A method for forming an oxide layer is provided to form an oxide layer having an excellent characteristic at a relatively low temperature by supplying oxygen gas and heavy hydrogen gas of a radical state to the surface of a silicon substrate. Oxygen gas and heavy hydrogen gas are formed as an oxygen radical and a heavy hydrogen radical(S110). The oxygen radical and the heavy hydrogen radical are supplied to the surface of a silicon substrate in a manner that the heavy hydrogen radical has a ratio of 1~55 percent in the oxygen radical and the heavy hydrogen radical(S120). The oxygen radical reacts with the heavy hydrogen radial to deposit an oxide layer on the silicon substrate(S130). The oxygen radical and the heavy hydrogen radical can be formed by applying RF to the oxygen gas and heavy hydrogen gas.
