Large-grain polycrystalline silicon films with low intragranular defect density by low-temperature solid-phase crystallization without underlying oxide
The solid-phase crystallization of an amorphous silicon film to polycrystalline silicon by a low-temperature (⩽600 °C) furnace anneal has been investigated in a suspended cantilever structure without underlying silicon oxide by transmission electron microscopy and Raman spectroscopy. The grain size of polysilicon increases up to ∼3.0 μm and the density of intragranular defects decreases one order of magnitude in the samples without underlying oxide, compared with those with underlying oxide. The main reasons for the high quality of the suspended structures are thought to be due to the lower stress in the films during crystallization and a reduced grain nucleation rate.
Structure character of fast growth polycrystalline silicon film from SiCl/sub 4//H/sub 2/
The polycrystalline silicon films with the deposition rate over 4.5 /spl Aring//s prepared at low temperature of 250 /spl deg/ were obtained from the hydrogen dilution of tetrachlorine silicon using PECVD technique. The results show that the growing surface of film contains a large amount of silicon crystalline grains with 30-100 nm in diameter. The crystalline fraction and the crystalline grain size strongly depend on the RF power and the hydrogen dilution ratio. The optimum RF power and the optimum hydrogen dilution ratio for the best crystalline character are related to the deposition rate. On the other hand, the crystalline fraction and the crystalline grain size are almost independent on the substrate temperature. It is considered that the space reaction processes and the Cl element play an important role in the initial stage of the crystalline formation and in the crystalline grain growth for the low-temperature crystallization of the films.
Extranasal type of nasal glioma
Summary A case of a rare congenital tumor; a nasal glioma of the extranasal type has been presented which seems sufficiently unusual to be worthy of reporting. The various theories as to the origin and nature of these lesions have been discussed in the paper by Hill6 and others, 1, 2, 5 but it is the belief of the authors that most or probably all of these lesions represent a congenital malformation.