Selected Papers

Block Copolymer Lithography toward
16-nm-technology Nodes and Beyond
Toru Yamaguchi† and Hiroshi Yamaguchi
Abstract
We report a combined top-down/bottom-up approach for nanopatterning using self-assembled
domains of a block copolymer. We have successfully demonstrated that these periodic domains with ahalf-pitch smaller than 16 nm can be ordered by using block copolymers with shorter chain lengths.
Moreover, we have devised a new approach for the lateral alignment of the lamellar domains of the
diblock copolymer by using a resist pattern as a guide for the alignment. This makes it possible to precisely control the alignment of the self-assembled domains. We are convinced that this approach ispromising for high-resolution lithography, which could be applicable to 16-nm half-pitch technology
nodes needed in about 2019.

1. Introduction
The remarkable progress in semiconductor fabrication technology has made it possible to manufacture
silicon chips using 65-nm process technology. This
dramatic advance in miniaturization technology islargely due to progress in lithographic technologies.
However, it is becoming difficult to maintain the
rapid pace of miniaturization because many difficult
challenges need to be overcome, such as criticaldimension (CD) control, overlay, defect control, andlow cost. The 2005 edition of the International Technology Roadmap for Semiconductors (ITRS
Roadmap), which is a fifteen-year assessment of thesemiconductor industry’s future technology requirements, offered no proposals for potential solutions
capable of meeting the requirement for the 16-nm
half-pitch technology node generation and beyond.
The forecast shows that this requirement should be
met by 2019. Therefore, innovative lithographic technologies need to be developed.
Recently, block copolymer lithography [1] has
attracted considerable attention as a combined topdown/bottom-up approach to nanopatterning. Thismethod involves the use of microphase-separated† NTT Basic Research Laboratories
Atsugi-shi, 243-0198 Japan
Email: guchan@NTTBRL.jp

Vol. 4 No. 11 Nov. 2006

nanometer-sized domains as lithography templates. It
is superior in that nanostructures can be fabricated inlarge quantities with approximately consistent sizes.
Its most important feature is that the sizes and periodsof the microphase-separated domains involved in thismethod are determined merely by the chain length of
the block copolymer. Therefore, this method has significant potential to exceed the resolution limit of the
top-down technologies such as electron-beam (EB)lithography, which is expected to be around 20 nm.
Diblock copolymers comprise two flexible, chemically incompatible and dissimilar polymer chain
blocks covalently bonded together at one end, as
shown in Fig. 1. Due to the incompatibility between
the two blocks and connectivity constraints, thechains spontaneously self-assemble into microphaseseparated nanometer-sized domains at a certain temperature. In ordered periodic structures, the size ofthe domains is governed by the dimensions of thechain, which is of the order of tens of nanometers.
The shape of the microphase-separated domains
depends on the composition of the polymer. Various
shapes ranging from spheres, cylinders, and lamellae
to inverse spheres (the matrix surrounding spheres ofthe other material) can be produced by changing thevolume fraction of block A, as illustrated in Fig. 2. In
block copolymer lithography, a monolayer of anordered structure is used as a patterning template. For
example, both spherical domains and vertical cylin17

Selected Papers

A-B diblock copolymer
A

B

Disordered structure

Ordered structure

Annealing

10–50 nmFig. 1. Self-assembly of diblock copolymer.

Increasing content of A
Spheres of A

Cylinders of A

Lamellae of A&B

Cylinders of B

Spheres of B

Dots

Dots/holes (vertical)
L&S (in-plane)

L&S

Dots/holes
L&S

Dots

Lithographic application

Fig. 2. Various shapes of microphase-separated domains.

der domains can be used to form dot and hole patterns.
With regard to dot and hole patterns, many attempts
have been made to apply these domains as dry-etching masks in the semiconductor fabrication process.
These structures are reported to have been used topattern magnetic media [2] and flash memory [3]. On
the other hand, research on line-and-space (L&S) patterns has just begun [4]-[6]. For L&S pattern formation, both in-plane cylindrical and lateral lamellar
domains can be applied. To apply these domains to
L&S pattern formation, the domain alignment should
be controlled more strictly.
Here, we report on our recent activity concerning
the alignment control of self-assembled domains of
diblock copolymers using graphoepitaxy. Graphoepi18

taxy is a technique that uses the surface topography ofthe substrate to direct epitaxial growth of the block
copolymer film.
Section 2 describes the alignment method of inplane cylindrical domains of an asymmetric diblock
copolymer using microtrench patterns. Section 3
reports a new approach to graphoepitaxy using a
resist pattern as the guide for alignment; this makes it
possible to laterally align the lamellar domain behaviors of symmetric diblock copolymers.
2. Alignment of in-plane cylindrical domains
inside a microtrench
2.1 Materials
We used an asymmetric diblock copolymer comNTT Technical Review

Selected Papers

PS0.3–b–PEP0.7
CH3
0.7

PS–PEP
Single molecule

2 × molecular size

Fig. 3. (a) Chemical structure of PS-b-PEP and (b) selfassembled cylinder structure.

