X-ray diffraction using the "sin(2) psi method" has been used to study the influence of the deposited thickness on the microstructural and mechanical state of 304L stainless steel films. The thin films are found to be in a high compressive stress state (2-3 GPa). Even though the microstructural state in films is identical, the film morphology is different according to the deposited thickness; when this increases from 175 to 500 nm, the film morphology evolves from an isotropic distribution to a columnar structure of grains. This sub-structure modification is clearly evidenced by X-ray diffraction measurements. The explanation of this modification is quite simple : the columnar structure provides tensile stresses which induce a stress relaxation in this part of the film.