JP4416574B2 - Substrate manufacturing method and bonding method - Google Patents

Description

  The present invention relates to a method and a structure for bonding minute (micro) electrodes provided on a substrate, that is, bonding between electrodes between a bump and a pad by bonding between the substrates.

  In recent years, with the increase in functionality and reduction in size and weight of MEMS (Micro-Electric-Micro-System), the elements themselves have become more complex and difficult to manufacture. For this reason, it is necessary to fabricate the electronic circuit and the MEMS on different substrates, and then electrically bond the wiring electrodes of the two substrates to each other and simultaneously integrate the two substrates.

  However, in bonding between substrates, it was difficult to bond all the minute electrodes formed on both substrates simultaneously.

  In Patent Document 1, bumps made of solder balls as surface mounting type semiconductor packaging, and bumps in which granular refractory metal is scattered on the upper surface of the bumps are pressed between opposing bumps, and the oxide film on the bump surface is formed with granular metal. The bumps are pierced and joined by heating.

Further, in Patent Document 2, tin / lead eutectic solder is reflowed in a nitrogen atmosphere reflow furnace to form a bump into a hemispherical shape and used as a bonding bump.
JP-A-9-167773 JP 11-163036 A

  However, since the low melting point metal In ball disclosed in Patent Document 1 described above is used, it is easy to form a hemispherical bump, and the bonding between the bump and the pad is made of In-Pd-Au. However, it is not easy to form bumps with fine dimensions because In is once melted to form hemispherical bumps. It is also possible to join under heating. It is also conceivable that distortion due to internal stress caused by the difference in linear expansion coefficient between the joined bodies is generated in the process of lowering the temperature to room temperature and this affects the dimensional accuracy.

  Further, the bump formation using the soft solder alloy disclosed in Patent Document 2 described above also forms hemispherical bumps by heating and melting means. In addition, since the bonding between the bumps / pads is also performed under heating, distortion due to the difference in linear expansion coefficient is generated, which may affect the dimensional accuracy.

Accordingly, the present invention consists face-centered cubic metal, the surface area of the bump side than the surface area of the bump top surface is rather large, electrode bumps grooves in the center part of the surface of the bump top is formed is formed by plating And a step of pressing the electrode bumps from above with a flat plate to make the upper surface of the electrode bumps hemispherical. A manufacturing method is provided.

  In the present invention, a pressing force is applied to Au bumps formed by plating on circuit terminals of a wiring board using a pressing plate. This causes slip deformation through a transition line in the slip system in which a shear stress greater than the yield shear stress acts in the slip system inherent to the material from the bump side surface, and the transition line extends from the bump side surface and the surface. Each time it exits, plastic deformation proceeds. For this reason, in the case of a bump having a large aspect ratio, the surface area is the largest on the side surface of the bump, the transition line tends to come out from the side surface of the bump, and plastic deformation is likely to occur. On the contrary, in the bump central portion that is far from the bump surface, it is difficult for the transition line to come off, so that large plastic deformation is difficult to occur, and elastic deformation becomes dominant. Therefore, when the pressing force acting on the bump is removed, the plastic deformation is large on the side surface of the bump, and conversely, it is small at the central portion of the bump. From the above, as a result, the bump is formed in a hemispherical shape.

  In the pressing process, it is possible to flatten and smooth the irregularities on the bump surface and the concave grooves that are inevitably produced in the center of the bump.

  After the bump surface is smoothed and hemispherical by the above method, the bumps that are work-hardened in the plastic deformation process are softened by heat treatment, so that the plastic deformability of the bumps can be increased during the main joining.

  By bringing the bump and the pad into contact and applying a pressing force between the bump and the pad, room temperature bonding can be performed at room temperature without heating. For this reason, it is possible to effectively bond the bumps without melting them and without causing distortion due to the difference in linear expansion coefficient.

  Further, in the normal temperature bonding process, when a load is applied, the contact between the pad and the bump starts from the convex portion of the bump hemisphere, and gradually proceeds in the radial direction of the bump as the applied load increases. Occurs.

  For this reason, since the non-joining part in the bump center part is eliminated and joining on the entire bump surface is possible, a large joining strength can be obtained.

  The present invention will be described more specifically below.

