JP2008041703A - Method for processing silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reuse a silicon wafer which has any cracking in its periphery, and thereby to improve the yield of the silicon wafer. <P>SOLUTION: A nozzle head 8 is reciprocated in a specified direction within a processing chamber 6. When a slurry 10 is jetted out for the upper side surface 11a of a lamination 11 from each of nozzles 7, the slurry 10 hits the peripheries 1a of respective silicon wafers 1. Thus, the chipped surface of the periphery 1a is polished and the surface is made smooth, so that the breakage of the silicon wafer 1 due to chipping is prevented. Therefore, the silicon wafer 1 is reused, and its yield is also improved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for processing a silicon wafer used in, for example, a solar cell.

  In recent years, solar cells have attracted attention as a power generation means that replaces thermal power generation, nuclear power generation, and the like from the viewpoint of protecting the global environment. In other words, power generation by this solar cell is possible as long as there is sunlight, and since it does not emit any harmful substances such as carbon dioxide and radioactive waste, it is attracting attention as a clean energy source.

  Such solar cells are manufactured through various processes such as cleaning of a silicon wafer, silver paste application, drying, and electrode formation.

  Silicon wafers are mainly rectangular and circular, but the silicon wafer 1 used for solar cells is mainly rectangular as shown in FIG. For example, as shown in FIG. 9, the silicon wafer 1 is obtained by slicing a prismatic silicon ingot 2 fixed to a glass substrate 4 with an adhesive 3 in a direction AA perpendicular to the long side with a wire saw or the like. Then, it peels from the adhesive agent 3 and is obtained by grinding and polishing a required part.

  By the way, conventionally, the peripheral portion of the silicon wafer (peripheral surface or chamfered portion of the peripheral surface edge) is prevented from generating dust from the peripheral portion, or cracks starting from minute unevenness of the surface roughness of the peripheral portion. Polishing is performed for the purpose of preventing the occurrence of chipping.

  For example, in Patent Document 1 below, in order to reduce cracking defects in a silicon wafer, the surface roughness present on the side surface of a silicon block or silicon stack (a cylindrical or prismatic block formed by stacking two or more silicon wafers). The minute unevenness (eg, Ry = 20 μm, 12 μm, paragraphs 0028, 0030, etc.) is flattened by mechanical polishing (eg, Ry = 5.8 μm, 2.8 μm, paragraphs 0028, 0030, etc.).

Further, in Patent Document 2 below, in order to prevent a silicon wafer from being chipped, the edge and side surfaces of the wafer are mirror-finished by polishing. Specifically, a plurality of wafers (10) are stacked via spacers (11), and a stacked body held by a clamp plate (12) is rotated around a shaft (13, 14). Mechanical polishing is performed by bringing the edge of (10) into contact with the pad (15a) on the surface of the rotating roller (15).
JP 2002-176014 A JP-A-5-182939

  It is possible to reduce the occurrence of chipping defects at the peripheral edge by polishing the peripheral edge of the silicon wafer and reducing its surface roughness, but in the silicon wafer manufacturing process and subsequent manufacturing processes, Depending on the circumstances, chipping defects may occur at the peripheral edge of the silicon wafer. This chip defect is a shape defect generally called chipping. For example, in the manufacturing process of a silicon wafer, after slicing a silicon block, when the silicon wafer is peeled off from the adhesive layer with the glass substrate, the chip defect May occur. Further, in the subsequent manufacturing process, when the silicon wafer is handled, the peripheral portion of the silicon wafer may come into contact with other members and a chip defect may occur.

  Conventionally, when a chip defect occurs at the peripheral edge, the silicon wafer has been disposed of as a defective product. This is because chipping defects at the peripheral edge cause cracking of the silicon wafer, but there is a problem that the yield of the silicon wafer is reduced by disposal as a defective product.

  Accordingly, an object of the present invention is to increase the yield of silicon wafers by reusing a silicon wafer having a chip defect at the peripheral edge.

