DE29800950U1 - Plasma detector with impingement flow for surface treatment - Google Patents

Description

Plasma reactor with impingement flow for surface treatment

The present invention relates to a plasma reactor for treating flat substrates, the gas flow of which is improved, as well as a method for plasma treatment of such substrates.

Plasmas are partially or completely ionized gases and vapors whose particles also contain a large number of excited states. They can be created and maintained by electromagnetic fields.

The ions, electrons, molecules in electronically excited states and the radiation present in the plasma activate and/or etch surfaces or, in the case of many (particularly organic) substances, initiate polymerization in the gas phase and the formation of layers on the surface of substrates.

Even compounds that are usually not very reactive can be stimulated to undergo chemical reactions in plasmas.

The main possibilities of plasma-substrate interaction are summarized in the following overview:

material

procedure

30 Removal

modification

organic

Cleaning,

e.g. degreasing

Activation,

inorganic

Etching e.g. plasma oxidation

e.g. hydrophilization structure ] plasma polymerization | plasma CVD

Plasma treatments are carried out under vacuum in special reactors. It is usually important that the substrate is treated evenly.

Fraunhofer Ges. eV
10194; Description

The most important prerequisite for uniform treatment (especially in layer deposition) is the uniform power and material input for all surfaces to be treated (or coated). This depends on the distribution of the electric fields and gas flows.

With the aim of achieving more uniform coatings, a so-called "radial flow reactor" [A.R. Reinberg, Ann. Rev. Mater. Sci., V.9, pp.341-372 (1979)] was developed. In this reactor, the process gas is either fed in or sucked out through an opening in the middle of an electrode. The gas flow is radially symmetrical.

However, the maximum substrate size for uniform coating must be much smaller than the reactor dimensions (e.g. 4-inch wafers in a 22-inch reactor). Uniform coating also requires precise adjustment of the gas flow and RF power, and the system is not easily scalable.

In a further modification, which is described in JP 59,02,375, a "shower electrode ^11" is used, ie the gas inlet is distributed over the surface of the electrode. In such a system, the impingement flow which is favorable for the plasma interaction (eg deposition) is partially realized. In addition, the undesirable concentration gradients in the gas phase are somewhat reduced, but not completely eliminated.

US 5614026 describes another "shower electrode" that is used in a device for removing photoresist. The plasma is generated outside the device because it should not contain any ions when it hits the surface to be treated. In this arrangement, the distance between the plasma generation chamber and the substrate must be greater than the recombination length of the excited particles.

However, such a device is not suitable if

Fraunhofer Ges. eV
10194; Description

a direct plasma effect on the substrate is necessary or desired.

The object of the invention is to provide a system for the treatment of flat substrates that are to be exposed to direct plasma exposure.

This object is achieved by a plasma reactor according to claim 1. Particularly preferred are reactors according to claim 5, &iacgr;&ogr; which have a modular structure.

Special embodiments of the reactor are shown in Figures 1 to , in which:

Figure 1 shows an embodiment according to the invention with a modular structure in a side section, in which a sheet separating the various gas spaces comprises a frame with gas distribution (supply) devices attached parallel to one another, which extend lengthwise over the sheet, with waveguides and antennas additionally being provided for feeding microwaves into the plasma treatment chamber,

Figure 2 shows the same design, but in the sectional planes K and L of Figure 1, - Figure 3 shows a detail of this design, from which one can see the fastening of the gas supply devices in the frame of the electrode

Figure 4 shows a gas supply device of Figure 1 in side section,
- Figure 5 shows the same device in lateral section IJ

Figure 6 shows the same device from above in two different cutting heights G, H, Figure 7 shows a device with a modular structure in a side section, in which the sheet separating the gas spaces comprises a frame with parallel gas supply devices as in Figure .1, which in this case, however, are in the form of elongated tubes with

Fraunhofer Ges. e.V.

10194; Description .". ·&iacgr;

inlet openings directed towards the plasma treatment chamber, and Figure 8 shows the device of Figure 7 from above at cutting height X,Y.

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The plasma reactor according to the invention is a closed vessel with a reactor gas inlet through which the gas is introduced into the reactor. Within the reactor wall, the gas then passes into a gas distribution chamber without obstructions such as constrictions or the like, so that it is distributed there with a constant pressure. The gas distribution chamber, like the gas extraction chamber, is separated from the plasma treatment chamber by a surface structure separating the gas chambers. The substrate is on a surface opposite the surface structure, e.g. on

í a plate. For example, it can rest on it (e.g. if, as is often the case, this plate extends horizontally, especially if it is impermeable and forms the floor of the plasma reactor). Of course, the substrate can also be attached to or near this surface, so that this surface does not necessarily have to form the floor of the system. However, this is preferred.

