JP2005321670A - Thin-film semiconductor device, liquid crystal display device, and image projector apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shield the unnecessary scattered light inside a substrate generated by miniaturization of a light valve and rising of photoirradiation density accompanying the same from a TFT. <P>SOLUTION: Each pixel electrode PE modulates incident light according to driving by the thin-film transistor TFT and has an opening emitting the modulated light. Each thin-film transistor TFT has an active layer consisting of a semiconductor thin film SL, and insulating films 1 to 5 of multiple layers superposed on each other from above to below on the active layer. The insulating films 1 to 5 of the multiple layers include the inner insulating films 2 and 3 having photoconductivity in contact with the semiconductor thin film SL, and the outer insulating films 1 and 4 superposed thereon. The inner insulating films 2 and 3 are set smaller in refractive index than the outer insulating films 1 and 4 in order to suppress the photoconductivity thereof and the amount of the unnecessary light guided to the semiconductor thin film SL through the inner insulating films 2 and 3 is suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thin film semiconductor device, an active matrix liquid crystal display device using the same as a substrate, and an image projector device using the same as a light valve. More specifically, the present invention relates to a technique for blocking or shielding a thin film transistor formed on a substrate from external light.

  In recent years, projectors using active matrix light valves such as LCD, DMD, and LCOS have been actively developed. In the future, it is considered that these image projector apparatuses will further increase in brightness, definition, image quality, and price. High definition is considered to be necessary for personal computer monitors compatible with SXGA, medical device monitors applied to the QXGA class, and full HD class displays as large screen devices. In addition, in data projectors, home projectors, rear projectors, etc., it is expected that the demand for cost reduction will increase further. For this reason, downsizing of the light valve is inevitably required. For the time being, there is a demand for miniaturization and high definition of the panel pixel structure.

For example, in the case of a transmissive liquid crystal display, taking an XGA class panel size as an example, it has been reduced from 1.3 inches to 0.9 inches, 0.7 inches, and 0.5 inches. . Along with this, the pixel pitch has been reduced to 23 μm, 18 μm, 14 μm, and 11 μm. The same tendency is observed not only in the liquid crystal display (LCD) but also in LCOS, DLP, and DMD.
JP 2000-298290 A

  However, as the above-described light valve is highly refined and miniaturized, the conventional thin film transistor (TFT) design concept cannot cope with various problems. For example, in order to maintain the brightness of the projection screen constant even when the projector panel is downsized, it is necessary to increase the light irradiation density on the panel. When the light intensity increases, the temperature of the light valve rises during driving, which may hinder normal operation. Further, as the light intensity increases, unnecessary light scattered and reflected in the panel increases, resulting in a decrease in screen contrast. Furthermore, unnecessary light horizontally diffused on the substrate penetrates into an active layer of a semiconductor element such as a thin film transistor, thereby deteriorating the light leakage characteristics of the device. Since these directly adversely affect the image quality of the display, they are important issues to be solved in advancing miniaturization and high definition.

In view of the above-described problems of the conventional technology, an object of the present invention is to provide a TFT structure capable of reducing light leakage in an active matrix light valve used for an LCD projector or the like. In particular, an object of the present invention is to block light that does not scatter in the substrate caused by downsizing of the light valve and accompanying increase in light irradiation density from the TFT. More specifically, an object is to remove the intrusion path of the light that does not require scattering in the substrate to the TFT. In order to achieve this purpose, the following measures were taken. That is, it comprises a substrate for forming matrix-like pixels and a thin film transistor formed on the substrate for driving each pixel, and each pixel modulates incident light according to driving by the thin film transistor and In the thin film semiconductor device having an opening for emitting modulated light, and each thin film transistor includes an active layer made of a semiconductor thin film and a multi-layer insulating film overlapping the active layer from above and below, the multi-layer insulating film comprises: An inner insulating film having a light guide property in contact with the semiconductor thin film and an outer insulating film overlapping therewith, and the inner insulating film is set to have a refractive index smaller than that of the outer insulating film in order to suppress the light guiding property. The amount of unnecessary light guided to the semiconductor thin film through the inner insulating film is suppressed.
Preferably, the multilayer insulating film includes an inner insulating film having a light guide property in contact with an upper surface of the semiconductor thin film and an inner insulating film having a light guide property in contact with a lower surface of the semiconductor thin film, In order for both insulating films to suppress light guiding properties, the refractive index is set smaller than that of the outer insulating film. The inner insulating film in contact with the upper surface of the semiconductor thin film and the inner insulating film in contact with the lower surface of the semiconductor thin film have the same refractive index. The inner insulating film and the outer insulating film are both made of a transparent oxide film and at least one of them contains a dopant, and the refractive index of the inner insulating film is made smaller than that of the outer insulating film by controlling the concentration of the dopant. To do. The dopant is selected from P, B, As, Ge, Al and F.

