KR101863752B1 - method of enhancing resolution for optical apparatus for inspecting pattern image of semiconductor wafer and method of acquiring TSOM image using the same - Google Patents
method of enhancing resolution for optical apparatus for inspecting pattern image of semiconductor wafer and method of acquiring TSOM image using the same Download PDFInfo
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- KR101863752B1 KR101863752B1 KR1020170050477A KR20170050477A KR101863752B1 KR 101863752 B1 KR101863752 B1 KR 101863752B1 KR 1020170050477 A KR1020170050477 A KR 1020170050477A KR 20170050477 A KR20170050477 A KR 20170050477A KR 101863752 B1 KR101863752 B1 KR 101863752B1
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- G01N21/8851—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges
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Abstract
Description
[0001] The present invention relates to an optical wafer inspection method, and more particularly, to an optical wafer inspection method, in which a wafer having a semiconductor circuit formed thereon is subjected to an inspection using an existing optical wafer inspection apparatus, A method for enhancing resolution of an optical wafer inspection apparatus and a method for acquiring a TSOM image using the same.
As one method for inspecting wafers, a wafer inspection apparatus for acquiring and inspecting images of a part of a wafer typically irradiates a single wavelength pulse illumination light with a predetermined period to a corresponding region of the wafer, . A field of view (FOV: Field Of View) in which a lens-attached image can be obtained by one pulse illumination is reflected and a reflected light of a target area passes through a lens portion, Once the imaging is performed on the imaging region of the wafer, the wafer moves so that the next imaging region adjacent to the imaging region can be imaged at the next pulse illumination time.
Assuming that the pulse illumination time is very short in order to capture all areas of the wafer, it is assumed that the wafer hardly moves during this time, and the wafer is irradiated during the pulse illumination period by the width of the imaging object area, It is possible to adopt a method of moving in the width direction.
On the other hand, a semiconductor device originally formed a circuit device by integrating circuit elements such as a device and a wire into a small-sized plane, and used a method of continuously reducing the size of devices and conductors in order to increase the degree of integration. However, as the degree of device integration increases, reducing the size of devices and wires has been hampered by various limitations in the process of making semiconductor devices, such as the optical limitations of photolithography processes. In addition, It is in a state that it can import.
In such a situation, in order to increase the device integration degree of the semiconductor device, a three-dimensional device configuration such as the layering of the semiconductor device and the solidification of the device configuration has been searched for.
When a semiconductor device is manufactured through a highly precise and complicated multi-step process step, the inspection work that confirms whether the semiconductor device can perform its function as it is designed according to the design, finds the process defect, corrects the problem, And play a very important role in enhancing effectiveness.
Among the conventional inspection apparatuses for semiconductor devices, an inspection apparatus using an optical image acquires an image of a part of a target semiconductor device and determines whether the image is normal or not to check whether the semiconductor device is defective. On the other hand, There is a problem in that the reduction of the CD causes the limitation of the inspection because the optical inspection apparatus does not have sufficient resolution for the inspection object. On the other hand, the three-dimensional configuration of the semiconductor device is a conventional inspection Method is causing problems that inspections can not be done adequately and appropriately.
First, in relation to a method of increasing the optical resolution of an existing inspection apparatus, resolution enhancement technology by pixel subsampling is known.
Normally, to increase the optical resolution, the number of pixels of a detector such as a CMOS or a CCD is increased. This can be understood as a concept involving increasing the detector area under the pixel density such as increasing the number of pixels within the same area, that is, the pixel density.
However, this has the aspect that it is difficult to adopt easily because it increases the cost for making the device and increases the installation space.
As a method for solving such difficulties, a technique of moving an image formed on a detector to a size smaller than a pixel of a detector and increasing the resolution in the moving direction is a resolution enhancement technique by pixel sub-stepping. It is known that it can be used in the field of astronomy and microscopy, and a piezoelectric driving scanning device using a piezoelectric element or a piezo element as a driving device for moving an image to a size smaller than a pixel of a detector is known.
In this way, image data processing can be used to superimpose or combine the images obtained at each position to be moved and finally to form a high resolution final image. This process is called super resolution imaging.
1 is an explanatory diagram for explaining a concept of resolution enhancement by pixel sub-stepping. As shown in the figure, the image area corresponding to a group of pixels of the scratch element by the movement of the image sensor itself in a plane moves from the initial position (A1) to a pixel shift the A3 position moved by the -y axis by 1/2 of the pixel size, and the A4 position moved by the -x axis by the half of the pixel size, Thereby obtaining a primary object image.
