  We present a method for fabricating Josephson junctions and superconducting
quantum interference devices (SQUIDs) which is based on the local anodization
of niobium strip lines 3 to 6.5 nm-thick under the voltage-biased tip of an
Atomic Force Microscope. Microbridge junctions and SQUID loops are obtained
either by partial or total oxidation of the niobium layer. Two types of weak
link geometries are fabricated : lateral constriction (Dayem bridges) and
variable thickness bridges. SQUIDs based on both geometries show a modulation
of the maximum Josephson current with a magnetic flux periodic with respect to
the superconducting flux quantum h/2e. They persist up to 4K. The modulation
shape and depth for SQUIDs based on variable thickness bridges indicate that
the weak link size becomes comparable to the superconducting film coherence
length which is of the order of 10nm.
