Die-to-wafer direct hybrid bonding method

Abstract

Title: Die-to-wafer direct hybrid bonding method The present invention relates to a method for producing a method for manufacturing a semiconductor device comprising the steps of: providing at least one die (10) comprising a first copper pad (11) and a first silicon oxide layer (12); providing a wafer (20) comprising a second copper pad (21) and a second silicon oxide layer (22); handling the die (10) so as to position the face (100) of the die (10) facing the area (210) for receiving the die on the wafer (20) by aligning the first and second pads (11, 21); depositing at least one water droplet (30) in the area (210) for receiving the die and / or on the face (100) of the die (10); and applying pressure from the water droplet (30) onto the die (10) to form a water film (31) between the surface (100) and the area (210) for receiving the die (10).

Description

[Technical Field]

[0001] The present invention relates to 3D integration, more particularly to die-to-wafer direct bonding, and more particularly to die-to-wafer direct hybrid bonding. [Background technology]

[0002] In the field of 3D integration of semiconductor components, methods for transferring and assembling wafers or dies onto other wafers are being developed. Among these methods, direct bonding and more specifically hybrid bonding make it possible to assemble two stacked integrated circuits and / or to establish a direct electrical connection between these two integrated circuits via the bonding interface. This makes it possible to increase the interconnect density of components manufactured by 3D integration.

[0003] In particular, copper / oxide hybrid bonding is an industrial bonding technique that involves the contact of two surfaces, typically consisting of copper pads surrounded by silicon oxide. Therefore, these surfaces, composed of two materials, are called hybrid. The purpose of the bonding is to achieve electrical contact between the copper pads on the two surfaces facing each other. The copper pads typically have a size of a few microns. Therefore, perfect alignment of the two surfaces is necessary before direct bonding. Initially developed for "wafer-to-wafer" bonding, this hybrid bonding has now been expanded to "die-to-wafer" bonding by using so-called "pick-and-place" equipment, as commonly understood by those skilled in the art. This allows for the combination of high placement accuracy and high speed. A document titled "A. Jouve et al., "Die to Wafer Direct Hybrid Bonding Demonstration with High Alignment Accuracy and Electrical Yields," International 3D Systems Integration Conference (3DIC), 2019, pp. 1-7" discloses a die-to-wafer direct hybrid bonding method with high placement accuracy and high yield. The drawback of this method is that the bond defect D is located on a specific die 10, as depicted in FIG. KO This can appear in the following cases: [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] A. Jouve et al., “Die to Wafer Direct Hybrid Bonding Demonstration with High Alignment Accuracy and Electrical Yields”, International 3D Systems Integration Conference (3DIC), 2019, p.1-7 Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, there is a need to reduce or even eliminate bond defects for direct bonding in general and more specifically for die-to-wafer direct hybrid bonding. It is an object of the present invention to fulfill this need. [Means for solving the problem]

[0006] To this end, according to one embodiment, at least the following steps are performed: - providing at least one die having a first flat surface, preferably provided with a first alignment mark; - providing at least one wafer having a second planar surface with an area for receiving a die and preferably having second alignment marks; - handling the die to position a first side of the die facing a die-receiving area on the second side of the wafer by aligning the die with respect to the wafer, preferably via first and second alignment marks; - placing a first surface of the die in contact with an area for receiving the die so as to bond the die onto the second surface of the wafer.

[0007] Advantageously, the method comprises, before the abutting, and preferably before handling the die, the deposition of at least one drop of water on the second side of the wafer in the area intended to receive the die and / or on the first side of the die, the drop not covering the alignment marks at this stage.

[0008] Advantageously, the method also includes applying pressure on the die during handling of the die and after deposition of the water droplets configured to form a water film from the deposited water droplets between the first surface and the area for receiving the die.

[0009] According to another embodiment, at least the following steps are performed: - providing at least one die including at least one first copper pad and a first silicon oxide layer, the die having a first planar surface formed by exposed portions of the first copper pad and the first silicon oxide layer; - providing at least one wafer including at least one second copper pad and a second silicon oxide layer, said wafer having a second planar surface including an area for receiving a die, said area being defined by exposed portions of the second copper pad and the second silicon oxide layer; - handling the die to position a first side of the die facing a die-receiving area on the second side of the wafer by aligning the first and second copper pads; - placing a first surface of the die against an area for receiving the die so as to bond the die onto the second surface of the wafer.

