CN102589692A - Vertical incidence broadband polarization spectrometer for splitting optical fiber bundle and optical measurement system - Google Patents

Abstract

The invention provides a vertical incidence broadband polarization spectrometer for splitting an optical fiber bundle and an optical measurement system. The vertical incidence broadband polarization spectrometer comprises a light source, the optical fiber bundle, a light detector and a polarization unit, wherein the optical fiber bundle comprises an incident optical fiber sub-bundle and an emergent optical fiber sub-bundle; the incident optical fiber sub-bundle is provided with a first port group and a second port group; the emergent optical fiber sub-bundle is provided with a third port group and a fourth port group; and the second port group of the incident optical fiber sub-bundle and the third port group of the emergent optical fiber sub-bundle are on a same cross section. According to the vertical incidence broadband polarization spectrometer and the optical measurement system disclosed by the invention, by the adoption of the optical fiber bundle splitting and the addition of a polarization element, the luminous flux efficiency of the spectrometer is improved and the control capability to polarization lights is enhanced.

Description

The vertical incidence wideband polarization spectrometer and the optical measuring system of fibre bundle beam split

Technical field

The present invention relates to field of optical measuring technologies, relate in particular to a kind of vertical incidence wideband polarization spectrometer and optical measuring system of fibre bundle beam split.

Background technology

Fast development along with semicon industry; The three-dimensional appearance that utilizes optical measuring technique to detect quickly and accurately the thickness of semiconductive thin film, material behavior and periodic structure is the control production run; The key link of boosting productivity is mainly used in integrated circuit, flat-panel monitor, hard disk, solar cell etc. and comprises in the industry of membrane structure.Utilize different materials, different structure film at different wave length the incident light of different polarization states is had different reflectivity, its reflectance spectrum has uniqueness.Current advanced film and three-dimensional structure measuring equipment; Like ellipsometer test and optics critical dimension measuring instrument (Optical Critical Dimension; Be called for short OCD) require satisfied spectral measurement ability of trying one's best wide to increase measuring accuracy, be generally 190nm to 1000nm.Under the known situation of membrane structure parameter, the light reflecting thin film spectrum can draw through calculated with mathematical model.When having the unknown structure parameter, film thickness for example, the Film Optics constant, surface three dimension structures etc. can be through regretional analysis, match measurement and analog computation spectrum, thus draw the unknown structure parameter.Measuring equipment is divided into respect to the optical system of sample surfaces vertical incidence with respect to the optical system of sample surfaces oblique incidence usually.The optical system of vertical incidence usually can be integrated with other process equipments because structure is compact more, realizes producing and integration of measuring and monitoring in real time.In the prior art, the optical system of vertical incidence spectrometer mainly through optical splitter, is separated detecting light beam with the sample folded light beam, make the sample folded light beam can't reversely return light source, and independently be incident to detector.Fig. 1 utilizes optical splitter for prior art and carries out the spectrometer of beam separation.As shown in Figure 1, in this spectrometer, the diverging light of light source 101 outgoing is behind lens 102, and parallel incident transmission focuses to sample 105 surfaces through optical splitter 103 after lens 104 are assembled; The reflected light on sample 105 surface after lens 104 reflections, vertical incidence optical splitter 103; Assemble through lens 106 after reflection, be incident to detector 107, obtain the reflectance spectrum of sample surfaces.

Adopt the subject matter of the spectrometer existence of optical splitter to be: 1) luminous flux is low, and in the whole measurement process, light beam needs through same optical splitter transmission by light source and reflects each once, the entering detector.The highlight flux ratio that can reach is 25%, promptly optical splitter be transmissivity and reflectivity each 50%; 2) if realize the spectral range of high-quality hot spot and broad simultaneously, then system complexity is higher, and cost is higher.Labor is following:

A) be under the situation of beam split thin slice at optical splitter, the beam split thin slice need become 45 ° of uses with the light beam key light, shown in U.S. Pat 6900900B2.The shortcoming of this structure is: under broadband light beam transmission situation, when light beam is parallel beam, can produce aberration; This problem can be provided with identical beam split thin slice correction aberration through other, but has increased system complexity, has reduced luminous flux.Another kind of optical splitter based on the beam split thin slice is that some lattice spectroscopes (Polka-dot Beamsplitter) (like United States Patent (USP) 5450240, EdmundOptics point lattice spectroscope) or thickness are merely 100 microns some lattice spectroscope (like U.S. Pat 6525884B2); The characteristics of its structure are: folded light beam can realize wide spectrum (comprising the deep ultraviolet scope), and self no chromatic dispersion; But the periodic structure of its surface point lattice can cause diffraction pattern, has influenced the accuracy of measuring greatly;

B) be under the situation of Amici prism (like U.S. Pat 6181427B1) at optical splitter; Its shortcoming is: Amici prism is difficult to realize simultaneously wide spectrum beam split, is divided into 400-700nm usually, 700-1100nm; The spectral range of measuring has been limited in three zones of 1100-1600nm;

C) be under the situation of polarization splitting prism at optical splitter, transmitted light/reflected light is fixing polarization direction, and changing polarization state needs rotatory polarization Amici prism or rotary sample or establish the polarizer in addition, realizes very complicacy;

D) be under the situation of pellicle beamsplitter (Pellicle Beamsplitter) at optical splitter, the shortcoming of its structure is that film thickness is merely 2 microns, and is affected by environment big, very easily damaged, can't clear up the surface, and cost is high; And there is absorption in film to ultraviolet band.

