Ultrafine lithography pattern inspection using multi-stage TDI image sensors with false image removability

A workpiece inspection apparatus includes a measured image generator unit configured to measure a pattern of a workpiece and generate a measured image; and a comparator unit configured to compare the measured image to a fiducial image, wherein said measured image generator unit includes a light-receiving device having an interconnection of two or more time delay integration (TDI) sensors each being arranged by two or more line sensors each being arranged by two or more pixels, for generating as the measured image an average value of pixel values excluding an abnormal pixel value from pixels of each TDI sensor with respect to a position of the pattern of the workpiece.

CROSS-REFERENCE TO RELATED APPLICATION(S)

Priority is claimed to Japanese Patent Application No. 2008-068918, filed Mar. 18, 2008, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to pattern inspection technologies and, more particularly, to a method and apparatus for inspecting ultrafine patterns of a workpiece, such as a photomask, wafer or substrate, which is used in the manufacture of highly integrated semiconductor devices and/or liquid crystal display (LCD) panels.

DESCRIPTION OF RELATED ART

In ultralarge-scale integrated (ULSI) circuit devices, such as one-gigabit (1 Gb) class dynamic random access memory (DRAM) chips, circuit patterns are becoming from submicron to nanometer orders in minimum feature sizes thereof. In the manufacture of such ULSI devices, production yields can decrease due to some causes, one of which must be the presence of defects in a photo-mask to be used in the process of exposing and transferring an ultrafine pattern onto semiconductor wafers by use of photolithography techniques. In particular, as ULSI patterns to be formed on semiconductor wafers decrease in size dimensions, pattern defects that must be detected by inspection tools become smaller in size accordingly. In view of this, an advanced pattern inspection apparatus capable of checking ULSI chips for such ultra-small defects has been developed.

Regarding LCD devices, recent advances in multimedia technology result in LCD panels becoming larger in substrate size to have a display area of 500 mm by 600 mm or greater and also becoming smaller in minimal line-width and feature size of patterns of thin-film transistor (TFT) circuitry to be formed on an LCD substrate. It is thus required to perform inspection of ultrasmall pattern defects extensively. This brings an urgent need to develop a high-accuracy workpiece inspection apparatus capable of efficiently checking for defects this large-area LCD pattern and a photomask for use in the manufacture of such large-area LCD panels in a short period of time.

Prior known pattern inspection tools are faced with a problem as to the lack of an ability to sufficiently perform the required inspection. One reason of this is that false images, which cause virtual presence of tiny patterns, are created at photoelectric sensors for acquisition of the image of a workpiece under inspection due to the presence of cosmic radiation rays or electrical noises internally occurring in the sensors. A technique for avoiding this false image-related problem is disclosed in Published Japanese Patent Application No. H05-312955, which employs a sensor for detecting collision of cosmic rays with image sensors to thereby remove baneful influence of such cosmic rays. Unfortunately, this advantages of the prior art technique does not come without accompanying penalties: an increase in apparatus configuration, an increase in structural complexity, and a failure to remove the influence of internal sensor noises.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a new and improved workpiece pattern inspection technique with increased accuracy. Another object of this invention is to provide a method and apparatus for performing workpiece inspection capable of excluding temporarily generated false images of an actually measured pattern image.

In accordance with one aspect of this invention, a workpiece inspection apparatus is provided which includes a measured image generator unit configured to measure a pattern of a workpiece and generate a measured image; and a comparator unit configured to compare the measured image to a fiducial image, wherein said measured image generator unit includes a light-receiving device having an interconnection of two or more time delay integration (TDI) sensors each being arranged by two or more line sensors each being arranged by two or more pixels, for generating as the measured image an average value of pixel values excluding an abnormal pixel value from pixels of each TDI sensor with respect to a position of the pattern of the workpiece.

