Proceedings Article | 28 May 2004
Jason Pan, John Viatella, Palash Das, Yasushi Yamasaki
KEYWORDS: Semiconducting wafers, Scanners, Laser scanners, 3D scanning, Lithography, Reticles, Attenuators, Mirrors, Control systems, Reliability
With the advent of advanced 193 nm systems processing 300 mm wafers, the production lithography cell is about to undergo a technology shift. This is because processing 300 mm wafers requires introduction of several new technologies. These include technologies that enable increasing light source power at 193 nm - the NA of the projection lens and the speed of scanner stages. Coupled with the need to maintaining high wafer throughput, the scanners must also deliver very tight CD control to within few nm, (typically less than 3 nm). Cymer, Inc. believes that certain key technologies - traditionally ignored at 248 nm for 200 mm wafers - must be revisited. This paper pertains to one such technology: the mechanism to deliver stable light from the light source to the input of the scanner. We refer to this as the Beam Delivery Unit (BDU). To support these changes, Cymer has developed a BDU that will guarantee a stable beam at the scanner entrance, during exposure. There are three aspects to beam stability: 1. Optical transmission, 2. Beam positioning and, 3. Beam angle. Position stability impacts dose stability (energy per pulse integrated over several pulses) at the wafer and pointing instability adversely affects the illumination uniformity at the reticle. To the lithography process engineers, the effects of beam stability are not new; both result in loss of CD control. At 130 nm node, the loss of CD control due to beam instability was insignificant, therefore ignored. However, below that node, we will show that unless the beam exiting the BDU is stabilized in position and pointing, the loss in CD control is of the order or 1 nm, which is a significant portion of the total CD control budget. For example, for MPU gate node of 65 nm, the ITRS roadmap allocates CD control of 3.7 nm. Thus, the 1 nm loss of CD control due to aforementioned instability alone is considered to be very significant. To address this critical loss in CD control, Cymer has implemented a novel beam stabilization control system in the BDU. Such beam stabilization maintains beam position and pointing during exposure of a die of a wafer, virtually eliminating CD control errors. Cymer has also incorporated reliable BDU materials technology that maintains stable transmission over several years of operation. Cymer's beam stabilization control system is the subject of this paper.
