Improving hole circularity via electro-optic beam modulation

Abstract

The present disclosure describes a system and method for providing electro-optical beam modulation to improve circularity in F-theta applications. The disclosed system utilizes an optical system, a Pockel cell, and a polarization control device. The optical system focuses a laser beam onto a workpiece to generate multiple spots within an optical field. The fast axis of the Pockel cell is aligned orthogonally to the corner of the optical field. The polarization control device reduces the circularity mismatch of the multiple spots by adjusting the polarization of the laser beam.

Description

Technology Field

[0001] The present application claims priority and benefit to U.S. provisional patent application No. 63 / 552,493, filed February 12, 2024, titled “ELECTRO-OPTIC BEAM MODULATION FOR IMPROVED CIRCULARITY IN F-THETA APPLICATIONS,” the entirety of which is incorporated herein by reference. Background Technology

[0002] The limitations and disadvantages of conventional electro-optic modulators (EOMs) will become apparent to those skilled in the art through a comparison of this approach with some aspects of the method and system described in the remainder of this disclosure with reference to the drawings.

[0003] The system and method provide electro-optical beam modulation for improved circularity in F-Theta applications, as more fully described in the claims, substantially as illustrated by and / or described in connection with at least one of the drawings. Brief explanation of the drawing

[0004] FIG. 1 illustrates an exemplary EOM system for improved prototyping in F-theta applications according to various exemplary implementations of the present disclosure. FIG. 2 illustrates examples of hole distortion and hole refinement according to various exemplary embodiments of the present disclosure. Specific details for implementing the invention

[0005] The following discussion provides various examples of systems and methods for improving circularity in F-theta applications using electro-optical beam modulation. These examples are not limiting, and the scope of the appended claims should not be limited to the specific examples disclosed. In the following discussion, the terms “examples” and “e.g.” are non-limiting.

[0006] The drawings illustrate general configurations, and descriptions and details regarding well-known features and technologies may be omitted to avoid unnecessarily obscuring the present disclosure. Additionally, elements within the drawings are not necessarily drawn to scale. For example, to aid in understanding the examples discussed in this disclosure, the dimensions of some elements in the drawings may be exaggerated compared to others. Identical reference numbers in different drawings indicate identical elements.

[0007] The term “or” means any one or more of the items in the list connected by “or”. For example, “x or y” means any element of the set of 3 elements {(x), (y), (x, y)}. As another example, “x, y or z” means any element of the set of 7 elements {(x), (y), (z), (x, y), (x, z), (y, z), (x, y, z)}.

[0008] The terms “comprise,” “comprised,” “include,” and / or “included” are “open” terms that specify the presence of the described feature but do not exclude the presence or addition of one or more other features.

[0009] Terms such as “first,” “second,” etc., may be used herein to describe various elements, and these elements should not be limited by these terms. Such terms are used solely to distinguish one element from another. Accordingly, for example, the first element discussed in this disclosure may be referred to as the second element without departing from the teachings of this disclosure.

[0010] Unless otherwise specified, the term “coupled” may be used to describe two elements in direct contact with each other, or two elements connected indirectly by one or more other elements. For example, if element A is coupled to element B, element A may be in direct contact with element B or connected indirectly to element B by an intervening element C. Similarly, the terms “on” or “on” may be used to describe two elements in direct contact with each other, or two elements connected indirectly by one or more other elements.

[0011] Light is a fundamental phenomenon with diverse characteristics and applications, spanning the electromagnetic spectrum from radio waves to gamma rays. While the human eye perceives only the visible spectrum, light extends beyond this range to include longer wavelengths, such as infrared, and shorter wavelengths, such as ultraviolet and X-rays. These variations in wavelength correspond to changes in energy and provide unique interactions with materials, enabling specialized technologies. For example, long-wave infrared (LWIR) light, characterized by lower energy and longer wavelengths compared to visible light, plays a significant role in fields such as imaging, industrial processing, and advanced optical instruments.

[0012] The primary property of light is polarization, which is the orientation of the electric field in space. Polarization can appear linear, circular, or elliptical depending on the interaction between the light wave and the material or filter. This characteristic is particularly important when working with coherent light sources, such as lasers, which propagate in a uniform direction and exhibit consistent wavelength and polarization. The ability to manipulate polarization can enable precise control over light for applications such as optical switching and modulation.

