JP2006077297A - Mask, film deposition method and method for producing organic el system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mask capable of obtaining an objective film pattern with high precision even if the mask members to be used are large. <P>SOLUTION: The mask comprises: a base member 2 having opening parts 7; and mask members 3 on the base member 2 each arranged at the position covering the opening part 7 and provided with a mask opening part 4 with a prescribed pattern. The mask opening part 4 has an opening area smaller than the area of a film to be formed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a mask, a film forming method, and a method for manufacturing an organic EL device.

  In recent years, with the development of electronic devices such as computers and portable information devices, the use of organic EL (electroluminescence) devices as color display devices has increased. In the manufacturing process of this type of organic EL device, for example, when an organic EL material for light emission or an electrode is patterned, deterioration of the organic material due to moisture or oxygen becomes a problem, so a vacuum evaporation method using a mask is used. ing.

In the manufacturing method of an organic EL device including such a vapor deposition process, it is possible to reduce the cost by generally increasing the number of panels from one substrate by increasing the size of the substrate. As the mask becomes larger, the mask manufacturing yield may be reduced. Therefore, for example, a technique such as Patent Document 1 or 2 is disclosed in order to improve the yield reduction.
JP 2001-237073 A JP 2001-273976 A

  In Patent Document 1, a plurality of members (unit masks) used as a vapor deposition mask and a base material to which the members are attached are positioned and fixed by alignment marks to increase the size of the mask. However, when vapor deposition is performed with the unit mask fixed to the deposition substrate, it is necessary to maintain good adhesion between the deposition substrate and the deposition mask during deposition in order to obtain good deposition pattern accuracy. However, as the deposition target substrate and the deposition mask increase in size, deformation due to its own weight increases, and it becomes difficult to maintain adhesion.

  In particular, the thickness of the area where the opening is formed in the unit mask needs to be thin (to prevent the mask from shadowing the vapor deposition particles) in order to improve the accuracy of the vapor deposition pattern. The rigidity is low, and deformation due to its own weight becomes significant. In addition, in a unit mask having a wide opening corresponding to a large panel, deformation due to its own weight becomes larger in a region where the opening is formed, and the deposition pattern accuracy on the deposition substrate is reduced.

  On the other hand, as shown in Patent Document 2, when the vapor deposition mask is made of a magnetic material, a magnet is disposed on the opposite side of the vapor deposition mask with the vapor deposition substrate sandwiched between the vapor deposition substrate and the vapor deposition substrate. Although there is a method to ensure adhesion, there is a large amount of displacement of the deposition substrate and the deposition mask (the state where the magnetic force is applied and the state where the magnetic force is acting), which causes defects such as scratches on the deposition substrate Is not sufficient.

  An object of the present invention is to solve these problems, and in particular, to provide a mask and a film forming method capable of accurately obtaining a target film pattern even when a mask member to be used is large. . A further object of the present invention is to provide a highly reliable organic EL device obtained by the film forming method.

  In order to solve the above-described problems, a mask of the present invention is a mask for forming a film having a desired shape on a substrate, and includes a base member having an opening formed of a plurality of openings, and the base. A mask member disposed on the member so as to cover the opening, and the mask member includes a mask opening formed of a plurality of openings, and the mask opening is formed on the substrate. The film has a shape smaller than the desired shape.

  According to such a mask, since the area of the opening forming region having a low strength is reduced compared to a conventional unit mask having a mask opening corresponding to the film shape, deformation due to its own weight is small. . That is, in the mask of the present invention, the area of the base member having relatively high strength is large, and the area of the mask member in the opening forming region having relatively low strength is small. Will be able to. Therefore, the mask of the present invention is highly reliable, and a vapor deposition film having a desired shape can be obtained by using the mask as a vapor deposition mask, for example.

  The strength referred to here can be exemplified with respect to the thermal expansion coefficient, and a mask member having a larger thermal expansion coefficient than the base member can be used. In order to obtain a film to be formed using the mask of the present invention, after forming a part of the film through the mask, the mask and the deposition target member are moved relative to each other, and the remaining film is formed through the mask. Should be formed.

  The mask opening is smaller than the area of the film formed on the substrate, and specifically has an opening area obtained by dividing the area of the film to be formed into n equal parts (where n is a natural number of 2 or more). It can be. In this case, the mask to be formed can be formed without any spots by moving the mask of the present invention n times.

