Strain Measurements from Single Grains in Passivated Aluminum Conductor Lines by X-Ray Microdiffraction During Electromi
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Strain Measurements From Single Grains In Passivated Aluminum Conductor Lines By X-Ray Microdiffraction During Electromigration K. J. Hwang, G. S. Cargill III, and T. Marieb† Materials Research Center, Lehigh University, Bethlehem, PA 18015, [email protected] † Components Research, Intel Corp., Hillsboro, OR 97124 ABSTRACT We describe a method for determining the local strain state of passivated aluminum metal lines from single grains within 2.6 µm x 7.0 µm x 0.75 µm sized regions along the line. X-ray microbeam diffraction is used to obtain localized measurements of thermal and electromigrationinduced strain during 37 hours of electromigration in a passivated 2.6 µm-wide, 300 µm-long pure Al conductor line at a current density of 4.2×105 A/cm2 and temperature of 270°C. Diffraction from single grains is used to measure both the in-plane and normal components of strain and their evolution during electromigration at several positions along the line. INTRODUCTION Mechanical strain in thin film interconnect structures has long been a reliability concern in VLSI devices. Thermally induced hydrostatic strain in narrow lines can result in cavitation and ultimately line failure [1,2]. In passivated narrow lines, hydrostatic strains in excess of 2×10-3 have been observed by bending beam [3] and predicted in finite-element calculations [4-5]. Most previous investigations have used conventional x-ray methods with millimeter-size x-ray beams to measure the macroscopic strain in arrays of aluminum lines encapsulated by passivation [6-10]. At present, obtaining information about local strain in interconnects is difficult, and few techniques are available. Wang et al. [11-13] and Chung et al. [14] have demonstrated the feasibility of x-ray microbeam diffraction for measuring local strain in Al lines. In the present studies, x-ray microbeams have been used to measure microscopic strain distributions from single grains at multiple regions along a 2.6 µm-wide, 300 µm-long, and 0.75 µm-thick passivated pure Al conductor line and for a 120 µm x 120 µm pure Al contact pad. The sampling volume for regions along the line was 2.6 µm x 7.0 µm x 0.75 µm. Initial results from these measurements are described in this paper. EXPERIMENT AND PROCEDURES X-ray microbeam diffraction measurements were made using NSLS beamline X6A, a bending magnet white (7keV - 30keV) x-ray synchrotron beamline. The instrumentation used for these measurements is shown in Fig. 1. The novel feature of the instrument is that rotation of the sample is not required in measuring different strain components, since the irradiated sample volume remains fixed while measuring various diffracting planes. The spatial resolution of the measurements in this configuration is limited solely by the x-ray beam size or by the sample dimensions, whichever are smaller. The instrument consists of the following parts: a customized Huber diffractometer, a pinhole collimator providing a 7 µm x 10 µm x-ray beam, a high precision x-y-z sample positioning mechanism, a sample heating stage, a liquid
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