JP2005251753A - Inspection method and inspection device of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the reliability of defect detection sensitivity and an inspection result by removing the noise of a high frequency component resulting from detailed unevenness produced in the case of processing a semiconductor device circuit pattern. <P>SOLUTION: An offset is applied to a focal position on a semiconductor device 28 by changing the diameter of an electron beam irradiated to the semiconductor device 28 by the operation of an objective lens 11 or regulating the height of alternatively the objective lens 11 or a test piece 14 in response to the unevenness generated in the case of processing the semiconductor device. Moreover, the pixel size is changed according to the unevenness of the semiconductor device processing surface at an image processing time in an image processing arithmetic unit 24. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a pattern inspection technique for a semiconductor device.

As for the method of inspecting the defect of the circuit pattern formed on the wafer, the method of comparing the same kind of circuit pattern of multiple LSIs using an optical image and the method of comparing circuit patterns using an electron beam image are reported. Has been. The contents are described below. In the method using an optical image, as described in JP-A-3-160348 and JP-A-3-167456, an optically illuminated region on a substrate is imaged by a time delay integration sensor, A method for detecting defects by comparing images with pre-input design characteristics, or image degradation during image acquisition as described in JP-A-61-82107 and detecting it A method of performing a comparative inspection with a stable optical image by correcting sometimes has been reported. As described in Japanese Patent Application Laid-Open No. 5-258703, a pattern comparison inspection apparatus using an electron beam irradiates a conductive substrate (such as an X-ray mask) with a secondary electron generated by A system for automatically detecting defects by detecting either reflected electrons or transmitted electrons and comparing and inspecting an image formed from the signal has been reported. The same content is described in J. Vac. Sci. Tech. B, Vol. 9, No. 6, pp. 3005-3009 (1991), J. Vac. Sci. Tech. B, Vol. 10, No. 6, pp. 2511-2515 (1992). In addition, pattern inspection using an electron beam image is performed by continuously irradiating an electron beam onto a wafer on a sample stage which is continuously disclosed in Japanese Patent Laid-Open No. 7-231022, and comparing the input image with an image of an adjacent repeated pattern with a time delay. A method is described. Japanese Patent Application Laid-Open No. 59-160948 describes a method of comparing and inspecting electron beam images by calculating the deviation between the reference coordinates on the wafer and the sample table coordinates and correcting the electron beam deflection to eliminate image distortion. In addition, Japanese Patent Laid-Open No. 4-337235 discloses a pattern inspection method using an electron beam in which a defect is detected by comparing a charge-up level with a reference image, Japanese Patent Laid-Open No. 59-13482, and Japanese Patent Laid-Open No. 62-161044. The publication discloses a pattern inspection method in which a defect is detected by comparing a reference pattern design data with an electron beam image.

Japanese Unexamined Patent Publication No. 3-160348

Japanese Unexamined Patent Publication No. 3-167456

When pattern defects in the manufacturing process of a fine-structure semiconductor device are inspected using the above-described conventional optical inspection method, the optical distance depending on the optical wavelength and refractive index used for inspection is optically transmissive material. Residues such as a sufficiently small silicon oxide film and photosensitive resist material cannot be detected, and it is possible to detect etching residues that are linear and whose short side width is less than the resolution of the optical system, or non-opening defects of minute conduction holes. It was difficult. In order to inspect these defects, an inspection technique that compares electron beam images using an electron beam having a shorter wavelength and higher spatial resolution than white light or the like has been studied. As a result, error factors that could not be seen below the resolution with white light, etc., that is, unevenness of high-frequency components on the machined surface that occurred during circuit pattern formation, were noticeable by inspecting with an electron beam with a higher resolution than that of light. It came to be able to. However, in the pattern defect inspection using the electron beam image, the unevenness of the high frequency component becomes a noise component. As a result of comparative inspection using the conventional method, it was found that since the noise component became large, the threshold for discriminating between defects and noise in the image signal had to be changed in order to avoid false detection. An object of the present invention is to suppress the influence of noise generated when inspecting using an electron beam, that is, the influence of unevenness of a circuit pattern processing surface generated during processing of a semiconductor device on an electron beam image, thereby making it possible to detect errors during defect inspection. It is to improve the accuracy of defect detection by reducing detection.

