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To: Falstaff who wrote (7096)	12/2/1998 2:52:00 PM
From: Starlight	Respond to of 9695

This is an article from SAL's newletter, Vol. 3 #5 - 1998 (current issue). I was unable to reproduce tables and photos, but this gives some interesting info. [This was very difficult to scan, so excuse any errors. I proofread it, but some scientific symbols don't reproduce here.) NGL: KEY ISSUES FOR X-RAY LITHOGRAPHY During the May 1998 NGL meeting, researchers in x-ray lithography were requested to focus on the following four issues. Projects are currently in various stages of completion. A full report is expected at the next NGL meeting. Issue# 1: Demonstration of technology capability at the 70 nm node at gap <10 microns. IBM and ASET have presented data showing resolution of 75 and 60 nm lines and spaces using a 10 micron gap, and isolated 50 nm lines using a 15 micron gap. This is good news from a manufacturing point of view. Many research facilities have shown the capability of XRL to produce lines smaller than 70 nm. In 1995 through 1997, Motorola's Scott Hector et al., studied the extendibility of x-ray lithography. They found that 100 nm ground rules could be printed at -<15 micron gaps using linewidth bias optimization and simple serifs. At 75 nm ground rules, patterns can be printed at gaps of 10 - 15 microns using more aggressive reticle enhancement techniques (RET) and negative tone resists. Issue #2: Demonstration of commercial mask manufacturing with yield comparable to 180 nm optical masks. IBM's Advanced Mask Facility (AMF) has accepted the challenge from International Sematech to produce 200 x-ray masks per year with a 25X25 mm field size and 180 nm ground rules. The AMF intends to produce 50 XRL masks during three months in 1998-in addition to various masks for other customers. The industry's decision makers are anxious to compare the yield to 248 DUV mask manufacturing. Issue #3: Demonstration of mask irradiation stability. * Irradiation stability >50k wafers * Mask usage - 3,000 wafers @ 15 micron gap with resist. This manufacturing insertion issue is the subject of several studies including one funded by International Sematech, These irradiation stability studies comprise the following: Uniformly exposing masks with very high doses of x-rays, equivalent to 40,000 wafers then measuring mask distortion. Exposure of 1,000 wafers at 20 micron gap, another 500 exposed with overlay at 20 micron gap, and 100 exposed at 15 micron gap. Each phase may use a different mask, or the same mask may be used for more than one phase. Wafer performance is then evaluated. Several studies have found that there is no mask damage if the mask is irradiated uniformly as in normal operations. This data correlates to a study done by Franco Cerrina of the Center for X-ray Lithography (CXRL) at University of Wisconsin.1 In Japan, similar results from a mask stability study by Ashikaga et al., were found, "No pattern displacements as well as [no] optical transmission changes were observed" after a dose equivalent to 40,000 exposure shots.2 Issue #4: Experimental verification of magnification correction capability. * Capability, reliability, and accuracy * Measure real time in coordinate measurement tool * 50k (magnification correction) flexes XRL will be used in mix-and-match with optical lithography steppers. Differences between optical steppers, along with process-induced errors, require XRL steppers to adjust magnification by up to plus or minus 5 ppm to meet overlay tolerances. Several experiments are being conducted to prove that magnification correction is not only feasible but also reliable. All x-ray stepper manufacturers have investigated and modeled magnification correction methods. SAL is working with the University of Wisconsin to implement productionworthy adjustability. ---------------------------- Footnotes: 1 - One Step Ahead, Vol. 2 No. 4 1997 2 - Ashikaga, K., Tsuboi, T, and Yamashita, Y., "SR Radiation Stability of X-ray Mask," Proc. XEL'95, Osaka, Japan (July 23-26,1995).