METHOD FOR POLISHING A SILICON WAFER AND METHOD FOR PRODUCING A SILICON WAFER

Abstract

Method for polishing a silicon wafer (W) comprising the following: a double-sided polishing step of performing polishing on a front surface and a rear surface of a silicon wafer (W); a notched part polishing step of performing a polishing on a beveled part of a notched part (N) of the silicon wafer, while a slurry (S) is delivered to the beveled part of the notched part (N) of the silicon wafer (W), after the double-sided polishing step; a chamfered peripheral part polishing step of performing a polishing on the chamfered part on a periphery of the silicon wafer (W) except for the chamfered part of the notched part (N) after the notched part polishing step; and a high-gloss polishing step of performing high-gloss polishing on the front surface of the silicon wafer (W) after the beveled peripheral part polishing step, the notch part polishing step is carried out in a state where the front surface is wet with water.

Description

Technical field

[0001] This disclosure relates to a method for polishing a silicon wafer and a method for producing a silicon wafer. background

[0002] Silicon wafers are commonly used as substrates for semiconductor devices. A silicon wafer is produced as follows: First, a single-crystal silicon ingot is formed by the Czochralski (CZ) process or similar methods. Next, the periphery of the grown single-crystal silicon ingot is ground to adjust the ingot's diameter to a predetermined value.

[0003] Next, a notch portion, indicating a certain crystal orientation, is formed on the peripheral surface of the single-crystal silicon ingot that has undergone peripheral grinding. For example, a notch portion that, for instance, <110> -direction, formed in a silicon wafer where the crystal plane is the (100) plane. This notch portion is formed, for example, as a groove with an arc shape or an approximate V-shape by moving a grinding stone in the axial direction of the ingot, with the grinding stone in contact with the periphery of the ingot.

[0004] Subsequently, the notched single-crystal silicon ingot is cut into blocks, a resulting single-crystal silicon block is cut using, for example, a wire saw device, and a resulting silicon wafer is subjected to chamfering, primary planarization (lapping), polishing, etc.

[0005] Chamfering adapts the shape of a peripheral end part of the silicon wafer to a predefined shape using a chamfering device. This chamfering is also performed on the notched part.

[0006] In primary planarization, the front surface of the silicon wafer (on which a device is manufactured) and its rear surface are subjected to coarse grinding using a lapping device, a double-disc grinding device, etc., thereby increasing the parallelism of the front and rear surfaces of the wafer.

[0007] Polishing involves polishing the front and back surfaces of the silicon wafer to increase its flatness. Polishing broadly falls into two processes: double-sided polishing, which polishes both the front and back surfaces of a silicon wafer simultaneously, and single-sided polishing, which polishes only the front surface.

[0008] In double-sided polishing, the front and back surfaces of a silicon wafer, loaded into a holding well of a substrate, are simultaneously polished to a desired thickness at a relatively high polishing rate using a relatively hard polishing cloth, such as one made of polyurethane. In contrast, single-sided polishing polishes the front surface of a silicon wafer using a relatively soft polishing cloth, such as suede, and fine abrasive grains, thereby reducing microsurface roughness on the silicon wafer surface, such as nanotopography or haze. The single-sided polishing, performed at the end of the process, is called fine polishing.

[0009] The polishing process described above typically employs chemical-mechanical polishing (CMP), in which a slurry, obtained by adding abrasive particles (e.g., silicon oxide) to an alkaline aqueous solution, is used as a polishing agent. The silicon wafer and the polishing cloth are rotated relative to each other. The CMP process combines the mechanical polishing action of the abrasive particles with the chemical polishing action of the alkaline aqueous solution. This combined effect results in a high-gloss polish of the silicon wafer surface, achieving a high degree of flatness.

[0010] Furthermore, during the polishing process described above, it is necessary to prevent the emission of particles not only from the front and back surfaces of the silicon wafer, but also from the beveled portion. Accordingly, polishing is also performed on the beveled portion at the periphery of the wafer to achieve a high-gloss finish, and polishing is carried out in the same manner on the beveled portion of the notched section.

[0011] If polishing of the beveled portion of the wafer periphery is performed before double-sided polishing, the inner circumferential surface of the wafer holding aperture of the substrate and the highly polished beveled surface will be in contact during double-sided polishing, causing scratches and thus damaging the beveled surface. To address this, the practice of polishing a beveled surface after double-sided polishing has been reported (see, for example, JP 2002 - 299 290 A (PTL 1)).

