Multidirectional illumination for hybrid bonding defect detection

A method of pre-bonding inspection, comprising:

• illuminating a surface of a sample by a first light source at a first oblique angle to the surface of the sample and by a second light source at a second oblique angle to the surface of the sample, the surface of the sample having a two dimensional (2D) periodic pattern and defects, wherein the first oblique angle and the second oblique angle have azimuthal directions that are orthogonal to each other in a plane parallel to the surface of the sample;
• acquiring a first optical image, of the surface of the sample, generated by the first light source and a second optical image, of the surface of the sample, generated by the second light source;
• and
• combining the first optical image and the second optical image, wherein
• a combined optical image generated from the first optical image and the second optical image specifies locations of the point defects on the surface of the sample.

A method of chip-to-substrate hybrid bonding, comprising:

• performing a pre-bonding inspection process on a substrate die having metallic bond pads, and a chiplet having metallic bond pads, comprising:
• generating dual optical images of a surface of the substrate die by dual-directional illumination, wherein each optical image of the dual optical images are formed using a different directional illumination of the surface of the substrate die;
• generating a composite optical image of point defects on the surface of the substrate die by combining the dual optical images of the surface of the substrate die;
• generating dual optical images of a surface of the chiplet by dual-directional illumination, wherein each optical image of the dual optical images are formed using a different directional illumination of the surface of the chiplet;
• and
• generating a composite optical image of point defects on the surface of the chiplet by combining the dual optical images of the surface of the chiplet;
• and
• inspecting the generated composite optical images, wherein inspecting the generated composite optical images comprises at least one of:
• determining a location of at least one of the point defects on the surface of the substrate die based on the composite optical image of the point defects on the surface of the substrate die;
• and
• determining a location of at least one of the point defects on the surface of the chiplet based on the composite optical image of the point defects on the surface of the chiplet.