低微管100mm碳化硅晶片

Abstract

A high quality single crystal wafer ofSiC is disclosed havinga diameter ofat least about 100 mm and a micropipe densityofless than about 25 cm-2.

BACKGROUND OF THE INVENTION

The present invention relates to low defect Silicon Carbidewafers and their use as precursors for semiconductor purposes, and to seeded sublimation growth oflarge, high-quality silicon carbide single crystals.Silicon carbide has found use as semiconductor materialfor various electronic devices and purposes in recent yearsSilicon carbide is especiallyuseful due to its physical strengthand high resistance to chemical attack. Silicon carbide alsohas excellent electronic properties, including radiation hard-ness, high breakdown field, a relatively wide band gap, highsaturated electron drift velocity, high-temperature operation.and absorption and emission of high-energy photons in theblue, violet, and ultraviolet regions ofthe spectrum.Single crystal silicon carbide is often produced by a seededsublimation growth process. In a typical silicon carbidegrowth technique, the seed crystal and a source powder areboth placed in a reaction crucible which is heated to thesublimation temperature of the source and in a manner thatproduces a thermal gradient between the source and the mar-ginally cooler seed crystal. The thermal gradient encouragesvapor phase movement ofthe materials from the source to theseed followed by condensation upon the seed and the result-ing bulk crystal growth. The method is also referred to asphysical vapor transport (PVT).

In a typical silicon carbide growth technique, the crucibleis made of graphite and is heated by induction or resistance.with therelevant coils and insulation being placed to establishand control the desired thermal gradient. The source powderis silicon carbide, as is the seed. The crucible is orientedvertically, with the source powder in the lower portions andthe seedpositioned at the top, typically on the seedholder; seeU.S.Pat. No.4,866,005 (reissued as No. Re 34,861) thecontents of which are incorporated entirely herein by refer-ence. These sources are exemplary, rather than limiting descriptions of modern seeded sublimation growth techniques.

The invention is also related to the following copendingandcommonly assignedU.S.application Ser.No.10/628,189filed Jul. 28,2003 for Growth of Ultra-High Purity SiliconCarbide Crystals in an Ambient Containing Hydrogen; SerNo.10/628.188 fled Jul. 28,2003 for Reducing NitrogenContent in Silicon Carbide Crystals by Sublimation Growthin a Hydrogen-Containing Ambient; Ser.No.10/707,898filed Jan.22.2004 for Silicon Carbideon Diamond Substratesand Related Devices and Methods: Ser.No.60/522.326 filedSep.15, 2004 for Seed Preparation for the Growth of HighQuality Large Size Silicon Carbide Crystals; Ser.No.10/915,095 filed Aug. 10, 2004 for Seed and Seedholder Combinations for High Quality Growth of Large Silicon Carbide Single Crystals; and Ser. No. 10/876,963 filed Jun. 25, 2004 for One Hundred Millimeter High Purity Semi-Insulating Single Crystal Silicon Carbide Wafer. The contents of these applications are likewise incorporated entirely herein by refrernce.

Although the density ofstructural defects in silicon carbidebulk crystals has been continually reduced in recent yearsrelatively high defect concentrations still appear and havebeen found to be difficult to eliminate, e.g. Nakamura et al..Ultrahigh quality silicon carbide single crystals,’NatureVol. 430, Aug. 26, 2004, page 1009. These defects can causesignificant problems in limiting the performance characteris-tics of devices made on the substrates, or in some cases canpreclude useful devices altogether. Current seeded sublima-tion techniques for the production oflarge bulk single crystalsof silicon carbide typically result in a higher than desiredconcentration ofdefects on the growing surface ofthe siliconcarbide crystal. Higher concentrations of defects can causesignificant problems in limiting the performance characteris-tics of devices made on the crystals, or substrates resultingfrom the crystals. For example, a typical micropipe defectdensity in some commercially available silicon carbidewafers can be on the order of 100 per square centimeter(cm-2). A megawatt device formed in silicon carbide, how-ever, requires a defect free area on the order of0.4 cm-2.Thusobtaining large single crystals that can be used to fabricatelarge surface area devices for high-voltage, high currentapplications remains a worthwhile goal.

Although small samples oflow-defect silicon carbide havebeen available,a broader commercial use of silicon carbiderequires larger samples, and in particular, larger wafers. Byway of comparison,100 mm (4") silicon wafers have beencommercially available since 1975 and 150 mm (6") siliconwafers became available in 1981.Gallium arsenide(GaAs)isalso commercially available in both 4"and 6" wafers.Thusthe commercial availability of 50 mm (2") and 75 mm (3")SiC wafers lags behind these other materials and to someextent limits the adoption and use ofSiC in a wider range ofdevices and applications.

Micropipes are common defects that develop or propagateduring the seeded sublimation production of SiC crystalsOther defects include threading dislocations, hexagonalvoids, and screw dislocations. If these defects remain in theSiC crystal, then resulting devices grown on the crystal mayincorporate these defects.

The nature and description of specific defects is generallywell understood in the crystal growth art. A micropipe is ahollow core super-screw dislocation with its Burgers vectorlying along the c-axis. A number of causes have been pro-posed or identified for the generation of micropipes. Theseinclude excess materials such as silicon or carbon inclusions.extrinsic impurities such as metal deposits, boundary defectsand the movement or slippage ofpartial dislocations.See e.gPowell et al, Growth ofLow Micropipe Density SiC WafersMaterials Science Forum, Vols.338-340,pp 437-440(2000)Hexagonal voids are flat, hexagonal platelet-shaped cavi-ties in the crystal that often have hollow tubes trailing beneaththem.Some evidence shows that micropipes are associatedwith hexagonal voids.A relatively recent discussion of suchdefects (exemplary and not limiting) is set forth in Kuhr et al.Hexagonal Voids And The Formation Of Micropipes DuringSiC Sublimation Growth, Journal of Applied Physics,Vol-ume 89, No.8, page 4625 (April 2001).