  The chipped defect at the periphery itself does not affect the electrical characteristics of the silicon wafer, so even if there is a chipped defect, it can be reused as a silicon wafer if it can be repaired to the extent that it does not cause cracking. is there. The inventors of the present application are proceeding with many experiments, and even if there is a chip defect on the periphery of the silicon wafer, if the surface of the chip defect has a smooth shape, the silicon wafer starting from the chip defect will be used. The knowledge that cracking can be prevented was obtained. The present invention has been proposed based on such knowledge. That is, the silicon wafer processing method of the present invention is characterized in that the surface of the chip defect is polished into a smooth shape by spraying slurry toward the peripheral part of the silicon wafer having a chip defect at the peripheral part. To do.

  Here, the “chip defect” at the peripheral edge of the silicon wafer is a shape defect generally called chipping, and in addition to exhibiting a concave defect shape as a whole, the surface thereof is sharp and relatively There are many large irregularities. The size of the irregularities on the chipping surface is considerably larger than the minute irregularities constituting the surface roughness of the peripheral edge.

  The slurry is a suspension in which abrasive grains are dispersed in a medium. As an abrasive grain, well-known abrasive grains, such as a diamond, GC (green carborundum), C (carborundum), CBN (cubic boron nitride), can be used, for example. As the medium for dispersing the abrasive grains, liquids such as water (particularly pure water), alkaline solution, mineral oil, and glycols (for example, polyethylene glycol, propylene glycol (PG)) can be used.

  At the time of processing, it is preferable that a plurality of silicon wafers are laminated so that the wafer surfaces directly overlap each other to form a laminated body, and the slurry is sprayed onto the laminated body. By doing so, since a plurality of silicon wafers can be processed simultaneously, the processing time is shortened. In addition, by laminating a plurality of silicon wafers so that the wafer surfaces directly overlap each other without interposing a spacer, a laminated body is formed, so that the wafer surface of each silicon wafer is unnecessarily polished by the sprayed slurry. Is prevented.

  The silicon wafer to be processed may be circular or rectangular. When processing a rectangular silicon wafer with a laminated body, it is desirable to install the laminated body so that the side surfaces of the laminated body formed by the peripheral portions of the plurality of silicon wafers are inclined with respect to the horizontal plane. If it does so, since the slurry injected to the side surface of the laminated body easily flows in the inclined direction of the side surface, new slurry can easily hit the peripheral portion of each silicon wafer, and the processing efficiency is improved. In this case, it is more desirable that the side surface of the laminated body be inclined in the direction along the peripheral edge of the silicon wafer with respect to the horizontal plane. Then, since the slurry sprayed to the side surface of the laminated body easily flows in the inclined direction along the peripheral edge portion of each silicon wafer forming the side surface, the new slurry easily hits the peripheral edge portion of each silicon wafer. , Processing efficiency is improved.

  When processing a silicon wafer with a laminated body, it is desirable to move relatively the nozzle which injects the said slurry, and the said laminated body. If it does so, the wide range of a laminated body can be processed with the nozzle of few installation numbers.

  According to the present invention, the surface of the chip defect is polished into a smooth shape by spraying the slurry toward the peripheral part of the silicon wafer having the chip defect at the peripheral part. The silicon wafer having a chipped defect at the peripheral edge, which has been conventionally disposed as a defective product, can be reused, and the yield of silicon wafers can be increased.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 1 is a schematic view of the entire silicon wafer processing apparatus used in this embodiment.

  This silicon wafer processing apparatus includes a processing chamber 6, a slurry tank 13, a pump 15, and a slurry pipe 18 connecting them. The processing chamber 6 is for processing by spraying the slurry 10 onto the silicon wafer 1 (laminated body 11), and its configuration and processing method will be described in detail later. The slurry tank 13 is for temporarily storing the slurry 10, and has a stirrer 14 for stirring the stored slurry 10. The pump 15 is for pumping the slurry 10 from the slurry tank 13 to the processing chamber 6. The slurry pipe 18 is constituted by a supply pipe 18a extending from the slurry tank 13 to the processing chamber 6 and a return pipe 18b extending from the processing chamber 6 to the slurry tank 13, and a flow rate of the slurry 10 is supplied to the supply pipe 18a. Appropriate devices such as a valve 16 for adjusting the pressure and a pressure gauge 17 for measuring the pressure of the slurry 10 are connected. The slurry 10 pumped through the supply line 18a by the discharge force of the pump 15 is sprayed from the nozzle 7 in the processing chamber 6 toward the silicon wafer 1 (laminated body 11), and then the slurry is passed through the return line 18b. It is collected in the tank 13.

