A reduction of the surface roughness, Ra, is required in various applications including electronic devic-es and / or optical devices. Although chemical-mechanical polishing (CMP) has been used to flatten the sur-faces, it is generally limited to reducing Ra to about 2 Å because the polishing pad roughness is as large as 10 m, and the polishing-particle diameters in the slurry are as large as 100 nm. We therefore developed a new polishing method, dressed-photon and phonon etching (DPP etching), that uses dressed photon based on an autonomous phonon-assisted process. DPP etching does not use any polishing pad, with which we obtained ultra-flat silica surface with angstrom-scale average roughness as small as Ra of 0.1 nm. Addi-tionally, we succeeded in reduction of the Ra for the three-dimensional structures.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3526

Ohtsu, M.

Yatsui, T.

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 2 No 1, 01PCSI09(3pp) (2013) 
 
 
2304-1862/2013/2(1)01PCSI09(3) 01PCSI09-1  2013 Sumy State University 
Dressed Photon-phonon Technology for Ultra Flat Surface 
 
T. Yatsui*, M. Ohtsu 
 
1School of Engineering, the University of Tokyo, 2-11-16 Yayoi, Bunkyo, 113-8656 Tokyo, Japan 
 
(Received 20 May 2013; published online 31 August 2013) 
 
A reduction of the surface roughness, Ra, is required in various applications including electronic devic-
es and / or optical devices. Although chemical-mechanical polishing (CMP) has been used to flatten the sur-
faces, it is generally limited to reducing Ra to about 2 Å because the polishing pad roughness is as large as 
10 m, and the polishing-particle diameters in the slurry are as large as 100 nm. We therefore developed a 
new polishing method, dressed-photon and phonon etching (DPP etching), that uses dressed photon based 
on an autonomous phonon-assisted process. DPP etching does not use any polishing pad, with which we 
obtained ultra-flat silica surface with angstrom-scale average roughness as small as Ra of 0.1 nm. Addi-
tionally, we succeeded in reduction of the Ra for the three-dimensional structures. 
 
Keywords: Dressed-photon method, Phonon etching method, Surface roughness. 
 
 PACS numbers: 81.16. – c, 81.16.Dn 
 
 
                                                          
* yatsui@ee.t.u-tokyo.ac.jp  
1. INTRODUCTION 
 
Ultra-flat substrate surfaces with sub-nanometer 
scale roughness are required for various applications, 
including optical components for the extreme ultravio-
let (UV) region and high-power lasers, and future opto-
electronics devices on a sub-100 nm scale. To obtain a 
flat surface, conventional methods have used chemical-
mechanical polishing (CMP) [1]. We have studied the 
application of the optical near-field to nanostructure 
fabrication using its properties of resolution beyond the 
diffraction limit and a novel nonadiabatic photochemi-
cal reaction. For chemical vapor deposition, we demon-
strated photodissociation with a light source, with a 
photon energy lower than the absorption band edge 
energy of the molecules. The optical near-field is a vir-
tual photon that can couple with an excited electron. In 
the coupled state, it is known as a dressed photon. Ad-
ditionally, it can be coupled with multiple-mode of pho-
nons, and thus, the quasi-particles of coupled state as 
dressed-photon-phonon (DPP). Thus, the energy of the 
DPP, is larger than the energy of a free photon due to 
coupling with and excited electron [2]. This DPP theory 
has been used to explain numerous experiments on 
topics such as photochemical vapour deposition [3], 
photolithography [4], and visible-light water splitting 
[5], as well as studies on photovoltaic devices [6] and 
energy up-conversion devices [7]. 
 
