Carrier concentration profiling on oxidized surfaces of Si device cross sections by resonant electron tunneling scanning probe spectroscopy

Abstract

Two-dimensional characterization of carrier concentration in metal-oxide-semiconductor field-effect transistors with the use of scanning tunneling microscopy Visualization of 0.1-μm-metal-oxide-semiconductor field-effect transistors by cross-sectional scanning tunneling microscopy Appl.Quantitative carrier concentration profiles of super-junction power metal-oxide-semiconductor field-effect transistor devices were obtained by resonant electron tunneling ͑RET͒ scanning probe spectroscopy making use of a discrete energy level of adsorbed C 60 molecules. RET voltage profiles measured on oxidized ͑100͒ surfaces of fine-polished cross sections revealed the presence of separated p-type islands in the n-type epitaxial layer and agreed well with the profiles obtained by local work function spectroscopy, although fluctuations were observed owing to surface defects and variations in the oxide and C 60 film thickness. The derived boron concentration coincides with the implanted boron density obtained by numerical simulations. These results verify that the C 60 RET scanning probe spectroscopy on oxidized surfaces has the ability of quantitative carrier concentration profiling of Si device cross sections, if flat surfaces with good quality are prepared.

Two Dimensional Dopant Profiling by Scanning Tunneling Microscopy

“…[36][37][38] We adopted the preparation of cross sectional surfaces of Si devices as follows. 41,43) First, dicing and ultra-ˆne polishing is used to expose either (100) or (110) surfaces of the device. The polished surfaces are cleaned by cycles of wet-oxidation in H 2 SO 4 :H 2 O 2 (3:1) and etching in diluted ‰uoric acid solution to remove a damage layer.…”

“…One promising STM-based spectroscopy to investigate nanometer-scale roughness of electric interfaces in actual devices is vacuum-gap modulation (VGM) spectroscopy, also called barrier-height spectroscopy. 21,23,41,52,55,56) In this method, while the STM probe was scanning the sample, small modulation of the STM probe-sample gap was introduced at a frequency of 10-20 kHz with a small amplitude dZ of 20 pm by applying a sinusoidal voltage to the STM piezo-scanner. Current response dI was measured with a lock-in ampliˆer at each point of the topographical image.…”

“…Current response dI was measured with a lock-in ampliˆer at each point of the topographical image. 41,53,56) On metal surfaces, the eŠective local work function (LWF) value is deˆned as…”

“…Thus, the LWF value re‰ects type and density of mobile carriers and electrostatic charges beneath the STM probe, leading to the ability to monitor the carrier concentration underneath oxidized Si surfaces. 41,53) Figure 5 shows LWF maps for cross sec- tions of CMOS devices with a gate length of 250 nm and 35 nm, where the source-drain extensions with high donor concentrations appeared brighter than the channel. Note that however the quantitative relation of measured LWF value with the doping concentration is not straight forward because the voltage applied to the probe is shared by the vacuum gap and the band bending region beneath the STM probe depending on type and doping level of the semiconductor.…”

Dopant and Potential Profiling with Atomic Resolution by Scanning Tunneling Microscopy (Invited)

“…This technique has been actually applied to quantitative analysis of doping profiles on cross sections of MOSFETs. [4]…”