JP5233643B2 - Shape measuring device - Google Patents

Description

  The present invention relates to a shape measuring apparatus that measures the shape of an object to be measured using multi-wavelength interference fringes, and more specifically, obtains the optical path length difference between two light fluxes that cause optical interference based on the interference color, and shapes the object to be measured. The present invention relates to a shape measuring apparatus that measures

2. Description of the Related Art Conventionally, a shape measuring method using a two-beam interference objective lens is known as a shape measuring technique that can measure the shape of an object to be measured with high accuracy without contact. In Patent Document 1 showing an example of a shape measuring method using a two-beam interference objective lens, the two-wavelength interference fringes obtained by interference of two systems of multiwavelength light divided into a measurement optical path and a reference optical path There has been disclosed a shape measuring method using multi-wavelength interference fringes in which the spectrum intensity peak for each color light is shifted little by little in the vicinity of the position of the optical path length difference 0 when obtaining the optical path length difference of the system. In this conventional technique, when the interference of the two systems of multi-wavelength light is observed using a two-beam interference objective lens, the optical thicknesses of the two reference plates are made different from each other. Further, in Patent Document 1, each color intensity peak is slightly shifted from the position of the optical path length difference 0 in the spectral distribution of interference colors due to the difference in optical thickness between the two reference plates. When the optical path length difference between two light fluxes is obtained, the absolute value and positive / negative are specified.
JP 2000-337836 A

  By the way, in the shape measuring method using the two-beam interference objective lens, in order to obtain a clear interference fringe, the optical path difference between the position where the object is in focus and the measurement optical path and the reference optical path is zero. It is necessary to match the position to be. In order to satisfy this relationship, the distance between the objective lens and the two reference plates is accurately set and built. However, even if the objective lens and the two reference plates that have been precisely built in this way are used, for example, when the object to be measured is coated with a protective film, or in the measurement optical path, a light transmitting body such as glass, etc. Is inserted, the position where the object to be measured is in focus and the position where the optical path difference between the measurement optical path and the reference optical path is zero do not match, and there is a problem that the accuracy of shape measurement is reduced.

  More specifically, in Patent Document 1, when the object to be measured is coated with a protective film, a light transmitting body such as glass is inserted between the two-beam interference objective lens and the object to be measured. In this case, the optical path length of the measurement optical path is changed, and the asymmetry of the spectral distribution is caused by the optical path length change caused by the protective film or the light transmitting body due to the component caused by the difference in optical thickness between the two reference plates. Components are superimposed, and it becomes impossible to specify the absolute value and positive / negative of the optical path difference between the measurement optical path and the reference optical path.

  In this way, the object to be measured is coated with a protective film, or a light transmitting body such as glass is inserted between the two-beam interference objective lens and the object to be measured. When the matching position and the position at which the optical path difference between the measurement optical path and the reference optical path is zero do not match, according to the prior art, a two-beam interference objective lens made with a different distance dimension can be used. Incurred high costs.

  The present invention has been made in view of the above-described problems, and matches the position where the object to be measured is in focus and the position where the optical path difference between the measurement optical path and the reference optical path is zero, regardless of the observation conditions. An object of the present invention is to provide a shape measuring apparatus capable of performing

The shape measuring apparatus according to claim 1 comprises:
A light source;
An objective lens for condensing the luminous flux from the light source;
Branching means for branching the light beam emitted from the objective lens into measurement light directed to the object to be measured and reference light;
Combining means for combining and emitting the measurement light reflected from the object to be measured and the reference light;
Observation means for observing the measurement light and the reference light synthesized by the synthesis means;
Have a, and adjusting means for adjusting the optical path length of the measuring light,
Between the objective lens and the object to be measured, two half mirrors that transmit a part of the light beam and reflect the remaining light beam are arranged, and the half mirror on the side close to the object to be measured Constituting a branching means, a half mirror closer to the objective lens constituting the combining means,
The adjusting means includes at least one of the half mirrors formed by combining two wedge-shaped plate members that can be relatively displaced, and the measurement light passes through the overlapping portion of the two wedge-shaped members, The optical path length of the measurement light is adjusted by displacing at least one of the wedge-shaped members with respect to the other .

  According to the present invention, even if the object to be measured is coated with a protective film or a light transmitting body such as glass is inserted between the two-beam interference objective lens and the object to be measured, the adjusting means Since the optical path length of the measurement light can be adjusted, the position where the object to be measured is in focus can be matched with the position where the optical path difference between the measurement optical path and the reference optical path is zero, so that the combined light High quality interference fringes and the like can be observed.

Also, pre-Symbol adjusting means comprises a combination of two wedge-shaped plate material capable displaced relatively comprise at least one of the half mirror, the measuring light is adapted to pass through the overlapping portion of the two wedge-shaped members Since the optical path length of the measurement light is adjusted by displacing at least one of the wedge-shaped members with respect to the other, for example, by displacing the wedge-shaped member in the optical axis orthogonal direction, By changing the thickness of the half mirror, the optical path length of the measurement light can be arbitrarily changed.

