WO2003060425A1

WO2003060425A1 - Optical apparatus for measuring the two and three-dimensional shape of an object

Info

Publication number: WO2003060425A1
Application number: PCT/KR2003/000045
Authority: WO
Inventors: Ssang-Gun Lim; Ki-Hong Kim; Sang-Hyun Cho; Ee-Bae Choi
Original assignee: Intek Plus Co., Ltd.; Lee, Sang-Yoon
Priority date: 2002-01-15
Filing date: 2003-01-10
Publication date: 2003-07-24
Also published as: CN1615426A; KR100449175B1; CN100510613C; JP4464137B2; KR20030061644A; JP2005515415A; AU2003203202A1

Abstract

Disclosed is a two-dimensional and three-dimensional optical measurement apparatus capable of alternately or selectively measuring two-dimensional sizes and three-dimensional features of an object, and measuring three-dimensional features of an object without using reflected light from a reference plane but only using a projection grating, thereby minimizing reducing measurement error. The apparatus comprises a CCD camera installed at an upper portion in a probe casing for producing a two-dimensional image and a three-dimensional image of an object through an image-forming lens, a first lighting system installed under the CCD camera and illuminating a measurement surface of the object to be measured when measuring a two-dimensional size of the object, a second lighting system installed under the first lighting system and attached to an image pick-up tube provided to the bottom of the probe casing 10 for illuminating corners of the object to be measured when measuring a two-dimensional size of the object, a third lighting system installed in a portion of the probe casing for illuminating the measurement surface of the object through a projection grating, a projection lens, a total reflection mirror and the image pick-up tube when measuring a three-dimensional feature of the object, and a piezoelectric actuator for finely moving the projection grating.

Description

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OPTICAL APPARATUS FOR MEASURING THE TWO AND THREE- DIMENSIONAL SHAPE OP AN OBJECT

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an optical measurement apparatus for measuring two-dimensional sizes and three-dimensional features of an object, and more particularly to a two-dimensional and three-dimensional optical measurement apparatus capable of selectively and alternately measuring two-dimensional sizes and three-dimensional features including surface roughness of an object to be measured.

Description of the Related Art

Generally, as electronics and mechanics are developed, miniaturization and refinement of electronic and mechanical components are accelerated. Therefore, to check process and fabrication status of the miniaturized fine electronic and mechanical components, sizes, features and surface roughness must be measured with high precision.

A two-dimensional size, a three-dimensional feature and surface roughness of a semiconductor wafer and fine patterns formed on the semiconductor wafer cannot be measured using known contact measurement apparatuses. Such a contact measurement apparatus particularly having a probe tip is disadvantageous in that the probe tip may make a scratch on the surface of an object to be measured while measuring a surface roughness of the object. Further, the contact measurement apparatus is disadvantageous in that it is difficult to measure the area of the surface of an object.

Accordingly, to measure sizes, features, and surface roughness of small electronic or mechanic components, two-dimensional and three-dimensional measurement apparatuses for measuring a two-dimensional size and a three- dimensional feature of an object by a non-contact method have been suggested. A known two-dimensional measurement apparatus only measures a two-dimensional size by using a light beam irradiated from a light source. A known three-dimensional measurement apparatus measures only three-dimensional features and surface roughness in such a manner that it collimates light beams irradiated from a light source, projects the collimated light beams to an object and compares a reference pattern acquired the collimated light beams and a deformed pattern acquired by measured light beams which are light beams reflected from the object.

However, such conventional two-dimensional measurement apparatuses and conventional three-dimensional measurement apparatuses are independently designed and separately implemented from each other. Therefore, to measure a two- dimensional size and a three-dimensional feature of an object, both of the conventional two and three-dimensional measurement apparatuses are utilized. Accordingly two-dimensional and three-dimensional measurement works are troublesome, and consume a lot of time and costs because both of two measurement apparatuses are used.

