APPLICATION OF NITROGEN IMPLANTATION TO ULSI

Nitrogen is not a commonly used ion species in Si ULSI. It cannot be u sed as an n-type dopant because of its low solubility in Si. However, it shows interesting properties such as the suppression of boron diffu sion when applied to source/drain doping and the nitridation of gate o xide when applied to gate doping. In this report, first, the effects o f nitrogen preimplantation to the formation of boron-doped shallow p()n junctions are described. The technique is successfully applied to 0 .25 mu m PMOSFETs, forming shallow junctions and thus suppressing shor t channel effects. Next, the effects of nitrogen implantation into p() poly-Si gates are studied. The implanted nitrogen diffuses to the ga te oxide during annealing and nitrides the gate oxide. As a result, bo ron penetration through the gate oxide is suppressed and the reliabili ty and hot carrier resistance are improved.