In order for the gas to strike the substrate essentially vertically, i.e. as an "impact flow", the surface structure through which the gas passes must have gas inlets distributed essentially over its surface. (The term "gas inlet" refers to the entry of the gas into the plasma treatment chamber). These can be distributed symmetrically or arranged in rows or the like; the geometry of the arrangement is not important. However, it is necessary that the number of gas inlets is sufficient so that the gas passing through the gas inlets, which essentially flows and diffuses in the direction of the substrate, strikes the entire surface of the substrate essentially evenly and in the same amount. It is particularly advantageous if the inlet cross sections of the individual gas inlets are kept as small as possible. Of course, the smaller the inlet cross sections, the greater the number of gas inlets. Preferably, the inlet cross sections of the individual gas inlets are not larger than about 15.5 mm ² , more preferably not larger than about 7 mm ² , and most preferably not larger than about 1 mm ² . The geometry of the gas inlets is not important, for example, they can be round or

Fraunhofer Ges. e.V.

10194; Description » ^&bgr;# · ··

be square or also be formed in the form of elongated slots. In the latter case, the inlet cross-section is usually somewhat larger than in the first two cases. Preferably, the characteristic distance between the inlet and outlet openings is smaller than the distance between the gas inlets and the substrate in order to avoid flows parallel to the substrate surface.

After the gas has hit the substrate with its components that change it, it should not be drawn off parallel to the substrate if possible, in order to avoid a concentration gradient being created along the substrate surface. Therefore, according to the invention, the gas can exit again via gas outlets in the same sheet-like structure separating the gas spaces, flow through a gas extraction space and then leave the reactor. The gas outlets and the gas extraction space must therefore be spatially separated from the gas distribution space and the gas inlets, which is done with the help of the sheet-like structure mentioned. This principle can be varied in a large number of designs, which are explained in detail below using individual examples. The gas is then extracted from the gas extraction space via a reactor gas outlet, for example with the help of a vacuum pump.

The principle of gas inlet and outlet being effected through the surface structure opposite the substrate to be treated enables an extremely simple construction of the entire reactor. It is not necessary for the components to be arranged in an external reactor chamber which communicates with the environment through a gas inlet and outlet. Rather, it is sufficient that the spaces required for treating the substrate are formed by the components which are necessarily present anyway. For example, the plasma treatment chamber can be formed by the surface structure provided with a fixed frame (which is equipped with the gas distribution systems described above), a

Fraunhofer Ges. eV
10194; Description

opposite base plate, which can support the substrate, and a frame in between. The external dimensions of these parts can be coordinated with each other. If these components are separated from each other by seals and connected to each other, a very simple modular structure is obtained. In a preferred, because very simple, way, it is then possible to form the spaces required for the gas supply or for the removal of the gas by one of these spaces being inside the

�iacgr;&ogr; surface structure, e.g. by grooves, other recesses or pipes or other structures within this surface structure, while the other of the two spaces is arranged on the side of the surface structure facing away from the plasma treatment chamber. To separate this last-mentioned space from the external environment, a cover can be used in a simple manner, which has a recess in its interior, so that when the cover is placed in a sealing manner on the surface structure separating the gas spaces, such a gas space is formed, which can be connected to a vacuum pump or a gas supply device or the like via a reactor gas inlet or outlet. The other of the two gas spaces can be connected to the environment via a gas inlet or outlet that is guided through the frame of this surface structure.

If the four components: (1) end or base plate, (2) intermediate frame, (3) surface structure provided with the gas passage openings (also with a fixed outer frame) and (4) cover have the same external dimensions, for example if they are rectangular or square when viewed from above, they can be simply used as modular components that are connected to one another by O-rings made of rubber or the like or other sealing parts. In a simple manner, individual of these modular parts can be exchanged for other parts if necessary, so that a high degree of variability of designs of the plasma reactor according to the invention is possible with a small number of components.

