Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-12-27
2001-10-16
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06303252
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to lithography, and particularly to a reticle for use in a lithography system.
2. Description of Related Art
Three main types of exposure techniques used for transferring patterns from the reticle to the photoresist include: contact type, proximity type and projection type. For the semiconductor technique of deep sub-micron, the precision of the exposure technique is highly limited to photo-resolution. This limitation may cause error or even failure to the pattern transferring. Taking proximity exposure technique as an example, the original pattern of the reticle lines are often different from the transferred pattern of the lines on the photoresist after the exposure step.
If the lines of the reticle are isolated, i.e., the gap spaces between the adjacent isolated lines are large such that the space/line ratio is higher than about 6.5, skilled persons locate assist features at the outside of every isolated line to gain sufficient process window thereof. A sufficient process window ensures that the pattern of the transferred lines are substantially the same as the pattern of the reticle lines. If the reticle lines of the reticle are dense, i.e., the gap spaces between the adjacent dense lines are small such that the space/line ratio is lower than about 3.0, skilled persons locate assist features at the outside edges of the extreme outer lines, but locate no assist feature between the dense lines. This is because locating an assist feature between dense lines easily induces sidelobe problems or increases mask-error factors.
However, in the semi-dense region of the reticle, i.e., the region where the space/line ratio is equal to about 3.0-6.5, skilled persons encounter a catch-22 situation. That is, inserting no assist feature between the semi-dense lines gains insufficient process window, however, on the other hand, inserting an assist feature easily induces sidelobe problems or increase mask-error factors.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a reticle having an assist feature between the adjacent lines of the reticle.
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.
The present invention is directed to a reticle having two adjacent, substantially parallel, and substantially equally spaced line segments of which each representing a portion of a main feature having a line width. Between two adjacent line segments of the group there exists a gap space. The reticle comprises at least one inside assist feature located between the two adjacent line segments, if the gap-space/line-width ratio is equal to about 3-6.5. The reticle further comprises two outside assist features located at the outside edges of the extreme left-hand and right-hand line segments, respectively, wherein each of the two assist features has a first width and is spaced apart from the nearest line segment by a distance.
The inside assist feature has a preferable second width substantially narrower than the first width if the gap-space/line-width ratio is equal to about 3-4. More preferably, the second width is equal to the first width multiplied a number of about 0.7-0.8. Most preferably, the second width is equal to the first width multiplied a number of about 0.75.
If the gap-space/line-width ratio is about 5.4-6.5,5, there are two inside assist features located between the two adjacent line segments, wherein each of the two inside assist features is spaced apart from the nearest line segment. Each of the two inside assist features has a preferable third width substantially narrower than the first width. More preferably, the third width is equal to the first width multiplied a number of about 0.7-0.8. Most preferably, the third width is equal to the first width multiplied a number of about 0.75.
REFERENCES:
patent: 5667918 (1997-09-01), Brainerd et al.
patent: 6165693 (2000-12-01), Lin et al.
Rosasco S.
United Microelectronics Corp.
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