Silicon Germanium (Si-Ge) LPCVD

Si-Ge devices extend the speed limit of about 3 GHz for standard silicon devices by at least another order of magnitude and have thus found applications in the rapidly expanding market for wireless multimedia devices. The Si-Ge technology uses a hetero-junction, bipolar transistor as it basic component. The speed advantage derives from the higher electron mobility of germanium as compared to silicon. With a few modifications the proven silicon fabrication technology can be used in contrast to the more difficult material and process technology for GaAs devices.

Si-Ge devices require the deposition of a thin, single crystalline layer of silicon with a small percentage of germanium blended in. These layers can be grown by epitaxial techniques, but require significantly better control of contamination from residual oxygen than what is available with the conventional LPCVD equipment used for silicon wafer processing. (Germanium does not deposit on oxides.) Commercial systems for Si-Ge thin film deposition require Ultra-High-Vacuum (UHV) equipment design concepts with the associated high equipment cost. The new Tystar Si-Ge LPCVD reactor is based on similar equipment developed for several universities for the hot wall deposition of silicon single crystalline epitaxial layers and the LPCVD of Si-Ge films with Ge concentrations from 0 to 100%. The design of a Si-Ge LPCVD reactor for the deposition of single crystalline films is accomplished in an upgraded LPCVD reactor to improve leak integrity and residual oxygen concentration.

The TYSTAR Si-Ge LPCVD Reactor system is a new development, based on Tystar's experience in CVD technology, equipment design and fabrication, including gas and vapor delivery control systems, process controllers and hot wall thermal reactors as well as on proven gas control equipment design.

The TYSTAR Si-Ge LPCVD reactor is designed for process loads of 25 wafers up to 8"/200mm size. The TYSTAR Si-Ge LPCVD reactor is primarily intended for applications in R&D laboratories, pilot line operations and small-scale manufacturing.

  • Deposition Temperature: 350 - 550 °C
  • Typical Film Thickness: 0.3 µm
  • Batch Size: 25
  • Deposition rate: 7 - 13 nm/min. (70 - 130 Å/min.)
  • Gases: Germane (GeH4), Disilane (Si2H6), Silane (SiH4), Phosphine (PH3), Boron Trichloride (BCl3)
  • Boron trichloride and phosphine respectively increase and decrease the deposition rate due to effects on the decomposition of the Si-Ge precursor gases.

Applications: GHz resonators, mixed signal circuit, heterojunction bipolar transistors, CMOS transistors, thermoelectric device, RF switches, and a variety of modern day electronic devices.

LPCVD Processes