JP7586012B2 - Surface treatment method, processing method, storage method for silicon blocks, manufacturing method for silicon wafers, and silicon ingots - Google Patents

Description

The present invention relates to a surface treatment method, a processing method, a storage method for silicon blocks, a manufacturing method for silicon wafers, and a silicon ingot.

Cu, a metal impurity, is known to induce various defects in silicon wafers. For example, Patent Documents 1 and 2 describe the change over time of OSF (Oxidation-Induced Stacking Fault). As a countermeasure, Patent Document 1 describes storing silicon single crystal ingots or blocks at low temperatures or cutting them early. Patent Document 2 describes specifying the Al and Cu concentrations of the quartz glass crucible used in manufacturing silicon single crystals, or doping with Al when manufacturing silicon single crystals. Patent Document 3 describes that "unevenly distributed LPD" is detected when the boron concentration and oxygen donor concentration in the silicon wafer are almost the same, and as a countermeasure, cutting the wafer within 50 days or performing heat treatment at 300°C or higher if the wafer is cut out after more than 50 days.

Japanese Patent Application Publication No. 5-58800 Japanese Patent Application Publication No. 8-73293 JP 2017-200878 A Japanese Unexamined Patent Publication No. 54-5378

"Investigation of Cu and Ni diffusion amount into Si substrate", Sales and Technology Department, DISCO Technical Review November 2018

However, the low-temperature storage method described in Patent Document 1 has the problem of being costly, and the method of limiting the number of days for cutting into wafers requires production management with restrictions on block inventory, making efficient production difficult. In addition, the method of changing the silicon single crystal manufacturing conditions (presence or absence of Al doping) depending on the Al concentration or Cu concentration of the quartz glass crucible described in Patent Document 2, and the method of changing the wafer manufacturing process (presence or absence of 300°C heat treatment) depending on the number of days until wafer cutting, as described in Patent Document 3, also require complicated process management and carry the risk of introducing errors.

Furthermore, Patent Document 4 only describes impurities that are introduced during crystal growth, so it is unclear what kind of impurities are intended, but as impurities promote the occurrence of stacking faults, a method is described in which lattice distortion is imparted to a silicon single crystal ingot, followed by annealing and etching the surface layer to remove the lattice distortion and silicon fracture layer as a countermeasure. As the method for introducing lattice distortion states that "the ingot is ground to form its outer shape and introduce lattice distortion," in other words, lattice distortion is introduced by cylindrical grinding. However, this method does not sufficiently remove the impurities, so new methods such as those in Patent Documents 1 to 3 have been proposed.

The present invention has been made to solve the above problems, and aims to provide a method for treating a silicon ingot that can easily and at low cost reduce the Cu concentration inside the ingot and produce a silicon ingot in which the occurrence of change over time in OSFs in the silicon wafers to be produced is suppressed even if the blocks cut from the ingot are stored for a long period of time before being processed into wafers, and a silicon ingot in which the Cu concentration inside the ingot is reduced and the occurrence of change over time in OSFs in the silicon wafers to be produced is suppressed even if the blocks are stored for a long period of time.

The present invention has been made to achieve the above object, and provides a method for treating the surface of a silicon ingot by subjecting the surface of the silicon ingot before cylindrical grinding to a physical impact treatment, thereby forming irregularities on the surface of the silicon ingot with an Rz of 50 μm or more.

This method of surface treatment of silicon ingots makes it possible to reduce the Cu concentration inside the ingot easily and at low cost. In addition, even if the blocks cut from the ingot are stored for a long period of time, it is possible to obtain silicon ingots in which the occurrence of changes over time in OSFs in the silicon wafers produced is suppressed.

In this case, the physical impact treatment can be a blasting treatment, which is a surface treatment method for silicon ingots.

This makes it extremely easy to form irregularities on the ingot surface, and reduces the Cu concentration inside the ingot more uniformly and stably throughout the entire ingot.

