JP2005033111A - Abrasive method of wafer having crystal orientation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abrasive method of a wafer having a crystal orientation whereby the wafer is so polished that no saw mark is formed in the direction of cracks being generated easily to the crystal orientation of the wafer. <P>SOLUTION: The abrasive method of a wafer having a crystal orientation is the one wherein the wafer having the crystal orientation is so held on a chuck table as to polish the top surface of the wafer by the end surface of a rotating abrasive grindstone acting on the top surface of the wafer. The abrasive method has a wafer positioning process for so mounting the wafer on the chuck table as to position the mark indicating the crystal orientation in a predetermined direction, an abrasive-grindstone positioning process for positioning the rotating abrasive grindstone in an abrasive acting position, and an abrasive process wherein the chuck table holding the wafer is so moved relatively to the abrasive grindstone positioned in the abrasive acting position and in parallel with the predetermined direction that the abrasive grindstone acts on the wafer from its outer periphery in the predetermined direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for polishing a wafer surface having a crystal orientation.

  In a semiconductor device manufacturing process, a large number of rectangular areas are defined by planned cutting lines called streets arranged in a lattice pattern on the surface of a substantially wafer-shaped semiconductor wafer, and a semiconductor circuit is formed in each of the rectangular areas. . Individual semiconductor chips are formed by separating the semiconductor wafer formed with such a large number of semiconductor circuits along the streets. A wafer in which a plurality of piezoelectric elements are arranged on a substrate such as lithium tantalate is also divided into individual chips by cutting along a predetermined street, and is widely used in electrical equipment.

  In order to reduce the size and weight of the individually divided chips as described above, the back surface of the wafer is usually polished prior to cutting the wafer along the street to separate the individual rectangular areas. To a predetermined thickness. Moreover, a cutting groove having a predetermined depth corresponding to the finished thickness of the chip is formed along the street without being completely divided into individual chips by a cutting device, and then the back surface of the wafer is polished until the cutting groove appears. A dividing method called so-called “first dicing” is generally performed to divide into individual chips.

  The polishing apparatus for polishing the back surface of the wafer described above includes polishing means including an annular polishing wheel for polishing the upper surface (back surface) of the wafer held by the chuck table that holds the workpiece, and rotates the chuck table. At the same time, the back surface of the wafer is efficiently polished so that the lower end surface, which is the grinding surface of the polishing wheel, passes through the center of the wafer held on the chuck table while being polished.

  Thus, a wafer formed of a material having a unique crystal orientation and weak with respect to the crystal orientation, such as lithium tantalate, is related to the crystal orientation when polished to a thickness of about 100 μm. There is a problem that breaks. According to experiments by the present inventors, it has been found that cracks that occur when a wafer having a crystal orientation is polished appear at a predetermined site. That is, when polished by the above-described polishing apparatus, as shown in FIGS. 8A and 8B, the surface to be polished of the wafer (W) has a radial shape from the rotation center (P) to the outer periphery as shown in the figure. A saw mark (S) is formed. 8A schematically shows a saw mark (S) when the workpiece mounting surface is polished by using a flat chuck table, and FIG. 8B shows a workpiece mounting surface. A saw mark (S) in the case of polishing using a chuck table having a conical surface is schematically shown. The polished wafer (W) is cracked in the region (A) where the orientation flat (F) or the notch (N) and the saw mark (S), which are marks indicating the crystal orientation, are in a substantially parallel relationship. I found out that In particular, when the wafer is divided by the above-described dicing, cracks appear remarkably in the chips in the region (A).

  The present invention has been made in view of the above facts, and the main technical problem thereof is a method for polishing a wafer having a crystal orientation for polishing so that a saw mark is not formed in a direction in which cracks tend to occur with respect to the crystal orientation. It is to provide.

In order to solve the above technical problem, according to the present invention, a wafer having a crystal orientation is held on a chuck table, and an end surface of a rotating grinding wheel is applied to the upper surface of the wafer held on the chuck table. A method for polishing a wafer having a crystal orientation for polishing the upper surface of the wafer,
A wafer positioning step of placing the wafer on the chuck table with a mark indicating a crystal orientation in a predetermined direction; and
A polishing wheel positioning step of rotating the polishing wheel and positioning it at a polishing action position;
A polishing step in which the chuck table holding the wafer is relatively translated toward the polishing grindstone positioned at a polishing action position, and the polishing grindstone is applied in a predetermined direction from the outer periphery of the wafer.
A method for polishing a wafer having a crystal orientation is provided.

  The polishing step is preferably performed by a polishing grindstone having an outer diameter that is twice or more the outer diameter of the wafer.

