Johan P. W. B. Duchateau

Improved High-Density Phase-Change Recording

By using a simple write strategy we have found that a wide range of linear velocities can be covered for direct overwrite in high-density phase-change recording. This is especially advantageous for data recording where the application of constant angular velocity facilitates fast seek and short random-access times. In the case of repeated overwriting, material flow will limit the number of cycles, particularly if a fixed pseudo-random data pattern is used. We studied how a random bit shift can reduce this problem and found that a relatively large shift of up to 100 bytes was required. Using these techniques in an optimized disc structure we achieved more than 100,000 overwrite cycles on a 2.6 Gbyte 12 cm phase-change disc.

Surface and interface effects in WSi2 formation

We studied the influence of a thin Fe interface layer between W and the substrate Si and of a surface W–oxide on the formation kinetics of WSi2. Auger depth profiling, Rutherford backscattering spectrometry and x‐ray diffraction have been used to investigate the reaction between the layers and the Si substrate. W layers with a thickness of 20 nm were deposited by electron beam evaporation on HF dipped Si(100) samples. If deposition and subsequent annealing are performed in ultrahigh vacuum, the complete conversion of a W layer into tetragonal WSi2 occurs within 1 h at 800 °C. The intercalation of a 5 nm‐thick Fe layer between the W layer and the substrate reduces the conversion temperature to 650 °C. Ironsilicide is formed at a relatively low temperature. This silicide acts as a medium through which Si can easily diffuse towards the surface, thus maintaining a fast Si supply to the W layer. This experiment indicates that reactions at the metal/Si interface are rate determining in the formation of WSi2. Bo...

A study of Pd–Ta on Si(100) using Auger electron spectroscopy, Rutherford backscattering spectrometry, and variable energy positron annihilation

The applicability of PdxTa1−x as a diffusion barrier on Si has been investigated. For this purpose PdxTa1−x films of 200‐nm thickness (x ranges from 0 to 1) were deposited on Si(100), and the reaction between overlayer and substrate was studied as a function of temperature. Interaction was found to occur at temperatures increasing with the Ta content. The as‐deposited PdxTa1−x films with 0.2≤x≤0.6 were found to be amorphous. The amorphous phase had a higher reaction temperature than the crystalline one, causing a discontinuous step in the reaction temperature. Rutherford backscattering spectrometry spectra revealed that for the Pd‐rich compositions, first a stoichiometric Pd2Si layer formed underneath a pure Ta layer. At higher temperatures TaSi2 formed at the surface. For Ta‐rich compositions Pd2Si formed first as well; however, the reaction temperature was so high that Pd2Si grains formed in a Si matrix. The defect density of the Ta layer, which remained after outdiffusion of Pd, was investigated using ...

High density phase-change recording beyond 2.6 GByte

We review the current status of high density phase-change optical recording at red wavelengths. A user bit capacity of 3.0 GByte has been realized on a 120 mm rewritable disk by using in-groove recording and a simple and reliable wobbled groove format. The headerless format shows excellent data and address integrity during cyclability tests and it has a high degree of compatibility with read-only DVD. In order to extend disk capacity even further, both radial and tangential densities must be increased. In increasing the radial density, land/groove recording appears more promising than in-groove recording because optical cross-talk between neighboring tracks can be largely cancelled. A reduction of the track pitch in land/groove recording below 0.74 micrometers results in thermal cross-talk, leading to partial erasure of data in the adjacent tracks. The minimum bit length which gives acceptable recording tolerances in both land and groove tracks is 0.32 micrometers . With the combination of a track pitch of 0.74 micrometers and a bit length of 0.32 micrometers , an areal density of 2.7 Gbit/in2 and a user capacity of 3.5 GByte should be possible in land/groove recording.

The reaction of amorphous Co–Zr layers with Si(100) and SiO2 substrates by annealing in vacuum and NH3

The reaction of amorphous Co–Zr films with Si(100) and SiO2 substrates has been investigated using in situ Rutherford backscattering spectrometry, Auger electron spectroscopy and x‐ray diffraction. For this purpose, CoxZr1−x (x=0.5 or 0.6) films were deposited on a substrate and annealed in vacuum or NH3. During annealing of an amorphous Co–Zr film on Si in vacuum at a temperature lower than 600 °C, Co reacts with Si, forming CoSi2 next to the substrate. Above 600 °C, the layer reacts completely with Si and the following structure develops: (ZrSi2+CoSi2)/CoSi2/Si. Annealing the same structure in NH3 above 600 °C causes two reactions to occur simultaneously: (i) CoSi2 formation at the film/substrate interface, and (ii) nitridation of the film surface, forming ZrN, which stops the diffusion of Si to the surface. It was found that a fraction of the CoSi2 grains was aligned with the Si(100) substrate, irrespective of the annealing ambient. This fraction increases with increasing annealing temperature. When an...

The reaction of extremely thin Co-Zr and Pd-Ta layers with Si(100)

Co-Zr films with thicknesses in the range 2.5-40 nm and with different compositions were electron-gun deposited on Si(100) substrates. In situ annealing, Auger analysis, and Rutherford backscattering spectrometry were performed to monitor the arrival of Si at the surface of the film. The temperature at which Si was observed at the film surface was found to vary quite considerably with the composition. A few experiments were performed on the Pd-Ta system as well. Both for the Co-Zr and Pd-Ta system the annealing temperature at which Si was detected at the surface was much higher for the amorphous than for the crystalline alloys