JP6414408B2 - Method for producing silicon single crystal - Google Patents

Description

  The present invention relates to a method for producing a silicon single crystal by the Czochralski (CZ) method.

  As a crystal defect introduced during the growth of a silicon single crystal, there is a twin. A twin is a surface defect in which atoms are arranged in such a manner that one of adjacent regions in the crystal is a mirror image of the other. For example, when a twin crystal is generated in a crystal having a <111> plane orientation, a plane defect with a <511> plane occurs. Twins are formed by applying stress in a certain direction to a single crystal.

  FIG. 1 is a photograph showing an example of a silicon wafer on which twins are formed. The diameter of the silicon wafer is 200 mm or more. In FIG. 1, the region on one side and the region on the other side form twins with respect to the vertical black streaks in the part surrounded by the ellipse. Since regions having different plane orientations have different brightness, it can be estimated that twins are formed when regions having different brightness are visually observed.

  As a method for suppressing the generation of twins, Patent Document 1 discloses a method of pulling a silicon single crystal from a silicon melt in a chamber by a Czochralski method and producing the silicon single crystal with a pulling speed V and a crystal temperature. The ratio V / G value to the gradient G is 0.2 to 0.5% larger than the boundary V / G value between the dislocation cluster region formed as an interstitial silicon aggregate and the defect-free region predominantly interstitial silicon. It has been proposed to perform control within a range that is smaller than the V / G value at which the OSF region appears.

  It is considered that twins are generated, for example, when foreign matter in the silicon melt is taken into the crystal growth interface during crystal growth and local overcooling occurs in the crystal being grown by the foreign matter. Examples of such foreign substances include carbon powder and metal powder adhering to the inner wall of the lifting device, and silicon powder generated from raw material silicon. In Patent Document 1, it is emphasized that even if a crystal is manufactured in a state where there is no foreign matter, twin defects are generated, and the reduction itself is not described.

  Conventionally, there has been a strong demand for reducing the manufacturing cost of silicon wafers. To that end, it is necessary to reduce the manufacturing cost of silicon single crystals.

JP 2011-225409 A

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a method for producing a silicon single crystal that can reduce the production cost of the silicon single crystal and is less likely to introduce twins.

The gist of the present invention is the following method (1) for producing a silicon single crystal.
(1) a filling step of filling the silicon material in the crucible;
A melting step of heating and melting the silicon raw material filled in the crucible in the filling step;
A method of producing a silicon single crystal by the Czochralski method, including a pulling step of pulling up a seed crystal after being immersed in a silicon melt produced by the melting step,
The filling step includes
As the silicon raw material, polysilicon material of the multi-grooved surface, ground, or cut the first silicon raw material is intended, a first filling step of filling a lower portion of the crucible,
A second filling step of filling, as the silicon raw material, a second silicon raw material obtained by pulverizing or cutting a polysilicon raw material having a non-multi-grooved surface onto the first silicon raw material in the crucible; seen including,
In the second filling step, the second silicon raw material is filled with a layer thickness of at least 10 mm so as to cover the first silicon raw material,
The method for producing a silicon single crystal , wherein the layer thickness of the second silicon material is the smallest of the distances in the height direction between the upper surface of the first silicon material and the upper surface of the second silicon material .

In the filling step, the ratio of the first silicon raw material in the silicon raw material is preferably 90% by mass or less .

The polysilicon raw material having a multi-groove surface is a raw material which contains a large amount of bubbles but can be obtained at low cost as compared with the polysilicon raw material having a non-multi-groove surface. Therefore, by using the first silicon raw material (obtained by pulverizing or cutting the polysilicon raw material having a multi-groove surface), the raw material cost can be reduced and the manufacturing cost of the silicon single crystal can be reduced. Further, the melt of the melt due to the first silicon raw material containing a large amount of bubbles is caused by the second silicon raw material (obtained by pulverizing or cutting the non-multi-grooved surface polysilicon raw material) on the first silicon raw material ( Preferably, it is prevented or suppressed by covering the first silicon material. That is, even if the first silicon raw material is foamed during melting and the silicon melt splashes, most of the silicon melt hits the second silicon raw material and does not jump above the second silicon raw material. . For this reason, silicon powder formed by solidification of silicon melt droplets is unlikely to be generated, and therefore, such silicon powder is rarely introduced into the silicon single crystal as a foreign substance.
Therefore, in the manufacturing method of the present invention, the manufacturing cost of the silicon single crystal can be reduced, and twins are not easily introduced into the silicon single crystal to be manufactured.

