VUV lithography based on SiC reflective optical systems and SASE FEL coherent light sources as a natural extension to shorter wavelengths of present-day optical lithography technology

The semiconductor industry growth is driven to a large extent by steady advancements in microlithography. According to the newly updated industry roadmap, the 50 nm generation is anticipated to be available in the year 2012. This paper discusses the basic concepts of VUV lithography (VUVL), a relatively new form of lithography that uses vacuum ultraviolet radiation (VUV) with a wavelength in a range of 50 to 100 nm to carry out projection imaging. This approach uses a self amplified spontaneous emission (SASE) free electron laser (FEL) as a source of radiation, a reflective mask, and a 4X reduction all reflective imaging system. The reflective elements for VUVL use SiC mirrors to produce normal incidence reflectivities nearly 40%. The mask in a VUV system also uses the same type of SiC material. Recent advances in SASE FEL systems suggest the feasibility of flexible sources for microelectronic production facilities. Any lithography must satisfy cost-ownership requirements. A VUV SASE FEL source is economical for high-volume production, because it can feed multiple steppers. The average SASE radiation on wafers is about 1 W, and throughput of each stepper is 90 wafer/hr. Estimated SASE FEL source portion of total cost is about $ 0.5 per 300 mm wafer. We believe that the underlying simplicity of the technology, particularly the mask and mirror and low source portion of total cost will make VUVL a cost effective solution for lithography at 100 nm and below. Since the wavelength of SASE FEL source is adjustable, selection of new materials needed for photoresists may be much easier than for the case of fixed wavelength source. SiC mirrors with characteristics required for VUVL optics are produced by industry. All components of the proposed SASE FEL source equipment have been demonstrated in practice. This is guaranteed success in the time requirement. (orig.)