Patent ID: 7022636

Claim:
A ceramic member for semiconductor manufacturing equipment which is formed of an alumina-based sinter comprising an yttrium-aluminum-garnet at the amount of 3 to 50 wt %, silicon oxide at the amount of not more than 0.2 wt % and the balance substantially alumina, wherein the sinter has dielectric loss of not more than 4×10 −4 in the frequency range of 10 MHz to 5 GHz, a 290 MPa or more four point bending strength, and a 15 GPa or more Vickers hardness, wherein the ceramic sinter comprises an alumina phase having mean crystal grain size in a range of 2 to 10 μm and a yttrium-aluminum-garnet phase having a mean crystal grain size in a range of 1.5 to 5 μm, wherein the ratio of the mean crystal grain size of the alumina phase to that of the yttrium-aluminum-garnet phase is larger than 1 and smaller than 7, wherein a starting mixture comprises an alumina powder having grain size of 1 to 15 μm and yttrium-aluminum-garnet powder having grain size of 0.6 to 1.2 μm and the mixture is fired at a temperature range of 1500 to 1750° C. where the crystal grains of alumina and yttrium-aluminum-garnet can not grow abnormally.