飛秒雷射微加工之應用

Abstract

由於超短雷射脈衝提供了極高的峰值功率(peak power)，使飛秒雷射加工在加工的過程中只有極小的熱效應，產生極小的熱效應區，所以被稱為冷加工。隨著科技的進步，當製造元件的尺寸越來越接近物理和長脈衝雷射製造的臨界尺度，飛秒雷射加工在工業應用上開始展露決定性的優勢。本論文針對3D IC製造，癌症治療，眼睛保護以及提高太陽能電池效率等令人關注的議題，研究飛秒雷射在材料微加工和奈米/微米結構製備中的應用。本論文針對三個不同的飛秒雷射微加工應用進行研究，分別為微加工、退火和沈積。 在本論文的第一部分，研究了飛秒雷射加工在3D IC製造中的應用，包括在中介層中形成高縱深比的微米級通孔，在銀膠上製造微米級導電通道，以及在非晶材料中研究對應力以及裂痕的控制。首先，我們在AlN基板上製備微米級通孔。藉由變更雷射功率、偏振以及在基板中的聚焦深度，製備不同圓度、直徑、錐度以及縱深比的微米級通孔。接著，針對鍍銀膠的PET 進行飛秒雷射加工，證實雷射功率的增加會導致加工區周圍的銀膠造成更大的影響。此外，為了精確控制應力，我們進一步發展一雙向雷射加工系統(專利編號：201611932），以此提高雷射加工的精度、減少了切割線的寬度，並且不需要進行後續處理，例如：拋光切割邊緣。另外，雙向雷射加工也同時適用於透明和不透明的材料。 在本論文的第二部分，則利用飛秒雷射退火，使氧化銦錫(ITO)薄膜變色，並研究其在可見範圍中的光學性質。通過改變雷射能量，在ITO膜表面產生具有棉花狀、波紋狀以及島狀的奈米結構，並改變薄膜顏色：青色、黃色和橙色。而這些雷射退火所產生的表面結構，在藍光區以外的可見光範圍，也保持〜90％的透明度，同時，由於其類金屬顆粒的特性，更進一步改善了導電性。除此之外，特定形貌的表面結構，可以在特定的視角範圍內產生繞射光，進而阻擋薄膜後面的圖像。於較斜的視角產生繞射光以及抗藍光的特性，使得這種具有特殊奈米結構的ITO薄膜，具有極大的潛力可以應用在面板或手機產業，讓使用者在觀看手機或面板的同時，可以降低藍光對眼睛的傷害，以及屏蔽旁人的目光以增加個人隱私。 最後，本論文也提出一種新穎的動能選擇奈米顆粒製備技術可以在室溫及室壓下，利用飛秒雷射照射Bi2Se3晶體的表面，以此產生具非晶相和晶相結構的硒奈米顆粒。硒奈米顆粒隨著噴濺距離的增加(原點為雷射照射的中心)，其形成的顆粒從直徑900 nm 降至 100 nm。我們進一步透過顯微拉曼光譜、原子級穿透式電子顯微鏡以及背向散射電子繞射儀來確定硒奈米顆粒的結晶性。另外，更利用研究雷射功率與噴濺距離的關聯性，來了解此新穎動能選擇奈米顆粒製備技術的物理機制。

Femtosecond laser processing has attracted intense interest because it delivers extremely high peak power in a very short duration, ablating most materials without heating and induced negligible heat affect zone. This is also called cold machining. This decisive advantage allows femtosecond laser processing to be potentially applied in industrial settings, as it operates below the critical scales of physical and long pulse laser manufacturing. In this thesis, the use of femtosecond lasers in material micromachining and nano-/ micro-structural fabrication is investigated for popular applications such as 3D IC manufacturing, cancer treatment, eye protection, and the efficiency enhancement of solar cells. It is separated into three Chapters, each focusing on different femtosecond laser processing applications: micromachining, annealing, and deposition. In the Chapter 5, machining using femtosecond lasers is investigated in 3D IC manufacturing, e.g., the formation of high-aspect-ratio microvias in an interposer substrate, the fabrication of narrow, conductive microchannels on Ag glue, and stress/crack control in amorphous materials. To carry out this goal, we initially produce microvias on AlN substrates. Femtosecond laser operating parameters including laser power, polarization, and focusing depth were modified to produce microvias with various circularity, diameter, taper, and aspect ratio. The results of femtosecond laser machining on PET coated with Ag glue are then reported, showing that the heat affect zone induced by the femtosecond laser active point enlarged as laser power increased. Additionally, to precisely control the stress, we developed a femtosecond laser machining system with counter-propagating femtosecond lasers (patent number: 201611932). This method significantly enhances the precision of femtosecond laser machining and reduces the cutting line width, with no need for post processing or polishing the cutting edges. Moreover, this method can be applied to both transparent and opaque substrates. In the Chapter 4, we investigate the optical properties of femtosecond laser-colorized indium-tin-oxide (ITO) thin films in the visible spectrum. By varying the laser fluences, nanostructures with cotton, brick and ripple forms are generated on the surface of ITO films, which produces cyan, yellow and orange colors. The femtosecond laser-induced structures on the films also remained ~90% transparent, except for a region of blue light, and the metal-like clusters on ITO films further led to greater local conductivity. Furthermore, the color of the regular nano-brick structure of the ITO films depended on the viewing angle, allowing that it can block an image behind a femtosecond laser-colorized ITO film. The fluence-dependent nanostructures on the surface of the films also significantly attenuated blue light, making these materials suited to eye protection or image screening to enhance information security. Finally, in the Chapter 5, we show that this novel approach prepares both the amorphous and crystalline Se nanoparticles by femtosecond laser pulse irradiation on the surface of topological insulator Bi2Se3 single crystals at room temperature and ambient pressure. The shape (spherical, rectangular) and size (100-900 nm) of Se nanoparticles can be reliably controlled through the kinetic energy obtained from laser pulse energy, thus providing the potential use as active components in nanoscale applications. Importantly, the growth strategy itself may also be extendable to other system.