Spectrometer defines the range of application of spectrometer to the control ability of polarization, especially for the anisotropy sample, for example, the sample of the structure of three-dimensional periodic.Through measuring the reflectance spectrum of polarized light, calculate phase characteristic, match numerical simulation result, the thickness and the optical constant of critical dimension (CD), three-dimensional appearance and the multilayer material of measuring samples surface periodic pattern at sample surfaces.Realize that spectrometer that critical dimension is measured requires the polarization state of control bundle in its light signal collection process, thus measuring samples exactly.

In realizing process of the present invention, the inventor recognizes that there is following defective in prior art: adopt the flux efficiency of spectrometer of traditional optical splitter low, lack the control ability to polarization.

Summary of the invention

The technical matters that (one) will solve

To the problem that exists in the prior art, the present invention proposes a kind of vertical incidence wideband polarization spectrometer and optical measuring system of fibre bundle beam split, to improve the flux efficiency of spectrometer, improve its control ability to polarization.

(2) technical scheme

The invention discloses a kind of vertical incidence wideband polarization spectrometer of fibre bundle beam split.This spectrometer comprises: light source, fibre bundle, polarization unit and photo-detector.Fibre bundle comprises incident optical bundle, outgoing optical fiber bundle, and incident optical bundle and the sub-Shu Jun of outgoing optical fiber comprise at least one optical fiber or fiber cores; Incident optical bundle has first port set and second port set, and outgoing optical fiber bundle has the 3rd port set and the 4th port set, and the 3rd port set of second port set of incident optical bundle and outgoing optical fiber bundle is on same xsect.Incident optical bundle is used to guide the detection light from the light emitted of the first port set incident, from the second port set outgoing, and incident sample surfaces behind polarization unit; Outgoing optical fiber bundle is used to guide behind polarization unit from the reflected light of the sample surfaces of the 3rd port set incident, from the 4th port outgoing, incident light detector.Polarization unit between same xsect and sample, is used to make the detection light from the second port set outgoing to form polarized light; And analyzing is from the reflected light of sample surfaces.

Preferably, in the vertical incidence wideband polarization spectrometer of fibre bundle beam split of the present invention, incident optical bundle is the preset optical fiber of reflection/backward scattering optical fiber bundle, and outgoing optical fiber bundle is the outer optical fiber of the preset optical fiber of reflection/backward scattering optical fiber bundle.And fibre bundle constitutes by a central optical fiber with around some branch optical fibers of central optical fiber, and the center of circle that some branch optical fibers are positioned on the same xsect is positioned on the donut of central optical fiber, and this annulus of five equilibrium.Central optical fiber is as incident optical bundle, and some branch optical fibers are as outgoing optical fiber bundle; Or central optical fiber is as outgoing optical fiber bundle, and some branch optical fibers are as incident optical bundle.

Preferably, the vertical incidence wideband polarization spectrometer of fibre bundle beam split of the present invention can also comprise: the polarization unit rotating control assembly.This polarization unit rotating control assembly is used to control the polarization direction of polarization unit.

Preferably, the vertical incidence wideband polarization spectrometer of fibre bundle beam split of the present invention can also comprise: diaphragm.This diaphragm between polarization unit and sample, is used to avoid the e light through producing behind the polarization unit to be incident to sample surfaces, and/or its reflected light reflected back polarization unit.

Preferably, the vertical incidence wideband polarization spectrometer of fibre bundle beam split of the present invention can also comprise: concentrating component.This concentrating component, between same xsect and sample, be used to assemble from the detection light of the second port set outgoing through behind the polarization unit to sample surfaces and the reflected light of assembling sample surfaces behind polarization unit to the 3rd port set.This concentrating component comprises: first light focusing unit and second light focusing unit.First light focusing unit, between same xsect and polarization unit, the detection light formation incident that is used to assemble from the first port set incident is similar to directional light to polarization unit; And outgoing linearly polarized photon to the three port set of convergence behind polarization unit.Polarization unit, being used for surveying light from the second port set outgoing partially is the incident linearly polarized photon; And to be used for analyzing be the outgoing linearly polarized photon from the reflected light of sample surfaces.Second light focusing unit between polarization unit and sample, is used to assemble the incident linearly polarized photon to sample surfaces; And the reflected light of assembling sample surfaces forms the approximate directional light of outgoing to polarization unit.Preferably, first light focusing unit is first condenser lens, and second light focusing unit is second condenser lens.First condenser lens and/or second condenser lens are for proofreading and correct three mirror assemblies, three balsaming lenss or cemented doublet.

(3) beneficial effect

The vertical incidence wideband polarization spectrometer of fibre bundle beam split of the present invention is through adopting the fibre bundle beam split, thereby its flux efficiency improves than the spectrometer of available technology adopting optical splitter greatly.Simultaneously; The vertical incidence wideband polarization spectrometer of fibre bundle beam split of the present invention has increased polarizer; Through measuring the parameter can obtain the polarization state of sample on the quadrature both direction, thus the optical parametric that can the calculation sample material and the three-dimensional appearance structure of analytic sample.

Description of drawings

Fig. 1 utilizes spectroscope for prior art and carries out the spectrometer of beam separation;

Fig. 2 is the synoptic diagram of the vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split;

Fig. 3 is the synoptic diagram in each port cross section of the preferred seven core fibre bundles of vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split;

Fig. 4 is the index path of the vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split;

Fig. 5 focuses on the index path that the time image plane is the mobile out-of-focus appearance of reference for the vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split with simple lens;

Object plane was the index path with reference to mobile out-of-focus appearance when Fig. 6 focused on simple lens for the vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split;

Object plane was the index path with reference to the out-of-focus appearance that moves when Fig. 7 focused on the vertical incidence wideband polarization spectrometer double lens of the embodiment of the invention one fibre bundle beam split;

Fig. 8 be the vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split under desirable case of lenses, the simulation drawing of the ZEMAX luminous flux of out-of-focus appearance;

Fig. 9 is the simulation result of ZEMAX software when adopting the EdmundOptics optical element in the vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split;

The synoptic diagram of Figure 10 for arranging according to the shape adjustments outgoing optical fiber bundle fiber port of spectrograph slit in the vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split;

Figure 11 is the optical schematic diagram of the embodiment of the invention one Rochon prism polarizer;

Figure 12 is the structural drawing of groove before the embodiment of the invention one crystal silicon;

Figure 13 is the absolute reflectance spectrogram of TE and TM in the absolute reflectance mensuration in the embodiment of the invention;

Figure 14 is TE and the TM/TE reflectivity ratio of TM and the spectrum of the phase differential between TM and the TE in the embodiment of the invention ellipsometric measurement method.

