JP2006308336A - Imaging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging system capable of displaying the images of the whole of the end edge of a semiconductor wafer over an azimuth of 180° on a monitor at the same time. <P>SOLUTION: The end edge of the semiconductor wafer is three-dimensionally scanned using an imaging head, which has light source devices (1, 2 and 3) for emitting linear laser beams, an object lens (10) for converging the linear laser beams to project the converged beam on a sample and a linear image sensor (13), and imaged from a plurality of angular directions. A plurality of the images taken from a plurality of the angular directions are synthesized in a signal processing circuit (16) to be displayed on an image display device (16). Further, since the end edge of the wafer is three-dimensionally scanned, the images of the end edge of the wafer are three-dimensionally displayed using the height data in a depth direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging system suitable for imaging an image of an edge of a semiconductor wafer having first and second surfaces parallel to each other and an edge located between the two surfaces.

  A semiconductor device is manufactured through various processes such as an etching process, an impurity implantation process, and a cleaning process in which various material films such as a semiconductor film, an insulating film, and a metal film are formed on a mirror-finished semiconductor wafer. In the semiconductor device manufacturing process, in order to improve the yield, it is necessary to perform the next process after the wafer surface on which various processes have been performed is in a clean state. For example, if the material used in the previous step remains, contamination occurs and the yield is significantly reduced. For this reason, after various processes are performed, a cleaning process is performed on the entire wafer, and the remaining material used in the previous process is removed, and the next process is executed after a clean state is obtained. However, the element formation area of the wafer is maintained in a clean state by the cleaning process, but the edge portion located at the periphery of the element formation area covers an azimuth angle of 180 °, so that the cleaning tends to be insufficient, such as foreign matter. May remain. In addition, the film formed in the previous step is removed by polishing processing (polishing) after various processes are performed on the peripheral portion of the wafer, but if the polishing amount is insufficient, foreign matter remains and is contaminated. Nation may occur, and excessive polishing may adversely affect the element formation region. Therefore, in order to increase the manufacturing yield of semiconductor devices, an imaging system capable of observing the state of the peripheral surface of the semiconductor wafer is required. On the other hand, in the current processing process, the edge of the semiconductor wafer is observed using an optical microscope.

  In the manufacturing process of a semiconductor device, it is desired to observe the entire edge of the wafer simultaneously. However, the edge of the wafer is defined by the element forming surface on which the device is formed and the back surface and spans an azimuth angle of 180 °. For this reason, when observing using a conventional microscope, it is necessary to separately capture images from the front surface side and the back surface side of the wafer, and it is difficult to simultaneously display an image of the entire edge on the monitor. Further, since the edge of the wafer is composed of a plurality of curved surfaces, the azimuth angle is greatly different for each surface. For this reason, when an image of the edge of a semiconductor wafer is to be taken with a normal optical microscope, the range on the wafer that is in focus is narrow, and the focus is at a position that is laterally separated from the focal point of the objective lens. There is a limit in capturing an image that is shifted and focused over the entire edge. In this case, there is a limit even if it tries to image using an objective lens with a deep focal depth.

  Further, when an edge image is captured with an optical microscope, the edge image is displayed only in a planar manner, and it is difficult to determine the properties or characteristics of the singular points displayed on the monitor. For example, even if a darker portion than the surroundings is displayed on the monitor, it is difficult to determine whether the portion is an image due to foreign matter adhesion or an image due to scratches. In addition, even if the adhesion of foreign matter is detected, it is difficult to obtain information on the nature and size of the attached foreign matter, and when a foreign matter of an optically transparent material is attached, a transparent foreign matter is detected. It was also difficult. Therefore, in the method of imaging the wafer edge with an optical microscope, there is a limit in obtaining image information useful for qualitative analysis and quantitative analysis necessary for improving the yield of the semiconductor device manufacturing process. Further, in order to determine whether or not the edge of the semiconductor wafer is polished accurately, it is necessary to obtain the cross-sectional shape of the wafer. However, in order to take an image of a cross-sectional shape using a normal optical microscope, the wafer must be broken, and when the wafer is broken, the wafer becomes a defective product.

  Furthermore, in order to image the edge of the wafer over an azimuth angle of 180 °, it is necessary to shoot from a large number of azimuth directions. Not only does the observation take a long time, but the work is complicated and more useful. Development of a simple imaging method is strongly demanded.

An object of the present invention is to provide an imaging system capable of simultaneously displaying an image of the entire edge of a disk-like or plate-like object over an azimuth angle of 180 ° on a monitor.
Furthermore, another object of the present invention is to realize an imaging system capable of obtaining image information useful for qualitative analysis and quantitative analysis of a manufacturing process with respect to an edge of a semiconductor wafer.