  In the present invention, when the film to be formed is rectangular, the mask opening can be formed in a stripe shape. In this case, after forming a part of the film through the mask, the mask is moved in the x-axis direction and / or the y-axis direction, and then the rest of the film is formed through the mask. A rectangular film can be obtained.

  In this invention, a mask member can be arrange | positioned on a base member so that the mask opening part of a mask member may be located on the opening part of a base member. Further, the base member can have a size that can completely cover the film forming member on which the film is to be formed during the film forming process.

  The mask member can be made of silicon, for example. In this case, the moldability of the mask member is improved, and a mask opening having a desired shape can be easily obtained. In addition, the mask member can be made of, for example, metal, and in this case, a high-strength mask member is obtained. Specifically, any of stainless steel, invar, 42 alloy, and nickel alloy can be used as a main component. The base member is preferably made of a material having a higher strength than that of the mask member, for example, a metal, and can be made of a metal material such as stainless steel or invar, or glass or ceramics.

  In the mask of the present invention, the mask member can be bonded to the base member. Each member can be positioned by an alignment mark attached to any member.

  Next, in order to solve the above problems, a film forming method of the present invention is a film forming method using the mask of the present invention described above, and a part of a film to be formed on a substrate through the mask is formed. A step of forming, a step of relatively moving the substrate and the mask, and a step of forming a remaining portion of a film to be formed on the substrate through the mask.

  According to such a film forming method, a film having a desired shape can be easily and reliably formed. And since the reliability of the mask is high, the yield is also high. In addition, since the area of the opening forming region having a low strength is smaller than that of a unit mask having a mask opening corresponding to the film shape as in the prior art, the mask used is less deformed by its own weight. In other words, the mask used in the film forming method of the present invention has a relatively high strength base member area, and a relatively low strength opening formation region mask member area. The amount of deformation can be minimized. The strength referred to here can be exemplified with respect to the thermal expansion coefficient, and a mask member having a larger thermal expansion coefficient than the base member can be used.

  Next, in order to solve the above-mentioned problem, the method for producing an organic EL device (organic electroluminescence device) of the present invention is a method for producing an organic EL device comprising an organic material layer between electrodes, And a step of forming the organic material layer for each different color by the film forming method described above. In this case, a highly reliable organic material layer can be formed, and the resulting organic EL device is extremely reliable.

  Further, as a manufacturing method of a different aspect, an organic layer is provided that includes a light emitting layer between a cathode and an anode, and an electron injection layer between the cathode and the light emitting layer of a specific color. A method for manufacturing an EL device, which may include a step of forming the electron injection layer by the film forming method described above. In this case, a highly reliable electron injection layer can be formed, and the resulting organic EL device is extremely reliable.

  Embodiments of the present invention will be described below with reference to the drawings. In each figure, the scale is different for each member in order to make each member recognizable on the drawing.

  FIG. 1 is a diagram schematically showing a planar configuration (a) and a cross-sectional configuration (b) of an embodiment of the mask of the present invention. The mask 1 of this embodiment is formed by joining a plurality of mask members 3 to a base member 2, and the mask member 3 has a mask opening 4. As shown in FIG. 1B, the mask member 3 is disposed so as to cover the opening 7 of the base member 2, and the mask opening 4 is located inside the opening 7. Such alignment is performed on the basis of alignment marks 5 (overlapped in FIG. 1) formed on both members 2 and 3. The base member 2 is formed with an alignment mark 6 for alignment with a substrate (film formation substrate) on which film formation or the like is performed using the mask 1.

  The base member 2 and the mask member 3 are fixed or joined together by an adhesive or spot welding. In order to configure the mask member 3 so as to be detachable with respect to the base member 2, both members may be integrated by, for example, engagement or fitting.

  The mask opening 4 formed in the mask member 3 has an opening area smaller than the area of the film desired to be formed on the substrate. Specifically, the area of the film to be formed is divided into n equal parts (where n is a natural number of 2 or more). Since the film to be formed has a rectangular shape, the mask opening 4 is formed. It is formed in a size that is half of the rectangular area.

