PhD Oral Defense -- Jen-Shiang Wang

Jen-Shiang Wang jenwang at
Mon Feb 13 12:47:07 PST 2006

Dear lab members,

I will have my oral defense presentation this afternoon at 4:15 PM at AP 200 (in Ginzton Lab).
I hope to see you there if you happen to have time.


University Ph.D. Oral Examination

Jen-Shiang Wang

Department of Electrical Engineering, Stanford University

Advisor: Prof. Olav Solgaard

4:15 PM, Monday, Feb 13th, AP 200. (Refreshments served at 4:00 PM).


“High-Resolution Optical Maskless Lithography Based on Micromirror Arrays”


The increasing cost of photo masks in optical lithography is identified as a key barrier for migrating to sub-100nm features in integrated circuit manufacturing.  An economical solution, called optical maskless lithography, has drawn broad interests in the IC industry.  In optical maskless lithography, an array of reconfigurable micromirrors replaces the traditional photo mask. Based on their mechanical motion, these micromirrors can be categorized into two groups: tilt mirrors and piston phase-shift mirrors.  These two types of mirrors have their own advantages and disadvantages, so the optimal mirror architecture has been a topic of debate over the past few years.  


We have developed a theoretical model and criteria to evaluate micromirror configuration and verified the model with the simulations (accuracy within ±1.5%).  We found that 4-piston mirror is the optimal micromirror configuration, which not only has the capability to generate high-resolution features with strong phase-shift effects, but also has a larger depth of focus and process window in arbitrary pattern generations.  


Then, I will present an optimal operation strategy for maskless lithography.  The strategy utilizes multiple exposures and takes advantage of inherent perfect alignment in maskless lithography system to achieve both high resolutions and large depths of focus.  The improvement is verified by an analytic model, and a maximum of 8X improvement in the depth of focus is demonstrated by simulations.  Other advantages including relaxing the requirement in the ratio between the minimum feature size and the mirror size, simplifying resolution enhancement, fixing twists in vortex patterns will also be presented.   In practice, an array of millions of micromirrors is needed for a high throughput production. To efficiently calibrate such a large number of mirrors, we proposed a method using high sensitive interferometric schemes.  The typical sensitivity improvement is about 3X to 4X when the optimized schemes are used.  


Lastly, I will present the design, process, fabrication, and characterization of an elastomer piston mirror array, or an elastomer spatial light modulator (SLM), that can be scaled to meet the requirements of extreme ultraviolet (EUV- 13nm wavelength) optical maskless lithography.  An array of 8-by-7 piston mirrors, a concept-proof device, having a localized piston-motion response with a maximum deflection of 10 nm in an effective area of 14mm-by-14mm will be presented.  
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