This method helps researchers in the semiconductor industry reduce contamination in the manufacturing process, which improves the yield and performance of their products
Agilent Technologies has announced a simple, reliable method for measuring metal impurities at ultratrace levels in photoresist samples.
This method helps researchers in the semiconductor industry reduce contamination in the manufacturing process, which improves the yield and performance of their products. Photoresists are photosensitive chemicals that play an important role in the manufacture of integrated circuits.
Minute amounts of metal impurities in the photoresist can distort electrical properties and significantly diminish product reliability. Consequently, current acceptable limits of metallic impurities in photoresist are in the range of 10 to 30 parts per billion (ppb) per element and are expected to become less than 10ppb. Agilent's new method provides photoresist detection limits of 0.2ppb or less for the full suite of impurities.
The usual approach to analysing photoresist samples is acid digestion or dry ashing, followed by graphite furnace atomic absorption spectroscopy.
This method is used extensively but it is time-consuming, potentially hazardous, and can introduce contaminants from the apparatus, acid mixture and other reagents. Inductively coupled plasma mass spectrometry (ICP-MS) offers a simpler, more accurate alternative, but several factors have limited its use in this application.
For example, the organic-rich matrix of the photoresist can cause the formation of many polyatomic species that affect the sensitivity of the ICP-MS analysis.
Another concern is the high carbon content in the matrix, which can cause instrument clogging and signal drift.
The method announced today uses an Agilent 7500cs ICP-MS system equipped with a high-sensitivity octopole reaction system (ORS). The ORS eliminates all matrix-based polyatomics that interfere with the measurement of difficult elements such as boron, magnesium, aluminum, titanium, chromium and zinc, as well as argon-based interferences on potassium, calcium and iron.
The sample-introduction system of the Agilent 7500cs is optimized to handle high sample matrices over extended periods and to break down the heavy photoresist matrix to prevent clogging.
Using this method, Agilent chemists measured positive photoresists for 35 typical metal impurities at 0.2ppb or less.
Results show the effectiveness of the ORS in preventing polyatomic ions from reaching the detector, with spike recoveries at 0.5ppb for all 35 elements tested.
Instrument stability over a two-hour period was excellent, with %RSD (percent relative standard deviation) typically less than 3% for the majority of elements.
For further information, request Agilent application note 'Direct analysis of photoresist and related solvents using the Agilent 7500cs ICP-MS', publication number 5989-0629EN, which is available without charge from any Agilent sales office or its website.
