JP5200353B2 - Periodic pattern unevenness inspection system - Google Patents

Description

  The present invention relates to a method and apparatus for inspecting pattern unevenness in a product having a periodic pattern, and is formed periodically on a substrate such as an aperture grill, a photomask, or a color filter used for a cathode ray tube of a color television. The present invention relates to a periodic pattern unevenness inspection method and an inspection apparatus capable of accurately detecting streak-like unevenness occurring in a pattern that is present.

For unevenness inspection of periodic patterns (hereinafter referred to as PM patterns) of substrates such as aperture grills, photomasks, and color filters used in color television CRTs, a transmittance image is captured using coaxial transmission illumination or planar illumination. Then, the unevenness portion and the normal portion are visually recognized by comparing the intensity (brightness) of light in each image. For this reason, in the PM pattern, the difference in light intensity between the uneven portion and the normal portion is originally small, that is, by devising an intensity difference processing method for images with low contrast, the difference is expanded and the uneven portion is extracted. , Have been inspected.

However, in the imaging of black matrix unevenness of a lattice-like periodic pattern, especially unevenness of a black matrix with a large opening, improvement in contrast between the uneven portion and the normal portion cannot be expected, and even if the intensity difference processing is devised In the inspection in the case of an image having a low contrast of the original image, there is a problem that only an inspection ability lower than the visual sensory inspection method can be achieved. The periodic pattern refers to an aggregate of slit patterns having a constant interval (hereinafter referred to as a pitch). For example, a striped periodic pattern in which one pattern is arranged at a predetermined pitch, or an opening. These patterns are a matrix-like periodic pattern in which these patterns are arranged at a predetermined pitch.

  On the other hand, due to the increase in electronic components with fine display and bright screen, the tendency to miniaturization or increase in the aperture ratio is progressing in the PM pattern. In the future, there will be a need for an inspection method and apparatus for periodic pattern irregularity inspection for a black matrix having a finer shape and a larger opening. That is, the conventional output with only the intensity (brightness) of the light intensity (brightness) based on the amplitude of the light is a limit, and unevenness cannot be clearly detected.

Therefore, an attempt has been made to apply a technique such as a projection method, which has a proven track record in coating color unevenness inspection, to the PM pattern unevenness inspection technology. For example, Patent Document 1 proposes a method for enhancing and detecting defects by image processing using a Laplacian filter.

  However, according to the method of Patent Document 1, when determining streak-like unevenness of the PM pattern, a pseudo defect caused by the light diffraction phenomenon is easily erroneously determined as streak-like unevenness, and it is difficult to say that the inspection accuracy is high. Therefore, the area to be imaged of the substrate on which the pattern is periodically formed is divided into two, the image is adjusted after the light source is adjusted, the imaged image data is connected and combined, and the combined image is used. A method for determining streaky unevenness on the substrate is conceivable.

  That is, first, two images are picked up by changing the position and angle of the light source. For example, as shown in FIGS. 4A and 4B, the images are divided into two and divided images (A1). , A2) and (B1, B2).

  At this time, a pseudo defect may occur in the imaging target area due to an alignment mark or a product information symbol outside the imaging target area on the substrate (hereinafter referred to as a drawing unit outside the captured image target area).

  By adjusting the light source at this time, as shown in FIGS. 4A and 4B, the area where the pseudo defect occurs is one side of the boundary line C, and the area where the pseudo defect occurs is two images. If the image can be reversed between the two, for example, as shown in FIG. 4C, the combined images (B1, A2) from which the pseudo defects are removed are synthesized by synthesizing the divided images B1 and A2 having no pseudo defects. Can do.

However, when a pseudo defect has occurred in both of the divided images A1 and A2 as shown in FIG. 5A, as shown in FIGS. 5C and 5D, the composite image from which the pseudo defect has been removed. Can't get.
Japanese Patent Laid-Open No. 9-264730

The present invention has been made to solve the above-described problem, and by covering a portion that is predicted to generate a pseudo defect in a drawing portion outside the imaging target area of a periodic pattern on a short substrate with a shielding plate. Another object of the present invention is to provide a periodic pattern unevenness inspection apparatus that prevents generation of pseudo defects and has high detection accuracy.

