CN103162831B - Broadband polarization spectrograph and optical measurement system - Google Patents

Abstract

The invention provides a broadband polarization spectrograph. The broadband polarization spectrograph comprises a first reflection unit, a first condensation unit, a second condensation unit, a polarizer, a first plane mirror, a first curved surface mirror, a second refection unit, and a detection unit. A vertical incidence broadband polarization spectrograph which comprises reference beams improves light flux efficiency of detection beams, and complete combination of non-detection beams which act as the reference beams and the detection beams after beam split is achieved at the front end of a detector. In addition, the detection beams can focus on the surface of a sample without chromatic aberration, and meanwhile a polarization state of the detection beams is further maintained, and the complexity of a system is lower compared with the prior art. The invention further provides an optical measurement system which comprises the broadband polarization spectrograph.

Description

Wideband polarization spectrometer and optical measuring system

Technical field

The present invention relates to optical field, particularly a kind of wideband polarization spectrometer and optical measuring system.

Background technology

Along with the fast development of semicon industry, the three-dimensional appearance that utilizes optical measuring technique to detect quickly and accurately thickness, material behavior and the periodic structure of semiconductive thin film is production control process, the key link of boosting productivity, is mainly used in the industry that integrated circuit, flat-panel monitor, hard disk, solar cell etc. comprise membrane structure.Utilize the film of different materials, different structure, at different wave length, the incident light of different polarization states is had to different reflectivity, its reflectance spectrum has uniqueness.Current advanced film and three-dimensional structure measuring equipment, as ellipsometer test and optics critical dimension measuring instrument (Optical Critical Dimension, be called for short OCD) be required to meet the spectral measurement ability of trying one's best wide to increase measuring accuracy, be generally 190nm to 1000nm.In the situation that membrane structure parameter is known, light reflecting thin film spectrum can draw by calculated with mathematical model.In the time there is unknown structure parameter, for example film thickness, Film Optics constant, surface three dimension structures etc., can be by regretional analysis, matching measurement and analog computation spectrum, thus draw unknown structure parameter.

In general, the optical measurement of semiconductive thin film is had to two kinds of methods conventionally, absolute reflectance mensuration and ellipsometric measurement method.Described in Chinese patent application 201110032744.8, while using absolute reflectance mensuration to measure, need to first use standard model to measure, and the measurement result of record standard sample is as reference value, and then measurement testing sample, and compared with the reference value that the measurement result of testing sample is measured with standard model, thereby obtain the relative actual value of testing sample.Due to light source itself, in actual measurement process, its spectral intensity may change (drift).The spectral intensity of generally supposing in theory light source is duplicate in the time of measurement standard sample and testing sample, but in fact, due to testing sample and standard model cannot be measured at synchronization, the spectral intensity of light source changes can affect measurement result.

In view of the foregoing, those skilled in the art has proposed to utilize reference beam to carry out regulation light source fluctuating.The light sending by light source is divided into two bundles, wherein a branch of optical information as surveying optical recording sample, another bundle conduct is with reference to light, by the measurement to reference beam, the spectral intensity of light source can record respectively witness mark sample and testing sample time, thereby the spectral intensity of light source changes in correction measurement process, improve measuring accuracy.

Measuring equipment is divided into conventionally with respect to the optical system of sample surfaces vertical incidence with respect to the optical system of sample surfaces oblique incidence.The optical system of vertical incidence, conventionally can be integrated with other process equipments because structure is compacter, realizes and producing and integration and the Real-Time Monitoring measured.In prior art, utilize the implementation method of the vertical incidence spectrometer of reference beam calibration to mainly contain following two kinds:

(1) as shown in Figure 1, the diverging light of light source 101 outgoing after lens 102, the parallel optical splitter 103 that is incident to, through optical splitter, the light of 103 transmissions after passing through is as detecting light beam, the light being reflected by optical splitter 103 is as with reference to light beam.Detecting light beam focuses to sample 105 surfaces after lens 104 are assembled, the reflected light on sample 105 surfaces after lens 104 reflections, vertical incidence optical splitter 103, detecting light beam after optical splitter 103 reflections, assemble through lens 107, be incident to detector 108, obtain the reflectance spectrum of sample surfaces; Reference beam vertical incidence is to plane mirror 106, vertical incidence optical splitter 103 after plane mirror 106 reflections, reference beam after optical splitter 103 transmissions is also assembled through lens 107, be incident to detector 108, the reference spectra (for example,, referring to U.S. Patent No. 7067818B2, No.7189973B2 and No.7271394B2, U.S. Patent Application Publication No.2005/0002037A1) that acquisition comprises light source light spectrum feature.In this spectrometer, can utilize control diaphragm to select the light beam of required measurement.This method has following benefit: can rise and fall by regulation light source, but owing to having adopted optical splitter, also there is following problem in this spectrometer: 1. luminous flux is low, in a whole measurement process, light beam need and be reflected respectively once through same optical splitter transmission by light source, enters detector.Suppose that optical splitter is that transmissivity and reflectivity are each 50%, the highlight flux ratio that detecting light beam and reference beam can reach is 25%; If 2. realize high-quality hot spot and wider spectral range simultaneously, need to solve the problem of dispersion, system complexity and cost are all higher.

(2) in light path, insert a plane mirror, the light part that light source sends is incided on plane mirror, another part passes through from the edge of plane mirror.Light beam after plane mirror reflection impinges perpendicularly on sample surfaces as surveying light, the light beam passing through from plane mirror edge is as with reference to light beam, detecting light beam and reference beam enter respectively two different spectrometers and measure (for example,, referring to U.S. Patent No. 5747813 and No.6374967B1) simultaneously.This method has following benefit: in measuring process, detecting light beam and reference beam can be measured simultaneously, has proofreaied and correct accurately spectrum and the Strength Changes of light source; In system, the loss of light intensity is less, and utilization factor is high.But owing to having used two different spectrometers, its electricity conversion is not quite similar, Wavelength distribution and resolution are also not quite similar, be difficult for calibration system, can reduce on the contrary measuring accuracy, on the other hand, the light channel structure more complicated of this scheme, be difficult for regulating, and two spectrometer meeting increasing device volumes, equipment cost increased.

In the time detecting general size and be the wafer of 150 millimeters, 200 millimeters or 300 millimeters, due to reasons such as the thin layer stress on wafer, wafer surface may be uneven.Therefore, in the time that whole wafer is detected, in order to realize the measurement of pinpoint accuracy and to ensure the Quick Measurement of semiconductor production line output, be, a crucial technology wherein to each measurement point automatic focus.And those skilled in the art is known, it is favourable that broadband detecting light beam is focused into relatively undersized hot spot on sample surfaces, because small size hot spot can be measured micro structured pattern, and broadband detecting light beam can improve measuring accuracy.In this case, in the time adopting lens to focus on, there are the following problems in meeting: lens have aberration conventionally, and such aberration can cause the focal position difference of the light of different wave length, increases error, reduces measuring accuracy; And, be difficult to find whole banded wavelength ranges is all had to good radioparent lens material.In view of the foregoing, those skilled in the art has proposed a kind of so method, use curved reflector, as elliptical mirror, toroidal reflectors (toroidal mirror), broadband detecting light beam is focused on (for example,, referring to U.S. Patent No. 5608526 and No.7505133B1, U.S. Patent Application Publication No.2007/0247624A1 and the open No.101467306A of Chinese patent application) on sample surfaces by off-axis parabolic mirrors etc.This method has following benefit: in whole banded wavelength ranges, catoptron can not produce aberration, and catoptron can all have high reflectance in wider wavelength coverage.But light beam can change through single catoptron reflection rear polarizer state.Here taking an aluminum catoptron as example.Reflectivity Rs and the Rp of S and P polarized light in two kinds of incident angle situations shown in Fig. 2 a.The reflectivity Rs that two curves are above S polarized lights, the reflectivity Rp that two curves are below P polarized lights.Solid line is corresponding to the incident angle of 45 degree, and dotted line is corresponding to the incident angle of 50 degree.Hence one can see that, and the reflectivity of S or P polarized light is unequal, and changes along with the difference of incident angle.S after reflection shown in Fig. 2 b and the phase differential between P polarized light, solid line is corresponding to the incident angle of 45 degree, and dotted line is corresponding to the incident angle of 50 degree.Hence one can see that, and the phase differential between the S after reflection and P polarized light changes, and changes along with the difference of incident angle, and relevant to wavelength.In a word, when broad band light beam is after catoptron reflection, the polarization state S orthogonal due to polarization direction has not identical reflectivity and phase place variation separately with P, the polarization state of light beam changes, cause being difficult to control the polarization variations (for example,, referring to U.S. Patent No. 6829049B1 and No.6667805) of light beam.

