氮化鎵基高電子遷移率晶體管逆壓電可靠性研究
發(fā)布時間：2018-08-17 18:23
【摘要】：由于GaN基高電子遷移率晶體管(HEMT)具有高擊穿電壓、高載流子密度、高載流子飽和速度等優(yōu)勢,目前已在高頻大功率器件應用領域取得了廣泛的關注。然而,目前可靠性問題仍然是阻礙GaN基HEMT器件進一步推廣的主要原因。由于GaN基HEMT器件通常工作于高壓大功率條件,逆壓電效應成為影響器件可靠性的重要因素之一。本文首先結合理論分析以及軟件仿真,建立了GaN基HEMT器件逆壓電效應的物理模型;其次通過合理設計實驗方法以及版圖結構,對器件的逆壓電效應進行了測試,并對逆壓電效應引起器件退化的物理機制進行了分析;再次研究了SiN鈍化介質對器件逆壓電效應的影響,以及在正向柵壓應力下器件特性的退化機制;最后研究了在機械應力作用下器件特性的變化規(guī)律。論文首先對GaN基HEMT器件做了簡要介紹,包括GaN材料相對其他半導體材料的優(yōu)勢、GaN基HEMT器件適用于高頻大功率應用的原因以及GaN材料外延生長技術和GaN基HEMT器件制造的發(fā)展歷程。對GaN基HEMT器件目前存在的主要可靠性問題,包括熱載流子效應、電流崩塌效應以及逆壓電極化效應等進行了分析,并對GaN基HEMT器件可靠性的國際研究現狀進行了討論。論文對GaN基HEMT器件的逆壓電效應理論進行了深入分析,并建立了GaN基HEMT器件逆壓電效應的物理模型。在對GaN材料的極化特性,包括自發(fā)極化、壓電極化以及逆壓電極化效應理解的基礎上,深入分析了AlGaN材料的逆壓電極化效應理論,推導了AlGaN材料晶格應力以及彈性能密度與電場關系。通過Silvaco-ATLAS器件仿真軟件,對GaN基HEMT器件的電場分布進行模擬,確定器件在任意工作模式下勢壘層材料中任意一點的電場強度。結合逆壓電效應的理論模型,計算出器件勢壘層中的彈性能分布,并與勢壘層材料所能承受的臨界彈性能密度進行對比,從而確定器件可靠性工作的臨界電壓。制備出了特性優(yōu)良的GaN基HEMT器件,并通過合理設計實驗,對器件的逆壓電效應進行了測試。通過對器件施加階躍應力,同時檢測應力過程中柵極應力電流隨應力時間的變化,確定器件發(fā)生逆壓電極化效應的臨界電壓。實驗發(fā)現,超過臨界電壓器件柵極反向泄露電流急劇增大,本文結合GaN基HEMT器件漏電機制分析對該現象進行了解釋。通過設計器件正反向測試實驗,并對應力前后器件特性對比分析,證明了逆壓電效應導致器件勢壘層陷阱產生的位置位于源極一側柵邊緣。通過合理設計器件結構,系統(tǒng)的研究了逆壓電效應對GaN基HEMT器件特性的影響,并對逆壓電效應引起器件特性退化的物理機制進行了深入分析。通過設計對稱結構GaN基HEMT器件,并對器件進行逆壓電效應測試,證明了柵極邊緣的高場峰值對逆壓電效應的產生至關重要。通過濕法腐蝕的方法去除器件鈍化介質以及金屬接觸,并通過掃描電子顯微鏡(SEM)對器件柵下材料形貌進行分析,證明了逆壓電效并不一定會引起器件柵下材料的物理損傷。研究了逆壓電效應的臨界電壓與器件偏置條件的關系,并結合不同偏置條件下器件勢壘層中的電場分布對該現象進行了解釋。采用能帶理論以及陷阱產生理論,對逆壓電效應引起器件退化的物理機制進行了詳細闡述。研究了SiN鈍化對器件逆壓電效應的影響,并結合器件瞬態(tài)特性測試以及表面漏電理論對實驗現象進行了深入的討論。實驗發(fā)現,去除SiN鈍化介質后在階躍應力測試過程中不會出現逆壓電極化效應的臨界電壓。瞬態(tài)測試表明,SiN介質鈍化會使得器件勢壘層表面的慢態(tài)陷阱得到抑制,但同時也會引入大量的快態(tài)陷阱。結合器件表面漏電機制以及橫向能帶分析,我們認為表面慢態(tài)陷阱俘獲電子并導致器件表面耗盡區(qū)的延伸,是導致上述實驗現象的根本原因。論文還對器件在正向柵壓下的退化規(guī)律進行了研究,并建立了應力作用下器件柵下界面氧化層消除理論。實驗表明,正向階躍應力后器件閾值電壓正向漂移,柵極漏電顯著增大。通過建立變頻電容-電導模型對器件柵下界面陷阱進行表征,證明了應力作用后器件柵下氧施主濃度的降低。通過X射線光電譜(XPS)對柵下材料組分進行分析,發(fā)現應力作用后勢壘層表面的Ga-O峰值顯著減弱。我們認為在應力作用下柵極金屬Ni會與界面氧發(fā)生反應,引起界面氧化層的消耗,從而導致器件特性的退化。發(fā)明了可以對芯片施加機械應力的測試裝置,并利用該裝置研究了GaN基HEMT器件在拉伸應力作用下特性的變化規(guī)律。實驗發(fā)現,在晶格發(fā)生拉伸時,器件的輸出電流密度和峰值跨導均出現增大趨勢。結合GaN材料的極化模型我們認為,晶格拉伸會導致材料能帶傾斜,使得更多的表面施主發(fā)生電離,從而引起溝道載流子濃度的增大以及溝道電阻的降低。
[Abstract]:GaN-based high electron mobility transistor (HEMT) has been widely used in high-frequency and high-power devices due to its high breakdown voltage, high carrier density and high carrier saturation speed. However, the reliability problem is still the main reason that hinders the further promotion of GaN-based HEMT devices. Inverse piezoelectric effect is one of the most important factors affecting the reliability of GaN-based HEMT devices. Firstly, the physical model of inverse piezoelectric effect is established by combining theoretical analysis and software simulation. Secondly, the inverse piezoelectric effect of GaN-based HEMT devices is carried out by reasonable design of experimental methods and layout structure. The physical mechanism of the device degradation caused by the inverse piezoelectric effect is analyzed. The influence of SiN passivation medium on the inverse piezoelectric effect and the degradation mechanism of the device characteristics under forward gate compressive stress are studied. Finally, the variation of the device characteristics under mechanical stress is studied. The advantages of GaN-based HEMT devices over other semiconductor materials, the reasons why GaN-based HEMT devices are suitable for high frequency and high power applications, and the development of GaN-based epitaxial growth technology and GaN-based HEMT devices manufacturing are briefly introduced. The inverse piezoelectric polarization effect of GaN-based HEMT devices is analyzed, and the research status of the reliability of GaN-based HEMT devices in the world is discussed. The inverse piezoelectric effect theory of GaN-based HEMT devices is analyzed in detail, and the physical model of inverse piezoelectric effect of GaN-based HEMT devices is established. Based on the understanding of piezoelectric polarization and inverse piezoelectric polarization effect, the theory of inverse piezoelectric