Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-03-16
2001-10-16
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C716S030000
Reexamination Certificate
active
06303253
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to photolithographic processing for a mask layout and more particularly to an improved method which eliminates optical proximity effects such a rounding of corners and line end foreshortening etc. through an improved hierarchy and domain-balanced serif mask design system and method.
2. Description of the Related Art
Microlithography is the technology of reproducing patterns using light. As presently used in the semiconductor industry, a photomask pattern for a desired circuit is transferred to a wafer through light exposure, development, etch, and resist strip, etc. As feature sizes on a circuit become smaller and smaller, the circuit shape on the wafer differs from the original mask pattern more and more. In particular, corner rounding, line end foreshortening, iso-dense print bias, etc. are typically observed. These phenomena are called optical proximity effects.
One of the main reasons for optical proximity effects is light diffraction. Optical proximity effects coming from light diffraction can be overcome partly by using a shorter wavelength source of light, with a projection system possessing a larger numerical aperture. In practice, the wavelength of an optical light source is typically fixed (365 nm for i-line, 248 nm and 193 nm for DUV, 157 nm, etc.) and there is a practical upper limit on numerical aperture. So other resolution enhancement methods, including the use of phase-shifting masks and masks with serifs, have been developed to correct optical proximity effects.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a structure and method for performing optical proximity correction in photolithographic mask layout that includes defining an inner band adjacent a mask edge within the photolithographic mask, defining an outer band adjacent that inner band, changing a transparency of part of the inner band and the mask structure to compensate for optical proximity effects using predefined transparency changes, determining whether the predefined transparency changes affect the outer band of the mask structure or outer bands of other mask structures on the photolithographic mask, and altering the predefined transparency changes to prevent the predefined transparency changes from affecting the outer side band and the outer bands.
The predefined transparency changes can include forming a square hole within the mask structure at interior right angles or forming a square serif external to the mask structure at exterior right angles. A serif has the same transparency as the mask structure. A hole has an opposite transparency as the mask structure.
The altering can include changing a transparency of part of the mask structure and regions adjacent the mask edge to form a negative complementary image along each edge of the structure. The altering may also identify quadrants around corners of the mask structure and change a transparency of the quadrants to form mirror images between diagonal quadrants. The altering can include adding a series of hole regions internal to the mask structure and parallel to an edge of the mask structure. The series of hole regions can decrease in size depending upon a positional distance from a corner of the mask structure.
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International Business Machines - Corporation
Kotulak, Esq. Richard M.
McGinn & Gibb PLLC
Rosasco S.
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