[0012] As silicon wafers become increasingly miniaturized and integrated, it has become essential in recent years for them to have a very flat surface. Differential interference contrast (DIC) microscopy has become widely used to evaluate the flatness of such silicon wafer surfaces. DIC microscopy is a technique that allows the determination of the number of step-forming microdefects on a wafer surface. These microdefects have a raised or depressed shape with a height (or depth) exceeding a predetermined threshold (e.g., 2 nm). It is worth noting that step-forming microdefects are typically defects with a width of 30 µm to 200 µm and a height of approximately 2 nm to 90 nm, which are rarely detected using other detection methods.

[0013] Fig. Figure 1 is a diagram illustrating the principle of detecting step-forming microdefects using DIC microscopy. As shown in this diagram, a laser L (for example, a He-Ne laser) is split by a beam splitter B, and the split laser beam illuminates the surface of a silicon wafer W. A photodiode P receives reflected light from the surface of the silicon wafer W via a mirror M. If the surface of the silicon wafer W exhibits a step-forming microdefect D with a raised or depressed shape, a phase contrast typical of step-forming microdefects will be found. The height information of the defect can be calculated from the difference in the optical path of the reflected light.In this patent specification, a step-forming microdefect with a raised or indented shape with a height of 2 nm or more, which is detected by DIC microscopy, is hereinafter simply referred to as a "step-forming microdefect".

[0014] If the number of step-forming microdefects is within a required range, the quality of the silicon wafer surface can be determined to be good. Conversely, silicon wafers that do not meet the required range are classified as unsuitable items and therefore cannot be shipped as products.

[0015] JP 2005 - 277 050 A discloses a method for polishing a silicon wafer with a peripheral part polishing step in which a front surface of the silicon wafer is wetted with water.

[0016] JP 2002 - 299 290 A discloses a method for double-sided polishing of a silicon wafer with a notched part polishing step in which a chamfered part of the notched part is polished at the same time or before a double-sided polishing step, a subsequent polishing step of a chamfered part of a periphery of the wafer other than the chamfered part of the notched part, followed by high-gloss polishing.

[0017] The JP 2010 – 40 950 A reveals the formation of notches on a single-crystal ingot. List of citations, patent literature

[0018] PTL 1: JP 2002 - 299 290 A Brief description (Technical problem)

[0019] However, if the beveled portion is subjected to polishing after double-sided polishing, followed by high-gloss polishing on a silicon wafer surface, it is found that step-forming micro-defects formed on the high-gloss polished silicon wafer surface increase.

[0020] It could therefore be helpful to provide a method for polishing a silicon wafer and a method for producing a silicon wafer that can reduce the formation of step-shaped microdefects on a silicon wafer. (Solution to the problem)

[0021] Regarding the solution to the above problem, we investigated the entire wafer production process to examine the cause of the formation of step-forming microdefects. As a result, we found that when a chamfered portion of a notched section formed on the periphery of a silicon wafer is polished after a slurry has been sprayed onto the wafer's front surface, the slurry spray dries, causing abrasive particles (for example, silicon dioxide) contained in the spray to adhere to the surface. Consequently, when high-gloss polishing is performed in the presence of this deposit, step-forming microdefects are created.

[0022] In light of this, we carefully investigated ways to prevent abrasive particles contained in the slurry, which splash onto the silicon wafer, from adhering to the wafer's front surface when polishing is performed on the beveled portion of the notched section. The study above found that performing polishing on the beveled portion of the notched section while the wafer's front surface is wet with water is significantly effective. This discovery led to this revelation.