In this case, the silicon ingot can be manufactured by the CZ method (Czochralski method) or the FZ method (floating zone melting method), and the physical impact treatment can be performed while the silicon ingot is held by a seed crystal.

When the ingot is held by the seed crystal, it can be easily rotated, making it easier and more stable to create unevenness evenly across the entire outer surface of the ingot and impart distortion.

The present invention also provides a method for processing a silicon ingot, which involves cylindrical grinding the silicon ingot that has been treated by the above-mentioned method for treating the surface of the silicon ingot.

This allows the Cu gettered to the strained layer on the surface of the silicon ingot to be removed from the ingot, resulting in an ingot with a reduced Cu concentration.

The present invention also provides a method for storing silicon blocks, in which the silicon ingot is cylindrically ground using the silicon ingot processing method, and then cut into blocks of a predetermined length for storage.

This storage method removes the Cu gettered into the strained layer, preventing Cu from diffusing into the block during storage.

The present invention also provides a method for producing silicon wafers by slicing the silicon block stored by the above-mentioned silicon block storage method.

This allows silicon wafers with reduced Cu concentration to be obtained.

The present invention also provides a silicon ingot in which the entire surface of the body portion is a physically impact treated surface having an unevenness of Rz of 50 μm or more.

This reduces the Cu concentration inside the ingot, suppresses the occurrence of changes in OSF over time in the silicon wafers produced even when stored for long periods of time, and results in a silicon ingot that does not deteriorate in quality for the silicon wafers produced.

In this case, the silicon ingot can have a blasted surface as the physical impact treatment surface.

This reduces the Cu concentration inside the ingot more uniformly and stably throughout the entire ingot.

As described above, according to the surface treatment method of the silicon ingot of the present invention, the Cu concentration inside the ingot can be easily reduced. Furthermore, even if the block cut from the ingot is stored for a long period of time before being processed into wafers, the occurrence of change over time in OSFs in the silicon wafers to be manufactured is suppressed, and it is possible to obtain a silicon ingot that does not deteriorate in quality. According to the silicon ingot of the present invention, the Cu concentration inside the ingot is reduced, and even if the block cut from the silicon ingot is stored for a long period of time, the occurrence of change over time in OSFs in the silicon wafers to be manufactured is suppressed, and the quality of the silicon wafers to be manufactured does not deteriorate.

1 shows an example of a silicon ingot according to the present invention.

The present invention is described in detail below, but is not limited to these.

As described above, there was a need to provide a silicon ingot in which the change in OSF over time is suppressed even when the blocks cut from the ingot are stored for a long period of time before being processed into wafers, a method for treating the silicon ingot that can easily and at low cost reduce the Cu concentration inside the ingot and produce a silicon ingot in which the change in OSF over time is suppressed even when the blocks cut from the ingot are stored for a long period of time before being processed into wafers, and a silicon ingot in which the Cu concentration inside the ingot is reduced and the change in OSF over time is suppressed even when the blocks cut from the silicon ingot are stored for a long period of time before being processed into wafers.

The inventors have thoroughly studied ways to solve the above problems, and have come up with the idea of a method for easily processing silicon wafers in bulk by processing them in ingot form rather than wafer by wafer, without imposing constraints on production management. This involves imparting distortion to the surface of the ingot before cylindrical grinding, so that Cu is gettered into this distortion layer, and then the Cu is removed from the silicon ingot by cylindrical grinding. This method does not require significant cost increases such as low-temperature storage, does not require a limit on the number of days until slicing, and does not require constraints on production management. It is also not necessary to change the manufacturing conditions depending on the quality of the quartz crucible used or the number of days until the wafer is cut out. It has been found that this method can easily and simply manufacture silicon wafers in which crystal defects caused by Cu are suppressed, without imposing constraints on production management.

