[en] Technique to control the composition of gas medium in the reactive magnetron discharge and the composition of the deposited films of niobium nitride using electrical parameters of discharge only, in particular, by δU = U_p - U_ar value at contant stabilized discharge current is described. Technique to select optimal condition for deposition of niobium nitride films when the films have composition meeting chemical formula, is suggested. Thin films of niobium nitride with up to 7 nm thickness and with rather high temperature of transition into superconducting state T_k > 10 K) and with low width of transition (δ < 0.6 K), are obtained. It is determined, that substrate material and dielectric sublayer do not affect. T_k value, while difference in coefficients of thermal expansion of substrate and of film affects δT_k value