E.F. Krimmel

Hydrogen profiles of thin PVD silicon nitride films using elastic recoil detection analysis

Abstract Thin silicon nitride films (e.g. D = 100 nm) produced by the ion beam sputtering technique show different depth profiles of hydrogen concentration depending on process parameters. The hydrogen profiles of these thin films can be varied within certain limits by annealing. Films prepared on a silicon substrate have been analysed with respect to the hydrogen content by the elastic recoil detection analysis method (ERDA) using a 10 MeV 20 Ne beam impinging on the target at an incident angle of φ = 10° relative to the ion beam axis. Comparison of the results of the ERDA with the results from analyses using the nuclear reaction 1 H( 15 N, αγ) 12 C shows good agreement. The experimental results illustrate the advantage of the PVD sputtering deposition technique in controlling the hydrogen concentration of thin silicon nitride films.

Chemical bonding and interface analysis of ultrathin silicon-nitride layers produced by ion implantation and Electron Beam Rapid Thermal Annealing (EB-RTA)

Abstract15N2+ions were implanted into c-Si with an energy of 5 keV/atom and fluences ranging from 5×1016 to 2×1017 atoms/cm2 at RT to form ultrathin silicon-nitride layers (SiNx) with different N/Si ratios depending on the fluences (up to an overstoichiometric N/Si ratio of 1.65). The 15N depth distributions were analysed by the resonant nuclear reaction 15N(p, αγ)12C(Eres=429 keV). The implanted samples were processed by Electron Beam Rapid Thermal Annealing (EB-RTA) at 1150° C for 15 s (ramping up and down 5° C/s). The chemical structure of the 15N implantation into Si was investigated by EXAFS and NEXAFS. Channeling-RBS (4He+, E0=1.5 MeV) measurements were performed to observe the transition region (disordered-Si layer, d-Si) being underneath of the SiNx layer (typical values of layer thicknesses:SiNx 24 nm, d-Si 6 nm).

In situ detection of rearrangement processes during electron beam annealing of ion implanted InP

Abstract Ion implantation and short-time electron beam annealing can be used as precise and reproducible tool for introducing controlled quantities of impurities into semiconductors. Measurement of the thermal radiation of ion implanted samples during the electron beam tempering process allows the in situ detection of changes in the surface structure and charge carrier density. In contrast to temperature controlled annealing methods, it is therefore possible to precisely control the annealing by the detection of rearrangement processes. We exemplify the method by the activation and diffusion of P during the temperature treatment for the well-known system of P implanted Si[2]. Furthermore, tempering of semi-insulating as well as of Mg+ implanted InP by means of electron beam irradiation is presented.

Nitrogen profiles of thin sputtered PVD silicon nitride films

Abstract Thin amorphous silicon nitride films (D= 100 nm ) were deposited on silicon substrates by means of argon ion beam sputtering under high vacuum conditions (residual gas pressure below 10 −5 Pa). The nitrogen depth profiles were measured by using the nuclear resonance reaction 15 N(p,αγ) 12 C at E res =429 keV ( Γ =120 eV ). The hydrogen concentration was determined by ERDA using a 10 MeV 20 Ne ion beam. Results show that the nitrogen concentration of thin films is inversely proportional to the hydrogen concentration . The nitrogen profiles obtained by NRA and by comparative RBS meaurements ( 4 He + , E 0 = 2.0MeV) showed good agreement. Annealing of the sample in nitrogen atmosphere at 600°C for 1 h did not influence the nitrogen concentration.

Investigations of ultrathin silicon nitride layers produced by low-energy ion implantation and EB-RTA

Abstract Ultrathin silicon nitride layers were produced by implanting 10 keV 15 N + 2 ions into 〈100〉 silicon at RT with fluences from 5.0 × 10 16 at/cm 2 to 5.0 × 10 17 at/cm 2 . The 15 N depth distributions were analysed by the resonant nuclear reaction 15 N(p, αγ) 12 C. The NRA of the silicon nitride layers show understoichiometric, stoichiometric, and overstoichiometric N/Si ratios depending on the fluences. The implanted samples were processed by electron beam rapid thermal annealing (EB-RTA) between 900 and 1130°C under high vacuum conditions. The layer thicknesses and the 15 N peak concentrations of EB-RTA samples varied with reference to non-annealed 15 N layers. The alteration of the chemical bonds of SiN x layers by EB-RTA was investigated by XPS. NRA analyses of the EB-RTA samples at tilt angles from 65 to 83° indicated a shift of the low-energy edge which represents the sample surface. This shift is attributed to a shadowing effect of the SiN x surface. AFM analyses confirmed that the surfaces of EB-RTA samples were covered with irregularly distributed vertical very elastic, needlelike structures. Their average height was 16 nm ( F = 5.0 × 10 16 at / cm 2 , EB-RTA at 900° C for 15 s).