  The present invention also includes a substrate for forming a matrix-like pixel and a thin film transistor formed on the substrate for driving each pixel. Each pixel receives incident light according to driving by the thin film transistor. In the thin film semiconductor device having an opening for modulating and emitting modulated light, each thin film transistor includes an active layer made of a semiconductor thin film, and a stacked insulating film overlapping the active layer from above and below, the stacked insulating film includes: A dopant for adjusting the refractive index is implanted into a region corresponding to the opening of each pixel, and the dopant has a concentration distribution in a direction perpendicular to the stacked insulating film. As a result, the laminated insulating film has the lowest refractive index in the vicinity of the interface with the active layer as a boundary, so that unnecessary light is guided from each opening through the laminated insulating film to the semiconductor thin film. And wherein the suppressing amount.

The present invention further includes a substrate for forming a matrix-like pixel and a thin film transistor formed on the substrate for driving each pixel. Each pixel receives incident light according to driving by the thin film transistor. Each of the thin film transistors has an active layer made of a semiconductor thin film and a stacked insulating film that overlaps the active layer from above and below, and has an opening region that emits modulated light and that emits modulated light. In the thin film semiconductor device, each thin film transistor is located in a non-opening region of each pixel, and the stacked insulating film extends over both the non-opening region and the open region. And the portion located in the opening region has a higher refractive index than the portion located in the non-opening region, thereby suppressing the light incident on the opening region from diffusing into the non-opening region. And it features.
Preferably, in the laminated insulating film, a dopant for adjusting the refractive index is implanted into one of a portion located in the opening region and a portion located in the non-opening region, and thus the portion located in the opening region. Has a higher refractive index than the portion located in the non-opening region.

  The present invention focuses on a multilayer interlayer insulating film that sandwiches an active layer of a thin film transistor from above and below as an intrusion path of unnecessary light in the substrate. In general, an interlayer insulating film has a laminated structure in which different and different materials are stacked, exhibits a light guide effect with total reflection at an interface (this may be referred to as an optical fiber effect in this specification), and It can be an intrusion route for unnecessary light. Therefore, the present invention eliminates the optical fiber effect by configuring the inner interlayer insulating film in contact with the TFT to have a refractive index lower than that of the outer interlayer insulating film. Thus, unnecessary light diffused in the horizontal direction of the substrate is prevented from propagating to the TFT. For example, by selectively injecting a dopant such as P, B, As, Ge, Al, F or the like into the laminated interlayer insulating film, the refractive index of each interlayer insulating film is controlled to thereby guide the TFT active layer. It eliminates the path and reduces light leakage. Such a basic inventive concept is applied to a two-dimensional structure in which pixels are arranged in a matrix. By controlling the vertical refractive index distribution and the horizontal refractive index distribution of the stacked insulating films included in the pixel array arranged in a matrix, light leakage to the TFT is reduced. When the present invention is applied to a projector, the propagation of unnecessary light to the TFT due to the optical fiber effect is reduced, and the light leakage failure of the TFT due to unnecessary light or stray light is drastically reduced. As a result, it is possible to realize a projector with high definition, high image quality and high brightness while corresponding to downsizing. Even if the amount of incident light increases, light leakage can be reduced, and an increase in contrast and prevention of flicker can be achieved. Furthermore, it is possible to prevent a bright spot defect of a pixel due to light leakage.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of an optical system of an image projector apparatus. As illustrated, the image projector apparatus includes a light source lamp 101, a first fly-eye lens 102, a second fly-eye lens 103, a PS separation / combination element 104, a condenser lens 105, and RGB color separation filters 106 (B reflection) and 107 ( G reflection / R transmission), a mirror 108, a field lens 109, relay lenses 110 and 111, a dichroic prism 112, a light valve 114, and a projection lens 116, and projects an enlarged image on a screen 117. In the present embodiment, the light valve 114 is composed of a liquid crystal display panel sandwiched between the front and rear polarizing plates 113 and 115.

  FIG. 2 is a schematic cross-sectional view showing the main part of the display panel shown in FIG. The display panel is basically a thin film semiconductor device, and includes a substrate B for forming matrix-like pixels and a thin film transistor TFT formed on the substrate B for driving each pixel. Each pixel is formed by a pixel electrode PE, and has an opening for modulating incident light according to driving by the thin film transistor TFT and emitting the modulated light. The pixel electrode PE is made of a transparent conductive film such as ITO, and almost the entire region forms an opening. The thin film transistor TFT has an active layer made of a semiconductor thin film SL such as polysilicon, and multilayer insulating films 1 to 5 overlapping the active layer from above and below.

