CN100524601C - Method and device for aligning a charged particle beam column - Google Patents

Abstract

The invention provides a method for automatically aligning a beam of charged particles with an aperture. Thereby, the beam is defelcted to two edges of the aperture. From the signals required to obtain an extinction, a correction deflection field is calculated. Furter, a method for automatically aligning a beam of charged particles with an optical axis is provided. Thereby a defocusing is introduced and a signal calculated based on an introduced image shift is applied to a deflection unit. Further, a method for correction of the astigmatism is provided. Thereby the sharpness is evaluated for a sequence of frames measured whilst varying the signals to a stigmator.

Description

Aim at the method and apparatus of beam of charged particles row

The field of the invention

The present invention relates generally to electric particle row, and be particularly related to the method and apparatus that produces beam of charged particles row aligning and aberrational correction.More particularly, the automatic aligning that the invention still further relates to beam of charged particles and difference from dynamic(al) correction.

Background of the present invention

In the worker, very high demand is arranged as technology such as microelectronics, micro mechanics and biotechnologys for the sample that constitutes and survey in the nanoscale.On so little yardstick, usually use electron beam to survey and construct, these electron beams produce in as charged particle bundle device such as sub-microscope or electron beam pattern generators and focus on.Beam of charged particles is because the wavelength of their weak point provides the very high spatial resolution that for example can compare with photon beam.

Yet because intrinsic aberration and the misalignment of beam of charged particles causes resolution to reduce, for example the spatial resolution that can arrive based on the wavelength that hangs down sub-0.01nm is restricted.

For example, in scanning electron microscopy (SEM), bundle focuses on size 1.5nm or littler dot.Bundle scans on whole sample.Thereby the resolution of the image that obtains is by the diameter restrictions during bundle is on the plane of sampling face.

The diameter of bundle can be limited by aberration, and is for example irrelevant with the aligning of bundle but change relevant aberration with electron beam energy.And then, the spiral aberration by the non-zero hole generation of imaging lens is arranged.Yet it is poorer that aberration may become, or even may be introduced with respect to the optical axis misalignment of each imaging element by bundle.Because high spatial resolution also requires very little franchise, bundle must be undertaken by a kind of rule with respect to each optic alignment.

Usually the beam of charged particles row are aimed at and need be undertaken by the operator.Thereby the operator regulates each signal that is applied to register correction means based on measured image.A defective of this process is its judgement that depends on the operator.Like this, cause different operators' inexactness and variation.And then manual adjustment is time-consuming, and is particularly particularly unfavorable for the in-service monitoring system of the high system throughput of needs.

In document US 5,627, in 373, a kind of method has been described, be used for aiming at electron beam axis automatically to the object lens axle in scanning electron microscopy.Thereby, measure first and second sample image of locating of object lens focusing scope.Produce the index signal of straight flange position in the field of microscope for each image.After also regulating aligning automatically from two input to an image transfer, this process repeats at an orthogonal direction.Whole sequence of operation iteration repeats, up to since resembling of occurring of misalignment move less than predetermined threshold value.

And then, in document US 5,627, propose to be used for a kind of method of automatic correct scan electron microscope electron beam astigmatism in 373.For the correction of astigmatism, around whole sample, boundary member is sampled in 30 ° of intervals.According to definition index signal identification bundle distortion axle among the sample.Distortion is conditioned and improves in iteration along this axle.

Document US 6,025,600 propose a kind of method, the astigmatic error that is used for calculating and proofreading and correct the charged particle beam system.Collect image in the single scan period that charged particle system object lens are provided with.Analyze the different sensing of image frame, such as the line in the spot target.The function that is provided with as object lens obtains best sharpness or best focal length value.By getting the linear combination of pointing to relevant optimum definition values with different image frame, calculate the suitable variation that the astigmatism correction device is provided with.

In document US 6,067, in 167, be used for realizing realizing the self-regulating a kind of scheme of electron-optical system, wherein stored by electron-optical arrangement owing to change the image of the defined amount that the object lens refractive index obtains in proper order at the sequential adjustment focus point such as electron-optical arrangements such as scanning electron microscopy.The amount of movement of calculating sampling image.Thereby, judge based on the amount of movement that calculates whether adjusting is necessary, and then regulate if desired.And then, a kind of scheme that realizes astigmatism correction in such as the beam of charged particles optical system of electron-optical arrangements such as flying-spot microscope is disclosed.

Yet, during particularly when consideration in-service monitoring system or at the wire harness write device, exist the further problem that relates to beam of charged particles row aligning, and the improvement needs that occur in the prior art are further perfect.

General introduction of the present invention

The present invention will overcome above problem.According to some mode of the present invention, a kind of method and the charged particle bundle device that are used for aiming at automatically beam of charged particles row and hole are provided at first direction.

From dependent claims, illustrate and accompanying drawing, the further advantage of the present invention, characteristic, mode and details are tangible.

According to the present invention, its advantage is the energy that changes beam of charged particles, aims at the required time to reduce.And then its advantage is to make the more automation and additional realized further improvement of necessary registration mark.

Like this, can overcome the following defective relevant with prior art.For example, in prior art, the iteration of each misalignment is regulated and is prompted.Thereby even for the automatic adjusting of beam of charged particles, the operator's of regulating system behavior is imitated.This imitation of operator's iterative process can be improved to the number of times of aiming to a certain degree, but regulating the needed time of charged particle system will be in the scope in 5 to 10 seconds.Owing to claims in the prior art and will change focal length, thereby this is particularly like this by the electric current that changes object lens.Yet object lens are usually installed with the form of magnetic or magnetic electrostatic lens.Like this, the self-induction of coil has hindered the quick variation of focal length, and thereby defines the further improvement of regulating the beam of charged particles required time.

In addition, in prior art, aim at the just part realization of automation of beam of charged particles.Like this, just each alignment procedures can be carried out automatically, and the aligning fully that what is also needed is whole row is realized automatically.Therefore, particularly in on-line measurement system, still need the operator, even its responsibility or necessary skill may reduce.

The present invention relates generally to the charged particle row, and be particularly related to the method and apparatus that produces beam of charged particles row aligning and aberrational correction.More particularly, the invention still further relates to the automatic aligning of beam of charged particles and aberration from dynamic(al) correction.

According to further mode of the present invention, provide a kind of method that in first direction, makes by the beam of charged particles mating holes of beam of charged particles rifle emission.Thereby bundle is deflected so that by blanking on first edge of Kong Zaikong, and measures and obtain the first required defection signal of delustring.In addition, bundle is deflected so that by blanking on second edge of Kong Zaikong, and measures and obtain the second required defection signal of further delustring.Calculate and provide a signal from first and second defection signals, so that alignment beams corresponding to the center, hole.Originally asking Shen Shuzhong, this alignment methods is also referred to as rifle and aims at.

Basic adjusting at beam of charged particles row is not enough to start under the situation of beam of charged particles and optical axis alignment, lessly needs the operator to have much to do.Because above-mentioned aligning can be improved to a kind of degree to the bad aligning of beam of charged particles automatically, it can begin to cause high-precision further aligning.And need not operator's intervention.And then, above-mentioned about also can be used for method of the present invention by the automatic aligning advantage of operator on aiming at.

In the application's book, phrase " beam of charged particles row " is meant all types device that wherein necessary beam of charged particles is aimed at.This can be an electron microscope, the device that electron beam is write device or used ion pair to answer.Said hole can be the Shu Dingyi hole or be introduced into to separate the hole of different vacuum chambers in the application's book.Yet the phrase Kongzui refers to the final hole of beam of charged particles row well.If for example do not mention in addition in a specific embodiment, beam steering field and beam steering unit are interpreted as static, magnetic or magnetic static.This unit can plate bias voltage, the form of coil or their combination realizes.Can use detector to carry out from measurements sample scattering or two amicrons with the form that is connected to scintillators such as photoelectric multiplier.Because the mode of measuring-signal does not generally influence idea of the present invention, this not should be understood to limitation of the present invention.