(a)Hole: L /2

(b)

(c)

Topography

Phase

50 µm

3L /2

0
100
200
300
400
3L /2
500

[nm]

0
100
200
300
400
L /2
500

L /2

0

Surrounding: 3L /2

400

20
[nm]

300

Cylindrical domain

[nm]

(b)

200

0.3

100

(a)

2.2 Self-assembly on a flat substrateFirst, we investigated the behavior of the selfassembly of this diblock copolymer on a flat substrate. Thermal annealing quantizes the film thickness of the block copolymer by separating it into terraces (i.e., islands and holes). An optical microscope
image exhibiting a hole morphology is shown in Fig.
4(a). From thickness measurements of the hole andsurrounding regions, we found that the block copolymer film on the silicon oxide surface exhibited asymmetric wetting: a PS block preferentially wet theoxide surface, whereas a PEP block covered the freesurface. The quantized thickness corresponds to odd
half-integer multiples of L, that is, (2n + 1)L/2, where
n is an integer and L is the thickness of a single layerof the cylinders.
A topographic image of the region near the boundary between the L/2 and 3L/2 terraces is shown in Fig.
4(b). In the 3L/2 terraces, a fingerprint pattern can beclearly observed. This implies that the cylinders lay
parallel to the substrate. Although a PS cylinder wasembedded in a PEP matrix, the cylinder structures
were observed even in the topographic image because
the surface immediately above the PS cylinderswelled up to a height of approximately 1 nm.
The phase image corresponding to the topographic
image of Fig. 4(b) is shown in Fig. 4(c). Phase imaging is a standard technique for mapping the spatial
variation in surface elasticity. The cylinder structures500

posed of polystyrene (PS) and poly(ethylene-altpropylene) (PEP). Its chemical structure is shown in
Fig. 3(a). The molecular weights of each PS and PEP
block were 6100 and 16,500 g/mol, respectively, witha polydispersity of 1.04. The molar ratio of PS:PEP
was 0.3:0.7, as shown in Fig. 3(a). In this polymer,
self-assembly involves the formation of cylinders of
PS embedded in a PEP matrix (Fig. 3(b)).

0100–70.948

200

300

[nm]
[deg]

400

500
–72.555(d)
Molecular brush layer

Cylinder layer~ L /2

~L

3L /2

L /2

Fig. 4. In-plane cylindrical structure: (a) optical microscope image, (b) AFM topological image,(c) AFM phase image, and (d) schematic diagram.

Vol. 4 No. 11 Nov. 200619

Selected Papers(a) Microtrench(b) Block copolymer film(c) Microphase separation

Fig. 5. Alignment process of cylindrical domains inside microtrench.

(b)

150

[µm]

100

0.4
0.2

–60.895

0.4

0.6

[µm]

[deg]

0.8

1

0

50

0.2
0
0

[nm]

0.6

200

0.8

250

1

(a)

0

50

100

150

200

250

[nm]

–63.399–59.901[deg]–63.383

Fig. 6. AFM phase images of cylindrical domains near theedge region of a trench.

can be observed due to the difference in elasticity
between the PS and PEP domains. The dark region in
the phase image corresponds to a PS cylinder domainthat is less elastic than a PEP domain. Neither the
topographic images nor the phase images showed any
specific structures due to the self-assembly on the L/2
terrace. This is because a self-assembled monolayer,
in which the PS block wets the substrate and the PEP
block faces the polymer/air interface, was formed on
the L/2 terrace. These results confirmed that the block
copolymer film on a flat surface covered with silicon
dioxide was quantized in units of odd half integers
and had a layer period L of about 20 nm, as illustrated in Fig. 4(d).
2.3 Alignment of cylindrical domains inside
microtrench
Next, we investigated the graphoepitaxy of selfassembled cylindrical structures on a micropatterned
substrate [7]. In graphoepitaxy, the self-assembled
structures are aligned with the sidewalls of the patterns.
A schematic diagram of the alignment process inthis approach is shown in Fig. 5. First, themicrotrench is formed on the substrate. A SiO2 layer
with a thickness of a few tens of nanometers isformed on the Si substrate by thermal oxidation in a20

