CN1225720A - Optical measurement - Google Patents

Optical measurement Download PDF

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Publication number
CN1225720A
CN1225720A CN 97196506 CN97196506A CN1225720A CN 1225720 A CN1225720 A CN 1225720A CN 97196506 CN97196506 CN 97196506 CN 97196506 A CN97196506 A CN 97196506A CN 1225720 A CN1225720 A CN 1225720A
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light
measuring device
optical measuring
optical
phase
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M·G·索梅克
C·W·西伊
刘书钢
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BTG International Ltd
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British Technology Group Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/30—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces
    • G01B11/306—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces for measuring evenness
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/21—Polarisation-affecting properties
    • G01N21/211—Ellipsometry

Abstract

Apparatus for phase contrast microscopy or ellipsometry has a source of coherent radiation with a beam divider (HDE) to derive an interrogating beam and a reference beam therefrom which are directed on to a surface under test. An objective receives two scattered or reflected beams which are combined to provide an optical signal indicative of the structure of the surface.

Description

Optical measurement
The present invention relates to optical measurement, particularly but not merely relate to ellipticity measurement and profile or profile is measured.
Propose the various optical systems that profile is measured that are used for, for example measured the thickness of the metal trace that covers on the silicon chip.
Because the untouchable and non-destructive of optical means is so they are very attractive methods.In addition, this method has wideer bandwidth than Contact methods.Particularly interference technique has the potentiality of measuring (in the 1MHz bandwidth) little height variation in the inferior nanometer range.Topmost problem is that the changes in material in the specimen material can cause the phase shift of light when using the little profile variation of these systematic surveys, and the variation that causes because of profile has been covered in this phase shift.Another difficulty that obtains precision measurement is such problem, even less external vibration (microphony) can both cause the big phase error of phase change that produces than profile variation.In order to overcome this problem, must under the environment of the influence of isolating exterior admirably, measure, or utilize common optical pathways technical design instrument, make reference and detecting light beam all pass through much at one light path thus, offsetting any microphony, and obviously do not offset the information of relevant sample.
According to the present invention, a kind of optical measuring device is provided, it comprises the optical emitter beam generated device, be used for producing main beam and secondary light beam from described optical emitter, wherein, object of described main beam directive is so that measure the partial structurtes of this object, and described secondary light beam is radiated on the described object as reference light; Light processor is used for producing three grades of light beams and level Four light beam after described object reflection from described main beam and described secondary light beam; And beam merging apparatus, make described three grades of light beams and level Four light beam close bundle, with near the light signal of the structure the described body surface of acquisition expression.
The present invention also provides polarized light ellipticity measurement mechanism, and it comprises lens devices, will focus on the back focal plane from the light of sample reflection; Selecting arrangement, the light of at least two different polarization states of selection from the light that arrives back focal plane; And measurement mechanism, be used to measure the parameter of selected light, can be to provide by the information of this calculation of parameter sample characteristics of for example.
Selecting arrangement preferably selects to arrive the s polarized light and the p polarized light component of back plane.
Measurement mechanism preferably also comprises the device that selected light is interfered mutually.Measurement mechanism is measured the amplitude and the phase place of the striped that is caused by mutual interference.
Selecting arrangement can comprise and being arranged on the back focal plane and at the shadow shield corresponding to the polarization position upper shed of selecting, thereby other polarized light is stopped by shadow shield.Shadow shield can comprise the opening of selecting s polarization and p polarized light is set.
Selecting arrangement preferably includes shadow shield, makes selecteed light pass opening on the shadow shield; And tripping device, be used to separate the p polarized light and the s polarized light component that pass the shadow shield opening.Tripping device can spatially separate this two components.Tripping device can comprise Wollaston prism (Wollaston prism).
Selecting arrangement can comprise the phase splitting device, is used for selected light is applied a differential phase shift.The phase splitting device can comprise general kerr cell (Pockel cell).Can operate general kerr cell selectively,, measure thereby allow to utilize measurement mechanism to carry out each group to change differential phase shift.
Can be provided with lens devices, with producing interference together so that the component that separates is focused at.Lens devices can comprise with it divides the polariscope device that the logical axle earlier of angle is aimed between p direction and the s direction equally.
The present invention also is provided with contour outline measuring set, comprises lens devices, is used for the light from the sample reflection is focused on conjugate planes; Selecting arrangement is used to select on the conjugate planes light on two diverse locations; And measurement mechanism, be used to measure the parameter of selected light, can obtain the profile information of relevant sample by this parameter.
