Transition from thermal- to electron-impact decomposition of diborane in plasma-enhanced chemical vapor deposition of boron films from B 2H6+He

Abstract

The apparent reaction orders for the growth of boron films in plasma-enhanced chemical vapor deposition from B2 H6 + He were measured as a function of the plasma power, which ranged from 0.4 to 1.6 kW. The conditions were as follows: substrate temperature, 890 °C; pressure, 200 Pa; and total flowrate of gases, 200 sccm. It was found that the reaction order (n) makes a transition from 1/2 to 1 at 900 W with an increase of the plasma power, and which accompanied a corresponding morphological transition. On the basis of a simple kinetic model, the observed reaction-order transition is related with a transition from thermal- to electron-impact decomposition of diborane occurring at 900 W: the n of 1/2 observed at the power range below 900 W is attributed to a pyrolysis-dominant growth mechanism in which the association of two BH3 into B2 H6 cannot be neglected, whereas the n of 1 observed at the power range above 900 W is related to a growth mechanism in which the electron-impact dissociation of diborane is dominant.