DE10322696B3 - Plasma-assisted treatment of given substrate surface area, e.g. for structurizing or coating metal, alloy, semiconductor, insulator or dielectric, uses insulator with opening, to form discharge gap, between electrode and substrate - Google Patents

Abstract

Plasma-assisted treatment of predetermined surface areas of a substrate involves operating a gas discharge without dielectric barriers by applying a potential at 2 electrodes and placing an insulator between one electrode and either the substrate or an ancillary electrode, so that there is a discharge gap at the given area, formed by openings in the insulator and ancillary electrode. An independent claim is also included for equipment used for this type of treatment.

Description

The The invention relates to a method and a device for plasma-assisted treatment of specifiable surface areas a substrate in which without masking or covering of subregions the surface a surface modification takes place, which has a lateral structuring.

The modification, ie the cleaning and activation of surfaces and the deposition of thin layers, has long been of great technological importance. The required expense of such methods is determined in particular by the technical means for generating and maintaining adequate vacuum conditions. Therefore, methods have been developed for a long time which allow surface modifications at atmospheric pressure. So will in the EP0732727B1 proposed to use plasmas, which are produced in dielectrically impeded discharges, for the surface treatment and deposition of thin layers.

there becomes an electrode facing the substrate to be treated, with a dielectric as insulator separated from the substrate surface. At sufficiently high field strengths, which are typically between 1 kV / mm and 5 kV / mm ignited a dielectrically impeded discharge, which on the treated Surface acts. Mostly the discharge with a pulsed DC voltage or operated an AC voltage.

adversely On the one hand, this method requires the high field strengths required the discharge over to ignite the dielectric barrier. Thereby is inherent given a high technical effort.

at the method described above is also the frequency of the applied High voltage preferably in the range of 10 to 50 kHz, but always below 1 MHz. This is the power density and thus the density low on reactive particles. A barrier discharge usually runs as filamentous discharge. An arbitrary increase in the frequency of the applied High voltage will therefore cause the following discharge pulse is connected to the discharge channel of the preceding one Pulse would follow. This decreases the inhomogeneity the coating to and the desired increase the deposition rate does not occur.

Therefore In the past, attempts were made to modify the surface at atmospheric pressure not with a dielectrically impeded discharge. In A. Ignatkov, A. Schwabedissen, G.F. Leu, J. Engemann, Studies of the atmospheric pressure jet matrix plasma source: Electrical properties and discharge stability, Hakone VIII Conference Proceedings, 2002, 58, is described as high frequency driven discharges in small channels for surface modification can be used. The disadvantage here is that a strong gas flow can be used must to stabilize the discharges at atmospheric pressure.

In Y.-B. Guo, F.C.-N. Hong, radio-frequency microdischarge arrays for large area cold atmospheric plasma generation, Applied Physics Letters, 82 (2003) 337, a device is shown which consists of a dielectric material is made, on both sides with a metal film is provided. By attaching several holes in this plate may be a plasma when a sufficiently high AC voltage is applied between the top and bottom of the dielectric plate over the Boreholes are fired away. Again, a strong gas flow is required to discharge to stabilize. This plasma is used for the large-scale modification of surfaces atmospheric pressure used.

For a large number However, technical application requires it only on certain surface elements the surface of a material to make modifications. Such a structured coating or functionalization of surfaces is primarily for applications of interest in the fields of biomedicine and bio-analytics, micro-optics, Microelectronics or microsystems technology lie.

If only certain, specifiable areas of the surface should be modified Most of the prior art are photolithographic processes applied. The surface is completely covered with covered by a photoresist. This is then exposed, developed and partially removed.

On this way can the surface first the whole area be modified, whereupon subsequently the modification again is eliminated at defined locations. Alternatively, the surface can also first be provided with a photoresist, whereupon the surface in the uncovered areas is modified. In any case, will the photoresist then in a so-called lift-off process again away.

