van Jl Hans Hemmen

Plasma and Thermal ALD of Al2O3 in a Commercial 200 mm ALD Reactor

The deposition of Al 2 O 3 by remote plasma atomic layer deposition (ALD) in the Oxford Instruments FlexAL reactor was studied and compared with results from thermal ALD in the same reactor. Trimethylaluminum [Al(CH 3 ) 3 ] was used as the metal precursor and O 2 plasma and H 2 O were used as oxidizing agents for the plasma and thermal processes, respectively. For remote plasma ALD with a total cycle time of 4 s, the growth per cycle decreased monotonically with substrate temperature, from 1.7 A/cycle at 25°C to 1.0 A/cycle at 300°C. This growth per cycle was consistently higher than that obtained for thermal ALD. For the latter a maximum growth per cycle of ∼ 1.0 A/cycle was found at 200°C. The film properties investigated were nearly independent of oxidant source for temperatures between 100 and 300°C, with a slightly higher mass density for the remote plasma ALD Al 2 O 3 films. Films deposited at 200 and 300°C were stoichiometric with a mass density of 3.0 g/cm 3 and low C (< 1 atom %) and H (<3 atom %) contents. At lower substrate temperatures, oxygen-rich films were obtained with a lower mass density and higher H-content. Remote plasma ALD produced uniform Al 2 O 3 films with nonuniformities of less than ±2% over 200 mm diam substrates. Excellent conformality was obtained for films deposited in macropores with an aspect ratio of ∼8 (2.0-2.5 μm diam). Preliminary results on electrical properties of remote plasma deposited films showed high dielectric constants of 7.8 and 8.9 for as-deposited and forming gas annealed Al 2 O 3 , respectively.

Deposition of TiN and HfO2 in a commercial 200mm remote plasma atomic layer deposition reactor

The authors describe a remote plasma atomic layer deposition reactor (Oxford Instruments FlexAL™) that includes an inductively coupled plasma source and a load lock capable of handling substrates up to 200mm in diameter. The deposition of titanium nitride (TiN) and hafnium oxide (HfO2) is described for the combination of the metal-halide precursor TiCl4 and H2–N2 plasma and the combination of the metallorganic precursor Hf[N(CH3)(C2H5)]4 and O2 plasma, respectively. The influence of the plasma exposure time and substrate temperature has been studied and compositional, structural, and electrical properties are reported. TiN films with a low Cl impurity content were obtained at 350°C at a growth rate of 0.35A∕cycle with an electrical resistivity as low as 150μΩcm. Carbon-free (detection limit <2at.%) HfO2 films were obtained at a growth rate of 1.0A∕cycle at 290°C. The thickness and resisitivity nonuniformity was <5% for the TiN and the thickness uniformality was <2% for the HfO2 films as determined over 200mm wafers.The authors describe a remote plasma atomic layer deposition reactor (Oxford Instruments FlexAL™) that includes an inductively coupled plasma source and a load lock capable of handling substrates up to 200mm in diameter. The deposition of titanium nitride (TiN) and hafnium oxide (HfO2) is described for the combination of the metal-halide precursor TiCl4 and H2–N2 plasma and the combination of the metallorganic precursor Hf[N(CH3)(C2H5)]4 and O2 plasma, respectively. The influence of the plasma exposure time and substrate temperature has been studied and compositional, structural, and electrical properties are reported. TiN films with a low Cl impurity content were obtained at 350°C at a growth rate of 0.35A∕cycle with an electrical resistivity as low as 150μΩcm. Carbon-free (detection limit <2at.%) HfO2 films were obtained at a growth rate of 1.0A∕cycle at 290°C. The thickness and resisitivity nonuniformity was <5% for the TiN and the thickness uniformality was <2% for the HfO2 films as determined over 20...