Embodiment

For making the object of the invention, technical scheme and advantage clearer, below in conjunction with specific embodiment, and with reference to accompanying drawing, to further explain of the present invention.

In one exemplary embodiment of the present invention, the vertical incidence wideband polarization spectrometer of fibre bundle beam split comprises: light source, fibre bundle, polarization unit and photo-detector.Fibre bundle comprises incident optical bundle, outgoing optical fiber bundle, and incident optical bundle and the sub-Shu Jun of outgoing optical fiber comprise at least one optical fiber or fiber cores; Incident optical bundle has first port set and second port set, and outgoing optical fiber bundle has the 3rd port set and the 4th port set, and the 3rd port set of second port set of incident optical bundle and outgoing optical fiber bundle is on same xsect.Incident optical bundle is used to guide the detection light from the light emitted of the first port set incident, from the second port set outgoing, and incident sample surfaces behind polarization unit; Outgoing optical fiber bundle is used to guide behind polarization unit from the reflected light of the sample surfaces of the 3rd port set incident, from the 4th port outgoing, incident light detector.Polarization unit between same xsect and sample, is used to make the detection light from the second port set outgoing inclined to one side; And analyzing is from the reflected light of sample surfaces.

In the middle of the spectrometer of Traditional use optical splitter; Under the situation of not considering the polarization unit influence; In the whole measuring process, light beam needs through same optical splitter transmission by light source and reflects each once, gets into detector; The highlight flux ratio that can reach is 25%, promptly optical splitter be transmissivity and reflectivity each 50%; If realize the spectral range of high-quality hot spot and broad, then system complexity is higher, and cost is higher simultaneously.Through simulation calculation, the vertical incidence wideband polarization spectrometer of fibre bundle beam split of the present invention, under the situation of not considering the polarization unit influence equally, flux efficiency can reach 50%, is higher than the spectrometer of Traditional use optical splitter far away.Simultaneously; The vertical incidence wideband polarization spectrometer of fibre bundle beam split of the present invention has increased polarizer; Through measuring the parameter that can obtain the polarization state of sample on the quadrature both direction; Thereby the optical parametric that can the calculation sample material and the three-dimensional appearance structure of analytic sample have been expanded the range of application of spectrometer greatly.

In the further embodiment of the present invention, the vertical incidence wideband polarization spectrometer of fibre bundle beam split comprises: light source, fibre bundle, photo-detector, first light focusing unit, second light focusing unit, polarizer.Fibre bundle comprises incident optical bundle, outgoing optical fiber bundle.Incident optical bundle and the sub-Shu Jun of outgoing optical fiber comprise at least one optical fiber or fiber cores.First light focusing unit and second light focusing unit are between fibre bundle and sample, and light beam is propagated for approximate directional light between first light focusing unit and second light focusing unit.Polarizer is between first light focusing unit and second light focusing unit; Incident optical bundle has first port set and second port set; Outgoing optical fiber bundle has the 3rd port set and the 4th port set, and the 3rd port set of second port set of incident optical bundle and outgoing optical fiber bundle is on same xsect.Incident optical bundle is used to guide the detection light from the light emitted of the first port set incident, from the second port set outgoing, through first light focusing unit, polarizer, the second light focusing unit vertical incidence sample surfaces; Outgoing optical fiber bundle is used to guide after the detection light process sample surfaces reflection of the 3rd port set incident, and the reflected light after second light focusing unit, polarizer, first light focusing unit is from the 4th port outgoing, incident light detector.Preferably, first light focusing unit and second light focusing unit are condenser lens.

In the preferred embodiment of the invention, the preset optical fiber of reflection/backward scattering optical fiber bundle is as incident optical bundle, and the outer optical fiber of the preset optical fiber of reflection/backward scattering optical fiber bundle is restrainted as outgoing optical fiber.Optimally; Fibre bundle constitutes by a central optical fiber with around some branch optical fibers of central optical fiber; The center of circle that some branch optical fibers are positioned on the said same xsect is positioned on the donut of central optical fiber; And this annulus of five equilibrium, central optical fiber is as incident optical bundle, and some branch optical fibers are as outgoing optical fiber bundle; Or central optical fiber is as outgoing optical fiber bundle, and some branch optical fibers are as incident optical bundle.