[0010] Advantageously, the method includes depositing at least one water droplet in the area for receiving the die on the second side of the wafer and / or on the first side of the die before abutting, and preferably before handling the die.

[0011] Advantageously, the method also includes applying pressure onto the die during handling of the die and after deposition of the water droplets, configured to form a water film from the deposited water droplets between the first surface and the area for receiving the die.

[0012] Within the scope of the development of the present invention, it has been observed that the formation of a water film by depositing a water droplet and applying pressure onto said droplet advantageously makes it possible to eliminate bonding defects between the die and the wafer.

[0013] In general, the formation of a liquid interface, particularly a water-based one, is to be avoided and / or is counterintuitive when achieving precise alignment of the die facing the wafer: it is reasonably assumed that the presence of water between the die and the wafer could modify the initial alignment typically achieved by "pick and place" type precision industrial equipment.

[0014] Within the scope of the present invention, it has surprisingly been observed that the application of pressure on the water droplets, which allows the formation of a thin water film, makes it possible to protect the initial alignment achieved by the device, so that the formation of the thin water film avoids any misalignment of the die relative to the wafer.

[0015] The presence of water in this thin layer reduces or eliminates bonding defects.

[0016] To avoid bonding defects, those skilled in the art of direct hybrid bonding may consider more complicated solutions, for example, by carrying out handling and abutting in a helium-based vacuum or regulated atmosphere, or also by bending the die during bonding. These solutions impose more constraints on the industrial equipment and are more expensive. They are not kept within the scope of the present invention.

[0017] Therefore, advantageously, the method according to the invention makes it possible to reduce or eliminate joint defects in direct joints and in direct hybrid joints while controlling costs.

[0018] The objects and aims of the present invention, as well as its features and advantages, will be best apparent from the following detailed description of the embodiments, illustrated by the accompanying drawings. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is an acoustic microscope image depicting, from a top view, a bond defect between a wafer and a particular die assembled by direct hybrid bonding according to the prior art. [Figure 2] FIG. 2 depicts, in cross-sectional view, a schematic depiction of a direct hybrid bonding process according to one embodiment of the present invention. [Figure 3] FIG. 3 is a top view that schematically depicts a direct hybrid bonding process according to one embodiment of the present invention. [Figure 4]FIG. 4 depicts, in cross-sectional view, a schematic depiction of a direct hybrid bonding process according to one embodiment of the present invention. [Figure 5] FIG. 5 is a top view that schematically depicts a direct hybrid bonding process according to one embodiment of the present invention. [Figure 6] FIG. 6 depicts, in cross-sectional view, a schematic depiction of a direct hybrid bonding process according to one embodiment of the present invention. [Figure 7] FIG. 7 is an acoustic microscope image depicting a top view of a die assembled on a wafer by direct hybrid bonding according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] The drawings are given by way of illustration and not by way of limitation of the present invention. They constitute primarily schematic representations, intended to facilitate understanding of the present invention, and are not necessarily drawn to scale for practical application. In particular, on the primary diagrams, the thicknesses and / or dimensions of the different layers, patterns, and elements mentioned are not representative of reality.

[0021] Before commencing a detailed review of embodiments of the present invention, optional features are described below that can be used optionally, in conjunction with, or as alternatives.

[0022] According to one example, the first flat surface and the area for receiving the die are based on one and the same material, for example Si, Ge, AsGa, InP, GaN, SiC, Al2O3, diamond, SiO2, Si3N4, SICN, Al2O3, TiN, TaN, WN, Cu, Ti, Ni, Au, W.

[0023] According to one example, the die includes at least one first pad based on a first material and a first layer based on a second material, and the first flat surface is formed by the first pad and an exposed portion of the first layer.

[0024] According to one example, the wafer includes at least one second pad based on the first material and a second layer based on the second material, and the area for receiving the die is formed by the second pad and the exposed portion of the second layer.

[0025] According to one example, the method is a die-to-wafer direct hybrid bonding method.