Selecting arrangement can be included in the shadow shield that opening is arranged on two positions.Two positions preferably are symmetrically located at the both sides of systematic optical axis.Measurement mechanism can comprise makes the selected interference of light, and measures the amplitude of the striped that is caused by interference and the device of phase place.Measurement mechanism also can comprise the transform lens device, is used for the Fourier transform of the light of scioptics is projected the plane that forms interference of light striped thereon.This device preferably also comprises the position of measuring striped and the device of contrast.
In third party's case, the invention provides as preceding two sections described contour outline measuring sets, also comprise polarized light ellipticity measurement mechanism by above-mentioned arbitrary scheme definition.This device preferably also comprises the device that obtains relevant sample characteristics of for example information from polarized light ellipticity measurement mechanism, utilizes this information to remove the information relevant with material from the measurement result that contour outline measuring set obtains, and basic real profile information is provided.
Below, only utilize example, and describe embodiments of the invention in detail with reference to accompanying drawing, wherein:
Fig. 1 is the schematic representation of apparatus according to the embodiment of the invention;
Fig. 2 is the phase place contrast microscope of the phase step of another program according to the present invention;
The part of Fig. 3 a and Fig. 3 b presentation graphs 2 shown devices;
Fig. 4 and Fig. 5 represent the synoptic diagram according to the ellipsometer structure of different embodiments of the invention;
Fig. 6 represents the synoptic diagram of the shadow shield that uses in the ellipsometer shown in Figure 5;
Fig. 7 represents the confocal microscopy mirror system;
Fig. 8 represents the variation of system shown in Figure 7;
Fig. 9 represents the common optical pathways optical interferometer according to further embodiment of this invention;
Figure 10 represent the full visual field ellipsometer that constitutes according to another program of the present invention and
Figure 11 represents the synoptic diagram according to the contour outline measuring set that ellipsometer is housed of specified scheme of the present invention;
Figure 12 represents the synoptic diagram of the shadow shield that uses in Figure 11 shown device;
Figure 13 a be illustrated in that light on the plane in the device shown in Figure 12 distributes and
Figure 13 b is illustrated in the synoptic diagram of the shadow shield that uses on this plane.
The device that will illustrate below can obtain basically the appearance information irrelevant with material information, this In its result is called " true profile " information. This device comprises that itself consists of the present invention one The polarised light ellipticity measurement component of individual scheme.
Can will be three critical stages for the Process Decomposition that obtains true profile:
(1) the common optical pathways interferometer of the phase information of the relevant sample of acquisition;
(2) information of the relevant specimen material characteristic of acquisition also keeps simultaneously by the lens numerical aperture The device of whole lateral resolutions that the footpath determines;
(3) response of common optical pathways interferometer can be converted to the response of not being with microphonics General counter-rotating algorithm utilizes the synthesis measuring profilometer device with same space frequency cutoff to obtain Must be somebody's turn to do response, for example with optics or non-optical device (for example, probe).
By realizing common optical pathways operation and obtained by the standard interference instrument in stage (1) and (3) The response of no microphonics. The phase shift compensation that stage (2) is relevant with material to offering sample.
Fig. 1 represents one embodiment of the present of invention.The core of this system is specially designed hologram diffraction parts HDE, its function is to be used for the parallel incident beam 2 of autoradiolysis source (not shown) to produce three output ranks: convergent beam that the collimation object beam of zero level is 4 ,+1 grade and-1 grade divergent beams (not shown).Design ± 1 output beam propagates with the very little angle θ with respect to optical axis.The effect of divergent beams is less, can be left in the basket.Zero order beam focuses on the sample 8 by micro objective 0L, is used to survey the partial structurtes of object.Object lens make+1 grade of beam collimation, and are radiated on the bigger object area.It is as phase reference, and when scanning object, its value remains unchanged.When from the sample surfaces reflex time, two light beams will be for the second time by holograph, and wherein each light beam produces and the slightly different collimation component in its direction of propagation.The phase place of the interference fringe (nominally parallel) that produces is corresponding to the average phase-difference of two light beams, and can obtain by carrying out Fourier transform to the intensity pattern that obtains.In addition, can use the photodiode array of four elements to obtain single striations.Then, use standard analog orthogonal signal disposal route, phase value is provided in real time.The common phase jitter of two light beams will not influence the position of striations, and not appear in system's output.
