A. E. T. Kuiper

Phase-change recording materials with a growth-dominated crystallization mechanism: A materials overview

The influence of phase-change material composition on amorphous phase stability, crystallization rate, nucleation probability, optical constants and media noise is reported for materials with a growth dominated crystallization mechanism. Two material classes have been studied, doped Sb–Te and doped Sb-based compositions. The material properties of both are greatly influenced by their composition, and in a similar way. For both materials systems hold that the antimony content especially influences the crystallization rate, amorphous phase stability and media noise of the phase-change material. Compositions rich in antimony generally show high crystallization rates, low archival life stability and high media noise. The material properties are further influenced by the presence of dopants like tellurium, germanium, gallium, indium or tin. Germanium and tellurium reduce the crystallization rate, but are essential to increase the amorphous phase stability. Dopants like tin or indium are added to increase the c...

Thermal nitridation of silicon dioxide films

Thermal SiO2 films, ranging in thickness from 200 to 1200 A, were thermally nitrided using NH3 at temperatures between 800 and 1160 °C and for times varying between 3 min and 5 h. The resulting films were analyzed with Auger electron spectroscopy in combination with argon ion sputtering, Rutherford backscattering spectrometry, spectroscopic ellipsometry, and infrared spectroscopy. The nitridation results in the formation of oxynitride layers in the oxide, the largest nitrogen concentration being found in the surface region and at the SiO2/Si interface. The reaction proceeds via a replacement of oxygen by nitrogen atoms under the action of hydrogen. Although the amount of nitrogen incorporated in the surface region is independent of the original oxide thickness, the interface nitrogen concentration is lower the larger the oxide thickness. This can be explained by assuming that the diffusion of NHx (0<x≤3) through the oxide limits the reaction rate. In the temperature range 1000–1160 °C the rate of the reac...

Robust giant magnetoresistance sensors

Abstract The giant magnetoresistance (GMR) effect offers interesting new possibilities for sensor applications. A short overview is given of the GMR effect in relation to its application in (automotive and industrial) field sensors. In the past the thermal and magnetic stability could not fulfil the requirements for use in automotive and industrial environments. Recently, a new, robust GMR material system has been developed that can withstand high temperatures (>200°C) and large magnetic fields (>200 kA/m). Using this material, GMR sensor elements have been fabricated and measured. Moreover, preliminary measurements on the first robust GMR sensor with a full Wheatstone-bridge configuration will be presented.

Hydrogen in low‐pressure chemical‐vapor‐deposited silicon (oxy)nitride films

Silicon (oxy)nitride films (SiOxNy) have been deposited onto silicon by low‐pressure chemical vapor deposition using SiH2Cl2, N2O and NH3 or ND3. Nuclear reaction analysis, elastic recoil detection, and Rutherford backscattering spectrometry have been used to determine the elemental composition of the films with emphasis on the hydrogen and deuterium content. In the as‐deposited, NH3‐grown films the bulk hydrogen concentration is about 3 at. % for an oxygen/nitrogen atomic ratio (O/N) smaller than 0.4, for O/N>0.4 it is lower. In 900 and 1000 °C vacuum annealed films the bulk hydrogen concentration as a function of O/N goes through a maximum at O/N≊0.4. By comparing this observation with the D content in ND3‐grown films as a function of O/N, a model is deduced which explains this behavior. This model involves an oxygen induced increase of the electronegativity of the atoms to which hydrogen/deuterium is bound. Annealing at 1000 °C in a H2/N2 gas mixture of NH3‐grown films results in bulk hydrogen concentr...

Robust GMR sensors for angle detection and rotation speed sensing

Magnetic sensors for automotive applications based on the giant magnetoresistance (GMR) effect have been developed. These sensors combine many of the advantageous properties of the GMR effect for sensor applications. The sensor characteristics have been optimised with respect to two different applications, namely angular position sensing and rotational speed sensing. Robust GMR sensors with a full Wheatstone-bridge configuration have been fabricated. The thermal and magnetic stability of our GMR sensors are excellent. The sensors show reliable performance at temperatures exceeding 170°C and at large magnetic fields (>200 kA/m). Lifetime tests at elevated temperatures also show very promising results.