When the image pickup device moves again by 1/2 of the pixel size on the y-axis, the image pickup device comes to the original position. In such a cycle of movement, the four primary object images are obtained at four different positions, .
In order to perform such a pixel sub-stepping technique, a detector in which an image is formed in a state in which a path of a light beam containing an image is maintained moves in sub-pixel units at an original position.
However, the detector having such an operation usually has a very heavy accessory structure, and it is not easy to move quickly and accurately and intermittently, and it has been difficult to increase the facility cost in order to make it possible.
On the other hand, when a pattern image is acquired and inspected by a conventional optical inspection apparatus, if the pattern is too small, the illumination beam is difficult to reach through the gap, and only when the optical microscope is larger than half of the wavelength size of light used In a small pattern inspection such as inspection of a semiconductor device, a microscope user can arrange a group of similar patterns at a certain distance and use a method of determining the size by observing how the light is dispersed among the groups In this way, there is a great deal of difficulty in measuring the new three-dimensional structure of a semiconductor device.
Of course, non-optical measurement methods can be considered, but non-optical image processing methods such as scanning probe microscopy are expensive and slow, making it difficult to use them as practical inspection devices.
Recently, Ravikiran Attota et al. Of the National Institute of Standards and Technology (NIST) has developed a technique for overcoming the limitations of an optical wafer inspection apparatus by a three-dimensional configuration of a semiconductor device, Through-Focus Scanning Optical Microscopy (TSOM) can be used to measure three-dimensional micropatterns ("TSOM method for semiconductor metrology", Proc. SPIE 7971, Metrology, Inspection, and Process Control for Microlithography XXV, 79710T, April 20, 2011)
This technique uses a conventional optical microscope, but uses a method of creating a three-dimensional image data space for an object by collecting two-dimensional images at different focus positions for the same object. Thus, the resulting two-dimensional images constitute a through-focus image comprising a plurality of in-focus images and out-of-focus images that are out of focus . Computer processing of such a three-dimensional image data space is performed. The computer extracts a brightness profile from a plurality of through-focus images for the same subject being collected and uses the focus position information to create a through-focus scan optical microscope (TSOM) image.
The image provided by the through-focus scanning optical microscope (TSOM) does not represent the object in detail but is slightly abstract, unlike ordinary photographs. However, the difference between the images is inferred from the fine difference in shape of the measured three- .
Through a simulation study, the through-focus scanning optical microscope (TSOM) is known to be capable of measuring characteristics below 10 nanometers and presents possibilities for fine three-dimensional structure shape analysis.
Fig. 2 shows an example of an optical wafer inspection apparatus for implementing such a method. Here, the table (XYZ stage) on which the wafer as the object is placed moves in the Z-axis direction, and the distance from the objective lens is changed, so that an image having a different focus position is obtained by the image pickup device (CCD). Here, the optical system constituted by the objective optical system and the tube lens can be regarded as a configuration equivalent to a kind of optical microscope. BS represents a beam splitter.
However, in order to take an image of an object through an optical microscope while changing the focal position, it is necessary to take an image while gradually changing the position of the focus direction of the optical system such as the object and the objective lens, and mechanical movement is required to move the position.
This position movement requires a considerable amount of time depending on the mechanical movement, and there is also a problem that the positional instability of the image becomes larger as the optical axis shifts due to the mechanical movement as the imaging is performed with respect to a very small object. It is time-consuming to acquire a large number of optical images with different focus positions for a very small subject, and the variation of the optical axis and the instability of the image position are inevitable due to the mechanical movement, So that the method used for the inspection of the semiconductor device is not yet adequately presented.
Korean Patent Laid-Open Publication No. 10-2014-0019737 discloses another method of obtaining and processing a plurality of defocused images without mechanical scanning of the object to be investigated with focus while using the TSOM method as a prototype. This method is based on the use of light sources with different wavelengths and the use of light sources with spatial spectral resolution.
FIG. 3 discloses an example of an optical wafer inspection apparatus for implementing such a method. Where L1 to L5 denote lenses and BS denotes beam splitter.
However, in this type of configuration, there is no need to mechanically move the object in the direction of the optical axis. However, there is a problem in that the amount of illumination is very low because one wavelength range of the entire illumination light is selected and used. In addition, there is instability caused by non-chromatic axial aberrations on imaging optics such as axial asymmetric aberrations.