Among the present invention, said light source can be for comprising the light source of multi-wavelength.Specifically, the spectrum of said light source can be at vacuum ultraviolet near infrared range, that is, and and in 190nm to 1100nm wavelength coverage.Light source can be xenon lamp, deuterium lamp, tungsten lamp, Halogen lamp LED, mercury lamp, comprise the composite broadband light source of deuterium lamp and tungsten lamp, comprise tungsten lamp and Halogen lamp LED the composite broadband light source, comprise mercury lamp and xenon lamp the composite broadband light source, or comprise the composite broadband light source of deuterium tungsten halogen, the light beam of this type of light source is a natural light usually.The example of this type of light source comprises Oceanoptics Company products HPX-2000, HL-2000 and DH2000, and Hamamtsu Company products L11034, L8706, L9841 and L10290.Light source also can be and utilizes depolariser that partial poolarized light or polarized light are transformed the natural light that the back forms.For example, depolariser can be Lyot depolariser (United States Patent(USP) No. 6667805).Said detector can be a spectrometer, specifically, can be to comprise grating; Catoptron; With the spectrometer of charge-coupled device (CCD) or photodiode array (PDA), for example, Ocean Optics QE65000 spectrometer or B&W Teck Cypher H spectrometer.Among the present invention, said polarizer can be thin film polarizer, glan thompson prism polarizer, Rochon prism polarizer, Glan Taylor prism polarizer, Glan laser polarization device.Especially, said polarizer is preferably the Rochon prism polarizer, and its material is preferably magnesium fluoride (MgF ₂).Preferably, the vertical incidence wideband polarization spectrometer of this fibre bundle beam split can also comprise: the polarizer rotating control assembly.This polarizer rotating control assembly is used to control the polarization direction of said polarizer.Preferably, the vertical incidence wideband polarization spectrometer of this fibre bundle beam split can also comprise: diaphragm.This diaphragm between said polarization unit and said sample, is used to avoid the e light through producing behind the said polarization unit to be incident to sample surfaces, and/or its reflected light reflected back polarization unit.

Below be example with concrete embodiment, the present invention is elaborated.

Embodiment one

Fig. 2 is the synoptic diagram of the vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split.As shown in Figure 2, the vertical incidence wideband polarization spectrometer of fibre bundle beam split comprises: light source 202, detector 203, fibre bundle 204, sample 205, condenser lens 206, polarizer 207, condenser lens 208.The concrete technical scheme of its committed step is following:

Fibre bundle 204 is divided into three end points; Terminal A comprises fibre bundle 204 whole paths; Promptly comprise second port set of incident optical bundle and the 3rd port set of outgoing optical fiber bundle; Terminal B comprises first port set of incident optical bundle and the 4th port set that end points C comprises outgoing optical fiber bundle; Light source 202 is connected with the fibre bundle terminal B, and the detecting light beam that sends is dispersed in second port set of A end incident optical bundle through first port set of terminal B incident optical bundle and is incident to condenser lens 206, and line focus lens 206 are assembled the back and formed parallel beam; Parallel beam forms linearly polarized photon behind polarizer 207; Linearly polarized photon line focus lens 208 are assembled vertical incidence to sample 205 surfaces.Its folded light beam line focus lens 208, polarizer 207 is incident to fibre bundle 204 terminal A after condenser lens 206 is assembled; The sample segment reflected light finally is incident to detector 203 through the 3rd port set of the outgoing optical fiber bundle of terminal A and the 4th port set of end points C outgoing optical fiber bundle.

In the present embodiment, fibre bundle 204 can be selected reflection/backward scattering optical fiber bundle for use.Fig. 3 is the synoptic diagram in each port cross section of the preferred seven core fibre bundles of vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split.As shown in Figure 3, optical fiber is made up of three fiber ports.The fibre bundle light path is divided into two groups; One group is dotted line fiber cores and the one group of solid line fiber cores that comprises a fiber cores that comprises six fiber cores; Form two independent light-pathes respectively, form incident path and reflex path in the present embodiment.At fibre bundle A end, the shared optical fiber interface of two-way light-path; At optical fiber B end and C end, two light-pathes are respectively the individual fibers interface.This enforcement middle port B is connected with light source, and port C is connected with detector.This type optical fiber, like Oceanoptics QR230-7-XSR/BX, fiber core diameter 230 μ m, spectral range can reach 180-900nm.In the present embodiment, light focusing unit also can be integrated in incident sub-optical fibre and/or the outgoing sub-optical fibre.

Fig. 4 is the index path of the vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split.Port A is positioned at the along of condenser lens 206, the central optical fiber among the port A, and the optical fiber that promptly is connected with the B end can be considered pointolite, and diverging light line focus lens 206 are assembled the back and are formed parallel beam; Parallel beam forms linearly polarized photon through polarizer 207; Line focus lens 208 are assembled vertical incidence to sample 205 surfaces.As shown in Figure 4; If the sample present position is the pairing picture of port A plane 205 '; The folded light beam line focus lens 208 of sample surfaces; Polarizer 207, the condenser lens 206 back overwhelming majority are returned the intrafascicular heart fiber port of optical fiber, can't be incident to in six fiber cores of central optical fiber distribution.In the case, through the distance between fine setting sample plane and the condenser lens 208, during to out of focus position 205, the partial reflection light of sample surfaces will be coupled in six fiber cores that center on the central optical fiber distribution among the port A, finally be incident to detector.

The light that below provides out-of-focus appearance is propagated relation.In the derivation, be the basis with the monofocal case of lenses earlier, expand to double focusing lens or poly focus lens situation.Under the monofocal case of lenses.The light of out-of-focus appearance is propagated relation, be divided into two kinds of situation by control method: (1) sample plane serves as with reference to moving to focus on the time image plane, and (2) optical fiber plane object plane when focusing on serves as with reference to moving.

Fig. 5 is under the monofocal case of lenses, and sample plane serves as the index path with reference to the out-of-focus appearance that moves to focus on the time image plane.As shown in Figure 5, being the point of d if the light of fiber optic hub emergence angle θ is reflexed to apart from the eye point horizontal range through optical system, in situation 1) sample plane is with reference to displacement h to focus on the time image plane, can draw by following steps:

$\frac{1}{f}=\frac{1}{s}+\frac{1}{t}---\left(1\right)$

s·tanθ＝t·tanθ ₁ (2)

$\tan {\mathrm{\θ}}_1=\frac{d_1}{h}---\left(3\right)$

$\frac{d}{h}=\frac{s}{t}---\left(4\right)$

Wherein, f is the focal length of lens, and apart from s, t is the image distance of object distance when being s to object plane apart from condenser lens, and h is a sample distance images plan range, and d is folded light beam and plane of incidence (object plane) intersection point and off-centring distance, and θ is an A end light beam shooting angle.

