CHEMICAL VAPOR DEPOSITION POL YMERIZATION

The Growth and Properties of Parylene Thin Films

CHEMICAL VAPOR DEPOSITION POL YMERIZATION

The Growth and Properties of Parylene Thin Films

by

Jeffrey B. Fortin, Ph.D. Rensselaer Polytechnic Institute

Department of Engineering Science Troy, NY

and GE Global Research Center

Niskayuna, NY

Toh-Ming Lu, Ph.D. R. P. Baker Distinguished Professor of Physics

Rensselaer Polytechnic Institute Department of Physics

Troy, NY

SPRINGER SCIENCE+BUSINESS MEDIA, LLC

Library of Congress Cataloging-in-Publication

Chemical Vapor Deposition Polymerization - The Growth and Properties of Parlyne Thin Films by Jeffrey B. Fortin, Ph.D. and Toh-Ming Lu, Ph.D. ISBN 978-1-4419-5413-8 ISBN 978-1-4757-3901-5 (eBook) DOI 10.1007/978-1-4757-3901-5

Copyright ©2004 by Springer Science+Business Media New York Originally published by Kluwer Academic Publishers in 2004 Softcover reprint of the hardcover 1 st edition 2004

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photo-copying, microfilming, recording, or otherwise, without the prior written permission of the publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Permissions ror books published in the USA: permissions@wkap.com Permissions for books published in Europe: permissions@wkap.nl Printed on acid-free paper.

Contents

List of Figures List of Tables Preface Acknowledgments

1. INTRODUCTION

1 Polymers and Their Applications

2

3

4

Polymerization Mechanisms

Polymerization Techniques

Parylene Family Polymers 4.1 Parylene History and the Gorham Method 4.2 Types of Parylene and Applications

2. DEPOSITION EQUIPMENT

1

2

3

4

Deposition System Design

Vacuum Systems

Pressure Measurement

Pump Speed, Flow Rate, and Contact Time 4.1 Determining the pumping speed and flow rate 4.2 Calculating the residence time

IX

xiii xv

xvii

1

1

2

2

4 4 4

9

9

11

11

11 12 14

5 Mass Spectrometry for in-situ Chemical Analysis and Process Monitoring/Control 15

6 Substrate Holders and Temperature Control 16

7 System-to-System Variations 17

8 Example Deposition System 18 9 Commercially Available Deposition Systems and Coating

Services 21

VI

3. STEP-I3Y-STEP GUIDE TO DEPOSITING PARYLENE 23

1

2

3

4

Equipment Preparation

Substrate and Source Preparation

Depositing a Film

Some Considerations

,1. PARYLENE-N PRECURSOR CHEMIS1'RY

1

2

3

DimeI' 1.1 1.2 1.3

Thernlodynamics Dimer purity Mass Spectrometer Fragmentation Pattern

Monomer 2.1 2.2

ThermociYI1<lUlics Mass Spectrometer Fragmentation Patterns

Dimer-to-Monomer Conversion

5. DEPOSITION KINETICS FOR POLYMERIZATION

23

23

24

25

27

27

28 29 33

3:3 34

36

:37

VIA THE GORHAM ROUTE 41

1

2

3

4

5

6

Introduction

Overview of CVD Kinetics

Identifying the Control Type

Identifying the Control Type for Parylene CVD 4.1 The Effect of Temperature on Deposition Rate 4.2 The Effect of Pressure on Deposition Rate 4.3 Summary

Kinetic Modeling of Parylene Thin Film Growth

5.1 5.2

Introduction The Chemisorption Model

Conclusion

6. FILM PROPERTIES

41

41

42

43 44 45 45

46

46

48

55

57

1 Overview 57

2 Adhesion 57

3 Cystallinity 60

4 Thermal Stability 61

5 Chemical Properties and I3iocompatihility 62

6 Properties and IVIeasmcment Techniques for Parylenc-N Films 63

Contents vii

6.1 Electrical Properties 63 6.2 Mechanical Properties 64 6.3 Optical Properties 65 6.4 Surface Morphology 66 6.5 Thermal Stability of Parylene-N 70 6.6 Summary 76

