Process Chemistries Research Articles

Significance of plasma-surface interactions in the etch behavior of low-k materials

Low-k materials are an integral component in the advancement of semiconductor device performance by reducing parasitic capacitance and enabling faster device switching for a given thickness compared to traditional dielectric materials such as SiO2. With the advances in logic scaling, low-k materials are increasingly more prominent in the structures of advanced devices. For example, low-k materials are essential as the spacer material to provide both etch selectivity between dielectric materials and electrical isolation in field effect transistors. Consequently, the integration of low-k materials requires that the etch behavior of these materials be well understood so that the device structures can be reliably and reproducibly fabricated. In this study, the authors used a high-density plasma reactor with benchmark CF4- and NF3-based process chemistries to etch low-k materials including SiCN, SiOCN, and SiBCN in addition to Si, SiO2, and SiN reference materials. Numerous characterization techniques were utilized to understand the relationships between the plasma conditions, the evolution of the surface chemistry of the materials, and the resulting etch behavior. These techniques consisted of optical emission spectroscopy, spectroscopic ellipsometry, x-ray photoelectron spectroscopy, and attenuated total reflection Fourier transform infrared spectroscopy. The etch behavior of low-k materials under a given etch process is vital for establishing the etch selectivities in multilayer structures that are required to yield complex device geometries. For example, a directly proportional correlation was observed between the etch rate and intrinsic nitrogen concentration of the low-k materials. Potential mechanisms for the observed etch behaviors were explored using modeling and found that the intrinsic nitrogen composition in the low-k materials can result in energetically favorable reactions that result in the weakening and volatilization of the Si–N bond. Identifying the underlying mechanisms for the etch behaviors of low-k materials will provide key guidance into the development of etch processes that integrate these materials in current and future device structures.

Direct Observation of the Ethyl Radical in the Pyrolysis of Ethane.

We report the first direct detection of ethyl radical in the pyrolysis of ethane. Observation of this vital intermediate was made possible in this extremely reactive environment by the use of a microreactor coupled with synchrotron radiation and photoelectron photoion coincidence (PEPICO) spectroscopy, despite its short lifetime and low concentration. Together with ab-initio master equation-calculated rates and fully coupled computational fluid dynamics simulations, our measurements show that even under the low pressures and short residence times in our experiment, ethyl formation can only be explained by bimolecular reactions; the most important is the catalytic attack of ethane by H atoms, which are then regenerated by decomposition of the nascent ethyl radicals. Our results complete the observation of all hypothesized intermediates in this industrially important process and highlight the need for further studies under additional conditions using similar methods to improve existing models and optimize process chemistries.

Direct Observation of the Ethyl Radical in the Pyrolysis of Ethane

AbstractWe report the first direct detection of ethyl radical in the pyrolysis of ethane. Observation of this vital intermediate was made possible in this extremely reactive environment by the use of a microreactor coupled with synchrotron radiation and photoelectron photoion coincidence (PEPICO) spectroscopy, despite its short lifetime and low concentration. Together with ab‐initio master equation‐calculated rates and fully coupled computational fluid dynamics simulations, our measurements show that even under the low pressures and short residence times in our experiment, ethyl formation can only be explained by bimolecular reactions; the most important is the catalytic attack of ethane by H atoms, which are then regenerated by decomposition of the nascent ethyl radicals. Our results complete the observation of all hypothesized intermediates in this industrially important process and highlight the need for further studies under additional conditions using similar methods to improve existing models and optimize process chemistries.

The Emergence of the Ubiquity of Cerium in Heterogeneous Oxidation Catalysis Science and Technology

Research into the incorporation of cerium into a diverse range of catalyst systems for a wide spectrum of process chemistries has expanded rapidly. This has been evidenced since about 1980 in the increasing number of both scientific research journals and patent publications that address the application of cerium as a component of a multi-metal oxide system and as a support material for metal catalysts. This review chronicles both the applied and fundamental research into cerium-containing oxide catalysts where cerium’s redox activity confers enhanced and new catalytic functionality. Application areas of cerium-containing catalysts include selective oxidation, combustion, NOx remediation, and the production of sustainable chemicals and materials via bio-based feedstocks, among others. The newfound interest in cerium-containing catalysts stems from the benefits achieved by cerium’s inclusion, which include selectivity, activity, and stability. These benefits arise because of cerium’s unique combination of chemical and thermal stability, its redox active properties, its ability to stabilize defect structures in multicomponent oxides, and its propensity to stabilize catalytically optimal oxidation states of other multivalent elements. This review surveys the origins and some of the current directions in the research and application of cerium oxide-based catalysts.

