Radiation imagery chemistry: process – composition – or product th – Including control feature responsive to a test or measurement
Reexamination Certificate
1999-07-01
2001-10-09
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Including control feature responsive to a test or measurement
C430S017000, C430S296000, C430S311000, C430S942000
Reexamination Certificate
active
06300023
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to microlithography apparatus and methods that employ an energy beam (light or charged particles) and a pattern-transfer optical system to transfer a pattern, defined by a reticle, onto a sensitized substrate. Such apparatus and methods are used, e.g., in the manufacture of integrated circuits, displays, and the like.
More specifically, the invention relates to, inter alia, methods for transferring a large pattern that exceeds the field dimensions of the pattern-transfer optical system, while achieving high throughput and high resolution of ultra-fine pattern features on the substrate.
Much of the following discussion is in the context of using a charged particle beam (specifically an electron beam) as the energy beam. However, it will be understood that the energy beam can be any of various other charged particle beams, such as an ion beam, or any of various beams of electromagnetic radiation, such as visible light, ultraviolet light, or X-rays.
BACKGROUND OF THE INVENTION
Current trends in which patterns for integrated circuits and displays are being made increasingly larger have resulted in the reticle pattern frequently being larger than the field of the exposure-optical system of the microlithography apparatus. This situation especially arises in charged-particle-beam (CPB) microlithography apparatus in which the field of the exposure-optical system typically is very small compared to the area of the reticle. In situations in which the pattern is larger than the optical field, the pattern is usually divided into multiple individual exposure units (e.g., “subfields”) that are separately exposed in an ordered manner to transfer the entire pattern. Microlithography performed using such a reticle is termed “divided” transfer-exposure.
During transfer of individual exposure units in divided transferexposure, the reticle and substrate (which are mounted on respective movable stages) are moved in a coordinated manner as required in respective planes that are perpendicular to the optical axis of the exposure-optical system. Also, as each exposure unit is exposed, one or more of certain parameters of the exposure-optical system (e.g., focus, image magnification, aberration correction, etc.) are optimized for the respective exposure field. The coordinated movements of the reticle stage and substrate stage can be according to either a “step-and-repeat” or a “continuous scanning” scheme. In step-and-repeat exposure, the stages move intermittently (e.g., to position the next exposure unit for exposure) and no exposures are made while the stages are moving. Rather, an exposure is made (of the positioned exposure unit) only when the stages are stationary. In continuous scanning exposure, exposures are made while the stages are moving at respective scanning velocities.
In CPB microlithography, the reticle can be a so-called “stencil” reticle or a so-called “membrane” reticle. With a stencil reticle, pattern features (i.e., pattern elements) are defined as respective through-apertures in a reticle plate. Certain features, such as “island” features, cannot be completely defined using a single respective aperture in a stencil reticle. Such features are usually divided into two complementary features defined in separate exposure units that are transferred onto the substrate in separate respective exposures (“shots”).
As is generally known, a current quest in integrated circuit technology is the manufacture of ever-larger memory chips. According to contemporary “roadmaps” of memory circuits, the anticipated dimensions of a 16-gigabit DRAM chip are approximately 40×20 mm. As explained in more detail below, the dimensions of a reticle (assuming a demagnification factor of ¼ and no complementary exposure units required) for such a chip would exceed 200×100 mm. If the pattern required any complementary exposure units, then the reticle would be even larger, and likely would not fit on a 12-inch diameter reticle plate.
SUMMARY OF THE INVENTION
In view of the problems of the prior art, as summarized above, the present invention provides, inter alia, transfer-exposure methods in which a complete reticle pattern (including complementary features) can be defined on a single reticle substrate such as a 12-inch diameter silicon wafer. Such a reticle can be used to transfer-expose the pattern onto a suitable substrate at acceptable throughput and transfer accuracy.
To such end, according to a first aspect of the invention, methods are provided for transferring a pattern, defined by multiple pattern portions on a segmented reticle, onto a substrate using an energy beam (e.g., light beam or charged particle beam). The reticle is mounted on a movable reticle stage and the substrate is mounted on a movable substrate stage. According to a representative embodiment of the method, during transfer-exposure of the pattern portions from the reticle to the substrate, the reticle stage and the substrate stage are moved at respective movement velocities with which the ratio of the movement velocities changes during the transfer-exposure. Thus, the pattern is transferred at velocities that can be varied to fit the characteristics of the various features or portions of the pattern being transferred, yielding higher throughput and transfer accuracy than obtainable with conventional methods.
According to second representative embodiment, a method is provided for transferring a pattern, defined by a segmented reticle, onto a substrate using an energy beam and a projection-optical system. The reticle is mounted on a movable reticle stage and the substrate is mounted on a movable substrate stage. The pattern is divided into multiple pattern portions individually definable on the reticle. The pattern portions are categorized as individually being of a first group or of a second group. The first group consists of pattern portions requiring division into primary and secondary pattern portions wherein each secondary pattern portion is complementary to a corresponding primary pattern portion. The second group consists of pattern portions not requiring division into primary and secondary pattern portions. On the reticle, a first region is formed containing the pattern portions of the second group and the primary pattern portions of the first group; a second region is also formed containing the secondary pattern portions of the first group. The pattern portions in the first region are transferred while moving the reticle stage at a velocity ratio of (M+&agr;):1 relative to the movement velocity of the substrate stage, wherein 1/M is the demagnification ratio of the projection-optical system and &agr; is a positive rational number denoting the proportion of the reticle occupied by non-patterned areas. The pattern portions in the second region are transferred while either moving the substrate stage at a velocity greater than the velocity used during transfer of the pattern portions in the first region or moving the reticle stage in a step-and-repeat manner. The pattern portions are desirably “scanning strips,” as defined herein, wherein the first region is a “primary stripe” containing multiple scanning strips, and the second region is a “secondary stripe” containing at least one scanning strip.
According to yet another representative embodiment, a method is provided for transferring a pattern, defined by a segmented reticle, onto a substrate using an energy beam and a projection-optical system. The reticle is mounted on a movable reticle stage and the substrate is mounted on a movable substrate stage. The pattern is divided into multiple stripes and scanning strips, wherein a scanning strip is a portion of a stripe. For each scanning strip, if a particular scanning strip contains one or more pattern features requiring splitting into primary features and corresponding secondary features, then the respective scanning strip is split into a primary scanning strip and a secondary scanning strip. The primary scanning strip contains the primary features and the secondar
Klarquist & Sparkman, LLP
Nikon Corporation
Young Christopher G.
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