Appendix D: Wafer Level Testing

Data is heavily utilized during product design to select the final configuration and to establish manufacturing controls and limits. Immediately after epitaxial growth, a vertical‐cavity surface‐emitting laser (VCSEL) wafer can be non‐destructively characterized and mapped to estimate the manufacturing yield. The spectrum is acquired at several hundred points across the wafer and is analyzed to extract physical properties such as the laser resonance wavelength and then mapped onto the wafer area. The wafer uniformity map is used by the epitaxial engineers to optimize the reactor growth uniformity; fitting of the measured spectrum can be a precise measurement of growth rate of the many VCSEL layers. In high‐power VCSEL array products, the beam divergence, and uniformity are critical to performance. The 2D arrays may be packaged similarly to the final customer assembly and tested for uniformity of emission and beam divergence, and the data is used to develop appropriate wafer level test limits.