Electronic chip including connection pillars for assembly by sintering

Abstract

Electronic chip comprising connection pillars for assembly by sintering The present description relates to an electronic chip (10) comprising a support (12) and connection pillars (15), each connection pillar (15) comprising a trunk (16) comprising an end portion (30) and an intermediate portion (20) connecting the end portion (30) to the support (12) and comprising a collar (17) at the junction between the end portion (30) and the intermediate portion (20). Figure for abstract: Fig. 1

Description

Title of the invention: Electronic chip comprising connection pillars for assembly by sintering Technical field

[0001] The present description relates to the field of electrical connection between an electronic chip and a package or between two electronic chips, and more particularly to the connection pillars of the electronic chip. Prior art

[0002] In an electronic chip, the connections are made by internal interconnection networks. To connect an integrated circuit chip to an external element, these interconnection networks are connected to pillars, generally located on one face of the chip. Thus, it is possible to bring the pillars into contact with conductive areas or connection tracks located on this other element. The element may correspond to a substrate, also called a package, particularly in the field of power electronics, for example a printed circuit. The element may also correspond to another electronic chip.

[0003] An exemplary method of assembling an electronic chip to another electronic chip or a package includes forming a block of sinter paste on each pillar, depositing the electronic chip onto the other electronic chip or the package, and sintering the sinter paste. For some applications, the sintering is carried out at a temperature below 200°C and without exerting pressure on the electronic chip. For such applications, the step of depositing the electronic chip onto the other electronic chip or the package is carried out before drying the sinter paste. Summary of the Invention

[0004] One embodiment overcomes all or part of the drawbacks of electronic chips comprising known connection pillars.

[0005] One embodiment provides an electronic chip comprising a support and connection pillars, each connection pillar comprising a trunk having an end portion and an intermediate portion connecting the end portion to the support and comprising a collar at the junction between the end portion and the intermediate portion.

[0006] According to one embodiment, the height of the end portion is between 10 μm and 100 μm.

[0007] According to one embodiment, the height of the intermediate portion is between 10 μm and 100 μm.

[0008] According to one embodiment, the difference between the maximum lateral dimension of the collar and the minimum lateral dimension of the end portion is between 1 μm and 7 μm.

[0009] According to one embodiment, the end portion comprises an end face on the side opposite the intermediate portion.

[0010] According to one embodiment, the end portion has a flared shape on the end face side.

[0011] According to one embodiment, the connection pillar comprises a finishing layer covering the end face.

[0012] According to one embodiment, the trunk is made of copper.

[0013] An embodiment also provides a method for assembling an electronic chip as defined above to another electronic chip or to a package, comprising the penetration of the connection pillars into a layer of sintering paste at least up to the collar of each connection pillar, the removal of the connection pillars from the layer of sintering paste, a block of sintering paste remaining attached to each connection pillar, the deposition of the electronic chip on the other electronic chip or on the package and the heating to obtain the sintering of the blocks of sintering paste.

[0014] An embodiment also provides a method for manufacturing an electronic chip as defined previously, comprising the formation of a first photosensitive resin mask comprising, for each connection pillar, a first through opening, the deposition of the material composing the trunk in the first through openings, the formation of a second photosensitive resin mask comprising a second through opening in the extension of each first through opening, and the deposition of the material composing the trunk in the second through openings. Brief description of the drawings

[0015] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0016] [Fig.l] schematically represents an embodiment of a connection pillar of a chip;

[0017] [Fig.2], [Fig.3], and [Fig.4] each schematically represent another embodiment of a connection pillar;

[0018] [Fig.5] and [Fig.6] are each an image obtained by scanning electron microscopy of the connecting pillar of [Fig.l];

[0019] [Fig.7], [Fig.8], [Fig.9], and [Fig. 10] represent structures obtained at successive stages of an embodiment of a method of assembling the chip of [Fig.l] to another chip or to a package;

