Integrated passive device maker OnChip Devices Inc of Santa Clara, CA, USA says that its wafer fabrication facility is offering backside metallization (BSM) of thin films for applications such as military, medical, and instrumentation.
Back-metal is required on a wide range of devices to form a solderable die-attach metal stack to ensure good electrical contact to the chip (ohmic contact) or proper bonding of the chips to their mounting cases. Specifically, power devices such as high-brightness light-emitting diodes (HB-LEDs) require backside metal for improved and reliable thermal conductivity. These metal layers are deposited using RF or DC sputtering and electron-beam evaporation.
In backside metallization of discrete devices, the typical layer stack consists of three to four metal layers. The most common metal stack consists of sputter-deposited titanium (500A) followed by nickel (3000A), and finally a flash of gold (200A). The metals offered by OnChip are: layers for providing good ohmic contact (gold, aluminium and titanium); barrier and superior adhesion layers (copper, chromium, palladium and titanium); and solder layers (nickel, gold and silver).
OnChip says that its systems deposit ultra-clean metal and dielectric films in a class-100 cleanroom. Generally, an in-situ RF etch is performed prior to sequential deposition of multi-layers to ensure good film adhesion and ohmic contact to underlying conductive layers or to the bare silicon. All sputter films are currently available on silicon wafer sizes up to 150mm (6") in diameter. Larger wafer sizes may be considered on a case-by-case basis.
BSM processing is available immediately worldwide. The lot charge ranges from $750 to $1450 (depending on metal stack, thickness of layers, wafer diameter, etc). Typical lot size is 11 for 100mm (4") wafers, 9 for 125mm (5") wafers, and 7 for 150mm (6") wafers. Typical lead times are two weeks after receipt of order.
