Conformal Platinum Thin Films Prepared by Chemical Vapor Deposition under High Oxygen Partial Pressure

Abstract

Conformal deposition of platinum thin films by chemical vapor deposition using ͑methylcyclopentadienyl͒trimethylplatinum as a liquid precursor, whose vapor was transferred by an argon carrier gas, is presented. Conformal coverages at thicknesses of less than 30 nm were obtained under the condition of high oxygen partial pressures and low temperatures. The surface morphology roughened and changed to a discontinuous grain growth when the film thickness and growth temperature were increased. The dense and smooth films with conformal coverage can be used in the storage nodes of capacitors in gigabit dynamic random access memories.Metal-insulator-metal ͑MIM͒ capacitors that consist of high dielectrics and noble metal electrodes are required in gigabit scale dynamic random access memories ͑DRAMs͒. However, MIM capacitors with high dielectrics do not allow for a simplified capacitor structure. Indeed, device shrinkage beyond the advantage of high permittivity requires a three-dimensional structure of capacitors to ensure a storage capacitance of over 20 fF/bit. A platinum electrode is widely used in a simple-stack capacitor of ferroelectric random access memories ͑FeRAM͒ having a 256 kbit density or less. 1 However, a platinum electrode complicates the patterning and fabrication of three-dimensional pillar-type storage nodes because of the difficulty in etching the thick film. Moreover, an additional protective layer is needed to suppress hydrogen diffusion in the back-end process, because platinum has a catalytic effect on reducing dielectric materials. A ruthenium electrode is another candidate for the noble metal electrode in DRAMs, because it enables fine patterning and suppresses such a hydrogen reduction effect. A chemical vapor deposition ͑CVD͒ process of the ruthenium electrode has recently been reported. 2 The oxidative condition is preferred to keep the dielectric layer insulating when the upper ruthenium electrode is deposited. However, the high oxygen partial pressure during the Ru-CVD changes the ruthenium metal to the oxide, RuO 2 . 2,3 Ruthenium dioxide is easily reduced under a reductive condition such as forming gas annealing, so the electrode may be deformed. 4 Therefore platinum, which is the most chemically stable metal in an oxidizing atmosphere, is still a promising candidate for the electrode of MIM capacitors. Moreover, CVD of platinum thin films enables a conformal electrode to be formed on various device structures, which solves the problem of the difficulty in etching a thick film. Among many precursors for the Pt CVD, an organometallic complex ͑methylcyclopentadienyl͒trimethylplatinum ͑MeCpPtMe 3 , Me ϭ methyl group, -CH 3 , Cp ϭ cyclopentadienyl ring, -C 5 H 4 ͒ is the most promising because it is a viscous liquid at room temperature, the vapor pressure is 0.2 Torr at 35°C, and it does not contain halogenide ions. [5][6][7] We reported in a previous paper that a CVD process using the MeCpPtMe 3 precursor is characterized by slow thermal decomposition in low oxygen partial pressure, and by ra...