Preparation and properties of antireflection coatings by chemical vapor deposition

Germanium films were deposited in the temperature region of 300 to 450 °C by the thermal decomposition of germane. Electron diffraction, electron microscopy, and infrared absorption studies were made on the films. The deposition parameters, germane concentration and growth temperature have a pronounced effect on surface topography and grain size and consequently on the infrared absorption. An increase in growth temperature results in an increase in grain size and surface roughness. This change in physical properties of the film results in a significant infrared absorption, 20% or greater depending upon the wavelength. Similarly, an increase in germane concentration causes an increase in grain size and surface roughness. Films were deposited on mechanically polished 〈111〉 silicon with 1000-Å oxide coating. The grain size is larger and more defined on the oxide substrates. Silane was thermally decomposed in the temperature region 525 to 575°C. The infrared absorption of the silicon films were obtained from transmission and reflectance measurements. Absorption was 5% or less for most of the films. Film properties, grain size, and surface topography, and effect of deposition parameters on growth of films for use as antireflection coatings by chemical vapor deposition are discussed.