In order to simplify this method, it is proposed in WO 01 / 69644A1 to modify the per se known surface modification by means of barrier discharges in such a way that the necessary electrical insulator is inserted between the two electrodes such that there is no positive contact between the insulator and the respective electrode in predetermined surface areas and in the remaining surface areas of the insulator and the respective electrode in contact. When applying a high voltage, which results in an electric field of 1 to 5 kV / mm and which has a frequency of 10 to 50 kHz, forms a cold, transient gas discharge exclusively in the predetermined surface areas.

On this type will be the textured surface modification without additional Cover and masking possible.

Because of the Barrier often surface sliding discharges ignited be filled the resulting plasma usually does not cover the entire cavity. The surface treatment becomes inhomogeneous.

Because completed the discharge zone by at least one insulator must be, is the supply of gases with layer-forming substances through pour in not possible in the discharge gap.

Farther remain the above-mentioned disadvantages of the coating process with barrier discharges also in the coating of partial areas of the surface consist.

Of the The invention is therefore based on the object, a method and to provide a device so that the treatment of a surface allows who will not uniform over this surface extends. Rather, this surface treatment is a lateral Have structuring. In the solution of this task should the known disadvantages of a local coating by means of barrier discharges be avoided.

The object is achieved by a method for plasma-assisted treatment of predeterminable surface areas of a substrate 1 ; 5 in which by applying a voltage to at least two electrodes 3 . 1 ; 6 ; 6a a gas discharge is operated and an insulator 2 either between the electrode 3 and the substrate 1 ; 5 or between the electrode 3 and an auxiliary electrode 6a is introduced such that at the predetermined surface areas discharge columns 4 emerge through recesses in the insulator 2 and the auxiliary electrode 6a be formed. Furthermore, the solution consists in a device for plasma-assisted treatment of predeterminable surface areas of a substrate 1 ; 5 consisting of at least two electrodes 3 . 1 ; 6 ; 6a is formed, which by an insulator 2 be separated, with recesses in the insulator discharge column 4 represent and these can be brought into contact with the predetermined surface areas.

A Treatment of surfaces In the context of this invention can be a coating, at the thin one Layers of a dissimilar material deposited on the surface become. Also treated as a surface modification, d. H. a change the equipment with chemical-functional groups. Furthermore suitable the process for purification, oxidation, reduction or for Material removal.

The surfaces to be treated can out Metal, an alloy, a semiconductor or insulators consist. An insulator in this sense is in particular also a dielectric.

The plasma used arises from a non-thermal discharge which takes place between at least two electrodes, which pass through at least one insulator 2 are separated from each other. In this case, at least one discharge gap 4 provided in the form of a continuous recess in the insulator, so that the plasma is formed in such a gap without a dielectric barrier.

Not Thermal discharge in this case means that through the energy input selectively the electron gas is heated and the heavy particles, such as For example, ions and neutrals remain relatively cold. Cold particles are characterized by low kinetic energy.

There the process does not use a dielectric barrier are the required Tensions to the ignition the gas discharge compared to barrier discharges low. typically, become field strengths from 0.1 to 2 kV / mm.

According to the invention, it has been recognized that the discharge can be limited to predefinable surface areas if the insulator provided with recesses or openings is brought into direct contact with the substrate to be coated, cf. 1 and 2 ,

When using an auxiliary electrode 6a this is provided with the same recesses as the insulator 2 and instead brought into direct contact with the substrate to be coated, see. 3 , The arrangement is suitable for 1 only for conductive substrates, while the devices after 2 and 3 are universally applicable.

The intended recesses or openings in the insulator and possibly to use the auxiliary electrode 6a can have any geometry. In question come next to circles, squares and rectangles also more complicated or irregular shapes.

The Structure widths of these breakthroughs are adaptable in a wide range of the required application. Typically, these are in the submillimeter range of about 1 micron to about 1 mm. Preferred in the application are feature widths of 50 μm to 500 μm.

