JP2009058377A - Inspection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of an inspection apparatus, such as, a minute line width measuring device, wherein an image of low contrast is provided dependently on a measured pattern because the black level of a camera is fixed and light quantity is adjusted by a dimmer. <P>SOLUTION: This inspection apparatus is provided with an image processing section, a microscope, a light source, the dimmer for adjusting the light quantity of the light source, a camera, and a control section for performing dimming by the dimmer based on the luminance value of the image and setting the black level of the camera at the optimal value with a measuring pattern. The black level of the camera is set at an optimal value for each measuring pattern, based on the number of the lowest luminance, thereby acquiring an image of high contrast. Thus, the dynamic range of the camera can be utilized effectively, and accurate measurements can be made. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a measurement apparatus for medical use, industrial use, etc., and more particularly to image adjustment of the measurement apparatus.

  The dimensional inspection device, line width measuring device, or visual inspection device related to the invention of the present application uses an optical microscope and an image sensor such as a CCD (Charge Coupled Device) camera, etc., and an IC (Integrated Circuit) wafer or LCD (Liquid Crystal). Device) is a device that performs non-contact measurement by image processing, such as measurement of line width and pattern interval of a film-like pattern formed on a TFT (Thin Film Transistor) substrate of Device) or pattern defect detection. In this document, the dimension inspection device, the line width measuring device, or the appearance inspection device is collectively referred to as an inspection device.

In the inspection apparatus as described above, a dimming function for controlling the amount of illumination light is indispensable so that the luminance level of an image acquired by an image sensor (hereinafter referred to as a camera) becomes a predetermined value.
However, when a pattern with a high reflectance (for example, a metal film pattern) and a pattern with a low reflectance (for example, a transparent film pattern) coexist, automatic light control is difficult. For this reason, several improvement plans have been proposed. For example, Patent Document 1 discloses an automatic light control device when a pattern having a high reflectance and a pattern having a low reflectance are mixed.
In the light control device as described above, the light amount is adjusted so that the peak value or average value of the image becomes the maximum value of the image level. However, since the black level of the camera at this time is fixed, an image with poor contrast is obtained depending on the pattern to be measured.

A conventional measurement processing operation will be described with reference to FIG. FIG. 5 is a flowchart for explaining a procedure for measuring an image captured using a conventional optical microscope and camera by image processing.
In executing this processing procedure, the image processing unit provided in the inspection apparatus registers in advance an optimal camera gain setting value and black level setting value for each lens of the optical microscope in the internal memory unit or the external memory unit. Because there is, you can refer to those data.
In FIG. 5, first, the measurement position is determined with a low-power lens having a wide field of view, and then measurement is performed with a high-power lens. Therefore, in the changing step 521, the lens of the optical microscope is changed. Note that the magnification when measuring with a high-magnification lens differs depending on the type of substrate (or measurement program) to be measured.
Next, in the gain setting step 522, the gain of the camera is set to an initial value. In a black level setting step 523, the current black level of the lens is set to an initial value.
Next, in the automatic light control step 524, the light amount is adjusted so that the peak value or the average value becomes the maximum value of the image level. In the imaging step 525, an image is captured, and in the measurement step 526, measurement processing is performed.

JP 2000-28319 A

As described above, in the conventional inspection apparatus, since the light amount is adjusted while the black level of the camera is fixed, an image with poor contrast may be obtained depending on the pattern to be measured.
In view of the above problems, an object of the present invention is to provide an inspection apparatus capable of dimming so that an image with good contrast is obtained regardless of a pattern to be measured.

In order to achieve the above object, the inspection apparatus of the present invention can obtain a high-contrast image by setting the black level of the camera to an optimum value for each measurement pattern.
That is, the inspection apparatus of the present invention is an inspection apparatus for inspecting the size or appearance of an object to be inspected, an optical microscope for enlarging an image of the object to be inspected, an image sensor for capturing an image enlarged by the optical microscope, In the inspection apparatus including a control unit that performs microscopic dimension measurement or appearance inspection of the sample by image processing from the image data of the sample imaged by the image sensor, the control unit increases the black level of the image sensor by a first predetermined value, Calculate the number of minimum brightness before and after the increase, and if the calculated number of minimum brightness is larger than before, the means to update the larger value as the number of minimum brightness and the minimum brightness even if the black level is increased If the number of images does not increase, the black level is lowered by the second predetermined value, the number of minimum luminances before and after the reduction is calculated, and before the calculated number of minimum luminances is decreased. If it is smaller, the means to update the smaller value as the number of minimum luminances, and if the calculated number of minimum luminances is larger than before, the black level at that time is set to the black of the image sensor when inspecting the object to be inspected. It is equipped with means for leveling.

