Vacuum metallization - technology description, device and reviews. Vacuum deposition of metals

Mari State Technical University

Department of design and production of radio equipment

Vacuum coating

EXPLANATORY NOTE

to the course work on the discipline

Fundamentals of solid state physics and microelectronics

Developed by: student of the EVS-31 group

Kolesnikov

Advised: Associate Professor

Igumnov V.N.

Yoshkar-Ola 2003

Introduction

1. Thermal vacuum spraying

1.1 Resistive sputtering

1.2 Induction spraying

1.3 Electron beam sputtering

1.4 Laser deposition

1.5 Arc spraying

2. Sputtering by ion bombardment

2.1 Cathodic sputtering

2.2 Magnetron sputtering

2.3 High frequency spraying.

2.4 Plasma ion sputtering in a non-self-sustaining gas discharge

3. Technology of thin films on orienting substrates

3.1 Mechanisms of epitaxial growth of thin films

3.2 Molecular beam epitaxy

Conclusion

Literature

INTRODUCTION

Thin films deposited in vacuum are widely used in the production of discrete semiconductor devices and integrated circuits (ICs).

Obtaining high-quality and reproducible in terms of electrical parameters thin-film layers is one of the most important technological processes formation of structures as discrete diodes and transistors, as well as active and passive elements of the IC.

Thus, the reliability and quality of microelectronic products, the technical level and economic indicators of their production depend to a large extent on the perfection of technological processes for the deposition of thin films.

Thin film technology is based on complex physical and chemical processes and the use of various metals and dielectrics. So, thin-film resistors, capacitor electrodes and interconnections are made by deposition of metal films, and interlayer insulation and protective coatings- dielectric.

An important stage is the control of the parameters of thin films (speed of their deposition, thickness and its uniformity, surface resistance), which is carried out using special devices, as in the performance of individual technological operations and at the end of the whole process.

The methods of ion-plasma and magnetron sputtering are widely used in modern microelectronics. High deposition rates and the energy of atoms incident on the substrate during deposition make it possible to use these methods to obtain films of various compositions and structures, and, in particular, for low-temperature epitaxy.

Currently, there is considerable interest in research in this area.

This term paper is a review of the main methods of deposition and spraying in vacuum, physical and chemical processes, as well as a description and operation of the installations used in these methods.

The process of applying thin films in a vacuum consists in creating (generating) a flow of particles directed towards the treated substrate, and their subsequent concentration with the formation of thin film layers on the surface to be coated.

Various modes of ion treatment are used to modify the properties of a solid surface. The process of interaction of the ion beam with the surface is reduced to the flow of interrelated physical processes A: condensation, spraying and embedding. The dominance of one or the other physical effect is determined mainly by the energy E 1 of the bombarding ions. When E 1 =10-100 eV, condensation prevails over sputtering, so the deposition of the coating takes place. As the ion energy increases to 104 eV, the sputtering process begins to predominate with the simultaneous introduction of ions into the metal. A further increase in the energy of the bombarding ions (E 1 >10 4 eV) leads to a decrease in the sputtering coefficient and the establishment of an ion implantation mode (ion doping).

The technological process of applying thin-film coatings in vacuum includes 3 main stages:

Generation of a stream of particles of the deposited substance;

Transfer of particles in rarefied space from the source to the substrate;

Deposition of particles upon reaching the substrate.

There are 2 methods of applying vacuum coatings, which differ in the mechanism of generation of the flow of deposited particles: thermal spraying and sputtering of materials by ion bombardment. Evaporated and sputtered particles are transferred to the substrate through a vacuum medium (or atmosphere reactive gases, thus entering into plasma-chemical reactions). To increase the degree of ionization of the deposited substance flow, special sources of charged particles (for example, a hot cathode) can be introduced into the vacuum chamber or electromagnetic radiation. Additional acceleration of the movement of ions to the treated surface can be achieved by applying a negative voltage to it.

The general requirements for each of these methods are the reproducibility of the properties and parameters of the obtained films and the provision of reliable adhesion (adhesion) of films to substrates and other films.

For understanding physical phenomena that occur during the deposition of thin films in vacuum, it is necessary to know that the process of film growth on a substrate consists of two stages: initial and final. Let us consider how deposited particles interact in vacuum space and on a substrate.

Particles of matter that have left the surface of the source move through vacuum (rarefied) space at high speeds (of the order of hundreds and even thousands of meters per second) to the substrate and reach its surface, giving it part of their energy upon collision. The fraction of the transferred energy is the smaller, the higher the substrate temperature.

While retaining a certain excess of energy, the substance particle is able to move (migrate) over the surface of the substrate. When migrating over the surface, the particle gradually loses its excess energy, tending to thermal equilibrium with the substrate, and the following may occur. If the particle loses its excess energy on the way, it is fixed on the substrate (condenses). Having met another migrating particle (or a group of particles) on the way, it will enter into a strong bond (metallic) with it, creating an adsorbed doublet. With a sufficiently large association, such particles completely lose the ability to migrate and are fixed on the substrate, becoming the center of crystallization.