  In the method for polishing a wafer having a crystal orientation according to the present invention, since a saw mark is not formed on the surface to be polished of the wafer in a direction in which cracks are likely to occur with respect to the crystal orientation, the wafer does not crack during polishing. At the same time, cracks do not occur in the chip when the wafer is divided by prior dicing.

  Preferred embodiments of a method for polishing a wafer having a crystal orientation according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view of a polishing apparatus for carrying out the polishing method according to the present invention.
The illustrated polishing apparatus is provided with an apparatus housing generally indicated by numeral 2. This device housing 2 has a rectangular parallelepiped main portion 21 that extends long and an upright wall 22 that is provided at the rear end portion (upper right end in FIG. 1) of the main portion 21 and extends substantially vertically upward. ing. A pair of guide rails 221 and 221 extending in the vertical direction are provided on the front surface of the upright wall 22. A polishing unit 3 as a polishing means is mounted on the pair of guide rails 221 and 221 so as to be movable in the vertical direction.

  The polishing unit 3 includes a moving base 31 and a spindle unit 32 attached to the moving base 31. The movable base 31 is provided with a pair of legs 311 and 311 extending in the vertical direction on both sides of the rear surface. The pair of legs 311 and 311 is slidably engaged with the pair of guide rails 221 and 221. Guided grooves 312 and 312 are formed. As described above, a support portion 313 protruding forward is provided on the front surface of the movable base 31 slidably mounted on the pair of guide rails 221 and 221 provided on the upright wall 22. The spindle unit 32 is attached to the support portion 313.

  The spindle unit 32 includes a spindle housing 321 mounted on the support portion 313, a rotating spindle 322 rotatably disposed on the spindle housing 321, and a servo motor as a driving unit for rotationally driving the rotating spindle 322. 323. The lower end of the rotary spindle 322 protrudes downward beyond the lower end of the spindle housing 321, and a disk-shaped tool mounting member 324 is provided at the lower end. The tool mounting member 324 is formed with a plurality of bolt insertion holes (not shown) at intervals in the circumferential direction. A polishing tool 325 is mounted on the lower surface of the tool mounting member 324. As shown in FIG. 2, the polishing tool 325 is mounted on an annular support member 326 in which a plurality of blind screw holes 326 a extending downward from its upper surface are formed at intervals in the circumferential direction, and on the lower surface of the support member 326. It is comprised from the cyclic | annular grinding | polishing grindstone 327 made. The annular polishing grindstone 327 is configured by disposing a plurality of grindstone pieces 327 a on the same circumference on the lower surface of the support member 326. The outer diameter of the annular polishing grindstone 327 is preferably at least twice the outer diameter of a wafer as a workpiece to be described later. The polishing tool 325 configured as described above is positioned on the lower surface of the tool mounting member 324, and the fastening bolt 328 is inserted into the blind screw hole 326a formed in the support member 326 through the through hole formed in the tool mounting member 324. By screwing, the tool mounting member 324 is mounted.

  Referring back to FIG. 1, the polishing apparatus in the illustrated embodiment moves the polishing unit 3 up and down along the pair of guide rails 221 and 221 (perpendicular to a holding surface of a chuck table described later). The polishing unit feed mechanism 4 is moved in the direction). The polishing unit feed mechanism 4 includes a male screw rod 41 disposed on the front side of the upright wall 22 and extending substantially vertically. The male screw rod 41 is rotatably supported by bearing members 42 and 43 whose upper end and lower end are attached to the upright wall 22. The upper bearing member 42 is provided with a pulse motor 44 as a drive source for rotationally driving the male screw rod 41, and the output shaft of the pulse motor 44 is connected to the male screw rod 41 by transmission. A connecting portion (not shown) that protrudes rearward from the center portion in the width direction is also formed on the rear surface of the movable base 31, and a through female screw hole that extends in the vertical direction is formed in the connecting portion, The male screw rod 41 is screwed into the female screw hole. Therefore, when the pulse motor 44 rotates in the forward direction, the moving base 31, that is, the polishing unit 3 is lowered or moved forward, and when the pulse motor 44 rotates in the reverse direction, the moving base 31, that is, the polishing unit 3 is raised or moved backward.

