In the sequence of photolithography for manufacturing semiconductor devices, the following processes are sequentially performed to form a predetermined resist pattern on a target substrate, such as a semiconductor wafer (which will be referred to as “wafer” hereinafter). Specifically, a resist coating process is performed such that a coating liquid or resist liquid is applied onto the wafer to form a resist film. Then, a pre-baking process (PAB) is performed such that a heat process is performed on the wafer treated by the coating process. Then, a light exposure process is performed such that the resist film is subjected to light exposure in accordance with a predetermined pattern. Then, a post-exposure-baking process (PEB) is performed such that a chemical reaction is promoted in the resist film treated by the light exposure. Then, a developing process is performed such that the resist film treated by the light exposure is developed.
After the photolithography sequence, an etching process is performed such that an underlying film, such as an oxide film, on the wafer is etched by use of the resist pattern as a mask to form a predetermined pattern.
A heat process, such as the pre-baking (PAB) or post-exposure-baking (PEB) described above, is performed in a heat processing unit. The heat processing unit includes a heating plate configured to heat a wafer placed thereon. For example, the heating plate is provided with a heater built therein to emit heat by electric supply, so that the heating plate is heated and adjusted by the heater to a predetermined temperature.
In the heat processing unit, the state of temperature is adjusted by setting, e.g., a heat process temperature, a heat process time, and a temperature increase/decrease value. These process conditions greatly affect the line width (CD) and sidewall angle (SWA) of a resist pattern formed on a wafer, and thus they need to be exactly controlled. The sidewall angle (SWA) means the inclination angle θ1 of a line sidewall, as shown by the sectional view of FIG. 11 that shows a line of a resist pattern.
In order to exactly control the temperature on the surface of a wafer in heating, the heating plate of the heat processing unit is segmented into a plurality of areas, which are respectively provided with independent heaters built therein, so that the temperatures of the heating areas can be respectively adjusted.
In this respect, if the heating areas of the heating plate are controlled by use of the same set temperature, the temperature on the surface of a wafer on the heating plate may become less uniform, due to the difference in thermal resistance between the heating areas, for example. In light of this problem, conventionally, the heating areas of the heating plate are respectively provided with temperature correction values (offset values) for fine adjustment of the temperature on the surface of a wafer. The set temperatures of the heating areas of the heating plate are prepared by correcting the heat process temperature with the respective temperature correction values (for example, Jpn. Pat. Appln. KOKAI Publication No. 2001-143850).
Where the heating areas of the heating plate are respectively provided with temperature correction values, so that the temperature is uniform all over the heating plate, the line width (CD) and sidewall angle (SWA) of a resist pattern are expected to be essentially uniform on the surface of a wafer after a photolithography sequence.
However, even where the line width (CD) and sidewall angle (SWA) of a resist pattern are uniform on a wafer after a photolithography sequence, the line width (CD) and sidewall angle (SWA) of a pattern of an oxide film below the resist pattern may become less uniform after the oxide film is etched by an etching process. This is due to fluctuations of process conditions in the etching process, such as the flow rate of a (etching) gas, which cause a difference in progress of the etching process between the wafer areas respectively corresponding to the heating areas.