JP2009182180A - Method of manufacturing semiconductor wafer, and semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor wafer that avoids the occurrence of processing distortion which tends to occur when silicon ingot is cut by a cutting device and silicon block is processed, and prevent the breaking and cracking of a thin sheet which tends to occur when silicon ingot is sliced into a thin sheet of silicon block, and to provide a semiconductor wafer. <P>SOLUTION: A method of manufacturing this semiconductor wafer includes (1) a block-forming step of cutting a semiconductor silicon ingot to form a silicon block in a predetermined size, (2) a film-forming step of thermally treating the silicon block in an oxidizing atmosphere to form a silicon dioxide film on a surface of the block, (3) a workpiece-mounting step of mounting the silicon block on a workpiece via the silicon dioxide film, and (4) a wafer-forming step of slicing the silicon block mounted on the workpiece into a thin flake having a predetermined thickness by a cutting device. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a semiconductor wafer and a semiconductor wafer, and more particularly, occurs when a silicon block of a predetermined size is cut from a semiconductor silicon ingot or when the silicon block is machined to be processed into a member having a required shape. The present invention relates to a method for manufacturing a semiconductor wafer particularly suitable for a solar cell and a semiconductor wafer manufactured by this method, which suppresses the occurrence of processing distortion, chipping, cracking, and the like that are likely to occur and ensures a high yield.

  Semiconductor silicon is used as a substrate material for semiconductor integrated circuits (ICs) and solar cells. In particular, as a substrate material of a solar cell that converts sunlight into clean electric energy, there is a material made of a thin film type organic substance, but a material made of a silicon semiconductor substrate is often used.

  A solar cell using a silicon semiconductor substrate is manufactured using a semiconductor wafer (hereinafter referred to as a wafer) obtained by processing a polycrystalline or single crystal silicon semiconductor material. This wafer is manufactured through a process in which a silicon ingot having a predetermined size is cut into a plurality of silicon blocks having a predetermined shape and then the individual blocks are sliced into thin plates having a predetermined thickness.

  Polycrystalline silicon ingots are usually manufactured by a casting method. In this casting method, a raw material polycrystalline silicon is filled into a quartz crucible, and the polycrystalline silicon raw material is melted by heating in a casting furnace, and the molten polycrystalline silicon is cast into a mold such as a graphite crucible. This is a method for producing a silicon ingot in a process of pouring into a solid and solidifying it. In this casting method, if the solidified silicon ingot is cooled as it is, a large residual stress is generated in the polycrystalline silicon ingot, causing cracks, cracks, and the like. A so-called in-furnace annealing process is performed to suppress the occurrence of cracks and cracks.

  Wafers are created through mechanical processing such as a block formation process that divides the silicon ingot into a plurality of pieces and a slicing process that slices the divided silicon block into thin pieces of a predetermined thickness. Distortion, undulation, etc. occur, and cracks, chipping, cracks, or chipping occur. Of course, if residual stress is generated in the silicon ingot in the manufacturing process of the above silicon ingot, the same cracking, chipping, cracking, etc. occur in the subsequent silicon block formation and slicing processes. Therefore, in the conventional silicon ingot casting method and silicon block processing method, measures are taken to prevent breakage such as distortion, cracking, chipping, cracking or chipping (for example, Patent Document 1 below). To 3).

  For example, a polycrystalline silicon ingot and a method for manufacturing a polycrystalline silicon member disclosed in Patent Document 1 below solve the above-mentioned problems by devising a heat treatment step after solidification in the prior art. Specifically, a silicon ingot sequentially performs a step of casting a crystalline silicon ingot, a step of taking out and holding a silicon ingot after casting from a mold, and a heat treatment step of raising the temperature to 1000 to 1400 ° C. and then cooling. To manufacture. The silicon member includes a step of machining the cast polycrystalline silicon ingot into a silicon block, a heat treatment step of cooling the silicon block after raising the temperature to 1000 to 1400 ° C., and a step of machining into a desired shape member after the heat treatment. The members in the required form are manufactured sequentially. Patent Document 2 below discloses a method of removing distortion generated when cutting into a silicon block by chemical etching. Further, Patent Document 3 below discloses a method for removing processing distortion on the surface of a silicon block by brush polishing.