[0020] [Fig.l 1] is an image obtained by scanning electron microscopy of the connecting pillar of [Fig.l] at the stage of the assembly process illustrated in [Fig.9];

[0021] [Fig. 12] is an image obtained by scanning electron microscopy of a section of the structure obtained at the stage of the assembly process illustrated in [Fig. 10]; and

[0022] [Fig.13], [Fig.14], [Fig.15], [Fig.16], [Fig.17], [Fig.18], [Fig.19], and [Fig.20] represent structures obtained at successive stages of an embodiment of a method for manufacturing the chip of [Fig.l]. Description of the embodiments

[0023] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0024] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, the various components of the chips, as well as the internal connections of the chips, are not detailed.

[0025] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") together, this means that these two elements can be connected or be connected by means of one or more other elements. Furthermore, the terms "insulator" and "conductor" are considered here to mean respectively "electrically insulating" and "electrically conducting".

[0026] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures or to an electronic circuit in a normal position of use.

[0027] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

[0028] [Fig.l] is a partial and schematic side view of an embodiment of an electronic chip 10 which is to be connected to a package or another electronic chip, not shown. The chip 10 comprises connection pillars 15, also called connection pads, made of a conductive material. Although two connection pillars 15 are shown in [Fig.l], the chip 10 comprises as many connection pillars 15 as connections to be made (depending on the intended application, only two, several tens, or even several thousand connection pillars 15 may be present). The chip 10 comprises, for example, a support 12 having a face 13 on which the electrical connections with the exterior of the chip 10 are made. By way of example, the support 12 comprises a substrate, for example made of silicon, covered with an interconnection structure comprising conductive elements not shown, for example vias and metallizations. Each connection pillar 15 is, for example, electrically connected to such conductive elements.

[0029] Each pillar 15 comprises a trunk 16 having an intermediate portion 20 and an end portion 30. The intermediate portion 20 is located between the support 10 and the end portion 30. The pillar 15 comprises a collar 17 at the junction between the intermediate portion 20 and the end portion 30. The intermediate portion 20 comprises a base 22, a connecting face 24 opposite the base 22, and a side wall 26 connecting the base 22 to the connecting face 24. The end portion 30 comprises a connecting face 32, an end face 34 opposite the connecting face 32, and a side wall 36 connecting the connecting face 32 to the end face 34. The base 22 of the intermediate portion 20 is in direct physical contact with the support 12. The connecting face 24 of the intermediate portion 20 is merged with the face connecting 32 of the end portion 30.According to one embodiment, the side wall 36 of the end portion 30 further comprises a flared portion 38 on the side of the upper face 32. According to one embodiment, the side wall 26 of the intermediate portion 20 further comprises a flared portion 28 on the side of the base 22.

[0030] The side wall 26 of the intermediate portion 20 is contained between an internal cylinder with a circular base Cint of axis A and an external cylinder Cext with a circular base of axis A, and is in contact with the internal cylinder Cint and the external cylinder Cext. According to one embodiment, the connecting face 24 of the intermediate portion 20 is substantially perpendicular to the axis A. The height H of the intermediate portion 20, measured along the axis A, is between 10 pm and 100 pm, and is preferably equal to approximately 50 pm. The diameter of the internal cylinder Cint is between 10 pm and 3 mm, and is preferably equal to approximately 50 pm. The difference between the radius of the external cylinder Cext and the radius of the internal cylinder Cint is between 1 pm and 100 pm, preferably between 1 pm and 7 pm. According to one embodiment, the pitch between the axes A of adjacent pillars 15 is between 20 μm and 7 mm, and is preferably equal to approximately 100 μm.According to one embodiment, except near the base 22 and the connecting face 24, the intermediate portion 20 has essentially a cylindrical shape with a circular base.

