Uniformity improvement of Josephson-junction resistance by considering sidewall deposition during shadow evaporation for large-scale integration of qubits
Tsuyoshi Takahashi, Norinao Kouma, Yoshiyasu Doi, Shintaro Sato, Shuhei Tamate, Yasunobu Nakamura
Abstract
Abstract The uniformity of Josephson-junction (JJ) characteristics is crucial in wafer-scale superconducting quantum-bit (qubit) integration. To achieve the level of accuracy demanded the circuits, every detail of the fabrication process needs to be optimized. Here we reveal that the junction-resistance ( R N ) variations of Al/AlO x /Al JJs are affected by the metal deposition on the sidewall of the resist mask during shadow evaporation. The effect is reproduced in numerical simulation using a simple model taking into account the resist structure and the evaporation angle. To overcome the issue, we introduce a two-step shadow evaporation method to reduce the variation of R N . As a result, the coefficient of variations across a 3-inch wafer decreases from 6.7% to 4.5%, achieving 1.1% in a chip with an area of 10 mm × 10 mm. This method is promising for developing large-scale superconducting quantum computers.