Ammonia Peroxide Mixture Research Articles

1/f noise reduction in PMOSFETs by an additional preoxidation cleaning with an ammonia hydrogen peroxide mixture

1/f noise magnitude in a 15 μm×0.5 μm PMOSFET was remarkably reduced by simply adding a cleaning step using an ammonia hydrogen peroxide mixture (APM) prior to gate oxidation. Gate input-referred noise level for APM-finished PMOSFETs at f=10 Hz was around -128 dBV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Hz whereas for standard, HF-finished devices, the level was around -114 dBV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Hz. Flat-band voltages (V/sub FB/s) determined by a capacitance-voltage (C-V) measurement were -0.19 V for an APM-finished PMOS and -0.34 V for a HF-finished PMOS. Based on the V/sub FB/ values, interface state densities were determined to be N/sub it/=3.02×10/sup 11/ cm/sup -2/ for APM-finished PMOS and N/sub it/=6.47×10/sup 11/ cm/sup -2/ for HF-finished PMOS. Lower interface state density obtained by the APM preoxidation cleaning is consistent with the remarkable reduction in the 1/f noise magnitude.

Quenching of Porous Silicon Photoluminescence by Ammonia Hydrogen Peroxide Mixture

Low resistivity p‐type porous silicon (PS) samples are subjected to oxidation treatment in an ammonia hydrogen peroxide mixture (APM) and to etching in 0.00035% and 0.0014% ammonia solutions at room temperature for 10 to 2700 s. Photoluminescence (PL) properties of the treated PS are correlated with chemical states and microstructures analyzed by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The intensity of the red PL from PS is increased by 0.00035% ammonia solution, decreased by 0.0014% ammonia solution, and almost completely quenched by an APM. FTIR analysis shows that the ammonia solutions do not affect the chemical states of the PS surface, which is terminated primarily by hydrogen. Immersion in an APM replaces the hydrogen‐terminated surface with an oxygen‐terminated surface. SEM observations indicate that the thickness of the PS layer is reduced with aqueous ammonia treatment for 2700 s, but not with APM treatment. These results suggest that the PL quenching by an APM may relate to the dehydrogenated surface. © 2000 The Electrochemical Society. All rights reserved.

Advances in silicon surface characterisation using light beam injection techniques

The development of new integrated circuits (IC) technologies demands a deeper knowledge of the effects of wet wafer cleaning treatments on microchemical, structural and physical surface properties for better device engineering procedures. In this paper, we report and discuss the results of measurements dealing with the effect of conventional hydrochloric acid peroxide mixture (HPM), ammonia peroxide mixture (APM) and dilute hydrofluoric acid (DHF) treatments on the surface recombination rate, measured using the light beam induced current (LBIC) technique in planar configuration and on surface microroughness by scanning tunnelling microscopy (STM). The results indicate that both APM and HPM produce a stable surface, whose recombination rate (around 10 3 cm s −1) remains constant for days after the cleaning. In contrast, the DHF treatment results in a low surface recombination rate (less than 10 2 cm s −1), which evolves, after an induction period of several hours, to steady-state conditions characterised by surface OH termination and a recombination rate of around 10 3–10 4 cm s −1. STM images and their derived power spectra are in agreement with the interpretation of the changes in surface recombination rates before and after DHF treatments.

Silicon Surface Roughening Mechanisms in Ammonia Hydrogen Peroxide Mixtures

Silicon wafers were exposed to a cleaning sequence containing an HF etching step prior to an ammonia hydrogen peroxide mixture (APM) (or SC1) cleaning treatment. These wafers are subject to roughening according to at least three mechanisms. One roughening mechanism is due to the vapor from the APM mixture, while the other two are strongly related to metal contamination. At first, ammonia vapor from a hot APM solution will condense on the cold hydrophobic wafer surface and will etch the surface. Second, iron‐ion contamination (present as iron hydroxide aggregates in the APM), will catalyze the hydrogen peroxide decomposition. During immersion of the wafer, these iron‐ion aggregates can deposit on the silicon surface. Therefore, local hydrogen peroxide depletion is created, as these aggregates continue to catalyze its decomposition. This causes local etching of the silicon in typical rings having a depth of 2–5 nm, while a rim of 3–8 nm of a silicon oxide is deposited next to the ring. Finally, metals such as copper and nickel can plate on the silicon wafer in the HF step prior to the APM step. They act as the cathode in a galvanic cell while the silicon surrounding the copper (or nickel) nuclei is dissolving anodically. © 2000 The Electrochemical Society. All rights reserved.

Impact of Iron Contamination and Roughness Generated in Ammonia Hydrogen Peroxide Mixtures (SC1) on 5 nm Gate Oxides

Immersion of hydrophobic (HF‐last) silicon wafers into iron‐contaminated ammonia peroxide mixtures (SC1 solution) results in the formation of so‐called clustered light point defects. At these sites, increased surface microroughness and local higher iron concentrations are observed. Also, device yield is strongly affected by the presence of iron contamination into SC1 solutions. It is demonstrated that only dHF/dHCl cleans are capable of completely eliminating any yield loss resulting from iron‐contaminated SC1 treatments. The experimental observations can be understood based on the following model. Hydrogen peroxide decomposition is catalyzed by iron. Iron contamination (present in SC1 solution as insoluble hydroxide aggregates) deposits on the silicon wafer surface upon immersion of the latter. While doing so, the adsorbed iron cluster continues to catalyze further hydrogen peroxide decomposition. Local hydrogen peroxide depletion exposes the bare silicon surface to the etching activity of the ammonia. Local etching of the silicon creates microroughness. Additionally, iron becomes inhomogeneously incorporated into the bulk of the chemical oxide formed. Gate oxide integrity degradation can be observed to correlate with these sites. A subsequent acid clean is only efficient in eliminating the induced yield loss, if the oxide layer (with built‐in iron) is completely removed.

Suppressed Si precipitation at an AlSi/Si contact by the presence of thin SiO2 film on the Si substrate

The effects of Si surface conditions on the susceptibility of Si precipitation at the AlSi (1 wt%)/Si interface have been studied. Conditions of the Si surface on which AlSi films are to be sputtered were varied by two wet cleanings, using an ammonium peroxide mixture (APM) and diluted hydrofluoric acid (HF). For AlSi/Si interfaces, Si precipitation after annealing at 400 degrees C for 2 h and that after AlSi sputtering were observed by scanning electron microscopy after removing AlSi films and by cross-sectional transmission electron microscopy (TEM) respectively. 1.0 mu m diameter contact resistance (Rc) was measured using Kelvin patterns. Complete suppression of Si precipitation at the AlSi/Si interface was observed by SEM for the APM-cleaned contacts resulting in a low and uniform Rc in a wafer, while large precipitates were observed resulting in high and non-uniform Rc for the HF-cleaned contacts. Furthermore, while Si precipitates on the substrate for the HF-cleaned AlSi/Si observed by TEM were epitaxially grown on the substrate, those precipitates for the APM-cleaned one were not grown and scarcely observed in the TEM image. Oxygen atoms formed by the APM cleaning were detected by energy dispersive X-ray spectroscopy at the AlSi/Si interface -even after annealing at 400 degrees C. A new model of the thin silicon oxide layer to suppress Si precipitation is proposed.