KR20080038796A - Methode for inspecting photo-mask cd trend - Google Patents

Abstract

A method for measuring a photomask CD(critical dimension) trend is provided to precisely measure a CD trend in a predetermined position even if a predetermined pattern partially gets out of a predetermined position, by calculating a CD trend using a plurality of images in which a predetermined pattern image is set in the periphery of a predetermined position. The surface of a photomask having a pattern is enlarged and projected by using an optical apparatus(S40). In the periphery of predetermined position coordinates of the photomask, a plurality of images including a pattern image corresponding to the pattern are acquired(S50). After light and darkness appearing in the plurality of images are added and divided by the number of the plurality of images, the average value of the light and darkness is obtained and a CD trend corresponding to the average value of the light and darkness is obtained(S80). The plurality of images can be acquired while being transferred by one or two pixel units defined by the minimum unit of an image pickup device for photographing the image of the pattern.

Description

Method for inspecting photo-mask CD trend

1 is a flowchart illustrating a CD trend measuring method of a photomask according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and in particular, a photo for measuring a trend of a critical dimension (hereinafter, referred to as "CD") by magnifying and projecting a pattern formed on a surface of a photomask using an optical device. CD trend measurement method of the mask.

BACKGROUND OF THE INVENTION The manufacturing process of a semiconductor integrated circuit generally includes a number of photographic processes performed to form circuit elements on the surface of a semiconductor substrate. In particular, in order to form a highly integrated circuit in a reliable photo process, the photomask must be able to define a fine pattern and be formed without defects.

The size of the line width required by the high integration of semiconductor devices is already approaching the limit of the resolution of exposure equipment. In such a situation, the uniformity of the CD of the pattern on the photomask, which becomes the disc for patterning a certain material layer, is very important. In this respect, CD measurement data for tens or hundreds of points is required in a patterning process using a photomask.

In the manufacture of semiconductor photomasks, defect inspection of photomasks and measurement of pattern CDs are generally performed in separate processes using different equipment. That is, in order to measure the CD of the photomask, facilities of an edge diffraction detection method using a scanning electron microscope (SEM), an optical system, or a laser are mainly used. This requires a lot of time and effort to obtain a large number of CD measurement data.

In addition, in order to inspect defects in a photomask, a mask to mask inspection comparing two photomasks manufactured in the same pattern and a die-to-two comparison of patterns repeated in one photomask are performed. Die to die inspection, die to data base inspection that compares the designed pattern and the actual photomask pattern is used.

Looking specifically at the die-to-database inspection method that compares the designed pattern and the actual fabricated photomask pattern among these methods, first, by using a facility designed to detect pixels on a pixel basis, light such as ultraviolet rays or visible light is detected. The amount of light transmitted or reflected by the pattern is irradiated to the photomask and stored as numerical information, and the stored information is processed to distinguish the difference between the actual photomask pattern and the designed pattern. You find a defect.

Conventionally, CD measurement and photomask defect inspection have been carried out in separate processes, but conventional inspection facilities are manufactured to obtain information on CD trends at the same time as photomask defect inspection. That is, a die to die inspection method for comparing repeated patterns in one photomask, and a die to data base for comparing a designed pattern with a photomask pattern actually produced. After processing the transmission or reflection data of light rays stored pixel by pixel during the inspection process, information on the CD trend can be obtained from the difference by comparing with the design pattern. The conventional CD trend measuring method compares and stores the CD between the design pattern and the actual photomask pattern with respect to the entire pattern of the inspection area at the same time as the inspection of the photomask. The advantage is that it can be obtained in real time. However, these methods have a disadvantage in that only the CD difference from the design pattern can be known for all the patterns on the photomask. That is, only the difference between the actual pattern and the design pattern of various shapes and sizes existing on the photomask is obtained. In practice, the pattern to be measured in the photomask is defined in a particular shape and size and only requires the results of the CD trend for that particular point. In addition, the CD trend measurement method in a certain range in which the various patterns on the photomask appear as follows. For example, the CD trend detects transmittance or reflectance in a set range of the photomask using an optical device to detect an opacity of brightness corresponding to lines and spaces formed on the photomask. Can be calculated and measured. In this case, the CD trend may be measured by acquiring a transmitted and reflected image of the photomask by the optical device at a position having a predetermined range and calculating a contrast ratio using the transmitted and reflected image.