[0031] The side wall 36 of the end portion 30 is contained between an internal cylinder Cint' with a circular base of axis A' and an external cylinder Cext' with a circular base of axis A', and is in contact with the internal cylinder Cint' and the external cylinder Cext'. The axis A is parallel to the axis A'. According to one embodiment, the axis A' coincides with the axis A. However, the axis A' may be offset relative to the axis A. The offset between the axis A' and the axis A may be between 0 pm and 6 pm. According to one embodiment, the connecting face 32 of the end portion 30 is substantially perpendicular to the axis A. According to one embodiment, the end face 34 of the end portion 30 is substantially perpendicular to the axis A. The height H' of the end portion 30 measured along the axis A' is between 10 pm and 100 pm, preferably between 10 pm and 40 pm, and is for example equal to approximately 20 pm.The difference between the radius of the external cylinder Cext' and the radius of the internal cylinder Cinf is between 1 pm and 7 pm, preferably between 1 pm and 4 pm. According to one embodiment, except near the connecting face 32 and the end face 34, the end portion 30 has essentially a cylindrical shape with a circular base.

[0032] The trunk 16 is made of metal, for example copper, nickel, silver, gold, or an alloy of these metals.

[0033] According to one embodiment, the pillar 15 further comprises a finishing layer 18 covering the end face 34 of the end portion 30 of the trunk 16. The thickness of the finishing layer 18 is between 10 nm and 1000 nm. The finishing layer 18 is made of a conductive material which improves the adhesion of the sintering paste. The finishing layer 18 is for example made of metal, in particular gold or silver, and optionally comprises one or more bonding layers and / or one or more barrier layers, comprising for example platinum (Pt), palladium (Pd), nickel (Ni), titanium (Ti), chromium (Cr), and / or tantalum (Ta), between the material of the trunk 16 and the material of the sintering paste which is subsequently deposited on the pillar 15. The finishing layer 18 also makes it possible to prevent oxidation of the end face 34 of the pillar 15 in the case where the assembly process is not carried out in a neutral or reducing atmosphere.

[0034] [Fig. 2] is a partial and schematic side view of another embodiment of the chip 10. Each pillar 15 of the chip 10 shown in [Fig. 2] comprises all of the elements of the pillar 15 of the chip 10 shown in [Fig. 1] with the difference that the end portion 30 of the trunk 16 does not comprise a flared part 38 on the side of the upper face 34.

[0035] [Fig. 3] is a partial and schematic side view of another embodiment of the chip 10. Each pillar 15 of the chip 10 shown in [Fig. 3] comprises all of the elements of the pillar 15 of the chip 10 shown in [Fig. 1] with the difference that the finishing layer 18 is not present.

[0036] [Fig.4] is a partial and schematic side view of another embodiment of the chip 10. Each pillar 15 of the chip 10 shown in [Fig.4] comprises all of the elements of the pillar 15 of the chip 10 shown in [Fig.2] with the difference that the finishing layer 18 is not present.

[0037] [Fig. 5] is an image obtained by scanning electron microscopy according to a perspective view of a pillar 15 according to the embodiment described previously in relation to [Fig. 1].

[0038] [Fig.6] is an image obtained by scanning electron microscopy of the pillar 15 of [Fig.5] seen along the axis A from the side of the bonding layer 18. In this example, the axis A is offset relative to the axis A'.

[0039] Figures 7 to 10 each comprise a sectional view on the left side and a side view on the right side of the structure obtained in successive steps of an embodiment of a method of assembling the chip 10 to another chip or to a package.

[0040] [Fig.7] illustrates the structure obtained after the formation of a layer 50 of sintering paste in a cavity 52. ​​The thickness of the layer 50 of paste is greater than the height H' of the end portion 30 of the pillar 15. The thickness of the layer 50 of paste is between 20 μm and 200 μm, and is for example equal to approximately 50 μm.

