Abrading – Precision device or process - or with condition responsive... – With feeding of tool or work holder
Reexamination Certificate
2001-12-27
2004-03-30
Hail, III, Joseph J. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
With feeding of tool or work holder
C451S019000, C451S024000, C451S307000
Reexamination Certificate
active
06712670
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to chemical mechanical planarization (CMP) techniques and, more particularly, to a method for applying downward force on a wafer during CMP and an apparatus for applying a wafer to a polishing surface during a CMP operation.
In the fabrication of semiconductor devices, there is a need to perform chemical mechanical planarization (CMP) operations. 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 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 then, metal CMP operations are performed to remove excess material.
A chemical mechanical planarization (CMP) system is typically utilized to polish a wafer as described above. A CMP system typically includes system components for handling and polishing the surface of a wafer. Such components can be, for example, an orbital polishing pad, or a linear belt polishing pad. The pad itself is typically 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 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. 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. The linear polishing apparatus
10
polishes 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 typically 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, semiconductor materials, etc. Typically, CMP may be utilized to polish the one or more of the layers on the wafer
16
to planarize a surface layer of the wafer
16
.
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
. The rollers 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 polishing head
18
. The wafer
16
is typically held in position by mechanical retaining ring and/or by vacuum. The polishing head
18
positions the wafer atop the polishing belt
12
and moves the wafer
16
down to the polishing belt
12
. The polishing head
18
applies the wafer
16
to the polishing belt
12
with pressure so that the surface of the wafer
16
is polished by a surface of the polishing belt
12
. The polishing head
18
is typically 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 polishing head
18
connected to a spindle
42
. The spindle
42
is attached to a force magnifier
34
that in one end is connected to a hinge
40
and in the other end is connected to an air cylinder
32
. The force magnifier
34
is typically an a machined aluminum arm that acts in a similar manner to a lever so force applied by the air cylinder
32
is magnified onto the spindle
42
. The spindle
42
then pushes down the polishing head
18
which in turn applies pressure to the wafer
16
for polishing action (as shown in FIG.
1
A).
Generally, a range of 3 psi to 10 psi can be applied to the wafer
16
by the spindle drive assembly
30
. Unfortunately, at pressures lower than 3 psi, the by the spindle drive assembly
30
is unable to apply a consistent, controlled pressure. The air cylinder
32
is typically controlled with a pneumatic servo valve that uses feedback from a load cell
36
inside the polishing head
18
. Problematically the weight of the spindle, head, and other hardware is not supported by anything other than the spindle. This makes the application of downward forces lower than the weight attached to the cylinder
32
very unstable. Also, because of the force magnifier
34
, small adjustments in pressure made at the cylinder
32
cause large pressure application changes in the polishing head
18
so control of pressure is very difficult. In certain circumstances, the inability to control low force application prevents a gentle touchdown of the wafer onto the polishing pad. This often occurs because of an inherent overshoot built into the spindle drive assembly
30
for a particular pressure setting. For example, if pressure of 4 psi is desired to be applied to the wafer, a pressure of 5 psi is generally applied to break friction within individual components of the spindle drive assembly
30
and move the spindle. Therefore, low polishing pressure application to the wafer using conventional pressure application systems is very problematic.
Additionally, because of the indirect linkage of air cylinder
32
to the rest of the spindle drive assembly
30
, reduced stability of the polishing head
18
often occurs. Therefore, consistent polishing pressure on a wafer, especially at low pressure levels is often difficult to attain.
Therefore, there is a need for an apparatus that overcomes the problems of the prior art by having a downward force application apparatus that can optimize control of polishing pressure applied by a polishing head to a wafer in CMP systems.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills this need by enabling the optimal control of downward force application in a chemical mechanical planarization (CMP) polishing process. 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 accordance with one aspect of the invention, an apparatus for applying a wafer to a polishing surface during a CMP operation is provided. The apparatus includes a spindle that has an upper end and a lower end. A wafer carrier is coupled to the lower end of the spindle. A linear force generator is disposed at the upper end of the spindle. A load cell is positioned between the linear force generator and the upper end of the spindle. A controller is coupled to the load cell for controlling the force applied by the linear force generator.
In one embodiment, the linear force generator includes a lower plate that is disposed on the load cell and an upper plate supported above the lower plate. The linear force generator also includes a bladder positioned between the lower plate and the upper plate. In another embodiment, a load cell plate is coupled to the upper end of the spindle, and a load cell is disposed on the load cell plate.
In accordance with another aspect of the invention, a method for
de la Llera Anthony
Luong Tony
Nguyen Tuan A.
Pham Xuyen
Siu Andrew
Hail III Joseph J.
Lam Research Corporation
Martine & Penilla LLP
Ojini Anthony
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