It is known that when a particle size of a metal particle is decreased to a size of 100 nm or less and the number of constituent atoms decreases, the ratio of the surface area to the volume of the particle increases abruptly and the melting point or the sintering temperature is greatly lowered compared with a case in a state of bulk. It has been studied to use a metal particle with a particle size of 1 to 100 nm as a bonding material by utilizing the low temperature sintering function (refer, for example, to Japanese Unexamined Patent Application: JP-A No. 2004-107728).
JP-A No. 2004-107728 discloses to conduct bonding by using a bonding material comprising metal particles with an average particle size of 100 nm or less in which a film of an organic material is formed to the periphery of core of the particle and decomposing the organic material by heating to sinter the metal particles to each other. In this bonding method, since the metal particles after bonding are bonded by metallic bonding at the bonding boundary, as well as they are converted into a bulk metal, they have extremely high heat resistance, reliability, and high heat dissipation property. Further, while lead-free solder has been demanded in the connection of electronic parts, etc, materials as a substitute for high temperature solders have not yet been available. In the mounting of electronic parts, since it is indispensable for using hierarchical solder, advent of a material in place of the high temperature solders has been desired. Accordingly, the bonding technique is also expected as a material capable of replacing the high temperature solder.
The present inventors have made a study on the bonding material using metal particles with a particle size of 100 nm or less as a main agent for bonding described in JP-A No. 2004-107728. As a result, it has been found that while the bonding material can provide satisfactory bonding strength to a mating electrode such as of Au, Ag, or Pd as a material to be bonded, no sufficient bonding strength can be obtained to Cu or Ni, which is applied frequently in the mounting of the semiconductors.
FIG. 9 shows the result for the evaluation of the bonding strength conducted for each of the electrode materials. Bonding to Au, Ag, Pd, Ni, and Cu electrodes were conducted at a constant bonding temperature of 250° C. and a pressure of 1.0 MPa using silver particles with an average particle size of 10 nm coated with an amine type organic material.
In FIG. 9, the ordinate shows a shearing strength, which is normalized with reference to the value of the Ag electrode. As a result, it has been found that while satisfactory bonding strength is obtained to Au, Ag, and Pd electrodes, no sufficient bonding strength can be obtained to Ni and Cu electrodes in the bonding in atmospheric air.
The organic material formed as the coating film for supermicro particles described in JP-A No. 2004-107728 is a material eliminated only by heating in atmospheric air and it is considered that while the material is effective for less oxidizing electrodes but it is not suitable to the bonding of easily oxidizable Cu, or Ni.
When the bonding surface by the method of JP-A No. 2004-107728 (using a bonding material comprising Cu as a metal core which is coated with an amine compound and heated in atmospheric air) is observed under a microscope, a nickel oxide layer is formed between a sintered pure copper layer and an Ni electrode as shown in FIG. 10 and it is considered that this lowers the bonding strength. Further, when the bonding boundary between the Cu electrode (underlayer) and the sintered pure copper layer using the bonding material is observed, a copper oxide layer is formed at the bonding boundary as shown in FIG. 11. It is considered that this lowers the bonding strength.
In a case of bonding an electronic part constituting a semiconductor device by using a bonding material comprising micro metal particles as a main agent for bonding, it is necessary to ensure electric conduction. Further, relaxation of thermal strain and heat conductivity are also required for the bonding material. Further, it is necessary that good bonding can be obtained also to Ni and Cu electrodes that are used most frequently used in the field of semiconductor devices.
The invention intends to improve the bonding reliability at a bonding portion between an electrode comprising a material selected from the group consisting of Ag, Au, Ni, Cu, or alloys thereof of a semiconductor devices and a bonding material using Cu particles as a main agent for bonding, and provides a semiconductor device utilizing the same, a manufacturing method thereof, a composite metal body and a manufacturing method thereof.
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