An imaging system according to the present invention includes an edge region of a semiconductor wafer having a first surface that is an element formation surface parallel to each other, a second surface that is a back surface, and an edge located between the two surfaces. An imaging system for imaging,
A light source device that generates a line-shaped light beam, a beam deflecting device that deflects the line-shaped light beam generated from the light source device in a direction orthogonal to the extending direction, and a line-shaped light beam emitted from the beam deflecting device An objective lens that projects toward the edge of the semiconductor wafer as a converging line-shaped light beam, an objective lens moving mechanism that moves the objective lens in the direction of the optical axis thereof, and an extension direction of the line-shaped light beam At least two imaging heads, including first and second imaging heads, each having a plurality of light receiving elements arranged along a direction and having a linear image sensor that receives reflected light from the semiconductor wafer; ,
A signal processing circuit for receiving an output signal from a linear image sensor of the imaging head and forming a video signal;
The imaging head is disposed on the same plane orthogonal to a central plane parallel to the first and second surfaces of the semiconductor wafer,
A converging line-shaped light beam emitted from the objective lens of each imaging head and incident on the edge of the semiconductor wafer is set so as to extend in a plane substantially orthogonal to the central plane of the semiconductor wafer,
Images of the edge region are sequentially taken while changing the relative distance between the objective lens and the semiconductor wafer from a plurality of angular directions along the periphery of the edge of the semiconductor wafer. A video signal representing an image of an edge region is output by combining images captured from directions.

  In the present invention, the edge of the disk-like object is imaged from a plurality of angular directions, a plurality of images captured by the signal processing circuit are combined, and the combined image is output as a video signal. An image of the entire edge can be simultaneously displayed on the monitor. Here, it is important that in the present invention, the edge region is illuminated with a line-shaped light beam, and the reflected light from the first surface and the second surface of the semiconductor wafer is received by the linear image sensor. That is. That is, if the laser beam is scanned in the main scanning direction using an acousto-optic device, it is extremely difficult to obtain a sufficient scanning length. If an attempt is made to obtain a sufficient scanning length, the optical path length is long. As a result, the entire apparatus becomes large. On the other hand, when two-dimensional scanning is performed using a line-shaped light beam, a sufficient scanning length can be obtained with a short optical path length. In particular, in order to image the entire edge region of the semiconductor wafer including the element formation surface and the back surface, a sufficiently long scanning length is necessary. Therefore, a compact imaging head can be obtained by using a linear light beam. Can be realized.

  In a preferred embodiment of the imaging system according to the present invention, the disk-like object to be observed is a semiconductor wafer, and the optical axis of the objective lens is centered on the optical axis of the objective lens from the element forming surface side and the back surface side across the central surface of the semiconductor wafer. Each of the images is picked up at an angle of 45 ° with respect to the surface, the two images are combined in the signal processing circuit, and an image of the entire edge including a part of the element forming surface and the back surface is displayed. And If an objective lens having an opening angle of 45 ° or more is used and the optical axis of the objective lens is set to an angle of 45 ° with respect to the center plane of the semiconductor wafer, imaging can be performed over an azimuth angle of 90 °. Therefore, an image of the entire edge can be displayed on the monitor at the same time by simply capturing images from the front side and the back side and combining the two images by the signal processing circuit. As a result, the imaging operation is facilitated and the load on the signal processing circuit is reduced. Furthermore, the edge of the semiconductor wafer is formed of a plurality of flat surfaces or curved surfaces having different azimuth angles. In the present invention, imaging is performed while changing the relative distance between the edge of the semiconductor wafer and the scanning spot. Therefore, it is possible to capture an image in which a plurality of surfaces having different azimuth angles are in focus.

  In a preferred embodiment of the imaging system according to the present invention, the signal processing circuit obtains the maximum luminance value from the luminance value obtained during imaging while changing the relative distance between the scanning spot and the edge of the semiconductor wafer. And means for obtaining position information in the direction of the optical axis that generates the maximum luminance, and storage means for storing the obtained maximum luminance value and the corresponding position information for each pixel. In the confocal microscope, among the converging line-shaped light beams incident on the edge of the semiconductor wafer, the maximum brightness is output when the focusing line is located on the sample surface, and the focusing line is displaced from the sample surface in the optical axis direction. In some cases, only a small amount of reflected light is incident on the linear image sensor. Therefore, if the maximum luminance value and the corresponding position information are output and the position information is used as the height information in the depth direction, the image of the wafer edge can be displayed three-dimensionally and attached to the edge of the wafer. Foreign matters and scratches can be clearly identified, and useful information for various analyzes of the manufacturing process can be obtained. In addition, an advantage that information such as the size and thickness of the adhered foreign matter can be obtained is achieved.

  In a preferred embodiment of the imaging system according to the present invention, the light source device is constituted by a combination of a laser light source and a micromirror device having a plurality of micromirrors arranged in a two-dimensional matrix. A beam is emitted. In this case, since the line-shaped light beam emitted from the micromirror device is a light beam having a random phase relationship and is a non-coherent beam, an advantage that no glare or flare occurs is achieved.

