JP3285054B2 - Polycrystalline silicon crushing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for crushing polycrystalline silicon which is a raw material of a semiconductor. More specifically, it relates to a method of crushing polycrystalline silicon, which is a raw material of single crystal silicon for semiconductors, into a lump having a size suitable for pulling a single crystal from a shape generated by precipitation in a reaction furnace while preventing contamination from atmosphere and tools. .

[0002]

2. Description of the Related Art Conventionally, methods of crushing polycrystalline silicon include a method of cutting with a diamond blade, a method of crushing with a hammer, a method of crushing with a crusher, and the like. In all of these methods, the crushing means is made of a material other than silicon, and it is unavoidable that polycrystalline silicon comes into contact with and contaminates them during crushing, and after crushing, cleaning with hydrofluoric nitric acid or the like is inevitable. ing.
In addition to the method of crushing by applying such a mechanical impact, there is also known a method of heating polycrystalline silicon to a high temperature, then dropping the same in water and quenching it, and crushing by thermal strain. Oxidation contamination and contamination in water pose a problem.

[0003] As a method of solving this disadvantage, Japanese Patent Application Laid-Open No.
The techniques of 0-33210 and JP-A-63-287565 have been proposed. The former is a method in which polycrystalline silicon is dielectrically heated and crushed by microwaves in an oven, and the latter is a method in which a cavity is attached to a microwave oven. These methods certainly prevent contamination of the silicon by the crushing means that do not come into contact with the silicon, but since they must be charged into the oven, anything larger than the oven cannot be crushed,
They must be cut to oven size beforehand. For example, at present, a long polycrystalline silicon rod having a length of about 2 m can be obtained by the Siemens method. However, in order to crush the rod by the above-described means, it is necessary to cut the rod into a size that can be put into an oven in advance. Surface contamination is inevitable. A possible solution to this problem is to make the oven larger, but it is expensive and far from practical. In addition, in the case of crushing by microwave, explosive crushing due to thermal expansion and the like extends from the inside of polycrystalline silicon in all directions, so it is difficult to predict the shape and size of the crushed material, and explosive scattering of crushed material In addition to the risk of inviting the oven, the oven may be damaged. Further, since the entire silicon rod is heated until thermal distortion occurs, oxidation contamination becomes severe.

Further, another crushing method is proposed in Japanese Patent Application Laid-Open No. 2-9706. This is silicon 600-1000 ℃
This is a method in which the silicon is heated and quenched to relax the silicon, and then mechanically crushed.However, there is a problem that the resistance heating element, which is the heating source, vaporizes at a high temperature and adheres to the silicon surface. Since it comes into contact with the mounting jig below, contamination from the jig cannot be ignored. In addition, this crushing method has the advantage that it can be crushed into many pieces at once because irregular strain is generated in the whole silicon, but fine powder is generated at the same time, resulting in a deterioration of the working environment due to floating in the air and loss of silicon. There is an easy disadvantage.

Japanese Utility Model Application Laid-Open No. 57-200385 and Japanese Utility Model Application Laid-Open No. 57-200386 disclose a device for cutting a thin plate with a laser. This device is designed to prevent cracks and cracks as much as possible. It is for processing, and the purpose is completely different from the crushing method. In the above-mentioned publication, it is described that a brittle material such as ceramic or silicon may cause cracks in processing by laser light. Although this can occur due to thermal shock due to a significant temperature difference between the laser light irradiation area and its surroundings, this type of crack occurs only near the laser light irradiation area, and breaks in thin materials such as silicon wafers. Despite the occurrence of cracks and the like, in the case of massive materials, even if cracks occur on the surface, they often stop partially and are not completely crushed. Therefore,
These materials are not easily crushed by laser light.

[0006]

SUMMARY OF THE INVENTION The present invention provides a crushing method which solves the above-mentioned problems of the prior art relating to a crushing method of polycrystalline silicon. The crushing method is free of impurities and contamination by surface oxidation, and is safe and easy to carry out. It is an object of the present invention to provide a crushing method that does not require processing.

As described above, even when a normal silicon crystal is irradiated with a high-density laser, cracks may be generated in the vicinity of the irradiated portion, but this does not cause crushing of the bulk material as a whole. However, according to the study of the present inventor, polycrystalline silicon deposited and grown in a rod shape by a thermal CVD method such as a Siemens method has a residual strain caused by its growth process and cooling process, and has The crystal grows in the radial direction from the core, and it has been found that if the internal strain and the crystal structure are properly used, the bulk or rod-like polycrystalline silicon can be crushed.

