Simultaneous Fabrication of Insulator and Contact Holes by Excimer Laser
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Growthing Mechanism of SiO2
NF3 gas has been widely used as etchant for Si. As illustrated in Fig. 1, NF3 gas has a strong absorption band in the vicinity of the wavelength of ArF laser light (193 nm); NF3 gas can be easily decomposed by ArF laser, since the bonding energy of N-F (72 kcal/mol) is smaller than the photon energy of ArF laser light (147 kcal). 100
r-F:472Kcal/
Fig. I UV Transmittance of Gaseous NF [8]
550
SNF3
200Torr
0i
4 00
30 0
200
5 00
WAVELENGTH (nm) G.L. Loper et al. [1] reported a photo-decomposition process given in the following equation: NF3
And,
T.
-
)
Ogura
of NF3 as
NF3-n + nF
et
al.
[2]
have
made
observation
by
the
Mat. Res. Soc. Symp. Proc. Vol. 236. 11992 Materials Research Society
XPS
(X-ray
10
photoelectron spectroscopy) analysis as follows: A fluorine layer with the thickness of approximate 10 X (SiFn:n=l-4) was adsorbed on the surface of the substrate, by irradiating a Si substrate with ArF laser beam in an atmosphere of NF3 ; with the laser irradiation repeated, n increased, and the etching rate of Si subsequently improved. This phenomenon occurs even if the ArF laser beam is not irradiated on a Si surface directly. Therefore, we suggest a new method which SiFn is oxidized to produce Si02 by introducing 02 gas into this reaction system. When ArF laser beam was irradiated the NF3 and 02 mixed gases, N02 and F were produced as formulated below.
Ji
NF3 + 02
N02 + 3F
This F radical etches the surface of Si wafer, producing SiFn; the SiFn chemically reacts with the N02 and fabricates a Si02 film on the substrate as well as NO and F gases as given in the next formula. SiFn + 2N02
Si02 + 2NO + nF
-
As shown in the above equations, this reaction suggests that the SiFn of the surface is oxidized and turned into Si02 film. In order to confirm this reaction mechanism, accordingly, the ultraviolet (UV) and infrared (IR) spectra were observed by the measuring devices as displayed in Fig. 2. Fig. 3 and 4 reveal the results of the experiment under the following conditions: NF3 :02 = 4:1; the total gas pressure, 100 torr; the ArF laser fluence, 30mJ/cm2 ; pulse repetition, 10 pps. The spectra were measured two times: immediately after 5000 shots of the laser irradiation, and after leaving it for 10 minutes. As for the UV spectra in Fig. 3, when the Si substrate was not set in the reaction cell, it was confirmed that NFO as an intermediate product was produced by photo-chemical reactions of NF3 and 02 immediately after the laser irradiation, and has been changed to N02 after being left for 10 minutes.
o sh1t
mirror
•rF Excimer Laser
5000 shots
-
a~'
NO,
6,_CNFO
sctro
sctro6 photometer
SRspectroafter notoeter
M
Si absence
tSmin-
=
-C
280
mix e ga se s
O0.
, 10 P
3
A. A,F :
SOnJ/týt
15000, 350
300
WAVELENGTH
N3+02
IRLam p
I
380
[nm]
UVLamp_0_ LWLamp
_5sa_ _t ..
1I00
Fig. 2 Measurement System of UV and IR Spectra with and
/ shots 5000
after "I-.
• .•.
. .
.
..
'4NO,
without Laser Irradiation in an atmosphere of NF3, 02
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