Somewhere around 40nm is the limit on the smallest half-pitch feature that can be formed with a single-exposure of 193-nm wavelength laser light using water immersion (193i) lithography. While multiple-patterning (MP) is needed to achieve tighter half-pitches, smaller features at the same pitch can be formed using technology extensions of 193i. “Chemistry is key player in lithography process,” is the title of a short video presentation by Dow Electronic Materials corporate fellow Peter Trefonas now hosted on the SPIE website (DOI: 10.1117/2.201608.02).
Trefonas as been working on chemistries for lithography for decades, including photoresists, antireflectant coatings, underlayers, developers, ancillary products, and environmentally safer green products. He is an inventor on 61 US patents, has over 25 additional published active U.S. patent applications, is an author of 99 journal and technical publications, and is a recipient of the 2014 ACS Heroes of Chemistry Award and the 2013 SPIE C. Grant Willson Best Paper Award in Patterning Materials and Processes. Now a Senior Member of SPIE, he earned his Ph.D. in inorganic chemistry with Prof. Robert West at the University of Wisconsin-Madison in 1985.
Trefonas explains how traditional Chemically-Amplified (CA) resists are engineered with Photo-Acid Generators (PAG) to balance the properties for advanced lithography. However, in recent years the ~40-nm half-pitch resolution limit has been extended with chemistries to shrink contact holes, smooth line-width roughness, and to do frequency-multiplication using Directed Self-Assembly (DSA). All of these resolution extension technologies rely upon chemistry to create the final desired pattern fidelity.
The mega-merger between Dow and DuPont has already shaken out an under-performing product line: Powerhouse(TM) solar singles. As reported at PVTech, over 100 jobs in Milpitas, California and in Midland, Michigan will be lost along with the production line that assembles the copper-indium-gallium-sulfide (CIGS) cells into thin-film Building-Integrated PhotoVoltaic (BIPV) rooftop shingles. BIPV markets are very slow to grow due to inherent risk-aversion in considering new building materials, and it has been difficult to cobble together sufficient consumer demand for upgrades to existing roofs to support a profitable business. Dow had offered a 20-year product warranty and optional financing to try to move the market.
“We’re looking at this one product that could generate $5 billion in revenue by 2015 and $10 billion by 2020,” Jane Palmieri, managing director of Dow Solar Solutions, told Reuters in a 2009 interview. Dow had used CIGS cells from Global Solar for a first-generation of the product line, and then acquired NuvoSun in 2013 to own it’s own thin-film CIGS manufacturing technology in anticipation of booming demand for large solar shingles with integrated internal electronics and easy rooftop installation.
When comparing the benefits of different PV product offerings, one factor dominates the decision: all PV installations are area-constrained, and rooftops are extreme examples. The cost of the panel hardware is typically only ~25% of the complete installed system, with Balance Of System (BOS) costs for electronics and installation and financing and permits and non-recurring engineering (NRE). CIGS BIPV may cost less than silicon BIPV, but reduced conversion efficiency means less power can be produced from the roof and when you “do the math” it is always more profitable to use the most efficient PV possible.
It is worth noting that the market for solar shingles had been poisoned by pathetic products from UniSolar leaving a severely negative impression on consumers. UniSolar was part of the Energy Conversion Devices portfolio of shell-companies that went bankrupt in 2012, and the UniSolar solar shingles had 6-8% cell efficiency using amorphous-silicon (a-Si) and no integration with electronics such that a hole had to be drilled through the roof for each shingle to connect to a micro-inverter (leading to extreme installation costs and an inherently leaky roof). So unfortunately, Dow faced a severe up-hill-battle in the roofing market to fight against a negative impression of all solar shingles.
Trefonas made major contributions to the development of many successful products which are used in the production of integrated circuits spanning device design generations from 2 microns to 14 nanometers. These include photoresists, antireflectant coatings, underlayers, developers, and ancillary products. At the most recent SPIE Advanced Lithography conference he was part of a team that presented on the use of a resolution extension material, “Chemical trimming overcoat: an enhancing composition and process for 193nm lithography.”
He is an inventor on 61 US patents, has over 25 additional published active U.S. patent applications, is an author of 99 journal and technical publications, and is a recent recipient of both the 2014 ACS Heroes of Chemistry Award and the 2014 SPIE Willson Award. His research career began at Monsanto, and moved via acquisitions by Shipley, Rohm&Haas, and Dow.