That is, by a surface treatment method for a silicon ingot in which the surface of the silicon ingot before cylindrical grinding is subjected to a physical shock treatment to form irregularities on the surface of the silicon ingot with an Rz of 50 μm or more, it is possible to reduce the Cu concentration inside the ingot easily and at low cost. In addition, it was found that even if a block cut from the ingot is stored for a long period of time before being processed into wafers, the occurrence of changes over time in OSFs in the silicon wafers to be manufactured is suppressed, and it is possible to obtain a silicon ingot in which the quality of the silicon wafers to be manufactured does not deteriorate, and thus the present invention has been completed.

The inventors also discovered that a silicon ingot in which the entire surface of the straight body portion is a physically impact treated surface having an unevenness of Rz of 50 μm or more reduces the Cu concentration inside the ingot, and even if a block cut from the silicon ingot is stored for a long period of time, the occurrence of changes over time in OSFs in the silicon wafers produced is suppressed, and the quality of the silicon wafers produced does not deteriorate, and thus the present invention was completed.

The present invention will be described in detail below.

(Silicon ingot)
First, a silicon ingot to be subjected to the silicon ingot surface treatment method according to the present invention will be described. The silicon ingot to be surface-treated will eventually be processed into a silicon wafer through processing steps such as slicing, and the method of manufacture is not particularly limited. The silicon ingot surface treatment method according to the present invention can be applied regardless of the method of manufacture of the ingot (crystal), such as the CZ method, the MCZ method, or the FZ method.

(Surface treatment method for silicon ingot)
Next, the method for surface treatment of silicon ingot according to the present invention will be described. A prepared silicon ingot is subjected to physical shock treatment on the surface of the silicon ingot before cylindrical grinding, and unevenness with Rz (maximum height) of 50 μm or more is formed on the surface of the silicon ingot to form a physical shock treatment surface. By forming such unevenness, a strain layer is formed near the ingot surface before cylindrical grinding, and Cu in the ingot can be gettered into this strain layer.

Figure 1 shows an example of a silicon ingot according to the present invention. In the silicon ingot 10 according to the present invention, the entire surface of the straight body portion 1 is a physically impact treated surface having an unevenness of Rz (maximum height) of 50 μm or more. Here, the physically impact treated surface refers to a surface in a state where it has been treated by physical impact. In a silicon ingot in which the entire surface of the straight body portion 1 is a physically impact treated surface 2 having an unevenness of Rz of 50 μm or more, Cu is gettered in the strain layer near the physically impact treated surface, so that the Cu concentration inside the silicon ingot except for the vicinity of the physically impact treated surface is extremely low. A block cut from such a silicon ingot has excellent long-term storage properties, and even if it is sliced into silicon wafers after long-term storage, various defects caused by Cu, especially OSFs, are not formed.

On the other hand, even if the entire surface of the straight body portion 1 is a surface that has been subjected to physical shock treatment, if the surface has irregularities with an Rz of less than 50 μm, the long-term storage properties will be particularly poor. This is because the effect of reducing the Cu concentration inside the silicon ingot is insufficient, and problems arise over time, such as the occurrence of OSFs in silicon wafers produced from the ingot as the storage period becomes longer.

The physical shock treatment surface may be any surface, but it is particularly preferable for it to be a blasted surface formed by blasting. The blasted surface can be easily formed over a wide area, and is provided with a strained layer capable of stably gettering Cu.

The unevenness (roughness) of the physical impact treatment surface is not particularly limited as long as Rz is 50 μm or more, but it can be preferably 75 μm or more, and more preferably 100 μm or more. There is also no particular upper limit, but for example, Rz can be 300 μm or less, and more preferably 200 μm or less.

The surface to be treated by physical shock may be any surface. It may be a surface in the as-grown state immediately after the ingot is grown, or a surface after other surface treatments or surface processing have been performed. In addition, if the silicon ingot and the seed crystal are still connected, it is preferable because the physical shock treatment can be performed at a high temperature before the ingot cools down, but the silicon ingot 10 according to the present invention may have the cone portion 3 and tail portion 4 removed. In the case of a silicon ingot 10 having a cone portion 3 and tail portion 4, not only the straight body portion 1 but also the surfaces of the cone portion 3 and tail portion 4 may be treated by physical shock.

