Imaging through semiconductor wafers and integrated circuit die 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 absorbtion of photons at visible and NIR wavelengths and does not absorb the lower energy SWIR wavelengths.
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Silicon is opaque to visible light, making it difficult to detect defects or alignment. |
Silicon's transparency to SWIR cameras is illustrated here by a sign viewed through a 12" silicon wafer. |
Producers of integrated circuits use SUI 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 viewing the wafer at the 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 presense 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 SUI InGaAs cameras and microscopes with SWIR optimized optics. Inspection using SUI cameras can characterize the optical beam properties of the waveguide outputs and identify any leakage along the sides of the waveguide.
View area camera products suitable for wafer inspection and line scan camera products.