Under Structure width should be the smallest dimension in one dimension be understood, so that a structure of for example 10 microns also a size length of For example, can reach several millimeters or centimeters.

When Insulator can also be used in particular a dielectric. Particularly preferred is the use of glass, ceramics or plastics. The required breakthroughs are preferred by drilling, milling, laser structuring or produced wet-chemically.

The insulator used has a thickness of about 1 micron to about 2000 microns. In order to minimize the voltage to be applied to ignite the gas discharge, the smallest possible thickness of the insulator 2 desirable. On the other hand, the mechanical stability of the structure requires larger thicknesses. Therefore, particularly preferred are insulators with thicknesses of about 50 microns to about 500 microns.

The Discharge is operated at frequencies above about 1 MHz. Operation is possible up to the microwave range at a few GHz.

Prefers is a procedure, in which the gas discharge at a frequency of about 1 MHz to about 200 MHz is operated. At these frequencies is coupled by the Performance particularly effective heating the electron gas. heavier By contrast, particles such as ions or neutral particles are moving, so to speak stationary in the alternating field of the discharge. The transfer of energy through collisions of the electrons is very inefficient due to the mass difference of the particles. Therefore contains the plasma is not a high energy heavy particle. sputtering, which damage the discharge assembly and the substrate also prevented by the small mean free path.

Especially advantageous is the operation of the gas discharge with a frequency from 10 MHz to 50 MHz. These frequencies can be achieved with little technical Create and shield effort, so that radio interference avoided become.

A preferred pressure range for the operation of the gas discharge is between about 10 ² Pa to about 10 ⁶ Pa. The working pressure used is adapted to the structural height of the recesses in the insulator. Particularly preferred is a working pressure in the order of the atmospheric pressure, that is from about 5 × 10 ⁴ Pa to 1, 5 × 10 ⁵ Pa.

The mean free path the free electrons hang directly from the selected one Working pressure decreases and amounts to at atmospheric pressure about 100 nm. Thus, correspondingly sharp structures can be produced, when the working pressure is sufficiently high. Furthermore, the Generation of excimer and other UV radiation at high working pressures especially effectively.

Of the Shelling of the surface to be treated with high-energy photons leads to stimulated desorption processes. This results in an increase the removal and coating rate and thus a faster treatment the substrates. The higher one Process speed causes in addition to a cost reduction of the coating a reduction of unwanted Contamination. This is because at given burst rate and Adhesion coefficient the number of atoms actually incorporated directly is proportional to the process time.

at huge structure heights or insulator thickness grows the insulation capacity of the enclosed gas volume. When the operation of the gas discharge thereby consuming is, so the working pressure can be reduced. This will match the breakdown field strength lowered the Paschen curve.

In order to perform targeted surface modifications, certain gas atmospheres are often necessary. For this purpose, in a further development, a gas supply device 7 provided, through which a process gas can be introduced into the discharge gap, cf. 4 , As in 4a In the simplest case, this can be shown through a nozzle 8th be formed, which passes the gas through a gas-permeable electrode 3 leads into the discharge gap. It is still possible, the process gas, as in 4c shown by milled or as in 4b through holes in the insulator 2 into the discharge column.

The gas stream may be in the range of about 1 to about 10 slm. Advantageously, the process is operated in a static atmosphere or with a low flow of less than about 2 slm. The unit slm designates standard liter per minute, ie a gas flow of one liter per minute at a temperature of 273.15 K and 1.013 × 10 ⁵ Pa. Due to the low gas flow no transport of the reactive gas components in the area covered by the insulator and the structure widths can be reduced.

Especially advantageous is a process management, in which the gas supply takes place only by diffusion. In this case the structure widths obtained are especially due to the lack of flow sharp.