[0041] The chip 10 is placed above the layer 50 of paste relative to a vertical direction and at a distance from the layer 50 of paste. The finishing layer 18 of each pillar 15 is oriented on the side of the layer 50 of paste. The dynamic viscosity of the layer 50 of paste is between 20 Pa.s and 60 Pa.s. The thixotropy of the layer 50 of paste is between 3 and 7. The layer 50 of paste is made of a material capable of being sintered. The layer 50 of paste comprises in particular an active filler comprising particles of a metallic material, for example silver, copper, or an alloy of silver and copper. The active filler may further comprise gold and other additives, for example polymers and / or ceramics, not participating in the sintering but facilitating the processes for implementing the paste to be sintered. The proportion of the active filler in the layer 50 of paste is from 60% to 97% by mass.

[0042] [Fig. 8] illustrates the structure obtained after the chip 10 has been driven into the layer 50 of paste until at least the entire end portion 30 of each pillar 15 has penetrated into the layer 50 of paste. According to one embodiment, the chip 10 is moved relative to the layer 50 of paste by means of a handling tool, not shown, for example according to a vertical displacement (arrow F1). According to one embodiment, the chip 10 is moved at a given initial speed. According to one embodiment, a force resisting the penetration of the chip 10 into the layer 50 of paste is measured and the movement of the chip 10 is stopped when the resistance force exceeds a threshold.

[0043] [Fig. 9] illustrates the structure obtained after the removal (arrow F2) of the chip 10 from the layer 50 of paste until each pillar 15 is entirely outside the layer 50 of paste. A block 52 of paste remains attached to each pillar 15. The finishing layer 18 is made of a material which promotes the adhesion of the block 52 of paste. The inventors have demonstrated that the presence of the collar 17 means that the volume of the block 52 of paste which remains attached to the pillar 15 is greater compared to the case where the collar 17 is not present. The minimum thickness of the block 52 of paste between each pillar 15 and the other chip / package 54 is greater than 4 μm, preferably between 7 μm and 15 μm. A high minimum thickness can be obtained due to the large volume of the block 52 of paste which is carried away by each pillar 15.

[0044] The [Fig. 10] illustrates the structure obtained after the deposition of the chip 10 on another chip or a package 54 in such a way that each pillar 15 is opposite a conductive track 55 of the other chip or the package 54, the block 52 of paste contacting the conductive track 55. According to one embodiment, the chip 10 is placed on the other chip / the package 54 (arrow F3), which causes a deformation of the blocks 52 of paste only under the action of the weight of the chip 10. According to one embodiment, the chip 10 is moved towards the other chip / the package 54 by a handling tool, not shown, until a criterion is reached, for example until the distance between the support 12 of the chip 10 and the other chip / the package 54 reaches a given distance, or until the force resisting the movement of the chip 10 exceeds a threshold. The deformation of the blocks 52 of dough is then also due to the action exerted by the handling tool on the chip 10.The minimum thickness of the paste block 52 between each pillar 15 and the other chip / package 54 after removal of the chip 10 from the paste layer 50 ensures that sintering paste remains present between each pillar 15 and the conductive track 55 despite any inhomogeneity in the height of the pillars present on the chip 10 and / or any curvature of the chip 10.

[0045] The method continues with a heating step resulting in the sintering of the paste block 52 and the adhesion of the chip 10 to the chip or to the package 54, for example at a temperature below 200°C. According to one embodiment, during the heating step, there is no pressure exerted on the chip 10 or only a pressure below 1 MPa. According to one embodiment, the heating temperature is between 130°C and 300°C, preferably between 150°C and 250°C.

[0046] [Fig. 11] is an image obtained by scanning electron microscopy according to a perspective view of a pillar 15 at the step described previously in relation to [Fig. 9], that is to say after the removal of the chip 10 from the layer 50 of paste. The intermediate portion 20 is located at the bottom of the image. The block 52 of paste completely covers the end portion of the pillar 15.

[0047] [Fig. 12] is an image obtained by scanning electron microscopy of a section of a pillar 15 at the step described previously in relation to [Fig. 10], that is to say after the deposition of the chip 10 on the other chip or the package 54.

