Thierry Conard

Nucleation and growth of atomic layer deposited HfO2 gate dielectric layers on chemical oxide (Si-O-H) and thermal oxide (SiO2 or Si-O-N) underlayers

A study was undertaken to determine the efficacy of various underlayers for the nucleation and growth of atomic layer deposited HfO2 films. These were compared to films grown on hydrogen terminated Si. The use of a chemical oxide underlayer results in almost no barrier to film nucleation, enables linear and predictable growth at constant film density, and the most two-dimensionally continuous HfO2 films. The ease of nucleation is due to the large concentration of OH groups in the hydrous, chemical oxide. HfO2 grows on chemical oxide at a coverage rate of about 14% of a monolayer per cycle, and films are about 90% of the theoretical density of crystalline HfO2. Growth on hydrogen terminated Si is characterized by a large barrier to nucleation and growth, resulting in three-dimensional, rough, and nonlinear growth. Thermal oxide/oxynitride underlayers result in a small nucleation barrier, and nonlinear growth at low HfO2 coverages. The use of chemical oxide underlayers clearly results in the best HfO2 layer...

Effective electrical passivation of Ge(100) for high-k gate dielectric layers using germanium oxide

In search of a proper passivation for high-k Ge metal-oxide-semiconductor devices, the authors have deposited high-k dielectric layers on GeO2, grown at 350–450°C in O2. ZrO2, HfO2, and Al2O3 were deposited by atomic layer deposition (ALD). GeO2 and ZrO2 or HfO2 intermix during ALD, together with partial reduction of Ge4+. Almost no intermixing or reduction occurs during Al2O3 ALD. Capacitors show well-behaved capacitance-voltage characteristics on both n- and p-Ge, indicating efficient passivation of the Ge∕GeOx interface. The density of interface states is typically in the low to mid-1011cm−2eV−1 range, approaching state-of-the-art Si∕HfO2∕matal gate devices.

Passivation of Ge ( 100 ) ∕ GeO2 ∕ high-κ Gate Stacks Using Thermal Oxide Treatments

The physical and electrical properties of Ge/GeO 2 /high-κ gate stacks, where the GeO 2 interlayer is thermally grown in molecular oxygen, are investigated. The high-K layer (ZrO 2 , HfO 2 , or Al 2 O 3 ) is deposited in situ on the GeO 2 interlayer by atomic layer deposition. Detailed analysis of the capacitance-voltage and conductance-frequency characteristics of these devices provides evidence for the efficient passivation of the Ge(100) surface by its thermal oxide layer. A larger flatband voltage hysteresis is observed in HfO 2 -based gate stacks, as compared to Al 2 O 3 gate stacks, which is possibly related to the more pronounced intermixing observed between the HfO 2 and GeO 2 .

Deposition of HfO2 on germanium and the impact of surface pretreatments

The deposition behavior of HfO2 by metalorganic chemical vapor deposition on germanium has been investigated. HfO2 films can be deposited on Ge with equally good quality as compared to high-k growth on silicon. Surface preparation is very important: compared to an HF-last, NH3 pretreatments result in smoother films with strongly reduced diffusion of germanium in the HfO2 film, resulting in a much better electrical performance. We clearly show that much thinner interfacial layers can be obtained, approximately half the thickness of what is typically found for depositions on silicon, suggesting the possibility of more aggressive equivalent oxide thickness∕leakage scaling.

Island growth in the atomic layer deposition of zirconium oxide and aluminum oxide on hydrogen-terminated silicon: Growth mode modeling and transmission electron microscopy

Atomic layer deposition (ALD) is used in applications where inorganic material layers with uniform thickness down to the nanometer range are required. For such thicknesses, the growth mode, defining how the material is arranged on the surface during the growth, is of critical importance. In this work, the growth mode of the zirconium tetrachloride∕water and the trimethyl aluminum∕water ALD process on hydrogen-terminated silicon was investigated by combining information on the total amount of material deposited with information on the surface fraction of the material. The total amount of material deposited was measured by Rutherford backscattering, x-ray fluorescence, and inductively coupled plasma–optical emission spectroscopy, and the surface fractions by low-energy ion scattering. Growth mode modeling was made assuming two-dimensional growth or random deposition (RD), with a “shower model” of RD recently developed for ALD. Experimental surface fractions of the ALD-grown zirconium oxide and aluminum oxid...

Ultra low-EOT (5 Å) gate-first and gate-last high performance CMOS achieved by gate-electrode optimization

A novel gate first integration approach enabling ultra low-EOT is demonstrated. HfO₂ based devices with a zero interface layer and optimized gate-electrode is used to achieve EOT and T_inv values of ˜5 Å and ˜8 Å respectively for both n and pMOS devices. The drive currents at I_off=100 nA/μm with V_DD=1 V is 1.4 mA/μm and 0.6 mA/μm (no SiGe source/drain) for n and pMOS respectively. The technology further offers low n/pMOS V_T of 0.3/-0.4V, good V_T-uniformity, and V_T-matching and very high cutoff frequencies at ˜290-340 GHz for 38 nm nMOS devices. A replacement poly gate process is used to further improve upon the pMOS effective work function. TDDB lifetimes over 10 years are reported while BTI indicates potential reliability challenges.

