Study On Ion Beam Polishing Of ZnS Optical Element

As a typical infrared optical material, zinc sulfide(ZnS) has an extremely unique value and its optical elements are widely used in optical, chemical, infrared window materials and many other areas. But with the development of innovative and high technology, such as microelectronics technology, laser technology, space application technology and so on, surface precision of optical components has become increasingly demanding, and the traditional processing methods for surface of the optical elements have been unable to meet the demanding.In this paper, using ion beam etching conducts the study of surface etching polishing process of ZnS. The variation curves of etching rate and surface roughness of ZnS are plotted by analyzing factors, including the energy of the ion beam, ion beam current density and ion beam incident angle. The sacrificial layer technology has also been led into ion etching polishing process in the article, which means a sacrificial layer film must be prepared firstly on the surface of zinc sulfide. The sacrificial layer surface will become ultra-smooth by planarization process, and then ultra-smooth surface will be transferred to the surface of zinc sulfide optical element by ion beam etching to reduce the surface roughness of ZnS wafer. In the process mainly includes the following sections:1) It is necessary to select the sacrificial layer materials which own the same speed or close speed point of ZnS material. Fixed ion beam energy and ion current density, the variation curves of sacrificial layer material and zinc sulfide material was drawn together by changing the ion beam incidence angle. If there is an intersection, the intersection is the same speed point of two kinds of materials.2) Prepare a thin film of sacrificial layer on the surface of ZnS. The surface of the planarization process is studied by solvent exposure mode used planarization reflow device, including flow control system, bubble system, the gas mixing chamber, sealed sample room and exhaust gas treatment system. In order to obtain optimal parameters of planarization process on the surface of sacrificial layer, analysis of influencing factors comprise solvent ventilation flow, mixed gas flow and solvent exposure time.The experimental results show that:1)The optimal technical parameters of ion beam directly processing ZnS are that the energy of ion beam is 400eV and the current density of ion beam is 35mA, and incident angle is 45°, used ion beam etching and polishing machine self-developed by Xi’an Technological University and equipped with a microwave ion source.2) Sacrifice layer materials of ZnS wafer’s surface can be selected photo-resist models: AZ4620 and EPG533. There are same speed etching points between ZnS and AZ4620, and close speed point between ZnS and EPG533.3) In the planarization process, the surface roughness of sacrificial layer can be maximally reduced with following parameters:heat treatment used before drying and after baking, solvent ventilation flow is 400mL/min, mixed gas flow selects 300mL/min and solvent exposure time is 15min.4) Fixed ion beam energy and ion current density, ZnS and EFG533 can be etched with close speed in ion beam incident angle 55°. ZnS and AZ4620 can be etched with same speed in ion beam incident angle 42° and 53°, and the result is better than former.