The Deposition of Molybdenum and Tungsten Films from Vapor Decomposition of Carbonyls

Abstract

Molybdenum and tungsten films formed by the pyrolytic decomposition of the respective carbonyls were investigated to determine their usefulness as conductors in microcircuit devices. The relations between deposition variables (such as pressure of carbonyls, pressure of the carrier gas, rate of gas flow, and substrate temperature) and deposition parameters (such as rate of film growth) or film properties (such as resistivity) were studied. The effects of carrier gas substitution on molybdenum film resistivity were determined. At a carbonyl pressure of 0.001 Torr, a hydrogen pressure of 0.01 Torr, a gas flow of 12 std cc/min, and a substrate temperature of 500°C, molybdenum films were deposited with a resistivity close to that of bulk (5.6 µohm cm), at a rate of 3.7 Aå/sec. In molybdenum films deposited at lower substrate temperatures the resistivity increased, presumably because of increased carbon within the films. The resistivity of tungsten film is always greater than the resistivity of Mo films deposited under equivalent conditions. The lowest resistivity achieved in a tungsten film was approximately twice the value for bulk tungsten (5.5 µohm cm). The structures of both molybdenum and tungsten films deposited under conditions that favored the formation of films with the lowest resistivities were examined by x‐ray diffraction as well as replica electron microscope techniques. Measured lattice parameters, when corrected for independently determined stress, were approximately equal to the parameters reported for pure molybdenum and tungsten. In all tungsten films studied, tensile stresses were found, but in molybdenum films the stresses were tensile for substrate temperatures greater than 500°C and compressive for lower temperatures.