rus
Issue #4/2022
S. V. Sidorova, K. M. Moiseev, D. D. Vasilev, M. V. Nazarenko, I. V. Mikhailova
Plasma Treatment of Material Surfaces for the Photonics Applications
Plasma Treatment of Material Surfaces for the Photonics Applications
DOI: 10.22184/1993-7296.FRos.2022.16.4.288.295
Plasma treatment is a powerful tool for cleaning the material surface from contamination, reducing the surface roughness, increasing the surface energy and surface modification. The use of plasma processing systems in the process equipment chain is a global trend. The article presents the results of high-frequency gas discharge plasma processing in the MPC RF‑12 plasma treatment systems. The influence of plasma treatment parameters and modes, namely power and time, on the treatment quality, determined by the contact angle, is studied. It is shown that in some cases it is possible to obtain the similar results with different ratios of plasma treatment parameters.
Plasma treatment is a powerful tool for cleaning the material surface from contamination, reducing the surface roughness, increasing the surface energy and surface modification. The use of plasma processing systems in the process equipment chain is a global trend. The article presents the results of high-frequency gas discharge plasma processing in the MPC RF‑12 plasma treatment systems. The influence of plasma treatment parameters and modes, namely power and time, on the treatment quality, determined by the contact angle, is studied. It is shown that in some cases it is possible to obtain the similar results with different ratios of plasma treatment parameters.
Теги: cleaning of optical elements low-temperature pulsed plasma plasma surface treatment technology for manufacturing optical components низкотемпературная импульсная плазма очистка оптических элементов плазменная обработка поверхности технология изготовления оптических компонентов
Plasma Treatment of Material Surfaces for the Photonics Applications
S. V. Sidorova2, K. M. Moiseev1,2, D. D. Vasilev1,2, M. V. Nazarenko3, I. V. Mikhailova1
GNtech LLC Moscow, Russia
Bauman Moscow State Technical University (BMSTU), Moscow, Russia
RTU-MIREA, Moscow, Russia
Plasma treatment is a powerful tool for cleaning the material surface from contamination, reducing the surface roughness, increasing the surface energy and surface modification. The use of plasma processing systems in the process equipment chain is a global trend. The article presents the results of high-frequency gas discharge plasma processing in the MPC RF‑12 plasma treatment systems. The influence of plasma treatment parameters and modes, namely power and time, on the treatment quality, determined by the contact angle, is studied. It is shown that in some cases it is possible to obtain the similar results with different ratios of plasma treatment parameters.
Keywords: low-temperature pulsed plasma, technology for manufacturing optical components, plasma surface treatment, cleaning of optical elements
Received on: 19.05.2022
Accepted on: 03.06.2022
Introduction
The laser technology development led to the emergence of photonics as a separate industrial branch and as a scientific field. The experts attribute the possible solution of many problems facing humanity in the field of information support, industrial production, energy, healthcare, environmental protection, and security to this technology [1].
Back in the 1960s‑1980s, photonics emerged as a separate region of science due to the new inventions: a laser, s laser diode, an optical fiber, and an optical fiber amplifier. In recent years, photonics has already penetrated into all spheres of our life. At present, this region of science covers a wide range of optical, electro-optical and optoelectronic devices, as well as their various applications. The main areas of research in photonics include the fiber optics and integrated optics, including nonlinear one, physics and technology of semiconductor compounds, semiconductor lasers, optoelectronic devices, high-speed electronic devices [2, 3]. The connection between photonics and quantum optics and quantum calculations has strengthened significantly.
To solve specific issues in all of the above fields of application, it is important that the structure of the material used and its surface quality remain unchanged that is related to the need to achieve the minimum optical losses in the devices and units. The performance limits of the optical losses of materials used for the photonics tasks can be established if the losses due to the intrinsic absorption and material scattering are considered. The significant losses occur when the materials are contaminated with impurities, as well as when there are impurities and microroughnesses on the contact surface. The availability of microroughnesses at the interface between the layers in devices entails double refraction and extrinsic optical losses [3].
To remove contaminants and microroughnesses from the material surface, the plasma treatment in a vacuum is increasingly used in addition to the classical mechanical and chemical treatment. It should be noted that the plasma surface treatment modifies the surface properties without changing the material properties that is important for optical and optoelectronic materials.