The distance between the said surface structure and the

Fraunhofer Ges. eV
10194; Description

The intermediate frame that creates the (base) plate that supports the substrate can be made of any material. If the plasma treatment chamber is also intended to generate plasma using direct or alternating current, the intermediate frame can or should be made of electrically insulating material. However, a metal component is sometimes recommended because the selection of vacuum and plasma-compatible electrically insulating materials is relatively small. Plastics should be avoided in the plasma treatment chamber because of the high

&iacgr;&ogr; Outgassing rate and degradation under plasma conditions should be avoided if possible. Glass and ceramics are therefore particularly suitable as insulating materials, but they are often brittle. Their processing options are usually limited and processing is often expensive. If metal or another conductive material is used instead, an insulator can be arranged on the side facing the plasma treatment chamber if necessary.

There are various ways to excite the plasma. For example, it is possible to design the surface structure separating the gas flows as the (first) electrode and to connect the (closing) plate or surface opposite this structure in the plasma treatment chamber, which will usually carry the substrate, as the counter electrode. Such a design is described in German patent application 197 27 857.4, the priority of which this application claims.

Additionally or alternatively, the energy supply for plasma generation can be provided by microwaves, which are fed in, for example, through coaxial or waveguides. The microwave conductors are preferably sealed by the lid and then guided through preferably free spaces in the surface structure separating the gas flows (between the gas distribution devices). The energy can then be radiated into the plasma treatment chamber through antennas. If the energy is generated exclusively through microwave treatment, electrodes can be dispensed with and the entire

Fraunhofer Ges. eV
10194; Description

Reactor can be connected to electrical ground.

In a special embodiment of the invention, the microwave feed devices (antennas) can each be operated at different frequencies so that no interference can occur between the antennas. The frequency difference can be, for example, a few hundred Hz up to a few percent of the frequency (at 2.48 GHz this would be a few hundred MHz).

The antennas can be stimulated additionally or alternatively one after the other in pulse mode.

In another embodiment of the invention, the plasma can also be generated by an electrical voltage difference, but not in the plasma treatment chamber itself, but in a room that is close to it and that is located in front of the plasma treatment chamber in terms of the gas flow. The gas distribution chamber is particularly suitable for this, preferably when it is formed by the space between the lid and the surface structure separating the gas flows. This space is located very close to the plasma treatment chamber. Excited species therefore have only short diffusion paths to the substrate. As a result, the losses of the excited species through recombination and other processes are minimal. On the other hand, the direct bombardment by high-energy ions, which can cause undesirable chemical reactions (such as chain rupture in polymers), is greatly suppressed. In order to completely exclude this bombardment, the ions can be stopped, for example, by attaching an electrically non-conductive fabric or the like, e.g. made of quartz fibers.

In the latter design, care must be taken to ensure that the gaps through which the gas passes through the sheet into the plasma treatment chamber are sufficiently small, as described above. This can be achieved, for example, by placing a close-meshed metal net or grid on the sheet, which also functions as an electrode.

Fraunhofer Ges. eV
10194; Description

The cover can then be connected as a counter electrode, for example. The surface structure itself can also be connected as an electrode. Instead of being excited by direct or alternating electrical voltage, or in addition to this, the plasma in the gas distribution chamber can also be excited using microwave energy. This can be done as described above for the excitation in the plasma treatment chamber.

The invention will now be explained in more detail using individual embodiments.

Figures 1 and 2 show a reactor with a lower plate 4, on which the substrate 5 to be treated is placed or otherwise fastened, the intermediate frame 6, e.g. made of an electrically insulating material such as glass or ceramic, and a surface structure 13 into which the gas distribution system is installed.

The cover 25 is mounted on the frame 16 of the sheet-like structure separating the gas spaces and has a recess within a frame with approximately the same frame width as that of the intermediate frame 6, so that a cavity 29 is formed between the cover and the sheet-like structure 13. The sheet-like structure 13 comprises the frame 16, on which parallel gas distributors 15 are mounted. Such a gas distributor is shown in Figs. 3 to ; it consists of a body 10 and a cover plate 11, which are glued together or connected in some other way. The deeper groove 30 allows the working gas to be evenly distributed over gas outlet gaps 12, which are formed between a depression in the body 10 and the cover plate 11. The width of the gaps 12 can be maintained very precisely by the webs 31. The webs 31 can be integral parts of the bodies 10 or the plates 11, but they can also be glued on or otherwise attached.

The gas is introduced into the gas distributor 15 through a pipe connection shown in Fig. 3.

The gas distributors are mounted on the frame 16 and

Fraunhofer Ges. eV
10194; Description

Screws 14. The pipe connection 9 ends in the gas channel 24 (a blind hole) which is connected to the gas inlet 7.

