JP4639808B2 - Measuring apparatus and adjustment method thereof - Google Patents

Description

  The present invention relates to an alignment optical system for various patterns formed on, for example, a wafer, a measurement apparatus used for a position measurement optical system, and an adjustment method thereof.

  For example, as disclosed in Patent Document 1, a position measuring optical system for various patterns formed on a wafer is conventionally provided with an illumination optical system, an imaging optical system, and an image processing unit as shown in FIG. Consists of. FIG. 4 is a schematic diagram of a position measuring optical system for various patterns according to the prior art.

  In the illumination optical system, the filament image of the light source (halogen lamp) 1 is projected onto the fiber entrance end face of the optical fiber 4 by the first and second relay lenses 2 and 3 for the light source. The illumination light is projected onto the illumination aperture stop 7 through the optical fiber 4 by the illumination first and second relay lenses 5 and 6. An optical diffusion plate (lemon skin) 20 is disposed between the emission end face of the optical fiber 4 and the first relay lens 6 for illumination.

  Thereafter, the light passes through the third relay lens 8 for illumination, the field stop 9 and the fourth relay lens 10 for illumination, is reflected by the incident prism 11 in the direction of 90 degrees, and passes through the imaging stop 12 and the first objective lens 13. The wafer 14 is illuminated. The wafer 14 is placed on the wafer holder 15 on the moving stage 16, and a measurement target pattern is formed on the wafer 14.

  In the imaging optical system, the light reflected by the measurement target pattern on the wafer 14 passes again through the first objective lens 13, the imaging aperture stop 12, the incident prism 11, the reflection mirror 21, and the second. After passing through the objective lens 17, an image is formed on the imaging surface of the CCD camera 18.

  In the image processing means, the measurement target pattern image projected on the imaging surface of the CCD camera 18 is converted into a digital signal, and then the image is sent to the image processing unit 19 where the measurement target pattern is placed on the position meter side. Is called.

  By the way, in a measuring apparatus using an optical microscope as described above, optical system errors (illumination telecentricity, imaging telecentricity, coma aberration) greatly affect measurement accuracy. Therefore, various adjustment methods have been devised so far to improve accuracy.

  For example, there is a method of using an adjustment pattern having a step of 1/8 of the illumination wavelength that is sensitive to an optical system error. If this reference pattern is used, the optical system error can be estimated from the change in the symmetry of the optical image with respect to the focus offset amount, so the adjustment mechanism (illumination aperture stop 7, imaging aperture stop 12, and second objective lens 17) is optimal. Can be adjusted to any position.

  However, the reflection glass parts (the epi-prism 11 and the reflection mirror 21) included in the optical system have not been regarded as a problem so far because the influence on the overall accuracy is small.

Conventionally, with respect to these reflective glass parts and the like, sufficient effects have been obtained by managing the precision of individual parts such as surface precision and dimensional precision.
JP 2001-317913 A

  However, in recent years, with the higher integration of semiconductor devices and the increase in storage capacity, the accuracy required for measuring devices has become extremely severe, and the accuracy of reflective glass components and the like cannot be ignored.

  Therefore, the accuracy required for reflective glass parts and the like is becoming higher and the manufacturing limit is approaching.

  For example, with respect to the epi-illumination prism 11, all factors such as reflection surface accuracy, glass surface accuracy, refractive index error, refractive index unevenness, laminated glass characteristic difference, adhesive property (adhesive layer thickness), and the like are measured accuracy. Affect. Regarding the reflection mirror 21, the accuracy of the reflection surface similarly affects the measurement accuracy.

  Also, when these reflective glass parts are arranged close to the optical image plane, they directly affect the quality of the optical image (distortion of the optical image), and when placed near the pupil plane, the pupil plane Affects the quality of the image and indirectly affects the quality of the optical image (distortion of the optical image).

  For example, FIG. 3A is a schematic diagram showing the state of an optical image, and an optical image formed on the imaging surface of the CCD camera 18 when a sample (ideal lattice object) is placed at the position of the wafer 14. It is. It is observed that the optical image of the sample is distorted due to the influence of surface accuracy of the reflective glass parts and the like.

  The present invention has been made in view of the circumstances as described above. For example, the influence of accuracy such as reflective glass parts that cannot be adjusted by the current method is eliminated as much as possible, and high integration and increase in storage capacity are achieved. An object of the present invention is to provide a highly accurate measuring apparatus and an adjustment method thereof that can suppress “distortion of an optical image” formed on the imaging surface of a CCD camera as much as possible.

