Effect of Organic Contamination on the Electrical Degradation of Hydrogen-Terminated Silicon upon Exposure to Air under Ambient Conditions

Abstract

The degradation of the electrical characteristics of hydrogen-terminated silicon ͑both n-and p-doped͒ under typical laboratory environments was investigated. When a hydrogen-terminated silicon ͑H-Si͒ surface was exposed to air under ambient conditions, the current density/bias voltage ͑J-V͒ curve of the mercury-silicon junction thus formed changed significantly during the first 50 h. For n-type H-Si surfaces, the J-V curve initially maintained ohmic characteristics for a period of 8-12 h, then evolved to diode behavior; for p-doped samples, the current density showed a rapid increase and reached a maximum in about 20 h. In both cases, the electrical property was recovered to some extent after sonication in organic solvents. In agreement with infrared spectroscopic results, organic contamination upon exposure to ambient air is suggested to play an important role in the change of the electrical performance of hydrogen-terminated silicon.

Long-Term Stability and Electrical Performance of Organic Monolayers on Hydrogen-Terminated Silicon

“…We note that the careful cleaning and drying steps involved before each measurement reduces such a possibility. Our previous studies revealed that cleaning hydrogen-terminated silicon with organic solvents after being exposed to ambient conditions can remove surface contamination effectively (as evidenced by both infrared spectroscopic and electrical measurements). , It has been previously shown that small amounts of oxidation significantly modify the optical properties of H−Si (Δ value changes); ,, the oxide growth occurring within the “pinholes” on unreacted silicon (Scheme ) would likely change the observed ellipsometric angles (Ψ, Δ), which leads to inaccurate modeling of the monolayer thickness. We believe that the construction of a more accurate model for the partially oxidized silicon−monolayer interface instead of the simple silicon−organic two-layer protocol is necessary.…”

“…To quantify the J − V properties and gain insight into the current transport mechanism through the junctions, the classical thermionic emission theory, a majority carrier model, has been frequently applied with varying degrees of success ,,,,,, ln true[ J 1 − e − q V / k T true] = ln ( A * T 2 ) − q ϕ eff k T + q V n k T where J is the measured current density, V the applied bias, A * the Richardson constant (110 A·cm −2 ·K −2 ), ϕ eff the effective barrier height, ,,,, q the electronic charge, k the Boltzmann’s constant, T the absolute temperature, and n the ideality factor. On the basis of the above equation, we would expect a linear relationship between ln J and V , and a change in the J − V curve at a low-forward bias would yield different values of ϕ eff and n .…”

“…For the fresh samples, both junctions allow a minimal, saturation current to flow under reverse bias, compared to that of the forward bias, indicating that these molecular junctions exhibit ideal rectifying properties. As time progresses, a significant increase in current is identified To quantify the J-V properties and gain insight into the current transport mechanism through the junctions, the classical thermionic emission theory, a majority carrier model, has been frequently applied with varying degrees of success 2,3,11,13,17,18,48 where J is the measured current density, V the applied bias, A* the Richardson constant (110 A • cm -2 • K -2 ), 18 φ eff the effective barrier height, 10,13,18,34,38 q the electronic charge, k the Boltzmann's constant, T the absolute temperature, and n the ideality factor. On the basis of the above equation, we would expect a linear relationship between ln J and V, and a change in the J-V curve at a low-forward bias would yield different values of φ eff and n. On fresh Hg|C12-Sit and Hg|C3Ph-Sit junctions, this linear relationship is evident between +0.15 and 0.45 V and is consistent with what has been observed previously.…”

Infrared spectroscopy of the organic monolayer sandwiched between a Hg electrode and a Si substrate

“…Several groups measured the current-voltage ͑I − V͒ characteristics for hydrocarbon monolayers with a liquid Hg electrode, [6][7][8][9][10][11][12][13][14][15][16] because Hg contacts softly and homogeneously with SAMs. 6,[8][9][10][11][12][13][14]16,19 On the other hand, Ohmic contacts were achieved for Hg/hydrogen-terminated n-type Si structures, 6,15,16,20 because the electron affinity of the hydrogen-terminated n-Si and the workfunction of Hg are energetically close. 6,[8][9][10][11][12][13][14]16,19 On the other hand, Ohmic contacts were achieved for Hg/hydrogen-terminated n-type Si structures, 6,15,16,20 because the electron affinity of the hydrogen-terminated n-Si and the workfunction of Hg are energetically close.…”

Failure Mechanism by Organic Contaminants in Si Device Fabrication

“…Thus far, studies of a few organic contaminants on silicon wafers have been carried out by identifying contaminants by thermal desorption-gas chromatography/mass spectroscopy (TD-GC/MS), 6,7 time of flight-secondary ion mass spectroscopy (TOF-SIMS), 8 X-ray photoelectron spectroscopy (XPS), 9 and Fourier transform-infrared spectroscopy (FT-IR). 10 The phenomenon has been explained by postulated degradation mechanisms but the causes of the device failure due to the organic contamination have not been experimentally studied.…”