DE102012107624A1 - Coating device for coating large-area substrates for producing thin atomic layers, comprises high frequency coil in communication with vaporization unit, and channel arrangement for discharging molecules from vaporization unit to substrate - Google Patents

Abstract

The coating device (10) comprises a chamber (15), which is connected to an evacuation unit for creating a vacuum. A vaporization unit (22) and a high frequency ionization unit (29) are arranged in the chamber. A high frequency coil (30) is provided, which is in communication with the vaporization unit to stimulate and to ionize the molecules of the vapor. A channel arrangement (33) with multiple channels (34) made of ceramic is provided for discharging the molecules from the vaporization unit in the direction of a substrate (11). A holder (12) is provided for the substrate. An independent claim is included for a method for producing epitaxial layers.

Description

The invention relates to a coating device for producing thin, preferably only one or a few atom layers comprehensive coatings and a method for producing such layers.

For example from the DE 10 2007 043 943 B4 For example, a method for coating substrates by means of vapor deposition in a vacuum coating chamber is known. The method is used for the production of thin-film solar cells. The coating is carried out by means of evaporation of the coating material in an open evaporation source, whereby a cloud of vapor is formed. A particle stream of the doping material is introduced into this cloud of vapor so that a doped semiconductor layer can form on the substrate.

It is an object of the invention to provide an apparatus and a method with which thin layers can be generated very controlled.

This object is achieved with the coating device according to claim 1 as well as with the coating method according to claim 15:
The device of the invention comprises a chamber connected to suitable pumping devices to create a vacuum in the chamber. Preferably, the corresponding pumping means are designed so that a high vacuum, preferably an ultra-high vacuum, with a pressure of 10 ^-10 mbar and below (10 ^-11 mbar) can be generated.

In the chamber, a vaporization device for a substance is arranged, from which the layer to be produced emerges. For example, the vaporizing substance may be a silicon compound, for example a silane, if a silicon layer is to be deposited. The substance to be evaporated may contain carbon, for example in the form of a hydrocarbon, if a carbon layer is to be deposited. The substance to be evaporated may be another compound or a mixture of compounds. It can be liquid or in solid state.

The evaporation device is preferably provided with a cooling or a heating device in order to set a desired temperature of the substance to be evaporated. The cooling or heating can for example be done by a coil, which is tempered, for example, with oil. Alternatively, an electrical heating and / or cooling device may be provided, for example a resistance heater, Peltier elements or the like. In the evaporation device can thus be set above or below 0 °, at which the substance to be vaporized develops the desired (low) vapor pressure.

The resulting thin vapor is transferred in the RF ionizer into a plasma, preferably with a low degree of ionization. It contains free electrons, neutral atoms, excited atoms and ions. If cyclopentasilane is used as starting material, it can be dissociated into silicon and hydrogen.

For discharging the neutral atoms, the excited atoms and the ions from the vapor space in the direction of the substrate, a channel arrangement is provided. This includes several channels that only conduct particles with velocity components towards the substrate holder. It is thus possible to generate a particle stream which moves uniformly on a broad front in the direction of the substrate and deposits there. The channels present in the channel arrangement are preferably oriented parallel to one another and are preferably of equal length to one another. The channels may have the same or different cross sections. In particular, it is possible to achieve a uniform particle current density over the entire cross-section of the particle flow through a suitable distribution of the tubes and the cross sections thereof over the entire cross section of the channel arrangement. In particular, it is possible to compensate for the radius dependence of the magnetic pressure of the RF coil in this way.

The resulting particle flow, z. B. Silicon may be provided according to the area of the substrate to be coated. The area can be several square centimeters to square decimeters or more.

The channels of the channel arrangement are preferably formed of a ceramic which transmits both electrical and magnetic fields, and preferably little or no influence. Thus, the number of neutral, excited and ionized particles in the channel array can be maintained. The channel arrangement can be arranged in the RF coil or protrude into it.

Between the substrate to be coated and the channel arrangement, a grid arrangement is preferably provided which has at least one grating lying at a defined electrical potential. Preferably, a plurality of grids may be provided. The voltages or potentials of these gratings can be set such that the ions are given a defined speed in the direction of the substrate. Thereby, the velocity of the particle flow can be influenced, in which all particles move within close tolerance limits at substantially the same speed and impact the substrate. Thus, the impact energy of the particles on the substrate can be controlled. This allows the growth conditions of the layer to be controlled.