Will be in the desirable details and the advantage of following detailed description rifle aligning.

Use preferably changes each deflection field according to the mode of the invention described above, and the best simultaneously form measurement image in succession with frame.Calculate the gray scale of the frame that produces.Extend required signal with gray scale measurement of correlation gray scale.Be more preferably by using threshold value, perhaps, measure never by the required signal of the location deflection beam of charged particles of hole blanking by using curve fit to gray-scale map for gray scale.Like this, can obtain first and second signals with automatic, effective and accurate way.

And then in the application's book, this word of frame is used as the single scanning in the charged particle bundle device visual field.Thereby, obtain image.Yet in general, an image for example can be by asking average acquisition to more than one frame.In addition, filter function etc. can be used to obtain final image.

When change is applied to the defection signal of deflection unit, obtain (imaging) or produce successive frames, promptly under the situation of frame sequence, preferably apply the deflection field of signal in one way with acquisition slope form, and at an interim measurement frame of ramp cycle.Be more preferably the slope, in other words signal or have the slope form the field variation and the imaging synchronization of frame.Like this, can even be more preferably duplicate measurements and the image that corresponds to each other asked average.

In the application's book, ramp function is interpreted as preferably having the monotonic function of good fixed gradient.Be to be understood that this can also be stepped function, preferably have good fixed height and the length of ladder.

As mentioned above, the mode that rifle is aimed at according to the present invention should be automatic.Like this, the incident that difference is possible must be by the process control unit reaction and/or the control that for example comprise CPU.Therefore,, preferably provide defection signal, make Kong Buhui blanking beam of charged particles as first step according to the present invention.This will make the flow chart of process control easy, if restraint at first with obstructed via hole its notice of preferably transmission being made mistakes.The for example this notice of makeing mistakes can be used for making further method flow to stop, or notifies the current alignment operator of charged particle device simply.

And then be preferably in additional second direction and realize above method.Be more preferably this second direction should with the first direction quadrature.

According to further mode of the present invention, a kind of method is provided, be used for aiming at automatically the optical axis of beam of charged particles and charged particle row.Thereby, change the energy of restrainting.A visual translation is fed back in defocusing of introducing thus under the situation of misalignment.Measurement is also estimated visual translation.Thus, derive a correction signal so that beam of charged particles is aimed at optical axis, and offer deflection unit.In this application, this alignment methods also is called the hole and aims at.

In the application's book, the variation of charged particle beam energy comprises the beam of charged particles row inner potential all changes that influence charging rate in the object lens.Like this, can change accelerating voltage in the rifle by changing any other current potential.Also can use any other voltage and current to revise, it influences the focussing property of object lens in the mode that is equipped with the row misalignment.In the application's book, carry out the variation of energy periodically thereby defocus.In the application's book, the energy of bundle this changes and is also referred to as " waving " swing one-period, and this is similar to for from supporting the operator use lens current cycle known to aiming to defocus employed phrase.Thereby the variation of carrying out energy periodically defocuses this fact, just because the restriction of existing electronic driver (waving sinusoidal generator).The preferably modern electronics setting of hypothesis is carried out energy changing as single linear ramp.

And then, should be appreciated that in the application's book phrase " estimation " for example also refers to the calculating of the algorithm that uses by computer.

Use this above-mentioned hole to aim at, can realize some advantages.The device of operating in production line specifically needs the availability of height and the long term accuracy of height, and the rapid alignment process importantly is provided.Owing in described method, do not need to change the electric current in the object lens, in the object lens coil, do not introduce self-induction, its cycle that focuses on of may slowing down is revised possible frequency.Like this, alignment procedures can be accelerated, and thereby increased having property, or can aim at more regularly to improve long-term accuracy.

In addition, by change lens current introduce a kind of magnetic hysteresis to the change of refractive of magnetic or magnetic static object lens.Therefore, must be by adding this magnetic hysteresis of corrected value local equalize of calculating to the electric current that applied, or attempt to avoid this magnetic hysteresis by the Current Control Technology alignment procedures that further slows down.Like this, can think favourable for the change of this further reason beam energy.

The hole is aimed at and is preferably measured golden template as benchmark.Opposite with the measurement that during visual translation (at this moment energy is modified) carries out, when remaining unchanged, energy produces golden image.By several frames are in succession asked on average, golden image manifests high signal noise ratio.Image processing module " pattern analyzer " can be analyzed this image, and search shows the little image region of strong marginal information in level and vertical direction.These selecteed zones are called golden template.They are used as benchmark in mode identification procedure.

In contrast, the measurement of moving for image is promptly because to visual translation, preferably there is a quick image sequence in misalignment institute.Preferably measure single frame and calculate the quasi-continuous mobile of these images (frame).Because this extremely, from a frame to next frame little visual translation can only be arranged.Like this, following between two frames in succession image moves than being easier to and more accurate.Thereby, two in succession between the image image move best less than 20 pixels, be more preferably two in succession the image between the image move less than 10 pixels, and the image that is more preferably less than 5 pixels moves.

And then it is preferably more measured to obtain each picture and the golden template of the mobile frame sequence of image.Preferably using mode tracking to measure image moves.Be more preferably and use Regression Model identification.Thereby, preferably select an initial frame, the most approaching golden template of its picture from the frame of being measured in succession.Owing to be initial frame, can obtain advantage from such fact, promptly the time synchronizedization between two frames is measured with to start the synchronization of waving better than starting usually.And then, can be more accurately and find out with higher certainty and to be used to measure each picture that image moves, because particularly for Regression Model identification, be merely able to take place visual little departing from for previous.Also cause the fuzzy of image because the periodicity of beam of charged particles looses to gather, thereby this is a particular importance.Like this, the figure astigmatism is poly-many more, then is difficult to more make pattern recognition detect the image frame of selection automatically.Preferably can compensate these difficulties by the way.

Preferably the image from succession image moves, calculate a frame position to.The frame index can provide the frame position direct translation of time-domain of vector time.What energy and frame position vector carried out is directly related (synchronization) for changing.Like this, based on the function of the cycle behavior of energy changing can with the match of frame position vector.The result of fit procedure provides the amplitude parameter that image moves, and with the corrected value translation for the beam steering unit.

Be preferably based on the signal that calibration calculations must be applied to deflection unit.This calibration provides the signal that is applied in and depends on the function that detected image moves.This calibration can once be carried out during the charged particle row are made, but also can repeat based on a kind of rule.

Just, can improve the ratio of measuring speed and certainty of measurement with upper type and details.Like this, can realize identical precision in the short period of time.Can be compared to most and be called the aligning that the hole is aimed at 3 seconds sooner, preferably faster than 1 second, and better faster than 0.5 second.Like this, can reduce the aligning time, promptly total process time, thereby and availability that can modifying device.

Because can use the calibration for the Shu Yidong desired signal, iteration generally not necessarily.Even it is more effective that this orientation ratio makes beam of charged particles regulate for the pure iteration of optical axis, but may be preferably with at least one iteration reregistration, to improve the precision of aiming at.

And then be preferably in a second direction and aim at.Be more preferably the about and first aligning direction quadrature of second direction.

And then preferably calibrate different instrument settings.Like this, the parameter that can be independent of the device in the use realizes aiming at.

