Method for measuring a covering defect; Associated instrumental system and computer program product.

Abstract

Method for measuring a covering defect; Associated instrumental system and computer program product. This method (100) GI-SAXS measures a defect affecting a pattern superimposing first and second line networks.It consists of: acquiring (110), in an observation plane, intensity measurements of the X-rays scattered by the pattern; reconstructing (120), from the intensity measurements, a reciprocal image; determining (130) a first position according to a first spatial frequency of a characteristic point on a first intensity curve corresponding to a section of the reciprocal image for a first value of a second spatial frequency, and a second position according to the first spatial frequency of the characteristic point on a second intensity curve corresponding to a section of the reciprocal image for a second value of the second spatial frequency; and, calculating (140) a defect from the difference between the first and second positions according to the first spatial frequency and the difference between the first and second values ​​according to the second spatial frequency. Figure for the abstract: Figure 6.

Description

Title of the invention: Method for measuring a covering defect; Associated instrumental system and computer program product.

[0001] The present invention relates to a method for measuring an error in the superposition of two line networks during the manufacture of a microelectronic component, this method implementing a grazing-incidence small-angle X-ray scattering technique or GISAXS (for "grazing-incidence small-angle X-ray scattering").

[0002] To continue increasing the density of microelectronic elements on a small surface, the superposition of successive levels for three-dimensional integration is expanding rapidly.

[0003] The manufacture of such a three-dimensional microelectronic component requires that the different levels which constitute it are superimposed with precision, so that the patterns carried by these different levels are correctly positioned relative to each other, so as to guarantee the correct functioning of the manufactured component.

[0004] It is known to control the precision of the superposition of two levels of a component by measuring, on a target provided for this purpose, an alignment error, called "overlay" (abusively using the English term as a person skilled in the art would do), corresponding to a translation between a first network of lines carried by a first level and a second network of lines carried by a second level of the component.

[0005] Documents US 9 885 962 B2 or FR 3133673 present a method for measuring the overlay by implementing a transmission X-ray scattering technique or T-SAXS. This involves illuminating the target carried by the component with an X-ray beam and evaluating the overlay from the transmitted intensity for different angles of incidence of the X-ray beam.

[0006] However, this technique remains difficult to implement since it requires the transmission of X-rays through the thickness of the component. This proves problematic because the different levels are deposited on a substrate, for example silicon, having a relatively large thickness, typically 700 μm.

[0007] A measurement of the overlay in transmission therefore requires that the X-ray beam has a high intensity. Only synchrotron sources are capable of delivering the required intensity. However, such sources are not compatible with deployment along a production line.

[0008] The aim of the present invention is to propose a method for measuring the overlay based on the implementation of a GISAXS X-ray reflection scattering technique.

[0009] For this purpose, the subject of the invention is a method for measuring a covering defect affecting a pattern resulting from the superposition of a first line array carried by a first level of a microelectronic component and a second line array carried by a second level of the microelectronic component, an orthonormal reference frame xoyoZo being associated with the microelectronic component, the lines of the first and second line arrays being oriented along the x0 direction, and the first and second line arrays being superimposed along the z0 direction, the measurement method implementing a small angle X-ray scattering technique by reflection - GLSAXS making it possible to illuminate the pattern at an angle of incidence ai, characterized in that the method comprises the steps of: acquiring, by means of a detector placed in an observation plane, an orthonormal reference frame xyz being associated with the detector so that the z axis is parallel to the z0 axis and the x axis,normal to the observation plane, coincides with the y0 axis for a zero illumination angle, a plurality of intensity measurements of an X-ray beam scattered by the pattern carried by the component, the illumination angle being defined as the angle, evaluated in the plane defined by directions x and z, between the direction x and the plane of incidence of the X-ray beam; reconstruct, from the plurality of intensity measurements,a reciprocal image in a reciprocal space of the spatial frequencies Qy and ^z associated respectively with the directions y and z; determining (130) at least a first position along the ^z direction of a characteristic point on a first intensity curve corresponding to a first section of the reciprocal image for a first value along the direction Vy and a second position along the ^z direction of the characteristic point on a second intensity curve corresponding to a second section of the reciprocal image in the reciprocal space for a second value along the direction Qy; and, calculating a value of the overlap defect from the difference between the first and second positions along the direction Qz and the difference between the first and second values ​​along the direction Qy.

