Polishing pad seasoning method, seasoning plate, and semiconductor polishing device

A seasoning plate is placed on a polishing pad and performs seasoning of the polishing pad by abrading the polishing pad through the friction caused by rotation of the polishing pad. The seasoning plate includes: conditioners that abrade the polishing pad; a round flexible substrate that has the conditioners attached to the lower face thereof; an O-ring that is placed on the upper face of the flexible substrate, the O-ring forming a circle concentric with the flexible substrate; and a weight plate serving as a weight portion that is placed on the O-ring and applies weight for deforming the flexible substrate.

BACKGROUND

(a) Field of the Invention

The present invention relates to a semiconductor polishing technique, and more particularly, to a semiconductor polishing technique by which a semiconductor wafer is brought into contact with a polishing pad.

(b) Description of the Related Art

Conventionally, a material wafer for manufacturing a semiconductor device is formed by growing a single-crystal semiconductor ingot of silicon or the like by the Czochralski method (CZ method) or the floating zone method (FZ method), abrading and shaping the outer periphery of the semiconductor ingot with the use of a cylindrical grinding machine or the like, and slicing the semiconductor ingot with a wire saw in a slicing process. After that, chamfering is performed on the wafer peripheral portions, and flattening and etching are also performed in a wrapping process. Primary polishing (rough polishing) and secondary polishing (finishing) are then performed to form a mirror wafer.

Circuits are formed on the surface of the mirror wafer obtained through the above-mentioned procedures, so as to form a semiconductor device. However, if the surface flatness of the wafer manufactured through the above-described procedures is low, part of the lens used in the exposure in a photolithography process for forming circuits does not come into focus, and it becomes difficult to form a minute circuit pattern.

Therefore, a very high degree of flatness is required in today's high-precision device manufacture. In the manufacture of wafers having a high degree of flatness, the wafer surface polishing is essential. As a polishing device for performing wafer surface polishing, a batch-type one-side polishing device has been widely known.

FIGS. 10-1and10-2show an example of the batch-type one-side polishing device (see Japanese Patent Application Laid-Open (JP-A) No. 2006-117775).FIG. 10-1is a vertical cross-sectional view of the batch-type one-side polishing device.FIG. 10-2is an enlarged cross-sectional view of essential components of the batch-type one-side polishing device. The batch-type one-side polishing device is a device that polishes only one side of each of the wafers in one polishing operation, and is capable of polishing more than one wafer at the same time.

InFIGS. 10-1and10-2, the batch-type one-side polishing device100includes: a disk-like fixed platen102that is capable of rotating in a predetermined direction (counterclockwise when seen from above, for example); a polishing pad104that is formed with unwoven fabric or urethane foam bonded onto the surface of the fixed platen102; polishing heads108that are placed above the polishing pad104and rotate about supporting axes106; carrier plates110that are placed under the lower faces of the polishing heads108; templates112that are fixed under the lower faces of the carrier plates110and hold wafers W with wafer positioning holes112a; and a slurry tube114that supplies slurry to the surface of the polishing pad104.

Each of the carrier plates110is the carrier for holding wafers, and is formed with porous resin such as polyurethane-resin porous solid. Each of the templates112is formed with glass epoxy resin, a polycarbonate sheet, a polyester sheet, or the like. Each of the templates112has five wafer positioning holes112afor holding five wafers W. As shown inFIG. 10-2, the diameter of each of the wafer positioning holes112ais larger than the wafer diameter. When the polishing heads108rotate, the wafers W freely rotate inside the wafer positioning holes112a.

In the batch-type one-side polishing device100shown inFIGS. 10-1and10-2, the templates112are provided to the carrier plates110, so as to allow the wafers W to freely rotate. However, instead of the templates112, an adhesive agent or wax may be used to bond and fix the wafers W to the lower faces of the carrier plates110.

Since chips generated during polishing operations and slurry abrasive grains remain on the polishing pad, the polishing pad deteriorate, and the wafer polishing efficiency drops rapidly, as the wafer polishing operations continue. More specifically, since the surface of the polishing pad becomes too smooth, the slurry retention rate (slurry remaining rate) becomes lower. As a result, the slurry does not spread evenly on the polishing pad, and this phenomenon causes variations of wafer surface polishing conditions and a decrease in wafer polishing removal efficiently.

