CN103293884B - 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, particularly relate to a kind of off-axis alignment system for lithographic equipment and alignment methods.
Background technology
Lithographic equipment is the major equipment manufacturing integrated circuit, and its effect is the position making different mask patterns be imaged onto the accurate aligning in substrate (as semi-conductor silicon chip or LCD plate) successively.But this aligned position but changes because of the physical and chemical changes that experiences of row graph, therefore needs an alignment system, to ensure that the aligned position of the corresponding mask of silicon chip can both be aimed at accurately at every turn.Along with the growth of the number of electronic components on substrate per unit surface area and the size of electronic component are synthesized more and more less, the accuracy requirement of integrated circuit is improved day by day, therefore mask is imaged on suprabasil position and must fixes more and more accurately successively, also more and more higher to the requirement of alignment precision during photoetching.
At present, mostly institute adopts lithographic equipment is alignment system based on optical grating diffraction interference.Such alignment system essential characteristic is: the illumination beam comprising single wavelength or multi-wavelength, on grating type alignment mark, diffraction occurs, and the diffraction lights at different levels of generation carry the positional information about alignment mark; The light beam of not at the same level time scatters from phase alignment grating with different angle of diffraction, the diffracted beam of at different levels times is collected by alignment system, make two symmetrical positive and negative orders of diffraction time (as ± 1 grade, ± 2 grades, ± level etc.) the image planes of alignment system or pupil face overlap relevant, form interference signal at different levels.When scanning mark grating, utilizing the Strength Changes of photodetectors register interference signal, by signal transacting, determining centering adjustment position.
At present, representative in 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 overlap and the coherent imaging of alignment mark multi-level diffraction light, and in image planes, imaging space is separated; Ruddiness is separated by a polarization beam splitter prism with the registration signal of green glow; By the transmitted light intensity of detection alignment mark picture through reference marker, obtain the sinusoidal registration signal exported.First, because this system adopts the beam splitting system of polarization beam splitter prism can only be separated the coloured light of two wavelength, then helpless to registration signal more than two wavelength; Secondly the multi-level diffraction light of this alignment system is at image plane interference, and when alignment mark reflectivity is uneven, the alignment error that the factors such as mark rotation, magnification error cause is larger; Finally, when this alignment system uses voussoir array, face type and the angle of wedge coherence request of two voussoirs of the positive and negative same stages of birefringence time are very high; And the requirement of the processing and manufacturing of wedge group, assembling and adjustment is also very high, specific implementation engineering difficulty of getting up is comparatively large, costs dearly, and poor to the Technological adaptability of alignment mark.
Another prior art is SMASH off-axis alignment system.This system rotates Self-referencing interferometer by one and produces the alignment mark picture that two revolve turnback relatively, detects the interference signal of the overlapping order of diffraction at pupil plane, and the relative phase change according at different levels the interference signals detected obtains aligned position signal.This alignment system have employed many principal sections, the rotation Self-referencing interferometer of space composite prism result, the processing of prism and to debug tolerance very high, and prism group gummed difficulty is larger.
Prior art is needed badly and is wanted a kind of new off-axis alignment system, effectively can overcome engineering difficulty comparatively large, the technological deficiency of processing cost costliness.
Summary of the invention
In order to overcome the defect existed in prior art, an object of the present invention is to provide a kind of off-axis alignment system and method, can regulate reference light and the energy Ratios of detection light, increase system to the adaptability of alignment mark.
Another object of the present invention is to provide a kind of off-axis alignment system for lithographic equipment and alignment methods, simple for structure and effectively according to the relative phase change of the interference signal that detects, aligned position information can be determined.
The present invention discloses a kind of off-axis alignment system for lithographic equipment, for measuring the aligned position information of an alignment mark, comprising: lighting module, providing illuminating bundle, polarization adjuster, for regulating the polarization direction of this illuminating bundle, make outgoing after the change of polarized direction predetermined angle theta of this illuminating bundle, this predetermined angle theta is the processing parameter setting according to this alignment mark, reference marker, image-forming module, comprise polarizing beam splitter, illuminating bundle through this polarization adjuster is divided into detecting light beam and reference beam by this polarizing beam splitter, this image-forming module collects this reference beam, this reference beam is made to produce first diffracted beam with multiple order of diffraction time beamlet at this reference marker place diffraction, and collect this detecting light beam, this detecting light beam is made to produce second diffracted beam with multiple order of diffraction time beamlet via this alignment mark and this reference marker re-diffraction, in this first diffracted beam and the second diffracted beam, respective stages time beamlet is at the pupil plane overlying interference of this image-forming module, form multiple order of diffraction time interfering beam, detecting module, detects the plurality of order of diffraction time interfering beam, and converts the plurality of order of diffraction time interfering beam to multiple order of diffraction time interference signal, and signal processing module, determine the aligned position information of this alignment mark according at least one pair of order of diffraction time interference signal in multiple order of diffraction time interference signal, wherein the order of diffraction time Symmetrical of this pair order of diffraction time interference signal.
