CN103293884A - Off-axis alignment system and method for photolithographic equipment - Google Patents
Off-axis alignment system and method for photolithographic equipment Download PDFInfo
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Abstract
The invention discloses an off-axis alignment system for photolithographic equipment, which is used for measuring alignment position information of an alignment mark. The off-axis alignment system comprises an illumination module, a polarization adjuster, a reference mark, an imaging module and a detection module, wherein the imaging module comprises a polarizing beam splitter. According to the off-axis alignment system, the energy ratio of reference light to detection light is adjusted through the polarization adjuster and the polarizing beam splitter, interfering beams of all levels of secondary diffraction light generated by secondary diffraction of the reference light and the detection light at a reference grating are detected, and then the position of an alignment mark is determined according to the detection result.
Description
Technical field
The present invention relates to a kind of integrated circuit equipment manufacturing field, relate in particular to a kind of off-axis alignment system and alignment methods for lithographic equipment.
Background technology
Lithographic equipment is the major equipment of making integrated circuit, and its effect is to make different mask patterns be imaged onto the position of the accurate aligning in the substrate (as semi-conductor silicon chip or LCD plate) successively.Yet this aligned position but changes because of the physics that row graph experiences and chemical change, therefore needs an alignment system, can both be aimed at accurately with the aligned position that guarantees the corresponding mask of silicon chip at every turn.Along with the growth of the number of electronic components on the substrate per unit surface area and the size of electronic component are synthesized more and more littler, accuracy requirement to integrated circuit improves day by day, therefore mask is imaged on suprabasil position and must fixes more and more accurately successively, and the requirement of alignment precision is also more and more higher during to photoetching.
At present, lithographic equipment adopts mostly and is based on the alignment system that optical grating diffraction is interfered.Such alignment system essential characteristic is: diffraction takes place at the grating type alignment mark in the illumination beam that comprises single wavelength or multi-wavelength, and the diffraction lights at different levels of generation carry the positional information about alignment mark; Not at the same level time light beam scatters from the phase alignment grating with different angle of diffraction, collect inferior diffracted beams at different levels by alignment system, make two symmetries the positive and negative order of diffraction time (as ± 1 grade, ± 2 grades, ± level etc.) overlapping relevant at image planes or the pupil face of alignment system, form interference signals at different levels.When the mark grating is scanned, utilize the Strength Changes of photodetectors register interference signal, handle by signal, determine the centering adjustment position.
At present, representative in the prior art is ATHENA off-axis alignment system, and this alignment system adopts ruddiness, green glow two-source illumination at the Lights section; And adopt voussoir array or wedge group to realize the overlapping and coherent imaging of alignment mark multi-level diffraction light, and on image planes, imaging space is separated; The registration signal of ruddiness and green glow is separated by a polarization beam splitter prism; By surveying the transmitted light intensity that the alignment mark picture sees through reference marker, obtain the registration signal of sinusoidal output.At first, because this system adopts the beam splitting system of polarization beam splitter prism can only separate the coloured light of two wavelength, then helpless to two registration signal more than the wavelength; Secondly the multi-level diffraction light of this alignment system is interfered in image planes, and when the alignment mark reflectivity was inhomogeneous, the alignment error that factors such as mark rotation, magnification error cause was bigger; At last, when this alignment system used the voussoir array, face type and the angle of wedge coherence request of two voussoirs that the positive and negative same stages of birefringence is inferior were very high; And the requirement of the processing and manufacturing of wedge group, assembling and adjustment is also very high, and the specific implementation engineering difficulty of getting up is bigger, cost dearly, and relatively poor to the Technological adaptability of alignment mark.
Another prior art is SMASH off-axis alignment system.This system produces the alignment mark picture of two relative Rotate 180 degree by a rotation self-reference interferometer, surveys the interference signal of the overlapping order of diffraction at pupil plane, changes obtaining the aligned position signal according to the relative phase of at different levels interference signals that detect.This alignment system has adopted many principal sections, space composite prism result's rotation self-reference interferometer, and the processing of prism and to debug tolerance very high, prism group gummed difficulty is bigger.
Prior art is needed badly and is wanted a kind of new off-axis alignment system, and it is bigger effectively to overcome the engineering difficulty, the technological deficiency of processing cost costliness.
Summary of the invention
In order to overcome the defective that exists in the prior art, a purpose of the present invention is to provide a kind of off-axis alignment system and method, can regulate reference light and the energy ratio of surveying light, and the increase system is to the adaptability of alignment mark.
