High Selectivity in Dry Etching of Silicon Nitride over Si Using a Novel Hydrofluorocarbon Etch Gas in a Microwave Excited Plasma for FinFET
Figure 1 shows the selectivity of SiNx to poly Si as a function of O2 flow rate. The flow rate of SSY525 and CH3F are 8 sccm and 10 sccm, respectively. The microwave power, the RF power of bottom electrode and the Ar gas flow rate were 1000 W, 60 W and 200 sccm, respectively. SiNx films were deposited by PECVD and LPCVD. Si/N ratio and density of SiNx by PECVD was lower than those by LPCVD . In the case of SSY525, a higher selectivity of SiNx by PECVD and LPCVD to poly Si was obtained with O2 flow rate from 0 to 50 sccm to CH3F. Low etch rate of poly Si less than 0.3 nm/min and high selectivity of SiNx to Si over 50 were obtained with O2 flow rate of 0 sccm and more than 30 sccm. Figure 2 shows the analysis of poly Si surface by XPS after dry etching using SSY525. A high intensity of C 1s was obtained with O2 flow rate of 0 sccm. It is considered that high selectivity of SiNx to poly Si was obtained due to carbon deposition on poly Si surface. The intensity of C 1s decreases and the intensity of O 1s increases as the O2 flow rate increases. It is considered that High selectivity of SiNx to poly Si is obtained with O2 flow rate more than 30 sccm due to an oxidation of poly Si surface. Figure 3 (a) shows the schematic of 3D-MISFET structure. Figure 3 (b)-(d) show the cross-section SEM images from A to B in Fig. 3 (a) with various SSY525 flow rate. A 40 nm-thick SiNx was overetched at (b) 8 sccm, (c) 12 sccm and (d) 15 sccm. Si near the SiNx sidewall was etched with SSY525 of 8 sccm. It was not etched with SSY525 more than 12 sccm. About 5 nm-thick film containing carbon was deposited on the Si surface with 15 sccm. In the cases of (c) and (d), high selectivity of SiNx over Si was obtained. It is confirmed that SSY525 is effective in order to form the SiNxgate spacer in the miniaturized MISFET.
 Y. Nishi, Handbook of Semiconductor Manufacturing Technology 2nd edition, CRC press (2008).  R. A. Gottscho et al., Thin Solid Films, 516 (2008).  S. U. Engelmann et al., Proc. the 58th AVS Int. Symp. (2011).  S. U. Engelmann et al., Proc. the 59th AVS Int. Symp. (2012).  E. A. Joseph et al., Proc. SPIE (2013).  S. U. Engelmann et al., Proc. the 60th AVS Int. Symp. (2013).  T. Ohmi et al., J. Phys. D, 39 (2006).  Y. Nakao et al., ECS Trans. 45 (2012).