Project Results

RF-SOI substrates are thought to be a good enabler to fabricate high performance superconducting qubit devices. In this intermediate report, relevant substrates parameters have been identified in order to maximize the performance of superconducting resonators, by limiting microwave losses. A new resonator process flow for 300mm SOI wafers has been developed, with a new dedicated mask set, including various structures designed by several partners, in order to investigate the losses over several orders of magnitude.

In this report IQM, VTT and IMEC have assessed the performances of different resonators taking into account variability. This is an important aspect in the long-term perspective of large-scale qubit integration since a tight control over resonator characteristics is needed. Besides that, assessing variability at cryogenic temperatures is a formidable task as the measurement throughput is very low compared to devices operated at room temperature. This task has been tackled evaluating the spread of resonator Q factors within a chip and across different wafers for different materials, geometries of the resonators and chips packaging. We have also obtained the distribution of the resonance frequencies of the different resonators that can ultimately serve as feedback to design and integration.

Standardized methodology for superconducting resonator testing was proposed across the consortium to enable unambiguous intercomparability across the different testing laboratories. Test resonator designs were created to support the activities by several partners aiming to find improved materials and fabrication processes for quantum computing applications.

Three different tailor-made high-performance photoresist-stripper formulations were developed within the MATQu project. All formulations are water-based and revealed no etching towards critical TiN layers. Comprehensive studies were carried out. Therefore, time dependent measurements and different types of plasma-etch pretreaments were investigated.

A transmon qubit is formed by shunting a Josephson junction with an extremely low-loss capacitor. In the vast majority of presently fabricated superconducting qubits, with coherence times comparable to state of the art, the Josephson junctions are superconductor-insulator-superconductor (SIS) junctions formed by shadow angle evaporation and lift-off of aluminum, typically on small coupons. In this report, we describe our progress in moving this conventional process onto full-wafer tools and in developing alternative junction fabrication process which does not use lift-off. Abandoning lift-off has the potential to improve yield, parameter control, and process compatibility with other processing steps. Here, we have, especially, investigated and utilized the side-wall spacer passivated (SWAPS) tunnel junction fabrication technique.

A transmon qubit is formed by shunting a Josephson junction with an extremely low-loss capacitor. In the vast majority of presently fabricated superconducting qubits, with coherence times comparable to state of the art, the Josephson junctions are superconductor-insulator-superconductor (SIS) junctions formed by shadow angle evaporation and lift-off of aluminum, typically on small coupons. In this report, we describe our progress in moving this conventional process onto full-wafer tools and in developing alternative junction fabrication process which does not use lift-off. Abandoning lift-off has the potential to improve yield, parameter control, and process compatibility with other processing steps. Here, we have, especially, investigated and utilized the side-wall spacer passivated (SWAPS) tunnel junction fabrication technique.

Indium deposition on copper and on superconductive substrates on wafer scale ongoing at imec.

This report presents the cabling specifications discussed with project partners and summarizes results of prototypes.

Kiutra has identified characterization tasks that could significantly benefit from a rapid test system for cryogenic temperatures and derived the adaptations to the cryostat prototype needed for their implementation. The results of our analysis were summarized in a report.

This report states the plan on the dissemination and communication activities of the project.

This report states an update on the dissemination and communication activities of the project.

The project Kick-off meeting took place on June 17th, 2021.

The first half-term report describes the work carried out in the MATQu project from project months one to six.

The second half-term report describes the work carried out in the MATQu project from project months 13 to 18.

Standardized methodology for superconducting resonator testing was proposed across the consortium to enable unambiguous intercomparability across the different testing laboratories. Test resonator designs were created to support the activities by several partners aiming to find improved materials and fabrication processes for quantum computing applications.

IFC successfully developed a prototype product for the fast removal of a pCAR photoresist from a Si-wafer. The prototype reveals a high compatibility towards TiN, proven by etch rate determination methods and surface roughening analyses.

See corresponding Deliverable D2.5

The consortium-level goals for resonator quality factor and coherence time metrics were consolidated and general instructions on data quality and statistics were created.

The Spherolyte In process was successfully adjusted and applied to deposit indium bumps on substrates with thin copper seed layers. Spherolyte In SC was successfully developed and applied to deposit indium on substrates with superconductive seed layers (e.g. Mo).

Optimization ongoing in collaboration with imec.

Technic Through Silicon Vias (TSV) cleaning blends, photoresist strippers, as well as wet etchant solutions (TiN, Nb, Cu) have been evaluated on wafers provided by partners (IMEC and CEA). Reduction of scallop effect in TSV has also been investigated.

Compatibility of the deposited indium with the CMP process could be shown in collaboration with imec.

Elevate Indium D4900 solution has been validated for indium deposition (thin film and bumps) over copper and ruthenium seed layers. New products have been developed for TSV cleaning: TechniClean D-BOS series. TechniStrip® solutions dedicated to photoresist stripping have been determined to be compatible with Indium and superconductor materials (Nb, NbN, TaN). A new wet etching solution is under development to etch Niobium selectively to Indium.

Indium plated wafers (blanket and patterned) have been provided to partners for further characterization analyses (critical temperature, intermetallic cross-section observation, and reflow tests). A new wet etching solution is under development to etch Ruthenium selectively to Indium, that will enable the optimization of the full process of deposition and etching.

Intelligent fluids has developed a highly performant water-based formulation for TSV cleaning. The novel formulation has passed the internal qualification process. First technical scale production of the prototype was produced for delivery of the material to the collaboration partner IMEC.

Technic provided all desired information (MSDS, TDS) to partners (imec, CEA) for the Elevate Indium D4900 before an upcoming supply. Technic is also ready to supply TechniClean D-BOS for TSV cleaning and TechniStrip® various solutions for photoresist stripping, such as P1331 and MLO07. Innovative selective wet etching solutions for Nb and Ru, while being compatible with In bumps were validated on patterned small size vehicles but necessitate complementary work with partners for industrial validation on full wafer.

Kiutra has completed the assembly of the basic ADR cryostat prototype and reported on its performance.

Various measurement types and methodologies were assessed to investigate how to best utilize the characterization tool development in MATQu. Resonator and qubit measurements were conducted in conditions emulating the ADR-based rapid turnaround measurement system to validate the compliance in screening measurements.

The first project year has been finished successfully and was stated in a corresponding report.