HCl defect revelation in 200 mm SiGe virtual substrates: A systematic study

Abstract

Gaseous HCl was used, instead of Secco or Schimmel etching solutions, to reveal the threading dislocations in thick SiGe virtual substrates (VS). The latters, which consisted in linearly graded layers (~8–9% Ge/μm) capped with more than 1μm thick constant composition SiGe layers, were grown at high temperatures on Si(001). Advantages of this revelation technique were obvious: HCl selective etching of the defects was indeed performed on full wafers in the very same chamber used for epitaxy, not on cleaved pieces of wafers in dedicated wet benches which contain toxic chromium ions. Reproducibility was thus better. The etch temperature was reduced from 772°C down to 700°C as the Ge content increased from 20% up to 50%, in order to have the same HCl etch rates (~14nmmin.−1). An automated light inspection tool was used to acquire polar maps of the inverted pyramid etch pits after the removal of ~120nm, 230 and 340nm of SiGe. The etch pit size increased linearly with the HCl etched thickness and somewhat linearly with the Ge content (20%, 30%, 40% or 50%). The Etch Pits Density (EPD) increased from the center towards the edges of the SiGe VS (~1.6×105cm−2 up to 6cm away from it ⇔ 2.7×105cm−2 2.7×105 cm−2 9cm away from it). Very similar mean EPDs, in the 1.75–2.05×105cm−2 range, were otherwise obtained irrespectively of the Ge content and the etched thickness. The EPD in SiGe VS depends instead on the growth temperature, the growth rate and the grading used.