Patent Application
20120305298
This application claims the priority benefit of Taiwan application serial no. 100119028, filed on May 31, 2011. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
The disclosure relates to a bump, a package structure of the same, and a manufacturing method of the same, more particularly to a bump with a nanolaminated structure, a package structure of the same, and a manufacturing method of the same.
Currently, the bonding process for a three dimensional integrated circuit (3D IC) is classified into two main types, which are tin soldering and direct copper bump thermal compression bonding. The advantage of tin solder bonding includes providing lower external pressure and bonding temperature than those required for thermal compression bonding. Typically, a tin solder is applied to a SnAgCu ternary alloy bump. The melting point of a tin solder is about 220° C., and an external pressure required for tin solder bonding is about several tens MPa. However, the biggest problem of employing a ternary alloy in a bump forming process is that electroplating is not applicable in forming a ternary alloy. Further, the smallest dimension of a structure can be formed by a printing process is about 25 μm. Therefore, to fabricate a 10 μm bump, some not only other bonding methods, such as immersion bumping, can fabricate to 10 μm bump but the fabrication temperature must be raised to about 250° C. Another approach for fabricating a bump is the application of a binary alloy. However, the melting point of a copper tin alloy is at least 230° C., and the bonding temperature of the binary or ternary alloy bump is at least 250° C. or above. Moreover, the resistance of a tin solder is higher (10 times of copper), and the formation of inter-metallic compounds also affect the reliability of the device.
Another bonding process is the direct copper bump thermal compression bonding, in which a metal is directly bonded on the copper bump. Accordingly, the resistance is low and the problem of inter-metallic compounds is also precluded. However, the process must be performed in a vacuum environment, mass production is thereby difficult. Further, the process must also be performed under a load (a large applied pressure of 100 MPa) at an elevated temperature (a bonding temperature of about 350° C. to 400° C.). Consequently, the bonding of thin wafers often results with the generation of thermal stress and cracks on the wafers.
To lower the applied pressure and the bonding temperature required in thermal compression bonding process, a plasma treatment process is performed to roughen the surface of the bump. However, a metal material is different from an organic material, and the surface roughen effect created by physical bombardment (Ar) is limited and the appearance of the roughened surface is also difficult to control. Further, no chemical plasma etching process is known to be appropriate for a typical copper bump. In simple terms, it is difficult to obtain a regular and uniform nanostructure surface using plasma etching.
A nanostructure has the characteristics of high surface energy, large contact area, etc. As described in a publication, an object of several kilograms may bond to a wall using carbon nanotubes without the application of a chemical adhesive substance. If the surface of a bump has a nanostructure, even in the absence of excessive heating and pressurization, the upper and lower bumps are tightly bonded together by diffusion bonding of the nanostructured metal atoms. Another publication revals that two pieces of stainless steel are completely bonded without any gap at the bonding interfaces by using Ni nanoparticles under a low pressure. Moreover, nanogold wires can be diffusion bonded in an acid solution at a temperature of 270° C., which is lower than a typical gold diffusion bonding temperature (430° C.). However, with the current process, it is not easy to form a nanostructure directly on a bump. Hence, the development of the technique using nanostructure for bonding is limited.
According to the current nanometal technique, nanometals are directly positioned on a substrate or a bump. To avoid the aggregation of nanometals, a large amount of “protecting agent” or “chelating agent” is applied to the peripheries of the nanometals. However, the application of a large amount of “protecting agent” or “chelating agent” would lead to the formation of voids in the package structure in the subsequent process.
An exemplary embodiment of the disclosure provides a bump having a nanolaminated structure, wherein by applying organic molecules having functional groups, metal ions are affixed to one of the functional groups through chemical bonding or physical bonding (such as, coordinate bonding, van der waals bonding, or hydrogen bonding) and are reduced to a metal. Ultimately, a nanolaminated structure is assembled on the bump.
An exemplary embodiment of the disclosure provides a package structure, wherein the nanometal and the bump have desirable bonding properties.