In order to achieve the above object, the semiconductor device inspection method according to the present invention adjusts the spatial resolution of the image to be equal to or less than the unevenness of the high-frequency component of the circuit pattern processing surface when forming an electron beam image. It is characterized by doing. The means for adjusting the resolution of the image will be specifically described below.

The first means is characterized by using a lens for converging the electron beam and adjusting the diameter of the electron beam on the sample surface to be equal to or larger than the unevenness of the high-frequency component on the circuit pattern processing surface. Since the resolution of the electron beam image depends on the electron beam diameter, the resolution can be lowered by increasing the electron beam diameter. Usually, in the processing of a semiconductor device, the size of a defect which is a problem is about 1/2 to 1/3 of the minimum line width of the pattern. Therefore, for example, by adjusting the diameter of the electron beam from 1/2 to 1/3 of the minimum line width of the pattern so that the resolution of the electron beam image is equal to or slightly smaller than the size of the defect in question. It is possible to reduce the influence of the unevenness of the pattern processing surface generated during the processing of the semiconductor device on the electron beam image.

The second means is to focus the electron beam so that the diameter of the electron beam becomes the smallest on the surface of the sample semiconductor device when converging the electron beam. In particular, the method is characterized in that the diameter of the electron beam irradiated onto the sample is adjusted. Two methods can be used to shift the focal position. First, when converging an electron beam, the electron beam diameter is adjusted by uniformly shifting the position where the electron beam diameter is minimized by the action of a lens upward or downward of the sample surface. Another method is to keep the electron beam convergence position constant, move the sample stage upward or downward, and adjust the position of the sample to a height that is uniformly separated from the position where the electron beam diameter is the smallest. Is. In either method, by adjusting the focal position, the diameter of the electron beam irradiated onto the sample is substantially adjusted. As described above, the resolution of the electron beam image resolution is a problem. By adjusting the diameter of the electron beam so as to be equal to or slightly smaller than the size, it is possible to reduce the influence of the unevenness of the pattern processing surface generated during processing of the semiconductor device on the electron beam image.

The third means detects the secondary electrons or backscattered electrons, forms an electron beam image, and before performing the comparison process, by adjusting the number of pixels when filtering the image, the image processing unit This is a method for adjusting the resolution of a stored electron beam image. By increasing the number of pixels when filtering an image, high frequency components in the electron beam image are reduced. Therefore, a pattern generated at the time of processing a semiconductor device by setting the number of pixels at the time of filtering so that an image signal having a size smaller than the size of a defect that is usually a problem in processing of the semiconductor device is averaged by filtering, for example. It is possible to reduce the influence of the image signal of the processed surface unevenness on the electron beam image signal at the time of comparison.

In order to realize the above inspection method, the configuration of the inspection apparatus of the semiconductor device according to the present invention includes an electron beam source for exciting secondary electrons or reflected electrons from a sample, a lens for converging the electron beam, A sample stage on which the sample is mounted, a deflector for controlling the scanning direction of the electron beam, an optical system for monitoring the focal position of the electron beam on the sample, and a detector for detecting secondary electrons or reflected electrons The semiconductor device inspection apparatus including an image processing unit that performs comparison processing on the detected signal has a function of adjusting the image resolution based on the detected electron beam signal. As a means for adjusting the image resolution, a semiconductor device inspection apparatus according to the present invention will be specifically described below. First, a function is provided that changes the voltage applied to the lens based on the detected signal level of secondary electrons or reflected electrons, and changes the position where the electron beam is converged. Further, the sample stage has a mechanism for driving up and down, and has a function of uniformly shifting the height of the sample with respect to the in-focus position being monitored. Further, the image processing unit has a function of changing a filtering size at the time of image processing as a parameter based on the signal level.

In order to set an appropriate electron beam diameter or focal point position and filtering size for image processing for various semiconductor devices using the inspection method and the inspection apparatus, first, the pattern size to be inspected and the defect to be detected Set the size and read the secondary electron beam image or reflected electron beam image of the sample semiconductor device by changing the electron beam diameter or focal position and processing pixel size in advance with reference to this data and referring to this data. This is possible by comparing images of the same circuit pattern and setting the various parameters so that the difference signal level of the images is within a predetermined range.

