高溫沉積之鋁閘極在非晶矽薄膜電晶體製程上之應用

Abstract

本研究是利用高溫濺鍍沈積之鋁薄膜做為非晶矽薄膜電晶體之閘極。因為 非晶矽薄膜電晶體之電特性會受介電層表面型態之影響，而介電層之平坦 度又由下層之鋁閘極所支配。而高溫沈積之鋁薄膜則可以抑制丘狀突起（ Hillocks）之成長，其平坦度和其沈積時的溫度和Al(111)晶向強度有關 。因為鋁閘極在高溫沈積時已有退火(Annealing)之效應，Al(111)晶向強 度會隨著沈積溫度的升高而變強。而於沈積溫度為300℃時有一最平坦之 表面型態。此外，氧化鋁/氮化矽雙介電層非晶矽薄膜電晶體之電特性亦 在討論之列。而在本研究中，介電層表面型態完全受下方鋁閘極表面型態 之影響，而介電層之平坦度會影響後續非晶矽薄膜之沈積。在介電層為氮 化矽之薄膜電晶體中，由最平坦的鋁閘極製成的元件，有最大的場效遷移 率（Field Effect Mobility = 0.71cm2/V-sec），最低的次臨界變動（ Subthreshold Swing = 0.32 V/decade），而在介電層為氧化鋁/氮化矽 時，則有最大的場效遷移率：0.78 cm2/V-sec，最低的次臨界變動：0.28 V/decade。 The electrical performances of hydrogenated amorphous silicon (a-Si:H), thinfilm transistors are affected by the surface roughness of SiNx/a-Si:H. If wecould get a smooth Al film, the SiNx and a-Si:H film would be more flatter.The high deposited temperature of Al film are expected to suppress hillocks formation. The surface roughness are related to Al(111) and it's deposited temperature. On the other hand, a suitable Al2O3/SiNx double layered insulatorsare applied to fabricate TFT. It has been found that the characteristics of a-Si:H TFT device is strong dependent on the morphology of Al film. When deposited temperature of Al film was 300℃, the surface roughness was most smoothest and for the double layered (Al2O3/SiNx) insulators, the MIM structure of anodized Al2O3 show a breakdown fields as high as 8.188 MV/cm and a low leakage current density of 8.35*10^-8 A/cm, As a result.The a-Si:H TFT fabricated on the smoothest Al/SiNx morphology shows the best performances : μ FET=0.71 cm2/V-sec, Ssub=0.32V/decade. For the double layered (Al2O3/SiNx) insulators TFT, has the best performances : μFET =0.78 cm2/V-sec, Ssub=0.28 V/decade.