Moreover, this optical aberration and light intensity profile varies according to the measurement equipment, varies from one imaging point to the next, and having a library of reference images for the new TSOM measurement for each setting is very time consuming.
As a result, it is not practical to apply the measurement method of Korean Patent Publication No. 10-2014-0019737 to the process at the present time.
The above-mentioned TSOM technique and pixel sub-stepping technique have common features in that they use optical equipment and can be used in inspection methods such as detecting defective positions of objects using them. However, these techniques are fundamentally different from each other , But it is a technology that has developed independently through other routes, and it does not have any significant correlation. Especially, in the case of TSOM technology, since the concept itself is not intended to directly increase the resolution of the pattern image, no consideration is given to the resolution improvement.
It is an object of the present invention to provide a method capable of alleviating the problems in conventional pixel sub-stepping while implementing a method of enhancing the resolution by the above-described pixel sub-stepping for wafer inspection above.
Another object of the present invention is to provide a method of acquiring a TSOM image using a resolution enhancement method using pixel sub-stepping in order to alleviate the problems of the semiconductor device inspection method using the conventional TSOM technology.
In this additional aspect, the present invention combines TSOM technology, which has been developed independently of each other, and resolution enhancement technology by pixel sub-stepping on the basis of device common elements, and both technologies use the optical system This is based on the fact that there are methods that can detect defects of microscopic size exceeding the optical resolution, so that a semiconductor device capable of increasing the capability of fine defect inspection through the same optical device as compared with each of the existing TSOM and pixel sub- It is also an object to provide a basis for a device inspection method.
According to an aspect of the present invention, there is provided a method for enhancing resolution of an optical wafer inspection apparatus,
An optical system for allowing an image light to pass through the wafer portion placed at a predetermined position with respect to the wafer placed on the table in order to acquire a semiconductor device image or a wafer image; And an image pickup element for acquiring image information by reaching the image light, that is, the reflection image, reflected by the adjustment reflecting portion and the adjustment reflecting portion,
It is possible to adjust the position or the reflection angle on the rotational displacement of the adjustment reflecting portion in a state in which the object (wafer, semiconductor device) and the optical system are fixed, that is, The image light is moved at least once to at least one of two different axial directions (for example, x-axis and y-axis directions orthogonal to each other) of the imaging plane of the imaging device to a sub-pixel (sub- Acquiring an image (primary object image) at each movement position,
And a step of deriving a resolution-enhanced result image (secondary object image) by the computer through the super resolution imaging program using the acquired image for each position.
In the present invention, the adjustment of the angle of the adjustment reflection part may be performed using a piezo element installed on the adjustment reflection part on the rear side. For example, in the present invention, the adjustment reflecting portion may be provided with a tip-tilt mirror, and the tip tilting mirror may be installed at four corners of the reflecting mirror, and the thickness may be varied by the applied voltage And a circuit portion capable of adjusting an applied voltage to the devices. The angle adjustment of the adjustment reflection portion adjusts the thickness of each of the piezoelectric materials by a given signal so that the direction in which the reflection mirror faces . ≪ / RTI >
At this time, the angle adjusting operation is predetermined by the moving program and is preferably associated with the super resolution imaging program so that the computer is periodically and automatically adjusted according to the program.
At this time, the reflection mirror of the adjustment reflection part rotates about two perpendicular vertical axes (x, y) of the plane formed by the reflection mirror while changing the direction of the image light that touches the adjustment reflection part through the optical system Reflection.
At this time, since the angle of the movement of the position of the image light to the detector, that is, the image pickup element by the angle of the adjustment reflection angle is very small, the shape change due to the phase change or angle becomes negligible.
According to another aspect of the present invention, there is provided a method for acquiring a TSOM image,
The step of obtaining a resolution-enhanced result image at a predetermined focal position by using the resolution enhancement method of the optical wafer inspection apparatus of the present invention is performed by adjusting the optical system or the target position, Obtaining a resolution enhanced image for each position;
And acquiring an integrated TSOM image by processing a resolution enhanced image for each focus position. As a matter of course, in the aspect of inspecting defects of an object as an inspection apparatus, it is further possible to further include a step of using the TSOM image and analyzing it to detect a defect in a semiconductor device in the corresponding region (position).
