High contrast imaging in bonded sample metrology using oblique illumination

A darkfield imaging system comprising:

• an imaging sub-system including an objective lens and a detector configured to image a buried target within a volume of a sample;
• an illumination sub-system, comprising:
• one or more illumination sources providing light with a first spatial profile;
• and
• two or more lens assemblies configured to direct the light from the one or more illumination sources as two or more illumination beams to the buried target along optical paths outside the objective lens, wherein the two or more illumination beams fully overlap at the buried target to provide a common illumination field, wherein the two or more lens assemblies limit numerical apertures of the two or more illumination beams to prevent specular reflection of the two or more illumination beams from entering the objective lens, wherein a respective one of the two or more lens assemblies includes a homogenizer to provide that a respective one of the two or more illumination beams has a second spatial profile with higher spatial uniformity than the first spatial profile according to a selected metric;
• and
• a controller communicatively coupled to the detector, the controller including one or more processors configured to execute program instructions causing the one or more processors to:
• receive one or more images of the buried target from the detector;
• and
• generate one or more measurements of the sample based on the one or more images.