Method for preparing a stack for gluing
The described process forms protrusions on substrates by selectively removing layers, addressing the challenges of thermal expansion and mechanical constraints in substrate assembly, enabling efficient and precise transfer of elements without high-temperature heating.
Patent Information
- Application Number
- FR2022013584
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2022-12-16
- Publication Date
- 2025-04-18
- Estimated Expiration
- 2042-12-16
AI Technical Summary
Existing substrate assembly techniques in microelectronics and optoelectronics face challenges such as material incompatibility due to differing thermal expansion coefficients and the need for high-temperature heating, which can cause distortions and mechanical constraints, especially when assembling substrates with copper-based elements and glass-based supports.
A process involving the preparation of a stack with structures having a stud and layers, where a portion of the second layer is selectively removed to form protrusions, allowing assembly without high-temperature heating, thus avoiding distortions and mechanical constraints.
The process enables effective assembly of substrates without requiring high-temperature heating, maintaining structural integrity and precise dimensional control, facilitating the transfer of elements like photo-elements between substrates.
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Abstract
Description
Title of the invention: Method for preparing a stack for bonding Technical field
[0001] The present invention relates to the preparation of a substrate, in particular with a view to bonding it with another substrate. It is particularly applicable to the manufacture of optoelectronic and microelectronic devices. It finds, for example, a particularly advantageous application in the field of assembling a substrate having copper-based elements with a substrate covered with a copper film. STATE OF THE ART
[0002] 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 photo-elements such as pixels, from one substrate to another.
[0003] 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 SiO2, 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 relative to the SiO2 protrusions 200'. During the step of assembling the two substrates, a heating step causes expansion of the copper pillars. The expansion of the SiO2 protrusions taking place in parallel is less significant than that of the copper pillars. Therefore, by correctly dimensioning the withdrawal of the pillars in relation to the SiO2 protrusions, the pillars are at the end of the heating step level with the SiO2 protrusions and in contact with the surface of the second substrate.
[0004] While this method is functional in certain contexts, it is not applicable to all substrates, and in particular not when the latter comprise materials whose melting temperature is lower than the temperature at which the material of the recessed elements can exhibit volume expansion. For example, the annealing temperature of copper is 350°C while certain materials used that may require such assemblies have melting temperatures of the order of 250°C. It is therefore impossible to implement this solution when these materials are involved.
[0005] The heating step can also cause problems of distortion 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.
[0006] Another disadvantage of this method lies in the precision required in the dimensioning of the shrinkage of the copper pillars in relation to the SiO2 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.
[0007] An objective of the present invention is therefore to propose a method for preparing a substrate for assembly with another substrate, this method not requiring the substrate to be subjected to high temperatures. SUMMARY
[0008] To achieve this objective, according to one embodiment, a method for preparing a stack is provided comprising the following steps: - provide a stack comprising a substrate topped with a plurality of structures separated by trenches, each structure comprising: • a pad comprising a top and at least one side, • a first layer based on a first material and covering 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 by being in direct contact with, an upper part of the side of the pad, the upper part of the side extending from the top of the pad, the withdrawal portion being formed by at least one of the first layer and the second layer, • a covering portion, covering, preferably by being in direct contact with, a lower part of the side of the pad and extending from the removal 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 side of the pad, the upper part of the side of the pad forming a protrusion beyond the covering portion.
[0009] The protrusion thus formed is suitable for bonding to another surface, for example the upper face of a transfer support.
[0010] 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 plot comprising a vertex and at least one side, 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 pad and leaving uncovered an upper part of the side of the pad, the upper part of the pad forming a protrusion relative to the first layer.
[0011] A third aspect of the invention relates to a method of bonding or transferring at least one pad included in a stack according to the second aspect of the invention onto a receiving stack: Providing a stack according to the second aspect of the invention, Provide a receiving stack with an upper face, Carry out direct bonding of the top of at least one pad of the stack onto the upper face of the receiving stack.
