A dual side electroluminescence measurement system for LED wafer manufacturing

The development of a system that evaluates the performances of an LED (light-emitting diode) wafer using a non-destructive test method after crystal growth and before chip processing is presented. The system measures electroluminescent characteristics of two sides of an epi-wafer. When a probe makes contact with an epi-wafer, a source meter drives an electric current, then emits LED light. Optical characteristics were measured by two spectrometers and two pico-am meters. The measured data were peak wavelength, FWHM (full width at half maximum), forward current, forward voltage and reverse current. The measuring devices are installed on the front and rear of the wafer. The probe and measuring devices were transferred by a 3-axis stage for the EL contact. Mapping images of the epi-wafer were obtained using these characteristics. The correlation between wafer state and chip state, and repeatability for an epi-wafer, were considered in the test.