JPH04133034A - Single crystal thin film semiconductor device for optical valve substrate - Google Patents

Abstract

PURPOSE:To obtain a subminiature optical valve device with high fineness having a high pixel density and a small picture size by forming integrally a pixel electrode and a switching element by using a LSI manufacturing technology for a semiconductor single crystal thin film layer formed on an insulated substrate. CONSTITUTION:On a surface of the electrically insulated substrate 1, the semiconductor single crystal thin film layer 2 is arranged. The pixel electrode 3 is formed by patterning the prescribed portion of the film layer 2 to a prescribed pattern and the switching element 4 is formed on the portion adjacent to the pixel electrode 3. Hence the switching element 4 is connected so as to hold the selective power supply to the corresponding pixel electrode 3. Namely in a portion of the thin film layer 2 adjacent to the pixel electrode 3, the drain region 7 of the switching element 4 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a flat plate light valve device used in direct-view display devices, projection display devices, and the like. More specifically, the present invention relates to a thin film semiconductor device on which a pixel array is formed, which is used as a substrate of a flat plate light valve device. The thin film semiconductor device is integrated into an active matrix device, for example, as a liquid crystal panel.

[Conventional technology]

The principle of an active matrix device is relatively simple; each pixel is provided with a switch element, and when a specific pixel is selected, the corresponding switch element is made conductive, and when not selected, the switch element is made non-conductive. It is something to keep. This switch element is formed on a glass substrate that constitutes a liquid crystal panel. Therefore, technology to reduce the thickness of switch elements is important. As this element, an insulated gate field effect thin film transistor is usually used.

Conventionally, in active matrix devices, thin film transistors have been formed on the surface of an amorphous silicon thin film or a polycrystalline silicon thin film deposited on a glass substrate. These amorphous silicon thin films and polycrystalline silicon thin films can be easily deposited on glass substrates using physical vapor deposition or chemical vapor deposition, making them suitable for manufacturing relatively large-screen active matrix devices. There is.

[Invention or problem to be solved]

However, conventional active matrix devices using amorphous silicon thin films or polycrystalline silicon thin films are not necessarily suitable for miniaturizing thin film elements and increasing pixel density. Recently, in addition to direct-view display devices, there has been an increasing demand for ultra-compact display devices or light valve devices having miniaturized, high-density pixels. Such a microscopic light valve device is used, for example, as a primary image forming surface of a projection type image device, and can be applied as a projection type high-definition television. It is believed that if micro semiconductor manufacturing technology or LSI technology can be used directly, it will be possible to create an ultra-compact light valve device that has pixel dimensions on the μ order and the size of the device as a whole.

However, when conventional amorphous or polycrystalline silicon thin films are used, it is difficult to actually apply LSI technology to form micro-order or sub-micro-order thin film elements. For example, in the case of an amorphous silicon thin film, the film formation temperature is about 300° C., so high-temperature processing required for LSI manufacturing technology cannot be performed. In addition, in the case of polycrystalline silicon thin films, the size of crystal grains is only about a few, which inevitably limits the miniaturization of thin film elements. Furthermore, the deposition temperature of the polycrystalline silicon thin film is approximately 600°C, and the
It is impossible to fully apply LSI manufacturing technology that requires high-temperature processing of 00° C. or higher. As mentioned above, the problem with conventional active matrix devices using amorphous or polycrystalline silicon thin films is that it is extremely difficult to achieve the same level of integration density and chip size as normal LSIs. was there.

In view of the above-mentioned problems of the prior art, it is a general object of the present invention to provide a semiconductor device for a light valve substrate that enables ultra-miniaturization of a light valve device of an active matrix device.

Incidentally, in conventional amorphous thin film semiconductor devices and polycrystalline thin film semiconductor devices for light valve substrates, pixel electrode groups arranged in a matrix are formed by patterning a transparent electrode thin film such as ITO.

This ITO thin film has a low heat resistance and does not have high etching accuracy. Although this is not a problem when the pixel size is relatively large, various problems arise when attempting to increase the density of pixels in accordance with the miniaturization of thin film elements. First, IT
Since the O thin film cannot withstand the high temperature treatment required for LSI manufacturing technology, it is not possible to apply a semiconductor process throughout, resulting in poor throughput. Second, the etching accuracy of the ITO thin film is low, making it difficult to form a high-definition pixel electrode group. Third, as elements become finer, the surface of the substrate inevitably becomes more uneven, and if a pixel electrode is placed on top of the unevenness, defects such as disconnections occur frequently.