  The base member 2 is made of a material having higher strength than the mask member 3, specifically, a material having a smaller thermal expansion coefficient than the mask member 3. In this embodiment, the mask member 3 is mainly composed of silicon, and the base member 2 is mainly composed of a metal (for example, stainless steel, invar, 42 alloy, nickel alloy, etc.) having a smaller thermal expansion coefficient than silicon. The mask member 3 can also be made of a metal material such as stainless steel, invar, 42 alloy, nickel alloy or the like in addition to silicon. In this case, a material having higher workability than the base member 2 is appropriately selected. It will be. The base member 2 can also be formed of glass, ceramics, or the like in addition to a metal material such as stainless steel or invar.

  Here, if silicon is used as the mask member 3, a highly accurate mask opening 4 can be formed by anisotropic etching. On the other hand, if a metal material such as Invar is used as the mask member 3, the mask opening 4 can be formed by ordinary etching.

  Further, the mask 1 of the present embodiment is configured as a multi-sided mask capable of obtaining a plurality of predetermined vapor deposition patterns (film patterns) from one mask 1. That is, as shown in FIG. 1, each mask member 3 disposed on the base member 2 has a mask opening 4 through which a vapor deposition material (film forming material) from a vapor deposition source (material supply source) can pass. The mask opening 4 has an opening pattern half the size of the film pattern corresponding to the film pattern to be acquired. In the present embodiment, a plurality of (for example, four) such mask members 3 are arranged on one base member 2, and a plurality of (for example, four) film patterns are obtained by one deposition process. It is possible.

  In the mask 1 having such a configuration, a film formation target substrate (not shown) is installed on a side different from the side in contact with the base member 2 of the mask member 3, and the film formation material generator (for example) disposed on the base member 2 side For example, a film is formed by supplying a film forming material (deposition material) from a vapor deposition source (not shown).

Next, an example of a film forming method using the mask of the present invention will be described.
2 uses a film area (film formation target area) 12 (area surrounded by a broken line) to be formed and a mask 1 shown in FIG. 1 on a substrate (film formation target substrate) 10 to be formed. It is the plane schematic diagram shown about the relationship with the film-forming area 11 (area | region enclosed with the continuous line) formed in this way. The size of the deposition target substrate 10 used here is 730 mm × 920 mm.

First, by performing the first film formation (first film formation step) on the film formation target area 12 using the mask 1 of FIG. 1, a part of the film formation target area 12 as shown in FIG. Film formation is performed for (half in this embodiment).
Then, after forming a film on a part of the film formation target area 12 in this way, the mask 1 and the substrate 10 are relatively moved. Here, it is assumed that the mask 1 is scanned so that the mask opening 4 is positioned on a region where no film is formed in the film formation target area 12.

After the relative movement between the mask 1 and the substrate 10, the second film is formed (second film forming step). FIG. 3 is a schematic plan view showing a film formation state on the substrate 10 after the second film formation. As shown in FIG. 3, the film formation area 14a and the film formation area 14b are formed in the first film formation process, and the film formation area 15a and the film formation area 15b are formed in the second film formation process.
That is, the same material can be formed without overlapping the desired film formation target area 12 by performing the film formation process twice using the mask 1 of FIG. 1 as in this embodiment. become able to.

  The conventional mask has a mask opening having the same size as that of the film formation target area 12, and the area of the mask member in the vicinity of the opening having a low strength is large, so that deformation due to its own weight increases. On the other hand, since the mask 1 of FIG. 1 has a large area of the base member 2 having a high strength and a small area of the mask member in the vicinity of the opening having a low strength, the amount of deformation due to its own weight can be minimized. . Therefore, according to the film forming method using the mask 1 of the present embodiment, since the deformation of the mask 1 is small, a film having a desired shape can be easily obtained, and the reliability of the obtained film is very high. It will be expensive.

On the other hand, FIG. 4A is a schematic plan view showing a modification of the mask, and FIG. 4B is a schematic plan view showing a pattern of a film formed when vapor deposition is performed using the mask.
The mask 100 shown in FIG. 4A has eight mask members 103 detachably assembled to the base member 102, and the mask member 103 has a mask opening 104 as in the mask 1 of FIG. Yes. The mask member 103 is disposed so as to cover an opening (not shown) of the base member 102, and the mask opening 104 is located inside the opening of the opening. Such alignment is performed with reference to alignment marks (not shown) formed on both members 102 and 103. The base member 102 is formed with an alignment mark (not shown) for alignment with a substrate (film formation substrate) on which film formation or the like is performed using the mask 100.

