FR2996052A1 - METHOD OF BONDING BY MOLECULAR ADHESION - Google Patents

Abstract

The invention relates to a molecular adhesion method comprising positioning a first plate (10) on the surface of a support (2), said surface comprising grooves (4), the application in the grooves (4). ) a first pressure lower than a second pressure as viewed by the exposed face of the first plate (10), and bringing a second plate (16) into contact with the exposed face of the first plate (10) followed by the initiation of the propagation of a bonding wave between the two plates, while maintaining the first and second pressures.

Description

BACKGROUND OF THE INVENTION The present invention relates to the manufacture of multilayer structures formed by assembling on a first plate (substrate or "support" plate) at least one second plate (or substrate) by molecular bonding. Such heterostructures are used in particular in microelectronics or optoelectronics. The invention relates more particularly to the molecular adhesion bonding of semiconductor plates in the context of the manufacture of multilayer structures, for example of the silicon on sapphire type AL203 (SOS for "Silicon-On-Sapphire") or GaN on sapphire (ganos).

Such multilayer structures (also called "multilayer semiconductor wafers") are typically produced according to 3D-integration technology, which implements the transfer on a first plate, called the final substrate, of at least one formed layer. from a second plate, this layer corresponding to the portion of the second plate in which elements have been formed, for example a plurality of microcomponents, the first plate may be blank or have other corresponding elements. In known manner, the molecular adhesion bonding on a first plate (support plate) of a second plate can generate deformations of different types in the multilayer structure obtained. Such bonding may for example generate inhomogeneous deformations in the first and second plates making it difficult to align components or other patterns formed in the second plate vis-à-vis the underlying support plate. The formation of these misalignments (or "overlay" in English) resulting from inhomogeneous deformations is described, for example, in patent application FR 2 965 398. Molecular adhesion bonding may also generate curvature deformation (s) ( or "bow" in English) on the assembled plates forming the multilayer structure. These curvature deformations can in particular occur during a heat treatment due to the differences in thermal properties (differences in thermal expansion coefficient (CTE) etc.) of the different plates assembled in the multilayer structure. For example, the application FR 2 954 585 describes the behavior of a heterostructure during a bonding reinforcement annealing carried out at a temperature of about 160 ° C., the heterostructure being formed by bonding a first plate corresponding to a SOI (Silicon on Insulator) structure on a sapphire substrate. The difference in CTE between the silicon, the main component of the SOI structure, and the sapphire leads, during a heat treatment, to a deformation in curvature of the assembly such that important detachment stresses are applied at the edges of the structure. the heterostructure. Due to these constraints, the transfer at the plate edge is insufficient, which can lead to the appearance of a crown (non-transferred area of the first plate on the support substrate) too wide and irregular, which can in particular cause peeling in edge of plates. The application FR 1 153 349 also describes the case of a transfer of a layer of a first substrate (called "donor substrate") to a second substrate (called "acceptor substrate"), this second substrate having previously undergone various technological treatments (cavity formation, etc.). This layer transfer requires bonding by molecular adhesion of the first and second substrates, the annealing of the multilayer structure thus obtained and the mechano-chemical thinning of this structure. The deformation in curvature generated in the final multilayer structure is imposed mainly by the initial deformation of the second substrate (ie the acceptor substrate), this initial deformation resulting from the technological treatment steps (etching, deposition etc.) to which this second substrate was subjected. before gluing. However, this phenomenon of curvature deformations imposed on multilayer structures has major disadvantages. The mechanical stresses (or stress) generated can in particular lead to the takeoff (partial or total) or to the breakage of the multilayer structure during a technological treatment (heat treatment, etc.) subsequent to the molecular adhesion bonding of the first and second plates. The post-bonding technological treatments (temperature treatment, thinning, etc.) carried out on the multilayer structure must thus be carefully parameterized so as to avoid excessive mechanical stresses, which substantially increases the complexity, the difficulty of control and therefore the cost of these treatments.

