Initial Study on the Polishing Performance of Nitrogen-Doped Silicon Carbide (SiC)
Authors: Qin Liqiao , Gu Sipeng , Kim Hong Jin , Han Ja-Hyung , Koli Dinesh R 
Published: February 2020

Nitrogen-doped silicon carbide (SiC) (Silicon carbonitride or SiCN) thin films which has been generally used as a etch stopping layer. Recently It becomes more and more attractive as capping dielectric layers and diffusion barriers due to their performance is similar to silicon nitride (SiN) but having lower dielectric constant and higher endurance on etching process. But high Carbon concertation SiCN film is hard to form and we have developed a process to form SiCN with tunable high Carbon concentration (5-15%). The SiCN film used in this study is deposited by 300mm Producer PECVD of applied materials at 400°C. The chemical composition and film property can be tuned by a tight control of gas flow and RF power. The overall chemical reaction occurring using TMS is as follows: Si(CH3)3-H + SiH4 + NH3 --> SiCN.  VASE analysis shown that the Refractive index (n) is around 2.18 at 633nm, higher than other PECVD SiCN films, while extinction coefficient (k) is comparable with others. Hg-probe for dielectric constant K value is determined and FTIR is used to measure the materials chemicals.

To enable this material use in the semiconductor manufacture scheme, such as poly opening polishing process, there is a need to study the other performance of this material, such as polishing performance. As the development of semiconductor manufacturing, chemical mechanical polishing (CMP) becomes a major process in IC integration. Nowadays, CMP is widely used in planarization structure and enable new structure and new material introduced in IC fabrication. To enable SiCN used in the new semiconductor scheme, we need to study the selectivity between removal rates of SiCN and silicon dioxide (SiO2) with silica particles. Two kind of silica nanoparticles slurries (one is acidic and the other one is alkaline) were used in this studied. The materials are polished with different downforce, platen and head rotation speed, as well as polishing time, aim to understand the polishing performance under different situation. In addition, the selectivity between removal rates of SiCN, SiN and Oxide was tested. The post CMP DFU information was also collected. The initial results of the investigations on the optimization of the consumables and process conditions would be given in this presentation.  Our study shown that, SiCN has higher removal rate at the beginning of polishing and then the removal rate drops off gradually as polishing longer.  The removal rate increase linear as process downforce increase which is similar as most dialectic materials. From defectivity points of view, with longer polishing time and higher downforce, CMP generated more defects. But with increasing RPM, higher removal rate and relative stable defectivity could be achived, which might be a knob to maitain specific removal rate as well as relative low defectivity. The selectivity between removal rates of SiCN and Oxide with acidic and alkaline silica nanoparticles nanoparticles slurry, shown the SiCN material is more prefer to be removed in the acidic slurry.  And acidic slurry has better SiCN to oxide selectivity compare to alkaline slurry.

 In conclusion, this is an initial study of the polishing performance of SiCN (5-15% carbon concentration), and we reported the material’s removal rate and defectivity corresponding polishing time, downforce and RPM with Silica nanoparticles slurry. It indicated that a new type of slurry is needed for this new materials and the slurry is prefer as acidic slurry.