JP4103808B2 - Wafer grinding method and wafer - Google Patents

Description

  The present invention relates to a grinding method for surface grinding a wafer using a cup-type grinding wheel.

  In general, a semiconductor wafer is produced by growing a single crystal ingot by the Czochralski method or the like, and cutting the grown single crystal ingot using an inner peripheral cutting machine or a wire saw to form a plate-like wafer. After fabrication, chamfering process to prevent chipping of the outer periphery of the wafer, lapping process to eliminate wafer thickness variation, etching process to remove processing distortion and contaminants, mirror the main surface of the wafer It is manufactured by sequentially performing a polishing process and the like.

  In recent years, miniaturization and high integration of semiconductor devices have been promoted, and the diameter of semiconductor wafers has been increased for reasons such as improving the performance of semiconductor devices and reducing costs. Currently, mass production of 300 mm diameter wafers has become mainstream. It is coming. As a result, demands for flatness of wafers have become stricter, and it has been demanded to manufacture high-quality wafers with even higher flatness. Therefore, recently, when manufacturing a semiconductor wafer, the above-mentioned lapping process is replaced with a grinding process to reduce the processing distortion of the wafer surface, and the allowance for etching and polishing in the next process is reduced as much as possible. Accordingly, a method for improving the flatness of the wafer has been proposed (see Patent Document 1).

  Usually, when a semiconductor wafer is ground, single-side grinding or double-side grinding is performed. Even in double-sided grinding, there are a method of grinding one surface and inverting and grinding the other surface, and a grinding method called double-sided simultaneous grinding or double-sided grinding in which both sides are ground simultaneously.

  In addition, when performing wafer grinding in this way, there are several methods for wafer grinding, and among them, creep feed grinding in which grinding is performed by passing the wafer between two pairs of cylindrical grinding wheels. In-feed grinding method, in which the cup-type grinding wheel and the wafer rotate together so that the grindstone passes through the center of the wafer using a cup-type grinding wheel, is the mainstream, especially the in-feed type This grinding method is often used for grinding semiconductor wafers because of the advantage that high flatness is easily obtained compared to the creep feed type.

  Such in-feed grinding can be performed using a grinding device 21 as shown in FIG. 8, for example. The grinding apparatus 21 includes a chuck table 23 that holds a wafer by vacuum suction and a cup-type grinding wheel 26 having a grinding head 25 to which a grinding wheel 24 is fixed. For example, a semiconductor wafer 22 that performs grinding. The semiconductor wafer can be ground by pressing the grinding wheel 24 against the wafer 22 while rotating the grinding head 25 with the rotation shaft 27 while adsorbing the chuck to the chuck table 23.

  At this time, on the surface of the wafer that has been ground, a grinding streak having a constant period is formed as a trajectory of the grindstone, or a concave portion that is depressed at the center of the wafer is formed. Grinding marks on the wafer surface can be removed in a subsequent polishing step, but if the amount of wafer polishing increases in this polishing step, the flatness of the wafer deteriorates and the productivity decreases. Problems arise. For this reason, in order to reduce the polishing amount in the polishing process, there has been proposed a method in which grinding is performed such that the period of grinding marks formed on the wafer is narrowed when the wafer is ground (see Patent Document 2). On the other hand, in order to prevent the concave shape formed at the center of the wafer, the grinding wheel is cut from the center of the wafer to advance from the center of the wafer toward the outer periphery, and is separated from the outer periphery of the wafer to grind the wafer. The method of doing is searched.

  However, when the semiconductor wafer is ground by cutting the cup-type grinding wheel from the wafer center as described above and separating the wafer from the outer periphery of the wafer, the diameter is 2 to 10 mm at the center of the ground wafer surface. There is a problem that protrusions having a protruding shape with a height of about 0.3 to 0.5 μm are formed, and improvement in wafer flatness is hindered.

  Therefore, in Patent Document 3, for example, when a semiconductor wafer is surface ground using a cup-type grinding wheel in order to remove the protrusion formed at the wafer center as described above, the grinding wheel is removed from the center of the semiconductor wafer. Disclosed is a method for manufacturing a semiconductor wafer in which a grinding wheel is cut at the outer peripheral edge of the wafer so that the semiconductor wafer is separated from the wafer, and the ground semiconductor wafer is polished by CMP (Chemical Mechanical Polishing). .

  On the other hand, when both surfaces of a wafer are ground in order using, for example, a cup-type grinding wheel as described above, first, when one surface of the wafer is ground, a protrusion is formed at the center of the wafer. When the other surface is ground by vacuum suction of the surface on which the surface is formed, the protrusions are transferred to the ground surface and grinding is performed in the same manner as described above. Therefore, the ground wafer is, for example, FIG. As shown in FIG. 4, a protrusion is formed on one surface, and the other surface is relatively flat.