  Further, the inspection apparatus such as the line width measuring apparatus of the present invention includes a microscope, a light source, a dimmer that adjusts the light amount of the light source, an image sensor, and dimming by the image processing unit dimmer. And an image processing unit that sets the black level of the image sensor according to the number of minimum luminances of the measurement pattern for each measurement position.

  Further, the inspection apparatus of the present invention controls the dimming by the microscope, the light source, the dimmer for adjusting the light quantity of the light source, the image sensor, and the image processing unit dimmer from the luminance value of the image, and the image sensor The black level is calculated by the number of minimum luminances of the measurement pattern for each measurement position, stored in a recipe in advance, and provided with an image processing unit that is set for each recipe.

  According to the present invention, it is possible to effectively use the dynamic range of a camera, and it is possible to perform measurement with higher accuracy than before.

  The inspection apparatus of the present invention includes a control unit that controls each component of the inspection apparatus in the inspection apparatus that inspects the size or appearance of the inspection object, and the control unit increases the black level setting of the image sensor, The number of minimum luminance before and after the increase is calculated, and if the calculated number of minimum luminance is larger than before the increase, it has means for updating the larger value as the number of minimum luminance, and further increasing the black level. However, if the number of minimum brightness does not increase, lower the black level setting, calculate the number of minimum brightness before and after the decrease, and if the calculated number of minimum brightness is smaller than before, decrease the value. Means of updating as the number of minimum luminances, and if the calculated number of minimum luminances is larger than before the decrease, the black level setting value of the image sensor when inspecting the object to be inspected at that time It is obtained and means for.

The inspection apparatus of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of a line width measuring apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the line width measuring apparatus mainly includes a camera 148, an optical microscope 141, a stage 142, a frame grabber (FG) 143, a dimmer 144, a light source 145, a control unit 146, a monitor 147, and a stage 142. The pedestal 150 is equipped with The control unit 146 includes an image capture / display unit 161, an image storage unit 162, and a CPU (Central Processing Unit) 163. The optical microscope 141 further includes an objective lens 151 having a plurality of magnifications, and the lens revolver mechanism is controlled by the control unit 146 to switch to an objective lens having a desired magnification, and the magnification of the sample 149 captured by the camera 148 is controlled. To change.
The control unit 146 may be a PC (Personal Computer).

On the stage 142, an inspection object (sample 149) is placed and fixed as a subject. The pedestal 150 includes a horizontal movement mechanism that moves the stage 142 in the X direction (left and right direction on the drawing) and the Y direction (depth direction on the drawing) and a height movement mechanism that moves the stage 142 in the Z direction (height direction). An image of a desired portion of the sample 149 can be taken by the control of the control unit 146.
The position of the stage 142 is controlled in the X, Y, and Z directions by the control of the control unit 146, but the operator manually operates the horizontal unit by operating an input unit (not shown) coupled to the control unit 146. Position control in the vertical direction and position control in the vertical direction can also be performed.

In FIG. 1, the control unit 146 controls each component of the inspection apparatus according to a processing program registered in the CPU 163.
Light from the light source 145 is output to the optical microscope 148 via the dimmer 144. The dimmer 144 is controlled by the control unit 146 to adjust the amount of light, and outputs the light with the adjusted amount of light to the optical microscope 141. For example, the dimmer 144 adjusts the light amount so that the peak value or average value of the image becomes the maximum value of the image level. The light input from the dimmer 144 is applied to the sample 149 through the optical microscope 141, and the sample 149 outputs reflected light when irradiated with the light, and the output reflected light passes through the optical microscope 141. Through the camera 148.
The camera 148 converts the incident light into an electrical signal, and outputs the converted image signal data to the FG 143. The FG 143 is an image input board for receiving the image signal data of the camera 148 and transferring the received image signal data to the image storage unit 162 of the control unit 146.

As described above, an enlarged image of the inspection target area of the inspection target object (sample 149) taken by the camera 148 is supplied to the control unit 146 as an image signal, and is supplied to the image capture / display unit 161 in the control unit 146. Entered. The control unit 146 further includes an image storage unit 162 and a CPU 163 in which a predetermined program is stored.
The image storage unit 162 is used to store images and data for calculation, and the CPU 163 executes control necessary for the operation of the entire system.
The program of the control unit 146 measures the pattern line width of the semiconductor substrate by performing image processing on the image signal, and outputs the result to the monitor 147.

