(24h) Plasma Enhanced Atomic Layer Deposition of Silicon Carbonitride

Conformal deposition of dielectrics is necessary for many applications, including as spacers for self-aligned multiple patterning and as charge trap layers in NAND memory features. Plasma enhanced atomic layer deposition (PEALD) of silicon nitride is promising for these applications, satisfying many requirements of deposition. However, silicon nitride films deposited with this technique typically have low hydrofluoric acid wet etch resistance, limiting its applications. Incorporating carbon into silicon nitride to form silicon carbonitride (SiCN) films can overcome this shortcoming by increasing wet etch resistance, but it also increases leakage currents. By incorporating small amounts of carbon to form silicon carbonitride films, a large increase in etch resistance can be achieved with only a small increase in leakage current. Finding a process that delivers a ternary component film with specific material properties is inherently complex as both stoichiometry and bonding nature need to be controlled through surface reactions. Managing the carbon content and nature of bonding within SiCN films are the focus of this talk.

We use PEALD to deposit silicon carbonitride by alternating a thermal exposure of a silane derived single source precursor, bis(dimethylamino)dimethylsilane, containing Si-N, Si-C, and N-C bonds at 100 °C and a plasma step as a model system for SiCN deposition. A plasma step is needed to create a surface on which the precursor can chemisorb leading to the desired film composition. An experimental capacitively coupled radio frequency plasma source is used to understand how different plasmas, including ammonia, hydrogen, nitrogen, and pure argon impact the nature of chemisorption and film nature. Films were characterized using in situ Fourier transform infrared spectroscopy (FTIR) and in situ X-ray photoelectron spectroscopy. First principles simulations are used to assess the fundamental mechanisms at play.

Changing the plasma condition had a large effect on carbon concentrations of deposited films, changing the C:Si ratio from 0 with an NH₃/Ar plasma to 4.3 with a N₂/Ar plasma. In addition to converting precursor-based adsorbates into a film, the choice of plasma changes the surface modalities (NH_x, undercoordinated Si-N, or Si-H modes), thereby altering the precursor-surface interactions during the adsorption step. This principle was exploited to tune film compositions to realize carbon concentrations ranging from C:Si ratios between 0.1 to 0.7 by using multiple plasma exposures to generate mixed modality surfaces for precursor adsorption.