Suvi Haukka

Electrical and materials properties of ZrO2 gate dielectrics grown by atomic layer chemical vapor deposition

Structural and electrical properties of gate stack structures containing ZrO2 dielectrics were investigated. The ZrO2 films were deposited by atomic layer chemical vapor deposition (ALCVD) after different substrate preparations. The structure, composition, and interfacial characteristics of these gate stacks were examined using cross-sectional transmission electron microscopy and x-ray photoelectron spectroscopy. The ZrO2 films were polycrystalline with either a cubic or tetragonal crystal structure. An amorphous interfacial layer with a moderate dielectric constant formed between the ZrO2 layer and the substrate during ALCVD growth on chemical oxide-terminated silicon. Gate stacks with a measured equivalent oxide thickness (EOT) of 1.3 nm showed leakage values of 10−5 A/cm2 at a bias of −1 V from flatband, which is significantly less than that seen with SiO2 dielectrics of similar EOT. A hysteresis of 8–10 mV was seen for ±2 V sweeps while a midgap interface state density (Dit) of ∼3×1011 states/cm eV wa...

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.

Diffusion Barrier Deposition on a Copper Surface by Atomic Layer Deposition

Diffusion barrier materials, TiN and WN, were deposited by atomic layer deposition (ALD). The chlorine concentration of the TiN film was as low as 1.2 at.-%, and resistivity was below 200 μΩ cm. Ultra high aspect ratio (AR=85) trenches were used to assess step coverage. Tungsten nitride film, deposited from WF 6 and ammonia, was found to have high resistivity, although the residue content was low. The barrier deposition compatibility was studied using the copper surface exposed on the bottom of vias in the copper dual-damascene structure. The deposition on copper of both TiN and WN was found to be very challenging.

Growth of Si nanocrystals on alumina and integration in memory devices

We present a detailed study of the growth of Si quantum dots (Si QDs) by low pressure chemical vapor deposition on alumina dielectric deposited by atomic layer deposition. The Si QDs density is very high, 1012 cm−2, for a mean diameter between 5 and 10 nm. Al2O3/Si QD stacks have been integrated in memory devices as granular floating gate. The devices demonstrate good charge storage and data retention characteristics.

Reduction of Copper Oxide Film to Elemental Copper

The reduction of copper oxide film was studied as a process step in the manufacturing of elemental copper film via copper oxide film. Alcohols, carboxylic acids, and aldehydes were tested as reducing agents. The copper oxide film was exposed to reducing agents below 400°C using nitrogen as a carrier gas. The reduction efficiency was studied by characterizing the oxide residues with ion beam analysis and measuring the electrical resistance of the films. Thermodynamic calculations were compared with the observations. Most of the reducing agents performed well and copper oxide film as thick as 300-400 nm was completely reduced to elemental copper.

Advanced Materials Processing by Adsorption Control

Precise control and knowledge of surface structures are essential inorder to meet the requirements of todays and future materials. One possiblegrowth technique capable of meeting the requirements is atomic layer epitaxy(ALE). ALE is based on sequentially applied saturated gas-solid reactions,which provide the means for adsorption controlled material deposition atatomic layer level. In this paper the potentiality of the use of porousmaterials in a detailed study of adsorption controlled growth is discussed.At the same time the study promotes the application of adsorption controlledmaterials processing for advanced catalysts manufacturing.

Atomic-layer-deposited WNxCy thin films as diffusion barrier for copper metallization

The properties of WNxCy films deposited by atomic layer deposition (ALD) using WF6, NH3, and triethyl boron as source gases were characterized as a diffusion barrier for copper metallization. It is noted that the as-deposited film shows an extremely low resistivity of about 350 μΩ cm with a film density of 15.37 g/cm3. The film composition measured from Rutherford backscattering spectrometry shows W, C, and N of ∼48, 32, and 20 at. %, respectively. Transmission electron microscopy analyses show that the as-deposited film is composed of face-centered-cubic phase with a lattice parameter similar to both β-WC1−x and β-W2N with an equiaxed microstructure. The barrier property of this ALD–WNxCy film at a nominal thickness of 12 nm deposited between Cu and Si fails only after annealing at 700 °C for 30 min.

Miscibility of amorphous ZrO2–Al2O3 binary alloy

Miscibility is a key factor for maintaining the homogeneity of the amorphous structure in a ZrO2–Al2O3 binary alloy high-k dielectric layer. In the present work, a ZrO2/Al2O3 laminate thin layer has been prepared by atomic layer chemical vapor deposition on a Si (100) wafer. This layer, with artificially induced inhomogeneity (lamination), enables one to study the change in homogeneity of the amorphous phase in the ZrO2/Al2O3 system during annealing. High temperature grazing incidence x-ray diffraction (HT-XRD) was used to investigate the change in intensity of the constructive interference peak of the x-ray beams which are reflected from the interfaces of ZrO2/Al2O3 laminae. The HT-XRD spectra show that the intensity of the peak decreases with an increase in the anneal temperature, and at 800 °C, the peak disappears. The same samples were annealed by a rapid thermal process (RTP) at temperatures between 700 and 1000 °C for 60 s. Room temperature XRD of the RTP annealed samples shows a similar decrease in...

Growth of aluminium nitride on porous silica by atomic layer chemical vapour deposition

Abstract Aluminium nitride (AlN) was grown on porous silica by atomic layer chemical vapour deposition (ALCVD) from trimethylaluminium (TMA) and ammonia precursors. The ALCVD growth is based on alternating, separated, saturating reactions of the gaseous precursors with the solid substrate. TMA and ammonia were reacted at 423 and 623 K, respectively, on silica which had been dehydroxylated at 1023 K and pretreated with ammonia at 823 K. The growth in three reaction cycles was investigated quantitatively by elemental analysis, and the surface reaction products were identified by IR and solid state 27Al and 29Si NMR measurements. Steady growth of about 2 aluminium and 2 nitrogen atoms/nmsilica2/reaction cycle was obtained. The growth mainly took place through (i) the reaction of TMA which resulted in surface Al–Me and Si–Me groups, and (ii) the reaction of ammonia which replaced the aluminium-bonded methyl groups with amino groups. Ammonia also reacted in part with the silicon-bonded methyl groups formed in the dissociative reaction of TMA with siloxane bridges. TMA reacted with the amino groups, as it did with surface silanol groups and siloxane bridges. In general, the Al–N layer interacted strongly with the silica substrate, but in the third reaction cycle AlN-type sites may have formed.

Characterization of Atomic Layer Deposited WNxCy Thin Film as a Diffusion Barrier for Copper Metallization

The film properties of WNxCy films deposited by atomic layer deposition (ALD) using WF6 ,N H 3, and triethylboron source gases were characterized as diffusion barrier for Cu metallization. It is noted that the as-deposited film shows an extremely low resistivity of about 350 µΩ-cm with a film density of 15.37 g/cm 3 . The film composition measured from Rutherford backscattering spectrometry shows W, C, and N of approximately 48, 32, and 20 at.%, respectively. Transmission electron microscopy analyses show that the as-deposited film is composed of face-centered-cubic phase with a lattice parameter similar to both β-WC1-x and βW2N with an equiaxed microstructure. The barrier property of this ALD-WNxCy film at a nominal thickness of 12 nm deposited between Cu and Si fails only after annealing at 700 o Cf or 30 minutes while the sputter-deposited Ta (12 nm) and ALD-TiN (20 nm) fail at 650 and 600 o C, respectively. It is thought that the superior diffusion barrier performance of ALD-WNxCyfilm is the consequence of both nanocrystalline equiaxed grain structure and the formation of high density film.