  1, 2, 3, 4, 5, 6, 7, and 8 are drawings that clearly illustrate the features of the present invention. In FIG. 1, 1 is one Si substrate and 2 is one. An insulating film made of a Si oxide film formed on the Si substrate 1, 3 is an electrical wiring made of Al formed on the insulating film 2, and 4 is an insulator formed on part of the insulating film 2 and the wiring 3. 5 is a bump made of Au that is electrically coupled to the wiring 3, 6 is a groove that must be generated by Au plating on the top of the Au bump 5, and 7 is a bump on the top of the bump 5. Surface, 8 is a pressing plate for pressing the upper part of the bump 5, 9 is an applied load acting on the pressing plate, 10 is a removing load for removing the pressing plate after pressing the pressing plate 8, and 11 is the other The Si substrate 12 is an electrode made of Au formed on the other Si substrate 11. Head, 14 shows a sliding surface where plastic deformation occurs accompanied by sliding the crystal surface through the transfer line when pushed bump 5 at an applied load of 9 by the pressing plate 8.

  Next, in the above configuration, the bump 5 formed by Au plating has a depth corresponding to the thickness obtained by subtracting the thickness of the wiring 3 from the thickness of the passivation film 4 in the Au plating step as shown in FIG. Since the groove 6 is inevitably generated, an applied load 9 is first applied on the bump 5 via a pressing plate 8 made of a flat plate as shown in FIG. When the applied load 9 is further increased, the bump 5 gradually increases in plastic deformation as seen in FIG. A transition line generated on the slip surface inside the material is easily removed from the side surface of the bump 5 which is not restrained, and plastic deformation occurs when the transition line comes out. Since the bump 5 made of Au is a face-centered cubic crystal, the slip system in which plastic deformation occurs is four equivalent planes {111} and three equivalent slip directions <110>. There is a slip system, and the slip of the slip surface 14 (FIG. 4) on the crystal plane having the slip system caused by the shear stress causes the bump 5 to be in a direction perpendicular to the applied load direction, that is, the radius of the bump 5. Plastic deformation is performed so as to increase, and at the same time, plastic deformation is greatly performed in a direction parallel to the applied load direction, that is, in a direction of shortening the height of the bump 5. In the bump 5, the transition line generated inside the material easily escapes from the side surface with a large surface area, so the plastic deformability in the vicinity of the side surface is large, and conversely, as it goes to the inside with a distance from the body surface of the bump 5, That is, as it goes closer to the center, the transition line becomes difficult to come out, and plastic deformation becomes difficult.

  Therefore, for the reason described above, when the pressing plate 10 is removed as shown in FIG. 5, the bump surface 7 of the bump 5 recovers the elastic strain at the central portion where the elastic deformation is relatively larger than the periphery. As shown in FIG. 6, the bump 5 is formed in a shape having a small plastic deformation amount at the center portion of the bump 5 having a relatively large elastic strain recovery amount, and conversely a large plastic deformation amount at the peripheral portion of the bump 5. That is, it is formed into a hemispherical bump shape.

  After going through the above process, one of the substrates 1 softens the bumps 5 that are work-hardened by plastic deformation by strain-removing heat treatment. Then, as shown in FIG. 7, the Au pad 12 formed on the other substrate and the hemispherical surface 7 of the bump 5 of one substrate are opposed to each other, and an applied load 9 is applied so that the bump 5 The pad 12 is firmly bonded (FIG. 8).

  In this example, in order to make a 50 μm square and 15 μm high bump 5 made of Au into a hemispherical surface, the bump 5 was pressed with an applied stress of 300 Mpa with an Si substrate 8, and then subjected to heat treatment for removing strain at 250 ° C. for 1 hour. However, the bump surface 7 was formed in a hemispherical shape having a radius of curvature of about 30 μm. Further, when the hemispherical sample was heat-treated, the Vickers hardness could be reduced to about 60 or less. When this hemispherical bump 5 and Au pad 12 were bonded at room temperature, good bonding was obtained at room temperature. After that, a tensile test was performed to obtain a bonding force having a large breaking stress of about 140 Mpa.

  In this embodiment, the aspect ratio of the bump was 0.3, but it is desirable that the bump shape has an aspect ratio of 0.5 or more at which the transition line can easily escape from the side surface of the bump.

In the present embodiment may be any material having a large plastic deformation as a bump 5, such as more face-centered elevational Akira Ho metal is preferably a slip system, preferably no oxide film in the atmosphere Au, In addition Also, for example, Al, Cu, or Sn may be used.

