ELECTRONIC CHIP WITH CONNECTING PILLARS FOR SINTERING ASSEMBLY

An electronic chip including a support and connection pillars, each connection pillar including a trunk including an end portion and an intermediate portion coupling the end portion to the support, and including a collar at the junction between the end portion and the intermediate portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to French application number 2309488, filed Sep. 8, 2023. The content of this application is incorporated herein by reference in its entirety.

TECHNICAL FIELD

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 connection pillars of the electronic chip.

BACKGROUND ART

In an electronic chip, connections are made by inner interconnection networks. To connect an integrated circuit chip to an outer element, these interconnection networks are connected to pillars, generally located on one face of the chip. In this way, it is possible to contact the pillars with conductive areas or connection tracks located on this other element. The element may correspond to a substrate, also known as a package, particularly in the field of power electronics, such as a printed circuit. The element could also correspond to another electronic chip.

An example of a method of assembling an electronic chip to another electronic chip or package comprises forming a block of sinter paste on each pillar, depositing the electronic chip on the other electronic chip or package, and sintering the sinter paste. In some applications, 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 on the other electronic chip or the package is carried out before drying the sinter paste.

SUMMARY OF INVENTION

One embodiment overcomes some or all of the drawbacks of electronic chips comprising known connection pillars.

One embodiment provides an electronic chip comprising a support and connection pillars, each connection pillar comprising a trunk including an end portion and an intermediate portion coupling the end portion to the support and comprising a collar at the junction between the end portion and the intermediate portion.

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

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

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.

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

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

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

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

One embodiment also provides a method of assembling an electronic chip as defined above to another electronic chip or to a package, comprising penetrating the connection pillars into a layer of sinter paste at least up to the collar of each connection pillar, removing the connection pillars from the layer of sinter paste, a block of sinter paste remaining attached to each connection pillar, depositing the electronic chip on the other electronic chip or on the package, and heating to obtain sintering of the blocks of sinter paste.

One embodiment also provides a method of manufacturing an electronic chip as defined above, comprising forming a first photosensitive resin mask comprising, for each connection pillar, a first through opening, depositing the material making up the trunk in the first through openings, forming a second photosensitive resin mask comprising a second through opening in the extension of each first through opening, and depositing the material making up the trunk in the second through openings.

DESCRIPTION OF EMBODIMENTS

For the sake of clarity, only the operations and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail. In particular, the various components of the chips, as well as the inner connections of the chips, are not described in detail.

Unless indicated otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements coupled together, this signifies that these two elements can be connected or they can be coupled via one or more other elements. Furthermore, the terms “insulator” and “conductor” are taken to mean “electrically insulating” and “electrically conductive” respectively.

FIG.1is a schematic, partial side view of an embodiment of an electronic chip10that is to be connected to a package or another electronic chip, not shown. The chip10comprises connection pillars15, also known as connection pads, made of a conductive material. Although two connection pillars15are illustrated inFIG.1, the chip10comprises as many connection pillars15as there are connections to be made (depending on the intended application, only two, several tens or even several thousands of connection pillars15may be present). The chip10comprises, for example, a support12with a face13on which the electrical connections to the outside of the chip10are made. By way of example, support12comprises a substrate, for example in silicon, covered with an interconnection structure comprising conductive elements not shown, for example vias and metallization. Each connection pillar15, for example, is electrically connected to such conductive elements.

Each pillar15comprises a trunk16having an intermediate portion20and an end portion30. The intermediate portion20is located between the support10and the end portion30. The pillar15comprises a collar17at the junction between the intermediate portion20and the end portion30. The intermediate portion20comprises a base22, a coupling face24opposite the base22, and a side wall26coupling the base22to the coupling face24. The end portion30comprises a coupling face32, an end face34opposite the coupling face32, and a side wall36coupling the coupling face32to the end face34. The base22of the intermediate portion20is in direct physical contact with the support12. The coupling face24of the intermediate portion20is coincident with the coupling face32of the end portion30. According to one embodiment, the side wall36of the end portion30further comprises a flared part38on the side of the top face32. According to one embodiment, the side wall26of intermediate portion20further comprises a flared part28on the side of base22.

