Nucleation and crystallization characteristics of phosphorus-doped amorphous silicon (a-Si) "slit nano wire" are studied, which is fabricated by conformal filling of a 100 nm wide trench by HLD (High temperature Low pressure chemical vapor Deposition) oxide, and measures about 10 nm in width and height. Nucleation rate and crystallization rate of the amorphous silicon layer, with a phosphorus doping concentration of 1 x 10(20) cm-3 are measured for samples annealed between 525 and 560-degrees-C between 3 and 120 h. The number of nuclei and the length of grains are observed by transmission electron microscopy with a magnification between 32,000 and 4,000,000. The activation energies of nucleation and crystallization are 1.15 and 1.53 eV, respectively, which are about one quarter and one half those measured for a-Si layers formed on flat SiO2. These characteristics are attributed largely to the effect of interaction of a-Si "slit nano wire" layers and the slit wall surface.