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Simulations of Silicon Carbide Chemical Vapor Deposition
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.ORCID iD: 0000-0001-8116-9980
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Most of the modern electronics technology is based on the semiconducting material silicon. The increasing demands for smaller electronic devices with improved performance at lower costs drive the conventional silicon technology to its limits. To meet the requirements from the industry and to explore new application areas, other materials and fabrication methods must be used. For devices operating at high powers, high temperatures and high frequencies, the so-called wide bandgap semiconductors can be used with great success. Silicon carbide (SiC) and III-nitrides are wide bandgap materials that have gained increased interest in recent years. One important technique in manufacturing of electronic devices is chemical vapor deposition (CVD), by which thin layers can be deposited. These layers may have different electrical properties, depending on the choice of material and doping. Generally in CVD, a reactive gas mixture flows through a heated reactor chamber, where the substrates are placed. Complex chemical reactions take place in the gas and on the substrate surface, leading to many intermediate species and by-products, and eventually to the desired deposition. For the growth of device quality material it is important to be able to control the properties of the grown layers. These properties generally depend on the growth conditions in the reaction chamber, and on the chemistry of the deposition process. So far, empirical trial-and-error methods have been employed in the development of growth processes. Due to the lack of basic understanding of the governing physical processes, progress is costly and time consuming. Improving and optimizing the CVD process, as well as improving the fundamental understanding of the whole process is of great importance when good quality material should be produced. For this, computer simulations of the relevant physical and chemical phenomena can provide the necessary tools. This thesis focuses on computer simulations of the CVD process, in particular CVD of SiC. Simulations can be used not only as a tool for optimizing growth processes and reactor designs, they can also give information about physical phenomena that are difficult to measure, such as the gas-phase composition or the flow paths inside the reactor.

Heating of the CVD susceptor is a central part of the process. For the growth of high quality SiC a relatively high temperature must be used. A convenient method for heating to high temperatures is by induction. A low resistive material, such as graphite, is placed inside a coil, which is given an alternating current. The graphite is then heated by the induced currents due to ohmic resistance. In this thesis the temperature distribution inside a CVD reactor, and how it is influenced by changes in coil frequency, power input to the coil and graphite thickness, is investigated. It is shown that by changing the placement and shape of the coil and by using insulation material correctly, a more uniform temperature distribution can be obtained.

A model for the growth of SiC is used to predict growth rates at various process parameters. A number of possible factors influencing the growth rate are investigated using this model. The importance of including thermal diffusion and the effect of etching by hydrogen is shown, and the effect of parasitic growth investigated. Simulations show a mass transport limited growth, as seen from experiments.

An improved susceptor design with an up-lifted substrate holder plate is investigated and compared to a conventional hot-wall reactor and to a cold-wall reactor. It is shown that stress induced by thermal gradients through the substrate is significantly reduced in the hot-wall reactor, and that stress due to backside growth can be diminished using the new design. Positive side effects are that slightly higher growth rates can be achieved, and that the growth temperature can be slightly lowered in the new susceptor.

The doping incorporation behavior is thoroughly investigated experimentally for intentional doping with nitrogen and aluminum. The doping incorporation on both faces of SiC, as well as on two different polytypes is investigated. Equilibrium calculations are preformed, giving possible candidates for species responsible for the doping incorporation. To predict nitrogen doping concentrations, a simplified quantitative model is developed and applied to a large number of process parameters. It is seen that the same species as predicted by equilibrium calculations are produced, but the reactions producing these species are relatively slow, so that the highest concentrations are at the outlet of the reactor. It is thus concluded that N2 must be the major specie responsible for the nitrogen incorporation in SiC.

For the growth of III-nitrides, ammonia is often used to give the nitrogen needed. It is well known that ammonia forms a solid adduct with the metalorganic gas, which is used as the source for the group III elements. It would thus be beneficial to use some other gas instead of ammonia. Since purity is of great importance, N2 gas would be the preferred choice. However, N2 is a very stable molecule and difficult to crack, even at high temperatures. It is shown that hydrogen can help in cracking nitrogen, and that growth of III-nitrides can be performed using N2 as the nitrogen-bearing gas, by only small changes to a conventional hot-wall CVD reactor.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2002. , 49 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 773
National Category
Polymer Chemistry Materials Chemistry Other Physics Topics
Identifiers
URN: urn:nbn:se:liu:diva-104594ISBN: 91-7373-423-3 (print)OAI: oai:DiVA.org:liu-104594DiVA: diva2:697853
Public defence
2002-10-25, 10:15 (English)
Opponent
Supervisors
Available from: 2014-03-14 Created: 2014-02-19 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Investigation of the temperature profile in a hot-wall SiC chemical vapour deposition reactor
Open this publication in new window or tab >>Investigation of the temperature profile in a hot-wall SiC chemical vapour deposition reactor
2002 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 235, no 1-4, 352-364 p.Article in journal (Refereed) Published
Abstract [en]

