CN116047707A

CN116047707A - Non-vertical autofocus system and corresponding optical instrument

Info

Publication number: CN116047707A
Application number: CN202211612465.3A
Authority: CN
Inventors: 王立峰; 高海军; 陈星�
Original assignee: Raintree Scientific Instruments Shanghai Corp
Current assignee: Raintree Scientific Instruments Shanghai Corp
Priority date: 2016-10-09
Filing date: 2016-10-09
Publication date: 2023-05-02
Also published as: CN107918184A

Abstract

Embodiments of the present disclosure relate to a non-vertical autofocus system including a light source and corresponding optical instrument; an incidence module configured to receive light emitted from the light source and focus the received light onto a sample; an exit module configured to receive light reflected from the sample and focus the received light onto a target surface of a light detector; and a photodetector configured to convert an optical signal focused on the target surface into an electrical signal and for calculation processing to automatically calculate and determine information of a focal position of the incidence module; wherein, the incident light path from the incident module to the sample and the emergent light path from the sample to the emergent module are not equal to zero in the included angle with the surface normal of the sample. The non-perpendicular autofocus system of the present disclosure advantageously expands the design space of existing optical instruments and enables accurate focusing of transparent samples.

Description

Non-vertical autofocus system and corresponding optical instrument

The present application is a divisional application filed on the date 2016, 10 and 09, with the application number 201610880380.1 and the name of "non-vertical autofocus system and corresponding optical device".

Technical Field

Embodiments of the invention relate to the field of optics, and more particularly to a non-vertical autofocus system and corresponding optical instrument, wherein the optical instrument particularly comprises a spectroscopic ellipsometer (Spectroscopic Ellipsometry, SE).

Background

As an example of an optical instrument comprising a focusing system, a spectroscopic ellipsometer is an optical measurement device for detecting film thickness, optical constants (refractive index n, extinction coefficient k) and material microstructure. The method has the characteristics of no damage, no contact, no need of vacuum, no need of reference sample and the like, so that the spectrum ellipsometer is widely applied to the fields of semiconductor chip manufacture, optical coating, material analysis and the like.

In order to shorten the detection time, the spectroscopic ellipsometer is provided with a set of Auto Focus (AF) system to realize the rapid positioning of the sample. An autofocus system is a system that converts signals such as force, heat, light, electricity, or sound into electrical signals for processing, and then automatically calculates and determines the focus position. The auto-focusing system for the spectroscopic ellipsometer generally adopts a reflective optical path system, that is, light emitted by a light source is focused on the surface of a sample by an incidence module and reflected, and finally received by a light detector by an emergent module.

At present, in an automatic focusing system for a spectrum ellipsometer, an incident light path and an emergent light path are perpendicular to a sample surface (namely, the incident light path and the emergent light path are coincident), and a microscope objective with high-power large numerical aperture is used as a focusing lens and a collimating lens. However, there are cases where there is no room for the sample to be vertically oriented to lay out such a vertical autofocus system, and where the reflected light from the second side of the sample may affect the measurement result when measuring a transparent sample, and thus may not be properly focused to the focus position. Therefore, a new type of autofocus optical system is proposed based on the above problems.

Disclosure of Invention

The present disclosure is directed to a novel Non-vertical autofocus system (Non-Vertical Auto Focus, NVAF) that at least overcomes or alleviates the technical problems of spatial layout in the prior art, and the real problem of incorrect focusing when measuring transparent samples.

According to a first aspect of the present disclosure, there is provided a non-vertical autofocus system comprising a light source; an incidence module configured to receive light emitted from the light source and focus the received light onto a sample; an exit module configured to receive light reflected from the sample and focus the received light onto a target surface of a light detector; and a photodetector configured to convert an optical signal focused on the target surface into an electrical signal and for calculation processing to automatically calculate and determine information of a focal position of the incidence module; and the included angles of the incident light path from the incident module to the sample and the emergent light path from the sample to the emergent module and the surface normal of the sample are not equal to zero.