When the support plate comprises, for example cavities, manufacturers generally require that the multilayer structure after bonding (the first plate bonded to the support plate being virgin of any component) meets certain criteria of deformation in curvature after thinning, so as to be able to perform subsequent technological treatments in good conditions. No satisfactory solution today makes it possible to control, at least to a certain extent, the direction and the amplitude of the curvature deformation imposed on the plates of a multilayer structure assembled by molecular bonding. OBJECT AND SUMMARY OF THE INVENTION To this end, the present invention relates to a molecular adhesion bonding method comprising: - positioning a first plate on the surface of a support, the surface comprising grooves; - Applying in the grooves a first pressure lower than a second pressure seen by the exposed face of the first plate; and contacting a second plate with the exposed face of the first plate followed by the initiation of the propagation of a bonding wave between the two plates, while maintaining the first and second pressures. The pressure difference AP thus applied induces local mechanical stresses in the first plate which deforms locally, in particular at its bonding surface with the second plate. During the propagation of the bonding wave, the second plate conforms to the curvature imposed by the first plate and is in turn subjected to the local mechanical stresses induced by the pressure difference P. The application of these local constraints to the bonding interface advantageously makes it possible to control to a certain extent the deformation in curvature (called "bow" in the rest of this document) that the multilayer structure exhibits after bonding. As explained in more detail below, the bow of the multilayer structure is systematically concave type vis-à-vis the reference plane formed by the surface of the support.

The final bow of the final structure is therefore less dependent on the clean curvatures (i.e. before gluing) of the first and second plates. A greater bow homogeneity can thus be obtained on a plurality of multilayer structures of the same batch for example. Controlling the direction of the curvature of the multilayer structure (and to a certain extent the amplitude of this curvature) makes it possible to meet the ever-increasing requirements of manufacturers and to avoid faulty collages or breaks, especially when subsequent technological steps (heat treatments ...) are performed on the multilayer structure. In a first variant, the grooves are arranged in the form of an orthogonal grid on the entire surface of the support.

In a second variant, the grooves are arranged in the form of concentric annular grooves centered on the center of the support. In a particular embodiment, the grooves are distributed uniformly over the entire surface of the support. Such a distribution makes it possible to apply homogeneous mechanical stresses to the bonding interface between the first and second plates. In another embodiment, the grooves are closer together in an area of the surface of the support with respect to the grooves on the remainder of the support surface. In this way, there is obtained a curvature of the multilayer structure more accentuated locally at the areas of the support where the grooves are closer together. This zone where the grooves are closer together may correspond for example to a ring at the periphery of the support in order to accentuate the curvature of the multilayer structure at the edge of the plate. Preferably, the pressure difference between the first and second pressures is greater than or equal to 3 mbar. In a particular embodiment, this pressure difference is between 3 and 10 mbar. In a particular embodiment, the support warms the first plate at least during the steps of contacting and initiation of propagation of the bonding wave. This heating can also be performed during the application step of the pressure difference. The bonding method according to the invention may further comprise: annealing of the multilayer structure resulting from molecular bonding of the first and second plates; and thinning the first plate or plate.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate an embodiment having no limiting character. In the figures: - Figures 1A to 1F are sectional views schematically showing each step (S10-S30) of a bonding method according to a particular embodiment of the invention; FIG. 2 represents, in the form of a flowchart, the main steps of the embodiment illustrated in FIGS. 1A-1F; FIGS. 3A and 3B show, in sectional view, two examples of plates having a curvature of the respective concave and convex type; and FIG. 4 is a graph representing in the form of a curve the evolution of the curvature deformation of a multilayer structure as a function of the pressure difference AP applied according to one particular embodiment of the invention. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION The present invention relates to the manufacture of multilayer structures by molecular bonding of a first plate (or carrier plate) with a second plate. The invention applies in particular to the formation of multilayer structures of the SOS or GaNOS type, for example. At least one of the plates forming the multilayer structure may comprise at least one microcomponent that has been produced before bonding. 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 patterns, making contact or interconnections, or nnicrochannels or cavities. In order to better control the curvature deformation of a multilayer structure formed by molecular bonding, the present invention proposes to apply mechanical stresses locally to the bonding interface.