[0026] According to one example, the first material is selected from the group consisting of copper, titanium, nickel, gold and tungsten.

[0027] According to one example, the second material is selected from the group consisting of SiO2, Si3N4, SICN, Al2O3, TiN, TaN, WN.

[0028] According to one example, the water film spreads across the second surface by remaining in the area for receiving the die.

[0029] According to one example, a second alignment mark is disposed within the area for receiving a die. Alignment is typically performed by inserting a microscope lens between the second alignment mark on the area for receiving a die and the first alignment mark on the first flat surface of the die. After alignment, the microscope lens is removed, and the die and the area for receiving a die are brought into contact with each other via a film of water. According to one example, deposition of at least one water droplet is configured such that the at least one water droplet does not completely cover the first and / or second alignment marks.

[0030] According to one example, the water film spreads over the second side outside the area for receiving the die. It is not necessary for the water film to be confined to the area for receiving the die. In particular, it is not necessary to provide a hydrophobic area around the area for receiving the die. This, in particular, avoids the need to prepare the second side of the wafer and / or the first side of the die to facilitate bonding.

[0031] According to one example, the second surface has a so-called peripheral area around the die-receiving area, and both the peripheral area and the die-receiving area are hydrophilic, which allows the water film to freely spread outside the die-receiving area, which allows excess water to be drained during the formation of the water film between the first surface of the die and the die-receiving area on the wafer.

[0032] According to one example, the water film has a thickness of 10 μm or less, preferably less than 1 μm, more preferably less than 100 nm or less than 50 nm, which makes it possible to avoid the die being moved by the water out of its alignment position with the area for receiving the die.

[0033] According to one example, the deposited water droplets are applied to the surface S corresponding to the area for receiving the die before the application of pressure. 210 a surface S on the area for receiving the die that is much smaller, i.e., at least two times smaller, than 30 Typically, the water droplet may be located in the center of the area for receiving the die. It is not necessary to cover the entire surface of the area for receiving the die during the deposition of the water droplet. According to one example, the water droplet is deposited on the first flat surface of the die, and before the application of pressure, the water droplet occupies a surface S on the first flat surface that is much smaller than the surface of said first flat surface of the die, i.e., at least two times smaller. 30 occupies the first place.

[0034] According to one example, the application of pressure allows a water droplet to spread over and outside the area for receiving the die, forming a water film between the first surface and the area for receiving the die. This pressure is typically applied automatically by a "pick and place" device. This pressure is not solely due to the weight of the die or the surface tension of the water droplet.

[0035] According to one example, the second surface and / or the first surface may include alignment marks, which typically allow for accurate alignment of the die to an area for receiving the die during use of "pick and place" type industrial equipment.

[0036] According to one example, the first surface includes a first alignment mark. According to one example, the second surface includes a second alignment mark in the area for receiving the die. According to one example, the first and / or second alignment mark are configured to align the die in the area for receiving the die through a microscope or semi-transparent lens inserted between the die and the area for receiving the die.

[0037] In one example, the deposited water droplet has a volume selected such that after the water droplet naturally spreads over the area for receiving the die, the water droplet does not cover the second alignment mark. In one example, the deposited water droplet has a volume selected such that after the water droplet naturally spreads over the first surface of the die, the water droplet does not cover the first alignment mark.

[0038] According to one example, the deposited droplets have a volume between 1 pL and 100 μL, preferably between 8 nL and 10 μL.

[0039] In one example, the deposited droplets have a volume of 100 μL or less. In one example, the deposited droplets have a volume of 8 nL or more. In one example, the deposited droplets have a volume of 10 μL or less.

[0040] According to one example, the applied pressure is maintained for a period between 100 ms and 10 s, preferably 1 s, which allows the water film to form, reducing the risk of this water film moving the die out of its initial alignment position, and also allows for a placement speed that meets industrial requirements.

[0041] According to one example, during die handling, the relative humidity of the atmosphere is controlled to be above 80%. This makes it possible to limit the evaporation of the deposited water droplets before applying pressure to said droplets. The increase in the volume of the droplets is therefore better controlled. It is therefore possible to reduce the volume of the droplets. This can be achieved, for example, by forming droplets of 100 x 100 μm. 2This makes it possible to apply the above method to very small size dies having a first surface area of ​​about 1000 nm.

