JP2009098053A - Apparatus and method for inspecting unevenness of periodic pattern - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and method for inspecting unevenness of a periodic pattern which can accurately image and detect unevenness even in an object to be inspected in which it is difficult to inspect by visible light, such as a periodic pattern, particularly a halftone mask. <P>SOLUTION: The apparatus comprises: a transmission lighting part 10; a reflection lighting part 20; an XY stage part 30 allowing transmission lighting and reflection lighting; a light source part 40; an imaging part 50 for picking up an image of a substrate 70 to be inspected; and a processing part 60 having functions to perform image input of the output from the imaging part 50 as digitalized image information, to perform computation such as image enhancement processing, and to display the image. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus and method for inspecting pattern unevenness in an inspection object having a periodic pattern. A periodic pattern refers to an aggregate of patterns having a constant interval. For example, a periodic pattern of stripes in which patterns are arranged at a predetermined pitch, or a pattern of openings is two-dimensionally arranged at a predetermined period. Such a matrix pattern corresponds to this. Examples of the inspection object having a periodic pattern include a photomask used in an exposure process of a photolithography process when manufacturing a semiconductor device, an imaging device, a display device, and the like.

  Conventionally, as a photomask used in a manufacturing process of a semiconductor device, an imaging device, a display device and the like, a photomask that is configured by partially removing a light shielding film such as chromium on a transparent substrate such as glass in a certain pattern is used. Are known.

  Uneven defects in periodic patterns such as photomasks are usually caused by the regular arrangement of fine pitch deviations and positional deviations, and are therefore difficult to find by individual pattern inspection. However, this is a defect recognized for the first time when the periodic pattern is observed in a wide area.

  In the conventional unevenness inspection of periodic patterns, a transmittance image is captured using coaxial transmission illumination or planar illumination, and the normal portion and the unevenness portion are visually recognized by comparing the light intensity in each image. . However, the difference in light intensity between the normal part and the uneven part is not always large, and the contrast of the obtained image is low. For this reason, the contrast difference is improved by devising an intensity difference processing method for an image having a low contrast, and a nonuniformity portion is extracted for inspection (see Patent Document 1).

  However, in the above-described conventional technique, in the imaging of the black matrix unevenness of the lattice-like periodic pattern, particularly the black matrix unevenness having a large opening, the contrast between the normal portion and the uneven portion is not expected to be improved. However, the inspection in the case of an image with a low contrast of the original image has a problem that only an inspection ability lower than the visual sensory inspection method can be achieved.

  On the other hand, due to the miniaturization of semiconductors and the increase in electronic components with fine displays and bright screens, the periodic pattern tends to be miniaturized or the ratio of openings is increased. In the future, a non-uniformity inspection apparatus and method for a periodic pattern having a finer shape and a larger opening will be required. That is, there is a limit in the conventional output with only the intensity (brightness) of light based on the amplitude of light.

  Therefore, for the purpose of providing a periodic pattern unevenness inspection apparatus capable of imaging and detecting a periodic pattern, for example, black matrix unevenness stably and with high accuracy, illumination light is irradiated onto the object to be inspected. For example, an inspection apparatus such as Patent Document 2 for inspecting transmitted diffracted light generated by a pattern has been proposed. In the normal part of the periodic pattern, the shape and pitch of the openings are constant, so that they interfere with each other and generate diffracted light in a certain direction. On the other hand, since the shape and pitch of the opening are irregular in the uneven portion, diffracted light is generated with various intensities in various directions according to the shape and pitch. In this inspection apparatus, a method of detecting a nonuniformity portion from the difference in diffracted light intensity contrast between the normal portion and the nonuniformity portion is adopted.

  By the way, in the periodic pattern, for example, photomask, the miniaturization of the pattern is progressing, and the resolution of the stepper is approaching the limit during the exposure process of the photolithography process, and the resolution is improved only by the lens reduction system. It is becoming difficult to do. For this reason, various resolution improvement techniques have been proposed, and one of them is a phase shift mask. The phase shift mask is a mask for resolving a fine pattern by shifting the transmission phase between the glass and the light shielding portion by 180 degrees and utilizing the light interference effect. Among them, a halftone mask having a light-shielding portion as a semitransparent film is often used. FIG. 1 schematically shows a comparison between a conventional Cr mask and a halftone mask.