[0012] The protrusions formed during the preparation process in fact 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 the 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 at which mechanical deformations can occur.
[0013] Furthermore, this bonding process does not require dimensional control. superior to the control commonly available in the industry. BRIEF DESCRIPTION OF THE FIGURES
[0014] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:
[0015] [Fig. 1A] Figures 1A to 1C show a method of assembling two substrates according to the prior art. [Fig. 1A] 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 laterally cover the pillars.
[0016] [Fig.IB] [Fig.IB] illustrates the reversal of the stack according to the prior art and its placement opposite a reception stack.
[0017] [Fig.lC] [Fig.lC] illustrates the assembly of the two stacks and their bonding by heating. [Fig.lC] illustrates in particular the expansion of the pillars.
[0018] [Fig.2A] Figures 2A to 2J illustrate a first embodiment of the method according to the invention. [Fig.2A] represents the provision of a primary stack comprising a substrate and a first primary layer overlying the substrate.
[0019] [Fig.2B] [Fig.2B] illustrates the formation of a first etching mask on the first primary layer.
[0020] [Fig.2C] [Fig.2C] represents the formation of cavities in the first primary layer.
[0021] [Fig.2D] [Fig.2D] illustrates the formation of a third primary layer in the cavities and on the first primary layer.
[0022] [Fig.2E] [Fig.2E] represents the thinning of the third primary layer so as to form pads extending into the cavities.
[0023] [Fig.2F] [Fig.2F] represents the formation of a second primary layer on the plots and the first primer layer.
[0024] [Fig.2G] [Fig.2G] represents the formation of a second etching mask on the second primary layer.
[0025] [Fig.2H] [Fig.2H] 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.
[0026] [Fig.21] [Fig.2I] illustrates the removal of the second etching mask.
[0027] [Fig.2J] [Fig.2J] illustrates the removal of the second layers and part of the first layers extending, prior to shrinkage, from the second layers.
[0028] [Fig.3A] Figures 3A to 3J illustrate a second embodiment of the method according to the invention. [Fig.3A] represents the provision of a stack comprising a substrate, a first primary layer overlying the substrate and a first primary sub-layer overlying the first primary layer.
[0029] [Fig.3B] [Fig.3B] represents the formation of a first etching mask on the first primary sub-layer.
[0030] [Fig.3C] [Fig.3C] represents the formation of secondary cavities in the first primary layer and in the first primary sub-layer through the first etching mask.
[0031] [Fig.3D] [Fig.3D] represents the formation of a third primary layer in the secondary cavities and on the first primary sub-layer.
[0032] [Fig.3E] [Fig.3E] 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.
[0033] [Fig.3F] [Fig.3F] illustrates the formation of a second primary sub-layer on the pads and on the first primary undercoat. The first primary undercoat and the second primary undercoat form a second primary coat.
[0034] [Fig.3G] [Fig.3G] represents the formation of a second etching mask on the second primary layer.
[0035] [Fig.3H] [Fig.3H] 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.
[0036] [Fig.31] [Fig.31] illustrates the removal of the second etching mask.
[0037] [Fig.3J] [Fig.3J] illustrates the removal of the second layers, thus forming a protrusion.
[0038] [Fig.4A] Figures 4A to 4H illustrate a third embodiment of the method according to the invention. [Fig.4A] represents the provision of a stack comprising a substrate and a first primary layer overlying the substrate. The first primary layer comprises cavities.
[0039] [Fig.4B] [Fig.4B] illustrates the formation of a third primary layer in the cavities and on the first primary layer.
[0040] [Fig.4C] [Fig.4C] illustrates the thinning of the third primary layer so as to distinguish the latter into individual plots protruding from the first primary layer.
[0041] [Fig.4D] [Fig.4D] represents the formation of a second primary layer on the pads and on the first primary layer.
[0042] [Fig.4E] [Fig.4E] represents the formation of a second etching mask on the second primary layer.
[0043] [Fig.4F] [Fig.4F] illustrates the formation through the second etching mask trenches extending through 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.