By using the information of the focal position of the incidence module or the sample position information relative to the focal position of the incidence module, the automatic focusing system disclosed by the invention can adjust the focal position of the incidence module to the sample surface or drive the sample surface to the focal position, thereby realizing an automatic focusing function, and the spatial layout of the non-vertical automatic focusing system is improved relative to that of the prior art because the included angles of the incident light path from the incidence module to the sample and the emergent light path from the sample to the emergent module and the surface normal of the sample are not equal to zero, and the accurate focusing of the transparent sample can be realized.

When the optical fiber guiding type light source is utilized, the light source guided by the optical fiber can be collimated into parallel light through the small hole and the collimating lens, and then focused on the surface of the sample through the focusing lens; the light reflected by the surface of the sample is collimated by the collimating lens and then focused on the target surface of the four-quadrant detector by the focusing lens; when a parallel light emergent light source (such as a laser) is utilized, a beam expanding lens and a collimating lens can be used for focusing light on the surface of a sample, and then the light is imaged on the target surface of a position detector through an imaging lens.

It should be noted that the lenses including the collimator lens, the focusing lens, the beam expanding lens, the imaging lens, and the like referred to herein may be single lenses or lens groups that achieve the same function. The collimating lens and the focusing lens mentioned in the present disclosure each cover both a single lens and a lens group including a plurality of lenses, respectively, unless otherwise specified.

According to a second aspect of the present disclosure, the above-described non-perpendicular autofocus system may be applied in optical instruments, in particular in spectroscopic ellipsometers. Optical instruments (such as spectroscopic ellipsometers) including the non-perpendicular autofocus systems of the present disclosure may have a wider design space and layout relative to existing focus systems.

Drawings

In the drawings, like/identical reference numerals generally refer to like/identical parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the drawings:

FIG. 1 schematically illustrates an optical path schematic diagram of a non-perpendicular autofocus system according to embodiments of the present disclosure;

FIG. 2 schematically illustrates a layout of a first embodiment of a non-perpendicular autofocus system according to the present disclosure;

FIG. 3A schematically illustrates a light intensity distribution on a four-quadrant detector with a sample in a focal position according to a first embodiment of the present disclosure;

FIG. 3B schematically illustrates a light intensity distribution on a four-quadrant detector when a sample is out of focus in accordance with a first embodiment of the present disclosure;

FIG. 4 schematically illustrates a layout of a second embodiment of a non-perpendicular autofocus system according to the present disclosure;

FIG. 5A schematically illustrates spot positions on a position detector when a sample is in a focus position according to a second embodiment of the present disclosure; and

fig. 5B schematically illustrates spot positions on a position detector when a sample is out of focus in accordance with a second embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

Various embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. One or more examples of the embodiments are illustrated by the accompanying drawings. The examples are provided by way of illustration of the present disclosure and are not intended as limitations of the present disclosure. For instance, features illustrated or described as part of one embodiment, can be used on another embodiment to yield a still further embodiment. The present disclosure is intended to include these and other modifications and variations as fall within the scope and spirit of the disclosure.

Furthermore, in the present disclosure, the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In the description of the present disclosure, the meaning of "a plurality" is at least two, such as two, three, etc., unless explicitly specified otherwise. For the drawings, directional terms, such as "upper", "lower", "left", "right", "front", "rear", etc., are used with reference to the orientation of the drawings as described. These directional terms are for purposes of illustration and not limitation, as the components of the embodiments of the present disclosure can be implemented in a variety of ways. The following specific embodiments are, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

Fig. 1 schematically illustrates an optical path schematic diagram of a non-perpendicular autofocus system according to various embodiments of the present disclosure. The non-perpendicular autofocus system of the present disclosure may find particular application in optical instruments such as spectroscopic ellipsometers, providing improved design space or layout for the optical instrument.

