次波長貝索光束直寫儀的研究與開發：從奈米光學元件的理論與製造到系統性能驗證的研究

2008-08-012024-05-17https://scholars.lib.ntu.edu.tw/handle/123456789/679728摘要：在過去十年來，半導體工業遵循著摩爾定律（Moore ’s law）每十八個月進步一倍的快速進程，非常迅速的增加每單位晶圓上電晶體的數目。而目前一般的光學微影方法所能達到的解析度，基本上還是受到光學繞射極限的限制，因此導致可以製作的最小圖形尺寸（critical dimension）仍舊維持在微米範圍左右。若要將圖形的最小尺寸進一步縮小到奈米範圍，除了 嘗試改進光學微影技術外，多數創新技術採用電子直寫儀(electron beam writer)和聚焦離子束 (focused ion beam)來追求更小的critical dimension。雖然這兩種儀器可以製作出奈米等級的圖形，但其製作的速度太慢，並且需要在真空環境下才能製作，因此具有應用成本太高的缺點。過去十年的創新技術中，還有許多團隊在努力的延伸光學微影術到可製作尺寸為奈米等級的圖形，其中最有名的當屬浸潤式微影術(immersion lithography)。雖然浸潤式微影術已經可以大量生產微小圖形，但光源和光阻之間還是需要有一層液體，在曝光的時候，仍舊需要極穩定的環境，否則在圖形附近將會有氣泡產生，進而導致整個圖形毀損。除此之外，浸潤式微影術的光源是利用遠紫外波長的雷射，其成本的花費並不是一般企業可以負擔的。相形之下，一般的雷射直寫儀所使用的光源約在可見光與紫外光之間，所以可以製作的critical dimension還是受到限制。縮短曝光波長雖然可以縮小聚焦光點尺寸，但隨著波長變短，原先可見光範圍的光學元件材料在短波長範圍並不透光，因此僅剩下少數的材料可用於紫外光範圍中。再加上由於波長變短，聚焦光點在接近次微米大小時，焦深將迅速縮小到接近一般試片的表面粗糙度，此些限制使得目前的雷射直寫儀必須加入快速自動對焦系統來進行光路修正，以避免在進行光學刻寫時出現離焦的現象，而使得曝光光點大小不如預期。綜合以上論 點，可知隨著波長的縮短，刻寫時的光機問題將愈顯複雜，因此生產成本也就愈來愈高。在非傳統光學現象中，當光與金屬次波長結構互動時，所產生的異常穿透現象與指向性效果是目前廣泛被討論與研究的課題。一般相信，其產生的原因與表面電漿有密不可分的關係，當入射光入射在結構上，在金屬表面就會產生表面電漿(surface plasmon)，進而使得穿透 率提高。另外，貝索光束(Bessel beam)也是另一個與傳統光學現象迥異的研究，此光束的焦深比一般透鏡聚焦光束大數十至數百倍。因此，本研究將利用由西元1998 年研究至今的異常穿透現象與貝索光束特性，充分運用次波長金屬結構與光之間的互動來提高光源穿透率，同時設計一種金屬奈米結構，使其穿透光也具有貝索光束之特性，換言之，本計畫將運用奈米結構來建構出同時具有長焦深以及次波長光束的可見光源。同時，本研究還將同時利用非均質偏極態光源入射至金屬奈米結構，並探討其特性。為了建立一套可靠的設計流程，本計畫將利用有限時域差分法以及有限元素法，來對光束特性做定性的預測。試片製作將同時利用聚焦離子束系統以及利用電子束微影定義圖形的 liftoff 製程。研究過程中，將利用本研究團隊所開發完成的整合heterodyne 干涉技術的近場光學顯微鏡(SNOM)來對光強與相位進行精確的定量分析，並將該光學頭整合到本研究團隊舊有的雷射直寫儀上，同時還將於本計畫中進一步的添加上顯微系統，以求能建構出全新的光學蝕刻系統，進而可以在一般環境中刻寫微小的自由圖形，並且藉由其岀射光的長焦深特性， 降低外界擾動對曝光流程的影響。最後本計畫還將嘗試微小化與模組化整個系統，除了光機的微小化外，還將運用金屬奈 米結構來改進光源的傳播特性，再配合上微小化的光機，將具有使得本計畫所完成技術落實於一般商用型的顯微鏡上使用的可能，同時還將嘗試充分運用本計畫所完成的次微米貝索光源來製作超高深寬比的奈米結構。<br> Abstract: Today, 3C (Communication, Computer, Consumer) industry is driven by the progress of semiconductor technology. One of the famous laws in semiconductor technology is Moore’s Law, which states that the number of transistors on a chip doubles about every 18 months. In other words, the critical dimension will become 0.7-fold every 18 months. By the push of Moore’s law, the critical dimension of line width has been shrunk from 5 micrometers in the late 1960 to 90 nanometers nowadays. But optical lithography faces the diffraction limit which constrains its best resolution. The common solution in the past is to reduce the wavelength of the light source. However, there are still plenty of disadvantages listed below that cannot be bypassed. To start, high cost associated with equipments developed based on short wavelength light source is detrimental at times. In addition, the light source, the photo-resist, and even the high vacuum environment are all of high cost. The second factor is time consuming as two of the most widely available techniques involve ion beam lithography or electron beam lithography within the process. With these two sources utilized, the throughput will certainly be low. Many research