[0048] Figures 13 to 20 are partial and schematic sectional views of the structures obtained at successive stages of an embodiment of a method for manufacturing the chip 10 of [Fig.l].

[0049] [Fig. 13] represents the structure obtained after the formation of an interconnection structure of the support 12. According to one embodiment, the support 12 comprises a substrate 60, for example a semiconductor substrate, covered with an insulating layer 62. A conductive track 64 extends on the insulating layer 62. The conductive track 64 can be connected to regions of the semiconductor substrate 60 by conductive vias not shown. An insulating layer 66 extends on the conductive track 64 and on the insulating layer 66. For each connection pillar to be produced, a through opening 68 extends over the entire thickness of the insulating layer 66, each through opening 68 exposing a portion of the conductive track 64. The interconnection structure depends on the desired connections of the connection pillars. In the example illustrated in [Fig. 13], the two connection pillars which will be formed are connected to the conductive track 34.

[0050] The substrate 60 is for example a substrate made of silicon, silicon carbide (SiC), III-V compounds, in particular gallium nitride (GaN), or diamond. The substrate 60 may have a single-layer or multi-layer structure, for example a structure of the silicon-on-insulator (SOI) type. According to one embodiment, the thickness of the substrate 60 is between 100 μm and 900 μm, and is for example equal to 200 μm. The insulating layer 62 is for example a layer of silicon oxide. According to one embodiment, the thickness of the insulating layer 62 is between 100 nm and 2 μm, and is for example equal to 200 nm. The conductive track 64 comprises for example a stack of metal layers. According to one embodiment, the metal track 64 can be made by depositing full-plate metal layers and etching the metal layers to form the metal track 64.According to one embodiment, the thickness of the metal track 64 is between 200 nm and 2 μm, and is for example equal to 500 nm. The metal layers of the metal track are for example made of materials chosen from copper, a copper alloy, titanium, a titanium alloy, titanium nitride, platinum, and a platinum alloy.

[0051] [Fig. 14] represents the structure obtained after the formation of a metal layer 70 over the entire structure obtained in the previous step. In particular, the metal layer 70 extends into the bottom of each opening 68 in contact with the metal track 64. According to one embodiment, the thickness of the metal layer 70 is between 10 nm and 1 pm. The metal layer 70 may comprise a layer of titanium or chromium, acting as an adhesion layer, and a layer of copper acting as a primer layer for the subsequent formation of the pillar 15.

[0052] [Fig. 15] represents the structure obtained after the formation of a first mask 72 of photosensitive resin on the metal layer 70 comprising through openings 74, each through opening 74 exposing the metal layer 70 in one of the openings 68. The through openings 74 can be produced by photolithography steps. The height of the first mask 72 is equal to the height H of the intermediate portion 20 of each pillar 15.

[0053] [Fig. 16] represents the structure obtained after the formation of at least a part of the intermediate portion 20 of each pillar 15. According to one embodiment, the part of the intermediate portion 20 of each pillar 15 may not completely fill the corresponding opening 74. The material composing each pillar 15 may be deposited by electrodeposition. The free face 75 of the part of the intermediate portion 20 may be set back relative to the upper face of the first mask 72, as illustrated in [Fig. 16].

[0054] [Fig. 17] shows the structure obtained after forming a second mask 76 of photosensitive resin on the first mask 72 comprising through openings 78, each through opening 78 exposing one of the openings 74 of the first mask 72. The second mask 76 may be made of the same photosensitive resin as that used for forming the first mask 72, and the through openings 78 may be made by photolithography steps. The height of the second resin mask 78 is greater than or equal to the height H' of the end portion 30 of each pillar 15.

[0055] [Fig. 18] represents the structure obtained after the formation of the remainder of the intermediate portion 20 of each pillar 15, the formation of the end portion 30 of each pillar 15, and the formation of the finishing layer 18 of each pillar 15. The material composing the trunk 16 of each pillar 15 can be deposited by electrodeposition.

