Large-area wafer bonding of GaAs using hydrogen and ultrahigh vacuum atmospheres

Uniform direct or fusion wafer bonding of GaAs wafers up to 4 inch in diame ter was achieved by means of two methods: (i) pre-heating, bonding at eleva ted temperatures and post-annealing in a H-2 atmosphere (gas environmental hot bonding) and (ii) bonding inside an UHV apparatus at temperatures as lo w as 150 degrees C after cleaning with atomic hydrogen. Both methods yield atomically abrupt interfaces as shown by cross-sectional TEM and by imaging the screw-dislocation network formed at low angles of twist between the wa fers. At large twist angles, additional "step" dislocations arising from bo nding across surface steps could be clearly imaged. The problem of occasion ally occuring microvoids, probably arising due to insufficient pre-cleaning or at excessive post-annealing, is addressed. Both bonding procedures neit her need mechanical loading of the wafers nor channel-patterning of the sur faces.