鎢金屬蝕刻製程中以C3F8取代SF6達到PFC減量之研究

Abstract

摘要 1980年代，科學界提出溫室氣體可能造成全球性暖化以及氣候變化的可能性，使得全球暖化(Global Warming) 現象議題逐漸受到重視全，隨著半導體工業的蓬勃發展，晶圓廠如雨後春筍紛紛在世界各地建立，生產晶圓的工廠雖然其產值相當吸引人但是其爲環境、健康、資源的耗用等層面所帶來的衝擊更大！但關於導致全球暖化現象的主因之ㄧ的全氟碳化物排放問題，實務上的改善大多止於消極的尾氣處裡工程上，對於製程替代物品之實務研究幾乎沒有。 現今全球仍保有相當數量的六吋晶圓製造廠以0.35 ~ 0.5毫米的製程，進行生產消費性積體電路這類需求，而製程當中的鎢金屬蝕刻(Tungsten Etch back)中所使用的PFC管制氣體SF6的使用量是佔蝕刻製程的68%，因此，希望能藉由製程替代物品取代的方式選擇以製程反應後全氟碳化物產出較低的C3F8氣體來取代現行製程中所使用的SF6氣體來進行研究實驗期能達成全氟碳化物排放的目的。 本研究將著重於如何以C3F8氣體來取代現行製程中所使用的SF6氣體，並且維持現有產品線上所有0.35 ~ 0.5毫米製程產品品質變異能控制在小於5個百分比之內為目摽，因此在成效的探討上將著重在以C3F8氣體取代後的製程配方是否符合量產的要求及取代過程中所發現在製程上相關副作用、克服方法為主。 研究中選定幾個製程之關鍵參數作為實驗參數:反應壓力(Pressure)、射頻功率(RF Power)、C3F8 / O2 反應氣體比例等，透過實驗設計法(DOE)找出影響製程的因素，並根據實驗結果探討出最佳的製程程式。 本研究在第一階段的實驗中發現：(1)反應壓力及 RF Power 與鎢金屬的蝕刻率有正相關，在3個水準的實驗中設定值愈大蝕刻率愈高，是為影響鎢金屬蝕刻率的主要因子； (2)反應壓力與鎢金屬的蝕刻均勻度有逆相關，在3個水準的實驗中設定值愈大蝕刻均勻度愈差；(3)反應氣體中C3F8 / O2比值與鎢金屬的蝕刻均勻度有正相關，在3個水準的實驗中設定比值愈大時其均勻度愈佳，是為影響鎢金屬蝕刻均勻度的主要因子。 第二階段的實驗透過反應氣體中C3F8 / O2比值做更精確的驗證，得到的結論為: (1)當C3F8 / O2比值在0.5 ~ 0.56的範圍時，製程獲得良好的蝕刻均勻度 2.3 % ~ 2.9%； (2) 當C3F8 / O2比值在0.38 ~ 0.44的範圍時，製程獲得良好的蝕刻率表現4300 Å/min ~ 4400 Å/min。 根據上述研究之結論，最後獲得之最佳化的鎢金屬蝕刻製程條件，以產品實際生產並通過SEM切片觀察、電性測試分析及良率檢視，最後投入量產兩年後證實是可應用於現今.35 ~ 0.5毫米產品線之鎢金屬蝕刻製程上的。

ABSTRACT

In 1980s, scientists proposed that the green house gases could cause global warming and climate change. The global warming phenomena have then attracted more attentions. Due to the booming of the semiconductor industry, wafer fabs were built like bamboos shooting after a spring rain. With the output value of wafer fabs increasing, the impact it brings to the environment and health is even bigger and the resource it consumes is even more. One of the major causes of global warming is the perfluorocarbons emission. However, most of the improvement actions are only passively on gas exhaust treatment engineering. Almost no research was done on process materials replacement. Nowadays, there are still a lot of 6 inches fabs using 0.35~0.5 □m process to produce consumer integrated circuit products. While it is necessary to controlled the PFC gas, SF6 usage amount in Tungsten Etch back process adds up to 68% of the PFC gases usage in the etch process. Therefore, the research is aimed at replacing the SF6 gas now used in the process with the C3F8 gas which produce less perfluorocarbons for the productive to reduce the perfluorocarbons emission. This research emphasizes on the use of the C3F8 gas to replace the SF6 gas currently used in the process, and still maintain product quality deviation within 5% for all the 0.35~0.5□m products. Therefore, the target is on if the replacement gas, C3F8, meets mass production requirements with no side effects. In the study, several key process parameters were chosen as the experimental parameters, such as the reaction pressure, RF power, and C3F8/O2 reaction gas ratio. Through DOE (design of experiment) to find out the factors that affect the process, while also look for optima process recipe based on the experimental results. In the first stage of the experiment, it is found that (1) the reaction pressure and RF power is positively correlated with the etching rate of Tungsten . In the 3 leveling experiments, the higher the set value is, the higher the etching rate will be. They are the major factors that affect the etching rate. (2) The reaction pressure is negatively correlated to the etching uniformity of Tungsten. In the 3 leveling experiments, the higher the set value is, the worse the etching uniformity. (3) The reaction gas C3F8/O2 ratio is positively correlated to etching uniformity of Tungsten. In the 3 leveling experiments, the higher the set value is, the better the uniformity. It is the major factor that affects the etching uniformity. In the second stage experiment, the optimum reaction gas C3F8/O2 ratio was investigated, the conclusions are , (1) When C3F8/O2 ratio is between 0.5~0.56, the good etching uniformity is achieved and the uniformity is between 2.3%~2.9%, (2) While the C3F8/O2 ratio is between 0.38~0.44, the good etching rate is achieved as the rate is 4300 Å/min ~ 4400 Å/min. According to the research conclusions above and by the optimized tungsten etching process conditions obtained attained, the products were manufactured based on there conditions and has passed the SEM slicing inspection, electric property test and analysis, and yield evaluation. Finally, the process was put into production and proved to be applicable to 0.35~0.5□m product line tungsten metal etch process.