FR3143841A1 - Process for preparing a stack for gluing - Google Patents

Abstract

Title: Method for preparing a stack for bonding The invention relates to a method for preparing a stack (1) comprising providing a stack comprising a substrate (10) surmounted by a plurality of structures (1000). Each structure comprises a pad (100) comprising a top (101) and at least one side (103), a first layer (200) surmounting the substrate, the first layer covering part of the side of the pad, a second layer (300) covering at least the top of the stud. The structure comprises a recess portion (500) covering an upper part (104) of the side of the pad and formed by at least one of the first layer and the second layer, and a covering portion (600), covering a part lower (105) of the sidewall and extending from the withdrawal portion. The withdrawal portion is then removed leaving the covering portion in place to form a protrusion. Figure for abstract: Fig.2J

Description

Process for preparing a stack for gluing

The present invention relates to the preparation of a substrate, in particular with a view to bonding it with another substrate. It is particularly involved in the manufacturing of optoelectronic and microelectronic devices. For example, it finds a particularly advantageous application in the field of assembling a substrate containing copper-based elements with a substrate covered with a copper film.

STATE OF THE ART

The assembly of two substrates is a very common operation in microelectronics and optoelectronics. Such an assembly may in particular have the objective of transferring elements, for example photoelements such as pixels, from one substrate to another.

A common technique for assembling two substrates illustrated in Figures 1A to 1C is based on direct bonding between protrusions 200' based on a dielectric, for example SiO ₂ , located on the surface of a first of the two substrates, and the second substrate 2'. Other elements of the first substrate 1', typically copper pillars 100', are set back from the SiO ₂ protrusions 200'. During the assembly step of the two substrates, a heating step causes expansion of the copper pillars. The expansion of the SiO ₂ protrusions occurring in parallel is less significant than that of the copper pillars. Therefore, by correctly sizing the shrinkage of the pillars in relation to the SiO ₂ protrusions, the pillars are at the end of the level heating step with the SiO ₂ protrusions and in contact with the surface of the second substrate. .

If this process is functional in certain contexts, it is however not applicable to all substrates, and in particular not when the latter include materials whose melting temperature is lower than the temperature at which the material of the recessed elements can present volume expansion. For example, the annealing temperature of copper is 350°C while certain materials used which may require such assemblies have melting temperatures of around 250°C. It is therefore impossible to implement this solution when these materials are involved.

The heating step can also cause problems with distortions and strong mechanical stresses within the substrates when the latter contain materials with thermal expansion coefficients that are too different from each other. This is particularly the case when the second substrate comprises a glass-based support covered with a thin copper film.

Another disadvantage of this method lies in the precision required in the dimensioning of the shrinkage of the copper pillars in relation to the SiO ₂ protrusions. Indeed, a variation in the value of this shrinkage, for example due to manufacturing hazards, could cause, at the time of expansion of the copper pillars, untimely detachments within the substrates.

An objective of the present invention is therefore to propose a process for preparing a substrate with a view to assembly with another substrate, this process not requiring subjecting the substrate to high temperatures.

SUMMARY

• fournir un empilement comprenant un substrat surmonté d’une pluralité de structures séparées par des tranchées, chaque structure comprenant :
  • un plot comprenant un sommet et au moins un flanc,
  • une première couche à base d’un premier matériau et surmontant le substrat, la première couche recouvrant une partie au moins du flanc du plot,
  • une deuxième couche à base d’un deuxième matériau et recouvrant au moins le sommet du plot,
  • une portion de retrait, recouvrant, de préférence en étant au contact direct de, une partie supérieure du flanc du plot, la partie supérieure du flanc s’étendant depuis le sommet du plot, la portion de retrait étant formée par au moins l’une parmi la première couche et la deuxième couche,
  • une portion de recouvrement, recouvrant, de préférence en étant au contact direct de, une partie inférieure du flanc du plot et s’étendant depuis la portion de retrait, la portion de recouvrement étant formée par la première couche,
• retirer la deuxième couche,
• retirer la portion de retrait en laissant en place la portion de recouvrement de sorte à mettre à découvert la partie supérieure du flanc du plot, la partie supérieure du flanc du plot formant une protrusion au-delà de la portion de recouvrement.

To achieve this objective, according to one embodiment, a method of preparing a stack is provided comprising the following steps:

• provide a stack comprising a substrate surmounted by a plurality of structures separated by trenches, each structure comprising:
  • a stud comprising a vertex and at least one flank,
  • a first layer based on a first material and surmounting the substrate, the first layer covering at least part of the side of the pad,
  • a second layer based on a second material and covering at least the top of the pad,
  • a withdrawal portion, covering, preferably being in direct contact with, an upper part of the flank of the stud, the upper part of the flank extending from the top of the stud, the withdrawal portion being formed by at least one among the first layer and the second layer,
  • a covering portion, covering, preferably being in direct contact with, a lower part of the side of the stud and extending from the withdrawal portion, the covering portion being formed by the first layer,
• remove the second layer,
• remove the withdrawal portion while leaving the covering portion in place so as to expose the upper part of the flank of the stud, the upper part of the flank of the stud forming a protrusion beyond the covering portion.

The protrusion thus formed is suitable for bonding to another surface, for example the upper face of a transfer support.

• un plot comprenant un sommet et au moins un flanc,
• une première couche à base d’un premier matériau et surmontant le substrat, la première couche recouvrant une partie au moins du flanc du plot,
• une portion de recouvrement formée par la première couche, recouvrant, de préférence en étant au contact direct de, une partie inférieure du flanc du plot et laissant à découvert une partie supérieure du flanc du plot, la partie supérieure du plot formant une protrusion par rapport à la première couche.

