JP2010253580A - Abrasive cloth with grooves, and method and device for polishing wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abrasive cloth suppressing a polishing trace on a polished surface and equalizing the amount of polishing over the entire polished surface; and method and device for polishing a single side of a wafer by using the abrasive cloth. <P>SOLUTION: The abrasive cloth with grooves is composed of a material obtained by wet foaming urethane, and 100 to 200 radial grooves are formed at predetermined intervals in the surface of the abrasive cloth. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a polishing technique, particularly a semiconductor wafer polishing technique, and a polishing cloth and a wafer polishing method for improving the flatness of a surface to be polished by suppressing variations in polishing marks on the surface to be polished and the polishing amount of the entire surface to be polished. And a wafer polishing apparatus.

  CMP (mechanochemical polishing) is used for surface polishing of wafers that require high flatness, such as semiconductor wafers. CMP is a polishing technique in which a polishing liquid that has an etching action on a workpiece that is a material to be polished is used, and the workpiece is mechanically polished by abrasive grains contained in the polishing liquid while the workpiece is being etched.

  A polishing apparatus as shown in FIG. 1 is usually used for CMP. A polishing apparatus 1 in FIG. 1 is an example of a wafer single-side polishing apparatus, and includes a head mechanism 2 that holds a wafer and a rotating surface plate 4 having a polishing cloth 3. In the single-side polishing apparatus 1, the head mechanism 2 presses the surface to be polished of the wafer against the polishing cloth 3 provided on the upper surface of the rotating surface plate 4 while holding the wafer, and the head mechanism 2 and the rotating surface plate 4. , The head mechanism 2 and the rotating surface plate 4 are moved relative to each other, and the polishing surface of the wafer is polished while supplying the polishing liquid 6 from the polishing liquid supply means 5.

  When CMP is performed using the polishing apparatus as described above, it is necessary to supply the polishing liquid uniformly over the entire surface to be polished in order to ensure the flatness of the polished wafer. Therefore, a groove having a predetermined pattern is provided on the polishing cloth, and the polishing liquid is held in the groove, thereby satisfying the above requirement.

  On the other hand, in the final polishing step such as finish polishing, it has been considered undesirable to use a polishing cloth provided with grooves. In the final polishing process, since there is no surface processing step in the subsequent process, it is necessary to avoid polishing marks as much as possible, and it is thought that if polishing is performed using a polishing cloth provided with grooves, polishing marks are likely to remain. This is because. For this reason, a polishing cloth without a groove is generally used for polishing cloth that can be mirror-polished for use in the final polishing process, such as a soft polishing cloth (suede) in which urethane is wet-foamed.

  A polishing cloth obtained by wet-foaming urethane has a characteristic of excellent absorbability like a sponge and therefore has a certain level of polishing liquid retention. However, as the line pattern formed on the semiconductor substrate has been miniaturized in recent years, the demand for the flatness of the wafer has become stricter, and the high flatness of the wafer with the conventional grooveless polishing cloth is no longer the limit. .

  In addition, regarding the technique of providing a groove in the polishing cloth, Patent Document 1 discloses that a grid-like, spiral, or turtle shell-like groove is formed in the polishing cloth, and the angle of the groove side surface with respect to the polishing cloth body is an obtuse angle. A technique for improving the stability of the polishing amount and the nanotopography has been proposed. In this technique, a certain degree of polishing mark suppression effect is exhibited by making the angle of the groove side surface with respect to the polishing cloth main body an obtuse angle. However, since the groove pattern has a lattice shape, a spiral shape, or a turtle shell shape, when polishing is performed by rotating the rotary platen, a polishing trace is left on the surface of the groove to be polished on the rotation locus wafer. Further, since the groove pattern is a lattice shape, a spiral shape, or a turtle shell shape, the flow of the polishing liquid to the grooves is difficult to make uniform, and it is difficult to make the polishing amount of the entire surface to be polished uniform.

  Patent Document 2 proposes a technique for uniformly dispersing a polishing liquid over the entire surface to be polished of a workpiece by providing grooves or holes in the polishing cloth. However, in such a technique, no consideration is given to polishing marks, and when polishing is performed by rotating a rotary platen, grooves or holes leave a polishing mark on the surface to be polished as in the technique described above. In addition, since it is difficult to supply the polishing liquid to the portion where the polishing surface of the wafer is in contact with the polishing cloth, it is difficult to make the polishing amount uniform.

