The present invention provides a high temperature chemical solution supply system for cleaning substrates. The system includes a solution tank, a buffer tank, a first pump and a second pump. The solution tank contains high temperature chemical solution. The buffer tank has a tank body, a vent line and a needle valve. The tank body contains the high temperature chemical solution. An end of the vent line connects to the tank body, and the other end of the vent line connects to the solution tank. The needle valve is mounted on the vent line, wherein the needle valve is adjusted to reach a flow rate to vent gas bubbles inside of the high temperature chemical solution out of the buffer tank through the vent line. An inlet of the first pump connects to the solution tank, and an outlet of the first pump connects to the buffer tank. An inlet of the second pump connects to the buffer tank, and an outlet of the second pump connects to a cleaning chamber in which a substrate is cleaned. The present invention also provides an apparatus including the high temperature chemical solution supply system and an ultra or mega sonic device for cleaning the substrate. The present invention also provides methods for cleaning the substrates.