The effects of ambient and dissolved oxygen concentration in ultrapure water ͑UPW͒ on native oxide growth were studied at room temperature using a silicon ͑100͒ surface. Studies focused on the initial stage of the surface oxidation immediately after the HF cleaning. The silicon surfaces were exposed at a fixed duration to the UPW with different dissolved oxygen concentrations, open air, and dry nitrogen, respectively. The SiO 2 equivalent thicknesses of the native oxides formed were then measured and compared. Results indicate that the ambient and the dissolved oxygen concentration in UPW dramatically affect the growth rate of the native oxide. Decreasing the dissolved oxygen concentration in UPW and using an inert and dry atmosphere for the ultracleaning is shown to reduce or eventually prevent the native oxide from growing on silicon surfaces. The SiO 2 equivalent thicknesses of the native oxide formed on these surfaces were characterized by a rapid acid extraction followed by a determination for extractable silicon. The extractable silicon was determined by a high-resolution magnetic-sector ICP mass spectrometer. This analytical method has been demonstrated for measurement of an oxide thickness on a silicon wafer surface down to a monolayer range with a possible 0.1 Å resolution.The presence of interfacial native oxide on a silicon surface has widely been recognized as an impediment to the formation of highquality ultrathin gate, atomic layer epitaxy, and small metal contacts on the surfaces. 1-3 Suppressing oxide growth during the surface cleaning and precisely controlling the interface prior to the advanced ULSI processes have become absolutely critical. This recognition has led to considerable efforts of studying the mechanism of the native oxide growth and developing new measuring techniques that are capable of detecting the ultrathin native oxide formed on a silicon surface.The objective of this paper is to extend our previous studies 4,5 of ultrathin native oxide growth on an HF-cleaned silicon ͑100͒ surface and to improve the technique used for oxide thickness measurements. Previous studies dealt with the effects of UPW exposure time on a bare wafer and showed that native oxide grew immediately during a UPW rinse. The growth rate was found to increase linearly with increasing exposure time during the first 10 min of the rinse. 4,5 The emphasis of this paper is, however, placed on the effects of the ambient and the dissolved oxygen concentration in UPW. The initial stage of the surface oxidation during the first 10 min of the UPW rinse is still the focus. It is the authors' belief that the initial surface oxidation may be closely related to the reaction mechanisms governing the initiation and kinetics of native oxide formation on a silicon wafer surface. This study of the initial surface oxidation is thereby of practical importance to better understand the mechanisms and to find the solutions to suppress the growth of native oxide during UPW rinse and storage processes.In order to carry out such a study,...
A highly sensitive multielement analytical method known as vapor phase decomposition flow injection inductively coupled plasma-mass spectrometry (ICP-MS) was developed and used to measure the concentration of trace metals on silicon wafer surfaces. The method uses hydrogen fluoride vapor to decompose and release metal contaminants from a surface oxide. These trace metals are then collected by scanning a small drop of dilute acid solution throughout the wafer surface. Trace metals in the solution are measured by ICP-MS using flow injection (FI) sample introduction. Potentially, 60 8 11 2 elements can be measured with detection limits ranging from 10 to 10 atom/cm. Typical surface concentrations of trace metals on silicon wafers with native oxides and dielectric oxides were measured and presented.The removal and control of metallic contaminants on silicon wafers is an important aspect of wafer and semiconductor device manufacturing. 1 Metallic contaminants cause deterioration in the performance and yield of semiconductor devicesY During high temperature processes, metals diffuse rapidly into silicon substrates and cause undesirable changes in electrical characteristics. In ULSI manufacturing, very low surface concentration of metals in the range of 10 l~ to 1011 atom/cm 2 or lower is required. This metal contamination level corresponds to less than 0.001% of a monolayer coverage on a wafer surface.Currently, metal impurities on silicon wafers are measured predominately by surface analytical techniques such as total reflection x-ray fluorescence spectroscopy (TXRF) and secondary ion mass spectrometry (SIMS). 4-9 The advantage of these techniques is that these are nondestructive techniques, do not require sample preparation, and they allow on-line or near-line measurements. 8 These techniques have relatively good sensitivity with detection limits in the range of 109 to 1012 atom/cm 2. Traditional TXRF technique has poor sensitivity (>1013 atom/cm 2) for some important low mass elements such as B, Na, Mg, K, and A1. 8 In addition, background interferences inhibit the measurement of other elements such as W-and Fe at usefully low detection limits. Also, the accurate quantitation is difficult due to the lack of representative reference standards.Furthermore, both SIMS and TXRF techniques measure only a very small area of the wafer and evaluate only the top 20 to 30 A layer of the wafer surface which limits their application for measuring metal contaminants in dielectric oxide layers with greater thickness.Another sensitive method currently used for metal analysis on silicon wafers is based on the use of g~'aphite furnace atomic absorption spectroscopy (GFAAS). 1~ In this technique, a silicon oxide layer is decomposed by HF vapor and the metal impurity on a silicon wafer is collected into a very small volume of solution and analyzed for one element at a time by GFAAS. Detection limits achieved are in the range of 109 to 1011 atom/cm 2. The main disadvantage of this method is that only one element can be analyzed at a tim...
Boron determination in borophosphosilicate glass films by the ICP-AES or ICP-MS technique can be performed after dissolution of the sample in HF solution. However, addition of HF to boric acid standard solution can cause a drift in the slope of the calibration curve. The signal change was correlated with the kinetics of the borontetrafluoride complex formation reaction. The mechanism was explained by the selectively increased boron transport into the plasma, which was caused by the more efficient diffusion of borontrifluoride gas through the aerosol particles into the nebulizer gas. With the kinetics of borontetrafluoride complex formation taken into consideration, an accurate and precise method was developed for the determination of boron in BPSG films.
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