An exemplary embodiment of the disclosure provides a fabrication method of a bump having a nanolaminated structure, wherein an organic layer is applied to form a nanolamianted structure on a bump.
An exemplary embodiment of the disclosure provides a bump having a nanolaminated structure. The bump having a nanolaminated structure includes at least a bump an organic layer, and a nanolaminated structure. The nanolaminated structure is formed with a plurality of nanometals on the bump. The organic layer is contiguous to the bump and the nanolaminated structure. The structure of the organic layer is G1-R-G2, wherein R is alkylene with less than 10 carbons; G1 is a first functional group, which forms a first metal bond with the bump; and G2 is a second functional group, which forms a second metal bond with the nanolaminated structure.
An exemplary embodiment of the disclosure provides a package structure, and the package structure includes a first member, a first bump, a first nanolaminated layer, a first organic layer fragment, a second member, a second bump, and a second nanolaminated layer. The first bump is configured on the first member. The first nanolaminated layer is configured on and is electrically connected with the first bump. The first organic layer fragment is configured between the first bump and the first nanolaminated layer, and the structure of the first organic layer G1-R-G2, wherein R is alkylene with less than 10 carbons; G1 is a first functional group, which includes one of the following groups:
wherein R1, R2 and R3 are each independently an alkyl with or without a substituted group, the substituted group includes, for example, carboxyl (—COOH), amino (—NH2), amide (—CONH2), cyano (—CN), —OH, or —Si—OH. The second member and the first member are configured opposite to each other. The second bump is configured on the second member. The second nanolaminated layer is configured between and is electrically connected with the first nanolaminated layer and the second bump.
An exemplary embodiment of the disclosure provides a fabrication method of a bump having a nanolaminated structure, and the method includes providing a surface having at least a bump. Then, a first self-assembling step is performed to assemble an organic layer on the bump. The structure of the first organic layer is G1-R-G2, wherein R is alkylene with less than 10 carbons; G1 is a first functional group and is bonded with the first metal atom of the bump, wherein the first functional group includes one of the following groups:
wherein R1, R2 and R3 are each independently an alkyl with or without a substituted group, the substituted group includes, for example, carboxyl (—COOH), amino (—NH2), amide (—CONH2), cyano (—CN), —OH, —Si—OH or —Si(OCxH2x+1)3, wherein x is 1, 2, or 3. Thereafter, a second self-assembling step is performed, wherein the second metal ions are bonded on the bump through the organic layer. Then, a redox reaction is performed to reduce the second metal ions to a second metal to form a plurality of nanometals. The plurality of nanometals is stacked to form a nanolaminated structure.
According to an exemplary embodiment of the disclosure, by applying an organic layer with a bifunctional group, a plurality of nanolaminated structure (nanometals) is selectively self-assembled on the bump.
According to a package structure of an exemplary embodiment of the disclosure, the nanolaminated structure and the bump include organic layer fragments therebetween. Nevertheless, bonding properties of the nanolaminated metals and the bump are desirable.
According to a fabrication method of a bump having a nanolaminated structure of an exemplary embodiment of the disclosure, a simple redox reaction is performed to reduce metal ions to a metal directly on a bump. Further, the size and the shape of the metal particles are adjustable to form a dense nanostructure on the bump.
The invention and certain merits provided by the invention can be better understood by way of the following exemplary embodiments and the accompanying drawings, which are not to be construed as limiting the scope of the invention.
Referring to
The plurality of nanolaminated structures 16 is configured on the bump 12. The material of the nanolaminated structures 16 includes a second metal, such as silver, gold, copper, nickel, platinum, or the alloys or composites thereof. During the package process, excessively high pressurization or excessively high temperature is not required for diffusion bonding of the metal atoms of the nanolaminated structures 16 to tightly bond the upper and lower bumps together because of the use of the nanolaminated structures 16. It is also not necessary for each nanometal of the nanolaminated structures 16 applied in diffusion bonding to have a very small particle diameter. Further, during the fabrication process, an excessive amount of the protecting agent for enclosing the surface of each nanolaminated structure 16 is not required and the total thickness of the nanolaminated structure 16 does not have to be too large. In one exemplary embodiment, the nanometal of each nanolaminated structure 16 has a dimension of about 30 nanometer to 200 nanometer. The nanometals of the nanolaminated structures 16 include nanowires, ball-shaped structures, flake-shaped structures, nanorods, nanocubes, structures with irregular shapes, or a combination thereof. The nanometals are stacked into two to three layers, and the thickness of each layer is less than 1 micron, for example, 100 nanometer to 1 micron.