By using these means to inspect the semiconductor device in the manufacturing process, depending on the degree of unevenness of the processed surface caused by the process processing, the unevenness is detected as an erroneous detection at the time of inspection. Appropriate inspection conditions are required so as not to occur, so that false detection in the inspection result is reduced. As a result, erroneous detection that occurs during the inspection, which has been a problem in the past, is reduced, so that highly accurate inspection is possible.

A typical effect obtained by the present invention will be briefly described below.

(1) In an inspection method and an inspection apparatus that irradiates an electron beam to a semiconductor device to be inspected, detects secondary electrons or reflected electrons generated from the semiconductor device to be inspected, forms an image, and compares them. By changing the diameter of the electron beam according to the degree of unevenness caused by process processing, pattern defects in the fine structure of the semiconductor device in the electron beam image, which were difficult to inspect due to frequent detection errors in the prior art, are erroneous. This is possible without detection.

(2) Similarly, the diameter of the electron beam on the surface of the semiconductor device to be inspected can be substantially changed by changing the focal position when irradiating the electron beam in accordance with the degree of unevenness caused by the process processing that has occurred in the semiconductor device to be inspected. In other words, the defect of the pattern in the fine structure of the semiconductor device in the electron beam image, which has been difficult to inspect due to frequent erroneous detection in the prior art, can be performed without erroneous detection.

(3) With respect to the semiconductor device to be inspected taken into the storage device, the conventional technology frequently causes false detection by changing the filtering size in the image processing unit in accordance with the degree of unevenness caused by process processing occurring in the semiconductor device to be inspected. Thus, pattern defects in the fine structure of the semiconductor device in the electron beam image that has been difficult to inspect can be made without erroneous detection.

(4) Due to the effects described above, the frequency of erroneous detection of surface irregularities due to process processing of the semiconductor device to be inspected is reduced, and highly accurate defect detection becomes possible.

(5) By applying the apparatus and the inspection method of the present invention to a semiconductor device due to the effects described above, it is possible to immediately detect the occurrence of an unexpected failure or unknown trouble of the semiconductor device, and prevent the occurrence of frequent failures. Is possible.

(6) Since it is possible to prevent defects in the semiconductor device, the yield of the semiconductor device is improved. As a result, the development efficiency of new products is improved and the manufacturing cost can be reduced.

(7) At the same time, defects in the semiconductor device are reduced due to the above effects, so that the reliability of the semiconductor device is improved.

Hereinafter, an example of an inspection method and an apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

(Example 1)
A first embodiment of the present invention will be described with reference to FIGS.
In the semiconductor device manufacturing process, a number of pattern forming steps are repeated as shown in FIG. One pattern formation process is roughly composed of steps of film formation, resist application, photosensitivity, development, etching, resist removal, and cleaning. A circuit pattern is formed on the wafer through these steps. When the pattern is processed, irregularities are formed on the processed surface as shown in FIG. For example, in the photosensitive / developing process, irregularities 1 may occur on the processed end face due to the influence of standing waves or the like. Further, in the process of cutting the film as in the etching process, the product may adhere to the processed surface or the surface may not be smooth, and fine irregularities 2 may be generated. Further, even in film formation processes such as sputtering and CVD, fine irregularities 3 may be formed on the film formation surface depending on temperature and other conditions. Hereinafter, a method for inspecting a semiconductor device having such irregularities will be described in order.

First, the inspection method and inspection apparatus of the present invention irradiates a sample semiconductor device in the inspection process with an electron beam, detects secondary electrons or reflected electrons generated from the sample semiconductor device irradiated with the electron beam, and displays an image. Form. A pattern shape defect is extracted by comparing this image with an image of the same pattern in the same process of a different place or different sample. FIG. 3 shows a configuration diagram of this type of inspection apparatus, and an outline of the inspection apparatus and an inspection method will be described.

