The control of photoresist thickness and uniformity is becoming more crucial factor as the wafer size increases and the minimum feature size decreases since the variation of resist thickness could affect the critical dimension variation. In general, spin coating technique is used to coat photoresist on a wafer. To obtain the wet resist thickness profile around a topographical feature, the analytical solution derived from mass continuity and lubrication approximation was used. Under the same spin coating condition, the formations of distributed photoresist were different among the shape and size of topology. The final dried resist thickness profile was obtained by applying the resist thickness reduction due to evaporation during soft bake. The photoresist thickness and distribution on an isolated topology were compared with those of a periodic topology. In case of periodic topology, the photoresist thickness and distribution are dependent on topology density. The resultant thickness variations were applied to our simulation tool to determine the line width variations around the topological feature. We found that the difference in resist thickness due to topography could induce a severe line width variation. Mask bias or other correctional method is necessary to get the desired line width for the whole area around the topology.
X-ray laminography and DT (digital tomosynthesis) are promising technologies to form a cross-section image of 3D objects and can be a good solution for inspection interior defects of industrial products. It has been known that digital tomosynthesis method has several advantages over laminography method in that it can overcome the problems such as blurring effect or artifact. The DT system consists of a scanning x-ray tube, an image intensifier as an x-ray image detector, and a CCD camera. To acquire an x-ray image of an arbitrary plane of objects, a set of images (8 images or more) should be synthesized by averaging or minimally calculating point by point. The images, however are distorted according to the configurations of the image intensifier and the x-ray source position. To get a clear and accurate synthesized image, the corresponding points in the distorted images should be accurately determined, and therefore, precise calibration of the DT system is needed to map the corresponding points correctly. In this work, a series of calibration methods for the DT system are presented including the correction of the center offset between the x-ray and the image intensifer, the x-ray steering calibration, and the correction of the distortion of the image. The calibration models are implemented to the DT system and the experiment results are presented and discussed in detail.