整合次波長圓環型孔洞與準分子雷射開發高深寬比光學鑽孔儀的先導性研究：以三維積體電路矽導通孔為應用平台

Abstract

本研究論文開發出一套整合次波長圓環型孔洞與KrF準分子雷射的光學鑽孔儀。由次波長圓環型孔洞可聚焦成突破繞射極限的微小光點與長焦深特性為出發點，以設計鈦、鋁之氧化物包覆其金屬之新型結構以及以矽薄膜為材料之次波長圓環型孔洞結構作為探討的方向，針對矽晶圓作為鑽孔對象進行雷射鑽孔。本論文中除了探討鈦與鋁金屬薄膜在烤箱氧化之情形以及實際以準分子雷射對不同材料進行雷射損壞閥值測試外，亦利用FDTD模擬找出上述材料在KrF準分子雷射248 nm波長下形成長焦深之點狀聚焦條件的最適膜厚，同時亦探討此結構半徑大小、波長、玻璃基板、表面電漿與膜厚對聚焦的影響，以此證明只需要改變圓環狹縫的膜厚，必能至少找出一組在遠場呈現點狀聚焦的似貝索光束，亦以能量計算及實際鑽孔測試說明即使不產生表面電漿使得穿透能量無額外增強，但由於此結構的聚焦光點極小提高能量密度仍能達到鑽孔目的。整合次波長圓環型孔洞與準分子雷射之鑽孔儀所鑽的孔洞，在重覆率10Hz、1000發脈衝下，可將矽晶圓鑽出孔徑小於1μm的孔洞，深度約140 nm，不到目前使用遠場雷射鑽孔最小孔徑的1/3，相當於進場雷射鑽孔的孔徑大小，但鑽孔深度確可達近場雷射的14倍以上。此研究對三維積體電路之矽導通孔提供一個更好的製程方式，可望鑽出高深寬比的孔洞，使之微小化並有更好的效能。

The main thrust of this thesis is to develop a high aspect ratio optical drill by integrating sub-wavelength annular aperture (SAA) and KrF excimer laser. The proposed new structure of SAA is made from metal, covered with metallic oxide by high temperature oxidation. This thesis discusses the effect of Ti/TiO2 and Al/Al2O3 composite layer and finds the optimal film thickness to be 110 nm and 200 nm when a 16μm diameter of SAA at wavelength of 248 nm is studied. Silicon thin film as the material of SAA is also discussed and the optimal film thickness is identified to be 100 nm. The SAA structure can render a quasi-Bessel beam and small focal spot with long depth of focus such that the designed structure can drill a high aspect ratio hole on silicon wafer by adjusting the energy of excimer laser. The drilled diameter of SAA is less than 1μm, which is about 30% of the smallest drilled diameter of present far-field laser driller. Moreover, the diameter is in close proximity to SNOM near-field driller, but the depth of the hole from SAA is more than 13 times to that from SNOM driller. This Silicon wafer optical drill can be applied to 3D IC through-silicon via (TSV) , and hopefully can reduce the size, power consumption, and time delay of an IC chip. Through this technique, performance of 3D IC may be improved.