Spectrometer defines the range of application of spectrometer to the control ability of polarization.For example, be widely used in now the optics critical dimension equipment OCD of integrated circuit production line technology controlling and process by measuring reflectance spectrum and the phase characteristic of polarized light at sample surfaces, matching Numerical Simulation Results, thickness and the optical constant of critical dimension (CD), three-dimensional appearance and the multilayer material of measurement sample surfaces periodic patterns.The spectrometer of realizing critical dimension measurement requires its focusing system must accomplish to control the polarization state of light beam in focusing and light signal collection process, thereby can measure exactly sample.

Summary of the invention

Technical matters to be solved by this invention is to provide a kind of no color differnece of realizing, and keeps polarization characteristic, and light logical efficiency is high and be easy to the wideband polarization spectrometer and the optical measuring system that realize.

According to an aspect of the present invention, provide a kind of wideband polarization spectrometer to comprise light source, the first reflector element, the first light focusing unit, the second light focusing unit, polarizer, the first plane mirror, first surface catoptron, the second reflector element, probe unit, wherein:

Described the first reflector element is divided into detecting light beam and reference beam two parts for the light beam that described light source is sent, and this two parts light beam is incident to respectively to described the first light focusing unit and described the second light focusing unit;

Described the second reflector element is used for receiving at the same time or separately from the detecting light beam of the described first surface catoptron of process successively of sample reflection, described the first plane mirror, described polarizer, described the first light focusing unit with by the reference beam of described the second light focusing unit, and received light beam is incident to described probe unit;

Described the first light focusing unit is used for receiving described detecting light beam, is incident to described polarizer after making this light beam become parallel beam;

Described polarizer is arranged between described the first light focusing unit and described the first plane mirror, for make described parallel beam by and be incident to described plane mirror;

Described the first plane mirror is used for receiving described parallel beam and this parallel beam is reflexed to described first surface catoptron;

Described first surface catoptron is used for and described parallel beam is become to convergent beam, and will after this convergent beam reflection, vertically focus on sample;

Described the second light focusing unit is used for receiving described reference beam, and is incident to described the second reflector element;

Described probe unit is for surveying the light beam being reflected by described the second reflector element.

According to another aspect of the present invention, provide a kind of optical measuring system to comprise described perpendicular incident broadband spectrometer.

The wideband polarization spectrometer that comprises reference beam provided by the invention has been realized the complete combination of the light beam after light splitting, improve the logical efficiency of light of detecting light beam, in addition, can also make detecting light beam no color differnece and focus on sample surfaces, keep the polarization state of light beam, and the complexity of system is lower than prior art simultaneously.

Brief description of the drawings

Fig. 1 realizes light splitting and the schematic diagram that closes light by optical splitter in prior art.

Fig. 2 a is S and the reflectivity Rs of P polarized light and the schematic diagram of Rp in two kinds of incident angle situations.

Fig. 2 b is the schematic diagram of the phase differential between S and the P polarized light illustrating after reflection.

Fig. 3 a to Fig. 3 c is for explaining by the basic principle schematic of the polarization characteristic of two plane mirrors or a plane mirror and an off-axis parabolic mirror maintenance polarized light.

Fig. 4 is the schematic diagram that the calculation level in incident light xsect distributes.

Fig. 5 can draw by curve the schematic diagram of the peaked position of quafric curve by the measured value of first three diverse location (, A, B and C position).

Fig. 6 is the optical schematic diagram that Rochon prism polarizer (Rochon Polarizer) is shown, in the figure, RP represents Rochon prism polarizer, and A represents diaphragm, S representative sample.

Fig. 7 a and 7b be in the present invention by two not coplanar flat catoptron realize the schematic diagram of light splitting.

Fig. 8 be in the present invention by two not coplanar flat catoptron realize and close the schematic diagram of light.

Fig. 9 a and Fig. 9 b are beam cross-section shape and the light beam imagings after light of closing obtaining by simulation.

Figure 10 is the periodically structural drawing of shallow trench of monocrystalline silicon.

Figure 11 is the periodically absolute reflectance spectrogram of shallow trench TE and TM of monocrystalline silicon in absolute reflectance mensuration.

Figure 12 a is the schematic diagram illustrating according to the vertical incidence wideband polarization spectrometer of first embodiment of the invention.

Figure 12 b utilizes optical splitter and the index path of pattern identification system to sample surfaces and detecting light beam focal imaging in the present invention.

Figure 13 a and Figure 13 b are the patterns arriving by pattern identification systematic observation.

Figure 14 is the schematic diagram illustrating according to the vertical incidence wideband polarization spectrometer of second embodiment of the invention.

Figure 15 is the schematic diagram illustrating according to the vertical incidence wideband polarization spectrometer of third embodiment of the invention.

Embodiment

For problems of the prior art, the present invention proposes a kind of no color differnece of realizing, keep polarization characteristic, the high and vertical incidence wideband polarization spectrometer that utilizes reference beam calibration that is easy to realize of light logical efficiency.In this spectrometer, the highlight flux ratio of detecting light beam and reference beam can reach 50%, and, vertical incidence wideband polarization spectrometer of the present invention only comprises a spectrometer, therefore, the spectrometer measurement precision that the present invention proposes is higher, and complexity and equipment cost are lower than prior art simultaneously.In addition, this vertical incidence light belt spectrometer at least comprises a polarizer, thereby can accurately measure anisotropy or non-homogeneous sample, as the three-dimensional appearance of the film that comprises periodic structure and material optical constant.

Explain by the ultimate principle of the polarization characteristic of two plane mirrors or a plane mirror and an off-axis parabolic mirror maintenance polarized light below with reference to Fig. 3 a, 3b and 3c.

As shown in Figure 3 a, suppose that S (or P) light beam taking the M1 plane of incidence as reference is incident on the first plane mirror M1 above with the incident angle of (90-θ) degree, and reflexed to the second plane mirror M2 by the first plane mirror M1.When the plane of incidence of the first plane mirror M1 and the plane of incidence of the second plane mirror M2 mutually vertical, and when M2 degree of tilt meets the reflected light that makes M1 and is incident to M2 with (90-θ) degree incident angle, change P (or S) polarized light taking the M2 plane of incidence as reference into through the S taking the M1 plane of incidence as reference (or P) polarized light of M1 reflection.

