JPS649415A - Production of thin ferroelectric film element - Google Patents

Abstract

PURPOSE:To enable uniform and rapid etching by diluting phosphoric acid with water and using such phosphoric acid in a stage for forming a diaphragm structure by removing a part of an MgO substrate by chemical etching with the phosphoric acid. CONSTITUTION:A thin ferroelectric film 2 is formed on the 100 face of the substrate 1 consisting of the MgO single crystal. An upper electrode 3 is then formed on the film 2. The part of the substrate corresponding to the part under a photodetecting part is removed by the hot phosphoric acid and thereafter, a photodetecting electrode 5 is formed on the rear face of the film 2. The etching is executed by diluting the phosphoric acid with water at the time of the etching of the substrate 1. The concd. phosphoric acid has a high viscosity and dissolved Mg ions are hardly diffusible therein so that the rate of the etching depends strongly on the flow rate of the liquid. Whereas, the viscosity decreases and the increased diffusion rate and the increased etching speed are obtd. if the etching is executed by diluting the phosphoric acid with water. The dependency of the speed on the flow rate is then decreased. As a result, the etching is uniformized and is progressed at a high speed. The dissolution and crack of the film 2 are thus prevented.