DE4421103A1 - Potential guiding electrode for plasma supported thin layer deposition for mfg. electric-electronic thin film components - Google Patents

Abstract

The potential-guiding electrode is cylindrical shaped and is sub-divided lengthwise into several, separately controlled electrode sections which are mutually electrically insulated from one another by isolation rings. The electrode has an integrated gas inflow line (2) for a gas (9) which decomposes in the plasma, and has perforations (5) in an external segment. Each electrode segment is independently actuated by a VHF potential fed in via supports (12). A cylinder rod opposite electrode (10) is disposed parallel to the potential-guiding electrode, onto a shielding substrate (11).

Description

For the production of layer systems for electrical and elec tronic thin-film components can be coated inline systems are used. A substrate runs through it different separation chambers in order, in each because at least one of the different layers will be divorced. Since this is a continuous process, the throughput speed of the overall process from the lowest throughput speed of one of the individual processes determined that is required to generate the layer system are.

Exemplary thin-film components in which a high Area throughput is desired are thin-film solar cells or so-called flat panel displays the base of amorphous silicon a-Si: H. These components have a diode structure (for example p-i-n), which by Deposition of differently doped individual layers is produced becomes. The throughput of the overall process is in this case determined by the deposition rate of the undoped i-layer.

To accelerate the deposition rate of this layer A number of measures have been tried so far. The promised The best results are achieved when used for deposition used plasma excitation frequencies not as usual in the HF area, but in the VHF area. Alone due to the higher plasma excitation frequency, increases can occur the deposition rate can be achieved by a factor of 7.

A disadvantage of the use of VHF plasma excitation frequencies is that the wavelength of the plasma excitation field approaches the dimension of the electrodes at a higher frequency. In the case of large-area electrodes, standing waves can then form, which lead to an inhomogeneous field, therefore to an inhomogeneous plasma and subsequently to inhomogeneous coating. This problem leads to the fact that the required electronic quality of an i-layer separated in VHF plasma has so far only been able to be maintained on small areas (F <100 cm²). Therefore, it has not been possible to take advantage of the high deposition rate in the VHF area and thus to achieve an increase in sales and consequently a reduction in the manufacturing costs of solar cells. In general, this problem also occurs in the deposition of other silicon-containing layers in which silane is also decomposed in the deposition process. Problems with PECVD deposition in the VHF region also occur, for example, with passivation layers made of SiO₂ or SiN _x if the deposition is to be carried out over a large area.

The object of the present invention is therefore a method ren and specify an associated device with which thin layers through plasma-supported deposits homogeneous and of high electronic quality and with improved Separation speed can be generated.

According to the invention, this object is achieved by a poten tial leading electrode with the features of claim 1 and by a method having the features of claim 8.

Further embodiments of the invention are the dependent claims Chen to take.

The basic idea of the invention is the potential-carrying Electrode of a plasma separator rod or cylin to train like this. This creates a linear plasma received source. To prevent anyone from getting taller the substrate widths of, for example, more than 20 cm form waves on the electrode, this is over the  Length in a corresponding number electrically against each other insulated and individually controllable electrode sections divided up. A standing wave can be in the electrode Only train if the length of the electrode covers the area reached by λ / 4, where λ is the wavelength at the VHF frequency in plasma used for plasma excitation trains. Since λ is also indirectly proportional to ε² in Plasma and excitation frequency can be critical Length at which standing waves can occur for one Electrode section for example between 10 and 30 cm (at 27 to 80 MHz). According to the length of the Electrode sections chosen smaller than the critical length.

The individual electrode sections are independent of one another which can be charged with VHF potential. With in-phase on Control of the individual electrode sections is thus a get extremely homogeneous excitation field, which is a homogeneous Generates plasma and enables homogeneous plasma separation light. So the total length of the plasma source can be reduced by Anein alternating a corresponding number of electrodes cuts can be increased almost arbitrarily. So that too at high VHF excitation frequencies a large area and homo gene layer generation. Great compared to known areal plasma deposition at RF frequencies, however the deposition rate and thus the growth rate of the deposited layer significantly increased.