[0023] In particular, we propose the following features. (1) A method for polishing a silicon wafer comprising: a double-sided polishing step of performing polishing on a front surface and a rear surface of a silicon wafer; a notched part polishing step of performing a polishing on a beveled part of a notched part of the silicon wafer after the double-sided polishing step; a chamfered peripheral part polishing step of performing a polishing on the chamfered part on a periphery of the silicon wafer other than the chamfered part of the notched part after the notched part polishing step; and a high-gloss polishing step of performing high-gloss polishing on the front surface of the silicon wafer after the beveled peripheral part polishing step, the notch part polishing step is carried out in a state where the front surface is wet with water. (2) The method for polishing a silicon wafer according to (1) above, wherein the water-wetted condition is achieved by subjecting the front surface to a hydrophilization process after the double-sided polishing step to obtain a hydrophilic surface and supplying water to the hydrophilic surface. (3) The method for polishing a silicon wafer according to (2) above, wherein the hydrophilization process is a chemical cleaning. (4) The method for polishing a silicon wafer according to (2) or (3) above, wherein the supply of water is carried out at a flow rate of 1 l / min or more and 10 l / min or less. (5) The method for polishing a silicon wafer according to (1) upwards, wherein the water-wetted condition is achieved by continuously supplying water to the front surface after the double-sided polishing step. (6) The method for polishing a silicon wafer according to (1) to (5) above, wherein the chemical cleaning is not carried out between the chamfered peripheral part polishing step and the high-gloss polishing step. (7) A method for producing a silicon wafer comprising the steps in the following order: forming a notched portion on a periphery of a single-crystal silicon ingot formed by the Czochralski process; cutting the ingot to obtain a silicon wafer; and subjecting the cut silicon wafer to the method for polishing a silicon wafer according to one of (1) to (6) above. (Beneficial effect)

[0024] According to this disclosure, polishing on a chamfered portion of a notched part of a silicon wafer is carried out in a condition in which the front surface of the silicon wafer is wetted with water, thereby preventing abrasive grains contained in a splash of slurry from adhering to the surface and reducing the formation of step-forming micro-defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The following applies to the accompanying drawings: Fig. Figure 1 is a diagram illustrating the principle of measuring step-forming microdefects using differential interference contrast microscopy; Fig. 2A to 2D are diagrams illustrating a typical polishing process performed on a chamfered part on the periphery of a silicon wafer; Fig. 3A and Fig. 3B are diagrams illustrating the principle of preventing slurry sprayed onto the front surface of a silicon wafer from adhering to the surface according to this embodiment; and Fig. Figure 4 is a diagram illustrating the number of step-forming microdefects in the conventional example and the example. Detailed description (method for polishing a silicon wafer)

[0026] Embodiments of this disclosure are described below with reference to the drawings. A method for polishing a silicon wafer according to this disclosure comprises: a double-sided polishing step of performing polishing on a front surface and a rear surface of a silicon wafer; a notched part polishing step of performing polishing on a chamfered portion of a notched portion of the silicon wafer after the double-sided polishing step; a chamfered peripheral part polishing step of performing polishing on the chamfered portion on the periphery of the silicon wafer (chamfered peripheral part) other than the chamfered portion of the notched part after the notched part polishing step; and a high-gloss polishing step of performing high-gloss polishing on the front surface of the silicon wafer after the chamfered peripheral part polishing step.Here, the notch polishing step is performed in a state where the front surface is wet with water.

[0027] As described above, the silicon wafer with the beveled part is subjected to double-sided polishing, polishing of the beveled part and high-gloss polishing in that order. Fig. 2A to 2D are diagrams illustrating a polishing process performed on a chamfered portion at the periphery of a silicon wafer. As illustrated in the diagrams, polishing the chamfered portion involves the following four steps.

[0028] First, the notched part polishing step is performed by polishing the chamfered part of the notched part. In particular, as shown in Fig. Figure 2A illustrates a small-diameter polishing pad 11. A slurry S is then delivered by a slurry supply 12 to a beveled portion of the notched part N of a silicon wafer W, and the notched part N is pressed against the polishing pad 11 while the angle of the silicon wafer W is changed. Consequently, the beveled portion of the notched part N is polished to a high gloss.

[0029] Next, the beveled peripheral polishing step is performed, in which the beveled portion on the periphery of the wafer, except for the beveled portion of the notched portion N, is subjected to polishing. In particular, as shown in Fig. Figure 2B illustrates a table 21 on which the silicon wafer W is placed and rotated. Polishing pads 23 are then pressed against the beveled peripheral portion of the silicon wafer W, while the slurry S is supplied by a slurry feeder 22 to a central portion of the silicon wafer W. Accordingly, the beveled portion on the periphery of the wafer, except for the beveled portion of the notched portion N, is polished to a high gloss.