The above organic layer 14 is configured between and bonded with the bump 12 and the nanolaminated structures 16. More specifically, the organic layer 14 includes a monolayer of organic molecules with bifunctional groups, and the structure thereof may be represented as G1-R-G2, wherein R is the backbone of the organic layer and is an alkylene group (CH2)n with a carbon number less than 10, and n is a natural number less than 10. When n is a natural number less than 10, G1-R-G2 degrades during thermal compression bonding to form small molecule fragments or to vanish. The bump 12 and the nanolaminated structures 16 are thus in contact, while the contact resistance between the bump 12 and the nanolaminated structures 16 is unaffected. However, when R of G1-R-G2 has a carbon number greater than 10, G1-R-G2 does not degrade into small molecule fragments or vanish during thermal compressing bonding process. Instead, the organic layer 14 remains between the bump 12 and the nanolaminated structure 16, causing the bump 12 and the nanolaminated structure 16 to be in poor or no contact and the contact resistance is affected. G1 is the first functional group, which may have a chemical bonding or physical bonding (such as coordinate bond, van der waals bond, or hydrogen bond) with the first metal of the bump 12. G2 is the second functional group, which may have a chemical bonding or physical bonding (such as coordinate bond, van der waals bond, hydrogen bond) with the second metal of the nanolaminated layer structures 16. The first functional group G1 includes one of the following groups:
wherein R1, R2 and R3 are each independently an alkyl with or without a substituted group, and the substituted group includes, for example carboxyl (—COOH), amino (—NH2), amide (—CONH2), cyano (—CN), —OH, —Si—OH, or —Si(OCxH2x+1)3, wherein x is a whole number ranging from 1 to 3. The second functional group G2 may alter the wetting and interfacial properties of the backbone R, and the second functional group G2 includes —COOH, —NH2, —CONH2, —CN, —OH, —Si—OH, —Si(OCxH2x+1)3, or —CHO, wherein x is 1, 2 or 3.
The organic layer 14 (G1-R-G2) includes HS—(CH2)n—COOH or HS—(CH2)n—Si(OCxH2x+1)3, wherein n is an integer from 1 to 10, x is 1, 2, or 3, OCxH2x+1 is, for example, OCH3, which can be totally or partially hydrolyzed into —OH. HS—(CH2)n—COOH is, for example, HS—C3H6—COOH. Alternatively speaking, G1-R-G2 includes, for example, alkanethiols, disulfides, dialkyl disulfides, dialkyl sulfides, alkylxanthates or dialkylthiocarbamates, and the terminal of the alkyl chain of the above-mentioned compounds is replaced by G2.
The first metal of the bump 12 may be the same as or different from the second metal of the nanolaminated structures 16. In one exemplary embodiment, the first metal of the bump 12 is copper, while the second metal of the nanolaminated structures 16 is silver. The first functional group G1 of the organic layer 14 includes, for example, a thiol group (—SH), the second functional group G2 includes, for example, a carboxyl group (—COOH), an amino group (—NH2), an amide group (—CONH2) or a cyano group (—CN), a hydroxyl group (—OH), or a silicon hydroxyl group (—Si—OH). In another example, the first metal of the bump 12 is gold, the second metal of the nanolaminated structures 16 is nickel, and the first functional group G1 is, for example, one of the following groups:
wherein R1, R2, and R3 are defined as above, and will not be further reiterated herein. The second functional group G2 is, for example, —COOH, —NH2, —CONH2, —CN, —OH, CHO or —Si—OH.