7 UV Degradation 77

7. OTHER CVD POLYMERS 83

1 Introduction 83

2 Polynaphthalene 83 2.1 Film deposition 83 2.2 Polynaphthalenc Film Properties 87

3 Polyimides 88

4 PolytetrafiuOl'oethylcne Family 89

List of Figures

1.1 The polymerization route for parylene-N. 5

1.2 The structure of Heveral different parylene repeat units. 6

2.1 The effective pumping speed versus chamber pressure. 13

2.2 The flow rate vcrHUH chamber preHHure. 14

2.3 The calculated contact time of the dimer III the pyrolysis wne. 15

2.4 The ion intensity of the 104 amu peak (parylene monomer) versus electron energy. 16

2.5 Pressure measured by a capacitance monometer and a thermocouple gauge for air and parylene-N monomer. 18

2.6 The Example Parylcne Deposition System. 19

2.7 Specialty Coating Systems PDS 2060PC produc­tion parylene deposition system, used with the per­mission of Specialty Coating Systems, Indianapo-lis, Indiana. 22

4.1 The measured and extrapolated dimer vapor pres-sure from reference [78]. 28

4.2 Deposition chamber presHure verSUH time for pyrol-ysis temperatureH of 665°C and 215°C. 30

4.3 The percentage of chamber preHHure due to dimer contamination VH. time for two dimer manufacturerH. 31

4.4 Mass spectra for (a) dimer contamination from ref­erence [45] and (b) p-xylene from the NIST vVeb-Book [44]. Inset in (b) shows the structure of p-xylene. ~~2

x

4.5

4.6

4.7

4.8

4.9

5.1

5.2

5.3

5.4

5.5

5.6

6.1

6.2

6.3

6.4

6.5

6.6

6.7

PARYLENE CVD

Mass spectra for (a) dimer from reference [45] (b) dimer from the NIST WebI300k [44].

The singlet and triplet states of the mOllomer with the asterisks signifying radicals.

The vapor pressure of the lllonOlller from reference [7] and for xylene.

.Fragmentation pattel'lls for the monomer llsing ion­i7.:ing electron energies of (a) 25 eV, (b) 45 eV, (c) 65 eV, (d) 85 eV, and (e) 105 eV.

Percent conversion of dimer to monomer vs. py­rolysis temperature for llluitiple tube linings.

The deposition process for parylcnc family poly­mers, not to scale.

Deposition rate vs. temperature for the exalllple deposition system at a pressure of 4.0 mTorr.

Deposition rate vs. pressure for the example depo­sition system at temperatures of -23°C and 22°C.

A molecule-surface potential diagram for a molec­ular chemisorption.

The fit of the chemisorption model to experimental data from the example deposition system.

The sticking coefficient vs. temperature from the chemisorption model.

The set-up for testing a film's electrical properties.

Leakage current density versus fidei strength for parylene-N.

The typical surface morphologies (4 x 4 j..lTr/2 ) mea­sured by AFM for growth time of t = 10 mill, 40 min, and 90 min at the growth rate R = 9.5 nrn/min.

Thc equal time height-height correlation function H(r, t) venms distance r for R = 5.5,9.5, and 13.9 nm/min, respectively.

The interface width 'lJ} and the lateral correlation length ~ versus film thickness d for various growth rates and substrate temperatures.

A diagram of the thermal desorption system.

The 104 amu ion intellsity measured by the TDS system as a function of sample temperat.ure for three film t.hicknesses at. a ramp rate of 7°C/min.

34

36

37

38

40

44

45

46

49

G2

65

67

68

69 71

List of Figu'T'cS Xl

G.8 The fragmentation pattern for the t.hermal decom-position products of parylene-N at 510°C. 74

6.9 The 91 amu ion intensity measured by the TDS system as a fUllction of sample temperature for ramp rates of 7, 10 and 20°C Imin, film thicknesses = 4500 A. 75

6.10 Final film thickness as a percentage of initial thick-ness versus annealing temperature. 76

6.11 The irradiance of the 6035 Hg(Ar) lamp at 50 cm. 78

6.12 Film Thickness change due to degradation from annealing for 2 hours under vacuum. Data is shown for as-deposited, 7 hour, and 24 hour UV-treated samples. 80

6.13 Direct current leakage density versus field strength for as-deposited, 7 hour, and 24 hour UV-treated samples. 80

7.1 The chemical structure of poly(l,4-naphthalene). 84 7.2 The precursor o-diethynylbenzne vapor is heated

in a CVD reactor at above 350°C to form poly-naphthalene via a diradical route. 84

