DD206722A3 - METHOD AND ARRANGEMENT FOR STRUCTURING EDGE DETERMINATION IN ELECTRON BEAM INSTRUMENTS - Google Patents

Abstract

A METHOD OF ASSOCIATED APPARATUS FOR CONTROLLING LOCATION, WIDTH OR SPACING, AND GUETE MICROELECTRONIC STRUCTURE IS USED IN ELECTRON BEAM INSTRUMENTS IN THE FIELD OF MICROLITHOGRAPHY. IT HAS THE GOAL, THE MEASUREMENT AND CONTROL OF SUCH STRUCTURES OF DIFFERENT SIZE AND SHAPE UP TO STRUCTURE WIDTH and spacing submicron HIGH PRODUCTIVITY AND AUTOMATICALLY, allowing objectified TO BEING THE TASK IS TO ONE FOR THE ACCURACY REQUIREMENTS SUFFICIENT HIGH NUMBER OF ELECTRON FOR EVALUATING TO USE , THE PRESENCE OF THE INVENTION IS THAT FIRST, A LINE OF VERTICAL HEADS FOR RADIATING DEVICE WILL BE MULTIPURELY DAMAGED, AND SECONDLY EACH MULTI ROWS ARE EASILY DAMAGED IN SPECIFIC DOWNSTREAM LENGTH OF THE ROLLING DIRECTION. MADE BY THE SUMMATION OF INDIVIDUAL SIGNAL CURVES WHICH GIVES THE COVERING PERFORMANCE. The edge retardancy is determined from the incline of two curves. TO CARRY OUT THE PROCEDURE, THE ELECTRONS EMITTING FROM THE OBJECT WHEN THE ELECTRON BEAM IS EMITTED, WILL BE ACCOMPANIED TO A RECIPIENT OF THE GENERAL CIRCUIT ARRANGEMENT.

Description

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Title of invention ;

Method and arrangement for structural edge beat in electron beam apparatus

Field of application of the invention :

The invention relates to a method and an arrangement for its implementation, which serve to control the position, width or spacing and quality of microlithographically produced structures by the course of the structural edges is automatically determined.

The invention is applicable in the field of microlithography in electron beam devices which serve to measure and control such structural patterns. The structures can lie as lacquer masks, in metallized glass bodies or as semiconductor wafers.

characteristics known teohniaohen solutions:

It is known to use light-optical measuring instruments for such measurements, as is apparent from brochures of the company Nikon / Japan to "Micro-Pattern Inspection Station" or "Laser Interferometry x-y Measuring Machine".

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However, these methods are only possible as long as the minimum element dimensions or distances are not less than a few microns.

For reasons of intensity, a light bundle with a rectangular cross-section, the narrow side of which measures up to 1 μm and its long side up to a few 100 μm, is guided over the edge of the structure and the transmitted or reflected light signal is evaluated via photodetectors.

The disadvantage is that thus demands on the geometric shape of the structures to be measured are connected and thus the diversity is significantly limited. Furthermore, it is known to use electron beam devices for controlling structures. For example, in the patent DD-ViP 124 091 is described that according to the principle of a scanning electron microscope, a fine electron probe over he led the object to be measured, an image of the object synchronously displayed on a screen and compared with a projected scale network. The measurement is carried out directly by means of the scale network or by a defined object displacement using a reference mark projected onto the fluorescent screen.

The disadvantage is that the measuring productivity is too low and the measurement accuracy is subjectively influenced.

aim the invention

The aim of the invention is to provide a means of measuring and controlling microlithographically prepared structures of different size and shape up to sub-micron feature widths and spacings. The process should be highly productive and run automatically and objectively.

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Presentation of the essence of the invention

The invention has for its object to develop such a method with an arrangement for its implementation, which allows on the one hand to carry out the measurement of structure widths in Submikroraeterbereich, on the other hand based on the accuracy requirements sufficiently high number of electrons of the evaluation, as well as statements about the quality to gain the structural edges.

In a method for determining the course of structural edges in measuring instruments for determining the position, the extent or the distance and the quality of preferably microlithographically produced structural patterns, wherein the signals generated during scanning with the electron beam are utilized for detecting the structure edges and the electron beam step by step is guided over the edge to be measured, the object is achieved according to the invention by the following method steps:

a) In the sweeping direction perpendicular to the edge extension, the structure pattern is scanned point by point along a line in constant predefined steps by shifting the electron beam, wherein the signal obtained at each point is digitized and stored in the memory of a computer. Since the diameter of the electron probe is small, therefore, only the property of the edge is detected in this small area and on the other hand, no requirement imposed on the longitudinal extent of the edge.

b) The step a) is repeated several times (η-fold), wherein the coordinate of the sweep in the edge direction is not changed in order to improve the signal-to-noise ratio of the signal obtained in a).

