AVS 53rd International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS1-WeA

Paper PS1-WeA3
Impact of Chamber Walls on Radical Densities in Cl@sub 2@ ICP Plasmas

Wednesday, November 15, 2006, 2:40 pm, Room 2009

Session: Plasma-Wall Interactions and Plasma Sources
Presenter: G. Cunge, CNRS-LTM, France
Authors: G. Cunge, CNRS-LTM, France
N. Sadeghi, CNRS, France
R. Ramos, Freescale Semiconductor Inc., France
O. Joubert, CNRS-LTM, France
Correspondent: Click to Email
The radical densities in low pressure high-density discharges are controlled mainly by chemical reactions occurring at the reactor walls. This sensitivity of halogen-based plasmas to the chamber walls conditions is known for long time and is at the origin of process drifts. By using laser absorption at 355 nm we have measured the absolute density of Cl@sub 2@ molecules in a typical Cl@sub 2@ plasma operating either in a clean reactor or in a reactor coated with a SiOCl, CCl@sub x@ or TiOCl@sub x@ layer. We report that under identical plasma operating conditions, the Cl@sub 2@ mole fraction in the plasma can vary from 0.1 to 0.6 depending on the chemical nature of the chamber wall coatings. We have then measured the time variation of Cl@sub 2@ and SiCl@sub x@ (x=0-2;4) etch products densities (by UV absorption and mass spectrometry (MS)) during silicon etching both in clean and SiOCl-coated reactor. From the Cl mass balance in the system and from MS measurements we concluded that several species are produced from the SiOCl-coated reactor walls, including heavy Si@sub x@O@sub y@Cl@sub z@ species (with x up to 4). Furthermore, it is obvious from these measurements that the quartz surface below the RF coil behaves differently than the other reactor walls surfaces, and plays an important role in controlling the plasma chemistry. As a matter of fact, due to electrostatic coupling, this part of the equipment is bombarded by more energetic ions than the floating walls of the chamber and is thus an efficient region of production (/loss) of reactive species. Furthermore, the sudden formation or disappearance of a thin conductive layer below the RF coil can lead to plasma instabilities by influencing the electromagnetic coupling between the RF coil and the plasma. The impact of these phenomenons on metal gate etching processes will be discussed in details.