Customizing continuous chemistry and catalytic conversion for carbon–carbon cross-coupling with 3dP

Abstract Support structures of various materials are used to enhance the performance of catalytic process chemistry. Typically, fixed bed supports contain regular channels enabling high throughput because of the low pressure drop that accompanies high flow rates. However, many fixed bed supports have a low surface-area-to-volume ratio resulting in poor contact between the substrates and catalyst. Three dimensional polymer printing (3dP) can be used to overcome these disadvantages by offering precise control over key design parameters of the fixed bed, including total bed surface area, as well as accommodating system integration features that are compatible with continuous flow chemistry. Additionally, 3dP allows for optimization of the catalytic process based on extrinsic constraints (e.g. operating pressure) and digital design features. These design parameters together with the physicochemical characterization and optimization of catalyst loading can be tuned to prepare customizable reactors based on objectives for substrate conversion and desired throughput. Using a Suzuki (carbon–carbon) cross-coupling reaction catalyzed by palladium, we demonstrate our integrated approach. We discuss key elements of our strategy including the rational design of hydrodynamics, immobilization of the heterogeneous catalyst, and substrate conversion. This hybrid digital-physical approach enables a range of pharmaceutical process chemistries spanning discovery to manufacturing scale.

Atomic layer deposition of metal phosphates

Because of their unique structural, chemical, optical, and biological properties, metal phosphate coatings are highly versatile for various applications. Thermodynamically facile and favorable functionalization of phosphate moieties (like orthophosphates, metaphosphates, pyrophosphates, and phosphorus-doped oxides) makes them highly sought-after functional materials as well. Being a sequential self-limiting technique, atomic layer deposition has been used for producing high-quality conformal coatings with sub-nanometer control. In this review, different atomic layer deposition-based strategies used for the deposition of phosphate materials are discussed. The mechanisms underlying those strategies are discussed, highlighting advantages and limitations of specific process chemistries. In a second part, the application of metal phosphates deposited through atomic layer deposition in energy storage and other emerging technologies such as electrocatalysis, biomedical, or luminescence applications are summarized. Next to this, perspectives on untangled knowledge gaps and opportunities for future research are also emphasized.

To decarbonize industry, we must decarbonize heat

Summary Industry is often termed “hard to decarbonize” because a vast, inhomogeneous array of processes comprise the sector. But developing new, decarbonized process heating technologies represents a single, broadly applicable pathway to eliminating a large portion of sectoral emissions—and approximately one-fifth of global CO2 emissions, overall. We begin this perspective with a brief review of the demand for and cost of industrial heat. Then, we highlight key challenges and R&D needs in developing zero-carbon industrial heating technologies. Technologies in four pathways are discussed: (1) zero-carbon fuels, (2) zero-carbon heat sources, (3) electrification of heat, and (4) better heat management. Finally, we identify cross-cutting challenges to the development and adoption of zero-carbon industrial heat technologies, the solution to any of which would constitute a significant breakthrough on the path to industrial decarbonization.