For example, it is known that Cu applied to one side of a silicon substrate (725 μm thick) is diffused to the opposite side by heat treatment at 350°C for 1 h (Non-Patent Document 1). Cu, which is so easily diffused, is sufficiently gettered into the strained layer even at room temperature if the ingot has a surface that has been subjected to physical shock treatment as described above.

The physical impact treatment may be blasting, barreling, or the like, with blasting being particularly preferred as it is simpler. Blasting can more easily and stably form irregularities over a wide area of the ingot surface. Examples of blasting include shot blasting and grit blasting.

When a silicon ingot is manufactured by the CZ method, MCZ method, or FZ method, it is preferable to perform the physical impact treatment while the silicon ingot is held by a seed crystal. If the seed crystal and the ingot remain connected and the ingot is held by the seed crystal, the ingot can be easily rotated, making it even easier to apply distortion evenly across the entire surface of the ingot.

(Silicon ingot processing method)
The method for processing a silicon ingot according to the present invention is a method for performing cylindrical grinding on a silicon ingot that has been treated by the above-mentioned method for treating the surface of a silicon ingot. By cylindrical grinding, Cu gettered into the strained layer is removed from the ingot. The silicon ingot that has been subjected to cylindrical grinding has an extremely low Cu concentration. At this time, the time from the physical shock treatment to the cylindrical grinding can be appropriately determined in consideration of the diffusion of Cu from the inside of the ingot to the strained layer and the past record of OSF generation.

(How to store blocks cut from ingots)
The blocks cut from the ingots can be stored in any state after the physical shock treatment. They may be stored either before or after cylindrical grinding, but it is particularly preferable to store them after cylindrical grinding. After cylindrical grinding, Cu gettered to the strained layer is removed, so that it is possible to prevent Cu from diffusing into the blocks during storage.

(Silicon Wafer Manufacturing Method)
The method for producing a silicon wafer according to the present invention is a method for producing a silicon wafer by slicing a block stored by the above-mentioned method for storing a block obtained by cutting a silicon ingot. After subjecting the surface of the silicon ingot to physical shock treatment to form irregularities of a predetermined size to give distortion and removing Cu from the ingot by cylindrical grinding, a normal silicon wafer production process including a slicing step is performed to produce a silicon wafer. For example, after the silicon ingot is separated from the seed crystal and cooled, the above-mentioned cylindrical grinding, removal of the cone and tail parts, block cutting, slicing of the straight body part, lapping of the sliced wafer, chamfering, etching, polishing, etc. are performed. The concentration of Cu contained in the silicon wafer produced in this way is extremely low compared to the conventional method, so that the formation of various defects caused by Cu is suppressed.

In this way, if the block is cut from a silicon ingot that has been surface-treated according to the present invention, problems such as the occurrence of OSFs can be suppressed even if the block is stored for a long period of time before slicing. Moreover, the only new process added is the process of distorting the surface of the ingot by physical impact treatment such as sandblasting, making it possible to manufacture silicon wafers with reduced Cu concentration with a simple method and only a slight increase in cost.

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

(Example)
By the MCZ method, 130 silicon single crystal ingots with a diameter of 300 mm and a length of 150 cm were pulled. The Al concentration in the depth direction from the inner surface of the quartz crucible used at this time was less than 40 ppmw on average within a range of 30 μm from the inner surface, and the silicon single crystal ingot was not doped with Al during production.

When removing the silicon single crystal ingot from the pulling machine, the ingot was held by the seed crystal and rotated at 6 rpm while sandblasting using a sandblasting device to form irregularities on the entire outer peripheral surface of the ingot. The abrasive used for sandblasting was glass beads with a grit size of 120. The air pressure for sandblasting was 0.5 to 0.7 MPa, the spray distance was 30 to 50 cm, the spray angle was 90 ± 30°, and the treatment time for the entire ingot was 10 minutes.

