X-ray diffraction study and electrical characterization of boron-implanted low-pressure chemical vapor deposited polycrystalline silicon layers

Abstract

The distribution of dopant atoms and the structure and the electrical properties of low-pressure chemical vapor deposited (LPCVD) polycrystalline silicon layers were studied as a function of layer thickness (0.35–2.0 μm), annealing temperature (800–1100 °C), and boron implantation dose (1015–1016 cm−2). The distribution of boron atoms was determined by secondary ion mass spectrometry. By means of x-ray diffraction, information about (i) preferred orientation of crystallites, (ii) crystallite size and short-range strain form the peak broadening, and (iii) lattice parameter from the peak position was obtained. The lateral grain size was determined by transmission electron microscopy. For electrical characterization Hall-effect measurements and resistivity measurements were performed. The redistribution of implanted boron in LPCVD polycrystalline silicon proceeds faster than in monocrystalline silicon, as expected. The as-deposited films exhibit an anisotropic structure: a 〈110〉 fiber texture was found and the crystallites with 〈110〉 perpendicular to the surface are larger than crystallites with other orientations. With increasing layer thickness the 〈110〉 texture becomes more pronounced and the 〈110〉 oriented crystallites increase in size, whereas the size of crystallites with other orientations slightly decreases. Annealing leads to a weaker texture and larger crystallites. Implantation and subsequent annealing at 800 °C results in a weaker 〈110〉 texture and smaller crystallites. A significant increase in crystallite size for the implanted layers is noted after the 1100 °C anneal only. Because of the multitude of parameters the interpretation of the electrical data is necessarily qualitative. The minimum in the mobility after annealing the implanted samples at 1000 °C correlates with a pronounced change in lattice parameter but its origin is not yet understood. The increase in mobility after the 1100 °C anneal can be explained by the significant increase in crystallite size mentioned above.