dry oxygen ambient. A 1.5-µm L&S pattern of theoxide is made by contact photolithography and subsequent reactive ion etching (Fig. 5(a)) Next, theblock copolymer film is formed over trenches (Fig.
5(b)). The spin-coated film is then annealed in anoven at 130°C under a nitrogen atmosphere for 15 h
to enable sufficient microphase separation (Fig. 5(c)).
The self-assembled domains are observed using an
atomic force microscope (AFM) in the dynamic forcemode.
AFM phase images of a self-assembled block
copolymer film near the edge region of a trench witha depth of 26 nm and width of 1.5 µm are shown in
Fig. 6(a). It is clear that the cylinder structure wasformed only within the trench. This is due to the formation of a 3L/2 terrace within the trench and an L/2
terrace on the mesa resulting from height quantization. To confine the formation of cylinders within atrench, a certain minimum height, which is probably
greater than L, is required. It is noteworthy that thecylinder structure is aligned with the sidewall of thetrench that is 800 nm long and 200 nm wide. A magnified view of Fig. 6(a) is shown in Fig. 6(b). We canclearly see that the bright domain corresponding to
the PS block is in contact with the sidewall of thetrench. This implies that a self-assembled monolayer
was formed on the sidewall of the trench as well as on
the bottom surface of the trench. This monolayer formation is the key to inducing the lateral alignment of
the cylinder structures. Moreover, it is clear that thecylinders having a 23-nm pitch are separated fromeach other, although the lines that they form are notcompletely straight.
We have demonstrated that cylindrical domains
with a pitch of 23 nm were aligned inside the oxide
trench. This already surpasses the resolution of the
16-nm half-pitch technology generation and confirmsthat block copolymer lithography has significant
potential for high-resolution lithography.
NTT Technical Review

Selected Papers

CH3

1
0.8
[µm]

0.6

PS

0
200
400
600
800

O

1 µm
µm

Phase

40
[nm]

0.5
O

C

(b)
1 µm

Topography

0.4

0.3

(a)

PS

[nm]

0
200
400
600
800

0.2

PS0.5–b–PMMA0.5
CH3

PMMA

0

(a)

0

0.2

–62.340

0.4

[µm]

0.6

0.8

[deg]

–63.788

1

PMMA–PS(b)(c)
Single molecule
3/2 L 0L0
1/2 L 0L0Lamellar domain

Native oxide

2 × molecular size

Fig. 7. (a) Chemical structure of PS-b-PMMA and(b) self-assembled lamellar structure.

3. Alignment of lateral lamellar domains in
confined spaces between resist patterns
From the viewpoint of pattern transfer processes
such as dry etching, lateral lamellar domains are
preferable to in-plane cylindrical domains because in
their case, an aspect ratio of at least 2 can be obtained.
Kim et al. successfully demonstrated that the lamellar domain made of symmetric poly(styrene-bmethylmethacrylate) could be perfectly aligned on
chemically nanopatterned substrates [4]. However, in
this method, lateral lamellar domains having a pitch
smaller than that of the chemically nanopatterned
substrates formed by conventional lithography cannever be aligned. To obtain a smaller pitch than theguide pattern, the graphoepitaxy technique should
also be used to align the lateral lamellar domain.
Therefore, we devised a new approach for graphoepitaxy using a resist pattern as the guide for alignment[8].
3.1 Materials
Diblock copolymers of PS and poly(methylmethacrylate) (PMMA), whose chemical structure isshown in Fig. 7(a), is the most suitable materials forblock copolymer lithography. This is because the PS
domain has a high dry-etching durability and the
PMMA domain can be easily removed by exposure to
deep-ultraviolet light and subsequent development.
The self-assembly of the symmetric diblock copolyVol. 4 No. 11 Nov. 2006

PS
PMMA
PS
PMMA

Fig. 8. Parallel lamellar structure: (a) AFM topographic
image, (b) AFM phase image, and (c) schematic
diagram.

