CN110244527A - A kind of overlay mark pattern and measuring condition optimization method - Google Patents
A kind of overlay mark pattern and measuring condition optimization method Download PDFInfo
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- CN110244527A CN110244527A CN201910510463.5A CN201910510463A CN110244527A CN 110244527 A CN110244527 A CN 110244527A CN 201910510463 A CN201910510463 A CN 201910510463A CN 110244527 A CN110244527 A CN 110244527A
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
- G03F7/70—Microphotolithographic exposure; Apparatus therefor
- G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
- G03F7/70605—Workpiece metrology
- G03F7/70616—Monitoring the printed patterns
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
- G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
- G03F9/7073—Alignment marks and their environment
- G03F9/708—Mark formation
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
- G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
- G03F9/7088—Alignment mark detection, e.g. TTR, TTL, off-axis detection, array detector, video detection
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- General Physics & Mathematics (AREA)
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- Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
- Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)
Abstract
The invention discloses a kind of overlay mark pattern and measuring condition optimization methods, belong to field of lithography.Firstly, determining overlay mark appearance structure and materials optical constant according to photoetching process.Secondly, alignment optical characterisation curve can be calculated by the modeling method of parsing or numerical value.Then, the expression formula of alignment measurement reproducibility precision and accuracy is obtained according to Taylor's formula.Then, variable to be optimized and suitable multi-objective Algorithm are selected, alignment measurement reproducibility precision and accuracy are optimized, obtains multiple Pareto optimization results.Finally, it is verified that the robustness of multiple Pareto optimization results, selects the preferable result of robustness as final optimization pass result.The overlay mark pattern and measuring condition of eDBO method is optimized in method disclosed by the invention simultaneously, final optimization pass result has the characteristics that repeatability precision is high, accuracy of measurement is high, measurement robustness is good, meets the needs that overlay error measures in photoetching process.
Description
Technical field
The invention belongs to field of lithography, more particularly, to a kind of overlay mark pattern and measuring condition optimization method.
Background technique
With the rapid development of integrated circuit technology, integrated circuit by developing to great scale, critical size on a small scale
(Critical Dimension, CD) is also constantly reduced 7nm node up to now by micron order.The manufacturing process packet of integrated circuit
Multiple processes such as material preparation, photoetching, cleaning, etching, doping, chemically mechanical polishing are included, wherein closing the most with photoetching process especially
Key.Photoetching process refers mainly to indicate resolution ratio, depth of focus, critical size, alignment and alignment precision etc..Wherein, alignment refers to
The aligned relationship of current photolithographic process layer and front layer process layer generally requires overlay error to be not more than the 1/3 of critical size, therefore
The rapid survey of overlay error and accurate assessment are the key that guarantee technique and device performance.
Haiyong Gao et al. is in document " Comparison study of diffraction-based overlay
It is summarized in and image-based overlay measurements on programmed overlay errors ", alignment
Measurement method can be roughly divided into two types: alignment based on figure measurement (Image-Based Overlay, IBO) and based on spreading out
The alignment measurement (Diffraction-Based Overlay, DBO) penetrated." super large-scale integration is advanced in document by Wei Yayi
Photoetching theory and application " in mention, in order to measure the overlay error of front and back process layer, both methods is required in mutual register
Front and back process layer on same position design overlay mark, then overlay mark is measured by alignment measuring device,
To obtain overlay error measurement result.These label be usually at the edge of exposure area, be called " scribeline " or
The region " kerf ".
Jie Li et al. people mentions in document " Evaluating Diffraction-Based Overlay ", DBO method
It mainly include eDBO and two kinds of mDBO (model-based DBO).For mDBO method, mentioned in patent CN103472004B,
Since it needs the positive optical property model of a large amount of building overlay marks, thus it is difficult to meet the time demand of actual measurement.
For eDBO method, this method is mentioned in patent CN103454861B has measuring speed fast, the small advantage of sampling area, together
When eliminate many error terms of traditional measurement method, such as position error, focal plane error, aberration factor and mechanical oscillation.This
Outside, Chinese patent CN200510091733, United States Patent (USP) US7173699B2, US7477405B2, US7428060B2 and
Such method is disclosed in US6985232B2.
