Browse Prior Art Database

Method to remove Mo/Si multilayers without damaging starting substrate

IP.com Disclosure Number: IPCOM000008275D
Original Publication Date: 2002-May-31
Included in the Prior Art Database: 2002-May-31
Document File: 5 page(s) / 186K

Publishing Venue

Motorola

Related People

Pawitter J.S. Mangat: INVENTOR [+2]

Abstract

Extreme ultraviolet lithography (EUVL) is a leading next generation lithography technology. The mask blank for EUVL consists of a low thermal expansion material substrate having a square photomask form factor (SEMI Standard P-37) that is coated with Mo/Si multilayers. One of the challenges in implementing EUVL is to economically fabricate multilayer-coated mask blanks with no printable defects. In the case of high defect or damaged multilayers, it is advantageous to recover the starting low thermal expansion material substrate. The starting substrates, due to the required specifications, have a very high manufacturing cost, and a method to recover these substrates without compromising the properties will enable a lower cost for the masks. This document details the method to remove the damaged multilayers from the substrates without compromising the morphology and characteristics of the starting substrate. The invention is also applicable to optical elements of the EUV projection optics system that has reflective Mo/Si mirrors of various shapes.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.

Method to remove Mo/Si multilayers without damaging starting substrate

Pawitter J.S. Mangat

A. Alec Talin

ABSTRACT

                    Extreme ultraviolet lithography (EUVL) is a leading next generation lithography technology.  The mask blank for EUVL consists of a low thermal expansion material substrate having a square photomask form factor (SEMI Standard P-37) that is coated with Mo/Si multilayers.  One of the challenges in implementing EUVL is to economically fabricate multilayer-coated mask blanks with no printable defects.  In the case of high defect or damaged multilayers, it is advantageous to recover the starting low thermal expansion material substrate.  The starting substrates, due to the required specifications, have a very high manufacturing cost, and a method to recover these substrates without compromising the properties will enable a lower cost for the masks.  This document details the method to remove the damaged multilayers from the substrates without compromising the morphology and characteristics of the starting substrate.  The invention is also applicable to optical elements of the EUV projection optics system that has reflective Mo/Si mirrors of various shapes.

Introduction

Extreme Ultra Violet Lithography (EUVL) mask substrates comprise low thermal expansion materials (e.g. ULE,  Zerodur) supplied by different commercial supplier.  The format described in the substrate standard is the same square form factor as the present optical photomask with 6.35 mm thickness and 152 mm edge length.  The main departures from the present optical photomask are the requirements for: (a) a near zero thermal expansion material with coefficient of thermal expansion (CTE) <30 ppb/K;(b) <0.15 nm rms surface roughness for spatial wavelengths <10 mm, (c) flatness over a 142 mm by 142 mm region of <50 nm peak-to-valley on the front and backsides of the substrate, and (d) zero defects >50 nm PSL equivalent size in a negotiated quality area.

Reflective multi-layers, which are 40 alternating layers of Molybdenum and Silicon with a period of approximately 7 nm, were deposited on the described substrates using ion-beam sputtering or other deposition methods.  The period of the multilayers was chosen to produce a centroid wavelength of 13.4 nm at 88.8° degrees from the multi-layer surface to match the multi-layers in exposure systems used to print the masks.  Obtaining a defect free multilayer deposition process is one of the key challenges faced by EUV lithography.

Mask blanks are defined as the substrates that have the defect-free multilayer stack present.  In an alternate embodiment, mask blanks include additional films known as absorber stack films as well as a resist layer.  In any case, Mo/Si film defectivity needs special attention.  If the Mo/Si films are not usable either due to defectivity issue or damage during mask fabrication ...