Study of the post-etch cleaning compatibility with dense and porous ULK materials – characterization of the process impact

Ultra low-K materials (ULK) are used as insulator between Cu interconnections. After via and line dry etching steps with a plasma, a cleaning step is generally mandatory. The cleaning solution and the process used have to be compatible with the ULK materials: structural, morphological and electrical modifications have to be minimized. In this investigation, we have studied the impact of this cleaning step on a dense (matrix and porogen) and porous spin-on ULK and on a porous ULK deposited by plasma enhanced chemical vapour deposition (PECVD). Several solutions containing diluted HF mixed with an organic acid and a supercritical CO2 process were tested. These results show that the material alteration depends on the nature of its surface and its porosity: the hydrophobic property of the porous PECVD material gives it a total compatibility with all the cleaning processes. However, the dense spin-on material, which is hydrophilic, is also compatible with the cleaning solutions. This is explained by the porogen content preventing the diffusion of the cleaning solution in the material. This explanation is confirmed also by the volumic dissolution of the porous spin-on material.