mer made of PS and PMMA with the same molar
ratio involves the formation of a lamellar structurecomposed of alternating stacked layers of PS andPMMA domains, as shown in Fig. 7(b). The lamellar
period L0 is twice the size of the molecule.
3.2 Self-assembly on a flat substrateFirst, we investigated the behavior of the selfassembly of this diblock copolymer on a flat substrate. Generally, the parallel lamellar structure of thisblock copolymer, in which the lamellar interface isparallel to the substrate surface, is formed on the silicon substrate. This is because a PMMA block preferentially wets the substrate surface, which has a strong
affinity with a PMMA block, whereas a PS block
covers the free surface because its surface tension islower than that of a PMMA block. As a result, theblock copolymer film is separated into terraces during annealing. Moreover, the block thicknesses arequantized in odd half-integer multiples of L0, that is,(2n + 1) L0/2, where n is an integer. In particular, at anincommensurate initial thickness, an island or hole
structure is clearly formed with a step height of L0.
Therefore, we only need to measure the height ofthese terraces to determine the value of L0.
A topographic AFM image of the region near theboundary between the L0/2 and 3L0/2 terraces of theself-assembled structures on a flat surface is shown in
Fig. 8(a). The figure shows that the terrace surfaces
were completely flat and exhibited no morphology.
21

Selected Papers(a) Neutralization layer(b) Guide pattern(c) Block copolymer film(d) Microphase separation

Fig. 9. Alignment process of lamellar domains.

The phase image corresponding to the topographic
image in Fig. 8(a) is shown in Fig. 8(b). The brightand dark regions correspond to the PS and PMMA
domains, respectively. It is clear that the PS domain
covered all the terraces, regardless of whether they
were L0/2 or 3L0/2 terraces. On the other hand, thePMMA domain appeared only as a streak around theboundary of a step. This is good evidence that parallel lamellae do actually form, as illustrated in Fig.
8(c). From the topographic image, we determinedthat the average step height between the L0/2 and3L 0 /2 terraces was approximately 28 nm. Thisimplies that this block copolymer should form L&S
patterns with a pitch of 28 nm.
3.3 Alignment of lamellar domains
As described above, a parallel lamellar structure ofthis block copolymer, in which the lamellar interface
is parallel to the substrate surface, was formed on thesilicon substrate. To align the lamellar domains laterally, we should align the lamellar interface in two
directions, i.e., perpendicular to the substrate surface
and parallel to the sidewall surface of the guide pattern. To achieve this, it is essential to create a difference between the surface affinities on the substratesurface and the sidewall surface of the guide pattern;in other words, the surface free energies of both thesurfaces must be controlled independently.
A schematic diagram of the alignment process inthis approach is shown in Fig. 9. First, a neutralization layer [9] is formed on the substrate (Fig. 9(a)).
Using a neutralization layer is an effective method ofaligning the lamellae perpendicularly. It prevents theother block domains from preferentially wetting thesubstrate because the surface affinity of the neutralization layer is approximately half that of either
domain of the block copolymer. This facilitates theperpendicular alignment of the lamellae to the substrate. We used a 10-nm-thick film of a cross-linked
alternating copolymer of α-methyl styrene andmethylmethacrylate as the neutralization layer.
22

Second, the resist pattern for the alignment guide isformed on the neutral surface (Fig. 9(b)). We usedhydrogen silsesquioxane (HSQ), which is an EB negative-tone resist [10], as the resist pattern guide. An
HSQ pattern with a width of 25 nm and height 40 nm
was delineated by 100-kV EB lithography. Since thesurface free energy of the HSQ pattern composed ofsiloxane is close to that of the PMMA domain, thisdomain preferentially wets the sidewall surface of theresist pattern guide. Therefore, lateral alignment of
the lamellar domain could be achieved.
Third, the block copolymer film is formed over the
resist pattern guide (Fig. 9(c)). We used symmetricpoly(styrene-b-methylmethacrylate) with a molecular weight of 36,000 g/mol. A 30-nm-thick block
copolymer film was prepared by spin coating on thesubstrates.
Finally, the film is baked to induce microphase separation (Fig. 9(d)). It is then annealed in an oven at
175°C under a N2 atmosphere for 16 h.
AFM phase images of the microphase-separated
domains near the boundary between a flat region anda guide pattern region are shown in Fig. 10. The lefthand image shows a magnified view of the flat region.
Although the alignment here was random, a laterallamellar domain had formed. This indicates that thelamellae were aligned vertically on the neutralization
layer. The right-hand image shows a magnified viewof the guide pattern regions. The arrows indicate thepositions of the guide patterns with pitches in therange from 104 to 108 nm. In the confined space
between the guide patterns, two dark PMMA
domains had partially formed parallel to the guide
pattern. Unfortunately, we could not observe a
PMMA domain directly wetting the sidewall because
there was a difference of approximately 10 nm in theheight between the top of the pattern and the surfaceof the film. These images demonstrate that the HSQ
patterns function as guides for lateral alignment.
We investigated how the degree of alignment
depends on the pitch of the guide pattern. AFM phase
NTT Technical Review

