EP2529182A1

EP2529182A1 - System and method for assessing inhomogeneous deformations in multilayer plates

Info

Publication number: EP2529182A1
Application number: EP11705922A
Authority: EP
Inventors: Marcel Broekaart; Arnaud Castex; Laurent Marinier
Original assignee: Soitec SA
Current assignee: Soitec SA
Priority date: 2010-01-25
Filing date: 2011-01-24
Publication date: 2012-12-05
Also published as: WO2011089368A1; KR20150006901A; US9733075B2; JP2013518401A; FR2955654B1; US20130054154A1; JP5633854B2; KR20120123105A; CN102741650B; SG182423A1; CN102741650A; FR2955654A1

Abstract

The invention relates to a method for assessing inhomogeneous deformations in a first plate (110), the first plate being adhered by molecular bonding to a second plate (120). Said method includes a step of recording a plurality of measurement points, each one of the measurement points being locally representative of the level of the surface of the first plate; a step of defining a surface profile of the first plate passing through a plurality of the measurement points; a step of processing the surface profile of the first plate in order to define a typical magnitude thereof; and a step of assessing a level of inhomogeneous deformations in the first plate according to the typical magnitude. The invention further relates to a device (147) for assessing such inhomogeneous deformations.

Description

System and method for evaluating inhomogeneous deformations in multilayer plates

Background of [invention

The present invention relates to the field of producing multilayer semiconductor plates or substrates (also called "multilayer semiconductor wafers") made by transferring at least one layer formed from an initial substrate onto a final substrate, the transferred layer corresponding to a portion of the initial substrate, the transferred layer may further comprise all or part of a component or a plurality of microcomponents.

The present invention relates to the problem of inhomogeneous deformations that appear in a bonded layer by molecular adhesion on a substrate, and more specifically, during the transfer of such a layer from an initial substrate called "donor substrate" on a final substrate called "substrate recipient". Such deformations have notably been observed in the case of 3D component integration technology which requires the transfer of one or more layers of microcomponents onto a final support substrate but also in the case of circuit transfer. or in the manufacture of illuminated imagers on the back. Due in particular to the very small size and the large number of microcomponents generally present on the transferred layers, each of them must be positioned on the final substrate with great precision in order to respect a very strict alignment with the underlying layer. In addition, it may be necessary to carry out treatments on the layer after its transfer, for example to form other microcomponents, to discover microcomponents on the surface, to make interconnections, etc.

However, the Applicant has noted that after such transfer, there are cases where it is very difficult, if not impossible, to form additional microcomponents in alignment with the microcomponents formed before the transfer.

This phenomenon of misalignment is described in relation to FIGS. 1A to 1E, which illustrate an exemplary embodiment of a structure three-dimensional method comprising the transfer, on a final substrate, of a layer of microcomponents formed on an initial substrate, and the formation of an additional layer of microcomponents on the exposed face of the initial substrate after bonding.

FIGS. 1A and 1B illustrate an initial substrate 10 on which is formed a first series of microcomponents 11. The microcomponents 11 are formed by photolithography by means of a mask making it possible to define the pattern formation zones corresponding to the microcomponents 11 to be produced.

As illustrated in FIG. 1C, the face of the initial substrate 10 comprising the microcomponents 11 is then placed in intimate contact with a face of a final substrate 20, thus forming the composite structure 25. The bonding between the initial substrate 10 and the substrate final 20 is made by molecular adhesion. Thus, a buried layer of microcomponents 11 is obtained at the bonding interface between the substrates 10 and 20. After bonding and as represented in FIG. 1D, the initial substrate 10 is thinned in order to remove a portion of material present in the substrate. above the microcomponent layer 11. A thinned composite structure 30 formed of the final substrate 20 and a layer 10a corresponding to the remaining portion of the initial substrate 10 is then obtained.

As shown in FIG. 1E, the following step in producing the three-dimensional structure consists in forming a second layer of microcomponents 12 at the exposed surface of the initial thinned substrate, or in carrying out complementary technological steps on this exposed surface. in alignment with the components included in the layer 10a (contacting, interconnections, etc.). For the sake of simplicity, the term "microcomponents" will be used later in this text, the devices or any other reasons resulting from the technological steps performed on or in the layers and whose positioning must be precisely controlled. It can therefore be active or passive components, simple contacts or interconnections.

Thus, in order to form the microcomponents 12 in alignment with the buried microcomponents 11, a photolithography mask similar to that used to form the microcomponents 11 is used. Here, similar masks are understood to mean masks. which have been designed for use in combination in a manufacturing process.

The transferred layers, like the layer 10a, typically comprise marks (or markers) both at the level of the microcomponents and at the level of the slice forming the layer which are used in particular by positioning and alignment tools during the steps of technological treatments such as those implemented during a photolithography.

However, even using positioning tools, offsets occur between some of the microcomponents 11 and 12, such as the offsets Δ11, Δ22, Δ33, Δ44, shown in FIG. 1E (respectively corresponding to the offsets observed between the pairs of microcomponents 111/121, 112/122, 113/123 and 114/124).

These shifts are not the result of elementary transformations (translation, rotation or their combinations) that could have originated in an imprecise assembly of the substrates. These offsets result from inhomogeneous deformations that appear in the layer from the initial substrate during its assembly with the final substrate. In fact, these deformations cause local and non-uniform displacements at the level of certain microcomponents 11. Also, some of the microcomponents 12 formed on the exposed surface 14b of the substrate after transfer present positional variations with these microcomponents 11 which may be order of several hundred nanometers, even micron.