To counter this problem, seasoning is performed to recover the slurry retention, where the smoothened surface of the polishing pad is put into almost an initial state. A semiconductor polishing device having a center roller at the center of a polishing pad is now described as an example. As illustrated inFIG. 11-1, a semiconductor polishing device200has an urethane-foam polishing pad206bonded onto a round platen204that rotates coaxially with a center roller202. The platen204rotates in the opposite direction (counterclockwise) from the rotation direction of the center roller202that rotates clockwise. Silicon wafers210having its polished surface facing downward are bonded to the lower face of a polishing plate208with wax. The polishing plate208has a smaller diameter than the radiuses of the platen204and the polishing pad206. The side face of the polishing plate208is brought into contact with the side face of the center roller202. A weight portion for facilitating the polishing of the silicon wafers210is placed on the polishing plate208, or weight is applied onto the upper face of the polishing plate208, so as to press the silicon wafers210against the polishing pad206. While slurry (not shown) is supplied onto the polishing pad206, the polishing pad206is rotated, and the polishing plate208is rotated counterclockwise by the friction caused by the rotation of the center roller202. The surfaces of the silicon wafers210are polished by the friction caused between the silicon wafers210and the polishing pad206(or the abrasive grains in the slurry) by the rotation of the polishing pad206and the polishing plate208. A ring-like conditioner (also called a dresser)212having an electrodeposited diamond grindstone is attached to a rotating member214, and, like the polishing plate208, the rotating member214is placed on the polishing pad206. The rotating member214is rotated counterclockwise, to perform toothing on the surface of the polishing pad206. In this manner, seasoning is performed. The seasoning is performed not only in the rough polishing process, but also in the CMP (Chemical Mechanical Polishing) process at a later stage (see JP-A No. 2002-208575 and 2003-151934).

However, if the seasoning with the use of the conditioner is repeated, the inner circumferential region206aand the outer circumferential region206cof the polishing pad206are selectively abraded.FIG. 11-2illustrates this phenomenon more specifically. Where the abscissa axis indicating the moving radial direction of the polishing pad206, and the ordinate axis indicates the abrasion depth in the polishing pad206, deeper abrasion is observed in the inner circumferential region206aand the outer circumferential region206c, and the curve inFIG. 11-2becomes a convex curve.

When a silicon wafer is polished with the use of a polishing pad having a shape represented by such a convex curve, the flatness of the surface of each silicon wafer becomes poorer, and more polishing is performed on the side of the silicon wafer positioned in the inner circumferential region of the polishing pad than on the side of the silicon wafer positioned in the outer circumferential region of the polishing pad. This phenomenon is called “inner abrasion”. This inner abrasion can be eliminated by lowering the rotation speed of the polishing pad. However, when the rotation speed becomes lower, the polishing efficiency also becomes lower. If the rotation speed of the polishing pad is lowered, “outer abrasion” might be observed, as opposed to the inner abrasion. However, depending on the surface condition of the polishing pad, a silicon wafer might have either inner abrasion or outer abrasion, even if the polishing pad is rotated at a fixed rotation speed. Therefore, it is difficult to control the flatness of the polished surface of each silicon wafer by adjusting the rotation speed of the polishing pad.

To solve this problem, JP-A No. 2003-151934 discloses a structure that controls the position of the polishing-pad seasoning conditioner on the polishing pad, and maintains the flatness of the polishing pad. However, this structure requires a mechanism for controlling the conditioner placed on the polishing pad. As a result, the structure becomes complicated, and the costs become higher. As shown inFIG. 12, Japanese Patent Publication No. 3,159,928 discloses a structure in which a quatrefoil hole306is formed in the lower face302of a conditioner300that has diamond abrasive grains304dispersed on the lower face302in contact with a polishing pad. The conditioner300is designed to flatten the polishing pad. In this structure, the efficiency of the seasoning of the polishing pad is increased in the inner circumferential region of the conditioner300, and the polishing pad is flattened. However, unlike a conventional ring-like conditioner, the conditioner300has a complicated structure, resulting in higher costs.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention aims to provide a seasoning method, a seasoning plate, and a semiconductor polishing device that can recover the flatness of a polishing pad with a simple structure, and can readily control the flatness of the polished surface by adjusting the rotation speed of the polishing pad.

To achieve the above objective, a first aspect of a polishing pad seasoning method according to the present invention is characterized as a polishing pad seasoning method for abrading a polishing pad by the friction caused by rotation of the polishing pad, the method including: attaching conditioners for abrading the polishing pad to the lower face of a round flexible substrate; and applying weight for deforming the flexible substrate to the flexible substrate from a ring placed on the upper face of the flexible substrate, the ring forming a circle concentric with the flexible substrate.