[0010] According to particular embodiments, the measuring method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0011] -the defect is a translation of the first network of lines relative to the second network of lines or “overlay” - OVL.

[0012] - the characteristic point is a minimum of intensity, preferably the first minimum intensity.

[0013] - the value of the defect is measured by exploiting a region of the reciprocal image corresponding to a diffusion angle substantially equal to the angle of incidence.

[0014] - the calculation step uses a relationship between the measurement of the defect, on the one hand, and the deviation between the first and second positions along the Qz direction and the difference between the first and second values ​​along the Qy direction, on the other hand, said relationship deriving from a modeling of the effects of multiple reflections of X-rays at the interface between the levels of the component and a substrate of the component.

[0015] - for a defect corresponding to a translation of the first line network with respect to the second network of lines or "overlay", the relationship is given by: tanct = Aq / Aq'oùa = ' with O VL the overlay, D the distance between the first and second line networks, A qz the gap between the first and second positions in the Qz direction and A qY the gap between the first and second positions in the % direction.

[0016] The invention also relates to an instrumental system of the small angle X-ray scattering by reflection type - GLSAXS, comprising an X-ray source, a detector, acquisition electronics and a computer, programmed for the implementation of the preceding measurement method.

[0017] According to particular embodiments, the system comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0018] - the X-ray source is a so-called laboratory source, preferably made of copper.

[0019] - the system makes it possible to exploit a region of the reciprocal image corresponding to a scattering angle substantially equal to the angle of incidence.

[0020] The invention finally relates to a computer program product comprising software instructions which, when executed by a computer of the preceding instrumental system, allows the latter to implement the preceding method.

[0021] The invention also relates to an instrumental system of the GISAXS type, comprising a computer and a detector connected to the computer, characterized in that the computer is suitably programmed so that the instrumental system implements the preceding method.

[0022] The invention also relates to a computer program product comprising software instructions which, when executed by the computer of an instrumental system conforming to the preceding system, allows the latter to implement a method for measuring the overlay conforming to the preceding method.

[0023] The invention and its advantages will be better understood upon reading the detailed description which follows of a particular embodiment, given solely for illustrative purposes. illustrative and non-limiting example, this description being made with reference to the attached drawings in which:

[0024] [Fig.l] [Fig.l] is a schematic representation of an instrumental system of the GIS AXS type for implementing the measuring method according to the invention;

[0025] [Fig.2] [Fig.2] is an image in reciprocal space obtained by means of the instrumental system of [Fig.l], for a zero overlay between the line networks carried by the illuminated component;

[0026] [Fig.3] [Fig.3] is an image in reciprocal space obtained by means of the instrumental system of [Fig.l], for a non-zero overlay between the line networks carried by the illuminated component;

[0027] [Fig.4] [Fig.4] is a graph superimposing a plurality of curves of the intensity as a function of the position coordinate qz obtained from the image of [Fig.3];

[0028] [Fig.5] [Fig.5] is a plot of the position coordinates qz as a function of the order of the first minimum of the curves of the graph of [Fig.4]; and,

[0029] [Fig.6] [Fig.6] is a block representation of an embodiment of the overlay measurement method according to the invention.

[0030] Generally speaking, the method according to the invention is based on the implementation of a measurement technique by small angle X-ray scattering at grazing incidence - GISAXS.

[0031] In this technique, the X-rays do not have to pass through the component, but are reflected at its surface.

[0032] The intensity required to carry out the measurement, i.e. to collect on the observation detector an intensity sufficient for a precise measurement, can then be provided by a less intense X-ray source, in particular a small so-called "laboratory" source, such as a Cu Ka source. Such a source is compatible with integration of the instrumental system and consequently with measurement of the overlay along a manufacturing line.

[0033] To be able to extract the overlay, there are nevertheless some difficulties associated with this technique, in particular the multi-reflection effects of the X-rays at the interface between the different levels of the component and the substrate.

[0034] [Fig.l] represents an instrumental system 1 making it possible to implement the method of measuring the overlay according to the invention on a sample 10.

