In this study, a planar type single turn inductively coupled plasma system was adapted for the deposition of TiN and Ti thin films with $H_2/Ar/TiCl_4$ and $N_2/H_2/Ar/TiCl_4$ gas mixtures. Major concerns of the study was the effect of the process variables like gas composition, pressure, and input power on the plasma parameters, such as plasma density, electron temperature and reactive species in the plasma and the resultant film properties including resistivity and chemical composition. Plasma density, electron temperature and plasma potential were monitored with Langmuir single probe and the distribution of positive ions in the plasma was examined with mass spectrometry.
Firstly, the inductively coupled plasma was characterized with each of Ar, $H_2$ and $N_2$ gases at the pressure range from 1 to 60mTorr and the input power range from 200 to 1000W. The plasma density and electron temperature showed critical dependence on the process gas, pressure and input power. Ar plasma showed the highest plasma density of $7\times10^{17}m^{-3}$ at the pressure of 60mTorr and input power of 800W. $N_2$ plasma showed maximum plasma density of $2\times10^{16}m^{-3}$ at 30mTorr and 800W. And the $H_2$ plasma showed the lowest plasma density of the three gases and had a maximum of $7\times10^{15}m^{-3} at 60mTorr and 800W. At the plasma density below a critical point (near $2\times10^{15}m^{-3}$) the power transfer efficiency to the plasma was low as a result of capacitive coupling. With plasma density over the critical point the power transfer was mainly by inductively coupling and the plasma density increased effectively with increasing pressure and input power. When the pressure increased, the plasma density of Ar and $H_2$ plasma increased monotonically while it had a maximum point near 30mTorr in $N_2$ plasma and the electron temperature and plasma potential decreased inversely proportional to the pressure in all gaseous system. Dissociation of the molecules occurred more with increasing pressure, especially in $H_2$ plasma. And the input power had the effect of increasing the plasma density without affecting the electron temperature.
Low temperature deposition of Ti and TiN films was possible with $H_2/Ar/TiCl_4$ and $N_2/H_2/Ar/TiCl_4$ plasmas. Ti films with no Cl and resistivity less than 300μ Ω cm was obtained at the substrate temperature of 415℃ with input power of 800W. TiN films with no Cl and resistivity as low as 110μΩcm was obtained at the substrate temperature of 410℃ with input power of 800W. The resistivity and impurity concentration of Ti and TiN films decreased with increasing input power and pressure of the system, which had the effect of increasing the plasma density and the overall density of $TiCl_x$, H, and N radicals.
The composition of the plasma forming gas had the effect of changing the plasma characteristics and affected the quality of the films greatly. In the Ti deposition system with $H_2/Ar/TiCl_4$ mixture, Ar had the effect of increasing the plasma density and dissociation of $H_2$ molecules and finally increasing the H radical density. As a result, high quality of Ti films were fabricated with high portion of Ar gas in the $H_2/Ar$ mixture. In the TiN deposition system with $N_2/H_2/Ar/TiCl_4$ mixture, the quality of the TiN films depended critically on the concentration of the N radical. The $H_2$ gas had the positive effect of reducing the Cl from the $TiCl_4$ but also had the negative effect of eliminating the N radical through the reactions to form molecular radicals of $N_xH_y$, as confirmed by the mass spectrometer. When Ar was added, the plasma density increased greatly and the production of ions and radicals from the $N_2$ and $H_2$ molecules were enhanced so that high quality of TiN films were obtained over a wide range of Ar portion in the plasma.