Now the right hand reference frame taking direction of beam propagation as+Z orientation determination is analyzed the propagation of light beam and the variation of polarization state.Said process is expressed with mathematical formulae:

$\left\{\begin{array}{c}\mathrm{Ex}=E_{1s}\\ \mathrm{Ey}=E_{1p}\end{array}\right.---\left(a\right).$

Polarized component E taking the M1 plane of incidence as reference _1s, E _1pbe defined as respectively in right hand reference frame+X and+Y-direction component.After M1 reflection,

$\left\{\begin{array}{c}{E}_{1s}^{\′}=r_{1s}{E}_{1s}\\ E_{1p}^{\′}=r_{1p}{E}_{1p}\end{array}\right.---\left(b\right).$

E ' _1s, E ' _1pbe respectively the reflected light polarized component taking the M1 plane of incidence as reference; Wherein, r _1sand r _1pbe respectively S taking the M1 plane of incidence as reference and P light polarization component and be incident on the reflectivity of the first plane mirror M1 with the angle of (90-θ).And,

$\left\{\begin{array}{c}{E}_{2s}=E_{1p}^{\′}\\ E_{2p}=-E_{1s}^{\′}\end{array}\right.---\left(c\right).$

E ' after M1 reflection _1s, E ' _1pbe respectively the incident polarization component-E taking the M2 plane of incidence as reference _2p, E _2s.After M2 reflection,

$\left\{\begin{array}{c}{E}_{2s}^{\′}=r_{2s}{E}_{2s}\\ E_{2p}^{\′}=r_{2p}{E}_{2p}\end{array}\right.---\left(d\right).$

E ' _2s, E _2pbe respectively the reflected light polarized component taking the M2 plane of incidence as reference, r _2sand r _2pbe respectively S taking the M2 plane of incidence as reference and P light polarization component and be incident on the reflectivity of the second plane mirror M2 with the angle of (90-θ).

Due to the right-hand rule, the S light polarization direction taking the M1 plane of incidence as reference is the P light negative direction taking the M2 plane of incidence as reference.Be defined in the be always+X-axis of S light polarization component taking the M1 plane of incidence as reference in the right hand reference frame taking direction of beam propagation as+Z orientation determination.This light beam is after M2 reflection, and the P light polarization direction taking the M2 plane of incidence as reference is X-axis positive dirction; So obtain, the S light polarization direction taking the M2 plane of incidence as reference is Y-axis negative direction.Have:

$\left\{\begin{array}{c}{E}_{2p}^{\′}=E_x^{\′}\\ E_{2s}^{\′}=-E_y^{\′}\end{array}\right.---\left(e\right).$

E ' _x, E ' _yfor emergent light polarized component.Have identical reflecting material and coating structure at M1 and M2:

$\left\{\begin{array}{c}{r}_{1s}=r_{2s}\\ r_{1p}=r_{2p}\end{array}\right.---\left(f\right).$

Comprehensive above formula has:

$\{\frac{E_x}{E_y}=\frac{E_x^{\′}}{E_y^{\′}}---\left(g\right).$

In above formula (a)-(g), all variablees are plural number.From formula (g), emergent light polarized component ratio equals incident light polarization component ratio.Therefore,, by above-mentioned two plane mirrors, can keep the polarization characteristic of polarized light.

According to above-mentioned formula (a)-(e), those skilled in the art will appreciate that as long as the first plane mirror M1 and the second plane mirror M2 meet r _2sr _1p=r _2pr _1srelation, just can obtain the relation of formula (g).That is to say, if two catoptrons meet r _2sr _1p=r _2pr _1srelation, by these two catoptrons, can keep the polarization characteristic of polarized light.Hence one can see that, can ideally keep polarization characteristic to incident light by two plane of incidences system that the vertical and identical plane mirror of incident angle forms mutually.

In the case of one of them in two plane mirrors above hypothesis is alternative by the reflecting material off-axis parabolic mirror identical with coating structure, the situation of small value aperture (NA, numerical aperture) is carried out to analog computation.Although light beam through having deviation on polarization characteristic after the system being made up of plane mirror and off-axis parabolic mirror, in the time that parallel beam is realized focusing with little NA, the deviation of polarization characteristic is not enough to the accuracy that impact is measured.For harsh polarization requirement, can further utilize numerical evaluation correcting measured results.

If first plane mirror M1 in above-mentioned two plane mirrors is replaced by off-axis parabolic mirror OAP, taking Fig. 3 b as example, directional light is circularly polarized light before inciding off-axis parabolic mirror OAP,, Ex=Ey, and Phase (Ex)-Phase (Ey)=90 degree, wherein, Ex and Ey are respectively the amplitudes of light beam electric vector in the x and y direction, and Phase (Ex) and Phase (Ey) are respectively the phase places of light beam electric vector in the x and y direction.After off-axis parabolic mirror focuses on, the cone half-angle that focused beam forms is 4.2 degree (NA=0.073).Lambda1-wavelength is 210nm, and the calculation level in incident light xsect distributes as shown in Figure 4, altogether 29 points (part is demarcated, and for example, (0,3) is to (0,0)).After numerical evaluation, change and listed by table 1 in the Strength Changes of the polarization at focus place and phase place.Polarization Strength Changes is defined as | and Ex/Ey|-1, phase place is changed to Phase (Ex)-Phase (Ey)-90.As can be seen from Table 1, with (0,0) there is quite approaching complementarity in light beam in a center of symmetry aspect polarization intensity and phase place variation, so can further be offset when incident light vertical incidence to the polarization deviation in the time that plane mirror M2, off-axis parabolic mirror OAP1 return after sample.

Table 1

If second plane mirror M2 in above-mentioned two plane mirrors replaced by off-axis parabolic mirror OAP1, taking Fig. 4 c as example, by the directional light after plane mirror M1 reflection, after off axis paraboloid mirror OAP1 focusing mirror, the cone half-angle that focused beam forms is 6.3 degree (NA=0.109734).In other conditions situation identical with table 1, after numerical evaluation, change and listed by table 2 in the Strength Changes of the polarization at focus place and phase place.As can be seen from the table, with (0,0) there is quite approaching complementarity in light beam in a center of symmetry aspect polarization intensity and phase place variation, with the point (3 of polarization phase deviation maximum, 0) be example, after the system of plane mirror and off-axis parabolic mirror formation, its phase deviation is 4.7508 degree, but in the time that detecting light beam is returned by sample surfaces, this calculation level light beam is reflected onto point (3,0), the phase deviation of this point can obtain the quite counteracting of size (4.3325 degree).So when incident light vertical incidence to the polarization deviation in the time that off-axis parabolic mirror OAP1, plane mirror M1 return after sample can further be offset.Be that the present invention can further offset the polarization impact that curved reflector causes on the whole.

Table 2

Therefore, adopt such system being formed by off-axis parabolic mirror and plane mirror not only can realize incident light and focusing at sample surfaces no color differnece, and substantially also can keep the polarization characteristic of polarized light.

Only enumerate the situation that substitutes one of above-mentioned two plane mirrors with the reflecting material off-axis parabolic mirror identical with coating structure above.Those skilled in the art will be appreciated that, not only plane mirror and off-axis parabolic mirror, comprise other curved reflector, if toroidal reflectors, ellipsoidal mirror or non-quadric surface catoptron etc. are interior, when any two kinds of catoptrons meet above-mentioned relation, can substantially keep the polarization characteristic of polarized light.

In sum, if it is identical mutually vertical (in the error range allowing in this area with plane of incidence that two catoptrons have approximately uniform reflecting material and approximately uniform coating structure and meet the incident angle of main beam,, include the approximate identical and approximate orthogonal situation of plane of incidence of firing angle) condition, random polarization light remains unchanged through its polarization characteristic after these two catoptrons.The example with the catoptron of identical reflecting material and coating structure is to remain on homogeneous plated film in same vacuum chamber and the catoptron that obtains.