However, the CD trend measurement method of the photomask according to the prior art has the following problems.

In the CD trend measurement method of the photomask according to the related art, an arbitrary position at which a CD trend is to be measured is set based on a predetermined pattern to be formed on the surface of the photomask, and the CD trend measurement is performed at a set position using an optical device. However, when the pattern is partially measured out of the set position, the CD trend measurement at the set position cannot be made more accurately.

An object of the present invention for solving the problems according to the prior art described above, even if the pattern measured at the set position is partially out of the CD trend measurement at the set position is accurately made to increase or maximize the production yield It is to provide a method for measuring CD trend of a mask.

According to an aspect of the present invention, there is provided a method of measuring a CD trend of a photomask, comprising: magnifying and projecting a surface of a patterned photomask using an optical device; Obtaining a plurality of images including a pattern image corresponding to the pattern around the set position coordinates of the photomask; And after summing the contrasts appearing in the plurality of images, dividing the number of images into a plurality of images to obtain an average value of the contrast, and obtaining a CD trend corresponding to the average value of the contrast.

Here, it is determined whether the entirety of the pattern image appears in the plurality of images, and if the entirety of the pattern image does not appear, capturing a portion in which the entirety of the pattern image appears, wherein the plurality of images includes the image of the pattern. It is preferably obtained while being moved by one pixel unit or two pixel units defined by the minimum unit of the imaging device to be picked up.

The method may further include mapping the CD trend corresponding to the average value of the contrast corresponding to each of the plurality of set position coordinates at which the CD trend is measured on the front surface of the photomask to form a database.

Hereinafter, a CD trend measuring method of a photomask according to an embodiment of the present invention will be described with reference to the accompanying drawings. The embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited by the embodiments described below. This embodiment is provided to more completely explain the present invention to those skilled in the art. Therefore, the shape of the elements in the drawings are exaggerated to emphasize a clearer description.

1 is a flowchart illustrating a CD trend measuring method of a photomask according to an embodiment of the present invention.

As shown in FIG. 1, first, in order to obtain information about a myriad of patterns formed in a design to be implemented on a photomask, information about the patterns is databased (S10). Here, the pattern is formed to be repeatedly arranged in accordance with a predetermined rule (rule). At this time, the pattern is made of a predetermined shape appearing in the same layer in a predetermined shape for making a semiconductor device formed on the wafer. The photomask is formed such that a myriad of lines and spaces are sequentially arranged according to a predetermined standard. Accordingly, the pattern to be formed on the photomask may be defined in a predetermined shape, size, and order, and the location to be formed on the photomask may be defined and made into a database. For example, the information corresponding to the pattern may be read as a predetermined picture file or a design file in the interface, and may be output as a flow chart or according to a predetermined form.

Next, the data corresponding to the pattern is coordinated in a plane coordinate system corresponding to the photomask in which the pattern is formed (S20). Here, the pattern is to provide the converted information to be represented in a matrix form on the photomask. For example, the pattern may be generally represented by a wire, and the wire may be represented by being coordinated as (X, Y) in a plane coordinate represented by a Cartesian coordinate system. In addition, the remainder except for the pattern may be processed as blanks and may not be calculated.

Then, the pattern is indexed on a predetermined transparent substrate according to coordinated data to complete the manufacturing process of the photomask (S30). Here, the pattern is indexed on the surface of the photomask according to the coordinated information. For example, the photomask includes a glass substrate made of a transparent material having a predetermined flat surface and a pattern film made of a material having excellent reflectance such as chromium on the glass substrate. Therefore, the photomask may be manufactured by removing chromium uniformly formed on the glass substrate with a laser beam or an electron beam according to predetermined position information. In this case, the pattern formed on the photomask may be transmitted or reflected depending on the type of photoresist patterned on the wafer. For example, when the photoresist is embossed, the pattern of the photomask should be formed with a highly reflective pattern film. On the other hand, when the photoresist is intaglio, the pattern of the photomask should be made of a portion from which the pattern layer is removed because of high transmittance. In this case, all of the patterns on the photomask are intended to be indexed with a constant line width, but there may be limitations of various laser beam or electron beam patterning techniques. In addition, it is necessary to check again the error or error of the worker or program generated in the process of database the pattern once again. Therefore, it is necessary to measure the CD trend to confirm whether the pattern is arranged on a photomask on a predetermined basis, and to determine whether the photomask is uniformly positioned within the entire photomask or within a predetermined range.

