  Thin pad detectors made from 75 $\mu$m thick epitaxial silicon on low
resistivity substrate were irradiated with reactor neutrons to fluences from
2.5$\times 10^{16}$ n/cm$^2$ to 1$\times 10^{17}$ n/cm$^2$. Edge-TCT
measurements showed that the active detector thickness is limited to the
epitaxial layer and does not extend into the low resistivity substrate even
after the highest fluence. Detector current was measured under reverse and
forward bias. The forward current was higher than the reverse at the same
voltage but the difference gets smaller with increasing fluence. Rapid increase
of current (breakdown) above ~ 700 V under reverse bias was observed. An
annealing study at 60$^\circ$C was made to 1200 minutes of accumulated
annealing time. It showed that the reverse current anneals with similar time
constants as measured at lower fluences. A small increase of forward current
due to annealing was seen. Collected charge was measured with electrons from
$^{90}$Sr source in forward and reverse bias configurations. Under reverse bias
the collected charge increased linearly with bias voltage up to 6000 electrons
at 2.5$\times 10^{16}$ n/cm$^2$ and 3000 electrons at 1$\times 10^{17}$
n/cm$^2$. Rapid increase of noise was measured above $\sim$ 700 V reverse bias
due to breakdown resulting in worse S/N ratio. At low bias voltages slightly
more charge is measured under forward bias compared to reverse. However better
S/N is achieved under reverse bias. Effective trapping times were estimated
from charge collection measurements under forward bias showing that at high
fluences they are much longer than values extrapolated from low fluence
measurements - at 1$\times 10^{17}$ n/cm$^2$ a factor of 6 larger value was
measured.
