A method of bonding a chip to a substrate by direct bonding

Abstract

A method for bonding a chip (100) to a substrate (101) by direct bonding includes a stage of providing a support (105) that contacts the chip (100), wherein the chips (100) in contact with the support (105) are separate from each other. The bonding method includes: a stage of forming a liquid film (103) on one side (104) of the substrate (101); a stage of contacting the chip (100) with the liquid film (103), wherein the action of contacting the chip (100) with the liquid film (103) causes the chip (100) to be attracted toward the substrate (101); and a stage of evaporating the liquid film (103) to bond the chip (100) to the substrate (101) by direct bonding.

Description

Technical Field

[0001] The technical field of this invention relates to bonding chips to substrates via direct bonding, particularly in the field of electronics, and more particularly in the field of microelectronics. Background Technology

[0002] The paper "Advances on III-V on Silicon DBR and DFB Lasers for WDM optical interconnects and Associated Heterogeneous Integration 200mm-wafer-scale Technology," presented by S. Menezo et al. at the 2014 IEEE Compound Semiconductor Integrated Circuits Symposium (CSIS), describes a method for bonding chips by directly bonding them to a receiving board using a mechanical jig with cavities for accommodating the chips to be bonded. A drawback of using a mechanical jig with cavities for accommodating chips before bonding is that if the chips do not have the same thickness and if the cavities do not have the same depth, the bonding surfaces of the chips will not be contained in the same plane. For the purpose of bonding the chips to the receiving board, some chips may fail to bond to the receiving board because there is no contact between the chips and the receiving board when the mechanical jig and the receiving board are combined. Furthermore, this chip bonding method cannot precisely align each chip with the receiving board.

[0003] In the case of direct chip bonding to a substrate, self-alignment techniques using capillary action and water droplets can be used to properly position the chips to be bonded, as described, for example, in the paper "Transfer and Non-Transfer Stacking Technologies Based on Chip-to-Wafer Self-Assembly for High-Throughput and High-Precision Alignment and Microbump Bonding" published by Takafumi Fukushima et al. at the IEEE 2015 International Conference on 3D Systems Integration TS7.4.1–TS7.4.4. However, implementing this self-alignment technique remains complex because it requires providing hydrophilic and hydrophobic regions on the chip to be bonded and providing an appropriate amount of water to ensure proper chip positioning during its bonding to the substrate, which can be achieved due to the evaporation of water between the substrate and the chip. Therefore, this solution is difficult to implement, especially if it must be applied to bonding multiple chips to a substrate. Furthermore, this solution presents a significant cost because it requires modifying the chip by forming a hydrophobic structure on it.

[0004] Therefore, there is a need to develop a reliable and easy-to-implement solution for bonding chips to substrates via direct bonding. Summary of the Invention

[0005] The purpose of this invention is to facilitate the bonding of several chips to a substrate.

[0006] Therefore, the present invention relates to a method for bonding a chip to a substrate by direct bonding, the bonding method including a stage of providing a support member in contact with the chip, the chip being separated from each other. The bonding method is characterized by including a stage of forming a liquid film on one surface of the substrate; a stage of contacting the chip with the liquid film, the action of contacting the chip with the liquid film causing the chip to be attracted toward the substrate; and a stage of evaporating the liquid film to bond the chip to the substrate by direct bonding.

[0007] This allows the bonding method to perform chip-to-substrate bonding (also known as collective chip bonding), while horizontal differences between the chips to be bonded can be absorbed via a liquid film. More specifically, horizontal differences are the differences in the horizontal planes between the bonding surfaces of the chips, which are designed to contact the substrate for bonding with it by direct contact.

[0008] Furthermore, bonding methods can include one or more of the following features:

[0009] -The liquid film is a deionized water film;

[0010] - The liquid film formation stage allows the liquid film to be deposited on the surface of the substrate by centrifugation;

[0011] - The stage of bringing the chip into contact with the liquid film is achieved by combining the substrate and the support.

[0012] - The bonding method includes using at least one support disposed between the substrate and the support to stop the bonding operation that brings the chip into contact with the liquid film, thereby causing that, when the bonding is stopped: the chip is in contact with the liquid film, and the liquid film separates each chip from the substrate.

[0013] - The support is a mechanical clamp on which the chip rests;

[0014] - The mechanical fixture includes a cavity, each chip is located in the cavity and protrudes from the cavity, and the bonding method includes a stage of removing the chip from the cavity, which is performed after the chip comes into contact with the liquid film and before the chip is bonded to the substrate;

[0015] - The stage of removing the chip from the cavity is performed by removing the support and the substrate;

[0016] - The bonding method includes an adhesive film on which the chip is bonded, the adhesive film being elastic to deform during the evaporation stage, and the bonding method includes a stage of removing the adhesive film after the chip is bonded to the substrate.

[0017] - The removal of the adhesive film includes stages of treating the adhesive film by heating it or by exposing it to ultraviolet radiation.

[0018] - The bonding method includes positioning the support on a mechanical jig, contacting the substrate with the support after the support has been positioned on the mechanical jig, and contacting the chip with the liquid film at the moment the substrate contacts the support.

[0019] - The bonding method includes bonding the support to the adhesive film, and after the support is bonded to the adhesive film, contacting the support with the substrate, and at the moment the support contacts the substrate, the chip contacts the liquid film.

[0020] - The substrate is kept at a level of ±1 degree, preferably ±0.1 degree, during the evaporation stage.

