THOMAS YOUNG CENTRE:
THE LONDON CENTRE FOR THEORY AND SIMULATION OF MATERIALS
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TYC Lunchtime Get-Together
Thursday 2nd February
Time: 1pm
Venue: Nyholm Room, Department of Chemistry, UCL
Contact: TYC Administrator
Tel: +44 (0)20 7679 9950
Email: tyc-administrator@ucl.ac.uk
TYC@UCL Lunchtime Get-Togethers consist of two short presentations from either students, visitors or academics talking place over lunch and drinks. They are a great opportunity to get to meet other students, catch up with your friends and colleagues, and listen to members and visitors talk about their research.
Food and drink will be provided so please just bring yourselves!
This month's talks are:
Simulations of Industrial Plasma Processes
Sergio Lopez-Lopez
We have performed realistic simulations of a relevant industrial process such as the SF6-based processing of Silicon. The goal of this work was to validate models of the gas and surface processes, and our results point to the need for more high-quality input on surface chemistry and feature profiling.
Electrically driven plasmas containing halogens are very used in different material modification and surface cleaning processes. Sulfur Hexafluoride (SF6) is used industry-wide in a range of processes for the dry etching of silicon or silicon dioxide for microelectronic feature definition, such as the Bosch process. However, the performance and efficiency of different processes and machines can vary widely, and the use of simulations can give us significant insight into the optimization problem and provide a low cost means for further development. That is especially relevant in the case of SF6, given its environmental impact, with a Greenhouse Warming Potential that is 22,000 times that of CO2. It is therefore vital to use SF6 sparingly and efficiently in every process, and simulation can help to find ways of remediating harmful waste gases and optimize the process for typical processing goals (e.g. etch rate, uniformity) as well as improving SF6 consumption efficiency and other environmental measures.
A key aspect of the plasma processes here considered is that some type of work is done at the plasma / surface boundary layer, and realistic simulations must therefore incorporate the surface material and the etch product chemistry. This increases drastically the complexity of the problem but is the only way to represent all of the appropriate physics. Radical species from the surface entering the gas phase will take part in the phase and surface reactions that are associated with the parent gas, including negative ion formation and electron dissociation among others.
Here we present 2D simulations of an inductively driven SF6 silicon etch process in the GEC Reference Cell, building upon previous calculations of SF6 plasma chemistries using Quantemol-P. Etch rate, pressure and power trends along with chamber wide contour plots of gas-phase species concentrations and fundamental plasma properties are considered. We have
found a good agreement with experimental results, which validates the underlying model and points to the important role of simulation-assisted plasma process development and optimization.
and
Controlling the bioactivity of modified silicate glass
Dr Jamieson Christie
A wide range of materials are implanted into the human body for medical reasons, from dental fillings to artificial hips. The material used for the implant must have the appropriate properties for the application. One property which is very relevant is bioactivity, that is, the tendency of a material to form a chemical bond to bone or soft tissue when placed in the body.
It has long been known that by changing the composition of modified silicate glasses, their bioactivity can be tuned. In this talk, I outline our recent classical and first-principles molecular dynamics simulations which have been used to elucidate the structure of various glasses, and to identify the microscopic structural features which correlate with the bioactivity. The required amount of bioactivity depends on the application, and I will discuss two applications in particular: (i) the incorporation of yttrium into different silicate glasses for in situ radiotherapy, and (ii) the incorporation of fluorine into bioactive 45S5 silicate glass for dental applications.
Food and drink will be provided so please just bring yourselves!
This month's talks are:
Simulations of Industrial Plasma Processes
Sergio Lopez-Lopez
We have performed realistic simulations of a relevant industrial process such as the SF6-based processing of Silicon. The goal of this work was to validate models of the gas and surface processes, and our results point to the need for more high-quality input on surface chemistry and feature profiling.
Electrically driven plasmas containing halogens are very used in different material modification and surface cleaning processes. Sulfur Hexafluoride (SF6) is used industry-wide in a range of processes for the dry etching of silicon or silicon dioxide for microelectronic feature definition, such as the Bosch process. However, the performance and efficiency of different processes and machines can vary widely, and the use of simulations can give us significant insight into the optimization problem and provide a low cost means for further development. That is especially relevant in the case of SF6, given its environmental impact, with a Greenhouse Warming Potential that is 22,000 times that of CO2. It is therefore vital to use SF6 sparingly and efficiently in every process, and simulation can help to find ways of remediating harmful waste gases and optimize the process for typical processing goals (e.g. etch rate, uniformity) as well as improving SF6 consumption efficiency and other environmental measures.
A key aspect of the plasma processes here considered is that some type of work is done at the plasma / surface boundary layer, and realistic simulations must therefore incorporate the surface material and the etch product chemistry. This increases drastically the complexity of the problem but is the only way to represent all of the appropriate physics. Radical species from the surface entering the gas phase will take part in the phase and surface reactions that are associated with the parent gas, including negative ion formation and electron dissociation among others.
Here we present 2D simulations of an inductively driven SF6 silicon etch process in the GEC Reference Cell, building upon previous calculations of SF6 plasma chemistries using Quantemol-P. Etch rate, pressure and power trends along with chamber wide contour plots of gas-phase species concentrations and fundamental plasma properties are considered. We have
found a good agreement with experimental results, which validates the underlying model and points to the important role of simulation-assisted plasma process development and optimization.
and
Controlling the bioactivity of modified silicate glass
Dr Jamieson Christie
A wide range of materials are implanted into the human body for medical reasons, from dental fillings to artificial hips. The material used for the implant must have the appropriate properties for the application. One property which is very relevant is bioactivity, that is, the tendency of a material to form a chemical bond to bone or soft tissue when placed in the body.
It has long been known that by changing the composition of modified silicate glasses, their bioactivity can be tuned. In this talk, I outline our recent classical and first-principles molecular dynamics simulations which have been used to elucidate the structure of various glasses, and to identify the microscopic structural features which correlate with the bioactivity. The required amount of bioactivity depends on the application, and I will discuss two applications in particular: (i) the incorporation of yttrium into different silicate glasses for in situ radiotherapy, and (ii) the incorporation of fluorine into bioactive 45S5 silicate glass for dental applications.