Selected Papers

On flat surface:random alignment

In confined spaces between guides:
lateral alignment
HSQ guide pattern
Pitch (nm)
106

108

200

300

0

200
[nm]

100

300

[µm]

0.6

0.8

[deg]

–65.413

300
[nm]

200

1
0

0.4

0

0.2

0

1 µm
0

100

100

0.2

200

0.4

[nm]

[µm]

0.6

300

0.8

104

0

–68.390Bright region: PS domain
Dark region: PMMA domain

100

[nm]

HSQ

HSQ

Fig. 10. Lateral alignment in confined spaces between guides.

300

0.6

[µm]

[deg]

0.8

1

–68.855

200

[nm]

152

156

0.8

1

–68.059

160

164
0.8
0.4

[µm]

0.6

0.8
0.4

[µm]

0.6

0.8
[µm]

0.6

[µm]

[deg]

300

1

148

200

[nm]

1

144

0.4
0.4

100

Random0.2
0.2–64.176

0
0

0
0

100

200
300

0.6

0.8
0.6

[µm]

0.4
0.4

200

[nm]

1

130 134 138 142

0.2
0.2

–64.953

100

Partial alignment

0
0

100
0

1

Pitch 104 108 112 116
(nm)

200

[nm]

Random

0.2

100

0

100
0
0

0

0.2

–64.446

0.4

0.6

[µm]

[deg]

0.8

1

–68.110

0

300

0.2

200

[nm]

Perfect alignment

0

100

[nm]

300
200

200

[nm]

[nm]

100
0
0

4.5L 0
300

4L 0
300

3.5L 0
300

3L 0

0

0.2

–63.950

0.4

0.6

[µm]

[deg]

0.8

1

–67.579

Fig. 11. Pitch dependence of self-assembly.

images of the microphase-separated domains in theconfined spaces between the guide patterns with various pitches are shown in Fig. 11. The lower images
are the original images covering a scan area of 1 µm
square and the upper ones are magnified views covering an area 400 nm square. For pitches in the range
from 112 to 116 nm, which corresponds to approximately 3L0, two PMMA domains were distinctly separated from each other. The repetition period of laterVol. 4 No. 11 Nov. 2006

al lamellar domains PL was about 29 nm, which was
obtained as PL = (Pg – Wg)/N, where Pg is the pitchof the guide patterns, Wg is the width of guide patterns (25 nm), and N is the repetition number. Thisvalue is consistent with the step height of parallel
lamellar domains L0 = 28 nm. In addition, we can seethat these domains were successively aligned over a
distance of 1 µm. For pitches in the range from 142 to
144 nm, which corresponds to approximately 4L0,23

Selected Papers

three PMMA domains were nearly aligned with eachother; however, defects interrupted the continuity. On
the other hand, at an incommensurate pitch such as
3.5L0 or 4.5L0 many defects appeared; consequently,
disordered domains were formed.
This result indicates that the degree of alignment
strongly depends on the pitch of the guide pattern andthat lamellae with a thickness of at least 3L0 can bealigned laterally in the confined spaces between theguide patterns under the experimental conditions
used in this study.
4. Conclusion
Block copolymer lithography is a powerful technique as a combined top-down/bottom-up approach
to exceed the resolution limit of conventional topdown lithography. We have succeeded in thegraphoepitaxy of a 23-nm-pitch cylindrical domainof asymmetric diblock copolymer PS-b-PEP inside
microtrenches made of silicon dioxide. The value of
this pitch is approximately equal to the current resolution limit of electron-beam lithography. We havealso devised a new approach for the graphoepitaxy of
the lamellar structures of a symmetric diblock
copolymer PS-b-PMMA by using a resist pattern as a
guide for alignment. We have successfully demonstrated lateral alignment of lamellae in confined
spaces with a thickness of at least 3L0 between thestraight guide patterns composed of an HSQ resist on
a neutral surface. This approach has the significant
advantage of differentiation between the surface
affinities on the substrate surface and the sidewall
surface of the guide pattern, which makes it possible
to achieve strict control of the alignment of selfassembled domains. We believe that the combinationof the artificial layout of the guide patterns and thebest choice of polymer materials could lead to a new
type of high-resolution lithographic technology.