[0044] [Fig.4G] [Fig.4G] illustrates the removal of the second etching mask.
[0045] [Fig.4H] [Fig.4H] illustrates the removal of the second layers, thus forming a protrusion.
[0046] [Fig.5A] Figures 5A and 5B are top views of the steps shown in Figures 21, 31 and 4G. [Fig.5A] illustrates an embodiment in which the studs are cylindrical with a square base.
[0047] [Fig.5B] [Fig.5B] illustrates the case of circular cylindrical plots.
[0048] The drawings are given as examples and are not limiting of 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
[0049] Before beginning a detailed review of the embodiments of the invention, optional features which may possibly be used in combination or alternatively are set out below:
[0050] 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 Eprot along a third direction perpendicular to said transverse plane, such that Eprot < 0.5*Eflanc, preferably Eprot < 0.3*Eflanc and preferably Eprot < 0.1*Eflanc, Eflanc being the height of the flank taken along the Z direction. Eprot is thus measured, along Z, between one end of the covering portion and the top of the pad.
[0051] According to one example, Eprot > 5 nm, preferably Eprot > 10 nm. Preferably, Eprot < 50 nm, Eprot < 30 nm.
[0052] 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.
[0053] According to one embodiment, the withdrawal portion is formed solely by the first layer.
[0054] 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.
[0055] 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.
[0056] According to one embodiment, the withdrawal portion is formed at least in part by the second layer. Thus, the second layer covers part of the sidewall.
[0057] According to one example, the shrinkage portion is formed solely by the second layer. This makes it possible to very precisely control the height of the protrusion obtained with the shrinkage of the shrinkage layer. This makes it possible to use only very common steps that are perfectly mastered in the industry. This also makes it possible to limit the number of steps to be implemented to remove the shrinkage portion. This thus results in a saving of time and an economic gain.
[0058] According to one example, the removal of the removal portion comprises etching the second layer selectively at the first layer. The removal of the removal portion is carried out for example by etching the second layer with a stop on the first layer.
[0059] According to a particular embodiment of the invention, the provision of the stack comprises the following steps: - Forming the first layer, - Form the plot, - Form the second layer, and the formation of the second layer includes the following sub-steps: - 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 forming the pad, form a second sub-layer of the second layer, the second sub-layer at least surmounting the pad.
[0060] According to a particular embodiment of the invention, the provision of the stack comprises the following steps: - Forming the first layer, - Form the plot, - Form the second layer, and the second layer is deposited on the pad and the first layer after the pad is formed.
[0061] According to one example, the pads are formed from a third material, the third material being based on one of copper, aluminum, tungsten and titanium.
[0062] According to one example, the first material is based on one of: SiO2, SiN and Si.
[0063] According to one example, the second material is based on one of SiN, SiO2, and Si.
[0064] It is specified that, in the context of the present invention, the terms "on", "overcomes", "covers", "underlying", "facing" and their equivalents do not necessarily mean "in contact with". Thus, for example, the deposition, transfer, bonding, 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.
[0065] A layer can also be composed of several sub-layers of the same material or different materials.
[0066] A substrate, a layer, a device, “based” on a material M, is understood to mean a substrate, a layer, a device comprising this material M only or this material M and possibly other materials, for example alloying elements, impurities or doping elements. Thus a material based on a III-N material may comprise a III-N material with added dopants. Similarly, a GaN-based layer typically comprises GaN and AlGaN or InGaN alloys.
[0067] The term "III-V material" refers to a semiconductor composed of one or more elements from column III and column V of Mendeleev's periodic table. Elements in column III include boron, gallium, aluminum, and indium. Column V contains, for example, nitrogen, arsenic, antimony, and phosphorus.
[0068] The term “selective etching with respect to” or “etching exhibiting selectivity with respect to” means etching configured to remove a material A or a layer A with respect to a material B or a layer B, and exhibiting an etching rate of the material A greater than the etching rate of the material B. The selectivity is the ratio between the etching rate of the material A and the etching rate of the material B. The selectivity between A and B is denoted SA:B.
