Semiconductor element and display device using the same

Abstract

A display device including a semiconductor element is provided. The semiconductor element includes: a semiconductor having an active layer; a gate insulating film which is in contact with the semiconductor; a gate electrode opposite to the active layer through the gate insulating film; a first nitride insulating film formed over the active layer; a photosensitive organic resin film formed on the first nitride insulating film; a second nitride insulating film formed on the photosensitive organic resin film; and a wiring provided on the second nitride insulating film, in which a first opening portion is provided in the photosensitive organic resin film, an inner wall surface of the first opening portion is covered with the second nitride insulating film, a second opening portion is provided in a laminate including the gate insulating film, the first nitride insulating film, and the second nitride insulating film inside the first opening portion, and the semiconductor is connected with the wiring through the first opening portion and the second opening portion.

Claims

1. A display device comprising: a semiconductor layer over a substrate; a first insulating film over the semiconductor layer, the first insulating film comprising a first opening; a wiring over the first insulating film, the wiring in contact with the semiconductor layer through the first opening; a second insulating film over the wiring, the second insulating film comprising a first inorganic insulating film and a second opening; a third insulating film over the second insulating film, the third insulating film comprising an organic insulating film and a third opening; a fourth insulating film over the third insulating film, the fourth insulating film comprising a second inorganic insulating film and a fourth opening; and a pixel electrode over the fourth insulating film, the pixel electrode in contact with the wiring through the second opening, the third opening, and the fourth opening, wherein the first opening and the third opening overlap with each other.

2. The display device according to claim 1, wherein the second insulating film is in contact with the wiring, wherein the third insulating film is in contact with the second insulating film, wherein the fourth insulating film is in contact with the third insulating film, and wherein the pixel electrode is in contact with the fourth insulating film.

3. The display device according to claim 1, wherein the first opening and the second opening overlap with each other, and wherein the first opening and the fourth opening overlap with each other.

4. A display device comprising: a semiconductor layer over a substrate; a first insulating film over the semiconductor layer, the first insulating film comprising a first opening; a wiring over the first insulating film, the wiring in contact with the semiconductor layer through the first opening; a second insulating film over the wiring, the second insulating film comprising a first inorganic insulating film and a second opening; a third insulating film over the second insulating film, the third insulating film comprising an organic insulating film and a third opening; a fourth insulating film over the third insulating film, the fourth insulating film comprising a second inorganic insulating film and a fourth opening; and a pixel electrode over the fourth insulating film, the pixel electrode in contact with the wiring through the second opening, the third opening, and the fourth opening, wherein the first opening and the third opening overlap with each other, and wherein the third insulating film has a curved inner wall surface adjacent to the third opening.

5. The display device according to claim 4, wherein the second insulating film is in contact with the wiring, wherein the third insulating film is in contact with the second insulating film, wherein the fourth insulating film is in contact with the third insulating film, and wherein the pixel electrode is in contact with the fourth insulating film.

6. The display device according to claim 4, wherein the first opening and the second opening overlap with each other, and wherein the first opening and the fourth opening overlap with each other.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the accompanying drawings:

(2) FIGS. 1A and 1B show a structure of a thin film transistor;

(3) FIGS. 2A to 2E show a process of manufacturing the thin film transistor;

(4) FIGS. 3A and 3B are an SEM photograph and a schematic view which show a cross sectional structure of an organic resin film;

(5) FIGS. 4A and 4B show dispersions in threshold voltages;

(6) FIGS. 5A and 5B are an SEM photograph and a schematic view which show a cross sectional structure of an organic resin film;

(7) FIGS. 6A and 6B are an SEM photograph and a schematic view which show a cross sectional structure of an organic resin film;

(8) FIGS. 7A and 7B are an SEM photograph and a schematic view which show a cross sectional structure of an organic resin film;

(9) FIGS. 8A and 8B show a structure of a thin film transistor;

(10) FIGS. 9A to 9D show a pixel structure of a light emitting device;

(11) FIGS. 10A and 10B show cross sectional structures of the light emitting device;

(12) FIGS. 11A to 11C show cross sectional structures of the light emitting device;

(13) FIG. 12 shows a structure of a thin film transistor;

(14) FIGS. 13A to 13D show a pixel structure of a liquid crystal display device;

(15) FIGS. 14A and 14B show cross sectional structures of the liquid crystal display device;

(16) FIGS. 15A to 15D show an outline structure of the light emitting device;

(17) FIGS. 16A to 16H show specific examples of electrical appliances; and

(18) FIGS. 17A and 17B show C-V characteristics of an MOS structure in the case where a silicon nitride film is used as dielectric.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

(19) In this embodiment, an example in which the formation position of the first opening portion 110 is changed in FIGS. 1A and 1B will be described using FIGS. 8A and 8B. Note that FIGS. 8A and 8B each show a cross sectional structure immediately after the formation of the second opening portion. In addition, the reference symbols used in FIGS. 1A and 1B are referred to if necessary.