A second aspect of the invention relates to a stack comprising a substrate surmounted by a plurality of structures separated by trenches, each structure comprising:

• a stud comprising a vertex and at least one flank,
• a first layer based on a first material and surmounting the substrate, the first layer covering at least part of the side of the pad,
• a covering portion formed by the first layer, covering, preferably by being in direct contact with, a lower part of the side of the stud and leaving exposed an upper part of the flank of the stud, the upper part of the stud forming a protrusion relative to to the first layer.

• Fournir un empilement selon le deuxième aspect de l’invention,
• Fournir un empilement de réception présentant une face supérieure,
• Réaliser un collage direct du sommet de l’au moins un plot de l’empilement sur la face supérieure de l’empilement de réception.

A third aspect of the invention relates to a method of gluing or transferring at least one pad included in a stack according to the second aspect of the invention onto a receiving stack:

• Provide a stack according to the second aspect of the invention,
• Provide a receiving stack having an upper face,
• Directly bond the top of at least one stud of the stack to the upper face of the receiving stack.

The protrusions formed during the preparation process indeed allow, during the bonding process, effective bonding. In particular, it is not necessary to carry out a heating step which risks causing distortions and/or strong mechanical stresses within the stacks, as was the case in the prior art. It is possibly possible to carry out consolidation annealing after direct bonding to improve adhesion between the tops of the pads and the upper face of the receiving stack, but such annealing is carried out at temperatures lower than the temperatures for which mechanical deformations may occur.

Furthermore, this bonding process does not require dimensional control greater than the control currently available in the industry.

BRIEF DESCRIPTION OF THE FIGURES

The aims, objects, as well as the characteristics and advantages of the invention will emerge better from the detailed description of an embodiment of the latter which is illustrated by the following accompanying drawings in which:

Figures 1A to 1C represent a method of assembling two substrates according to the prior art. There illustrates a stack according to the prior art comprising a substrate surmounted by pillars set back relative to protrusions based on a dielectric. The protrusions cover the pillars laterally.

There illustrates the reversal of the stack according to the prior art and its placement opposite a receiving stack.

There illustrates the assembly of the two stacks and their bonding by heating. There illustrates in particular the expansion of the pillars.

Figures 2A to 2J illustrate a first embodiment of the method according to the invention. There represents the provision of a primary stack comprising a substrate and a first primary layer overlying the substrate.

There illustrates the formation of a first etching mask on the first primary layer.

There represents the formation of cavities in the first primary layer.

There illustrates the formation of a third primary layer in the cavities and on the first primary layer.

There represents the thinning of the third primary layer so as to form pads extending into the cavities.

There represents the formation of a second primary layer on the pads and the first primary layer.

There represents the formation of a second etching mask on the second primary layer.

There illustrates the formation through the second etch mask of trenches extending into the second primary layer and the first primary layer. A plurality of second layers are thus formed from the second primary layer and a plurality of first layers from the first primary layer.

There illustrates the removal of the second engraving mask.

There illustrates the removal of the second layers and a portion of the first layers extending, prior to the removal, from the second layers.

Figures 3A to 3J illustrate a second embodiment of the method according to the invention. There represents the provision of a stack comprising a substrate, a first primary layer overlying the substrate and a first primary sublayer overlying the first primary layer.

There represents the formation of a first etching mask on the first primary sublayer.

There represents the formation of secondary cavities in the first primary layer and in the first primary sublayer through the first etching mask.

There represents the formation of a third primary layer in the secondary cavities and on the first primary sublayer.

There illustrates the thinning of the third primary layer so as to form pads extending into the secondary cavities and level with the first primary sub-layer.

There illustrates the formation of a second primary sub-layer on the pads and on the first primary sub-layer. The first primary sublayer and the second primary sublayer form a second primary layer.

There represents the formation of a second etching mask on the second primary layer.

There illustrates the formation through the second etch mask of trenches extending into the second primary layer and the first primary layer. A plurality of second layers are thus formed from the second primary layer and a plurality of first layers from the first primary layer.

There illustrates the removal of the second engraving mask.

There illustrates the removal of the second layers, thus forming a protrusion.

Figures 4A to 4H illustrate a third embodiment of the method according to the invention. There represents the provision of a stack comprising a substrate and a first primary layer overlying the substrate. The first primary layer includes cavities.

There illustrates the formation of a third primary layer in the cavities and on the first primary layer.

There illustrates the thinning of the third primary layer so as to single out the latter into individual studs projecting relative to the first primary layer.

There represents the formation of a second primary layer on the pads and on the first primary layer.

There represents the formation of a second etching mask on the second primary layer.

There illustrates the formation through the second etch mask of trenches extending into the second primary layer and the first primary layer. A plurality of second layers are thus formed from the second primary layer and a plurality of first layers from the first primary layer.

There illustrates the removal of the second engraving mask.

There illustrates the removal of the second layers, thus forming a protrusion.

Figures 5A and 5B are top views of the steps shown in Figures 2I, 3I and 4G. There illustrates an embodiment in which the pads are cylindrical with a square base.

There illustrates the case of circular cylindrical pads.

The drawings are given as examples and are not limiting to the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of practical applications. In particular, the dimensions are not representative of reality.

DETAILED DESCRIPTION

Before beginning a detailed review of the embodiments of the invention, the following are set out as optional characteristics which may possibly be used in combination or alternatively:

According to one example, the substrate has a lower face extending mainly along a transverse plane defined by a first direction and a second direction, the protrusion having a height E_protectionin a third direction perpendicular to said transverse plane, such that E_protection ≤ 0.5*E_flank , preferably E_protection ≤ 0.3*E_flankand preferably E_protection ≤ 0.1*E_flank, E_flankbeing the height of the side taken in the direction Z. E_protectionis thus measured, along Z, between one end of the covering portion and the top of the stud.

According to one example, E _prot ≥ 5 nm, preferably E _prot ≥ 10 nm. Preferably, E _prot ≤ 50 nm, E _prot ≤ 30 nm.

