A Study of Ultra-thin Gate Oxides on Deep Sub-micron Devices

• Main Authors: Hsien, Szu-Kang, 鮮思康
• Other Authors: Huang, Tsung-Shiew
• Format: Others
• Language: en_US
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/75833927342385018421

碩士 === 國立清華大學 === 材料科學與工程研究所 === 85 === As the device dimensions scaled down,t he thickness of gate oxides must decrease in order to suppress short-channel effects, improves device speed, and increase current drivability. However, the decreasing of gat oxides can lead to an intolerable degradation in reliability. The reliability of 2.5 nm gate oxides is important because it isneeded for devices with channel length below 0.1 μm. Besides, if we scale down gate oxides more aaggressively than required and if we can by the same time control the reliability issues, we get very good device performance as compared to those using thicker oxides. In our exzperiments, we can see that devices perform well as predicted by the theory. Hence, the reliability of ultra-thin gate oxides is an important issue for deep sub-micron MOSFET devices. In this thesis, we have developed 2.5 nm- thick, high quality oxide. The mean value of charge-to-breakdown. QBD, for 2.5 nm sample is 435 C/cm2 by using gate injection current density of 0.4 A/cm2 and 8150 C/cm2 by using substrate injectioncurrent density of 0.4 A/cm2. The mean value of breakdown field EBD is 15.9 MV/cm. On the hand, the mean value of charge-to-breakdown, QBD, for 3 nm sample is 0.028 C/cm2 by using gate injection current density of 0.02 A/cm2 and 2462 C/cm2 by using substrate injection current density of 0.02 A/cm2. The mean value of breakdown field EBD is 16 MV/cm. Also Oxide breakdown mechanism, oxide thickness effects, various stress current dependence and stress induced leakage current are studied. The ratio of Ig/Id for 2.5 nm-thick gate oxide device decreases as Lg falls in proportion to Lg1.8, which is very consistent with the device physics theory. The performance of various channel length devices of 2.5 nm-thick oxide is good as compared to those made by 4nm-thick oxide. For 0.3μm NMOSFET device, the drain urrent drive, the transconductance and the subthreshold swing are 0.6 mA/μm,358 S/mm, 71 mV/dec, respectively. We have also confirmed that hot-carrier relability mproves as the gate oxide thickness is reduced to the 2.5 nm case.