  In a preferred embodiment of the imaging system according to the present invention, the imaging head combines three light sources of R, G and B and R, G and B light beams generated from these light sources into a line light beam of three primary colors. And an image of an edge region of the semiconductor wafer is output as a color video signal. Since the semiconductor wafer may be polished to various colors, the edge image is output as a color image, thereby making it easier to identify the semiconductor wafer. In addition, when a foreign substance such as a resist is not attached, the foreign substance can be specified based on the color of the foreign substance, which is suitable for foreign substance determination. Furthermore, since three color light sources are used, there is an advantage that an image can be captured with an appropriate color beam according to the type of the semiconductor wafer.

  FIG. 1 is a diagram showing an example of an imaging system according to the present invention. In this example, the image of the edge of a semiconductor wafer is imaged using two imaging heads. Since the two imaging heads have the same configuration, only the configuration of one imaging head is shown. In this example, a mercury lamp 1 is used as the light source 1. A xenon lamp can also be used as a light source. A linear light beam for illumination is generated from the mercury lamp 1. The light generated from the mercury lamp 1 is converted into a linear light beam extending in the first direction by the optical fiber 2 and emitted as a linear light beam shaped through the slit 3. In the drawing, it is assumed that the line-shaped light beam extends in the direction of the arrow in the drawing. The line-shaped light beam passes through the beam splitter 4 and enters the vibrating mirror 6 which is a beam deflecting device through the imaging lens 5. The oscillating mirror 6 periodically deflects the incident light beam in a second direction (direction orthogonal to the paper surface) orthogonal to the first direction. The light beam emitted from the oscillating mirror 6 enters the objective lens 9 via the relay lenses 7 and 8. The incident light beam is converged by the objective lens 9 and enters the edge region of the semiconductor wafer 10 which is a sample to be observed. The semiconductor wafer is arranged so as to extend in a direction orthogonal to the paper surface. Therefore, the focused line-shaped light beam extends in a plane orthogonal to the central plane Sc parallel to the element formation surface and the back surface of the semiconductor wafer. As a result, the edge of the semiconductor wafer 10 to be imaged is two-dimensionally scanned at a predetermined scanning frequency by the converging line light beam. The semiconductor wafer is supported on a stage (not shown), and the illumination beam can be incident on the front side and the back side of the semiconductor wafer by rotating the stage.

  In this example, two-dimensional scanning is performed while changing the relative distance between the focused line light beam and the edge of the semiconductor wafer. Therefore, in this example, a stepping motor 11 that is a displacement means for displacing the objective lens 9 in the optical axis direction is provided, and two-dimensional scanning is performed while displacing the objective lens in the optical axis direction by the stepping motor. Further, the amount of displacement of the objective lens in the optical axis direction is detected by an encoder, and the amount of displacement of the objective lens is stored in the memory as position information in the depth direction. The objective lens may be fixed, and the stage supporting the semiconductor wafer may be displaced in the optical axis direction of the objective lens to displace the relative distance between the objective lens, that is, the scanning spot and the wafer edge.

  The light reflected by the edge of the semiconductor wafer 10 is collected by the objective lens 9, enters the oscillating mirror 6 through the relay lenses 8 and 7, is descanned, and enters the beam splitter 4 through the imaging lens 5. The reflected light from the wafer surface is reflected by the beam splitter and enters the linear image sensor 12. The linear image sensor 12 is arranged at the imaging position of the imaging lens 5, and a first direction which is a scanning direction on the wafer surface so as to receive reflected light from the semiconductor wafer for each line in the main scanning direction. A plurality of light receiving elements arranged in the corresponding direction are read out, and charges accumulated in each light receiving element are read out at a predetermined reading frequency. Since the reflected light from the wafer surface is descanned by the vibrating mirror 6, it is not displaced in the sub-scanning direction. Therefore, each light receiving element of the linear image sensor is periodically scanned by the reflected light from the wafer surface. Become. As a result, the charge accumulated in each light receiving element of the linear image sensor is read out at a predetermined readout frequency, whereby two-dimensional image information of the wafer edge is output.

As described above, the edge of the semiconductor wafer 10 is scanned with the light beam converged in a spot shape, and the reflected light from the edge is received by each light receiving element of the linear image sensor. A focal optical system can be configured to capture a wafer edge image with high resolution.
Since the second imaging head has the same configuration as the first imaging head described above, description thereof is omitted, and only the objective lens and the λ / 4 plate of the second imaging head are illustrated.

  FIG. 2 is a diagram showing the relationship between the orientation of the edge of the semiconductor wafer to be imaged and the optical axis of the objective lens. In FIG. 2, it is assumed that the semiconductor wafer extends in a direction orthogonal to the paper surface. The peripheral edge of the semiconductor wafer 10 has a first surface 10a constituting an element formation region and a second surface 10b which is a parallel back surface facing the first surface. These first surface and second surface An edge is formed between the surface and the surface. Here, a plane located between the two surfaces 10a and 10b and passing through the center of the wafer is defined as a center plane Sc. The end edge is constituted by a surface 10c orthogonal to the center surface Sc and two surfaces 10d and 10e located on both sides thereof. Each surface forming the edge is a flat surface or a slightly curved surface.

