光電化學蝕刻反應下n型（100）矽與氫氟酸溶液界面間之能帶圖研究

Energy Bands for the Interface between n-type Si (100) and HF Solution in the Photoelectrochemical Etching Reaction

本研究之目的在建立不同照光強度下n-Si /HF界面平衡的能帶圖，並配合不同偏壓下的光電流–時間曲線圖，推導出照光與偏壓對Si/HF電化學蝕刻系統之影響。n型矽／氫氟酸界面間能帶圖之建立，乃藉由量測在HF蝕刻液中n-Si的開路電位（Open circuit potential, OCP）與平坦電位（Flatband voltage; Vfb）後，依據半導體能帶中EF（Fermi energy）與Ec（Conduction band energy）、Ev（Valence band energy）的位置，而描繪出能帶定量關係圖。實驗結果顯示：在黑暗中施正偏壓於n-Si /HF系統，其電化學蝕刻速率極慢，此系統經照光後其電化學蝕刻速率會大幅提升；當光的功率固定時，蝕刻反應會隨正偏壓增加而加速，但施加的正偏壓超過一臨界範圍後，其蝕刻之反應速率維持定值，並不隨正偏壓的增加而加快。

The aim of this work is to construct an energy band diagram for the electrochemical etch of n-Si(100) in hydrofluoric acid in the absence and presence of illumination. Experimental measurements of the open circuit potential (OCP) and Flatband voltage (Vfb) were combined with theoretical calculation of the conduction band (Ec), valence band (Ev) and Fermi level energies (EF) to establish the band diagram. By means of diagrams established and kinetic data measured we successfully estimated the activation energy of the photoelectrochemical reaction and explored the singular and combinative effect of illumination and electrical bias on this reaction. The dissolution rate under an anodic bias of 0.250 VSCE was extremely low in the dark but it could be speeded up to a few tenfold when a lamplight from 15 to 45 W was illuminated. For systems illuminated at constant power, the etching rate increased to a plateau and leveled off with an increase of anodic bias.