#Jounol of PhotopolymerSclence qnd Technology
Volu me 16, Number2( 2003)163-164
O2003TAPJ

Gommunkation

Room TemperaturePhotochemicalFabricationof Silica GlassCoatings
using VacuumUltraviolet Excimer Lamps
Chihiro Kato, Satomi Tanaka, Yasuhiro Naganuma and Toyohiko Shindo*Kanagawa Industrial TechnoIogy Research I nstitute,
705-I, Shimo-imaizumi,Ebina, Kanagawa, Japan* Contamination Control Services,-3,529 Shimohtzawa,Sagamihara, Kanagawa, Japancoating
SiO2,photochemical,
Keywords: excimerlamp,VUV, polysilazane,

L. Introduction
Recently it becomes possible to fabricate silica
glass coatings onto various kinds of materials byheating coated polysilazane films ; (-SiHz-NH-)"
This technique attracts much interestsin[-3].
wide area of industry for making protective hardcoatings, electrical insulating layers, thermal orchemical resistive films, highly transparentor antiToreflection coatings, and gas barrier coatings.
produce high quality silica glass coatings from thepolysilazane precursor, heating processes above
600 C' are necessary to remove residual nitrogen
Lowering of theatoms or Si-OH impurities.
process temperature is necessary for fabricatinghigh quality silica glass coatings onto thermallyunstable substrates such as plastics orsemiconductivedevices.
In this paper, we demonstrate a room
temperature photochemical fabrication of silica
glass coatings by utilizing a vacuum ultraviolet(V[JV) light inadiation obtainable by recently
developed high power xenon excimer lamps.
The quality of the photochemically fabricatedcoatings are elucidated here by spectroscopicallyinvestigating their chemical structwes, ffid
comparedwith the thermally fabricated coatings.
2. Experimental
Polysilazane solutions, used as received from
Clariant Japan without further purification, werediluted with toluene, and spin-coatedonto Si (100)substrates(10 x l0 x 0.5 rnrn, both sidespolished).
The Si substratesare carefully wiped with ethanol,and then photolytically cleaned by the VUVReceived
Accepted

April 1, 2003
May 28, 2003

Spin-coating wasinadiation just before using.
performed at 1500 rpm for 120 s, yielding film
thicknesses- 500 nm after drying onto a hot plate
at 50 C' for 10 minutes.
A xenon excimer lamp (Quark Systems,QEX230SX, 172 nm, -8 mWcm2) was employed toirradiate VUV light on the sample. Irradiation
The larnp was placed
time was about I hour.
within a small stainless chamber together with thepolysilazane-coatedSi substrate, and then filledwith atmosphericpressureddry air at -5 l/min flow
The distance between the larnp and the Sirate.
substratewas kept about 2 - 3 mm.
A quartz tube muffle oven (Asahi Rika ARF50K) was used to thermally fabricating thecoatings. In this case,sampleswere kept heatedin air for about I hour.
An X-ray photoelectron spectrometer(Ulvac-PhiPHI-5500) was used to measure the X-ray
photoelecfron specfra ()(PS) with aluminum Kq, Xray source. An FT-IR spectrometer (ShimadzuFTIR-8200PC) was used to obtain infrared (IR)absorption spectra with wavenumber resolution of4 cm-I.
3. Results and discussion
3.1 XPS specfra
Figure I shows Si2p, Nls and Ols XPS spectraof thermally (a-f) or photochemically (g) fabricatedcoatings from polysilazane, respectively. )(PS
give
information
about
atomicspecûa
concentrations and chemical bonds at the surface(1 - 4 nm depth). As shown in the fig. l(a-f),chemical shifts toward higher binding energy \Mere163

l. Plntopolym.Sci.Techtnl.,Vol.16,No.2, 2003
observedfor the Si2p spectraas increasingprocesstemperaturesfrom "as depo" to 600 C', indicatingthat Si-N bonds in the heated polysilazanesurface
were dissociated and recombined with oxygen
In consistent withatoms to form Si-O bonds.
the Si2p shifts, intensities of the Nls or Ols
specha were decreasedor increasedwith process
The surface of thetemperatures, respectively.
thermally fabricated coatings at 600 C' werecompletely converted to SiO2 without any residual
nitrogen atoms.
As shown in the fig. 1(g), the surfaces ofphotochemically fabricated coatings are found tobe equivalent to that of the thermally fabricatedcoatings at 600 C', becauseno residual nitrogen
atom was detectedfor thesecoatings.

fabricated coatings across the depth is nearly equal
to the thermally fabricated coatings between 200 -300c'.

(rtE
7ct
Oo(tl€U)

3000

2000

1500

1000

s00/ cm-l
Wavenumber

Fig. 2. IR absorptionspecta of thermally (a-f) or
photochemically(g) fabricatedcoatings : (a) as dcpo,(b) 200C', (c) 300C', (d) 400C', (e) 500C', (f) 600C",(g) VUV irradiated.

((Ét{>rvtaÉ

106
100
N2396/ eVBinding
EnergyFig. l.
X-ray photoelectron
spectraof thermally(a-f)
or photochemically(g) fabricatedcoatings: (a) as depo,(b) 200C', (c) 300C', (d) 400C", (e) 500C', (0 600C',(g) VUV inadiated.
536

530

3.2 IR absorptionspectra
Figure 2 shows IR absorption spectra ofthermally (a-f) or photochemically (S) fabricatedIRcoatings from polysilazane, respectively.
givesaverage chemicalabsorption spectroscopySoinformation across the film depth.
complementary information can be extractablefrom the )(PS and IR spectraof the coatings. As
shown in the fig. z(a-f), N-H stretching bands at3370 cffi-r, Si-H shetchingbands at 2160 cmr, and
Si-N bands at 830 cm-l were decreased as'Whereas
increasing processing temperatures.
Si-O bands at 1060 and 450 cm-r were increased.
These spechal changes are reasonably explainablewith the structural change from (-SiH2-NH-)"(polysilazane) to SiO2 (silica glass) occurring allover the film.
As shown in the fig. 2(g), it was found that theaverage chemical structure of photochemically161

3.3 Discussion
From the XPS and IR
spectroscopic
investigationsof photochemically fabricated silica
glass coatings at room temperatures,there fbund adifference in quality between the surface nnd theFor thebulk state of the coatings.
process
photochemicallrom
conversion
polysilazaneto SiO2, it needs any kind of oxygen
supply from gas phase such as Oz molecule in dry
ar, Ol or O radicals produced by VUV photolysisof 02, becausepolysilazaneitself does not include
oxygen atoms in its molecular structure. Thus
that difference is explainable to the oxygen gas
barrier characteristicsof the photogeneratedsilica
glasslayer at the top of the silica glasscoating.
4. Conclusion
In this study, the 172 nm VUV photoirradiationfrom recently developed high pov/er xenon
excimer lamps is found to be useful to achieveroom temperature photochemical fabrication ofqvartz glasscoatings from polysilazane.
References
1. D. Seyferth et al., J. Am. Ceram. Soc., 66[1](1e83)
C13-Cr4.
2. Funayamaet al., J. Ceram. Soc. Jpn., 98 (1990)
104.
3. Suzuki et â1., Proc. Znd Japan International
SAMPE Symposium,216 (1991).