Dry etching of sacrificial oxide and residueremoval using supercritical carbon dioxide

Abstract

In this work, we used dry etching process using supercritical carbon dioxide (scCO₂), which possesses zero surface tension, liquid like density, gas like diffusibility and environmentally benign. As a result, this green solvent is being considered for use to advantage etching of sacrificial layers (SiO₂, TEOS) with high selectivity toward SiN structural layers. Moreover, scCO₂-based solutions in wafer etching would eliminate the water-based drying step and prevent structural damage to materials in microelectronic devices. In our work, etching experiments were carried out using HF-pyridine and various cosolvents (methanol, ethanol, butanol and iso-propyl alcohol) mixture in scCO₂. The experimental parameters were changed namely concentration of etchant, kind of cosolvents and changing the experimental conditions. Also, we developed a two chamber etching reactor (e.g. etching chamber and pre-chamber) that could provide better efficiency. The pre？\chamber is designed for pre-treating the etchant as per demanded by the samples. We measured the etching rate, selectivity and uniformity for BPSG and SiN under various experimental parameters and found improved results. Finally, our developed etching method might have a great beneficiary in microelectronic industry in case of silicon wafer and in surface micro-machining for the release of component parts in micro？\electromechanical system (MEMS) devices. Further more, to meet the challenges posed by shrinking future sizes, a novel cleaning technology for removing sacrificial oxide residue from semiconductor wafer is introduced. In the key excitement in this paper is we introduced specifically formulated surfactants (which must be compatible with the acidic residues produced in the wafer) along with polar solvent can be added in small amount into CO₂ to form water in CO₂ (w/c) microemulsion in the circulated chamber system to perform sacrificial oxide residue removal. In a typical experiment, we introduced a specially designed surfactants into water in CO₂ microemulsion. The surfactants create a nanometer scale heterogeneous system of discrete polar microdomains dispersed in a continuous phase of non polar CO₂. The surfactants added to CO₂ have a polar head group that points inward and a CO₂-philic tail that forms micells, which remove process residue. Cleaning with scCO₂ is a ‘dry in - dry out’ process technology, consisting of a cleaning and a rinsing /drying step performed in the same chamber. A novel approach to clean single wafer with supercritical carbon dioxide process has been described. A major benefit of this process is from an environmental perspective. It allows dramatic reductions in water and chemical consumption while enabling achievement of the ITRS (International Technology Roadmap for Semiconductors) goals.