To the gas supply through a simple outlet nozzle 8th In order to allow into the discharge column, the first electrode must 3 gas permeable, see. 4a , This happens in the simplest case in that this electrode consists of a metal grid. Commercially available, etched grids or those wound from thin wire onto a carrier body can be used for this purpose. Particularly advantageous is an arrangement in which the gap between the electrodes 3 . 6a and insulator 2 is avoided. This is made possible by forming an electrode by forming a metal layer by sputtering methods or by vacuum evaporation on the insulator 2 is deposited directly. Since there is no gap between insulator and electrode in this case, no parasitic surface discharges can form at this point.

A further development of the device for the treatment of predeterminable surface areas is characterized in that one of the electrodes is a protective layer 9 having. An embodiment is without limitation of generality in 5 shown. This layer is chosen such that the damage to the electrode is reduced or prevented by the gas discharge. For example, an oxide or nitride layer on the electrode surface is suitable for this purpose. The layer thickness is preferably 10 nm to 10 μm

Particularly simple can be treated by the process according to the invention conductive substrates. As 1 In this case, the substrate can be directly used as an electrode. Of particular technological importance is the use of a semiconductor material that simultaneously the substrate and the electrode 1 represents.

A possible Use of the method according to the invention represents the surface treatment with silicon-containing precursors. In this case is called layer-forming Substance a silicon-containing compound together with a carrier gas in introduced the discharge gap. Suitable carrier gases are, for example Noble gases and nitrogen. Possible is also the addition of oxygen.

preferred Silicon-containing compounds are organically modified silanes and / or organically modified disiloxanes and / or organically modified Disilazane and / or organically modified disilane. Especially preferred are there, without restriction generality, hexamethyldisilazane, tetraethoxysilane, tetramethoxysilane, Hexamethyldisi-Loxan, Hexamethyldisilane, tetramethylsilane, aminopropyltrimethoxysilane, Aminopropyltriethoxysilane Be radically polymerizable substances used as precursors, so allows the inventive method the deposition of plasma polymers, which are characterized by a high concentration distinguish functional groups.

Prefers contains the process gas thereby an acrylic and / or a methacrylic and / or an allyl and / or a propargyl and / or a vinyl compound and / or maleic acid derivatives and / or Maleic anhydride.

Especially preferred is the use of methacrylic acid or a methacrylic acid ester.

By the treatment of the substrate with fluorine-containing hydrocarbons can surfaces laterally structured be hydrophobized. By the supply cyclic Siloxane precursors the formation of functional groups is suppressed and the surface tension the treated surface continues reduced.

To is used as a process gas in addition to the carrier gases already mentioned a fluorine-containing Hydrocarbon and / or carbon compound with less than 20 carbon atoms used. Because volatile compounds easier penetrate into the discharge gap and a higher diffusion speed are small molecules preferred with few carbon atoms.

Examples for such preferred precursors are partially or fully fluorinated Alkanes and / or alkenes having a chain length of 3 to 20 carbon atoms and / or cycloalkanes and / or cycloalkenes having a ring size of each 3 to 8 carbon atoms and / or aromatics.

Especially Partially or completely fluorinated alkanes and / or are preferred Alkenes of one chain length each of 3 to 8 carbon atoms.

By Supply of oxygen or oxygen-containing gas mixtures can the inventive method be used for the oxidation of substrates. Exemplary called the oxidation of silicon in electronic components. In this way, the gate insulator of a metal oxide semiconductor (MOS) Component be formed.

By introducing chlorinated or fluorinated alkanes into the discharge gap, silicon substrates may be subjected to an etching process. One Such structured etching of the surface is possible even if the silicon surface has been pretreated and consists of, for example, silicon oxide SiO _X or silicon nitride SiN _X.

One last example for the structured modification of a surface according to the inventive method represents the amination of a polymer surface. Possible process gases for these Modification are nitrogen, ammonia, hydrazine or mixtures these gases.

following the invention will be explained in more detail with reference to embodiments.

