The etching of polysilicon by low energy Cl2+HBr plasma beam was studied, and the etching yield as a function of composition, ion impingement energy and ion incident angle was measured. The etching yield by HBr plasma beam is slightly lower than Cl2 plasma beam. The angular dependence of etching yield by both Cl2 and HBr beam strongly suggests the mechanism of ion induced chemical etching, with highest etching yield at normal incident angle. For Cl2 beam, the etching yield almost keeps constant until the off-normal incident angle of ions increased to 45°, while for HBr beam, the etching yield starts dropping even with small off-normal angle. The angular dependence of etching yield by Cl2+HBr plasma at different composition exhibits similar trend as pure HBr. Using x-ray photoelectron spectroscopy, the coverage of Cl and Br on polysilicon surfaces after etching in Cl2+HBr plasmas was measured. The Cl coverage after etching with pure Cl2 plasma beam is about 1.4 times higher than the Br coverage after etching with pure HBr plasma beam, due to the larger size of Br atom. The instantaneous sputtering yields of polysilicon by Ar+ ions after Cl2 and HBr plasma etching are similar, indicating that the lower Br coverage is not responsible for the lower etching rate in HBr plasma. The effect of the angular dependent etching yield difference between Cl2 and HBr on feature profile evolution, as identified with Monte Carlo simulation, might contribute to the more anisotropic etching in HBr plasma.

The introduction of copper interconnects has increased the use of dual damascene etching processes, which leads to new challenges for feature profile control. Oxide fencing around vias during the trench etch of the via-first dual damascene scheme can be detrimental to the device performance and therefore need to be eliminated. A systematic study of oxide fencing formation during via-first dual damascene etching processes is presented. A Monte Carlo technique associated with surface kinetics and cell removal algorithm is used to simulate the profile evolution, and the simulation results qualitatively agree with the experimental results taken from literature. The simulation indicated that the feature profile evolution is controlled by both the ion and neutral flux distribution along the etching surface and angular dependent etching yield. The shape of via, the SiO 2 :BARC etching selectivity, and etching chemistry can affect the oxide fencing. Bowed via can eliminate the oxide fencing, and tapered via will result in severe oxide fencing. Reducing etching selectivity can also control the height of oxide fencing, but it does not seem to be a practical solution. Less polymerizing chemistry causes much less severe oxide fencing than does more polymerizing chemistry. The simulation can thus serve as a useful guide for searching optimal profile evolution control conditions.

A Monte Carlo based profile simulator was constructed that incorporated the dominant reaction mechanisms of surface chlorination under simultaneous neutral and ion bombardment, surface etching, and ion reflection. The profile simulation is based on the kinetics model developed from beam studies that measured the ion energy, ion and neutral fluxes and ion angular dependencies of Cl+ ion-enhanced etching with Cl. The profile evolution of patterned samples with oxide hard mask etched in an inductively coupled plasma etcher were simulated. The mechanisms of undercutting and microtrenching forming were discussed. Ions scattered from the neighboring hardmask were primarily responsible for the undercutting, while ions reflected from bowed feature sidewalls were primarily responsible for the microtrenching. The profile evolutions under different processing conditions were compared with experimental results and some etching artifacts were characterized and discussed. The neutral-to-ion ratio was found to influence the surface chlorination significantly, thus causing variation of profile evolution. Higher ion energy would give more ideal profiles due to increased ion directionality. However, higher ion energy also increased the etching rate and reduced the chlorination at the bottom of the feature. The reduced chlorination of the feature bottom relative to the sidewall increases the ratio of lateral etching to vertical etching, and decreases the etching anisotropy. The influence of SiCl2 deposition and mask angle on feature profile evolution were also investigated.

High density fluorocarbon plasma for silicon oxide etching has various ion and neutral species. Profile evolution modeling can provide understanding of many difficulties caused by the complexity of the plasma in etching. In this research we have measured etching and deposition rates as functions of ion impinging angle, sample temperature, which are necessary for profile evolution modeling of silicon oxide etching in inductively coupled plasma. Angular dependence of etching yield of oxide in fluorocarbon plasma shows very unique behavior unlike typical ion-induced chemical etching or physical sputtering. Ion-induced deposition model is suggested and tested.