The inspection apparatus is roughly divided into an electron optical system, a sample chamber, a control unit, and an image processing unit. The electron optical system includes an electron gun 4, an electron beam extraction electrode 5, a condenser lens 6, a blanking deflector 7, a scanning deflector 8, a diaphragm 10, and an objective lens 11. The sample chamber is composed of an XY stage 13, a rotary stage 12, a position monitor length measuring device 16, and a semiconductor device height measuring device 15 to be inspected, and a secondary electron detector 9 is located above the objective lens 11. The output signal of the secondary electron detector 9 is amplified by the preamplifier 20 and converted into digital data by the AD converter 21. The image processing unit includes image storage units 22 and 23, a calculation unit 24, and a defect determination unit 25. The captured electron beam image is displayed on the monitor 26. Operation commands and operating conditions of each part of the inspection apparatus are input / output from the control unit 27, and conditions such as an electron beam acceleration voltage, an electron beam deflection width, a deflection speed, a sample stage moving speed, and a detector signal capturing timing are input in advance. ing.

A method for forming a secondary electron beam image will be described below. A voltage is applied to the extraction electrode 5 to extract an electron beam from the electron gun 4. The electron beam is accelerated by applying a high voltage negative potential to the electron gun. As a result, the electron beam travels in the direction of the sample stage 14 with energy corresponding to the potential, is converged by the condenser lens 6, is further narrowed down by the objective lens 11, and is mounted on the XY stage 13. The device 28 is irradiated. While the semiconductor device 28 is irradiated with the electron beam, the generated secondary electrons are detected by the detector 9. Immediately after detection, it is converted and digitized by the AD converter 21 and transmitted to the image processing unit. Then, for each time corresponding to a desired pixel size at the electron beam irradiation position given from the control unit 27, the detection signal is stored in the storage unit 22 or 23 as a gradation value of the brightness information. This is repeated, and a two-dimensional secondary electron image of the semiconductor device 12 to be inspected is formed by taking the correspondence between the electron beam irradiation position and the secondary electron capture amount. Next, a method for actually inspecting a semiconductor device will be described.

Prior to the inspection, the rotation stage 12 corrects the rotation so that the pattern of the semiconductor device 28 to be inspected installed on the sample stage 14 in the inspection apparatus is parallel or orthogonal to the stage moving direction. Next, from the circuit pattern image of the semiconductor device 28 to be inspected, the position of the chip on the wafer and the distance between the chips, for example, the repetitive pitch of a repetitive pattern such as a memory cell are measured in advance, and a value is input to the control unit 27. Then, the inspected chip on the wafer and the inspected area in the chip are set from the image on the monitor 26. When this is completed, an image of a part of the inspection region of the semiconductor device 28 to be inspected is acquired under exactly the same conditions as the actual inspection conditions, and the brightness information of the image depending on the material and shape and the range of variation thereof are calculated. Store as a table. A condition for determining whether or not the defect is to be detected is determined with reference to this table.

When the setting of the inspection area and the defect determination condition is completed by the above method, the inspection is started. At the time of inspection, the XY stage 13 on which the semiconductor device 28 to be inspected is moved continuously at a constant speed in the X direction. During this time, the electron beam is scanned linearly in the Y direction by the scanning deflector 8. In this way, it is possible to form an image suitable for the size and shape of the inspection region by irradiating the electron beam onto the circuit pattern region of the semiconductor device 28 set in advance. Regarding the region or position where the electron beam is irradiated, the position monitor length measuring device 16 provided on the XY stage 13, the XY stage 13, the motor rotational speed of the rotary stage 12, the scanning signal generator 17, etc. Can be grasped in detail by transferring the information to the correction control circuit 19, and control can be performed to correct the measured positional deviation. Further, the height of the semiconductor device 28 to be inspected is measured in real time by means other than the electron beam, the focal length of the objective lens 11 for narrowing the electron beam is dynamically corrected, and the inspected region is always in focus. The configuration is such that an electron beam is irradiated. In this embodiment, the optical sample height measuring device 15 of the method for measuring the change in the position of the reflected light is used. In this way, a secondary electron beam image of the semiconductor device 28 to be inspected is formed, and then image processing, comparison, and defect extraction are performed on the inspection region. For example, when performing a comparison inspection between chips on a wafer, a secondary electron image of the inspection area of chip A is first stored in the storage unit 22 and various statistics are calculated by the calculation unit 24. Next, the same part and the same circuit pattern of adjacent chips B are stored in the storage unit 23, and at the same time, various statistical processes are similarly performed by the calculation unit. The signals of the storage unit 22 and the storage unit 23 subjected to these processes are transferred to the defect determination unit 25, compared to extract a difference signal, and refer to the defect determination conditions already obtained and stored to determine the Separate signals other than. This is repeated to inspect all inspection chips / inspection areas, detect defects, and store information such as positions and sizes.

