A comprehensive review on convex and concave corners in silicon bulk micromachining based on anisotropic wet chemical etching

Pal, Prem; Sato, Kazuo

doi:10.1186/s40486-015-0012-4

Cited by 96 publications

(83 citation statements)

References 164 publications

(197 reference statements)

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“…The photolithographic mask, shown in Figure b, was composed of a periodic lattice ( p = 1.8 mm) of squares 1.404 × 1.404 mm 2 in size. It is well known that the etching in alkali solution of <100> oriented silicon wafers protected by a crystallographically aligned square or rectangular SiO 2 mask results in convex corner undercutting unless compensation techniques are employed . In our specific case, the undercutting is intentionally exploited to produce dodecagonal or octagonal features.…”

Section: Experimental Demonstration Of a Silicon Metasurface With Submentioning

confidence: 99%

All‐Dielectric Silicon Metasurface with Strong Subterahertz Toroidal Dipole Resonance

Zografopoulos

Ferraro

Algorri

et al. 2019

Advanced Optical Materials

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properties of propagating electromagnetic waves, such as wave front, polarization, intensity, or spectrum, in ways unachievable by bulk materials of the same subwavelength thickness. [1][2][3] The constituent elements of a metasurface can be either metallic or dielectric and they are usually patterned on a low-loss, dielectric substrate. All-dielectric metasurfaces, in particular, which are composed of elements made of a high-refractive index dielectric material, have been lately attracting more attention, as they show a very high diversity of exploitable properties, while being free from ohmic losses associated with the presence of metals. [4] The potential of dielectric metasurfaces as a platform for low-loss, compact, functional components has been extensively demonstrated in numerous applications, such as reflection/refraction control and wave-front shaping, [5][6][7][8] lensing, [9] control of light emission [10,11] or photoluminescence, [12,13] polarization control [14,15] and polarimetry, [16] generation of vortex beams, [17] highly selective filtering, [18,19] or enhancement of nonlinear processes. [20,21] In addition to offering novel solutions in practical applications, metasurfaces can also provide insight in theoretical physics, optics, and the investigation of phenomena based on particular light-matter interaction conditions. One such case is that of toroidal modes, which have been under intense investigation, thanks to their unusual electromagnetic properties. The toroidal dipole, the simplest toroidal mode, is generated by a current flowing in a solenoid, which is bent into a torus. Under certain conditions, the excitation of the toroidal dipole can interfere destructively with the electric dipole mode and cancel the far-field scattering radiation of dielectric particles, in the so-called "anapole" state. [22] Since decades ago, toroidal modes were employed in physics, for instance, to explain the parity violation of the weak interactions in atomic nuclei, [23] to propose models of stable atoms, [24] or to describe dark matter. [25] In recent years, though, the interest on electromagnetic toroidal moments is rapidly increasing as, apart from the fundamental physical insight, they can be harnessed in numerous applications. [26,27] Toroidal modes in individual dielectric particles or small clusters have been theoretically proposed for the excitation of toroidal response, [28] cloaking, [29] enhanced absorption, [30] and nanolasing [31] or experimentally demonstrated as nonradiating sources [32] and for the enhancement of nonlinear effects. [33,34] Moreover, it A single-layer, all-dielectric metasurface exhibiting a strong toroidal resonance in the low-atmospheric loss radio window of the subterahertz W-band is theoretically proposed and experimentally demonstrated. The metasurface is fabricated on a high-resistivity floating-zone silicon wafer by means of a singleprocess, wet anisotropic etching technique. The properties of the toroidal mode of both the constituent dielectric elements and the metasur...

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Section: Experimental Demonstration Of a Silicon Metasurface With Submentioning

confidence: 99%

All‐Dielectric Silicon Metasurface with Strong Subterahertz Toroidal Dipole Resonance

Zografopoulos

Ferraro

Algorri

et al. 2019

Advanced Optical Materials

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“…Undercutting rate increases as the concentration of NH 2 OH increases up to 15% NH 2 OH and is around four times more than that in pure 20 wt% KOH. The undercutting at convex corners takes place mainly due to the emergence of high index planes [29,[46][47][48][49][50][51][52]. The main reason behind the increase in undercutting is the increase of the etch rate of high index planes appearing at convex corners during etching process.…”

Section: Undercutting At Convex Cornermentioning

confidence: 99%

“…Although both types of corners (concave and convex) are shaped by the intersection of {111} planes, they have opposite etching characteristics. Concave corners do not encounter any kind of undercutting, while convex corners face severe undercutting, depending on the type of etchant, in all kinds of alkaline solutions [46][47][48][49][50][51][52]. Si{110} wafer is a primary choice when the microstructures with vertical sidewalls formed by {111} planes are fabricated using wet anisotropic etching [28][29][30][31][32][33][34]52].…”

