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Illuminators for Microlithography
Published in Fred M. Dickey, Scott C. Holswade, David L. Shealy, Laser Beam Shaping Applications, 2018
All lithographic projection lenses are designed to be telecentric on the image side, in order to maintain the same magnification through the DOF (Figure 1.2). A telecentric lens in the most basic terms is defined as one that has the chief ray normal at the image plane. This is the ray that emits from the edge of the field and passes through the center of the aperture stop. In more precise terms, it is the illuminator’s angular radiance distribution at the wafer that defines the telecentricity of imaging at the wafer. Typically, the projection lens has insignificant variations over the imaging field, so it is the illuminator that determines the degree of telecentricity correction. This is discussed in greater detail in Section II.C and Section III.E. The illuminator not only maintains the magnification of the image through the DOF, but can also increase the depth by tailoring the pupil profile for the specific objects being imaged. This is discussed in more detail in Section II.D. The DOF along with the exposure latitude defines the total process window. In the absence of other factors, the process window is usually illustrated as an exposure defocus (ED) window. Factors such as reticle flatness, wafer flatness, thermal drift, aberration correction of the projection lens, flare, and other characteristics can reduce the DOF. A larger ED window generally means a more robust lithography process and more wafers per hour.
Illuminators for Microlithography
Published in Fred M. Dickey, Todd E. Lizotte, Laser Beam Shaping Applications, 2017
In order to maintain the same magnification through the DOF, lithographic projection lenses are designed to be telecentric on the image side (Figure 2.2). A telecentric lens, in the most basic terms, is defined as one that has the chief ray normal at the image plane. This is the ray that emits from the edge of the field and passes through the center of the aperture stop. In more precise terms, it is the illuminator’s angular radiance distribution at the wafer that defines the telecentricity of imaging at the wafer. Typically, the projection lens has insignificant NA variations over the imaging field, so it is the illuminator that determines the degree of telecentricity correction. This is discussed in greater detail in Sections 2.2.3 and 2.3.5. The illuminator not only maintains the magnification of the image through the DOF, but can also increase the depth by tailoring the pupil profile for the specific objects being imaged. This is discussed in more detail in Section 2.2.4. The DOF along with the exposure latitude defines the total process window. In the absence of other factors, the process window is usually illustrated as an exposure defocus (ED) window. Factors such as reticle flatness, wafer flatness, thermal drift, aberration correction of the projection lens, flare, and other characteristics can reduce the DOF. A larger ED window means a more efficient and robust lithography process.
Industrial Machine Vision
Published in Richard L. Shell, Ernest L. Hall, Handbook of Industrial Automation, 2000
Telecentric lens systems have the characteristic that the size of the image does not vary as the scene is moved toward or away from the lens, within limits. Thus they have an advantage in making measurements or matching reference shapes in those cases where the image is likely to vary in distance. They also have an advantage in that if the object of interest is in different places in the FOV there is no prospective distortion or occluding of the image. For instance, one can look right down a hole, even if the hole is not on the optical axis. These lens systems still have depth-of-field limitations and light-gathering limitations based on F-stop values. Because the optics diameter must encompass the entire FOV, telecentric optics are most practical from a cost standpoint for smaller FOV, including particularly microscopes, where the image on the CCD is larger than the actual scene.
A dual-projector three-dimensional measurement model for shading problem of micro-scale object complex surface
Published in Journal of Modern Optics, 2023
Cheng Gui, Huikai Zhong, Yanjun Fu, Kejun Zhong, Baiheng Ma, Zhanjun Yan
According to the properties of orthogonal projection telecentric lens, the presence of the object to be tested in 2D coordinates (x, y) of analyte taken by a camera and the image pixel coordinates (u, v) for fixed magnification of linear relationship between (within the scope of a certain height), so in the face of the object to be tested coordinates can be directly by the pixel coordinates through linear transformation. Finally, the three-dimensional coordinates (x, y, z) of the object can be obtained by combining the phase-height relationship. According to the above phase – height relationship, the microscopic 3D measurement model for double telecentric fringe projection only needs to calibrate the horizontal fringe spacing and the angle included angle α between the projector's optical axis and the camera's optical axis to solve the Z height coordinate of the measured object, calibrate the magnification of the telecentric camera m to solve the in-plane coordinates (x, y) of the measured object, and finally get the three-dimensional coordinates of the measured object.