The mechanism of formation of a “Si recess” that appears during gate poly-Si etching was studied. Hydrogen in HBr plasma penetrates through a thin gate oxide film and generates dislocated sites in the Si substrate. We developed a molecular dynamics (MD) simulation to clarify both the penetration depth of H and O and the dislocation of Si. The damage was successfully minimized by controlling the high energy peak in the ion energy distribution function (IEDF) to be lower than the threshold energy of ion penetration.

Low dielectric constant (low-k) films have been widely used as insulating materials in ultra-large-scale integrated circuits. Low-k films receive heavy damage during the plasma processes of etching or ashing, resulting in an increase in their dielectric constant. In order to realize damage-free plasma processes for low-k films, it is essential to determine the influence of radiation, radicals, and ions emitted in the plasma process on the characteristics of low-k films. We have developed a technique to evaluate the influence of radiation, radicals, ions, and their synergies on films in real plasma processes and have named it pallet for plasma evaluation (PAPE). Using the PAPE, plasma-induced damage on porous SiOCH films were investigated in dual-frequency capacitively coupled H2∕N2 plasmas. The damage was characterized by ellipsometry, Fourier-transform infrared spectroscopy, and thermal desorption spectroscopy. On the basis of the results, the damage mechanisms associated with vacuum ultraviolet (VUV) and UV radiation, radicals, and ions were clarified. The damage was caused not only by ions and radicals but also by VUV and UV radiation emitted by the plasmas. Moreover, it was found that the synergy between the radiation and the radicals enhanced the damage.

Gas mixtures based on C4F8 are promising for the development of high-performance SiO2 plasma etching processes. Measurements of important gas phase species, thin film etching rates and surface chemistry changes were performed for inductively coupled plasmas fed with C4F8/Ar and C4F8/O2 gas mixtures. The addition of Ar to C4F8 causes a strong increase of the plasma density relative to that of pure C4F8 (by up to a factor of 4× at 90% Ar). For O2 addition the changes in plasma density are small up to 90% O2 relative to pure C4F8. Infrared laser absorption spectroscopy was used to determine the absolute densities of neutral CF, CF2 and COF2 radical species as a function of the gas composition. The densities of CF and CF2 were enhanced for certain operating conditions when Ar was added to C4F8 as long as the amount of Ar remained below 20%. For instance, the partial pressure of CF was 0.1 mTorr for a 20 mTorr 1400 W source power discharge for pure C4F8, and increased to 0.13 mTorr at 20% Ar. Above 20% Ar it decreased, roughly following the gas dilution. The CF2 partial pressure was about 5 mTorr for the same conditions, and increased by about 10% at 20% Ar. Above 20% Ar the CF2 partial pressure decreased roughly linearly with the amount of Ar added, to about 2 mTorr at 50% Ar. Of particular interest was the analysis of the difference in behavior of CF, CF2 and COF2 partial pressures over SiO2 and Si surfaces, with and without rf bias power (in the latter case a self-bias voltage of −100 V was used). For pure C4F8 discharges at 20 mTorr and 1400 W inductive power without rf bias the partial pressures of CF, CF2 and COF2 radicals are comparable over SiO2 and Si surfaces. Upon applying a rf bias, the CF2 partial pressure over a SiO2 surface is reduced much more strongly than for a Si surface. The overall reduction appears to be consistent with the relative SiO2/Si etch rate ratios observed for these conditions. These results indicate that CF2 is consumed during the etching of SiO2 and Si. We also measured fluorocarbon deposition rates without rf bias and etching rates of blanket SiO2, silicon, resist and deposited fluorocarbon films as a function of the rf bias and feed gas composition. Important differences in the response of the etching rates of those materials upon the addition of O2 and Ar to C4F8 were observed. In particular, we show that the SiO2/Si and SiO2/resist etching selectivities can be doubled by adding up to 90% Ar to C4F8, without inducing an unacceptably large reduction of the SiO2 etching rate. The change in etch rate ratios is at least in part due to strong surface chemical changes seen for Ar-rich fluorocarbon gas mixtures. The surface chemical changes of Si and SiO2 surfaces were investigated by real-time ellipsometry and x-ray photoelectron spectroscopy. A strong reduction of the fluorine content of the fluorocarbon steady-state layer and an increase in thickness is seen when up to 90% Ar was added to C4F8, and this coincides with an increase of the SiO2/Si etching selectivity. The change in fluorocarbon surface chemistry can be explained by the strongly increased ion/neutral flux ratio that is characteristic of Ar-rich C4F8/Ar gas mixtures.

Si surface damage induced by H 2 plasmas was studied in detail by optical and electrical analyses. Spectroscopic ellipsometry (SE) revealed a decrease in the pseudo-extinction coefficient hi in the region of photon energy higher than 3:4 eV upon H 2 -plasma exposure, which is attributed to the disordering of crystalline silicon (c-Si). The increase in hi in the lower energy region indicates the presence of trap sites for photogenerated carriers in the energy band gap in the E -k space of Si. The current-voltage (I-V ) measurement of metal-contacted structures was performed, revealing the following characteristic structures: thinner surface (SiO 2 ) and thicker interface (SiO 2 :c-Si) layers on the Si substrate in the case of H 2 -plasma exposure than those with Ar-and/or O 2 -plasma exposure. The structure assigned on the basis of both SE and I-V was further analyzed by a layer-by-layer wet-etching technique focusing on the removability of SiO 2 and its etch rate. The residual damage-layer thickness for the H 2 -plasma process was thicker (10 nm) than those for other plasma processes (<2 nm). Since the interface layer plays an important role in the optical assessment of the plasma-damage layer, the present findings imply that a conventional two-layer (SiO 2 /Si) optical model should be revised for in-line monitoring of H 2 -plasma damage. #

Hydrogen in hydrofluorocarbon plasmas plays an important role in silicon nitride (Si 3 N 4 ) reactive ion etching. This study focuses on the elementary reactions of energetic CHF þ 2 and CH 2 F þ ions with Si 3 N 4 surfaces. In the experiments, Si 3 N 4 surfaces were irradiated by monoenergetic (500-1500 eV) beams of CHF þ 2 and CH 2 F þ ions as well as hydrogen-free CF þ 2 and CF þ ions generated by a massselected ion beam system and their etching yields and surface properties were examined. It has been found that, when etching takes place, the etching rates of Si 3 N 4 by hydrofluorocarbon ions, i.e., CHF þ 2 and CH 2 F þ , are higher than those by the corresponding fluorocarbon ions, i.e., CF þ 2 and CF þ , respectively. When carbon film deposition takes place, it has been found that hydrogen of incident hydrofluorocarbon ions tends to scavenge fluorine of the deposited film, reducing its fluorine content.