The specific configuration of the thin film semiconductor device will be described with reference to FIG. The substrate B is made of a transparent plate material such as quartz or glass, and its surface is covered with two layers of interlayer insulating films 1 and 2. In this embodiment, the interlayer insulating films 1 and 2 are made of SiO ₂ and function as a buffer layer. A light shielding layer 7 made of WSi or the like is formed between the interlayer insulating films 1 and 2. A semiconductor thin film SL made of polysilicon is formed on the interlayer insulating film 2. On top of that, a gate electrode 10 is formed via a gate insulating film 9 to constitute a so-called TFT. The gate insulating film 9 is made of, for example, a thermal oxide film, and the gate electrode 10 is an electrode material whose resistance is reduced by doping, for example, polysilicon with phosphorus. On the substrate B, an auxiliary capacitor CS is also formed in addition to the TFT. The auxiliary capacitor CS has the semiconductor thin film SL as one electrode and the phosphorus-doped polysilicon 10a overlaid on the thermal oxide film 9a as the other electrode. The TFT and CS are covered with an interlayer insulating film 3, and a source electrode 11 and a drain electrode 12 are formed of metal aluminum or the like thereon. The source electrode 11 is connected to the signal wiring. The source electrode 11 and the drain electrode 12 are covered with an interlayer insulating film 4, and a black mask 13 made of metal titanium or the like is formed thereon. The black mask 13 is covered with an interlayer insulating film 5 on which the above-described pixel electrode PE is formed. The pixel electrode PE is electrically connected to the drain electrode 12 through the black mask 13. Interlayer insulating film 3, 4 and 5 is formed of a transparent oxide film such as SiO _2. The uppermost interlayer insulating film 5 functions as a flattening layer, and the pixel electrode PE is formed on the flattened surface filling the unevenness of the TFT and CS.

  FIG. 3 is a schematic partial cross-sectional view showing the overall configuration of the liquid crystal display panel. As shown in the figure, the liquid crystal display panel includes a matrix-shaped pixel electrode PE and one substrate B on which the thin film transistor TFT for driving each pixel electrode PE is formed, and the other substrate 20 on which the counter electrode 21 is formed. The pixel electrode PE, the counter electrode 21 and the liquid crystal 30 positioned between the pixel electrode PE and the liquid crystal 30 are formed on the substrates B and 20 joined to each other with a predetermined gap therebetween. As described in detail with reference to FIG. 2, one substrate B is a thin film semiconductor device, and TFTs and CSs are integrated. The opposite substrate 20 is made of quartz, glass, neo-serum or the like and is transparent. The counter electrode 21 formed on the inner surface of the counter substrate 20 is also made of a transparent conductive film such as ITO.

  FIG. 3 depicts typical light guides (1)-(4). Of these, the light guide (1) is the original one, and light incident from the light source of the projector through the counter substrate 20 is modulated by the pixels of the panel and emitted from the substrate B side. The other light guides (2), (3), and (4) guide light that does not contribute to display and can cause stray light. The light guide path (2) is a case where incident light is directly reflected by the black mask 13. The light guide path (3) represents a case where incident light is reflected at the end of the aluminum electrode 11, propagates through the interlayer insulating films 2 and 3, and is diffused in the horizontal direction. The light guide (4) represents a case where light partially reflected on the back surface of the substrate B is blocked by the light shielding film 7.

  Of the four light guides, the light guides (2) and (4) have been the main cause of light leakage of the TFT. These stray lights can now be dealt with by sandwiching the TFT from above and below with light shielding layers 7 and 13 such as metal. However, considering the further progress of higher brightness in projector optical systems or the increase in light density accompanying the downsizing of panel pixel pitch, light that propagates in the interlayer insulating film in the horizontal direction through the light guide (3) will be increasingly used in the future. This is expected to increase the number of TFT leakage defects due to the above, and become a more obvious issue than before. In FIG. 3, typical light guides (1) to (4) are shown. However, in an actual system, it is not necessary to enter from the reflection variation due to the surface roughness at the interface of each layer, the end face of the substrate glass, and other optical systems. It is expected that light will enter the TFT at various angles and cause leak defects. The influence of such stray light is expected to become stronger as the projector brightness increases.

