ANALYTICAL MODELING AND SIMULATION OF THE CHEMICAL ETCHING PROCEss OF THE BORON-DOPED SILICON LAYERS FROM BBr3 SOURCE in the micromachining technology

The boron-doped silicon layers commonly used to fabricate various micro-mechanical elements, particularly silicon membranes, are efficient stop-etching barriers, so their control is crucial in the bulk micromachining technology. As the properties of the boron doped layers depends on the type of the doping source and on the diffusion depth in the silicon bulk, a particular analysis should be applied in each specific case. In this paper there are reported the results of an analytical modeling of the boron diffusion profile in silicon, which are applied to simulate the boron diffusion profile at high diffusion temperatures (1050°C, 1100°C, 1150°C and 1200°C), emphasizing a dependence of the diffusion coefficient as a square root of the boron diffusion concentration. It is shown that the comparison of the theoretical results and some experimental diffusion data after diffusion at 1050°C shows a very good agreement, well supporting the analytical modeling. On this basis, the chemical etching rate and the etching time are simulated as a function of the boron diffusion depth in silicon for various etching solutions and etching conditions, providing suitable guiding curves for practical applications in the bulk micromachining technology