矽在氫氧化鉀溶液的電化學蝕刻和保護層的研究

Abstract

使用電漿助長型化學氣相沉積(PECVD)，在矽晶片上成長一層 500nm 的氮 化矽，研究氮化矽經過不同溫度回火後其阻擋氫氧化鉀的效果。使用紅外 線光譜儀和歐傑電子光譜儀來量測氮化矽的組成，紅外線光譜儀量測得知 ，氮化矽存在三個主要 (Si-N)s , (Si-N)w , (N-H)s的鍵結， 歐傑電子 光譜儀量測得知， 氮與矽的比值為 2 是氮豐富的氮化矽 。 由實驗結果 ， 回火在600℃的氮化矽其阻擋氫氧化鉀的效果不錯。 在氮豐富的氮 化矽中存在很多未飽合鍵 (K-center) ， 當回火在800℃以下時 ， (Si- N)s 的鍵結濃度增加 ， 而且氮化矽的厚度亦減少，所以氮化矽的結構變 密集，這就是氮化矽經過回火後其阻擋氫氧化鉀效果變好的原因 。但回 火在1000℃時，由於應力的產生，其阻擋氫氧化鉀的效果反而變差。 再來， 不同的氫氧化鉀濃度和溫度下 ， 量測矽晶片蝕刻速率和表面的 平坦度，當溫度升高時， 蝕刻速率亦上升， 由假的光罩模型中得知，其 表面的平坦度亦變差。最後，使用三極電化學蝕刻停止的方法， 精確得 到一個薄膜。 A 500nm silicon nitride film are grown by PECVD on n-type silicon wafer. We have studied the anneal behavior of PECVD nitride film in the KOH solution. Thecomposition of annealing of PECVD nitride film is determined by Fourier transform infrared spectroscopy (FTIR) and Auger electron spectroscopy (AES). FTIR spectra reveal the presence of (Si-N)s, (Si-N)w and (N-H)s bonds. AES indicating a ratio of N/Si is about 2 and it is the N-rich nitride film. The nitride film is also good passivation in the KOH solution after annealing at 600℃. A dangling bond termed K-center is dominant charge trapping center in N-rich nitride film. The height of stretching N-H mode decreases after annealing. Due to the K-center, the height of stretching Si-N mode increases after annealing below 800℃ .We also find that thickness of the nitride film decreases after annealing. So the structure of the nitride film becomes dense. This is the main reason that annealing of PECVD nitride film is good passivation in KOH solution. But annealing at 1000℃, due to the stress, the nitride film is left off in KOH solution. Then, we determine the etch rate and roughness for various KOH concentration and temperature. It is clear that the etch rate increases when raising the temperature at the same concentration. From pseudomasking model, the roughness increases when rasing the etch rate. Finally we precise obtain a membrane by using etch- stop system.