Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Electron beam imaging
Reexamination Certificate
2003-02-05
2004-03-02
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Electron beam imaging
C430S311000, C430S396000
Reexamination Certificate
active
06699639
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to microlithographic projection-exposure methods and apparatus for use principally in the manufacture of semiconductor integrated circuits and display devices. In such methods and apparatus, a pattern for a circuit or display array is defined by a reticle or the like and is projected onto a semiconductor wafer or other suitable substrate using an energy beam so as to transfer the pattern to the substrate.
BACKGROUND OF THE INVENTION
In conventional projection-microlithographic techniques, a pattern (e.g., for a semiconductor chip or display device) is defined on a reticle or other suitable “original plate.” At least a portion of the reticle is illuminated using an energy beam. As the energy beam passes through the reticle, the beam carries an image of the illuminated portion. The image is focused onto a corresponding region of a suitable substrate (termed herein a “wafer”). The wafer is normally coated with an appropriate resist that is imprinted with the projected image.
As used herein, “throughput” means the number of wafers, product devices, or other product units that can be manufactured per unit time using the subject method or apparatus; a “pattern original” is a plate, film, or the like that defines a pattern to be transferred to a substrate and encompasses masks, reticles, and analogous structures; an “energy beam” is a medium used to transfer an image of the pattern from the pattern original to the substrate and encompasses visible light, ultraviolet light, X-rays, electron beam, and ion beam; and a “charged particle beam” can be an electron beam, ion beam, or analogous beam. Hence, an “optical system” as referred to herein is not limited to an optical system for light (e.g., visible light, ultraviolet light, X-rays), but also encompasses optical systems for a charged particle beam.
As used herein, a “field of view” of an optical system or the like is, unless otherwise specified, an imaging region in which aberrations are within specification.
At present, projection-microlithographic exposures made in the mass-production of semiconductor chips are mainly performed using a “stepper” that utilizes visible light or ultraviolet light as the energy beam. As feature sizes have continued to decrease with the need to achieve increasingly higher circuit densities on semiconductor chips and displays, the wavelength of light used as the exposure energy beam in steppers is becoming increasingly shorter. This has placed severe limits on the optical materials that can be used in the optical systems (e.g., illumination-optical systems and projection-optical systems) in contemporary steppers.
Aberrations impose limitations to the field of view of optical systems that must satisfy a requirement for high resolution. I.e., whenever fine features must be transferred with high resolution, optical systems exhibiting excessive aberrations have a field of view that is confined to more paraxial regions compared to otherwise similar optical systems in which aberrations are better corrected.
In addition to demands for increased resolution, there is also a demand for ever larger semiconductor devices. Whereas meeting such demands could be achieved using correspondingly larger optical systems, larger optical systems capable of achieving high resolution are more difficult to manufacture to close tolerances than smaller optical systems. Hence, optical systems tend to have a field of view that is too small to project the entire pattern in one “shot. ”
Therefore, especially when higher integration densities and/or larger devices are the goal, exposing the entire pattern simultaneously with a single exposure “shot” is impractical. To make exposures in such situations, exposure methods have been derived during which the reticle and the wafer are synchronously scanned as in the so-called “lens-scanning”, methods.
Exposure using a charged particle beam (e.g., electron beam) offers prospects of higher resolution than obtainable using visible or ultraviolet light. Unfortunately, conventional charged-particle-beam (CPB) exposure systems exhibit low throughput because of the impracticality of exposing the entire pattern simultaneously in one exposure “shot.” Various approaches have been devised to increase throughput of such systems. One conventional approach is termed “cell projection” which involves combining exposures of limited types of pattern portions. (This technique is also termed a “character projection” method.) Unfortunately, this method exhibits a throughput that is inadequate for practical use in the mass-production of semiconductor chips.
Another conventional approach is a “reduction” (i.e., producing a demagnified image on the wafer relative to the pattern on the reticle) projection-exposure method utilizing an electron beam. This method is disclosed, e.g., in Japanese Kôkai patent document no. JP Hei 05-160012. To increase throughput, an electron beam irradiates a reticle defining a circuit pattern for one entire semiconductor chip (i.e., an entire “die”). A demagnified image of the die pattern is transferred to the wafer using a projection lens. In most instances, an extremely large projection-lens field would be required to projection-expose the entire die simultaneously in a single shot. Unfortunately, aberration control over such a large field of view is extremely difficult to achieve with CPB optical systems. Hence, exposure is normally performed by dividing the pattern on the reticle into multiple pattern portions. The pattern portions are successively transferred in an ordered manner from the reticle to the wafer. During each exposure, one or more parameters of the charged particle beam can be changed as required to obtain the best aberration reduction for each exposure. The images on the wafer are “stitched” together by appropriate positioning during exposure to form the entire reticle pattern on the wafer. Certain methods utilizing this approach are termed “step-and-scan” methods or “divided” projection-transfer methods, as disclosed, for example, in U.S. Pat. No. 5,260,151.
Currently, CPB projection-exposure apparatus for mass production utilizing the “step-and-scan” method are not generally available. Also, CPB projection-exposure apparatus utilizing “divided” projection-transfer methods are still in development. In any event, utilizing such methods for forming a plurality of semiconductor chips on a wafer typically requires that the reticle stage be moved over distances (each separate movement consuming a certain amount of time) that prohibit the attainment of satisfactory throughput levels.
Certain types of scanning-type exposure apparatus for mass production are currently available in which the reticle stage exhibits one-dimensional movement. With such apparatus, changing the scanning direction for various die patterns can be performed. However, stitching together of portions of a die pattern as projected onto the wafer to form larger chips has not yet been practicably realized.
SUMMARY OF THE INVENTION
In view of the shortcomings of conventional technology as summarized above, an object of the present invention is to provide projection-exposure methods and apparatus that exhibit improved throughput. Such an object is achieved by certain improvements in the manner in which the reticle stage and wafer stage (on which the reticle and wafer, respectively, are mounted during exposure) undergo movement during exposure.
According to a first aspect of the invention, methods are provided for projection-exposing a die pattern, defined by a pattern original and comprising multiple pattern portions for individual exposure, onto multiple locations on a substrate. According to a representative embodiment of such a method, an energy beam is directed to impinge on a pattern portion of the die pattern defined by the pattern original, and to form a patterned beam from the energy beam passing through and propagating downstream of the illuminated pattern portion. (The patterned beam carries an image of the illuminated pattern portion.) The pat
Huff Mark F.
Klarquist & Sparkman, LLP
Mohamedulla Saleha
Nikon Corporation
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