次微米n-MOS在低汲極偏壓下,因電子間的交互作用所產生之閘極漏電流

Abstract

隨著深次微米領域的迅速開發, 元件電壓也必須持續的降低, 故 低汲極電壓下之熱載子效應已成為深次微米領域的技術開發所無法避免的 問題. 探討次微米元件在低汲極電壓下熱載子產生之機制即為論文之目 的. 當汲極電壓低於 Si/SiO2 之能障電壓時 (約3eV), 元件所測 得之閘極電流已無法用橫向電場加速所獲致之能量來解釋, 因為此時載子 由上述之能量並無法穿越閘極氧化層; 再者, 由實驗結果發現, 在越低汲 極電壓之情況下, 熱載子因 Auger recombination 而發生之可能性亦越 大為降低. 因此, 必然存在著某一新機制主導著低汲極電壓下次微米元件 中熱載子的產生. 為了配合低汲極電壓下閘極漏電流產生的理論 機制, 我進行閘極漏電流量測方面的探討. 由於閘極漏電流值甚小 (小 於1pA), 無法經由直接量測而得, 我利用 flash (EPROM) 中 floating gate 之結構, 以間接的方式測得次微米 n-MOS 極小之 gate current, 其精密度可達 1e-17 Amp, 並由此方法與直接量測之交集證明此方法具極 高之準確度. 理論方面則建立了 "電子和電子碰撞後能量轉換之 物理模式", 並由模擬結果發現, 上述之微小漏電流主要是因電子和電子 碰撞所產生之熱載子所引發的, 亦即:Electron-Electron Scattering 將 是低汲極電壓下熱載子發生之一極重要之機制. Due to the rapid progress of deep submicron technology, the power supply voltage used in the MOS circuits is expected to scale down continually. Hot carrier effects at low drain voltages have received much attention in recent years. The purpose of this thesis is to investigate the hot carrier generation mechanisms at low drain voltages. As the supply voltage is scaled below the Si/SiO2 interfacial barrier height (about 3eV), the gate current injection in a MOSFET cannot be simply explained by lateral channel field heating because the energy gained from channel field heating is not enough to overcome the Si/SiO2 interface barrier. In addition, the probability of hot carrier generation caused by Auger recombination declines as the drain voltage is lowered. In order to investigate the hot carrier generation mechanisms at low drain voltages, the gate leakage current at low drain voltages is characterized. Since the gate current level is extremely low, a floating gate measurement technique is employed. This technique can provide a sufficient resolution in gate current measurement to 1e-17 Amp. In the theoretical respect, we develop a model for conduction band electron- electron interaction enhanced gate current injection. Good agreement between the measured and theoretically calculated results is obtained. It is concluded that electron-electron interaction is directly responsible for the electron high energy tail exceeding the interface barrier height and plays an important role in hot carrier generation at low drain voltages.