H Norström

A comparative study of the diffusion barrier properties of TiN and ZrN

Abstract The usefulness of Ti/TiN and Zr/ZrN bilayers as low resistivity contacts and diffusion barriers between doped silicon and aluminium was examined. The metal nitride layers were formed by reactive sputtering from elemental targets in Ar-N2 mixtures. Analytical results obtained using Rutherford backscattering spectroscopy (RBS) showed that the as-deposited layers were stoichiometric. X-ray diffactometry revealed that the as-deposited films were polycrystalline. The respective RBS spectra showed that no detectable intermixing occured between aluminium and silicon after heat treatment up to 550°C for 30 min for either combinations. Furthermore, RBS analysis indicated that arsenic implanted in the silicon was snow ploughed during the formation of zirconium silicide, which is essential for the formation of low resistivity ohmic contacts. In contrast, arsenic was observed to diffuse through the titanium silicide layer during its formation. Finally, the possibility of in situ deposition of a multilayered structure of Zr/ZrN/Al and the formation of zirconium silicide during the post-metal anneal without aluminium-silicon intermixing was examined.

Implanted collector profile optimization in a SiGe HBT process

Abstract Optimization of implanted collector doping profiles for a high-speed, low-voltage SiGe HBT process has been investigated experimentally and by device simulations. A low-energy antimony implantation has been combined with a standard selectively implanted collector using phosphorous, to achieve improved control of the collector doping profile. The simulations indicate that the narrow n-type doping peak formed by the antimony implantation allows the cut-off frequency f T to be increased without degrading the collector emitter breakdown voltage BV CEO . The fabricated devices demonstrate a highest f T of 60 GHz. Depending on the collector profile BV CEO values between 1.5 and 2 V were obtained.

Thermal degradation of TiSi2/poly-Si gate electrodes

Abstract The influence of high temperature processing steps on the integrity of a polycide metal-oxide-semiconductor system has been investigated. At temperatures exceeding 900°C the TiSi 2 /poly-Si (where poly-Si is polycrystalline silicon) system is not stable, and the dielectric strength of an underlaying gate oxide deteriorates. Degradation of the silicide-poly-Si interface was detected by backscattering spectrometry. Scanning and transmission electron microscopy revealed silicon precipitation and silicide film deformation.

Dry etching of n‐ and p‐type polysilicon: Parameters affecting the etch rate

The etch rate of doped polycrystalline silicon films (polysilicon) was studied as a function of dopant concentration, degree of dopant activation, and dopant type, in a parallel‐plate reactor, using a CFCl3 plasma. The significant difference in etch rate between n‐doped and p‐ or undoped polysilicon observed indicates that the electrical activity of the bulk (and surface) plays an important role when etching at a plasma frequency of 13.56 MHz. However, at lower frequencies this difference in etch rate for n‐ and p‐doped polysilicon is less pronounced.

R.f. sputtering characteristics and power supply coupling conditions

Abstract R.f. power systems are being increasingly used in thin film technology for sputtering as well as for plasma chemistry. In order to design impedance-matching networks for capacitively coupled r.f.-excited plasmas (as used for sputtering and in some types of chemical reactors) it is necessary to know the values of the plasma parameters, i.e. the capacitance and the conductance of the discharge, and the variations in these with the operating conditions of the system, i.e. the pressure, the frequency and the input power. In this paper the effects on the glow discharge characteristics of different gases are shown. The values of the glow discharge parameters obtained in the presence, and in the absence, of a magnetic field are compared. The results can be used to design suitable matching networks.

Si/Ti/TiB2/Al structures investigated as contacts in microelectronic devices

Abstract The metallization system Ti/TiB2/Al to silicon has been investigated. TiB2 was reactively sputter deposited in an Ar/B2H6 mixture. With this technique it is possible to study the stability of both Ti/TiB2 and TiB2 contacts to both n- and p-type silicon. In general Ti/TiB2 contacts showed significantly smaller contact resistances than TiB2 contacts. Upon annealing we found that current crowding at the periphery became predominant. This current crowding effect was more pronounced on n-type silicon. Diode structures of Ti/TiB2/Al annealed up to 500°C exhibited no junction leakage. The TiB2/Al contact remained intact up to 525°C. Barrier height measurements on Schottky contacts annealed at different temperatures was also performed. The barrier height value of 0.6 eV, close to that reported for TiSi2, was recorded after annealing at 525°C. The usefulness of these contact structures in microelectronic metallization was discussed. The difference between the two metallization systems was also investigated by Rutherford Backscattering Spectroscopy and X-Ray Diffraction measurements.