2. DPP ETCHING 
 
Chlorine gas was used as the etching gas source. A 
continuous wave (CW) laser (   532 nm) was used as 
the light source to dissociate the Cl2. Since its photon 
energy is lower than the absorption band edge energy 
of Cl2 (   400 nm [5]), this avoids conventional adia-
batic photo-etching. However, since the substrate sur-
face has nanometer-scale protrusions, depending on its 
roughness, a strong optical near-field can be generated 
at the edge of such a protrusion (Fig. 1a). Since the 
optical near-field has a steep spatial gradient, a higher 
molecular vibrational state can be excited in the Cl2, 
although the photon energy is lower than the absorp-
tion band energy of Cl2, which cannot be excited by a 
uniform optical far-field. As a result, Cl2 is selectively 
photodissociated and the activated Cl atoms etch away 
the protrusions on the substrate. Finally, the etching 
process automatically comes to a halt when the surface 
becames sufficiently flat so that the optical near-field 
disappears (Fig. 1b). 
 
 
 
Fig. 1 – Schematic of DPP etching 
 
We used silica substrates. The Cl2 pressure was 
100 Pa. Figures 2(a) and 2(b) show typical atomic force 
microscopy (AFM) images of a 10 m  10 m of the 
scanning area of the silica substrate before and after 
DPP etching, respectively. By comparing these images, 
the drastic decrease in surface roughness was realized. 
Additonally, the cross-sectional profiles revealed this 
technique can reduced the pits, as well as bumps [8]. 
DPP etching does not require the polishing pad, it 
can be applicable to the three dimensional structures 
(Figs. 3(a) and 3(b)). We performed DPP etching on the 
grating structures of the soda lime glass. The compari-
son between Figs. 3(a) and 3(b) of before and after DPP 
etching confirmed that the DPP etching can etch the 
side wall of the three dimensional structures [9]. 
 
 T. YATSUI, M. OHTSU PROC. NAP 2, 01PCSI09 (2013) 
 
 
01PCSI09-2 
 
 
Fig. 2 – AFM images: (a) before and (b) after DPP etching. (c) Cross-sectional profiles along the dashed white lines in (a), and (b) 
 
 
 
Fig. 3 – (a and b) Schematic of DPP etching on three dimensional structure. AFM images: (c) before and (d) after DPP etching 
 
3. CONCLUSION 
 
We reviewed recent developement of DPP etching. 
DPP etching is based on photo-chemical reaction, it can 
be applicable to other materials, including semiconduc-
tor, metal, plastic, and so on. 
 
AKNOWLEDGEMENTS 
 
A part of this work was supported by the “Develop-
ment of Next-generation High-performance Technology 
for Photovoltaic Power Generation System” Program, 
NEDO, Japan. 
 
 
 DRESSED PHOTON-PHOTON TECHNOLOGY FOR ULTRA FLAT SURFACE PROC. NAP 2, 01PCSI09 (2013) 
 
 
01PCSI09-3 
REFERENCES 
 
1. L.M. Cook, J. Non-Crystalline Solids 120, 152 (1990). 
2. A. Sato, Y. Tanaka, F. Minami, K. Kobayashi, J. Lumin. 
129, 1718 (2009). 
3. T. Kawazoe, K. Kobayashi, S. Takubo, M. Ohtsu J. Chem. 
Phys. 122, 024715 (2005). 
4. H. Yonemitsu, T. Kawazoe, K. Kobayashi, M. Ohtsu. J 
Lumin. 122-123, 230 (2007). 
5. T.H.H. Le, K. Mawatari, Y. Pihosh, T. Kawazoe, T. Yatsui, 
M. Ohtsu, T. Kitamori, Appl. Phys. Lett. 99, 213105 (2011). 
6. S. Yukutake, T. Kawazoe, T. Yatsui, W. Nomura, 
K. Kitamura, M. Ohtsu. Appl. Phys. B: Lasers O. 99, 415 
(2010). 
7. T. Kawazoe, H. Fujiwara, K. Kobayashi, M. Ohtsu, Appl. 
Phys. B: Lasers O. 15, 1380 (2009). 
8. T. Yatsui, K. Hirata, W. Nomura, Y. Tabata, M. Ohtsu, 
Appl. Phys. B: Lasers O. 93, 55 (2008) 
9. T. Yatsui, K. Hirata, Y. Tabata, Y. Miyake, Y. Akita, 
M. Yoshimoto, W. Nomura, T. Kawazoe, M. Naruse, 
M. Ohtsu, Appl. Phys. B: Lasers O. 103, 527 (2011). 
 


