Nanoliquid Processes for Electronic Devices: Developments of Inorganic Functional Liquid Materials and Their Processing

594 Pages·2019·35.83 MB·English

by  Tatsuya Shimoda

Tatsuya Shimoda
Nanoliquid
Processes for
Electronic
Devices
Developments of Inorganic Functional
Liquid Materials and Their Processing
Nanoliquid Processes for Electronic Devices
Tatsuya Shimoda
Nanoliquid Processes
for Electronic Devices
Developments of Inorganic Functional Liquid
Materials and Their Processing
Tatsuya Shimoda
Japan Advanced Institute of Science
and Technology
Nomi, Ishikawa, Japan
ISBN 978-981-13-2952-4 ISBN 978-981-13-2953-1 (eBook)
https://doi.org/10.1007/978-981-13-2953-1
Library of Congress Control Number: 2018959442
© Springer Nature Singapore Pte Ltd. 2019
This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of
the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,
broadcasting, reproduction on microfilms or in any other physical way, and transmission or information
storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology
now known or hereafter developed.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication
does not imply, even in the absence of a specific statement, that such names are exempt from the relevant
protective laws and regulations and therefore free for general use.
The publisher, the authors, and the editors are safe to assume that the advice and information in this book
are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the
editors give a warranty, express or implied, with respect to the material contained herein or for any errors
or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims
in published maps and institutional affiliations.
This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd.
The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721,
Singapore
Preface
This book summarizes the research outcomes of the “ERATO Shimoda nano liquid
process project” and its extended research, both of which aimed to fabricate nano-
sized devices directly through creating a novel printing technology. The project was
sponsored by the Japan Science and Technology Agency. Because the outcomes
were produced by many researchers involved, I have used “we” instead of “I” in the
descriptions of the research-related contents. The researchers who led each research
project can be found in the corresponding literatures.
In the project, Si-based and oxide-based transistors were selected as target nano-
sized devices. The first work in the project was the development of a series of solu-
tion materials together with their proper processes to realize solid films with high
performance, followed by research works to create a direct printing method using
the developed solutions and to fabricate devices using it. In the case of fabricating a
Si-based transistor, i.e., a metal-oxide semiconductor field-effect transistor (MOS-
FET), the necessary solution materials have been systematically synthesized using
cyclopentasilane as a raw material. Specifically, precursor solutions that can be
transformed by proper treatment to an i-type, p-type, or n-type Si semiconductor
film, a SiO insulator film, or a CoSi conductor film were developed. We also devel-
2 2
oped a SiC precursor solution using cyclopentasilane.
In the case of oxide transistors, several kinds of insulators, semiconductors, and
conductors were developed. In both Si-based and oxide-based materials, the struc-
ture of the solution and its solution-to-solid transformation behavior have been
intensively studied; an intermediate state from solution to solid, i.e., a gel state in
the case of oxide, was investigated in particular detail.
Concerning the direct printing, a novel method named nano-rheology printing
(n-RP) was developed using nanoimprinting. This method involves the direct
imprinting of a precursor gel material that has a plastic deformation ability and can
retain its imprinted shape fairly well after post-annealing. Our reasons for adopting
an imprinting method will be explained together with its advantages in Chap. 12 in
Part I (Introduction of Liquid Process). The n-RP method enabled direct printing of
precise patterns in both Si-based and oxide-based materials. In the case of oxide-
based materials, we found that some gels had an imprinting ability, i.e., plastic
v
vi Preface
deformation ability, at elevated temperatures (below 200 °C) when its structure was
an aggregate of tiny clusters. This behavior was fully exploited to fabricate thin-film
transistors (TFTs) with a short channel and TFT integrated circuits. In the case of
Si-based materials, polysilane derived from cyclopentasilane was found to be
imprinted under certain conditions, and patterns with a high aspect ratio were suc-
cessfully fabricated.
With respect to the devices, before we developed transistors, we developed thin-
film solar cells with a pin structure as a preliminary study of Si-based transistors. In
the case of oxide-based devices, a TFT with memory function, i.e., a ferroelectric
gate–insulator transistor (FGT), was developed together with a normal switching
transistor. Not only transistors but also capacitors were developed, as described in
the chapter on oxide-based devices, because we found a novel dielectric material,
BiNbO, which had an extremely high relative dielectric constant εr.
This book first outlines a liquid process as background information about the
technology of the project. To make clear the technological placement of this book,
I divide the existing liquid processes into three categories according to the liquid to
solid conversion manner and show that the technological category handled by the
project belongs to Type 6 in Category 3, as described later. The necessity of creating
of a new direct printing method is explained with reference to the limitation of the
conventional direct printing technology named “printed electronics (PE).”