According to one example, the removal of the second layer and the removal of the removal portion are carried out during a single etching step.

According to one embodiment, the shrinkage portion is formed only by the first layer.

According to one example, prior to the removal step, the first layer extends to the top of the pad. In particular, the second layer may not cover the sidewall.

According to one example, the removal of the removal portion is carried out by time control, as well as preferably by the etching selectivity of the different materials

According to one embodiment, the shrinkage portion is formed at least in part by the second layer. Thus, the second layer covers part of the sidewall.

According to one example, the shrinkage portion is formed only by the second layer. This allows very precise control of the height of the protrusion obtained with the removal of the shrinkage layer. This allows us to use only very common steps that are perfectly mastered in the industry. This also limits the number of steps required to remove the withdrawal portion. This translates into time and economic savings.

According to one example, removing the removal portion includes etching the second layer selectively to the first layer. The withdrawal portion is removed, for example, by etching the second layer with stopping on the first layer.

• Former la première couche,
• Former le plot,
• Former la deuxième couche,

et la formation de la deuxième couche comprend les sous-étapes suivantes :

• Après la formation de la première couche et préalablement à la formation du plot, former une première sous-couche de la deuxième couche, la première sous-couche surmontant la première couche,
• Après la formation du plot, former une deuxième sous-couche de la deuxième couche, la deuxième sous-couche surmontant au moins le plot.

According to a particular embodiment of the invention, the supply of the stack comprises the following steps:

• Form the first layer,
• Form the block,
• Form the second layer,

and the formation of the second layer includes the following substeps:

• After the formation of the first layer and prior to the formation of the pad, form a first sub-layer of the second layer, the first sub-layer surmounting the first layer,
• After the formation of the stud, form a second sub-layer of the second layer, the second sub-layer surmounting at least the stud.

• Former la première couche,
• Former le plot,
• Former la deuxième couche,

et la deuxième couche est déposée sur le plot et la première couche après la formation du plot.According to a particular embodiment of the invention, the supply of the stack comprises the following steps:

• Form the first layer,
• Form the block,
• Form the second layer,

and the second layer is deposited on the pad and the first layer after the formation of the pad.

According to one example, the pads are formed of a third material, the third material being based on one of copper, aluminum, tungsten and titanium .

According to one example, the first material is based on one of: SiO2, SiN and Si.

According to one example, the second material is based on one of SiN, SiO2, and Si .

It is specified that, in the context of the present invention, the terms "on", "surmounts", "covers", "underlying", "vis-à-vis" and their equivalents do not necessarily mean "at the contact of”. For example, the deposition, transfer, gluing, assembly or application of a first layer on a second layer does not necessarily mean that the two layers are in direct contact with each other, but means that the first layer at least partially covers the second layer by being either directly in contact with it or by being separated from it by at least one other layer or at least one other element.

A layer can also be composed of several sub-layers of the same material or of different materials.

By a substrate, a layer, a device, “based” on a material M, is meant a substrate, a layer, a device comprising this material M only or this material M and possibly other materials, for example elements alloy, impurities or doping elements. Thus a material based on a III-N material can include a III-N material with added dopants. Likewise, a GaN-based layer typically comprises GaN and AlGaN or InGaN alloys.

The term "III-V material" refers to a semiconductor composed of one or more elements from column III and column V of the Mendeleev periodic table. The elements in column III include boron, gallium, aluminum and indium. Column V contains, for example, nitrogen, arsenic, antimony and phosphorus.

By “selective etching with respect to” or “etching exhibiting selectivity with respect to” is meant an etching configured to remove a material A or a layer A with respect to a material B or d. 'a layer B, and having an etching speed of material A greater than the etching speed of material B. The selectivity is the ratio between the etching speed of material A to the etching speed of material B. The selectivity between A and B is denoted SA:B.

The roughness of a surface is a parameter characterizing the state of this surface. It is most often associated in tribology with the characteristic depth of the striations crisscrossing the surface. The roughness of a surface is noted Ra and is typically expressed in µm (1 µm = 10 ^-6 m) or nm (1 nm = 10 ^-9 m).

A reference frame, preferably orthonormal, comprising the axes X, Y, Z is represented in Figures 1A, 2A, 3A, 4A, 5A and 5B. This reference is applicable by extension to other figures.

In this patent application, we will preferentially speak of thickness for a layer and height for a structure or a device. The height is taken perpendicular to the transverse plane XY. The thickness is taken in a direction normal to the main extension plane of the layer. Thus, a layer typically has a thickness along Z, when it extends mainly along the transverse plane XY, and a projecting element, for example an insulation trench, has a height along Z. The relative terms "on », “under”, “underlying” refer preferentially to positions taken in the Z direction.

The terms “substantially”, “approximately”, “of the order of” mean “within 10%, preferably within 5%”.

A first step of the method according to the invention consists of providing a stack 1 comprising a substrate 10 and a plurality of structures 1000 surmounting the substrate 10 and separated by the trenches 400.

The substrate 10 has a lower face 12 extending mainly in a transverse plane XY defined by a first direction The photoemitting elements can for example be active nanowires or microwires forming LEDs or micro-LEDs. These can, for example, be standard two-dimensional LEDs (2D LEDS). The photoemitting elements typically have an elongated shape in a third direction Z perpendicular to the transverse plane XY.

The structures 1000 have a cylindrical shape, preferably that of a straight cylinder whose generating lines extend in the third direction Z. The structures 1000 typically have a rectangular section, preferably square, in a plane parallel to the transverse plane XY , as shown in Figures 5A and 5B.

The structures 1000 are separated from each other by trenches 400. These trenches are typically rectilinear. The trenches 400 may for example comprise a first series of trenches 400a and a second series of trenches 400b, the trenches 400b of the second series being perpendicular to the trenches 400a of the first series. The trenches 400a of the first series extend for example in the first direction X and those of the second series in the second direction Y, as shown in Figures 5A and 5B.

