Work function engineering using lanthanum oxide interfacial layers

Abstract

A La2O3 capping scheme has been developed to obtain n-type band-edge metal gates on Hf-based gate dielectrics. The viability of the technique is demonstrated using multiple metal gates that normally show midgap work function when deposited directly on HfSiO. The technique involves depositing a thin interfacial of La2O3 on a Hf-based gate dielectric prior to metal gate deposition. This process preserves the excellent device characteristic of Hf-based dielectrics, but also allows the realization of band-edge metal gates. The effectiveness of the technique is demonstrated by fabricating fully functional transistor devices. A model is proposed to explain the effect of La2O3 capping on metal gate work function.

Band alignment at the SiO2/HfO2interface: Group IIIA versus group IIIB metal dopants

“…Overall, our results summarized in table VI are in a qualitative agreement with the recent experiments [6][7][8][9][10][11][12][13][14][15][16][17], and we need to identify the microscopic mechanism of the doping effect.…”

“…In particular, group III metals have been suggested to modify the interfacial dipole. For example, La has been used for the n-type silicon field effect transistors (FETs) [6,[8][9][10][11] and Al for the p-type FETs [7,[12][13][14][15][16][17]. The doping can be achieved, for instance, via the ion diffusion from a thin metal oxide capping layer deposited on top of the HfO 2 -based dielectric.…”

Growth of Dysprosium‐, Scandium‐, and Hafnium‐based Third Generation High‐κ Dielectrics by Atomic Vapor Deposition

“…Recent experiments into the possibility of shifting the threshold voltage to more desirable values incorporating rare earth elements (e.g., lanthanum) in the gate stack have shown encouraging results. [5][6][7][8] This can be accomplished, for example, by mixing the element in the bulk dielectric, such as in the case of HfLaO x materials, [5][6][7] or by adding a cap layer on top of the HfSiO x dielectric. [8] In addition, reports have been published describing scandate materials where a rare earth element is combined with scandium instead of hafnium.…”

“…[5][6][7][8] This can be accomplished, for example, by mixing the element in the bulk dielectric, such as in the case of HfLaO x materials, [5][6][7] or by adding a cap layer on top of the HfSiO x dielectric. [8] In addition, reports have been published describing scandate materials where a rare earth element is combined with scandium instead of hafnium. [9][10][11][12][13][14] Besides the benefits for threshold voltage control originating from the incorporation of the rare earth element in the gate stack, these materials are reported to have a high dielectric constant (j ∼ 20), [10,15] and a band gap comparable to HfO 2 [9,16] in combination with a high thermal stability, which makes them a very interesting class of materials.…”

The Progress and Challenges of Applying High-k/Metal-Gated Devices to Advanced CMOS Technologies

“…34 illustrates the effect of a band offset change between the high-k and interfacial oxide induced by incorporating metal ions into the interfacial layer. A metallic element can be incorporated in the IL by diffusion during thermal processing, specifically www.intechopen.com In nFETs, La is found to be the most effective dopant based on its overall effect on V t , EOT scaling, mobility, and reliability [50,53,54]. An Al 2 O 3 cap has been widely used for pFETs, but it increased the EOT [52] (since it has a relatively lower dielectric constant value) as well as raises reliability concerns due to Al diffusing into the interfacial oxide layer [52].…”