teams continue to pursue breakthrough idea with a hope to bypass the diffraction limit within the lithographic field. One of the latest and most successful fabrication process technology developed so far is called immersion lithography, which can have both tiny feature size and large throughput. But there is a problem exists in this newly developed process. When the liquid contacts the resist, it could suffer from the bubbles present and cause failure in the exposure process. It costs more to remove all these bubbles during production. Two of the nontraditional optical properties that may provide insight to bypass the above mentioned dilemma are extraordinary transmission and directional beaming effects. These two phenomena, which demonstrate the interaction between light beams and sub-wavelength metallic/dielectric structures had been widely discussed since 1998. It is believed that these two nontraditional effects were caused by surface plasmon resonances. After further study, it is believed that the sub-wavelength sized optical beam with focal depth beyond the diffraction limit generated from the two above-mentioned effects can be attributed to Bessel beams. In other words, it is a nondiffracting beam. The objective of this proposal is to apply the extraordinary transmission and nondiffracting beam to develop a novel lithographic tool. Utilizing these nontraditional phenomena, an optical head possesses both ultralong depth of focus and few hundreds of nanometer spot size will be designed and fabricated. At the same time, the interactions between inhomogeneous incident light beam and subwavelength metalic as well as dielectric surface structures will be discussed. Finite-difference time domain method (FDTD) and finite element method will be applied within the design processes. In order to fabricate the optical head, ion beam lithography and electron beam lithography with metal liftoff process will be integrated and implemented. The optical properties of optical head will be measured by using our newly developed scanning near-field optical microscope with heterodyne interferometry to simultaneously measure the intensity and the phase distributions precisely. In addition, the optical head will be integrated with microscopic nanowriter system to produce ultrahigh aspect ratio patterns. Finally, an integrated optical head and a module for miniaturized laser writing system will be designed and fabricated. In summary, this proposal plans to initiate a three-year project to develop the fundamental theory, to design, and to uncover all of the fabrication know-hows, etc. in order to develop a direct writing system prototype that can produce ultrahigh aspect ratio pattern easily and conveniently within an atmospheric environment.表面電漿非均質偏極態光源貝&#63850光束超長焦深貝&#63850光束直寫儀Surface plasmoninhomogeneous polarization lightBessel beamultralong depth of focusBessel Beam Laser Writer次波長貝索光束直寫儀的研究與開發：從奈米光學元件的理論與製造到系統性能驗證的研究