奈米金屬鎳/鎳矽化物晶粒之非揮發性記憶體製程與研究

Abstract

在非揮發性金屬記憶體的研究方面，本論文所選取的金屬量子點材料為鎳及鎳矽化物。然而金屬的量子點記憶體在近年來受到矚目，其相對於傳統半導體材料用於量子點記憶體上，有諸多的優勢，其優勢包含低功率耗損、高密度的能階、沒有明顯的量子侷限效應(carrier confinement)、有效降低元件尺度、且可調變的空間大，因為隨不同的金屬有不同的功函數。除此之外，我們在選擇金屬的材料上，在線上製程中有其他的應用及良好的熱穩定度，是我們選擇鎳及鎳矽化物的一個主要的原因。 然而，我們在實驗中發現一些鎳量子點記憶體所存在的機制，我們合理的獲得一些結論去解釋我們的記憶體特性，發現其中存在兩種重要的機制，就是鎳金屬的擴散問題及其有機會與我們的介電質材料(氧化矽)作反應。此機制在高溫時便成不可忽略的問題，也是造成高溫時記憶體特性不佳的主要原因。 但在同時，我們也發現鎳矽化物的量子點記憶體卻可以改善在高溫時鎳量子點的問題，因為鎳層偏愛與矽反應成矽化物，所以並沒有殘存的鎳可以造成上述的問題，因此成功的獲得高溫的鎳矽化物量子點記憶體。此外，我們發現層積薄的矽(僅提供反應成矽化物)，可以較有效的控制量子點的大小及均勻性。最後，我們透過矽/鎳/矽的結構，去反應成鎳矽化物的量子點及上下的絕緣層，發現在氧化溫度800度時，獲得兩位元(two-bit)的記憶體特性。

We have studied experimentally and theoretically two kinds of nonvolatile metal nanocrystal memories: nickel nanocrystal memories and nickel-silicide nanocrystal memories. The metal nanocrystals memories come into notice as so many advantages. The advantages of metal nanocrystals over their semiconductor counterparts include low power consumption, higher density of states, smaller energy perturbation due to carrier confinement, stronger coupling with the channel, better size scalability, and the design freedom of engineering the work functions to optimize device characteristics. The reasons why nickel/nickel-silicide is chosen as the materials for the nanocrystals are the compatibility with current manufacturing technology of semiconductor industry and thermal stability of the nickel silicide. In our experiments, we would discuss some mechanisms about the nickel nanocrystals as memory storage medium. We obtained some conclusions to explain the memory effects for the different annealing temperatures. The two important mechanisms were nickel diffusion problem and the reaction between nickel and silicon dioxide. So these would be become the terrible problems as the high temperature processes. At the same time, we observed the nickel-silicide nanocrystal memories to improve the disadvantages of the nickel nanocrystal memories. The nickel film was only prepared to silicidation, so the high temperature processes were suitable for nickel silicide formation. The thin nickel/silicon film was exact to be controlled the dot size and observed good uniformity at the same time. However, another good result was obtained the one cell two bit memory from the silicon/nickel/silicon structure at 800℃ annealing.