Deflection Reduction of GaN Wafer Bowing by Coating or Cutting Grooves in the Substrates

GaN films on sapphire substrates are obtained using the metal-organic chemical vapor deposition growth technique. We present two methods to reduce the GaN wafer bowing caused by the mismatch of the thermal expansion coefficients (TECs) between the film and the substrate. The first method is to use coating materials on the back side of the substrate whose TECs are smaller than that of the GaN films. The second is to cut grooves on the back side of the sapphire substrate and filling the grooves with appropriate materials (e.g., tungsten, silicon nitride). For each method, we minimize wafer bowing and even reduce it to zero. Moreover, the two methods can reduce stress concentration and suppress the propagation of cracks in the GaN/sapphire structure.