  Since the edge of the wafer is formed by five surfaces 10a to 10e, the optical axis of the objective lens is set to be perpendicular to each surface, the image is captured by five imaging operations, and the five images are synthesized. It is also possible to display an edge image. However, the imaging operation needs to be performed many times, and there is a disadvantage that imaging takes a long time. In order to eliminate this drawback, two imaging heads are used, an objective lens having an aperture angle of 45 ° or more (numerical aperture is 0.95) is used as the objective lens, and the optical axis of the objective lens is approximately 45 with respect to the center plane Sc. The angle is set to an angle of 0 ° or an angle close thereto, and two imaging heads are used to make 45 ° with respect to the center plane from two sides of the first surface 10a side and the opposite second surface 10b side, respectively. Each edge is imaged at an angle of. In this case, images of the three surfaces 10a, 10d, and 10c constituting one half region of the wafer edge are simultaneously captured by the first imaging head, and images 10b, 10e, and 10c are captured by the second imaging head. To do.

  Next, the relationship between the converging line light beam emitted from the objective lens and each surface of the semiconductor wafer edge will be described. In this example, since an image of an object having an azimuth angle of 180 ° is captured by two imaging heads, it is necessary to capture an image of 90 ° azimuth by one imaging head. Therefore, one limit light beam 20a of the line-shaped light beam passing through the objective lens 9 is incident substantially perpendicular to the first surface 10a, and the other limit light beam 20b is approximately perpendicular to the third surface 10c. Set to enter. One limit light ray 20a is incident on the surface 10a perpendicularly, is reflected by the surface, and is condensed by the objective lens 9 again. On the other hand, when the limit light ray 20a is incident on the surface 10a at an angle smaller than perpendicular, it is no longer condensed by the objective lens and cannot be imaged. The same applies to the other limit ray 20b. In this way, by setting the limit light beam so as to be perpendicularly incident on each surface of the semiconductor wafer, an image of the edge can be taken.

  In addition, by using one imaging head and rotating the stage supporting the wafer by 90 °, images of the three opposite surfaces 10b, 10e, and 10c can be simultaneously captured. As a result, the wafer edge having an azimuth angle of 180 ° can be imaged by two imaging operations, and an image of the entire edge can be displayed on the monitor simply by combining the two images. Further, by fixing the stage of the semiconductor wafer and rotating the imaging head by 90 °, an image of the wafer edge having an azimuth angle of 180 ° can be taken.

  When imaging is performed by setting the optical axis of the objective lens to an angle of 45 ° with respect to the center plane Sc of the wafer, the optical axis of the objective lens is not perpendicular to each surface forming the edge, but is relative to the optical axis. Each surface becomes an inclined surface. For this reason, the distance from the objective lens to each part of each surface is greatly different, and the focused part is in a narrow range. Therefore, in the present invention, two-dimensional scanning is performed while changing the relative distance between the linear light beam focused by displacing the objective lens and the edge of the wafer. In a confocal microscope, when a focused line-shaped light beam is positioned on the sample surface, strong reflected light is incident on the corresponding light receiving element of the linear image sensor, and the focused line of the line-shaped light beam extends in the optical axis direction from the sample surface. When it is displaced, that is, when the focusing line of the linear light beam is located on the front side or the rear side of the sample surface, only a small amount of reflected light is incident on the light receiving element of the linear image sensor. By taking advantage of the unique properties of this confocal microscope and taking images while displacing the focusing line of the line-shaped light beam in the direction of the optical axis, even if each surface of the wafer edge is tilted with respect to the optical axis, the image is taken. A focused image can be obtained over the entire edge image. That is, when imaging is performed from the first surface side, it is possible to capture an image in which the first surface 12a and the entire two surfaces 12c and 12d constituting the edge are focused. Therefore, even if a foreign object adheres to any part of the edge or a flaw exists, all of the foreign substance, the flaw, and the like can be clearly imaged and displayed on the monitor.

Referring to FIG. 1, the output signal from the linear image sensor 13 is amplified by an amplifier 14 and supplied to a signal processing circuit 15. Then, various signal processing is performed in the signal processing circuit to create a video output, which is supplied to the image display device 16, and an image of the wafer edge is displayed on the image display device. The signal processing circuit can perform the following processing as an example.
First, in the present invention, the edge image of the wafer is taken from a plurality of directions, the images taken from the respective angular directions are stored in the frame memories, and the images stored in the respective frame memories are synthesized by the image synthesis means. Then, it is supplied to the image display device 16 as a video output. As described above, when imaging is performed by setting the optical axis of the objective lens at an angle of 45 ° with respect to the center plane of the wafer, two images captured from the two sides by the two imaging heads are combined to generate a video signal. To the image display device. By this image composition processing, an image of the entire edge of the wafer including the element formation surface and the back surface can be simultaneously displayed on the image display device.

