高介電係數介電質在金屬-絕緣層-金屬結構電容上的應用

Abstract

由於製程技術的快速發展再加上元件尺寸不斷的縮微，使得高介電係數介電質材料的應用已受到很大的注意。目前，在高介電係數介電質材料的領域中已投入非常多的研究和進展。而此技術亦獲得了相當的成功。在積體電路方面，電容面積往往消耗了大部分的晶片面積，且電容值也隨著操作頻率的不同而變化。因此，在未來射頻積體電路的應用上，使用高介電係數介電質材料以縮小電容面積進而增加晶片中電路的密度以及在高頻時維持電容特性是必須面對的問題。而使用具有高介電係數介電質、高傳導電極和低寄生電容特性的金屬-絕緣層-金屬電容將成為改善射矽頻積體電路特性的一個重要關鍵，尤其在無線通訊射頻積體電路。 在此研究中，我們發展出了一種沈積介電薄膜的方法，先利用物理氣相沈積的方式蒸鍍金屬薄膜，接著將其氧化並在400 oC的溫度下回火。應用此方法，我們使用氧化鉭鋁（AlTaOx）介電質材料製造適用於高頻量測且具有高電容密度特性的金屬-絕緣層-金屬電容。為了研究此元件在高頻範圍的電容特性，而量測其高頻散射參數。接著，運用數學模擬軟體去模擬在不同頻率下的等效電路並粹取出其所具有的電容大小。從元件的量測結果顯示得到非常高的電容密度值10 fF/um2、非常低的電容下降率從一萬赫茲（10K Hz）到三百億赫茲（30G Hz）以及低於0.03的正切損耗。同時也從十億赫茲（1G Hz）所量測的散射參數計算得到低於600ppm的電壓相關電容值。由數據可知，使用這項製程方法，此高介電質金屬-絕緣層-金屬結構電容可適用於操作在射頻範圍的高精密積體電路上。此外，此製程方法也與目前的超大型積體電路後段製程技術相容。

Process technology improving rapidly and the devices are continuous scaling down. The application of high-k dielectric materials has attracted a great attention. At present, there are large amounts of researches and developments for high-k dielectric materials and the high-k technology has reached a colossal success. In integrated circuits, the total capacitor area usually consumes a large portion of the whole chip size and the capacitance will change as different operating frequency. For this reason, there will be a required challenge in the application of radio frequency (RF) ICs for using high-k dielectric materials to make capacitor area small, further increase the circuit density in chip and maintain the capacitance characteristics at high frequency (or RF). The capacitor using MIM structure and high-k dielectric will play a very important and critical role in order to improve the property of RF silicon integrated circuits or wireless communication RF integrated circuits, which is due to the high conductive electrode and the low parasitic capacitance. In this study, we have developed the approach to deposit high-k dielectric films. We deposited the thin metal film using PVD followed by subsequent oxidation and annealing at 400 oC. Applying this method, we have fabricated higher density MIM capacitors using high-k AlTaOx dielectrics and suitable for RF measurement. In order to investigate the characteristics of capacitors at RF region, the S-parameters is measured. The capacitance of the device at different frequencies was extracted from equivalent circuit model by simulation software. From the measurement of devices, a very high capacitance density of 10 fF/□m2 is obtained, with small capacitance reduction of 5 % from 10KHz to 30GHz, low loss tangent < 0.03. Small voltage dependence of capacitance < 600 ppm, mathematical derived from S-parameters, is obtained at 1 GHz, which ensures this MIM capacitor useful for high precision circuits operated at RF regime and process compatible with existing VLSI back-end integration.