The silicon single crystal ingot was then separated from the seed crystal, cooled, cylindrically ground, and cut into blocks. Before cylindrical grinding, the roughness of the ingot surface was measured at 10 points using a surface roughness measuring device (Mitutoyo, Surftest SJ-210), and the Rz was found to be 55 to 65 μm.

The storage period of the blocks was set at one-month intervals, from 0 months (3 days left standing) to 12 months, and 10 silicon single crystal ingots were sliced, lapped, chamfered, etched, polished, etc., for each month to produce silicon wafers. Every 50th silicon wafer was taken out and heat-treated at 1150°C/100 min. to check for the occurrence of OSFs. Not a single silicon wafer had OSFs, regardless of storage period.

(Comparative Example 1)
Surface treatment and processing of silicon single crystal ingots, manufacture and evaluation of silicon wafers were performed in the same manner as in the Example, except that the size of the glass beads used as the abrasive in sandblasting was 150. The roughness of the silicon single crystal ingot surface before cylindrical grinding was 35 to 45 μm in Rz. No OSFs occurred when the block storage period was 0 months (3 days) to 3 months, but OSFs occurred in 80% or more of the silicon wafers after 4 months.

(Comparative Example 2)
By the MCZ method, 130 silicon single crystal ingots with a diameter of 300 mm and a length of 150 cm were pulled. The Al concentration in the depth direction from the inner surface of the quartz crucible used at this time was less than 40 ppmw on average within a range of 30 μm from the inner surface, and the silicon single crystal was not doped with Al during production.

The silicon single crystal ingot was separated from the seed crystal and cooled, then cylindrically ground and cut into blocks. Before cylindrical grinding, the roughness of the ingot surface was measured at 10 points using a surface roughness measuring device (Mitutoyo Surftest SJ-210), and the Rz was 5 to 15 μm.

The storage period of the blocks was set at one-month intervals, from 0 months (3 days left standing) to 12 months, and 10 silicon single crystal ingots were sliced, lapped, chamfered, etched, polished, etc., for each month to produce silicon wafers. Every 50th silicon wafer was sampled and heat-treated at 1150°C/100 min. to check for the occurrence of OSFs. No OSFs occurred after 0 and 1 month storage, but after 2 months OSFs occurred in more than 80% of the silicon wafers.

As described above, according to the embodiment of the present invention, it is possible to reduce the Cu concentration in a silicon ingot easily and at low cost, and to improve the long-term storage properties of blocks cut from the ingot.

The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included within the technical scope of the present invention.

1...straight body portion, 2...physical impact treatment surface, 3...cone portion, 4...tail portion,
10...Silicon ingot.

Claims (8)

A surface treatment method for a silicon ingot, comprising: subjecting a surface of the silicon ingot before cylindrical grinding to a physical impact treatment, thereby forming irregularities on the surface of the silicon ingot having an Rz of 50 μm or more and 300 μm or less . The method for treating the surface of a silicon ingot according to claim 1, characterized in that the physical impact treatment is a blasting treatment. The method for treating the surface of a silicon ingot according to claim 1 or 2, characterized in that the silicon ingot is manufactured by the CZ method or the FZ method, and the physical impact treatment is performed while the silicon ingot is held by a seed crystal. A method for processing a silicon ingot, comprising performing cylindrical grinding on the silicon ingot that has been treated by the method for surface treatment of a silicon ingot according to any one of claims 1 to 3. A method for storing silicon blocks, comprising cutting the silicon ingot into blocks of a predetermined length after cylindrical grinding using the silicon ingot processing method described in claim 4, and storing the blocks. A method for producing silicon wafers, comprising slicing the silicon block stored according to the method for storing silicon blocks described in claim 5 to produce silicon wafers. A silicon ingot,
A silicon ingot, wherein the entire surface of a straight body portion is a physically impact treated surface having an unevenness of Rz of 50 μm or more and 300 μm or less . The silicon ingot according to claim 7, characterized in that the physical shock treated surface is a blasted surface.

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