  2 shows a front sectional view of the processing chamber 6, and FIG. 3 shows a side sectional view.

  A nozzle head 8 is installed in the upper part of the processing chamber 6, and a laminated body 11 of the silicon wafer 1 is accommodated and fixed in the lower part. A plurality (for example, a plurality of rows and a plurality of rows) of nozzles 7 are attached to the nozzle head 8. The slurry 10 pumped from the pump 15 enters the nozzle head 8 and is ejected from each nozzle 7 through a passage (not shown) of the nozzle head 8. The laminated body 11 is configured by laminating a plurality of silicon wafers 1 so that the wafer surfaces 1b directly overlap each other without interposing a spacer, and fixing with a suitable fixing jig 9. As schematically shown in FIG. 6A, each silicon wafer 1 has chipping 5 as a chip defect at the peripheral edge 1a (in the figure, the size of the chipping 5 is exaggerated). In the laminated body 11, the silicon wafers 1 are laminated so that the peripheral edge 1a having the chipping 5 is on the upper side. Accordingly, the upper side surface 11 a of the stacked body 11 is formed by the peripheral edge portion 1 a having the chipping 5 of the silicon wafer 1. A discharge hole 12 for the slurry 10 is formed in the lower surface corner of the processing chamber 6.

  As shown in FIG. 4, in this embodiment, the processing chamber 6 is inclined with respect to the horizontal plane C at a predetermined angle γ. The direction of inclination is a direction along the peripheral edge 1 a of the silicon wafer 1 in the stacked body 11. As a result, the upper side surface 11a of the stacked body 11 formed by the peripheral edge portion 1a of the silicon wafer 1 is inclined with respect to the horizontal plane C by an angle γ in the direction along the peripheral edge portion of the silicon wafer 1.

  As shown in FIG. 5, the processing chamber 6 may be installed parallel to the horizontal plane, and the laminate 11 may be fixed in a state where it is inclined with respect to the processing chamber 6 by a predetermined angle. In this case, the nozzle head 8 is also preferably installed in a state inclined by a predetermined angle with respect to the processing chamber 6.

  The nozzle head 8 is moved and driven in the processing chamber 6 by an appropriate driving means (not shown). Thereby, relative movement is given between each nozzle 7 of the nozzle head 8 and the laminated body 11. In this embodiment, the nozzle head 8 reciprocates in the direction D shown in FIG. 3, that is, in the direction orthogonal to the wafer surface 1 b of each silicon wafer 1 in the stacked body 11. By reciprocating the nozzle head 8, it is possible to cover the entire range of the upper side surface 11 a of the laminate 11 with a small number of nozzles 7.

  The slurry 10 sprayed from the nozzle 7 is, for example, one in which GC (green carborundum) having an abrasive grain size # 200 to 800 is dispersed in pure water at a concentration of 30 to 50% by weight. Moreover, the pressure of the slurry 10 injected from the nozzle 7 is, for example, 0.3 to 0.5 MPa, and the injection angle of the nozzle 7 is, for example, 65 °.

  When the slurry 10 is sprayed from the respective nozzles 7 toward the upper side surface 11a of the laminated body 11 while the nozzle head 8 is reciprocated in a predetermined direction in the processing chamber 6, the slurry 10 of each silicon wafer 1 having the chipping 5 is obtained. It hits the peripheral edge 1a. Thereby, the surface of the chipping 5 of the peripheral part 1a is grind | polished and becomes a smooth shape. FIG. 6A schematically shows the shape of the chipping 5 before processing, and FIG. 6B schematically shows the shape of the chipping 5 after processing.