Another object of the present invention is to provide a kind of off-axis alignment system and alignment methods for lithographic equipment, simple for structure and can be effectively change according to the relative phase of the interference signal that detects, determine aligned position information.
The present invention discloses a kind of off-axis alignment system for lithographic equipment, is used for measuring the aligned position information of an alignment mark, and comprising: lighting module provides illuminating bundle; Polarization adjuster be used for to be regulated the polarization direction of this illuminating bundle, makes outgoing after the change of polarized direction predetermined angle theta of this illuminating bundle, and this predetermined angle theta is the processing parameter setting according to this alignment mark; Reference marker; Image-forming module, comprise polarizing beam splitter, this polarizing beam splitter will be divided into detecting light beam and reference beam through the illuminating bundle of this polarization adjuster, this image-forming module is collected this reference beam, make this reference beam produce first diffracted beam with a plurality of orders of diffraction time beamlet at this reference marker place diffraction, and collect this detecting light beam, make this detecting light beam produce second diffracted beam with a plurality of orders of diffraction time beamlet via this alignment mark and this reference marker secondary diffraction, respective stages time beamlet forms a plurality of orders of diffraction time interfering beam in the overlapping interference of the pupil plane of this image-forming module in this first diffracted beam and second diffracted beam; Detecting module is surveyed these a plurality of orders of diffraction time interfering beam, and should convert a plurality of orders of diffraction time interference signal to by a plurality of orders of diffraction time interfering beam; And signal processing module, determine the aligned position information of this alignment mark, the wherein inferior positive and negative symmetry of the order of diffraction of this a pair of order of diffraction time interference signal according to time interference signal of at least one pair of order of diffraction in a plurality of orders of diffraction time interference signal.
Further, this polarization adjustment module is the magnetic opticity device or rotates adjustable deflection film.
Further, this image-forming module also comprises: first
Wave plate, first lens,
Wave plate, second lens, the 3rd lens, this detecting light beam via this first
Wave plate, first this alignment mark of lens incident, and at this alignment mark place generation diffraction first time, the diffraction light of diffraction is via these first lens, first for the first time
Wave plate, polarization spectro element,
Wave plate, second this reference marker of lens incident, the 3rd lens with time beamlet of respective stages in this first diffracted beam and second diffracted beam in the overlapping interference of the pupil plane of the 3rd lens.This image-forming module also comprises the space diaphragm, and this space diaphragm is positioned at the pupil plane place of these first object lens.This image-forming module also comprises analyzer, is arranged on this polarization spectro element and this first
Between the wave plate.This image-forming module also comprises second
Wave plate, reflecting element, this reference beam via this second
Wave plate be incident to this reflecting element return by by this second
Wave plate, polarization spectro element,
Wave plate, second this reference marker of lens incident.
Further, this lighting module comprises light source, the polarizer, the 3rd lens, aperture diaphragm, the 4th lens, and the light that this light source sends is successively through producing this illuminating bundle outgoing behind this polarizer, the 4th lens, aperture diaphragm, the 5th lens.This light source is multi wave length illuminating source, comprises the polychromatic light piece-rate system of the light separation that this light sources with different wavelengths is sent in this detecting module.
Further, this detecting module comprises a plurality of detection light paths, surveys the isolated different wavelengths of light of this polychromatic light piece-rate system respectively.In these a plurality of detection light paths each is surveyed light path and is comprised the 6th lens, spatial light filter, the 7th lens, a plurality of detection optical fiber and a plurality of photodetector in regular turn along optical propagation direction, the incident end of this detection optical fiber closes on this pupil plane, and the exit end of this detection optical fiber is connected with this photodetector.
The present invention discloses a kind of off-axis alignment method for lithographic equipment simultaneously, it is characterized in that, comprising: an alignment mark and reference marker are provided; Illuminating bundle is provided, and makes change of polarized direction one predetermined angle theta of this illuminating bundle, this predetermined angle theta is the processing parameter setting according to this alignment mark; This illuminating bundle is divided into detecting light beam and reference beam; This reference light is incident to a reference marker, generation comprises first diffracted beam of a plurality of orders of diffraction time beamlet, this detecting light beam produces second diffracted beam that comprises a plurality of orders of diffraction time beamlet through this alignment mark and this reference marker secondary diffraction, and the corresponding order of diffraction time beamlet forms a plurality of orders of diffraction time interfering beam in the overlapping interference of a pupil plane in this first diffracted beam and second diffracted beam; Survey these a plurality of orders of diffraction time interfering beam, and it is turned to a plurality of orders of diffraction time interference signal; At least one pair of order of diffraction time interference signal in these a plurality of orders of diffraction time interference signal is carried out the signal treatment step to determine the positional information of this alignment mark, wherein the order of diffraction time positive and negative symmetry of this a pair of order of diffraction time interference signal.