As shown in fig. 1, the non-vertical autofocus system mainly includes four parts, namely, a light source 10, an incident module 20, an exit module 30, and a light detector 40.

The light source 10 may be a broad spectrum light source or a narrow spectrum light source such as a single wavelength light source depending on design requirements and actual conditions. The light source 10 may also be a fiber guided light source or a parallel-emitting light source if classified by the emitting mode of the light source. Wherein the optical fiber guided light source, i.e. the light source is guided out by an optical fiber; in the case where the non-perpendicular autofocus system is applied to an optical instrument such as a spectroscopic ellipsometer, the fiber guided light source may be taken from the spectroscopic ellipsometer's own light source (such as a xenon lamp light source) and guided out of the fiber; whereas the parallel-emitting light source may be, for example, a laser.

The incidence module 20 is configured to receive light emitted from the light source 10 and focus the received light onto the sample S. For example, the incident module 20 may collimate the light emitted from the light source 10 into parallel light and then focus the parallel light on the sample surface or the measured surface. The incident module is used for collimating and/or focusing the light emitted by the light source on the tested surface of the sample. The design of the incident module varies according to the actual situation of the light source. If the light source is a fiber guided light source, such as from a xenon light source or a laser coupled with an optical fiber, the incidence module may consist of an aperture, a collimating lens and a focusing lens; if the light source is a parallel-emitting light source such as a laser, the entrance module may include a beam expanding lens and a focusing lens.

The exit module 30 is configured to receive light reflected from the sample S and focus or image the received light onto a target surface of the light detector 40. For example, the exit module 30 may focus the light reflected from the sample surface or the surface under test to the target surface of the photodetector 40. The exit module is different according to different working modes of the light detector. There are two main types of photodetectors, one is a four-quadrant detector (Quadrant Photodiode, QP) and the other is a position detector (Position Sensitive Device, PSD). The optical aberration control requirement of the four-quadrant detector on the emergent module is not very high, but the working range of the four-quadrant detector is smaller. The position detector has a larger working range, but has higher requirements on optical aberration control of the emergent module. The detector is specifically selected, and the measurement and selection are required according to actual conditions. If a four-quadrant detector is selected, the size of a light spot irradiated on the detector through the emergent module is required to be half (millimeter level) of the diameter of the detector; if a position detector is chosen, it is desirable that the spot size impinging on the detector is as small as possible, which requires that the various optical aberrations of the exit module be controlled to a minimum.

The optical parameters of the optical elements comprised in the entrance and exit modules may vary as the case may be. For example, in the case of a fiber guided light source, in some embodiments, the core diameter of the optical fiber may be greater than 100um (e.g., 300 um), the numerical aperture NA may be greater than 0.18 (e.g., 0.23), and may include an optical fiber splice such as SMA 905; the diameter of the small holes may be between 50um and 200um (e.g., 100 um) and cannot be larger than the core diameter of the optical fiber. In some embodiments, the collimating lens of the incident module may be an infinity flat field microscope objective, such as a 4 x infinity flat field microscope with a parfocal distance of 45 mm; the focusing lens of the incidence module may be a single lens or a lens group, such as a lens or a lens group with a focal length of 25mm and a numerical aperture of 0.12, for example an apochromatic lens group in the visible light band. In some embodiments, the collimating lens of the exit module may be a single lens or a lens group, such as a lens or a lens group with a focal length of 25mm and a numerical aperture of 0.12, for example an apochromatic lens group in the visible light band. Furthermore, in some embodiments, the focusing lens of the exit module may be a doublet lens composed of two glass materials, BK7 and F5.

The photodetector 40 is configured to convert the optical signal focused on the target surface into an electrical signal and is used for calculation processing to automatically calculate and determine information of the focal position of the incidence module 20 or information of the sample position relative to the focal position of the incidence module. The light detector 40 may be any detector suitable for detecting the above-described focal position, including but not limited to a four-quadrant detector and a position detector. Where the photodetector is a four-quadrant detector, the photosensitive region thereof may be circular, such as a circle having a diameter of 5 mm.