A second aspect of the polishing pad seasoning method according to the present invention is characterized as a polishing pad seasoning method for abrading a polishing pad by the friction caused by rotation of the polishing pad, the method including: attaching conditioners for abrading the polishing pad to the lower face of a round flexible substrate; mounting a weight portion on the upper face of the flexible substrate, to press the conditioners against the polishing pad; and applying weight for deforming the flexible substrate to the flexible substrate by a ring placed between the flexible substrate and the weight portion, to eliminate inflection points in the pad surface of the polishing pad, the inflection points appearing during the abrasion of the polishing pad by the conditioners, the ring forming a circle concentric with the flexible substrate.

A third aspect of the polishing pad seasoning method according to the present invention is characterized in that the conditioners are arranged in such a manner that the centers of the conditioners form a circle concentric with the flexible substrate.

A fourth aspect of the polishing pad seasoning method according to the present invention is characterized in that grooves extending along radial lines extending from the center of each of the conditioners are formed in the surface of each of the conditioners, the surface being in contact with the polishing pad.

A first aspect of a seasoning plate according to the present invention is characterized as a seasoning plate that is placed on a polishing pad and performs seasoning of the polishing pad by abrading the polishing pad through the friction caused by rotation of the polishing pad, the seasoning plate including: conditioners that abrade the polishing pad; a round flexible substrate that has the conditioners attached to the lower face thereof; a ring that is placed on the upper face of the flexible substrate, the ring forming a circle concentric with the flexible substrate; and a weight portion that is placed on the ring and applies weight for deforming the flexible substrate.

A second aspect of the seasoning plate according to the present invention is characterized as a seasoning plate that is placed on a polishing pad and performs seasoning of the polishing pad by abrading the polishing pad through the friction caused by rotation of the polishing pad, the seasoning plate including: conditioners that abrade the polishing pad; a round flexible substrate that has the conditioners attached to the lower face thereof; a weight portion that applies weight to the flexible substrate; and a ring that is placed between the flexible substrate and the weight portion, and applies weight for deforming the flexible substrate to the flexible substrate, the ring forming a circle concentric with the flexible substrate, the ring eliminating inflection points in the pad surface of the polishing pad, the inflection points appearing during the abrasion of the polishing pad by the conditioners.

A third aspect of the seasoning plate according to the present invention is characterized in that the conditioners are arranged in such a manner that the centers of the conditioners form a circle concentric with the flexible substrate.

A fourth aspect of the seasoning plate according to the present invention is characterized in that grooves extending along radial lines extending from the center of each of the conditioners are formed in the surface of each of the conditioners, the surface being in contact with the polishing pad.

A fifth aspect of the seasoning plate according to the present invention is characterized in that the material of the flexible substrate is polyvinyl chloride.

A sixth aspect of the seasoning plate according to the present invention is characterized in that the material of the ring is silicon rubber or resin.

A seventh aspect of the seasoning plate according to the present invention is characterized as a seasoning plate that is placed on a polishing pad and performs seasoning of the polishing pad by abrading the polishing pad through the friction caused by rotation of the polishing pad, the seasoning plate including: conditioners that abrade the polishing pad; a round flexible substrate that is made of polyvinyl chloride and has the conditioners attached to the lower face thereof; grooves that extend along radial lines extending from the center of each of the conditioners, and are formed in the surface of each of the conditioners, the surface being in contact with the polishing pad; a ring that is made of silicon rubber or resin, and is placed on the upper face of the flexible substrate, the ring forming a circle concentric with the flexible substrate; and a weight portion that is placed on the ring and applies weight for deforming the flexible substrate.

An eighth aspect of the seasoning plate according to the present invention is characterized as a seasoning plate that is placed on a polishing pad and performs seasoning of the polishing pad by abrading the polishing pad through the friction caused by rotation of the polishing pad, the seasoning plate including: conditioners that abrade the polishing pad; a round flexible substrate that is made of polyvinyl chloride and has the conditioners attached to the lower face thereof; grooves that extend along radial lines extending from the center of each of the conditioners, and are formed in the surface of each of the conditioners, the surface being in contact with the polishing pad; a weight portion that applies weight to the flexible substrate; and a ring that is made of silicon rubber or resin, and is placed between the flexible substrate and the weight portion, the ring forming a circle concentric with the flexible substrate, the ring applying weight for deforming the flexible substrate to the flexible substrate, the ring eliminating inflection points in the pad surface of the polishing pad, the inflection points appearing during the abrasion of the polishing pad by the conditioners.