English

Dressed Photon-phonon Technology for Ultra Flat Surface

A reduction of the surface roughness, Ra, is required in various applications including electronic devic-es and / or optical devices. Although chemical-mechanical polishing (CMP) has been used to flatten the sur-faces, it is generally limited to reducing Ra to about 2 Å because the polishing pad roughness is as large as 10 m, and the polishing-particle diameters in the slurry are as large as 100 nm. We therefore developed a new polishing method, dressed-photon and phonon etching (DPP etching), that uses dressed photon based on an autonomous phonon-assisted process. DPP etching does not use any polishing pad, with which we obtained ultra-flat silica surface with angstrom-scale average roughness as small as Ra of 0.1 nm. Addi-tionally, we succeeded in reduction of the Ra for the three-dimensional structures

T. Yatsui

M. Ohtsu

CiteSeerX

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 2 No 1, 01PCSI09(3pp) (2013)   2304-1862/2013/2(1)01PCSI09(3) 01PCSI09-1  2013 Sumy State University Dressed Photon-phonon Technology for Ultra Flat Surface  T. Yatsui*, M. Ohtsu  1School of Engineering, the University of Tokyo, 2-11-16 Yayoi, Bunkyo, 113-8656 Tokyo, Japan  (Received 20 May 2013; published online 31 August 2013)  A reduction of the surface roughness, Ra, is required in various applications including electronic devic-es and / or optical devices. Although chemical-mechanical polishing (CMP) has been used to flatten the sur-faces, it is generally limited to reducing Ra to about 2 Å because the polishing pad roughness is as large as 10 m, and the polishing-particle diameters in the slurry are as large as 100 nm. We therefore developed a new polishing method, dressed-photon and phonon etching (DPP etching), that uses dressed photon based on an autonomous phonon-assisted process. DPP etching does not use any polishing pad, with which we obtained ultra-flat silica surface with angstrom-scale average roughness as small as Ra of 0.1 nm. Addi-tionally, we succeeded in reduction of the Ra for the three-dimensional structures.  Keywords: Dressed-photon method, Phonon etching method, Surface roughness.   PACS numbers: 81.16. – c, 81.16.Dn                                                             * yatsui@ee.t.u-tokyo.ac.jp  1. INTRODUCTION  Ultra-flat substrate surfaces with sub-nanometer scale roughness are required for various applications, including optical components for the extreme ultravio-let (UV) region and high-power lasers, and future opto-electronics devices on a sub-100 nm scale. To obtain a flat surface, conventional methods have used chemical-mechanical polishing (CMP) [1]. We have studied the application of the optical near-field to nanostructure fabrication using its properties of resolution beyond the diffraction limit and a novel nonadiabatic photochemi-cal reaction. For chemical vapor deposition, we demon-strated photodissociation with a light source, with a photon energy lower than the absorption band edge energy of the molecules. The optical near-field is a vir-tual photon that can couple with an excited electron. In the coupled state, it is known as a dressed photon. Ad-ditionally, it can be coupled with multiple-mode of pho-nons, and thus, the quasi-particles of coupled state as dressed-photon-phonon (DPP). Thus, the energy of the DPP, is larger than the energy of a free photon due to coupling with and excited electron [2]. This DPP theory has been used to explain numerous experiments on topics such as photochemical vapour deposition [3], photolithography [4], and visible-light water splitting [5], as well as studies on photovoltaic devices [6] and energy up-conversion devices [7].  