[0008]

The present invention is based on the above findings, and according to the present invention, the following crushing method is provided. (1) A method of crushing polycrystalline silicon deposited and grown in a rod shape by a thermal CVD method, in which a high-density laser beam is locally radiated to the polycrystalline silicon surface in an axial direction or a radial direction for a short time. A method for crushing polycrystalline silicon, wherein a crack generated on the surface by an impact is advanced into the polycrystalline silicon by internal strain and crushed. (2) The crushing method according to (1), wherein the irradiation direction is switched from the axial direction to the radial direction or from the radial direction to the axial direction when irradiating the rod-shaped polycrystalline silicon surface with the high-density laser light. (3) Power density of high-density laser light is 1 to 500 kW / cm
^2. The crushing method according to (1) or (2) above, wherein the diameter of the irradiation spot is 1 to 30 mm. (4) The above (1) to (3), wherein the laser is a carbon dioxide laser.
Any of the crushing methods.

[0009]

DETAILED DESCRIPTION OF THE INVENTION Polycrystalline silicon, which is the subject of the present invention, has been deposited and grown in a rod shape by a thermal CVD method represented by the Siemens method. Specifically, a raw material gas such as trichlorosilane is supplied to an airtight container having a rod-shaped silicon core, and silicon is deposited by thermal decomposition of the raw material gas on the surface of the red-heated silicon core, and is grown into a rod shape. . Since this precipitation growth reaction is an endothermic reaction, even if the central silicon core is energized and heated, the temperature of the outer peripheral portion is lower than that of the central portion. Also, at the time of cooling after completion of the reaction, the outer peripheral portion is cooled first, and the central portion remains at a high temperature. For this reason, polycrystalline silicon has internal strain caused by its growth process and cooling process. Further, since the crystal grows from the central silicon core to the outside, the crystal grows in the circumferential direction from the silicon core, and two planes, a plane perpendicular to the axis of the silicon rod and a plane including the axis, are included. It is easy to cleave at the seed surface.

The crushing method of the present invention utilizes the above-mentioned internal strain of polycrystalline silicon and the presence of a plane which is easily cleaved. The state of crushing of polycrystalline silicon varies greatly depending on the irradiation direction of the laser beam, and is most easily crushed when irradiated along its axial direction or radial direction, and crushing does not occur when irradiated from other directions. In addition, the surface is melted or oxidized due to irradiating laser light of excessive power for crushing. In the present invention, cracks are caused to progress along the internal strain by irradiating the laser light along the axial direction or the radial direction of the polycrystalline silicon.

In order to crush the polycrystalline silicon into a size suitable for pulling a single crystal by making good use of the internal strain and the existence of a surface which is easily cleaved, first, the outer peripheral surface of the rod-shaped silicon is irradiated with a laser beam from the radial direction. To form a columnar mass of a desired length. Next, when the cut surface of the columnar silicon is irradiated with laser light from the axial direction, the silicon rod is broken into a semi-cylindrical shape along a straight line connecting the center and the irradiated portion. In addition, when the irradiation location is the center of the columnar silicon, the direction in which it is broken cannot be predicted. Therefore, when controlling the crushing direction, it is desirable to irradiate a laser beam shifted from the center of the cylindrical silicon. Then, by irradiating near the center of this semicircular surface, the cross section is broken into a fan-shaped column shape. The regularity of the crushing described above is due to the internal strain and the presence of a plane that is easily cleaved in the polycrystalline silicon. By switching the irradiation direction of the laser light between the axial direction and the radial direction and crushing, the rod-shaped polycrystalline silicon can be processed to a desired size.

As described above, the present invention is a method in which cracks are generated on the surface of polycrystalline silicon, and the cracks are caused to progress inside due to internal strain, so that the laser light to be irradiated is applied to the surface of the polycrystalline silicon. Any material may be used as long as it has an output and a power density that cause cracks due to thermal shock. Excessive irradiation is not preferred because it causes the surface to melt and cause a mirror surface. Therefore, it is preferable to irradiate the laser light with high density or high luminance for a short time, for example, several seconds.

When the surface of polycrystalline silicon is irradiated with high-density laser light, its energy is converted into heat and a sharp rise in temperature occurs locally. The temperature rise of the irradiated portion occurs at the moment of irradiating the laser beam. On the other hand, the temperature around the irradiated portion is delayed due to heat conduction. For this reason, a remarkable thermal stress acts between the irradiated portion and its surroundings, and cracks occur on the surface. The cracks generated on the surface progress into the polycrystal due to internal strain accumulated during the process of depositing the polycrystalline silicon, leading to crushing of the entire polycrystalline silicon. Since stress such as internal strain of the polycrystalline silicon tends to concentrate on a defect such as a crack, once a crack occurs, the crack proceeds linearly due to the internal strain. For this reason, the crushing is mainly concentrated on one surface, and the crushing surface becomes a substantially linearly continuous surface, and is rarely crushed into many small pieces.

