<title>New dry-development process of trilayer resist systems for advanced lithography</title>

Abstract

A parametric study of the pattern transfer step in a trilevel resist system using oxygen-based plasmas has been made using a distributed electron cyclotron resonance reactor with independent r.f. biasing. In pure oxygen plasmas, critical dimension loss is always present in the O pressure and ion bombardment energy ranges investigated. The mechanisms most likely to be responsible for these defects during the jttern transfer process are presented and discussed. Perfect anisotropy can only be obtained at substrate tempemwres below -60°C. A novel plasma etching process based on sidewall passivation by sulfur is proposed using SOJO2 mixtures. Perfect anisotropy without CritiCal dimension loss is obtained at room temperature by using a 80% SOJ 20% O mixture and a moderate ion bombardment energy. The ultimate resolution using this new plasma process in conjunction with deep U.V. exposure and a phase..shift mask is presentet 1.INTRODUCTIONConventional single-layer lithography can resolve sub half-micron linewidths on planar, nonreflective substrates.However, lithographic processes for integrated circuit fabrication still have to be optimized f the high aspect ratio (height to width ratio) with a reflective topographyL2. When conventional single-layer resists are applied over a reflective topography, thickness variations in the resist layer result in poor linewidth control, whereas reflections of topographic sidewalls can cause "notching" effects1'2. A good method for dealing with a reflective topography is to coat the substrate with a material that planarizes the topography while eliminating reflections. Multilayer lithographic methods use an optically absorbing organic polymer as the planarizing antireflective layer. Planarizing materials provide a planar surfsee coated by the imaging layer in a subsequent spin coating step. This improves control of the critical dimensions (CD) by eliminating variations in the imaging layer. The focus latitude is also improved by allowing the use of a thinner imaging layer.