G.R. Sagatelyan1, K.N. Bugorkov2, A.B. Solomashenko3, A.S. Kuznetsov4

1–4 Bauman Moscow State Technical University (National Research University) (Moscow, Russia)
 

As far as the process of plasma chemical etching (PCE), is characterized by poor reproducibility of results, which, in turn, is due to the multiplicity of physical and chemical processes that eventually lead to the removal of the processed material, the PCB process should be considered in the form of a "black box" model, a distinctive feature of which is the consideration of feedbacks that arise due to formation of hidden process factors – such as pressure in the vacuum chamber, surface temperature of the workpiece, electrical the impedance of the plasma. The factors of the PCE process are divided into modes and conditions of technological operations, which ensures their reasonable development. Modes are those factors that can be purposefully changed during the course of the process itself. The conditions of technological operations include the design features of the technological system and consider the purpose of each technological transition.

Purpose of the study – to describe the relationships available in the technological system, a mathematical model based on the analysis of the rate of chemical reactions calculated by the Arrhenius formula must be developed to predict the numerical values of the main output parameters of the PCE process, namely, the etching rate and the achievable depth of the relief layer. The distinctive feature of this model is the consideration of changed reaction rate due to passivation of the treated surface caused by the occurrence of side gas transport reactions on it.

As a result of experimental studies, a number of empirical formulas have been obtained that can be entered into the universal database being created. Such models allow to establish and evaluate the degree of influence on the output parameters of the process of the main characteristics of the plasma – its ionic and electron temperature, as well as the degree of ionization. Along with this, some requirements for the design of the technological system are experimentally justified – in particular, it is shown that the workpiece should be located as close as possible to the plane of the inductor. In addition, the expediency of dividing the PCE process into the actual etching of the workpiece material, performed during the implementation of functional transitions, and cleaning (in particular, by oxygen) of the treated surface from its passivating film, performed at the preparatory and final transitions, is shown. The structure of the technological operation of PCE is substantiated as consisting of alternating preparatory-final and functional transitions.
The proposed model is adapted mainly for the technological operation of PCTs performed on installations with inductively coupled plasma created by a flat inductor when the workpiece is placed directly in the plasma volume. This scheme is used for double-sided etching of quartz glass with sulfur hexafluoride during the formation of functional relief on both surfaces of flat parts. As an extension of the scope of applications of PCE and its dissemination to mass production, the possibility of creating holographic and diffraction optical elements (HOE-DOE) from optically transparent compounds has been experimentally shown. Such HOE-DOE are replicas removed from the relief surface of a matrix made of quartz glass.

Sagatelyan G.R., Bugorkov K.N., Solomashenko A.B., Kuznetsov A.S. Plasma-chemical etching of quartz glass by sulfur hexafluoride. Nanotechnology: development and applications – XXI century. 2023. V. 15. № 3. P. 32–46. DOI: https://doi.org/10.18127/j22250980-202303-04 (in Russian)

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