Abrading – Precision device or process - or with condition responsive... – By optical sensor
Reexamination Certificate
2000-02-28
2002-02-19
Hail, III, Joseph J. (Department: 3103)
Abrading
Precision device or process - or with condition responsive...
By optical sensor
C451S041000, C451S182000, C451S258000, C451S285000, C451S287000, C451S298000
Reexamination Certificate
active
06347977
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to chemical mechanical polishing (CMP) systems and techniques for improving the performance of CMP operations.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform chemical mechanical polishing (CMP) operations, buffing and wafer cleaning. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, 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 increases. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to the higher variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material, and then metal CMP operations are performed to remove excess metallization.
FIG. 1A
shows a schematic diagram of a chemical mechanical polishing (CMP) process
10
, consisting of a CMP system
14
, a wafer cleaning system
16
, and post-CMP processing
18
. After a semiconductor wafer
12
undergoes a CMP operation in the CMP system
14
, the semiconductor wafer
12
is cleaned in a wafer cleaning system
16
. The semiconductor wafer
12
then proceeds to post-CMP processing
18
, where the wafer may undergo one of several different fabrication operations, including additional deposition of layers, sputtering, photolithography, and associated etching.
A CMP system
14
typically includes system components for handling and polishing the surface of the wafer
12
. Such components can be, for example, an orbital or rotational polishing pad, or a linear belt polishing pad. The pad itself is typically made of a polyurethane material. In operation, the belt pad is put in motion and then 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. Similarly, in rotational or orbital CMP systems, a polishing pad is located on a rotating planar surface, and slurry is introduced. The wafer, mounted on a polishing carrier is lowered onto the surface of the polishing pad. In this manner, the wafer surface that is desired to be planarized is substantially smoothed. The wafer is then sent to be cleaned in the wafer cleaning system
16
.
With the increasing necessity for multi-layered complex structures fabricated on larger wafer substrates, more accurate measurement and control of the CMP process is required than provided by current technology. The goal of the CMP process should be to maximize the removal rate and uniformity. As is well known, the removal rate can be determined by Preston's Equation: Removal Rate=KpPV, where the removal rate of material in Angstroms/minute is a function of Downforce (P) and Linear Velocity (V), with Kp being the Preston Coefficient, a constant determined by the chemical composition of the slurry, the process temperature, and the pad surface.
Therefore, one way to increase the removal rate can be to apply the wafer against the polishing pad with increased amounts of pressure (e.g., downforce). However, when the wafer is applied to the pad with excessive force, the wafer can suffer in that stress will be transferred to the brittle wafer which could cause the wafer to break, and excessive force can cause non-uniform removal rates. In addition, a high downforce is limited by stall friction produced by high pressure on the surface of the wafer, and by motor torque, Further, it has been shown that increasing downforce can actually decrease both local and global uniformity.
Another way to increase removal rates and uniformity is to increase the velocity of the polishing pad. The increase in velocity can also be done in conjunction with the application of more pressure. The limiting factors for achieving increased linear velocity include carrier size and mass, the larger physical size of the CMP system and motor torque. For example, some belt-type CMP systems can be quite large, thus requiring more torque and power to move the belt. Consequently, linear velocity in conventional CMP systems cannot be efficiently increased.
If linear velocity were somehow increased, a hydroplaning effect could start to occur between the surface of the wafer and the polishing pad. Hydroplaning is believed to occur due to the increased linear velocity of the wafer and the fact that a film of chemical s (e.g., slurry) cover the polishing pad surface.
To illustrate another problem with conventional CMP systems, reference will now be made to
FIGS. 1B-1C
. As is well known, present CMP systems are used to remove metallization material, such as copper, to isolate metal lines in an oxide layer. In
FIG. 1B
, an oxide layer
102
is shown over a substrate
100
. Trenches
102
a
-
102
d
have been etched in the oxide layer
102
that will be used to create metal lines within the oxide layer
102
. Prior to applying the metal layer
104
, a thin barrier or liner layer (not shown) is deposited over the entire surface. As is known, materials such as silicon nitride, titanium itride, and the like are used for the barrier. Then, the metal layer
104
is applied over the oxide layer
102
completely filling the illustrated trenches
102
a
-
102
d
. In
FIG. 1C
, conventional CMP has been performed on the metal layer
104
to remove the excess metal, and barrier, and smooth the surface at the oxide layer
102
such that the trenches
102
a
-
102
d
stay filled with the remaining metal from the metal layer
104
, and running throughout the oxide layer
102
as metal lines.
As shown in
FIG. 1C
, deformities known as “erosion” and “dishing” occur on the planarized surface at points
106
and
108
respectively. In current technology CMP systems, the entire surface of the wafer is always in contact with and polished by the polishing belt or pad and slurry. Because of the differences in hardness of the oxide, the barrier, and the metal layers, rate of removal changes significantly as the layers are processed and the different layers are exposed. The softer metal layer
104
is removed at a higher rate than both the harder barrier and oxide. Once the metal layer is removed in the oxide regions
106
between the metal lines
104
, continued processing can result in the dishing shown in the metal lines at
108
. Continued processing, however, is necessary to remove the barrier layer over the oxide. The process known as “over-polishing” is often needed to compensate for variations in thickness, but too much over-polish can result in erosion or localized thinning of the oxide illustrated at points
106
. As is well known, dishing and erosion
106
can have a negative impact on the performance of a finished integrated circuit fabricated from the wafer.
In view of the foregoing, there is a need for CMP systems that efficiently allow increases in linear velocity and also allow increased amounts of force to be applied against the wafer without the disadvantages of the prior art. The increases in linear velocity and force should be controlled to achieve increased removal rates and uniformity of the planarized surface of the wafer.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing a CMP system that provides increased, uniform, and controllable removal rates. The CMP system allows for significant increases in linear velocity over the prior art without the previously associated detrimental effects of dishing, erosion, and hydroplaning, and can incorporate real-time in-situ monitoring of material removal to provide precise an
Hail III Joseph J.
Lam Research Corporation
Martine & Penilla LLP
McDonald Shantese
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