The laser device used in the present invention only needs to have an output, a power density and an irradiation time sufficient to apply a thermal shock to the polycrystalline silicon and to cause cracks on the surface. Since polycrystalline silicon has a sufficient thickness, laser light is absorbed around the surface and most of the light is converted into heat. Since the surface of polycrystalline silicon is generally not a mirror surface, reflection of light does not matter. For this reason, most commercially available laser devices such as a carbon dioxide laser, a carbon monoxide laser, an iodine laser, a YAG laser, an argon laser, and an excimer laser can be used as the laser device used in the present invention. A carbon dioxide laser and a YAG laser are desirable from the viewpoint of operation cost and the like. As described above, since excessive laser irradiation melts the surface and makes it mirror-finished, it is preferable to irradiate high-density laser light for a short time, and a pulsed laser is desirable. In addition, the YAG laser can use an optical fiber, and assembling and operation of the device are easy.

Since silicon easily transmits near-infrared rays and infrared rays, when these lights are irradiated, the light reaches a certain extent from the surface to the inside and turns into heat. However, when irradiated with ultraviolet or visible light, it is absorbed only on the silicon surface without reaching the inside, causing damage to the silicon near the surface, causing melting or oxidation, or ionization of the silicon called ablation, and the laser light is emitted. The effect of thermal shock required for crushing cannot be exhibited. From these facts, a near infrared or infrared laser such as a YAG laser or a carbon dioxide laser is more preferable as the laser light. Also, in this type of laser, light also reaches inside silicon,
Since the heat generation region has a conical shape not only from the surface of the irradiated portion but also from the irradiated portion toward the inside of the member, the cracks extend in the irradiation direction. Therefore, when the laser beam is irradiated from the axial direction or the radial direction, cracks are generated along a surface that is easily cleaved, so that crushing is facilitated and controllability of the crushing direction is improved.

The irradiation of the laser beam may be performed at such a high density as to cause cracks on the surface of the silicon mass as described above.
The strength of the polycrystalline silicon rod varies depending on the crystal growth direction. In both the radial direction and the axial direction, the power density of the laser beam is 1 to 500 kW / cm ² and the diameter of the irradiation spot is 1 to 500 kW / cm ^2. It may be 30 mm. If the power density is too low, no cracks will occur, and if it is too high, the surface will melt, evaporate, oxidize, cut or ablate, etc., which is undesirable for crushing. Also, if the irradiation area is small, even if the power density is large, the total energy to be irradiated is small, so that crushing is difficult to occur. Conversely, if the irradiation area is large, many cracks are generated in various directions, and crushing is difficult to occur. In addition, the direction of crushing cannot be controlled. As for the irradiation time, a short time of about 10 seconds or less is sufficient because the crushing is caused by a thermal shock due to a remarkable temperature difference between the irradiated portion and the periphery. Long-time irradiation not only causes the surface to melt and oxidize due to excessive energy, but also causes the temperature of the whole silicon mass to rise, reducing the temperature difference during the next irradiation, making crushing difficult, and cooling after crushing. A process is required.

EXAMPLE 1 A diameter of 100 mm and a length of 1800 mm manufactured by the Siemens method
Place several polycrystalline silicon rods on the movable stage,
Using a carbon dioxide laser device (Mitsubishi Electric 50C type), 5 kW laser light is applied vertically to the side surface of each polycrystalline silicon rod at a power density of 5 to 100 kw / cm ² and a spot diameter of 2 to 2.
When irradiation was performed at 10 mm for 5 seconds, a crack was formed on the circumferential surface from the moment of irradiation, and some of them cracked into two by making a sound, and others cracked immediately when they were tapped lightly. It was the same even if the irradiation place was changed sequentially. The fracture surfaces were generated in the radial direction, and were all smooth.

Example 2 Using the same laser device as in Example 1, a laser beam of 3 to 5 kW was applied to the vicinity of the center of the crushed surface perpendicular to the crushed surface of the sliced polycrystalline silicon lump obtained in Example 1. 3 to 100 kw / cm
^When irradiation was performed at a power density of 2 and a spot diameter of 2 to 10 mm for 2 seconds, a sample having a thickness of less than 100 mm cracked through the irradiated portion at the moment of irradiation, and was broken into two into a semi-cylindrical shape. The cracks were in only one direction and did not split into many pieces. Thereafter, when irradiation was performed near the center of this semicircular surface, the cross section was broken into a fan-shaped column. On the other hand, thickness 100
In the case of the mm sample, a phenomenon was observed in which a part of the sample cracked obliquely from the irradiated part. By repeating the crushing of Example 1 and the crushing of this example, a standard silicon lump used as a raw material for pulling single crystal silicon was obtained. Example 1
The same unprocessed polycrystalline silicon rod as used in (1) could be similarly crushed by using a sample cut in a circle with a diamond cutter.

