Photomask and manufacturing method of the same, and pattern forming method

#The present invention relates to a photomask used to manufacture a semiconductor device, a liquid crystal, and so forth and a manufacturing method of the same, and a pattern forming method.

#Along with the advance in the integration of semiconductor elements, the patterns formed by lithography systems are making progress in microfabrication. In the progress, however, it is considered to be difficult to form contact holes arranged at smaller pitches. In order to form the contact holes at smaller pitches by conventional technologies, there is used a technique in which a square mask pattern is formed by biasing a mask data or design data and the mask is transferred onto a wafer. For instance, in order to form contact holes arranged at pitches of 240 nm and each having a diameter of 120 nm by an ArF aligner under the illumination conditions of numeral aperture (NA)=0.7 and σ=0.7, the patterns on the mask come to be a square pattern each having a diameter of 160 nm, which requires a bias of approximately 40 nm to be stably formed.

#This technique allows the contact holes to be formed, however, it increases the light intensity at a light shielding part to sometimes cause a failure such as a reduction in resist film thickness or disconnection.

#FIG. 1A is a schematic plan view showing a mask image when forming a conventional contact hole;

#FIG. 1B is a contour map of a light intensity derived from a simulation of the mask image in FIG. 1A;

#FIG. 2A a schematic plan view showing a mask image when a mask pattern is formed into a polygon having more vertexes by the present invention;

#The previously-described problems, specifically, the reduction in a resist film thickness and a disconnection caused when forming an actual pattern, and the optimal optical proximity corrections required depending on each of the mask manufacturing processes come to obvious when forming the actual pattern having a circular or oval outline such as a contact hole. When reviewing this from a general view point, the problems can be deemed to be attributable to the requirement that, when forming a micro actual pattern having an outline including at least partly a curve, such a part of the mask pattern that corresponds to the curve of the actual pattern be formed to approximate to the curve using a plurality of line segments (polygonal line segments).

#The present inventor has conceived that the above-described problems can be prevented by the use of a photomask having an approximated curve to the curve of the actual pattern, in other words, by approximating such a part of the mask pattern that corresponds to the curve of the actual pattern thereto by way of the above-described approximation using polygonal line segments (polygonal approximation) beforehand in the step of a mask data to form a mask pattern of the photomask (depending on cases, however, the polygonal approximation employs for example a hexagon, octagon, or a polygon having more vertexes when forming an actual pattern of a circular shape). That is, the polygonal approximation for approximating the outline of a mask pattern to a curve is a technique capable of approximating such a part of the mask pattern that corresponds to the curve of an actual pattern to the curve, and differs depending on the modes of mask pattern drawing, various conditions, and so forth in addition to the shape of the mask pattern. Accordingly, a desired mask pattern can be formed based on an individual and specific polygonal approximation in accordance with the shapes, the conditions, or so forth.

#It should be noted that, as an electron-beam aligner to draw a circular pattern, there is disclosed one in Japanese Patent Application Laid-Open No. Sho60-136225 that draws the circular pattern based on information on a center position and radius. However, as a background of the present invention, it is extremely difficult to form a micro pattern of recent-days by such a simple technique, so that the present invention has been made to practically respond to the demands to form a desired micro pattern. Specifically, in order to practically form a micro actual pattern of a circular shape, as in the present invention, an approximated pattern that matches with the shape to form, the mode of mask pattern drawing, the various conditions, and so forth is necessary to be formed, and in this case, a mask pattern approximated to a circle is necessary to be formed.