Patent Application
20120107506
1. Field of the Invention
The present invention relates to a film formation method and a film formation apparatus for forming a predetermined thin film pattern on a substrate according to an aperture pattern of a mask which is placed so as to be in intimate contact with a front surface of the substrate.
2. Description of the Related Art
Conventionally, in a manufacturing process of an organic electroluminescent (EL) thin film, a mask film formation method is often employed in which a mask having a predetermined aperture pattern is placed so as to be in intimate contact with a glass substrate when a film is formed. A known example of the mask film formation method is the following mask evaporation method.
The mask evaporation method is a method in which a substrate front surface (surface on which a film is to be formed) is placed downward, and an evaporation material evaporated from an evaporation source placed so as to be opposed to the substrate front surface is evaporated onto the substrate front surface via a mask, thereby forming a predetermined organic EL thin film on the substrate front surface. When such organic EL thin film is used as a color display panel, in order to form a thin film pattern having pitches similar to those of pixels in the display panel, a mask having apertures corresponding to the pattern is used. Pixel pitches of a display panel are several tens of micrometers, and pixels of three colors, i.e., red, green, and blue are regularly placed, and thus, the mask apertures are formed so as to correspond thereto. For example, with regard to the shape of the mask apertures, a slit-like shape in which the slit ranges multiple pixels or a dot-like shape in which the dot-like aperture is provided in each pixel is used.
In recent years, the resolution of an organic EL panel becomes higher and higher, and the pixel pitches become finer and finer accordingly, which requires the mask apertures to become finer. When the thickness of the mask is relatively large (0.5 mm to 1.0 mm), portions in the mask apertures near the evaporation pattern are shaded with the mask, which causes the film thickness at the portions to be smaller than that of center portions in the mask apertures. In order to reduce or eliminate nonuniformity due to such a film thickness distribution (edge blur), it is better that the mask is as thin as possible. For example, thin masks having thicknesses of 0.01 mm to 0.4 mm are used. Meanwhile, a substrate on which an organic EL thin film is to be formed becomes larger and larger. For use in a large flat panel display, a substrate with the size of, for example, about 370 mm×470 mm or larger becomes available.
On the other hand, in the above-mentioned evaporation method for forming an organic EL thin film, both the mask and the substrate warp, the extent of which differs, and thus, a gap is liable to occur between the mask and the substrate. In particular, in a large-sized substrate, the difference in deflection between the mask and the substrate becomes larger, and the gap caused between the mask and the substrate becomes as large as several tens of micrometers or more (which is close to the pixel pitches or the mask aperture width). When a gap is caused between the mask and the substrate in this way, the evaporation material enters the gap to blur the edges of the evaporation pattern, resulting in a vague evaporation pattern. Therefore, there are problems that the evaporation accuracy is lowered and that the evaporation material enters an adjacent pixel to cause failure.
Therefore, as disclosed in Japanese Patent Application Laid-Open No. H11-158605, a vacuum film formation apparatus is known in which a mask formed of a magnetic material is attached to a substrate front surface and the mask is brought into intimate contact with the substrate front surface in a horizontal state by magnetic attraction caused by a magnet holder provided on a rear surface side of the substrate.
However, when the substrate and the mask are brought into intimate contact with each other using only magnetic attraction of a magnet, the following problems occur. A mask aperture for forming an evaporation pattern which corresponds to pixels of an organic EL panel has a problem that the shape thereof is deformed when a magnet approaches, and thus, a predetermined thin film pattern may not be formed. The reason for this is, when the mask is to be attracted by magnetic force, it is necessary that the mask contain a ferromagnetic metal such as Fe, Ni, or Co as a mask formed of a magnetic material. Such ferromagnetic metal is liable to be magnetized and, in the ferromagnetic metal, correspondingly to an applied magnetic field of the magnet, force (for example, repulsive force) acts between fine mask patterns. As a result, deformation is caused to locally widen or narrow the mask aperture. Further, such deformation of the mask aperture results in abnormal display in the organic EL panel due to a pixel defect, a line defect, or the like. In particular, while the weight of the substrate itself becomes heavier as the size becomes larger, when a mask which is thinned to respond to higher resolution of the display panel is used, an intense magnet is necessary in order to pull up the thin mask from a rear surface of the substrate and to hold the mask in intimate contact with the substrate. Therefore, the problem of the deformation of the mask apertures becomes more liable to occur.
Accordingly, an object of the present invention is to provide a film formation apparatus capable of causing a substrate and a mask to be in intimate contact with each other in a substantially horizontal state without deforming mask apertures as described above, and also provide a film formation method using the film formation apparatus.