JP 2004-161575 A (paragraphs [0018] to [0021]) JP 2006-278701 A (paragraphs [0034] to [0037], FIG. 1) JP 2004-356657 A (paragraphs [0016] to [0019], FIG. 1)

  According to the manufacturing method disclosed in Patent Document 1, the silicon block surface distortion can be removed by treating the silicon block at a high temperature (1000 to 1400 ° C.). However, this method is not preferable because heat treatment is performed in an air atmosphere, while treatment in an oxygen atmosphere is not preferable because impurities diffuse into the silicon. Moreover, although the method of the said patent document 2 removes the distortion which generate | occur | produced by cutting out into a block by chemical etching, since this method uses strong acid, there exists a subject that control of etching is difficult. Furthermore, although the method of the above-mentioned patent document 3 is to remove processing distortion on the surface of the silicon block by brush polishing, this method can suppress chipping or the like that tends to occur in the wire saw process. It is difficult to suppress the occurrence of chipping.

  The present invention has been made to solve the above-described problems of the prior art, and the object of the present invention is to occur when a silicon block is processed by cutting a silicon ingot with a cutting device. An object of the present invention is to provide a method for manufacturing a semiconductor wafer and a semiconductor wafer, in which cracks and chips of the thin plate, which tend to occur when removing the processing distortion and slicing a silicon block into a thin plate, are suppressed.

In order to achieve the above object, the method for producing a semiconductor wafer of the present invention includes the following steps (1) to (4).
(1) a block forming step of dividing a semiconductor silicon ingot to form a silicon block of a predetermined size;
(2) A film forming step of heat-treating the silicon block in an oxidizing atmosphere to form a silicon dioxide film on the surface thereof.
(3) a workpiece mounting step of mounting the silicon block on the workpiece via the silicon dioxide film;
(4) A slicing step of slicing the silicon block mounted on the workpiece into thin pieces having a predetermined thickness with a cutting device.

  According to the invention related to the method for manufacturing a semiconductor wafer, the film is formed when the silicon block is cut into a silicon block of a predetermined size by heat-treating the silicon block in an oxidizing atmosphere in the film forming step (2). It is possible to alleviate the surface processing distortion that tends to occur, that is, lattice defects near the block surface. At the same time, in this step, since a silicon dioxide film is formed on the surface of the silicon block, it is possible to bond without attaching the adhesive directly to the silicon material when it is attached to the workpiece, for example, with an adhesive. Therefore, stress is not applied to the silicon material. Further, slicing by the cutting device in the next slicing step (4) or subsequent wafer peeling from the adhesive becomes easy. As a result, in each process, chipping and cracking defects of the silicon material are reduced and quality and yield are improved, and workability of the bonding process, slicing process, and subsequent peeling process can be improved.

  In the method for manufacturing a semiconductor wafer, the thickness of the silicon dioxide film is preferably 0.5 μm to 2.0 μm.

  According to the said preferable aspect, said effect can be show | played appropriately by making the thickness of a silicon dioxide film into the range of 0.5 micrometer-2.0 micrometers. In addition, when the film thickness is within this range, the film formation time can be shortened and the productivity is not reduced.

  In the semiconductor wafer manufacturing method, the slicing step uses a wire saw cutting machine for the cutting device, and the wire saw cutting machine sets a cutting speed when cutting the silicon dioxide film to the silicon block. It is preferable to slice at a speed slower than the cutting speed when cutting the silicon material.

  According to the preferred embodiment, a wire saw cutting machine is used as the cutting device, the cutting speed of the cutting machine is changed to two speeds, and the cutting speed of the silicon dioxide film is made slower than the cutting speed of the silicon material. The occurrence of defects such as chipping and cracking that tend to occur when slicing a block can be suppressed. That is, if the cutting speed of the silicon dioxide film is increased to be equal to or faster than the cutting speed of the silicon material, cutting with a lot of vibration occurs at the stage where the cutting location is not determined, and as a result, the wafer thickness is thin at the peripheral portion However, the defects such as chipping and cracking are increased, but these defects can be suppressed by slowing down as described above.