[0030] Subsequently, a cleaning step is performed in which the silicon wafer W, which has undergone polishing of the beveled portion as described above, is subjected to a wafer cleaning step. In particular, as described in Fig. Figure 2C illustrates a (not shown) table 21 on which the silicon wafer W is placed and rotated. Subsequently, while air and pure water are sprayed onto the periphery of the silicon wafer W from a dual-fluid nozzle 31, which is positioned outside the wafer in the wafer plane direction, a brush 32 is pressed against the periphery of the silicon wafer W as it is rotated, with pure water being supplied to the front surface of the silicon wafer W by a water supply 33. Accordingly, the front surface and the entire periphery of the silicon wafer W are cleaned.

[0031] Finally, a drying step is performed on the cleaned silicon wafer W. As in Fig. To illustrate this in 2D, this step can be carried out, for example, by centrifugal drying. A table (not shown) on which the silicon wafer W is placed is rotated at high speed to dry the surface of the silicon wafer W by blowing away any water deposited on the surface, and the blown-away water is collected by an absorbent 41.

[0032] In the process of investigating the cause of step-forming microdefects, we discovered that when polishing the beveled part of the notched portion N, which is located in Fig. As shown in Figure 3A, abrasive grains contained in splash H adhere to the surface of the silicon wafer W. During polishing of the chamfered portion of the notched part N, the silicon wafer W is not rotated. Furthermore, the slurry S is delivered only locally to the notched part N. Consequently, a portion of the front surface, except for a portion surrounding the notched part N, remains dry during polishing of the chamfered portion of the notched part. If the slurry S is injected in such a way as to be deposited on the front surface of this dry silicon wafer W, the splash H of the deposited slurry S dries, and abrasive grains contained in the splash H may adhere to the surface.

[0033] If the polishing on the beveled peripheral part except for the beveled part of the notched part N, which is in Fig. As illustrated in Figure 2B, the slurry S is delivered to a central part of the rotating silicon wafer W; accordingly, the slurry S is delivered to the entire front surface, and the front surface of the silicon wafer W is wet. Therefore, the abrasive grains contained in the slurry S would not adhere to any part of the surface during the polishing of the beveled portion.

[0034] We have found that when a silicon wafer W, in which abrasive grains adhere to the front surface as described above, is subjected to the next step, which is the high-gloss polishing step, the rate of polishing on one part of the surface to which the abrasive grains adhere is lower than on the other part, resulting in the formation of a step-forming microdefect.

[0035] We have therefore found that when polishing the beveled part of the notched part N, the splash H of the slurry S, which is sprayed onto the front surface of the silicon wafer W, dries and the abrasive grains contained in the splash H adhere to a part of the surface, contributing to the formation of step-forming micro-defects.

[0036] To address this, we carefully investigated ways to prevent the abrasive grains contained in the slurry H of the slurry S from adhering to the front surface when polishing is performed on the chamfered portion of the notched part N. Consequently, we considered performing the polishing in a condition where the front surface of the silicon wafer is wetted with water.

[0037] Here, “state in which the front surface of the silicon wafer is wetted with water” refers to a state in which a water layer F is formed on the front surface of the silicon wafer W, as in Fig. This is illustrated in Figure 3B. This water layer F can prevent the splash H from drying on the front surface of the silicon wafer W, even if the slurry S is splashed onto the front surface of the wafer, which can inhibit the adhesion of the abrasive grains contained in the splash H to the surface.

[0038] In a specific example, the water layer F described above can be formed by subjecting the front surface of the silicon wafer W to a hydrophilization process to obtain a hydrophilic surface, and then supplying water to this hydrophilic surface. Incidentally, the front surface of the silicon wafer W is hydrophobic after undergoing double-sided polishing, which is a preceding step. Such a hydrophobic front surface repels water, even when water is supplied to it; consequently, the water layer F is hardly formed. Therefore, the front surface, which is hydrophobic after double-sided polishing, is first subjected to a hydrophilization process to obtain a hydrophilic surface.

[0039] The hydrophilization process described above can be carried out, for example, by chemical cleaning. Specifically, the front surface of the silicon wafer W, for example SC-1, is exposed to ozonated water to oxidize it, forming a silicon oxide film. This silicon oxide film is hydrophilic; therefore, the front surface, which is hydrophobic immediately after double-sided polishing, can be made hydrophilic.

