TWI394247B - Metal post chip connecting device and method free to use soldering material - Google Patents

Description

Metal pillar wafer connection structure and method without solder

The present invention relates to semiconductor devices, and more particularly to a metal pillar wafer connection structure and method that is free of solder.

According to Flip-Chip, an advanced chip packaging technology can shorten the transmission distance between the wafer and the substrate, and has become more popular than the electrical performance of the wire connection. In particular, IBM has developed an innovative flip chip packaging technology that replaces the solder balls on the wafer with metal posts and solders the metal posts on the wafer to the pads on the substrate. There is no change in the shape of the ball into the ball in the past, so the spacing of the metal columns can be allowed to shrink more densely (the bump spacing can reach less than 50 microns, such as 30 microns), to achieve higher density or to omit RDL (heavy The bump configuration of the configuration circuit layer is called "metal pillar soldered wafer connection", which is called the MPS-C2 (Metal Post Solder-Chip Connection) technology. This MPS-C2 related art is described in U.S. Patent No. 6,229,220 B1, "Bump structure, bump forming method and package connecting body".

As shown in FIG. 1 , a conventional metal pillar wafer connection structure 100 of the MPS-C2 architecture mainly includes a wafer 110 and a substrate 120 . The wafer 110 is provided with a plurality of metal pillars 112 and protrudes from a surface 111 of the wafer 110. One of the upper surfaces 121 of the substrate 120 has a plurality of pads 122 and corresponding to the metal pillars 112, respectively. In detail, the metal pillars 112 are soldered to the pads 122 by a plurality of solders 150, and an underfill layer 140 is formed to cover the metal pillars 112, the pads 122, and the Some solder 150. The electrical connection between the wafer 110 and the substrate 120 is achieved by using the solders 150 as soldering interfaces, which are different from the metal pillars 112 and the pads 122 in material and melting point, and are susceptible to solder joint breakage. The risk of increased impedance.

Therefore, the conventional MPS-C2 technology uses the solder 150 to make a wafer connection when the wafer 110 is combined with the substrate 120. Among them, the solder 150 can be selected from a solder ball or other solder different from the bump component, so that the diffusion and wettability of the metal between different materials need to be considered when the wafer is connected, and nickel is often used. Ni)/gold (Au) and the like are used as the surface plating of the bumps, which increases the welding cost. In addition, in the subsequent reflowing step, when the solders 150 are heated to the reflow temperature, the solders 150 are melted to have fluidity, and when the solders 150 are squeezed or vibrated, overflow may occur, and It may cause the metal posts 112 to be soldered to the wrong pads 122, which will result in failure of the electrical connection.

In order to solve the above problems, the main object of the present invention is to provide a solder-free metal pillar wafer connection structure and method, which does not require the use of conventional solder for wafer connection, thereby improving the conductivity of the solder joint, especially for MPS-C2. The (metal post soldered wafer connection) product can save the cost of using solder joints.

The main object of the present invention is a solder-free metal pillar wafer connection structure and method, which establishes a U-shaped metal bonding cross section without solder between the metal pillar and the pad, and greatly improves the bonding strength of the solder joint.

The object of the present invention and solving the technical problems thereof are achieved by the following technical solutions. The invention discloses a solder-free metal pillar wafer connection structure, which mainly comprises a wafer and a substrate. The wafer is provided with a plurality of metal pillars protruding from one surface of the wafer, each metal pillar having a top surface and two parallel sidewalls. The substrate has an upper surface and a plurality of pads on the upper surface, each of the pads having a bottom surface of the recess and a side of the recess on both sides. Wherein, the wafer is bonded to the upper surface of the substrate, and the top surfaces of the metal pillars are self-welded to the bottom surfaces of the recesses, and the portions of the two parallel sidewalls of the metal pillars are self-welded to the two side recesses. The side is such that a U-shaped metal bonding cross section of the metal pillar and the pads is formed without solder. The present invention further discloses a method of connecting the above-described solder-free metal pillar wafer connection structure.

