Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
1999-12-22
2001-10-02
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S394000
Reexamination Certificate
active
06296991
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to lithography, and particularly to an exposure process.
2. Description of Related Art
Integrated circuit fabrication requires high precision techniques to achieve. Any minute errors in the fabrication process cause the fabricated wafer to be unreliable or even unusable, which worsens wafer yield.
Photolithography technology is the most important process in semiconductor fabrication. This technology prints mask patterns onto wafers for fabrication of various circuit components including MOS (metal-oxide semiconductor) components, doped areas, and other else in the integrated circuit. IC fabrication typically requires several photolithography processes to complete. Each of the photolithography processes comprises three basic steps: coating, exposure, and development.
Current photolithography technique uses fixed illumination condition, exposure energy and defocus, to print mask patterns onto wafers. However, as IC dimension shrinks, photolithography is pushed to its resolution limit due to narrow pitch of patterns. Double-exposure operation using two masks is proposed to solve the narrow pitch issue. However, this operation suffers low throughput caused by mask exchanging. Moreover, it is difficult to align the second mask precisely to the previously exposed areas on the wafers using the first mask. Furthermore, the two masks inherently possess mask errors between them, thereby worsening this double-exposure operation.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an exposure process that can be performed on a wafer.
Other objects and advantages of this invention will become apparent to those of ordinary skill in the art having reference to the following specification in conjunction the drawings.
A bi-focus exposure process for exposing a wafer through a mask is described. The mask comprises a plurality of first transparent hole features having a phase shift of about 0 degrees and a plurality of second transparent hole features having a phase shift of about 180 degrees, the first and the second hole features are alternatively located on a transparent substrate, and each of the hole features is substantially and adjacently surrounded by a lightly transparent material having a phase shift of about 90 degrees on the transparent substrate. The patterns of the first hole features are printed on the wafer by exposing the wafer through the mask at a first defocus. The patterns of the second hole features are printed on the wafer by exposing the wafer through the mask at a second defocus.
The above first defocus and the second defocus are preferably about −0.3 &mgr;m and +0.3 &mgr;m defocuses, respectively. The above lightly transparent material has a preferable transmission of about 6%.
By exposing through only one previously described mask, a double exposure can be performed on the wafer without mask exchanging, thereby increasing the throughput. Moreover, this double exposure has no mask errors and alignment issues, because the double exposure is performed using only one mask. Furthermore, this invention increases the width of the pitch without affecting the final patterns printed on the wafer, thereby improving the exposure resolution.
REFERENCES:
patent: 5637424 (1997-06-01), Haruki et al.
Rosasco S.
United Microelectronics Corp.
LandOfFree
Bi-focus exposure process does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Bi-focus exposure process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bi-focus exposure process will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2605846