  9, FIG. 10, FIG. 11, FIG. 12, FIG. 13 and FIG. 14 are drawings that clearly show the features of the present invention. In FIG. 9, 1 is formed on one Si substrate and 2 is formed on one Si substrate 1. Insulating film made of Si oxide film, 3 is an electrical wiring made of Al formed on the insulating film 2, and 4 is a passivation film made of an insulator formed on part of the insulating film 2 and the wiring 3. Reference numeral 5 denotes a bump made of Au electrically coupled to the wiring 3, 7 denotes a bump surface on the upper part of the bump 5 formed by pressing with the applied load 9 with the pressing plate 8, and 8 presses the upper part of the bump 5. , 9 is an applied load acting on the pressing plate, 11 is the other Si substrate, and 12 is a pad as an electrode made of Au formed on the other Si substrate 11.

  Next, in the above configuration, a large number of bumps 5 formed simultaneously by Au plating are forced to form grooves on the upper surface in the Au plating process when the bumps 5 are formed as described in the first embodiment. 8 is placed on the bump 5 and an applied load 9 is applied. In this load application process, the bump 5 becomes hemispherical as described in the first embodiment. This hemispherical phenomenon occurs regardless of the number of the bumps 5, and occurs in all the bumps at the same time in the single bump 5 or the plurality of bumps 5. In the step of applying a load to the pressing plate 8, the bumps 5 become hemispherical as described in the first embodiment and are smoothed at the same time, and the height of the bumps 5 can be made substantially uniform as seen in FIG. However, in our experiment in this embodiment, when a plurality of bumps 5 are pressed with an applied load 9 using a flat pressing plate, the center of the substrate 1 is not uniform over the entire surface. The height of the bump 5 in the portion is large, and the height of the bump 5 gradually decreases as it goes to the peripheral portion of the substrate 1, that is, in the radial direction. However, the bump surface 7 of the bump 5 was formed in a hemispherical shape, and at the same time, the outermost surface layer was smoothed. Then, a pad 12 was formed on the other substrate 11, and then, as shown in FIG. 14, when an applied load 9 was applied to the substrate 11, strong inter-electrode bonding occurred between the substrates.

  In this embodiment, when 2048 bumps 5 consisting of a plurality of bumps were applied with a flat pressing plate, all the bumps were deformed into a hemispherical shape. Thereafter, the Si substrate 1 having the bumps 5 deformed into the hemispherical shape is subjected to heat treatment for removing strain at 250 ° C. for 1 hour, and thereafter, both of the bonding surfaces, that is, the bumps 5 and the pads 12 are formed by Ar ion plasma etching. After the bonding surfaces were cleaned and an applied load 9 was applied at room temperature as shown in FIG. 14, the Si substrate 1 having bumps 5 and the Si substrate 11 having pads 12 were firmly bonded.

  In this embodiment, the number of bumps 5 is 2048, the size is a rectangular cross section of 19 μm square, the height is 15 μm, and when an applied load 9 is applied for making a hemisphere, the bump surfaces 7 of all the bumps 5 are applied. Was formed in a hemispherical shape having a radius of curvature of about 30 μm. At the same time, a smooth bump surface 7 without residual grooves 6 could be obtained.

  In the present embodiment, the cross-sectional shape of the bumps is rectangular.

  15, FIG. 16, FIG. 17, FIG. 18, FIG. 19, FIG. 20, FIG. 21, FIG. 22, and FIG. 23 are drawings that clearly show the features of the present invention. Is a bump made of Au electrically coupled to the wiring (not shown) of one substrate 1, 8 is a pressing plate for pressing the upper portion of the bump 5, 9 is an applied load acting on the pressing plate, and 13 is a substrate 1 Auxiliary bumps 15 and 15 are pressing plates used to adjust the height of the bumps 13.

  Next, in the above configuration, the bumps 5 and auxiliary bumps 13 formed simultaneously by Au plating are not uniform in height but rich in irregularities. First, as shown in FIG. 16, the pressing plate 15 is used. It is pressed with the applied load 9 to the required height (FIG. 17). Then, as shown in FIG. 18, the pressing plate 8 is placed on the bump 5 and pushed in with the applied load 9 to reach the height of the reinforcing bump 13 whose height has been adjusted to the required height in advance. Then, the pushing of the applied load 9 is stopped (FIG. 18). By this height adjustment step, the height of the bump 5 is formed to the height of the auxiliary bump 13 as shown in FIG. Further, as shown in FIG. 20, a pressing plate 15 is placed on the auxiliary bump 13 on the reinforcing bump 13 and pushed with an applied load 9, and the pad 12 of the other substrate 11 and the bump of one substrate 1 are pressed. The bump 5 is pushed in until it becomes lower than the height of the bump 5 that is plastically deformed at the time of joining (FIG. 21). Then, the bonding surfaces are cleaned with Ar ion plasma in the same manner as in Example 1 and Example 2, and then the bumps 5 of one substrate 1 and the pads 12 of the other substrate 11 are aligned with each other, and Then, the pads 12 and the bumps 5 were joined by applying and applying the applied load 9 from both sides of the Si substrate 1 and the Si substrate 11 at room temperature.