In addition, those skilled in the art can know, detecting light beam is in the time that sample surfaces focuses on, in order to make detecting light beam obtain less spot size and better image quality at sample surfaces, the numerical aperture that makes the numerical aperture of sample surfaces focused beam be more than or equal to pointolite place light beam is more favourable, and for fixing distance, the numerical aperture of pointolite place light beam is larger, the actual light beam light flux of collecting is larger, therefore, adopt the focus method of Fig. 4 c can make detecting light beam obtain larger numerical aperture compared with Fig. 4 b, , can obtain larger luminous flux, improve measuring accuracy.

As described below, in broadband light spectrometer of the present invention, there are two kinds of methods to realize focusing.

First method is that the catoptrical change in signal strength of collecting by observation realizes focusing.Than focus state, in spectrograph slit position, after calibration, out of focus can cause the part light of hot spot periphery to lose in collection optical system.On the preliminary basis focusing on, can obtain focusing the most accurately by finding light signal maximal value.Mathematical method and the basic step of fast searching focus can be: near focus, the relation of light signal strength and out of focus distance is approximately to quafric curve type, that is and, parabola shaped: I=-A (x-x ₀) ²+ B, wherein, I is light signal strength, x ₀for focal position, A, B is coefficient.As shown in Figure 5, can draw the peaked position of quafric curve by curve by the measured value of first three diverse location (, A, B and C position); Taking the measured value of this position as newly-increased numerical point, again matched curve; With the method iteration until in theory meet | x _n+1-x _n| < σ, wherein x _nbe the position of the n time focusing, x _n+1for the n+1 time focusing position simulating in the measured value situation increasing by the n time focusing position, σ is the degree of accuracy that system is adjusted.

Second method is that the imaging definition by observing sample surfaces in described pattern identification system is realized focusing.At desirable focus state, at pattern identification alliance after calibration, sample surfaces while focusing, have the most clearly as.In the situation that image resolution ratio is definite, the sharpness of image is determined by the acutance (Sharpness) of image.The contrast at acutance presentation video edge.Or rather, acutance is the derivative amplitude of brightness for space.On the preliminary basis focusing on (that is, sample surfaces can identify in described pattern identification system), can lead to adjusting focal length and synchronously calculate image definition.So, can obtain focusing the most accurately in conjunction with mathematical method and the basic step of above-mentioned fast searching focus

For the polarizer adopting in the present invention, can adopt Rochon prism polarizer RP as shown in Figure 6.The material of Rochon prism polarizer can be MgF ₂, a-BBO, kalzit, YVO ₄or quartz.Rochon prism polarizer utilizes birefringece crystal (o light is different from the refractive index of e light) to make the outgoing that forms an angle during by 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.Different materials has different transmitted spectrum scopes, MgF ₂can reach the spectral range of 130-7000nm.Because different materials has different o light and e optical index, so the angle of the o light in transmitted light and e light is not identical yet.For example,, for MgF ₂or quartz, the angle of o light and e light is 1 to 2 degree, but, for a-BBO or YVO ₄, this angle can reach 8 to 14 degree.This angle also partly depends on the corner cut θ of Rochon prism.When detecting light beam transmission is by after polarizer, o light is vertically incident to sample S, and e light is incident to sample S obliquely with angle α; When e light is in the time that the folded light beam of sample surfaces can enter within the scope of polarizer optical aperture, its e reflection of light light beam can reflex to polarizer equally, then enters detector, thereby impact is measured.For the larger polarizer in e light drift angle, its e light is difficult for reentering polarizer at the reflected light of sample surfaces.In order to improve measuring accuracy, avoid the impact of e reflection of light light, the position that the o light above sample surfaces separates with e light can arrange diaphragm A (as shown in Figure 6), to avoid e light to be incident to sample surfaces or its reflected light is reflected back polarizer.

Describe by respectively comprising two not the first reflector element of coplanar flat catoptron and the processes that the second reflector element is realized respectively light splitting and closed light below with reference to Fig. 7 a, Fig. 7 b and Fig. 8.

(1) realize light splitting: as shown in Figure 7a, suppose: from the divergent beams of pointolite, after light source light focusing unit, as, toroidal reflectors (M6) (or achromat), form convergent beam, and after deflecting, be incident to the first reflector element in the plane of incidence.The first reflector element is made up of two not coplanar plane mirror M4 and M5, plane mirror M4 contains a linear edge, and in the light path of this linear edge in above-mentioned convergent beam, the half of this convergent beam, be incident on plane mirror M4, after plane mirror M1 reflection, in the plane of incidence, deflect, form convergent beam B1.Another part convergent beam passes through from the linear edge of plane mirror M1, is incident to plane mirror M5, after plane mirror M5 reflection, in the plane of incidence, deflects, and forms convergent beam B2.The major axes orientation of plane mirror M5 tilts slightly with respect to plane mirror M4 in the plane of incidence, can make respectively convergent beam B1 after plane mirror M4 and M5 reflection and the main beam of B2 first intersect, and then separates, as shown in Figure 7a; Or, convergent beam B1 and B2 are directly separated, as shown in Figure 7b.Since then, from the light of pointolite, through the first reflector element, after plane mirror M4 and M5, being divided into can be respectively as the two-beam of surveying light and reference light.Before and after the light splitting, the key light of this two-beam is all the time in same plane, and the linear edge of plane mirror M5 is vertical with this plane.

In addition, if the transmitting light beam that pointolite sends is assembled (as toroidal reflectors or achromat) without light focusing unit, but directly incident, through the first reflector element of plane mirror M5 and M6 composition, can realize the effect of above-mentioned light splitting equally.

(2) realize and close light: as shown in Figure 8, the detecting light beam after sample reflection, Yan Yuanlu is back to reference beam institute planar time, is convergent beam.The second reflector element is made up of two not coplanar plane mirror M2 and M3, the detecting light beam returning from sample surfaces and reference beam are incident to respectively the plane mirror M2 and M3 of composition the second reflector element, plane mirror M2 at least contains a linear edge shape, and this linear edge is crossing with the main beam of detecting light beam, detecting light beam is after plane mirror M2 reflection, and incident also focuses in spectrometer SP.This spectrometer SP is positioned over the focus place of the detecting light beam of this convergence.Reference beam in same plane, through lens L or other collective opticses, as become convergent beam after reflecting objective, through plane mirror M2 reflection, deflects, and is incident in same spectrometer SP in the plane of incidence.By rotation and/or along direction of light (or in the other direction) plane of motion mirror M 3, can change the direction of propagation and/or the inflection point of reference beam, thereby the main beam that makes reference beam overlaps with the main beam of surveying light light beam, and reference beam and detecting light beam are independent of each other.The focal position of reference beam can be by regulating along reference beam direction of light (or in the other direction) mobile convergence lens L (not shown)., regulate plane mirror M3 and condenser lens L can make reference beam incident and focus in same spectrometer SP.Since then, can incident after the second reflector element reflection from the detecting light beam of different directions and reference beam and focus in same spectrometer SP.

According to the photoreduction process that closes shown in Fig. 8, the detecting light beam that simulation obtains and the reference beam beam cross section after the second reflector element reflection is as shown in Fig. 9 a, by suitable light path design, detecting light beam and reference beam incide in same spectrometer simultaneously to be surveyed, and in this process, their propagation each other that is independent of each other.Detecting light beam and reference beam focus on imaging as shown in Fig. 9 b on spectrometer, in Fig. 9 b, survey the focal beam spot that detecting light beam and reference beam form on spectrometer and vary in size, and this is due to due to the magnification difference in two-beam during focusing.In actual detection process, need to select the suitably measurement window (entrance slit) of size for spectrometer, so that reference beam can be detected as much as possible, thereby improve the signal to noise ratio (S/N ratio) of reference beam spectrum, reach the object that improves measuring accuracy.

