1. Field of the Invention
The present invention relates to the lithographic technology. More particularly, the present invention relates to a customer illumination aperture (CIA) structure for lithographic exposure, which can improve the resolution in simultaneous formation of dense, semi-dense and isolated patterns.
2. Description of the Related Art
In advanced semiconductor processes, especially those of 90 nm generation or below, resolution-enhanced technologies (RET) are required to achieve fine pitch resolution. Many methods have been proposed to overcome the issue of lower k1 value, such as, the methods using alternating phase-shift masks (Alt-PSM), chromeless masks, vertex masks or half-tone masks in exposure, and multiple exposure methods.
Other RET methods include judicious applications of mask biasing and inclusion of additional assisting features. However, these methods suffer from high cost and low throughput on mask manufacturing since circuit designs are often too complex to be handled by optical proximity correction (OPC) software.
Another RET method is to use optimal customer illumination apertures (CIAs), as described in U.S. Pat. No. 6,839,125. For example, the illumination aperture of
In view of the foregoing, this invention provides a customer illumination aperture (CIA) structure for lithographic exposure, which can improve the resolution in simultaneous formation of dense, semi-dense and isolated patterns.
The CIA structure of this invention includes a central part and at least one off-axis part around the central part. The at least one off-axis part is disposed in a symmetric manner with respect to the central part.
In the above CIA structure of this invention, the central part may have a ring shape. The off-axis part may be a single region having a ring shape, or includes a number “n” (n≧2) of regions arranged in n-fold symmetry around the central part. In addition, there may be multiple off-axis parts arranged in two or more circles around the central part. Combinations of two or all of the three additional features are also allowed.
Since the central part is good for definition of isolated and semi-dense patterns and the off-axis part good for that of dense patterns, the overall quality of pattern transfer can be improved. By comparing the simulated aerial images and the real resist profiles obtained in experiments, it is confirmed that the through-pitch CD uniformity, mask error enhancement factor (MEEF), line-end shortening problem, pattern linearity and depth of focus (DOF) can be improved by using the illumination aperture of this invention with reduced OPC loading and cost.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
FIGS. 6 illustrates another exemplary CIA structure of this invention, wherein the off-axis part includes 3 regions arranged in 3-fold symmetry that are connected with the central part.
Referring to
Moreover, there may be more than one off-axis parts arranged in two or more circles around the central part 200, wherein any off-axis part can be a single region having a ring shape or includes n regions (n≧2) arranged in n-fold symmetry. As shown in
Referring to
Referring to
Referring to
Referring to
Furthermore, when the off-axis part include n regions in n-fold symmetry, the n regions of the off-axis part may be connected with the central part of the CIA structure, as shown in
In addition, any combination of two or al! of the three features about the shape of the central part 200, the number of off-axis parts and the geometry (single or n regions) of an off-axis part is also possible, depending on the shapes and arrangements of the patterns to be transferred to the photoresist layer.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.