乾膜光阻應用於微結構滾輪製作之探討

Abstract

滾輪微壓印兼具製程快速、大量連續生產的優點，重要性與日俱增。滾輪製作是關鍵技術，各式製作微結構滾輪之方法，大都製程繁瑣，需要高檔昂貴之設備。一般壓印滾輪是以微結構薄金屬版包覆在滾輪上，緊密附著不易，因此在滾壓時常有模具位移、翹曲等問題；若以軟性模具進行壓印，則有強度不足、不耐高溫等問題。 本研究以創新方法直接在滾輪上製作微結構：利用乾膜光阻直接貼附於滾輪表面，並以簡易可撓式塑膠光罩包覆於上，進行曲面曝光微影製程，在滾輪上製作出微米級光阻微結構，再利用濕式蝕刻、或無電鍍技術，在滾輪上直接產生剛性微結構。用CAD設計印刷光罩極為簡便，製作之微結構圖形彈性大，大幅降低製作微結構滾輪之門檻；直接在滾輪上製作微結構，避免包覆式模具與滾輪本體滑移之問題，大幅提升微結構滾輪之耐用性。 研究中使用乾膜光阻開發出三種不同製作微結構滾輪之製程：一、直接將乾膜光阻貼附到滾輪進行曲面曝光微影，用蝕刻產生微結構；二、直接將乾膜光阻貼附到滾輪進行曲面曝光微影，用無電鍍產生微結構；三、將乾膜光阻曝光後，再貼附到滾輪進行顯影，用蝕刻產生微結構。首先探討製程中「貼合」、「曲面曝光」兩步驟之適當參數，接著探討各個製程中，光罩圖案的重現性與各自之優缺點。 乾膜光阻有其曝光極限線寬，本研究進一步提出以兩次貼合、分別進行對位微影製程來產生比極限更小之線寬結構。 微結構滾輪製作完成後，實際用在滾輪擠出微壓印製程，成功在PC塑膠薄膜上製作出均勻成型、焦距為682μm之微透鏡陣列。證實此製程製作出之微結構滾輪，確實可以應用在微結構之連續性大量複製生產上。

The importance of roller embossing for mass production is increasing because of its rapid, continuous production. The fabrication of microstructure rollers is the key technology. Most of the microstructure rollers fabrication methods are very complicated and costly, demanding high-end facilities. Furthermore, mold sliding and warping problems are frequently encountered because of the weak adhesion between molds and rollers. Soft rollers with microstructures have problems such as poor durability and temperature endurance. This study proposes a novel fabrication method of rollers with microstructure. This method takes advantage of the excellent adhesion of dry film photoresist on metal. By laminating it uniformly onto the curvy surface of metal rollers, micro-scale photoresist patterns can be directly fabricated on the surface of rollers. Non-planer lithography with flexible film photomask is first performed; wet etching or electroless plating process is followed. A roller with rigid metal microstructures can be obtained. The flexible film photomask can be easily designed using CAD software; it enhances the design flexibility and reduces the cost and time. In this study, three kinds of roller fabrication processes using dry film photoresist are developed: The first two methods start with laminating dry film photoresist onto the surface of the roller, followed by non-planer lithography. Then the microstructures are fabricated by wet etching and electroless plating, respectively. Another method is to expose the dry film photoresist first, then laminate it onto the roller surface. The microstructure is fabricated by wet etching. The proper process parameters during dry film photoresist laminating process and non-planer lithography process are first investigated. Then the reproducibility between film photomask and the fabricated microstructure by the feature size difference in each process is studied. After the roller fabrication, the metal rollers with microstructures are used in a hybrid extrusion embossing system. Microlens arrays on PC film have been successfully fabricated. The measured focal length is 682μm. This result proves that the rollers fabricated in this method can be used in roller embossing for microstructure mass production. Dry film photoresist has its exposure limitation. To broaden the application range of dry film photoresist, the study also proposes a novel method. Microstructures with feature size smaller than the original limitation can be fabricated. This method is carried out by performing the dry film photoresist laminating twice and aligning exposure after each laminating step.