The plasma treatment makes it possible to influence the surface wettability and allows to develop a hydrophobic, hydrophilic surface, i. e., a surface with the required properties. Such processes are possible as a result of the surface layer formation with certain chemical properties.
The degree and level of material surface modification depends on the parameters of the plasma treatment process. It is possible to perform both cleaning and etching in plasma (removal of contaminants and removal of the material layers), as well as deposition (material coating), surface activation (development of active centers on the metal surfaces for subsequent treatment).
It should be noted that there is a significant tendency in photonics development towards the wave optics, where a wide range of polymeric materials is used. Thus, during the waveguide production process, three optical layers, namely the lower cover, the core and the upper cover, are made on the substrates by the successive build-up method. Each optical layer is subject to the subsequent coating, imaging and curing cycles. As a result, the higher index polymer routing patterns (optical cores) are completely surrounded by the lower index optical material (optical jacket) [4, 5].
It is important to maintain an even polymer surface at each layer. It will be advisable to perform additional treatment between the coating stages to achieve the required surface modification degree and prepare it for the next layer application that improves the adhesive properties.
The article evaluates the plasma treatment effect on the glass substrates used for the production of photonics devices.
Materials and their quality assessment methods
In the photonics devices and units, the range of material application is very extensive: optical glasses, polycrystalline glasses, semiconductor materials, polymers, optical coatings, optical fiber, etc.
The plasma treatment quality can be determined by the water film breaking, by sputtering technique, by the contact angle measuring, or by comparing the substrate cleanliness [6]. Most commonly, an assessment based on the contact angle is used to determine the quality of the material surface treatment against contamination.
Wetting is the physical interaction of a liquid with the surface of a solid body or other liquid. In the case when there is a contact between a liquid and a solid body, we consider the contact wetting. It depends on the ratio between the adhesion forces of liquid molecules with the wetted body molecules (or atoms) (adhesion) and the mutual adhesion forces of liquid molecules (cohesion).
If a liquid is in contact with a solid body, then there are two possibilities:
the liquid molecules are attracted to each other more strongly than to the solid body molecules. As a result of the attractive force between the liquid molecules, the drop is made. In this case, the liquid does not wet the surface. The surface is hydrophobic.
the liquid molecules are attracted to each other more weakly than to the solid body molecules. As a result, the liquid tends to cling to the surface and spreads over it. In this case, the liquid wets the surface. The surface is hydrophilic.
The wetting degree is specified by the contact angle. The contact angle (or the limiting contact angle) is the angle generated by the tangent planes to the interfacial areas that limit the wetting liquid, and the angular vertex is located along the boundary line of the three phases.
There are many types of surface wettability measurements. The most common is the sessile drop method. This method was used to assess the plasma treatment quality of glass samples during the drop study using a goniometer.
Plasma surface treatment equipment
The studies were performed using a plasma treatment system MPC RF‑12 (Fig. 1) manufactured by the Russian company GNtech (GNtech LLC, a resident of the Skolkovo Innovation Center) [7].
The system is a mass-produced home-grown technology and, in terms of its specifications and functionality, fully complies with the foreign analogues (see table).
For the dielectric materials that prevail in the photonics products, it is advisable to use treatment in a radio frequency (RF) discharge plasma. This is due to the fact that in such an RF variable field with a frequency of 13.56 MHz, the electrons provide efficient neutralization of the positive charge occurred on the substrate surface during their interaction with the positively charged ions of the working gas.
For the treatment of metal components of the photonics products, for example, the LED case frames, as well as for more mass processing, other MPC series systems can be applied (Fig. 2), for example, with a low-frequency plasma of 40 kHz, with an increased chamber volume up to 100 liters or more, or with the increased plasma generator power up to 1 kW.
Results and discussion
The plasma treatment of polymer samples was performed in an argon atmosphere at a pressure of 50 mT. During the experiment, the power (50, 100, and 200 W) and the treatment duration (30, 60, and 90 s) were varied. The processed samples were examined using a goniometer. The obtained images confirm that with an increase in the glass plasma treatment duration, the contact angle is decreased (Fig. 3).