(20) In FIG. 8A, reference numeral 801 denotes a first opening portion having a diameter of 1 and 802 denotes a second opening portion having a diameter of 2. A characteristic in FIG. 8A is that the first opening portion 801 is provided to protrude from the end portion of the source region 103. The photosensitive organic resin film 109 can be formed in a position as indicated in this embodiment because the first passivation film 108 becomes an etching stopper, thereby stopping the progress of etching. In addition, in FIG. 8B, reference numeral 803 denotes a first opening portion having a diameter of 3 and 804 denotes a second opening portion having a diameter of 2. A characteristic in FIG. 8B is also that the first opening portion 803 is provided to protrude from the side end portion of the source region 103. Even in this case, with respect to the photosensitive organic resin film 109, the first passivation film 108 becomes an etching stopper, thereby stopping the progress of etching.

(21) As described above, the inorganic insulating film which can become an etching stopper is located under the photosensitive organic resin film used as the interlayer insulating film. Thus, even when the diameter of the first opening portion is increased, there is no problem, so that it is very useful because a design margin in the formation of the contact hole can be widened.

Embodiment 2

(22) In this embodiment, an example in which the present invention is applied to a light emitting device such as an EL display device will be described. FIG. 9A is a plan view of a pixel of the light emitting element (note that a state up to the formation of a pixel electrode is indicated), FIG. 9B is a circuit diagram thereof, and FIGS. 9C and 9D each are a cross sectional view along a line A-A or B-B.

(23) As shown in FIGS. 9A and 9B, a display portion of the light emitting device includes a plurality of pixels which are surrounded by gate wirings 951, data wirings 952, and power source wirings (wirings for supplying a constant voltage or a constant current) 953 and arranged in matrix. In each of the pixels, a TFT 954 serving as a switching element (hereinafter referred to as a switching TFT), a TFT 955 serving as means for supplying a current or a voltage for producing light emission of an EL element (hereinafter referred to as a driver TFT), a capacitor portion 956, and an EL element 957 are provided. Although not shown here, the EL element 957 can be formed by providing a light emitting layer over a pixel electrode 958.

(24) Note that, in this embodiment, an n-channel TFT having a multi-gate structure is used as the switching TFT 954 and a p-channel TFT is used as the driver TFT 955. However, it is not required that the pixel structure of the light emitting element is limited to this. Thus, the present invention can be applied to various known structures.

(25) In the cross sectional view of FIG. 9C, the n-channel TFT 954 and the capacitor portion 956 are shown. Reference numeral 901 denotes a substrate, and a glass substrate, a ceramic substrate, a quartz substrate, a silicon substrate, or a plastic substrate (including a plastic film) can be used. In addition, reference numeral 902 denotes a silicon nitride oxide film, 903 denotes a silicon oxynitride film, and they are laminated to serve as base films. Of course, it is not required that the present invention is limited to these materials. Further, an active layer of the n-channel TFT 954 is provided on the silicon oxynitride film 903. The active layer has a source region 904, a drain region 905, LDD regions 906a to 906d, and channel formation regions 907a and 907b. In other words, it has two channel formation regions and four LDD regions between the source region 904 and the drain region 905.

(26) Also, the active layer of the n-channel TFT 954 is covered with a gate insulating film 908, and a gate electrode (gate electrode layers 909a and 909b) and another gate electrode (gate electrode layers 910a and 910b) are provided thereon. In this embodiment, a silicon oxynitride film is used as the gate-insulating film 908. When the above nitride insulating film such as an aluminum nitride film having a high relative dielectric constant is used, an occupying area of an element can be reduced. Thus, it is effective for the improvement of the scale of integration.

(27) Also, a tantalum nitride film is used for the gate electrode layers 909a and 910a and a tungsten film is used for the gate electrode layers 909b and 910b. With respect to these metallic films, ii selection ratio is high. Thus, the structure as shown in FIG. 9B, can be obtained by selecting an etching condition. The etching condition is preferably referred to JP 2001-313397 A according to the present applicant.

(28) Also, a silicon nitride film or a silicon nitride oxide film is provided as a first passivation film 911 covering the gate electrodes, and a photosensitive organic resin film 912 (in this embodiment, a positive type photosensitive acrylic film is used) is provided thereon. Further, a second passivation film 913 is provided on the photosensitive organic resin film 912 so as to cover a first opening portion (see FIG. 1A). A second opening portion (see FIG. 1A) is provided to the bottom of the first opening portion. In this embodiment, a silicon nitride film or a silicon nitride oxide film is used as the second passivation film 913. Of course, another nitride insulating film such as an aluminum nitride film or an aluminum nitric oxide film can be also used.

(29) Also, the data wiring 952 is connected with the source wiring 904 through the second opening portion, and a connection wiring 915 is connected with the drain region 905 through the second opening portion. The connection wiring 915 is a wiring connected to a gate electrode of the driver TFT 955. A structure in which a wiring containing mainly low resistance metal such as aluminum or copper is sandwiched by other metallic films or an alloy film of these metals is preferably used for the data wiring 952 and the connection wiring 915.

