Laser induced implanted oxide (Ll2Ox) and polycrystalline silicon film
simultaneously fabricated by excimer laser irradiation
Cheol-Min Park, Byung-Hyuk Min, Juhn-Suk Yoo, Jae-Hong Jun, Hong-Seok Choi,
and Min-Koo Hana)
School of Electrical Engineering, Seoul National University, Seoul, Korea
͑Received 23 September 1996; accepted for publication 15 November 1996͒
A method to form the gate oxide and recrystallize the polycrystalline silicon ͑poly-Si͒ active layer
simultaneously is proposed. During the irradiation of excimer laser, the poly-Si film is recrystallized
while the oxygen ion impurities injected into the amorphous silicon (a-Si͒ film are activated by laser
energy and react with silicon atoms to form SiO2. Our experimental results show that a high quality
oxide and a poly-Si film with fine grain have been fabricated successfully by the proposed method.
High quality interface between oxide and poly-Si films has also been obtained. © 1997 American
Institute of Physics. ͓S0003-6951͑97͒03703-0͔
The polycrystalline silicon thin film transistors ͑poly-Si
TFTs͒ are widely used for active matrix liquid crystal dis-
plays ͑AMLCDs͒. The characteristics of poly-Si TFTs are
determined by not only the quality of gate insulator but also
polycrystalline silicon ͑poly-Si͒ active layer.1,2 Recrystalliza-
tion of amorphous silicon (a-Si͒, which is usually deposited
by either plasma-enhanced chemical-vapor deposition
͑PECVD͒ or low-pressure chemical-vapor deposition
͑LPCVD͒, is a critical factor to enhance the performance of
poly-Si, TFTs.3 The excimer laser-induced recrystallization
is a promising tool for fabricating poly-Si TFTs on low-cost
glass substrates.4 It is well known that the surface roughness
of poly-Si layer recrystallized by excimer laser increases
with the energy density of excimer laser. The CVD, such as
PECVD or atmospheric pressure chemical vapor deposition
͑APCVD͒, oxides are usually employed to fabricate gate in-
sulators in low temperature processed poly-Si TFTs. The ox-
ides for poly-Si TFTs are required to exhibit low leakage
current, high dielectric strength, and good interface with the
poly-Si active layers.
obtained by the proposed fabrication method.
The process sequences of the proposed method are as
follows. The a-Si film of 3000 Å thickness was deposited on
the substrate by LPCVD at 550 °C. A dose of 5
ϫ1017 cmϪ2 oxygen ions at 10 KeV were implanted into
a-Si layer. The excimer laser irradiation was carried out at an
energy density from 254 to 371 mJ/cm2. The energy of the
laser is absorbed in the oxygen-rich a-Si film, and the ab-
sorbed thermal energy becomes a heat source for the oxygen
impurities to react with the silicon atoms. As a result of
excimer laser irradiation, structure of oxide-on-
polycrystalline silicon film was formed at the same time. We
entitle the oxide fabricated by proposed method as laser in-
duced implanted oxide (LI2Ox). It should be noted that, al-
though we employed relatively high temperature process for
our convenience such as LPCVD 550 °C, the deposition of
a-Si layer may be altered to PECVD which can be processed
below 350 °C with dehydrogenation process in order to get a
similar material property to LPCVD a-Si layer in hydrogen
content.
It is reported that the field effect mobility of TFTs is
affected by the roughness of the gate insulator.5 In most low
temperature processed poly-Si TFTs, the gate oxide is depos-
ited after recrystallization of poly-Si active layer so that in-
terface between gate insulator and active layer may be easily
contaminated and the performance of poly-Si TFTs is de-
graded. The poly-Si active layer which has smooth surface
roughness and good electrical characteristics is required. Be-
sides the quality of poly-Si active layer, a high quality
SiO2 which has good interface with the poly-Si active layer
is needed to improve the performance of poly-Si TFTs.6
We propose a new method to form the gate oxide and to
recrystallize the poly-Si active layer simultaneously by irra-
diation of the XeCl excimer laser on an oxygen implanted
amorphous silicon(a-Si͒ thin film. By the thermal energy of
the excimer laser, the poly-Si film is recrystallized, while the
oxygen ion impurities injected into the a-Si film react with
the silicon atoms to form SiO2.
The Auger electron spectroscope ͑AES͒ analyzed atomic
concentration of the oxygen implanted a-Si film before and
after the laser irradiation is shown in Fig. 1. In the sample,
which is not irradiated by excimer laser, the oxygen concen-
tration peak is observed at depth about 250 Å with a Gauss-
ian distribution. The constant concentration up to about
500 Å, which implies that stoichiometry of SiO2 is well
matched, is observed in excimer laser annealed sample.
Those data show that oxygen ions have reacted with the sili-
con atoms to form SiO2 by the laser energy and a sharp
oxide/poly-Si interface is obtained.
The cross-sectional TEM image of the oxide
(LI2Ox)/poly-Si structures fabricated by a proposed method
is shown in Fig. 2. The samples in Fig. 2 were irradiated by
three shots with the energy density of 371 mJ/cm2. As shown
in Fig. 2, the grains of poly-Si have not any internal defects
such as micro twins. The fully recrystallized poly-Si from
the bottom poly-Si/substrate interface to top interface with
oxide (LI2Ox) layer is formed by proposed method. The
sharp and clear interface between poly-Si layer and oxide
(LI2Ox) is obtained as shown in Fig. 2.
Our experimental results show that a high quality oxide,
a poly-Si film with fine grain, and a smooth and clear inter-
-face between oxide and poly-Si film have been successfully
The roughness of the interface between poly-Si and ox-
ide measured by atomic force microscope ͑AFM͒ are shown
a͒
Electronic mail: mkh@eesrc-09.snu.ac.kr
372 Appl. Phys. Lett. 70 (3), 20 January 1997 0003-6951/97/70(3)/372/3/$10.00 © 1997 American Institute of Physics
137.189.170.231 On: Sun, 21 Dec 2014 06:25:04
Park, Cheol-Min