Around individual centers of crystallization, crystallites grow, which subsequently coalesce and form a continuous film. The growth of crystallites occurs both due to particles migrating over the surface and as a result of direct deposition of particles on the surface of crystallites. It is also possible to form doublets in a vacuum space upon collision of two particles, which are eventually adsorbed on the substrate.

The formation of a continuous film ends First stage process. Since from this moment on, the quality of the substrate surface ceases to affect the properties of the deposited film, the initial stage has crucial in their formation. At the final stage, the film grows to the required thickness.

Under other constant conditions, an increase in the substrate temperature increases the energy, i.e. the mobility of adsorbed molecules, which increases the probability of meeting migrating molecules and leads to the formation of a film with a coarse-grained structure. In addition, with an increase in the density of the incident beam, the probability of the formation of doublets and even polyatomic groups increases. At the same time, an increase in the number of crystallization centers contributes to the formation of a film with a finely crystalline structure.

The rarefied state of the gas, i.e. a state in which the pressure of a gas in a certain closed hermetic volume is lower than atmospheric pressure is called a vacuum.

Vacuum technology takes important place in the production of IC film structures. To create a vacuum in working chamber gases must be evacuated from it. The ideal vacuum cannot be achieved, and in evacuated working chambers technological installations there is always a certain amount of residual gases, which determines the pressure in the evacuated chamber (depth, or degree of vacuum).

Essence this process deposition of thin films consists in heating the substance in a vacuum to a temperature at which, increasing with heating, kinetic energy atoms and molecules of a substance becomes sufficient for them to detach from the surface and spread in the surrounding space. This occurs at a temperature at which the pressure of the substance's own vapors exceeds by several orders of magnitude the pressure of the residual gases. In this case, the atomic flow propagates in a straight line and, upon collision with the surface, evaporated atoms and molecules condense on it.

The evaporation process is carried out according to the usual scheme: solid phase - liquid phase - gaseous state. Some substances (magnesium, cadmium, zinc, etc.) pass into the gaseous state, bypassing the liquid phase. This process is called sublimation.

The main elements of the installation vacuum deposition, a simplified diagram of which is shown in Fig. 1, are: 1 - a vacuum cap made of of stainless steel; 2 - damper; 3 - pipeline for water heating or cooling of the cap; 4 - needle leak for feeding atmospheric air into the camera; 5 - substrate heater; 6 - substrate holder with a substrate on which a stencil can be placed; 7 - sealing gasket made of vacuum rubber; 8 - an evaporator with a substance placed in it and a heater (resistive or electron beam).

The main functional purpose of the vacuum unit is to create and maintain a technical vacuum, which is achieved by pumping the mixture out of the system. Vacuum plants are widely used in the metallurgical, textile, chemical, automotive, food and pharmaceutical industries. The main parts of the installation include a pump, a panel with filters, a camera control unit.

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The use of vacuum plants

Vacuum installations can be used for laboratory research. Included in microscopes, chromatographs, evaporators and filtration systems. For these purposes, an aggregate that will not occupy large area. The performance of such units is not in the first place. Most often it is a forevacuum or turbomolecular pump. When working with aggressive gases the best way- diaphragm pump.

Vacuum systems play an important role in test equipment. They provide the necessary rate of climb for aircraft. In order for the takeoff or landing process to proceed successfully, it is necessary to ensure fast speed pumping.

Dry pumps are used for semiconductor and sputtering vacuum installations, for the deposition of materials. Perfect for creating ultra-high vacuum. These include turbomolecular and cryogenic pumps.

In the metallurgical industry, pumps are actively used, which have sufficient throughput. They must be wear-resistant, as there is dust and dirt in the system. Perfectly cope with tasks in the industrial sphere claw and screw pumps performing forevacuum pumping. Diffusion pumps may be used.

The 976A vacuum unit is a laboratory type. It is designed to determine the water saturation of asphalt concrete in the laboratory. The working volume of the chamber is 2 liters. The vacuum unit is capable of creating a final vacuum of 1x10-2.

Elements of vacuum installations

Vacuum installations create and maintain a working vacuum in a certain hermetic volume. As a rule, elements that have the same purpose in various types installations. They include a control unit with a control stand, a vacuum unit, a hood device, cooling systems and a vacuum system and a bell lift drive. The vacuum system consists of a pump of any type, a vacuum unit, pipelines, a vacuum gauge and an electromagnetic leak.

Busch vacuum systems

Busch vacuum systems are, first of all, high-quality vacuum pumps. The company manufactures units such as the R5 rotary vane vacuum pump. It is of high quality and performance. The limiting pressure of the unit is from 0.1 to 20 hPa. The medium pumping speed reaches 1800 m3/h. Secondly, these are lobe pumps and compressors. One of these is the Mink model. Widely used in industry. Especially where it is necessary to maintain a constant level of vacuum. The limiting pressure is from 20 to 250 hPa. The pumping speed can reach 1150 m3/h.

