POLISHING PAD AND POLISHING METHOD

Abstract

According to one embodiment, there is provided a polishing pad having a surface for the polishing processing of a polishing workpiece. Here, the polishing pad is made of a plate-shaped thermal shrinking material, and it has a half-cut portion cut to a particular depth from one principal surface.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-067679, filed on Mar. 23, 2012, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate to a polishing pad and a polishing method.

BACKGROUND

In the manufacturing process of semiconductor devices, as the flattening technology, the chemical-mechanical polishing method (Chemical Mechanical Polishing, to be referred to as CMP) is mainly used. Usually, a groove is processed on the surface of the polishing pad used in the CMP method for feeding and exhausting the slurry to/from the polishing surface.

However, when the polishing pad is worn off due to dressing (conditioning of the polishing pad), the depth of the groove gradually becomes shallower and the shape of the groove changes, so that the polishing characteristics also change. That is, the groove formed on the surface of the polishing pad is a major factor in determining a lifetime of the polishing pad.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view illustrating an example of the constitution of the CMP apparatus for which the polishing pad of the embodiment of the present disclosure is used.

FIGS. 2A and 2B are partial cross-sectional views illustrating an example of the constitution of the polishing pad in the embodiment.

FIG. 3 is a top view illustrating an example of the constitution of the polishing pad in the embodiment.

FIGS. 4A and 4B are schematic cross-sectional views illustrating the state of the polishing pad after a certain time of use.

FIGS. 5A and 5B are schematic partial cross-sectional views illustrating the state of use of the polishing pad after a certain time of use of the polishing pad having a conventional groove structure in a comparative example.

DETAILED DESCRIPTION

In general, according to one embodiment, the polishing pad and polishing method of the embodiment will be explained in detail with reference to attached figures. However, the present disclosure is not limited to the embodiment.

The embodiment has an aim to provide a polishing pad and a polishing method for reducing variation of polishing characteristics even when a polishing pad is polished.

According to the embodiment, there is provided a polishing pad having a polishing surface for polishing a workpiece. The polishing pad is made of a plate-shaped thermal shrinking material, and it has a half-cut portion cut to a particular depth from one principal surface.

FIG. 1 is a schematic side view illustrating an example of the constitution of the CMP apparatus for which the polishing pad of the embodiment is used. FIGS. 2A and 2B include schematic partial cross-sectional views illustrating the constitution of the polishing pad in the embodiment. FIG. 2A shows the normal state and FIG. 2B shows the state in the polishing operation. FIG. 3 is a top view illustrating an example of the constitution of the polishing pad in the embodiment.

The CMP apparatus includes a rotatable polishing table 21, a polishing pad 22 bonded via a bonding layer, not shown in the figure, on the polishing table 21, a polishing head 23 arranged on the polishing pad 22 and that holds a semiconductor substrate or other polishing workpiece 20, a chemical solution feeding nozzle 24 for feeding polishing slurry 241 or other chemical-solution in the polishing operation, and a dresser 25 made of, for example, a diamond disk or the like, arranged above the polishing pad 22 for dressing the polishing pad 22.

The polishing head 23 holds the polishing workpiece 20 by a vacuum chuck holder or similar part so that the surface for polishing faces the polishing pad 22 on the polishing table 21. The polishing head 23 and the dresser 25 have a structure such that they can be rotated in the same plane as the polishing table 21 and, at the same time, they can be driven to move in the direction perpendicular to the surface of the polishing table 21 so that the surface of the polishing head 23 or dresser 25 can make contact with the surface of the polishing pad 22. In addition, although not shown in the figure, a polishing slurry feeding tank is connected with the chemical-solution feeding nozzle 24.

The polishing pad 22 in this embodiment has a half-cut portion 31. Here, the half-cut portion 31 is cut to a particular depth from the surface of the polishing pad 22, and it does not go through to reach the back surface of the polishing pad 22. Here, the half-cut portion 31 differs from the groove in that it does not have a particular width. In the normal state, not in the polishing operation, the two side surfaces with half-cut portion 31 held between them are in contact with each other. As shown in FIG. 3, the half-cut portion 31 is formed in, for example, a lattice shape on the surface of the polishing pad 22. Also, the half-cut portion 31 may be formed in a vortex shape, or concentric circular shape or the like, instead of the lattice shape on the surface of the polishing pad 22. The depth of the half-cut portion should be appropriate to ensure that it does not cut through to reach the bonding layer as the underlying layer of the polishing pad 22.

The polishing pad 22 is made of a material that shrinks under the heat generated in the polishing operation as to be explained later. An example of such a thermal shrinking material is the thermal shrinking polyurethane. Also, the polishing pad 22 may be made of either a foaming material or a non-foaming material.

