Eutectic bonding

Ultrasonic image of a blank Au-Si eutectic bonded wafer [1]
Ultrasonic image of a patterned Au-Si eutectic bonded wafer [1]

Eutectic bonding, also referred to as eutectic soldering, describes a wafer bonding technique with an intermediate metal layer that can produce a eutectic system. Those eutectic metals are alloys that transform directly from solid to liquid state, or vice versa from liquid to solid state, at a specific composition and temperature without passing a two-phase equilibrium, i.e. liquid and solid state. The fact that the eutectic temperature can be much lower than the melting temperature of the two or more pure elements can be important in eutectic bonding.[citation needed]

Eutectic alloys are deposited by sputtering, dual source evaporation or electroplating. They can also be formed by diffusion reactions of pure materials and subsequently melting of the eutectic composition.[2]

Eutectic bonding to transfer epitaxial materials such as GaAs-AlGaAs onto Si substrates with high yields for the general purpose of optoelectronics integration with Si electronics as well as to overcome fundamental issues such as lattice mismatch in hetero-epitaxy, was developed and reported by Venkatasubramanian et al. in 1992, and the performance of eutectic-bonded GaAs-AlGaAs materials for solar cells was further validated and reported by the same group in 1994.[3][4]

Eutectic bonding is able to produce hermetically sealed packages and electrical interconnection within a single process (compare ultrasonic images)[further explanation needed]. This procedure is conducted at low temperatures, which results in low resultant stress induced in final assembly, high bonding strength, large fabrication yield and a good reliability. These attributes are dependent on the coefficient of thermal expansion between the substrates.[1]

The most important parameters for eutectic bonding are:

  1. ^ a b c Cite error: The named reference LBH+2009 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference FS2008 was invoked but never defined (see the help page).
  3. ^ Venkatasubramanian, Rama (1992). "High Quality Eutectic-Metal-Bonded AlGaAs-GaAs Thin Films on Si Substrates". Appl. Phys. Lett. 60 (7): 886–889. Bibcode:1992ApPhL..60..886V. doi:10.1063/1.106494.
  4. ^ Venkatasubramanian, Rama (1994). "Optoelectronic Properties of Eutectic-Metal-Bonded (EMB) GaAs-AlGaAs Structures on Si Substrates". Solid State Electronics. 37 (11): 1809–1815. Bibcode:1994SSEle..37.1809V. doi:10.1016/0038-1101(94)90171-6.