A process of manufacturing a semiconductor device in which a stacking structure of an integrated circuit is formed on the surface of a substrate to be processed such as a semiconductor wafer (hereinafter, referred to as a “wafer”) includes a liquid process of processing a wafer surface using a liquid to remove minute dusts or native oxide layers on the wafer surface using a cleaning liquid such as, for example, a chemical solution.
For example, a single type spin cleaning apparatus for cleaning a wafer removes dusts or native oxides on the wafer surface by rotating the wafer while supplying, for example, alkaline or acid chemical solutions to the wafer surface using a nozzle. In this case, the wafer surface is dried by, for example, a spin drying in which remaining chemical solutions are removed from the wafer surface by rinse cleaning using, for example, deionized water (DIW), and then remaining liquids are brushed away while rotating the wafer.
However, as a semiconductor device is highly integrated, a problem such as so-called a pattern collapse has grown serious in a processing of removing such liquids. The pattern collapse is a phenomenon in which the balance of a surface tension horizontally pulling a convex portion is lost, and as a result, the convex portion falls down toward a side where more liquids remain at the time of drying the remaining liquids on the wafer surface, as the liquids which remain at, for example, the left and right sides of the convex portion of concave-convex portions forming a pattern, are unevenly dried.
A drying method has been known, which uses a fluid of supercritical state (a supercritical fluid), which is a kind of high temperature and high pressure fluids, as a method for removing the remaining liquid from the wafer surface while suppressing the occurrence of the above-described pattern collapse. The supercritical fluid has viscosity which is lower than that of a liquid and a high level of capability to dissolve a liquid. In addition, there is no interface between a supercritical fluid and a liquid or a gas which is in an equilibrium state with the supercritical fluid. In a wafer attached with a liquid, the liquid is substituted with a supercritical fluid, and then the supercritical fluid is changed to a gaseous state. As a result, the liquid can be dried without being influenced by a surface tension.
Applicant is developing a single type wafer processing apparatus which repeats a series of operations including heating a raw material in a liquid state (“a liquid raw material”) to generate a supercritical fluid and supplying the supercritical fluid into an atmosphere where a wafer is disposed, to dry a liquid on the wafer surface for every wafer processing. At this time, if a necessary amount of supercritical fluid is generated for every wafer processing, there is no need to prepare and store much supercritical fluids in advance, and thus, it may cause a compact wafer processing apparatus.
As a method for preparing a necessary amount of supercritical fluid for every wafer processing, a method may be considered in which a liquid raw material is transported to, for example, a metallic vessel, the vessel is sealed, and then the temperature and pressure of the liquid raw material are raised by heating the body of the vessel to indirectly heat the liquid raw material. However, the vessel of which inside becomes a high temperature and high pressure atmosphere has to get a sufficient pressure-resistant property, the thermal capacity thereof is high, and the responsibility thereof at the time of performing a temperature control is poor.
When a liquid raw material for the next processing is transported to a vessel which is once heated to a supercritical temperature or more, the liquid raw material that contacts with the vessel body begins a vaporization to raise the inner pressure of the vessel. For that reason, a high pressure pump is necessary for a transportation of the liquid raw material or a cooling mechanism that cools a vessel body is necessary, and as a result, the facility cost may be increased or the supercritical fluid needs to be prepared for a long time.
Herein, Japanese Patent Application Laid-Open No. 2008-72118 (see, e.g., paragraphs [0025] to [0029], paragraphs [0038] and [0039], and FIG. 1) discloses a technology in which a substrate to be processed is dried by transporting a substrate cleaned in a cleaning unit into a dry processing chamber, raising the pressure inside the dry processing chamber in advance to be equal to or higher than a critical pressure of a dry processing fluid (in the present exemplary embodiment, a carbon dioxide), and thereafter, supplying a supercritical fluid into the dry processing chamber. However, Japanese Patent Application Laid-Open No. 2008-72118 does not disclose a technology for preparing a supercritical fluid from a liquid raw material, and does not disclose a method for solving the problems as described above.