SELECTIVE Reactive Ion Etching of Tungsten Films in Fluorinated Gases
Abstract
The use of reactive ion etching (RIE) with fluorinated gas plasmas, such as SF6, CHF3 and CF4 mixed with oxygen, to achieve selective patterning of tungsten films is reported. Rapid thermal annealing (RTA) was used to improve the properties of sputtered films. The resistivity of W films was found to decrease rapidly with annealing time (within 10sec) and to exhibit an Arrhenius behaviour with annealing temperature. The etch rates of W, Si and SiO2 were measured as a function of oxygen percentage in the fluorinated gas plasma. The results on optimum selectivity indicate that a CHF3/70%O mixture results in W:Si and W:SiO2 etch rate ratios of 2.4:1 and 2.1:1 for unannealed W films, and 1.6:1 and 1.8:1 for annealed samples, respectively. A higher W etch rate selectivity over SiO2 was obtained in an SF6/ 5% O2 plasma where the etch rate ratio is 11. 6:1 for unannealed W films and 3:1 for annealed W samples. For reverse selectivity, the optimum W:SiO2 etch rate ratios measured are 1:7.7 in pure CHF3 gas for unannealed W and 1:4.6 for annealed W. The optimum W:Si reverse selectivity of 1:10 is obtained with an SF6/30%O2 mixture plasma for both annealed and unannealed films. Satisfactory anisotropic edge profiles were obtained with CHF3 /70%O2 and SF6/5%O2 where vertical-to-later etch ratios of 3. 5:1 and 2:1 were measured. Keywords: Tungsten films, Reactive ion etching, Selectivity, fluorinated gases.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 1987
- Accession Number
- ADA183263
Entities
People
- Andrew Steckl
- Wen-sen Pan
Organizations
- Rensselaer Polytechnic Institute