HALODISILANES Si2H6-xHalx

Dichlorodisilane Si2H4Cl2

Fig. Si2H4Cl2 vs SiH2Cl2 (DCS) - growth rate of Si vs deposition temp

     Use of mixture of dichlorodisilane Si2H4Cl2 (DCDS), and chlorine as the etchant is a new approach for the selective deposition of silicon-based heteroepitaxial layers. Dichlorodisilane as a candidate based on thermodynamic and practical considerations.

     The issue with using mixtures of silanes and halogens (f.e. trisilane and chlorine) in a selective process is that the gas phase reaction can be highly exothermic under certain conditions (Si3H8 + 10Cl2 => 3 SiCl4 + 8 HCl + 833.8 kcal/mol @ 550°C). The more preferred approach is to use more stable DCDS precursor that releases intermediates such as SiH2 which contribute to epitaxial deposition, leaving less reactive species such as SiH2Cl2 in the gas phase that have a low rate of reaction with Cl2 (Si2H4Cl2 + 5Cl2 => 2SiCl4 + 4 HCl + 324.6 kcal/mol @ 550°C). In this way, the deposition advantages of trisilane (high deposition rate, low temperature decomposition) without the drawbacks of the Cl2/Si3H8 interaction (exothermicity), are obtained.

     The comparison of silicon growth rate vs temperature (from 700°C down to 450°C) under varying process pressure from dichlorosilane and dichlorodisilane is presented in Fig. The growth rate from DCDS is orders of magnuitude higher than from DCS (matched to have an identical amount of Si atoms) and is on the same order as using Si3H8. At low temperatures (<600°C), and reduced pressure (100 Torr), the growth rate for dichlorodisilane is  75-500 times higher than with DCS, making DCDS an attractive precursor for low temperature selective epitaxy of silicon based films.

Hexachlorodisilane Si2Cl6

    Hexachlorodisilane Si2Cl6 and other chlorosilanes are useful precursors for low-temperature applications: deposition of SiN, SiO2, polycrystalline and monocrystalline Si as spacers, etch stop, cap nitrides, gap fill, engineered source/drain and engineered substrates, epitaxial Si layers. [534]

    Hexachlorodisilane is used mostly for the deposition of silicon nitride at low temperature   (~ 550°C) by LPCVD, along with ammonia, and for the deposition of silicon dioxide by CVD or ALD. HCDS is a corrosive, water reactive colorless liquid, that requires extreme handling care due to the shock sensitive nature of some partial hydrolysis products ("poppy gels").

The usual synthetic route to HCDS involves the reaction of chlorine on silicon alloys, which is likely to yield metal contamination. Titanium is notably difficult to separate due to the close BP of TiCl4 and HCDS. ALOHA's HCDS is made from semiconductor grade silane disproportionation process, which ensure the best purity and lowest specification on the market. It has lowest metal specification, 12 months shelf life guarantee.

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