By studying the mechanism of formation of the deformations generated in multilayer structures as described above, the applicant has indeed observed that the application of certain mechanical forces to the bonding interface during the bonding operation by molecular adhesion allows to some extent control the curvature deformation of the resulting multilayer structure. The control of this deformation in curvature advantageously makes it possible to correct the general shape of the plates forming the multilayer structure and to anticipate the shape of the structure even before its assembly by molecular adhesion. Also, the applicant has developed a molecular adhesion bonding method for applying such mechanical stresses so as to control the curvature deformation of multilayer structures. As explained in more detail below, this method makes particular use of a support (or "chuck" in English) comprising grooves on its contact surface (ie the surface of the support intended to be in contact with the first plate of the multilayer structure to be produced).

A particular embodiment of the invention is now described with reference to FIGS. 1A to 1F and 2. FIG. 1A represents a support 2 (or "chuck") comprising grooves 4 distributed here uniformly over the set of the contact surface 6 of the support 2.

In this example, the grooves 4 are in the form of an orthogonal grid consisting of two series 4A and 4B of parallel grooves uniformly distributed over the entire surface 6, these two series of grooves being perpendicular to one another. to the other. As indicated in more detail later, variations with regard to the distribution of the grooves and / or the dimensions and shapes of these grooves can however be envisaged within the scope of the invention. In the example considered here, the grooves 4 each have a width of 5 mm and a depth of 1 mm. However, it will be understood that other groove dimensions can be envisaged within the scope of the invention.

The grooves 4 are here equipped with suction means 8 which will be described in more detail later. Figure 1B shows a first plate 10 (or support plate) with a diameter of 150 mm which is positioned on the surface 6 of the support 2 (S10). Other diameters (200 mm, 300 mm etc.) or plate shapes are naturally conceivable.

In this example, the plate 10 is of the SOI (Silicon on Insulator) type and comprises a silicon layer on a support also made of silicon, a buried oxide layer (for example made of SiO 2) being placed between the layer and the support in silicon. However, it will be understood that the first plate 10 may consist of a multilayer structure of another type or a monolayer structure. Furthermore, the support plate 10 has here a curvature Ki, i.e. an initial curvature before bonding. It is recalled here that before bonding, each plate has a clean curvature that can be concave as for the plate 100 of Figure 3A or convex as for the plate 110 of Figure 3B. This curvature determines the bending deformation of the plates which is designated by the English term "bow" in semiconductor technology. A bow may for example be of paraboloidal shape (in particular of spherical shape).

As illustrated in FIGS. 3A and 3B, the bow Az of a plate or wafer corresponds to the distance (arrow) between a reference plane P (typically perfectly flat) on which the plate and the plate itself rest freely. At the scale of the diameters of plates usually used in the field of semiconductors, namely between a few tens of millimeters and 300 millimeters, the bow is measured in micrometers (μm) while the curvature is generally measured in m-1 or km-1 because the curvature of the plates used in the field of semiconductors is very small and, consequently, the corresponding radius of curvature is very important. In the example of Figure 1B, the support plate 10 has a bow K1 of concave shape with respect to the surface 6 of the support 2 (K1 <0). Once the first plate 10 positioned on the support 2, is generated (S15) in the grooves 4 a first pressure P1 with the suction means 8 (Figure 1C). This pressure P1 is thus applied locally to the surface 10a of the support plate 10 at each groove 4. The suction effect is here obtained by suction of the air 12 present in the grooves between the plate 10 and the support 2 this air 12 being discharged through orifices of the suction system 8 arranged at the bottom of the grooves 4 of the support 2. Alternatively, it may be possible to use any other suitable means for locally applying the pressure Pl at the grooves.

