Patent ID: 8396281

Claim:
A method for inspecting substrate internal defects, comprising: providing a solar cell substrate having an upper surface, a lower surface and a plurality of lateral sides connected between the upper surface and the lower surface; providing at least one light source disposed on one of the lateral sides on the substrate and configured to emit a light beam to the lateral side for correspondingly penetrating the substrate; and providing an image capturing module disposed above the substrate for retrieving an image of the upper surface; wherein an incident angle of the light beam to the respective lateral side is limited within a first predetermined angle, and the first predetermined angle is a critical angle to allow the light beam to have total reflection in the substrate and is defined by an included angle between a light ray propagation direction and a normal line to the lateral surface; wherein the incident angle of the light beam to the respective lateral side is limited within a second predetermined angle, the second predetermined angle is the far half of the first predetermined angle away from the image capturing module; wherein a center of the light source is located substantially at an angle-bisecting line of the second predetermined angle; wherein a width of the lateral side is defined by a thickness of the substrate, and a diameter of the light source is larger than the width of the lateral side; and wherein the light beam emits the light beam towards the lateral side of the substrate via a condensing lens to have the light beam focus on the lateral side so that the light beam emitted by the light source illuminates only on part of the lateral side instead of illuminating on whole lateral side.