EDBO method extracts overlay error based on the local linear relationship of alignment optical characterisation curve.In alignment optical characterisation
At 200 origin O of curve, alignment offset delta is approximate with optical characterisation amount I in a linear relationship:
I=K δ (1)
Wherein, alignment offset delta and measurement sensitivity K are unknown quantity, it is difficult to the number of the two is determined by single measurement
Value.For this purpose, eDBO realizes the extraction of overlay error with calculus of finite differences by way of introducing known alignment offset.
As shown in 300,301 and 304 are used to measure the overlay error in X-direction typical eDBO overlay mark top view,
302 and 303 are used to measure the overlay error in Y-direction.By taking X-direction as an example, overlay error to be asked is ε, in two overlay marks
Known alignment offset+D and-D is introduced on unit 301,304 respectively, corresponding sectional view is shown in Fig. 3 (b) and 3 (c), then two lists
The total alignment offset delta of member±Respectively D+ ε and-D+ ε.Therefore according to the optical characterisation amount of (1) two overlay mark unit of formula point
Not such as following formula:
I+=K (D+ ε) (2)
I?=K (- D+ ε) (3)
Then overlay error ε are as follows:
Therefore, only need to open measurement to overlay mark unit 301 and 304 point obtains I+、I?, so that it may it is covered by above formula
Carve error ε.In view of the influence of noise △ I in the measurement of practical alignment, formula (2), (3) are rewritten are as follows:
I+=K (D+ ε)+△ I+ (5)
I-=K (- D+ ε)+△ I- (6)
Therefore, the overlay error value such as following formula that actual measurement obtains:
Use σm△ I in (the apparatus measures noise criteria that alignment characterizes optical quantities I is poor) substituted (7)++△I-, and ignore
△ I in denominator+-△I-Obtain the repetition measurement precision σ of eDBO method:
It can be seen that the noise level of measurement sensitivity K and instrument has codetermined the repetition measurement precision of overlay error.
The key of eDBO method is in alignment offset delta ∈ [- D+ ε, D+ ε] range that approximation meets linear in formula (1)
Relational assumption.However, alignment optical characterisation curve is periodic odd function (see 201), therefore characterize the non-linear meeting of curve
It introduces alignment offset and characterizes error delta δ1(see 202) influence accuracy of measurement μ.In addition, other asymmetric factors of overlay mark
It can make the curvilinear translation of alignment optical characterisation and introduce alignment offset characterization error delta δ2(see 203), it is quasi- that this also will affect measurement
Exactness μ.
Overlay error characterization curve depends not only on the pattern of overlay mark, and (such as measurement wavelength, enters with measuring condition
Firing angle, azimuth) it is related, therefore to realize the good overlay error measurement of high repeatability precision, accuracy height, robustness, having must
Study a kind of eDBO overlay mark pattern and measuring condition optimization method.
Summary of the invention
Aiming at the above defects or improvement requirements of the prior art, the present invention provides a kind of overlay mark patterns and measurement item
Piece optimization method, it is intended that considering that overlay mark topography optimization is distributed rationally with measuring condition, simultaneously with overlay error weight
Renaturation measurement accuracy σ and accuracy μ is two optimization aims, obtains the good multiple Pareto optimalities of robustness as a result, thus
Solve the technical issues of existing overlay error measurement reproducibility precision is low, accuracy is low, poor robustness.
To achieve the above object, the present invention provides a kind of overlay mark pattern and measuring condition optimization method, features
It is, includes the following steps:
Step 101, overlay mark appearance structure and materials optical constant are determined；
Step 102, the parameter and materials optical constant of the overlay mark appearance structure determined according to step 101, Yi Jishe
Fixed measuring condition calculates single optical characterisation amount I by parsing or numerical modeling method, by continuously changing alignment offset
Alignment optical characterisation curve is calculated in δ；Alignment optical characterisation curve characterization optical characterisation amount I and alignment offset delta
Functional relation；
Step 103, Taylor's formula is unfolded in the origin of the alignment optical characterisation curve, obtains alignment measurement reproducibility essence
Spend the expression formula of σ and accuracy μ；
Step 104, variable to be optimized is selected from the parameter and the measuring condition of the overlay mark appearance structure, with
Alignment measurement reproducibility precision σ and accuracy μ as optimization aim, using multi-objective optimization algorithm to the variable to be optimized into
Row iteration selection, obtains the Pareto optimization result comprising alignment measurement reproducibility precision σ and accuracy μ described in multiple groups.