In accordance with another aspect of the invention, a workpiece inspection apparatus is provided, which includes a measured image generator unit configured to measure a pattern of a workpiece and generate a measured image, and a comparator unit for comparison of the measured image to a fiducial image. The measured image generator unit includes a light-receiving device having an interconnection of two or more TDI sensors, each of which is arranged by two or more line sensors, each being arranged by two or more pixels. The measured image generator unit generates as the measured image the average value of pixel values excluding as the abnormal pixel value a pixel value greater than a fiducial value from pixels of each TDI sensor with respect to a position of the pattern of the workpiece.

In accordance with still another aspect of the invention, a workpiece inspection apparatus is provided which includes a measured image generator unit configured to measure a pattern of a workpiece and generate a measured image, and a comparator unit configured to compare the measured image to a fiducial image. The measured image generator unit includes a light-receiving device which has an interconnection of two or more TDI sensors each be arranged by two or more line sensors, each of which is arranged by two or more pixels, uses as a fiducial value a sum of an average value of pixel values and a predetermined value and generates as the measured image the average value of pixel values excluding as the abnormal pixel value a pixel value greater than the fiducial value from pixels of each TDI sensor with respect to a position of the pattern of the workpiece.

In accordance with a further aspect of the invention, a workpiece inspection apparatus is provided which includes a measured image generator unit configured to measure a pattern of a workpiece and generate a measured image, and a comparator unit configured to compare the measured image to a fiducial image. The measured image generator unit includes a light-receiving device which has three or more of the TDI sensors, and generates as the measured image the average value of pixel values excluding as the abnormal pixel value a pixel value such that an absolute value of a difference between the pixel value and an average value of pixel values of all the three or more TDI sensors at the position is greater than a fiducial value, from pixels of each TDI sensor with respect to a position of the pattern of the workpiece.

In accordance with another further aspect of the invention, a workpiece inspection apparatus is provided which includes a measured image generator unit configured to measure a pattern of a workpiece and generate a measured image, and a comparator unit configured to compare the measured image to a fiducial image. The measured image generator unit includes a light-receiving device which has three or more of the TDI sensors. when calculating as the measured image the average value of pixel values, if an average value difference which is an absolute value of a difference between a pixel value of an i-th TDI sensor and an average value calculated using pixel values of first to (i−1)th TDI sensors is less than or equal to a fiducial value, the measured image generator unit sets as a new pixel value an average value of a pixel value of the i-th TDI sensor and pixel values of the first to (i−1)th TDI sensors, and if the average value difference is not less than the fiducial value then the measured image generator unit performs processing for preventing updating of the average value as the abnormal pixel value. And the measured image generator unit repeats execution of this processing with respect to pixels of all the TDI sensors to thereby obtain an average value and then lets this average value be the measured image.

In accordance with another further aspect of the invention, a workpiece inspection method is provided, which includes measuring a pattern of a workpiece using a light-receiving device including an interconnection of two or more time delay integration (TDI) sensors each being arranged by two or more line sensors each being configured from two or more pixels; generating as a measured image an average value of pixel values excluding an abnormal pixel value from pixels of each TDI sensor with respect to a position of the pattern of the workpiece; and comparing the measured image to a fiducial image to output a compared result.

According to at least one of these invention, it is possible to perform accurate workpiece pattern inspection. Another advantage of the at least one of these invention lies in its ability to perform pattern inspection capable of excluding temporarily created false images of a measured image of a workpiece being tested.

DETAILED DESCRIPTION OF THE INVENTION

Currently preferred embodiments of this invention will be described in detail with reference to the accompanying figures of the drawing below.

