This paper focuses on the study of reactive magnetron sputtering thin NbN films for sensitization of hot electron bolometers. HEB will be utilized in the Millimetron space observatory. The main principle of operation is a superconductivity that is experimentally observed when NbN film is cooled to the temperature of a liquid helium. At a critical temperature of superconductive transition a resistance of the film falls to zero and film becomes sensitive to light radiation of infrared and millimeter wavelength range. It is important to note that a thickness of film greatly affects on the sensitivity of film. When the thickness of film is decreased, the heat capacity decreases and with it the sensitivity of detectors based on superconductive film increases. In this research dependencies of the critical temperature from various parameters of fabrication technology were identified. Subsequently, parameters of reactive magnetron sputtering with the highest critical temperature at the lowest thickness of film were discovered.