Optimization of deep silicon etching process for microstructures fabrication

The paper presents the study of cyclic process of deep anisotropic silicon etching, called Oxi-Etch, in which the steps of etching and oxidation alternate, allowing deep etching of silicon with an anisotropic profile. This process forms typical for cyclic etching process sidewall profile called scalloping. Opportunities for modification and optimization of the process for specific application were investigated. The effects of optimization of the bias voltage and the duration of the etching step on the parameters of the resulting structures, such as the etching depth, wall roughness, and the accuracy of transferring the lithographic size, are considered. Balance between etch rate and scalloping was established.

Single-step alkaline etching of deep silicon cavities for chip-scale atomic clock technology

This paper presents the results of experiments on the development of the technology of MEMS alkali vapor cells for a miniature quantum frequency standard. The classical design of a two-chamber silicon cell containing an optical chamber, shallow filtration channels and a technical container for a solid-state alkali source was implemented in a single-step process of wet anisotropic silicon etching. To prevent the destruction of the filtration channels during etching of the through silicon cavities, the shapes of the compensating structures at the convex corners of the silicon nitride mask were calculated and the composition of the silicon etchant was experimentally found. The experiments results were used in the manufacture of chip-scale atomic clock cells containing vapors of 87Rb or 133Cs isotopes in the neon atmosphere.

ИССЛЕДОВАНИЕ ПРОЦЕССА ГЛУБОКОГО ТРАВЛЕНИЯ КРЕМНИЯ С МИНИМАЛЬНОЙ ШЕРОХОВАТОСТЬЮ СТЕНОК И ДНА СТРУКТУР

Данная работа посвящена исследованию процессов глубокого анизотропного травления кремния. В качестве предложенных методов были проанализированы два подхода - Bosch и Cryo. Представлено феноменологическое описание вышеупомянутых методов, проведен анализ эксперимента по криогенному травлению кремния, полученный на базе ФТИАН, также предложена аналитическая модель Cryo-процесса. This work is devoted to the study of the processes of deep anisotropic silicon etching. Two approaches (Bosch and Cryo) have been analyzed as proposed methods. The phenomenological description of the above mentioned methods has been presented, the analysis of the experiment on cryogenic etching of silicon obtained on the basis of FTIAN has been carried out, as well as an analytical model of Cryo process has been proposed.

Wet Etching Technique to Reduce Pyramidal Hillocks for Anisotropic Silicon Etching in NaOH/IPA Solution

The various methods of silicon wet etching techniques, which utilize ultrasonic agitation to reduce pyramidal hillocks in etched patterns, were evaluated in NaOH+IPA solution. The comparison of the etching methods composed of; 1.) no agitation + sample horizontally orientated, 2.) ultrasonic agitation + sample horizontally orientated, 3.) ultrasonic agitation + sample vertically orientated, and 4.) ultrasonic with rotation agitation + sample vertically orientated. It was found that the percentages of the etched patterns presenting hillocks after etching were 100%, 79.77%, 32.67% and 2.62%, respectively. Ultrasonic coupled with rotation agitation along with the sample vertically orientated is the most powerful etching technique, offering a high yield of smooth etched surface. The difference in etch rate between without agitation and applying ultrasonic agitation was not observed in this experiment, as it was operated in a solution temperature 60-65°C and a 275nm/min etch rate was achieved. The theories that relate to each evaluated method are also discussed.

Wet Anisotropic Etching Characteristics of Si{100} in TMAH+Triton at near the Boiling Point

The anisotropic silicon etching characteristics of TMAH(tetramethyl ammonium hydroxide)+Triton at near the boiling point were investigated. The etch rate of Si {100}, the convex corners, and the roughness of the etched surface contact with the fabrication of bulk microstructures and thus micromechanical devices in silicon. This study presents that the etch rate of Si {100} in 25 wt.% TMAH with 0.1% Triton at near boiling point (112°C) is 1.37μm/min, it is three times higher than it at 80°C. The surface roughness and convex corners of Si {100} after etching at different temperature were investigated by optical microscope, scanning electron microscope (SEM) and atomic force microscope (AFM). The etching rate and smoothness of an etched surface can be improved simultaneously at near boiling point, meanwhile, the undercutting on convex corner should be accepted.

Feasibility to Fabricate the 45° Slant with Anisotropic Silicon Etching in NaOH Solution

The experiments to study the feasibility to fabricate the 45 slant on p-type (100)-oriented silicon wafer were done. The various mask shapes, rectangular, cross, circle and boomerang, were patterned on the SiO2 mask by utilizing the conventional photolithography and dry etching process for investigating the anisotropic wet etch characteristic. The edge of masks were align in two crystal direction, 110 and 100 that is allowable to get a better understanding about the crystal orientation and the angle between planes in a crystal system. The very low etch rate,  50 nm/min, process regime was selected to fabricate the 45 slant with the concept is the lowest of an overall etch rate in the system to reach the level that is possible to detect the (110) plane. The etch recipe can be used for the next development work to built a housing of the laser light source for applying in a data storage technology.