The further mode according to the present invention provides a kind of method, is used to proofread and correct the aligning of iteration particle beam equipment.Change the energy of iteration particle beam so that sample is arrived in bundle automatic focus.And then, during electric current in changing stigmator, make the frame imaging.Estimate the definition of the frame of imaging, and stigmator is set for corresponding to the electric current of image the most clearly.

Use this method, can realize some advantages.Special because the device of operating in production line needs high availability and high long term accuracy, it is important that the rapid alignment process is provided.Owing to do not need to change the electric current in the object lens in the described method, in the object lens coil, can not induce the self-induction of the possible frequency of focal length cycle modification that will slow down.Like this, alignment procedures can be accelerated, thereby and improved availability, maybe can have more regularly and aim at, improved long-term accuracy.

In addition, cause magnetic hysteresis by the change of refractive that changes lens current magnetic or magnetic static object lens.Therefore, must be by adding this magnetic hysteresis of corrected value local equalize of calculating to the electric current that applies, or by the Current Control Technology of attempting to avoid this magnetic hysteresis alignment procedures that further slows down.Like this, can think that to this further reason the beam energy periodically-varied is favourable.

Preferably repeat the step of the definition that changes electric current and be estimated picture frame for stigmator second.Such two stigmators, each is used for direction four utmost points arranges, if both direction rotates 45 ° each other, will form an ends of the earth better.

The electric current that preferably is applied to stigmator is with the slope variation.Thereby, can be implemented in the synchronization of frame number when making each frame imaging and the electric current that applies easilier.

Use above method, the variation of stigmator electric current will cause the translation of image in addition.In general, must between them, distinguish two different principles of drawing for estimate seeing.Usually, select each picture, and estimate the definition of image based on the definition of these pictures from image.Yet the translation of above-mentioned image also will be moved and be wanted each analyzed picture.Do not considering to occur the misjudgment of image definition probably under this situation that moves of drawing.Thereby, preferably use to focus on the definition that histogram is determined frame or image respectively.Thereby, analysis be not each picture, but whole image or the image some parts.Like this, need not focus on sign for the visual shift calibrating of introducing.Be more preferably the definition of using two slope focus analysis to be used for estimating image.Thereby at least two images measuring under similar condition compare each other, and definition based on this relatively.Thereby, preferably calculate the covariance of each frame.Measure these at least two frames during being preferably in two ramp cycle of separating.Being more preferably the slope has the ladder form, and measures at least two images during a slope.Use these modes, in general, can estimate picture for the definition of image, and need not to consider the translation of image.

In the better accuracy of needs or avoid preferably can using pattern recognition to detect because the image that the variation of stigmator electric current causes moves, and preferably can proofreading and correct under the out of use situation of above method of the influence that image moves to it.

Above-mentioned for the optimal way and the details that are used for proofreading and correct the imaging system alignment, can also be used for according to the present invention relates to further two modes of the following stated alignment correction.

Further a kind of mode according to the present invention, provide and be used to proofread and correct a kind of method that beam of charged particles is aimed at, make the series of frames imaging when being included in the electric current that changes first group of astigmatism correction coil, and the definition of estimating successive frames is to find out and the most visual relevant electric current, and the electric current that first group of astigmatism correction coil be set for and the most clearly circle resemble the step of relevant electric current, focus on histogram and estimate definition thereby use.Thus, focus at sample surfaces with the similar beam of charged particles that preferably at first makes of the first astigmatism correction method.

Further a kind of mode according to the present invention, provide and be used to proofread and correct a kind of method that beam of charged particles is aimed at, make the series of frames imaging when being included in the electric current that changes first group of astigmatism correction coil, and the definition of estimating successive frames is to find out and the most visual relevant electric current, and the electric current that first group of astigmatism correction coil be set for the step of the electric current that image is relevant the most clearly, thereby use two slope focus analysis estimation definition.Thus, similar with the first astigmatism correction method, beam of charged particles is focused at sample surfaces.

Further a kind of mode according to the present invention provides a kind of method that is used for aiming at automatically beam of charged particles in the charged particle device.Thereby, make bundle be deflected, make by hole blanking, and measure and obtain the first required defection signal of delustring at first edge in hole.In addition, bundle is deflected, and makes by the hole blanking at second edge in hole, and measures and obtain the second required defection signal of further delustring.From first and second defection signals, calculate corresponding to the signal of center, hole and supply with alignment beams.And then, for the focusing of sample surfaces by cyclomorphosis.This defocuses and present visual translation under the situation of misalignment.Measurement is also estimated visual translation.Thus, deriving makes beam of charged particles aim at the correction signal of optical axis, and offers deflection unit.And then, during electric current in changing stigmator, make the frame imaging.Estimate the definition of the frame of imaging, and stigmator is set to electric current corresponding to sharp image.

Use this method of aiming at beam of charged particles in the charged particle device automatically,, and do not rely on operator's judgement although the beginning misregistration can be aimed at the charged particle row.This can carry out with improved speed, and can improve the availability of this device like this.

And then, more than for rifle is aimed at, the hole is aimed at and the astigmatism correction mode is described all advantage feature and the details of invention, can be respectively or be used for row aligning automatically in combination fully.

The present invention also aims to carry out the equipment of disclosed method, and comprise the equipment unit of the method step that is used to carry out each description.These method steps can pass through hard assembly, by the computer of suitable software programming, carry out by both any combinations or with any alternate manner.In addition, the present invention also aims to the method for described operation of equipment.It comprises the method step of each function of actuating equipment.

Brief description of drawings

Above-indicated some and the more details of other the present invention aspect will illustrate in the following description and part is explained with reference to the drawings.Wherein:

Fig. 1 illustrates a block diagram of the charged particle bundle device that is suitable for carrying out variety of way of the present invention;

Fig. 2 a illustrates the block diagram that the expression rifle is aimed at; Fig. 2 b illustrates the curve chart that rifle is aimed at, promptly as the gray scale of the function of beam steering;

Fig. 3 is illustrated in that rifle is aimed at and corresponding rifle is aimed at some cardinal principle of beam steering during the curve chart;

Fig. 4 illustrates the flow chart of expression rifle alignment procedures;

Fig. 5 a and 5b illustrate the principle that the hole is aimed at; How its bundle that misalignment is shown introduces the translation of the image of generation;

Fig. 6 illustrates the flow chart of hole alignment procedures;

Fig. 7 a and 7b illustrate the ripple match curve match of the translation vector of measurement;

Fig. 8 illustrates astigmatic principle;

Fig. 9 illustrate for both direction be combined as ends of the earth stigmator the block diagram of two four utmost point stigmators;

Figure 10 illustrate focal length sign experimental result with owing to proofread and correct obtainable improvement;

Figure 11 a and 11b illustrate the principle of two slopes analyses that are used for the evaluation graph seeing;

Figure 12 a and 12b illustrate the extension principle that two slopes are analyzed, and wherein produce the frame of two correspondences during a slope;

The explanation of preferred embodiment

At first, those skilled in the art should see that the present invention can be used in any charged particle device.Yet for convenience, will the present invention be described for its realization in scanning electron microscopy (SEM).Those skilled in the art can see that also all be meant relative rather than absolute relation about the discussion of voltage and current potential here.For example, by connecting negative electrode to " ground connection " and apply 3Kv to sample and quicken bundle and be equivalent to negative electrode and apply negative 3Kv and place sample and arrive ground connection.Thereby, be to provide in some discussion for convenience by means of specific voltage, should be appreciated that benchmark is relative current potential.

