Chemical investigations of GaAs wafer bonded interfaces

Abstract

The bonding chemistry of various GaAs-to-oxide/GaAs bonded samples was investigated using multiple internal transmission Fourier transform infrared spectroscopy for thermally annealed and thermocompression annealed samples. The oxides used in these investigations included a native GaAs oxide as well as two compositions of borosilicate glass ͑BSG͒ deposited by low-pressure chemical vapor deposition ͑LPCVD͒. For the thermally annealed samples, the hydrogen-bonded H 2 O/OH groups on the hydrophilic surface form a room temperature bond without the application of pressure. Chemical changes at the wafer-bonded interface occur in two temperature regions. For anneals between 200 and 400°C for 1 h in N 2 , the H 2 O/OH groups react and evolve H that becomes absorbed within the oxide. The LPCVD BSG oxide was chemically unaltered during anneals in this temperature range, however, the GaAs native oxide underwent chemical modification. Initially, the GaAs oxide consisted of As͑III͒-O and Ga-O related oxides. The As͑III͒-O oxides react to form free As and Ga-O during annealing between 200 and 400°C. For anneals between 500 and 600°C, the reaction of H 2 O/OH groups continue and the H becomes infrared inactive, most likely forming H 2 voids at the bonded interface. In addition, As͑V͒-O related oxides were observed during thermal annealing in this temperature range. No detectable chemical changes in the BSG were observed over the temperature range investigated. Samples that were annealed under an estimated 1-10 MPa of pressure had similar chemical changes to thermally annealed samples.

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

“…The GaAs-related vibrational modes and those from carbon-based contamination are listed in Table I and are based on literature assignments. 8,[15][16][17] Changes in interfacial bonding chemistry were studied as a function of annealing temperature. Individual FTIR samples were annealed at temperatures of 200°C, 300°C, 400°C, and 500°C, for 1 h in N 2 .…”

“…The absorbance was obtained by where p sample , s sample , p background , and s background represented the p-and s-polarized sample and background signals. 8 The background spectra were measured by placing a mirror in the sample position. The ratio of p-to-s polarized sample spectra was used to reduce the contribution to the measured signal from the outer prism surfaces.…”

“…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.…”

“…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.…”

“…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).…”