According to a first aspect of the present invention, there is provided a method for forming a film on a substrate surface on which a film is to be formed, via a mask including therein multiple apertures, in a manner that the mask is fixed to a mask frame under tension at least in one direction and the mask is brought into intimate contact with the substrate surface on which a film is to be formed, the substrate being placed above the mask, the method including pressing the substrate from a rear surface side of the substrate in lines along at least two opposing sides of the substrate at least in a region inside the mask frame.
According to a second aspect of the present invention, there is provided a film formation apparatus including: a mask frame for fixing thereto a mask under tension; a substrate support member for holding a substrate above the mask, with a substrate surface on which a film is to be formed facing on the mask; and a pressing body for pressing the substrate from a rear surface side in lines along at least two opposing sides of the substrate at least in a region inside the mask frame.
According to the present invention, the mask and the substrate may be brought into intimate contact with each other in a substantially horizontal state without deforming the mask apertures. Therefore, a thin film pattern may be formed according to a predetermined mask aperture pattern. Further, a high-quality thin film pattern may be obtained which has no edge blur and the like caused by an evaporation material that enters through a gap between the mask and the substrate.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
The present invention is described in the following based on embodiments illustrated in the attached drawings.
A mask holder (not shown), which is located in an evaporation apparatus for holding a mask 10 and a mask frame 11, is coupled to a mask position controller (not shown). By driving the mask position controller, movement of the mask held by the mask holder in directions of the X axis and the Y axis and rotation of the mask about the Z axis may be controlled independently. Note that, the mask as used in the present invention includes multiple predetermined apertures and is, under tension in at least one direction, fixed to the rectangular, rigid mask frame 11. The tension on the mask 10 is at least in a direction along two opposing sides of a substrate 20, and is, ordinarily, at least in a long side direction of the mask apertures.
Further, a substrate support member (not shown) for supporting the substrate 20 is coupled to a substrate position controller (not shown). By driving the substrate position controller, movement of the substrate 20 supported by the substrate support member in the directions of the X axis and the Y axis and rotation of the substrate 20 about the Z axis may be controlled independently.
As illustrated in
Note that, in the present invention, the positions at which the pressing body 30 presses the substrate 20 from the rear surface side thereof are in lines along at least two opposing sides of the substrate 20. The lines as used herein may be continuous or intermittent. Examples of the layout of the pressing positions of the pressing body 30 are illustrated in
Note that, it is desired that the ball-like bodies 31 placed on the pressing body 30 be rotatable. The reason is that, if the ball-like bodies 31 are rotatable, friction between the ball-like bodies 31 and the substrate 20 in the in-plane direction of the substrate 20 may be alleviated to prevent adverse effects on the positional accuracy between the substrate 20 and the mask 10 which is adjusted at a previous process step. Further, it is desired that, in the pressing body 30, the ball-like bodies 31 be combined with an elastic body so that force applied by the ball-like bodies 31 to the substrate 20 may be arbitrarily adjusted.
In the above-mentioned pressing body 30, the ball-like bodies 31 are described as exemplary members to be brought into contact with the substrate 20, but the present invention is not limited thereto. Any structure having a basic function capable of pressing a selected region may be employed, and it is desired that the structure have a curved surface which is to be brought into contact with the substrate 20 so as not to damage the substrate 20.
Further, in the above, the case in which the pressing body 30 is in contact with the substrate 20 at multiple points within the rear surface of the substrate 20 is described by way of example, but a ring-like structure may be used so that the pressing body 30 may be brought into contact with the substrate 20 in lines along the four sides thereof. Further, as a material of the members to be brought into contact with the substrate 20 (for example, the ball-like bodies 31), a metal, a resin, a glass, or the like may be appropriately used.
In the present invention, a more exemplary embodiment is a structure in which the pressing force applied to the rear surface of the substrate 20 in lines is larger in a direction perpendicular to the direction of maximum tension on the mask 10 than in a direction in parallel therewith. More specifically, referring to
Further, in this case, the ball-like bodies 31 for pressing the substrate 20 in lines along the X direction and the ball-like bodies 31 for pressing the substrate 20 in lines along the Y direction are separately structured so that the pressing forces thereof may be independently adjusted. Alternatively, the multiple ball-like bodies 31 arranged in the respective directions in lines may be separately structured so that the pressing forces thereof may be individually adjusted. In this case, adjustments according to the conditions of the deflection of the mask and the deflection of the substrate may also be made. This may avoid pressing with excess force, and thus, may avoid damage to the substrate and the mask.