Workpiece Inspection Basics

SeeFIG. 1, which shows in block diagram form a principal data flow in workpiece inspection to be performed by a pattern inspection apparatus10embodying the invention. The workpiece inspection apparatus10is the one that performs inspection of a circuit pattern12of a workpiece under testing, such as a photomask, wafer or substrate of liquid crystal display (LCD) panel. The workpiece inspection apparatus10is especially the one that checks the workpiece pattern12for defects by generating a measured image, which is for use as an object to be compared, while excluding therefrom unwanted influenceability of false images of an output image. These false images are locally created temporarily due to the presence of radiation rays, such as cosmic rays, or internal production of electrical noises in sensors. The workpiece inspection apparatus10includes a measured image generation unit14, which measures transmitted light and/or reflection light of the workpiece pattern12to thereby generate a measured image of any one of a transmitted image and a reflection image or both of them. The inspection apparatus10also includes a reference image generation unit22, which processes design data20of the workpiece pattern to thereby produce a referencing image that resembles the measured image.

The workpiece inspection apparatus10has a comparison unit24, which receives a measured image from which any false images are removed away and compares this false image-excluded measured image to the reference image to determine whether a difference therebetween is in excess of a predetermined value: if the difference exceeds this value, then decide that the measured image must contain defects therein. The comparator24uses the reference image which was produced by the reference image generator22as a standard or fiducial image to perform die-to-database (D-DB) comparison with the false image-excluded measured image. Alternatively, the comparator24uses as the fiducial image a measured image which is obtained by the measured image generator14through image pickup of the same pattern of the workpiece at a different location on its surface and from which any possible false images are removed, thereby performing die-to-die (D-D) comparison with the false image-excluded measured image.

Measured Image Generator

The measured image generator unit14includes a light-receiving device30, such as a photoelectric imaging device, and a false image removing unit40. The light-receiving device30has a photosensitive module which is generally made up of a serial combination of a plurality of time delay integration (TDI) image sensors32as shown inFIG. 4. Typical examples of these TDI sensors32are photodiodes, charge-coupled device (CCD) photo-sensing elements and like sensors, which are for integrating a packet of electrical charge carriers by an integration stage number in the charge transfer direction. Use of the TDI sensors32makes it possible to improve the sensitivity in proportion to the stage number, thereby reducing noises otherwise occurring due to element variations and/or irregularities of illumination light brightness.

The false image remover40is operatively responsive to receipt of an output value of an image that was picked up by each of the TDI sensors32, for performing comparison of it with the fiducial value and applying thereto arithmetic processing, such as average value calculation or the like, to thereby remove therefrom an abnormally large output value which is not normally detected from the intensity of light, i.e., an abnormal pixel value that exceeds the fiducial value. By doing this, any possible false or “fake” images are moved away. Note here that the fiducial value is obtained by taking into consideration either the normally non-detected large output values or those values which are obtained through various arithmetic computation processes, e.g., the average value of all output values involved.

Workpiece Inspection Apparatus

Turning toFIG. 2, an internal configuration of the workpiece inspection apparatus10is shown. This workpiece inspection tool10is the one that checks a workpiece100for pattern defects. An example of the workpiece is a photomask or a silicon wafer or else. The workpiece inspection tool10includes an optical image acquiring unit110and a system control unit150. The optical image acquisition unit110is generally made up of an automatic loader112, an illumination device114for emitting illumination light, a movable table structure116, which is slidable in directions of X and/or Y axis while rotating about Z axis by an angle θ, an electrical motor118for driving the X-Y-θ table116, a laser-used length measurement system120, a magnifying optical system122, a piezoelectric element124, the light-receiving device30having the TDI sensors32for sensing received light rays which passed through or reflected from the workpiece surface, such as CCD image sensor, photodiode array, etc., the false image removing unit40, and a sensor circuit128associated therewith.

The system controller150includes a central processing unit (CPU) for use as a control computer, which is connected via a data transfer bus154to a large-capacity storage device156, semiconductor memory158, display device160, printer162, auto-loader control circuit170, table control circuit172, auto-focus control circuit174, pattern generation circuit176, reference image generation circuit178, comparator circuit180, position control circuit182and others. The false image remover40may alternatively be disposed within the sensor circuit128. The pattern generator circuit176, reference image generator circuit178, comparator circuit180and positioning circuit182are operatively connected together as better shown inFIG. 2.