To solve such problems of the conventional measurement apparatuses, the present applicant disclosed an optical measurement device capable of selectively or alternately measuring a two-dimensional size and a three-dimensional feature including surface roughness of an object in Korean patent 284080, which is incorporated herein as a reference. Fig. 1, Fig. 2 and Fig. 3 illustrate an optical measurement device in accordance with a prior art, the device capable of selectively and alternately measuring a two-dimensional size and a three-dimensional feature including surface roughness of an object. Fig. 1 is a perspective schematic view of the optical measurement device in accordance with the prior art. Referring to Fig. 1, the optical measurement device comprises input devices such as a keyboard 114 and a mouse 116, a controller 112 for controlling and managing the entire optical measurement device to be operated in a specified mode set by the keyboard 114 or the mouse 116, and output devices such as a monitor 118 and a printer 120 for outputting the measured result so as for an operator to know the result.

The optical measurement device in accordance with the prior art further comprises a measurement unit 130 connected to the controller 112 for measuring a two-dimensional size and a three-dimensional feature of an object P to be measured. The measurement unit 130 includes a controller block 130a. The measurement unit

130 further includes a vibration isolation system 136, a granite surface plate 138, an X-Y table 140, and a tilt table 142, which are stacked on the controller block 130a in order. The measurement unit 130 further comprises a support 44 fixed on the granite surface plate 138 at an edge portion, wherein the support 44 has a probe 146 therein, which is used to measure a feature of the object P and arranged to move linearly up and down.

The probe 146 has a first optical system 150 for measuring a two-dimensional size of the object P and a second optical system 152b for measuring a three- dimensional feature of the object P therein. Fig. 2 illustrates the first optical system 150 and Fig. 3 illustrates the second optical system 152a. Referring to Fig. 2, to measure a two-dimensional size of the object P using the first optical system 150, a turret 148 (shown in Fig. 1) of the optical measurement device is turned backward or forward so as for an objective lens 172 to face the object P placed on the controller block 130a. After the turret 148 is turned and operation of the measurement device is initiated, white light beams are emitted from a light source

160 and are made incident onto a beam splitter 170 through a first lens 162, a second lens 164, a third lens 166 and a total reflection lens 168.

The white light beams incident onto the beam splitter 170 are irradiated to the object P to be measured through the objective lens 172, and then reflected from the object P. The reflected light passes back through the objective lens 172, is focused by an image- forming lens 174 installed on the optical path of the reflected lightj and then enters a Charge Coupled Device (CCD) camera having a CCD therein, so that a two-dimensional image is acquired and a two-dimensional size can be measured.

On the other hand, with reference to Fig. 3, to measure a three-dimensional feature of the object P using the second optical system 152a, the turret 148 (shown in

Fig. 1) is turned so as for the objective lens 172, a reference plane 178 and a beam splitter 180 to face the object P placed on the controller block 130a. After the turret 148 is turned and the operation of the optical measurement device is initiated, white light beams are emitted from a light source 160 and are made incident onto the beam splitter 170 through a first lens 162, a second lens 164, a third lens 166 and a total reflection lens 168.

The white light beams incident onto the beam splitter 170 are irradiated to the object P to be measured through the objective lens 172, the reference plane 178 and the beam splitter 180. At this time, the reference plane 178 forms a reference beam with respect to condensed light beams condensed by the objective lens 172 and the 03 00045

beam splitter forms a measured beam for measuring features/surface roughness of the object P.

The reference beam and the measured beam are incident onto the reference plane 178 and a measurement surface of the object, respectively, and then respectively reflected from the reference plane 178 and the measurement surface. At this time, interference is caused between the reflected reference beam and the reflected measured beam, thereby forming a fringe. The CCD camera 176 photographs the fringe through the image-forming lens 174 and produces a three-dimensional image, thereby measuring a three-dimensional feature and surface roughness. The conventional optical measurement device shown in Figs. 1 to 3 is advantageous in that the first and second optical systems 150, 152b share common elements so that the device structure is simplified. However, the conventional optical measurement device shown in Figs. 1 to 3 is disadvantageous in that the first optical system 150 and the second optical system 152b must be selected by turning the turret 148 backward or forward every time measurement parameters such as the two- dimensional size and the three-dimensional feature are changed, so that the device is inconvenient to use.