A ninth aspect of the seasoning pad according to the present invention is characterized in that the conditioners of the seventh and eighth aspects are arranged in such a manner that the centers of the conditioners form a circle concentric with the flexible substrate.

A first aspect of a semiconductor polishing device according to the present invention is characterized as a semiconductor polishing device on which a seasoning plate can be mounted, the seasoning plate being placed on a polishing pad and performing seasoning of the polishing pad by abrading the polishing pad through the friction caused by rotation of the polishing pad, the seasoning plate including: conditioners that abrade the polishing pad; a round flexible substrate that has the conditioners attached to the lower face thereof; a ring that is placed on the upper face of the flexible substrate, the ring forming a circle concentric with the flexible substrate; and a weight portion that is placed on the ring and applies weight for deforming the flexible substrate.

A second aspect of the semiconductor polishing device according to the present invention is characterized as a semiconductor polishing device on which a seasoning plate can be mounted, the seasoning plate being placed on a polishing pad and performing seasoning of the polishing pad by abrading the polishing pad through the friction caused by rotation of the polishing pad, the seasoning plate including: conditioners that abrade the polishing pad; a round flexible substrate that has the conditioners attached to the lower face thereof; a weight portion that applies weight to the flexible substrate; and a ring that is placed between the flexible substrate and the weight portion, and applies weight for deforming the flexible substrate to the flexible substrate, the ring forming a circle concentric with the flexible substrate, the ring eliminating inflection points in the pad surface of the polishing pad, the inflection points appearing during the abrasion of the polishing pad by the conditioners.

A third aspect of the semiconductor polishing device according to the present invention is characterized in that the conditioners are arranged in such a manner that the centers of the conditioners form a circle concentric with the flexible substrate.

A fourth aspect of the semiconductor polishing device according to the present invention is characterized in that grooves extending along radial lines extending from the center of each of the conditioners are formed in the surface of each of the conditioners, the surface being in contact with the polishing pad.

A fifth aspect of the semiconductor polishing device according to the present invention is characterized in that the material of the flexible substrate is polyvinyl chloride.

A sixth aspect of the semiconductor polishing device according to the present invention is characterized in that the material of the ring is silicon rubber or resin.

A seventh aspect of the semiconductor polishing device according to the present invention is characterized as a semiconductor polishing device on which a seasoning plate can be mounted, the seasoning plate being placed on a polishing pad and performing seasoning of the polishing pad by abrading the polishing pad through the friction caused by rotation of the polishing pad, the seasoning plate including: conditioners that abrade the polishing pad; a round flexible substrate that is made of polyvinyl chloride and has the conditioners attached to the lower face thereof; grooves that extend along radial lines extending from the center of each of the conditioners, and are formed in the surface of each of the conditioners, the surface being in contact with the polishing pad; a ring that is made of silicon rubber or resin, and is placed on the upper face of the flexible substrate, the ring forming a circle concentric with the flexible substrate; and a weight portion that is placed on the ring and applies weight for deforming the flexible substrate.

An eighth aspect of the semiconductor polishing device according to the present invention is characterized as a semiconductor polishing device on which a seasoning plate can be mounted, the seasoning plate being placed on a polishing pad and performing seasoning of the polishing pad by abrading the polishing pad through the friction caused by rotation of the polishing pad, the seasoning plate including: conditioners that abrade the polishing pad; a round flexible substrate that is made of polyvinyl chloride and has the conditioners attached to the lower face thereof; grooves that extend along radial lines extending from the center of each of the conditioners, and are formed in the surface of each of the conditioners, the surface being in contact with the polishing pad; a weight portion that applies weight to the flexible substrate; and a ring that is made of silicon rubber or resin, and is placed between the flexible substrate and the weight portion, the ring forming a circle concentric with the flexible substrate, the ring applying weight for deforming the flexible substrate to the flexible substrate, the ring eliminating inflection points in a pad surface of the polishing pad, the inflection points appearing during the abrasion of the polishing pad by the conditioners.

A ninth aspect of the semiconductor polishing device according to the present invention is characterized in that the conditioners are arranged in such a manner that the centers of the conditioners form a circle concentric with the flexible substrate.