The object of the present invention and solving the technical problems thereof can be further achieved by the following technical measures.

In the aforementioned metal pillar wafer connection structure, the U-shaped metal bonding cross section may be a copper-copper interface.

In the aforementioned metal pillar wafer connection structure, the surface of the wafer may be an active surface.

In the aforementioned metal pillar wafer connection structure, the metal pillars may penetrate the wafer more.

In the foregoing metal pillar wafer connection structure, an underfill adhesive may be further included between the wafer and the substrate to seal the metal pillars.

In the foregoing metal pillar wafer connection structure, the recess depth of the pads may be no more than one third of the height of the metal pillars.

It can be seen from the above technical solutions that the solder-free metal pillar wafer connection structure and method of the present invention have the following advantages and effects:

1. A specific combination of metal pillars and pads can be used as one of the technical means, since each metal pillar has a top surface and two parallel side walls, and each of the pads has a concave bottom surface and two concave sides. The side of the hole, and the top surface of the metal post is self-welded to the bottom surface of the recess, and the portions of the two parallel side walls of the metal post are self-welded to the side of the recess on both sides, so that a solder-free U is formed between the metal post and the pad. Shaped metal bond cross section. Therefore, it is not necessary to use conventional solder as a wafer connection to improve the conductivity of the solder joint, and in particular, when it is applied to an MPS-C2 (metal pillar soldered wafer connection) product, the cost of using the solder joint can be saved.

Second, the specific combination relationship between the metal post and the pad can be used as one of the technical means, since each metal post has a top surface and two parallel side walls, and each of the pads has a concave bottom surface and two concave sides. The side of the hole is applied to the wafer by heat, pressure and ultrasonic waves to establish a solder-free U-shaped metal bond cross section between the metal post and the pad. Therefore, the bonding strength of the solder joint can be greatly improved.

The embodiments of the present invention will be described in detail below with reference to the accompanying drawings in which FIG. The components and combinations related to this case, the components shown in the figure are not drawn in proportion to the actual number, shape and size of the actual implementation. Some size ratios are proportional to other related sizes or have been exaggerated or simplified to provide clearer description of. The actual number, shape and size ratio of the implementation is an optional design, and the detailed component layout may be more complicated.

According to a first embodiment of the present invention, a solder-free metal pillar wafer connection structure is illustrated in a cross-sectional view of FIG. 2 and a cross-sectional view of the elements in the flip-chip bonding process in FIGS. 3A to 3C. The solder-free metal pillar wafer connection structure 200 mainly includes a wafer 210 and a substrate 220.

As shown in FIG. 2, the wafer 210 is provided with a plurality of metal pillars 212 protruding from a surface 211 of the wafer 210. Each of the metal pillars 212 has a top surface 213 and two parallel sidewalls 214. In detail, the wafer 210 has formed an integrated circuit (IC) component such as a memory, a logic component, and an application specific integrated circuit (ASIC), which can be divided into a pellet by a wafer. In this embodiment, the surface 211 of the wafer 210 can be an active surface, that is, a forming surface of the integrated circuit. In detail, a plurality of solder pads (not shown) may be formed on the surface 211 (ie, the active surface) for the metal pillars 212 to be disposed between the solder pads and the metal pillars. A metal layer under the bump (not shown) to avoid metal diffusion of the components in the metal pillar. The material of the metal pillars 212 may include gold, copper, aluminum or an alloy thereof, and may be formed into a columnar shape by electroplating. Preferably, the top surface 213 is flat and has the same height using abrasive or surface flattening techniques.

