Wafer Inspection

SWIR Backside or Frontside Wafer Alignment and Failure Analysis

Imaging through semiconductor wafers and integrated circuit die for wafer defect inspection with InGaAs cameras is easy because semiconductor materials such as silicon and gallium arsenide are transparent in the short-wave infrared wavelength spectrum. This is due to the bandgap of the molecules, which results in absorption of photons at visible and NIR wavelengths and does not absorb the lower energy SWIR wavelengths.

Producers of integrated circuits use Sensors Unlimited's InGaAs cameras to inspect the quality of pure semiconductor crystals after expitaxial growth into an ingot or boule. Similarly, wafers cut from the boule can be inspected for internal defects or cracks. As the wafers are processed with successive layers to make transistors and memory cells used in modern integrated circuits, SWIR cameras are used to check alignment of the layers. High resolution scans of complete wafers are often accomplished with line scan cameras at the wafer defect inspection stage.

Once circuits are completed, microscope inspection of the circuits operated on wafer probe stations reveals defects due to photonic emissions; photon counting APDs can detect the presence of these faint emissions, then cooled InGaAs cameras see through the backside of the circuit to find the layer and circuit location of the fault. Micro-machining of Micro-Electro-Mechanical Systems (MEMS) devices and silicon optical waveguides require inspection of the engineered structures at various points of their fabrication, which is readily accomplished with Sensors Unlimited InGaAs cameras and microscopes with SWIR optimized optics. Wafer defect inspection using Sensors Unlimited cameras can characterize the optical beam properties of the waveguide outputs and identify any leakage along the sides of the waveguide.