According to the invention, the first applied pressure Pi must be such that P1 is less than P2, where P2 is the pressure seen by the exposed face 10b of the first plate 10. In the present case, P2 corresponds to the pressure of the chamber where the bonding process of the invention is carried out. The pressure difference AP = P2-P1 imposed locally (S15) on the first plate 10 at each groove 4 induces local mechanical stresses (or stresses) 14 to the first plate 10. Under the effect of these constraints, the first plate 10 then deforms locally especially at its exposed surface 10b, as shown schematically in Figure 1C. A magnification (magnifying effect) in FIG. 1C represents one of the zones of the first plate 10 at a groove 4 as well as the mechanical stresses 14 locally induced. It will be understood here that the mechanical stresses 14 physically translate into a force pressing the plate 10 locally against the support 2, which leads to slight deformations of the plate 10 mainly in the grooves area (slight bending of the plate 10 towards the bottom grooves). These slight deformations generate a curvature deformation on the whole of the plate 10, in particular at its exposed surface 10b, this deformation being a function of the physical arrangement of the grooves (width, orientation, distribution of the grooves on the surface 6 , amount of grooves etc.). In this example, the difference AP applied locally to the plate 10 is preferably greater than or equal to APmin = 3 mbar, and even more preferably between 3 and 10 mbar inclusive. By applying a differential pressure AP greater than or equal to APmin, it is ensured that the plate 10 is firmly fixed against the support 2 (clamping effect). Note that several procedures can be envisaged to achieve the desired AP. According to one particular embodiment, a pressure P1 is first applied by suction of the air under the plate 10, then the pressure P2 is reduced in the chamber until the desired AP is obtained. Once the desired pressure difference AP is applied locally to the first plate (515), the pressures P1 and P2 are kept constant and the molecular adhesion bonding of a second plate 16 to the first plate is carried out (520). 10 deformed (Figure 1D). The same pressure difference AP as that imposed in the previous step S15 is thus maintained during the bonding step S20 in the regions of the plate 10 in correspondence with the grooves 4.

Molecular adhesion bonding is a well-known technique in itself. As a reminder, the principle of molecular bonding is based on the direct contact of two surfaces, that is to say without the use of a specific material (glue, wax, solder, etc.). Such an operation requires that the surfaces to be bonded are sufficiently smooth, free of particles or contamination, and that they are sufficiently close together to allow initiation of contact, typically at a distance of less than a few nanometers. In this case, the attractive forces between the two surfaces are high enough to cause the propagation of a bonding wave which results in molecular adhesion (bonding induced by all the attractive forces (Van Der Waals forces)). electronic interaction between atoms or molecules of the two surfaces to be glued). During this step S20, the second plate 16 is then brought into contact with the surface 10b of the first plate 10, and then the propagation of a bonding wave is initiated at the interface between the plates 10 and 16. The setting in contact and the initiation of the wave propagation are performed while maintaining the same AP as that instituted locally in step S15. The technique of initiating a bonding wave is well known per se and therefore will not be further developed here. The second plate 16 is in this sapphire example and also has a diameter of 150 mm. The second plate could, however, consist of a monolayer structure of another type or a multilayer structure. As shown in FIG. 1D, the second plate 16 had a clean bow K2 before convex-shaped gluing (K2> 0). A bow K2 for example concave or approximately flat would have been possible. Once the propagation of the bonding wave initiated, the second plate 16 conforms to the curvature imposed by the first plate 10 during the progression of the bonding wave (Figure 1D). Once the bonding has been completed, a multilayer structure 20 (or stacked structure) of the SOS type comprising the first plate 10 and the second plate 16 is obtained, this structure having the desired curvature deformation KF 30. The amplitude of the KF bow obtained is directly related to the local deformations imposed on the plates 10 and 16 during the bonding process of the invention. According to the invention, whatever the type of clean bow (concave, flat or convex) of the first and second plates 10 and 16 before bonding, at the end of the bonding operation S20, a multilayer structure 20 is obtained. presenting a KF bow of concave shape.