Temperature-Dependent Structural Transformations of Electrodeposited Al from Acidic Imidazolium-Based Tetrachloroaluminate Ionic Liquid

The electrodeposition of aluminum (Al) has been extensively investigated for a range of emerging applications in electrical, electronic, and automotive industries due to its excellent corrosion and wear tolerance. One highly prospective process is the Al electrodeposition from an electrolytic bath comprised of an air and moisture-stable ionic liquid, such as 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl), and an aluminum precursor, which is normally aluminum chloride (AlCl3). Recent spectroscopic studies have shown that Al deposition results from electrochemical reduction of chloroaluminate complexes. In general, the chloroacidity determines reactivity and electrochemistry in the ionic liquid electrolyte. However, the Al deposition chemistry has been complicated by the chemical nature of different chloroaluminate complexes species, their chemical equilibria, and interconversion [20, 21]. The [AlCl4]-, [Al2Cl7]-, and Cl- are the main anions in the solution of alkylimidazolium chloride and AlCl3. More complicated anions such as [Al3Cl10]-, [Al4Cl13]-, and [Al2OCl5]-, have also been detected when the AlCl3 concentration is high.The distribution of the chloroaluminate complexes in the AlCl3/[EMIm]Cl system is heavily dependent on AlCl3 concentration and reaction temperatures. When the molar ratio is less than 50%, [AlCl4]- is the only chloroaluminate complex present. In contrast, when is greater than 50%, the [AlCl4]- concentration decreases and [Al2Cl7]- is formed. When is further increased to 75%, the [Al3Cl10]- concentration reaches 48%, accompanied by [Al2Cl7]-, [Al4Cl13]- and Al2Cl6. Our thermodynamic calculations indicate that increasing temperature mainly affects the distribution of [AlCl4]-, [Al2Cl7]- and [Al4Cl13]- when is higher than 50%.As of now, standardized and reproducible procedures have not yet been established due to challenges with the sensitivity of the process chemistries to environments and operation conditions. The properties of Al deposits were affected by many factors such as: the composition of the mixture (AlCl3-to-IL ratio), substrate-pretreatment, stirring, additives, and reaction temperatures. In order to elucidate how the temperature affects the quality of Al deposits, we have focusedly investigated microstructure changes of Al thin films deposited from an acidic imidazolium-based tetrachloroaluminate bath as a function reaction temperature using several materials characterization techniques. Our presentation will introduce the interesting structural changes of Al films with increasing temperatures, and their correlation with the process chemistry and the kinetics of the electrodeposition.

(Invited) Electrochemical Characterization of the Interface between Atmospheric Noble Gas Plasma Jet and Aqueous Solution

Elucidation of general features of the interface between atmospheric pressure plasma jets and aqueous solutions would be beneficial to environmental, agricultural and biomedical applications. Such fundamental descriptions are critically important to design process chemistries and scale-up production. In this presentation, our recent efforts towards that end will be discussed. The focus of the talk will be on free jets of low temperature radiofrequency (RF) plasma generated using noble gas in contact with water, in contrast to the often used two-electrode configuration with e.g. micro-plasmas. Experiments will be presented in support of a perspective that views the plasma-liquid interface as a boundary condition that locally constrains the reduction potential, which can be controlled using parameters such as the plasma gas composition, applied RF power, and jet stand-off distance. A unique spatial distribution of the reduction potential that develops to maintain charge neutrality in the aqueous solution will be presented. The consequences for process design and scale-up will be expanded upon.

Deficiencies frequently encountered in the management of process safety information

Process Safety Information (PSI) provides the fundamental information necessary for developing the elements of Process Safety Management (PSM). We report the PSI management deficiencies found in PSM audits of more than 70 plants. It should be noted that the PSM audits were not limited to OSHA requirements. The deficiencies found were frequently encountered in the management of the PSI element. The chemical hazards information provided on the Safety Data Sheets (SDS) are not sufficient and may not be appropriate for the process condition used; therefore, the chemical hazards information should not be limited to only the SDS. Although the information provided by the SDS satisfies the OSHA requirements, it is suggested that management further develop the chemical hazards information necessary to ensure the safety of the process. Process incidents resulting from undesired reactions are more frequent than from the desired reaction. Therefore, in terms of safety, the process chemistry of the undesired reactions is essential information for the process technology. However, such undesirable reactions are not identified, and their process chemistries are lacking for most processes. The frequently encountered problem for the information of the process equipment is the inconsistency between the piping and instrument diagram and the actual process. Summarily, the necessary information of the PSI should be developed based upon the characteristics of the process.

