Micro- and Nanopatterning Polymers 9780841235816, 9780841216884, 0-8412-3581-3

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Micro- and Nanopatterning Polymers

In Micro- and Nanopatterning Polymers; Ito, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

In Micro- and Nanopatterning Polymers; Ito, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

Downloaded by 89.163.35.42 on October 31, 2012 | http://pubs.acs.org Publication Date: September 1, 1998 | doi: 10.1021/bk-1998-0706.fw001

Downloaded by 89.163.35.42 on October 31, 2012 | http://pubs.acs.org Publication Date: September 1, 1998 | doi: 10.1021/bk-1998-0706.fw001

ACS

SYMPOSIUM

SERIES

Micro- and Nanopatterning Polymers Hiroshi Ito, EDITOR IBM Almaden Research Center

Elsa Reichmanis, EDITOR Bell Laboratories, Lucent Technologies Omkaram Nalamasu, EDITOR Bell Laboratories, Lucent Technologies

Takumi Ueno, EDITOR Hitachi Ltd.

Developed from a symposium sponsored by the Division of Polymeric Materials: Science and Engineering at the 214 ACS National Meeting Las Vegas, Nevada, September 7-11, 1997 th

American Chemical Society, Washington, DC In Micro- and Nanopatterning Polymers; Ito, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

706

Library of Congress Cataloging-in-Publication Data Micro- and nanopatterning polymers / Hiroshi Ito, editor ... [et al.]. p. cm.—(ACS symposium series, ISSN 0097-6156 ; 706)

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"Developed from a symposium sponsored by the Division of Polymeric Materials: Science and Engineering at the 214th ACS National Meeting, Las Vegas, Nevada, September 7-11, 1997." Includes bibliographical references and index. ISBN 0-8412-3581-3 1. Microelectronics—Materials. 2. Polymeric composites. 3. Photoresists— Materials. I. Ito, Hiroshi. II. American Chemical Society. Division of Polymeric Materials: Science and Engineering. III. American Chemical Society. Meeting (214 : 1997 : Las Vegas, Nev.) IV. Series. th

TK7871.15.P6M517 1998 621.381—dc21

98-25955 CIP

The paper used in this publication meets the minimum requirements of American National Standard for Information Sciences—Permanence of Paper for Printed Library Materials, ANSI Z39.48-1984. Copyright © 1998 American Chemical Society Distributed by Oxford University Press All Rights Reserved. Reprographic copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Act is allowed for internal use only, provided that a per-chapter fee of $20.00 plus $0.25 per page is paid to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. Republication or reproduction for sale of pages in this book is permitted only under license from ACS. Direct these and other permissions requests to ACS Copyright Office, Publications Division, 1155 16th Street, N.W., Washington, DC 20036. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. Registered names, trademarks, etc., used in this publication, even without specific indication thereof, are not to be considered unprotected by law. PRINTED IN THE UNITED STATES OF AMERICA

In Micro- and Nanopatterning Polymers; Ito, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

Advisory Board

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ACS Symposium Series

Mary E. Castellion ChemEdit Company

Omkaram Nalamasu AT&T Bell Laboratories

Arthur B. Ellis University of Wisconsin at Madison

Kinam Park Purdue University

Jeffrey S. Gaffney Argonne National Laboratory

Katherine R. Porter Duke University

Gunda I. Georg University of Kansas

Douglas A. Smith The DAS Group, Inc.

Lawrence P. Klemann Nabisco Foods Group Richard N. Loeppky University of Missouri Cynthia A. Maryanoff R. W. Johnson Pharmaceutical Research Institute Roger A. Minear University of Illinois at Urbana-Champaign

Martin R. Tant Eastman Chemical Co. Michael D. Taylor Parke-Davis Pharmaceutical Research Leroy B. Townsend University of Michigan William C. Walker DuPont Company

In Micro- and Nanopatterning Polymers; Ito, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