In the present invention, an optical system is usually formed by arranging and combining at least one lens, and here, it is meant to consist of a combination of optical elements between the object wafer and the regulating reflector, but an optical element such as a lens is limited It is not. Therefore, a lens constituting an imaging optical system for converging the reflection image of the regulated reflection portion to the size of the image pickup element may be provided between the regulated reflection portion and the image pickup element.
As a specific method of changing the focus position in the present invention, there is a method of moving the table of the table on which the target wafer is mounted in the direction of the optical axis, or moving the objective lens system constituting at least a part of the optical system in the direction of the optical axis, A lens between the wafer and the regulating reflector, or an optical element system, which can be considered to be composed of one objective lens) is a method of moving the distance between the objective lenses constituting the objective lens system and a method of moving the objective lens system itself As a whole.
By mechanically moving the table or table holder on which the wafer is placed, the holder can also be quickly moved by adjusting the voltage applied to the piezo element using the piezo element.
In the present invention, in the process of mechanically moving the table stand to move the target in the direction of the optical axis, the position of the image in the surface of the imaging element can be changed even in the state where the adjustment reflecting portion is not moved, Corrections to these unwanted changes can be made through additional configurations.
For example, in the present invention, a reflection image dividing means such as a beam splitter is provided in an optical path before a subsequent image pickup element of the regulated reflection portion, at least a part of the divided light is input to a position sensor for detecting a shift of the optical axis, And the direction of the reflected image can be adjusted to the correct position by inserting the detected optical axis deviation information into the adjustment reflecting unit. For example, the reflected image is divided by the beam splitter in the path to the imaging element, the divided reflected image is sensed in a quadrant cell, and the result is transmitted to the regulated reflector, So that the reflection direction can be adjusted.
When the deviation of the optical axis due to the change in the distance between the optical system and the wafer due to the mechanical movement forms a constant relationship after the entire setting of the inspection apparatus, the adjustment by the input of the detection result of the orientation sensor according to the relational expression or trend indicating this relationship It is also possible to interlock the mechanical movement and the adjustment amount of the adjustment reflecting portion without adjusting the reflection portion so that the reflection image is placed in the correct position of the image pickup element.
In the present invention, a reflection image splitting means such as a beam splitter is provided in the optical path before the image pickup element of the control reflection portion, and at least a part of the split light can be inputted to a defocus measurement means such as a Shark-Hartmann sensor. The detection result of the Shark-Hartman sensor can be used to measure or confirm the relationship between the relative mechanical displacement and the amount of defocus on the optical axis of the wafer and optical system for TSOM, or to determine the wavefront state or phase, .
If the relationship between the mechanical movement amount and the defocus amount is secured in this way and a constant relationship is established between the above-mentioned mechanical movement amount and the optical axis deviation, the defocus amount measurement value is input to the adjustment reflecting portion It is also conceivable to use it for adjusting the projection angle of the reflection image of the adjustment reflection part.
In the present invention, the image pickup device does not simply mean an image pickup device such as a CCD or a CMOS. It interprets or reconstructs image information input to an image pickup device in a narrow sense to produce a visible image, Can be interpreted as a concept that includes both computer hardware and software that are associated with, processed, processed, or compared with a reference image.
Although not specifically referred to in the present invention, a known illuminating device may also be incorporated in the present invention to form a part of the entire inspection apparatus. When the illuminating light source supplies light in a pulsed manner or other intermittent manner, the illumination period can be interlocked with a moving program for the mirroring operation of the reflex control section.
According to the present invention, it is possible to increase the resolution of the optical image obtained by adding or modifying the method of moving the adjustment reflector and the method of processing the resultant image in the optical inspection apparatus having the conventional adjustment reflector, The work can be performed more accurately and effectively.
According to a further aspect of the present invention, even when a wafer (semiconductor device) is inspected using an optical inspection apparatus for TSOM technology, a more accurate TSOM image is acquired by increasing the resolution of the optical image of each focal position, It is possible to derive and utilize more accurate results in various tests such as discovery of process defects in semiconductor devices.
This additional aspect improves the resolution of the optical image at locations that are out of focus in the existing TSOM technology, so even though the non-focused image has a higher resolution, it contains more three-dimensional information It is possible to obtain better inspection results even when the TSOM technology is applied to the same optical inspection apparatus.