Vacuum installations Bulat

One example of installations for applying thin-film coatings is the Bulat model. It produces the application of the film in a vacuum-plasma way. Can be coated with other electrically conductive materials. These are molybdenum, zirconium, nitride and carbonitride. Initially, the model was developed for coating metal dentures. The installation includes a pumping station, a fore vacuum tool and related electrical equipment.

Other manufacturers of vacuum systems

Agilent Technologies is one of the largest manufacturers of vacuum equipment. The enterprise launched the production vacuum pumps, leak detectors, vacuum gauges, vacuum oils and other components of systems.

Air Dimensions Inc. specializes in the mass production of high quality diaphragm pumps that sample corrosive gases, as well as dry diaphragm compressors.

Edwards manufactures laboratory and industrial vacuum technology. Among them are vacuum pumps, vacuum gauges and more. auxiliary equipment. Famous for release a wide range different types of pumps.

Vacuum coating plants

With the help of the installation of vacuum deposition (UVN) coating is made various parts coatings that perform conductive, insulating, wear-resistant, barrier and other functions. This method is the most common among other microelectronics processes in which metallization is used. Thanks to such installations, it is possible to obtain antireflection, filtering and reflective coatings.

Aluminum, tungsten, titanium, iron, nickel, chromium, etc. can be used as coating materials. If necessary, acetylene, nitrogen and oxygen can be added to the medium. Activation chemical reaction during heating, ionization and dissociation of gas. After the coating procedure, additional processing not required.

The UVN-71 P-3 installation is capable of testing technological spraying. It is involved in the mass production of various film circuits. With its help, thin films are produced under high vacuum conditions. The applied method is resistive evaporation of metals.

Vacuum unit UV-24 performs laboratory tests of asphalt concrete. Helps to determine its quality. Distinctive feature of this unit - the presence of two evacuated tanks, which are interconnected.

Magnetron sputtering

In magnetron sputtering, a thin film is deposited by means of cathode sputtering. Devices using this method are called magnetron sputters. This installation can spray many metals and alloys. When used in various working environments with oxygen, nitrogen, carbon dioxide, etc. films with different compositions are obtained.

ion sputtering

The principle of operation of the ion installation in vacuum is the bombardment of solids by ions. When the substrate is placed in a vacuum, atoms hit it and a film is formed.

Other spraying methods

Vacuum deposition can be carried out using batch and continuous equipment. Batch plants are used for a certain number of workpieces. In mass or serial production, continuous installations are used. There are single and multi-chamber types of spraying equipment. In multi-chamber installations, the deposition modules are arranged in series. In all chambers, a certain material is sprayed. Between the modules there are lock chambers and a transporting conveyor device. They carry out the operations of creating a vacuum, evaporation of the film material, transportation separately.

Vacuum units

Vacuum water ring pumping unit type VVN 12 extracts air, non-aggressive gases and other mixtures that are not cleaned from moisture and dust. The gas entering the plant does not require purification.

The AVZ 180 vacuum spool unit is universal, has good indicator limiting residual pressure, low weight and is characterized by speed and compactness.

Technical characteristics of the AVZ 180 vacuum spool unit.

The AVR 50 vacuum unit is capable of pumping air, non-aggressive gases, vapors and vapor-gas mixtures from vacuum spaces. It is not intended for pumping the above compositions from one container to another. It consists of two pumps: NVD-200 and 2NVR-5DM.

THEORETICAL DATA

The rapid development of the production of microelectronic devices (MEDs) in the last decade has led to the creation of working equipment that would have the least possible effect on the process of forming thin films and would allow controlling their parameters. As a result, there is currently big choice vacuum plants, component parts, as well as materials and methods of installation that allow solving complex technological problems in the manufacture of MEP.

The process of obtaining thin films takes place in the vacuum environment of the cap device of the vacuum unit. Two principles can be used to reduce the pressure in the cap device. In the first, the gas is physically removed from the vacuum chamber and thrown out. An example of this mode of action are mechanical and steam jet, steam oil pumps. Another pumping method is based on the condensation or entrapment of gas molecules on some part of the surface of the vacuum chamber without removing the gas to the outside. On this principle, cryogenic, getter and getter - ion pumps are designed.

A quantitative measure of the transfer or absorption capacity of a gas by a pump is its capacity (Q). The performance depends on the pressure in the evacuated device and is defined as the amount of gas that flows through the suction pipe of the operating pump per unit time at t = 20 0 C:

Q = fp · P,

where Fp – pumping speed, l/s; P is the pressure of pumped gases, mm Hg. Art.

Another parameter that characterizes the operation of the pump is the pumping speed Fp, which is defined as the ratio of the pump performance to the partial pressure of a given gas near the pump inlet:

Fp = Q/P

Most vacuum pumps have an almost constant pumping speed over several orders of magnitude of gas pressure. Above and below this area, it drops sharply, so pumping with this kind of vacuum pump becomes inefficient.