polarization effect of AlGaN material is deeply analyzed, and the relationship between lattice stress, elastic energy density and electric field of AlGaN material is deduced. The elastic energy distribution in the barrier layer of GaN-based HEMT devices is calculated and compared with the critical elastic energy density that the barrier material can withstand to determine the critical voltage for the device reliability. The inverse piezoelectric effect of the device is tested by a reasonable design experiment. The critical voltage for the inverse piezoelectric polarization effect of the device is determined by applying step stress to the device and measuring the change of the grid stress and current with stress time. This phenomenon is explained by the leakage mechanism analysis of GaN-based HEMT devices. Through the forward and backward testing experiments of GaN-based HEMT devices and the comparative analysis of device characteristics before and after stress, it is proved that the position of barrier layer trap caused by inverse piezoelectric effect is located at the edge of the grid on the source side. By designing the device structure rationally, the system is designed. The influence of inverse piezoelectric effect on the characteristics of GaN-based HEMT devices is studied, and the physical mechanism of the degradation of GaN-based HEMT devices caused by inverse piezoelectric effect is analyzed. The passivation medium and metal contact were removed by wet etching and the morphology of the material under the gate was analyzed by scanning electron microscopy (SEM). It was proved that the inverse piezoelectric effect did not necessarily cause the physical damage of the material under the gate. The relationship between the critical voltage of the inverse piezoelectric effect and the bias condition of the device was studied. This phenomenon is explained by the electric field distribution in the barrier layer of the device under different bias conditions. The physical mechanism of the device degradation caused by the inverse piezoelectric effect is described in detail by using the energy band theory and the trap generation theory. The effect of SiN passivation on the inverse piezoelectric effect of the device is studied. The experimental phenomena are discussed in detail by the leakage theory. It is found that the critical voltage of inverse piezoelectric polarization will not occur during the step stress test after removal of SiN passivating medium. Based on the mechanism of surface leakage and the analysis of transverse band, we consider that the slow trapping of electrons on the surface leads to the extension of the depletion zone on the surface of the device, which is the fundamental cause of the above experimental phenomena. Experiments show that the threshold voltage drifts forward and the gate leakage increases significantly after the forward step stress. A variable frequency capacitance-conductance model is established to characterize the interface traps under the gate. It is proved that the oxygen donor concentration under the gate decreases after the stress action. The material components under the gate are fed by X-ray photoelectron spectroscopy (XPS). It is found that the Ga-O peak value on the barrier layer surface decreases remarkably after the stress action. We believe that the gate metal Ni will react with the interface oxygen under the stress action, resulting in the consumption of the interface oxide layer, which leads to the degradation of the device characteristics. The experimental results show that the output current density and peak transconductance of the HEMT devices increase with the tensile stress. Combined with the polarization model of GaN material, it is found that the crystal extension leads to the tilt of the energy band of the material, which leads to the ionization of more surface donors, and thus causes the groove. The increase of carrier concentration and the decrease of channel resistance.