Preferably, the overlay mark pattern and measuring condition optimization method further include step 105, tired to multiple pas
Hold in the palm optimum results carry out overlay error extract emulation, verify corresponding alignment measurement reproducibility precision, accuracy of measurement and
Robustness chooses the best alternatives and measures experiment.
Preferably, the expression formula of the alignment measurement reproducibility precision σ and accuracy μ is,
Wherein, σmFor the apparatus measures standard deviation of optical characterisation amount, D is the alignment offset of setting, and K is that alignment is sensitive
Degree, ε are overlay error value to be measured, ΔaFor other influences of the asymmetric factor to optical characterisation amount,
In formula, I " (ξ+) it is alignment optical characterisation curve in δ=ξ+The second derivative values at place, I " (ξ-) it is alignment optics table
Curve is levied in δ=ξ-The second derivative values at place, ξ+∈ [0, D+ ε], ξ?∈[0,-D+ε]。
Preferably, step 103 specifically,
According to Taylor's formula by I+、I?It is modified to following formula:
Wherein, Δ I+、ΔI?For apparatus measures noise, I (0) is value of the alignment optical characterisation curve in origin；
According to formula (13) and formula (14), shown in the measurement error △ ε of eDBO method such as formula (15):
With the apparatus measures standard deviation sigma of optics token statem△ I in alternate form (15)++△I-, obtain the alignment measurement
The expression formula (9) and expression formula (10) of repeatability precision σ and accuracy μ.
Preferably, in step 102, the parameter of the overlay mark appearance structure includes the line width CD of top layer grating1, bottom
The line width CD of grating2, the period Pitch of top layer grating and bottom grating, the high H of the wall of top layer grating1, the high H of the wall of bottom grating3,
The sum of intermediate thin thicknesses of layers and bottom grating wall height H2, alignment offset delta, bottom grating left side wall angle LSWA and bottom light
Grid right side wall angle RSWA；The materials optical constant refers to the complex refractivity index of material.
Preferably, in step 102, the measuring condition includes measurement incidence angle θ, azimuthMeasure wavelength X and polarization
One or more of combinations of angle Ψ；The optical characterisation amount I refers to reflectivity, ellipsometric parameter or Muller matrix.
Preferably, in step 104, selected variable to be optimized is all parameters in overlay mark appearance structure parameter
Any combination and measurement incidence angle θ, azimuthMeasure any combination of one or more of wavelength X and angle of polarization Ψ.
Preferably, the parsing or numerical modeling method use rigorous couple-wave analysis, finite element method, Element BEM
Or finite time-domain calculus of finite differences.
Preferably, the multi-objective optimization algorithm uses multi-objective particle swarm algorithm, multi-objective Evolutionary Algorithm or multiple target
Genetic algorithm.
In general, through the invention it is contemplated above technical scheme is compared with the prior art, can obtain down and show
Beneficial effect:
1, characterization light is calculated by parsing or numerical modeling method in the optimization method provided by the invention based on eDBO
The alignment optical characterisation curve for learning the functional relation of token state I and alignment offset delta, passes through alignment optical characterisation curve and Taylor
Formula is unfolded to obtain the expression formula of alignment measurement reproducibility precision σ and accuracy μ, which considers alignment optics table simultaneously
Levy the non-linear of curve, apparatus measures noise and other influences of asymmetric factor to eDBO method.Then it is measured with alignment
Repeatability precision σ and accuracy μ is iterated choosing to the variable to be optimized as optimization aim, using multi-objective optimization algorithm
It selects, obtains Pareto optimization result.The present invention considers overlay mark topography optimization simultaneously and distributes rationally with measuring condition, thus
So that overlay error measurement has better performance in terms of accuracy and accuracy, high duplication measurement accuracy, high survey are realized
Measure accuracy and robustness it is good overlay error measurement.
2, the present invention provides multiple Pareto optimization results according to measurement reproducibility precision σ and accuracy μ two indices.
Consider actual processing, measurement process influence, can by emulate further to optimum results carry out alignment measurement reproducibility precision,
Accuracy of measurement and robustness verifying, selection meet needs and the good scheme of robustness, guarantee optimum results in actual measurement
Validity in the process.
