Nutech Canister Sampling and Preconcentration System for Detecting VOCs in Semiconductor Cleanrooms

Background

With the rapid development of semiconductor process technology, chip linewidths have entered the nanoscale, imposing increasingly stringent environmental requirements on cleanrooms. Gaseous molecular contaminants, known as airborne molecular contaminants (AMCs), which are smaller than particulate pollutants, can penetrate the microstructures of semiconductor devices and deposit on wafer surfaces, affecting device performance and yield. This significantly impacts the semiconductor manufacturing process. Research has shown that to minimize the impact of AMCs on process yield, the concentration of key AMCs in cleanrooms needs to be controlled at parts per trillion by volume (pptv) levels.

The primary sources of AMCs in semiconductor production cleanrooms are external environmental air and internal process activities. Internally generated AMCs may originate from the release of chemicals used during manufacturing (such as cleaning agents), emissions from cleanroom construction materials, and personnel activities. External environmental air can enter the cleanroom through air purification and filtration systems, affecting the cleanroom’s air quality. By monitoring the gases inside and outside the cleanroom, it is possible to determine whether AMCs originate from external or internal sources. Additionally, monitoring AMCs during different production processes can help trace their impact. Monitoring AMCs inside and outside cleanrooms is crucial for controlling AMC levels in the semiconductor industry.

Nutech Solution

As a global leader in VOCs analysis and testing solutions, Nutech leverages its deep understanding of VOCs analysis challenges and extensive experience to address the unique requirements of AMC analysis in cleanrooms. Nutech pioneered the application of canister sampling and a three-stage cryogenic preconcentration system for VOCs analysis in cleanrooms.

Figure 1: Nutech Sampling and Preconcentration System

Currently, there are no specific standard methods for VOCs detection in the quality control of wafer manufacturing in the semiconductor industry. Nutech refers to the existing TO-15 method by US EPA.

Using Summa canisters, Nutech collects air samples from both inside and outside cleanrooms. The samples are then analyzed qualitatively and quantitatively using a three-stage cryogenic preconcentration technique. Qualitative analysis is performed with reference to the NIST library, while quantitative analysis employs the internal standard method.

Figure 2: Schematic Diagram of Three-Stage Cold Trap Pre-concentration System

Air samples collected from inside and outside cleanrooms using canisters are introduced into the preconcentration system via an autosampler. The sample undergoes water-removal in trap 1, followed by concentration and enrichment in trap 2. The sample is then reverse desorbed and cryogenically focused in trap 3. Upon heating, the sample in trap 3 is rapidly flash vaporized and injected into the GC.

Ultralow temperature water-removal prevents compound loss and overcomes the issue of low efficiency in low-temperature water-removal. The use of spiral adsorbents for low-temperature enrichment (cold trap) addresses the problem of selective compound enrichment, increases safe sampling volume, and enhances system sensitivity. Purely physical cryogenic focusing ensures small-volume, rapid, splitless injection, resulting in sharp peak shapes and improved separation efficiency.

Test Results

TO-15 Standard Gas and Characteristic Compounds in the Semiconductor Industry.

Figure 3: TO-15 and Characteristic Compound Standard Gas Chromatograms for the Semiconductor Industry

We have developed a rapid analysis method targeting key VOC components relevant to the semiconductor industry. This method allows for the completion of analysis within 25 minutes per sample, significantly enhancing analytical efficiency.

Figure 4: Rapid Analysis Chromatogram of Characteristic Compounds in the Semiconductor Industry

Information on Linearity, Detection Limits, and Precision for Selected Compounds

Table 1: Information for Selected Compounds
No.Compound NameCAS No.Average RF RSD (%)Detection Limit (SCAN nmol/mol)Precision (%)
1Dichlorodifluoromethane75-71-83.260.0301.54
21,1,2,2-Tetrachloro-1,2-difluoroethane76-14-22.620.0281.23
3Chloromethane74-87-32.660.0190.79
4Vinyl Chloride75-01-41.480.0261.72
4Chlorotrifluoromethane75-69-42.620.0281.39
5Acrolein107-02-84.490.0612.34
61,1-Dichloroethylene75-35-41.480.0231.47
71,2,2-Trifluoro-1,1,2-trichloroethane76-13-11.310.0201.29
8Acetone67-64-17.040.0582.40
9Carbon Disulfide75-15-01.310.0301.59
10Dichloromethane75-09-23.590.0331.66
11Cyclohexane110-82-72.230.0342.07
12Carbon Tetrachloride56-23-51.640.0322.00
13Benzene71-43-22.460.0342.15
141,2-Dichloroethane107-06-22.720.0372.18
15n-Hexane142-82-52.590.0322.02
16Propylene Glycol Methyl Ether107-98-28.720.0511.69
17Toluene108-88-32.230.0281.69
18Ethylbenzene100-41-43.620.0392.63
19m/p-Xylene108-38-3/106-42-35.590.0412.76
20Propylene Glycol Methyl Ether Acetate108-65-63.910.0470.17
21o-Xylene95-47-65.080.0392.68
221,3,5-Trimethylbenzene108-67-84.830.0330.17

Canister blank TIC and cleanroom outdoor ambient air TIC

Figure 5: Total Ion Chromatogram (TIC) of Cleanroom Outdoor Air (black) and Blank (red).

Conclusion

Using canister sampling and pre-concentration with a three-stage cold trap technology, we conducted air quality assessments inside and outside cleanrooms. This method effectively screens for major VOC species in cleanrooms, identifies VOC sources, and provides data support for VOC control measures in cleanrooms, thereby reducing VOC pollution and improving wafer yield. Nutech’s canister sampling and pre-concentration system is well-established in the semiconductor industry. We specialize in developing customized VOC rapid analysis methods tailored to the semiconductor industry’s need for quick analysis of target compounds.

Note: Due to the confidentiality nature of the semiconductor industry, air quality data from inside cleanrooms cannot be disclosed.