The role of pre-anneal conditions on the microstructure of Ge+ implanted Si after high temperature milli-second flash annealing

The effect of the pre-anneal conditions on the final defect microstructure after flash annealing of Ge implanted Si is investigated using transmission electron microscopy. (100) Si wafers were implanted with 30keV Ge⁺ implant at a dose of 1 × 10¹⁵/cm² followed by a 500eV B implant at a dose of 1 × 10¹⁵/cm². The germanium implant produces an amorphous layer 480Å thick and the boron implant is completely contained within the amorphous layer. The wafer was subsequently subjected to an impulse anneal at ramp rates between 50°C/sec and 400°C/sec to temperatures between 700 and 900°C followed by a flash anneal to temperatures between 1100°C and 1300°C. The flash anneal occurred over a microsecond time scale so the ramp rates and the cooling rates are estimated to be 10⁶°C/sec. It was found that the ramp rate and temperature of the impulse pre-anneal has a remarkable effect on the final microstructure and sheet resistance of the implant. For the 760°C pre-anneal impulse temperature, followed by a 1300°C flash, decreasing the ramp rate of the impulse anneal from 400°C/sec to 50°C/sec increases the end of range defect density by 270% while the sheet resistance increased from 613 to 704 ohms/square. As the impulse temperature is increased the effects of the impulse ramp rate appear to decrease. The changes in the electrical and microstructural properties of the Si imply that the relatively low temperature impulse conditions play an increasingly important role as the high temperature flash anneals become shorter.