Microscratch and load relaxation tests for ultra-thin films
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The microindenter has proven to be a powerful device in the characterization of the mechanical properties of thin films. The machine has both high resolution in the applied load and penetration depth measurements, as well as the versatility to perform different types of testing. The former provides the capability to deal with extremely thin films, while the latter allows for other mechanical properties, in addition to hardness, to be acquired. Four types of tests, namely indentation, scratch, load relaxation, and indentation fatigue tests can currently be conducted using the microindenter via different operating procedures. Only the scratch and load relaxation techniques will be covered in this paper. In a microscratch test, the normal load, tangential load, scratch length, and acoustic emission are monitored simultaneously during an entire scratch process for the purposes of measuring the critical load and studying the failure mechanisms of the deposited films. The adhesion strength, scratch hardness, fracture toughness, and friction are the mechanical properties which are possible to obtain by using this technique. Results from aluminum, carbon, and zirconia coatings will be discussed. The load relaxation test provides information on the creep properties of the films and results in an empirical constitutive relation between the applied stress and plastic strain rate. The creep properties of DC sputtered Al films will be used as an illustration of this.
I. INTRODUCTION
Today's technology has demanded a device not only with a very high functional capability but also with a miniaturized size. However, the development of the understanding of the mechanical properties of materials at extremely small dimensions and/or in multilayered structures lags far behind the fabrication process advances. The insufficient understanding of the mechanical issues results in so-called micromechanical type failures. One example of this has occurred in VLSI technology where cracking, notching, or voiding has been observed on Al-Si metallization stripes after a certain service period, and these failures have resulted in open or closed circuits.1'2 Another example is from magnetic recording technology. To fulfill a high bit density requirement, the flying height of the magnetic head has to be reduced. This reduction in spacing between the head and disk can potentially result in intermittent contacts.3'4 The interactions during a contact, such as impact, scratch, wear, or in combinations, impose strong requirements on the disk mechanical durability to ensure the reliability of the disk file. Several testing schemes have been developed in laboratories to measure various mechanical properties of thin film type samples, such as the miniaturized tensile test,5'6 bulge test,5'7 microbeam deflection,8 vibrating resonance method,9 and microindentation test.10"13 Among these techniques, the microindentation or the depth sensing mechanical probing technique still reJ. Mater. Res., Vol. 6, No. 2, Feb 1991 http://journals.cambridge.org
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