Effects of Resist Thickness and Substrate Reflectance on Critical Dimension Bias of Isolated-Dense Pattern

The critical dimension (CD) uniformity of an isolated-dense pattern has been the most critical issue in optical lithography below the wavelength of the illumination source and much effort has been exerted to improve it. The CD difference between isolated and dense patterns (ID bias), which is caused by proximity effects, is known to be one of the key factors leading to the deterioration of CD uniformity. Because ID bias is such a complicated phenomenon and affected by many factors, it would be very difficult to control it even though we understand all the factors that lead to it. Much research on ID bias has been conducted; however, the effect of resist thickness on ID bias has not yet been clearly studied. From our investigations, we have investigated the effects of resist thickness on ID bias and found that ID bias is strongly affected by resist thickness. ID bias changes periodically with resist thickness and the minimum ID bias is obtained by controlling the resist thickness for a specified pattern. We also found that the antireflective coating (ARC) process is an effective method for controlling ID bias.