Embodiment 1

In a first embodiment, in a ceramic dielectric board, 100 holes having a diameter of 400 μm were arranged in a regular array of 10 × 10 holes. The thickness of the ceramic plate is 0.5 mm and the structured area has a size of 13 × 13 mm ² . This dielectric plate is brought into direct contact with the conductive substrate to be coated, cf. 1 , In a first experiment, this was a metal plate. On the opposite side of the structured dielectric is a metallic electrode in the form of a grid. By applying a voltage of about 195 V at a frequency of 13.56 MHz, a gas discharge is simultaneously ignited in the 100 openings of the insulator. The required electrical power in this case is about 16 W. With the aid of a commercial matching network, an optimal coupling of the electrical power to the unloading device is achieved.

In same way this arrangement operate with a silicon wafer as the substrate. To a treatment time of 60 seconds are treated on the area Hydrophilic round areas detected by hydrophobic areas are separated from each other. The hydrophobically activated areas correspond to the geometry of the structured insulator. The hydrophilic areas are round and have a diameter of about 400 microns.

Embodiment 2

In a second embodiment, the counter electrode 3 replaced by a titanium layer of 50 nm thickness, which is evaporated in vacuo directly on a ceramic plate of 1 mm thickness. Subsequently, a regular arrangement of 10 × 10 holes with a diameter of 400 microns in the metal-coated ceramic plate is made again. In direct contact with a silicon wafer according to 1 succeeds in igniting a gas discharge in all recesses with a coupled power of about 35 W at a voltage of 275 V. The discharge is also operated in this case with a frequency of 13.56 MHz.

The total volume of the 100 discharge gap is 1.3 × 10 ^-2 cm ³ . The power density of the discharge is thus 2.8 kW / cm ³ . Barrier discharges, as described in WO 01/69644 A1 for structured surface treatment, have a mean power density of 0.1-1 W / cm ³ . To the same extent, the proportion of reactive particles in the gas discharge increases, which sets the advantages according to the invention in the surface treatment.

Embodiment 3

In a further embodiment, a laterally structured coating with silicon oxide was applied to an 80 μm thick polypropylene film. For this purpose, the polypropylene film was introduced between the structured ceramic plate described in the above examples and a metallic counterelectrode, cf. 2a ,

The process gas consisted of 0.01 vol .-% tetraethoxysilane (TEOS), which was introduced together with oxygen as a second layer forming substance and helium as a carrier gas at a total pressure of 10 ⁵ Pa and a gas flow of 1 slm in the discharge column. The spatially resolved elemental analysis of these layers was performed by Scanning Electron Microscopy (SEM) and Electron Beam Microprobe (EPMA).

Depending on the coating time was some of the detected coating thickness 10 nm to several 100 nm. The lateral structuring of this coating again corresponded with good accuracy of the geometry of the structured Insulator.

The thus-deposited silicon oxide layers can be derivatized so that various functional groups can be introduced based on the silicon oxide deposition. As an example, the direct layer deposition with aminopropyltrimethoxysilane (APTMS) can be mentioned as a precursor. Such process control provides aminofunctionalized surfaces. To determine the density of functional groups on the surface, the surface-coupled amino groups were labeled with fluorescein isothiocyanate (FITC). The density of functional groups on the surface can then be readily determined by measuring fluorescence over a fluorescein zenz reader read or the characteristic absorption spectrum of the dye is measured using a spectrometer.

