Selective mask deposition using SiCl4 plasma for highly selective etching process

Abstract

We developed an area-selective deposition process for forming protective layers on top of masks generated using a microwave electron-cyclotron-resonance etching system. A deposition layer is formed only on SiO2 masks without forming an unnecessary deposition layer on the Si surfaces in the etching area, such as the bottoms of the patterns and isolated etching area. The protection layers were selectively formed on a SiO2 mask without forming on a Si etching area by using a SiCl4/H2/Cl2 plasma. The pretreatment to clean the Si and SiO2 surfaces before deposition was important for achieving selective deposition because selectivity appeared by nucleation delay on the cleaned Si surface. On the Si surface, adsorbed SiClx easily desorbed again by reacting with the Cl generated from the plasma. However, adsorbed SiClx on SiO2 was more difficult to desorb by reacting with Cl due to Si–O having a larger binding energy than Si–Si. After the deposition layer was selectively formed on the SiO2 mask, the layer was oxidized by using O2 plasma treatment to improve the etching resistance during the subsequent Si etching. We also investigated a Si etching process using selective deposition during the etching of a 25 nm-pitch line-and-space Si pattern with a SiO2 mask. Extremely highly selective etching was achieved using selective deposition without forming an unnecessary deposition on an isolated Si area.