In view of the various problems caused by the conventional pixel electrode structure due to the miniaturization of thin film elements, the present invention has been developed so that the semiconductor process can be consistently applied, has high dimensional accuracy, and is not affected by the adverse effects of irregularities on the substrate surface. A distinctive object of the present invention is to provide a semiconductor device for a light valve substrate that has a pixel electrode structure that is free from problems.

[Means for Solving the Problems] In order to achieve the above-mentioned general purpose and characteristic purpose, a thin film semiconductor device for a light valve substrate according to the present invention comprises an electrically insulating substrate and a thin film semiconductor device disposed on the surface of the substrate. A composite substrate consisting of a semiconductor single crystal thin film layer is used. The pixel electrode group is composed of a semiconductor single crystal thin film layer patterned into a predetermined shape. Furthermore, a group of switching elements is also formed integrally on the semiconductor single crystal thin film layer. Each switch element is composed of a single crystal thin film element, and the single crystal thin film element is directly connected to the corresponding pixel electrode through the semiconductor single crystal thin film layer.
7 for selective power supply.

According to one aspect of the invention, each single crystal thin film device is comprised of an insulated gate field effect transistor having a gate electrode and a pair of impurity diffusion regions. One impurity diffusion region, for example, a drain region, is continuous with the corresponding pixel electrode through a common semiconductor single crystal thin film layer.

According to another aspect of the invention, preferably the semiconductor single crystal thin film layer comprises a polished semiconductor single crystal thin film layer adhered to the substrate surface. That is, for example, after bonding a high quality silicon wafer to the surface of an electrically insulating substrate, the bonded silicon wafer is thinned by mechanical polishing or chemical polishing to form a silicon single crystal thin film layer.

[Action of the invention]

As described above, according to the present invention, a composite substrate having a two-layer structure in which a semiconductor single crystal thin film layer is formed on the surface of an electrically insulating substrate carrier layer is used, and the semiconductor single crystal thin film layer is made of, for example, silicone. It has the same quality as silicon wafers made of single crystal bulk. Therefore, it is possible to integrally form a pixel electrode group and a corresponding switch element group on such a liquid conductor single crystal thin film layer by making full use of LSI manufacturing technology. The resulting semiconductor device has an extremely high pixel density and an extremely small pixel size, and can be used to construct an ultra-small, high-definition light valve device.

In particular, the individual pixel electrodes are formed by patterning a common semiconductor single crystal thin film layer similarly to the switch element group. Therefore, unlike structures using conventional ITO thin films, LSI manufacturing technology can be applied as is, and a consistent semiconductor process is possible.
Became iJ Noh. Since the pixel electrode group is formed by patterning the conductor single crystal thin film layer itself, it is not affected by irregularities on the substrate surface that occur after the switch element group is formed.

〔Example〕

Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic partial cross-sectional view showing an embodiment of a single crystal thin film semiconductor device for a light valve substrate, and only one pixel is cut out and shown. As shown in the figure, this semiconductor device uses an electrically insulating substrate 1. This substrate is made of, for example, transparent quartz glass. A semiconductor single crystal thin film layer 2 is arranged on the surface of the substrate 1 . This semiconductor single crystal thin film layer 2 is made of silicon single crystal, for example, and its film thickness is set to about 0.1□□□. By reducing the film thickness, it is possible to make the film substantially transparent to incident light. A certain portion of the semiconductor single crystal thin film layer 2 is patterned into a predetermined shape to constitute a pixel electrode 3. A switch element 4 is formed in a portion of the semiconductor single crystal thin film layer 2 adjacent to the pixel electrode 3.

This switch element 4 is composed of integrated single crystal thin film elements, and each single crystal thin film element selectively supplies power directly to the corresponding pixel electrode 3 through the semiconductor single crystal thin film layer 2. It is connected. The switching element 4 or single crystal thin film element is composed of, for example, an insulated gate field effect transistor having a gate electrode 5 and a pair of impurity diffusion regions, that is, a source region 6 and a drain region 7. One impurity diffusion region, that is, the drain region 7 is continuous with the corresponding pixel electrode 3 (indicated by -. In other words, the train region 7 and the pixel electrode 3 are formed of impurity diffusion regions formed in a common semiconductor single crystal thin film layer 2. This semiconductor monocrystalline thin film layer 2 consists of, for example, a high quality polished silicon single crystal thin film layer adhered to the surface of the substrate 1.