(30) Also, reference numeral 916 denotes a source region of the driver TFT 955, with which the power source wiring 953 is connected. In a contact portion for this connection, the first opening portion and the second opening portion are formed by carrying out the present invention. In addition, the power source wiring 953 is opposite to a gate wiring 917 of the driver TFT 955 through the first passivation film 911 and the second passivation film 913, so that a storage capacitor 956a is formed. Further, the gate wiring 917 is opposite to a semiconductor film 918 through the gate insulating film 908 so that a storage capacitor 956b is formed. Because the power source wiring 953 is connected with a semiconductor layer 919, a charge is supplied therefrom, so that the semiconductor film 918 serves as an electrode. Thus, the capacitor portion 956 becomes a structure in which the storage capacitors 956a and 956h are connected in parallel, thereby obtaining a large capacity with a very small area. Furthermore, with respect to particularly the storage capacitor 956a, a silicon nitride film having a high relative dielectric constant is used for dielectric, so that a large capacity can be ensured. Because the dielectric of the storage capacity 956a is composed of a laminate structure of the first passivation film 911 and the second passivation film 913, a probability of occurrence of a pinhole is extremely low. Thus, a capacitor with high reliability can be formed.

(31) When the present invention is carried out, the number of masks used in a photolithography process is increased to form the second opening portion as compared with a conventional case. However, when the increase in the number of masks is advantageously used, a new storage capacitor can be formed as described in this embodiment. Such a point is also one of important characteristics of the present invention. The characteristic of the present invention more than compensates for a demerit resulting from the increase in the number of masks, so that it greatly contributes to industrial progress. For example, when high definition image display is obtained, it is required that a relative occupying area of the storage capacitor to an area of each pixel is reduced in a display portion to improve an aperture ratio. Therefore, it is extremely useful to increase a storage capacity.

(32) Also, in FIG. 9D, reference numeral 920 denotes a drain region of the driver TFT 955, which is connected with a drain wiring 921. The drain wiring 921 is connected with a pixel electrode 958 to compose a pixel. In this embodiment, an oxide conductive film which is transparent with respect to visible light (typically, an ITO film) is used as the pixel electrode 958. However, the present invention is not limited to such a film.

(33) An example after an EL element is actually formed in the light emitting device having the above pixel structure is shown in FIGS. 10A and 10B. FIG. 10A is a cross sectional view corresponding to the cross section shown in FIG. 9D and shows a state in which the EL element 957 is formed on the pixel electrode 958. Note that, when the structure shown in FIG. 10A is used, the pixel electrode 958 corresponds of the anode of the EL element 957. In addition, in this specification, an EL element indicates an element in which an EL layer is provided between a cathode and an anode and a voltage is applied to the EL layer or a current is injected thereto to emit light.

(34) The end portion of the pixel electrode 958 is covered with a photosensitive organic resin film 961. The photosensitive organic resin film 961 is provided in a grid shape so as to frame each pixel or provided in a stripe shape in row unit or column unit. In any case, when it is formed on the contact hole, a concave portion can be efficiently embedded and the entire surface can be also leveled. Note that, in this embodiment, the same material as the photosensitive organic resin film (first photosensitive organic resin film) 912 used as the interlayer insulating film described above (in this embodiment, the positive type photosensitive acrylic film) is used for the photosensitive organic resin film (second photosensitive organic resin film) 961. Thus, manufacturing facilities can be minimized. In addition, although not shown, the negative type photosensitive acrylic film which becomes an S-shaped cross section as shown in FIGS. 6A and 6B may be used. Of course, in this time, it is desirable that a curvature radius in a top end portion and a bottom end portion of the opening portion is set to 3 m to 30 m (typically, 10 m to 15 m). In addition, in this case, when a length of the tail portion indicted by W is not minimized, it is not preferable because an aperture ratio is reduced. Further, a known resist material (polymer material containing chromophore) can be also used.

(35) Also, the surface of the photosensitive organic resin film 961 is covered with a nitride insulating film as a third passivation film 962, so that degassing from the photosensitive organic resin film 961 can be suppressed. In addition, the third passivation film 962 is etched on the pixel electrode 958 to provide an opening portion. In the opening portion, an EL layer 963 is in contact with the pixel electrode 958. The EL layer 963 is generally composed by laminating thin films such as a light emitting layer, a charge injecting layer, and a charge transporting layer. However, various structures and various materials in which light emission has been observed can be used. For example, SAlq (in which one of three ligands of Alq.sub.3 is substituted for a triphenylsilanol structure) as an organic system material containing silicon can be also used as a charge transporting layer or a hole blocking layer.

(36) Of course, the EL layer is not necessarily composed of only organic thin film, and a structure in which an organic thin film and an inorganic thin film are laminated may be also used. A polymer thin film or a low molecular thin film may be used. In addition, a forming method is changed according to whether a polymer thin film or a low molecular thin film is used. However, the thin film is preferably formed by a known method.

(37) Also, a cathode 964 is formed on the EL layer 963, and a nitride insulating film as a fourth passivation film 965 is finally provided thereon. A metallic thin film containing an element belonging to group 1 or 2 of the periodic table is preferably used as the cathode 964. A metallic film in which lithium of 0.2 wt % to 1.5 wt % (preferably, 0.5 wt % to 1.0 wt %) is added to aluminum is suitable in view of a charge injecting property and the like. Note that, if lithium is diffused, it is concerned that the operation of a TFT is influenced thereby. However, according to this embodiment, the TFT is completely protected by the first passivation film 911, the second passivation film 913, and the third passivation film 962, so that it is unnecessary to concern the diffusion of lithium.

