Micropipes

Micropipes, silicon carbide, 22 532 Micropipette solution deposition fabrication method for inorganic materials, 7 415t... 

It is also interesting to note that the technique is shown to reduce micropipes by 80% during each run [35]. The micropipes close at the interface by some type of hollow core-closing effect. Very low micropipe densities have been recorded using this technique, which is clearly much faster in improving material quality than seeded sublimation growth. 

Figure 1.11 Simuiation of the yieid of various sizes of Schottky diodes versus micropipe density for randomiy distributed micropipes. The right-hand figure is a detaii of the ieft-hand figure. Micropipes iocated on the active area or JTE region render a faiied device, however, micropipes iocated in between the devices are considered harmiess.

Figure 1.11 is a simulation of randomly distributed micropipes, however, there is normally a tendency to cluster the micropipes, which would give somewhat better yields. Also, a significant amount of micropipes land in between the devices where the wafers are diced and these are considered harmless in the simulation. 

Similar research has been done on planes perpendicnlar to the [0001] basal plane. Micropipe-free material has been grown, however, new defects appear as reported by the authors [60]. 

The sublimation sandwich method (SSM) is similar to the sublimation method, except for the small distance between source powder and substrate, 2-5 mm [10-12], Ga or GaN was used as a source and the substrate was sapphire or 6H-SiC. The optimal growth temperature was around 1200°C as temperatures lower than 1150°C caused the formation of structural defects such as voids and micropipes. Polycrystalline GaN was grown under 1050°C. At higher temperatures, GaN was thermally decomposed. The growth rate is much higher, up to 300 pm/hr [10] or 0.2 - 1.1 mm/hr [12], and crystalline GaN with the maximum thickness of 500 pm could be obtained. 

Celata, G.P., Single-phase heat transfer and fluid flow in micropipes. T Int. Conf. on Microchannels and Minichannels, Rochester, N.Y., AprU 24-25, (2003). 

Tunc, G., and Bayazitoglu, Y., (2002) Convection at the Entrance of Micropipes with Sudden Wall Temperature Change, Proceedings of the ASME IMECE. 

Aydm, O. and Avci, M., Heat and Fluid Flow Characteristics of Gases in Micropipes, Int. J. Heat Mass Transfer, vol. 49, pp. 1723-1730, 2006. 

G. Tunc and Y. Bayazitoglu, Convection at the entrance of micropipes with sudden wall temperature change, Proceedings of IMECE, November 17-22, 2002, New Orleans, Louisiana. 

In order to produce SiC material of the level of quality required for device applications, chemical vapor deposition (CVD) is currently used as the primary growth technique for SiC epitaxy [2], Due to the continuous improvements in commercial substrate quality, the presence of micropipes in SiC epilayers is not the device yield limiting issue as it was a decade ago. However, the epitaxially grown SiC films still suffer from other extended defects such as basal plane and threading edge dislocations as well as point defects. The vision of growing SiC on porous SiC was to reduce the concentration of these defects and thus improve the epitaxial layer quality for device applications. 

No Hall data 1016 Undoped, p>2000Qcm micropipes 102 to 103cm2, [14]... 

SiC power devices are expected to be superior to Si devices even at room temperature. However, the practical difficulties are related to a limited yield of large area devices due to the existence of so-called micropipes (or voids) [10]. The density of these micron size defects has steadily decreased over the years reaching approximately 100 to 400 cm 2 in the state-of-the-art 6H-SiC substrates [11]. These defects are formed during the substrate growth. They... 

High ohmic contact resistances in SiC devices present a serious limitation for high frequency performance. Furthermore, the problem of ohmic and Schottky contact thermal stability has not been solved. Contacts (and, sometimes, packages) usually limit the maximum SiC device operating temperatures. The existence of micropipes in 6H- and 4H-SiC material leads to a low yield for power devices. Improvements in material quality, the development of bulk 3C-SiC for 3C-SiC homoepitaxy, and the development of better contacts are of primary importance for the advancement of the SiC device technology. 

Recent topics in SiC research in Japan are micropipes in wafers, control of polytype in epitaxy, surface analysis of epitaxial layers, application for power devices, device simulation, and others [10]. 

Recent reviews on the growth of high-purity SiC single crystals and their properties have been given by Muller et al. [195] and Augustine et al. [196]. Today, wafer diameters up to 50 mm are feasible on an industrial scale for the polytypes 4H and 6H the density of micropipe defects can be reduced to less than 100 cm (down to about 1 cm ). 

Figure 12.27a Reprinted with permission from Gutkin, M.Y., Sheinerman, A.G., Argunova, T.S., Mokhov, E.N., Je, J.H., Hwu, Y, Tsai, W-L., and Margaritondo (2003) Micropipe evolution in silicon carbide , Appl. Phys. Lett. 83, 2157. Copyright 2003, American Institute of Physics. Figure 12.27b Reprinted with permission from Qian, W., Rohrer, G., Skowronski, M., Doverspike, K., Rowland,...

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