Analysis of impurities in semiconductor grade hydrochloric acid by dynamic reaction cell ICP-MS
Hydrochloric acid (HCl) is widely used in the semiconductor industry. Semiconductor devices are currently being
designed with smaller line widths and are more susceptible to low-level impurities. In more critical processes, the impurities in HCl need to be monitored for continuous performance at desired and achievable levels of quality.
SEMI Standard C27-07081 specifies the maximum contaminant levels for each metal ranging from ppt to 0.1 ppm depending upon the grade or tier.
Inductively coupled plasma mass spectrometry (ICP-MS) traditionally has been an indispensable analytical tool for
quality control because of its ability to rapidly determine analytes simultaneously at the ultratrace (ng/L or parts-pertrillion) level in various process chemicals. However, it should be pointed out that under conventional plasma conditions, argon ions combine with matrix components to generate polyatomic interferences. Some of the chloride-based interferences observed during the analysis of HCl are <sup>37</sup>Cl<sup>1</sup>H<sub>2</sub> on <sup>39</sup>K, <sup>35</sup>Cl<sup>1</sup>6O on <sup>51</sup>V, <sup>35</sup>Cl<sup>16</sup>O<sup>1</sup>H on <sup>52</sup>Cr, <sup>37</sup>Cl<sup>16</sup>O on <sup>53</sup>Cr, <sup>37</sup>Cl<sup>16</sup>O<sup>16</sup>O on <sup>69</sup>Ga, <sup>40</sup>Ar<sup>35</sup>Cl on <sup>75</sup>As.
While cold plasma has been shown to be effective in reducing argon based interferences, it is even more prone to matrix suppression than hot plasma. Additionally, because of the low plasma energy, other polyatomic interferences which are not seen under hot plasma conditions may be preferentially formed. Collision cells using multipoles and low reactive gases have proven useful in reducing polyatomic interferences. This approach necessitates the use of kinetic energy discrimination to remove the unwanted by-products. However kinetic energy discrimination results in the loss of sensitivity, which is an issue when analyzing ng/L levels. Additionally, sensitivity loss is more significant for lighter analytes.