【學位授予單位】：西安電子科技大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TN386
本文編號：2188503
[Abstract]:GaN-based high electron mobility transistor (HEMT) has been widely used in high-frequency and high-power devices due to its high breakdown voltage, high carrier density and high carrier saturation speed. However, the reliability problem is still the main reason that hinders the further promotion of GaN-based HEMT devices. Inverse piezoelectric effect is one of the most important factors affecting the reliability of GaN-based HEMT devices. Firstly, the physical model of inverse piezoelectric effect is established by combining theoretical analysis and software simulation. Secondly, the inverse piezoelectric effect of GaN-based HEMT devices is carried out by reasonable design of experimental methods and layout structure. The physical mechanism of the device degradation caused by the inverse piezoelectric effect is analyzed. The influence of SiN passivation medium on the inverse piezoelectric effect and the degradation mechanism of the device characteristics under forward gate compressive stress are studied. Finally, the variation of the device characteristics under mechanical stress is studied. The advantages of GaN-based HEMT devices over other semiconductor materials, the reasons why GaN-based HEMT devices are suitable for high frequency and high power applications, and the development of GaN-based epitaxial growth technology and GaN-based HEMT devices manufacturing are briefly introduced. The inverse piezoelectric polarization effect of GaN-based HEMT devices is analyzed, and the research status of the reliability of GaN-based HEMT devices in the world is discussed. The inverse piezoelectric effect theory of GaN-based HEMT devices is analyzed in detail, and the physical model of inverse piezoelectric effect of GaN-based HEMT devices is established. Based on the understanding of piezoelectric polarization and inverse piezoelectric polarization effect, the theory of inverse piezoelectric polarization effect of AlGaN material is deeply analyzed, and the relationship between lattice stress, elastic energy density and electric field of AlGaN material is deduced. The elastic energy distribution in the barrier layer of GaN-based HEMT devices is calculated and compared with the critical elastic energy density that the barrier material can withstand to determine the critical voltage for the device reliability. The inverse piezoelectric effect of the device is tested by a reasonable design experiment. The critical voltage for the inverse piezoelectric polarization effect of the device is determined by applying step stress to the device and measuring the change of the grid stress and current with stress time. This phenomenon is explained by the leakage mechanism analysis of GaN-based HEMT devices. Through the forward and backward testing experiments of GaN-based HEMT devices and the comparative analysis of device characteristics before and after stress, it is proved that the position of barrier layer trap caused by inverse piezoelectric effect is located at the edge of the grid on the source side. By designing the device structure rationally, the system is designed. The influence of inverse piezoelectric effect on the characteristics of GaN-based HEMT devices is studied, and the physical mechanism of the degradation of GaN-based HEMT devices caused by inverse piezoelectric effect is analyzed. The passivation medium and metal contact were removed by wet etching and the morphology of the material under the gate was analyzed by scanning electron microscopy (SEM). It was proved that the inverse piezoelectric effect did not necessarily cause the physical damage of the material under the gate. The relationship between the critical voltage of the inverse piezoelectric effect and the bias condition of the device was studied. This phenomenon is explained by the electric field distribution in the barrier layer of the device under different bias conditions. The physical mechanism of the device degradation caused by the inverse piezoelectric effect is described in detail by using the energy band theory and the trap generation theory. The effect of SiN passivation on the inverse piezoelectric effect of the device is studied. The experimental phenomena are discussed in detail by the leakage theory. It is found that the critical voltage of inverse piezoelectric polarization will not occur during the step stress test after removal of SiN passivating medium. Based on the mechanism of surface leakage and the analysis of transverse band, we consider that the slow trapping of electrons on the surface leads to the extension of the depletion zone on the surface of the device, which is the fundamental cause of the above experimental phenomena. Experiments show that the threshold voltage drifts forward and the gate leakage increases significantly after the forward step stress. A variable frequency capacitance-conductance model is established to characterize the interface traps under the gate. It is proved that the oxygen donor concentration under the gate decreases after the stress action. The material components under the gate are fed by X-ray photoelectron spectroscopy (XPS). It is found that the Ga-O peak value on the barrier layer surface decreases remarkably after the stress action. We believe that the gate metal Ni will react with the interface oxygen under the stress action, resulting in the consumption of the interface oxide layer, which leads to the degradation of the device characteristics. The experimental results show that the output current density and peak transconductance of the HEMT devices increase with the tensile stress. Combined with the polarization model of GaN material, it is found that the crystal extension leads to the tilt of the energy band of the material, which leads to the ionization of more surface donors, and thus causes the groove. The increase of carrier concentration and the decrease of channel resistance.
【學位授予單位】：西安電子科技大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TN386
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