  The semiconductor wafer of the present invention is manufactured by the above-described method for manufacturing a semiconductor wafer.

  According to the invention relating to the semiconductor wafer, a high-quality semiconductor wafer free from defects such as chipping and cracks can be obtained.

  The best mode of the present invention will be described below. However, the embodiment shown below exemplifies a semiconductor wafer manufacturing method and a semiconductor wafer for embodying the technical idea of the present invention, and is not intended to specify the present invention. Other embodiments within the scope of the claims are equally applicable.

First, a manufacturing process of a semiconductor wafer according to an embodiment of the present invention will be described mainly with reference to FIG. FIG. 1 is a process diagram showing a manufacturing process of a semiconductor wafer according to an embodiment of the present invention.
In the semiconductor wafer manufacturing process, as shown in FIG. 1, first, a silicon ingot manufactured by a silicon ingot manufacturer or the like is accepted by a processing manufacturer, that is, a specialized slice manufacturer (S1). In this slice specialized manufacturer, the silicon ingot is divided into, for example, a plurality of prismatic silicon blocks having a predetermined size using a large band saw such as a diamond band saw (S2). These silicon blocks are formed into silicon blocks having a predetermined shape by cutting off the end portions using the same small band saw (S3). Next, the silicon block is transferred to, for example, a heat treatment apparatus 3 or 3A as shown in FIGS. 2 and 3, and the heat treatment apparatus 3 or 3A takes silicon for a predetermined time at a predetermined temperature in a predetermined oxidizing atmosphere. A silicon dioxide film having a predetermined thickness is formed on the surface of the block (S4).

  The oxidizing atmosphere will be described in detail. The oxidizing atmosphere is an atmosphere that can oxidize non-oxide (silicon), and is formed of a gas such as oxygen that is dry or contains a small amount of water vapor. Among these gases, the former oxygen is generally called dry oxygen. By using this gas, a dense silicon dioxide film can be formed although the oxidation rate is slightly slowed down. In addition, the latter oxygen, which contains a small amount of water vapor in oxygen, is also called wet oxygen. Since this oxygen accelerates the oxidation reaction due to the presence of water vapor, the oxidation reaction is fast and a thick film is formed. Can be formed.

  The concentration of oxygen constituting the oxidizing atmosphere is preferably 100%, but may be mixed with other gas, for example, air. The air mixing rate is preferably adjusted so that at least the oxygen concentration is 30% or more. With such an oxygen concentration, even if the flow rate of these gases is reduced, a silicon dioxide film with little variation in thickness can be formed on the silicon block. However, so-called dry air, in which only air is used, is not preferable. The reason is that air is generally composed of a mixed gas of 21% by weight of oxygen and 79% by weight of nitrogen. Since the partial pressure of oxygen is low and it does not contain water vapor, the oxidation rate is very slow and a film having a predetermined thickness is formed. This is because they cannot. That is, if only the silicon block strain is removed, dry air is also effective, but in this embodiment, by performing heat treatment in an oxidizing atmosphere, not only the silicon block strain is removed, but also the silicon block surface. A silicon dioxide film with a predetermined thickness is formed on this, and when this film is bonded to the wire saw work in the next process, it is used as an adhesion interface with the work. However, dry air that takes a long time and is difficult to form a predetermined thickness cannot be used. The relationship with this work will be described later.

  Of the heat treatment conditions, the treatment temperature is preferably determined in consideration of the manufacturing process of a semiconductor device made from a silicon wafer. That is, the temperature is preferably 30 to 50 ° C. higher than the maximum temperature in the semiconductor device manufacturing process, and this temperature is about 1100 to 1150 ° C. The treatment time is in the range of 1 to 10 hours, and about 3 hours is preferable even in this time zone. Furthermore, the film thickness to be formed is preferably 0.5 μm to 2.0 μm. If it is out of this range, there are few effects, and problems such as the time required for film formation appear.