[0069] 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 furrowing the surface. The roughness of a surface is noted Ra and is typically expressed in pm (1 pm = 106 m) or nm (1 nm = 109 m).
[0070] A reference frame, preferably orthonormal, comprising the axes X, Y, Z is represented in figures 1A, 2A, 3A, 4A, 5A and 5B. This reference frame is applicable by extension to the other figures.
[0071] In the present patent application, we will preferably speak of thickness for a layer and of 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 isolation trench, has a height along Z. The relative terms “on”, “under”, “underlying” preferably refer to positions taken along the Z direction.
[0072] The terms “substantially”, “approximately”, “of the order of” mean “to within 10%, preferably to within 5%”.
[0073] 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.
[0074] The substrate 10 has a lower face 12 extending mainly in a transverse plane XY defined by a first direction X and a second direction Y. The substrate 10 may also comprise an emitting layer 15 comprising a plurality of photoemitting elements. The photoemitting elements may for example be active nanowires or microwires forming LEDs or micro-LEDs. They may 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.
[0075] The structures 1000 have a cylindrical shape, preferably that of a right 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 FIGS. 5A and 5B.
[0076] 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 FIGS. 5A and 5B.
[0077] Each of the structures 1000 surmounting the substrate 10 comprises a pad 100 having a top 101 and at least one flank 103 having a height Eflanc in the third direction Z. Eflanc is advantageously greater than 500 nm, typically substantially equal to 1 pm.
[0078] The top 101 of the pad 100 advantageously extends in a so-called upper plane 501, preferably parallel to the transverse plane XY.
[0079] The pad 100 typically has the shape of a cylinder, preferably a right cylinder whose generating lines defining one or more lateral faces of the pad 100 preferably extend in the third direction Z. The pad 100 may for example have a polygonal shape in the transverse plane XY. The pad 100 then has several lateral 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 [Fig.5A]. The pad 100 may also have a circular cylindrical shape, as illustrated in [Fig.5B]. It then has only one lateral face. In the case of a cylindrical pad, the at least one flank 103 of the pad 100 corresponds to one or the lateral face of the pad 100.
[0080] The pad 100 is preferably based on a metallic material, for example copper, aluminum, tungsten or even titanium.
[0081] Each pad 100 advantageously covers at least one photoemitting element included in the emitting layer 15. The photoemitting elements are thus located at right angles to the pads 100 in projection along the transverse plane XY. They may be in direct contact with the pads 100, possibly via a layer called contact layer 16 which may for example be based on aluminum, titanium or titanium nitride.
[0082] 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 E20o in the third direction Z. The first layer 200 covers at least a portion of the flank 103 of the pad 100. It is thus in contact with the pad 100 over a non-zero height Ecoverment less than or equal to the height of the flank Eflanc.
[0083] 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.
[0084] The stack 1 provided during the method according to the invention can for example be obtained according to the steps below: - Provide a primary stack comprising it, as illustrated in [Fig.2A]: • The substrate 10, • A first primary layer 200a based on the first material and covering the substrate 10. - Forming in the first primary layer 200a cavities 250 passing entirely 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). - Forming 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.
[0085] It is understood, however, that stack 1 can be obtained according to any other embodiment.
[0086] Following the provision of the stack 1, a step of removing a removal portion 500 is implemented at the level of each structure 1000.
[0087] 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 flank 103 of the pad 100. In other words, it is adjacent, in a plane parallel to the XY plane, to the flank 103 of the pad 100, and this at any point of the upper part 104 of the flank 103. The withdrawal portion 500 is preferably in direct contact with the upper part 104 of the flank 103 of the pad 100. In the particular case of a pad 100 having several flanks, the upper part 104 advantageously extends into each of the flanks 103 of the pad 100.
