The World’s Most Powerful Lenses
A day without a cell phone, computer or laptop. Unimaginable for many. In an increasingly fasterpaced world, no one wants to do without these electronic marvels in either their professional or private lives.
Every user values the performance of modern electronics. However, only a few are aware that highly precise optics are required for the manufacture of these electronic gadgets. Today, state-of-the-art controllers and memory modules based on semiconductors can be found in virtually all areas of daily life: in industrial operations and hospitals, in transportation vehicles and private households. The semiconductor industry manufactures millions of microchips annually for these modules. The heart of the wafer steppers used, or semiconductor production machines, is an enormous lens with practically unimaginable power.
It is virtually unknown that the ZEISS Planar camera lens is the forefather of these special optics. Carl Zeiss employee Paul Rudolf (1858 – 1935) developed this lens in 189. The result was a lens featuring uniformly high definition throughout the entire image field. This property is still the hallmark of Planar lenses, and it is precisely this property that is so vital to semiconductor manufacture where a plane surface must be uniformly exposed by the lens.
Enhanced for industrial applications
An important milestone in the historical development of the Planar lenses occurred in the 1960s when they were redesigned for industrial applications. The name of mathematician and optical designer Erhard Glatzel (1925 – 2002) is now inseparably associated with this event. In 1969, he also developed the S-Planar line of lenses for microlithography – the process used to produce integrated circuits (now, entire microchips).
Although derived from camera lenses and very similar to them in the beginning, the lenses now used in microlithography are becoming increasingly different from their predecessors. In the 1970s, a good dozen single lens elements with a total weight of 50 kg were assembled to form a lithography lens. This led to the development of new S-Planar lenses in rapid succession. During the 1970s, S-Planar lenses worked with light in the 400 – 600 nm spectral range (10-9 m, billionth of a meter). This enabled structural widths of approximately 2 micrometers. A human hair is 30 times as thick. The structures became increasingly smaller within only a few years. The 5/0.42 S-Planar lens from 1982 enabled structures smaller than 0.5 micrometers for the first time.
This development adhered to Moore’s Law. Gordon Moore, a co-founder of Intel, predicted in the mid 1960s that the performance of microchips will double about every two years. Back then it was impossible for him to know that the „law“ later named after him would dictate the rate of development of semiconductor chips into the next century.
Current technology level
Now, almost 30 years later, semiconductor lenses are specified for light with a wavelength of 258 or 193 nm, for example. The numerical apertures of immer-sion lenses for chip fabrication, Starlith i, reach values above 1. This results in ever finer semiconductor structures that enable microchips with greater storage capacity and computing speed. The performance of the Starlith 1700i lithography lens is outstanding. It is the first system of its kind with a combination of lens elements and mirror systems. It features a numerical aperture of 1.2 and enables resolution down to 45 nanometers. This resolution makes it possible to store the content of 7.4 bibles on a surface no larger than one square millimeter.
A new field of business emerges
The first semiconductor lenses were developed as “special lenses” in what was then the department for camera lenses. Business was so successful that the later Semiconductor Technology Business Group was founded. This later became Carl Zeiss SMT AG. For many years, Carl Zeiss has maintained a strategic partnership with Holland-based ASML, the world‘s largest provider of lithography systems. This cooperation holds a market share of more than 50 percent. This means that more than half of the microchips produced around the globe are created with a lens from Carl Zeiss. The chances are good that the monitor you are looking at right now works with such microchips.
The world in which the precision optics for microlithography are created is a world of records: the lens elements are cemented in the mounting rings with an accuracy of 0.5 arc seconds, or the equivalent of 1 meter variance over 400 kilometers of altitude (International Space Station). A one meter tall lens must not be tipped more than 6 micrometers out of its longitudinal axis; at this degree of accuracy, the tip of the 165 meter tall cathedral in Ulm would be exactly 1 millimeter outside its longitudinal axis.
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