3, multi-objective optimization algorithm changes simultaneously to two optimization aims of alignment measurement reproducibility precision σ and accuracy μ
Generation selection, finally obtains the Pareto optimization result of alignment measurement reproducibility precision σ and accuracy μ described in multiple groups.Optimum results
The non-linear of alignment optical characterisation curve, apparatus measures noise and other asymmetric factors are considered to eDBO method simultaneously
It influences, repetition measurement precision and accuracy are more preferable, and robustness is more preferable.
Detailed description of the invention
Fig. 1 is overlay mark pattern and measuring condition optimization method flow chart in present pre-ferred embodiments；
Fig. 2 (a) is the local line in present pre-ferred embodiments between typical alignment optical characterisation curve and alignment offset
Sexual intercourse；
Fig. 2 (b) is the non-linear shadow to overlay error characterization of alignment optical characterisation curve in present pre-ferred embodiments
It rings；
Fig. 2 (c) is other asymmetric factors of overlay mark in alignment optical characterisation curve in present pre-ferred embodiments
Influence to overlay error characterization；
Fig. 3 (a) is typical case eDBO overlay mark pattern top view in present pre-ferred embodiments；
Fig. 3 (b) is the overlay mark unit section figure introduced after setting alignment offset+D in present pre-ferred embodiments；
Fig. 3 (c) is the overlay mark unit section figure introduced after setting alignment offset-D in present pre-ferred embodiments；
Fig. 4 is the schematic diagram of the section structure of each overlay mark unit in present pre-ferred embodiments；
Fig. 5 is overlay error measuring condition schematic diagram in present pre-ferred embodiments；
Fig. 6 (a) is the process for seeking Pareto optimality result in present pre-ferred embodiments using multi-objective optimization algorithm
Figure；
Fig. 6 (b) is the measurement reproducibility precision and accuracy of overlay error before optimizing in present pre-ferred embodiments；
Fig. 6 (c) is the measurement reproducibility precision and accuracy of overlay error after optimizing in present pre-ferred embodiments；
Fig. 7 (a) is the robustness of the repetition measurement precision σ of Pareto optimization result in present pre-ferred embodiments；
Fig. 7 (b) is the robustness of the accuracy of measurement μ of Pareto optimization result in present pre-ferred embodiments.
Specific embodiment
In order to make the objectives, technical solutions, and advantages of the present invention clearer, with reference to the accompanying drawings and embodiments, right
The present invention is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, and
It is not used in the restriction present invention.As long as in addition, technical characteristic involved in the various embodiments of the present invention described below
Not constituting a conflict with each other can be combined with each other.
The present invention is based on diffraction overlay error measurement method (the Empirical Diffraction-Based of empirical relation
Overlay, eDBO) provide a kind of overlay mark pattern and measuring condition optimization method based on eDBO method.This method with
Overlay error repetition measurement precision σ and accuracy μ are two optimization aims, have obtained multiple Pareto optimalities as a result, then
Can be with the robustness of simulating, verifying optimum results to be screened, the result obtained after screening is overlay mark structural parameters
With the final optimization pass result of measuring condition.
Firstly, according to the technique of semiconductors manufacture, it is thus necessary to determine that the topological structure of eDBO overlay mark, i.e. each layer of structure
Optical constant (refractive index n and the extinction coefficient k) of shape (such as film or grating) and respective material.On this basis, lead to
The modeling methods such as RCWA, FEM, BEM, FDTD are crossed, positive optical property model can be established, it is bent to calculate alignment optical characterisation
Line.Secondly, the table of overlay error the repetition measurement precision σ and accuracy of measurement μ of eDBO method can be obtained according to Taylor's formula
Up to formula, the numerical approximation of the two can be calculated according to alignment optical characterisation curve.All due to repetition measurement precision and accuracy
It is very important index in alignment measurement, and the two are index related weaker, it is therefore desirable to be calculated using multiple-objection optimization
Method simultaneously optimizes two indices.The structural parameters and measuring condition for selecting overlay mark as variable to be optimized, with
Multi-objective optimization algorithm is iterative strategy, and Pareto optimality measurement reproducibility precision σ and accuracy μ, the two indexs can be obtained
Corresponding overlay mark structural parameters and measuring condition are optimum results.
Finally, can also carry out overlay error to multiple optimum results extracts simulating, verifying.Emulation includes analog semiconductor
Processing error, measuring condition in technique is uncertain, and the random noise of measurement, to verify Different Optimization result
Performance and its robustness select overlay mark pattern and measuring condition to measure experiment according to specific needs.