Simplify the block diagram that an electron microscope is shown among Fig. 1.Electron microscope 100 comprises an electron gun 103 of divergent bundle 101, and electron beam is extracted by anode 104.Object lens 112 make electron beam focus on sample surfaces 105a.In order to obtain an image from whole visual field, use scan deflection unit 102 scanning beam on whole sample.Bundle can be realized by deflection unit 108 to 111 for the aligning of hole 106 or optical axis 113 respectively.As the arbitrary coil of deflection unit, can use the static module of belt electrode form or the combination of coil and static deflecter.By using detector 16 to detect backscattered or secondary electron, and make detected signal and electron beam scanning synchronous, formation one image in scanning electron microscopy.

For the research of sample or for the very important secondary product of the formation of image is secondary electron, and they have low relatively energy (3 to 50eV) from sample 105 with various angles and escape.These secondary electrons arrive detector 16 and detected.By the output of scanning beam on whole sample 105 101 and demonstration/record detector 16, form the surface image of sample 105a.

The different parts of equipment are connected to corresponding power subsystem, it is high voltage source unit 21, rifle aim detecting control unit 22, hole aim detecting control unit 23, scanning coil power subsystem 27, object lens power subsystem 24, stigmator control (with electric current supply) unit 28, sample voltage source unit 25, and platform power unit 26, they are by 31 controls of parameter regulation unit.Parameter regulation unit 31 is provided with unit 35 and analysis and/or synchronization control unit 32 with standard and is connected, and it provides the basic parameter collection to parameter regulation unit 31.

Fig. 2 a and 2b illustrate rifle alignment so according to an embodiment of the invention.It is that electron beam is for hole 106 symmetric test and adjustings that this rifle is aimed at.Thereby electron beam 101 is aimed at hole 106.Electron beam 101 is aligned in other words, makes its center by the hole.This aligning may further comprise the steps.At first drive rifle deflection unit 108 so that restraint to direction 205 deflections.Under the situation of electron beam through-hole, with bundle irradiation sample, and make secondary or the back-scattered signal imaging.Like this, can see bright image.First rifle is aimed at deflection unit and is driven so that restraint further deflection has bundle up to the edge in the hole blanking.Thereby the brightness of image will reduce.Like this, if the gray scale of image is expressed as the function for the beam steering or the field intensity deflection of defection signal 202 respectively, then gray scale will drop to threshold value below 203.Aim at other signal of this branch of deflection unit for first rifle and for example will be stored as first signal.This process in the opposite direction 207 repeats.Thereby, the blanking of an electron beam will be arranged on another edge in hole, and will drop to below the threshold value once more, thereby obtain secondary signal for defection signal 202b gray scale.From these two signals, calculate guiding electron beam 101 and pass through moving of the required bundle in 106 centers, hole, and be applied to first rifle aligning deflection unit 108.In above (one dimension) occasion, to aim at owing to describe the x-direction, the center should be understood to the centre of the projection of hole in the x-z-plane.

Yet the present invention is appreciated that two-dimensional object for the hole.In other words, the above-mentioned second direction that is aligned in is favourable.Aim at both direction x and y, the centrally aligned in electron beam and hole.This second direction should be different from first direction at least.Second direction preferably is orthogonal to first direction.Like this, above-mentionedly preferably also repeat in the y-direction in x-direction rifle alignment methods.Thereby, for example can find out center in the x-of circular port direction and y-direction.The hole is preferably circular.In order to aim in the y-direction, advantageously make the deflection of third and fourth rifle aligning in place like this, make it possible to realize the deflection of second direction correspondence.

Yet first rifle is aimed at deflection unit 108 center of Shu Xiangkong is moved, but make beam steering, thereby introduce the inclination of bundle.In other words, bundle for the angle of for example optical axis owing to deflection changes.The deflection of this constraint is aimed at deflection unit 109 compensation by second rifle at least in part.Second rifle is aimed at deflection unit 109 preferably makes Shu Yitong first rifle aim at the identical angle of deflection unit in opposite direction inclination.For example, this can realize having the deflection field of same absolute to have opposite direction by two similar deflection units being arranged and being electrically connected them like this.Yet, the invention is not restricted to similar first and second rifles and aim at deflection unit 108,109.Also can make by correction factor etc. and to be applied to the signal deflection angle difference that deflection unit is equal to and to equate.

In general, the above-mentioned fact about Shu Yidong all is suitable for using all modes, alignment methods and the embodiment of deflection unit among the present invention.In other words, when beam of charged particles when single deflection unit is deflected, bundle is additionally tilted.Thereby two degrees of freedom that influence the beam of charged particles aligning are coupled to each other.Because this coupling makes the aligning of bundle complicated.For fear of this situation, preferably use second deflection unit to redirect bundle to its original direction.Like this, redirect should be understood to before first deflection unit basically (after second deflection unit) rebulid the direction of beam of charged particles.Be more preferably the mode of propagating along its original direction and redirect bundle.

The fact that this process is assumed to be automation causes the state notifying processing that needs the advanced person.Owing to can not accurately determine the initial state aimed at, flow chart as shown in Figure 4 should comprise contingent all possible state during the automated system.Some measurable situation is shown in Fig. 3.

Show beam steering path 301 in the plane in hole in the mode of arrow among Fig. 3.From top to bottom, express following situation.Beam steering path 301a is outside the opening (hole) of orifice plate 303.Bundle is by blanking.During the central motion in hole 106, rifle to directrix curve 201a in as seen, the translation to the bundle of non-blanking appears.Beam steering path 301b is similar to beam steering path 301a to begin.Yet this bundle does not pass the edge in hole 106.Thereby rifle has low-light level to directrix curve 201b for the image of all measurements.Beam steering path 301c begin and do not have the bundle blanking.Yet, Shu Congwei by orifice plate 303 along its deflection path blanking.Like this, rifle is read a little for all directrix curve 201c and is become clear, and produces a frame.At last, beam steering path 301d illustrates the preferred deflection option according to the present invention.Can find out this point with reference to Fig. 4, because this beam steering path does not produce the notice of makeing mistakes.Beam steering path 301d begins in the position of a branch of not blanking, and is finished by the bundle position of orifice plate 303 blankings at electron beam 101.Rifle illustrates from high brightness by the function behavior of translation to the low-light level correspondence directrix curve 201d.

Fig. 4 illustrates the flow chart of the state notifying of considering that automation is necessary.This flow chart illustrates by means of the rifle deflection unit and carries out the necessary step of deflection in a direction.Like this, this flow chart is carried out four times with two edges of each side of measurement of x-direction and two edges of each side of y-direction.In step 401, this process is the order by providing from outer computer etc. for example.In step 402, measure.Thereby, producing several frames and for example send to a frame, first and second rifles aligning deflection unit is operated the deflection field to change continuously simultaneously.Like this, in the step 403, each frame can be estimated corresponding to the gray scale of the frame of deflection field strength by calculating each.Thereby, will obtain as Fig. 2 b or rifle seen in fig. 3 directrix curve.The variation of deflection field during measuring, the form on slope preferably, the situation that reaches capacity even continued by the slope of controller request in other words, can not reach further deflection, sends the III that makes mistakes in step 405 to master controller.Each steps in decision-making 404 otherwise will proceed to steps in decision-making 406.If blanking reaches from the bright translation that acquires dark gray scale in other words, then be given in step 407 and finish.Whether all images are dark otherwise in steps in decision-making 408 checks.Situation (" not having blanking " like this and " not all image dark ") if not so, calculate the further slope of continuing last slope by controller, and electron microscope 100 will continue to carry out to step 402, measure to use the further deflection command of controller.Under the situation that steps in decision-making 408 continues with " yes ", in further steps in decision-making 409 decision-making this whether be first iteration, promptly whether this process enters 402 from step 408.To directrix curve 201b, and the I that makes mistakes is sent by controller in step 410 state according to the rifle among Fig. 3 under the situation of first iteration.Like this, do not run into preferably there not to be the initial conditions of black out start.Under the situation of carrying out before this, the II that makes mistakes sends in step 411 in the step of further iteration.The II that makes mistakes notifies the blanking that is occurred but does not have by system identification.

