T. G. M. Oosterlaken

In situ sensitive measurement of stress in thin films

A method for the in situ measurement of mechanical stress in thin films deposited in a vacuum system is presented. The bending of the substrate, a measure for mechanical stress in the deposited layer, is detected by reflecting two parallel laser beams off the surface of the substrate and measuring the angle between the two reflected beams. A hollow mirror in the path of the reflected beams acts as an ‘‘optical cantilever’’ and increases the sensitivity of this method. In the present setup it is possible to detect the difference between a flat substrate and a substrate with a radius of curvature of 6.5 km.

Growth kinetics and inhibition of growth of chemical vapor deposited thin tungsten films on silicon from tungsten hexafluoride

The growth kinetics and inhibition of growth of chemical vapor deposited thin W films on Si(100) from WF6 was studied with in situ growth stress and reflectivity measurements and ex situ weight gain measurements. A systematic series of experiments at varying WF6 flow, total pressure, and temperature show that the thickening kinetics and inhibition of the growth are controlled by two processes: WF6 diffusion through the gas phase and Si diffusion through the thickening columnar film. The steady state growth kinetics are controlled by WF6 diffusion in the gas phase whereas inhibition of the growth occurs at the transition from WF6 gas diffusion limited to Si solid state diffusion limited growth. A simple model based on WF6 gas phase diffusion and Si solid state diffusion is presented which gives a quantitative description of the experimental results.

The evolution of growth stresses in chemical vapor deposited tungsten films studied by in situ wafer curvature measurements

An in situ study of the evolution of the biaxial state of intrinsic stress during nucleation and growth of polycrystalline tungsten chemical vapor deposition films deposited by the hydrogen reduction of tungsten hexafluoride is presented. The evolution of biaxial stress was determined from in situ wafer curvature measurements. It is shown that the intrinsic stress is a growth stress, i.e., a stress developing in close vicinity to the advancing surface of the film due to metastable film growth processes. The stress developing depends strongly on the thickness of the film. High tensile stress (≊4 GPa) is observed during the initial stage of growth, compressive stress (up to −1 GPa) is observed in an intermediate thickness regime after film closure and tensile stress (0.1–1 GPa) is observed in the thick film regime. The associated stress gradients in the film are preserved during and after growth. The development of growth stress is determined by deposition temperature and growth rate. The tensile stress in ...

Deformation of Si(100) wafers during rapid thermal annealing

In this paper in situ wafer curvature measurements are presented that were performed during rapid thermal annealing of silicon wafers. The wafer curvature due to thermal stress originating from a nonuniform temperature distribution was measured as a function of time for a fixed setting of the illumination source power. The presence of thermal stress was clearly demonstrated. It was found that wafers deform during the complete annealing cycle and moreover that, the deformation is largest during the heating and cooling transients. The influence of various wafer supports on the deformation was investigated. The use of a susceptor and a guard ring reduce the wafer deformation compared to a free‐standing wafer by a factor of 6 and 10, respectively.

Stress in Al, AlSiCu, and AlVPd films on oxidized Si substrates

Abstract Electromigration and stress migration in Al metallization are major reliability issues for advanced ICs. Recently it has been shown that, compared to AlSiCu alloy films, alloys containing Si, V and Pd combine excellent plasma etchability with good corrosion resistance, while a high resistance against electromigration is maintained [1]. It is commonly accepted that the resistance against stress migration, i.e. the creep strength, of Al can be improved by addition of alloying elements in combination with appropriate heat treatments (e.g. precipitation hardening). We present data on the influence of alloying elements on the behaviour of stress as a function of temperature for a number of Al-alloy films. Pure mono- and polycrystalline Al, AlSi(1.0 at%)Cu(1.0 at%) and AlV(0.1 at%)Pd(0.1 at%) films were studied. The sputter conditions, the film thickness and the annealing conditions were similar to reliability tests described in the literature. These films are subjected to thermal cycles from 50 to 425°C in a vacuum furnace, while the stress behaviour was measured by means of wafer curvature measurements.