Further, this polarization adjustment module is magnetic opticity device or rotates adjustable deflection film.
Further, this image-forming module also comprises: first
wave plate, the first lens,
wave plate, the second lens, the 3rd lens, this detecting light beam via this first
wave plate, this alignment mark of the first lens entrance, and there is first time diffraction at this alignment mark place, the diffraction light of diffraction is via these the first lens, first for the first time
wave plate, polarization beam splitter,
wave plate, this reference marker of the second lens entrance, the 3rd lens are by the pupil plane overlying interference of time beamlet of respective stages in this first diffracted beam and the second diffracted beam at the 3rd lens.This image-forming module also comprises space diaphragm, and this space diaphragm is positioned at the pupil plane place of these the first object lens.This image-forming module also comprises analyzer, be arranged on this polarization beam splitter and this first
between 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 after through by this second
wave plate, polarization beam splitter,
wave plate, this reference marker of the second lens entrance.
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 produces this illuminating bundle outgoing successively after this polarizer, the 4th lens, aperture diaphragm, the 5th lens.This light source is multi wave length illuminating source, and this detecting module comprises the polychromatic light piece-rate system of the light separation sent by this light sources with different wavelengths.
Further, this detecting module comprises multiple detection light path, detects the isolated different wavelengths of light of this polychromatic light piece-rate system respectively.Each detection light path in the plurality of detection light path sequentially comprises the 6th lens, spatial light filter, the 7th lens, multiple detection optical fiber and multiple photodetector along optical propagation direction, the incidence 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: provide an alignment mark and reference marker; There is provided illuminating bundle, and make 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, produce the first diffracted beam comprising multiple order of diffraction time beamlet, this detecting light beam produces the second diffracted beam comprising multiple order of diffraction time beamlet through this alignment mark and this reference marker re-diffraction, in this first diffracted beam and the second diffracted beam, the corresponding order of diffraction time beamlet forms multiple order of diffraction time interfering beam at a pupil plane overlying interference; Detect the plurality of order of diffraction time interfering beam, and turned to multiple order of diffraction time interference signal; Signal transacting step is carried out to determine the positional information of this alignment mark at least one pair of order of diffraction time interference signal in the plurality of order of diffraction time interference signal, wherein the order of diffraction time Symmetrical of this pair order of diffraction time interference signal.
Further, this signal transacting step is the positional information of this alignment mark of phase difference calculating of the interference signal utilizing the order of diffraction time Symmetrical.This signal transacting step be utilize the order of diffraction time Symmetrical interference signal intensity and the positional information of this alignment mark of phase calculation.This signal transacting step is the positional information of this alignment mark of phase calculation of the interference signal intensity difference utilizing the order of diffraction time Symmetrical.
The open alignment system of the present invention is based on double grating re-diffraction principle.Namely illuminating bundle incides alignment mark first time diffraction occurs, the diffracted beams at different levels of generation with different angle of diffraction from alignment mark surface scattering; After imaging system, diffraction light at different levels converges to reference marker and produces second time diffraction, and the re-diffraction light beam with identical angle of diffraction is relevant in finder lens pupil face overlap, and the relative phase according to the interference signal detected changes, and determines aligned position information.Compared with prior art, this alignment system tool has the following advantages: the first, adopt polarization adjuster and polarization beam apparatus, make isolated reference beam energy dynamics adjustable, improves the contrast of detectable signal, increases the Technological adaptability of alignment system to mark.The second, this alignment system structure is simple, and the voussoir array (or wedge group) of Structure of need complexity and Self-referencing interferometer, do not utilize the re-diffraction of reference marker can obtain interference signal at different levels in pupil face.Reference marker processing and manufacturing, assembling and modulation difficulty are less.Three, this alignment system is in the detection of pupil face, and the overlap that registration signal comes from the light beam of same space frequency is concerned with.The factors such as incident light tilts, mark inclination out of focus, rotation are less on alignment precision impact.Four, pass through at lens pupil face usage space diaphragm, the strange level time diffraction light needed for only selecting, avoid even level time diffraction light to enter detectable signal and produce multiple harmonic components; Reduce the impact of parasitic light on the other hand.
