Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
1999-04-30
2001-05-22
Rose, Robert A. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S288000, C451S443000, C451S072000
Reexamination Certificate
active
06234868
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for conditioning polishing pads for polishing semiconductor wafers.
DESCRIPTION OF THE RELATED ART
Chemical mechanical polishing (CMP) is an essential process in the production of integrated circuits (ICs). CMP is used to refine the surfaces of semiconductor wafers during fabrication. This process, known as planarization, serves to remove any excess or unwanted material from the surface of the wafer, and thus allows more circuits to be created on each wafer. The polishing is typically accomplished by applying the semiconductor wafer to a rotating polishing pad. The wafer is typically attached to a stationary shaft which is driven against a rotating polishing platen which has the polishing pad affixed to its upper surface. In alternative configurations, the drive shaft and semiconductor wafer may also be rotated. In most conditioning processes, a slurry (i.e. chemical liquid) is added to the surface of the polishing pad in order to assist in the polishing process. The slurry usually contains a polishing agent, such as alumina or silica, as well as various other chemicals which serve to etch or oxidize specific portions of the wafer during polishing.
A principal problem which occurs during the polishing process is the phenomenon known as “glazing.” Glazing occurs when abrasive particles from the polishing slurry and the semiconductor wafers become embedded in the surface of the polishing pad. Often glazing results in a significant reduction in the efficiency of the polishing pad.
In addition to glazing, the polishing pad also often becomes worn in certain areas due to extended use. This wear also impacts on the effectiveness of the polishing process. Since the slurry is held by small depressions in the surface of the polishing pad, when areas become worn, the slurry is no longer effectively held, and the polishing process suffers.
In order to restore the polishing pad to its optimum condition, various “conditioning” processes are employed in the prior art. Conditioning is a process by which the polishing pad is treated with a conditioning device to increase its lifetime. Most conditioning processes use a conditioning head pressed against the polishing pad to accomplish the conditioning. The conditioning head usually includes an abrasive surface, for example, diamonds embedded in a nickel plating. The abrasive surface of the conditioning head is driven against the polishing pad in much the same way as the semiconductor wafers are during polishing. The conditioning head removes excess particulate material from the surface of the polishing pad and roughens (i.e. places new depressions) in worn areas, thereby restoring the polishing pad to its optimum condition.
There are two basic types of conditioning processes: in-situ and ex-situ. In-situ conditioning processes condition the polishing pad at the same time that wafers are being polished. Essentially, two separate heads, one for polishing and one for conditioning, overlie the polishing pad simultaneously. An ex-situ conditioning process takes place in between wafer polishings. In an ex-situ-process, only one of the conditioning and polishing heads overlies the polishing pad at any one time. Generally, in-situ conditioning processes are favored because valuable polishing time is not wasted on conditioning. However, in-situ processes often experience problems because particulate material removed by the conditioning head often strays onto the polishing portion of the polishing pad, thereby interfering with the polishing process.
One of the main problems experienced by both in-situ and ex-situ conditioning processes is a lack of consistency in the amount of pressure applied to the conditioning head during conditioning. The amount of pressure applied to the conditioning head is directly related to the amount of conditioning which is accomplished. Thus, the more pressure that is applied to the conditioning head, the more vigorous the conditioning process will be, and vice versa. Too much or too little conditioning can result in decreased lifetime for polishing pads. Therefore, there is currently a need for a conditioning process which accurately and efficiently controls the amount of conditioning which the polishing pad experiences.
FIG. 1
shows a prior art conditioning device generally designated by reference numeral
100
. The device
100
is an example of an ex-situ conditioning device, however, the following explanation applies equally as well to an in-situ conditioning device. The device
100
includes a polishing platen
110
, a polishing pad
140
, a conditioning head
130
, conditioner
170
, and a support arm
190
. The conditioning head
130
is supported by a first rotatable shaft
137
, which is rotated about axis A
1
, by first drive motor
180
. The polishing platen
110
is supported by a second rotatable shaft
120
, which is rotated about axis A
2
by second drive motor
150
. The conditioner
170
is held to the conditioning head
130
by a retaining member (not shown), such as bolts, glue, or magnets. Preferably, the conditioner
170
is held to the conditioning head with bolts, so that the conditioner
170
may be easily changed or replaced. The support arm
190
performs a dual function, it serves to rotate the conditioning head
130
onto and off of the polishing pad
140
, and it also serves to force the conditioning head
130
against the polishing pad
140
. Since the device
100
is an ex-situ device, the conditioning head
130
only overlies the polishing pad
140
when conditioning is required. The conditioning head
130
is rotated on and off of the polishing pad
140
by rotation of the support arm
190
about axis A
3
. If the device
100
were in-situ, the conditioning head
130
would overly the polishing pad at all times, even during polishing.
The forcing of the conditioning head
130
against the polishing pad is accomplished by displacing a first shaft portion
192
of the support arm
190
in the vertical direction. Note that the first shaft portion
192
lies inside a second shaft portion
194
of the support arm
190
. The second shaft portion
194
allows the first shaft portion
192
to be displaced within the second shaft portion
194
to thereby force the conditioning head
130
against the polishing pad
140
. A control circuit (not shown) controls the vertical displacement of the first shaft portion
192
in the holder
194
. This displacement of the first shaft portion
192
causes the conditioning head
130
to either be pressed against the polishing pad
140
or removed from it, depending on the direction of displacement. For example, an upward movement of the first shaft portion
192
moves the conditioning head
130
away from the polishing pad
140
, whereas a downward movement moves the conditioning head
130
closer to the polishing pad
140
. The amount of displacement directly controls the amount of conditioning which the polishing pad
140
will experience. Thus, as the conditioning head
130
is pressed more firmly against the polishing pad
140
, more particles are cleared away and more depressions are formed in the polishing pad. In order to optimize the conditioning process, it is necessary to accurately control the force applied to the conditioning head
130
.
SUMMARY OF THE INVENTION
The present invention is a method and apparatus for improving the process for conditioning a polishing pad. A stationary support arm and a force control mechanism accomplish the conditioning. The force control mechanism is attached to the conditioning head and is used to raise and lower the head with respect to the polishing pad. The force control mechanism comprises a force control mechanism, such as a piston or magnet, which accurately controls the amount of force applied to the conditioning head.
The above and other advantages and features of the present invention are better understood from the following detailed description of the preferred embodiments of the invention which is provided in connection with the ac
Easter William Graham
Maze John Albert
Miceli Frank
Duane Morris & Heckscher LLP
Lucent Technologies - Inc.
Rose Robert A.
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