Prototype of an EUVL wafer stepper by the Lawrence Livermore National Laboratory, California, USA.
SCHOTT LITHOTEC, Mainz, Germany
Fit for Future Chip Technology
SCHOTT LITHOTEC is a world leader in high-tech optical materials for lithography. In a new project the company is now also developing key materials and components for Extreme Ultraviolet Technology (EUVL).
According to Moore’s Law the power of computer chips doubles approximately every 18 months by continually miniaturizing their structure. This is only possible if appropriate lithography processes are available to treat the silicon wafers. Inevitably continuously smaller light wavelengths are used in the exposure machines (wafer steppers) which transfer the complicated design of the electronic components and circuits. Nowadays mass production is handled by eximer lasers which work with wavelengths of 248 and 193 nanometers (nm = one-billionth of a meter) and thus belong in the invisible, short-wave UV range. For the next generation of chips, which will be going into production beginning in 2005, wavelengths of 157 nm are foreseen, which can be produced using fluorine lasers. Back in 1999, a German consortium started work on 157 nm lithography. As the world’s leading manufacturer of calcium fluoride crystals, SCHOTT LITHOTEC is playing an important role in the consortium.
Innovation Tempo High
The use of ever smaller light wavelengths reduces the structure gaps on computer chips and thus increases their performance.
Masks, Lenses, Mirrors
Lithography is not just a question of the radiation sources, but above all the suitable materials for components and systems. SCHOTT LITHOTEC AG of Jena is the only manufacturer at the present time supplying all the technologies currently in use. These materials include high homogeneity optical glasses, fused silica and calcium fluoride. The substrate requirements for 13 nm lithography represent a further challenge. For example the material must have an extremely low thermal expansion so that it does not distort when warmed up. Based on optical simulations, the expansion would have to remain below just a few ppb (parts per billion) per Kelvin range. One ppb per Kelvin means that a body 100 millimeters long may not expand more than 0.1 nanometers when heated up by one degree – this greatly surpasses all previous demands on so-called zero expansion materials. It calls for the development of a new material and enhanced measurement techniques if the required material properties, with regard to expansion behavior, flatness, surface finish and freedom from imperfections, are to be verified with absolute certainty.
Extremely Clean Rooms
The fused silica substrates are lapped, then polished and then under clean room conditions finally coated with more than 100 layers, each only a few atoms thick.
A further prerequisite is a degree of material homogeneity which can only be achieved with the special processes used for the manufacture of optical glasses. With its “ZERODUR®” glass ceramic and its proven performance in scientific and industrial applications, SCHOTT is in an excellent starting position, since this material already comes very near to meeting these requirements. Nevertheless some fundamental work still needs to be done.
Sights on Higher Market Shares in Lithography
The goal of SCHOTT LITHOTEC and SCHOTT GLAS is clear. If the broad industrial introduction of the EUV technology is imminent from 2006 onwards, key materials and components should come from SCHOTT. These include the substrate material for masks and optical elements plus the complete mask blanks. The share of the lithography market is set to be expanded continuously. SCHOTT LITHOTEC plans to transfer its current world leadership in the manufacture of calcium fluoride to the technologies of future lithography generations too.