  Then, when double-side polishing was performed on the wafer having the protrusions formed on one side, as shown in FIG. 2B, the wafer was formed at the center of the wafer on one side. The protrusion cannot be completely removed and remains, and the other surface is transferred with the shape of the back surface and polished to form a dent. Further, as shown in FIG. 2C, even if the wafer surface side on which the device is manufactured is polished and finished by CMP or the like, it is hardly improved. Then, as shown in FIG. When the wafer is attracted to the chuck table 30, the shape of the back surface of the wafer is transferred to the front surface, so that there is a problem that the flatness of the wafer is lowered and the yield is lowered.

JP-A-10-180599 JP 2000-158304 A International Publication No. WO 01/022484 Pamphlet

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to suppress the formation of a protruding shape at the center of the wafer when grinding on both surfaces of the wafer. It is an object of the present invention to provide a method for grinding a wafer which can be processed to a high flatness with a uniform thickness.

  In order to achieve the above object, according to the present invention, in a method of grinding both surfaces of a wafer one side at a time using a cup-type grinding wheel, first, when grinding one surface of the wafer, the grinding wheel is Grinding is performed by cutting from the outer periphery of the wafer, proceeding toward the center from the outer periphery of the wafer, and detaching from the center of the wafer. Then, when grinding the other surface of the wafer, the grinding wheel is removed from the wafer. There is provided a wafer grinding method characterized in that grinding is performed by cutting from the center, proceeding from the wafer center toward the outer periphery, and detaching at the outer periphery of the wafer (claim 1).

Thus, when grinding both surfaces of the wafer using a cup-type grinding wheel, grinding of one surface of the wafer is performed by cutting the grinding wheel from the outer periphery of the wafer and progressing from the outer periphery of the wafer toward the center. Performing by separating at the wafer center, and then grinding the other surface of the wafer by cutting the grinding wheel from the wafer center, proceeding from the wafer center toward the outer periphery, and separating at the outer periphery of the wafer Can suppress the formation of protrusions protruding in the center of the wafer, and both surfaces of the wafer can be processed to be flat. A high-quality wafer having a high degree can be stably obtained.
In the present invention, the convex shape and the concave shape are a shape depending on the wafer thickness, that is, a shape of a portion where the wafer thickness expressed with reference to the back surface (or front surface) of the wafer is increased and a decrease. The shape of the portion, and the protrusion and the dent refer to the surface shape of the portion protruding from the wafer surface and the surface shape of the recessed portion.

At this time, it is preferable to rotate the wafer at a rotational speed of 20 rpm or more when grinding is performed by cutting the grinding wheel from the outer peripheral edge of the wafer and detaching it from the center of the wafer (claim 2).
In this way, when the grinding wheel is cut from the outer periphery of the wafer and separated from the wafer center to perform grinding, the grinding wheel is cut from the outer periphery of the wafer by rotating the wafer at a rotation speed of 20 rpm or more. However, since the taper shape of the grindstone is worn down during grinding of the wafer, the grinding residue generated when the grindstone is detached at the center of the wafer can be reduced, and the flatness of the wafer can be further improved. it can.

In addition, it is preferable to rotate the wafer at a rotation speed of 10 rpm or less when grinding is performed by cutting the grinding wheel from the center of the wafer and detaching it from the outer periphery of the wafer.
Thus, when grinding is performed by cutting the grinding wheel from the center of the wafer and separating it from the outer peripheral edge of the wafer, by rotating the wafer at a rotational speed of 10 rpm or less, particularly 5 rpm or less, the grinding is performed on the wafer surface. The period of the grinding streak appearing as a trajectory of the grindstone can be reduced. Thus, if the period of the grinding streaks appearing on the wafer surface is small, for example, when polishing the wafer after that, it becomes possible to easily remove the grinding streaks on the wafer surface with a small polishing allowance. It is possible to prevent the flatness of the wafer from being deteriorated during polishing, and to improve productivity.

  In this case, the grinding wheel is cut from the outer peripheral edge of the wafer, and grinding is performed on the back surface of the wafer, and the grinding wheel is cut from the central part of the wafer and is released from the outer peripheral edge of the wafer. Is preferably applied to the surface of the wafer.

  In this way, grinding is performed on the back surface of the wafer so that the grinding wheel advances from the wafer outer periphery to the wafer center, and grinding is performed on the wafer surface so that the grinding wheel advances from the wafer center to the wafer outer periphery. It is possible to suppress the formation of convex shapes on the wafer, to increase the flatness of the wafer, and to reduce the period of grinding marks formed on the wafer surface. Therefore, for example, by subsequently performing mirror polishing on the wafer surface, grinding marks on the wafer surface can be easily removed with a small polishing allowance, so a high-quality mirror-polished wafer having high flatness can be produced with high productivity. It becomes possible to obtain stably.

