用于超导共面波导谐振器的溅射TiN薄膜
Sputtered TiN films for superconducting coplanar waveguide resonators
摘要：
本文系统地研究了在超高真空反应磁控溅射室中通过改变沉积条件制备TiN薄膜的性能。当保持Ti（1-x）N（x）（x=0.5）接近化学计量比时，通过将沉积压力从2 mTorr增加到9 mTorr，膜电阻率增加，主晶体取向从（100）变为（111），晶界变得更清晰，并且强压缩应变变为弱拉伸应变。TiN膜在沉积后暴露于空气时吸收高浓度的污染物，包括氢、碳和氧。当靶-衬底距离设置为88 mm时，污染物水平随着压力从2 mTorr增加到9 mTorr而从~0.1%增加到~10%。污染物浓度也与从衬底的中心的平面内的距离，并增加了大约两个数量级的目标-衬底的距离从88 mm增加到266 mm。这些污染物被发现强烈影响TiN薄膜的性能。例如，当氧含量从0.1%增加到11%时，化学计量膜的电阻率增加约5倍。这些结果表明，溅射TiN粒子的能量是决定TiN膜性能的关键，并且重要的是要控制该能量以获得高质量的TiN膜。由一系列在2 mTorr到7 mTorr的压力下生长的接近化学计量比的薄膜制成的超导共面波导谐振器显示出随着压缩应变的大小从接近3800 MPa减小到大约150 MPa以及氧含量从0.1%增加到8%，本征品质因数从~10^4增加到~10^6。具有较高氧含量的膜表现出较低的损耗，但氧掺入的不均匀性阻碍了溅射TiN在较大电路中的使用。
英文摘要：
We present a systematic study of the properties of TiN films by varying the deposition conditions in an ultra-high-vacuum reactive magnetron sputtering chamber. By increasing the deposition pressure from 2 to 9 mTorr while keeping a nearly stoichiometric composition of Ti(1-x)N(x) (x=0.5), the film resistivity increases, the dominant crystal orientation changes from (100) to (111), grain boundaries become clearer, and the strong compressive strain changes to weak tensile strain. The TiN films absorb a high concentration of contaminants including hydrogen, carbon, and oxygen when they are exposed to air after deposition. With the target-substrate distance set to 88 mm the contaminant levels increase from ~0.1% to ~10% as the pressure is increased from 2 to 9 mTorr. The contaminant concentrations also correlate with in-plane distance from the center of the substrate and increase by roughly two orders of magnitude as the target-substrate distance is increased from 88 mm to 266 mm. These contaminants are found to strongly influence the properties of TiN films. For instance, the resistivity of stoichiometric films increases by around a factor of 5 as the oxygen content increases from 0.1% to 11%. These results suggest that the sputtered TiN particle energy is critical in determining the TiN film properties, and that it is important to control this energy to obtain high-quality TiN films. Superconducting coplanar waveguide resonators made from a series of nearly stoichiometric films grown at pressures from 2 mTorr to 7 mTorr show an increase in intrinsic quality factor from ~10^4 to ~10^6 as the magnitude of the compressive strain decreases from nearly 3800 MPa to approximately 150 MPa and the oxygen content increases from 0.1% to 8%. The films with a higher oxygen content exhibit lower loss, but the nonuniformity of the oxygen incorporation hinders the use of sputtered TiN in larger circuits.
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