Photon emission microscopy (PEM) is a powerful failure analysis technique that detects extremely faint infrared light emitted by transistors and other devices on a semiconductor die. This light emission occurs when current flows through defective or stressed regions, making PEM invaluable for pinpointing the exact location of failures on complex chips.

How It Works

• Physics: When current flows through a semiconductor junction — especially under abnormal conditions like leakage paths, oxide breakdown, or latch-up — photons in the near-infrared spectrum (wavelengths around 1,000–1,500 nm) are emitted.
• Detection: A highly sensitive InGaAs camera or superconducting nanowire detector mounted on a microscope captures these faint emissions while the chip is powered and operating.
• Overlay: The emission image is overlaid on an optical or layout image of the die, precisely localizing the defect site to within microns.

Key Applications

• Leakage Current Localization: Finding transistors or junctions with abnormal leakage that cause excessive power consumption.
• Gate Oxide Defects: Detecting spots where thin gate dielectrics are breaking down.
• Latch-Up Detection: Identifying parasitic thyristor structures that have triggered.
• Short Circuit Localization: Finding metal-to-metal or via shorts causing current paths.

Backside Emission

For modern flip-chip packages where the die is mounted face-down, PEM is performed through the silicon substrate (backside). Since silicon is transparent to infrared wavelengths, emissions can still be detected, though the substrate must often be thinned to improve signal strength.

PEM is considered one of the most effective non-destructive FA techniques for localizing electrical defects on production ICs.