I. Radu

GaAs on Si heterostructures obtained by He and/or H implantation and direct wafer bonding

Transfer of GaAs layers onto Si by helium and/or hydrogen implantation and wafer bonding was investigated. The optimum conditions for achieving blistering/splitting only after postimplantation annealing were experimentally obtained. It was found that specific implantation conditions induce large area exfoliation instead of blistering after annealing of unbonded GaAs. This effect is related to a narrow size and/or a depth distribution of the platelets in as-implanted GaAs and their evolution with annealing. The influence of substrate orientation in blistering/splitting of GaAs was also investigated. Thin GaAs layers were transferred onto silicon by a combination of He and/or H implantation, wafer bonding and low temperature annealing.

Strain relaxation in nanopatterned strained silicon round pillars

Periodic arrays of strained Si (sSi) round nanopillars were fabricated on sSi layers deposited on SiGe virtual substrates by electron-beam lithography and subsequent reactive-ion etching. The strain in the patterned sSi nanopillars was determined using high-resolution UV micro-Raman spectroscopy. The strain relaxes significantly upon nanostructuring: from 0.9% in the unpatterned sSi layer to values between 0.22% and 0.57% in the round sSi pillars with diameters from 100 up to 500nm. The strain distribution in the sSi nanopillars was analyzed by finite element (FE) modeling. The FE calculations confirm the strain relaxation after patterning, in agreement with the results obtained from Raman spectroscopy.

Low-temperature layer splitting of (100) GaAs by He+H coimplantation and direct wafer bonding

The present letter introduces a low-temperature GaAs layer splitting approach by He+H coimplantation which—in combination with direct wafer bonding—enables monolithic integration of GaAs with different substrates. The influence of He+H coimplantation on blistering and layer splitting of GaAs is studied and the optimum coimplantation conditions are determined. Thin GaAs layers are transferred onto Si after bonding of He+H coimplanted GaAs and Si substrates via a spin-on glass intermediate layer and subsequent annealing at only 225 °C for 14 h. Cross-sectional transmission electron microscopy investigations show a high quality of the GaAs/SOG bonding interface.

Formation of nanovoids in high-dose hydrogen implanted GaN

The formation of nanovoids upon high-dose hydrogen implantation and subsequent annealing in GaN is investigated by transmission electron microscopy. The epitaxial GaN layers on sapphire were implanted at room temperature with H2+ ions at 100keV with a dose of 13×1016cm−2. Cross section transmission electron microscopy investigations revealed that nanovoids about 2nm in diameter had formed during hydrogen implantation at room temperature while large microcracks (∼150–200nm long) occurred upon annealing (1h at 700°C) leading to surface blistering. The nanovoids serve as precursors to the microcrack formation and are essential for the blistering process.

Single-Crystalline Ferroelectric Thin Films by Ion Implantation and Direct Wafer Bonding

Layer splitting by helium and/or hydrogen implantation and wafer bonding was applied to transfer thin single-crystalline ferroelectric layers onto different substrates. The optimum conditions for achieving blistering/splitting after post-implantation annealing were experimentally obtained for LiNbO3, LaAlO3, SrTiO3 single crystals and PLZT ceramic. Under certain implantation conditions large area exfoliation instead of blistering occurs after annealing of as-implanted substrates. Small area single-crystalline layer transfer was successfully achieved.

Enhancement in wafer bow of free-standing GaN substrates due to high-dose hydrogen implantation: implications for GaN layer transfer applications

Two-inch free-standing GaN wafers were implanted by 100 keV H+2 ions with a dose of 1.3 × 1017 cm−2 at room temperature. The hydrogen implantation induced damage in GaN extends between 230 to 500 nm from the surface as measured by cross-sectional transmission electron microscopy (XTEM). The wafer bow of the free-standing GaN wafers was measured using a Tencor long range profilometer on a scan length of 48 mm before and after the hydrogen implantation. Before implantation the bow of two different free-standing GaN wafers (named A and B) with different thicknesses was 1.5 µm and 6 µm, respectively. Initially, both wafers were concave in shape. After implantation the bow changed to convex with a value of 36 µm for wafer A and a value of 32 µm for wafer B. High dose hydrogen implantation leads to an in-plane compressive stress in the top damaged layer of the GaN, which is responsible for the enhancement of wafer bow and change of bow direction. The high value of bow after implantation hinders the direct wafer bonding of the free-standing GaN wafers to sapphire or any other handle wafers. Tight bonding between hydrogen implanted GaN wafers and the handle wafers is a necessary requirement for the successful layer transfer of thin GaN layers onto other substrates based on wafer bonding and layer splitting (Smart-cut).

Ferroelectric Oxide Single-Crystalline Layers by Wafer Bonding and Hydrogen/Helium Implantation

Layer splitting by helium and/or hydrogen and wafer bonding was applied for the transfer of thin single-crystalline ferroelectric oxide layers onto different substrates. The optimum conditions for achieving blistering/splitting after post-implantation annealing were experimentally obtained for LiNbO3, LaAlO3, SrTiO3 single crystals and transparent PLZT ceramic. Under certain implantation conditions large area exfoliation instead of blistering occurs after annealing of as-implanted oxides. Small area single-crystal oxide layer transfer was successfully achieved.

Si/GaAs heterostructures fabricated by direct wafer bonding

Si/GaAs heterostructures were obtained by a low temperature direct wafer bonding (DWB) method which uses spin-on glass (SOG) intermediate layers. The use of intermediate SOG layers allows the fabrication of Si/GaAs heterostructures at processing temperatures lower than 200°C. The achieved bonding energy permits thinning down to a few microns of Si and GaAs wafers, respectively, using grinding procedures followed by chemical mechanical polishing (CMP). After thinning, the heterostructures sustained annealing temperatures of 450°C without damaging of the bonded interface. The above bonding procedure was successfully applied for bonding GaAs wafers to Si wafers with structured surfaces. A technology was developed based on this bonding method for producing universal GaAs-on-Si or Si-on-GaAs substrates.

Blistering and exfoliation of hydrogen and helium implanted (100) GaAs

Blistering and exfoliation of hydrogen and helium implanted GaAs was studied. The influence of the dose and implantation temperature on the formation of microcracks during implantation and their evolution at subsequent annealings were investigated. Layer splitting instead of blistering of helium implanted GaAs was demonstrated.

Comparison of SiGe Virtual Substrates for the Fabrication of Strained Silicon-On- Insulator (sSOI) Using Wafer Bonding and Layer Transfer

Different methods of preparing sSOI wafers have been analyzed. The initial virtual substrate wafers are characterized by a 17 20 nm thick strained silicon layer grown either on a thick relaxed SiGe layer on a graded buffer or on a thin SiGe buffer relaxed by He implantation. Bonding and layer transfer experiments using different oxide layers proved that strained silicon layers are completely transferred if designed PE-CVD oxide layers were used. For both types of virtual substrates the oxide layers are deposited on top of the strained silicon and bonded to non-oxidized (blank) silicon wafers. A perfect layers transfer is obtained for virtual substrates having thick SiGe buffer layers (type A) even at 350°C, while annealing at 450 °C is required for substrates with thin SiGe buffer layers (type B). The lower annealing temperature for substrates of type A is caused by the lower activation energy for blistering. The hydrogen implantation is here into the SiGe. For type B substrates the hydrogen implantation is into the underlying Si requiring a higher temperature for layer splitting (higher activation energy for Si).