  Unlike a conventional Cr mask, the halftone mask has the film transmittance and phase determined so that a high contrast can be obtained at the exposure wavelength. As a semi-permeable film material, a MoSi-based single layer film is widely used, and its spectral transmittance may reach 50 to 60% in the visible range, and has a characteristic that is higher than that of a Cr light shielding film. Have.

  In the above-described inspection apparatus using transmitted diffracted light, visible light is used as illumination light. Therefore, when a halftone mask is used as an inspection target, most light components are transmitted without being blocked by the pattern portion. In the inspection image obtained as a result, the contrast between light and dark becomes low, and the contrast between the normal part and the uneven part becomes extremely low. Therefore, it becomes difficult to detect the uneven part from the difference in the contrast of the diffracted light intensity.

The known literature is described below.
JP 2002-148210 A JP 2006-208084 A

  The present invention has been made in view of the above problems, and its object is to provide an object to be inspected that is difficult to inspect with visible light, such as a periodic pattern, particularly a halftone mask. In contrast, an object of the present invention is to provide a periodic pattern unevenness inspection apparatus and method capable of capturing and detecting unevenness with high accuracy.

  The invention according to claim 1, which has been made in order to solve the above-described problem, is a non-uniformity inspecting using a diffracted light generated by a periodic pattern, with a pattern substrate having a periodic pattern formed on the substrate as a substrate to be inspected. An inspection apparatus, which is a vertical angle of an illumination head unit with respect to the periodic pattern on a substrate to be inspected installed on the substrate to be inspected and having a mechanism for driving in the X-axis and Y-axis directions And a illuminating means having a transmissive illumination part and a reflective illuminating part, each of which can be adjusted so that the angle of the horizontal direction can be adjusted and the irradiation position of the illumination is constant; Imaging means for imaging diffracted light generated in the periodic pattern that has been reflected and illuminated, image input means for converting the output of the imaging means into digitized image information, and Image processing means for performing defect portion extraction / determination processing on the image information obtained by the image input means, and display means for displaying an image captured by the imaging means and a processed image by the image processing means. In addition, the illumination means includes: a light source capable of irradiating visible light; a light source capable of irradiating ultraviolet light; a light guide means switching mechanism from the light source; and a light on / off means for each light source. And a non-uniformity inspection apparatus including the illumination head unit for irradiation with visible light and the illumination head unit for irradiation with ultraviolet light in the transmission illumination unit and the reflection illumination unit, respectively. .

  The invention according to claim 2 is characterized in that the imaging means has a light receiving sensitivity capable of imaging at least in an ultraviolet range to a visible range, and an ultraviolet light guide means in the illumination means and an illumination head unit for ultraviolet light irradiation. The nonuniformity inspection apparatus according to claim 1, wherein the unevenness inspection apparatus comprises an optical member having ultraviolet light transmission characteristics.

  The invention according to claim 3 is the unevenness inspection apparatus according to claim 1, wherein the light source in the illumination means is a metal halide lamp and a mercury xenon lamp. .

  According to a fourth aspect of the present invention, the illumination unit irradiates the periodic pattern with parallel light, and the imaging unit extracts only transmitted diffracted light and reflected diffracted light perpendicular to the periodic pattern. The unevenness inspection apparatus according to claim 1, wherein the unevenness inspection apparatus has an optical system.

  The invention according to claim 5 is the unevenness inspection apparatus according to any one of claims 1 to 4, wherein a light amount fluctuation range with respect to an operation time of the light source in the illumination unit is 1% or less. Is.

  According to a sixth aspect of the present invention, in the light source of the illumination means, a plurality of band pass filters can be installed therein, and a filter changer portion capable of switching the band pass filter is incorporated. The unevenness inspection apparatus according to any one of claims 1 to 5 is provided.

