Research on a New Lithography Method Utilizing Laser Speckles for Printing Random Patterns

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Simple and low-cost optical lithography method utilizing speckles was researched for printing random patterns on wafer surfaces coated with thick resist films. Patterning characteristics were investigated using a handmade exposure system. In the system, a laser beam was irradiated on a transparent diffuser plate, and generated speckles were projected onto a wafer coated with 50-100 μm thick resist. As a result, the resist was sensitized, and patterns with random needle-like shapes were formed after development. Pattern sizes were between several microns and several hundred microns. The sizes and number of patterns were controllable by adjusting the exposure time. It was demonstrated also that the pattern sizes and the number of patterns were varied by changing the distance between the diffuser plate and the wafer. Maximum aspect ratios for various exposure conditions were also investigated. Although patterns were inclined or curved, very high aspect ratio of 14 was obtained for a 100-μm thick resist film.

Section: Methods Of Exposure Utilizing Specklesmentioning

confidence: 99%

“…As a related research, speckle lithography has been reported to be applied to creation of nonreflective silicon structures [28]. Authors have also demonstrated the feasibility of random hole patterning using the speckle lithography [29].…”

Section: Introductionmentioning

confidence: 98%

Printing of Random Needle-like Resist Patterns Utilizing Laser Speckle Lithography

Kobayashi,

Kataoka,

Komiya

et al. 2024

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Miniaturization of Scattered Random Patterns Formed by Lens·less Speckle Lithography

Iwaoka,

Horiuchi,

Kobayashi

2023

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A new method without using a projection lens for easily and inexpensively forming random micro-patterns on large area surfaces and three-dimensional shapes such as steps and curved surfaces was developed in the past research. In the method named "Speckle lithography", speckle light was used for forming scattered random patterns on surfaces coated with a resist film. In this paper, further miniaturization of patterns was investigated. In a renovated handmade exposure system, the beam diameter of laser beam irradiated to the diffusion plate was expanded from 4 mm to 17 mm using a beam expander. And, the distance between the diffusion plate and the wafer was shortened from 45 mm to 1 mm. As a result, random dot resist patterns with a minimum size of 1 μm or less were successfully formed on entire exposed areas limited to 10×10 mm.

Printing of Random Patterns on Stepped Surfaces Using Speckle Lithography

Kikuchi,

Taura,

et al. 2024

Speckle lithography has the potential to print random micro-patterns over an area of 10 mm 2 without using a projection lens. In this paper, this speckle lithography technique was used for basically researching on how to print random patterns on stepped surfaces. Experiments were conducted based on the idea that patterns could be printed over a wide area in the depth direction simultaneously if the speckle light generated by irradiating a laser beam onto a diffuser plate is collimated by a lens. Collimating lenses with various focal lengths were used in the experiment. As a result, it was found that almost same patterns were formed on a silicon wafer coated with 1 µm thick resist when the distance between the collimating lens and the wafer was changed between 40 and 200 mm under the same exposure time condition.