Paper AP+PS+TF-ThM10
Thermal Atomic Layer Etching (ALE) of Germanium-Rich SiGe Films

Thursday, October 24, 2019, 11:00 am, Room B130

The thermal atomic layer etching (ALE) of germanium-rich SiGe was demonstrated using an oxidation and “conversion-etch” mechanism (See Supplemental Figure 1). In this process, the SiGe surface was oxidized to a SiGe oxide layer using O₂. The SiGe oxide layer was then converted to an Al₂O₃ layer using trimethylaluminum (TMA). The Al₂O₃ layer was fluorinated by HF to an AlF₃ layer prior to the removal of the AlF₃ layer by ligand-exchange using TMA. The thermal ALE of SiGe films will be important for the fabrication of advanced MOSFET devices.

This study explored the thermal ALE of germanium-rich Si_0.2Ge_0.8 films. In situ spectroscopic ellipsometry was employed to monitor the thickness of both the Si_0.2Ge_0.8 and the surface oxide layer during ALE. These studies showed that the Si_0.2Ge_0.8 film thickness decreased linearly with number of reaction cycles while the surface oxide thickness remained constant. Using an O₂-HF-TMA reaction sequence, the Si_0.2Ge_0.8 ALE etch rate was 0.57 Å/cycle at 290°C. This etch rate was obtained using optimal reactant pressures of 25, 0.2 and 0.4 Torr, and dose times of 1.5, 1 and 1 s, for O₂, HF and TMA, respectively.

The Si_0.2Ge_0.8 ALE etch rate was lower at lower temperatures. Using an O₂-HF-TMA reaction sequence, the Si_0.2Ge_0.8 etch rate was reduced from 0.57 Å/cycle at 290°C to 0.07 Å/cycle at 225°C. The order of the reactant sequence also affected the Si_0.2Ge_0.8 etch rate. Changing the reactant sequence from O₂-HF-TMA to O₂-TMA-HF reduced the Si_0.2Ge_0.8 etch rate from 0.57 to 0.45 Å/cycle at 290°C. Si_0.2Ge_0.8 could also be etched selectively in the presence of Si and Si₃N₄. The Si_0.2Ge_0.8 etch rate was >10 times faster than the etch rate for Si or Si₃N₄ at 290°C (See Supplemental Figure 2).