The present invention relates to a periodic pattern unevenness inspection apparatus for inspecting streaky unevenness generated in a periodic pattern on a rectangular substrate, the substrate being held substantially horizontally, and the substrate being held in a two-dimensional plane. An XY stage having a moving mechanism for moving in the X-axis direction and the Y-axis direction within the field of view, and four light sources that individually illuminate obliquely transmitted light with respect to the periodic pattern of the substrate on the XY stage, An imaging unit that is disposed on the opposite side of the light source across the XY stage, and that images diffracted light in the periodic pattern illuminated obliquely by the light source;
A moving unit that individually moves each of the light sources within a two-dimensional planar field of view with respect to the substrate on the XY stage, and the periodic pattern to be inspected when the light source is moved by the moving unit. On the other hand, posture moving means for changing the direction of the light source in conjunction with the moving means so that obliquely transmitted light is illuminated from the light source, and illumination light from the light source on a portion outside the imaging target area of the substrate 4 shielding plates that are arranged in four directions around the substrate between the substrate and the light source so that they can move independently, and at least two areas to be imaged on the substrate And adjusting the relative positional relationship between the XY stage and the light source and adjusting the brightness level of each of the divided areas by individually adjusting the light quantity of the light source. Each divided area is imaged by the imaging means at the brightness level, each captured image data is captured, the captured segmented images are connected to each other and synthesized, and stripe-like unevenness is determined using the synthesized image. An object of the present invention is to provide a periodic pattern irregularity inspection apparatus. Thereby, a pseudo defect does not occur, and the irregularity of the periodic pattern can be determined with high accuracy.

  In the present invention, the brightness level is adjusted by covering with a shielding plate that shields the illumination light from being applied to a portion that is predicted to generate a pseudo defect in drawing outside the imaging target area, and irradiating only the imaging target area with the illumination light. Each captured area is imaged, each captured image data is captured, connected and combined under the conditions according to the size of the captured divided image capturing area, and streaky unevenness is determined using the combined image This makes it possible to provide a periodic pattern unevenness inspection apparatus having high detection accuracy.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  The periodic pattern non-uniformity inspection apparatus of the present invention includes an optical condition 4-axis setting function, an individual setting / saving function for each axis, a reference condition / reference condition setting function, and an illumination center position described in Patent Document 1 In addition to these basic functions, there are alignment functions, product information, etc. in addition to these basic functions. Then, the mechanism which shields the site | part to which it is estimated is provided in the determination conditions as an additional function.

  As shown in FIG. 1, the unevenness inspection apparatus includes an oblique transmission illumination unit 10, an XY stage unit 20, an imaging unit 30, a processing unit 40, and a shielding plate 60. The processing unit 40 has a function of emphasizing the image captured by the imaging unit 30, determining whether the image is uneven, and displaying the unevenness so that the operator can easily recognize the emphasized image. Yes.

  The oblique transmission illumination unit 10 includes four lamps 11A to 11D. Each of the lamps 11A to 11D is movably supported on the linear guide 14 by a swing mechanism 12 as a posture changing unit and a linear slider 13 as a moving unit. The linear guide 14 is composed of two X guides and Y guides which are arranged so as to be orthogonal to each other within a plane field of view. One of the two X guides is provided with a first ramp 11A so as to be able to slide in the X direction, and the other is provided with a second ramp 11B so as to be capable of sliding in the X direction. Also, one of the two Y guides is provided with a third ramp 11C that can slide in the Y direction, and the other has a fourth ramp 11D that can slide in the Y direction.

The linear slider 13 is drivably engaged with the linear guide 14 and supports the lamps 11 </ b> A to 11 </ b> D via the swing mechanism 12. Further, each of the lamps 11A to 11D is provided with means for switching on and off (changing the point light source), and the distance to the inspection target substrate, the incident angle of illumination light, and the direction can be switched.

  The head swing mechanism 12 includes a micro motor, a horizontal shaft connected to the motor rotation drive shaft, and a holder that rotates around the horizontal axis together with the lamps 11A to 11D. Each of the lamps 11A to 11D swings as shown in FIG. As a result, the light projection angle θ of the light from the lamps 11A to 11D changes variously, and illumination from various angles and directions is possible. Each of the lamps 11A to 11D can be detachably mounted with an optical filter that transmits light having a desired wavelength. The optical filter is prepared in one-to-one correspondence with the wavelength of light, and can be replaced with a desired optical filter corresponding to each change in customer specifications and inspection recipes.

  For the lamps 11A to 11D, a linear light source including a parallel optical system including a telecentric lens is used. This type of light source has uneven brightness and uneven illuminance, and if the illumination intensity is high, the captured image may be affected. In the inspection apparatus of the present embodiment, an illumination center position adjustment function is added as a measure for preventing luminance unevenness and illuminance unevenness.

  In the XY stage unit 20, a mask 50 as an inspection target substrate is placed and held at a predetermined position on the XY stage 21. The XY stage unit 20 has a measurement function, recognizes the position, and superimposes the optical axis of the apparatus on the inspection start position of the mask 50. The XY stage 21 is supported by an X drive mechanism 22 and a Y drive mechanism so as to be movable in the X direction and the Y direction in a horizontal plane.

  The imaging unit 30 includes an imaging-side parallel optical system 31 parallel to the optical axis, and shares functions such as a means for capturing an image, for example, a camera with a CCD, image data conversion, data storage and transmission. The imaging side parallel optical system 31 includes an optical system or a projection optical system that can image the inspection target pattern 51 at a desired magnification (including enlargement or reduction, and equal magnification).

