Kinetics of Radicals in CF ₄ and C ₄F ₈ Electron Cyclotron Resonance Plasmas

Abstract

Temporal variations in densities of CF and CF2 radicals were measured at rising phases of plasma ignition in CF4 and C4F8 electron-cyclotron-resonance (ECR) plasmas by infrared diode laser absorption spectroscopy. It was found that CF2 radical densities at the rising phase briefly became larger than those at the steady state in the C4F8 plasma. This finding shows that the CF2 is generated in abundance by the rapid dissociation of C4F8 molecules at the discharge ignition. The variations of CF2 and CF radical densities were demonstrated using a computer calculation to characterize the chemistry in the CF4 and C4F8 plasmas numerically. Chemical models in the CF4 and C4F8 ECR plasmas were presented based on the results obtained by the experiment and calculation. The models suggested that the higher fluorocarbons, that is CXFY (X ≥2), were important in the C4F8 plasma as dissociation paths from C4F8 molecules to CFX (X=1–3) radicals and as polymer precursors.

High-performance silicon dioxide etching for less than 0.1-μm-high-aspect contact holes

“…The higher molecular weight radicals cause a polymer deposition on the top and side wall of contact holes because these radicals have a higher sticking coefficient than the CF 2 radicals in the hole. 18,19 As a result of this, we observed an imbalance between the polymerization and etching, and microloading and etching stop occurred in the high-aspect contact holes. Also, the CF 3 ϩ ion density, the SiO 2 etching rate, and the selectivity were dramatically decreased.…”

“…However, the polymer deposition rate did not correspond to the CF 2 radical density in the C 4 F 8 /Ar plasma. The other radicals, such as the higher-molecular-weight radicals (C x F y ), 18,19 play a very important role for the polymerization in the C 4 F 8 /Ar plasma. The higher molecular weight radicals cause a polymer deposition on the top and side wall of contact holes because these radicals have a higher sticking coefficient than the CF 2 radicals in the hole.…”

Precursors of fluorocarbon film growth studied by mass spectrometry

“…The sticking probabilities of ions are as high as unity, as in the case of analogue C:H film growth chemistry, 21 hence ⌫ ion Ϸ⌫ ion * . If the s 1 , s 2 , and s 3 values of 5ϫ10 Ϫ4 , 6ϫ10 Ϫ5 , and 2ϫ10 Ϫ3 , respectively, cited from a simulation study under similar low ion flux conditions, 22 are employed, each ⌫ x * is estimated on the order of 10 13 -10 14 cm Ϫ2 s Ϫ1 . The justification of these s x values is at present difficult, since the reliable values can only be established by in situ measurements.…”

Study for plasma etching of dielectric film in semiconductor device manufacturing. Review of ASET research project

“…The net flux is the ratio of the number of species that actually react with the etched material to the total number of incident species. So we calculate the net radical flux of CF, CF 2 and CF 3 , respectively using the reported values of s, 5 × 10 -4 , 6 × 10 -5 , and 2 × 10 -3 [30]. The calculated values of net radical flux were on the order of 10 14 cm -2 s -1 .…”