以新式光電化學氧化法成長砷化鎵金氧半場效電晶體閘極氧化層之特性研究

Investigation of the GaAs MOSFETs gate oxide by using photoelectrochemical oxidation method

林元富(Yuan-Fu Lin)

國立虎尾科技大學/電機資訊學院/光電與材料科技研究所/碩士(2007年)

摘要

本論文主要目的是以新式光電化學法(photoelectrochemical oxidation method)成長直接於n型砷化鎵表面成長氧化層作為金氧半場效電晶體(MOSFET)閘極氧化層之特性研究。
於論文中，探討以不同光電化學氧化條件成長n型砷化鎵的氧化層，其中調整電解液之酸鹼值，以控制n型砷化鎵的成長速率，並對氧化層進行熱處理，在氧氣環境下，分別以200、300及400oC分別熱處理10、20、30及40分鐘，藉由氧化層厚度變化分析，發現於熱處理30分鐘後氧化層厚度趨於穩定，並由原子力顯微鏡(AFM)分析可得該氧化層經300oC熱處理後可得最佳之表面平整度，並經由能量散射光譜儀(EDX)、X光繞射分析儀(XRD)、歐傑電子能譜儀(AES)及X光光電子能譜儀(XPS)分析確認該氧化層為三氧化二鎵(Ga2O3)及三氧化二砷(As2O3)所組成，並經X光光電子能譜儀分析可得經氧氣熱處理200、300及400oC，其氧化層之氧化態有随熱處理溫度上升，而有逐漸增加之趨勢。
最後，將此氧化層應用於金氧半二極體及砷化鎵金氧半場效電晶體之製作，因利用光電化學氧化法所成長之砷化鎵氧化層(簡稱PEC oxide)，其有無熱處理之砷化鎵氧化層皆易溶於酸鹼溶液中，故於元件製作過程中為了保護砷化鎵氧化層，故於其上成長一層薄的氧化矽(SiOx)作為保護層，阻擋酸鹼容易蝕刻砷化鎵氧化層。於本論文中，製作六組不同氧化層條件之金氧半二極體(No.1~No.6)，其氧化層依序分別是PEC oxide (40nm)、SiOx(10nm)+PEC oxide(40nm)、SiOx(10nm)+PEC oxide(200oC, 33.6nm)、SiOx(10nm)+PEC oxide(300oC, 26.4nm)、SiOx(10nm)+PEC oxide(400oC, 22.8nm)及SiOx(50nm)，藉由電容-電壓量測，得到元件No.1~No.6之氧化層介電常數分別為7.7、7.2、8.2、8.9、9.1及3.9，而元件No.1~No.5之氧化層與半導體之間的界面態密度分別為8.22×1011、7.85×1011、7.47×1011、7.28×1011及7.45×1011cm2eV。
另外，於本論文中，製作一組無經熱處理之光電化學氧化法所成長之砷化鎵氧化層作為金氧半場效電晶體之閘極電極，並對元件進行汲極-源極飽合電流(IDS)電流-電壓量測，在閘極-源極偏壓(VGS)為0V時，汲極-源極飽合電流為101mA/mm，且在VDS=2.4V及VGS=-0.3V時互導值(gm)為65mS/mm。

並列摘要

In this study, we investigated the performance of the n-GaAs MOSFET that the gate oxide was directly grown on the semiconductor surface using photoelectrochemical (PEC) oxidation method.
To investigate different PEC oxidation conditions for n-GaAs by PEC method, adjust pH value to control growth rate of n+-GaAs. To annealed PEC oxide under 200, 300 and 400oC in the oxygen ambiance of 10, 20, 30 and 40 minutes respectively by furnace, respectively. After annealed 30 minutes that the depth tend to become stable, then we got a smooth surface that after 300oC annealed by AFM, and analysis the compose of oxide are oxidation of gallium and arsenic by EDX, XRD, AES and XPS. We find the oxidation state of oxide increase comply with temperature of 200, 300 and 400oC by XPS.
Finally, the PEC oxidation method was used to grow the GaAs oxide layer as the gate oxide of the MOS diodes and GaAs MOSFETs. Unfortunately, the PEC oxide layers were easily dissolved in the acid and alkali solutions. Therefore, the SiOx layers were deposited on the PEC oxide layers as the protected of the PEC. In this thesis, we fabricated six MOS diodes with different gate oxide (No.1~No.6). The six kinds of gate oxide were PEC oxide (40nm), SiOx(10nm)+PEC oxide(40nm), SiOx(10nm)+PEC oxide(200oC, 33.6nm), SiOx(10nm)+PEC oxide(300oC, 26.4nm), SiOx(10nm)+PEC oxide(400oC, 22.8nm) and SiOx(50nm), respectively. From the C-V measurement, the dielectric constant of the six kinds MOS diodes (No.1 to No.6) is 7.7, 7.2, 8.2, 8.9, 9.1 and 3.9. The interface state density of five kinds MOS diodes (No.1 to No.5) is 8.22×1011, 7.85×1011, 7.47×1011, 7.28×1011 and 7.45×1011 cm2eV, respectively.
We also fabricated a GaAs MOSFET with non-anneal PEC oxide layer as the gate oxide. The drain-source situation current-drain-source voltage (IDS-VDS) and the associated extrinsic transconductance (gm) of the MOSFET were measured by Agilent 4156C semiconductor parameter analyzer. When the MOSFETs were biased at VDS=2.4V, the output current was equal to 101mA/mm at VGS=0V. At VGS=?2.5V, the drain current was close to zero. This phenomenon indicated that the MOSFETs could be biased in a cut-off mode. The maximum associated extrinsic transconductance was 65mS/mm at VGS = ?0.3V.

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