In Reply to: darker colour problem in cr sputtering on glass posted by c.s.lee on 08/26/02 at 1:23 AM:
Dark color in Cr films is mostly due to hydrocarbon backstreaming of either the rough pumping system or the diffusion pump. The person who advised you to install a liquid Nitrogen trap was on the right track. You should seriously consider it. You might also investigate the crossover pressure for rough pumping as well as to monitor the foreline pressure of the diffusion pump. (Do you have a rough pump trap?)
The time to reach to 10-6 range seems excessive. If your pumping system is inadequate you may be spending too much time in rough pumping.
In addition, there may be outgassing of your substrates which affect the coating quality.
As you may have discovered, the secret to good films is good, clean vacuum. Sources of contamination are many and you must eliminate them one by one until your system performs as you want it to.