Details

Autor(en) / Beteiligte

• Tolpygo, Sergey K.
• Bolkhovsky, Vladimir
• Weir, T. J.
• Wynn, Alex
• Oates, D. E.
• Johnson, L. M.
• Gouker, M. A.

Titel

Advanced Fabrication Processes for Superconducting Very Large-Scale Integrated Circuits

Ist Teil von

• IEEE transactions on applied superconductivity, 2016-04, Vol.26 (3), p.1-10

Ort / Verlag

New York: IEEE

Erscheinungsjahr

2016

Quelle

IEL

Beschreibungen/Notizen

• We review the salient features of two advanced nodes of an 8-Nb-layer fully planarized process developed recently at MIT Lincoln Laboratory for fabricating single flux quantum (SFQ) digital circuits with very large-scale integration on 200-mm wafers: the SFQ4ee and SFQ5ee nodes, where "ee" denotes that the process is tuned for energy-efficient SFQ circuits. The former has eight superconducting layers with 0.5-μm minimum feature size and a 2-Ω/sq Mo layer for circuit resistors. The latter has nine superconducting layers: eight Nb wiring layers with the minimum feature size of 350 nm and a thin superconducting MoN x layer (T c ~ 7.5 K) with high kinetic inductance (about 8 pH/sq) for forming compact inductors. A nonsuperconducting (T c <; 2 K) MoN x layer with lower nitrogen content is used for 6-Ω/sq planar resistors for shunting and biasing of Josephson junctions (JJs). Another resistive layer is added to form interlayer sandwich-type resistors of milliohm range for releasing unwanted flux quanta from superconducting loops of logic cells. Both process nodes use Au/Pt/Ti contact metallization for chip packaging. The technology utilizes one layer of Nb/AlO x -Al/Nb JJs with critical current density J c of 100 μA/μm 2 and minimum diameter of 700 nm. Circuit patterns are defined by 248-nm photolithography and high-density plasma etching. All circuit layers are fully planarized using chemical mechanical planarization of SiO 2 interlayer dielectric. The following results and topics are presented and discussed: the effect of surface topography under the JJs on the their properties and repeatability, I c and J c targeting, effect of hydrogen dissolved in Nb, MoN x properties for the resistor layer and for high-kinetic-inductance layer, and technology of milliohm-range resistors.