- 學位論文
氮化鎵高電子遷移率電晶體之磊晶結構材料特性分析
Characterizations of GaN Based HEMT Epitaxial Structure
摘要
隨著5G產業的迅猛發展和電動車技術的興起，市場對於耐高壓和高頻材料的需求日益增長。在這樣的時空背景下，三五族半導體因其優越的特性，成為各研究團隊積極研究的焦點。其中，高電子遷移率電晶體（High Electron Mobility Transistor, HEMT）因其高效能、高功率、高頻率的優點，使得氮化鎵HEMT成為許多先進電力設備的理想選擇。 在氮化鎵（Gallium nitride, GaN）元件的基板選擇上，目前主流的選擇包括碳化矽（SiC）、藍寶石（Sapphire）和矽（Si）三種材料。儘管矽基板的晶格常數與熱膨脹係數與氮化鎵之間存在較大的差異，這種不匹配會導致一定程度的應力和缺陷，但因矽基板在成本和製程技術上的優勢，它仍然是氮化鎵基板的首選。 為了緩解因晶格常數差異而產生的應力，同時兼顧二維電子氣（2DEG）的品質，HEMT元件通常會在其緩衝層中安排多層且複雜的磊晶結構。在此多層磊晶結構若引入不預期的缺陷，將對元件的性能發揮有所影響。因此，探索磊晶片內部存在的缺陷，並提出有效的解決方案，將可抑制晶格不匹配的影響，同時可提高二維電子氣的品質。 在本研究中，我們利用光致發光（PL）、拉曼光譜（Raman）、X射線繞射（XRD）和原子力顯微鏡（AFM）等儀器，對國內知名半導體公司提供的GaN HEMT磊晶片進行了「倒敘法」全面分析。有系統地結合這些光性和物性的檢測能使我們追蹤製程的品質，並以簡易的電性測試來驗證分析結果。上述的分析方法不僅有助於提高元件的性能，還能提升元件製程效率，因此對於HEMT半導體製程的優化具有重要意義。 透過本研究系統性的分析，我們能夠辨識出磊晶結構中存在的具體缺陷，並將這些發現回報廠商且提供建議改善製程。這些建議不僅有助於改善元件的性能，還能提高製程的穩定性和可靠性，從而提升國內在GaN HEMT技術開發方面的競爭力。 關鍵字：高電子遷移率電晶體、氮化鎵、二維電子氣、缺陷。
並列摘要
With the rapid development of the 5G industry and the rise of electric vehicle technology, there is a growing demand for high voltage and high frequency resistant materials. Against this backdrop, III-V semiconductors have become the focus of active research by various research teams due to their superior characteristics. Among them, High Electron Mobility Transistor （HEMT） has become the ideal choice for many advanced power devices due to its high performance, high power, and high frequency. In terms of substrate selection for Gallium nitride （GaN） devices, the three main choices are silicon carbide （SiC）, sapphire and silicon （Si）. Although the lattice constants and coefficients of thermal expansion of Si substrates differ significantly from those of GaN, and this mismatch can lead to a certain degree of stress and defects, Si substrates are still the preferred choice for GaN substrates due to their cost and process technology advantages. In order to mitigate the stress caused by the difference in lattice constants and to maintain the quality of the 2DEG, HEMT devices usually have multiple layers of complex epitaxial structures in the buffer layer. The introduction of undesired defects in this multilayer epitaxial structure will affect the performance of the device. Therefore, exploring the defects inside the epitaxial wafers and proposing effective solutions will suppress the effect of lattice mismatch and improve the quality of 2D EGs at the same time. In this study, GaN HEMT epitaxial wafers supplied by a well-known semiconductor company in Taiwan were comprehensively analyzed using photoluminescence（PL）, Raman spectroscopy（Raman）, X-ray diffraction （XRD）, and atomic force microscopy （AFM） instruments by the "inverse method". The systematic combination of these optical and physical tests enables us to trace the quality of the process and verify the analysis results with simple electrical tests. The above analysis method is not only helpful for improving the performance of the device, but also enhances the efficiency of the device process, and is therefore important for the optimization of the HEMT semiconductor process. Through the systematic analysis in this study, we were able to identify specific defects in the epitaxial structure and report these findings back to the vendors with recommendations to improve the process. These recommendations will not only help to improve the performance of the devices, but also increase the stability and reliability of the process, thus enhancing the competitiveness of GaN HEMT technology development in Taiwan. Keywords: HEMT, GaN, 2DEG, defects.