Plasma Behaviors Of Inductively Coupled Fluorocarbon Discharges And Fluorinated Carbon Films Growth Mechanism

Nowadays, in the manufacturing of microelectronic components fluorocarbon plasma was widely used in low K a-C:F:H film deposition and the etching of SiO₂, Si and other related materials. With the advantage of low pressure, high density and sufficient uniformity, inductively coupled fluorocarbon plasma was widely studied for the decreasing in the dimension of the devices, the increasing of the substrate. Using ICP method, we have prepared the low K fluorocarbon films and carried out research on the characteristics of the discharge of the fluorocarbon gas, the behavior of the fluorocarbon radicals and the growth mechanism of films. Part 1: Characteristics of fluorocarbon plasmas discharge Characteristics of the low-pressure inductively coupled CF₄ plasma have been investigated using a Langmuir probe method. Results in CF4 gas have shown that two electron populations: one with low temperature and high density and the second with higher temperature and lower density. Fast electron temperature The, slow electron temperature Tce and mean electron temperature Te decrease, while their densities nhe, nce, ne increase with the increasing r.f. input power. Our findings suggest that the dependence of two-electron-temperature on r.f. input power can be explained by the thermodynamic equilibrium of the collision between the electrons and the particles. Part 2: Behavior of the fluorocarbon radicals in ICP Actinometric optical emission spectroscopy (AOES) is used to investigate the discharge of CF₄ and CH₄ mixtures. Relative concentrations of radicals in ICP plasma are determined as a function of r.f. input power, pressure and the gas flow ratio R (R=CH₄/(CH₄+CF₄)). It is found that CF,CF₂,CH,H and F radicals exist in the CF4/CH4 plasma as well as C₂ radical. The relative concentration of C₂ increases with increasing power, and shows a reverse "U"shape tendency with increasing pressure. As R is increased, the variation of the relative concentration of C2 is not monotonous. It reaches a maximum value when R =7.5%, then decreases followed by almost no change with the further increase of R. Based on these results, it is concluded that gas-phase reaction from the reaction of CF and CH (C F + CH→C2 +HF) contributes to the production of C2 radical. At the same time, activation reaction model of radical collision is suggested. Result of simulation agrees well with that of experiment. C4F8 plasma with the addition of H2 is generated by ICP method. The results show that plasma activity increases firstly and then decreases with increasing R (R=H2/(H2+C4F8)). As the gas flow rate ratio R ranges from 0 to 0.625, relative densities of both CF and CF2 decrease, and the relative [CF] has a similar tendency with the calculated [CF], indicating that CF radicals are generated mainly by the electron impact dissociation of CF2 radicals. Production of HF is also discussed. Part 3: Growth mechanism of films. a-C:F:H films were deposited by ICP using CH4 and CF4 gases. The relationship between the film deposition and precursor radicals in the plasma was discussed. It was shown that CH radical, as well as CF, CF2, C2 radicals are of the precursors, contributing to a-C:F:H film growth. Thus, the "adsorbed layer model limited by precursor radicals"of the growth mechanism of a-C:F:H films was suggested.