FIG. 1 is a photograph showing an example of a silicon wafer on which twins are formed. FIG. 2 is a surface photograph of an example of high-speed grown polysilicon. 3A is a cross-sectional view showing a filling state of silicon raw material in a crucible in Comparative Example 1. FIG. FIG. 3B is a cross-sectional view showing a filling state of the silicon raw material in the crucible in Comparative Example 2. FIG. 3C is a cross-sectional view showing a filling state of the silicon raw material in the crucible in the example of the present invention. FIG. 4 is a perspective view showing the relationship between a block cut out from a silicon single crystal and a sample for measuring twin generation rate.

  The inventor of the present invention manufactured a silicon single crystal of polysilicon manufactured at a high growth rate (hereinafter also referred to as “high-speed growth polysilicon”) in order to reduce the manufacturing cost of polysilicon as a raw material for the silicon single crystal. The application to was examined. High-speed grown polysilicon is manufactured at a growth rate of 1.1 to 1.5 times, for example, as compared with polysilicon conventionally used for silicon single crystals. For this reason, high-speed grown polysilicon can be obtained at a lower cost than a polysilicon raw material manufactured at a normal growth rate.

  A polysilicon raw material for a silicon single crystal is obtained by, for example, a CVD (Chemical Vapor Deposition) method so as to fill the inside of a container and then pulverizing it into chips. When forming polysilicon, if the temperature of the container is lowered to increase the growth rate, a large amount of bubbles are introduced into the polysilicon (especially adjacent to the container). The resulting polysilicon material contains countless bubbles.

  Moreover, the surface condition of the high-growth polysilicon is greatly different from that of a polysilicon material manufactured at a normal growth rate. FIG. 2 shows an example of the surface of the fast growth polysilicon before pulverization. Specifically, the surface of the fast-growing polysilicon is filled with a small piece of polysilicon to give a popcorn-like appearance. Among the small pieces, those having a diameter of 2 mm to 50 mm occupy 50% or more, and among the adjacent small pieces, those having a groove having a depth of 3 mm or more occupy 50% or more. Hereinafter, such a surface property is referred to as a “multi-groove surface”, and a polysilicon material having such a surface is referred to as a “poly-groove surface polysilicon material”. On the other hand, a polysilicon material manufactured at a normal growth rate does not become the above-mentioned polysilicon material having a multi-groove surface. A polysilicon material that is manufactured at a normal growth rate and does not satisfy the requirements for the polysilicon material having the multi-groove surface is hereinafter referred to as “polysilicon material having a non-multi-groove surface”.

  When such a multi-grooved surface polysilicon material is melted for use in the production of a silicon single crystal, bubbles contained in the multi-grooved surface polysilicon material are foamed by repelling in the melt. When the polysilicon raw material having a multi-groove surface is melted alone, minute droplets are scattered. These droplets solidify into silicon powder and soar in the lifting device. Such silicon powder becomes the above-mentioned foreign matter and can introduce twins into the silicon single crystal.

  On the other hand, the conventionally used polysilicon material (polysilicon material having a non-multi-grooved surface) contains significantly fewer bubbles than the polysilicon material having a multi-groove surface. For this reason, when the conventionally used polysilicon raw material is melted, droplets are not substantially scattered due to the bubble repelling. The present inventor reduces the manufacturing cost of silicon single crystal by using a raw material derived from a polysilicon material having a multi-grooved surface and a raw material originating from a polysilicon material having a non-multi-grooved surface at the time of melting, It has been found that the dispersion of melt droplets can be remarkably reduced to suppress the formation of twins in the silicon single crystal.

  The method for producing a silicon single crystal of the present invention is based on the Czochralski method, in which a crucible is filled with a silicon raw material, and the silicon raw material filled in the crucible in the filling step is heated. A melting step of melting, and a pulling step of pulling up the seed crystal after being immersed in the silicon melt produced by the melting step. In the filling step, as the silicon raw material, a first filling step of filling a lower portion in the crucible with a first silicon raw material obtained by crushing or cutting a polysilicon raw material having a multi-grooved surface; and the silicon raw material And a second filling step of filling a second silicon material, which is obtained by crushing or cutting a polysilicon material having a non-multi-grooved surface, onto the first silicon material in the crucible.

  In the filling step, the second silicon material (non-multi-grooved surface polysilicon material) is covered in the crucible so as to cover the first silicon material (a material obtained by pulverizing or cutting the poly-grooved surface polysilicon material). Pulverized or cut) is filled. In this state, when the silicon raw material is melted, the second silicon raw material serves as a lid for the first silicon raw material, and depending on the foaming of the first silicon raw material, the silicon raw material may be on the top of the silicon raw material or on the liquid surface of the silicon melt. These droplets are unlikely to scatter. For this reason, silicon powder due to solidification of the droplets hardly occurs, and therefore twins are not easily introduced into the silicon single crystal to be manufactured.