With the polishing pad seasoning method, the seasoning plate, and the semiconductor polishing device according to the present invention, the variations in abrasion depth in the inner circumferential region and the outer circumferential region of polishing pad can be reduced with a simple structure, while using conventional conditioners. Also, appearance of inflection points in the pad surface of the polishing pad due to the conditioners can be prevented, and the variations in abrasion depth of the polishing pad can be made uniform. In this manner, the flatness of the polished surface can be readily maintained by controlling the rotation speed of the polishing pad. Thus, the duration of use (the life) of the polishing pad can be prolonged, and costs can be lowered.

DETAILED DESCRIPTION OF EMBODIMENTS

The following is a description of an embodiment of a polishing pad seasoning method, a seasoning plate, and a semiconductor polishing device according to the present invention, with reference to the accompanying drawings. The components and the types, combinations, shapes, and relative positions of the components described in the embodiment are merely examples and do not restrict the scope of the invention to those examples, unless otherwise specified.

FIG. 1-1is a perspective view of a seasoning plate and a semiconductor polishing device according to this embodiment.FIG. 1-2is a partial cross-sectional view of the structures shown inFIG. 1-1, andFIG. 1-3is a plan view of the structures shown inFIG. 1-1. By a polishing pad seasoning method according to this embodiment, a polishing pad is ground by the friction caused by rotating the polishing pad. Conditioners for grinding the polishing pad are attached to the bottom face of a round flexible substrate, and a ring that is concentric with the flexible substrate is placed on the upper face of the flexible substrate. Weight for deforming the flexible substrate is applied onto the ring. As a result, a seasoning plate10is formed. The seasoning plate10includes a flexible substrate12, conditioners14, an O-ring16, and a weight plate18serving as a weight portion. A semiconductor polishing device20has a fundamental structure in which a polishing pad26made of urethane foam is attached to a round-shape fixed platen24that is coaxial with a rotating center roller22and can have a rotation speed adjusted independently of the center roller22. This embodiment is to be applied to the polishing pad that is used in primary polishing (rough polishing) of the surface of each silicon wafer after the processes for wrapping and etching the silicon wafers cut out of ingot.

The flexible substrate12is formed with a flexible material such as polyvinyl chloride (hereinafter referred to as PVC). The flexible substrate12is a round-shape substrate that has a certain thickness, and has a diameter smaller than the radius of the polishing pad26. This flexible substrate12can be deformed by weight applied from the later described weight plate18serving as a weight portion.

FIG. 2-1andFIG. 2-2illustrate the conditioners14. As shown inFIG. 2-1, the conditioners14that have ring-like shapes or ashtray-like shapes are attached to the bottom face of the flexible substrate12. The conditioners14have diamond abrasive grains or the like electrodeposited onto their surfaces, and each have a diameter smaller at least than the radius of the flexible substrate12. As shown inFIG. 2-2, a ring-like bank14ais formed on the outer circumferential region on the opposite face of each conditioner14from the face to be attached to the flexible substrate12. The ring face14bof the bank14ais to be brought into contact with the polishing pad26. In the ring face14b, grooves14eare formed at locations where lines14dextending radially from the center14cof the conditioner14across the ring face14b. In this embodiment, eight grooves14eare formed to divide the ring face14binto eight. As shown inFIG. 2-1, the conditioners14are attached to the bottom face of the flexible substrate12. In this embodiment, five conditioners14are attached to the bottom face of the flexible substrate12in such a manner as to form a circle concentric with the flexible substrate12.

The O-ring16is placed on the upper face of the flexible substrate12in such a manner as to form a circle concentric with the outer circumference of the flexible substrate12. The round weight plate18serving as the weight portion has the same diameter as the flexible substrate12, and is placed on the O-ring16. The weight plate18applies weight onto the flexible substrate12via the O-ring16, and presses the conditioners14against the polishing pad by the weight. It is preferable that the weight plate18is made of ceramics. On the other hand, any material may be used for the flexible substrate12, and a metal or the like may be used, as long as the predetermined weight can be applied to the flexible substrate12. It is preferable that the O-ring16is made of silicon rubber. However, any other material such as resin may be used, as long as the weight plate18can be held by the friction, that is, the weight plate18and the O-ring16do not deviate from each other due to the later described rotation of the seasoning plate10.

