碳化硅单晶的制造方法

The soft surfaced particles in slurries according to embodi-ments of the invention have been found to unexpectedly pro-vide high polishing rates considering the much harder andhighly inert silicon carbide comprising surface, such asremoval rates ofz200 nm/hr. Moreover, slurries according toembodiments of the invention have been found to signifi-cantly reduce surface and sub-surface damage present fromearlier processing.Accordingly, embodiments of the inven-tion provide new CMP slurries and related methods for pol-ishing silicon carbide comprising materials which signifi-cantly increase the polishing rate and decrease damage to thesilicon carbide comprising surface.

FIELD OF THE INVENTION

The present invention relates to a monocrystalline siliconcarbide with a uniform concentration of a dopant element, awafer of the monocrystalline silicon carbide with a uniformconcentration of a dopant element and a manufacturingmethod thereof. This invention is particularly suitable forhigh-resistance monocrystalline silicon carbideSilicon carbide (SiC) is a wide-gap semiconductor with awide width of forbidden gap ranging from 2.2 to 3.3 eV. SiChas been studied as an environment-resistant semiconductormaterial since SiC has excellent physical and chemical prop-erties.In particular, SiC has been recently actively researchedwith a focus on its application to short-wavelength opticaldevices andhigh frequency, high power electronic devices. Inthe application ofmonocrystalline SiC to the semiconductorfield,high quality monocrystals with a large area aredemanded. Also, for use as a substrate for a high frequencydevice, high electrical resistance is also required in additionto high crystal quality.

Conventionally, for research purposes,sublimationmethod (Lely method) has been used for obtaining monoc-rystalline SiC of a size that enables the preparation of asemiconductor element. However, this method can provideonly an area ofmonocrystal that is small in size.In additionit is diffcult to control the dimension, shape, crystal poly-types and concentration of carrier impurities. On the otherhand, a CVD method has been used to form and grow cubicmonocrystalline SiC on a heterogeneous substrate, such as Siusing heteroepitaxial growth. This method can provide anarea of monocrystal that is large in size. However, since thelattice mismatch between SiC and Si reaches about 20%, theobtained monocrystalline SiC includes many defects (up to10%cm2), which is far from a high quality monocrystal. Tosolve these problems, a modified Lely method where subli-mation-re-crystallization is performed using monocrystallineSiC as a seed crystal is proposed (Yu. M. Tairov and V. F.Tsvetkov, Journal ofCrystal Growth, Vol. 52 (1981) pp.146-150). This modified Lely method enables the growth ofmonocrystalline SiC with control of crystal polytypes (6Htype, 4Htype, 15R type etc.), shape, carrier type and concen-tration.

Currently, monocrystalline SiC wafers of diameters ranging from 2 inches (50 mm) to 3 inches (75 mm) are cut froma monocrystalline SiC made by the modified Lely methodThis is used for manufacturing devices in the field of powerelectronics.In the practical application to devices, dependingupon the intended purpose, it is necessary to adjust the conductivity type and/or resistivity ofthe crystal. This is usuallyaccomplished by controlling the kind and concentration ofdopant. However it is very difficult to uniformly dope thecrystal when the vapor pressure of the dopant is greatly different from that of SiC.As an example, a SiC wafer for highfrequency devices is described below.

Recently, gallium nitride (GaN), which has superior properties to that of silicon (Si) or gallium arsenide (GaAs), hasdrawn attention. Rutberg & Co., Gallium Nitride: A MaterialOpportunity (2001) discusses gallium nitride as a material forhigh frequency semiconductor devices.In order to make aGaN device, it is necessary to form a monocrystalline thinfilm of GaN on a monocrystalline substrate. A sapphire sub-strate is one ofthe more common substrates. Sapphire has theadvantage ofbeing useful to stably manufacture a monocrys-tal with fairly good quality. However, the difference in latticeconstant value between sapphire and GaN is 13.8%. Thistends to cause deterioration of the GaN thin film. Also, sap-phire has a problem concerning heat release during operationof the device since the heat conductivity is as low as 0.42W/cmK.Thus, at present, GaN high frequency devices donot allow perfect function. On the other hand, the differencein the lattice constant value between monocrystalline SiC andGaN is as small as 3.4%, which makes it possible to form ahigh quality GaN thin film. Also, the heat conductivity ofmonocrystalline SiC is as high as 3.3 W/cm·K, which provides good heat release. Therefore, since major improve.ments can be expected if monocrystalline SiC is used as asubstrate, the employment of monocrystalline SiC substrateshave been recently desired in the field of GaN high frequencydevices.