Fig. 2 represents the phase place contrast microscope of the phase step of another program according to the present invention.This system in combination the optical technology that in phase place contrast microscope and phase step interferometer, adopts, thereby stable and sensitive profile measurement is provided.On the image plane 222 that uses core structure far away, wherein, plane 224 is confocal of two lens 223,225 object 220 imaging.This plane also is the Fourier plane of object.Utilize phase place contrast technology, phase-plate (the 226b part shown in the plane 226a shown in Fig. 3 b and Fig. 3 c) is inserted Fourier plane.This makes bias light and scattered light (because of the object characteristic produces) carry out phase interference, and produces high contrast image.In order to finish quantitative surface measurement, altering system like this: use the ccd array that on detection plane 222, is provided with to obtain a plurality of optical images, insert Fourier plane with different optical phase plates at every turn.Required minimum number of images is that three, three phase-plates are set like this, first block of plate be uniformly and its phase shift be zero degree, second block of plate provides pi/2 phase shift between bias light and scattered light, the 3rd block of plate provides π phase shift.Therefore, the class of operation of system is similar to the operation of phase step interferometer, wherein produces a plurality of interferograms, and each interferogram has the known interference condition of variable quantity.Then, utilize one group of simple conversion formula, can obtain surface profile and reflected by objects rate by the interferogram that obtains.Utilize phase step phase place contrast technology, adopt not conversion formula on the same group.This system can be used for shining upon the object surfaces height change.System compares with phase step, and the technology that is proposed does not need independent reference arm (arm), so it is compacter.In addition, two interfering beams (bias light and scattered light) pass identical lens set, and any common mode noise (microphony and thermograde) influences two light beams in the same manner, and its result is cancelled.Therefore, under the situation that does not need expensive light isolation, just can obtain stable and high-precision optical measurement.
Fig. 4 and Fig. 5 represent two replacement forms of ellipsometer.
Structure 70 among Fig. 4 has shadow shield 72 to be used for replacing shadow shield 52 among Fig. 1 on back plane.Optical texture before the shadow shield 72 is identical with structure shown in Figure 1.
The shadow shield of simple form only is made of a pin hole.With p-line and s-line as vertical and transverse axis, should be along 45 ° of lines, 90 fixing single pin holes.Therefore, the light beam that passes this hole is made of the p polarized component and the s polarized component that equate, and these two components will be subjected to the influence of the complex index of detected material respectively.In order to measure this two plural reflectivity, use Wollaston prism 74 (Wollaston prism) on angle, two components to be separated.Lens L is set 1And L 2, two divergent beams are converted to two parallel beams that intersect by low-angle mutually.Polariscope 76 is set between two lens, and therefore its logical optical axis (pass axis) five equilibrium P and S direction allow two light beams to interfere.Two major advantages of this structure are:
Since p and s component all from same position, so the heterogeneity of input beam on distributing can not cause measuring error; With
2. because the interference between two light beams produces one group of parallel striped,, allow to use one dimension (1-D) detector array so can use post lens compression striped length.Using with digital signal processor (DSP) plate can the approximate real-time sample measurement of generation.
Can constitute shadow shield by a plurality of pin holes, the optical phase reference to be provided and to improve measuring accuracy.
As can be seen, this structure utilizes Wollaston prism to select two different polarized lights, spatially separate the s polarized component and the polarized component of the light that arrives back plane, utilize lens combination to make the selected interference of light then, cause the interference fringe of on detection plane, measuring.Single pin hole on optical axis, back are Wollaston prisms, and the effect of pin hole is " void " pin hole that causes corresponding to Fig. 1 structure, promptly leaves lens L 1Light equal to leave the light of the shadow shield 52 among Fig. 1.
Fig. 5 represents to use shadow shield 82 to replace another structure 80 of the shadow shield 52,72 among Figure 11 and Fig. 4, but the part before the shadow shield 82 is identical.Shadow shield 82 has single pin hole on optical axis 84.
Long-focus lens L 3Be used to make beam collimation, be provided with for example general kerr cell 86 of electro-optical device in the lens back by after the pin hole.The second lens L 4Be used for light beam is focused on detecting device 88.The combination two lens effectively with pinhole imaging on detector plane.The orientation of general kerr cell makes two the p direction that is parallel to light beam respectively and s direction, thereby when being applied to suitable voltage on the device, differential phase shift can be applied on two polarized components.Make the logical optical axis of polarizer and p direction and s direction at 45, therefore allow two components to interfere.
