Numerical Simulation Method for Plasma-Induced Damage Profile in SiO₂ Etching

Abstract

We developed a numerical simulation method for the depth profiles of plasma-induced physical damage to SiO2 and Si layers during fluorocarbon plasma etching. In the proposed method, the surface layer is assumed to consist of two layers: a C–F polymer layer and a reactive layer. Physical and chemical reactions in the reactive layer divided into several thin slabs and in the deposited C–F polymer layer, which depend on etching parameters, such as etching time, gas flow rate, gas pressure, and ion energy (V pp), are considered in detail. We used our simulation method to calculate the SiO2 etch rate, the thickness of the C–F polymer layer (T C–F), and the selectivity of SiO2 to Si during C4F8/O2/Ar plasma etching. We confirmed that the calculated absolute values and their behavior are consistent with experimental data. We also successfully predicted depth profiles of physical damage to the Si and SiO2 layers introducing our re-gridding method. We found that much Si damage is generated in the pre- and early stages of the overetching step of SiO2/Si layer etching despite the high selectivity. These simulation results suggest that the T C–F value and the overetching time must be carefully controlled by process parameters to reduce damage during fluorocarbon plasma etching. The results have also provided us with useful knowledge for controlling the etching process.

Advanced simulation technology for etching process design for CMOS device applications

“…On the other hand, this was not observed in the case of high flow rate owing to the thick polymer layer (4 nm) at the hole bottom in which the ion energy was largely reduced. It was also previously reported that the time evolution of the damage distribution during SiO 2 =Si multilayer etching is predicted well, and that even in the case of high selectivity (∼20), considerable Si damage can be observed just before overetching occurs because of the thin polymer and SiO 2 layers 69,114) used, as shown in Fig. 20, and this agrees with the results of MD calculations.…”

“…16. By using a voxel model 113) connected to the slab model, 114) which is then called the voxel-slab model, a simulation technology for the SiN SW etching process with new concepts for gas transportation, detailed surface reactions that are dependent on the H=N ratio, and etch front evolution has recently been reported; 115) this technology can calculate the etched profile and damage distribution simultaneously in a 3D space with a short calculation run time. Figure 17 shows a schematic image of the calculation flow of the 3D voxelslab model described above.…”

“…114) The dangling bond ratio θ is calculated using SiN dði; j; tÞ dt ¼ ½1 À ði; j; tÞ X i Y iSiN ðV net ÞÀ i À ði; j; tÞÀ ER DB ð j; tÞ; ð20Þ…”

“…Here, L + is the effective slab depth after correction using the etch rate, and α is a parameter used to represent the channeling effects of small particles such as H. Using the derived θ value, the time variation in the effective etch rate ERði; j; tÞ and the total etch rate ERði; tÞ were calculated as 114) ERði; j; tÞ…”

Investigation of SiO2 Etch Characteristics by C6F6/Ar/O2 Plasmas Generated Using Inductively Coupled Plasma and Capacitively Coupled Plasma

“…4 nm) measured as a function of oxygen flow rate are shown in Figure 4a for the ICP system and b for the CCP system. In general, during the etching of SiO 2 by fluorocarbon plasmas, F radicals react with Si on the SiO 2 surface and are removed from the surface as SiF x while C radicals react with O on the SiO 2 surface and are removed from the surface as CO x [20]. As shown in Figure 4a,b, the increase in densities of radicals such as CF 2 , CO, C 2 , and F with increasing oxygen flow rate could be observed in both the ICP system and the CCP system due to the increased dissociation of fluorocarbon by oxygen radicals in the plasmas.…”