Further, this signal treatment step is the positional information of this alignment mark of phase difference calculating of utilizing the interference signal of the order of diffraction time positive and negative symmetry.This signal treatment step be utilize the order of diffraction time positive and negative symmetry interference signal intensity and the positional information of this alignment mark of phase calculation.This signal treatment step is the positional information of this alignment mark of phase calculation of utilizing the interference signal intensity difference of the order of diffraction time positive and negative symmetry.
The open alignment system of the present invention is based on double grating secondary diffraction principle.Be that illuminating bundle incides alignment mark diffraction for the first time takes place, the diffracted beams at different levels of generation with different angle of diffraction from the alignment mark surface scattering; After imaging system, diffraction lights at different levels converge to reference marker and produce diffraction for the second time, and the secondary diffracted beam with identical angle of diffraction is overlapping relevant at finder lens pupil face, according to the relative phase variation of the interference signal that detects, determine aligned position information.Compared with prior art, this alignment system has following advantage: the first, adopt polarization adjuster and polarization beam apparatus, make isolated reference beam energy dynamics adjustable, improve the contrast of detectable signal, increase alignment system to the Technological adaptability of mark.The second, this alignment system is simple in structure, does not need baroque voussoir array (or wedge group) and self-reference interferometer, utilizes the secondary diffraction of reference marker to obtain interference signals at different levels at the pupil face.Reference marker processing and manufacturing, assembling and modulation difficulty are less.Three, this alignment system is surveyed at the pupil face, and registration signal comes from the overlapping of light beam of same space frequency and is concerned with.Factors such as incident light inclination, mark inclination out of focus, rotation are less to the alignment precision influence.Four, by at lens pupil face usage space diaphragm, only select required strange level time diffraction light, avoid idol level time diffraction light to enter detectable signal and produce a plurality of harmonic componentss; Reduced the influence of parasitic light on the other hand.
Description of drawings
Can be by following detailed Description Of The Invention and appended graphic being further understood about the advantages and spirit of the present invention.
Fig. 1 is the structural representation of first embodiment of alignment system involved in the present invention;
Fig. 2 is the lighting module light channel structure synoptic diagram of alignment system involved in the present invention;
Fig. 3 is the structural representation of the polarization adjustment module of alignment system involved in the present invention;
Fig. 4 is the secondary diffraction interference structural representation of alignment system involved in the present invention;
Fig. 5 is the pupil face mechanism of diaphragm synoptic diagram of alignment system involved in the present invention;
Fig. 6 is based on the light-dividing principle figure of the polychromatic light piece-rate system of blazed grating;
Fig. 7 is the structural representation of the detection light path module of alignment system involved in the present invention;
Fig. 8 is the aligning process flow diagram of alignment system involved in the present invention;
Beam interference synoptic diagram when Fig. 9 is alignment mark inclination out of focus;
Figure 10 is the structural representation of second embodiment of alignment system involved in the present invention.
Embodiment
Describe specific embodiments of the invention in detail below in conjunction with accompanying drawing.
Fig. 1 is the alignment system structural representation of first embodiment of the invention.This off-axis alignment system mainly is made up of lighting module 200, image-forming module 300 and detecting module 400, polarization adjuster 205 and reference marker 312 etc.The major technique characteristics of this off-axis alignment system are: illuminating bundle is imaged onto plane, reference marker 312 place the secondary diffraction takes place behind alignment mark 307 diffraction on the silicon chip, the secondary diffracted beam that all diffraction direction are identical is overlapping relevant at pupil face 315, by the intensity of detection system record interference signal, obtain the positional information of alignment mark according to the phase place variation of signal.
