  We provide a theoretical framework to analyze the properties of frontal
collisions of two growing interfaces considering different short range
interactions between them. Due to their roughness, the collision events spread
in time and form rough domain boundaries, which defines collision interfaces in
time and space. We show that statistical properties of such interfaces depend
on the kinetics of the growing interfaces before collision, but are independent
of the details of their interaction and of their fluctuations during the
collision. Those properties exhibit dynamic scaling with exponents related to
the growth kinetics, but their distributions may be non-universal. These
results are supported by simulations of lattice models with irreversible
dynamics and local interactions. Relations to first passage processes are
discussed and a possible application to grain boundary formation in
two-dimensional materials is suggested.