In the present invention, it is preferable to use a resin-bonded grindstone using diamond abrasive grains as the cup-type grinding wheel.
Thus, as the cup-type grinding wheel used in the grinding method of the present invention, by using a resin-bonded grindstone using diamond abrasive grains, the resin-bonded grindstone has a slight elasticity, so that grinding is performed. Sometimes the grinding stone itself contracts slightly due to the pressure, so that good grinding can be performed stably.

At this time, in recent years, a wafer having a diameter of 200 mm is required to have a high flatness specification similar to that of 300 mm, and the diameter of the wafer to be ground can be 200 mm or more (Claim 6). The wafer to be processed can be a semiconductor wafer.
In the present invention, when grinding a wafer having a large diameter of 200 mm or more, further 300 mm or more, or particularly when grinding a semiconductor wafer, a very excellent flatness is obtained, and a large diameter of 200 mm or more is obtained. It is suitable for processing a silicon semiconductor wafer.

According to the present invention, a wafer ground by the wafer grinding method can be provided (Claim 8), and a mirror-polished wafer obtained by subjecting the ground wafer to a mirror-polishing process is provided. (Claim 9).
The wafer ground by the present invention has a very small convex shape formed at the center of the wafer, and can be a high-quality wafer in which both surfaces of the wafer are ground flat. Further, a mirror-polished wafer having a surface finished by subjecting the wafer thus ground to mirror-polishing by double-side polishing, CMP, or the like to a very high-quality mirror-polished wafer having extremely high flatness. be able to.

  As described above, according to the present invention, one surface of the wafer is ground by cutting the grinding wheel from the outer periphery of the wafer and separating it from the wafer center, and then the other surface of the wafer is Grinding is performed by cutting the grinding wheel from the center of the wafer and separating it from the outer periphery of the wafer to perform grinding on both sides of the wafer, so that the formation of protrusions at the center of the wafer is suppressed and both sides of the wafer are flattened. Can be processed. Therefore, a high-quality wafer having excellent flatness with a reduced convex shape at the center of the wafer can be stably obtained.

Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to these.
The inventors of the present invention have earnestly studied and studied a method for suppressing the formation of a protrusion having a shape protruding at the center of the wafer when grinding on both sides of the wafer. As a result, when a wafer is ground using a cup-type grinding wheel, the grinding amount decreases due to the upslip phenomenon caused by the elasticity of the grinding wheel at the position where the grinding wheel contacts the wafer and starts cutting. In the vicinity of the incision start position, the grinding surface slightly rises, and on the other hand, at the position where the incision by the grinding wheel is finished (that is, the position at which the grinding wheel comes off), the grinding amount increases due to a sharp decrease in grinding resistance. Therefore, it became clear that the ground surface was slightly recessed.

  Therefore, the inventors of the present invention grind the wafer to a high flatness by appropriately using the above-described phenomenon caused by the start and release of the grinding wheel when grinding using a cup-type grinding wheel. Therefore, further examination was repeated. As a result, when grinding one surface of the wafer, the grinding wheel is cut from the outer peripheral edge of the wafer, advanced from the outer periphery of the wafer toward the center, and separated from the central portion of the wafer, so that the protrusion at the central portion of the wafer is removed. By finding that it is possible to perform grinding while suppressing formation, and then grinding the other surface of the wafer, by grinding so that the direction of cutting the grinding wheel is opposite to the above, The present invention has been completed by finding that it is possible to perform grinding while suppressing the formation of protrusions or dents in the center of the wafer, and that both surfaces of the wafer can be ground flat.

  That is, the grinding method of the present invention is a method in which both sides of a wafer are ground one by one using a cup-type grinding wheel. First, when grinding one surface of the wafer, the grinding wheel is cut from the outer periphery of the wafer. The grinding wheel is ground from the wafer outer periphery, and then ground at the center of the wafer, and then separated from the center of the wafer. Then, when grinding the other surface of the wafer, the grinding wheel is cut from the center of the wafer. However, it is characterized in that the grinding is performed by proceeding from the wafer center toward the outer periphery and separating from the outer periphery of the wafer.

Hereinafter, the wafer grinding method of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.
The grinding apparatus used in the wafer grinding method of the present invention is not particularly limited as long as it can grind both surfaces of the wafer one side at a time using a cup-type grinding wheel. For example, a grinding apparatus as shown in FIG. Can be used. First, an example of a grinding apparatus that can be used when carrying out the grinding method of the present invention will be described with reference to FIG.

