37 Willow Street
Washington, N.J. 07882
TEL (973) 386-0053
Goldfilm is designed for application with a
spinner. After 10 or 15 seconds of spinning, a fairly hard film
will form on the wafer which contains gold atoms attached through
suitable groupings to the carbon-carbon backbone forming the
polymer. At the selected diffusion temperature the polymer
decomposes releasing gold to diffuse into the wafer and CO2
and H2O which pass out the diffusion tube. The gold
concentration achieved does not depend upon the atmosphere
selected for the diffusion.
Goldfilm is applied to the reverse (unpolished) surface of the wafer. When used as a diffusion source, the concentration profile obtained is not dependent on the spin speed or film thickness, because the gold concentration is sufficient that any continuous film will supply enough gold to saturate the wafer. Goldfilm may also be used to deposit thin metallic films on the reverse surface to facilitate child to package bonding. The metallic film will vary with spin speed. At 6000 rpm a 20 angstrom thick film will result, while a spin speed of 1000 rpm will yield a 100 angstrom film.
Diffusion Characteristics of Gold
The following data will be useful in determining the gold concentration which may be obtained in silicon as a result of the diffusion process.
|Temperature (oC)||Gold Saturation Solubility (atoms/cm3)||Diffusion Coefficient
The trapping cross sections obtained with Goldfilm are similar to the values obtained with evaporated or electroplated gold films. For reference, the following data shows the reverse recovery time for a p-n junction in which the high resistivity side was n type:
|Diffusion temp.||tr (nanosecond)|
Process For Plating Out Metallic Films
As noted above 20 to 100 angstroms of gold may be deposited as a continuous film on a wafer by applying the material as directed. The wafer is then heated to 250o to 300oC. In 5 to 10 minutes film decomposition will occur, and a yellow film characteristic of gold will result.
Goldfilm with Boron and Goldfilm with Phosphorous are handled in a manner similar to the pure Goldfilm. These were designed for simultaneous gold and phosphorous or gold and boron diffusion yielding a deep penetration of gold to create an intrinsic region and a p+ or n+ surface layer as required in PIN devices.