[0013] Electro-optical effects, specifically the Pockels effect, are central to the operation of electro-optical modulators (EOMs) that allow for dynamic control of optical polarization. This effect occurs in certain non-central symmetry crystals, where an applied electric field induces a change in the refractive index, thereby altering the polarization state of the transmitted light. Materials such as cadmium telluride (CdTe), gallium arsenide (GaAs), zinc selenide (ZnSe), zinc sulfide (ZnS), and boron arsenide (BAs) are some of the materials capable of supporting this effect in the LWIR and mid-wave infrared (MWIR) spectra due to their specific optical and structural properties.

[0014] The Pockel cell, a key component of the EOM, utilizes these electro-optical materials to modulate light at high speeds without moving parts. By applying voltage across the crystal, the birefringence of the material can be controlled, thereby enabling phase modulation of the laser beam with nanosecond precision. This capability is important in advanced applications such as extreme ultraviolet (EUV) lithography, where precise timing and modulation of light are essential for producing state-of-the-art microchips.

[0015] The present disclosure relates to a system and method for controlling optical polarization to improve precision in laser drilling, particularly to applications requiring consistent hole circularity, such as microchip substrate processing. The present disclosure utilizes electro-optical modulation to resolve the ellipticity of a laser beam spot caused by optical aberrations in a scanning system, thereby enabling improved control and uniformity in laser-drilled features.

[0016] F-theta lenses can be used in laser systems for precision drilling due to their ability to maintain a constant focal length across the scanning field. However, when a laser passes through such a lens, the resulting beam spot often exhibits elliptical distortion, particularly at the edges of the scanning field. This distortion results in inconsistencies in the drilled holes, which is unacceptable in high-precision applications such as microchip substrate processing. Conventional approaches can use circularly polarized light to mitigate this distortion and achieve uniformity, but limit flexibility in compensating for material or process-specific requirements.

[0017] The disclosed electro-optical modulation (EOM) system dynamically controls the polarization state of a laser beam to correct the ellipticity at the laser spot. By adjusting polarization to offset elliptical distortion at different scan field positions, the system can achieve consistent hole circularity across the entire field. Unlike previous methods, this system allows the use of linearly or elliptically polarized light tailored to specific locations on the scan field, enabling compensation without compromising beam quality or cutting efficiency.

[0018] FIG. 1 illustrates an exemplary EOM system (100) for improved circularity in F-theta applications according to various exemplary embodiments of the present disclosure. Referring to FIG. 1, the EOM system (100) comprises a polarization control device (101), one or more Pockel cells (103), a Galvo mirror (105), and an F-theta lens (107).

[0019] The polarization control device (101) can be operated for initial polarization adjustment. The polarization control device (101) may include, for example, a thin film polarizer, a Fresnel rhomb, a Faraday rotator, a wire grid polarizer and / or a polarization-dependent chromatic dispersion (PCD) wave plate.

[0020] One or more pokel cells (103) can enable dynamic polarization changes according to an applied electric field. One or more pokel cells (103) are configured so that their fast axes are aligned in a specific direction. The pokel cells (103) can be configured to dynamically change beam polarization (111, 113, 115) in response to voltage changes. This capability compensates for spot ellipticity at different scan field positions, as illustrated in FIG. 2.

[0021] To achieve optimal results, the polarization control device (101) and the Pockel cell (103) may need to be aligned with the scan field geometry. Additional optical components, such as a Faraday rotator or a Fresnel ROM, may be integrated to extend the range of polarization adjustment. The system is compatible with CO2 lasers and other laser types operating in the long-wave infrared spectrum, providing flexibility in material processing.

[0022] The galvo mirror (105) can enable beam steering across the scan field. The F-theta lens (107) can maintain focus consistency. The EOM system (100) can be used for workpieces (109), such as microchip substrates, that require precision hole drilling.

[0023] FIG. 2 illustrates examples of hole distortion and hole refinement according to various exemplary embodiments of the present disclosure. FIG. 2 illustrates how the system (100) (of FIG. 1) resolves spot distortion. The beam spot (203) at the edge of the scan field often exhibits an elliptical shape due to lens aberrations. The system (100) (of FIG. 1) can effectively round the drilled hole (207) by modifying the polarization axis of the beam to be orthogonal to the major axis of the ellipse. This process can be achieved by dynamically adjusting the voltage across the Pockel cell (103) (of FIG. 1), which changes the polarization state of the light. The resulting rounded spot (205) can ensure uniform cutting across the scan field.

