Mask tech advances attract new members to Leepl consortium

By Paula Doe
Contributing Editor WaferNews

Two more potential big users have signed on to the Low Energy E-Beam Projection Lithography consortium (Leepl). Matsushita Electric Industrial and Sharp will now join Sony, Rohm, NEC, and Texas Instruments in working on developing the low-cost alternative next generation lithography technology. Nippon Control Systems, which makes mask data conversion systems, will also join the group, bringing member companies to 19.

Leepl’s eccentric 1x e-beam exposure system has started to look more feasible with recent progress in technology for making the required ultra-thin stencil masks. Toppan Printing and HOYA have now each separately developed masks for the system made of silicon, instead of the diamond film that had been used in demonstration masks so far. Both use technology developed by Sony to support the weaker silicon with a lattice of beams so it can be made thinner, reportedly much as Nikon does in its e-beam masks. Sony researchers say the lattice support system makes it easy to produce very thin masks.

Much work, however, still remains before the system is practical for chip production.
These first silicon masks are 2-microns thick, and that will have to be brought down to at least 0.5-microns to make 70nm lines. And the group is putting support beams across the mask blocks sections of the pattern, so the masks must be exposed four times through four subfields formed by different complementary lattice arrangements to make the complete pattern.
Toppan’s dry-process mask shown at Semicon Japan has a subfield of 1mm square. HOYA’s wet-process version has a 3.8mm-square subfield. Though the four-fold multiplex exposure process drastically reduces throughput, Leepl researchers have told Nikkei Microdevices Online that with efficient arrangement they can actually get 60% of single-exposure throughput, not the 25% one might expect from the four-fold process. Leepl officials have said previously that their system’s throughput was about 30 wph. Tokyo Seimitsu researchers say work is advancing on making masks of silicon carbide and silicon nitride, and getting thickness down to 0.2- to 0.3-microns. They expect to have a patterned mask ready for exposure by mid-year.

Leepl also claims good progress over the last six months in developing thinner resists specifically for its e-beam projection system, and says it can make 30nm lines. It plans to install a beta tool at Sony this year, and to begin investing in producing for the commercial market in April 2003. Tokyo Seimitsu recently bought out more of the two Leepl founders’ share, to take control of 67% of the company. TSK is making the tool the first step in its strategy to diversify from its probers and dicers into the front-end equipment market.

Other current Leepl consortium members are NTT Advanced Technologies, Dainippon Printing, Toppan, HOYA, Tokyo Ohka, JSR, Fuji Film Arch, Toshiba Machine, Shin-Etsu Chemical, Shipley Far East.-P.D.


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