7.3 A schematic diagram showing the design of a cold-wall reactor used to grow polynaphthalene film from o-diethynylbenzene precursor. 85

7.4 A schematic diagram showing the design of a hot-wall reactor used to grow polynaphthalene film from o-diethyny lbenzene precursor. 86

7.5 This figure shows the measured temperature along the furnace plotted with the film thickness data collected a different positions along a 30 inch sec-tion of a hot wall deposition chamber. 87

7.6 Synthesis of fluorinated polynaphthalene from 1,2-diethynyltetrafluorobenzene. 87

7.7 Example of a diamine (ODA) and a dianhydride (PMDA) monomer. 88

7.8 Chemical structure of Teflon and Teflon-AF. 89

List of Tables

4.1 Identity of major peaks appearing in the fragmen-tation pattern of the dimer shown in figure 4.5. 35

4.2 Identity of major peaks appearing in the fragmen-tation pattern of the monomer shown in figure 4.8. 39

5.1 Values of the fitting parameters for the chemisorp-tion model. 53

6.1 Typical properties of the parylene family polymers. 58 6.2 Thermal degradation temperatures (DC) of the pary-

lene family polymers. 61 6.3 Calculated irradiance and dose of the Hg( Ar) arc

lamp for 7 and 24 hour exposures. Irradiance from the sun outside the earth's atmosphere is given as a reference. 79

6.4 Capacitors exhibiting dielectric breakdown and the associated field strength for as-deposited, 7 hr. UV, and 24 hr. UV-treated samples. 81

6.5 Dielectric constant and dissipation factor values for as-deposited, 7 h1'. UV, and 24 hr. UV-treated samples. 81

Preface

The interest and research in the parylene family polymers has re­mained strong since their invention in 1947. To date there have been a handful of reviews and encyclopedia articles covering parylene and its properties but no textbook devoted to the subject. The authors are attempting to fill the void with this textbook that provides a solid intro­duction to the parylene family polymers, their deposition, the deposition apparatus, and film properties.

Chapter 1 is an introduction to polymerization, parylene family poly­mers, the unique parylene deposition process, and the application space. Chapter 2 provides an overview of parylene deposition equipment and process control instrumentation, as well as details on an example depo­sition system. Chapter 3 provides the reader with a step-by-step process for depositing parylene, that, although is not meant to be applied to ev­ery system, points out the critical factors to depositing a high quality film in a well controlled mannel'. Chapter 4 provides details on parylene-N precursor thermodynamics and mass spectrometry fragmentation pat­terns for both the monomer and the dimer. Chapter 5 then goes deep into providing an understanding of the kinetics of the chemical vapor deposition process itself and presents a rate model for parylene-N depo­sition that can be extended to other parylcne family polymers. Chapter 6 contains property data for many of the parylene family polymers as well as detailed property testing methods and results for multiple prop­erties of thin parylene-N films. The testing methods can be used broadly for property measurement of other thin dielectric films. Chapter 7 gives an overview of non-parylene polymers that have been deposited via dif­ferent forms of chemical vapor deposition.

This book is intcnded to bc useful to both users and researchers of parylene thin films. It should be particularly useful for those setting up and characterizing their first research deposition system. It provides a

xvi PARYLENE CVlJ

good picture of the deposition process and equipment as well as informa­tion on system-to-system variations that is important to consider when designing a deposition system or making modifications to an existing one. Also included are methods to characterize a deposition system's pumping properties as well as monitor the deposition process via mass spectrometry. There are many references that will lead t.he reader to further information on the topic being discussed. This text should serve as a useful reference source and handbook for scient.ists and engineers interested in depositing high quality parylene thin films.

JEFFREY FORTIN

TOIl-MING Lu

Acknow ledgments

We would like to thank Dr. Chung Lee and Dr. Jay Senkevich for many valuable discussions. We appreciate the contributions from many former group members including Dr. Lu You, Dr. G.-R. Yang, Dr. Y.-P. Zhao, and Dr. Peter Wu. The support of an NSF grant, IBM, and the Semiconductor Research Corporation over the years is deeply appreciated. The support of a fellowship for Dr. Fortin from Applied Materials during his study at Rensselaer is greatly appreciated. This text could not have been completed without the support of our families.