[0040] Water is delivered to the resulting hydrophilic surface, thus forming a water layer F on the front surface of the silicon wafer W. The above water delivery can be accomplished using a water supply device, such as a shower. Furthermore, the water to be delivered is either pure water or ultrapure water, which has a higher degree of purity than pure water.

[0041] Furthermore, the above water supply is preferably carried out at a flow rate of 1 l / min or more and 10 l / min or less. If the flow rate is set to 1 l / min or more, a good water layer F can be formed across the entire front surface of the silicon wafer W. Moreover, a higher water flow rate is effective for the formation of the water layer F; however, the water supply flow rate need not be excessively high, and with regard to production costs, the flow rate is preferably 10 l / min or less.

[0042] Alternatively, the water layer F can be formed by immersing the silicon wafer W, which has undergone the hydrophilization process, in water.

[0043] This disclosure can prevent deposits from adhering to the front surface of the silicon wafer when polishing is performed on the beveled portion of the notched part N. This eliminates the need to remove deposits adhering to the front surface of the silicon wafer by performing a chemical cleaning between the beveled peripheral polishing step and the start of the high-gloss polishing step, steps that were conventionally performed. Consequently, the cost of agents used for chemical cleaning can be reduced.

[0044] It is noted that drying and adhesion of the slurry S sprayed onto the front surface can also be inhibited by continuously supplying water to the front surface of the silicon wafer W during the polishing of the chamfered portion of the notch, as described above, instead of performing the water layer F formation described above. Accordingly, the condition obtained through this feature is also included in the "condition in which the front surface of the silicon wafer is wetted with water" specified here. In this case, the front surface of the silicon wafer S can remain hydrophobic or can be a hydrophilic surface obtained by performing the hydrophilization process.

[0045] The above supply of water is not necessarily carried out continuously and can be carried out periodically, as long as the splash H of the slurry S, which is sprayed onto and adheres to the front surface of the silicon wafer W, does not dry.

[0046] Accordingly, the formation of step-forming microdefects on the front surface of the silicon wafer can be reduced. (Method for producing a silicon wafer)

[0047] A method for producing a silicon wafer is now described. In a method for producing a silicon wafer according to this disclosure, a silicon ingot is grown by the Czochralski process, the grown ingot is cut to obtain a silicon wafer, and a chamfered portion of a notched part of the resulting silicon wafer is subjected to polishing under predetermined conditions by the silicon wafer polishing method disclosed above. Accordingly, this method is not limited in any way except that the double-sided polishing step, the notched part polishing step, the chamfered peripheral part polishing step, and the high-gloss polishing step are performed in that order, and that the notched part polishing step is performed in a condition in which the front surface of the silicon wafer is wetted with water.An example of the disclosed method for producing a silicon wafer is described below.

[0048] First, polycrystalline silicon, loaded into a quartz crucible, is melted at approximately 1400 °C. Then, a seed crystal is immersed in the molten silicon and subsequently pulled upwards while being rotated, producing a single-crystal silicon ingot in which the crystal plane is, for example, the (100) plane. The silicon ingot is then doped with, for example, boron or phosphorus to achieve the desired resistivity. Furthermore, the oxygen concentration of the silicon ingot can be controlled by the magnetic Czochralski process (MCZ process), in which a magnetic field is applied during ingot formation.

[0049] Next, grinding is performed on the periphery of the resulting single-crystal silicon ingot to make its diameter uniform. Then, a grinding stone of a suitable shape is pressed against the peripheral surface of the ingot, and the grinding stone is repeatedly moved in the axial direction, thereby forming a notched portion that, for example, <110> -direction. The ingot with the notched section is then machined by cutting it into blocks.

[0050] The single-crystal silicon ingot in which the notched part is formed is then cut into silicon wafers using a wire saw or an ID blade slicer.

[0051] Next, a peripheral end of the silicon wafer undergoes a primary beveling procedure (coarse beveling). This can be done by: grinding using a fine grinding wheel in which a groove with a shape corresponding to the bevel shape is previously formed by dressing; contouring; etc. For example, a cylindrical grinding wheel, such as a coarse-grit diamond wheel, is pressed against the periphery of the silicon wafer while it is rotated, thus performing the primary beveling procedure. In this way, the periphery of the silicon wafer is brought into a predetermined round shape.