The substrate 220 has an upper surface 221 and a plurality of pads 222 on the upper surface 221. Each of the pads 222 has a recess bottom surface 223 and two side pocket sides 224. In detail, the substrate 220 can be a printed circuit board (PCB) as a medium for carrying and electrically connecting the wafers in the semiconductor package structure. In a preferred embodiment, the distance between the two pocket sides 224 of each pad 222 may be no greater than the distance between the two parallel sidewalls 214 of each of the corresponding metal posts 212 to ensure the parallel sidewalls in the flip chip bond. 214 can frictionally contact the pocket sides 224. The material of the pads 222 may comprise copper, and the formation of the recess bottom surface 223 and the two side pocket sides 224 may be achieved by pattern etching or pattern plating. In a preferred embodiment, the depth of the recesses of the pads 222 may be no more than one third of the height of the metal pillars 212 to prevent the metal pillars 212 from being excessively embedded in the pads 222. And maintaining a gap between the wafer 210 and the substrate 220 that is not in frictional contact. In addition, in the present embodiment, the metal pillars 212 and the pads 222 may have the same material. For example, the metal pillars 212 may be Cu posts, and the pads 222 may also be used. It is a copper cave.

In addition, the wafer 210 is bonded to the upper surface 221 of the substrate 220. The top surface 213 of the metal pillars 212 is self-welded to the bottom surfaces 223 of the recesses. Solder to the two side pocket sides 224 to form a solder-free U-shaped metal bond cross section 230 between the metal posts 212 and the pads 222. In other words, the U-shaped metal bonding section 230 is at least three bonding interfaces and is non-planar. The above-mentioned "joining interface" is located between the top surface 213 and the bottom surface 223 of the recess and the two parallel sidewalls 214 and corresponding Between the two pocket sides 224. The term "self-welding" refers to the use of metal atoms on the surface of the metal pillars 212 to activate diffusion, and form a mutual metal bond with the pads 222, without the need for additional solder, bump plating or other bonding agents. The U-shaped metal bonding section 230 generates an intermittent metal lattice interface, so that the impedance between the metal pillars 212 and the pads 222 does not rise after self-welding, The U-shaped metal bonding cross section can achieve better conductivity as a solder joint. In this embodiment, the U-shaped metal bonding section 230 can be a copper-copper interface or a gold-gold interface, wherein the copper-copper interface is less expensive. Therefore, the U-shaped metal bonding section 230 does not have other impurities, a fragile cast structure or a metal-containing compound, and can form a relatively flat joint surface without using conventional solder for wafer bonding. Improve the electrical conductivity of the solder joints.

In addition, the solder-free metal pillar wafer connection structure 200 may further include an underfill material formed between the wafer 210 and the substrate 220 to seal the metal pillars 212. The high fluidity of the underfill 240 prior to curing is used to avoid void formation between the wafer 210 and the substrate 220. In a preferred embodiment, the underfill 240 is selected from a higher hardness material, and in addition to protecting the metal posts 212, the overall structural strength can be enhanced.

Therefore, the present invention utilizes a specific combination of metal pillars and pads as one of the technical means, and does not require conventional solder for wafer bonding, particularly for MPS-C2 (metal pillar soldered wafer bonding) products, which can save the cost of using solder joints. . This is because each of the metal posts 212 has a top surface 213 and two parallel side walls 214, and each of the pads 222 has a recess bottom surface 223 and two side pocket sides 224, and the top surfaces of the metal pillars 212 213 is self-welded to the bottom surface 223 of the recess, and the portions of the two parallel sidewalls 214 of the metal pillars 212 are self-welded to the corresponding side pockets 224 of the two sides, so that the metal pillars 212 and the pads 222 are 222. A U-shaped metal bond cross section 230 is formed between the solders. In addition, the bonding strength and conductivity of the solder joints are greatly improved, which eliminates the risk of solder joint breakage and impedance increase when solder joints are conventionally used.

The present invention also discloses a possible but non-limiting manufacturing method of the solder-free metal pillar wafer connection structure 200, illustrating a cross-sectional view of the components in the process of FIGS. 3A to 3C for clearly demonstrating one of the effects of the present invention. The detailed steps are as follows.

First, as shown in FIG. 3A, the wafer 210 is provided with a plurality of metal pillars 212 protruding from a surface 211 of the wafer 210. Each of the metal pillars 212 has a top surface 213 and two parallel sidewalls. 214. The top surfaces 213 do not need to adhere to the solder used in the prior art, and in addition to worrying about solder contamination problems, the installation cost of the solder can be saved.