One embodiment of the light control processing operation of the inspection apparatus of the present invention will be described with reference to FIG. FIG. 2 is a flowchart for explaining the measurement procedure of the inspection apparatus of the present invention.
In executing this processing procedure, an image processing unit (see control unit 146 in FIG. 1) included in the inspection apparatus previously stores an optimal camera gain setting value and black level setting value for each lens of the optical microscope in the internal memory. Since the data is registered in the external memory unit or the external memory unit, the data can be referred to.
In FIG. 2, first, usually, after a measurement position is determined with a low-power lens with a wide field of view, measurement is performed with a high-power lens. Therefore, in a change step 521, the lens of the optical microscope is changed. Note that the magnification when measuring with a high-magnification lens differs depending on the type of substrate (or measurement program) to be measured.
Next, in a gain setting step 522, an optimal value for executing the subsequent processing steps is set as an initial value of the camera gain. In a black level setting step 523, a black level corresponding to the lens magnification currently set is set. The initial value of the black level is set for each lens having a different magnification. For this reason, the black level is always set in accordance with the lens magnification change.
Next, in the automatic light control step 524, the amount of light input to the optical microscope is adjusted so that the peak value or the average value becomes the maximum value of the image level.

In the minimum luminance number (LVL1) calculation step 105, the minimum luminance number LVL1 of the designated area is calculated for each inspection program that differs depending on the type of the inspection object.
Black level UP In step 106, the black level of the camera is increased by a predetermined value C from the current black level setting value.
In the lowest luminance number (LVL2) calculation step 107, the lowest luminance number LVL2 of the area designated for each inspection program is calculated.
Minimum luminance number comparison A In step 108, the size of the minimum luminance number LVL1 calculated in step 105 and the minimum luminance number LVL2 calculated in step 107 are compared. If LVL1 ≦ LVL2, proceed to LVL1 update step 109. If LVL1> LVL2, proceed to black level return step 110.
LVL1 update A In step 109, the value of the minimum luminance number LVL1 is replaced (updated) with the value of the minimum luminance number LVL2, and the procedure returns to black level UP step 106, and the camera black level is set to the current black level. Increase the value by C by more than the value and continue processing.

In the black level returning step 110, the black level of the camera is returned to the black level before being raised in the black level UP step 106, and the process proceeds to the black level down step 111.
Black level DOWN In step 111, the black level of the camera is lowered by a predetermined value D from the current black level setting value.
In the lowest luminance number (LYL3) calculation step 112, the lowest luminance number LYL3 of the designated area is calculated.
Minimum luminance number comparison B In step 113, the size of the minimum luminance number LVL1 at the time of processing of step 108 is compared with the minimum luminance number LVL3 calculated in step 112. If LYL1 ≧ LVL3, the process proceeds to LVL1 update B step 112. If LYL1 <LVL3, the process proceeds to black level determination step 114.
LVL1 Update B In Step 112, replace (update) the value of the lowest luminance number LVL1 with the value of the lowest luminance number LVL3, return to the black level DOWN step 111, and set the camera black level to the current black level setting. Decrease the value by a predetermined value D and continue processing.

In a black level determination step 114, the black level of the current camera is determined as the final black level, that is, the black level applied at the time of inspection.
In the image capturing step 525, an image is captured, and in the measuring step 526, a measurement process is performed.
In the above embodiment, the black level is increased by a predetermined value C in step 106, and the black level is decreased by a predetermined value D in step 111. The predetermined value C and the predetermined value D may be the same value or different values. Further, it may be changed according to the value of the black level instead of a constant value. Moreover, these predetermined values may differ for every inspection program, and may be the same.

Next, referring to FIGS. 3 and 4, when the processing operation for setting the black level of the camera to an optimum value is executed for each pattern to be inspected according to the processing procedure described in the flowchart of FIG. 2, the conventional black level is fixed. Then, the case where the light is adjusted will be described. FIG. 3 is a diagram for explaining the relationship between the change in the black level of the camera and the number of pixels with the lowest luminance (LVL1, etc.). FIG. 4 is a diagram showing an image and a luminance waveform when the same pattern is dimmed according to the conventional technique and when dimming is performed according to the procedure of the flowchart of FIG.
FIG. 3A shows a change in the set value of the black level for each elapsed time when the black level of the camera is gradually increased. FIG. 3 (b) shows the number of pixels with the lowest luminance in the designated area when the black level of the camera is raised.
In FIG. 3 (a), the black level increases with a linear characteristic having a predetermined slope as time passes. Therefore, in FIG. 3B, the horizontal axis may be considered as the set value of the black level of the camera.

