Synthesis of cubic boron nitride thin films by low-energy ion beam assisted deposition by applying substrate bias

Abstract

Cubic boron nitride (c-BN) films are synthesized with low-energy ions of 100eV from a gridless ion gun by applying negative substrate bias. Boron is evaporated by an electron beam at rates of 0.8 to 2.3Å/sec onto silicon substrate. Substrate temperature and bias are varied from 400 to 800°C and from 0 to -700V, respectively. Due to the low-operating pressure of the ion beam assisted deposition (IBAD) process, applying substrate bias efficiently accelerates ions enough for synthesis of the c-BN phase. With increasing substrate bias, the major phase changes in the sequence of hexagonal boron nitride (h-BN) to c-BN to h-BN. The reappearance of the hexagonal phase at high bias voltage is thought to be due to the stress annealing effect. Intermediate temperatures have produced higher c-BN contents. Far-off stoichiometric film (N/B≈0.72) consists of h-BN phase even under the c-BN parameter but a little off stoichiometry has led to higher c-BN contents. The maximum contents of c-BN phase is about 70%. DC type bias and oxygen/hydrogen incorporation into the films are presumed to limit the content. The IBAD process with proper substrate bias is promising for large areas of and high rate growth of the c-BN phase.