Chemistry researchers at Eindhoven University of Technology (TUE), funded by NWO’s Chemical Sciences Council, recently discovered a way to determine the chemical composition of chips or coatings which are only a few nanometers across. This technique makes a major contribution to further miniaturisation in the field of micro-electronics and semiconductors, in which the smallest structural details are about 200 nanometers in size.
The method which the Eindhoven have developed is based on the radiation emitted by an object when it is irradiated by a beam of electrons. The measurable phenomenon occurs because the electrons in the beam collide with electrons in the atoms making up the object so that they enter an excited state. When the electrons return to the free state, with lower energy, X-rays are emitted. The wavelength of this radiation is characteristic of the chemical element, while the intensity of the radiation depends on the overall composition of the material.
The Dutch researchers combined a model for determining the chemical composition on the basis of the measured intensity with the use of a high resolution electron microscope. The beam of electrons which the microscope produces irradiates a minimum area of 10 by 10 nanometers. Using the X-rays emitted from this area, it is possible to determine precisely which chemical elements occur at that location and in what quantity.
Using this technique, research is now being carried out on a new type of electrical contact within chips constructed of a thin layer of cobalt deposited on a semiconductor. The cobalt forms an electrical connection for the semiconductor. When heat is applied, a chemical reaction takes place between the cobalt and the semiconductor, improving the mechanical strength and the electrical conductivity of the contact. The new chemical technique allowed the researchers to determine accurately where chemical changes had developed as a result of the heat-treatment.
In industry, micro-electronics or semiconductor components with a diameter of less than 1 micrometre are now commonplace. Further miniaturisation of the smallest structures within equipment, such as electrical connections and junctions within a chip, will only be possible if researchers are in a position to measure the chemical composition of the smallest details of the new materials.
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