From point Pa to point Pb in Fig. 3 (b), even if the black level is raised, the number of pixels with the lowest luminance does not rise above LVL0 (a constant value). From point Pb to point Pc, there is a proportional relationship with Fig. 3 (a). When the black level is from the Pa point to the Pb point, the black level approaches the Pb point by the flow from the black level UP step 106 to the LVL1 update A step 109 in FIG.
When the black level passes the Pb point and is from the Pb point to the Pc point, the black level approaches the Pb point by the flow from the black level DOWN step 111 to the LVL1 update B step 112.

In FIG. 4, FIG. 4 (a) is an image and luminance waveform obtained by dimming (for example, see FIG. 5) with the camera black level fixed in the prior art, and FIG. 4 (b) is a flowchart of FIG. It is a figure which shows the image and luminance waveform which were acquired by the light control which sets the black level of this camera to an appropriate value. In FIG. 4, a case will be described in which the pattern 1 and the inspection target area in which the pattern 2 is partially overlapped with the pattern 1 are enlarged and imaged in the area.
In FIG. 4 (a), the upper part shows an image 501a, and the lower part shows a luminance level waveform on the scanning line SL of the image 501a. Also in FIG. 4B, the upper part shows an image 501b and the lower part shows a luminance level waveform on the scanning line SL of the image 501b. Images 502a and 502b are pattern 1 images, and images 503a and 503b are pattern 2 images. 504a and 504b are luminance waveforms, and 505a and 505b are black levels.

When the flowchart of FIG. 2 is used, an image with a black level, such as an image 502a of pattern 1 and an image 503a of pattern 2 shown in FIG. As shown in the second image 503b, an appropriate black level is obtained. Therefore, it can be seen that range b is wider than range a, and the dynamic range of the camera is effectively used.
Measurement by image processing with inspection equipment such as line width measurement is based on the height of the luminance waveform (the difference between the lowest luminance level and the highest luminance level). Affects accuracy. Therefore, according to the present invention, highly accurate measurement processing is possible.

Also, instead of the above-described flow for automatically determining the black level of the camera, the black level is determined in advance for each product inspection program by executing a flowchart as shown in FIG. 2 when creating a recipe. It is also possible to save the optimal black level at the position to be performed. It goes without saying that it is possible from the configuration of the present invention to perform inspections such as measurement of a minute line width by using a recipe created in advance and performing the camera with its settings at the time of measurement or inspection.
In the embodiment of FIG. 4, the number of pixels with the lowest luminance is calculated on the scanning line, but it may be within a predetermined area instead of on the scanning line.

The block diagram which shows the structure of the line | wire width measuring apparatus of one Example of this invention. The flowchart for demonstrating one Example of the measurement procedure of the test | inspection apparatus of this invention. The figure for demonstrating the relationship between the change of the black level of a camera, and the pixel number of the minimum brightness | luminance. The figure for demonstrating the difference of the image and luminance waveform by a prior art and this invention. The flowchart for demonstrating the procedure which measures the image imaged using the conventional optical microscope and camera by image processing.

Explanation of symbols

  141: optical microscope, 142: stage, 143: FG, 144: dimmer, 145: light source, 146: control unit, 147: monitor, 148: camera, 149: sample, 150: pedestal, 151: objective lens, 161 : Image capture / display unit 162: Image storage unit 163: CPU, 501a, 501b: Image of inspection target area, 502a, 502b: Pattern 1 image, 503a, 503b: Pattern 2 image, 504a, 504b: Luminance waveform, 505a, 505b: Black level.

Claims (1)

In an inspection device that inspects the dimensions or appearance of an object to be inspected,
An optical microscope for enlarging the image of the object to be inspected;
An image sensor that captures an enlarged image of an optical microscope;
In an inspection apparatus having a control unit that performs microscopic measurement or appearance inspection of a sample by image processing from image data of the sample imaged by an image sensor,
The control unit increases the black level of the image sensor by a first predetermined value, calculates the number of minimum luminances before and after the increase, and if the calculated minimum luminance number is larger than before the increase, the larger value is set to the lowest value. Means for updating as the number of luminances;
If the number of minimum brightness does not increase even if the black level is raised, the number of minimum brightness before and after the black level is lowered by the second predetermined value is calculated. If it is smaller than before lowering, means for updating the smaller value as the minimum luminance number,
An inspection apparatus comprising means for setting the black level at that time to a black level of an image sensor when inspecting an object to be inspected if the calculated number of minimum luminances is larger than before.

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