  Next, when capturing a two-dimensional image while changing the relative distance between the objective lens and the wafer edge, position information for generating a maximum luminance value and a maximum luminance value for each pixel of the two-dimensional image at the wafer edge is obtained. Store in memory. Then, by supplying the maximum luminance value and the position information to the image display device and using the position information as the height information in the depth direction, the image of the wafer edge can be displayed three-dimensionally. This maximum luminance value is updated when each output from the linear image sensor that is sequentially input is compared with the data stored in the frame memory and the input value is greater than the value stored in the frame memory. Can be obtained more easily. As a result, it is possible to clearly grasp the appearance shape of an image portion that has been displayed only with singular points that differ from the surroundings in the conventional microscope, for example, the displayed specific image portion is at the edge of the wafer. It is possible to clearly determine whether the foreign matter is attached or a scratch formed on the surface of the edge. In addition, since foreign matter and scratches can be displayed three-dimensionally, the size and thickness of the foreign matter can be determined from the display image. Furthermore, even if the foreign matter is an optically transparent material, when the scanning spot is located on the surface of the transparent foreign matter, reflected light is generated by the reflection action on the surface of the transparent foreign matter and is incident on the linear image sensor. Even if it is a foreign material of a transparent material, the surface shape can be imaged. Therefore, based on these determination results, useful information regarding the quality of the polishing process performed after the end of each process and the time required for the polishing process can be obtained, and as a result, it is useful for quantitative analysis and qualitative analysis of the manufacturing process. Image information can be provided.

  Further, the cross-sectional shape of the wafer edge can be obtained by obtaining the positional information for generating the maximum luminance by displacing the objective lens in the optical axis direction using the vibrating mirror 6 as a stationary mirror. That is, in the confocal microscope, when the line-shaped light beam is irradiated while displacing the objective lens, the maximum luminance value is output from the light receiving element of the linear image sensor when the line-shaped light beam is positioned on the wafer surface. Therefore, by plotting the position information for generating the maximum luminance value of the synthesized one-dimensional image on the image display device, the cross-sectional shape of the wafer edge can be displayed. When this cross-sectional shape measurement is used together with the display of a two-dimensional image, more useful information can be obtained. For example, when adhesion of foreign matter is observed in a two-dimensional image displayed on the image display device, the cross-sectional shape and thickness of the foreign matter can be quantitatively obtained by obtaining the cross-sectional shape of the portion. Of course, it is also possible to obtain a cross-sectional shape by reading data corresponding to one line of the frame memory in which the maximum luminance value is stored in a state where the vibrating mirror 6 is driven without being fixed.

  FIG. 3 is a diagram showing a second embodiment of the imaging system according to the present invention. In this example, a color imaging head is used, and a combination of a laser light source and a micromirror device in which a plurality of micromirror elements are arranged in a two-dimensional array is used as a light source device. A light beam is generated. The color of the polished surface of the semiconductor wafer varies, and by obtaining color information, more useful information about the edge of the semiconductor wafer can be obtained. In FIG. 3, only one imaging head will be described, and description of the other imaging heads will be omitted.

  In this example, all the optical elements are arranged on the same plane, and the complexity of adjusting the optical system is eliminated. As the R, G, and B light sources, a laser light source 31 that generates a red light beam, a laser light source 32 that generates a green light beam, and a laser light source 33 that generates a blue light beam are used. These three laser light sources are constituted by semiconductor lasers, and the optical axes of the emitted laser beams are set so as to be located on the same plane. The wavelengths of the red laser light, the green laser light, and the blue laser light are, for example, 660 nm, 530 nm, and 440 nm. Expander optical systems 34 to 36 are arranged on the front surfaces of the laser light sources 1 to 3, respectively, and converted into expanded parallel light beams. The red laser beam emitted from the first laser light source 31 is converted into an expanded parallel light beam by the expander optical system 34, and the first dichroic mirror 37 that transmits red light and reflects green light, and red and red The light passes through the second dichroic mirror 38 that transmits green light and reflects blue light, and enters the first polarizing beam splitter 40 through the first cylindrical lens 39. The green laser beam emitted from the second laser light source 2 is made into an expanded parallel light beam by the expander optical system 35, reflected by the first dichroic mirror 37, transmitted through the second dichroic mirror 38, and the first Then, the light enters the first polarizing beam splitter 40 through the cylindrical lens 39. Further, the blue laser beam emitted from the third laser light source 33 is reflected by the second dichroic mirror 38 through the expander optical system 36, passes through the first cylindrical lens 39, and is then supplied to the first polarizing beam splitter 40. Incident. Accordingly, the first and second dichroic mirrors 37 and 38 constitute a beam combining optical system that combines the R, G, and B color beams. The first cylindrical lens 39 converges the incident light beam only in the second direction (a direction orthogonal to a beam divergence direction of a line-shaped light beam generator 42 described later, in this example, a direction orthogonal to the paper surface). It has a lens action.

