Energy filter multiplexing

A method for determining an interface between a first material and a second material on a specimen by detecting electrons that scatter from the specimen, the method comprising:

• scanning and directing an electron beam to irradiate a spot on the specimen, the electron beam causing the electrons to scatter from the irradiated spot on the specimen;
• setting a high pass filter at a first voltage level, the first voltage level being predetermined;
• detecting the scattered electrons with the high pass filter that is set at the first voltage level, the high pass filter detecting a first electron intensity level of the scattered electrons;
• setting the high pass filter at a second voltage level, the second voltage level being predetermined;
• detecting the scattered electrons with the high pass filter that is set at the second voltage level, the high pass filter detecting a second electron intensity level of the scattered electrons;
• determining a differential electron intensity level, which is the difference between the first electron intensity level and the second electron intensity level, the first voltage and the second voltage setting the limits to an electron energy range within which the first and second material emit different electron intensity levels;
• repeating each of the setting, detecting and determining operations to obtain additional differential electron intensity levels for successively irradiated spots along the scanned specimen;
• and
• evaluating each of the additional differential electron intensity levels that are determined for a change in intensity levels between subsequently determined differential electron intensity levels, whereby the change between subsequently determined differential electron intensity levels indicates an interface between the first and second materials.

A method for performing spectroscopy on a specimen by detecting electrons that scatter from the specimen comprising:

• directing an electron beam to irradiate a spot on the specimen, the electron beam causing the electrons to scatter from the irradiated spot on the specimen;
• setting a high pass filter at a first voltage level, the first voltage level being predetermined;
• detecting the scattered electrons with the high pass filter that is set at the first voltage level, the high pass filter detecting a first electron intensity level of the scattered electrons;
• setting the high pass filter at a second voltage level, the second voltage level being predetermined;
• detecting the scattered electrons with the high pass filter that is set at the second voltage level, the high pass filter detecting a second electron intensity level of the scattered electrons;
• determining a differential electron intensity level, which is the difference between the first electron intensity level and the second electron intensity level, whereby the differential electron intensity level is the electron intensity level in an energy window between the first and second voltage level;
• and
• repeating each of the setting, detecting and determining operations to obtain additional differential electron intensity levels such that during each repeated cycle of setting, detecting and determining, the first voltage level is set to the second voltage level and the second voltage level is increased a determined increment, each of the successively determined differential electron intensity levels providing information as to an electron intensity spectrum for the specimen.

A method for inspecting a specimen by detecting electrons that scatter from the specimen comprising:

• directing an electron beam to irradiate an inspected region on the specimen, the electron beam causing the electrons to scatter from the inspected region;
• setting a high pass filter at a first voltage level, the first voltage level being predetermined;
• detecting the scattered electrons with the high pass filter while set at the first voltage level, the high pass filter detecting a first electron intensity level of the scattered electrons that is used to generate a first image of the inspected region;
• setting the high pass filter at a second voltage level, the second voltage level being predetermined;
• detecting the scattered electrons with the high pass filter while set at the second voltage level, the high pass filter detecting a second electron intensity level of the scattered electrons that is used to generate a second image of the inspected region;
• determining a first differential electron intensity level, which is the difference between the first electron intensity level and the second electron intensity level, wherein the first differential electron intensity level is the electron intensity level in an energy window between the first and second voltage level;
• and
• generating a first resulting image of the inspected region from the differential electron intensity level.

An inspection system comprising:

• a beam generator for generating an electron beam;
• a detector having a high pass filter for detecting scattered electrons;
• and
• a controller arranged to:
• set the high pass filter at a first voltage level such that the detector detects the scattered electrons with the high pass filter while set at the first voltage level, the first voltage level being predetermined, the high pass filter detecting a first electron intensity level of the scattered electrons that is used to generate a first image of the inspected region;
• set the high pass filter at a second voltage level such that the detector detects the scattered electrons with the high pass filter while set at the second voltage level, the second voltage level being predetermined, the high pass filter detecting a second electron intensity level of the scattered electrons that is used to generate a second image of the inspected region;
• determine a first differential electron intensity level, which is the difference between the first electron intensity level and the second electron intensity level, wherein the first differential electron intensity level is the electron intensity level in an energy window between the first and second voltage level;
• and
• generate a first resulting image of the inspected region from the differential electron intensity level.