Furthermore, the incident light path from the incident module to the sample and the exit light path from the sample to the exit module are arranged in principle in a relationship in which the incident angle is equal to the exit angle. In this case the angles of the incident and the exit light paths to the normal of the sample surface are typically more than 45 degrees, which may for example be designed to be 67 deg. each, however in other embodiments other angles are possible.

Further, the autofocus system of the present disclosure may further include a driving unit (not shown) that may drive the surface to be measured of the sample to the focal position according to the focal position determined by the light detector.

Fig. 2 schematically illustrates a layout of a first embodiment of a non-perpendicular autofocus system according to the present disclosure. As an example, this first embodiment corresponds to the case where the light source 10 is configured as a fiber-guided light source.

As shown in fig. 2, the light source 10 may be configured to be guided out via an optical fiber 101, in which case the light source 10 is connected to a broad spectrum or narrow spectrum light source carried by the optical instrument, for example, by a fiber optic connector (such as SMA905, not shown). Light guided out through the optical fiber 101 is collimated into parallel light by the aperture 201 and the collimator lens 202 to be vertically incident on the focusing lens 203, the light focused by the focusing lens 203 is obliquely incident on the surface of the horizontally placed sample S, the light reflected by the surface of the sample S is incident (such as vertically incident) on the collimator lens 301, the collimator lens 301 collimates the light into parallel light and then is incident (such as vertically incident) on the focusing lens 302, and the focusing lens 302 focuses the parallel light on the target surface of the photodetector 401 such as a four-quadrant detector.

To demonstrate the principle of a four-quadrant detector, fig. 3A and 3B schematically show the light intensity distribution on the four-quadrant detector when the sample is in and out of a focal position according to a first embodiment of the present disclosure.

If the sample is in the focal position, the light intensity distribution on the target surface of the four-quadrant detector 401 is schematically shown in fig. 3A, and the light intensity values irradiated on the quadrants i, ii, iii, and iv are equal, namely: a+b=c+d, where A, B, C, D represents the intensity values of the light impinging on quadrants i, ii, iii, and iv of the four-quadrant detector 401, respectively. If the sample deviates from the focal position, the intensity values in the quadrants I, II and III, IV of the four-quadrant detector 401 are no longer equal, i.e. A+B+.C+D, as schematically shown in FIG. 3B. The four-quadrant detector 401 may take as a signal the normalized (a+b-C-D)/(a+b+c+d) value in order to indicate the position information of the sample out of focus, thereby determining the position of the sample, and may then drive the sample to the focus position by the driving unit.

It should be noted that the kind and the number of elements included in the non-perpendicular type autofocus system shown in fig. 2 are merely illustrative, and those skilled in the art can make appropriate modifications to the kind and the number of elements in this first embodiment under the principles of the present disclosure. For example, any suitable beam shaping element or the like may be further added to the optical path of fig. 2; for another example, the collimator lens 201, the focusing lens 203, the collimator lens 301, and the focusing lens 302 may be implemented by a lens group including a plurality of lenses.

As a further example, fig. 4 schematically shows a layout of a second embodiment of a non-perpendicular autofocus system according to the present disclosure, wherein the second embodiment corresponds to the case where the light source is a parallel-emitting light source.

As shown in fig. 4, the laser 102 as a parallel-emitting light source emits parallel light, which is incident (e.g., vertically incident) on the focusing lens 203 after passing through the beam expander lens 204, and the light beam focused by the focusing lens 203 is obliquely incident on the surface of the horizontally placed sample S, and the light reflected by the surface of the sample S is imaged on the target surface of the photodetector 402 such as a position detector by the imaging lens 303.

To illustrate the principle of the position detector, fig. 5A and 5B schematically show the spot position on the position detector when the sample is in the focus position and is offset from the focus position, respectively, according to a second embodiment of the present disclosure.