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c) The digitized signal values obtained in steps a) and b), which belong to the same locations along the sweep direction, are summed to form a signal curve.

d) I η different locations at predetermined distances a along the structural edge, which is perpendicular to the Sweeprichtung, is in each case the step a) again

: fetches to reduce the influence of the edge roughness on the measuring signal.

e) The scanning signals obtained in step d) are digitized and summed in sweep direction for all sampling points of the same coordinate. The signal thus obtained presents itself as a spatiotemporal average over an edge range of n.a. The distance a is chosen so that the sweep offset matches the edge extent, i. n.a ^, 1, 1 = edge extension.

f) In the signal formation in step e) signals are superimposed with finite edge roughness, which are shifted to each other in Sweeprichtung on the order of the edge roughness. The resulting edge signal is thus generally flatter than that in which a = O holds.

The steepness of the signal curve obtained according to c), i. for a = O, the steepness of the signal curve obtained according to e), i. for a + 0, and this quotient is linked to a constant determined from test objects. This creates a value that is a measure of the edge roughness of the structure to be measured.

In order to carry out the method according to the invention, an arrangement is used in an electron beam apparatus in which the electron beam impinges on the structure to be measured and, as a function of this structure, emits an emerging electric element.

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tronen formed signal is supplied to a receiver. The arrangement is characterized by the following features: The receiver signal, which may be very different in size and contains a disturbing ground level, is supplied to a normalizing means. The normalized signal is digitized in an AD converter, which is read in via a gate circuit from the central unit of a computer, and supplied to the central unit.

For the digital displacement of the electron beam for the x and y coordinate direction, a position counter is provided in each case, which determines the position of the electron beam via a deflection system via the DA converter and the power amplifier. At one input of each position counter is information about start or end values in sweep direction. When the final value of a position counter is reached, a message is sent to the central unit. At the same time, the position counter is reset to the initial value and a clock pulse is output to the position counter of the second coordinate direction. This allows a new Abtastsweep done on a line that is parallel to the previous, both lines have a predetermined distance a.

Between both position counters is an electronic switching device for selecting the scanning sweep in the x or y coordinate direction. Serve as clock pulses, the read-in pulses of the signal digitization, which are also fed via a delay element as a start signal to the AD converter.

The digitizing signal transfers the digitized signal to the central unit. The trailing edge of this pulse increases the position counter _} and the electron beam takes the next position. After a delay time, the AD converter is designed and the new signal value is digitized.

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To smooth out noisy signals is used before the normalization ungsgli ed switched low-pass filter whose time constant is tuned to the delay time of the AD converter.

In order to improve the edge signal with regard to readability, it may be advantageous to mix the signals of different receivers additively or subtractively.

To improve the accuracy of electron beam positioning serve the following features of the circuit arrangement;

The adaptation of the step size to the structure to be measured and the deflection sensitivity of the deflection system via a Impulsvervielfacherstufe and a digitally adjustable analog Dämpfunsglis d.

The skew of the object against the direction of the deflection systems is taken into account by rotational correction units.

The position counter with step size adjustment and fast M; converter is used only for the actual grid sweep symmetrically to the assumed edge position, and the basic deflection of the beam to this assumed Kantenpßsition set by a second DA converter before the beginning of the series. This DA converter is more accurate and slower, its output is additively added to the screened deflection voltage.

Ausfuhrunftsbeiapiel

In the following the invention will be explained with reference to an embodiment and the accompanying drawings. In the drawing show

FIG. 1 representation of the structure edge profile,

FIG. 2 shows a circuit arrangement for detecting structural edges,

FIG. 3 shows a circuit arrangement for improving the edge signal,

Figure 4 circuit arrangement for improving the electron beam positioning.

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The inventive solution for detecting structural edges assumes that an electron beam is shifted digitally and the signal obtained from a receiver is digitized.

Pig. 1a shows in cross-section a structure 1 on a carrier material 2.

