Paper PS1-TuA11
Process Induced Damages and Their Recovery for Highly-Porous Self-Assembled Porous Silica Low-k Film

Tuesday, October 16, 2007, 5:00 pm, Room 606

To realize the low-k film of k<2.1 with silica material, it is necessary to achieve the porosity higher than 50%. We have been developing porous silica materials. The characteristics of the porous silica is; (a) scalability of the k-value by controlling pore structure with self-assembled process, and (b) post reinforcing and hydrophobizing treatment.¹ The new process technologies to apply such highly porous low-k films to the interconnect module process have been developed, simultaneously. Especially, introduction of the damage recovery process is inevitable.² This paper describes about damage recovery process for the porous silica materials. The porous silica blanket films with k~2.07 and E~6.5 GPa were formed on 300 mm wafers. They were half-etched by fluorocarbon plasma, and were exposed to high-temperature He/H₂ down flow ashing plasma. Then, wet clean by two different types of chemical were examined, followed by the damage recovery process by TMCTS vapor annealing. The samples were evaluated by k-value measurement, FT-IR, and TDS after each step. The porous silica films after the etching and the ashing were first treated by the organic acid type wet chemical solution. The k-value of the films increased from 2.07 (pristine) to 2.66 (etching), 2.67 (ashing), and 2.96 (wet clean). The TDS spectrum showed the desorption of the species originated in the wet chemical solution. In contrast to that, the k-value increased to 2.78 after the treatment by the dilute aqueous solution type chemical. The FT-IR and TDS spectra showed almost no change compared with those after the ashing. The recovery process at the pressure of 4 kPa or 30 kPa were evaluated. The recovery of the k-value was remarkable under the high pressure 30 kPa conditions (k=2.17). The collision probability enhancement between silanol groups on the pore surface and TMCTS molecules diffusing into the pore is important to improve recovery effect. When the incident ion-energy during etching was reduced to change the initial damage level with keeping final film thickness, the k-value recovered clearly at the lower ion-energy condition. The recovery effects by the other molecules, and electrical properties of Cu interconnect structure will be presented. Part of this work was assisted by NEDO.

¹K. Kohmura, et al., Thin Solid Films, 515, 5019 (2007)
²T. Ono, et al., Jpn. J. Appl. Phys., 45, 6231 (2006).