Determination of the silica polymorphs thermally grown on silicon carbide as a function of temperature and time using X-ray photoelectron spectroscopy (XPS)
EMSL Project ID
16692
Abstract
Electronic devices based on silicon carbide (SiC) represent a good choice for the next generation of high temperature, high power electronics applications. Conditions are extreme and this all but rules out only a handful of materials and materials systems.Like silicon, it is possible to grow a thermal SiO2 oxide over SiC. While this enables SiC MOS technology to somewhat follow the highly successful path of Si MOS technology, there are nevertheless important differences in insulator quality and device processing that are presently preventing SiC MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) from realizing their full beneficial potential.
4H-SiC and 6H-SiC are of considerable technological interest due to their large band gaps and high electron mobilities. Recently, high quality wafers have been grown. Moreover, polycrystalline SiC may soon be used as an electronic packaging material because it exhibits high hardness, high thermal conductivity, low coefficient of thermal expansion and excellent resistance to erosion and corrosion.
Both polycrystalline (slip casted SiC) and single crystal (4H-SiC) silicon carbide samples have been annealed (oxidized) in air for up to 100 hours between 800oC and 1700oC resulting in the formation of an oxide layer.
Silica occurs in many phases and XPS allows their distinction (e.g., cristobalite, quartz, tridymite) by acquiring C1s, O1s, and Si2p. The literature has proved possible to distinguish between polymorphs of silica. As evident from the Si2p and O1s spectra peak positions already reported there are modest but measurable differences between the photoelectron spectra of quartz and the various other SiO2 polymorphs. Therefore, chemical shifts of Si2p and O1s XPS binding energies offer a tool for probing the chemical bonds for polymorphs of silica minerals. If it is possible to collect data on the Si KLL Auger line, this would provide more information as one can often see differences in the coordination of oxygen.
Running a set of standards would probably be helpful as the data in the literature varies in reliability and accuracy. On an absolute basis it is very difficult to distinguish between polymorphs based on peak position alone if the initial data was collected on different systems by different people.
Also, as the surface material formed is a glass (or a crystal), I would not be concerned about collecting XPS data long after the oxidation as each of the principal crystalline phases can persist for an indefinite time, under certain conditions of temperature and pressure outside its range of stability or its usual range of formation. The reconstructive conversions of silica are very unlikely due to the leptonic sluggishness at room temperature.
The flood gun (or the magnetic lens available on the Kratos spectrometer) will prevent sample charging.
I have exchanged numerous emails with Don Baer and Mark Engelhard about the feasibility of these experiments. This study shall be fairly quick; say 2 days at most. I plan on using the Kratos XPS equipment. The samples are ready. Slight cleaning of the surface with sputtering will be required.
Project Details
Project type
Exploratory Research
Start Date
2005-10-01
End Date
2006-04-18
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Oxidation of silicon carbide and the formation of silica polymorphs