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Gan epitaxy with migration enhancement and surface energy modification

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Gan epitaxy with migration enhancement and surface energy modification


Methods and apparatus for depositing thin films incorporating the use of a surfactant are described. Methods and apparatuses include a deposition process and system comprising multiple isolated processing regions which enables rapid repetition of sub-monolayer deposition of thin films. The use of surfactants allows the deposition of high quality epitaxial films at lower temperatures having low values of surface roughness. The deposition of Group III-V thin films such as GaN is used as an example.
Related Terms: Surfactant Enhancement

Browse recent Intermolecular, Inc. patents - San Jose, CA, US
USPTO Applicaton #: #20130313566 - Class: 257 76 (USPTO) - 11/28/13 - Class 257 
Active Solid-state Devices (e.g., Transistors, Solid-state Diodes) > Specified Wide Band Gap (1.5ev) Semiconductor Material Other Than Gaasp Or Gaalas

Inventors: Philip A. Kraus, Boris Borisov, Thai Cheng Chua, Sandeep Nijhawan, Yoga Saripalli

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The Patent Description & Claims data below is from USPTO Patent Application 20130313566, Gan epitaxy with migration enhancement and surface energy modification.

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CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation claiming priority to U.S. patent application Ser. No. 13/399,695 filed 29 Dec. 2011, which is entirely incorporated by reference herein for all purposes.

FIELD OF THE INVENTION

The present disclosure relates generally to methods and apparatus for forming metal nitride films, such as epitaxial gallium nitride (GaN) films, and in particular to methods and apparatus for forming GaN films with migration enhancement and surface energy modification.

BACKGROUND OF THE INVENTION

The growth of high-quality crystalline semiconducting thin films is a technology of significant industrial importance, with a variety of microelectronic and optoelectronic applications, including light emitting diodes and lasers. The current state-of-the-art deposition technology for gallium nitride (GaN), indium nitride (InN) and aluminum nitride (AlN) thin films, their alloys and their heterostructures (collectively “InGaAlN” herein) is metal-organic chemical vapor deposition (MOCVD), in which a substrate is held at high temperature and gases which contain the elements comprising the thin film flow over and are incorporated into the growing thin film at the surface of the wafer. In the case of GaN, the state-of-the-art may include growth temperatures of approximately 1050° C. and the simultaneous use of ammonia (NH3) and a Group III alkyl precursor gas (e.g., trimethylgallium, triethylgallium).

While methods exist for forming InGaAlN films, there are limitations associated with current methods. First, the high processing temperature involved in MOCVD may require complex reactor designs and the use of refractory materials and only materials which are inert at the high temperature of the process can be used in the processing volume. Second, the high temperature involved may restrict the possible substrates for InGaAlN growths to substrates which are chemically and mechanically stable at the growth temperatures and chemical environment, typically sapphire or silicon carbide substrates. Notably, silicon substrates, which are less expensive and are available in large sizes for economic manufacturing, may be less compatible. Third, the expense of the process gases involved as well as their poor consumption ratio, particularly in the case of ammonia, may be economically unfavorable for low cost manufacturing of InGaAlN based devices. Fourth, the use of carbon containing precursors (e.g., trimethylgallium) may result in carbon contamination in the InGaAlN film, which may degrade the electronic and optoelectronic properties of the InGaAlN based devices. Fifth, MOCVD reactors may have a significant amount of gas phase reactions between the Group III and the Group V containing process gases. The gas phase reactions may result in undesirable deposition of the thin film material on all surfaces within the reaction volume, and in the undesirable generation of particles. The latter may result in a low yield of manufactured devices. The former may result in a number of practical problems, including reducing the efficacy of in-situ optical measurements of the growing thin film due to coating of the internal optical probes and lens systems, and difficulty in maintaining a constant thermal environment over many deposition cycles as the emissivity of reactor walls will change as deposition builds up on the reactor walls. These problems may be common to all the variants of MOCVD, including plasma enhanced MOCVD and processes typically referred to as atomic layer deposition (ALD) or atomic layer epitaxy (ALE).