Can draw by formula (1), (2), (3), (4),

$d=\frac{2h{(s-f)}^2\tan \mathrm{\θ}}{f^2}---\left(5\right)$

Fig. 6 is under the monofocal case of lenses, and optical fiber input plane object plane when focusing on is the index path with reference to out-of-focus appearance under the situation of movement.In situation 2) sample plane serves as with reference to moving h to focus on the time image plane, can be by situation 1) similar step draws:

$d=\frac{2h{(s+h-f)}^2\tan \mathrm{\θ}}{(s+h-f)(s-f)}---\left(6\right)$

Under the situation of double focusing lens or poly focus lens, can focus lens group be converted into the single condenser lens that is equal to and consider that as shown in Figure 7, its focal length does

$\frac{1}{f}=\frac{1}{f_1}+\frac{1}{f_2}-\frac{d}{f_1{f}_2}---\left(7\right)$

Wherein d is for focusing on the distance between two lens, f ₁, f ₂It is the focal length of two condenser lenses

Its object distance s is the distance of object distance object space interarea, and interarea is with respect near the distance X of the condenser lens f1 of object space _HFor

$X_H=-\frac{\mathrm{fd}}{f_2}---\left(8\right)$

In the present invention, the keeping parallelism light beam because the light beam that is incident to the polarizer 207 need be tried one's best; Thus, fibre bundle 204 exit ends are preferably placed on the focal length of lens f1, that is, preferred through regulating as planimetric position adjusting out of focus; Formula (7) (8) is brought in the formula (5) and can be obtained,

$d=\frac{2h\tan \mathrm{\θ}}{{f_2}^2}---\left(9\right)$

Wherein, f ₂Be lens f2 focal length, h is a sample distance images plan range, and θ is an A end light beam shooting angle.According to the cross section structure of seven fiber cores reflection/backward scattering optical fiber bundles,, carried out luminous flux and calculated simulation 200 microns situation of fiber core diameter.Consider that the f1 focal length is 100mm, the f2 focal length is the perfect lens of 50mm, promptly ignores aberration and aberration, has carried out the ZEMAX luminous flux analog computation of out-of-focus appearance.

Fig. 8 be the vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split under desirable double lens situation, the simulation drawing of the ZEMAX luminous flux of out-of-focus appearance.As shown in Figure 8, when center optical fiber output intensity is 100%, remove incident light fibre core area occupied, light intensity is 71.429% in 100 microns to 300 microns annular regions of radius on every side.Comprised six fiber cores in the annular region, its area occupied is than being 3/4 of annulus area; So final luminous flux is about 53.6%; Far above utilizing spectroscopical optical system (like the listed simulation 1 of table one).

The out of focus method of above-mentioned simulation 1 is: fixed fiber bundle 204A end keeps fibre bundle 204A end to be positioned at lens f1 focal position, the position h=0.1 millimeter of adjustment sample surfaces.In the simulation 2, only change two distances between the condenser lens, become 25 millimeters by 50 millimeters, do not influence the integral light flux, this conclusion can be drawn by formula (9).In the simulation 3, with respect to the focal length that simulation 1 and simulation 2 have changed condenser lens f1 and condenser lens f2 respectively, fibre bundle 204A end position and image distance change thereupon, and promptly the magnification ratio of hot spot changes; Luminous flux almost remains unchanged with simulation 1 and situation about simulating in 2.The method can be used for adjusting the detecting light beam spot size, realizes measurement uneven or the conditional sample of sampling area.In the simulation 4,, realize six core fibre bundle outgoing through being connected of exchange fibre bundle 204 port B and port C; In the case, the coupling efficiency of monochromatic light fibre core centering heart fiber cores is 11%, and when supposing that 6 optical fiber connect light source, the luminous flux of each fiber cores equals the luminous flux that single fiber cores connects light source, then total efficiency 11% * 6=66%.Table 1 is the out of focus analog result table of the vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split.

The out of focus analog result table of the vertical incidence wideband polarization spectrometer of table 1 fibre bundle beam split

Simulation

Structure

The f1 focal length

The f2 focal length

Spacing d

h

Total efficiency

Optical fiber cross section efficient

1

1 core → 6 cores

100mm

50mm

50mm

0.1mm

71％

54％

2

1 core → 6 cores

100mm

50mm

25mm

0.1mm

71％

54％

3

1 core → 6 cores

175mm

35mm

50mm

0.1mm

75％

56％

4

6 cores → 1 core

175mm

35mm

50mm

0.1mm

66％

66％

Can find out that by table 1 flux efficiency of light path system part is promptly utilized the vertical incidence wideband polarization spectrometer of optical splitter realization all greater than prior art in the vertical incidence wideband polarization spectrometer of fibre bundle beam split of the present invention.The beam split ratio of supposing optical splitter is x, and its light path flux efficiency is (1-x) x, when x=50%, reaches maximal value 25%.All be lower than technical scheme of the present invention.According to above description, can find out that the straightforward procedure of regulating system does, regulate sample 205 surface elevations separately, make detector reach peak signal.And, can be through different object distances and image distance ratio be set, the adjustment spot size is realized the measurement (small light spot) to limited area.

At light source is that lens can cause chromatic dispersion under the wide spectrum situation; Under the vertical incidence situation,, can influence degree of accuracy although do not influence measurement result accuracy.Can select for use chromatic dispersion to correct the preferable lens combination of ability in the reality and realize the different influence of focal length that maximized rectification chromatic dispersion causes.Lens are for example proofreaied and correct three mirror assemblies, three balsaming lenss or cemented doublet.Existing is example with ultraviolet to three mirror assemblies of infrared correction, like Edmund Optics, and NT64-837 and NT64-840.