Gate electrode 5 is placed over the channel formation region of thin film transistor switch element 4 with gate insulating film 8 interposed therebetween. This channel forming region is sandwiched between a pair of source regions 6 and train regions 7.

A wiring button 10 made of metal aluminum or the like is formed above the switch element 4 with an insulating film 9 interposed therebetween. This wiring button 10 is electrically connected to the source region 6 of the switch element 4 via a contact hole formed in the insulating film 9. This wiring button lO is further connected to a signal line (not shown), and transmits the image signal to the switch element 4.
to be applied. This image signal is selectively supplied to the pixel electrode 3 via the channel forming region and drain region 7 which are in a conductive state. A protective film 11 is formed on the surface of the wiring button 10. This protective film 11 covers the surface of the substrate 1 except for the portion where the pixel electrode 3 is formed, and protects the switch element 4 from external stress. Finally, the entire surface of the substrate is coated with an alignment film 12. This alignment film 12 is necessary, for example, when incorporating the present single crystal thin film semiconductor device for a light valve substrate as a liquid crystal panel.

Incidentally, FIG. 1 shows an example in which a liquid crystal panel is constructed using the single crystal thin film semiconductor device for a light valve substrate described above. As shown in the figure, a counter substrate 13 is placed with respect to the substrate 1 with a predetermined gap therebetween. The counter substrate 13 has a laminated structure composed of a glass carrier 14, a common electrode 15 formed on the inner surface thereof, and an alignment film 16 covering the common electrode 15. A predetermined gap between the composite substrate 1 and the counter substrate 13 is filled with a liquid crystal layer 17 . The liquid crystal layer 17 is sandwiched between a pair of alignment films 12 and 16 from above and below, and has a predetermined alignment structure of liquid crystal molecules. A predetermined voltage is applied between the common electrode 15 and the pixel electrode 3 according to the amount of selectively supplied electric charge, and the alignment state of liquid crystal molecules in the liquid crystal layer I7 changes. The transmittance of incident light is adjusted according to this change, and each pixel performs a light valve function.

FIG. 2 is a schematic partial sectional view showing a modification of the single crystal thin film semiconductor device for a light valve substrate shown in FIG.

Components that are the same as those shown in FIG. 1 are given the same reference numerals, and their explanations will be omitted. The difference from the embodiment shown in FIG. 1 is that the thickness of the semiconductor single crystal thin film layer 2 in the portion constituting the pixel electrode 3a is different from that in the portion where the corresponding thin film switch element 4 is integrated. This means that the layer thickness is set smaller than the layer thickness of . That is, the semiconductor single crystal thin film layer 2 is selectively etched along a predetermined pattern to form a pixel electrode 3a whose film thickness is partially reduced. In this way, the transmittance of the pixel electrode 3a can be significantly improved, and at the same time, there is no need to make the thickness of the semiconductor single crystal thin film layer 2 on which the switch element 4 is formed extremely thin in advance, so the formation process is simplified. Ru.

FIG. 3 is a schematic partial sectional view showing another modification of the single crystal thin film semiconductor device for a light valve substrate according to the present invention. Components that are the same as those in the embodiment shown in FIG. 1 are given the same reference numerals and their descriptions will be changed. The difference from the embodiment shown in FIG. 1 is the thickness of the semiconductor single crystal thin film layer 2 in the portion constituting the pixel electrode 3b, or the thickness of the semiconductor single crystal thin film layer 2 in the portion where the corresponding thin film element 4 is integrated. This is smaller than the layer thickness of . However, unlike the modification shown in FIG. 2, the semiconductor single crystal thin film layer 2 is partially thermally oxidized along a predetermined pattern and converted into an optically transparent oxide film 3c. Therefore, in the region of the pixel electrode 3b, the thickness of the semiconductor single crystal thin film layer 2 is reduced so that its transmittance is substantially 100%. Unlike the example shown in FIG. 2, since the surface of the substrate 1 is flattened, there is an advantage that post-processing, such as alignment film treatment, is facilitated.

FIG. 4 is a schematic partial sectional view showing still another modification of the single crystal thin film semiconductor device for a light valve substrate according to the present invention.