The measured image generator14ofFIG. 1may be configured from the optical image acquisition unit110shown inFIG. 2. The reference image generator22is configurable from the pattern generator circuit176and reference image generator circuit178. The comparator unit24is arrangeable by the comparator circuit180. The workpiece inspection apparatus10of the illustrative embodiment may be designed to include other known functional units or components, which are not specifically illustrated herein.

Operation of Image Acquisition Unit

The workpiece100to be inspected, such as a mask for light exposure or photolithography, is conveyed by the auto-loader112which is driven by the auto-loader control circuit170and is then loaded into a processing chamber (not shown) of the workpiece inspection tool10so that it is placed onto the XYθ table116in an automated way. The workpiece100has a top surface which is irradiated with incoming light from the illumination device114overlying this workpiece in order to obtain transmitted light, and has a back surface onto which light is irradiated from its downside in order to obtain reflected light, although not specifically shown inFIG. 2. Disposed beneath the workpiece100are the magnifying optical system122, light-receiving device30, false image remover40and sensor circuit128. The transmitted light that passed through the workpiece100or the light reflected therefrom is guided by the magnifying optical system122to be focused onto the light-receiving device30as an optical image. The auto-focus control circuit174controls the piezoelectric element124to perform image focussing adjustment relative to the workpiece100in order to absorb arcuation of the workpiece100and fluctuation of the XYθ table116into Z axis, which is at right angles to X and Y axes.

A perspective view of the workpiece100is shown inFIG. 3for explanation of a procedure of acquiring the measured image. The workpiece100has on its top surface an area to be inspected, which is virtually subdivided by a scan width W in Y-axis direction. More specifically, the workpiece100's inspection area is virtually divided into a plurality of strip-like portions102, each of which has a width corresponding to the scan width W. The XYθ table116is controlled so that these divided strips102are continuously scanned one-by-one in a serpentine fashion which follows. Firstly, the XYθ table116moves along the X axis so that a measured image of one strip102is acquired. This strip102is of a narrow elongate rectangle shape which has the scan width W along Y-axis direction and its length along the X-axis direction as shown inFIG. 3. The light that passed through the workpiece100or the light reflected therefrom travels through the magnifying optical system122to fall onto the light-receiving device30. Part of the strip-like surface area of the virtually divided pattern shown inFIG. 3is focused as a magnified optical image on the light-receiving device30. The light-receiving device30continuously picks up images each having the scan width W such as shown inFIG. 3. After having acquired the image of the first strip102, the light-receiving device30senses an image of second strip102having the scan width W while moving in the opposite direction at this time. When sensing an image of third strip102, it acquires this image while moving in the opposite direction to that when it acquired the image of the second strip102—that is, the direction same as that when obtained the image of the first strip102. The scan width W may be set to about 2,048 pixels, for example.

The XYθ table116is driven by the table control circuit172under the control of CPU152. This table becomes movable by use of a drive system having the three-axis (X-Y-θ) motor assembly118including three electric motors for driving the table116in X-axis direction, Y-axis direction and θ direction, respectively. Examples of these motors are stepper motors. A moved position of the XYθ table116is measured by the laser length measurement system120. This system generates an electrical signal indicative of a present table position, which signal is then supplied to the position circuit182. The light-receiving device30obtains electronic data of the same pattern by means of the plurality of TDI sensors32. The false image remover40uses the electronic data of the same pattern of each TDI sensor to exclude a false image which can take place due to cosmic rays and/or electrical noises. The sensor circuit128outputs as a measured image the electronic data of an optical image with false images being excluded therefrom. The measured image as output from the sensor circuit128is sent to the comparator circuit180along with output data of the position circuit182which indicates the position of the workpiece100on XYθ table116. After having completed pattern inspection, the workpiece100on the XYθ table116is automatically ejected under control of the auto-loader control circuit170. An example of the measured image is unsigned 8-bit data indicative of the gradation or “tone” of the brightness of each pixel.

