Inventors at the Cornell Research Foundation have devised a method of selective metallization of high-temperature semiconductors to produce ohmic or rectifying contacts. The process consists of three phases: a lithographic step to define the areas of contact, preparation of the semiconductor surface, and deposition of the metallization via chemical vapor deposition.
The invention provides a method for forming electrical contacts on high-temperature wide-bandgap semiconductors such as diamond and silicon carbide. Because such semiconductors are not attacked by WF6 or other CVD gases, the CVD metals or DVD refractory metal silicides normally will not seed on the surface in the areas exposed during the lithographic step. This problem is overcome by modifying the semiconductor surface in the exposed areas by using an ion beam to implant ions of a refractory metal. Depending on the materials used and the energy of the beam, either damaged surface regions or buried layers below the semiconductor surface will be produced. Buried layers will be exposed by a subsequent etching step. A CVD may now be performed to deposit metallization, which will make contact directly with the semiconductor at the sites of the damaged surface or buried layer.
The process has been successfully demonstrated on silicon dioxide. To elaborate, a surface which would not allow seeding of tungsten has been successfully modified by implantation to cause it to seed tungsten and allow the growth of layers thick enough for interconnects. Developmental effort is required to implement the patented concept with wide-bandgap semiconductors, but this result indicates that the effort would be successful.
This invention overcomes the difficulties in attaching metallization to wide-bandgap semiconductors of the kind that have become important in high-temperature applications, lasers, and LEDs. The process is self-aligned and permits high-purity depositions. The use of refractory materials for the metallization provides good resistance to electromigration and permits high process temperatures. The process can be applied to a variety of semiconductors, including silicon carbide, silicon nitride, boron nitride, and diamond.