Silicon germanium

from Wikipedia, the free encyclopedia

Siliciumgermanium (technical language; standard language silicongermanium ), SiGe for short, is an IV-IV compound semiconductor consisting of the elements silicon (Si) and germanium (Ge).

Manufacturing

Due to the relationship with silicon technology , many processes can be transferred. For the production of conventional silicon are wafer used, the similar strained silicon are a SiGe layer expanded. The process engineering is realized by means of epitaxy . A solid SiGe layer is deposited from silane (SiH 4 ) and German (GeH 4 ) at temperatures around 600 ° C. The Ge content of the SiGe layer can be adjusted with the gas flows (5 to 30  atomic percent ). The monocrystalline SiGe layer is stressed as a result. Only when a critical layer thickness is exceeded does the layer relax (relax) and undesired crystal dislocations arise.

In addition, carbon is preferably introduced into boron - doped base zones of bipolar transistors , which is why SiGe technology is often also referred to as SiGe: C. This significantly reduces the rate of diffusion of the dopant boron in the base zone during subsequent temperature processes and prevents the boron from diffusing out of the SiGe layer. It is possible to design the epitaxial process in such a way that a layer stack consisting of a Si start layer, the p-conducting SiGe base zone and an n-conducting Si cover layer (emitter) is deposited.

application

The transistors have a hetero-junction ( heterojunction bipolar transistor , HBT). The main application is the high-frequency - Electronics and the area fast digital technology .

Research at the Ruhr University Bochum in 2003 in the working group of Hans-Martin Rein paved the way for SiGe for the high-frequency range at 77 GHz by developing circuits on this process that could fully exploit the potential of the SiGe process . For this reason, SiGe is suitable, for example, for use in the area of ​​vehicle radars at 77 GHz for frequency generation or signal conversion. SiGe is used, for example, in a distance warning radar from Robert Bosch GmbH (start of series production in the first quarter of 2009) and the Infineon chipset (RXN774x family) used by him. In addition to SiGe as the base material for high-frequency applications around 77 GHz, gallium arsenide (GaAs) should also be mentioned, which, however, in the current state of technology (2006) does not come close to the limit frequency of SiGe and is also considerably more expensive. Since, in contrast to SiGe, power levels are also possible with GaAs, it can be interesting to stick with GaAs as long as this material still has the required frequency.

Developments in the years 2008 to 2010 showed achievable transit frequencies of 250 GHz up to 500 GHz.

At the beginning of the 2000s, SiGe was also used in conventional processors for desktop PCs (Intel, IBM / AMD). This makes use of the fact that the charge carrier mobility of electrons and defect electrons can be increased by mechanical stresses (so-called strained silicon ). For electrons and holes, this effect depends on the type of strain and the crystal orientation; compressive stress, for example, worsens the charge carrier mobility of electrons in <100> -Si but improves that of the hole. The silicon germanium is not used here as a channel material. Instead, it is used to brace the canal. For this purpose, after the production of the polysilicon gate, the silicon of the actual source-drain regions in the vicinity of the channel is etched out (by reactive ion etching, etc.) and then refilled with an epitaxial CVD -SiGe. Due to the different volume expansion of SiGe and Si, the area between the source and drain area (i.e. the channel) is stressed (compressive stress) during cooling. In principle, this technique can also be used in conjunction with conventionally constructed gate stacks (silicon dioxide and polysilicon). With the high-k + metal gate technology , however, greater stresses can be achieved by first removing the polysilicon gate after the stressing; later this space will be filled again with metal.

Individual evidence

  1. ↑ Hao Li, H.-M. Pure: Millimeter-wave VCOs with wide tuning range and low phase noise, fully integrated in a SiGe bipolar production technology . In: IEEE Journal of Solid-State Circuits . tape 38 , no. 2 , 2003, p. 184-191 , doi : 10.1109 / JSSC.2002.807404 .
  2. ↑ Hao Li, H.-M. Rein, T. Suttorp, J. Bock: Fully integrated SiGe VCOs with powerful output buffer for 77-GHz automotive radar systems and applications around 100 GHz . In: IEEE Journal of Solid-State Circuits . tape 39 , no. 10 , 2004, p. 1650-1658 , doi : 10.1109 / JSSC.2004.833552 .
  3. ↑ Dotfive project - Towards 0.5 TeraHertz Silicon / Germanium Heterojunction bipolar technology. Retrieved January 25, 2013 .
  4. ↑ Chris Auth, Mark Buehler, Annalisa Cappellani, Chi-hing Choi, Gary Ding, Weimin Han, Subhash Joshi, Brian McIntyre, Matt Prince, Pushkar Ranade, Justin Sandford, Christopher Thomas: 45nm High-k + Metal Gate Strain-Enhanced Transistors . In: Intel® Technology Journal . tape 12 , no. 01 , 2008, p. 77-85 , doi : 10.1109 / VLSIT.2008.4588589 ( PDF ).
  5. ↑ W. Chee, S. Maikop, CY Yu: Mobility-enhancement technologies . In: IEEE Circuits Devices Mag . tape 21 , no. 3 , 2005, p. 21-36 , doi : 10.1109 / MCD.2005.1438752 .