This phenomenon of misalignment (also called "overlay") between the two layers of microcomponents 11 and 12 can be the source of short circuits, distortions in the stack or connection faults between the microcomponents of the two layers. Thus, in the case where the transferred microcomponents are imagers formed of pixels and the post-transfer processing steps aim at forming on each of these pixels color filters, a loss of the colorization function has been observed for some of these pixels. pixels.

This phenomenon of misalignment thus leads to a reduction in the quality and value of the multilayer semiconductor plates manufactured. The impact of this phenomenon is becoming more and more critical because of the ever increasing demands on miniaturization of microcomponents and their integration density per layer.

The method currently used today to determine whether significant inhomogeneous deformations are present in a multilayer plate consists in determining the positioning of a certain number of microcomponents by optically performing positioning measurements at marks formed on or near these microcomponents (verniers,.,.).

However, it is possible to perform these positioning tests only after the thinning of the initial substrate and the realization of complementary technological steps on the exposed surface 14b of the initial substrate 10.

In addition, if misalignments are detected in the initial substrate after thinning, they can not be corrected. In this case, the initial thinned substrate is not recyclable. Ultimately, when positioning tests reveal unacceptable misalignments in terms of reliability and / or performance in a thinned composite structure, the final substrate is lost which significantly increases the cost of producing the multilayer plates.

A technique for determining misalignments in a semiconductor wafer has also been described in WO 2007/103566 A2. More specifically, this technique aims to evaluate misalignments that may occur in a plate during a photolithography step, these misalignments resulting from mechanical stresses generated in the plate.

In practice, this technique consists in making curvature measurements on one side of a layer produced by deposition on a substrate. From the curvature data obtained at different points of the layer, the internal mechanical stresses of this layer with respect to the substrate are determined. From the knowledge of these constraints, it is possible to evaluate the "displacements" of this layer with respect to the substrate. The evaluation of these displacements before or during a photolithography step notably makes it possible to determine how to compensate or correct the parameters of the photolithography so as to minimize the misalignments. However, this technique only concerns the evaluation of the deformations generated on the whole of a layer produced by deposition on a substrate (or possibly by ion implantation, annealing or etching). These deformations, said homogeneous, are in fact the result of a mechanical equilibrium obtained over the entire layer deposited on the substrate. This type of deformation has a behavior that is today relatively predictable thanks to the use of models taking into account in particular the laws of mechanics and the thicknesses involved (see equation 5 presented on page 5 of the document WO 2007/103566 A2).

The technique described in document WO 2007/103566 A2 is however not designed to evaluate inhomogeneous deformations resulting from a bonding of two plates, and in particular of a bonding of the molecular adhesion type whose mechanisms are still very poorly known. today.

The Applicant has indeed found that the behavior of inhomogeneous deformations resulting from bonding by molecular adhesion is random, and in any case very different from that of conventional homogeneous deformations. To date, no model reliably assesses the level of inhomogeneous deformations generated in a bonded layer by molecular adhesion to a substrate. There is therefore a need to evaluate simply and effectively the level of inhomogeneous deformations in multilayer structures manufactured by molecular bonding adhesion, and at an earlier stage of their manufacture, that is to say after bonding.

Object and summary of the invention

One of the aims of the invention is to propose a solution that makes it possible to meet the need formulated above. For this purpose, the present invention provides a method of evaluating inhomogeneous deformations in a first plate, the first plate being adhesively bonded to a second plate by molecular adhesion, the evaluation method comprising;

a step of reading a plurality of measuring points, each of the measuring points being locally representative of the level of the exposed surface of the first plate; a step of determining at least one surface profile of the first plate passing through a plurality of measurement points;

a step of processing the surface profile of the first plate to determine a characteristic magnitude of the treated surface profile; and

a step of evaluating a level of inhomogeneous deformations in the first plate as a function of the characteristic quantity.

Thanks to the evaluation method of the invention, it is possible to evaluate the level of inhomogeneous deformations in an initial substrate and immediately after its bonding on a final substrate.

From the evaluation of a level of inhomogeneous deformations, it is possible to estimate the shifts that occurred between the buried surface and the exposed surface of the initial substrate. More particularly, the method of the invention makes it possible to estimate the level of misalignments that would be likely to occur if microcomponents were manufactured on the exposed surface of the initial substrate.

A simple and effective evaluation of the inhomogeneous deformations is thus possible before proceeding to the thinning of the initial substrate. Indeed, the evaluation method according to the invention does not require the presence of microcomponents on the exposed surface of the initial substrate or even the presence of microcomponents buried in the initial substrate so as to be optically observable through a relatively small thickness of the initial substrate remaining. The evaluation of a level of inhomogeneous deformations can therefore be performed very far upstream in the method of manufacturing a three-dimensional structure.

The evaluation method according to the invention is preferably carried out just after bonding by molecular adhesion of the initial substrate to the final substrate. In this way, it is avoided to carry out additional technological steps (thinning, making micro-components, etc.) which could be unnecessary and expensive in the case where excessive misalignments would subsequently be detected in the initial substrate.

When undesirable inhomogeneous deformations are detected in an initial substrate after bonding, it is then possible to separate the initial substrate from the final substrate and to attempt a new one. bonding by molecular adhesion. The evaluation method according to the invention therefore allows the reuse (that is to say the recycling) of an initial substrate, when the bonding has led to inhomogeneous deformations.

