微量分子污染對元件特性之影響

Abstract

空氣中分子的污染包括的範圍相當地廣泛，常見的為:揮發性的有機分子、金屬離子及無機分子等多種微污染物，而這些通常來自於無塵室裡的建築材料、儀器設備或過濾系統的濾網所揮發出來。所以在本論文中我們將找出現在或未來無塵室中最大量的微污染分子種類並且試著去隔離或減少它，然後更進一步的探討微污染分子對於元件特性的影響。 一般而言，空氣中污染分子所造成的影響有:薄閘極氧化層的劣化,氧化層成長速率的改變，硼的微量摻雜及深紫外光光阻的變質等等。而無塵室中所使用的玻璃纖維濾網一般須藉由有機黏膠來固定濾網纖維及填補縫隙增加過濾效果，不過由於空氣中微量酸性氣體的腐蝕，這將使濾網本身成為微分子污染的污染源並且對元件特性造成影響。 實驗中我們利用自製的迴風槽，並且更換不同種類的濾網以模擬不同的無塵室環境，為了更明顯的比較出新型鐵氟龍材質濾網及玻璃纖維濾網的差別，就在迴風槽內加入約1ppm的氫氟酸氣體。然後量測空氣中微分子污染的含量，以GC/MS、Ion Chromatograph 及ICP-MS分別進行有機分子、無機離子跟金屬離子的分析，此外我們也用TRXRF、SIMS及TDS-APIMS來分析附著在晶圓表面金屬離子，硼的微量摻雜以及有機分子種類跟含量。當空氣中污染分子的含量及種類已知後，我們再藉由實際製作薄氧化層的MOS電容元件以了解其對元件特性的影響，在此我們刻意在清洗晶圓和成長薄閘極氧化層前暴露在不同的環境下讓微污染分子能附著在晶圓表面，而藉由電性量測如: J-E、 Qbd 和C-V等方法來評測元件電特性的改變。 由實驗結果證實了空氣中微量的污染分子確實會對元件造成的影響，並且可以發現到:在玻璃纖維濾網下曝露的晶圓表面附著了更多的有機污染，而MOS電容元件的氧化層劣化將使得漏電流上升和崩潰電壓下降，以及硼的微量摻雜發生；然而在新型鐵氟龍(PTFE)濾網下則無劣化的情形產生，此外我們也針對化學濾網的過濾效果加以評測，發現化學濾網將可過濾掉有機及無機的微污染分子。 所以由本實驗發現新型鐵氟龍(PTFE)材質的濾網並不會釋出微污染分子且其與化學濾網的組合將提供我們優良的超大型積體電路製造環境。

AMC is the outgassing of construction materials, equipments, or filter itself, and covers a wide range of contaminations, including volatile organic compounds, metallic and inorganic species [2]. In our thesis, we will find out what kind of contamination is the main quantity in present or future clean room and try to isolate or eliminate it. Then we can discuss its influence on device performance further. Generally, the AMC can cause the changes of oxide growth rate, damage thin oxide quality, trace boron doping, and effect deep UV photoresists. Because Low-Boron glass fibers need mix some binders, which mainly consist with acrylic fibers, to reduce the gaps between fibers and to increase particle-isolating ability. The trace acid atmospheres, however will corrode binders, make filter itself be the organic compounds contamination source and influence device reliability. A specially designed clean bench with different ULPA filter modules was used to supply different kinds of environment. In order to obviously compare the difference of Low-Boron glass fiber filter and NEUROFINE PTFE filter, we add 1ppm HF Vapor gas into clean bench for simulating corrosion of glass fibers and organic binders. Then measuring the quantities of AMC, the AMC was analyzed by GC/MS, Ion Chromatography, and ICP-MS to detect organic compounds, inorganic ions and metallic ions, respectively. And then the metallic ions on wafer were analyzed by TRXRF and SIMS method, while the organic compounds were analyzed by TDS-APIMS method. After sampling, we also fabricated MOS capacitor devices and measure its electrical performance to evaluate the actual effects from AMC. Between RCA cleaning and thin gate oxide growing, the devices were exposed in different environments to absorb AMC on wafer. After manufacturing, we measured the leakage current density (J-E), V-ramp stress test (Qbd) and C-V to evaluate the changes of device performance and reliability. As the results of experiments, we proved that AMC really affect the device performance. There are many organic compounds and metallic ions absorbing on wafer surface when exposing under Low-Boron glass-fiber filter. Then it produces many defects in thin gate oxide of MOS capacitor device, which will increase leakage current increasing, decrease breakdown voltage and trace boron doping. But the NEUROFINE PTFE filter will not. Besides ULPA filter modules, the chemical filter is also evaluated in effective ability. Finally, we consider that NEUROFINE PTFE filter will not be the source of AMC, and the combination of NEUROFINE PTFE filter and chemical filter will have excellent control ability of AMC in future ULSI manufacturing environment.