Analytical and mechanical evaluation of diamond films on silicon

Abstract

A diamond film commercially deposited on a 10 cm diameter silicon wafer has been evaluated by a variety of analytical and mechanical procedures. The film is nominally 2.5 µm thick and is very smooth with a surface roughness of only 28.1 nm, as measured by atomic force microscopy. The grain size is very small, with grains from 10 nm to about 100 nm in diameter. A sharp diamond diffraction pattern is obtained across at least 98% of the surface area, as measured by transmission electron diffraction. Raman spectra show a strong diamond band at 1330 cm^–1, as well as a strong graphite band at 1580 cm^–1. Additional bands are seen near 1500 cm^–1 and 1200 cm^–1 and are attributed to non-diamond, non-graphite carbon and to microcrystalline diamond, respectively. Intensity in the graphite band decreases toward the outer edge of the wafer. Elastic recoil detection shows the bulk hydrogen content of the film to range from 1 at. % near the edge of the wafer to 3 at. % near the center. The film is considerably harder than the silicon substrate and is highly adherent. During acoustic emission scratch adhesion testing, the film exhibits a critical load for failure of 11.2 N. At this load the film spalls from the substrate, at the film interface. Almost 50% of the scratch tests also show limited local failure (partial film loss) at a critical load of 2.6 N. Both failure modes may be similar to cohesive failure modes in the underlying silicon substrate which shows critical loads of 4.1 and 10.0 N. The separate failure loads may be related to processes with different friction coefficients.