In addition, a shutter may be disposed between the channel assembly and the substrate holder to release or shut off the particle flow. In this way, the coating process can be selectively switched on and off.

Preferably, a cryoshield is arranged in the chamber. This is, for example, a hollow cylinder and surrounds the RF coil. The cryoshield can be used for gettering the residual gases in the vacuum chamber. This allows a high vacuum or ultrahigh vacuum to be maintained during the coating process.

Further details of advantageous embodiments of the invention are the subject of the description of the drawing or claims. Show it:

1 a coating device, in a schematic representation

2 a plan view of the channel arrangement of the coating device according to 1 in a schematic representation.

In 1 is a coating device 10 for coating large-area substrates 11 illustrated. The substrate 11 For example, it may be a sheet-like substrate made of a metal such as semiconductive monocrystalline disc, a plate, a metal-coated non-metal plate, or a non-metallic plate having a non-metallic surface, a ceramic material, plastic or the like. The substrate 11 is from a substrate holder 12 carried. This can be a heater 13 have, in 1 is indicated only schematically. It may be a resistance heater that is adapted to the substrate 11 to bring to a suitable temperature for the desired shutdown. This can be in the range of several 100 ° to over 1200 °.

The substrate holder 12 is in an interior 14 a vacuum chamber 15 arranged, which is connected to a not further illustrated lifting device. In the vacuum chamber 15 is an ultra-high vacuum generated. It has an entrance 16 and an exit 17 on, which are connected to a Einschleusekammer and discharge chamber. In these preferably prevail pressures of about 10 ^-6 mbar. The Einschleusekammer and the discharge chamber are not shown. Also all other bushings through the wall of the chamber 15 are preferably equipped with double seals, between which in turn an extraction is arranged.

To create the vacuum in the chamber interior 14 serve a dry-running backing pump, a turbomolecular pump and a getter system 18 which serves to bind residual gases. The getter device 18 can in the form of a cryo shield 19 be formed, which is designed here as a hollow cylindrical body. He has an entrance 20 and an exit 21 via which the cryoshield can be fed with a cryogenic coolant, for example liquid nitrogen. Gas and vapor residues are deposited on the cold surface of the cryo shield.

In the chamber 15 is an evaporation device 22 arranged, can be selectively released with the small amounts of a material to be evaporated. The evaporation device 22 includes a vessel 23 , which is set up to receive the substance to be vaporized. Is this liquid, he can over a line 24 into the vessel 23 be initiated. The material to be vaporized may be a silicon compound, mixtures of silicon compounds, a carbon compound, mixtures of carbon compounds and silicon compounds, or other compounds or mixtures. These may be, inter alia, silanes and / or hydrocarbons. The evaporation of other substances is possible.

In the vessel 23 is a tempering device 25 arranged. The tempering device 25 may be a heater or a cooling device. For example, it may be a pipe coil, which is a tempering fluid, eg. As oil, can flow. The corresponding coil is with its input 26 and their exit 27 in 1 illustrated schematically. If you want to evaporate substances that require an elevated temperature, the tempering device is required 25 that is, as a heater, an electric heating coil or the like may be used as the tempering device 25 be provided for heat dissipation. Other evaporation devices, eg. As electron beam evaporator, Laserstrahlverdampfungseinrichtungen or the like can also be used.

The container 23 is preferably a cup-like vessel with an upstanding wall 28 , The cup thus formed is preferably in one of the cryoshield 19 surrounded zone.

The evaporation device 23 is an ionization device 29 assigned. This is arranged to match that of the evaporator 22 produced, under very low pressure (eg., 10 ^-10 mbar or less) standing steam in a plasma can transfer. All it takes is the generation of a plasma with a low degree of ionization. As ionization device 29 can, for example, an RF coil 30 serve, their connections 31 . 32 from the vessel 15 led out. The connections 31 . 32 are electrical connections of the coil 30 forming conductor. This is, for example, tubular, so that it can be flowed through by a cooling fluid. At the connections 31 . 32 Thus, both electrical RF power as well as cooling fluid can be in and out.

In the from the cup wall 28 enclosed space is preferably in the upper region thereof a channel arrangement 33 provided that several channels 34 that is from the evaporation device 22 to the substrate 11 point. The channels 34 are preferably oriented in parallel. They are also preferably parallel to the central axis of the RF coil 30 oriented. In the present embodiment, the channels 34 vertically oriented. They have, for example, round cross sections. The channel arrangement 33 may be formed by a ceramic body or the like, as for example 2 is visible in plan view. The channels 34 can over the cross section of the channel arrangement 33 be evenly or unevenly distributed. In particular, the density of the channels 34 increase or decrease from center to edge, as desired, to produce a particular density distribution in the generated particle stream. The cross sections of the channels 34 can be equal to each other or even vary, for example, from the center to the edge, for example, increase or decrease.

