Highly Oriented Growth of AlxSc1-X N Ferroelectric Film on W Bottom Electrodes
Authors: Tsai Sung-Lin , Hoshii Takuya , Wakabayashi Hitoshi , Tsutsui Kazuo , Kakushima Kuniyuki 
Published: December 2020

Ferroelectric materials have been utilized for non-volatile memory applications [1]. Beside extensive works on ferroelectric HfO2 thin film [2, 3], recent works on nitride-based materials have proven that AlxSc1-xN (ASN) also shows ferroelectricity with a box-like characteristic [4]. A high remnant polarization of over 100 µC/cm2 is attractive for future non-volatile memory applications. However, the leakage current is still high for ASN thin films. Thus, a better-oriented growth method or an insulator is needed. The purpose of this study is to evaluate the impact of adding an AlN seed layer which also acts as an insulator for ASN thin film.

ASN films, AlN films, and ASN films with 3nm AlN seed layer, three samples were fabricated in this research. A W layer was deposited on an n+Si substrate. Then, 50-nm-thick films of ASN and AlN films were deposited by DC reactive sputtering, respectively. For ASN films with a 3nm AlN seed layer, a W layer was deposited on an n+Si substrate. Then, 3-nm-thick AlN films were deposited by DC reactive sputtering. In the end, 50-nm-thick ASN films were deposited by DC reactive sputtering. All fabrication processes were kept constant at 400oC. XRD and XRC measurements were performed on these three samples. The source of the x-ray was CuKa with a divergence angle of 0.04o.

The out-of-plane and in-plane XRD patterns of these three samples are shown in fig. 1(a) and (b), respectively. In out of plane XRD patterns, the (002) peak for the ASN sample is at 35.52 o, yielding parameter c = 0.505nm, which is slightly larger than the reported value of c = 0.4989 ± 0.0005nm [5]. On the other hand, in in-plane XRD patterns, the (100) peak for the AlN sample is at 33.07 o, yielding parameter a = 0.313nm, which is in perfect agreement with the reported value for pure AlN [6]. The (100) peak for the ASN sample is at 31.64 o, yielding parameter a = 0.327nm, which the composition of Sc x= 0.205 by following the reported Gaussian fitting [5]. However, the results didn't show any improvement in the oriented growth of adding the AlN seed layer. Further analyses such as JV, CV, and PV measurements are needed. XRC results of the AlScN (002) plane are shown in fig. 1(c). The results revealed a full-width half-maximum (FWHM) of 7.28o, 15.90o, and 16.17 for ASN, AlN, and ASN/AlN samples, respectively, indicating the oriented growth for these films. Moreover, the seven times higher intensity obtained with the ASN sample suggests a highly oriented film to (00l) plane.

In conclusion, XRD and XRC results for ASN films, AlN films, and ASN films with a 3nm AlN seed layer were performed. The results for AlN films met the reported value for pure AlN. ASN grew highly oriented when directly deposited on W electrodes. Further measurements such as JV, CV, and PV are needed.

References

[1] T. S. Böscke, et al., Appl. Phys. Lett., 99, 102903 (2011). [2] S. Kundu, et al., Nature Scientific Reports, 5, 8494 (2015). [3] M. Kobayashi, et al., IEEE J. Electron Dev. Soc., 7, 134 (2018). [4] S. Fichtner, et al., J. Appl. Phys., 125, 114103 (2019). [5] R. Deng, et al., Appl. Phys. Lett., 102, 112103 (2013). [6] Inorg. Mater.,1976,12,,371-374,Kuzenkova M.A., Kislyi P.S., Pshenichnaya O.V.

Figure 1