Thereafter, in order to measure the CD trend of the pattern formed on the surface of the photomask, the surface of the photomask at a predetermined position is enlarged and projected using an optical device (S40). The optical device enlarges and projects the surface of the photomask on which the pattern is formed at a high magnification. For example, the photomask is supported on a stage having a predetermined flat surface and the surface of the photomask is projected at high magnification using an optical microscope or an electron microscope. In this case, the optical microscope or the electron microscope may enlarge and project the pattern formed at a predetermined position on the surface of the photomask while the stage is moved with the center of the photomask as a predetermined reference point.

Thereafter, a plurality of images including a pattern image corresponding to the pattern of the photomask is acquired not only in the position coordinates of a predetermined range by the operator but also around the set position coordinates (S50). Here, the plurality of images may be enlarged and projected by the optical device and captured by the image sensor. The image sensor can be roughly divided into an image tube and a solid-state image pickup device. The former includes a beacon or a plum beacon, and the latter is a complementary metal oxide semiconductor (CMOS) type image sensor and a charge coupled device. Device (CCD) type image sensor. For example, complementary metal oxide semiconductor (CMOS) image sensors, charge coupled device (CCD) image sensors, and the like. Here, the imaging tube has the advantages of low cost and long life, but it is difficult to be mounted in the exposure equipment because of the low resolution and large volume. On the other hand, the solid-state imaging device is a semiconductorized and integrated imaging device, also referred to as an imaging plate corresponding to the imaging tube. The solid-state image pickup device includes a two-dimensionally arranged pixel group having a function of accumulating photoelectric conversion and charge on a semiconductor substrate on which the visible light is incident. Combined with a scanning function that reads the charge images stored in the pixels in a certain order, so that all of them are solidified to form an integrated structure. Is easy. In this case, the semiconductor substrate is almost a single crystal silicon substrate, and the pixel is formed to have a matrix array on the semiconductor substrate. Therefore, the solid state image pickup device is sequentially read in accordance with the scanning method of the pixel charge amount which is the smallest constitutional unit on the telephone to generate an output signal current. The solid-state image pickup device is a photoelectric conversion-accumulation-scanning (reading) function, and the basic method is a charge transfer method in which each pixel is sequentially transferred to each pixel through a scanning signal generator for reading. . In this case, a metal oxide semiconductor transistor is used as a complementary metal oxide semiconductor image sensor for signal transmission of a light receiving unit that receives the corrected laser beam in the visible light region, and a charge coupled device (CCD) is used as a charge coupled device. It is called a type image sensor. In this case, the charge coupled device type image sensor is composed of an integrated circuit having a basic element, a passive element such as a diode or a resistor mainly composed of a semiconductor thin film and a plurality of electrodes provided on the surface. Here, the charge coupling device is a semiconductor device. An insulating layer having a thickness of about 0.1 m is formed on the surface of the n-type semiconductor substrate, and the metal electrodes are arranged to control the voltage of the metal electrodes, thereby moving the lower portion of the semiconductor surface potential to the left and right to sequentially accumulate charges accordingly. It can also be used as a shift register or storage device because it can be transferred. The charge coupling device is a device having a simple structure similar to that of a metal oxide semiconductor transistor, and is widely used in industrial fields because it has two functions of memory storage by charge accumulation and transfer by charge transfer.

Accordingly, the image sensor is shifted by one pixel unit, two pixel units, or more pixels around the set position of the photomask that is enlarged and projected by the optical device, and includes a plurality of images including the pattern image. Can be obtained.

