CN111486952A - Optical measurement system - Google Patents

Abstract

The invention discloses an optical measurement system, which comprises a shared objective lens, an emission side objective lens, a receiving side objective lens and a light source. The light beam emitted by the light source enters the common objective lens after passing through the emission side objective lens, the light beam emitted by the common objective lens enters the common objective lens again after being reflected or scattered by a measured object, the light beam received by the common objective lens enters the receiving side objective lens, the light beam emitted by the emission side objective lens is used for acquiring information of the measured object, and the emission side objective lens and the common objective lens have different axes with spatial offset. The invention realizes that the transmitting and receiving light beams have controllable inclination angles, thereby reducing the crosstalk between optical signals; because the transmitting light path and the receiving light path are not coaxial, and no light splitting element is arranged in the system, the light energy utilization rate of the system is improved, and the resolution of the system is improved.

Description

an optical measurement system

technical field

The invention relates to an optical measurement system, in particular to an optical measurement system for measuring surface topography, thickness refractive index of transparent substances, back structure of transparent substances and the like.

Background technique

Spectral confocal has many applications in the measurement of displacement, thickness, refractive index, multilayer transparent material structure or three-dimensional topography. As early as the 1970s, scholars Courtney Pratt and others proposed a chromatic aberration that can be used with microscope objectives The technology of surface topography detection; Molesini and other scholars then used a set of specially designed lenses with chromatic aberration to build a surface profiler based on the principle of spectral confocal; Boyde.A et al. applied it to the field of microscopy. Come to the revolutionary change in confocal microscopy technology. Since then, many foreign scholars have carried out in-depth research on the measurement technology based on the principle of spectral confocal, and derived many application examples in the field of measurement: such as the measurement of surface profile and topography, the measurement of micro- and nano-scale fine structures, the semiconductor industry Displacement measurement in the automotive industry, thickness measurement of optical glass and biofilms, color measurement in the paint and printing industry, etc. At present, developed countries have a very mature grasp of this technology, and industrial-grade spectral confocal related products have appeared on the market, with a working frequency response of more than kHz.

The spectral confocal displacement sensor is a non-contact sensor based on the confocal principle and uses a broad-spectrum light source. Its highest accuracy can reach the sub-micron level, and it can measure almost all material surfaces. One of the key technologies of spectral confocal is to use spectral wavelength to encode the distance, and then use the photoelectric conversion element to decode the code. Most of the currently published and commercialized spectral confocal sensors are point measurement methods. For example, a Chinese patent with publication number CN107044822A entitled "Spectral confocal sensor and measurement method", a Chinese patent with publication number CN110260799A named "A Spectral Confocal Displacement Sensor", publication number US10197382B2, named " "chromatic confocal sensor" US patent, the disclosed spectral confocal sensor and measurement method realize the measurement of point displacement through spectral decoding. To obtain two-dimensional properties, it is necessary to cooperate with a motion scanning device. Therefore, the development of line scanning devices has always been the pursuit of the industry.

In 2014, the US Patent No. US9476707B2 published by Focalspec OY Company disclosed a method for realizing linear measurement. In this scheme, the progressive filter has a spatial inclination angle with the surface of the measured object and the optical lens. The optical system is complex, bulky, and has a relatively small working distance. The transmitting and receiving systems are not coaxial. Usually the numerical aperture of the measurement optical path is relatively small.

In 2018, PrecitecOptronik GmbH disclosed a method for realizing linear measurement in US Patent Publication No. US10228551B1. In this method, the confocal pinholes at key points reduce the lateral resolution of the X-axis measurement due to the limitation of pinhole spacing. If slits are used, signal crosstalk at different depths will be caused, which will also reduce the resolution. At the same time, the use of the beam splitting prism reduces the utilization rate of light energy of the system, resulting in a large power of the light source, which brings a large amount of heat, which brings challenges to the heat dissipation design of the system.

In 2019, PrecitecOptronik GmbH also published a light splitting solution using gratings or beam splitting prisms in US Patent Publication No. US10466357B1 (Patent No. US 10466357B1). However, in order to maintain a certain angle between the transmitting part and the receiving part and the measured surface, the use of two spectroscopic elements results in a bulky system and a large number of spectroscopic elements.

SUMMARY OF THE INVENTION

In view of the above problems in the prior art, the present invention provides a method for surface topography measurement, transparent material thickness measurement, refractive index measurement, multilayer transparent material structure measurement, etc. optical measurement system.

