Dopant Diffusion during Amorphous Silicon Crystallization

Abstract

We have investigated the redistribution of B during the crystallization of an amorphous Si layer homogeneously doped with P. The redistribution of B only occurs for concentrations lower than 2 × 1020 at cm−3. Crystallization leads to a non “Fickian” redistribution, allowing an abrupt interface between the regions doped and undoped with B. Once the crystallization is ended, B diffuses through the layer in the type B regime with a coefficient which is in agreement with the literature data for diffusion in polycrystalline Si. Although the P distribution is homogeneous in the entire layer, for a temperature as high as 755 °C, P diffuses towards the region the most concentrated in B. The B and P interactions are interpreted as chemical interactions.

B diffusion in implanted Ni2Si and NiSi layers

“…Three following samples were produced: two samples were made for B diffusion studies either in Ni 2 Si or in NiSi, and one sample was made to observe B redistribution resulting from the sequential formation of Ni 2 Si and NiSi. [17][18][19] The a͒ Author to whom correspondence should be addressed. These silicides were produced through the reaction of a Ni layer deposited at room temperature by magnetron sputtering on a Si layer grown by low pressure chemical vapor deposition at 550°C on the 30 nm-thick oxide ͑see Ref.…”

Anomalous B diffusion profiles in nanocrystalline Si

“…Once this shoulder has reached the SiO 2 layer at the depth 250 nm, the B concentration profile becomes quasi-linear. This type of profile was not observed previously [11][12][13], probably because the nc-Si film being thinner (100 nm), the observations were performed at the end of the phenomena, when the shoulder had already reached the SiO 2 layer. This type of shoulder observed in dopant diffusion profiles measured in monocrystalline Si is usually explained by a diffusion coefficient varying with dopant concentration (C B in our case) due to the variation of the Si Fermi level with dopant concentration (change in charge carrier and point defect concentrations) [14].…”

“…This thermal treatment allows the layer to be crystallized, but is not sufficient for significant B diffusion in the nc-Si layer. As noted in previous experiments [12,13], Si crystallization leads to the formation of a shoulder in the B concentration profile, located at a depth of $75 nm and corresponding to a concentration close to the B solubility limit in Si in this http://dx.…”

“…This profile (red line in Fig. 1) can be considered as the initial B distribution in the sample before B diffusion for temperature annealing higher than 600°C [12,13]. Figure 1 shows that B atoms diffused in the nc-Si layer for annealing performed at temperatures > 550°C.…”

“…Figure 1 shows B profiles measured by SIMS in the sample after annealing for different times at temperatures between 550 and 800°C. The profile measured after annealing at 550°C for 24 h results mainly from diffusion and redistribution during the first stage of Si crystallization [11][12][13]. This thermal treatment allows the layer to be crystallized, but is not sufficient for significant B diffusion in the nc-Si layer.…”