News Column

Patent Issued for Micro Bump and Method for Forming the Same

August 26, 2014



By a News Reporter-Staff News Editor at Journal of Technology -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Uang, Ruoh-Huey (Zhudong Township, TW); Cheng, Yi-Ting (Kaohsiung, TW), filed on March 27, 2013, was published online on August 12, 2014.

The assignee for this patent, patent number 8802557, is Industrial Technology Research Institute (Hsinchu, TW).

Reporters obtained the following quote from the background information supplied by the inventors: "With the development of semiconductor technology, three-dimensional (3D) packaging has become more widely used. An integrated circuit employing 3D packaging technology may be called a 3D-IC. In a 3D-IC, chips may be vertically stacked on top of each other, with different chips being interconnected using interconnects such as through-silicon-vias (TSVs), bumps, and/or redistribution layers.

"Among different kinds of 3D-ICs, those having logic chips and memory chips stacked in one package may be challenging to manufacture. Since there are many TSVs in such a 3D-IC, a large number of bumps may also be required to connect the TSVs in one chip and wirings on another chip. However, since chip area may be limited, the large number of bumps may require reducing a horizontal size of the bumps, such as a diameter of a circular bump, a side length of a square bump, or a length of a short side of a rectangular bump. The horizontal size of the bumps may need to be reduced to about 10 .mu.m or even smaller. The traditional method of manufacturing lead-free solder bumps by a printing process may not be suitable for manufacturing bumps of such size.

"Generally, a 3D-IC packaging process may require low temperature (such as a temperature lower than about 200.degree. C.), low pressure (such as a pressure lower than 10 MPa), and non-vacuum condition during bonding of two chips. Moreover, bumps between the chips may need to have high strength and low resistivity. Currently, there are two categories of bonding methods that may be used for 3D-IC packaging. One is solder bonding, and the other is thermocompression bonding using copper bumps. However, the existing techniques cannot achieve a bump having a horizontal size of about 10 .mu.m or smaller, which may be used to bond two chips at a bonding temperature lower than 200.degree. C. and a bonding pressure smaller than 10 MPa in a non-vacuum environment. For example, use of SnAgCu solder can only achieve a bump having a horizontal size larger than 25 .mu.m. Solder bonding using CuSn solder may be used to manufacture bumps having smaller size, but the temperature required for bonding using CuSn solder may need to be higher than 250.degree. C. The thermocompression bonding method using copper bumps may need a higher temperature of about 400.degree. C., a pressure higher than 10 MPa, and a vacuum environment. Also, a 3D-IC packaged using thermocompression bonding method may have large stresses built up in the chips. This may be especially true for an IC package composed of chips with small thickness and the stresses may cause the chips to crack.

"Recently, metal nano particles have been employed as bonding material for microelectromechanical systems (MEMS), surface mount diodes (SMD), and light emitting devices (LED). Due to their small size, metal nano particles may have a low melting temperature, so that the bonding process using metal nano particles may be performed at a low temperature. However, in most existing methods, metal nano particles are coated on chips in a form of paste or ink, These methods may not be able to form micro bumps having a horizontal size smaller than 10 .mu.m, and thus may also not be suitable for the fabrication of a 3D-IC including logic and memory chips.

"Further, since space exists between metal nano particles due to, for example, non-uniform nano-particle size and protective agents such as polyvinylpyrrolidone (PVP), if the metal nano particles are directly subjected to a bonding process, voids may appear in the bumps so formed. For micro bumps having a horizontal size smaller than 10 .mu.m, such voids may undesirably decrease bond strength. The resistivity of the micro bumps may also increase due to the voids. To prevent voids from forming, the metal nano particles may be first melted and solidified, and then subjected to the bonding process. However, in this method, since the melting/solidifying process may cause formation of larger crystal grains, the temperature required for bonding may be increased."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "In accordance with the present disclosure, there is provided a method for forming a micro bump including forming a first nano-particle layer on a substrate and forming a second nano-particle layer on the first nano-particle layer. The first and second nano-particle layers include a plurality of first nano particles and a plurality of second nano particles, respectively. The method further includes irradiating a laser beam onto the second nano-particle layer, the laser beam penetrating through the second nano-particle layer and being at least partially absorbed by at least some of the first nano particles to generate heat. The first nano particles and the second nano particles have different absorption rates with respect to the laser beam.

"Also in accordance with the present disclosure, there is provided a method for forming a micro bump including forming a first nano-particle layer on a substrate, patterning the first nano-particle layer to form a plurality of adhesion pads, and forming a second nano-particle layer over the adhesion pads and the substrate. The first and second nano-particle layers include a plurality of first nano particles and a plurality of second nano particles, respectively. The method further includes irradiating a laser beam onto the second nano-particle layer, the laser beam penetrating the second nano-particle layer and being at least partially absorbed by the first nano particles in the adhesion pads to generate heat. The first nano particles and the second nano particles have different absorption rates with respect to the laser beam.

"Also in accordance with the present disclosure, there is provided a micro bump including an adhesion layer formed of a first metal and a bump layer formed on the adhesion layer. The bump layer includes a plurality of nano particles formed of a second metal and a filling material filling space between the nano particles, the filling material being formed of the first metal. A weight ratio of the filling material to the nano particles decreases from an interface between the bump layer and the adhesion layer to a top surface of the bump layer.

"Also in accordance with the present disclosure, there is provided a package including a first substrate comprising a first electrode, a second substrate comprising a second electrode, a first adhesion layer formed on the first substrate, and a second adhesion layer formed on the second substrate. The first and second adhesion layers are formed of a first metal. The package also includes a bump layer formed between the first adhesion layer and the second adhesion layer. The bump layer includes a bump material and a filling material filling space in the bump material. The bump material is formed of a second metal and the filling material is formed of the first metal. A weight ratio of the filling material to the bump material decreases from an interface between the bump layer and the first adhesion layer to a middle of the bump layer, and increases from the middle of the bump layer to an interface between the bump layer and the second adhesion layer.

"Features and advantages consistent with the present disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present disclosure. Such features and advantages will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

"It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

"The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention."

For more information, see this patent: Uang, Ruoh-Huey; Cheng, Yi-Ting. Micro Bump and Method for Forming the Same. U.S. Patent Number 8802557, filed March 27, 2013, and published online on August 12, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8802557.PN.&OS=PN/8802557RS=PN/8802557

Keywords for this news article include: Industrial Technology Research Institute.

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Source: Journal of Technology


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