In general, as an interlayer insulating film included in a TFT structure, in particular in the case of a transmissive LCD, an SiO ₂ insulating film used in a semiconductor process is frequently used in consideration of transparency and insulating properties. Among them, PSG (a silica glass (SG) made of SiO ₂ doped with phosphorus (P)) or BPSG (a silica glass SG doped with boron B and phosphorus P in consideration of heat flow, flatness, etc.) ) Has been widely used. A specific configuration example will be described with reference to FIG. As shown, interlayer insulating films 1 to 5 are laminated on the TFT substrate B. The lowermost interlayer insulating film 1 is formed to prevent contamination from the surface of the quartz substrate B, and is called a buffer layer. In many cases, SiO ₂ is used as the buffer layer rather than the one containing a dopant. If a dopant is injected into the buffer layer in the manufacturing process, there is a risk of the influence of adsorption of moisture or the like, or contamination of the TFT active layer due to deposition of the dopant. A light shielding layer 7 is formed on the interlayer insulating film 1, and an interlayer insulating film 2 is formed thereon. The interlayer insulating film 2 also functions as a buffer layer. Further, a semiconductor thin film SL is formed on the interlayer insulating film 2, and TFTs and CS are formed. The fabricated TFT and CS are covered with an interlayer insulating film 3. A PSG film is used as the interlayer insulating film 3. The doping amount of P is, for example, several weight percent. Here, annealing at about 1000 ° C. is performed in order to activate and planarize impurities injected into the semiconductor thin film SL. Contacts are formed on the interlayer insulating film 3, and a source electrode 11 and a drain electrode 12 made of metal aluminum or the like are formed thereon. This is covered with an interlayer insulating film 4, and a black mask layer 13 is formed thereon. A PSG film or a SiO ₂ film is used as the interlayer insulating film 4. Finally, the black mask layer 13 is covered with the interlayer insulating film 5, and the pixel electrode PE made of ITO or the like is formed thereon. At this time, the surface of the interlayer insulating film 5 may be planarized by CMP or the like. As the interlayer insulating film 5, SiO ₂ formed by AP-CVD or P-CVD is frequently used. As described above, the interlayer insulating films 1 to 5 that are in direct or indirect contact with the active layer of the TFT are mostly NSG (silica glass SG containing no dopant), PSG, and BPSG. This is because it is easy to form a film and has a track record in LSI manufacturing.

For example, SiO ₂ (NSG) containing no impurities is used as the interlayer insulating films 1 and 2 (buffer layers). Next, as an interlayer insulating film 3 that covers the TFT, PSG containing a dopant of several weight% in terms of P ₂ O ₅ is formed. PSG is known to have a higher refractive index than NSG. Further, when annealing at about 1000 ° C. is performed to activate impurities implanted into the semiconductor thin film SL of the TFT, the interlayer insulating film 3 made of PSG is densified and the refractive index is further increased. Another interlayer insulating film 4 is formed on the densified interlayer insulating film 3. Basically, the interlayer insulating film 4 is made of PSG having the same composition as that of the interlayer insulating film 3, but is not densified because it is not annealed. Therefore, the refractive index of the interlayer insulating film 4 is lower than the refractive index of the interlayer insulating film 3. Accordingly, these refractive index distributions have the same configuration as an optical fiber in which the interlayer insulating film 3 is used as a core layer and the upper and lower sides thereof are sandwiched between low-refractive index insulating films 4 and 2 and are used as cladding layers. Therefore, as shown by the light guide path (3), the amount of stray light reflected at the end of the metal aluminum electrode 11 or the like is horizontally diffused by this optical fiber effect, and the amount of intrusion into the active layer of the TFT increases. This horizontal diffusion of stray light due to the optical fiber effect is caused by the lower refractive index of the interlayer insulating film 4 located outside the interlayer insulating film 3 in contact with the active layer of the TFT, and therefore the interlayer insulating film 3 and the interlayer insulating film 4 This is because total reflection occurs between them. Such horizontal diffusion of stray light through the light guide path (3) occurs everywhere in pixels formed with a pitch of several tens of μm forming an active matrix even when viewed two-dimensionally. It diffuses and enters the TFT, causing light leakage.

  FIG. 4 is a schematic cross-sectional view showing a first embodiment of a thin film semiconductor device according to the present invention. For ease of understanding, the same reference numerals are assigned to portions corresponding to the thin film semiconductor device according to the reference example shown in FIG. As shown in the figure, the thin film transistor TFT has an active layer made of a semiconductor thin film SL, and multilayer insulating films 1 to 4 overlapping the active layer from above and below. The multilayer insulating film includes inner insulating films 2 and 3 having light guiding properties in contact with the semiconductor thin film SL, and outer insulating films 1 and 4 overlapping therewith. The inner insulating films 2 and 3 are set to have a refractive index smaller than that of the outer insulating films 1 and 4 in order to suppress the light guide property, and are guided to the semiconductor thin film SL through the inner insulating films 2 and 3. The amount of unnecessary light is suppressed.

