Polishing liquid for polishing compound semiconductor substrate
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.
1 . A polishing method for a compound semiconductor substrate for polishing the compound semiconductor substrate, comprising:
a holding step of holding the compound semiconductor substrate by a chuck table of a polishing apparatus; and
a polishing step of polishing the compound semiconductor substrate while supplying a polishing liquid from a polishing pad to the compound semiconductor substrate in a state in which the polishing pad is brought into contact with one surface of the compound semiconductor substrate, wherein:
the polishing pad is a fixed abrasive grain polishing pad having abrasive grains fixed in a main body of the polishing pad,
the polishing liquid includes an aqueous solution in which a sodium permanganate and a water-soluble compound obtained by combination of a strong acid and a transition metal element are dissolved,
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,
a concentration of the sodium permanganate is equal to or less than 4.8 wt %, and
free abrasive grains are not contained in the polishing liquid during the polishing step.
2 . The polishing method according to claim 1 , wherein a concentration of the water-soluble compound is equal to or less than 2.4 wt %.
3 . The polishing method according to claim 2 , wherein the concentration of the sodium permanganate is equal to or more than 0.6 wt %, and the concentration of the water-soluble compound is equal to or more than 0.3 wt %.
4 . The polishing method according to claim 3 , wherein the concentration of the sodium permanganate is equal to 0.8 wt %.
5 . The polishing method according to claim 3 , wherein the concentration of the sodium permanganate is equal to 1.2 wt %.
6 . The polishing method according to claim 3 , wherein the concentration of the sodium permanganate is equal to 2.4 wt %.
7 . The polishing method according to claim 3 , wherein the water-soluble compound includes lanthanum nitrate.
8 . The polishing method according to claim 2 , wherein the concentration of the sodium permanganate is twice as large as a concentration of the water-soluble compound.
9 . The polishing method according to claim 2 , wherein the water-soluble compound includes lanthanum nitrate.