(Invited) Enabling 5nm and Beyond Device Fabrication with New Etch Technologies

All logic device roadmaps predict significant change in the form and nature of logic at 5 nm. III-V’s, SiGe, Ge, nanowires and nano-sheets, while attractive as device options, bring pause to process and integration teams that need to integrate new materials or new material forms. Research grade devices are certainly possible today but high volume manufacturing of new devices in whatever form they may take requires change to unit processes available in today’s fabrication facilities. The question is whether something entirely new is needed or it is a matter of enhancing the capabilities of process and equipment that exists today. A key of those responsible for next generation logic is damage in one form or another by the (plasma) etch unit process. III-V’s, SiGe and Ge devices are particularly sensitive to damage. This has motivated calls for a complete move to thermal etch processes potentially upending available integration approaches. Unfortunately, thermal processes are themselves not damage free in that it is impossible not to leave interfaces and the immediate sub-surfaces unaltered. Fortunately, advances in plasma etch technology allow plasma etch to meet and exceed thermal process performance. Pulsing technology went a long way to mitigating damage caused during silicon device fabrication more than a decade ago. Now, advanced pulse technology applied to advanced plasma sources delivers performance equivalent to thermal processes by precise control of surface passivation, surface volatilization and surface reaction by-products. Concurrent advances in applying novel process chemistries (plasma based self-limited material removal and deposition processes) are also ready for new logic materials. Key is the availability of advanced materials chemistry simulations for use in process development. The research opportunities for new etch technology for “selective area etching” in advanced logic manufacturing will be the next frontier of R&D activities.

Systematic Framework for Design of Environmentally Sustainable Pharmaceutical Supply Chain Network

The current push towards sustainability has pressurized pharmaceutical companies to reduce greenhouse gas (GHG) emissions in their manufacturing supply chains (SCs). However, the heavily regulated nature of the pharmaceutical industry has necessitated decisions such as sourcing of raw materials including names and addresses of suppliers and siting of plants to be locked early during the registration of a new drug. This could result in SC inefficiencies during the drug commercial life leading to higher than necessary GHG emissions. This paper presents a systematic framework for design of a more sustainable pharmaceutical SC network at the commercial stage that can be performed during the early stages of drug development. The framework comprises the following steps. First, basic SC information including process chemistries, outsourcing strategies, and potential supplier and manufacturer sites is consolidated. Next, an analytic hierarchy process (AHP) is performed to identify the most suitable supplier and manufacturer sites followed by mapping the entire SC network by connecting all the sites that have been identified as high priority. Subsequently, a set of indicator metrics—namely, cost, lead time, and GHG emissions—is calculated to evaluate the economic and environmental performances of the network. The framework has been applied to an industrially motivated case study. Two network alternatives were proposed and analyzed based on their metrics together with synergies and trade-offs highlighted. The findings demonstrate the efficacy of the framework in generating different network alternatives and identifying the most sustainable one on the basis of economic and environmental benefits. As such, the framework is applicable to the early stages of drug development where information is very limited.

