Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
2000-06-07
2001-04-24
Bueker, Richard (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
Reexamination Certificate
active
06221166
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to apparatus for processing of a semiconductor wafer, and more particularly to an edge exclusion apparatus employing a multi-thermal zone shield to provide a multi-zone temperature profile for the shield while shielding a portion of a hot workpiece in a high temperature processing system.
BACKGROUND OF THE INVENTION
During the deposition of materials on a semiconductor wafer, it is desirable to exclude the materials from depositing on the edge of the front surface, the end edges and the backside of the wafer. This is important when the wafer requires surface treatment to improve the adhesion of the deposited material as in the case of tungsten deposition. The wafer surface needs to be coated with a adhesion promoter material such as titanium tungsten (TiW), or titanium nitride (TiN) before the deposition of tungsten to ensure proper adhesion. When tungsten is deposited on the front edge, end edges or backside of the wafer where there is no TiW or TiN, the deposited tungsten does not adhere properly and flakes off as particles. The generation of particles such as these could be damaging to subsequent wafer processing. Edge and backside exclusion is also of particular importance when the deposited materials requires a diffusion barrier layer to prevent the deposited materials from reaching the silicon wafer, creating device degradation. For example, copper is deposited on a diffusion barrier layer such as TiN, tantalum nitride, tungsten nitride. Without the diffusion barrier layer, copper could migrate to the silicon area and degrade the device performance. Deposition of copper on the backside, end edges and front edge where there is no diffusion barrier material severely affects the device properties.
FIG. 1
shows a prior art edge exclusion apparatus employing purging gas to prevent edge and backside deposition. Deposition precursor enters the inlet
20
, and deposits on the wafer
10
. The inlet
20
could be a showerhead, providing precursor flow
16
to the wafer
10
at a more uniform distribution. Purging gas
15
enters the gap between the wafer holder
30
and the blocker
24
to prevent material deposition at the wafer
10
edge and backside. Precursor flow
16
ff continues to
26
and purging gas
15
continues to
25
to reach the exhaust. The major drawback of this prior art apparatus is the high purging gas required to prevent edge and backside deposition, typically in the range of liter per minute flow. Therefore this apparatus is not suitable for system using low precursor flow.
Another prior art apparatus is U.S. Pat. No. 4,932,358 of Studley et al. Studley et al. disclosed a seal ring which presses down against a wafer on a CVD chuck continuously around the outer periphery of the wafer, and with sufficient force to hold the backside of the wafer against the chuck. This apparatus requires a complicated mounting mechanism to move the seal ring in and out of clamping engagement with the wafer and to maintain alignment between the seal ring and the wafer. Furthermore, the seal ring can only be as wide as the diameter of the chuck.
FIG. 2
shows a prior art apparatus from U.S. Pat. No. 5,851,299 of Cheng et al. Cheng et al. disclosed a shield ring
50
normally rests on a ring support
72
. The shield ring
50
engages the front side edge of the wafer
10
when the wafer support
40
is raised into the contact position by the susceptor lift
46
. The wafer edge and backside is shielded from the precursor flow from the showerhead
20
. Cheng et al. also disclosed an additional purging gas flow
1
retained in the cavity between the wafer support
40
, the wafer
10
and the shield ring
50
. The purging gas exhausts through the gap
2
between the ring support
72
and the shield ring
50
, and combines with the precursor exhaust
3
to reach the vacuum pump.
As with the other prior art, the major drawback of this shield ring is that eventually there will be some deposition at the edge of the shield ring at the locations where the shield ring contacts the wafer. This gap between the shield ring and the wafer caused by material deposit will be widen quickly with time due to more and more material deposition. This process causes the shield ring to lose contact with the wafer and thus no longer perform the shielding action. The apparatus will need to shut down, the chamber vented, and the shield ring manually replaced. Then the chamber will be pump down and the system needs conditioning for process qualification before running again. This causes a significant lost in productivity.
The purging gas is helpful in reducing the built up of material deposit at the shield ring edge. However in prior art Cheng et al. apparatus, as seen in
FIG. 2
, the purging gas escapes easily through the big gap between the shield ring
50
and the ring support
72
. In Cheng et al. apparatus, this gap is required for proper shielding of the wafer. The minimum gap size is probably 0.1″ to allow adequate separation between the shield ring and the wafer for the removal of the wafer. Assuming a 10″ diameter for the shield ring for the processing of a 8″ wafer, the purging gas area is 0.1×10, translated into an equivalent diameter D of 1.1″. The 1.1″ diameter opening would requires a very high flow rate to retain the purging gas at the connection of the wafer and the shield ring to prevent material deposition there, especially when the typical inlet of the purging gas is only 0.25″ in diameter.
One major draw back of the prior art apparatus is the uniform temperature profile of the shield ring in high temperature processing systems. In these systems, the wafer is heated for the process reaction to take place, but it is desirable to have the shield ring cooler than the wafer to prevent reaction at the shield ring. Using high thermal conductivity material will raise the temperature of the shield ring through the transfer of thermal energy from the heated wafer. Using low thermal conductivity material will lower the temperature of the shield ring, but the wafer temperature will no longer be uniform because of the heat loss at the contact area with the cool shield ring. Using a high thermal reflectivity material will solve the problem because all the heat will be reflected back, and the shield will be cool without draining the thermal energy from the wafer edge. However, there is currently no effective high thermal reflectivity material available.
It would be advantageous to develop a shielding apparatus that has variable temperature profile.
It would be advantageous to develop a shielding apparatus that do not cause the heat loss at the wafer edge.
It would be advantageous to develop a shielding apparatus that reduces the down time of the system.
It would be advantageous to develop an apparatus with smaller purging gas escape flow.
SUMMARY OF THE INVENTION
Accordingly, a multi-thermal zone shielding apparatus is provided. The apparatus includes a shield with multiple zones having different thermal property. In the shield area to be in contact with the workpiece for shielding purpose, the shield material has low heat transmitivity property to retain heat in the workpiece. In the rest of the shield area, the shield material has high heat transmitivity property to prevent the shield from absorbing the heat.
The multi-thermal zone shielding apparatus for shielding a portion of a hot workpiece in a high temperature processing system while keeping the workpiece temperature hot at the shielded area and maintaining the rest of the shield cooler comprises:
a) a heater means for heating the workpiece within the system;
b) a multi-thermal zone shield for engaging a portion of the workpiece and shielding the engaged portion of the workpiece during processing thereof to prevent processing on the engaged portion of the workpiece, the multithermal zone shield comprising
a low thermal transmitivity section in the portion of the shield to be engaged and shielding the workpiece, the low transmitivity section pr
Bercaw Craig Alan
Nguyen Tue
Bueker Richard
Fieler Erin
Simplus Systems Corporation
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