JP 2003-163192 A JP 2003-260657 A

  As described above, in the prior art, in the final polishing process such as finish polishing, it is possible to suppress polishing traces on the surface to be polished and uniformize the amount of polishing over the entire surface to be polished to manufacture a wafer with high flatness. It was difficult. In addition, it is essential to improve the polishing cloth under the situation that the flattening of the wafer becomes more difficult as the size of the wafer is increased to 300 mm or more.

  The present invention has been developed in view of the above-described situation, and provides a polishing cloth capable of suppressing polishing marks on a work surface to be polished and uniformizing the polishing amount over the entire surface to be polished, and the polishing cloth. An object of the present invention is to provide a single-side polishing method and a single-side polishing apparatus for a wafer.

The present inventor obtained the following knowledge (a) to (c) as a result of intensive studies to solve the above problems.
(a) In the case of polishing using a polishing cloth made of a material obtained by foaming urethane, in order to supply the polishing liquid over the entire surface to be polished of the workpiece, which is a material to be polished, It is effective to provide a groove.
(b) By making the groove a radial groove pattern, polishing marks that have been regarded as a problem when polishing with a grooved polishing cloth are effectively suppressed.
(c) When the radial grooves are set to an appropriate number, the polishing liquid is supplied uniformly over the entire surface to be polished of the workpiece.

The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) A polishing cloth made of a material obtained by wet foaming of urethane, wherein 100 to 200 radial grooves are formed at predetermined intervals on the surface of the polishing cloth. .

(2) The planar shape of the polishing cloth is circular, and a radial groove is formed from the circumferential portion toward the outer peripheral portion where the ratio of the groove-free portion to the groove forming portion is 25% or more. The grooved polishing cloth according to (1) above.

(3) The grooved polishing according to (1) or (2) above, wherein the depth of the groove from the surface of the polishing pad is more than 0.2 mm and the groove width is more than 0.5 mm. cloth.

(4) The grooved polishing cloth according to any one of (1) to (3), wherein the polishing cloth is used for polishing a wafer.

(5) The grooved polishing cloth according to (4), wherein the polishing cloth is used for a large wafer having a diameter of 300 mm or more.

(6) By pressing the wafer held by the polishing head against a polishing cloth fixed to the surface of the rotating surface plate, and rotating the polishing head and the rotating surface plate while supplying the polishing liquid onto the polishing cloth. In the single-side polishing method for a wafer in which the polishing surface of the wafer is polished, the polishing cloth according to (4) or (5) is used as the polishing cloth, and the polishing process is performed with a polishing amount of 1.0 μm or less. A method for polishing a single side of a wafer.

(7) The single-side polishing of a wafer according to (6), wherein the polishing liquid is supplied to the groove forming portion of the polishing cloth, and the surface to be polished of the wafer is pressed against the groove forming portion. Method.

(8) A wafer single-side polishing apparatus comprising a polishing head for holding a wafer and a rotating surface plate having a polishing cloth fixed to the surface, the polishing cloth according to (4) or (5) A single-side polishing apparatus for a wafer, characterized by using a polishing cloth.

  According to the present invention, since the polishing trace on the workpiece surface can be suppressed and the polishing liquid can be supplied uniformly over the entire surface to be polished, a mirror surface having a uniform polishing amount over the entire surface to be polished can be obtained. It is done. Therefore, the present invention is extremely effective in performing finish polishing and the like that need to avoid polishing marks as much as possible.

It is the schematic of a wafer single-side polish apparatus. It is a top view of the polishing cloth of the example of the present invention. It is a figure for demonstrating the groove dimension at the time of providing a groove | channel in polishing cloth. It is sectional drawing of the surface of the typical abrasive cloth of this invention. 1 is a schematic plan view of a wafer single-side polishing apparatus. It is a figure which shows the relationship between the number of the radial groove | channel formed in circular shaped polishing cloth, the variation in the grinding | polishing amount in a to-be-polished surface, and an average grinding | polishing amount.

Hereinafter, the present invention will be described in detail.
The polishing cloth of the present invention is a polishing cloth made of a material obtained by wet foaming of urethane, and is characterized in that 100 to 200 radial grooves are formed at predetermined intervals on the surface of the polishing cloth.
The polishing cloth of the present invention is made of a material (suede) obtained by wet foaming urethane, and is a polishing cloth used mainly in a final polishing process such as finish polishing. Since the polishing cloth having such a material absorbs the polishing liquid like a sponge, it is effective in supplying the polishing liquid over the entire surface to be polished of the wafer. In addition, in this invention, a well-known thing can be used as an abrasive cloth which consists of the raw material which carried out the wet foaming of urethane.

  However, when further flattening the wafer or polishing a large wafer having a diameter of 300 mm or more, even if the polishing cloth is made of the above material, it does not have grooves, and the entire surface to be polished of the wafer is covered. It was insufficient to supply the polishing liquid. Therefore, in the present invention, grooves are formed in the polishing cloth.