Further, the conventional optical measurement device is disadvantageous in that images remaining in the reference plane may cause measurement error, so that it is difficult to ensure reliability of the measurement result, because the three- dimensional image acquired by the conventional optical measurement device CCD is a fringe formed by interference of light beams reflected from the reference plane and the measurement surface.

SUMMARY OF THE INVENTION Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a two-dimensional and three-dimensional optical measurement device capable of selectively and alternately measuring two-dimensional sizes and three-dimensional features including surface roughness, without using a reference plane but only using a projection grating.

In accordance with the present invention, the above and other objects can be accomplished by the provision of a two-dimensional and three-dimensional optical measurement apparatus comprising a CCD camera installed at an upper portion in a probe casing for producing a two-dimensional image and a three-dimensional image of an object through an image-forming lens, a first lighting system installed under the

CCD camera and illuminating a measurement surface of the object to be measured when measuring a two-dimensional size of the object, a second lighting system installed under the first lighting system and attached to an image pick-up tube provided to the bottom of the probe casing 10 for illuminating corners of the object to be measured when measuring a two-dimensional size of the object, a third lighting system installed in a portion of the probe casing for illuminating the measurement surface of the object through a projection grating, a projection lens, a total reflection mirror and the image pick-up tube when measuring a three-dimensional feature of the object, and a piezoelectric actuator for finely moving the projection grating. Preferably, the first lighting system may include a body having a ring shape so as for image information of the object to be acquired by the CCD camera, and a plurality of light emitting diodes installed with a tilt angle in corresponding grooves formed at a lower part of the body along external edge portions.

Preferably, the second lighting system may include: a body having ring shape so as for image information of the object to be acquired by the CCD camera; a plurality of grooves formed at a lower part of the body along external edge portions; and a plurality of light emitting diodes placed on corresponding slanted panels installed in the corresponding grooves.

Preferably, in accordance with the present invention, three-dimensional feature information of the obj ect may be obtained by unwrapping a Moire phase which is a difference phase between a reference phase which is acquired by applying bucket algorithm to a reference grating pattern projected to a reference plane of a transportation to receive the object to be measured thereon, and an object phase which is acquired by applying the bucket algorithm to a deformed grating pattern projected to a measurement surface of the object.

Preferably, in accordance with the present invention, a two-dimensional size information of the object may be acquired by selectively using a first lighting image which is taken when the first lighting system is lit up and a second lighting image which is taken when the second lighting system is lit up, or comparing the first lighting image with the second lighting image.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a perspective schematic configuration diagram of a conventional optical measurement device;

Fig. 2 is a schematic view of a first optical system included in the conventional optical measurement device shown in Fig. 1 ; Fig. 3 is a schematic view of a second optical system included in the conventional optical measurement device shown in Fig. 1;

Fig. 4 schematically illustrates an interior of a two-dimensional and three- dimensional optical measurement apparatus in accordance with the present invention; Fig. 5 is an enlarged view of a first lighting systemshown in Fig. 4;

Fig. 6 is an enlarged view of a second lighting systemshown in Fig. 4;

Fig. 7 is an explanation diagram for explaining the operation of the apparatus in accordance with the present invention;

Fig. 7A is a diagram for explaining a method for measuring a three- dimensional feature using the apparatus in accordance with the present invention; and

Fig. 7B and 7C are diagrams explaining a method for measuring a two- dimensional size using the apparatus in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will be described below in detail with reference to accompanying drawings.

