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Determning lithographic parameters to optimise a process window

  • US 20060206851A1
  • Filed: 12/18/2003
  • Published: 09/14/2006
  • Est. Priority Date: 12/30/2002
  • Status: Abandoned Application
First Claim
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1. A method of determining best process variables setting that provides optimum process window for a lithographic production process comprising transferring a mask pattern into a substrate layer, which process window is constituted by latitudes of controllable process parameters and which method comprises the steps of:

  • acquiring a data set of a focus-exposure matrix for a feature of the mask pattern having critical dimension (CD), which feature has a predetermined design CD value being the CD value that should be approximated as close as possible when transferring the feature to the substrate layer, and checking whether transferred images of the feature meet design tolerance condition, and determining which combination of values of controllable process variables provides the CD value closest to the design value and the best process latitude, characterized in that the process of checking and determining the best combination comprises the steps of;

    1) defining a statistical distribution of relevant process variables, the parameters of the distribution being determined by estimated or measured variations of the process variables;

    2) fitting the coefficients (b1-bn) of an analytical model (CD(E, F)) that describes the CD value as a function of the process variables focus (F) and exposure dose (E);

    3) calculating the average CD value and the variance of the CD distribution using the analytical model CD(E, F) of step

         1);

    4) determining quantitatively how the CD distribution fits to a desired process control parameter Cpk; and

    5) determining the best process setting for the design feature by determining the exposure-dose value and the focus value which provide a maximum Cpk value.

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