Important film parameters:

• uniformity

• step coverage:

• a conformal film is deposited when the film has uniform thickness in the trenches as well as on the plateau
• a film has good step coverage if it is able to cover the surface topology

• in a reactor where the molecules move in all directions (normal situations for medium and high pressure) the deposition takes place more on the top surfaces, and less in the trenches,

• voids can be created, when the two bumps shown above unite, while the trench remains unfilled

• the explanation: the film thickness depends on the arriving angle (the bigger the angle, the more molecules hit that point - the rule is valid only for high pressure, when the particle movement is randomised due to often collisions)

• the arriving angle is pictured in the image below (90o for the corner of the trench, 270o for the top)

• a few definitions:

• Aspect ratio = h/w

• Conformity = b/c

• Sidewall step coverage = b/a

• Bottom step coverage = d/a

• 

• for improving step coverage, there are a few solutions:
• a layer can be etched back by plasma etching or CMP
• enhanced surface migration by increasing the temperature
• moving the substrate
• adhesion:
• for poor adhesion, the film can be easily removed from the substrate, peeling off
• improved by cleaning, plasma sputtering which removes the surface oxide