When operating system, four different voltages are applied on the general kerr cell continuously, produce 0 °, 90 °, 180 °, 270 ° differential phase shift respectively.After applying each magnitude of voltage, the output of detector for measuring.Therefore, four are output as
I 1=E 1 2[ρ P 2+ρ S 2+2ρ Pρ Scos(Δ)]
I 2=E 1 2[ρ P 2+ρ S 2+2ρ Pρ Scos(Δ+90°)]
I 3=E 1 2[ρ P 2+ρ S 2+2ρ Pρ Scos(Δ+180°)]
I 4=E 1 2[ρ P 2+ ρ S 2+ 2 ρ Pρ SCos (Δ+270 °)] wherein, E 1Be the amplitude of light beam, ρ PAnd ρ SIt is respectively the amplitude reflectance of p component and s component.Therefore, by finding the solution the equation of four simultaneous, can obtain ellipticity parameter Δ and tan Ψ=ρ P/ ρ S, can utilize personal computer to finish this and find the solution (when finding the solution simultaneous equations, intrinsic ambiguity being arranged between value).Like this, the operating process of system is identical with the phase step interferometer, therefore can use the phase step number and different phase-shift value that is not four.The advantage of this ad hoc structure is
1. similar with said structure, the heterogeneity in input beam distributes will not cause any measuring error; With
2. can use along cornerwise single pin hole more than one.
Certainly, for many application, preferred shadow shield structure can comprise the seam 90 (Fig. 6) at two diagonal angles, replaces detecting device 88 with ccd array.In addition, in order to obtain more precise material feature measurement, the successive range of angular frequency component will provide information for the more complicated sample structure of for example multilayer film and so on.Under some measurement situation,, can remove shadow shield characteristic not being had under the situation of negative interaction.
As can be seen, the structure of Fig. 5 is come separated light by apply differential phase shift on general kerr cell, promptly operates general kerr cell selectively, with the change differential phase shift, thereby allows to utilize different differential phase shifts to carry out one group of measurement on detector plane.Perhaps, the position of general kerr cell can be moved on to the position of blocking from the light beam of radiation source ejaculation.
Structure 70,80 does not require that the beam cross section of irradiation sample 12 is evenly distributed.In addition, structure 70 has potential enough big ability, so that allow to measure in real time, therefore estimates that it is specially adapted to monitor the variation of material behavior or is used to make the substrate image.Structure 80 can be made material behavior and measure, and is therefore particularly useful for the research of sandwich construction.
The final stage of this process comprises that the response that will measure converts the equivalence response that the enough independently systems of energy obtain to.This can realize (Figure 11) in processor 34.
Importantly recognize because above-mentioned ellipsometers structure can be used separately, provide the useful information of the material behavior of relevant sample 12, thus under the situation that does not have profile measurer (profiler) 28 this part of operative installations separately.
Below, referring to Fig. 7, it has provided the synoptic diagram of conventional confocal microscope.By the light from light source 170 of partial reflection prism 172 transmission, focus on the sample 176 and utilize another lens 180 that have back focal plane 182 to pass pin hole 178 imaging backward by object lens 174.The spatial filtering effect of pin hole makes confocal microscope have the characteristic of the spatial resolution of well-known good axial resolution and improvement.Testing process in the confocal microscope can think and be divided into two stages, wherein, focused on after pin hole collimates again by the light of object lens reflection again.Because radial position is relevant with the incident angle on the sample, and horizontal angle determined the illumination polarized state of light, so the distribution of any plane of its conjugation (or with) comprises information by the ellipsometer acquisition on back focal plane.
Pick-up unit 178,180 is shown among the square B of Fig. 7.In another embodiment of the present invention, additional shearing (shearing) element 184 has strengthened the function of the confocal microscope of Fig. 7.Shearing elements generally is an acousto-optic modulator, and it is divided into two bundles to incident light, and introduces relative frequency displacement between light beam.Then, two light beams pass confocal lens 180, and these lens focus on two light beams and form two adjacent hot spots on the detection plane 186.It is clear to be noted that in order to illustrate, and has amplified the shear distance between the two light beams, and importantly on detection plane two focus points be overlapping.Then, before for example photodetector detects with suitable pick-up unit, overlapping focus point is carried out spatial filtering with the pin hole of appropriate size.To produce interference between two focus points, produce the signal that frequency is the difference frequency of two focus points.Shearing means that the different piece that is actually focus interferes mutually, thereby causes high stability differential phase response.Can control the degree of shearing, with the difference component of by control the driven by power of shear being guaranteed to expect.In addition, the sharpest edges of system are, under the situation of the reference beam that does not have to separate, can access the interferometry response, and this will provide very simple and stable system.
