rus
Issue #2/2023
M. A. Bogachev, D. D. Vasiliev, K. M. Moiseev, M. V. Nazarenko
Processing of Optical Crystals and LEDs in Glow Discharge Plasma
Processing of Optical Crystals and LEDs in Glow Discharge Plasma
DOI: 10.22184/1993-7296.FRos.2023.17.2.108.112
Glow discharge plasma treatment is increasingly being used to clean the surfaces of materials from contamination, reduce surface roughness, increase surface energy and surface modification. The article presents the results of plasma processing of high-frequency and low-frequency gas discharge in the MPC RF‑12 plasma processing unit of optical crystal disks and cassettes of solid-state LEDs. The influence of parameters and modes of plasma treatment, namely power, time and type of working gas on the quality of treatment is estimated. It is shown that plasma treatment is a powerful tool for influencing the surface properties of optical crystals, is effective for removing metal oxide layers and is safe for adhesive joints of crystals with a base.
Glow discharge plasma treatment is increasingly being used to clean the surfaces of materials from contamination, reduce surface roughness, increase surface energy and surface modification. The article presents the results of plasma processing of high-frequency and low-frequency gas discharge in the MPC RF‑12 plasma processing unit of optical crystal disks and cassettes of solid-state LEDs. The influence of parameters and modes of plasma treatment, namely power, time and type of working gas on the quality of treatment is estimated. It is shown that plasma treatment is a powerful tool for influencing the surface properties of optical crystals, is effective for removing metal oxide layers and is safe for adhesive joints of crystals with a base.
Теги: cleaning of optical elements low-temperature pulsed plasma optical crystals plasma surface treatment solid-state leds низкотемпературная импульсная плазма оптические кристаллы очистка оптических элементов плазменная обработка поверхности твердотельные светодиоды
Processing of Optical Crystals and LEDs in Glow Discharge Plasma
M. A. Bogachev 1, 2, D. D. Vasiliev 1, 2, K. M. Moiseev 1, 2, M. V. Nazarenko 1, 3
GNtech LLC, Moscow, Russia
Bauman Moscow State Technical University, Moscow, Russia
Russian Technological University MIREA (RTU-MIREA), Moscow, Russia
Glow discharge plasma treatment is increasingly being used to clean the surfaces of materials from contamination, reduce surface roughness, increase surface energy and surface modification. The article presents the results of plasma processing of high-frequency and low-frequency gas discharge in the MPC RF‑12 plasma processing unit of optical crystal disks and cassettes of solid-state LEDs. The influence of parameters and modes of plasma treatment, namely power, time and type of working gas on the quality of treatment is estimated. It is shown that plasma treatment is a powerful tool for influencing the surface properties of optical crystals, is effective for removing metal oxide layers and is safe for adhesive joints of crystals with a base.
Key words: low-temperature pulsed plasma, optical crystals, solid-state LEDs, plasma surface treatment, cleaning of optical elements
The article received: January 19, 2023
The article accepted: February 03, 2023
Introduction
The range of materials used in photonics products is extremely diverse. The technological process of creating photonic products usually includes a plasma processing operation, the purposes of which differ: this includes cleaning the surface from organic contaminants, activating the surface for subsequent application of thin-film optical coatings, modifying the surface structure, reducing roughness (ion polishing), and hydrophilization and hydrophobization. It is possible to distinguish such large market niches of industrial products, the manufacture of which involves plasma processing operations, as laser technology [1], closely related integral [2–4] and fiber optics [5, 6], polycrystalline optical materials [7] and many others. Plasma processing of optical crystals [8, 9] and solid-state LEDs [10, 11] is of particular interest.
The article presents the results of the effect of glow discharge plasma processing on the properties of ZnGeP2 optical crystals and cassettes with solid-state LED chips.
Equipment for plasma surface treatment
The experiments were carried out in MPC plasma processing units (Fig. 1) manufactured by the Russian company GNtech (GNtech LLC, resident of the Skolkovo Innovation Center) [12]. The units are a domestic development, they are mass-produced and in their characteristics and functionality fully correspond to foreign analogues.
For processing ZnGeP2 optical crystals, plasma processing of a radio-frequency (RF) discharge in the MPC RF‑12 unit is used. This is due to the fact that the material is a dielectric, and in such an RF-alternating field with a frequency of 13.56 MHz, the electrons provide effective neutralization of the positive charge that occurs on the surface of the substrates when they interact with positively charged ions of the working gas.
For the processing of metal materials, an MPC LF‑12 installation with a low-frequency plasma of 40 kHz is used. For example, it is used to process cassettes with LED chips. The reason is that the main element of the product that requires cleaning is the metal frames of the LEDs. They need to be cleaned both from possible organic contaminants and from the resulting oxides, which degrade the optical properties (reflection coefficient) of the final LED product.
Research results
and their discussion
Samples of ZnGeP2 optical crystals are disks with a diameter of 30 mm and a thickness of 2 mm.