[0021] Other features and advantages will become apparent from the following detailed description. Attached Figure Description

[0022] A better understanding of the invention will be gained by reading the following detailed description, which is given by way of non-limiting example only and with reference to the accompanying drawings listed below.

[0023] Figure 1A chip is shown bonded to a substrate using the bonding method according to the present invention.

[0024] Figure 2 The stages of the bonding method according to a specific embodiment of the present invention are illustrated graphically.

[0025] Figure 3 The illustration shows a substrate viewed from the side, on which a liquid film is formed.

[0026] Figure 4 The image shows a support for a chip, viewed from the side, which supports the chip to be bonded to a substrate.

[0027] Figure 5 A stage of the bonding method according to a first embodiment of the present invention is shown, wherein, Figure 4 The support components are placed inside the machine.

[0028] Figure 6 The first embodiment illustrates the transfer of the liquid film and the substrate on the support.

[0029] Figure 7 The first embodiment illustrates the clamping of a substrate by an upper support element of a machine.

[0030] Figure 8 The first embodiment shows the movement and separation of the substrate and the support member.

[0031] Figure 9 The first embodiment illustrates the result of liquid film evaporation leading to chip bonding to the substrate.

[0032] Figure 10 A cross-sectional view of a support for a chip, comprising an adhesive film to which the chip is bonded, is shown in the context of a second embodiment of the bonding method.

[0033] Figure 11 It shows Figure 10 Top view of the support component.

[0034] Figure 12 According to the second embodiment, it is shown that... Figure 10 Support components Figure 3 Positioning of the substrate and liquid film in a machine used to perform the bonding method.

[0035] Figure 13 The second embodiment illustrates the contact between a chip bonded to an adhesive film and a liquid film formed on a substrate.

[0036] Figure 14 The second embodiment illustrates the result of liquid film evaporation leading to chip bonding to the substrate.

[0037] Figure 15 The second embodiment illustrates the treatment of the adhesive film of the support for the purpose of separating the adhesive film from the chip.

[0038] Figure 16 The second embodiment illustrates the peeling of the adhesive film, ensuring separation of the adhesive film from the chip.

[0039] Figure 17 The thickness (in micrometers) of the deionized water film that can be obtained by centrifugation deposition on a substrate is shown as a function of centrifugation time (in seconds).

[0040] In these figures, the same reference numerals are used to indicate the same elements. Detailed Implementation

[0041] Direct bonding corresponds to bonding through molecular adhesion, in which two surfaces are bonded together without the use of an intermediate adhesive.

[0042] In this specification, the term "between two values" is understood to mean that the boundary defined by the two values ​​is included within the range of the values ​​under consideration.

[0043] In this specification, the combination of two elements, or the engagement between two elements, corresponds to bringing them closer in space by moving one of the two elements toward the other, which remains fixed, or by moving the two elements together. The same principle applies to the separation of the two elements.

[0044] For example, a method of bonding chip 100 to substrate 101 by direct bonding can achieve the following: Figure 1 As can be seen, chip 100 is bonded to substrate 101. The bonding process can include... Figure 2 The visible stages. An example of a first embodiment of this bonding method is shown in... Figures 3 to 9 The second embodiment of the bonding method is shown, particularly in a side view. Figure 3 as well as Figures 10 to 16 The text shows, in particular, examples of... Figure 10 as well as Figures 12 to 16 Side view of a partial cross-section with support member 105 and Figure 11 Top view.

[0045] Chip 100 may or may not have undergone microelectronics stages (e.g., material deposition, photolithography, etching). For example, a chip that has undergone microelectronics stages can include circuitry and routing levels. Chip 100 can include or be based on silicon, indium phosphide (InP), gallium arsenide (GaAs), silicon carbide (SiC), silicon dioxide, germanium, or sapphire, and these chips 100 can present material layers (e.g., silicon dioxide, silicon nitride, metals (e.g., copper or titanium)) and all other layers known in microelectronics (e.g., hafnium dioxide (HfO2) layer, silicon-on-aluminum (SiOC) layer, aluminum nitride (AlN) layer, or aluminum oxide (Al2O3) layer) on its surface. Chip 100 can be an electronic chip, also known as a "bare die".

[0046] The substrate 101 may preferably include electronic components 102. Figure 1 The electronic component is linked to or connected to, preferably electrically connected to, the chip 100 by directly bonding the chip 100 to the substrate 101. The substrate 101 can be a wafer, also known as a slice (e.g., a silicon wafer, obtained after dicing a silicon ingot), on which a technological stage has been applied to form the electronic component 102. The substrate 101 including the electronic component 102 is also referred to as a functionalized substrate 101. Figure 1 In particular, a chip 100 is shown directly bonded to a substrate 101 including electronic components 102, with each electronic component 102, for example, bonded to only one of the chips 100. According to Figure 1 The non-limiting example shown has each of the eighteen chips 100 connected to a corresponding electronic component 102.

[0047] The bonding method includes a stage E1 in which a liquid film 103 is formed on surface 104 of substrate 101. Therefore, prior to stage E1, the bonding method can include a stage of providing substrate 101. For example, in Figure 3 In this configuration, surface 104 of substrate 101 is the surface on which chip 100 must be bonded via direct bonding. Surface 104 of substrate 101 is preferably planar. The liquid film 103 serves to attract chip 100 toward substrate 101, particularly through capillary action.

