提高离子束刻蚀亚微米光栅侧壁陡直度的方法

现代亚微米光栅的应用通常要求栅脊侧壁陡直。通过比较两种配备不同离子源的刻蚀机的反应离子束刻蚀结果,认为影响亚微米光栅侧壁陡直度的一个重要因素是离子束发散角(束散角),且小束散角有利于获得陡直的光栅侧壁。国内应用最广泛的双栅考夫曼刻蚀机束散角较大(大于13°),致使用常规方法获得的熔石英光栅的侧壁倾角仅为77°。针对此刻蚀机,尝试了三种提高侧壁陡直度的方法:旋转倾斜刻蚀法、交替倾斜刻蚀法和二次金属掩模法,分别把侧壁倾角提高到86°、86°和82°。最后从掩模侧壁收缩速率和槽底部与顶部离子通量的差异对束散角对侧壁陡直度的影响给予解释,并说明了上述三种方法的工作机理。

Methods for Increasing Sidewall Steepness of Reactive Ion-Beam Etched, Sub-Micrometer-Period Gratings

Modern applicaiton of sub-micrometer-period gratings often requires the grating profile to be rectangular with steep sidewalls. By comparing cross sections of gratings made by reactive ion-beam etching in two etchers equipped with different types of ion-beam sources, we find that the divergence of ion-beam strongly influences the sidewall steepness of sub-micrometer-period gratings fabricated by using reactive ion-beam etching. All conditions being equal, a smaller divergence angle renderes higher sidewall steepness. The divergence angle of the two-grid Kaufman ion-beam source that is widely used in China at present is typically larger than 13°, limiting the attainable sidewall angle of gratings in etched fused silica to be only 77°, unless a special measure is taken. Using such an ion-beam source, we experimented with three etching methods (rotation-tilt method, alternate-tilt method and metallic-mask recoating method), and increased the sidewall angle of sub-micrometer-period fused silica gratings to 86°, 86° and 82°, respectively. Two mechanisms by which the ion-beam divergence affects the sidewall steepness are considered: the shrinkage rate of the mask's sidewalls and the difference between the ion fluxes at the bottom and the top of the grooves. The roles of these two mechanisms in the three etching methods are also explained.