Nomi, Ishikawa, Japan Tatsuya Shimoda
Contents
Part I Introduction to Liquid Process
1 Liquid Process ......................................................................................... 3
1.1 Liquid and Its Formability ............................................................. 3
1.2 Categories of Liquid Process ......................................................... 4
1.2.1 First Step: Conversion Way from Liquid to Solid ........... 4
1.2.2 Second Step: Direct Forming Process ............................. 7
Part II Silicon-Based Materials
2 Guide to Silicon-Based Materials .......................................................... 15
3 Liquid Silicon .......................................................................................... 21
3.1 CPS ................................................................................................ 21
3.1.1 Hydrosilanes and CPS ..................................................... 21
3.1.2 Structures of a CPS Molecule .......................................... 23
3.1.3 Electronic Structure of Isolated CPS Molecule ............... 24
3.1.4 I nteraction Between CPS Molecules ............................... 24
3.2 Silicon Ink ...................................................................................... 28
3.2.1 Silicon Ink from CPS ....................................................... 28
3.2.2 Polymer Structure in Silicon Ink ..................................... 30
3.2.3 D oped Silicon Inks .......................................................... 32
References ................................................................................................. 33
4 Thin Film Formation by Coating .......................................................... 35
4.1 Coating Process and Molecular Forces .......................................... 35
4.2 The Origin of Molecular Forces .................................................... 36
4.2.1 T heory of van der Waals Free Energy.............................. 36
4.2.2 M easurement of Refractive Index n ................................. 39
4.2.3 Molecular Forces of CPS and Silicon Compounds ......... 39
4.3 Coating of Si Ink ............................................................................ 42
4.3.1 G eneral Remarks on Si Ink Coating ................................ 42
4.3.2 Observations of Liquid Films .......................................... 42
vii
viii Contents
4.3.3 Hamaker Constant and Coating Property ........................ 44
4.4 Conversion from Polysilane to Amorphous Si by Pyrolysis .......... 45
4.4.1 Film Appearance During Pyrolysis and TG/DTA
Analysis of Si Ink ............................................................ 45
4.4.2 Raman Scattering Analysis .............................................. 46
4.4.3 FT-IR and SIMS Analyses ............................................... 47
4.4.4 Properties of Amorphous Films ....................................... 49
References ................................................................................................. 50
5 Liquid Vapor Deposition Using Liquid Silicon (LVD) ......................... 53
5.1 Formation of I-, N-, and P-Type Silicon Film by LVD .................. 54
5.1.1 L VD Method and Experiment .......................................... 54
5.1.2 CPS Deposition Process .................................................. 55
5.1.3 Film Properties ................................................................. 57
5.1.4 C onclusion ....................................................................... 62
5.2 High-Quality Amorphous Silicon Film with LVD......................... 62
5.2.1 N ew Equipment for LVD ................................................. 62
5.2.2 F ilm Quality with Processing Temperature ..................... 63
5.2.3 Film Quality with CPS Supply Speed ............................. 65
5.2.4 E lectronic Properties of a-Si:H Films .............................. 66
5.2.5 Oxygen Contamination in a-Si:H Film ............................ 67
5.2.6 Summary .......................................................................... 68
References ................................................................................................. 68
6 Liquid Silicon Family Materials(1): SiO, CoSi, and Al .................... 71
2 2
6.1 SiO Fabrication from Liquid Silicon ............................................ 71
2
6.1.1 F orming SiO Films from Liquid Silicon Material .......... 72
2
6.1.2 The Sole Solution-Processed SiO Film for TFTs ........... 75
2
6.1.3 Multiuse of Solution-Processed SiO Films for TFTs ..... 77
2
6.1.4 Conclusions ...................................................................... 78
6.2 CoSi Fabrication from Liquid Silicon .......................................... 78
2
6.2.1 Metal Silicide from Solution ........................................... 78
6.2.2 S ynthesis of Cobalt Silicide Ink ...................................... 79
6.2.3 Formation of CoSi Films ................................................ 79
2
6.2.4 T EM Observation ............................................................ 80
6.2.5 Comparison of this Process with the
Conventional Ones ........................................................... 81
6.2.6 More Detailed Analyses ................................................... 81
6.2.7 C onclusion ....................................................................... 83
6.3 Al Fabrication Via Solution Process .............................................. 83
6.3.1 Triethylamine Alane as a Precursor of Metal Al .............. 84
6.3.2 D eposition Process and Reaction ..................................... 85
6.3.3 Analysis of Film Structure and Al Growth Manner ......... 86
6.3.4 Selective Deposition of Al ............................................... 87
6.3.5 Conclusion ....................................................................... 90
References ................................................................................................. 90
Contents ix
7 Liquid Silicon Family Materials(2): SiC ............................................... 93
7.1 SiC Fabrication via Liquid Process ............................................... 94
7.1.1 Preparation and Characterization of SiC Precursor
Polymer ............................................................................ 94
7.1.2 a-SiC Film Formation and Analyses of Films ................. 98
7.1.3 Polymer Structure ............................................................ 102
7.1.4 Polymer-to-Ceramic Conversion ..................................... 103
7.1.5 Conclusion ....................................................................... 104
