Abrading – Precision device or process - or with condition responsive... – With indicating
Reexamination Certificate
2001-03-30
2003-05-13
Hail, III, Joseph J. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
With indicating
C451S041000, C451S288000
Reexamination Certificate
active
06561870
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to chemical mechanical planarization (CMP) systems, and more particularly, to systems having force applying air platens.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform Chemical Mechanical Planarization (CMP) operations, including polishing, 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.
In the prior art, CMP systems typically implement belt, orbital, or brush stations in which belts, pads, or brushes are used to scrub, buff, and polish one or both sides of a wafer. Slurry is used to facilitate and enhance the CMP operation. Slurry is most usually 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.
FIG. 1
illustrates an exemplary prior art CMP system
10
. The CMP system
10
in
FIG. 1
is a belt-type system, so designated because the preparation surface is an endless belt-type polishing pad
18
mounted on two drums
24
which drive the pad in a rotational motion as indicated by belt rotation directional arrows
26
. A wafer
12
is mounted on a carrier
14
. The carrier
14
is rotated in direction
16
, which can be either clockwise or counterclockwise. The rotating wafer
12
is then applied against the polishing pad
18
with a force F to accomplish a CMP process. Some CMP processes require significant force F to be applied and monitored. A platen
22
is provided to stabilize the polishing pad
18
and to provide a support onto which to apply the wafer
12
. The platen
22
is designed with an air bearing
23
, which is designed to supply a constant flow of air during movement of the polishing pad
18
. The constant flow of air therefore provides a consistent cushion over which the polishing pad
18
can traverse. To facilitate polishing, slurry
28
composed of an aqueous solution such as NH
4
OH or DI containing dispersed abrasive particles is introduced upstream of the wafer
12
.
Typically, a load cell (LC) is integrated as part of the carrier
14
to enable monitoring of the pressure being applied to the wafer during processing. In practice, the carrier
14
is lowered onto the polishing pad
18
while the wafer is rotated in the direction
16
. In addition to being lowered, the load cell (LC) is designed to provide pressure data to monitoring electronics. If more or less pressure is needed for a particular process, the spindle is instructed to make the pressure adjustment. Accordingly, not only is the spindle designed to move up and down, rotate at a particular rate, but also continuously adjust the force on the wafer (in the form of pressure) as transmitted by the carrier
14
to achieve the appropriate CMP parameters.
Because the carrier
14
is designed to place a force onto a moving polishing pad
18
, frictional forces will build at the spindle so as to generate mechanical hysteresis. These frictional forces are known to reduce an actuator's (which is designed to apply a force to the carrier
14
) ability to maintain a constant force during small amplitude variations in carrier
14
vertical position during polishing. The challenge of maintaining a constant force during precision polishing operations therefore complicates the design of the carrier
14
and its accompanying electronics and controls. In some cases, even very expensive an complex controls are unable to ensure a uniform application of force since the carrier, which is measuring the forces, is continuously under frictional stress from the moving polishing pad
18
.
In view of the foregoing, a need exists for a chemical mechanical planarization system that can provide a stable and accurate force to a substrate being planarized.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing a chemical mechanical planarization system that has an adjustable platen. The adjustable platen is designed to apply a force to an underside of the polishing pad during operation, while the carrier is simply lowered into position over the polishing pad to achieve the appropriate planarization result. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a chemical mechanical planarization (CMP) system having a polishing pad, a wafer carrier, and an adjustable platen is disclosed. The adjustable platen includes a platen body and an air bearing that is integrated in the platen body for applying air pressure to an underside of the polishing pad. A set of bearings are connected to the platen body to enable movement of the platen body closer and further from the underside of the polishing pad. A load cell is connected to the platen body, and the load cell is configured to output a load signal that is indicative of a force being applied to the underside of the polishing pad. An air supply for applying air flow to the air bearing is also provided. The air flow is adjustable in response to changes in the force being applied to the underside of the polishing pad.
In another embodiment, an adjustable platen is disclosed. The adjustable platen includes a platen body having a top region and a bottom region. The platen body is oriented under a linear polishing pad. An air bearing is integrated with the platen body at the top region, and the air bearing is configured to apply an air pressure to an underside of the linear polishing pad. A set of bearings are connected to the bottom region of the platen body to enable controlled movement of the top region of the platen body closer or further from the underside of the linear polishing pad depending on the applied air pressure. The applied air pressure is configured to exert a controllable force to the underside of the linear polishing pad.
In yet another embodiment, another platen is disclosed. The platen includes a platen body having a top region and a bottom region. The platen body is positioned under a linear polishing pad of a chemical mechanical polishing (CMP) system, and the CMP system is designed to receive a wafer to be polished on a top surface of the linear polishing pad when positioned for processing by a spindle and carrier of the CMP system. An air bearing is coupled with the platen body at the top region, and the air bearing is configured to deliver an air flow to an underside of the linear polishing pad. A set of linear bearings are coupled to the bottom region of the platen body to enable controlled vertical movement of the platen body closer and further from the underside of the linear polishing pad. The vertical movement of the platen body is determined by the air flow, and the air
Owczarz Aleksander A.
Saldana Miguel A.
Hail III Joseph J.
Lam Research Corporation
Martine & Penilla LLP
Thomas David B.
LandOfFree
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