Provided is a phase shift mask including a substrate, a phase shift layer, and a shielding layer. The phase shift layer is located on the substrate. A pattern of the phase shift layer includes a main pattern and sub-resolution assist features (SRAFs). The SRAFs are disposed around the main pattern. The phase shift layer has a transmission, and the transmission is larger than 6%. The shielding layer at least covers the SRAFs of the phase shift layer.

Provided is a phase shift mask including a substrate, a phase shift layer, and a shielding layer. The phase shift layer is located on the substrate. A pattern of the phase shift layer includes a main pattern and sub-resolution assist features (SRAFs). The SRAFs are disposed around the main pattern. The phase shift layer has a transmission, and the transmission is larger than 6%. The shielding layer at least covers the SRAFs of the phase shift layer.

A phase shift mask including a substrate, a phase shift layer and a transparent layer is provided. The phase shift layer is disposed on the substrate and has an opening. The transparent layer is disposed in the opening. The phase shift mask can have a large DOF window.

A phase shift mask including a substrate, a phase shift layer and a transparent layer is provided. The phase shift layer is disposed on the substrate and has an opening. The transparent layer is disposed in the opening. The phase shift mask can have a large DOF window.

An extreme ultraviolet lithography (EUVL) method includes providing at least two phase-shifting mask areas having a same pattern. A resist layer is formed over a substrate. An optimum exposure dose of the resist layer is determined, and a latent image is formed on a same area of the resist layer by a multiple exposure process. The multiple exposure process includes a plurality of exposure processes and each of the plurality of exposure processes uses a different phase-shifting mask area from the at least two phase-shifting mask areas having a same pattern.

An extreme ultraviolet lithography (EUVL) method includes providing at least two phase-shifting mask areas having a same pattern. A resist layer is formed over a substrate. An optimum exposure dose of the resist layer is determined, and a latent image is formed on a same area of the resist layer by a multiple exposure process. The multiple exposure process includes a plurality of exposure processes and each of the plurality of exposure processes uses a different phase-shifting mask area from the at least two phase-shifting mask areas having a same pattern.

Manufacturing of semiconductor devices often involves performed photolithography to pattern and etch the various features of those devices. Such photolithography involves masking and focusing light onto a surface of the semiconductor device for exposing and etching the features of the semiconductor devices. However, due to design specifications and other causes, the semiconductor devices may not have a perfectly flat light-incident surface. Rather, some areas of the semiconductor device may be raised or lowered relative to other areas of the semiconductor device. Therefore, focusing the light on one area causes another to become unfocused. By carefully designing a photomask to cause phase shifts of the light transmitted therethrough, focus across all areas of the semiconductor device can be achieved during photolithography, which results in sharp and accurate patterns formed on the semiconductor device.

Manufacturing of semiconductor devices often involves performed photolithography to pattern and etch the various features of those devices. Such photolithography involves masking and focusing light onto a surface of the semiconductor device for exposing and etching the features of the semiconductor devices. However, due to design specifications and other causes, the semiconductor devices may not have a perfectly flat light-incident surface. Rather, some areas of the semiconductor device may be raised or lowered relative to other areas of the semiconductor device. Therefore, focusing the light on one area causes another to become unfocused. By carefully designing a photomask to cause phase shifts of the light transmitted therethrough, focus across all areas of the semiconductor device can be achieved during photolithography, which results in sharp and accurate patterns formed on the semiconductor device.

A reflective mask blank for EUV lithography includes: a substrate; a multilayer reflective film for reflecting EUV light; and a phase shift film for shifting a phase of EUV light, the multilayer reflective film and the phase shift film formed on or above the substrate in this order. The phase shift film includes a layer 1 including ruthenium (Ru) and at least one selected from the group consisting of oxygen (O) and nitrogen (N). Among diffraction peaks derived from the phase shift film observed at 2θ: from 20° to 50° by out-of-plane XRD method, a peak having the highest intensity has a half value width FWHM of 1.0° or more.

The present invention is directed to the provision of an interferometer and a phase shift amount measuring apparatus that can precisely operate in the EUV region. The interferometer according to the invention comprises an illumination source for generating an illumination beam, an illumination system for projecting the illumination beam emitted from the illumination source onto a sample, and an imaging system for directing the reflected beam by the sample onto a detector. The illumination system includes a first diffraction grating for producing a first and second diffraction beams which respectively illuminate two areas on the sample where are shifted from each other by a given distance, and the imaging system includes a second grating for diffracting the first and second diffraction beams reflected by the sample to produce a third and fourth diffraction beams which are shifted from each other by a given distance.