Formation ofCuAlO₂at theCu/Al₂O₃Interface and its Influence on Interface Strength and Thermal Conductivity

Abstract

The criteria for the formation of a CuAlO 2 reaction phase at the Cu/Al 2 O 3 interface are explored. Oxygen solutes up to 2 wt% were introduced into the copper first. The bonding was carried out at 1075°C. The reaction phase was observed only when the oxygen solute in copper before bonding was higher than 1.3 wt%. The CuAlO 2 phase is polycrystalline and covers only part of the interface. The CuAlO 2 grains interact with the crack, which improves the interface strength. As CuAlO 2 is not continuous at the interface, the thermal conductivity of the Al 2 O 3 /Cu/Al 2 O 3 laminate is affected little.

Eliminating Voids at Al2O3–Cu Interface During Direct Bonding

“…17,18 The substrates fabricated with the technique exhibit both high interface strength and high thermal conductivity. 7 The substrates are currently used as the heat-dissipation substrates for power transistors. 8 For such application, chemical etching routine is employed first on the top copper layer to produce electric circuit; the transistor is then mounted.…”

“…More importantly, the laminates prepared with the technique exhibit both high interface strength and high thermal conductivity. 6,7 However, many large pores (voids), with the size from 10 to 500 lm, are present at the interface after bonding. [8][9][10][11][12][13][14][15] The presence of such large pores at interface is detrimental to the long-term reliability of laminate.…”

“…This technique is a powerful one for its economic feasibility to prepare Al 2 O 3 /Cu laminates. More importantly, the laminates prepared with the technique exhibit both high interface strength and high thermal conductivity . However, many large pores (voids), with the size from 10 to 500 μm, are present at the interface after bonding .…”

Use of a Ni Interlayer to Improve the Thermal Cycling Reliability of Cu/Sapphire Bilayers

“…A reaction phase, CuAlO 2 , may be formed, as the dissolved oxygen is higher than a critical value. Many previous studies suggested that interface strength increased with the formation of CuAlO 2 . The CuAlO 2 crystal exhibits anisotropic thermal expansion characteristics.…”

“…Despite huge elastic and thermal expansion mismatches between copper and alumina, many studies have demonstrated that alumina can be bonded to copper using a eutectic bonding technique . The process takes the advantage of eutectic liquid formation in the Cu‐O system.…”