CN102253609A - Method for processing alignment mark measuring signals - Google Patents

Abstract

The invention provides a method for processing alignment mark measuring signals. The method comprises the following steps of: after sampling an alignment signal, fitting the signal by a fitting model to solve the best alignment position; performing model fitting by using a result acquired by light intensity sampling and position sampling; fitting the period of the signal while fitting model parameters so as to determine the phase of the signal; and finally solving and determining the best alignment position.

Description

Alignment mark measuring-signal disposal route

Technical field

The present invention is relevant with the lithographic equipment that integrated circuit or other microdevice are made the field, particularly a kind of alignment mark measuring-signal disposal route.

Background technology

In the semiconducter IC ic manufacturing process, complete chip need just can complete through photolithographic exposure repeatedly usually.Except the photoetching first time, before exposure, the photoetching of all the other levels all will accurately be located the figure of this level and the figure that level exposure in the past stays, to guarantee the correct relative position between two layer patterns, i.e. alignment.The alignment error only allows within 1/3 scope of photolithography resolution usually.The factor that influences alignment precision is numerous, comprise the bearing accuracy of work stage, measuring error, mask and the silicon pad alignment error of position measuring system, the alignment error of machine etc., wherein the alignment precision between the silicon chip different process layer also is one of significant effects factor.Because silicon chip finishes on lithographic equipment after one deck graph exposure, the processing that needs down follow-up semiconductor technologies such as sheet cures, development, and then go up again slice to lithographic equipment, carry out the photoetching of next layer pattern.Before carrying out this layer pattern photoetching, the first-selected needs by alignment system, set up the position coordinates relation between this layer mark and the last layer mark, could guarantee between two figures that alignment concerns accurately.In the actual production, for fear of the propagation of error of markers align between layer and the layer, the normal zero layer mark that adopt is as reference mark.Each layer mark aimed at zero layer mark, promptly sets up the position coordinates relation between each layer mark and the zero layer mark.Among the present invention, the aligning of mark is the measurement of mark, and registration signal is the measuring-signal that measurement markers obtains.

Patent CN03164859.2, CN200710045495X, CN2007100454964 and US6297876B1 etc. have introduced silicon chip (from the axle) alignment system of a class based on optical grating diffraction.This alignment system adopts the alignment mark (as 16 microns and 17.6 microns) that comprises two different cycles sub-gratings, by survey two sub-gratings ± 1 grade of interference of light picture sees through the light intensity signal with reference to grating, through the match of signal, comprehensively determine the coarse alignment position of mark; Simultaneously, utilize the senior interference of light imaging (as ± 5 grades of light) of meticulousr grating ± 1 grade interference of light picture or 16 microns periodic optical gratings,, on coarse alignment (measurement) basis, determine fine alignment (measurement) through the match of signal.In such patent, the match of registration signal is the phase place of determining signal, adopts following model of fit usually:

In the formula, I is a light intensity, and x is the position, coefficient a ₀, a ₁, Λ, a _i, b ₀, b ₁, Λ, b _jAnd phase place

Be the model undetermined parameter, P is the cycle of signal, needs predetermined constant.Match promptly be right by positions different on the registration signal and luminosity sampling, and signal period P determines the undetermined parameter of model by least square fitting.In patent CN200510030807.0, CN200810035115.9, CN200910055927.4, CN200510030577.8, signal period P is pre-set machine constant.This machine constant can utilize design load directly to introduce, or demarcates acquisition by surveying the school.Alignment mark on the datum plate is little with environmental change, and the cycle of the registration signal of generation is also constant substantially, and it is feasible adopting fixing signal period P to carry out model fitting.Yet,, be subject to processing technology and environmental change influence big (as the thermal expansion of silicon chip etc.) for the alignment mark on the silicon chip.Different process layer mark on mark on the different silicon chips, the same silicon chip, and the cycle of the registration signal that the zones of different mark produces on the same silicon chip all be different.At this moment, adopt same fixed signal cycle P to carry out model fitting, will cause the match deviation as continuing.As shown in Figure 1, this moment actual cycle and the match cycle of registration signal do not match, and actual signal and matched curve deviation are very big.In addition, when there are deviation in signal actual cycle and match cycle, will there be dependence in peak point (obtaining from matched curve) with sampling point distributions, promptly utilize the different section matches of registration signal, and it is different obtaining a series of peak points.And registration signal match section is closely related with the prealignment position that the last process of aiming at provides mark, thereby makes alignment result have very big uncertainty.

