Doping of trench capacitors by rapid thermal diffusion

A new rapid thermal diffusion process for shallow, heavily doped trench junctions in high density dynamic RAMs is described. Planar dopant sources are formed by spin-coating rigid substrates, such as silicon wafers or solid dopant sources, with liquid dopants. Diffusion takes place at high temperatures when the source, placed in proximity to the silicon wafer, releases dopant via evaporation followed by diffusion to the silicon surface. Well-controlled, heavily doped shallow junctions are readily obtained for B, P, and As. The doping process is shown to provide uniform doping of high-aspect-ratio trenches. Process control is achieved by controlling the wafer temperature and duration of the process. Junction depths near 0.1 mu m have been demonstrated over the entire surface of trenches 0.7 mu m in diameter and 6 mu m in depth.