Because plane mirror self does not affect the converged state of incident light and do not produce aberration, so adopt catoptron can change the direction of propagation of light beam in ensureing convergent beam quality.Detecting light beam and reference beam can focus in same spectrometer after above-mentioned two plane mirrors simultaneously.On the other hand, plane mirror can be realized the high reflectance within the scope of broadband spectral, very low on light intensity impact, in the present invention, the design of a spectrometer does not reduce the detection efficiency of spectrometer to detecting light beam and reference beam, therefore, the present invention, by suitable light path design, has realized the complete combination of the light beam after light splitting, thereby realized when improving the logical efficiency of light, the complexity of system is lower than prior art.

The present invention can adopt absolute reflectance mensuration, measures the absolute reflectance of two polarization states of sample on orthogonal directions.If measure the absolute reflectance of a sample, should do as follows:

A. the dark numerical value I of measure spectrum instrument _d0, the reading of spectrometer while entering spectrometer without light signal;

B. load reference sample, for example, naked silicon wafer, obtains spectrum numerical value I _si, and before or after witness mark sample the spectrum numerical value I of witness mark light beam at once _r0;

C. load and measure testing sample, obtain spectrum numerical value I, and before or after measuring testing sample the spectrum numerical value I of witness mark light beam at once _r;

D. the dark numerical value I of measure spectrum instrument _d;

In above-mentioned steps, step a and b only need operation once within a period of time, for example, and in one hour, in one day, in one week or several weeks.And step c and d should again operate in the time of each measurement.If environment temperature is constant, or the not change in time of the dark numerical value of spectrometer, I _dcan use I _d0replace.

Like this, the reflectivity of sample is:

$R=\frac{{I-I}_d}{(I_{\mathrm{Si}}-I_{d0})f\left(r\right)}R\left(\mathrm{Si}\right)=\frac{{I-I}_d}{(I_{\mathrm{Si}}-I_{d0})\left(\frac{I_R-I_d}{I_{R0}-I_{d0}}\right)}R\left(\mathrm{Si}\right)$

Wherein R (Si) is the absolute reflectance of reference sample, and R (Si) can obtain from other measurements, or logical the property calculation of reference sample is drawn, is generally the reflectivity of naked silicon chip; the correction of reference beam to sample reflectivity.

For example, periodically in shallow ditch groove structure, as shown in figure 10, two orthogonal polarization directions are defined as respectively perpendicular to the direction TM of linear structure 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 is 50 nanometer, as shown in figure 11, wherein dotted line is TE polarization direction reflectivity to its reflectivity, and solid line is TM polarization direction reflectivity.

Measure after TE, TM absolute reflectance, by returning and calculate with Numerical Simulation Results comparison and numerical value, can measure thickness and the optical constant of critical dimension, three-dimensional appearance and the multilayer material of sample surfaces periodic patterns.In this case, described perpendicular incident broadband spectrometer can also comprise computing unit, this computing unit is for by calculated with mathematical model and the curvilinear regression matching of reflectivity, the optical constant of calculation sample material, film thickness and/or critical dimension characteristic or three-dimensional appearance for the periodic structure of analytic sample.Conventional periodic structure electromagnetical analogies computing method are rigorous couple-wave analysis (Rigorous Coupled-Wave Analysis, RCWA) now, and regression algorithm is Levenberg-Marquardt algorithm.In the present invention, except theoretical measuring method, measuring process also relates to the processing that has the variation that polarization sensitivity causes for polarizer rotation etc., and problems can solve by numerical method, and more specifically content can be with reference to U.S. Patent No. 6522406B1 and U.S. Patent No. 6665070B1.In the present invention, determined by the polarizer anglec of rotation through the linear polarization direction of the light beam of polarizer, the light source that is incident to polarizer can be the light beam of random polarization state.Light through sample reflection is linearly polarized light after polarizer, be incident in the process of detector at this light beam, reference sample reflected light all experiences identical polarization variations with measurement sample reflected light, thus do not require maintenance polarization state, to the Polarization-Sensitive no requirement (NR) of optics.

Taking concrete embodiment as example, the present invention is described in detail below.

Embodiment mono-

Shown in Figure 12 a according to the perpendicular incident broadband spectrometer of the first embodiment of the present invention.As shown in Figure 12 a, this perpendicular incident broadband spectrometer comprises broadband pointolite SO, the first reflector element (comprising plane mirror M4, M5), active catch tabula rasa D, diaphragm A, the first light focusing unit (off-axis parabolic mirror OAP2), polarizer P, the first plane mirror M1, the first off-axis parabolic mirror OAP1, the second light focusing unit (lens L), the second reflector element (comprising plane mirror M2, M3), broadband spectral meter SP, movably beam-splitter BS (its particular location can be with reference to Figure 12 b) and pattern identification system IRS.This pattern identification system IRS comprises lens L ', lighting source (not shown) and CCD imager (not shown).Broadband pointolite SO can launch the divergent beams that comprise broadband spectral, this broadband spectral conventionally at deep ultraviolet near infrared range (approximately 190nm to 1100nm wavelength coverage in).In practice, broadband pointolite SO can be xenon lamp, deuterium lamp, tungsten lamp, Halogen lamp LED, mercury lamp, the composite broadband light source that comprises deuterium lamp and tungsten lamp, the composite broadband light source that comprises tungsten lamp and Halogen lamp LED, the composite broadband light source that comprises mercury lamp and xenon lamp and the composite broadband light source that comprises deuterium tungsten halogen lamp.The light beam of these wideband light sources can be natural light (, degree of polarization equals zero).But this broadband pointolite can be also the natural light pointolite that the degree of polarization that produces by depolariser is zero.The example of broadband pointolite SO comprises the product HPX-2000 of Ocean Optics company, HL-2000 and DH2000, and the product L11034 of Hamamatsu company, L8706, L9841 and L10290.Broadband spectral meter can be charge-coupled image sensor (CCD) or photodiode array (PDA) broadband spectral meter, for example, and Ocean Optics QE65000 spectrometer or B & W TeckCypher H spectrometer.The example of pattern identification system IRS comprises the product NT59-839 of EDMUND company, NT59-743, the FVL-5X-120D-C of SEIWA company, FVL-6X-120D-C, product XF-T6X-110D of Can Rui Optical Co., Ltd etc.

The divergent beams of broadband pointolite SO transmitting are incident to plane mirror M3 and M4 can be divided into two bundles, and wherein a branch of for surveying light, another bundle is reference light.As preferably, this embodiment also comprises light source light focusing unit (curved reflector M6), this curved reflector M5 is set between pointolite SO and plane mirror M 3, M4 to form convergent beam, this convergent pencil of rays is divided into two bundles by plane mirror M3 and M4, wherein a branch of for surveying light, another bundle is reference light.Introduce respectively the light path of this two-beam below: the convergent beam of the light key light that (1) is reflected through plane mirror M4 in surface level is as surveying light, and diaphragm A is placed in the focus place of this convergent beam.Detection light after diaphragm is dispersed again, and be incident to the first light focusing unit, be off-axis parabolic mirror OAP2, the focus of off-axis parabolic mirror OAP2 overlaps with the focus of these divergent beams, these divergent beams are by the rear parallel beam that forms along continuous straight runs of axle parabolic mirror OAP2 reflection, this parallel beam is incident to plane mirror M1 after polarizer P, plane mirror M1 makes this parallel beam in surface level, after 90-degree rotation, be incident to the first off-axis parabolic mirror OAP1, the first off-axis parabolic mirror OAP1 makes this parallel beam half-twist degree in perpendicular, be key light convergent beam vertically by the light beam after off-axis parabolic mirror OAP1 reflection, this convergent beam vertical incidence and focusing on sample surfaces.The reflected light of sample surfaces is got back to successively and is incident to for the first time the OAP2 plane at light beam place before after the first off-axis parabolic mirror OAP1, the first plane mirror M1, polarizer P, off-axis parabolic mirror OAP2, and form convergent beam, this convergent beam, after plane mirror M2 reflection, is incident to broadband spectral meter SP straight up.This broadband spectral meter SP will be placed on the focus place of detecting light beam of the convergence after plane mirror M2 reflection.(2) pass through from the edge of plane mirror M4, through the light of plane mirror M5 reflection as with reference to light.Plane mirror M5 tilts slightly with respect to M4, and the reference light after plane mirror M5 reflection separates again after crossing with the detection light reflecting through plane mirror M4 immediately.Reference light is assembled to becoming divergent beams after a bit, and these divergent beams are incident to the second light focusing unit, after condenser lens L, form again convergent beam, are incident to straight up broadband spectral meter SP after plane mirror M3.

