19 Leslie Court
Whippany, New Jersey 07981
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
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.
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