[0035] According to this technique, a source S illuminates the sample 10 and the light reflected by the sample 10 is imaged in an observation plane PO.

[0036] A reference frame x, y, z of the instrumental system 1 is for example attached to the origin O of the observation plane PO, so that the direction normal to this plane is the direction x and the plane itself is defined by the directions y and z.

[0037] The sample 10 is for example a microelectronic component on the flat surface of which a target 12 is provided. The target 12 comprises a first level carrying a first line network and a second network having a second line network. Each network is for example etched by implementing a lithography process during the manufacture of the level which carries it.

[0038] A reference frame x0, y0, z0 is attached to the center A of the target 12, so that the direction z0 (which corresponds to the stacking direction of the levels of the component 10) corresponds to the normal to the surface of the sample 10, that the direction x0 corresponds to the direction of the lines of the line network of the target 12, and that the direction y0 is orthogonal to the directions z0 and x0, i.e. orthogonal to the direction of the lines of the line network.

[0039] The sample 10 is placed on a support 30 of the instrumental system 1. Preferably and to simplify the present description, the sample 10 is oriented so that the zO axis is parallel to the z axis of the instrumental system 1, and the xoyo plane of the surface of the sample 10 coincides with the xy plane. However, and more generally, there may be an angle between these two directions, which must then be taken into account during the analysis.

[0040] The X-ray source S emits an X-ray beam in a direction of incidence D on the target 12 of the sample 10.

[0041] The incidence plane PI corresponds to the xz plane. The y direction is therefore the direction normal to the incidence plane PI.

[0042] A GISAXS measurement is carried out with a small angle of incidence ai, between the x and D directions, for example a few radians (between 0.1-10 degrees).

[0043] The support 30 makes it possible to rotate the sample 10 around the direction z0 so as to modify an illumination angle q> between the direction x0 and the direction x, which is also the angle between the direction y0 and the direction y. The illumination angle (p), when it is not zero, causes there to be a misalignment between the direction of the lines of the line network (direction x0) and the plane of incidence PI.

[0044] The incident beam falls at point A of the sample 10. It is diffused by the target 12 so as to form an image in the observation plane PO.

[0045] A detector 20 is placed in the observation plane PO. It is for example composed of a matrix of X-ray sensors, the lines of which are arranged in the y direction and the ranks in the z direction. Each sensor is capable of measuring an intensity.

[0046] The intensity I at point B of the observation plane PO, measured by the sensor located at point B, depends on the angle 20, defined between the direction AO and the projection of the direction AB in the horizontal xy plane, and on the angle af between the direction AB and the projection of the direction AB in the horizontal xy plane.

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[0059] The detector 20 is connected to an electronic device, represented schematically in [Fig.l] by a cube bearing the reference 40. The device 40 comprises control electronics making it possible to control the support 30 so that it positions the sample 10 according to a set value of the illumination angle. The device 40 also includes acquisition electronics making it possible to carry out suitable pre-processing on the signals delivered by each of the sensors of the detector 20 and to digitize them. The device 40 further comprises a computer for processing the pre-processed and digitized signals. The computer is a computer comprising calculation means, such as a processor, and storage means, such as a memory. The memory stores in particular the instructions of computer programs, in particular a program whose execution allows the implementation of the measurement method according to the invention. Rather than analyzing an image (collected for a particular illumination angle) in the observation plane PO, that is, in the direct space of x, y and z coordinates, it is known to convert it in such a way as to obtain a reciprocal image. This reciprocal image belongs to the reciprocal space whose reciprocal coordinates are the spatial frequencies Qx, 9y and Qz. The spatial frequencies Qx, Qy and Qz, respectively associated with the directions x, y and z of the reference frame linked to the observation plane PO, are written: qx = ^[cos(cq).cos(29)-cos^](1) qy = Ÿ[œs(af).sin(2e)] W qz= ^ [ sin(«f) + 8111(¾)] (3) where ai is the angle of incidence of the X-rays on the sample, is the angle of the ray reflected out of the xy plane, 20 is the angle of rotation around the zO axis of the reflected ray, and X is the wavelength. On the reciprocal image, the key information is found at the level of the Bragg spots (i.e., the scattering peaks). For each illumination angle cp, the p-order Bragg spot is located at a unique combination of values ​​(q^, q^'). This was shown in the article M. Yan et al. “on the intersection of grating truncation rods with the Ewald sphere studied by grazing-incidence small-angle X-ray scattering”, J. Appl. Cryst. (2007). 40, 1050-1055: , ( r , t A] 14) n 2jrcos( <p) 27Tsm(a+cos(®)cos(®) J X~p- / 2bsin(<p) \ p v 7 qp —- ..................,.,.,.1...... _ ................................................................................... IJI JA [ [ b sin(«j) costcpy \ L / J

