Study on the influence of electron angular distribution on mask pattern damage in plasma etching

Abstract

The perfect pattern transfer from mask to substrate during the plasma‐etching process is strongly limited by the charging effect on the mask surface, which is increased by the accumulation of negative charges on the surface. These are mainly caused by high‐velocity isotropic electrons impinging on the mask surface faster than ions. These anisotropic ions thus bombard the undesired locations of the mask under the influence of the electric field (E‐field) established by electrons. This problem leads to significant damages to the mask pattern and causes deformations of etched features due to failure pattern transfer. This study examined that electron angular distribution (EAD; relative to the vertical direction, which can be regulated by voltage waveform tailoring) displays a close relationship with the mask pattern damage. Based on a modeling framework that consists of a surface etching module, a surface charging module, and a profile evolution module, the effects of changing the EAD on distributions of spatial E‐field and etching rate were studied focusing on an isolated rough mask hole surface. It is revealed that by narrowing the EAD shape, the E‐field strength and the etching rate around the mask hole edge can be reduced strongly, meanwhile, the number of electrons penetrating into the bottom of the trench can be greatly increased. These developments will supposedly reduce the mask‐pattern damage and improve the etching of high‐aspect‐ratio (HAR) features into the substrate. The simulated evolution rates of profile of a rough mask hole and the profile of E‐field strength inside the hole under various EAD shapes verify the above conclusions. The mechanism behind these results was analyzed systematically. This study provides a significant point for further investigation into the optimization of the etching technique.

Deep neural network-based reduced-order modeling of ion–surface interactions combined with molecular dynamics simulation

“…For example, complex 3D structures with HAR patterns are commonly implemented in memory devices whose fabrication requires advanced plasma techniques, which presents many challenges in controlling the process conditions to achieve uniform profiles with a high yield for the mass production of semiconductor devices. Typically, highly collimated ions are needed to produce fine HAR contact holes during plasma processing [6,7]. To guarantee the precise shape of the HAR pattern, the effects of localized disturbances in the process should be considered, such as variations in the mask pattern shape [4,8], sheath curvature at the wafer edge [5,7], and the local charging effect inside the trench [9,10], as these disturbances significantly influence the trajectories of energetic ions, thus altering the etched profile substantially.…”

Control of electron velocity distributions at the wafer by tailored voltage waveforms in capacitively coupled plasmas to compensate surface charging in high-aspect ratio etch features

“…Moreover, the mask can charge up negatively in the presence of a wide angular distribution of the electron velocities at the wafer. This can lead to an attraction of positive ions, which causes mask distortion [20,21]. These issues represent significant limitations of modern HAR plasma etching and lead to a continuous increase of driving voltages to ensure even higher ion energies to overcome retarding potentials inside etch features.…”

“…This approach, however, only treats the symptoms of a problem, whose origin can be removed by ensuring in-feature surface charge neutralization. This requires the generation of a significant flux of electrons with high velocities directed normal to the electrode [20,21]. This would also reduce the negative charge-up of the mask.…”

“…In this way, electrons can penetrate deeply into HAR trenches to neutralize positive wall charges. Zhang et al [20,21] used the velocity and angular distributions obtained in their work as input for a feature scale model and demonstrated that this technology indeed leads to surface charge neutralization inside HAR etch features and reduces mask distortion. This concept is similar to the effects of peaksand valleys-waveforms in micro atmospheric pressure plasma jets [37,55,56] and is also similar to the effects of highly emissive boundary surfaces in dc plasmas [57,58], which both lead to the generation of electric fields close to boundary surfaces that accelerate electrons towards this surface to balance the ion flux on time average.…”

Study on the modified effect of polyvinylidene fluoride membrane by remote argon plasma

“…During the discharge process of the plasma equipment, gas molecules are dissociated in the reaction chamber, generating charged ions, free electrons and free radicals [31,32]. These active particles are beneficial to the improvement of the membrane properties, and the plasma-etching effect is mainly caused by the strong impact of high-speed electrons on the material surface [33,34]. Tsai C Y [35] found that the hydrophilicity of the membrane was significantly improved by a plasma technology, but the pore size of the modified membrane material increased by about 25% compared with the original membrane, which was due to the plasma-etching effect on the membrane surface.…”