Reflective mask blank for EUV lithography, and process for its inspection and process for its production

Patent metadata

Field	Value
Publication number	US-9739722-B2
Application number	US-201514878181-A
Country	US
Kind code	B2
Filing date	Oct 8, 2015
Priority date	Oct 20, 2014
Publication date	Aug 22, 2017
Grant date	Aug 22, 2017

Abstract

A process for inspecting an EUV mask blank capable of distinguishing phase defects and amplitude defects and capable of detecting small amplitude defects, a process for producing an EUV mask blank using the inspection process, and an EUV mask blank obtainable by such a process. A process for inspecting a reflective mask blank for EUV lithography having a multilayer reflective film and an absorber layer. The process includes a first step of detecting in-plane defects in the multilayer reflective film by applying EUV light to the surface of the multilayer reflective film, a second step of detecting in-plane defects from the absorber layer by applying light having a wavelength of from 150 to 600 nm to the surface of the absorber layer, and a step of distinguishing phase defects and amplitude defects in the reflective mask blank by comparison between the first and second in-plane defect data.

First claim

What is claimed is:

1. A process for inspecting a reflective mask blank for EUV lithography having a multilayer reflective film for reflecting EUV light and an absorber layer for absorbing EUV light formed in this order on a substrate, which comprises:
a first defect distribution storing step of detecting an in-plane distribution of defects in the multilayer reflective film by, at a stage where the multilayer reflective film is formed on the substrate, applying EUV light to the surface of the multilayer reflective film and storing the detected first defect in-plane distribution data,
a second defect distribution storing step of detecting an in-plane distribution of defects from the absorber layer by, at a stage where the absorber layer is formed on the multilayer reflective film, applying light having a wavelength of from 150 to 600 nm to the surface of the absorber layer and storing the detected second defect in-plane distribution data, and
a defect distinguishing step of distinguishing phase defects and amplitude defects in the reflective mask blank for EUV lithography by comparison between the first defect in-plane distribution data and the second defect in-plane distribution data.

2. The process for inspecting a reflective mask blank for EUV lithography according to claim 1 , wherein a protective layer for the multilayer reflective film is further formed between the multilayer reflective film and the absorber layer of the reflective mask blank for EUV lithography, and the first defect distribution storing step is carried out at a stage where the protective layer for the multilayer reflective film is formed.

3. The process for inspecting a reflective mask blank for EUV lithography according to claim 1 , wherein a low reflective layer for inspection light to be used for inspection of a mask pattern is further formed on the absorber layer of the reflective mask blank for EUV lithography, and the second defect distribution storing step is carried out at a stage where the low reflective layer is formed.

4. A process for producing a reflective mask blank for EUV lithography, which comprises:
a step of forming a multilayer reflective film for reflecting EUV light on a substrate,
a first defect distribution storing step of detecting an in-plane distribution of defects in the multilayer reflective film by applying EUV light to the surface of the multilayer reflective film and storing the detected first defect in-plane distribution data,
a step of forming an absorber layer for absorbing EUV light on the multilayer reflective film,
a second defect distribution storing step of detecting an in-plane distribution of defects from the absorber layer by applying light having a wavelength of from 150 to 600 nm to the surface of the absorber layer and storing the detected second defect in-plane distribution data, and
a defect distinguishing step of distinguishing phase defects and amplitude defects in the reflective mask blank for EUV lithography by comparison between the first defect in-plane distribution data and the second defect in-plane distribution data.

5. The process for producing a reflective mask blank for EUV lithography according claim 4 , which further has a step of forming a protective layer for the multilayer reflective film on the multilayer reflective film, and wherein the first defect distribution storing step is carried out after the step of forming the protective layer.

6. The process for producing a reflective mask blank for EUV lithography according to claim 4 , which further has a step of forming a low reflective layer for inspection light to be used for inspection of a mask pattern, on the absorber layer of the reflective mask blank for EUV lithography, and wherein the second defect distribution storing step is carried out after the step of forming the low reflective layer.

7. The process for producing a reflective mask blank for EUV lithography according to claim 4 , wherein the pressure in the step of forming the absorber layer is at least 3.0×10 −2 [Pa] and at most 1.5×10 [Pa].

8. The process for producing a reflective mask blank for EUV lithography according to claim 4 , wherein of the absorber layer, the light reflectivity at a wavelength of inspection light within a wavelength range of from 150 to 600 nm is at least 20%.

9. The process for producing a reflective mask blank for EUV lithography according to claim 4 , wherein the angle of growth of defects on the absorber layer is at least 0 [deg].

10. The process for producing a reflective mask blank for EUV lithography according to claim 4 , wherein the root mean square roughness Rq of the surface of the multilayer reflective film is at most 0.30 [nm], and the root mean square roughness Rq of the surface of the absorber layer is at most 0.50 [nm].

11. A reflective mask blank for EUV lithography having a multilayer reflective film for reflecting EUV light and an absorber layer for absorbing EUV light formed in this order on a substrate, wherein the ratio of the size of a local irregularity on the surface of the absorber layer resulting from an amplitude defect present in the vicinity of the surface of the multilayer reflective film, to the size of the amplitude defects, is at least 1 and at most 2.

12. A reflective mask blank for EUV lithography having a multilayer reflective film for reflecting EUV light and an absorber layer for absorbing EUV light formed in this order on a substrate, wherein the ratio of the size of a local irregularity on the surface of the absorber layer resulting from an amplitude defect present in the vicinity of the surface of the multilayer reflective film, to the size of the amplitude defects, is at least 1 and at most 1.5.

Assignees

• Asahi Glass Co Ltd

Inventors

• Nakanishi Hiroshi
• Kageyama Junichi
• Ikuta Yoshiaki

Classifications

• G03F1/84

  Inspecting · CPC title

• G01N21/8851

  Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges (G01N21/8806 and G01N21/93 - G01N21/95692 take precedence; optical measurement of dimensions G01B11/00; optical scanning G02B26/10; image transformation G06T3/00; computerised image enhancement G06T5/00; image processing per se for flaw detection G06T7/0002) · CPC title

• G01N21/956 Primary

  Inspecting patterns on the surface of objects {(contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)} · CPC title

• G01N2021/95676

  Masks, reticles, shadow masks · CPC title

• G03F1/24

  Reflection masks; Preparation thereof · CPC title