[0048] The bonding method also includes a stage E2 of providing a support 105, during which the chip 100 to be bonded to the substrate 101 contacts the support 105. In other words, the stage E2 can provide the support 105 and the chip 100 that subsequently contacts the support 105. Figure 4 and Figure 10Two specific embodiments of the support member 105 are shown, which will be described in more detail below and can be used in the first and second embodiments, respectively. The advantage of this support member 105 is that it can simultaneously present the chip 100 for bonding the chip to the substrate 101, thereby achieving the purpose of jointly bonding these chips 100 to the substrate 101.

[0049] The chips 100 in contact with the support 105 are separated from each other. "Separated chips 100" is understood to mean that these chips 100 are not arranged within a wafer or slice, which makes their formation possible. In particular, the separated chips 100 are chips 100 cut from one or more wafers, which may result in the chips 100 to be bonded to the substrate 101 not all having the same thickness, thus making the co-bonding of these chips 100 to the substrate 101 more difficult.

[0050] The bonding method includes bringing the chip 100 into contact with the liquid film 103 (according to the first embodiment). Figure 6 and according to the second embodiment Figure 13 This leads to stage E3, in which the chip 100 comes into contact with the liquid film 103, resulting in the chip 100 being attracted toward the substrate 101. This attraction is generated by capillary action.

[0051] In particular, once there is contact between the chip 100 and the liquid film 103, the capillary force will cause attraction so that the chip 100 is at an equilibrium distance relative to the substrate 101.

[0052] exist Figure 2 In this context, stage E2 indicates that it follows stage E1, but the order is not important.

[0053] The bonding method also includes a stage E4 in which the liquid film 103 is evaporated to bond the chip 100 to the substrate 101 by direct bonding. Specifically, the evaporation stage E4 evaporates the liquid film 103 in contact with the chip 100. Therefore, at the end of the evaporation stage E4 of the liquid film 103, the chip 100 is bonded to the substrate 101, particularly to surface 104 of the substrate 101, by direct bonding. Figure 9 and Figure 14 The evaporation stage E4, which leads to the bonding of chip 100, is described in the context of the first embodiment by... Figures 8 to 9 The paragraph and in the context of the second embodiment by Figures 13 to 14The paragraph illustrates this. This is because during the evaporation stage E4, the capillary action between the liquid film 103 and the chip 100 keeps the chip 100 fixed relative to the liquid film 103 until the chip 100 contacts the surface 104 of the substrate 100, especially after the evaporation stage E4, which leads to the implementation of direct bonding. In other words, the bonding method can include stage E5, which involves bonding the chip 100 by direct bonding after the evaporation stage E4.

[0054] The evaporation of the liquid film 103 allows for a reduction in the volume of the liquid film 103, while capillary action continues to ensure the attraction of the chip 100 toward the substrate 101.

[0055] Due to the implementation of stages E1, E2, E3, and E4, the use of liquid film 103 can compensate for thickness differences in chip 100 or, more generally, compensate for horizontal differences in the bonding surfaces 106 of chip 100. The bonding surfaces 106 of chip 100 are the surfaces that contact the substrate 101 for bonding chip 100. Each chip 100 therefore includes a bonding surface 106 (…). Figures 4 to 16 Each bonding surface 106 is preferably orthogonal to the direction of thickness measurement of the chip 100 including the bonding surface 106. Since the bonding surfaces 106 do not need to be on the same plane when the chip 100 contacts the support 105, the liquid film 103 can accommodate horizontal differences between the bonding surfaces 106 for the purpose of allowing all chips 100 to contact the substrate 101. Furthermore, contacting the chips 100 with the liquid film 103 can clamp them by capillary action so that the chips and the substrate 101 are subsequently bonded as the liquid film 103 evaporates until the chips 100 contact the substrate 101, thereby producing the desired direct bonding.

[0056] For example, it is possible to Figure 3 In the example seen, the liquid film 103 is preferably a deionized water film. Deionized water has the advantage of leaving no residue after evaporation. The thin film form of deionized water offers the advantages of compatibility with substrate 101 when it is completely hydrophilic or its surface 104 is hydrophilic; and compatibility with chip 100 when it is completely hydrophilic or at least the bonding surface 106 is hydrophilic. Therefore, it eliminates the need to provide a complex structure with both hydrophilic and hydrophobic regions; the bonding method is then readily applicable.

[0057] Preferably, the liquid film 103 is continuous, that is, it exists on the entire surface of the substrate 101, for example, the surface of the face 104 of the substrate 101, and the thickness of the liquid film 103 may vary locally.

[0058] The thickness of the liquid film 103 can be from 10 μm to 100 μm. Of course, the thickness of the liquid film 103 will be adapted to the horizontal differences between the bonding surfaces 106 of the different chips 100, especially to prevent any direct contact between one of the chips 100 and the surface of the substrate 101 before the evaporation stage E4. For example, a liquid film 103 with a thickness of 100 μm can compensate for the horizontal differences between the bonding surfaces 106 of the different chips to be bonded, which can be ±50 μm without actually reaching the required thickness.