  The mask opening 104 formed in one mask member 103 has an opening area smaller than the film area of the film formation target area 12 (FIG. 2) to be formed. Specifically, it has an opening area obtained by dividing the film area of the film formation target area 12 (FIG. 2) to be formed into eight equal parts. The base member 102 is made of a material having higher strength than the mask member 103, specifically, a material having a smaller thermal expansion coefficient than the mask member 103. In this embodiment, the mask member 103 is mainly composed of silicon, and the base member 102 is mainly composed of a metal (here, 42 alloy) having a smaller thermal expansion coefficient than silicon.

  Further, the mask 100 of the present embodiment is configured as a multi-sided mask capable of obtaining a plurality of predetermined vapor deposition patterns (film patterns) from one mask 100. That is, as shown in FIG. 4A, each mask member 103 disposed on the base member 102 has a mask opening 104 through which a vapor deposition material from a vapor deposition source can pass, and the mask opening The unit 104 is configured to have an opening pattern having a size of 1/8 of the film pattern corresponding to the film pattern of the film formation target area 12 (FIG. 2) to be acquired. In this embodiment, eight such mask members 103 are arranged on one base member 102.

  In the mask 100 having the above-described configuration, deformation due to its own weight in the vicinity of the opening formation region is further reduced as compared with the mask 1 shown in FIG. In addition, when performing vapor deposition using this mask 100, the following processes can be included.

  First, by performing the first vapor deposition on the substrate 10, as shown in FIG. 4B, a film is formed on a part of the film formation target area 12, here the film formation areas 14a, 14b, 14c, and 14d. Is done. Then, after forming a film on a part of the film formation target area 12 in this way, the mask 100 and the substrate 10 are relatively moved. Here, it is assumed that the mask 100 is scanned so that the mask opening 104 is positioned on an area where the film formation target area 12 is not formed (film formation areas 15a, 15b, 15c, and 15d).

  After the relative movement between the mask 100 and the substrate 10, the second vapor deposition is performed. As a result, film formation is performed on the film formation areas 15a, 15b, 15c, and 15d, and the same material can be formed on the film formation target area 12 without overlapping.

  As shown in FIG. 5, one mask opening 204 is formed so as to have an opening area divided into eight equal parts of the film to be formed with respect to the film formation target area 12 (FIG. 2). Two mask members 203 having 204 may be formed on the base member 202. In this case, a desired film can be obtained by four times of vapor deposition, and the proportion of the mask opening 204 in the entire mask 200 is small. Therefore, the influence of deformation due to its own weight is less than that of the mask 100 of FIG. It can be further reduced. Note that although the number of film formation increases and the processing time becomes long, the rigidity of the mask can be obtained, so that it is possible to deposit on a large substrate with high accuracy.

  Further, as shown in FIG. 5B, a plurality of mask openings 304 may be formed for one mask member 303. Further, as shown in FIG. 6, the mask opening is formed so as to be parallel to the longitudinal direction of the film formation target area 12, and the film formation areas 14 a and 14 b are formed by the first vapor deposition using this. 15a and 15b may be formed by the second vapor deposition.

  Here, the manufacturing method of the mask member used in the above embodiment will be briefly described. As described above, the mask member can be made of a metal material such as stainless steel, nickel alloy, or invar, a silicon material, or the like. In the case of a metal material, etching or electroforming is effective for forming the mask opening. On the other hand, in the case of silicon, the opening can be formed by a process as shown in FIG.

In FIG. 7, silicon having a plane orientation (110) is taken as an example.
First, as shown in FIG. 7A, a silicon wafer 30 is prepared, and a silicon oxide film 31 is formed on the surface of the silicon wafer 30 with a thickness of about 1 μm by a thermal oxidation method. The film formed on the surface of the silicon wafer 30 is not limited to the silicon oxide film 31, but can be nitrided by the CVD method as long as it is a film that is durable in the subsequent crystal anisotropic etching of silicon performed using an alkaline aqueous solution. A silicon film or a film made of gold or platinum by sputtering may be used.