Accompanying drawing explanation
Can be further understood by following detailed Description Of The Invention and institute's accompanying drawings about the advantages and spirit of the present invention.
Fig. 1 is the structural representation of the first embodiment of alignment system involved in the present invention;
Fig. 2 is the lighting module light channel structure schematic 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 re-diffraction interference structure schematic diagram of alignment system involved in the present invention;
Fig. 5 is the pupil face mechanism of diaphragm schematic diagram of alignment system involved in the present invention;
Fig. 6 is the light-dividing principle figure of the polychromatic light piece-rate system based on 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 schematic diagram when Fig. 9 is alignment mark inclination out of focus;
Figure 10 is the structural representation of the second embodiment of alignment system involved in the present invention.
Embodiment
Specific embodiments of the invention are described 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 is primarily of compositions such as lighting module 200, image-forming module 300 and detecting module 400, polarization adjuster 205 and reference markers 312.The technical characteristics of this off-axis alignment system is: alignment mark 307 image after diffraction of illuminating bundle on silicon chip is to reference marker 312 place plane generation re-diffraction, the re-diffraction light beam that all diffraction direction are identical is relevant in pupil face 315 overlap, by the intensity of detection system record interference signal, obtain the positional information of alignment mark according to the phase place change of signal.
Lighting module 200 in described alignment system mainly comprises light source 100, shutter, optoisolator and the phase-modulator (not shown in FIG.) etc. that provide multi-wavelength.Described light source prioritizing selection high brightness, the laser instrument that coherence is good, such as semiconductor laser, or fiber laser etc.; Phase-modulator is used for illuminating bundle phase-modulation, effectively can suppress the coherence of parasitic light and flashlight, reduces the contrast of posting and interfering carded sliver line, improves signal to noise ratio (S/N ratio).
Described alignment system adopts coherent light illumination between multi-wavelength space, has four wavelength at least (such as
,
,
,
), wherein there are two wavelength at infrared band.Multi wave length illuminating source transmits through single-mode polarization maintaining fiber 101, is then coupled into traffic pilot 103 through fiber coupler 102, then by single-mode polarization maintaining fiber 104, multi-wavelength illuminating bundle is outputted to lighting module 200.Utilize multi-wavelength light source lighting, effectively can suppress the impact interfering cancellation effect, improve Technological adaptability; Use the light illumination of near infrared and far infrared wavelength, effectively can solve the absorption problem of dielectric material in limit of visible spectrum of low k-value, and can be used for the marker detection of polysilicon process layer, thus improve registration signal intensity.
In a first embodiment, the light beam that light source 100 exports enters lighting module 200, successively through the polarizer 201, lens 202, illuminating aperture diaphragm 203, lens 204 and polarization adjuster 205.Kohler illumination system is formed to object lens 303, as shown in Figure 2 from illuminating aperture diaphragm 203.Lens 202 are collector lens, by the scope regulating illuminating aperture diaphragm size can change alignment mark 307 place illumination field of view.Polarization adjuster 205 for changing the polarization direction of light beam 105, with polarization beam apparatus 301 with the use of, can the energy ratio of accommodation reflex light beam 106 and transmitted light beam 107, improve the contrast of detectable signal.As shown in Figure 3.The light beam of vertical polarization is after polarization adjuster 205, and polarization direction turns over angle and is
if in the vertical direction, then folded light beam 106 and transmitted light beam 107 amplitude ratio are polarization beam apparatus optical axis
, energy Ratios is
.Polarization adjuster prioritizing selection magnetic opticity device, avoids luminous energy loss.In other embodiments, rotatable polaroid also can be selected as polarization adjuster.
