In immersion lithography, it is necessary that the surface of wafer has high hydrohybicity in order to prevent the residue of immersion fluid, i.e. pure water, that cause watermark defect. Usage of a cover material film over the resist film is effective to consistent with high hydrohybicity of the surface and high performance of resist film. But it was problem that much pattern deformation defects was observed with the use of an alkali-soluble type cover material film and an immersion exposure tool. As a result of the examination, it was identified that the fraction of film which caused the pattern deformation in the area of several micrometers were the fraction of the cover material. And the fractions of cover coat material were oriented in the coating defects of the cover material film and in the film peeling after scan of the immersion nozzle at the wafer bevel. The coating defects were improved with the chemical of the cover material. An adhesion process was effective to prevent the film peeling of cover material.
The impact of wafer warpage on critical dimension (CD) control is getting larger in ArF lithography. The product wafers with stacked films are warped due to the stress caused by the difference in the film stack structure between the top side and the back side of the wafers. A typical warpage of the product wafers is of convex shape, and the amount of the warpage is larger than 50 μm for 200mm wafer. On the other hand, proximity bake method is widely used in the Post Exposure Bake (PEB). When the warped wafer is placed on the hot plate, the gap between the wafer and the hot plate varies across the wafer. That is, the temperature of the wafer center is lower than that of wafer edge. Such a temperature variation affects CD uniformity within wafer. In particular the fact is obvious in ArF chemical amplified resist because PEB sensitivity of ArF resist is larger than 5nm/degree. In this study we optimize PEB zone temperature within wafer to suit the wafer warpage. This method is based on controlling zone temperature of the PEB hot plate with concentrically divided heaters. We carry out that the CD uniformity for the warped wafer is improved by 70% compared with the conventional process.
In the liquid immersion lithography, uses of the cover material (C/M) films were discussed to reduce elution of resist components to fluid. With fluctuation of exposure tool or resist process, it is possible to remain of waterdrop on the wafer and watermark (W/M) will be made. The investigation of influence of the W/M on resist patterns, formation process of W/M, and reduction of pattern defect due to W/M will be discussed. Resist patterns within and around the intentionally made W/M were observed in three cases, which were without C/M, TOK TSP-3A and alkali-soluble C/M. In all C/M cases, pattern defect were T-topped shapes. Reduction of pattern defects due to waterdrop was examined. It was found that remained waterdrop made defect. It should be required to remove waterdrop before drying, and/or to remove the defect due to waterdrop. But new dry technique and/or unit will be need for making no W/M. It was examined that the observation of waterdrop through the drying step and simulative reproduction of experiment in order to understand the formation mechanism of W/M. If maximum drying time of waterdrop using immersion exposure tool is estimated 90 seconds, the watermark of which volume and diameter are less than 0.02 uL and 350um will be dried and will make pattern defect. The threshold will be large with wafer speed become faster. From result and speculations in this work, it is considered that it will be difficult to development C/M as single film, which makes no pattern defects due to remained waterdrop.
Two kinds of development processes were investigated. One is two-step development in which surface treatment using ozonated water was employed between the two steps of the development. The other is development in which ozonated water and hydrogenated water were employed in the pre-treatment step and the post-treatment step. The above-mentioned processes were applied to KrF resist process of 130nm generation. By pre-treatment using ozonated water and two-step development using ozonated water in inter-treatment, the shot-to-shot CD variation of isolated line (line width = 180nm) and the intra-shot variation were improved from 6.6nm to 4.4nm and from 13.5nm to 8.6nm, respectively. And the total variation was greatly improved from 15.0nm to 8.6nm. Moreover, the number of defects was greatly decreased by post-treatment using ozonated water and hydrogenated water continuously.
In the tri-level resist process, it is sometimes difficult to detect the alignment mark because of the anti-reflection performance of the organic thick anti-reflective (ARL). Laser ablation in running water was one of the most effective techniques for removing the organic thick ARL on the alignment mark. Generally, the ablation process produces many particles. The results of our experiment indicate that the particle distribution area greatly depends on the dome-shape bubble on the ablation area. The particle distribution area could be minimized by optimizing some ablation conditions according to the estimated size of the dome-shape bubble. By optimizing a shift of the narrow slit-laser-beam and its energy so as to keep the ablation/initial thickness ratio to less than 20%, fine ablation area could be obtained. This novel ablation technique is very useful for particle-free selective removal of the organic thick ARL film.