HCl selective etching of SiGe versus Si in stacks grown on (1 1 0)

Abstract

We have investigated the lateral HCl selective etching of SiGe versus Si in various patterned (1 1 0) SiGe/Si stacks. Given that Si(1 1 0) vertical etch rates are roughly four times higher than Si(1 0 0) ones for T < 850 °C, a moderate HCl partial pressure (0.4 Torr) was adopted for this study, which was conducted in the 600–700 °C temperature range. A definite SiGe versus Si etch selectivity has conclusively been demonstrated on (1 1 0) for 30–40% of Ge. SiGe could not however be selectively removed in stacks with 20% of Ge. SiGe lateral etch rates 1.5–4 times higher in the [1 −1 0] direction than in the [0 0 1] direction have also been evidenced. A definite increase of both [1 −1 0] and [0 0 1] lateral etch rates occurred when increasing the Ge content (up to ×90 along [1 −1 0] for 15 nm thick Si0.6Ge0.4 layers compared to Si(1 1 0)). Increasing the etch temperature also led to a dramatic increase of those etch rates. Given that etch rate activation energies were lower for SiGe than for Si, selectivity increased as temperature decreased. Mean selectivities for 15 nm thick layers were however not that high, 20 for Si0.7Ge0.3 and 60 for Si0.6Ge0.4. Thicker SiGe layers were otherwise etched faster than thinner ones. The etch rate increase with thickness was however more important in the [0 0 1] direction than in the [1 −1 0] direction, partially compensating the etch anisotropy. Finally, increasing the total etch pressure from 20 up to 100 Torr (same HCl flow) led to roughly a doubling of the SiGe lateral etch rates together with a decrease of the etch anisotropy.