Illuminating bundle 105 is divided into polarization direction orthogonal reflected light 106(S polarization through polarization beam apparatus 301 beam-splitting surface) and transmitted light 107(P polarization).Transmitted light beam 107 reflects through catoptron 309, passes twice through achromatism
become S polarized light after wave plate 308, entered achromatism at polarization beam apparatus beam-splitting surface by reflection
wave plate 310, its optical axis direction becomes 45 degree with S polarization direction, can make the light beam polarization direction 90-degree rotation of S polarization, become P polarized light 111.Light beam 111 arrives reference marker 312 as with reference to light beam through lens 311.This reference beam can replace together with non-zero order time diffraction light that 0 order diffraction light 109 that reflected light 106 produces after alignment mark 307 diffraction and alignment mark produce and produces re-diffraction at reference marker 312 place.
Folded light beam 106 is first by analyzer 302, and its polarization is identical with S polarization direction through direction.Achromatism
incident light is converted to circularly polarized light by wave plate 303, impinges perpendicularly on alignment mark 307 and first time diffraction occurs, produce each order diffraction and folded light beam after object lens 306.For obtaining higher alignment precision, object lens 306 should have enough large numerical aperture (such as NA=0.8) and produce more senior diffraction light to collect alignment mark 307.Work as NA=0.8, when the alignment mark cycle is 8 microns, can ensure object lens 306 detect described four illumination wavelengths ± 7 order diffraction light.
Achromatism in described alignment system
wave plate 302 Main Function is: one is that illuminating bundle is converted to circular polarization, improves the adaptability of described alignment system to minor cycle alignment mark.When the screen periods of alignment mark with illumination light wavelength in identical magnitude time, grating diffration efficiency is relevant with the polarization characteristic of illumination light.If adopt linearly polarized light incident, the risk that grating diffration efficiency sharply declines on this polarization direction may be faced.Utilize circularly polarized light to throw light on and can effectively avoid this risk.Circular polarization comprises the orthogonal linearly polarized light of both direction, and guaranteeing always has a polarization direction can produce high efficiency diffraction light.Two be alignment mark 307 is produced each order diffraction and reflected light through achromatism
after wave plate 303, circularly polarized light changes P polarized light into.
Each order diffraction that alignment mark 307 produces and folded light beam (such as light beam 108,109,110), collected by object lens 306 and pass through achromatism
wave plate 303 is converted to linearly polarized light (P polarization).Folded light beam 109(is also called 0 order diffraction light) absorbed by analyzer 302, other orders of diffraction time light beam (such as light beam 108,110) arrives lens 311 through polarization beam apparatus 301, and converges to reference marker 312.Described reference marker is not limited to transmission-type grating, can be the diffraction grating of other types, such as reflective gratings, blazed grating etc.All light beams converging to reference marker 312 are (as diffracted beam 108,110, reference beam 111) there is second time diffraction, the re-diffraction light beam with identical angle of diffraction is collected through lens 313, form-n to+n level interfering beam (as 112,113,114), enter detecting module 400 through catoptron 314 reflection.
Space diaphragm 305 is positioned over pupil face 304 place of object lens 306, and the light beam of the order of diffraction required for selection time passes through, and can reduce parasitic light, improves the signal to noise ratio (S/N ratio) of detection system.Object lens 306 and lens composition 4f imaging system, can by the front surface being imaged onto reference marker 312 of alignment mark 307 equal proportion.
Fig. 5 is that the re-diffraction of described alignment system interferes schematic diagram.Illuminating bundle impinges perpendicularly on alignment mark 307 and first time diffraction occurs, and produces each order diffraction and reflected light.For convenience of description, in Fig. 2, illuminating bundle only comprises single wavelength, and only indicate 0, ± 1, ± 3 grades of light beams, more Advanced Diffraction light does not illustrate in the drawings.According to grating equation, the n order diffraction light of alignment mark
angle of diffraction be
（1）
In formula
for alignment mark screen periods,
for illumination wavelengths.In the present embodiment, the dutycycle of alignment mark is set to 1:1, in theory even level time diffraction light
diffraction efficiency is zero, and namely even level light deficient phenomena occurs.Therefore, 0 grade of reflected light is only indicated in Fig. 5
, ± 1 diffraction light
,
, ± 3 diffraction lights
,
, even level time does not illustrate with higher strange level time diffraction light.It is worthy of note, in the present embodiment, the zero order light reflected that alignment mark produces
absorbed by analyzer 302, the actual light beam inciding reference marker
for light beam 111(and above-mentioned reference beam).