[0088] The upper part 104 of the flank 103 extends from the top 101 of the pad 100. More precisely, the upper part 104 extends from the edge(s) of the pad 100 delimiting its top 101 and its flank 103. It has a height E104 in the third direction Z. The recessed portion 500 extends in the third direction Z over a distance less than the height of the flank 103. We thus have E104 <Eflanc.
[0089] 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.
[0090] During the step of removing the removal portion 500, a covering portion 600 is left in place.
[0091] The covering portion 600 is formed by the first layer 200. It covers a lower part 105 of the flank 103 of the pad 100. In other words, it is adjacent, in a plane parallel to the XY plane, to the flank 103 of the pad 100, and this at any point of the lower part 105 of the flank 103. The covering portion 600 is preferably in direct contact with the lower part 105 of the flank 103 of the pad 100.
[0092] 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 flank 103 of the pad 100 are in contact.
[0093] The lower part 105 of the flank 103 has a height E105 along the third direction Z. According to one example, the withdrawal portion 500 and the covering portion 600 together cover the flank 103 of the pad 100 over the entire height. We then have E104 + E105 = Efianc.
[0094] The lower part 105 of the flank 103 is, when the withdrawal portion 500 is removed, left covered by the covering portion 600.
[0095] Once the withdrawal portion 500 has been removed, the upper part 104 of the flank 103 forms a protrusion beyond the covering portion 600. The pad 100 thus projects in the third direction Z relative to at least one remaining part of the first layer 200 corresponding to the covering portion 600.
[0096] The formed protrusion has a height Eprot in the third direction. Advantageously, Eprot is greater than or equal to 5 nm.
[0097] Different embodiments of the method according to the invention will now be described in more detail.
[0098] First example of implementation of the method according to the invention
[0099] A first embodiment of the method according to the invention will now be described with reference to FIGS. 2A to 2J.
[0100] A first step consists of providing a primary stack 1a comprising the substrate 10 and a first primary layer 200a overlying the substrate 10 ([Fig.2A]). A first etching mask 50 is then deposited on the upper face 201a of the first primary layer 200a ([Fig.2B]) and a removal of certain parts of the first primary layer 200a is carried out through openings 55 in the first etching mask 50, then, preferably, the latter is removed ([Fig.2C]). This removal makes it possible to form cavities 250 in the first primary layer 200a. Preferably, the shrinkage in the first primary layer 200a is done over its entire thickness in the third direction Z. In other words, preferably, the cavities 250 extend to the upper face 11 of the substrate 10. This gives an assembly comprising the substrate 10 surmounted by the first primary layer 200a comprising the cavities.
[0101] 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 into the cavities 250, directly above the cavities 250 in the third direction Z and above the first primary layer 200a ([Fig.2D]). A portion 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 ([Fig.2E]). 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 removal of the pads 100 relative to the first primary layer 200a.
[0102] As illustrated in [Fig.2F], 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, according to the third Z direction a thickness E300a. Advantageously, E300a is less than or equal to 200 nm and / or greater than or equal to 20 nm, preferably substantially equal to 60 nm.
[0103] A second etching mask 60 is then formed on the second primary layer 300a ([Fig.2G]). The second etching mask 60 has openings 65 located directly above the first primary layer 200a.
[0104] 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 ([Fig.2H]). Preferably, the second etching mask 60 is then removed. The trenches 400 separate the structures 1000 described previously. Preferably, the trenches pass through the entire thickness along 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 intended applications, to single out different zones of the substrate 10, for example to electrically isolate them from each other.
[0105] 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. This gives 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.
[0106] In this embodiment, in each structure 1000, the first layer 200 and the pad 100 are substantially level along the third direction Z. The second layer 300 does not cover the flank 103 of the pad 100. Thus, as illustrated in [Fig.2I], the withdrawal portion 500 is formed solely by a portion of the first layer 200. The upper portion 104 of the flank 103 of the pad 100 is solely covered by the first layer 200. The lower portion 105 of the flank 103 is advantageously covered solely by the first layer 200.
[0107] 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 from each structure 1000. This remark extends to the mention of all the other elements common to all the structures 1000.