An internal structure of the light-receiving device30is shown inFIG. 4, wherein three separate TDI image sensors32a,32band32care serially connected together. Each TDI sensor has a predetermined number, e.g., 256 or 512, of stages of line sensors34, although six stages of line sensors34ato34fare shown inFIG. 4for purposes of convenience in illustration. Each line sensor34a,34b, . . . ,34fhas a linear array of a great number of—e.g., 1,024 or 2,048—pixels36, although ten pixels are shown inFIG. 4for illustration purposes only. TDI sensors32ato32chave buffer memories38ato38c, respectively. Electrical charge carriers that are produced in TDI sensor32a,32b,32cis ejected or “drained” to its associated buffer memory38a,38b,38c. Each buffer memory38a,38b,38cis for temporary storage of the data of an image as sensed by TDI sensor32a,32b,32cassociated therewith.

An exemplary pattern of the workpiece100which is sensed by the light-receiving device30is shown inFIG. 4, wherein an optical image of a pattern of alphabetical letter “A” is projected onto the light-receiving device30while moving from its downside to upside. When doing so, the individual TDI sensor32a,32b,32cof light-receiving device30picks up the pattern image “A”, causing its produced charge carriers to sequentially transfer upward as indicated by a black-painted arrow inFIG. 4. The carriers that have reached an upper end of TDI sensor32a,32b,32care drained to its corresponding buffer memory38a,38b,38c. The first stage TDI sensor32asenses the pattern image “A” faster than the remaining, second and third TDI sensors32b-32cso that its produced carriers are drained to the buffer memory38aassociated therewith. Then, the second stage TDI sensor32bsenses this pattern “A” to drain its produced carriers to its associated buffer memory38b. Lastly, the third TDI sensor32csenses this pattern “A” to drain produced carriers to its own buffer memory38c.

Turning toFIG. 5, there is shown a sequence of steps S1to S5in the process of sensing the pattern image of alphabetical letter “A”, which process is performed by one TDI sensor32having five (5) line sensors34ato34efor example. At step S1, the first line sensor34aoptically picks up uppermost part of the pattern “A” and produces a corresponding amount of charge carriers, which are then accumulated therein. At the next step S2, the carriers accumulated in the first line sensor34aare transferred to the second line sensor34bthat is placed next thereto. It is noted here that inFIG. 5, a pattern with an increased amount of received light is illustrated by a heavy line segment having a likewise thicker line width—i.e., a proportionally thickened line.

Then, at step S3, the second line sensor34bsenses a pattern of the upper end of the pattern “A” and, at the same time, the first line sensor34asenses its following pattern part which is slightly below the upper end of this pattern “A” so that a corresponding amount of charge carriers are accumulated therein. Due to this, the upper edge of the pattern “A” of second line sensor34bis such that its corresponding sensed carrier accumulation becomes greater in amount. Regarding the pattern which is little lower than the upper edge of the pattern “A” of the first line sensor34a, its charge accumulation amount is not greater than that of the upper edge thereof. Subsequently, in step S4, the carriers that were accumulated in the second line sensor34bare transferred to the third line sensor34cat the next stage while at the same time causing the carriers stored in first line sensor34ato be sent forth toward the second line sensor34b.

At step S5ofFIG. 5, the third line sensor34csenses incoming light of the upper end of the pattern “A”; at the same time, the second line sensor34bsenses a subsequent pattern part which is below the upper end of the pattern “A”; and, simultaneously, the first line sensor34asenses a part which is further below the upper end of the pattern “A”, resulting in a corresponding amount of charge carriers being accumulated therein. Accordingly, the sensed upper end of the pattern “A” of third line sensor34cis further greater in carrier accumulation amount; the pattern slightly below the upper end of the pattern “A” of second line sensor34bis greater in carrier accumulation; and, the pattern which is further below the upper end of the pattern “A” of first line sensor34ais relatively less in carrier accumulation amount.

