M. Rennau

Thermal conductivity of ultra low- k dielectrics

The so-called 3ω measurement technique (transient hot wire method) was established to determine the thermal conductivity of thin films. Measurements of standard substrates and films validate the found thermal conductivity values and agree with published, commonly accepted values. The method was successfully applied to determine the thermal conductivity of porous low-k dielectric materials using special test structure fabrication. The thermal conductivity of the porous low-k dielectrics thus measured is only between 7 and 13% of the thermal conductivity of thermally grown silicon dioxide.

TiN diffusion barriers for copper metalization

Summary form only given. The requirements of future integrated circuits will result in shrinking dimensions and consequently new materials like copper or low k materials. TiN films are an interesting candidate as diffusion barriers because of their well known compatibility to semiconductor technology. Moreover TiN films were already shown to be stable barriers against copper diffusion. Based on a series of tests including the stochiometry variation of films deposited by reactive magnetron sputtering on Si and SiO/sub 2/ and annealing in different atmospheres the interaction between film properties and barrier stability is studied. The applicability of optical, mechanical and analytical thickness measurement methods for thin TiN films is investigated. Advantages and drawbacks of the used measurement techniques given by method related boundary conditions are discussed.

Investigation of copper metallization induced failure of diode structures with and without a barrier layer

Different metallization systems Cu/Si, Cu/Ti/Si, Cu/W/Si and Cu/TiN (N/Ti ratio < and 1 )/Si were prepared on n + p-diodes. After sequential annealing in H 2 -atmosphere these structures were investigated by electrical and analytical methods. For a metallization without barrier layer the electrical breakdown is caused by the formation of Cu 3 Si. Randomly distributed reaction spots are visible on the silicon surface. For Ti and W the electrical failure occurs after annealing at 450°C in H 2 -atmosphere. The breakdown of diodes with TiN is first found for barrier layers with a N/Ti-ratio < 1 after annealing at 650°C. Stoichiometric TiN-barriers are stable after annealing at 650°C. The electrical breakdown can be assigned to failure mechanisms determined by the barrier film properties.

Electrical and adhesion properties of plasma-polymerised ultra-low k dielectric films with high thermal stability

New intermetal dielectrics with dielectric constants (k) less than the dielectric constant of the conventionally used SiO2 (k=3.9) are required for the fabrication of low voltage integrated circuits due to their ability to decrease signal delay time, crosstalk and power dissipation. In this paper results of depositing and investigating CF polymers will be presented. The films were deposited in a single wafer PECVD (plasma enhanced chemical vapor deposition) equipment (Secon 251) using a mixture of C, F and H containing gases. The polymer films are stable for temperatures as high as 425°C (shrinkage <1%) maintaining a dielectric constant k even lower than 2.0 (depending on the deposition parameters and annealing processes). Furthermore, the adhesion of the CF films on top of several inorganic materials could be proved by tape test and following CMP processing. ICP patterned vias (polymer thickness: 1 μm; aspect ratio: 5) showed strong vertical profile.

Influence of different treatment techniques on the barrier properties of MOCVD TiN against copper diffusion

Abstract The barrier property of MOCVD produced TiN is assessed by use of analytical and electrical methods. A pn-diode was used as the electrical test device. TiN was varied by the application of different TiN treatments. Untreated TiN failed at 350°C annealing temperature. Plasma treatment raised the failure temperature to 500°C. It is shown that etch pit tests and Rs measurement do not indicate barrier failure at an early stage.

Evidence of a high density of fixed negative charges in an insulation layer compound on silicon

Abstract For drift field generation, IS structures with a positive interface charge in an insulator compound were developed in the 1980s and employed mainly on field effect solar cells. While there has been a large number of publications about the positively biased insulator–semiconductor structure there has been very little interest in its antipolar counterpart — the negatively biased insulator–semiconductor structure — so far. However, by using that structure as a second drift field source for field effect solar cells their conversion efficiency could be improved. The conventional rear surface passivation of silicon active layers by shallow ultrahigh aluminium doping in order to form a back surface field involves a high density of lattice and surface defects which increase recombination rates. The structure introduced herein is put onto a silicon layer and acts thus as an external negative drift field source, thereby avoiding the drawbacks of ultrahigh doping. The layer arrangement aluminiumfluoride–silicon dioxide on silicon seems to be a good candidate for a negative drift field source. Experimental results which led to a fixed interface charge of up to −1.6×10 12 cm −2 at the interface aluminiumfluoride∣∣silicon dioxide are presented and an interpretation of the fixed negative charge is given.

W/TiN double layers as barrier system for use in Cu metallization

Abstract The properties of Cu/W/TiN film stacks were studied. Adding at thin W layer to a known stable TiN diffusion barrier significantly affects the whole metallization system. The introduction of a thin W interlayer causes a significant change of the Cu texture, while the film stress remains stable. The adhesion of Cu on W is excellent, if deposited without vacuum break. The poor adhesion of Cu on air exposed W/TiN is improved by a subsequent annealing step in H2. The performed analytical and electrical barrier tests demonstrate the tandem barrier to be stable up to 650°C.

Comparison of different emitter diffusion methods for MINP solar cells: Thermal diffusion and RTP

A solar cell technology with an extremely small thermal budget was developed for MINP cells. MINP solar cells with efficiencies of up to 15.3% have been achieved by rapid thermal processing (RTP). An emitter diffusion process was simulated and developed that yields a doping profile with a tunnelling oxide in a single furnace step. The P concentration profile was investigated by SIMS measurements and compared to the calculated profile. The SIMS results of the 850°C processing temperature differ from the calculated profile, but the 800°C values showed an excellent conformity. The surface passivation can be improved by an increase of the deposition temperature of the antireflection film. The maximum temperature was appointed with 400°C for MINP and 300°C for pn cells. In comparison with pn cells the temperature stability of MINP cells is significantly higher.

Localization length of integrated multi-walled carbon nanotubes

We prepared CNT based vias on wafer scale. Based on the electrical characterization we extracted the localization length of the CNTs. While for short CNTs the classical transport regime is valid, the Anderson localization regime applies for longer CNTs. Supplementary the characteristic length scales were estimated based on the structure of the CNTs being in good agreement with the parameters extracted from the electrical measurements.