  As shown in FIG. 1, the grooves formed in the polishing cloth are uniformly supplied with the polishing liquid supplied from one place (several places in some cases) from the center side to the outer peripheral side of the polishing cloth. And a function of holding the polishing liquid on the polishing cloth. Therefore, by forming the groove on the polishing cloth, the polishing amount of the entire surface to be polished of the workpiece can be made uniform.

  What is important here is the pattern of grooves formed in the polishing pad. When the groove pattern formed on the polishing cloth is not appropriate, even if the polishing amount of the entire surface to be polished of the workpiece can be made uniform, a polishing mark is left on the surface to be polished of the workpiece. Therefore, in the present invention, the grooves formed in the polishing cloth are formed in a radial pattern. This is because by making the groove pattern radial, for example, when a workpiece is polished by a polishing apparatus as shown in FIG. 1, polishing marks generated on the surface to be polished of the workpiece are drastically reduced. In the present invention, the “radial groove” is formed over a part or the entire length of a line drawn radially (preferably linearly) from the center position of the polishing cloth toward the outer peripheral edge of the polishing cloth. Means a groove to be made.

  The number of grooves formed in the polishing cloth is 100 to 200. When the number of grooves is less than 100, for example, when a workpiece (for example, a wafer) is polished by a polishing apparatus as shown in FIG. 1, the polishing liquid supplied to the outer peripheral side of the polishing cloth becomes insufficient. The polishing amount of the entire surface to be polished cannot be made uniform. On the other hand, if the number of grooves exceeds 200, the area where the polishing cloth comes into contact with the surface to be polished of the workpiece becomes small, particularly in the central portion of the polishing cloth where the grooves are concentrated, and the polishing processing efficiency is lowered. The number of grooves in the present invention specifically means the number of grooves counted on the outer periphery of the polishing pad.

  With respect to the plurality of grooves formed on the polishing pad, the distance between the grooves is not particularly limited. However, from the viewpoint of uniform polishing amount, it is preferable to form a plurality of grooves at equal intervals. Especially when the size of the polishing cloth is 220 to 2000 mm, the arrangement angle of the adjacent grooves is determined by the polishing cloth. It is preferable that the center position of the angle be 3.6 ° or less. Note that the cross-sectional shape of the groove is not particularly limited, and grooves having various shapes can be formed. In particular, a U shape or a V shape is preferable in terms of suppressing polishing marks.

  In addition, the grooved polishing cloth of the present invention includes various methods such as a method of forming polishing grooves on the polishing cloth by grinding, a method of forming press grooves by applying heat and pressure to the polishing cloth with a mold or the like, and the like. It can be manufactured by a method.

  When the planar shape of the polishing pad is circular, it is preferable to form a radial groove from the circumferential portion toward the outer peripheral portion where the ratio of the groove-free portion to the groove forming portion is 25% or more. When the radial grooves are formed over the entire length from the center to the outer periphery of the polishing pad, the grooves are concentrated in the center. That is, there are cases where a plurality of grooves overlap each other at the center, and the surface of the polishing cloth for polishing the surface to be polished of the workpiece is lost. Further, even when the grooves do not overlap each other, when the grooves are extremely close to each other, the strength of the polishing cloth becomes insufficient, and it is assumed that the surface of the polishing cloth is broken during polishing or dressing. The Therefore, in the present invention, a radial groove is formed from the circumferential portion toward the outer peripheral portion in which the ratio of the groove-free portion to the groove forming portion is 25% or more, that is, the center side from the circumferential portion. In order to avoid the above-mentioned problem, it is preferable not to form a groove.

  An example of the polishing cloth of the present invention when the planar shape is circular is shown in FIG. In the polishing cloth 3 of FIG. 2, a plurality of grooves 30 are formed radially from a predetermined circumferential portion toward the outer peripheral portion, and the inner side of the circumferential portion is a groove-free region. The diameter D of the circumference depends on the number of grooves 30 and the groove width. For example, when 100 grooves having a groove width of 1.0 mm are formed, the diameter D (mm) of the circumferential portion satisfies a value satisfying 1.0 (mm) × 100 (pieces) × 1.25 ≦ πD, that is, 39.8 mm or more. It becomes.

