Improvement of Ag sintering Quality on Cu surface at Hydrogen atmosphere

Wide-bang gap (WBG) semiconductors such as SiC and GaN have many advantages including energy saving and high power capability and are expected as the new semiconductors substituting traditional Si. To bond these SiC/GaN dies to substrates securely, the die-bonding materials are required to stand high-temperature environment and possess superior heat and electronic-conducting properties as well as excellent reliability. Recently, Ag micron particle paste has been developed to show good performance such as high-temperature raliability and high electronic conductivity. Direct copper bonding (DCB) is the commonly used substrate, of which a Cu face is bonded with dies. Since Cu is easy to be oxidized in air, the substrates have to be coated with a thin layer of Ag to realize bonding and to improve the mechanical property. In this work, a simple two-step sintering process was proposed to omit the complicated Ag-coating process and achieve the stable direct bonding between a Cu surface and a die. The two-steps sintering process included first-step in the air and second-step in hydrogen atmosphere. Shear strength over 20 MPa has been achieved by an opti-mized sintering condition with an affordable Ag micron paste.