[0108] 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 the third material forming the pads 100. This etching also preferably has a selectivity between the first material and the second material. If we denote by Vi the etching speed of the first material, V2 the etching speed of the second material and V3 the etching speed of the third material, we thus preferably have: V2 > Vi and V2 > V3. Preferably, V2 > 10*Vi and / or V2 > 100*V3.
[0109] The selectivity between the first, second and third materials has as a direct consequence the height Eprot of the protrusion formed during the withdrawal of the withdrawal portion 500. Thus, the height Eprot can be controlled by the choice of these materials.
[0110] This embodiment is characterized by its simplicity of implementation, in particular because relatively few steps are necessary for the formation of the protrusions.
[0111] 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 are also transposable to other embodiments. It is in particular possible to use selective etching between the first, the second and the third material as described above for the formation of the protrusion during other variants of the method according to the invention.
[0112] Second example of implementation of the method according to the invention
[0113] A second embodiment of the method according to the invention will now be described with reference to FIGS. 3A to 3J.
[0114] A first step consists of providing a stack comprising the substrate 10, a first primary layer 200a overlying the substrate 10 and a first primary sub-layer 310a overlying the first primary layer 200a ([Fig.3A]). The first primary sub-layer 310a is preferably in direct contact with the first primary layer 200a.
[0115] A first etching mask 50 having openings 55 is then deposited on the upper face 311a of the first primary sub-layer 310a ([Fig.3B]). The parts of the first primary sub-layer 310a and of the first primary layer 200a located at the openings 55 are removed ([Fig.3C]), then, preferably, the etching mask 50 is removed. This removal makes it possible to form secondary cavities 250'. The secondary cavities 250' preferably extend to the upper face 11 of the substrate 10.
[0116] 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 FIGS. 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 primary sub-layer 310a ([Fig. 3D]). The deposition of the third primary layer 100a is preferably conformal. The third primary layer 100a can then be thinned, for example by CMP, so that it is level with the first primary sub-layer 310a ([Fig. 3E]).
[0117] A second primary undercoat 320a is then formed on, and preferably at, direct contact with the upper face 31 IA of the first primary sub-layer 310a and on, and preferably in direct contact with, the top 101 of the pads 100 ([Fig.3F]). The assembly consisting of the first primary sub-layer 310a and the second primary sub-layer 320a is called the second primary layer 300a.
[0118] 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.
[0119] 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 intended applications, to single out different zones of the substrate 10, for example to electrically insulate them from each other.
[0120] 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 ([Fig.31]).
[0121] As described in the context of the first embodiment, the trenches 400 may be formed through openings 65 of a second etching mask 60 deposited on the second primary layer 300a (FIGS. 3G and 3H). This second etching mask 60 is advantageously removed after the formation of the trenches 400.
[0122] In the context of the second embodiment, the second layer 300 - more precisely the first sub-layer 310 of the second layer 300 - covers a portion of the flank 103. Prior to the removal step, the first layer 200 extends over only a portion of the flank 103 of the pad 100 and does not extend to the top 101 of the pad 100. Thus, for a structure 100, the removal portion 500 is at least formed by the first sub-layer 310 of the second layer 300. According to an advantageous example illustrated in [Fig. 31], the removal portion 500 extends only in the first sub-layer 310 of the second layer 300. However, it is also possible to remove a portion of the first layer 200 to form the protrusion.
[0123] The withdrawal portion 500 is selectively withdrawn relative to the pad 100 after the formation of the trenches 400.
[0124] As illustrated by the passage from [Fig.31] to [Fig.3J], the removal of the removal portion 500 advantageously comprises the removal of the entirety of the second layer 300, always selectively with respect to the pad 100.
[0125] In this second embodiment, the pads 100 are protruding relative to 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 Eprot of the protrusion obtained after removal of the removal portion 500 is therefore typically defined by the thickness E 300a, measured along the third direction Z, of the first primary sub-layer 310a. In particular, if, for a structure 1000, the removal layer 500 corresponds to the first sub-layer 310 of the third layer 300, we have substantially Eprot = E310a.
