PROCESS FOR FORMING COMPOSITIONALLY-GRADED THIN FILMS

A compositionally-graded thin film is formed on a substrate by atomic layer deposition. A mixing system provides a homogeneous gaseous mixture having a controllable ratio of first and second reactive gaseous species. The first and second reactive gaseous species each react with a third reactive gaseous species but do not react with each other. A deposition unit includes first and second reactive gas zones. The homogeneous gaseous mixture is provided to the first reactive gas zone, and the third reactive gaseous species is provided to the second reactive gas zone. The mixing system is controlled to change the ratio of the first and second reactive gaseous species as a function of time as the substrate is moved relative to the deposition unit such that the deposited material has a variable composition as a function of height above the substrate.