AVS 47th International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS2-ThA

Paper PS2-ThA8
Selective Etching of SiO@sub 2@ in High Density Fluorocarbon Plasmas for Applications in Micro-systems

Thursday, October 5, 2000, 4:20 pm, Room 311

Session: Dielectrics I
Presenter: Ch. Cardinaud, CNRS-University of Nantes, France
Authors: F. Gaboriau, CNRS-University of Nantes, France
M.-C. Peignon, CNRS-University of Nantes, France
G. Turban, CNRS-University of Nantes, France
Ch. Cardinaud, CNRS-University of Nantes, France
Correspondent: Click to Email
In the recent years, plasma processes using high density sources have been extensively developed to meet the more and more stringent constraints required by integrated circuits fabrication. Among the various steps, dielectric etching is the more challenging as processes rely on polymerizing hydrofluorocarbon gases that produce simultaneously deposition and etching. It is thus difficult to achieve adequate SiO@sub 2@/mask etch selectivity and to continue etching in high aspect ratio features at the same time. Our aim is to develop new plasma processes concerning the oxide etching step for micro-machining device elaboration. Fabrication of MEMS (micro electro mechanical systems) and O-MEMS (optical MEMS) requires several conditions : i) a higher etch rate, ii) an extreme selectivity, iii) much longer etching processes. Previous studies have shown that adding methane to a fluorocarbon gas (CHF@sub 3@, C@sub 2@F@sub 6@, CF@sub 4@) yields to a significant improvement of the selectivity from 4 to 20 with no significant loss in the SiO@sub 2@ etch rate (300 nm/min). The present study using in-situ real time measurements by ellipsometry and quasi in-situ XPS analysis is focused on the influence of gas flow rate on the SiO@sub 2@ and Si (acting as a mask) etching using a mixture C@sub 2@F@sub 6@-CH@sub 4@. C@sub 2@F@sub 6@ was chosen due to a higher oxide etch rate compared to CHF@sub 3@ and CF@sub 4@. Increasing the gas flow rate when using pure C@sub 2@F@sub 6@ yields to an increase of both material etch rates ; the selectivity is thus unchanged and equal to 2. In contrast, using C@sub 2@F@sub 6@-CH@sub 4@ mixtures with 40% of methane leads to a significant improvement of the selectivity (from 4 to 15) when increasing total gas flow rate ; indeed, oxide etch rate shows the same behavior as before whereas silicon etch rate decreases when increasing gas flow rate. Besides, XPS analysis exhibits a dependence between the silicon etch rate and the fluorocarbon layer thickness pointing out that this overlayer controls the silicon etching. Influence of the gas flow rate on the gas phase is under study using mass spectrometry, optical emission spectroscopy and Langmuir probe ; these diagnostics will allow us to determine the ion flux on the surface and to correlate the different evolutions of plasma species with the etch rate evolution for a better understanding of SiO@sub 2@ and Si etch mechanisms.