JPH06147866A - Optical surface profile measuring equipment - Google Patents

Abstract

PURPOSE:To provide an optical surface profile measuring equipment for optically measuring microundulation on the surface of an object in which downsizing and shortening of measuring time are realized by allowing the measurement of distance upto the surface of a sample without requiring vertical movement of the sample or the measuring equipment by taking advantage of the characteristics of a cofocal optical system. CONSTITUTION:The optical surface profile measuring equipment comprises a cylindrical lens 11 for focusing reflection light condensed through an objective lens 44 on a focal plane as an image of parallel lines, and an image sensor 12 for receiving the image light while inclining by a micro-angle against the focal plane of the cylindrical lens 11 and detecting the position of the line image from a pixel position for obtaining maximum output thus calculating the distance upto the surface of a sample.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical surface shape measuring device for optically measuring minute undulations on an object surface.

[0002]

2. Description of the Related Art A method using a confocal optical system is known as a method capable of accurately measuring minute undulations on the surface of an object.

FIG. 4 is a diagram showing a schematic configuration of a conventional optical surface profile measuring apparatus using a confocal optical system. In the figure, a conventional optical surface profile measuring apparatus has a laser light source 41, a collimator lens 42, a beam splitter 43 and an objective lens 44 arranged on one optical axis, and an optical axis orthogonal to the optical axis in the beam splitter 43. An image forming lens 45, a pinhole 46 and a light receiving element 47 are arranged on the top. Here, the light emitting end surface of the laser light source 41 coincides with the focal position of the collimator lens 42, and the laser light source 4
The light emitted from No. 1 becomes a parallel beam by the collimator lens 42. The parallel beam is further focused on the surface of the sample 40 via the beam splitter 43 and the objective lens 44. The center of the pinhole 46 coincides with the focal position of the imaging lens 45.

In such a structure, the objective lens 44
In the state where the focal point of is on the surface of the sample 40, the light emitted from the laser light source 41 is condensed at one point on the surface of the sample 40, and a part of the reflected light scattered there is captured by the aperture of the objective lens 44. The light is then incident on the beam splitter 43, where the optical path is bent and reaches the light receiving element 47 via the imaging lens 45 and the pinhole 46 (thin solid line in the figure).

On the other hand, as shown by the thin broken line in the figure, the sample 40
When the surface of the object is out of focus of the objective lens 44, a spot condensed on the surface of the sample spreads, and most of the reflected light cannot pass through the pinhole 46, is removed, and is detected by the light receiving element 47. The signal strength is significantly reduced.

FIG. 5 shows an example of the signal intensity of the light receiving element 47 depending on the distance between the objective lens 44 and the surface of the sample 40. In the figure, the horizontal axis represents the distance between the objective lens 44 and the surface of the sample 40, and the vertical axis represents the signal intensity detected by the light receiving element 47. At the position A where the signal intensity detected by the light receiving element 47 has a peak, the focal plane of the objective lens 44 is the sample 4
A point corresponding to the surface of 0 is shown.

By the way, in FIG. 4, when the surface of the sample 40 changes to the position of the broken line, the position of the objective lens 44 is moved to the position shown by the broken line to detect the peak at the position B in FIG. be able to. The same applies when the sample 40 itself is relatively moved instead of moving the position of the objective lens 44. The amount of movement of the objective lens 44 or the sample 40 at this time corresponds to the amount of change in the height of the surface of the sample 40. Therefore, by monitoring the peak of the signal intensity detected by the light receiving element 47 while moving the objective lens 44 or the sample 40 itself, the relative movement amount of the objective lens 44 or the sample 40 is determined as the change amount of the surface of the sample 40. Can be detected.

As described above, in the method using the confocal optical system, the focused state can be detected with high accuracy, and therefore the height direction with respect to the sample surface (hereinafter referred to as "vertical direction").
Can be measured with excellent resolution. Further, the sample or the optical surface shape measuring device is moved in a plane direction parallel to the sample surface (hereinafter referred to as “horizontal direction”) to scan the sample surface, thereby performing highly accurate three-dimensional shape measurement. You can

[0009]

However, in order to move the sample or the optical surface profile measuring apparatus (objective lens) in the vertical direction, conventionally, there is only a mechanical moving method, which makes the apparatus complicated and large. Was unavoidable. Further, since the scanning speed is slow, it takes a long time for measurement.

