fourier transform infrared spectroscopy (ftir)
**Fourier Transform Infrared Spectroscopy (FTIR)** is a non-destructive analytical technique that measures the absorption of infrared radiation by a material as a function of wavelength (typically 400-4000 cm⁻¹), producing a spectrum that reveals molecular bond vibrations, chemical compositions, and thin-film properties. FTIR uses an interferometer to collect all wavelengths simultaneously, then applies a Fourier transform to extract the frequency-domain spectrum, providing high throughput and excellent signal-to-noise ratio.
**Why FTIR Matters in Semiconductor Manufacturing:**
FTIR is a **workhorse characterization tool** in semiconductor fabs, providing rapid, non-destructive measurement of film composition, thickness, impurity concentrations, and bonding chemistry critical for process control.
• **Thin film composition** — FTIR identifies and quantifies bonding configurations in deposited films: Si-O stretching (~1070 cm⁻¹), Si-N stretching (~830 cm⁻¹), Si-H bonds (~2100 cm⁻¹), and C-H bonds indicate film stoichiometry and hydrogen content
• **Interstitial oxygen in silicon** — The 1107 cm⁻¹ absorption peak measures interstitial oxygen concentration in CZ silicon wafers per ASTM F1188, critical for controlling oxygen precipitation and internal gettering
• **Carbon in silicon** — Substitutional carbon at 607 cm⁻¹ is quantified to ensure wafer specifications are met (typically <0.5 ppma for prime wafers)
• **Low-k dielectric monitoring** — FTIR tracks Si-CH₃ bonding (~1275 cm⁻¹), porosity-related OH groups (~3400 cm⁻¹), and carbon depletion during integration that indicates plasma damage to porous low-k films
• **Epitaxial layer characterization** — FTIR measures SiGe composition via mode positions, epitaxial thickness via interference fringes, and dopant activation via free-carrier absorption in the far-IR region
| Application | Absorption Band | Wavenumber (cm⁻¹) | Detection Limit |
|------------|-----------------|-------------------|-----------------|
| Interstitial O in Si | Si-O-Si asymmetric | 1107 | 0.1 ppma |
| Carbon in Si | C-Si | 607 | 0.05 ppma |
| SiO₂ Film | Si-O stretch | 1070 | ~1 nm thickness |
| Si₃N₄ Film | Si-N stretch | 830 | ~2 nm thickness |
| Moisture/OH | O-H stretch | 3200-3600 | ppm level |
| SiGe Composition | Si-Ge mode | 400-500 | ±0.5% Ge |
**FTIR spectroscopy is the semiconductor industry's primary non-destructive technique for monitoring thin-film composition, impurity concentrations, and bonding chemistry, providing rapid, quantitative process control data that ensures film quality and wafer specifications across every stage of device fabrication.**