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Reticle Analysis

The imaging of the pattern reticle to the substrate is perhaps one of the few "magical" elements remaining in Lithography. Aberrational contributors such as lens distortions, proximity, scatter, mechanical and base manufacturing stability of the reticle all support the aura of this mystique. Even the most detailed simulators add in mystic enhancement factors (MEF) that are empirically derived for each process rather than predicted from the physical setup.

Reticle variations predominate the critical feature error budget in the process. Until now, even when each feature was directly measure at the mask shop it has been difficult to see their signature variations on the wafer because of the influence of the lens aberrations, films and substrate.

Scanners add in a whole new level of contributors through their potential for deformation during the mechanical scan-exposure. Reticles now experience high scan velocities and extreme acceleration during the bidirectional scan process. This often leads to bow-deformation, direction dependant tilt and scan-path-height and pellicle turbulence vibration.

Accurate derivations of the contributions of the reticle are critical not only to estimating lens and tool performance but also for deriving a meaningful set of process control variables.

Two typical applications include:

Reticle Signature (Top) and Deformation During Exposure

 

Top: Wafer errors removed, SEM reticle data is compared against isolated and dense structures on the wafer.

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Bottom: Reticles can be tilted and deformed during exposure. This is one row on a wafer with all fields exposed on the "Down" or "-" scan direction. Notice the classic lens "M" shaped signature is both tilted and flattened by the reticle stage.

Reticle Qualification

  • Functions
    • Qualification of new binary and Optical Proximity Correction (OPC) reticles
    • Verify feature sizes and quality on new reticles
    • Estimate mask size from wafer printed image for qualification and removal during process analysis studies.
  • Method
    • Expose Focus matrix
    • Run Weir PW or LithoWorks PW
  • Weir PW/LithoWorks PW outputs:
    • Reticle library entries for Photolith removal of reticle signature.
    • Focus uniformity across field (for that exposure tool)
    • Depth of Focus uniformity across field (for exposure tool and feature size/limits)
    • Process Window characterization for full-profile films and features within the mask shop
    • Critical Feature Size map
      • Focus errors will be removed resulting in no feature-size changes from focus variations
        • Size is only influenced by reticle and dose
      • Size of printed feature on reticle is estimated for each site
      • Reticle Scan-speed uniformity can also be estimated from this.
        • scan-speed influences dose

Automated Mask Error Function (MEF) Analysis

  • Function
    • Calculation of process constants and individual exposure tool influence on dense patterning
  • Method
    • Import, derive, model and store reticle data into the Weir Reticle library.
      • From SEM measurements or from Reticle Qualification or from process described above
    • Remove reticle-library elements from raw or modeled data for enhanced process analyses and tuning.
    • Accurately derive mask error enhancement (MEF) factors
      • from wafer and reticle measured features
      • Estimate reticle signatures from wafer-only metrology.
  • Outputs
    • Characterization of mask-shop performance and process precision from reticle-measured data.
    • Characterization of exposure tool contributed errors such as  bow, tilt and scan-direction induced errors.
    • Characterization of and tool-matching for phase-shift and other reticle enhancement techniques (RET).
Select a product solution according to your needs below or directly click on a product name on the lower-right for more information.

By Solution

Products

  • Overlay & Registration Control

  • Critical Feature Analysis

  • Focus Control

  • Post Exposure Bake

  • Reticle Analysis

    • Vector Raptor

      • Advanced Model applications using TEA Systems proprietary adaptive modeling tools.
      • Exposure Tool corrections
      • Import ANY overlay or registration data
      • Import ANY metrology data (in addition to overlay data)
      • Comparative performance tools
      • Precision analysis
      • Covariance tools
      • Deconvolve error sources of the reticle, metrology, process and exposure tool
    • Weir PW (feature & process window models)
    • Import, derive, model and store reticle data into the Weir Reticle library.
    • Work with data from the Photomask Supplier or from the wafer-fab
    • Remove reticle-library elements from raw or modeled data for enhanced process analyses and tuning.
    • Incorporate film-thickness and feature profiles into Weir Models to optimize etch-depth for OPC Reticles
    • Employ full-profile mask-feature measured data from ellipsometer and scatterometry to determine films and edge profiles.
    • Qualify OPC and other RET Reticles using wafer-measured data.
    • Accurately derive mask error enhancement (MEF) factors from wafer and mask-shop data for each site in the exposure field.
    • Estimate reticle signatures from wafer-only metrology.
    • Employ mask-shop provided reticle data into the Weir Reticle library to allow improved Semiconductor Process Setup using Weir Reticle Signature Removal.
    • Model reticle flatness and signatures from critical feature metrology.
    • Characterize the Across-Reticle/ Across-Field Depth-of-Focus and Best Focus uniformity of the RET features.
    • Model reticle feature uniformity from wafer data when vendor data is not available or for plate incoming inspection.
    • Characterize and optimize mask-shop performance and process precision from reticle-measured data.
    • Characterize exposure tool contributed errors such as  bow, tilt and scan-direction induced errors.
    • Characterize and tool-match phase-shift and other reticle enhancement techniques (RET).
    • Mask-Suppliers can use Weir Reticle data workbooks to provide a standard format data for measured reticle signatures.
    • Weir PSFM (Focus)
      • Characterize reticle-scan performance.
      • Measure deformation due to heating, scan direction and clamping.
      • Measure plate-boxing due to reticle-platen errors.
    • Weir DM / Weir DMA (Automation)
      • Incorporate any of the above applications into a custom Weir Macro.
      • Call Weir DMA from factory control software or any APC or other software for automated  process control.
      • Output data to Internet sites in HTML format or to other programs in ASCII or Weir Spreadsheet formats.
  • Tool Characterization

  • Metrology

  • Process Setup & Control

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Weir PW
Process window, metrology and spatial feature modeling.

 

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Weir PSFM
Focus analysis from commercial patterns and programs.

 

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Weir DMA
Trend charts and automated analyses of raw or modeled data.

 

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Vector Raptor
Overlay and Registration for Double Patterning

 

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LithoWorks PEB
Thermal wafer analysis PLUS correlation to feature profile.

  
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