[0059] In summary, a solution is needed, preferably for forming a liquid film 103 on the surface 104 of substrate 101, while ensuring an appropriate thickness of the liquid film 103. To meet this need, stage E1 for forming the liquid film 103 enables the liquid film 103 to be deposited on substrate 101 by centrifugation, particularly on the surface 104 of substrate 101. The technique of centrifugal deposition is particularly suitable for obtaining the desired liquid film 103, especially when the liquid film 103 is formed from deionized water. For example, a deionized water film with a thickness on the order of 50 μm to 75 μm can be obtained on substrate 101 by centrifugation for 20 seconds at a speed of 30 rpm. Figure 17 An example of the thickness (thickness of water (μm)) of the liquid film 103 formed from deionized water is given, which can be obtained according to the centrifugation time during this centrifugation process. Therefore, the rotation time and rotation speed of the substrate 101 can centrifugally deposit the liquid film 103 on the substrate 101, thereby controlling the thickness of the liquid film 103, for example, from 10 μm to 100 μm.

[0060] Preferably, the liquid film 103 exhibits a contact angle of less than 10 degrees, preferably less than 5 degrees, on the substrate 101. Similarly, the liquid film 103 exhibits a contact angle of less than 10 degrees, preferably less than 5 degrees, on each of the chips 100. This contact angle provides the advantage of ensuring very good hydrophilicity, thereby exhibiting high capillary force, which is particularly suitable for the implementation of bonding methods.

[0061] The stage E3, which brings the chip 100 into contact with the liquid film 103, can be ensured by bonding the substrate 101 and the support 105. This bonding offers the advantage of simultaneously bonding the chip 100 and the substrate 101, with the aim of bringing these chips 100 into contact with the liquid film 103, subsequently enabling the desired direct bonding due to the evaporation of the liquid film. According to the first embodiment, Figure 6 This demonstrates that this bonding allows chip 100 to contact liquid film 103 formed on surface 104 of substrate 101. In the context of the second embodiment, from... Figures 12 to 13 The paragraph illustrates this combination.

[0062] Compared to not using a liquid film at all, the evaporation of the liquid film 103 makes slow bonding of the chip to the substrate to which it must be bonded possible. Without the liquid film, bonding would therefore be rapid and lead to defects, while the liquid film 103 limits the occurrence of these defects.

[0063] As mentioned above, the evaporation of the liquid film 103 can bring the chip 100 into contact with the substrate 101. Therefore, it is necessary to ensure that at a given moment, the chip 100 is in contact with the liquid film 103, which is then placed between each of the chips 100 and the substrate 101 so that the evaporation of the liquid film 103 brings the chip 100 into contact with the substrate 101. To meet this requirement, the bonding method can include using at least one support 107a, 107b (also referred to as a wedge) arranged between the substrate 101 and the support 105 to stop bonding, thereby ensuring that the chip 100 is in contact with the liquid contact 103, resulting in the chip 100 contacting the liquid film 103 at the moment bonding stops, and the liquid film 103 separating each chip 100 from the substrate 101. Therefore, one or more supports 107a, 107b facilitate stopping bonding at the correct time. Figures 5 to 9 and Figures 12 to 16 The use of two supports 107a and 107b is shown. Subsequently, the slow evaporation of the liquid film 103 can bond the chip 100 and the substrate 101 until a bonding of the chip 100 to the substrate 101 is achieved. This can limit the occurrence of the aforementioned defects and is characterized by allowing the chip to directly contact the substrate without using a liquid film.

[0064] Preferably, when the support 105 and the substrate 101 are joined, each of the support 105 and the substrate 101 maintains a horizontal level of ±1 degree, preferably ±0.1 degrees. This horizontality of the substrate 101 prevents the liquid film 103 from sliding on the substrate 101. This horizontality also offers the advantage of not requiring an excessively thick liquid film 103 to contact all the chips 100. In particular, this horizontality is maintained at least until the chips 100 are directly bonded to the substrate 101. The liquid film 103 can be maintained using capillary forces on the substrate 101, for example, when the substrate 101 is flipped. Horizontality can also be maintained using one or more supports 107a, 107b, and an excessively thick liquid film 103 is not required to contact all the chips 100.

[0065] Therefore, in a preferred embodiment, during the evaporation stage E4, the substrate 101, preferably its flat surface 104, is maintained at a level of ±1 degree, preferably ±0.1 degree, to prevent the liquid film 103 from sliding on the substrate 101, which would also cause the chip 100 to be misaligned relative to the substrate 101.

[0066] The support 105 can be a mechanical clamp, such as one formed of a particularly rigid plate, on which the chip 100 rests. Therefore, the contact between the chip 100 and the substrate 101 can be, for example, a gravity contact, thus eliminating the need to fix the chip 100 to the substrate 101. In the context of the first embodiment, the mechanical clamp serves as the support 105. An advantage of using a mechanical clamp is that techniques for cleaning the chip 100 can be applied before it is bonded to the substrate 101 without degrading the performance of the mechanical clamp supporting the chips 100; for this purpose, the mechanical clamp can be made of silicon, silicon dioxide, sapphire, germanium, silicon carbide, aluminum oxide, or silicon nitride. The clamp can be constructed of only one of these materials or at least coated with one of these materials. One cleaning technique can be O2 plasma, which can remove any hydrocarbon contaminants from the surface of the chip 100. Another cleaning technique can be ultrasonic treatment, which can remove particulate contamination from the chip 100 generated during cutting. Ultrasonic cleaning is a process known to those skilled in the art, for example, as illustrated in the paper “Innovative megasonic cleaning technology evaluated through direct wafer bonding” published by F. Fournel et al. in ECS Transactions, 33(4), 495-500 (2010).

