Test key design to enable X-ray scatterometry measurement

A method comprising:

• forming an array of semiconductor fins, wherein the semiconductor fins have a same length, and the array has a plurality of rows and a plurality of columns;
• forming additional features over the semiconductor fins, wherein the additional features comprise at least a plurality of columns, with each column over a column of the semiconductor fins;
• obtaining an X-ray diffraction pattern from the array of semiconductor fins and the additional features;
• and
• determining dimensions of the additional features from the X-ray diffraction pattern.

A method comprising:

• forming a test key comprising:
• forming an array of semiconductor fins, wherein the semiconductor fins have a same length, and the array has a plurality of rows and a plurality of columns;
• forming a plurality of gate structures overlying the semiconductor fins, wherein the plurality of gate structures is distributed substantially uniformly throughout the array, and the plurality of gate structures has a lengthwise direction perpendicular to a lengthwise direction of the semiconductor fins;
• and
• etching portions of the semiconductor fins not covered by the plurality of gate structures to form recesses extending into isolation regions;
• obtaining an X-ray diffraction pattern from the test key;
• and
• determining dimensions of the semiconductor fins and the plurality of gate structures from the X-ray diffraction pattern.