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12наиболее обоснованный способ осреднения - способ осреднения по массовому расходу. При использовании этого способа величины интегральных характеристик осредненных канонических воздушных и газовых потоков О, О , Е , I * , I , и
их статическое давление сохраняются равными соответствующим параметрам действительных неравномерных потоков.
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Дружинин, Л. И. Швец, Н. С. Малинина // Двигатели авиационные и газотурбинные: Руководящий техн. материал авиационной техники. 1983. 1667 -83. 68 с.
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8. Кофман, В. М. Экспериментальное определение потерь и неравномерности полного давления в радиально-осевом входном устройстве ВГТД / В. М. Кофман, Р. Г. Ахметов // Вопросы авиационной науки и техники. Серия Авиационное двигателе-строение : науч.-техн. сб. ЦИАМ. 1992. Вып.4. С. 59.
9. Кофман, В.М. Методы оценки показателей эффективности работы узлов ГТД по результатам измерений параметров неравномерных воздушных и газовых потоков / В. М. Кофман // Наука и технологии. Труды XXVIII Российской школы. М.: РАН, 2008. Т.1, С. 108-120.
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11. Кофман, В. М. Свид. РФ о гос. рег. программы для ЭВМ № 2013661093. Осреднение параметров неравномерных воздушных и газовых потоков при обработке результатов испытаний газотурбинных двигателей и их узлов; Заявл. 03.10.2013; Зарег. в Реестре программ для ЭВМ 28.11.2013.
MAGNETRON SPUTTERING OF METALS IN THE PRESENCE OF JET GASES
Dubonosov V.
The Senior teacher Krichkovskaya L.
Doctor of Biology, the Full Professor of the Department of Organic Synthesis and Nanotechnologies, Kharkiv
Petrova I.
Doctor of Technology of the Department of Organic Synthesis and Nanotechnologies/
Abstract
Specificities of magnetron sputtering of metals in the presence of jet gases are represented in the paper. Oxygen or atmospheric air in the environment of inert gas argon was used as jet gases. Influence effects of quantity of oxygen and also atmospheric air in the gas mixture on discharge voltage and sedimentation rate of oxides during sputtering were analyzed.
Keywords: magnetron sputtering.
Problem of modern material technology is creating of new materials with multipurpose coatings which find wide application in various fields of technics (power engineering, microelectronics, aircraft and others) [1-3].
Today the method of magnetron sputtering is widely applied for drawing various industrially significant (attrition-resistant or protective) coatings in millimeter range, as well as for obtaining of complex, multilayer constructions with layer thickness in range of several tens of nanometers [4].
Magnetron sputtering is characterized by high repeatability and stability of precipitated coatings both in sputtering velocity and performances of obtained coatings. This feature of magnetron systems as opposed, for example, to electron beam evaporation allows to gain multilayer constructions complex enough and without systems monitoring thickness of a precipitated coating. Due to high energy efficiency and ionization degree magnetron sputtering allows to achieve obtaining of "dense" layers of a substance, for example, oxides with
high refraction index, on a cold substrate that has essential value for materials of substrates which can't be exposed to heating [3].
In the paper specificities of magnetron sputtering of titan and also silicon in presence of jet oxygen and atmospheric air are presented.
Development of technological modes for drawing of titan oxide coatings gained by sputtering of a metal target in the environment of jet gas (oxygen) and in the environment of atmospheric air was provided in vacuum equipment of the "Bulat" type.
Before process starting the vacuum chamber was pumped out until residual pressure not more than 5 • 103 Pa, working pressure was 2,5 10-1 Pa. Feeding of working gases was provided by means of two inlet valves with stabilized controllers of the gas rate flux. The device for coat drawing was represented by planar magnetron with size of the cathode-target 600*100 mm. The flux rate of working gases was regulated by means of the controllers. Pressure was measured in the chamber by means of vacuum gauges. Before coat drawing the substrate surface was cleaned with alcohol dissolved in distilled water. After placing substrates into the chamber their working area was processed with high-voltage source of ions in the environment of argon containing 5% of oxygen.
Working pressure 0,25 Pa corresponded to the optimum for stable magnetron work as reduction of working pressure can lead to unstable work of magnetron, and pressure increase does not influence operating conditions of a magnetron and can lead only to excessive flux rate of working argon gas.
Results and discussion
At obtaining of coatings by magnetron sputtering method, film growth occurs as the result of sublimation of the target atoms which precipitate both on a substrate surface and on fittings of vacuum equipment. To make the working pressure enough for stable magnetron operation, it's necessary to use inert working gas of high purity such as argon as a rule. The sputtering of metal targets in the environment of pure argon will lead to formation of metal film which characteristics will depend in great degree on purity of residual vacuum. Presence of various jet gases impurities in residual vacuum, such as oxygen or nitrogen, which can react with volatilized stream of metal, leads to formation on substrate
surface a coating containing compounds of the volatilized target atoms with these gases.
Obtaining of a film in the oxygen environment.
If it's necessary to gain metal oxide on a substrate surface into the chamber jet gas oxygen is fed through separate inlet valve. Process of target sputtering is changed into reactive process with formation of chemical compounds of volatilized substance with oxygen on a substrate, vacuum fittings and, the most important, on a surface of volatilized target that cardinally changes modes of magnetron sputtering. Formation of oxide compounds on a surface of magnetron target causes essential decrease in velocity of target sputtering that leads to change in rate of inert to reactive gases inside the working chamber.