The side wall26of intermediate portion20is contained between a circular-based inner cylinder Cint of axis Δ and a circular-based outer cylinder Cext of axis Δ, and is in contact with inner cylinder Cint and outer cylinder Cext. According to one embodiment, the coupling face24of the intermediate portion20is substantially perpendicular to the axis Δ. The height H of the intermediate portion20, measured along the axis Δ, is between 10 μm and 100 μm, and is preferably equal to approximately 50 μm. The diameter of the inner cylinder Cint is between 10 μm and 3 mm, and is preferably equal to about 50 μm. The difference between the radius of the outer cylinder Cext and the radius of the inner cylinder Cint is between 1 μm and 100 μm, preferably between 1 μm and 7 μm. According to one embodiment, the pitch between the axes A of adjacent pillars15is between 20 μm and 7 mm, and is preferably equal to approximately 100 μm. According to one embodiment, except in the vicinity of the base22and coupling face24, intermediate portion20is essentially cylindrical in shape with a circular base.

The side wall36of the end portion30is contained between a circular-based inner cylinder Cint′ of axis Δ′ and a circular-based outer cylinder Cext′ of axis Δ′, and is in contact with the inner cylinder Cint′ and the outer cylinder Cext′. The axis Δ is parallel to the axis Δ′. According to one embodiment, the axis Δ′ is coincident with the axis Δ. However, the axis Δ′ can be offset from the axis Δ. The offset between the axis Δ′ and the axis Δ can be between 0 μm and 6 μm. According to one embodiment, the coupling face32of the end portion30is substantially perpendicular to the axis Δ. According to one embodiment, the end face34of the end portion30is substantially perpendicular to the axis Δ. The height H′ of the end portion30measured along the axis Δ′ is between 10 μm and 100 μm, preferably between 10 μm and 40 μm, and is for example equal to approximately 20 μm. The difference between the radius of the outer cylinder Cext′ and the radius of the inner cylinder Cint′ is between 1 μm and 7 μm, preferably between 1 μm and 4 μm. According to one embodiment, except in the vicinity of coupling face32and end face34, end portion30is essentially cylindrical in shape with a circular base.

Trunk16is made of metal, for example copper, nickel, silver, gold or an alloy of these metals.

According to one embodiment, the pillar15further comprises a finishing layer18covering the end face34of the end portion30of the trunk16. The thickness of the finishing layer18is between 10 nm and 1,000 nm. Finishing layer18is made of a conductive material that improves the adhesion of the sinter paste. For example, finishing layer18is made of a metal, in particular gold or silver, and optionally comprises a bonding and/or barrier layer(s), comprising for example platinum (Pt), palladium (Pd), nickel (Ni), titanium (Ti), chromium (Cr), and/or tantalum (Ta), between the material of trunk16and the material of the sinter paste subsequently deposited on pillar15. The finishing layer18also allows oxidation of the end face34of the pillar15to be prevented in the case where the assembly method is not carried out in a neutral or reducing atmosphere.

FIG.2is a partial schematic side view of another embodiment of chip10. Each pillar15of the chip10illustrated inFIG.2comprises all the elements of the pillar15of the chip10illustrated inFIG.1, with the difference that the end portion30of the trunk16does not comprise a flared part38on the side of the end face34.

FIG.3is a partial schematic side view of another embodiment of chip10. Each pillar15of the chip10illustrated inFIG.3comprises all the elements of the pillar15of the chip10illustrated inFIG.1, with the difference that the finishing layer18is not present.

FIG.4is a partial schematic side view of another embodiment of chip10. Each pillar15of the chip10illustrated inFIG.4comprises all the elements of the pillar15of the chip10illustrated inFIG.2, with the difference that the finishing layer18is not present.

FIG.5is an image obtained by scanning electron microscope in perspective view of a pillar15according to one embodiment as described above in relation toFIG.1.

FIG.6is an image obtained by scanning electron microscope of the pillar15shown inFIG.5viewed along the axis Δ from the side of the bonding layer18. In this example, the axis Δ is offset from the axis Δ′.

FIGS.7to10each comprise a left-hand cross-sectional view and a right-hand side view of the structure obtained in successive steps of an embodiment of a method of assembling chip10to another chip or to a package.