Examples of the organic layer 14 include:
Referring to both
Thereafter, referring to
More specifically, in step 104, the member 10 with the already formed organic layer 14 is placed in a first solution containing second metal ions. The second metal ions in the first solution are adsorbed on the bump 12 of the member 10 through the organic layer 14. The second metal ions include, for example, silver ions, gold ions, copper ions, nickel ions, or platinum ions. In one exemplary embodiment, the second metal ions are silver ions, for example, the first solution containing the second metal ions further include the ingredients of sodium borohydride, silver nitrate, and sodium citrate. In the exemplary embodiment, as shown in
In the first stage 108 of the synthesis of the nanolaminated structures 16, the second metal ions on the bump 12 are directly reduced with the reducing agent in the first solution to form second nanometal atoms with small particle diameters. Since the second nanometal atoms are highly reactive with the second function group of the organic layer 14 and are not reactive with the dielectric layer (not shown), a bonding is generated between the second nanometal atoms and the second functional group of the organic layer 14 to form crystal seeds 15. In one exemplary embodiment, the second metal ions are silver ions, the first solution containing the second metal ions also includes the ingredients of sodium borohydride, silver nitrate, and sodium citrate. Sodium borohydride reduces the silver ions of silver nitride to silver particles. In the exemplary embodiment as shown in
According to another exemplary embodiment, if a denser structure is desired, the second stage 110 of the step 106 is performed to synthesis the nanolaminated structures 16. In the second stage 110, the bump 12 with the crystal seeds 15 already formed thereon is placed in the second solution containing the second metal ions for a redox reaction to occur. By controlling the reduction rate of the second metal ions, the second metal ions are reduced to a second metal, and grown on the crystal seeds 15, to form the second metal nanolaminated structures 16. In another exemplary embodiment, the second metal ions are silver ions, and the second solution containing the second metal ions also includes the ingredients of silver nitrate, ascorbic acid, and sodium hydroxide. The silver ions of silver nitrate are reduced by ascorbic acid to silver particles, which will grow on the crystal seeds to form silver nanolaminated structures. In this exemplary embodiment of the disclosure, instead of forming the nanometal particles directly on the organic layer 14 above the bump 12, the second metal ions are received on the organic layer 14 above the bump 12 and are reduced to second metal. Accordingly, the application of a large amount of protecting agent to prevent the aggregation of the nanoparticles is precluded. However, to prevent the aggregation of second metal ions and to also control the growing mechanism of the nanometal particles for the isotropic growing of the crystal seeds, a small amount of protecting agent may still be required. However, the required amount of the protecting agent is very small. The protecting agent, which includes, but not limited to, cetyltrimethylammonium bromide (CTAB) or polyvinylpyrrolidone (PVP), may be added to the second solution. In one exemplary embodiment, the mole ratio of silver nitrate to cetyltrimethylammonium bromide is, for example, less than 1:250. In another exemplary embodiment, the mole ratio of silver nitrate to cetyltrimethylammonium bromide is, for example, 1:250 to 1:750.
The nanolaminated structures formed according to the above the exemplary embodiment of the disclosure include nanowires, ball-shaped structures, flake-shaped structures, nanorods, nanocubes, structures with irregular shapes, or a combination thereof. The size of the second metal of the nanolaminated structures is, for example, 50 nm to 200 nm. In the exemplary embodiment as shown in
Thereafter, as shown in
During the fabrication process of the above nanolaminated structures 16, the reduction rate is adjustable by manipulating the reaction conditions, such as the concentration of the second metal ions, the concentration of the protecting agent, and the concentration of the reducing agent. Further, by controlling of the reduction time, the formation of nanolaminated structures with different sizes, shapes, and densities is achieved. The details of the synthesis of a nanolaminated structure may be referred to “Wet Chemical Synthesis of Silver Nanorodes and Nanowires of Controllable Aspect Ratio” by Nikhil R. Jana, et al. in Chem. Commun., page 617-618 and is incorporated herein as reference.
The above member having a bump may directly bond with another member having a bump with a nanolaminated structure thereon without the application of a solder.