  The depth of the groove is preferably 0.2 mm or more from the surface of the polishing pad (the portion where no groove is formed). When a workpiece is polished using a polishing apparatus as shown in FIG. 1, the polishing cloth receives a load from a head mechanism that holds the workpiece, and the polishing cloth sinks. That is, if the groove formed in the polishing cloth is too shallow, the height of the polishing cloth surface (the part where no groove is formed) and the groove bottom are approximately the same, and the height is substantially the same as polishing with a grooveless polishing cloth. Tend. Here, although depending on polishing conditions and the type of polishing cloth, the sinking of the polishing cloth is usually about 0.2 mm. Therefore, if the depth of the groove is more than 0.2 mm from the surface of the polishing pad (the portion where no groove is formed), the function of the groove can be more reliably exhibited. The upper limit value of the depth of the groove is not particularly limited, but it is preferably 1 mm or less from the viewpoint of maintaining the hardness of the polishing pad and suppressing deformation of the polishing pad.

  The polishing cloth of the present invention has a cross-sectional structure as shown in FIG. The polishing cloth of the present invention is obtained by impregnating a base 32 such as a nonwoven fabric with urethane and performing wet foaming, and the foamed portion 31 is formed on the base 32. In the present invention, a groove 30 having a depth: d and a width: w is formed in the foamed portion 31. In the present invention, “the depth of the groove from the surface for the polishing cloth” refers to the distance from the surface of the polishing cloth (where the groove 30 is not formed) to the deepest portion of the groove 30 as shown in FIG. The distance d means a distance perpendicular to the surface of the polishing pad.

  The groove width w is preferably more than 0.5 mm. FIG. 4 is an enlarged cross-sectional view of the surface portion of the polishing cloth of the present invention. The polishing cloth of the present invention made of a material obtained by wet foaming of urethane has a nap (fluff) 311 on the surface. When a polishing cloth having the nap 311 is used to polish a workpiece by the polishing apparatus shown in FIG. 1, the nap 311 falls down as the head mechanism 2 and the rotating surface plate 4 rotate. Here, when the groove width w is too narrow with respect to the length of the nap 311, the groove is blocked by the fall of the nap 311 and there is a possibility that the supply of the polishing liquid may be hindered. Therefore, in view of the fact that the length of the nap 311 is usually about 0.5 mm, it is preferable that the groove width w is more than 0.5 mm in order to effectively exhibit the function of the groove. The upper limit value of the groove width w is not particularly limited, but is preferably 3 mm or less in terms of controlling the flow of the polishing liquid and suppressing polishing marks on the wafer.

  According to the polishing cloth of the present invention having the above-described configuration, it is possible to suppress polishing marks on the workpiece surface and uniformly supply the polishing liquid over the entire surface to be polished. A mirror surface with a uniform polishing amount can be obtained. Therefore, the polishing cloth of the present invention is suitably used for polishing a wafer such as a semiconductor wafer that requires high flatness. Further, even when polishing a large-diameter wafer having a wafer size of φ300 mm or more, for example, a wafer having φ300 mm or φ450 mm, the polishing cloth of the present invention exhibits the above effects sufficiently.

  The polishing cloth of the present invention is applied to a known wafer single-side polishing apparatus as illustrated in FIG. 1, that is, a polishing apparatus 1 having a head mechanism 2 for holding a wafer and a rotating surface plate 4 having the polishing cloth 3. can do. Further, since the polishing cloth of the present invention is made of a material obtained by wet foaming of urethane, it is suitably used for CMP such as finish polishing of wafers whose polishing amount is 1.0 μm or less, SOI polishing, LPD removal polishing and the like. .

  The polishing apparatus according to the present invention is mainly composed of a head mechanism (polishing head) 2 and a rotating surface plate 4. The head mechanism 2 presses the surface to be polished of the wafer against the groove forming portion of the polishing pad 3 provided on the upper surface of the rotating surface plate 4 while holding the wafer, and rotates the head mechanism 2 and the rotating surface plate 4 together. As a result, the head mechanism 2 and the rotating surface plate 4 are moved relative to each other, and the polishing surface of the wafer is polished while supplying the polishing liquid 6 from the polishing liquid supply means 5. As the polishing liquid 6, for example, an alkaline polishing liquid containing colloidal silica or the like as abrasive grains is used.

  Although the place where the polishing liquid 6 is supplied is not particularly limited, as shown in FIG. 5, if the polishing liquid is supplied to the groove forming portion of the polishing cloth, the polishing liquid is easily supplied uniformly over the entire surface to be polished. It is preferable in order to make it easier. Further, it is more preferable to supply the polishing liquid 6 in the vicinity of the rotation track of the center portion of the head mechanism 2 which is a groove forming portion of the polishing cloth.

