We show that post anneals of short duration at high temperature can markedly
improve the quality of CaF2 films grown by molecular beam epitaxy
(MBE) on Si (100). Anneals at 1100°C for 20 sec in an Ar ambient improved
χmin, the ratio of backscattered 1.8 MeV He4 ions
in the aligned to random direction, from as-grown values of .07 to .26, to
post post-anneal values of .03 to .045. This is the best χmin yet reported
for the CaF2:Si system. The post-annealed films also show
improved resistance to chemical etching and mechanical stress, and increased
dielectric breakdown voltages.