Textures of Cu and Dilute Binary Cu(Ti) and Cu(In) Thin Films

Abstract

The development of texture in thin Cu and dilute binary Cu(Ti) and Cu(In) films has been investigated as a function of annealing history. The textures are comprised of , and fiber in different proportions for the three films. Annealing strengthens the texture for all films. For the annealed films, alloying with Ti strengthens the component, whereas alloying with In weakens it compared to pure copper. Two different approaches were used to derive volume fractions of texture components, namely fiber plots and orientation distributions. For strong mono-textured films of materials such as aluminum, fiber plots are most effective. For weaker, poly-textured films such as the copper alloys studied here, orientation distributions derived from pole figures provide the most reliable basis for quantitative characterization. Introduction As dimensions of very narrow copper interconnections reach the 100 nm range, the control of microstructural features such as texture and grain size becomes increasingly important. In a recent study we addressed the impact of alloying elements on the decomposition and resistivity of a series of dilute binary Cu alloy films annealed at a constant heating rate up to 950 C [1]. In this work, we focus on the impact of isothermal annealing at 400 C on the texture of pure Cu and dilute binary Cu(Ti) and Cu(In) films. In addition to the detailed behavior of the films, we briefly discuss the advantages and disadvantages of various x-ray based methods for the analysis of the texture of Cubased films. Experiment Pure Cu and dilute binary Cu(Ti) and Cu(In) alloy films were electron beam evaporated onto thermally oxidized silicon wafers. The composition and thickness of the films are listed in Table 1. X-ray diffraction (XRD) experiments were conducted using Cu Kα radiation in a Rigaku powder diffractometer with a curved graphite monochromator. These patterns were used to give a qualitative indication of the texture in the films. For the quantitative analysis of film texture, fiber plots and pole figures were used. Pole figures and fiber plots were obtained in a Philips X’Pert Pro diffractometer, utilizing an X-ray lens and 0.27 Soller slits in the path of the incident beam and a flat graphite monochromator in the path of the diffracted beam. The fiber plots were measured in 0.1 intervals per second as is commonly done in texture studies of Al films [2], while the pole figures were determined at 5 intervals every two seconds. Three pole figures {111}, {200} and {220} were obtained for each sample. In order to ensure that the use of 5 intervals for the collection of pole figures did not affect the resolution of intensity data used for the calculation of the orientation distribution functions (ODFs), sections through the pole figures were compared with 2 Title of Publication (to be inserted by the publisher) the fiber plots. Three such sections for the annealed Cu film have been overlaid on their respective fiber plots in Fig. 1 and show no discernible difference. Table 1 Composition and thickness of the films. Sample Solute [at%] Thickness [nm] Cu(Ti) 3.0 488 Cu(In) 2.6 520 Cu 420 0 20 40 60 80 0 500