Patent GB-1404383-A (GB)
Title: Mounting terminals for semiconductor devices and a method of fabricating same
IPC: H01L21/60
Filed: 1973-05-01
Abstract: 1404383 Semi-conductor devices MICROSYSTEMS INTERNATIONAL Ltd 1 May 1973 [6 June 1972] 20704/73 Heading H1K A terminal for a semi-conductor device comprises a beam lead with a portion made adherent to an anchor region of a chip surface, and a pliant non-adherent arm extending over the chip surface within its boundary to a raised land connected by thermocompression to a registering terminal pad or bump adherent to a substrate (Figs. 1, 2, not shown). Multiple such terminals may be connected to metallization paths of active devices of a bipolar integrated circuit chip (Fig. 3, not shown). In fabrication (Figs. 4B, 4D) integrated circuits (not shown) with N and P doped regions are conventionally formed in a Si wafer 1 thermally coated with SiO 2  at 10, in which contact windows are photolithographically formed. A layer (not shown) of Si 3 N 4  is formed thereon by reaction of SiH 4  and NH 3  and the contact windows are photolithographically reopened for ohmic contacts of Pt silicide to the underlying Si. The water surface is then coated with a layer of Ti 11 overlain by Pt 12; the latter being etched in aqua region over a photolitho mask to form an interconnection pattern having the Ti layer unaffected and the anchorage regions 13 protected. A photoresist pattern identical in geometry but with opposed contrast is applied to the Pt interconnection pattern to cover all exposed Ti areas and leave areas exposed for electroplating with Au at 14. The photoresist is removed and the wafer surface electrolessly plated with Ni, washed and coated with a further photoresist mask exposing anchorage areas 13 and a beam lead region extending therefrom on which Au 16 is again electrodeposited. The photoresist is again removed and a further mask applied to expose the beam lead regions to be built up to thermocompression lands 5 by further Au electrodeposition. After removal of this photoresist the wafer is etched in warm ethylene diamine tetracetic acid, NH 4 OH, and H 2 O 2  to remove all Ni and Ti from between the Au plated areas and from the area underlying the Au beam lead 16 (Fig. 4D) except for the anchorage region 13. The wafer is then probe tested and scribed for breakage along chip separation channels in conventional manner. Similarly, in a MOSFET integrated circuit structure for a Si random access memory circuit (Figs. 5A to 5H) a chip 1 with prediffused P and N regions protected by a SiO 2  layer 18 overlain by vacuum deposited Al 19 is photolitho etched to leave a continuous metallized grid 20 disposed within separation channels 17 electrically connecting the terminal anchorage areas 21. The wafer is then passivated by P doped SiO 2  28 from low temperature pyrolysis of SiH 4  and holes are etched over photolitho mask to access the anchorage areas 21 of the required beam leads, after which the wafer is immersed in alkaline zincate solutions to remove oxide from the exposed aluminium and deposit zinc, after which Ni layer 22 is electrolessly plated therein. A further Ni layer 23 is then electrolessly deposited over the entire surface of the wafer to overlie the exposed Ni and SiO 2  surfaces 28 (Fig. 5E) and photolitho masked to expose the anchorage areas and beam lead areas 24, which are then electroplated with Au at 25; the grid 20 being unaffected within the separation channels 17 to connect the several beam anchorage areas inter se and to the active integrated circuit regions (not shown), while the wafer surface is passivated by the SiO 2  layer 28 except for the anchorage areas, which provides a non-adherent interface with Ni layer 23. The beams 25 are further electroplated over photolitho mask to produce leads 5 without deposition on the Al metallization protected by the SiO 2  mask, which is then etched off in buffered HF to expose the Al grid and connections thereto over the separation channels 17. After washing in H 2 O, H 3 PO 4  etchant removes the Al grid and beam connections (Fig. 5H) and after removal of the photoresist and washing the wafer is heated in air to anneal the Au-Ni adhesion in the beam anchorage areas. Subsequent to test probing the wafer is scribed and broken into chips. The beam leads may alternatively be circular with the centre or a peripheral ring adherent to thechip, U-shaped, rectangular, or spiral. Agmay replace Ni as an electrode metal. The contacts of the chip and the substrate may be mechanically wobble bonded in sequence, and ultrasonic energy may be applied during bonding.