  The grinding apparatus 1 shown in FIG. 3 is configured as an apparatus that inverts and grinds both surfaces of a wafer such as a semiconductor wafer one by one, and holds and rotates the rotating cup-type grinding wheel 9 and one surface of the wafer W. The first chuck table 6 and the second chuck table 7 that rotate, the turntable 8 that supports and rotates the wafer, the wafer reversing means 10 that reverses the wafer W, and the wafer transfer robot that carries the wafer W into and out of the grinding apparatus. 11.

  As shown in the side view of FIG. 4A, the cup-type grinding wheel 9 is composed of a cup-shaped base 20, a grindstone portion 18 to which the grindstone is joined, and a grindstone rotating shaft 19 for rotating them. Thus, the main surface of the wafer can be ground by contacting the front surface (or back surface) of the wafer W while the grindstone rotates. Further, the semiconductor wafer W and the cup-type grinding wheel 9 are rotated at a predetermined rotational speed, and the grinding liquid is usually supplied from the center hole (not shown) of the grinding wheel rotating shaft or is poured over the inside of the grinding wheel. Yes.

  At this time, as a grindstone to be joined to the grindstone portion of the cup-type grinding grindstone 9, it is preferable to use a resin bond grindstone using diamond abrasive grains. Since such a resin-bonded grindstone has some elasticity, the grindstone itself slightly contracts due to the pressure during grinding, and therefore, good grinding can be stably performed on a semiconductor wafer.

  Further, in the grinding apparatus 1, the first chuck table 6 and the second chuck table 7 have a conical shape with a height of about 10 μm with a slight inclination centered at the center, as shown in FIG. have. Therefore, after vacuum-sucking the semiconductor wafer W onto the conical chuck table, the grindstone portion 18 of the cup-type grinding wheel 9 is rotated, for example, as shown in FIG. 4B while rotating the wafer W and the cup-type grinding wheel 9. As shown in the plan view, the entire surface of the semiconductor wafer W can be ground smoothly and effectively by bringing the wafer W into contact with the arc wire portion 17.

Next, a method for grinding the semiconductor wafer W using the grinding apparatus 1 as described above will be described.
First, the semiconductor wafer W to be ground is accommodated in the wafer cassette 14 and is carried into a predetermined position in the apparatus by the transfer robot 11. This is caught by the reversing means 10, and first attracted and held by the first chuck table 6 positioned at a predetermined position with the back surface of the wafer W facing up at the reversing position 12, and moved to the grinding position 13 by the turntable 8. . Here, by rotating the first chuck table 6 and rotating the cup-type grinding wheel 9, the entire back surface of the semiconductor wafer W can be ground by bringing the grindstone portion into contact with the back surface of the semiconductor wafer W.

  At this time, in the grinding method of the present invention, first, when grinding one surface (back surface) of the wafer, the grinding wheel is cut from the outer periphery of the wafer and is advanced from the outer periphery of the wafer toward the center. The wafer is ground by separating it with. For example, as shown in FIG. 4B, when the cup-type grinding wheel 9 and the back surface of the semiconductor wafer W are brought into contact with each other at the arc line portion 17 of the semiconductor wafer W, the cup-type grinding wheel 9 is rotated clockwise as viewed from above. The grindstone 9 of the cup-type grinding wheel 9 is cut from the outer periphery of the wafer, is advanced from the outer periphery of the wafer toward the center, and is separated from the center of the wafer for grinding the wafer. it can.

  In this way, by grinding the wafer by cutting the grinding wheel from the outer periphery of the wafer and separating it from the wafer center, the grinding amount of the wafer is reduced by reducing the grinding resistance at the wafer center from which the grinding wheel is detached. Can do a lot. As a result, it is possible to effectively suppress the formation of a protrusion protruding at the center of the back surface of the wafer when the back surface of the wafer is ground. For example, as shown in FIG. As shown in FIG. 2A, the convex shape formed at the center of the back surface of the wafer is extremely small compared to the conventional FIG. A wafer having a flat back surface can be obtained (Note that FIG. 1 is provided for easy understanding of the features of the present invention, and the dimensions and shape thereof are different from the actual ones. The present invention is not limited to this).

In this case, it is preferable to rotate the semiconductor wafer sucked and held on the chuck table at a rotation speed of 20 rpm or more.
Here, when the semiconductor wafer is rotated at various rotational speeds, the grinding wheel is cut from the outer peripheral edge of the wafer and separated from the wafer center so that the back surface of the semiconductor wafer is ground. In order to investigate the size of the convex shape generated at the center, the following experiment was conducted.