The present invention makes it possible to measure the distance to the sample surface without moving the sample or the optical surface profile measuring device in the vertical direction while making use of the characteristics of the confocal optical system. It is an object of the present invention to provide an optical surface profile measuring device that realizes shortening.

[0011]

An optical surface shape measuring apparatus according to a first aspect of the present invention is a cylindrical lens that forms reflected light condensed by an objective lens into a linear image parallel to a focal plane. And an image used to calculate the distance to the sample surface by detecting the image formation position of the linear image from the pixel position where the maximum output is received by tilting the cylindrical lens at a slight angle with respect to the focal plane. And a sensor.

An optical surface profile measuring apparatus according to a second aspect of the present invention is the optical surface profile measuring apparatus according to the first aspect, wherein the effective diameter of the collimating lens is smaller than the effective diameter of the objective lens. Is characterized by.

[0013]

By collecting the reflected light from the sample surface with the cylindrical lens, a linear image parallel to the focal plane of the cylindrical lens is formed. This linear image moves before and after the focal plane of the cylindrical lens according to the distance between the sample surface and the objective lens.

On the other hand, by arranging the image sensor at a slight angle with respect to the focal plane of the cylindrical lens, the position of the image that moves back and forth on the focal plane of the cylindrical lens according to the distance between the sample surface and the objective lens. Is
It can be grasped as a change in the pixel position where the output level shows the maximum value in the image sensor. That is, by detecting the image forming position of the cylindrical lens from the pixel position that changes one-dimensionally on the image sensor without moving the sample or the optical surface shape measuring device (objective lens) in the vertical direction, the result is obtained. The distance between the sample surface and the objective lens can be calculated from the image position.

[0015]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of the invention described in claim 1. In FIG. In the figure, a laser light source 41, a collimator lens 42, a beam splitter 43, and an objective lens 44 have the same arrangement configuration as that of the conventional optical surface shape measuring apparatus shown in FIG. The features of the present invention are that the imaging lens 45, the pinhole 46, and the light receiving element 4
In place of No. 7, in this embodiment, a cylindrical lens 11 and a linear image sensor 12 are used. The linear image sensor 12 used in the present embodiment has a plurality of light receiving elements arranged with a predetermined opening width on the line that is the focal point of the cylindrical lens 11. However, in the two-dimensional image sensor, the focal point of the cylindrical lens 11 is reduced. The light receiving element on the line corresponding to may be regarded as it.

The light emitted from the laser light source 41 becomes a parallel beam at the collimator lens 42 and is converged on the surface of the sample 40 via the beam splitter 43 and the objective lens 44. Further, the light scattered on the surface of the sample 40 is captured by the aperture of the objective lens 44 and is condensed again, and the optical path is bent by the beam splitter 43 so that the cylindrical lens 11 is formed.
Be led to.

The cylindrical lens 11 forms a linear image parallel to the focal plane, and the image is formed before and after the focal plane of the cylindrical lens 11 according to the distance between the surface of the sample 40 and the objective lens 44. To do. Here, the objective lens 4
Focal length f ₁ of 4, the focal distance f ₂ of the cylindrical lens 11, objective lens 44 and the cylindrical lens 1
If the optical axis distance of 1 is L and the distance between the surface of the sample 40 and the focus of the objective lens 44 is x, the cylindrical lens 11
The distance y between the linear image and the linear image is given by y = f ₂ ² × x / {f ₁ ² + (f ₁ + f ₂ −L) × x}, and particularly when L = f ₁ + f ₂ . Is y = f ₂ ² × x / f ₁ ² . In this way, the surface of the sample 40 and the objective lens 44
The linear image moves before and after the focal plane of the cylindrical lens 11 according to the distance x from the focal point of the.

The linear image sensor 12 receives the linear image, but by arranging the linear image sensor 12 at a slight angle θ with respect to the focal plane of the cylindrical lens 11, the linear image sensor 12 is arranged according to the image forming position. The pixel position at which the output level of is at the maximum value changes.

FIG. 2 is a diagram showing an output example corresponding to each pixel of the linear image sensor 12. In the figure, the horizontal axis represents the pixel number of the linear image sensor 12, and the vertical axis represents the output level. The maximum value of the output level is obtained at the pixel at the point C where the linear image formed by the cylindrical lens 11 intersects with the linear image sensor 12. The point C changes according to the distance x between the surface of the sample 40 and the focal point of the objective lens 44.

