The present invention relates to new and useful methods for atomic layer deposition.
Atomic layer deposition (ALD) is an enabling technology for next generation conductor barrier layers, high-k gate dielectric layers, high-k capacitance layers, capping layers, and metallic gate electrodes in silicon wafer processes. ALD has also been applied in other electronics industries, such as flat panel display, compound semiconductor, magnetic and optical storage, solar cell, nanotechnology and nano materials. ALD is used to build ultra thin and highly conformal layers of metal, oxide, nitride, and others one monolayer at a time in a cyclic deposition process. Oxides and nitrides of many main group metal elements and transition metal elements, such as aluminum, titanium, zirconium, hafnium, and tantalum, have been produced by ALD processes using oxidation or nitridation reactions. Pure metallic layers, such as Ru, Cu, Ta, and others may also be deposited using ALD processes through reduction or combustion reactions.
A typical ALD process is based on sequential applications of at least two precursors to the substrate surface with each pulse of precursor separated by a purge. Each application of a precursor is intended to result in a single monolayer of material being deposited on the surface. These monolayers are formed because of the self-terminating surface reactions between the precursors and surface. In other words, reaction between the precursor and the surface should proceed until no further surface sites are available for reaction. Excess precursor is then purged from the deposition chamber and the second precursor is introduced. Each precursor pulse and purge sequence comprises one ALD half-cycle that theoretically results in a single additional monolayer of material. Because of the self-terminating nature of the process, even if more precursor molecules arrive at the surface, no further reactions will occur. It is this self-terminating characteristic that provides for high uniformity, conformality and precise thickness control when using ALD processes.
However, in practice, it has been found that ALD processes are often limited to film growth rates of half a monolayer or less. In particular, film growth rates can be influenced by the choice of precursor and by temperature and pressure limits for the selected precursor. In addition, steric hindrances from the size and shape of precursor ligands can limit the film growth rate given because of the fixed surface density of active reaction sites. These less than complete growth rates for ALD operations present production problems in wafer throughput and cost of manufacturing. In addition, sub-monolayer growth can result in island type growth and thus higher surface roughness.
There remains a need in the art for improvements to ALD processes.
The present invention provides an ALD process that allows for thin film growth rate to be tuned to the needs of a particular deposition process by precursor composition (metal precursor concentration and solvent selection) or manipulation of process conditions (pressure, temperature).
In addition, the present invention provides an ALD process that allows for thin film growth rate to be tuned during the deposition by manipulation of process conditions (e.g. pressure).
The present invention relies on solvent based precursors. Suitable solvent based precursors are disclosed in applicants co-pending U.S. patent application Ser. No. 11/400,904, filed Apr. 10, 2006. Examples of precursor solutes that can be selected from a wide range of low vapor pressure solutes or solids as set forth in Table 1.
Other examples of precursor solutes include Ta(NMe2)5 and Ta(NMe2)3(NC9H11) that can be used as Tantalum film precursors.
The selection of solvents is critical to the ALD precursor solutions. In particular, examples of solvents useful with the solutes noted above are given in Table 2.
Another example of a solvent useful for the present invention is 2,5-dimethyloxytetrahydrofuran.
The present invention is directed to methods of using solvent based precursors, such as those noted above in order to obtain a fixed ALD thin film growth rate. The method of the present invention is described as follows.
In accordance with the present invention, specific film growth rates can be achieved by establishing particular operation parameters for the precursor/solvent combination. For example, Table 3 shows parameters that can be varied depending on the precursor/solvent combination, as long as they are kept within ranges where ALD growth occurs.
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The present invention also provides a method of performing variable growth rates of an ALD film by adjusting one or more operation parameters; e,g, temperature or pressure during deposition. It is preferred according to the present invention to change deposition pressure during an ALD deposition process. In one example, the growth rate of ALD thin films can be altered during deposition by the following method.
It is believed that the advantages of the present invention are provided at least in part because within certain ranges, the solvent partial pressure in the deposition chamber forms a temporary surface layer that does not react with surface reactive sites chemically. The solvent also acts to carry the precursor to the surface and helps remove ligand fragments from the deposition surface, thus opening up free reaction sites for more complete saturation and reaction with the precursor molecules. The total pressure in the deposition chamber can be varied from 0.1 to 50 Torr. The preferred deposition pressure is between 1 and 15 Torr.
It is anticipated that other embodiments and variations of the present invention will become readily apparent to the skilled artisan in the light of the foregoing description, and it is intended that such embodiments and variations likewise be included within the scope of the invention as set out in the appended claims.
This application claims priority from international Application Serial No. PCT/US2007/015917, filed 12 Jul. 2007 (published as WO 2008/010941 A2, with publication date 24 Jan. 2008), which claims priority from U.S. Application No. 60/832,209 filed 20 Jul. 2006.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US07/15917 | 7/12/2007 | WO | 00 | 7/29/2009 |
Number | Date | Country | |
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60832209 | Jul 2006 | US |