Speckle in optical lithography and its influence on linewidth roughness

Noordman, O.F.J.

doi:10.1117/1.3256131

Cited by 14 publications

(5 citation statements)

References 4 publications

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“…Speckle noise is detrimental to full-field imaging applications such as displays [3], microscopy, optical coherence tomography, and holography [4]. It also poses as a problem for laserbased applications like material processing, photolithography [5], and optical trapping of particles [6].Various approaches to mitigate speckle artifacts have been developed. A traditional method is to average over many independent speckle patterns generated by a moving diffuser [7,8], colloidal solution [9], or fast scanning micromirrors [10].…”

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Electrically pumped semiconductor laser with low spatial coherence and directional emission

Kim

Bittner

Zeng

et al. 2019

Applied Physics Letters

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We design and fabricate an on-chip laser source that produces a directional beam with low spatial coherence. The lasing modes are based on the axial orbit in a stable cavity and have good directionality. To reduce the spatial coherence of emission, the number of transverse lasing modes is maximized by fine-tuning the cavity geometry. Decoherence is reached in a few nanoseconds. Such rapid decoherence will facilitate applications in ultrafast speckle-free full-field imaging.The high spatial coherence of conventional lasers can introduce coherent artifacts due to uncontrolled diffraction, reflection and optical aberration. A common example is the speckle formed by the interference of coherent waves with random phase differences [1,2]. Speckle noise is detrimental to full-field imaging applications such as displays [3], microscopy, optical coherence tomography, and holography [4]. It also poses as a problem for laserbased applications like material processing, photolithography [5], and optical trapping of particles [6].Various approaches to mitigate speckle artifacts have been developed. A traditional method is to average over many independent speckle patterns generated by a moving diffuser [7,8], colloidal solution [9], or fast scanning micromirrors [10]. However, the generation of a series of uncorrelated speckle patterns is time-consuming and limited by the mechanical speed. A more efficient approach is to design a multimode laser that generates spatially incoherent emission, thus directly suppressing speckle formation [11]. Low spatial coherence necessitates lasing in numerous distinct spatial modes with independent oscillation phases. For example, a degenerate cavity [12][13][14] allows a large number of transverse modes to lase, but the setup is bulky and hard to align. Complex lasers with compact size such as random lasers [15][16][17][18] have low spatial coherence and high photon degeneracy, but are mostly on optically pumped. For speckle-free imaging applications, wave-chaotic semiconductor microlasers [19] have the advantages of electrical pumping and high internal quantum efficiency. However, disordered or wave-chaotic cavity lasers typically have no preferential emission direction, and the poor collection efficiency greatly reduces their external quantum efficiency. Our goal is creating an electrically pumped multimode semiconductor microlaser without disordered or wave-chaotic cavity to combine low spatial coherence and directional emission.Moreover, the speed of speckle suppression is crucial for imaging applications. For instance, time-resolved optical imaging to observe fast dynamics requires specklefree image acquisition with a short integration time, so * hui.cao@yale.edu the oscillation phases of different spatial lasing modes must completely decorrelate during the integration time to attain decoherence. The finite linewidth ∆ν of individual lasing modes leads to their decoherence on a time scale of 1/∆ν. The frequency difference between different lasing modes can lead to even faster decoherence....

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confidence: 99%

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confidence: 99%

Electrically pumped semiconductor laser with low spatial coherence and directional emission

Kim

Bittner

Zeng

et al. 2019

Applied Physics Letters

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“…However, due to the coherence of the collimated laser, speckles appear and influence the quality of the lithographic structures [17,18]. In order to minimize the speckle effect, various techniques have been applied, e.g., multiple exposure [19], or the use of a rotating, holographic diffuser [20] to reduce the spatial coherence of the laser light.…”

Section: Lau Effect For Optical Lithographymentioning

confidence: 99%

Lau Effect Using LED Array for Lithography

2021

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Illumination with LEDs is of increasing interest in imaging and lithography. In particular, compared to lasers, LEDs are temporally and spatially incoherent, so that speckle effects can be avoided by the application of LEDs. Besides, LED arrays are qualified due to their high optical output power. However, LED arrays have not been widely used for investigating optical effects, e.g., the Lau effect. In this paper, we propose the application of an LED array for realizing the Lau effect by taking into account the influence of the coherence properties of illumination on the Lau effect. Using spatially incoherent illumination with the LED array or a single LED, triangular distributed Lau fringes can be obtained. We apply the obtained Lau fringes in the optical lithography to produce analog structures. Compared to a single LED, the Lau fringes using the LED array have significantly higher intensities. Hence, the exposure time in the lithography process is largely reduced.

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“…It can originate from a myriad of factors such as the photon or chemical shot noise, molecular stacking, development process, and low image contrast [1,[13][14][15][16][17][18][19][20][21]. Recently, mask roughness gained significant attention as one of the contributors to the wafer LER [2-9, 22, 23].…”

Section: Introductionmentioning

confidence: 99%

Mitigating mask roughness via pupil filtering

et al. 2014

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The roughness present on the sidewalls of lithographically defined patterns imposes a very important challenge for advanced technology nodes. It can originate from the aerial image or the photoresist chemistry/processing [1]. The latter remains to be the dominant group in ArF and KrF lithography; however, the roughness originating from the mask transferred to the aerial image is gaining more attention [2-9], especially for the imaging conditions with large mask error enhancement factor (MEEF) values. The mask roughness contribution is usually in the low frequency range, which is particularly detrimental to the device performance by causing variations in electrical device parameters on the same chip [10][11][12]. This paper explains characteristic differences between pupil plane filtering in amplitude and in phase for the purpose of mitigating mask roughness transfer under interference-like lithography imaging conditions, where onedirectional periodic features are to be printed by partially coherent sources. A white noise edge roughness was used to perturbate the mask features for validating the mitigation.

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Speckle in optical lithography and its influence on linewidth roughness

Cited by 14 publications

References 4 publications

Electrically pumped semiconductor laser with low spatial coherence and directional emission

Electrically pumped semiconductor laser with low spatial coherence and directional emission

Lau Effect Using LED Array for Lithography

Mitigating mask roughness via pupil filtering

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