The influence of the crystal orientation difference between (100) and (110) silicon substrates on characteristics of La 2 O 3 -and Al 2 O 3 -capped HfO 2 dielectric metal-oxide-semiconductor field-effect transistors has been investigated. We observed that the equivalent oxide thickness of the capped devices varies according to the crystal orientation, indicating that the two substrates are not equal in the gate stack scalability within a subnanometer regime. We found that the mobility dependency on the crystal orientation is reduced by additional scattering associated with the capping films, suggesting the difficulty to derive maximum benefit from an inherent difference in the mobility depending on the crystal orientation.A s traditional metal-oxide-semiconductor fieldeffect transistor (MOSFET) scaling is facing difficulty in the continued performance improvement, novel solutions are required especially for the channel and gate stack technologies. The extreme reduction in equivalent oxide thickness of dielectrics, EOT, can be achieved by the implementation of high-k dielectrics. 1) In the development of the complementary MOSFET, a control of the threshold voltage, V t , governed by the effective work function of the gate stack, W eff , is the issue of greatest concern, because of the inflexibility of the W eff under the given MOSFET fabrication process. 2,3) One of the promising solutions is the deposition of capping films on top of the base dielectric, 4) which provides the dynamic W eff change. 5) The La 2 O 3 and Al 2 O 3 films stacked on the bulk HfO 2 is commonly used as negative and positive V t shifter, respectively, while those capping films affect the EOT and the inversion carrier mobility, . 6,7) On the other hand, regarding the channel technology, the selection of appropriate surface orientation of silicon substrates is necessary for improving the MOSFET's drive current. Whereas the (100)-oriented substrate is conventionally used, the (110)-oriented substrate is attracting considerable attention for its excellent hole transport property. 8,9) Since the nature of the silicon surface and its surface oxide layer differ between the two substrates, 10,11) the orientation difference is potentially influential on the high-k dielectric properties stacked on the substrates. Therefore, it is very important to assess the functionally of the capping films in the (110) MOSFETs. However, few studies have been carried out. In this letter, we present the effects of the La 2 O 3and Al 2 O 3 -capping films on the characteristics of HfO 2 dielectric MOSFETs fabricated on the two different silicon substrates.N-and p-channel bulk planer MOSFETs were fabricated on the (100) and (110) silicon substrates through a standard gate first process to the first back-end metal layer. After the device isolation process, n-and p-type wells were formed. The impurity concentration of the wells is $6 Â 10 16 cm À3 , irrespective of the well type. The thin oxide interface layer was prepared, followed by the deposition of $2-nm HfO 2 by ato...