Fig. 9 is the simulation result of ZEMAX software when adopting the EdmundOptics optical element in the vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split.Be that optical fiber to sample surfaces distance is under the 293mm situation shown in a group among Fig. 9; 230nm, 500nm and three wave bands of 900nm optical efficiency separately; The average flux efficient of considering three wave bands can reach 39.1%, still is higher than to utilize under the spectroscope situation 25% optical efficiency.When optical fiber to sample surfaces distance not simultaneously, the luminous flux of each wave band is closely not identical, can be according to the spectral distribution of light source intensity, through adjustment optical fiber to sample surfaces apart from optimizing whole measurement effect.Under individual cases, can SPECTRAL REGION be divided into plurality of sections according to dispersion situation, get different out of focus distances respectively for every section and measure, reach the optimum measurement result; Usually 190nm-1000nm is divided into two sections is enough to satisfy measurement requirement.Shown in b group among Fig. 9, when optical fiber to sample surfaces distance is under the 294mm situation, the optical efficiency of 230nm wavelength will greatly improve, and the signal of 500nm and 900nm wavelength is very low.

Preferably, a plurality of ports of some branch optical fibers of the vertical incidence wideband polarization spectrometer outgoing optical fiber of fibre bundle beam split of the present invention bundle are arranged as said photo-detector light inlet shape corresponding shape, to improve the lighting efficiency of photo-detector.In the present embodiment, when fibre bundle 204 port C are connected to spectrometer,, can fibre bundle 204 port C be held many fiber cores word order, to obtain higher coupling efficiency according to the structure of spectrograph slit.The synoptic diagram of Figure 10 for arranging according to the shape adjustments outgoing optical fiber bundle fiber port of spectrograph slit in the vertical incidence wideband polarization spectrometer of the embodiment of the invention one fibre bundle beam split.

For the polarizer that is adopted among the present invention, can adopt Rochon prism polarizer RP shown in figure 11.The material of Rochon prism polarizer can be MgF ₂, a-BBO, kalzit, YVO ₄Or it is quartzy.The Rochon prism polarizer utilizes birefringece crystal (o light is different with the refractive index of e light) to make the outgoing that forms an angle during through the Rochon prism interface of two bundle polarized lights of incident beam orthogonal directions; Wherein o light and incident direction are consistent, with the outgoing of linear polarization light state.Adopt MgF ₂The Rochon prism polarizer of material can reach the spectral range of 130-7000nm.Because material different has different o light and e optical index, so the angle of o light in the transmitted light and e light is also inequality.For example, for MgF ₂Or quartzy, the angle of o light and e light is 1 to 2 degree, yet, for a-BBO or YVO ₄, this angle can reach 8 to 14 degree.This angle also partly depends on the length of the corner cut θ and the polarizer of Rochon prism.When polarizer was passed through in the detecting light beam transmission, o light vertically was incident to sample S, and e light is incident to sample S obliquely; In the time of in e reflection of light light beam can get into polarizer optical aperture scope, its e reflection of light light beam can reflex to polarizer equally, gets into detector then.For the bigger polarizer in e light drift angle, its e light is difficult for getting into again polarizer at the reflected light of sample surfaces.In order to improve measuring accuracy, avoid the influence of e reflection of light light, the position that the o light above sample surfaces separates with e light can be provided with diaphragm D (shown in figure 11), is incident to sample surfaces or reflected light reflected back polarizer to avoid e light.

In the vertical incidence wideband polarization spectrometer of above-mentioned fibre bundle beam split; Light beam between polarizer and sample in the communication process polarization characteristic can remain unchanged; Through suitable measuring method, but correct measurement goes out the change of sample to polarization state, and then calculates the various attributes of sample itself.

Through the vertical incidence wideband polarization spectrometer of above-mentioned fibre bundle beam split, can implement two kinds of measuring methods:

The absolute reflectance of (1) absolute reflectance mensuration, measuring samples two polarization states on orthogonal directions.If will measure the reflectivity of a sample, should do as follows:

A. the dark numerical value I of measuring light spectrometer _d

B. witness mark sample reflectivity, for example, naked silicon wafer, and obtain spectrum numerical value I _r

C. measuring samples, and acquisition numerical value I;

Like this, the reflectivity of spy's amount sample is:

R＝(I-I _d)/(I _r-I _d)×R(ref)

Wherein R (ref) is the absolute reflectance of reference sample.R (ref) can measure obtain from other, or logical property calculation to reference sample draws, and is generally the reflectivity of naked silicon chip.

For example in the one-dimensional grating structure, shown in figure 12, two polarization directions of quadrature are defined as perpendicular to the direction TM of linear structure respectively and are parallel to the direction TE of linear structure.When period p is 100 nanometers, live width w is 50 nanometers, and when gash depth t was 50 nanometers, its reflectivity was shown in figure 13, and wherein dotted line is a TE polarization direction reflectivity, and solid line is a TM polarization direction reflectivity.

