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Keywords:

  • LPCVD;
  • Tantalum pentoxide;
  • High dielectric constant;
  • ULSI devices

Abstract

A laminar flow low-pressure chemical vapour deposition (LPCVD) system (LAM IntegrityTM) has been used to deposit tantalum pentoxide (Ta2O5) from Ta(OEt)5 films in the presence of oxygen (O2) at 470 °C at a typical deposition rate of 4 nm min−1. Uniformities of <1.5% (SD 1σ) over a 150 mm silicon substrate were obtained. The layers were annealed under different conditions. It was discovered that the films did not change their stoichiometry as determined by Rutherford backscattering (RBS). The as-deposited films were amorphous but became crystalline (β-Ta2O5) at temperatures > 700 °C. The transmission electron microscopy (TEM) results on crystallisation behaviour were supported by X-ray diffraction data. The electrical properties of the Ta2O5 films have been characterised using MIS (metal/insulator/silicon) capacitor structures. Leakage values of <10−6 A cm−2 at 6 MV cm−1 equivalent applied electric field and breakdown strengths of >7 MV cm−1 at 1.6 μA were obtained for annealed layers. Compound dielectric constants (native silicon oxide thickness of about 2.5 nm plus Ta2O5 of various thicknesses) between 14 and >30 have been measured. The electrical properties reveal the potential use of Ta2O5 as a storage capacitor dielectric in 64 and 256 Mbit DRAM (dynamic random access memory) devices.