  The processing unit 40 comprehensively manages the imaging unit 30, the XY stage unit 20, and the transmitted illumination unit 10, and also comprehensively manages means for sequentially processing the inspection process of the periodic pattern unevenness. The processing unit 40 includes a personal computer main body 41 having a CPU and a memory, a display unit 42 including a liquid crystal display or a CRT display, and a keyboard input unit 43. The processing unit 40 receives image data picked up from the image pickup unit 30, extracts and compares the features of the image according to a predetermined data processing procedure, calculates the difference, and determines pass / fail.

The shielding plate 60 used when it is not desired to apply illumination light to the imaging target area is made of a material that does not transmit illumination light, for example, a metal such as stainless steel or iron, or a resin such as plastic.
Further, under the XY stage 21 on which the substrate is set, four shielding plates 60 that are movable independently of each other are installed in parallel to the four directions of the outer frame of the mask 50.

Accordingly, the shielding plate 60 can select the image detection area in the vertical direction of the imaging target area by sliding in parallel with the center line C that bisects the image target area vertically, for example, and the other shielding plate. 60 can slide in the direction perpendicular to the center line C to select the horizontal imaging target area of the imaging target area.

  Further, the shielding plate 60 used when it is not desired to apply illumination light to areas other than the imaging target area has a structure that can be stopped independently and at arbitrary positions by motor control in the vertical and horizontal directions. It is possible to select a desired imaging target area while observing the screen. Naturally, by moving the respective shielding plates 60 so as to cover the drawing area outside the imaging target area, it is possible to prevent the occurrence of multiple reflection images by the drawing section outside the imaging target area.

Next, the outline of the control system of the inspection apparatus will be described with reference to FIG.
The inspection apparatus of the present invention is constituted by five subsystems 40a to 40e. The data input unit 40a includes a sensor unit 411, an illumination unit 412, a position fixing unit 413, and a position control unit 414. The sensor unit 411 includes a plurality of sensors such as a position sensor for position detection, a distance sensor for detecting a moving distance (including an encoder and a counter), and a light detection sensor for detecting luminance.

The data processing unit 40b includes an image processing unit 415 that processes imaging data input from the sensor unit 411 of the data input unit 40a, and a data management unit 416 that manages the processed data. Detection signals are sent to the image processing unit 415 from each sensor of the sensor unit 411 as needed. The image processing unit 415 may be a part of the function of the personal computer 41 of the processing unit 40 or may be a processing unit independent of the personal computer 41.

  The illumination unit 412 controls the lamps 11A to 11D. The position fixing unit 413 controls the XY stage unit 20. The position control unit 414 individually controls the swing mechanism 12 and the linear slider 13 of the lamps 11A to 11D.

  The machine interface unit 40c includes a machine interlocking unit 417 that transmits / receives data to / from an external device such as a transport mechanism (not shown) that transports the mask 50 to be inspected, and an automatic supply / discharge unit that transfers the mask. 418. The human interface unit 40e includes an information display unit 42 that displays a processed image processed by the data processing unit 40b, and an interpersonal operation unit 43 that exchanges information with an operator. The system bus 40d is an interface between the human interface unit 40e and the other subsystems 40a to 40c for data transmission / reception.

The substrate inspection procedure is the same as that in Patent Document 2, and is therefore omitted.

Next, an outline of the generation principle of pseudo defects will be described.
FIG. 3 is a schematic diagram for explaining the principle of generation of a shadow (ghost) due to multiple reflection (bottom reflection) light. When the illumination light 2 enters the mask 50 and illuminates the pattern 51, a real image 34 of the pattern is formed on the image plane 33 of the imaging unit 30. On the other hand, the bottom surface reflected light from the pattern 51 is reflected again (multiple reflection) by the bottom surface 50 b of the mask 50, and this multiple reflection image is formed on the image surface 33 to become a shadow (ghost) 35. If this shadow (ghost) 35 appears on the image surface 33 as an image of a pseudo defect, it causes a decrease in the accuracy of the pass / fail judgment of the real image 34.

The pseudo defect removal method will be described.
As shown in FIG. 4, in the image synthesis for pseudo defect removal, for example, a pseudo defect removal image is obtained by dividing the imaging target area into left and right with a center line C that bisects the imaging target area and combining the A2 image and the B1 image. However, in the case where the imaging target area width X as shown in FIG. 5 is extremely narrow or there is some out-of-area drawing such as an alignment mark, pseudo defects occur on both the left and right sides with respect to the center C of the imaging target area. Sometimes.

  In such a case, if the illumination light applied to the drawing outside the imaging target area is blocked by the shielding plate 60, it is possible to prevent reflection of a pseudo defect in the imaging target area.