  Continuing the description with reference to FIGS. 1 and 3, the chuck table mechanism 5 is disposed in the main portion 21 of the housing 2. The chuck table mechanism 5 includes a support base 51 and a chuck table 52 disposed on the support base 51. The support base 51 is formed on a pair of guide rails 23 and 23 extending on the main portion 21 of the housing 2 in the direction indicated by the arrows 23a and 23b in the front-rear direction (the direction perpendicular to the front surface of the upright wall 22). The workpiece mounting area 24 shown in FIG. 1 (position indicated by a solid line in FIG. 3) and a polishing tool 325 constituting the spindle unit 32 are mounted by a chuck table moving mechanism 56 described later. The polishing wheel 327 is moved between the polishing surface (lower end surface) of the polishing grindstone 327 and the polishing area 25 (position indicated by a two-dot chain line in FIG. 3). The chuck table 52 is made of an appropriate porous material such as porous ceramics, and is connected to a suction means (not shown). Therefore, by selectively communicating the chuck table 52 with a suction means (not shown), a wafer, which will be described later, which is a workpiece placed on the upper surface, that is, the placement surface, is sucked and held. The illustrated chuck table mechanism 5 includes a cover member 54 having a hole through which the chuck table 52 is inserted and covering the support base 51 and the like. The cover member 54 is configured to be movable together with the support base 51. ing.

  Continuing the description with reference to FIG. 3, the polishing apparatus in the illustrated embodiment includes a chuck table moving mechanism 56 that moves the chuck table mechanism 5 along the pair of guide rails 23 in the directions indicated by the arrows 23 a and 23 b. It has. The chuck table moving mechanism 56 includes a male screw rod 561 that is disposed between the pair of guide rails 23 and extends in parallel with the guide rail 23, and a servo motor 562 that rotationally drives the male screw rod 561. The male screw rod 561 is screwed into a screw hole 511 provided in the support base 51, and the tip end portion thereof is rotatably supported by a bearing member 563 attached by connecting a pair of guide rails 23 and 23. ing. The servo motor 562 has a drive shaft connected to the base end of the male screw rod 561 by transmission. Accordingly, when the servo motor 562 rotates in the forward direction, the support base 53, that is, the chuck table mechanism 5 moves in the direction indicated by the arrow 23a. When the servo motor 562 rotates in the reverse direction, the support base 53, that is, the chuck table mechanism 5 moves in the direction indicated by the arrow 23b. It can be moved.

  Returning to FIG. 1, the description will be continued. On the both sides in the moving direction of the support base 51 constituting the chuck table mechanism 5, the cross-sectional shape is a reverse channel shape, and the pair of guide rails 23, 23 and male screws Bellows means 61 and 62 are attached to cover the rod 561, the servo motor 562, and the like. The bellows means 61 and 62 can be formed from any suitable material such as campus cloth. The front end of the bellows means 61 is fixed to the front wall of the main portion 21, and the rear end is fixed to the front end surface of the cover member 54 of the chuck table mechanism 5. The front end of the bellows means 62 is fixed to the rear end surface of the cover member 54 of the chuck table mechanism 5, and the rear end is fixed to the front surface of the upright wall 22 of the apparatus housing 2. When the chuck table mechanism 5 is moved in the direction indicated by the arrow 23a, the bellows means 61 is expanded and the bellows means 62 is contracted, and when the chuck table mechanism 5 is moved in the direction indicated by the arrow 23b, the bellows means. 61 is contracted and the bellows means 62 is extended.

A polishing method for polishing a wafer having a crystal orientation using the polishing apparatus configured as described above will be described.
A wafer 10 having a crystal orientation shown in FIG. 4 is made of a lithium tantalate substrate, and a plurality of regions are defined on a surface 10a thereof by a plurality of streets (division lines) arranged in a lattice pattern. A circuit 102 is formed in the partitioned area. In this wafer 10, an orientation flat (F) or notch (N) is formed as a mark indicating a crystal orientation at a predetermined portion on the outer periphery. A protective tape 11 is attached to the surface 10a of the wafer 10 thus configured.

  Next, the wafer 10 with the protective tape 11 adhered to the front surface 10a is placed on the chuck table 52 positioned in the workpiece placement area 24 with the back surface 10b facing upward as shown in FIG. At this time, the orientation flat (F) or notch (N) formed on the outer periphery of the wafer 10 is positioned so as to be parallel to the movement direction arrow 23a and the arrow 23b of the chuck table 52 (wafer positioning step). The wafer 10 placed on the chuck table 52 in this manner is sucked and held on the suction chuck 52 by suction means (not shown). Note that the direction in which the orientation flat (F) or notch (N) indicating the crystal orientation easily breaks depends on the material of the wafer. Therefore, the relationship between the wafer positioning direction, that is, the moving direction of the chuck table 52 depends on the wafer material. Set each.

  When the wafer 10 is sucked and held on the chuck table 52, the chuck table moving mechanism 56 (see FIG. 3) is operated to move the chuck table mechanism 5 in the direction indicated by the arrow 23a, and the solid line in FIG. Positioned at the indicated polishing start position. Next, the pulse motor 44 of the polishing unit feed mechanism 4 is driven forward so that the polishing unit 3 is positioned from the standby position indicated by the two-dot chain line in FIG. 6 to the polishing action position indicated by the solid line (polishing tool positioning step). This polishing action position is set to a height position where the lower end surface, which is the polishing surface of the polishing grindstone 327 of the polishing tool 325, is 2 to 4 μm below the upper surface of the wafer 10 held on the chuck table 52.