[0042] According to one example, the method further comprises a drying step configured to remove the water film after the application of pressure. Then, the abutment, i.e., direct bonding or direct hybrid bonding, is performed. This drying can be performed in a simple container under ambient atmosphere. Alternatively, drying can be performed under a dry atmosphere in a dryer, for example, or under a neutral gas atmosphere, for example, under nitrogen, argon, or helium. This allows a relative humidity of less than 1% to be obtained. This drying can also be performed by placing the wafer under vacuum, for example, at 21°C and a pressure of 20 mbar. It is preferable not to drop below the saturated vapor pressure of water. It is also possible to raise the temperature to, for example, 75°C. It is preferable not to exceed the boiling point of water.

[0043] According to one example, the method further comprises an annealing step after the abutting, intended to improve or strengthen the bond.

[0044] Within the scope of the present invention, a method for transferring and bonding one or more dies onto a single and unique wafer is described. Preferably, this method is intended for industrial implementation to transfer and bond multiple dies onto each wafer of multiple 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 after final bonding, the bonding interface directly corresponds to the bonding surfaces, without the presence of a bonding layer such as a polymer adhesive inserted between the two bonding surfaces.

[0045] In this application, "die" typically refers to an integrated circuit containing a microelectronic or optoelectronic component, or also an electrochemical microsystem (MEMS). "Wafer" typically refers to a substrate containing or carrying multiple dies. Die also refers to a wafer piece without components. Alignment can be performed using alignment marks or, more recently, simply with the precision of mechanical movements. Alignment is typically performed to an accuracy of 100 μm or better.

[0046] The area for receiving the die is hereinafter also referred to as the bonding area.

[0047] It is specified that within the scope of the present invention, the terms "on", "overlying", "covering", "underlying", "opposite" and their equivalents do not necessarily mean "in contact". Thus, for example, depositing, transferring, joining, assembling or applying a first layer onto a second layer does not necessarily mean that the two layers are in direct contact with one another, but rather means that the first layer at least partially covers the second layer, either by being in direct contact with it or by being separated from it by at least one other phase or at least one other element.

[0048] Furthermore, the layer can consist of several sublayers of one and the same material or of different materials.

[0049] By substrate, film, layer "based on" material A, this means a substrate, film, layer comprising only this material A, or this material A and optionally other materials, for example doping or alloying elements.

[0050] The water droplet according to the invention is preferably composed of pure or deionized water (DI water), in particular does not contain particles with a size greater than 20 nm, and preferably has a resistance greater than 1 Mohm.

[0051] The hybrid surface of a die or wafer can be composed of different materials: for example, copper, titanium, nickel, gold, tungsten, for example (these metals may or may not be oxidizable on the surface), SiO2, Si3N4, SICN, Al2O3, TiN, TaN, WN.

[0052] The surface of the die cannot be a hybrid and can be composed of one single material (e.g., Si, Ge, AsGa, InP, GaN, SiC, Al2O3, diamond, SiO2, Si3N4, SiC, Al2O3, TiN, TaN, WN, copper, titanium, nickel, gold, tungsten).

[0053] The surface of the wafer may not be hybrid and may consist of one single material (e.g., Si, Ge, AsGa, InP, GaN, SiC, Al2O3, diamond, SiO2, Si3N4, SiC, Al2O3, TiN, TaN, WN, copper, titanium, nickel, gold, tungsten).

[0054] Several embodiments of the invention are described below that practice sequential steps in the manufacturing process. Unless specified, the adjective "sequential" does not necessarily imply that the steps immediately follow one another, even if this is generally preferred; intermediate steps may separate them.

[0055] Furthermore, the term "step" refers to the performance of part of a method and can refer to a set of substeps.

[0056] Furthermore, the term "step" does not necessarily imply that actions performed during a step are simultaneous or immediately consecutive. In particular, a particular action in a first step can be followed by an action associated with a different step, and then another action in the first step can be resumed. Thus, the term "step" does not necessarily imply separate and inseparable actions over time and in the sequence of phases of a method.

