Polishing method

Details Polishing method Polishing method

2002-12-30

2004-12-07

Shakeri, Hadi (Department: 3723)

Abrading

Abrading process

Glass or stone abrading

C451S067000, C451S057000, C451S287000

Reexamination Certificate

active

06827633

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polishing method, and more particularly to a polishing method of polishing a workpiece such as a semiconductor wafer with a fixed abrasive.
2. Description of the Related Art
As semiconductor devices become more highly integrated in recent years, circuit interconnections have become finer and distance between those circuit interconnections becomes smaller. In case of photolithography which can form interconnections that are at most 0.5 &mgr;m wide, it is required that surfaces on which pattern images are to be focused by a stepper should be as flat as possible because a depth of focus of an optical system is relatively small. A polishing apparatus for performing chemical mechanical polishing (CMP) has been used for planarizing a semiconductor wafer.
This type of chemical mechanical polishing (CMP) apparatus comprises a polishing table having a polishing pad attached thereon, and a top ring for holding a workpiece, to be polished, such as a semiconductor wafer. The workpiece is disposed between the polishing pad and the top ring and pressed against the polishing pad under a certain pressure by the top ring while the polishing table and the top ring are being rotated. The workpiece is polished to a flat mirror finish while a polishing liquid (slurry) is being supplied onto the polishing pad.
When the aforementioned chemical mechanical polishing process is continuously performed, polishing particles or polishing wastes are attached to the polishing pad, resulting in a change in properties of the polishing pad and a deterioration in polishing performance. Therefore, if an identical polishing pad is repeatedly used for polishing semiconductor wafers, problems such as lowered polishing rate and uneven polishing are caused. In order to overcome such problems, conditioning called dressing is performed before, after or during polishing of a semiconductor wafer to regenerate the polishing pad.
In a chemical mechanical polishing process using a polishing liquid as described above, a workpiece is polished while a polishing liquid containing a large amount of abrasive particles is being supplied onto a relatively soft polishing pad. Therefore, a problem of pattern dependence arises. Pattern dependence means that gentle irregularities are formed on a surface of a semiconductor wafer after a polishing process due to irregularities on the surface of the semiconductor wafer that existed before the polishing process, thus making it difficult to planarize the surface of the semiconductor wafer to a completely flat surface. Specifically, a polishing rate is higher in an area where irregularities have small pitches (a density of irregularities is large) and is lower in an area where irregularities have large pitches (a density of irregularities is small), and existence of areas of the higher polishing rate and areas of the lower polishing rate causes gentle irregularities to be formed on the surface of the semiconductor wafer. Further, during the polishing process using the polishing pad, since not only convexities but also concavities of the irregularities on the surface of semiconductor wafer are polished, it is difficult to stop the polishing process when the convexities of the irregularities are polished to a flat surface.
It has also been practiced to polish a semiconductor wafer with use of a fixed abrasive (grindstone) which comprises abrasive particles of cerium oxide (CeO
2
) or the like fixed by a binder such as phenolic resin. A polishing process utilizing the fixed abrasive is advantageous in that polishing material, i.e., the fixed abrasive, is harder than a polishing pad used in a conventional CMP process, and tends to polish convexities of the irregularities more than concavities thereof, for thereby achieving a higher absolute level of planarity. Depending on composition of the fixed abrasive, the fixed abrasive provides a self-stop function which considerably lowers a polishing rate and practically stops a polishing process when the convexities of the irregularities are polished to a flat surface. The polishing process utilizing the fixed abrasive is also advantageous in that environmental load can be reduced because of no use of a suspension liquid (slurry) containing a large amount of abrasive particles.
However, when a dressing process is performed on the aforementioned fixed abrasive, massive particles (masses of polishing particles) tend to be produced on a surface of the fixed abrasive. The massive particles may enter a boundary between the semiconductor wafer and the fixed abrasive to cause scratches to be produced on a surface of the semiconductor wafer. After the semiconductor wafer is polished with the fixed abrasive, abrasive particles contained in the fixed abrasive are attached to the surface of the semiconductor wafer. Therefore, it is necessary to prevent the semiconductor wafer from being contaminated by the abrasive particles.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above drawbacks. It is therefore an object of the present invention to provide a polishing method which can effectively remove massive abrasive particles produced on a surface of a fixed abrasive, by performing a dressing process, to prevent scratches from being produced on a surface of a workpiece, and can remove abrasive particles attached to a surface of a workpiece after a polishing process to prevent the workpiece from being contaminated.
According to a first aspect of the present invention, there is provided a method comprising: polishing a workpiece by pressing the workpiece against a fixed abrasive and bringing the workpiece into sliding contact with the fixed abrasive; dressing a surface of the fixed abrasive so as to generate free abrasive particles thereon; and ejecting (or atomizing) a liquid or a gas, composed of a mixture of liquid or inert gas and pure water or chemical liquid, onto the surface of the fixed abrasive during or after the dressing of the surface of the fixed abrasive.
As described above, when the dressing process is performed on the fixed abrasive, massive particles (masses of polishing particles) tend to be produced on the surface of the fixed abrasive. According to the present invention, atomization is performed on the surface of the fixed abrasive during the dressing process or immediately after the dressing process. Therefore, even if massive particles, which cause scratches on a surface of the wafer, are produced on the surface of the fixed abrasive by the dressing process, the atomization can remove the massive particles from the surface of the fixed abrasive to prevent the workpiece from being scratched.
It is free fine abrasive particles present on the surface of the fixed abrasive that contribute to a polishing process of the workpiece. These free fine abrasive particles are unlikely to be removed by atomization. Therefore, while massive particles are removed as described above, the free fine abrasive particles which contribute to a polishing rate are not removed, and the polishing rate is not affected by atomization. However, if pressure of an inert gas is higher than 0.5 MPa, then the fine abrasive particles are likely to be removed to thereby lower the polishing rate. Therefore, it is desirable that a flow rate of the liquid is within a range of from 200 to 5000 cm
3
/min, and pressure of the inert gas is within a range of from 0.05 to 0.5 MPa. More preferably, the flow rate of the liquid is about 1000 cm
3
/min, and the pressure of the inert gas is about 0.15 MPa.
Such atomization may be performed in either case of an in-situ dressing process in which a dressing process is performed during a polishing process of a workpiece, or an ex-situ dressing process in which a dressing process is performed when the workpiece is not polished. The atomization should preferably be performed during the dressing process. Particularly, in the case of the in-situ dressing process, it is necessary to perform the atomization during the dressing process.
The

Affiliated with

Also associated with

Rating

Polishing method does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Polishing method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polishing method will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3301088