The Kinetics of Tungsten Etching by Atomic and Molecular Chlorine

Balooch, M.; Fischl, D. S.; Olander, D.R.; Siekhaus, W. J.

doi:10.1149/1.2096215

Cited by 20 publications

(9 citation statements)

References 7 publications

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“…This difference in the probability to form dissociative adsorbed chlorine on the respective metal surface explains the often observed phenomenon of atomic chlorine showing a much more pronounced attack on molybdenum, tungsten, niobium, and tantalum than molecular chlorine, whereas there is no difference between the two species on nickel surfaces .…”

Section: Reaction Mechanisms Of the High Temperature Chlorination Of mentioning

confidence: 84%

“…They can be described by the mechanisms of heterogeneous catalysis . According to these theories, the chlorination of the refractory metals tungsten, molybdenum, niobium, and tantalum follows most probably a Rideal‐type of mechanism where the surface is first covered with dissociated chlorine atoms and the chlorine layer is subsequently attacked by further chlorine from the surrounding gas phase .…”

Section: Reaction Mechanisms Of the High Temperature Chlorination Of mentioning

confidence: 99%

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Refractory metals and nickel in high temperature chlorine‐containing environments ‐ thermodynamic prediction of volatile corrosion products and surface reaction mechanisms: a review

Galetz

Rammer

Schütze

2015

Materials & Corrosion

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Thermodynamic calculations are an important tool for prediction of chemical reactions. In many cases the results help to understand and describe the experimental observations. In others, especially if reaction kinetics play a major role, their predictive value can be rather limited and the projected results have to be treated with care. One such case are high temperature chlorine corrosion conditions. For example, thermodynamically a similar corrosion behavior of nickel and molybdenum is predicted in chlorine‐containing atmospheres at low oxygen partial pressures. In contrast to their calculated similarity, experimental results showed much higher resistance of molybdenum against the chlorinating attack. Above 800 °C nickel is rapidly consumed, whereas molybdenum remains almost inert. This paper reviews the literature on the corrosion mechanisms and kinetics of nickel and molybdenum in chlorine‐containing environments as well as in mixed oxygen‐chlorine‐containing atmospheres. Based on the literature review, differences in their reaction kinetics are discussed, taking into account the deviation from an ideal thermodynamic correlation between the partial pressure and the reaction kinetics via the often used Hertz‐Langmuir equation. Finally it is shown that the findings concerning the special characteristics of molybdenum and nickel and the conclusions drawn from experimental observations on high temperature chlorine corrosion can also be transferred to other metals.

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Section: Reaction Mechanisms Of the High Temperature Chlorination Of mentioning

confidence: 84%

Section: Reaction Mechanisms Of the High Temperature Chlorination Of mentioning

confidence: 99%

Refractory metals and nickel in high temperature chlorine‐containing environments ‐ thermodynamic prediction of volatile corrosion products and surface reaction mechanisms: a review

Galetz

Rammer

Schütze

2015

Materials & Corrosion

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“…To develop a mathematical model for the determination of this rate determining step, the single steps have to be defined and their reaction rates mathematically described. The major steps for the formation and removal of a volatile corrosion product from the surface are the following, according to : 1. gas phase diffusion of the chlorine molecule to the metal surface; 2.…”

Section: Mathematical Approachmentioning

confidence: 99%

Kinetics of volatilization of high temperature corrosion products and its application to chlorine corrosion

Rammer

Galetz

2016

Materials & Corrosion

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Operating atmospheres of many industrial high temperature processes contain a certain amount of halogens, in most cases chlorine. Halogens have the tendency of forming volatile metal chlorides of the general formula MxCly, which are well known to play a critical role in high temperature corrosion processes, when present at a significant amount. Thermodynamic calculations give a valuable hint, whether a reaction product can occur and how volatile such products can potentially be, when the partial pressures are calculated. However, such calculations reflect thermodynamically stable conditions, while in open systems the local kinetics control the process of surface reactions. For each specific condition, the reaction rates and thus the corrosion rates have to be determined. In previous work, we have shown that corrosion kinetics which lead to the formation of volatile products follows different steps. In this work, a mathematical model is developed in which the different steps, which are required for the formation of metal chlorides and their removal from the surface are described. It is assumed that the slowest of such formation or transport steps determines the kinetics of high temperature corrosion. The application of this model on the literature data shows that by this model it becomes possible to identify the slowest and therefore rate determining step.