Each of the structures 1000 surmounting the substrate 10 comprises a pad 100 having a vertex 101 and at least one flank 103 having a height E _flank in the third direction Z. E _flank is advantageously greater than 500 nm, typically substantially equal to 1 µm.

The top 101 of the stud 100 advantageously extends in a so-called upper plane 501, preferably parallel to the transverse plane XY.

The pad 100 typically has the shape of a cylinder, preferably a straight cylinder whose generating lines defining one or more lateral faces of the pad 100 extend preferably in the third direction Z. The pad 100 can for example have a shape polygonal in the transverse plane XY. The pad 100 then has several side faces. In the particular case of a pad 100 having a rectangular or even square shape in the transverse plane XY, the pad 100 has four lateral faces 103a, 103b, 103c, 103d, as shown in the . The pad 100 can also have a circular cylindrical shape, as illustrated in . It then has only one side face. In the case of a cylindrical stud, the at least one side 103 of the stud 100 corresponds to one or the side face of the stud 100.

The pad 100 is preferably based on a metallic material, for example copper, aluminum, tungsten or even titanium.

Each pad 100 advantageously covers at least one photo-emitting element included in the emitting layer 15. The photo-emitting elements are thus located to the right of the pads 100 in projection along the transverse plane XY. They can be in direct contact with the pads 100, possibly via a layer called contact layer 16 which can for example be based on aluminum, titanium or titanium nitride.

Each of the structures further comprises a first layer 200 having an upper face 201 preferably extending in a plane parallel to the transverse plane XY. According to one example, the first layer 200 directly surmounts the substrate 10, that is to say that its lower face 202 is in contact with the substrate 10. It has a thickness E₂₀₀in the third direction Z. The first layer 200 covers at least part of the side 103 of the pad 100. It is thus in contact with the pad 100 over a height E_recovery non-zero less than or equal to the height of the sidewall E_flank.

Each of the structures 1000 further comprises a second layer 300 covering at least the top 101 of the pad 100. It can also cover at least part of the first layer 200. The second layer 300 is preferably in direct contact with the top 101 of the pad 100 and possibly the first layer 200. It has an upper face 301 preferably extending in a plane parallel to the transverse plane XY.

• Fournir un empilement primaire 1a comprenant, comme illustré à la :
  • Le substrat 10,
  • Une première couche primaire 200a à base du premier matériau et recouvrant le substrat 10.
• Former dans la première couche primaire 200a des cavités 250 traversant entièrement la première couche primaire 200a selon la troisième direction Z. Cette étape est illustrée par les figures 2B et 2C.
• Remplir les cavités 250 par le troisième matériau, formant ainsi les plots 100 (figures 2E, 4C).
• Former une deuxième couche primaire 300a à base du deuxième matériau et surmontant les plots 100 et les premières couches 200 (figures 2F, 3A, 3F, 4D).
• Former les tranchées 400 traversant entièrement la deuxième couche primaire 300a et la première couche primaire 200a selon la troisième direction Z. La formation des tranchées 400 permet de singulariser et former les structures 1000, comme illustré en figures 2H, 3J, 4F. Elles séparent notamment les premières couches 200 formées dans la première couche primaire 200a, et les deuxièmes couches 300 formées dans la deuxième couche primaire 300a, qui feront chacune partie d’une structure 1000.

The stack 1 provided during the process according to the invention can for example be obtained according to the steps below:

• Provide a primary stack 1a comprising, as illustrated in :
  • The substrate 10,
  • A first primary layer 200a based on the first material and covering the substrate 10.
• Form cavities 250 in the first primary layer 200a completely passing through the first primary layer 200a in the third direction Z. This step is illustrated by Figures 2B and 2C.
• Fill the cavities 250 with the third material, thus forming the pads 100 (Figures 2E, 4C).
• Form a second primary layer 300a based on the second material and surmounting the pads 100 and the first layers 200 (Figures 2F, 3A, 3F, 4D).
• Form the trenches 400 completely crossing the second primary layer 300a and the first primary layer 200a in the third direction Z. The formation of the trenches 400 makes it possible to single out and form the structures 1000, as illustrated in Figures 2H, 3J, 4F. They separate in particular the first layers 200 formed in the first primary layer 200a, and the second layers 300 formed in the second primary layer 300a, which will each be part of a structure 1000.

It is understood, however, that stack 1 can be obtained according to any other embodiment.

Following the supply of stack 1, a step of removing a withdrawal portion 500 is implemented at each structure 1000.

The withdrawal portion 500 is formed by at least one of the first layer 200 and the second layer 300. It covers an upper part 104 of the side 103 of the pad 100. In other words, it is adjacent, in a plane parallel to the plane XY, at the side 103 of the stud 100, and at any point of the upper part 104 of the side 103. The withdrawal portion 500 is preferably in direct contact with the upper part 104 of the side 103 of the stud 100. In the particular case of a pad 100 having several sides, the upper part 104 advantageously extending into each of the sides 103 of the pad 100.

The upper part 104 of the sidewall 103 extends from the top 101 of the stud 100. More precisely, the upper part 104 extends from the edge(s) of the stud 100 delimiting its top 101 and its sidewall 103. It presents according to the third direction Z a height E ₁₀₄ . The withdrawal portion 500 extends in the third direction Z over a distance less than the height of the sidewall 103. We thus have E ₁₀₄ <E _sidewall .

The withdrawal portion 500 can thus extend, in the third direction Z, between the upper plane 501 in which the top 101 of the pads 100 extends, and a lower plane 502 extending, in the third direction Z, between the transverse plane XY and the upper plane 501.

During the step of removing the removal portion 500, a covering portion 600 is left in place.