According to the study results, the contact angle dependences on the plasma treatment duration were plotted at various powers of the working gas (Fig. 4).
An analysis of the experimental results demonstrates that in the case of a short-term treatment of about 30 s, i. e., at its initial stage, the contact angle is increased with an increase in power. In the case of a relatively long-term treatment (about 60 s in this case), the treatment time ceases to have an effect. There is also a certain threshold power value in the range between 50 and 100 W, after which it ceases to affect the contact angle, provided a sufficient treatment time of 90 s.
Conclusion
The conducted experiments relating to the influence of plasma treatment parameters confirm that the treatment is an efficient tool for cleaning and property control of the surfaces of dielectric materials used in the photonics devices.
It can be noted that in some cases it is possible to obtain similar results with less power, but with longer treatment duration. However, such results were achieved under the condition that the power was above a certain threshold value.
The search for optimal treatment parameters is almost always performed experimentally, and the data presented in this and other articles can be used to determine the start points or boundaries of the variation ranges. The MPC plasma treatment systems manufactured by GNtech allow to vary the process parameters in a wide range of values, as well as to save the experimentally selected combinations of such parameters in the form of recipes (up to 50 pcs.) that makes them a convenient tool both for scientific research, and for mass production.
AUTHORS
Moiseev Konstantin M., Cand. of Scien. (Engineering), Associate Professor of the Department of Electronic Technologies in Mechanical Engineering, Bauman Moscow State Technical University (BMSTU); technical director of GNtech LLC, info@gnaxel.ru, Moscow, Russia.
ORCID 0000-0002-8753-7737
Vasilev Denis D., Cand. of Scien. (Engineering), Associate Professor of the Department of Electronic Technologies in Mechanical Engineering, Bauman Moscow State Technical University (BMSTU); Lead Engineer of GNtech LLC, Moscow, Russia.
ORCID 0000-0003-2147-4216
Mikhailova Irina V., project manager of GNtech LLC, Moscow, Russia.
ORCID 0000-0002-4558-261X
Sidorova Svetlana V., Cand. of Scien. (Engineering), Associate Professor of the Department of Electronic Technologies in Mechanical Engineering, Bauman Moscow State Technical University (BMSTU), Moscow, Russia.
ORCID 0000-0002-3002-1246
Nazarenko Maria V., PhD student, Department of Nanoelectronics, Institute of Advanced Technologies and Industrial Programming (IPTIP), Russian Technological University MIREA (RTU-MIREA), Moscow, Russia.
ORCID 0000-0003-1707-8587
CONTRIBUTION OF THE AUTHORS
The article was prepared on the basis of the work of all members of the team of contributors.
CONFLICT OF INTEREST
The authors herewith declare that there is no conflict of interest. All authors participated in the writing of the manuscript in terms of the contribution of each of them to the work and agree with the full text of the manuscript.
S. V. Sidorova2, K. M. Moiseev1,2, D. D. Vasilev1,2, M. V. Nazarenko3, I. V. Mikhailova1
GNtech LLC Moscow, Russia
Bauman Moscow State Technical University (BMSTU), Moscow, Russia
RTU-MIREA, Moscow, Russia
Plasma treatment is a powerful tool for cleaning the material surface from contamination, reducing the surface roughness, increasing the surface energy and surface modification. The use of plasma processing systems in the process equipment chain is a global trend. The article presents the results of high-frequency gas discharge plasma processing in the MPC RF‑12 plasma treatment systems. The influence of plasma treatment parameters and modes, namely power and time, on the treatment quality, determined by the contact angle, is studied. It is shown that in some cases it is possible to obtain the similar results with different ratios of plasma treatment parameters.
Keywords: low-temperature pulsed plasma, technology for manufacturing optical components, plasma surface treatment, cleaning of optical elements
Received on: 19.05.2022
Accepted on: 03.06.2022
Introduction
The laser technology development led to the emergence of photonics as a separate industrial branch and as a scientific field. The experts attribute the possible solution of many problems facing humanity in the field of information support, industrial production, energy, healthcare, environmental protection, and security to this technology [1].
