Method for measuring by T-SAXS a cover defect affecting a control pattern carried by a microelectronic component; associated instrumental system and computer program product.

Abstract

A method for measuring, by T-SAXS, a coverage defect affecting a control pattern carried by a microelectronic component; associated instrument system and computer program product. This method (100) measures, by a small-angle X-ray scattering technique by transmission, a defect affecting a pattern resulting from the superposition of two line arrays carried by a microelectronic component, an xyz coordinate system being associated with the component, the lines being oriented along the y direction and the arrays being superimposed along the z direction.This method consists of: acquiring (110) intensity measurements for a plurality of X-ray beam incidence angles; reconstructing (120) two Bragg rods from the intensity measurements; determining (130) a translation angle from the spatial frequency qz position difference of the principal maxima of the two Bragg rods; and determining (140) a deformation angle from the spatial frequency qz position difference of the i-th secondary maxima of the two Bragg rods. Figure for the abstract: Figure 7.

Description

Title of the invention: Method for measuring by T-SAXS a covering defect affecting a control pattern carried by a microelectronic component; associated instrumental system and computer program product.

[0001] The present invention relates to a method for measuring a defect affecting the production of a pattern resulting from the superposition of two networks of lines carried by a microelectronic component.

[0002] The present invention relates more particularly to a method of measuring by small angle X-ray scattering - CD-SAXS (according to the English "Critical-Dimension Small Angle X-ray Scattering") by transmission (called T-SAXS for "transmission - Small Angle X-ray Scattering").

[0003] The manufacturing by stacking of a microelectronic component requires that the different levels constituting it be superimposed with precision, so that the elements carried by these different levels are correctly positioned relative to each other to guarantee the correct functioning of the final component.

[0004] It is known to control the manufacturing precision by using a control pattern resulting from the superposition of a second network of lines produced on a second level of the component, above a first network of lines produced on a first level of the component. The first network of lines, respectively the second network of lines, is for example etched during the production of the elements of the first level, respectively of the second level.

[0005] This control is carried out by measuring a covering defect, or "overlay" (abusively using the English term as a person skilled in the art would do), affecting this control pattern.

[0006] On this subject, the applicant filed patent application FR 22 02371, in which it was a question of measuring the overlay by implementing a T-SAXS technique.

[0007] In this document, the overlay is defined as a translation of the second network of lines relative to the first network of lines. This translation is characterized by an angle α between first and second directions: the first direction being the direction normal to the lines of a network, in the plane of this network; and the second direction passing through the geometric centers of the cross sections of a line of the first network and a line of the second network, the lines considered having to be perfectly superimposed when the angle α is equal to 90°.

[0008] However, the control pattern can be altered in ways other than a simple translation shifting one array of lines relative to the other.

[0009] The aim of the present invention is thus to propose a measurement method allowing the extraction of other information on the geometry of the control pattern.

[0010] For this purpose, the invention relates to a method for measuring a covering defect affecting a pattern resulting from the superposition of a first network of lines carried by a first level of a microelectronic component and a second network of lines carried by a second level of the microelectronic component, an orthonormal xyz reference frame being associated with the microelectronic component, the lines of the first and second network of lines being oriented in the y direction, and the first and second network of lines being superimposed in the z direction, the measurement method implementing a technique of small angle X-ray scattering by transmission, the method comprises the steps of:

[0011] - acquiring, by illuminating the pattern, a plurality of intensity measurements of a beam of X-rays transmitted for a plurality of angles of incidence of the X-ray beam, the angle of incidence being defined as the angle, evaluated in the plane defined by the x and z directions, between the z direction and the direction of incidence of the X-ray beam;

[0012] - reconstructing, from the plurality of intensity measurements, at least two rods of Bragg of interest of a diffraction pattern according to spatial frequencies Qx and associated respectively with the directions x and z;

[0013] - determine a translation angle from a difference between the positions according to the direction of the principal maxima of the two Bragg rods; and / or,

[0014] - determine a deformation angle from a difference between the positions according to the direction of the ith secondary maxima of the two Bragg rods.

[0015] According to particular embodiments, the method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0016] - the translation angle is the angle a defined between the x direction and the direction connecting the geometric centers of the cross-sections of a line of the first line network and a corresponding line of the second line network.