In order to achieve the above object, a measuring apparatus according to claim 1 of the present invention includes an illumination optical system having a light source for supplying illumination light to a sample;
An imaging optical system for observing an optical image of the sample;
An image processing unit that captures the optical image with an imaging unit and performs image processing;
Analyzing means for calculating the distortion amount of the optical image of the sample imaged on the imaging surface of the imaging means;
Based on the analysis result of the analysis means, the position of the distortion factor optical component that has a substantially flat entrance and exit surface and causes distortion of the optical image on the optical axis of the illumination optical system or the imaging optical system. characterized by comprising a position adjusting mechanism for adjusting the no position change of the optical image, and moving in the direction parallel to the entering exit surface so that the reflected point is shifted before entry exit surface.

In the measurement apparatus according to claim 2 of the present invention, the distortion factor optical component is at least one of an epi-prism, a reflection mirror, an indicator plate, color correction glass, and a protective surface of the imaging unit. It is characterized by.

An adjustment method for a measuring apparatus according to claim 3 of the present invention includes an illumination optical system having a light source for supplying illumination light to a sample;
An imaging optical system for observing an optical image of the sample;
An image processing unit that captures the optical image with an imaging unit and performs image processing;
An analysis step of calculating a distortion amount of the optical image of the sample imaged on the imaging surface of the imaging means;
Based on the analysis result of the analysis step, the position of the distortion factor optical component that has a substantially flat entrance and exit surface and causes distortion of the optical image on the optical axis of the illumination optical system or the imaging optical system. characterized by comprising a position adjustment step of adjusting the no position change of the optical image, and moving in the direction parallel to the entering exit surface so that the reflected point is shifted before entry exit surface.

According to a fourth aspect of the present invention, there is provided the measuring apparatus adjustment method, wherein the distortion factor optical component is at least one of an epi-illumination prism, a reflecting mirror, an index plate, color correction glass, and a protective surface of the imaging means. It is characterized by being.

  According to the present invention, the sample is placed at the position to be inspected on the object surface, and the amount of distortion of the optical image of the sample imaged on the imaging surface of the imaging means is calculated and analyzed. Reflective glass that cannot be adjusted by the current method, for example, because it is configured to adjust the position of the distortion factor optical component that causes distortion of the optical image on the optical axis of the illumination optical system or the imaging optical system. A high-precision measuring device that eliminates the effects of surface accuracy of parts, etc. as much as possible, and minimizes the distortion of the optical image that forms an image on the imaging surface of the imaging means with high integration and increased storage capacity. Can be provided.

  Hereinafter, a measuring device and an adjustment method thereof according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram of a position measurement optical system for various patterns according to an embodiment of the present invention.

  2A is a front view of the position adjusting mechanism, FIG. 2B is a side view thereof, and FIG. 2C is a plan view thereof.

  FIG. 3A is a schematic diagram showing the state of the optical image before the “distortion of optical image” adjustment, and FIG. 3B shows the state of the optical image after the adjustment of “distortion of optical image”. It is a schematic diagram.

  As shown in FIG. 1, for example, a position measuring optical system for various patterns formed on a wafer includes an illumination optical system, an imaging optical system, and image processing means.

  In the illumination optical system, the filament image of the light source (halogen lamp) 1 is projected onto the fiber entrance end face of the optical fiber 4 by the first and second relay lenses 2 and 3 for the light source. The illumination light is projected onto the illumination aperture stop 7 through the optical fiber 4 by the illumination first and second relay lenses 5 and 6. An optical diffusion plate (lemon skin) 20 is disposed between the emission end face of the optical fiber 4 and the first relay lens 6 for illumination.

  Thereafter, the light passes through the third relay lens 8 for illumination, the field stop 9 and the fourth relay lens 10 for illumination, is reflected by the incident prism 11 in the direction of 90 degrees, and passes through the imaging stop 12 and the first objective lens 13. The wafer 14 is illuminated. The wafer 14 is placed on the wafer holder 15 on the moving stage 16, and a measurement target pattern is formed on the wafer 14.

  In the imaging optical system, the light reflected by the measurement target pattern on the wafer 14 passes again through the first objective lens 13, the imaging aperture stop 12, the incident prism 11, the reflection mirror 21, and the second. After passing through the objective lens 17, an image is formed on the imaging surface of the CCD camera 18.

  In the image processing means, the measurement target pattern image projected on the imaging surface of the CCD camera 18 is converted into a digital signal, and then the image is sent to the image processing unit 19 where the measurement target pattern is placed on the position meter side. Is called.