  Next, the silicon oxide film 31 is patterned by photolithography as shown in FIG. A buffered hydrofluoric acid solution is used for patterning.

  Next, crystal anisotropic etching of the silicon wafer 30 is performed using a 35 wt% aqueous potassium hydroxide solution heated to 80 ° C. As a result, as shown in FIG. 7C, the portion of the silicon wafer 30 that is not covered with the silicon oxide film 31 is removed to form the opening 33, and the portion corresponding to the opening 33 is thick. Becomes smaller. Further, the lower edge portion is etched in a tapered shape by crystal anisotropic etching. Note that the thickness of the opening 33 and the taper amount can be controlled by adjusting the etching time.

  Finally, by removing the silicon oxide film 31 using, for example, a buffered hydrofluoric acid solution, a mask member having an opening 33 as shown in FIG. 7D can be obtained.

Then, the example which manufactures an organic EL apparatus (organic electroluminescent apparatus) using the film-forming method mentioned above is demonstrated.
With regard to the mask 1 and the like described above, a matrix-like vapor deposition pattern can be formed on the deposition target substrate depending on the shape of the mask opening of the mask member. Such a matrix-like deposition pattern formation is suitable for forming a pixel of a display device, for example. Specifically, an organic material or an electrode material constituting the pixel is used by a film forming method using the above-described mask. It is preferable to do so.

  FIG. 10 is a plan view schematically showing a schematic configuration of the organic EL device, and reference numeral 270 in FIG. 10 denotes an organic EL panel. Such an organic EL panel can be obtained by forming each pixel (R pixel, G pixel, B pixel) including each color light emitting layer on the organic EL device substrate 55. The organic EL panel 270 includes a substrate 55 made of glass or the like, a large number of organic EL elements forming pixels 271 (R pixels, G pixels, B pixels) arranged in a matrix, and a sealing substrate (not shown). And is configured.

  The substrate 55 is made of a transparent substrate such as glass, for example, and includes a display region 202a positioned at the center of the substrate 55 and a non-display region positioned outside the display region 202a at the periphery of the substrate 55. 202b. The display area 202a is an area formed by organic electroluminescence elements arranged in a matrix, and is also referred to as an effective display area.

  FIG. 8A is a schematic plan view showing an arrangement pattern of each color pixel R (red), G (green), and B (blue) of the organic EL device, and shows a display area of one organic EL panel. . FIG. 8B is an explanatory diagram showing a pixel B (blue) that is a target for depositing the same material. Note that the two areas surrounded by the dotted line in FIG. 8B indicate the areas where the film is formed in two steps using a mask.

  On the other hand, FIG. 9 is a schematic plan view showing a mask for forming the pixel B shown in FIG. 9A shows a mask member 400 having a mask opening 404 corresponding to the pattern of the pixel B, and FIG. 9B shows a mask member having a slit-like opening 504 corresponding to a plurality of pixels B. 500 and FIG. 9C show a mask member 600 in which the mask member of FIG. 9B is formed by two mask members 603a and 603b. In the case where a plurality of organic EL panels are formed from a single substrate, these mask members are assembled to a base member to form a mask.

  When forming the pixel of such an organic EL device, each of the pixels can be simply configured in a matrix by applying the film forming method described above. Moreover, it can be suitably used for large organic EL devices. Moreover, it can be suitably used when a striped electrode is formed on each substrate of the panel.

Specifically, the low molecular organic EL device to be manufactured has a structure in which an anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode are laminated in this order. . The polymer organic EL device has a structure in which an anode / hole transport layer / light emitting layer / electron transport layer / cathode are laminated in this order.
In the case of a low molecular organic EL device, the characteristics of the light emitting layer are improved by putting a small amount of guest material (dopant material) into the host material by co-evaporation. Different colors can be emitted by changing materials used for the light emitting layer. For display applications, as shown in FIG. 8A, R, G, and B pixels are arranged in stripes, and a light emitting material is formed using the above-described masks at positions corresponding to the respective colors. Can do. In particular, it is effective to use the above-described mask for large substrates and large panels.