(Experiment)
Using the grinding apparatus shown in FIG. 3, the grinding wheel is cut from the outer peripheral edge of the wafer while rotating the semiconductor wafer W attracted to the chuck table 6 at the grinding position 13 under four conditions of 5, 10, 20, and 40 rpm. However, the back surface of the semiconductor wafer was ground so as to be separated from the center of the wafer. Thereafter, the size of the convex shape formed in the wafer center portion on the wafer back surface (grind surface) was measured using a capacitance type thickness measuring instrument (SBW-330 manufactured by Kobelco Research Institute). The measurement results are shown in FIG. As shown in FIG. 5, grinding is performed from the outer periphery toward the center and the semiconductor wafer is ground while rotating at a rotational speed of 5 rpm, thereby reducing the size of the convex shape formed at the center of the wafer to 0. It has been found that the size of the convex shape can be reduced to 15 μm or less, and the size of the convex shape can be reduced to an extremely small size of 0.04 μm or less by further increasing the rotation speed of the wafer to 20 rpm or more.

  This is because, as described above, when the cup-type grinding wheel is cut from the outer periphery of the wafer and separated from the wafer center to perform grinding, the wafer is rotated at a high rotational speed of 20 rpm or more, for example, 6 (a) to (c), it is considered that the grinding wheel cut from the outer peripheral edge of the wafer is worn during the grinding of the wafer and the cross-sectional taper shape of the grinding wheel is gradually reduced. . Thus, by reducing the tapered shape of the cross section of the grinding wheel at the center of the wafer, it becomes possible to reduce the grinding residue that occurs when the grinding wheel is detached from the center of the wafer and to reduce the size of the convex shape. Further improvement in wafer flatness can be achieved. At this time, if the rotational speed of the semiconductor wafer is increased too much, the grinding wheel wears greatly, and the life of the grinding wheel is shortened. It is preferable to be 40 rpm or less.

  Then, after grinding the back surface of the semiconductor wafer W as described above, the wafer W is moved to the reversal position 12 in FIG. 3 and reversed by the wafer reversing means 10, and then the first surface with the front surface of the semiconductor wafer facing upward. After attracting and holding the chuck table 6 again, the chuck table 6 is moved to the grinding position 13 by the turntable 8. At this time, since a slight protrusion is formed on the back surface of the wafer, when the wafer is attracted to the chuck table, the shape of the wafer back surface is transferred to the wafer surface and slightly protrudes to the center of the surface. .

  Thereafter, the entire surface of the semiconductor wafer W is ground by rotating the first chuck table 6 and bringing the grinding wheel portion of the cup grinding wheel 9 into contact with the surface of the semiconductor wafer W while rotating the cup grinding wheel 9. be able to.

In the present invention, when grinding the surface of the wafer in this way, the grinding wheel is cut from the center of the wafer, advanced from the center of the wafer toward the outer periphery, and separated from the outer periphery of the wafer to grind the wafer. Do.
For example, as shown in FIG. 4B, when the cup-type grinding wheel 9 and the surface of the semiconductor wafer W are brought into contact with each other at the arc line portion 17 of the semiconductor wafer W, the cup-type grinding wheel 9 is viewed from above. If the cup-type grinding wheel 9 and the surface of the semiconductor wafer W are brought into contact with each other at the arc line portion 17 ′ of the semiconductor wafer W, the cup-type grinding wheel 9 is moved upward. By rotating it clockwise as viewed from the top, the grinding wheel portion of the cup-type grinding wheel 9 can be cut from the center of the wafer and separated from the outer periphery of the wafer to grind the wafer.

  By grinding the surface of the wafer in this manner, even if the protrusion shape on the back surface is transferred to the center portion of the wafer surface as described above, the center portion of the wafer is excessively used by utilizing the sliding phenomenon of the grinding wheel. It is possible to suppress the formation of a concave shape by grinding, and on the other hand, it is possible to suppress the formation of a convex shape at the center of the wafer by utilizing the fact that this projection shape is transferred. Therefore, the protrusion protruding on the surface of the wafer can be reduced. Thereby, for example, the wafer shape as shown in FIG. 1B is obtained, and the height of the convex shape formed at the center of the wafer is as small as 0.15 μm or less, further 0.04 μm or less. The wafer of the degree can be obtained.

