In the related art, in processes of manufacturing a semiconductor device that is configured via the stacking of semiconductor elements, a technique of forming Sn-based (SnAg or the like) micro-solder bumps is used so as to connect the respective electrodes of the stacked semiconductor elements.
FIG. 1 is a view schematically illustrating a technique of forming Sn-based micro-solder bumps that are used so as to stack semiconductor elements in the related art.
As illustrated in FIG. 1, a portion of an Al PAD 2 on a first semiconductor element, that is, one semiconductor element, is exposed, and Ni or the like is formed as a barrier metal 3 thereon. A Sn-based micro-solder bump 6 is formed on a second semiconductor element 4, that is, the other semiconductor element, and the barrier metal 3 and the Sn-based micro-solder bump 6 are diffusion connected to each other via formic acid reduction.
FIG. 2 is a graph illustrating the theoretical diffusion distance (at 200 degrees Celsius) of each of various metals vs. time, the metals being obtainable from Sn and barrier metals. As is apparent from FIG. 2, in a case where the diffusion connection is made via the above-mentioned formic acid reduction, it is necessary to form the barrier metal 3 having a thickness on the order of a micrometer, specifically, a thickness of 3 micrometers or greater, when taking into consideration the diffusivity of a Sn-based solder.
However, it is difficult to fluidize the barrier metal 3 having a thickness on the order of a micrometer in a wafer process among the processes of manufacturing the semiconductor device.
In a case disclosed in PTL 1, Ti is adopted as a barrier metal for a Sn-based solder, and Ti having a thickness of approximately 200 nanometers, which can be fluidized in a wafer process, is formed using a sputtering technique as a die bond technology.