In the present invention, signal period P does not introduce as fixed value, but participates in match as a parameter for the treatment of match.Because match cycle this moment is found the solution acquisition by match, rather than it is directly given as the machine constant, to not have the match cycle in the technology formerly and the inconsistent problem of actual cycle of signal, the matched curve of acquisition also will be more identical with the actual conditions of signal, phase place

Solving precision will obtain to improve, and then reduce alignment error.

Summary of the invention

The object of the present invention is to provide a kind of new alignment mark measuring-signal disposal route, this signal processing system is carried out model fitting to the signal (comprising luminosity sampling and position sampling) that measurement markers obtains, the process of match is carried out match to the cycle of signal simultaneously, thereby determines the phase place of signal.

Alignment mark measuring-signal disposal route provided by the invention, after utilizing alignment system that registration signal is sampled, utilize following model of fit to carry out signal fitting and solve best aligned position:

In the formula, I is a light intensity, and x is the position, a ₀, a ₁, Λ, a _i, b ₀, b ₁, Λ, b _jBe model coefficient, i, j are non-negative integer,

Be phase place, P is the cycle of signal;

Utilize light intensity and position sampling, carry out determining model coefficient a behind the numerical solution ₀, a ₁, Λ, a _iWith b ₀, b ₁, Λ, b _j, signal period P and phase place

Value.

Wherein, described method of value solving adopts successive approximation approach.

Wherein, described successive approximation approach adopts Gauss-Newton method or wheat quart method.

Wherein, in solution procedure, at first provide model coefficient a ₀, a ₁, Λ, a _iWith b ₀, b ₁, Λ, b _j, signal period P, phase place

Initial value a ₀ ⁽⁰⁾, a ₁ ⁽⁰⁾, Λ, a _i ⁽⁰⁾, b ₀ ⁽⁰⁾, b ₁ ⁽⁰⁾, Λ, b _j ⁽⁰⁾, P ⁽⁰⁾,

And near this initial value, model of fit is carried out platform labor and launch, omit second order and above higher order term, then model of fit is converted into linear equation and is:

In the formula,

$\frac{\∂I}{{\∂a}_i}{\mathrm{\Δa}}_i=x^i{\mathrm{\Δa}}_i,i=\mathrm{0,1,2},\mathrm{\Λ},$

Δ a _i, Δ b _j, Δ P and

Poor between true value and the initial value, that is: Δ a _i=a _i-a _i ⁽⁰⁾, Δ b _j=b _j-b _j ⁽⁰⁾, Δ P=P-P ⁽⁰⁾, At this moment, the commentaries on classics of the parametric solution of model of fit just turns to Δ a _i, Δ b _j, Δ P and

Linear equation find the solution.

Wherein, a _i, b _j,

Initial value determine by experience or determine at random that the initial value of the cycle P of signal is determined according to the design parameter of used alignment system.

Wherein, utilize least square method to iterate and find the solution Δ a _i, Δ b _j, Δ P and

Until calculate | Δ a _i|, | Δ b _j|, | Δ P| and

Less than threshold value separately.

Wherein, described threshold value is definite by experience, or according to a after upgrading through first round iteration _i ⁽⁰⁾, b _j ⁽⁰⁾, P ⁽⁰⁾,

Value determine.

In the disposal route that the present invention adopts, the cycle P of signal is also as treating fitting parameter, with a ₁, a ₂, Λ, a _i, b ₁, b ₂, Λ, b _kWith

Carry out match together, thereby obtain and the model fitting of coupling under the cycle of registration signal, and then can improve aligning (measurement) precision of silicon chip mark effectively.

Description of drawings

Figure 1 shows that the match cycle influences synoptic diagram to signal accuracy;

Figure 2 shows that the alignment system that the present invention is used.

Embodiment

Below, describe in detail according to a preferred embodiment of the invention in conjunction with the accompanying drawings.For convenience of description and highlight the present invention, omitted existing associated components in the prior art in the accompanying drawing, and will omit description these well-known components.