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“…Methods for spontaneous tungsten etching utilize plasmas containing various halogens such as fluorine 27−29 or chlorine. 28,30,31 Tungsten etching occurs through formation of volatile chlorides or fluorides. Tungsten can also be etched by Cl 2 or XeF 2 gases.…”

Section: Introductionmentioning

confidence: 99%

WO₃ and W Thermal Atomic Layer Etching Using “Conversion-Fluorination” and “Oxidation-Conversion-Fluorination” Mechanisms

Johnson

George

2017

ACS Appl. Mater. Interfaces

117

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The thermal atomic layer etching (ALE) of WO and W was demonstrated with new "conversion-fluorination" and "oxidation-conversion-fluorination" etching mechanisms. Both of these mechanisms are based on sequential, self-limiting reactions. WO ALE was achieved by a "conversion-fluorination" mechanism using an AB exposure sequence with boron trichloride (BCl) and hydrogen fluoride (HF). BCl converts the WO surface to a BO layer while forming volatile WOCl products. Subsequently, HF spontaneously etches the BO layer producing volatile BF and HO products. In situ spectroscopic ellipsometry (SE) studies determined that the BCl and HF reactions were self-limiting versus exposure. The WO ALE etch rates increased with temperature from 0.55 Å/cycle at 128 °C to 4.19 Å/cycle at 207 °C. W served as an etch stop because BCl and HF could not etch the underlying W film. W ALE was performed using a three-step "oxidation-conversion-fluorination" mechanism. In this ABC exposure sequence, the W surface is first oxidized to a WO layer using O/O. Subsequently, the WO layer is etched with BCl and HF. SE could simultaneously monitor the W and WO thicknesses and conversion of W to WO. SE measurements showed that the W film thickness decreased linearly with number of ABC reaction cycles. W ALE was shown to be self-limiting with respect to each reaction in the ABC process. The etch rate for W ALE was ∼2.5 Å/cycle at 207 °C. An oxide thickness of ∼20 Å remained after W ALE, but could be removed by sequential BCl and HF exposures without affecting the W layer. These new etching mechanisms will enable the thermal ALE of a variety of additional metal materials including those that have volatile metal fluorides.

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The Kinetics of Tungsten Etching by Atomic and Molecular Chlorine

Cited by 20 publications

References 7 publications

Refractory metals and nickel in high temperature chlorine‐containing environments ‐ thermodynamic prediction of volatile corrosion products and surface reaction mechanisms: a review

Refractory metals and nickel in high temperature chlorine‐containing environments ‐ thermodynamic prediction of volatile corrosion products and surface reaction mechanisms: a review

Kinetics of volatilization of high temperature corrosion products and its application to chlorine corrosion

WO₃ and W Thermal Atomic Layer Etching Using “Conversion-Fluorination” and “Oxidation-Conversion-Fluorination” Mechanisms

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The Kinetics of Tungsten Etching by Atomic and Molecular Chlorine

Cited by 20 publications

References 7 publications

Refractory metals and nickel in high temperature chlorine‐containing environments ‐ thermodynamic prediction of volatile corrosion products and surface reaction mechanisms: a review

Refractory metals and nickel in high temperature chlorine‐containing environments ‐ thermodynamic prediction of volatile corrosion products and surface reaction mechanisms: a review

Kinetics of volatilization of high temperature corrosion products and its application to chlorine corrosion

WO3 and W Thermal Atomic Layer Etching Using “Conversion-Fluorination” and “Oxidation-Conversion-Fluorination” Mechanisms

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WO₃ and W Thermal Atomic Layer Etching Using “Conversion-Fluorination” and “Oxidation-Conversion-Fluorination” Mechanisms