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[0074] 27rsiti(ai)cos(c!i)eos(cp) I [ 2bsin(«>) \ T =---; >------ X 1 + ......1 - ~T~~ “z A [ [ b cos((p) \ PÀ / where X is the X-ray wavelength, b is the periodicity of the pattern, p is the order of the scattering peak, and ai is the angle of incidence and is the illumination angle. The left part of [Fig.2] represents, in the direct space of the coordinates yO and zO (or z), a fraction of the pattern carried by the target 12 of the component 10. This is the superposition, in the thickness of the component 10 (that is to say in the direction zO), of a first network of lines 40 and a second network of lines 50. For example, two lines 41 and 42 of the first network and two lines 51 and 52 of the second network are represented. The lines of each of these networks extend in the direction xO, orthogonal to the plane of the figure. A line has a substantially rectangular section in the plane zOyO, of width 1 and depth p. Two neighboring lines of the same network of lines are spaced by a pitch d. The two networks of lines 40 and 50 are separated from each other by a distance D. In [Fig.2], the first and second line networks are perfectly superimposed along the zO direction. The GIS AXS illumination of the configuration shown in the left part of [Fig.2], leads, in the reciprocal space qzet qy to the reciprocal image shown in the right part of [Fig.2]. More precisely, to obtain this configuration, the angle of incidence ai is 0.2 degrees and one line of the line array has a width and depth of 40 nm. The pitch d is 100 nm and the distance D is 40 nm, with the two line arrays directly superimposed on each other. [Fig.3] is similar to [Fig.2] except that the first and second line arrays 40 and 50 are now slightly offset from each other along the yO direction of an OVL overlay. The lines of the second network 50 are angularly offset relative to the lines of the first network 40 by an angle α such that: tg(a) Or, as a first approximation, for small values ​​of a: OVL / aï and = -gr W With such an overlay, the obtained reciprocal image is shown on the right part of Figure 3. It is a representation in the reciprocal space of the spatial frequencies*^ and Qz, respectively conjugate of the y and z coordinates. It can be seen that the GISAXS signal is only obtained for positive Qz. Indeed, the exit angles, af, less than 0 are masked from the detector by the sample.

[0075] Figure 4 is a graph superimposing a set of curves giving the intensity I as a function of the coordinates Qz.

[0076] Each curve is indexed by the index i, or order, i is a non-zero relative integer.

[0077] Each curve corresponds to a vertical section in the reciprocal image of the [Fig.3],

[0078] Each cut is associated with a particular value q( according to the direction Qy of the reciprocal image of [Fig.3].

[0079] The chosen values ​​of qÿ are distributed equidistantly along the Qy direction.

[0080] For example, in Figure 3, values ​​of q^ retained are represented for i integer between -5 and 5. These vertical cuts are here made for a step A every 0.3 nm '.

[0081] Advantageously, the step A between two successive values ​​of q(, is equal to the distance between two Bragg rods, but this is not necessary.

[0082] If we follow the evolution of the position qd according to the direction Qz of the first minimum (n=l) as a function of the order i, we obtain the graph of [Fig.5].

[0083] The graph in Figure 5 shows a linearity between qb and i.

[0084] A similar linear relationship could be obtained by following the evolution of the position q^ of the nth minimum as a function of the order i, or of any other characteristic point of the intensity curves:

[0085] qn.i = a'i+b'(7)

[0086] Since order i can also be associated with a position q[, (multiple of step A), we have the following general linear relationship:

[0087] q'd = aqi, + b (8)

[0088] Now we need to link the parameters a and b to the OVL overlay.