Above the channel arrangement 33 is a grid arrangement 35 intended. This comprises at least one, but preferably several grids 36 , which can be placed at the same or different electrical potentials. This is preferably the substrate 11 closest upper grid 36 connected to 0 V or a slightly negative potential. The other grids 36 can be applied to other voltages, for example. Between 0 and +100 V. At the bars 36 are preferably DC voltages.

Between the grid arrangement 35 and the substrate holder 12 can be a shutter 37 be arranged. This is formed, for example, by a pivotable aperture, which is the path between the evaporation device 22 and the substrate holder 12 can release or lock. The shutter 27 , the substrate holder 122 and all parts that are heated are preferably made of materials such as tantalum, molybdenum or boron nitride.

To influence the chemical composition of the resulting vapor, in particular to ensure a complete dissociation of all chemical compounds, a UV lamp (or more) or another UV light source 38 be provided by means of those of the evaporation device 22 to the substrate 11 flowing molecules, atoms or ions are exposed to ultraviolet radiation.

In the chamber 15 In addition, an analysis device for determining the structure of the on the substrate 11 be provided layer formed. Such an analysis device can, for example, by an electron source 39 be formed with an electron beam at a shallow angle of 0.5 ° to 2 ° to the surface of the substrate 11 can be directed. The electrons reflected from the substrate surface can be placed on a fluorescent screen 40 to produce a diffraction pattern resulting from electron scattering. The diffraction pattern indicates the surface crystallography. A not further illustrated camera can be used to monitor the screen and to record the diffraction patterns.

The coating device described so far 10 works as follows:
It is assumed that on the holder 11 a substrate 11 attached is that the substrate 11 for example, to be provided with a silicon layer which is to grow epitaxially. The interior 14 is evacuated by means not further illustrated pumping device, so that an ultra-high vacuum of, for example, about 10 ^-11 mbar is generated. About the line 24 is a precursor substance of the layer to be produced, for example Cyklopentasilan in the evaporation device 22 filled. With the tempering device 25 the existing amount of the precursor substance is now tempered so that the vapor pressure is sufficient to produce a thin vapor. With the ionization device 29 this is at least weakly ionized. This is the RF coil 30 over the connections 31 . 32 with high frequency, for example. In the range of 1 MHz to 500 MHz and a power of some 100 watts fed. The resulting plasma contains neutral molecules, excited molecules and ions. The ions release energy to the molecules through collisions. It creates a uniform energy distribution. The ions are transmitted through the grid 25 towards the substrate 11 accelerated. They pass through the channels 34 the channel arrangement 33 and thus become a uniform ion current or molecular stream. This can be from the shutter 37 specifically switched on and off, ie intercepted or released. At the same time the cryoshield 19 chilled to to keep the residual gas pressure low by gettering. The substrate 11 is brought to a suitable temperature for coating, for example. Several 100 ° brought.

That in the ionizer 29 generated plasma contains silicon and optionally also Cyklopentasilanringe, by the UV light of the UV source 38 can be split. On the substrate 11 Thus, silicon atoms and / or silicon ions with a defined composition and defined energy arrive, which are due to the voltage of the grid arrangement 35 The ionization and the available temperatures can be regulated. By the temperature of the substrate 11 the crystallization can be further influenced. The grids 36 the grid arrangement 35 serve the extraction of ions. When the polarization of the lattice strains change, electrons can also be extracted whose energy is released by collisions with the atoms of the forming layer, so as to achieve the uniform distribution of energy during crystallization. With the applied voltage, the energy of the ions can be influenced.

Once the coating conditions are stationary, the shutter opens 37 and the epitaxial coating process begins. The growth of the layer can be in situ with the electron source 39 and the screen 40 be monitored. In addition, via not further illustrated temperature sensors on the evaporation device 22 , in particular their bottom, the evaporation temperature can be regulated. The ionization and thus the splitting of the cyclopentasilane rings takes place predominantly in the ionization device 29 , The UV source 38 may possibly break any remaining compounds in the molecules and ensure that on the substrate 11 only single atoms and ions strike.

