Gas heating and throw distance for the sputter deposition of aluminum and tungsten

The throw distance of Al and W atoms was determined (A) by investigating the pressure-dependent deposition rate and applying the Keller–Simmons one-dimensional model. The power density at the target as a parameter was varied over more than one order of magnitude. Whereas the values determined for Al are not influenced by power, the values for tungsten strongly increase with power. This effect is related to strong gas density reduction related to gas heating for W sputtering, which reduces the probability of collisions between sputtered atoms and the gas. The gas heating was experimentally determined by simultaneous measurements of the pressure in the sputtering chamber and at the end of a tubular probe inserted into the hot plasma region. For tungsten, a strong heating and related gas density reduction was found. An analytical expression describing the spatially resolved temperature profile in a sputtering discharge is developed by means of the Keller–Simmons formulas. The influence of various process parameters on gas heating can be easily studied by the model. There is good agreement between the model calculations with the experiments performed as well as with Monte Carlo simulations and experimental findings from the literature. Forward simulations by the model result in a power-independent throw distance (B) for both elements, which are in agreement with the values (A) resulting from the pressure-dependent deposition rate. Existing differences are explained by the rough assumptions of the model, which is critically discussed.