Measurement of Trace Metallic Contaminants on Silicon Wafer Surfaces in Native and Dielectric Silicon Oxides by Vapor Phase Decomposition Flow Injection Inductively Coupled Plasma‐Mass Spectrometry

Abstract

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...

Calibrated Contamination Spiking Method for Silicon Wafers in the 1010 – 1012 Atom / cm2 Range

“…Analyses were carried out with VPD-ICP/MS. 26 For copper, three systems were examined: a modified cleaning solution prepared by 60 g ammonium hydroxide (30%) and 200 g hydrogen peroxide (30%) in 14 L of water at 30ЊC. The second system was a modified cleaning solution prepared by 60 g TMAH (30%) and 200 g hydrogen peroxide (30%) in 14 L of water.…”

Monitoring metal contamination of silicon by multiwavelength room temperature photoluminescence spectroscopy

“…10 TXRF is a nondestructive characterization technique capable of mapping metal contamination. However, it has limited sensitivity to low Z (atomic number or proton number) elements (such as Na, Mg and Al) and no sensitivity to Li, Be and B.…”

“…The VPD technique can be integrated in TXRF systems and ICP-MS systems. 9,10 In VPD TXRF, the water droplet, containing surface contaminants, is dried and its residue is analyzed with various X-ray sources. The benefit of VPD TXRF is that concentrated contaminants, from the entire surface, are dissolved and present in the residue, which significantly lowers the detection limits of elements per unit area, but at the cost of losing local information.…”

Dynamic Reaction Cell ICPMS for Trace Metal Analysis of Semiconductor Materials

“…In this technique, trace metal contaminants in the decomposed silicon oxide layer are concentrated into a droplet of HF, which is usually collected for analysis with a small amount of HF and H 2 O 2 . The sample, typically 200-1000 µL in total volume, is then analyzed by graphite furnace atomic absorption, X-ray fluorescence, or ICPMS (18).…”