X-ray rocking curve characterization is a relatively fast and nondestructive technique that can be utilized to evaluate the crystal quality of SiC substrates. The contribution of lattice curvature to rocking curve broadening is estimated, and shown to be the major contribution to the measured broadening (FWHM). The feedback on lattice quality is used to optimize our SiC growth process. In the optimized growth runs, the typical variation in rocking curve sample angle Ω across the entire 3” diameter wafer is about 0.2 degrees. Possible mechanisms leading to changes in the lattice curvature are discussed.