[0052] The main surfaces of the silicon wafer then undergo a primary planarization procedure. In this procedure, the silicon wafer is placed between a pair of parallel lapping plates. While a lapping fluid, such as a mixture of abrasive particles like aluminum oxide, a dispersion medium, and water, is supplied between the plates, the plates are rotated and slid under a predetermined pressure. This mechanically lappes the front and back surfaces of the silicon wafer, increasing the parallelism of the wafer surfaces. For the primary planarization procedure, the front and back surfaces of the wafer can be ground using a dual-disc grinding machine, or they can be subjected to both lapping and dual-disc grinding.

[0053] Next, the notched portion of the silicon wafer, which has undergone the primary planarization procedure, is chamfered. Specifically, for example, a metal-bonded or resin-bonded grinding wheel is pressed against the notched portion of the silicon wafer while it is rotated, and the grinding wheel is moved along the contour of the notched portion, thereby performing the chamfering on the notched portion of the silicon wafer. The chamfered notched portion can further be subjected to known strip chamfering.

[0054] Subsequently, the periphery of the silicon wafer, which has undergone the primary planarization procedure, is subjected to a secondary beveling procedure. Specifically, for example, a metal-bonded or resin-bonded grinding wheel with a finer grit than the grinding wheel used in the primary beveling procedure is pressed against the periphery of the silicon wafer while it is rotated, thereby performing the secondary beveling procedure (final beveling) on ​​the silicon wafer. The beveled periphery can further be subjected to known strip beveling.

[0055] Next, the silicon wafer, which has undergone the secondary beveling procedure, is etched. Specifically, any warping of the wafer caused by the procedures in the previous steps is eliminated by: acid etching using an aqueous solution containing hydrofluoric acid and / or nitric acid and / or acetic acid and / or phosphoric acid; alkaline etching using a potassium hydroxide solution, a sodium hydroxide solution, etc.; or a combination of the above acid etching and alkaline etching.

[0056] It is noted that the silicon wafer, after etching, can undergo surface grinding to further improve its flatness. This surface grinding can utilize a single-disc or double-sided surface grinding machine.

[0057] The front and back surfaces of the silicon wafer are then subjected to double-sided polishing using a double-sided polishing device. Double-sided polishing is performed as follows: the silicon wafer is inserted into an opening in a carrier plate; the carrier plate is then held between an upper and a lower plate, each with a polishing cloth attached; a slurry, containing, for example, abrasive grains of colloidal silicon dioxide or similar materials in an alkaline solution, is poured into the space between the upper and lower plates and the wafer; and the upper and lower plates and the carrier plate are rotated in opposite directions. This process reduces surface irregularities on the wafer, resulting in a wafer with high flatness.

[0058] The chamfered portion on the periphery of the silicon wafer is then polished. First, the chamfered portion of the notched part is polished. This polishing is performed by pressing a urethane polishing wheel, shaped like a disc with one end having a conical shape, against the chamfered portion of the notched part while the polishing wheel is rotated. It is noted that polishing the chamfered portion of the notched part can also be achieved by pressing a rotating polishing belt against the notched part.

[0059] In this disclosure, it is important to perform the polishing on the beveled portion of the notched part while the front surface of the silicon wafer is wetted with water. Accordingly, polishing the beveled portion of the notched part prevents the splash H of slurry S, which is sprayed onto the front surface of the silicon wafer, from drying and prevents the abrasive particles contained in the splash H from adhering to the surface. Consequently, the formation of step-forming micro-defects in the silicon wafer during high-gloss polishing can be reduced.

[0060] Polishing is performed in a similar manner on the beveled portion of the periphery, excluding the beveled portion of the notched part. For example, the silicon wafer is rotated, with the rear surface of the wafer held by a suction step, and a polishing wheel, made of urethane for example, is pressed against the peripheral end of the rotating wafer, thereby highly polishing the beveled portion on the periphery of the silicon wafer.

[0061] The front surface of the silicon wafer, which has undergone polishing on the beveled portion, is then subjected to high-gloss polishing using a single-sided polishing device. This high-gloss polishing can be performed using a polishing cloth made of a suede material and, for example, an alkaline polishing compound containing colloidal silicon dioxide.