The chemical vapor deposition (CVD) technique is widely used to grow epitaxial layers of silicon carbide. To meet the demands for high quality epitaxial layers, which have good morphology and a minimum variation of the doping and thickness, a good knowledge of the CVD process is essential. The present work uses a simulation tool to investigate several parameters influencing the heating of <!--[if !vml]--><!--[endif]-->a hot-wall CVD reactor. The simulations are set up as 2D axisymmetric problems and validation is made in a 2D horizontal hot-wall CVD reactor. By applying the knowledge achieved from the simulations, the temperature profile is optimized to give as large area as possible with homogeneous temperature. New susceptor and coil designs are tested. A very good agreement between the simulated and the measured results is obtained. The new design has a temperature variation of less than 0.5% over more than 70% of the total susceptor length at an operating temperature of 1650°C. In addition, the power input needed to reach the operating temperature is decreased by 15% compared to the original design. 3D simulations are performed to show that the changes made in the 2D case give similar results for the real 3D case.

Place, publisher, year, edition, pages
ScienceDirect, 2002
Keyword
A1. Computer simulation, A1. Heat transfer, A3. Chemical, vapor deposition, A3. Hot-wall epitaxy, B2. Semiconducting silicon carbide
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:liu:diva-15064 (URN)10.1016/S0022-0248(01)01831-0 (DOI)
Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2017-12-11Bibliographically approved
2.
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3. Predicted nitrogen doping concentrations in silicon carbide epitaxial layers grown by hot-wall chemical vapor deposition
Open this publication in new window or tab >>Predicted nitrogen doping concentrations in silicon carbide epitaxial layers grown by hot-wall chemical vapor deposition
2003 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 250, no 3-4, 471-478 p.Article in journal (Refereed) Published
Abstract [en]

A simple quantitative model for the surface adsorption of nitrogen has been developed to simulate the doping incorporation in intentionally doped 4H-SiC samples during epitaxial growth. Different reaction schemes are necessary for the two faces of SiC. The differences are discussed, and implications to the necessary model adjustments are stressed. The simulations are validated by experimental values for a large number of different process parameters with good agreement.

Keyword
A1. Doping, A1. Growth models, A3. Chemical vapor deposition, A3. Hot wall epitaxy, B2. Semiconducting silicon carbide
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46680 (URN)10.1016/S0022-0248(02)02513-7 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
4. Reducing stress in silicon carbide epitaxial layers
Open this publication in new window or tab >>Reducing stress in silicon carbide epitaxial layers
2003 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 252, no 1-3, 289-296 p.Article in journal (Refereed) Published
Abstract [en]

A susceptor for the epitaxial growth of silicon carbide, with an up-lifted substrate holder, is investigated and compared to other susceptor designs both experimentally and by the use of computational fluid dynamics simulations. It is shown that the wafer bending due to temperature gradients is diminished in a hot-wall reactor compared to growth in a cold-wall reactor. The substrate backside growth is diminished using the up-lifted substrate holder, limiting the substrate bending due to the backside growth. Thereby the stress built into the epitaxial layers during growth is significantly reduced. Simulations indicate a lower effective C/Si ratio over the wafer, and a lower preferable growth temperature, as compared to the original susceptor design. In addition a slightly higher growth rate is achieved

Place, publisher, year, edition, pages
Elsevier, 2003
Keyword
A1. Computer simulation; A3. Chemical vapor deposition; A3. Hot wall epitaxy; B2. Semiconducting silicon carbide
National Category
Condensed Matter Physics Other Physics Topics
Identifiers
urn:nbn:se:liu:diva-104590 (URN)10.1016/S0022-0248(03)00938-2 (DOI)
Available from: 2014-02-19 Created: 2014-02-19 Last updated: 2017-12-06Bibliographically approved
5. Using N2 as precursor gas in III-nitride CVD growth
Open this publication in new window or tab >>Using N2 as precursor gas in III-nitride CVD growth
2003 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 253, no 1-4, 26-37 p.Article in journal (Refereed) Published
Abstract [en]