The on the substrate 11 flowing silicon ions accumulate randomly distributed on the substrate surface and form crystallization nuclei. These seeds then undergo further layer growth. For energetic reasons, the growth takes place in a lateral direction until the plane is completely filled. Only then does growth begin in the next level.

By absorbing energy of the silicon ions as it passes through the grid array 35 In addition, energy for crystal growth can be introduced. By adding a gaseous boron compound, for example diborane, P-type layers can be produced. By adding a phosphorus compound (phosphine) or an arsenic compound (arsine), N-type silicon layers can be formed.

Similarly, graphene layers can be created. There are then used as a precursor substance no silanes, but hydrocarbon compounds, for example. Benzene or benzene compounds.

For the epitaxial production of large-area layers, an ion source is provided, which is an epitaxy system with a plurality of Knudsen cells, which are connected by a channel arrangement 33 with a variety of channels 34 are formed. These are collimated and serve to rectify a plasma beam or stream having a large cross section of preferably several square decimeters. The individual channels 34 have a cross section of a few square millimeters to square centimeters.

LIST OF REFERENCE NUMBERS

10

coater

11

substratum

12

substrate holder

13

heater

14

inner space

15

chamber

16

entrance

17

output

18

getter

19

cryoshield

20

Entrance of the cryoshield

21

Exit of the cryoshield

22

Evaporation device

23

vessel

24

management

25

tempering

26

Input of the coil of the tempering device

27

Output of the coil of the tempering device

28

cup wall

29

ionization

30

RF coil

31, 32

connections

33

channel arrangement

34

channels

35

grid array

36

grid

37

shutter

38

UV-light source

39

electron source

40

umbrella

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007043943 B4 [0002]

Claims (15)

Coating device ( 10 ), with a chamber ( 15 ), which is connected to an evacuation device for generating a vacuum, with an evaporation device ( 22 ) in the chamber ( 15 ) is arranged with an RF ionization device ( 29 ) in the chamber ( 15 ) and an RF coil ( 30 ), with the evaporator device ( 22 ) in order to stimulate or ionize the molecules of the vapor, with a channel arrangement ( 33 ) for discharging the molecules from the evaporator device ( 22 ) in the direction of a substrate ( 11 ) and with a holder ( 12 ) for the substrate ( 11 ). Coating device according to claim 1, characterized in that the channel arrangement ( 35 ) several channels ( 34 ), which are oriented parallel to each other. Coating device according to claim 2, characterized in that the channels ( 34 ) are equal to each other. Coating device according to claim 2 or 3, characterized in that the channels ( 34 ) have the same cross sections. Coating device according to one of claims 2 to 4, characterized in that, the channels ( 34 ) Have cross-sections which depend on the distance of the channel ( 34 ) to the coil center of the RF coil ( 30 ) are dependent. Coating device according to one of claims 2 to 5, characterized in that the channels ( 34 ) parallel to a coil axis of the RF coil ( 30 ) are arranged. Coating device according to one of claims 2 to 6, characterized in that, the channels ( 34 ) are formed of ceramic. Coating device according to one of claims 1 to 7, characterized in that, the channel arrangement ( 33 ) is formed in the shape of a one-piece body. Coating device according to one of claims 1 to 8, characterized in that, the density of the channels ( 34 ) over the cross section of the channel arrangement ( 33 ) is variable. Coating device according to one of claims 1 to 9, characterized in that, the channel arrangement ( 33 ) from the RF coil ( 30 ) is surrounded or protrudes into this. Coating device according to one of claims 1 to 10, characterized in that, at one end of the channel arrangement ( 33 ) a grid arrangement ( 35 ), which has at least one grid ( 36 ), which is at a defined electrical potential. Coating device according to claim 11, characterized in that, the grating arrangement has at least two grids ( 36 ), which are at different electrical potentials. Coating device according to one of Claims 1 to 13, characterized in that, between the HF ionization device ( 22 ) and the substrate holder ( 12 ) a shutter ( 37 ) is arranged. Coating device according to one of claims 1 to 14, characterized in that, in the chamber ( 15 ) a cryoshield ( 19 ) is arranged. Process for producing epitaxial layers, in which: a starting material in a chamber ( 15 ) and is converted by means of electromagnetic energy at least 0se in ionized molecules, the ionized molecule is exposed to an electric field to accelerate positively charged ions in the direction of a substrate, and the accelerated ions through channels ( 34 ) of a channel arrangement to unify the direction of movement of the ions.

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