A simple and robust model to explain convex corner undercutting in wet bulk micromachining

Pal, Prem; Singh, Sajal

doi:10.1186/2213-9621-1-1

Cited by 23 publications

(19 citation statements)

References 28 publications

(44 reference statements)

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“…Hence the fabrication of structures with protected convex corner is a tedious task for both {100} and {110} silicon wafers. The mechanism of undercutting [79][80][81][82][83][84][85][86][87] and the fabrication of convex corners [24, are widely investigated. Although we have published a review article in 2007 on the fabrication of convex corners, it covers the techniques reported upto 2005 for Si{100} wafers only [109].…”

Section: Introductionmentioning

confidence: 99%

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

Pal

Sato

2015

Micro and Nano Syst Lett

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Section: Introductionmentioning

confidence: 99%

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

Pal

Sato

2015

Micro and Nano Syst Lett

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“…The silicon atoms at concave corners do not contain any break bond and therefore the shape of concave corner is not distorted. Recently, a simple model is developed to describe the etching characteristics of concave and convex corners on {100} and {110} surfaces in all kinds of wet anisotropic etchants [79,87]. This model is based on the etching behavior of the tangent planes at the convex edge and the role of dangling bonds in etching process.…”

Section: Why Does Undercutting Starts At Convex Corners?mentioning

confidence: 99%

“…The orientation of the facets appearing at the convex corners mainly depend on types of etchant, concentration and additives [79][80][81][82][83][84][85][86][87]. The etching time and temperature also affect the shape and orientation of beveled planes.…”

Section: Figure 19mentioning

confidence: 99%

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

Pal¹,

Sato²

2016

Nano Online

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Wet anisotropic etching based silicon micromachining is an important technique to fabricate freestanding (e.g. cantilever) and fixed (e.g. cavity) structures on different orientation silicon wafers for various applications in microelectromechanical systems (MEMS). {111} planes are the slowest etch rate plane in all kinds of anisotropic etchants and therefore, a prolonged etching always leads to the appearance of {111} facets at the sidewalls of the fabricated structures. In wet anisotropic etching, undercutting occurs at the extruded corners and the curved edges of the mask patterns on the wafer surface. The rate of undercutting depends upon the type of etchant and the shape of mask edges and corners. Furthermore, the undercutting takes place at the straight edges if they do not contain {111} planes. {100} and {110} silicon wafers are most widely used in MEMS as well as microelectronics fabrication. This paper reviews the fabrication techniques of convex corner on {100} and {110} silicon wafers using anisotropic wet chemical etching. Fabrication methods are classified mainly into two major categories: corner compensation method and two-steps etching technique . In corner compensation method, extra mask pattern is added at the corner. Due to extra geometry, etching is delayed at the convex corner and hence the technique relies on time delayed etching. The shape and size of the compensating design strongly depends on the type of etchant, etching depth and the orientation of wafer surface. In this paper, various kinds of compensating designs published so far are discussed. Two-step etching method is employed for the fabrication of perfect convex corners. Since the perfectly sharp convex corner is formed by the intersection of {111} planes, each step of etching defines one of the facets of convex corners. In this method, two different ways are employed to perform the etching process and therefore can be subdivided into two parts. In one case, lithography step is performed after the first step of etching, while in the second case, all lithography steps are carried out before the etching process, but local oxidation of silicon (LOCOS) process is done after the first step of etching. The pros and cons of all techniques are discussed.

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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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A simple and robust model to explain convex corner undercutting in wet bulk micromachining

Cited by 23 publications

References 28 publications

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

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

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

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

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