In a further embodiment of the invention, the gas supply is line for the gas to be decomposed in the plasma into the Hollow cylinder trained electrode integrated. So the gas evenly into the space between the electrode and the substrate can occur, the electrode is at least in an outer Perforated segment or alternatively sufficiently porous to egg to allow gas passage. In the simplest version is the gas supply line a perforated hollow cylinder, which is formed from electrode material and in several  Electrically insulated electrode sections un is divided.

Alternatively, it is also possible to use one of the gas Initiate electrode independent device, for example via a gas shower, which can be annular.

The inventions exist for reasons of mechanical stability inventive electrode preferably from at least two mated hollow cylinders, at least one of which electrically insulating material is formed. Is possible it, for example, the gas supply line from a tube from a to form porous or perforated ceramic material. The electrode sections can then, for example, as Hollow cylinders or sleeves that are simply formed over the gas supply pipe is inserted or pushed. The electrical insulation is provided by thin, between the elec Electrically insulating rings arranged on the electrode sections or discs made of electrically insulating material, for example made of ceramic or Teflon.

It is also possible to use the gas supply as a perforated meter Train tall pipe with an insulating sleeve Ceramic or a suitable plastic to provide and via in turn the electrodes designed as hollow cylinders clip sections.

It is also possible to remove the potential-carrying electrodes to form cuts as a hollow cylinder and over this one further, but continuous and therefore mechanically stabilized renden hollow cylinder made of electrically insulating material plug in. Since the electrically insulating surface is on construction of the VHF field does not interfere, nor is it metallic or otherwise electrically conductive outer electrode surface required.  

To the plasma generated in the VHF field largely to mate rialabscheid and therefore to produce the thin layer the electrode is turned away from the substrate shielded side. This is done at a distance from the elec trode surface on the side facing away from the substrate shield following the shape of the electrode surface, a so-called dark room cover attached. Because of the Zylin the shape of the electrode is more open on one side Hollow cylinder designed to shield the load consists of metal or is at least coated with metal. The dark room cover is against the electrode or the po electrically conductive electrode sections. The distance to the electrode surface is such that the Energy from charges not accelerating over this distance is sufficient for the impact ionization of further particles. In Ab depending on the other deposition conditions a maximum distance of, for example, approx. 1.5 mm to the Electrode surface should be sufficient.

To use the electrode according to the invention for plasma deposition to perform, a counter electrode is parallel to the potenti arranged leading electrode. The counter electrode is with grounded as short a line as possible, so that no Po potential difference to the zero potential Can build reactor housing. The two electrodes are then arranged in a reactor housing which is used to generate supply of a vacuum inside or at least for opening maintaining an atmosphere other than air is not. To create the separation conditions is white then a substrate heating is required, with which the Ab optimal substrate temperature is generated.

Since the rod-shaped electrode is a line source, the substrate has to be flat stratification "under" the potential-carrying electrode or between led through the electrode and the counter electrode become. It can be an advantage if the counter elec  trode is also rod-shaped. A parallel Alignment of two rod-shaped electrodes is essential easier than that of two large, plate-shaped elec tread. Especially when the counter bearing the substrate electrode is plate-shaped and large area can it when the counter electrode is heated on the separator temperature to slight thermal deformations, in the consequence of which is an absolute parallelism of the two plates electrodes are no longer guaranteed. Because a homo separation, however, only with absolute plane parallelism of the electrodes is ensured, this leads to the deposition inhomogeneous and thus electronically deteriorated layer This problem is solved with the rod-shaped electrodes avoided.

In the following, the invention is illustrated by means of an embodiment game and the associated four figures explained in more detail.

Figs. 1 to 3 show schematic Aufrißzeichnungen ver VARIOUS embodiments of the electrode of the invention.

Fig. 4 shows a device for depositing shows in a schematic perspective view of thin layers using the electrode of the invention.

