Characteristics of the Surface-State Charge (Qss) of Thermally Oxidized Silicon

Abstract

The nature of the surface-state charge (Qss) associated with thermally oxidized silicon has been studied experimentally using MOS structures. The effects of oxidation conditions, silicon orientation, annealing treatments, oxide thickness, and electric field were examined, as well as the physical location of the surface-state charge. The results indicate that the surface-state charge can be reproducibly controlled over a range 1010-1012 cm -2, and that it is an intrinsic property of the silicon dioxide-silicon system. It appears to be due to an excess silicon species introduced into the oxide layer near the silicon during the oxidation process.In much of the early work on the properties of semiconductor surfaces, experimental results were interpreted within the framework of two quantities: fast and slow surface states (1). "Fast surface states" are electronic states within Che forbidden gap of the semiconductor, located at the surface, which are in good electrical communication with the semiconductor bulk. Because of this, they can act as surface recombination centers. Their density per unit area for both clean germanium and silicon surfaces has been generally found to be of the same order as the surface atom density. If the semiconductor is covered by an adsorbed layer, or an oxide, the density of fast states has been found to decrease to 1011-101~ cm-2. "Slow states," in contrast, have been attributed to ionic contamination within an oxide covering the semiconductor surface. Because of their relatively large distance from the semiconductor, they are in poor electrical communication with it. Their density is a strong function of the ambient and surface treatment of the sample, but generally ranges in the neighborhood of 1012-1013 am-2 In the past several years, the thermally oxidized silicon surface has been investigated very intensively, partly due to its extreme technological importance and partly to the ease with which its characteristics can be studied (2). As a result of these investigations, a detailed picture of this system has emerged which is not explainable strictly within the framework of fast and slow surface states. Vol. 114, No. 3 SURFACE-STATE CHARGE OF OXIDIZED Si 267An idealized representation of the current picture of the thermally oxidized silicon system is depicted in Fig. 1. Fast surface states have been identified, but in many cases their density has been found to be less than 5 x 10 TM cm-2 (3), considerably lower than in other systems, thus leading to the low surface recombination velocity of passivated silicon devices (4). While slow surface states, in the customary sense, have not been evident, ionic space charges within the oxide have been observed. These were found to result from either contamination by relatively mobile ions such as sodium (5, 6), or from exposure to ionizing radiation (7). They are evidently in poor electrical contact with the underlying silicon even when located very near the oxide-silicon interface.These charges within the oxide, which have general...

A non-volatile MOSFET memory device based on mobile protons in SiO2 thin films

“…The fixed positive species is remarkably similar to oxidation induced fixed charge [3] and have recently been attributed to near-interracial over-coordinated oxygen sites induced by interaction with hydrogen [4]. The mobile species, which will be discussed in this work, have only been observed to date in Si/Si02/Si structures and are identified as mobile protons imprisoned inside the oxide of these layered structures [5].…”

Analysis of interface workfunction and process-induced damage of reactive-plasma-deposited ITO/SiO2/Si stack

“…The interface workfunction of ITO electrode was estimated from the obtained C-V curves as follows. [7][8][9][10]21 The relation between flat-band voltage (V FB ) and SiO 2 thickness (t ox ) for experimental samples was plotted. The value of V FB was determined as the voltage at which the measured capacitance becomes the flat-band capacitance (C FB ).…”

“…Although there have been some earlier reports on workfunction values determined by capacitance-voltage (C-V) analysis, the materials of interest were the electrode materials used in the clean metal-oxide-semiconductor (MOS) technology such as doped polysilicon and hafnium-silicide. [7][8][9][10] Furthermore, although the damages induced by the TCO deposition processes determine the electrical properties at the interface, there are few reports on these issues but not with the interface workfunction measurement. In the fabrication process of optoelectronic devices such as solar cells, TCO films are deposited by electron-beam (EB) deposition, 11 sputtering, 12-14 atomic-layer deposition (ALD), 15 reactive-plasma deposition (RPD) [16][17][18] etc.…”

Microelectronic Processing Laboratory at NBS

“…Additionally, a dry nitrogen annealing of the grown oxide layer decreases its hydroxyl content and improves the ability of the photoresist to adhere to the oxide for the subsequent photolithographic process. The annealing of oxide layers after growth has been shown to decrease the fixed charge [8] with an improvement of the junction leakage characteristics.…”