In this embodiment, the interlayer insulating films 1 to 4 are all made of PSG, and a desired vertical refractive index distribution is obtained by adjusting the phosphorus concentration. The composition, film thickness, and refractive index of each interlayer insulating film 1 to 4 are summarized in Table 1 below. In general, the PSG concentration is expressed as follows.
[P ₂ O ₅ ] mol% = 6010 · W / (6200-81.9 · W) [W]: wt%
For example, 4 wt% = 4.09 mol%.
Further, 2 wt% = 1.99 mol%.

In this embodiment, the interlayer insulating films 1 to 4 surrounding the TFT are PSG films, and the phosphorus concentration is lower in the inner interlayer insulating films 2 and 3 than in the outer interlayer insulating films 1 and 4, and as a result, the refractive index is low. It is designed to be smaller. These PSG films can be easily formed using SiH ₄ and PH ₃ gas by AP-CVD. By changing the composition of both source gases, the phosphorus concentration of PSG can be controlled to a desired value. In this embodiment, the TFT substrate B is made of quartz, and the uppermost insulating film 5 is made of SiO ₂ . In this way, the light guide including the TFT is not formed, and the fiber effect generated in the light guide (3) in FIG. 3 is eliminated. In this embodiment, the optical fiber effect is removed simply by controlling the concentration of PSG. More practically, the interlayer insulating films 2 and 3 are preferably SiO ₂ rather than PSG. This is because this has a larger refractive index difference and is more convenient for suppressing the fiber effect.

Even when the interlayer insulating film 3 is a SiO ₂ film and the interlayer insulating film 2 is PSG, the desired effect can be obtained if the phosphorus concentration is less than about 1% by weight. The refractive indexes of the upper and lower insulating films 2 and 3 sandwiching the TFT active layer are not necessarily exactly the same. The TFT structure is made of a multilayer film, and the refractive index difference between the inner insulating film and the outer insulating film is important. By providing this refractive index difference, it is possible to suppress the optical fiber effect and prevent stray light from entering the TFT. However, the refractive index difference between the interlayer insulating film 3 and the interlayer insulating film 2 is preferably small in practice.

Examples of materials such as PSG and SiO ₂ (NSG) have been given as the material of the interlayer insulating film, but the material of the insulating film is limited to this as long as the difference in refractive index is such that the optical fiber effect cannot be obtained. It is not a thing. For example, BPSG or AsSG may be used as the insulating film. Incidentally, FIG. 5 is a graph showing the relationship between the refractive index and the dopant concentration. When P ₂ O ₅ , GeO ₂ , Al ₂ O ₃ and TiO ₂ are used as dopants for the silica glass SG, the refractive index of the silica glass increases in proportion to the doping amount. On the other hand, when F or B ₂ O ₃ is used as a dopant, it acts in the direction of decreasing the refractive index. Here, the refractive index of silica glass shows dependency on the concentration of various dopants, but in fact, it should be noted that the refractive index may vary depending on the film formation method and thermal history such as annealing. There must be. However, under the same film formation method and the same thermal history, the dopant concentration dependence of the refractive index of doped SiO ₂ maintains the tendency of the graph shown in FIG. Therefore, by utilizing this tendency, it is possible to control the vertical refractive index distribution of the multilayer interlayer insulating film to be low in the middle and high in the vertical direction. In the case of an optical fiber, the refractive index difference Δn of the core / cladding layer is about 0.01, but in a high-definition and high-density LCD, the pixel width is about 10 μm, and the distance is very short. Since the amount of incident light is 20 million lx or more, even if the difference in refractive index is about 0.001, there is a sufficient effect in reducing light leakage.

As the SiO ₂ film forming method, the AP-CVD method or the P-CVD method is suitable. Both films are formed at a temperature of about 100 ° C. to 500 ° C., and SiH ₄ , GeH ₄ , BH ₃ , PH _{3 and the} like can be used as the source gas. Instead of these inorganic raw material gases, tetraethoxysilane, tetramethoxysilane, tetraethoxygermanium, tetramethoxygermanium, triethyl meborate, trimethyl phosphate, triethyl phosphate, trimethyl phosphate, or the like can be used as the organic raw material gas.

