Low-energy e-beam proposed for next-generation lithography
By Yoshiko Hara, EE Times
Dec 14, 2001 (7:44 AM)
URL: eetimes.com
TOKYO — A beta prototype system for low-energy e-beam proximity projection lithography (LEEPL) is being pitched here for use at the 70- and 50-nanometer process nodes.
While LEEPL has been excluded from most next-generation lithography R&D projects to date, the prototype equipment, shown by Leepl Corp. (Tokyo) earlier this month at the Semicon Japan show, is garnering attention as a low-cost, simple approach to next-generation lithography.
"In the coming year, we expect that we can prepare LEEPL equipment and the infrastructure for volume production lines," said Kiyoaki Tsuta, chief technology officer of Tokyo Seimitsu Co. Ltd. and director of Leepl Corp. , an R&D joint venture backed by Tokyo Seimitsu, and NTT Advanced Technology Corp., which provides technology support. Since its founding in June 2000, Leepl has been proposing the low-energy e-beam technology as a solution for advanced lithography processes below 100-nm (0.10-micron) design rules.
In parallel with the equipment development, Leepl Consortium founders Leepl Corp., Tokyo Seimitsu and Sony Corp. have marshaled the group's membership to prepare the infrastructure for LEEPL-based lithography.
"The infrastructure [for lithography] in Japan is marvelous," Tsuta said. "Through the activity of the Leepl Consortium, member companies developed silicon stencil masks. [Initially] there had been no adequate resist materials, because the speed of the electrons is slow, at 2 kV. But just in the last 10 months, development of resists [has also progressed] smoothly.
"We will continue to evaluate the system and want to expand the promotion of LEEPL to overseas device manufacturers as well."
Leepl Corp. put prototype equipment for its lithography technology on public view at the Semicon Japan show.
At Semicon Japan, Leepl exhibited the beta version of the lithography system and silicon stencil masks as well as an earlier, diamond stencil mask. The beta machine prints 45-nm lines and forms 50-nm contact holes. It is said to achieve overlay adjustment accuracy at 25 nm, which is required for the 70-nm node in the International Technology Roadmap for Semiconductors (ITRS 2001).
The beta system is equipped with an automatic loader and changer for volume production and has a claimed throughput of more than thirty 300-mm wafers per hour. The equipment handles both 300-mm and 200-mm wafers via a loader change.
Leepl is pushing for evaluation of the equipment's suitability at the 70- and 50-nm nodes. The venture hopes to offer the system "for a 70-nm process at less than 1 billion yen [about $8 million]," said Tsuta. With next-generation steppers expected to cost tens of millions of dollars, low cost is LEEPL's strong suit, its proponents said.
LEEPL combines the best of X-ray and e-beam lithography technologies, its proponents claim. The technology employs real-size proximity projection instead of the widely proposed demagnification projection method. The stencil mask and wafer are placed as close as 50 microns apart, and a low-energy parallel e-beam prints the 1x mask patterns onto the wafer. Real-size proximity projection does not require the use of lenses and thus yields a low-cost, simple system, backers said.
Leepl chairman Takao Utsumi and president Nobuo Shimazu developed the core LEEPL technologies, for which U.S. patents were obtained in 1998. Developers demonstrated the alpha prototype of the lithography system at Semicon Japan 2000.
The Leepl Consortium was established in June with 13 members. The membership now stands at 16 and includes four device manufacturers (NEC Corp., Rohm Co. Ltd., Sony and Texas Instruments Inc.), four mask manufacturers (Dai Nippon Printing Co. Ltd., Hoya Corp., NTT Advanced Technology Corp. and Toppan Printing Co. Ltd.), five manufacturers of resists and materials (Fiji Film Arch Co. Ltd., JSR Corp., Shin-Etsu Chemical Co. Ltd., Shipley Far East Ltd. and Tokyo Ohka Kogyo Co. Ltd.) and three equipment manufacturers (Leepl, Tokyo Seimitsu and Toshiba Machine Co. Ltd.).
Next-generation potential
"Sony sees LEEPL as one of most [promising] potential next-generation lithography systems," a spokesman for that company said. "To develop lithography technology, device manufacturers' input is important. We believe Sony can contribute extensively, and [Sony] is aggressively participating in the activity."
Three masks were exhibited at Semicon Japan. One was a diamond membrane mask; the two others were silicon stencil masks. Early systems used diamond membranes to maintain rigidity. But Sony proposed a structure in which a mask would be divided into four quadrants, with each quadrant having beams and crossbeams in a grid pattern to lend rigidity to the silicon masks. As beams are placed in a complementary position in each of the quadrants, multiplex exposure of the four quadrants yields one complete pattern.
Hoya and Toppan Printing developed the mask blanks using the complementary beam structure. The beams radiate heat efficiently and enable the membrane to be made thinner. The thickness of the membrane used in the prototype is 2 microns (2,000 nanometers), but the beam structure enables membranes to be made as thin as 500 or even 300 nm.
Heat radiation will eventually enable beams to be used in the diamond membranes as well, Tsuta said. "For the LEEPL mask, we want to make 50 mm x 50 mm the standard size," he said. That size accommodates today's largest chip.
Tokyo Seimitsu plans to put a factory next to its Hachioji works in Tokyo to build the LEEPL printer system. The production target is about 30 units a year. |
