Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1999-08-30
2001-07-31
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C359S230000, C204S298110
Reexamination Certificate
active
06268908
ABSTRACT:
TECHNICAL FIELD
This invention relates, in general, to the manufacture of integrated circuits and the like. More particularly, this invention relates to an illumination aperture or stop plate used to vary a distribution of light in a lithographic projection exposure device during the manufacture of integrated circuits.
BACKGROUND ART
Integrated circuits are commonly manufactured through utilization of photolithographic projection exposure devices (e.g., step reduction or step and repeat reduction exposure devices and scanning reduction projection exposure devices). One example of such a photolithographic projection exposure device is a device entitled Micrascan which is offered by Silicon Valley Group of San Jose, Calif. With these types of exposure devices, a substrate or wafer having a photosensitive resist layer formed on one of its surfaces is exposed to ultraviolet light irradiated from an illumination source which may be, for instance, a mercury lamp. In this process, light irradiated from the illumination source is first passed through a photomask or mask of the exposure device and then onto the photosensitive resist layer of the substrate. A circuit pattern which is to be transferred onto the substrate is formed on the mask and by irradiating light through the particular pattern formed on the mask, the circuit pattern may be projected or transferred onto the substrate for use in creating the integrated circuit.
Needless to say, the capacity of an integrated circuit may be increased by transferring finer or higher density circuit patterns onto the underlying substrates. To transfer these higher density circuit patterns, projection exposure devices have been implemented which reduce the size of the patterns projected from the mask onto the substrate. However, by reducing the size of the pattern to be transferred, due to the diffraction effects of light and consequent reduction in resolution, the pattern detrimentally becomes distorted and, in some cases, results in the transfer of an inaccurate circuit or a circuit which is not true with respect to the original circuit pattern.
Thus, a need exists for a device which transfers or projects a reduced circuit pattern or image from a mask onto an underlying substrate with a minimal loss of resolution and minimal reduction of fidelity.
SUMMARY OF THE INVENTION
The shortcomings of the prior art are overcome and additional advantages are provided through the provision of an illumination aperture in a projection exposure device. More particularly, the illumination aperture is positioned between an illumination source and a set of optical elements so that light irradiated from the illumination source must first pass through the illumination aperture before reaching the optical elements. To reach the optical elements, light from the illumination source passes through the illumination aperture through an opening having a given size, shape, and transmissivity. The particular size, shape, and transmissivity of the opening alters the distribution of onto the optical elements. The illumination aperture is used to alter the distribution of light that subsequently passes through the mask because it has been discovered that certain illumination aperture openings can markedly improve the printability of certain circuit patterns. For instance, the annular openings shown in
FIGS. 11
a
-
13
c
increase the fidelity of the transfer of many types of tightly packed, or nested, circuit patterns. Likewise, a square shaped opening (not shown) increases the fidelity of a pattern consisting of horizontal and vertical lines. Thus in accordance with the principles of the present invention, the fidelity of a circuit pattern is maintained and an accurate pattern is transferred by varying the size and shape of the illumination aperture opening according to the type of pattern to be transferred.
As has been discussed in a number of published articles (see, for example, E. Barouch, S. Knodli, M. S. Young, “Illuminator Optimization for Projection Printing,” Proc. SPIE 3679, edited by Luc Vanden Hove, 1999; N. Shiraishi, S. Hirukawa, et al., “New Imaging for 64M DRAM,” Proc. SPIE 1674, pp. 741-752, edited by J. D. Cuthbert, 1992), modified illuminator aperture openings can significantly change the printability of most patterns. However, the optimal aperture structure is closely tied to the type of patterns being imaged, thereby necessitating different aperture structures to achieve optimal printability for different mask patterns.
Additional shortcomings of the prior art are overcome and further advantages are provided through the provision of an illumination aperture having a variably sized and shaped opening. In particular, an illumination aperture is provided having a plurality of apertures which may be opened and closed to the passage of light, independently of one another, to form an opening having a desired size and shape according to the pattern intended to be transferred.
In one example of the present invention, an apparatus for forming variably sized and shaped openings is provided. The apparatus includes: a main body having formed therein a plurality of apertures; and a plurality of shutters associated with the apertures, each shutter having an open position and a closed position such that the open position allows light to pass through the associated aperture and the closed position prevents light from passing through the associated aperture; wherein the shutters may be opened and closed independently of one another.
Accordingly, the present invention advantageously allows an opening having a desired size and shape to be formed in a single illumination aperture. As a result, instead of requiring a particularly sized and shaped illumination aperture to be manually replaced with a differently sized and shaped illumination aperture each time a new circuit pattern is to be transferred, the plurality of apertures formed in the illumination aperture of the instant invention are opened and closed according to the particular circuit pattern to be transferred to form an opening having any desired shape and size. Consequently, the illumination aperture of the present invention facilitates the transfer of accurate and true circuit patterns from a mask onto a substrate and therefore effectively transfers fine and high density integrated circuit patterns.
Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention.
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E. Barouch, S. Knodli, M.S. Young, “Illuminator Optimization for Projection Printing,” Proc. SPIE 3679, edited by Luc Vanden Hove, 1999.
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Bula Orest
Cole Daniel C.
Conrad Edward W.
Horak David Vaclay
Rankin Jed Hickory
Adams Russell
Fuller Rodney
Heslin & Rothenberg, P.C.
International Business Machines - Corporation
Radigan, Esq. Kevin P.
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