SBIR-STTR Award

Aluminum Nitride (AlN) substrates are attractive for III-nitride epitaxial growth due to their high thermal conductivity, close lattice and thermal expansion match to III-nitride compositions used for opto-electronic and electronic devices and their relative ease of growth when compared to Gallium Nitride (GaN). A comprehensive program which integrates the manufacturing of starting material feedstock, single crystal growth and wafering process development. The overall program objective is to develop a process for synthesizing high purity, consistent AlN powder for use a feedstock for the sublimation growth of single crystals. Seeded AlN single crystal growth using a unique vertical furnace provided through DURIP will be used to study the impact of crucible material and design on crystal growth and quality. Crystal slicing and polishing processes will be developed to prepare the substrates for epitaxial growth. Initial studies will be carried out in Phase I which will establish the basis for the Phase II crystal growth technology transfer from Kansas State University to American Xtal Technology. In Phase III AXT will fully commercialize AlN substrate technology. We have proposed a unique program which integrates all aspects of technology which are required to achieve a commercially viable AlN substrate manufacturing process. Successful development of a large-area, high-quality AlN substrate will have significant impact on the development and availability of blue and green III nitride lasers and nitride-based high temperature, high power electronics. Conservative estimates of the potential market for these devices is in the billions of dollars within the next 5-10 years. The devices are important for many military and commercial applications such as high density data storage, solar-blind detectors, high resolution printing, underwater communications, etc.

Keywords:
Powder-Synthesis, Aluminum-Nitride, Single-Crystal, Sublimation, Aln, High-Yield, Wafer-Process, Lar

A1N is an attractive substrate material for electronic applications of III-nitriides since it is a good insulator and has very high thermal conductivity. A1N can be grown by sublimation and condensation as was demonstrated by Slack. Scaling the A1N growth to commercially viable substrates requires improvements in furnace, crucible, seeding, slicing and polishing. AXT with its technology transfer partner, KSU, proposed a comprehensive development for A1N substrates which included source material, crystal growth and wafer preparation. In Phase I, we successfully demonstrated the feasibility of all aspects of the program. Sources of high purity A1N were identified and samples.. The sublimation rate of A1N powder as a function of temperatures was measured and was shown to be sufficiently high for large crystal growth at high temperature. PBN was demonstrated as a suitable crucible and reactor furniture material for A1N growth. A high density of small, unseeded crystals was spontaneously nucleated in the crucible. Small samples of epitaxially grown GaN, as a proxy for A1N, were mechanically and chem-mechanically polished to a high quality surface finish. In summary, all key elements required to grow large A1N crystals and prepare wafers were demonstrated in Phase I. In Phase II, we propose to implement seeded crystal growth by using seed crystals prepared by epitaxial growth of A1N on SiC or sapphire and by controlled spontaneous nucleation, to modify the reactor to give more controlled temperature zones for sublimation and crystallization, to scal up the furnace to allow growth of crystals up to 50 mN diameter by 100mN length and to slice and polish A1N wafers. We will also demonstrate epitaxy growth on the substrates and distribute substrates to users.

Keywords:
A1n Sublimation Condensation Seeded Growth Slicing Chem-Mechanical Polishing Semiconductor