Fig. 1 shows a simple embodiment of the invention with reference to a cross section parallel to the longitudinal axis of the electrode. In the figure, two of the electrode sections 1 formed as a hollow cylinder are shown. With an assumed length of the electrode sections of, for example, 10 cm, a corresponding number of electrode sections is strung together until a desired total length of the electrode is reached. The total length is adapted to the width of the substrate to be coated in the plasma. For example, 10 electrode sections 1 are required for a 1 m wide substrate.

Another hollow cylinder 2 , which is adapted to the inner diameter of the electrode sections 1 , is used for mechanical stabilization and at the same time represents the gas supply line for the reactive gas to be decomposed in the plasma. So that the reactive gas can emerge evenly from the electrode, both the inner hollow cylinder 2 and the electrode sections 1 perforations 4 and 5 , which are evenly distributed over the surface. The electrode sections 1 are pushed over the inner hollow cylinder 2 , a narrow and approximately 1 to 2 mm wide insulation ring or an insulation disk, which consists of an electrically insulating material, for example ceramic or Teflon, being arranged between each two electrode sections 1 . The electrode sections 1 consist of a conventional electrode material which is sufficiently electrically conductive and is stable against the plasma to be generated. Suitable materials are, for example, aluminum or copper.

Fig. 2 shows a similarly simple embodiment of the electrode according to the invention, but in which the electrode sections 1 form an inner hollow cylinder, which are inserted into an outer hollow cylinder 2 made of an insulator material. The insulator material can also be a ceramic. In this embodiment, the lined-up electrode sections 1 serve simultaneously as a gas supply line, while the outer hollow cylinder 2 serves for mechanical stabilization. For electrical isolation, electrically insulating insulating rings 3 are also arranged between the electrode sections 1 . A perforation 7 and 6 in the electrode sections 1 and the outer hollow cylinder 2 enable a uniform gas outlet of the reactive gas from the electrode.

In Fig. 3, an embodiment is shown, which has an egg gene and ausgebil Dete gas supply line 13 in the form of a perforated hollow cylinder. The electrode sections 1, which are also designed as a perforated hollow cylinder, are fitted over the gas supply line 13 , with an insulation layer 14 arranged between them for electrical insulation, which in turn can be designed as a hollow cylinder. However, the insulation layer 14 can also be an insulating coating of the gas supply line 13 . It consists, for example, of an insulator ceramic or an insulating plastic material, for example made of Teflon. Insulation rings 3 are used for electrical insulation of the individual electrode sections 1 against each other.

Fig. 4 shows a schematic perspective view of how the electrode according to the invention can be arranged in a plasma deposition to the substrate and to the counterelectrode. The electrode shown in FIG. 4 corresponds to the embodiment according to FIG. 1, although the embodiments according to FIG. 2 or 3 can also be used.

A counter-electrode 10, which is also cylindrical or rod-shaped, is arranged parallel to the potential-carrying electrode. Since the two electrodes can be aligned vertically or horizontally in the reactor. On the side of the electrode facing away from the counterelectrode 10 is the dark room cover 8 , which in the simplest case is a sheet metal arranged at a distance of approximately 1 mm from the surface of the electrode sections 1 . The dark room cover 8 has the shape of a hollow half cylinder, which follows the surface of the electrode sections and is open towards the counter electrode 10 .

The substrate 11 to be coated is arranged on the counter electrode 10 and is preferably an “endless substrate”, for example a tape to be unwound from a supply roll. However, any other plate-shaped substrates 11 can also be coated using the electrode in accordance with the invention. In all cases, however, it is necessary to pass the substrate 11 at a constant distance under the electrode. For this purpose, the counter electrode 10 can be designed as a roller over which the substrate 11 can be guided. While the counter electrode is grounded directly as possible to 10, the electrical be denabschnitte 1 of the electrode through independent control of a VHF potential establish which of the columns can be fed in the electrode portions 1 12, for example, intra-half. The reactive gas to be decomposed in the plasma is fed into the gas feed line 2 (see arrow 9 ). In the area of the electrode portions 1 is in the gas feed line or a perforation 5 can escape before hands, by the gas in the region between the electrode and the counter electrode 10 in the electrode portions. 1 To deposit a silicon layer, the reactive gas consists, for example, of silane, which can be diluted in hydrogen.

