Characterization of Laminated CeO[sub 2]–HfO[sub 2] High-k Gate Dielectrics Grown by Pulsed Laser Deposition

Abstract

The electrical and physical properties of CeO 2 -HfO 2 nanolaminates on Si͑100͒, by pulsed laser deposition, are investigated. Layers were deposited using pure CeO 2 and HfO 2 targets at various substrate temperatures ranging from 220 to 620°C at Ar + H 2 and O 2 and in situ postdeposition anneal of nanolaminates performed by controlled cooling from deposition temperature to room temperature under high oxygen pressure. After layer growth and anneal, top and bottom Au electrodes were deposited by sputtering. Electrical characterization was done by C-V and I-V measurements. The highest k value of 30 was found for the laminates deposited at 520°C in Ar + H 2 ambient. It is found that the properties of CeO 2 -HfO 2 nanolaminates deposited at reducing atmosphere are dependent on the layer thickness. Thicker layers showed a higher dielectric constant and higher leakage current densities than thinner layers.As a result of aggressive scaling of the dimensions of complementary metal-oxide silicon ͑CMOS͒ devices, research on new high dielectric constant ͑high-k͒ materials for replacing SiO 2 has become a major issue in materials science of dielectrics in recent years. HfO 2 is the most promising candidate, and has been investigated intensively by the semiconductor industry and research institutions. CeO 2 is also one of the promising candidates because it is thermodynamically stable on silicon, which is advantageous for reducing interfacial SiO 2 regrowth. 1 CeO 2 with its fluorite structure has a very small lattice mismatch of 0.35% on silicon that allows epitaxial or highly oriented crystalline layers. CeO 2 also has a k value of 20-26 and a bandgap of approximately 6 eV. 2 Laminated structures are used for tailoring the electrical and physical properties of oxides. 3 Conduction and valence band offsets the dielectric constant and in particular the leakage current properties of the resulting composite dielectric can be engineered by lamination. Pulsed laser deposition ͑PLD͒ is known for its flexibility and precision for growing atomically smooth alternating layers on various substrates. 4 In this work, first results of laminated CeO 2 -HfO 2 dielectric layers deposited by PLD are presented. ExperimentalCeO 2 -HfO 2 nanolaminates were grown on HF-dipped silicon ͑100͒ substrates at temperatures varying from 220 to 620°C by PLD from high-density, pure ͑above 99.99% purity͒ CeO 2 and HfO 2 targets in an ultrahigh vacuum ͑UHV͒-PLD system ͑with a base pressure below 5 ϫ 10 −9 mbar͒. A 248 nm KrF laser is used for PLD at 1 and 3 J/cm 2 for CeO 2 and HfO 2 targets, respectively. Target-tosubstrate distance was 45 mm and laser repetition rate was 5 Hz for all deposited layers. These settings resulted in a deposition rate of 0.125 nm/s. A 0.1 mbar Ar + H 2 ͑5%͒ gas mixture was used as deposition ambient to create a reducing atmosphere to prevent excessive silicon oxide formation during deposition, as well as to reduce the CeO 2 first layer to Ce 2 O 3 . The latter is thermodynamically more stable on silicon than CeO 2 toward SiO 2...

Maxwell–Wagner Relaxation-Driven High Dielectric Constant in Al2O3/TiO2 Nanolaminates Grown by Pulsed Laser Deposition

“…Several oxide NL combinations such as Al 2 O 3 /TiO 2 , Al 2 O 3 /ZnO, ZrO 2 /HfO 2 , ZrO 2 /Gd 2 O 3 , HfO 2 /Ta 2 O 5 , CeO 2 /HfO 2 , HfO 2 /LaAlO 3 , Al 2 O 3 /ZrO 2 , Al 2 O 3 /MgO, , Al 2 O 3 /HfO 2 , , and so forth have been investigated to achieve improved electrical and dielectric properties required for aforementioned applications. Among these, the Al 2 O 3 /TiO 2 /Al 2 O 3 (ATA) NL has emerged as the most preferred candidate for high- k applications, owing to its low cost, excellent thermal stability, and superior electrical and dielectric properties. , Initial studies on ATA NLs with layer thicknesses of the order of a few nanometers have reported k values less than that of TiO 2 ; , however, significantly enhanced k values were achieved when thicknesses of Al 2 O 3 and TiO 2 layers were reduced to the subnanometric regime. − Although dielectric constants of ∼1000 and 850 have been reported for atomic layer deposition (ALD)-grown ATA NLs with sublayer thicknesses ∼0.2 and 0.5 nm, these structures suffered from high dielectric losses of ∼10 and 2, respectively. , Furthermore, the observed high- k values for ATA NLs have been attributed to charge accumulation across the heterogeneous interfaces of insulating (Al 2 O 3 ) and semiconducting (TiO 2 ) sublayers due to the well-known Maxwell–Wagner (M–W) relaxation .…”

“…7−9 Among these, multilayered NLs consisting of alternate ultrathin sublayers of two high-k dielectrics have recently garnered significant attention owing to their superior electrical and dielectric properties, suitable for a wide range of potential applications in next-generation data and energy storage devices, metal-oxide-semiconductor capacitors, and field-effect transistors. 10−13 Several oxide NL combinations such as Al 2 O 3 /TiO 2 , 14 Al 2 O 3 /ZnO, 15 ZrO 2 /HfO 2 , 16 ZrO 2 /Gd 2 O 3 , 17 HfO 2 /Ta 2 O 5 , 18 CeO 2 /HfO 2 , 19 HfO 2 /LaAlO 3 , 20 Al 2 O 3 /ZrO 2 , 21 Al 2 O 3 / MgO, 22,23 Al 2 O 3 /HfO 2 , 24,25 tigated to achieve improved electrical and dielectric properties required for aforementioned applications. Among these, the Al 2 O 3 /TiO 2 /Al 2 O 3 (ATA) NL has emerged as the most preferred candidate for high-k applications, owing to its low cost, excellent thermal stability, and superior electrical and dielectric properties.…”

Sol–gel deposited ceria thin films as gate dielectric for CMOS technology

“…The film's structure and interface properties depend upon deposition processes. Several deposition techniques have been reported in literature for the preparation of CeO 2 films on Si for CMOS devices, including sputtering (Wang et al 2001), vacuum evaporation (Inoue et al 1990), MBE (Joumori et al 2004), PLD (Karakaya et al 2006), MOCVD (Ami and Suzuki 1998), and E-beam evaporation (Inoue et al 1999), etc. All these techniques require high temperature treatments which usually induces a deterioration of the device performance and reliability.…”

Conduction Mechanism and Reliability Characteristics of a Metal–Insulator–Metal Capacitor with Single ZrO2 Layer

“…However, the energy band-gap (E g ) of the HK dielectric and its conduction-band offset (ÁE C ) to the metal electrode become worse with increasing HK dielectric constant, 6) which can cause poor electrical performance, poor reliability, and thermal leakage current. In the literature, [7][8][9][10][11][12] zirconium oxide (ZrO 2 ) has emerged as one of the most promising HK dielectrics for MIM capacitors due to its outstanding characteristics including high dielectric constant, low leakage current, and high electrical performance. 13) However, there have been few reports on a MIM capacitor with single ZrO 2 layer, which would be necessary for high-density capacitors, although a stacked dielectric with ZrO 2 has been reported.…”