Described alignment system adopts coherent light illumination between multi-wavelength space, (for example has four wavelength at least
,
,
,
), two wavelength are wherein arranged at infrared band.Multi wave length illuminating source is coupled into traffic pilot 103 through fiber coupler 102 then through single-mode polarization maintaining fiber 101 transmission, by single-mode polarization maintaining fiber 104 the multi-wavelength illuminating bundle is outputed to lighting module 200 again.Utilize the multi-wavelength light source lighting, can effectively suppress to interfere the influence of cancellation effect, improve Technological adaptability; Use the light illumination of near infrared and far infrared wavelength, can effectively solve the dielectric material of low k value in the absorption problem of limit of visible spectrum, and can be used for the marker detection of polysilicon process layer, thereby improve registration signal intensity.
In first embodiment, the light beam of light source 100 outputs enters lighting module 200, passes through the polarizer 201, lens 202, illuminating aperture diaphragm 203, lens 204 and polarization adjuster 205 successively.303 constitute the Kohler illumination system from illuminating aperture diaphragm 203 to object lens, as shown in Figure 2.Lens 202 are collector lens, can change the scope of alignment mark 307 place's illumination field of view by adjusting illuminating aperture diaphragm size.Polarization adjuster 205 is used for changing the polarization direction of light beam 105, is used with polarization beam apparatus 301, can accommodation reflex light beam 106 and the energy ratio of transmitted light beam 107, improve the contrast of detectable signal.As shown in Figure 3.The light beam of vertical polarization is through behind the polarization adjuster 205, and the polarization direction turns over angle and is
, establish the polarization beam apparatus optical axis in the vertical direction, then folded light beam 106 and transmitted light beam 107 amplitude ratios are
, the energy ratio is
Polarization adjuster is preferentially selected the magnetic opticity device, avoids the luminous energy loss.At other embodiment, also can select rotatable polaroid as polarization adjuster.
Folded light beam 106 is at first by analyzer 302, and it is identical with the S polarization direction that its polarization sees through direction.Achromatism
Wave plate 303 is converted to circularly polarized light with incident light, through impinging perpendicularly on alignment mark 307 behind the object lens 306 diffraction for the first time takes place, and produces each order diffraction and folded light beam.For obtaining higher alignment precision, object lens 306 should have enough big numerical aperture (for example NA=0.8) and produce more senior diffraction light to collect alignment mark 307.Work as NA=0.8, the alignment mark cycle is when being 8 microns, can guarantee object lens 306 detect described four illumination wavelengths ± 7 order diffraction light.
Achromatism in the described alignment system
Wave plate 302 mainly act as: the one, illuminating bundle is converted to circular polarization, and improve described alignment system to the adaptability of minor cycle alignment mark.When grating cycle of alignment mark with the illumination light wavelength during in identical magnitude, grating diffration efficient is relevant with the polarization characteristic of illumination light.If adopt linearly polarized light incident, may face the risk that grating diffration efficient sharply descends on this polarization direction.Utilize the circularly polarized light illumination can effectively avoid this risk.Circular polarization comprises the orthogonal linearly polarized light of both direction, guarantees always to have a polarization direction can produce high efficiency diffraction light.The 2nd, each order diffraction and reflected light process achromatism that alignment mark 307 is produced
Behind the wave plate 303, circularly polarized light changes the P polarized light into.
Each order diffraction and folded light beam (for example light beam 108,109,110) that alignment mark 307 produces are collected and are passed through achromatism by object lens 306
Wave plate 303 is converted to linearly polarized light (P polarization).Folded light beam 109(also is called 0 order diffraction light) absorbed by analyzer 302, other orders of diffraction time light beam (for example light beam 108,110) sees through polarization beam apparatus 301 and arrives lens 311, and converges to reference marker 312.Described reference marker is not limited to transmission-type grating, can be the diffraction grating of other types, for example reflective gratings, blazed grating etc.All converge to the light beam of reference marker 312 (as diffracted beam 108,110, reference beam 111) diffraction for the second time takes place, secondary diffracted beam with identical angle of diffraction is collected through lens 313, formation-n enters detecting module 400 to+n level interfering beam (as 112,113,114) through catoptron 314 reflections.
