A semiconductor fabrication method comprises steps of providing a
semiconductor structure. The semiconductor structure includes a
semiconductor substrate, a trench in the semiconductor substrate. The
trench comprises a side wall which includes {100} side wall surfaces and
{110} side wall surfaces. The semiconductor structure further includes a
blocking layer on the {100} side wall surfaces and the {110} side wall
surfaces. The method further comprises the steps of removing portions of
the blocking layer on the {110} side wall surfaces without removing
portions of the blocking layer on the {100} side wall surfaces such that
the {110} side wall surfaces are exposed to a surrounding ambient.