[0057] A preferred orthonormal system including the x, y, and z axes is depicted in the accompanying drawings. When a single system is depicted on one and the same set of figures, this system applies to all figures in the set.

[0058] In this patent application, thickness will preferably be referred to for a layer or film. The thickness is taken along a direction perpendicular to the main plane of extension of the layer or film. Thus, a layer or film typically has a thickness along the z-axis. The relative terms "above", "overlying", "below", and "underlying" refer to a position taken along the z-axis.

[0059] An element positioned "vertically aligned with" or "to the right of" another element means that these two elements are both positioned on the same line perpendicular to the plane in which the lower or upper surface of the substrate mainly extends, i.e., across the same line oriented perpendicularly into the cross section of the drawing.

[0060] 1 corresponds to an ultrasonic microscope image obtained after direct hybrid bonding of a die 10 on a wafer 20 according to a standard direct hybrid bonding method. On this wafer 20 area, six dies 10 are bonded on the new die 10. OK The die had good bonding with no obvious defects, and three die 10 KO has bonding defects D. The method according to the present invention aims to remove these bonding defects.

[0061] The principle of the method according to the invention is to insert a water droplet between the die and the wafer and apply pressure to this droplet so as to form a thin water film between the die and the wafer. Surprisingly, the alignment of the die to the wafer is preserved even in the presence of this thin water film. During drying of the water film, the die comes into direct contact with the wafer and bonding is carried out without defects.

[0062] 2-6 depict certain steps of the direct hybrid bonding method according to the present invention.

[0063] 2, a die 10 including copper pads 11 at least partially embedded in a silicon oxide layer 12 is presented by a "pick and place" device 1 facing a wafer 20. A face 100 of the die 10 is flat and is composed, among other things, of exposed portions of the copper pads 11 and exposed portions of the silicon oxide layer 12. Face 100 is thus a composite or hybrid surface having a surface formed in part by the copper pads 11 and portions of the exposed layer 12 without creating a step.

[0064] The face 200 of the wafer 20 facing the die 10 is substantially identical to the face 100, at least in the region 210 intended to receive the die 10. In this region 210, the face 200 is flat and consists, in particular, of exposed portions of the copper pads 21 and exposed portions of the silicon oxide layer 22. Thus, in the region 210, the face 200, like the face 100, is a composite or hybrid surface having a surface formed in part by the copper pads 21 and portions of the exposed layer 22 without creating a step.

[0065] The "pick-and-place" device 1 allows handling of the die 10 so as to align the pads 11 of the die 10 vertically with the pads 21 of the wafer 20. This alignment can typically be performed through a first alignment mark (not depicted) located on the die 10 and / or a second alignment mark 40 located on the wafer 20 in area 210, as depicted in a top view in FIG. 3. Alignment is typically performed using a microscope placed between the die 10 and the wafer 20, allowing simultaneous observation of the first and second alignment marks. After alignment, the microscope is removed, and the die 10 is lowered until it abuts the receiving area 210 by flattening a water drop to form a water film interposed between the die 10 and area 210. Pick-and-place devices are generally installed with such a microscope. This is the case, for example, with the NEO HB device commercialized by SET. In FIG. 3, the first and second alignment marks are cross-shaped and overlap after alignment. In a variant, the first and second alignment marks may be complementary, for example, the second alignment mark 40 may consist of a cross (as in FIG. 3) and the first alignment mark may consist of four separated squares, positioned complementary to form a square from the cross after alignment.

[0066] Before or during handling of the die 10 by the "pick and place" device 1, a water droplet 30 is deposited on at least one of the surfaces 100, 200 facing each other. According to one option, the water droplet 30 is deposited only in the area 210, for example in the center of the area 210. According to another option, the water droplet 30 is deposited or formed only on the surface 100 of the die 10, for example in the center of the surface 100. According to another option, a first water droplet 30 is deposited or formed on the surface 100 and a second water droplet 30 is deposited or formed on the area 210. The principle of this step of the method is to insert at least one water droplet between the surface 100 and the area 210 that are intended to be in contact with each other.

[0067] Preferably, the volume of the droplets 30 is very small. Generally, this volume can be between 1 pL and 100 μL, preferably between 8 nL and 10 μL. These values ​​typically correspond to the drop volume obtained in one single deposition. The droplet deposition process can be repeated multiple times to increase the total deposited volume.

