1. Field of the Invention
The present invention relates to a pattern inspection apparatus and a pattern inspection method, to a pattern inspection technique for inspecting a pattern defect of an object serving as a target used in, for example, semiconductor manufacturing, and to an apparatus which inspects a defect of an extremely small pattern of a photomask, a wafer, or a liquid crystal substrate used when a semiconductor element or a liquid crystal display (LCD) is manufactured and an inspection method therefor.
2. Related Art
In recent years, with increases in integration density and capacity of a large-scale integrated circuit, a circuit linewidth required for a semiconductor element becomes narrower. The semiconductor elements are manufactured by exposing a pattern to transfer the pattern onto a wafer by a reduced projection exposure apparatus so-called a stepper while using an original pattern (also called a mask or a reticle, to be generally called as a mask hereinafter) to form a circuit. Therefore, a pattern writing apparatus which can write a fine circuit pattern is used to manufacture a mask for transferring a fine circuit pattern onto a wafer. The pattern circuit may be directly written on a wafer by using the pattern writing apparatus. For example, the pattern is written by using an electron beam or a laser beam.
An increase in yield is necessary for manufacture of an LSI which requires huge manufacturing cost. However, as typified by a 1-Gigabit DRAM (Random Access Memory), a pattern configuring an LSI is now changing from an order of sub-micron meter to a nanometer. A pattern defect of a mask used when a super-fine pattern is exposed and transferred on a semiconductor wafer by a photolithography technique is one of great factors for reducing a yield. In recent years, with miniaturization of a size of an LSI pattern formed on a semiconductor wafer, a size which must be detected as a pattern defect is also very small. For this reason, a pattern inspection apparatus which inspects a defect of a transfer mask used in manufacture of an LSI is required to be precise.
On the other hand, with the advance of multimedia, in an LCD (Liquid Crystal Display), a liquid crystal substrate size is increased to 500 mm×600 mm or more, and miniaturization of a pattern for a TFT (Thin Film Transistor) or the like formed on a liquid crystal substrate is advanced. Therefore, a very small pattern defect in wide area is required to be inspected. For this reason, a pattern inspection apparatus which efficiently inspects a defect of a photomask used in manufacture of a pattern for the large-area LCD and a large-area LCD within a short period of time has been urgently needed.
For example, as a pattern inspection method, a “die to die inspection method in which optical image data obtained by imaging an identical pattern at different places on the same mask are compared with each other and a “die to database inspection” method in which image data (design image data) serving as a comparative reference is generated based on writing data (design pattern data) obtained by converting CAD data used when a mask pattern is written into an inspection apparatus input format and the image data is compared with measurement data (optical image data) obtained by imaging a pattern are known. In the inspection methods in the inspection apparatus, a target object is placed on a stage, and a beam scans the target object by moving the stage, thereby performing inspection. A beam is irradiated on the target object from a light source and an illumination optical system. A light transmitted through or reflected by the target object is focused on a sensor through the optical system. An image captured by the sensor is sent to a comparing circuit as optical image (measurement image) data. In the comparing circuit, after the images are aligned to each other, reference image data is compared with the optical image data according to an appropriate algorithm. When these data do not match with each other, it is determined that a pattern defect is present.
In this case, it has been primarily assumed that the pattern formed on the mask is transferred onto a semiconductor wafer or the like at its position on the mask when the pattern is transferred onto the semiconductor wafer or the like by an exposure apparatus. However, when a pattern is transferred by the exposure apparatus, a pattern shape or the like may be distorted by the optical system of the exposure apparatus, so that a patterned misaligned from the pattern formed on the mask is transferred onto the semiconductor wafer or the like. In order to utilize this fact, a technique, in which a pattern formed on a mask it self is distorted in advance such that the transferred pattern is at an ideal position according to transfer conditions of the exposure apparatus is developed.
When the mask on which a pattern is formed at a position distorted in advance as described above is inspected, the following problem occurs. In the die-die inspection, first, a mask is virtually divided into a plurality of inspection stripe regions of a strip shape, and image acquisition is performed for each of the inspection stripe regions. For one inspection stripe image, dies on which the identical pattern is formed exist to be compared with each other. The corresponding dies are cut out and compared with each other (for example, see Japanese Patent Laying-Open No. 2007-088375). In the die-die inspection, it is assumed that reference Y coordinates of the dies laterally arranged are equal to each other.
However, when a mask on which the distorted pattern is formed is inspected, positions (Y coordinates) of the corresponding patterns vary in an inspection stripe. For this reason, the positions of the dies to be compared with each other do not match with each other. For this reason, disadvantageously, accurate inspection cannot be executed.
As described above, when the die-die inspection is performed on a target object to be inspected on which a pattern distorted in advance is formed, the positions (Y coordinates) of the patterns of the corresponding dies vary. For this reason, the positions of the dies to be compared with each other do not match with each other. For this reason, disadvantageously, accurate inspection cannot be executed. In the past, a method that sufficiently solves the problem has not been established.