The present invention adopts following technical scheme:

An optical measurement system includes a common objective lens, an emission side objective lens, a receiving side objective lens, and a light source. The light beam emitted by the light source enters the common objective lens after passing through the emission side objective lens. Focusing in the axial direction, after being reflected or scattered by the measured object, it enters the same common objective lens again. The beam emitted by the common objective lens enters the receiving side objective lens, and the beam exiting from the receiving side objective lens is used to obtain the measured object information after the back-end spectral decoding. , the optical axes of the transmitting side objective lens and the common objective lens, and the optical axes of the receiving side objective lens and the common objective lens are not coaxial, and have a spatial offset.

Furthermore, the common objective lens is a dispersive objective lens with an axial dispersion function and having axial chromatic aberration.

Further, the light source is a continuous spectrum light source.

Furthermore, the light beam emitted by the light source enters the emission-side objective lens after passing through a confocal diaphragm, and the confocal diaphragm is a first slit that does not include an array of spaced pinholes.

Further, the three optical axes of the transmitting side objective lens, the shared objective lens, and the receiving side objective lens are not coaxial, and the beam emitted by the shared objective lens and the beam entering the shared objective lens after being reflected or scattered by the measured object are between the Z axis. All have an inclination angle, the inclination angle of which is adjustable.

Further, the common objective lens and/or the transmitting-side objective lens and/or the receiving-side objective lens is a single optical element or an objective lens group including multiple optical elements.

Furthermore, there is no spectroscopic element in the optical measurement system before acquiring the topographic information of the surface of the object to be measured.

Furthermore, the common objective lens and the transmitting side objective lens form a dispersive objective lens group with axial linear dispersion and perfect focusing, and the receiving side objective lens and the common objective lens form a dispersive objective lens group with axial linear dispersion and perfect focusing.

Furthermore, the front end of the common objective lens also includes a turning optical element for realizing the turning of the optical path.

Further, the light beam received by the objective lens on the receiving side forms a linear light spot on the confocal diaphragm; the linear light spot is transformed by the first lens and divided into two parts by the beam splitting element: one part is focused by the second lens on the linear array. On the photoelectric conversion element, it is used to collect the overall light intensity information; the other part is dispersed and emitted according to different wavelengths and different exit angles after passing through the dispersion element. Above, the information of the measured object can be obtained after the area array light intensity information received by the area array photoelectric conversion element is processed.

The beneficial effects of the present invention are as follows:

In the present invention, the transmitting and receiving objective lenses use the same objective lens element, and the objective lens element includes at least one objective lens, the optical axis of the objective lens element is different from the optical axis of the light source emitting end, and the optical axis of the objective lens element is not on the axis of the receiving lens group. There is a controllable tilt angle between the transmit and receive beams, thereby reducing signal crosstalk. Since the transmitting optical path and the receiving optical path do not share the same optical axis, there is no optical splitting element in the system, so the utilization rate of the optical energy of the system is improved. At the same time, there is no need to use an array of small holes with intervals, and a slit can be used, thereby improving the resolution of the system.

Description of drawings

Fig. 1 is the spatial light path layout diagram of Embodiment 1;

Fig. 2 is the X-axis scanning schematic diagram of embodiment one;

FIG. 3 is a diagram of an alternative scheme of the refracted optical path of the second embodiment.

Fig. 4 is the spatial light path layout diagram of embodiment three;

FIG. 5 is a spatial optical path layout diagram of the fourth embodiment.

Labels in the figure: 1. Continuous spectrum light source; 2. The first slit; 3. The objective lens on the emission side; 4. The objective lens on the dispersive side; 5. The measured object; 6. The objective lens on the receiving side; a lens; 9, a beam splitter prism; 10, a second lens; 11, a linear array photoelectric conversion element; 12, a diffraction grating; 13, a third lens; 14, an area array photoelectric conversion element; 15, a first folding optical element; 16. The second folding optical element; 17. A prism.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings.

Example 1

This embodiment takes surface topography measurement as an example, and provides an optical measurement system as shown in FIG. 1 . The optical measurement system includes a common objective lens, an emitting side objective lens 3, a receiving side objective lens 6, and a light source. Wherein, the common objective lens in this embodiment is preferably a dispersive objective lens 4 having an axial dispersion function and having axial chromatic aberration, and the light source in this embodiment is preferably a continuous spectrum light source 1 .