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Foreword THE ACS SYMPOSIUM SERIES was first published in 1974 to provide a m e c h a n i s m for p u b l i s h i n g s y m p o s i a q u i c k l y i n b o o k form. T h e pur­ pose o f the series is to p u b l i s h timely, comprehensive books d e v e l ­ oped from A C S sponsored s y m p o s i a based o n current scientific re­ search. O c c a s i o n a l l y , books are developed from s y m p o s i a sponsored b y other organizations w h e n the topic is o f keen interest to the c h e m ­ istry audience. Before agreeing to p u b l i s h a book, the proposed table o f contents is r e v i e w e d for appropriate and comprehensive coverage and for i n ­ terest to the audience. S o m e papers m a y be e x c l u d e d i n order to better focus the b o o k ; others m a y be added to provide comprehensiveness. W h e n appropriate, o v e r v i e w or introductory chapters are added. Drafts o f chapters are peer-reviewed p r i o r to final acceptance or re­ j e c t i o n , and manuscripts are prepared i n camera-ready format. A s a rule, o n l y o r i g i n a l research papers and o r i g i n a l r e v i e w pa­ pers are i n c l u d e d i n the v o l u m e s . V e r b a t i m reproductions o f p r e v i ­ ously p u b l i s h e d papers are not accepted. ACS BOOKS DEPARTMENT

In Micro- and Nanopatterning Polymers; Ito, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

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Preface

r olymers have p l a y e d an important role i n the electronics industry as c o m p o ­ nent structures and i n manufacturing o f microelectronics devices such as m i c r o ­ processors and m e m o r y chips. T h e wide-spread use o f p o l y m e r i c materials arises from its f i l m - f o r m i n g properties, ease o f fabrication, and especially the ability to synthesize and modify such materials for specific functionalities. Furthermore, patterning o f such p o l y m e r i c materials i n a j i m - n m scale is a k e y technology i n electronic device manufacturing. In the last decade, the performance advancement and price reduction o f consumer electronic devices have been astounding, w h i c h was made possible b y shrinking the m i n i m u m feature size o n integrated circuits i n microlithographic i m a g i n g technology, where radiation-sensitive p o l y m e r i c materials c a l l e d "resists" play a k e y role. A major shift i n the technology has occurred re­ c e n t l y — a shift from 365 to 248 n m and an accompanied shift from n o v o l a c diazoquinone resists to c h e m i c a l l y amplified resist systems. T h e c h e m i c a l l y amplified 2 4 8 - n m resists designed to resolve 2 5 0 - n m features for manufacture o f 256-megabit r a n d o m access memory and related l o g i c devices are n o w ex­ pected to support 1-gigabit (175-nm) and even 4-gigabit (150-nm) generations i n the near future. T h u s , refinement o f c h e m i c a l l y amplified 2 4 8 - n m resists is critical, w h i c h c o u l d be a c c o m p l i s h e d through fundamental understanding o f chemistry and physics o f resist materials and i m a g i n g processes. Further reduction o f the wavelength to 193 n m ( A r F e x c i m e r laser) has be­ c o m e the major thrust i n the last several years, w h i c h has necessitated a d e v e l ­ opment o f new c h e m i c a l l y amplified resists, spawning a massive research effort and p r o v i d i n g enormous challenges and opportunities to resist chemists and en­ gineers. X - r a y and electron-beam lithographic technologies are also expected to c o m e into the scene i n the not-far future. In parallel to the fast progress o f the " c o n v e n t i o n a l " lithographic technol­ ogy, n e w p o l y m e r i c materials must also be developed for n e w patterning tech­ nologies for process simplication, environmental consideration, and so o n . Furthermore, the patterning technology is not confined i n the electronics indus­ try but finds its use i n other areas such as b i o l o g y and m e d i c i n e . W e hope that this v o l u m e provides valuable information o n the current status, future directions, challenges, and opportunities i n the area o f p o l y m e r i c materials for use i n |Lim-and nm-scale patterning.

xi In Micro- and Nanopatterning Polymers; Ito, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

Acknowledgments T h i s v o l u m e is based o n the s y m p o s i u m " P o l y m e r i c Ma te ria ls for M i c r o - and Nano-Patterning Science and T e c h n o l o g y , " w h i c h w a s sponsored b y the A m e r i ­ can C h e m i c a l Society ( A C S ) D i v i s i o n o f P o l y m e r i c M a t e r i a l s : Science a n d E n ­ gineering, Inc. ( P M S E ) , and h e l d i n L a s V e g a s i n September 1997.

W e thank

the P M S E D i v i s i o n for sponsoring the s y m p o s i u m , the authors for their valuable contributions to both the s y m p o s i u m and this v o l u m e , and the referees for care­

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fully r e v i e w i n g the manuscripts. vided

by Olin

F i n a n c i a l support for the s y m p o s i u m w a s pro­

Microelectronic

Materials,

Inc., Hoechst-Celanese, Inc.,

S E M A T E C H , L u c e n t Technologies B e l l Laboratories, I B M , the P M S E D i v i ­ sion, and the Petroleum Research F u n d administered b y A C S , w h i c h is grate­ fully a c k n o w l e d g e d . O u r sincere thanks are also extended to A n n e W i l s o n , T r a c i e Barnes, and the production staff o f the A C S B o o k s Department for their efforts i n assem­ b l i n g the v o l u m e .