According to a first particular embodiment, the surface profile is determined by measurement points arranged along a diameter of the first plate. This case applies of course when the first plate has a substantially cylindrical shape.

It is thus possible to take measurements of measuring points of different diameters of the first plate in order to obtain data representative of inhomogeneous deformations on the whole of the first plate.

In this first mode, the characteristic quantity is preferably the second derivative of the surface profile.

In addition, the evaluation step of the evaluation method may comprise at least one of the following tests;

a first test to determine if the second derivative has at least one sign change; and

a second test to determine if the second derivative has at least one absolute value greater than a predetermined value.

Each of these two tests makes it possible to evaluate in a simple and effective way a level of inhomogeneous deformations in an initial substrate after bonding by molecular adhesion on a final substrate.

In one embodiment of the invention, only one of the two tests described above is performed.

In an alternative, both tests are performed to evaluate a level of inhomogeneous deformations in the first plate.

According to a second embodiment, the surface profile is determined by measuring points arranged along a circle whose center coincides with the center of said first plate.

In a particular implementation, the evaluation method comprises carrying out the following steps:

determining a plurality of surface profiles of the first plate,

for each surface profile of the plurality of surface profiles, performing a processing step to determine a characteristic quantity of the processed profile, in which, during the step the level of inhomogeneous deformations is determined according to the determined characteristic quantities.

In an alternative, a plurality of measurement point readings can be made, the readings being spaced from each other and made in the same direction. In this way, all measured measurement point readings are parallel to each other in a first direction. In particular, it is possible to envisage the case where the readings are uniformly spaced from each other and oriented in the same first direction.

Moreover, still in the context of this alternative, it is possible to carry out a plurality of additional surveys, in which the measurement points of each of these surveys follow the same second direction, this second direction being different from the first direction mentioned above. -above. For example, measurements of measurement points can be made according to a grid formed by lines parallel to the first and second directions. This grid may be uniform and the first and second directions may be chosen so as to be perpendicular.

On the other hand, the measurement points of each reading can be measured in a measurement step, the measurement step being determined according to a dimension of at least one pattern of the first plate.

In a particular embodiment, the measurement step may correspond substantially to half a dimension of a pattern of said first plate. In a particular case, a pattern has a rectangular shape on the exposed surface of the initial substrate, the measurement step substantially corresponding to half of one side of this pattern.

The choice of a suitable measurement step, and this according to a size of a pattern of the first plate, is advantageous in that it makes it possible to not take into account any minute variations in the level of the exposed surface of the first plate, these variations causing very localized sign changes of the second derivative of the corresponding surface profile.

In addition, the reading of a plurality of measurement points can be performed by acoustic microscopy.

The present invention also relates to a method for selecting at least one structure comprising a first glued plate by molecular adhesion to a second plate, the selection process comprising:

a step of evaluating inhomogeneous deformations in the first plate of each structure according to an evaluation method as described above;

a step of selecting one or more structures from the characteristic quantities determined for each evaluated structure.

Thus, when for example the first test and the second test are performed during the evaluation step, a structure is selected only when these two tests are negative,

The selection method according to the invention makes it possible to retain, among a batch of a plurality of multilayer structures, satisfactory structures, that is to say those which have an acceptable level of inhomogeneous deformations and to eliminate structures having a level inhomogeneous deformations unacceptable.

The present invention also relates to a device for evaluating inhomogeneous deformations in a first plate, the first plate being adhesively bonded to a second plate by molecular adhesion, the evaluation device comprising:

measuring means for raising a plurality of measurement points, each of the measuring points being locally representative of the level of the exposed surface of the first plate;

computing means for determining at least one surface profile of the first plate passing through a plurality of measurement points and for determining a characteristic magnitude thereof; and

evaluation means for evaluating a level of inhomogeneous deformations in the first plate as a function of the characteristic quantity.

It will be noted that the advantages and comments stated with reference to the various embodiments of the evaluation method and to the selection method according to the invention apply in a similar manner to the various embodiments of the evaluation device and to the selection device. of the invention.

In a particular embodiment, the characteristic quantity is the second derivative of the surface profile. In this embodiment, the evaluation means may be configured to perform at least one of the following tests:

The measuring means can be configured so that the measuring points of each reading are measured along a diameter of the first plate,

In an alternative, the measuring means are configured to perform a plurality of measurement point readings, the readings being spaced from each other and made in the same direction.

The measuring means can also be configured so that the measuring points of each reading are measured in a measurement step, the measurement step being determined according to a dimension of at least one pattern of the first plate.

In a particular embodiment, the measurement step corresponds substantially to half a dimension of a pattern of the first plate.

Moreover, the measuring means of the invention may comprise an acoustic microscope.

Brief description of the drawings

Other features and advantages of the invention will become apparent from the following description of particular embodiments of the invention, given by way of example, with reference to the appended drawings, in which;

- Figures 1A to 1E, are schematic views showing the realization of a three-dimensional structure according to the prior art; - Figure 2 is a half-sectional perspective of a composite structure comprising a first plate bonded to a second plate;

FIG. 3 represents, in the form of a flowchart, the main steps of an evaluation method and a selection method according to a particular embodiment of the invention; FIGS. 4A, 4B, 4C and 4D respectively represent a schematic view of a first example of bonding a first plate to a second plate, the curve of a surface profile corresponding to this first example, the curve of the corresponding second derivative according to a determined diameter and a curve representative of the misalignments present in the first plate according to a determined radius;