Figure 2 shows that the used alignment system of signal processing method according to the present invention.This alignment system comprises: light source and lighting module 1; Image-forming module 2; With reference to grating 3; Signals collecting and processing module 4; Alignment mark 5 comprises datum plate mark and the silicon chip mark that is positioned on the silicon chip 6; Work stage 7; Motion platform 8; Station acquisition and motion-control module 9; Alignment function and administration module 10.Light source and lighting module 1 provide illumination beam to alignment mark, form the diffraction light that carries label information, and diffraction light is imaged onto with reference on grating 3 surfaces by image-forming module 2.Station acquisition and motion-control module 9 are gathered the positional information of the work stage 7 of carrying silicon chip, and negotiate synchronously with alignment function and administration module 10, the planning movement locus, the motion of controlled motion platform 8, simultaneously, the positional information that will be used to aim at is transferred to alignment function and administration module 10 after treatment.The motion of motion platform 8 makes alignment mark imaging scan reference grating 3 and produce light intensity signal.Signals collecting and processing module 4 are gathered light intensity signal, and are transferred to alignment function and administration module 10 after treatment.Alignment function and administration module 10 comprehensive light intensity signal and the positional informations in order to aim at from a plurality of mark sub-gratings through signal fitting, calculate the aligned position of asking for mark.Concrete alignment procedures can be introduced as known technology here with reference to formerly patent CN200710045495X, CN2007100454964 etc.

Fitting within alignment function and the administration module 10 of registration signal carried out, and adopts as drag:

In the formula, I is a light intensity, and x is the position, a ₀, a ₁, Λ, a _i, b ₀, b ₁, Λ, b _jBe model coefficient, i, j are non-negative integer,

Be phase place, P is the cycle of signal.

The purpose of registration signal match is exactly to obtain light intensity and position sampling according to the alignment scanning process, determines the phase place of signal

And and then determine a series of peak points of this registration signal.Formerly among patent CN200510030807.0, CN200810035115.9, the CN200510030577.8, model coefficient a only ₀, a ₁, Λ, a _i, b ₀, b ₁, Λ, b _jAnd phase place

As treating that fitting parameter finds the solution, and signal period P directly introduces as pre-set fixed value.When there are deviation in the predefined fixed value of P and signal actual cycle, the cycle of the matched curve that obtains by match and the inconsistent (see figure 1) of actual cycle of registration signal, the phase place that obtains

Error also will be become greatly, and then influence alignment precision.Among the present invention, signal period P is also as treating fitting parameter, with model coefficient a ₀, a ₁, Λ, a _i, b ₀, b ₁, Λ, b _jAnd phase place

Find the solution together by match, can guarantee that the cycle of the matched curve that obtains is consistent with the cycle of actual signal, also improved phase place simultaneously

Solving precision, and then improved alignment precision.

Because formula (2) is a nonlinear function, can't directly find the solution.In the numerical evaluation, the method that common employing approaches is one by one handled, as Gauss-Newton method, wheat quart method etc.The present invention has only provided the embodiment that Gauss-Newton method is handled, and those skilled in the art can adopt other method for solving to handle with condition as required.

Solution procedure at first provides model coefficient a ₀, a ₁, Λ, a _iWith b ₀, b ₁, Λ, b _j, signal period P, phase place

Initial value a ₀ ⁽⁰⁾, a ₁ ⁽⁰⁾, Λ, a _i ⁽⁰⁾, b ₀ ⁽⁰⁾, b ₁ ⁽⁰⁾, Λ, b _j ⁽⁰⁾, P ⁽⁰⁾,

And near this initial value, formula (2) is carried out platform labor and launch, omit second order and above higher order term, then formula (2) is converted into linear equation:

$\frac{\∂I}{{\∂a}_i}{\mathrm{\Δa}}_i=x^i{\mathrm{\Δa}}_i,i=\mathrm{0,1,2},\mathrm{\Λ}$

Here, Δ a _i, Δ b _j, Δ P and Poor between true value and the initial value, that is: Δ a _i=a _i-a _i ⁽⁰⁾, Δ b _j=b _j-b _j ⁽⁰⁾, Δ P=P-P ⁽⁰⁾,

The parametric solution of formula (2) also just is converted into Δ a _i, Δ b _j, Δ P and Find the solution.