  At this time, when grinding the surface of the semiconductor wafer as described above, the semiconductor wafer sucked and held on the chuck table is rotated at a rotational speed slower than the rotational speed of the wafer when the back surface of the wafer is ground, for example, It is preferable to rotate at a rotation speed of 10 rpm or less, and further 5 rpm or less. In this way, when the cup-type grinding wheel is cut from the wafer center and separated from the outer periphery of the wafer for grinding, the wafer is rotated to a wafer surface by rotating at a low rotational speed of 10 rpm or less. The period of the grinding striations that appear can be reduced. As a result, for example, when polishing the wafer surface after that, it becomes possible to easily remove the grinding marks on the wafer surface with a small polishing allowance, preventing deterioration of the flatness of the wafer in the polishing process, and producing It is possible to improve the performance. At this time, if the rotational speed of the semiconductor wafer is too slow, it may be impossible to uniformly grind the wafer surface. Therefore, the rotational speed of the semiconductor wafer is preferably 1 rpm or more.

  After the front and back surfaces of the semiconductor wafer W are ground as described above, the wafer W is removed from the first chuck table 6 by the wafer reversing means 10 at the reversing position 12 and transferred to the transfer robot 11 at a predetermined position. Into the wafer cassette 14. In the present invention, for example, additional steps such as wafer centering means 15 and cleaning / drying means 16 before and after grinding can be provided.

  Further, when grinding another semiconductor wafer after that, after the next semiconductor wafer to be ground is sucked and held on the first chuck table 6, the wafer back surface and the wafer surface can be sequentially ground one by one in the same manner as described above. it can. At this time, a plurality of wafers can be efficiently ground in a short time by loading the wafers alternately into the first chuck table 6 and the second chuck table 7 and performing the grinding.

  As described above, by grinding both surfaces of the semiconductor wafer one by one, it is possible to suppress the formation of a convex shape at the center of the wafer and to process the wafer with high flatness. Specifically, for example, when the wafer is ground in the conventional method, as described above, a convex shape of 0.3 to 0.5 μm is formed at the center of the wafer. By carrying out the grinding method, the size of the convex shape formed at the center of the wafer can be easily reduced to 0.15 μm or less, further 0.04 μm or less. A quality wafer can be obtained stably.

  And since the wafer ground by the grinding method of the present invention becomes a wafer with high flatness such that the size of the convex shape formed at the center of the wafer is as small as 0.15 μm or less, for example, Then, by performing double-side polishing on this highly flat wafer, as shown in FIG. 1C, the convex shape at the center of the wafer is reduced to a size of 0.01 μm or less, which is hardly detected, with a small polishing allowance. Can be made. Therefore, it is possible to stably obtain a high-quality mirror-polished wafer having extremely high flatness without deteriorating the flatness of the wafer during polishing and without causing a decrease in productivity. Further, by polishing and finishing the wafer surface of the polishing wafer having such extremely high flatness by CMP or the like, the flatness of the wafer can be further improved as shown in FIG. For example, the wafer subjected to CMP in this manner is adsorbed to the chuck table 30 by a device process or the like as shown in FIG. 1E, so that the wafer surface becomes very flat. Therefore, a device can be manufactured with a high yield. Can be done.

  In the present invention, the above-mentioned grinding wheel is cut from the outer peripheral edge of the wafer, and the grinding is separated from the wafer center, and the grinding is performed by cutting the grinding wheel from the wafer central part and separated from the wafer outer periphery. It is not particularly limited as to whether it is applied to the front surface or the back surface of the wafer, and can be appropriately selected as necessary. For example, as described above, the grinding wheel is cut from the outer peripheral edge of the wafer, and the wafer center Protrusions are formed at the center of the wafer surface by applying grinding on the backside of the wafer, grinding the grinding wheel from the center of the wafer, and grinding the wafer on the wafer outer periphery. Not only can the wafer be flattened, but also the cycle of grinding marks formed on the wafer surface can be reduced, which is more preferable. .

  If the protrusions formed on the wafer surface can be reduced in this way and the period of the grinding marks can be reduced, for example, when mirror polishing is subsequently performed on the wafer surface, the grinding marks on the wafer surface can be easily obtained with a small polishing allowance. Therefore, it is possible to prevent the deterioration of the flatness of the wafer in the polishing process, and to obtain an advantage that a highly flat and higher quality mirror-polished wafer can be stably produced. On the other hand, even if some grinding marks remain on the back surface, no problem occurs.

  Furthermore, the wafer grinding method of the present invention can be applied very effectively when grinding a wafer with a large diameter having a high flatness specification of 200 mm or more, and more than 300 mm, which has been increasing in demand in recent years. it can. By grinding such a large diameter wafer according to the present invention, it is possible to suppress the formation of a convex shape at the center of the wafer and stably obtain a large diameter wafer having high flatness.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Example 1)
The both sides of the silicon wafer were ground one by one with the grinding apparatus 1 shown in FIG.
First, as a silicon wafer to be ground, a silicon single crystal ingot grown by the CZ method was sliced with a wire saw, and then a chamfered 300 mm diameter wafer was prepared.

