DALLAS -- Several months later than originally planned, Texas Instruments Inc. has qualified a 900-MHz 64-bit RISC processor, with copper and low-k interconnects, for volume shipment to Sun Microsystems Inc., which will now use the central processing units in workstations within the next 90 days (see July 30 story).
The new UltraSparc III is TI's first all-copper, low-k processor and the latest step towards 64-bit RISC chips that operate with speeds up to 1.5 GHz, according to a roadmap disclosed by Sun last year (see Sept. 27, 2000, story). The roadmap last fall showed the 900-MHz processors to be ready for products in the first quarter of 2001. Sun's roadmap showed a 2.1-GHz UltraSparc V being targeted for 2003.
In disclosing the achieved 900-MHz milestone, TI and Sun managers told SBN that even faster UltraSparc III processors are now being produced with the current CMOS process, which uses 0.10-micron channel-length transistors in a 0.15-micron class technology. The new processor has seven layers of copper metal and a low-k dielectric insulator of fluorinated silicate glass (FSG).
At 900 MHz, the UltraSparc III maintains its status as the world's fastest commercially available 64-bit central processor for workstations and servers, according to TI and Sun. The two companies claim that the UltraSparc III CPU beats IBM Corp.'s existing high-end Power4 processors in terms of frequency and low-power dissipation and Intel Corp.'s targets for its 64-bit Itanium processor.
To take Sun's RISC processor to higher speeds, TI is preparing a next-generation 0.13-micron process technology node, which will feature 0.065-micron (65-nanometer) transistors that can eventually be shrunk to 0.055-micron (55-nm) length.
After initially trying spin-on dielectrics for copper interconnects, TI has decided to pursue chemical vapor deposition (CVD) for low-k films in next-generation copper interconnect processes. "We have decided that spin-on has too many problems in uniformity, yields, and other issues," said Dennis D. Buss, vice president of silicon technology development at TI.
Consequentially, TI is now planning to integrate copper dual damascene processes with low-k dielectrics in the form of organosilicate glasses (OSG) using CVD tools and processes from Novellus Systems Inc. The next-generation 0.13-micron copper process will employ 193-nm lithography scanners and OSG dielectrics with a k rating of 2.7 (compared to the current 3.7 using FSG).
TI's work on Sun's 64-bit UltraSparc processors is setting the pace for its own processes used in digital signal processors. The Dallas company exclusively develops a ultra-high performance transistor and interconnect version of its leading-edge processes for Sun's central processing units, under a 13-year partnership in RISC chips, said Julie Spicer England, vice president and general manager of TI's Sun Microsystems Business unit. The transistor gate lengths are slightly relaxed for cost/performance-optimized TI's high-end DSP chips, she said.
In the foreseeable future, TI and Sun plan to continue to use bulk silicon substrates for high-performance RISC processors, and there are no plans to eventually shift to silicon-on-insulator (SOI) wafers, Buss said. "We have exchanged Spice design models and evaluated SOI, but we have determined there is little benefit in performance as the voltages are reduced," he said. "The higher costs--eventually 10% over bulk silicon--has little payback. The higher costs come from both the design infrastructure changes and manufacturing costs," Buss explained.
The issue of using SOI in processors has been raised recently after Advanced Micro Devices Inc. announced it planned to move 100% of its personal computer microprocessors to silicon-on-insulator substrates to lower power consumption and boost speeds (see July 13 story). IBM Microelectronics has also been pursuing greater use of SOI substrates for several years.
Sun has already seen some chip speed exceeding 1 GHz with the current copper processes at TI, said David W. Yen, vice president and general manager of Sun's Processor Products Group based in Palo Alto, Calif. Those higher frequency processors will eventually make their way into Sun systems and products once testing qualify the higher speed grades. At 900-MHz speeds, the 29 million-transistor UltraSparc III has a maximum power dissipation of just 75 watts.