Below in conjunction with attached drawing and example to overlay mark pattern provided by the invention and measuring condition optimization method carry out into
One step detailed description.
Fig. 1 illustrates the process flow 100 of overlay mark provided by the invention and measuring configuration optimization method.The present invention is real
Applying example will be by taking three layers of overlay mark 400 as an example, to be specifically described the concrete operations process of method provided by the invention:
(1) overlay mark structure and materials optical constant are determined
Shown in overlay mark structure top view such as Fig. 3 (a) provided in this embodiment, overlay mark 300 includes four lists
Member, horizontal raster unit 302,303 are used to measure the overlay error of Y-direction, and vertical raster unit 301,304 is for measuring the side X
To overlay error.Wherein, the sectional view in the vertical raster direction of each unit is as shown in Figure 4.Its bottom is Si grating layer
(trapezoidal protrusion), middle layer SiO2Film layer, top layer are photoresist grating (square protruding), substrate Si.Wherein cover blaze
Remember that the parameter of section appearance structure is as follows, CD1Indicate the line width of top layer photoresist grating, CD2Indicate the line of bottom Si grating layer
Width, Pitch indicate the period of grating, H1Indicate wall height, the H of top layer photoresist grating3Indicate that the wall of bottom Si grating layer is high, H2
Indicate that the sum of intermediate thin thicknesses of layers and bottom grating layer wall height, δ indicate alignment offset, LSWA and RSWA respectively indicate bottom
Grating left and right sidewall angle.The parameter of overlay mark section appearance structure is not limited only to the above-mentioned parameter enumerated, the common skill in this field
Art personnel can be configured according to actual needs, herein not exclusive list one by one.In addition, also needing to obtain material by measurement means
Optical constant.Materials optical constant refers to the complex refractivity index of material, i.e. refractive index and extinction coefficient.
(2) calculation method of alignment optical characterisation curve is determined
Measured in 500 in the overlay mark structural parameters and materials optical constant and Fig. 5 obtained according to step (1) into
Firing angle θ, azimuthWavelength X is measured, angle of polarization Ψ can calculate single optical characterisation by parsing or numerical modeling method
Measure I.Alignment optical characterisation curve can be calculated by continuously changing alignment offset delta.
Utilizable modeling method includes rigorous couple-wave analysis (RCWA), finite element method (FEM), boundary element side
Method (BEM) or finite time-domain calculus of finite differences (FDTD) etc..Optical characterisation amount I includes reflectivity, ellipsometric parameter, in Muller matrix
Any one.
(3) alignment measurement reproducibility precision and accuracy are obtained based on Taylor's formula
As shown in Fig. 2 (b), alignment optical characterisation curve 201 is periodical odd function, therefore its non-linear will lead to measurement
Inaccurate (see in Fig. 2 (b) 202).Secondly because overlay error is substantially one of non-symmetrical factor, so set blaze
Remember that other asymmetric factors (such as left side wall angle LSWA ≠ right side wall angle RSWA) in technical process can also make entire alignment light
It learns characterization curvilinear translation and keeps overlay error measurement result inaccurate (see in Fig. 2 (c) 203).The two factors can all cause eDBO
There is accuracy of measurement in method.Consider the non-linear of aforementioned alignment optical characterisation curve and other asymmetric factors, I
Based on Taylor expansion by I+、I?It is modified to following formula:
Wherein, ε is overlay error value to be measured, and D is the alignment offset of setting, ΔaIt is other asymmetric factors to alignment
The influence of optical characterisation amount, Δ I+、ΔI?For apparatus measures noise, I (0) is alignment optical characterisation curve in origin (corresponding set
Carving offset is value 0), and generally 0, K is alignment sensitivity.I″(ξ+) and I " (ξ-) it is respectively that alignment optical characterisation curve exists
ξ+、ξ-Second derivative values, by Taylor-expansion theorem it is found that ξ+∈ [0, D+ ε], ξ?∈[0,-D+ε]。
According to formula (13) and formula (14), shown in the measurement error △ ε of eDBO method such as formula (15):
N in formula (15)+And N?Such as following formula:
Use σm△ I in (the apparatus measures standard deviation of alignment optical characterisation amount) alternate form (15)+-△I-, set can be obtained
Carve the repetition measurement precision σ and accuracy μ of error:
Due to N+And N?It is not that a determining value chooses its average value only in the present embodiment to calculate σ and μ.
