Epitaxial Growth of Y2O3-doped High-K Cubic HfO2 on GaAs Utilizing ALD-HfO2/Y2O3 Super-Cycles
Lawrence Boyu Young1*, Chao-Kai Cheng2, Yen-Hsun Lin1, Keng-Yung Lin1, Chia-Hung Hsu3, Jueinai Kwo4, Minghwei Hong1,2
1Department of Physics, National Taiwan University, Taipei, Taiwan
2Graduate Institute of Applied Physics, National Taiwan University, Taipei, Taiwan
3National Synchrotron Radiation Research Center, Hsinchu, Taiwan
4Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
* Presenter:Lawrence Boyu Young
Si-based complementary metal-oxide-semiconductor (CMOS) technology has reached its physical limit as the scaling is no longer available since the 22-16 nm node. To push better devices, one approach is to replace the Si channel by high carrier mobility InGaAs with high-k gate dielectrics. Among the InGaAs compound semiconductors, GaAs(001) is a promising candidate to be integrated with the conventional Si(001) platform because of the smallest lattice mismatch to Si. We urgently need materials with higher dielectric constant > 30 for the sub 5-nm CMOS technology. In our previous work, we have successfully grown single crystal cubic Y2O3-doped HfO2 (YDH) on GaAs(001) by using molecular beam epitaxy (MBE) through 19% Y2O3-doping. For technological applications, it is necessary to grow the YDH by utilizing atomic layer deposition (ALD), a thin film deposition method with capability for mass production, featuring uniform growth over a large area, precise thickness control down to angstrom, and conformal deposition over artificial structures.
In this work, we have epitaxially grown cubic YDH on GaAs(001) substrate using ALD-HfO2/Y2O3 super-cycles. The reflection high energy electron diffraction (RHEED) patterns revealed that the surface of the deposited YDH on GaAs(001) exhibited four-fold symmetry. We have performed synchrotron radiation x-ray diffraction (SR-XRD) to study the crystal structure of the films. From the radial scan along the substrate normal, the two strong and sharp peaks located at 31.62o and 66.04o are attributed from the substrate GaAs(002) and (004). Another two peaks centered at 29.96o and 61.78o were identified to be the diffraction from cubic Hf0.8Y0.2O1.9(111) and (222) according to the inter-plane d-spacing of 0.298 nm and 0.150 nm. The other two peaks at 34.88o and 73.53o have the corresponding d-spacing of 0.257 nm and 0.128 nm, which probably came from the diffractions of monoclinic HfO2(002) and (004), or cubic Hf0.8Y0.2O1.9(002) and (004). The off-normal φ-cone scan confirmed the symmetry of the structure; the 90o equally spaced peaks indicated the structure exhibited a four-fold symmetry, consistent with the off-normal symmetry of a (001) cubic structure. Moreover, an in-plane radial scan along GaAs[100] was taken to further rule out the possibility of the monoclinic phase. Furthermore, the clear Pendellösung fringes indicated an excellent crystallinity of cubic YDH, which is consistent with the narrow FWHM of 0.034o and 0.059o observed in the θ-rocking scan of cubic YDH(111) and YDH(002), respectively.

Keywords: Atomic Layer Deposition, Epitaxial growth, Doping induced phase stabilization, High-k dielectrics, III-V semiconductor.