[0024] The disclosed system and method can enable dynamic polarization control. Unlike a static polarizer, the system allows for continuous adjustment of polarization, thereby enabling customized compensation for aberrations at different scan positions.

[0025] The disclosed system and method can improve hole circularity. By aligning polarization with elliptical distortion, the system can consistently generate circular holes even at the edges of the scan field.

[0026] The disclosed system and method can improve flexibility. The system can support various polarization states, including linear, elliptical, and circular, to accommodate different materials and applications.

[0027] The disclosed system does not require moving parts. The use of electro-optical modulation eliminates the need for mechanical components, ensuring high-speed operation and reliability.

[0028] The disclosed system and method are suitable for hole drilling on microchip substrates where precision and consistency are important. However, the disclosed system can also be applied to any application requiring high-precision laser drilling, such as industrial cutting, medical device manufacturing, and optical component manufacturing.

[0029] The disclosed system and method represent an advancement in laser drilling technology and provide control over polarization to correct spot ellipticity and improve hole circularity. By combining electro-optical modulation with advanced optical instruments, the disclosed system and method solve challenges in precision manufacturing, enabling performance and reliability.

[0030] Although the present method and / or system has been described with reference to a specific implementation, those skilled in the art will understand that various modifications may be made and equivalents replaced without departing from the scope of the present method and / or system. Furthermore, without departing from its scope, many modifications may be made to adapt a specific situation or material to the teachings of the present disclosure. Accordingly, the present method and / or system is not limited to the specific implementation disclosed, and the present method and / or system is intended to include all implementations falling within the scope of the appended claims.

Claims

Claim 1 A system comprising: an optical system configured to focus a laser beam on a workpiece to generate a plurality of spots within an optical field; a Pockels cell configured to align a fast axis orthogonal to a corner of the optical field; and a polarization control device configured to reduce circularity inconsistencies of the plurality of spots by adjusting the polarization of the laser beam. Claim 2 A system comprising a plurality of Pockel cells in claim 1. Claim 3 A system according to claim 1, wherein the polarization control device comprises a thin-film polarizer. Claim 4 A system according to claim 1, wherein the optical system comprises an F-theta lens. Claim 5 A system according to claim 1, wherein the parameters of the laser beam are adjusted according to the material absorption of the workpiece. Claim 6 A system according to claim 1, wherein the wavelength of the laser beam is in the mid-wave infrared (MWIR) spectrum. Claim 7 A system according to claim 1 configured to compensate for distortion in a rectangular scan field. Claim 8 A system according to claim 1, wherein the polarization is adaptively adjusted according to real-time feedback. Claim 9 A system according to claim 1, wherein the system comprises a computer numerical control (CNC) machine. Claim 10 A system according to claim 1, wherein the polarization control device comprises a Faraday rotator. Claim 11 A method comprising the steps of: aiming a laser beam at a workpiece to create a plurality of spots within an optical field; aligning the fast axis of a forkel cell orthogonally to a corner of the optical field; adjusting the polarization of the laser beam according to the misalignment of the plurality of spots; and drilling holes according to the plurality of spots. Claim 12 A method according to claim 11, comprising the step of aligning the rapid axes of a plurality of Pockel cells. Claim 13 A method according to claim 11, wherein a thin film polarizer is configured to adjust the polarization of the laser beam. Claim 14 A method according to claim 11, wherein the F-theta lens is configured to direct the laser beam. Claim 15 A method according to claim 11, comprising the step of adjusting the parameters of the laser beam according to the material absorption of the workpiece. Claim 16 A method according to claim 11, wherein the wavelength of the laser beam is in the mid-wave infrared (MWIR) spectrum. Claim 17 A method according to claim 11, wherein the step of adjusting the polarization of the laser beam is to compensate for distortion in a rectangular scan field. Claim 18 A method according to claim 11, wherein the polarization is adaptively adjusted according to real-time feedback. Claim 19 A method according to claim 11, wherein a computer numerical control (CNC) machine is configured to drill the hole. Claim 20 A method according to claim 11, wherein a Faraday rotator is configured to adjust the polarization of the laser beam.

Images