Example 3 A continuous wave output of 400 W was applied vertically to the side of a polycrystalline silicon rod having a diameter of 100 mm using a YAG laser device (type SL117-2C manufactured by NEC Corporation) that oscillates continuous waves and pulse waves. ,
When laser light was irradiated with a pulse wave peak value of 250 kW and a spot diameter of 2 mm, the laser irradiation surface of the silicon rod cracked and split into two within 5 seconds from the moment the laser was irradiated, whether continuous or pulsed. Was. Since this YAG laser beam was sent by an optical fiber, the operation was performed by changing the irradiation location and direction. However, in any of the axial and radial directions, and at any location, it was possible to crush and crush as desired. Was completed. On the other hand, when the side face and the crushed face of the silicon lump were irradiated with the laser beam from an oblique direction, the surface portion was peeled off and cracks did not progress inside.

[0020]

According to the crushing method of the present invention, the following effects can be obtained. (1) Since it is a non-contact crushing method by laser irradiation, no impurities are mixed in from a crushing tool or the like. (2) There is no surface oxidation by heating or impurities from the atmosphere at the time of heating, such as volatile contamination of the material of the heating furnace, which gives thermal shock to a very small part of the surface of polycrystalline silicon. Therefore, there is no danger of damage or contamination by the jigs installed in the apparatus. (3) Since the crushing is caused by internal strain of the polycrystalline silicon, the crushing surface is smooth, and impurities are less likely to adhere to the surface during bagging, so that the product is kept clean. Also, the energy used is minimal and there is no danger of explosive crushing. Moreover, since no fine powder is generated, the air can be kept clean and the working environment can be favorably maintained. (4) Since the crushing direction can be predicted from the directionality of the strain in the polycrystalline silicon, it can be processed into a desired size and shape. (5) After laser irradiation, the temperature rises slightly near the irradiated part, but it is about 100 ° C at the maximum, and the irradiated surface does not change,
There is no need to cool or wash the product as in the conventional method, and the product can be inspected and packaged as it is after crushing classification. Therefore, the process can be largely omitted, and the trouble of treating wastewater containing silicon fine powder and a solvent, which is a problem in the conventional method, can be omitted. (6) It can be easily carried out without being limited by the size and shape of the polycrystalline silicon. (7) Since the laser light can be easily changed in the optical path or split by a mirror or optical fiber, continuous crushing can be performed by sequentially moving the irradiation location, and several crushing devices can be operated with one laser device. It is. The focusing of the laser light can be automatically adjusted by light, and the work can be automated.

Continuation of the front page (72) Inventor Masayuki Tekei 5 Mita-cho, Yokkaichi-shi, Mie Inside High Purity Silicon Co., Ltd. (56) References JP-A-60-33210 (JP, A) JP-A-58-213623 ( JP, A) JP-A-1-140690 (JP, A) JP-A-2-9706 (JP, A) JP-A-2-152554 (JP, A) JP-A-63-287565 (JP, A) Showa 57-200385 (JP, U) Actually open Showa 57-200386 (JP, U) Japanese Patent Publication No. 51-48688 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01B 33 / 00-33/193 B02C 19/18 WPI / L (QUESTEL)

Claims (4)

(57) [Claims] 1. A method for crushing polycrystalline silicon deposited and grown in a rod shape by a thermal CVD method, comprising irradiating a polycrystalline silicon surface with a high-density laser beam for a short time locally in an axial direction or a radial direction thereof. A method of crushing polycrystalline silicon, wherein a crack generated on the surface by the thermal shock is advanced into the polycrystalline silicon by internal strain and crushed. 2. When irradiating a rod-shaped polycrystalline silicon surface with high-density laser light, the irradiation direction is changed from an axial direction to a radial direction.
The crushing method according to claim 1, wherein the irradiation is performed by switching from the radial direction to the axial direction. 3. The high-density laser beam has a power density of 1 to 50.
0 kW / cm ² and the irradiation spot diameter is 1 to 30
3. The crushing method according to claim 1 or 2, wherein 4. The crushing method according to claim 1, wherein said laser is a carbon dioxide gas laser.