For the alignment mark with periodic structure, its transmission function
discrete Fourier is transformed to
（2）
Wherein,
for the Fourier conversion coefficient of alignment mark, be defined as
（3）
Theoretical according to Fourier optics, when plane wave illumination is penetrated, the far-field distribution of grating is proportional to the Fourier conversion of its transmission function, i.e. the n order diffraction light of alignment mark
amplitude proportional in
, its light field can be described as
（4）
Diffraction light at different levels, after object lens 306, lens 311, converges to reference marker 312 and second time diffraction occurs.Here, the reference marker cycle is identical with the alignment mark cycle, and dutycycle is also 1:1.The m order diffraction light beam that n-th order diffraction light of alignment mark produces through reference marker is designated as
, its angle of diffraction is
（5）
Such as light beam
0 grade that produces, ± 1 grade, ± 3 order diffraction light are designated as respectively
,
,
.Re-diffraction light beam
light field has following form
（6）
Wherein
for the Fourier conversion coefficient of reference marker,
for alignment mark is relative to the displacement of reference marker in x direction.
According to formula (2), twice order of diffraction time and (namely
) equal light beam has identical angle of diffraction, relevant in pupil face 315 overlap after lens 313.As shown in Figure 5, re-diffraction light beam
with
form+3 grades in pupil face and interfere hot spot;
with
form+1 grade in pupil face and interfere hot spot;
,
,
,
with
form 0 grade in pupil face and interfere hot spot;
with
form-1 grade in pupil face and interfere hot spot;
with
form-3 grades in pupil face and interfere hot spot.
Due to the disappearance of the even level of reference marker time diffraction light, the strange level in pupil face 315 place time n(n=2k+1) signal is only by two light beams
with
be concerned with and form, its signal intensity
for
（7）
Wherein,
represent two light beams
with
at alignment mark and the normal phase differential of reference marker.By the motion of alignment mark in x direction, the strange level time scan-data of m detectable signal in x direction can be obtained, utilize computing machine to carry out curve fitting, can extract
phase information
（8）
The signal intensity of symmetrical strange level time-n
for
（9）
phase place be
（10）
According to formula (8) and (10), utilize symmetrical positive and negative level time signal
phase differential, the displacement information of obtainable alignment mark
（11）
In addition, the intensity difference of positive and negative level time signal and intensity and calculating alignment mark displacement information can also be utilized.
In theoretical analysis above, deriving, thinking when grating dutycycle is 1:1 for simplifying, even level time diffraction efficiency is zero.And under actual conditions, alignment mark is the phase grating of multilayer technology structure, even if when dutycycle is 1:1, although even level time diffraction efficiency is very little, non-vanishing.Now, the strange level in pupil face 315 place time signal will be the result of multiple (being greater than 2) re-diffraction beam interference, this level time signal will be caused to comprise multiple harmonic components, be unfavorable for phase extraction.Under avoiding actual working conditions, even level time diffraction light, on the impact of detectable signal, at lens pupil face 304 place placement space diaphragm 305, (can only illustrate the secondary distribution in pupil face 304 of each order of diffraction of two wavelength) as shown in Figure 6 in figure.Space diaphragm blocks even level time diffraction light, allows strange level time diffracted beam to pass through.When using multi-wavelength illumination, may occur that strange level time diffraction light and the even level time diffraction light of another wavelength of a certain wavelength partly overlap in position, pupil face 304, as shown in Figure 6,6 order diffraction light of 532nm wavelength and the 5 order diffraction light of 633nm partly overlap in pupil face 304.Now, can adopt at 5 order diffraction light-beam positions of 633nm wavelength the band pass filter only allowing 633nm light transmission, thus stop passing through of 6 order diffraction light of 532nm wavelength.When using filter plate effectively can solve multi-wavelength illumination, the Aliasing Problem of the odd even order diffraction light of different wave length.
When adopting multi wave length illuminating source (such as
,
,
,
) simultaneously throw light on alignment mark time, the multi-level diffraction light of different wave length is overlapped.Therefore, need polychromatic light piece-rate system 401 to be separated by different wavelength, so that subsequent optical path detection.Described polychromatic light piece-rate system can adopt blazed grating, echelon grating or other diffraction optical elements etc. to realize multi-wavelength and be separated.Fig. 7 is the light-dividing principle figure of the polychromatic light piece-rate system based on blazed grating, and after the light beam comprising 4 wavelength is by blazed grating 403, each wavelength is by with different angle of diffraction outgoing.