Characterisation of ALCVD Al2O3-ZrO2 nanolaminates, link between electrical and structural properties

Al 2 O 3 and ZrO 2 mixtures for gate dielectrics have been investigated as replacements for silicon dioxide aiming to reduce the gate leakage current and reliability in future CMOS devices. Al 2 O 3 and ZrO 2 films were deposited by atomic layer chemical vapor deposition (ALCVD) on HF dipped silicon wafers. The growth behavior has been characterized structurally and electrically. ALCVD growth of ZrO 2 on a hydrogen terminated silicon surface yields films with deteriorated electrical properties due to the uncontrolled formation of interfacial oxide while decent interfaces are obtained in the case of Al 2 O 3 , Another concern with respect to reliability aspects is the relatively low crystallization temperature of amorphous high-k materials deposited by ALCVD. In order to maintain the amorphous structure at high temperatures needed for dopant activation in the source drain regions of CMOS devices, binary Al/Zr compounds and laminated stacks of thin Al 2 O 3 and ZrO 2 films were deposited. X-ray diffraction and transmission electron microscope analysis show that the crystallization temperature can be increased dramatically by using a mixed oxide approach. Electrical characterization shows orders of leakage current reduction at 1.1-1.7 nm of equivalent oxide thickness. The permittivity of the deposited films is determined by combining quantum mechanically corrected capacitance voltage measurements with structural analysis by transmission electron microscope, X-ray reflectivity, Rutherford backscattering, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectroscopy. The k-values are discussed with respect to formation of interfacial oxide and possible silicate formation.

Atomic layer deposition of hafnium oxide on germanium substrates

Germanium combined with high-κ dielectrics has recently been put forth by the semiconductor industry as potential replacement for planar silicon transistors, which are unlikely to accommodate the severe scaling requirements for sub-45‐nm generations. Therefore, we have studied the atomic layer deposition (ALD) of HfO2 high-κ dielectric layers on HF-cleaned Ge substrates. In this contribution, we describe the HfO2 growth characteristics, HfO2 bulk properties, and Ge interface. Substrate-enhanced HfO2 growth occurs: the growth per cycle is larger in the first reaction cycles than the steady growth per cycle of 0.04nm. The enhanced growth goes together with island growth, indicating that more than a monolayer coverage of HfO2 is required for a closed film. A closed HfO2 layer is achieved after depositing 4–5HfO2 monolayers, corresponding to about 25 ALD reaction cycles. Cross-sectional transmission electron microscopy images show that HfO2 layers thinner than 3nm are amorphous as deposited, while local epita...

Characterization of Cu surface cleaning by hydrogen plasma

When a Cu surface is exposed to a clean room ambient, a surface layer containing Cu2O, CuO, Cu(OH)2, and CuCO3 is formed. Thermal treatment in a vacuum combined with hydrogen plasma can remove this layer. Water and carbon dioxide desorb during the thermal treatment and the hydrogen plasma reduces the remaining Cu oxide. Ellipsometric, x-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectroscopy analyses indicate that the mechanism of interaction of the H2 plasma with this layer depends on temperature. When the temperature is below 150 °C, H2 plasma cannot completely reduce Cu oxide. Hydrogen diffuses through the oxide and hydrogenation of the Cu layer is observed. The hydrogenated Cu surface has a higher resistance than a nontreated Cu layer. The hydrogen plasma efficiently cleans the Cu surface when the substrate temperature is higher than 150 °C. In this case, hydrogen atoms have enough activation energy to reduce Cu oxide and adsorbed water forms as a byproduct of Cu oxide reduction. When the wafer temperature is higher than 350 °C, the interaction of the Cu film with hydrogen and residual oxygen is observed.When a Cu surface is exposed to a clean room ambient, a surface layer containing Cu2O, CuO, Cu(OH)2, and CuCO3 is formed. Thermal treatment in a vacuum combined with hydrogen plasma can remove this layer. Water and carbon dioxide desorb during the thermal treatment and the hydrogen plasma reduces the remaining Cu oxide. Ellipsometric, x-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectroscopy analyses indicate that the mechanism of interaction of the H2 plasma with this layer depends on temperature. When the temperature is below 150 °C, H2 plasma cannot completely reduce Cu oxide. Hydrogen diffuses through the oxide and hydrogenation of the Cu layer is observed. The hydrogenated Cu surface has a higher resistance than a nontreated Cu layer. The hydrogen plasma efficiently cleans the Cu surface when the substrate temperature is higher than 150 °C. In this case, hydrogen atoms have enough activation energy to reduce Cu oxide and adsorbed water forms as a byproduct of Cu oxide reduc...

Characterization of ALCVD-Al2O3 and ZrO2 layer using X-ray photoelectron spectroscopy

The atomic layer chemical vapor deposition (ALCVD) deposited Al 2 O 3 and ZrO 2 films were investigated by ex situ X-ray photoelectron spectroscopy. The thickness dependence of band gap and valence band alignment was determined for these two dielectric layers. For layers thicker than 0.9 nm (Al 2 O 3 ) or 0.6 nm (ZrO 2 ), the band gaps of the Al 2 O 3 and ZrO 2 films deposited by ALCVD are 6.7 ± 0.2 and 5.6 ± 0.2 eV, respectively. The valence band offsets at the Al 2 O 3 /Si and ZrO 2 /Si interface are determined to be 2.9 ± 0.2 and 2.5 ± 0.2 eV, respectively. Finally, the escape depths of Al2p in Al 2 O 3 and Zr 3p3 in ZrO 2 are 2.7 and 2.0 nm, respectively.