High speed silicon wet anisotropic etching for applications in bulk micromachining: a review

Abstract

Wet anisotropic etching is extensively employed in silicon bulk micromachining to fabricate microstructures for various applications in the field of microelectromechanical systems (MEMS). In addition, it is most widely used for surface texturing to minimize the reflectance of light to improve the efficiency of crystalline silicon solar cells. In wet bulk micromachining, the etch rate is a major factor that affects the throughput. Slower etch rate increases the fabrication time and therefore is of great concern in MEMS industry where wet anisotropic etching is employed to perform the silicon bulk micromachining, especially to fabricate deep cavities and freestanding microstructures by removal of underneath material through undercutting process. Several methods have been proposed to increase the etch rate of silicon in wet anisotropic etchants either by physical means (e.g. agitation, microwave irradiation) or chemically by incorporation of additives. The ultrasonic agitation during etching and microwave irradiation on the etchants increase the etch rate. However, ultrasonic method may rupture the fragile structures and microwave irradiation causes irradiation damage to the structures. Another method is to increase the etching temperature towards the boiling point of the etchant. The etching characteristics of pure potassium hydroxide solution (KOH) is studied near the boiling point of KOH, while surfactant added tetramethylammonium hydroxide (TMAH) is investigated at higher temperature to increase the etch rate. Both these studies have shown a potential way of increasing the etch rate by elevating the temperature of the etchants to its boiling point, which is a function of concentration of etch solution. The effect of various kinds of additives on the etch rate of silicon is investigated in TMAH and KOH. In this paper, the additives which improve the etch rate have been discussed. Recently the effect of hydroxylamine (NH2OH) on the etching characteristics of TMAH and KOH is investigated in detail. The concentration of NH2OH in TMAH/KOH is varied to optimize the etchant composition to obtain improved etching characteristics especially the etch rate and undercutting which are important parameters for increasing throughput. In this article, different methods explored to improve the etch rate of silicon have been discussed so that the researchers/scientists/engineers can get the details of these methods in a single reference.

Fabrication of SiNx Nanopore Filters Using Combined Process of Nanoimprint and Dual‐Side Aligned Photolithography for Purified Cs3MnBr5 Green Phosphors

“…Si residue is etched by tetramethylammonium hydroxide (TMAH) wet etching and is also removed by two-step wet etching of buffered oxide etchant (BOE) and EKC solution as a photoresist stripper. [34,35] scanning electron microscopy (SEM) images indicate that SiO 2 particles remain after BOE wet etching and are clearly removed by EKC wet etching. So, it can be clearly seen that the nanopore size and pore size uniformity of the final 2D SiN x nanohole-arrayed nanofilter chip are well matched to our designed nanofilter chip structure.…”

Addition of Carboxylic Acids to Superheated Water for the Environmentally Benign Removal of Silicon Nitrides

“…Even when different OH – concentrations were obtained by adding different amounts of additives to superheated water, the results were consistent with previous results (Figure ), where the etching rate of Si 3 N 4 in superheated water is proportional to the OH – concentration. However, it is well known that Si substrates, which are widely used as starting materials for electronic devices, are vigorously etched in basic solutions. − This is because Si is thermodynamically stable in the form of HSiO 3 – or SiO 3 2– under basic conditions . For this reason, a region of higher OH – concentration, which produces faster Si 3 N 4 etching in superheated water, is undesirable for the Si substrate.…”

Recent Advancements in Microneedle Technology for Multifaceted Biomedical Applications

“…For longer periods and deeper etching (>100 μm), silicon nitrides are an enhanced etch mask as it etches more gradually in the KOH. TMAH has good etching discernment between silicon dioxide and silicon [ 159 ]. On the requirement of a deep etching with a thickness of a silicon wafer (500 μm), a thermally developed oxide layer could be used as a mask.…”