Described interfering beam enters polychromatic light piece-rate system 401 after catoptron 314, enters detection light path 402a-402d after being separated by the interfering beam of different wave length.Polychromatic light piece-rate system 401 is based on dispersion element, and it comprises the beam splitting systems such as blazed grating, echelon grating or other diffraction optical elements.Detection light path comprises the (not shown in FIG.) such as lens, optical fiber, photodetector.
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 produced in alignment system.Lens 406 are by the beam separation of different order of interference and project the emergent pupil face 315 of lens 313.The beam signal of each order of interference is collected by detection optical fiber 406 and is transferred to photodetector 409.
The aligning flow process of the present embodiment as shown in Figure 9, comprises S801 light source control, S802 acquisition light intensity signal, S803 acquisition position signalling, the computing of S804 signal and S805 and exports aligned position.S801 light source control comprises the modulation to source phase, amplitude, and the beam orthogonal of output is irradiated to alignment mark.In S802 intensity collection process, alignment mark is along X(or Y) to uniform motion, photodetector receives each wavelength secondary coherent light not at the same level with given sample frequency.After opto-electronic conversion, signal receiving, filtering, each wavelength secondary light intensity value at different levels can be obtained.The movement position of S803 alignment mark directly obtains by measurement mechanism, and described measurement mechanism can be laser interferometer, grating scale or both hybrid measurement systems etc.The movement position of alignment mark
by measuring position
deduct reference position
obtain,
。（12）
Reference position is commonly defined as nominal alignment position.
In existing patent US 6876436 B2 and US 2006/0007446 A1, alignment mark displacement information can be obtained by selecting single or multiple level time interference signal Strength Changes.And in the present invention, must detect simultaneously a pair (or multipair) symmetrical order of interference (such as ± 1 grade, ± 3 grades ...), utilize relative intensity change (or relative phase change) of symmetrical positive and negative level time interference signal to calculate aligned position.
The computing of S804 signal.For single wavelength, there are three kinds of signal computation processing methods.The first is the phase place calculating symmetrical positive and negative level time interference signal 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), known detectable signal is cosine function, 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 following formula
measure 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
（15）
Adopt above-mentioned identical method, the phase place of-n class survey signal of this wavelength can be obtained
（16）
According to formula (11), can try to achieve relative alignment position is
（17）
The second signal processing mode utilizes the intensity of symmetrical positive and negative level time interference signal and calculates aligned position.According to formula (7) and (9), the intensity of symmetrical positive and negative level time signal and there is following form
(18)
Equally by trigonometric function to the intensity of positive and negative level time signal with carry out matching, ask for its phase place
, thus produce relative alignment position
（19）
The first signal processing mode utilizes the intensity difference of symmetrical positive and negative level time interference signal to calculate aligned position.According to formula (7) and (9), the intensity difference of symmetrical positive and negative level time signal has following form
(20)
Carry out matching by the intensity difference of trigonometric function to positive and negative level time signal equally, ask for its phase place
, thus produce relative alignment position
（21）
The positive and negative level time diffraction efficiency that the first signal computation processing method effectively can eliminate the alignment mark symmetry that the mark factors such as reflectivity is uneven cause is asymmetric, reduces systematic error; The second signal computation processing method can detector produce stochastic error, reduce measuring error; The first signal processing mode can eliminate the background noise of interference signal, improves signal fitting computational accuracy.In actual signal process, one or more disposal routes can be selected to calculate relative alignment position.
S805 exports aligned position.In conjunction with reference position
with the relative alignment position calculating generation
, exporting actual aligned position is
（22）
Because light intensity signal is in the detection of pupil face, the measuring accuracy of described alignment system tilts by incident light, mark inclination out of focus, and the factor impacts such as rotation are less.To as shown in Figure 10, when alignment mark out of focus
, pitch angle is
time, it produces ± n order diffraction light
angle of diffraction become
。（23）
the re-diffraction light beam that light beam produces by reference to mark 313
to be similar in detection pupil face 315
position offsets.Because light beam has certain bulk, light beam
,
respectively with light beam
,
major part is overlapping relevant.Two light beams, in the incomplete coincidence in pupil face, cause interference region area to reduce, and cause detectable signal contrast to decline to some extent, but do not affect the phase place of detectable signal, therefore less on the measuring accuracy impact of alignment system.