Claims (26)

Process for the plasma-assisted treatment of predefinable surface areas of a substrate ( 1 ; 5 ), in which by applying a voltage to two electrodes ( 3 . 1 ; 6 ; 6a ) a gas discharge without dielectric barrier is operated and an insulator ( 2 ) either between the electrode ( 3 ) and the substrate ( 1 ; 5 ) or between the electrode ( 3 ) and an auxiliary electrode ( 6a ) is introduced in such a way that at the predetermined surface areas discharge gaps ( 4 ), which through recesses in the insulator ( 2 ) and the auxiliary electrode ( 6a ) are formed. Method according to claim 1, characterized in that that the gas discharge operated at a frequency of 1 MHz to 200 MHz becomes. Method according to claim 2, characterized in that that the gas discharge operated at a frequency of 10 MHz to 50 MHz becomes. Method according to one of the preceding claims, characterized in that the gas discharge is operated at a pressure of 10 ² Pa to 10 ⁶ Pa. A method according to claim 4, characterized in that the gas discharge at a pressure of 5 · 10 ⁴ Pa to 1.5 · 10 ⁵ Pa is operated. Method according to one of the preceding claims, characterized in that a process gas in the discharge column ( 4 ) is supplied. Method according to Claim 6, characterized that the process gas is supplied by diffusion. Method according to one of claims 6 or 7, characterized in that a silicon-containing compound is used as the process gas. Method according to claim 8, characterized in that that as the process gas organically modified silanes and / or organic modified disiloxanes and / or organically modified disilazanes and / or organically modified disilane-containing gases used become. Method according to claim 8 or 9, characterized that the silicon-containing compound is selected from hexamethyldisilazane, Tetraethoxysilane, tetramethoxysilane, hexamethyldisiloxane, hexamethyldisilane, Tetramethylsilane, aminopropyltrimethoxysilane, aminopropyltriethoxysilane. Method according to one of claims 6 or 7, characterized that as the process gas, a fluorine-containing hydrocarbon and / or Carbon compound containing less than 20 carbon atoms Gases are used. Method according to claim 11, characterized that as a process gas partially or completely fluorinated alkanes and / or Alkenes of one chain length each of 3 to 20 carbon atoms and / or cycloalkanes and / or Cycloalkenes having a ring size of each 3 to 8 carbon atoms and / or aromatics-containing gases used become. Method according to claim 12, characterized that as a process gas partially or completely fluorinated alkanes and / or Alkenes of one chain length used gases each containing 3 to 8 carbon atoms become. Method according to one of claims 6 or 7, characterized that as the process gas one or more radically polymerizable Compounds containing gases are used. Method according to claim 14, characterized that as the process gas is an acrylic and / or a methacrylic and / or an allyl and / or a propargyl and / or a vinyl compound and / or maleic acid derivatives and / or maleic anhydride containing gases are used. Method according to claim 15, characterized that as the process gas methacrylic acid or methacrylic containing gases are used. Device for the plasma-assisted treatment of predefinable surface areas of a substrate ( 1 ; 5 ), which two electrodes ( 3 . 1 ; 6 ; 6a ) through an insulator ( 2 ) are separated, wherein by recesses in the insulator discharge column ( 4 ) and the insulator can be brought into contact with the substrate such that the discharge gaps come to lie on the predetermined surface areas of the substrate, characterized in that the recesses are made continuous. Device according to claim 17, characterized in that the insulator has a thickness of about 1 μm to about 2000 μm. Device according to claim 18, characterized in that the insulator has a thickness of about 50 μm to about 500 μm. Device according to one of claims 17 to 19, characterized the recesses have a structure width of 1 μm to 1000 μm. Device according to claim 20, characterized in that the recesses have a structure width of 50 μm to 500 μm. Device according to one of claims 17 to 21, characterized in that one of the electrodes ( 3 . 1 ; 6 ; 6a ) consists of a metal grid. Device according to one of claims 17 to 22, characterized in that one of the electrodes ( 3 . 1 ; 6 ; 6a ) consists of a semiconductor. Device according to one of claims 17 to 23, characterized in that one of the electrodes ( 3 . 1 ; 6 ; 6a ) by depositing a metal layer on the insulator ( 2 ) is available. Device according to one of Claims 17 to 24, characterized in that one of the electrodes has a protective layer ( 9 ) having. Device according to one of claims 17 to 25, characterized that a gas supply device is present is, by which a process gas in the discharge gap can be introduced is.