Expression formula (9), (10) advantage be to consider simultaneously alignment characterization the non-linear of curve, apparatus measures noise and
Other influences of asymmetric factor to eDBO method.
(4) optimize overlay mark pattern and measuring condition
From the foregoing it will be appreciated that σ and μ and alignment optical characterisation curvilinear correlation, and alignment optical characterisation curve is by overlay mark knot
Structure structural parameters and measuring condition are got by optical model calculating namely every group of overlay mark structure and morphology parameter and measurement item
Part corresponds to the σ and μ of every group of determination.In the present embodiment, we select Pitch in overlay mark sectional view (see in Fig. 4 400),
CD1、CD2And incidence angle θ, azimuth are measured in the 500 of alignment measuring condition schematic diagram 5Wavelength X is measured as optimization
Variable, using σ and μ as optimization aim.Optimized variable in the present embodiment for explaining only the invention, other optimized variable packets
Include θ,λ、Ψ、Pitch、CD1、CD2Any combination.
Due to optimization aim containing both σ and μ and variable to be optimized it is more, it is therefore desirable to using strong more of ability of searching optimum
Objective optimization algorithm optimizes iteration of variables selection.Common multi-objective optimization algorithm has multi-objective particle swarm algorithm
(MOPSO), multi-objective Evolutionary Algorithm (MOEA), multi-objective genetic algorithm (MOGA) etc..The present embodiment selects multi-target evolution to calculate
For method as optimization algorithm, multi-objective optimization algorithm is global optimization approach, has preferably optimization effect relative to Local Optimization Algorithm
Fruit.Multi-objective optimization algorithm is iterated selection simultaneously to two optimization aims of alignment measurement reproducibility precision σ and accuracy μ,
Finally obtain the Pareto optimization result of alignment measurement reproducibility precision σ and accuracy μ described in multiple groups.
As shown in Fig. 6 (a), before multi-objective Evolutionary Algorithm iteration starts, multiple groups optimized variable initial value is firstly generated,
Then alignment optical characterisation curve is calculated according to optical model to obtain optimized variable initial value corresponding σ and μ, then root
According to optimisation strategy (ordinary priority selects the smaller optimized variable of σ or μ value) selection optimized variable of multi-objective Evolutionary Algorithm.In order to
The number for guaranteeing optimized variable will carry out some variations on the basis of filial generation also usually to generate new individual and maintain every generation
Individual amount and diversity of individuals.After the completion of each iteration, it is optimal to judge whether optimization aim σ and μ have reached, if reaching
It is optimal, then stop optimization algorithm.
More specifically, Fig. 6 (b) and Fig. 6 (c) show respectively change to be optimized for the overlay mark structure 400 in this example
Amount before optimization with σ, μ value corresponding after optimization.It can be seen that in this example, selecting by optimization algorithm iteration, the size of σ, μ are original
/ 10th come.In Fig. 6 (c), σ and the corresponding optimized variable of μ (θ,λ、Pitch、CD1、CD2) it is obtained optimization knot
Fruit.
(5) optimum results simulating, verifying
In semiconductor fabrication, it is difficult to guarantee overlay mark structural parameters Pitch, CD in optimum results1、CD2And survey
Amount condition θ,λ is ideal value.So also needing to consider actual processing, the influence of measurement process covers optimum results
Measurement reproducibility precision, accuracy of measurement and robustness verifying are carved, to guarantee its validity during actual measurement.
More specifically, the R in Fig. 7 (a) and Fig. 7 (b) characterizes 50 respectively for the overlay mark structure 400 in this example
The robustness of the repetition measurement precision σ and accuracy of measurement μ of a Pareto optimization result.As it can be seen that some optimum results are difficult to
The complex effects of processing technology and actual measurement condition are resisted, therefore in practical applications, need to be selected from Pareto optimization result
The good result of robustness is selected as final optimum results, carries out overlay error measurement experiment.
As it will be easily appreciated by one skilled in the art that the foregoing is merely illustrative of the preferred embodiments of the present invention, not to
The limitation present invention, any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should all include
Within protection scope of the present invention.