[0062] Next, the silicon wafer, which has undergone high-gloss polishing, is transferred to a cleaning step in which particles, organic matter, metal, etc. are removed from the wafer surface using, for example, an SC-1 cleaning solution, which is a mixture of aqueous ammonia, a hydrogen peroxide solution and water, or an SC-2 cleaning solution, which is a mixture of hydrochloric acid, a hydrogen peroxide solution and water.

[0063] Finally, the cleaned silicon wafer is transferred for inspection, where the wafer's flatness, the number of LPDs on the wafer surface, any damage, surface contamination, etc., are examined. Only wafers that pass these inspections and meet specified product quality requirements are shipped as finished products.

[0064] It is noted that the wafer obtained by the above steps may optionally be subjected to annealing or epitaxial film growth, in which case an annealed wafer, an epitaxial wafer or a silicon-on-insulator (SOI) wafer may be obtained.

[0065] Accordingly, a silicon wafer with reduced step-forming microdefects can be produced. EXAMPLES (Example)

[0066] A silicon wafer was produced by the disclosed method for producing a silicon wafer. First, grinding was performed on the periphery of a single-crystal silicon ingot grown by the CZ process to adjust the diameter, and then a notched portion was created that <110> -direction, formed on the periphery of the ingot. Subsequently, after the single-crystal silicon ingot was cut into blocks, one of the blocks with a notched portion was cut to obtain a silicon wafer with a diameter of 300 mm.

[0067] Next, the periphery of the silicon wafer underwent a primary beveling procedure using a beveling machine. Specifically, the periphery of a silicon wafer was pressed against a coarse-grit metal-bonded grinding wheel while the wafer was rotated, thereby performing a primary beveling procedure on a peripheral end portion of the silicon wafer.

[0068] Subsequently, the silicon wafer, which had undergone the primary beveling procedure, was transferred to a lapping device and the front and rear surfaces of the silicon wafer were subjected to a primary planarization procedure.

[0069] Subsequently, the notched portion of the silicon wafer, which had undergone the primary planarization procedure, was chamfered. Specifically, a metal-bonded grinding wheel was pressed against the notched portion while it was rotated, and the grinding wheel was moved along the contour of the notched portion, chamfering it to form a beveled section. Next, the wafer periphery, excluding the notched portion, was subjected to a secondary chamfering procedure to form a chamfered section using a grinding wheel made from a resin-bonded fine-grinding grinding wheel with a finer grit than the grinding wheel used in the primary chamfering procedure.

[0070] Subsequently, the front and back surfaces of the silicon wafer, in which the beveled portion was formed, were subjected to double-sided polishing. This double-sided polishing was performed while an alkaline polishing slurry containing abrasive particles was supplied from the side of the top plate. The silicon wafer, loaded into a wafer-holding well of a carrier plate, was held between an upper and lower plate, each with a polyurethane polishing cloth bonded to it. The upper and lower plates were rotated in opposite directions under predetermined pressure. The carrier plate was rotated by a gear mechanism in the same direction as the upper plate, and the front and back surfaces of the silicon wafer loaded into the carrier plate were polished to achieve a predetermined wafer thickness.

[0071] Subsequently, the beveled portion of the silicon wafer, which had undergone double-sided polishing, was polished using the beveled portion polishing unit, resulting in Fig. The process shown in Figures 2A to 2D involved the following steps: First, the chamfered portion of the notched section was polished. Prior to this polishing, the front surface of the silicon wafer underwent a hydrophilization process using a hydrogen peroxide solution to make it hydrophilic. Then, pure water was sprayed onto the hydrophilic surface at a flow rate of 1.8 L / min, creating a layer of water across the entire front surface. It should be noted that alternative hydrophilization agents include ozone and a usage agent.

[0072] After the water layer was formed, a urethane polishing wheel, shaped like a disc with one end conical, was pressed against the beveled portion of the notched section while rotating at 600 rpm. Simultaneously, an alkaline slurry containing colloidal silicon was supplied as a polishing agent at a flow rate of 1.5 l / min to the beveled portion of the notched section. Polishing was performed while the wafer was tilted at an angle between +55° and -55° to ensure the entire beveled portion was polished. Subsequently, the silicon wafer was rotated with its rear surface held by a suction stage, and a urethane polishing wheel was pressed against the beveled peripheral end of the rotating wafer. This resulted in high-gloss polishing of the beveled portion on the periphery of the silicon wafer, excluding the beveled portion of the notched section.