In addition, the larger the pressure difference AP, the larger the KF bow of the resulting multilayer structure 20 will be. FIG. 4 represents the evolution of the bow as a function of the value of the AP imposed during the steps S15 and S20 in the embodiment envisaged here.

As indicated above, the pressure difference applied in steps S15 and S20 is chosen so that AP APmin. The value of APmin varies, however, depending in particular on the materials and the thickness of the plates and 16 to be glued. In the present case, the plates 10 and 16 are made of silicon and each have a thickness of 775 μm, and APrnin is set at about 3 mbar. In this particular example, the multilayer structure 20 has after gluing a concave bow between 38 pm and 85 pm for a pressure difference AP ranging respectively between 3 mbar and 900 mbar (see Figure 4). In order to enhance the adhesion strength between the two plates 10 and 16, it is possible to subject (S25) thereafter the multilayer structure 20 to a moderate heat treatment (less than 500 ° C for example). In this example, stabilization annealing of the bonding interface at a temperature between 140 and 150 ° C is achieved. This heat treatment makes it possible to increase the bonding energy between the plates 10 and 16 and makes possible the subsequent thinning of one of them under good conditions. The bonding energy may, for example, reach 400 m 3 / m 2 after such annealing. As shown in FIG. 1F, the first plate 10 is then thinned (S30) according to a conventional method in order to be reduced to the plate 11. In this example, an upper layer of the first SOI plate 10 is removed by chemical mechanical polishing. (CMP), the buried insulating layer of the plate 10 advantageously serving as a chemical etch stop layer for delineating the thickness of the remaining plate 11. The final thickness of the plate 11 may for example be between 4 and 10 μm. Alternatively, the thinning of the plate 10 can be achieved by other methods such as by chemical etching or by fracture along a weakening plane previously formed in the plate 10, for example by ion implantation (eg implantation of H or He impurities and fracture according to Smart CutC technology)). In the example of Figure 1F, it is the first plate that is thinned. However, it is possible to envisage the alternative according to which it is the second plate 35 which is thinned in step 530.

Thus, a three-dimensional structure 20 of SOS type formed of the second plate (now serving as a support substrate) and a layer 11 corresponding to the remaining portion of the first plate 10. Microcomponents (not shown) can then be formed in the transferred layer 11. These microcomponents are formed according to conventional methods, typically by photolithography by means of at least one mask defining the pattern formation zones corresponding to all or part of the microcomponents to be produced. A selective irradiation tool of the stepper type is generally used to irradiate the zones where the patterns to be made. Ultimately, the application of local mechanical stresses in the first plate, and more particularly to the bonding interface with the second plate, advantageously makes it possible to control to a certain extent the deformation in curvature (or bow) that the multilayer structure presents. after collage. As indicated above, the bow of the multilayer structure is always of the concave type (like the plate 100 in FIG. 3A) with respect to the reference plane formed by the contact surface 6 of the support 2. The final bow KF is no longer as dependent on the curvature K1 and K2 of the first and second plates. A greater homogeneity of KF bow between a plurality of multilayer structures of the same batch can thus be achieved. This facilitates in particular the realization of subsequent technological steps on the multilayer structures thus produced. Controlling the direction of the curvature of the multilayer structure (and to a certain extent the amplitude of this curvature) makes it possible to respect the ever-increasing requirements of manufacturers and to avoid faulty collages or possible fractures, especially when subsequent technological steps (heat treatments, etc.) are performed on the multilayer structure. In a variant, the support 2 (or chuck) is configured so as to heat the support layer 10 during the step S20 of contacting and initiation of the bonding wave (and possibly also during the step S15 application of .8P above). Warming with chuck 2 enhances the effect of concave bow formation on the final multilayer structure over the same process without heating. The chuck is preferably heated to a temperature between room temperature (eg 20 ° C) and 200 ° C.

