Epitaxial film growth using low pressure MOCVD

Abstract: A method for growing high quality epitaxial films using low pressure MOCVD that includes providing a substrate that is misoriented from a singular plane, placing the substrate into an MOCVD reactor at a total pressure of less than 0.2 atmospheres and then growing an epitaxial film on the substrate. When providing a misoriented gallium arsenide substrate, the MOCVD reactor is set at a temperature in the range of 650 to 750 degrees centigrade to grow an aluminum gallium arsenide film. This temperature is substantially lower than that at which aluminum gallium arsenide epitaxial films are commonly grown and the resulting film has a smooth surface morphology and enhanced photoluminesence properties.

Description: Background of the Invention This invention relates, in general, to a method for growing epitaxial films, and more particularly to a method for growing high quality epitaxial films using low pressure metalorganic chemical vapor deposition (MOCVD). The quality of epitaxial film surface morphology is extremely important in high performance electronic and optoelectronic III-V and II-VI compound devices. Film smoothness influences the quality of submicron lithography and a rough surface morphology at heterointerfaces may degrade electron mobility. Smooth epitaxial film morphology also plays an important role in the operation of optoelectronic devices in such areas as the interfacial recombination velocity, scattering from optical waveguides and the line width of emission from quantum wells. Epitaxial film morphology is dependent upon various growth parameters such as substrate temperature, substrate orientation, ambient pressure and reagent mole fraction. The growth of epitaxial films on substrates that are critically misoriented from a singular plane is well known in the art. Misorientation effects have been previously observed in liquid phase epitaxy (LPE), chloride-transport vapor phase epitaxy (VPE) and molecular beam epitaxy (MBE). Most recently, atmospheric pressure MOCVD has been used to grow epitaxial films on critically misoriented substrates (E.S. Johnson and G.E. Legg, J. Crystal Growth, vol. 88, no. 1, (1988), p.53-66). The above methods of growing epitaxial films on misoriented substrates have lead those skilled in the art to believe that high quality epitaxial films may be grown on substrates having small (less than 3.0 degrees) misorientations from a singular plane. However, it has been shown by low pressure MOCVD that the growth of epitaxial films on substrates being slightly misoriented from the origin of a singular plane will provide rough, faceted epitaxial films due to long range reordering which lowers step surface energy near a singular plane. Therefore, to build high quality electronic and optoelectronic devices, it is critical that a method of growing high quality epitaxial films be provided. Summary of the Invention Accordingly, it is an object of the present invention to provide a method for growing high quality epitaxial films that uses low pressure MOCVD. Another object of the present invention is to provide a method for growing high quality epitaxial films that have a superior surface morphology. It is an additional object of the present invention to provide a method for growing high quality epitaxial films that provides for superior optical properties. Yet a further object of the present invention is to provide a method for growing high quality epitaxial films that is not dependent on a clean or unflawed substrate. Another object of the present invention is to provide a method for growing high quality epitaxial films wherein the films may be grown at relatively low temperatures. A further object of the present invention is to provide a method for growing high quality epitaxial films that employs a lesser quantity of reagents. The foregoing and other objects and advantages are achieved in the present invention by one embodiment in which, as a part thereof, includes the steps of providing a substrate being misoriented from a singular plane to the critical angle or beyond, placing the substrate into an MOCVD reactor having a total pressure of less than 2.10⁴ Pa (0.2 atmospheres) and growing an epitaxial film layer on the substrate. Detailed Description of the Invention Disclosed herein is a method for growing high quality epitaxial films using low pressure MOCVD. Initially, a substrate must be provided. Although the specific embodiment discussed herein will employ a gallium arsenide substrate, one skilled in the art will understand that an indium phosphide substrate or other III-V material substrates or II-VI material substrates of a material such as mercury cadmium telluride may be employed. The substrate provided must be misoriented from a singular plane to the critical angle or beyond. One skilled in the art will understand that a singular plane is a plane wherein the step surface energy has a singular point exactly at the low index orientation. One skilled in the art will also understand that the critical angle is the minimum angle at which long-range reordering ceases to produce rough surface morphology. In employing a gallium arsenide substrate, the singular planes are the {100}, {111}A and {111}B crystallographic orientations. Specific misorientations of gallium arsenide substrates upon which high quality epitaxial films may be grown include a 3.0 to 8.5 degree misorientation from the {100} plane towards the {111}A plane, a misorientation of 4.5 to 12.5 degrees from the {100} plane towards the {111}B plane and a misorientation of at least 4.0 degrees from the {100} plane generally towards the {110} plane. Growing epitaxial films on gallium arsenide substrates having misorientations from the {100} plane less than 3.0 degrees towards the {111}A plane, less than 4.5 degrees towards the {111}B plane and less than 4.0 degrees generally towards the {110} plane will result in epitaxial films having rough surface morphologies. Although misorientations from the {100} plane towards the {111}A, {111}B and {110} planes have been disclosed herein, one skilled in the art will understand that high quality epitaxial films may be grown at misorientations between these planes. These specific misorientations may be determined by extrapolation. Further, misorientations from the {100} plane greater than 8.5 degrees and 12.5 degrees towards the {111}A and {111}B planes, respectively, will cause the growth of epitaxial films having rough surface morphology. Once a gallium arsenide substrate having the proper misorientation from a singular plane has been provided, it is placed into an MOCVD reactor having a total pressure of less than 2.10⁴ Pa (0.2 atmospheres) with an ideal pressure being 4.10³ Pa (0.04 atmospheres). For optimal film growth, a ratio of Group V to Group III source flows of 30 or less should be employed. In order to grow an aluminum gallium arsenide epitaxial film on the gallium arsenide substrate, the reactor should have a temperature in the range of 650 to 750 degrees centigrade with an ideal temperature of approximately 700 degrees centigrade. One skilled in the art will realize that this temperature is well below the approximately 800 degrees centigrade temperature usually required to grow an aluminum gallium arsenide epitaxial film of high quality. It should be understood that the aluminum gallium arsenide epitaxial film grown herein comprises in the range of 10 to 40 percent aluminum. An advantage of the present invention is that the misoriented substrate provided need not be totally cleaned or unflawed. It has been shown that the method described herein will result in the growth of high quality epitaxial films even when grown on slightly defected substrates. One skilled in the art will understand that this will greatly increase yield as well as increasing the quality of devices manufactured.

