FOCUSED ION-BEAM LITHOGRAPHY

Lithography for microelectronics, that is, the exposure and development of resist, is already being carried out in research laboratories at dimensions well below 0.1 mum. In production the minimum dimensions are likely to approach 0.1 mum before the end of the decade. This review will examine the use of focused ion beams for ultrafine lithography. Minimum dimensions down to 0.015 mum have been reported as well as exposure of 0.25 mum thick resist with 0.05 mum linewidth for the making of X-ray lithography masks. At this time there are only two techniques for writing original patterns (as opposed to replicating them) at 0.1 mum and below: electron beams and ion beams. Electron beams are at a mature state of development and have advantages in absence of shot noise and in fast deflection capability. Ion beams on the other hand have demonstrated absence of proximity effect and high resist sensitivity, i.e. potentially faster writing speed. The development of the gas field ion source promises hundredfold increase in current density of light ions (H-2+, He ... ) in the beam focal spot. In addition, these light ion beams at high energy can be deflected at the speeds needed for lithography. Thus focused ion beam lithography is a serious candidate for future fine pattern writing.