  With the grinding wheel 327 thus positioned at the polishing action position, the servo motor 323 is driven to rotate the polishing tool 325 at 2000 to 3000 rpm, and the chuck table mechanism 5 is moved to 6 to 10 cm in the direction indicated by the arrow 23a. Is moved parallel to the polishing grindstone 327 at a grinding feed rate of / min and moved to a polishing end position indicated by a two-dot chain line in FIG. 6 (polishing step). The polishing end position is set to a predetermined position where the rear end passes through the lower end surface of the polishing grindstone 327 when viewed in the grinding feed direction indicated by the arrow 23a of the wafer 10. As a result, the upper surface (that is, the back surface) of the wafer 10 is polished by the rotating polishing grindstone 327. When the chuck table mechanism 5 is moved to the polishing end position in this way, the polishing grindstone 327 is positioned at a standby position indicated by a two-dot chain line in FIG. 6, and the chuck table mechanism 5 is set at a polishing start position indicated by a solid line in FIG. Position. Then, the wafer 10 is polished to a predetermined thickness by repeatedly executing the above-described polishing tool positioning step and polishing step. As shown in FIG. 7, a saw mark (S) substantially perpendicular to the orientation flat (F) or notch (N) is formed on the surface to be polished, which is the upper surface (that is, the back surface) of the wafer 10 polished in this way. It is formed. That is, in the above polishing process, a saw mark substantially parallel to the orientation flat (F) or notch (N) is not formed in a portion corresponding to the region (A) where the crack is likely to occur as shown in FIG. Is prevented. It is desirable that the saw mark (S) be closer to a straight line. Therefore, it is desirable that the outer diameter of the polishing grindstone 327 is twice or more the outer diameter of the wafer 10.

  A wafer made of a lithium tantalate substrate having a diameter of 75 mm and a thickness of 260 μm is polished on the back surface as described above using a polishing tool equipped with a polishing wheel having a diameter of 200 mm until the thickness of the wafer reaches 100 μm. When polished, there was no cracking. Further, a cutting groove having a depth of 110 μm was formed along the street from the surface of the wafer, and then the wafer was polished as described above until the thickness became 100 μm (until the cutting groove was exposed). There was no outbreak.

The perspective view of the polish device for enforcing the polish method by the present invention. The perspective view which shows the grinding | polishing tool which comprises the grinding | polishing unit with which the grinding | polishing apparatus shown in FIG. 1 is equipped. The perspective view which shows the chuck table mechanism and chuck table moving mechanism with which the grinding | polishing apparatus shown in FIG. 1 is equipped. 1 is a perspective view of a wafer to be polished by a polishing method according to the present invention and a protective tape to be attached to the surface of the wafer. Explanatory drawing of the wafer positioning process in the grinding | polishing method by this invention. Explanatory drawing of the grinding-wheel positioning process and grinding | polishing process in the grinding | polishing method by this invention. Explanatory drawing which shows the grinding | polishing surface of the wafer grind | polished by the grinding | polishing method by this invention. Explanatory drawing which shows the grinding | polishing surface of the wafer grind | polished by the conventional grinding | polishing method.

Explanation of symbols

2: Device housing 3: Polishing unit 31: Moving base 32: Spindle unit 321: Spindle housing 322: Rotating spindle 323: Servo motor 324: Tool mounting member 325: Polishing tool 326: Support member 327: Polishing grindstone 4: Polishing unit Feed mechanism 44: Pulse motor 5: Chuck table mechanism 51: Support base 52: Chuck table 53: Servo motor 54: Cover member 56: Chuck table moving mechanism 61, 62: Bellows means 10: Wafer (member to be processed)

Claims (2)

Polishing a wafer having a crystal orientation in which a wafer having a crystal orientation is held on a chuck table, and the upper surface of the wafer held on the chuck table is made to act on an end surface of a rotating grinding wheel to polish the upper surface of the wafer. A method,
A wafer positioning step of placing the wafer on the chuck table with a mark indicating a crystal orientation positioned in a predetermined direction;
A polishing wheel positioning step of rotating the polishing wheel and positioning it at a polishing action position;
A polishing step in which the chuck table holding the wafer is relatively translated toward the polishing grindstone positioned at a polishing action position, and the polishing grindstone is applied in a predetermined direction from the outer periphery of the wafer.
A method for polishing a wafer having a crystal orientation.   The method for polishing a wafer having a crystal orientation according to claim 1, wherein the grinding step is performed by a polishing grindstone having an outer diameter that is twice or more the outer diameter of the wafer.

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