Claims (9)
1. a kind of overlay mark pattern and measuring condition optimization method, which comprises the steps of:
Step 101, overlay mark appearance structure and materials optical constant are determined；
Step 102, the parameter and materials optical constant of the overlay mark appearance structure determined according to step 101, and setting
Measuring condition calculates single optical characterisation amount I by parsing or numerical modeling method, by continuously changing alignment offset delta meter
Calculation obtains alignment optical characterisation curve；The function of alignment optical characterisation curve characterization the optical characterisation amount I and alignment offset delta
Relationship；
Step 103, Taylor's formula is unfolded in the origin of the alignment optical characterisation curve, obtains alignment measurement reproducibility precision σ
With the expression formula of accuracy μ；
Step 104, variable to be optimized is selected from the parameter and the measuring condition of the overlay mark appearance structure, with alignment
Measurement reproducibility precision σ and accuracy μ changes to the variable to be optimized as optimization aim, using multi-objective optimization algorithm
Generation selection, obtains the Pareto optimization result comprising alignment measurement reproducibility precision σ and accuracy μ described in multiple groups.
2. a kind of overlay mark pattern according to claim 1 and measuring condition optimization method, which is characterized in that further include
Step 105, overlay error is carried out to multiple Pareto optimization results and extracts emulation, verify corresponding alignment measurement weight
Renaturation precision, accuracy of measurement and robustness choose the best alternatives and measure experiment.
3. a kind of overlay mark pattern according to claim 1 or 2 and measuring condition optimization method, which is characterized in that institute
State the expression formula of alignment measurement reproducibility precision σ and accuracy μ are as follows:
Wherein, σmFor the apparatus measures standard deviation of optical characterisation amount, D is the alignment offset of setting, and K is alignment sensitivity, and ε is
Overlay error value to be measured, ΔaFor other influences of the asymmetric factor to optical characterisation amount.
In formula, I " (ξ+) it is alignment optical characterisation curve in δ=ξ+The second derivative values at place, I " (ξ-) it is that alignment optical characterisation is bent
Line is in δ=ξ-The second derivative values at place, ξ+∈ [0, D+ ε], ξ?∈[0,-D+ε]。
4. a kind of overlay mark pattern according to claim 1 or 2 and measuring condition optimization method, which is characterized in that step
Rapid 103 specifically, according to Taylor's formula by I+、I?It is modified to following formula:
Wherein, Δ I+、ΔI?For apparatus measures noise, I (0) is optics table of the alignment optical characterisation curve in coordinate origin δ=0
The value of sign amount；
According to formula (13) and formula (14), shown in the measurement error △ ε of eDBO method such as formula (11):
With the apparatus measures standard deviation sigma of optics token statem△ I in alternate form (15)++△I-, obtain the alignment measurement and repeat
The expression formula (9) and expression formula (10) of property precision σ and accuracy μ.
5. a kind of overlay mark pattern according to claim 1 or 2 and measuring condition optimization method, which is characterized in that step
In rapid 102, the parameter of the overlay mark appearance structure includes the line width CD of top layer grating1, the line width CD of bottom grating2, top layer
The period Pitch of grating and bottom grating, the high H of the wall of top layer grating1, the high H of the wall of bottom grating3, intermediate thin thicknesses of layers and bottom
The sum of layer grating wall height H2, alignment offset delta, bottom grating left side wall angle LSWA and bottom grating right side wall angle RSWA；It is described
Materials optical constant refers to the complex refractivity index of material.
6. a kind of overlay mark pattern according to claim 5 and measuring condition optimization method, which is characterized in that step
In 102, the measuring condition includes measurement incidence angle θ, azimuthMeasure the one or more of of wavelength X and angle of polarization Ψ
Combination；The optical characterisation amount I refers to reflectivity, ellipsometric parameter or Muller matrix.
7. a kind of overlay mark pattern according to claim 6 and measuring condition optimization method, which is characterized in that step
In 104, selected variable to be optimized is any combination of all parameters and measurement incidence angle in overlay mark appearance structure parameter
θ, azimuthMeasure any combination of one or more of wavelength X and angle of polarization Ψ.
8. a kind of overlay mark pattern according to claim 1 or 2 and measuring condition optimization method, which is characterized in that institute
Parsing or numerical modeling method are stated using rigorous couple-wave analysis, finite element method, Element BEM or finite time-domain difference
Method.
9. a kind of overlay mark pattern according to claim 1 or 2 and measuring condition optimization method, which is characterized in that institute
Multi-objective optimization algorithm is stated using multi-objective particle swarm algorithm, multi-objective Evolutionary Algorithm or multi-objective genetic algorithm.
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