Abstract: A polishing method for a gallium nitride wafer includes a holding step of holding a first surface side of the gallium nitride wafer by a holding table, and a polishing step of polishing the gallium nitride wafer while supplying a polishing liquid to an area between a polishing pad and the gallium nitride wafer in a state in which the polishing pad is in contact with a second surface located on a side opposite to the first surface side of the gallium nitride wafer held by the holding table. The polishing liquid contains dissolved therein permanganate and a water-soluble ionic compound including one of or both nitrate ions and cerium(IV) ions.

Abstract: A resin member for supporting a workpiece has urethane linkages deriving from a reaction between a polyether polyol and an aliphatic isocyanate. Note that, preferably, the resin member has transmittance of not less than 74.88 for light of a wavelength of 550 nm. In addition, preferably, the resin member has Shore A hardness of 50 to 90.

Abstract: A polishing liquid for polishing a compound semiconductor substrate includes an aqueous solution in which a permanganate and a water-soluble compound of a weak acid and a Group III element, a lanthanoid, or a Group IV element are dissolved. Preferably, the pH of the polishing liquid is 3 to 7. In addition, preferably, the concentration of the permanganate is not less than 2.50 wt %, and the concentration of the water-soluble compound is 0.55 wt % to 5.50 wt %.

Abstract: A polishing liquid for polishing a compound semiconductor substrate includes an aqueous solution in which a permanganate is dissolved, and abrasive grains which are dispersed in the aqueous solution and an electrokinetic potential (zeta potential) of which is plus. Preferably, the polishing liquid has a pH of 3 to 7. In addition, preferably, a concentration of the permanganate is not less than 2.5 wt %, and a concentration of the abrasive grains is not less than 4.5 wt %. Besides, preferably, the abrasive grains include silica grains having an average primary grain diameter of 12 nm to 60 nm.

Abstract: A polishing liquid for polishing a compound semiconductor substrate includes an aqueous solution in which a permanganate and a water-soluble compound are dissolved. The water-soluble compound is obtained by combination of a strong acid and a transition metal element. The transition metal element includes at least one element of Group III elements, lanthanoid, or Group IV elements. Concentrations of ammonium ions and ammonia contained in the aqueous solution are equal to or less than concentrations of the Group III elements, the lanthanoid, and the Group IV elements.

Abstract: Provided is a polishing liquid that is used when one surface of a wafer is polished by use of a fixed abrasive grain polishing pad with abrasive grains fixed in the pad, in which an organic salt that exhibits a basic property by hydrolysis and contains no metal and an organic base that contains no metal are dissolved, and no abrasive grains are contained. Preferably, the organic salt includes a strong basic cation and a weak acidic anion, and the organic base contains at least one of ammonia, an amine, and a basic amino acid.