Irrelevant with certain embodiments, advantageously the slope form of deflection field is by initial value and amplitude definition.Thereby, definable resolution, this is the function of the sum of the frame measured during a ramp cycle and/or the slope amplitude.With regard to this mode, be more preferably the measurement that allows at least one further slope, thereby the intensity of the deflection field on slope in succession is overlapping.Like this.Under the situation of notice of makeing mistakes, can realize the process flow simplified, not make speed pass through the edge deflection in hole corresponding to the deflection field on first slope.Compare this with other process flow and will additionally cause aligning time of shortening, and improved alignment methods like this.

With reference to Fig. 5 a, 5b, 6,7a, 7b describes a further embodiment who aims at electron beam 101 and electron microscope 100 shown in Figure 1.Object lens 112 focus on the sample electron beam 101.Electron beam 101 was before formed by hole and collector lens.Because the object lens 112 main final spot sizes of being responsible for realizing resolution limiting, Shu Bixu accurately aims at object lens.In general, object lens define an optical axis.After restrainting mating holes 106, also do not aim at this optical axis 113 usually as mentioned above by object lens 112 definition.

Can better understand the principle whether bundle is accurately aimed at reference to Fig. 5 a.In the left side, draw electron beam 101a profile, this aims at optical axis 113 symmetries.Deliberately introducing under the situation that defocuses, focal length moves in the direction vertical with sample plane.If measure during being called the periodic focusing of waving, the visual vestige of each of acquisition is with as follows.The feature of image will be described with focusing and misconvergence periodically.Yet owing to the focusing of electron beam 101a just changes in the direction perpendicular to sample surfaces, image will be by translation, just stands the periodicity of the image feature of image or correspondence and blurs.

On the other hand, if bundle not as aiming at well shown in Fig. 5 a right-hand side for electron beam 101b, then focus not only moves in the direction perpendicular to sample surfaces, and and then moves in the direction that is parallel to the surface.Like this, for image in succession, except image or feature fuzzy, also will experience the translation of image/mobile.This further is shown in Fig. 5 b.Good focusing image feature 502 is corresponding to the focus state 503b among Fig. 5 a in the visual field 501.If realized defocusing of focusing 503b, then image feature moves for the visual field and blurs owing to defocusing.Like this, will see that image feature for example is similar to 502b.On the other hand, for according to the 503c focus, image feature is as for the translation of rightabout shown in the 502c.Except fuzzy, obtain this translation again.

Yet first hole is aimed at deflection unit 110 and is not moved bundle to optical axis 113, but deflection beam, thereby introduce the inclination of restrainting.In other words, bundle for the angle of for example optical axis owing to deflection changes.This a branch of deflection is aimed at deflection unit 111 compensation by second hole at least in part.Deflection unit 111 is aimed in second hole preferably makes the identical angle of Shu Yitong first rifle aligning deflection unit in the opposite direction tilt.For example this can realize that making has the deflection field of same absolute to have opposite direction by two similar deflection units being arranged and being electrically connected them like this.Yet, the invention is not restricted to similar first and second holes and aim at deflection unit 110 and 111.Difference for the deflection angle that is applied to the deflection unit equivalent signals also can be by equilibriums such as correction factors.

According to the present invention, advantageously realize a kind of periodicity focal length owing to the variation of electron beam 101 energy and the calibration aberration of in object lens, introducing thus.This is better than using defocusing of object lens electric current.Thereby the cyclic variation of focus is not limited to the self-induction in the scioptics.And then in object lens, there is not magnetic hysteresis to take place.

Example for automation process is following description with reference to Fig. 6.Master controllers etc. start the beginning of alignment function in step 601.At first, activate automatic focus in step 602.Thereby focal point settings is on the surface of sample.Like this, generally the image quality by current alignment restriction can be modified.A failure or a success status returned in automatic focus, and this makes a strategic decision when steps in decision-making 603.Under the situation of failure notification (step 604), can expect have SEM imaging state in subject matter, and alignment procedures withdraws from an error messages.Under the situation that success is notified, alignment procedures continues with step 605.

In general, it is favourable adding the step that additional adjusting beam of charged particles focuses on.Thereby, preferably estimate the result of this focus steps.In other words, based on the result of state notifying, can whether be enough to further aim at automatically by the decision maker alignment.Like this, for example can use the status of fail prior warning operator of focusing process, status of fail may be not enough to aim at automatically.This has been avoided waste of time under the complete misalignment situation of system once more.

Preferably produce high-quality image in step 605.Thereby for example use the average generation benchmark image of several frames, thereby and improvement signal noise ratio.In addition, can adopt the method for further improvement image quality.This can be filtering method or any other suitable method.This high quality image, the image of bursting is used for pattern analyzer in step 606.In step 606, antithetical phrase for example has necessary contrast so that be used as the pattern analysis image of benchmark image feature.Pattern analyzer is determined the position and the sensing of so-called golden template.The position of golden template and golden template itself are used as the input of the following stated mode tracking, and offer mode tracking by step 611.Can find out that golden image satisfies by pattern analyzer as the situation of enough contrast, suitable sensing or appropriate brightness condition under, send the notice of makeing mistakes to master controller.Thereby at step 608 notice master controller, the current visual field of making a strategic decision on wafer is inapplicable for alignment procedures.Based on this notice for example master controller can move the stand that sample is housed on it, and this process that starts anew.Like this because 607 of stepss in decision-making extremely, can check the sample position that is applicable to alignment procedures by imaging.

In step 609, activation is waved, and periodically defocus in other words and introduce visual moving, and image produces.Thereby, produce frame sequence and obtain by presentation manager.Preferably change energy or any current potential that influences beam energy of beam of charged particles by rights.Preferably carry out imaging to wave the period of oscillation time greater than one.For example, 1.5 durations of oscillation of waving in the cycle are obtained 32 frames.

In step 610, the mode tracking algorithm receives this 32 images (frame), golden template and position thereof.No matter because how fuzzy moving both vertically of focus be, the mode tracking program must be followed the translation of the benchmark image feature of introducing.Thereby, also may use in the visual field more than one image as benchmark.The preferably at first more golden template of mode tracking algorithm and all 32 frames, and find out the frame of approaching golden image.This frame of approaching golden image be called as initial frame.In addition, in order to find out this frame, also to find out each frame index.The advantage of this process is not need to control to activate to wave and activate the initial synchronization of image.Ideally, initial frame will be similar to the image of bursting, and be turned off as waving.Under the situation of sufficiently high visual original frequency, initial frame is very similar to the image of bursting.Have only visual sub-fraction, each frame is compared, and the time that promptly golden template, this fact cause being used to estimate reduces.

In general, can use several possibilities, for example the relevant of template image be kept the score, classification, one of neural net or other pattern recognition program carry out pattern recognition.

Because frame in succession has only a little image to move, preferably use recursive schema to follow the tracks of, thereby the next frame of the initial frame of index k and index k+1 relatively.Error logging between two of frame sequence successive frames is only limited to the pixel of a view like this, preferably less than 10 pixels.Record has the vector of each image feature position among x and the template position sensing frame k+1 of y component from frame k.Next recurrence uses the k+1 frame to carry out as template.Each template of each frame compares with golden template after discerning.In bad relevant surpassing under the situation of certain threshold value, frame is designated as invalid.Like this, for example because too many fuzzy institute to coarse image, does not consider to be used for estimation.

