Design, Fabrication and Characterization of a Microwave Resonator ...

4 Fabrication and Measurement SetupCleaning the substratesThe substrates were ultrasonic-cleaned in each of the following solvents:• Acetone technical• Acetone p.a.• IsopropanolSputtering NiobiumAfter the cleaning process, the substrates are ready to be sputtered with Niobium. Theyare screwed into a specially designed carrier in order deposit Niobium on both sides of thesubstrate for CBCPW, without scratching the Niobium layer.The carrier is then placed in the sputtering chamber and positioned in front of the desiredtarget, in our case Niobium.The sputtering is done with the following parameters:• process pressure: ≈ 2.7 · 10 −3 mbar• argon flow rate: 10 sccm/min• power: 200 W• duration: 5 min + presputtering 60 sDuring presputtering the power stabilizes. With these sputtering parameters we achieve alayer thickness of 200 nm.Spincoat the resistIn the cleanroom the substrate coated with Niobium is cleaned again as describedabove, in order to remove eventually captured particles (e.g. dust). After this, the sample isspincoated with photo resist (AZ 5214E, Microchemicals 2 ). The spin coating is done with4000 rpm for 40 seconds, resulting in a resist thickness of 1.4 µm.Afterwards, the sample is baked for 120 seconds at 110 ◦ C (soft bake) to improve theadhesion of the resist.Mask exposureThe UV-exposure is done with the mask aligner (MJB3, Karl Süss GmbH). Themask is carefully cleaned under flowing acetone and isopropanol and placed in themask holder. The substrate is aligned with the desired resonator structure.We used the high precision modus to have optimum accuracy of the structure on thesample. The samples are exposed with UV radiation for 4 seconds.2 www.microchemicals.com32