[0056] [Fig. 19] represents the structure obtained after the removal of the second mask 76 and the removal of the first mask 72. This can be achieved by dissolving the resin in a solvent or by a dry etching step. The inventors have demonstrated that each pillar 15 obtained comprises the collar 17 located at the interface between the first mask 72 and the second mask 76.

[0057] [Fig.20] represents the structure obtained after the removal of the metal layer 70 around the pillars 15.

[0058] In the embodiment described previously in relation to figures 13 to 20, the formation of the trunk 16 of each pillar 15 comprises two deposition steps by electrodeposition, the first deposition step comprising the partial filling of the openings 74 of the first mask 72 and the second deposition step comprising the end of the filling of the openings 74 of the first mask 72 and the total or partial filling of the openings 78 of the second mask 76. As a variant, the formation of the trunk 16 of each pillar 15 comprises a single deposition step by electrodeposition comprising the total filling of the openings 74 of the first mask 72 and the total or partial filling of the openings 78 of the second mask 76. Such a variant can be implemented when the form factor of the openings 74 and 78 is compatible with the electrodeposition method.

[0059] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. Finally, the practical implementation of the described embodiments and variations is within the ability of those skilled in the art from the functional indications given above.

Claims

Claims

1. A method of manufacturing an electronic chip (10) comprising a support (12) and connection pillars (15), each connection pillar (15) comprising a trunk (16) having an end portion (30) and an intermediate portion (20) connecting the end portion (30) to the support (12) and comprising a collar (17) at the junction between the end portion (30) and the intermediate portion (20), the method comprising the formation of a first mask (72) made of photosensitive resin comprising, for each connection pillar (15), a first through opening (74), the deposition of the material composing the trunk (16) in the first through openings (74), the formation of a second mask (76) made of photosensitive resin comprising a second through opening (78) in the extension of each first through opening (74), and the deposition of the material composing the trunk (16) in the second through openings (78).

2. A manufacturing method according to claim 1, wherein the height (H1) of the end portion (30) is between 10 pm and 100 pm.

3. Manufacturing method according to claim 1 or 2, wherein the height (H) of the intermediate portion (20) is between 10 pm and 100 pm.

4. A manufacturing method according to any one of claims 1 to 3, wherein the difference between the maximum lateral dimension of the collar (17) and the minimum lateral dimension of the end portion (30) is between 1 pm and 7 pm.

5. A manufacturing method according to any one of claims 1 to 4, wherein the end portion (30) comprises an end face (34) on the side opposite the intermediate portion (20).

6. A manufacturing method according to claim 5, wherein the end portion (30) has a flared shape (38) on the end face (34) side.

7. A manufacturing method according to claim 5 or 6, wherein the connecting pillar (15) comprises a finishing layer (18) covering the end face (34).

8. A manufacturing method according to any one of claims 1 to 7, wherein the trunk (16) is made of copper.

9. Method for assembling an electronic chip (10) manufactured according to the manufacturing method according to any one of claims 1 to 8 to another electronic chip or to a package (54), comprising the penetration of the connection pillars (15) into a layer (50) of sintering paste at least up to the collar (17) of each connection pillar (15), the removal of the connection pillars (15) from the layer (50) of sintering paste, a block (52) of sintering paste remaining attached to each connection pillar (15) at least over the height (H1) of the end portion (30), preferably over a height equal to 50 μm, the deposition of the electronic chip (10) on the other electronic chip or on the package (54) and the heating to obtain the sintering of the blocks (52) of sintering paste.

10. An assembly method according to claim 9, wherein, during heating to obtain sintering of the blocks (52) of sintering paste, there is no pressure exerted on the electronic chip (10).

11. Assembly method according to claim 9 or 10, wherein the quantity of sintering paste after bonding, between each connection pillar (15) and the other electronic chip or the package (54), is greater than 4 pm, preferably between 7 pm and 15 pm.

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