Core Technology The core technology developed for the HexScan system is based on a well-proven design3-5 which is schematically illustrated in Figure 2. The wafer and mask are rigidly mounted on a single-planar scanning stage that moves them synchronously in both x and y directions. The illumination system uses an excimer laser light source and a beam-processing optical system. The laser typically emits 45 watts of UV radiation at 351nm, a wavelength ideally suited for imaging conventional photoresists designed for i-line exposures. The beam-processing system illuminates the mask from below (through a cutout in the stage) in a uniform-intensity, hexagon-shaped illumination region that is typically 50 mm in size (vertex-to-vertex). The mask pattern within the illuminated hexagonal region is imaged onto the wafer by a unit-magnification projection lens through a folded image path. The projection lens, the illumination system and all other optical components are stationary. The sole moving component is the single-planar stage, which is scanned in a serpentine fashion in the x-y plane in order to achieve complementary overlap between adjacent hexagonal scans. The HexScan system, by combining seamless 1:1 projection imaging and high-speed scanning with a single-planar stage, delivers the capability of high-resolution imaging on 300 mm wafers. This feature permits a choice of different user-specified system configurations, as well as future upgradability as requirements change with product migration. System Description Table 2 shows the specifications of the HexScan 2100 SPE lithography system, a tool that can currently meet all of the lithography requirements for WLP.
The HexScan 2100 SPE uses a xenon fluoride (XeF) excimer laser light source, operating at 351 nm-a wavelength compatible with all conventional photoresists and solder-mask resists currently used with the 365 nm wavelength (i-line) of Hg arc lamps. It is capable of aligning the mask and wafer rapidly and automatically to better than ±1 micron. Demonstrated Results The HexScan 2100 SPE provides an exposure time of 12 sec for 300 mm wafers with common photoresists. With an overhead time of 10 sec (for load, unload and align), the system delivers a net imaging throughput of 165 wafers/hr. The throughput value of 165 wafers/hr is realized with the HexScan 2100 SPE for any photoresist with a dose requirement of 150 mJ/cm2 or less. Wafer-level packaging processes are currently under investigation at several research facilities, including the Packaging Research Center (PRC) at the Georgia Institute of Technology, Atlanta, where an Anvik HexScan 2150 SXE lithography tool is installed. Conclusion The new laser projection imaging (LPI) system described in this paper provides not only very high resolution, large depth-of-focus and precise alignment, but also high yield and high throughput. Demonstrated results show that the Anvik HexScan™ series of LPI machines eliminates many of the limitations of proximity printers and stepper systems. References 1. R. Iscoff, "Steppers vs. Aligners: Two Technologies Race for the Finish Line in Wafer-Level Packaging," Chip Scale Review, p. 45, July 2001. 2. M. Töpper, et al., "Is Wafer-Level Packaging Ready for 300 mm?" Advanced Packaging, p. 39, July 2001. 3. K. Jain, "Large-Area, High-Throughput, High-Resolution, Projection Imaging System," U.S. Patent 5,285,236, issued Feb. 8, 1994. 4. K. Jain, "Large-Area, High-Throughput, High-Resolution Lithography Systems for Flat-Panel Displays and Microelectronic Modules," Proc. SPIE, Vol. 3331, p. 197, 1998. 5. M. Robertsson, et al., "Large-area Patterning of High-Density Interconnects by Novel UV-Excimer Lithography and Photo Patternable ORMOCERTM-dielectra," IMAPS Conference, Strassbourg, France, May 30-June 1, 2001. Dr. Klosner is a project manager at Anvik Corp. He holds a bachelor's degree from Cornell University in physics and a master's and Ph.D. in optical sciences from CREOL at the University of Central Florida, Tallahassee. [mklosner@anvik.com]
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