  The chipping 5 has a concave defect shape as a whole, and on its surface, there are many sharp and relatively large irregularities, which cause cracks in the silicon wafer 1. Conceivable. The surface of the chipping 5 is polished by spraying the slurry 10 to smooth the concave shape as a whole, and the uneven portions existing on the surface are flattened, or the uneven portions are rounded to obtain a height (depth). ) Can be prevented from cracking the silicon wafer 1 starting from the chipping 5. Thereby, the silicon wafer 1 in which the chipping 5 has occurred can be reused, and the yield of the silicon wafer 1 is improved.

  The test was performed by changing the particle size (abrasive grain number) of the abrasive grains of the slurry 10 and the spray pressure of the slurry 10 in various ways. The abrasive grains of the slurry 10 are GC, the medium is pure water, and the GC concentration is 30% by weight. The silicon wafer 1 is a single crystal and is a square with a side length of 104 mm. The processing time was 30 minutes, and the number of samples was 5 under each test condition. The test results are summarized in FIG.

  As shown in the test results of FIG. 7, when the grain size of the abrasive grains is as large as F80, the peripheral edge 1a of the silicon wafer 1 tends to be excessively polished, and conversely, the grain size of the abrasive grains is # 800. When it is small, it was recognized that the chipping 5 of the peripheral edge 1a tends to be insufficiently polished. On the other hand, even when the grain size of the abrasive grains is F220 (about 80 to 90 μm) and # 400 (about 35 to 40 μm), there is a tendency that the polishing pressure of the slurry 10 causes excessive polishing or insufficient polishing. Admitted. To summarize the test results, the grain size of the abrasive grains is good for F220 (about 80 to 90 μm) and # 400 (about 35 to 40 μm), and the spray pressure of the slurry 10 is 0.30 MPa for F220 and # 400. It can be seen that 0.35 to 0.40 MPa is good.

  The present invention can also be applied to a circular silicon wafer.

1 is an overall schematic view of a silicon wafer processing apparatus according to an embodiment. It is front sectional drawing of the processing chamber of a silicon wafer processing apparatus. It is side surface sectional drawing of the processing chamber of a silicon wafer processing apparatus. It is front sectional drawing of the processing chamber of a silicon wafer processing apparatus. It is front sectional drawing of the processing chamber of the silicon wafer processing apparatus which concerns on other embodiment. (A) is a perspective view schematically showing a state before chipping of the peripheral portion of the silicon wafer, and (b) is a perspective view schematically showing a state after chipping of the peripheral portion of the silicon wafer. It is a figure which shows the result of a test. (A) is a front view of a square silicon wafer, (b) is a side view of the square silicon wafer. It is a perspective view of a prismatic silicon ingot bonded to a glass substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon wafer 1a Peripheral part 1b Wafer surface 5 Chipping (chip defect)
7 Nozzle 10 Slurry 11 Silicon wafer laminate 11a Upper side surface

Claims (8)

  A method of processing a silicon wafer, comprising polishing a surface of the chip defect to a smooth shape by spraying slurry toward the peripheral part of the silicon wafer having a chip defect at the peripheral part.   The silicon wafer processing method according to claim 1, wherein a plurality of silicon wafers are stacked so that wafer surfaces directly overlap each other to form a stacked body, and the slurry is sprayed onto the stacked body.   The silicon wafer processing method according to claim 1, wherein the silicon wafer is square. 3. The processing of a silicon wafer according to claim 2, wherein the silicon wafer is square, and the stacked body is installed so that a side surface of the stacked body formed by peripheral portions of the plurality of silicon wafers is inclined with respect to a horizontal plane. Method. The silicon wafer processing method according to claim 4, wherein the side surface of the stacked body is inclined in a direction along a peripheral edge of the silicon wafer with respect to a horizontal plane. The method for processing a silicon wafer according to claim 2, wherein the nozzle for injecting the slurry and the laminate are relatively moved.   The method for processing a silicon wafer according to claim 1, wherein the silicon wafer is used for a solar cell. A silicon wafer processed by the processing method according to claim 1.

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