感光性聚亞醯胺減量塗佈製程對積體電路鈍化層均勻性與品質之影響

Abstract

據估計IC製造的關鍵材料光阻，約佔總化學品成本20%以上，基於降低生產成本及減少環境污染考量，使得光阻減量的研究受到普遍重視，本文使用8吋晶圓，以最佳化聚亞醯胺(Polyimide，PI)減量製程為導向，探討旋塗製程參數對薄膜均勻性的影響，包含初轉速度、降轉速度、主轉速度、PI噴出量，並且分析量產的可行性，由實驗得知在不改變製程條件下，執行PI減量將導致薄膜均勻性變差，然而降低初轉速度搭配提高主轉速度對於PI減量所造成的塗佈不均有正面改善，本文最後PI噴出量由3.5g減量至2.7g，針孔測試、剖面結構分析，均與PI減量前無差異，預計可減少22.8%的材料成本。 歸納旋塗製程參數與PI均勻性的關係如下，初轉速度對於PI厚度影響不明顯，但對PI均勻性影響明顯，過高的初轉速度將引起塗佈不良，而在某一範圍內的初轉速度，PI均勻性較佳，主因為過低的初轉速度使得邊緣光阻量不夠形成中凸輪廓，過高的初轉速度使得光阻在一開始時，大量旋至邊緣形成中凹輪廓，嚴重時將導致塗佈不良；利用冪次趨勢線回歸計算得PI厚度與降轉速度的-0.07次方成正比，雖然增加降轉速度可以使PI厚度變薄，但達到某一值後，PI的均勻性會隨之變差，主因為過高的降轉速度導致回流現象減少；利用冪次趨勢線回歸計算得PI厚度與主轉速度的-1.01次方成正比，雖然增加主轉速度可以使PI厚度變薄，但PI均勻性會隨之變差，主因為過高主轉速度導致光阻中心與邊緣所受的離心力差異變大；當PI噴出量只要超出一定值時，PI噴出量的多寡對於PI厚度與均勻性影響不明顯，主因為過多的溶液在一開始就已經被旋出晶圓表面。

The expense of photoresist materials is estimated to occupy more than 20% of the total cost of chemicals used for IC fabrication. In order to reduce the fabrication cost and environmental pollution, the reduction of the photoresist quantity has recently become a popular research topic. This thesis reports the influence of optimization of the spin-coating process of the polyimide (PI) on 8-inch wafers, including spin-up speed, deceleration, spin-off speed and the control of the dispensed PI weight, on the film uniformity, and verifies the feasibility of the optimized PI reduction process for the on-line mass production. The study shows that the PI reduction without any process optimization may degrade the uniformity of the PI film. However, the decrease in the spin-up speed combined with an increase in the spin-off speed can mitigate the non-uniformity problem. We can produce a stable PI passivation film, which passes the pin-hole test and the cross-sectional examination, by reducing the used PI weight from 3.5 g to 2.7g per wafer, saving the material cost by 22.8%. The dependence of the PI uniformity on the optimized spin-coating parameters is summarized as follows. The spin-up speed greatly affects the film uniformity although a direct relation between the speed and the film thickness is not obvious. It is important to set the spin-up speed within an appropriate range for a better film uniformity. The increase in the deceleration speed reduces the film thickness, and the deceleration speed is found to be related to the film thickness by a power of -0.07. However, the film uniformity becomes worsen after the speed is increased to a critical value; this is due to the occurrence of PI backflow at the high speed, deteriorating the film uniformity. The increase in the spin-off speed reduces the film thickness, and the speed is related to the thickness by a power of -1.01. The film uniformity, however, degrades with increasing spin-off speed; this may result from an unbalance between the center and the edge centrifugal forces. The increase in the PI amount used for the spin coating has little effect on the film thickness and uniformity. This is because the excessive PI solution is spun out of the wafer at the beginning of the spin process and, therefore, the PI amount has a small influence on the film quality of the PI layer.