碳化硅的化学机械抛光

Abstract

Slurry compositions and chemically activated CMP methodsfor polishing a substrate having a silicon carbide surfaceusing such slurries.In such methods, the silicon carbide sur-face is contacted with a CMP slurry composition that com-prises i) a liquid carrier and ii) a plurality of particles havingat least a soft surface portion, wherein the soft surface portionincludes a transition metal compound that provides a Mohshardness <6, and optionally iii) an oxidizing agent. The oxi-dizing agent can include a transition metal. The slurry ismoved relative to the silicon carbide comprising surfacewherein at least a portion of the silicon carbide surface isremoved.

BACKGROUND

Silicon carbide possesses unique electrical and physicalproperties that make it suitable for high power, high fre-quency and high temperature electronic devices includingICs. Such properties have fueled an intense research effort inthe last several years that has prompted the need to developlarger sized,epi-ready and substantially defect/damage-freesilicon carbide wafers.

The preparation of silicon carbide wafers is known torequire multiple polishing steps including a mechanical pol-ishing step in which particles which are typically harder thansilicon carbide (Mohs hardness of 9, Knoop hardness 2,4003,000 Kg/mm), such as boron nitride(BN; Mohs hardness of9.9,Knoop hardness 4,500-5,000 Kg/mm2) or diamond(Mohs hardness of 10, Knoop hardness 8,000-12,000Kg/mm2) or Boron Carbide (Mohs hardness 9.35, Knoophardness 2.900-3,580 Kg/mm~) are used to achieve reason-able silicon carbide polishing rates. The very hard particlesrequired for the mechanical polishing step generally results ina high degree of damage to the silicon carbide surface includ.ing scratches and dislocations which generally develop bothat the surface and sub-surface of the wafer. The mechanicalpolishing step is typically followed by a CMP step which usesparticles that are still abrasive, but are less abrasive as com-pared to diamond or BN,such as aluminum oxide (Mohshardness about 9,Knoop hardness 1,800-2,200 Kg/mm).titania (Mohs hardness of5.5 to 6.5 Knoop Hardness 500-600Kg/mm~), or Garnet Mohs hardness about 8, Knoop hardness1360 Kg/mm2,silica/quartz (Mohs hardness of 7, KnoopHardness 900-1,200 Kg/mm2),or zirconia (Mohs hardnessabout 8, Knoop hardness 1,120 Kg/mm2 to polish the surfaceregions and attempt to reduce the surface and sub-surfacedamage induced by the mechanical polishing.

Typically the abrasives that are harder than silicon carbideprovide reasonably high polishing rates, but cause significantsurface and sub-surface damage. The abrasives which aresofter than silicon carbide typically provide low polishingrates, and significantly less damage. Since the CMP particlesused are still significantly abrasive, new damage is generatedduring the CMPprocess.Moreover, since silicon carbide andsilicon carbide comprising materials are generally chemicallyinert materials, the CMP process typically is very slow, andthus requires a long cycle time, as the slurry chemicals do notreact with the silicon carbide comprising surface. Therefore.there is a need to develop new CMP slurries and/or methodsfor polishing silicon carbide comprising materials whichdecrease damage and increase the polishing rate.

SUMMARY

This Summary is provided to comply with 37 C.F.R.S1.73presenting a summary of the invention to briefly indicate thenature and substance ofthe invention.It is submitted with theunderstanding that it will not be used to interpret or limit thescope or meaning of the claims.Embodiments ofthe present invention describe slurry com-positions and chemically activated CMP methods for polish-ing a substrate having a silicon carbide comprising surfaceusing such slurries.In such methods, the silicon carbide com-prising surface is contacted with a CMP slurry compositionthat comprises i) aliquid(e.g. water) carrier, ii) and apluralityofparticles having at least a soft surface portion, wherein thesoft surface portion comprises a transition metal compoundthat provides a Mohs hardness 6 or Knoop Hardness less than900 Kg/mm2.Optionally, iii) an oxidizing agent can beadded. The slurry is moved relatively near or close to thesilicon carbide comprising surface, wherein at least a portionofthe silicon carbide comprising surface is removed.

The soft surfaced particles can be what are referred toherein as “coated particles” in some embodiments of theinvention or“soft functionalized particles”in other embodi-ments ofthe invention.Soft functionalized particles generallycomprise a thin soft surface coating comprising a waterinsoluble compound ofa transition metal on an abrasive sur-face. Soft functionalization is defined herein as the arrange-ment where the thickness of the transition metal comprisingcoating on the core particles is between 0.001 monolayers to10monolayers, and comprised oftransition metal comprisingmaterials that have a Knoop Hardness of 900 Kg/mm2 whenmeasured in their bulk form. The soft surface coating of thesoft functionalized particles can be a discontinuous or con-tinuous coating, and its thin nature results in its surface prop-erties generally being different from the core but having ahardness that will generally be similar to the core. In contrast,coated particles have a coating that is generally a continuouscoating that is thicker and is typically much thicker (e.g.>10monolayers to 100,000 monolayers (about 30 microns)) ascompared to the coating for the soft functionalized particlesand its surface properties surface properties and hardness willgenerally be controlled by the coating and thus be differentfrom the core.

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.