The pseudo defect removal method will be described in detail with reference to FIG.
FIG. 6A shows that the pseudo-defect 35 is generated in the imaging target area a-1 divided by the center line C by the imaging target area outside drawing unit 51. Further, another pseudo defect is also generated in one of the divided imaging target areas b-1.
Here, as shown in FIG. 6B, the pseudo defect 35 generated in the imaging target area a-1 is caused by the illumination light emitted from below to the imaging target area outside drawing unit 62, and the imaging target outside area drawing unit. The light reflected by the bottom surface of 62 is reflected by the bottom surface of the glass substrate of the substrate 60 and is combined with the drawing pattern portion 64 to generate a pseudo defect.
Therefore, as shown in FIG. 6C, if the shielding plate 60 is moved to prevent the illumination light outside the imaging target area drawing unit 62 from being irradiated from below, it is possible to prevent the occurrence of pseudo defects. Become.

  In the apparatus of the present embodiment, the pseudo defect removal function is called using the reference condition / reference condition function to perform the pseudo defect removal processing. The operator determines the unevenness level (luminance level on the image) for the composite image, and determines and evaluates the presence or absence of streaky unevenness defects based on the determined unevenness level. When performing this judgment and evaluation, it is possible to evaluate the pseudo defect using only the captured image without the operator displaying a review and displaying the pseudo defect image (sample) on the screen. In addition, the function of pseudo defect removal is only for the designated area when an image that seems to be a pseudo defect is obtained from the result of measurement with the mode that performs automatic measurement and automatic judgment after setting in the recipe and the previous recipe. It is assumed that there are two modes: a manual mode for displaying a pseudo defect-removed image and determining one image. In the automatic mode, conditions preliminarily registered as recipes (light quantity of illumination light, camera magnification, light projection angle, etc.) are read out, and the inspection is automatically executed in accordance therewith.

  The present invention can be used, for example, to inspect streaky irregularities generated in shadow masks used for color television CRTs, color filters for liquid crystal display panels, photomasks, Fresnel lenses, and the like.

1 is a structural block perspective view showing an outline of an inspection apparatus of the present invention. The block diagram which shows the control system of the test | inspection apparatus of this invention. Schematic diagram for explaining the principle of generation of pseudo defects due to multiple reflection (bottom reflection) light Pseudo defect removal composite image part 1 Pseudo defect removal composite image part 2 Diagram showing the outline of the pseudo defect removal method

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Oblique transmission illumination part, 11A-11D ... Light source, 12 ... Attitude change means, 13 ... Movement means, 14 ... Guide way, 20 ... XY stage part, 21 ... XY stage, 22 ... X drive mechanism (movement mechanism), 23 ... Y drive mechanism (moving mechanism), 30 ... imaging unit, 31 ... CCD camera (imaging means), 32 ... camera optical axis (center line), 34 ... real image, 35, 35a, 35b ... pseudo defect, 40 ... processing , 41 ... PC, 42 ... display screen, 43 ... keyboard, 50 ... mask (imaging target substrate), 51 ... drawing area outside imaging target area, 52 ... streaky unevenness, 53 ... periodic pattern area, 56 ... imaging target Area, 58 ... center line (camera optical axis), 60 ... shielding plate C1, light source C2, light source C ... center line

Claims (1)

A periodic pattern unevenness inspection apparatus for inspecting streaky unevenness generated in a periodic pattern on a rectangular substrate,
An XY stage comprising a moving mechanism for holding the substrate substantially horizontally and moving the substrate in the X-axis direction and the Y-axis direction within a two-dimensional planar field of view;
A light source including four telecentric lenses that individually illuminate obliquely transmitted light with respect to the periodic pattern of the substrate on the XY stage, and having an illumination center position adjustment function ;
An imaging unit that is disposed on the opposite side of the light source across the XY stage, and that images diffracted light in the periodic pattern illuminated obliquely by the light source;
Moving means for individually moving each of the light sources in a two-dimensional planar field of view relative to the substrate on the XY stage;
When the light source is moved by the moving means, the direction of the light source is changed in conjunction with the moving means so that the periodic pattern to be inspected is illuminated with obliquely transmitted light from the light source. Posture moving means for causing
Arranged in four directions around the substrate between the substrate and the light source so that illumination light from the light source is not applied to a portion outside the imaging target area of the substrate,
With four shielding plates that can move independently ,
The imaging target area on the substrate is divided into at least two areas, the relative positional relationship between the XY stage and the light source is adjusted, and the light intensity of each of the light sources is individually adjusted to adjust the luminance level of each of the divided areas. Each divided area is imaged by the imaging means with the adjusted brightness level, the captured divided image data is captured, the captured divided images are connected to each other and synthesized, and a streak shape is formed using the synthesized image. A periodic pattern unevenness inspection apparatus characterized by determining unevenness.