Dry etching of sapphire substrate for device separation in chlorine-based inductively coupled plasmas

In this study, sapphire wafers were etched using magnetized inductively coupled plasmas (MICP) and their etch characteristics were investigated as a function of gas combination of Cl2/BCl3, operation pressure, and additive gases such as Ar, Xe and SiCl4. The characteristics of plasmas were estimated using a Langmuir probe and optical emission spectroscopy, and the profiles of the etched sapphire wafers were evaluated with a scanning electron microscopy (SEM). The increase of BCl3 in Cl2/BCl3 increased the etch rate and improved the etch selectivity over photoresist, SiO2 and Cr until 80% BCl3 was reached. The decrease of operating pressure also increased the sapphire etch rate. The maximum etch rate over 3300 °C min−1 could be obtained using 20%Cl2/80%BCl3 and, by the addition of 10%Ar or 10%Xe in this mixture, the etch rates increased further to over 3500 °C min−1 at 2.0 Pa of operating pressure, 1.6 kW of inductive power, −250 V of bias voltage, and 70 °C of substrate temperature. When the sapphire etching was performed with 10% Ar in 20%Cl2/80%BCl3, sharp sidewall trenches required for stress concentration during the device separation could be observed on the sapphire etch profiles.