The covering portion 600 is formed by the first layer 200. It covers a lower part 105 of the side 103 of the pad 100. In other words, it is adjacent, in a plane parallel to the plane XY, to the side 103 of the pad 100, and this at any point of the lower part 105 of the sidewall 103. The covering portion 600 is preferably in direct contact with the lower part 105 of the sidewall 103 of the stud 100.

The covering portion 600 extends from the withdrawal portion 500, that is to say that the upper part 104 and the lower part 105 of the side 103 of the pad 100 are in contact.

The lower part 105 of the sidewall 103 has a height E ₁₀₅ in the third direction Z. According to one example, the withdrawal portion 500 and the covering portion 600 together cover the side 103 of the stud 100 over the entire height. We then have E ₁₀₄ +E ₁₀₅ = E _flank .

The lower part 105 of the sidewall 103 is, when removing the withdrawal portion 500, left covered by the covering portion 600.

Once the withdrawal portion 500 has been removed, the upper part 104 of the sidewall 103 forms a protrusion beyond the covering portion 600. The stud 100 thus projects in the third direction Z with respect to at least one remaining part of the first layer 200 corresponding to the covering portion 600.

The protrusion formed has a height E _prot in the third direction. Advantageously, E _prot is greater than or equal to 5 nm.

Different embodiments of the method according to the invention will now be described in more detail.

First example of implementation of the method according to the invention

A first embodiment of the method according to the invention will now be described with reference to Figures 2A to 2J.

A first step consists of providing a primary stack 1a comprising the substrate 10 and a first primary layer 200a surmounting the substrate 10 ( ). A first etching mask 50 is then deposited on the upper face 201a of the first primary layer 200a ( ) and certain parts of the first primary layer 200a are removed through openings 55 in the first etching mask 50, then, preferably, the latter is removed ( ). This withdrawal makes it possible to form cavities 250 in the first primary layer 200a. Preferably, the shrinkage in the first primary layer 200a takes place over its entire thickness in the third direction Z. In other words, preferably, the cavities 250 extend up to the upper face 11 of the substrate 10. We thus obtain a assembly comprising the substrate 10 surmounted by the first primary layer 200a comprising the cavities.

The cavities 250 are then filled with the third material. It is for example possible to deposit a third primary layer 100a of third material extending in the cavities 250, directly above the cavities 250 in the third direction Z and above the first primary layer 200a ( ). A part of the third primary layer 100a can then be removed, for example by chemical mechanical polishing (CMP), so as to make it level in the third direction Z with the first primary layer 200a ( ). The remaining portions of the third primary layer 100a, separated by the first primary layer 200a, constitute the pads 100. This way of proceeding, by deposition then polishing, makes it possible to reduce or even avoid any possible protrusion or withdrawal of the pads 100 relative to each other. to the first primary layer 200a.

As illustrated in , a second primary layer 300a is then deposited on the upper face 201a of the first primary layer 200a and the top 101 of the pads 100. The second primary layer 300a has a thickness E _300a in the third direction Z. Advantageously, E _300a is less than or equal to 200 nm and/or greater than or equal to 20 nm, preferably substantially equal to 60 nm.

A second etching mask 60 is then formed on the second primary layer 300a ( ). The second etching mask 60 has openings 65 located directly above the first primary layer 200a.

Following the deposition of the second etching mask 60, trenches 400 are formed through the openings 65 in the second primary layer 300a, the first primary layer 200a, and possibly a portion of the substrate 10 ( ). Preferably, the second etching mask 60 is then removed. The trenches 400 separate the structures 1000 described above. Preferably, the trenches pass through the entire thickness in the third direction Z of the second primary layer 300a and the first primary layer 200a. Advantageously, at least some of the trenches 400 extend into the substrate 10. This can make it possible, depending on the targeted applications, to single out different zones of the substrate 10, for example to electrically isolate them from each other.

The formation of the trenches 400 makes it possible to divide the first primary layer 200a into a plurality of first layers 200 and the second primary layer 300a into a plurality of second layers 300. We thus obtain the stack 1 comprising the substrate 10 surmounted by the structures 1000 , each structure 1000 comprising a pad, a first layer 200 and a second layer 300.

In this embodiment, in each structure 1000, the first layer 200 and the pad 100 are substantially level in the third direction Z. The second layer 300 does not cover the side 103 of the pad 100. Thus, as illustrated in the , the shrinkage portion 500 is only formed by part of the first layer 200. The upper part 104 of the side 103 of the pad 100 is only covered by the first layer 200. The lower part 105 of the side 103 is advantageously covered only by the first layer 200.

Advantageously, in this embodiment, when removing the removal portion 500, a portion of the second layer 300 is also removed. It is understood that the removal of the second layer 300 is understood as the removal of the second layers 300 of each structure 1000. This remark extends to the mention of all other elements common to all structures 1000.

The removal of the removal portion 500 is done for example during the same step as the removal of the second layer 300. It is for example possible to implement an etching of the first material and of the second material selective with respect to of the third material forming the pads 100. This etching also preferably presents selectivity between the first material and the second material. If we note V ₁ the etching speed of the first material, V ₂ the etching speed of the second material and V ₃ the etching speed of the third material, we thus preferably have: V ₂ > V ₁ and V ₂ > V ₃ . Preferably, V ₂ > 10*V ₁ and/or V ₂ > 100*V ₃ .

The selectivity between the first, second and third materials has as a direct consequence the height E _prot of the protrusion formed during the withdrawal of the withdrawal portion 500. Thus, the height E _prot can be controlled by the choice of these materials.

This embodiment is characterized by its simplicity of implementation, in particular because relatively few steps are necessary for the formation of protrusions.

All the steps described in the context of this first embodiment can be implemented in other embodiments of the method according to the invention. The advantages presented by these steps can also be transposed to other embodiments. It is in particular possible to use selective etching between the first, second and third material as described above for the formation of the protrusion during other variants of the process according to the invention.

