Nanoindentation Instrumentation

Abstract

Interest in nanoindentation has spawned a number of nanoindentation instruments that compete on a world market. Purchasers of such instruments are usually universities , private and government research organisations, and quality control laboratories. There is particular interest within the semiconductor industry that is concerned with the mechanical properties of a wide range of thin films. The instruments typically measure depth of penetration using either an induc-tance or capacitance displacement sensor. A typical nanoindentation test instrument, or "nanoindenter", has a depth resolution of less than a tenth of a nanometre and a force resolution of several nanonewtons. Load can be applied by the expansion of the piezoelectric element, the movement of a coil in a magnetic field, or electrostati-cally. Maximum loads are usually limited to the millinewton range. The minimum load is usually less than a micronewton. Nanoindentation instruments are typically load-controlled machines. A common question asked by the novice is the specification of the minimum thickness of film or specimen that can be measured. This is difficult to answer since it is the minimum load that is the important parameter. When operated at the minimum load, the resulting depth depends upon the mechanical properties of the specimen. The minimum load quoted in manufacturer's specifications is very important and gives an indication of the minimum load range for testing on actual specimens. Force and displacement resolutions are not so important, since they are limited in practice by the noise floor of the instrument and, more importantly, the mechanical, electrical and thermal environment in which it is placed. Table 11.1 provides a description of the most commonly quoted specifications for nanoindentation instruments. The remainder of this chapter is concerned with discussing those elements of instrument design so as to educate the reader as to what is on the market, the strengths and weaknesses of various design philosophies, and how different manufacturers approach similar design problems in order to make these exacting measurements.