Replaceable shielding apparatus

Details Replaceable shielding apparatus Replaceable shielding apparatus

2002-07-16

2003-11-04

Edwards, Laura (Department: 1734)

Coating apparatus

Gas or vapor deposition

Having means to expose a portion of a substrate to coating...

C118S503000, C118S504000, C118S505000

Reexamination Certificate

active

06641672

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 replaceable shield with comparable weight as the semiconductor wafer for allowing the replacement of the shield in the same way as the replacement of the semiconductor wafer.
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
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
1
also 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.
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 replaceable shielding apparatus is provided. The apparatus includes a replaceable shield of comparable weight as the wafer, thus allowing the replacement of the shield in the same way as the replacement of the wafer. With this replaceable shielding apparatus, the system no longer needs to be shut down for shield replacement. The shield replacement can be performed at every wafer, or at every 25 wafers, or one a day, or one a week, depend on the degradation of the shield ring due to material deposited at the shield ring edge.
The apparatus for replaceably shielding a portion of a workpiece in a processing system comprises:
a) a workpiece support for supporting the workpiece within the system;
b) a replaceable shield of comparable weight as the workpiece for allowing replacement of the shield in the same way as the replacement of the workpiece, the shield 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;
c) a moving means for engaging the shield with the portion of the workpiece.
The apparatus includes a workpiece support to support the workpiece, a replaceable shield ring of comparable weight as the workpiece to permit the use of workpiece replacement mechanism for replacing the shield ring, and a moving means for engaging the shield with the workpiece. The workpiece replacement mechanism allows the workpiece to be replaced without the need to shut down the system, thus by using the workpiece replacement mechanism to replace the shield ring, the system will not need to be shut down for shield ring replacement service. The moving means could be permanently connected to the workpiece support for moving the workpiece support to engage the shield with the workpiece. The moving means could be connected to the shield for moving the shield to engage the shield with the workpiece. In this case, when the shield is engaged with the workpiece, the moving means could be disconnected from the shield.
The present invention further provides a shield restraint clamp for holding the shield against the portion of the workpiece. In the applications that the workpiece is lightweight, such as that of a silicon wafer, the shield ring could benefit from a shield restr

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