In Pig. Ib is the structural edge 3, which is to be measured, shown. The location of the structure edges was chosen to be the y-coordinate direction. The sweep direction is perpendicular to this, in which the structural edge 3 is scanned in predetermined steps, for example 5 mm. The signal from backscattered electrons, secondary electrons or a mixture of the two obtained in each sampling point is digitized and stored. Since the diameter of the electron probe is small, ie typically 10 nm, only the edge is detected in this small area, on the other hand, no requirement imposed on the linear expansion of the edge. The residence time per point is for example 4 μs. Due to the small number of registered electrons, the signal of Fig. 16 has a small signal-to-noise ratio. To improve this, the sampling is repeated at y = constant η-fold (eg, η = 50) and the digitized signal values are summed to form a signal curve 5 shown in FIG. 1d. In this example, capturing the edge takes n.2ms = 0,1 &. In this type of signal formation, the edge roughness is not taken into account. Therefore, after the scan sweep has taken place at y.sup.n, further measurements are carried out after shifting the electron beam along the y direction by. The resulting signals are superimposed to a signal curve 6, which is shown in Fig. 1 · f and a spatial-temporal means over the edge region η. Δ y, where Ay is chosen such that n. ^ Y ^ l (1 = edge extension) holds. The steepness of the signal curve 5 is divided by the steepness of the signal curve 6 and this quotient with a constant

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linked, which was determined from test objects. This creates a liiert, which is a measure of the edge roughness.

FIG. 2 shows a circuit arrangement for carrying out the method, in which a signal of a receiver 7 in a normalization element 8 is normalized by additive level shifting and multiplicative gain change. To digitize this signal is an AD-Y / andler 9, which is read via a gate 10 of the CPU 11 of a computer. A delay element 21 receives the read-in pulse EI from the central unit 11 and outputs a start signal St to the AD converter 9. The digital shift is realized per coordinate direction by a position counter 12 and 13, which via a DA-V / andler 14 and 15 and a respective output amplifiers 16 and 17, a deflection system 18 for dia χ- direction and a deflection system 19 for the y Influence direction. The initial and final values Aw and Ew a raster sweep are given the position counters 12} 1.3 by the central unit 11, they describe t he putative edge position. An electronic switching device 20 can optionally generate an x or y line. As clock pulses serve the Einleseimpulse El the signal digitization. Upon reaching the final value of a line, which is in the example in the x direction, a signal M is given to the central unit 11 by the position counter 12. At the same time, this position counter is reset to the initial value and a clock pulse is output to the position counter 13. A new scanning sweep thereby takes place on a line which is offset parallel to the first by the distance 4y.

FIG. 3 shows a circuit arrangement for improving the edge signal, in which two receivers 22 and 23 for backscattered electrons and a receiver 24 for secondary electrons are provided. The output signals of the receivers 22 and 23 are mixed additively or subtractively in a summing element 25, the resulting signal and the output signal of the receiver 24 for smoothing over, respectively

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a low-pass filter 26 and 27 the Normierungaglia countries 28 and 29 fed, the output signals are combined additively or subtractively in another summing 30 and digitized in an A / D converter 31.

 The. .Ze it constant dee low pass 26 and the low pass 2? is tuned to the delay time of the ad-Wan diers 31.

The circuit arrangement of FIG. 3 effects an improvement of the electron beam positioning for carrying out the method according to the invention. The adaptation of the distance Δ y to the structural edge of the length 1 to be measured and to the deflection sensitivity of the deflection systems 18; 19 via a Impulsvervielfacherstufe 33, which iat the position counter 13 iat. In addition, iat provided an analog attenuator 35, which is connected downstream of the DA converter 15.

Similarly, the step size in the x direction by a Impulsvervielfacherstufe 32, which is the position counter 12 upstream, and by an analog attenuator 34, the DA converter H downstream realized.

The skew of the structure to be measured against the direction of the deflection systems 18; 19 is rotated by Drehkorrektureinheiten 36; 37 taken into account. In this case, an adjustable part of the deflection voltage of one coordinate is additively or subtractively added to the other coordinate.

A significant increase in accuracy in the positioning of the electron beam is achieved in that the position counter 12 with the fast DA · * -Wan dl he 14 and the attenuator 34 only for the actual sweep, which takes place in the example in the x-direction and symmetrically to the edge position, is being used. The basic deflection of the electron beam to this assumed edge position is set by a second DA converter 38 or 39 for the x- or y-coordinate direction ν or the beginning of the series of measurements. These work more accurately and slowly, e.g. with 16 bit.