  In order to sufficiently exhibit such an effect, it is preferable that the ratio of the first silicon raw material in the silicon raw material in the filling step (hereinafter referred to as “first silicon raw material use ratio”) is 90 mass% or less. . In general, when the use ratio of the first silicon material exceeds 90% by mass, it becomes difficult to suppress the first silicon material from foaming and the silicon melt from being scattered by the second silicon material.

  However, the upper limit of the use ratio of the first silicon material that can suppress the generation of twins depends on the foamability (porosity) of polysilicon used as the first silicon material, the manufacturing conditions of the silicon single crystal, and the like. Therefore, the upper limit of the first silicon raw material usage ratio is determined for each of these conditions, and even if it exceeds 90% by mass, the generation of twins may be suppressed.

  Since the first silicon raw material can be made cheaper than the second silicon raw material, by using the first and second silicon raw materials together by the manufacturing method of the present invention, the raw material cost can be reduced. The manufacturing cost of the silicon single crystal can be reduced. If the first silicon raw material usage ratio is too low, the effect of reducing the raw material cost cannot be sufficiently obtained. The lower limit of the first silicon raw material usage ratio is determined based on the price of each of the first and second silicon raw materials, the target raw material cost reduction range, and the like. As an example, the lower limit of the first silicon raw material usage ratio is 10% by mass.

  The form of the first silicon raw material is not particularly limited, and may be, for example, a chip shape or a cut lot (for example, a cylindrical shape) before being formed and pulverized by CVD. The form of the second silicon raw material is not limited as long as it can be filled on the first silicon raw material in the crucible, and can be, for example, in a chip shape.

  The presence or absence of foamability of the silicon raw material in the melting step can be confirmed based on the following method. That is, when silicon raw material is put in a quartz crucible and the silicon raw material is melted in a state where the quartz crucible is installed in a pulling device (furnace), if the silicon raw material adheres to the parts in the furnace after pulling up The silicon raw material shall be “foamable”, while if the silicon raw material does not adhere to the parts in the furnace after pulling up, the silicon raw material may be slightly foamed, It shall be “not foamable”.

  In the present invention, the method for melting the raw material in the melting step is not limited, and a known method such as resistance heating can be employed. In the melting step, the usage ratio of the first silicon raw material is set so that a part of the first silicon raw material does not melt at the end, and the first and second silicon raw materials can be appropriately arranged in the crucible. preferable. This is because when the first silicon raw material floats and foams on the surface of the silicon melt of the previously melted silicon raw material, the silicon melt droplets scatter and silicon powder is formed.

  In the present invention, the pulling method in the pulling step is not limited, and at the time of pulling, rotation of the seed crystal and / or crucible, application of a magnetic field to the silicon melt, and the like can be appropriately performed.

In order to confirm the effect of the present invention, the following tests were conducted.
A first silicon material and a second silicon material were prepared. It was confirmed that the first and second silicon raw materials had foamability or not at the time of melting, respectively, by the above-described method.

  As a comparative example (Comparative Example 1) to be compared with the present invention example, the first silicon raw material and the second silicon raw material are weighed at a mass ratio of 85:15, and these are uniformly mixed as shown in FIG. 3A. Then, the quartz crucible 1 having an inner diameter of about 800 mm and a height of about 500 mm was filled. Then, these silicon raw materials were heated and melted, and after immersing the seed crystal in the resulting silicon melt, the seed crystal was pulled up to produce a silicon single crystal having a straight barrel portion with a diameter of about 300 mm. .

  As Comparative Example 2, the first silicon material and the second silicon material are weighed at a mass ratio of 85:15, and the second silicon material is filled in the lower part (bottom part) of the crucible 1 as shown in FIG. 3B. On top of this, the first silicon raw material was filled. Except this, a silicon single crystal was produced in the same manner as in Comparative Example 1.

  As an example of the present invention, the first silicon raw material and the second silicon raw material are weighed at a mass ratio of 85:15, and the first silicon raw material is filled in the lower part of the crucible 1 as shown in FIG. On top, the second silicon raw material was filled. In this state, the layer thickness of the second silicon raw material was about 10 mm to 50 mm. Except this, a silicon single crystal was produced in the same manner as in Comparative Example 1.

