Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
1999-06-01
2002-07-30
Hail, III, Joseph J. (Department: 3729)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S006000, C451S008000, C451S041000, C451S285000, C451S287000, C451S288000, 36
Reexamination Certificate
active
06425801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus of monitoring a polishing process of a semiconductor wafer, which are suitably applied to the well-known Chemical Mechanical Polishing (CMP) process, a method of detecting an endpoint of the polishing process, and a polishing machine equipped with the monitoring apparatus.
2. Description of the Prior Art
To form wiring or interconnecting lines, contact plugs penetrating via holes, and so on, for electronic devices or elements formed on a semiconductor wafer, conventionally, the so-called CMP process has been used. In this case, typically, a dielectric layer is formed on or over the entire wafer to cover the electronic devices or elements and then, a metal layer is formed to overlay the whole dielectric layer. Subsequently, an upper, unnecessary part of the metal layer is globally polished away by a polishing machine until the remaining metal layer has a desired pattern designed for the wiring lines, contact plugs, and so on.
It is important for the CMP process to be monitored for the purpose of detecting an optimum endpoint for the desired pattern at which the polishing operation is stopped. If the degree of polishing is insufficient, in other words, the polishing operation is stopped prematurely, the metal layer tends to be partially left on the underlying dielectric layer, causing electrical short circuit between the wiring lines and/or contact plugs. On the other hand, if the degree of polishing is excessive, in other words, the polishing operation is stopped belatedly, the remaining metal layer tends to have less cross-sections than those desired at the respective wiring lines and contact plugs.
The Japanese Non-Examined Patent Publication No. 7-235520 published in September 1995, which corresponds to the U.S. Pat. No. 5,433,651 issued on July 1995, discloses a technique for monitoring the polishing process of a semiconductor wafer.
FIG. 1
shows schematically a prior art polishing process monitoring apparatus using the technique disclosed in the Japanese Non-Examined Patent Publication No. 7-235520.
In
FIG. 1
, the prior-art in-situ monitoring apparatus is equipped with a circular polishing table
102
rotatable in a horizontal plane, a polishing pad
103
placed on the surface of the table
102
, a wafer holder
104
rotatable in a horizontal plane, a laser
106
as a light source for emitting a light beam
105
, a photodiode
140
for receiving a reflected light beam
107
, and a monitoring means
113
. The table
102
has a viewing aperture
138
with a specific size, which allows the incident light beam
105
from the laser
106
to reach a semiconductor wafer or workpiece
101
held onto the bottom surface of the wafer holder
104
. A view window
138
a
is fixed to the aperture
138
to prevent a polishing slurry
116
from flowing out through the aperture
138
while allowing the light beams
105
and
107
to penetrate.
The light beam
105
emitted from the laser
106
is irradiated to the polishing surface of the wafer
101
, on which the beam
105
forms a beam spot having a specific diameter. The incident light beam
105
is reflected by the polishing surface of the wafer
101
, forming the reflected light beam
107
. The reflected light beam
107
is received by the photodiode
140
.
The photodiode
140
measures the amount of the reflected light beam
107
and outputs an electric signal s to the monitoring means
113
according to the amount thus measured. The monitoring means
113
samples the electric signal s at specific time intervals to generate an electric detection signal through specific signal processing. Then, the monitoring means
113
displays a time-dependent change of the detection signal on a screen (not shown), in which the ordinate axis is defined as the amount of the detection signal and the abscissa axis as the polishing time.
Next, the operation of the prior-art in-situ monitoring apparatus shown in
FIG. 1
is explained below.
The incident light beam
105
emitted from the laser
106
is irradiated through the viewing apertures
138
and
139
and the view window
138
a
to the polishing surface of the semiconductor wafer
101
held by the wafer holder
104
. The irradiated light beam
105
is reflected by the polishing surface of the wafer
101
, generating the reflected light beam
107
. The reflected light beam
107
travels through the viewing apertures
138
and
139
and the view window
138
a
to be received by the photodiode
140
, in which the amount of the beam
107
is measured and the electric detection signal s is generated according to the amount thus measured. The detection signal s from the photodiode is sampled and averaged in the monitoring means
113
, displaying the time-dependent change of the signal s, i.e., the reflected light beam
107
. The reflected light beam
107
is generated by “specular reflection” of the incident light beam
105
.
During the time period from the start of polishing to the exposure of the underlying dielectric layer, the strength of the detection signal s, i.e., the amount of the reflected light beam
107
, is kept approximately constant. This is because almost all the incident light beam
105
is specularly reflected by the metal layer having a comparatively high reflectance. When the underlying dielectric layer begins to be exposed from the metal layer due to the progressing polishing operation, a part of the incident light beam
105
is specularly reflected by the remaining metal layer and received by the photodiode
140
. Thereafter, the amount of the reflected light beam
107
thus received gradually decreases with the progressing polishing operation because of the decreasing surface area of the remaining metal layer. At the same time as this, another part of the incident light beam
105
is specularly reflected by the structure formed below the dielectric layer and received by the photodiode
140
. The remainder of the incident light beam
105
is scattered and/or diffracted by the remaining metal layer (i.e., the wiring lines and/or contact plugs) or the structure formed below the dielectric layer, which is not received by the photodiode
140
. As a result, after the time the underlying dielectric layer begins to be exposed from the metal layer, the strength of the detection signal s, i.e., the amount of the reflected light beam
107
, decreases gradually with time.
At the time when the polishing process reaches a desired endpoint, the dielectric layer is exposed from the remaining metal layer forming the desired wiring lines and/or contact plugs. At this stage, the amount of the reflected light beam
107
has a minimum value. After the time corresponding to the endpoint, the surface-area reduction of the metal layer is substantially zero even if the polishing process further progresses. Thus, the amount of the reflected light beam
107
has substantially a same value as that at the endpoint. In other words, the strength of the detection signal s is kept substantially constant after the corresponding time to the endpoint.
With the prior-art in-situ monitoring apparatus shown in
FIG. 1
, however, there is a problem that the polishing process may be unable to be monitored correctly according to the material of the semiconductor wafer
101
, the thickness of the layered structure on the wafer
101
, or the pattern (i.e., geometry or closeness/coarseness) of the wiring lines and/or contact plugs. This problem is due to the following reason.
For example, if the wafer
101
is made of a specific semiconductor material, the reflectance value of the metal layer may have a small difference from that of the underlying layered structure of the wafer
101
. In this case, even if the surface area of the metal layer is decreased according to progress of the polishing process, the amount of the reflected light beam
107
(i.e., the strength of the detection signal s) varies only within a narrow range due to the small difference in reflectance. As a result, the endpoint of the polishing
Hayashi Yoshihiro
Mitsuhashi Hideo
Ohkawa Katsuhisa
Onodera Takahiro
Takeishi Akira
Hail III Joseph J.
McDonald Shantse
Michael Best & Friedrich LLC
NEC Corporation
Whitesel J. Warren
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