The shrinking device dimensions in integrated circuits combined with the introduction of 3-D device architectures has created a need for novel atomic layer deposition (ALD) processes for a variety of materials including Si-based dielectrics such as SiNx. Development of new ALD techniques that can meet the demands for semiconductor manufacturing requires an atomistic level understanding of the surface reaction processes. In our lab, we use in situ optical diagnostic techniques including highly surface sensitive attenuated total reflection Fourier transform infrared spectroscopy and multi-wavelength ellipsometry to study the surface processes that occur during ALD.
In this presentation, I will discuss the low-temperature plasma-assisted ALD of SiNx films where one of the key challenges has been to grow conformal films in high-aspect-ratio nanostructures such that the sidewall structure and composition is the same as the top surface. I will discuss the surface reactions that occur during ALD of SiNx using chlorosilanes and aminosilanes as the Si precursors with an NH3 and N2 plasma, respectively, as the nitrogen source. The NH3-plasma based processes show >95% conformality, but the wet-etch rate in dilute HF is much higher for the sidewalls compared to the planar surface. While N2 plasma based processes show a low wet-etch rate for both the sidewalls and the planar surface, the conformality is ~50%. Based on these observations, we have developed a new three-step ALD process for SiNx growth using Si2Cl6 followed by CH3NH2, and then an N2 plasma. I will show that in this three-step ALD process because nitrogen is supplied to the surface partially in a thermal step followed by an N2 plasma, the films are more conformal with a sidewall wet etch rate that is intermediate between NH3 and N2 plasma based ALD processes.