Articles you may be interested inSurface loss rates of H and Cl radicals in an inductively coupled plasma etcher derived from time-resolved electron density and optical emission measurements Auger electron spectroscopy study of reactor walls in transition from an O 2 to a Cl 2 plasma Effects of wall recombination on the etch rate and plasma composition of an etch reactorThe effect of chamber wall conditions on the Cl and Cl 2 concentrations in a Cl 2 discharge was studied in an inductively coupled plasma reactor. Cl and Cl 2 mole fractions were determined using optical emission spectroscopy in conjunction with actinometry, while the state of the reactor walls was monitored using a surface probe that enables detection of films and adsorbates that deposit on these walls. Prolonged exposure of the chamber walls to a Cl 2 plasma increases the Cl concentration in the discharge. This increase is due to the decreasing recombination probability of Cl atoms on the walls which with time are covered with a thin SiO 2 film. The source of the SiO 2 is the quartz dielectric window which is sputtered by ion bombardment. A SF 6 /O 2 plasma etches the SiO 2 film from the chamber walls and restores the chamber walls to a ''clean'' state. The Cl concentration in the reactor with these two different states of the wall conditions, under otherwise identical plasma operating conditions, was dramatically different and implied that the wall recombination probability of Cl atoms on the SiO 2 covered walls is considerably lower than that on the clean anodized Al. Changing the state of the walls also changes the rate controlling step for Cl recombination from diffusion limited for the reactor with the clean walls to surface reaction limited for the SiO 2 covered walls. This change in the rate controlling step changes the dependence of the plasma composition on the power, pressure, and gas flow rate.

Articles you may be interested inEvolution of titanium residue on the walls of a plasma-etching reactor and its effect on the polysilicon etching rate

Films and adsorbates that deposit on reactor walls during plasma etching and deposition affect the discharge properties such as the charged particle and reactive radical concentrations. A systematic study of this plasma–wall interaction is made difficult by a lack of diagnostic methods that enable one to monitor the chemical nature of the reactor wall surface. A new diagnostic technique based on multiple total internal reflection Fourier transform infrared (MTIR-FTIR) spectroscopy was developed to monitor films and adsorbates on plasma etching and deposition reactor walls with monolayer sensitivity. Applications of this MTIR-FTIR probe are demonstrated. Specifically, we use this probe to (i) detect etch products and films that deposit on the reactor walls during Cl2 plasma etching of Si, (ii) determine the efficacy of a SF6 plasma to clean films deposited on reactor walls during Cl2/O2 etching of Si, and (iii) monitor wafer-to-wafer etching reproducibility.

Silicon oxychloride films deposited on plasma etching reactor walls during the Cl2/O2 plasma etching of Si must be removed to return the reactor to a reproducible state prior to etching the next wafer. Using multiple surface and plasma diagnostics, we have investigated the removal of this silicon oxychloride film using an SF6 plasma. In particular, a diagnostic technique based on the principles of multiple total internal reflection Fourier transform infrared spectroscopy was used to monitor the films that formed on the reactor walls. The silicon oxychloride film etching proceeds by incorporation of F, which also abstracts and replaces the Cl atoms in the film. If the SF6 plasma is not maintained for a sufficiently long period to remove all the deposits, the F incorporated into the film leaches out into the gas phase during the subsequent etch processes. This residual F can have undesirable effects on the etching performance and the wafer-to-wafer reproducibility. The removal of the silicon oxychloride film from the reactor walls is inherently nonuniform and the end of the cleaning can be detected most easily by monitoring reactor averaged F and SiF emissions.