FIG. 6 shows a second embodiment of the present invention, and parts corresponding to those of the first embodiment shown in FIG. 4 are given corresponding reference numerals. In the present embodiment, the lowermost interlayer insulating film 0 and the upper insulating film 4 are formed of PSG, while the intermediate insulating films 1 to 3 are formed of SiO ₂ . The composition, film thickness and refractive index of each insulating film are shown in Table 2 below. As shown in FIG. 6, the refractive index distribution is low in the middle of the laminated insulating film and high on both the upper and lower sides, so that the optical fiber effect does not appear.

FIG. 7 is a schematic partial sectional view showing a third embodiment of the present invention. In order to facilitate understanding, parts corresponding to those of the previous embodiment are given corresponding reference numbers. In this embodiment, the interlayer insulating films 2 and 3 are formed of SiO ₂ and the interlayer insulating film 4 is formed of PSG. The composition, film thickness and refractive index of each insulating film are shown in Table 3 below.

  In the present embodiment, the refractive index of the outer interlayer insulating film 4 is higher than that of the interlayer insulating film 3 in contact with the upper surface of the semiconductor thin film SL. In this way, by removing the optical fiber effect on at least one of the upper and lower sides, it is possible to suppress the light leak defect of the TFT.

  For introducing the dopant into the silica glass, ion implantation other than CVD can be used. A desired refractive index distribution can be obtained by ion-implanting a dopant into the laminated insulating film. FIG. 8 is a schematic plan view showing the specific method. As shown in the figure, a resist is formed leaving the opening of each pixel. The resist covers the TFT and the signal line 11 connected thereto. The black mask 13 formed on the substrate is also covered. By using this resist as a mask, dopant can be ion-implanted only into the opening of the pixel, so that a desired refractive index profile can be formed in the laminated insulating film.

FIG. 9 is a schematic partial sectional view showing the above-described ion implantation method. In this embodiment, F is used as a dopant, and F is implanted into the stack of the interlayer insulating films 2, 3, and 4 at a stage after the black mask 13 is formed. In this example, the average flight distance Rp of F is set at the interface between the buffer layer 2 and the interlayer insulating film 3, and F ions are implanted. The doping amount is about 10 ¹⁵ / cm ² . F is ion-implanted only into the opening using the resist as a mask. Therefore, the TFT is not damaged. An electron shower or the like may be used together for the purpose of preventing charge-up at the same time as ion implantation. If implanted the F in the interlayer insulating film 2, 3, 4 made of SiO _2, the refractive index decreases. At this time, by setting Rp at the interface between the buffer layer 2 and the interlayer insulating film 3, the F concentration in this portion reaches a peak. Conversely, the refractive index distribution in the vertical direction is minimal at this interface. Thereby, the optical fiber effect is suppressed.

  As described above, in the present embodiment, each pixel is divided into an opening region and a non-opening region other than this in advance by a resist. The TFT has an active layer made of a semiconductor thin film SL, and laminated insulating films 2, 3, and 4 overlapping the active layer from above and below. The TFT is located in the non-opening region of each pixel, and the laminated insulating films 2, 3, and 4 extend over both the non-opening region and the opening region. As a characteristic matter, a dopant for adjusting the refractive index is implanted into a portion of the laminated insulating films 2, 3, and 4 that extends into the opening region. The dopant F has a concentration distribution in the vertical direction of the laminated insulating films 2, 3, and 4, whereby the laminated insulating films 2, 3, and 4 have the lowest refractive index near the interface with the active layer as a boundary, Accordingly, the amount of unnecessary light guided from each opening to the semiconductor thin film SL through the laminated insulating films 2, 3, 4 is suppressed.

  FIG. 10 also shows a refractive index control method using ion implantation. Unlike the previous examples shown in FIGS. 8 and 9, the refractive index control method is intended to give a horizontal distribution to the refractive index. This ion implantation is performed at a stage after the signal line 11 is formed on the substrate. As shown in the figure, a resist is formed so as to cover the signal line 11 in the column direction, the gate line 10 in the row direction, and the auxiliary capacitance line 10a. This resist also covers the TFT. An exposed opening is left in the center of each pixel.

  FIG. 11 schematically shows an ion implantation process, and P is used as a dopant. The dopant P is ion-implanted into the interlayer insulating films 2, 3, and 4 through a resist, thereby providing a refractive index distribution in the horizontal direction. That is, the refractive indexes of the laminated insulating films 2 to 4 are high in the opening region and low in the non-opening region. Thereby, most of the light incident on the interface between the opening region and the non-opening region is totally reflected and does not enter the non-opening region. Thereby, the TFT under the non-opening region can be effectively shielded from light. The P ion Rp is set at the interface between the buffer layer 2 and the interlayer insulating film 3. However, the present invention is not limited to this.

