DESIGN OF A MEDIUM-POWER X-RAY-LITHOGRAPHY SYSTEM

A medium-power x-ray-lithography system has been developed. The system includes an inexpensive stationary water-cooled x-ray source and a modified Cobilt aligner system. The exposure system is capable of printing 1- mu m lines with an edge accuity of 2000 A over a 5-cm-diam wafer. The alignment is compatable with this tolerance of line definition. The x-ray source uses a defocused electron beam on a water-cooled anode. For cooling purposes the anode is a thin copper plate with an evaporated aluminum film. The 10-kV electron beam creates a similar 1-cm-diam x-ray source able to handle more than 1 kW of power without detrimental effects on the aluminum film. The system uses an electrostatic shield to prevent over heating a 25- mu m-thick beryllium vacuum window by stray electron bambardment. The x rays pass through the beryllium window into a helium atmosphere where they expose the wafer through the x-ray mask. The wafer is printed with the mask in contact to avoid alignment problems arising from wafer warpage. In this geometry the pattern to wafer distance is kept constant at 3 mu m or less which allows the use of the large x-ray source and thus, the high x-ray flux.