2. DPP ETCHING  Chlorine gas was used as the etching gas source. A continuous wave (CW) laser (   532 nm) was used as the light source to dissociate the Cl2. Since its photon energy is lower than the absorption band edge energy of Cl2 (   400 nm [5]), this avoids conventional adia-batic photo-etching. However, since the substrate sur-face has nanometer-scale protrusions, depending on its roughness, a strong optical near-field can be generated at the edge of such a protrusion (Fig. 1a). Since the optical near-field has a steep spatial gradient, a higher molecular vibrational state can be excited in the Cl2, although the photon energy is lower than the absorp-tion band energy of Cl2, which cannot be excited by a uniform optical far-field. As a result, Cl2 is selectively photodissociated and the activated Cl atoms etch away the protrusions on the substrate. Finally, the etching process automatically comes to a halt when the surface becames sufficiently flat so that the optical near-field disappears (Fig. 1b).    Fig. 1 – Schematic of DPP etching  We used silica substrates. The Cl2 pressure was 100 Pa. Figures 2(a) and 2(b) show typical atomic force microscopy (AFM) images of a 10 m  10 m of the scanning area of the silica substrate before and after DPP etching, respectively. By comparing these images, the drastic decrease in surface roughness was realized. Additonally, the cross-sectional profiles revealed this technique can reduced the pits, as well as bumps [8]. DPP etching does not require the polishing pad, it can be applicable to the three dimensional structures (Figs. 3(a) and 3(b)). We performed DPP etching on the grating structures of the soda lime glass. The compari-son between Figs. 3(a) and 3(b) of before and after DPP etching confirmed that the DPP etching can etch the side wall of the three dimensional structures [9].   T. YATSUI, M. OHTSU PROC. NAP 2, 01PCSI09 (2013)   01PCSI09-2   Fig. 2 – AFM images: (a) before and (b) after DPP etching. (c) Cross-sectional profiles along the dashed white lines in (a), and (b)    Fig. 3 – (a and b) Schematic of DPP etching on three dimensional structure. AFM images: (c) before and (d) after DPP etching  3. CONCLUSION  We reviewed recent developement of DPP etching. DPP etching is based on photo-chemical reaction, it can be applicable to other materials, including semiconduc-tor, metal, plastic, and so on.  AKNOWLEDGEMENTS  A part of this work was supported by the “Develop-ment of Next-generation High-performance Technology for Photovoltaic Power Generation System” Program, NEDO, Japan.    DRESSED PHOTON-PHOTON TECHNOLOGY FOR ULTRA FLAT SURFACE PROC. NAP 2, 01PCSI09 (2013)   01PCSI09-3 REFERENCES  1. L.M. Cook, J. Non-Crystalline Solids 120, 152 (1990). 2. A. Sato, Y. Tanaka, F. Minami, K. Kobayashi, J. Lumin. 129, 1718 (2009). 3. T. Kawazoe, K. Kobayashi, S. Takubo, M. Ohtsu J. Chem. Phys. 122, 024715 (2005). 4. H. Yonemitsu, T. Kawazoe, K. Kobayashi, M. Ohtsu. J Lumin. 122-123, 230 (2007). 5. T.H.H. Le, K. Mawatari, Y. Pihosh, T. Kawazoe, T. Yatsui, M. Ohtsu, T. Kitamori, Appl. Phys. Lett. 99, 213105 (2011). 6. S. Yukutake, T. Kawazoe, T. Yatsui, W. Nomura, K. Kitamura, M. Ohtsu. Appl. Phys. B: Lasers O. 99, 415 (2010). 7. T. Kawazoe, H. Fujiwara, K. Kobayashi, M. Ohtsu, Appl. Phys. B: Lasers O. 15, 1380 (2009). 8. T. Yatsui, K. Hirata, W. Nomura, Y. Tabata, M. Ohtsu, Appl. Phys. B: Lasers O. 93, 55 (2008) 9. T. Yatsui, K. Hirata, Y. Tabata, Y. Miyake, Y. Akita, M. Yoshimoto, W. Nomura, T. Kawazoe, M. Naruse, M. Ohtsu, Appl. Phys. B: Lasers O. 103, 527 (2011).  

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Dressed Photon-phonon Technology for Ultra Flat Surface

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