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EP-4741920-A1 - REFLECTIVE PHOTOMASK BLANK, AND METHOD FOR MANUFACTURING REFLECTIVE PHOTOMASK

EP4741920A1EP 4741920 A1EP4741920 A1EP 4741920A1EP-4741920-A1

Abstract

A reflective photomask blank including a substrate, a multilayer reflection film, a protection film and a light absorbing film that has a phase shift function is provided. The light absorbing film contains ruthenium and chromium and is free of oxygen and nitrogen, and has a ruthenium content of 5 to 15 at%, a chromium content of 85 to 95 at%, a thickness of 40 to 56 nm, and a reflectance of 2 to 5% and a phase shift of 200 to 230 degrees with respect to exposure light being light in extreme ultraviolet range.

Inventors

  • KAWAMURA, Ryoto

Assignees

  • SHIN-ETSU CHEMICAL CO., LTD.,

Dates

Publication Date
20260513
Application Date
20250926

Claims (4)

  1. A reflective photomask blank comprising a substrate, a multilayer reflection film that is formed on the substrate and reflects exposure light being light in extreme ultraviolet range, a protection film that is formed on the multilayer reflection film to protect the multilayer reflection film, and a light absorbing film that is formed on the protection film, absorbs the exposure light, and has a phase shift function, wherein the light absorbing film comprises ruthenium (Ru) and chromium (Cr) and is free of oxygen (O) and nitrogen (N), and has a ruthenium (Ru) content of not less than 5 at% and not more than 15 at%, a chromium (Cr) content of not less than 85 at% and not more than 95 at%, a thickness of not less than 40 nm and not more than 56 nm, a reflectance of not less than 2% and not more than 5% with respect to the exposure light, and a phase shift of not less than 200 degrees and not more than 230 degrees with respect to the exposure light.
  2. The reflective photomask blank of claim 1 wherein the light absorbing film further comprises niobium (Nb), and has a niobium (Nb) content of not more than 4 at%.
  3. The reflective photomask blank of claim 1 or 2 wherein the protection film has a thickness of not less than 1 nm and not more than 6 nm.
  4. A method for manufacturing a reflective photomask comprising a pattern of the light absorbing film from the reflective photomask blank of any one of claims 1 to 3 wherein the method comprises the steps of: (A) forming a resist film in contact with the light absorbing film at the side remote from the substrate, (B) patterning the resist film to form a resist pattern, (C) patterning the light absorbing film to form a light absorbing film pattern by dry etching using a chlorine-based gas, and the resist pattern as an etching mask, and (D) removing the resist pattern.

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a reflective photomask that is used in manufacturing semiconductor devices and others, and a reflective photomask blank that is used as a material for manufacturing the reflective photomask. BACKGROUND It is required that projection exposure has high pattern resolution in accordance with miniaturization of semiconductor devices, particularly, in accordance with high integration of large-scale integrated circuits. So, as a photomask, a phase shift mask has been developed as a means for improving the resolution of a transfer pattern. A principle of phase shift method is that, by adjusting so as to invert a phase of transmitted light that has been passed through an opening of a phase shift film of a photomask by about 180 degrees with respect to a phase of transmitted light that has been passed through the portion of the phase shift film adjacent to the opening, interference between the transmitted lights reduces a light intensity at the boundary of the opening and the portion adjacent to the opening. As a result, resolution and depth of focus of a transfer pattern are improved. A photomask utilizing this principle is generally called a phase shift mask. The phase shift mask in this case is a type of transmissive photomask that transmits exposure light. A most common phase shift mask blank, as a material for the phase shift mask, that is used for manufacturing the phase shift mask has a structure in which a phase shift film is laminated on a transparent substrate such as a glass substrate, and a film composed of a material containing chromium (Cr) is laminated on the phase shift film. The phase shift film usually has a phase shift of about 175 to 185 degrees and a transmittance of about 6 to 30% with respect to exposure light, and a mainstream phase shift film is composed of a material containing silicon (Si), particularly a material containing molybdenum (Mo) and silicon (Si). Generally, the film composed of a material containing chromium (Cr) is adjusted so as to have a thickness that provides a desired optical density together with the phase shift film, and the film composed of a material containing chromium (Cr) is provided as a light-shielding film, and is also used as an etching mask in etching the phase shift film. As a general method for manufacturing a phase shift mask by patterning a phase shift film from a phase shift mask blank in which a phase shift film that is composed of a material containing silicon (Si), and a light-shielding film that is composed of a material containing chromium (Cr) are formed in this order on a transparent substrate, the following method is exemplified. First, a resist film is formed on the light-shielding film composed of a material containing chromium (Cr) of the phase shift mask blank, and a resist pattern is formed by drawing a pattern onto the resist film by light or an electron beam, and developing. Next, the light-shielding film composed of a material containing chromium (Cr) is dry-etched with using the resist pattern as an etching mask, and a chlorine-based gas to form a pattern of the light-shielding film. Further, the phase shift film composed of a material containing silicon (Si) is dry-etched with using the pattern of the light-shielding film as an etching mask, and a fluorine-based gas to form a pattern of the phase shift film. Then, the resist pattern is removed, and the pattern of the light-shielding film is removed by dry etching using a chlorine-based gas. In this case, the light-shielding film is left at the portion outside the portion in which the pattern of the phase shift film (a circuit pattern) is formed, and a light-shielding portion (light-shielding pattern) having an optical density of not less than 3 in the combination of the phase shift film and the light-shielding film is formed at the outer periphery portion of the phase shift mask. This is to prevent irradiation of exposure light caused by leaking the exposure light at the outer periphery portion of the phase shift mask to the resist film on an adjacent chip on a wafer from the portion located outside the circuit pattern in transferring the circuit pattern to the wafer with using a wafer exposure apparatus. In a general method for forming such a light-shielding pattern, after forming the pattern of the phase shift film and removing the resist pattern, a resist film is anew formed, and a resist pattern that remains at the outer periphery portion of the light-shielding film is formed by drawing a pattern and developing. Then, the film composed of a material containing chromium (Cr) is etched with using the resist pattern as an etching mask to left the light-shielding film at the outer periphery portion of the phase shift mask. A mainstream etching in a phase shift mask blank that requires pattern formation with highly accurate is dry etching using gas plasma. Dry etching using a chlorine-based gas (chlorine-based dry