When potential is applied to the electrode sections 1 and reactive gas is introduced into the electrode, a plasma is formed in which the reactive gas is broken down into radicals and ions. The dark room cover 8 prevents the plasma from burning in the direction turned away from the counter electrode 10 .

Since the device used for plasma deposition is only shown schematically in FIG. 4, it is clear that a functional system has further details not shown. Not shown is, for example, the reactor chamber, pumps and vacuum systems, substrate heating, devices for guiding and transporting the substrate 11 and control devices for checking the deposition conditions. A VHF generator with a matching network is also required, which can generate an excitation of, for example, 30 to 100 MHz. Already at 30 MHz, an accelerated layer growth compared to HF deposition is observed. However, the deposition is preferably carried out with a higher excitation frequency of, for example, 50 to 100 MHz.

Claims (12)

1. Potential-carrying electrode for plasma-assisted deposition of thin layers with excitation frequencies in the VHF region, the electrode being cylindrical and divided over the length into several, individually controllable, electrode sections ( 1 ) which are electrically insulated from one another. 2. Electrode according to claim 1 with an integrated gas supply line ( 2 , 13 ) for a gas to be decomposed in the plasma, the cylindrical electrode having a perforation ( 4 , 5 , 6 , 7 ) at least in an outer segment. 3. Electrode according to claim 1 or 2, in which the gas feed line ( 2 , 13 ) and the electrode sections are designed as plug-in units, the perforations ( 4 , 5 , 6 , 7 ) pointing towards hollow cylinders. 4. An electrode according to claim 3, a ceramic hollow cylinder (2) comprising, sections on or are plugged (1) in or on which the, likewise designed as a hollow cylinder electrodes, the electric denabschnitte (1) by intervening inserted insulating rings (3 ) are isolated from each other. 5. Electrode according to one of claims 1 to 4, which also has an outer, open on one side, go through the metallic or metallic coated half cylinder as a dark room cover ( 8 ) which is arranged at a distance of at most about 1.5 mm from the effective electrode surface . 6. Electrode according to one of claims 1 to 5, in which an insulating layer ( 14 ) made of ceramic or an insulating plastic material is arranged between the internal gas supply line ( 13 ) and external electrode sections ( 1 ). 7. Electrode according to one of claims 1 to 6, wherein the length of the electrode sections ( 1 ) is small ge gene the wavelength of the VHF excitation field. 8. A method for the plasma-assisted deposition of thin layers on a substrate ( 11 ),

• - In which a rod-shaped, designed as a hollow cylinder potential-conducting electrode is arranged above the substrate,
• in which a gas to be decomposed in the plasma is passed through the hollow cylinder forming the electrode ( 1 , 2 ),
• - in which the gas exits through a perforation ( 5 ) in the hollow cylinder into the space between the electrode ( 1 , 2 ) and the substrate ( 11 ),
• - in which the electrode is divided over the length into several electrode sections ( 1 ) which are separated from one another but approximately in phase with a VHF potential,
• - In which a grounded counterelectrode ( 10 ) is arranged under the substrate ( 11 ), and
• - In which the heated to a deposition temperature substrate ( 11 ) is moved between the electrode and counter electrode ( 10 ) at constant distance from the electrode.

9. The method according to claim 8, in which a band-shaped "endless" substrate is used. 10. The method according to claim 8 or 9,  with another one for the deposition of thin layers required gas outside the rod-shaped electrode a gas shower is supplied. 11. The method according to any one of claims 8 to 10, in which a likewise rod-shaped counter electrode ( 10 ) is used ver. 12. Use of the electrode according to one of claims 1 to 7 for a plasma-based deposition process for manufacturing large-area thin-film solar cells.