FIG.7illustrates the structure obtained after forming a layer50of sinter paste in a cavity52. The thickness of the paste layer50is greater than the height H′ of the end portion30of the pillar15. The thickness of the paste layer50is between 20 μm and 200 μm, and is, for example, equal to approximately 50 μm.

The chip10is positioned above the paste layer50in a vertical direction and at a distance from the paste layer50. The finishing layer18of each pillar15is oriented towards the paste layer50. The dynamic viscosity of the paste layer50is between 20 Pa·s and 60 Pa·s. The thixotropy of the paste layer50is between 3 and 7. Paste layer50is made of a sinterable material. In particular, paste layer50comprises an active filler comprising particles of a metallic material, for example silver, copper, or an alloy of silver and copper. The active filler could also comprise gold and other additives, such as polymers and/or ceramics, which do not participate in the sintering process but facilitate the methods for implementing the sinter paste. The proportion of active filler in the paste layer50is between 60% and 97% by weight.

FIG.8illustrates the structure obtained after the chip10has been pressed into the paste layer50until at least the entire end portion30of each pillar15has penetrated the paste layer50. According to one embodiment, the chip10is moved relative to the paste layer50by means of a handling tool, not shown, for example in a vertical movement (arrow F1). According to one embodiment, chip10is set in motion at a given initial speed. According to one embodiment, a penetration resistance effort of the chip10into the paste layer50is measured, and the movement of the chip10is stopped when the resistance effort exceeds a threshold.

FIG.9illustrates the structure obtained after removing the chip10(arrow F2) from the paste layer50until each pillar15is completely outside the paste layer50. A paste block52remains attached to each pillar15. The finishing layer18is made of a material that favors adhesion of the paste block52. The inventors have shown that the presence of collar17causes that the volume of paste block52remaining attached to pillar15is greater than in the case where collar17is not present. The minimum thickness of the paste block52between each pillar15and the other chip/package54is greater than 4 μm, preferably between 7 μm and 15 μm. A high minimum thickness may be achieved due to the large volume of paste block52carried by each pillar15.

FIG.10illustrates the structure obtained after depositing the chip10on another chip or package54in such a way that each pillar15faces a conductive track55of the other chip or package54, with the paste block52contacting the conductive track55. According to one embodiment, the chip10is placed on the other chip/package54(arrow F3), that causes the paste blocks52to be deformed only by the weight of the chip10. According to one embodiment, chip10is moved towards the other chip/package54by a handling tool, not shown, until a criterion is reached, for example until the distance between the support12of chip10and the other chip/package54reaches a given distance, or until the movement resistance effort of chip10exceeds a threshold. The deformation of the paste blocks52is then also caused by the action exerted by the handling tool on the chip10. The minimum thickness of the paste block52between each pillar15and the other chip/package54after removing the chip10from the paste layer50allows to ensure that sinter paste remains present between each pillar15and the conductive track55despite any height inhomogeneity of the pillars present on the chip10and/or any curvature of the chip10.

The method goes on with a heating step that causes the paste block52to sinter, and the chip10to adhere to the chip or package54, for example at a temperature below 200° C. According to one embodiment, during the heating step, no pressure is exerted on chip10, or only a pressure of less than 1 MPa. According to one embodiment, the heating temperature is between 130° C. and 300° C., preferably between 150° C. and 250° C.

FIG.11is an image obtained by scanning electron microscopy in perspective view of a pillar15at the step previously described in relation toFIG.9, i.e. after removing chip10from paste layer50. The intermediate portion20is at the bottom of the image. The paste block52completely covers the end portion of pillar15.

FIG.12is an image obtained by scanning electron microscopy of a section of a pillar15at the step previously described in relation toFIG.10, i.e. after depositing the chip10on the other chip or package54.

FIGS.13to20are schematic partial sectional views of the structures obtained at successive steps of an embodiment of a method of manufacturing the chip10shown inFIG.1.