[4]

S. O. Kim, H. H. Solak, M. P. Stoykovich, N. J. Ferrier, J. J. de Pablo,
and P. F. Nealey, “Epitaxial self-assembly of block copolymers on
lithographically defined nanopatterned substrates,” Nature, Vol. 424,
pp. 411-414, 2003.
[5] D. Sundrani, S. B. Darling, and S. J. Sibener, “Guiding Polymers to
Perfection: Macroscopic Alignment of Nanoscale Domains,” Nano
Lett., Vol. 4, No. 2, pp. 273-276, 2004.
[6] H. -W. Li and W. T. S. Huck, “Ordered Block-Copolymer Assembly
Using Nanoimprint Lithography” Nano Lett., Vol. 4, No. 9, pp. 16331636, 2004.
[7] T. Yamaguchi and H. Namatsu, “Graphoepitaxy of Diblock Copolymer on Micropatterned Substrates,” J. Photopolym. Sci. Technol.,Vol. 18, No. 3, pp. 421-423, 2005.
[8] T. Yamaguchi and H. Yamaguchi, “Resist-Pattern Guided Selfassembly of Symmetric Diblock Copolymer,” J. Photopolym. Sci.
Technol., Vol. 19, No. 3, pp. 385-388, 2006.
[9] P. Mansky, Y. Liu, E. Huang, T. P. Russel, and C. Hawker, “Controlling Polymer-Surface Interactions with Random Copolymer Brushes,” Science, Vol. 275, pp. 1458-1460, 1997.
[10] H. Namatsu, Y. Takahashi, K. Yamazaki, T. Yamaguchi, M. Nagase,and K. Kurihara., “Three-dimensional siloxane resist for the formation of nanopatterns with minimum linewidth fluctuations,” J. Vac.
Sci. Technol., Vol. B16, No. 1, pp. 69-76, 1998.

Toru Yamaguchi
Senior Research Scientist, Physical Science
Laboratory, NTT Basic Research Laboratories.
He received the B.S. and M.S. degrees inchemistry from the University of Tokyo, Tokyo,
in 1990 and 1992, respectively. He joined NTT
LSI Laboratories in 1992. He has been engaged
in research on surface modification by high-energy ion-beam irradiation and resist materials fornanolithography. His current interest is nanofabrication using the self-assembly of block copolymers. He is a member of the Japan Society ofApplied Physics (JSAP).

Hiroshi Yamaguchi

References
[1]

[2]

[3]

24

M. Park, C. Harrison, P. M. Chaikin, R. A. Register, and D. H. Adamson, “Block Copolymer Lithography: Periodic Arrays of ~1011 Holesin 1 Square Centimeter,” Science, Vol. 276, No. 5317, pp. 1401-1404,
1997.
K. Asakawa, T. Hiraoka, H. Hieda, M. Sakurai, Y. Kamata, and K.
Naito, “Nano-Patterning for Patterned Media using Block-Copolymer,” J. Photopolym. Sci. Technol., Vol. 15, No. 3, pp. 465-470,
2002.
K. W. Guarini, C. T. Black, Y. Zhang, I. V. Babich, E. M. Sikorski,
and L. M. Gignac, “Low voltage, scalable nanocrystal FLASH memory fabricated by templated self assembly,” International Electron
Devices Meetings, Technical Digest, pp. 541-544, 2003.

Executive Manager of Physical Science Laboratory, Group Leader of Nanodevice ResearchGroup and Nanostructure Technology ResearchGroup, Distinguished Technical Member, NTT
Basic Research Laboratories.
He received the B.S. and M.S. in physics andthe Ph.D. degree in engineering from Osaka University, Osaka, in 1984, 1986, and 1993, respectively. He joined NTT Basic Research Laboratories in 1986. He was a visiting research fellow at
Imperial College, University of London, UK,during 1995-1996. Since 1986 he has been
engaged in the study of compound semiconductor surfaces prepared by molecular beam epitaxy
mainly using electron diffraction and scanningtunneling microscopy. His current interests are
the mechanical and elastic properties of semiconductor low-dimensional structures. He is a member of JSAP and the Physical Society of Japan.

NTT Technical Review