FIGS. 5A, 5B, 5C and 5D respectively represent a schematic view of a second example of bonding a first plate to a second plate, the curve of a surface profile corresponding to this second example, the curve of the corresponding second derivative according to a determined diameter and a curve representative of the misalignments present in the first plate according to a determined radius;

FIGS. 6A, 6B, 6C and 6D respectively represent a schematic view of a third example of bonding a first plate to a second plate, the curve of a surface profile corresponding to this third example, the curve of the corresponding second derivative according to a determined diameter and a curve representative of the misalignments present in the first plate according to a determined radius;

FIG. 7 schematically represents an example of acoustic microscopy technique for measuring a surface profile;

FIG. 8A represents a half-section perspective of a composite structure comprising a first plate glued to a second plate; and

FIG. 8B represents a view from above of the structure of FIG. 8A

Detailed description of an embodiment

The present invention provides a solution for evaluating a level of inhomogeneous deformations in a first plate corresponding to an initial substrate bonded by molecular adhesion to a second plate corresponding to a final substrate. The case of the composite structure 125 as described in FIG. 2 is considered here. In this example, the composite structure 125 is formed by adhesively bonding a first plate 110, comprising microcomponents 111 on its bonding surface 114a, on a surface. second plate 120, so as to bury the microcomponents 111 at the bonding interface.

In the examples described here, the plates used to form the composite structure 125 have a diameter of 300 mm. It will be understood, however, that the invention applies to other dimensions and / or shapes of the plates.

With reference to FIG. 3, the main steps of the evaluation method (steps E1 to E3) are described according to one embodiment of the invention, this method making it possible to evaluate a level of inhomogeneous deformations in the composite structure. illustrated in Figure 2.

The Applicant has found, surprisingly, that it is possible to obtain information on the inhomogeneous deformations in the first plate 110 by studying the reliefs of the exposed surface 114b of the first plate 110.

Firstly, a step E1 of reading a plurality of measurement points is carried out, each measurement point being locally representative of the level of the exposed surface of the plate 110. Each survey carried out thus corresponds to a surface profile. of the first plate 110 in a given direction or curve and over a predetermined length.

The term "surface profile" is here understood to mean a profile representative of the relief (or level) of a surface along a determined direction or curve and over a determined length.

In the present case, each measurement point survey is locally representative of the level or relief of the exposed surface 114b of the first plate 110 with respect to a Z axis perpendicular to said exposed surface 114b.

The measurement point (s) is (are) typically made using mechanical or optical profilometry equipment (for example, interferometry). The readings will preferably be made using an acoustic microscopy technique. technique to advantageously reduce the measurement time of each record.

FIG. 7 schematically represents an example of an acoustic microscopy technique for measuring a profile of the exposed surface 114b of the first plate 110.

A probe 147 comprises a source 148 configured to emit an incident acoustic wave 140 in the direction of the composite structure 125. This acoustic wave propagates in the first plate 110 and then in the second plate 120, thus meeting three successive interfaces, namely the surface exposed 114b of the first plate 110 and the buried surface 114a of the first plate 110 and finally the rear face of the second plate 120. The acoustic wave 140 is reflected partially at each interface, giving rise each time to an echo which is sent back to the acoustic sensor 150 of the probe 147. Thus, the acoustic sensor 150 detects the reception of the echoes 142, 144 and 146 coming respectively from the reflection of the acoustic wave 142 on the rear face of the second plate 120, on the buried surface 114a and on the exposed surface 114b.

The distance between the probe 147 and the exposed surface 114b of the first plate 110 can then be determined from the time required for the echo 146 to reach the probe 147. Alternatively, the thickness of the first plate can be measured. a given position from the time offset between the reception of the echo 146 and the reception of the echo 144.

By moving the probe towards the composite structure 125, it is thus possible to take a measurement point survey corresponding to a profile of the exposed surface 114b of the first plate 110.

In the example described here, the measuring points are measured along a diameter D of the first plate 110. In a second example, the measurement points are measured along a circle (or an arc of circle) whose center coincides with the center of the plate 110 and whose radius is smaller than the radius of the plate.

However, it is possible to perform more than one measurement point reading, in any directions and / or distances. In addition, the direction and length of each survey can be chosen according to the constraints and needs of a given situation. (the technology considered, the level of reliability required, the equipment used, etc.). To continue the second example above, the readings can consist of a series of concentric circles whose centers coincide with the center of the plate 110 and whose radii are chosen so as to distribute the measurement points on the surface of the plate.

A step E2 of determining at least one surface profile of the plate 110 is then carried out, each profile passing through a plurality of measurement points of a reading made in step E1. A surface profile can thus correspond to all or part of the measuring points of a reading made in step E1. When several measurement readings have been made in step E1, a measurement profile is determined for each of them in step E2.

Once step E2 has been carried out, a treatment is carried out (step E3) for each surface profile obtained in step E2 in order to deduce therefrom a corresponding characteristic quantity. As explained in more detail below, this characteristic magnitude may be of different nature.

More specifically, the Applicant has determined that different treatments make it possible, from the surface profile determined in step E2, to obtain information representative of the level of inhomogeneous deformations present in the plate 110.

According to a first embodiment of the invention, during step E3, a second derivative is calculated from the measuring points obtained along the diameter D of the plate 110. The second derivative thus calculated provides information on the variations the slope of the surface profile along this diameter.