[0089] For the region of the reciprocal image corresponding to high angles, the effect related to multiple reflections is reduced and the GIS AXS image becomes very close to a TSAXS image. Overlay measurements can be made in GIS AXS as they are in TSAXS.

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[0092] Under these conditions, we show that: tana = a = Aqy / Aqz^9) where A qv is the position difference in Qy between two orders i and j ( Aqy= (ij). A ) and A q is the difference in position in Qz between these same two orders i and j ( A qz = q“-q"'j )'

[0093] However, for accurate measurement at wide angles, multi-reflections must be taken into account.

[0094] Furthermore, this approach only takes a small advantage of the grazing illumination configuration, since only angles af greater than three times the angle of incidence a; (i.e. qz > 0.6 nm1) are considered.

[0095] Finally, the signal intensity in this region is low. It is difficult to exploit, unless the exposure time is increased, which is not compatible with integration on a manufacturing line and the multiplication of measurements.

[0096] We therefore seek to exploit the image in the region close to a;=af (diffusion angle substantially equal to the angle of incidence), that is to say the reciprocal image for qz between 0.2 and 0.3 nm ', that is to say the lower, most intense part of the reciprocal image, that is to say between lines L1 and L2.

[0097] The horizontal line L1 is commonly called Yoneda and corresponds to af equal to the critical angle of the substrate (here in this example a Si wafer), or total angle of reflection. It is in this angular range that the multi-reflection effects are the most intense.

[0098] The effects of multiple reflections of X-rays at the interface between the medium (the levels of the component being probed) and the substrate can be taken into account through modeling based on the Bom approximation of distorted waves -DWBA ("Distorted Wave Born Approximation").

[0099] To evaluate the total signal, it is shown that four events are in the majority and must be taken into account for the theoretical calculations: a first simple diffusion event through the levels of the component; a second reflection event on the substrate after diffusion; a third reflection event before diffusion; and a fourth event with a reflection before diffusion and a reflection after diffusion.

[0100] We then theoretically establish the following relationship, which is ultimately similar to that usable in the upper part of the reciprocal image: [OWi] tana = a= Aqy / Aqz(10)

[0102] Given this theoretical relationship, the straight line joining the points in [Fig.5] allows the value of the overlay to be extracted very precisely: OVL = 0.501+0.0130 nm.

[0103] The method for measuring the overlay according to the invention will now be presented with reference to [Fig.6].

[0104] The method 100 first consists of reconstructing the reciprocal image in the reciprocal space.

[0105] For this, in a first acquisition step 110, by means of the detector 10, the intensity is measured in the observation plane for a value of the angle

[0106] The method 100 continues with a second step 120 consisting of reconstructing the reciprocal image in the reciprocal space described by the coordinates Qy and Qz.

[0107] Once the reciprocal image has been reconstructed, the method 100 continues with a step 130 of determining the position along the 9Z axis of the nth minimum intensity for at least two vertical sections of the reciprocal image obtained in step 120. Preferably, this is the first minimum since it has a strong contrast and can therefore be located precisely.

[0108] For example, we measure the position qb of the first minimum of the curve of order i (cut in qp and the position qU of the first minimum of the curve of order -i (cut in

[0109] Advantageously, more than two cuts are used to obtain more points and determine with greater precision the coefficients of the straight line connecting these points (for example by a least squares type regression method).

[0110] Finally, in a fourth step 140, the difference in position in Qz of the minimum tracked as a function of the difference in position in 9y makes it possible to extract the overlay OVL. If we are interested in the most intense region of the reciprocal image, that is to say one of the first minima of the intensity curves (close to the line Ll) equation (10) is used.

[0111] Advantageously, the method 100 can be iterated by modifying the illumination angle ç.

[0112] Indeed, from several images collected for different illumination angles q>, and converted into reciprocal space, a mapping of the pattern can be obtained.

[0113] Since the information is contained at the Bragg task level, it is therefore preferable to scan in order to access different %, clz, and thus obtain more information on the pattern.

[0114] Looking only at the part around the Yoneda, the pattern information is contained for a small angular range between -5 and 5°, preferably between -2 to 2, and more preferably -0.5 and 0.5. It is therefore this range if it is then advantageous to scan accurately.

