This study concerns the quality of Ta absorber patterns on EUVL masks. Experiments revealed that the sidewall angle of the absorber pattern strongly affects pattern printability because the mask is a reflective type and the wavelength is very short (lambda = 13.5 nm). When a resist pattern is transferred to a Ta film by etching, the quality of the Ta pattern generally depends on the properties of the resist and resist pattern (etching durability, angle of sidewall, etc.). To control the sidewall angle of Ta patterns, we need to pay close attention to the interface between the resist and the Ta film, and also to the side etching characteristics of Ta crystal, because the feature size of printed patterns will be as small as 50 nm or below in the EUVL era. We found that it is possible to control the sidewall angle of Ta patterns through the introduction of an additional gas and adjustment of the radio frequency conditions during plasma etching. This paper also discusses the effect of the thermal conductivity of a substrate. Though Si wafers were used in our experiments, we simulated the thermal effects of using a quartz substrate, since quartz has a much larger thermal conductivity than Si. The results showed the temperature rise during plasma etching to be less than 150 deg. Celsius. This work is supported by NEDO.