側向擴散電流對超薄氧化層金氧半元件之反轉區電流特性影響與其相關應用

Abstract

本篇論文主要藉由側邊擴散電流來討論其對於超薄氧化層p型及n型矽基板金氧半電容元件之周邊相關電流的影響與其應用。在論文的第二章，利用不同的元件閘極圖案的設計，來證明元件側邊的擴散電流在超薄氧化層p型矽基板金氧半電容元件中扮演了重要的角色，即反轉區電流的周邊相關現象係來自於側邊擴散電流的作用，透過側邊擴散電流的補充，元件邊緣的電子濃度較中間處大，使得氧化層壓降增加，以及電洞之蕭基位障下降，造成大量電洞電流流經元件周邊。同時，也可以同樣的概念來解釋金氧半電容與金氧半場效電晶體之閘極漏電流的差異。在論文的第三章，我們利用側邊擴散電流受溫度調變的特性，製作了金氧半穿隧溫度感測器，由於側邊擴散電流的影響，金氧半穿隧溫度感測器之反轉區電流亦呈現周邊相關的特性，此周邊相關之電流特性係無法以空乏區內熱激發電流來解釋，而電流對溫度的相依性亦呈現與熱激發電流不同的趨勢。藉由側邊擴散電流引起的邊緣電洞電流即可解釋周邊相關現象以及溫度相依性。在論文的第四章，我們亦利用側邊擴散電流來製作金氧半光二極體，透過比較不同氧化層厚度元件的光電流，我們發現當厚度越大，其光電流越大，此現象不能由傳統認為的邊緣空乏區光激發電流機制來解釋，利用TCAD模擬亦可知當厚度越大，其側邊延伸的空乏區寬度越小，即集光區越小，光電流理當應隨厚度增大而減小，但實驗觀察並非如此。如同溫度感測器，在文獻及本論文實驗中可知金氧半光二極體電流亦呈周邊相關特性，此一現象僅能由側邊擴散電流所引起的邊緣電洞電流來解釋。在論文的第五章，我們比較了p型和n型矽基板金氧半電容元件之電流特性，在n型矽基板金氧半元件中，由於其具與p型矽基板不同的能帶結構，故側邊擴散電流對於暗電流的影響並不顯著，然而對於光電流卻有極明顯的影響，造成光敏度在具較厚氧化層之元件中急劇上升，此一現象僅能由側邊擴散電流引發之氧化層壓降增加，並允許大量電子由金屬穿隧至矽基板來解釋。

In this thesis, we demonstrate the importance of the lateral diffusion current in the current behavior of MOS(p) capacitor with ultrathin oxide and the applications by utilizing the lateral diffusion current. In chapter 2, through comparing the current phenomenon of MOS(p) capacitors with different gate patterns, we can verify that the lateral diffusion current plays an important role in the current characteristic of MOS(p) capacitor. In other words, the perimeter-dependent current behavior is caused by the lateral diffusion current. By the supplement of the lateral diffusion current, the electron concentration is higher in the edge region than in the bulk region, leading to the increase in the edge oxide voltage and smaller Schottky barrier height of holes which allows massive Schottky diode hole current to flow through the edge of the device. Furthermore, the concept of supplement of electrons can be used to explain the difference of gate leakage currents of MOSCAP(p) and NMOSFET. In chapter 3, due to the change of the lateral diffusion current with temperature, we make use of the lateral diffusion current to detect temperature in MOS(p) tunneling temperature sensor whose inversion current is perimeter-dependent. This perimeter-dependent current phenomenon cannot be explained by the thermal generation current in the depletion region, and the temperature dependence of current does not agree with the experimental data. Instead, the edge Schottky diode hole current can be used to well explain the current behavior. In chapter 4, we demonstrate MOS(p) photodiodes by utilizing the lateral diffusion currents. Through fabricating MOS(p) photodiodes with different oxide thicknesses, we find that when the oxide is thicker, the light current is larger. This cannot be explained by the conventional explanation, i.e., the edge photo-generation current in depletion region. Moreover, by using TCAD simulation, it is proved that the edge depletion width will decrease with thicker oxide, indicating that the collection region of light is smaller and the light current also should be smaller. Just like the MOS(p) tunneling temperature sensor, the perimeter-dependent current characteristic of MOS(p) photodiode can be found in some papers and experiments in chapter 4, and this phenomenon only can be explained by the edge Schottky diode hole current. In chapter 5, we compare the current characteristics of MOS(p) and MOS(n) capacitors. In MOS(n), due to its different band structures compared to MOS(p), the lateral diffusion cannot affect the dark current behavior but can influence the light current significantly, leading to strong sensitivity enhancement in the device with thicker oxide. This phenomenon only can be explained by the oxide voltage tuning, which introduce large electron direct tunneling current, induced by the lateral hole diffusion current.