In this case, the plurality of images should be verified whether the entire pattern image is included (S60). This is because if the CD trend is to be measured at the portion where the pattern image appears, but the entire pattern image does not appear, it is impossible to calculate the correct contrast of the portion where the pattern image appears later.

Next, when there is a portion in which the entirety of the pattern image does not appear in the plurality of images, the portion in which the pattern image appears in the plurality of images is captured. For example, the plurality of images may be processed in software using a program called Matlab to capture a portion where the pattern image appears (S70).

Next, the contrasts of the plurality of images are summed, divided by the number of images, and the average value of the contrast is calculated, and the CD trend corresponding to the average value of the contrast is calculated (S80). Here, the plurality of images have a predetermined transmittance or reflectance according to the degree of light and dark. Thus, the contrast may correspond to the transmittance or reflectivity. For example, the plurality of images obtained by the optical device and the image sensor using the transmitted light that is shielded through the pattern film of the photomask and then passes through the glass substrate of the transparent material has a constant contrast corresponding to a predetermined transmittance. On the other hand, the plurality of images obtained by the optical device and the image sensor by using the reflected light reflected from the pattern film of the photomask film has a constant contrast corresponding to a predetermined reflectivity. In addition, the interface calculates an average value of the contrast by dividing all the contrasts of each of the plurality of images by the number of the plurality of images. In addition, the average value of the contrast corresponds to the CD trend. In this case, since the CD trend is calculated using a plurality of images acquired around the set position as well as the set position, the CD trend can be measured more accurately than in the related art.

Therefore, the photomask CD trend measuring method according to an embodiment of the present invention calculates a CD trend using a plurality of images including a predetermined pattern image around the set position and sets the set position even if the pattern measured at the set position deviates partly. CD trends can be measured precisely, increasing or maximizing production yields.

Finally, after calculating the CD trend corresponding to the average value of the contrast in the same manner as described above in a plurality of set locations across the entire surface of the photomask (S90) is mapped to the database. Here, the database CD trend map can be used as various data to evaluate the performance of the mask to be applied to the process. For example, the CD trend map may be used to evaluate the quality of a mask, to calculate a CD trend for each area on the mask surface, to extract a CD trend distribution, or to manage a CD trend maximum and minimum.

As described above, in the CD trend measuring method of the photomask according to the embodiment of the present invention, the CD trend is calculated using a plurality of images including a predetermined pattern image around the set position, and the pattern image measured at the corresponding position is partially. It is possible to increase or maximize the production yield by accurately measuring CD trends even if they are off, and by obtaining a plurality of CD trends on the front of the photomask and mapping the CD trends to a database of the CD trends on the front of the photomask.

In addition, the inventive concepts and embodiments disclosed herein may be used by those skilled in the art as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. In addition, such modifications or altered equivalent structures by those skilled in the art may be variously changed, substituted, and changed without departing from the spirit or scope of the invention described in the claims.

As described above, according to the present invention, a CD trend using a plurality of images including a predetermined pattern image around a set position is calculated, and the CD trend at the set position even if a part of the pattern measured at the set position deviates. Since the measurement can be made accurately, there is an effect to increase or maximize the production yield.

Claims (4)

Magnifying and projecting the surface of the patterned photomask using an optical device; Obtaining a plurality of images including a pattern image corresponding to the pattern around the set position coordinates of the photomask; And Summing the contrasts appearing in the plurality of images, dividing by the number of images to obtain the average value of the contrast, and obtaining a CD trend corresponding to the average value of the contrast. . The method of claim 1, And determining whether the entire pattern image appears in the plurality of images, and if the entire pattern image does not appear, capturing a portion in which the entire pattern image appears. The method of claim 1, And the plurality of images are acquired while moving in a unit of 1 pixel unit or 2 pixel unit defined as the minimum unit of the image pickup apparatus for imaging the image of the pattern. The method of claim 1, Mapping the CD trend corresponding to the average value of the contrast corresponding to each of the plurality of set position coordinates at which the CD trend is measured on the front side of the photomask, and converting the database into a CD trend of the photomask. How to measure.

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