探討低溫氮化鋁鎵插入層對成長厚氮化鎵在矽基板上之影響

Abstract

由於氮化鎵(GaN)材料具有高崩潰電場、寬能隙、高電子遷移率與極佳的熱傳導性，使得氮化鎵材料成為摩爾定律極限下，能取代矽元件成為次世代高功率電子元件。其中，又以氮化鎵可成長在大尺寸矽基板上最具為優勢。然而，要運用於高功率電子元件，必須具備高崩潰電壓，而在磊晶成長上，則必須具備厚的氮化鎵磊晶層。 本次實驗中首先是藉由即時量測系統建立一套磊晶薄膜品質之判斷標準，藉由此標準可直接在磊晶實驗過程中判斷磊晶薄膜品質之優劣。並且，藉由此判斷標準輔助下，順利成長實驗中所需之氮化鎵薄膜。當獲得高品質氮化鎵薄膜後，於其磊晶層上成長氮化鋁鎵薄膜，形成二維電子氣層(2DEG)，以進行高電子遷移率電晶體(HEMT)的電性量測。 然而，本次實驗之主題為探討低溫氮化鋁鎵引入層之研究最佳化成長條件，其為950 °C下成長90秒。在此條件下，成功地成長出高品質無裂痕之2.87 μm磊晶薄膜。其中XRD (002)面 rocking curve半高寬為450 arcsec，XRD (102)面 rocking curve半高寬為661 arcsec。經霍爾量測得到電子遷移率為1300 cm2/V-s，載子濃度為0.81x1013 cm-2 。為了進一步成長厚之氮化鎵薄膜，必須先探討氮化鎵之第二層磊晶層極限厚度，藉此實驗發現，必須於氮化鎵之第二層磊晶層成長1500秒後，導入第二層低溫氮化鋁鎵引入層。最後可順利成長出總厚度為4.4 μm無裂痕之磊晶薄膜。在此厚度下，雖然磊晶薄膜產生塑性變形，但其磊晶品質仍然相當優異，其中XRD (002)面 rocking curve半高寬為493 arcsec，XRD (102)面 rocking curve半高寬為836 arcsec。 藉由即時量測系統所建立磊晶薄膜判斷標準，可以在實驗過程中，即時瞭解磊晶品質好壞，以省下後續材料分析所需之時間。另外，藉由最佳化低溫氮化鋁鎵引入層之導入，可以成功地成長出厚且高品質之磊晶薄膜。

GaN material with high breakdown field, high energy bandgap, high electron mobility and good thermal conductivity is the most attractive alternative over Si, due to developments of Si semiconductor technology are close in the limit of the Moore’s Law. The most advantage is that GaN could be grown on large-sized Si substrate. In order to achieve high breakdown voltage for high power electronic device, it’s equipped wih thick epilayer of GaN for epitaxial growth. In this study, firstly, we establish a series of criterions of epitaxy quality by in-situ measurement system. Based on criterions, we could identify epitaxy quality during experimental process. All samples in experiment followed the criterions. Besides, when 2DEG channel was formed at AlGaN / GaN interface, we could do the hall measurement. Topics of experiment are optimizations of growth parameters of LT-AlGaN interlayers. The 2.87 μm crack-free epilayer was grown with optimization of LT-AlGaN for 90 seconds at set temperature of 950°C. From rocking curve scan of XRD analysis, FWHM of GaN (002) is 450 arcsec and GaN (102) is 661 arsec. For hall measurement, the electron mobility of 1300 cm2/V-s, carrier concentration of 0.81x1013 cm-2 were measured. Furthermore, find the criticalthickness of the second GaN. After the second GaN was deposited for 1500 seconds, the second LT-AlGaN interlayer was inserted. Then, 4.4 μm crack-free epilayer was grown. Despite of the substrate is plastic deformation, the crystal quality is good. From rocking curve scan of XRD analysis, FWHM of GaN (002) is 493 arcsec and GaN (102) is 836 arsec. Based on criterions, we could indentify epitaxy quality during experimental process; it could save time of ex-situ material analysis. Moreover, when LT-AlGaN interlayer was inserted, thick and high quality of epilayer could be grown.