A method for determining long nucleotide sequences of double-stranded DNA is being developed. It involves (a) the synchronous digestion of the DNA from the 3' ends with EL coli exonuclease III (Exo III) followed by (b) resynthesis with labeled nucleotides and DNA polymerase. A crucial factor in the success of this method is the degree to which the enzyme digestion proceeds synchronously under proper conditions of incubation (step a). Dark field EM is used to obtain accurate measurements on the lengths and distribution of the DNA molecules before and after digestion with Exo III, while gel electrophoresis is used in parallel to obtain a mean length for these molecules. It is the measurements on a large enough sample of individual molecules by EM that provides the information on how synchronously the digestion proceeds. For length measurements, the DNA molecules were picked up on 20-30 Å thick carbon-aluminum films, using the aqueous Kleinschmidt technique and stained with 7.5 x 10-5M uranyl acetate in 90% ethanol for 3 minutes.
ABSTRACTPure aluminum films are deposited under a variety of conditions to vary the crystallographic texture. After patterning and annealing at 400°C for 1 hour, electromigration tests are performed at several temperatures. Failure data are compared on the basis of t50 and standard deviation. Microstructure is quantified by transmission electron microscopy for grain size and grain size distribution and by X-ray diffraction for texture. A strong (111) texture significantly improves the electromigration lifetime and decreases the standard deviation in time to failure. This improvement correlates with both the fraction and sharpness of the (111) texture component.
ABSTRACTThe technique of picosecond electron diffraction is used to time resolve the
laser-induced melting of thin aluminum films. It is observed that under
rapid heating conditions, the long range order of the lattice subsists for
lattice temperatures well above the equilibrium point, indicative of
superheating. This superheating can be verified by directly measuring the
lattice temperature. The collapse time of the long range order is measured
and found to vary from 20 ps to several nanoseconds according to the degree
of superheating. Two interpretations of the delayed melting are offered,
based on the conventional nucleation and point defect theories. While the
nucleation theory provides an initial nucleus size and concentration for
melting to occur, the point defect theory offers a possible explanation for
how the nuclei are originally formed.
The aluminum film with high reflectivity and low absorption in the visible wavelength region has been widely used in optical applications. In this investigation, aluminum films were prepared on glass substrates by electron-beam vapor deposition. The reflectivity of the Al thin film was measured by a Perkin-Elmer Lambda spectrophotometer in the wavelength region of 450-680 nm. The experimental measurements of reflectivity were validated with the numerical results using the Essential Macleod software. The surface topology and microstructure of the film were examined by means of atomic force microscope (AFM). The effects of the temperature and humidity on the reflectivity of the Al film were examined by the environmental test. Nanoindentation tests were employed to determine the hardness and Young’s modulus of the film. The measured hardness of the Al thin films were found to depend on the penetration depth.
IntroductionElectromigration in aluminum films has been identified as an increasing concern for integrated circuit reliability. Electromigration is the mass transport of atoms in a conductor under a current stress. Electromigration occurs in conductors experiencing current densities greater than 105 A/cm2 and is accelerated by high temperature. The damage to aluminum films manifests itself in the formation of voids, hillocks and whiskers along the conductor. This paper presents a test vehicle preparation procedure which can be used to investigate electromigration.
AbstractAlumina formed by the electrochemical anodization of bulk aluminum has a regular porous structure [1]. Sub-100 nm pores with aspect ratios as high as 1000:1 can easily be formed [2] without elaborate processing. Anodization of aluminum thus provides the basis for the inexpensive, high throughput microfabrication of structures with near vertical sidewalls [2]. In this work we explore the patterned anodic oxidation of deposited aluminum thin films, facilitating the integration of this technique with established microfabrication tools. An anodization barrier of polymethylmethacrylate (PMMA) is deposited onto 300 nm thick aluminum films. The barrier film is subsequently patterned and the exposed aluminum anodized in a 10% sulfuric acid solution. Barrier patterning techniques utilized in this study include optical exposure, ion-beam milling and nano-imprint lithography. Sharp edge definition on micron scale patterns has been achieved using optical methods. Extension of this technique to smaller dimensions by ion-beam milling and nano-imprint lithography is presented. We further report on the observation of contrast reversal of anodization with very thin PMMA barriers, which provides a novel means of pattern transfer. Potential applications and challenges will be discussed.
Measurement of elastic precursor decay in pre-heated aluminum films under ultra-fast laser generated shocks