1. Field of the Invention
The present invention relates to a charged particle beam writing method and a charged particle beam writing apparatus. More specifically, for example, the present invention relates to a method for increasing the accuracy of the writing position of the electron beam writing apparatus.
2. Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. For forming a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a high-precision master pattern.
FIG. 22 is a conceptual diagram explaining operations of a variable shaping type electron beam writing or “drawing” apparatus. The variable shaping electron beam (EB) writing apparatus operates as described below. A first aperture plate 410 has a quadrangular aperture 411 for shaping an electron beam 330. A second aperture plate 420 has a variable shape aperture 421 for shaping the electron beam 330 having passed through the aperture 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the aperture 411 is deflected by a deflector to pass through a part of the variable shape aperture 421 of the second aperture plate 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g., the x direction) during the writing. In other words, a quadrangular shape that can pass through both the aperture 411 and the variable shape aperture 421 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the x direction. This method of forming a given shape by letting beams pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) system.
In electron beam writing, there is a problem in that if a pattern density greatly varies during writing, the position accuracy of a pattern is degraded at the place of varying. As a cause of this problem, for example, charging of an extraneous matter adhered to the deflector is described (refer to, e.g., “Proc. of SPIE Vol. 8441 84410C-2”). Then, as a solution to this problem, it has been attempted to improve the decrease of the position accuracy by setting the stripe width to be small in order to lessen the writing area per stripe. However, if the stripe width is set to be narrow, there occurs a problem in that the throughput is reduced because the number of stripes set in the target object is greatly increased. Therefore, this method is not desirable. Accordingly, conventionally, the problem described above has been coped with by periodically measuring a beam drift amount to correct the beam drift. However, with respect to the place where the pattern density sharply changes, drift correction has difficulty in following the beam position variation. Therefore, required position accuracy has not been obtained. Although it is necessary to set the time interval to measure a beam drift amount to be very short for dealing with even the case of the sharp variation of a pattern density, the writing operation needs to be stopped when measuring the beam drift amount, which poses a problem of throughput decrease. Therefore, this method is not desirable, either.