Referring to FIG. 3B, the substrate 220 is provided. The upper surface 221 of the substrate 220 is provided with a plurality of pads 222. Each of the pads 222 has a recess bottom surface 223 and two side pocket sides 224. Specifically, each of the pocket bottom surface 223 and the corresponding two side pocket sides 224 can form a structure like a U-shaped groove.

Referring to FIG. 3C, a flip chip bonding step is performed to bond the wafer 210 to the upper surface 221 of the substrate 220. Heat, pressure and ultrasonic waves are transmitted to the wafer 210 via an adsorption thermocompression fixture (not shown) so that the top surfaces 213 of the metal pillars 212 are self-welded to the bottom surfaces of the recesses. 223, a portion of the two parallel sidewalls 214 of the metal pillars 212 are self-welded to the two side pocket sides 224, so that the metal pillars 212 and the pads 222 are formed as a solderless U-shaped metal. Bonding section 230. Here, the term "ultrasonic" means that the vibration frequency is not less than 20,000 Hz, and the wafer 210 and its metal pillar 212 are subjected to high-frequency lateral vibration of 20,000 to 40,000 times per second, so that the metals The joint surface of the pillar 212 and the pads 222 is surface-welded by high-frequency vibration, and the atom diffusion is induced to form atomic bonding of the mutual metal, so that no flux and no electric current and heating to the melting point of the metal pillars 212 are required. . By properly heating the wafer 210 but not reaching the melting points of the metal pillars 212, the metal pillars 212 connected to the wafer 210 are simultaneously heated and expanded, and the distance between the two parallel sidewalls 214 of the same metal pillar 212 may be slightly larger than the corresponding connection. The distance between the two parallel sidewalls 214 of the pad 222 is to increase the frictional contact between the portions of the two parallel sidewalls 214 of the metal posts 212 and the two side pocket sides 224 to achieve vertical self-welding of the sides. By applying pressure to the wafer 210, the top surface 213 of the metal pillars 212 is brought into frictional contact with the recessed bottom surfaces 223 to achieve a central horizontal self-welding. Therefore, by applying heat, pressure and ultrasonic waves to the wafer 210, a solder-free U-shaped metal bonding cross section 230 can be established between the metal pillars 212 and the pads 222, which can greatly improve the bonding strength of the solder joints. .

4A-4C are schematic views showing the metal post wafer connection structure 200 showing the combination of the metal post and the pad and the flip chip bonding process. As shown in FIG. 4A, the top surface 213 of each metal pillar 212 may be rectangular, and each metal pillar 212 may have a pair of parallel wall surfaces in addition to the two parallel sidewalls 214 described above, thereby The metal pillars 212 are formed in a rectangular parallelepiped shape. In addition, as shown in FIGS. 4B and 4C, the area of the bottom surface 223 of each of the pads 222 may not be larger than the area of the corresponding top surface 213. More specifically, when the metal pillars 212 are bonded to the pads 222, the wafers 210 are applied by heat, pressure and ultrasonic waves, the top surfaces 213 and the corresponding recess bottom surfaces 223 and the parallel sidewalls 214. Quickly vibrating friction with the corresponding pocket side 224 to self-weld the top surface 213 of the metal posts 212 to the bottom surfaces 223 of the recesses, and the partial self-welding of the two parallel sidewalls 214 of the metal posts 212 To the two side pocket sides 224. The direction indicated by the arrow in Fig. 4C is the direction of vibration using the ultrasonic waves, which is parallel to the parallel side walls 214 and the pocket sides 224.

