一種利用鉿矽酸鹽結晶化形成的新穎氧化鉿非揮發性奈米晶體記憶體

Abstract

在本論文中，我們將研究一種關於在鉿矽酸鹽薄膜中形成氧化鉿奈米晶體的新穎技術。本實驗是利用在氬氣/氧氣的環境中，共同濺鍍高純度的鉿靶與矽靶來沉積鉿矽酸鹽薄膜。之後，薄膜進行高溫900 °C氧氣環境下熱退火處理，氧化鉿奈米晶體將在鉿矽酸鹽薄膜中結晶產生。其奈米晶體尺寸為7.8 nm而密度分佈為9.2×1011 cm-2。此外，我們也發現到奈米晶體的產生將造成表面崎嶇不平。當鉿矽酸鹽薄膜發生結晶現象時，薄膜中將分離出複晶氧化鉿和氧化矽，這是因為在薄膜中發生相分離的關係。從電性分析中顯示，在900 °C熱退火處理樣本中可獲得大的記憶窗口以及小的漏電流。這是因為在氧氣環境中高溫熱退火有助於形成奈米晶體和修補矽酸鹽薄膜中的氧空缺。此外，當增加所施加負閘極電壓時，有更多的電子注入並被奈米晶體補抓故可獲得更大的記憶窗口。本實驗中，奈米晶體記憶體是經由閘極注入電子來執行寫入操作。從900 °C熱退火處理樣本施予–1 mA/cm2定電流壓迫前與後的電流-電壓量測計算可得出其距心 等於2.2 nm和補抓電荷密度Qt為4.78×10-7 C/cm2。我們也發現當提高熱退火溫度將使距心減少以及補抓電荷增加。最後，我們利用Frenkel-Poole傳導來討論奈米晶體的傳導機制。結果顯示，900 °C沉積後熱退火處理樣本的等效阻礙高度 為0.684 eV。因此，我們相信經由鉿矽酸鹽薄膜發生結晶現象所產生的氧化鉿奈米晶體記憶體將是下個世代非揮發性記憶體最有可能的候選人之一。

We have investigated a novel technique to form the HfO2 nanocrystals in Hf-silicate film. The Hf-silicate films are deposited by co-sputtering the hafnium and silicon targets in Ar/O2 ambience. From the material analysis, we have found that the HfO2 nanocrystals with a size of 7.8 nm and a dot density of 9.2×1011 cm-2 are formed by Hf-silicate crystallization when it is annealed in O2 ambience at 900 °C. In addition, the surface roughness is dramatically increased when the nanocrystals are formed. When the Hf-silicate is crystallized, HfOx and SiOx (x<2) phases are separated, and the polycrystalline HfO2 are obtained. Therefore, we believe that the formation of nanocrystals is induced by the phase separation of Hf-silicate. The electrical characteristics of HfO2 nanocrystal memory are also investigated by measuring C–V and I–V curves. The wide memory window and low leakage current of the sample with 900 °C annealing are obtained because annealing in O2 ambience is helpful for forming nanocrystals and repairing the oxygen vacancies in Hf-silicate. Moreover, we have found that more electrons are injected into the nanocrystals as increasing the negative gate voltages to widen the memory window. Thus, the nanocrystal memory should be programmed by gate injection. The centroid ( ) of 2.2 nm and the trap charge density (Qt) of 4.78□10-7 C/cm2 are calculated by the double-IV measurement with CCS of –1 mA/cm2 for the sample with 900 °C annealing. We also find that is decreased and Qt is increased as raising the annealing temperature. Finally, the conduction mechanism of the nanocrystal memory is dominated by the Frenkel-Poole emission, and the effective FP barrier heights of 0.684 eV is extracted for the nanocrystals formed in 900 °C annealing. Therefore, the HfO2 nanocrystal memory formed by Hf-silicate crystallization should be one of the most promising candidates for nonvolatile memory applications.