Measuring and testing – Instrument proving or calibrating – Dynamometer
Reexamination Certificate
2002-03-27
2004-07-27
Raevis, Robert (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Dynamometer
Reexamination Certificate
active
06766679
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to semiconductor manufacturing equipment, and more specifically to spindle downforce calibration using an internal load cell inside a carrier.
2. Description of the Related Art
Often, in the fabrication of semiconductor devices, there is a need to perform chemical mechanical planarization (CMP) operations. By way of background, integrated circuit devices are in the form of multi-level structures, wherein transistor devices having diffusion regions are formed at the substrate level. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define desired functional devices. In addition, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide.
As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material grows. Without planarization, fabrication of further metallization layers becomes substantially more difficult due to the variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material and metal CMP operations are performed to remove excess material.
Typically, a chemical mechanical planarization (CMP) system is utilized to polish a wafer as described above. A CMP system generally includes system components for handling and polishing the surface of a wafer, such as an orbital polishing pad, or a linear belt polishing pad. The pad itself often is made of a polyurethane material or polyurethane in conjunction with other materials such as, for example a stainless steel belt. In operation, the belt pad is put in motion and a slurry material is applied and spread over the surface of the belt pad. Once the belt pad having slurry on it is moving at a desired rate, the wafer is lowered onto the surface of the belt pad. In this manner, wafer surface that is desired to be planarized is substantially smoothed, much like sandpaper may be used to sand wood. The wafer may then be cleaned in a wafer cleaning system.
FIG. 1A
shows a linear polishing apparatus
10
, which is typically utilized in a CMP system to polish away materials on a surface of a semiconductor wafer
16
. The material being removed may be a substrate material of the wafer
16
or one or more layers formed on the wafer
16
. Such a layer generally includes one or more of any type of material formed or present during a CMP process such as, for example, dielectric materials, silicon nitride, metals (e.g., aluminum and copper), metal alloys, and semiconductor materials.
In operation, the linear polishing apparatus
10
utilizes a polishing belt
12
, which moves linearly in respect to the surface of the wafer
16
. The belt
12
is a continuous belt rotating about rollers
20
, which are typically driven by a motor so that the rotational motion of the rollers
20
causes the polishing belt
12
to be driven in a linear motion
22
with respect to the wafer
16
.
The wafer
16
is held by a wafer carrier
18
, generally using a mechanical retaining ring and/or by vacuum. The wafer carrier
18
positions the wafer atop the polishing belt
12
and moves the wafer
16
down to the polishing belt
12
, applying the wafer
16
to the polishing belt
12
with pressure such that the surface of the wafer
16
is polished by a surface of the polishing belt
12
. Typically, the wafer carrier
18
is part of a spindle drive assembly
30
(shown in
FIG. 1B
) that enables application of polishing pressure to the wafer
16
.
FIG. 1B
shows a conventional spindle drive assembly
30
that may be utilized to apply the wafer
16
to the polishing belt in the CMP apparatus
10
(as shown above in FIG.
1
A). The spindle drive assembly
30
includes the wafer carrier
18
connected to a spindle
42
. The spindle
42
is attached to a force magnifier
34
, which is connected to a hinge
40
and an air cylinder
32
. Typically, the force magnifier
34
is a machined aluminum arm that acts in a manner similar to a lever such that force applied by the air cylinder
32
is magnified onto the spindle
42
. The spindle
42
then pushes down the wafer carrier
18
, known as applying downforce, which in turn applies pressure to the wafer
16
for polishing action (as shown in FIG.
1
A).
During a planarization process, the wafer removal rate profile is highly dependent on the wafer carrier
18
downforce pressure exerted by the spindle
42
. Thus, if the wafer carrier
18
downforce pressure is too high for a particular process, the overall effect of the polishing is diminished. Hence, the downforce pressure exerted by the spindle
42
is generally calibrated prior to use of the CMP system.
FIG. 1C
is diagram showing a prior art spindle force downforce calibration system
50
. As shown in
FIG. 1C
, the spindle force downforce calibration system
50
attaches to the wafer carrier
18
, and includes an alignment plate
54
positioned below a polishing plate
52
, and a load cell holder
56
that holds a button load cell
58
above the polishing belt
12
. In normal operation, the polishing plate
52
is used to hold a wafer during the polishing process. However, during calibration, the alignment plate
54
is positioned below the polishing plate
52
to align placement of the load cell holder
56
. In particular, the alignment plate
54
includes a beveled center
60
, in which the top portion load cell holder
56
is inserted. In this manner, the load cell holder
56
can be positioned in the center of the carrier
18
to equalize the downforce measured.
The load cell holder
56
holds the button load cell
58
, which is used to measure downforce for calibration. As mentioned above, the load cell holder
56
is located above the polishing belt
12
and below the alignment plate
54
. Thus, in operation, the spindle drive assembly
42
applies downward force to the wafer carrier
18
, which in turn transfers the downforce to the button load cell
58
via the alignment plate
54
and the load cell holder
56
. In this manner, the button load cell
58
measures the downforce at the center of the polishing plate
52
. Typically, the button load cell
58
is attached to a hand-held meter, which can be read to determine the measured downward force.
Unfortunately, the prior art spindle force downforce calibration system
50
requires the wafer carrier
18
to be positioned approximately three inches above the polishing belt
12
. Since the wafer carrier
18
is not located at the position of the polishing belt during calibration, the measured downforce will be different than what is actually applied during normal CMP operation. More specifically, linkage is used to apply downforce to the spindle drive assembly
42
. However, the force applied by the linkage, or force amplifier, varies depending on the position of the linkage when the downforce is applied. The linkage has a different position when the wafer carrier
18
is located three inches above the polishing belt
12
than when the wafer carrier
18
is positioned approximately at the same level as the polishing belt
12
. As a result, 20-30 psi calibration errors can occur during calibration using the prior art spindle force downforce calibration system
50
.
In view of the foregoing, there is a need for a CMP calibration system capable of providing accurate calibration results. Hence, the CMP calibration system should measure downforce during calibration at approximately the wafer carrier height used during normal CMP operation.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing a spindle drive downforce calibration apparatus that includes a load cell located within the calibration wafer carrier. In one embodiment, a method is disclosed for spindle downforce calibration. A calibration wafer carrier is provided having a calibration load cell recess. A calibration load cell is positioned within the calibration load cell recess.
Bryand, Jr. Justo
Judd Clayton E.
Lam Research Corporation
Martine & Penilla LLP
Raevis Robert
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