H. Kupfer

Structure and properties of titanium nitride thin films deposited at low temperatures using direct current magnetron sputtering

Titanium nitride layers on silicon substrates have been deposited by magnetron sputtering at a constant temperature of 200 °C using nitrogen partial pressures (pN2) from 0.001 to 0.36 Pa. Distinct dependences between pN2 in the reactive gas and the mechanical and structural properties of the layers could be found by x‐ray diffraction and other methods. The general absence of the Ti2N phase in layers deposited at low temperatures can be explained by the high energy impact of energetic particles during the deposition process as well as by the limited mobility of adatoms due to the low substrate temperature. Two different cases of lattice distortions were detected for low and high pN2, respectively. In the higher pressure range the lattice parameters a1110 are greater than the a2000. For this the variable density of interstitial sites in different planes together with the macroscopic film stress was found to be responsible. At lower pN2 the a1110 was smaller than the a2000. This effect could be explained by ...

Optical properties and mechanical stress in SiO2/Nb2O5 multilayers

Abstract The aim of this work is the formation of stress-controlled reflection layers which are suitable for application on micromechanical elements without bending them out of shape. Thin films of Nb 2 O 5 and SiO 2 have been deposited by magnetron sputtering of an oxide target (SiO 2 ) and reactive sputtering of a niobium target in an oxygen containing atmosphere, respectively. Silicon and niobium oxide had been selected on the basis of preliminary experiments out of nine different thin film oxides since they yielded sufficiently low absorption coefficients of magnetron sputtered films. Both optical parameters and film stress have been investigated in dependence on deposition parameters. In particular, by varying the substrate bias voltage (for Nb 2 O 5 ) and the sputtering pressure (for SiO 2 ) the film stress could be influenced to a large extent without deterioration of the optical properties. In Nb 2 O 5 , the stress could be varied between compressive and zero stress, whereas in SiO 2 compressive stress was always obtained. Hence, a complete stress-compensation in the multilayers necessitates the application of an additional underlying metal layer having tensile stress. We found magnetron-sputtered chromium films most suitable for that purpose since they provided the highest line stress in comparison to their additional mass per area. To demonstrate our approach we present as an example a layer stack of six SiO 2 and six Nb 2 O 5 films which were designed for maximum reflection at the wavelengths 446, 532 and 629 nm. The film stack was formed after a chromium film (nominal thickness 143 nm) was deposited onto a thin (thickness 30 μm) single-crystal silicon mirror plate. Reflectivity at the wavelengths given above was between 96 and 98%. The multilayer was highly stress-compensated with a typical residual bow of 0.4 μm for a 3.5×3.5 mm 2 mirror.

Optical properties of nitrogen-rich carbon films deposited by d.c. magnetron sputtering

Abstract Nitrogen-rich carbon films were grown by d.c. magnetron sputtering from a graphite target in various nitrogen/argon gas mixtures using two different substrate temperatures. Infrared spectroscopical investigations were carried out in order to determine differences in the film composition and structure caused by the variation of the deposition conditions. The spectra are interpreted in terms of two bands which are typically found in the Raman spectra of CN α films. While the band at 1280 cm −1 only slightly increases in absorption intensity with increasing nitrogen incorporation, the band at 1520 cm −1 becomes much more pronounced. Both bands shift to higher wavenumbers with increasing nitrogen content. Additionally, the films show a decrease in the absorption above 2500 cm −1 . The existence of different functional groups absorbing at 2130 cm −1 can be suppressed by substrate heating up to 400°C during preparation, CN groups absorbing above 2200 cm −1 , however, remain in the samples. In order to support the IR results additional ellipsometric measurements, investigations of film density and stoichiometry were performed. Heating the substrates during deposition leads to a reduced nitrogen incorporation.

Two N2+(B2 u+) populations with different Boltzmann distribution of the rotational levels found in different types of N2/Ar discharges—improved estimation of the neutral gas temperature

We investigated the rotational excitation of the nitrogen molecule ion in a pulsed magnetron sputter discharge (Mg target, pressure 0.1–2.0 Pa) and a 150 Pa dc glow discharge in dependence on various process parameters. For this purpose we used optical emission spectroscopy of the 0–0 band of the first negative system of the (FNS0–0) and calculated the rotational temperature by fitting the spectra. Often, the best fit could be achieved assuming two populations of the molecules having two different rotational temperatures. These temperatures and their contributions to the spectrum of the FNS0–0 show a significant dependence on the process parameters. The lower temperature is in the range of 370–800 K and is believed to be equal to the translational temperature of the neutral gas. The higher temperature is in the order of 1500–3000 K and its origin is most probably the excitation of the state by heavy particle impact connected with rotational excitation.

