以原子層磊晶與電子束退火成長高品質氮化鋁磊晶薄膜及氮化鋁/氮化鎵超晶格

Abstract

三族氮化物半導體由於具有寬能隙、較強的鍵結、以及良好導熱特性等優越的物理性質，因此於高頻、高功率的應用具有良好的前景。本論文透過電漿輔助原子層沉積結合創新的原子層退火技術，開發高品質的氮化鋁磊晶薄膜以及氮化鋁/氮化鎵超晶格結構，並利用大面積電子束退火成長出高品質氮化鋁磊晶薄膜。本論文第一部分，我們透過原子層退火技術進行原位、逐層電漿退火處理，成功於攝氏300度的低溫，於碳化矽基板上成長出厚度僅20奈米的高品質氮化鋁磊晶薄膜。本論文第二部分的研究主題為電子束退火技術。我們利用大面積電子束照射位於藍寶石基板上的氮化鋁奈米薄膜，大幅提高氮化鋁薄膜的結晶品質。研究結果顯示大面積、快速的電子束退火，對於低熱預算的退火製程是相當關鍵的技術。接下來，本論文利用電漿增強原子層沉積技術成長氮化鋁/氮化鎵超晶格結構，並透過原子層退火處理來提升磊晶品質。我們能透過改變氮化鋁與氮化鎵的厚度以達到微調其能隙的目的。本研究將原子層退火技術的應用從薄膜擴展到超晶格結構，成功在低溫下成長出能隙可調控的高品質氮化鋁/氮化鎵超晶格磊晶層。最後，我們透過對三甲基鋁前驅物時進行電漿處理，使得使用原子層沉積技術所成長之氮化鋁薄膜的成長速度得到提升，並大幅提升氮化鋁薄膜的結晶品質。

Because of excellent physical properties such as wide bandgap, strong bonds, and good thermal conductivity, group-III nitride semiconductors have been wide recognized as very promising materials for high-frequency and high-power applications. By utilizing plasma enhanced atomic layer deposition (PEALD) along with the atomic layer annealing (ALA) technique, we are able to deposit AlN and AlN/GaN superlattice with excellent epitaxial quality in this thesis. In addition, high quality AlN epilayers are achieved via the large-area electron beam annealing (EBA) technique. In the first part of this thesis, the growth of high quality AlN epilayers on SiC wafer at a temperature as low as 300 °C were realized by incorporating the in-situ, layer-by-layer plasma treatment referred to as the ALA technique. In the second part of this thesis, electron irradiation in a large EBA system was used to greatly improve the crystalline quality of the AlN thin films on sapphire substrates. The research results demonstrate that the large-area, rapid EBA system is a critical technique for the annealing process with a low thermal budget. Next, we utilized the PEALD and ALA techniques to deposit AlN/GaN superlattice structure with a high crystallinity. The bandgap energy can be tailored by changing the thickness of each layer. The result indicates that the applications of the ALA technique have been extended from nanoscale thin films to superlattice structures, and high-quality superlattice epilayers with adjustable bandgap energy have also been achieved. Finally, the growth per cycle (GPC) and the crystallinity of AlN thin films prepared by PEALD were significantly enhanced by the plasma treatment on the trimethylaluminum precursor. This research demonstrates that the growth rate and the crystal quality of nanoscale thin films can be tailored by the plasma treatment on the precursors used in the ALD process.