The Applicant has observed that, surprisingly, the second derivative of a surface profile provides information representative of the level of inhomogeneous deformations existing in the first plate 110 bonded by molecular adhesion to the second plate 120. According to a second embodiment of the invention, during the processing step E3, the dispersion of a surface profile determined in step E2 is determined, this surface profile corresponding to a circle-shaped survey. The Applicant has observed that, surprisingly, the dispersion (as measured by a standard deviation or the difference between the maximum and minimum value) of a surface profile corresponding to a survey in circle shape also provides information representative of the level of inhomogeneous deformations existing in the first plate adhered by molecular adhesion to the second plate 120.

An evaluation (step E4) of the inhomogeneous deformation levels of the first plate 110 is then carried out as a function of the characteristic quantity obtained in step E3. This evaluation makes it possible to estimate the misalignments which are likely to occur in the continuation of the manufacture of a heterostructure such as that described with reference to FIG. 1E.

With reference to the case of FIG. 1, for example, the invention makes it possible to estimate the level of the misalignments Δ11, Δ22, Δ33 and Δ44 that would be obtained by manufacturing the microcomponents 12 with a photolithography mask similar to that used for the manufacture of microcomponents 11.

For this purpose, the Applicant has found that there are different ways of exploiting the characteristic magnitude (i.e. the second derivative or the dispersion) of a surface profile to evaluate a level of inhomogeneous deformations in a plate.

Examples of exploitation of a second derivative of a surface profile allowing evaluation of a level of inhomogeneous deformations (first embodiment) are firstly described in relation with the examples of FIGS. 4A, 5A and 6A.

In all the examples considered here, the first plates 210, 310 and 410 have a slightly concave shape before their respective bonding on the second plates 220, 320 and 420. For the sake of clarity, the curvature of the first plates 210, 310 and 410 has was intentionally exaggerated in Figures 4A, 5A and 6A, respectively. In addition, in each of these examples, microcomponents (211, 311 and 411) are present on the surface (214a, 314a and 414a) of the first plate (210, 310 and 410).

In the first and second cases illustrated respectively in FIGS. 4A and 5A, the first plates 210 and 310 are placed on a support S (commonly called "chuck") and have a concave shape on this support. The curvature of the first plates 210 and 310 is directed opposite the support S so that the surfaces 214a and 314a including the microcomponents 211 and 311 are exposed. The second plates 220 and 320 are then placed on the surfaces 214a and 314a of the first plates 210 and 310 respectively, in order to proceed to bonding.

A contact force is applied to a region (or point) of the second plates 220 and 320 with the aid of an application tool (denoted 231 and 331, respectively). The contact force generated by the application tools 231 and 331 makes it possible in each case to initiate a bonding wave between the first and second plates. The first plates 210 and 310 are thus bonded by molecular adhesion to the second plates 220 and 320, respectively. In each case, the microcomponents are then buried at the bonding interface between the first and second plates.

In the first case (FIG. 4A), the contact force is applied at the peripheral edge of the second plate 220. On the other hand, in the second case (FIG. 5A), the contact force is applied to the center of the second plate 320.

The third case illustrated in FIG. 6A differs from the first and second cases in that the second plate 420 is positioned directly on the support S. The first plate 410 is then placed on the second plate 420, the face 414a of the first plate 410 comprising the microcomponents 411 being directed towards the second plate 420.

A contact force is then applied to the center of the first plate 410 by means of an application tool 431 to initiate the propagation of a bonding wave between the first plate 410 and the second plate 420.

In the three cases considered here, a composite structure is thus obtained comprising a first plate bonded by molecular adhesion to a second plate (as illustrated in FIG. 2). Note that in the examples described here, a contact force of 3.7N is applied for 6 seconds to initiate the bonding wave.

Inherent deformations are then likely to appear in the first plates 210, 310 and 410 as a result of their respective assembly with the second plates 220, 320 and 420.

Note also that in the three cases shown in figures

4A, 5A and 6A, the second plates 220, 320 and 420 are planar. However, the second plate may have in each case a non-planar shape, such as, for example, a similar concave shape or different from the first plate with which it is assembled.

Once the molecular bonding has been performed in each of the three cases considered above, the inhomogeneous deformation levels are evaluated in the first plate of each of the composite structures obtained.

First, a measurement of a plurality of measuring points is made on the exposed surface of the first plate of each of the composite structures (step E1).

In the cases described here, the measuring points are measured along a determined diameter D of the first plates 210, 310 and 410 by acoustic microscopy.

Each measurement point corresponds to a height Z of the exposed surface of the first plate relative to a predetermined reference height, each height being associated with a given position on the surface of the first plate. In the examples described here, the position of each measuring point is defined by a position X along the diameter D considered.

Alternatively, each measurement point may also be associated with a pair of coordinates (X, Y) corresponding to a two-dimensional position on the exposed surface of the first plate.

Moreover, in each of the examples described here, the step E1 of carrying out the measurement point readings further comprises the preparation of a curve representative of the surface profile thus obtained.

On the other hand, the following steps of the process of the invention can be carried out without the elaboration of such curves being necessary.

Figures 4B, 5B and 6B show the surface profiles 232, 332 and 432 that have been observed respectively for the three cases considered.

The study of surface profiles 232, 332 and 432 showed height variations of the order of 25 μπη in the example of FIG. 4A, of 12 μηη in the example of FIG. 4B and of 30 μηι in FIG. the example of Figure 4C. Next, step E2 is used to calculate the second derivatives from the surface profiles obtained in step E1.

As indicated above, the elaboration of the curves 232, 332 and 432 is not necessary, each second derivative can be calculated directly from the measurement points of the corresponding reading.

