In Situ Monitoring of Surface Reactionsduring Atomic Layer Etching of Silicon Nitride Using Hydrogen Plasmaand Fluorine Radicals

The atomic layer etching (ALE) of silicon nitride (SiN) via a hydrogen plasma followed by exposure to fluorine radicals was investigated using in situ spectroscopic ellipsometry and attenuated total reflectance Fourier transform infrared spectroscopy to examine the surface reactions and etching mechanism. FTIR spectra of the surface following exposure to the hydrogen plasma showed an increase in the concentration of Si-H and N-H bonds, although the N-H bond concentration plateaued more quickly. In contrast, during fluorine radical exposure, the Si-H bond concentration decreased more rapidly. Secondary ion mass spectrometry demonstrated that the nitrogen atom concentration was decreased to a depth of 4 nm from the surface after the hydrogen plasma treatment, and indicated a structure consisting of N-H rich, Si-H rich, and mixed layers. It appears that Si-H bonds were primarily present near the surface, with N-H bonds mainly located deeper into the film. The formation of these N-H and Si-H rich layers are i...