System and method of characterizing micro-fabrication processes
A system for assessing a structure and the tools and processes used to form the structure is described. 2D images of the structure are captured and processed to obtain 3D information concerning the structure. Both 2D and 3D information is then used to identify and analyze selected characteristics of the structure. This analysis allows for a quality assessment of the structure. The selected characteristics are correlated with information relating to the operation of the tool that carried out the process that at least in part created the structure. The correlation of tool/process information to structure characteristics allows for the generation of feedback that may be used to modify the tool or processed used to form the structure.
1. A system for assessing structures formed by microfabrication processes and the microfabrication processes themselves comprising:
an imaging system comprising a camera, optics and illumination for obtaining 2D images of a structure at multiple focal positions of the imaging system relative to the structure to substantially characterize both 2D and 3D geometries of the structure;
a mechatronic support for moving the structure relative to the imaging system to address a field of view of the camera to the structure; and
a controller coupled to the imaging system and to the mechatronic support for coordinating operation thereof and for receiving images from the imaging system, for identifying in focus portions of individual received images of the structure at multiple different focal positions of the imaging system relative to the structure, for forming a concatenated image from the in focus portions of the received images, each pixel of the concatenated image having an XY position identical to its XY position in the image from which it is derived and a Z position derived from the focal position of the image from which it is derived and for identifying features of the structure in the concatenated image that are indicative of the operation of a microfabrication tool.
2. The system of claim 1 , wherein the controller is constructed and arranged to identify characteristics of the structure selected from a group consisting of: roughness, inclination, skew, pitch, height, aspect ratio, presence/absence of discontinuities, and size.
3. The system of claim 1 , wherein the controller is further programmed to:
generate a 2D model of the structure comprising at least a range of acceptable values for each pixel in the concatenated image; and
compare a subsequent test image of a structure with the 2D model on a pixel by pixel basis to identify potentially discrepant portions of the structure in the test image.
4. The system of claim 1 , wherein the controller is further programmed to:
identify a 2D location of a feature of the structure in the concatenated image;
determine a 3D characteristic of the feature of the structure using the X, Y and Z positions of the pixels that represent the feature of the structure; and
assess the characteristic of the feature of the structure to determine whether the structure satisfies a predetermined criteria.
5. The system of claim 4 , wherein the controller is further programmed to:
identify a first edge and a second edge of the structure in the concatenated image;
determine a 3D position of each of the first and second edges relative to one another; and
assess whether the relative positions of the first and second edges satisfy a predetermined geometric criteria.
6. The system of claim 5 , wherein the predetermined geometric criteria is selected from a group consisting of a vertical critical dimension, a horizontal critical dimension, a Euclidian distance, a pitch and a slope.
7. The system of claim 1 , wherein the controller is further programmed to:
identify an edge of the structure present in the concatenated image;
determine a shape in 3D space of the edge of the structure; and
assess a dimensional variability of the shape of the edge of the structure in at least one of XY, XZ, and YZ planes.
8. The system of claim 1 , wherein the controller is further programmed to:
identify a feature of interest and a fiducial feature of the structure present in the concatenated image;
determine a shape and a position in 3D space of the feature of interest of the structure relative to the fiducial feature; and
assess alignment of the feature of interest relative to the fiducial feature.
9. The system of claim 8 , wherein the controller is further programmed to:
determine an alignment between the feature of interest and the fiducial feature in at least one of XY, XZ and YZ planes.
10. The system of claim 1 , wherein the imaging system has a depth of field, and further wherein the Z position of each pixel of the concatenated image is derived from a position of the depth of field of the imaging system for the individual received image otherwise providing an in-focus pixel from which a corresponding pixel of the concatenated image is derived.
11. The system of claim 10 , wherein the Z position of each pixel of the concatenated image is assigned an error related to a size of the depth of field of the imaging system.
12. The system of claim 1 , wherein the imaging system is configured to provide greyfield illumination of the structure.