  In this example, the height of the bump 5 and the auxiliary bump 13 produced by plating are both about 15 μm in height, and the height of the bump 5 is adjusted to about 13 μm as described above using the auxiliary bump. Thereafter, the height of the auxiliary bump 13 is further adjusted to 5 μm by the above method, and both surfaces of the pad 12 and the bump 5 are previously cleaned by Ar ion plasma etching and further bonded at room temperature, Joined. Thereafter, when a bonding strength test was performed, a large bonding strength of 180 Mpa was obtained. When the fracture surface was observed, the bump 5 and the pad 12 were bonded all over. Then, electrical continuity was confirmed using lead electrodes (not shown) formed on the Si substrate 1 and the Si substrate 11.

  As described above, in the present invention, a plurality of electrode bumps formed by plating on the wiring of one substrate are pressed with a pressing plate made of a flat plate, so that it is inevitably formed on the surface of minute bumps and bumps. The plastic deformation caused by the smoothing of the groove and the pressing process increases as it proceeds in the radial direction of the bump, and the surface of the upper part of the bump is made hemispherical by the plastic deformation, and at the same time, smoothed. The bumps are softened, both the bonding surfaces are cleaned by Ar ion plasma etching, and then contact at the time of bonding of the bumps and the pads is performed at room temperature bonding between the bumps of one Si substrate and the pads of the other Si substrate. Starts at the center of the hemispherical surface of the bump and gradually proceeds in the radial direction of the bump. In this process, the plastic deformation of the bump Because proceeds, bonding is performed simultaneously, firmly bonded over the said bump entirely is performed. Since this bonding is room temperature bonding performed at room temperature, bonding between substrates having different linear expansion coefficients is also possible.

It is a figure explaining the joining method and structure between board | substrate electrodes of Example 1 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 1 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 1 of this invention. FIG. 4 is an enlarged view of a bump electrode side surface portion A in FIG. 3 when the bump electrode of Example 1 of the present invention is pressed with a flat plate. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 1 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 1 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 1 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 1 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 2 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 2 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 2 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 2 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 2 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 2 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 3 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 3 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 3 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 3 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 3 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 3 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 3 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 3 of this invention. It is a figure explaining the joining method and structure between board | substrate electrodes of Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 11 Si substrate 2 Insulator film 3 Wiring 4 Passivation film 5 Bump 6 Groove 7 Bump surface 8, 15 Press plate 9 Applied load 10 Removal load 12 Pad 13 Auxiliary bump 14 Slip surface

Claims (5)

Consist face-centered cubic metal, the surface area of the bump side than the surface area of the bump top surface is rather large, the step of the bump top surface central electrode bumps grooves are formed in the providing a substrate which is formed by plating When,
And a step of pressing the electrode bump from above with a flat plate to make the upper surface of the electrode bump hemispherical. A method of manufacturing a substrate on which an electrode bump is formed. 2. The manufacturing method according to claim 1, wherein the face-centered cubic metal is any one of Au, Al, Cu, Sn, and alloys thereof.   The manufacturing method according to claim 1, wherein the substrate on which the electrode bump is formed is heat-treated after the step of pressing the electrode bump with a flat plate.   The step of making the electrode bumps hemispherical is characterized in that the transition line is pulled out from the side surface of the electrode bump, so that the bump is plastically deformed, and the plastic deformation is such that the bump side surface is larger than the bump central portion. The manufacturing method according to claim 1. Consist face-centered cubic metal, the surface area of the bump side than the surface area of the bump top surface is rather large, the substrate on which the electrode bumps grooves in the center part of the surface of the bump top is formed is formed by plating, pad Preparing a formed substrate; and
The substrate on which the electrode bump is formed and the substrate on which the pad is formed are opposed to each other, and by pressing both the substrates, the electrode bump and the pad are joined.
Before the bonding of the electrode bump and the pad, the electrode bump is formed by pressing the electrode bump with a flat plate from above to make the upper surface of the electrode bump hemispherical. Substrate bonding method.

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