  By the heat treatment under this condition, the silicon block can remove distortion generated in the previous process and the like, and a silicon dioxide film having a predetermined thickness can be formed on the surface of the block. With this film formation, when the silicon block is bonded to the workpiece with an adhesive, the silicon block is not directly contacted with the adhesive, so that the silicon block is not stressed and the wafer can be easily peeled off from the wire saw and the adhesive. become. As a result, it is possible to suppress the occurrence of defects such as chipping and cracking at the time of the wire saw and subsequent peeling.

Next, a heat treatment apparatus for performing this heat treatment will be described with reference to FIGS. 2 is a schematic plan view showing a heat treatment apparatus, and FIG. 3 is a schematic view of another heat treatment apparatus.
The heat treatment apparatus 3 in FIG. 2 is an example of an apparatus that performs heat treatment using dry oxygen. As shown in FIG. 2, the heat treatment apparatus 3 has an electric furnace 4 provided with a space S having a size capable of accommodating the silicon block 1 therein. The electric furnace 4 includes a furnace body 5 having a space S and a door 6 that covers the opening 5b of the furnace body 5 so as to be freely opened and closed. Both the furnace body 5 and the door 6 are heat-resistant materials. It is formed with. The furnace body 5 has an inlet 5a connected to an oxygen supply source at one end, and an opening 5b having a size capable of carrying in and out the silicon block 1 at the other end. The door 6 is provided with an outlet 6a for leading oxygen inside the furnace body 5 to the outside. Around the furnace body 5, a heater 7 for heating the inside is provided. The electric furnace 4 is connected to an oxygen supply source 10 and a gas processing device 11 by pipes P ₁ and P ₂ .

  The usage state of the heat treatment apparatus 3 will be described. First, the door 6 of the electric furnace 4 is opened, and the silicon block 1 is inserted into the space S in the furnace body 5. Thereafter, the opening 5b of the furnace body 5 is closed with the door 6, the energization of the heater 7 is started, and the space S is heated to a predetermined temperature. In this state, a predetermined amount of dry oxygen is continuously supplied from the oxygen supply source 10 into the electric furnace 4 for a predetermined time, and oxygen sent from the electric furnace 4 is sent to the gas processing device 11 for processing. The heat treatment apparatus 3 removes strain and the like from the silicon block 1 and forms a silicon dioxide film 2 having a predetermined thickness on the surface thereof.

The heat treatment apparatus 3A in FIG. 3 is an example of an apparatus for performing heat treatment using wet oxygen. The heat treatment apparatus 3A is different from the above-described treatment apparatus 3 only in the configuration in which the accelerated oxidation water container 8 is disposed between the oxygen supply source 10 and the electric furnace 4, and the other configurations are the same. Yes. That is, the acceleration oxidation water container 8 is constituted by a container large enough to store a predetermined amount of water 9, the container by a pipe P ₁₁ is the oxygen supply 10, and the pipe P is to the electric furnace 4 ₁₂ are connected to each other.

  By bubbling the water 9 stored in the container, oxygen containing a small amount of water vapor can be supplied to the electric furnace 4 to form a silicon dioxide film having a predetermined thickness on the silicon block 1.

  The manufacturing process of the semiconductor wafer will be described again with reference to FIG. 1. The silicon block heat-treated in step S4 is bonded and fixed to the workpiece (base) 12 with an adhesive 13 as shown in FIG. 4 in the next step S5. . FIG. 4 is a perspective view of the silicon block bonded to the workpiece.

  As shown in FIG. 4, a glass plate (not shown) is fixed to the work 12, and a predetermined adhesive, for example, an adhesive 13 made of an epoxy resin is applied to the glass plate to fix the silicon block 1 as shown in FIG. Place and bond. By this adhesion, the workpiece 12 and the silicon block 1 are bonded and fixed via a silicon dioxide film formed on the surface of the silicon block 1.

