利用虛擬金屬降低負光阻製程中極紫外光閃焰變異量之方法

Abstract

目前IC製造中，最重要的過程之一是光顯影技術，目前業界所廣泛運用之193nm的紫外光，已經到達其物理極限，若要往次20nm以下之製程節點走，極紫外光光刻技術是其中一種很有希望的次世代光刻技術。目前世界上之晶圓製造公司也正往此技術上投入了大量的研究資源；但是在極紫外光中仍有很許多問題必須解決，在此篇論文中我們將討論因極紫外光光蝕刻的光學系統散射產生令人困擾的極紫外光閃焰效應(EUV flare effect)。 高含量與高差異量的極紫外光閃焰會影響臨界尺度(CD)的控制上的問題，在之前的研究中顯示0.2%的閃焰改變量就會影響2nm的臨界尺度。在正光阻製程中已經有使用虛擬金屬(dummy fill)來降低高含量閃焰與高差異量的閃焰，我們運用相似的想法在負光阻製程中來降低高差異量的閃焰。正光阻製程與負光阻製程之間在光罩上的定義有所不同，負光阻製程所使用的是暗場光罩。在暗場光罩中，電路設計上原本所需要的圖案或虛擬金屬都會增加光罩上的反光面積也會使晶圓上的閃焰含量增加。因此我們無法藉由加入虛擬金屬降低閃焰含量，所以我們需要設法不要使用太多的虛擬金屬增加不必要的閃焰含量。加入虛擬金屬的區域也會因為正、負光阻不同而不同的趨向，負光阻提升四周的閃焰含量會分散在邊緣跟角落的區域。我們可以利用個二維的高斯分布來模擬閃焰含量與光罩上反射光源的區域之間的轉積核心，藉由把光罩上反射的區域與用來模擬閃焰的高斯分布摺積的運算得到閃焰含量的分布。我們用一個漸進式的方法，盡量在低含量閃焰的地方加入虛擬金屬來降低閃焰的差異量。實驗結果顯示我們的方法可以有效地降低40%閃焰的差異量，成功讓臨界尺度達到比較好的控制。此外我們是第一個在負光阻製程中考量降低閃焰的差異的研究。

In the semiconductor manufacturing process, one of the most important techniques is photo lithography. The light with 193nm wavelength has the physical limitation problem on resolution. Extreme Ultraviolet Lithograph (EUVL) is one of the promising Next Generation Lithography (NGL) technologies. Most of foundries have invested considerable resources in the NGL technology. In this thesis we will mention one of the critical issues is EUV flare which is an undesirable scattered light due to the optical surface roughness. The high level EUV flare and the large flare variation could affect the control of critical dimension (CD) uniformity. However, previous work has reported that 0.2% change in flare level may cause 2 nm change in CD. There is a way to reduce flare variation and flare level for the process by using dummy fill for positive-tone photoresist process. We used the similar idea to reduce flare variation for negative- tone photoresist process. There is a mask different between negative-tone and positive-tone photoresist that negative-tone photoresist used dark field mask. For dark field mask process, the pattern or dummy fill are increasing the reflective area on the mask and the flare level on wafer, so we cannot decrease flare level by adding dummy fill. The distribution of dummy fill will be different that the dummy fill will accumulate in the middle for bright field mask, but in our case the dummy fill will accumulate on the edge for dark field mask process. We use a progressive method to reduce flare variation by insert dummy fill on low flare level region. Experimental results show that our process can reduce the flare variation by 40%, which may contribute to the better control of CD uniformity. This thesis presents the first work that reduce the flare variation for the negative-tone photoresist process.