Relation between texture and stress in thin sputtered molybdenum layers
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Relation between texture and stress in thin sputtered molybdenum layers Ilse M. van den Berk1, Léon J. Seijbel2 and Rob Delhez1 1
Laboratory for Materials Science, Delft University of Technology, Rotterdamseweg 137, 2628 AL Delft, Netherlands 2 Netherlands Institute for Metals Research, Rotterdamseweg 137, 2628 AL Delft, Netherlands email: [email protected] ABSTRACT X-ray diffraction was used to measure the stress and the texture in thin molybdenum layers. The 500 nm thick layers were sputter deposited at various argon sputter pressures. All crystallites in the layers showed a strong tendency to develop a direction perpendicular to the surface of the sample. Depending on the sputter pressure, a different fraction of the Mo crystallites developed a preference for a direction parallel to the tangential direction of the rotating sputter table. The stresses found in the layer are best described when it is recognized that the crystallites in the layer belong to two groups: one group with both directions preferred and one group with only the out-of-plane direction preferred. For the intermediate sputter pressures the highest stresses were observed.
INTRODUCTION It is generally observed that refractory metal layers can contain high residual stresses that change from compressive to tensile on increasing the sputter gas pressure [1]. Other properties of the layer, such as density and conductivity, are also influenced by this sputter pressure [2]. Also the textures of these layers depend on the sputter conditions. Karpenko et al. [3] found that a strong out-of-plane texture (fiber texture) developed within 1000 Å, whereas a strong inplane texture (biaxial texture) did not develop until a thickness of about 1 µm. In this paper we examine the relation between the textures and the stresses in 500 nm thick molybdenum layers on silicon (001)wafers deposited at various argon sputter pressures.
EXPERIMENT Sample preparation Pure molybdenum layers were deposited by magnetron sputtering at room temperature on an oxidized silicon wafer (001) at four argon sputter pressures: 0.25 Pa, 0.5 Pa, 1.0 Pa and 2.0 Pa respectively. The thickness of the deposited layers is 500 nm, the deposition rate was 16.7 nm/min at a power of 510 W (DC). Substrates where placed under the cathode on a table rotating with 6 revolutions per minute. A -direction of the wafer was parallel to the tangential direction, which is ϕ = 90° in the sample coordinate system as given in Figure 1. Prior to deposition the target was cleaned by presputtering for 5 minutes under the same conditions as applied by the deposition to remove the oxide layer on the target and to prevent incorporation of O3.22.1
σ33 ψ σ22
ϕ σ11
Figure 1: Definition of angles in the stress and specimen systems, the direction of σ33 is perpendicular to the specimen surface, σ22 is parallel to the tangential direction of the sputter table.
impurities in the layer. The substrate was not heated and during the deposition the temperature did not exceed 330 K. X-ray diffraction The stresses a
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