When choosing a pump for a vacuum installation, it must be remembered that the pumps themselves, under certain conditions, are sources of residual gases in the vacuum chamber. different types pumps differ greatly from each other both in the amount and in the nature of the emitted gases. Particularly harmful are traces of vapors of organic compounds due to the working fluids used in pumps.

The main parameters of the pump also include the ultimate pressure Pg - this is the minimum pressure that can be obtained using a vacuum pump if the pump itself does not emit gases.

For rotary pumps, Pg depends on the "bad volume" of the pump (that is, that part of the compression chamber from which the gas coming from the pumped object cannot be displaced) and the vapor pressure of the substances, such as oil, used for sealing. For steam jet pumps, Pg depends on the speed of the steam molecules in the nozzle, the speed of the gas molecules in the pumped volume, and the molecular weight of the gas.

Permissible external (inlet) pressure is the maximum allowable pressure gas at the outlet of the pump, that is, a pressure at which the pumping speed is still equal to the maximum value. For foreline pumps that compress gas to atmospheric pressure, the allowable outlet pressure is equal to atmospheric pressure, for high-vacuum pumps, the allowable outlet pressure is equal to the foreline pressure.

The pumping process of a cap device with a volume V and an initial pressure Po performed by any pump with a pumping speed Fp and a limiting pressure Pg can be described using a differential equation derived on the basis of the Boyle-Mariotte law. The pressure drop over time is described by the following equation:

DP/dt = Fp/V(P - Pg) (1)

The solution of this differential equation will give a characteristic of the change in time t of the pressure P in the evacuated vessel.

In the case of an “ideal” pump, Fp = Fp max = const, the pump characteristic P is a straight line. Pumping speed Fp all technical pumps unlike “ideal” ones, it depends on pressure , and therefore, the time characteristics of pressure changes are usually obtained not by calculation, that is, by integrating equation 1, but are determined from the experiment.

VACUUM SPRAYER INSTALLATION DEVICE

The vacuum unit is designed to create and maintain a vacuum in the working volume (cap device). The installation consists of a vacuum unit and a control rack. Structurally, the vacuum block (Fig. 1.1) is a body 1, on which a cap device 2 is installed. A vacuum system, a cooling system, gas system and hydraulic hood lift. In the cap device, the working pressure of gases is set from 1·10 -3 to 5·10 -4 mm Hg. Art. and the materials of the sputtered target are deposited on the substrate using a sputtering device.

The vacuum system of the installation (Fig. 1.2) consists of a mechanical pump NVR-5D and a vacuum unit VA-2-3R-N, a valve box, an electromagnetic leak, pipelines and sensors for measuring pressure.

Fig.1.1. Appearance installations: 1 - housing; 2 - cap; 3 - system

vacuum; 4 - cooling system; 5 – mixing mechanism;

6 - spray device; 7 - valve box; 8 - vacuum gauge

The pipelines of the vacuum system connect it to a mechanical pump, a cap device and an outlet pipe of a steam-oil pump. The valve - leak valve is designed to depressurize the working volume.

The pumping means of the vacuum system of the installation are controlled by the control unit vacuum system.

To start a mechanical pump, you must turn on the appropriate toggle switch on the control panel. In this case, a magnetic starter is activated, which with one normally open contact becomes self-locking, and with three other contacts it turns on the electric motor for driving the electromechanical pump in the vacuum unit.

Fig.1.2. Vacuum installation system: 1 - mechanical pump NVR-5D;

2 - the lower handle of the valve box; 3 - electromagnetic leak;

4 - the upper handle of the valve box; 5 - valve box;

6 - thermocouple; 7 - manometric sensor; 8 - valve-leak;

9 - shutter; 10 - vacuum unit type VA-2-3RM; 11 - pipelines

To turn on a mechanical pump, you must turn on the corresponding toggle switch on the control panel. In this case, a magnetic starter is activated, which

one normally open contact becomes self-locking, and the other three contacts turn on the electric motor for driving the electromechanical pump in the vacuum unit

Turning on the heater of the steam oil pump EN-1 is possible only after turning on the mechanical pump, since the magnetic starter is powered through the normally open contact of the magnetic starter, while the signal lamp lights up on the control panel.

With the help of the valve box 2, all switching of the vacuum system necessary for the operation of the unit is provided. The valve box control is placed on the front post of the unit (Fig.1.1). When the upper handle is pulled out, the mechanical pump pumps out the working volume of the cap device, when the lower handle is pulled out, the cavity of the steam-oil pump is pumped out.

The electromagnetic valve is located on the valve box 5 and is designed to let atmospheric air into the pipeline of the mechanical pump.

