p 與n 基板超薄閘極氧化層金氧半結構元件之深空乏現象與氧化層不均勻現象探討

Abstract

本篇論文主要藉由深空乏現象來討論p 型基板與n 型矽基板超薄閘極氧化層 金氧半結構的不均勻效應。首先，主要應用李建緯學長的超薄氧化層金氧半電容 模型來解釋p 型與n 型矽基板金氧半電容本質上的差異，其中最主要的議題是對於p 型矽基板的金氧半電容而言，金屬和矽基板間的蕭基位障是不能被忽略的，但對於n 型基板的金氧半電容而言，蕭基位障的影響較小。此外，邊際電場效應會使得p 型基板的金氧半電容具有邊緣相關的電流特性，而n 型基板的金氧半電容的電流則是與面積相關；在第二部分有電流及電容對電壓的作圖來驗證此模型。n 型基板比起p 型基板的金氧半電容較快進入空乏區且具有較低的電容值，這個特性也與它本身漏流比較全面有關。為了再進一步討論及比較p 型與n 型基板的金氧半電容電荷的不均勻性，我們將元件照光來增加少數載子的數量。我們發現對於n 型基板的金氧半電容而言，在高頻下電容卻具有低頻的特性，這是由於n型基板內的少數載子具有較快的反應時間，儘管其本身漏流較p 型基板更大，而在p 型基板上則不會看到此低頻現象。在第三部分，我們使用後金屬退火與氧化層蝕刻來討論氧化層不均勻現象。我們發現到後金屬退火可以增加局部薄氧化層的面積且使氧化層的等效厚度減小，而對超薄閘極氧化層金氧半電容而言，甚至可能因為金屬穿透而使元件崩潰。對小面積的元件而言，因為不均勻面積占全部面積之比例較大，所以後金屬退火會使元件特性影響更為嚴重。同樣的，氧化層蝕刻也是對於小面積元件有較嚴重的影響。對大面積元件而言，因為它有較高比例會覆蓋到缺陷，所以它本身漏流較大且較早進入深空乏區域。此外，隨著閘極電壓增大，對於厚的氧化層元件而言，因為壓降主要在氧化層，所以厚的氧化層容易在量測過程中被破壞，而對於薄的氧化層元件而言，壓降主要在矽基板上，所以元件較不易被破壞。

In this thesis, the non-uniformity effect of MOS (p) and MOS (n) capacitors with ultra-thin oxide were thoroughly investigated through deep depletion analysis. In the first part, the theoretical model of ultra-thin oxide MOS capacitors proposed by Chien-Wei Lee was used to explain the abnormal behavior regarding MOS (p) and MOS (n) capacitors. The main issue is the Schottky barrier between metal and the silicon substrate could not be ignored for MOS (p) capacitors but would be less pronounced for MOS (n) capacitors. In addition, the effect of fringing field would further enhance the edge-dependent current conduction of MOS (p) capacitors. For MOS (n) capacitors, the current are area-dependent. In the second part, both I-V and C-V measurements were performed to verify this model. It was found that MOS (n) capacitors enter into the deep depletion much quickly and show lower capacitance values than those of MOS (p) capacitors. These could also refer to the comprehensive leakage characteristics of MOS (n) capacitors. To further investigate the effect of charge non-uniformity in MOS (p) and MOS (n) capacitors, incandescent light was applied to enhance the amount of minority carriers. For the MOS (n) capacitors, they reveal a low frequency effect at the 1MHz under light illumination due to a shorter minority carrier response time despite the intrinsic leakier characteristic, but MOS (p) capacitors are not. In the third part, post-metallization annealing (PMA) and oxide etching were applied to discuss the oxide non-uniformity. It was found that PMA would extend the oxide local thinning area and reduce the effective thickness of the oxide layer. For ultra-thin oxide MOS (p) capacitors, it may further breakdown due to the metal spiking effect. For small-area devices, the effect of PMA would be much serious since the ratio of the non-uniform area to the entire area is higher. Similarly, oxide etching would cause serious oxide non-uniformity, particularly for small-area devices. For large-area devices, more defects are covered, the deep depletion occurs much quickly and are intrinsically leakier than small-or medium-area devices. Besides, it is noticed that thick oxide would encounter higher probability of breakdown during measurements since the voltage drop is mainly on oxide layer for thick-oxide MOS (p) capacitors, while mainly at silicon for thin oxide MOS (p) capacitors.