If the sample is in the focus position, the spot position on the target surface of the position detector 402 is in the target surface neutral position, as shown in FIG. 5A. If the sample deviates from the focal position, the spot position on the target surface of the position detector 402 also deviates from the target surface median position, as shown in FIG. 5B. In this way, the distance that the sample is off focus can be translated into a distance that the spot is off center on the target surface of the position detector 402. Therefore, the position of the sample can be judged, and finally the sample is moved to the focus position by the driving unit.

Similarly, the types and numbers of elements included in the non-perpendicular autofocus system shown in fig. 4 are also merely illustrative, and those skilled in the art can make appropriate modifications to the types and numbers of elements in this second embodiment under the principles of the present disclosure. For example, any suitable beam shaping element may be further added to the optical path of fig. 4; for another example, the beam expander lens 204, the focusing lens 205, and the imaging lens 303 may be lens groups including a plurality of lenses, respectively. Accordingly, unless otherwise indicated, all lenses in this disclosure may be made up of a single lens or lens group.

The above-described non-perpendicular autofocus systems of the present disclosure may be included in a number of optical instruments including, but not limited to, the above-mentioned spectroscopic ellipsometer. Wherein the light source of the non-vertical automatic focusing system can be connected to the light source of the optical instrument by an optical connector, thereby realizing the automatic focusing control of the optical instrument on the surface of the sample; meanwhile, due to the non-vertical automatic focusing system, the design space inside the optical instrument is expanded, so that the space layout of the optical instrument can be better optimized, and precise focusing can be realized on transparent samples.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In this specification, a description of the terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.

In the claims, the word "comprising" does not exclude other elements, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain features are recited in mutually different embodiments or in dependent claims does not indicate that a combination of these features cannot be used to advantage. The scope of the present application encompasses any possible combination of the features recited in the various embodiments or the dependent claims without departing from the spirit and scope of the present application.

Any reference signs in the claims shall not be construed as limiting the scope of the invention.

Claims

1. A non-vertical autofocus system comprising:

a light source (10);

an incidence module (20) configured to receive light emitted from the light source and focus the received light onto a sample (S);

an exit module (30) configured to receive light reflected from the sample and focus the received light onto a target surface of a light detector (40);

the light detector (40) is configured to convert the optical signal focused on the target surface into an electrical signal, and when the light detector is a four-quadrant detector, the four-quadrant detector determines information of the focal position of the incidence module based on the light intensity distribution on the target surface of the four-quadrant detector, or when the light detector is a position detector, the position detector determines information of the focal position of the incidence module based on the distance of a light spot on the target surface of the light detector from the center position of the target surface; and

a driving unit configured to drive a measured surface of the sample to the focal position according to information of the focal position determined by the photodetector;

wherein, the incident light path from the incident module to the sample and the emergent light path from the sample to the emergent module are not equal to zero in the included angle with the surface normal of the sample.

2. The non-perpendicular autofocus system of claim 1, wherein when the light source is a fiber guided light source (101), the incidence module comprises an aperture (201), a collimating lens (202), and a focusing lens (203).

3. The non-perpendicular auto-focusing system according to claim 1, wherein when the light source is a parallel-emitting light source, the incidence module comprises a beam expanding lens (204) and a focusing lens (205).

4. The non-perpendicular autofocus system of claim 2, wherein the aperture diameter is no greater than a core diameter of an optical fiber.

5. The non-perpendicular autofocus system of claim 1, wherein when the light source is a fiber guided light source, the exit module includes a collimating lens (301) and a focusing lens (302).

6. The non-perpendicular autofocus system of claim 1, wherein when the light source is a parallel-emitting light source, the emitting module comprises an imaging lens (303).

7. An optical instrument comprising the non-perpendicular autofocus system of any one of claims 1-6.

8. A spectroscopic ellipsometer comprising the non-perpendicular autofocus system according to any one of claims 1-6.