As described above, the method for inspecting a semiconductor device using an electron beam has been described. Since an electron beam can be narrowed down by the action of a lens or the like as described above, an electron beam image is a space compared with a conventional optical image. The resolution is remarkably improved, and information on the detailed structure of the circuit pattern can be obtained. Therefore, as described above with reference to FIG. 2, when the pattern processing surface has irregularities, the minute shape of the high frequency component does not match between the adjacent identical circuit pattern and the circuit pattern of the region to be inspected. Therefore, when the images are compared by the conventional method, many mismatched portions are generated and appear as false detections, so that the accuracy of the inspection result is low and it is difficult to detect only the defect. For this reason, in this embodiment, the diameter of the electron beam is adjusted so as to be larger than the minute unevenness of the patterned surface and smaller than the defect size to be detected by the lens action, and an electron beam image is acquired.

In the present embodiment, as an example, the inspection of a semiconductor device after completion of etching / resist removal in which a pattern minimum line width is 0.3 μm and the surface is a polysilicon film and a line pattern is formed will be described. In general, since the size of a defect that is a problem in pattern processing corresponds to 1/2 to 1/3 of the pattern line width, the defect detection size is set to 0.1 μm in this embodiment. At this time, when the unevenness on the side surface of the pattern was observed in detail, the size of the unevenness was about 1/3 of the defect size in question. This semiconductor device was inspected in the case of an electron beam diameter of 10 nm or less, which is the same as that of a conventional SEM, and in the case of 0.1 μm. At this time, only the diameter of the electron beam is changed, the other electron beam scanning width, the moving speed of the XY stage, and the pixel size when performing signal processing / comparison / defect determination after taking the secondary electron image Were the same conditions. As a result, with the conventional electron beam diameter, irregularities on the patterned surface of the pattern were erroneously detected, but when the electron beam diameter was adjusted, almost no false detection was detected, and no defects were detected. It was.

FIG. 4 shows a top view of a pattern 29 in the semiconductor device 28 to be inspected and a pattern 30 in the same location as the pattern 29 in an adjacent chip. In the pattern 29, a pattern short has occurred. In addition, both the pattern 29 and the pattern 30 have fine irregularities because the surface polysilicon film is grained, and irregularities are formed on the processed end face of the line pattern during etching. FIG. 5 shows the density signal profile when the electron beam diameter is reduced to 10 nm and the secondary electron images of the pattern 29 and the pattern 30 are captured, and the difference signal profile when the pattern 29 and the pattern 30 image are compared. Show. FIG. 6 shows a profile when a secondary electron beam image is similarly taken with the electron beam diameter of 0.1 μm, and FIG. 7 shows a similar profile when the electron beam diameter is 0.3 μm.

In FIG. 5, since the diameter of the electron beam is narrowed to be much finer than the pattern or the unevenness of the pattern, the unevenness on the surface or side is reflected as it is in the image density signal. Since the uneven portions are different between the pattern 29 and the pattern 30, when the difference signal of the image is taken, it becomes as shown in (c), and a fine signal but a high gray signal level remains at the pattern edge portion, which is erroneously detected. . FIG. 6 shows an example in which the diameter of the electron beam is adjusted to 0.1 μm as described above. Therefore, it is adjusted to be about three times larger than the size of the pattern irregularities. In the image density signal profiles of the patterns 29 and 30, the change in the density at the pattern edge portion is gradual, but the signal of the high frequency component is reduced. Adjacent identical patterns have almost the same image profile, and if the difference signal is taken, there is no signal difference between the patterns, and the contrast between the pattern portion and the defect portion is maintained, so that erroneous detection is eliminated. Defects are detected. Further, FIG. 7 shows the result of inspection after adjusting the diameter of the electron beam much larger than the unevenness of the pattern. Although the influence of the unevenness of the pattern surface and the edge portion has been eliminated, the contrast between the pattern portion and the background is lowered, and as a result, the pattern edge portion becomes unclear, making it difficult to recognize the pattern portion. In addition, since the contrast between the defective portion and the normal portion is lowered, it is difficult to detect the defect.