This additional aspect makes it possible to improve existing problems on the application of the TSOM technology and the application of the pixel sub-stepping technology without the need for any hardware changes of the optical inspection equipment by effectively operating the regulating reflector. In other words, the use of an additional sensor system can compensate for undesired positional changes in the imaging device due to mechanical and physical movements in the relative movement of the focus position in the direction of the optical axis in the TSOM, through adjustment of the adjustable reflector, By appropriately adjusting the direction of the weighing control reflection part, fine movement of a desired direction and size of an image in an image pickup device can be accurately implemented to obtain an accurate (higher resolution) image and enhance the inspection ability of the inspection apparatus.
FIG. 1 is an explanatory diagram for explaining a concept of resolution enhancement by pixel sub-stepping,
2 is a configuration diagram showing an example of a configuration of a conventional wafer inspection apparatus of the TSOM system,
3 is a structural conceptual diagram showing an example of a conventional wafer inspection apparatus configuration of a conventional TSOM system eliminating a mechanical movement for changing a distance between a wafer and an optical system;
Figure 4 is a flow chart illustrating the important steps of an embodiment of the method of the present invention.
Figure 5 is a flow chart illustrating the important steps of an embodiment incorporating an additional aspect of the method of the present invention;
FIG. 6 is a configuration diagram showing a configuration of a wafer inspection apparatus according to the present invention,
FIG. 7 is a conceptual diagram illustrating the configuration of the regulated reflector of FIG. 6 and the coupling relationship with quadrants,
8 is a plan view showing in greater detail the reflective mirror and the piezoelectric element configuration of the adjustable reflector among the wafer apparatus configurations suitable for practicing the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Figure 4 is a flow chart illustrating the important steps of an embodiment of the method of the present invention.
Before explaining each step of the method of the present invention, a basic configuration of a wafer inspection apparatus for carrying out the method of the present invention will be described. A wafer inspection apparatus includes a table on which a wafer is placed to obtain a semiconductor device image or a wafer image, An optical system that is placed at a predetermined position with respect to the wafer placed on the wafer and allows the image light to pass through the wafer portion, an adjusting reflecting portion provided behind the optical system for reflecting the image light passing through the optical system by adjusting the angle, Light, that is, a reflection image, and acquires image information.
For example, the reflection control unit is provided such that a plurality of piezo elements are distributed in the rear of the mirror, and a proper voltage is applied to each of the piezo elements to change the length of each piezo element, so that the angle of the mirror is changed as a whole. It is preferable that the distribution of the piezo elements is such that the image light is easily moved in the directions of the two axes orthogonal to each other like the x-axis and y-axis of the plane of the imaging element. Of course, it is also possible to use a step motor other than the piezoelectric element as a displacement means to adjust the direction of another mirror, but it is not excluded.
A more specific configuration of the wafer inspection apparatus will be described later with reference to the embodiments.
Next, the method of this embodiment will be described. First, an optical wafer inspection apparatus is prepared (S10). In this preparation process, the target wafer is mounted on the table. The table is moved in the horizontal direction so that imaging can be performed for one area of the wafer so that the area is positioned below the objective lens system of the optical system.
The illumination light starts from the light source, is reflected by the splitter, illuminates the area through the objective lens system, and the image light reflected from the area passes through the objective lens system and the splitter and is reflected from the mirror surface of the reflection control part.
The reflected image light is focused on a specific pixel area on the surface of the imaging element through the imaging lens system, and the imaging element sends the electrical signal by the imaging light to a computer or other signal processing device, (S30).
Next, the mirror of the reflection control unit is rotated to move the image light in the image pickup element below the pixel (S60). Then, the process of acquiring the primary object image as in S30 is repeated at the moved position. Such movement is performed by a moving program, and repetition of the process of acquiring an image for each movement position can be performed through program type logic steps for increasing and decreasing the number of times such as S20, S40, and S50 of FIG. The NF in the step S50 can be given in advance through the input when creating the moving program.
The mirror of the reflection control unit is finely rotated by the action of the piezo element distributed on the rear surface. Rotating the mirror of the reflection adjusting part in the present invention is very simple and effective compared with the conventional method of adjusting the mirror part when comparing the general configuration of the reflection adjusting part and the image pickup part, . For example, the piezo element can adjust the angle of rotation very finely according to the applied voltage and adjust the distance between the mirror and the element so that the moving degree of the image light in the imaging plane can be easily controlled according to the angle of rotation. , The image light can be easily moved from a large distance to a small distance in each axial direction while being easily adjusted within the imaging plane (ease of adjustment). Further, the reflection control unit including the mirror and the piezo element for driving the mirror can be made into a very small and simple structure, and can only consume very little electric power for driving. (Simplicity of configuration and economy)
When the rotary movement is completed, the pulsed light is emitted in the illumination. In the absence of any change in position or state of the illumination, the optical system, the target, and the image pickup element, the rotation of the mirror causes the image light to shift (shift) in the x-axis direction by a quarter distance of the pixel size, for example.