[0073] Next, the silicon wafer, which had undergone beveled polishing, was transferred to a single-sided polishing unit, and the main surfaces of the silicon wafer were subjected to high-gloss polishing. The single-sided polishing was performed using a polishing cloth made of suede material and, for example, an alkaline slurry containing colloidal silicon dioxide as a polishing agent.

[0074] The silicon wafer, which had undergone high-gloss polishing, was then subjected to final cleaning using a wafer cleaning device. A silicon wafer was thus obtained.

[0075] Another silicon wafer obtained when the above block was cut was also subjected to the same procedures described above to obtain another silicon wafer. (Conventional example)

[0076] Two silicon wafers were prepared in a manner similar to the example. However, it should be noted that the water layer was not applied to the front surface of the silicon wafer prior to polishing on the chamfered portion of the notched section. All other conditions were the same as those in the example. < Evaluation of DIC defects >

[0077] The surface of each silicon wafer fabricated according to the example and the conventional example was measured in DIC mode (measurement mode based on DIC microscopy) using a wafer surface inspection device (Surfscan SP2, manufactured by KLA-Tencor Corporation). In the measurement, the height threshold for step-forming microdefects with a raised or depressed shape was set to 3 nm, and the number of step-forming microdefects with a height exceeding this threshold was determined. The results are presented in Fig. 4 given.

[0078] As in Fig.As illustrated in Figure 4, the number of step-forming microdefects in the conventional example was 9 and 16, whereas the number of step-forming microdefects in the example was 0 and 2. Accordingly, it can be seen that the formation of step-forming microdefects can be reduced by performing polishing on the chamfered portion of the notch in a condition where the front surface of the silicon wafer is wetted with water. INDUSTRIAL APPLICABILITY

[0079] According to this disclosure, polishing on a chamfered portion of a notched part of a silicon wafer is performed in a condition where the front surface of the silicon wafer is wetted with water, thereby preventing abrasive particles contained in a splash of slurry from adhering to the surface and reducing the formation of step-forming microdefects. Therefore, the disclosed methods are beneficial in the semiconductor manufacturing industry. REFERENCE MARK LIST 11, 23 Polishing pad 12, 22 Slurry supplies 13, 33 Water supply equipment 21 Table 31 Dual-fluid nozzle 32 brush B Beam splitter D Step-forming microdefect F Water layer H Spritzer L Laser M mirror P photodiode S Slurry W silicon wafer

Claims

A method for polishing a silicon wafer (W) comprising: a double-sided polishing step of performing polishing on a front surface and a rear surface of a silicon wafer (W); a notched part polishing step of performing polishing on a beveled part of a notched part (N) of the silicon wafer while a slurry (S) is supplied to the beveled part of the notched part (N) of the silicon wafer (W) after the double-sided polishing step; a beveled periphery part polishing step of performing polishing on the beveled part on a periphery of the silicon wafer (W) other than the beveled part of the notched part (N) after the notched part polishing step;and a high-gloss polishing step of performing high-gloss polishing on the front surface of the silicon wafer (W) after the beveled peripheral part polishing step, wherein the beveled part polishing step is performed in a condition in which the front surface is wetted with water. Method for polishing a silicon wafer according to claim 1, wherein the water-wetted state is achieved by subjecting the front surface to a hydrophilization process after the double-sided polishing step to obtain a hydrophilic surface and supplying water to the hydrophilic surface. Method for polishing a silicon wafer according to claim 2, wherein the hydrophilization process is a chemical cleaning process. Method for polishing a silicon wafer according to claim 2 or 3, wherein the supply of water is carried out at a flow rate of 1 l / min or more and 10 l / min or less. Method for polishing a silicon wafer according to claim 1, wherein the water-wetted state is achieved by continuously supplying water to the front surface after the double-sided polishing step. Method for polishing a silicon wafer according to any one of claims 1 to 5, wherein no chemical cleaning is performed between the beveled peripheral part polishing step and the high-gloss polishing step. A method for producing a silicon wafer (W) comprising the steps in the following order: forming a notched portion (N) on a periphery of a single-crystal silicon ingot formed by the Czochralski process; cutting the ingot to obtain a silicon wafer (W); and subjecting the cut silicon wafer (W) to the method for polishing a silicon wafer (W) according to any one of claims 1 to 6.

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