Finally be converted to the frame position vector in step 610 for the vector of error logging, it sends to the ripple matcher of step 612 in step 613.

In step 612, the periodic phenomena of observation and the cycle of induction change match each other.Thereby, wave the cycle of generation and the phenomenon of observation and be equal to.Service time t and rolling period T.Energy can be expressed as:

$E\left(t\right)=E_0+A_{\mathrm{Wobble}}\·\cos (\frac{2\mathrm{\π}}{T}t+\mathrm{\Φ})$

Wherein, Ф is an arbitrary phase.For the discrete frames for imaging has a kind of expression formula that is equal to, can use frame index I and the number N of the frame that in a rolling period, produces, thereby obtain following expression formula:

$E\left(i\right)=E_0+A_{\mathrm{Wobble}}\·\cos (\frac{2\mathrm{\π}}{N}i+\mathrm{\Φ})$

The index vector position is the tolerance for the target pattern position of each frame.Thereby, on x and y axle, being marked with the projection of Px and Py, can separately see.Suppose that Px and Py also are sinusoidal wave, for example Px can be expressed as

$P_x\left(i\right)=A_x\·\cos (\frac{2\mathrm{\π}}{N}i+\mathrm{\Φ})+C_x$

Can obtain following expression formula from discrete fourier transition:

$A_x=\frac{2}{N\cos \left(\mathrm{\Φ}\right)}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{P}_x\left(i\right)\·\cos \left(\frac{2\mathrm{\π}}{N}i\right)$

And

$A_x=\frac{2}{N\sin \left(\mathrm{\Φ}\right)}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{P}_x\left(i\right)\·\sin \left(\frac{2\mathrm{\π}}{N}i\right)$

Parameter A x (A thus _x), and Cx (=C _x) can be calculated as follows.

${\mathrm{<figure-callout\; id="2"\; label="Ax"\; filenames="C02822953E00301.png,C02822953E00391.png"\; state="\{\{state\}\}">Ax</figure-callout>}}^2=\frac{4}{N^2}[{(\underset{l=1}{\overset{N}{\mathrm{\&Sigma;}}}{P}_x\left(i\right)*\mathrm{Cos}(\frac{2\mathrm{\&pi;}}{N}*i))}^2+{(\underset{l=1}{\overset{N}{\mathrm{\&Sigma;}}}{P}_x\left(i\right)*\mathrm{Sin}(\frac{2\mathrm{\&pi;}}{N}*i))}^2]$

$\mathrm{Tan}\left(\mathrm{\&Phi;}\right)=-\frac{(\underset{l=1}{\overset{N}{\mathrm{\&Sigma;}}}{P}_x\left(i\right)*\mathrm{Sin}(\frac{2\mathrm{\&pi;}}{N}*i))}{(\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{P}_x\left(i\right)*\mathrm{Cos}(\frac{2\mathrm{\&pi;}}{N}*i))}$

$\mathrm{Cx}=\frac{1}{N}\underset{l=1}{\overset{N}{\mathrm{\&Sigma;}}}{P}_x\left(i\right)$

These parameters are used as the initial value of second approximating method.Thereby, preferably only consider valid frame, and mean square deviation match computing being by finding out Ax, Ф and Cx minimize following formula:

$\underset{i=\mathrm{ValidFrame}}{\overset{N}{\mathrm{\&Sigma;}}}{[P_x\left(i\right)-A_x\mathrm{Cos}(\frac{2\&CenterDot;\mathrm{\&pi;}}{N}\&CenterDot;i+\mathrm{\&Phi;})+C_x]}^2$

In Fig. 7 a, can see each result for the y-direction for the x-direction and in Fig. 7 b.Curve 703 illustrates the frame position of measurement, comprises the valid frame that is labeled as circle.These valid frames are used for the mean square deviation match.Curve 701 illustrates the SIN function that match is measured.Aiming at each signal that will introduce in the deflection unit 110,111 in the hole can be from magnitude determinations.Two values all provide at Fig. 7 a and each top of 7b.Thereby, the calibration of having carried out before using.Know Δ l=f (Δ x/ Δ V from calibration _Acc) behavior of function, wherein I is the electric current that will be applied to deflecting coil, x is the translation of image, and V _AccIt is the accelerating voltage that changes beam energy.This calibration can once be carried out during row are made, and maybe can be undertaken by a kind of rule.Preferably there is one group of calibration to can be used for different system parameterss.Calibration function can be any polynomial function; Preferably use the linear gauging function.

Say further embodiment of description with reference to Fig. 8 in more detail to 11b.Except rifle was aimed at, the astigmatism of preferably also proofreading and correct object lens was used charged much Lie Keda, the image quality that arrives so that improve.The use of word x-and y-direction means that not necessarily both direction is orthogonal in astigmatism is described.If but the correction that relates to astigmatism thinks that preferably x-and y-direction rotate 45 ° each other.

Can astigmatism be described with reference to Fig. 8.Under the situation that astigmatism takes place, point-like object 801 imaging ideally is not because the focus 811 in the focus 809 in first image plane 803 and second image plane 805 is equal to.Like this, if do not find best focal point 807, then must find out a kind of compromise.For this reason, the image 808 at best focal point has a diameter that amplifies.Under the situation that defocuses, the image of dotted picture no longer is circular, but oval-shaped.It still is afterwards relevant before that oval sensing is positioned at best focal point 807 with image plane.In addition, burnt if image loses, then will differ from one another by the resolution in the both direction of first and second image planes definition.

In electron beam equipment, the distortion of bundle is proofreaied and correct by a kind of stigmator.Preferably any to carrying out this correction on time, because astigmatic correction changes with interior the aiming at relatively of electron beam 101 of e-beam column whenever having carried out.Thereby the distortion of x-direction is corrected owing to coil groups 902.It is the form of four utmost points that coil groups is preferably arranged.In general, coil is used for forming four utmost points.Yet, also can use the combination of coil and static board.In order to proofread and correct, preferably use second four utmost point to arrange as one group of coil 903 with the direction of x-orientation independent.Arranging by the ends of the earth of such formation like this can be in each correction for direction bundle distortion.Yet, can also only use the stigmator of four utmost points, its rotatable and be adjusted to bundle 101 distortions each point to.

Shown in 9, Shu Bubi is by the center 901 of stigmator.And then, if apply electric current, also produce moving of electric field driven electron beam 101 to coil.Its implication will be referred to following.

For correction of astigmatism, preferably make fully little and complete feature imaging in the visual field.This feature preferably should show several edges, so that obtain image contrast in the several separate direction.For example this can be features such as circle, and its position is known in the visual field.For automatic correction of astigmatism, carry out following process.At first, the visual field and location feature are set.Then, thus changing beam energy and line goes into to calibrate aberration and makes visual automatic focus.After the automatic focus success, change first group of electric current in the stigmator coil 902, thereby produce several images.By calculate focusing on the definition of sign drawing for estimate elephant, and first group of electric current in the astigmatism correction coil 902 is set is the value with optimum focusing sign.Focusing on sign is a kind of tolerance of image definition.Then, repeat this process for second group of astigmatism correction coil 903.For secondary iteration reduced field of view and rotary scanning direction, be preferably 45 °.Meticulous mobile at image with after locating each feature, the process that repeats automatic focus and proofread and correct two stigmators.Can be similar to optional the 3rd iteration of secondary iteration, further reduced field of view and further rotary scanning direction.