The image sensing device senses the shifted image light and transmits the electrical signal by the shifted image light to the computer or other signal processing device in the same manner as described above to acquire the primary object image data at the second position.
The next rotation operation of the mirror is repeatedly causing the image light to move further (shift) in the x-axis direction by 1/4 of the pixel size in the imaging element plane, to further move in the y-axis direction, or to return to the original position It is also possible to do. For example, as shown in FIG. 1, after taking an image at the home position, the image is shifted in the x-axis by 1/2, the second image is picked up, -1/2, so that the fourth imaging is performed to complete the imaging of the wafer with the four primary object images as one set. In addition, 16 primary object images were obtained at 16 positions in four sections in the x-axis direction and four sections in the y-axis direction while making a distance of one movement to each of the x and y axes to 1/4 of the pixel, .
The mirror rotation operation and thus the image light movement on the image pickup device surface are automatically performed by changing the periodic periodical computer signal to the reflection adjustment unit according to the movement program built in the computer and changing the applied voltage of the piezo element of the reflection adjustment unit When the pulse light is used as the illumination, the pulse period can be interlocked with the pulse period.
In this way, a plurality of (one set of) primary object images for the region are obtained while displacing the mirror to move to a position determined by the movement program, and processed by a conventional super resolution imaging program to obtain a resolution An enhanced secondary object image is obtained (S70).
In order to further enhance the resolution, the number of primary object images acquired for each movement, that is, the number of primary object images constituting one set, until the image light travels at a single time in the plane of the imaging element is further reduced and returned to the home position It is possible to use a method of increasing the resolution by associating these images with a super resolution imaging program.
Such a super resolution imaging program may be performed in consideration of the moving order and the moving position by the moving program or may be a single integrated program together with the moving program to process a plurality of primary object images, The explanation will be omitted here.
Figure 5 is a flow chart illustrating the key steps of an embodiment incorporating an additional aspect of the method of the present invention.
In this embodiment, in applying the TSOM technology, the method of FIG. 4 is applied as one element.
The conventional TSOM technology will be described first. In an optical inspection apparatus, a wipers are installed on a table so that an optical pattern image for a corresponding region is formed at a specific focus position with respect to a corresponding region, After acquiring the image and then changing the focus position, the optical pattern image for each focal position is obtained as a basic image, and then the basic image at these different focal positions is combined through image processing processing to obtain a TSOM image as a result The TSOM image is compared with the TSOM reference image obtained for the normal pattern to determine whether the corresponding area pattern is normal or not.
At this time, since the basic image obtained as the basic data for obtaining the TSOM image is composed of those which are not focused on the optical viewpoint and the resolution is determined by the optical inspection device for the unfocused image, It was treated as not being an object.
In the method of FIG. 5, the resolution enhancement method as in the embodiment of FIG. 4 is used in the process of acquiring the basic image in implementing the conventional TSOM technology. That is, when acquiring an image that is out of focus for each focus position while changing the focus position for applying the TSOM technology to the corresponding region of the wafer, We obtain a plurality of primary object images and process them through a super resolution imaging program to obtain a secondary object image and use it as the base image of the TSOM image.
Referring to the drawings, first, an optical wafer inspection apparatus is prepared (SS110). At this time, an object (wafer) is placed on the table, and the corresponding region of the object is placed under the objective lens system to prepare for imaging.
The position between the objective lens system and the object is adjusted to achieve a specific focus position (SS130). Then, the secondary object image of the focus position is obtained through the process of steps S20 to S70 of the embodiment of FIG. That is, by moving the position of the image pickup element plane with respect to the corresponding area in the x-axis or y-axis direction by the pixel distance or less, the primary object image is formed at every position, ). A super-resolution imaging program is used to process the primary object image, substantially the associated electrical signal (data), to obtain a secondary object image with enhanced resolution.