(2) ellipsometric measurement method: the vertical incidence spectrometer of fibre bundle beam split of the present invention etc. is all the ellipsometer test of a polarizer-sample-analyzer (PSA) structure, and wherein, the analyzer and the polarizer are the situation of same polarizer.The ellipsometric measurement method can be measured reflectivity ratio and the sample of two kinds of TM/TE under the polarization state at TM, the last phase differential that causes of TE.But concrete measuring principle reference book HANDBOOK OF ELLIPSOMETRY, Harland G.Tompkins, 2005; Spectroscopic Ellipsometry Principles and Applications, Hiroyuki Fujiwara, 2007; The principle formula that United States Patent(USP) No. 7115858B1 and United States Patent(USP) No. 7330259B2 are illustrated. following only the work briefly described.Total transmitance is provided by Jones matrix,

i(out)＝J _AR(A)J _SR(-P)i(in)，

Wherein

$J_s=\left(\begin{array}{cc}{r}_{\mathrm{xx}}& r_{\mathrm{xy}}\\ r_{\mathrm{yx}}& r_{\mathrm{yy}}\end{array}\right)$

Be the Jones matrix of sample reflection, x and y are the polarization direction of two quadratures;

Work as A=P, for r _Xy+ r _Yx=0 situation (for example, referring to Li Lifeng, J.Opt.Soc.Am.A17 is in 881 (2000)), above equality can be reduced to:

$I=I_0[r_{\mathrm{xx}}^2{\cos }^{4}p+r_{\mathrm{yy}}^2{\sin }^{4}p+2{\left(r_{\mathrm{xx}}{r}_{\mathrm{yy}}\right)}^{1/2}\cos \mathrm{\Δ}{\sin }^{2}p{\cos }^{2}p]$

$=I_0{r}_{\mathrm{xx}}^2[\frac{3{\tan }^2\mathrm{\φ}+3+2\tan \mathrm{\φ}\cos \mathrm{\Δ}}{8}+\cos \left(2p\right)\frac{{\tan }^2\mathrm{\φ}-1}{2}+\cos \left(4p\right)\frac{{\tan }^2\mathrm{\φ}+1-2\tan \mathrm{\φ}\cos \mathrm{\Δ}}{8}]$

$=a_0+a_2\cos \left(2p\right)+a_4\cos \left(4p\right)$

Wherein,

$a_0=I_0{r}_{\mathrm{xx}}^2\frac{3{\tan }^2\mathrm{\φ}+3+2\tan \mathrm{\φ}\cos \mathrm{\Δ}}{8}$

$a_2=I_0{r}_{\mathrm{xx}}^2\frac{{\tan }^2\mathrm{\φ}-1}{2}$

$a_4=I_0{r}_{\mathrm{xx}}^2\frac{{\tan }^2\mathrm{\φ}+1-2\tan \mathrm{\φ}\cos \mathrm{\Δ}}{8}$

a ₀, a ₂, a ₄Be Fourier coefficient, can calculate according to Fourier expansion or linear fit.Δ is because x that sample reflection causes and the phase differential between the y polarized light, R _XxBe reflectivity, r _XxBe reflection constant, tan φ=| r _Xx/ r _Yy|.At last,

$\tan \mathrm{\φ}=\sqrt{\frac{a_0+a_2+a_4}{a_0-a_2+a_4}}$

$\cos \mathrm{\Δ}=\frac{-a_0+3a_4}{\sqrt{{(a_0+a_4)}^2-a_2^2}}$

The concrete operations of ellipsometric measurement method comprise following three key steps: 1) owing to the existence of rotary system, system need calibrate to get rid of the measurement light intensity deviation that the polarizer rotation causes.Bearing calibration is the even sample of use standard, and for example silicon chip is measured the light intensity of even sample under different polarization device angle; In theory, light intensity should be identical; The variation relation of this light intensity and angle can be used as reference value, removes the light intensity influence of system in different polarization device angle through ratio.Specifically can be, every rotation 1 degree of polarizer writes down the reflective light intensity spectrum of each angle lower silicon slice, and accomplishes the whole scanning of 360 degree, and these data are worth preservation as a reference.When 2) measuring, the reflective light intensity of all angles is compared with reference value, obtained the relative actual value of light intensity in all angles.Because in the ellipsometric measurement, evaluation is the relative ratio of light signal strength and phase place, but not absolute strength does not influence data processing and measurement result.3) calculate the spectrum of the phase differential between TM/TE reflectivity ratio and TM and the TE.With structure shown in figure 12 is example, and its spectrum is shown in figure 14.

The amplitude that measures TE, TM absolute reflectance or TM/TE is when behind the phase differential, through relatively reaching the numerical value regression Calculation with the numerical simulation result, but the thickness and the optical constant of critical dimension, three-dimensional appearance and the multilayer material of measuring samples surface periodic pattern.In this case; The vertical incidence wideband polarization spectrometer of said fibre bundle beam split can also comprise computing unit; This computing unit is used for through the calculated with mathematical model of reflectivity and curvilinear regression match, the optical constant of calculation sample material and/or be used for the critical dimension characteristic or the three-dimensional appearance of the periodic micro structure of analytic sample material.

Above-described specific embodiment; The object of the invention, technical scheme and beneficial effect have been carried out further explain, and institute it should be understood that the above is merely specific embodiment of the present invention; Be not limited to the present invention; All within spirit of the present invention and principle, any modification of being made, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (17)

1. the vertical incidence wideband polarization spectrometer of a fibre bundle beam split is characterized in that, comprising: light source, fibre bundle, polarization unit and photo-detector,

Said fibre bundle comprises incident optical bundle, outgoing optical fiber bundle, and said incident optical bundle and the sub-Shu Jun of said outgoing optical fiber comprise at least one optical fiber or fiber cores; Said incident optical bundle has first port set and second port set; Said outgoing optical fiber bundle has the 3rd port set and the 4th port set, and the 3rd port set of second port set of said incident optical bundle and said outgoing optical fiber bundle is on same xsect;

Said incident optical bundle is used to guide the detection light from the said light emitted of the said first port set incident, from the said second port set outgoing, incident sample surfaces behind said polarization unit; Said outgoing optical fiber bundle is used to guide behind said polarization unit from the reflected light of the said sample surfaces of said the 3rd port set incident, from said the 4th port outgoing, the said photo-detector of incident;

Said polarization unit between said same xsect and said sample, is used to make the detection light from the said second port set outgoing to form polarized light; And analyzing is from the reflected light of said sample surfaces.

