Patent Application
20100186671
The invention relates to an arrangement for the working of substrates by means of plasma.
Plasma enhanced chemical vapor deposition (Plasma Enhanced Chemical Vapor Deposition=PECVD) is a special form of chemical vapor deposition=CVD), in which the deposition of thin layers is enhanced through chemical reaction by means of CVD. Instead of the thermal activation in CVD, the surface reaction is regulated or highly modified via the plasma properties (Liebermann and Lichtenberg: Principles of Plasma Discharges and Materials Processing, 2nd Edition, 2005, p. 621 ff.). The plasma can burn directly at the substrate to be coated or in a separate chamber. In the first case, the method is referred to as direct plasma method, in the second case as remote plasma method.
In the direct plasma method between the substrate and a counterelectrode a strong electric field is applied, through which a plasma is ignited. The plasma causes the opening of the bonds of a reaction gas, for example SiH4, and decomposes it into radicals which are deposited on the substrate and cause here the chemical deposition reaction. A higher deposition rate at lower deposition temperatures, for example 200-300° C., than with the CVD method can thereby be attained.
In the remote plasma method the plasma is so disposed that it has no direct contact with the substrate. It is hereby possible to excite selectively individual components of a process gas mixture. The probability of damage of the substrate surface through the plasma is, moreover, low. Of disadvantage are the possible loss of radicals on the path between the remote plasma and the substrate; in addition, gas phase reactions can already occur before the reactive gas molecules reach the substrate surface.
PECVD plasmas can also be generated inductively or capacitively through the irradiation of alternating electric fields, making electrodes superfluous.
The PECVD method is applied in the semiconductor production and also in the production of solar cells or capacitors. Gases to be considered for use in plasma processes are, for example N2O, NH3, N2, SiH4 or other silanes. If there is the wish to produce, for example SiO2 layers by means of hexamethyidisiloxane=HMDSO═C6H18O2Si2, a mixture of HMDSO, oxygen and perhaps an inert gas as excitation gas is introduced into a reaction chamber. The plasma subsequently breaks down the HMDSO molecules into their components, and substantially H2O, CO2 and SiO2, however also byproducts, are produced in the reaction. Only the SiO2 fraction contributes to the formation of the layer. The volatile or gaseous molecules, such as for example water and carbon dioxide, are pumped off.
An arrangement for the generation of plasma is already known, which includes two first electrodes connected to a voltage source and two grounded electrodes, with the first of the two grounded electrodes located in front of the first of the other electrodes and the first of the other electrodes disposed in front of the second grounded electrode (EP 1 475 824 A1). A first passage between a central first electrode permits the inlet of raw gas (first gas) which serves for the formation of a film on a substrate. A plasma discharge space of a second passage is provided between the first and second electrode, and specifically on both sides, whereby the excitable gas (second gas) can pass through. The raw gas can subsequently form a film, while the excitable gas itself is only excited and not utilized for the formation of a film.
An arrangement for the deposition of a substance out of the gas phase onto a substrate is furthermore disclosed (JP 2002-158219). This arrangement comprises several electrodes and between the electrodes two gas inlet channels and two gas outlet channels are provided.
A system for the working of substrates by means of plasma is furthermore known, with which the occurrence of flash-overs between an electrode in a dielectric is to be prevented (EP 1 796 442 A1). This system includes two working units, between which a gap is formed through which process gas is conducted.
Furthermore is known a PECVD installation with which photovoltaic materials can be applied onto a substrate (US 2006/0219170 A1). This installation includes a cathode with two opposing surfaces, with a system distributing a process gas being integrated in the electrode.
Lastly, a plasma working arrangement is also known with which a substrate can be worked effectively (JP 2005-026062). In this arrangement a substrate is transported parallel to three successively disposed electrodes. Between the electrodes gas supply means and gas drainage means are provided. Two of the electrodes are connected to a common voltage source.
The invention addresses the problem of providing a cost-effective arrangement for a PECVD working method.
This problem is solved according to the features of claim 1.
The invention relates thus to an arrangement for the working of substrates by means of plasma (PECVD), wherein at least two electrodes are provided, which are disposed in a common plane and are spaced apart from one another. Between each of the electrodes are provided interspaces which serve as gas inlets or gas outlets.
The advantage attained with the invention comprises in particular that an arrangement with several electrodes is provided, which has a small overall size since it is not necessary to provide each electrode with its own plasma source.