From these examples, it is possible to maintain the contrast between the pattern part and the ground, and adjust the diameter of the electron beam so that it is equal to or slightly larger than the unevenness of the pattern surface and the edge part. Defects can be detected. FIG. 8 shows an excerpt of the electron optical system at this time from FIG. By inputting conditions to the objective lens 11 from the control unit 27 via the objective lens power supply 18, the diameter of the electron beam on the surface of the sample semiconductor device 28 is adjusted, and each of the conditions shown in FIGS. 5 to 7 is realized. Yes.

A method for setting an appropriate electron beam diameter or focal position and filtering size for image processing for various semiconductor devices using the methods and apparatuses described so far will be described. First, the pattern size to be inspected and the defect size to be detected are set as parameters, and the electron beam diameter or focal position and processing pixel size are changed in advance before inspection while referring to the data of the defect determination criteria already described. Then, an electron beam image of the sample semiconductor device 28 is captured, images of the same circuit pattern adjacent to each other are compared, and a gradation histogram is monitored for the signal of the difference image. FIG. 9 shows this histogram. As shown in FIG. 5, when high-frequency noise due to pattern irregularities remains in the electron beam image, the noise component also remains in the difference signal. In the same manner as in the low region, signals are distributed. On the other hand, when the high frequency component noise in the electron beam image is reduced by the inspection methods described so far, as shown in FIG. In the histogram, the frequency is high in a low gradation area. Therefore, in order to appropriately set the electron beam diameter, the focal position, and the image processing filter size for the irregularities of various semiconductor devices, the difference signal gradation and frequency are determined from the difference signal gradation histogram of the image captured by the above method. This can be done by setting various parameters so that is within a predetermined range.

A method of setting an appropriate electron beam diameter for the sample semiconductor and obtaining the image resolution or the defect detection size corresponding to the setting condition will be described with reference to FIGS. FIG. 10 shows a layout of a test pattern 31 that is known and has a plurality of pattern sizes. This test pattern 31 is mounted on the sample stage 14 of the inspection apparatus shown in FIG. 3, and the coordinates of each pattern are known. After setting various electron beam irradiation conditions, the stage is moved to the pattern portion of FIG. 10A, and the electron beam image of the pattern is captured while moving the stage at a constant speed. The contrast of the pattern is obtained from the grayscale signal of the captured image. In order to determine the image resolution in advance, a predetermined threshold is set for the contrast of the image signal. When the contrast of the pattern (a) is compared with the threshold and it is confirmed that the contrast is equal to or higher than the threshold, the pattern moves to the pattern portion of the next pattern (b). This is repeated. For example, when the contrast is equal to or higher than the threshold value at 0.2 μm, but is less than the threshold value at 0.17 μm, the resolution of the image is determined to be 0.2 μm.

FIG. 11 shows a test pattern 32 in which protrusions / chips and isolated defects of a known size are formed in a line pattern having a predetermined width. This test pattern 32 is also mounted on the sample stage 14 of the inspection apparatus, similarly to the test pattern 31 of FIG. Similarly to the above method, after setting various electron beam irradiation conditions, the stage is moved to the pattern portion of FIG. 11 and the electron beam image of the test pattern is captured while moving at a constant speed. At that time, the repetition pitch of the line patterns is input in advance, and the images of the adjacent line patterns are compared by the same method as at the time of inspection. As a result, the coordinates of the location detected as a defect are compared with the coordinates of the defect actually created, and the size of the detected defect and its detection rate are displayed on the screen. By these methods, even if various electron beam irradiation conditions are set / changed, the influence on the image resolution and the defect detection size can be quantitatively grasped as a result, and the inspection accuracy can be improved.

(Example 2)
A second embodiment of the present invention will be described with reference to FIG. Since the detailed configuration of the inspection apparatus is the same as that of the first embodiment, it is omitted here.

