rus
Issue #3-4/2022
Yu.V.Panfilov, L.L.Kolesnik
MICRO-CONTAMINATION OF NANOSTRUCTURES AT MANUFACTURING IN VACUUM
MICRO-CONTAMINATION OF NANOSTRUCTURES AT MANUFACTURING IN VACUUM
DOI: 10.22184/1993-8578.2022.15.3-4.224.231
Main sources of micro-contamination of the micro- and nanoelectronic devices in vacuum cluster-type processing equipment were analysed. Generation mechanism of microparticles flows at locks and processing vacuum chambers, molecular contamination and metal particles as a results of construction materials wear and tribo-desorption were shown.
Main sources of micro-contamination of the micro- and nanoelectronic devices in vacuum cluster-type processing equipment were analysed. Generation mechanism of microparticles flows at locks and processing vacuum chambers, molecular contamination and metal particles as a results of construction materials wear and tribo-desorption were shown.
Теги: micro and nanoelectronics micro-contamination molecules contamination tribo-desorption vacuum equipment вакуумное оборудование ключевые слова: привносимая дефектность микро- и наноэлектроника молекулярные загрязнения трибодесорбция
Received: 17.05.2022 | Accepted: 27.05.2022 | DOI: https://doi.org/10.22184/1993-8578.2022.15.3-4.224.231
Original paper
MICRO-CONTAMINATION OF NANOSTRUCTURES AT MANUFACTURING IN VACUUM
Yu.V.Panfilov1, Doct. of Sci. (Tech), Prof., ORCID: 0000-0001-6861-2028 / panfilov@bmstu.ru
L.L.Kolesnik1, Cand. of Sci. (Tech), Docent, ORCID: 0000-0002-1037-997X
Abstract. Main sources of micro-contamination of the micro- and nanoelectronic devices in vacuum cluster-type processing equipment were analysed. Generation mechanism of microparticles flows at locks and processing vacuum chambers, molecular contamination and metal particles as a results of construction materials wear and tribo-desorption were shown.
Keywords: micro-contamination, vacuum equipment, micro and nanoelectronics, molecules contamination, tribo-desorption
For citation: Yu.V. Panfilov, L.L. Kolesnik. Micro-contamination of nanostructures at manufacturing in vacuum. NANOINDUSTRY. 2022. V. 15, no. 3–4. PP. 224–231. https://doi.org/10.22184/1993-8578.2022.15.3–4.224.231
INTRODUCTION
The claim that the fight against introduced defects in microelectronics products cannot be won [1] is clearly demonstrated in the nanoelectronics production. For example, with the minimum element sizes of modern super large integrated circuits (VLSI) of 7–18 nm, not only fine particles (FP) [2], but also so-called molecular contamination becomes critical in terms of VLSI yield [3]. The purpose of this paper is to analyse the sources of introduced defects in micro- and nanoelectronic s products in the vacuum cluster-type process equipment.
Cluster production systems (Fig.1) integrate different technological operations in a single vacuum cycle and today they are used to produce the most advanced micro- and nanoelectronic products. One of the main challenges in designing and operating such equipment is to ensure the quality of the vacuum process environment, namely, to minimise the introduced defectiveness of the manufactured micro- and nanostructures. While for the microstructures with dimensions of 1 µm the main cause of defects is solid or liquid fine particles [2], for the nanostructures with dimensions of tens or even several nanometres the molecular contamination [3] in the form of degradation products of polymer structural materials and organic compounds as well as products of gas emission of rubber mixtures are critical in terms of good quality yield. In addition, as a result of high-temperature and frictional influence (tribodesorption [4]), on the materials of intra-chamber devices and mechanisms, the atoms and molecules of oxygen, methane, mono- and carbon dioxide, sulfur compounds as well as, metals and their oxides get on the processed nanostructures. In the cluster type equipment there is another cause of defects related to penetration of gaseous reagents and products of plasma chemical reactions from one process module into the other process modules through the high-vacuum transport module.
