Electric heating – Metal heating – By arc
Reexamination Certificate
2002-12-02
2004-09-21
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121710, C219S121720
Reexamination Certificate
active
06794605
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polishing pad used in a chemical mechanical polishing process, and more particularly to a method for forming micro-holes, perforations, or grooves on a polishing pad by a laser.
BACKGROUND ART
Generally, chemical mechanical polishing (CMP) is a high precision/mirrored surface polishing method used to obtain global planarization in a semiconductor device manufacturing process. In accordance with such CMP, a slurry is supplied between a polishing pad and a wafer to be polished, so as to chemically etch the surface of the wafer. Using the polishing pad, the etched surface of the wafer is mechanically polished.
Referring to
FIG. 1
, a typical CMP machine, which is denoted by the reference numeral
1
, is schematically illustrated. Also, a CMP method using the CMP machine
1
is schematically illustrated in FIG.
2
. The CMP method includes a chemical etching reaction process and a mechanical polishing process, which are conducted using a polishing pad
10
included in the CMP machine
1
. The chemical etching reaction is carried out by a slurry
42
. That is, the slurry
42
serves to chemically react with the surface of a wafer
30
to be polished, thereby making it possible for the mechanical polishing process, following the chemical etching reaction, to be easily carried out. In the mechanical polishing process, the polishing pad
10
, which is fixedly mounted on a platen
20
, rotates. The wafer
30
, which is firmly held by a retainer ring
32
, rotates while oscillating. A Slurry containing abrasive particles is supplied to the polishing pad
10
by a slurry supply means
40
. The supplied slurry is introduced between the polishing pad
10
and the wafer
30
. The introduced abrasive particles come into frictional contact with the wafer
30
by virtue of a relative rotating speed difference between the polishing pad
10
and the wafer
30
, so that they conduct mechanical polishing. The slurry
42
is a colloidal liquid containing abrasive particles having a grain size of nanometers. This slurry
42
is spread on the polishing pad
10
during the polishing process. As the polishing pad
10
rotates during the polishing process, the slurry
42
supplied to the polishing pad
10
is outwardly discharged from the periphery of the polishing pad
10
due to a centrifugal force caused by the rotation of the polishing pad
10
. In order to achieve an enhanced polishing efficiency, many abrasive particles should remain for a desirable lengthy period of time on the upper surface of the polishing pad
10
so that they participate in the polishing of the wafer. That is, the polishing pad
10
should make the slurry
42
be held on the surface thereof for as long a period of time as possible.
In order to make the slurry be held on the polishing pad for a long period of time, there may be used a method of forming spherical microcells having a size of micrometers (Em) or a method of forming perforations or grooves at the surface of the polishing pad. Such microcells, perforations and grooves act to control the flow and distribution of the slurry continuously supplied during the polishing process.
Conventionally, the formation of microcells at the polishing pad is achieved using a physical method or a chemical method. As the physical method, there is a method in which hollow microelements each having a cavity are incorporated in a polymeric matrix to form microcells. As the chemical method, there is a foaming method in which bubbles are chemically formed to form microcells.
The incorporation of microelements in a polymeric matrix is achieved by impregnating a large amount of microelements each having a cavity into a polymeric matrix in such a fashion that the microelements are uniformly distributed in the polymeric matrix, thereby forming microcells. The polymeric matrix is prepared by mixing a curing agent with a resin such as urethane, polyester, fluorinated hydrocarbon, or a mixture thereof. For the microelements, inorganic salt, sugar, water soluble gum, or resin is mainly used. Such microelements are made of polyvinylalcohol, pectin, polyvinyl pyrrolidone, polyethylene glycol, polyurethane or a combination thereof. Such microelements have an average diameter of about 150 Em. The microelements are uniformly distributed over the polymeric matrix in accordance with a high shear mixing process, so that they form uniform microcells. Referring to
FIG. 3
, microcells formed using the cavity bodies are illustrated. The pad formed with microcells in the above mentioned manner is subsequently cut into pieces each having a desired thickness to obtain a polishing pad. In each cut piece, microcells randomly distributed in the pad are opened at the cut surfaces of the cut piece, so that they are exposed in the form of a circular or oval cross section at the cut surfaces of the cut piece. The sizes and positions of the micro-cell cross sections exposed at the polishing surface of each polishing pad are random. Such random size and position of the exposed microcell cross sections serves to degrade a desired uniformity among polishing pads.
In accordance with the chemical method in which cells are formed using a foaming process, a polymeric matrix is formed by mixing a curing agent with a liquid-phase polyurethane forming substance having a low boiling point. Water or liquefied gas, which directly takes part in a chemical reaction to generate gas, is also used as a foaming agent, thereby producing bubbles to form cells in the polymeric matrix. The production of bubbles is achieved by way of a nucleation caused by a high shear mixing operation. A surfactant, which serves to achieve a reduction in surface tension, is also used to adjust the size of microcells, thereby achieving a desired uniformity of micro-cells. Microcells formed using the foaming process are shown in FIG.
4
. Where cells are formed in accordance with the foaming process, however, there are problems in that the cells are too large to be applied to a CMP pad, that those cells have a non-uniform distribution, and that there is no method capable of adjusting the size and distribution of the cells.
The microcells formed using microelements each having a cavity or a foaming process have a spherical structure having a circular or oval cross-sectional shape. Due to such a shape, the microcells have a cross section varying in the thickness direction of the polishing pad. For this reason, the cross section of each microcell exposed at the polishing surface of the polishing pad is varied as the polishing pad is abraded during a polishing process. In other words, circular or oval microcells exposed at the polishing surface of the polishing pad are gradually reduced in diameter as the polishing process proceeds, and finally disappear. Eventually, microcells existing below the surface of the polishing pad without being exposed, are newly exposed at the polishing surface of the polishing pad.
Thus, the cross section of each microcell exposed at the polishing surface of the polishing pad is varied as the polishing pad varies in thickness during the polishing process. For this reason, there is a problem in that the polishing rate is non-uniform.
In order to form perforations or grooves at the polishing surface of the polishing pad, a mechanical machining method has been used which uses a cutting or milling process.
Referring to
FIG. 5
a,
a cutter
70
for forming grooves is illustrated. When a polishing pad is machined using the cutter
70
mounted to a tool die on a lathe under the condition in which the polishing pad is rotated, grooves are formed on the upper surface of the polishing pad in the form of concentric circles, as shown in
FIG. 5
b.
FIG. 5
c
is a cross-sectional view taken along the line A—A of
FIG. 6
b.
Referring to
FIG. 6
b,
an exemplary form of grooves formed using the cutter is illustrated. In
FIG. 6
b,
the grooves are denoted by the reference numeral
75
. An example of grooves having the form of concentric circles is disclosed in U.S. Pat. No. 5,984,769.
Referring t
Hwang In-Ju
Kim Jae-seok
Kwon Tae-Kyoung
Park Inha
Abelman ,Frayne & Schwab
Heinrich Samuel M.
SKC Co., LTD
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