Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-11-18
2001-05-29
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06238825
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mask with alternating scattering bars. More particularly, the present invention relates to a low duty ratio mask.
2. Description of the Prior Art
In the semiconductor industry, the lithography process is a very important and common fabrication process. Structures of MOS devices such as layout patterns and doping regions of thin films are defined by the lithography process.
Scattering bars are employed in the lithography process to reduce or eliminate proximity effects. Rectangular openings are disposed next to edges of masked layout patterns. During an exposure process, diffraction arises at the rectangular openings and eliminates the proximity effects of adjacent layout patterns.
Resolution of the lithography process determines a line width in the semiconductor manufacture. How to increase the resolution is an important issue for the semiconductor industry. Duty ratio for a patterning is one of the features which affects the resolution. The duty ratio represents the ratio of a line width and a pitch width in a semiconductor device being fabricated. In the lithography process, a duty ratio of 1 gives the best resolution.
When the integration is further increased, for example, contact holes of a giga-bit DRAM cell, the duty ratio is less than 1 (that is, the pitch width is larger than the line width). Such patterning has a poor resolution even when the scattering bars are employed.
FIG. 1
A illustrates an exposed pattern of contact holes in a DRAM cell employing a conventional mask. Circular patterns represent positions of the contact holes. It is noted that some of the adjacent circular patterns overlap along their edges.
FIG. 1B
illustrates an exposed pattern of
FIG. 1A
after a 0.3 microns defocus. Overlapping of edges is more serious, and hence, the masking process cannot be employed.
FIG. 2A
illustrates an exposed pattern of contact holes in a DRAM cell employing a conventional mask with scattering bars.
FIG. 2B
illustrates an exposed pattern of
FIG. 2A
after a 0.3 microns defocus. Circular patterns represent positions of the contact holes. Rectangular bars indicate positions of the scattering bars. Overlapping of edges still exists. Therefore, the resolution is not improved even by employing the scattering bars.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a mask with alternating scattering bars which enhance the resolution of an exposed pattern, allowing attainment of proper layout patterns even for a less-than-1 duty ratio patterning.
Another object of the present invention is to provide a mask with alternating scattering bars which defines layout patterns having a less-than-1 duty ratio. The mask with alternating scattering bars has a larger process window than a conventional mask with or without scattering bars. High resolution is still maintained even after a 0.3 microns defocus.
Based on the foregoing, the present invention provides a mask with alternating scattering bars, which includes a plurality of masked layout patterns and a plurality of alternating scattering bars placed next to edges of each masked layout pattern. A phase shift of 180° exists between the alternating scattering bars and the corresponding masked layout pattern.
In accordance with a preferred embodiment of the present invention, if the alternating scattering bars have a phase of 180°, then the corresponding masked layout pattern will have a phase of 0°.
In accordance with the preferred embodiment of the present invention, if the alternating scattering bars have a phase of 0°, then the corresponding masked layout pattern will have a phase of 180°.
REFERENCES:
patent: 5821014 (1998-10-01), Chen et al.
patent: 6114071 (2000-09-01), Chen et al.
Rosasco S.
United Microelectronics Crop.
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