  The R, G, and B laser beams pass through the first polarizing beam splitter 40, pass through the λ / 4 wavelength plate 41, and converge vertically on the light incident surface of the line-shaped light beam generator 42 according to the present invention. Incident. This line-shaped light beam generator is arranged in a two-dimensional matrix, and is composed of, for example, a micromirror device having a plurality of micromirror elements having a rectangular aluminum reflecting surface of 14 μm × 14 μm on the light incident surface. As will be described later, since the mirror surface of each micromirror element is reciprocally rotated or reciprocated at high speed by a drive pulse supplied from a drive circuit, the incident laser beam is vibrated at high speed in the first direction. . Therefore, when viewed as the entire laser beam, the light is emitted from the micromirror device 42 as a light beam that diverges in the first direction (the direction extending in the drawing). Further, since the mirror surface of each micromirror element of the micromirror device is rotated or tilted in a random state, a minute beam portion incident on each micromirror element of the incident laser beam is reflected in a random state. . As a result, the light beam emitted from the micromirror device has a random phase relationship when viewed as a whole beam, and the coherence is no longer maintained and is converted into a divergent non-coherent light beam. As a result, the occurrence of glare or the like can be prevented, and a clear sample image can be taken.

  The non-coherent divergent light beam emitted from the line-shaped light beam generator 42 passes through the λ / 4 wavelength plate 41, is reflected by the polarization plane of the first polarization beam splitter 40, and enters the convergent spherical lens 43. Then, it is converted into a parallel light beam expanded in the first direction by the convergent spherical lens. The parallel light beam is converged in the second direction by the second cylindrical lens 44, and enters the second polarization beam splitter 46 through the imaging lens 45. Therefore, at the image forming position of the second cylindrical lens 44, a parallel line-shaped light beam that is enlarged in the first direction and converged in the second direction orthogonal to the first direction is formed.

  The thin line-shaped light beam incident on the second polarization beam splitter 46 enters the vibrating mirror 48 via the relay lens 47. The oscillating mirror 48 deflects the incident line-shaped light beam in a second direction orthogonal to the extending direction thereof, for example, at a television rate sub-scanning frequency under the control of the drive circuit 49. The light beam deflected by the vibration mirror 48 enters the objective lens 53 through the relay lenses 50 and 51 and the λ / 4 wavelength plate 52. The objective lens focuses the incident linear light beam, places it on the stage, and projects it onto the edge of the semiconductor wafer 54 extending in the direction perpendicular to the paper surface. Therefore, the edge 54 of the semiconductor wafer is scanned one-dimensionally by the line-shaped light beam focused in the second direction.

  The reflected beam reflected by the edge region of the semiconductor wafer 54 is collected by the objective lens 53 and enters the vibrating mirror 48 again through the λ / 4 wavelength plate 52 and the relay lenses 51 and 50. The reflected beam from the sample is descanned by the vibrating mirror 48 and enters the second polarizing beam splitter 46 via the relay lens 47. Since the reflected beam from this sample passes through the λ / 4 wavelength plate 52 twice, it is separated from the illumination beam that passes through the second polarizing beam splitter 46 and travels from the light source to the sample, and enters the light receiving device 56. . The light receiving device 56 receives the reflected beam from the sample and generates R, G, B video signals. There are various methods for generating R, G, and B video signals, the specific contents of which will be described later. The R, G, and B video signals generated from the light receiving device 56 are supplied to the signal processing circuit 57, and the R, G, and B video signals are combined to output a color video signal.

  Next, a light receiving device that generates R, G, and B video signals will be described. FIG. 4 shows a first embodiment of the light receiving device. In this example, the color separation optical system having the first and second dichroic mirrors 60 and 61 is used to separate the reflected beam from the sample into R, G, and B color lights, and the respective color lights are lined up. A video signal is generated by being incident on the image sensor. That is, the reflected beam from the sample is incident on the first dichroic mirror 60 that transmits red and green light and reflects blue light, and the blue light is incident on the first linear image sensor 62. Since the incident light is descanned by the vibrating mirror 48, the incident light is kept stationary on the first linear image sensor 62. The red and green light is incident on the second dichroic mirror 61 that reflects the green light and transmits the red light, the green light is incident on the second linear image sensor 63, and the red light is the first light. 2 passes through the dichroic mirror 2 and enters the third linear image sensor 64. The first to third linear image sensors have a plurality of light receiving elements arranged along a direction corresponding to the first direction. The electric charge accumulated in each light receiving element is read out at a television rate, for example, by a readout signal from a linear image sensor readout circuit 66 controlled under the control signal supplied from the controller 65, and R, G, B Video signals are generated respectively. These R, G, and B video signals are amplified by an amplifier and supplied to a signal processing circuit 57, where they are combined and a color video signal is output. In this way, a line confocal optical system is constructed by scanning the sample surface with a focused line-shaped light beam and allowing the reflected beam from the sample to enter the linear image sensor in a focused state, thereby forming a high-resolution sample image. Can be output.

