Resistless Etching of SiO 2 by Two Color Excimer Lasers
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RESISTLESS ETCHING OF Si0 2 BY TWO COLOR EXCIMER LASERS. T.Obara* and M.Murahara** *Graduate Student of Tokai Univ., Faculty of Eng. "**Faculty of Eng., Tokai Univ., 1117, Kitakaname, Hiratuka, Kanagawa 259-12, Japan ABSTRACT
Resistless etching of thermal oxide silicon filmes were demonstrated by ArF & KrF excimer lasers, and CC12 F2 gases. CC12F 2 was decomposed by ArF excimer laser light, and CF2 radicals were produced. These radicals, which have absorption band nearby 250nm, were vary stable. Then the circuit pattarned KrF laser light was irradiated on the Si0 2 in an atomsphere of CF2 radicals. As thse result, the etching pattern of 2 u m width was performed. Introduction Use of resists is indispensable to etch Si02 of insulation film in the semiconductor process. The studies on resistless etching of Si0 2 by synchrotron radiation (SR) or vacuumed ultraviolet light have been reported recently [1.2]; however, to be exact, they are not essential etching due to the decomposition of liberated Si. Here, we tried an resistless selective pattern etching of Si0 2 using ArF and KrF excimer lasers. This etching mechanism is to irradiate CC12F 2 gas with ArF excimer laser (193 nm) in order to produce very stable CF2 radicals, and then to excite the CF2 radicals in the vicinity of the Si0 2 substrate with KrF excimer laser (249 nm) so that the activated CF2 radicals pull out 0 atoms from Si0 2 . It results in etching the selective area irradiated with the KrF excimer laser. With this method, we achieved a resistless selective. pattern etching of Si0 2 with the line and space of 2 um and the depth 2000 A. Photo-decomposition of Etchant Gas CC12F 2 gas has an laser (193 nm), and its ArF laser (147 kcal). CF2 with ArF excimer equation [3,4,5]:
absorption band at the wavelength of ArF excimer bonding energy is lower than the photon energy of Accordingly, CC1 2 F2 photo decomposes into C12 and laser irradiation as expressed in the following
CCI 2 F2 + hp (193 nm) --- > CF2 * + C12 (1) In order to clarify this photo decomposition mechanism, the UV absorption and luminescence spectra of CCl 2 F2 gas irradiating with ArF and KrF lasers were observed by the device shown in Fig. 1.
A.
Photo Reaction of Etchant Gas with ArF Laser Irradiation
Fig. 2(a) shows that CC1 2 F2 has very strong absorption band below 230 rum[6]. When this gas was irradiated with ArF laser light, the absorption of 2CF 2 0 + Si (2) Si + 2C1 2 --- > SiCl4
(3)
Here, if the CF2 * excited by KrF laser were extremely short lived, its reaction would occur only on the irradiated part of the substrate surface. Namely, a selective photo etching would be possible in the presence of Si0 2. If possible, a material without absorption band at the wavelength of irradiation light could be etched. Moreover, no photoresist would be required.
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perpendicular irradiation I
KrF(249nm) vapor
irradiationI
phase
(1para7lel (147 Kcal)
Fig.4
reaction
I
(114 Kcal)
excitation of CF2 radicals
Can,F---CF+ a,
I Si02
Flow chart of the photoetching mechanism for Si0 2 e
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