Abstract
半導體與電解液接觸造成半導體能帶圖彎曲的情形與半導體/金屬接觸時 能帶彎曲的情形相類似，因此我們利用元件物理中半導體/金屬接觸的能 帶彎曲理論來考察半導體與電解液接觸後的能帶圖彎曲變化，由該能帶圖 彎曲的情形來探討半導體電極的電化學行為。本論文並且利用電化學的技 術開發出矽半導體在KOH與NH4OH電解液中的選擇性蝕刻技術，同時也開發 出選擇性無電鍍鎳的技術。 用半導體與金屬接觸時能帶彎曲的理論研究 矽半導體在KOH電解液中能帶圖彎曲的情形，利用測量半導體的開路電壓( OCP)與平坦電壓(flatband voltage)來作為繪製能帶圖的依據。n-Si在2 M KOH電解液中的平坦電壓是利用光敏感法(photocurrent susceptivity) 測量得為 -1.04 V/SCE，其開路電壓-1.25 V/SCE，根據這兩個數據我們 繪製 n-Si與2M KOH接觸達到平衡後的能帶圖。由該能帶圖可以發現n-Si 的能帶是向下彎曲的情形，並使得n-Si表面呈現電子累積(electrons accumula- tion)的狀態，因此為歐姆接觸的特性，該特性由電壓-電流 (證。p-Si與2M KOH接觸後達到平衡的能帶圖則顯示其表面是電洞空乏( ho- le depletion)的狀態，並且表現出蕭基二級體(Schottky diode)的 行為，此行為也由電壓-電流圖得到驗證。由於這兩個能帶圖的建立，使 得我們能夠了解矽半導體在KOH中的電化學現象與載子的傳遞機構，同時 也讓我們能夠解釋高濃度摻雜的蝕刻截止的原因。利用n-Si與p-Si在電化 學性質上的不同，我們開發出在矽晶片上選擇性蝕刻技術。從矽晶片在 KOH電解液中的電壓-電流圖中可以發現n-Si與 p-Si的開路電壓(OCP)與鈍 化電壓的位置都不一樣，因此能夠外加一個位於n-Si與p-Si鈍化電位之間 的偏壓 (bias)，在這個偏壓下n-Si已經開始發生鈍化反應，而p-Si仍然 可以進行蝕刻反應，使得具有選擇性的蝕刻得以進行。此外由於n-Si與p- Si在不同的外加電壓下蝕刻速率不同，我們成功的設計出「突出」或「陷 入」的3D元件。 The energy band model of semiconductor/electrolyte was used to explain the electrochemical reaction of a semiconductor The electrochemical technology was then applied to the device fabrications which include selective etching of p-n junction Si in aqueous KOH and in aqueous ammonia and selective electroless nickel deposition on to p-n junction Si substrate. The energy band diagram of n-Si in aqueous 2M KOH was constructed by the measured open circuit potential (OCP) and the flatband voltage. A photocurrent susceptivity method was proposed to determine the flatband voltage.The transport of these carriers which participate in the electrochemical reaction can be explained by the energy band diagram.The etch-stop for heavily doped Si is attributed to the enhanced growth rate of oxide film under high carrier concentration. Since the passivation potential and open circuit potential are different for p-Si and n-Si in aqueous KOH, selective anisotropic etching can be achieved by applying a proper external potential. Both sunken and protruded cross- patterned n-type zone on a p-type substrate have been fabricated by applying proper potential on the p-n junction. A systematic method to etch either the n-type zone or the p-type zone on silicon substrate in ammonia was selectively proposed. Very good etching selectivity can be achieved with proper applied external bias. Smooth and hillock-free etched surfaces are achieved. The energy band model of Si/electroless nickel deposition solution was used to explain the mechanism of electroless nickel deposition on n-Si and p-Si. In the p-n junction Si, the electroless nickel deposition occurs only on the n-type zone. Hence, selective electroless nickel deposition on the p-n junction Si was successfully performed.The mechanism of selective electroless nickel deposition on the p-n junction Si was discussed