Abrading – Precision device or process - or with condition responsive... – By optical sensor
Reexamination Certificate
2001-03-29
2003-09-02
Eley, Timothy V. (Department: 3724)
Abrading
Precision device or process - or with condition responsive...
By optical sensor
C451S009000, C451S010000, C451S041000
Reexamination Certificate
active
06612902
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to chemical mechanical polishing apparatuses, and more particularly to methods and apparatuses for end point triggering with integrated steering in a chemical mechanical polishing system.
2. Description of the Related Art
In the prior art, chemical mechanical polishing (CMP) systems typically implement belt, orbital, or brush stations in which belts, pads, or brushes are used to scrub, buff, and polish a wafer. To facilitate and enhance the CMP operation, slurry is used. Slurry generally is introduced onto a moving preparation surface, e.g., belt, pad, brush, and the like, and distributed over the preparation surface as well as the surface of the semiconductor wafer being buffed, polished, or otherwise prepared by the CMP process. The distribution is generally accomplished by a combination of the movement of the preparation surface, the movement of the semiconductor wafer and the friction created between the semiconductor wafer and the preparation surface. In addition, end point detection mechanisms are used to determine when to end the CMP process. The end point detection mechanism senses the wafer layers through an end point window when triggered by an end point trigger mechanism.
FIG. 1A
is diagram showing a prior art CMP system
100
a
. The CMP system
100
a
includes a polishing belt
101
and rollers
102
, which physically rotate the belt and provide belt steering. During the CMP process, a wafer is positioned at wafer position
106
, generally via a carrier having a retainer ring that holds the wafer in position during polishing. Beneath the wafer position
106
is a platen
104
for wafer support during polishing. To facilitate end point detection, an end point window
108
is disposed within the polishing belt
101
.
Further disposed within the polishing belt
101
is a trigger slot
110
, which is used in conjunction with an end point trigger mechanism. In operation, the end point trigger mechanism detects the trigger slot
110
whenever the trigger slot
110
passes over the end point trigger mechanism. Then, as will be described in greater detail with respect to
FIG. 2
, the end point trigger mechanism provides a signal to a CMP controller, which controls end point detection. In this manner, the prior art CMP system
100
a
can synchronize end point detection sensing with the end point window
108
in the polishing belt
101
. To help maintain the centralized position of the end point window
108
with respect to the wafer position
106
and platen
104
, limit sensors are used.
FIG. 1B
is a diagram showing a top view of a prior art CMP system
100
b
. The prior art CMP system
100
b
includes rollers
102
, and a polishing belt
101
having an end point window
108
and a trigger slot
110
to facilitate end point detection control. The end point detection mechanism performs best when the end point window
108
is centered above the end point detection sensor. Thus, limit sensors
112
are used to detect the lateral position of the polishing belt
101
during operation. When the polishing belt
101
moves off center, the limit sensors detect the position of the polishing belt
101
and provide the positional information to a belt steering mechanism. The belt steering mechanism then adjusts the lateral position of the polishing belt
101
using the rollers
102
.
FIG. 2
is a diagram showing a conventional end point trigger mechanism
200
. The end point trigger mechanism
200
includes a polishing belt
101
having an end point window
108
and a trigger slot
110
. Further included are a trigger sensor
206
, which detects light from a light source
204
, and a CMP controller, which receives information from the trigger sensor
206
and an end point detection sensor
208
. The end point detection sensor
208
senses the current layer status of the wafer
202
in a CMP process.
Generally, the trigger sensor
206
is an optical sensor that detects the presence of the trigger slot
110
by the intensity of the light detected from the light source
204
. Specifically, the polishing belt
101
blocks light from the light source
204
, except when the trigger slot is
110
present above the trigger sensor
206
. Thus, when the trigger sensor
206
detects a light intensity above a predefined threshold, a message is sent to the CMP controller
212
that the trigger slot
110
is presently positioned above the trigger sensor
206
. Since the trigger slot
110
is positioned a know distance from the end point window
108
and the belt speed is known, the appropriate delay can be calculated that will trigger end point data acquisition when the end point window
108
is aligned with the platen window
210
of the platen
104
.
As previously mentioned, belt steering is provided using limit sensors. End point signal strength in part depends upon both the alignment of the end point window
108
above the platen window
210
in the direction transverse to belt travel and the alignment in the belt travel direction. However, conventional CMP systems
100
a
and
100
b
use two separate, unrelated methods to position the end point window
108
and synchronize the end point data acquisition. Specifically, the alignment in the direction transverse to belt travel is determined using the limit sensors, while the alignment in the belt travel direction is determined by the synchronization of the end point window
108
with the platen window
210
using the trigger sensor
206
.
Using two independent methods to align the end point window
108
with the platen window
210
causes problems in both the reliability of the end point detection system and the system set up time. Thus, there is a need for reliable systems and methods for improved end point trigger mechanisms that improve end point detection reliability and reduce system setup time.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing a sensor array that determines the longitudinal and transverse position of the end point window, as well as the belt speed of the polishing belt. In one embodiment, a method for end point triggering in a chemical mechanical polishing process is disclosed. A sensor array is positioned beneath a polishing belt having an end point window. The polishing belt is then rotated during the CMP process, and a transverse position of the end point window is determined based on a portion of the sensor array covered by a particular portion of the polishing belt. The particular portion of the polishing belt can be the end point window, a trigger slot, or a portion of the polishing belt covered by a reflective material. Further, the sensor array can optionally be a charged coupled device (CCD), or a linear array of sensors. In operation, the positional information is determined based on which sensors are covered by the particular portion of the polishing belt. The positional information is then communicated to a belt steering system, which corrects the transverse position of the end point window based on which sensors are covered by the particular portion of the polishing belt. The time to begin end point detection is based on a longitudinal position of the end point window, and the speed of the belt can be determined based on intensities sensed by the sensor array.
In another embodiment, an apparatus for end point triggering in a chemical mechanical polishing process is disclosed. The apparatus includes a sensor array that is disposed beneath a polishing belt, which includes an end point window. The apparatus determines a position of the end point window based on a portion of the sensor array covered by a particular portion of the polishing belt. As above, the particular portion of the polishing belt can be the end point window, a trigger slot, or a portion of the polishing belt covered by a reflective material, and the sensor array can optionally be a charged coupled device (CCD), or a linear array of sensors.
A system for end point triggering in a chemical mechanical polishing pr
Boyd John M.
Litvak Herbert E.
Eley Timothy V.
Lam Research Corporation
Martine & Penilla LLP
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