JP2005028550A - Method for polishing wafer having crystal orientation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for polishing a wafer having a crystal orientation, which restrains a saw mark from being formed in such a direction to the crystal orientation as to cause a crack, without lowering polishing efficiency. <P>SOLUTION: The method comprises: a process of positioning the wafer held on the chuck table in a polishing zone below a polishing abrasive wheel; a first polishing process for polishing an upper surface of the wafer while turning a chuck table holding the wafer and revolving a polishing abrasive wheel so as to pass through the center of the wafer; a positioning process for positioning the wafer polished by the first polishing step with a mark showing the crystal orientation on the chuck table directed in a prescribed direction; a positioning process for positioning the polishing abrasive wheel at a position for polishing action; and a second polishing process for polishing the upper surface of the wafer by relatively moving the chuck table holding the wafer in parallel with the polishing abrasive wheel positioned at the position for polishing action and revolving, and by causing the polishing abrasive wheel to act on the upper surface of the wafer in a prescribed direction from the periphery of the wafer. <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 polishing surface of the polishing grindstone, passes through the center of the wafer held on the chuck table while rotating the polishing grindstone.

  Thus, when the bending strength of the chips that are polished and individually divided as described above is measured, there is a problem in that there are quantitatively chips having extremely low bending strength. According to the experiments by the present inventors, it has been found that, when the wafer having the crystal orientation is polished as described above, a chip having a low bending strength exists quantitatively at a predetermined portion. That is, when polished by the above-described polishing apparatus, as shown in FIGS. 9A and 9B, 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. 9A schematically shows a saw mark (S) when the workpiece mounting surface is polished using a chuck table having a flat surface, and FIG. 9B 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. In the polished wafer (W), the orientation flat (F) or notch (N) which is a mark indicating the crystal orientation and the saw mark (S) have a predetermined relationship (for example, 45 degrees in the case of silicon). It was found that chips with low bending strength were quantitatively generated in the region.

  The present invention has been made in view of the above-mentioned facts, and the main technical problem thereof is polishing of a wafer having a crystal orientation that can prevent generation of a chip having low bending strength without reducing polishing efficiency. It is to provide a method.

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 step of positioning the wafer held on the chuck table in a polishing region below the polishing wheel, and rotating the chuck table holding the wafer and passing through the center of the wafer while rotating the polishing wheel. A first polishing step comprising: a step of polishing the upper surface of the wafer by acting as described above;
The step of positioning the wafer polished by the first polishing step on the chuck table with a mark indicating a crystal orientation in a predetermined direction, the step of positioning the polishing grindstone at a polishing action position, and holding the wafer The chuck table is positioned in a polishing position and relatively translated toward the rotating polishing wheel, and the polishing wheel is applied in a predetermined direction from the outer periphery of the wafer to polish the upper surface of the wafer. A second polishing step comprising:
A method for polishing a wafer having a crystal orientation is provided.

  The second 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, the chuck table holding the wafer in the first polishing step is rotated and the polishing grindstone is rotated so as to pass through the center of the wafer so as to have a predetermined thickness. Since it grind | polishes until it becomes, it can grind | polish, without reducing polishing efficiency. Then, since the wafer polished to a predetermined thickness is polished in the second polishing step, the saw mark is not formed in the direction in which the bending strength is likely to decrease with respect to the crystal orientation. It is possible to prevent a decrease in the bending strength.

  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 attached to 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 a lower surface of the support member 326. And an annular polishing grindstone 327. 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 chuck table 52 is rotatably supported by the support base 51. The chuck table 52 is rotated by a servo motor 53 as a rotation driving means connected to a rotation shaft (not shown) mounted at the lower end thereof. 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 silicon substrate, and a plurality of regions are defined on a surface 10a by a plurality of streets (division lines) 101 arranged in a lattice pattern. A circuit 102 is formed in the region. 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 having 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. 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).

  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 held on the chuck table 52. The wafer 10 is positioned in the polishing area 25 below the polishing wheel 327. In this state, the wafer 10 held on the chuck table 52 is positioned at a position where the polishing grindstone 327 passes through the center (P) thereof as shown in FIGS. 5 (a) and 5 (b). When the wafer 10 is positioned in the polishing area 25 in this way, the servo motor 53 is driven to rotate the chuck table 52 at 100 to 300 rpm, and the servo motor 323 is driven to set the polishing tool 325 to 3000. While rotating at ˜6000 rpm, the pulse motor 44 of the polishing unit feed mechanism 4 is driven in the normal direction to lower the polishing unit 3 from the standby position indicated by a two-dot chain line in FIG. The lower end surface, which is a polishing surface, is allowed to act on the upper surface (back surface) of the wafer 10 held on the chuck table 52. Then, the polishing grindstone 327 is lowered by a predetermined amount, and the wafer 10 is polished to a predetermined thickness (first polishing step). This predetermined thickness is set to a dimension about 5 to 10 μm thicker than the finished dimension.