[0067] The mechanical fixture can include cavities 108, each of which contains... Figures 4 to 9 The image schematically shows, with dashed lines, each chip 100 positioned within and protruding from a cavity 108, particularly before stage E3, where the chip 100 contacts the substrate 101. Preferably, each cavity 108 of the mechanical fixture accommodates only one chip 100. In this case, before the chip 100 is bonded to the substrate 101... Figure 8 Before bonding to the substrate 101, the chip 100 is extracted / removed from the cavity 108. Therefore, the bonding method can include a stage of removing the chip 100 from the cavity 108, whereby the chip 100 can be removed from the cavity 108, and the chip 100 removal stage is performed after the chip 100 has contacted the liquid film 103, before bonding the chip 100 to the substrate 101. The cavity 108 can be suitably positioned for bonding the chips 100 to the substrate 101. The fact that the chip 100 protrudes from the cavity 108 allows the liquid film 103 to contact the chip 100 without contacting the support 105, for example, by using the aforementioned supports 107a, 107b. Subsequently, before bonding to the substrate 101... Figure 8Removing chip 100 from cavity 108 previously can prevent chip 100 from being mechanically locked in cavity 108 during bonding. Figure 9 This is because if the chip 100 remains at least partially within the cavity 108 during the bonding process to the substrate 101, it could lead to locking of the substrate 101 relative to the support 105 if multiple chips 100 press against the substrate 101 when in contact with the sidewalls of the cavity 108. The chip 100 can be easily removed from the cavity 108 by removing the substrate 101 and the support 105, preferably by at least a distance equal to the thickness of the thickest chip 100 among those to be bonded to the substrate 101. Of course, during removal, capillary action between the liquid film 103 and the chip 100 ensures retention of the chip 100 within the liquid film 103. Of course, the depth of the cavity 108 is adapted to the chips 100, and especially to their thickness: in order for each chip 100 to protrude from its cavity 108, the thickness of the chip 100 is strictly greater than the depth of the cavity 108 in which the chip 100 is located (the chip 100 extends along its thickness from the bottom of the cavity 108 before contacting the liquid film 103). For example, the cavity 108 can have a depth of 400 μm to 500 μm, such a cavity is suitable for receiving chips 100 with a thickness of 500 μm to 600 μm.

[0068] In particular, each cavity 108 is an open cavity 108, which includes a bottom and a sidewall connecting the bottom to the cavity opening. In this case, each chip 100 resting on the support 105:

[0069] - Its bonding surface 106 is located outside the cavity 108, and

[0070] - A surface that is exposed along the thickness of the chip 100 and opposite its bonding surface 106, which contacts the bottom of the cavity 108.

[0071] For example, in order to remove chip 100 from cavity 108, support 105 and substrate 101 can be removed, for example, by moving support 105 and / or substrate 101. In other words, the stage of removing chip 100 from cavity 108 can be performed by removing support 105 and substrate 101. Therefore, such removal can meet the need to remove chip 100 from cavity 108.

[0072] Alternatively, if the depth of cavity 108 allows, chip 100 can be simply brought into contact with liquid film 103, and the resulting attraction of chip 100 toward substrate 101 makes it possible to extract chip 100 from cavity 108. All chips 100 are then removed from cavity before being bonded to substrate 101.

[0073] The bonding method can include positioning supports 107a and 107b on a mechanical jig when using supports 107a and 107b, and then contacting the substrate 101 with the supports 107a and 107b after positioning the supports 107a and 107b on the mechanical jig. This ensures perfect parallelism and an appropriate distance between the chip 100 and the substrate 101, thereby ensuring that the liquid film 103 will contact the different chips 100 in the same way. In this case, at the moment of contact, that is, when the substrate 101 contacts the supports 107a and 107b, the chip 100 contacts the liquid film 103. Figure 6 ).

[0074] In the context of using a mechanical clamp as a support 105, a machine 109 provided with a lower support element 110 and an upper support element 111 can be used, the upper support element being movable relative to the lower support element 110, for example, by using guide rails 114a, 114b belonging to the machine 109. Figures 5 to 9 Each of the lower support element 110 and the upper support element 111 can also be referred to as a "chuck". In this case, the bonding method allows the support 105 holding the chip 100 to be positioned on the lower support element 110, and the chip 100 to face the upper support element 111. Figure 5 Subsequently, the substrate 101 is positioned relative to the supports 107a and 107b. Figure 6 Before that, position supports 107a and 107b on support member 105. Figure 5 This causes the liquid film 103 to come into contact with the chip 100. Therefore, here the substrate 101 approaches the support 105. The upper support element 111 can then descend along the direction of the lower support element 110. Figure 7 ), until it contacts the substrate 101 to hold it, for example, by suction, as it rises ( Figure 8 To remove the chip 100 from the cavity 108 before removing the substrate 101 and the support 105, so as to remove the chip 100 from the cavity 108 before bonding the chip 100 to the substrate 101. Figure 9 The advantage here is that it ensures the levelness of the substrate 101 to prevent the chip 100 from sliding.

[0075] Supports 107a and 107b may not be used, preferably if the displacement of the upper support element 111 is precisely controlled: the substrate 101 can then be fixed to the upper support element 111, and the support element 111 is then lowered to a selected height so that the liquid film 103 contacts the chip 100. Subsequently, the upper support element 111 is raised to fix the chip 100 with the liquid film 103. Then, the liquid film 103 is allowed to evaporate, thereby bonding the chip 100 to the substrate 101.

