Suppression of cobalt silicide agglomeration using nitrogen (N/sub 2//sup +/) implantation
In this paper, the effects of nitrogen coimplantation with boron into p/sup +/-poly gate in PMOSFETs on the agglomeration effects of CoSi/sub 2/ are studied. The thermal stability of CoSi/sub 2//poly-Si stacked layers can be significantly improved by using nitrogen implantation. Samples with 40-nm cobalt silicide (CoSi/sub 2/) on 210-nm poly-Si implanted by 2/spl times/10/sup 15//cm/sup 2/ N/sub 2//sup +/ are thermally stable above 950/spl deg/C for 30 s in N/sub 2/ ambient. If the dose of nitrogen is increased up to 6/spl times/10/sup 15//cm/sup 2/, the sheet resistance of CoSi/sub 2/ film is not increased at all, and TEM photographs show that the agglomeration of CoSi/sub 2/ film is completely suppressed.
Direct CoSi2 thin-film formation with homogeneous nanograin-size distribution by oxide-mediated silicidation
By annealing at 460°C for 120s followed by 600°C120s, nanocrystalline CoSi2 thin film with an average grain size of 5nm can be directly formed from a Co∕SiOx∕Si multilayer with the SiOx as a mediated layer. It is found that annealing at 460°C for enough time is crucial for generating enough diffusion channels within the SiOx layer. After these channels are created, subsequent annealing at 600°C keeps these channels open and is responsible for rapid grain growth. In other words, by using two-step annealing, nucleation and growth processes can be effectively controlled and, hence, the resulting microstructure. The homogeneous nanograin-size distribution is important for ultralarge-scale integration technology below 90nm to prevent resistance degradation induced by CoSi2 agglomeration.
Interactions in the Co/Si thin‐film system. II. Diffusion‐marker experiments
The Kirkendall effect in thin‐film Co/Si couples is investigated by He backscattering using diffusion markers. The couples contain the compounds Co2Si and CoSi. The markers used are Xe implanted into Si, C, or Co2Si and a discontinuous W film between Si and Co. In the case of Xe implantation into Co, the experiments can be explained by dragging of Xe bubbles by the moving Co/Co2Si phase boundary. Xe implanted into Si is located at the Si/CoSi interface after the reaction and W is found at the Co/Co2Si interface after the reaction. The same applies to Xe implanted through Co into Co2Si. The results are evidence for predominant Co diffusion in Co2Si growth and Si diffusion in CoSi growth. Grain‐size measurements suggest that grain‐boundary diffusion plays a role in the growth of the silicide layers. The results of a Xe implantation into Co2Si without Co suggests that at the Co2Si/CoSi interface both Si and Co diffusion currents flow.