Method of forming a semiconductor device

A method of forming a semiconductor device includes forming a trench in a semiconductor body; at least partially filling the trench with a filling material, the filling material; introducing dopants into a portion of the filling material, where the dopants have a first diffusion coefficient relative to the filling material and have a second diffusion coefficient relative to the semiconductor body, where the first diffusion coefficient is greater than the second diffusion coefficient, and where a ratio of the first diffusion coefficient to the second diffusion coefficient is greater than 10; and applying thermal processing to the semiconductor body configured to spread the dopants in the filling material along a vertical direction between a bottom side and a top side of the filling material by a diffusion process.