离子束刻蚀改善膜厚均匀性的研究(特邀)

Study of Ion Beam Etching to Improve Film Thickness Uniformity(Invited)

为了提高光学透镜表面的膜厚均匀性,用离子束刻蚀原理修正膜厚均匀性,用法拉第探针测试不同参数离子源的离子束密度,并研究不同离子束密度对Ti_(3)O_(5)膜层均匀性的影响。采用电子束与离子辅助沉积技术在未安装修正挡板的三级公自转行星盘真空镀膜机进行实验,对测试结果用Optilayer进行膜厚拟合,并用Zygo干涉仪测量粗糙度,分析离子束刻蚀对透镜表面形貌的影响。结果表明通过离子束的刻蚀,可见光波段Ti_(3)O_(5)单层膜的均匀性为0.36%,粗糙度由0.036 nm变为0.037 nm。

Optical lenses are commonly used in security,optical instruments,digital camera lenses,etc.,and the spherical surface of the lens has a large difference in film thickness due to the large curvature of the projection at its centre and the different angles of incidence between the lens apex and edge positions.For large spherical optics,film thickness uniformity can be corrected in two ways:1)by optimising simple or planetary rotation fixtures;2)by installing fixed or moving correction baffles to improve film thickness uniformity.Correction baffles are used to correct the film thickness uniformity by selectively blocking the faster deposition rates on the optical element.Due to the small size of small spherical optical elements,the correction baffle is not able to improve the film thickness uniformity very well.In this paper,the principle of ion beam etching is applied to correct the film thickness uniformity by using electron beam and ion assisted deposition techniques in a three-stage metric rotating planetary disk vacuum coater without correction baffles.Two etching methods are used to improve the film thickness uniformity,the first method is deposition moment etching,where an ion beam is used to bombard the film material molecules while the vapour phase deposition coating is being applied.Variables were controlled to investigate the effect of different ion source currents and different ion source voltages on the film thickness uniformity.At constant ion source voltage values,the film uniformity of Ti_(3)O_(5)first decreases and then increases as the ion source current increases.At ion source voltage values of 1500 V,the ion source current increases,the BC value increases from 1300 mA to 1400 mA,and the ion beam density increases from 63.6μA/cm^(2) to 67.1μA/cm^(2) and its uniformity increases from 1.26%to 0.53%.The uniformity of the Ti_(3)O_(5)film layer increased with increasing ion source voltage at constant ion source current values.Comparative analysis revealed that changing the ion source current value had a greater effect on the film thickness uniformity,as the ion source current value mainly affected the ion beam density,which increased more and the number of ions per unit area per unit area of time increased more.The second method is etching at the end of the deposition,where the film thickness at the end of deposition(without etching)and after etching are fitted by the OptiLayer to obtain the difference in film thickness and etching rate at different locations before etching,and to calculate the optimum coating time.The two etching methods were compared and it was found that the etching rate of the first one was significantly greater than that of the second method,because at the moment of deposition,the molecules of the film material just reach the surface of the substrate when the film is formed,and the dense structure is not yet formed when it is Ar^(+)The film atoms need less energy to detach at this time.The second method is limited by the slow etching speed and the difference in thickness between the top of the lens and the edge of the film is fixed at the end of deposition,with a maximum thickness uniformity of 1.14%.Lens roughness was measured using a Zygo interferometer for uncoated,etched while deposited,and etched after film formation.The effect of ion beam etching on the surface morphology of the lenses was analysed.The results show that the Ti_(3)O_(5)monolayer was coated by deposition etching at an inclination angle of 68°without a correction baffle,and that the film thickness uniformity reached 0.36%and the roughness changed from 0.036 to 0.037 nm.