Next, an evaporation method according to an embodiment of the present invention is described with reference to
After the above-mentioned alignment is completed, the substrate 20 is further lowered toward the mask 10, and, as illustrated in
After that, as illustrated in
Therefore, according to the present invention, the substrate 20 and the mask 10 may be brought into intimate contact with each other in a wide range without a gap and without deforming the fine mask aperture pattern. Further, even when the size of the substrate 20 used is large, deflection of the center portion thereof due to its own weight may be suppressed to maintain the horizontal state by the method described above, and thus, the substrate 20 and the mask 10 may be brought into intimate contact with each other in a wide range without a gap.
Further, according to the present invention, there is exemplified another configuration in which a support body supports the substrate 20 from the side of the surface of the substrate 20 on which a film is to be formed.
In the support body 40 in the above description, a member to be brought into contact with the mask 10 is a member having a round shape in cross section as an example, but the present invention is not limited thereto. Any structure having a basic function capable of supporting, or further, lifting up a selected area may be employed, and it is desired that the structure have a curved surface which is to be brought into contact with the mask 10 so as not to damage the substrate 20 or the mask 10. Further, in order to prevent damage to the mask 10 at the positions at which the support body 40 is brought into contact therewith, the thickness of the mask 10 may be locally increased at the positions.
Further, here, the support body 40 is brought into contact with the mask 10. Alternatively, a contact member may be brought into contact with the substrate 20. In the mask 10 used in this case, an aperture is formed in advance in the mask 10 at a portion at which the support body 40 is brought into contact with the substrate 20. Further, as the material of the support body 40, a metal, a resin, a glass, or the like may be appropriately used.
By the method described above, the substrate 20 and the mask 10 are caused to be in a horizontal state in a wide range, and the substrate 20 and the mask 10 are brought into intimate contact with each other without a gap. In this state, the multiple CCD cameras are used to measure the misalignment between the alignment marks of the substrate 20 and the mask 10, and confirm again that the accuracy of the misalignment is in the predetermined range. Note that, in a process step described with reference to
Then, in the state in which the pressing body 30 presses the rear surface of the substrate 20 to bring the mask 10 into intimate contact with the surface on which a film is to be formed of the substrate 20, an evaporation source (not shown) provided below the mask 10 is used to evaporate an organic EL material onto the front surface of the substrate 20 via the mask 10 having the predetermined aperture pattern formed therein. Note that, when an organic EL thin film for color display is to be formed on the front surface of the substrate 20, masks 10 for red, green, and blue, respectively, are used and the alignment of the mask, the intimate contact between the mask and the substrate 20, and the film formation described above are carried out with regard to each of the masks.
In this way, the thin film pattern may be formed according to a predetermined mask aperture pattern. Further, a high-quality thin film pattern may be obtained which has no edge blur and the like caused by an evaporation material that enters through a gap between the mask 10 and the substrate 20.
Using the film formation apparatus illustrated in
An organic EL material was loaded in an evaporation source (not shown) placed in the film formation apparatus, and the substrate 20 was located in the film formation apparatus so that the surface on which a film is to be formed thereof faced downward. The vacuum degree in the film formation apparatus was 2×10−4 Pa. As the substrate 20, a glass substrate formed of alkali-free glass having a thickness of 0.5 mm and the size of 400 mm (X)×500 mm (Y) was used. The substrate 20 had multiple arranged thin film transistors (TFTs) and electrode wiring formed thereon. The size of each of pixels arranged in the display region was 30 μm (Y)×120 μm (X), and the size of the display region of each of the organic EL display devices including multiple such pixels was 60 mm (X)×70 mm (Y). In the substrate 20, 25 display devices described above were placed so as to form a matrix of 5 rows×5 columns correspondingly to the aperture regions 12 illustrated in
The mask 10 had a thickness of 40 μm and the size of 460 mm (X)×560 mm (Y), and was fixed by welding under tension to the mask frame 11. The mask frame 11 had a thickness of 20 mm and the width of the region inside the mask frame 11 was 396 mm (X)×496 mm (Y). The tension in the X direction as the long side direction of the apertures in the mask 10 was adjusted to be 1.5 times as large as that in the Y direction. An Invar material was used as the mask 10 and the mask frame 11. Further, in the aperture regions 12 of the mask 10, multiple apertures in which the dimension in the X direction was 60 mm and the dimension in the Y direction was 30 μm were provided.
