Laser Direct Write of Conducting and Insulating Tracks in Silicon Carbide
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within the temperature range 250-450'C, the proposed use environment for silicon carbide devices. In addition, metal conductors can oxidize and react with chemical species in hostile environments degrading their conductivity properties and further creating chemical product that can attack the device. Because of these limitations, platinum and silicide conductors are currently being developed for silicon carbide. A laser direct write technology [12,13,14] that can convert insulating silicon carbide exhibiting resistivities greater than 1011 ohm-cm to conductors without the need for external metallization and the effect of pure oxygen gas assist during laser irradiation of silicon carbide are demonstrated. This technology which is applicable to SiC substrates provides a solution to silicon carbide metallization problems and enables the creation of planar and three-dimensional monolithic silicon carbide devices. LASER PROCESSING OF SILICON CARBIDE Bulk 0.025cm thick insulating a-SiC substrates were processed using controlled boron carbide concentrations and a proprietary pressureless sintering thermal treatment cycle. The Carborundum Company processed these substrates [12,13,14]. Experiments were conducted using a modified Nd:YAG laser system with an emission wavelength of 1064 nm and pulse repetition rates from 1000-10000 Hz. The pulse duration time was 70 nsec and the TEM00 or multimode was used. The effect of pure oxygen gas assist was studied using a continuos wave Nd:YAG laser operating at a power density of -50W/cm 2. Pattern formation was achieved by moving the substrate with a programmable x-y table at speeds ranging from 0.1 to 2 cm/sec. For pure oxygen gas assist studies, the substrate was moved at a rate of 0.01 cm/sec. Also, 248 nm KrF excimer laser has been successfully used to obtain the conversion of electrical properties in silicon carbide. Pulse duration was 30 nsec and pulse repetition rates ranged from 100010000Hz. The sample to be irradiated was mounted on a stepper motor driven stage allowing the laser spot to be translated across the sample surface at a controlled rate. Evaluation of the mechanism for the electrical property conversion in these laser-processed materials requires the application of analytical procedures. Scanning electron microscopy (SEM), JOEL Super probe 733 operated at 12KV was used for the structural and chemical characterization. Conventional direct write processes are multi-step requiring at least one addition process to change conductive properties. Laser synthesis direct-write is a one step process; the electrical property conversion is a phase transformation Laser in the substrate resulting from selective rapid Optic system grain grain refinement, solidification, Oxygen recrystallization, and chemical transitions. The fact that selective and controlled electrical g property transitions can be imparted to wide bandgap ceramics, such as silicon carbide and aluminum nitride, by laser excitation is a Fixture "44smart" material behavior. Laser synthesis sic : = , Substrate ena
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