1. Field of the Invention
The present invention relates to a pattern forming method, and more particularly, to a pattern forming method for use in a lithography process for fabricating a semiconductor device, and a semiconductor device manufacturing method.
2. Description of the Related Art
With downsizing of a semiconductor element, there has been a demand for a high resolution for a pattern in a lithography process, as described in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2000-277423. To this demand, shorting of the wavelength of an exposure light to be used is promoted. In optical lithography, an ArF excimer laser (wavelength: 193 nm) has been widely used as an exposure light source. On the other hand, with the shorting of the wavelength of the exposure light, a chemically amplified resist has been practically used as a material for a photo resist (resist film) to which a pattern is to be transferred. The chemically amplified resist film contains an acid generator which generates an acid in the resist by exposure. The acid generator decomposes the chemically amplified resist (in the case where the resist is of a positive type) or cross-links the resist (in the case where the resist is of a negative type). As a result, solubility of the resist by a developing solution changes. This feature is utilized to obtain high resolution.
In the lithography process using the chemically amplified resist film, it is practical to carry out a heating process called PEB (Post-Exposure Baking) for diffusing the acid generated at the time of exposure. In the PEB process, since there is an intimate relationship between an amount of heat supplied and a dimension of a resist film pattern formed after exposure, severe temperature uniformity is required with reduction of the size of a pattern to be formed.
In a conventional PEB process, there has been widely used a so-called proximity baking method in which a substrate to be treated is placed above a hot plate heated by a heater to supply heat to the substrate from its back surface. It is general to set a distance (gap) between the hot plate and the substrate to be about 100 μm to shorten the heat time. However, since the substrate having undergone a film forming process or the like has a warp due to a stress of a film, the gap between the hot plate and the substrate becomes non-uniform within the plane of the substrate. This becomes a factor of degrading temperature uniformity within the plane of the substrate.
As another heating method, there is proposed a lamp heating method in which a light is irradiated onto a substrate from a lamp installed above the substrate to heat the substrate. With this method, a substrate warp is not so problematic as compared with the proximity baking method. However, there is a problem that it is difficult to ensure luminance uniformity of the lamp and thus good temperature uniformity within the plane of the substrate cannot be obtained.
There is a demand for a pattern forming method capable of forming a pattern having good dimensional uniformity within the plane of the substrate against a substrate having a warp.