  Further, when light from the light emitting layer is extracted, a color change is caused by the interference effect of the stacked films. Interfering film thickness varies depending on each color of R, G, B, and the effect on color change also varies. However, by optimizing at least the film thickness of the electron transport material for each R, G, B pixel, The color purity of each color of G and B can be improved. Thus, by using the above-described mask, an electron transport material having an optimum film thickness can be formed for each of the R, G, and B pixels. As a result, display characteristics can be improved.

  Furthermore, depending on the color, display properties can be improved by inserting a layer of alkali metal fluoride or alkaline earth metal fluoride, specifically lithium fluoride, between the light emitting layer and the cathode. it can. In particular, when the lithium fluoride layer is formed on the blue pixel B, the effect of improving the characteristics becomes remarkable. However, such a lithium fluoride layer can be formed by vapor deposition, and the above-described mask is used. By vapor deposition, a film can be selectively formed on the pixel B.

  In addition, in the organic EL device, by forming a translucent reflective film on the light extraction side and forming a reflective film on the opposite side, multiple interference of light from the light emitting layer occurs, resulting in a half of the spectrum of the extracted light. The value range is reduced and the color purity is improved (see, for example, JP-A-2002-373776). Such a configuration can be realized by adjusting the distance between the translucent reflective film and the reflective film to the wavelength of the emission color. Among the R, G, and B pixels, by forming a translucent reflective film on the pixel whose characteristics are to be improved, for example, the pixel B, the color purity is improved, the luminance load as a display is reduced, the life is improved, etc. Improved characteristics can be realized. Thus, in the process of forming the translucent reflective film only on the pixel B, if the above-described mask is used, it is possible to improve display characteristics on a large substrate or a large panel.

  As mentioned above, although each embodiment was shown, the present invention is not restricted to the above-mentioned embodiment, and can be suitably changed in the range which does not contradict the gist or idea of the invention which can be read from a claim and the whole specification, Masks, film forming methods, and organic EL device manufacturing methods involving such changes are also included in the technical scope of the present invention.

The top view (a) and sectional drawing (b) which show typically the mask which is one Embodiment of this invention. Explanatory drawing shown about the usage condition of the mask of FIG. Explanatory drawing which shows the usage condition of a mask following FIG. The top view (a) typically shown about the modification of a mask, and explanatory drawing (b) shown about a use aspect. The top view shown typically about the modification of a mask. Explanatory drawing shown about the usage condition of a different mask. Explanatory drawing shown about the manufacturing process of a mask member. The top view which shows typically the pixel structure of an organic electroluminescent apparatus. FIG. 9 is a schematic plan view of a mask having an opening corresponding to the pixel configuration of FIG. 8. The top view which shows an example of the organic electroluminescent apparatus obtained by the manufacturing method to which the film-forming method of this embodiment is applied.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Mask, 2 ... Base member, 3 ... Mask member, 4 ... Mask opening part, 5 ... Alignment mark

Claims (8)

A mask for forming a film of a desired shape on a substrate,
A base member having an opening composed of a plurality of openings, and a mask member disposed on the base member so as to cover the opening;
The mask member includes a mask opening composed of a plurality of openings,
The mask opening has a shape smaller than the desired shape of the film formed on the substrate.   The mask according to claim 1, wherein an area of the mask opening is smaller than an area of the film formed on the substrate.   The mask according to claim 1, wherein the mask member is configured to be detachable from the base member.   The mask according to any one of claims 1 to 3, wherein the mask member is made of silicon.   5. The mask opening according to claim 1, wherein the mask opening has an opening area obtained by dividing an area of a film to be formed into n equal parts (where n is a natural number of 2 or more). mask of. A film forming method using the mask according to any one of claims 1 to 5,
Forming a part of a film to be formed on the substrate through the mask, moving the substrate and the mask relative to each other, and forming a remaining part of the film to be formed on the substrate through the mask. The film-forming method characterized by having. An organic EL device manufacturing method comprising an organic material layer between electrodes,
A method for producing an organic EL device, comprising the step of forming the organic material layer for each different color by the film forming method according to claim 6. A method for producing an organic EL device comprising a light emitting layer between a cathode and an anode, and an electron injection layer between the cathode and the light emitting layer of a specific color among the light emitting layers,
A method for manufacturing an organic EL device, comprising the step of forming the electron injection layer by the film forming method according to claim 6.

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