磊晶成長高阻值氮化鎵緩衝層在矽(111)基板

Abstract

氮化鎵(GaN)成長在矽基板近年來逐漸被大家注意，因為氮化鎵的材料特性具有寬能隙、高載子遷移率和良好的導熱性，所以具有高崩潰電場、高的電子速度及具有高的操作溫度，所以氮化鎵為基礎的相關元件是相當適合作為次一世代高功率元件。藉由磊晶成長的方法提升氮化鎵高功率元件的崩潰電壓，是本論文中所討論的。 從文獻中可得知，藉由磊晶成長提升氮化鎵高功率元件的崩潰電壓主要有三種方法：增加磊晶層的厚度、摻雜碳原子作為受體雜質、成長氮化鋁鎵/氮化鎵/氮化鋁鎵雙異質磊晶結構(DH-FET)。然而在先前的經驗可得知，當成長總厚度超過4.4μm時的氮化鎵磊晶層，矽基板會產生塑性變形，這將會造成製作元件上的困難，並影響到元件的電流特性。故在本次實驗中，藉由摻雜類似P型的碳原子雜質在氮化鎵緩衝層中，來提升崩潰電壓，並且在氮化鋁鎵/氮化鎵/氮化鋁鎵雙異質磊晶結構(DH-FET)內插入一層低溫成長的氮化鋁層，增加磊晶層的總厚度來增加崩潰電壓。 在碳摻雜氮化鎵方法中，改變氮化鎵成長壓力由原本的100 torr降至30 torr，碳濃度成功地由原本的7 x 1016 atoms/cm3 增加至1 x 1019 atoms/cm3，並且增加氮化鋁鎵過渡層(transition layer)的厚度，成功地成長出3.3μm無裂痕的磊晶薄膜。其中XRD (002)面 rocking curve半高寬為501 arcsec，XRD (102)面 rocking curve半高寬為993 arcsec。最終結構的片電阻值，量測結果為1643 Ω/□。 電性量測方面，量測出電極間距在20μm時，崩潰電壓為510 V，超過了原本總厚度3μm無碳摻雜氮化鎵元件的崩潰電壓320 V。 在雙異質磊晶結構中，在原本雙異質磊晶結構中插入低溫氮化鋁插入層，讓磊晶薄膜的厚度達到3.3μm。量測其中XRD (002)面 rocking curve半高寬為578 arcsec，XRD (102)面 rocking curve半高寬為1105 arcsec。崩潰電壓在電極間距20μm時則是超過600 V。 在此實驗中，藉由改變兩種不同的磊晶結構，成功成長出高阻值與高能障的緩衝層，提升元件的崩潰電壓。

In recent years, growing GaN on Si has attracted a lot of attention. Due to wide band gap, high electron mobility and thermal conductivity, GaN has high electron breakdown field and high current velocity and high operating temperature. GaN-based devices are able to be the high power devices in the next generation. In this thesis, epitaxial methods that can increase breakdown voltage of GaN devices are discussed. From the literature, there are three main epitaxial methods to increase breakdown voltage: increasing growth thickness of epitaxial wafer, doping carbon in GaN buffer layer (C-doped GaN) and growing AlGaN/GaN/AlGaN double heterostructure field effect transistor (DH-FET). In the previous experience, when the total thickness of GaN biffer layer is over 4.4μm, plastic deformation of silicon substrate occurs. It will make fabrication process more difficult and degrade device performance. For this reason, we should increase breakdown voltage by C-doped GaN and DH-FET. In the C-doped GaN method, we change the growth pressure of 2nd GaN layer from 100 torr to 30 torr, the carbon concentration increases from 7 x 1016 atoms/cm3 to 1 x 1019 atoms/cm3. The total thickness is 3.3 μm and the wafer is creak-free. From XRD analysis, the FWHM of GaN (002) is 501 arcsec and (102) is 993 arcsec. The resistance of final structure is 1643 Ω/□. In the DC measurement, the breakdown voltage of C-doped GaN HEMT is 510 V at 20 μm spacing gap. It is higher than traditional GaN HEMT. In the DH-FET method, we insert one LT-AlN interlayer, so the total thickness increases to 3.3 μm. From XRD analysis, the FWHM of AlGaN (002) is 578 arcsec and (102) is 1105 arcsec. The breakdown voltage of DH-FET is over 600 V at t 20 μm spacing gap. In my experiments, we use C-doped GaN and DH-FET to increase breakdown voltage for high voltage applications.