  A second embodiment of the light receiving device is shown in FIG. In the second embodiment, R, G, and B video signals are generated using a single linear image sensor. As a linear image sensor, as shown in FIG. 5A, R, G, B color filter elements are sequentially arranged on the front surface of the light receiving element, and R, G, B light is selectively received. A linear image sensor in which light receiving elements for G and B are sequentially arranged in a line along a direction corresponding to the first direction is used. When this linear image sensor is used, R, G, and B video signals can be output by separating and outputting the charges accumulated in the R, G, and B light receiving elements. A color image can be output by combining the video outputs of G and B in the signal processing circuit 57.

  As a third embodiment, as shown in FIG. 5B, three light receiving element arrays are provided in a second direction orthogonal to the first direction that is the arrangement direction of the light receiving elements of the linear image sensor. R, G, and B reflected beams from the sample are respectively incident on the light receiving element array. In this example, the optical axes of the R, G, and B laser light sources 1 to 3 are tilted by a minute angle in the second direction with respect to the basic optical axis of the microscope, and the R, G, and B illumination beams are converted into semiconductors. The light is incident on the same position on the wafer. In the light receiving device that receives the reflected beam from the sample, the three light receiving element arrays are arranged slightly shifted in the second direction. Then, R, G, and B reflected beams from the sample are respectively incident on the respective light receiving element arrays, and R, G, and B video signals output from the respective light receiving element arrays are combined in the signal processing circuit 57 to obtain a color. An image can be taken. In this case, it is also possible to arrange three linear image sensors in a direction orthogonal to the arrangement direction of the light receiving elements, and make R, G, B reflected beams from the sample enter each linear image sensor. is there.

  Furthermore, as a fourth embodiment of the light receiving device, an example in which a color image is picked up by driving R, G, B laser light sources by a time division method will be described. In this example, R, G, and B laser light sources are sequentially driven by a time-division drive system, and R, G, and B reflected beams that are sequentially reflected by the sample are sequentially received by a single linear image sensor. G and B video signals are output. FIG. 6 shows the emission waveforms of the first, third, and third light sources of R, G, and B and the video output waveform read from the linear image sensor. As shown in FIG. 6, under the control of a light source driving circuit (not shown), only the R light source 1 is caused to emit light, the other two light sources are stopped, and red is emitted during a predetermined light emission period. The sample is irradiated with only the laser beam. Next, the red laser light source 1 is stopped, and the light source 2 is driven to irradiate the sample with only the green illumination beam. The charge accumulated in the linear image sensor 56 during the irradiation period of the green illumination beam is read out to form a red video output. Next, only the blue light source is driven to irradiate the sample with a blue laser beam, and the charges accumulated from the linear image sensor during this light emission period are read out to form a green video output. In this way, the luminance information of R, G, B is sequentially output and synthesized in the signal processing circuit 57, whereby a color image of the sample can be formed. By using this time division method, only one linear image sensor is required, and an advantage that a color separation optical system is not required is achieved.

  Next, an example using a laser light source that generates white light as a laser light source will be described. In the above-described embodiment, three laser light sources that respectively generate R, G, and B color lights are used as laser light sources. However, a color laser microscope is configured using a single laser light source that emits a white laser beam. It is also possible to do. In this embodiment, a laser light source that generates white laser light is used, and a sample is scanned with a white line light beam via a line light beam generator and a beam deflector. The white beam reflected by the sample surface enters the light receiving device again via the beam deflecting device and the second beam splitter. In the light receiving device, as shown in FIG. 4, the reflected beam from the sample is separated into R, G, and B components by a color separation optical system, respectively, and incident on a linear image sensor, and R, G, and B videos are obtained. Output can be generated. Alternatively, a single linear image sensor shown in FIG. 5A, that is, a linear image sensor in which light receiving elements that selectively receive R, G, and B component lights are sequentially arranged in the first direction. Can be used to generate R, G, B video outputs. Thus, by using a laser light source that generates white laser light as a light source, an advantage that a color video signal can be formed only by using a single laser is achieved.

The present invention is not limited to the above-described embodiments, and various modifications and changes can be made. For example, in the above-described embodiment, the edge of the semiconductor wafer is taken as an example of the sample to be observed, but the present invention can also be applied to capturing edge images of various disk-like objects.
The signal processing in the signal processing circuit is an example, and a desired image can be displayed on the monitor using various information obtained by three-dimensional scanning.
Furthermore, in the above-described embodiment, the example in which the edge of the semiconductor wafer is imaged using two imaging heads has been described, but it is also possible to image using three imaging heads.

