Advanced Fabrication Processes for Superconducting Very Large-Scale Integrated Circuits

作者：Tolpygo Sergey K^*; Bolkhovsky Vladimir; Weir T J; Wynn Alex; Oates D E; Johnson L M; Gouker M A

来源：IEEE Transactions on Applied Superconductivity, 2016, 26(3): 1100110.

DOI：10.1109/TASC.2016.2519388

• ERSFQ
• Josephson junctions
• kinetic inductance
• MoNx
• Nb/AlOx/Nb Josephson junctions
• RQL
• RSFQ
• SFQ digital circuits
• superconducting electronics
• superconductor integrated circuits

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-mu m minimum feature size and a 2-Omega/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 MoNx layer (T-c similar to 7.5 K) with high kinetic inductance (about 8 pH/sq) for forming compact inductors. A nonsuperconducting (T-c < 2 K) MoNx layer with lower nitrogen content is used for 6-Omega/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/AlOx-Al/Nb JJs with critical current density J(c) of 100 mu A/mu m(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 SiO2 interlayer dielectric. The following results and topics are presented and discussed: the effect of surface topography under the JJs on the their properties

• 出版日期2016-4