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UV excimer lasers are enabling tools in the formation of ultra shallow junctions (USJ) for ever smaller CMOS logic devices such as CPUs and memory chips, of power devices such as insulated gate bipolar transistors (IGBTs) and of advanced CCD or CMOS based image sensors. The respective functional structures are activated by diffusion-controlled UV excimer annealing with low-thermal-budget. The excimer laser wavelength, fluence and pulse width can be chosen to match the individual process window.
Laser Used:VarioLas Family
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The 308nm excimer laser beam can be applied via a homogeneous line which is scanned along the surface or a via rectangular homogeneous field. The energy density scales with the field size on substrate and can be scaled up to several J/cm², enabling melt and non-melt annealing. Next to mask imaging, line-beam techniques are applied. The pulsed excimer beam activates shallow implants of tens of nm.
A commercial 308nm excimer laser annealing system (ELIAS, Ficontec GmbH) has been tested and qualified for full surface implant activation of a Boron ion implant dose of 1.6E+14cm-², implanted at E=15keV on a 5” Si wafer. Lot-to-lot surface resistance of 120mV/mA (± 10%) on Si(100) wafers are measured after annealing at 3J/cm² with one pulse per area with a square field (2.7x2.7mm2) homogeneity better than ±3% (2s).
Fig. 1 - One shot, 308nm excimer activation of doped Si wafer surface in the melt regime.
Click on image for larger view.
Fig. 2 - Implant activation via melt and non-melt surface annealing works via line-beam scanning (left) or large-field mask imaging (right).
Pulse expanders can be utilized in order to achieve deeper melt zones where thicker layers need to be activated. A throughput of up to 50 wafers per hour can be achieved with high energy excimer lasers.