High-aspect-ratio amorphous carbon mask etch profile control through plasma and surface chemistry optimization

The etch profile control for the amorphous carbon layer (ACL) is an important step in the 3D NAND fabrication process. Because ACL is the mask material for defining the pattern of the high-aspect-ratio-contact (HARC) dielectric ONON layer etch process, precise control of its etch profile is necessary. Specifically, an ideal ACL mask profile should be free of symptoms such as hole circularity distortion, profile twisting, bowing, and undercutting. In order to achieve this desired etch performance, knowledge of various etch contributing factors must be systematically derived and applied, including etch surface chemistry, high-aspect-ratio (HAR) etchant transport, ion flux and ion energy angle distribution function (EADF) control, etc. In this work, we investigate the ACL etch fundamental characteristics through combined 2D chamber-scale plasma simulations with the hybrid plasma-equipment model (HPEM) and 3D etch profile simulations with the Monte-Carlo Feature Profile Model (MCFPM) for an inductively-coupled-plasma (ICP) reactor with RF bias at the substrate. In particular, we focus on the profile trends under different reactant fluxes and energies. Our findings indicate that maintaining a neutral-starved (ion-rich) etch regime is essential for mitigating both the channel hole etch circularity distortion and the slit etch profile twisting. To achieve this desired etch regime, the HAR ion, and neutral transport must controlled by the RF bias power and frequency, substrate temperature, etc. Furthermore, especially in this neutral-limited etch regime which is necessary for distortion and twisting mitigation, the control of the consequent aspect-ratio dependent etching (ARDE), as well as maintaining the critical dimension (CD) and reducing bowing and undercutting are also necessary. For this purpose, atomistic density functional theory (DFT) calculations have been applied to compare the reaction energetics for various ALD-like sidewall passivation chemistries. Specifically, we propose a new process based on its favorable reaction energetics. Experimental cross-section images have matched simulation results. In conclusion, our insights have provided guidance for process optimization and tool design to meet industrial demands.