The purpose of the treatment is to study the effect of the technological parameters of RF plasma treatment of the surface of an optical crystal on the efficiency of removing residual products of crystal polishing (organic contaminants), which in turn affects the value of the laser destruction threshold (LDT). LDT is directly related to the amount of contamination of the crystal surface [9], therefore, its value may also be used to judge the quality of plasma treatment. The standard “S-on‑1” technique is used to determine the LDT of crystals (see international standard ISO 11254-2), according to which the probabilistic nature of the optical breakdown is estimated.
RF plasma treatment is carried out in the medium power range (50 W and 100 W) provided by the MPC RF‑12 plasma treatment unit, mainly in an oxygen environment. To assess the effect of the gas type, one of the experiments was carried out in an argon medium. The parameters of the RF plasma treatment and the results of the LDT measurement are given in the table.
As measurements have shown, the LDT has a higher value in a crystal processed at a higher power of 100 W in an oxygen medium. An increase in processing time from 1 to 5 minutes, but at a lower power of 50 W does not show an increase in LDT.
The purpose of plasma treatment of cassettes with LED crystals is to remove oxides from metal frames (copper with silver coating) to restore the reflectivity of silver, as well as to check the effect of plasma treatment on the strength of the adhesive connection of the crystal and the base.
The treatment is carried out in a low-frequency (40 kHz) glow discharge plasma at capacities of 50, 100 and 200 W. The processing time is 3 minutes. The working gas is argon. Images of samples before and after processing are shown in the Fig. below.
There is a visual change in color – from yellowish (oxide) to silver. At the same time, there was no visual difference in the quality of surface treatment (i. e., a more noticeable color change) between samples processed at different capacities. The strength of the adhesive connection is not affected.
For an additional assessment of the effect of plasma treatment on the strength of the adhesive connection, RF discharge plasma treatment was carried out at a power of 200 W and a duration of 10 minutes. It is confirmed that the strength of the adhesive connection is not affected and is preserved. Visually, the sample looks the same as samples processed over a shorter period of time.
Conclusion
Analysis of the results of the experiments conducted to study the effect of plasma processing parameters showed that the plasma formed in the unit is an effective tool for influencing the physical and mechanical properties of the surface of optical crystals. The selection of suitable process parameters (RF discharge power, processing time and composition of the gas medium) needs be carried out experimentally, which requires the use of equipment, for example, plasma processing units of GN tech MPC series. These installations make it possible to vary the values of the maximum number of operating parameters when choosing optimal plasma treatment conditions and save these data as recipes corresponding to the high reproducibility of the characteristics of the products being created during mass production.
For processing more plasma-resistant materials, such as metal frames of solid-state LEDs, the MPC LF‑12 installation provides a choice of process conditions in a fairly wide power range from 50 to 200 W. An additional advantage of plasma treatment is also the preservation of the strength of adhesive joints present in products of this type.
AUTHORS
Bogachev Maksim A., 1st year master’s student of the Department of Electronic Technologies in Mechanical Engineering, Bauman Moscow State Technical University (BMSTU); Engineer of GN tech LLC, Moscow, Russia.
ORCID 0000–0001–6580–0103
Vasiliev 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 GN tech LLC, Moscow, Russia.
ORCID 0000–0003–2147–4216
Nazarenko Maria V., PhD student, Department of Nanoelectronics, Institute of Advanced Technologies and Industrial Programming (IPTIP), Russian Technological University MIREA (RTU-MIREA), Process Engineer of GN tech LLC, Moscow, Russia.
ORCID 0000–0003–1707–8587
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 GN tech LLC, Moscow, Russia.
ORCID 0000–0002–8753–7737
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.
M. A. Bogachev 1, 2, D. D. Vasiliev 1, 2, K. M. Moiseev 1, 2, M. V. Nazarenko 1, 3
GNtech LLC, Moscow, Russia
Bauman Moscow State Technical University, Moscow, Russia
Russian Technological University MIREA (RTU-MIREA), Moscow, Russia
Glow discharge plasma treatment is increasingly being used to clean the surfaces of materials from contamination, reduce surface roughness, increase surface energy and surface modification. The article presents the results of plasma processing of high-frequency and low-frequency gas discharge in the MPC RF‑12 plasma processing unit of optical crystal disks and cassettes of solid-state LEDs. The influence of parameters and modes of plasma treatment, namely power, time and type of working gas on the quality of treatment is estimated. It is shown that plasma treatment is a powerful tool for influencing the surface properties of optical crystals, is effective for removing metal oxide layers and is safe for adhesive joints of crystals with a base.
Key words: low-temperature pulsed plasma, optical crystals, solid-state LEDs, plasma surface treatment, cleaning of optical elements
The article received: January 19, 2023
The article accepted: February 03, 2023
Introduction
The range of materials used in photonics products is extremely diverse. The technological process of creating photonic products usually includes a plasma processing operation, the purposes of which differ: this includes cleaning the surface from organic contaminants, activating the surface for subsequent application of thin-film optical coatings, modifying the surface structure, reducing roughness (ion polishing), and hydrophilization and hydrophobization. It is possible to distinguish such large market niches of industrial products, the manufacture of which involves plasma processing operations, as laser technology [1], closely related integral [2–4] and fiber optics [5, 6], polycrystalline optical materials [7] and many others. Plasma processing of optical crystals [8, 9] and solid-state LEDs [10, 11] is of particular interest.
