1.  Field of the Invention
The present invention relates to a substrate treatment method and a substrate treatment apparatus.  Exemplary substrates to be treated include semiconductor wafers, substrates for liquid crystal display devices, substrates for plasma display devices, substrates for FED (Field Emission Display) devices, substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks, substrates for photo masks, ceramic substrates and substrates for solar cells. 
2.  Description of Related Art
In production processes for semiconductor devices, liquid crystal display devices and the like, a phosphoric acid etching process is performed on a substrate having a silicon nitride film and a silicon oxide film formed in a front surface thereof, as required, to selectively remove the silicon nitride film by supplying a higher temperature phosphoric acid aqueous solution as an etching liquid to the front surface of the substrate (see, for example, JP2007-258405A1). 
In a substrate treatment apparatus of a batch type adapted to collectively treat a plurality of substrates, the substrates are immersed in a higher temperature phosphoric acid aqueous solution retained in a treatment bath for a predetermined period.  In a substrate treatment apparatus of a single substrate treatment type adapted to treat a single substrate at a time, on the other hand, a higher temperature phosphoric acid aqueous solution is spouted from a nozzle toward a substrate held by a spin chuck.  The phosphoric acid aqueous solution is supplied to the front surface of the substrate to flow on the front surface of the substrate. 
In the substrate treatment apparatus of the batch type, it is necessary to immerse the substrates in the higher temperature phosphoric acid aqueous solution retained in the treatment bath for the predetermined period or longer in order to uniformly perform the phosphoric acid etching process.  Therefore, whether the plurality of substrates are collectively treated or a single substrate is treated in the substrate treatment apparatus of the batch type, the same treatment period is required.  In the substrate treatment apparatus of the single substrate treatment type, the single substrate can be uniformly treated in a shorter period of time than in the batch type substrate treatment apparatus. 
The phosphoric acid etching process can be performed at the highest treating rate (etching rate) when the phosphoric acid aqueous solution is supplied at about its boiling point to the substrate.  In the substrate treatment apparatus of the single substrate treatment type, however, the temperature of the phosphoric acid aqueous solution is reduced before the phosphoric acid aqueous solution is supplied to the substrate, even if the phosphoric acid aqueous solution is temperature-controlled at about its boiling point in a tank.  This reduces the etching rate of the silicon nitride film to increase the time required for the phosphoric acid etching process, thereby reducing the throughput.