Jaakko Niinistö

Structural and dielectric properties of thin ZrO2 films on silicon grown by atomic layer deposition from cyclopentadienyl precursor

ZrO2 thin films with thicknesses below 20 nm were deposited by the atomic layer deposition process on Si(100) substrates at 350u200a°C. An organometallic precursor, Cp2Zr(CH3)2 (Cp=cyclopentadienyl, C5H5) was used as the zirconium source and water or ozone as oxygen source. The influence of oxygen source and substrate pretreatment on the dielectric properties of ZrO2 films was investigated. Structural characterization with high-resolution transmission electron microscopy was performed to films grown onto HF-etched or native oxide covered silicon. Strong inhibition of ZrO2 film growth was observed with the water process on HF-etched Si. Ozone process on HF-etched Si resulted in interfacial SiO2 formation between the dense and uniform film and the substrate while water process produced interfacial layer with intermixing of SiO2 and ZrO2. The effective permittivity of ZrO2 in Al/ZrO2/Si/Al capacitor structures was dependent on the ZrO2 layer thickness and oxygen source used. The interfacial layer formation incre...

Controlled growth of HfO2 thin films by atomic layer deposition from cyclopentadienyl-type precursor and water

HfO2 thin films have been deposited onto p-Si(100) substrates by atomic layer deposition (ALD) using Cp2Hf(CH3)2 n (Cp = cyclopentadienyl) and water as precursors at 300–500 °C. Processing parameters were optimised and the ALD type growth mode corroborated at 350 °C where a deposition rate of 0.42 A cycle−1 was obtained. The crystallinity, morphology and chemical composition of the deposited films were characterised. Films deposited at 300–450 °C were polycrystalline with monoclinic (−111) as the preferred orientation. Impurity levels of the stoichiometric HfO2 films deposited at 350 and 400 °C were very low, or below 0.4 and 0.25 atom% for carbon and hydrogen, respectively. In addition, ultrathin HfO2 films showed good dielectric properties such as low hysteresis and nearly ideal flatband voltage.

Deposition of yttria-stabilized zirconia thin films by atomic layer epitaxy from β-diketonate and organometallic precursors

Yttria-stabilised zirconia (YSZ) films were deposited by atomic layer epitaxy (ALE) using Zr(thd)4, Cp2Zr(CH3)2 and Cp2ZrCl2 as zirconium precursors. Y(thd)3 and ozone were used as yttrium and oxygen sources, respectively. YSZ films were grown at 375 °C from Y(thd)3/O3–Zr(thd)4/O3. Deposition temperatures were 310–365 °C for the Y(thd)3/O3–Cp2Zr(CH3)2/O3 and 275–350 °C for the Y(thd)3/O3–Cp2ZrCl2/O3 precursor combinations. Growth rates with a Y to Zr pulsing ratio of 1xa0∶xa01 were 0.56, 0.79 and 0.89 A n(cycle)−1 when Zr(thd)4, nCp2Zr(CH3)2 and Cp2ZrCl2 were used as zirconium precursors, respectively. Crystallinity and surface morphology of the deposited films were characterised by XRD and AFM while TOF-ERDA, XRF and SEM-EDX were used to analyse stoichiometry and possible impurities. The YSZ films were (100) oriented when deposited with a Y to Zr pulsing ratio of 1xa0∶xa01. Only thinner films (<60 nm), deposited from Y(thd)3/O3–Zr(thd)4/O3, showed the (111) preferred orientation. The lattice parameter was in the range of 5.09–5.28 A when the Y2O3 content was 5–89 mol%. When Cp2ZrCl2 was used as zirconium precursor, 0.1–1.7 mol% chlorine was observed in the films. According to the AFM analysis, roughness was dependent on the pulsing ratio of the nY and Zr precursors.

