Analysis of Anionic Contamination on Wafer Surfaces Manual
Contents
1. Analysis of Anionic oo Contamination on 2 e ec Wafer Surfaces a e Thomas Ehmann j e and Maria Serwe Semiconductor Industry Abstract The quality of a wafer can be seriously affected by ionic impurities on its surface As part of quality control programs in most semiconductor facilities anions cations metals and amines are routinely measured to determine the level of contamination Anionic impurities have increasingly attracted attention because they lead to additional etching of the oxide layer causing light point defects and affecting the amount of metals that adhere to the wafer surface Low sample consumption and cost per analysis together with high speed and short turnover times make capillary electrophoresis CE very suitable for the analysis of low ppb levels of anions on wafer surtaces Conditions Sample 500 ul out of 3 ml ultrapure water used for complete wetting of 1 Chloride 5 Oxalate a 200 mm wafer 2 Sulfate itrate ISTD 25 ppb 5 s Absorbance 8 ae ae ee Injection 125 mbar s 10 mM NaOH mAU 1 4 Nitrate 8 Formate 5 s water dip followed by 10 kV x 10s 25 sample injection AA E Capillary effective length 40 cm total length 48 5 cm t aa internal diameter 50 um 1 0 gt Buffer 2 25 mM pyromellitic acid ig 6 5 mM sodium hydroxide 3 5 0 75 mM hexamethoniumhydroxide 1 6 mM triethanolamine pH 7 7 0 5 buffer replenishment prior to each run 20 25 30 35 40 45 Voltage 30 kV negative polarit2. 5966 4601E es Agilent Technologies
3. rected peak areas Table 1 shows linear ranges and detection limits of the assay using electrokinetic injection Linearity ranges given are based on correlation coefficients r gt 0 996 The data obtained here correlated well with results from ion chromatography IC However CE is more suitable in terms of cost per analysis and ease of use Anion Linear Range ppb Detection Limit ppb Bromide 4 40 01325015 Chloride 2 18 04202 Sulfate 5 48 1 0 0 2 Nitrite 2 23 0 5 0 3 Nitrate 3 31 0 6 0 4 Oxalate 4 44 0 9202 Chlorate 4 42 0 8 0 6 Fluoride 1 10 02072 Formate 2 23 Use 05 Phosphate 5 49 O90 Table 1 Linearity ranges and detection limits of the anions analyzed Innovating the HP Way Literature Ehmann et al Optimization of the Electrokinetic Sample Introduction in Capillary Electrophoresis for the Ultra Trace Determination of Anions on Silicon Wafer Surfaces Chromatographia 1997 Vol 45 301 311 available as Agilent publication number 5966 1991E Equipment Agilent Capillary Electrophoresis system TTT Thomas Ehmann is a chemist at Wacker Siltronic AG Central Analytical Laboratories Burghausen Germany Maria Serwe is an application chemist at Agilent Technologies Waldbronn Germany For more information on our products and services visit our worldwide website at http www agilent com chem Copyright 1998 Agilent Technologies Released 02 98 Publication Number
4. y Time min Temperature 20 C Detection signal 350 60 nm Figure 1 reference 245 10 nm Analysis of anions on wafer surfaces by capillary Preconditioning flush with 0 25 M electrophoresis HCI for 0 5 min flush with buffer for 3 min prior to each run oe Agilent Technologies p Innovating the HP Way Experimental and Results Anion analysis was performed on a Agilent Capillary Electrophoresis system equipped with diode array detector and controlled through a PC based Agilent ChemStation The analysis was based on the Agilent inorganic anion analysis kit see figure caption for more details All vials glass vials for buffer polypropylene vials for samples and clear polyurethane caps were washed with ultrapure water UPW which fulfilled the requirements of the SEMI guidelines Anion stock solutions and electrolyte were prepared in a class 10 000 flow box Calibration standards were prepared daily immediately before use in a clean room under a class 10 laminar flow hood Prior to first use new capillaries were treated by a 30 min flush with 0 5 M NaOH a 30 min flush with electrolyte and 60 min conditioning at 30 kV A capillary was considered to be equilibrated when migration time repeatability of 5 consecutive runs using hydrodynamic injection was lt 2 RSD A typical electropherogram of the analysis is shown in figure 1 Repeatability n 20 with internal standard was lt 0 5 RSD for migration times and lt 3 RSD for cor
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Analysis of Anionic Contamination on Wafer Surfaces Manual