The open alignment system of the present invention is based on double grating re-diffraction principle.Namely illuminating bundle incides alignment mark first time diffraction occurs, the diffracted beams at different levels of generation with different angle of diffraction from alignment mark surface scattering; After imaging system, diffraction light at different levels converges to reference marker and produces second time diffraction, and the re-diffraction light beam with identical angle of diffraction is relevant in finder lens pupil face overlap, and the relative phase according to the interference signal detected changes, and determines aligned position information.Compared with prior art, this alignment system tool has the following advantages: the first, adopt polarization adjuster and polarization beam apparatus, make isolated reference beam energy dynamics adjustable, improves the contrast of detectable signal, increases the Technological adaptability of alignment system to mark.The second, this alignment system structure is simple, and the voussoir array (or wedge group) of Structure of need complexity and Self-referencing interferometer, do not utilize the re-diffraction of reference marker can obtain interference signal at different levels in pupil face.Reference marker processing and manufacturing, assembling and modulation difficulty are less.Three, this alignment system is in the detection of pupil face, and the overlap that registration signal comes from the light beam of same space frequency is concerned with.The factors such as incident light tilts, mark inclination out of focus, rotation are less on alignment precision impact.Four, pass through at lens pupil face usage space diaphragm, the strange level time diffraction light needed for only selecting, avoid even level time diffraction light to enter detectable signal and produce multiple harmonic components; Reduce the impact of parasitic light on the other hand.
Just preferred embodiment of the present invention described in this instructions, 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., for an off-axis alignment system for lithographic equipment, for measuring the aligned position information of an alignment mark, comprising:
Lighting module, provides illuminating bundle;
Polarization adjuster, for regulating the polarization direction of described illuminating bundle, make outgoing after the change of polarized direction predetermined angle theta of described illuminating bundle, this predetermined angle theta is the processing parameter setting according to described alignment mark;
Reference marker;
Image-forming module, comprise polarizing beam splitter, illuminating bundle through described polarization adjuster is divided into detecting light beam and reference beam by described polarizing beam splitter, described image-forming module collects described reference beam, described reference beam is made to produce first diffracted beam with multiple order of diffraction time beamlet at described reference marker place diffraction, and collect described detecting light beam, described detecting light beam is made to produce second diffracted beam with multiple order of diffraction time beamlet via described alignment mark and described reference marker re-diffraction, in described first diffracted beam and the second diffracted beam, respective stages time beamlet is at the pupil plane overlying interference of described image-forming module, form multiple order of diffraction time interfering beam,
Detecting module, detects described multiple order of diffraction time interfering beam, and converts described multiple order of diffraction time interfering beam to multiple order of diffraction time interference signal; And
Signal processing module, determines the aligned position information of described alignment mark according at least one pair of order of diffraction time interference signal in multiple order of diffraction time interference signal, the order of diffraction time Symmetrical of wherein said a pair order of diffraction time interference signal.
2. off-axis alignment system as claimed in claim 1, it is characterized in that, described polarization adjustment module is magnetic opticity device or rotates adjustable deflection film.
3. off-axis alignment system as claimed in claim 1, it is characterized in that, described image-forming module also comprises: first
wave plate, the first lens,
wave plate, the second lens, the 3rd lens, described detecting light beam is via described first
alignment mark described in wave plate, the first lens entrance, and there is first time diffraction at described alignment mark place, the diffraction light of diffraction is via described first lens, first for the first time
wave plate, polarization beam splitter,
reference marker described in wave plate, the second lens entrance, described 3rd lens are by the pupil plane overlying interference of time beamlet of respective stages in described first diffracted beam and the second diffracted beam at described image-forming module.
4. off-axis alignment system as claimed in claim 3, it is characterized in that, described image-forming module also comprises space diaphragm, and described space diaphragm is positioned at the pupil plane place of described first lens.
5. off-axis alignment system as claimed in claim 3, it is characterized in that, described image-forming module also comprises analyzer, is arranged on described polarization beam splitter and described first
between wave plate.
6. off-axis alignment system as claimed in claim 3, it is characterized in that, described image-forming module also comprises second
wave plate, reflecting element, described reference beam is via described second
wave plate be incident to described reflecting element return after through by described second
wave plate, polarization beam splitter,
reference marker described in wave plate, the second lens entrance.
