Influence of annealing conditions on threading dislocation density in Ge deposited on Si by reduced pressure chemical vapor deposition

Abstract

The influence of annealing conditions on the crystallinity of Ge deposited on Si(001) is investigated. Ge deposited with postannealing at 800 °C and 850 °C, five cycles of postannealing at 750 °C and 850 °C (temperature-swing postannealing) and several cycles of annealing at 800 °C or 850 °C during the Ge growth by interrupting the deposition step (cyclic annealing) are compared. To check the threading dislocation density (TDD) of the deeper part of the Ge, thinning by HCl vapor phase etching (VPE) followed by Secco defect etching is performed for 5 μm thick Ge of all three annealing variants. By comparing the TDD of the same Ge thickness with and without HCl VPE, TDD reduction by VPE is observed for the sample using the cyclic annealing process only. Lower TDD is observed at higher postannealing temperature. By the five cycles of temperature swinging, TDD becomes around a half compared to conventional postannealing at 850 °C. In the case of the cyclic annealing process significant improvement of TDD is observed with increasing Ge thickness. Even at a maximum temperature of 800 °C, the same or lower TDD levels were observed for higher than 2 μm thick Ge compared to that with five cycles of temperature-swing postannealing. For the sample with cyclic annealing at 800 °C, a lower Si diffusion length into Ge is also observed for the cyclic annealing process indicating a lower thermal budget. A lower amount of tilted Ge planes at the interface is confirmed showing higher crystal quality also in the deeper part of the Ge layer.