In the first embodiment, when the pattern processing surface is uneven when the semiconductor device to be inspected is processed, in the first embodiment, the diameter of the electron beam irradiated to the semiconductor device 28 to be inspected by the action of the objective lens 11 is set. The method of changing was adopted. On the other hand, in this embodiment, a method of shifting the in-focus position from the sample surface is adopted. When designing the electron optical system in advance, the lens conditions at the in-focus position when various electron beam irradiation conditions are set and the lens conditions for shifting the focal position are stored. The height position of the sample is measured in real time by a method of irradiating the surface of the semiconductor device 28 to be inspected with, for example, white light and measuring the change in the position of the reflected light. Normally, the focus position of the electron beam is fed back from the sample height measurement result to the objective lens conditions so that the sample surface is always in focus. In the case of detection, for example, the objective lens condition is corrected so that the focus is adjusted to a height shifted by 0.5 μm from the in-focus position. By shifting the focal position, the diameter of the electron beam irradiated onto the semiconductor device 28 to be inspected is substantially changed, so that the same effect as that obtained in the first embodiment can be obtained. In addition, a method of adjusting the height of the sample stage 14 instead of the action of the objective lens can be used to adjust the focal position. In this embodiment, the focal position is measured in real time by irradiating white light or the like and detecting the position change of the reflected light. In this case, the condition of the objective lens 11 is fixed, and the sample surface height is always constant from the in-focus position by moving the position in the height direction of the sample stage 14 on which the semiconductor device 28 to be inspected is installed. The offset height is set as follows. By this method, the position of the sample stage 14 is adjusted so that the focus is uniformly shifted from the in-focus position as in the case of changing the objective lens condition. As a result, since the diameter of the electron beam irradiated onto the semiconductor device 28 to be inspected substantially changes, the same effect as that obtained in the first embodiment can be obtained. In this manner, the focal position or the sample height that does not cause erroneous detection and does not impair the defect detection performance is obtained corresponding to the irregularities of the pattern surface or the processed surface in the semiconductor device 28 to be inspected. In order to obtain an appropriate condition, similar to the method described in the first embodiment, the semiconductor device to be inspected is inspected by changing the focal position, and the secondary electron image of the same circuit pattern and the density signal thereof at the two taken-in locations And a difference signal profile obtained by comparing two circuit pattern images, a condition for maintaining the contrast between the pattern portion and the ground and eliminating false detection is obtained. The method for obtaining the image resolution and the defect detection size corresponding to the focus position conditions set in accordance with the above contents is also the same as in the first embodiment, and is therefore omitted here.

(Example 3)
A third embodiment of the present invention will be described with reference to FIG. In the present embodiment, by using the inspection apparatus of FIG. 3, the secondary electron beam image of the semiconductor device to be inspected is captured, and after the image information is stored in the storage device, by changing the filter size when performing various data processing, This is a method of reducing the influence of irregularities on the pattern surface and the processed surface. FIG. 13 shows the set pixel size for the captured image and the signal level of the comparative image at each pixel size. When the set pixel size is very small compared to the unevenness of the pattern surface or processing surface generated in the semiconductor device to be inspected, the unevenness is different when compared with the image of the adjacent same pattern location, It causes false detection. Therefore, after acquiring and storing the secondary electron beam image of the sample semiconductor device by the method described in the first embodiment, the pixel size when calculating and filtering various statistics is equivalent to the size of the unevenness of the sample semiconductor. Set it to a larger size. Specifically, for example, while the pixel size at the time of image capture is 0.1 μm, at the time of processing, an average value of 3 × 3 pixels including each surrounding pixel is first taken and used as data of the pixel. As a result, the same effect can be obtained as if the image was captured with an electron beam of 0.3 μm. Since the pixel size when performing the defect determination comparison is set to 0.1 μm which is the same as that at the time of capture, the defect detection size is not affected. In this way, in the same manner as in the first embodiment, the apparent pixel size is increased before image data processing according to the pattern surface or unevenness of the processed surface caused by the process processing in the semiconductor device to be inspected, By processing with a predetermined pixel size at the time of defect determination, it is possible to eliminate the erroneous detection due to the unevenness of the pattern surface or the processed surface and to detect the defect with high sensitivity. Also in this embodiment, the subsequent resolution / defect detection sensitivity evaluation method is the same as that in the first embodiment, and is omitted here.

As described above, the diameter of the electron beam irradiated to the sample and the height of the sample are adjusted according to the configuration of the representative apparatus of the present invention and the degree of unevenness of the surface or processed surface of the semiconductor device to be inspected. Although some embodiments of the inspection method and inspection apparatus for forming a secondary electron image and automatically detecting defects on the semiconductor device from the image have been described, it is claimed without departing from the scope of the present invention. The same applies to an inspection method and an inspection apparatus that combine a plurality of features listed in the items.

