The biggest semiconductor trade show in North America, SEMICON WEST 2008 has concluded couple of days ago (15-17 July). One of impending issues facing the semiconductor industry is the lithography solutions for 32nm and 22nm. It is pretty obvious now that EUV lithography will not be deployed for 32nm, and most likely will not be ready for 22nm as well. On the other hand, the immersion lithography technology which has served the semiconductor industry pretty well for 45-40nm will face its own limitations for 32nm and beyond. To bridge the gap for 32nm and 22nm before EUV lithography comes on board, the semiconductor industry is now betting on double patterning lithographic technology coupled with 193nm immersion lithography. However, as AMD Fellow Harry Levinson aptly summarized the current challenges of DP technology as “double patterning doubles the troubles” (Ref).

There are a number of variants for double patterning technology, such as double-exposure; trench double-patterning; line double-patterning; litho-etch-litho-etch, spacer and others. Whatever the variants, the biggest concerns with double-patterning technology are cost and overlay, particularly the overlay between the two exposures. To mitigate the overlay constraints, AMAT has introduced the Self-Aligned Double Patterning (SADP) Scheme. Samsung Electronics and Hynix Semiconductor Corp have announced they would use SADP for their 3x generation NAND flash. The IM Flash also reported that it would employ something similar to SADP for the 34nm memory devices (Ref).

During the SEMICON WEST 2008, IMEC announced a new variant of the double patterning technology which significantly reduces the cost. The new process first exposes the resist with the first pattern, apply a chemical enhancement to freeze that pattern into the material, expose the second pattern, and then develop and etch the resist normally. The big advantage of this approach is that the wafer stays on the litho track for both exposures. It doesn’t have to go off to a separate etch track and then back onto the litho track. (Ref)

On the other note, ASML has rolled out a new generation of 193-nm immersion scanner for double-patterning applications, Twinscan XT:1950i during the SEMICON WEST. It has an overlay below 4-nm and throughput of 175 wafers an hour. The system uses a lens with the same 1.35 numerical aperture (NA) as its predecessor, however the resolution has improved from 40 nm to 38 nm, which effectively provides a 10% gain in wafer area available for chips (Ref). You can watch a videos ads from ASML of this system below.

In Chinese, water symbolizes wealth. Therefore, the Chinese believes no splashing of water out of the house. In the semiconductor industry, water has also brought great fortune to ASML, a Dutch-based litho tool company that invested early in water-based immersion lithography R&D. The company has benefited on the rapidly growing trend of water-based immersion lithography which is now widely accepted by the industry as the most viable solution to extend the life of 193nm DUV lithography beyond 45nm to even 22nm.

According to the latest equipment companies ranking by Gartner, AMSL has strengthened its top spot in litho suppliers and maintained number 3 position in the overall equipment market. In contrast, its rivals Nikon and Canon have slided to number 6 and 13, respectively (Ref). In particular, the market share of Canon has slumped significantly in recent years.

One key success factor of ASML’s immersion systems is attributed to its TWINSCAN platform which incorporates two wafer stages in one lithographic system. One wafer stage is used for exposing the wafer, while the other wafer stage is used for wafer alignment in parallel. Once the imaging is completed on the first wafer, the two stages are swapped and the aligned wafer moves into the exposure position. This eliminates virtually all overhead time, allowing continuous patterning of product wafers for maximum productivity. In addition, the “dry measurement, the wet exposure” approach is particularly conducive for accurate wafer measurement. ASML’s latest immersion tool, TWINSCAN XT:1900Gi takes full advantage of the TWINSCAN platform, and offers the highest NA (1.35) in the industry. Besides the hardware improvement, 1900Gi also bundled with software capabilities to enhance lithographic process, such as QUASAR XL, LithoGuide ILIAS, DoseMapper, Reticle Shape Correction, CDFEC and Focus Spot Monitor (Ref).