Fig. 5 is the secondary diffraction interference synoptic diagram of described alignment system.Illuminating bundle impinges perpendicularly on alignment mark 307 diffraction for the first time takes place, and produces each order diffraction and reflected light.For convenience of description, illuminating bundle only comprises single wavelength among Fig. 2, and only indicate 0, ± 1, ± 3 grades of light beams, more senior diffraction light does not illustrate in the drawings.According to grating equation, the n order diffraction light of alignment mark
Angle of diffraction be
In the formula
Be the alignment mark grating cycle,
Be illumination wavelengths.In the present embodiment, the dutycycle of alignment mark is made as 1:1, in theory idol level time diffraction light
Diffraction efficiency is zero, and idol level light deficient phenomena namely takes place.Therefore, only indicate 0 grade of reflected light among Fig. 5
, ± 1 diffraction light
,
, ± 3 diffraction lights
,
, the strange level time diffraction light that the idol level is inferior and higher does not illustrate.It is worthy of note, in the present embodiment, the zero order light reflected that alignment mark produces
Absorbed the actual light beam that incides reference marker by analyzer 302
For light beam 111(is above-mentioned reference beam).
For the alignment mark with periodic structure, its transmission function
Discrete Fourier is transformed to
（2）
Wherein,
Fourier conversion coefficient for alignment mark is defined as
According to the Fourier optics theory, when plane wave illumination was penetrated, the far-field distribution of grating was proportional to the Fourier conversion of its transmission function, i.e. the n order diffraction light of alignment mark
Amplitude is proportional to
, its light field can be described as
Behind diffraction lights process object lens 306 at different levels, the lens 311, converge to reference marker 312 diffraction for the second time take place.Here, the reference marker cycle is identical with the alignment mark cycle, and dutycycle also is 1:1.The n order diffraction light of alignment mark is designated as through the m order diffraction light beam that reference marker produces
, its angle of diffraction is
Light beam for example
Produce 0 grade, ± 1 grade, ± 3 order diffraction light are designated as respectively
,
,
The secondary diffracted beam
Light field has following form
Wherein
Be the Fourier conversion coefficient of reference marker,
For alignment mark with respect to the displacement of reference marker in the x direction.
According to formula (2), twice order of diffraction is inferior to (namely
) light beam that equates has identical angle of diffraction, and is overlapping relevant at pupil face 315 through lens 313 backs.As shown in Figure 5, secondary diffracted beam
With
Form+3 grades at the pupil face and interfere hot spot;
With
Form+1 grade at the pupil face and interfere hot spot;
,
,
,
With
Form 0 grade at the pupil face and interfere hot spot;
With
Form-1 grade at the pupil face and interfere hot spot;
With
Form-3 grades at the pupil face and interfere hot spot.
Because the disappearance of reference marker idol level time diffraction light, the strange level time n(n=2k+1 in pupil face 315 places) signal is only by two light beams
With
Be concerned with and form its signal intensity
For
Wherein,
Represent two light beams
With
At alignment mark and the normal phase differential of reference marker.By the motion of alignment mark in the x direction, can obtain strange level time m detectable signal at the scan-data of x direction, utilize computing machine to carry out curve fitting, can extract
Phase information
The signal intensity of strange grade time-n of symmetry
For
According to formula (8) and (10), utilize the positive and negative level time signal of symmetry
Phase differential, the displacement information of obtainable alignment mark
In addition, also can utilize intensity difference and intensity and the calculating alignment mark displacement information of positive and negative level time signal.
In the theoretical analysis in front, derive for simplifying, think when the grating dutycycle is 1:1, idol level time diffraction efficiency is zero.And under the actual conditions, alignment mark is the phase grating of multilayer technology structure, even when dutycycle is 1:1, though idol level time diffraction efficiency is very little, non-vanishing.At this moment, the strange level time signal in pupil face 315 places will be the result that a plurality of (greater than 2) secondary diffracted beam is interfered, and will cause this level time signal to comprise a plurality of harmonic componentss, be unfavorable for phase extraction.For avoiding under the actual working conditions, idol level time diffraction light is to the influence of detectable signal, can be at lens pupil face 304 place's placement space diaphragms 305, (each order of diffraction time of two wavelength only is shown in the distribution of pupil face 304 among the figure) as shown in Figure 6.The space diaphragm blocks idol level time diffraction light, allows strange level time diffracted beam to pass through.When using the multi-wavelength illumination, strange level time diffraction light and another wavelength idol level time diffraction light that a certain wavelength may occur are overlapped in pupil face 304 positions, as shown in Figure 6, the 5 order diffraction light of 6 order diffraction light of 532nm wavelength and 633nm are overlapped at pupil face 304.At this moment, can adopt the band pass filter that only allow the 633nm light transmission at 5 order diffraction light-beam positions of 633nm wavelength, thereby stop the passing through of 6 order diffraction light of 532nm wavelength.When using filter plate can effectively solve the multi-wavelength illumination, the aliasing problem of the odd even order diffraction light of different wave length.