Second example of implementation of the method according to the invention

A second embodiment of the method according to the invention will now be described with reference to Figures 3A to 3J.

A first step consists of providing a stack comprising the substrate 10, a first primary layer 200a surmounting the substrate 10 and a first primary sublayer 310a surmounting the first primary layer 200a ( ). The first primary sublayer 310a is preferably in direct contact with the first primary layer 200a.

A first etching mask 50 having openings 55 is then deposited on the upper face 311a of the first primary sublayer 310a ( ). The parts of the first primary sub-layer 310a and the first primary layer 200a located in line with the openings 55 are removed ( ), then, preferably, the etching mask 50 is removed. This withdrawal makes it possible to form secondary cavities 250'. The secondary cavities 250' preferably extend to the upper face 11 of the substrate 10.

Following the formation of the secondary cavities 250' in the first primary layer 200a and in the first primary sub-layer 310a, the latter are filled with the third material. As illustrated in Figures 3F and 3G, it is for example possible to form a third primary layer 100a extending into the secondary cavities 250', directly above the secondary cavities 250' in the third direction Z and on the first sub-cavity. primary layer 310a ( ). The deposition of the third primary layer 100a is preferably compliant. The third primary layer 100a can then be thinned, for example by CMP, so that it is level with the first primary sublayer 310a ( ).

A second primary sub-layer 320a is then formed on, and preferably in direct contact with, the upper face 311A of the first primary sub-layer 310a and on, and preferably in direct contact with, the top 101 of the pads 100 ( ). The assembly consisting of the first primary sub-layer 310a and the second primary sub-layer 320a is called second primary layer 300a.

Trenches 400 are then formed in the second primary layer 300a and the first primary layer 200a. The trenches 400 pass through the second primary layer 300a over its entire thickness. They preferably also pass through the first primary layer 200a over its entire thickness.

The formation of the trenches 400 makes it possible to divide the first primary layer 200a into a plurality of first layers 200 and the second primary layer 300a into a plurality of second layers 300. More precisely, the first primary sub-layer 310a is divided into a plurality of first sub-layers 310 of the second layers 300, and the second primary sub-layer 320a is divided into a plurality of second sub-layers 320 of the second layers 300. Advantageously, at least some of the trenches 400 extend into the substrate 10. This can make it possible, depending on the targeted applications, to single out different zones of the substrate 10, for example to electrically isolate them from each other.

We thus obtain the stack 1 comprising the substrate 10 surmounted by the structures 1000, each structure 1000 comprising a pad, a first layer 200 and a second layer 300 ( ).

As described in the context of the first embodiment, the trenches 400 can be formed through openings 65 of a second etching mask 60 deposited on the second primary layer 300a (Figures 3G and 3H). This second etching mask 60 is advantageously removed after the formation of the trenches 400.

In the context of the second embodiment, the second layer 300 – more precisely the first sub-layer 310 of the second layer 300 – covers part of the sidewall 103. Prior to the removal step, the first layer 200 extends on only a portion of the side 103 of the pad 100 and does not extend to the top 101 of the pad 100. Thus, for a structure 100, the shrinkage portion 500 is at least formed by the first sub-layer 310 of the second layer 300. According to an advantageous example illustrated in , the withdrawal portion 500 extends only in the first sub-layer 310 of the second layer 300. It is however also possible to remove part of the first layer 200 to form the protrusion.

The withdrawal portion 500 is selectively removed with respect to the pad 100 after the formation of the trenches 400.

As illustrated by the passage from to the , the removal of the removal portion 500 advantageously comprises the removal of the entire second layer 300, always selectively with respect to the pad 100.

In this second embodiment, the pads 100 project from the first primary layer 200 as soon as they are formed. This comes from the fact that the pads 100 are formed in the secondary cavities 250', delimited, in any plane parallel to the transverse plane XY, on the one hand by the first primary layer 200a and on the other hand by the first primary sub-layer 310a. The height E _prot of the protrusion obtained after removal of the shrinkage portion 500 is therefore typically defined by the thickness E _310a , measured in the third direction Z, of the first primary sub-layer 310a. In particular, if, for a structure 1000, the shrinkage layer 500 corresponds to the first sub-layer 310 of the third layer 300, we have approximately E _prot = E _310a .

An advantage of the second embodiment is the excellent control of the height E _against protrusion. As mentioned previously, this height can be defined as soon as the first primary sub-layer 310a is deposited, but the thickness of a layer when it is deposited is a very well-controlled parameter in the industry. We can therefore precisely control E _310a and therefore E _prot .

This embodiment can also make it possible to form a protrusion having a particularly large height E _prot . The removal of the second material forming the removal portion 500 selectively from the third material forming the pad 100 can in fact be carried out without difficulty over a significant height, typically from 50 to 200 nm.

All the steps described in the context of this second embodiment can be implemented in other embodiments of the method according to the invention. The advantages presented by these steps can also be transposed to other embodiments. It is in particular possible to use the principle of deposition of the second layer 300 in two stages (first sub-layer 310 and second sub-layer 320) and the formation of the pad 100 between the formation of the first primary sub-layer 310a and the formation of the second primary sublayer 320a during other variants of the method according to the invention.

Third example of implementation of the method according to the invention

A third example of an embodiment of the method according to the invention will be described with reference to Figures 4A to 4H.

The steps making it possible to obtain the substrate 10 surmounted by the first primary layer 200a comprising cavities 250 ( ) can be similar to those described for the first embodiment with reference to Figures 2A to 2C.

A third primary layer 100a is then formed in the cavities 250 and on the upper face 201a of the second primary layer 200a. The third primary layer 100a is preferably compliant. Its upper face 101a preferably extends in a plane parallel to the transverse plane XY.