7.2 Correlation of Si/C Stoichiometry Between SiC-Ink
and a-SiC Film ............................................................................... 105
7.2.1 P olymer and Film Preparation ......................................... 105
7.2.2 Correlation Between PSH and a-SiC ............................... 106
7.2.3 Structural Properties of an a-SiC Film ............................. 108
7.2.4 O ptical and Electrical Properties of an a-SiC Film ......... 111
7.2.5 Conclusion ....................................................................... 113
7.3 n-Type a-SiC by Coating ............................................................... 114
7.3.1 P olymer and Film Preparation and Their Analyses ......... 114
7.3.2 P olymer Analysis ............................................................. 115
7.3.3 Thin-Film Formation ....................................................... 117
7.3.4 E ffect of Carbon Content on Film ................................... 118
7.3.5 Effect of Phosphorous Concentration on Film ................ 120
7.3.6 Conclusion ....................................................................... 123
7.4 P-Type a-SiC via LVD Method ...................................................... 123
7.4.1 S iC-Ink Preparation and Film Deposition ....................... 123
7.4.2 I nk Analysis ..................................................................... 125
7.4.3 Film Analysis ................................................................... 126
7.4.4 D iscussion ........................................................................ 132
7.4.5 Conclusion ....................................................................... 134
References ................................................................................................. 134
8 Nano-pattern Formation Using Liquid Silicon .................................... 137
8.1 Area-Selective Deposition of Silicon Family Materials ................ 137
8.1.1 A rea-Selective Deposition of Silicon Using
the Difference of Molecular Force ................................... 138
8.1.2 Selective Deposition Using the Reactive Difference ....... 139
8.2 Beam-Assisted Deposition of Silicon ............................................ 140
8.2.1 Free Writing of Silicon by FIB-CVD
and Advantage of CPS for a Source Material .................. 140
8.2.2 Experimental .................................................................... 141
8.2.3 Deposition of Silicon Patterns ......................................... 141
8.2.4 Characterization of the Deposited Patterns ...................... 142
8.2.5 Summary .......................................................................... 144
8.3 Direct Imprinting of Silicon Using Liquid Silicon ........................ 145
8.3.1 Nanoimprinting and Silicon ............................................. 146
8.3.2 Experimental Section ....................................................... 146
x Contents
8.3.3 Imprinted Patterns with Mold 1 ....................................... 150
8.3.4 Influence of Baking Temperature on Imprinting
in Mold 2 .......................................................................... 154
8.3.5 Raman and FTIR Analyses .............................................. 157
8.3.6 Solid-Phase Crystallization of Si Nano-patterns ............. 161
8.3.7 Discussion ........................................................................ 164
8.3.8 Conclusion ....................................................................... 168
References ................................................................................................. 169
9 Development of Solar Cells Using Liquid Silicon ................................ 171
9.1 Thin-Film Solar Cells by Coating .................................................. 171
9.1.1 Solution Preparation and Film Formation ....................... 171
9.1.2 Characteristics of Coated Films and Their
Improvement by Hydrogen-Radical Treatment ............... 172
9.1.3 F abrication of Solar Cells and Their Properties ............... 173
9.1.4 Conclusion ....................................................................... 177
9.2 Thin-Film Solar Cells by LVD ...................................................... 178
9.2.1 Solar Cell Fabrication Using LVD ................................... 178
9.2.2 S olar Cell Fabrication Using the Improved LVD ............ 181
9.2.3 C onclusion ....................................................................... 182
9.3 Application of Liquid Silicon for HBC-Type Solar Cells ............. 182
9.3.1 E xperimental Procedure ................................................... 183
9.3.2 Thermal Stability of LVD a-Si Passivation Films ............ 184
9.3.3 Storage Stability of c-Si Wafers Passivated
with LVD a-Si Films ........................................................ 186
9.3.4 F eature of LVD a-Si Passivation Films
and Advantage of LVD Method ....................................... 186
9.4 Conclusion ..................................................................................... 188
References ................................................................................................. 188
10 Development of Thin-Film Transistors Using Liquid Silicon ............. 189
10.1 Poly-Si Thin-Film Transistor (TFT) .............................................. 189
10.1.1 P reparation of Liquid Silicon ........................................... 190
10.1.2 Poly-Si TFT ..................................................................... 190
10.1.3 I nk-Jet Printing of a Channel ........................................... 191
10.1.4 Conclusion ....................................................................... 193
10.1.5 Experimental Methods ..................................................... 193
10.2 Single-Grain Si-TFT ...................................................................... 194
10.2.1 F orming Single Grains from Liquid Si ............................ 195
10.2.2 Fabrication of Single-Grain TFTs .................................... 198
10.2.3 Single-Grain TFTs on Flexible Substrates ....................... 203
10.2.4 Conclusion ....................................................................... 208
10.3 TFT on Paper ................................................................................. 208
10.3.1 Poly-Si Film from Polysilane .......................................... 209
10.3.2 TFT Fabrication on Paper ................................................ 210
10.3.3 Properties of TFT on Paper .............................................. 211