新穎高介電常數材料與奈米微晶粒非揮發性記憶體之研究

Abstract

此論文製作許多不同的非揮發性快閃記憶體，將使用數種材料、不同的製程方法及結構來製備捕陷電荷層，來取代現今傳統氮化矽 (Si3N4) 材料。再用不同的寫入/抹除的操作方式，在低電壓下來操作快閃記憶體。以達成電荷捕捉效率佳、有快速的寫入/抹除速度、大的記憶窗口、儲存資料持久性、以及寫入、清除操作造成的性能退化少的非揮發性快閃記憶體。 首先，我們利用氧化鉿 (HfO2) 奈米微晶粒作為捕陷電荷層來製作新潁的SONOS型非揮發性快閃記憶體。此氧化鉿奈米微晶粒快閃記憶體在一萬次的寫入/抹除下，還是擁有好的儲存資料持久性、以及寫入、清除操作造成的性能退化少。其電荷儲存方式可以很區域性，使其一個單元儲存2個位元，並具有高密度之優點，可用於相關記憶體及半導體產業中。 再者，利用氧化鉿 (HfO2)薄膜作為捕陷電荷層隨著後處理溫度的不同來製作SONOS型非揮發性快閃記憶體。我們發現到隨著退火的溫度愈高，記憶窗口愈大而儲存資料持久性愈差且寫入、清除操作造成的性能退化變多了。此為高溫下結晶額外產生的淺能量的捕陷電荷所造成。之後我們也討論了溫度變化，以及其記憶體在一般操作時和其旁元件的電性影響。 接著，我們使用三種高介電常數材料成功的製作出了SONOS型非揮發性快閃記憶體於低溫多晶矽薄膜電晶體上，材料包含氧化鉿，氧化鉿矽化物以及氧化鋯矽化物。我們在其低溫製程中，達成電荷捕捉效率佳、有快速的寫入/抹除速度、大的記憶窗口、儲存資料持久性、以及寫入、清除操作造成的性能退化少的非揮發性快閃記憶體。而且，我們也成功的設計一個單元儲存2個位元的記憶體操作。 在論文的最後，我們製作出五十奈米的氧化鉿 (HfO2) 奈米微晶粒記憶體在SOI的晶片上。此可以完全和現今CMOS的製程互相配合，來製作電荷非常有區域性的記憶體。如此一來，我們可以把現今的非揮發性快閃記憶體來縮小到七十個奈米以下，在次世代的小線寬記憶體的應用上將會完善。

In this thesis, we design various nonvolatile memory with a high-k charge-trapping layer and nanocrystals. This high-k layer replaces the silicon nitride layer in the SONOS structure. Different program/erase methods are also proposed for low power applications. This nonvolatile memory structure will have superior characteristics in terms of considerably large memory window, high speed program/erase, long retention time, and excellent endurance. First, we present a novel nonvolatile SONOS-type flash memory that was fabricated using hafnium oxide (HfO2) nanocrystals as the trapping storage layer. These HfO2 nanocrystal memories exhibit excellent data retention, endurance, and good reliability, even for the cells subjected to 10k P/E cycles. These features suggest that such cells are very useful for high-density two-bit nonvolatile flash memory applications. Then, we demonstrate the effect of the post-deposition annealing for the HfO2 trapping layer on the performance of the SONOS-type flash memories. It was found that the memory window becomes larger while the retention and endurance characteristics get worse as the annealing temperature increases. This was ascribed to the larger amount and the shallower energy levels of the crystallization-induced traps as compared to the traps presented in the as-fabricated HfO2 film. Finally, in the aspect of disturbances, we show only insignificant read, drain and gate disturbances presented in the three samples in the normal operation. Next, we have successfully fabricated SONOS-type poly-Si-TFT memories employing three kinds of high-k dielectrics, including HfO2, Hf-silicate and Zr-silicate, as the trapping layer with low-thermal budget processing. It was demonstrated that the fabricated memories exhibit good performance in terms of relatively large memory window, high program/erase speed (1ms/10ms), long retention time ( >106s for 20% charge loss) and negligible read/write disturbances. In particular, 2-bit operation has been successfully demonstrated. Finally, we demonstrate 50nm nonvolatile HfO2 nanocrystal memory on SOI wafer. With this technique, which is fully compatible to current CMOS technologies, to form the very local HfO2 nanocrystals for the application of the nonvolatile flash memories. For aggressively scaling the conventional nonvolatile floating gate memories below sub-70nm node, we can successfully achieve the nano-devices for the application in the next-generation nonvolatile memories