(Invited) Plasma Process Simulation for Advanced Semiconductor Applications

Next generation semiconductor device technology node logic and advanced memory fabrication etch [1] deposition [2] and functionalization [3,4] unit processes require management of process chamber species’ nature, flux and energy at all facets of a substrate and feature being fabricated. Management of profile (conformality), selectivity, deposition or etch rate, uniformity, damage and/or sub-surface and film “quality” needs via continuous or quasi-continuous processes is difficult as process chemistries and plasma source characteristics drive trade-offs innate to their combination. Fortified by more than two decades of progress in modelling and simulation, concurrent process and equipment development has overcome these difficulties. It is evident now to meet trade-off born difficulties in the future that self-limiting process technology will need to be used. In this case, chemistry control may mean parsing individual process steps into adsorption and desorption components [5]. Segregating processes include rapid cyclic etch and atomic layer deposition (ALD). Other examples of self-limiting processes include radical driven plasma doping. This presentation will discuss each of these processes in the context of their needs and how simulation drives their development. Simulation models discussed are based on an integrated approach (chamber through feature) with fluxes to surfaces from plasma source simulations (e.g., HPEM [6]) mated to feature scale simulations such as MCFPM. [7] Atomic layer etching for front end applications will be described that use this suite of simulation models. [8] While atomic layer deposition is more mature than it’s etch counterpart, plasma assisted ALD comes with mechanistic complexity both in the plasma and at surface. [9] Fortunately, quantum chemistry methods, [10] surface and plasma chemistry models can be linked to equipment simulations for concurrent process design. Three dimensional devices require source drain engineering to being about conformal electrical properties. An example is fin extension doping. Radical driven plasma doping can be conformal because of the self-passivating nature of a saturation layer created all around the surface of the fin during the doping process. Functionalizing topographic structures such as silicon, Ge or III-V fins sets severe constraints on the plasma itself. Fins must not erode but sufficient ion energy is required to disorder a single surface layer so that dopants may be infused. Plasma equipment simulations show that high microwave power and high pressure operation are sufficient to generate sufficient dopant radicals with a sufficient non-damaging flux of light ions to the surface to meet functionalization requirements. [11] The properties of the surface layer are very important. Using arsenic doping of silicon as an example, first principles calculations of ternary dopant silicon oxygen system were used to explore the surface film properties. [12] The calculations show that trade-offs between strain relaxation of the amorphous and the evolution of penalty energy as arsenic is introduced to the amorphous silica system creates a preferred stoichiometry film. This is one ingredient to maintaining conformality in the presence of different flux compositions all around a feature. The presentation will close with a look forward at how the new norm in modeling and simulation will involve addition of first-principles (quantum chemistry through device) to the integrated source through feature approach of the last two decades. [1] C. T. Carver et al., ECS J. Sol. St. Sci. Tech., 4 N5005-N5009 (2015) [2] S. M. George, Chem. Rev., 110, 111 (2010) [3] K. J. Kuhn, IEEE Trans. Elec. Dev., 59, 1813 (2012) [4] T. Tatsumi and J. Lee, Jpn. J. Appl. Phys., 53, 06JE06 (2014) [5] K. Ono and M. Tuda, Thin Solid Films, 374, 208 (2000) [6] M. Wang and M. J. Kushner, J. Appl. Phys 107, 023308 (2010) [7] A. Agarwal and M. J. Kushner, J. Vac. Sci. Technol. A 26, 498 (2008) [8] A. Ranjan et al., Proc. SPIE 9428, Advanced Etch Technology for Nanopatterning IV, 94280O (2015) [9] S. King, J. Vac. Sci. Technol. A, 29, 041501(2011) [10] J. Yoshikawa, AVS 60th Annual Symposium, Paper TF+PS-ThM12(2013) [11] H. Ueda et al., J. Appl. Phys., 115, 214904 (2014) [12] P. Ventzek et al., Appl. Phys. Lett., 105, 262102 (2014)

Efficient and flexible Focused Ion Beam micromachining of Solid Immersion Lenses in various bulk semiconductor materials – An adaptive calibration algorithm

Focused Ion Beam (FIB) micromachining of Solid Immersion Lenses (SILs) in substrate material offers optical analysis solutions for current and future technologies without the limitations of external SIL systems. This work presents an efficient single iteration calibration algorithm. This algorithm enables the implementation of FIB created SILs using a variety of substrate materials, process chemistries and most importantly different SIL shapes to match sample thicknesses. The successful application on silicon and silicon carbide is presented by creating a 50μm wide refractive lens segment with a radius of curvature of 60μm. Laser scanning microscope images of a silicon sample demonstrate the optical benefit with a measured resolution of 274nm.

Recovery of rhenium from molybdenum and copper concentrates during the Looping Sulfide Oxidation process

Rhenium is recovered during pyrometallurgical processing of molybdenum sulfide and copper sulfide ores; the traditional technology involves removing rhenium(VII) oxide, Re2O7, from the sulfurous gas phase generated during multiple hearth roasting (in molybdenum processing) and smelting (in copper processing). A new technology platform called Looping Sulfide Oxidation (LSO) has been proposed to produce molybdenum and copper using alternative process chemistries. A detailed thermodynamic study of the reaction conditions used in LSO process indicates that rhenium recovery is possible at higher rates than currently realized in the industry. Conditions at which Re2O7 is reduced to rhenium metal by S2 have been identified and key process conditions are outlined to maximize performance of the LSO scheme and rhenium recovery.