After the formation of the third primary layer 100a, the portions of the third primary layer 100a surmounting the first primary layer 200a are removed. This makes it possible to update the upper face 201a of the first primary layer 200a. This withdrawal also makes it possible to single out the third primary layer 100a into blocks 100.

This removal can be carried out by thinning, for example by CMP, of the first primary layer 200a of the third primary layer 100a. A CMP process can in fact make it possible to thin the first primary layer 200a selectively to the third primary layer 100a, by means of a judicious choice of the slurry (English term meaning "mud") of CMP and the buffer (commonly referred to as English for “pad”) of CMP.

According to another example, this removal is carried out, for example by wet etching, through a mask having openings overhanging the first primary layer 200a (not shown in the figures).

As illustrated in , a second primary layer 300a is then formed on the pads 100 and the first primary layer 200A. The second primary layer 300a is preferably in contact with the top 101 of the pads 100 and the upper face 201A of the first primary layer 200A.

Trenches 400 are then formed in the second primary layer 300a and the first primary layer 200a ( ). The trenches 400 pass through the second primary layer 300a over its entire thickness. They preferably also pass through the first primary layer 200a over its entire thickness.

The formation of the trenches 400 makes it possible to divide the first primary layer 200a into a plurality of first layers 200 and the second primary layer 300a into a plurality of second layers 300. More precisely, the first primary sub-layer 310a is divided into a plurality of first sub-layers 310 of the second layers 300, and the second primary sub-layer 320a is divided into a plurality of second sub-layers 320 of the second layers 300.

We thus obtain the stack 1 comprising the substrate 10 surmounted by the structures 1000, each structure 1000 comprising a pad, a first layer 200 and a second layer 300 ( ).

As described in the context of the first embodiment, the trenches 400 can be formed through openings 65 of a second etching mask 60 deposited on the second primary layer 300a (Figures 4E and 4F). This second etching mask 60 is advantageously removed after the formation of the trenches 400.

In the context of the third embodiment, the second layer 300 covers part of the sidewall 103. Prior to the removal step, the first layer 200 extends over only a portion of the sidewall 103 of the stud 100 and does not extend not until summit 101 of plot 100.

Thus, for a structure 100, the shrinkage portion 500 is formed at least by part of the second layer 300. According to an advantageous example illustrated in , the withdrawal portion 500 extends only in the second layer 300. However, it is also possible to remove part of the first layer 200 to form the protrusion.

The withdrawal portion 500 is selectively removed with respect to the pad 100 after the formation of the trenches 400.

As illustrated by the passage from to the , the removal of the removal portion 500 advantageously comprises the removal of the entire second layer 300, always selectively with respect to the pad 100.

This embodiment can also make it possible to form a protrusion having a particularly large height E _prot , potentially even greater than by implementing the second embodiment described previously. The removal of the second material forming the removal portion 500 selectively from the third material forming the pad 100 can in fact be carried out without difficulty over a significant height, typically 50 to 200 nm.

All the steps described in the context of this second embodiment can be implemented in other embodiments of the method according to the invention. The advantages presented by these steps can also be transposed to other embodiments. It is in particular possible to use the principle of thinning by CMP to form pads 100 projecting relative to the third primary layer 100a then protection of the top 101 of the pads 100 during other variants of the process according to the invention.

In all the embodiments described above, during the formation of the trenches 400, the top 101 of the pads 100 is covered by the second primary layer 300a. This has the advantage of protecting this summit 101 and in particular of making it possible to maintain its level of surface roughness, which could be strongly impacted during the formation of the trenches 400.

The surface roughness obtained after thinning the second primary layer 300a or the pads 100, depending on the embodiment, can be controlled by adjusting certain thinning parameters. In particular, the CMP suspension, sometimes called CMP mud, CMP paste or more commonly "slurry" (English term meaning "mud") of CMP, used during the thinning step can be chosen according to the roughness surface area targeted for the pads 100. This choice can particularly be made according to the characteristic dimension, often nanometric, of the abrasive particles contained in the CMP suspension. The CMP suspension is advantageously chosen so that the surface roughness of the pads 100 is compatible with their bonding with a specific object, depending on the targeted applications. It can for example be a thin film based on the third material.

The roughness R ₁₀₁ of the vertex 101 of the pads 100 is advantageously less than 2 nm, preferably less than 1.5 nm.

Furthermore, another characteristic common to the embodiments described is the fact that the step of thinning the third primary layer 100A making it possible to obtain the pads 1 (passage of the to the in the first embodiment, the to the in the second embodiment and the at 4C in the third embodiment) takes place before the step of forming the trenches 400. This makes it possible to avoid that, during a CMP step subsequent to a step of singularization of the structures 1000 (ie a step of forming trenches 400), CMP suspension residues do not remain in the trenches 400. These residues are in fact very difficult to remove and constitute pollution for the rest of the process. They could in particular harm the good adhesion of the pads 100 with a surface on which one would try to stick them.

The previously mentioned removals of material (formation of cavities 250, formation of trenches 400, removal of the removal portion 500, removal of the second layer 300, etc.) can be carried out by wet etching. The removal of the different etching masks 50, 60 can in particular be done by stripping, more commonly referred to by the English term “stripping”.

Through the different embodiments described above, it clearly appears that the invention proposes a method of preparing a stack with a view to assembly with another stack or substrate that is simple to implement. It makes it possible to place, at the level of each structure 1000, a portion of the pad 100 in protrusion relative to the first layer. These protrusions can be used for gluing or transferring the stack to another stack or substrate. In particular, as mentioned previously, the top 101 of the pads 100 is protected during the process and maintains a roughness suitable for direct bonding.