When (for example adopting multi wave length illuminating source
,
,
,
) when throwing light on alignment mark simultaneously, the multi-level diffraction light of different wave length is overlapped.Therefore, need polychromatic light piece-rate system 401 that different wavelength is separated, so that subsequent optical path is surveyed.Described polychromatic light piece-rate system can adopt blazed grating, echelon grating or other diffraction optical elements etc. to realize that multi-wavelength separates.Fig. 7 is based on the light-dividing principle figure of the polychromatic light piece-rate system of blazed grating, and after the light beam that comprises 4 wavelength passed through blazed grating 403, each wavelength will be with different angle of diffraction outgoing.
Described interfering beam enters polychromatic light piece-rate system 401 behind catoptron 314, enter after the interfering beam separation with different wave length and survey light path 402a-402d.Polychromatic light piece-rate system 401 is based on dispersion element, and it comprises beam splitting systems such as blazed grating, echelon grating or other diffraction optical elements.Survey light path and comprise (not illustrating among the figure) such as lens, optical fiber, photodetectors.
The detection light path of described alignment system as shown in Figure 8.With wavelength
Detection light path 402a be example, incident beam converges to spatial light filter 405 through lens 404, to eliminate the parasitic light that produces in the alignment system.Lens 406 are with the beam separation of different order of interferences and project the emergent pupil face 315 of lens 313.Photodetector 409 is collected and be transferred to the beam signal of each order of interference by detection optical fiber 406.
The aligning flow process of present embodiment comprises that S801 light source control, S802 obtain light intensity signal, S803 obtains position signalling, the processing of S804 calculated signals and S805 output aligned position as shown in Figure 9.The S801 light source control comprises the modulation to light source phase place, amplitude, and the light beam vertical irradiation of output is to alignment mark.In the S802 intensity collection process, alignment mark is along X(or Y) to uniform motion, photodetector receives each wavelength inferior coherent light not at the same level with given sample frequency.After opto-electronic conversion, signal demodulation, filtering, can obtain each wavelength inferior light intensity values at different levels.The movement position of S803 alignment mark can directly obtain by measurement mechanism, and described measurement mechanism can be laser interferometer, grating chi or both hybrid measurement systems etc.The movement position of alignment mark
Can pass through the measuring position
Deduct the reference position
Obtain,
The reference position is commonly defined as the nominal alignment position.
In existing patent US 6876436 B2 and US 2006/0007446 A1, can obtain the alignment mark displacement information by selecting single or multiple level time interference signal Strength Changes.And in the present invention, must survey the order of interference (for example ± 1 grade, ± 3 grades ...) of a pair of (or many to) symmetry simultaneously, utilize the relative intensity of the positive and negative level time interference signal of symmetry to change (or relative phase variation) and calculate aligned position.
The S804 calculated signals is handled.Be example with single wavelength, three kinds of calculated signals disposal routes are arranged.First kind is the phase place of calculating the positive and negative level time interference signal of symmetry respectively, utilizes phase differential to obtain aligned position.If the intensity of the n class survey signal of this wavelength is
The value of individual sampled point is
, corresponding relative position is
According to formula (7), detectable signal is cosine function as can be known, is constructed as follows the trigonometric function of form for this reason
（13）
Wherein, A
n, B
n, C
nBe fitting coefficient, p is the alignment mark cycle.Utilize least square method, ask for parameter A
n, B
n, C
nMake in the following formula
Amount is minimum
（14）
Wherein N is total hits.When asking for parameter A
n, B
n, C
nAfter, the phase place of this wavelength n class survey signal is
Adopt above-mentioned identical method, can obtain this wavelength-phase place of n class survey signal
（16）
According to formula (11), can try to achieve relative aligned position and be
Second kind of signal processing mode is to utilize the intensity of the positive and negative level time interference signal of symmetry and calculate aligned position.According to formula (7) and (9), the intensity of the positive and negative level of symmetry time signal and have following form
Can ask for its phase place by trigonometric function to the intensity of positive and negative level time signal with carry out match equally
Thereby, produce relative aligned position
First kind of signal processing mode is to utilize the intensity difference of the positive and negative level time interference signal of symmetry to calculate aligned position.According to formula (7) and (9), the intensity difference of the positive and negative level time signal of symmetry has following form
(20)
Can carry out match to the intensity difference of positive and negative level time signal by trigonometric function equally, ask for its phase place
Thereby, produce relative aligned position
It is asymmetric that first kind of calculated signals disposal route can effectively be eliminated the positive and negative level time diffraction efficiency of the alignment mark symmetry that factors such as the mark reflectivity is inhomogeneous cause, and reduces systematic error; The stochastic error that second kind of calculated signals disposal route can detector produces reduces measuring error; First kind of signal processing mode can be eliminated the background noise of interference signal, improves the signal fitting computational accuracy.Actual signal can select one or more disposal routes to calculate relative aligned position in handling.
