非矽基垂直式梳狀元件之製程研究

Abstract

由於優異的出平面運動特性，垂直式梳狀致動器如今已成為熱門的微機電元件。至今為止，所有被發展出來的垂直式梳狀致動器皆以矽基微加工技術進行製作，並以矽作為結構的材料。然而，這些必須由深反應離子蝕刻(DRIE)進行加工，並以SOI晶片為主的技術，也意味著較高的製作成本。相對於矽基材料，金屬與高分子正發展成為極具吸引力的替代性材料，可用來製作低成本的微元件以取代矽基元件。然而，至今仍未見有文獻利用高分子或金屬製作垂直式梳狀致動器。 本論文提出兩種新式的製作方法用以製作高分子與金屬垂直式梳狀致動器，這兩種方法皆屬低溫及低成本的製程，在僅需類LIGA製程基礎設備的狀況下，提供了高可適性以及容易負擔的製作方案。首先，論文中對垂直式梳狀致動器進行理論及有限元素分析，以便進行尺寸上的設計。接著，為了製作高分子垂直式梳狀致動器，此處提出一雙面多重部分曝光(DoMPE)的製程平台，此平台經由正面及背面的多階曝光，可有效擴充懸浮光阻結構的外形複雜度。經由此平台及其所建立的參數資料庫，各種複雜的三維光阻結構及垂直式梳狀致動器皆被成功製作及展示。在比較理論分析及實驗結果之後，以高分子製作垂直式梳狀致動器的可行性已被成功驗證。 在金屬垂直式梳狀致動器的製作方面，首先對電鑄鎳進行材料特性調查，並發現電鑄鎳的材料特性會隨著厚度及電流密度的變化而有明顯的改變，這對設計鎳元件而言將很有幫助。在製程上，電鑄鎳與銅分別被用來當作結構層及犧牲層，在交替電鑄鎳與銅之下建構出垂直式梳狀致動器的結構，最後再由濕式蝕刻進行結構釋放。此外，經由控制光阻的斜角，亦可藉由此方法製作具有斜角的垂直式梳狀致動器。

In recent MEMS research, vertical comb drives (VCDs) have attracted lots of attention due to their superior characteristics in out-of-plane motion. To date, all the reported VCDs were fabricated by silicon-based micromachining with using silicon as the structural material, and exhibit a high cost solution with the DRIE process and the mainly required SOI-wafers. In contrast to silicon, the metals and polymers are becoming attractively alternative materials for fabricating the low cost micro devices and components to their silicon or glass-based counterparts. However, no polymer or metal-based VCDs have been reported yet. In this dissertation, novel fabrication methods are proposed to fabricate the VCDs in different materials―polymer and metal. Both of them are low temperature and low cost techniques, and provide a flexible and affordable solution with the basic equipment of LIGA-like process. First, the operation model of VCD is performed with theoretical analysis and FEM simulation for dimensional design. For the fabrication of polymer-based VCD, the double-side multiple partial exposure (DoMPE) method is developed to extend the multi-level morphology on both the front and back sides of the suspended photoresist microstructures. Depending on the established processing data, different 3D photoresist microstructures made of photoresist AZ9260® are successfully demonstrated, as well as the polymer-based VCD. By comparing the analytical and experimental results, the feasibility on fabricating polymer-based VCD is verified. For the fabrication of metal-based VCD, the properties of electroplated nickel are first characterized with different thicknesses and current densities, and obvious variations on material properties are observed, which would be helpful in designing micro devices by using electroplated nickel as structural material. To fabricate the metal-based VCD, electroplated nickel and copper are used as the structural and sacrificial layers. By electrodepositing nickel and copper in turn with thick photoresist as the molds, the VCD structures are constructed with the final release performed by wet etching. Also, the VCD with angled fingers could be further realized by controlling the angle of photoresist sidewall by this approach.