In this way, the TDI sensor32accumulates therein a sensed image of the workpiece pattern with the elapse of time. Accordingly, even when a temporary false image takes place in this sensor due to the presence of cosmic radiation rays or electrical noises, it is possible to lessen the influenceability thereof. In addition, in this embodiment, it is also possible by use of the plurality of TDI sensors32to remove or at least greatly suppress baneful influences of temporarily creatable false images.

Reference Image Generation

The design data that was used in the process of forming the pattern of the workpiece100is stored in the large-capacity storage device156. The design data20is input from the large-capacity storage device156to the pattern generator circuit176under the control of CPU152. This design data is subjected to pattern generating in a way which follows. The pattern generator circuit176converts the design data of workpiece100into two-value or multi-value image data indicative of the original pattern image. This original image data is sent to the reference image generator circuit178. The reference image generator178applies appropriate filtering to the original image data to thereby produce an image to be referenced—say, reference image. It can be said that the measured image as obtained from the sensor circuit128is in the state that the filtering acts thereon owing to the image resolution characteristics of the magnifying optics122and aperture effects of the light-receiving device30. In this state, a difference must exist between the measured image and the original image data on the design side. Thus, by applying the filtering by the reference image generator circuit178to the original image data on the design side, it becomes possible to fit or “tune” it to the measured image.

First Embodiment

FIG. 6shows a relation of the light-receiving device30and the false image remover unit40in a first embodiment of the workpiece pattern inspection. The light-receiving device30as used herein is arranged to have a prespecified number of TDI sensor32a,32b, . . . ,32n(where “n” is a positive integer), each of which includes two or more stages of line sensors. As shown inFIG. 5, the TDI sensors32perform measured data accumulation while transferring the measured data in a way synchronous with the movement of the pattern “A” of a workpiece.

Usually, noises are temporarily generated with respect to a local pixel due to the irradiation of cosmic rays or else. In view of this, the false image remover40applies arithmetic processing to this pixel's output value of abnormal brightness for removing such noises to thereby obtain a measured image. Thereafter, inspection is performed with this image being used as a measured image corresponding to the pattern of the workpiece under testing. This makes it possible to achieve high-sensitivity inspection without being influenced by false images.

An example of this noise removal processing is as follows. In the case of the light-receiving device30having a serial combination of N TDI sensors32a,32b, . . . ,32neach having n stages of line sensors34, the cosmic ray-caused noise appearing in each TDI sensor32i(1≦i≦n) becomes N times greater than that occurrable at a single TDI sensor having n×N stages of line sensors. In view of this, as shown inFIG. 6, the average value of an ensemble of TDI sensors32each having its output value less than or equal to a predetermined fiducial value is computed with respect to a position of the pattern of the workpiece; then, inspection is performed with this average value being used as the measured image corresponding to the pattern of the to-be-tested workpiece with respect to the position of the workpiece. By executing this processing, it becomes possible to achieve high-sensitivity inspection without being influenced by false images. The fiducial value is determined by taking account of a value which is not normally measured from the strength of light or the like—for example, it is set to 240 gradation levels, or more or less.

More specifically, in the false image remover40, an output value (pixel value) of each pixel36of the first TDI sensor32aat a position of the pattern of the workpiece is compared to the fiducial value: if this output value greater than the fiducial value, it is determined to be a false image and thus discarded or “wasted.” Similarly, as for the individual one of the second to N-th TDI sensors (TDI1to TDIN)32bto32nat the position also, a decision is made as to whether its output value is less than or equal to the fiducial value (at step S10). Any pixel value which is not less than the fiducial value is wasted as a false image (at step S11). Those pixel values less than or equal to the fiducial value are summed together for calculation of the average value thereof (at step S12). This average value is sent to the comparator unit24as the measured image which contains no false images and then compared with the fiducial image for inspection to determine whether defects are present or absent with respect to the position, and the compared result is output. (at step S13). This processing is performed with respect to each position of the pattern of the workpiece.

