EN
The X-ray diffraction and atomic force microscopy are used to examine the microstructure of La_{1.85}Sr_{0.15}CuO_4 films grown by pulsed laser deposition on LaSrAlO_4 substrates. The films grow with different degrees of built-in strain, ranging from a large compressive to a large tensile in-plain strain. The tensile strain cannot be attributed to a substrate-related strain. The possible origins of the tensile strain are discussed.