5A to 5C are diagrams showing a metal pillar wafer connection structure 200 in a modified embodiment, illustrating a metal pillar, a pad and a combination in a flip chip bonding process, to illustrate that the top surface of the metal pillar is not limited. The shape of the bottom surface of the pad. As shown in FIG. 5A, the top surface 213a of each of the metal posts 212 can be square and can have two pairs of mutually parallel and equal parallel sidewalls 214a. Moreover, as shown in FIG. 5B, each of the pads 222 is recessed to form a shape like a receiving groove, and has two pairs of parallel side walls in addition to the side pocket sides 224a. Further, the shape of the bottom surface 223a of the pads 222 may be a rectangle, and the area of the bottom surface 223a of the pads 222 may be larger than the area of the top surface 213a of the metal pillars 212. The top surface 213a of the metal pillars 212 is self-welded to the recess bottom surfaces 223a. In addition, the shorter sides of the bottom surfaces 223a of the recesses (ie, the distances between the two recess sides 224a of the pads 222) are not greater than the corresponding side lengths of the top surfaces 213a of the corresponding metal pillars 212 (ie, the two parallel sidewalls of the metal pillars 212). 214a), when the wafer 210 is bonded to the substrate 220, according to the ultrasonic vibration direction indicated by the arrow in FIG. 5C, the two parallel sidewalls 214a of the metal pillars 212 can be ultrasonically vibrated to the corresponding ones. The two recess sides 224a of the pad 222 are used to self-weld the two parallel sidewalls 214a of the metal posts 212 to the two side recess sides 224a.

In accordance with a second embodiment of the present invention, another solder free metal pillar wafer connection configuration 300 is illustrated in cross-section in FIG. The same elements as those in the first embodiment will be denoted by the same reference numerals and will not be described in detail.

Referring to FIG. 6, the solder-free metal pillar wafer connection structure 300 mainly includes a wafer 210 and a substrate 220. The wafer 210 is provided with a plurality of metal pillars 212 protruding from a surface 211 of the wafer 210. Each of the metal pillars 212 has a top surface 213 and two parallel sidewalls 214. The substrate 220 has an upper surface 221 and a plurality of pads 222 on the upper surface 221. Each of the pads 222 has a recess bottom surface 223 and two side pocket sides 224. The wafer 210 is bonded to the upper surface 221 of the substrate 220. The top surface 213 of the metal pillars 212 is self-welded to the bottom surface 223 of the recess. The two parallel sidewalls 214 of the metal pillars 212 are self-contained. Solder to the two side pocket sides 224 to form a solder-free U-shaped metal bond cross section 230 between the metal posts 212 and the pads 222. Preferably, the metal pillars 212 can penetrate the wafer 210 more. Further, a plurality of through holes 315 may be formed in the through hole of the metal pillars 212, and a plating layer 316 is disposed on the hole walls of each of the through holes 315. The plating layer 316 may be selected from a conductive material such as copper (Cu). In detail, the through holes 315 are also called so-called through silicon vias (TSVs). The structure of the metal pillars 212 extending through the wafer 210 can provide vertical electrical conduction and stabilize the metal pillars 212, thereby facilitating ultrasonic vibration conduction of the wafer 210 to the metal pillars 212 to promote the The U-shaped metal bond section 230 is formed. In this embodiment, the protruding surface 211 of the metal pillars 212 can be the back surface of the wafer 210, so that the active surface of the wafer 210 is away from the substrate 220 for better heat dissipation. In addition, the exposed end faces of the metal pillars 212 can vertically stack another wafer.

The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Although the present invention has been disclosed in the above preferred embodiments, it is not intended to limit the present invention. Any simple modifications, equivalent changes and modifications made without departing from the technical scope of the present invention are still within the technical scope of the present invention.

100. . . Metal column wafer connection structure

110. . . Wafer

111. . . surface

112. . . Metal column

120. . . Substrate

121. . . Upper surface

122. . . Pad

140. . . Underfill

150. . . solder

200. . . Metal pillar wafer connection structure without solder

210. . . Wafer

211. . . surface

212. . . Metal column

213. . . Top surface

213a. . . Top surface

214. . . Parallel side wall

214a. . . Parallel side wall

220. . . Substrate

221. . . Upper surface

222. . . Pad

223. . . Underside of the pocket

223a. . . Underside of the pocket

224. . . Pocket side

224a. . . Pocket side

230. . . U-shaped metal bonding section

240. . . Underfill

300. . . Metal pillar wafer connection structure without solder

315. . . Through hole

316. . . Plating

Fig. 1 is a schematic cross-sectional view showing a conventional metal column wafer connection structure.