Next, the effects of the present invention will be described by way of examples of the present invention and comparative examples. However, the examples of the present invention are merely examples for explaining the present invention, and do not limit the present invention.
A φ100mm (100) silicon wafer (P type, 1-20Ωcm) is a circular polishing cloth (φ770mm) of wet foamed urethane material, and various radial grooves from the φ80mm circumference to the outer circumference Finish polishing was performed by using a single-side polishing apparatus shown in FIG. The number of the radial grooves and the polishing conditions are as follows.
<Number of radiation grooves>
Example of the present invention: 100, 144, 200 Comparative example: 0, 40, 80 <Polishing conditions>
Rotating surface and head mechanism speed: 20rpm
Wafer whole surface pressure: 17kPa
Polishing allowance: 0.1μm (target value)
Polishing time: 210sec.
Polishing liquid: Alkaline polishing liquid (containing colloidal silica)
In the above, the rotation direction of the rotating surface plate and the head mechanism are the same direction. Further, polishing was performed while pressing the surface to be polished of the wafer against the groove forming portion of the polishing cloth and supplying the polishing liquid to the rotating track portion at the center of the head mechanism 2.

(Evaluation)
About each silicon wafer after grinding | polishing, the variation in the grinding | polishing amount and the grinding | polishing amount in a to-be-polished surface was measured. The measurement results are shown in FIG. For measurement of the polishing amount, “Nanospec 8300” manufactured by Nanometrics Co., Ltd. was used. In addition, the wafer thickness was measured at 121 locations before and after polishing, and the average value of thickness differences before and after polishing was taken as the polishing amount. Further, the difference between the maximum value and the minimum value of the thickness difference was defined as the variation in the polishing amount.

  As shown in FIG. 6, the present invention examples 1 to 3 and comparative examples 1 to 3 show a large difference in the amount of polishing in the surface to be polished, although the amount of polishing is equivalent (about 1030 mm). In comparison with Comparative Examples 1 to 3, Examples 1 to 3 of the present invention have extremely good polishing amount variation. In Comparative Example 1 using the grooveless polishing cloth, the variation was 125 mm. Further, the number of grooves formed in the polishing cloth is 40 and 80, respectively. In Comparative Examples 2 and 3 which are less than the scope of the present invention, the above-described variation is different from Comparative Example 1 using the grooveless polishing cloth. Although the value is improved somewhat, the values are 102 依然 と し て and 107Å. On the other hand, in Examples 1 to 3 which are examples of the present invention, the above variation is 51 mm or less, and the above variation is less than half of Comparative Examples 2 and 3.

  Provided are a polishing cloth capable of suppressing polishing marks on a surface to be polished and making the polishing amount uniform over the entire surface to be polished, and a single-side polishing method and a single-side polishing apparatus for a wafer using the polishing cloth. .

1… Polishing equipment
2… Head mechanism
3… Abrasive cloth
4… Rotating surface plate
5… Polishing liquid supply means
6… Polishing liquid
7… Head lifting axis
8… Head lifting bearing

Claims (8)

  A polishing cloth made of a material obtained by wet-foaming urethane, wherein 100 to 200 radial grooves are formed at predetermined intervals on the surface of the polishing cloth.   The planar shape of the polishing cloth is circular, and a radial groove is formed from the circumferential portion toward the outer peripheral portion where the ratio of the groove-free portion to the groove forming portion is 25% or more. The grooved polishing cloth according to 1.   3. The grooved polishing cloth according to claim 1, wherein a depth of the groove from the surface of the polishing cloth is more than 0.2 mm, and the groove width is more than 0.5 mm.   The grooved polishing cloth according to any one of claims 1 to 3, wherein the polishing cloth is used for polishing a wafer.   The grooved polishing cloth according to claim 4, wherein the polishing cloth is used for a large wafer having a diameter of 300 mm or more.   The wafer held on the polishing head is pressed against a polishing cloth fixed to the surface of the rotating surface plate, and the polishing head and the rotating surface plate are rotated while supplying the polishing liquid onto the polishing cloth. In a single-side polishing method for a wafer in which polishing is performed on a surface to be polished, the polishing cloth according to claim 4 or 5 is used as the polishing cloth to perform polishing with a polishing amount of 1.0 μm or less. Single-side polishing method.   The single-side polishing method for a wafer according to claim 6, wherein the polishing liquid is supplied to the groove forming portion of the polishing cloth, and the surface to be polished of the wafer is pressed against the groove forming portion.   A wafer single-side polishing apparatus comprising a polishing head for holding a wafer and a rotating surface plate having a polishing cloth fixed to the surface, wherein the polishing cloth according to claim 4 or 5 is used as the polishing cloth. A single-side polishing apparatus for wafers.

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