Surface Studies on Single-Crystal Germanium

100

The (100) silicon etch-rate dependence on boron concentration in ethylenediamine-pyrocatechol-~ater (EPW) solutions at 110~ has been measured by successive etching of boron-diffused silicon. The etch rate begins to decrease near 10'9cm -3 and decreases approximately as the fourth power of doping over three orders of magnitude in etch rate. The etch-rate ratio between heavily and lightly doped silicon appears insensitive to pyrazine concentration from 0.01 to 6.0g/liter E, oxygen exposure of the etch solution, and light. The etch-rate decrease is sensitive to hole concentration and not to atomic concentration of boron or stress. The etch-rate dependence may be explained by assuming that the hydrogen-evolution cathodic half-reaction of the oxidation-reduction reaction is the rate-determining step. The reason for the etch-rate decrease as the hole concentration increases is given in terms of increased Auger recombination of large numbers of electrons chemically produced at the silicon surface during etching. Excellent agreement with experiment is obtained. Similarities of this etch system and the phenomenon of silicon staining are discussed in terms of oxidation-reduction reactions. Application to control of thickness and uniformity of boron-doped silicon membranes is discussed.Boron-doped silicon membranes have been fabricated using ethylenediamine-pyrocatechol-water (EPW) etching solutions for a variey of purposes: as thin substrates to reduce backscattering in electron (1) or ion beam lithography (2), to reduce scattering of transmitted radiation in x-ray lithography (3), as thin highly doped barriers for Josephson junctions or super-Schottky diodes (4), as ink-jet nozzles (5), and for the fa~iqation of micromechanical beams used in accelerometers (6, 7). In almost all cases, boron diffusions are used to stop the EPW-etchant attack on silicon. Thus far, there has been very little work reported on the etch-rate dependence on boron or on the basic etchant system itself. Finne and Klein (8) first reported the etchant but did not find any etchrate dependence up to 8 • 1017 cm -3 boron. It was reported later that the etchant stopped at 7 • 1019 cm -3 (9), but there was no detailed measurement of the transition region. Reisman et al. (10) discovered the effect of pyrazine and oxygen-induced benzoquinone catalysts on the etch rate for lightly doped silicon in EPW solutions. This is important, since the pyrazine and quinone concentration in commercially available ethylenediamine and pyrocatechol, respectively, varies from lot to lot. They briefly report the etch-rate dependence on boron in bulk silicon wafers at two levels of heavy doping for high pyrazine/low benzoquinone etch solutions and find the etch rate to be small but finite in the 102o cm -3 range. Seidel and Csepregi (11) reported a stronger etch-rate dependence on doping in epitaxial layers than that reported by Reisman et al. They used a similar etch solution, except with somewhat lower pyrazine concentration and unknown benzoquinone content. Initial experime...

Section: January 1984mentioning

confidence: 96%

(100) Silicon Etch‐Rate Dependence on Boron Concentration in Ethylenediamine‐Pyrocatechol‐Water Solutions

Raley

Sugiyama

Duzer

1984

100

“…2. Four regions can be distinguished: (I) the etch triangles are well developed, the crystals having a shiny appearance; (II) the HF deficiency gives rise to somewhat dull surfaces in which the triangular pits are still present; (III) after etching a slight oxide film becomes visible (2). This film is readily soluble in H~O~; underneath the film small etch triangles are present; (IV) gives thicker oxide layers after etching, also soluble in H~O~.…”

