The present invention relates to a low temperature chemical vapor deposition process for producing indium-containing semiconductor materials employing triisopropylindium as the source of indium.
Indium containing semiconductor materials have been grown by organometallic vapor phase epitaxy (OMVPE) using conventional organoindium precursors such as trimethylindium, triethylindium, ethyldimethylindium and cyclopentadienylindium. The most common OMVPE indium precursor presently employed is trimethylindium. However, there are several problems associated with the use of trimethylindium. Since trimethylindium is a solid at or below room temperature, the effective vapor pressure of trimethylindium in a bubbler changes with time due to changes in the surface area of solid. This results in transport problems in a OMVPE system. Since trimethylindium decomposes slowly at temperatures lower than 400.degree. C. in an atmospheric reactor, semiconductor film growth below 400.degree. C. is typically inefficient because trimethylindium is too stable at these low film growth temperatures. Furthermore, the use of trimethylindium in low temperature film growth can result in significant unintentional carbon impurity incorporation--due to the formation of methyl radicals during pyrolysis--which can be deleterious to the performance of a semiconductor device.
Additionally, the incorporation of Bi into InAs, useful for far infrared device applications, requires growth temperatures as low as 275.degree. C. At this low growth temperature, trimethylindium decomposition is not complete so the growth rates of InAs and InAsBi are too low.
While ethyldimethylindium is a liquid, its relative compositional stability as a pure molecular compound is questionable. Furthermore, ethyldimethylindium is too stable for low temperature film growth and its use can also result in unintentional carbon incorporation due to the formation of methyl radicals during pyrolysis. Although triethylindium is a liquid, it has been reported to be marginally stable and has been observed to decompose in the "bottle" during storage. Furthermore, triethylindium undergoes parasitic reactions with Group V hydrides such as AsH.sub.3 and PH.sub.3 to form nonvolatile adducts upstream of the substrate in the atmospheric pressure OMVPE reactors. Cyclopentadienylindium is a solid with a vapor pressure an order of magnitude less than trimethylindium and appears to be thermally more stable than trimethylindium which rules out its use for low temperature film growth of indium-containing semiconductor materials.
Therefore, there is a need for an alternative organoindium precursor without methyl groups or substituents that result in unintentional carbon incorporation for the low temperature chemical vapor deposition of indium-containing semiconductor materials. The availability of alternative chemical vapor deposition organoindium precursors with lower pyrolysis temperatures and lower carbon incorporation characteristics would greatly enhance the development of indium containing semiconductor materials and devices.
One object of the present invention is the provision of an improved process for forming indium-containing semiconductor materials using chemical vapor deposition.
Another object is to provide such process employing an indium precursor with a lower pyrolysis temperature than organoindium precursors heretofore used.
Still another object is the employment in the above process of an indium precursor that is more efficiently pyrolyzed at lower film growth temperatures than organoindium precursors heretofore used.
A still further object is to provide a process of the above type employing an organoindium precursor that results in less unintentional carbon impurity incorporation at lower film growth temperatures than with the use of conventional organoindium precursors such as trimethylindium and ethyldimethylindium precursors.
Another object is the provision of an improved indium-containing semiconductor material obtained by the invention process.
Other objects and advantages of the invention will appear hereinafter.