Direct Evidence of the Si Interstitialicy Injection and Fast diffusion effect in Si During Pulsed Laser Melt Process
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DIRECT EVIDENCE OF THE Si INTERSTITIALICY INJECTION AND FAST DIFFUSION EFFECT IN Si DURING PULSED LASER MELT PROCESS
YIH CHANG*, J. CHEN**~, S. TALWAR*, E. Y. SHU*, and THOMAS. W. SIGMON*
*Solid State Laboratory and Department of Electrical Engineering, Stanford University, Stanford, CA 94305. **Technology and Manufacturing Group, Intel Corp., Santa Clara, CA 95051. ABSTRACT High temperature gradient induced fast diffusion effect during pulsed laser melt processes is reported for the first time in the Si semiconductor. We use both the oxidationinduced stacking faults and dislocation loops as markers to determine the degree of enhanced diffusion in the unmelted Si substrate by tracing their movement after laser melt. The crosssectional transmission electron microscope is employed to investigate the defect structures before and after laser melt. The expanded dislocation loops exhibit a significant diffusion and climb occurring during the nanosecond-scale processing duration. We also formulate and solve the governed diffusion equation, based on a high temperature gradient induced electric field, to simulate the dislocation movement. The agreement between the experimental and simulated results verifies that the fast diffusion effect indeed occurs in the Si semiconductor during the pulsed laser melt period. INTRODUCTION An anomalous point defect injection and fast diffusion effect is reported during the characterization of the redistribution behaviors of each atomic species in the heteroepitaxial InxGai~xAs/n+-GaAs(100) layers fabricated using pulsed laser induced epitaxy (PLIE) [1]. A hypothesis, based upon the combined effects of concentration impulse and huge temperature gradient across the liquid/solid (l/s) interface, is proposed to explain the significant solid phase diffusion observed during the pulsed laser melting process. In other words, the impulse of Ga, As, In, and Si exerted by the pulsed laser is believed to pile up at the I/s interface during the nanosecond-scale melting period. As the melt front reaches and regrows from the position of the maximum melt depth, these atoms are then injected into the unmelted GaAs substrate by a high temperature gradient induced fast diffusion effect. In order to understand and confirm this fast diffusion effect, in this presentation, we describe an experiment designed to examine this phenomenon in detail. For this purpose we choose Si substrate material for this experiment. If the proposed high temperature gradient induced fast diffusion effect in fact exists, this phenomenon will also occur in Si semiconductor because of the high thermoelectric power [2]. The advantage of choosing Si is that the diffusion parameters of Si interstitialicy (Si1 ) are established for certain temperature ranges, whereas we are far from understanding the diffusion of Ga and As interstitialicies in GaAs substrate. Therefore, we can formulate the diffusion equation and simulate the fast diffusion effect by using Si as the medium. This study employs the modified processing steps for the format
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