1. Field of the Invention
The present invention relates to an atomic layer deposition method using a novel group IV metal precursor. More particularly, the present invention relates to an efficient atomic layer deposition method which comprises forming a metal oxide thin film on a substrate by using a group IV metal precursor which is thermally and chemically stable in a carrier gas and highly reactive with a reaction gas.
2. Description of the Prior Art
Recently, there have been performed many studies on the application of an atomic layer deposition method to the formation of a high-k gate oxide film or a dielectric thin film for a capacitor, because the atomic layer deposition method is generally advantageous over a chemical vapor deposition method with respect to the insurance of a uniform composition and thickness of the thin films so deposited.
Metal precursors to be used in the atomic layer deposition method should meet the following qualifications. First, the precursors should be highly volatile as well as thermally and chemically stable in a carrier gas such as N2 or Ar so that they can be efficiently and steadily delivered from a vaporizer to a deposition chamber. Secondly, the precursors should be highly reactive with a reaction gas such as O2 and the like so that the dissociation of ligands from a central metal ion can occur rapidly and completely upon effecting the reaction. Thirdly, the bulkiness or the molecular weight of the precursors should be small so that the deposition rate can be increased, which is defined as the film thickness per one deposition cycle composed of chemical absorption-purge-reaction-purge. Currently, the deposition rate is regarded as a critical defect of the conventional atomic layer deposition method.
The conventional precursors which have been used in the atomic layer deposition method include metal alkoxides such as titanium tetrakis(iso-propoxide), Ti(O-iPr)4; Cp compounds such as cyclopentadienyl titanium; and metal halides such as TiCl4. These prior precursors have small bulkiness due to their low molecular weight and have high reactivity with a reaction gas such as O2. However, the prior precursors are problematic because of their instability in that they are inferior in thermal and chemical stabilities under a carrier gas atmosphere. In particular, the metal halide-based precursors are unsuitable for a semiconductor process. In order to solve these problems, metal xcex2-diketonate-based precursors such as Ti(thd)2(O-iPr)2 (titanium bis(iso-propoxide) bis(2,2,6,6,-tetramethyl-3,5-heptanedionate)) have been developed as an alternative precursor. These metal xcex2-diketonate-based precursors, however, are not desirable in that dissociation of the xcex2-diketonate ligands from the metal ion is difficult because of their low reactivity with a reaction gas, and also the deposition rate is low because of their high molecular weight. Under these circumstances, there has been a continuous need for a precursor appropriate for atomic layer deposition, which is thermally and chemically stable under a carrier gas atmosphere and highly reactive with a reaction gas.
A feature of the present invention is an atomic layer deposition method using a novel group IV metal precursor made by coordinating, as a ligand, N-alkoxy-xcex2-ketoiminates with a group IV metal ion, the precursor being thermally and chemically stable in a carrier gas and easy to disassociate the ligands from the metal ion due to its high reactivity with a reaction gas.
In accordance with one aspect of the present invention, there is provided an atomic layer deposition method which comprises forming a metal oxide thin film by using, as a group IV metal precursor, a complex of the formula M(L)2, in which M is a group IV metal ion having a charge of +4 and L is a tridentate ligand having a charge of xe2x88x922, the ligand being represented by the following formula (I): 
wherein each of R1 and R2, independently, is a linear or branched C1-4 alkyl group; and R3 is a linear or branched C1-5 alkylene group.