Those skilled in the art can know, by adjusting and/or rotational plane mirror M 3, can make reference beam vertical incidence to spectrometer SP; By along or against the position of the incident direction mobile focusing lens L2 of reference beam, can make reference beam focus in spectrometer SP after the reflection of plane mirror M2.

In the embodiment of the present invention, before detecting light beam is emitted to arrival off-axis parabolic mirror OAP2 from wideband light source SO, and through leaving off axis paraboloidal mirror OAP2 after sample reflection to before arriving broadband spectral meter SP, reference beam is all in same perpendicular P1 before being emitted to arrival broadband spectral meter SP from wideband light source SO.Detecting light beam to before arriving off-axis parabolic mirror OAP1, and leaves off-axis parabolic mirror OAP1 to before arriving plane mirror M2, in the parallel plane of sample surfaces after plane mirror M4 reflection after sample reflection.

In the present invention, the light that pointolite sends has been divided into detecting light beam and reference beam two-beam through the first reflector element (after being plane mirror M4 and M5 reflection), the detecting light beam returning from sample surfaces and reference beam are after the second reflector element (being plane mirror M2 and M3), synthesize again the light beam of beam cross-section shape as shown in Fig. 4 a, thereby realized the object of detecting light beam and the public spectrometer of reference beam.

In the present invention, shifting board D can move by automatic or manual control, cuts off reference light or/and survey light.And when shifting board D in survey light/or the light path of reference light outside time, on corresponding light path, without any impact,, after light beam has switched, the light path that do not need to reset can be carried out spectral measurement.Therefore vertical incidence spectrometer of the present invention, can realize the quick switching between reference beam and detecting light beam in measuring process easily.

In the present invention, polarizer can be thin film polarizer, glan thompson prism polarizer, Rochon prism polarizer, Glan-Taylor prism polarizer, Glan Laser polarizers.Especially, described polarizer is preferably Rochon prism polarizer, and its material is preferably magnesium fluoride (MgF ₂).In the present embodiment, beam-splitter BS and mirror M 2 and M4 are the plane reflection elements that at least contains a linear edge shape, as, semicircle plane mirror, or square reflector.Those skilled in the art can know, the linear edge of beam-splitter BS, plane mirror M2 and M4 is parallel, and this linear edge is crossing with the key light of light beam.Preferably acute angle shape of this linear edge, to avoid the reflection to reference beam.

In addition, vertical incidence wideband polarization spectrometer of the present invention can also comprise polarizer rotating control assembly, rotates to adjust light beam polarization direction for controlling polarizer.This polarizer rotating control assembly can adopt the various automatic rotating devices (manually also can realize measurement) of Electric Machine Control, as Newport Precision Rotation Stage URS150.

The sample of measuring is placed on an adjustable sample stage conventionally, as X-Y-Z-Theta or R-Theta-Z worktable.At semicon industry, the size of sample is the wafer of diameter 8 inches (200 millimeters) or 12 inches (300 millimeters) normally.In flat-panel monitor industry, sample has 1 meter of above size conventionally.For wafer, due to reasons such as the thin layer stress on wafer, surface may be uneven.For large scale sample, the distortion of sample surfaces possibility, or example platform may be uneven.Therefore,, in the time that sample is detected, in order to realize the measurement of pinpoint accuracy and the Quick Measurement of guarantee semiconductor production line output, can again focus on each measurement point.

In the present invention, for fear of the optically focused effect of off-axis parabolic mirror OAP1, CCD imager imaging definition in pattern identification system IRS is impacted, pattern identification system IRS and optical splitter BS are positioned between off-axis parabolic mirror OAP1 and sample.

Before measuring sample, need be to utilizing pattern identification system that the measurement point of sample surfaces is identified, located, this process only need need optical splitter to move in light path and can realize along direction as shown in arrow in Figure 12 b.Concrete operations are: removable beam-splitter is moved in the described detecting light beam light path of (comprising the sample folded light beam of detecting light beam), its non-reflecting surface covers detecting light beam completely, illuminating bundle is incident to sample surfaces by its reflecting surface, now the pattern of sample surfaces can imaging in CCD imaging system, by calculation sample surface imaging definition, taking the pattern identification system IRS that calibrates as benchmark, sample is focused, can in CCD imaging system, obtain the chip sample picture on surface as shown in Figure 13 a, in figure, darker square region is measurement point.After measurement point has been identified, beam-splitter part can be shifted out to the light path of described detecting light beam, its non-reflecting surface shaded portions detecting light beam, its reflecting surface can reflex to sample surfaces by illuminating bundle, detecting light beam and the illuminating bundle of sample surfaces reflection are reflexed to CCD imaging system, its light path is as shown in Figure 12 b simultaneously.Now detecting light beam and sample surfaces pattern all can imagings in CCD imaging system, thereby by example platform movably, can aim at hot spot and measurement point.When hot spot and measurement point are on time, the image observing in CCD imaging system is as shown in Figure 13 b, and bright spot of view-field center is become image by detecting light beam.After above step completes, can implement to measure to measurement point.When measurement, beam-splitter BS need be shifted out completely to light path in described detecting light beam (now in CCD imaging system without image), make detecting light beam Free propagation to sample surfaces, thereby carry out spectral measurement.

In addition,, except the variation judgement by light intensity in observation spectrum meter focuses on, the present invention also has the another kind of determination methods that focuses on, that is, focus by the imaging definition of observing CCD imager in described pattern identification system IRS.And deposit two kinds of focusing systems and improved the degree of accuracy that equipment focuses on.And, can realize the function that sample surfaces detecting light beam hot spot is aimed at sample surfaces pattern.

According to the present embodiment, those skilled in the art can know, if plane mirror M1 and off-axis parabolic mirror OAP1 have identical reflecting material and coating structure and meet the identical and orthogonal condition of plane of incidence of the incident angle of light beam, in the time propagating in the light path of detecting light beam between polarizer and sample surfaces, arrive polarization characteristic when sample surfaces and remain unchanged when leaving polarizer, the reflected light of sample, be generally elliptically polarized light, the polarization characteristic while returning to polarizer also remains unchanged when leaving sample.,, when light beam is propagated between polarizer and sample surfaces, its polarization characteristic is only because the reflection of sample changes to some extent.In the present invention, focusing system and focusing process do not affect light polarization, described twin-beam vertical incidence Intensity modulation can be measured anisotropic film sample or non-uniform film sample according to measuring method mentioned above, as measures thickness and the optical constant of critical dimension (CD), three-dimensional appearance and the multilayer material of surperficial periodic patterns.

