Sbs Stephan Heil

Ultralow surface recombination of c-Si substrates passivated by plasma-assisted atomic layer deposited Al2O3

Excellent surface passivation of c-Si has been achieved by Al2O3 films prepared by plasma-assisted atomic layer deposition, yielding effective surface recombination velocities of 2 and 13cm∕s on low resistivity n- and p-type c-Si, respectively. These results obtained for ∼30nm thick Al2O3 films are comparable to state-of-the-art results when employing thermal oxide as used in record-efficiency c-Si solar cells. A 7nm thin Al2O3 film still yields an effective surface recombination velocity of 5cm∕s on n-type silicon.

Plasma-assisted atomic layer deposition of Al2O3 moisture permeation barriers on polymers

Thin Al2O3 films of different thicknesses (10–40nm) were deposited by plasma-assisted atomic layer deposition on substrates of poly(2,6-ethylenenaphthalate) (PEN), and the water vapor transmission rate (WVTR) values were measured by means of the calcium test. The permeation barrier properties improved with decreasing substrate temperature and a good WVTR of 5×10−3gm−2day−1 (WVTRPEN=0.5gm−2day−1) was measured for a 20nm thick Al2O3 film deposited at room temperature using short purging times. Such ultrathin, low-temperature deposited, high-quality moisture permeation barriers are an essential requirement for the implementation of polymeric substrates in flexible electronic and display applications.

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.

In situ reaction mechanism studies of plasma-assisted atomic layer deposition of Al2O3

Reaction mechanisms during plasma-assisted atomic layer deposition (ALD) of Al2O3 from Al(CH3)3 and O2 plasma were studied by time-resolved quartz crystal microbalance measurements, mass spectrometry, and optical emission spectroscopy. Al(CH3)3 chemisorption on the oxide surface after the plasma pulse releases CH4 products while from the detection of CO, CO2, and H2O in the O2 plasma it is established that surface –CH3 groups are predominantly removed by O radical-driven combustionlike reactions. Also a second pathway exists for –CH3 removal driven by H2O generated in this plasma step. These reaction pathways are expected to be generic for plasma-assisted ALD of oxides from metal organic precursors.

Optical emission spectroscopy as a tool for studying, optimizing, and monitoring plasma-assisted atomic layer deposition processes

In this note it is demonstrated that optical emission spectroscopy (OES) is an easy-to-implement and valuable tool to study, optimize, and monitor thin film growth by plasma-assisted atomic layer deposition (ALD). The species in the plasma can be identified through the analysis of the light emitted by the plasma. OES provides therefore information on the reactant species delivered to the surface by the plasma but it also yields unique insight into the surface reaction products and, as a consequence, on the reaction mechanisms of the deposition process. Time-resolved measurements reveal information about the amount of precursor dosing and length of plasma exposure needed to saturate the self-limiting half reactions, which is useful for the optimization of the ALD process. Furthermore, time-resolved OES can also be used as an easy-to-implement process monitoring tool for plasma-assisted ALD processes on production equipment; for example, to monitor reactor wall conditions or to detect process faults in real time.

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...

Low-Temperature Deposition of TiN by Plasma-Assisted Atomic Layer Deposition

Titanium nitride (TiN) films were deposited by a plasma-assisted atomic layer deposition (PA-ALD) process, based on TiCl 4 precursor dosing and remote H 2 -N 2 plasma exposure, at temperatures ranging from 100 to 400°C. The plasma, the PA-ALD process, and the resulting TiN material properties were extensively investigated. The plasma was studied by optical emission spectroscopy and Langmuir probe, revealing an ion density of 10 9 cm -3 and an electron temperature of 3.5 eV just above the substrate. Under floating conditions there is thus a considerable ion flux towards the substrate per ALD cycle with a typical ion energy of ∼ 15 eV. TiN film growth was studied by in situ spectroscopic ellipsometry, revealing self-limiting surface reactions for the complete temperature range. At 100°C the growth rate of 0.3 A/cycle was found to be significantly lower than the growth rate of 0.6 A/cycle at 400°C. The stoichiometry of the films varied with the plasma exposure time, while the Cl content was mostly affected by the deposition temperature (2.1 atom % at 100°C to 0.07 atom % at 400°C). Resistivities as low as 71 μΩ cm were obtained at a temperature of 400°C, while at 100°C a fair resistivity of 209 μΩ cm was reached. These results show that PA-ALD with TiCl 4 and H 2 -N 2 plasma is well suited for low-temperature deposition of high-quality TiN films.

In situ spectroscopic ellipsometry study on the growth of ultrathin TiN films by plasma-assisted atomic layer deposition

The growth of ultrathin TiN films by plasma-assisted atomic layer deposition (PA-ALD) was studied by in situ spectroscopic ellipsometry (SE). In between the growth cycles consisting of TiCl4 precursor dosing and H2–N2 plasma exposure, ellipsometry data were acquired in the photon energy range of 0.75–5.0eV. The dielectric function of the TiN films was modeled by a Drude-Lorentz oscillator parametrization, and the film thickness and the TiN material properties, such as conduction electron density, electron mean free path, electrical resistivity, and mass density, were determined. Ex situ analysis was used to validate the results obtained by in situ SE. From the in situ spectroscopic ellipsometry data several aspects related to thin film growth by ALD were addressed. A decrease in film resistivity with deposition temperature between 100 and 400°C was attributed to the increase in electron mean free path due to a lower level of impurities incorporated into the films at higher temperatures. A change in resist...

Plasma-assisted atomic layer deposition of TiN monitored by in situ spectroscopic ellipsometry

In situ spectroscopic ellipsometry has been employed to determine the properties of titanium nitride (TiN) films during plasma-assisted atomic layer deposition by alternating TiCl4 precursor dosing and H2–N2 plasma exposure. Besides monitoring the film thickness when optimizing the half reactions, it is shown that spectroscopic ellipsometry is a very valuable tool for in situ studies of (air-sensitive) film properties such as resistivity, and for investigating the nucleation phase during initial film growth.