The Controlled Etching of Silicon in Catalyzed Ethylenediamine‐Pyrocatechol‐Water Solutions

Abstract

The etching of single crystal silicon in ethylenediamine-pyrocatecholwater solutions (EPW) has been examined as a function of gross and trace contaminant concentrations, etching bath design, bath silicon content, and oxygen exposure in the temperature interval from 50~176 It has been found that trace quantities of 1,4-and 1,2-diazine catalyze the etch rate on (100) surfaces dramatically while affecting (111) etch rate to a lesser extent. This results in a (100)/(111) anisotropy ratio increase from 13.5, in the absence of pyrazine, to about 19 in the 5g pyrazine/liter ethylenediamine range at 115~ Coincident with this effect, there is a decrease in the apparent activation energy of etching from 10.8 to 8.4 kcal/mole, making the solution less temperature sensitive. In addition, surface morphology improves with addition of the catalyst. EPW solutions are subject to residue formation in many composition-temperature intervals, and conditions necessary to avoid this undesirable side effect have been defined. Oxygen contamination of EPW solutions also increases silicon etch rate significantly, and this effect appears to be due to the formation of 1,4-benzoquinone which also functions as a catalyst. It has been found, however, that EPW solutions containing 1,4-diazine (pyrazine) are relatively oxygen stable and residue free and can be employed as controlled etchants for single and polycrystalline silicon over the temperature range from 50~176 Two specific quaternary concentrations have been defined for use where (i) high etch rate processes are required, "F" etch, and (ii) where slower removal rates and/or lower etching temperatures are desired, "S" etch.Ethylenediamine-pyrocatechol-water solutions (EPW) find extensive use in the etching of polycrystalline silicon layers in integrated circuit fabrication, generally in the temperature range from 100~176 Disadvantages in the use of such solutions for the etching of polycrystalline silicon layers are that they etch too rapidly at 100~ or higher (20 sec for a 3500A layer) making tolerance control difficult, develop insoluble residues when used at lower temperatures, and tend to "age" rapidly. This aging manifests itself in an uncontrolled continued increase in etch rate with use. EPW solutions have, however, been shown to be excellent anisotropic etchants for single crystal silicon in chemical milling applications, e.g., the formation of ink jet nozzle arrays in silicon (1-3).The open literature dealing with this etchant system is small (4-7). The work discussed in Ref. (4) focused on (111) etching for which a temperature dependency of "approximately" 11 kcal/mole (0.48 eV) was determined. Etch rate ratios of 50:30:3 ~m/hr at an unspecified temperature were reported for (100): (110):(111) orientations in an EPW solution containing 17 ml E: 3g P: 8 m.1 W, [35.1, 3.7, and 61.2 mole percent (m/o), respectively]. The authors proposed what appears to be a reasonable over-all reaction sequence, Eq. [1], based on an oxidation stage involving ethylenediamine, water, and silicon, and...

Electrochemical Etching Methods for Producing Porous Silicon

“…These pre-and post-treatments make it possible to design and engineer a broad range of pSi structures. The most widespread alkaline etchants used to etch silicon are potassium hydroxide (KOH) and tetramethyl ammonium hydroxide (TMAH), although other inorganic and organic compounds such as lithium hydroxide (LiOH), sodium hydroxide (NaOH), rubidium hydroxide (RbOH), caesium hydroxide (CsOH), ammonium hydroxide (NH 4 OH), cholin and ethylenediamine have been used as well [33,[40][41][42][43][44][45][46][47][48][49][50][51][52][53]. It is worthwhile mentioning that the etching rate of silicon in these etchants is highly dependent on Porous silicon structures featuring a broad range of pore geometries, sizes and morphologies can be produced by electrochemical etching of silicon wafers.…”

A comprehensive review on convex and concave corners in silicon bulk micromachining based on anisotropic wet chemical etching

“…The anisotropic etchants etch materials much faster in one direction than in another, exposing the slowest etching crystal planes over time [1,2,4,10,[23][24][25][26][27]. Several kinds of aqueous alkaline solutions such as potassium hydroxide solution (KOH) [23][24][25][26][28][29][30][31][32][33][34][35], tetramethylammonium hydroxide (TMAH) [27,[36][37][38][39][40][41][42][43][44][45], ethylenediamine pyrocatechol water (EDP or EPW) [26,35,46,47], hydrazine [23,48,49], ammonium hydroxide [50], and cesium hydroxide (CsOH) [51] are employed for silicon wet anisotropic etching. Among these etchants, potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) are most frequently used.…”

Postprocessing Technologies, Interface Circuits and Packaging Strategies for CMOS Compatible Gas Flow Sensors

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