Etching a substrate: processes – Masking of a substrate using material resistant to an etchant – Mask resist contains organic compound
Reexamination Certificate
2002-05-09
2003-09-30
Niebling, John P. (Department: 2812)
Etching a substrate: processes
Masking of a substrate using material resistant to an etchant
Mask resist contains organic compound
Reexamination Certificate
active
06627097
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a shadow mask which is applicable to forming film having predetermined patterns. The present invention also relates to a method of forming the shadow mask. The present invention further relates to a method of manufacturing a semiconductor device with using the shadow mask.
2. Description of the Related Art
An organic EL (Electroluminescence) display, which is one of semiconductor devices, has been employed in a television, a computer, and the like.
In order to realize color display, a plurality of light emission layers are electively formed in predetermined areas in the organic EL display device. Each of the light emission layers emits light of red, green or blue. The formation of the light emission layers requires a metal sheet having apertures as a mask (shadow mask). The light emission layers are formed by evaporation.
For example, techniques disclosed in Unexamined Japanese Patent Application KOKAI Publications Nos. H3-250583 and H8-227276 relate to a method of manufacturing the organic EL display device.
FIG. 7
is a cross sectional view showing a state of forming the light emission layers with using a shadow mask described above.
A transparent anode
502
is formed on a transparent glass substrate
501
, and a hole transfer layer
503
is formed on the anode
502
. As shown in
FIG. 7
, a shadow mask
504
is arranged so as to be slightly distant from the hole transfer layer
503
. An evaporation material
505
is placed so as to face the hole transfer layer
503
so that the shadow mask
504
intervenes between them.
The evaporation material
505
is heated, thus, light emission layers
506
are formed on predetermined regions of the hole transfer layer
503
. Thereafter, an electron transfer layer and a cathode (not shown) are formed on the hole transfer layer
503
and the light emission layers
506
, thus, the organic EL display device is completed.
In such the case using the shadow mask, a thinner shadow mask with finer apertures is required to form finer light emission layers. However, thinner the shadow mask becomes, harder to realize the fine apertures, because the shadow mask is made of the metal sheet. The thin shadow mask may be bent by heat for evaporation. Accordingly, it is difficult to form the light emission layers with precise dimensions.
Moreover, the light emission layers or the like may be broken when the shadow mask contact it, because of the shadow mask is made of metal. In such a case, yield of the organic EL display device may be deteriorated. Unexamined Japanese Patent Application KOKAI Publications Nos. S53-75858, S62-297457 and H4-236758, and Unexamined Japanese Utility Model Application KOKAI Publication No. S64-45160 disclose masks for solving the above problems.
Unexamined Japanese Patent Application KOKAI Publication No. S53-75858 discloses a mask (evaporation mask) which comprises a thin silicon plate including boron and a support plate for reinforcing the silicon plate so as to have enough mechanical strength. Those thin silicon plate and support plate are formed unitarily. The thin silicon plate has a first hole whose side wall is perpendicular to a major surface of the thin silicon plate. The support plate have a second hole whose side wall is perpendicular to a major surface of the support plate. The second hole is larger than the first hole. In a case of forming a film on a substrate by evaporation, the mask is arranged so that its thin silicon plate faces the substrate.
In the case of forming the film on the substrate by the evaporation, some of evaporated particles slant toward the substrate. Since the side wall of the hole in the mask is perpendicular to the major surface of the mask (or the substrate) as described above, edge of the hole in the mask prevents the evaporated particles slanting toward the substrate from reaching the substrate. As a result, the formed film does not always have correct dimensions.
The mask and the substrate may be expanded by temperature variation or the like during the film formation. If the material of the substrate differs from that of the thin silicon plate of the mask, the thermal expansion rate of the substrate also differs from that of the thin silicon plate. In a case where, for example, the thin silicon plate includes boron as described above, such the problem may occur when the material of the substrate is not silicon including boron. As a result, the dimensions of the formed film may differ from the planned value. Especially in the semiconductor device whose pattern is very fine, minute difference may cause short circuit or the like, and yield of the semiconductor device may be deteriorated.
Unexamined Japanese Patent Application KOKAI Publication No. S62-297457 discloses a mask (mask for evaporation) has the thickness of 50 to 400 micrometers and a hole whose side wall is perpendicular to a major surface of the mask.
Such the mask is too thick to manufacture an organic EL color display device or the like. Since the side wall of the hole in the mask is perpendicular to the major surface of the mask, the mask prevents the evaporated particles slanting toward the substrate from reaching the substrate. Accordingly, a film having inappropriate dimensions may be formed.
Moreover, it is difficult to precisely form fine apertures necessary for forming a film having fine patterns even if anisotropic etching is carried out to form the apertures.
Unexamined Japanese Utility Model Application KOKAI Publication No. S64-45160 discloses a mask (mask for forming a film) which comprises stacked first and second masks. The first mask, which is relatively thin, has an opening whose shape is the same as that of a film to be formed, and the second mask, which is relatively thick, has an opening which is larger than the opening in the first mask. Since those first and second masks are stacked with each other, they are formed separately. Therefore, the first mask may slide away from the second mask and vice versa, or the thinner first mask may be bent because of thermal expansion caused by temperature variation or the like during the film formation.
Moreover, it is difficult to form a hole (an opening) in a very thin film because such a film does not have enough strength. Therefore, the film must have appropriate thickness (for example, 100 micrometers). Therefore, the first mask is made so as to be thinner than the second mask, however, the first mask is not very thin (approximately 10 micrometers, for example). As a result, edge of the hole in the mask prevents the evaporated particulars slanting toward the substrate from reaching the substrate, thus, it is difficult to form a film having appropriate dimensions.
Unexamined Japanese Patent Application KOKAI Publication No. H4-236758 discloses a mask (mask for evaporation) which is made of a (
100
) surface single crystal silicon wafer. Firstly, a region including an area which will mask apertures are applied (to-be-aperture area) of the (
100
) surface single crystal silicon wafer is processed so as to be thinner than surrounding regions. Then an SiO
2
film is formed on regions other than the to-be-aperture area. Then apertures each of whose side wall is a (
111
) surface are formed by anisotropic etching the to-be-aperture area which is not covered with the SiO
2
.
Since there is an interrelation between the dimension of the aperture whose side wall is the (
111
) surface and the thickness of the mask, the above described mask is not suitable for forming a film having fine patterns.
Moreover, since the region including the to-be-aperture area is thinned first and then the apertures are formed as described above, the etching process is required twice. However, it is difficult to complete the first etching so that the single crystal silicon wafer has a predetermined thickness without failure, therefore, the to-be-aperture area may be too thin or too thick. As a result, the strength of the mask may decrease or apertures having appropriate dimensions are hardly to be formed.
Ac
Fukuzawa Shinichi
Ootsuki Shigeyoshi
Niebling John P.
Stevenson Andre′ C.
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