The image formation by photo – reaction of Ag or Al with glassy chalcogenides: mechanisms and application
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TSIULYANU , Dumitru. The image formation by photo – reaction of Ag or Al with glassy chalcogenides: mechanisms and application. In: Materials Science and Condensed Matter Physics. Editia a 8-a, 12-16 septembrie 2016, Chişinău. Chişinău: Institutul de Fizică Aplicată, 2016, p. 365. ISBN 978-9975-9787-1-2.
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Materials Science and Condensed Matter Physics
Editia a 8-a, 2016
Conferința "International Conference on Materials Science and Condensed Matter Physics"
8-th Edition, Chişinău, Moldova, 12-16 septembrie 2016

The image formation by photo – reaction of Ag or Al with glassy chalcogenides: mechanisms and application

Pag. 365-365

Tsiulyanu Dumitru
Technical University of Moldova
Disponibil în IBN: 7 august 2019


The mechanisms and application of photo-dissolution (PD) of silver in chalcogenide glassy semiconductors  (ChGS) , as well as of   electrically controlled photoreaction (ECPR) of aluminum with  ChGS are extensive reviewed  and discussed. It is shown that one of the main interesting application of these phenomena is due to possibility of their use for image formation, followed by appearance of differential chemical etching rate between exposed and unexposed portions of either ChGS - Ag or Al - ChG – metal wafers.  This property is utilized to form the surface relief, which results in a wide application of Ag (Al) – ChGS structures in the microelectronic lithography as high-resolution inorganic photoresists. The advantages of these photoresists are: the possibility to obtain layers with high homogeneity and low concentration of defects on a large area, the possibility of wet and dry processing, the high absorption coefficient of light, which enhance the accuracy of simultaneous or successive etching. It is significant that the spectral range of photosensitivity is very wide and includes UV, visible and IR regions. The sensitivity of ChGS to electron or ion beams has also been discovered and possibility of their application  in sub-micron lithography was demonstrated. Along with traditional use of Ag - ChGS - Ag wafers in optics and optoelectronics their modern application in Programmable Metallization Cell (PMC) technologies is considered. Although the mechanisms of PD and ECPR effects are still not completely understood, it is clear that they are rather different.  One of the aims of this presentation is to give a brief consideration of mechanisms of the mentioned effects. Based on the experimental results concerning the kinetics of Ag photo -dissolution in glassy As2S3 [1] and As-S-Ge alloys [ 2 ], the mechanism and regularities of the phenomenon in question is explained in terms of Elliott’s model [3], which asserts a simultaneous ionic and electronic charge transport controlled by chalcogenide properties, illumination and temperature. This mechanism comprises at least three processes: 1)  A solid state chemical reaction between Ag and the chalcogenide, which results in formation of a superionic conductor with a high (10-5 – 10-3 Ohm-1cm-1) ionic conductivity: 2) Photo-creation of free holes at the doped / undoped  chalcogenide interface, followed by their drift through superionic chalcogenide to Ag layer and production of ions by reaction    Ago + h → Ag+: 3) Motion of Ag+ ions in opposite direction i.e. towards the boundary doped / undoped  chalcogenide through the doped (superionic region). As far as the   ECPR effect is concerned, it    occurs in metal - ChGS structures based on metals (such as Al), which do not actively interact with ChGS in normal conditions. The interaction appears only when a transversal electrical field is applied.  The rate of interaction is influenced by direction and density of electrical current flowing through interface Al - ChGS, hence it is controlled by electrical field strength and by all factors which lead to the ChGS conductivity variation, such as heating, illumination, radiation et al.   Showed by X-ray photoelectron spectroscopy [4]   the    ECPR   phenomenon is due to the transfer matter with the subsequent chemical interaction both at the interface and inside the chalcogenide glass. By this transfer matter, the Al atoms diffuse through the whole thickness of ChGS, showing almost a linear decreasing profile. Simultaneously the intensive oxidation of aluminum atoms occurs at the interface and as a result, an essential part of aluminum electrode is transformed into Al2O3. As Al diffuse inside of ChGS and Al2O3 is a wide-gap insulator the structure becomes more transparent and less reflective that consists a key for optical image formation.