The working gas enters through the reactor gas inlet 7 and is evenly distributed over the described gas space, which is located in the gas distributor 15 and represents the gas distribution space here. It is then evenly guided through the gas outlet gaps 12 into the plasma treatment space 26.

&iacgr;&ogr; A uniform distribution is given, for example, when the total cross section of the passages of a column 12 is significantly smaller than the cross section of a groove 3 0 and therefore the pressure drop only occurs in the passages.

The working gas enters the plasma treatment chamber 26 from the openings 12 and strikes the substrate 5 essentially vertically. If the openings 12 are small enough and the working pressure is selected accordingly, the gas dynamic effects ("impact flow") can, for example, lead to excellent deposition of plasma polymerization products on the opposite side, i.e. on the substrate. This is a desired effect. An impingement flow effect is achieved, for example, if the exit area of the openings is approximately 0.5 mm^ with a distance between the sheet 13 and the substrate 5 of approximately 4 cm, the gas pressure during treatment in the plasma chamber being 100 Pa and the gas flowing at 0.5 sccm (standard cubic centimeter) per inlet opening.

For evacuating the reactor and extracting the reaction products, passages 19 are provided in the surface structure 13. These passages extend parallel to the gas distributors 15. The gas flow then passes through the extraction chamber 29 in the cover 25 to the reactor gas outlet 1, which e.g.

connected to a vacuum pump.

The sealing between the reactor components 4, 6, 13 and 25 is achieved by rubber O-rings 3.

Fraunhofer Ges. eV _# , . ..

10194; Description

The advantage of this system is that the gas outlet gaps 12 through which the gas enters the plasma treatment chamber 16 can be made very narrow. This allows the advantageous gas dynamic effects to be achieved in a particularly effective manner. In addition, this design is very simple and economical to manufacture, since a large number of gas inlets can be created by connecting only two parts, the body 10 and the cover plate 11. The

&iacgr;&ogr; Drilling a large number of small holes is not necessary here.

The energy is fed in by microwaves that are fed in through coaxial (or waveguide) feedthroughs 21, which are sealed by the cover 25 and then introduced into the plasma treatment room 26 through the spaces between the gas distributors 15. They can be radiated into the room 26, for example, by antennas 22.

In addition to exciting the plasma using microwave energy, it can also be excited by applying direct or alternating voltage. In this case, the surface structure 13 is connected as an electrode and the (base) plate 4 as a counter electrode. The plasma efficiency is significantly increased by the combined effect of microwave and high frequency energy, which is desirable in some cases.

Figures 7 and 8 show a design in which the gas guidance and distribution are implemented in the opposite direction. The gas inlet is now through the cover 25, the cavity between the cover 25 and the surface structure 13 functions as the gas distribution chamber 17. The chamber components plate 4, frame 6 and surface structure 13 are located below ground potential. The surface structure 13 comprises the frame 16, parallel pipes 34 and, if necessary, a metal grid 39 pointing towards the gas distribution chamber (for metallic shielding). An electrical (e.g. RF) voltage can be applied to these components on the cover 25 so that the plasma is generated in the chamber 17.

Fraunhofer Ges. e.V. 10194; Description

and can then immediately flow into the plasma treatment chamber.

If required, an electrically non-conductive, permeable structure 37, e.g. a fabric or mat made of quartz or other fibers, can be arranged behind the metal grid 39 in order to capture ionic species. The pipes 34 with the openings 35 are used here to extract the gas. The use of pipes 34 instead of a system as shown in Fig. 1 also has the advantage of being particularly simple in terms of construction.

In an alternative embodiment, not shown, the plasma in the gas distribution chamber 17 can be excited with microwave energy, either as an alternative to or in addition to electrical excitation. In this case, the microwave energy is fed in in a similar way to that shown in Fig. 1; however, the conductors only reach into the gas distribution chamber

If only microwave energy is used for excitation, there is no need to form a cover and a surface structure as electrodes. These can then be made of any material, including non-conductive ones.

