Cubic Structured HfLaO Dielectrics for MIM Capacitor for RF IC Applications
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Metal-Insulator-Metal (MIM) capacitors with various thickness as (22 nm, 30 nm, 37 nm and 44 nm) of La (8%) doped HfO2 deposited using atomic layer deposition were fabricated. A high dielectric constant value of 38 can be obtained when 8% La doped HfO2 is crystallized into cubic structure. While amorphous HfLaO demonstrates a quadratic voltage linearity <1000 ppm/V2 up to a capacitance density of 9fF/µm2, both amorphous and crystallized HfLaO film shows good leakage current characteristics. The higher k value of HfLaO benefits MIM capacitor for RF ICs.Keywords:
High-κ dielectric
Metal-insulator-metal
We fabricate ultrathin HfO2 gate stacks of very high permittivity by atomic layer deposition (ALD) and oxygen-controlled cap post-deposition annealing. The HfO2 layer is directly deposited on a wettability-controlled Si surface by ALD. To enhance permittivity, a cubic crystallographic phase is generated in ALD-HfO2 by short-time annealing with a Ti capping layer. The Ti layer absorbs residual oxygen in the HfO2 layer, which suppresses the growth of the interfacial SiO2 layer. The dielectric constant of ALD-HfO2 is increased to ∼40, and a gate stack of extremely scaled equivalent oxide thickness (∼0.2 nm) is obtained.
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The atomic layer deposition (ALD) method was applied for fabricating high permittivity (high-k) dielectrics, viz. HfO2, ZrO2 and rare earth oxides, which can be used to replace SiO2 as gate and capacitor dielectric. The dielectrics were processed by ALD using novel cyclopentadienyl (Cp, -C5H5) precursors together with water or ozone as the oxygen source. ALD, which has been identified as an important thin film growth technique for microelectronics manufacturing, relies on sequential and saturating surface reactions of alternately applied precursors, separated by inert gas purging. The surface-controlled nature of ALD enables the growth of thin films of high conformality and uniformity with an accurate thickness control. The ALD technique is introduced and ALD processes for HfO2, ZrO2 and rare earth oxide films, as well as the applications of the high-k dielectrics in microelectronics are reviewed. The need for developing new ALD processes for the high-k materials is emphasized. ALD processes for HfO2 and ZrO2 were developed using Cp-type precursors. The effect of different oxygen sources, namely water or ozone, on the film growth characteristics and properties of the ALD-processed films was examined in detail. The oxide films were stoichiometric, with impurity levels below even 0.1 at-% for C or H. Electrical measurements showed promising dielectric properties such as high permittivity values and low leakage current densities. Other properties, such as structure, interfacial layer thickness and morphology, were also characterized. Compared to films processed by water, the ozone-processed films on H-terminated Si showed improved dielectric properties, as well as higher density, lower roughness and better initial growth rate. In addition, in situ gasphase measurements by quadrupole mass spectrometry (QMS) were performed in order to study the ZrO2 growth mechanism. A number of Cp-precursors were tested for the ALD of several rare earth oxide films. The thermal stability of many of the precursors was limited, but nevertheless, ALD-type processes were developed for Y2O3 and Er2O3 films. High reactivity of the Cp-precursors towards water resulting in high growth rates (1.2-1.7 A/cycle) and purity of the Y2O3 and Er2O3 films were realized. Despite the detected partial decomposition of the (CpMe)3Gd precursor, Gd2O3 films with high growth rate and purity as well as effective permittivity of about 14 were deposited. Finally, promising processes for ternary scandates, namely YScO3, GdScO3, and ErScO3, were developed using either Cpor β-diketonate-based processes. These as-deposited ternary films were amorphous exhibiting high effective permittivity (14-15), low leakage current density, and resistance towards crystallization upon annealing even up to 800°C.
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Atomic Vapor Deposition (AVD) and Atomic Layer Deposition (ALD) techniques were successfully applied for the depositions of perovskite type dielectrics, namely, Sr-Ta-O, Ti-Ta-O, Sr-Ti-O, Ba-Hf-O, Nb-Ta-O and Ce-Al-O. Thin films were investigated as alternative dielectrics for Metal-Insulator-Insulator (MIM) capacitors. Structural and electrical properties are investigated after depositing the metal oxides on 200 mm TiN/Si (100) substrates within the temperature range of 225-400 ºC. Electrical properties, investigated after sputtering Au top electrodes, revealed that the main characteristics are different for each dielectric. The highest dielectric constants were achieved for crystalline SrTiO3 (k=95), crystalline CeAlO3 (k = 60) and amorphous Ti-Ta-O (k = 50) films. However, Sr-Ta-O based MIM capacitors showed the lowest leakage current densities as well as the smallest capacitancevoltage linearity coefficients.
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A semi-empirical, stacked capacitor model was developed to calculate the dielectric constants (k) and deposition rates of hafnium silicate (HfSiO) deposited by nano-laminated atomic layer deposition (NL-ALD) from the HfO2 and SiO2 ALD cycles (m and n, respectively). The calculations agree well with the experimental data, with an accuracy of 90%. The model enables the deposition of HfSiO with desired thicknesses and any dielectric constants ranging from 7 to 19 using proper combinations of m and n. The systematic study on the effects of various combinations of m and n that give similar dielectric constants showed that increasing m and n enhances the dielectric scalability due to less defects formed at the high- k/IL oxide interface during NL-ALD, but degrades the electrical stability due to more severe charge trapping. Changing m and n has no significant effect on thermal stability and electron mobility.
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Hafnium
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Atomic Vapor Deposition (AVD) technique was successfully applied for the depositions of amorphous HfO2, Sr-Ta-O and Ti-Ta-O thin films, which were investigated as alternative dielectrics to replace the standard SiO2 or Si3N4 dielectrics used in Metal-Insulator-Insulator (MIM) capacitors. Metal oxides were grown on 200 mm TiN/Si (100) substrates within the thermal budget of back-end-of-line (BEOL) process. Electrical properties, investigated after sputtering Au top electrodes, revealed that the main characteristics are different for each dielectric. On one hand, Ti-Ta-O based MIM capacitors possessed a dielectric constant of 50, which is more than a factor of 2 higher compared to the ones of Sr-Ta-O (20) and HfO2 (18). On the other hand, Sr-Ta-O based MIM capacitors showed the lowest leakage current densities as well as the smallest capacitance-voltage linearity coefficients.
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We fabricate ultra-thin HfO2 gate stacks of very high permittivity value by using atomic layer deposition (ALD) and Ti-cap post deposition annealing. The HfO2 layer is directly deposited on hydrophilicized Si surface by ALD. A cubic crystallographic phase is generated in ALD-HfO2 by short time annealing with Ti capping layer. The Ti layer absorbs residual oxygen in HfO2 layer. The reduced oxygen concentration during annealing suppresses the growth of the interfacial SiO2 layer. The dielectric constant of ALD-HfO2 is enhanced to ～40, and extremely scaled ～0.2 nm equivalent oxide thickness of total gate stack is obtained.
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