  The layer thickness of the second silicon raw material is defined as follows. That is, first, the top vertex of the individual material located at the top of each of the second silicon material arranged to cover the first silicon material and the first silicon material covered with the second silicon is identified. Here, the “raw material individual located at the top” means a raw material individual that can visually recognize the appearance shape of the raw material individual without being obstructed by the adjacent raw material individual when viewed from directly above. In the case of the first silicon raw material, when the second silicon is virtually removed and the first silicon raw material is viewed from directly above, the raw material individual of the adjacent first silicon raw material is not obstructed by the raw material individual. The raw material individual that can visually recognize the appearance shape is the “highest material individual”. Then, with respect to each of the first and second silicon raw materials, when the upper surface is defined as the upper surface, a surface consisting of a set of polygons having a line connecting the vertices of adjacent ones of the uppermost raw material individual is defined as the first silicon. The minimum distance in the height direction between the upper surface of the raw material and the upper surface of the second silicon raw material is defined as the layer thickness of the second silicon raw material.

  For each of Comparative Example 1, Comparative Example 2, and Example of the present invention, 50 or more silicon single crystals were produced. About each obtained silicon single crystal, the twin crystal generation rate was calculated | required with the following method.

  First, a block having a length of 100 mm to 300 mm was cut out from the silicon single crystal, and a sample for measuring twin generation rate was cut out from the block. FIG. 4 is a perspective view showing the relationship between a block cut out from a silicon single crystal and a sample for measuring twin generation rate. Both end portions in the axial direction of the block 2 were cut into a disk shape, and these were used as a sample 3 for measuring twin generation rate.

  These samples were heat-treated at 1140 ° C. for 2 hours and then selectively etched. The etching amount was 10 μm. For selective etching, Seco solution was used for samples with a resistivity of 1Ω or more, and light solution was used for samples with a resistivity of less than 1Ω. Table 1 shows the composition of the etching solution used.

  The sample subjected to the above treatment was visually observed under a condenser lamp to confirm the presence or absence of twins. When there is even one sample in which twinning is observed for one silicon single crystal, the single crystal is assumed to contain twins. For each of Comparative Example 1, Comparative Example 2, and Example of the present invention, The ratio of silicon single crystals containing twins to the number of silicon single crystals whose presence or absence of twins was confirmed was defined as the twin generation rate. Table 2 shows the twin rate of silicon single crystals for each manufacturing method. Compared to Comparative Examples 1 and 2, it can be seen that the twin crystal generation rate can be greatly reduced in the inventive example.

  As a modification of the inventive example, a silicon single crystal was produced in the same manner as the inventive example, changing only the ratio of the first silicon raw material and the second silicon raw material, and the twin generation rate was determined. Table 3 shows the relationship between the first silicon raw material usage ratio and the twinning rate. A material containing 85% of the first silicon raw material is the above-described example of the present invention. The layer thickness of the second silicon raw material filled on the first silicon raw material in the crucible 1 is about 10 mm to 15 mm when the first silicon raw material usage ratio is 90% by mass, and the first silicon raw material usage ratio is When it was 95% by mass, it was about 5 mm to 10 mm.

  Under the present test conditions, even if the usage ratio of the first silicon raw material is increased to 90% by mass, the twinning rate can be sufficiently reduced as compared with Comparative Examples 1 and 2, but the usage ratio of the first silicon raw material is high. It can be seen that the twin generation rate cannot be reduced as compared with Comparative Example 1 when the content is increased to 95% by mass.

    1: crucible

Claims (2)

A filling process for filling the crucible with silicon raw material;
A melting step of heating and melting the silicon raw material filled in the crucible in the filling step;
A method of producing a silicon single crystal by the Czochralski method, including a pulling step of pulling up a seed crystal after being immersed in a silicon melt produced by the melting step,
The filling step includes
A first filling step of filling a lower portion in the crucible with a first silicon material obtained by pulverizing or cutting a polysilicon material having a multi-grooved surface as the silicon material;
A second filling step of filling, as the silicon raw material, a second silicon raw material obtained by pulverizing or cutting a polysilicon raw material having a non-multi-grooved surface onto the first silicon raw material in the crucible; seen including,
In the second filling step, the second silicon raw material is filled with a layer thickness of at least 10 mm so as to cover the first silicon raw material,
The method for producing a silicon single crystal , wherein the layer thickness of the second silicon material is the smallest of the distances in the height direction between the upper surface of the first silicon material and the upper surface of the second silicon material . A method for producing a silicon single crystal according to claim 1,
The method for producing a silicon single crystal, wherein, in the filling step, a ratio of the first silicon raw material in the silicon raw material is 90% by mass or less.