The light beam emitted by the continuous spectrum light source 1 is shaped and then irradiated on the first slit 2 , and the light beam emitted from the first slit 2 is refracted by the emission side objective lens 3 and then enters the dispersive objective lens 4 . Since the optical axis of the emission side objective lens 3 and the optical axis of the dispersive objective lens 4 are not coaxial, there is a spatial offset, so after being focused by the dispersive objective lens 4, the light spots of different wavelengths are arranged along the Z-axis direction, and the dispersive objective lens 4 exits The light beam has a certain inclined angle with the Z axis, and the arrangement of this inclined angle reduces the crosstalk of the optical path signal.

Part or all of the light beams reflected (scattered) by the measured object 5 return to the dispersive objective lens 4 and then exit to the receiving side objective lens 6. The optical axis of the receiving side objective lens 6 is not coaxial with the optical axis of the dispersive objective lens 4, and there is a spatial offset, After passing through the incident side objective lens 6, the light beam forms a linear light spot on the second slit 7. The linear light spot is transformed by the first lens 8 and then divided into two parts by the beam splitter prism 9: one part is focused by the second lens 10 for linear photoelectric conversion. On the element 11 (for example, a linear array CCD or a linear array CMOS), it is used to collect the overall light intensity information; the other part is dispersed and emitted on the diffraction grating 12 according to different wavelengths and different emission angles after passing through the beam splitter prism 9. The light beam is focused by the third lens 13 on the area array photoelectric conversion element 14 (for example, area array CCD or area array CMOS) in a two-dimensional space, and the area array light intensity information received by the area array photoelectric conversion element 14 is processed by the computer or control. After the system processes, the relevant information of the measured object 5 can be obtained.

FIG. 2 illustrates the propagation path of the chief ray in the X-axis direction. The figure shows the schematic diagram of the chief ray having the same wavelength, and the remaining wavelengths are referenced in order. As an industry consensus, no further description is given here.

The transmitting side objective lens 3 and the dispersive objective lens 4 form a dispersive objective lens group with axial linear dispersion and perfect focusing, and the receiving side objective lens 6 and the dispersive objective lens 4 also form a dispersive objective lens group with axial linear dispersion and perfect focusing.

Embodiment 2

This embodiment provides an optical measurement system as shown in FIG. 3 . The composition of the optical measurement system is basically the same as that of the first embodiment, and the first folding optical element 15 and the second folding optical element 16 are respectively added to the front end of the common objective lens. The first folding optical element 15 is used to realize the inversion of the optical path between the emission side objective lens 3 and the dispersive objective lens 4 , and the second folding optical element 16 is used to realize the optical path between the receiving side objective lens 6 and the dispersive objective lens 4 . 's inversion.

It should be noted that any turning of the optical path at the front end of the common objective lens can realize the change of the optical axis direction, which is inseparable from the protection scope of the present invention, and this embodiment is only one of the expected solutions. The inflections of many optical paths are not listed here.

Embodiment 3

This embodiment provides an optical measurement system as shown in FIG. 4 by taking the measurement of the thickness of a transparent substance as an example. The structure of the optical measurement system is the same as that of the first embodiment. After the light wave signal reflected from the upper surface of the measured object 5 is de-spectrified by the de-spectrification system, the corresponding height h1 is obtained. The physical thickness h=n*(h2-h1) corresponding to the measured object 5, where n is the corresponding refractive index of the lower surface reflection wavelength corresponding to the material.

Embodiment 4

This embodiment provides an optical measurement system as shown in FIG. 5 by taking the acquisition of the overall image information of the measured area as an example. The composition of the optical measurement system is basically the same as that of the first embodiment, and the main difference lies in the spectral decoding system at the rear end of the second slit. After the received light wave signal is collimated by the first lens 8 (this embodiment preferably adopts a collimating objective lens group), it is incident on the prism 17, and the incident surface of the prism 17 is coated with a certain proportion of the beam splitting film, and part of the light wave before dispersion is absorbed by the prism 17. Partial reflection, after passing through the second lens 10, is focused on the line array photoelectric conversion element 11, and is used to obtain the overall image information of the measured area. Part of the transmitted light waves are dispersed by the prism 17, the prism 17 can be a single prism, or the prism combination is not limited to the structure shown, and the components with the dispersion function are included in the protection scope of the present invention, and will not be listed one by one here. Repeat. The light wave dispersed by the prism 17 is focused on the area array photoelectric conversion element 14 by the third lens 13, and after photoelectric conversion, is provided to the control system for corresponding information processing. The third lens 13 is a lens, a lens group or a mirror.

