Audio Pixels - Research Report - 24th Of June 2020, page-88

You may recall in a previous presentation they showed that certain structural features that had been fabricated by material deposition had been crushed and some bits were broken off and the dislodged pieces were stuck to the surface. It was then said that these can get into the space where the membrane moves and would disrupt function and cause further damage. These broken off pieces were described as debris. If I recall correctly this damage was occurring when the wafers get inverted so the back side can be etched out to create the cavity in which the membrane moves. We were told that they had devised a nifty solution to the way this was done so it would not occur in future production.

In the most recent presentation we were shown patches of residue that had flowed or been deposited and left behind across the surfaces around some of the features. These were described as chemical residues from the processes and their cleaning steps. The implication was that the cleaning processes had not been done to an adequate level, but that the processor would be able to make adjustments to the process so that these were completely removed. This was a fabrication issue, not a design issue, and the FAB would be dealing with it. i.e. it is a routine issue rather than a problem as such.

This is how I understood the presentation, so this is my opinion only.