Mask inspection

About: Mask inspection is a research topic. Over the lifetime, 1072 publications have been published within this topic receiving 8696 citations.

Impact of MEEF on low k 1 lithography and mask inspection

Abstract: In this paper, we present a comparative simulation study of mask defect impact in a high MEEF process and its detectability under a mask inspection too. A simulation mode for a mask inspection system is constructed and validated by comparing the simulated signal with data collected from an inspection tool. With this calibrated mode, defect images and scan signals from programmed defect pattens are studied. The corresponding wafer CD variations caused by programmed defects are simulated using a photolithography simulator. We find that for a mask defect of a given size, its impact on wafer varies greatly from location to location, depending on the MEEF of the host patterns surrounding the defect. In comparison, the signal from a high-resolution inspection tool varies linearly with defect size and is nearly independent of the host patterns. Once the MEEF starts its sharp increase, the sensitivity of the inspection tool is required to increase at the same rate. An inspection tool operating at its resolution limit generally could not follow the sharp increase in MEEF once the wafer process starts to degrade. It is therefore important to control the MEEF in the original pattern design to ensure that residual defect does not cause circuit malfunction. Extra margins may have to be introduced in the design rule to account for the impact of residual defects.

Aerial-image-based inspection on subresolution scattering bars

Abstract: The paper presents the results of a study to define a production-worthy inspection technique for subresolution solid and hollow scattering features used in 193-nm lithography. Masks are inspected using conventional high-NA and aerial-imaging-based mask inspection tools. Inspection results are compared regarding capture rate and nuisance defect rate.

Through-pellicle defect inspection of EUV masks using an ArF-based inspection tool

Abstract: The use of EUV photomasks in a semiconductor manufacturing environment requires their periodic inspection to ensure they are continually free of defects that could impact device yield. Defects typically occur from fall-on particles or from surface degradation such as “haze”. The proposed use of a polycrystalline-based EUV pellicle to prevent fall-on particles would preclude periodic through-pellicle mask defect inspection using e-beam, as well as, DUV inspection tools (the pellicle is opaque at DUV wavelengths). Thus, to use these types of defect inspection tools would require removal of the EUV pellicle before inspection. After inspection, the pellicle would need to be re-attached and the mask re-qualified using a test wafer, thus causing expense and delays. While EUV-wavelength inspection tools could inspect through such a pellicle precluding the need to remove the pellicle, these tools are not likely to be available in the commercial marketplace for many years. An alternate EUV pellicle material has been developed that is semi-transparent to 193nm wavelengths, thus allowing through-pellicle inspection using existing ArF-based, or other 193nm wavelength mask inspection tools. This eliminates the requirement to remove the pellicle for defect inspection and the associated time and expense. In this work, we will conduct an initial evaluation of through-pellicle EUV mask defect inspection using an existing 193nm mask inspection tool. This initial evaluation will include durability of the pellicle to defect inspection, and impact of the pellicle on inspection tool performance.

Automating defect disposition in fabs and maskshops

Abstract: ADAS (Automated Defect Analysis Software) is the first product to fully automate mask defect analysis for mask shops and fabs. ADAS classifies and dispositions photomask defects quickly and accurately. Disposition is based on defect size and printability measurements from simulation. Full analysis of inspection reports with 100 defects requires 2 seconds. Printability measurements match AIMS within 6 percent at 3 sigma on 45 nm test masks. Repeatability is 5 percent at 3 sigma over multiple inspections. ADAS can reduce the need for production AIMS measurements by 90% and eliminate operator review errors and the repelliclizations they cause. ADAS increases overall inspection efficiency for mask shop first-inspection and final inspection. It can automate fab requalification inspections and eliminate the need for incoming inspection.

Evaluation of 32nm advanced immersion lithography pellicles

Abstract: Advanced immersion lithography utilizes higher numerical aperture (NA) stepper lenses resulting in higher angles of light illumination through photomasks. Transmission in conventional pellicles (830 nm thickness) is generally maximized at 0 degree illumination and decreases significantly at the higher angles. Most pellicle suppliers have developed thinner pellicle membranes (~280 nm) which allow considerably improved transmission of light at angles up to 20 degrees. In addition, aluminum frames have been shortened, potentially allowing inspection closer to the inside of the frame and reduced mask flatness distortion upon pellicle mount. Suppliers have also developed advanced adhesives which reduce outgassing even beyond the low levels obtained with current 45 nm pellicles. In this paper, advanced immersion pellicles from several suppliers are evaluated and compared with conventional 45 nm pellicles for the following quality parameters: physical durability, foreign material, ease of demounting and glue removal, chemical outgassing, mask flatness distortion and susceptibility to radiation damage. Improvements in mask inspection and pellicle optical transmission at higher incident angles are also evaluated and are discussed. Keywords : Mask flatness, pellicle, adhesive, frame