[0076] For example, chip 100 protrudes an average of 100 μm from cavity 108 at the surface of the mechanical fixture. Chip 100 can exhibit a variable thickness of ±50 μm. According to this example, supports 107a and 107b can have a thickness of 150 μm to form a spacer separating substrate 101 from support 105 by 150 μm when the supports are in contact with support 105 on one side and substrate 101 on the other. In this case, without liquid film 103, no chip 100 can be pressed onto substrate 101. With liquid film 103 of 100 μm thickness, through capillary action, after liquid film 103 evaporates, all chips 100 are attracted to substrate 101 and bonded to substrate 101.

[0077] According to a separate embodiment of the mechanical clamp, the provided support 105 may include an adhesive film 112, to which the chip 100 is bonded by adhesive bonding. Figures 10 to 15 The adhesive film 112 exhibits elasticity, allowing it to deform during the evaporation stage E4, thus enabling the chip 100 to approach the substrate 101 as the liquid film 103 evaporates. The advantage of using the adhesive film 112 is that the positioning of the chips 100 relative to each other is optimized, while particularly preventing movement of the chips 100 relative to the adhesive film 112 during bonding or evaporation of the liquid film 103; therefore, this results in more precise bonding because any slippage of the chip 100 on the liquid film 103 is avoided compared to using a mechanical jig with a cavity 108. After the chip 100 is bonded to the substrate 101, the bonding method can include a stage of removing the adhesive film 112 relative to the chip 100. Figure 15 and 16 The stage of removing the adhesive film 112 can include a stage of processing the adhesive film 112. Figure 15 This process allows the adhesive film to be separated from the chip 100. For example, this stage can reduce the adhesion of the adhesive film to facilitate its removal, such as by peeling off the adhesive film 112 by pulling it in accordance with arrow F2. Figure 16 ).

[0078] For example, the stage of removing the adhesive film 112 can include a stage of treating the adhesive film 112 by heating the adhesive film 112 or exposing the adhesive film 112 to ultraviolet radiation (by...). Figure 15 The middle arrow F1 points to the adhesive film 112. When the adhesive film 112 is loosened by heat, heating makes it easy to remove. Exposing the adhesive film 112 to ultraviolet radiation can facilitate its removal when the adhesive film loosens due to exposure to UV (short for ultraviolet) radiation.

[0079] When the support 105 includes an adhesive film 112, the adhesive film 112 can be fixed to its periphery by adhering to the guide frame 113 (also called an annulus). Figures 10 to 15 This provides support for the adhesive membrane 112. Figure 10 and Figures 12 to 16 In order to make these figures easier to understand, support 105 is shown along a side section.

[0080] When the support 105 includes an adhesive film 112, the bonding method can include bonding the supports 107a and 107b to the adhesive film 112, and then contacting the supports 107a and 107b with the substrate 101 after they are bonded to the adhesive film 112. In this case, at the moment of contact, that is, at the moment the supports 107a and 107b contact the substrate 101, the chip 100 contacts the liquid film 103, which allows for easy control of the distance and parallelism between the chip 100 and the substrate 101. In other words, the presence of the supports 107a and 107b ensures an appropriate distance between the chip 100 and the substrate 101, thereby ensuring that the liquid film 103 contacts the different chips 100 in the same way. Preferably, the frame 113, the supports 107a and 107b, and the chip 100 are bonded to the same surface of the adhesive film 112. For example, the presence of supports 107a and 107b for the adhesive film 112 bonded to and also bonded to the chip 100 ensures that when the supports 107a and 107b contact the substrate 101, the chip 100 contacts the liquid film 103, without having to take into account the thickness of the adhesive film 112 in the dimensions of the supports 107a and 107b: thus, adhesive films 112 of different thicknesses can be used.

[0081] When using the adhesive film 112, during the process of bonding the support member 105 and the substrate 101 described above, the support member 105 can be placed above or below the substrate 101. Figures 12 to 14 In the example shown, the support member 105 is placed above the substrate 101, thereby connecting the substrate 101 and the support member 105 by displacement of the support member 105 toward the substrate 101, and then the substrate 101 remains fixed. As long as the chip 100 faces the liquid film 103, the support member 105 and the substrate 101 can be reversed, thereby allowing the chip 100 to come into contact with the liquid film 103.

[0082] The machine 109 described above, including the lower support element 110, the upper support element 111, and the guide rails 114a and 114b, can also be used for a support member 105 with an adhesive film 112. However, if the upper support element 111 holds the support member 105 by suction, the suction must not be generated in the area where the chip 100 is attached to the adhesive film 112, so that the adhesive film 112 can deform to move toward the substrate 101 along with the chip 100 during the evaporation of the liquid film 103. Therefore, the bonding method enables:

[0083] - The support member 105, which bonds the chip 100 to the adhesive film 112 by adhering it thereto, can be positioned to contact the upper support element 111, and then the support member 105 is fixed to the adhesive film area without the chip 100 and to contact the frame 113 by the suction of the adhesive film 112. Figure 12 ).

[0084] - Place the substrate 101 on the lower support element 110. Figure 12 ).

[0085] - Optionally, supports 107a and 107b are bonded to adhesive membrane 112. Figure 12 (or positioned on substrate 101.)

[0086] - The upper support element 111 descends toward the lower support element 110 to bring the chip 100 into contact with the liquid film 103; preferably, this descent is restricted by supports 107a, 107b. Figure 13 ).

