矽奈米粒子於深紫外區間所展現的非線性極化子散射和超解析顯微術的應用

Abstract

矽是被廣泛研究的材料，並由於其容易取得的特性以及和互補金屬氧化物半導體 (CMOS) 的相容性而被廣泛應用於半導體產業。半導體產業正致力於縮小芯片尺寸以形成具有更多功能的積體電路。隨著製造技術的提升以及生產的加速，我們需要新的顯微技術來更快地檢查半導體結構。一般業界所使用的掃描式電子顯微鏡（SEM）具有低吞吐量、僅能掃描樣品表面，所使用的高能電子束能量也容易傷害樣品表面，和傳統光學顯微鏡（OM）所具有的高吞吐量、三維樣品的觀測範圍，並和使用低能量的光照檢測相比，OM不但能避免對樣品造成更多損害同時也提供相較SEM大的觀測吞吐量。因此，隨著半導體尺寸日漸縮小至光學的繞射極限無法分辨時，電子顯微鏡反倒得以達成遠小於繞射極限的奈米解析度，因此我們需要超解析光學顯微技術，用以觀測奈米尺度的半導體晶片。 在2020年，我們通過結合飽和激發顯微鏡（SAX）和矽奈米結構的光學非線性，達成了132奈米的空間解析度。米氏共振有效加熱了矽奈米方塊，使之展現了比矽塊材大了五個數量級的等效光熱非線性指數n2，並在可見光區域達成了兩倍的解析度提升。在這篇研究裡面我們預期使用更短的波長來進一步突破繞射極限，以提高SAX的光學解析度。最近的研究揭示，在深紫外（DUV）波段光照射下，矽展現了表面極化子共振。在這項研究中，我們模擬了266奈米的紫外光激發下，矽奈米粒子基於表面極化子共振，所展現的光熱非線性效應。我們也最佳化矽奈米圓盤結構的半徑，達成6%的散射強度差異。我們預期這種非線性散射可以應用於SAX顯微鏡並提升至70奈米的解析度。 此外，我們製作了隨機排列的矽奈米圓盤樣品，並架設了一個配備了光偵測器的光學截斷器系統，以初步檢測非線性現象是否存在。經深紫外光譜儀檢測的矽樣品顯示在約270奈米處有共振峰。在實驗中，我們優化了系統的穩定性，以確保良好的可逆性。然而，重複性仍然存在爭議，因此未能於實驗上應證非線性的存在。而均一化的實驗數據顯示其趨勢更接近線性。因此，下一步仍需改善實驗系統，以驗證模擬的結果。

Silicon material has been widely studied due to its natural abundance and compatibility with complementary metal-oxide semiconductors (CMOS). The semiconductor industry strives to miniaturize chips and develop circuits with enhanced functionality. With the advancement of fabricating techniques and accelerating production, scanning electron microscopy (SEM)'s low throughput, surface-only scanning, and potential sample damage make it insufficient for high-demand semiconductor inspection, necessitating a faster alternative. In contrast, optical microscopes (OM) provide high throughput, a three-dimensional (3D) inspection range, and low-energy illumination, which avoids sample damage. However, OM is limited by the diffraction limit, thus, the resolution is typically 200 nm or worse. Therefore, the development of super-resolution optical microscopy that breaks through resolution limits is highly desired. In 2020, by combining saturated excitation (SAX) microscopy and optical nonlinearity of a silicon nanostructure, our group achieved 132 nm lateral resolution. Silicon nanoblock with Mie resonance enhanced heating offers an equivalent photothermal nonlinear index n2 that is five orders larger than bulk silicon, and the nonlinearity provides more than two-fold resolution enhancement. To further enhance optical resolution by SAX, a shorter wavelength is explored in this work. Although silicon has a large imaginary refractive index below 300 nm that reduces the quality factor of resonance, recent studies have shown that silicon exhibits polaritonic resonance under deep ultraviolet (DUV) excitation. Here, we simulated the enhancement of photo-thermo-optical nonlinearity of a single silicon nanostructure excited at 266 nm wavelength based on polaritonic resonance. An optimized radius of a silicon nanodisk shows a backward scattering intensity difference as large as 17%. We expect this nonlinear scattering can be used in SAX microscopy and yield a 70 nm spatial resolution in the future. Additionally, we fabricated silicon nanodisks with diameters ranging from 65 nm to 75 nm and built a 266 nm laser light path equipped with a chopper to control exposure time and a photodetector to detect whether nonlinearity exists. The silicon sample inspected by a DUV spectroscope demonstrated a resonant peak at around 270 nm. Even though the system's stability was optimized to ensure good reversibility, reproducibility remains controversial. As a result, the experimental data failed to confirm whether nonlinearity was present. The normalized experimental data indicate a trend that is closer to linearity. The experiment needs further refinement to examine the simulation results.