Second Embodiment

SeeFIG. 7, which shows a second embodiment including the light-receiving device30which is configured from a serial combination of TDI sensors32a,32b, . . . ,32neach having two or more line sensors34, wherein a specific value which is equal to a sum of the average value of outputs of all the TDI sensors32a-32nand a prespecified value is used as the fiducial value. While in the first embodiment an attempt was made to judge whether an output value of a respective sensor is used as the measured pattern data by using a single fiducial value as a standard for each sensor output value, noises occurring due to cosmic rays significantly affect the sensor output in such a way that it becomes greater undesirably in most cases. Therefore, the second embodiment is arranged so that the specific value that is obtained by adding together the average value of outputs of all the TDI sensors32a-32nand the prespecified value is used as the fiducial value. Regarding an output image used for workpiece pattern inspection, the average value of an ensemble of those TDI sensors each being less than or equal to the fiducial value is calculated and used as the measured image. With this arrangement, it is possible to exclude false images more precisely. The prespecified value as used herein is set by taking into consideration the stability of output characteristics of TDI sensors32—for example, it is set at about 20 gradation levels. Thus it becomes possible to remove noises occurring due to cosmic radiation rays, which are less in energy than those in the first embodiment.

More specifically, in the false image remover40, what is done first is to calculate the average value of output values of all the TDI sensors (TDI1to TDIN)32a-32nwith respect to a position of the pattern of the workpiece (at step S20). A sum of the average value thus calculated and a predetermined value is obtained for use as the fiducial value, which is then compared to an output value of each pixel of the first to N-th TDI sensors32a-32n(at step S21) If the output value is in excess of the fiducial value then this is judged to be a false image and then discarded (at step S22). The remaining pixel values each of which is less than or equal to the fiducial value are added together for calculation of their average value (at step S23). This average value is sent to the comparator unit24as a measured image which contains no false images at the position of the pattern of the workpiece and then compared to the fiducial image for execution of the inspection for defects with respect to the position, and the compared result is output. (at step S13). These steps are performed with respect to each position of the pattern of the workpiece.

Third Embodiment

Referring next toFIG. 8, there is shown a third embodiment which includes its light-receiving device30having three or more TDI sensors32a,32b, . . . ,32neach having two or more stages of line sensors34. In a case where the absolute value of a difference between the average value of output values of all the TDI sensors32a-32nand an output value of the individual TDI sensor32ibecomes greater than a predetermined fiducial value, such output value is discarded and the average value of output values of the other TDI sensors32is used as the measured image. Whereby, it becomes possible to remove noises by means of majority decision in case a number of noise-affected TDI sensors32is less than the half of a total number of TDT sensors involved. The fiducial value in this case is set at about 20 gradation levels as an example.

More precisely, in the false image remover40, the processing to be done first is to calculate the average value of output values of respective pixels36of the first to N-th TDI sensors (TDI1to TDIN)32a-32nwith respect to a position of the pattern of the workpiece (at step S30). Then, the absolute value of a difference between the average value thus computed and an output value of each pixel of each TDI sensor is calculated and then compared to a predetermined fiducial value (at step S31). If this absolute value is not less than the fiducial value, it is determined that it must be a false image and then wasted (at step S32). Those pixel values each of which is less than or equal to the fiducial value are added together for calculation of their average value (at step S33). This average value is sent to the comparator unit24as a measured image that contains no false images and then compared with the fiducial image for inspection for pattern defects with respect to the position, and the compared result is output. (at step S13). These steps are performed with respect to each position of the pattern of the workpiece.

