In-situ probe for optimizing electron beam inspection and metrology based on surface potential

A method of controlling charge on a sample, the method comprising:

• (a) directing a charged particle beam substantially towards a portion of the sample under a set of operating conditions that result in a surface charge value on the sample portion;
• (b) measuring the surface charge value of the sample portion under the first set of operating conditions;
• (c) comparing the measured surface charge value to an optimum surface charge value;
• (d) when the measured charge value does not substantially equal the optimum surface charge value and the optimum surface charge value cannot be extrapolated from previously measured charge values, adjusting the set of operating conditions to a current set of operating conditions and repeating operations (a) through (d);
• and
• (e) when the measured charge value does substantially equal the optimum surface charge value or the optimum surface charge value can be extrapolated from previously measured charge values, defining the current set of operating conditions as an optimum set of operating conditions and inspecting the sample portion with the charged particle beam under the optimum set of operating conditions.

A computer readable medium containing program instructions for controlling charge build up on a sample while an image is being generated of a portion of the sample with a charged particle device having a source unit for directing a charged particle beam substantially towards the sample, a detector for detecting particles that are output from the sample, and an image generator for generating the image of the sample from the detected particles, the computer readable medium comprising:

• computer code for (a) directing a charged particle beam substantially towards a portion of the sample under a set of operating conditions that result in a surface charge value on the sample portion;
• computer code for (b) measuring the surface charge value of the sample portion under the first set of operating conditions;
• computer code for (c) comparing the measured surface charge value to an optimum surface charge value;
• computer code for adjusting the set of operating conditions to a current set of operating conditions and repeating operations (a) through (d) when the measured charge value does not substantially equal the optimum surface charge value and the optimum surface charge value cannot be extrapolated from previously measured charge values;
• and
• computer code for defining the current set of operating conditions as an optimum set of operating conditions and inspecting the sample portion with the charged particle beam under the optimum set of operating conditions when the measured charge value does substantially equal the optimum surface charge value or the optimum surface charge value can be extrapolated from previously measured charge values.

A method of controlling charge build up on a test sample that is to undergo a metrology or inspection procedure within a charged particle device, the method comprising:

• (a) in a charged particle device, calibrating a focus setting of a charged particle device to obtain a first optimum image of a reference sample having a known surface charge value, the first optimum image corresponding to a first optimum focus setting;
• (b) selecting a set of operating conditions for the charged particle device;
• (c) in the charged particle device, directing a charged particle beam towards a test sample under the selected set of operating conditions, the test sample being the same or substantially identical to the reference sample;
• (d) in the charged particle device, calibrating the focus setting of the charged particle device to obtain a second optimum image of the test sample, the second optimum image corresponding to a second optimum focus setting;
• (e) comparing the second optimum focus setting to the first optimum focus setting;
• (f) when the second optimum focus does not substantially equal the first optimum focus setting, adjusting the set of operating conditions and repeating operations (c) through (f) under the adjusted set of operating conditions;
• and
• (f) when the second optimum focus setting substantially equals the first optimum focus setting, commencing with inspection or metrology of the test sample by directing the charged particle beam towards the test sample under the adjusted set of operating conditions to thereby result in the test sample having a surface charge substantially equal to the known surface charge value of the reference sample.