2 is a cross-sectional view showing a solder-free metal pillar wafer connection structure in accordance with a first embodiment of the present invention.

3A to 3C are cross-sectional views showing the elements in the flip chip bonding process of the metal post wafer connection structure according to the first embodiment of the present invention.

4A to 4C are views showing a metal post wafer connection structure according to a first embodiment of the present invention, showing a combination of a metal post and a pad and a bonding process in a flip chip bonding process.

5A to 5C are views showing a metal post wafer connection structure according to a variant embodiment of the present invention, showing a combination of a metal post and a pad and a bonding process in a flip chip bonding process.

Figure 6 is a cross-sectional view showing another solder-free metal post wafer connection structure in accordance with a second embodiment of the present invention.

200. . . Metal pillar wafer connection structure without solder

210. . . Wafer

211. . . surface

212. . . Metal column

213. . . Top surface

214. . . Parallel side wall

220. . . Substrate

221. . . Upper surface

222. . . Pad

223. . . Underside of the pocket

224. . . Pocket side

230. . . U-shaped metal bonding section

240. . . Underfill

Claims (10)

A solder-free metal pillar wafer connection structure comprising: a wafer having a plurality of metal pillars protruding from a surface of the wafer, each metal pillar having a top surface and two parallel sidewalls; and a substrate Having an upper surface and a plurality of pads on the upper surface, each pad having a bottom surface of the recess and a side of the recess on both sides; wherein the wafer is bonded to the upper surface of the substrate, the metal The top surface of the column is self-welded to the bottom surface of the recesses, and the portions of the two parallel side walls of the metal posts are self-welded to the side of the two side pockets to form a gap between the metal pillars and the pads. It is a U-shaped metal bond cross section without solder. The metal pillar wafer connection structure of the solder-free solder according to the first aspect of the patent application, wherein the U-shaped metal bonding cross section is a copper-copper interface. The metal pillar wafer connection structure of the solder-free solder according to the first aspect of the patent application, wherein the surface of the wafer is an active surface. The metal pillar wafer connection structure of the solder-free solder according to the first aspect of the patent application, wherein the metal pillars penetrate the wafer. The metal pillar wafer connection structure of the solder-free solder according to the first, second, third or fourth aspect of the patent application, further comprising an underfill layer formed between the wafer and the substrate to seal the metal pillars. A metal pillar wafer connection structure exempt from solder according to claim 1, 2, 3 or 4, wherein the pads have a recess depth not greater than one third of the height of the metal posts. A solder-free metal pillar wafer connection method includes: providing a wafer with a plurality of metal pillars protruding from a surface of the wafer, each metal pillar having a top surface and two parallel sidewalls; The substrate has an upper surface and a plurality of pads on the upper surface, each of the pads having a bottom surface of the recess and the side of the recess on both sides; and bonding the wafer to the upper surface of the substrate, utilizing heat and pressure Applying to the wafer with ultrasonic waves, the top surfaces of the metal pillars are self-welded to the bottom surfaces of the recesses, and the portions of the two parallel sidewalls of the metal pillars are self-welded to the side of the two recesses so that the A metal-free metal-bonded cross section is formed between the metal pillars and the pads. A method of joining metal pillar wafers excluding solder according to the first aspect of the patent application, wherein the U-shaped metal bonding cross section is a copper-copper interface. A method of joining a solder-free metal pillar wafer according to claim 1, wherein the surface of the wafer is an active surface. A metal pillar wafer bonding method for solder-free, according to the first aspect of the patent application, wherein the metal pillars penetrate the wafer.