HIROSHI ITO

IBM Almaden Research Center 650 Harry Road San Jose, C A 95120

E L S A REICHMANIS

Bell Laboratories, Lucent Technologies 600 Mountain Avenue Murray Hill, NJ 07974

OMKARAM NALAMASU

Bell Laboratories, Lucent Technologies 600 Mountain Avenue Murray Hill, NJ 07974

TAKUMI UENO

Hitachi, Ltd. Hitachi Research Laboratory 1-1 Omika-cho 7-Chome Hitachi, Ibaraki 319-12, Japan

In Micro- and Nanopatterning Polymers; Ito, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

Chapter 1

Lithography with a Pattern of Block Copolymer Microdomains as a Positive or Negative Resist 1

1

1

2

Christopher Harrison , Miri Park , Paul M . Chaikin , Richard A. Register , and Douglas H. Adamson Downloaded by 89.163.35.42 on October 31, 2012 | http://pubs.acs.org Publication Date: September 1, 1998 | doi: 10.1021/bk-1998-0706.ch001

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1

2

3

Department of Physics, Department of Chemical Engineering, and Princeton Materials Institute, Princeton University, Princeton, NJ 08544 Dense, periodic arrays of holes and troughs have been fabricated in silicon, silicon nitride, and germanium, at a length scale inaccessible by conventional lithographic techniques. The holes are approximately 20 nanometers (nm) wide, 20 nm deep, spaced 40 nm apart, and uniformly patterned with 3X10 holes on a three inch silicon wafer. To access this length scale, self-assembling resists were synthesized to produce either a layer of hexagonally ordered polyisoprene (PI) spheres or polybutadiene (PB) cylinders in a polystyrene (PS) matrix. The PI spheres or PB cylinders were then chemically modified by either degradation or stained with metal compounds to produce a useful mask for pattern transfer by fluorine­ -based reactive ion etching (RIE). A mask of spherical microdomains was used to fabricate a lattice of holes or posts and a mask of cylindrical voids was used to produce parallel troughs. This technique accesses a length scale difficult to produce by conventional lithography and opens a route for the patterning of surfaces via self-assembly. 12

Recent advances in photolithography have pushed the feature size down to 150 nm in production processes(7), and even smaller feature sizes have been reported in experimental research(2,5,4). However, dramatic improvements in the circuit density with photolithographic processes are not anticipated because the minimum feature size is limited by the wavelength of light, typically 193 or 248 nm in current processes. A s an alternative to photolithography, self-assembled structures, such as monolayers of spheres or cylinders(5,6), have been advanced by researchers due to their nanoscopic feature sizes and the control demonstrated in uniformly coating substrates. Though these morphologies do not allow one

2

© 1 9 9 8 American Chemical Society In Micro- and Nanopatterning Polymers; Ito, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

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3

the high degree of pattern control necessary for microelectronic circuits, there are a variety of applications in which regular patterning or texturing of a surface at the 10 nm lengthscale is ideal: for example, the periodic patterning of an electric potential on a two-dimensional electron gas system(7,#,9,70,77), fabrication of quantum dots or anti-dots(72), synthesis of D N A electrophoresis media(73), filters with nanometer pore sizes, and creation of quantum confinements for light emission. For these applications, the self-assembled structures observed in ordered diblock copolymer thin films would seem ideal as lithography templates because of their self-assembly and the ability to parallel-process wafer-sized areas. B l o c k copolymers with a narrow polydispersity (the chains are of near uniform length) and with %N>10 microphase separate above their glass transition temperature, where % is the Flory-Huggins interaction parameter and N is the degree of polymerization(74). Macroscopic phase separation of the components of the block copolymer is prevented by a covalent bond which connects the unlike blocks. The resulting morphology depends largely on the relative volume fraction of the components. Some of the more commonly seen microdomain morphologies are lamellae, cylinders, and spheres (Figure 1). The periodicity of these structures is determined by the length of the polymer chains and is typically on the order of 20-100 nm. (a) A

A

A' ' 'V block A

/

A

,

B

,

B

J

!

\

B-B

block B

Figure 1: (a) A block copolymer consists of two or more homogeneous blocks, drawn here as blocks A and B . (b) Microphase separation typically produces a lamellar morphology for equal lengths of blocks A (light) and B (dark). A s block B is shortened with respect to block A , hexagonally packed cylinders are typically observed. For an even shorter block B , packed spheres on a body centered-cubic lattice are observed.