Fundamental mechanisms of titanium nitride formation by d.c. magnetron sputtering

Abstract The dependences of the structure and properties of titanium nitride layers deposited using reactive d.c. magnetron sputtering on the substrate bias voltage and substrate position were investigated. The plasma parameters and particle fluxes towards the substrate surface were analysed using in-situ methods. The microstructure of the layers as well as important properties strongly depend on the impact of energetic particles on the surface of the growing film. The formation of the TiN compound, on the contrary, depends mainly on the neutral atomic and excited molecular nitrogen species arising within the magnetron discharge.

A time-resolved Langmuir double-probe method for the investigation of pulsed magnetron discharges

Langmuir probes are important means for the characterization of plasma discharges. For measurements in plasmas used for the deposition of thin films, the Langmuir double probe is especially suited. With the increasing popularity of pulsed deposition discharges, there is also an increasing need for time-resolved characterization methods. For Langmuir probes, several single-probe approaches to time-resolved measurements are reported but very few for the double probe. We present a time-resolved Langmuir double-probe technique, which is applied to a pulsed magnetron discharge at several 100 kHz used for MgO deposition. The investigations show that a proper treatment of the current measurement is necessary to obtain reliable results. In doing so, a characteristic time dependence of the charge-carrier density during the “pulse on” time containing maximum values of almost 2∙1011cm−3 was found. This characteristic time dependence varies with the pulse frequency and the duty cycle. A similar time dependence of the...

Structure and secondary electron emission properties of MgO films deposited by pulsed mid-frequency magnetron sputtering

A pulsed mid-frequency magnetron sputtering technique was used to deposit MgO films. Atomic force microscopy, Rutherford backscattering, x-ray diffraction, and a diode discharge device were used to characterize surface morphology, oxygen content, crystalline structure, and the secondary electron emission (γ) coefficient of the films, respectively. The oxygen content (56 at. %) in all the films remained constant. However, surface morphology, crystalline structure, and the secondary electron emission properties of the films are strongly dependent on the O2 flow rate. As the O2 flow rate is increased from 3 to 10 sccm, a sudden decrease in the grain size and the γ coefficient of the films can be observed, and the crystalline orientation evolves from a strong (200) preferred orientation continuously to a fully (220) preferred orientation. Further increase of O2 flow rate results in a slight change in the grain size and the crystalline orientation, but a considerable increase in the full width at half maximum ...

Intrinsic stress in dielectric thin films for micromechanical components

Abstract The film stress in coated micromechanical elements may cause bending of such elements and thus impair their performance. In these cases, stress reduction within a single layer by proper choice of deposition parameters or stress compensation within multilayer systems is necessary. In this paper, possibilities for stress reduction in high-reflection (Nb 2 O 5 /SiO 2 ) n quarterwave multilayers for thin silicon laser mirrors have been investigated. Film deposition was performed by reactive direct-current (Nb 2 O 5 ) and non-reactive radio-frequency magnetron sputtering (SiO 2 ), respectively. The film stress was investigated as a function of process gas pressure, substrate temperature and ion bombardment of the growing film. At zero bias voltage, a total stress of about −30 MPa was obtained in the Nb 2 O 5 films. Utilization of an additional electrode to reduce the plasma density in front of the substrate did change the stress to a small tensile value. SiO 2 films show a compressive stress that could not be reduced below 100 MPa within the parameter range investigated. Complete stress compensation in the multilayer film systems was only possible by application of an additional tensile-stressed metal interlayer. Chromium films deposited prior to the growth of a (4×2) stack of Nb 2 O 5 and SiO 2 did compensate — within the error of measurement of ±25 MPa — the average stress in the multilayer system to zero.

Influence of aluminum additions on phase formation in boron nitride films deposited by magnetron sputtering

Boron nitride (BN) thin films have been deposited by magnetron sputtering of an hexagonal BN (h-BN) target with an additional flux of aluminum provided by a special Al sputtering target. Up to an aluminum percentage of about 1.0 at. % the formation of the cubic BN (c-BN) phase was not influenced by the aluminum addition. An Al content of 1.3 at. % was connected with a remarkable delay in the transition from h-BN to c-BN growth as well as a certain deterioration in the crystal quality. An aluminum flux causing a concentration of 1.5 at. % did prevent the growth of the cubic BN phase completely. The dynamics of impurity incorporation were investigated using secondary ion mass spectrometry measurements. We found that the aluminum electrode plays an important role in the incorporation of hydrogen in the films. In connection with other results it can be concluded that for both h-BN and c-BN strong evidence for substitutional incorporation of aluminum on boron sites exists. Cross-section transmission electron m...

Deposition and properties of TiN/carbon multilayers for corrosion protection of steel

TiN/carbon multilayers for corrosion protection of steel were deposited using d.c. magnetron sputtering. Cross-section TEM pictures revealed a dense and fine-grained polycrystalline TiN structure whereas the carbon sublayers proved to be amorphous. Nodular growth defects connected with deep gaps were frequently observed; these are due to macroscopic carbon particles emitted from the graphite target. These defects are the most important cause for a corrosive attack. The pitting potential of the multilayers was increased in comparison with both TiN and carbon single layers.