The seasoning plate10having the above structure has the conditioners14that face the polishing pad26and are in contact with the polishing pad26of the semiconductor polishing device20. The side faces of the flexible substrate12and the weight plate18of the seasoning plate10are brought into contact with the side face of the center roller22of the semiconductor polishing device20rotating clockwise. Subjected to the friction with the side face22aof the center roller22and the counterclockwise rotation from the center roller22, the seasoning plate10(the flexible substrate12and the weight plate18) rotates counterclockwise in the opposite direction from the direction of rotation of the center roller22. Although rotating coaxially with the center roller22, the polishing pad26is capable of rotating counterclockwise, independently of the rotation of the center roller22. As shown inFIG. 1-3, the seasoning plate10is held by the contact between a rotational contact roller30fixed at the top end of an arm28extending toward the seasoning plate10from the opposite direction from the direction of rotation of the polishing pad26and the side faces of the flexible substrate12and the weight plate18. Held in that position, the seasoning plate10is in rotational contact with the center roller22and the rotational contact roller30, and rotates counterclockwise, with its axis of rotation being the center of the flexible substrate12and the weight plate18. Here, the wafer to be polished such as a silicon wafer (not shown) and the polishing plate (not shown) have the same arrangement and structures as those of the conventional art, and therefore, explanation of them is omitted herein.

Next, the background to the development of the structure and the effects and advantages of the seasoning plate10according to this embodiment are described.

FIG. 3-1shows the shapes of the pad surface of the polishing pad in predetermined “pad lives”. Here, a “pad life” means a polishing time of the polishing pad. The pad shapes are indicated by the displacement from the best-fit surface of an inner circumference region26aof the polishing pad26, and the pad shapes of the polishing pad shown in the other drawings are also shown in the same manner, unless otherwise specified. The “best-fit surface” is a virtual surface in which the later described GFLR becomes smallest. As shown inFIG. 3-1, as the pad life passes, deeply ground portions appear in the inner circumferential region26aand the outer circumferential region26cof the polishing pad26, and convex pad face portions are formed in the inner circumferential region26aand the outer circumferential region26cacross the center region26b. In this case, the surface polished by the polishing pad26tends to have abrasion in the inner circumferential region.

FIG. 3-2shows the relationship between the pad life and the GBIR of the polished surface plotted in a graph. Here, GBIR (Global Back-side Ideal Range) is used to evaluate the flatness of the polished surface, with the back surface of the polished surface of the polished wafer being the reference surface. Normally, the GBIR does not indicate a negative value. However,FIG. 3-2shows both positive and negative values, based on the GBIR index to check variations in flatness. More specifically, the value of the GBIR is adjusted so that the polished surface has abrasion in the outer circumferential region when the GBIR indicates a positive value, and the polished surface has abrasion in the inner circumferential region when the GBIR indicates a negative value. The surface polishing is performed, with the rotation speed of the polishing pad26being fixed at 21 rpm, and the polishing time being 10 minutes. It becomes apparent from the observation result that the abrasion of the polished surface switches from the outer circumferential region to the inner circumferential region when the pad life first exceeds a certain period of time.

FIG. 4-1shows the polishing pad displacement observed when the center region26bof a polishing pad is abraded.FIG. 4-2shows the GBIR of the surface polished with the use of the polishing pad shown inFIG. 4-1. As shown inFIG. 4-1, the inventor formed a polishing pad that had a concave portion extending from the inner circumferential region to the outer circumferential region across the center region, with the use of conditioners. As shown inFIG. 4-2, the GBIR of the polished surface of the polished wafer was measured and plotted in a graph. A polishing pad almost in an initial state was prepared, and the center region of the polishing pad was abraded at the rotation speed of 45 rpm. The rotation speed of the polishing pad and the center roller22before and after the abrasion in the polishing process was set at 21 rpm, and the polishing time of the polished wafer was set at 10 minutes. It became apparent that the surface polished by the polishing pad26after the abrasion had a higher GBIR value and greater outer-circumferential abrasion than the surface polished by the polishing pad26before the abrasion (in the outer circumferential region). In view of this, the inventor considered that a polishing pad26that has less inner-circumferential abrasion in the polished surface could be formed by performing the same processing as above on a polishing pad26having inner-circumferential abrasion in the polished surface and flattening the convex portion.

FIG. 5-1shows the shape of a seasoning plate having conditioners attached to a ceramic plate.FIG. 5-2shows the abrasion amount observed when a polishing pad is abraded with the seasoning plate shown inFIG. 5-1. The inventor formed a seasoning plate36that had five conditioners34attached to a round-shape ceramic plate32as shown inFIG. 5-1, so as to flatten the convex portions formed in the polished pad26due to abrasion. The seasoning plate36was placed on the polishing pad26, and is rotated around the center of the ceramic plate32to abrade the polishing pad26in the same manner used for the seasoning plate10. As shown inFIG. 5-2, it became apparent that the polishing pad26had the largest abrasion at the location corresponding to the position of the rotational axis of the seasoning plate36. This is because the weight from the ceramic plate32is applied uniformly to the conditioners34, and the contact area between the polishing pad26and the conditioners34becomes larger in the inner circumferential region of the rotating ceramic plate32.

