We report on a study of the morphology of (100) silicon surfaces etched in aqueous alkaline solutions. It is shown that the formation of pyramidal hillocks during etching can be influenced in two different ways: by the presence of an oxidizing agent (ferricyanide or oxygen) in the etchant solution, or by etching under anodic bias. In both cases pyramid formation is suppressed without a significant change of the etch rate. The addition of ferricyanide does not markedly change the etching anisotropy. The formation, stability, and suppression of the pyramids are discussed. The large anisotropy makes it possible to etch structures such as V-grooves in (100)Si wafers.3 Unfortunately, a maximum in the etch rate f or 4.0 M KOH is accompanied by an extremely rough surface,2 Several groups26 report that this roughness is due to the formation of pyramidal hillocks during etching. Since for many applications smooth surfaces are of the utmost importance, these defects can cause serious problems.7 In micromachining, pyramid formation is avoided by etching at increased KOH concentration.2'8 The improved surface morphology, however, is achieved at the expense of the etch rate which decreases with increasing KOH concentration above 4.0 M. 2 To raise the etch rate, a higher temperature is required. With Si02 as a masking material the combination of high KOH concentration and higher temperature constitutes a problem for the chemical stability of the mask.In this paper we describe a study of the surface morphology of Si etched in 4.0 M KOH solutions at 70°C. It is Electrochemical Society Active Member shown how hillock formation can be suppressed without drastically changing the etch rate or the etching anisotropyThe results suggest that it should be possible to obtain a more acceptable compromise with respect to the requirements of high etch rate, surface smoothness, and good mask stability. ExperimentalThe p-type (100)Si samples were boron-doped with a resistivity of 8 to 12 111 cm. Prior to each experiment the samples were standard RCA cleaned9 and the native oxide layer was removed by a 10 s dip in a 2 M HF solution followed by rinsing with deionized water. Samples used in electrochemical experiments were provided with an ohmic contact (Ga/In eutectic) on the back side. The samples were mounted with an 0-ring in a Teflon holder exposing 0.5 cm2 to the solution. All experiments were performed at 70°C. The chemicals used were of p. a. grade (Merck).Electrochemical experiments were performed in the dark using a Bank POS7 3 Potentioscan. The thermostatically controlled cell contained a working electrode whose surface faced upward, a Pt counterelectrode, and a saturated calomel electrode (SCE) as reference. All potentials are quoted with respect to SCE. The etch rate was determined by measuring the etched depth as a function of etching time using a Tencor Alpha-Step 500 surface pro-

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We report on a study of transparent conducting tin-doped indium oxide (ITO) electrodes in propylene carbonate solutions containing lithium ions. The system was studied using electrochemical methods in combination with in situ techniques: ultraviolet-visible spectroscopy, X-ray diffraction, and quartz crystal microbalance. The results show that the cathodic process at E 1.0 V vs. Li/Lit mainly involves the reduction of the electrolyte solution, leading to the formation of a thin, lithium-rich surface film. At potentials 1.0 V vs. Li/Li, degradation of ITO and the formation of metallic indium take place. No evidence was obtained that lithium-ion intercalation into ITO, which has been suggested by several workers, occurs to a significant extent. We conclude that ITO probably cannot be used as a combined ion-storage layer and transparent conductor for all-solid-state and laminated electrochromic switching devices in view of long-term stability.