Through the different embodiments described above, it clearly appears that the invention proposes a stack and a method of manufacturing this stack allowing efficient transfer of structures from one stack to another. The presence of protrusions according to the invention in fact allows effective bonding of one or more pads or structures towards a receiving stack, not requiring dimensional control greater than the control currently accessible in the industry, and not requiring The heating step risks causing distortions and/or strong mechanical stresses within the stacks.

The invention is not limited to the embodiments previously described and extends to all the embodiments covered by the invention.

Claims (18)

Method for preparing a stack (1) comprising the following steps:

• provide a stack (1) comprising a substrate (10) surmounted by a plurality of structures (1000) separated by trenches (400), each structure comprising:
  • a stud (100) comprising a top (101) and at least one side (103),
  • a first layer (200) based on a first material and surmounting the substrate (10), the first layer (200) covering at least part of the side (103) of the pad (100),
  • a second layer (300) based on a second material and covering at least the top (101) of the pad (100),
  • a recess portion (500), covering an upper part (104) of the sidewall (103) of the stud (100), the upper part (104) of the sidewall (103) extending from the top (101) of the stud (100) ), the shrinkage portion (500) being formed by at least one of the first layer (200) and the second layer (300),
  • a covering portion (600), covering a lower part (105) of the side (103) of the stud (100) and extending from the withdrawal portion (500), the covering portion (600) being formed by the first layer,
• remove the second layer (300),
• remove the withdrawal portion (500) leaving the covering portion (600) in place so as to expose the upper part (104) of the sidewall (103) of the stud (100), the upper part (104) of the sidewall (103) of the stud (100) forming a protrusion beyond the covering portion (600).

Method according to the preceding claim in which the substrate (10) has a lower face (12) extending mainly along a transverse plane (XY) defined by a first direction (X) and a second direction (Y), the protrusion having a height E_protectionin a third direction (Z) perpendicular to said transverse plane (XY), such that E_protection ≤ 0.5*E_flank , preferably E_protection ≤ 0.3*E_flankand preferably E_protection ≤ 0.1*E_flank, E_flankbeing the height of the side (103) of the stud (100) taken in the third direction (Z). Method according to any one of the two preceding claims, in which E _prot ≥ 5 nm, preferably E _prot ≥ 10 nm. Method according to any one of the preceding claims, in which the removal of the second layer (300) and the removal of the removal portion (500) are carried out during a single etching step. Method according to any one of the preceding claims in which the shrinkage portion (500) is formed solely by the first layer (200). Method according to the preceding claim, in which, prior to the removal step, the first layer (200) extends to the top (101) of the pad (100). Method according to any one of the two preceding claims in which the withdrawal of the withdrawal portion (500) is carried out by time control. Method according to any one of claims 1 to 4, in which the shrinkage portion (500) is formed at least in part by the second layer (300). Method according to the preceding claim in which the withdrawal portion (500) is formed solely by the second layer (300). A method according to any one of the two preceding claims wherein removing the removal portion (500) comprises etching the second layer (300) selectively to the first layer (200). Method according to any one of claims 8 to 10 in which the supply of the stack (1) comprises the following steps:

• Form the first layer (200),
• Form the plot (100),
• Form the second layer (300),

and in which the formation of the second layer (300) comprises the following substeps:

• After the formation of a first primary layer (200a) intended to form the first layer (200) and prior to the formation of the pad (100), forming a first primary sublayer (310a) of a second primary layer (300a ) intended to form the second layer (300), the first primary sub-layer (310a) overlying the first primary layer (200a), the first primary sub-layer (310a) being shaped so that after formation of the trenches (400) separating the structures (1000) it forms a first sub-layer (310) of the second layer (300) covering part of the side (103) of the pad (100) and forming the withdrawal portion (500),
• After the formation of the pad (100), form a second primary sub-layer (320a) of the second primary layer (300a), the second primary sub-layer (320a) covering the first primary sub-layer (310a), the second primary sub-layer (320a) being shaped so that after the formation of the trenches (400) separating the structures (1000) it forms a second sub-layer (320) of the second layer (300) surmounting at least the plot (100).

Method according to any one of claims 8 to 10 in which the supply of the stack (1) comprises the following steps:

• Form the first layer (200),
• Form the plot (100),
• Form the second layer (300),

and in which a second primary layer (300a), shaped so as to form the second layer (300) after formation of the trenches (400) separating the structures (1000), is deposited:

• on the pad (100) and
• on a first primary layer (200a) shaped so as to form the first layer (200) after the formation of the trenches (400)

after the formation of the stud (100). Method according to any one of the preceding claims in which the pads (100) are formed of a third material, the third material being based on one of copper, aluminum, tungsten and titanium. Method according to any one of the preceding claims in which the first material is based on one of: SiO ₂ , SiN and Si. Method according to any one of the preceding claims in which the second material is based on one of SiN, SiO ₂ and Si. Stack (1) comprising a substrate (10) surmounted by a plurality of structures (1000) separated by trenches (400), each structure comprising:

• a stud (100) comprising a top (101) and at least one side (103),
• a covering portion (600) formed by a first layer (200) based on a first material and surmounting the substrate (10), covering a lower part (105) of the side (103) of the pad (100) and leaving discovered an upper part (104) of the side (103) of the pad (100), the upper part (104) of the pad (100) forming a protrusion relative to the first layer (200).

Stack (1) according to the preceding claim in which the protrusion has a height E _prot greater than 5 nm, preferably greater than 10 nm, the height E _prot being taken along a third dimension (Z) perpendicular to a transverse plane (XY) in which mainly extends a lower face (12) of the substrate (10). Method of gluing or transferring at least one pad (100) included in a stack (1) according to any one of the two preceding claims onto a receiving stack (20):

• Provide a stack (1) according to any one of the two preceding claims,
• Providing a receiving stack (20) having an upper face (21),
• Directly bond the top (101) of the at least one pad (100) of the stack (1) to the upper face (21) of the receiving stack (20).