Low-energy 15N implantation in carbon for the synthesis of carbon nitride layers

15N2+ molecular ions with an energy of 12 keV were implanted in glassy carbon and 40 keV 15N+ ions were implanted into different carbon forms (glassy carbon, graphite and polycrystalline diamond) at room temperature in order to form thin carbon nitride layers. The nitrogen depth profiles were measured using the resonant nuclear reaction 15N(p, αγ)12C (Eres = 429 keV, Γ = 120 eV) by varying the projectile energy during the analysis. In the case of the 6 keV implantation the saturation dose was 8 × 1016 at./cm2 whereas for the 40 keV implantation the saturation dose was found to be 3.9 × 1017 at./cm2. A maximum nitrogen concentration of 25 at.% was measured at both implantation energies. The saturation dose, the maximal attainable nitrogen concentration and the form of the 15N depth distribution are not dependent on the used carbon form. Sputtering yield measurements showed that the sputter process (measured sputtering yield < 0.2) is not responsible for the saturation dose (4 × 1017 at./cm2) and the maximal attainable nitrogen concentration (25 at.%). For the formation of carbon-nitrogen bonds, samples with an implanted fluence of 6 × 1017 ions/cm2 were rapidly heated for 120 s using an electron beam. A reduction of the dose from 4 × 1017 at./cm2 to 1.3 × 1017 at./cm2 was observed indicating the formation of a carbon nitride phase stable to temperatures up to 1000°C.

Height control of silicon nano-whiskers embedded in ultra thin silicon nitride layers by rapid thermal annealing

Abstract Two steps are necessary to produce nanometre sized silicon whiskers rising out of ultra thin silicon nitride layers: (i) production of under-stoichiometric silicon nitride surface layers by ion implanting of silicon wafer material, (ii) growth of silicon whiskers by the formation of silicon nitride bonds in the surface region through rapid thermal electron beam annealing. Depending on the implantation and annealing conditions, whiskers of different height and width can be produced. As an example, 25 nm high whiskers were formed by implanting 10 keV 15 N 2 + ions into silicon (fluence 5×10 16 cm −2 ) followed by rapid thermal electron beam annealing at 900°C for 15 s . In atomic force microscope studies, it was observed that the structures became more pronounced with increased temperature. Resonant nuclear reaction analysis revealed the absence of nitrogen in the whiskers and the stoichiometry of the silicon nitride layer formed by implantation.

Characterisation of thin sputtered silicon nitride films by NRA, ERDA, RBS and SEM

SummaryThin, amorphous silicon nitride (a-SINx) films were deposited on n-type (100) silicon substrates using an argon ion beam for sputtering a HPSN block under high vacuum conditions. The substrates were kept at room temperature. Nitrogen depth distributions were determined by NRA using the resonance reaction 15N(p,αγ)12C at 429 keV. Hydrogen profiles were analysed by NRA (1H(15N,αγ)12C at Eo=6.385 MeV) and by ERDA (20Ne2+, Eo=10 MeV). The NRA was used to determine the depth distributions (concentration vs. areal density) of nitrogen and hydrogen taking calibration standards into consideration. The silicon depth distributions and the N/Si ratios of the deposited a-SiNx films were determined by RBS (4He+, Eo=2.0 MeV). Film thicknesses were obtained by SEM. The density of the deposited a-SiNx films was found to be ϱ=2.7 (±0.1) g/cm3 by correlating RBS data and real film thicknesses as obtained by SEM.

Surface-near analyses of ultra thin silicon nitride layers by NRA, channeling RBS, FT IR ellipsometry and AFM

Homogeneous ultra thin silicon nitride layers (SiNx layers) close to the surface have been produced by 10 keV 15N2+molecular ion implantation and an ion current density of 10 μA/cm2, into single crystal silicon at room temperature. Stoichiometric SiNx layers with thicknesses of about 28 nm (analyzed by NRA) were obtained at fluences of 1.5×1017 at/cm2. NRA analyses of samples annealed by EB-RTA at T=1150° C for 15 s indicated that the N/Si ratio and the layer thickness did not change drastically. FT IR ellipsometry analyses indicated the existence of Si3N4 bonds in as-implanted specimens. A disordered Si layer (d-Si, typically 15 nm thick) underneath the implantation region caused by the ion implantation was found by channeling RBS analyses. The d-Si layer partly recrystallized during EB-RTA showing a thickness of 6 nm afterwards. The SiNx layers showed no decomposition and detachment after EB-RTA. Due to EB-RTA, however, the smooth surface of the as-implanted specimens changed into a surface with remaining whisker-like structures surrounded by circular recesses as shown by AFM analyses. A model for the growth of these whisker-liker structures caused by low energy ion implantation and EB-RTA is presented on the basis of the thickness of the SiNx layer, the existence of the d-Si layer and the special annealing process.

Nitrogen depth distribution, interface and structure analysis of SiNx layers produced by low-energy ion implantation

Thin silicon nitride (SiNx) layers with the stoichiometric N/Si ratio of 1.33 in the maximum of the concentration depth distributions of nitrogen were produced by implanting 10 keV15N2+ in 〈100〉 silicon at room temperature under high vacuum conditions. The depth distribution of the implanted isotope was measured by resonance nuclear reaction analysis (NRA), whereas the layer structure of the implanted region and the geometrical thickness of the layers were characterised by high resolution transmission electron microscopy (TEM). SiNx layers with a thickness of about 30 nm were determined by NRA. Channeling Rutherford backscattering spectrometry was used to determine the disorder in the silicon substrate. Sharp interfaces of a few nanometers between the highly disordered implanted region and the crystalline structure of the substrate thickness were observed by TEM. The high thermal stability of SiNx layers with N/Si ratios from under to over stoichiometric could be shown by electron beam rapid thermal annealing (1100 °C for 15 s, ramping up and down 5 °C/s) and NRA.