Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2002-07-01
2004-03-09
Wilson, Lee D. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S008000, C451S021000, C451S056000, C451S443000
Reexamination Certificate
active
06702646
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of polishing, in particular chemical mechanical polishing in the manufacture of semiconductor wafers and integrated circuits. More particularly, the invention relates to a method and apparatus for controlling chemical-mechanical polishing processes by monitoring the results and process of polishing plate wear and conditioning.
BACKGROUND OF THE INVENTION
Polishing processes play significant role in modern technologies, in particular in semiconductor fabrication. For example, at certain stages in the fabrication of devices on a substrate, it may become necessary to polish or planarize a surface of the substrate before further processing. Polishing may also be performed with chemically active abrasive slurry, such polishing is commonly known as a chemical mechanical polishing (also called chemical mechanical planarization, or just CMP). In a polishing process, a polishing plate repetitively passes over the surface of the substrate; abrasive particles are either present on the plate or supplied with the slurry. In contrast with mechanical polishing, the CMP slurry provides an increased removal rate of a substrate material and the capability to selectively polish certain films on the substrate.
Chemical mechanical planarization may be used as a preparation step in the fabrication of substrates or semiconductor wafers to provide substantially planar front and backsides thereon. CMP is also used to remove high elevation features and other discontinuities, created on the outermost surface of a substrate during fabrication of a microelectronic circuitry.
The planarization method typically requires that the substrate be mounted in a wafer head or carrier, with the substrate surface to be polished exposed. The substrate supported by the head is then placed against a moving polishing pad mounted on a platen. The head may also move, for example rotate, to provide additional motion between the substrate and the polishing pad. Polishing slurry is supplied onto the pad to provide an abrasive chemical solution at the interface between the pad and the substrate. Pressure is applied on the carrier to effectuate polishing. In some polishing machines the substrate rotates while the polishing pad is stationary, in others the pad moves while the wafer is stationary, and in yet another type both the wafer carrier and the pad move simultaneously. The polishing pad may be pre-soaked and continually re-wet with slurry.
DESCRIPTION OF THE RELATED ART
U.S. Pat. No. 5,597,341 issued on Jan. 28,1997 to Kodera, et al, U.S. Pat. No. 5,234,867 issued on Aug. 10, 1993 to Schultz, et al., and U.S. Pat. No. 5,232,875 issued on Aug. 3, 1993 to Tuttle, et al illustrate several techniques and corresponding types of CMP systems for chemical mechanical planarization of semiconductor wafer surfaces.
One type of CMP systems, used in the apparatuses of the type disclosed in the aforementioned references, is shown schematically in
FIG. 1
a
. In this system a polishing pad
10
a
is mounted on a platen
12
a
, which rotates by means of a first motor
14
a
through a transmission
16
a
. A wafer
20
a
with a front surface
22
a
to be polished is held on a head
24
a
. In the illustrated apparatus, the polishing pad
10
a
has a diameter significantly larger than that of the wafer
20
a
(
FIG. 1
a
). The polishing head
24
a
is rotated by means of a second motor
26
a
through a transmission
28
a
and comprises a retaining ring
30
a
which prevents the wafer from slipping out of the head during polishing. A slurry feeding system
32
a
pours slurry on the top working surface of the pad
10
a.
FIG. 1
b
illustrates another embodiment of the aforementioned known CMP system. In this embodiment, a polishing pad
11
b
is mounted on a platen
12
b
, which is rotated by means of a first motor
14
b
through a transmission
16
b
. A wafer
20
b
with a front surface
22
b
to be polished is held on a head
24
b
. In the illustrated apparatus, the polishing pad
1
b
has a diameter significantly smaller than that of the wafer
20
b
(
FIG. 1
b
). The polishing head
24
b
is rotated by means of a second motor
26
b
through a transmission
28
b
and comprises a retaining ring
30
b
, which prevents the wafer from slipping out of the head during polishing. A slurry feeding system
32
b
pours slurry on the front surface of the wafer
22
b.
In order to provide uniformity of polishing, in the CMP systems of the types shown in
FIGS. 1
a
and
1
b
, the distance between the polishing pad rotational axis and the wafer rotational axis is typically varied in an oscillatory manner. For this purpose, the substrate is repeatedly moved back and forth relative to the polishing pad. In
FIGS. 1
a
and
1
b
the oscillatory movement is shown by arrows
25
a
and
25
b
, respectively. Another type of the CMP system, shown schematically in
FIG. 2
, is disclosed, e.g., in U.S. Pat. No. 5,899,800, issued on May 4, 1999 to Shendon and in U.S. Pat. No. 6,184,139, issued on Feb. 6, 2001 to Adams, et al. In the CMP apparatus of these patents, the lower head comprising a polishing pad
10
c
mounted on a platen
12
c
is driven into orbital movements by means of an orbital drive
34
with a motor
36
, while the carrier
24
c
holding the wafer
20
c
rotates about its central axis by a motor
26
c
via a transmission
28
c
. The pad diameter is slightly larger than the diameter of the wafer
20
c
. Polishing slurry is introduced directly through the openings
38
a
,
38
b
. . .
38
n
in the polishing pad
10
c
with point-of-use mix, which may result in better wafer uniformity and reduced slurry consumption.
Important characteristics of a planarization process in semiconductor wafer fabrication are a wafer material removal rate and uniformity of material removal. There are several factors that may affect these parameters. Since various materials of the wafer, polishing pad, slurry, and retaining ring interact in a course of polishing, a combination of their characteristics and process parameters, such as compression force or pressure, speed, temperature, etc., can provide specific polishing characteristics Typically, the material combination is selected based on a trade off between the polishing rate, which determines in large part the throughput of wafers through the polishing apparatus, and the need to provide a particular desired finish and flatness on the surface of the wafer.
The efficiency of polishing greatly depends on the pad surface conditions and may reduce with time as a polishing pad is contaminated, its pores jammed with various waste, and worn out. Therefore in the course of polishing, the pad surface should be refreshed or “conditioned” after a period of use to provide for both a more uniform polishing rate from wafer to wafer and better planarization uniformity across a single wafer. During the pad conditioning process, a pad conditioner with an abrasive surface is forced to come in contact with the working surface of the pad while both the pad and the conditioner move at pre-determined speeds and pressure. While the operation of conditioning is an effective way of deterring the wear of the polishing pad, the pad requires replacement when either its surface conditions are not recovered by conditioning or its thickness drops below a pre-determined level.
The pad conditioning can be done, for example, with a conditioning device described in U.S. Pat. No. 5,486,131 issued in January 1996 to Cesna, et al. The conditioner has an either circular or ring configuration and is provided with a combination of vertical motion, rotation around a vertical axis, and oscillating horizontal movement.
To ensure good pad flatness during the above conditioning process, the U.S. Pat. No. 5,868,605 issued in February 1999 to Cesna, suggests supplying both pad and conditioner with oscillating radial motions, with a stroke of reciprocation sufficient to have the conditioner extending over the edges of the polishing pad.
Another way of conditioning with optimum pad shape is suggested
Dorfman Vlad
Faynberg Mikhail
Gitis Norm
Meyman Aleksandr
Vinogradov Michael
Nevmet Corporation
Shakeri Hadi
Wilson Lee D.
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