Optimal Conditions for Micromachining Si1 − xGex at 210 °C

This paper investigates the possibility of reducing the deposition temperature of silicon-germanium (Si_1-xGe_x) thin films to 210degC and tuning the physical properties of the film locally to achieve optimal mechanical and electrical properties that are suitable for a wide range of microelectromechanical systems that can be postprocessed on top of standard prefabricated electronics or onto more exotic substrates, such as polymer films. First, the effect of the Ge content, layer thickness, and deposition pressure on the mechanical properties of as-deposited Si_1-xGe_x films, which are deposited at 210degC, is analyzed in detail, and the optimal deposition conditions are experimentally determined. Then, the possibility of using pulsed excimer laser annealing to control the electrical and mechanical properties of such films is demonstrated. It is shown that the low deposition temperature imposes many constraints on the laser-annealing conditions, particularly for optimizing the mechanical properties. Moreover, the Ge content and the film thickness have a significant influence on the optimal laser-annealing conditions. It is illustrated that eliminating stress gradient implies very shallow crystallization, which is accompanied by relatively high electrical resistivity. Using the optimal laser-annealing conditions, the stress gradient can be as low as 1 times 10^-6 mum^-1 for a 0.3-mum-thick film. The optimal electrical resistivity, on the other hand, depends on the Ge content. For 70% Ge, the minimum resistivity is 80 mOmega ldr cm; decreasing the Ge content to 30% results in a resistivity of 3 Omega ldr cm.