S805 exports aligned position.In conjunction with the reference position
With the relative aligned position that calculates generation
, export actual aligned position and be
Because light intensity signal is surveyed at the pupil face, the measuring accuracy of described alignment system is subjected to incident light inclination, mark inclination out of focus, and factor affecting such as rotation are less.To as shown in figure 10, when the alignment mark out of focus
, the pitch angle is
The time, its generation ± n order diffraction light
Angle of diffraction become
The open alignment system of the present invention is based on double grating secondary diffraction principle.Be that illuminating bundle incides alignment mark diffraction for the first time takes place, the diffracted beams at different levels of generation with different angle of diffraction from the alignment mark surface scattering; After imaging system, diffraction lights at different levels converge to reference marker and produce diffraction for the second time, and the secondary diffracted beam with identical angle of diffraction is overlapping relevant at finder lens pupil face, according to the relative phase variation of the interference signal that detects, determine aligned position information.Compared with prior art, this alignment system has following advantage: the first, adopt polarization adjuster and polarization beam apparatus, make isolated reference beam energy dynamics adjustable, improve the contrast of detectable signal, increase alignment system to the Technological adaptability of mark.The second, this alignment system is simple in structure, does not need baroque voussoir array (or wedge group) and self-reference interferometer, utilizes the secondary diffraction of reference marker to obtain interference signals at different levels at the pupil face.Reference marker processing and manufacturing, assembling and modulation difficulty are less.Three, this alignment system is surveyed at the pupil face, and registration signal comes from the overlapping of light beam of same space frequency and is concerned with.Factors such as incident light inclination, mark inclination out of focus, rotation are less to the alignment precision influence.Four, by at lens pupil face usage space diaphragm, only select required strange level time diffraction light, avoid idol level time diffraction light to enter detectable signal and produce a plurality of harmonic componentss; Reduced the influence of parasitic light on the other hand.
Described in this instructions is preferred embodiment of the present invention, and above embodiment is only in order to illustrate technical scheme of the present invention but not limitation of the present invention.All those skilled in the art all should be within the scope of the present invention under this invention's idea by the available technical scheme of logical analysis, reasoning, or a limited experiment.
Claims (14)
1. off-axis alignment system that is used for lithographic equipment is used for measuring the aligned position information of an alignment mark, comprising:
Lighting module provides illuminating bundle;
Polarization adjuster be used for to be regulated the polarization direction of described illuminating bundle, makes outgoing after the change of polarized direction predetermined angle theta of described illuminating bundle, and this predetermined angle theta is the processing parameter setting according to described alignment mark;
Reference marker;
Image-forming module, comprise polarizing beam splitter, described polarizing beam splitter will be divided into detecting light beam and reference beam through the illuminating bundle of described polarization adjuster, described image-forming module is collected described reference beam, make described reference beam produce first diffracted beam with a plurality of orders of diffraction time beamlet at described reference marker place diffraction, and collect described detecting light beam, make described detecting light beam produce second diffracted beam with a plurality of orders of diffraction time beamlet via described alignment mark and described reference marker secondary diffraction, respective stages time beamlet forms a plurality of orders of diffraction time interfering beam in the overlapping interference of the pupil plane of described image-forming module in described first diffracted beam and second diffracted beam;
Detecting module is surveyed described a plurality of order of diffraction time interfering beam, and converts described a plurality of orders of diffraction time interfering beam to a plurality of orders of diffraction time interference signal; And
Signal processing module is determined the aligned position information of described alignment mark, the order of diffraction time positive and negative symmetry of the wherein said a pair of order of diffraction time interference signal according to time interference signal of at least one pair of order of diffraction in a plurality of orders of diffraction time interference signal.
