Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
1999-07-30
2003-06-10
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S492220
Reexamination Certificate
active
06576914
ABSTRACT:
TECHNICAL FIELD
The field of the invention is that of microlithographic patterning, especially using charged particle beam projection systems.
BACKGROUND OF THE INVENTION
In the field of lithography a reticle may contain stencil shapes, sometimes referred to as “doughnut” shapes, that are open areas having a “closed” configuration that permit the passage of the exposing radiation, but contain within them areas that are required to be opaque to the exposing radiation. A simple example is the letter “O”, which has an closed oval line surrounding a central area. With chrome on glass masks, there is no problem in using such configurations, because the glass substrate supports the central opaque section. If such a shape is to be used in a particle beam system that employs a stencil reticle (a reticle having “opaque” regions that remove particle from the beam and open areas that permit the beam to pass though without scattering) there is the known problem of supporting the central area.
In the prior art, two complementary reticles were used to define stencil shapes, each reticle carrying a supported partial pattern that combined with the other pattern to define the correct shape, each reticle being exposed with the full exposure dose of electrons. Such reticles suffered from certain problems explained below.
SUMMARY OF THE INVENTION
The invention relates to a stencil mask for e-beam lithography that includes more than one set complementary sub-field reticle, each of which is exposed with one nth of the total dose.
A feature of the invention is that stencil (or “doughnut”) shapes have n different patterns of struts, so that an area that is blocked in one shape is exposed in (n−1) other shapes.
An advantageous feature of the invention is that, when used with a photoresist with sufficient contrast, the areas having (n−1)
exposure are not significantly different from the areas having the full exposure.
Another feature of the invention is the provision of areas of the reticle that are used several times for printing repetitive arrays.
Yet another feature of the invention is the provision of areas of the reticle that carry alternative versions; i.e. the wafer can be exposed with version A or with version B.
REFERENCES:
patent: 5557110 (1996-09-01), Itoh
patent: 5874198 (1999-02-01), Okino
patent: 5936252 (1999-08-01), Stickel et al.
patent: 6262429 (2001-07-01), Richton et al.
patent: 6323500 (2001-11-01), Yamashita
Elimiation of mask-induced defects with vote-taking lithography by C-C Fu, et al. in SPIE vol. 633 Optical Microlithography V (1986).
International Business Machines - Corporation
Neff Daryl K.
Nguyen Kiet T.
Petraske Eric W.
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