As mentioned above, the electric current at first and second groups of coils that are used for stigmator x-and y-direction changes also moving of driving image.By calculating the solution along feasible that focuses on sign estimation definition is the covariance of observing two successive frames.Yet moving in the visual field of image will influence covariance.Therefore, moving of image can only be ignored its little moving, and for example is limited in 2 or 3 pixels etc.Like this, move for the image that surpasses this, the estimation of definition will use improved method to carry out.

The further embodiment according to the present invention carries out following process.At first, the visual field is set and the location is held and levied.Then, make visual automatic focus.After the automatic focus success, change first group of electric current in the stigmator coil 902, thereby produce several images.Focus on the definition of sign drawing for estimate elephant by calculating as described below, and first group of electric current in the astigmatism correction coil 902 is set is the value with optimum focusing sign.Then, repeat this process for second group of astigmatism correction coil 903.For secondary iteration reduced field of view and rotary scanning direction, be preferably 45 °.Meticulous mobile at image with after locating each feature, the process that repeats automatic focus and proofread and correct two stigmators.Can be similar to optional the 3rd iteration of secondary iteration, further reduced field of view and further rotary scanning direction.

Thereby, calculate and focus on sign, wherein recording picture moves and is similar to the measurement that is applied to the Shu Yidong that aims in the hole.Thereby, can use one of various pattern recognitions.Image move be corrected after, can calculate the correlation of successive frames.Owing to proofread and correct institute extremely, can improve focusing on the sign curve, be about to more measure on the certain noise level, and like this improvement found out the accuracy and the repeatability of image the most clearly.Focusing sign curve 909a and 909b fixing among focusing sign curve 908a more originally and 908b and Figure 10 can see more.

The further embodiment according to the present invention carries out following process.At first, the visual field and location feature are set.Then, make visual automatic focus.After the automatic focus success, change first group of electric current in the stigmator coil 902, thereby produce several images.Focus on the definition of sign drawing for estimate elephant by calculating as described below, and first group of electric current in the astigmatism correction coil 902 is set is the value with optimum focusing sign.Then, repeat this process for second group of astigmatism correction coil 903.For secondary iteration reduced field of view and rotary scanning direction, be preferably 45 °.Meticulous mobile at image with after locating each feature, the process that repeats automatic focus and proofread and correct two stigmators.Can be similar to optional the 3rd iteration of secondary iteration, further reduced field of view is also selected a step rotary scanning direction.

Thereby, use grey level histogram to calculate and focus on sign.Thereby, use whole image to be used for estimating.Estimate to be based on high-contrast gradient quantitative analysis in the image.Suppose that image is clear more, the edge amount with certain contrast gradient is high more, because fuzzy less.And then, suppose under the situation of better definition in the first derivative grey level histogram, have preferably between noise and the imaging edge feature and separate.Because the location independent of feature moves almost without any correlation image in this method and the image.The sample top edge be evenly distributed in the area of visual field and the visual field around situation under, to image fully without any correlation because the motion in the visual field do not change may be by the number of edges of imaging.

Grey level histogram for example can calculate from compound directional derivative

$S(i,j)=\sqrt{S_x^2(i,j)+S_y^2(i,j)}$

Wherein focus on sign and estimate that following formula calculates

$F_{j=\mathrm{Frame}\ln \mathrm{dex}}=\underset{i=k}{\overset{\max }{\mathrm{\&Sigma;}}}{i}^2{h}_i$

Wherein k provides as certain percentage α of gray scale.Item h _iIt is the histogram value that provides divided by the pixel sum as number of picture elements at gray scale i.If make each frame normalization for intensity profile, then frame preferably can be estimated independently of one another.

In further embodiment, carry out following process according to the present invention.At first, the visual field and location feature are set.Then, make visual automatic focus.After the automatic focus success, change first group of electric current in the stigmator coil 901, thereby produce several images.Focus on the definition of sign drawing for estimate elephant by calculating as described below, and first group of electric current in the astigmatism correction coil 902 is set is the value with optimum focusing sign.Then, repeat this process for second group of astigmatism correction coil 903.For secondary iteration reduced field of view and rotary scanning direction, be preferably 45 °.Meticulous mobile at image with after locating each feature, the process that repeats automatic focus and proofread and correct two stigmators.Can be similar to optional the 3rd iteration of secondary iteration, further reduced field of view and further rotary scanning direction.

Thereby, because the influence that the variation institute of electric current to image moves in the stigmator is compensated during following definition estimation.Two slopes 904 of the stigmator electric current of generation shown in Figure 11 b.The frame 907 that produces shown in Figure 11 a is similarly producing under the condition each other.Like this, can calculate being correlated with between each frame with conditions of similarity.To these two frames, for each other will be less than moving of moving or almost do not have to be corrected.The frame that is compared is not in succession.The frame that is compared is the frame that is equal to from each slope.Like this, can overcome the translation problem of each analyzed feature.By accumulating more frame or using plural slope can further improve signal noise ratio.If the slope is by its initial value 905 and its amplitude 906 definition, this so that be considered to favourable.Like this, if one of slope is not enough to find out maximum in focusing on sign, two slopes can be easy to make up in overlapping mode.Use is from the analysis of two slopes, 904 a pair of frames or a framing, owing to above reason can obviously be improved the focusing sign.

In further embodiment of the present invention, further expanded the notion of the frame of relatively under conditions of similarity, being got.After the visual field and location feature are set, make visual automatic focus.After the automatic focus success, change first group of electric current in the stigmator coil 902, thereby produce several images.Focus on the definition of sign drawing for estimate elephant by calculating as described below, and first group of electric current in the astigmatism correction coil 902 is set is the value with optimum focusing sign.Then, repeat this process for second group of astigmatism correction coil 903.For secondary iteration reduced field of view and rotary scanning direction, be preferably 45 °.Meticulous mobile at image with after locating each feature, the process that repeats automatic focus and proofread and correct two stigmators.Can be similar to optional the 3rd iteration of secondary iteration, further reduced field of view and further rotary scanning direction.

With reference to the ratio of Figure 12 a and 12b descriptor frame.In this embodiment, the slope 904 that is applied to stigmator is stepped functions.Substitute and in the slope that separates, get similar frame, in a ladder on stepped slope, produce two or more frames 907.In order to make condition similar as far as possible, must consider a relaxation time for each ladder on slope 904.In Figure 12 b, point out that the horn shape ladder of drawing with dotted line relatively has circular edge this slack time.

Shown in Figure 12 a, this embodiment can followingly realize.Each grade at the stigmator electric current produces two frames 907, and is sent to the frame getter.After finishing the slope, use frame 1 and 1 ', 2 strange and idol and 2 ' etc. to focus on sign for each rating calculation of the means for correcting current ramp of loosing.Thereby, calculate the covariance between per two each frames and the noise grade of frame.Calculate the focusing sign according to following equation:

$F_{u,k}=\mathrm{COVARIANCE}(\frac{{\&PartialD;I}_k}{\&PartialD;u},\frac{{\&PartialD;I\&prime;}_k}{\&PartialD;u})$

$=\mathrm{COVARIANCE}(S_{u,k},{S\&prime;}_{u,k})$

$=\mathrm{Mean}(S_{u,k}*{S\&prime;}_{u,k})-\mathrm{Mean}\left(S_{u,k}\right)\mathrm{Mean}\left({S\&prime;}_{u,k}\right)$

$=\frac{1}{N_x{N}_y}\underset{i,j}{\overset{\mathrm{IMG}}{\mathrm{\&Sigma;}}}(S_{u,k}(i,j)*{S\&prime;}_{u,k}(i,j))$

I _kAnd I ' _kBe corresponding image, and N _xAnd N ' _yIt is the sum of pixel in all directions.

