Deposition rate of polysilicon using silane in a low pressure reactor

temp       temperature of deposition in °C
conc       concentration of silane in the gas, it could be be any value between 0% and 100%
pres        total pressure of deposition
sel          deposition rate


Polysilicon is sometimes used as a structural material in MEMS devices to make suspended structures formed by surface micromachining. They could also be used for making resistors or conductors. Polysilicon is deposited by pyrolyzing Silane (SiH4) in a low pressure reactor generally referred to as LPCVD or Low Pressure Chemical Vapor Deposition. This is done between 575°C and 650°C, by regulating a gas flow of either 100% silane or silane diluted in nitrogen . The deposition rate of polysilcon mainly depends on the temperature and partial pressure of silane.

This design interface can be used to calculate the deposition rate of polysilicon on a flat silicon substrate at a given temperature, % of silane in the gas and the total pressure. Based on the % of silane and total pressure, the partial pressure of silane is calculated. If the silane concentration is 100%, the partial pressure of silane is equal to the total pressure, otherwise it will be a percentage of the total pressure. The deposition rate is found to increase exponentially with temperature.

In reality the deposition rate depends on a few other factors that are specific to the reactor like gas flow, the wafer load and its arrangement. The calculated deposition rate should be adjusted to suit the individual reactor.

The plot shows the variation of deposition rate with silane partial pressure at the specified temperature. If the silane concentration is 100%, the result will correspond to the silane partial pressure equal to total pressure. Using the cross hair  the deposition rate corresponding to any partial pressure upto 750mTorr can be read out.


-The influence of reactor specific parameters are not considered.
-The gas is assumed to be free of dopants. Doping will change the deposition rate.
-The wafer is flat silicon substrate.
-The deposition is assumed to be surface-reaction limited with enough supply of silane gas to sustain reaction.
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