Introduced defectiveness of microelectronic products in the form of fine particles was investigated sufficiently in detail in the 90’s of the last century, which was reflected in many publications, including [5]. There were studies of FP distribution on the semiconductor wafer surface after pumping of vacuum, including sluice chambers, pumping air into them for depressurization, and also after wafer transfer in vacuum process chambers with the help of, for example, conveyors. Figure 2 shows the results of the induced defect measurements on the semiconductor wafer surface in the 01NI-7-015 gateway-type device developed by RIPMM, Zelenograd.
Molecular contamination of semiconductor wafers with formed nanostructures in vacuum chambers of technological equipment can appear, firstly, during their depressurization from CR atmosphere, and consist of organophosphates, silicones, cresols, hydrocarbons and other compounds [3], secondly, emissions from organic materials and friction pairs, desorption of water vapors from the walls of a vacuum chamber, gas leakage through mobile and fixed contacts, thirdly, corrosion products (about 100 Å/30 days) and oxidation of the technological equipment surface and the walls of the vacuum chamber. The intensity of molecular contamination, e.g. by phosphorus, can be 2.5 . 1011 atoms/cm2 per hour [3].
According to SEMI F21-951, molecular contamination in vacuum can include condensable compounds (CC) and trace metals (TM). GOST R ISO 14644-9-2013 characterizes surface roughness classes according to particle concentration, which define maximum permissible concentration of particles of certain sizes on the semiconductor wafer surface. Measurement of mass concentration of surface contaminants is based on determining characteristic wavelengths of the main functional groups of contaminants and signal power. With the help of modern methods it is possible to monitor contamination at the level of 0.1 ng/cm2 [3].
Traces of metals on the semiconductor wafers surface in a vacuum can theoretically appear as a result of sublimation of metal armature atoms. Sublimation is a multi-step process that requires additional thermal energy. When it is supplied, particles of solid material migrate to the solid phase surface from the highest bond strength state to a state with lower bond strength and then to the gas phase. At the same time the particles desublimate from it. The maximum sublimation rate and desublimation processes in a vacuum can be calculated from the Hertz-Knudsen equation:
(1)
where Nи is the number of evaporated (sublimated) atoms or molecules, t is time, s, A is the evaporation (sublimation) area, m2, aи is the evaporation coefficient (for pure materials aи = 1), m is mass of an evaporated (sublimated) atom or molecule, kg, Tи is the evaporation temperature, K.
The saturated vapour pressure over the surface of a solid body is described by the Clapeyron – Clausius equation:
, (2)
where pнас is saturated vapour pressure of material to be vaporised, Pa; T is material temperature, K; H is enthalpy of gas (г) and liquid (ж), kcal/kmol; V is volume of gas (г) and liquid (ж), m3 (Vг>>Vж); DH is heat of vaporisation, kcal/kmol.
However, the saturated vapour pressure at temperatures below the evaporation temperature is very low. For example, the saturated vapour pressure of a metal, e.g. neptunium, at room temperature in a vacuum is [6]:
lgpнас= 5,1 – 2,06 . 104/T, (3)
where T is the absolute temperature, K.
At T = 1,000 K the saturated vapour pressure is pнас = 10–15 Pa, and at room temperature 293 K the saturated vapour pressure is only pнас = 10–65 Pa. At these pressures the speed of sublimation processes is approximately 107 and 10–39 atoms/(m2s), respectively. It follows that at room temperature contamination of micro- and nanostructures with atoms and molecules by structural materials of vacuum technological equipment can be disregarded.
Introduced defects in the form of atoms and molecules in structural materials can have a marked effect on performance of nanostructures, up to and including rejection, as a result of tribodesorption [4] from intra-cavity friction pairs.
As the experience of design and operation of vacuum transport and loading modules showed, the main sources of contamination in the form of chemically active gases and fine particles are friction pairs of mechanisms, guides, motion inputs, located in high and ultra-high vacuum [7].