An overall structure of a two-dimensional and three-dimensional optical measurement apparatus in accordance of the present invention is the same as the structure of the conventional optical measurement device shown in Fig. 1 except for the probe having the first and second optical systems therein. Accordingly, to avoid duplication of explanation, a description is provided only with respect to the probe relating to the preferred embodiment of the present invention below.

Fig. 4 is a cross-sectional view of a probe included in a two-dimensional and three-dimensional optical measurement apparatus in accordance with the present invention. Referring to Fig. 4, a probe includes a probe casing 10 and a CCD camera 11 placed on a mount 12 in the probe casing 10. The probe further comprises an image-forming lens 13 fixed to a portion of the probe casing 10 via a lens mount 14 and installed under the CCD camera 11. The probe further comprises a first lighting system 15 fixed to a portion of the probe case 10 via a first illumination mount 16 and installed under the image-forming lens 13. The first lighting system 15 is used to acquire a two-dimensional image of an object.

The first lighting system 15 includes a body 15a having a ring shape so as for an image information of an object to be acquired by the CCD camera 11, a plurality of grooves 15b formed at a lower part along external edge portions of the body 15a, and a plurality of light emitting diode (LED) 15c installed in corresponding grooves 15b and inclined toward the object with a tilt angle, wherein the object is placed right under the center of the image-forming lens 13.

Further, the probe further includes an image pick-up tube 17 provided under the first lighting system 15 at a lower part of the probe casing 10, and a second lighting system 18 provided under the image pick-up tube 17 and used for measuring a three- dimensional size of an object.

Referring to Fig. 6, the second lighting system 18 includes a body 18a formed to have a ring shape so as for image information of an object to be acquired by the CCD camera 11, a plurality of grooves 18b formed at a lower part of the body 16a along external edge portions of the body 16a, a plurality of slanted panels 18c with a tilt angle, which is installed in the corresponding grooves 18b for receiving respective LEDs 18d thereon, and a plurality of LEDs 18d placed on the respective slanted panels.

The probe further includes a total reflection mirror 19 separately installed at a portion of the interior of the probe casing 10 from the first lighting system 15 and to 0045

face the image pick-up tube 17, and a projection lens 20 fixed to the internal wall of the probe casing 10 via a lens mount 21 above the total reflection mirror 19. The projection lens 20 is used to measure a three-dimensional feature of an object.

Further, a projection grating 22 movable by a piezoelectric actuator (PZT) (not shown) is installed above the projection lens 20, and a third lighting system 23 which is used in measuring a three-dimensional feature of an object is installed above the projection grating 22 and fixed to the probe casing 10 via a third lighting mount 24.

Methods for measuring a two-dimensional size and a three-dimensional feature will be described below using the apparatus in accordance with the preferred embodiment of the present invention with reference to Fig. 7, Fig. 7A, Fig. 7B and Fig.

7C.

First, a measurement parameter of a three-dimensional feature is set using an input device such as a keyboard and a mouse.

Then, with reference to Fig. 7A, to acquire a reference phase with respect to the reference plane, light beams irradiated from the third lighting system 23 are made incident onto a reference plane of a transportation table through the projection grating 22, the projection lens 20 and the total reflection mirror 19.

The light beams irradiated from the third lighting system 23 projects a grating pattern of the projection grating 22 onto the reference plane while the projection grating 22 finely moves by a piezoelectric actuator 25, so that a reference grating pattern is formed on the reference plane and photographed by the CCD camera 11 through the image-forming lens 13. Therefore, a reference grating image is acquired. Further, by applying the bucket algorithm to the reference grating image, reference phase with respect to the reference plane is acquired. Next, an object P to be measured is placed on the transportation table and light P T/KR03/00045

beams irradiated from the third lighting system 19 are incident onto a surface to be measured of an object through the projection grating 22, the projection lens 20 and the total reflection mirror 19.