  Then, the rear surface of the prepared silicon wafer is attracted and held on the first chuck table 6 and moved to the grinding position 13 by the turntable 8, and then the first chuck table 6 is rotated and the cup type grinding is performed. While the grindstone 9 was cut from the outer peripheral edge of the wafer and rotated in such a direction as to be detached from the center of the wafer, the grindstone was brought into contact with the silicon wafer and the back surface of the silicon wafer was ground with a grinding allowance of 7 μm.

  At this time, as the cup-type grinding wheel 9 of the grinding apparatus 1, a resin bond # 3000 grindstone using diamond abrasive grains is used, the rotational speed of the cup-type grinding wheel is 2700 rpm, and the feed amount of the grinding wheel is 12 μm / Grinding was performed with the rotation speed of the chuck table set to 5 rpm.

  After the back surface of the silicon wafer is ground as described above, the silicon wafer is moved to the reversal position 12 and reversed by the wafer reversing means 10 so that the surface of the semiconductor wafer is faced up and again attracted to the first chuck table 6. It was held and moved again to the grinding position 13 by the turntable 8. After that, the first chuck table 6 is rotated at a rotational speed of 5 rpm, and the grindstone 9 is rotated in a direction such that the cup-type grinding grindstone 9 is cut from the wafer center and separated from the outer periphery of the wafer. The surface of the silicon wafer was ground with a grinding allowance of 7 μm in contact with the wafer. Also at this time, a resin bond # 3000 grindstone using diamond abrasive grains is used as the cup-type grinding wheel 9, the rotation speed of the cup-type grinding wheel is set to 2700 rpm, and the feed amount of the grinding wheel is set to 12 μm / min. And then grinding.

  After grinding both sides of the silicon wafer in this way, the size of the convex shape generated at the center of the front and back surfaces of the wafer is measured using a capacitance type thickness measuring instrument (SBW-330 manufactured by Kobelco Kaken Co., Ltd.). did. As a result, it was found that the size of the convex shape formed at the center of the wafer was about 0.15 μm.

(Example 2)
A silicon wafer similar to that in Example 1 was prepared, and both surfaces of the wafer were ground one by one.
In Example 2, both sides of the silicon wafer were ground under the same conditions as in Example 1 except that the rotation speed of the chuck table when grinding the back surface of the wafer was set to 20 rpm.

  Then, as a result of measuring the size of the convex shape generated at the wafer center after the wafer grinding by using a capacitance type thickness measuring instrument, the size of the convex shape formed at the wafer center is about 0. 0. It was found to be 04 μm.

(Comparative example)
A silicon wafer similar to that in Example 1 was prepared, and both surfaces of the wafer were ground one by one with the grinding apparatus 1 shown in FIG.
First, the rear surface of the prepared silicon wafer is suction-held on the first chuck table 6, moved to the grinding position 13 by the turntable 8, and then the first chuck table 6 is rotated at a rotation speed of 5 rpm. The cup-type grinding wheel 9 is cut from the center of the wafer and rotated in the opposite direction to that of the first embodiment so as to be detached at the outer periphery of the wafer, while the grinding wheel is brought into contact with the silicon wafer so that the back surface of the silicon wafer is covered. Grinding was performed with a grinding allowance of 7 μm. At this time, as the cup-type grinding wheel 9 of the grinding apparatus 1, a resin bond # 3000 grindstone using diamond abrasive grains is used, the rotational speed of the cup-type grinding wheel is 2700 rpm, and the feed amount of the grinding wheel is 12 μm / Grinding was performed by setting to min.

  After grinding the back surface of the wafer, the silicon wafer is moved to the reversal position 12 and reversed by the wafer reversing means 10, so that the surface of the semiconductor wafer is held up again by the first chuck table 6. It was moved to the grinding position 13 again. Thereafter, the first chuck table 6 is rotated at a rotational speed of 5 rpm, and the cup-type grinding wheel 9 is cut in the same direction as when the back surface of the wafer is ground, that is, from the center of the wafer and separated from the outer periphery of the wafer. The surface of the silicon wafer was ground with a grinding allowance of 7 μm by rotating in such a direction. Also at this time, a resin bond # 3000 grindstone using diamond abrasive grains is used as the cup-type grinding wheel 9, the rotation speed of the cup-type grinding wheel is set to 2700 rpm, and the feed amount of the grinding wheel is set to 12 μm / min. And then grinding.

  Then, after grinding both sides of the wafer, the size of the convex shape formed at the center of the wafer was measured using a capacitance type thickness measuring instrument. As a result, the size of the convex shape formed at the center of the wafer was measured. Was found to be approximately 0.30 μm.