Claims: A method for growing high quality epitaxial films using low pressure metalorganic chemical vapor deposition comprising the steps of: providing a substrate that is misoriented to the critical angle or beyond from a singular plane; placing said substrate into an MOCVD reactor, said reactor having a total pressure of less than 2.10⁴ Pa (0.2 atmospheres); and growing an epitaxial film on said substrate. The method of claim 1 wherein the providing a substrate step includes providing a substrate comprising one of the group comprising III-V and II-VI materials. The method of claim 1 wherein the providing a substrate step includes providing a gallium arsenide substrate and the growing an epitaxial film step includes growing an aluminum gallium arsenide epitaxial film. The method of claim 3 wherein the MOCVD reactor has a temperature in the range of 650 to 750 degrees centigrade. The method of claim 4 wherein the MOCVD reactor has a temperature of approximately 700 degrees centigrade. The method of claim 4 wherein the providing a substrate step includes providing a substrate that is misoriented 3.0 to 8.5 degrees from the {100} plane towards the {111}A plane. The method of claim 4 wherein the providing a substrate step includes providing a substrate that is misoriented 4.5 to 12.5 degrees from the {100} plane toward the {111}B plane. The method of claim 4 wherein the providing a substrate step includes providing a substrate that is misoriented at least 4.0 degrees from the {100} plane generally towards the {110} plane. The method of claim 4 wherein the providing a substrate step includes providing a substrate that is misoriented from the {100} plane towards planes between the {111}A, {111}B and {110} planes. The method of claim 4 wherein the MOCVD reactor has a Group V to Group III source flow ratio of 30 or less.

Inventors: JOHNSON ERIC S, JOHNSON, ERIC S.
Applicants: MOTOROLA INC, MOTOROLA, INC.
Application year: 1990
Main classification: C30B25
IPC codes: H01L21, C30B29, C30B25, H01S5