Ion implantation is employed for trench sidewall doping. Aspect ratios of trenches for high Mbit DRAM become very large, so that very small grazing incidence ion implantation to sidewall is necessary to avoid shadowing effect. In this case, ion reflection in trenches occurs at a high rate and these reflected ions are implanted to the opposite sidewall, so it is very important to know this effect to apply real devices. We have studied these ion reflection effects in trenches by SIMS, and spatial and energy distributions by Monte Carlo Simulation. It is found that reflected atoms were concentrated at the specular reflection angle. The reflected ions were also scattered with large angles because of diffuse and inelastic scattering. These diffusely scattered atoms are implanted to the region facing to the directly implanted region. The experimental results are reproduced well by using distribution functions for an amorphous surface.