Suppose detecting device is located at the point ' a ' last (Fig. 8) of the back focal plane of collimator 180.Produce interference signal so on the difference frequency between the two light beams, this interference will occur in the center of a light beams, and towards the external diameter of another Shu Guang.Therefore, in fact occurring interfering along the light of method line reflection with between with the light of oblique angle reflection by sample.Therefore, the phase differential of measuring from this interference signal is correlated with the different reflection coefficients under different incidence angles.This will provide the index of sample characteristics of for example.Obviously, different detection positions will provide the information of different incidence angles and the information of polarization state.
Therefore, simply additional element provides dual-use function very easily.A function provides sample structure has been changed the very stable differential phase image with sensitivity, another function provides ' measurement of difference ellipticity ' pattern, this pattern is to the reacting condition sensitivity on the material behavior, and this pattern will provide for example index of oxide thickness variations of sample variation rapidly.Therefore, this system will find actual application in semi-conductor industry.
Below, with reference to Fig. 9, it represents another embodiment of the present invention, this embodiment comprises the scanning common optical pathways optical interferometer that microphonics is had good insensitivity (immunity) and has good low spatial frequency to respond.Comprise certain lenses 190 in this device, it is the spherical lens of replacing its core with parallel glass wafer.This can polish by the central area 191 to a plano-convex lens, reaches the smooth smooth finish of optics and obtains.Temporarily ignore the inclination angle of lens this moment, the parallel beam that enters lens is divided into two parts: inside part passes without change then and focuses on the sample through micro objective 192, therefore, and the partial structurtes of this light beam detection object 194; The Outboard Sections of incident beam passes lens ring, and focuses on the P.Overlapping by the back focus that makes P and object lens 192, the annular beam that collimates is incided on the body surface.Because compare the area of annulus with the lateral resolution of system bigger, so this system will provide average reference phase value, when scanning object, this phase value will keep ' constant '.After surface reflection, light beam passes through this system for the second time with backpropagation.As mentioned above, two light beams do not overlap.By specific lens 190 is tilted with respect to system's axle, provided the compact design that can cause two beam interferences among the figure.These two light beams are after secondary passes certain lenses, and its direction of propagation is mutually certain angle.In two light beam overlapping areas, form interference fringe.Any surface elevation changes the change of the optical phase value that will cause focused beam, and this is again with the position of moving striation.By at first using CCD camera (not shown) pickup light striped can measure the latter, then the data of taking are carried out Fourier transform, the measurement that provides.In addition, can use photodetector array (four elements are just enough) to take a striations.Then, can adopt standard analog orthogonal signal disposal route that fringe position is provided in real time.Because two light beams are by same light path, so microphonics will influence two light beams in the same manner, thereby its influence will be offset in interventional procedures and be constituted a very stable system.Compare with other common optical pathways structure, its another advantage is that there is better low spatial frequency response in described system.Therefore, can convert measured profile to meet international measurement standard profile with high precision.
Figure 10 represents the full visual field ellipsometer according to another program formation of the present invention.Can regard it as the full visual field optical microscope of a standard, wherein, can accurately control the angle and the polarization state of irradiates light.Control initial polarization state by for example half-wave plate 200 such devices.By the incident angle of illumination optics 204,206,208 control input beams 202, these optical device focus on incident light on the point ' a ' on the back focal plane 210 of object lens 212.The input optical device comprises spatial filter 206 and beam splitter 207.The incident angle of the illumination beam on the sample 214 has been determined in the radial position of this point.Is r as fruit dot ' a ' apart from the distance of the axis of lens, and the focal length of object lens is f, and incident angle is sin so -1(r/f).For accurate measurement, need to adopt object lens with large-numerical aperture.
According to this point, can regard this system the conventional microscope of imaging as to detector array.Dotted line is represented the opticpath from a point on the sample surfaces 216.Change the input polarization state that arrives sample and will change the image that on CCD camera 218, obtains.By at least three kinds of different polarization states of combination, can use this system to reproduce the map of material behavior.
