高介電常數介電質的電性及其在元件上的應用

Abstract

由於元件尺寸的不斷縮微，閘極氧化層的厚度也必須隨之減少。然而，隨之而來的高閘極漏電流卻使電晶體的特性變差，並且使元件消耗的功率變大。因此，用高界電常數介電質取代傳統熱氧化層是無可避免的。雖然高界電常數介電質的使用能有效的減少閘極漏電流，但仍然有一些相關的問題必須解決。我們已經發展出一種沈積介電質的方法，先利用物理氣相沈積的方式蒸鍍金屬薄膜，再將其氧化及退火。利用這種方法，我們可以在高介電常數介電質下方先成長一層氧化鋁，這層氧化鋁不但可以解決介面氧化層的問題，同時能在介電質中加入一些鋁的摻雜，進而減少介電質的高溫結晶現象。在我們研究中，我們將氧化鋁鈦及氧化鋁沈積在矽基版上，並製作成可量測高頻特性的電容。為了瞭解其被應用為閘極介電質且被操作在射頻時的特性，我們量測了散射參數以及雜訊。運用數學模擬軟體，我們淬取出元件在不同頻率所具有的電容大小。結果顯示，氧化鋁以及氧化鋁鈦在某種厚度比時，具有和氧化矽相似的電容下降率，然而，就雜訊的部分而言，氧化鋁所具有的雜訊和氧化矽的相似，而氧化鋁鈦的較高。在定電壓應力後，漏電流的增加和雜訊的增加具有相同的趨勢，我們藉此可以推斷雜訊生成的機制。此外，我們也使用氧化鋁以及氧化鋁鈦製作高頻電容，量測結果顯示，雖然氧化鋁鈦可以使電容密度大為提升，但在高頻時，這個優點會因為氧化鈦所具有的介電常數下降特性而被抵銷。然而這個問題可以藉由調整氧化鋁和氧化鈦的厚度比來解決。因此，我們使用的這項製程方法，可以製作出適合射頻範圍所使用的介電質，此外它同時具有簡單，並且與現有製程技術相容的優點。

According to the continuous scaling of device, the thickness of gate oxide has to be reduced. However, the high leakage current degrades the performance of transistors and enlarges the power consumption of the devices. Therefore, the replacement of conventional thermal oxide with high k dielectrics is inevitable. Although utilizing high k dielectrics reduced the gate leakage current effectively, there are still some issues that we have to overcome. We have developed a approach to deposit high k dielectrics. We deposited the ultra thin metal film using PVD followed by oxidation and annealing. Using this method, we can deposit Al2O3 under the other high k dielectrics. This Al2O3 layer can not only prevent from the formation of interface oxide, but also provide Al-doping into high k dielectrics to reduce the high temperature crystallization. In this study, we deposited both Al2O3 as well as AlTiOx on Si substrate and fabricate the capacitors suitable for RF measurement. To investigate the characteristics of them used as gate dielectric at RF region, we measured the S-parameters and the noise figure. Using the simulation software, the capacitance of the device at different frequencies was extracted. The result indicates that Al2O3 and AlTiOx having some thickness ratio of Al to Ti, exhibits the similar capacitance reduction rate with SiO2. Form the point of view of noise figure, Al2O3 exhibits the similar noise figure with SiO2, but AlTiOx shows the higher noise figure than others. After constant voltage stress, the increase of leakage current tends to increase the noise figure. We can deduce the mechanism of noise generation. Besides, we also fabricated RF capacitors using Al2O3 and AlTiOx. The measurement results suggest that capacitors using AlTiOx exhibits higher capacitance density, but this merit is compensated by the capacitance reduction at high frequency. However, this issue can be overcome by tuning the thickness ratio of Al2O3 and TiO2. Therefore, using this approach, we can fabricate the high k dielectric that is suitable in RF application. More important, this approach is simple and fully compatible with current VLSI technology.