本研究使用鎢靶和碳靶，以共濺鍍法製備W1-xCx和Wtop/C/Wbottom，二種「摻碳鎢薄膜」。搭配SiO2/p-Si成為金屬-氧化物-半導體(簡稱MOS)電容器，並進行900 °C真空退火一小時，探討各種條件閘極電極之材料性質及電性表現。
本實驗利用電子微探儀對W1-xCx薄膜進行定量分析；使用低掠角X光繞射儀對W1-xCx薄膜進行薄膜晶體結構分析；以X光光電子能量分析儀對W1-xCx薄膜進行化學鍵結分析；利用穿透式電子顯微鏡及歐傑電子能譜分析儀對MOS疊層結構進行微結構及成份深度分佈分析；並對MOS電容器進行電容-電壓曲線及電流密度-電場曲線的量測。
材料分析結果顯示，W1-xCx薄膜在初鍍時為非晶型態，在經過900 °C真空退火後，轉變為α-W和W2C共存。而成分方面，則藉由改變靶材的濺鍍功率，成功將W1-xCx薄膜中的碳含量控制在0～20%之間。不論是穿透式電子顯微鏡或是歐傑電子能譜分析的結果，皆顯示出MOS電容器的疊層結構在真空退火前後，均相當穩定，並無明顯的變動。
電性量測分析結果顯示，初鍍的W1-xCx薄膜做為閘極電極時，其等效功函數（Φm,eff）會隨著碳含量的比例增加而上升，推測是由於碳的電負度較高，可提升鎢對其電子的束縛力，使其不易脫離至真空能階，故功函數因而提高。而初鍍的Wtop/C/Wbottom薄膜做為閘極電極時，當Wbottom的厚度越小時，其等效功函數會降低，推測是由於較高電負度的碳，聚集於金屬閘極/介電層界面，使得界面的電子均勻分布不均，形成「碳誘發偶極」，不僅改變了能帶圖的排列，也同時改變了等效功函數。而真空退火後的MOS電容器則出現了電容-電壓曲線扭曲的現象，因而無法針對退火處理後的「摻碳鎢薄膜」進行等效功函數的擷取。
本研究首次發現在「摻碳鎢薄膜」中，改變功函數的機制有二種，且同時存在，主要是看何者佔優勢。經由精確的控制W1-xCx的成分和Wbottom的厚度，絕對可以同時滿足NMOS和PMOS的需求。

Carbon-added tungsten thin films of two configurations, W1-xCx and Wtop/C/Wbottom, were fabricated by co-sputtering tungsten and carbon targets. The metal-oxide-semiconductor (MOS) capacitors of carbon-added tungsten/SiO2/p-Si layered structure were fabricated, in order to investigate their material and electrical characteristics.
The composition of W1-xCx thin films is examined by electron probe X-ray microanalyzer (EPMA). The crystal structure of W1-xCx thin films is identified by grazing incident angle x-ray diffractometer (GIAXRD). X-ray photoelectron spectroscopy (XPS) is applied for chemical bonding analysis of W1-xCx thin films. Transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) are employed to analyze the microstructure and compositional depth profiles of the MOS capacitors, respectively. The C-V curves and J-E curves are measured to find the electrical characteristics of MOS capacitors.
Based on the EPMA results, the carbon content of W1-xCx thin films can be modulated from 0 to 20%, by controlling the sputtering power on the targets. According to the X-ray diffraction patterns, as-deposited W1-xCx thin films are amorphous. After vacuum annealing at 900 °C, the diffraction patterns show the coexistence of α-W and W2C phases in W1-xCx thin films. TEM and AES results indicate that there is no significantly structural change between as-deposited and annealed MOS capacitors.
The effective work function of the as-deposited W1-xCx thin films increases with increasing carbon content. Incorporation of carbon atoms enhances the electron binding energy for tungsten atoms because tungsten lose part of electrons to carbon due to its higher electronegativity than that of tungsten. In as-deposited Wtop/C/Wbottom system, the effective work function decreases by reducing the thickness of the Wbottom layer. The carbon-induced dipoles are responsible for this case. The MOS capacitors after annealing showed distorted C-V curves; therefore, it is impossible to extract effective work function in this situation.
In this work, we demonstrated that there are two mechanisms to explain the modulation of the effective work function of carbon-added tungsten thin film. Actually, these mechanisms should coexist in the carbon-added tungsten thin film, and the way of adding carbon determines which mechanism is dominated. By precisely controlling the carbon content in W1-xCx and the thickness of Wbottom, the effective work function will meet the requirement of PMOS and NMOS.

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