Paper PS2-ThA11
Plasma Etch Chamber Wall Deposits – Impact on Etch Species Density and Evaluation of Cleaning Procedures

Thursday, November 12, 2009, 5:20 pm, Room B2

During the last ten years there has been a growing awareness about the impact of the plasma etch chamber wall condition on the density of reactive species in the etch chamber. This is especially the case for ICP chambers at low pressure (5-80mTorr) where gas phase diffusion and recombination at the reactor wall can be a dominant loss mechanism for reactive species. The majority of the studies are carried out for reaction chambers, coated with SiOCl or CF_x -based polymers.

In this paper we expanded the study to metal deposits such as titanium and tantalum which are frequently used for metal gate application in front-end-of-line, or as hard mask material for low-k etching in back-end-of-line. Additionally we made an evaluation of the cleaning procedures to remove these metals from the reactor walls.

CF_x-based polymers where deposited by igniting a polymerizing plasma, while Si, Ti and Ta were deposited by etching Si, TiN and TaN, respectively, in Cl₂/HBr/O₂ plasmas. The composition of the chamber wall deposits was investigated by XPS analysis of so-called ‘floating samples’. Relative density variation of reactive species (Cl, Br, O and F) in “contaminated” chambers was analyzed by actinometry. For the actinometry experiments we added 5% Ar to respectively Cl₂, HBr, O₂ and SF₆ plasmas and we related the peak intensities to the Ar 750nm peak. Our results indicate that the effect of the metal deposits is very similar to the CF_x-based deposits. We can summarize this as a lowering of all tested species densities when the chamber walls contain metal(oxide) traces. By comparing our data with previously published results we can also estimate a recombination probability.

Next to the study on density variations of reactive species we investigated how these metals are best cleaned from the chamber walls. This is again done with actinometry, by comparing the data of ‘clean’ and ‘coated’ chamber walls. For CF_x based coatings and SiOCl coated chambers the cleaning procedure is well known and is mostly done with O₂ and SF₆ based plasmas respectively. For the metals however we found that titanium should be cleaned with Cl₂ plasma and for Ta we observed that none of the tested chemistries was able to quickly remove it. Since our XPS data indicate that the Ti and Ta on the walls is partially in the form of TiO₂ and Ta₂O₅ this is not a surprising result. Finally, we did observed that it’s possible to clean both metals with BCl₃ or SiCl_x containing plasmas but this is beyond the scope of this work.