Diagram showing the manufacturing process flow of a semiconductor device Schematic diagram of the patterned surface of the semiconductor device during the manufacturing process Configuration diagram of an automatic defect inspection system for semiconductor devices using electron beams Top view of semiconductor device circuit pattern The figure which shows the profile of the light and shade signal of the circuit pattern The figure which shows the profile of the light and shade signal of the circuit pattern The figure which shows the profile of the light and shade signal of the circuit pattern Diagram showing adjustment of electron beam diameter Histogram showing the gradation of the difference image of the electron beam image Top view and detection signal diagram of test pattern for image resolution evaluation Top view of defect detection sensitivity test pattern and distribution of detection results Diagram showing how to adjust the focal position and sample height The figure explaining the filtering size at the time of electron beam image processing

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Pattern unevenness | corrugation which generate | occur | produced in exposure process etc. 2. Pattern unevenness | corrugation 3 which generate | occur | produced in etching process etc .... Pattern unevenness | corrugation 4 which generate | occur | produced in film-forming etc .... Condenser lens 7 ... Blanking deflector 8 ... Scanning deflector 9 ... Secondary electron detector 10 ... Aperture 11 ... Objective lens 12 ... Rotating stage 13 ... XY stage 14 ... Sample stage 15 ... Optical sample Height measuring instrument 16 ... Position monitor length measuring instrument 17 ... Scanning signal generator 18 ... Objective lens power supply 19 ... Correction control circuit 20 ... Amplifier 21 ... AD converter 22 ... Image storage section 23 ... Image storage section 24 ... Calculation section 25 ... Defect determination unit 26 ... Monitor 27 ... Control unit 28 ... Inspected semiconductor device 29 ... Circuit pattern 30 ... Circuit pattern 31 of adjacent chip ... Test pattern 32 ... Test pattern

Claims (11)

  A method for inspecting a semiconductor device, wherein a defect of a circuit pattern is detected by irradiating a sample with an electron beam and comparing the formed electron beam images. An inspection method for a semiconductor device, wherein the resolution of an electron beam image is changed based on a signal level of a frequency component.   2. The method for inspecting a semiconductor device according to claim 1, wherein the resolution of the electron beam image is changed by changing the diameter of the electron beam applied to the sample.   3. The semiconductor device inspection method according to claim 2, wherein the diameter of the electron beam is changed by the action of a lens.   2. The method for inspecting a semiconductor device according to claim 1, wherein the resolution of the electron beam image is changed by uniformly shifting the focal position of the electron beam applied to the sample.   5. The method of inspecting a semiconductor device according to claim 4, wherein the focal position is shifted evenly by the action of a lens.   5. The method for inspecting a semiconductor device according to claim 4, wherein the focal position is shifted evenly by changing the position of the sample stage.   2. The method of inspecting a semiconductor device according to claim 1, wherein the resolution of the electron beam image at the time of image processing is changed by changing a filter size when the electron beam image is compared.   An electron beam source that excites secondary electrons or reflected electrons from the sample, a lens for converging the electron beam, a sample stage on which the sample is placed, a deflector for controlling the scanning direction of the electron beam, An inspection apparatus for a semiconductor device comprising an optical system for monitoring the focal position of an electron beam on a sample, a detector for detecting the secondary electrons or reflected electrons, and an image processing unit for comparing and processing the detected signals. A semiconductor device inspection apparatus having a function of adjusting an image resolution in order to adjust a signal level of a frequency component within a predetermined range based on a detected electron beam signal.   9. The semiconductor device inspection apparatus according to claim 8, wherein the semiconductor device inspection device has a function of adjusting resolution by changing an electron beam condensing position by a lens.   9. The semiconductor device inspection apparatus according to claim 8, wherein the semiconductor device inspection device has a function of adjusting resolution by moving a sample stage up and down.   9. The inspection apparatus for a semiconductor device according to claim 8, wherein the inspection apparatus for a semiconductor device has a function of adjusting an image resolution at the time of image processing by changing a filter size of signal processing in an image processing unit.

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