FIG. 6-1shows the shapes of the pad surface of the polishing pad26observed when the polishing pad26is abraded with the use of the seasoning plate36shown inFIG. 5-1.FIG. 6-2shows the GBIR of the surface polished with the polishing pad26ofFIG. 6-1.FIG. 6-3shows the GFLR of the surface polished with the polishing pad26ofFIG. 6-1. The rotation speed of the polishing pad26in the process of abrading the polishing pad26was 45 rpm. In the polishing process, on the other hand, the rotation speed of the polishing pad26and the center roller22before and after abrasion was 21 rpm, and the polishing time was 10 minutes. The polishing pad26having the pad shape shown inFIG. 3-1was used as the polishing pad (the reference polishing pad) before abrasion. As can be seen fromFIG. 6-1, the convex portions of the polishing pad26were flattened, and not only the center region26bbut also the inner circumferential region26aand the outer circumferential region26cwere abraded. As can be seen fromFIG. 6-2, the mean GBIR value of the surface polished with the use of the polishing pad26after the abrasion by the seasoning plate36was higher than the mean GBIR value observed before the abrasion (increased from −6.73 μm to −3.44 μm), and accordingly, the inner-circumferential abrasion tendency of the polished surface was reduced.

However, as can be seen fromFIG. 6-3, the mean value of the GFLR (Global Front Least squares Range) for evaluating the flatness of the polished surface was rather degraded, compared with the mean GFLR value observed before the abrasion, with the reference surface being the virtual polished surface (the best-fit surface) expected to have the lowest flatness of all polished surfaces. The reason for this phenomenon can be considered as follows. The convex portions of the polishing pad26were flattened by abrading the polishing pad26having the convex portions with the use of the seasoning plate36as shown inFIG. 6-1, and the GBIR was improved as the entire flatness became higher. However, as indicated by the arrows27inFIG. 6-1, two noticeable inflection points appeared in the inner circumferential region26aand the outer circumferential region26cof the polishing pad26, and the shapes of the inflection points were transferred onto the polished surface. As a result, the GFLR deteriorated.

FIG. 7shows the pad shapes of the outer circumferential region26cof the polishing pad26ofFIG. 6-1observed where the reference surface is the best-fit surface of the circumferential region26c. As shown inFIG. 7, the outer circumferential region26cis abraded, while maintaining a shape greatly different from the best-fit surface both before and after the abrasion of the polishing pad26. This shape is considered as the main cause of the deterioration of the GFLR.

To eliminate the two inflection points (indicated by the arrows27), the inner circumferential region26aand the outer circumferential region26chaving the inflection points in the polishing pad26were selectively abraded, and the GFLR of the polished surface of the wafer polished by the abraded polishing pad26was measured, as shown inFIG. 8-1. In the process of abrading the polishing pad26, the rotation speed of the polishing pad26was 45 rpm, and the regions having the inflection points in the polishing pad26were abraded. In the polishing process, on the other hand, the rotation speed of the polishing pad26and the center roller22both before and after the abrasion was 21 rpm, and the polishing time was 10 minutes. As can be seen fromFIG. 8-2, there was not a large difference in the mean GFLR value when the inflection point in the inner circumferential region26awas eliminated. However, when the inflection point in the outer circumferential region26cwas eliminated, the mean GFLR value was greatly improved (before the abrasion: 1.04 μm, after the abrasion of the inner circumferential region: 1.11 μm, after the abrasion of the outer circumferential region: 0.44 μm).

In view of the above facts, the inventor invented the seasoning plate10that flattens the entire polishing pad26, and eliminates the inflection points (particularly, the inflection point in the outer circumferential region) as shown inFIGS. 1-1,1-2, and1-3. More specifically, the seasoning plate10is placed on the polishing pad26, and performs seasoning of the polishing pad26by abrading the polishing pad26by the friction caused by the rotation of the polishing pad26. The seasoning plate10includes: the conditioners14for abrading the polishing pad26; the round flexible substrate12having the conditioners14attached to its bottom face; the O-ring16that is placed on the upper face of the flexible substrate12in such a manner as to form a circle concentric with the flexible substrate12; and the weight plate18serving as the weight portion that is placed on the O-ring16and applies weight so as to deform the flexible substrate12.

