Electrical simulation of scanning capacitance microscopy imaging of the pn junction with semiconductor probe tips

Scanning capacitance microscopy (SCM) enables the imaging of the two-dimensional carrier profiles of small transistors. Initial imaging utilized metal-coated probe tips but the limited resolution achievable with these tips due to their size led us to investigate micromachined silicon tips with a smaller tip diameter. Electrical simulations of a pn junction structure probed with semiconducting tips indicate that image improvements result from the semiconductor nature of the silicon tips as well as from the smaller tip size. The tip becomes active in the imaging process as the capacitance–voltage responses of the tip and sample interact to improve image contrast and decrease the Vbias dependence of the pn junction locations. SCM images of a 60 nm gate length n-metal–oxide–semiconductor device, obtained using a boron-doped silicon tip, demonstrate these effects.