  In the present embodiment, a position adjustment mechanism 30 that adjusts the position of the epi-illumination prism 11 and a position adjustment mechanism 31 that adjusts the position of the reflection mirror 21 are provided.

  2 illustrates the position adjusting mechanism 31 for the reflecting mirror 21, but the position adjusting mechanism 30 for the epi-illuminating prism 11 can be configured in the same manner. Further, the position adjustment direction of the reflection mirror 21 is a direction along the reflection surface and is one direction, but may be two directions.

  As shown in FIG. 2, the basic components of the position adjustment mechanism 30 are a pedestal component 51 and a moving table 52.

  That is, the moving table 52 is configured to move in one direction with respect to the pedestal component 51, and the reflecting mirror 21 is attached to the moving table 52.

  By moving the moving table 52 with the adjustment knob 55, the reflection point of the reflection mirror 21 is shifted to adjust the position. After the position of the reflection mirror 21 is adjusted, the moving table 52 is fixed by a fixing screw 53.

  Next, in the present embodiment, FIG. 3A is an optical image of the sample imaged on the imaging surface of the CCD camera 18 when the sample (ideal lattice object) is placed at the position of the wafer 14. . As shown in FIG. 3A, when distortion is observed in this optical image, the positions of the reflection glass parts (the epi-prism 11 and the reflection mirror 21) are adjusted as shown below. , “Optical image distortion” is suppressed as much as possible.

  When a sample (ideal lattice object) whose lattice shape is defined in advance is placed on the position of the wafer 14 on the moving stage 16, an optical image of this sample is formed on the imaging surface of the CCD camera 18. The image processing unit 19 calculates and analyzes the distortion amount of the optical image of the imaged sample.

  At this time, when the optical image is an optical image 41 as shown in FIG. 3A, based on the analysis result of the image processing unit 19, a reflective glass component (which causes distortion of the optical image 41) ( The positions of the epi-illumination prism 11 and the reflection mirror 21) are adjusted. As a result, an optical image 42 with “less distortion” as shown in FIG. 3B is searched for, and in this state, the position of the reflective glass component (the epi-prism 11 and the reflective mirror 21) is fixed. Thereby, “distortion of the optical image” can be suppressed as much as possible.

  Specifically, an optical image of the sample imaged on the imaging surface of the CCD camera 18 is calculated and analyzed by the image processing unit 19 and the “distortion of the optical image” is quantified. It is determined whether or not the numerical value is within an allowable value. This quantification and determination can be performed using a predetermined evaluation function or a flowchart.

  If the determination is NG (when the distortion of the optical image is large), the position of the reflective glass component (the epi-prism 11 and the reflective mirror 21) is adjusted.

  In this adjustment, the position adjustment direction is the direction of the reflection surface of the reflective glass component (the epi-prism 11 and the reflection mirror 21) so that the optical image position does not shift. This is because the state of the optical image depends strictly on the position of the reflecting surface.

  In this way, the operation of searching for the optical image 42 as shown in FIG. 3B is repeated a plurality of times while considering the analysis result of the image processing unit 19, and the position of the moving table 52 is repeatedly adjusted.

  As a result, when the determination is OK (when the distortion of the optical image is within the allowable value range), the position of the moving table 52 is fixed. Thereby, “distortion of the optical image” can be suppressed as much as possible.

  As described above, according to the present embodiment, the distortion amount of the optical image of the sample imaged on the imaging surface of the CCD camera 18 is calculated and analyzed, and based on the analysis result, the illumination optical system or the imaging optical system is calculated. Since it is configured to adjust the position of the reflective glass parts (the incident prism 11 and the reflective mirror 21) that cause distortion of the optical image on the optical axis, the reflective glass parts that cannot be adjusted by the current system Provides a highly accurate measurement device that minimizes the “distortion of the optical image” that forms an image on the imaging surface of the CCD camera 18 with high integration and increased storage capacity. can do.

(Modification)
In the above-described embodiment, the position of the reflective glass parts (the epi-prism 11 and the reflective mirror 21) is adjusted, the influence of the surface accuracy is eliminated, and the “image of the optical image” is formed on the imaging surface of the CCD camera 18. Although “distortion” is suppressed, as shown below, the position of another distortion factor optical component that causes distortion of the optical image may be adjusted. Also in this case, if the position of the distortion factor optical component is adjusted, the influence can be eliminated as much as possible, and “distortion of the optical image” can be suppressed.