The article presents the results of the effect of glow discharge plasma processing on the properties of ZnGeP2 optical crystals and cassettes with solid-state LED chips.
Equipment for plasma surface treatment
The experiments were carried out in MPC plasma processing units (Fig. 1) manufactured by the Russian company GNtech (GNtech LLC, resident of the Skolkovo Innovation Center) [12]. The units are a domestic development, they are mass-produced and in their characteristics and functionality fully correspond to foreign analogues.
For processing ZnGeP2 optical crystals, plasma processing of a radio-frequency (RF) discharge in the MPC RF‑12 unit is used. This is due to the fact that the material is a dielectric, and in such an RF-alternating field with a frequency of 13.56 MHz, the electrons provide effective neutralization of the positive charge that occurs on the surface of the substrates when they interact with positively charged ions of the working gas.
For the processing of metal materials, an MPC LF‑12 installation with a low-frequency plasma of 40 kHz is used. For example, it is used to process cassettes with LED chips. The reason is that the main element of the product that requires cleaning is the metal frames of the LEDs. They need to be cleaned both from possible organic contaminants and from the resulting oxides, which degrade the optical properties (reflection coefficient) of the final LED product.
Research results
and their discussion
Samples of ZnGeP2 optical crystals are disks with a diameter of 30 mm and a thickness of 2 mm.
The purpose of the treatment is to study the effect of the technological parameters of RF plasma treatment of the surface of an optical crystal on the efficiency of removing residual products of crystal polishing (organic contaminants), which in turn affects the value of the laser destruction threshold (LDT). LDT is directly related to the amount of contamination of the crystal surface [9], therefore, its value may also be used to judge the quality of plasma treatment. The standard “S-on‑1” technique is used to determine the LDT of crystals (see international standard ISO 11254-2), according to which the probabilistic nature of the optical breakdown is estimated.
RF plasma treatment is carried out in the medium power range (50 W and 100 W) provided by the MPC RF‑12 plasma treatment unit, mainly in an oxygen environment. To assess the effect of the gas type, one of the experiments was carried out in an argon medium. The parameters of the RF plasma treatment and the results of the LDT measurement are given in the table.
As measurements have shown, the LDT has a higher value in a crystal processed at a higher power of 100 W in an oxygen medium. An increase in processing time from 1 to 5 minutes, but at a lower power of 50 W does not show an increase in LDT.
The purpose of plasma treatment of cassettes with LED crystals is to remove oxides from metal frames (copper with silver coating) to restore the reflectivity of silver, as well as to check the effect of plasma treatment on the strength of the adhesive connection of the crystal and the base.
The treatment is carried out in a low-frequency (40 kHz) glow discharge plasma at capacities of 50, 100 and 200 W. The processing time is 3 minutes. The working gas is argon. Images of samples before and after processing are shown in the Fig. below.
There is a visual change in color – from yellowish (oxide) to silver. At the same time, there was no visual difference in the quality of surface treatment (i. e., a more noticeable color change) between samples processed at different capacities. The strength of the adhesive connection is not affected.
For an additional assessment of the effect of plasma treatment on the strength of the adhesive connection, RF discharge plasma treatment was carried out at a power of 200 W and a duration of 10 minutes. It is confirmed that the strength of the adhesive connection is not affected and is preserved. Visually, the sample looks the same as samples processed over a shorter period of time.
Conclusion
Analysis of the results of the experiments conducted to study the effect of plasma processing parameters showed that the plasma formed in the unit is an effective tool for influencing the physical and mechanical properties of the surface of optical crystals. The selection of suitable process parameters (RF discharge power, processing time and composition of the gas medium) needs be carried out experimentally, which requires the use of equipment, for example, plasma processing units of GN tech MPC series. These installations make it possible to vary the values of the maximum number of operating parameters when choosing optimal plasma treatment conditions and save these data as recipes corresponding to the high reproducibility of the characteristics of the products being created during mass production.
For processing more plasma-resistant materials, such as metal frames of solid-state LEDs, the MPC LF‑12 installation provides a choice of process conditions in a fairly wide power range from 50 to 200 W. An additional advantage of plasma treatment is also the preservation of the strength of adhesive joints present in products of this type.
AUTHORS
Bogachev Maksim A., 1st year master’s student of the Department of Electronic Technologies in Mechanical Engineering, Bauman Moscow State Technical University (BMSTU); Engineer of GN tech LLC, Moscow, Russia.
ORCID 0000–0001–6580–0103
Vasiliev 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 GN tech LLC, Moscow, Russia.
ORCID 0000–0003–2147–4216
Nazarenko Maria V., PhD student, Department of Nanoelectronics, Institute of Advanced Technologies and Industrial Programming (IPTIP), Russian Technological University MIREA (RTU-MIREA), Process Engineer of GN tech LLC, Moscow, Russia.
ORCID 0000–0003–1707–8587
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 GN tech LLC, Moscow, Russia.
ORCID 0000–0002–8753–7737
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.
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