METHOD FOR FABRICATING SEMICONDUCTOR DEVICE
A semiconductor device fabrication method by which a desired pattern can be formed. After a conductive layer which is a material for a gate electrode is formed, a SiN layer to be used as a hard mask is formed. Then a photoresist layer is formed as a second mask. Then patterning is performed on the photoresist layer. Then patterning is performed on the SiN layer with the photoresist layer as a mask. After the photoresist layer is removed, surface portions of the SiN layer are transmuted and are selectively removed. The conductive layer under the SiN layer is etched with the reduced SiN layer as the hard mask. By doing so, the photoresist layer does not, for example, deform during the process and a minute gate electrode pattern can be formed stably.
1 . A method for fabricating a semiconductor device, the method comprising:
forming a first mask layer over a conductive layer;
forming a second mask layer over the first mask layer;
performing patterning on the second mask layer;
performing patterning on the first mask layer by the use of the second mask layer patterned;
transmuting exposed surface portions of the first mask layer;
reducing the first mask layer by removing the transmuted surface portions; and
performing patterning on the conductive layer by the use of the reduced first mask layer.
2 . The method according to claim 1 , wherein in transmuting the exposed surface portions of the first mask layer, the exposed surface portions are oxidized to form an oxide film.
3 . The method according to claim 1 , further comprising removing the second mask layer patterned between the patterning of the first mask layer by the use of the second mask layer patterned and the transmuting of the exposed surface portions of the first mask layer.
4 . The method according to claim 1 , wherein in the patterning of the second mask layer:
the second mask layer is formed by the use of photoresist; and
dimensions of the patterning of the second mask layer are set such that a shape of the second mask layer patterned can be kept until the patterning of the first mask layer by the use of the second mask layer patterned.
5 . The method according to claim 1 , further comprising forming an anti-reflection coating over the first mask layer after forming the first mask layer over the conductive layer, wherein in forming the second mask layer over the first mask layer, the second mask layer is formed over the anti-reflection coating by the use of photoresist.
6 . The method according to claim 1 , further comprising forming over the first mask layer a layer of a material which can be removed together with the transmuted surface portions at the time of transmuting and removing the surface portions of the first mask layer after forming the first mask layer over the conductive layer, wherein in forming the second mask layer over the first mask layer, the second mask layer is formed over the layer.
7 . The method according to claim 6 , wherein:
after the second mask layer is formed over the layer, patterning is performed on the second mask layer and patterning is performed on the layer and the first mask layer by the use of the second mask layer patterned;
in transmuting the exposed surface portions of the first mask layer after the patterning of the layer and the first mask layer, exposed side surface portions of the first mask layer over which the layer patterned is formed are transmuted; and
in reducing the first mask layer by removing the transmuted surface portions, the first mask layer is reduced by removing the layer formed over the first mask layer together with the surface portions.
8 . The method according to claim 7 , further comprising forming an anti-reflection coating over the layer after forming the layer, wherein in forming the second mask layer over the first mask layer, the second mask layer is formed over the anti-reflection coating by the use of photoresist.
9 . The method according to claim 1 , wherein the first mask layer is formed of SiN, SiC, SiOC, or SiO 2 .
10 . The method according to claim 1 , wherein the transmuted surface portions are formed of SiON, SiOC, or SiO 2 .
11 . The method according to claim 6 , wherein the layer is formed of photoresist or SiO 2 .
12 . The method according to claim 2 , wherein when the surface portions are oxidized to form an oxide film, oxidization treatment is performed at a temperature of 400° C. or less.