High-permittivity YScO3 thin films by atomic layer deposition using two precursor approaches

Amorphous YScO3 thin films have been deposited by atomic layer deposition using two types of volatile metal precursors, viz. n β-diketonate-type metal complexes M(thd)3 (M = Y, Sc; thd = 2,2,6,6-tetramethyl-3,5-heptanedionato) and organometallic cyclopentadienyl compounds tris(methylcyclopentadienyl)yttrium (C5H4CH3)3Y and tris(cyclopentadienyl)scandium Cp3Sc (Cp = C5H5). Ozone and water were used as oxygen sources in the M(thd)3 and cyclopentadienyl precursor-based processes, respectively. Deposition temperatures were 335–350 °C for the M(thd)3 precursor-based process and 300 °C for the cyclopentadienyl precursor-based process. Metal ratio and film thickness were easily controlled by varying the metal precursor pulsing ratio and the number of deposition cycles. Stoichiometric YScO3 films contained less than 1 atom% hydrogen and less than 0.2 atom% carbon regardless of the precursors used. The as-deposited stoichiometric films were smooth, amorphous and they had high permittivity (14–16). Films deposited using the cyclopentadienyl precursor-based process started to crystallize at 800 °C while films deposited using the M(thd)3 precursor-based process still remained amorphous at this temperature. Films deposited using the latter process crystallized at 1000 °C. Crystallization significantly deteriorated the dielectric properties of the films, however.

HfO2 Films Grown by ALD Using Cyclopentadienyl-Type Precursors and H2O or O3 as Oxygen Source

HfO 2 thin films have been deposited onto p-Si(100) substrates by atomic layer deposition (ALD) using Cp 2 Hf(CH 3 ) 2 (Cp = cyclopentadienyl) or Cp 2 HfCl 2 and water or ozone as precursors. The purity of HfO 2 films was better when ozone instead of water was used as oxygen precursor. The use of Cp 2 Hf(CH 3 ) 2 together with ozone in the ALD window range, viz. 350-400°C, yielded HfO 2 films with less than 0.1 atom % C and H impurities. Cp 2 HfCl 2 /H 2 O-processed film contained C and Cl, but again the use of ozone considerably reduced the impurity levels. When using Cp 2 Hf(CH 3 ) 2 as the metal source, the higher reactivity of ozone as compared to H 2 O yielded slightly higher growth rate, smoother morphology, higher degree of crystallinity for thicker films, and a close to ideal density. Furthermore, with ozone no inhibition of the growth during initial ALD cycles could be detected. The growth of HfO 2 film on H-terminated Si with the Cp 2 Hf(CH 3 ) 2 /H 2 O process was retarded and the initial island-like growth took place resulting in rougher surface. With the Cp 2 Hf(CH 3 ) 2 /O 3 process, the films showed the best leakage current density characteristics. Slightly higher capacitance equivalent oxide thickness values were calculated for the ozone-processed films.

Electrical properties of thin zirconium and hafnium oxide high-k gate dielectrics grown by atomic layer deposition from cyclopentadienyl and ozone precursors

ZrO2 and reference HfO2 films grown by atomic layer deposition from metal cyclopentadienyls and ozone as precursors to thicknesses ranging from 3.6to13.1nm on etched silicon showed electrical characteristics adequate to high-k dielectrics. The best results in terms of low interface state densities were obtained when (CpMe)2ZrMe2 precursor was used, with Cp denoting the cyclopentadienyl group (C5H5), and Me the methyl group (CH3). The ZrO2 films grown from (CpMe)2Zr(OMe)Me possessed nearly an order of magnitude higher trap state densities. Similar dependence on the precursor chemistry was observed upon recording the flatband voltage time transients. The flatband voltage transients, originating from phonon-assisted tunneling between localized states at oxide silicon interface, were the lowest in HfO2 films grown from (CpMe)2Hf(OMe)Me. The leakage current densities were also lower in the HfO2 films, compared to ZrO2. On the other hand, interfacial trap state densities in HfO2 based capacitors remained higher...

Influence of precursor chemistry and growth temperature on the electrical properties of SrTiO3-based metal-insulator-metal capacitors grown by atomic layer deposition

SrTiO3 thin films were grown to thicknesses in the range of 18–30 nm by atomic layer deposition using Sr(Pir3Cp)2 and (CpMe5)Ti(OMe)3 as strontium and titanium precursors at 250 and 300u2009°C. Water or ozone was used as oxygen precursor. The films were amorphous in as-deposited state, but crystallized as cubic SrTiO3 after annealing at 650u2009°C. The highest permittivity values, 60–65, were achieved in the films deposited with ozone at 300u2009°C. The films grown at 250u2009°C tended to possess markedly lower leakage currents than those grown at 300u2009°C.

Chapter 4:Atomic Layer Deposition

Atomic layer deposition (ALD) is a special variant of chemical vapour deposition (CVD) technology used to grow high-quality thin films through alternate self-limiting surface reactions (Figure 4.1). ALD has gained considerable interest in recent years as a thin film deposition method to overcome man...