Liquid supply method

A liquid supply method for supplying a solution to be inspected to a spot formed on a substrate, the method comprising:

• preparing a liquid supply pipe in which the solution to be inspected, air, and oil are disposed in this order;
• and
• installing the liquid supply pipe above the substrate at an angle such that the solution to be inspected is positioned on a lowermost side and the solution to be inspected, the air, and the oil flow onto a front surface of the substrate by gravity,
• wherein
• a cross-sectional area of the liquid supply pipe is designed such that the air continues to be present between the solution to be inspected and the oil while the solution to be inspected, the air, and the oil are flowing through the liquid supply pipe, and
• after the solution to be inspected is supplied to the spot, the solution to be inspected present on the front surface of the substrate is replaced with the air, and then the liquid supply progresses such that the oil covers the front surface of the substrate.