In situ end-point detection during development of submicrometer grating structures in photoresist

Britten, Jerald A.; Boyd, Robert; Shore, Bruce W.

doi:10.1117/12.194046

Cited by 21 publications

(3 citation statements)

References 4 publications

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“…Polarization independent gratings with high diffraction efficiency are necessary in a fiber laser spectral beam combining system. e substrate [4] . I proposed a method of monitoring the diffraction efficiency ratio of the +1st order to -1st order in both TE and TM polarizations to get groove depth and duty cycle of a binary grating mask [5] .…”

Section: Introductionmentioning

confidence: 99%

In situ estimate of duty cycle of surface-relief holographic gratings during development by measuring TM/TE diffraction efficiency ratio

Shen

Zeng

2015

SPIE Proceedings

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Holographic exposure (i.e., exposure of a photoresist coated substrate in an interference field of two light beams), followed by development in alkaline solution and subsequent ion-beam etching, remains to be the most important technique for fabricating diffraction gratings, especially large-area gratings, despite the advance of other techniques. In this process as an intermediate product the photoresist grating serves as a mask for ion-beam etching. The shape and critical dimensions of the photoresist mask directly determine the shape and critical dimensions of the etched end product, which in turn determine the performance parameters of the grating. In a crude and yet often effective approximation the shape of the mask can be taken as rectangular and the critical dimension is duty cycle (ratio of ridge width to period). The groove depth is not critical, as long as it is large enough, and it can be controlled easily by adjusting the photoresist layer thickness during spin coating and by detecting the critical turning point of the diffraction efficiency curve of one of the grating's dispersive orders during development when the photoresist in the trough is completely removed. Once the maximum groove depth has been reached the following development process predominantly manifests as reduction of duty cycle. While the efficiency monitoring method is effective for detecting the point of trough clearing, it is ineffective for measuring duty cycle. A one-dimensionally periodic grating is an optically anisotropic structure when the groove period and light wavelength are comparable. Diffraction efficiencies of TE and TM polarizations are different and their ratio is a monotonic function of duty cycle in the range of duty cycle of interest. We propose to use this property to estimate the duty-cycle of surface-relief holographic gratings during development. We will present our theoretical simulation results and experimental results.

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Section: Introductionmentioning

confidence: 99%

In situ estimate of duty cycle of surface-relief holographic gratings during development by measuring TM/TE diffraction efficiency ratio

Shen

Zeng

2015

SPIE Proceedings

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“…A different application based on the above method in photoresist grating fabrication was reported thereafter 4 . All of these works did not concern quantitative measurement, but focused on controlling the qualitative features of the gratings, such as clean grating troughs 2,3 and sufficient diffraction efficiency 4 6 was employed as the analysis tool, but the experimental results were not satisfactory. By duplicating Zhao's work, we found the reason was that the thickness of the photoresist layer was not well controlled before development, inducing discrepancies between the theoretically predicted and experimental diffraction efficiency curves.…”

Section: Introductionmentioning

confidence: 99%

On-line measurement of profile parameters of rectangular holographic photoresist gratings during development

Wei

2009

SPIE Proceedings

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This paper presents a method for on-line measuring photoresist grating profiles during the development process by detecting the diffraction efficiencies of surface-relief photoresist gratings on transparent substrates. A He-Ne laser of 594.1 nm wavelength is employed as the monitoring light source. Firstly, the groove depth of a grating is determined from the minimum value of the monitoring curve of the 0 th -order transmission intensity. Then, with the groove depth known, the duty cycle of the grating is measured from the -1 st -order transmission intensity. The feasibility of our method has been demonstrated through fabrication of many rectangular photoresist gratings of 1200, 2200, and 3000 lines/mm on glass substrates. Good agreement between the on-line, real-time measured results and the scanning electron microscopy results is obtained.

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“…The substrate is then coated with a thin (≈500 nm) film of photoresist, using a meniscus coating process 8 , then baked in a convection oven overnight. The grating pattern was exposed into the photoresist layer using LLNL's large laser interference lithography station 9 , shown in Figure 2, utilizing 1.1 meter-diameter collimating lenses and 413 Kr-ion laser light. The surface relief pattern spacing d is produced in the photoresist by intersecting two plane-wave laser beams, each of exposure λ and each incident at an angle θ according to the following relationship, where φ is the angle between the normal to the substrate and the bisector of the incident laser beams.…”

Section: Grating Fabricationmentioning

confidence: 99%

Gratings for high-energy petawatt lasers

et al. 2005

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To enable high-energy petawatt laser operation we have developed the processing methods and tooling that produced both the world's largest multilayer dielectric reflection grating and the world's highest laser damage resistant gratings. We have successfully delivered the first ever 80 cm aperture multilayer dielectric grating to LLNL's Titan Intense Short Pulse Laser Facility. We report on the design, fabrication and characterization of multilayer dielectric diffraction gratings.

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In situ end-point detection during development of submicrometer grating structures in photoresist

Cited by 21 publications

References 4 publications

In situ estimate of duty cycle of surface-relief holographic gratings during development by measuring TM/TE diffraction efficiency ratio

In situ estimate of duty cycle of surface-relief holographic gratings during development by measuring TM/TE diffraction efficiency ratio

On-line measurement of profile parameters of rectangular holographic photoresist gratings during development

Gratings for high-energy petawatt lasers

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