Effects of Al film thickness and annealing temperature on the aluminum-induced crystallization of amorphous silicon and carrier mobility

Si crystallization arising in Al(20, 50, 150 nm)/amorphous silicon (a-Si) (200 nm)/glass specimens prepared by the aluminum-induced crystallization (AIC) technique and the rapid thermal annealing (RTA) process is investigated. Compared with specimens with amorphous aluminum (a-Al), specimens with micro-crystallized aluminum (μc-Al) underwent Si crystallization at either a lower annealing temperature or with a thinner Al film. Si crystallization started only when the compressive annealing stress (σan) of the composite film formed in the annealing process reached a critical value which is independent of the Al film thickness. The compressive stress in specimens increased with increasing annealing temperature and Al film thickness. With decreasing Al film thickness the Si crystallization density increased in proportion to the hillock density, but in inverse proportion to the average micro-crystallized silicon (μc-Si) grain size. The product value (R∗) of the mean area and the number of nano voids in a unit area increased with increasing difference between the stresses formed during and after annealing (Δσ = σf − σan). For the Al(50 nm)/a-Si(200 nm)/glass specimens an increase in annealing temperature resulted in a decrease in R∗ but an increase in the mean μc-Si size. For the Al(150 nm)/a-Si(200 nm)/glass specimens the behavior is exactly opposite to that for the Al(50 nm)/a-Si(200 nm)/glass specimens. For all 10 specimens an increase in R∗ led to an increase in the tensile Δσ and a decrease in the mean μc-Si size. The carrier mobility of a specimen decreased with increasing tensile Δσ, irrespective of the Al film thickness. The mean μc-Si size and thus the carrier mobility increased significantly with increasing Al film thickness.