Do not relying under the sample scan condition, native system just can obtain to have the oval symmetrical material information of good spatial resolution.It will provide for example quick map of semiconductor wafer of material surface.It is contemplated that with this system provides such as the quick spatial discrimination map of oxide thickness variations on the semiconductor wafer.Can monitor variation like this, the statistics of the standard deviation etc. of for example average thickness, thickness is provided simultaneously.Owing to adopt the mean value on a large amount of pixels, so thickness average value will have especially little uncertainty.Because the good visual field that the acquisition that single measurement had is observed is so this system also is provided at the possibility that scans on the large tracts of land.
Figure 11 represents to be used to obtain the device 10 of the true profile information of relevant sample 12.Laser instrument 14 produces linearly polarized light 16, and this polarized light is by beam splitter 18 and object lens 20 back irradiation samples 12.
Reflected light leaves beam splitter at 22 places, passes lens 24, then by 26 beam splitting of second beam splitter, passes on profile measurer (generally representing with 28) and the ellipsometer (generally representing with 30).As described below, profile measurer 28 produces the data that comprise true profile information and relevant material information.Give processor 34 this information (being expressed as 32 among the figure), this processor also receives (being expressed as 36 among the figure) information from the relevant material of ellipsometer, therefore, can provide true profile information in output 38.
Profile measurer partly is used to obtain differential phase information.Projecting with lens 24 on the plane with the sample plane conjugation that makes object lens 20 focusing thereon from the light of sample 12 reflection.Shadow shield 40 is arranged on these conjugate planes.It is the amplification that focuses on cross direction profiles on the sample that light on these conjugate planes distributes.If the phase place that relatively should distribute on the diverse location that the optical axis symmetria bilateralis is provided with, the phase differential between the two positions will be represented the phase differential on sample surfaces so.By (for example, the edge of washing layer on) the sample, understanding this point by a phase step focusing on imaging.Half of reflected light class image is reflected in phase value on one side of this hot spot, and the opposite side of focal beam spot image will be phase reflection on the opposite side of phase step simultaneously.Obviously, phase differential is represented the structures of samples feature.On the other hand, if sample is uniform (smooth), the phase place of each hot spot will be identical on the conjugate planes so, will not produce phase differential.In order to measure differential phase, must measure the phase place on two complimentary positions.This can adopt interferometer structure to finish.
Shadow shield 40 is used to selective light on two positions of conjugate planes.These positions are provided with the both sides of axle formerly symmetrically.Then, the light of selection passes transform lens 41, will project on the charge-coupled device (CCD) camera 42 from the photodistributed Fourier transform that shadow shield 40 penetrates.On the shadow shield two named a person for a particular job and produce one group of interference of light striped on the CCD camera, and its degree of modulation and phase place are represented from the amplitude ratio and the phase differential of the light of two holes ejaculations.Interfere the spacing in hole and the cycle and the direction of orientation decision striated pattern by two.The simple numerical Fourier transform can promptly be calculated amplitude ratio and phase differential.
Use profile measurer 28, shadow shield is arranged on the plane with the focussing plane conjugation.Below, we suppose to adopt the detecting device of placing on two diverse locations of conjugation image plane, and we can measure as the amplitude of scanning position function and the response of phase place.In fact, this can utilize have two holes separating in the optical axis both sides and on optical axis the shadow shield of the 3rd standby reference bore realize.Then, if possible, to the amplitude of the striped that forms and phase place is measured or with the comparing of axial setting.Figure 12 represents suitable shadow shield configuration.Suppose that we have and corresponding two the independently outputs of the slightly different transition function that is produced by different hole sites, we can write two outputs and pluralize so:
i 1(x s)=a 1(x s)exp(jφ 1(x s))
i 2(x s)=a 2(x s)exp(jφ 2(x s))
These two outputs can be expressed as object function T (m) and two transition function C 1(m) and C 2(m) Fourier transform, this output is corresponding to the response of using two detecting devices that separate 37,39.Therefore, response i 1(x s) and i 2(x s) can be expressed as:
i 1(x s)=F -1{C 1(m)T(m)}
i 2(x s)=F -1{C 2(m)T(m)}
Obviously, do not having under the situation of microphony, allowing to be finally inversed by function T (m) with simple Fourier transform from the response of each detecting device.Problem is that microphony has destroyed this information, therefore need obtain the method for transfer function T (m), keeps shared path information simultaneously.If two responses are divided by, can offset the microphony that each arm all has so.After two outputs were divided by, expression formula can be written as: i 0 ( x s ) = i 0 ( x s ) i 2 ( x s ) = a 1 ( x s ) a 2 ( x s ) exp ( j ( Φ 1 ( x s ) - Φ 2 ( x s ) ) )
Employing is to i 1(x s) and i 2(x s) the Fourier expression formula can calculate T (m) by integral formula.
