{"id":13972,"date":"2024-02-20T08:00:35","date_gmt":"2024-02-20T14:00:35","guid":{"rendered":"https:\/\/www.thermofisher.com\/blog\/materials\/?p=13972"},"modified":"2024-02-14T11:13:28","modified_gmt":"2024-02-14T17:13:28","slug":"analyzing-hydrogen-concentration-in-silicon-nitride-films-using-ftir-spectroscopy","status":"publish","type":"post","link":"https:\/\/www.thermofisher.com\/blog\/materials\/analyzing-hydrogen-concentration-in-silicon-nitride-films-using-ftir-spectroscopy\/","title":{"rendered":"Analyzing Hydrogen Concentration in Silicon Nitride Films Using FTIR Spectroscopy"},"content":{"rendered":"

In the world of semiconductor fabrication<\/a>, understanding the hydrogen concentration within silicon nitride (SiNx:H) films has become increasingly important. These films exhibit excellent physical, mechanical, and optoelectronic properties, making them a popular choice in industries like automotive, aerospace, and medical devices.<\/p>\n

Understanding the hydrogen concentration within these films can influence their processing and performance, including aspects like etch rate, refractive index, and film stress.<\/p>\n

Traditionally, two techniques, Nuclear Resonance Analysis-Rutherford Backscattering Spectroscopy (NRA-RBS) and Secondary Ion Mass Spectrometry (SIMS), have been used to analyze the composition of solid surfaces and thin films. However, these methods are both destructive and not well-suited for a production environment where samples need to be analyzed in every deposition cycle.<\/p>\n

Enter Fourier Transform Infrared Spectroscopy<\/a> (FTIR), a non-destructive, fast, precise, and reliable analytical technique for characterizing dielectric films in semiconductor wafer processing.<\/p>\n

What is FTIR?<\/h2>\n

Fourier transform infrared is the preferred method of infrared spectroscopy. When IR radiation is passed through a sample, some radiation is absorbed by the sample and some passes through (is transmitted). The resulting signal at the detector is a spectrum representing a molecular \u2018fingerprint\u2019 of the sample. The usefulness of infrared spectroscopy arises because different chemical structures (molecules) produce different spectral fingerprints.<\/p>\n

FTIR spectrometers<\/a> offer a vast array of analytical opportunities in academic, analytical, QA\/QC, and forensic labs. Deeply ingrained in everything from simple compound identification to process and regulatory monitoring, FTIR covers a wide range of chemical applications, especially for polymers and organic compounds, and is well suited for semiconductor metrology and Silicon thickness measurement.<\/p>\n

Why is FTIR Important to Semiconductor Wafer Analysis?<\/h2>\n

The FTIR method uses the unique IR absorption bands of N-H and Si-H at 3350 cm-1 (N-H stretching) and 2170 cm-1 (Si-H stretching) regions, respectively, as the basis for quantitative analysis on hydrogen concentration in SiNx:H films.<\/p>\n

The Lanford and Rand method is a commonly used approach for computing hydrogen concentration in SiNx:H films based on FTIR measurements. This method allows the determination of bond densities and hence, hydrogen concentration from FTIR measurements. It correlates the hydrogen content determined by NRA-RBS absorption on a series of SiNx:H samples with different compositions, the IR absorption cross sections of Si-H and N-H bonds, and the proportionality factor between N-H and Si-H.<\/p>\n

In a recent study, silicon nitride films on silicon wafers with thickness ranging from 2990 to 5150 were measured by transmission FTIR spectroscopy. The resulting atomic % hydrogen (at.% H) values were compared with those obtained from NRA-RBS measurements. The results showed a general agreement within 5%, suggesting the reliability of the FTIR method using the Lanford and Rand equations.<\/p>\n

However, for a more rigorous and often more accurate approach to quantitatively determine the hydrogen concentration, the partial least squares (PLS) modeling approach is recommended. This approach requires careful considerations, including ensuring the wafer type of the calibration set matches those to be analyzed, maintaining low variability in wafers, controlling backside finish and resistivity, and ensuring the hydrogen concentration and thickness range of the calibration set bracket those of the samples.<\/p>\n

Summary<\/h2>\n

FTIR spectroscopy, particularly the Lanford and Rand method, is a valuable tool for non-destructive, fast, and reliable analysis of hydrogen concentration in silicon nitride films. With careful calibration and consideration, this approach can provide valuable insights for process monitoring in semiconductor fabrications<\/a>.<\/p>\n

To get more details, including sampling methods, equations, FTIR instruments<\/a> used, examples, and spectra, read the application note, Quantitative determination of hydrogen concentration in silicon nitride dielectric films on silicon wafers using FTIR spectroscopy<\/em><\/a><\/p>\n

Additional Resources<\/h2>\n