Semiconductor device manufacturing: process – With measuring or testing
Reexamination Certificate
1999-03-29
2001-08-21
Chaudhuri, Olik (Department: 2814)
Semiconductor device manufacturing: process
With measuring or testing
C118S721000, C257S797000, C438S401000
Reexamination Certificate
active
06277658
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a monitor wafer and method used to monitor the use of clamp ring shielding tabs to preserve alignment marks by shielding the alignment marks during deposition of material on a wafer.
(2) Description of the Related Art
The preservation of alignment marks after the deposition of layers of material on a wafer is of primary importance in photolithographic processing of integrated circuit wafers. One method used to preserve the alignment marks is to place shielding tabs on the clamp rings used to hold the wafer in place during material deposition. The effectiveness of the shielding tabs depends on the location of the shielding tabs when material is deposited, and continual monitoring of this location is important.
U.S. Pat. No. 5,456,756 to Ramaswami et al. and U.S. Pat. No. 5,614,446 to Ramaswami et al. describes the use of shielding tabs on the clamp ring used to hold wafers in place during material deposition to shield the alignment marks during material deposition. This shielding prevents material from being deposited over the alignment marks and obscuring the alignment marks.
U.S. Pat. No. 5,320,728 to Tepman describes a planar magnetron sputtering source used to produce a uniform coating of material during material deposition on a wafer.
SUMMARY OF THE INVENTION
FIG. 1
shows a top view of an integrated circuit wafer
10
having two alignment marks
12
and an alignment notch
14
.
FIG. 2
shows a top view of a clamping ring
16
used to hold the wafer in place during material deposition.
FIG. 2
shows the shielding tabs
18
which prevent material from being deposited on the alignment marks.
FIG. 3
shows the clamping ring
16
assembled in place with the wafer
10
. The shielding tabs are located directly over the alignment marks on the wafer and prevent material from being deposited on the alignment marks.
The shielding tabs are an effective means to preserve the alignment marks during material deposition steps but problems can arise if the clamping ring is not properly aligned to the wafer so that the shielding tabs are not properly aligned to the alignment marks. This can be a particular problem when robotic equipment is used to align the clamping ring to the wafer. Many wafers can be processed before the problem is detected.
It is a principle objective of this invention to provide a method of monitoring the alignment of the shielding tabs to the alignment marks.
This objective is achieved using a monitor wafer, which is an oxide wafer having monitor marks formed thereon. The monitor wafer has the same size and shape as the product wafers and the monitor marks are located so that the centers of the monitor marks are in the same position on the oxide wafer as the centers of the alignment marks on the product wafers. The monitor marks are configured so that the distance from the center of the monitor marks can be readily determined by means of visual observation without the use of measuring equipment.
Periodically, such as after a fixed number of product wafers or after preventive maintenance on the equipment, an oxide wafer is processed through the step of material deposition. The same processing steps and equipment used for the product wafers are used for the oxide wafer. After the clamping ring is removed the monitor marks are observed to determine the shortest distance between the center of the monitor marks and the edge of the deposited material. If this distance is greater than a critical distance processing of product wafers continues. If the distance is not greater than a critical distance corrective action must be taken.
REFERENCES:
patent: 4592308 (1986-06-01), Shih et al.
patent: 4599970 (1986-07-01), Peterson
patent: 5118742 (1992-06-01), Burkhardt et al.
patent: 5320728 (1994-06-01), Tepman
patent: 5456756 (1995-10-01), Ramaswami et al.
patent: 5525840 (1996-06-01), Tominaga
patent: 5614446 (1997-03-01), Ramaswami et al.
patent: 5877036 (1999-03-01), Kawai
patent: 6120607 (2000-09-01), Taravade
Chen Jeng-Horng
Jeng Shwangming
Yu Chen-Hua
Ackerman Stephen B.
Chaudhuri Olik
Pizarro-Crespo Marcos D.
Prescott Larry J.
Saile George O.
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