In each of the examples considered here, the calculation step E2 further comprises the development of a curve representative of the second derivative thus obtained. The curves 234, 334 and 434 respectively correspond to the second derivatives of the three surface profiles 232, 332 and 432.

It is however possible to evaluate a level of inhomogeneous deformations without producing a graphical representation of the second derivatives. It is possible to limit the calculation and exploitation of the values of each second derivative.

The second derivatives calculated in step E2 make it possible to evaluate a level of inhomogeneous deformations in the first plate for the three cases considered (evaluation step E3).

The Applicant has indeed found that the second derivative of a surface profile is representative of the surface deformations of the first plate and that by studying these deformations on the surface, it was possible to evaluate a level of inhomogeneous deformations in the first one. plate.

For example, it has been found that the presence of at least one change of direction of curvature in the same surface profile demonstrates the existence of significant inhomogeneous deformations in the first plate.

In a particular embodiment of the invention, a first test is thus performed consisting of determining whether a second derivative of a surface profile has at least one sign change. If this first test is positive, it is deduced that significant inhomogeneous deformations exist in the first plate considered.

The ^{effectiveness} of this first test has been verified experimentally by evaluating the level of inhomogeneous deformations in the three composite structures tested, in accordance with acoustic microscopy technique described above in connection with Figure 7, More precisely, in the first case (FIG. 4A), the majority of misalignments on the surface 214b of the first plate 210 are observed to be less than 100 nm, or even less than 50 nm, in the center of the plate. Only about 15% of surface 214b has misalignments greater than 150 nm. These significant misalignments are distributed at the peripheral edge of the plate, in particular in the region close to the point of contact of the application tool 231.

In the second case (FIG. 5A), misalignments greater than 150 nm have been observed over approximately 50% of the exposed surface 314b of the first plate 310. These major misalignments are distributed for the most part in the center and at the peripheral edges of the surface. 314b. The remaining 50% of the surface 314b mainly have misalignments of between 50 and 150 nm.

In the third case (FIG. 6A), it has been observed that about 75% of the surface 14b of the first plate 10 has misalignments of less than 100 nm. Larger misalignments, generally between 100 and 150 nm, are present in the center of the first plate 410.

FIGS. 4D, 5D and 6D represent, in the form of curves, the respective misalignments measured according to a determined radius of each of the first plates 210, 310 and 410.

In these three cases, the misalignments present on the first plate were measured from a conventional measurement method, as described in relation with FIGS. 1A to 1E: the first plate is thinned after gluing, then the misalignments present are measured. between microcomponents buried at the bonding interface between the two plates and microcomponents manufactured on the exposed surface of the first thinned plate.

The abscissa axis in FIGS. 4D, 5D and 6D represents the distance (in mm) from the center of the first plate.

Finally, the samples tested according to the second case (Figure 5A) are those with the largest inhomogeneous deformation levels. This is confirmed by the fact that only the second derivative 334 of the surface profile 332 has at least one sign change. More specifically, it has been found that the derivative second 334 has two sign changes, which reveals large surface slope variations of the first plate 310.

Conversely, for the samples tested according to the first and third cases, the second derivatives do not show a sign change, which indicates that these cases lead to lower levels of inhomogeneous deformations than the second case.

It will be noted that the number of sign changes detected in the second derivative of the same surface survey can also provide information on the level of inhomogeneous deformations existing within the first plate.

Moreover, the Applicant has observed that a surface profile exhibiting steep slope variations, and thus high second derivative values, could also correspond to significant inhomogeneous deformations within the first plate.

Thus, in a variant of this first embodiment of the invention, the evaluation of a level of inhomogeneous deformations in the first plate is performed as a function of the values of the second derivative obtained in step E2.

For example, during the evaluation step E3, a second test is performed consisting of determining whether a second derivative of a surface profile has at least one value greater than a predetermined threshold value. When this second test is positive, it means that significant inhomogeneous deformations are present in the first plate.

It should be noted that this predetermined value can be chosen in particular according to the constraints and needs of the situation considered (technology considered, level of reliability required, equipment used, etc.).

The tests described above are however provided by way of example so that other methods of using the second derivative of a surface profile can be used depending on the situation. For example, it is possible to take into account the number of times a second derivative of a surface profile is exceeded with respect to a predetermined value, etc.

One can also consider evaluating a level of inhomogeneous deformations by combining different tests relating to the second derivative of surface profiles, for example, by combining the first and second tests described above.

An implementation example is described in which the characteristic quantity obtained in the processing step E3 corresponds to a dispersion of a surface profile (second embodiment), this profile determined in the step E2 corresponding to a measurement of measuring points in the form of a circle.

More specifically, a composite structure 525 having a structure similar to the structure 125 described above (FIG. 8A) is considered here. The structure 525 thus comprises a first plate 510 adhered by molecular adhesion to a second plate 520. The first plate 510 also comprises in this example microcomponents 511 on its bonding surface 514a, these microcomponents being thus buried at the interface of bonding.

In the measuring step E1, the measurement points are arranged along at least one circle whose center coincides with the center CT of the first plate 510 (FIGS. 8B). In the example described here, a survey is carried out along three concentric circles denoted C1, C2 and C3, these circles respectively having a radius R1, R2 and R3 (these radii being less than that of the plate 510).