In the present embodiment, determined by the polarizer anglec of rotation through the linear polarization direction of the detecting light beam of polarizer, the light that is incident to polarizer can be the light beam of random polarization state.Light through sample reflection is linearly polarized light after polarizer, be incident in the process of detector at this light beam, reference sample reflected light all experiences identical polarization variations with measurement sample reflected light, thus do not require maintenance polarization state, to the Polarization-Sensitive no requirement (NR) of optics.

Use the vertical incidence wideband polarization spectrometer of the present embodiment not only can realize to make detecting light beam no color differnece and focus on sample surfaces, accurately control the polarization variations of detecting light beam simultaneously,, can keep the effect of random polarization polarisation of light characteristic, can also proofread and correct the measuring error that the spectrum change of wideband light source in absolute reflectance method measuring process causes by shirtsleeve operation, in addition, owing to only needing, with a spectrometer, not increase cost.

Embodiment bis-

The index path of twin-beam perpendicular incident broadband spectrometer according to a second embodiment of the present invention shown in Figure 14.The twin-beam vertical incidence wideband polarization spectrometer of the light path element of the present embodiment and measuring method and the first embodiment is basic identical, but light path feature is slightly different, for simplicity, only light path light path is done to concise and to the point description.

The light beam of broadband pointolite SO transmitting is after curved reflector M6 reflection, form convergent beam, the first reflector element, be that light beam is divided into detecting light beam and reference beam two bundles by plane mirror M4 and M5, the second reflector element, plane mirror M2 and M3 are incident in same spectrometer SP light beam is combined into light beam by the detecting light beam returning from sample surfaces and reference beam again.Different from the first embodiment, the light beam after M4 reflection is reference light, and passes through from the edge of M4, and the light beam after M5 reflects is to survey light, and in the present embodiment, after two-face mirror, process is crossing with surveying light for reference light, but directly separates.Reference beam is assembled to becoming divergent beams after a bit, and these divergent beams are incident to the second light focusing unit (condenser lens L), form again convergent beam, and after plane mirror M3 reflection, vertical incidence is to broadband spectral meter SP.And pass through from the edge of M5, the light beam after M4 reflection is for surveying light.Surveying light is the convergent beam of key light in surface level, and diaphragm A is placed in the focus place of this convergent beam.Detection light after diaphragm is dispersed again, and be incident to the first light focusing unit (off-axis parabolic mirror OAP2), these divergent beams are spent at the plane of incidence (surface level) intrinsic deflection 90 after being reflected by off-axis parabolic mirror OAP2, form the parallel beam of along continuous straight runs, this parallel beam is incident to plane mirror M1 after polarizer P, plane mirror M1 makes this parallel beam form convergent beam after surface level intrinsic deflection 90 degree, this convergent beam focuses on sample surfaces after the first off axis paraboloidal mirror OAP1 reflection, and its key light is that vertical incidence is to sample surfaces.The reflected light of sample surfaces, after the first off-axis parabolic mirror OAP1, the first plane mirror M1, polarizer P, off-axis parabolic mirror OAP2, return successively and be incident to for the first time before OAP2 light beam place plane and form convergent beam, this convergent beam is spent at plane of incidence intrinsic deflection 90 after plane mirror M2 reflection, and vertical incidence is to broadband spectral meter SP.This broadband spectral meter SP is placed on the focus place of the detecting light beam of the convergence after plane mirror M2 reflection.Those skilled in the art can know, by adjusting and/or rotational plane mirror M 3, can make reference beam vertical incidence to spectrometer SP; By along or against the position of the incident direction mobile focusing lens L2 of reference beam, can make reference beam focus in spectrometer SP after the reflection of plane mirror M3.

Identical with the first embodiment is, before detecting light beam is emitted to arrival off-axis parabolic mirror OAP2 from wideband light source SO, and through leaving the second off axis paraboloidal mirror OAP2 after sample reflection to before arriving broadband spectral meter SP, reference beam is all in the same plane vertical with sample surfaces before being emitted to arrival broadband spectral meter SP from wideband light source SO.Detecting light beam to before arriving off-axis parabolic mirror OAP1, and leaves off-axis parabolic mirror OAP1 to before arriving plane mirror M2, in the parallel plane of sample surfaces after plane mirror M4 reflection after sample reflection.

The present embodiment also can increase pattern identification system as the first embodiment.The present embodiment can be implemented to measure identical measurement with described in the first embodiment.

Embodiment tri-

The twin-beam perpendicular incident broadband spectrometer of a third embodiment in accordance with the invention shown in Figure 15.The light path element of the present embodiment and measuring method and first and second embodiment are basic identical.For simplicity, only the light path of the present embodiment is done to concise and to the point description below.

As shown in figure 15, the light beam of broadband pointolite SO transmitting, after curved reflector M6, is divided into two bundles by plane mirror M5 and M6, and wherein a branch of for surveying light, another bundle is reference light.Survey light through diaphragm A, off-axis parabolic mirror OAP2, is incident to plane mirror M1 after polarizer P, off-axis parabolic mirror OAP1, and rear vertical incidence is to sample surfaces.Through the detection light of sample surfaces reflection, through off-axis parabolic mirror OAP1, plane mirror M1, polarizer P, after off-axis parabolic mirror OAP2, plane mirror M2, be incident in spectrometer SP; Reference light, through lens L, is incident to after plane mirror M3 in spectrometer SP.Different from the first embodiment, the plane of incidence of detecting light beam on plane mirror M1 is mutually vertical with the plane of incidence at off-axis parabolic mirror OAP2.

In addition, before detecting light beam is emitted to arrival off-axis parabolic mirror OAP2 from wideband light source SO, and through leaving plane mirror M1 after sample reflection to before arriving broadband spectral meter SP, reference beam is all in the same plane vertical with sample surfaces before being emitted to arrival broadband spectral meter SP from wideband light source SO.In the light path of detecting light beam between off-axis parabolic mirror OAP2 and off-axis parabolic mirror OAP1 time, in the plane parallel with sample surfaces.

The present embodiment also can increase pattern identification system as the first embodiment.The present embodiment can be implemented to measure identical measurement with described in the first embodiment.

Described vertical incidence wideband polarization spectrometer also comprises a diaphragm between described polarizer and described sample in the above-described embodiments, for avoiding the e light producing after described polarizer to be incident to sample surfaces, and/or its reflected light is reflected back polarizer.In addition, in any one section of light path in above-described embodiment, diaphragm all can be set, this diaphragm in and diaphragm center vertical with key light by the position of key light, to regulate the actual numerical value aperture of surveying light.

In addition, vertical incidence wideband polarization spectrometer of the present invention can also comprise computing unit, and this computing unit is for the optical constant of calculation sample material and/or for critical dimension characteristic or the three-dimensional appearance of the periodic micro structure of analytic sample material.

In above embodiment, the first off-axis parabolic mirror OAP1 can also can move against direction of light along direction of light, thereby can measure the different point of sample.

Please note, according to the instruction of this instructions, those skilled in the art will should be appreciated that, vertical incidence wideband polarization spectrometer of the present invention is not limited to disclosed concrete form in above-described embodiment, as long as under general plotting of the present invention, can carry out various distortion to broadband light spectrometer of the present invention.Broadband light spectrometer of the present invention can be applied to the thickness, optical constant of probing semiconductor film, optical mask, metallic film, thin dielectric film, glass (or plated film), laser mirror, organic film etc. and critical dimension and the three-dimensional appearance of the periodic structure that these materials form, and especially can be applied to and measure whole yardsticks of the three-dimensional structure planar with a peacekeeping two-dimensional and periodic that multilayer film form and the optical constant of layers of material.In addition, adopt broadband light spectrometer of the present invention, can realize automatic focus, also can realize Manual focusing.

