Bruce,

I personally do not believe, based on my experience, that you cannot
precisely control the slope of your sidewall in a specific angle like 85
deg. You can get a sloped sidewall with various methods or tricks but this
slope will vary in some margin. It is very difficult to specify a profile
angle to some value with uniformity and repeatability. Like thin film
deposition, you don't get the film thickness exactly the same everywhere
on the wafer (maybe 5% variation). The only angle that you may comfortably
reproduce is 90 deg, that is, fully anisotropic. 90 deg is about 5%
deviation from 85 deg. Perhaps it is still acceptable for you, no?

Yours sincerely,

Isaac Chan, Ph.D.
University of Waterloo