Oxide uniformity and dimer ratio effects on overall phosphorous dose uniformity in a non-mass resolved ion implanter

In low-temperature polysilicon thin film transistor (LTPS) fabrication, a non-mass resolved implanter is used. The primary application is for flat-panel displays, where it is often required to implant through an oxide layer for lightly doped drain (LDD) and threshold adjust steps. It was generally accepted that to ensure good implant uniformity over a large substrate area, a low dimer ratio (P₂H_x⁺/PH_x⁺) in the PH₃ beam is generally required for LDD doping. In this work PH₃ implants were performed in an Orion NV6072 flat-panel implanter. The sheet resistance non-uniformity as a function of the non-uniformity of oxide thickness under different dimer ratio was studied. It was found that the implant uniformity depends strongly on the capping oxide uniformity. Beams with higher dimer ratios resulted in higher dose non uniformity when implanting through oxide films. The relationship between dose uniformity and implant energy was also explored