Since the polishing pad26is abraded in the condition that the conditioners14are attached to the single flexible substrate12, the total contact area between the conditioners14and the center region26bof the polishing pad26becomes larger. Accordingly, the abrasion of the center region26bis also performed efficiently, and the convex portions of the pad surface can be flattened. Thus, the GBIR can be improved. Furthermore, more weight is applied to the portions of the conditioners14overlapping the outer circumferential region of the flexible substrate12, with the conditioners14being attached to the flexible substrate12. Accordingly, the pad-surface inflection points which may appear in the inner circumferential region26aand the outer circumferential region26cof the polishing pad26can be eliminated, and the shape of the entire pad surface is made smooth. In this manner, transfer of the inflection points onto the polished surface can be prevented, and the GFLR can be improved.

The distribution of weight applied to the conditioners14depends on the thickness of the flexible substrate12, the degree of flexibility, and the diameter of the O-ring16. For example, in a case where the thickness of the flexible substrate is small or the degree of flexibility is high, the deformation of the flexible substrate becomes larger. In this case, the weight applied to the conditioners14concentrates on the portion directly below the O-ring16, and the position of the concentric weight concentrating portion varies with the diameter of the O-ring16. In a case where the thickness of the flexible substrate12is large or the degree of flexibility is low, the deformation of the flexible substrate12is smaller. In this case, the weight applied to the conditioners14scatters in conformity with the shape of the concentric circle formed with the O-ring16(or the flexible substrate12), with the portion immediately below the O-ring being the center. Accordingly, the three parameters should be varied so as to adjust the GBIR and GFLR of each polishing object to preferred values.

FIG. 9-1shows the shapes of the pad surface observed when the polishing pad26is abraded with the use of the seasoning plate10according to this embodiment.FIG. 9-2shows the GBIR of the surface polished by the polishing pad26ofFIG. 9-1.FIG. 9-3shows the changes in the GFLR of the surface polished by the polishing pad26ofFIG. 9-1. In the process of abrading the polishing pad26, the rotation speed of the polishing pad26and the center roller22was 45 rpm, and the abrasion was performed for 10 minutes in one case and 20 minutes in another. In the polishing process, on the other hand, the rotation speed of the polishing pad26and the center roller22was 21 rpm, and the polishing time was 10 minutes.

As shown inFIG. 9-1, in the entire pad surface, the convex portions are flattened as in the pad surface shape illustrated inFIG. 6-1. As can be seen fromFIG. 9-1, the abrading performance of the seasoning plate10near the center12bof the flexible substrate12is substantially the same as that of the seasoning plate36even in a case where the conditioners14are attached to the flexible substrate12. Also, since the convex portions in the pad surface are flattened, the tendency represented by the GBIR value also switches from the inner abrasion to the outer abrasion, as the abrading time becomes longer, as can be seen fromFIG. 9-2. Thus, the GBIR is improved. Meanwhile, as can be seen fromFIG. 9-1, where the abrading time in the inner circumferential region26aand the outer circumferential region26cis longer, the above mentioned inflection points disappear. Accordingly, where the abrading time is longer, the GFLR value shown inFIG. 9-3is also improved.

As described above, with the method for seasoning the polishing pad26, the seasoning plate10, and the semiconductor polishing device20according to this embodiment, the variations of abrasion depths in the inner circumferential region26aand the outer circumferential region26cof the polishing pad26can be reduced with simple structures using conventional conditioners, and the abrasion depths in the polishing pad26can be made more uniform. Accordingly, the flatness of the polished surface can be readily maintained by controlling the rotation speed of the polishing pad26. Thus, the life of the polishing pad26in use can be prolonged, and the costs are lowered.

Since this embodiment is not affected by the shape of the polishing pad26before abrasion, this embodiment can be applied to cases where convex portions are already formed in the inner circumferential region26aand the outer circumferential region26cacross the center region26b, and the once-lost control of the flatness of the polished surface through the adjustment of the rotation speed of the polishing pad26can be resumed. In this embodiment, seasoning is performed on the polishing pad to be used for rough polishing as described above. However, this embodiment may also be applied to the seasoning of polishing pads to be used for finishing and polishing pads to be used for CMP. As described so far, this embodiment can provide a polishing pad seasoning method, a seasoning plate, and a semiconductor polishing device, with which appropriate seasoning can be performed at low cost.