A new optical system has recently been developed for large area lithography applications. The new optical system is referred to as scanning array lens lithography (SALLY) and is based on the well-known Wynne-Dyson 1:1 projection lens configuration that has found widespread use in the IC, thin- film head and micromachining industries. The array lens is designed to project essentially a single elongated field that can be extended to span the width of any substrate. This enables a substrate to be exposed in a single scanning motion. The array lens is composed of multiple, compact catadioptric lens relays having trapezoidal shaped image fields that are positioned in an alternating and overlapping fashion. The resulting imaging capability is comparable to that of a single very large well-corrected lens. Features exposed in the transition between separate fields exhibit no visible variations in their structures. This paper describes the system configuration and test results for a three-field prototype SALLY system composed of lens relays with a numerical aperture (NA) of 0.10. This NA was selected to provide a useful combination of resolution, depth-of-focus (DOF) and exposure irradiance for large area and thick resist applications. SEM results from field-to-field measurements demonstrate that a seamless transition between separate image fields can be achieved. Resolution of equal line/space patterns down to 2.3 micrometer has been attained. In addition, thick resist imagery showing thickness to linewidth aspect ratios of greater than 8.5:1, in 33 micrometer thick resist is shown.
A new optical system has recently been designed, built, and tested to meet the demands of large area lithography applications. The new optical system is referred to as Scanning Array Lens LithographY (SALLY) and is based on the well-known Wynne Dyson 1:1 projection lens configuration that has found widespread use in the IC, thin-film head, and micromachining industries. Recent advances in the areas of optical design, alignment, assembly and packaging have led to the development of an array lens that essentially projects a single elongated field that can be extended to span the width of any substrate. This enables a substrate to be exposed in a single scanning motion. The array lens is composed of multiple compact, catadioptric lens relays having trapezoidal shaped image fields that are positioned in an alternating and overlapping fashion. The resulting imaging capability is indistinguishable from that which would be accomplished by a single very large, well-corrected lens. Features exposed in the transition between separate fields exhibit no visible variations in their structures. This paper describes a three field prototype SALLY system composed of lens relays with a numerical aperture (NA) of 0.10 designed to include the g- and h-lines of the mercury spectrum. This NA was selected to provide a useful combination of resolution, depth-of-focus, and exposure irradiance for a range of applications including micromachining. Test results demonstrate a seamless transition between separate image fields and resolution of equal line/space patterns down to 2.3 micrometers . Thick resist film imagery showing thickness to linewidth aspect ratios of up to 4:1 using conventional application and development techniques are also shown.
Ion figuring is an efficient and deterministic process for fabricating high quality optical surfaces. The simultaneous phase shifting interferometer is a helium-neon laser-based Twyman-Green system capable of data acquisition at shutter speeds of up to 1/10,000th of a second, which eliminates vibration effects. Ion figuring and simultaneous phase shifting interferometry were successfully combined to produce an aspheric, 18 inch diameter, f/2, ULE mirror of exceptional surface figure quality. Through iterative cycles of SPSI testing and ion figuring, the mirror surface was processed to a final figure quality of 0.007 (lambda) rms (95% of data <EQ 0.028 (lambda) p-v). The radius of curvature of the mirror was held to within 0.00008 inch of the design radius. Details of the testing/figuring cycles are discussed along with information regarding the mirror mounting scheme, interferometer calibration, and data analysis techniques.
We have explored two-level, or `twin' masks as a mask-based means of increasing depth of focus. Simulations have shown that the technique offers substantial gains for a variety of pattern types. To verify this experimentally, we have fabricated a test mask containing two- level as well as conventional mask patterns. We have performed through-focus series of photoresist exposures and demonstrated the expected improvement in focus latitude.
The optical performance of Markle-Dyson projection optics is now well established. Here we describe options for 1X reflective optical masks that might achieve the desired linewidth control. One option is the use of aluminum as the reflecting material. A film less than 50 nm thick has nearly twice the reflectivity of the silicon used until now, and so it should be possible to develop an etching process (for such a thin film) that is adequately precise. Moreover options exist for repairing both opaque and clear defects. An interesting alternative configuration, that eliminates the need to etch the aluminum, is to use a patterned absorber on the substrate and to deposit the aluminum over the patterned absorber.
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