Information on tribodesorption in vacuum from various steels, polymeric materials, minerals, solid lubricants, soft metals (silver, lead) is accumulated, with tribodesorption having both thermal and athermal (at low loads and friction speeds) character. The compositions of polypropylene, ethylene propylene, chlorobutylene and fluorocarbon rubbers stand out in the friction of synthetic rubbers. Low molecular weight compounds such as methane, mono and carbon dioxide, non-polymerised monomers and volatile components of impurities are found in the mass spectrum.
Tribo-emission phenomena include various physical and chemical processes occurring in and around the contact zone of rubbing bodies and leading to emission of atoms and molecules out of the bodies themselves, occluded gases and nanoparticles [5]. These properties of tribo-emission phenomena made the basis for a number of developments of the fundamentally new technological processes, materials and methods with given properties, including:
Two types of solid-lubricant coatings based on molybdenum disulphide were developed for use in UHV equipment by RITI Ryazan in 1980s: chemical-thermal coating "Dimolit-4" developed by All-Russian Scientific Research Institute optical-physical measurements and ion-plasma coating "IPN MoS2" developed by Mechanical Engineering Research Institute of the Russian
Academy of Sciences. However, in a spectrum of gas emissions from friction pair with "Dimolit-4" there were traces of sulphur and its compounds that turned out to be unacceptable for processes of molecular beam epitaxy as it led to overlegging of GaAs-based heterostructures. Therefore, the friction assemblies of manipulators and slideways coated with MoS2 IPN were taken into use and no traces of sulphur and its compounds were detected in their gas emission spectrum even at 773 K (Fig.3).
In research of brought defectiveness from units and mechanisms in vacuum chambers of the process equipment, in particular, from sliding bearings with solid lubricant coating (SLC) on the basis of molybdenum disulphide, applied by vacuum ionic-plasma method, traces of metals and sulphur on surface of control plates which have been placed in immediate proximity of a sliding bearing (Fig.4) were found. The quantity and composition of these traces varied with operating time, expressed as the total number of revolutions of the bearing shaft.
CONCLUSIONS
Thus, the analysis of causes and sources of the introduced defects in micro- and nanoelectronics products, as well as occurrence and spread of molecular contaminants in cluster-type vacuum processing equipment show that:
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Original paper
MICRO-CONTAMINATION OF NANOSTRUCTURES AT MANUFACTURING IN VACUUM
Yu.V.Panfilov1, Doct. of Sci. (Tech), Prof., ORCID: 0000-0001-6861-2028 / panfilov@bmstu.ru
L.L.Kolesnik1, Cand. of Sci. (Tech), Docent, ORCID: 0000-0002-1037-997X
Abstract. Main sources of micro-contamination of the micro- and nanoelectronic devices in vacuum cluster-type processing equipment were analysed. Generation mechanism of microparticles flows at locks and processing vacuum chambers, molecular contamination and metal particles as a results of construction materials wear and tribo-desorption were shown.
Keywords: micro-contamination, vacuum equipment, micro and nanoelectronics, molecules contamination, tribo-desorption
For citation: Yu.V. Panfilov, L.L. Kolesnik. Micro-contamination of nanostructures at manufacturing in vacuum. NANOINDUSTRY. 2022. V. 15, no. 3–4. PP. 224–231. https://doi.org/10.22184/1993-8578.2022.15.3–4.224.231
INTRODUCTION
The claim that the fight against introduced defects in microelectronics products cannot be won [1] is clearly demonstrated in the nanoelectronics production. For example, with the minimum element sizes of modern super large integrated circuits (VLSI) of 7–18 nm, not only fine particles (FP) [2], but also so-called molecular contamination becomes critical in terms of VLSI yield [3]. The purpose of this paper is to analyse the sources of introduced defects in micro- and nanoelectronic s products in the vacuum cluster-type process equipment.