To sum up, in the present invention, the emission optical axis of the light source is not coaxial with the focusing optical axis, and the rear end optical axis of the receiving is not coaxial with the focusing optical axis. The objective lens part realizes perfect focusing of two parts of light waves with different optical axes. The light waves focused on the measured surface and reflected (scattered) back to the receiving light path have a certain angle. This ingenious structure realizes the controllable existence of the transmitted and received beams. Therefore, the crosstalk of the signal is reduced. At the same time, since the transmitting optical path and the receiving optical path do not share the same optical axis, there is no optical splitting element in the system, so the utilization rate of the optical energy of the system is provided. The confocal diaphragm does not need to use an array of small holes with spacing, but can use slits, thereby improving the resolution of the system.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For example, it should be noted that the emission-side objective lens 3, the dispersive objective lens 4, the receiving-side objective lens 6, the first lens 8, the second lens 10, etc. used in the present invention are not limited to a single lens or multiple lenses, they may be It is a single optical element, or a combination of multiple optical elements; for another example, in the spectral decoding system at the rear end of the second slit 7, the implementation of the dispersion element is not limited to reflection gratings, diffraction gratings or prisms. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. An optical measurement system, characterized by: the light beam emitted by the light source enters the shared objective lens after passing through the emission side objective lens (3), the light beam emitted by the shared objective lens is focused in different wavelengths along the optical axis direction of the shared objective lens, reflected or scattered by a measured object (5) and then enters the same shared objective lens again, the light beam emitted by the shared objective lens enters the receiving side objective lens (6), the light beam emitted by the receiving side objective lens (6) is subjected to rear end spectrum decoding and then is used for acquiring information of the measured object (5), and the optical axes of the emission side objective lens (3) and the shared objective lens and the optical axes of the receiving side objective lens (6) and the shared objective lens are not coaxial and have spatial offset.

2. An optical measuring system according to claim 1, characterized in that: the common objective lens is a dispersion objective lens (4) with axial dispersion function and axial chromatic aberration.

3. An optical measuring system according to claim 1, characterized in that: the light source is a continuous spectrum light source (1).

4. An optical measuring system according to claim 1, characterized in that: the light beam emitted by the light source enters an emission side objective lens (3) after passing through a confocal diaphragm, wherein the confocal diaphragm is a first slit (2) which does not comprise an interval small hole array.

5. An optical measuring system according to claim 1, characterized in that: the optical axes of the emission side objective lens (3), the common objective lens and the receiving side objective lens (6) are not coaxial, and the light beam emitted by the common objective lens, the light beam entering the common objective lens after being reflected or scattered by the measured object (5) and the Z axis all have inclination angles, and the inclination angles of the inclination angles can be adjusted.

6. An optical measuring system according to claim 1, characterized in that: the common objective lens and/or the emission-side objective lens (3) and/or the reception-side objective lens (6) are a single optical element or an objective lens group comprising a plurality of optical elements.

7. An optical measuring system according to claim 1, characterized in that: the optical measurement system is free of spectroscopic elements prior to obtaining topographical information of the surface of the object (5) to be measured.

8. An optical measuring system according to claim 1, characterized in that: the shared objective lens and the transmitting side objective lens (3) form a dispersive objective lens group with axial line dispersion and perfect focusing, and the receiving side objective lens (6) and the shared objective lens form a dispersive objective lens group with axial line dispersion and perfect focusing.

9. An optical measuring system according to claim 1, characterized in that: and a folding optical element is also arranged at the front end of the common objective lens and used for realizing the folding of the optical path.

10. An optical measuring system according to claim 1, characterized in that: the light beam received by the receiving side objective lens (6) forms a linear light spot on the confocal diaphragm; the linear light spot is converted by the first lens (8) and then is divided into two parts by the light splitting element: one part of the light is focused on the linear array photoelectric conversion element (11) by the second lens (10) and is used for collecting total light intensity information; and the other part of the light beams are dispersed and emitted according to different wavelengths and different emission angles after passing through the dispersion element, the light beams emitted by dispersion are focused on an area array photoelectric conversion element (14) by a third lens (13) on a two-dimensional space, and the area array light intensity information received by the area array photoelectric conversion element (14) is processed to obtain the information of the measured object (5).

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