It is a diagram showing an example of an imaging system according to the present invention. It is a diagram which shows the relationship between a wafer edge and the optical axis of an objective lens. It is a diagram showing a second embodiment of the imaging head according to the present invention. FIG. 2 is a diagram showing a first embodiment of a light receiving device that generates R, G, and B video signals. It is a diagram which shows the 2nd and 3rd Example of a light-receiving device. FIG. 6 is a waveform diagram of an embodiment in which three laser light sources of R, G, and B are driven in a time-division drive system to generate R, G, and B video outputs from a single linear image sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mercury lamp 2 Optical fiber 3 Slit 4 Beam splitter 5 Imaging lens 6 Vibration mirror 7, 8 Relay lens 9 Objective lens 10 Semiconductor wafer 11 Step motor 12 Linear image sensor 13 Amplifier 14 Signal processing circuit 15 Image display apparatus

Claims (7)

An imaging system for imaging an edge region of a semiconductor wafer having a first surface that is an element forming surface parallel to each other, a second surface that is a back surface, and an edge located between the two surfaces. ,
A light source device that generates a line-shaped light beam, a beam deflecting device that deflects the line-shaped light beam generated from the light source device in a direction orthogonal to the extending direction, and a line-shaped light beam emitted from the beam deflecting device An objective lens that projects toward the edge of the semiconductor wafer as a converging line-shaped light beam, an objective lens moving mechanism that moves the objective lens in the direction of the optical axis thereof, and an extension direction of the line-shaped light beam At least two imaging heads, including first and second imaging heads, each having a plurality of light receiving elements arranged along a direction and having a linear image sensor that receives reflected light from the semiconductor wafer; ,
A signal processing circuit for receiving an output signal from a linear image sensor of the imaging head and forming a video signal;
The imaging head is disposed on the same plane orthogonal to a central plane parallel to the first and second surfaces of the semiconductor wafer,
A converging line-shaped light beam emitted from the objective lens of each imaging head and incident on the edge of the semiconductor wafer is set so as to extend in a plane substantially orthogonal to the central plane of the semiconductor wafer,
Images of the edge region are sequentially taken while changing the relative distance between the objective lens and the semiconductor wafer from a plurality of angular directions along the periphery of the edge of the semiconductor wafer. An imaging system characterized in that images taken from directions are combined to output a video signal representing an image of an edge region.   The objective lens of the first imaging head is arranged so that a part of the first surface of the semiconductor wafer is desired, and one limit light beam of the linear light beam emitted from the objective lens is substantially perpendicular to the first surface. And the objective lens of the second imaging head is arranged so that a part of the second surface of the semiconductor wafer is desired, and one limit light beam of the linear light beam emitted from the objective lens The imaging system according to claim 2, wherein the imaging system is arranged so as to be substantially perpendicularly incident on the second surface.   3. The imaging system according to claim 1, wherein the light source device includes a shared mercury lamp or xenon lamp, and converts light emitted from the mercury lamp or xenon lamp into a line-shaped light beam by an optical fiber. An imaging system that emits light as a line-shaped light beam through a slit having a cylindrical opening.   3. The imaging system according to claim 1, wherein the light source device includes a combination of a laser light source and a micromirror device having a plurality of micromirrors arranged in a two-dimensional matrix, and the line from the micromirror device. Imaging system characterized by emitting a light beam   5. The imaging system according to claim 1, wherein the signal processing circuit outputs a cross-sectional shape of an edge region of the semiconductor wafer as a video signal. 6. An imaging system for imaging an edge region of a semiconductor wafer having a first surface that is an element forming surface parallel to each other, a second surface that is a back surface, and an edge located between the two surfaces. ,
A light source device that generates a line-shaped light beam, a beam deflecting device that deflects the line-shaped light beam generated from the light source device in a direction orthogonal to the extending direction, and a line-shaped light beam emitted from the beam deflecting device An objective lens that projects toward the edge of the semiconductor wafer as a converging line-shaped light beam, an objective lens moving mechanism that moves the objective lens in the direction of the optical axis thereof, and an extension direction of the line-shaped light beam An imaging head having a plurality of light receiving elements arranged along a direction and a linear image sensor that receives reflected light from the semiconductor wafer;
A signal processing circuit that receives an output signal from a linear image sensor of the imaging head and forms a video signal; and
A rotation drive mechanism for rotating the imaging head and the edge of the semiconductor wafer relative to each other is provided, and the semiconductor wafer or the imaging head is rotated relative to each other so that the objective lens and the semiconductor wafer can be rotated from a plurality of angular directions. An image pickup system that captures an image of an edge while changing the relative distance of the image and outputs a video signal by synthesizing images picked up from a plurality of angular directions in the signal processing circuit. 7. The imaging system according to claim 1, wherein the imaging head includes three light sources of R, G, and B, and R, G, and B light beams generated from these light sources in three primary colors. An imaging system characterized in that an image of an edge region of a semiconductor wafer is output as a color video signal.