During alignment scanning, can obtain a series of sampled point on the registration signal, measurement sampled point as shown in Figure 1, these measurement points are formed light intensity-position sampling to { I _n, x _n, n=1,2,3, Λ.By least square method, find the solution Δ a easily _i, Δ b _j, Δ P and

Value.When | Δ a _i|, | Δ b _j|, | Δ P| and

During greater than separately threshold value, upgrade initial value and be: a _i ⁽⁰⁾=Δ a _i+ a _i, b _j ⁽⁰⁾=Δ b _j+ b _j, P ⁽⁰⁾=Δ P+P,

Again utilize least square to find the solution Δ a then _i, Δ b _j, Δ P and

So iterate, up to | Δ a _i|, | Δ b _j|, | Δ P| and

Less than threshold value separately.The a of this moment _i ⁽⁰⁾, b _j ⁽⁰⁾, P ⁽⁰⁾,

Be finally and separate.The phase place of match acquisition registration signal is so: The cycle of registration signal is: P=P ⁽⁰⁾

Peak value (crest) position is:

In this embodiment, a _i, b _j, Initial parameter can be determined by experience, also can determine at random, for example sets a _i ⁽⁰⁾=0, b _j ⁽⁰⁾=0, The initial value of cycle P is determined according to design parameter.For example, for the grating marker of 8.0 microns live widths, its ± theoretical value of 1 grade of optical registration signal is 8.0 microns, so set P ⁽⁰⁾=8 microns.

Δ a _i, Δ b _j, Δ P and

Threshold value can determine by experience, also can be according to taking turns after iteration upgrades a of this moment through one _i ⁽⁰⁾, b _j ⁽⁰⁾, P ⁽⁰⁾,

Value determine.For example, set Δ a _iThreshold value is a _i ⁽⁰⁾/ 10, other threshold value is similar.

Described in this instructions is several preferred embodiment of the present invention, and only in order to technical scheme of the present invention to be described but not limitation of the present invention, for example, the present invention also can use on the double-workpiece-table lithographic equipment above embodiment.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 (7)

1. alignment mark measuring-signal disposal route is characterized in that utilizing following model of fit to carry out signal fitting solves best aligned position after utilizing alignment system that registration signal is sampled:

In the formula, I is a light intensity, and x is the position, a ₀, a ₁, Λ, a _i, b ₀, b ₁, Λ, b _jBe model coefficient, i, j are non-negative integer,

Be phase place, P is the cycle of signal;

Utilize light intensity and position sampling, carry out determining model coefficient a behind the numerical solution ₀, a ₁, Λ, a _iWith b ₀, b ₁, Λ, b _j, signal period P and phase place

Value.

2. alignment mark measuring-signal disposal route according to claim 1 is characterized in that: described method of value solving adopts successive approximation approach.

3. alignment mark measuring-signal disposal route according to claim 2 is characterized in that: described successive approximation approach adopts Gauss-Newton method or wheat quart method.

4. alignment mark measuring-signal disposal route according to claim 3 is characterized in that:

In solution procedure, at first provide model coefficient a ₀, a ₁, Λ, a _iWith b ₀, b ₁, Λ, b _j, signal period P, phase place

Initial value a ₀ ⁽⁰⁾, a ₁ ⁽⁰⁾, Λ, a _i ⁽⁰⁾, b ₀ ⁽⁰⁾, b ₁ ⁽⁰⁾, Λ, b _j ⁽⁰⁾, P ⁽⁰⁾,

And near this initial value, model of fit is carried out platform labor and launch, omit second order and above higher order term, be converted into Δ a _i, Δ b _j, Δ P and

Linear equation:

In the formula,

$\frac{\∂I}{\∂a_i}\mathrm{\Δ}{a}_i=x^i\mathrm{\Δ}{a}_i,i=\mathrm{0,1,2},\mathrm{\Λ},$

Δ a _i, Δ b _j, Δ P and

Poor between true value and the initial value, that is: Δ a _i=a _i-a _i ⁽⁰⁾, Δ b _j=b _j-b _j ⁽⁰⁾, Δ P=P-P ⁽⁰⁾,

5. alignment mark measuring-signal disposal route according to claim 4 is characterized in that: a _i, b _j,

Initial value determine by experience or determine at random that the initial value of the cycle P of signal is determined according to the design parameter of used alignment system.

6. alignment mark measuring-signal disposal route according to claim 5 is characterized in that: utilize least square method to iterate and find the solution Δ a _i, Δ b _j, Δ P and

Until calculate | Δ a _i|, | Δ b _j|, | Δ P| and

Less than threshold value separately.

7. alignment mark measuring-signal disposal route according to claim 6 is characterized in that: described threshold value is definite by experience, or according to a after upgrading through first round iteration _i ⁽⁰⁾, b _j ⁽⁰⁾, P ⁽⁰⁾,

Value determine.

Images