Shallow p-type source/drain extension formation using B 2 H 6 plasma doping for deep submicron CMOS

Abstract

In this paper, we studied the feasibility of using a commercial etch chamber to perform plasma doping to form shallow p<SUP>+</SUP>-n junction. The plasma doping has the advantage of high wafer throughput compared to conventional low energy implanters. Ultra-shallow boron implantation was done in a plasma reactor with a Helicon plasma source and a gas mixture of He+B<SUB>2</SUB>H<SUB>6</SUB>. 0.18 micrometer class PMOS devices were fabricated using the plasma doping and compared with devices with a conventional BF<SUB>2</SUB> S/D extension implant (10 keV BF<SUB>2</SUB> implant, X<SUB>j</SUB> approximately equals 650 Angstrom). The key results are as follows. (1) Shallow boron implant with good process uniformity on a wafer was achieved using the plasma doping process. Boron dose of approximately 5E14 cm<SUP>-2</SUP> and junction depth (X<SUB>j</SUB>) of approximately 250 Angstrom was achieved after S/D annealing. (2) The pMOS devices fabricated using the plasma doping have much better short channel effect (SCE) characteristics than the devices fabricated with 10 keV BF<SUB>2</SUB> implant. The improvement of X<SUB>j</SUB> in the vertical direction of a transistor (from approximately 650 angstrom to approximately 220 angstrom) using the plasma doping resulted in an improvement of approximately 450 angstrom in the lateral direction shown in L<SUB>g</SUB><SUP>min</SUP>. (3) Degradation in gate-depletion was observed for the plasma doping devices; however, the degradation can be recovered by using an extra gate implant step. (4) Compared to devices with the conventional implant, higher R<SUB>sd</SUB> was found in devices with the plasma doping process. This higher R<SUB>sd</SUB> for the B<SUB>2</SUB>H<SUB>6</SUB> cases was most likely due to the less gate-to-drain overlap and carbon/oxygen contaminants introduced during the plasma doping process. (5) Higher gate- edge diode leakage was also observed in the plasma doping devices. The high diode leakage was believed also due to the contaminants.