  According to the seventh aspect of the present invention, a pattern substrate having a periodic pattern formed on a substrate is used as an inspection target substrate, and a pattern substrate having a periodic pattern formed on the substrate is used as an inspection target substrate. A nonuniformity inspection method in which light is obliquely incident on the inspection target substrate and inspected by using diffracted light generated by a periodic pattern, and depending on the inspected substrate, transmitted illumination light or reflected diffraction light, visible light An inspection condition setting step for setting light or ultraviolet light, an illumination angle, an imaging step for switching the illumination means in accordance with the inspection condition, and imaging diffracted light generated in the periodic pattern that is transmitted or reflected and illuminated, An image input process in which the output at the imaging stage is digitized image information, and a defect extraction / determination process for the image information obtained by the image input stage. To have an image processing step of performing is obtained by the unevenness inspection method comprising.

According to the periodic pattern unevenness inspection apparatus and method of the present invention, unevenness can be generated even for a periodic pattern, particularly an object to be inspected that is difficult to inspect with visible light, such as a halftone mask. Imaging and detection can be performed with high accuracy.
That is, according to the unevenness inspection apparatus and unevenness inspection method of the present invention,
1) Optimum because the contrast of the diffracted light pattern is small in the conventional wavelength range of the irradiated light, and it is difficult to detect the object to be inspected in the wavelength range from the visible light region to the ultraviolet region. The correct wavelength was selected and the detection accuracy was improved.
2) Selection of visible light and ultraviolet light, and further, selection of irradiation with reflected light and transmitted light can be appropriately set according to the characteristics of the object to be inspected by the light guide switching mechanism, etc. This makes it possible to handle a wide variety of test objects.
3) Since the illumination angle can be changed without changing the projection position of illumination by having the vertical angle and horizontal angle of each illumination head unit, and the illumination driving unit, the light source wavelength and the period of the substrate Observational inspection was possible according to the sex pattern.
4) Further, by using a light source having a light amount fluctuation range of 1% or less with respect to the operation time and a high light amount stability, it becomes possible to ensure the stability of the image acquired by inspection and the reproducibility of the inspection result.

  An embodiment of a periodic pattern unevenness inspection apparatus to which the present invention is applied will be described. FIG. 2 is a schematic configuration diagram of the unevenness inspection apparatus 1 according to the present invention. As shown in FIG. 2, the present apparatus captures images of a transmission illumination unit 10, a reflection illumination unit 20, an XY stage unit 30 capable of transmission illumination and reflection illumination, a light source unit 40, and an inspected substrate 70. An image capturing unit 50, and a processing unit 60 having a function of inputting an image as digitized image information, performing an image enhancement process, and further displaying an image. Yes. It is desirable that this apparatus be operated in a dark environment where disturbance light and stray light are reduced as much as possible and in a clean environment that prevents foreign matter from adhering to the substrate to be inspected.

  In the transmitted illumination unit 10, an arc rail 12 is installed on the turntable 11, and a visible light irradiation illumination head 13 and an ultraviolet light irradiation illumination head 14 are provided on the arc rail 12, respectively. The turntable 11 can be rotated to adjust the irradiation angle in the horizontal direction, and the arcuate rail 12 can be driven to adjust the irradiation angle in the vertical direction. With these functions, transmitted illumination from various angles and directions can be performed on the inspected substrate 70 on the XY stage unit 30. Each illumination head unit is provided with a parallel optical system. For the ultraviolet light irradiation head 14 and the light guide 16, an optical member having an ultraviolet light transmission characteristic is selected.

  Similarly, the reflection illumination unit 20 is provided with arc rails 22 and 23 on the turntable 21. The arc rail 22 has a visible light irradiation illumination head 24, and the arc rail 23 has an ultraviolet light irradiation illumination head 25. Each is provided. The turntable 21 can be rotated to adjust the irradiation angle in the horizontal direction, and the arcuate rail 22 can be driven to adjust the irradiation angle in the vertical direction. With these functions, reflected illumination from various angles and directions can be performed on the substrate 70 to be inspected on the XY stage unit 30. Each illumination head unit is provided with a parallel optical system. For the ultraviolet light irradiation head 25 and the light guide 27, an optical member having an ultraviolet light transmission characteristic is selected.

  In the XY stage unit 30, the inspected substrate 70 is placed at a predetermined position of the XY stage unit. The XY stage unit 30 has a measurement function, recognizes the position, and superimposes the optical axis of the apparatus on the inspection start position of the substrate 70 to be inspected. Using the means for driving in the X-axis and Y-axis directions, the XY stage is driven in the X-axis and Y-axis directions according to a preset operation procedure.

