Computers have been shrinking ever since their conception almost two centuries ago, and the trend is set to continue with the latest developments in microchip manufacturing. The earliest prototype of a mechanical computer was called the Difference Engine, and was invented by an eccentric Victorian called Charles Babbage. It weighed over 15 tons and had 26,000 parts. Colossus, the first electronic computer, did not appear until the end of WWTI, and with its 1,500 vacuum tubes was even more complex and much heavier than its mechanical predecessor.

It was only when the silicon-based microchip was invented in the early 1950s that computers started to become more compact. The first microchip computers were very complex and had more than 100,000 transistors, or electronic switches; however, they were still rather bulky and measured several metres across. Nowadays microchips are measured in nanometres (nm)-that is, in billionths of a metre-and the search for even smaller microchips continues as scientists work on new methods of microchip production.

Today, most microchips are shaped by a process called lithographic etching, which uses ultraviolet (UV) light. A beam of UV light with a wavelength of only 193 nm is projected through a lens on to an etching mask, a micro device with slits, or long narrow cuts. When the UV light hits the surface of silicon chips, it removes microscopic layers of silicon to create patterns for the microchips circuits. Microchips with features as small as 65 nm can be created with this wavelength.

However, lithographic etching is unable to make chips much smaller than 65 nm due to the fundamental properties of light. If the slit in the mask were made narrower, the air and nitrogen used in the space between the lens and the etching mask would diffuse the light, causing a blurred image. This means that 193-nm UV light cannot be used to produce microchips with features smaller than 65 nm. Manufacturers know that they need to go even smaller for the technological demands of this century, and they are looking for new methods of making microchips.

One approach to solving the problem is to use microscopic mirrors to focus X-rays rather than ultraviolet light. X-rays with a wavelength of less than 25 nm can be created, allowing engineers to make components smaller than 15 nm. The process is known as X-ray lithography etching. However, this technology is extremely expensive, so manufacturers are continuing to search for a cheaper alternative.

A technology called immersion lithography might be the solution. Although liquids are not commonly associated with computers, a tiny drop of water may be all it takes to make microprocessors smaller and more powerful. Intel and IBM, who made the first microprocessors, have recently developed a unique method of microchip production, which uses water droplets to enable manufacturers to shrink the chips-and at a reasonable price! The new microchip is produced by using a drop of water to narrow the gap between the light source and the etching mask, and shorten the wavelength of the UV light to less than 34 nm. This process can be used to manufacture microchips as small as 45 nm, or possibly even smaller.

Initially, engineers feared that air bubbles and other contaminants in water drops would distort the light and ruin the microchip etching process, and the first experiments proved these fears to be well-founded. The problem was overcome by using high-purity water, free of air and other substances. Scientists are also experimenting with liquids other than water-denser liquids such as hydrofluoric acid-which may allow the wavelength to be shrunk still further, thus producing even smaller chips.

IBM have already successfully implemented immersion lithography on some of their production lines and created a fully-functioning microprocessor. IBM also claim that they are able to produce microchips with very few defects.

Although immersion lithography is very new, it is highly promising as it will make the production of 45 nm and 32 nm chips commercially viable. It is a significant milestone in chip manufacturing and will help to bring the costs of the chip down without fundamentally changing the microchip production processes.

In the near future, the ground-breaking technology of immersion lithography will enable computer manufacturers to make powerful microchips that will be used in electronic devices smaller than a coin. This will open up new opportunities in the ever-shrinking world of digital technology.