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TIC OF THE METALORGANIC DEPOSITION PROCESS

SPIN-COAT

V SUBSTRATE

PRE-BAKE

PYROLYZE AND ANNEAL

Figure 1. Schematic of the metalorganic déposition (MOD) process, consisting of: spin-coating, pre-baking, pyrolysis, and annealing.

sition process including a prebake and annealing (if necessary). Metalorganic déposition can be used to form films of uniform composition over large areas having complicated shapes and geometries. The metalorganics, when dissolved in solvent, may be used to coat a suitable substrate in a variety of ways: dispensing the liquid from a standard resist coater, screen printing, and spray or dip coating. The concentration ratios of the chemical constituents or dopants may be adjusted by varying the concentration of precusor materials added to solution. AH this adds up to a simple, inexpensive means of film déposition which is compatible with very-large-scale integrated circuit (VLSI) technology. Metalorganic déposition has been used to deposit a wide variety of thin film materials: YBa 2 Cu 3 0 7 , u Pt, SnOx,3 Au,4 Ag,5 Pd, PbTi03,6 ITO,7 BaTi03,8 and SrTi0 3 . It can provide a rapid means of studying substrate interactions with deposited films, 9 grain growth,10 the effects of dopants, and mapping out multicomponent phase diagrams. In addition, a variety of patterning techniques permits the fabrication of novel sensors and electronic devices. Metalorganics are described as coordinate covalent compounds with a métal atom bonded to an organic liquid via a bridging oxygen, sulfur, phosphorus, or nitrogen atom. Of the many metalorganics from which to choose, only a few of the octoates, neodecanoates, aminés, and mercaptides are commercially available.1112 Other precursor materials must be synthesized in-house. Metalorganic precursors formed by the bonding of a métal ion to a carboxylic acid are referred to as carboxylates. Figure 2a shows a typical carboxylate structure, where M is a métal atom bonded to oxygen and R is a hydrocarbon chain. The numO ber of —O—C—R bonded to M is a funcrion of the valence of M. The solubility, viscosity, and volatility of a carboxylate strongly dépends on the species of métal atom used and the length, number, and structure of the hydrocarbon chain (R) attached to the métal atom. 2ethyl-hexanoates (also called octoates) and neodecanoates, both shown in Figure 2b, are two commonly used ligands. 13 Metalorganics formed using thèse hydrocarbon chain groups hâve been found to hâve high solubility in many solvents and wet most substrates. We hâve successfully synthesized over

MRS BULLETIN/OCTOBER1989

Metalorganic Déposition (MOD)

Carboxylates-

O II M-O-C-R R- Hydrocarbon chain

M- Métal atom

(a) -

CHCH CH CH CH |

2

2

2

3

CH2CH3

x o

2-ethyl-hexanoates, also called octoates

-Ç-R-,

?•

m

C+R 1 +R 2 +R 3 =9 carbons

Neodecanoates

TEMPERATURE ( °C) (b) Figure 3a. Thermogravimetric analysis (TCA) of the décomposition, in air, of Sn (IV) neodecanoate.

Figure 2. (a) Typical carboxylate structure, where M is a métal atom and R is a hydrocarbon chain. (b) Two co