G. J. Leusink

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 ...

Selective chemical vapor deposition of tungsten using WF6 and GeH4

Germane (GeH4) has, for the first time, been used as a reducing agent for tungsten hexafluoride in selectively depositing tungsten on silicon. As shown by x‐ray diffraction, films deposited below 400 °C consist of the β‐W phase with A15 cubic crystal structure. This A15 structure proved to be stabilized by germanium which is probably incorporated in the film as a hitherto unknown W3Ge compound. Annealing for 1 h at 575 °C did not change the β‐W structure to the low‐resistivity body‐centered‐cubic α phase of tungsten. The superconducting transition temperature of the films is ≊3 K. The growth rate dependence on temperature, total pressure, and WF6, GeH4, and H2 partial pressure has been investigated. At deposition temperatures above 400 °C the deposited films consist of a mixture of the β and α‐W phase.

A thermodynamic and kinetic study of chemical vapor deposition of tungsten from WF6 and GeH4

In this paper a thermodynamic and kinetic study of the deposition of tungsten on silicon (100) from tungsten hexafluoride (WF6) and germane (GeH4) is presented. Thermodynamic calculations, as well as experiments with a closed reactor, indicate that the reaction occurring during deposition is WF6+3GeH4→W+3GeF2+6H2. The growth rate as a function of process parameters is obtained for depositions in the temperature range from 600 to 800 K and a total pressure range from 150 to 1000 mTorr. Experiments show that the germane reduction of tungsten hexafluoride is of 0.9 order in WF6, −0.2 order in GeH4, and zero order in H2. The activation energy is 34 kJ/mol. The deposition rate does not change when SiH4 is added to the GeH4/WF6 mixture, while, on the contrary, a small amount of GeH4 reduces the growth rate from a SiH4/WF6 mixture considerably. The kinetic data indicate that the formation of GeF2 might be the rate‐limiting step.

Control of the Microstructure of Al Metallization by Graphoepitaxy

Microstructure is an important factor determining the lifetime of Al metallization lines. Deposition conditions, substrate material, alloying elements, and anneal treatments are the key parameters that influence microstructure. In this work we explore the use of graphoepitaxy as a tool for additional control over the grain structure of metallization lines. Onto a submicrometer topography in SiO 2 (viz., a large number of parallel grooves), a pure Al film is grown by dc magnetron sputtering, followed by an in situ rapid thermal anneal. The topography of the annealed Al is investigated by cross section SEM. It is observed that if it is heated up to its melting point, Al fills the grooves and leaves the ridges between the grooves uncovered. X-Ray Diffraction, TEM, and Backscatter Kikuchi Diffraction are used to determine the global as well as the local crystallographic orientation of the grains in the quenched aluminum. The analyses are performed for various anneal and cool down treatments. Depending on the treatment, the Al lines in the grooves are either polycrystalline with an almost perfect (111) texture, or single crystalline but with a gradual change of 0.067°/μm in orientation. In the latter case, there is no preferred orientation. The single crystalline Al lines will be used as a starting point for the fabrication of model systems for fundamental electromigration studies.

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.