GaAs wafer bonding by atomic hydrogen surface cleaning

Abstract

A method of large-area wafer bonding of GaAs is proposed. The bonding procedure was carried out in an ultrahigh vacuum. The wafer surfaces were cleaned at 400 and 500°C by application of atomic hydrogen produced by thermal cracking. The wafers were brought into contact either immediately after the cleaning, or at temperatures as low as 150°C, without application of a load, and successfully bonded over the whole area. High-resolution transmission electron microscopy revealed that the wafers could be directly bonded without any crystalline damage or intermediate layer. From a mechanical test, the fracture surface energy was estimated to be 0.7-1.0 J/m 2 , which is comparable to that of the bulk fracture. Furthermore, this bonding method needs no wet chemical treatment and has no limits to wafer diameter. Moreover, it is suitable for low temperature bonding.

Changes in interfacial bonding energies in the chemical activation of GaAs surfaces

“…1,[3][4][5][6][7][8] However, an increase in the bond strength using some of these techniques is often compromised by a degradation of the interfacial electrical and structural properties. For example, postbonding thermal treatments can increase the bond strength and alter the interfacial chemistry but may, however, also lead to bubble formation, the formation of an enhanced thickness of interfacial oxide, and even structural damage (Ն500°C).…”

“…For example, postbonding thermal treatments can increase the bond strength and alter the interfacial chemistry but may, however, also lead to bubble formation, the formation of an enhanced thickness of interfacial oxide, and even structural damage (Ն500°C). 5,7,8 Compressive loading can lead to the structural damage of the near-interface region. 8 In contrast, chemical pretreatments can be used as an alternative method to enhance the bond strength without many of these side effects.…”

Frequency dispersion reduction and bond conversion on n-type GaAs by in situ surface oxide removal and passivation

“…13,14 Atomic hydrogen exposure removes As-O and Ga-O bonds by producing water and unstable As and Ga oxides that desorb at the 430°C substrate temperature used here. 7 Figures 1͑a͒ and 1͑b͒ show the striking difference in the concentrations of As-O and Ga-O bondings, respectively, for each of the two treatments with both peaks being below the detection limit after H exposure. Figure 1͑c͒ illustrates the reduction in the total amount of oxygen after exposure to the atomic hydrogen.…”

“…One set of samples was degreased in acetone, methanol, and isopropyl alcohol for 1 min each, followed by a 3 min etch in 29% NH 4 OH, 6 and dried with N 2 , while another set was prepared, in situ with no chemical treatment, using a hydrogen cracker source ͑cell temperature of 1400°C, P H 2 =1 ϫ 10 −6 mbar͒ producing atomic H with a substrate temperature of 430°C for 30 min. 7,8 Silicon of various thicknesses was deposited at room temperature on treated GaAs by e-beam evaporation ͑deposition rate= 18-132 Å / min in a multitechnique deposition/characterization system ͑base pressure= 2 ϫ 10 −11 mbar͒. 9 MOS capacitors were made using such treated surfaces followed by atomic layer deposition ͑ALD͒ of 10 nm of Al 2 O 3 using trimethylaluminum ͑TMA͒ and H 2 O at 300°C in an adjacent chamber and ex situ, rf sputtered TaN as the gate metal using shadow masks.…”

Interfacial Chemistry of InP/GaAs Bonded Pairs

“…Previously employed treatments include postbonding thermal treatments, compressive loading, chemical pretreatments, oxygen plasma or ozone treatments, hydrogen surface cleaning before bonding, and the use of ultrahigh vacuum during bonding. [21][22][23][24][25][26][27][28] However, some of these techniques that increase bond strength often compromise the interfacial electrical and structural properties. For example, postbonding thermal treatments can increase the bond strength by altering the interfacial chemistry but may also lead to bubble formation, the formation of an enhanced thickness of interfacial oxide, and even structural damage at high annealing temperatures.…”