DOPING AND CRYSTALLOGRAPHIC EFFECTS IN CL-ATOM ETCHING OF SILICON

Absolute rates for the intrinsic reaction between Cl atoms and surfaces of P-doped polycrystalline silicon, P-doped Si(100) and As, Sb-doped Si(111) substrates were measured for the first time as a function of dopant concentration (Ne) and substrate temperature in a downstream reaction system. This study clearly shows that when there is no ion bombardment, increasing Ne increases the Si-Cl reaction rate even when silicon is lightly doped (∼1015 cm-3), in contrast to in-discharge studies. Moreover, results showed that crystal orientation influences the Cl-Si reaction more than Ne, for N e<1020 cm-3. The data are fitted to a modified Arrhenius expression, R=νNγ enClT1/2e -E/kT, with R the etch rate and nCl the gas phase Cl concentration. The calculated values of the activation energy E are 4.1-4.7 kcal/mole for all doping levels and crystallographic orientations. Therefore, the doping effect is manifested solely in the preexponential (νN γe) of the Arrhenius expression, and the data qualitatively agree with a charge-transfer mechanism which facilitates chemisorption of chlorine.