1. Field of the Invention
The present invention relates to a photo mask used for exposure to form a pattern of a semiconductor device on the sample, and in particular, to a photo mask having an improved proximity effect correction pattern for an oblique line pattern, and a method of manufacturing the photo mask. The present invention also relates to a method of generating mask data used to manufacture a photo mask.
2. Description of the Related Art
In the prior art, a photo mask is used for light exposure in order to form a device pattern on a semiconductor wafer. The photo mask is produced using an electron beam lithography technique. The electron beam lithography technique uses electron beams to draw a design pattern of a semiconductor device on a mask substrate. A problem with the electron beam lithography technique is that when resolution is close to its limit, a proximity effect or the like may prevent an actual design pattern from being formed on a mask substrate. To solve this problem, a proximity effect correction pattern is added to the design pattern so as to accurately form a desired pattern (refer to, for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-83757).
However, such a method has the problems described below. Since the proximity effect correction pattern is added to the design pattern, the number of figures used for shot divisions for electron beam drawing increases. This increases the time required for the drawing and the amount of data required. Consequently, data handling becomes difficult and other various problems may occur. Further, for example, fine figures that require a resolution higher than the one used may be generated at, for example, edges of the correction pattern. Thus, disadvantageously, these figures may not be resolved on the mask, the accuracy of defect inspections may decrease, or inspection throughput may decrease.
Further, when the pattern of the photo mask is transferred to a wafer by optical lithography, the optical proximity effect may curl edges of a pattern formed on the wafer or may thicken or thin the pattern. Consequently, the pattern formed on the pattern may differ from the original pattern. Thus, an OPC (Optical Proximity Correction) technique is required to add a correction pattern to the pattern to be formed on the photo mask in order to correct the optical proximity effect.
Accordingly, to more precisely create mask data for electron beam drawing, it is necessary to add, to a design pattern, both a correction pattern for correcting the proximity effect when the pattern is drawn on the photo mask, and a correction pattern for correcting the proximity effect when the pattern is transferred to the wafer. In this case, the above problems, including an increase in the number of figures and the generation of fine figures, are more significant.
Thus, in the prior art, when a correction pattern is added to a design pattern in order to correct the proximity effect, this may increase the number of figures required and thus the time required for drawing or may produce very fine figures that are not actually resolved. The increase in the time required for drawing may lead to a decrease in drawing throughput. The generation of fine figures may contribute to reducing the inspection throughput.