以有機金屬化學氣相沉積法成長磷化銦鎵及砷化鎵異質接面雙載子電晶體之銅金屬化研究

Abstract

本論文主要研究以有機金屬化學氣相沉積法成長磷化銦鎵及砷化鎵的異質接面雙載子電晶體之銅金屬化製程和以鉭為擴散障礙層的銅/鉭/砷化鎵結構經退火後擴散機制和熱穩定性之研究。 首先，異質接面雙載子電晶體以有機金屬化學氣相沉積法成長之，其磷化銦鎵及砷化鎵異質接面之特性和控制方法將先被討論。本論文中，接面的陡峭和磷化銦鎵的有序排列效應係利用光激發光譜、雙晶X-射線繞射、掃描式電子顯微鏡、拉曼散射光譜來加以鑑定。一個平滑的接面可以藉著控制三、五族前驅物的開關時間和五/三比來獲得。從光激發光譜得到的帶寬和拉曼光譜判斷的有序排列效應，可以清楚解釋磷化銦鎵的有序排列現象。在成長溫度730度時，其帶寬為1.93伏特顯示出較無序排列的特性，而620度成長時其帶寬1.83伏特則對應到一個原子分佈較有序排列的特性。 第二，研究無序排列的磷化銦鎵磊晶製作的銅金屬化磷化銦鎵/砷化鎵異質接面雙載子電晶體特性並和以金為金屬化的異質接面雙載子電晶體電子特性比較。在本研究中，一個新的銅/鉬/鍺/鈀毆姆接觸將被使用到n型的砷化鎵上作為異質接面雙載子電晶體的應用。銅/鉬/鍺/鈀毆姆接觸在經過350度的退火之後可以達到2.8□10-7Ωcm2最低的接觸電阻。然而，經過400度的退火之後，此毆姆接觸因為銅和下面的金屬層作用而遭到破壞。片電阻、X-射線繞射、歐傑電子光譜和穿透式電子顯微鏡的分析結果，顯示鉬是一個理想的障礙層，可以在銅金屬化的毆姆接觸中穩定到350度。含此銅/鉬/鍺/鈀毆姆接觸的元件也被施以250度、24小時的熱穩定性測試，經此測試，元件特性並沒有顯著的改變。在高電流密度120KA/cm2、24小時的測試下，元件特性也沒有顯著的改變。 第三，研究鉭作為銅和砷化鎵之間擴散障礙層的機制。一層薄的30nm濺鍍形式之鉭薄膜作為障礙層阻擋砷和鎵擴散到銅層。經過片電阻、X-射線繞射、歐傑電子光譜和穿透式電子顯微鏡的分析，在砷化鎵上的銅/鉭膜可以穩定到500度。然而，經過550和600度的退火之後，由於障礙層的破壞和接面的不穩定性，一些額外的化合物如: TaAs2, Cu3Ga, and TaAs將會形成。

In this thesis, copper metallization of InGaP/GaAs heterojunction bipolar transistor grown by metal-organic chemical vapor deposition (MOCVD) and the diffusion mechanism and the thermal stability for the Cu/Ta/GaAs structure with Ta as the barrier are studied. First, the characterization and control of InGaP/GaAs heterostructure grown by MOCVD for HBT application were studied. Interface abruptness and the ordering effect of InGaP were characterized by photoluminescence (PL), Double crystal X-ray diffraction (DCXRD), scanning electron microscopy (SEM), Raman scattering spectra. A very smooth interface can be obtained by controlling the switching time of III and V precursors and V/III ratio. The PL data and the Raman spectra clearly evidenced the ordering phenomenon of the InGaP layer. A high band gap of 1.93 eV showing a more disorder characteristic was obtained when the film was grown at 730℃ and a low band gap of 1.83 eV corresponding to an atomically ordered distribution was obtained when grown at 620℃. Second, the Cu-metallized InGaP/GaAs HBT, with lattice-matched disordered InGaP structure was manufactured, this device exhibited comparable device performances with Au-metallized HBT. In this study, a novel Cu/Mo/Ge/Pd ohmic contact was characterized and applied to the n+-GaAs for HBT applications. The Cu/Mo/Ge/Pd ohmic contact structure reached the lowest contact resistance and was measured to be 2.8□10-7Ωcm2 after annealing at 350℃. However, the contact structures deteriorated owing to the interfacial reactions between Cu and the underlying layers when annealed at 400℃. The sheet resistance, XRD, AES and TEM analysis data also indicate that Mo is a reliable diffusion barrier for the Cu-based ohmic contacts to n+-GaAs up to 350℃ annealing. The devices with the Cu/Mo/Ge/Pd ohmic contacts were also thermally annealed at 250℃ for 24 hours for thermal stability study and showed no obvious electrical degradation after the thermal test. Under the high current density of 120kA/cm2 at a VCE of 1.5V for 24 hours, the HBTs with the novel Cu/Mo/Ge/Pd ohmic contacts show little change in electrical characteristics. Third, the mechanism of tantalum inserting as a barrier between Cu and GaAs is investigated. A thin 30 nm tantalum layer was sputtered as a diffusion barrier to block the Ga and As diffusion into the Cu layer. Judging from the data of sheet resistance measurement, X-ray diffraction analysis, Auger electron spectroscopy and transmission electron microscopy, the Cu/Ta films on GaAs were found to be very stable up to 500 □C without Cu migration into GaAs. However, after annealing at 550 and 600□C, some extra compounds such as TaAs2, Cu3Ga, and TaAs formed owing to barrier deterioration and interfacial instability.