In Micro- and Nanopatterning Polymers; Ito, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

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Researchers have recently studied thin films of block copolymers because of both the rich set of phenomena that have been observed(75,76,77) and because of their application to lithography(7#,79,20). Earlier work with poly(styrene-fcbutadiene), P S - P B , and subsequent work with poly(styrene-£-isoprene), PS-PI, block copolymers showed that by choosing the appropriate film thickness, a single layer of spherical or cylindrical microdomains (a monolayer of spheres or cylinders, see Figure 2) could be produced as a lithographic template. Brush­ like wetting layers of P B or PI (collectively referred to as the diene component) on the free and confined surfaces were shown to sufficiently decouple the microdomains from the substrate to allow the microdomains to order with a grain size of up to 25 by 25 unit cells, or about 1 square micron. Subsequent dynamic secondary ion mass spectrometry analysis confirmed the existence of wetting layers of P B on the free and confined surface of films spin coated onto silicon wafers(27). The diene component preferentially wets the free surface due to its lower surface tension(22) while the confined surface is wet by the diene component due to a combination of a lower interfacial tension and a possible silica-poly diene chemical bonding(23,24).

Figure 2: (a) A monolayer of PI spheres in a PS matrix, with accompanying free and confined surface PI wetting layers, (drawn for SI 68/12) (b) A monolayer of P B cylinders in a PS matrix, with accompanying free and confined surface P B wetting layers, (drawn for S B 36/11) The microdomain template as shown above (Figure 2) is not an effective mask for R I E because the P S , PI, and P B blocks etch approximately at the same rate under either C F or CF4/O2 R I E , which we find to be the most effective etching process for pattern transfer. Therefore, further modification of the microdomains is necessary to make a useful mask. B y allowing the monolayer to act as a template and taking advantage of the different chemical properties of the component blocks, we found that the template could function as either a positive or negative resist for pattern transfer. 4

In Micro- and Nanopatterning Polymers; Ito, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

5

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Sample Preparation Asymmetric P S - P B and PS-PI diblock copolymers were synthesized (designated S B 36/11 and SI 68/12 respectively, with the molecular weights of the blocks in kilograms per mole) by standard high-vacuum anionic techniques(25). In bulk, S B 36/11 microphase separates into a cylindrical morphology and produces hexagonally ordered P B cylinders in a PS matrix. SI 68/12 adopts a spherical morphology and produces PI spheres in a PS matrix with body-centered-cubic order, as shown in Figure l b . Thin polymer films were produced by spin-coating solutions of polymer dissolved in toluene onto various substrates, and the film thickness was controlled by varying the spinning speed and polymer concentration. The films were annealed in vacuum between 130°C and 170°C, a temperature above the glass transition temperatures of both blocks, for 24 hours to obtain well-ordered morphologies. Pattern Transfer as a Positive Resist For pattern transfer, thin films of spherical or cylindrical microdomain monolayers were directly spin coated on silicon wafers. Previous work on imaging the microdomain pattern on silicon wafers with a combination of lowvoltage, high resolution S E M and a REE allowed us to determine the optimum film thickness deposited by spin coating to form a monolayer of spheres or cylinders(27). T o make a monolayer of spheres with SI 68/12, a 70 nm thick-film was required, and for a monolayer of cylinders using S B 36/11, a 50 nm film was required (see Figure 2). For silicon nitride patterning, - 6 0 nm of silicon nitride was deposited on silicon wafers at 250°C by plasma enhanced chemical vapor deposition ( P E C V D ) , followed by spin coating polymer films. T o pattern germanium, we first evaporated germanium on silicon wafers, then deposited a - 1 0 nm isolation layer of P E C V D silicon nitride, and subsequently spin coated polymer solutions. W e found it necessary to protect the germanium during the ozonation (discussed in the following paragraph) process with silicon nitride to prevent the formation of germanium oxides which damage the sample. During pattern transfer, the microdomain pattern was etched through the silicon nitride and into the germanium underneath. B y selectively degrading and removing the PI or P B microdomains, the template functioned as a positive resist on the substrate, making a mask of microdomain voids. The positive resist was created by placing the coated wafers in an aqueous environment through which ozone was bubbled for .four minutes(26). The ozone cleaved the carbon-carbon double bonds of the diene component and the degradation fragments dispersed in the water(27,2