|
After decades of binary mask manufacturing using Cr absorber the material spectrum was extended by phase shift
material in late 90's during introduction of Half Tone Phase Shift Masks (HT-PSM). This change had strong impact on
manufacturing flow as well as several unit processes.
A consequences of phase shifter introduction was the necessity of introducing a second level litho process, as well as
introducing of dry etch processes due to poor etch properties of MoSi using wet chemistry. Less obvious and rather
unremarkable was the impact of this change to clean processes, except the impact of the clean process on the phase
shift.
In recent years we've seen several new materials based on varying chemical composition as well as thickness of the
absorber developed by various mask blank vendors namely Hoya and ShinEtsu. These materials are improving
resolution, pattern fidelity and to some degree also mask lifetime. Adding the EUV mask blank materials increases
further the spectrum of materials, taking into account all the absorber stacks available today on market.
Thorough investigation of the clean process performance as a function of surface material shows significant variation in
the critical parameters as defectivity, susceptibility to recontamination and relative cleaning efficiency.
Goal of this work is to
1) Compare the already mentioned clean related properties together with feature damage and impact on the critical
dimension (CD) shift for different materials.
2) Find a compromise between the technology requirements and process limitations resulting from the combination of
available processes with material properties.
Some aspects of the new materials such as stack height and interface between absorber and substrate are making this
task easier, especially with respect to feature damage. On the other hand the most critical parameter - the cleaning
efficiency, dropped due to the introduction of the new materials, mainly due to unfavorable sticking coefficients of
these materials.
|
