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SYNOPSISTo enhance polyimide-to-polyimide adhesion, we have investigated the effect of surface modification in water vapor plasma. The use of a water vapor plasma to treat a fully cured polyimide ( PMDA-ODA) surface before subsequent layers of polyimide are applied results in dramatically enhanced interfacial adhesion. The polyimide-to-polyimide interfacial adhesion strength attained following water vapor plasma treatment exceeds the cohesive strength of the applied polyimide layer. The effect of surface modification in water vapor plasma on metal-to-polyimide adhesion has also been investigated. The use of a water vapor plasma to treat a fully cured polyimide (PMDA-ODA) surface prior to metallization results in increased metal-to-polymer interfacial adhesion. A study of both electroless and vacuum-deposited metal was conducted. The use of contact-angle measurements, peel tests, Fourier transform infrared spectroscopy, optical emission spectroscopy, nuclear forward scattering, and X-ray photoelectron spectroscopy has led us to a preliminary understanding of the resulting surface modification and the subsequent effect of adhesion promotion.

Qubit information processors are increasing in footprint but currently rely on e-beam lithography for patterning the required Josephson junctions (JJs). Advanced optical lithography is an alternative patterning method, and we report on the development of transmon qubits patterned solely with optical lithography. The lithography uses 193 nm wavelength exposure and 300-mm large silicon wafers. Qubits and arrays of evaluation JJs were patterned with process control which resulted in narrow feature distributions: a standard deviation of 0.78% for a 220 nm linewidth pattern realized across over half the width of the wafers. Room temperature evaluation found a 2.8 − 3.6% standard deviation in JJ resistance in completed chips. The qubits used aluminum and titanium nitride films on silicon substrates without substantial silicon etching. T1 times of the qubits were extracted at 26 µs -27 µs, indicating a low level of material-based qubit defects. This study shows that large wafer optical lithography on silicon is adequate for high-quality transmon qubits, and shows a promising path for improving many-qubit processors.

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