[0115] The instrumental system 1 is adapted to implement the measurement method 100 just presented. In particular, the computer of the system 1 is suitably programmed to carry out the calculation steps, i.e. the steps other than the acquisition step, in particular calculating the overlay from equation (10).

[0116] With the GIS AXS, the grazing incidence geometry makes it possible to circumvent the limitations of the TSAXS, since the X-ray beam is no longer sent through the substrate but is reflected by it.

[0117] Furthermore, in order not to be restricted to a few specific GISAXS conditions, in particular at high incidence angles, multiple reflection effects are taken into account.

[0118] The measurements are more precise and do not depend on the experimental conditions, since they allow the overlay to be extracted even at low angles of incidence.

[0119] This possibility makes it possible to exploit the intense region of the reciprocal image and consequently to authorize measurements with reduced acquisition times.

Claims

1. Claims Method (100) for measuring a covering defect affecting a pattern resulting from the superposition of a first line array (40) carried by a first level of a microelectronic component (10) and a second line array (50) carried by a second level of the microelectronic component, an orthonormal reference frame xoyoZo being associated with the microelectronic component, the lines of the first and second line arrays being oriented along the x0 direction, and the first and second line arrays being superimposed along the z0 direction, the measurement method implementing a small-angle X-ray scattering technique by reflection making it possible to illuminate the pattern at an angle of incidence ai, characterized in that the method comprises the steps of: - acquiring (110), by means of a detector placed in an observation plane, an orthonormal xyz reference frame being associated with the detector so that the z axis is parallel to the z0 axis and the x axis, normal to the observation plane, coincides with the y0 axis for a zero illumination angle, a plurality of intensity measurements of an X-ray beam diffused by the pattern carried by the component, the illumination angle being defined as the angle, evaluated in the plane defined by directions x and z, between the direction x and the plane of incidence of the X-ray beam; - reconstructing (120), from the plurality of intensity measurements, a reciprocal image in a reciprocal space of the spatial frequencies Qy and associated respectively with the directions y and z; - determining (130) at least a first position along the direction of a characteristic point on a first intensity curve corresponding to a first section of the reciprocal image for a first value along the direction ^y and a second position along the direction ^z of the characteristic point on a second intensity curve corresponding to a second section of the reciprocal image in the reciprocal space for a second value along the direction Qy; and, - calculating (140) a value of the overlap defect from the difference between the first and second positions in the direction Qz and the difference between the first and second values ​​in the direction Qy.

2. The method of claim 1, wherein the defect is a translation of the first line array relative to the second line array or overlay (OVL).

3. A method according to any preceding claim, wherein the characteristic point is an intensity minimum, preferably the first intensity minimum.

4. A method according to any preceding claim, wherein the value of the defect is measured by exploiting a region of the reciprocal image corresponding to a scattering angle substantially equal to the angle of incidence.

5. Method according to any one of the preceding claims, in which the calculation step uses a relationship between the measurement of the defect, on the one hand, and the difference between the first and second positions in the Qz direction and the difference between the first and second values ​​in the cly direction, on the other hand, said relationship deriving from a modeling of the effects of multiple reflections of the X-rays at the interface between the levels of the component and a substrate of the component.

6. Method according to claim 5, in which, for a defect corresponding to a translation of the first network of lines relative to the second network of lines or "overlay", the relation is given by: tana = A q / A where a = , with 0VL the overlay, D the distance between the first and second networks of lines, A qz the difference between the first and second positions in the direction Qz and A qv the difference between the first and second positions in the direction cly.

7. Instrumental system (1) of the small angle X-ray scattering by reflection (GI-SAXS) type, comprising an X-ray source, a detector, acquisition electronics and a computer, programmed for the implementation of a measurement method according to any one of the preceding claims.

8. Instrumental system according to claim 7, wherein the X-ray source is a so-called laboratory source, preferably made of copper.

9. Instrumental system according to claim 7 or claim 8, making it possible to exploit a region of the reciprocal image corresponding to a diffusion angle substantially equal to the angle of incidence. 14

10. Computer program product comprising software instructions which, when executed by a computer of an instrumental system according to claim 7 or claim 9, allows the latter to implement a method according to any one of claims 1 to 6.

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