Simulation and experimental study of maskless convex corner compensation in TMAH water solution

Abstract

Maskless etching with convex corner compensation in the form of a ⟨1 0 0⟩ oriented beam is investigated using both experiments and simulations. The maskless convex corner compensation technique is defined as a combination of masked and maskless anisotropic etching of {1 0 0} silicon in 25 wt% TMAH water solution at a temperature of 80 °C. This technique enables fabrication of three-level micromachined silicon structures with compensated convex corners at the bottom of the etched structure. All crystallographic planes that appear during etching are determined and their etch rates are used to calculate the etch rate value in an arbitrary crystallographic direction necessary for simulation by an interpolation procedure. A 3D simulation of the profile evolution of the etched structure during masked and maskless etching of silicon based on the level set method is presented. All crystallographic planes of the etched silicon structures determined in the experiment are recognized in the corresponding simulated etching profiles obtained by the level set method.

Etching of Uncompensated Convex Corners with Sides along <n10> and <100> in 25 wt% TMAH at 80 °C

“…A pattern formed of two adjoined symmetrical parallelograms, which shared one side along a <100> crystallographic direction, was analyzed. The etched convex corners of the pattern represent the free end of convex corner compensation bounded by {100} and {311} planes [15][16][17][18]. Convex corner compensations formed as the <100> beams for the etching of square or rectangular patterns with sides along <110> crystallographic directions can be related with parallelograms in the case of n = 3.…”

“…The etch rate angular dependence model function must interpolate through the given etch rates and directions while maintaining only C0 continuity, since empirical studies have shown cusps in etch rate diagrams. The simulations presented here are performed using our 13-parameters model, described in detail in [38], with the parameters' values given in [15].…”

“…Convex corners of the island patterns in the masking layer can be distorted during etching. The fabrication of complex 3D silicon structures requires knowledge of the mechanisms behind the evolution of convex corner compensation during etching [14][15][16][17][18][19][20][21][22][23][24]. Appropriate convex corner compensation depends on the design of the 3D silicon structure.…”

“…Most of the results were obtained for the etching of square or rectangular patterns in the masking layer with sides along <110> crystallographic directions. Additionally, convex corner compensation techniques for TMAH water solution etching have been developed for patterns with sides along <110> crystallographic directions [14][15][16][17][18][19][20][21][22][23][24]. The etching of a (100) silicon substrate in TMAH water solution using square, rectangular and octagonal mask patterns with sides along different crystallographic directions was explored in [9,27].…”

Study, Modelling and Implementation of the Level Set Method Used in Micromachining Processes

“…Consequently, several implementations based on the LS method has been presented in last years since this calibration process can be avoided [223][224][225][226]. In chapter 4 the LS implementation developed for wet etching of silicon and quartz is explained.…”