2. the vertical incidence wideband polarization spectrometer of fibre bundle beam split according to claim 1; It is characterized in that: said incident optical bundle is the preset optical fiber of reflection/backward scattering optical fiber bundle, and said outgoing optical fiber bundle is the outer optical fiber of the preset optical fiber of reflection/backward scattering optical fiber bundle.

3. the vertical incidence wideband polarization spectrometer of fibre bundle beam split according to claim 2 is characterized in that:

Said fibre bundle constitutes by a central optical fiber with around some branch optical fibers of said central optical fiber, and the center of circle that said some branch optical fibers are positioned on the said same xsect is positioned on the donut of said central optical fiber, and this annulus of five equilibrium;

Said central optical fiber is as incident optical bundle, and said some branch optical fibers are as outgoing optical fiber bundle; Or said central optical fiber is as outgoing optical fiber bundle, and said some branch optical fibers are as incident optical bundle.

4. the vertical incidence wideband polarization spectrometer of fibre bundle beam split according to claim 3; It is characterized in that: when said some branch optical fibers were restrainted as outgoing optical fiber, said the 4th port set of said some branch optical fibers was arranged as and said photo-detector light inlet shape corresponding shape.

5. the vertical incidence wideband polarization spectrometer of fibre bundle beam split according to claim 1 is characterized in that this spectrometer also comprises: the polarization unit rotating control assembly,

This polarization unit rotating control assembly is used to control the polarization direction of said polarization unit.

6. the vertical incidence wideband polarization spectrometer of fibre bundle beam split according to claim 5 is characterized in that this spectrometer also comprises: diaphragm,

This diaphragm between said polarization unit and said sample, is used to avoid the e light through producing behind the said polarization unit to be incident to sample surfaces, and/or its reflected light reflected back polarization unit.

7. the vertical incidence wideband polarization spectrometer of fibre bundle beam split according to claim 5; It is characterized in that said polarization unit is thin film polarizer, glan thompson prism polarizer, Rochon prism polarizer, Glan Taylor prism polarizer or Glan laser polarization device.

8. the vertical incidence wideband polarization spectrometer of fibre bundle beam split according to claim 7 is characterized in that said polarization unit is the Rochon prism polarizer, and its material is a kind of in the following material:

MgF ₂, a-BBO, kalzit, YVO ₄Or it is quartzy.

9. the vertical incidence wideband polarization spectrometer of fibre bundle beam split according to claim 1 is characterized in that, also comprises: concentrating component,

This concentrating component; Between said same xsect and said sample; Be used to assemble from the detection light of the said second port set outgoing through behind the said polarization unit to said sample surfaces and the reflected light of assembling said sample surfaces behind said polarization unit to the 3rd port set.

10. the vertical incidence wideband polarization spectrometer of fibre bundle beam split according to claim 9 is characterized in that said concentrating component comprises: first light focusing unit and second light focusing unit;

Said first light focusing unit, between said same xsect and said polarization unit, the detection light formation incident that is used to assemble from the said first port set incident is similar to directional light to said polarization unit; And the outgoing linearly polarized photon of convergence behind said polarization unit is to said the 3rd port set;

Said polarization unit, being used for said partially is said incident linearly polarized photon from said second port set outgoing detection light; And to be used for the said reflected light from said sample surfaces of analyzing be said outgoing linearly polarized photon;

Said second light focusing unit between said polarization unit and said sample, is used to assemble said incident linearly polarized photon to said sample surfaces; And the reflected light of assembling said sample surfaces forms the approximate directional light of outgoing to said polarization unit.

11. the vertical incidence wideband polarization spectrometer of fibre bundle beam split according to claim 10 is characterized in that said first light focusing unit is first condenser lens, said second light focusing unit is second condenser lens.

12. the vertical incidence wideband polarization spectrometer of fibre bundle beam split according to claim 11 is characterized in that, said first condenser lens and/or second condenser lens are for proofreading and correct three mirror assemblies, three balsaming lenss or cemented doublet.

13. the vertical incidence wideband polarization spectrometer of fibre bundle beam split according to claim 11 is characterized in that: said second port set is positioned at the said first condenser lens focal position, when sample plane to serve as when moving as the plane, satisfy relational expression:

$d=\frac{2h\tan \mathrm{\θ}}{{f_2}^2},$

Wherein, said picture plane is the total picture plane of said first condenser lens and second condenser lens, f ₂It is the focal length of second condenser lens; H is a sample distance images plan range; D surveys eye point that light is positioned at second port set and this outgoing beam after the sample reflection, and with the offset distance of eye point, θ is the angle of detection light from the second port set outgoing in exit plane.

14. the vertical incidence wideband polarization spectrometer according to each described fibre bundle beam split among the claim 1-13 is characterized in that: said photo-detector is a spectrometer.

15. the vertical incidence wideband polarization spectrometer of fibre bundle beam split according to claim 14 is characterized in that said spectrometer also comprises:

Computing unit; The said sample that is used for measuring according to said spectrometer is in the absolute reflectance of TE, TM direction; And/or said sample is at the amplitude of TE, TM direction phase differential when; Through relatively calculated with mathematical model and curvilinear regression match, the optical constant of calculation sample material, film thickness and/or be used for the sample critical dimensional properties or the three-dimensional appearance of analytical cycle property structure.

16. the vertical incidence wideband polarization spectrometer according to each described fibre bundle beam split among the claim 1-13 is characterized in that said light source is the light source that comprises multi-wavelength.

17. an optical measuring system is characterized in that, comprises the vertical incidence wideband polarization spectrometer of each described fibre bundle beam split among the claim 1-16.

Images