Abrading – Accessory – Dressing
Reexamination Certificate
2000-05-17
2003-08-26
Hail, III, Joseph J. (Department: 3723)
Abrading
Accessory
Dressing
C451S056000, C451S444000
Reexamination Certificate
active
06609962
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dressing apparatus for dressing a polishing surface of a polishing table used for polishing a workpiece in a polishing apparatus, and a polishing apparatus having such dressing apparatus for polishing a workpiece such as a semiconductor wafer to a flat mirror finish.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnection is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 &mgr;m wide, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small.
It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening the surfaces of semiconductor wafers is to polish them with a polishing apparatus for performing Chemical Mechanical Polishing (CMP).
Conventionally, as shown in
FIG. 43
, such a polishing apparatus has a polishing table
102
having a polishing cloth (polishing pad)
100
attached to the upper surface thereof, and a top ring
104
for holding a substrate W such as a semiconductor wafer and pressing the substrate W against the polishing cloth
100
on the polishing table
102
. A polishing liquid containing abrasive particles is supplied from a nozzle
106
onto the polishing cloth
100
and retained on the polishing cloth
100
. The polishing cloth
100
on the polishing table
102
constitutes a polishing surface. During operation, the top ring
104
exerts a certain pressure, and the surface of the substrate W held against the polishing surface of the polishing table
102
is therefore polished to a flat mirror finish while the top ring
104
and the polishing table
102
are rotating. The polishing liquid comprises abrasive particles such as silica particles, and chemical solution such as alkali solution in which the abrasive particles are suspended. Thus, the substrates W is chemically and mechanically polished by a combination of a mechanical polishing action of abrasive particles in the polishing liquid and a chemical polishing action of chemical solution in the polishing liquid.
When the polishing process is finished, the polishing capability of the polishing cloth
100
is gradually deteriorated due to a deposition of the abrasive particles and ground-off particles removed from the substrate, and due to changes in the characteristics of the surface of the polishing cloth. Therefore, if the same polishing cloth is used to repeatedly polish the substrates W, the polishing rate of the polishing apparatus is lowered, and the polished substrates tend to suffer polishing irregularities. Therefore, it has been customary to condition the polishing cloth according to a process called “dressing” for recovering the surface of the polishing cloth before, or after, or during polishing.
In order to dress the surface of the polishing cloth
100
which has been deteriorated by polishing, a dressing apparatus
108
having a dressing surface is provided adjacent to the polishing table
102
. In operation, the dressing surface of the dressing apparatus
108
is pressed against the polishing surface of the polishing table
102
, and the dressing surface and the polishing table
102
are rotated relatively to each other for thereby bringing the dressing surface in sliding contact with the polishing surface. Thus, the polishing liquid and the ground-off particles attached to the polishing surface are removed, and planalization and regeneration of the polishing surface are conducted.
In order to primarily remove the polishing liquid and the ground-off particles from the polishing surface, the dressing apparatus
108
having a dressing surface composed of a nylon brush is mainly used. In order to primarily planalize the polishing surface by scraping off the polishing surface slightly, the dressing apparatus
108
having a diamond dresser is mainly used. The uniformity of the polishing surface which has been dressed affects greatly polishing precision of the workpiece.
However, the above-mentioned polishing apparatus has the following problems:
The first problem is that in case of polishing a substrate by a polishing table which rotates on its own axis, there is no relative movement between the polishing surface and the substrate on the rotation center of the polishing table, and hence the substrate is polished on an area of the polishing surface away from the rotation center of the polishing table. Therefore, the diameter of the polishing table
102
should be at least two times the diameter of the substrate W. Thus, the size of the polishing apparatus becomes large, and a large installation space of the polishing apparatus is required and the cost of facilities is high. This drawback is becoming significant with increasing diameter of the substrate W.
The second problem is presented by the polishing cloth
100
made of material having elasticity such as urethane. In general, a device pattern on the upper surface of the semiconductor wafer (substrate) W has various irregularities having various dimensions and steps, and is composed of different material. When the semiconductor wafer W having step-like irregularities is planarized by the polishing cloth
100
having elasticity, not only raised regions but also depressed regions are polished, and hence a large amount of material is removed from the semiconductor wafer and a long period of time is required until the semiconductor wafer is planarized. Thus, the operation cost in the polishing process is increased and irregularities of the polished surface of the semiconductor wafer are difficult to be eliminated, with the result that a high flatness of the polished surface cannot be obtained.
Further, regions on which microscopic irregularities are concentrated are polished at a high polishing rate, and regions on which macroscopic irregularities exist are polished at a low polishing rate. Thus, a large undulation is formed on the polished surface of the semiconductor wafer.
The third problem is presented by operating cost in the polishing process and environmental pollution. In order to polish the semiconductor wafer to a high degree of flatness, a polishing liquid needs to be supplied abundantly onto the polishing cloth
100
. However, the supplied polishing liquid is discharged from the polishing cloth
100
at a high rate without being used in an actual polishing process. This leads to a high operating cost in the polishing process because the polishing liquid is expensive. Further, since the polishing liquid contains a large amount of abrasive particles such as silica particles, and may contain chemicals such as acids or alkalis to thus form slurry-like material, it is necessary to treat waste liquid discharged from the polishing process for thereby preventing environmental pollution. This also leads to a high operating cost in the polishing process.
In order to solve the first problem, it is conceivable that the polishing apparatus incorporates the polishing table
102
which makes a circulative translational motion (scroll motion) along a circle having a certain radius. In this case, every point on the polishing surface of the polishing table makes the same motion, and hence the diameter of the polishing surface on the polishing table may be equal to the dimension obtained by adding two times radius of gyration of the polishing table
102
to the diameter of the semiconductor wafer (substrate).
Thus, the polishing apparatus may be small in size and the installation space of the polishing apparatus may be reduced to lower the overall cost including manufacturing cost of the polishing apparatus, operating cost in the plant and cost of equipment.
In order to solve the second and thir
Nabeya Osamu
Takada Nobuyuki
Togawa Tetsuji
Wakabayashi Satoshi
Yamaguchi Kuniaki
Ebara Corporation
Hail III Joseph J.
Thomas David B.
Wenderoth , Lind & Ponack, L.L.P.
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