F{i 0(x s)}*C 2(m)Tm(m)=C 1(m)T(m)
Then, can by standard step for example singular value decomposition separate and find the solution this equation.In case T (m) is obtained,, can easily obtain this response if the response of using another transition function to obtain is carried out suitable Fourier transform by the transition function with expectation so.
In order to realize the present invention, need two independent inputs.This can utilize the above-mentioned interference instrument to realize.
If do not obtain two independently values and only know and accurately to carry out division so by phase differential.But for weak phase object, the amplitude on each arm is identical, thereby phase differential has provided the good approximation to quotient, and when only knowing phase differential, above-mentioned steps is feasible.
At last, be noted that this method can not need differential configuration, any common optical pathways structure that can be used for input separately can be used.
The differential interferometer that can use other form is obtaining phase differential, the processing stage of finishing (1).
Stripe measurement result on the CCD camera is sent to processor 34, carries out digitized processing in this processor.
Use ellipsometer 30 can finish the obtaining step (2) of above-mentioned true profile.This comprises transform lens 50, and these lens form with lens 24 and object lens 20 and have the lens combination that is positioned at the back focal plane on second shadow shield 52.The back focal plane of lens comprises the information of being represented by the position of the light that arrives shadow shield 52, shown in Figure 13 a.Light can arrive any position around optical axis 54, for example in-position 56 and 58.The radial position of distance axis 54 is corresponding to the incident angle of the light of irradiation sample 12, and the position angle is corresponding to the irradiation polarized state of light.For the linear polarization incident light along Y-axis, the s polarized light will arrive certain point (for example, position 56) along the x axle, and the p polarized light will arrive the point (for example, the position 58) along Y-axis.Focus light on the charge-coupled image sensor 55 with lens 53.
Therefore, the light field on this plane comprises oval symmetric parameter ψ and needed all information of Δ obtained.We advise realizing that a kind of method of this purpose is the shadow shield configuration of adopting shown in Figure 13 b, so that according to the amplitude and the phase place that project the striped on the CCD camera through transform lens 50, obtain amplitude ratio (tan ψ) and phase difference.These values allow to obtain the refractive index of material, thereby can promptly calculate the phase shift relevant with material behavior.
The Fourier plane ellipsometry allows to obtain material information, keeps the whole lateral resolution relevant with the numerical aperture of lens simultaneously, and other method also can be used for get parms ψ and Δ, comprises interferometer or polarizer.Above-mentioned hatch method allows phase difference is expressed as skew in the interference fringe, and this striped is not subjected to heteropical influence of any intensity of light beam.
Yet for successfully obtaining profile, can enough whole spatial resolution relevant determine that material behavior is important with lens, if do not consider the detection method that uses in back focal plane, for this, the Fourier plane ellipsometry is effective method.
Although specific embodiment of the present invention has been described specially, can carry out various changes within the scope of the invention.For example, although illustrated with lens radiation is focused on above the specimen, also can use other method, for example holographic method in order to reach this purpose.When test surfaces was essentially on-plane surface, this replacement method had special meaning.

Claims (23)

1. optical measuring device, comprise optical emitter (2) beam generated device (HDE), be used for producing main beam (4) and secondary light beam (6) from described optical emitter, it is characterized in that, described main beam (4) directive object (8), so that survey the partial structurtes of object, described secondary light beam (6) is radiated on the described object as reference light; Light processor (HDE) is used for producing three grades of light beams and level Four light beam by described main beam and described secondary light beam from described object reflection back; And beam merging apparatus (HDE), described three grades of light beams and level Four light beam are closed bundle, with near the light signal of the structure the described body surface of acquisition expression.
2. according to the optical measuring device of claim 1, it is characterized in that, described beam generated device comprises hologram diffraction unit (HDE), be fit to produce the parallel object beam of zero level (4), with as with reference to light beam+1 grade of convergent beam, also comprise treating apparatus (HDE), be used for being created in each the parallel component light beam that has difference on its direction of propagation according to from described described light beam and described reference beam with reference to reflection; Beam merging apparatus is with the beam splitting of described two parallel component light beams, so that obtain near the conoscope image of the architectural feature the described reference surface of expression.
