Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-07-06
2001-09-04
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S296000, C430S942000
Reexamination Certificate
active
06284415
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to methods and apparatus for charged-particle-beam pattern transfer for transferring patterns defined by a mask onto a sensitized wafer or other substrate.
BACKGROUND OF THE INVENTION
The so-called “resist-heating effect” has been observed in electron-beam microlithography with a variable-shaped electron beam. See, e.g., Japanese Laid-Open Patent Document No. Hei 2-143516. The resist-heating effect causes a pattern transferred with a large diameter electron beam to be larger than the same pattern transferred with a smaller diameter electron beam even though the dose is constant. The electron beam irradiating the resist heats the resist, increasing the resist's sensitivity. This effect is most often observed in processes involving direct electron-beam writing of patterns.
In electron-beam writing using a variable-shaped electron beam, the resist-heating effect can be reduced or compensated by changing the exposure time for each of the various beam sizes to achieve a selected dose that produces a corresponding pattern dimension.
While adjusting dose is adequate to compensate the resist-heating effect in direct writing of patterns, dose adjustment is generally impossible in projection or proximity pattern transfer in which patterns are transferred from a mask. A mask pattern used to define a circuit pattern typically contains a mixture of large and small circuit features. When the mask is illuminated, both large and small pattern features are illuminated simultaneously and the dose cannot be optimally selected for both. Under such conditions, the resist-heating effect cannot be eliminated.
Accordingly, methods and apparatus for reducing or compensating for the resist heating effect in CPB pattern transfer from a mask to wafer are needed. There is also a need for such methods and apparatus that avoid the so-called “stencil” or “donut” problem.
SUMMARY OF THE INVENTION
An object of the invention is to provide apparatus and methods for reducing the effects of resist heating in charged-particle-beam (CPB) projection-exposure apparatus and methods, including such apparatus and methods employing a segmented mask or an un-segmented mask (as described in, e.g., U.S. Pat. No. 5,260,151) with minimal reduction in throughput.
The present invention cures the deficiencies of conventional apparatus and methods summarized above. A circuit pattern is divided into low-resolution (i.e., large) circuit features and high-resolution (i.e., small) circuit features. These features are defined in separate regions or subfields of a mask. This permits selection of the dose to correspond to the feature size. With such pattern division, the resist-heating effect can be reduced or corrected.
According to one aspect of the invention, methods for transferring a pattern to a wafer or other substrate using a CPB are provided. In one representative embodiment, the pattern is divided into low-resolution features and high-resolution features. A low-resolution mask pattern is used to define, on a mask or an area of a mask, the low-resolution features. Similarly, a high-resolution mask pattern is used to define, on a separate mask or a separate region of the same mask, the high-resolution features. Patterns from the low-resolution mask pattern and the high-resolution mask pattern are projected onto the substrate with respective doses.
In any of various embodiments, a circuit pattern can be divided into low-resolution and high-resolution features based on a threshold feature size. By “feature size” is meant a width dimension, or an area of the subject feature, as appropriate.
In another embodiment, a CPB projection-pattern-transfer method is provided in which a pattern to be transferred is divided into a first pattern and a second pattern that are defined as first and second mask patterns in separate areas of a mask. The first pattern includes patterns corresponding to low-resolution features of the pattern to be transferred as well as at least a portion of the patterns for the high-resolution features. The first and second mask patterns are transferred to the wafer by projecting images of the respective patterns with a CPB, producing respective first and second doses at the wafer, wherein the first dose is less than the second dose. At least some areas of the wafer are exposed by both the first and second mask patterns and the dose in such areas is the sum of the first and second doses.
In other embodiments, the pattern to be transferred includes features such as line segments and intersections of line segments. Such a pattern is divided into a first set and second set of features so that the first set of features includes intersections of at least some of the line segments and the second set of features includes at least portions of the line segments. The first and second sets of features are defined by first and second mask patterns, respectively, and transferred to the wafer by projecting images of the mask patterns onto the wafer. The wafer receives first and second doses, corresponding to the first and second mask patterns, respectively, wherein the first dose is less than the second dose. By way of example, the pattern includes rectangular features having sides and corners, and the pattern is divided so that the first set of features includes the corners and the second set of features includes the sides.
According to another aspect of the invention, masks are provided for transferring a pattern to a substrate with a charged-particle beam. The mask comprises first and second areas that define low-resolution and high-resolution features of the pattern, respectively. The low-resolution and high-resolution features can be designated based on a threshold feature size. In one example, the threshold feature size is a width dimension smaller than 0.2 &mgr;m.
A charged-particle-beam projection-pattern-transfer method for transferring a pattern to a wafer or other substrate is provided. The method comprises dividing the pattern into a low-resolution pattern and a high-resolution pattern based on a threshold feature size and defining a first mask pattern that includes the low-resolution pattern and at least a portion of the high-resolution pattern. A second mask pattern is defined to include at least a portion of the high-resolution pattern, and the first and second mask patterns are defined in separate areas on a mask or masks. The first and second mask patterns are transferred to the wafer with respective first and second doses, wherein the first dose is less than the second dose and the second mask pattern is transferred either prior to or after transfer of the first mask pattern.
In yet another embodiment, the portion of the high-resolution pattern defined by the first mask pattern or the portion of the low-resolution pattern defined by the second mask pattern can be selected to avoid the “donut” problem.
In yet another embodiment, the portion of the high-resolution pattern defined by the first and second mask patterns can include a common pattern portion.
According to another aspect of the invention, methods for making a mask for transferring a pattern to a wafer or other substrate by projection-exposure using a charged-particle beam are provided. A representative embodiment of such a method comprises dividing a mask pattern into low-resolution features and high-resolution features and defining such features in respective first and second mask patterns on separate areas of a mask. The patterns can be divided into low-resolution features and high-resolution features based on a threshold feature size.
The foregoing and additional features and advantages of the p resent invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
REFERENCES:
patent: 5260151 (1993-11-01), Berger et al.
patent: 5912096 (1999-06-01), Hada
patent: 5935744 (1999-08-01), Nakajima
Kratschmer et al., “Resist Heating Effects in 25 and 50 kV e-Beam Lithography on Glass Masks,”J. Vac. Sci. Technol. B. 8:1898-1902 (N
Klarquist Sparkman Campbell & Leigh & Whinston, LLP
Nikon Corporation
Young Christopher G.
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