The inclusion of the electromagnetic valve is made by the switch "leak" located in the control unit of the vacuum system. The valve only works if the mechanical pump is switched off. When the lower handle of the valve box is extended, atmospheric air is admitted into the cavity of the oil-steam pump by the same leak valve. Structurally, the leak valve is a solenoid, the end part of which is made in the form of a sealing valve. The inlet has a porous glass filter that traps dust particles from the air.

Vacuum control is carried out by a VIT-2 vacuum gauge from sensors connected to it by the “Sensor selection” switch.

When the “Sensor Selection” switch is set to “1”, the vacuum gauge measures the low vacuum in the foreline. When set to position “2”, the high vacuum in the cap device is measured using an ionization pressure sensor, when switched to position “0”, both sensors are switched off.

Mechanical vacuum pump. A rotary vane pump with an oil seal is designed for pumping air, chemically inactive gases and vapor-gas mixtures that do not affect the construction materials and the working fluid. Such pumps can normally pump out condensable vapors and vapor-gas mixtures of acceptable concentration.

The process of pumping gases in rotary vane pumps is based on the mechanical suction of gas due to the periodic increase in the working chamber.

The principle of operation of such a pump is illustrated in Figure 1.3 and occurs in the following way.

Fig.1.3. Rotary vane pump: 1 - cylinder; 2 - rotor; 3 - blades;

4 - spring; 5 - valve; A and B - cavities

In cylinder 1, in the direction indicated by the arrow, an eccentrically mounted rotor 2 rotates. Blades 3 are placed in the slot of the rotor, which are pressed against the spring 4 inner surface cylinder. When the rotor rotates, the blades slide along the inner surface of the cylinder, the cavity formed by the cylinder, the rotor and the blades is divided into cavity A and cavity B.

When the rotor rotates, the volume of cavity A periodically increases and gas from the evacuated system enters it; the volume of cavity B periodically decreases and compression occurs in it. The compressed gas is expelled through valve 5. The seal between the suction chambers A and compression chambers B is carried out by an oil film. This is how a single-stage pump works. In a two-stage version, the outlet of the first stage is connected to the inlet of the second stage, and the gas is released into the atmosphere through a valve.

All rotary vane pumps have a similar design, but differ in size, which determines the pumping speed of the pumps. The design of a single-stage rotary vane pump is shown in Figure 1.4.

When connecting the pump to a vacuum system, the pipeline must have a short length and a large diameter, not less than the diameter of the pump inlet. Failure to comply with these conditions leads to a decrease in the pumping speed of the pump.

The mechanical rotary vane pump VN-05-2 used in the installation has the following main performance characteristics:

Pumping speed 0.5 l/s

Residual pressure 5·10 -3 mm Hg. Art.

High vacuum steam oil pump. The high-vacuum steam-oil pump H-05 is designed for pumping air, non-aggressive gases, vapors

and steam-gas mixtures.

The pump must only be operated in conjunction with an auxiliary pre-discharge pump. The location of the steam oil pump in a high vacuum system is shown in Figure 1.5.

Widely used three-stage oil-steam pumps consist of the following main units: a casing, a steam line, an electric heater, an oil deflector and a hydraulic relay. The design of the pump is shown in Figure 1.5.

Pump housing 1 is a steel cylinder with a bottom welded to it, an inlet flange 2, an outlet pipe with a flange 3. To install the ejector parts, there is a plunged flange 4 on the outlet pipe.

Fig.1.5. General form pump: 1 - electric heater; 2 - steam pipeline; 3 - body; 4 - oil deflector; 5 - nozzle; 6 - podsolnik;

7 - nozzle; 8 - podsolnik; 9 - ejector nozzle

The main structural part of the pump is a steam pipeline in which oil is circulated in such a way that oil vapors from the boiler located in the lower part of the housing through the steam channels enter the upper, lower and ejector nozzles, leaving where they condense on the cold walls of the pump housing and outlet pipe . Flowing into the boiler, the oil first enters the section of the boiler associated with the last (outlet) nozzle, and only lastly, passing through the labyrinth, it enters the section associated with the most important internal steam pipeline supplying steam to the high-vacuum nozzle. As a result, the high-vacuum nozzle closest to the object being pumped works only with oil having the lowest saturation vapor pressure, while the nozzle closest to the pre-vacuum pump works with the lightest fractions.

The steam line of the pump is three-stage. The first two stages are umbrella type, the third stage is ejector. Oil vapors from the boiler through steam pipelines enter the nozzles of the three stages of the pump and, flowing from them, form jets. The evacuated gas diffuses into the steam jets and is carried by them to the area of ​​preliminary discharge. The steam, having reached the cooled wall of the pump, condenses and flows back into the boiler.

The pump is started in the following sequence:

a) turn on the foreline pump and, by opening the valve, pump out the system

with a steam-oil pump up to a pressure of 5·10 -2 - 1·10 -2 mm Hg. Art.;

b) let water in to cool the pump housing;

c) turn on the electric heater of the steam-oil pump.

