矽基微光學平台若需光路垂直轉折，例如使雷射光束垂直入射矽基板後轉折90°方向至平面微光學平台上，即需具光學品質且寬度足夠的45°矽基微反射面。一般在(100)矽晶片上以氫氧化鉀(KOH)蝕刻，會留下晶面鍵結較強的(111)面，主要原因在於KOH溶液對該晶向面蝕刻速率相對其他晶向面最為緩慢，因此，欲在(100)矽晶片蝕刻出45°斜面，則須修正晶向面間蝕刻速率，使(110)晶向面的蝕刻速率小於(111)晶向面。在本篇論文中，利用KOH添加IPA之蝕刻液，在特定溫度與濃度下，抑制(110)面的蝕刻速率，進而得到一個深度具97 μm且表面粗糙度達光學品質之矽基45°微反射面。 接著，在矽基45°微反射面上設計一個繞射元件，藉由繞射光柵週期的調整設計，使得繞射元件對徑向面與子午面之聚焦能力不同，而改善光線入射45°微反射面所引起的像差，並且經由微製程技術將繞射式光學元件整合於矽基45°微反射面上。此一體化(monolithic)之微光學元件，將使得單模光纖的發散光場經由45°矽基微反射面偏折同時亦能夠達到準直、聚焦在特定位置之效果，同時減化微光學系統對位封裝之需求，在積體化、三維化之微光學平台上，深具發展與應用潛力。 A Si-based 45° micro reflector with very deep depth more than 100 μm and RMS surface roughness less than 20 nm by using the anisotropic wet etching process was demonstrated. In general, the etch rate of {110} planes on a (100) silicon wafer is fastest than that of the other crystalline planes. The corner compensation method in the fabrication of 45° slants is developed for suppressing the etching rate of {110} planes. Therefore, this Si-based 45° micro reflector can be etched to deep depth more than 100 μm with surface roughness less than 20 nm. This micro reflector makes the in-plane light on the general optical bench to successfully deflect to the out-of-plane. Moreover, for reducing the following assemble process of macro and micro optical elements in such a 3-D optical setup, a monolithic integration of this Fresnel lens based on this Si-based 45° micro reflector is also developed. For eliminating the astigmatic aberration due to this inherent off-axis optical setup, an aspherical Fresnel lens with different refraction power in the tangential and saggital direction is designed and fabricated. The measurement result is also discussed in this paper.
