Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
2001-05-09
2003-09-30
Nguyen, George (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
Reexamination Certificate
active
06626734
ABSTRACT:
TECHNICAL FIELD
The present invention relates to methods and devices for the wireless transfer of measurements made during chemical-mechanical planarization of semiconductor wafers.
BACKGROUND OF THE INVENTION
Chemical-mechanical planarization (“CMP”) processes remove material from the surface of a semiconductor wafer in the production of integrated circuits.
FIG. 1
schematically illustrates a CMP machine
10
with a platen
20
, a wafer carrier
30
, a polishing pad
27
, and a planarizing liquid
28
on the polishing pad
27
. The polishing pad
27
may be a conventional polishing pad made from a continuous phase matrix material (e.g., polyurethane), or it may be a new generation fixed abrasive polishing pad made from abrasive particles fixedly dispersed in a suspension medium. The planarizing liquid
28
may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the wafer, or the planarizing liquid
28
may be a planarizing solution without abrasive particles that contains only chemicals to etch and/or oxidize the surface of the wafer. In most CMP applications, conventional CMP slurries are used on conventional polishing pads, and planarizing solutions without abrasive particles are used on fixed abrasive polishing pads.
The CMP machine
10
also has an underpad
25
attached to an upper surface
22
of the platen
20
and the lower surface of the polishing pad
27
. In one type of CMP machine, a drive assembly
26
rotates the platen
20
as indicated by arrow A. In another type of CMP machine, the drive assembly
26
reciprocates the platen
20
back and forth as indicated by arrow B. Since the polishing pad
27
is attached to the underpad
25
, the polishing pad
27
moves with the platen
20
.
The wafer carrier
30
has a lower surface
33
to which a wafer
12
may be attached, or the wafer
12
may be attached to a resilient pad
34
positioned between the wafer
12
and the lower surface
33
. The wafer carrier
30
may be a weighted, free-floating wafer carrier, or an actuator assembly
40
may be attached to the wafer carrier to impart axial and/or rotational motion (indicated by arrows C and D, respectively).
To planarize the wafer
12
with the CMP machine
10
, the wafer carrier
30
presses the wafer
12
face-downward against the polishing pad
27
. While the face of the wafer
12
presses against the polishing pad
27
, at least one of the platen
20
or the wafer carrier
30
moves relative to the other to move the wafer
12
across the planarizing surface
29
. As the face of the wafer
12
moves across the planarizing surface
29
, the polishing pad
27
and the planarizing liquid
28
continually remove material from the face of the wafer
12
.
CMP processes must consistently and accurately produce a uniform, planar surface on the wafer to enable precise circuit and device patterns to be formed with photolithography techniques. As the density of integrated circuits increases, it is often necessary to accurately focus the critical dimensions of the photo-patterns to within a tolerance of approximately 0.1 &mgr;m. Focusing photo-patterns of such small tolerances, however, is difficult when the planarized surface of the wafer is not uniformly planar. Thus, CMP processes must create a highly uniform, planar surface.
One problem with CMP processing is that the planarized surface of the wafer may not be sufficiently uniform across the whole surface of the wafer. The uniformity of the planarized surface is a function of several variables, including the pressure between the wafer and the planarizing surface, the temperature of the wafer and/or the planarizing surface, and the temperature and pH of the planarizing liquid. One conventional approach to addressing this problem has been to measure some or all of the above variables and adjust the CMP processing conditions to improve the uniformity of the wafers. This approach has created additional problems. For example, if the measurements are made while the CMP machine is stationary, they may not be representative of the actual conditions present during planarization. On the other hand, if sensors are placed on the wafer carrier to make measurements during planarization, mechanical means, such as slip rings and the like may be required to transmit electrical signals from the moving sensors to a stationary display.
One conventional approach for obtaining in situ measurements is to use remote sensing means. For example, an infrared gun may be used to measure the temperature of the wafer during planarization. This approach suffers from several drawbacks. One drawback is that the temperature readings obtained from the infrared gun may be distorted by the presence of the planarizing liquid. A second drawback is that remote sensing means may not be readily available for some types of sensors, for example, pressure transducers. Accordingly, it may be difficult to determine the pressure between the wafer and the polishing pad during planarization.
One conventional approach for obtaining in situ pressure measurements is to place the pressure transducer on a mechanical linkage between the wafer carrier and a fixed reference point. This approach may suffer from still further drawbacks. For example, the weight of the mechanical linkage may distort the pressure measurement, and the linkage itself may have such a high inertia that it is unable to respond quickly to sudden pressure changes.
Still a further drawback with the foregoing conventional approaches is that each approach may require that a sensor and associated peripheral hardware be installed on a large number of CMP machines, although the planarizing characteristics may need to be monitored only periodically. As a result, the cost for sensors, peripheral hardware, and maintenance may be higher than is necessary.
In the competitive semiconductor industry, it is also desirable to maximize the throughput of finished wafers. One factor that affects the throughput of CMP processing is the ability to accurately stop planarizing a given wafer or type of wafers at a desired endpoint. To determine whether a wafer is at its desired endpoint, conventional CMP processes typically stop planarizing the wafer and measure the change in thickness of the wafer with an interferometer or other distance measuring device. If the wafer is under-planarized, CMP processing is resumed and the wafer is periodically measured until the wafer reaches its desired endpoint. If the wafer is over-planarized, the wafer may be partially or fully damaged. The throughput of finished wafers is accordingly greatly affected by the ability to accurately and quickly determine the endpoint of individual wafers and/or types of wafer.
SUMMARY OF THE INVENTION
The present invention is directed toward a method and apparatus for the wireless transfer of measurements made during chemical-mechanical planarization of a semiconductor substrate with a planarizing device. The planarizing device may have a support, a platen assembly connected to the support, and a carrier movable relative to the platen assembly and the support to remove material from a semiconductor substrate positioned between the carrier and the platen assembly. In one embodiment, the apparatus may comprise a sensor connected to the platen assembly, the carrier, or the semiconductor substrate. The sensor generates a signal corresponding to a value of a selected property of the planarizing device or the semiconductor substrate. For example, the property may be a force exerted against the semiconductor substrate by the carrier, a temperature or resistance of the semiconductor substrate, or the pH of planarizing liquid surrounding the semiconductor substrate. The apparatus may further include a display spaced apart from the sensor and a wireless communication link coupled between the sensor and the display to transmit the signal from the sensor to the display. The wireless communication link may include an infrared, radio, or acoustic transmitter and receiver, or a pair of inductors.
In one embodiment, the signal may be
Dorsey & Whitney LLP
Micro)n Technology, Inc.
Nguyen George
LandOfFree
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