chapter 3, EUV Source Technology

Excerpt

3.1 Introduction

EUV lithography (EUVL) is the leading technology, beyond 193-nm-based optical lithography, for printing circuits at the 32-nm node and below in a high volume manufacturing (HVM) environment fab. In EUVL, a 13.5-nm radiation wavelength generated by an EUV source is used to print circuits. Because light is strongly absorbed at this wavelength, the entire EUVL scanner system must be in a vacuum environment, and all optics must be reflective instead of refractive. Based on the HVM requirements of 100 wafers per hour (WPH) throughput and other system requirements for optics, resist sensitivity, and overhead (see Sec. 3.2.3), a power requirement of 115 to 180 W, based on resist sensitivity, has been specified for HVM EUVL scanners. Besides power, EUV sources must meet additional specifications (Sec. 3.2.2). The production-level requirements for EUV sources (Table 3.1) have been jointly agreed upon by major EUVL scanner manufacturers. Table 3.2 shows the change in EUV source requirements over time.

Discharge-produced plasma (DPP) and laser-produced plasma (LPP) are the leading technologies for generating high-power EUV radiation at 13.5 nm. In both technologies, hot plasma of ~30 eV of the chosen fuel material is generated, which produces EUV radiation. In DPP, magnetic pinching of low-temperature plasma generates the high-temperature plasma. In LPP, the target material is heated by a laser pulse to generate the high-temperature plasma. Today, tin (Sn) is the leading fuel for HVM-level EUV sources, with xenon (Xe) still being used to meet the lower power requirements of metrology sources, microexposure tools (METs), and alpha-level scanners.