Silicon-germanium

SiGe (ˈsɪɡɪː), or silicon-germanium, is a general term for the alloy Si_1-xGe_x which consists of any molar ratio of silicon and germanium. It is commonly used as a semiconductor material in integrated circuits (ICs) for heterojunction bipolar transistors or as a strain-inducing layer for CMOS transistors. This relatively new technology offers opportunities in mixed-signal circuit and analog circuit IC design and manufacture.

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Production

SiGe is manufactured on silicon wafers using conventional silicon processing toolsets. SiGe processes achieve costs similar to those of silicon CMOS manufacturing and are lower than those of other heterojunction technologies such as gallium arsenide. Recently, organogermanium precursors (e.g. isobutylgermane, alkylgermanium trichlorides, and dimethylaminogermanium trichloride) have been examined as less hazardous liquid alternatives to germane for MOVPE deposition of Ge-containing films such as high purity Ge, SiGe, and strained silicon.^{[1] [2]}

SiGe foundry services are run by companies including IBM, STMicroelectronics, TSMC, Freescale (originally Motorola Semiconductor), Sony, Atmel, Chartered Semiconductor, Micrel, Infineon, TI, IHP, and Jazz Semiconductor (originally Conexant). AMD disclosed a joint development with IBM for a SiGe stressed-silicon technology^[3], targeting the 65-nm process.

SiGe Transistors

SiGe allows CMOS logic to be integrated with heterojunction bipolar transistors, making it suitable for mixed-signal circuits. Heterojunction bipolar transistors have higher forward gain and lower reverse gain than homojunction bipolar transistors. This translates into better low current and high frequency performance. Being a heterojunction technology, the opportunity for band gap tuning exists which has normally been available only to compound semiconductors. Silicon Germanium-on-insulator (SGOI) is a technology similar to the Silicon-On-Insulator (SOI) technology currently employed in computer chips. SGOI increases the speed of the transistors inside microchips by stretching the space between the atoms, which forces the electricity to travel faster.

SiGe also is used in MOSFETs where it is found to increase carrier mobilities and to reduce junction leakage.

References

1. ^ E. Woelk, D. V. Shenai-Khatkhate, R. L. DiCarlo, Jr., A. Amamchyan, M. B. Power, B. Lamare, G. Beaudoin, I. Sagnes (2006). "Novel Organogermanium MOVPE Precursors". Journal of Crystal Growth 287 (2): 684-687. doi:10.1016/j.jcrysgro.2005.10.094.
2. ^ Deo V. Shenai, Ronald L. DiCarlo, Michael B. Power, Artashes Amamchyan, Randall J. Goyette, Egbert Woelk (2007). "Safer alternative liquid germanium precursors for relaxed graded SiGe layers and strained silicon by MOVPE". Journal of Crystal Growth 298: 172-175. doi:10.1016/j.jcrysgro.2006.10.194.
3. ^ AMD And IBM Unveil New, Higher Performance, More Power Efficient 65nm Process Technologies At Gathering Of Industry’s Top R&D Firms retrieved at March 16, 2007