摻雜不同濃度的硼在金屬誘發結晶前對矽奈米晶SONOS記憶體的影響

Abstract

金屬誘發側向結晶的技術是利用金屬可在低溫下控制結晶的位置使非晶矽重新結晶為多晶矽。Hayzelden在1992年發現鎳金屬具有兩個優點。一個是快速遷移的特性；另一個是鎳的矽化物和結晶的矽有較小的晶格常數誤差。因此金屬誘發側向結晶中的金屬常常使用鎳。為了得到更大的結晶的晶粒，使晶格缺陷減少並讓載子可以更快速的移動，許多方法針對加大結晶晶粒做研究。在金屬誘發側向結晶前摻雜硼是否能幫助鎳金屬更快速的遷移至今仍是一個具爭議性的議題。支持的團隊認為硼可以降低鎳的矽化物形成的能量並修補結晶矽和鎳的矽化物0.4%的晶格常數誤差，因而可加快鎳及其矽化物遷移，使得結晶更有效率且得到較大的結晶晶粒。然而，反對的團隊認為在金屬誘發側向結晶前摻雜硼，硼會是一個干擾因子阻礙鎳金屬側向遷移，導致結晶速率緩慢以及晶粒變小。 我們好奇硼是否真的能幫助金屬鎳結晶。因此在SONOS記憶體的通道中應用金屬誘發側向結晶的技術，並在結晶前摻雜不同濃度的硼 (〖5*10〗^14 〖cm〗^(-2),〖1*10〗^15 〖cm〗^(-2)) 做比較。這兩組樣本，我們會分別從物性以及電性做討論，包括XRD分析、電導值、載子寫入和抹除速度、漏電流比較、源極和集極電阻值量測、可靠度探討。 在此研究中我們證實在SONOS記憶體通道中先摻雜硼會幫助鎳擴散，使結晶的晶粒更大。摻雜硼濃度〖1*10〗^15 〖cm〗^(-2)的樣本金屬側向結晶長度為摻雜硼濃度〖5*10〗^14 〖cm〗^(-2)的兩倍；對比T. Ma發現當摻雜濃度為〖3*10〗^15 〖cm〗^(-2)時金屬側向結晶長度為濃度〖3*10〗^14 〖cm〗^(-2)的兩倍的結果，在SONOS記憶體中我們可將硼的濃度下修正至〖1*10〗^15 〖cm〗^(-2)。此外，摻雜硼濃度較高的樣品具有較大的晶粒、不同尺寸下有較小的變異性、較高的載子遷移率、較快的寫入和抹除速度、較低的源極和集極電阻值，較長的資料保存時間。本論文中我們將逐步的檢驗並證明硼幫助鎳擴散的現象，且此現象會提升SONOS記憶體物性以及電性的性質。

Metal Induced Lateral Crystallization (MILC) technique has been purposed due to metal can be used to cause crystallization at controlled locations with low temperature. In 1992 Hayzelden et al. found nickel shows two advantages. One is fast migration property. The other is small lattice constant mismatch between NiSi_2 and crystal silicon (c-Si). So nickel is common used as MILC source in experiments now. Large crystal grain size can reduce defects and enhance carriers mobility, many research focus on how to increase grain size. But boron enhanced nickel crystallization is a controversial issue. The support groups think boron can reduce 〖NiSi〗_2 formation energy and modify lattice constant mismatch between crystal silicon and 〖NiSi〗_2 resulting in 〖NiSi〗_2 faster migration, longer metal induced lateral crystallization (MILC) length and larger grain size. However, the opposite groups think boron atoms are interrupt factor for crystallization. They believe doping boron with MILC process would block nickel crystallization causing short MILC length and small grain size. Weather boron enhance or reduce nickel diffusion is what we curious. So the experiments are designed by different boron doping concentration (〖5*10〗^14 〖cm〗^(-2),〖1*10〗^15 〖cm〗^(-2)) samples with MILC crystallization on SONOS memories. We discuss this effect in physical and electrical parts, including XRD analysis, conductance measurement, program/erase speed, source/drain resistance extraction, GIDL current, retention and endurance researches. The boron enhanced nickel diffusion effect is successfully proved in SONOS memories. We also found with double difference of boron doping concentration (〖5*10〗^14 〖cm〗^(-2),〖1*10〗^15 〖cm〗^(-2)) leading to double difference of grain size. Therefore, T. Ma et al. found MILC length double increase effect between boron dosages 〖3*10〗^14 〖cm〗^(-2) and 〖3*10〗^15 〖cm〗^(-2) can be modified to 〖1*10〗^15 〖cm〗^(-2) in SONOS memories. In addition, the high boron doping device shows better performance presenting large grain size, small variation, high mobility, fast program/erase speed, low resistance and long retention time. In this thesis, we gradually examine and verify boron enhanced nickel diffusion phenomenon which can promote SONOS memories physical and electrical characteristics.