[0126] An advantage of the second embodiment is the excellent control of the height E prot of the protrusion. As mentioned previously, this height can be defined from the deposition of the first primary sub-layer 310a, but the thickness of a layer during its deposition is a parameter that is very well controlled in the industry. It is therefore possible to precisely control E3i0a and therefore Eprot.
[0127] This embodiment can also make it possible to form a protrusion having a particularly large height Eprot. The removal of the second material forming the removal portion 500 selectively to 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.
[0128] 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 are also transposable 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 of the formation of the pad 100 between the formation of the first primary sub-layer 310a and the formation of the second primary sub-layer 320a during other variants of the method according to the invention.
[0129] Third example of implementation of the method according to the invention
[0130] A third example embodiment of the method according to the invention will be described with reference to FIGS. 4A to 4H.
[0131] The steps for obtaining the substrate 10 topped with the first primary layer 200a comprising cavities 250 ([Fig.4A]) may be similar to those described for the first embodiment with reference to FIGS. 2A to 2C.
[0132] 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 conformal. Its upper face 101a preferably extends in a plane parallel to the transverse plane XY.
[0133] After the formation of the third primary layer 100a, the portions of the third primary layer 100a overlying the first primary layer 200a. This makes it possible to expose the upper face 201a of the first primary layer 200a. This removal also makes it possible to distinguish the third primary layer 100a into pads 100.
[0134] 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 method 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 CMP slurry (English term meaning “mud”) and the CMP pad (commonly referred to by the English term “pad”).
[0135] 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).
[0136] As illustrated in [Fig.4D], 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.
[0137] Trenches 400 are then formed in the second primary layer 300a and the first primary layer 200a ([Fig.4G]). 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.
[0138] 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.
[0139] 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 ([Fig.4G]).
[0140] As described in the context of the first embodiment, the trenches 400 may be formed through openings 65 of a second etching mask 60 deposited on the second primary layer 300a (FIGS. 4E and 4F). This second etching mask 60 is advantageously removed after the formation of the trenches 400.
[0141] In the context of the third embodiment, the second layer 300 covers a portion of the flank 103. Prior to the removal step, the first layer 200 extends over only a portion of the flank 103 of the pad 100 and does not extend to the top 101 of the pad 100.
[0142] Thus, for a structure 100, the withdrawal portion 500 is at least formed by a part of the second layer 300. According to an advantageous example illustrated in [Fig.4G], the withdrawal portion 500 extends only in the second layer 300. It is however also possible to remove a part of the first layer 200 to form the protrusion.
[0143] The withdrawal portion 500 is selectively withdrawn relative to the pad 100 after the formation of the trenches 400.
[0144] As illustrated by the transition from [Fig.4G] to [Fig.4H], the removal of the removal portion 500 advantageously comprises the removal of the entirety of the second layer 300, always selectively with respect to the pad 100.
[0145] This embodiment can also make it possible to form a protrusion having a particularly large height Eprot, potentially even larger than when implementing the second embodiment described previously. The removal of the second material forming the removal portion 500 selectively to the third material forming the pad 100 can in fact be carried out without difficulty over a significant height, typically 50 to 200 nm.
[0146] 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 are also transposable 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 and then a protection of the top 101 of the pads 100 during other variants of the method according to the invention.
[0147] In all the embodiments previously described, 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 top 101 and in particular of making it possible to preserve its level of surface roughness, which could be strongly impacted during the formation of the trenches 400.
[0148] 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 slurry, CMP paste or more commonly CMP slurry, used during the thinning step can be chosen according to the surface roughness targeted for the pads 100. This choice can in particular 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 to a given object, depending on the applications. targets. For example, it could be a thin film based on the third material.
[0149] The roughness RiOi of the top 101 of the pads 100 is advantageously less than 2 nm, preferably less than 1.5 nm.
[0150] 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 from [Fig.2D] to [Fig.2E] in the first embodiment, from [Fig.3D] to [Fig.3E] in the second embodiment and from [Fig.4B] to 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 singulating the structures 1000 (i.e. a step of forming the trenches 400), residues of CMP suspension remain in the trenches 400. These residues are in fact very difficult to remove and constitute pollution for the rest of the process. In particular, they could harm the good adhesion of the 100 pads to a surface on which one would try to stick them.
[0151] The previously mentioned material removals (formation of the cavities 250, formation of the 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 various etching masks 50, 60 can in particular be carried out by stripping, more commonly referred to by the English term “stripping”.
[0152] Through the various embodiments described above, it is clear that the invention proposes a method for preparing a stack for 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 bonding or transferring the stack onto another stack or substrate. In particular, as mentioned previously, the top 101 of the pads 100 is protected during the method and retains a roughness suitable for direct bonding.
[0153] Through the various embodiments described above, it is clear that the invention proposes a stack and a method for manufacturing this stack allowing an efficient transfer of structures from one stack to another. The presence of protrusions according to the invention in fact allows an efficient bonding of one or more pads or structures to a receiving stack, not requiring dimensional control greater than the control commonly accessible in the industry, and not requiring a heating step risking causing distortions and / or strong mechanical stresses within the stacks.
[0154] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention.
Claims
Claims
1. A method of 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 pad (100) comprising a top (101) and at least one side (103), - a first layer (200) based on a first material and covering 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 withdrawal portion (500), covering an upper part (104) of the flank (103) of the pad (100), the upper part (104) of the flank (103) extending from the top (101) of the pad (100), the withdrawal 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 flank (103) of the pad (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) while leaving the covering portion (600) in place so as to expose the upper part (104) of the flank (103) of the stud (100), the upper part (104) of the flank (103) of the stud (100) forming a protrusion beyond the covering portion (600).
2. 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 Eprot in a third direction (Z) perpendicular to said transverse plane (XY), such that Eprot< 0.5*Eflanc, preferably Eprot< 0.3*Eflanc and preferably Eprot< 0.1*Eflanc, Eflanc being the height of the flank (103) of the stud (100) taken in the third direction (Z).
3. Method according to any one of the two preceding claims, wherein Eprot > 5 nm, preferably Eprot >10 nm.
4. A method according to any preceding claim, wherein the removal of the second layer (300) and the removal of the removal portion (500) are performed in a single etching step.
5. A method according to any preceding claim wherein the removal portion (500) is formed solely by the first layer (200).
6. 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).
7. A method according to any one of the two preceding claims wherein the removal of the removal portion (500) is carried out by time control.
8. A method according to any one of claims 1 to 4, wherein the shrinkage portion (500) is formed at least in part by the second layer (300).
9. Method according to the preceding claim in which the withdrawal portion (500) is formed solely by the second layer (300).
10. 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).
11. A method according to any one of claims 8 to 10 wherein providing the stack (1) comprises the following steps: • Forming the first layer (200), • Forming the pad (100), • Forming the second layer (300), and wherein forming the second layer (300) comprises the following sub-steps: • After forming 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 sub-layer (310a) of a second primary layer (300a) intended to form the second layer (300), the first primary sub-layer (310a) surmounting 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 a portion of the flank (103) of the pad (100) and forming the withdrawal portion (500), • After the formation of the pad (100), forming 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 pad (100).,
12. Method according to any one of claims 8 to 10 wherein the provision of the stack (1) comprises the following steps: • Forming the first layer (200), • Forming the pad (100), • Forming the second layer (300), and wherein 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 formation of the trenches (400) after formation of the pad (100).
13. A method according to any preceding claim wherein the pads (100) are formed from a third material, the third material being based on one of copper, aluminum, tungsten and titanium.
14. A method according to any preceding claim wherein the first material is based on one of: SiO2, SiN and Ci
15. ol. A method according to any preceding claim wherein the second material is based on one of SiN, SiO2 and Si.