OPTICAL ILLUMINATION AND INSPECTION SYSTEM FOR WAFER AND SOLAR CELL DEFECTS

摘要

An embodiment of an optical inspection system for detecting cracks in a silicon wafer or in intermediate layers of a solar ceil is disclosed including a laser for providing a coherent light beam. The laser may be a typical HeNe laser. A video camera sensitive to near infrared frequency light is disposed co-linear with the laser and includes a macro-zoom lens. The solar panel that is to be inspected is located in a test plane and in the field of view of video camera. The laser is used to aid in directing the camera onto the solar panel. A first quartz-halogen collimated light source is projected through and filtered by a long pass filter which passes wavelengths of 1.0 micron. The filtered collimated light from the light source is projected onto the surface of a white paper panel. The source of the white paper contains irregularities on the same order as the 1.0 micron wavelength of the light through the long pass filter. These irregularities cause the light reflected from the white paper to diffuse. The white paper is positioned such that the diffuse light reflected therefrom falls upon the surface of the solar panel in the test plane. Because the light rays reflected from white paper are diffuse they strike the surface of the solar panel at a plurality of various angles. As the light rays pass through the solar cell layer interfaces will be reflected in the direction of the camera. Those rays which fall in the path of the field of view of the camera, become the object image from which a real image is created and may be viewed on a control monitor. Cracks in the solar cell silicon layer or glass covers can be observed on the control monitor, and printed by a video graphics printer or stored via a VCR for permanent documentation purposes.