  Next, the pulse motor 44 is driven in reverse to raise the polishing tool 325 to the standby position indicated by a two-dot chain line in FIG. 5A, and the servo motor 323 is stopped to rotate the polishing tool 325. To stop. Further, the drive of the servo motor 53 is stopped to stop the rotation of the chuck table 52, and the servo motor 562 is driven in the reverse direction to position the chuck table 52 in the workpiece placement area 24. As shown in FIG. 6, the orientation flat (F) or notch (N) formed on the outer periphery of the wafer 10 held on the chuck table 52 has a moving direction arrow 23a and an arrow 23b of the chuck table 52. Position them so that they are parallel. The positioning of the wafer 10 may be performed by rotating the chuck table 52, or may be performed by releasing the suction and holding of the wafer 10 once.

  When the wafer 10 held on the chuck table 52 is positioned in a predetermined direction as described above, the chuck table moving mechanism 56 (see FIG. 3) is operated to indicate the chuck table mechanism 5 with an arrow 23a. It moves in the direction and is positioned at the polishing start position indicated by the solid line in FIG. Next, the servo motor 323 is driven to rotate the polishing tool 325 at 2000 to 4000 rpm, and the pulse motor 44 of the polishing unit feed mechanism 4 is driven to rotate forward so that the polishing unit 3 is shown by a two-dot chain line in FIG. The polishing position is indicated by the solid line from the standby position shown. This polishing action position is set to a height position where the lower end surface, which is the polishing surface of the polishing wheel 327 of the polishing tool 325, is 5 to 10 μm below the upper surface of the wafer 10 held on the chuck table 52.

  With the polishing grindstone 327 positioned at the polishing position in this way, the rotation speed of the servo motor 53 is set to zero (0) to restrict the rotation of the chuck table 52, and the chuck table mechanism 5 is moved by the arrow 23a. It moves in parallel to the polishing wheel 327 at a grinding feed rate of 6 to 10 cm / min in the direction shown, and moves to the polishing end position indicated by the two-dot chain line in FIG. 7 (second 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. 7, and the chuck table mechanism 5 is set at a polishing start position indicated by a solid line in FIG. Position. If the predetermined finishing thickness is not reached by executing the second polishing step once, the wafer 10 is made to the predetermined finishing thickness by repeatedly executing the second polishing step described above several times. Grind. As shown in FIG. 8, 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 as described above. Is formed. That is, in the second polishing step, a region where a chip having a low bending strength as shown in FIG. 9 is likely to occur (for example, in the case of silicon, orientation flat (F) or notch (N) and 45 degrees direction). A saw mark is not formed in the direction corresponding to the orientation flat (F) or notch (N) and 45 degrees in a portion corresponding to the region. 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.

  As an example of a method for restricting the rotation of the chuck table 52 in the second polishing step described above, an example in which the rotation speed of the servo motor 53 that rotationally drives the chuck table 52 is set to zero (0) has been shown. It is desirable to use a mechanical brake mechanism to ensure 52 rotation regulation. In the above-described embodiment, an example in which the first polishing process and the second polishing process are performed by one polishing apparatus having a mechanism that rotationally drives the chuck table 52 has been described. The polishing step and the second polishing step may be performed by separate polishing apparatuses.

  As described above, according to the present invention, the chuck table holding the wafer in the first polishing step is rotated and the polishing grindstone is rotated so as to pass through the center of the wafer until the predetermined thickness is reached. Since the polishing is performed, the wafer can be polished to a predetermined thickness without reducing the polishing efficiency. Then, the polished surface of the wafer polished to a predetermined thickness is polished in the second polishing step to remove the saw mark in the direction in which cracking is likely to occur with respect to the crystal orientation, so that the wafer is cracked during polishing. In addition, the die strength of the divided chip is improved as compared with a chip manufactured by polishing according to a conventional method.

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 1st grinding | polishing process in the grinding | polishing method by this invention. Explanatory drawing of the process of positioning a wafer on the chuck | zipper table in the 2nd grinding | polishing process of the grinding | polishing method by this invention. Explanatory drawing of the 2nd 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 step of positioning the wafer held on the chuck table in a polishing region below the polishing wheel, and rotating the chuck table holding the wafer and passing through the center of the wafer while rotating the polishing wheel. A first polishing step comprising: a step of polishing the upper surface of the wafer by acting as described above;
The step of positioning the wafer polished by the first polishing step on the chuck table with a mark indicating a crystal orientation in a predetermined direction, the step of positioning the polishing grindstone at a polishing action position, and holding the wafer The chuck table is positioned in a polishing position and relatively translated toward the rotating polishing wheel, and the polishing wheel is applied in a predetermined direction from the outer periphery of the wafer to polish the upper surface of the wafer. A second polishing step comprising:
A method for polishing a wafer having a crystal orientation.   2. The method for polishing a wafer having a crystal orientation according to claim 1, wherein the second polishing 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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