Device scaling predicts that copper barrier layers of under 3 nm in thickness will soon be needed in back-end processing for integrated circuits, motivating the development of new barrier layer materials. In this work, nanoscale organic thin films for use as possible copper diffusion barrier layers are deposited by molecular layer deposition (MLD) utilizing a series of self-limiting reactions of organic molecules. MLD can be used to tailor film properties to optimize desirable barrier properties, including density, copper surface adhesion, thermal stability, and low copper diffusion. Three systems are examined as copper diffusion barriers, a polyurea film deposited by the reaction of 1,4-phenylene diisocyanate (PDIC) and ethylenediamine (ED), a polyurea film with a sulfide-modified backbone, and a polythiourea films using a modified coupling chemistry. Following deposition of the MLD films, copper is sputter deposited. The copper diffusion barrier properties of the film are tested through adhesion and annealing tests, including 4-point bend testing and TEM imaging to examine the level of copper penetration. The promise and challenges of MLD-formed organic copper diffusion barriers will be discussed.