Computational fluid dynamics simulations have been performed to explore the possibility of using nitrogen gas as a precursor to III-nitride growth. A chemical model for the gas-phase decomposition of N2 has been used to show that large enough amounts of reactive species can be formed under conditions not far from those used in normal metalorganic chemical vapor deposition. Simulations were performed in 2D for various concentrations of N2, and comparisons with the use of NH3 were made. A modified reactor design needed to achieve high enough concentrations of reactive species is suggested. The possibility to increase the growth rate and material quality in III-nitride growth is discussed.

Place, publisher, year, edition, pages
Elsevier, 2003
Keyword
A1. Computer simulation; A1. Growth models; A3. Hot wall epitaxy; A3. Metalorganic chemical vapor deposition; B2. Semiconducting III–V materials
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-104589 (URN)10.1016/S0022-0248(03)00971-0 (DOI)
Available from: 2014-02-19 Created: 2014-02-19 Last updated: 2017-12-06Bibliographically approved
6. Nitrogen doping of epitaxial Silicon Carbide
Open this publication in new window or tab >>Nitrogen doping of epitaxial Silicon Carbide
Show others...
2002 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 236, no 1-3, 101-112 p.Article in journal (Refereed) Published
Abstract [en]

Intentional doping with nitrogen of 4H- and 6H-SiC has been performed using a hot-wall CVD reactor. The nitrogen doping dependence on the temperature, pressure, C/Si ratio, growth rate and nitrogen flow has been investigated. The nitrogen incorporation for C-face material showed to be C/Si ratio independent, whereas the doping decreased with increasing C/Si ratio for the Si-face material in accordance with the “site-competition” model. The nitrogen incorporation was constant in a temperature “window” of 75°C on Si-face material indicating a mass transport limited incorporation. Increasing the growth rate resulted in a decrease of nitrogen incorporation on Si-face but an increase on C-face material. Finally, a comparison between previously published results on cold-wall CVD-grown material and the present hot-wall-grown material is presented.

Place, publisher, year, edition, pages
ScienceDirect, 2002
Keyword
A1. Doping, A3. Hot wall epitaxy, B2. Superconducting materials
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:liu:diva-15068 (URN)10.1016/S0022-0248(01)02198-4 (DOI)
Note
The status of this article on the day of the defence was: Submitted and the title of the article was "Nitrogen doping of Silicon Carbide: Effect of Process Parameters"Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2017-12-11Bibliographically approved
7. Aluminum doping of epitaxial Silicon Carbide
Open this publication in new window or tab >>Aluminum doping of epitaxial Silicon Carbide
Show others...
2003 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 253, no 1-4, 340-350 p.Article in journal (Refereed) Published
Abstract [en]

Intentional doping of aluminum in 4H and 6H SiC has been performed using a hot-wall CVD reactor. The dependence of aluminum incorporation on temperature, pressure, C/Si ratio, growth rate, and TMA flow has been investigated. The aluminum incorporation showed to be polarity dependent. The high aluminum incorporation on the Si-face is closely related to the carbon coverage on the SiC surface. Changes in process parameters changes the effective C/Si ratio close to the SiC surface. Increased growth rate and C/Si ratio increases the aluminum incorporation on the Si-face. Diffusion limited incorporation occurs at high growth rate. Reduced pressure increases the effective C/Si ratio, and at low growth rate, the aluminum incorporation increases initially, levels off at a critical pressure, and continues to decrease below the critical pressure. The aluminum incorporation showed to be constant in a temperature range of 50°C. The highest atomic concentration of aluminum observed in this study was 3×1017 and 8×1018 cm−3 in Si and C-face, respectively.

Place, publisher, year, edition, pages
ScienceDirect, 2003
Keyword
A1. Doping; A1. Growth models; A3. Chemical vapor deposition processes; A3. Hot wall epitaxy; B2. Semiconducting silicon carbide
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:liu:diva-15055 (URN)10.1016/S0022-0248(03)01045-5 (DOI)
Note
The status of the article on the defence day was: Submitted and the original title was "Aluminum doping of Silicon Carbide: Effect of Process Parameters".Available from: 2008-10-13 Created: 2008-10-13 Last updated: 2017-12-11Bibliographically approved

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