Achieving selective etching of SiN and SiO₂ over amorphous carbon during CF₄/H₂ by controlling substrate temperature

The effects of substrate temperature (T_s, from 50 to –20 ^oC) on the etch rates (ER) of the PECVD-prepared SiN and SiO₂, and their selectivity were investigated with a CF₄/H₂ plasma. The chemical composition and physical properties of the films were analyzed with a RBS and XRR. The ERs for the SiN at all T_s were higher than that for the SiO₂ films. As T_s was decreased from 50 to –20 ^oC, the ER for the SiN decreased. Contrarily, the ER of the SiO₂ films increased. The etch selectivity of SiN over SiO₂ reached to near unity when the T_s was –20 ^oC. Simultaneously, the polymer deposition for the amorphous carbon (a-C) irrespective of T_s was found, suggesting the process which is applicable to the etching of 3D NAND structure composed of alternatively multilayered structure of SiN/SiO₂. The angular-resolved XPS results revealed that fluorocarbon (FC) thickness was thicker for the SiO₂ films than that of the SiN. The lower ER for the SiO₂ was therefore attributed to the thicker FC layer and resultant etching mechanism. As the T_s was decreased, the FC thickness on the both series of films decreased. This led to the fact that the ER of the SiO₂ slightly increased. On the contrary, the decrease of ER for the SiN at the low temperature was likely due to the formation of N–H bonding layer.