Pulsed excimer‐laser processing of amorphous silicon on non‐crystalline substrates is an important processing technology for large‐area polysilicon electronics, such as flat‐panel displays and two‐dimensional imaging arrays. It also allows for the integration of amorphous silicon and polysilicon devices on the same glass substrate and provides procedures for the doping of self‐aligned thin‐film transistors. Materials studies show that laser‐crystallized polysilicon exhibits a narrow peak in the average grain size as a function of the excimer laser energy density, with a corresponding peak in the electron mobility. This is of particular significance for devices since large grains imply high electron mobility. On the other hand, the peak in the grain size is very narrow and is also accompanied by a peak in the surface roughness of the film. These relationships force a compromise between large grain size for high mobility and homogeneous size distribution for uniformity of device characteristics. A window exists in process parameter space where good‐quality devices with uniform characteristics have been obtained. Also, laser‐processing enhancements, such as laser doping and fabrication of self‐aligned transistors, provide additional tools to fabricate unique devices.
The rapid annealing of ion implantation damage in silicon using the radiation from a graphite heater has been demonstrated. Complete 3-in.-diam wafers were annealed in a single 10-sec exposure with high activation for implants of boron (50 keV; 1×1015 cm−2) and moderate activation for high-dose arsenic implants (140 keV; 6×1015 cm−2). Dopant redistribution was ∼1000 Å for boron and ∼200 Å for arsenic. Leakage currents of implanted p+n and n+p diodes were comparable to those of furnace-annealed control wafers and indicate good crystallinity in the depletion region near the junction. Diode leakage uniformity across the wafers was also excellent. C-V measurements on oxides annealed by this technique showed flatband voltages within 0.5 V of those measured on control wafers. This method of annealing implant damage is a practical alternative to those involving more elaborate power sources such as lasers, electron beams, or high-intensity arc lamps.
We report that continuous, incoherent light from a xenon arc lamp can be used to completely activate implanted Si (100) samples (75As+:100 keV, 1×1015 cm−2) with negligible dopant redistribution and excellent uniformity (sheet resistivity variation less than ±2% over a 3-in.-diam wafer). An entire 3-in. wafer could be activated in only about 10 sec without relative motion of wafer and light beam. The extent to which implant damage was removed by the incoherent light anneal is qualitatively indicated by the carrier mobilities which were within 10% of single-crystal values.
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