To stop the pump, turn on the electric heater of the pump and supply water to cool the bottom. After the pump has cooled down, close the valve, turn off the foreline pump and stop the water supply.

The main characteristics of the steam oil pump:

Maximum residual pressure is not more than 5·10 -7 mm Hg. Art.

Pumping speed Fp 500 l/s

The maximum outlet pressure is not less than 0.25 mm Hg. Art.

Leakage of atmospheric air is not more than 0.02 l×mm Hg. st./s

Oil grade VM-1 GOST 7904-56

preliminary discharge VN-2MG or NVR-5D

WORK PROCEDURE

1. Turn on the unit, for which the “network” machine is switched to the “On” position.

2. Turn on the mechanical pump by moving the switch knob to the “On” position.

3. Pump out the volume of the steam-oil pump, open the bottom valve of the valve box.

4. Turn on the steam oil pump heater with the toggle switch “On”.

5. After 35-40 minutes after turning on the oil-steam pump heater, turn on the nitrogen feeder.

6. After warming up the steam-oil pump, close the bottom valve and preliminarily pump out the volume under the cap by opening the top valve of the valve box.

7. Record and plot the characteristic P(t) during pumping out on a mechanical pump; for this, within one hour, record the readings of a thermocouple vacuum gauge every 10 minutes. Bring the data into a table and draw a curve P(t).

8. Remove and plot the characteristic P(t) for the diffusion pump. The experiment is carried out in the same way as in paragraph 7.

9. Evaluate the capabilities of both pumps when the pre-vacuum level is reached: mechanical for 40 minutes, high vacuum for 1 hour.

10. Give a conclusion about the preliminary vacuum that can be obtained with the proposed pumping system.

11. The data obtained during the experiment should be presented in the form of tables and graphs.

TEST QUESTIONS

1. How vacuum is classified. Explain the principle of operation of the vacuum deposition unit, the purpose of the nodes.

2. Explain correct sequence switching on and off the vacuum pumps in vacuum plant. Explain what limits the ultimate vacuum that can be obtained on such an installation.

3. Explain the operation of the steam oil pump.

4. Explain the operation of a mechanical pump.

5. Explain the principle of vacuum measurement and the operation of thermionic and ionization sensors.

6. Explain the purpose and operation of the valve - leak.

7. Explain the principle of operation and arrangement of nitrogen and electromagnetic traps.

8. Comment on the obtained vacuum characteristics of the installation.

Hello, friends.

So, the story began a little earlier, when we got a vacuum chamber. Her path to us was not close and can be described in a separate story, but this, as they say, is "a completely different story." I can only say that even earlier it brought people some benefit in one of the laboratories of the University of Göttingen.

The first thing we started to use the vacuum chamber with was to try out the method of thermal deposition of metals on substrates. The method is simple and as old as the world. The target of the sputtered metal, for example, silver, is placed in the molybdenum crucible. Placed around it a heating element. We used tungsten-rhenium alloy wire, which was wound in a spiral.

The complete thermal spray device looks like this:

Tooling for thermal spraying of metals. a. Assembled (protective screen and valve removed). Designations: 1 – crucible, 2 – heating element, 3 – steam line, 4 – current lead, 5 – thermocouple, 6 – sample frame.

After the current is passed (it goes into the vacuum chamber through the pressure seals), the spiral heats up, heats the boat, in which the target material also heats up and evaporates. A cloud of metal vapor rises along the steam pipeline and envelops the body, on which it is necessary to deposit a metal film.

The method itself is simple and good, but there are also disadvantages: high energy consumption, it is difficult to place surfaces (bodies) in the vapor cloud on which the film needs to be deposited. Adhesion is also not the best. applied to different materials, including for metals, glass, plastic, etc. Basically - for research purposes, since we only mastered vacuum equipment.

Now it's time to talk about the vacuum system. The experiments were carried out in a vacuum chamber equipped with a vacuum system consisting of a rotary fore-vacuum and turbomolecular pump and providing a residual pressure of 9.5 10 -6 - 1.2 10 -5 mm Hg.
If at first glance it seems that it is not difficult, then in fact it is not. First, the chamber itself must have the tightness necessary to maintain a high vacuum. This is achieved by sealing all functional flanges and openings. The upper and lower flanges-covers have the same, in principle, rubber seals, as well as the smallest holes designed for installing windows, sensors, devices, pressure seals and other flange covers, only with a much larger diameter. For example, for reliable sealing of such a hole

Requires flange, gasket and fasteners as shown in this photo.

This sensor measures the vacuum in the chamber, the signal from it goes to the device, which shows the level of high vacuum.

Vacuum required level(eg 10-5 mmHg) is achieved as follows. First, a low vacuum is pumped out by a fore-vacuum pump to a level of 10-2. Upon reaching this level, a high-vacuum pump (turbomolecular) is switched on, the rotor of which can rotate at a speed of 40,000 rpm. At the same time, the foreline pump continues to work - it pumps out pressure from the turbomolecular pump itself. The latter is a rather capricious unit and its “thin” device played a certain role in this story. We use Japanese Osaka vacuum turbomolecular pump.