  The light source unit 40 includes a visible light irradiation light source 41, an ultraviolet light irradiation light source 42, an illumination light switching mechanism unit 43 for switching transmitted / reflected light and visible / ultraviolet light, a light source on / off switching operation, and It is comprised from the light source part control apparatus 44 which performs illumination light switching mechanism part operation control. The visible light irradiation light source 41 is provided with a filter changer mechanism, and a plurality of wavelength selection filters can be used. The UV light irradiation light source 42 is equipped with a UV bandpass filter. In this embodiment, a metal halide lamp is used as the light source 41 for visible light irradiation, and a mercury xenon lamp is used as the light source 42 for ultraviolet light irradiation. In either light source, the light amount fluctuation range with respect to the operating time is 1% or less. The feature is that one with high stability is selected. As shown in FIG. 3, the illumination light switching mechanism 43 is provided with two light guide attachment ports on the incident side and four places on the emission side, and rotates the incident side disk in the direction shown in FIG. In addition, by switching on / off the two lights, it is possible to switch between the transmitted light and the reflected light as shown in FIG. By utilizing the above functions, it is possible to set an optimum inspection wavelength according to product information such as the pattern density, layout, and film type of the substrate 70 to be inspected.

  The imaging unit 50 includes a camera 51 as a means for capturing an image and an imaging side parallel optical system 52 parallel to the optical axis. Various cameras can be used as the camera 51, and an area camera, a line camera, or the like can be selected according to the application. In this embodiment, the camera 51 uses an area camera, but it is desirable to select an area camera having an optimal imaging resolution in consideration of the pattern density, layout, etc. of the substrate to be inspected. In addition, by providing a plurality of cameras with different performances and a camera switching mechanism, it may be possible to select an optimal one for each inspection by switching the camera used. The imaging side parallel optical system 52 may have functions such as a magnification adjustment function and an automatic aperture adjustment function.

  The processing unit 60 performs operation management and control of the transmission illumination unit 10, the reflection illumination unit 20, the XY stage unit 30, the light source unit 40, and the imaging unit 50. Further, the processing unit 60 takes the output from the imaging unit 50 as image information digitized by the image input device 64, performs predetermined data processing on the image information, and digitizes the feature amount of the image information. Judge the pass / fail. Examples of the data processing procedure include noise removal processing such as shading correction and expansion / contraction processing, image enhancement processing such as filtering processing, feature amount extraction processing such as a projection method, and composite processing thereof.

  FIG. 5 is a flowchart showing an inspection method according to an embodiment of the present invention. The inspection method according to the embodiment of the present invention is performed by a series of steps S1 to S15. Hereinafter, the contents of each step will be described in the order of steps.

  The entire apparatus is started up such as turning on the power and turning on the light source (S1).

  Set initial conditions before setting inspection conditions. At this stage, whether to use transmitted light or reflected light is also determined (S2).

  Product information such as pitch, L / S, chip layout, etc. on the inspected substrate 70 is input. At this stage, a combination of a light source and a filter to be used is determined (S3).

  The stage 31 is moved to the initial condition setting position set in S2 (S4).

  The inspected substrate 70 is placed at a predetermined position on the stage 31 (S5).

  The stage 31 is moved to the set inspection start position (S6).

  For the transmission illumination unit 10, the reflection illumination unit 20, and the light source unit 40, the setting of the light amount, the horizontal direction angle, the vertical direction angle, and the light projection position on the inspected substrate 70 are performed (S7a to S7d).

  The imaging magnification of the imaging unit 50 used at the time of inspection is set (S8).

  After the setting of the inspection conditions in S5 to S8 is completed, the XY stage is driven according to a predetermined operation, and image information is acquired by imaging with the camera 51.

  Further, a plurality of inspection images may be acquired by repeating imaging in the same range a plurality of times. When performing the imaging a plurality of times, the settings of the transmission illumination unit, the reflection illumination unit, and the imaging unit may be changed to different settings for each imaging, and inspection images under a plurality of different inspection conditions may be acquired. (S9).