Cluster production systems (Fig.1) integrate different technological operations in a single vacuum cycle and today they are used to produce the most advanced micro- and nanoelectronic products. One of the main challenges in designing and operating such equipment is to ensure the quality of the vacuum process environment, namely, to minimise the introduced defectiveness of the manufactured micro- and nanostructures. While for the microstructures with dimensions of 1 µm the main cause of defects is solid or liquid fine particles [2], for the nanostructures with dimensions of tens or even several nanometres the molecular contamination [3] in the form of degradation products of polymer structural materials and organic compounds as well as products of gas emission of rubber mixtures are critical in terms of good quality yield. In addition, as a result of high-temperature and frictional influence (tribodesorption [4]), on the materials of intra-chamber devices and mechanisms, the atoms and molecules of oxygen, methane, mono- and carbon dioxide, sulfur compounds as well as, metals and their oxides get on the processed nanostructures. In the cluster type equipment there is another cause of defects related to penetration of gaseous reagents and products of plasma chemical reactions from one process module into the other process modules through the high-vacuum transport module.
Introduced defectiveness of microelectronic products in the form of fine particles was investigated sufficiently in detail in the 90’s of the last century, which was reflected in many publications, including [5]. There were studies of FP distribution on the semiconductor wafer surface after pumping of vacuum, including sluice chambers, pumping air into them for depressurization, and also after wafer transfer in vacuum process chambers with the help of, for example, conveyors. Figure 2 shows the results of the induced defect measurements on the semiconductor wafer surface in the 01NI-7-015 gateway-type device developed by RIPMM, Zelenograd.
Molecular contamination of semiconductor wafers with formed nanostructures in vacuum chambers of technological equipment can appear, firstly, during their depressurization from CR atmosphere, and consist of organophosphates, silicones, cresols, hydrocarbons and other compounds [3], secondly, emissions from organic materials and friction pairs, desorption of water vapors from the walls of a vacuum chamber, gas leakage through mobile and fixed contacts, thirdly, corrosion products (about 100 Å/30 days) and oxidation of the technological equipment surface and the walls of the vacuum chamber. The intensity of molecular contamination, e.g. by phosphorus, can be 2.5 . 1011 atoms/cm2 per hour [3].
According to SEMI F21-951, molecular contamination in vacuum can include condensable compounds (CC) and trace metals (TM). GOST R ISO 14644-9-2013 characterizes surface roughness classes according to particle concentration, which define maximum permissible concentration of particles of certain sizes on the semiconductor wafer surface. Measurement of mass concentration of surface contaminants is based on determining characteristic wavelengths of the main functional groups of contaminants and signal power. With the help of modern methods it is possible to monitor contamination at the level of 0.1 ng/cm2 [3].
Traces of metals on the semiconductor wafers surface in a vacuum can theoretically appear as a result of sublimation of metal armature atoms. Sublimation is a multi-step process that requires additional thermal energy. When it is supplied, particles of solid material migrate to the solid phase surface from the highest bond strength state to a state with lower bond strength and then to the gas phase. At the same time the particles desublimate from it. The maximum sublimation rate and desublimation processes in a vacuum can be calculated from the Hertz-Knudsen equation:
(1)
where Nи is the number of evaporated (sublimated) atoms or molecules, t is time, s, A is the evaporation (sublimation) area, m2, aи is the evaporation coefficient (for pure materials aи = 1), m is mass of an evaporated (sublimated) atom or molecule, kg, Tи is the evaporation temperature, K.
The saturated vapour pressure over the surface of a solid body is described by the Clapeyron – Clausius equation:
, (2)
where pнас is saturated vapour pressure of material to be vaporised, Pa; T is material temperature, K; H is enthalpy of gas (г) and liquid (ж), kcal/kmol; V is volume of gas (г) and liquid (ж), m3 (Vг>>Vж); DH is heat of vaporisation, kcal/kmol.
However, the saturated vapour pressure at temperatures below the evaporation temperature is very low. For example, the saturated vapour pressure of a metal, e.g. neptunium, at room temperature in a vacuum is [6]:
lgpнас= 5,1 – 2,06 . 104/T, (3)
where T is the absolute temperature, K.
At T = 1,000 K the saturated vapour pressure is pнас = 10–15 Pa, and at room temperature 293 K the saturated vapour pressure is only pнас = 10–65 Pa. At these pressures the speed of sublimation processes is approximately 107 and 10–39 atoms/(m2s), respectively. It follows that at room temperature contamination of micro- and nanostructures with atoms and molecules by structural materials of vacuum technological equipment can be disregarded.