In the following, a brief account will be given on the CMP processing method using the CMP apparatus. Here, as an example, a semiconductor substrate on which a silicon oxide film is formed will be taken as the polishing workpiece 20 for explanation. In this case, it is supposed that bumps/dips are formed on the surface of the silicon oxide film as the surface for polishing.

Before the polishing operation, the semiconductor substrate is held on the polishing head 23 so that the silicon oxide film faces the polishing pad 22. In addition, a polishing slurry 241 containing, for example, cerium oxide grains and a surfactant is fed from the chemical-solution feeding nozzle 24 onto the polishing pad 22.

As the polishing pad 23 is driven to move in the direction towards the polishing table 21, the semiconductor substrate is pressed on the surface of the polishing pad 22 and, while the polishing table 21 and the polishing pad 23 are driven to rotate, the surface of the semiconductor substrate is subjected to a polishing operation. After the start of the polishing operation, while the polishing pad 22 and the polishing workpiece 20 are in contact with each other, they are driven to rotate in the in-plane direction, so that friction leads to a rise in the temperature near the surface of the polishing pad 22. Depending on the types of polishing workpiece 20 and the polishing slurry 241 as well as the polishing conditions, the temperature of the surface of the polishing pad 22 may rise to about 60 to 80° C. in the polishing operation.

As shown in FIG. 2B, because the polishing pad 22 is made of thermal shrinking polyurethane or other thermal shrinking material, due to the rise in the temperature on the surface of the polishing pad 22 in the polishing operation, the polishing pad 22 shrinks in the in-plane direction and in the direction perpendicular to the polishing surface on the surface of the polishing pad 22. Also, as the position moves deeper from the surface of the polishing pad 22, the temperature of the polishing pad 22 decreases, so that the shrinkage degree of the thermal shrinking material becomes smaller. As a result, at a particular depth d1 position from the surface of the polishing pad 22 where no thermal shrinking takes place, the side surfaces that hold the half-cut portion 31 between them are in contact with each other. As the position becomes shallower (as the position moves towards the surface), the shrinkage degree in the in-plane direction increases, so that the side surfaces of the half-cut portion 31 are separated from each other. Consequently, a groove 32 is formed at the half-cut portion 31. The polishing slurry 241 fed from the chemical solution feeding nozzle 24 is then fed into the formed groove 32, and the polishing slurry 241 is exhausted from the groove 32 as the polishing operation is executed.

With the progress of polishing, cerium oxide grains generated in the polishing operation and the coagulated polishing grains formed due to coagulation by the surfactant as well as polishing-generated chaff, etc., are accumulated in a large quantity on the polishing pad 22 and the groove 32. As a result, clogging of the polishing pad 22 takes place, so that the polishing speed falls. At this point, in order to eliminate this problem, a dressing treatment should be carried out.

In the dressing treatment, the surface of the dresser 25 is pressed on the surface of the polishing pad 22 and, as the polishing table 21 and the dresser 25 are driven to rotate, the surface of the polishing pad 22 is polished. As a result, while the coagulated polishing grains and polishing-generated chaff on the surface of the polishing pad 22 are removed, dressing is carried out in this treatment. As explained above, in the CMP treatment, the polishing treatment and dressing treatment are carried out.

FIGS. 4A and 4B include schematic cross-sectional views illustrating the state of use after a certain time of use from the start of use of the polishing pad. FIG. 4A is a schematic cross-sectional view illustrating the initial state before use. FIG. 4B is a schematic cross-sectional view illustrating the state during the polishing treatment after a certain time of polishing. After use of the polishing pad 22, the polishing pad 22 with the initial state shown in FIG. 4A becomes the state shown in FIG. 4B, with a reduced thickness of the polishing pad 22 due to the thermal shrinking and dressing treatment. When the polishing treatment is carried out in such a state, as explained above, due to the heat generated in the polishing, the portion of the polishing pad 22 from the top surface to a particular depth is deformed due to thermal shrinking, and groove 32 is formed on the half-cut portion 31. The depth d2 of the groove 32 formed in this case is similar to the depth dl of the groove 32 formed using the polishing pad 22 in the initial state shown in FIG. 2B. The shape and size of the groove 32 as shown in FIG. 4B are similar to those shown in FIG. 2B. This remains true and is independent of the thickness of the polishing pad 22 until the position of height d1 from the end point 311 of the half-cut portion 31 (d2) becomes the top surface of the polishing pad 22.

