InP微透镜的设计与制作

Design and Fabrication of an InP Microlens

高速光电探测器采用芯片背面带微透镜的背入射结构,利用微透镜对光的汇聚提高芯片与光纤的耦合效率。软件模拟发现,光敏面直径为30μm的芯片采用背入射结构时,其等效光敏面直径大于50μm,并且透镜拱高为8～15μm时,能更好实现对光的汇聚。对于InP微透镜的制作,首先要制作出透镜形状的光刻胶胶型,然后通过电感耦合等离子体（ICP）刻蚀将光刻胶图形转移到InP衬底上。光刻胶坚膜温度与坚膜时间对光刻胶形成透镜形状有很大影响。通过优化条件,150℃坚膜3 min的光刻胶呈规则透镜形状,并且表面光滑无褶皱。通过调节反应离子刻蚀（RIE）功率和ICP功率找到了合适的InP刻蚀速率,调节Cl2和BCl3的体积流量比改变了InP和光刻胶的刻蚀选择比,从而制作出不同拱高的微透镜。

A back-illuminated structure with microlens on the back of the chip was used in the high speed photodetector,the coupling efficiency between the chip and fiber was improved by light convergence with the microlens.The software simulation shows that when the back-illuminated structure was used in the chip with photosensitive surface with a diameter of 30μm,the diameter of the equivalent photosensitive surface is larger than 50μm and the arch height of lens is 8-15μm,then the light can converge better.For the fabrication of the InP microlens,the shape of the lens-shaped photoresist was fabricated at first,then the photoresist pattern was transferred on the InP substrate by inductively coupled plasma（ICP）etching.The hardening temperature and hardening time of the photoresist have a great influence on the formation of the lens-shaped photoresist.Through the optimization of conditions,the photoresist is a regular lens shape after hardening at 150℃for 3 min,and the surface is smooth and no fold.The proper InP etching rate was found by adjusting the reactive ion etching（RIE）power and ICP power,and the etching selectivity of the InP and photoresist can be changed by adjusting the volume flow ratio of Cl2 and BCl3,thus the microlens with different arch heights were fabricated.