  In this bonding and fixing, the silicon block 1 is bonded via the silicon dioxide film 2 without directly contacting the adhesive 13, so that stress is not applied to the silicon block 1, and the wafer is peeled off from the wire saw and the adhesive. It becomes easy. As a result, it is possible to suppress the occurrence of defects such as chipping and cracking during slicing with a wire saw and subsequent peeling. That is, since the epoxy resin used for the bonding surface of the silicon block is hard, stress is often applied to the silicon at the bonding portion during and after slicing with a wire saw to cause breakage. As a result, small cracks called chipping are generated in the periphery of the sliced wafer, resulting in a decrease in quality and a decrease in yield. However, such problems can be solved by bonding through film formation.

  The silicon block fixed to the workpiece 12 is sliced into thin pieces having a predetermined thickness using, for example, a multi-wire saw device 15 as shown in FIG. 5 (S6). In addition, FIG. 5 is the schematic which showed the principal part of the multi-wire saw apparatus.

  As shown in FIG. 5, the multi-wire saw device 15 includes three rollers 16 </ b> A to 16 </ b> C around which one wire 18 is wound. Among these rollers 16A to 16C, the roller 16A is connected to a drive source 19 composed of a motor or the like to become a drive roller, and the other two rollers 16B and 16C follow the rotation of the drive roller 16A. It is a driven roller that rotates. The driving roller 16A is rotated by the driving source 19 at a set speed. A plurality of grooves 17a to 17c are formed at a predetermined pitch on the outer peripheral surfaces of the rollers 16A to 16C, and one wire 18 is wound around the grooves 17a to 17c. The pitch of the grooves 17a to 17c is set by the thickness of a thin plate cut out by cutting. The wire 18 is formed of, for example, a hard steel wire (piano wire), and a thickness of about 0.06 to 0.25 mm is used. One end 18A of the wire 18 is wound around a delivery reel (not shown), and the other end 18B is wound around a take-up reel (not shown).

  The wire 18 is guided while receiving tension of several kilograms according to the rotation of the driving roller 16A, and is wound around the take-up reel from the feed reel while traveling along a predetermined direction at a predetermined speed.

The silicon block cutting process using the multi-wire saw device 15 is performed by moving the silicon block at a predetermined speed V ₀ to the portion of the wire 18 that runs on the workpiece 12 that is stretched between the driven rollers 16B and 16C. Press 1 against the wire. The pressing wire 18 which are arranged at a constant pitch as a multi-wire saw, first, cutting the silicon dioxide film 2 of silicon block surface at a cutting speed V _1. Then, it cuts at the cutting speed V ₂ by pressing a silicon block 1 the wire 18. After the silicon block 1 is cut, the silicon dioxide film 2 of the portion bonded with the adhesive is cut again, and finally, a part of a glass plate (not shown) fixed to the work 12 is cut to form a wire array. A plurality of wafers having a thickness determined by the pitch and the wire thickness are cut out simultaneously. The cut wafer is bonded to the workpiece 12 by an adhesive 13. This cutting is performed by supplying slurry to the roller and the silicon block.

Relationship between the cutting speed V ₂ of the cutting speed V ₁ and the silicon block 1 of silicon dioxide film 2 is preferably set to V ₁ <V _2. Become cutting speed V ₁ of the cutting speed V ₂ equal to or higher than the advancing and high cutting vibration which remains cut portion is not fixed to the silicon block 1 of silicon dioxide film 2, as a result, easily wafer thickness becomes thinner at the peripheral portion Chipping This is because defects such as cracks and chips occur.

  Referring to FIG. 1 again, the semiconductor wafer manufacturing method will be described. The silicon block 1 after slicing is immersed in a predetermined stripping solution to strip the wafer from the workpiece 12 (S7). At this time, each wafer is fixed to the work 12 in a state of being bonded by the adhesive 13. In order to remove the slurry and the adhesive 13 used in step S6, each wafer is immersed in a predetermined cleaning solution to remove the slurry and peel off the adhesive 13 (S8). The cleaned wafer is shipped to a solar cell manufacturer or the like as a product after undergoing a predetermined inspection process (S9) (S10).