Subsequently, the process of S20 to S70 is repeated while shifting the focus position (SS160). Thus, a secondary object image having enhanced resolution for the corresponding region at the focus position is obtained. The secondary object image enhanced in resolution for the corresponding region at each focal position is obtained while performing the focal position variation as much as predetermined. For this iterative process, programmable formal logic steps can be used to increase and decrease the number of times such as SS120, SS140, and SS150, which sequentially increase the focus position from 1 to M, a natural number less than MF. Here too, the MF can be automatically determined by changing the focus between the wafer and the optical system, signaling the focal position to change, processing the base image, and entering the TSOM program into the computer and the TSOM program.
The secondary object image at each focal point becomes a basic image for obtaining the TSOM image, and the TSOM image is obtained by processing the TSOM image with the TSOM program (SS 170).
In order to obtain N basic images (secondary object images) for the TSOM image, it is N-1 times to correct the focus position at a specific focus position.
The subsequent TSOM image acquisition operation can be performed in the same manner as the conventional method of acquiring the TSOM image. That is, a computer having an image processing program for acquiring a TSOM image executes this image processing program to obtain a single TSOM image by processing a basic image of an object corresponding area at N different focal positions.
The following process compares the reference TSOM image obtained by applying the embodiment of FIG. 5 of the present invention and the one TOSM image obtained in advance to the corresponding region of the wafer having the normal pattern to determine whether the region includes a normal defect . Of course, such determination can also be made through an image processing program of a computer.
Hereinafter, a specific configuration of a wafer inspection apparatus suitable for the practice of the present invention will be described with reference to the drawings. In addition, in order to acquire an image having a different focal position with respect to an object corresponding area in the present invention, even if the focal position is changed, the image light must reach the same position of the image pickup device so that there is no distortion of the basic image and a proper TSOM image can be obtained Assumption. Accordingly, the description and the method of preventing and correcting the position of the image light due to the mechanical or physical movement of the object or the optical system when the focus position is different are also mentioned. In addition, this correcting method can be used to precisely control the amount of movement of the image light in sub-pixel shift (pixel sub-stepping) in the imaging element plane in the step of obtaining the resolution enhanced image Should be considered.
6 and 7 show an example of a wafer inspection apparatus capable of carrying out the method of the present invention.
The
The illumination device is provided with a
Reflected light produced by reflection of the illumination light on the wafer includes an image for the wafer and passes through the objective
The image light is reflected by the
The adjustment of the
The reflecting
8, in order to rotate the
Here, the
The adjustment operation of the
The reflected image arrives at the
As shown in FIG. 7, the position sensor senses a change in the position of the reflection image when the reference state occurs and a position of the reflection image sensed when the table is moved along the Z axis or a deviation of the optical axis, (Circuit board: 330) of the regulating part. According to the information, the control unit adjusts the amount of voltage applied to the piezoelectric element so that the position where the divided reflection image is formed returns to the original position in the position sensor.
The amount of voltage applied to the
This adjustment can be made continuously through feedback rather than at once. That is, while the Z-axis movement of the table 220 is being performed, the position sensor detects the distance from the original position in a short time period, and the control unit of the
When the deviation of the optical axis due to the change in distance between the objective optical system and the wafer due to the mechanical movement forms a constant relationship after the entire setting of the inspection apparatus, the detection result of the orientation sensor is inputted according to the relational expression or trend indicating this relationship It is also possible to interlock the mechanical movement and the adjustment amount of the regulating reflector without adjusting the regulating reflector so that the reflected image is placed in the correct position of the image capturing element.
In this case, after the setting, it is possible to remove the position sensor and the beam splitter therefrom in the configuration of FIG. 6 to increase the amount of light reaching the image pickup element.
In this embodiment also, a beam splitter is installed in the optical path of the regulating
The Shark-Hartman sensor is a kind of wavefront sensor that measures wavefronts, and can simultaneously measure both defocus and tilt, so if a Shark-Hartman sensor is present, a separate quartile sensor There is no need, but here it is shown as being included for convenience, and it has been made a kind of extraordinary composition.
The detection result of the Shark-
If the relationship between the mechanical movement amount and the defocus amount is secured in this way and a constant relationship is established between the above-mentioned mechanical movement amount and the optical axis deviation, the defocus amount measurement value is input to the adjustment reflecting portion It is also conceivable to use it for adjusting the projection angle of the reflection image of the adjustment reflection part.
The Shark-
Even in this case, it is possible to remove the Shark-Hartman sensor and the beam splitter therefrom after the setting in the configuration of FIG. 6 to increase the amount of light reaching the imaging element.
