Reflective photomask blank and reflective photomask
A reflective photomask blank ( 10 ) of a first aspect includes a substrate ( 1 ); a reflective layer ( 2 ) formed on the substrate ( 1 ); and a light absorbing layer ( 4 ) formed on the reflective layer ( 2 ) and including a tin oxide film with a film thickness of 17 nm or more and less than 25.0 nm. Consequently, the shadowing effect of a reflective photomask for pattern transfer using extreme ultraviolet light as a light source is suppressed or reduced to improve the performance of transfer to a semiconductor substrate, and further, pattern collapse due to cleaning of the reflective photomask is suppressed.
1. A reflective photomask blank for producing a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, the reflective photomask blank comprising:
a substrate;
a reflective layer including a multilayer film and formed on the substrate; and
a light absorbing layer formed on the reflective layer, the light absorbing layer including a tin oxide film with a film thickness of 17 nm or more and less than 25.0 nm; wherein
an atomic ratio (O/Sn) of oxygen (O) to tin (Sn) contained in the tin oxide film is 1.0 or more and 2.0 or less; and
given that Rm is a reflected light intensity from the reflective layer and that Ra is a reflected light intensity from the light absorbing layer, an OD (Optical Density) defined by a formula (1) below is 1 or more and less than 1.5,
OD=−log( Ra/Rm ) (1).
2. The reflective photomask blank according to claim 1 , wherein a material forming the tin oxide film contains 80 at % or more of tin (Sn) and oxygen (O) in total.
3. The reflective photomask blank according to claim 1 , further comprising a capping layer formed between the light absorbing layer and the reflective layer.
4. The reflective photomask blank according to claim 2 , further comprising a capping layer formed between the light absorbing layer and the reflective layer.