In this way, by using the thermal shrinking material, it is possible to ensure that the shape and size of the groove 32 formed in the half-cut portion 31 are kept the same even when the thickness of the polishing pad 22 changes. As a result, it is possible to ensure a constant quantity of the polishing slurry 241 fed to the groove 32 in the polishing operation, and it is possible to ensure stable polishing characteristics independent of the remaining thickness of the polishing pad 22.

FIGS. 5A and 5B include partial cross-sectional views schematically illustrating the state of variation over time of the conventional polishing pad as a comparative example due to the polishing operation. FIG. 5A is a partial cross-sectional view illustrating the state of the polishing pad in the initial state. FIG. 5B is a partial cross-sectional view illustrating the state of the polishing pad after use for a certain time. As shown in FIG. 5A, for the conventional polishing pad 22, a groove 35 with a width of W (>0) and depth of d3 is formed on it. As shown in FIG. 5B, after use for a certain time, because the polishing pad 22 is worn off due to the dressing treatment or the like, the groove 35 on polishing pad 22 has a width of W and a depth of d4.

When the polishing pad 22 is in use, the polishing slurry 241 enters the groove 35 while the polishing operation is carried out. However, the groove 35 shown in FIG. 5A is deeper than the groove 35 shown in FIG. 5B, so that the polishing slurry 241 is fed into the groove 35. As a result, in the polishing operation, the quantity of the polishing slurry 241 changes corresponding to the difference in depth (d3−d4) of the two grooves 35, so that a significant difference takes place in the polishing characteristics between them. That is, because the polishing characteristics depend on the thickness of the polishing pad 22, it is necessary to carry out the polishing operation with the thickness of the polishing pad 22 taken into consideration.

On the other hand, for the polishing pad 22 in the embodiment, the shape and size of the groove 32 formed for the half-cut portion 31 in the polishing operation are kept constant and independent of the thickness of the polishing pad 22. Consequently, the quantity of the polishing slurry 241 enclosed in the groove 32 during the polishing operation is kept constant. As a result, there is no difference in the polishing characteristics depending on the thickness of the polishing pad 22, and it is possible to realize stable polishing characteristics over the entire lifetime.

Also, it is possible to carryout the polishing operation under conditions without considering the thickness of the polishing pad 22. That is, there is no need to determine the optimum polishing conditions for each thickness value of the polishing pad 22. More specifically, for the conventional polishing pad 22 shown in FIGS. 5A and 5B, the lifetime of the polishing pad 22 is taken as the time when the depth of the groove 35 reaches a certain level, so that the lifetime of the polishing pad 22 depends on the polishing characteristics that vary depending on the depth and shape of the groove 35. On the other hand, according to the present embodiment, the position of the end point 311 of the half-cut portion 31 is selected as the depth without going through the polishing pad 22. Consequently, compared with the case of the polishing pad 22 having the groove 35 shown in FIGS. 5A and 5B, it is possible to prolong the lifetime. This is an effect of the present embodiment. During the period until the lifetime of the polishing pad 22 is reached, the polishing rate and evenness can be kept constant independent of the thickness of the polishing pad 22. This is another effect of the present embodiment.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein maybe made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

Claims

1. A polishing pad comprising: a surface for polishing processing of a workpiece, anda half-cut portion cut to a particular depth from one principal surface, whereinthe polishing pad is made of a plate-shaped thermal shrinking material.

2. The polishing pad according to claim 1, wherein the thermal shrinking material is a thermal shrinking polyurethane.

3. The polishing pad according to claim 1, wherein the half-cut portion has a lattice shape, vortex shape, or concentric circular shape.

4. A polishing apparatus comprising: a rotatable polishing table;a polishing pad provided on the polishing table;a feeding nozzle configured to feed a slurry to the polishing pad;a polishing head that can hold a workpiece;

5. The polishing apparatus according to claim 4, wherein the thermal shrinking material is a thermal shrinking polyurethane.

6. The polishing apparatus according to claim 4, wherein the half-cut portion has a lattice shape, vortex shape, or concentric circular shape.

7. A polishing method comprising: feeding slurry to a principal surface of a plate-shaped polishing pad while the polishing pad is driven to rotate in the in-plane direction, the polishing pad being made of a thermal shrinking material and having a half-cut portion cut to a particular depth from one principal surface, andpolishing a surface of a workpiece with being in contact with the principal surface of the polishing pad, shrinking the polishing pad in the region from the surface of the principal surface of the polishing pad to a particular depth, thereby forming a groove with a certain shape and a certain size on the contact portion of the half-cut portion with the polishing workpiece.

8. The polishing method according to claim 7, wherein the thermal shrinking material is a thermal shrinking polyurethane.

9. The polishing method according to claim 7, wherein the half-cut portion has a lattice shape, vortex shape, or concentric circular shape.