As the industry develops processes for the 65 and 45 nm technology nodes, post etch/ash cleaning faces new challenges with far more stringent requirements on surface cleanliness and materials loss. The introduction and integration of new materials, such as metal hard mask, creates additional requirements for wafer cleaning due to the occurrence of new defect modes related to metal hard mask. These include organometallic residue and metal fluorite compounds precipitating with time. We have developed a novel aqueous solution (AQ) based single wafer cleaning process to address these new defect modes. Physical characterization results and process integration electrical data and reliability data (TEM cross section review of the vias) are presented in this paper.
The main conclusions can be summarized as follows: (1) In the dual damascene Cu/low-k process flow with hard mask, there are three typical residues after etch/ash: generic polymer residue, organometallic residue strongly bonded to metal maks, and time-dependent metal fluoride residue. (2) Generic polymer residue is very well characterized [1,2] and is usually easy to remove with solvent or aqueous solution [2,3]. (3)We developed an oxidizing chemistry based process to undercut the hard mask for the organometallic residue removal, which proved highly effective. (4)The time-dependent metal fluoride reside makes queue time control after etch/ash very critical (<1 hour). We developed a process with a fluorine based aqueous chemistry to address the metal fluoride residue, which proved highly effective. With this new process, queue time control is not required. (5) The post etch/ash cleaning for the Cu/low-k structure with metal hard mask typically employs the solvent/dry plasma ash multi-step procedure . The new process developed in this research reduced the multi-step process to one wet clean step with two different aqueous chemistries in sequence. (6) The integration electrical data shows that the new single step aqueous cleaning process performance is comparable to, or even better than that from the solvent/dry plasma ash multi cleaning process. (7) Blanket Cu loss with the new process is about 23A/min, however TEM analysis of the vias after full integration shows Cu loss, we are working to improve the integration related Cu loss.