A hybrid model is used to simulate the characteristics of a collisional sheath in a capacitively coupled plasma （CCP） driven by a dual frequency source including a RF and a pulsed current source applied to the same electrode. The hybrid model includes a fluid model used to simulate the characteristics of the collisional sheath, and a Monte-Carlo （MC） method to obtain both ion energy and ion angular distributions （IEDs and IADs） impinging on the substrate. The effects of the low frequency of the pulsed source and the gas pressure on the characteristics of the sheath, as well as the IEDs and IADs, are studied. The results show that the ratio of pulse/RF frequency and the gas pressure are crucial for the characteristics of the sheath and the IEDs. The IADs are significantly more sensitive to the gas pressure.
We have developed a plasma etching simulator to investigate the evolution of pattern profiles in SiO2 material under different plasma conditions. This model focuses on energy and angular dependent etching yield （physical sputtering in this paper）, neutral and ion angular distributions, and reflection of ions or neutrals on the surface of a photoresist or SiO2. The effect of positive charge accumulation on the surface of insulated mask or SiO2 is studied and the charge accumulation contributes to a deflection of ion trajectory. The wafer profile evolution has been simulated using a cellular-automata-like method under radio-frequency （RF） bias and direct-current （DC） bias, respectively. On the basis of the critical role of angular distribution of ions or neutrals, the wafer profile evolution has been simulated for different variances of angles. Observed microtrenching has been well reproduced in the simulator. The ratio of neutrals to ions has been considered and the result shows that because the neutrals are not accelerated by an electric field, their energy is much lower compared with ions, so they are easily reflected on the surface of SiO2, which makes the trench shallower.
We present a model which is used to study ion transport in capacitively coupled plasma （CCP） discharge driven by a radio-frequency （rf） source for an etching process. The model combines a collisional sheath model with a trench model. The sheath model can calculate the ion energy distributions （IEDs） and ion angular distributions （IADs） to specify the initial conditions of the ions incident into the trench domain （a simulation area near and in the trench）. Then, considering the charging effect on the photoresist sidewalls and the rf-bias applied to the substrate, the electric potentials in the trench domain are computed by solving the Laplace equation. Finally, the trajectories, IEDs and IADs of ions impacting on the bottom of the trench are obtained using the trench model. Numerical results show that as the pressure increases, ions tend to strike the trench bottom with smaller impact energies and larger incident angles due to the collision processes, and the existence of the trench has distinct influences on the shape of the IEDs and IADs. In addition, as the bias amplitude increases, heights of both peaks decrease and the IEDs spread to a higher energy region.
Ion＇s behavior plays an important role in plasma etching processes and is determined by the local electric potential in the etched trenches. In this study, with the trench powered by a radio frequency （rf） source, the Laplace equation is solved to obtain the electric potential. The ion trajectories and the ion energy distribution （IED） at the bottom of the trench are obtained self-consistently by tracking the ions in the trench. The results show that the aspect ratio of depth- to-width of the photoresist trench and the voltage amplitude of the rf source applied to the electrode are important parameters. The larger the aspect ratio and the smaller the amplitude are, the more ions hit the sidewalls, which results in a notching phenomenon. Meanwhile, there are a higher high-energy peak and a lower low-energy peak in the IED with the increase in aspect ratio.