[0068] When the droplet is placed before alignment, the volume of the water droplet 30 is the surface S of the joining area. 210 The surface S of the joining area is so covered that at least more than 1%, even 10%, or 25% of its surface, or more specifically at least 50% of its surface is partially covered by the droplet by considering its natural spreading. 210 , but in order to be alignable, the alignment marks must not be covered.

[0069] If the droplets are placed after alignment, there are fewer constraints on their volume.

[0070] In any case, after the flattening of the water droplet, the water film 31 thus formed is applied to the surface S of the joining area (as depicted in FIGS. 4 and 5). 210 It may cover the whole or only a part of this surface (10%, 25%, even 50%).

[0071] The smaller the volume of the water droplet 30, the faster it will evaporate. Handling of the die 10 and its precise alignment with respect to the area 210 can take a certain time, for example, on the order of a few seconds or even tens of seconds. The volume of the water droplet 30 can be chosen to take into account this handling time, at which the droplet 30 begins to evaporate. The volume of the water droplet 30 is preferably such that it compensates for the loss of water due to evaporation and the evaporation of the surface S of the bonding area under the influence of the pressure exerted by the die 10 during the following steps of the method. 210 or at least 1%, or more specifically, at least 10, 25, or 50% of the bond area.

[0072] Thus, a compromise in choosing the volume of the water droplet 30 can be found according to the size of the die 10, and / or according to the distance between the initial position of the droplet and the alignment mark, and / or according to the distance between the areas 210 for receiving two adjacent dies, and / or according to the handling and alignment times. 2 For a die 10 of this size and for an alignment mark 40 located 100 μm inside a corner or edge of the area 210, a reasonable volume of the water droplet 30 is on the order of 520 nL. According to one option, the surface S occupied by the droplet 30 on the area 210 during deposition and after its natural spreading is 30 The dispensed drop volume is chosen according to the surface S occupied by the drop 30 after its natural spreading without any particular compression. 30 is preferably the surface S of the region 210 210 It is at least two times smaller, and even at least ten times smaller.

[0073] The evaporation kinetics of the water droplets 30 can be slowed down by increasing the relative humidity of the atmosphere of the "pick and place" equipment. This allows the required droplet volume to be reduced. In an atmosphere with a relative humidity RH value of around 90%, for example, the droplets 30 may have a volume of only a few tens of picoliters (pL). The size of the droplets 30 is therefore reduced. This can be achieved, for example, by reducing the droplet size to 100 x 100 μm. 2 This allows the method to be implemented for very small die sizes.

[0074] Once the droplet has been deposited or formed, and once alignment has taken place, the "pick and place" device 1 is lowered towards area 210. Thus, in the case depicted in Figure 2, face 100 first comes into contact with droplet 30, which has the effect of spreading droplet 30 across area 210.

[0075] Then, the "pick-and-place" device 1 applies pressure to the droplet 30 so that it spreads over the entire area 210, or over at least 1%, or more specifically, over 50% of the area 210, to form a water film 31 between the surface 100 and the area 210, as depicted in FIGS. 4 and 5 . During the application of this pressure, some of the water is typically expelled outside the bonding area 210. The water film 31 spreads beyond the area 210. This does not interfere with the present invention. It is not necessary to confine the water or the water film 31 to the area 210. The area 220 surrounding the area 210 can be hydrophilic like the area 210. This avoids the need to specially prepare the surrounding area 220. In particular, it is not necessary to provide hydrophobic areas or even specific topography, such as steps, in the surrounding area 220 that would allow the droplet to be confined to the area 210. This makes the above method easier to implement.

[0076] The pressure exerted by the "pick and place" device 1 is 31 The thickness of the remaining water film 31 must be sufficient to obtain a thickness e 31 is typically less than 5 μm, preferably less than 1 μm, and more specifically less than 100 nm or less than 50 nm. 31 To obtain this, a force between 0.1 N and 1 kN, preferably between 1 N and 300 N, is applied to the "pick and place" device, so that a pressing pressure of several tens to several thousands of Pascals (Pa) is exerted on the water film 31.

