Photolithography on bulk micromachined substrates

Venstra, Warner J.; Spronck, Jo W.; Sarro, P.M.; Eijk, J. van

doi:10.1088/0960-1317/19/5/055005

Cited by 9 publications

(6 citation statements)

References 15 publications

(18 reference statements)

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“…Subsequent to the deposition of masking layer, second step of lithography is performed using mask # 2 to pattern the masking layer on the sidewalls as well as top surface. Due to uneven surface topography, it is very hard to coat the photoresist of a uniform thickness using spin coating technique [167][168][169]. The use of standard liquid photoresist deposited by a spincoating process results in non-uniform thickness, especially on sloping sidewalls and convex edges/ corners.…”

Section: Perfect Convex Corners Using Two-step Etching Techniquesmentioning

confidence: 99%

“…3D nature of the microstructure makes it very difficult to transfer the pattern [168,169,[171][172][173][174]. There are three major issues in lithography process on 3D topography: Figure 45 SEM photographs of (a) acute and (b) obtuse convex corners fabricated using triangular compensation patterns in 42.5 wt% KOH at 80°C [116].…”

Section: Perfect Convex Corners Using Two-step Etching Techniquesmentioning

confidence: 99%

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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: Perfect Convex Corners Using Two-step Etching Techniquesmentioning

confidence: 99%

Section: Perfect Convex Corners Using Two-step Etching Techniquesmentioning

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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“…Subsequent to the deposition of masking layer, second step of lithography is performed using mask # 2 to pattern the masking layer on the sidewalls as well as top surface. Due to uneven surface topography, it is very hard to coat the photoresist of a uniform thickness using spin coating technique [167][168][169]. The use of standard liquid photoresist deposited by a spin-coating process results in non-uniform thickness, especially on sloping sidewalls and convex edges/corners.…”

Section: Perfect Convex Corners Using Two-step Etching Techniquesmentioning

confidence: 99%

“…In order to coat the constant thickness photoresist, spray coating method is employed. The thickness, uniformity and surface roughness of spray-coated photoresist depend on several parameters such as viscosity of the photoresist, orifice of the spray nozzle and the air pressure applied to the nozzle [169][170][171]. After the patterning of masking layer using second step of lithography (Figure 49(c)), the next step of anisotropic etching is carried out (Figure 49(d)).…”

Section: Perfect Convex Corners Using Two-step Etching Techniquesmentioning

confidence: 99%

“…However this technique provides protected convex corners, the second step of lithography is onerous as it is performed on 3D surface topography. 3D nature of the microstructure makes it very difficult to transfer the pattern [168,169,[171][172][173][174]. There are three major issues in lithography process on 3D topography: uniform photoresist coating, reflection of UV light from tilted sidewalls and the uneven gap between mask and bottom surface.…”

Section: Perfect Convex Corners Using Two-step Etching Techniquesmentioning

confidence: 99%

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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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MEMS Process Integration

Franssila

2010

Introduction to Microfabrication

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MEMS devices come in a bewildering variety, in regard to structures, materials and functions. Whereas all CMOS technologies are close relatives, MEMS devices are made with a multitude of closely related, distantly related and unrelated technologies. Pressure sensor operation can be based on piezoresistive, capacitive, thermal conductance or resonance mechanisms, and while the first three share some structural features and fabrication steps, the fourth bears more resemblance to gyroscopes and RF oscillators. Accelerometers are made of single crystal silicon, of bulk, epitaxial and SOI type, of polycrystalline silicon and of electroplated metals. Electrospray emitters have been realized in silicon, glass, quartz, SU-8, PDMS, PMMA and many other polymers. Microneedles have been made in both out-of-plane and in-plane configurations, from single crystal and polysilicon, silicon dioxide, metals, polymers. Micromirrors are most often made of silicon, but also of metals or metallized nitride membranes. Mirrors come in in-plane (horizontal) and out-of-plane (vertical) versions too.Bulk and SOI MEMS structures have high aspect ratios and highly complex 3D shapes resulting from etching and wafer bonding. These put new requirements on subsequent lithography, doping and thin-film steps, and introduce novel metrology requirements. MEMS devices with through-wafer holes pose process limitations: for instance, in spinning a vacuum chuck holds the wafer, and DRIE reactors use backside helium cooling. Through-wafer structures require double-sided processing and even without through-holes, there is often a need to align structures on the two sides of the wafer. Double-sided alignment is also mandatory for structured wafer bonding.MEMS devices are not solid state devices: they have free-standing, moving, rotating and vibrating structures, like the grids of old-fashioned vacuum tubes. These moving structures create challenges for the subsequent processing and packaging steps. Capillary forces in drying, silicon dust and vibrations during dicing, or stresses in encapsulation may damage delicate mechanical structures. Closed cavities can sometimes be handled without problems, but high temperatures and changing pressures during fabrication can cause some design limitations, especially when the cavity roof is a thin diaphragm. Despite this seeming variety, there are many generic structures, design principles and widely used techniques for realizing them. These are the topics of this chapter.

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Photolithography on bulk micromachined substrates

Cited by 9 publications

References 15 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

MEMS Process Integration

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