It will be understood that it is possible to play on the spatial configuration of the grooves on the surface of the chuck and on the difference AP applied to control to a certain extent the KF value of the final bow. In particular, it is possible to adjust at least one of these parameters in order to tend towards the desired bow level: the width of the grooves; the quantity (or density) of the grooves formed on the surface of the support; - the orientation of the grooves; the distribution of the grooves on the whole of the contact surface of the support ... (alternatively, one or more grooves may be arranged in spirals or the grooves may take the form of a spider web). As indicated above, the orientation of the grooves may correspond to an orthogonal (or possibly non-orthogonal) grid (or checkerboard). Alternatively, the grooves may be arranged in the form of concentric annular grooves. In addition, the grooves may advantageously be arranged uniformly over the entire surface of the support in order to apply the most homogeneous mechanical stresses possible to the bonding interface. For example, it is possible to arrange the grooves in the form of a uniform orthogonal grid (or not) or, alternatively, in the form of uniform concentric annular grooves, so that the grooves have the same spacing with one another over the entire length of the groove. surface of the support.

However, variations may be envisaged in which the grooves are non-uniformly disposed on the surface of the support. The grooves may for example be configured to be closer to each other in a particular area of the surface of the support with respect to the grooves on the rest of the support surface. This configuration makes it possible to obtain a curvature of the multilayer structure that is more accentuated locally at the regions of the support where the grooves are closer together. This zone where the grooves are closer together may correspond for example to a ring at the periphery of the support in order to accentuate the curvature of the multilayer structure at the edge of the plate. Other areas of support may be considered according to the needs of each situation.

Moreover, any grooves or other recesses of the same order can act as grooves in the sense of the invention insofar as their dimensions allow the first plate to locally deform by application of the pressure difference to, P described below. above. The dimension chosen for the grooves can thus also be a function of the mechanical properties of the first plate (and possibly also of the second plate). The grooves of the invention may for example be arranged in the support (chuck) by removing material on the surface thereof by machining or the like. Alternatively, the grooves may be formed by adding material to the surface of the chuck or forming on the surface of the reliefs delimiting the contours of the different grooves.

Claims (9)

REVENDICATIONS1. A method of molecular adhesion comprising: - positioning (S10) a first plate (10) on the surface (6) of a support (2), said surface comprising grooves (4); - the application in the grooves of a first pressure (P1) less than a second pressure (P2) seen by the exposed face (10b) of the first plate (10); and contacting (S20) a second plate (16) with the exposed face (10b) of the first plate (10) followed by initiation of the propagation of a bonding wave between the two plates, while maintaining said first and second pressures. 2. Bonding method according to claim 1, wherein the grooves (4) are arranged in the form of an orthogonal grid on the entire surface (6) of the support (2). 3. Bonding method according to claim 1, wherein the grooves (4) are arranged in the form of concentric annular grooves centered on the center of the support (2). 4. Bonding method according to any one of claims 1 to 3, wherein the grooves (4) are distributed uniformly over the entire surface (6) of the support (2). The method of bonding according to any one of claims 1 to 3, wherein the grooves are closer to each other in an area of the surface of the support with respect to the grooves on the rest of the surface of the support . 6. Bonding method according to any one of claims 1 to 5, wherein the pressure difference between said first and second pressures (P1, P2) is greater than or equal to 3 mbar. 35 The method of bonding according to claim 6, wherein said pressure difference is between 3 and 10 mbar. 30 8. Bonding method according to any one of claims 1 to 7, wherein the carrier (2) heats the first plate (10) at least during the steps of contacting and initiation of the propagation of the wave lift-off. 5 9. A method of bonding according to any one of claims 1 to 8 further comprising: - the annealing (S25) of the multilayer structure (20) resulting from the bonding by molecular adhesion of the first and second plates; and thinning (S30) the first plate (10) or the second plate (16).