[0087] -After the liquid film 103 in contact with chip 100 evaporates, chip 100 is bonded to substrate 101. Figure 14 ), and can raise the upper support element 111 so that the assembly formed by the substrate 101, the chip 100 and the support 105 can be removed from the machine 109. Figure 15 ), so that the support 105 can be separated from the chip 100 by removing the adhesive film 112. Figure 16 ).

[0088] When using the adhesive film 112, supports 107a and 107b may not be used. Preferably, if the displacement of the upper support element 111 is precisely controlled, the adhesive film 112 can be fixed to the upper support element 111 only at the bottom of the frame 113, and then the upper support element 111 is lowered to a selected height so that the liquid film 103 contacts the chip 100. Subsequently, it is only necessary to wait for the evaporation of the liquid film 103 and the bonding of the chip 100 without changing the distance between the upper support element 111 and the frame 113. Figure 14 As the liquid film 103 evaporates, the support element 111 can also gradually decrease.

[0089] A specific example of the first embodiment is now described. According to this specific example of the first embodiment, the thickness of three indium phosphide (InP) wafers, each 50 mm in diameter, is measured. These wafers are to be diced to form chip 100. The measured thickness of these three wafers is between 325 μm and 375 μm. Chip 100 is formed by dicing from these three InP wafers. Each of these chips 100 exhibits a 10 mm × 10 mm square profile orthogonal to its thickness. Chip 100 is then placed in a mechanical fixture (…). Figure 4In the cavity 108, the measurement direction of the thickness of the chip 100 is parallel to the measurement direction of the depth of the cavity 108. The mechanical fixture is 200 mm in size. Each cavity 108 has a depth of 250 μm, and each cavity includes a sidewall extending from the bottom of the cavity to the opening of the cavity 108, the sidewall having a 10.2 mm by 10.2 mm square profile orthogonal to the bottom of the corresponding cavity 108. The chip 100 is placed in the cavity 108 by a processing device (also called a "pick-and-place machine") for processing the chip 100 without contacting the bonding surface 106 to be directly bonded to the substrate 101. This processing device can include a pyramid-shaped tool that only contacts the edge of each chip being gripped, a claw-shaped tool that grips each chip through its side-cut edges, or a tool that uses the Venturi effect to grip each chip 100. Subsequently, chip 100 is placed in cavity 108 of the mechanical gripper, and the InP chip can be surface-prepared with O2 plasma for 20 seconds to remove hydrocarbon contamination on chip 100. This preparation can also include removing particulate contamination by ultrasonic treatment of chip 100. This ultrasonic treatment can be performed using ultrasound and a deionized aqueous solution with 2% ammonia, as is known to those skilled in the art, for example, as shown in the paper “Innovative megasonic cleaning technology evaluated through direct wafer bonding” published by F. Fournel et al. in ECS Transactions, 33(4), 495-500 (2010). Optionally, supports 107a, 107b, formed of silicon and 150 μm thick, are placed, particularly at the end of the surface preparation of chip 100, around the surface of the support 105 forming cavity 108. Figure 5 The component is placed on the completely flat lower support element 110 inside the aforementioned machine. Figure 5 The horizontality of the lower support element 110 is preferably ±0.1 degrees. The substrate 101 can also be prepared using conventional direct bonding methods, for example, in the paper "Low Temperature Wafer Bonding" published by F. Fournel et al. in ECS Transactions, 16(8), 475-488 (2008). Subsequently, a thin film of deionized water is deposited on the surface of the substrate 101 to form a liquid film 103. Figure 3A liquid film 103 can be formed using a centrifugation process of 30 rpm for 20 seconds, leaving only a deionized water film with a thickness of approximately 50 μm to 75 μm on the surface of the substrate 101. When the support 105 (mechanical clamp) and the substrate 101 are separated by supports 107a and 107b, they can contact the chip 100. The substrate 101 is immediately flipped over and placed above the mechanical clamp, allowing the chip 100 to contact the liquid film 103. Figure 6 If necessary, this positioning corresponds to placing the substrate 101 on the supports 107a, 107b on the mechanical gripper. Within the machine 109, the suction-type upper support element 111 is lowered (…). Figure 7 The liquid film 103 is formed on the surface of the substrate 101, opposite to the surface 104 on which it is formed. Once the substrate 101 is lifted by the upper support element 111, the upper support element 111 will rise 300 μm while maintaining the levelness of the substrate 101, for example, ±1 degree, to prevent the liquid film 103 from sliding above the surface of the substrate 101. This will produce the effect of misaligning the chip 100 to be bonded to the substrate 101. Once the time required for the liquid film 103 to evaporate has passed (e.g., within 4 hours or within 30 minutes to 6 hours under ambient pressure and temperature of 45% humidity), the chip 100 is directly bonded to the substrate 101. Figure 9 The substrate 101 can be removed from the machine 109.

