Optics: measuring and testing – By light interference – For dimensional measurement
Utility Patent
1998-11-25
2001-01-02
Kim, Robert (Department: 2812)
Optics: measuring and testing
By light interference
For dimensional measurement
C356S517000
Utility Patent
active
06169603
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a reticle inspection system and a method of inspecting a reticle used for forming a predetermined pattern on a semiconductor wafer.
Conventionally, in a manufacturing process of a Large Scale Integration(LSI) circuit, a reticle is used for forming the predetermined pattern on the semiconductor wafer constituted by a silicon or the like. The pattern is formed on the semiconductor wafer by exposing the semiconductor wafer to a light through the reticle and an optical lens. Therefore, when the reticle has a pattern defect in itself, the defective pattern is transferred on all the wafers manufactured by using the reticle. As a results a large amount of defective LSI circuits are manufactured. Accordingly, the pattern inspection of the reticle is very important and essential for manufacturing LSI circuits. Moreover, since the more fine pattern has come to be formed in recent years, a high accuracy inspection of a defect detecting sensitivity of less than 0.2 &mgr;m is required in a reticle inspection system.
In inspection methods of the reticle for manufacturing LSI circuits, there are two kinds of the methods. One is a die-to-die inspection method for comparing identical patterns formed at different positions on the same reticle to each other while another is a die-to-database inspection method for comparing draft data used when plotting the reticle pattern with the pattern on the actual reticle. Herein, “die” means a certain grouping of pattern areas or the detection image thereof, which is defined as a unit of a pattern comparison inspection. Further, “database” means a reference image synthesized from the draft data with respect to an actual pattern image detected by an optical system.
Conventionally, an ordinarily reticle inspection system comprises an X-Y stage for setting a reticle, a laser interferometer for detecting a position of the X-Y stage with a high accuracy, a laser-scanning optical-device for scanning a laser beam in the direction of the Y-axis of the reticle, a transmitted-light detection section for detecting the transmitted light, an optical image input section for receiving an optical image from the transmitted-light detection section, a data conversion section for converting the draft data used where plotting the reticle to synthesize the reference image, an image comparison section for comparing the optical image with the reference image to detect a pattern defect, and a controller for controlling the entire system.
However, via a conventional method of inspecting a reticle using the ordinarily reticle inspection system, it takes several hours to detent one sheet of the reticle. Therefore, error is inevitably caused to occur in detection of the travel of the X-Y stage by the laser interferometer due to changes of environment (temperature, humidity, atmospheric pressure) during inspection. When the error is included in the detected results by the laser interferometer, the X-Y stage cannot be made to travel correctly by a certain pitch. Consequently, a deviation is generated between the optical image and the reference image, even though the reticle has actually no defect in the pattern thereof.
In order to avoid this problem, it is considered that the entire reticle inspection system is placed in an temperature control chamber to hold the air flow constant as well as to hold the temperature and the humidity constant. In addition, a wavelength compensator (a correcting means) is provided foot detecting the change in a refractive index in the vicinity of the optical path of the laser interferometer. Thereby, an effective refractive index is calculated to correct the reference image in. real time. Accordingly, the optical image is compared with the reference image corrected in real time. In the wavelength compensator, a wavelength in an actual environment is compared with that in vacuum by the use of a vacuum tube with a certain distance to detect the change in a refractive index and to correct it. However, this method requires a very large temperature control chamber surrounding the entire system and the wavelength compensator. The method therefore brings disadvantages in that the system becomes large in size and very expensive.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a reticle inspection system and a method of inspecting a reticle in which the reticle car be inspected with a high accuracy, by synthesizing the reference image corrected appropriately to compare with the optical image, even in the case that the laser interferometer is subjected to the influence of changes in the environment.
Other objects of the present invention will become clear as the description proceeds.
According to an aspect of the present invention, there is provided a method of inspecting a reticle comprising the steps of: irradiating a light bean on a reticle having a pattern in advance to receive the transmitted light and to form an optical image, while measuring the relative position of the X-Y table placing the reticle by a laser interferometer; comparing the optical image with a reference image synthesized by converting draft data used when forming the pattern; and detecting defects of the pattern. The method further comprising the steps of: providing a scale to which changes in an environmental condition is less than that of the laser interferometer and detecting the position of the X-Y table; obtaining deviation data of measurement errors of the laser interferometer due to the changes in the environmental condition using the scale; and synthesizing the reference image which is corrected from the draft data by the amount of the deviation data. Therefore, a visual inspection of the reticle can be performed accurately corresponding to the changes in the environmental condition.
More particularly, the deviation data is calculated by: storing position data of the laser interferometer and the scale in a light-beam irradiating initiation position to the reticle, and position data of the laser interferometer and the scale in a light-beams irradiating completion position; obtaining in advance an initial distance value of the difference between the position data of the laser interferometer in the light-beam irradiating completion position and the position data of the laser interferometer in the light-beam irradiating initiation position; moving the X-Y table, placing the reticle of an inspection object so that the position data detected by the scale matches with the stored position data of the light-beam irradiating initiation position stored to store the initiation position data of the laser interferometer at that time; subsequently, initiating the light-beam irradiation to the reticle while moving the X-Y table; storing the completion position data of the laser interferometer at that time as well as stopping the light-beam irradiating, at the time ill which the position data detected by the scale reaches a position matching with the position data of the light-beam irradiating completion position; and calculating a distance data of the difference between the completion position data of the laser interferometer and the initiation position data of the laser interferometer to obtain the difference between the distance data and the initial distance value.
Moreover, the laser interferometer cancels vibration difference in phase between a lens of the laser-scanning optical system irradiating the light beam and the X-Y table. Thus, both the effects can be obtained using in combination of the laser interferometer and the scale.
The detection of the defects in the pattern in a plurality of points of the reticle is performed sequentially, and when, in a reference image synthesizing process, the correction is designed to be performed based on the deviation data obtained at the preceding detection of the defect, the synthesis of the reference image is efficiently corrected corresponding to the changes in the environment.
According to another aspect of the present invention, there is provided a
Foley & Lardner
Kim Robert
Lee Andrew H.
NEC Corporation
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