Microtexture Measurements of Aluminum VLSI Metallization
- PDF / 345,524 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 32 Downloads / 224 Views
Introduction Electromigration and stress induced voiding continue to be serious reliability issues in integrated circuit design and manufacture. Several groups have inferred that microstructure may play an important role in determining why failure occurs at one aluminum grain and not at another[I-3]. Evidence given for this is based on x-ray texture measurements, which show that the reliability of aluminum metallization increases as the texture increases. However, x-ray measurements give an average over many grains. Direct measurements of microtexture are required to determine if specific grain orientations are responsible for reliability degradation. There are at present two methods for measuring the orientations of individual grains in small grain polycrystalline materials. The first method, transmission electron microscopy (TEM), has been used for many years. It presents several difficulties. First, since the test sample has to be electron transparent, considerable preparation has to take place before a sample can be viewed, or special membrane structures must be prepared initially. Second, accurate determination of crystallite orientation is time consuming and may be ambiguous, given the small solid angle subtended by the detector. Another method for measuring crystal orientations is electron backscatter diffraction (EBSD) in an SEM[4]. The detection arrangement is shown in figure 1. Details of this detector design can be found in reference 5. In this technique, an electron probe is
347 Mat. Res. Soc. Syrup. Proc. Vol. 391 ©@1995 Materials Research Society
CHANNEL PLATE MULTIPLIER
Figure 1. EBSD detector arrangement generated in an SEM and held fixed on a single Al grain. A small fraction of these electrons scatter at large angles and are diffracted on their outward trajectories by the crystal planes. An imaging detector, in this case a channel plate, is used to view the diffracted electrons. The patterns generated are recorded with a video camera. An EBSD pattern resembles a TEM Kikuchi pattern in that lines are formed by the diffraction of the electrons by the crystal planes, and the principal directions are formed by the intersections of these diffraction lines. EBSD Kikuchi patterns are "locked" to the crystal orientation, as are TEM patterns. EBSD patterns typically subtend 45-60 degrees of arc, making pole identification simple compared to transmission electron microscopy, where patterns only subtend a few degrees. The appropriate orientation of a single grain can be determined by direct inspection of this backscatter pattern. EBSD requires little or no sample preparation, but it cannot be used for films that are covered with a passivating oxide. Such a film must be stripped before EBSD is performed. A crystallite orientation is precisely determined by first computer enhancing the EBSD image. The image is inspected, two crystallographic poles are identified, and the positions of these two poles in the image are input to a computer with cross hairs and a mouse. The absolute orientation matrix is then ca
Data Loading...