In general, preferably consider according to a following process.During the focus steps of preferably carrying out automatically in this mode of the present invention, image processing unit etc. can be estimated the result of image.This focusing sign can be used as a kind of tolerance, so that a process judges that relatively focusing on the average system performance is to produce good or bad result.Like this, preferably make system's decision whether will carry out the renewal or the adjusting of charged particle equipment based on focusing on sign.At reproducting periods, old system parameters is used as initial value, and for example the stigmator electric current changes from this value.Estimating that focusing on sign points out under bad result's the situation, for example preferably carries out the stigmator electric current from the initial adjusting of default value.Thereby for example system value can be used as the starting point that stigmator changes.Thereby, be more preferably by different service areas and draw performance of subsystems.Like this, select further to handle based on focusing on the sign result, can be dependent on the service area that reaches.

With regard to above general mode, of the present invention one further embodiment, the estimated result of the focus steps of before the stigmator electric current changes, carrying out according to following use.Based on the focusing sign that produces by automatic focus, astigmatism correction must be upgraded or regulate to decision whether.Yet, can also manually make by the operator its decision-making, under the situation of upgrading, detecting during aimed at or proofreaied and correct last time is that best current value is used as initial value.With the amplitude ratio that is used to regulate be little than the amplitude on slope 904.In order to regulate, system is reset to its original parameter, and (scratch) begins respectively to aim at or proofread and correct from the working area.Like this, use for the bigger amplitude in slope, and carry out the more aligning or the correction of time-consuming respectively.Thereby,, for example consider the number of edges in the visual field for the setting of accurate system.Estimate that based on it if the visual field can reduce and still have the fact of enough number of edges in its visual field in other words, the sample of the position on the sample is refused by system.In the error handling processing process, require the operator to change sample or sample position respectively.

In the present invention one further embodiment, rifle is aimed at, the hole is aimed at and the correcting mode aimed at is combined and finish the aligning of electron beam device.Thereby, at first make the centrally aligned (rifle aligning) of bundle at last for the hole.Then, bundle is aligned to the optical axis (hole aligning) by the object lens definition.This hole aligning is aimed at relatively even more important for the imaging behavior with rifle.Like this, as stating among above several embodiment, this aligning must be very accurate.Proofread and correct at last and aim at.Like this, as long as satisfy some primary condition, the charged particle device can be aimed at automatically from the working area.

The favorable characteristics of the slope form that for example changes from the signal that is applied to deflection unit that relates to and mention for a method of the present invention, the details that pattern recognition and pattern are extracted, the using and be connected of two deflectors to obtain Shu Yidong, rather than bundle tilts or the focusing of the variation change beam of charged particles of current potential, not should be understood to only be suitable for for this mode, but, then also can be used for alternate manner of the present invention if transferable.

Claims (23)

1. one kind is used for comprising step in the automatic method of aiming at a beam of charged particles and a hole of first direction:

A) aim at deflection unit to first rifle and apply first deflection field, up to the delustring that obtains at the described bundle of first edge in described hole,

B) measure required first signal that offers described first rifle aligning deflection unit of the described delustring of acquisition;

C) aim at deflection unit to described first rifle and apply second deflection field, up to the further delustring that obtains at the described bundle of second edge in described hole;

D) measure the required secondary signal that offers described first rifle aligning deflection unit of the described further delustring of acquisition;

E) use the center of the described bundle of described first and second calculated signals for described hole;

F) aim at deflection unit to described first rifle correction deflector field is provided, with the center of described beam of charged particles of leading by described hole.

2. according to the process of claim 1 wherein by regulating the energy that accelerating voltage changes described beam of charged particles.

3. change to produce a framing according to the process of claim 1 wherein in one of described first and second deflection fields each, and obtain described first and second signals based on the gray scale of each frame of this framing.

4. according to the method for claim 3, wherein use the threshold value of gray scale to estimate described first and second signals.

5. according to the method for claim 3, wherein use with the curve of intensity profile match and estimate described first and second signals.

6. according to each method in the claim 1 to 5, wherein step f) also comprises:

Apply and be positioned at the further deflection field that second rifle on the described beam of charged particles direction is aimed at deflection unit after the described hole, to redirect described beam of charged particles.

7. according to the method for claim 6, wherein rebulid described beam of charged particles is aimed at deflection unit optical axis before with respect to described first rifle angle by described further deflection field.

8. according to each method in the claim 3 to 5, wherein said first and second deflection fields apply with the form on slope, and produce each frame during a ramp cycle.

9. method according to Claim 8, wherein said first or the slope of second deflection field and the generation synchronization of frame.

10. method according to Claim 8, the slope of described first and second deflection fields of at least twice measurement wherein, and ask average for the frame of each frame correspondence.

11. method according to Claim 8, wherein the slope is by the resolution definition of the variation in one of an initial value, amplitude and described first or second deflection field.

12., wherein improve the resolution of the variation in one of described first and second deflection fields by the definition totalframes according to the method for claim 11.

13., wherein improve the resolution of the variation in one of described first and second deflection fields by the amplitude on definition slope according to the method for claim 11.

14. according to the method for claim 11, wherein use the slope that different at least initial values are arranged more than, and the field intensity of the deflection field on slope overlaps each other.

15. according to each method in the claim 1 to 5, wherein in step a) to f) carry out following steps before:

H) aim at deflection unit to described first rifle and apply deflection field, make the described bundle of described not blanking of hole.

16. according to each method in the claim 1 to 5, wherein separately aim at, thereby carry out aligning with respect to the center in described hole for the second direction that is different from first direction.

17., also comprise step according to each method in the claim 1 to 5:

G) use another rifle to aim at the deflection unit repeating step for second direction a) to f), wherein said second direction is different from first direction, thereby carries out the aligning with respect to the center in described hole;

I) change the focal position of described beam of charged particles with respect to sample surfaces;

J) measuring image moves;

K) moving based on the required bundle of the optical axis of image estimation described beam of charged particles of aligning and charged particle row;

L) at sample surfaces described beam of charged particles is focused on;

M) electric current in first group of astigmatism correction coil of change;

N) definition of estimating image to be finding out and the relevant electric current of image the most clearly, and the electric current that described first group of astigmatism correction coil be set is and the relevant electric current of sharp image;

O) for second group of astigmatism correction coil repeating step m) and n).

18., wherein carry out step I by the energy that changes described beam of charged particles according to the method for claim 17) and l).

19. according to the method for claim 17, wherein in step a) to g) carry out step I afterwards) to k), and in step I) to k) carry out step l afterwards) arrive o).

20. a charged particle bundle device comprises

A source (103) is used to launch beam of charged particles (101);

A hole (106);

At least one lens (112) between sample position and described source;

Aim at deflection unit (108) in described source with first rifle between the described hole for one, and second rifle aligning deflection unit (109) that is positioned at described hole reverse side, deflection unit aimed at by wherein said first rifle and described second rifle is aimed at deflection unit between described source and described lens;

A control unit (22), control is used for the signal that described first and second rifles are aimed at deflection unit;

An estimation unit (32) is estimated the described beam of charged particles of blanking and is calculated the center required signal of described beam of charged particles for described hole (106).

21. according to the device of claim 20, deflection unit (108) aimed at by wherein said first rifle and described second rifle aligning deflection unit (109) is electrically connected to each other.

22. according to each device in the claim 20 to 21, wherein said first and second rifles aim at deflection unit each comprise one group of coil.

23. according to each device in the claim 20 to 21, wherein said first and second rifles aim at deflection unit each comprise an electrostatic deflection module.

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