To overcome the resolution limits of the current generation of steppers, mask makers are forced to include an ever-growing number of OPC features on 65 nm node masks. Although lithography techniques have improved significantly in the last five years, they have not kept pace with the needs of 65 nm technology. To produce viable OPC features at the 65 nm node, the etch process must be capable of accurately defining on the mask features as small as 100 nm. The etch must also show reasonable linearity to prevent distortion of the primary features. To this end, a four factor, irregular fraction factorial design was performed using a 4th generation mask etch system. The factors in this design include RIE power, RIE coupling efficiency, ICP power, and pressure. These factors were selected for their influence on CD bias, CD uniformity, and CD linearity. The results of this design will be presented, along with an optimized solution. This solution is demonstrated on an asymmetric test pattern representative of logic or ASIC devices, as well as an evenly loaded pattern more representative of memory devices.
The ITRS roadmap indicates that significant improvements in photomask dry etching will be necessary to achieve the design goals of 90nm and 65nm technology node masks. Although some existing dry etch systems are capable of R&D work on these masks, a new dry etch system is needed to achieve production worthy results. To this end, a new 4th generation mask etch system was designed and built by Unaxis USA, Inc. In early testing, the Unaxis Mask Etcher 4 has demonstrated significant improvements in CD uniformity and linearity compared to earlier systems. A designed experiment (DoE) was performed on this new system to more fully characterize its performance window. The results of these experiments are presented and compared to a standard process performed on a Unaxis Mask Etcher 3.
As the 193 nm generation of steppers reaches the limit of its capability, alternating aperture phase shift masks (altPSMs) are necessary to extend the lifetime of these tools. The fabrication of a production-worthy altPSM requires that the quartz dry etch satisfy many conditions. The etched quartz features must not only show excellent phase uniformity, but they should have near vertical sidewalls and good etch depth linearity across a wide range of feature sizes. Surface roughness must also be low enough that transmission is unaffected. To this end, Unaxis USA performed a series of quartz photomask dry etch experiments utilizing a Unaxis Mask Etcher III. Etch depth uniformity and etch depth linearity are studied for each experiment. SEM cross-sections of the etched profiles and AFM analysis of surface roughness are also provided. Various models were constructed by IBM that demonstrate the importance of some of the etch responses, and the results from the optimized Unaxis process will be shown.