The pressing body 30 was adapted to apply pressing force by means of ball-like rotating bodies using the elastic body. As the ball-like rotating bodies, the ball-like bodies 31 formed of SUS304 and having a diameter of 10 mm were used, and, as the elastic body, a spring formed of SUS304 was used. The strength of the spring was selected so that the spring might apply pressing force of about 0.196 N (20 gf) when the ball-like bodies 31 pressed the substrate 20 in the film formation. Such ball-like bodies 31 were placed at 20 locations in the region inside the mask frame 11 with the same pitches as those of the mask apertures as illustrated in
Next, a process step of forming the organic EL material is described. First, in the previous process step, pixel electrodes electrically connected to driving TFTs were formed at positions corresponding to the pixel regions on the substrate 20, respectively. The alignment marks were simultaneously formed in the layer in which the pixel electrodes were formed.
Then, in the film formation apparatus, the above-mentioned mask 10 was aligned with predetermined pixels in the panel. After that, the organic EL material was formed. Note that, in the following, a process step of forming the organic EL material is described, but a similar method may be used to form a film of other materials forming an organic EL element.
First, from the state illustrated in
After the above-mentioned alignment was completed, as illustrated in
After that, as illustrated in
With the pressing body 30 pressing the rear surface of the substrate 20, the gap between the surface on which a film was to be formed of the substrate 20 and the mask was 10 μm or smaller. In this way, with the mask 10 being in intimate contact with the surface on which a film was to be formed of the substrate 20, the organic EL material was evaporated onto the front surface of the substrate 20 via the mask 10 from the evaporation source provided below the mask 10. After the evaporation, the shape of the organic EL thin film formed on the substrate 20 at a thickness of about 50 nm was investigated. The width of the film formed was almost equal to the mask aperture width and no edge blur was observed. Further, it was confirmed that the organic EL material did not enter a pixel placed adjacently.
In the organic EL display device manufactured by the film forming process step described above, lack of a pixel due to light emission failure and a malfunction were not observed.
The ball-like bodies 31 were placed at positions along the long sides of the substrate 20 (in the Y direction) as illustrated in
After the evaporation, the shape of the organic EL thin film formed on the substrate 20 at a thickness of about 50 nm was investigated. The width of the film formed was almost equal to the mask aperture width and no edge blur was observed. Further, it was confirmed that the organic EL material did not enter a pixel placed adjacently.
In the organic EL display device manufactured by the film forming process step described above, lack of a pixel due to light emission failure and a malfunction were not observed.
The evaporation process step was carried out similarly to the case of Example 1 except that the support body 40 illustrated in
Next, a process step of forming the organic EL material is described.
Similarly to the case of Example 1, the misalignment between the alignment marks of the mask 10 and the substrate 20 was measured and adjusted to ±2 μm or smaller. After that, the substrate 20 was further lowered toward the mask 10 and the front surface of the substrate 20 was brought into contact with the mask 10. After the contact, the multiple CCD cameras were used to measure the misalignment between the alignment marks of the substrate 20 and the mask 10, and confirm that the accuracy was ±2 μm or smaller. In this state, the pressing body 30 stood still above the rear surface of the glass substrate 20. Further, the support bodies 40 stood still below the surface on which a film was to be formed of the substrate 20.
After that, the support bodies 40 was raised and was stopped in a state of being in contact with the mask 10. Further, the pressing body 30 was lowered to press the rear surface of the substrate 20 to be put into the state illustrated in
As described above, in this example, by using both the support bodies 40 and the pressing body 30, deflection of the center portion of the substrate 20 due to its own weight was able to be suppressed. With this, the substrate 20 and the mask 10 were able to be caused in a substantially horizontal state.
Next, the pressing body 30 was caused to press the rear surface of the substrate 20, and the support bodies 40 supported the mask 10, so that the gap between the surface on which a film was to be formed of the substrate 20 and the mask was 10 μm or smaller. In this way, with the mask 10 being in intimate contact with the surface of the substrate 20, the organic EL material was evaporated onto the front surface of the substrate 20 via the mask 10 from the evaporation source provided below the mask 10.
After the evaporation, the shape of the organic EL thin film formed on the substrate 20 at a thickness of about 50 nm was investigated. The width of the film formed was almost equal to the mask aperture width and no edge blur was observed. Further, it was confirmed that the organic EL material did not enter a pixel placed adjacently.
In the organic EL display device manufactured by the film forming process step described above, lack of a pixel due to light emission failure and a malfunction were not observed.
A pressing body including structures 32 elongated along the directions of the sides of the substrate as illustrated in
After the evaporation, the shape of the organic EL thin film formed on the substrate 20 at a thickness of about 50 nm was investigated. The width of the film formed was almost equal to the mask aperture width and no edge blur was observed. Further, it was confirmed that the organic EL material did not enter a pixel placed adjacently.
In the organic EL display device manufactured by the film forming process step described above, lack of a pixel due to light emission failure and a malfunction were not observed.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2010-240759, filed Oct. 27, 2010, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-240759 | Oct 2010 | JP | national |
