Experimental and theoretical study of ion distributions near 300 m tall steps on rf-biased wafers in high density plasmas J.
Articles you may be interested inSurface loss rates of H and Cl radicals in an inductively coupled plasma etcher derived from time-resolved electron density and optical emission measurements Auger electron spectroscopy study of reactor walls in transition from an O 2 to a Cl 2 plasma Effects of wall recombination on the etch rate and plasma composition of an etch reactorThe effect of chamber wall conditions on the Cl and Cl 2 concentrations in a Cl 2 discharge was studied in an inductively coupled plasma reactor. Cl and Cl 2 mole fractions were determined using optical emission spectroscopy in conjunction with actinometry, while the state of the reactor walls was monitored using a surface probe that enables detection of films and adsorbates that deposit on these walls. Prolonged exposure of the chamber walls to a Cl 2 plasma increases the Cl concentration in the discharge. This increase is due to the decreasing recombination probability of Cl atoms on the walls which with time are covered with a thin SiO 2 film. The source of the SiO 2 is the quartz dielectric window which is sputtered by ion bombardment. A SF 6 /O 2 plasma etches the SiO 2 film from the chamber walls and restores the chamber walls to a ''clean'' state. The Cl concentration in the reactor with these two different states of the wall conditions, under otherwise identical plasma operating conditions, was dramatically different and implied that the wall recombination probability of Cl atoms on the SiO 2 covered walls is considerably lower than that on the clean anodized Al. Changing the state of the walls also changes the rate controlling step for Cl recombination from diffusion limited for the reactor with the clean walls to surface reaction limited for the SiO 2 covered walls. This change in the rate controlling step changes the dependence of the plasma composition on the power, pressure, and gas flow rate.
In situ attenuated total reflection Fourier transform infrared spectroscopy was used to study the H bonding on the surfaces of a-Si:H and nc-Si:H during plasma enhanced chemical vapor deposition from SiH4/H2/Ar containing discharges. Well-resolved SiHx (1⩽x⩽3) absorption lines that correspond to the vibrational frequencies commonly associated with surface silicon hydrides were detected. During deposition of a-Si:H films using SiH4 without H2 dilution, the surface coverage was primarily di- and trihydrides, and there are very few dangling bonds on the surface. In contrast, during deposition of nc-Si:H using SiH4 diluted with H2, the amount of di- and trihydrides on the surface is drastically reduced and monohydrides dominate the surface. Furthermore, the vibrational frequencies of the monohydrides on nc-Si:H film surfaces match well with the resonant frequencies of monohydrides on H terminated Si (111) and Si (100) surfaces. The decrease of higher hydrides on the surface upon H2 dilution is attributed to increased dissociation rate of tri- and dihydrides on the surface through reaction with dangling bonds created by increased rate of H abstraction from the surface. Results presented are consistent with SiH3 being at least one of the precursors of a-Si:H deposition.
A compact retarding field ion energy analyzer has been designed and built to measure the energy distribution of ions bombarding the wafer surfaces placed on radio frequency (rf) biased electrodes in high-density plasma reactors. The analyzer was used to measure the energy distribution of ions impinging on the rf-biased electrostatic chuck in a high-density transformer coupled plasma (TCP) reactor. The effects of TCP power, rf bias, gas composition, and ion mass on the ion energy distributions (IEDs) were demonstrated through Ar, Ne, Ar/Ne, O2 and CF4/O2 discharges. In the operating range studied, the average ion energy increased linearly with increasing rf bias while the ion flux remained constant indicating that independent control of ion flux and energy was achieved in the TCP reactor. Bimodal ion energy distributions resulting from ion energy modulation in the sheath were observed and multiple peaks in the IEDs measured in gas mixtures were identified as ions with different masses falling through the sheath.
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