Maybe this is why the Hamster/SludgePumper has been delayed until 2003 !!!
Price remains obstinate barrier to SOI usage
By Paul Kallender, EE Times
Oct 9, 2001 (3:05 PM)
URL: eetimes.com
TOKYO — Silicon-on-insulator technology is coming of age, but high wafer costs continue to hold back its widespread adoption even at companies that are its strongest proponents, according to attendees of last week's Solid State Devices and Materials conference.
Though defect problems with SOI wafers improved by three orders of magnitude in the late 1990s, some issues still remain, said Motorola Inc. senior principle staff scientist Michael Mendicino, speaking to an audience about SOI for microprocessor applications.
SOI wafers were typically riddled with as many as 10,000 defects as recently as 1997, but have been reduced to a fraction of that level and now nearly match those of bulk silicon wafers, Mendicino said. But even the best separation by implanted oxygen (Simox) wafers have pinholes and crystalline defects beneath the buried oxide layer that must be addressed, he said.
SOI's reduced junction capacitance, lack of reverse body effect and radiation hardness all indicate a bright future for the technology in limited applications, Mendicino said. He was bullish about its prospects for high-end devices, but bearish on its use in memory, ASIC and low-power communications devices. SOI costs will never be low enough to compete in the memory sector, and the ASIC market moves too fast for SOI-based designs, he said.
"But everyone is agreed that for high-performance logic, SOI is top of the list," he said. "The intrinsic performance advantage is 30 percent and this works out to x plus 20 percent in high-end chips."
Researchers at SSDM showcased a series of advances that will give SOI power beyond the scaling limits of CMOS and will hopefully make the wafers cheaper.
Jean-Pierre Colinge, a professor at the department of electrical and computer engineering at the University of California at Davis, outlined a new "ð" gate MOSFET he has built that use what he called a "virtual" back gate to form something like a four gate device.
Researchers are pressing to develop practical multiple-gate MOSFETs that boost current while keeping the drain's electric fields from encroaching on the channel region. The more the gate surrounds the channel region, the better the shielding. While quadruple gates are difficult to fabricate, the "ð" gate, which has two side gates buried 10 nanometers into the oxide, performs nearly as well as a "real" quadruple gate, Colinge said.
"A triple-gate is easy, but etched a little bit into the oxide for the two side gates, and the extensions give you extra field lines from the drain to give you a virtual fourth gate," he told EE Times.
After patenting the device, Colinge asked Taiwan Semiconductor Manufacturing Co. to build some prototypes. This work has been temporarily shelved "because of the economy," he said. The devices would eventually have 30-nm gate lengths and work on 0.3 volts, Colinge said.
"We don't think there are any fundamental challenges to eventually manufacturing these, but we will have to wait for the lithography tools to catch up first," he said.
SSDM featured 16 SOI-related papers that featured new devices and attacked existing process problems. One paper described ways to fabricate a double-gate SOI MOSFET. Mitsubishi Electric revealed a potential process for making 0.18-micron SOI CMOS for 3.3/1.8-volt operation that the company may develop for commercial production.
Researchers at NTT Laboratories reported efforts to develop 0.5-volt SOI CMOS for mobile devices. The Japanese government has been aiding development of low-power SOI as part of a national program involving eco-friendly technologies, which sprung up following the 1997 Kyoto Protocol, said NTT Labs' Takakuni Douseki. NTT's ultralow voltage SOI project hopes to develop SOI chips that operate at 100 MHz and dissipate from 1 to 10 milliwatts of power, he said.
Atsushi Ogura of NEC Corp.'s Silicon Systems Research Labs unveiled a light ion implantation process he believed could spurn a cheap alternative to the Simox process. While Simox is highly compatible with the VLSI process, the substrate is damaged during high-temperature annealing, which occurs at 1,350°C. Ogura's technique causes less damage, and allows the substrate to be annealed at room temperature for a shorter period of time than the standard Simox process, he said.
"This small-damage process definitely provided a good effect on crystal quality, and the room temperature implantation may give us a further advantage in developing a low-cost process," Ogura said.
Such promising techniques are vitally important if SOI is to come of age, said Yoshio Miura, retired former director of R&D at Nippon Motorola.
"We think [SOI] is a strong candidate for the future, but these days the most important point is the cost of the substrate," Miura said. "When I was working at Motorola, we used to say that if the price could drop to 3x that of bulk, SOI use would increase dramatically. But today that price is still between 5x and 10x."
Motorola, IBM, Advanced Micro Devices and Texas Instruments are heavy backers of SOI for 0.13-micron and 0.10-micron logic. But industry has been sending mixed signals of late on the merits of SOI compared to bulk CMOS. Recently, Sun Microsystems Inc. and Texas Instruments Inc. decided not to use SOI for Sun's next-generation microprocessor. On the other hand, IBM said it will use SOI to make its upcoming 0.13-micron Power4 processor.
Motorola has stated its commitment to SOI and intends to develop a future generation of SOI-based DSPs, said Mendicino. Having shouldered most of the costs to develop the technology, Motorola wants SOI in place for the upturn, he said.
Cost is the only remaining frontier, Mendicino said.
"Five years ago I could show you road maps that said costs would be competitive with bulk at the volumes we have today," he said. "We have the volumes now, but we don't have the prices. Cellular phone makers would love SOI's 20 percent performance benefit and dynamic power, but they can't afford the price." |