It is a schematic diagram which shows the optical system of an image projector apparatus. It is a fragmentary sectional view which shows the reference example of a thin film semiconductor device. It is a fragmentary sectional view which shows the reference example of a liquid crystal display device. It is a fragmentary sectional view showing a 1st embodiment of the present invention. It is a graph which shows the relationship between a refractive index and dopant concentration. It is a fragmentary sectional view showing a 2nd embodiment of the present invention. It is a fragmentary sectional view showing a 3rd embodiment of the present invention. It is a top view which shows other embodiment of this invention. It is a fragmentary sectional view showing other embodiments of the present invention. It is a top view which shows another embodiment of this invention. It is a fragmentary sectional view showing another embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Buffer layer, 2 ... Interlayer insulation film, 3 ... Interlayer insulation film, 4 ... Interlayer insulation film, 5 ... Interlayer insulation film, 7 ... Light shielding film, 11 ... Source electrode (signal line), 12 ... drain electrode, 13 ... black mask, 20 ... counter substrate, 21 ... counter electrode, 30 ... liquid crystal, TFT ... thin film transistor, CS ...・ Auxiliary capacitor, SL ... Semiconductor thin film, PE ... Pixel electrode

Claims (14)

A substrate for forming matrix-like pixels and a thin film transistor formed on the substrate for driving each pixel,
Each pixel has an opening that modulates incident light according to driving by the thin film transistor and emits the modulated light.
Each thin film transistor includes a thin film semiconductor device having an active layer made of a semiconductor thin film and a multilayer insulating film overlapping the active layer from above and below,
The multilayer insulating film includes an inner insulating film in contact with the semiconductor thin film and an outer insulating film overlapping therewith,
2. The thin film semiconductor device according to claim 1, wherein the inner insulating film has a refractive index smaller than that of the outer insulating film.   The multilayer insulating film includes an inner insulating film in contact with the upper surface of the semiconductor thin film and an inner insulating film in contact with the lower surface of the semiconductor thin film, and both the inner insulating films are set to have a refractive index smaller than that of the outer insulating film. The thin film semiconductor device according to claim 1, wherein the thin film semiconductor device is formed.   3. The thin film semiconductor device according to claim 2, wherein the inner insulating film in contact with the upper surface of the semiconductor thin film and the inner insulating film in contact with the lower surface of the semiconductor thin film have the same refractive index.   Both the inner insulating film and the outer insulating film are made of a transparent oxide film and at least one of them contains a dopant, and the refractive index of the inner insulating film is made smaller than that of the outer insulating film by controlling the concentration of the dopant. The thin film semiconductor device according to claim 1.   5. The thin film semiconductor device according to claim 4, wherein the dopant is selected from P, B, As, Ge, Al, and F. A substrate for forming matrix-like pixels and a thin film transistor formed on the substrate for driving each pixel,
Each pixel has an opening that modulates incident light according to driving by the thin film transistor and emits the modulated light.
Each thin film transistor includes a thin film semiconductor device having an active layer made of a semiconductor thin film and a laminated insulating film overlapping the active layer from above and below,
The laminated insulating film extends to a region corresponding to the opening of each pixel, and a dopant for adjusting the refractive index is implanted into this portion,
2. The thin film semiconductor device according to claim 1, wherein the dopant has a concentration distribution in a direction perpendicular to the laminated insulating film, whereby the laminated insulating film has the lowest refractive index in the vicinity of the interface with the active layer as a boundary. A substrate for forming matrix-like pixels and a thin film transistor formed on the substrate for driving each pixel,
Each pixel has an opening region that modulates incident light according to driving by the thin film transistor and emits the modulated light, and a non-opening region other than this,
Each thin film transistor has an active layer made of a semiconductor thin film, and a laminated insulating film overlapping the active layer from above and below,
Each thin film transistor is located in a non-opening region of each pixel, and the laminated insulating film extends over both the non-opening region and the opening region.
2. The thin film semiconductor device according to claim 1, wherein the stacked insulating film has a horizontal distribution in refractive index, and a portion located in the opening region has a higher refractive index than a portion located in the non-opening region.   In the laminated insulating film, a dopant for adjusting the refractive index is implanted into one of a portion located in the opening region and a portion located in the non-opening region, so that the portion located in the opening region is the non-opening. 8. The thin film semiconductor device according to claim 7, wherein the thin film semiconductor device has a higher refractive index than a portion located in the region. A matrix-shaped pixel electrode and one substrate on which a thin film transistor for driving each pixel electrode is formed, and the other substrate on which a counter electrode is formed are held on both substrates bonded to each other with a predetermined gap. Consisting of a liquid crystal, a pixel is composed of a pixel electrode, a counter electrode, and a liquid crystal positioned between the two,
Each pixel has an aperture that modulates the incident light and emits the modulated light,
