應用於金氧半電晶體閘極氧化層的氧化鋯薄膜電性之研究

The Electrical Properties of Zirconium Oxide Thin Films for Metal-Oxide-Semiconductor Field Effect Transistor Gate Dielectric Applications

王明璁(Ming-Tsong Wang)

指導教授 ： 李雅明

國立清華大學/電機資訊學院/電子工程研究所/博士(2006年)

https://doi.org/10.6843/NTHU.2006.00016

摘要

當金氧半電晶體，通道長度小於0.1 um，閘極氧化層厚度小於1.5nm時，直接穿隧電流將過大而使得晶片的功率消耗太大而無法使用。高介電常數薄膜因為可以用來取代二氧化矽作為金氧半電晶體的閘氧化層並壓抑直接穿隧電流而受到注目。其中，高介電常數薄膜氧化鋯(ZrO2)由於具有高介電常數(20~25)，高崩潰電場(7-15 MV/cm)，低漏電電流，因而更加有可能可以取代二氧化矽。在本論文中，我們製作出金屬鋁/氧化鋯/p型矽的電容及金氧半電晶體並研究其相關特性。
為了研究及區分氧化鋯薄膜的在不同溫度及外加偏壓下的傳導機制，我們使用變溫來量測金屬鋁/氧化鋯/p型矽的電容。在金屬鋁電極為負偏壓時 我們發現在不同溫度及外加偏壓區間的傳導機制分別為(1)修正型Schottky發射；(2)修正型Poole-Frenkel發射；(3) Fowler-Nordheim穿透；(4)及缺陷所造成穿透發射。藉由不同傳導機制的方程式，我們萃取出相關電性參數。並建構出能帶圖。
接著，我們探討以氧化鋯作為閘氧化層金氧半電晶體特性，並量測IDS-VDS 及 IDS-VGS 。同時，我們研究有效載子移動率 (effective mobility)退化。有效垂直電場(effective vertical field)隨溫度改變的情況，經過系統化的分析，發現氧化鋯N通道場效電晶體在庫侖散射(Coulomb scattering)、表面平坦度散射(surface roughness scattering)與聲子散射(phonon scattering)的情況均較二氧化矽電晶體嚴重許多。這種情況可用soft optical phonon散射來加以解釋。最後，經由電導法(conductance method)，以氧化鋯作為閘氧化層的二極體(gated diode)之量測，得到氧化鋯與矽介面的場空乏區介面缺陷電荷密度Dit (interface trapped charge densities)約為5.79×10^12 cm^-2-eV^-1，表面結合速度為941 cm/s，及少數載子活期為1.32×10-6 sec。並且與二氧化矽和氧化鉭做比較。
總結，首先我們分析氧化鋯薄膜的在不同溫度及外加偏壓下的傳導機制。其次，我們研究有效載子移動率 (effective mobility)退化。最後，我們量測並獲得氧化鋯與矽介面的場空乏區的相關電性參數。

關鍵字

高介電常數 ； 氧化鋯介電層 ； 傳導機制 ； 歐姆傳導 ； 修正型Schottky發射 ； 修正型Poole-Frenkel發射 ； Fowler-Nordheim穿透 ； 缺陷所造成穿透發射 ； 載子移動率退化 ； 庫侖散射 ； 表面平坦度散射 ； 聲子散射

並列摘要

When the channel length of the MOSFET is scaled below 0.1 μm and SiO2 gate oxide thickness below 1.5 nm, tunneling current will increase significantly. Zirconium oxide (ZrO2) is considered as a potential replacement of SiO2. In this thesis, metal-insulator-semiconductor (MIS) capacitors, and MOSFETs with ZrO2 gate dielectrics were fabricated. The temperature dependence of the conduction current for Al/ZrO2/p-Si MIS capacitors was studied. With the Al electrode biased negative, the conduction mechanisms are found to be: (1) modified Schottky emission; (2) modified Poole-Frenkel emission; (3) Fowler-Nordheim tunneling; and (4) tunnel emission of trapped electrons under different temperature and electric field regions. The related electrical parameters are extracted from the I-V characteristics.
The transistor properties were characterized. The IDS-VDS and IDS-VGS characteristics were measured. The degradation of electron mobility was studied. The temperature dependence of the electron mobility on vertical field reveals that Coulomb scattering, surface roughness scattering and phonon scattering of ZrO2-gated n-MOSFETs are more severe than that of SiO2-gated n-MOSFETs in the temperature range from 300 K to 420 K. Transverse soft optical phonons was used to explain the extra source of phonon scattering in ZrO2-gated n-MOSFETs.
The interface trapped charge density, the surface recombination velocity, and the minority carrier lifetime in the field-induced depletion region measured from gated diodes were 5.79×1012 cm-2-eV-1, 941 cm/s, and 1.32×10-6 sec, respectively. A comparison with MOSFETs using SiO2 and Ta2O5 gate oxides was made.
In summary, the conduction mechanisms in ZrO2 thin films were analyzed. The degradation of electron mobility was studied. The parameters in the field-induced depletion region of the ZrO2 gated diodes were obtained.

並列關鍵字

High k ； ZrO2 gate dielectric ； Conduction mechanism ； ohmic conduction ； modified Schottky emission ； modified Poole-Frenkel emission ； Fowler-Nordheim tunneling ； tunnel emission of trapped electrons ； mobility degradation ； Coulomb scattering ； surface roughness scattering ； phonon scattering

參考文獻

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