Section: Surface Structuresmentioning

confidence: 97%

“…Much work has already been done on the etching of Ge single crystals with mixtures of HF-H~O~ and H~O (1)(2)(3)(4)(5)(6)(7)(8)(9). This work has been extended by studying the etch rates on (111) oriented Ge crystals at room temperature as a function of etchant composition and by a study of the surface structures after etching.…”

mentioning

confidence: 99%

Etching Ge with Mixtures of HF-H[sub 2]O[sub 2]-H[sub 2]O

Bloem

Vessem

1962

Etch rate vs. composition of the etchant (HF-H~O~-H20) was studied, together with the surface structures after etching Ge single crystals. Conclusions concerning the orientation dependence and the kinetics of the etching process are given. The ratio of the etch rate on different faces depends on the value of CH~o/CHF in the etchant independent of the H~O~ concentration, whereas visible oxide films are formed for a CH..,oJCH~ ratio smaller than the stoiehiometric ratio given by the over-all reaction:Much work has already been done on the etching of Ge single crystals with mixtures of HF-H~O~ and H~O (1-9). This work has been extended by studying the etch rates on (111) oriented Ge crystals at room temperature as a function of etchant composition and by a study of the surface structures after etching.The Ge pellets used (dimensions 3 x 3 x 0.25 ram, 2-3 ohm-cm N-type) were cut along (111) planes to within 0.5 degree, the surfaces were polished with No. 500 carborundum abrasive powder. Etching was performed in a polyethylene vessel, rotating in a constant temperature bath (25~The vessel was inclined in order to be sure of adequate stirring. About 50 crystals at a time were etched in 250 cc of etchant.After etching the etchant was quenched with water and poured off After washing and drying the thickness of the pellets was measured to within 1;,. Etching times were used to give a total decrease in thickness of about 100m in each case. This procedure essentially follows that during fabrication, and the influence of damaged surface layers on the etch rate is small. The etch rate has been defined as that on a single surface in ~/min, thus half the decrease in thickness per unit time. Etch RatesThe results are plotted in a tri-axial diagram (Fig. 1), where the basic components in the three corners correspond to pure water, concentrated HF (50%), and H~O~ (30%), respectively. The concentrations are expressed volume percent. Each composition corresponds to a certain point in the diagram to which in turn the appropriate etch rate can be attached. In Fig. 1 contour lines of equal etch rates, at room temperature, on a single Ge surface are given.Maximum etch rates are found for about equal volume parts of HF and H~O.~; on dilution with water the etch rate decreases. As the I-IF contains 28.8 moles HF/1 and the H.~O~ used 9.8 moles/l, equal volume parts of both compose a nearly stoichiometric etchant according to the over-all reaction:Ge + 2H~O._, + 6HF ~ H~GeF~ + 4H~O[ 1 ]Figure 1 also shows that for low H~O~ or HF concentrations the etch rates vary proportional to this H20~ or HF content. The etch rates are strongly temperature dependent; a plot of log R over 1/T shows that for the stoichiometric etchants a variation in etch rate of about 6% per degree at room temperature is found (activation energy of 10.7 kcal/mole). It is quite possible that with less H~O~ or HF another activation energy is obtained, as other reaction steps may then become rate limiting. The experimental results at room temperature can be described by the...

“…[4] and [5] or by [6] and [7] gives OE.~/OpH =-0.0591 v/pH unit. Assuming symmetrical energy barriers (rio----fl,----0.5), the mechanism represented by Eq.…”

Section: Mechanism Of the Dissolution Reactionmentioning

confidence: 99%

The Reaction of Germanium with Aqueous Solutions

Harvey

Gatos

1960

The dissolution of single-crystal germanium has been studied in electrolyte solutions containing dissolved oxygen. The following electrolytes were considered: KF, KC1, KBr, KI, NaNOs, Na~SO,, CsC1, BaCh, and LaCh. In the range 10 -6 to 1.0N, the dissolution rate typically goes through a maximum as ExperimentalThe experimental techniques employed were, in many respects, similar to those described earlier (1). The reagent grade salts employed were not further purified, since consistent results were obtained with such salts from different sources. The KHF~ was purified by recrystallization. Certain improvements in the procedure for single-crystal samples, as well as the technique employed with powdered samples, will be described briefly. Powdered samples.--These experiments were performed using a conventional Warburg apparatus. 65 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.192.114.19