1. Field of the Invention
The present invention relates to a manufacturing apparatus for a semiconductor device and a manufacturing method for a semiconductor device, used for etching treatment of a semiconductor substrate, for example, with phosphoric acid solution.
2. Description of the Related Art
In the manufacturing processes of semiconductor devices, there is a process of etching a silicon nitride (SiN) film formed on a wafer with phosphoric acid solution, hereinafter referred to as “H3PO4 solution”. This process uses a batch processing bath subjected to etching treatment, for example, with a plurality of wafers as one lot. Usually, H3PO4 solution is maintained at a temperature of approximately 160° C. next to boiling point in the processing bath, and is used while being circulated for treatment of a plurality of lots.
When etching treatment of a SiN film formed on a wafer using H3PO4 solution is performed in the batch processing bath, etching residue resulting from silica (SiO2) generated by an etching reaction remains in the H3PO4 solution. By circulating the H3PO4 solution and repeatedly using the solution for H3PO4 treatment, etching residue gathers in the H3PO4 solution as the number of lots to be treated increases, and the amount of etching residue increases.
The etching residue causes dust generation and fluctuates SiN etching rate and etching selectivity to oxide film with the amount of etching residue gathered in H3PO4 solution. Accordingly, to restrain process fluctuations, there have been studied various methods for controlling the concentration of etching residue (Si concentration) dissolved in H3PO4 solution.
For example, U.S. Pat. No. 6,780,277 has disclosed a method for additionally supplying H3PO4 solution by directly monitoring Si concentration in H3PO4 solution and discarding a required amount of solution when the concentration has reached a predetermined concentration. For this method, a dedicated Si concentration measurement unit for measuring Si concentration in high-temperature H3PO4 solution with the in-situ technique is essential. However, such a unit exists in reality, but is very expensive and has questionable reliability.
There has been known a method for controlling Si concentration in H3PO4 solution to have a desired concentration by adding an appropriate amount of hydrofluoric acid (HF) into H3PO4 solution and vaporizing SiO2 by reaction with HF. This method requires measurement of Si concentration in H3PO4 solution. However, it is difficult to control H3PO4 solution in real time, as described above.
US2005/0263488 has disclosed a method for re-precipitating silicate by cooling H3PO4 solution and removing the re-precipitated silicate by filtration. However, the method requires use of a dedicated cooling system.
Japanese Patent Application Laid-Open No. 2004-288963 (paragraph numbers [0030] to [0033], FIG. 3 and others) has proposed a method for determining a current etching rate of H3PO4 solution based on the use history of H3PO4 solution up to now and data showing a relationship between the use history and etching rate and correcting etching time in accordance with the etching rate. This method requires no actual measurement of Si concentration by the in-situ technique during etching treatment.
However, this method allows completion of etching treatment of a desired depth, but requires long treatment time and therefore a desired aperture shape may be difficult to obtain due to a relationship with etching selectivity to oxide film.