Oxide layer forming on a target surface during jet sputtering has lower sputtering coefficient than pure metal. In process of increase in quantity of supplied oxygen into the working chamber on a target surface thickness of the formed oxide layer grows that causes reduction of film growth rate on a substrate and fittings of the vacuum chamber. Together with reduce in film growth rate, the uptake of fed oxygen becomes lower that will lead to its excess and full coating of a target surface with oxide film [5].
Under operation of magnetron sputtering system in current stabilization mode, it's possible to monitor the condition of a target surface and its covering degree with oxide layer by change of discharge voltage. At sputtering of titanic target the discharge voltage (at current stabilization) will grow with increase of quantity of submitted oxygen and growth of oxide layer on a target surface, that is related to secondary emission coefficient of pure metals and oxides forming on target surfaces (fig. 1, 2).
Reduce of oxygen supply influences when on a target surface the sites free from oxide layer start to form owing to which rate of target sputtering and film sedimentation on a substrate and chamber fittings, that causes increase of jet gas uptake with precipitating film and decrease in its residual pressure in the chamber, that causes, in its turn, drastic transition from a target surface coated with layer of a chemical compound to almost pure metal surface.
V 470
420
320
270
—- 2
X
\ 15
15
Flux rate of oxygen, cm3
Fig. 1 Influence of the 02 flux rate in the gas mixture on discharge voltage at sputtering of silicon (1), TiN (2)
and TiCN (3).
S. nm/min 10.0
7.5
5.0
2 «
> v -1
N
<2
--3
\
\
\
V\
V y
6 Î 1 2 15
Flux rate of oxygen, cnr
Fig. 2 . Influence of the oxygen flux rate in the gas mixture on sedimentation rate of TiN (1), TiCN (2
The range of jet gas flux rate between two extreme states of a target - (pure metal surface and completely oxide-coated one) is the range within which the process mode is labile and characterized by abrupt transition from oxidized target surface containing films with too low sedimentation rate to the metal target surface free from oxide compounds with formation of almost metal films with high drawing rate, however required operating conditions for obtaining of high-quality optical layers lie namely within this gap.
State transition, for example, of titanic metal target during jet sputtering from metal surface to the surface coated with dielectric layer can be accelerated sharply at formation of oxide layer on a small site of a target that can be caused by non-uniform oxygen distribution near target surface. It imposes additional requirements
to the uniform oxygen delivery - to obtain not only uniform coating on a substrate surface, but also to provide conditions for maintenance of uniform formation of oxide layer on the whole target surface.
Choice for modes of oxygen delivery for uniform formation of oxide layer on a target surface depends on its area - the more is the area, the more difficult is to support stable the same quantity of oxygen near its surface and, accordingly, formation of oxide layer. For narrow enough and difficultly controllable range of working oxygen pressure to achieve optimum drawing rates and performances of gained coatings, magnetron systems (using targets of large areas) need for necessity of maintenance of uniform oxygen quantity near their surface to provide uniform growth of oxide layer and to
prevent formation of the sites completely coated with compounds [6].
Sputtering in the environment of air
Moving from oxygen use to atmospheric air leads to increase in the volume content of jet gas within working space of the chamber due to presence of elements in air other than oxygen. To maintain optimum state of a target the difference in flux rate of pure oxygen and air makes 1,5-2 times. Thus increase in quantity of working gas leads to its uniform distribution near target surface, and low oxygen content allows to carry out the control of formation of oxide layer on a target surface more uniformly. Thus, use of air as oxygen-containing mixture allows to check state of a target during its staying between two stable states - change of air pressure and other process conditions makes not such an essential impact as under operation in pure oxygen.
When the sites free from oxide layer start forming on a target surface, rates of target sputtering and of film sedimentation on a substrate and chamber fittings grow, that causes increasing uptake of jet gas with precipitated film and decrease in its residual pressure inside the chamber. After a while this can cause sharp transition from a target surface coated with layer of chemical compound to almost pure metal surface. Operating conditions in the range between two states of a tar-get -completely metal surface and completely oxide-coated - are achieved at the highest rates of sedimentation of optically transparent films under stable operation of a magnetron. However, providing of the magnetron operating mode within the range between two these states by control of oxygen stream inlet is rather difficult, because even small changes of process conditions lead to fast covering of a target surface with layer of a chemical compound and to transition of a target surface into state of being coated with dielectric layer or to fast clearing of a target surface from layer of a chemical compound and its transition into pure metal state. Thus, the range of the flux rate of jet gas between two extreme states of a target is the range within which the process mode is labile and characterized by abrupt transition from oxidized target surface obtaining films with insignificant sedimentation rate to metal target surface cleared of oxide compounds with formation of almost metal films with high drawing rate, however namely within this gap
operating conditions required for obtaining of high-quality optical layers lie.
Conclusions
In the paper specificities of magnetron sputtering of aluminium and titan in the environment of jet oxygen and air gases are presented. It has been shown that presence of jet gas in the working chamber at the moment of target sputtering leads to formation of oxides including on surface of a sprayed target that essentially reduces evaporation rate of a substance and leads to unstable work of a magnetron. The influence of oxygen replacement to air on modes of producing of oxide coatings was discussed. Use of air as jet gas for obtaining of optically transparent coatings is possible in case of higher affinity of metal to oxygen. If occurring 1-3% absorption does not render essential influence on required performances of a coating, use of air as jet gas allows to monitor state of a target more smoothly during magnetron sputtering, that makes the main effect on characteristics and drawing rates of a coating.
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