Therefore, by detecting the pixel C point where the output level is maximum on the linear image sensor 12, the distance between the objective lens 44 and the sample 40 is not physically changed, and the objective lens 44 and the sample 40 are not changed. Can be calculated as a function of the coordinates of point C and θ.

The linear image sensor 12 is preferably a slit-shaped one having an opening width of several tens of μm, but a CCD linear image sensor, a fiber array, a PSD (Position Sensitive Device), a diode array and others. It can be easily realized by the element. In addition to limiting the width of the opening depending on the shape of the light receiving element, the same applies to the configuration in which a mechanical slit is brought into close contact with the front surface when a two-dimensional image sensor is used.

FIG. 3 is a schematic diagram showing the configuration of an embodiment of the invention described in claim 2. In the figure, a laser light source 41,
The collimator lens 42, the beam splitter 43, and the objective lens 44 have the same arrangement configuration as that of the conventional optical surface shape measuring apparatus shown in FIG. The feature of the present invention lies in that, instead of the imaging lens 45, the pinhole 46 and the light receiving element 47, the cylindrical lens 11 is used in the present embodiment.
In addition to the configuration using the linear image sensor 12, a configuration in which the aperture 31 is inserted between the collimator lens 42 and the beam splitter 43 as means for making the effective diameter of the collimator lens 42 smaller than the effective diameter of the objective lens 44. It is in. The same applies when the collimator lens 42 having a diameter smaller than the effective diameter of the objective lens 44 is used.

The functions of the cylindrical lens 11 and the linear image sensor 12 are similar to those of the embodiment shown in FIG. Therefore, the function of the aperture 31 will be described below.

Since the effective diameter of the collimating lens 42 is limited by the aperture 31, the diameter of the parallel beam is smaller than the effective diameter of the objective lens 44. Therefore, the effective N of the objective lens 44 with respect to the light irradiated to the sample 40 is
A becomes smaller, and the light condensed by the objective lens 44 has a uniform intensity distribution. As a result, a large dynamic range can be realized in the vertical direction. Note that N
Even when an objective lens with a small A is used, the intensity distribution of the condensed light can be made uniform, but in this case, the NA for the reflected light scattered on the surface of the sample 40 is also small, and the resolution is reduced. It causes deterioration. However, as in the configuration of the present invention, by limiting only the light that illuminates the sample 40, a sufficient NA for the reflected light can be secured, and deterioration of resolution can be avoided.

[0025]

As described above, according to the present invention, the distance to the sample surface can be measured with high accuracy in a short time without performing the scanning in the vertical direction on the sample. Further, since it is not necessary to scan the sample in the vertical direction, the entire apparatus can be made compact and lightweight.

Further, the undulation of the sample surface is measured with high accuracy and at high speed by scanning the optical surface shape measuring device of the present invention in a horizontal direction with high speed and high accuracy using, for example, an AOM (acoustic optical deflector). be able to.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an embodiment of the invention described in claim 1.

FIG. 2 is a diagram showing an output example corresponding to each pixel of a linear image sensor 12.

FIG. 3 is a schematic diagram showing a configuration of an embodiment of the invention described in claim 2.

FIG. 4 is a diagram showing a schematic configuration of a conventional optical surface profile measuring apparatus using a confocal optical system.

FIG. 5 is a diagram showing an example of signal intensity of the light receiving element 47 according to the distance between the objective lens 44 and the surface of the sample 40.

[Explanation of symbols]

 11 Cylindrical lens 12 Linear image sensor 31 Aperture 40 Sample 41 Laser light source 42 Collimating lens 43 Beam splitter 44 Objective lens 45 Imaging lens 46 Pinhole 47 Light receiving element

Claims (2)

[Claims] 1. A light emitted from a laser light source is collimated by a collimator lens to be a parallel beam, which is then condensed by an objective lens to irradiate the sample surface, and reflected light scattered on the surface is captured again by an aperture of the objective lens. In an optical surface shape measuring device using a confocal optical system for calculating a distance to a sample surface using condensed reflected light, reflected light condensed by the objective lens is linearly parallel to a focal plane. And a cylindrical lens for forming an image on the image of the linear lens, and the image forming light is received by inclining the cylindrical lens at a minute angle with respect to the focal plane of the cylindrical lens, and the image forming position of the linear image is detected from the pixel position where the maximum output is obtained. And an image sensor for calculating the distance to the sample surface. 2. The optical surface profile measuring apparatus according to claim 1, wherein the effective diameter of the collimator lens is smaller than the effective diameter of the objective lens.