3. according to the optical measuring device of claim 2, it is characterized in that it comprises by the intensity pattern that obtains is carried out Fourier transform, obtains the device of the average phase-difference of parallel component light beam.
4. according to the optical measuring device of claim 2, it is characterized in that it comprises the analogue orthogonal signal treating apparatus that is used to obtain the photodiode array of the single striped of described conoscope image and is used to derive its phase value.
5. optical measuring device, comprise optical emitter (2) beam generated device, be used for producing main beam (4) and secondary light beam (6) from described optical emitter, it is characterized in that, it comprises the ellipticity measurement mechanism, this device comprises lens devices (20), to focus on the back focal plane from the light of sample reflection, selecting arrangement (40), from the light that arrives back focal plane, select the light of at least two different polarization states, and measurement mechanism (42), be used to measure the parameter of selected light, can be to provide according to the information of its calculation sample characteristic.
6. according to the optical measuring device of claim 5, it is characterized in that measurement mechanism also comprises the device that makes the selected interference of light.
7. according to the optical measuring device of claim 6, it is characterized in that measurement mechanism can be measured the amplitude and the phase place of the striped that is caused by interference.
8. according to the optical measuring device of claim 5, it is characterized in that selecting arrangement comprises the shadow shield that is located on the back focal plane, it has opening on the position with respect to the polarization state of selecting, thereby other polarized light is blocked by shadow shield.
9. according to the optical measuring device of claim 5, it is characterized in that selecting arrangement comprises shadow shield, the opening that selected light is passed through is arranged in shadow shield; And tripping device, the p polarized component of the light that passes the shadow shield opening is separated with the s polarized component.
10. according to the optical measuring device of claim 9, it is characterized in that tripping device is used for spatially separating polarized component.
11. the optical measuring device according to claim 10 is characterized in that tripping device comprises Wollaston prism.
12. the optical measuring device according to claim 5 is characterized in that, selecting arrangement comprises the phase splitting device, is used for selected light is applied differential phase shift.
13. the optical measuring device according to claim 12 is characterized in that, the phase splitting device comprises general kerr cell.
14. the optical measuring device according to claim 13 is characterized in that, controls general kerr cell selectively, to change differential phase shift, measures thereby allow to carry out each group with measurement mechanism.
15. the optical measuring device according to claim 5 is characterized in that it comprises lens devices, with producing interference so that the component that separates merges together.
16. the optical measuring device according to claim 15 is characterized in that, lens devices comprises that its logical optical axis divides the polariscope device of p direction and s direction equally.
17. optical measuring device, comprise optical emitter (2) beam generated device, be used for producing main beam (4) and secondary light beam (6) from described optical emitter, it is characterized in that, it comprises contour outline measuring set, this contour outline measuring set comprises lens devices, in order to focus on by the light of sample to the reflection conjugate planes; Selecting arrangement is in order to select in the conjugate planes light on two diverse locations; And measurement mechanism, be used to measure the parameter of selected light, from this parameter, can obtain relevant sample profile information.
18. the optical measuring device according to claim 17 is characterized in that, selecting arrangement can be included in the shadow shield that two positions have opening.
19. the optical measuring device according to claim 18 is characterized in that, two positions are symmetrically located at the both sides of systematic optical axis.
20. the optical measuring device according to claim 19 is characterized in that, measurement mechanism comprises the device that causes the selected interference of light.
21. the optical measuring device according to claim 20 is characterized in that, measurement mechanism also comprises the transform lens device, in order to the Fourier transform of the light of scioptics is projected on the plane that forms interference of light striped thereon.
22. optical measuring device, comprise and have the optical emitter that is used for the device (207) of described radiation directive sample, it is characterized in that described device comprises selecting arrangement (200,204,208,212), in order to select to be incident on the polarization and the direction of the described light beam on the described sample; And sniffer (218), be used to survey the radiation of the described light beam of the selected regional scattering that comes free described sample surfaces.
23. the optical measuring device according to claim 20 is characterized in that, the device that produces described main beam and secondary light beam is included in the plano-convex lens (190) that has center plane region on its shaped form surface.
CN 97196506 1996-05-18 1997-05-16 Optical measurement Pending CN1225720A (en)

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EP0900356A1 (en) 1999-03-10

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