  The distortion factor optical component that causes the distortion of the optical image is limited to an optical component having a flat entrance / exit surface. This is because when the position of a lens or the like whose curved surface is curved is adjusted, the optical axis of the illumination optical system or the imaging optical system is shifted, and aberrations may appear.

  For example, when an index plate (glass plate) is disposed at the position of the primary image and a CCD camera is disposed on the optical downstream side of the index plate via a relay optical lens system, on the imaging surface of the CCD camera, An indicator plate is projected together with a conjugate secondary optical image of the sample (ideal lattice object). At this time, if the position of the index plate is adjusted, the influence can be eliminated as much as possible to suppress “distortion of the optical image”.

  Further, when a color correction lens is disposed between the second objective lens 17 and the CCD camera 18 on the optical axis of the illumination optical system or the imaging optical system, for example, the inclination angle of the color correction lens is adjusted. Thus, it is possible to correct the chromatic aberration of the lens and the like, and to eliminate the influence as much as possible and to suppress “distortion of the optical image”.

  Furthermore, since the distortion of the protective surface (protective glass) of the CCD camera may affect the “distortion of the optical image”, the CCD camera is moved along the protective surface (protective glass). It is possible to suppress the “distortion of the optical image” by eliminating the influence as much as possible.

  Note that the present invention is not limited to the above-described embodiment, and is intended for “distortion of an optical image” by an optical component made of flat glass. There are various modifications.

It is a schematic diagram of the position measurement optical system of various patterns according to the embodiment of the present invention. (A) is a front view of the position adjusting mechanism, (b) is a side view thereof, and (c) is a plan view thereof. (A) is a schematic diagram showing the state of the optical image before the “optical image distortion” adjustment, and (b) is a schematic diagram showing the state of the optical image after the “optical image distortion” adjustment. It is. It is related and is a schematic diagram of the position measurement optical system of various patterns.

Explanation of symbols

1 Light source (halogen lamp)
DESCRIPTION OF SYMBOLS 2,3 1st and 2nd relay lens for light sources 4 Optical fiber 5,6 1st and 2nd relay lens for illumination 7 Illumination aperture stop 8 3rd relay lens for illumination 9 Field stop 10 4th relay lens 11 for illumination Incident light Prism 12 Imaging diaphragm 13 First objective lens 14 Wafer 15 Wafer holder 16 Moving stage 17 Second objective lens 18 CCD camera (imaging means)
19 Image processor 20 Optical diffuser (lemon skin)
21 Reflection mirror 30, 31 Position adjustment mechanism 41 Optical image (before adjustment)
42 Optical image (after adjustment)
51 Pedestal 52 Moving table 53 Fixed screw 55 Adjustment knob

Claims (4)

An illumination optical system having a light source for supplying illumination light to the sample;
An imaging optical system for observing an optical image of the sample;
An image processing unit that captures the optical image with an imaging unit and performs image processing;
Analyzing means for calculating the distortion amount of the optical image of the sample imaged on the imaging surface of the imaging means;
Based on the analysis result of the analysis means, the position of the distortion factor optical component that has a substantially flat entrance and exit surface and causes distortion of the optical image on the optical axis of the illumination optical system or the imaging optical system. , measured, characterized in that it comprises a position adjusting mechanism for adjusting the no position change of the optical image, and moving in the direction parallel to the entering exit surface so that the reflected point is shifted before entry exit surface apparatus.   The measuring apparatus according to claim 1, wherein the distortion factor optical component is at least one of an epi-illumination prism, a reflection mirror, an index plate, color correction glass, and a protective surface of the imaging unit. . An illumination optical system having a light source for supplying illumination light to the sample;
An imaging optical system for observing an optical image of the sample;
An image processing unit that captures the optical image with an imaging unit and performs image processing;
An analysis step of calculating a distortion amount of the optical image of the sample imaged on the imaging surface of the imaging means;
Based on the analysis result of the analysis step, the position of the distortion factor optical component that is substantially flat on the optical axis of the illumination optical system or the imaging optical system and causes the distortion of the optical image is determined. , measured, characterized in that it comprises a position adjustment step of adjusting the no position change of the optical image, and moving in the direction parallel to the entering exit surface so that the reflected point is shifted before entry exit surface Device adjustment method.   The measuring apparatus according to claim 3, wherein the distortion factor optical component is at least one of an epi-illumination prism, a reflection mirror, an index plate, color correction glass, and a protective surface of the imaging unit. Adjustment method.

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