Back in the 1960s‑1980s, photonics emerged as a separate region of science due to the new inventions: a laser, s laser diode, an optical fiber, and an optical fiber amplifier. In recent years, photonics has already penetrated into all spheres of our life. At present, this region of science covers a wide range of optical, electro-optical and optoelectronic devices, as well as their various applications. The main areas of research in photonics include the fiber optics and integrated optics, including nonlinear one, physics and technology of semiconductor compounds, semiconductor lasers, optoelectronic devices, high-speed electronic devices [2, 3]. The connection between photonics and quantum optics and quantum calculations has strengthened significantly.
To solve specific issues in all of the above fields of application, it is important that the structure of the material used and its surface quality remain unchanged that is related to the need to achieve the minimum optical losses in the devices and units. The performance limits of the optical losses of materials used for the photonics tasks can be established if the losses due to the intrinsic absorption and material scattering are considered. The significant losses occur when the materials are contaminated with impurities, as well as when there are impurities and microroughnesses on the contact surface. The availability of microroughnesses at the interface between the layers in devices entails double refraction and extrinsic optical losses [3].
To remove contaminants and microroughnesses from the material surface, the plasma treatment in a vacuum is increasingly used in addition to the classical mechanical and chemical treatment. It should be noted that the plasma surface treatment modifies the surface properties without changing the material properties that is important for optical and optoelectronic materials.
The plasma treatment makes it possible to influence the surface wettability and allows to develop a hydrophobic, hydrophilic surface, i. e., a surface with the required properties. Such processes are possible as a result of the surface layer formation with certain chemical properties.
The degree and level of material surface modification depends on the parameters of the plasma treatment process. It is possible to perform both cleaning and etching in plasma (removal of contaminants and removal of the material layers), as well as deposition (material coating), surface activation (development of active centers on the metal surfaces for subsequent treatment).
It should be noted that there is a significant tendency in photonics development towards the wave optics, where a wide range of polymeric materials is used. Thus, during the waveguide production process, three optical layers, namely the lower cover, the core and the upper cover, are made on the substrates by the successive build-up method. Each optical layer is subject to the subsequent coating, imaging and curing cycles. As a result, the higher index polymer routing patterns (optical cores) are completely surrounded by the lower index optical material (optical jacket) [4, 5].
It is important to maintain an even polymer surface at each layer. It will be advisable to perform additional treatment between the coating stages to achieve the required surface modification degree and prepare it for the next layer application that improves the adhesive properties.
The article evaluates the plasma treatment effect on the glass substrates used for the production of photonics devices.
Materials and their quality assessment methods
In the photonics devices and units, the range of material application is very extensive: optical glasses, polycrystalline glasses, semiconductor materials, polymers, optical coatings, optical fiber, etc.
The plasma treatment quality can be determined by the water film breaking, by sputtering technique, by the contact angle measuring, or by comparing the substrate cleanliness [6]. Most commonly, an assessment based on the contact angle is used to determine the quality of the material surface treatment against contamination.
Wetting is the physical interaction of a liquid with the surface of a solid body or other liquid. In the case when there is a contact between a liquid and a solid body, we consider the contact wetting. It depends on the ratio between the adhesion forces of liquid molecules with the wetted body molecules (or atoms) (adhesion) and the mutual adhesion forces of liquid molecules (cohesion).
If a liquid is in contact with a solid body, then there are two possibilities:
the liquid molecules are attracted to each other more strongly than to the solid body molecules. As a result of the attractive force between the liquid molecules, the drop is made. In this case, the liquid does not wet the surface. The surface is hydrophobic.
the liquid molecules are attracted to each other more weakly than to the solid body molecules. As a result, the liquid tends to cling to the surface and spreads over it. In this case, the liquid wets the surface. The surface is hydrophilic.
The wetting degree is specified by the contact angle. The contact angle (or the limiting contact angle) is the angle generated by the tangent planes to the interfacial areas that limit the wetting liquid, and the angular vertex is located along the boundary line of the three phases.
There are many types of surface wettability measurements. The most common is the sessile drop method. This method was used to assess the plasma treatment quality of glass samples during the drop study using a goniometer.
