We study a thin film which is composed of antiferromagnetic triangular sheets stacked along the $y$ direction with {\it quantum} Heisenberg spins 1/2 by a Green function technique. We calculated self-consistently the spin-wave spectrum and the local magnetization as a function of the temperature for several surface exchange interactions and film thicknesses. Monte Carlo simulations of the same system but with classical Heisenberg spins are also performed for comparison.[no postscript.gz available]