(38) Here, data indicating a blocking effect of a silicon nitride film formed by a sputtering method using high frequency discharge with respect to lithium are shown in FIGS. 17A and 17B. FIG. 17A shows a C-V characteristic of an MOS structure in the case where a silicon nitride film formed by a sputtering method using high frequency discharge (indicated as RF-SP SiN) is used as dielectric. Note that Li-dip means that a solution containing lithium is spin-coated on the silicon nitride film and means that contamination is intentionally caused using lithium for a test. In addition, FIG. 17B shows a C-V characteristic of an MOS structure in the comparative case where a silicon nitride film formed by a plasma CVD method (indicated as CVD SiN) is used as dielectric. Note that, with respect to data shown in FIG. 17B, an alloy film in which lithium is added to aluminum is used as a metallic electrode. A general BT test is conducted for these films (specifically, heat treatment is conducted at 150 C. for 1 hour in addition to the application of a voltage of 1.7 MV). As a result, as shown in FIG. 17A, a change in C-V characteristic in the case where the silicon nitride film formed by the sputtering method using high frequency discharge is hardly observed. On the other hand, a large change in C-V characteristic in the case where the silicon nitride film formed by the plasma CVD method is observed. Accordingly, contamination of lithium is recognized. These data suggest that the silicon nitride film formed by the sputtering method using high frequency discharge has a very effective blocking effect to lithium diffusion.

(39) Further, when a nitride insulating film is used as the second passivation film 913 or the third passivation film 962, a heat radiation effect can be expected. For example, if it is assumed that a thermal conductivity of a silicon oxide film is 1; that of a silicon nitride film is about 5 and that of an aluminum nitride film is about 35 to 130, thereby obtaining a very high thermal conductivity. Thus, even when the EL element generates heat, heat is effectively radiated, so that the deterioration of the EL layer 963 resulting from self heat radiation can be suppressed.

(40) Note that the same material as the nitride insulating film used for the first passivation film 911 and the second passivation film 913 can be used for the third passivation film 962 and the fourth passivation film 965.

(41) When the structure shown in FIG. 10A is used, light emitted from the EL element transmits the pixel electrode 958 and exits from the substrate 901 side. At this time, the transmitting light transmits through the photosensitive organic resin film 912. Thus, it is required that sufficient decolorization processing is conducted for the photosensitive organic resin film 912 so that it is made sufficiently transparent.

(42) Next, FIG. 10B shows an example in which a metallic film 971 having a reflecting property is used instead of the pixel electrode 958. As the metallic film 971 having the reflecting property, a film of metal such as platinum (Pt) or gold (Au) having a high work function is used to serve as an anode. In addition, because such a metal is expensive, it may be laminated on a suitable metallic film such as an aluminum film or a tungsten film to form a pixel electrode in which at least platinum or gold is exposed onto an uppermost surface. Reference numeral 972 denotes an EL layer, and various structures and various materials in which light emission has been observed can be used as in the case shown in FIG. 10A. In addition, reference numeral 973 denotes a metallic film having a small film thickness (preferably, 10 nm to 50 nm). A metallic film containing an element belonging to group 1 or 2 of the periodic table is used to serve as a cathode. Further, an oxide conductive film (typically, an ITO film) 974 is provided by laminating it on the metallic film 973 and a fourth passivation film 975 is provided thereon.

(43) When the structure shown in FIG. 10B is used, light emitted from the EL element is reflected by the pixel electrode 971, transmits through the metallic film 973, the oxide conductive film 974, and the like, and exits from the substrate. At this time, because the light does not transmit through a portion under the pixel electrode 971, a memory element, a resistor element, or the like may be provided therein and the photosensitive organic resin film 912 may be colored. Thus, a degree of flexibility in a design is high and a manufacturing process can be also simplified. Therefore, it can be said that the structure generally contributes to a reduction in manufacturing cost.

Embodiment 3

(44) In this embodiment, an example is indicated in which a connection structure between the drain wiring 921 and the pixel electrode 958 is modified in the light emitting device described in Embodiment 2. Note that the fundamental structure is not changed as compared with that shown in FIG. 9C. Thus, in this embodiment, reference symbols are provided to only necessary portions and the description will be made.

(45) As shown in FIG. 11A, a pixel electrode 501 made from an oxide conductive film is formed and then a drain wiring 502 is formed, so that a structure in which the drain wiring 502 is in contact with the pixel electrode 501 so as to cover the end portion thereof is obtained. When such a structure is obtained, the pixel electrode 501 may be formed after the formation of a second opening portion 503. Alternatively, the second opening portion 503 may be formed after the formation of the pixel electrode 501. In any case, even when dry etching processing is conducted, the photosensitive organic resin film 912 is always protected by the second passivation film 913 from plasma damage. Thus, there is no case where electrical characteristics of a thin film transistor are adversely influenced.