FIG.13illustrates the structure obtained after forming an interconnection structure on support12. According to one embodiment, support12comprises a substrate60, for example a semiconductor substrate, covered by an insulating layer62. A conductive track64extends over the insulating layer62. The conductive track64could be connected to regions of the semiconductor substrate60by conductive vias not shown. An insulating layer66extends over the conductive track64and the insulating layer66. For each connection pillar to be made, a through opening68extends through the entire thickness of the insulating layer66, each through opening68exposing a part of the conductive track64. The interconnection structure depends on the desired connections of the connection pillars. In the example illustrated inFIG.13, the two connection pillars to be formed are connected to the conductive track64.

Substrate60may, for example, be made of silicon, silicon carbide (SIC), III-V compounds, in particular gallium nitride (GaN), or diamond. Substrate60could have a single-layer or multi-layer structure, for example of the Silicon-On-Insulator (SOI) type. According to one embodiment, the thickness of substrate60is between 100 μm and 900 μm, for example 200 μm. The insulating layer62is, for example, a silicon oxide layer. According to one embodiment, the thickness of the insulating layer62is between 100 nm and 2 μm, and is for example equal to 200 nm. The conductive track64comprises, for example, a stack of metal layers. According to one embodiment, the metal track64could be performed by whole-wafer depositing metal layers and etching the metal layers to form the metal track64. According to one embodiment, the thickness of the metal track64is between 200 nm and 2 μm, and is for example equal to 500 nm. The metal layers of the metal track are made, for example, of materials selected from copper, a copper alloy, titanium, a titanium alloy, titanium nitride, platinum and a platinum alloy.

FIG.14illustrates the structure obtained after forming a metal layer70over the entire structure obtained in the previous step. In particular, metal layer70extends into the bottom of each opening68in contact with metal track64. According to one embodiment, the thickness of metal layer70is between 10 nm and 1 μm. Metal layer70could comprise a titanium or chromium layer, acting as an adhesion layer, and a copper layer acting as a primer layer for the subsequent formation of pillar15.

FIG.15illustrates the structure obtained after forming a first photosensitive resin mask72on the metal layer70comprising through openings74, each through opening74exposing the metal layer70in one of the openings68. The through openings74could be performed by photolithography steps. The height of the first mask72is equal to the height H of the intermediate portion20of each pillar15.

FIG.16illustrates the structure obtained after forming at least part of the intermediate portion20of each pillar15. According to one embodiment, the part of the intermediate portion20of each pillar15may not completely fill the corresponding opening74. The material making up each pillar15could be deposited by electroplating. The free face75of the part of the intermediate portion20may be set back from the upper face of the first mask72, as illustrated inFIG.16.

FIG.17illustrates the structure obtained after forming a second mask76of photosensitive resin on the first mask72, comprising through openings78, each through opening78exposing one of the openings74of the first mask72. The second mask76can be made of the same photosensitive resin as that used to form the first mask72, and the through openings78could be performed by photolithography steps. The height of the second resin mask78is greater than or equal to the height H′ of the end portion30of each pillar15.

FIG.18illustrates the structure obtained after forming the remaining of the intermediate portion20of each pillar15, forming the end portion30of each pillar15, and forming the finishing layer18of each pillar15. The material making up the trunk16of each pillar15could be deposited by electroplating.

FIG.19illustrates the structure obtained after removing the second mask76and removing the first mask72. This could be performed by dissolving the resin in a solvent or by a dry etching step. The inventors have shown that each pillar15obtained comprises the collar17located at the interface between the first mask72and the second mask76.

FIG.20illustrates the structure obtained after removing the metal layer70around the pillars15.

In the embodiment previously described in relation toFIGS.13to20, forming the trunk16of each pillar15comprises two electrodeposition steps, the first deposition step comprising partial filling of the openings74of the first mask72, and the second deposition step comprising completion of filling of the openings74of the first mask72, and total or partial filling of the openings78of the second mask76. Alternatively, forming the trunk16of each pillar15comprises a single electrodeposition step comprising the total filling of the openings74of the first mask72, and the total or partial filling of the openings78of the second mask76. Such an alternative could be implemented when the form factor of the openings74and78is compatible with the electroplating method.

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these embodiments can be combined and other variants will readily occur to those skilled in the art. Finally, the practical implementation of the embodiments and variants described herein is within the capabilities of those skilled in the art based on the functional description provided hereinabove.