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10194; Description · ; ·; ; ; ·; j ;·,.·

14 Legend of the figures

I Reactor gas outlet 3 O-ring

4 Base plate

5 Substrat

6 intermediate frames

7 Reactor gas inlet 9 Pipe connection

&iacgr;&ogr; 10 Gas distributor body

II Gap inlet cover plate

12 Gas outlet gap

13 gas-permeable fabric

14 Screw

15 Gas distributor

16 Frame of the surface structure

17 Groove (gas channel)

19 Extraction ports

21 MW feedthrough (coax or waveguide)

2 2 MW antenna

23 Insulator

25 lids

26 Plasma room

29 Gas exhaust chamber

3 0 Groove

31 Spacer (bridge)

32 Metal sieve

33 electrically insulating or conductive spacer

34 Pipe gas collector

35 Gas inlet opening

39 metal grilles

Claims (11)

Fraunhofer Ges. e.V. 10194; Protection claims Protection claims: 1. Plasma reactor, comprising - arranged one after the other in the gas flow direction - :
- a reactor gas inlet (7) , a gas distribution chamber (17), a plasma treatment chamber (26), a gas extraction chamber (29), and a reactor gas outlet (1),
Î wherein the gas distribution chamber (17) and the gas extraction chamber (29) are separated from the plasma treatment chamber (26) by a surface structure (13) which is provided with gas inlets (12) distributed substantially over its surface, through which the gas from the gas distribution chamber (17) into the Plasma treatment chamber (26) can flow, as well as gas outlets (19,35) distributed essentially over its surface through which the gas can flow from the plasma treatment chamber (26) into the gas extraction chamber (29), characterized in that the gas distribution space (17) and/or the plasma treatment chamber (26) is/are provided with means for plasma generation. 2. Plasma reactor according to claim 1, characterized in that the means for generating plasma are the formation of opposing wall surfaces as electrode and counter electrode. 3. Plasma reactor according to claim 1 or 2, characterized in that the means for generating plasma are microwave guides or antennas. Fraunhofer Ges. eV _#> . 10194; Protection claims · J ·; i I ". I J*.." 4. Plasma reactor according to one of the preceding claims, characterized in that the area of the inlet cross sections of the individual gas inlets (12) is not larger than about 16 mm ² , preferably not larger than about 4 mm ² and most preferably not larger than about 2.5 mm ² . 5. Plasma reactor according to one of the preceding claims, comprising a closure plate (4) and a &iacgr;&ogr; intermediate frames (6) which are sealingly connected to one another together with a frame (16) of the sheet structure (13) to form the plasma treatment chamber (26), and a cover (25) which has a recess and is provided with a reactor gas inlet (7) or gas outlet (1), the cover (25) being placed sealingly on the frame (16) of the sheet structure (13) in such a way that a gas extraction space (29) or a gas distribution space (17) is formed between the cover (25) and the sheet structure (13). 6. Plasma reactor according to claim 5, characterized in that the base plate (4), the intermediate frame (6), the frame (16) of the flat structure (13) and the cover (25) have essentially the same dimensions and are sealingly connected to one another by O-rings. 7. Plasma reactor according to one of the preceding claims, characterized in that a gas extraction chamber (29) is formed between the cover (25) and the sheet-like structure (13), and in that the sheet-like structure (13) comprises a reactor gas inlet (7) extending laterally through its frame (16) and gas distribution devices (15) forming the gas distribution chamber, which communicate with the reactor gas inlet (7), wherein coaxial or waveguides (21) are guided through the sheet-like structure (13) into the plasma treatment chamber (26), through which microwave energy can be introduced into the plasma treatment chamber (26). Fraunhofer Ges. eV
10194; Protection claims 8. Plasma reactor according to claim 7, wherein the gas distribution devices (15) are mounted substantially parallel to each other on the frame (10), while the coaxial or waveguides (21) are arranged in the gaps formed thereby. 9. Plasma reactor according to claim 7 or 8, wherein the gas distribution devices are elongated tubular gas distributors with gas outlet openings or made of a ‘ a grooved elongated cuboid (10) and an elongated, also cuboid-shaped cover plate (11) are gas distributors, the latter being connected to one another in a sealing manner in such a way that gas outlet gaps 12 are formed. 10. Plasma reactor according to one of claims 1 to 6, characterized in that a gas distribution space (17) is formed between the cover (25) and the sheet-like structure (13), and the sheet-like structure (13) has a reactor gas outlet (1) extending laterally through its frame (16) and gas outlets (34, 35) which communicate with the reactor gas outlet (1), a grid (39) being arranged on the sheet-like structure (13) towards the gas distribution space and, if appropriate, a sheet-like fiber structure (37) being arranged between the grid (39) and the sheet-like structure (13), and the cover (25) being designed as a counter electrode to the component group consisting of the base plate (4), the intermediate frame (6), the sheet-like structure (13) and the metal grid (39). 11. Plasma reactor according to claim 10, characterized in that the gas outlets (34, 35) are elongated tubes with inlet openings (35) directed towards the plasma treatment chamber.