(46) Next, as shown in FIG. 11B, an interlayer insulating film 504 made from an inorganic insulating film is provided on the first passivation film 911, and a drain wiring 505 is provided thereon. A connection wiring 506 is formed simultaneous with the drain wiring. The connection wiring 506 is connected with a capacitor wiring 917 of a lower layer. The drain wiring 505 and the connection wiring 506 are covered with a photosensitive organic resin film 508 having a first opening portion 507. The first opening portion 507 is covered with a second passivation film 509 made from a nitride insulating film. The second passivation film 509 has a second opening portion 510 in the bottom of the first opening portion 507. A pixel electrode 511 made from an oxide conductive film are connected with the drain wiring 505 through the first opening portion 507 and the second opening portion 510.

(47) In this time, a storage capacitor 512 which is composed of the connection wiring 506, the second passivation film 509, and the pixel electrode 511 is produced on the connection wiring 506. In the case of the structure shown in FIG. 11B, only the second passivation film 509 having a high relative dielectric constant is used as dielectric, so that a storage capacitor having a large capacitance value can be produced. Of course, a storage capacitor using the pixel electrode 511 and the capacitor wiring 917 as a pair of electrodes can be also produced. However, in this case, because the second passivation film 509, the interlayer insulating film 504, and the first passivation film 911 are used as dielectric, a capacitance value becomes lower than that in the structure shown in FIG. 11B.

(48) Next, FIG. 11C shows an example in which a nitride insulating film 513 is provided as another passivation film after the formation of the drain wiring 505 and the connection wiring 506 in FIG. 11B. In such a case, a storage capacitor 514 is composed of the connection wiring 506, the nitride insulating film 513, the second passivation film 509, and the pixel electrode 511. In this case, the film thickness is increased as compared with that in FIG. 11B, thereby slightly reducing a capacitance value. However, when a laminate is used for dielectric, a problem related to a pinhole, and the like can be reduced, so that the reliability of the storage capacitor is improved.

(49) As described above, the present invention is not limited to the structure described in Embodiment 2, and therefore can be applied to various transistor structures using the organic resin film as the interlayer insulating film. Note that, in the structure described in this embodiment, the nitride insulating film described in Embodiments 1 and 2 above can be used for the second passivation film 509 and the nitride insulating film 513.

Embodiment 4

(50) In this embodiment, an example in which a bottom gate thin film transistor (specifically, an inverse staggered TFT) is used as a thin film transistor in Embodiments 1 to 3 will be described. In other words, even when an inverse staggered TFT is used for the switching TFT and the driver TFT in Embodiment 2 or 3, the present invention can be carried out.

(51) This embodiment will be described using FIG. 12. In FIG. 12, reference numeral 301 denotes a substrate, 302 denotes a gate electrode, 303 denotes a gate insulating film, 304 denotes a source region, 305 denotes a drain region, 306a and 306b denote LDD regions, and 307 denotes a channel formation region. The source region, the drain region, the LDD regions, and the channel formation region are made from a semiconductor film provided on the gate insulating film 302 covering the gate electrode 302. In addition, reference numerals 308 and 309 denote inorganic insulating films. In this embodiment, 308 denotes a silicon oxide film and 309 denotes a silicon nitride film. The silicon nitride film 309 serves as a first passivation film. The silicon oxide film 308 serves as a buffer layer between a semiconductor layer which becomes a lower layer and the first passivation film 309 made of silicon nitride. A known thin film transistor structure is described up to here. Various known materials can be used for materials of respective portions.

(52) Next, a photosensitive organic resin film, specifically, a positive type photosensitive acrylic film is provided as an interlayer insulating film 310 on the first passivation film 309. A first opening portion (indicated by a diameter of 1) 311 is provided in the photosensitive organic resin film 310. Further, a second passivation film 312 made from an inorganic insulating film is provided so as to cover the top surface of the photosensitive organic resin film 310 and the inner wall surface of the first opening portion 311. A second opening portion (indicated by a diameter of 2) 313 is provided in the second passivation film 312 in the bottom of the first opening portion 311. Reference numeral 314 denotes a source electrode and 315 denotes a drain electrode.

(53) Even in this embodiment, as in Embodiment 1, a silicon nitride film, a silicon nitride oxide film, a silicon oxynitride film, an aluminum nitride film, an aluminum nitric oxide film, or an aluminum oxynitride film can be used for the first passivation film 309 and the second passivation film 312. In addition, a laminate film including these films in at least a portion thereof can be used. It is desirable that the diameter of 1 is set to 2 m to 10 m (preferably, 3 m to 5 m) and the diameter of 2 is set to 1 m to 5 m (preferably, 2 m to 3 m). It is preferable that a relationship of 1>2 is satisfied. Note that, because the cross sectional shape of the first opening portion 311 has been described in detail in Summary of the Invention, it is omitted here. It is desirable that an inner wall surface of the first opening portion is a gradual curved surface and has a continuously changed curvature radius. Specifically, when three points of curvature radii of R1, R2, and R3 are noted in order, it is desirable that a relationship among the respective curvature radii becomes R1<R2<R3 and these numerical values each become within 3 m to 30 m (typically, 10 m to 15 m). In addition, an angle (contact angle ) formed by the photosensitive organic resin film 310 and the first passivation film 309 in the bottom of the first opening portion 311 is preferably kept within a range of 30<<65 (typically, 40<<50).

