emiconductor Physics, Quantum Electronics & Optoelectronics, 5 (2), P. 188-192 (2002)

Semiconductor Physics, Quantum Electronics & Optoelectronics. 2002. V. 5, N 2. P. 188-192.

The effect of doping methods on electrical properties and micromorphology
of polysilicon gate electrode in submicron CMOS devices

I. Ahmad1), A. Omar2), A. Mikdad1)

1) Dept. of Electrical, Electronic and Systems Engineering, Faculty of Engineering, 43600 University Kebangsaan Malaysia, Malaysia
Phone: 6-03-89296309; fax: 6-03-89296146; e-mail: ibrahim@vlsi.eng.ukm.my, anuar@vlsi.eng.ukm.my,
2) MIMOS Semiconductor (M) Sdn Bhd, MIMOS Berhad, Technology Park Malaysia Kuala Lumpur, Malaysia
Phone: 6-03-89965000; fax: 6-03-89960387; e-mail: abdullah@mimos.my

Abstract. Two doping methods for introducing phosphorus atoms into polysilicon to form a gate electrode for 0.5 mm CMOS were investigated. These methods were ion implantation and the ”in-situ” one (it is also known as thermal diffusion). For the in-situ method, the concentration of 1.8.1020cm-3 for Si2H6 and phosphane (PH3) were used, in the course of ion implantation applying two different doses: 2.0.1016 and 3.1016cm-2 at 40 keV. The micromorphology of the polysilicon surface was studied using the atomic force microscopy (AFM). The polysilicon thickness obtained via the in-situ method ranged between 12.35 and 26.08 nm, with an average value thickness of 18.0 nm, and its sheet resistance value was 21±1 ohm/square. As for the ion implantation method, at the lower doses the thickness ranged at about 12.00 upto 46.0 nm with an average value of 24.0 nm, and its sheet resistance values were of 36±13 and 45±21 ohm/square, respectively. At the higher doses, the thickness varied from 12.16 to 47.84 nm with an average meaning 23.96 nm, and its sheet resistance value was between 25 to 40 ohm/square. Therefore, polysilicon doped by the in-situ method has smoother and thinner surface and possesses better electrical properties.

Keywords: polysilicon gate, micromorphology, ion implantation.

Paper received 12.02.02; revised manuscript received 15.04.02; accepted for publication 25.06.02.

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