Characterization of low‐pressure chemical‐vapor‐deposited and thermally‐grown silicon nitride films

Low‐pressure chemical vapor‐deposited (LPCVD) silicon nitride films on silicon have been characterized by means of Rutherford backscattering (RBS), Auger electron spectroscopy (AES) combined with ion sputtering, and spectroscopic ellipsometry. It appeared that all LPCVD samples in the examined thickness range of 50 –500 A had an oxygen‐containing layer equivalent to 15–20 A of SiO2 at the nitride‐silicon interface. This interfacial layer originates from the native silicon oxide present at the silicon substrate when the deposition of nitride is started. For comparison, oxide‐free silicon substrates were nitrided in ammonia at temperatures between 800–1160 °C. The thermal nitride films were found to be very thin, at the most 30 A, even after 5 h of nitridation. Both the LPCVD and thermal nitride films oxidize slightly when transferred into the ambient; a surface layer equivalent to 8 A of SiO2 was detected. Auger and RBS results agree very well for all nitride films investigated. It is shown that RBS can be...

In situ investigation of TiN formation on top of TiSi2

TiN formation on TiSi2 has been studied using in situ Rutherford backscattering spectroscopy and Auger electron spectroscopy. Two systems were investigated: (i) the reaction of Ti with nitrogen and (ii) the nitridation of TiSi2. When a Ti film on Si is annealed in N2 or NH3, two reactions occur simultaneously: TiN forms at the surface and TiSi2 at the interface. Oxygen, dissolved in the original Ti film, is expelled from the growing silicide and is piled up at the TiN/TiSi2 interface. Around 600 °C, the complete conversion of the upper nitrogen‐containing layer into TiN is retarded by this oxygen and a TiNxO1−x layer remains detectable between the TiN and TiSi2 layers. At 750 °C, the TiN layer is formed very rapidly and further growth is blocked by the TiSi2 layer that has developed underneath. Nitridation of TiSi2 requires a temperature of at least 800 °C. Starting at the exposed surface, the silicide layer is gradually converted into TiN. Some of the Si released in this reaction segregates to the surfac...

Plasma oxidation of thin aluminum layers for magnetic spin-tunnel junctions

This article presents results of a study initiated to characterize the plasma-oxidation process of very thin Al films, a technology commonly used to produce good barrier layers for magnetic spin-tunnel junctions. The behavior of oxygen in the oxidizing Al layer is determined using both quantitative (Rutherford backscattering spectrometry, transmission electron microscopy) and qualitative (x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry) analytical techniques. We have applied in situ XPS and experimented with 18O2 to unravel details of the oxidation mechanism. In addition, the influence of the oxygen pressure on the oxidation rate was established, both with and without a plasma being present. From optical emission spectra it is concluded that this pressure has a minor effect on the relative abundance of excited species in the oxygen plasma. When combined, these data constitute the basis of a model that distinguishes several steps in the plasma oxidation of Al. At the start, oxygen p...

Nitrogen and oxygen incorporation during rapid thermal processing of Si in N2O

Using a special detector setup in elastic recoil detection measurements, the incorporation of nitrogen during rapid thermal processing of Si(100) in N2O has been quantified for the first time. During oxidation at 1150 °C, the equivalent of a monolayer of silicon nitride is formed at the SiO2/Si interface. This retards the oxidation rate but it does not inhibit further oxide growth, which implies that gate oxides with thicknesses up to several tens of nm can be produced in N2O.

Hydrogenation during thermal nitridation of silicon dioxide

The incorporation of nitrogen and hydrogen during nitridation of SiO2 was studied over the temperature range of 800–1000 °C and for ammonia pressures of 1, 5, and 10 atm. The nitrogen content of the nitrided films was determined with Rutherford‐backscattering spectrometry and elastic‐recoil detection. Nitrogen in‐depth profiles were obtained applying Auger analysis combined with ion sputtering. Hydrogen profiles in the films were measured using nuclear‐reaction analysis. Both the nitrogen and hydrogen incorporation were found to increase with temperature in this range. A higher ammonia pressure primarily increases nitridation of the bulk of the oxide films. Depending on the nitridation conditions, up to 10 at.% of hydrogen may be incorporated. As distinct from the nitrogen profiles, the hydrogen in‐depth profiles are essentially flat. The concentration of hydrogen in the films, however, was always found to be smaller than that of nitrogen: measured H/N ratios varied between 0.25 and 0.85, the smaller valu...