(54) As described above, when the present invention is carried out, the structure of a thin film transistor is not necessarily limited to only a top gate type or only a bottom gate type. Thus, the present invention can be applied to a thin film transistor having any structure. Further, the present invention is not necessarily limited to a thin film transistor, and may be applied to a transistor having a MOS structure which is formed using a silicon well.

Embodiment 5

(55) In this embodiment, an example in which the present invention is applied to a liquid crystal display device will be described. FIG. 13A is a plan view of a pixel of a liquid crystal display device (note that a state up to the formation of a pixel electrode is indicated), FIG. 13B is a circuit diagram thereof, and FIGS. 13C and 13D each are a cross sectional view along a line A-A or B-B.

(56) As shown in FIGS. 13A and 13B, a display portion of the liquid crystal display device includes a plurality of pixels which are surrounded by gate wirings 851 and data wirings 852 and arranged in matrix. In each of the pixels, a TFT 853 serving as a switching element (hereinafter referred to as a switching TFT), a capacitor portion 854, and a liquid crystal element 855 are provided. In the circuit shown in FIG. 13B, both the capacitor portion 854 and the liquid crystal element 855 are connected with a constant potential line 856. However, they are not necessarily kept to the same potential, i.e., one may be kept to a common potential and the other may be kept to a ground potential (earth potential). In addition, although not shown here, the liquid crystal element can be formed by providing a liquid crystal layer over a pixel electrode 857. Note that, although in this embodiment, an n-channel TFT having a multi-gate structure is used as the switching TFT 853, a p-channel TFT may alternatively be used. The layout of the switching TFT is preferably determined as appropriate by an operator.

(57) In the cross sectional view of FIG. 13C, the switching TFT 853 and the capacitor portion 854 are shown. Reference numeral 801 denotes a substrate, and a glass substrate, a ceramic substrate, a quartz substrate, a silicon substrate, or a plastic substrate (including a plastic film) can be used. In addition, reference numeral 802 denotes a silicon nitride oxide film, 803 denotes a silicon oxynitride film, and they are laminated to serve as base films. Of course, the present invention is not necessarily limited to these materials. Further, an active layer of the switching TFT 853 is provided on the silicon oxynitride film 803. The active layer has a source region 804, a drain region 805, LDD regions 806a to 806d, and channel formation regions 807a and 807b. In other words, it has two channel formation regions and four LDD regions between the source region 804 and the drain region 805.

(58) Also, the active layer of the switching TFT 853 is covered with a gate insulating film 808, and a gate electrode (gate electrode layers 809a and 809b) and another gate electrode (gate electrode layers 810a and 810b) are provided thereon. In this embodiment, a silicon oxynitride film is used as the gate insulating film 808. In addition, a tantalum nitride film is used for the gate electrode layers 809a and 810a and a tungsten film is used for the gate electrode layers 809b and 810b. With respect to these metallic films, a selection ratio is high. Thus, the structure as shown in FIG. 13B can be obtained by selecting an etching condition. The etching condition may be referred to JP 2001-313397 A according to the present applicant.

(59) Also, a silicon nitride film or a silicon nitride oxide film is provided as a first passivation film 811 covering the gate electrodes, and a photosensitive organic resin film 812 (in this embodiment, a positive type photosensitive acrylic film is used) is provided thereon. Further, a second passivation film 813 is provided on the photosensitive organic resin film 812 so as to cover a first opening portion (see FIG. 1A). A second opening portion (see FIG. 1A) is provided to the bottom of the first opening portion. In this embodiment, a silicon nitride film or a silicon nitride oxide film is used as the second passivation film 813. Of course, another nitride insulating film such as an aluminum nitride film or an aluminum nitric oxide film can be also used.

(60) Also, the data wiring 852 is connected with the source region 804 through the first opening portion, and the drain wiring 815 is connected with the drain region 805 through the second opening portion. The drain wiring 815 is used as an electrode composing a storage capacitor in the capacitor portion and electrically connected with the pixel electrode 857. Note that, in this embodiment, an oxide conductive film which is transparent with respect to visible light (typically, an ITO film) is used as the pixel electrode 857. However, the present invention is not limited to such a film. In addition, a structure in which a wiring containing mainly low resistance metal such as aluminum or copper is sandwiched by other metallic films or an alloy film of these metals is preferably used for the data wiring 852 and the drain wiring 815.

(61) The drain wiring 815 is opposite to a capacitor wiring 816 which is formed together with the gate electrodes (that is, which is formed on the same surface as the gate electrodes) through the first passivation film 811 and the second passivation film 813, so that a storage capacitor 854a is produced. Further, the capacitor wiring 816 is opposite to a semiconductor film 817 through the gate insulating film 808 so that a storage capacitor 854b is produced. Because the semiconductor film 817 is electrically connected with the drain region 805, when a constant voltage is applied to the capacitor wiring 816, the semiconductor film serves as an electrode. Thus, the capacitor portion 854 becomes a structure in which the storage capacitors 854a and 854b are connected in parallel, thereby obtaining a large capacity with a very small area. Furthermore, with respect to particularly the storage capacitor 854a, a silicon nitride film having a high relative dielectric constant is used for dielectric, so that a large capacity can be ensured.