Reaction mechanisms during plasma-assisted atomic layer deposition of metal oxides: A case study for Al2O3

Plasma-assisted atomic layer deposition (ALD) of metal oxide films is increasingly gaining interest, however, the underlying reaction mechanisms have rarely been addressed. In this work, a case study is presented for the plasma-assisted ALD process of Al2O3 based on Al(CH3)3 dosing and O2 plasma exposure. A complementary set of time-resolved in situ diagnostics was employed, including spectroscopic ellipsometry, quartz crystal microbalance, mass spectrometry, and optical emission spectroscopy. The saturation of the Al(CH3)3 adsorption reactions was investigated, as well as the reaction products created during both the precursor dosing and the plasma exposure step. The generality of the observations was cross-checked on a second commercial ALD reactor. The main observations are as follows: (i) during the precursor dosing, the Al(CH3)3 predominantly binds bifunctionally to the surface at 70°C through a reaction in which H is abstracted from the surface and CH4 is released into the gas phase; (ii) during the...

Dielectric Properties of Thermal and Plasma-Assisted Atomic Layer Deposited Al2O3 Thin Films

A comparative electrical characterization study of aluminum oxide (Al2O3) deposited by thermal and plasma-assisted atomic layer depositions (ALDs) in a single reactor is presented. Capacitance and leakage current measurements show that the Al2O3 deposited by the plasma-assisted ALD shows excellent dielectric properties, such as better interfaces with silicon, lower oxide trap charges, higher tunnel barrier with aluminum electrode, and better dielectric permittivity (k = 8.8), than the thermal ALD Al2O3. Remarkably, the plasma-assisted ALD Al2O3 films exhibit more negative fixed oxide charge density than the thermal ALD Al2O3 layers. In addition, it is shown that plasma-assisted ALD Al2O3 exhibits negligible trap-assisted (Poole-Frenkel) conduction unlike the thermal ALD Al2O3 films, resulting in higher breakdown electric fields than the thermal ALD prepared films

Opportunities for plasma-assisted atomic layer deposition

Within the method of atomic layer deposition (ALD), additional reactivity can be delivered to the surface in the form of plasma-produced species. The application of such a low- temperature plasma in the ALD cycle can therefore open up a processing parameter space that is unattainable by the strictly thermally driven process. In this contribution several possible benefits of plasma-assisted ALD will be reviewed showing bright prospect for plasma-assisted ALD for a large variety of applications, also far beyond the typical use in semiconductor devices.

Downstream ion and radical densities in an Ar-NH3 plasma generated by the expanding thermal plasma technique

A full characterization of the Ar–NH3 expanding thermal plasma source applied in industrial processes for high-rate silicon nitride deposition is presented in terms of absolute densities of reactive species such as ions and radicals. The ion composition of the plasma was identified by mass spectrometry, while absolute ion density information was obtained by Langmuir probe measurements. N radicals were detected by threshold ionization mass spectrometry, whereas NH and NH2 radicals were measured by cavity ringdown spectroscopy. It was found that the ion density decreases from 1013 cm−3 in a pure Ar plasma to 1010–1011 cm−3 when NH3 is injected, with ArH+, , , and being the most abundant ions. The densities of N and NH both saturate at a level of 3 × 1012 cm−3 at NH3 flows above 3 sccs while the density of NH2 increases linearly with the NH3 flow and reaches a level of 4 × 1012 cm−3. When the plasma source current is increased, the densities of N and NH increase linearly, while the NH2 density remains approximately constant. Furthermore, it is revealed that most of the consumed NH3 is converted into N2 and H2 in the plasma.

Remote plasma and thermal ALD of Al2O3 for trench capacitor applications

The remote plasma ALD process of Al 2O3 from Al(CH 3)3 and O 2 plasma was characterized and compared to the well established thermal ALD process of Al 2O3 employing H 2O as the oxidant. The growth per cycle, saturation of the surface reactions and material properties were investigated for substrate temperatures between 25 and 300 °C. It was demonstrated that high-quality films can be obtained for substrate temperatures above 100 °C. For these temperatures the mass densities of the remote plasma ALD films are slightly higher than those of the thermally deposited films. Remote plasma ALD also yields fair material properties below 100 °C at a relatively high growth per cycle and short cycle times. With remote plasma ALD conformal films were achieved in high-aspect ratio structures. Together with the first results on electrical characterization, it was shown that the Al 2O3 deposited is promising for the application in metal-oxide-semiconductor “trench” capacitors.