Etalon for Nanometrology Produced by Anisotropic Etching

Possibilities and results of using relief structures produced by anisotropic etching as etalons for linear measurements in nanorange are discussed. Two types of the structures with different profiles and with two approaches to estimation of influence of its sophistication degree on measurement results are considered. Analyze of methods and means of measurements of its geometric parameters and comparison of uncertainness of measurement results are conducted. The important condition for diminishing the measurements uncertainness is taking into account irregularities of a sample surface. These irregularities were evaluated by TEM and CD-AFM. Results of harnessing these types of structures are different also. The bureau International des Poids et Mesures recommended the structure with rectangular profile and its attestation procedure as an example for all national committees on linewidth metrology in nanorange. The structure with trapezoid profile that induced hopes for decision of basic tasks of nanometrology in past is occurred to be poorly in demand even on national scale.

Study of Black Silicon Wafer through Wet Chemical Etching for Parametric Optimization in Enhancing Solar Cell Performance by PC1D Numerical Simulation

Black silicon (BSi) fabrication via surface texturization of Si-wafer in recent times has become an attractive concept regarding photon trapping and improved light absorption properties for photovoltaic applications. In this study, surface texturization has been conducted on mono-crystalline Si(100) wafer using a wet chemical anisotropic etching process with IPA:KOH solution to form micro-pyramidal surface structures. Moreover, the optimized properties of the fabricated BSi wafers are used for numerical simulation using PC1D software to analyze the performance of the solar cell and establish the correlation among relevant parameters. Effects such as doping concentration, texturization, passivation, and anti-reflection coating of BSi on the solar cell performance have numerically been investigated. Results show that textured surface obtained from the wet chemical anisotropic etching process has successfully reduced the reflectance of the BSi wafer and surpassed the solar cell efficiency by 2%, which is mainly attributed to the optical confinement of the textured pyramids on the surface with a height of 1–2 μm and angles of 70 degrees. Furthermore, the doping concentration of the p-type wafer and n-type emitter were optimized to be 1 × 1016 cm−3 and 1 × 1018 cm−3, respectively. In the case of device optimization, the SiO2 passivation layer with a refractive index of 1.48 and the Si3N4 ARC layer with a refractive index of 2.015 has been identified as the best combination for the solar cell performance. These optimized parameters eventually result in 23.14% conversion efficiency from numerical simulation for solar cells that use black silicon wafers as fabricated in this study.

Geometry of Structures Developed by Anisotropic Etching in the Nanometer Range

Geometric disadvantages of nanostructure surface developed by anisotropic etching of silicon are discussed. These disadvantages increase uncertainness of its sizes and impeded its using as an etalons for linear measurements. The greatest uncertainness are observed for structures with trapezoid profile. They make up due to defects on sidewalls of etched structures. The surface of a sidewall is proposed to be disposed in the [111] plane and so be absolutely flat. Really parts of a sidewall surface are deflected in stepwise way from the plane [111]. This phenomenon leads to deflection of angles between converging flat sections of etched structure from its known values for silicon. Consequence of this is most drastic to a measure MShps-2K due to its structure, technology of anisotropic etching and absence of required control. Sources of these surface disadvantages induced by anisotropic etching are discussed. Possibilities to decrease disadvantages are evaluated.

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

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.

Breaking the symmetry of nanosphere lithography with anisotropic plasma etching induced by temperature gradients

A strongly anisotropic etching process mediated by temperature is presented to create nano mushroom arrays from a monolayer of spheres.