The air pumped out from the chamber with oil vapors is recommended to be discharged into the atmosphere, since fine droplets of oil can “splatter” the entire room.

Having dealt with the vacuum system and worked out the thermal deposition, we decided to try another method of film deposition - magnetron. We had a long experience of communication with one large laboratory, which applied us functional nanocoatings for some of our developments using the magnetron sputtering method. In addition, we have fairly close ties with some departments of MEPhI, Moscow Higher Technical School and other universities, which also helped us to master this technology.

But over time, we wanted to use more of the possibilities that the vacuum chamber provides.

Soon we had a small magnetron, which we decided to adapt for film deposition.

It is the magnetron vacuum method of deposition of thin metal and ceramic films that is considered one of the most productive, economical and easy to operate among all physical deposition methods: thermal evaporation, magnetron, ion, laser, electron beam. The magnetron is installed in one of the flanges, which is convenient for use. However, this is still not enough for deposition, since it requires a certain voltage, cooling water, and gases to be supplied to ensure plasma ignition.

Theoretical excursion

Simplistically, the magnetron is arranged as follows. On the base, which also serves as a magnetic circuit, strong magnets are placed, which form a strong magnetic field. On the other hand, the magnets are covered with a metal plate, which serves as a source of the sputtered material and is called the target. Potential is applied to the magnetron, and earth is applied to the body of the vacuum chamber. The potential difference formed between the magnetron and the chamber body in a rarefied atmosphere and magnetic field leads to the following. An atom of the plasma-forming argon gas falls into the action of magnetic and electric field and ionized under their influence. The ejected electron is attracted to the chamber body. A positive ion is attracted to the magnetron target and, having accelerated under the action of magnetic field lines, hits the target, knocking out a particle from it. It flies out at an angle opposite to the angle at which the ion of the argon atom hit the target. A metal particle flies away from the target towards a substrate located opposite it, which can be made of any material.

Our university friends made a DC power supply with a power of about 500 W for this magnetron.

We also built a gas supply system for the plasma-forming argon gas.

To accommodate the objects on which the films will be sprayed, we have built the following device. There are technological holes in the chamber lid, into which various devices can be installed: electrical power feedthroughs, traffic pressure feedthroughs, transparent windows, sensors, and so on. In one of these holes, we installed a pressure seal of a rotating shaft. Outside the chamber, we brought rotation to this shaft from a small electric motor. By setting the speed of rotation of the drum on the order of 2-5 hertz, we have achieved good uniformity in the application of films around the circumference of the drum.

From below, i.e. inside the chamber, we mounted a light metal basket on the shaft, on which objects can be hung. In a stationery store, such a standard drum is sold as a waste basket and costs about 100 rubles.

Now we had in stock almost everything needed for film deposition. We used the following metals as targets: copper, titanium, stainless steel, aluminum, copper-chromium alloy.

And they started to dust. Through the transparent windows into the chamber, one could observe the plasma glow on the surface of the magnetron target. In this way, we controlled “by eye” the moment of plasma ignition and the deposition intensity.

The way to control the thickness of the spraying came up with a fairly simple one. The same piece of foil with the measured surface area was placed on the drum, and its mass was measured before and after the spraying session. Knowing the density of the deposited metal, the thickness of the deposited coating was easily calculated. The coating thickness was controlled either by changing the deposition time or by adjusting the voltage at the magnetron power source. This photo shows a precision balance that allows you to measure the mass of samples with an accuracy of ten-thousandths of a gram.

We applied to various materials: wood, metals, foil, plastics, paper, polyethylene films, fabrics, in short, everything that could be placed in the chamber and attached to the drum. Basically, we focused on obtaining decorative effects - changing the color or tactile perception of the surface. On these samples of organic and inorganic origin, you can see the difference in color before and after applying different metal films.

Even more clearly the difference in color before and after spraying is visible on fabrics and films. Here is the right piece of the usual polyethylene film- not sprayed, but the left one is covered with a layer of copper.

Another effect that can be used for various needs is the conductivity of thin films on substrates. This photo shows the resistance of a piece of paper (in ohms) with a thin layer of titanium just over a micron thick.

For further development, we have chosen several directions. One of them is to improve the efficiency of film deposition by magnetrons. We are going to "swing" at our own development and manufacture of a more powerful magnetron with a height of a camera and a power 2 times greater than that shown in this essay. We also want to test the technology of reactive deposition, when, together with the plasma-forming gas argon, oxygen or nitrogen are fed into the chamber, and during the deposition of films on the surface of the substrate, not pure metal films are formed, but oxides or nitrides, which have a different range of properties than pure ones. metal films.

