In situ stress measurements during the MOCVD growth of AlN buffer layers on (1 1 1) Si substrates

Stress evolution during MOCVD growth of AlN buffer layers and GaN epilayers on (1 1 1) Si substrates was investigated using in situ wafer curvature measurements in order to understand the impact of growth conditions on thin film stress. AlN layers up to 400nm thick were deposited over a temperature range of 600-1100°C at growth rates of 0.1-1nm/s. In all cases, the growth stresses were tensile and the stress value did not change during growth. A sharp drop in the value of the tensile growth stress is observed between 900°C and 800°C from >1GPa to <0.4GPa. This drop is due a transition in the structure of the film from an epitaxially oriented crystalline film above 900°C to a highly defective polycrystalline film at 600°C. At a constant temperature however, the tensile stress in the film remained relatively constant with a change in growth rate. The origin of these stress differences and their impact on residual stress in GaN epitaxial layers grown on Si are discussed.