Conformal Silicon Nitride Etching in Superdeep and Narrow Patterns

Despite the silicon nitride (SiN) etching in both narrow critical dimension (CD) and high aspect ratio feature requires extreme precision for the structural integration of NAND Flash device, pattern dimension-dependent chemical kinetics and thermodynamics cause fluctuation in the SiN etch rate. Here we tackle both wet and gaseous process control methods to achieve the conformal SiN etching in superdeep and narrow pattern. Firstly, we studied the boundary layer and electric double layer in nanoconfined patterns to understand their significant impact on CD-dependent wet etching. Additionally, gaseous etching in Knudsen flow regime has been discussed to address the CD independent etching. Next, we investigated thermodynamic strategies to minimize the accumulation of byproducts during phosphoric acid-based SiN wet etching, which can reduce the etch rate lag at the bottom of superdeep holes. These strategies were experimentally validated, supported by computational calculations. Furthermore, we investigated the improvement in local etch rate lag within the top layer of superdeep holes, with a particular emphasis on the effusion of SiN gaseous etching products. This led to the demonstration of excellent top-bottom uniformity, characterized by a ratio of nearly ~1.