Referring to
Referring to
In the above exemplary embodiment, the two members respectively have a bump, an organic layer, and a nanolaminated structure. Moreover, the two members being bonded by a solder layer is used as an exemplary illustration. In another exemplary embodiment, one of the member includes a bump, an organic layer, and a nanolaminated structure, while another member includes a bump having the above nanolaminated structure thereon, wherein the bump and the nanolaminated structure do not include an organic layer therebetween.
An etching solution is used to clean the surface of the copper electrode to remove the oxide layer on the surface of the copper electrode. Pure water is then used to remove the etching solution remaining on the surface of the copper electrode. Thereafter, the copper electrode, already formed with HSC2H4COOH, is placed in an aqueous solution of silver nitrate, sodium borohydride, and PVP. The mole ratios of silver nitrate, sodium borohydride, and PVP in the exemplary embodiments are shown in Table 1, wherein the mole ratio of silver nitrate to PVP changes with the area of the copper electrode, for example, 1:0.05 to 1:0.5, and the mole ratio of silver nitrate to sodium citrate is, for example 1:0.5 to 1:3.
The particle diameters illustrated in Table 1 are the average particle diameters. Appropriate mixing is performed during the experiment to promote the growing of the seed and heating is occasionally required. After the completion of the reaction, water or alcohol is used to perform the cleaning.
An etching solution is used to clean the surface of the copper electrode to remove the oxide layer on the surface of the copper electrode. Pure water is then used to remove the etching solution remaining on the surface of the copper electrode. Thereafter, the copper electrode, already formed with HSC2H4COOH, is placed in 0.25 mM silver nitrate, 5 ml of 10 mM of sodium borohydride and 0.25 mM of sodium citrate for the redox reaction to proceed. The mole ratio of silver nitrate to sodium citrate is not limited to the ratio disclosed above; in one example, the ratio of silver nitrate to sodium citrate is about 1:0.5 to 1:3. After the reaction is completed, water or alcohol is used to perform the cleaning process. The resulting nanosilver structure has a small particle diameter of about 5 to 20 nm, for example. The previously formed copper electrode is placed in a mixture solution containing 50 ml of 80 mM cetyltrimethylammonium bromide (CTAB), 0.5 ml of 10 mM silver nitrate, 0.5 mL of 100 mM ascorbic acid, and 0.1 ml of 1M sodium hydroxide for a redox reaction to proceed. The mole ratio of silver nitrate to cetyltrimethylammonium bromide is not limited to the ratio disclosed above. In one example, the mole ratio of silver nitrate to cetyltrimethylammonium bromide is about 1:250 to 1:750. Appropriate mixing is performed during the experiments to promote the growing of the seed and heating is occasionally required. After the reaction is completed, water or alcohol is used to perform the cleaning.
The dimensions of the nanoparticles synthesized in the above Examples 1-7 are summarized in Table. Pictures from scanning electron microscope (SEM) of the above Examples 1-5, 6 and 7 are respectively presented in
According to the exemplary embodiments of the disclosure, the organic layer has a bifunctional group, which selectively bonds with metal ions through chemical or physical bonding and allows the metal ions to reduce to metal directly on the bump to form a dense nanolaminated structure.
According to the packaging structure of the exemplary embodiment of the disclosure, at least one of the two members includes an organic layer. Further, by using one terminal function group of the organic molecule of the organic layer, the organic layer is selectively bonded with the bump via chemical or physical bonding. Another terminal functional group is bonded with the metal ions in the solution. The metal ions are further reduced to a metal via a redox reaction to form a dense nanolaminated structure. Because of the low melting point characteristic of the nonmetals, a low temperature bonding is performed. Although voids may form between the nanomainated structure and the bump or in the nanolamianted structure after the degradation of the organic layer, desirable bonding between the nanometals and the bump is still achieved.
According to the fabrication method of a bump having a nanolamianted structure, wherein by relying on the formation of an organic layer and the occurrence of a redox reaction, metal ions are reduced to metals, and dense nanolaminated structures are formed on a bump.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 100119028 | May 2011 | TW | national |
