Macromolecules, Vol. 37, No. 22, 2004
Photosensitive Semi-Alicyclic Poly(benzoxazole)s 8257
was purified by recrystallization from mixture of toluene and
Sch em e 1. Syn th esis of
N-Ad a m a n tyl-2-h yd r oxyben za m id e Der iva tive a s a
P AHA Mod el
THF. The yield was 3.1 g (64%). Sublimation point: 348-350
1
°C. H NMR (DMSO-d6, δ, ppm): 10.32 (s, 2H, OH), 8.39 (s,
2H, NHCO), 8.11 (s, 2H, Ar), 6.87 (dd, J ) 12.9, 8.4 Hz, 4H,
Ar), 2.01 (s, 6H, CH), 1.88 (s, 12H, COC(CH2)3), 1.69 (s, 12H,
CHCH2CH). Elemental analysis: Calcd for C37H40F6N2O4: C,
64.34; H, 5.84; N, 4.06; Found: C, 64.62; H, 6.07; N, 4.07.
Syn th esis of P AHA fr om 6F AP a n d ADC. To a solution
of lithium chloride (0.0933 g, 2.20 mmol) and 6FAP (0.366 g,
1.00 mmol) in 1.5 mL of NMP under nitrogen was added ADC
(0.261 g, 1.00 mmol) at once. And the mixture was stirred at
0 °C for 12 h under a nitrogen atmosphere. The resulting
solution was poured into water. The precipitated polymer was
filtered off and washed with water several times, followed by
drying in vacuo. The yield was almost quantitative (>98%).
1H NMR (DMSO-d6, δ, ppm): 10.28 (s, 2H, OH), 8.53 (s, 2H,
NHCO), 8.08 (s, 2H, Ar), 6.94 (d, J ) 8.7 Hz, 2H, Ar), 6.87 (d,
J ) 8.7 Hz, 2H, Ar), 2.19-1.67 (m, 14H, CH2 or CH). IR (KBr,
ν, cm-1): 3424 (OH), 2915, 2857 (CH2, CH), 1654 (CdO), 1253
(CF3). Elemental analysis: Calcd for C27H24F6N2O4‚1.13H2O:
C, 56.41; H, 4.61; N, 4.87; Found: C, 56.98; H, 4.50; N, 4.30.
Sch em e 2. Syn th esis of P AHA a n d P ABO
Dissolu tion Ra te. TVEB and DIAS were added to a PAHA
solution in cyclohexanone to construct a photosensitive poly-
mer. The polymer film spin-cast from the solution (15 wt %
concentration) on a silicon wafer was prebaked at 90-140 °C
for 5 min and then exposed to a filtered super-high-pressure
mercury lamp at 365 nm (i-line), followed by postexposure
baking at the same temperature for 5 min. The exposed film
was developed with 2.38 wt % of tetramethylammonium
hydroxide (TMAHaq) solution at 25 °C to determine a dissolu-
tion rate (Å/s).
P h otosen sitivity. A 2.0 µm thick photosensitive polymer
film on a silicon wafer was exposed to i-line and then developed
with 2.38 wt % of TMAHaq at 25 °C for 60 s followed by rinsing
with water. A characteristic curve was obtained by plotting a
normalized film thickness as a function of exposure dose (mJ /
cm2).
the corresponding o-hydroxybenzamide increases in the
area of i-line because of decreasing conjugation between
2-hydroxybenzamide and the N-substituent group. Ada-
mantane is known as a robust alicyclic compound with
relatively high thermal resistance. Thus, an adamantyl
group was selected as an N-substituent (Scheme 1). The
UV-vis spectra of N-phenyl-2-hydroxybenzamide and
N-adamantyl-2-hydroxybenzamide derivatives shown in
Figure 1 clearly indicate that the N-adamantyl group
is very effective to improve the transparency of N-
substituent-o-hydroxybenzamide.
Mea su r em en ts. The infrared spectroscopy (IR) was taken
1
with Horiba FT-210 spectrophotometer. The H nuclear mag-
netic resonance (NMR) spectrum was recorded on a Bruker
GPX300 (300 MHz) spectrometer. Thermogravimetric (TG) and
differential scanning calorimetry (DSC) were performed on a
Seiko TG/DTA 6300 and DSC 6200, respectively, at a heating
rate 5 °C/min under a nitrogen stream. Ultraviolet-visible
spectroscopy (UV-vis) was performed on
a J asco V-650
spectrophotometer. Number- and weight-average molecular
weights (Mn and Mw) were determined by gel permeation
chromatography (GPC) with a Tosoh HLC-8120 GPC system
Syn th eses a n d Ch a r a cter iza tion s of P AHA a n d
P ABO. Polycondensation of 6FAP with ADC was car-
ried out in the presence of lithium chloride in NMP at
0 °C for 12 h (Scheme 2). Polycondensation proceeded
smoothly to give a desired PAHA with a weight-average
molecular weight of 24 100 and a polydispersity of 3.2.
The structure of the polymer was identified as the
equipped with polystyrene gel columns (TSK GELs; GMHHR
M, and GMHHR-L) at 40 °C in DMF (containing 0.01 M LiBr)
at a flow rate of 1.0 mL/min, calibrated with polystyrene
standards. The film thickness on silicon wafers was measured
by a Veeco Instrument Dektak3 surface profiler. The field
emission scanning electron microscope (SEM) was taken with
a Hitachi S-800 scanning electron microscope with 15 kV
accelerating voltage for imaging. Refractive indices of PABO
-
1
corresponding PAHA by H NMR and IR spectroscopy.
films formed on quartz substrates were measured at
a
wavelength of 1.320 µm at room temperature with a Metricon
model PC-2000 prism coupler. Using linearly polarized laser
with parallel (TE: transverse electric) and perpendicular
(TM: transverse magnetic) polarization to the film plane, the
in-plane (nTE) and out-of-plane (nTM) refractive indices and the
film thickness of the samples were determined. The dielectric
constant (ꢀ) at 1.0 MHz frequency was calculated from the
equation as follows: ꢀ ) 1.10 nAV2, where nAV is average
refractive index (i.e., nAV ) (2nTE + nTM)/3).
Resu lts a n d Discu ssion
Since i-line is used as exposure source in PSPBOs,
the transparency of PAHA in the region of i-line is
important to improve the sensitivity. When N-substitu-
ent groups of o-hydroxybenzamide are replaced from
aryl derivatives to alicyclic ones, the transparency of
F igu r e 1. Transparencies of (a) alicyclic compound (adaman-
tyl) and (b) aromatic compound (phenyl) as N-substituent
groups of o-hydroxybenzamide in THF at 1.0 µM. Inset shows
chemical structures of (a) and (b).