Abstract
The continued scaling in transistors and memory elements has necessitated the development of atomic layer deposition (ALD) of silicon nitride (SiNx), particularly for use a low k dielectric spacer. One of the key material properties needed for SiNx films is a low wet etch rate (WER) in hydrofluoric (HF) acid. In this work, we report on the evaluation of multiple precursors for plasma enhanced atomic layer deposition (PEALD) of SiNx and evaluate the film’s WER in 100:1 dilutions of HF in H2O. The remote plasma capability available in PEALD, enabled controlling the density of the SiNx film. Namely, prolonged plasma exposure made films denser which corresponded to lower WER in a systematic fashion. We determined that there is a strong correlation between WER and the density of the film that extends across multiple precursors, PEALD reactors, and a variety of process conditions. Limiting all steps in the deposition to a maximum temperature of 350 °C, it was shown to be possible to achieve a WER in PEALD SiNx of 6.1 Å/min, which is similar to WER of SiNx from LPCVD reactions at 850 °C.
Highlights
To improve thin film properties rapid thermal annealing (RTA) is commonly used
We report on the evaluation of multiple precursors for plasma enhanced atomic layer deposition (PEALD) of SiNx and evaluate the film’s wet etch rate (WER) in 100:1 dilutions of HF in H2O
We determined that there is a strong correlation between WER and the density of the film that extends across multiple precursors, PEALD reactors, and a variety of process conditions
Summary
To improve thin film properties (crystallinity, morphology, density, trap density) rapid thermal annealing (RTA) is commonly used. Plasma annealing or extensions of in-cycle plasma during PEALD have shown similar improvements in thin film properties of high k oxide-based dielectrics.[11]. We report on PEALD of SiNx films with three different precursor chemistries (TSA, tris(dimethylamino)silan (3DMAS), dichrolosilane (DCS)) and the WER performance achieved with each. We note the strong correlation found between film density and WER regardless of precursor chosen, PEALD reactor utilized, or variation of several process parameters. We present two methodologies for increasing film density and lowering WER by use of in-cycle and post-deposition plasma processing within the PEALD reactor
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