微影用光罩的二種新設計：相移干涉條與交錯式相移光罩與193奈米浸入式微影之光罩誤差放大因子之模擬分析

Abstract

在193奈米浸入式微影下，由於光強度太低的關係所以很難在不依靠任何解像度增進技術的幫助下在晶圓上印出精確的縮小4倍密集圖案(如接觸孔)，過去最常用的方法是加上干涉條，其可增加接觸孔的光強度，然而在製造更小的圖案時，干涉條與接觸孔的距離會變得相當的近，因此縮小了光罩的誤差容忍度，另一方面，這種方法有可能造成圖案扭曲而造成圖案交連，為了解決這個問題，我提出一種新的光罩設計方法，我將其稱之為“相移干涉條”，其在一維陣列圖案上表現出比傳統干涉條更好的效果，但是當面對更小的圖案時，也不容易在光罩上加上這些干涉條，因此我提出另外一種“交錯式相移光罩” 來處理此類微小的密集圖案，在此設計中，主要圖案亦是臨近圖案的干涉條，因此就不需要額外的細小干涉條，光罩製備也變得比較容易，這二種設計方式在修飾與增強晶圓上的光強度都很有用的工具，影像對比度均可獲得大幅提升，也就可以在不更換微影機臺的情況下得到更好的解析度與更大的製程視窗。 一般而言，當數值孔徑增加時，解析度會變好且光罩誤差放大因子也較小，然而，本研究的模擬計算結果卻顯示，當使用Y偏振光和偏軸發光時，在193奈米浸入式微影中較小而密集的圖案其光罩誤差放大因子會隨數值孔徑增加而增加，此光罩誤差放大因子的反轉現象被清楚的觀測到，尤其是在雙孔發光的條件下，而當圖案接近解像度極限時，光罩誤差放大因子會急速增加，本研究的模擬計算也顯示出在大多數的情況下，光罩誤差放大因子與影像對比度的立方根成反比。

For 193 nm immersion lithography, it is hard to print clear 4X nm dense images (e.g. contact holes) on wafer without any modifications due to lower light intensity. In the past, the most common method is to add the scattering bars, which can enhance the light intensity of contact holes. However, with tinier pattern, the distance between scattering bars and contact holes will get quite close. Hence, the error tolerance for mask making was reduced. On the other hand, this method may also cause the pattern twist which will induce pattern crosslink. To solve this issue, a new design method for lithography mask was proposed, which is named “Phase-shifting Scattering Bar”, and it shows better performance in 1D chain array patterns than those with traditional scattering bars. However, for even tinier patterns, it is quite difficult to put these scattering bars on mask. Hence, another special design named “Interlaced Phase-shifting Mask” was proposed to handle such tiny dense patterns. In this design, main patterns are also the scattering bars for adjacent patterns. Hence, there is no need for additional tiny scattering bars, and the mask making requirement can be also relaxed. Both of these two mask design are useful tools to trim and modify light intensity profile on wafer. The image contrast was largely enhanced which means a better resolution and a larger process window can be gained without the cost of new illumination equipments. In general, better resolution and lower mask error enhancement factor (MEEF) are obtained when a higher numerical aperture (NA) is used. However, simulations in this study show that, if Y-polarized light and off-axis illuminations were used, higher NA leads to higher MEEF for smaller and dense feature line sizes in 193 nm immersion lithography. The reversal of the MEEF was clearly observed, especially in the presence of a dipole. When the feature size decreased to the resolution limit, the MEEF rose enormously. Simulations also show that the MEEF is inversely proportional to the cubic root of image contrast in most cases in this study.