  Hereinafter, the Example which implemented the manufacturing method of the semiconductor wafer of this invention which consists of the process mentioned above is described.

[Example 1]
A silicon block 1 having a side of about 16 cm and a length of 25 cm was cut with a band saw from a polycrystalline silicon ingot having a length of 70 cm, width 85 cm, and height 25 cm. It should be noted that steps, saw marks, and surface irregularities could be observed with the naked eye on the surface of the cut silicon block 1. The silicon block 1 was kept at 1100 ° C. for 3 hours using the heat treatment apparatus 3 shown in FIG. 2 and then slowly cooled at 10 ° C./min. By this heat treatment, a silicon dioxide film 2 having a thickness of 0.5 μm was formed on the surface of the silicon block 1. The silicon dioxide film 2 on the silicon block 1 and the wire saw work 12 (pedestal) were bonded with an epoxy adhesive 13 interposed therebetween (see FIG. 4).

  Thereafter, as shown in FIG. 4, a wire saw (abrasive grain: # 1200, piano wire diameter: 140 μm, piano wire moving speed: 5 m / sec, silicon dioxide 2 part work moving speed: 0.1 m / sec) Using this, the wafer was sliced to obtain a wafer having a thickness of 200 μm. The work moving speed of the silicon block 1 portion is 3 m / sec. The results are as shown in Table 1 below.

[Example 2]
A silicon block 1 having a side of 16 centimeters and a length of 40 centimeters is cut out from a cylindrical silicon single crystal having a diameter of 20 centimeters with a band saw, and then heat treated with a heat treatment apparatus 3A shown in FIG. The silicon dioxide film 2 having a thickness of 1.3 μm was obtained by holding at 1150 ° C. for 5 hours in an oxygen atmosphere that had been submerged (bubbling). The silicon block 1 was bonded to the work 12 in the same manner as in Example 1, and then cut with a wire saw. The results are as shown in Table 1 below.

FIG. 1 is a process diagram showing a manufacturing process of a semiconductor wafer according to an embodiment of the present invention. FIG. 2 is a schematic plan view showing a heat treatment apparatus used in the process of FIG. FIG. 3 is a schematic plan view of another heat treatment apparatus different from the treatment apparatus of FIG. FIG. 4 is a perspective view of the silicon block bonded to the workpiece. FIG. 5 is a schematic view of the main part of the multi-wire saw device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon block 2 Silicon dioxide film 3, 3A Heat processing apparatus, quartz jig 4 Electric furnace 5 Furnace main body 6 Door 7 Heater 8 Water container for accelerated oxidation 9 Water 10 Oxygen supply source 11 Gas treatment apparatus 12 Work 13 Adhesive 15 Multi-wire saw Equipment 16A-16C Roller 17a-17c Groove 18 Wire

Claims (4)

The manufacturing method of a semiconductor wafer characterized by including the process of (1)-(4) below.
(1) a block forming step of dividing a semiconductor silicon ingot to form a silicon block of a predetermined size;
(2) A film forming step of heat-treating the silicon block in an oxidizing atmosphere to form a silicon dioxide film on the surface thereof.
(3) a workpiece mounting step of mounting the silicon block on the workpiece via the silicon dioxide film;
(4) A slicing step of slicing the silicon block mounted on the workpiece into thin pieces having a predetermined thickness with a cutting device.   2. The method of manufacturing a semiconductor wafer according to claim 1, wherein a thickness of the silicon dioxide film is 0.5 μm to 2.0 μm.   The slicing step uses a wire saw cutting machine for the cutting device, and the wire saw cutting machine uses a cutting speed when cutting the silicon dioxide film to a cutting speed when cutting the silicon material of the silicon block. The method for manufacturing a semiconductor wafer according to claim 1, wherein the slicing is performed at a slower speed.   A semiconductor wafer manufactured by the method for manufacturing a semiconductor wafer according to claim 1.

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