Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
1999-01-19
2002-05-28
Johns, Andrew W. (Department: 2621)
Image analysis
Applications
Manufacturing or product inspection
C382S145000
Reexamination Certificate
active
06396944
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a method of die to die or die to database inspection of phase shifting masks for defects in the transparent phase shifting mask elements.
(2) Description of the Related Art
In order to inspect masks having phase shifting mask elements, some means must be employed to make defects in the phase shifting mask elements detectable. The detectability of these defects is made difficult because the phase shifting mask elements are transparent and difficult to distinguish from the transparent mask substrate. The phase shifting mask elements are often the same material as the transparent mask substrate.
U.S. Pat. No. 5,446,540 to Lin describes the use of a phase-contrast microscope for the inspection of a phase shifting mask.
U.S. Pat. No. 5,786,112 to Okamoto et al. describes a method of inspecting photomasks having phase shifting mask elements using a first anomaly discrimination step, a second anomaly discrimination step, and an anomaly extraction step in inspecting the mask.
U.S. Pat. No. 5,439,767 to Yamashita et al. describes a method of inspection a phase shifter for transmittance error and phase shift angle error by exposing a layer of photoresist several times at varying focus, developing the photoresist, and measuring the width of the lines in the resulting pattern.
SUMMARY OF THE INVENTION
Levenson type phase shifting masks use quartz or other transparent phase shifting mask elements. The quality of these masks is very important so that inspection of the masks for mask defects is very important. Inspection of the masks is quite difficult, however, since the light transmission through the phase shifting mask elements is the same as through the transparent mask substrate. The phase shifting mask elements and the transparent mask substrate are often formed of the same material.
It is a principle objective of this invention to provide a method of inspecting for defects in transparent phase shifting mask elements using die to die inspection.
It is another principle objective of this invention to provide a method of inspecting for defects in transparent phase shifting mask elements using die to data base inspection.
These objectives are achieved by forming a layer of partially transmitting material, such as a layer of anti-reflective material, on the mask covering the phase shifting mask elements. The mask is then illuminated by a light source and the light transmitted through the mask is detected. Defects in the pattern of phase shifting mask elements will cause a difference in the amount of light transmitted through the defect when compared to a defect free phase shifting mask element. This difference can be used to perform a die to die inspection or a die to database inspection of the pattern of phase shifting mask elements.
REFERENCES:
patent: 4618938 (1986-10-01), Sandland et al.
patent: 5439767 (1995-08-01), Yamashita et al.
patent: 5446540 (1995-08-01), Lin
patent: 5563702 (1996-10-01), Emery et al.
patent: 5786112 (1998-07-01), Okamoto et al.
patent: 6084716 (2000-07-01), Sanada et al.
Ackerman Stephen B.
Azarian Seyed
Prescott Larry J.
Saile George O.
Taiwan Semiconductor Manufacturing Company
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