Growth and characterization of silicon thin films employing supersonic jets

Supersonic jets of $Si2H6$ have been employed to grow single crystalline silicon thin films on Si(100) and polysilicon surfaces at substrate temperatures of 500–650 °C. Films deposited on Si(100) employing high and low kinetic energy jets are epitaxial as determined by reflection high energy electron diffraction. The uniformity and growth of films deposited on polysilicon by high energy ∼2 eV (1% $Si2H6$ in hydrogen) and low energy ∼0.09 eV (pure $Si2H6) Si2H6$ jets are compared to silicon growth employing ultrahigh vacuum chemical vapor deposition (UHV-CVD). To ascertain the influence of high kinetic energy on the growth of silicon from disilane, the reaction probability is estimated from growth measurements for all techniques and compared. The high energy jet is found to have a substantially higher reaction probability compared to the low energy jet and UHV-CVD indicating that the growth is enhanced by the high energy disilane. The disilane flux distribution employing the high energy jet is sharply peaked along the centerline causing a peaked growth profile across the 4 in. wafer. The silicon growth profile obtained from the high energy jet broadens slightly as the substrate temperature decreases. The higher flux at the centerline results in a higher hydrogen coverage compared to the wafer edge which affects the reaction probability in the two locations relative to one another. As the substrate temperature decreases, the growth profile flattens since the lower hydrogen desorption rate, and resulting higher hydrogen coverage, reduces the disilane adsorption probability at the centerline more than at the wafer edge. The growth distribution from the high energy jet is found to become slightly less peaked when the carrier gas is changed from hydrogen to helium.