It will be understood, however, that the number of circles along which the measurement points are measured can be arbitrary. This number can be chosen in particular according to the accuracy and / or reliability of the evaluation that is then desired in step E4. The number of circles and their respective radius are preferably chosen so as to distribute the measurement points uniformly over the surface of the plate, so as to obtain data representative of the inhomogeneous deformations on the whole of the plate 510. In a variant, it is possible to record measurement points along at least one circular arc whose center of curvature coincides with the center CT. It is also possible to record measuring points along at least one spiral centered on CT.

At least one surface profile of the first plate 510 is then determined in step E2, each of these profiles passing through a plurality of measurement points of a corresponding reading made in the previous step El. In this example, three surface profiles PI, P2 and P3 are thus determined in step E2, these corresponding to all the measuring points respectively taken along the circles C1, C2 and C3.

The dispersion of each surface profile obtained in step E3 (step E4) is then determined. This dispersion calculation can be implemented in different ways.

According to a first variant, the minimum value Vmin (i) and the maximum value Vmax (i) of each of the surface profiles Pi (i = 1, 2, 3) are determined. These values Vmin (i) and Vmax (i) respectively correspond to the measurement points of the profile Pi representative locally of the lowest and the highest level of the exposed surface of the plate 510. Then, for each profile Pi, the difference is determined. Ai such that Ai = Vmax (i) - Vmin (i).

From the values Ai, a third test is carried out to evaluate the level of the inhomogeneous deformations present in the first plate 510. A predetermined limit value Amax is for example fixed. The third test then consists in determining if Ai> Amax (for i = 1, 2 or 3). If so, the level of inhomogeneous deformations present in the plate 510 is considered important. Otherwise, the level of deformation is considered low. The acceptability criterion Amax associated with each value of the index i may be variable, in particular increasing as the diameter of the circles C1 to C3 increases. For example for circles of diameter 65 and 145 mm, the values of Amax may be equal to approximately 5 and 15 microns respectively.

A variant of the third test consists first of all in making the sum of the differences Ai, then in dividing this result by what is commonly called the "warp" of the structure, defined by the difference between the overall maximum height of the surface where the surveys are operated and its overall minimum height. For example, for a uniformly curved structure in a paraboloid of revolution, the "warp" is equal to the "bovv" of the structure. The second step of this variant of the third test consists in determining whether the coefficient between the sum of the Ai and the "warp" is less than a predetermined value, for example of the order of 0.7. If yes, the level of inhomogeneous deformations is considered low. In the opposite case, the level of deformations is considered important. According to a second variant, the standard deviation ai is determined for each surface profile Pi. A fourth test is then performed which consists in determining whether a is greater than or equal to a predetermined maximum standard deviation (for i = 1, 2 or 3 ). If so, the plate 510 is considered to have a significant level of inhomogeneous deformations. Otherwise, the level of deformation is considered low.

The variants described above are only non-limiting examples of implementation of the invention and those skilled in the art will understand that other alternatives are conceivable for determining the dispersion of a surface profile without departing from the framework of the invention.

The processing step E3 and the evaluation step E4 of the method of the invention may be implemented, for example, by a computer, a computer or any other equipment capable of calculating a second derivative or a dispersion from measuring points of a surface profile and performing a test relating to a second derivative or a dispersion, for example, one of the tests described above.

The present invention further relates to a method of selecting (steps E1 to E5) composite structures comprising a first plate adhered by molecular adhesion to a second plate.

The main steps of the selection method according to a particular embodiment are illustrated in FIG.

A level of inhomogeneous deformations is first evaluated in a first plate by successively performing steps E1, E2, E3 and E4 of the evaluation method of the invention on the composite structure.

Then, during a selection step E5, one or more composite structures identified in step E4 are selected as having a low level of inhomogeneous deformations.

For example, it is possible to perform the first and second tests or the third and fourth tests as described above. The composite structure or structures are then selected when the result of the tests carried out is negative.

It is also possible to perform only one of these tests. In this particular case, the composite structure or structures are selected when the test performed is negative. The selection method according to the invention is however not limited to the two test examples described above. Indeed, other selection criteria relating to the second derivative of a surface profile may be used, individually or in combination,

The measurement point readings in step E1 of the evaluation method may further be made according to different plots on the exposed surface of the first plate.

In particular, it is possible to make "star" readings, that is to say according to several diameters of the first plate. This technique makes it possible to obtain a good representation of inhomogeneous deformation levels in a first plate with a limited number of readings made.

In a particular example, a plurality of measurement point readings is carried out in step E1, the readings being made along first parallel lines spaced apart from one another. It is also possible to perform additional surveys along second parallel lines spaced apart and which may be, for example, perpendicular to the first lines. Surveys are thus made according to a grid, this grid being able to be on all or part of the exposed surface of the first plate considered.

Furthermore, when for example the first test described above is carried out, only the sign changes of the second derivative on the macroscopic scale are considered. Indeed, it is possible that in practice the exposed surface of the first plate has minute level variations which result in very localized sign changes of the second derivative of the corresponding surface profile (s). s). These minute variations may have for origin, for example, very slight variations in thickness of the first plate. This type of variation does not give usable information on the level of inhomogeneous deformations in the first plate of a composite structure.

In order to avoid taking negligible surface defects into account, it is possible to take readings in step E1 so that the measurement points are measured according to a measurement step. This measurement step can be chosen according to the situation considered. It will preferably be chosen according to a dimension of a pattern of the first plate.

"Pattern" here means a geometric arrangement arranged, or intended to be arranged, on the exposed surface of a first plate, this geometric arrangement being repeated several times on the surface of this plate. A pattern may for example correspond to a cell of one or more microcomponents arranged at several locations on the exposed surface of the first plate considered.