[0017] - the step of determining the translation angel uses the relation: 100181 a = arctanm there# /

[0019] where A q? = qnx - q™ and A q® = q'^ - m and n being the respective orders of the two reconstructed Bragg rods.

[0020] - the deformation angle is the angle defined as the average between a first edge angle and a second edge angle, the first edge angle being the angle between the x-direction and the direction joining the lower right corner of a line of the first line array and the upper right corner of the corresponding line of the second line array and the second edge angle being the angle between the x-direction and the direction joining the lower left corner of a line of the first line array and the upper left corner of the corresponding line of the second line array.

[0021] - the step of determining the deformation angel uses the relation: 0^ = arctaii^

[0022] where A qx — q'^-q™ and A q'_ = q^' - q”u, m and n being the respective orders of the two reconstructed Bragg rods.

[0023] The invention also relates to an instrumental system of the T-SAXS type, comprising a detector, acquisition electronics and a computer, characterized in that the computer is suitably programmed so that said instrumental system implements the preceding measurement method.

[0024] Preferably, the instrumental system comprises a detector adapted to measure the intensity of the transmitted beam over a reduced diffraction angle range making it possible to follow the at least two Bragg rods of interest during the acquisition step.

[0025] The invention also relates to a computer program product comprising software instructions which, when executed by a computer of the preceding instrumental system, allow the latter to implement the preceding measurement method.

[0026] The invention and its advantages will be better understood on reading the detailed description which follows of a particular embodiment, given solely by way of non-limiting example, this description being made with reference to the appended drawings in which:

[0027] [Fig-1] [Fig.l] is a schematic representation of an instrumental system of overlay measurement by implementing a T-SAXS technique;

[0028] [Fig.2] [Fig.2] is a representation of the Fourier transform of a pattern for which the overlay is zero;

[0029] [Fig.3] [Fig.3] is a schematic representation of two geometries associating deformation of the lines of the two superimposed networks and translation of the two superimposed networks;

[0030] [Fig.4] Figure 4B is a simulation of the form factors according to qz for the two shapes shown in Figure 4A, making it possible to illustrate the impact of the variation of the angle a on the form factor, the angles [31 and [32 being similar for these two shapes;

[0031] [Fig.5] Figure 5B is a simulation of the form factors according to qz for the two shapes shown in Figure 5A, making it possible to illustrate the impact of the variation of the angles [31 and [32 on the form factor, the angle a being similar for these two shapes;

[0032] [Fig.6] [Fig.6] is an illustration of the extraction of angles a and [3moy respectively from the position of the main maximum and the first maximum; and,

[0033] [Fig.7] [Fig.7] is a block representation of a mode of realization implementation of the overlay measurement method according to the invention.

[0034] [Fig.l] represents an instrumental system 1 for measuring the overlay.

[0035] An X-ray source S emits an X-ray beam in a direction z0, perpendicular to an observation plane P. The incident beam falls at an origin point O of the observation plane P. Directions x0 and y0 define an orthonormal reference frame of the plane P.

[0036] A microelectronic component C is interposed between the source S and the observation plane P.

[0037] The component C is provided with a control pattern Z allowing the determination of the overlay. The control pattern Z consists of a first level comprising a first network of lines and, superimposed on the first level, a second level comprising a second network of lines.

[0038] Preferably, the surface of the control pattern Z is flush with the rest of the surface of the component C.

[0039] The center A of the control pattern Z is placed on the axis of incidence of the X-ray beam.

[0040] An orthonormal xyz frame is associated with component C. This frame is attached to the center A of the control pattern Z so that the y direction corresponds to the y0 direction, and the z direction is normal to the surface of the control pattern Z.

[0041] As specified below, the lines of the line networks which make it possible to measure the overlay are arranged parallel to the y0 axis, so as to obtain Bragg peaks along the x0 axis.

[0042] The component C is placed on a support 30 allowing the component C to be rotated around the direction y so as to modify the angle of incidence (P) of the X-ray beam on the control pattern Z, i.e. the angle between the direction z and the direction z0, which is also the angle between the direction x and the direction x0.

[0043] A detector 10 is placed in the observation plane P. It is for example composed of a strip of sensors arranged in the direction x0.

[0044] The intensity at point B of the x0 axis, measured by the sensor located at point B, depends on the angle 20 between the AO direction and the AB direction. This intensity is noted / (0).