Introduced defects in the form of atoms and molecules in structural materials can have a marked effect on performance of nanostructures, up to and including rejection, as a result of tribodesorption [4] from intra-cavity friction pairs.
As the experience of design and operation of vacuum transport and loading modules showed, the main sources of contamination in the form of chemically active gases and fine particles are friction pairs of mechanisms, guides, motion inputs, located in high and ultra-high vacuum [7].
Information on tribodesorption in vacuum from various steels, polymeric materials, minerals, solid lubricants, soft metals (silver, lead) is accumulated, with tribodesorption having both thermal and athermal (at low loads and friction speeds) character. The compositions of polypropylene, ethylene propylene, chlorobutylene and fluorocarbon rubbers stand out in the friction of synthetic rubbers. Low molecular weight compounds such as methane, mono and carbon dioxide, non-polymerised monomers and volatile components of impurities are found in the mass spectrum.
Tribo-emission phenomena include various physical and chemical processes occurring in and around the contact zone of rubbing bodies and leading to emission of atoms and molecules out of the bodies themselves, occluded gases and nanoparticles [5]. These properties of tribo-emission phenomena made the basis for a number of developments of the fundamentally new technological processes, materials and methods with given properties, including:
- special tribological coatings with self-repairing ability and adaptable to operating conditions;
- new lubricants for vacuum and space systems and particularly clean environments;
- a new method for analysing the content and distribution of gases in materials and coatings.
Two types of solid-lubricant coatings based on molybdenum disulphide were developed for use in UHV equipment by RITI Ryazan in 1980s: chemical-thermal coating "Dimolit-4" developed by All-Russian Scientific Research Institute optical-physical measurements and ion-plasma coating "IPN MoS2" developed by Mechanical Engineering Research Institute of the Russian
Academy of Sciences. However, in a spectrum of gas emissions from friction pair with "Dimolit-4" there were traces of sulphur and its compounds that turned out to be unacceptable for processes of molecular beam epitaxy as it led to overlegging of GaAs-based heterostructures. Therefore, the friction assemblies of manipulators and slideways coated with MoS2 IPN were taken into use and no traces of sulphur and its compounds were detected in their gas emission spectrum even at 773 K (Fig.3).
In research of brought defectiveness from units and mechanisms in vacuum chambers of the process equipment, in particular, from sliding bearings with solid lubricant coating (SLC) on the basis of molybdenum disulphide, applied by vacuum ionic-plasma method, traces of metals and sulphur on surface of control plates which have been placed in immediate proximity of a sliding bearing (Fig.4) were found. The quantity and composition of these traces varied with operating time, expressed as the total number of revolutions of the bearing shaft.
CONCLUSIONS
Thus, the analysis of causes and sources of the introduced defects in micro- and nanoelectronics products, as well as occurrence and spread of molecular contaminants in cluster-type vacuum processing equipment show that:
- For microstructures with dimensions of the order of 1 µm, the main causes of rejects due to introduced defects are fine particles entering vacuum chambers with process gas flows, particles of films and layers being deposited on and peeled off the walls and tools and particles generated by the mechanisms operating in vacuum;
- For nanostructures smaller than 100 nm (down to 5–10 nm), molecular contamination in the form of degradation products of polymer construction materials and organic compounds, outgassing products of rubber compounds, etc., becomes critical;
- Atoms and molecules of chemically active gases such as oxygen, methane, carbon monoxide and carbon dioxide, as well as sulphur compounds, traces of metals and oxides negatively affecting the characteristics of formed nanostructures appear on semiconductor wafers as a result of high temperature and friction effects (tribodesorption) on materials of in-cell devices and mechanisms as well as their wear;
- The cause of defects in nanostructures processed in cluster-type equipment are atoms and molecules of gaseous reagents and products of plasma chemical reactions diffusing from one process module to another through transport and loading and intermediate modules.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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