  For the inspection image obtained as described above, the processing unit 40 performs noise removal processing such as shading correction and expansion / contraction processing, image enhancement processing by filtering processing, feature amount extraction processing by projection method, etc. Various data processing is performed, the feature amount of the inspection image is digitized, and pass / fail judgment of the inspected substrate 70 and result output are performed (S10 to S13).

  After the inspection of the substrate 70 to be inspected by these procedures, the substrate 70 to be inspected is unloaded from the stage 31, the entire apparatus is lowered, and all steps of periodic pattern unevenness inspection in this apparatus are completed ( S14, S15).

  A series of operations in each process described above is executed by an operation by the interpersonal operation device 63 or by a program incorporated in advance, and the inspection progress information and output results are displayed on the display device 62.

  In the periodic pattern unevenness inspection apparatus provided with the above-described means, the periodic pattern is characterized by imaging transmitted diffracted light or reflected diffracted light in the periodic pattern, which is generated by performing light projection from an oblique direction. This is a non-uniformity inspection apparatus.

  In the periodic pattern unevenness inspection apparatus configured as described above, the light emitted from the transmission illumination unit 10 or the reflection illumination unit 20 is diffracted by the periodic pattern of the substrate 70 to be inspected of the periodic pattern, and the diffraction Light is captured by the imaging unit 50 as an image. The diffracted light has an effect of enhancing the difference in the shape and pitch of the slit or opening, and the difference in the diffracted light is also enhanced by changing the incident angle of illumination little by little.

  If the diffracted light diffracted by the substrate 70 to be inspected has a slight variation in the line width or slit width of the photomask or black matrix, the dimension of the pattern, the positional deviation, etc., the diffraction angle of the light at the variation portion Therefore, the image captured by the imaging unit 50 is an image in which unevenness caused by the changing unit is emphasized (schematically shown in FIG. 6). Furthermore, by using a parallel optical system for the transmission illumination unit 10, the reflection illumination unit 20, and the imaging unit 50, it is possible to capture an image that emphasizes the fluctuation of the diffracted light with higher accuracy.

  FIG. 7 schematically shows an example of visualizing unevenness with visible light and an example of visualizing unevenness with ultraviolet light when a halftone mask is inspected as the substrate 70 to be inspected. Unlike the conventional Cr mask, the halftone mask has the transmittance and phase of the semipermeable membrane so that a high contrast can be obtained at the exposure wavelength. Therefore, as shown in FIG. 7A, for example, when visible light having a wavelength of 550 nm is irradiated, most light components are transmitted without being blocked by the pattern portion. In the inspection image obtained as a result, the contrast between light and dark becomes low, the contrast between the normal part and the uneven part becomes extremely low, and it becomes difficult to determine pass / fail. However, as shown in FIG. 7B, when ultraviolet light relatively close to the exposure wavelength is irradiated, a certain amount of light component is shielded by the pattern portion, and the extraction of the diffracted light generated in the pattern portion is relatively It becomes easy. Therefore, in the inspection image, a contrast difference between the normal part and the uneven part is ensured, and it is possible to determine whether or not it is acceptable.

  In this way, the optimum inspection light / inspection wavelength band is determined each time from the product information of the substrate 70 to be inspected, and the optimum inspection conditions are set. Can be detected.

  In addition, by adopting a light source that has a light amount fluctuation range of 1% or less with respect to the operation time and a high light amount stability, it is possible to ensure the stability of the image acquired by inspection and the reproducibility of the inspection result.

  Then, by displaying the determined position and level of the unevenness portion on the display device 62 simultaneously with the unevenness image, the use for unevenness monitoring is also effective.

  As described above, according to the embodiment of the present invention, it is possible to detect the irregularity of the periodic pattern stably and with high accuracy.