[0077] According to one example, the pressure exerted on the water film 31 for a 10 mm x 10 mm square die resulting in a force of 1 to 300 N is 10 4 ~3×10 6 For a 1 mm x 1 mm die, the pressure is about 10 6 ~3×10 8 Varies with Pa.

[0078] The pressure exerted on the water film 31 is maintained for a period of 100 ms to 10 s, preferably 500 ms to 5 s. According to one example, the pressure exerted on the water film 31 is maintained for a period of about 1 s, which is perfectly compatible with the industrial implementation of the method. The "pick and place" device 1 is then removed, typically to go to another die, handle it, and perform another bonding according to the method. Advantageously, during removal of the "pick and place" device 1, the alignment between the die 10 and the region 210 is preserved by the presence of the thin film 31.

[0079] As depicted in FIG. 6, the water film 31 disappears upon drying, and the die 10 is in direct contact with the region 210. Thus, direct hybrid bonding of the die 10 on the region 210 is at least partially achieved. Drying of the water film 31 can correspond to a simple container in an atmosphere with a relative humidity (HR) of less than 100%, and preferably less than 50%. Drying in a very dry atmosphere (HR<1%) and / or in a neutral gas atmosphere, such as nitrogen, argon, or helium, is also possible. Dry air can also be obtained using a dryer. This drying can also be performed by placing the wafer under vacuum in an atmosphere with a pressure less than ambient pressure, e.g., 20 mbar at an ambient temperature of 21° C. It is preferable not to lower the temperature below the saturated vapor pressure of water. During drying, it is also possible to increase the temperature, e.g., to 75° C. It is preferable not to exceed the boiling point of water.

[0080] After drying, conventional annealing for direct hybrid bonding may be performed, for example, for 2 hours at 300° C. This bond-reinforcing annealing is advantageously performed at temperatures above 200° C., even 250° C., and advantageously between 200° C. and 400° C., and typically between 250° C. and 350° C.

[0081] According to a specific example of implementation of the method, all steps are carried out in a clean room at 21° C. and 45% relative humidity. The hybrid surfaces of face 100 and region 210 consist of copper pads surrounded by silicon oxide, typically according to the embodiment described in the document "A. Jouve et al., "Die to Wafer Direct Hybrid Bonding Demonstration with High Alignment Accuracy and Electrical Yields", International 3D Systems Integration Conference (3DIC), 2019, pp. 1-7." The size of each die 10 is 3×3 mm. 2 A SET NEO HB "pick and place" machine was used. It was modified to include a Microdrop NanoJet water droplet dispenser (using an NJ-K-4010 piezoelectric valve). Before alignment of the die 10 and wafer 20 began, a 520 nL water droplet 30 was deposited on the wafer 20 in the center of the die 10 receiving area 210. The droplet 30 did not cover the alignment marks 40 located beyond the corners of the bonding area 210. Alignment was performed for at least 5 seconds, and the die 10 was then brought into contact with the water droplet 30. A force of 20 N was applied to the die 10, which corresponds to a pressure of approximately 2.2 GPa. The pressure was maintained for 1 second. The process was repeated to bond multiple dies 10 onto the wafer 20. The wafer 20 was then removed from the "pick and place" machine and stored in a clean room atmosphere for 24 hours. After storage, it was annealed in a furnace at 300°C for 2 hours.

[0082] FIG. 7 shows an image obtained using a scanning acoustic microscope (SAM) on a wafer 20 carrying dies 10 to characterize the quality of the direct hybrid bond. OK It is clearly shown that the method according to the present invention achieves perfect bonding without any interfacial defects.

[0083] In view of the above description, it is clearly evident that the proposed method provides an effective solution, especially for die-to-wafer direct hybrid bonding.

