高質液相沈積絕緣膜暨其微污染膜質探討

Abstract

隨著半導體製程對空氣中微污染的影響日益注重，關於微污染對元件特性所產生的退化將是我們要盡力避免的。我們利用迴風槽來模擬無塵室內的迴風系統，並更換槽內的濾網模組，透過製作MOS電容測試結構，在氧化層成長前於迴風槽內作暴露，經由氧化層的漏電流密度，崩潰電場強度及崩潰電荷等來探討微污染對氧化層可靠度的影響。由實驗中比較的三種濾網發現，新型的鐵氟龍(PTFE)濾網較其餘兩種濾網：低硼元素玻璃纖維濾網(Low Boron Glass-Fiber filter A/B)為優秀。透過電性分析我們可以看出相同時間內，元件暴露在新型鐵氟龍(PTFE)材質的濾網下仍能較其它兩種濾網保持較佳的漏電流密度以及崩潰電場而不至於過度退化。 為了更準確評估微污染對元件特性的影響，我們必須採用更高品質且特性更好的液相沉積氧化膜。我們採用了的新式技術是以蒸餾法製備高純度的六氟矽酸溶液，並使用來自日本的高純度二氧矽粉末(99.9999%)，這種工業級的粉末與之前所使用的醫藥級二氧化矽(99.99%)相較之下，雜質的含量更大幅降低。因此可預期的，經過蒸餾法所收集到的六氟矽酸溶液配合高純度二氧化矽粉末的使用，確實可以看出電特性的改善。漏電流密度明顯的降低，以及崩潰電場小幅增加。另外，蒸餾前配製溶液的比例改變，不但會影響蒸餾時的蒸餾速率，對於之後成長液相沉積氧化膜時的沉積速率以及氧化膜的特性也有顯著的影響。由實驗中的觀察得到蒸餾前配製溶液中的二氧化矽比例越高，則蒸餾速率越慢，且在成長液相沉積氧化膜時的沉積速率也越慢，但所成長的氧化膜特性卻越好。經過特殊的方法分析蒸餾所得的六氟矽酸濃度以及實驗中的過程觀察，在此一併討論可能的反應機制並嘗試提出解釋。

As we pay more attention to effects of AMC in semiconductor manufacturing process, degradation of devices characteristics due to AMC should be avoided. We use the specially designed clean bench with different filter modules to supply different kinds of environment. In order to evaluate effect of AMC on oxide reliability, we expose samples in CB before LPD oxide film deposited. We fabricate MOS capacitor to measure the leakage current density (J-E), V-ramp stress test (Qbd) and C-V to evaluate the changes of device performance and reliability. After our experiments, we have found that NEUROFINE PTFE filter performs better than Low-Boron Glass-Fiber Filters (A/B). Through the analysis of electrical characteristics, samples exposed under NEUROFINE PTFE filter have higher breakdown field and lower leakage current density than those exposed under Low-Boron Glass-Fiber filters (A/B) in the same exposure time. In order to evaluate effects of AMC on devices characteristics precisely, we must use high quality and high performance low temperature LPD oxide films. We propose a novel LPD process by distilling high purity H2SiF6 solution. High purity SiO2 powder (99.9999%) form Japan is used, too. New industrial class SiO2 powder has fewer impurities than medical class SiO2 powder used before. It is expectable that using distilled H2SiF6 and high purity SiO2 powder can improve device electrical properties effectively. Leakage current density is lowered obviously, and breakdown field is slightly increased. Moreover, different ratios of pre-distilled solution will affect distillation rate and deposition rate very much. LPD oxide film quality has concern with the ratio, too. From experiments, the higher SiO2 proportion in pre-distilled solution, the lower distillation and deposition rate but the higher quality of LPD oxide film is observed. We also propose a reasonable mechanism to explain distillation method by analyzing the concentration of H2SiF6 and observation during whole process in this thesis.