The portion of the beam splitter which is not divided through some reflection but goes straight is focused by the imaging optical system and is input to the imaging element. The image pickup device is usually in the form of a CCD (charge coupled device) or a CMOS (complimentary metal oxide semiconductor) chip, but does not mean only an image pickup device in a narrow sense such as a CCD or a CMOS. The concept is interpreted as a concept that includes both computer hardware and software that interprets or reconstructs image information to produce a visible image, processes it, processes it in association with other data as needed, or compares it with a reference image.
An image pickup device in a narrow sense sends a video signal generated by receiving a reflected video image to a device computer (not shown), and the processor of the device computer processes the video signal by a dedicated program (super resolution imaging program) And acquires a TSOM image by processing the acquired TSOM image, thereby detecting a defective pattern.
At this time, most of the images have no sharp edges depending on the defocus amount. Therefore, the pattern defects of the semiconductor device formed on the wafer itself can not be found immediately, but a plurality of images of different defocus amounts are processed by the TSOM method The composite TSOM image is obtained, and compared with the reference TSOM image, the original pattern defect is detected.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. That is, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
211: laser (light source) 213, 217, 219: lens
215: pinhole 220: table (wafer stage)
230: objective optical system 240: imaging lens system (tube lens)
250: image pickup element 300:
310:
330: circuit board 400: quadrant cell
500: Shack Hartmann sensor
Claims (7)
The angle of the adjustment reflecting portion is adjusted in a state in which the wafer and the optical system are fixed so that the image light in the image pickup element is shifted to at least the pixel size of the image pickup element by at least one axis So as to obtain a plurality of images at an initial position and at each movement position of the imaging element plane,
A method for enhancing resolution of an optical wafer inspection apparatus, comprising: obtaining a resolution-enhanced result image by a computer having a super resolution imaging program using a plurality of acquired images.
The angle adjusting operation of the adjustment reflecting portion is automatically performed in the order determined by the moving program,
Wherein the moving program is associated with the super resolution imaging program,
Wherein the angle adjustment operation of the adjustment reflection unit is performed periodically automatically by a signal transmitted to the adjustment reflection unit by the computer.
So as to allow the direction of the image light (reflection image) to be adjusted in the regulating reflector of the optical wafer inspecting apparatus so as to divide the image light on the back of the regulating reflector and on the optical path in front of the image sensing device A position sensor installed to detect at least a part of the light split by the reflection image dividing means and to detect a shift of the optical axis, a shift sensor for detecting shifts of the optical axis detected by the position sensor, (Signal line) provided so as to be able to be inserted into the optical wafer inspection apparatus.
Wherein the orientation sensor comprises at least one of a quartic cell and a Shark Hartmann sensor.
The adjustment reflector may be a tip-tilt mirror,
The tip tilt mirror includes a quadrangular plane reflecting mirror, a piezoelectric element provided at four corners of the reflecting mirror, the thickness of which can be varied by an applied voltage, and a circuit part capable of adjusting an applied voltage to the piezoelectric element. (Circuit board) on the surface of the optical wafer inspecting apparatus.
A first step of fixing the wafer and the optical system to each other at a first position so as to be in a first focus position,
Adjusting the angle of the adjustment reflecting portion so that image light in the image pickup element moves at least once in at least one axis among two different axial directions of the image pickup element plane to a level of the pixel size of the image pickup element, A second step of acquiring a plurality of images at a position and each movement position,
And a third step of the computer having the super resolution imaging program incorporating the plurality of acquired images to derive a resolution-enhanced result image to be a base image of the current focus position,
A fourth step of performing the second step and the third step for each different focal position while changing the wafer and the optical system to mutually different positions to obtain a basic image for the different focal positions, ,
And a fifth step of processing a base image for the different focus positions to obtain a TSOM image. The method for acquiring a TSOM image using the resolution enhancement method of an optical wafer inspection apparatus, comprising:
The image pickup element may be a CCD or a CMOS image pickup element having a narrow meaning,
And a computer apparatus including hardware and software for processing a signal by the reflection image received by the image pickup device in the narrow sense to acquire an image,
Wherein the computer apparatus is configured to obtain a TSOM image (TSOM image) for a wafer by integrating a plurality of images obtained by changing the relative distance (distance on the optical axis) between the optical system and the wafer TSOM Image Acquisition Method Using Resolution Enhancement Method.
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