|
Extreme ultraviolet lithography (also known as ''EUV'' or ''EUVL'') is a next-generation lithography technology using an extreme ultraviolet (EUV) wavelength, currently expected to be 13.5 nm. EUV is currently targeted for possible future use below 15 nm resolution after the 7 nm node, in 2018–19.〔(Globalfoundries to develop 7nm and 10nm in-house )〕〔(TSMC plans EUV for 5nm )〕 The primary EUV tool maker, ASML, projects EUV at 5 nm node to require a higher numerical aperture than currently available and multiple patterning to a greater degree than immersion lithography at 20 nm node.〔(ASML - Many ways to shrink (Nov 2014) )〕 It was first targeted for 100 nm conventional patterning. While source power is the chief concern due to its impact on productivity, significant changes in mask infrastructure, including blanks, pellicles and inspection, are also under study. Particle contamination would be prohibitive if pellicles were not stable above 200 W, i.e., the targeted power for manufacturing.〔(EUVL activities in South Korea (including Samsung and SKHynix) )〕 Without pellicles, particle adders would reduce yield, which has not been an issue for conventional optical lithography with 193 nm light and pellicles. ==Light source== Neutral atoms or condensed matter cannot emit EUV radiation. Ionization must precede EUV emission in matter. Electrons must be bound to multicharged positive ions; for example, to remove an electron from a +3 charged carbon ion (three electrons already removed) requires about 65 eV.〔(【引用サイトリンク】title=WebElements Periodic Table of the Elements )〕 Such electrons are more tightly bound than typical valence electrons. The thermal production of multicharged positive ions is only possible in a hot dense plasma, which itself strongly absorbs EUV. Xe or Sn plasma sources are either discharge-produced or laser-produced. Discharge-produced plasma is made by discharging a lightning bolt's worth of electric current through a tin vapor. Laser-produced plasma is made by microscopic droplets of molten tin heated by powerful laser. Laser-produced plasma sources (e.g., ASML's NXE:3300B scanner) outperform discharge-produced plasma sources. Power output exceeding 100 W is a requirement for sufficient throughput. While state-of-the-art 193 nm ArF excimer lasers offer intensities of 200 W/cm2, lasers for producing EUV-generating plasmas need to be much more intense, on the order of 1011 W/cm2. This indicates the enormous energy burden imposed by switching from 193 nm light (power output approaching 100 W) to EUV light (10 kW).〔V. Bakshi, 2009 EUVL Workshop Summary, Sheraton Waikiki, Hawaii, July 13–17, 2009.〕 An EUV source driven by a 200 kW CO2 laser with ~10% wall plug efficiency〔(Cymer presentation at 2007 EUV Source Workshop )〕 consumes an electrical power of ~2 MW, while a 100 W ArF immersion laser with ~1% wall plug efficiency consumes an electrical power of ~10 kW. A state-of-the-art ArF immersion lithography 120 W light source requires no more than 40 kW〔T. Asayama ''et al.'', Proc. SPIE vol. 8683, 86831G (2013).〕 while EUV sources are targeted to exceed 40 kW.〔(ASML update Nov. 2013, Dublin )〕 A further characteristic of the plasma-based EUV sources under development is that they are not even partially coherent,〔(【引用サイトリンク】title=A New Light Source for EUV Lithography )〕 unlike the KrF and ArF excimer lasers used for current optical lithography. Further power reduction (energy loss) is expected in converting incoherent sources (emitting in all possible directions at many independent wavelengths) to partially coherent (emitting in a limited range of directions within a narrow wavelength band) sources by filtering. Coherent light poses a risk of monochromatic reflection interference and mismatch of multilayer reflectance bandwidth. , development tools had a throughput of 4 wafers per hour with a 120 W source.〔(ASML update on ADT )〕 For a 100 WPH requirement, therefore, a 3 kW source would be needed, which was not expected to be available in the foreseeable future. However, EUV photon count is determined by the number of electrons generated per photon that are collected by a photodiode. This is essentially the highly variable secondary yield of the initial photoelectron, yielding highly variable dose measurement. Data by Gullikson ''et al.'' indicated ~10% natural variation of the photocurrent responsivity. More recent data for silicon photodiodes agree with this assessment. Calibration of the EUV dosimeter remained a nontrivial unsolved issue. The secondary electron number variability is the well-known root cause of noise in avalanche photodiodes. The highly relativistic vacuum tube free-electron lasers and synchrotron radiation sources can give better light quality than material sources, though high intensity may require development work. Existing dedicated industrial synchrotron light facilities with applications including semiconductor device fabrication. Free electron lasers offer light that is monochromatic and coherent, as well as narrow in space and angle spread. Both also offer a continuous range of available wavelengths, allowing seamless progress into the X-ray band.〔Robert W. Hamm and Marianne E. Hamm, "The Beam Business: Accelerators in Industry", ''Physics Today'', June 2011, pp. 49–50〕 At SPIE 2014, TSMC reported that the 200 kW CO2 laser for their NXE:3100 EUV tool light source had a misalignment problem.〔(【引用サイトリンク】title=Intel, TSMC Revive EUV Hopes )〕 The laser was supposed to focus on a tin droplet that absorbs the power to generate EUV light. Missing the droplet directed the power elsewhere, leading to component damage and downtime. As of September 2015, ASML demonstrated EUV tools with light source power of 130W and over 70% uptime at multiple customer sites, but only for limited one-week periods, over four weeks in one case. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Extreme ultraviolet lithography」の詳細全文を読む スポンサード リンク
|