| AVS 58th Annual International Symposium and Exhibition | |
| Electronic Materials and Processing Division | Monday Sessions |
| Session EM-MoM |
| Session: | Dielectrics for Novel Devices and Process Integration |
| Presenter: | J.J.M. Law, University of California, Santa Barbara |
| Authors: | J.J.M. Law, University of California, Santa Barbara A.D. Carter, University of California, Santa Barbara G.B. Burek, University of California, Santa Barbara B. Thibeault, University of California, Santa Barbara M.J.W. Rodwell, University of California, Santa Barbara A.C. Gossard, University of California, Santa Barbara |
| Correspondent: | Click to Email |
As electronic device areas scale with each generation by 1:4, resistances must remain constant, so contact resistivities must scale by 1:4. The high dopant concentrations achievable by molecular beam epitaxy (MBE) provide a method for creating low-resistance ohmic contacts; however, line-of-sight deposition and low desorption of atomic species may hinder the self-alignment of such regrowth. Careful control over growth conditions makes MBE a suitable technique for creating self-aligned, low resistance ohmic contacts to InGaAs.
Samples were grown by solid source MBE lattice matched to semi-insulating InP with layer structure as follows from the substrate: 400 nm InAlAs, 3 nm of Si-doped 2 and 3×1019 cm-3 InAlAs, and 25 and 15 nm of InGaAs, respectively. 300 nm of SiO2 and 20 nm of Cr were deposited by PECVD and e-beam evaporation. A combination of electron beam and photolithography followed by ICP dry etching was used to define dummy spacer pillars. Oxidation and oxide removal of exposed InGaAs was done with UV o-zone and a dilute 10 H2O:1 HCL dip. Samples were heated to 420 °C and treated with thermally cracked hydrogen (≈1×10-6 Torr) for 40 minutes prior to regrowth. 70 nm of 5×1019 Si-doped InAs was grown on the exposed InGaAs regions with quasi-migration enhance epitaxy (MEE) at 500 °C with V:III beam equivalent pressures of 4.0, 5.6, and 8.0. After regrowth, shorts over the dummy pillar were removed, and samples were metalized with lifted-off e-beam evaporated Ti/Pd/Au and mesa isolated. Contact resistances were extracted by transmission line measurements (TLM).
RHEED images during regrowth showed 4x2 surface reconstructions for regrowths with V:III ratios of 4.0 and 5.6 indicating a group In-rich surface reconstruction. SEM of regrowths at V:III ratios of 4.0 and 5.6 showed no faceting and fill-in to the dummy pillar edge. AFM showed roughened surfaces possibly due to high Si incorporation and lattice mismatch between InGaAs and InAs. Regardless of the V:III ratio during growth, 25 nm thick InGaAs channels showed contact resistances of 190 Ω μm while 15 nm thick InGaAs showed contact resistances of 105 Ω μm. Metal-semiconductor contact resistances were 2.1 Ω μm. Local electrode atom probe shows that the regrowth carries some of the Ga along with it creating a varying InGaAs alloy concentration throughout the regrowth.