[0045] As known per se, the image in the observation plane P is related to the spatial Fourier transform of the control pattern Z illuminated by the incident beam.

[0046] In reciprocal space, the coordinate associated with the x0 direction is the spatial frequency defined by:

[0047] „ = (1) has

[0048] Let, still in the reciprocal space, but considering the spatial frequencies clx and respectively associated with the x and z directions of the reference frame linked to the Z control pattern:

[0049] g - q^ cos^ (2)

[0050] q^ _ q^ sin^ (3)

[0051] The detector 10 is connected to an electronic device, represented schematically in [Fig.l] by a cube bearing the reference 20.

[0052] The device 20 comprises control electronics making it possible to control the support 30 so that it positions the component C according to a set value of the angle of incidence V.

[0053] The device 20 also comprises acquisition electronics making it possible to carry out suitable pre-processing on the signals delivered by each of the sensors of the detector 10 and to digitize them.

[0054] The device 10 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 method for measuring the overlay, that is to say a defect affecting the control pattern.

[0055] From a theoretical point of view, it is possible to calculate exactly the spatial Fourier transform of the control pattern.

[0056] Thus, part A of [Fig.2] represents, in the direct space of the x and z coordinates (the xz plane being the plane transverse to the first and second line networks), a fraction of the control pattern Z carried by the component C. For example, the transverse sections of two lines 41 and 42 of the first line network 40 and two lines 51 and 52 of the second line network 50 are represented. The lines of each of these networks extend in the y direction.

[0057] In the case of a zero overlay, that is to say when the control pattern Z respects an ideal geometry, a line of a network has a rectangular cross-section, the side walls of a line being perpendicular to the bottom of this line.

[0058] A line has a width of 1 and a depth of p.

[0059] Two lines of the same network are spaced by a step d.

[0060] The pitch between a line of the first grating and a line of the second grating is noted D. This pitch according to the thickness of the component is considered to be equal to p in the remainder of this description (the two gratings being superimposed directly on top of each other), because this pitch according to the thickness has no measurable effects on the diffraction pattern.

[0061] Still according to the ideal geometry, the first and second networks of lines are by completely superimposed in x, that is to say in a direction normal to the lines of a network, in the plane of this network.

[0062] The exact calculation of the spatial Fourier transform of this pattern leads to part B of Figure 2. This is a representation in the reciprocal space of the spatial frequencies and Qz, which are respectively conjugates of the x and z coordinates.

[0063] For a zero value of Qz, the Fourier transform presents, along the Qx direction, a succession of principal maxima, or Bragg peak. Each Bragg peak is identified by an integer n, called the Bragg order. The Bragg peak of order n is positioned at

[0064] For a given value, that is to say for the Bragg peak of order n, the intensity along the direction forms what is called the Bragg rod of order n. A Bragg rod presents an alternation of local maxima and minima.

[0065] For i integer greater than unity, the ith secondary maximum of the upper part of the Bragg rod of order n is located at q^ (q™ positive) and the ith secondary maximum of the lower part of the Bragg rod of order n is located at q1^1 (q"'1 negative). We can note q1^ the position of the principal maximum of the Bragg rod of order n.

[0066] In part B of Figure 2, the Bragg rod of order n is symmetrical with respect to the elx axis. Thus, the position of the ith secondary maximum of the upper part of the Bragg rod of order n corresponds to the position of the ith secondary maximum of the lower part of the Bragg rod of order n: = - q^.

[0067] In part B of figure 2, we see that, when there is no overlay, the position along the Qz axis of the ith secondary maximum of a Bragg rod is constant, whatever the Bragg order n considered (q”J = q'.').

[0068] The present invention makes it possible to measure the parameters of an overlay resulting from the combination of two types of defect which can affect the Z control pattern so that it deviates from the ideal geometry of [Fig.2]:

[0069] - a translation of one network of lines relative to the other network of lines, described by a translation angle a; and

[0070] - a deformation of the lines of the two networks, described by a deformation angle PfHOV

[0071] The control pattern Z may have a defect resulting from the translation of one network of lines relative to the other in a direction normal to the lines of a network, in the plane of this network.

