微污染與電漿製程對奈米電晶體元件特性影響

Abstract

在超大型積體電路中，電晶體元件的尺寸必須持續微縮以降低成本及提升元件特性，在奈米世代元件的研發上，電晶體的重要製程，包括微污染、閘極氧化層、超淺接面及銅製程等，都是元件製作成敗的關鍵。本論文主要研究微污染防治及電漿製程兩大主題，分別就潔淨室中微污染及電漿製程對奈米電晶體元件特性的影響，並分別提出改良的新式製程。

在微污染防治方面，首先我們架設一組清洗工作台，在工作台內裝置可更換的濾網模組，分別使用新的鐵氟龍材質空氣濾網與傳統玻璃纖維空氣濾網，探討兩種濾網對微污染的控制能力。在定性與定量分析工作台內微污染的成分及含量後，發現兩種空氣濾網皆可有效控制包括無機離子、有機離子及金屬等微污染物，但是傳統玻璃纖維空氣濾網由於內含黏著劑，在循環迴風下，產生了相關的有機污染物。另外，我們製作了金氧半電容元件來評測暴露在不同濾網下，微污染對元件閘極氧化層的影響，結果發現鐵氟龍材質空氣濾網相較於傳統玻璃纖維空氣濾網，可有效改善元件特性。

接著，我們在工作台內使用氫氟酸氣體加速實驗來模擬潔淨室中酸性氣體的腐蝕過程，鐵氟龍與玻璃纖維材質的空氣濾網，分別安裝在工作台內進行實驗以分析兩種空氣濾網的抗腐蝕能力，空氣採樣、晶片採樣及元件暴露實驗分別使用來探討兩種空氣濾網在腐蝕過程中所釋放污染物的成分及含量，以及這些污染物對元件特性的影響，結果證明鐵氟龍材質空氣濾網可有效抵抗潔淨室中酸性氣體的腐蝕，而傳統玻璃纖維材質的空氣濾網在氫氟酸氣體的腐蝕下，釋放了包括硼及有機離子等污染物，造成元件特性的退化。

在電漿製程研究方面，首先我們開發製作矽化鎳的製程，分別針對鎳金屬沉積厚度、快速熱退火溫度及製作於不同結晶的矽基板上等，尋找最佳化條件，發現在單晶矽及非晶狀複晶矽上，200□厚度的鎳在400℃到650℃快速熱退火下形成的矽化鎳，有較低且穩定的片電阻值。接著我們將矽化鎳製作於不同線寬的複晶矽閘極上，探討閘極線寬對矽化鎳阻值的影響，結果顯示矽化鎳的最佳製程溫度在400℃到550℃之間。然後，我們研究矽化鎳在第二次快速熱退火的熱穩定性，發現矽化鎳製作於單晶矽與非晶狀複晶矽有較佳的熱穩定性。

在矽化鎳製程最佳化後，我們將矽化鎳製程應用於超淺接面的製作，實驗發現接面二極體漏電流隨著矽化鎳製程溫度增加而減少，這是由於矽化鎳完全形成所致，另外，漏電流也會隨著矽化鎳厚度增加而增加，這是由於矽化鎳越來越接近接面二極體的空乏區。接著，我們使用新式選擇性液相沉積法來取代傳統活性離子蝕刻法製作接觸孔，研究二極體元件在電漿環境下元件特性退化的機制，結果發現利用選擇性液相沉積法製作接觸孔可以抑制電漿製程對接面深度1000□以下元件造成的退化。

在本研究中，我們分別探討微污染及電漿製程對電晶體元件特性的影響，並提出改良製程，經實驗結果證實新式鐵氟龍材質空氣濾網及選擇性液相沉積法可有效改善元件特性，此兩項技術對應用於奈米世代元件製程，應該具有相當大的潛力。

In ULSI, the dimension of device must be scaled down to reduce the cost and improve the device performance. For the development of nanometer generation devices, the important issues, including microcontamination, gate insulator, ultra-shallow junction, copper interconnection, etc., are the key processes to successfully fabricate devices. In this thesis, the microcontamination control and the plasma process of silicide shallow junction were the main topics. The influences of microcontamination and plasma process to device performance were studied and the new improvement methods were developed.

In the microcontamination control aspect, first the specially designed clean bench was set up in the cleanroom. The main filter of the clean bench was changeable and two kinds of air filter modules, including the PTFE and the glass-fiber ULPA filters, were used as the main filter, respectively. After the air sampling, wafer sampling and device exposure experiments, it was found that two kinds of air filters can effectively control the contaminants, including inorganic ions, organic ions and metals, in the cleanroom. The glass-fiber ULPA filter, however, presented some organic contaminants released from the binder of the filter in air recycling condition. Besides, the MOS capacitors were also used to investigate the effects of contaminations to gate insulator when the device were exposed under different ULPA filters. The results revealed that the PTFE ULPA filter can control the contamination and improve the device performance.

Next, the hydrofluoric acid (HF) vapor was used in the clean bench to simulate the acid vapor corrosion in the cleanroom. The PTFE and glass-fiber ULPA filters were used to investigate the corrosion-resistant ability, respectively. From the air sampling, wafer sampling and device exposure experiments, the PTFE ULPA filter showed better resistance to HF vapor corrosion. On the contrary, the glass-fiber ULPA filter released organic ions and boron contaminants in the HF vapor environment and resulted in the degradation of device performance.

In the plasma process aspect, first the optimum process conditions of nickel silicide were developed according to the nickel film thickness, rapid thermal annealing (RTA) temperature and different crystallization substrates. The nickel silicide formed with the 200□-thick nickel and the RTA temperature between 400℃ to 650℃ showed the low and stable sheet resistance when fabricated on the c-Si and apoly-Si substrates. The nickel silicide was also fabricated on the poly-gate with different linewidth and the results showed that the optimum process temperatures were between 400℃ to 550℃. Finally, the stability of nickel silicide processed with second RTA was studied and it was found that the nickel silicide formed on c-Si and apoly-Si substrates have the better thermal stability.

The optimum processes of nickel silicide were then used to fabricate on the ultra-shallow n+/p junction. The leakage current of junction diode decreased with the increasing RTA temperature and this was due to the complete formation of nickel silicide. Besides, the leakage current of junction diode increased with the increasing nickel silicide thickness and this is because the silicide grew close to the junction depletion region. Finally, the selective liquid-phase deposition (S_LPD) method was used to replace the traditional reactive-ion etching (RIE) for the formation of contact holes. The degradation mechanism of diodes exposed under the plasma environment was investigated and the results displayed that diodes with the contact-holes formed by the S_LPD method can suppress the degradation of device with the junction depth shallower than 1000□.

In this study, the influences of microcontamination and plasma process to device performance were investigated and the new improvement methods were also proposed. The experimental results revealed that the PTFE ULPA filter and the selective liquid-phase deposition method can effectively improve the device performance and they may become the potential technologies for the fabrication of nanometer generation devices.