Surface treatment by vacuum deposition with metals makes it possible to enhance positive characteristics products from various materials. metal parts are protected from corrosion, conduct electricity better, become more aesthetically pleasing. Metallization of plastic products allows you to get high-quality and beautiful parts from lighter and cheaper materials. This is especially true for the automotive industry, because metallization plastic components can significantly reduce the weight of vehicles. A metallized fur gives the fur coat exclusivity, originality and is the new trend of the season.

In the company "Alfa-K" you can order vacuum metal spraying for products from various materials, including fur.

Methods

The essence of the technology lies in the fact that under vacuum conditions on special equipment the smallest metal particles are transferred to work surface blanks. During the formation of coatings, the original metal evaporates, condenses, absorbs and crystallizes in a gaseous medium, creating a stable coating. Depending on the type of workpiece, the properties of the metal film and the selected deposition mode, a wide variety of effects are obtained. Almost any metal can be sprayed: aluminum, nickel, chromium, copper, bronze, gold, titanium, etc. Taking into account the specific properties and features, each metal requires different modes and techniques. For example, due to low wear resistance, a special technology requires vacuum deposition of aluminum. That is why our company employs only highly qualified and experienced professionals. Metallization is carried out in different ways.

Vacuum plasma

In such systems, under a certain gas pressure, a metallized coating is created by high heat metal source, resulting in its evaporation, and the particles are deposited on the workpiece. The camera can be metal, glass, necessarily with a water cooling system. To heat the sprayed element, the following evaporators are used:

• wire or tape tungsten or molybdenum direct-heated evaporator;
• electron-radial, creating heating with the help of electric bombardment.

In accordance with the source metal or alloy that needs to be sprayed onto the part, the heating temperature in the heat exchanger is set, it can reach 20 thousand ° C. If the metal to be sprayed is not very good adhesion with the workpiece material, first a primary layer of metal with higher adhesive properties is applied.

Ion-vacuum

Main advantage this method it is considered that there is no need to heat the evaporator very much. The metal is sprayed under the influence of bombardment with negatively charged gas ions. The creation of such an environment is possible due to special discharges inside the working chamber. To do this, the equipment uses a magnetic system with cooling. A glow discharge for spraying the sprayed element is created between 2 electrodes due to the supply of high voltage up to 4 kV. In the working chamber, a gaseous medium is created with a pressure of up to 0.6 Pascal. By similar principle vacuum ion-plasma spraying is also carried out on specialized equipment.

Surfaces suitable for spraying

Any items that can withstand heat up to 80 ° C and exposure to specialized varnishes. The advantage of the technology is that in order to give the products the effect of copper coatings, mirror chrome plating, gilding, nickel plating, it is not necessary to pre-polish the surfaces. More often by vacuum metallization cover parts made of plastic, glass, metal alloys, various polymer and ceramic products. Less commonly, but still technology is used to more soft materials such as wood, textiles, fur.

Treatment metal blanks and products made of metal alloys due to the good compatibility of the base and coatings does not require the use of additional Supplies. While polymers must first be primed with protective and adhesive compounds. To prevent deformation of polymer blanks and reduce stress in the working environment during vacuum metallization, special modifying components and material diffusion modes are used.

Stages of metallization

The technological process of vacuum deposition of metal on various products includes several successive stages:

• Detail preparation. It is important that the workpiece has the maximum simple form, without hard-to-reach places for condensate to settle.
• Applying protection. It is necessary to apply an anti-diffusion coating on polymer bases containing low molecular weight fillers.
• Drying. For 3 hours, the parts are dried at 80 degrees Celsius, which allows you to remove the absorbed moisture.
• Degreasing. In a vacuum chamber, the workpiece is degreased using a glow discharge. This is especially good for the structure of polymers.
• activation processing. The processing method is selected depending on the material of the product, it is necessary to increase the adhesion of the surface before metallization.
• Metal spraying. By condensation, a metallized layer is created on the workpiece.
• Coating quality control. decorative details inspected for uniformity of spraying and its strength. Technical products are additionally tested with adhesive tape, ultrasonic vibrations, friction, etc.

Metallization plants are quite complex and expensive equipment that consumes a lot of electricity. To create a complex technological cycle, a fairly spacious room is required, since several multifunctional devices should be placed. The main components of the vacuum system:

• Power supply and control unit in conjunction with a source of condensed metals.
• Gas distribution system that creates a vacuum space and regulates gas flows.
• Working chamber for vacuum metallization.
• Block of thermal control, control of deposition thickness and speed, properties of coatings.
• The conveying unit is responsible for changing the position of the workpieces, their supply and removal from the chamber.
• Unit blocking devices, gas filters, dampers and other ancillary equipment.

Magnetron and ion-plasma vacuum equipment can be of different sizes, from small ones, with chambers of several liters to very large ones, with chamber volumes of several cubic meters.

Alfa-K has sufficient production capacity and appropriate equipment to ensure various ways vacuum deposition. We can order ion-plasma coating of products from any materials with metals such as titanium, copper, aluminum, brass, chromium, various alloys, etc. We guarantee high quality work and reasonable prices.