Mechanism study and solution to photo resist poor coating induced by implant process

The IC manufacture implant process produces a rough wafer surface and thus induces photo resist poor coating of the subsequent photo process due to larger resistance when photo resist spins on the wafer. This paper describes how the implant process induces photo resist poor coating, the correlation of photo resist poor coating and Vt-implant process parameters (dosage, energy), and proposes a solution to solve this issue. We discovered the correlation of roughness to implant energy to be a hyperbolic curve. We also observed similar correlation of roughness to implant dosage. Photo resist poor coating occurred in larger rough wafer surface due to larger interfacial fraction force when photo resist was sprayed on the wafer. The more rough wafer surface, the larger wafer surface area. The more photo resist amount is necessary to cover the whole wafer surface. APM (Ammonia Hydrogen-Peroxide Mixture) pre-treatment could recover the wafer surface gate oxide roughness induced by the implant process and thus eliminate photo resist poor coating significantly with the following two mechanisms: 1. APM solution did not consume oxide film, but would reach a dynamic equilibrium state in the SiO₂-NH₄OH-H₂O₂ tri-component system shown by the following reversible chemical reaction: Oxide dissolution <=>Oxide deposition 2. The reversible chemical reaction functioned like "anneal" to thin gate oxide film. It changed the atom crystal arrangement on gate oxide surface and thus recovered the wafer surface roughness from the Vt-implant process. The APM composition we used was NH₄OH:H₂O₂:H₂O=1:4:20, with temperature at 45°C, power at 250 W and dip time of 10 minutes.