Charged particle beam apparatus and methods for capturing images using the same
View Patent ↗The present invention provides a charged particle beam apparatus used to measure micro-dimensions (CD value) of a semiconductor apparatus or the like which captures images for measurement. For the present invention, a sample for calibration, on which a plurality of polyhedral structural objects with known angles on surfaces produced by the crystal anisotropic etching technology are arranged in a viewing field, is used. A beam landing angle at each position within a viewing field is calculated based on geometric deformation on an image of each polyhedral structural object. Beam control parameters for equalizing the beam landing angle at each position within the viewing field are pre-registered. The registered beam control parameters are applied according to the position of the pattern to be measured within the viewing field when performing dimensional measurement. Accordingly, the present invention provides methods for reducing the variation in the CD value caused by the variation in the electron beam landing angle with respect to the sample with an equal beam landing angle and methods for reducing the instrumental error caused by the difference in the electron beam landing angle between apparatuses.
1. A method for imaging a sample by use of a charged particle beam apparatus, the method comprising the steps of:
imaging a test sample with a first magnification ratio sufficient for including polyhedral patterns formed the test sample within a viewing field by applying a charged particle beam to the test sample and by detecting secondary electrons generated from the test sample, the polyhedral patterns having a known shape;
imaging each polyhedral pattern with a second magnification ratio which is higher than the first magnification ratio by sequentially moving and applying the charged particle beam;
obtaining first relationships between a position irradiated with the charged particle beam within the viewing field and the beam landing angle for each of the polyhedral patterns using images obtained during the step of imaging each polyhedral pattern;
obtaining second relationships between other positions within the viewing field and beam landing angles through interpolation; and
imaging the sample by applying the charged particle beam to the sample with a pattern formed on the surface thereof to scan the sample while controlling beam incidence conditions of the charged particle beam to allow a beam landing angle to be maintained within a viewing field based on the first and second relationships.
2. The method for imaging a sample by use of a charged particle beam apparatus as defined in claim 1 , wherein a polyhedral pattern with a known shape on the test sample has a shape of a quadrangular pyramid, a quadrangular frustum, or an almost quadrangular pyramid with a round top surface.
3. The method for imaging a sample by use of a charged particle beam apparatus as defined in claim 1 ,
wherein a plurality of polyhedral patterns with a known shape are formed on the test sample; and
wherein a control quantity for controlling a beam landing angle of a charged particle beam is obtained from images of a plurality of polyhedral patterns of the test sample.
4. The method for imaging a sample by use of a charged particle beam apparatus as defined in claim 1 ,
wherein the charged particle beam is applied to the sample with the pattern formed on the surface thereof to scan the sample while controlling the beam incidence condition of the charged particle beam; and
wherein dimensions of the pattern formed on the surface thereof are obtained by use of images obtained by imaging the sample irradiated and scanned by the charged particle beam.
5. A charged particle beam apparatus comprising:
a charged particle beam irradiation means for applying a focused charged particle beam to a sample to scan the sample;
an image capturing means for capturing images of the sample by detecting secondary charged particles generated from the sample irradiated with a charged particle beam emitted from the charged particle beam irradiation means with a first magnification ratio and a second magnification ratio, the second magnification ratio being higher than the first magnification ratio;
an image processing means for processing images captured by the image capturing means, and for obtaining first relationships between positions irradiated with the charged particle beam within a viewing field and a beam landing angle in a plurality of directions for polyhedral patterns detected with the first magnification ratio, and obtaining second relationships between other positions within the viewing field and beam landing angles through interpolation;
a display means for displaying images of the sample captured by the image capturing means; and
a control means for controlling the charged particle beam irradiation means, the image capturing means, the image processing means, and the display means,
wherein the image processing means causes beam incidence conditions of the charged particle beam allowing a beam landing angle to be maintained within a viewing field to apply the charged particle beam to the test sample, and obtains the first relationships between a positions irradiated by the charged particle beam and the beam landing angle in a plurality of directions; and
wherein the control means controls the charged particle beam irradiation means based on the first and second relationships.
6. The charged particle beam apparatus as defined in claim 5 , wherein a plurality of polyhedral patterns with a known shape of a quadrangular pyramid, a quadrangular frustum, or an almost quadrangular pyramid with a round top surface are formed on the test sample.
7. The charged particle beam apparatus as defined in claim 5 , wherein the image processing means processes images captured by the image capturing means, by use of the sample with the pattern formed on the surface thereof, thereby obtaining dimensions of the pattern of the sample.