It should be noted last that, above embodiment is only unrestricted in order to technical scheme of the present invention to be described, although the present invention is had been described in detail with reference to example, those of ordinary skill in the art is to be understood that, can modify or be equal to replacement technical scheme of the present invention, and not departing from the spirit and scope of technical solution of the present invention, it all should be encompassed in the middle of claim scope of the present invention.

Claims (27)

1. a wideband polarization spectrometer, is characterized in that, comprises light source, the first reflector element, the first light focusing unit, the second light focusing unit, polarizer, the first plane mirror, first surface catoptron, the second reflector element, probe unit, wherein:

Described the first reflector element is divided into detecting light beam and reference beam two parts for the light beam that described light source is sent, and this two parts light beam is incident to respectively to described the first light focusing unit and described the second light focusing unit;

Described the first light focusing unit is used for receiving described detecting light beam, is incident to described polarizer after making this light beam become parallel beam;

Described polarizer is arranged between described the first light focusing unit and described the first plane mirror, for make described parallel beam by and be incident to described the first plane mirror;

Described the first plane mirror is used for receiving described parallel beam and this parallel beam is reflexed to described first surface catoptron;

Described first surface catoptron is used for described parallel beam to become convergent beam, and will after this convergent beam reflection, vertically focus on sample;

Described the second reflector element is used for receiving at the same time or separately from the detecting light beam of the described first surface catoptron of process successively of sample reflection, described the first plane mirror, described polarizer, described the first light focusing unit with by the reference beam of described the second light focusing unit, and received light beam is incident to described probe unit;

Described the second light focusing unit is used for receiving described reference beam, and is incident to described the second reflector element;

Described probe unit is for surveying the light beam being reflected by described the second reflector element.

2. wideband polarization spectrometer according to claim 1, is characterized in that, described wideband polarization spectrometer also comprises:

Light source light focusing unit, described light source light focusing unit is arranged between described light source and described the first reflector element, becomes convergent beam for the light that described light source is sent.

3. wideband polarization spectrometer according to claim 2, is characterized in that, described light source light focusing unit comprises:

At least one lens and/or at least one curved reflector.

4. wideband polarization spectrometer according to claim 1, is characterized in that, described wideband polarization spectrometer also comprises:

Movably optical splitter and pattern identification system;

Described optical splitter and pattern identification system are between described first surface catoptron and sample;

Described pattern identification system comprises lens, lighting source and CCD imager;

Described movably optical splitter reflexes to sample surfaces and the folded light beam of sample surfaces is reflexed to described CCD imager for the sample illuminating bundle that described pattern identification system is provided; And can be by observing the light intensity of described probe unit and/or focusing by the sharpness of observing the image in described pattern identification system in described wideband polarization spectrometer.

5. according to the described wideband polarization spectrometer of claim 4, it is characterized in that:

Described movably optical splitter is the plane mirror with at least one linear edge, this plane mirror can be completely in, part in or completely not in the light path in described detecting light beam.

6. wideband polarization spectrometer according to claim 1, is characterized in that, described wideband polarization spectrometer also comprises:

For switching the light beam switch unit of described detecting light beam and described reference beam.

7. wideband polarization spectrometer according to claim 6, is characterized in that:

Described light beam switch unit is the movably light barrier being arranged between described the first reflector element and the second reflector element, and described light barrier can block respectively or simultaneously detecting light beam and reference beam.

8. wideband polarization spectrometer according to claim 1, is characterized in that, described wideband polarization spectrometer also comprises:

For carrying adjustable example platform of sample.

9. wideband polarization spectrometer according to claim 2, is characterized in that, described wideband polarization spectrometer also comprises:

Diaphragm, described diaphragm is placed in any one section of light path of whole optical system.

10. wideband polarization spectrometer according to claim 9, is characterized in that, described wideband polarization spectrometer also comprises:

At least one diaphragm, described diaphragm is placed in the detecting light beam focus place that the convergent beam that formed by described light source light focusing unit separates.

11. wideband polarization spectrometers according to claim 1, is characterized in that, described wideband polarization spectrometer also comprises:

At least one diaphragm, described diaphragm, between described polarizer and described sample, is incident to sample surfaces and/or its reflected light is reflected back described polarizer for the e light of avoiding producing after described polarizer.

12. wideband polarization spectrometers according to claim 1, is characterized in that, described wideband polarization spectrometer also comprises:

Polarizer rotating control assembly, this polarizer rotating control assembly is for controlling the polarization direction of described polarizer.

13. wideband polarization spectrometers according to claim 1, is characterized in that, described wideband polarization spectrometer also comprises:

Computing unit, this computing unit is for the optical constant of calculation sample material, film thickness and/or for critical dimension characteristic or the three-dimensional appearance of the periodic structure of analytic sample.

14. according to the wideband polarization spectrometer described in claim 1-13 any one, it is characterized in that:

Described the first plane mirror and described first surface catoptron have identical reflecting material and coating structure, and meet identical or approximate identical and the plane of incidence vertical or approximately perpendicular condition mutually of the incident angle of key light.

15. wideband polarization spectrometers according to claim 14, is characterized in that:

The incident angle of the main beam of described detecting light beam on described the first plane mirror differs and is no more than 5 degree with the incident angle on described first surface catoptron;

The orthogonal error of plane of incidence of the plane of incidence of described the first plane mirror incident beam and described first surface catoptron incident beam is less than 5 degree.

16. according to the wideband polarization spectrometer described in claim 1-13 any one, it is characterized in that:

Described the first reflector element is made up of at least two plane mirrors, wherein, has at least a catoptron to have at least one linear edge and this linear edge is crossing with the key light of light path.

17. according to the wideband polarization spectrometer described in claim 1-13 any one, it is characterized in that:

Described the first light focusing unit is off-axis parabolic mirror or toroidal reflectors.

18. according to the wideband polarization spectrometer described in claim 1-13 any one, it is characterized in that:

Described the second light focusing unit is lens, lens combination, off-axis parabolic mirror or toroidal reflectors.

19. according to the wideband polarization spectrometer described in claim 1-13 any one, it is characterized in that:

Described polarizer is Rochon prism polarizer.

20. according to the wideband polarization spectrometer described in claim 1-13 any one, it is characterized in that:

Described first surface catoptron is off-axis parabolic mirror or toroidal reflectors.

21. according to the wideband polarization spectrometer described in claim 1-13 any one, it is characterized in that:

The angle of inclination of described the first plane mirror and/or locus are adjustable.

22. wideband polarization spectrometers according to claim 21, is characterized in that:

Described the first plane mirror moves along the direction of propagation of the key light of described convergent beam.

23. according to the wideband polarization spectrometer described in claim 1-13 any one, it is characterized in that:

Described the second reflector element is made up of at least two plane mirrors, forms in the plane mirror of described the second reflector element, has at least a catoptron to have at least one linear edge and this linear edge is crossing with the key light of light path.

24. according to the wideband polarization spectrometer described in claim 1-13 any one, it is characterized in that:

Described probe unit is spectrometer.

25. according to the wideband polarization spectrometer described in claim 1-13 any one, it is characterized in that:

Described light source is the light source that comprises multi-wavelength.

26. according to the wideband polarization spectrometer described in claim 1-13 any one, it is characterized in that:

Described light source is xenon lamp, deuterium lamp, tungsten lamp, Halogen lamp LED, mercury lamp, the composite broadband light source that comprises deuterium lamp and tungsten lamp, the composite broadband light source that comprises tungsten lamp and Halogen lamp LED, the composite broadband light source that comprises mercury lamp and xenon lamp or the composite broadband light source that comprises deuterium tungsten halogen, or described light source is the natural light pointolite that the degree of polarization that produces by depolariser is zero.

27. 1 kinds of optical measuring systems, comprise according to the wideband polarization spectrometer described in claim 1-13 any one.