CVD of TixSi1-xO2 films:: Precursor chemistry impacts film composition

Thin films of composition Ti(x)Si(1-x)O(2) were grown by low-pressure (LP) CVD on silicon (100) substrates using tetraethyl orthosilicate (TEOS), [Si(OC(2)H(5))(4)], and either titanium isopropoxide (TTIP), [Ti(O-(i)Pr)(4)], or anhydrous titanium tetranitrate (TN), [Ti(NO(3))(4)], as the sources of SiO(2) and TiO(2), respectively. The substrate temperature was varied between 300 degreesC and 535 degreesC, and the individual precursor delivery rates ranged from 5 seem to 100 seem. Under these conditions, growth rates ranging from 0.6 nm min(-1) to 90.0 nm min(-1) were observed. As-deposited films were amorphous to X-rays, and cross-sectional transmission electron microscopy (TEM) images showed no compositional inhomogeneity. Rutherford backscattering (RBS) spectrometry revealed that the relative concentration of TiO(2) and SiO(2) was dependent upon the choice of TiO(2) precursor. Possible multi-precursor deposition scenarios are presented and discussed in relation to the observed variation of film stoichiometry. For the TTIP-TEOS pair, the systematic variation of Ti content with deposition conditions could be accounted for by a growth scenario that limits SiO(2) growth to TiO(2) sites within the composite film. For the case of TN-TEOS the Ti content remained close to 50 % for all conditions studied. A specific chemical reaction between TN and TEOS prior to film deposition accounts for the observed composition.