  Quantum tunneling through a two-dimensional static barrier becomes unusual
when a momentum of an electron has a tangent component with respect to a border
of the prebarrier region. If the barrier is not homogeneous in the direction
perpendicular to tunneling a fraction of the electron state is waves
propagating away from the barrier. When the tangent momentum is zero a mutual
interference of the waves results in an exponentially small outgoing flux. The
finite tangent momentum destroys the interference due to formation of caustics
by the waves. As a result, a significant fraction of the prebarrier density is
carried away from the barrier providing a not exponentially small penetration
even through an almost classical barrier. The total electron energy is well
below the barrier.