Process to Etch Ni and Pt Residues during Silicide Contact Electrode Processing Using Low Temperature Aqueous Solutions

During NiPtSi contact electrode processing and after the first thermal treatment to form Ni rich silicide, excessive Ni is removed by a strong acid mixture such as piranha (mixture of sulfuric acid and hydrogen peroxide. The post salicidation clean process has to be selective to all exposed materials: Si3N4, SiO2, NiPtSi, and NiPtSiGe (contact electrodes of source/drain for strain applications)). Performing a partition process with RTA1 (rapid thermal annealing) followed by Ni strip, followed by RTA2, and then with Pt strip is one method to check for NiPt removal. The Ni strip was performed using dilute nitric acid (20:1) and dilute aqua regia (1:5:4) and showed completed NiPt removal. A queue time study was also investigated after the Ni strip and after RTA2 for defect formation. Also, Pt removal using aqua regia solutions of various shelf-lives were tested. The result led to the conclusion that solutions of aqua regia with longer shelf-lives were also shown to be less effective in Pt residue removal. Using a High Productivity Combinatorial materials/process screening technique to reduce the number of product wafers used for evaluation process development, the etch rates of all the materials of interest were tested on blanket wafers. The chemistry consists of varying acid and base types and the relative combinations of these chemistries. Process conditions that consisted of various process chemistries, process temperatures, and degrees of fluid agitation (e.g. stirrer speed) were done on the same substrate.

Unconventional Chemistry for Unconventional Natural Gas

New process chemistries will be needed to replace petroleum with abundant natural gas as the most economical feedstock for fuels and chemicals.

Electron beam excitation method to study gas phase during etch processes

In process optical emission spectroscopy (OES) measurements, excitation mechanisms as dictated by the process plasma can be complex to analyze optical signals quantitatively. Applications of a new electron beam excitation method demonstrate distinct merits for plasma process diagnostics and process control. The electron energy control attribute of the method provides the means to optimize and monitor specific species optical emission in process chemistries to achieve process control such as endpoint. The authors present gas phase results from photoresist ash and SiO2 etch using O2 and CF4/Ar discharges, respectively. The effluent density variations as measured with the e-beam method during process stages demonstrate process endpoint detection. Simultaneous measurements with FTIR spectroscopy and direct plasma OES is also presented for comparison.

Controllable optical emission spectroscopy diagnostic system for analysis of process chemistries

Optical emission spectroscopy (OES) diagnostics have been employed for many years in plasma etch end point detection schemes. Unfortunately some newer process systems have much lower optical emission or limited optical access. To overcome such limitations, an OES diagnostic system making use of variable e-beam has been developed. That system is described and initial experimental results are presented. A strong correlation is observed between the optical emission intensity and e-beam current, a measurable electrical parameter. This correlation offers means to normalize optical signal and to be used as a feedback input to the electronics that control the plasma source. In addition there is a measurable response from the different lines due to energy of the electrons, indicating a new degree of freedom in the diagnostic that can be tapped for more precise analysis of end point.

Effect of Competing Reversible Reactions on Optimal Operating Policies for Plants with Recycle

A simple classification procedure for determining optimal steady-state operating policies for plants with recycle has recently been developed by Griffin et al. to cover complex process chemistries. (Griffin, D. W.; Mellichamp, D. A.; Doherty, M. F. AIChE J. 2008, 54, 2597). This procedure classifies a process chemistry into one of two groups of operating policies based solely on the reaction kinetics. The optimal operating policy for a bounded chemistry is to operate the reactor completely full for all production rates while a nonbounded chemistry may have a variable reactor volume subject to system constraints. The current work focuses on process chemistries with reversible reactions and demonstrates that the optimal operating policy can change depending on which reaction(s) is(are) reversible and the magnitude of the equilibrium constant(s). Process chemistries with a reversible desired reaction also exhibit multiple steady-states, but only one of the steady-states corresponds to feasible operating conditions.