Cyclohexasilane as a Higher Order Silane
Typical CVD processes used to create p-type MOSFETs (metal oxide field effect transistors) have included high concentrations of germanium which improves hole mobility due to the induced strain of embedding the germanium into the silicon lattice. However, as the industry drives to smaller devices, the needed concentrations of germanium, along with typical deposition temperatures of greater than 700 °C has caused severe lattice mismatch issues, leading to structural defects, and ultimately device failure.
While silane has traditionally been the silicon precursor of choice, in an effort to reduce necessary deposition temperatures, higher order silanes such as trisilane, tetrasilane, and neopentasilane have been explored in an effort to obtain lower deposition temperatures. While these precursors DID allow deposition at lower temperatures, the resulting depositions are generally plagued by the presence of silicon hydride clusters in the deposited layers, and additional adjustments had to be made to the partial pressures, thus having the overall effect of lowered growth rates.
Cyclohexasilane (CHS), in contrast to the other higher order silanes mentioned above, is a ring structure, and as such has lower Si-Si and Si-H bond strengths, contributing to lower deposition temperatures. Initial studies, in fact, have shown that CHS deposited at ~300°C has a 10X higher growth rate than SiH4 deposited at 700 °C. There is also empirical evidence that CHS does not produce silicon hydride clusters.
CHS also has the attributes of being stable during storage and handling, is readily vaporized or is amenable to solution processing at ambient temperatures, and may be delivered to a reaction zone without the need for a carrier gas. Co-deposition of germanium, or a wide variety of other dopants, is readily achieved with CHS and the lower deposition temperatures allows the formation of amorphous structures which can then be annealed at temperatures as low as 400 °C if crystalline materials are desired.
The Coretec Group will be offering evaluation samples available for early 2021. If you would like a conversation about the potential benefits of this low temperature silicon precursor, please reach out to Michelle Tokarz at email@example.com to see how we can work with you!