ISSN 1063-7397, Russian Microelectronics, 2016, Vol. 45, No. 6, pp. 410–413. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © V.I. Lebedev, V.E. Kotomina, S.V. Zelentsov, 2016, published in Mikroelektronika, 2016, Vol. 45, No. 6, pp. 448–451.
Ways of Increasing the Service Life of Positive Photoresists
V. I. Lebedev, V. E. Kotomina, and S. V. Zelentsov
Lobachevsky State University, pr. Gagarina 23, GSP-20, Nizhny Novgorod, 603950 Russia
Received December 16, 2015
Abstract—The change in the functional properties of positive photoresists during their storage is a serious
issue in photolithography. The recovery of the functional properties of photoresists, and especially, the qual-
ity of the edge of the formed elements and changes in their sizes compared to the sizes in the photostencil, is
possible by the introduction of additives into the composition of positive photoresists which form hydrogen
bonds with the novolak resins constituting them prior to their usage. Experimental verification of the correla-
tion between the density of the hydrogen bonds and the photoresist resolution has been obtained.
Photolithography holds a central position in mod-
ern microelectronics technology . It is photolithog-
raphy that most often determines the possibility of
obtaining various semiconductor devices, especially
when the sizes of the device’s elements and the thick-
nesses of their active layers are close to the critical val-
ues, i.e., the utmost values for the modern level of
development of photolithography.
It is well known that the functional characteristics
of positive photoresists, which serve as the main tool
for forming photoresist masks, deteriorate during stor-
age ; in particular, the edge of a photoresist mask
becomes more uneven. It appears immensely import-
ant to minimize the influence of this feature of posi-
tive photoresists . To decrease the aging rate,
hydroquinone , which is an inhibitor of radical oxi-
dation, is added to the photoresist composition .
One might assume that hydroquinone acts as an agent
that reduces the contribution of the reactions of
novolak resin’s radical oxidation by molecular oxygen
during the process of positive photoresist aging .
There are several viewpoints on the mechanism of
obtaining the resist mask in positive photoresists. We
consider the dissolution of a novolak polymer is inhib-
ited due to the formation of intermolecular hydrogen
bonds between novolak macromolecules and a light-
sensitive ortho-naphthoquinone derivative  to be
one of the most adequate suppositions. Such bonds
hamper the penetration of the dissolvent molecules
deep into the polymer , which leads to the loss of its
dissolubility. The UV light action results in disturbance
of the system of the intermolecular hydrogen bonds and
is one of the reasons for the emergence of the dissolubil-
ity of the exposed areas of the photoresist layer.
In work  it was found that the use of meta-
methyl-substituted (especially 3,5-dimethyl-substituted)
phenols is an effective way of increasing the propor-
tion of intra- and intermolecular hydrogen bonds;
moreover, this proportion is controlled by the chemi-
cal nature of the phenol component of the novolak
resin. There is an optimal proportion that allows
obtaining photoresists with the best characteristics. It
was shown that the formation and strength of the
hydrogen bonds between the OH groups of the
novolak resin and ortho-naphthoquinone diazide
molecules play a decisive role in the loss of photoresist
dissolubility in the aqueous solutions of alkalies.
The aim of the present work is to investigate the
influence that the additives of substances forming
hydrogen bonds have on the increase of the service life
of positive photoresists.
As the additives recovering the photoresist proper-
ties, 1,3-dinitrobenzylidene urea and 6-azauracil were
used. These substances were dissolved immediately in
the photoresist (10% from the ortho-naphthoquinone
diazide derivative mass).
An aged (with a storage time longer than the work-
ing life, several years) photoresist of grade FP-383
(TU 2378-005-29135749-2007) was applied. The
image was developed in it by dipping in a 0.26 N
tetramethyl ammonium hydroxide aqueous solution.
A photoresist film was applied by centrifugation on
an SM-180-BT SAWATEC centrifuge at 3500 rpm for
30 s. The substrates with the applied photoresist layer
were dried in a convection-type drying cabinet for
40 min at 80°C. The photoresist was exposed on an
EM-5026M1 system. As a photostencil, a test pattern