Other methods for forming InGaAlN thin films include plasma-assisted molecular beam epitaxy (PAMBE), in which fluxes of evaporated Ga, In, or Al are directed in high vacuum at a heated substrate simultaneously with a flux of nitrogen radicals (either activated molecular nitrogen, atomic nitrogen, or singly ionized nitrogen atoms or molecules) from a nitrogen plasma source. The method may be capable of producing high quality InGaAlN thin films and devices, but the method may suffer from a tendency to form metal agglomerations, e.g., nano- to microscopic Ga droplets, on the surface of the growing film. See, for example, “Homoepitaxial growth of GaN under Ga-stable and N-stable conditions by plasma-assisted molecular beam epitaxy”, E. J. Tarsa et al., J. Appl. Phys 82, 11 (1997), which is entirely incorporated herein by reference. As such, the process may need to be carefully monitored, which may inherently result in a low yield of manufactured devices.

Other methods employed to make GaN films include hydride vapor phase epitaxy, in which a flow of HCl gas over heated gallium results in the transport of gallium chloride to a substrate where simultaneous exposure to ammonia results in the growth of a GaN thin film. The method may require corrosive chemicals to be used at high temperatures, which may limit the compatible materials for reactor design. In addition, the byproducts of the reaction are corrosive gases and solids, which may increase the need for abatement and reactor maintenance. While the method may produce high quality GaN films at high growth rates (tens to hundreds of microns per hour have been demonstrated, exceeding those commonly achieved with MOCVD), the reactor design and corrosive process inputs and outputs are drawbacks.

One approach being considered to lower the cost of manufacturing of InGaAlN thin films and devices is to develop methods that lower the energy barrier for surface diffusion (herein referred to as the “surface energy”) of species involved in the growth of the film, thereby allowing high quality films to be formed at lower temperatures. Therefore, there is a need to develop methods and apparatus for delivering beneficial species that lower the surface energy for adatom diffusion on the growth front of InGaAlN thin films in a cost effective manner.

SUMMARY

OF THE DISCLOSURE

The following summary of the invention is included in order to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention and as such it is not intended to particularly identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below.

In some embodiments of the present invention, surfactants are disposed on the surface during the growth of a thin film wherein the surfactants lower the surface energy and increases the lateral diffusion of species involved in the growth of the film.

The deposition of a Group III-V film such as GaN is used as a non-limiting example. In some embodiments of the present invention, apparatus are provided that allow the investigation of the influence of the surfactant on the growth of the film in a combinatorial manner.

BRIEF DESCRIPTION OF THE DRAWINGS

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The drawings are not to scale and the relative dimensions of various elements in the drawings are depicted schematically and not necessarily to scale.

The techniques of the present invention can readily be understood by considering the following detailed description in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a schematic diagram for implementing combinatorial processing and evaluation using primary, secondary, and tertiary screening.

FIG. 2 is a simplified schematic diagram illustrating a general methodology for combinatorial process sequence integration that includes site isolated processing and/or conventional processing in accordance with some embodiments of the present invention.

FIG. 3 presents a flow chart for the deposition of a film according to some embodiments.

FIG. 4 illustrates a schematic diagram illustrating four processing regions and a substrate according to some embodiments.

FIG. 5 presents a graph of the calculated average time needed for a Ga atom to diffuse 5 nm as a function of temperature illustrating the benefits of using a surfactant.

FIG. 6 presents a graph of the calculated reflectivity for a bare sapphire substrate, a GaN layer, and a GaN layer with 2 ML of In.



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stats Patent Info
Application #
US 20130313566 A1
Publish Date
11/28/2013
Document #
13957380
File Date
08/01/2013
USPTO Class
257 76
Other USPTO Classes
257615, 438478
International Class
01L21/02
Drawings
10


Surfactant
Enhancement


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