1. Field of the Invention
The present invention relates to a resist pattern forming method by immersion exposure of a lithography step in a semiconductor manufacturing process, and a manufacturing method of a semiconductor device.
2. Description of the Related Art
Immersion exposure is a technology in which a space between the surface of a resist film and a lens of an exposure device is filled with a liquid to perform exposure on the resist film formed on a substrate to be treated. A device for use in such an exposure process is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 10-303114. In Jpn. Pat. Appln. KOKAI Publication No. 10-303114, there is disclosed a device in which a substrate to be treated is all immerged into water in a stage to which water can be supplied, and the exposure is performed while this stage is relatively moved with respect to the exposure device. In the device having such configuration, the liquid is supplied to the whole stage. Therefore, there is a problem that the liquid overflows from the stage, when the stage is moved at a high speed. The stage cannot be driven at a high speed.
In Immersion Lithography; its Potential Performance and Issues, Proc. of SPIE Vol. 5040, pp. 724 to 733 by Soichi Owa and Hiroyuki Nagasaka, as a measure against disturbance of the liquid due to the movement of the stage, there is disclosed a technology to drive the stage while locally supplying the liquid to a portion to be exposed. According to this technology, it is possible to move the stage at a high speed. When such technology to supply the liquid locally is used, water is left in an exposed region and the like of a portion from which the lens is detached. In consequence, when the resist film is exposed and thereafter heated in this state, there is a problem that a watermark is generated, or an abnormality is generated in a resist pattern owing to a temperature drop in the portion where water exists.
On the other hand, in New Cover Material Development Status for Immersion Lithography, Web Publication of International Symposium on Immersion and 157 nm Lithography by Keita Ishizuka et al., it is disclosed that components of a resist are eluted from the resist film into the liquid in the immersion exposure. According to this document, such elution can be avoided by disposing a cover film on the surface of the resist film. As to a state of the surface of the cover film, it is preferable that a contact angle of the surface to water is 90° or more. However, in a case where the cover film having such a large contact angle is used, there might occur a problem that the watermark is easily generated on the cover film, and a defect due to the watermark is generated in the resist pattern. In this document, there is also disclosed an example in which a film having a contact angle of 68° or 78° to an immersion liquid (pure water) is used as a hydrophilic cover film.