[0090] A specific example of the second embodiment is now described. According to this specific example of the second embodiment, the thickness of three indium phosphide (InP) wafers, each 50 mm in diameter, is measured. These wafers are to be diced to form chip 100. The measured thickness of each of the three wafers is between 325 μm and 375 μm. Chip 100 is formed by dicing from these three InP wafers. These chips 100 exhibit a 10 mm by 10 mm square profile orthogonal to their thickness. Chip 100 is then placed on an adhesive film 112, which is, for example, sensitive to ultraviolet radiation, and stretched onto a frame 113. Figure 10 and 11 The thickness measurement direction of chip 100 is orthogonal to the plane of adhesive film 112. Such adhesive film 112 can be Lintec's Adwill D-650 UV-sensitive film. Chip 100 can be bonded to adhesive film 112 using the same processing apparatus described above. Subsequently, surface preparation of chip 100 can be performed by exposing the chip to ultraviolet radiation in an ozone-containing atmosphere, for example, for 10 minutes, to remove organic contaminants such as hydrocarbons from chip 100. Subsequently, to prepare the surface of chip 100 for direct bonding, particulate contaminants can be removed by ultrasonic treatment, particularly as described above. Supports 107a and 107b, made of silicon and 400 μm thick, can be placed on adhesive film 112. Figure 12 On the surface of chip 100, especially at the end of the surface preparation, chip 100 is positioned between these supports. The portion of adhesive film 112 that contacts frame 113 remains in contact with upper support element 111 of machine 109, for example, as described above. This contact is achieved by upper support element 111 applying suction force only to this portion of adhesive film 112, and upper support element 111 is completely flat, with a levelness of, for example, ±1 degree. Substrate 101 can also be prepared in a conventional manner using direct bonding. Subsequently, a thin film of deionized water, particularly the pre-prepared one, is deposited on the surface of substrate 101 to form liquid film 103. Figure 3 The system can utilize a centrifugation process of 30 rpm for 20 seconds to leave only a deionized water film with a thickness of approximately 50 μm to 75 μm on the surface of the substrate 101, which can contact the chip 100 when the support 105 and the substrate 101 are separated by supports 107a and 107b. Immediately after forming the liquid film 103, the substrate 101 is placed on the lower support element 110. Figure 12 On the substrate 101, the lower support element 110 is flat and horizontal, for example, ±0.1 degrees. The upper support element 111 is lowered toward the surface 104 of the substrate 101, to which the substrate 100 must be bonded until the supports 107a, 107b contact the surface 104 of the substrate 101. Figure 13 After the chip 100 comes into contact with the liquid film 103, the liquid film 103 evaporates, for example, within 4 hours or within 30 minutes to 6 hours at ambient pressure and temperature and 45% humidity. Once the time required for the liquid film 103 to evaporate has elapsed, the upper support element 111 releases the support 105 to which the chip 100 is adhered, for example, by ceasing its suction and returning to its elevated position. Figure 14 After removing the assembly consisting of support 105, substrate 101, and chip 100 bonded to substrate 101 and support 105 from machine 109, the adhesive film 103 is exposed to ultraviolet radiation in an appropriate manner. Figure 15 ), so as to facilitate peeling (e.g., for Lintec's Adwill D-650 UV-sensitive film, appropriate UV radiation can be 160 mJ / cm2), and then peeling ( Figure 16 ), so as to separate the adhesive film 112 from the chip 100.

[0091] The bonding method according to the invention offers the advantage of providing a technique for collectively transferring the chip 100 so as to bond the chip by direct bonding to the substrate 101, while taking into account the thickness differences between the chips 100, ranging from ±50 μm.

[0092] The bonding method described herein has industrial applications in the field of bonding chips directly to a substrate.

Claims

1. A method of bonding chips to a substrate by direct bonding, the bonding method comprising a stage of providing a support comprising an adhesive film in contact with the chips, the chips being separate from one another in contact with the adhesive film, the bonding method comprising: - placing the support in contact with an upper support element, - placing the substrate on a lower support element, - a stage of forming a liquid film on one face of the substrate, - a stage of bringing the chips into contact with the liquid film, the action of bringing the chips into contact with the liquid film causing an attraction of the chips towards the substrate, - a stage of evaporating the liquid film so as to bond the chips to the substrate by direct bonding, - wherein the upper support element holds the support by suction of the adhesive film, the suction not being generated in the area of the adhesive film to which the chips are attached, so as to enable the adhesive film to deform in order to accompany the chips towards the substrate during the evaporation of the liquid film, wherein the bonding method comprises a stage of separating the upper support element from the adhesive film after the evaporation stage, the adhesive film remaining connected to the chips.

2. The bonding method according to claim 1, wherein The liquid film is a film of deionized water.

3. The bonding method according to claim 1, wherein The stage of forming the liquid film is such that the liquid film is deposited on the face of the substrate by centrifugation.

4. The bonding method according to claim 1, wherein The stage of bringing the chips into contact with the liquid film is performed by coupling the substrate and the support.

5. The bonding method according to claim 1, wherein The bonding method comprises using at least one support arranged between the substrate and the support to stop the coupling operation of bringing the chips into contact with the liquid film, whereby, at the moment of stopping this coupling: - the chips are in contact with the liquid film, and - the liquid film separates each chip from the substrate.

6. The bonding method according to claim 1, characterized in that: the chips are bonded on the adhesive film, - the adhesive film exhibits elasticity, so that the adhesive film deforms during the evaporation stage, - the bonding method comprises a stage of removing the adhesive film after bonding the chips to the substrate.

7. The bonding method according to claim 6, wherein The stage of removing the adhesive film comprises a stage of treating the adhesive film by heating the adhesive film or by exposing the adhesive film to ultraviolet radiation.

8. The bonding method according to claim 5, wherein The bonding method comprises bonding the support to the adhesive film, and bringing the support into contact with the substrate after the support is bonded to the adhesive film, and at the moment of bringing the support into contact with the substrate, the chips are in contact with the liquid film.

9. The bonding method according to claim 1, wherein The substrate remains horizontal to within plus or minus 1 degree during the evaporation stage.

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