Chemical vapour deposition tungsten film growth studied by in situ growth stress measurements

Abstract In this paper we present in situ measurements of the wafer curvature during nucleation and growth of W films deposited by chemical vapour deposition (CVD) on Si substrates. Because of the absence of stress relaxation mechanisms in the films, these measurements directly reflect the growth stress in the W films. The growth stress development is measured during self-limiting W film growth by the Si(100) reduction of WF6 and during continuous W film growth by the H2, SiH4, and GeH4 reduction of WF6. It is shown that these measurements provide detailed information on the growth kinetics (for the Si reduction of WF6) as well as the (high) growth stresses themselves. High stress gradients are observed in the growth direction of the films. In general the growth stresses range from highly tensile during the initial stages of growth, to compressive in an intermediate region and tensile again in the thick film regime. The average film stress decreases with increasing deposition temperature. The process-dependent growth stresses reported in this paper can be used to engineer the magnitude of the average film stress in W CVD metallization of integrated circuits.

The growth of ultra-thin amorphous WGex films on Si by the GeH4 reduction of WF6

Ultra-thin amorphous WGex layers were deposited by the GeH4 reduction of WF6. In-situ reflection measurements, resistance and RBS measurements consistently showed that a closed film is formed at a thickness of about 3 nm and that subsequent growth occurs layer-by-layer with a constant growth rate. From the measured time-dependent layer thickness, reflectivity and resistivity during the growth of the 3 nm thin film it is speculated the growth starts by nucleation and growth of WGex islands. In contrast to films deposited by the H2 reduction of WF6 the Si substrate is not consumed during the GeH4 reduction of WF6. Preliminary results indicate this is caused by a Ge layer which is formed during the initial stage of the growth. In comparison with other W-LPCVD processes the GeH4 reduction of WF6 is extremely reproducible.

Influence of temperature gradients on partial pressures in a low‐pressure chemical‐vapor‐deposition reactor

Measurements and calculations of the influence of temperature gradients on the partial pressures of the gas species in a cold‐wall chemical‐vapor‐deposition reactor are presented. The experiments were performed at low pressures (300–500 Pa total pressure) and gas mixtures consisting of hydrogen, nitrogen, and tetrafluoromethane. The partial pressures were determined by Raman spectroscopy. The Soret effect (or thermal diffusion) has a large influence on the partial pressures of heavy gases in the vicinity of the heated wafer. In some cases a decrease in partial pressure of 20% compared to the inlet partial pressures was observed. Numerical calculations were performed to predict the behavior of the gas mixture. For mixtures under investigation the gas temperatures as well as the changes in partial pressures due to the Soret effect were predicted correctly.

Characterization of Tungsten Deposited by GeH4 Reduction of WF 6, and Its Application as Contact Material to Si

W deposition by GeH 4 reduction of WF 6 is a promising alternative for W deposition from H 2 /WF 6 and SiH 4 /WF 6 The structure and composition of W layers deposited from WF 6 and GeH 4 , are determined mainly by the deposition temperature. At temperatures between 300 and 400 o C, W layers with the A15 bcc β-W crystal structure are formed. These β-W layers contain a substantial amount of homogeneously distributed Ge, roughly between 10 and 15 atomic percent (a/o). At higher temperatures , films are formed which consist of a mixture of β-W and α-W. At temperatures greater than 500°C, the layer consists exclusively of α-W, and the Ge concentration is less than 1 a/o.

Step coverage of tungsten films deposited by germane reduction of WF6

Abstract The step coverage of tungsten films deposited by the germane reduction of WF 6 is investigated. The step coverage modulus for the germane process is influenced only by the deposition temperature. It hardly depends on the partial pressures of the reactive species. These results are confirmed by experiments on structures with a large internal surfaces as compared to the access area. The stepcoverage of the films deposited by this process is excellent and sufficient to fill small (0.5 μm) contact holes with a high aspect ratio.