It is the figure which showed typically the comparison of Cr mask and a halftone mask. It is a schematic diagram which shows schematic structure of the nonuniformity inspection apparatus of the periodic pattern of this invention. It is a schematic diagram of the illumination light switching mechanism unit 43 in the present invention. It is a schematic diagram of the illumination light switching operation | movement by the illumination light switching mechanism part 43 in this invention. It is a flowchart figure which shows embodiment of the test | inspection method of this invention. It is a schematic diagram of the unevenness visualization of the periodic pattern by diffracted light in the present invention. It is the figure which showed typically the difference in the non-uniformity visualization in the case of using visible light and ultraviolet light when a halftone mask is used as a substrate to be inspected in the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transmission illumination part 11 Turntable 12 Arc rail 13 Illumination head 14 for visible light irradiation Illumination head 15 for ultraviolet light irradiation 15 Light guide 16 Light guide 20 Reflection illumination part 21 Turntable 22 Arc rail 23 Arc rail 24 Visible light illumination head 25 UV light irradiation head 26 Light guide 27 Light guide 30 XY stage unit 31 Stage 32 X drive mechanism 33 Y drive mechanism 40 Light source unit 41 Light source for visible light irradiation 42 Light source for ultraviolet light irradiation 43 Illumination light switching mechanism unit 44 Light source Control device 45 Light guide 46 Light guide 50 Imaging unit 51 Camera 52 Imaging side parallel optical system 60 Processing unit 61 Arithmetic processing device 62 Display device 63 Interpersonal operation device 64 Image input device 70 Substrate to be inspected

Claims (7)

A non-uniformity inspection apparatus that inspects a pattern substrate in which a periodic pattern is formed on a substrate as an inspection target substrate, and inspects using diffracted light generated by the periodic pattern,
Conveying means comprising a mechanism for driving in the X-axis and Y-axis directions;
The vertical angle and horizontal angle of the illumination head can be adjusted with respect to the periodic pattern on the substrate to be inspected installed on the transport means, and the illumination irradiation position can be controlled to be constant. Illuminating means having a transmissive illuminating unit and a reflective illuminating unit, each of which includes a lighting drive
Imaging means for imaging diffracted light generated in the periodic pattern that is transmitted or reflected by the illumination means;
Image input means for converting the output of the imaging means into digitized image information;
With respect to the image information obtained by the image input means, image processing means for performing defect portion extraction / determination processing;
Display means for displaying an image captured by the imaging means and a processed image by the image processing means;
And in the lighting means,
A light source capable of emitting visible light and a light source capable of emitting ultraviolet light;
A light guide switching mechanism from the light source;
Illumination light switching means comprising lighting and extinguishing means for each light source;
In the transmitted illumination unit and the reflected illumination unit, the illumination head unit for visible light irradiation and the illumination head unit for ultraviolet light irradiation, respectively,
A nonuniformity inspection apparatus comprising:   The imaging means has a light receiving sensitivity capable of imaging at least in an ultraviolet range to a visible range, and an ultraviolet light guide means and an illumination head portion for ultraviolet light irradiation in the illumination means are from an optical member having ultraviolet light transmission characteristics. The unevenness inspection apparatus according to claim 1, wherein the unevenness inspection apparatus is formed.   The unevenness inspection apparatus according to claim 1, wherein a light source in the illumination unit is a metal halide lamp and a mercury xenon lamp.   The illumination unit irradiates the periodic pattern with parallel light, and the imaging unit includes an optical system that extracts only transmitted diffracted light and reflected diffracted light perpendicular to the periodic pattern. The nonuniformity inspection apparatus in any one of Claims 1-3.   The unevenness inspection apparatus according to claim 1, wherein a light amount fluctuation range with respect to an operation time of the light source in the illumination unit is 1% or less.   The light source in the illuminating means includes a plurality of band-pass filters therein and a built-in filter changer unit capable of switching the band-pass filters. The unevenness inspection apparatus described in 1. This is a non-uniformity inspection method in which a pattern substrate on which a periodic pattern is formed is used as an inspection target substrate, illumination light is obliquely incident on the inspection target substrate by an illuminating means, and inspection is performed using diffracted light generated by the periodic pattern. And
According to the substrate to be inspected, for the illuminating means, transmitted diffraction light or reflected diffracted light, visible light or ultraviolet light, an inspection condition setting step for setting an illumination angle, and
An imaging step of imaging the diffracted light generated in the periodic pattern that has been switched in accordance with the inspection conditions and that is transmitted or reflected and is illuminated.
An image input step for converting the output of the imaging stage into digitized image information;
For the image information obtained by the image input step, an image processing step for performing defect extraction / determination processing;
A method for inspecting unevenness, characterized by comprising: