Chip-to-sheet direct hybrid bonding method

Abstract

The invention relates to a method for the direct hybrid bonding of chip (10) to sheet (20), comprising the following steps: Providing at least one chip (10) comprising a first copper pad (11) and a first layer (12) of silicon oxide, Providing a sheet (20) comprising a second copper pad (21) and a second layer (22) of silicon oxide, Manipulating the chip (10) so as to position the face (100) of the chip (10) facing the area (210) for receiving the chip on the sheet (20), aligning the first and second pads (11, 21), Depositing at least one water drop (30) in the area (210) for receiving the chip and / or on the face (100) of the chip (10), Applying pressure to the chip (10) to form, from the water drop (30), a water film (31) between the face (100) and the area (210) for receiving the chip (10).

Description

[0001] "Direct hybrid chip-to-wafer bonding process"

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to 3D integration, more particularly to direct chip-to-wafer bonding and more particularly to direct hybrid chip-to-wafer bonding.

[0004] STATE OF THE ART

[0005] In the field of 3D integration of semiconductor components, processes are being developed to transfer and assemble a wafer or chip onto another wafer. Among these processes, direct bonding and more specifically hybrid bonding allow two integrated circuits to be assembled in a stack, and / or a direct electrical connection to be established between these two integrated circuits via the bonding interface. This makes it possible to increase the interconnection density of components manufactured by 3D integration.

[0006] In particular, hybrid copper / oxide bonding is an industrial bonding technique typically consisting of placing two surfaces composed of copper pads surrounded by silicon oxide opposite each other. These surfaces composed of two materials are thus called hybrid. The objective of the bonding is to make electrical contact between the copper pads of the two surfaces facing each other. The copper pads have a typical size of a few microns. It is therefore necessary to perfectly align the two surfaces prior to direct bonding. Initially developed for “plate-to-plate” bonding, this hybrid bonding is now being developed to perform “chip-to-plate” bonding using so-called “pick and place” machines (which can be translated as “grasp and position” or “take and deposit” or “pick and place” according to the usual meaning used by those skilled in the art).This allows for high placement accuracy and high throughput. The paper “Die to Wafer Direct Hybrid Bonding Demonstration with High Alignment Accuracy and Electrical Yields, A. Jouve et al., in 2019 International 3D Systems Integration Conference (3DIC), pp. 1-7” discloses a die-to-wafer direct hybrid bonding process with high alignment accuracy and high throughput. A disadvantage of this process is that D-bonding defects can occur on some 10KB chips, as shown in Figure 1.

[0007] There is therefore a need to reduce, or even eliminate, bonding defects for direct bonding in general and more particularly for direct hybrid chip-to-plate bonding. One objective of the invention is to meet this need.

[0008] SUMMARY OF THE INVENTION

[0009] To achieve this objective, according to one embodiment, a direct chip-to-plate bonding method is provided comprising at least the following steps:

[0010] - Provide at least one chip having a first flat face preferably comprising first alignment marks,

[0011] - Provide at least one plate having a second flat face comprising a chip receiving area and preferably second alignment marks,

[0012] - Manipulate the chip so as to position the first face of the chip opposite the chip receiving area on the second face of the plate, aligning the chip with the plate, preferably via the first and second alignment marks,

[0013] - Bring the first side of the chip into contact with the chip receiving area, so as to stick the chip to the second side of the plate.

[0014] Advantageously, the method comprises, before contacting and preferably before handling the chip, a deposit of at least one drop of water in the receiving area of ​​the chip on the second face of the plate and / or on the first face of the chip. The drop of water does not cover the alignment marks at this stage.

[0015] Advantageously, the method also comprises, during the handling of the chip and after depositing the drop of water, an application of pressure on the chip configured to form, from the deposited drop of water, a film of water between the first face and the receiving zone of the chip.

[0016] According to another embodiment, a direct hybrid chip-to-plate bonding method is provided comprising at least the following steps:

[0017] - Providing at least one chip comprising at least a first copper pad and a first silicon oxide layer, said chip having a first planar face formed by exposed portions of the first copper pad and the first silicon oxide layer,

[0018] - Providing at least one plate comprising at least a second copper pad and a second silicon oxide layer, said plate having a second flat face comprising a chip receiving area, said area being formed by exposed parts of the second copper pad and the second silicon oxide layer,

[0019] - Manipulate the chip so as to position the first face of the chip opposite the chip reception area on the second face of the plate, aligning the first and second copper pads,

[0020] - Bring the first side of the chip into contact with the chip receiving area, so as to stick the chip to the second side of the plate.

[0021] Advantageously, the method comprises, before contacting and preferably before handling the chip, a deposit of at least one drop of water in the reception area of ​​the chip on the second face of the plate and / or on the first face of the chip.

[0022] Advantageously, the method also comprises, during the handling of the chip and after depositing the drop of water, an application of pressure on the chip configured to form, from the deposited drop of water, a film of water between the first face and the receiving zone of the chip.

[0023] In the context of the development of the present invention, it was found that the formation of the water film by depositing a drop of water and applying pressure to said drop of water advantageously made it possible to eliminate bonding defects between the chip and the plate.

[0024] In general, it is contraindicated and / or counterintuitive to form a liquid interface, especially water-based, when performing precise alignment of the chip with respect to the wafer. It is indeed assumed that the presence of water between the chip and the wafer will modify the initial alignment typically performed by precision industrial equipment such as "pick and place".

[0025] In the context of the present invention, it has been surprisingly found that applying pressure to the water droplet, which allows a thin film of water to be formed, allows the initial alignment carried out by the equipment to be maintained. Thus, the formation of a thin film of water prevents misalignment of the chip with respect to the plate. This presence of water in a thin film reduces or eliminates bonding defects.

[0026] To avoid bonding defects, those skilled in the art of direct hybrid bonding could consider more complex solutions, for example by carrying out the handling and contacting under vacuum or under a controlled atmosphere based on helium or by bending the chips at the time of bonding. These solutions impose more constraints on industrial equipment and are more expensive. They have not been retained within the scope of the present invention.

[0027] The method according to the invention thus advantageously makes it possible to reduce or eliminate bonding defects in direct bonding and direct hybrid bonding, while controlling costs.

[0028] BRIEF DESCRIPTION OF THE FIGURES

[0029] 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:

[0030] Figure 1 is an acoustic microscopy image illustrating in top view bonding defects between a plate and certain chips assembled by direct hybrid bonding, according to the prior art.

[0031] Figures 2, 4 and 6 schematically illustrate in cross-section steps of direct hybrid bonding, according to an embodiment of the present invention. Figures 3 and 5 schematically illustrate in top view steps of direct hybrid bonding, according to an embodiment of the present invention.

[0032] Figure 7 is an acoustic microscopy image illustrating a top view of chips assembled on a plate by direct hybrid bonding, according to an embodiment of the present invention.

[0033] 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, on the schematic diagrams, the thicknesses and / or dimensions of the different layers, patterns and reliefs are not representative of reality.

[0034] DETAILED DESCRIPTION OF THE INVENTION

[0035] Before commencing a detailed review of embodiments of the invention, optional features which may optionally be used in combination or alternatively are set out below:

[0036] According to one example, the first planar face and the receiving area of ​​the chip are based on the same material, for example Si, Ge, AsGa, InP, GaN, SiC, AI2O3, diamond, SiO2, Si3N4, SIGN, AI2O3, TiN, TaN, WN, Ou, Ti, Ni, Au, W.

[0037] According to one example, the chip comprises at least a first pad based on a first material and a first layer based on a second material, and the first planar face is formed by exposed portions of the first pad and the first layer.

[0038] According to one example, the plate comprises at least a second pad based on the first material and a second layer based on the second material, and the chip receiving area is formed by exposed portions of the second pad and the second layer,

[0039] In one example, the method is a direct hybrid chip-to-wafer bonding method.

[0040] According to an example, the first material is chosen from copper, titanium, nickel, gold, tungsten.

[0041] According to one example, the second material is selected from SiO2, Si3N4, SIGN, AI2O3, TiN, TaN, WN.

[0042] In one example, the water film extends onto the second face, remaining within the chip receiving area.

[0043] According to one example, the second alignment marks are arranged in the receiving area of ​​the chip. The alignment is typically performed by inserting a microscope objective between the second alignment marks of the receiving area of ​​the chip, and the first alignment marks of the first planar face of the chip. After alignment, the microscope objective is removed and the chip and the receiving area of ​​the chip are brought into contact via the water film. According to one example, the deposition of the at least one water droplet is configured such that the at least one water droplet does not completely cover said first and / or second alignment marks.

[0044] According to one example, the water film extends onto the second face, outside the chip receiving area. It is not necessary for the water film to be confined to the chip receiving area. In particular, it is not necessary to provide hydrophobic areas around the chip receiving area. This avoids having to specifically prepare the second face of the wafer and / or the first face of the chip for bonding.

[0045] According to one example, the second face has a so-called peripheral zone surrounding the chip receiving zone, said peripheral zone and the chip receiving zone both being hydrophilic. This allows the water film to extend freely outside the chip receiving zone. This allows excess water to be evacuated during the formation of the water film between the first face of the chip and the chip receiving zone on the wafer.

[0046] According to one example, the water film has a thickness less than or equal to 10 μm, preferably less than 1 μm and more preferably less than 100 nm or less than 50 nm. This makes it possible to prevent the chip from being carried by the water outside its alignment position with the receiving area of ​​the chip.

[0047] According to one example, the deposited water droplet initially occupies, before applying the pressure, a surface area S30 on the receiving area of ​​the chip that is much smaller, i.e. at least twice smaller, than the surface area S210 corresponding to the receiving area of ​​the chip. The water droplet may typically be centered on the receiving area of ​​the chip. It is not necessary to cover the entire surface area of ​​the receiving area of ​​the chip when depositing the water droplet. According to one example, the water droplet is deposited on the first planar face of the chip and initially occupies, before applying the pressure, a surface area S30 on the first planar face that is much smaller, i.e. at least twice smaller, than the surface area of ​​said first planar face of the chip.

[0048] In one example, applying pressure spreads the water droplet onto and off the chip receiving area to form the water film between the first face and the chip receiving area. This pressure is applied deliberately, typically by pick and place equipment. This pressure is not solely due to the weight of the chip or the surface tension forces of the water droplet.

[0049] In one example, the second side and / or the first side include alignment marks. This allows the chip to be precisely aligned with the chip receiving area, typically when using industrial pick and place equipment.

[0050] According to one example, the first face includes first alignment marks. According to one example, the second face includes second alignment marks in the receiving area of ​​the chip. According to one example, the first and / or second alignment marks are configured to align the chip with the receiving area of ​​the chip, via a microscope or semi-transparent optics interposed between the chip and the receiving area of ​​the chip. According to one example, the deposited water droplet has a volume chosen such that after natural spreading of the water droplet on the receiving area of ​​the chip, the water droplet does not cover the second alignment marks. According to one example, the deposited water droplet has a volume chosen such that after natural spreading of the water droplet on the first face of the chip, the water droplet does not cover the first alignment marks.

[0051] According to one example, the deposited water droplet has a volume of between 1 pL and 100 pL, preferably between 8 nL and 10 pL.

[0052] According to one example, the deposited water droplet has a volume less than or equal to 100 pL. According to one example, the deposited water droplet has a volume greater than or equal to 8 nL. According to one example, the deposited water droplet has a volume less than or equal to 10 pL.

[0053] In one example, the applied pressure is maintained for a duration of between 100 ms and 10 s, preferably for 1 s. This allows a water film to be formed while reducing the risk of this water film dragging the chip out of the initial alignment position of the chip. This also allows a placement rate compatible with industrial requirements to be achieved.

[0054] In one example, the relative humidity of the atmosphere is controlled so that it is greater than or equal to 80% when handling the chip. This limits the evaporation of the deposited water droplet, before applying pressure to said water droplet. The evolution of the volume of the water droplet is thus better controlled. The volume of the water droplet can thus be reduced. This makes it possible to apply the method to very small chips, for example having a first face surface of the order of 100*100 pm 2 .

[0055] According to one example, the method further comprises a drying step after applying pressure, configured to remove the water film. Contacting, i.e. direct bonding or direct hybrid bonding, is thus carried out. This drying can be carried out by simple storage under ambient atmosphere. Alternatively, it can be carried out under dry atmosphere, in a desiccator for example, or under neutral gas atmosphere, for example under nitrogen, or under argon or under helium. A relative humidity of less than 1% can thus be obtained. It is also possible to carry out this drying by placing the plate under vacuum, for example at 20 mbar pressure at 21°C. It is preferable not to go below the saturated vapor pressure of water. It is also possible to increase the temperature, for example to 75°C. It is preferable not to exceed the boiling temperature of water.According to one example, the method further comprises an annealing step intended to improve or strengthen the bonding, after contacting.

[0056] In the context of the present invention, a method for transferring and bonding one or more chips onto a single wafer is described. This method is preferably intended for industrial implementation, for transferring and bonding a plurality of chips onto each wafer of a plurality of wafers. It belongs to the field of direct hybrid bonding. "Hybrid" means that the bonding surfaces are composed of at least two materials. "Direct" means that the bonding interface corresponds, after final bonding, directly to the two bonding surfaces, without there being a bonding layer, such as a polymer glue, interposed between the two bonding surfaces.

[0057] In the present application, a “chip” typically refers to an integrated circuit comprising microelectronic or optoelectronic components or microelectromechanical systems (MEMS). A “plate” or “wafer” typically refers to a substrate comprising or carrying a plurality of chips. A chip can also, by extension, refer to a piece of plate devoid of components. Alignment can be done with alignment marks or, in the latter case, simply with the precision of machine movement. Alignment is typically done with an accuracy of 100 pm or better.

[0058] The chip receiving area is also called the bonding area in the following.

[0059] 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.

[0060] A layer can also be composed of several sub-layers of the same material or of different materials.

[0061] A substrate, film or layer "based on" a material A means a substrate, film or layer comprising this material A only or this material A and possibly other materials, for example doping elements or alloying elements.

[0062] A water droplet according to the invention is preferably composed of pure or deionized water (DI water). In particular, it does not comprise particles larger than 20 nm. It preferably has a resistivity greater than 1 MOhm.

[0063] The hybrid surface of the chip or wafer can be made of different materials:

[0064] Copper, titanium, nickel, gold, tungsten for example (these metals can be oxidized on the surface or not)

[0065] SiO2, Si3N4, SIGN, AI2O3, TiN, TaN, WN for example.

[0066] The chip surface may not be hybrid and may be composed of a single material (Si, Ge, AsGa, InP, GaN, SiC, AI2O3, diamond, SiO2, Si3N4, SIGN, AI2O3, TiN, TaN, WN, Copper, titanium, nickel, gold, tungsten for example).

[0067] The surface of the plate may not be hybrid and may be composed of a single material (Si, Ge, AsGa, InP, GaN, SiC, AI2O3, diamond, SiO2, Si3N4, SIGN, AI2O3, TiN, TaN, WN, Copper, titanium, nickel, gold, tungsten for example).

[0068] Several embodiments of the invention implementing successive steps of the manufacturing process are described below. Unless explicitly stated, the adjective “successive” does not necessarily imply, even if this is generally preferred, that the steps follow one another immediately, intermediate steps being able to separate them.

[0069] Furthermore, the term "step" means the carrying out of a part of the process, and can designate a set of sub-steps.

[0070] Furthermore, the term "step" does not necessarily mean that the actions carried out during a step are simultaneous or immediately successive. Certain actions of a first step may in particular be followed by actions linked to a different step, and other actions of the first step may be repeated subsequently. Thus, the term "step" does not necessarily mean actions that are unitary and inseparable in time and in the sequence of phases of the process.

[0071] A preferably orthonormal reference frame, comprising the x, y, z axes, is shown in the attached figures. When a single reference frame is shown on the same sheet of figures, this reference frame applies to all the figures in this sheet.

[0072] In this patent application, we will preferably speak of thickness for a layer or a film. The thickness is taken along a direction normal to the main extension plane of the layer or film. Thus, a layer or a film typically has a thickness along z. The relative terms "on", "overcomes", "under", "underlying" refer to positions taken along the z direction.

[0073] An element located "perpendicular to" or "in line with" another element means that these two elements are both located on the same line perpendicular to a plane in which a lower or upper face of a substrate mainly extends, that is to say on the same line oriented vertically in the cross-sectional figures.

[0074] Figure 1 corresponds to an acoustic microscopy image produced after direct hybrid bonding of chips 10 on a plate 20, according to a standard direct hybrid bonding method. Of the nine chips 10 bonded on this area of ​​plate 20, six 10OK chips have normal bonding, without apparent defects, and three 10KO chips have bonding defects D. The method according to the invention aims to eliminate these bonding defects.

[0075] One principle of the method according to the invention is to insert a drop of water between the chip and the plate and to apply pressure on this drop of water so as to form a thin film of water between the chip and the plate. Surprisingly, the alignment of the chip with respect to the plate is maintained in the presence of this thin film of water. When the water film dries, the chip comes into direct contact with the plate and the bonding is done without defects.

[0076] Figures 2 to 6 illustrate certain steps of the direct hybrid bonding process according to the invention.

[0077] As illustrated in Figure 2, a chip 10 comprising copper pads 11 at least partly integrated within a silicon oxide layer 12 is brought by a “Pick and Place” device 1 opposite a plate 20. The face 100 of the chip 10 is flat and is composed in particular of the exposed parts of the copper pads 11 and the exposed parts of the silicon oxide layer 12. The face 100 is therefore a composite or hybrid face having a surface formed in part by the flush copper pads 11 and the parts of the exposed layer 12.

[0078] The face 200 of the plate 20 facing the chip 10 is substantially identical to the face 100, at least at the level of the zone 210 for receiving the chip 10. In this zone 210, the face 200 is flat and is composed in particular of the exposed parts of the copper pads 21 and the exposed parts of the silicon oxide layer 22. At the level of the zone 210, the face 200 is therefore, like the face 100, a composite or hybrid face having a surface formed in part by the copper pads 21 in flush contact and the parts of the exposed layer 22.

[0079] The “Pick and Place” device 1 makes it possible to manipulate the chip 10 so as to align the pads 11 of the chip 10 in line with the pads 21 of the plate 20. This alignment can typically be done by means of first alignment marks positioned on the chip 10 (not illustrated) and / or second alignment marks 40 positioned on the plate 20, in the area 210, as illustrated in a top view in FIG. 3. The alignment is typically carried out using a microscope which is placed between the chip 10 and the plate 20, and which allows simultaneous observation of the first and second alignment marks. After alignment, the microscope is withdrawn and the chip 10 is lowered until it comes into contact with the receiving area 210, crushing the water droplet to form a water film interposed between the chip 10 and the area 210. Pick and place devices are generally equipped with such a microscope.This is the case, for example, of the NEO HB device marketed by the company SET. In Figure 3, the first and second alignment marks are in the form of crosses which overlap after alignment. Alternatively, the first and second alignment marks may be complementary. For example, the second alignment marks 40 consist of a cross (as in Figure 3) and the first alignment marks consist of four separate squares which, after alignment, are positioned in addition to the cross to form a square.

[0080] Before or during the manipulation of the chip 10 by the “Pick and Place” device 1, a drop of water 30 is deposited on at least one of the faces 100, 200 facing each other. According to one possibility, the drop of water 30 is deposited only in the zone 210, for example in the center of the zone 210. According to another possibility, the drop of water 30 is deposited or formed only on the face 100 of the chip 10, for example in the center of the face 100. According to another possibility, a first drop of water 30 is deposited or formed on the face 100, and a second drop of water 30 is deposited or formed on the zone 210. The principle of this method step is to insert at least one drop of water between the face 100 and the zone 210 intended to come into contact with each other.

[0081] The volume of the water drop 30 is preferably quite small. Generally, this volume can be between 1 pL and 100 pL, preferably between 8 nL and 10 pL. These values ​​typically correspond to a drop volume obtained in a single deposition. The drop deposition step can be repeated several times to increase the total volume deposited.

[0082] If the drop is placed before alignment, the volume of the water drop 30 must be adapted according to the surface S210 of the bonding zone, so that the surface S210 of the bonding zone is partially covered at least over 1%, or even 10% or 25% of its surface, or more particularly at least 50% of its surface by the drop, taking into account its natural spreading, but must not cover the alignment marks in order to allow alignment.

[0083] If the drop is arranged after alignment, there is less constraint on its volume.

[0084] In all cases, after crushing the water droplet, the water film 31 thus formed can cover the entire surface S210 of the bonding area (as illustrated in FIG. 4 and FIG. 5) or only a portion (10% or even 25% or even 50%) of this surface. The smaller the volume of the water droplet 30, the faster it will evaporate. The handling of the chip 10 and the precise alignment of the chip 10 with respect to the area 210 can take a certain amount of time, for example approximately a few seconds or tens of seconds. The choice of the volume of the water droplet 30 can take into account this handling time during which the droplet 30 begins to evaporate.The volume of the water droplet 30 is preferably large enough to compensate for water losses through evaporation and to cover the entire surface S210 or at least 1%, or more particularly at least 10, 25 or 50%, of the bonding area under the effect of the pressure exerted by the chip 10 during the following step of the method.

[0085] A compromise in the choice of the volume of the water drop 30 can therefore be found as a function of the size of the chip 10, and / or as a function of the distance between the initial position of the drop and the alignment marks, and / or as a function of the distance between two reception areas 210 of neighboring chips, and / or as a function of the handling and alignment time. According to an example, for a chip 10 of 3*3 mm 2and for alignment marks 40 located 100 pm inside the corners or edges of the zone 210, a reasonable volume for the water drop 30 is approximately 520 nL. According to one possibility, it is as a function of the surface S30 that the drop 30 occupies on the zone 210 during deposition and after its natural spreading that the volume of drop to be dispensed is chosen. The surface S30 that the drop 30 occupies after its natural spreading without specific support is preferably at least two times smaller than the surface S210 of the zone 210, or even at least ten times smaller.

[0086] It is possible to slow down the evaporation kinetics of the water droplet 30 by increasing the relative humidity of the atmosphere of the pick and place machine. This makes it possible to reduce the volume of droplet required. In an atmosphere with a relative humidity value RH of the order of 90% for example, the droplet 30 may have a volume of only a few tens of picoliters (pL). The size of the droplet 30 is thus reduced. This makes it possible to implement the method for very small chips, for example of the order of 100*100 pm 2 .

[0087] When the drop is deposited or formed and the alignment is carried out, the “Pick and Place” device 1 is lowered towards the zone 210. In the case illustrated in Figure 2, the face 100 therefore first comes into contact with the drop 30, which has the effect of spreading the drop 30 over the zone 210.

[0088] The “Pick and Place” device 1 then applies pressure to the drop 30 so that the drop 30 spreads over the entire area 210, or at least over 1% or more particularly over 50% of the area 210, to form a water film 31 between the face 100 and the area 210, as illustrated in Figures 4 and 5. When this pressure is applied, some of the water is typically ejected outside the bonding area 210. The water film 31 extends beyond the area 210. This does not hinder the invention. It is not necessary to confine the water or the water film 31 in the zone 210. The zone 220 at the periphery of the zone 210 may be hydrophilic, like the zone 210. This avoids having to specifically prepare the peripheral zone 220. In particular, it is not necessary to provide hydrophobic zones at the peripheral zone 220 or even a particular topography such as a step which could confine the drop in the zone 210.The implementation of the process is facilitated.

[0089] The pressure exerted by the “Pick and Place” device 1 must be sufficient to obtain a water film 31 of low thickness 631. The thickness 631 of the residual water film 31 is typically less than 5 μm, preferably less than 1 μm and more precisely less than 100 nm or less than 50 nm. To obtain such a thickness 631, a force of between 0.1 N and 1 kN, preferably between 1 N and 300 N, is applied to the “Pick and Place” device 1. A bearing pressure of a few tens to a few thousand pascals (Pa) is thus exerted on the water film 31.

[0090] According to one example, the pressure exerted on the water film 31 is of the order of 10 4 at 3.10 6 Pa for a 10mm*10mm square chip subjected to a force of 1 to 300 N. For a 1mm*1mm chip, the pressure varies from 10 6 at 3.10 8 Pa.

[0091] The pressure exerted on the water film 31 is maintained for a duration of between 100 ms and 10 s, preferably between 500 ms and 5 s. According to one example, the pressure exerted on the water film 31 is maintained for a duration of the order of 1 s. This duration is perfectly compatible with the industrial implementation of the method. The “Pick and Place” device 1 is then removed, typically to handle another chip and perform another bonding according to the method. Advantageously, when the “Pick and Place” device 1 is removed, the alignment between the chip 10 and the area 210 is maintained in the presence of the thin film 31.

[0092] As illustrated in Figure 6, the water film 31 disappears by drying and the chip 10 is in direct contact with the area 210. The direct hybrid bonding of the chip 10 on the area 210 is thus at least partially achieved. The drying of the water film 31 may correspond to simple storage in an atmosphere having a relative humidity (RH) of less than 100%, and preferably less than 50%. It is also possible to carry out the drying in a very dry atmosphere (RH < 1%), and / or in an atmosphere of neutral gas such as nitrogen, argon or helium for example. It is also possible to obtain dry air with a desiccator. It is also possible to carry out this drying by placing the plate under vacuum, in an atmosphere having a pressure lower than ambient pressure, for example at 20 mbar pressure and at an ambient temperature of 21°C. It is preferable not to go below the saturated vapor pressure of water.It is also possible to increase the temperature during drying, for example up to 75°C. It is best not to exceed the boiling temperature of water.

[0093] After drying, a conventional annealing for direct hybrid bonding can be carried out, for example at 300°C for 2 hours. This bond strengthening annealing is advantageously carried out at a temperature above 200°, or even 250°C, and advantageously between 200°C and 400°C, and typically between 250°C and 350°C.

[0094] According to a particular example of implementation of the method, all the steps are carried out in a clean room at 21°C and 45% relative humidity. The hybrid surfaces of the face 100 and the area 210 are composed of copper pads surrounded by silicon oxide, typically according to an embodiment described in the document “Die to Wafer Direct Hybid Bonding Demonstration with High Alignment Accuracy and Electrical Yields, A. Jouve et al., in 2019 International 3D Systems Integration Conference (3DIC), pp. 1-7”. The size of each chip 10 is 3*3mm 2. A NEO HB pick and place machine from SET is used. It is modified to include a NanoJet water droplet dispenser (with a NJ-K-4010 piezoelectric valve) from Microdrop. Before starting the alignment of the chip 10 and the plate 20, a 520 nL water droplet 30 is deposited on the plate 20 in the center of the receiving area 210 of the chip 10. The water droplet 30 does not cover the alignment marks 40 which are located beyond the corners of the bonding area 210. The alignment is carried out in less than 5 s and the chip 10 is brought into contact with the water droplet 30. A force of 20 N is applied to the chip 10, which corresponds to an exerted pressure of approximately 2.2 GPa. The pressure is maintained for 1 s. The process is repeated to bond a plurality of chips 10 to the wafer 20. The wafer 20 is then removed from the pick and place machine and stored in the clean room atmosphere for 24 hours.After storage, annealing at 300°C for 2 hours is carried out in an oven.

[0095] Figure 7 is an image produced using a scanning acoustic microscope SAM (acronym for Scanning Acoustic Microscopy in English) on the plate 20 carrying the chips 10, in order to characterize the quality of the direct hybrid bonding. It is clear that all the chips 10, 10OK are perfectly bonded without interface defects by the method according to the invention.

[0096] In view of the foregoing description, it is clear that the proposed method offers a particularly effective solution for direct hybrid chip-to-plate bonding. The invention is not limited to the embodiments previously described.

Claims

CLAIMS 1. Method for direct bonding of chip (10) to plate (20) comprising at least the following steps: - Provide at least one chip (10) having a first flat face (100), - Provide at least one plate (20) having a second flat face (200) comprising an area (210) for receiving the chip (10), - Manipulate the chip (10) so as to position the first face (100) of the chip (10) opposite the zone (210) for receiving the chip (10) on the second face (200) of the plate (20), aligning the chip with respect to the plate, - Bringing the first face (100) of the chip (10) into contact with the area (210) for receiving the chip (10), so as to bond the chip (10) to the second face (200) of the plate (20), the method being characterized in that it further comprises the following steps: - before contacting, a deposit of at least one drop of water (30) in the zone (210) for receiving the chip (10) on the second face (200) of the plate (20) and / or on the first face (100) of the chip (10), and - when handling the chip (10) and after depositing the drop of water (30), applying pressure to the chip (10) configured to form, from the deposited drop of water (30), a film of water (31) between the first face (100) and the zone (210) for receiving the chip (10), said application of pressure to the chip being configured so that the position of the chip with respect to the plate is not modified due to the presence of water between the chip and the plate - a drying step after application of the pressure, configured to remove the water film (31) and bring the chip into contact with the plate, said drying step being carried out at a temperature strictly lower than 100°C, - after the drying step, an annealing step configured to strengthen the bonding of the chip (10) on the plate (20).

2. Method according to the preceding claim in which: • the chip (10) comprises at least a first pad (11) based on a first material and a first layer (12) based on a second material, and the first planar face (100) is formed by exposed parts of the first pad (11) and the first layer (12), • the plate (20) comprises at least a second pad (21) based on the first material and a second layer (22) based on the second material, and the area (210) for receiving the chip (10) is formed by exposed parts of the second pad (21) and of the second layer (22), the method being a direct hybrid bonding method of chip (10) to plate (20).

3. Method according to the preceding claim in which the first material is chosen from copper, titanium, nickel, gold, tungsten, and in which the second material is chosen from SiO2, Si3N4, SIGN, AI2O3, TiN, TaN, WN.

4. Method according to any one of the preceding claims wherein the first planar face (100) comprises first alignment marks and the second planar face (200) comprises second alignment marks (40), and wherein the alignment of the chip with respect to the plate is carried out via said first and second alignment marks.

5. Method according to the preceding claim in which the second alignment marks (40) are arranged in the area (210) for receiving the chip (10), and in which the deposition of the at least one drop of water (30) is configured so that the at least one drop of water (30) does not completely cover said second alignment marks (40).

6. Method according to any one of the preceding claims in which the water film (31) extends on the second face (200), outside the zone (210) for receiving the chip (10).

7. Method according to any one of claims 1 to 4 in which the water film (31) extends over the second face (200), remaining within the zone (210) for receiving the chip (10).

8. Method according to any one of the preceding claims in which the second face (200) has a so-called peripheral zone (220) around the area (210) for receiving the chip (10), said peripheral zone (220) and the area (210) for receiving the chip (10) both being hydrophilic.

9. Method according to any one of the preceding claims in which the water film (31) has a thickness 631 less than 5 pm, preferably less than 1 pm and more preferably less than 100 nm or less than 50 nm.

10. Method according to any one of the preceding claims in which the deposited water drop (30) initially occupies, before application of the pressure, a surface S30 on the zone (210) for receiving the chip (10) which is much smaller, that is to say at least twice less than the surface S210 corresponding to the zone (210) for receiving the chip (10), and the application of the pressure makes it possible to spread said drop of water (30) on and outside the zone (210) for receiving the chip (10), to form the film of water (31) between the first face (100) and the zone (210) for receiving the chip (10).

11. Method according to any one of the preceding claims in which the drop of water (30) deposited has a volume less than or equal to 100 pL.

12. Method according to any one of the preceding claims in which the drop of water (30) deposited has a volume of between 8 nL and 10 pL.

13. Method according to any one of the preceding claims in which the applied pressure is maintained for a duration of between 100 ms and 10 s.

14. Method according to any one of the preceding claims in which the relative humidity of the atmosphere is controlled so as to be greater than or equal to 80% during handling of the chip (10).

15. Method according to any one of the preceding claims in which the drying step is carried out at room temperature.

16. Method according to any one of the preceding claims in which the annealing step is carried out at a temperature greater than or equal to 300°C for a duration greater than or equal to 2 hours.

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