In high-tech as well, packaging counts alongside content, as a DEMCON project for Mapper Lithography shows. In this case, the packaging serves not to impress by means of glossy appearance, but rather to keep out electromagnetic radiation – to less than a thousandth of the strength of the earth’s magnetic field. DEMCON has developed a sophisticated ‘biscuit tin’ for this and is also taking care of production.
Mapper Lithography is developing and building a machine for electron beam lithography as an alternative to conventional optical lithography. From the outset, DEMCON has been closely involved in the systems engineering and for example contributed to ideas on the solution for the metrology frame. DEMCON was also in at the launch of a crucial module, the Wafer Positioning System (WPS).
The design tasks for the WPS lay in the wafer throughput speed and the wafer positioning. The prescribed accuracy requires maximum suppression of the disturbances between the wafer (in the WPS) and the electron source (attached to the metrology frame). For that reason, apart from vibration insulation with respect to the floor, a position measuring system with feedback mechanism to the wafer positioning is used. DEMCON was involved in drawing up the specifications and concept, and in its own cleanroom built a proof-of-principle, a prototype and later an operational industrial system. The challenge was, despite the complexity – which is inherent in electron beam lithography – to make the module as passive as possible, while keeping the concept simple.
For a subsequent version, DEMCON focussed on a critical component of the WPS, the short-stroke stage, that had to achieve sub-nanometre resolution. Important points of focus included assembly and service friendly cabling, minimal heat dissipation from electric motors and magnetic screening of the electron beam. Electric motors with permanent magnets that could disturb the electron beams are after all used to move the WPS.
A special screen around each motor with the aid of a complex shaped cylinder with extremely precise tolerances is to prevent this disturbance. DEMCON, along with its manufacturing partners, developed the sophisticated manufacturing procedure for this ‘biscuit tin’. The cylinder is constructed of layers of so-called mu-metal: initially cut out of plate, subsequently rolled and then attached to each other through laser welding. The whole is annealed to remove any mechanical tension, as the mu-metal works as magnetic screen only if it is completely free of tension.
DEMCON is responsible for series production, including qualification, of the complex short-stroke stage and its special packaging. Mapper is now offering DEMCON the opportunity to sell this stage, or variants of it, in other markets. The aim is increasing volume for DEMCON, with a resultant decline in cost price for Mapper. This was always the central thread running through the laborious development process: to achieve a competitive cost price while retaining sub-nanometre performance. In this way, Mapper and DEMCON have built up a durable and close relationship.