Charged Particle Beam Processing System with Visual and Infrared Imaging

• US 20120006987A1
• Filed: 07/08/2011
• Published: 01/12/2012
• Est. Priority Date: 07/08/2010
• Status: Active Grant

• Current Assignee: FEI Company (Thermo Fisher Scientific Incorporated)
• Original Assignee: FEI Company (Thermo Fisher Scientific Incorporated)
• Inventors: Rue, Chad, Agorio, Enrique, Crowley, Daniel
• Granted Patent: US 8,610,092 B2
• Time in Patent Office: Days
• US Class Current: 250/332
• CPC Class Codes: G01J 3/0208 using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction
• CPC Class Codes: G01J 3/0262 Constructional arrangements for removing stray light
• CPC Class Codes: G01J 3/0278 Control or determination of height or angle information for sensors or receivers
• CPC Class Codes: G01N 2021/8825 Separate detection of dark field and bright field
• CPC Class Codes: G01N 2021/95653 Through-holes
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G01N 21/95684 Patterns showing highly reflecting parts, e.g. metallic elements
• CPC Class Codes: H01J 2237/31749 Focused ion beam
• CPC Class Codes: H01J 37/226 Optical arrangements for illuminating the object; optical arrangements for collecting light from the object
• CPC Class Codes: H01J 37/3005 Observing the objects or the point of impact on the object
• CPC Class Codes: H01J 37/3056 for microworking, e. g. etching of gratings or trimming of electrical components

Abstract

A charged particle beam system for processing substrates is disclosed, comprising a charged particle column, combination infrared radiation and visible light illumination and imaging subsystems, in-vacuum optics, and a precision stage for supporting and positioning the substrate alternately under the charged particle column and the imaging system. The axes of the charged particle column and imaging system are offset to enable much closer working distances for both imaging and beam processing than would be possible in a single integrated assembly. A method for extremely accurately calibrating the offset between the column and imaging system is disclosed, enabling beam processing at precisely-determined locations on the substrate. The imaging system is capable of locating sub-surface features on the substrate which cannot be seen using the charged particle beam. Two illumination modes are disclosed, enabling both bright-field and dark-field imaging in infrared radiation and visible light.

Claims

1. A charged particle beam system for processing a substrate, comprising:

a charged particle column, configured to produce a beam of charged particles which can be focused on the surface of the substrate;

an in-vacuum optical subsystem, configured to collect scattered infrared radiation and visible light from the surface and regions near the surface of the substrate;

a precision stage, configured to transport the substrate alternately between a location under the in-vacuum optical subsystem and a location under the charged particle column;

an illumination subsystem, configured to provide infrared radiation and visible light to the surface of the substrate; and

an imaging subsystem, configured to focus the scattered infrared radiation and visible light collected by the in-vacuum optical subsystem onto one or more detectors.

2. The charged particle beam system of claim 1, wherein:

the illumination subsystem is configured to provide near-infrared radiation and visible light to the surface of the substrate;

the in-vacuum optical subsystem is configured to collect scattered near-infrared radiation and visible light from the surface and regions near the surface of the substrate; and

the imaging subsystem is configured to focus the scattered near-infrared radiation and visible light collected by the in-vacuum optical subsystem onto one or more detectors.

3. The charged particle beam system of claim 1, wherein the charged particle column is a focused ion beam column, and wherein the processing of the substrate is focused ion beam milling.

4. The charged particle beam system of claim 1, wherein the charged particle column is an electron beam column.

5. The charged particle beam system of claim 4, further comprising a gas feed assembly, configured to provide an etchant gas to the vicinity of the intersection of the electron beam with the substrate, and wherein the processing of the substrate is electron beam induced etching.

6. The charged particle beam system of claim 4, further comprising a gas feed assembly, configured to provide a deposition precursor gas to the vicinity of the intersection of the electron beam with the substrate, and wherein the processing of the substrate is electron beam induced deposition.

7. The charged particle beam system of claim 1, wherein the illumination subsystem comprises a single light source, configured to provide both infrared radiation and visible light.

8. The charged particle beam system of claim 1, wherein the illumination subsystem comprises:

a first light source configured to provide principally infrared radiation;

a second light source configured to provide principally visible light radiation; and

optics for combining the radiation from the first and second radiation sources into a parallel beam.

9. The charged particle beam system of claim 1, further comprising optics for directing the infrared radiation and visible light from the illumination subsystem at a glancing angle to the surface of the substrate for enabling dark-field imaging of the substrate.

10. The charged particle beam system of claim 1, further comprising optics for directing the infrared radiation and visible light from the illumination down through the in-vacuum optical subsystem at approximately normal incidence to the surface of the substrate for enabling bright-field imaging of the substrate.

11. The charged particle beam system of claim 1, further comprising a tilted vacuum viewport to reduce the amount of reflected radiation entering at least one of the detectors.

12. The charged particle beam system of claim 1 in which the imaging subsystem comprises a broad spectrum camera having a single detector that can form an image using infrared radiation or visible light.

13. The charged particle beam system of claim 1 in which the imaging subsystem comprises a single camera having two detector, one that can form an image using infrared radiation and one that can form an image using visible light.

14. The charged particle beam system of claim 1 in which the imaging subsystem comprises a first camera for forming an image using scattered infrared radiation and a second camera for forming an image using visible light.

15. A method for calibrating the distance between the axis of an optical imaging subsystem and the axis of a charged particle column, comprising the steps of:

configuring a charged particle column to produce a focused charged particle beam on a substrate surface;

configuring an optical imaging system to form an image of the substrate surface;

configuring a stage to transport the substrate alternately between a location under the optical imaging subsystem and a location under the charged particle column;

mounting the charged particle column and the optical imaging system with a fixed relative offset distance;

positioning the substrate using the stage initially under the imaging system and centering an expendable feature on the axis of the imaging subsystem;

transporting the substrate to a location under the charged particle column, where the transport distance corresponds to the expected offset between the imaging subsystem and the charged particle column;

forming a first structure on the substrate using charged particle beam processing;

transporting the substrate to a location under the imaging subsystem, where the transport distance is exactly opposite to the expected offset between the imaging subsystem and the charged particle column;

imaging the first structure formed by charged particle beam processing and determining the offset of the first structure with respect to the expendable feature, wherein the offset corresponds to the difference between the actual and the expected offset between the imaging subsystem and the charged particle column;

transporting the substrate to a location under the charged particle column, wherein the transport distance is calibrated using the offset just determined, thereby enabling the stage to position the expendable feature much more precisely under the charged particle column;

forming a second structure on the substrate using charged particle beam processing;

transporting the substrate to a location under the imaging subsystem, where the transport distance is exactly opposite to the calibrated offset between the imaging subsystem and the charged particle column;

imaging the second structure formed by charged particle beam processing, thereby verifying the accuracy of the offset calibration;

transporting the substrate to a location under the charged particle column, wherein the transport distance is modified by the offset between a critical feature to be processed and the expendable feature, thereby positioning the critical feature directly under the charged particle column; and

forming a third structure on the substrate using charged particle beam processing, wherein the third structure has the required size, shape for the desired processing, and wherein the third structure is directly above the critical feature.

16. The method of claim 15, further comprising:

a multiplicity of additional expendable features on the substrate, wherein the offsets of each of the multiplicity of expendable features with respect to a critical feature to be processed are known;

forming a multiplicity of structures above the multiplicity of expendable features on the substrate; and

imaging the multiplicity of structures, thereby verifying a correct calibration of the exact spacing between the imaging subsystem and the charged particle column.