(62) An example, up to the actual formation of a liquid crystal element of the liquid crystal display device having the above pixel structure is shown in FIGS. 14A and 14B. FIG. 14A is a cross sectional view corresponding to the cross section shown in FIG. 13C and shows a state in which the liquid crystal element 855 is formed on the pixel electrode 857. A spacer 821 made of an organic resin is provided on the drain wiring 815, and an alignment film 822 is provided thereon. The formation order of the spacer 821 and the alignment film 822 may be reverse. Further, a light shielding film 824 made from a metallic film, a counter electrode 825 made from an oxide conductive film, and an alignment film 826 are provided on another substrate (counter substrate) 823, and then the alignment film 822 and the alignment film 826 are bonded opposite to each other using a sealing material (not shown). Furthermore, a liquid crystal 827 is injected from a liquid crystal injection port provided in the sealing material, and the liquid crystal injection port is then sealed to complete the liquid crystal display device. Note that a general liquid crystal cell assembly process is preferably applied to a process after the formation of the spacer 821. Thus, the detailed description is not particularly made.

(63) When the structure shown in FIG. 14A is used, light is made incident from the counter substrate 823 side, modulated through the liquid crystal 827, and exits from the substrate 801 side. At this time, the transmitting light transmits through the photosensitive organic resin film 812 used as the interlayer insulating film. Thus, it is required that sufficient decolorization processing is conducted for the photosensitive organic resin film 812 so that it is made sufficiently transparent.

(64) Next, FIG. 14D shows an example in which a drain wiring 831 made from a metallic film having a reflecting property is used without modification instead of the pixel electrode 857. As the metallic film having the reflecting property, an aluminum film (including an aluminum alloy film) or a conductive film having a silver thin film at least on its surface can be used. The description related to other portions for which the same reference symbols as in FIG. 14A are provided is omitted here. When the structure shown in FIG. 14B is used, light is made incident from the counter substrate 823 side, modulated through the liquid crystal 827, and outputted from the counter substrate 823 side again. At this time, because the light does not transmit through a portion under the drain wiring 831, a memory element, a resistor element, or the like may be provided therein and the photosensitive organic resin film 812 may be colored. Thus, a degree of flexibility in a design is high and a manufacturing process can be also simplified. Therefore, it can be said that the structure generally contributes to a reduction in manufacturing cost.

Embodiment 6

(65) In this embodiment, a structure of the entire light emitting device shown in FIGS. 9A to 9D will be described using FIGS. 15A to 15D. FIG. 15A is a plan view of a light emitting device produced by sealing an element substrate in which thin film transistors are formed with a sealing material. FIG. 15B is a cross sectional view along a line B-B in FIG. 9A. FIG. 15C is a cross sectional view along a line A-A in FIG. 15A.

(66) A pixel portion (display portion) 402, a data line driver circuit 403, gate line driver circuits 404a and 404b, and a protective circuit 405, which are provided to surround the pixel portion 402, are located on a substrate 401, and a seal material 406 is provided to surround them. The structure of the pixel portion 402 preferably refers to FIGS. 10A and 10B and its description. As the seal material 406, a glass material, a metallic material (typically, a stainless material), a ceramic material, or a plastic material (including a plastic film) can be used. As shown in FIGS. 10A and 10B, it can be also sealed with only an insulating film. In addition, it is necessary to use a translucent material according to a radiation direction of light from an EL element.

(67) The seal material 406 may be provided to partially overlap with the data line driver circuit 403, the gate line driver circuits 404a and 404b, and the protective circuit 405. A sealing material 407 is provided using the seal material 406, so that a closed space 408 is produced by the substrate 401, the seal material 406, and the scaling material 407. A hygroscopic agent (barium oxide, calcium oxide, or the like) 409 is provided in advance in a concave portion of the sealing material 407, so that it has a function of absorbing moisture, oxygen, and the like to keep an atmosphere clean in an inner portion of the above closed space 408, thereby suppressing the deterioration of an EL layer. The concave portion is covered with a cover material 410 with a fine mesh shape. The cover material 410 allows air and moisture to pass therethrough but not the hygroscopic agent 409. Note that the closed space 408 is preferably filled with a noble gas such as nitrogen or argon, and can be also filled with a resin or a liquid if it is inert.

(68) Also, an input terminal portion 411 for transmitting signals to the data line driver circuit 403 and the gate line driver circuits 404a and 404b is provided on the substrate 401. Data signals such as video signals are transferred to the input terminal portion 411 through a FPC (flexible printed circuit) 412. With respect to a cross section of the input terminal portion 411, as shown in FIG. 15B, an input wiring having a structure in which an oxide conductive film 414 is laminated on a wiring 413 formed together with a gate wiring or a data wiring is electrically connected with a wiring 415 provided in the FPC 412 side through a resin 417 to which conductors 416 are dispersed. Note that a spherical polymer compound for which plating processing using gold or silver is conducted is preferably used for the conductors 416.