Each thin film transistor is a liquid crystal display device having an active layer made of a semiconductor thin film, and a multilayer insulating film overlapping the active layer from above and below,
The multilayer insulating film includes an inner insulating film in contact with the semiconductor thin film and an outer insulating film overlapping therewith,
The liquid crystal display device according to claim 1, wherein the inner insulating film has a refractive index set smaller than that of the outer insulating film. A matrix-shaped pixel electrode and one substrate on which a thin film transistor for driving each pixel electrode is formed, and the other substrate on which a counter electrode is formed are held on both substrates bonded to each other with a predetermined gap. Consisting of a liquid crystal, a pixel is composed of a pixel electrode, a counter electrode, and a liquid crystal positioned between the two,
Each pixel has an aperture that modulates the incident light and emits the modulated light,
Each thin film transistor includes a liquid crystal display device having an active layer made of a semiconductor thin film and a laminated insulating film overlapping the active layer from above and below,
The laminated insulating film extends to a region corresponding to the opening of each pixel, and a dopant for adjusting the refractive index is implanted into this portion,
The liquid crystal display device according to claim 1, wherein the dopant has a concentration distribution in a direction perpendicular to the laminated insulating film, whereby the laminated insulating film has the lowest refractive index in the vicinity of the interface with the active layer as a boundary. A matrix-shaped pixel electrode and one substrate on which a thin film transistor for driving each pixel electrode is formed, and the other substrate on which a counter electrode is formed are held on both substrates bonded to each other with a predetermined gap. Consisting of a liquid crystal, a pixel is composed of a pixel electrode, a counter electrode, and a liquid crystal positioned between the two,
Each pixel has an opening region that modulates incident light and emits the modulated light, and a non-opening region other than this,
Each thin film transistor has an active layer made of a semiconductor thin film, and a laminated insulating film overlapping the active layer from above and below,
In the liquid crystal display device in which each thin film transistor is located in a non-opening region of each pixel and the laminated insulating film extends over both the non-opening region and the opening region,
2. The liquid crystal display device according to claim 1, wherein the laminated insulating film has a horizontal distribution in refractive index, and a portion located in the opening region has a higher refractive index than a portion located in the non-opening region. In an image projector device in which a light source, a display panel, and an enlarged projection optical system are arranged in order along the optical axis,
The display panel includes a substrate for forming matrix-like pixels, and a thin film transistor formed on the substrate for driving each pixel.
Each pixel has an opening that modulates light incident from the light source according to driving by the thin film transistor and emits the modulated light to the enlarged projection optical system,
Each thin film transistor has an active layer made of a semiconductor thin film, and a multilayer insulating film overlapping the active layer from above and below,
The multilayer insulating film includes an inner insulating film in contact with the semiconductor thin film and an outer insulating film overlapping therewith,
The image projector apparatus according to claim 1, wherein the inner insulating film is set to have a refractive index smaller than that of the outer insulating film. In an image projector device in which a light source, a display panel, and an enlarged projection optical system are arranged in order along the optical axis,
The display panel includes a substrate for forming matrix-like pixels, and a thin film transistor formed on the substrate for driving each pixel.
Each pixel has an opening that modulates light incident from the light source according to driving by the thin film transistor and emits the modulated light to the enlarged projection optical system,
Each thin film transistor has an active layer made of a semiconductor thin film, and a laminated insulating film overlapping the active layer from above and below,
The laminated insulating film extends to a region corresponding to the opening of each pixel, and a dopant for adjusting the refractive index is implanted into this portion,
The dopant has a concentration distribution in a direction perpendicular to the laminated insulating film, whereby the laminated insulating film has the lowest refractive index in the vicinity of the interface with the active layer as a boundary. In an image projector device in which a light source, a display panel, and an enlarged projection optical system are arranged in order along the optical axis,
The display panel includes a substrate for forming matrix-like pixels, and a thin film transistor formed on the substrate for driving each pixel.
Each pixel has an opening region that modulates light incident from the light source according to driving by the thin film transistor and emits the modulated light to the enlarged projection optical system, and a non-opening region other than this,
Each thin film transistor has an active layer made of a semiconductor thin film, and a laminated insulating film overlapping the active layer from above and below,
Each thin film transistor is located in a non-opening region of each pixel, and the laminated insulating film extends over both the non-opening region and the opening region,
An image projector apparatus, wherein the laminated insulating film has a horizontal distribution in refractive index, and a refractive index is higher in a portion located in the opening region than in a portion located in the non-opening region.

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