Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Patent
1994-08-09
1997-06-03
Crane, Sara W.
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
257772, 257779, H01L 2348
Patent
active
056357648
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD:
The present invention relates to a solder joint of a case with a substrate or ground metal having an inferior solder wettabillty.
For instance, the present invention relates to (A): a semiconductor electrode structure for connecting a semiconductor substrate to a mount base by a Pb-Sn (lead-tin) solder and (B): a no-flux soldering method for connecting a small solder joint part of a pressure sensor unit or the like requiring high airtightness to a metallic part without using flux to attain excellent joint quality.
BACKGROUND ART:
Conventionally, as a surface treatment for improving solder wettability of a solder joint part, a Ni/Au (nickel/gold) laminated thin film structure is used. However, there are problems such as (1): requiring two stages of film forming steps and (2): the solder wettabllity is unequivocally decided depending on an Au film thickness and thus cannot be freely controlled.
Further, in the case of the semiconductor electrode structure or the pressure sensor unit, the respective technical backgrounds are as follows: factor for various semiconductor devices is how to electrically connect with an external member. In particular, owing to an inferior operational environment very hard conditions are imposed on semiconductor devices of electrical components of automobiles and the like, which are different from OA (office automation) equipment components.
The requirements for the electrodes of such semiconductor devices are as follows: devices, a contact resistance between the semiconductor and the electrode should be small, particularly, the contact resistance should be sufficiently small at low temperature operation. impurity causing a malfunction or an unstable operation of an electronic device should not diffuse into the electrode. with good stability and reproducibility and the connection should have a large adhesive strength, and excellent heat resistant and corrosion resistant properties over a long period of operation.
Hitherto, as a structure for carrying out an electrical connection of such a semiconductor device, a semiconductor substrate is connected to a mount base using solder to carry out an electrical connection with an external member. In this case, first a Cr (chromium) or Ti (titanium) layer is formed on the rear surface of the semiconductor substrate and an Ni layer and an Au layer are successively formed on the Cr or Ti layer. These electrode layers are coupled with the mount base via a solder layer. In this instance, the Cr or Ti layer acts as a contact layer with the semiconductor to form an ohmic electrode along with the semiconductor of the electrode layers, with the result of a reduction in the contact resistance. The Ni/Au layers improve the solder wettability not only to ensure the soldering capability but also to play a role of a diffusion preventing layer for preventing the tin within the solder from diffusing into the semiconductor substrate side. With this structure, while the electrical connection can be sufficiently kept, the diffusing of the impurity (the tin within the solder) into the semiconductor substrate can be prevented.
On the other hand, with the progress of the recent semiconductor technique, in order to accomplish a higher accurate operation, an electrode having a low contact resistance and an excellent ohmic property in a substrate having a low dopant concentration, that is, a high resistivity in a semiconductor has been desired. In the above-described electrode structure, the use of the material Cr or Ti permits an increase of a contact resistivity against Si (silicon), and no ohmic electrode having a sufficiently low electric resistance can be formed, and hence an unstable operation in the semiconductor device is caused. In particular, in the electric components for the automobiles, when they are used at a low temperature, the contact resistance at the interface between the semiconductor and the electrode turns out to be large and no ohmic electrode having a sufficiently low resistance can be formed.
Moreover, because of the r
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"The Formation of Silicides From Thin Films of Some Rare-Earth Metals" J.E. Baglin F.M. D'Heurle, and C.S. Petersson, pp. 594-596.
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Fujikawa Hisayoshi
Kondo Ichiharu
Kondo Kenji
Ohwaki Takeshi
Taga Yasunori
Crane Sara W.
Nippondenso Co. Ltd.
Potter Roy
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