- 學位論文
利用三維積體電路技術實現兆赫波光學零件開發及應用
Development and Applications of Terahertz Optical Components Using 3D-IC Technologies
摘要
本論文旨在設計新形兆赫波光學零件(THz optical component)，並使用三維積體電路(3D-IC)製程技術實現；兆赫波的波長範圍約落在10μm到1000μm左右，這意味著兆赫波光學零件結構落在微米等級，故半導體製程技術及三維積體整合(3D-Integration)技術非常適合用來開發微米等級之光學結構，本論文將透過對三維積體電路之關鍵技術之研究，如低溫晶圓接合(low temperature wafer bonding)、微凸塊(micro-bump)、矽深蝕刻(Si Deep-RIE)，來實現兆赫波光學零件之開發，如高穿透偏振器、濾波器、共振腔…等，並推廣其應用，來達到低成本之光學零件。 傳統的兆赫波零件，如金屬柵欄偏振器(wire-grid polarizer)，為提高其穿透功率，採用無基板或薄膜基板的設計，大大減少其機械強度；厚基板的設計可提高機械強度，但因抗反射處理的難度，造成穿透功率下降，本論文一開始將透過晶圓接合技術，及鎳超薄緩衝層(ultra-thin buffer layer, UBL)，成功開發次微米厚度銅對銦錫非對稱低溫接合，將銅金屬柵欄偏振器封裝在矽基板中，此整合方式提供了基板所有表面得已經抗反射處理，而提高穿透率；此外，銅對銦錫接合提供了電性連接方式，能夠應用到光學零件與元件之整合，在本實驗中，銅-銦錫有良好的接合良率和特徵接觸電阻(specific contact resistance, 約10-6 ohm-cm)，並且通過溫度循環(temperature cycling test)及高速壽命(highly accelerated stress test)可靠度測試。 再者，根據等效介質理論(effective medium theory)，利用矽深蝕刻控制蝕刻深度以及蝕刻圖形，能在矽基板兩外表面製作人造介質層，形成單層抗反射層，藉此達到特定頻率的高穿透率，實現抗反射的兆赫波偏振器，此研究透過嚴格耦合波分析(Rigorous Coupled Wave Analysis, RCWA)來驗證設計之結構，並使用兆赫波時域光譜(THz time-domain spectroscopy, TDS)來量測實驗結果，實驗結果顯示兆赫波偏振器在特定的頻率可達到100%的穿透率，並擁有約30dB之消光比(extinction ratio)；而結合不同中心頻率之抗反射層，可達到較均勻的穿透頻譜，進而減少訊號的失真，並維持一定的高穿透率；除此之外，亦能透過此方式，將多層金屬柵欄與抗反射層整合，得到高穿透率和極高之消光比。而本研究開發之整合堆疊方式，也能夠將抗反射層推廣至兆赫波濾波器之應用。 本論文展示了一個低成本、堅固、高效能之兆赫波偏振器製程方式，透過次微米厚度之銅-銦錫封裝方式，成功將銅金屬柵欄封裝在矽基板中，並且在基板之外表面蝕刻出抗反射層結構，達到在特定頻率完全穿透之高消光比偏振器，透過結合不同中心頻率之抗反射層，在稍微犧牲穿透率的情況下，可得到更均勻的穿透頻譜減少訊號的失真；最後結合實驗結果以及電性連接，本論文提出一線性偏振法布里-珀羅共振腔(Fabry-Pérot resonator)結構，能在未來應用在面射型線性偏振兆赫波雷射(Vertical-Cavity Surface-Emitting Linearly polarized THz Laser)上。
並列摘要
The purpose of this study is to demonstrate the new THz optical components using 3D-IC technologies. Because of THz wavelength between 10μm and 1000μm, the order of optical structure of THz components is in micro-meter. Therefore, semiconductor manufacture and 3D-integration technologies are very suitable for developing micron-level optical structure. In this thesis, THz optical components are developed by key technologies of 3D-integration, such as low temperature wafer bonding, micro-bumping, Si deep reactive etching (DRIE), to achieve low-cost THz components. The fabrication method can realize high-transmittance THz polarizers, and is further proposed to apply to THz filter and resonator. Some of commercial THz optical components, such as free-standing or thin-film wire-grid polarizers, are fabricated without substrate or with thin-film to achieve high transmittance. However, the free-standing or thin-film structure are fragile. Wire-grid polarizer fabricated on thick-substrate is with high mechanical strength, but low transmittance. Also, wire-grid fabricated on substrate is hard to apply anti-reflection coating on both outward surfaces because of occupied surface by wire-grid. In this study, Cu-In/Sn asymmetric low temperature bonding with submicron thickness using Ni ultra-thin buffer layer (UBL) is demonstrated to seal Cu wire-grid into Si substrate. Therefore, this integration method provides both of outward surfaces of polarizer to fabricate anti-reflection layers. Besides, Cu-In/Sn interconnects can be further applied to integrate THz components and devices. In bonding results, Cu-In/Sn bonding structure with Ni UBL has excellent bonding yield and good specific contact resistance about 10-6 ohm-cm, and passes temperature cycling test (TCT) and highly accelerated stress test (HAST). Next, the single-layer artificial layer were fabricated on outward surfaces of substrate for anti-reflection by Si DRIE. The THz polarizer with high transmittance at selected frequency can be accomplished by designed etching depth and pattern according to effective medium theory. The THz polarizers with designed parameter are verified by rigorous coupled wave analysis (RCWA) and measured by THz time-domain spectroscopy (TDS). The results show 100% transmittance at selected frequency and about 30dB extinction ratio of THz polarizer. Broad-band THz polarizer can be achieved by stacking two anti-reflection layers with different central frequency. Although the transmittance slightly degrade, the transmittance spectrum is much uniform, which means less distortion of propagated signal. Furthermore, ultra-high extinction ratio polarizer with high transmittance could be realized by stacking multi-layer of wire-grid and two anti-reflection layers. The same integration concept could be also applied to multiple anti-reflection layers to attain THz filter. In conclusion, this thesis demonstrates a new fabrication method of THz polarizer with advantages such as robust structure, low cost and high performance. The wire-grid polarizer is successfully sealed into Si substrate through sub-micron Cu-In/Sn bonding. 100% transmittance at selected frequency of polarizer can be achieved by anti-reflection process through Si DRIE. By combining two different AR layers, the transmittance spectrum of polarizer is slightly degraded but much uniform. The transmission signal with efficient power could pass through without distortion. Finally, a new structure of linearly polarized Fabry-Pérot resonator is proposed for the future vertical-cavity surface-emitting linearly polarized THz laser according to results of this thesis.