation in the wafer surface increases, and the occurrence of slip becomes remarkable.
From the viewpoint of preventing the decrease in oxygen concentration on the wafer surface layer, the presence of COP, and the occurrence of slip from affecting the yield of semiconductor devices, the temperature rise / fall rate is 400 ° C./second or more and 800 ° C./second or less. More desirable.

The heat treatment atmosphere is a reducing gas, an inert gas, or a mixed gas atmosphere of a reducing gas and an inert gas. In other atmospheres, movement of silicon in the silicon wafer occurs. This is because the COP is difficult to disappear. In addition, the heat treatment in the above atmosphere allows the surface silicon atoms to be reconstructed, and a flat silicon wafer surface at the atomic level can be formed.
As the heat treatment atmosphere, for example, it is more desirable to perform in an inert gas atmosphere such as argon gas or nitrogen gas. This is because, from the viewpoint of reducing the COP density, it is desirable to carry out in a reducing gas atmosphere such as hydrogen gas, but in the reducing gas atmosphere such as hydrogen gas, the decrease in oxygen concentration in the surface layer is also promoted. Also, from the viewpoint of safety, an inert gas atmosphere is preferable to a reducing atmosphere such as hydrogen gas.

The reason why the heat treatment temperature is set to 1200 ° C. or more and 1400 ° C. or less is that COP does not disappear effectively in a range lower than this. Moreover, it is because the metal contamination of a silicon wafer increases in the range higher than this. Furthermore, in the high temperature range, the possibility of occurrence of slip to the silicon wafer is increased, and the member life of the heat treatment apparatus is shortened, which is not realistic.
And, from the viewpoint of sufficiently reducing the COP density so as not to affect the yield of the semiconductor device and surely suppressing the decrease in mechanical strength due to the decrease in oxygen concentration, the heat treatment is performed in the range of 1250 ° C. or higher and 1350 ° C. or lower. It is more desirable to be performed at.

  The reason for setting the heat treatment time to 5 seconds or more and 5 minutes or less is that if the temperature is below this range, the disappearance of COP becomes insufficient, and if it exceeds this range, the oxygen concentration of the wafer surface layer is significantly reduced.

  In addition, the pressure of the heat treatment atmosphere is not particularly limited, but from the viewpoint of suppressing an increase in process cost by applying an expensive processing furnace capable of pressure control, it should be performed under normal pressure. Is desirable.

  The heat treatment of this embodiment is preferably the first high-temperature heat treatment (heat treatment at about 100 ° C. or higher) after slicing a silicon single crystal ingot to form a silicon wafer. This is because if there is a high temperature heat treatment before the heat treatment of the present embodiment, oxygen on the surface layer of the silicon wafer is lost by the heat treatment.

The oxygen concentration of the silicon wafer before the heat treatment is not particularly limited, but from the viewpoint of maintaining the mechanical strength of the silicon wafer, the interstitial oxygen concentration ([Oi]) is 1.2 atoms / cm ³ or more 1 It is desirable to use a silicon wafer having a high oxygen concentration of 8 × 10 ¹⁸ atoms / cm ³ or less.

  The embodiments of the present invention have been described above with reference to specific examples. In the description of the embodiments, the description of the semiconductor substrate, the method for manufacturing the semiconductor substrate, etc., which is not directly necessary for the description of the present invention is omitted, but the required semiconductor substrate and the method for manufacturing the semiconductor substrate are omitted. It is possible to appropriately select and use elements related to the above.

  In addition, all semiconductor substrate manufacturing methods that include the elements of the present invention and that can be appropriately modified by those skilled in the art are included in the scope of the present invention.

  Examples of the present invention will be described below, but the present invention is not limited by these examples.

(Example)
First, a silicon single crystal ingot having a crystal plane orientation (100) of φ200 mm (8 inches) was manufactured by the chocolate ski method (CZ method). Then, this silicon single crystal ingot was sliced so that the off angle with respect to (100) on the surface of the silicon wafer was 0.2 degrees to prepare a silicon wafer.