According to a second aspect of the present invention, in the invention according to the first aspect , the shape measuring apparatus includes an actuator that drives at least one of the wedge-shaped members. However, at least one of the wedge-shaped members may be manually displaced.

According to a third aspect of the present invention, in the shape measuring apparatus according to the first aspect , the adjusting means includes a half mirror having a different plate thickness or material, and is replaced with a half mirror having a specific plate thickness or material. Therefore, the optical path length of the measurement light can be easily changed without requiring a particularly complicated mechanism. A half mirror having a specific thickness or material may be replaced manually, or a plurality of half mirrors may be mounted on a rotatable turret and mechanically replaced by rotating the turret. Also good.

The shape measuring apparatus according to a fourth aspect of the present invention is the invention according to any one of the first to third aspects, wherein the observation unit calculates an image sensor that images the combined light and a signal from the image sensor. And a device. Incident light incident on the objective lens is split into two light beams by the branching unit, one as measurement light reflected by the object to be measured, the other as reference light having a known optical path length, and the combining unit. After being synthesized, it is taken into the imaging device. Therefore, the shape of the object to be measured can be obtained by performing arithmetic processing with the arithmetic device based on the image and the interference fringes according to the signal from the imaging device.

  According to the present invention, it is possible to provide a shape measuring apparatus that can match the position where the object to be measured is focused and the position where the optical path difference between the measurement optical path and the reference optical path is zero, regardless of the observation conditions. It becomes possible.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing a shape measuring apparatus according to the present embodiment, but a lens barrel and the like are omitted. In FIG. 1, divergent light emitted from a light source 20 as inspection light passes through an illumination optical system 21, is further reflected by a beam splitter 24, and enters a two-beam interference objective lens system OBJ. The two-beam interference objective lens OBJ receives the light beam from the light source 20 and branches it into two systems of reference light and measurement light toward the object to be measured 14, and further reflects the reflected light from the object to be measured 14 to the reference light. And has a function of emitting light. The combined light emitted from the two-beam interference objective lens system OBJ passes through the beam splitter 24, is collected by the sensor lens 23, and enters the light receiving surface of the CCD sensor 22 that is a solid-state imaging device. The image data obtained by the CCD sensor 22 is output to a calculation unit 25 such as a personal computer, and the calculation unit 25 performs calculation processing to obtain the shape data of the object 14 to be measured. It can be observed with the attached monitor shown. The CCD sensor 22 and the calculation means 25 constitute an observation means. The principle of the shape measurement and the calculation based on the image data are described in detail in, for example, Japanese Patent Application Laid-Open No. 2000-337836 and will not be described below.

  FIG. 2 is a sectional view of the two-beam interference objective lens system OBJ. FIG. 3 is an enlarged view of the half mirror 12. In FIG. 2, the two-beam interference objective lens system OBJ houses an objective lens 10 and two half mirrors 11 and 12 in a cylindrical barrel 15. The first half mirror (combining means) 11 on the objective lens 10 side is a parallel flat plate orthogonal to the optical axis, and a semi-transmissive film is deposited on the lower surface. On the other hand, the second half mirror (branching means) 12 on the measured object 14 side has two wedge-shaped members 12a and 12b whose slopes face each other. However, the second half mirror 12 may be a parallel plate, and the first half mirror 11 may be constituted by two wedge-shaped members.

  In the state shown in FIG. 2, the overlapping portions of the wedge-shaped members 12 a and 12 b are parallel flat plates orthogonal to the optical axis (meaning that the upper surface and the lower surface of the overlapping portions are parallel), and the wedge-shaped members on the side closer to the objective lens 10. A semi-transmissive film is deposited on the upper surface of 12b.

  In FIG. 2, the lens barrel 15 has an opening 15a on a side surface, and an actuator 16 is disposed in the opening 15a. The actuator 16 is composed of, for example, a piezoelectric element (piezo actuator). By supplying electric power from the outside, the actuator 16 illuminates the wedge-shaped member 12b with respect to the wedge-shaped member 12a fixed to the lens barrel 15 as indicated by a dotted line in FIG. It functions to be displaced in the direction perpendicular to the axis. As the actuator 16, in addition to the piezoelectric actuator, a motor or a screw that can be manually operated may be used as a drive source.

  The function of the two-beam interference objective lens system OBJ will be described with reference to FIG. A light beam incident on the two-beam interference objective lens system OBJ from the light source 20 (FIG. 1) is converted into convergent light L by the objective lens 10, passes through the first half mirror 11, and reaches the upper surface of the second half mirror 12. Part of the light beam (referred to as reference light) L1 is reflected, reflected back to the first half mirror 11, then reflected back to the second half mirror 12, and again toward the first half mirror 11. On the other hand, the remaining light beam L <b> 2 (measurement light) L <b> 2 that has passed through the second half mirror 12 is reflected by the surface of the DUT 14, passes through the second half mirror 12 again, and travels toward the first half mirror 11. . Therefore, the reference light L1 and the measurement light L2 are combined by the first half mirror 11, and an interference fringe is generated in a portion where the optical path length is equal. The combined light passes through the objective lens 10 and interferes with two beams. After exiting from the objective lens system OBJ, the interference fringes are observed by forming an image on the light receiving surface of the CCD sensor 22. Therefore, originally, the objective lens 10 and the half mirror 11 are arranged so that the position where the surface of the object to be measured 14 is in focus and the position where the optical path length difference between the reference light L1 and the measuring light L2 is zero match. , 12 are determined.

