Behavior of Metal-Induced Negative Oxide Charges on the Surface of N-type Silicon Wafers Using Frequency-Dependent AC Surface Photovoltage Measurements

Abstract

The metal-induced negative charge on the surface of n-type silicon (Si) wafers, previously reported in the atomic bridging model as (AlOSi)- and (FeOSi)- networks, was investigated using AC surface photovoltage (SPV) as a function of the frequency ( f) of a chopped photon beam, with the aid of an AC SPV instrument developed in-house. A frequency-dependent AC SPV in Al-contaminated wafers was observed immediately after the rinsing. In the early stages of exposure to air at room temperature after rinsing, the induced AC SPV at frequencies of less than approximately 100 Hz was flat with frequency. This indicated that majority carrier conduction was the dominant mechanism, suggesting that the surface was depleted and/or weakly inverted. With the passage of time, the AC SPV in the lower frequency region increased, yielding an AC SPV vs frequency relationship approaching 1/ f. This demonstrated that the Al-induced negative charge [(AlOSi)-] increased and finally became limited by the depletion layer capacitance (strongly inverted state). The frequency-dependent AC SPV caused by Fe-induced negative charge [(FeOSi)-] was identified as being dependent on Fe concentration on the Si surface. The higher the Fe concentration, the more strongly inverted the Si surface became. The metal-induced oxide charge could be observed, together with other oxide charges such as fixed oxide charge.

Analysis of Au/Si Schottky barrier type AC surface photovoltage in silicon wafer surface dipped into Au aqueous solution

“…The surface Au concentration of the "Au" samples was 2.0 × 10 15 atoms/cm 2 . On the surface of Au-contaminated samples, concentrations of iron (Fe) and Cu on the order of 10 11 atoms/cm 2 were present, but at these levels, the influence of these surface impurities on the AC SPV properties shown in this paper can be ignored [13,14].…”

“…In this device, a resistance and a capacitance between the lower transparent electrode and ground is larger than 100 MΩ and less than 220 pF, respectively. This device is placed in a black box to avoid the interference of stray light from outside [14].…”

Au/N‐type Si Schottky‐barrier contact and oxidation kinetics in Au‐contaminated and thermally oxidized N‐type Si (001) surfaces

“…The frequency-dependent AC SPV was measured with a new instrument, developed in-house, [5] on the basis of the theory reported by Munakata et al [7,8] This instrument evaluates charged states by irradiating the wafer with a blue PB (with a wavelength peak at 470 nm) and an optical power of the order of microwatts. The incident PB power was actually adjusted to 2.5 µW.…”

“…[3,4] When Q mi Q f + Q it + Q ot + Q m holds in the oxide, quantitative analyses of an alternating current surface photovoltage (AC SPV) have already been performed. [5] AC SPV is excited by a chopped photon beam (PB) in semiconductor wafers and has already been proposed for nondestructive evaluation of Si wafers. [5 -8] The AC SPV appears when a depletion and/or inversion layer is formed on the wafer surface.…”

Analyses of Au/Si Schottky Barrier-Induced AC Surface Photovoltages in N-Type Silicon Wafers Rinsed in Au Aqueous Solution

“…Based on AC SPV method, this proposal has been demonstrated to induce the negative charge on Al-contaminated n-type Si (13,14,15) and developed into an atomic bridging mechanism (14,16).…”