[0072] For example, in part 1 of [Fig.3], the upper line 51 is translated in the x direction by a distance e relative to the lower line 4L

[0073] This first type of defect (or overlay) is described by the angle a, or translation angle, between the normal direction x and the direction connecting the geometric centers Gi and G2 of a pair of lines.

[0074] The control pattern may also have a defect resulting from the deformation of the lines of the line networks, each line then having a diamond-shaped section (in other words, the side walls of a line are no longer at right angles to the bottom of this line).

[0075] For example, in part B of [Fig.3], the edges between corners 44 and 46, on the one hand, and 43 and 44, on the other hand, of the lower line 41 are inclined, and the edges between corners 54 and 56, on the one hand, and 53 and 54, on the other hand, of the upper line 51 are inclined.

[0076] A first edge angle is defined as the angle between the x direction and the direction joining the lower right corner 43 of the first line 41 and the upper right corner 57 of the second line 51.

[0077] A second edge angle is defined as the angle between the x direction and the direction joining the lower left corner 44 of the first line 41 and the upper left corner 56 of the second line 51.

[0078] The deformation angle Pm<;y characterizing this second type of defect (or overlay) is then defined as the average of the first and second edge angles: „ _ . Pmoy— 2

[0079] In the case where the pattern is affected by a translation defect but not by a deformation defect (part A of Figure 3), we show that — a, so that these two parameters then make it possible to extract the same information on the geometry of the pattern.

[0080] On the other hand, when the pattern is affected by a translation defect and by a deformation defect (part B of Figure 3), we lose the equality Pmï)y = a, and the two parameters |3 , and a then make it possible to extract different information on the overlay.

[0081] Figures 4 and 5 show that the two parameters pmoy and a are independent of each other and can be extracted from a diffraction pattern independently of each other.

[0082] In part A of [Fig.4], two patterns are superimposed with different overlays.

[0083] Pattern a, shown in solid lines, corresponds to an overlay caused solely by a translation. Pattern b, shown in dotted lines, corresponds to an overlay caused not only by a translation, but also by a deformation of the lines. These two patterns have different values ​​of the angle a (respectively aa and at>\ but identical values ​​of the angle &moy.

[0084] In part B of [Fig.4], the Bragg rods of the same order n are represented for each of the two patterns a and b of part A of [Fig.4].

[0085] We note that the position of the main maximum of the intensity is no longer identical for the two patterns (^.o and that the positions of the secondary maximums of the intensity are identical — qÿ for the second secondary maximum by example).

[0086] On part A of [Fig.5], two patterns are superimposed.

[0087] Pattern a, shown in solid lines, corresponds to an overlay caused solely by a translation. Pattern b, shown in dotted lines, corresponds to an overlay caused not only by a translation, but also by a deformation of the edges of the lines.

[0088] These two patterns have identical values ​​of the angle a, but different values ​​of the angle Pmov (respectively and secondary maxima of the intensity (nn2 ny^-az

[0089] In part B of [Fig.5], the Bragg rods of the same order n are represented for each of these two patterns.

[0090] We note that if the position of the main maximum of the intensity is identical for the two patterns a and b (qn^ _ qn,Gy there is now a shift between the positions «,2Y bz)

[0091] Part IA of [Fig.6] represents, for the same pattern affected by a translation defect and a deformation defect, different Bragg rods, in this case the rods of order -1, 1 and 2.

[0092] The measurements carried out on the positions of the principal maxima of the different Bragg rods make it possible to establish a linear relationship between the position of these maxima in the plane <7? and (part B of [Fig.6]).

[0093] Thus, the angle a can be expressed as follows:

[0094] tan(tt)=^

[0095] With A q® = q^° - q™$ and A q* — q" - q™, where n and m are the orders of the Bragg rods used for extracting information on the overlay.

[0096] The measurements carried out on the positions of the secondary maxima of the different Bragg rods make it possible to establish a linear relationship between the position of these maxima in the plane and (Z* (part C of [Fig.6]).

[0097] Thus, the angle p„K?v can be expressed as follows:

[0098] so 6

[0099] With A q\ = q'^ - qr^' and A qx — qtlx - q™, where n and m are the orders of the Bragg rods used for the extraction and i the ith secondary maximum considered.

[0100] Checks show a very good fit between these relationships and the angles real.