Embodiment examples of the invention are shown in the drawing and will be described in further detail in the following. In the drawing depict:
Below the quartz plates 4, 5 is depicted a counterelectrode 17. Above the counterelectrode 17 is located a substrate 26 which is transported in the direction of arrow 18. Between the quartz plates 4, 5 and the substrate 26 can be seen plasma clouds 19, 20, and beneath the counterelectrode 17 optionally heating elements 21, 22 are provided, which ensure a temperature-controlled counterelectrode 17. A matched housing 23 encompassing the two electrodes 2, 3 on the atmospheric side is indicated by means of dashed lines. Outside and underneath this housing 23 atmospheric pressure obtains, while beneath the quartz plates 4, 5 and the heating elements 21, 22 vacuum obtains. The housing 23 serves for high-frequency radiation shielding and as a contact guard against energized structural parts.
By 10 and 11 are denoted insulators encompassing the T-shaped electrodes 2, 3.
Although only two electrodes are shown in
The quartz plates 4, 5 are of advantage in terms of processing technique particularly if higher current and power densities are utilized, for example in a μc-Si process. In particular when the discharge switches to the so-called “gamma regime”, quartz plates 4, 5 are of advantage. In the case of an “alpha regime”, i.e. at low voltage or power density, such as are characteristic of a-Si, the ionization is mainly localized in the plasma, such that the role of the quartz plates can be neglected. Instead of quartz plates 4, 5, plates of another electrically non-conducting material, for example plates of ceramic, can also be utilized.
With the aid of quartz plates 4, 5 is attained that the emission of secondary electrons due to the ion bombardment effects a local increase of the plasma density. A higher plasma density, which corresponds to a high plasma stream, leads to a reduction of the plasma voltage. The plasma-ground voltage regulates the energy with which the ions bombard the substrate, i.e. a higher plasma voltage corresponds to higher energy. During the settling of amorphous silicon at energies of >˜15 eV electrical and optical defects form. If, due to the quartz plates, the ion energy is decreased, an improvement in the material quality results at a constant input power density. The transition from good electrical-optical a-Si:H quality, which is referred to as alpha-gamma transition, is in general observed at ˜15 eV, which in a PECVD installation can correspond to an electrode voltage of approximately 200 to 300 Volt. The use of quartz plates consequently makes possible a relative increase of the power and therewith of the coating rate. The quartz plates, moreover, isolate the expensive mechanical structural parts—the electrodes and the insulators—from the process volume proper, i.e. no chemical-thermal reaction takes place between the plasma and these components. Only the quartz-glass sheets are directly exposed to this process. However, if necessary, they can be readily exchanged. These are furthermore of great advantage, for example during a plasma cleaning etching by means of NF3, since here the quartz glass can additionally play out its excellent resistance properties. Added to this is the fact that during the process atomic components are knocked out of the source itself, i.e. a sputtering or disintegration process occurs. These atomic components are consequently also incorporated in the generated layers on the substrate. If this substrate is an electrically conducting material, this leads, for example in the production of a solar cell active layer, to the result that microscopically small shortcircuits form which, in turn, can have a negative effect on the efficiency of the finished solar cell. By applying the quartz plates, the major portion of the metallic source surface is covered such that the sputter effect is mainly limited to atomic quartz particles. Since quartz is an insulator, this does not present a problem for most applications.
By 40 is denoted a power connector bolt, which leads to a, not shown, matching network. An adapter flange 41 rests on a source flange 43, which terminates in a VCR threaded connector 45, 46 for a gas pipework. Of this adapter flange 41 only lateral regions 75, 76 are evident. On each side a gas supply bar 47, 48 is provided which is provided over its entire length with holes or slits or nozzles, through which process gases are introduced. Through the appropriate distances of these holes with respect to one another and through appropriate cross sections of the holes a mixed gas distribution in the plasma volume is attained. The holes extend into the plane of drawing of
The source flange 43 includes a central region 49 as well as two lateral regions 42, 44. In this source flange 43 is provided a gas outlet channel 50 which can be provided at the suction side, for example, with DN40 ISO-KF connectors. Such a connector 73 is evident in
On the left electrode 2 is disposed a cooling water return flow tube 56, 58 implemented as a hose assembly, as well as a cooling water forward flow tube 55, 57, also implemented as a hose assembly. Above the second electrode 3 are correspondingly disposed a cooling water forward flow tube 59, 61 on a cooling water return flow tube 60, 62. The cooling water serves for the temperature control of the electrode bodies.
Into the adapter flange 41 lead several securement bolts, of which one is provided with the reference number 63.
In
Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications and alternative constructions fall within the scope and spirit of the disclosed invention as expressed in the claims.
