With the development of ultra-large-scale integrated circuits, a bottleneck problem will eventually appear due to further shrinking of device feature sizes, which is the thickness of Cu interconnect diffusion barrier layer fail to continuously reducing. Therefore, it is imperative to develop a new barrierless structure Cu alloy thin film (Cu seed layer), that needs keeping high stability (no interdiffusion occurs) and low resistivity in a moderate temperature environment (400~500 ℃) of subsequent processes for a long period. In present paper, the current state and problem of the barrierless structures were summarized firstly. Then, the research work of the barrierless Cu-Ni-M films based on the stable solid solution cluster model was reviewed, and the selection principle of the third element M and its influence on the thermal stability were discussed through the comparison of the microstructure, resistivity and stability of the multi-series films. Finally, the changes of the second element were discussed to further verify the validity of the stable solid solution cluster model. The results show that the films have excellent ability to inhibit diffusion under the condition of the third element M with a slightly larger atomic radius than Cu and difficult to diffuse and insoluble in Cu. When M/Ni=1/12, i.e., the alloying elements are completely dissolved into the Cu matrix in the form of clusters, the comprehensive performance of the film reaches the optimal, which can meet the requirements of the microelectronics industry. All these studies indicate that the stable solid solution cluster model is very effective in the composition design of the barrierless Cu thin film, and this model is also expected to be widely used in the composition design of high temperature resistant Cu alloy and radiation resistant materials.