For example, the measurement step may correspond substantially to half a dimension of a pattern of the first plate.

It will also be noted that the number of readings made during step E1 of the evaluation method may depend on various parameters, such as, for example, the constraints of the manufacturing process in terms of cost, of the time allocated to the tests for each lot of plates, level of reliability required, etc.

Moreover, a given level of inhomogeneous deformations may be acceptable for a given microcomponent technology (because it is not very restrictive in terms of the positioning of the photolithography masks), and unacceptable for another technology. As a result, the following parameters may be chosen depending on the situation:

- the choice of the number of readings to be made,

- the layout of each survey (length, direction),

- the number of measurement points per survey,

- the measurement step used,

the method (s) of exploitation of the second derivatives obtained in step E2, and

- the criterion (s) of selection of the composite structures. It will be noted here that many mechanisms can cause misalignments (or "overlay") in a first plate bonded by molecular adhesion to a second plate.

When a first plate is adhesively bonded to a second plate by molecular adhesion, the inhomogeneous deformations generated in the first plate can result in particular from the combination of the deformations originally present in the first and second plates. before gluing. The method according to the invention can thus make it possible to obtain relevant information on the deformations of the two plates before their assembly by molecular adhesion (degree of concavity, flatness defects, etc.).

The present invention can also reveal, for example, the presence of foreign bodies as a particle between the support S and the plate directly in contact therewith. These elements can indeed be at the origin of inhomogeneous deformations in the first plate and thus of misalignments.

The invention can also highlight problems of calibration of the gluing machine (especially at the application of the contact force by the application tool).

Moreover, as indicated above, once the composite structure is formed by molecular adhesion, the first plate generally undergoes thinning. However, after thinning, the evaluation of inhomogeneous deformations using the process of the invention is no longer representative. It is therefore preferable to carry out step E1 of the process of the invention before thinning of the first plate.

Claims

A method of evaluating inhomogeneous deformations in a first plate (110), said first plate being adhesively bonded to a second plate (120), said evaluation method comprising:

a step (E1) of reading a plurality of measuring points, each of the measuring points being locally representative of the level of the exposed surface of the first plate;

a step (E2) of determining at least one surface profile of the first plate passing through a plurality of measurement points;

a step (E3) of processing the surface profile of the first plate to determine a characteristic magnitude of the treated surface profile; and

a step (E4) of evaluating a level of inhomogeneous deformations in said first plate as a function of said characteristic quantity.

The evaluation method according to claim 1, wherein the surface profile is determined by measurement points disposed along a diameter of said first plate.

3. Measuring method according to claim 2 wherein the characteristic quantity is the second derivative of the surface profile.

The measuring method according to claim 3, wherein the evaluating step comprises at least one of the following tests:

a first test for determining whether said second derivative has at least one sign change; and

a second test to determine if said second derivative has at least one absolute value greater than a predetermined value.

The evaluation method according to claim 1, wherein the surface profile is determined by measuring points arranged along a circle (R1-R3) whose center coincides with the center of said first plate.

6. Evaluation method according to claim 5 wherein the characteristic quantity is the dispersion of the surface profile,

7. Evaluation method according to any one of claims 1 to 6, wherein the following steps are carried out:

determining a plurality of surface profiles (C1-C3) of the first plate,

for each surface profile of the plurality of surface profiles, carrying out a processing step to determine a characteristic quantity of the processed profile, in which, during the evaluation step, the level of inhomogeneous deformations is determined according to said determined characteristic quantities.

8. Evaluation method according to any one of claims 1 to 7, wherein the measurement points of each record are measured in a measurement step, said measurement step being determined according to a dimension of at least a pattern of said first plate.

The evaluation method according to claim 8, wherein said measurement step corresponds substantially to half a size of a pattern of said first plate.

10. Evaluation method according to any one of claims 1 to 8, wherein the reading of a plurality of measuring points is performed by acoustic microscopy.

A method of selecting at least one structure comprising a first molecular adhesively bonded plate (110) on a second plate (120), said selection method comprising:

a step of evaluating inhomogeneous deformations in the first plate of each structure according to the method evaluation system as defined in any one of claims 1 to 10; and

a step (E5) for selecting one or more structures from the characteristic quantities determined for each evaluated structure,

12. Device for evaluating inhomogeneous deformations in a first plate; said first plate being adhesively bonded to a second plate, said evaluation device comprising:

measuring means for raising a plurality of measuring points, each of said measuring points being locally representative of the level of the exposed surface of the first plate;

evaluation means for evaluating a level of inhomogeneous deformations in said first plate as a function of said characteristic quantity.

13. Evaluation device according to claim 12, wherein the characteristic quantity is the second derivative of the surface profile.

The evaluation device according to claim 13, wherein said evaluating means is configured to perform at least one of the following tests:

15. Evaluation device according to one of claims 12 to 14, wherein the measurement points of each survey are measured along a diameter of said first plate.

16. Evaluation device according to any one of claims 12 to 15, wherein said measuring means are configured to perform a plurality of measurement point readings, said readings being spaced from each other and made in the same direction .

17. Evaluation device according to any one of claims 12 to 16, wherein said measuring means are configured so that the measurement points of each reading are measured in a measurement step, said measurement step being determined according to a dimension of at least one pattern of said first plate.

The evaluation device according to claim 17, wherein said measurement step substantially corresponds to half a size of a pattern of said first plate.

19. Evaluation device according to any one of claims 12 to 18, wherein said measuring means comprise an acoustic microscope.