以草酸溶液作MESFET AlAs/GaAs 磊晶選擇性侵蝕的研究

Abstract

我們使用三種不同的蝕刻溶液C6H8O7.H2O/H2O2,C6H8O7/H2O2,C4H6 O4/NH4OH/H2O2對 GaAs/AlAs及GaAs/Al0.32Ga0.68As結構做選擇性蝕刻 的研究.並將最後所得到的結果應用 在異質結構金屬半導體場效電晶體( MESFET)閘極蝕刻上.且量測其直流特性,觀察其蝕刻後 的均勻性. 在選擇性蝕刻方面,我們得到蝕刻溶液C6H8O7.H2O/H2O2在體積比為7;1時, 對GaAs/AlAs 有最高的選擇性,S 值超過600.且C6H8O7.H2O/H2O對AlAs 蝕刻後的表面狀態,在掃描式電子 顯微鏡中觀察,亦較其他的溶液均勻及 平坦. 將蝕刻溶液C6H8O7.H2O/H2O2體積比為7:1,應用在具有蝕刻 終止層AlAs的金屬半導體 場效電晶體閘極侵蝕上,並且量取其直流特性. 得到其電流密度約為376mA/mm;互導值Gm 為160mS/mm;夾止電壓為4.38V. 又利用夾止電壓值在整片晶片上的分佈狀況,求得其標準 偏差值,並且和 沒有蝕刻終止層的MESFET做比較.發現具有蝕刻終止層的MESFET比沒有蝕 刻 終止層的MESFET蝕刻後的均勻性更好. 我們得到的結論是:使用 蝕刻溶液C6H8O7.H2O/H2O2體積比為7:1時,應用在具有蝕刻終止 層AlAs 的金屬半導體場效電晶體的閘極選擇性侵蝕上,在蝕刻後將會有較好的均 勻性.而且 由所量得的直流特性得知,AlAs的存在並不會降低元件的特 性. Three different type of solutions including C4H6O4/NH4OH/H2 O2,C6H8O7.H2O/ H2O2,C6H8O7/H2O2,were used as selective etching solutions for GaAs/AlAs,GaAs/ Al0.32Ga0.68As structure. The results of this study were applied to gate recess of the heterojunction MESFET. The DC characteristics of the MESFET using this selective etch were studied in this research. In this study,it is found that the C6H8O7.H2O/H2O2 solution with 7:1 ratio offers the highest selectivity for GaAs/AlAs layers, the selectivity is 600. The surface morphology of the AlAs after etched by C6H8O7.H2O/H2O2 was may smooth. The 7:1 C6 H8O7.H2O/H2O2 solution was applied to the gate recess of the MESFET with an etch stop layer of AlAs.The DC characteristics of the 1um MESFET with etch stop layer were measured. The maximum transconductance of the device was over 160mS/mm and the current density was about 376mA/mm. The average pinch-off voltage was -4.38V. The standard devition was measured for the whole wafer.It is found that the uniformity of MESFET with an etch stop layer was better than the MESFET without an etch stop layer. The experiment results indicate that the 7:1 C6H8O7/ H2O/H2O2 solution is ideal for selective etch of GaAs/AlAs layer.The MESFET that has an etch stop layer of AlAs for gate recess gives better uniformity after selective etching. From the DC characteristics,we also find that the existence of the AlAs layer does not reduce the performance of the MESFET device.