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The digital value of this basic deflection is determined by the central unit 11 and output in two buffer memories 40j 41 respectively upstream of the DA converters 38j 39. The output signals of the DA converters 38} 39 are each summed with the output signal of the DA converter 14 or 15 of the corresponding coordinate in a summing element 40 or 41, to which the output signal of the respective rotational correction unit 36 or 37 is supplied and which with one of the power amplifiers 16 or 17 is connected.

To achieve a high degree of automation, it is convenient to all digital units, d.ft. characterized in Figures 3 and 4 by d, to be controlled by the central unit 11 and to provide additional feedback to the central unit, e.g. Maximum and minimum value of the normalized signal, position of the position counter and readiness of the AD converter.

By appropriate adjustment of the pulse multiplier 33, the distance .DELTA.y between the rows can be varied or maintained the same row for repeated sampling.

If a further increase in Δy is required, the clock pulses can be fed into a higher-order bit position of the position counter. The message to the central unit 11 about the probable edge position can be made by the target position is entered into the central unit 11. This method is used to measure known structures at predetermined measuring points. On the other hand, the message can be made by displaying the object on a screen and marking the edge to be measured in an appropriate manner. For bildqrzeugenden screening while the position counter 12; 13 used. The marking can be made, for example, by a superimposed, movable mark.

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Claims (5)

- 11 Brfindunaaanapruch 234526 Method for determining the course of structural edges in measuring instruments for determining the position, the extent or the distance and the quality of preferably microlithographically produced structural patterns, wherein the signals generated during scanning with the electron beam are utilized for detecting the dtrukturkanten and the electron beam gradually over the zu measuring edge is characterized by the following method steps: a) in the sweeping direction perpendicular to the edge extension, the structure pattern is scanned pointwise by means of an electron beam along a line in constant predefined steps, the scanning signals are digitized and stored, b) the step a) is repeated several times, wherein the coordinate is not changed in the edge direction, c) the signal values obtained and digitized in steps a) and b), which in each case belong to the same locations along the sweep direction, are summed to form a signal curve, d). for η different locations at predetermined distances a along the edge of the structure, perpendicular to the sweeping direction, step a) is repeated in each case e) the scanning signals obtained and digitized in step d) are summed in the sweeping direction for all sampling points of the same coordinate, and signals are formed as spatial-temporal mean values over a selectable structural edge region n.a, 3883 234526 7 f) the steepness of the signal curve obtained according to c) is divided by the steepness of the signal curve obtained according to e), and this quotient is linked to a constant determined from test objects to a value which is a measure of the edge roughness of the structure to be measured. , Arrangement for carrying out the method according to item 1 in an electron beam measuring device, in which the electron beam impinges on the structure to be measured and, depending on this structure, a signal formed from escaping electrons is supplied to a receiver, characterized in that the receiver signal via a normalization element and a AD converter, which is read via a gate circuit from the central processing unit of a computer, the central unit is supplied, that an input pulse is supplied via a delay element as a start signal to the ^ D converter that for digital displacement of the electron beam for the x and y Coordinate direction is provided for each position counter, 'that at an input of each position counter predetermined initial or End values of Rastersweep abut that in each case a first output of the position counter via a respective DA converter and a power amplifier is supplied to a deflection system for positioning the electron beam in the relevant coordinate direction and in each case a second output of each position counter is connected to the central unit, wherej these two output Signa Ie information on reaching the final value in Sweeprichtung included that between two Poaitionszählern an electronic switching device is provided for selecting the Sweeprichtung in x- or y-coordinate direction, serving as clock pulses, the Einleseimpulse the signal digitization, 3883 234526 7 in that the wide outputs of the position counters are respectively connected to the other position counter via the changeover device. 3. Arrangement according to point 2 », characterized in that a plurality of receivers are provided which are each connected via a delay element acting as a low-pass filter with a normalization member, and the output signals of all normalizing members via an additively or subtractively acting summation with the AD-Y / andler supplied are. 4. Arrangement according to item 3, characterized that at least a portion of the receiver is followed by a summation and this is connected to a delay element. 5. Arrangement according to item 2, characterized in that for adjusting the step size in Sweeprichtung and iibstandea a in the edge direction of the structure to be measured in the clock input line of the position counter, an adjustable Impulsvervielfacherstufe and each between the DA converter and the Bndverstärker an adjustable analog attenuator is connected, that are provided for correcting the skew of the object Drehkorrektureinheiten that each coordinate direction, a second, more accurate and slower than the first working DA converter is provided, the output signal is additively linked to the rasterized deflection voltage. For this 5 pages drawings. 3883 • UüDl -4QUC * UUOQQA