2. off-axis alignment as claimed in claim 1 system is characterized in that described polarization adjustment module is the magnetic opticity device or rotates adjustable deflection film.
3. off-axis alignment as claimed in claim 1 system is characterized in that described image-forming module also comprises: first
Wave plate, first lens,
Wave plate, second lens, the 3rd lens, described detecting light beam is via described first
Wave plate, the described alignment mark of the first lens incident, and at the described alignment mark place generation diffraction first time, the diffraction light of diffraction is via described first lens, first for the first time
Wave plate, polarization spectro element,
Wave plate, the described reference marker of the second lens incident, described the 3rd lens with time beamlet of respective stages in described first diffracted beam and second diffracted beam in the overlapping interference of the pupil plane of described the 3rd lens.
4. off-axis alignment as claimed in claim 3 system is characterized in that described image-forming module also comprises the space diaphragm, and described space diaphragm is positioned at the pupil plane place of described first object lens.
5. off-axis alignment as claimed in claim 3 system is characterized in that described image-forming module also comprises analyzer, is arranged on described polarization spectro element and described first
Between the wave plate.
6. off-axis alignment as claimed in claim 3 system is characterized in that described image-forming module also comprises second
Wave plate, reflecting element, described reference beam is via described second
Wave plate is incident to described reflecting element and returns by by described second
Wave plate, polarization spectro element,
Wave plate, the described reference marker of the second lens incident.
7. off-axis alignment as claimed in claim 1 system, it is characterized in that, described lighting module comprises light source, the polarizer, the 3rd lens, aperture diaphragm, the 4th lens, and the light that described light source sends is successively through producing described illuminating bundle outgoing behind the described polarizer, the 4th lens, aperture diaphragm, the 5th lens.
8. off-axis alignment as claimed in claim 7 system is characterized in that described light source is multi wave length illuminating source, comprises the polychromatic light piece-rate system that light that described light sources with different wavelengths is sent separates in the described detecting module.
9. off-axis alignment as claimed in claim 8 system is characterized in that described detecting module comprises a plurality of detection light paths, surveys the isolated different wavelengths of light of described polychromatic light piece-rate system respectively.
10. off-axis alignment as claimed in claim 9 system, it is characterized in that, in described a plurality of detection light path each is surveyed light path and is comprised the 6th lens, spatial light filter, the 7th lens, a plurality of detection optical fiber and a plurality of photodetector in regular turn along optical propagation direction, the incident end of described detection optical fiber closes on described pupil plane, and the exit end of described detection optical fiber is connected with described photodetector.
11. an off-axis alignment method that is used for lithographic equipment is characterized in that, comprising:
One alignment mark and reference marker are provided;
Illuminating bundle is provided, and makes change of polarized direction one predetermined angle theta of this illuminating bundle, this predetermined angle theta is the processing parameter setting according to described alignment mark;
This illuminating bundle is divided into detecting light beam and reference beam;
Described reference light is incident to a reference marker, generation comprises first diffracted beam of a plurality of orders of diffraction time beamlet, described detecting light beam produces second diffracted beam that comprises a plurality of orders of diffraction time beamlet through described alignment mark and described reference marker secondary diffraction, and the corresponding order of diffraction time beamlet forms a plurality of orders of diffraction time interfering beam in the overlapping interference of a pupil plane in described first diffracted beam and second diffracted beam;
Survey described a plurality of order of diffraction time interfering beam, and it is turned to a plurality of orders of diffraction time interference signal;
At least one pair of order of diffraction time interference signal in described a plurality of orders of diffraction time interference signal is carried out the signal treatment step to determine the positional information of described alignment mark, the order of diffraction time positive and negative symmetry of the wherein said a pair of order of diffraction time interference signal.
12. off-axis alignment method as claimed in claim 11 is characterized in that, described signal treatment step is the positional information of the described alignment mark of phase difference calculating of utilizing the interference signal of the order of diffraction time positive and negative symmetry.
13. off-axis alignment method as claimed in claim 11 is characterized in that, described signal treatment step be utilize the order of diffraction time positive and negative symmetry interference signal intensity and the positional information of the described alignment mark of phase calculation.
14. off-axis alignment method as claimed in claim 11 is characterized in that, described signal treatment step is the positional information of the described alignment mark of phase calculation of utilizing the interference signal intensity difference of the order of diffraction time positive and negative symmetry.
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