鑽石的區域選擇沉積法在場效發射陣列上的應用

Abstract

本實驗是利用微波電漿化學氣相沉積法,藉由超音波振盪鑽石粉末懸浮液 的前處理以提高成核密度,並使用甲烷-氫氣系為反應氣體源,在附有熱絕 緣層(非晶質二氧化矽)圖樣化(pattern)的矽基板上沉積區域選擇多晶鑽 石薄膜,因鑽石薄膜的區域選擇成長對於鑽石欲應用於電子元件上是一相 當重要的步驟,選擇性佳的鑽石薄膜可說是製作電子元件的首要基礎.將此 種選擇成長的方法,應用於場效發射陣列上.在本實驗中,將嘗試發展出一 種不同於一般場效發射陣列的新方法.此外,亦利用摻硼與摻磷的鑽石膜來 增加場效發射電流.由實驗結果得知,鑽石的選擇成長可以利用圖樣化後的 二氧化矽當作遮蔽物(mask).試片先經由鑽石懸浮液的超音波振盪後,將其 置於緩衝液(BOE)數秒鐘,以除去二氧化矽薄層及其成長在薄膜上之鑽石晶 種.再將其置於甲烷-氫氣系的系統中成長,即可得選擇性良好的鑽石薄膜. 另一方面,本實驗也嘗試將使用上述之方法製作選擇性良好的多結晶鑽石 顆粒陣列可推廣至場效發射陣列的應用上.場效發射陣列的工作原理和陰 極射線管相同,但是它並沒有笨重的高壓電子槍,也不需要液晶顯示器的背 光設計,祇需使用低壓射極陣列激發磷質照亮螢幕,所產生的對比程度較液 晶顯示器為低.而鑽石因具有負電子親和力所以較一般的金屬鍍層在相同 的工作電壓下會大大提供了工作電流.因此,鑽石應用在場效發射陣列將是 未來研究發展上大家所認定的主流.場效發射陣列的電流-電壓值(Ie-Va) 與鑽石膜的品質有很大的關係.當鑽石薄膜的品質較佳的時候,得到的電流 值較小;也就是說,品質較差的鑽石薄膜其電流值相對較大.但是,品質較差 的鑽石薄膜經高電壓且長時間的時效下,發現其電流值會隨測量時間的增 加而有逐漸衰退的現象,而品質較佳者則會維持在某一定的固定值,不會有 太大的改變.此結論告訴我們,如果要實際將鑽石薄膜應用在場效發射陣列 上,必須要被覆品質較佳的鑽石薄膜,雖然其電流值較小.此外,吾人亦發現 圖式的陣列模樣與形狀的改變也會影響場效發射陣列的電流.吾人推測,具 有負電子親和力的鑽石(111)面較易在有尖銳的基板上成核;(111)面愈多, 其電流值愈大.同時,經摻硼和摻磷的鑽石薄膜因為可額外提供的電洞或電 子,所以其利用在場效發射陣列上的電流值比沒有摻雜的鑽石膜大. Modern electronic applications demand diamond films with selected growth patterns.Film patterning is one technique used to fabricate such devices.In this thesis,we present two new processes for producing field emitter display tips coated with diamond synthesized using microwave plasma chemical vapor deposition method(MPCVD).We also report on fabricating impurity doped diamond to get larger emisson currents.Our results indicate selective diamond growth can be achieved using SiO2- masks.We used masks of different sizes and shapes on Si(100) substrates.We first lithographically patterned and chemically etched SiO2 layers in buffered solutions(HF:NH4F:H2O=3:6:10).We then used ultrasonic agitation with diamond powder and shallow etching of SiO2 masks to remove diamond nuclei from the masks. Finally,we grew diamond films using CH4-H2 gas mixtures, obtaining excellent selectivity.Upon investigating the Current- Voltage(Ie-Va)characteristics of the diamond-coated field emitter arrays,we found that those with good quality diamond films exhibited low but stable current intensities,and those with poor quality films exhibited high intensities that tended to decay over time.In general,the better the film is,the lower the current;the poorer the film is,the higher the current.We thus determined using higher quality films to be desirable,even in spite of their lower current.We also found that shape influenced current emission.Trench-shaped devices produced higher currents than either square-shaped or circular ones.We attributed this to (111) surface nucleation tendencies toward negative electron affinities present on prominent substrate features;e.g.,protruding sharp edges and apexes;the greater the (111) surface areas,the larger the currents.Since extra electrons or holes would be present in impurity-doped diamond films,the Current-Voltage(Ie-Va)characteristics of those films could be expected to differ from those of undoped films.So, boron-doped and phosphorus-doped films were introduced among the field emitter arrays and secondary ion mass spectroscopy(SIMS), Raman spectroscopy,and scanning electron microscopy(SEM)were used to examine these films.