Nutech Pre-Concentration System for PGME and PGMEA Monitoring in Semiconductor Manufacturing

Background

As semiconductor manufacturing technology advances towards smaller nodes (e.g., 3nm, 2nm) and high-density integration, the precision and stability of the photolithography process have become critical factors determining chip performance. Propylene Glycol Methyl Ether (PGME) and Propylene Glycol Methyl Ether Acetate (PGMEA), as key components of photoresist solvents, developers, and cleaning agents, are used throughout the entire photolithography process. Fluctuations in PGME/PGMEA concentrations within the cleanroom can lead to uneven photoresist thickness or pattern defects during development, directly impacting chip yield. This is particularly critical in advanced processes such as Extreme Ultraviolet (EUV) lithography, where nanometer-scale errors can cause device failure. Furthermore, upon volatilization, PGME and PGMEA can form airborne molecular contaminants (AMCs). Similar to other gaseous pollutants, these AMCs can penetrate high-aspect-ratio regions of nanoscale semiconductor structures and deposit on the wafer surface through physical adsorption or chemical reactions, leading to degradation of dielectric layer performance, metal line shorts, and ultimately affecting device reliability and production yield. Therefore, monitoring PGME, PGMEA, and other volatile organic compounds (VOCs) in the cleanrooms of chip manufacturing facilities is essential.

The concentrations of PGME and PGMEA in the cleanroom air of chip manufacturing facilities are typically in the parts-per-billion (ppb) or sub-ppb range. Traditional Gas Chromatography-Mass Spectrometry (GC-MS) methods often struggle to meet the required sensitivity and usually need to be coupled with pre-concentration techniques to enhance detection limits. Air pre-concentration technology has been widely applied for the analysis of VOCs in ambient or indoor air. PGME is a polar compound with a boiling point of 120°C and is miscible with water. PGMEA is a moderately polar compound with a boiling point around 152°C and a water solubility ratio of approximately 1:5 at 20°C. Both compounds have relatively high boiling points and are significantly affected by water, which leads to short calibration curve validity periods when using pre-concentration GC-MS techniques. Therefore, ensuring consistent water removal by the pre-concentrator while improving the consistency and recovery rates of PGME and PGMEA has become a key challenge that needs to be addressed.

Nutech Solutions

As a global leader in VOCs analysis and testing solutions, Nutech, leveraging its profound understanding of the challenges in VOCs analysis and accumulated application experience, and considering the physicochemical properties of PGME and PGMEA, has successfully applied its pre-concentration system for the detection and analysis of PGME, PGMEA, and other VOCs in the cleanrooms of chip manufacturing facilities. This was achieved by modifying relevant modules of the pre-concentrator, optimizing method parameters, and employing a highly efficient water removal mode, resulting in favorable application outcomes.

This system exhibits the following features: It utilizes a three-stage cold trap pre-concentration technique. Helical sorbent low-temperature enrichment (cold trapping) addresses the issue of compound enrichment selectivity, allowing for larger safe sampling volumes and achieving higher system sensitivity. A purely physical cryogenic focusing trap ensures rapid splitless injection of small volumes, resulting in sharp peak shapes and improved separation. Stable flash vaporization temperatures further enhance the repeatability of PGME and PGMEA analysis. The highly efficient water removal performance significantly reduces the trace amounts of water entering the GC-MS, thereby improving the long-term stability of the GC-MS system.

Figure 1. Technical Schematic Diagram of the Three-Stage Cold Trap Pre-Concentration System

Test Results

HJ759-2023 standard gas and PGME/PGMEA standard gases were mixed, diluted, and humidified to prepare a standard working gas with a concentration of 10.0 nmol/mol. Aliquots of 30 mL, 60 mL, 120 mL, 300 mL, 600 mL, and 750 mL of the standard working gas were sampled separately to create a standard series with target compound mole fractions of 1.0 nmol/mol, 2.0 nmol/mol, 4.0 nmol/mol, 10.0 nmol/mol, 20.0 nmol/mol, and 25.0 nmol/mol, with an internal standard concentration of 5.0 nmol/mol. Calibration curves were established by plotting the ratio of the quantitative ion peak area of the target compound to that of the corresponding internal standard (y-axis) against the mole fraction (x-axis), and quantification was performed using the calibration curve method. The correlation coefficients (R²) of the linear equations for the target compounds were all above 0.995 (Table 1). The Total Ion Chromatogram (TIC) and Extracted Ion Chromatograms (EICs) of the target compounds are shown in Figure 2 and Figure 3.

Figure 1. Chromatogram (TIC) of PGME, PGMEA and other VOCs

Figure 1. Chromatogram (EIC) of PGME, PGMEA and other VOCs

Table 1. Method Information for PGME, PGMEA, and Selected VOCs

Conclusion

Addressing the issue of short calibration curve validity for PGME and PGMEA, Nutech achieved stable test results by upgrading the pre-concentrator hardware structure and optimizing method parameters. The correlation coefficients (R²) of the calibration curves for PGME, PGMEA, and other key VOC components of concern to chip manufacturing facilities were all above 0.995, with a significantly improved validity period, meeting the stringent quality control and low maintenance requirements of chip manufacturing enterprises. This method provides a valuable reference for the monitoring of PGME and PGMEA in the cleanrooms of chip manufacturing facilities.