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[0110] [YES]

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[0115] Therefore, by measuring two diffraction orders n and m, whatever they are, the shift observed on the main maximum, as well as on a secondary maximum allows the extraction of both the angle a and the angle these two parameters allowing a description of the shape of the lines and therefore of the overlay. Taking these considerations into account, an embodiment of the method for measuring the overlay according to the invention will now be presented with reference to [Fig.7]. The method 100 first consists of reconstructing at least two Bragg rods of interest, for example orders n and m. For this, in a first acquisition step 110, by means of the detector 10, the measurement of the intensity is iterated for different angles of incidence q>. For example, the angle of incidence is varied in steps of 1° in the range from +60° to -60° and for each value of the angle of incidence the intensity is measured as a function of the position along the axis x0 of the observation plane P, i.e. as a function of the diffraction angle 0. Then, in a step 120, the diffraction pattern is reconstructed in the reciprocal space described by the coordinates Qx and Once the Bragg rods of interest have been reconstructed, the method 100 continues with a step 130 of determining the angle a: - we first calculate: Âq^ — q™- q'” ; - we then calculate: A q^ = q”-® - q'^ - and finally we determine the translation angle: . / 4^' \ 6 a = arctan-“ The method 100 continues with a step 140 of determining the angle 0we)y: - the value of A q calculated previously is taken; - we then calculate: A q{ = q™ - q™> (for example i is equal to 2); - and finally we determine the deformation angle: R Pwpy -aician^ The present invention makes it possible to measure the characteristic parameters of translation and deformation defects potentially affecting a pattern. In the present description, attention is paid to a control pattern, specifically made on the component to carry out measurements of the manufacturing quality. However, as a variant, the pattern can be developed from functional elements of the component, such as for example lines of transistors belonging to different levels of the component.

Claims

Claims

1. 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 (C) and a second line array (50) carried by a second level of the microelectronic component, an orthonormal xyz reference frame being associated with the microelectronic component, the lines of the first and second line arrays being oriented in the y direction, and the first and second line arrays being superimposed in the z direction, the measurement method implementing a transmission small angle X-ray scattering (T-SAXS) technique, characterized in that the method comprises the steps of: - acquiring (110), by illuminating the pattern, a plurality of intensity measurements of a transmitted X-ray beam for a plurality of angles of incidence of the X-ray beam, the angle of incidence being defined as the angle, evaluated in the plane defined by the x and z directions, between the z direction and the direction of incidence of the X-ray beam; - reconstructing (120), from the plurality of intensity measurements, at least two Bragg rods of interest of a diffraction pattern according to spatial frequencies Qx and associated respectively with the directions x and z; - determining (130) a translation angle from a difference between the positions according to the direction of the principal maxima of the two Bragg rods; and / or, - determine (140) a deformation angle from a difference between the positions according to the direction of the ith secondary maxima of the two Bragg rods, the translation angle being the angle a defined between the x direction and the direction connecting the geometric centers of the cross sections of a line of the first network of lines and a corresponding line of the second network of lines and the step of determining the translation angle using the relation: \ a = arctan hh where A gv = g„ - g™ and A g® = g"® - m and n being the respective orders of the two reconstructed Bragg rods, the strain angle being the angle &moy defined as the average between a first edge angle and a second edge angle, the first edge angle being the angle between the x direction and the direction joining the lower right corner of a line of the first line grating and the upper right corner of the corresponding line of the second line grating and the second edge angle being the angle between the x direction and the direction joining the lower left corner of a line of the first line grating and the upper left corner of the corresponding line of the second line grating and the step of determining the strain angle using the relation: « . / \ P,„v = arctan^ where A q = qnx - q"1 and A q[ — q1^ - q™'1, m and n being the respective orders of the two reconstructed Bragg rods.

2. Instrumental system (1) of the transmission small angle X-ray scattering (T-SAXS) type, comprising a detector, acquisition electronics and a computer, characterized in that the computer is suitably programmed so that said instrumental system implements a method for measuring a covering defect according to claim 1.

3. Instrumental system according to claim 2, comprising a detector adapted to measure the intensity of the transmitted beam over a reduced diffraction angle range making it possible to follow the at least two Bragg rods of interest during the acquisition step.

4. Computer program product comprising software instructions which, when executed by a computer of an instrumental system according to any one of claims 6 and 7, allows the latter to implement a method for measuring a covering defect according to claim 1.

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