  Next, the silicon wafer subjected to double-side grinding in the above Example 2 and Comparative Example is subjected to alkali etching to remove the grinding strain layer, and further, 14 μm on both sides of the wafer using a mirror polishing apparatus. Double-side polishing was applied at the polishing allowance. Thereafter, the flatness of each mirror-surface silicon wafer was measured using a capacitance type thickness measuring instrument (ADE / U9G9700). As a result, as shown in FIG. 7, when the wafer of Example 2 was mirror-polished, the shape protruding at the wafer center was hardly observed. On the other hand, in the case of the wafer of the comparative example, the wafer center was It was confirmed that the convex shape was still formed.

  The present invention is not limited to the above embodiment. The above embodiment is merely an example, and the present invention has the same configuration as that of the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  For example, in the above description, the case of grinding a semiconductor wafer is mainly described as an example. However, the present invention is not limited to this, and a precision substrate such as a quartz substrate or an oxide single crystal is ground. The same applies to the case. Further, in the present invention, the conditions for the grinding fluid supplied when grinding the wafer, the grinding allowance of the wafer, the rotation direction of the chuck table, etc. can be appropriately set according to the wafer to be ground, It is not particularly limited.

It is a schematic diagram showing typically the shape of the wafer ground and polished by the grinding method of the present invention. It is a schematic diagram which represents typically the shape of the wafer which was ground and polished by the conventional method. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram showing an example of a grinding apparatus that can be used when carrying out a wafer grinding method of the present invention. It is the expansion schematic which expanded and showed roughly the chuck table and the cup type grinding wheel currently installed in the grinding device, (a) is a side view, (b) is a top view. It is the graph which showed the relationship between the rotational speed of a wafer, and the magnitude | size of the convex shape formed in the center part of a grinding surface. It is a schematic explanatory drawing explaining abrasion of the grinding wheel which grinds a wafer. It is a figure which shows the result of having measured the surface shape of the wafer after performing mirror polishing to the silicon wafer ground in Example 2 and a comparative example. It is the structure schematic which shows an example of the conventional grinding apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Grinding device, 6 ... 1st chuck table, 7 ... 2nd chuck table,
8 ... Turntable, 9 ... Cup type grinding wheel, 10 ... Wafer reversing means,
11 ... Wafer transfer robot, 12 ... Reverse position, 13 ... Grinding position,
14 ... wafer cassette, 15 ... wafer centering means, 16 ... cleaning / drying means,
17, 17 '... the arc wire part where the wafer contacts the grinding wheel,
18 ... Grinding wheel part, 19 ... Grinding wheel rotating shaft, 20 ... Cup-shaped base,
21 ... Grinding device 22 ... Semiconductor wafer 23 ... Chuck table,
24 ... grinding wheel 25 ... grinding head 26 ... cup type grinding wheel,
27 ... Rotating shaft, 30 ... Chuck table, W ... Wafer (semiconductor wafer).

Claims (9)

  In the method of grinding both surfaces of a wafer one side at a time using a cup-type grinding wheel, first, when grinding one surface of the wafer, the grinding wheel is cut from the outer periphery of the wafer and directed from the outer periphery of the wafer toward the center. Then, when grinding the other surface of the wafer, the grinding wheel is cut from the wafer center, and from the wafer center toward the outer periphery. A method of grinding a wafer, wherein the grinding is performed by being advanced and separated at an outer peripheral edge of the wafer.   2. The wafer according to claim 1, wherein the grinding wheel is rotated at a rotational speed of 20 rpm or more when grinding is performed by cutting the grinding wheel from an outer peripheral edge of the wafer and detaching the grinding wheel at a wafer central portion. Grinding method.   3. The method according to claim 1, wherein the grinding wheel is rotated at a rotational speed of 10 rpm or less when grinding is performed by cutting the grinding wheel from a wafer central portion and detaching the grinding wheel from the outer periphery of the wafer. The wafer grinding method as described.   Grinding by cutting the grinding wheel from the outer peripheral edge of the wafer and removing it at the wafer center, and performing grinding on the back surface of the wafer, cutting the grinding wheel from the wafer central part and releasing it at the outer edge of the wafer, The wafer grinding method according to any one of claims 1 to 3, wherein the method is performed on a wafer surface.   5. The wafer grinding method according to claim 1, wherein a resin-bonded grindstone using diamond abrasive grains is used as the cup-type grinding grindstone. 6.   6. The wafer grinding method according to claim 1, wherein a diameter of the wafer to be ground is 200 mm or more.   7. The wafer grinding method according to claim 1, wherein the wafer to be ground is a semiconductor wafer.   A wafer ground by the wafer grinding method according to any one of claims 1 to 7.   A mirror-polished wafer obtained by subjecting the wafer according to claim 8 to a mirror-polishing process.

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