Fourth Embodiment

A fourth embodiment shown inFIG. 9is such that it employs three or more TDI sensors32a-32neach having two or more stages of line sensors34. Unlike the above-stated second and third embodiments each being arranged so that the comparison judgment with an output value of the individual TDI sensor32is performed after having computed the average value of all the TDI sensors32a-32n, the fourth embodiment is arranged in a way which follows: as shown inFIG. 9, at N TDI sensors32a-32n(where N is an integer), an output value of the i-th TDI sensor32and an average value using output values of the first to (i−1)th TDI sensors are compared to each other. If the absolute value of a difference therebetween (referred to hereinafter as the average value difference) is not lower than a fiducial value having a predetermined specific value, the output value of the i-th TDI sensor32is wasted. If the average value difference is lower than the fiducial value then add thereto the output value of the i-th TDI sensor32to thereby update the currently established average value. This process will be repeatedly executed sequentially from an output value of the second TDI sensor32up to the last, N-th TDI sensor32. With this processing, it is possible to eliminate the average calculation process to be first performed in the second and third embodiments; so, it is no longer necessary to wait until completion of outputting of pixel values from all the TDI sensors32involved, thereby enabling successful execution of more effective pattern inspection. The fiducial value is set by taking account of the stability of output characteristics of all the TDI sensors of the light-receiving device30—for example, it is set to about 20 gradation levels.

More specifically, in the false image remover40, initialization processing is done first while letting a pointer “i” be equal to 2 (i.e., i=2) and letting the average value be equal to an output value of the first TDI sensor32awith respect to a position of the pattern of the workpiece (at step S40). Then, an output value of the second (i=2) TDI sensor32bat the position is read out (at step S41) for comparison with the average value. If its average value difference is not lower than the fiducial value (step S42), the output value of the second sensor is discarded (step S43). On the contrary, if the average value difference is lower than the fiducial value (step S42), an output value of the second TDI sensor32bis added thereto to thereby update the average value with respect to the position of the pattern of the workpiece (step S44). Next, checking is performed to determine whether a presently designated TDI sensor32is the last one (step S45). If it is not the last TDI sensor then add one (1) to the pointeri(step S46). Then, an output image of the next TDI sensor32at the position of the pattern of the workpiece is read out (step S41), followed by repeated execution of similar processing up to the last TDI sensor32nwith respect to the position of the pattern of the workpiece. The finally obtained average value at the position of the pattern of the workpiece in this way is sent to the comparator unit24as a measured image which contains no false images and is then compared with the fiducial image for inspection for pattern defects with respect to the position, and the compared result is output. (step S13). These steps are performed with respect to each position of the pattern of the workpiece.

In the illustrative embodiments stated supra, degradation of image quality due to the mixture of false images occurrable by cosmic radiation or internal electrical sensor noises badly behave to affect the pattern defect detectability and sensitivity in the process of inspecting workpieces being tested; so, in order to increase the sensitivity, it is important to perform such inspection by use of specific sensors of the type outputting no false images. Accordingly, by detecting false images due to cosmic rays falling onto sensors and/or electrical noises generated within these sensors and removing them from accumulated data, it is possible to suppress or minimize pseudo-defects otherwise occurring due to the presence of such noises, thereby making it possible to perform high-sensitivity inspection. The inspection in any one of these embodiments may be performed with respect to every pixel of a measured image or, alternatively, performed only for selected pixels which particularly require higher precision when the need arises or, still alternatively, performed only for certain pixels that are high in probability of false image creation.

Any one of the functional units and circuits plus process steps as stated in the description above may be configured from a computer-executable software program or programs. Alternatively, any one of them is configurable from possible combinations of software programs and hardware components or, still alternatively, combinations with firmware assemblies. In the case of being configured from software programs, these may be prestored or temporarily stored in storage media, such as a magnetic disk drive device, such as a hard disk drive (HDD), magnetic tape recorder device, floppy diskette (FDD) or read-only memory (ROM).

Although the invention has been disclosed and illustrated with reference to particular embodiments, the principles involved are susceptible for use in numerous other embodiments which will be apparent to persons skilled in the art. For example, while in each embodiment the testing position is scanned by driving the XYθ table116to move accordingly, this table may be modified to be fixed at a prespecified location while designing its associated optics to move relative thereto. In other words, relative motion methodology is employable for the workpiece table and the optics associated therewith. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.