Section: Undercutting At Convex Cornermentioning

confidence: 99%

Etching characteristics of Si{110} in 20 wt% KOH with addition of hydroxylamine for the fabrication of bulk micromachined MEMS

Rao

Swarnalatha

Pal

2017

Micro and Nano Syst Lett

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Anisotropic wet etching is a most widely employed for the fabrication of MEMS/NEMS structures using silicon bulk micromachining. The use of Si{110} in MEMS is inevitable when a microstructure with vertical sidewall is to be fabricated using wet anisotropic etching. In most commonly employed etchants (i.e. TMAH and KOH), potassium hydroxide (KOH) exhibits higher etch rate and provides improved anisotropy between Si{111} and Si{110} planes. In the manufacturing company, high etch rate is demanded to increase the productivity that eventually reduces the cost of end product. In order to modify the etching characteristics of KOH for the micromachining of Si{110}, we have investigated the effect of hydroxylamine (NH 2 OH) in 20 wt% KOH solution. The concentration of NH 2 OH is varied from 0 to 20% and the etching is carried out at 75 °C. The etching characteristics which are studied in this work includes the etch rates of Si{110} and silicon dioxide, etched surface morphology, and undercutting at convex corners. The etch rate of Si{110} in 20 wt% KOH + 15% NH 2 OH solution is measured to be four times more than that of pure 20 wt% KOH. Moreover, the addition of NH 2 OH increases the undercutting at convex corners and enhances the etch selectivity between Si and SiO 2 .

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“…The zoomed view shows that there is no underetching and oversizing (or additional overhang) when the mask is accurately aligned with ⟨110⟩ direction, while additional overhang occurs due to the misalignment of mask patterns. The additional overhanging leads to coupling between adjacent beams including wet etching [8,100], dry etching [21], microvalves [92], micropumps [95,97], microfluidics [101], etc., there is no review article till date which extensively discusses various techniques to identify different crystallographic directions on silicon wafers along with their associated pros and cons. Given the importance of precise alignment as discussed above, it is very important to understand the role of alignment as well as the methodologies to ensure precise mask alignment.…”

Section: Diaphragmmentioning

confidence: 99%

“…These arrays are fabricated either by front side etching or backside etching. In order to fabricate using front side etching, the phenomenon of convex corer undercutting is used for their release from substrate [8,100]. Etching stops when it encounters the {111} planes at the anchoring point of the beam.…”

Section: Cantilever Beamsmentioning

confidence: 99%

Determination of precise crystallographic directions for mask alignment in wet bulk micromachining for MEMS

Singh

Pal

Pandey

et al. 2016

Micro and Nano Syst Lett

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In wet bulk micromachining, the etching characteristics are orientation dependent. As a result, prolonged etching of mask openings of any geometric shape on both Si{100} and Si{110} wafers results in a structure defined by the slowest etching planes. In order to fabricate microstructures with high dimensional accuracy, it is vital to align the mask edges along the crystal directions comprising of these slowest etching planes. Thus, precise alignment of mask edges is important in micro/nano fabrication. As a result, the determination of accurate crystal directions is of utmost importance and is in fact the first step to ensure dimensionally accurate microstructures for improved performance. In this review article, we have presented a comprehensive analysis of different techniques to precisely determine the crystallographic directions. We have covered various techniques proposed in the span of more than two decades to determine the crystallographic directions on both Si{100} and Si{110} wafers. Apart from a detailed discussion of each technique along with their design and implementation, we have provided a critical analysis of the associated constraints, benefits and shortcomings. We have also summed up the critical aspects of each technique and presented in a tabular format for easy reference for readers. This review article comprises of an exhaustive discussion and is a handy reference for researchers who are new in the field of wet anisotropic etching or who want to get abreast with the techniques of determination of crystal directions.

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A comprehensive review on convex and concave corners in silicon bulk micromachining based on anisotropic wet chemical etching

Cited by 96 publications

References 164 publications

All‐Dielectric Silicon Metasurface with Strong Subterahertz Toroidal Dipole Resonance

All‐Dielectric Silicon Metasurface with Strong Subterahertz Toroidal Dipole Resonance

Etching characteristics of Si{110} in 20 wt% KOH with addition of hydroxylamine for the fabrication of bulk micromachined MEMS

Determination of precise crystallographic directions for mask alignment in wet bulk micromachining for MEMS

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