Study on x-ray irradiation stability of absorber materials for x-ray masks by stress measurement

We fabricated photomasks by means of a surface imaging technique using electron beams. For this purpose, a bi-level resist process was used. The resist consisted of three- dimensional polysilphenylenesiloxane (TSPS), a negative resist containing silicon, at the top and sulfonated polyaniline (SPAn), an electrically conductive polymer film, at the bottom. TSPS is known to be sensitive to electron beams. It swells slightly during development and it is easily oxidized. These features together make TSPS a good top coat substance. It is also know that the bottom layer substance SPAn reduces substrate charging because it is electrically conductive. By taking advantage of this resist system, we used O2-RIE (oxygen reactive ion etching) for transferring surface images from the top to bottom layer. This paper discusses the performance of photomasks which we fabricated by combining this bi-level resist process with variable-shaped electron-beam lithography system (acceleration voltage of 20 keV and current density of 10 A/cm2). By using this process, we succeeded in obtaining 0.2 micrometer line/space patterns. In addition since the multilayer resist system could reduce proximity effect, it was possible to produce reticles for 1-Gbit DRAM devices without any data correction.