  Here, a case is considered where the object to be measured 14 is coated with a protective film 13 having a refractive index different from that of air. In such a case, since the optical path length of the measuring light L2 changes according to the thickness of the protective film 13, the position where the surface under the film of the object to be measured 14 is in focus and the optical path length difference between the reference light L1 and the measuring light L2 The position where becomes 0 does not match.

  In such a case, according to the present embodiment, the CCD sensor 22 is configured such that the optical path difference between the two systems of the reference light L1 and the measuring light L2 becomes 0 at the position where the surface under the film of the object to be measured 14 is in focus. While observing an image based on the signal from the actuator 16, the actuator 16 can be driven to move the wedge-shaped member 12 b in the direction perpendicular to the optical axis. Thereby, as shown in FIG. 3, since the thickness of the overlapping portion of the wedge-shaped members 12a and 12b having a refractive index different from that of air changes (Δ), the distance of the measurement light L2 passing through the overlapping portion changes, Thereby, the optical path length of the measurement light L2 can be changed. Specifically, when the protective film 13 is coated on the device under test 14, the thickness of the second half mirror 12 is reduced. As is apparent from FIG. 3, when the wedge-shaped member 12b is moved in the direction perpendicular to the optical axis, the optical path length of the reference light L1 also changes. However, if one of the optical path lengths becomes longer, the other optical path length becomes shorter, so the position where the optical path difference becomes 0 is uniquely determined.

  As described above, the optical path length of the measurement light L2 is not limited to the case where the object to be measured 14 is coated with the protective film 13, but for example, between the object to be measured 14 and the two-beam interference objective lens system OBJ. In addition, there may be a case where a light transmitting body such as glass is inserted, but also in this case, the optical path length can be adjusted by moving the wedge-shaped member 12b in the direction perpendicular to the optical axis. Further, the wedge-shaped member 12a on the side close to the device under test 14 may be moved. Furthermore, the optical path difference of 0 may be realized by changing the optical path length of the reference light after fixing the optical path length of the measuring light.

  As described above, in order to adjust the optical path length, instead of using a half mirror made of two wedge-shaped members as described above, a plurality of types of half mirrors having different thicknesses and refractive indexes are prepared, and the protective film of the object to be measured is prepared. Depending on the thickness, etc., select and replace an appropriate half mirror so that the optical path difference between the two systems of the reference light and measurement light becomes 0 at the position where the surface under the film of the object to be measured is in focus. It is possible to use it. As described above, the structure capable of replacing the half mirror cannot be continuously adjusted, but an actuator or the like for moving the wedge-shaped member is not required, and thus the apparatus can be reduced in size.

It is the schematic which shows the shape measuring apparatus of this Embodiment. It is sectional drawing of the two-beam interference objective lens system OBJ. FIG. 3 is an enlarged view of the half mirror 12.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Objective lens 11 ... 1st half mirror 12 ... 2nd half mirror 12a ... Wedge-like member 12b ... Wedge-like member 13 ... Measured object protection film 14 ... Measured object 15 ... Lens barrel 16 ... Actuator 20 ... Inspection light source 21 ... Illumination optical system 22 ... CCD sensor 23 ... Condensing lens 24 ... Beam splitter 25 ... Calculation unit

Claims (4)

A light source;
An objective lens for condensing the luminous flux from the light source;
Branching means for branching the light beam emitted from the objective lens into measurement light directed to the object to be measured and reference light;
Combining means for combining and emitting the measurement light reflected from the object to be measured and the reference light;
Observation means for observing the measurement light and the reference light synthesized by the synthesis means;
Have a, and adjusting means for adjusting the optical path length of the measuring light,
Between the objective lens and the object to be measured, two half mirrors that transmit a part of the light beam and reflect the remaining light beam are arranged, and the half mirror on the side close to the object to be measured Constituting a branching means, a half mirror closer to the objective lens constituting the combining means,
The adjusting means includes at least one of the half mirrors formed by combining two wedge-shaped plate members that can be relatively displaced, and the measurement light passes through the overlapping portion of the two wedge-shaped members, A shape measuring apparatus for adjusting an optical path length of the measuring light by displacing at least one of the wedge-shaped members with respect to the other . The shape measuring apparatus according to claim 1 , further comprising an actuator that drives at least one of the wedge-shaped members. Said adjusting means includes a different half mirror having the plate thickness or material, by exchanging a half mirror having a certain thickness or material, to claim 1, characterized by adjusting the optical path length of the measurement light The shape measuring apparatus described. It said observation means includes: an imaging device for imaging the combined light, the shape measuring apparatus according to any one of claims 1-3, characterized in that with a calculating device for calculating a signal from the imaging device.

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