(69) Also, an enlarged view of a region 418 surrounded by a dot line in FIG. 15C is shown in FIG. 15D. The protective circuit 405 is preferably composed by combining a thin film transistor 419 and a capacitor 420, and any known structure may be used therefor. The present invention has such a feature that the formation of the capacitor is possible without increasing the number of photolithography steps together with the improvement of contact holes. In this embodiment, the capacitor 420 is formed utilizing the feature. Note that the structure of the thin film transistor 419 and that of the capacitor 420 can be understood if FIGS. 10A and 10B and description thereof are referred to, and therefore the description is omitted here.

(70) In this embodiment, the protective circuit 405 is provided between the input terminal portion 411 and the data line driver circuit 403. When an electrostatic signal such as an unexpected pulse signal is inputted therebetween, the protective circuit releases the pulse signal to the outside. At this time, first, a high voltage signal which is instantaneously inputted can be dulled by the capacitor 420, and other high voltages can be released to the outside through a circuit composed of a thin film transistor and a thin film diode. Of course, the protective circuit may be provided in other location, for example, a location between the pixel portion 402 and the data line driver circuit 403 or locations between the pixel portion 402 and the gate line driver circuits 404a and 404b.

(71) As described above, according to this embodiment, when the present invention is carried out, an example in which the capacitor used for the protective circuit for electrostatic measures and the like which is provided in the input terminal portion is simultaneously formed is indicated. This embodiment can be carried out by being combined with any structure of Embodiments 1 to 5.

Embodiment 7

(72) Examples of electronics employing a display apparatus of the present invention to a display portion are: a video camera; a digital camera; a goggle type display (head mounted display); a navigation system; an audio reproducing apparatus (car audio, an audio component, and the like); a laptop computer, a game machine; a portable information terminal (a mobile computer, a cellular phone, a portable game machine, an electronic book, etc.); and an image reproducing apparatus including a recording medium (specifically, an appliance capable of processing data in a recording medium such as a Digital Versatile Disk (DVD) and having a display apparatus that can display the image of the data). Specific examples of the electronics are shown in FIGS. 16A to 16H.

(73) FIG. 16A shows a television, which comprises a casing 2001, a supporting base 2002, a display unit 2003, speaker units 2004, a video input terminal 2005, etc. The present invention is applied to the display unit 2003. The term television includes every television for displaying information such as one for a personal computer, one for receiving TV broadcasting, and one for advertisement.

(74) FIG. 16B shows a digital camera, which comprises a main body 2101, a display unit 2102, an image receiving unit 2103, operation keys 2104, an external connection port 2105, a shutter 2106, etc. The present invention is applied to the display unit 2102.

(75) FIG. 16C shows a laptop computer, which comprises a main body 2201, a casing 2202, a display unit 2203, a keyboard 2204, an external connection port 2205, a pointing mouse 2206, etc. The present invention is applied to the display unit 2203.

(76) FIG. 16D shows a mobile computer, which comprises a main body 2301, a display unit 2302, a switch 2303, operation keys 2304, an infrared ray port 2305, etc. The present invention is applied to the display unit 2302.

(77) FIG. 16E shows a portable image reproducing apparatus equipped with a recording medium (a DVD player, to be specific). The apparatus comprises a main body 2401, a casing 2402, a display unit A 2403, a display unit B 2404, a recording medium (such as DVD) reading unit 2405, operation keys 2406, speaker units 2407, etc. The display unit A 2403 mainly displays image information whereas the display unit B 2404 mainly displays text information. The present invention is applied to the display units A 2403 and B 2404. The term image reproducing apparatus equipped with a recording medium includes domestic game machines.

(78) FIG. 16F shows a goggle type display (head mounted display), which comprises a main body 2501, display units 2502, and arm units 2503. The present invention is applied to the display unit 2502.

(79) FIG. 16G shows a video camera, which comprises a main body 2601, a display unit 2602, a casing 2603, an external connection port 2604, a remote control receiving unit 2605, an image receiving unit 2606, a battery 2607, an audio input unit 2608, operation keys 2609, etc. The present invention is applied to the display portion 2602.

(80) FIG. 16H shows a cellular phone, which comprises a main body 2701, a casing 2702, a display unit 2703, an audio input unit 2704, an audio output unit 2705, operation keys 2706, an external connection port 2707, an antenna 2708, etc. The present invention is applied to the display unit 2703. If the display unit 2703 displays white characters on a black background, power consumption of the cellular phone can be reduced.

(81) As described above, the display apparatus obtained by applying the present invention may be used as the display units of every electronics. Low-cost display apparatus can be provided and the electronics parts cost can be lowered. Since the stability of the performance of the display apparatus can be improved and the design margin in the circuit design can be expanded in the present invention, the low-cost display apparatus can be provided and the electronics parts cost can be lowered. Also, the electronics of the present Embodiment may use any configuration of the display apparatuses shown in Embodiments 1 to 6.

(82) According to the present invention, a display device can be manufactured without varying a threshold voltage of a thin film transistor by a process having a high design margin in a circuit design, so that the improvement of stability of operating performance of the display device can be achieved. Further, a large capacitor can be produced with a small area together with the above thin film transistor without increasing the number of photolithography steps, thereby improving an image quality of the display device.