At this time, while the projection grating 22 finely moves by a piezoelectric actuator 25a, a grating pattern of the projection grating 22 is projected on the surface to be measured of the object P by the light beams irradiated from the third lighting system 19. The original grating pattern of the projection grating 22 is deformed along the curved surface of the object. This deformed grating pattern is taken by the CCD camera 11 through the image-forming lens 13, so that a deformed grating image is acquired.

Further, by applying bucket algorithm to the deformed grating image, an object phases is acquired. Next, a Moire phase is acquired by calculating phase difference between the reference phase and the object phase, and actual height information of the object can be acquired by unwrapping the Moire phase. That is, the three-dimensional feature information, height information, of the object is obtained.

Further, in the case of selecting a measurement parameter of a two-dimensional size by using the input device such as the mouse and the keyboard, with reference to Fig. 7B, the LED 15c installed in the body 15c of the first lighting system 15 irradiates white light beams, and the white light beams are incident onto the object P, reflected from the measurement plane of the object P and enter the CCD camera 11.

Then, the first lighting system 15 is extinguished, and the LED 18d installed in the body 18a of the second lighting system 18 are lighted up and illuminate light beams. The light beams are reflected from corners of the object P and enter the CCD camera 11 through the image-forming lens 13. Accordingly, by selectively using a first lighting image acquired using the first lighting system and a second lighting image acquired using the second lighting system or comparing them with each other, a size, two- dimensional shape information, of the object P can be obtained.

As apparent from the above description, the present invention provides a two- dimensional and three-dimensional optical measurement apparatus capable of selectively or alternately measuring two-dimensional sizes , and three-dimensional features. Further, the present invention provides a two-dimensional and three- dimensional optical measurement apparatus capable of measuring a three-dimensional feature without using light beams reflected from the reference plane but only using a projection grating, so that the apparatus is unlikely to cause measurement error and can be implemented in compact size at low cost. Further, the apparatus of the present invention is convenient to use.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

"WHAT IS CLAIMED IS:

1. A two-dimensional and three-dimensional optical measurement apparatus capable of selectively and alternately measuring sizes and features of an object using an optical system, the apparatus comprising: a CCD camera installed at an upper portion in a probe casing for producing a two-dimensional image and a three-dimensional image of an object through an image- forming lens; a first lighting system installed under the CCD camera and illuminating a measurement surface of the object to be measured when measuring a two-dimensional size of the object ; a second lighting system installed under the first lighting system and attached to an image pick-up tube provided to the bottom of the probe casing for illuminating corners of the object to be measured when measuring a two-dimensional size of the object ; a third lighting system installed in a portion of the probe casing for illuminating the measurement surface of the object through a projection grating, a projection lens, a total reflection mirror and the image pick-up tube when measuring a three-dimensional feature of the object ; and a piezoelectric actuator for finely moving the projection grating .

2. The apparatus as set forth in claim 1, wherein the first lighting system includes: a body having a ring shape so as for image information of the object to be acquired by the CCD camera; and a plurality of light emitting diodes installed with a tilt angle in corresponding grooves formed at a lower part of the body along external edge portions.

3. The apparatus as set forth in claim 1, wherein the second lighting system includes: a body having a ring shape so as for image information of the object to be acquired by the CCD camera; a plurality of grooves formed at a lower part of the body along external edge portions; and a plurality of light emitting diodes placed on corresponding slanted panels installed in the corresponding grooves.

4. The apparatus as set forth in claim 1, wherein a three-dimensional feature information of the object is obtained by unwrapping a Moire phase which is a difference phase between a reference phase which is acquired by applying bucket algorithm to a reference grating pattern projected to a reference plane of a transportation to receive the object to be measured thereon, and an object phase which is acquired by applying the bucket algorithm to a deformed grating pattern projected to a measurement surface of the object.

5. The apparatus as set forth in claim 1, wherein a two-dimensional size information of the object is acquired by selectively using a first lighting image which is taken when the first lighting system is lit up and a second lighting image which is taken when the second lighting system is lit up, or comparing the first lighting image with the second lighting image.