Measurement technique for determining the width of a structure on a mask
AssigneeInfineon Technologies AG
InventorThomas Schätz
Life of this patent
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Abstract
A measurement technique for determining the width of a structure on a mask is described. During a focus sweep, the width of the structure on a photomask, and an edge slope thereof or the structure contrast thereof are measured on a scanning electron microscope by controlling a current through a flow in a magnetic lens by a control unit. To determine the best focus, a function is fitted to the measured values for the contrast and the angle of edge inclination and the focus is read off at the extreme value thereof. A further function is adapted to the values, measured in each case as a function of the focus for the structural width, and the functional value relating to the previously determined best focus is determined.
Claims7
A measurement technique for determining a width of a structure on a photomask, which comprises the steps of:
- a) bringing the photomask with the structure into an object chamber of a scanning electron microscope;
- b) adjusting a first focus value of a magnetic lens of the scanning electron microscope;
- c) measuring a first width of the structure;
- d) measuring a first value for a further parameter characterizing the structure;
- e) adjusting a second focus value of the magnetic lens of the scanning electron microscope;
- f) measuring a second width of the structure;
- g) measuring a second value for the further parameter characterizing the structure;
- h) adjusting a third focus value of the magnetic lens of the scanning electron microscope;
- i) measuring a third width of the structure;
- j) measuring a third value for the further parameter characterizing the structure;
- k) adapting a first function with exactly one extreme value to the first, second and third values for the further parameter as a function of the first, second and third focuses, respectively, such that deviations of the first, second and third values from the first function are minimized;
- l) determining a focus value assigned to the extreme value of the first function as a best focus;
- m) adapting a second mathematical function with exactly one extreme value to the first, second and third widths of the structure as a function of the first, second and third focuses, respectively, such that deviations of the first, second and third widths from the second function are minimized;
- and
- n) determining the width of the structure in relation to a functional value of the second mathematical function which is assigned to the best focus.
Dependencies are inferred from the claim text.