7. off-axis alignment system as claimed in claim 1, it is characterized in that, described lighting module comprises light source, the polarizer, the 4th lens, aperture diaphragm, the 5th lens, and the light that described light source sends produces described illuminating bundle outgoing successively after the described polarizer, the 4th lens, aperture diaphragm, the 5th lens.
8. off-axis alignment system as claimed in claim 7, it is characterized in that, described light source is multi wave length illuminating source, and described detecting module comprises the polychromatic light piece-rate system of the light separation sent by described light sources with different wavelengths.
9. off-axis alignment system as claimed in claim 8, it is characterized in that, described detecting module comprises multiple detection light path, detects the isolated different wavelengths of light of described polychromatic light piece-rate system respectively.
10. off-axis alignment system as claimed in claim 9, it is characterized in that, each detection light path in described multiple detection light path sequentially comprises the 6th lens, spatial light filter, the 7th lens, multiple detection optical fiber and multiple photodetector along optical propagation direction, the incidence 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. 1 kinds, for the off-axis alignment method of lithographic equipment, is characterized in that, comprising:
One alignment mark and reference marker are provided;
There is provided illuminating bundle, and make 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, produce the first diffracted beam comprising multiple order of diffraction time beamlet, described detecting light beam produces the second diffracted beam comprising multiple order of diffraction time beamlet through described alignment mark and described reference marker re-diffraction, in described first diffracted beam and the second diffracted beam, the corresponding order of diffraction time beamlet forms multiple order of diffraction time interfering beam at a pupil plane overlying interference;
Detect described multiple order of diffraction time interfering beam, and turned to multiple order of diffraction time interference signal;
Signal transacting step is carried out to determine the positional information of described alignment mark at least one pair of order of diffraction time interference signal in described multiple order of diffraction time interference signal, the order of diffraction time Symmetrical of wherein said a pair order of diffraction time interference signal.
12. off-axis alignment methods as claimed in claim 11, is characterized in that, described signal transacting step be the interference signal utilizing the order of diffraction time Symmetrical phase difference calculating described in the positional information of alignment mark.
13. off-axis alignment methods as claimed in claim 11, is characterized in that, described signal transacting step be utilize the order of diffraction time Symmetrical interference signal intensity and phase calculation described in the positional information of alignment mark.
14. off-axis alignment methods as claimed in claim 11, is characterized in that, described signal transacting step be the interference signal intensity difference utilizing the order of diffraction time Symmetrical phase calculation described in the positional information of alignment mark.
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| CN104460247A (en) * | 2013-09-18 | 2015-03-25 | 上海微电子装备有限公司 | Alignment device and alignment method |
| CN104460248B (en) * | 2013-09-18 | 2019-05-31 | 上海微电子装备（集团）股份有限公司 | Alignment device |
| CN104950584B (en) * | 2014-03-25 | 2018-01-30 | 上海微电子装备（集团）股份有限公司 | Imaging is to Barebone |
| CN105807573B (en) | 2014-12-31 | 2017-12-29 | 上海微电子装备（集团）股份有限公司 | Apparatus and method for overlay error detection |
| CZ307520B6 (en) * | 2017-09-21 | 2018-11-07 | Vysoké Učení Technické V Brně | An imaging module for off-axis recording of polarized wavelengths |
| CN109725466A (en) * | 2017-10-31 | 2019-05-07 | 上海微电子装备（集团）股份有限公司 | Polarization illuminator, light orientation equipment and polarized illumination control method |
| CN110262058B (en) * | 2019-06-19 | 2021-11-23 | 中国工程物理研究院应用电子学研究所 | Auxiliary pupil optical axis adjusting device and method |
| CN110954007B (en) * | 2019-11-27 | 2022-06-07 | 长江存储科技有限责任公司 | Wafer detection system and detection method |
| CN113448192B (en) * | 2020-03-26 | 2022-08-30 | 上海微电子装备（集团）股份有限公司 | Alignment system and photoetching machine |
| CN113448191B (en) * | 2020-03-26 | 2022-11-29 | 上海微电子装备（集团）股份有限公司 | Alignment system and photoetching machine |
| CN114755838B (en) * | 2022-04-01 | 2024-04-05 | 北京半导体专用设备研究所（中国电子科技集团公司第四十五研究所） | Optical alignment system |
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