Chemical Vapor Deposition of Oxides from Alkoxides
- PDF / 324,434 Bytes
- 5 Pages / 414.72 x 648 pts Page_size
- 75 Downloads / 268 Views
249
Mat. Res. Soc. Symp. Proc. Vol. 415 01996 Materials Research Society
OR\RO 1 NO/i•ý
/-
OR
LH
OR Rd
R=n-C
10'OLiO/ ]OR R OR
Figure 1. The link between metal elements are established through tridentate oxygens in some of the alkoxy groups 3 . The subsequent reactions used to effect deposition of the oxides are sufficiently mild so that breaking of the tridentate oxygen bond is hindered for steric reasons, thus allowing for the preservation of the metal-to-metal ratio throughout the deposition process. Such deposition reaction scheme is made possible through hydrolysis-assisted pyrolysis or hydrolysis-polycondensation of alkoxide complex at varying water partial pressure. It was suggested 4 ,5 that concerted processes, such as the SN2 type hydrolysis reaction of alkoxide complex, occur preferentially at the terminal alkoxy groups due to steric hindrance. Polycondensation occurs after the hydrolysis, causing the stoichiometric deposition of hydrolyzed alkoxide complex on the substrate( equation 1): AB, (OR)2m + 2kH20 ABJ(H)2k(OR)2-m-k)
,por-phase
AB (OH)2k (OR)2(.-) + 2kHOR
on-substrate, AB,,Ok(OR)2tmek)+
AB,,Ok(OR) 2(mk) + (m - k)H 20
on -,suIstrate
W20
;AB, O,, + 2(m - k)HOR.
(la)
(lb) (lc)
The deposition of precisely stoichiometric LiTaO3 and MgAI204 showed for the first time the successful control of stoichiometry through the selection and control of the precursor structure, along with control over the deposition reactions. Vapor deposition of this kind is referred to as autostoichiometric vapor deposition (AVD) 4 ,5 . The use of alkoxides and alkoxide complexes for MOCVD of oxides is worthy of further investigation for an additional benefit. Hydrolysis reactions conducted at low water partial pressure leads to a well known reaction referred to as the hydrolysis-assisted pyrolysis. 7 Such reactions involving alkoxides are typically milder than free-radical pyrolysis. Carbon contamination can be reduced to minimum level if the reaction is carried out correctly. In this paper, we review the history of alkoxide precursors for the deposition of oxides, the characteristics of different deposition reactions and provide examples of oxide depositions from these precursors to illustrate the advantages and disadvantages of alkoxide precursors. The earliest report on the use of volatile alkoxide precursors for the deposition of oxides were by K. J. Sladek and W. W. Gilbert 8 . They have reported low temperature deposition of A1203, Sb203, TiO2, ZrO2, VOx and BOx by low temperature hydrolytic reactions. The as-deposited films were amorphous in nature. Annealing at higher temperatures resulted in crystallization. In the early 70's, deposition of Si02 from pyrolysis of tetraethylorthosilicate (TEOS) has become popular for good step coverage and convenient operations. 9 Comparing to diketone compounds and other volatile metalorganic precursors, alkoxides have relatively well known chemical characteristics, particularly under hydrolytic conditions. The hydrolysis-polycondensation reactions of alkoxides are
Data Loading...
