HCl Selective Etching of SiGe versus Si in Stacks Grown on (110)

Abstract

We have investigated the lateral HCl selective etching of SiGe versus Si in various patterned (110) SiGe/Si stacks. Given that Si(110) vertical etch rates are roughly 4 times higher than Si(100) 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 (110) for 30-40% of Ge. SiGe could however not be selectively removed in stacks with 20% of Ge. SiGe lateral etch rates 1.5 to 4 times higher in the [1-10] than in the [001] direction have also been evidenced. A definite increase of both [1-10] and [001] lateral etch rates occurred when increasing the Ge content (up to x90 along [1-10] for 15 nm thick Si 0.6 Ge 0.4 layers compared to Si (110)). Increasing the etch temperature also led to a dramatic increase of those etch rates (with roughly 40 and 50 kcal. mol. -1 activation energies along [001] and [1-10], respectively). Given that etch rate activation energies were lower for SiGe than for Si (75 kcal. mol. -1 ), selectivity increased as temperature decreased. Mean selectivities for 15 nm thick layers were however not that high, 20 for Si 0.7 Ge 0.3 and 60 for Si 0.6 Ge 0.4 . Thicker SiGe layers were otherwise etched faster than thinner ones. The etch rate increase with thickness was however more important in the [001] than in the [1-10] direction (x 5 and x 3 when switching from 10 to 20 nm thick Si 0.6 Ge 0.4 layers, respectively), partially compensating the etch anisotropy.

Kinetic Model of SiGe Selective Epitaxial Growth using RPCVD Technique

“…The etching of Cl atoms have been previously studied and reported by many groups. [29][30][31][32][33] But, Eq. 11 represents Cl etch during the epitaxy growth, which differs remarkably from a simple Si vapor etching.…”