[0084] The present invention is not limited to the above embodiments. [Explanation of symbols]

[0085] 1 device 10 Die 11 First copper pad 12 First silicon oxide layer 20 wafers 21 Second copper pad 22 Second silicon oxide layer 30 water drops 31 Water film 40 Second Alignment Mark 100 1st flat surface 200 2nd flat surface 210 Joint area 220 Surrounding Area

Claims

1. At least the following steps: - providing at least one die (10) having a first flat surface (100); - providing at least one wafer (20) having a second planar surface (200) including an area (210) for receiving said die (10); handling the die (10) by aligning it with respect to the wafer so that the first side (100) of the die (10), facing the area (210) for receiving the die (10), is located on the second side (200) of the wafer (20); - placing the first surface (100) of the die (10) against the area (210) for receiving the die (10) so as to bond the die (10) onto the second surface (200) of the wafer (20); A die (10) to wafer (20) direct bonding method comprising: The method comprises the following steps: - depositing at least one water droplet (30) in the area (210) intended to receive the die (10) on the second side (200) of the wafer (20) and / or on the first side (100) of the die (10) before the abutment; - application of pressure on the die (10) during the handling of the die (10) and after deposition of the water droplets (30) configured to form a water film (31) from the deposited water droplets (30) between the first surface (100) and the area (210) for receiving the die (10), the application of pressure being configured such that, due to the presence of water between the die and the wafer, the application of pressure on the die does not change the position of the die relative to the wafer; the second surface (200) has a so-called peripheral area (220) around the area (210) for receiving the die (10), and both the peripheral area (220) and the area (210) for receiving the die (10) are hydrophilic; and a drying step after the application of pressure to remove the water film (31) and bring the die into contact with the wafer, said drying step being carried out at a temperature strictly below 100°C; - after said drying step, an annealing step configured to strengthen said bonding of said die (10) on said wafer (20).

2. the die (10) comprises at least one first pad (11) based on a first material and a first layer (12) based on a second material, the first flat surface (100) being formed by the first pad (11) and the exposed portion of the first layer (12); the wafer (20) comprises at least one second pad (21) based on the first material and a second layer (22) based on the second material, the area (210) for receiving the die (10) being formed by the second pad (21) and the exposed portion of the second layer (22), The method of claim 1, wherein the method is a die-to-wafer direct hybrid bonding method.

3. The first material is selected from the group consisting of copper, titanium, nickel, gold, and tungsten, and the second material is SiO ２ , Si ３ N ４ , SICN, Al ２ O ３ 3. The method according to claim 2, wherein the material is selected from the group consisting of TiN, TaN, and WN.

4. 2. The method of claim 1, wherein the first flat surface (100) includes a first alignment mark and the second flat surface (200) includes a second alignment mark (40), and the alignment of the die to the wafer is performed via the first and second alignment marks.

5. 5. The method of claim 4, wherein the second alignment mark (40) is disposed within the area (210) for receiving the die (10), and the deposition of the at least one water droplet (30) is configured such that the at least one water droplet (30) does not completely cover the second alignment mark (40).

6. 2. The method of claim 1, wherein the water film (31) extends over the second surface (200) outside the area (210) for receiving the die (10).

7. 2. The method of claim 1, wherein the water film (31) spreads across the second surface (200) by remaining in the area (210) for receiving the die (10).

8. The water film (31) has a thickness e of less than 5 μm, preferably less than 1 μm, and more preferably less than 100 nm or less than 50 nm. ３１ 2. The method of claim 1, comprising:

9. The deposited water droplets (30) are formed on the surface S corresponding to the area (210) for receiving the die (10) before the application of pressure. ２１０ a surface S on the area (210) for receiving the die (10) that is much smaller than ３０ 2. The method of claim 1, wherein the first surface (100) is initially occupied by a pressure application means, and the application of pressure makes it possible to spread the water droplet (30) over and outside the area (210) for receiving the die (10) to form the water film (31) between the first surface (100) and the area (210) for receiving the die (10).

10. The method of claim 1 , wherein the deposited droplets (30) have a volume of 100 μL or less.

11. The method of claim 1, wherein the deposited droplets (30) have a volume between 8 nL and 10 μL.

12. The method of claim 1 , wherein the applied pressure is maintained for a period of between 100 ms and 10 s.

13. 2. The method of claim 1, wherein the relative humidity of the atmosphere is controlled to be greater than or equal to 80% during the handling of the die (10).

14. The method of claim 1 , wherein the drying step is carried out at ambient temperature.

15. 10. The method of claim 1, wherein the annealing step is carried out at a temperature of 300°C or greater for a period of 2 hours or greater.

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