This silicon single crystal ingot is a p-type silicon single crystal having boron as an impurity, the resistivity is 9 to 22 Ωcm, and the interstitial oxygen concentration ([Oi]) is 1.2 to 1.8 × 10 ¹⁸ atoms / cm. ^{It was set to 3} .

Next, the silicon wafer formed by slicing was mirror-polished after RCA cleaning.
Then, the silicon wafer subjected to mirror polishing was subjected to high-speed heating / cooling heat treatment by RTA using an RTP apparatus. The maximum temperature was 4 conditions of 1100 ° C., 1200 ° C., 1250 ° C., 1300 ° C., and the time was 1 condition of only 5 minutes, and the temperature raising / lowering rate was changed in the range of 20 ° C./second to 1000 ° C./second.

  The COP density and wafer surface oxygen concentration were measured for the heat-treated sample. The results are shown in FIGS. 2 (a) and 2 (b), respectively.

(Comparative example)
Under the same conditions as in the Examples, except that the maximum temperature is 1 condition at 1250 ° C., the heating / cooling rate is 700 ° C. to 1000 ° C. at 10 ° C./min, and 1000 ° C. to 1250 ° C. is 2 ° C./min. Heat treatment was performed in a mold diffusion furnace. The results are shown in FIGS. 2 (a) and 2 (b), respectively.

As shown in FIG. 2A, the COP density tends to decrease as the maximum temperature of the heat treatment increases. When the temperature raising / lowering rate is in the range of 200 to 1000 ° C./second, the change in the COP density is small. However, when the temperature is higher than 1000 ° C./second, the COP density rapidly increases when the maximum temperature is in the range of 1100 to 1300 ° C. This is because COP is difficult to disappear if the temperature rising rate is fast.
On the other hand, as the maximum temperature of the heat treatment increases from the example of FIG. 2B, the surface oxygen concentration tends to decrease in the same manner as the COP density. When the temperature raising / lowering rate is in the range of 50 ° C./second or less, the temperature rising rate decreases and the surface oxygen concentration decreases. However, when the temperature is higher than 50 ° C./second, the surface oxygen concentration does not change when the maximum temperature is in the range of 1100 to 1300 ° C. It is presumed that if the heating / cooling speed is high, oxygen atoms / molecules on the wafer surface are less likely to diffuse out into the atmosphere.

  According to the present embodiment, according to the present invention, it is possible to realize a high yield of semiconductor devices by reducing the COP of the semiconductor substrate surface layer while suppressing the decrease in oxygen concentration of the semiconductor substrate surface layer. It was done.

Explanatory drawing of the effect | action and effect of embodiment. The figure which shows the temperature increase / decrease rate dependence of the COP density and wafer surface oxygen concentration of an Example.

Claims (4)

Slicing a semiconductor single crystal ingot;
The semiconductor wafer obtained by the slicing step is heated and lowered at a rate of 100 ° C./second to 1000 ° C./second in a reducing gas, an inert gas, or a mixed gas atmosphere of a reducing gas and an inert gas. A method for manufacturing a semiconductor substrate, comprising a step of performing a heat treatment at a temperature of 1200 ° C. to 1400 ° C. for a time of 5 seconds to 5 minutes.   2. The method of manufacturing a semiconductor substrate according to claim 1, wherein in the heat treatment step, the heat treatment is performed at a temperature increase / decrease rate of 400 ° C./second to 800 ° C./second and a temperature of 1250 ° C. to 1350 ° C. ^3. The semiconductor substrate according to claim 1, wherein an interstitial oxygen concentration of the semiconductor wafer is 1.2 × 10 ¹⁸ atoms / cm ³ or more and 1.8 × 10 ¹⁸ atoms / cm ³ or less. Production method.   4. The method of manufacturing a semiconductor substrate according to claim 1, wherein the heat treatment is performed in an argon gas or nitrogen gas atmosphere.

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