Plasma surface treatment equipment
The studies were performed using a plasma treatment system MPC RF‑12 (Fig. 1) manufactured by the Russian company GNtech (GNtech LLC, a resident of the Skolkovo Innovation Center) [7].
The system is a mass-produced home-grown technology and, in terms of its specifications and functionality, fully complies with the foreign analogues (see table).
For the dielectric materials that prevail in the photonics products, it is advisable to use treatment in a radio frequency (RF) discharge plasma. This is due to the fact that in such an RF variable field with a frequency of 13.56 MHz, the electrons provide efficient neutralization of the positive charge occurred on the substrate surface during their interaction with the positively charged ions of the working gas.
For the treatment of metal components of the photonics products, for example, the LED case frames, as well as for more mass processing, other MPC series systems can be applied (Fig. 2), for example, with a low-frequency plasma of 40 kHz, with an increased chamber volume up to 100 liters or more, or with the increased plasma generator power up to 1 kW.
Results and discussion
The plasma treatment of polymer samples was performed in an argon atmosphere at a pressure of 50 mT. During the experiment, the power (50, 100, and 200 W) and the treatment duration (30, 60, and 90 s) were varied. The processed samples were examined using a goniometer. The obtained images confirm that with an increase in the glass plasma treatment duration, the contact angle is decreased (Fig. 3).
According to the study results, the contact angle dependences on the plasma treatment duration were plotted at various powers of the working gas (Fig. 4).
An analysis of the experimental results demonstrates that in the case of a short-term treatment of about 30 s, i. e., at its initial stage, the contact angle is increased with an increase in power. In the case of a relatively long-term treatment (about 60 s in this case), the treatment time ceases to have an effect. There is also a certain threshold power value in the range between 50 and 100 W, after which it ceases to affect the contact angle, provided a sufficient treatment time of 90 s.
Conclusion
The conducted experiments relating to the influence of plasma treatment parameters confirm that the treatment is an efficient tool for cleaning and property control of the surfaces of dielectric materials used in the photonics devices.
It can be noted that in some cases it is possible to obtain similar results with less power, but with longer treatment duration. However, such results were achieved under the condition that the power was above a certain threshold value.
The search for optimal treatment parameters is almost always performed experimentally, and the data presented in this and other articles can be used to determine the start points or boundaries of the variation ranges. The MPC plasma treatment systems manufactured by GNtech allow to vary the process parameters in a wide range of values, as well as to save the experimentally selected combinations of such parameters in the form of recipes (up to 50 pcs.) that makes them a convenient tool both for scientific research, and for mass production.
AUTHORS
Moiseev Konstantin M., Cand. of Scien. (Engineering), Associate Professor of the Department of Electronic Technologies in Mechanical Engineering, Bauman Moscow State Technical University (BMSTU); technical director of GNtech LLC, info@gnaxel.ru, Moscow, Russia.
ORCID 0000-0002-8753-7737
Vasilev Denis D., Cand. of Scien. (Engineering), Associate Professor of the Department of Electronic Technologies in Mechanical Engineering, Bauman Moscow State Technical University (BMSTU); Lead Engineer of GNtech LLC, Moscow, Russia.
ORCID 0000-0003-2147-4216
Mikhailova Irina V., project manager of GNtech LLC, Moscow, Russia.
ORCID 0000-0002-4558-261X
Sidorova Svetlana V., Cand. of Scien. (Engineering), Associate Professor of the Department of Electronic Technologies in Mechanical Engineering, Bauman Moscow State Technical University (BMSTU), Moscow, Russia.
ORCID 0000-0002-3002-1246
Nazarenko Maria V., PhD student, Department of Nanoelectronics, Institute of Advanced Technologies and Industrial Programming (IPTIP), Russian Technological University MIREA (RTU-MIREA), Moscow, Russia.
ORCID 0000-0003-1707-8587
CONTRIBUTION OF THE AUTHORS
The article was prepared on the basis of the work of all members of the team of contributors.
CONFLICT OF INTEREST
The authors herewith declare that there is no conflict of interest. All authors participated in the writing of the manuscript in terms of the contribution of each of them to the work and agree with the full text of the manuscript.
Readers feedback