Components that are the same as those in the embodiment shown in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted. Also in this modification, the layer thickness of the semiconductor single crystal thin film layer 2 in the portion constituting the pixel electrode 3d is smaller than the layer thickness of the semiconductor single crystal thin film layer 2 in the portion where the corresponding thin film switch element 4 is integrated. It is set. However, unlike the example shown in FIG. 2, in this example, a table-shaped step 3e is previously formed on the surface portion of the substrate 1 that defines the pixel area. Semiconductor single crystal thin film layer 2 that is flat against the stepped surface
Cover. As a result, the thickness of the semiconductor single crystal thin film layer 2 is reduced by the height of the stepped portion 3e. By appropriately setting the height dimension of this stepped portion, it is possible to make the transmittance of the pixel electrode 3d substantially 100%.

Next, FIG. 5 is a schematic exploded perspective view showing an active matrix liquid crystal device constructed using the single crystal thin film semiconductor device for a light valve substrate according to the present invention. As shown in the figure, the liquid crystal device is composed of a composite substrate 1, a counter substrate 13 disposed opposite to the composite substrate with a predetermined gap in between, and an electro-optic material layer, that is, a liquid crystal layer 17 disposed in the gap. ing. The composite substrate 1 includes a group of pixel electrodes 3 that define pixels;
A drive circuit for driving the pixel electrode group 3 in response to a predetermined signal is formed.

Composite substrate 1 is made of quartz glass, and its surface is covered with silicon single-crystal thin film layer 2 .

Furthermore, an alignment film 12 is formed thereon. In addition, a polarizing plate 18 is bonded to the back side of the quartz glass substrate. The drive circuit is formed using this silicon single crystal thin film layer 2.
It consists of an integrated circuit formed in

This integrated circuit includes a switch element group 4 formed corresponding to a pixel electrode group 3 arranged in a matrix. This switch element 4 is composed of an insulated gate field effect transistor, and its drain electrode is connected to the corresponding pixel electrode 3.
Similarly, the gate electrode is connected to the scanning line 19, and the source electrode is similarly connected to the signal line 20. The integrated circuit further includes an X driver 21 and is connected to a column-shaped signal line 20. Furthermore, it includes a Y driver 22 and is connected to the row scanning line 19 . The counter substrate 13 is composed of a glass carrier 14, a polarizing plate 23 bonded to the outer surface of the glass carrier 14, and a common electrode 15 formed on the inner surface of the glass carrier 14.

In addition, the surface of the common electrode 15 is covered with an alignment film 16.

As described above, the pixel electrode 3 is composed of a silicon single crystal thin film layer 2 patterned into a predetermined shape. or,
A corresponding switch element 4 is similarly formed integrally on the silicon single crystal thin film layer 2.

As a result, the train region of the insulated gate field effect transistor constituting the switch element 4 and the pixel electrode 3 are continuously connected via the silicon single crystal thin film layer 2.

Next, the operation of the active matrix liquid crystal device shown in FIG. 5 will be briefly explained. The gate electrode of each thin film transistor switch element 4 is connected to a scanning line 19,
A scanning signal is applied by the Y driver 22 to control conduction and cutoff of the individual switch elements 4 line sequentially. The image signal output from the X driver 21 is applied via the signal line 20 to the selected transistor 4 which is in a conductive state. The applied image signal is transmitted to the corresponding pixel electrode 3, and selective power supply is performed. As a result, the pixel electrode 3 is excited and acts on the liquid crystal layer 17, increasing its transmittance to substantially 100%.
shall be. On the other hand, when not selected, the transistor switch element 4 becomes non-conductive and maintains the image signal written to the pixel electrode 3 as a charge. Note that the liquid crystal layer 17 has a high specific resistance and normally operates as a capacitor.

The on/off current ratio is used to express the switching performance of these thin film transistors. The current ratio required for liquid crystal operation can be easily determined from the write time and retention time. For example, if the image signal is a television signal,
90% of the image signal during approximately 60 μsec of one scanning line period
You have to write the above. On the other hand, more than 90% of the charge must be retained for about 16 m5ec, which is one field period. As a result, the current ratio needs to be five orders of magnitude or more. At this time, since the switching element 4 made of a thin film transistor is formed on the silicon single crystal thin film layer 2 having extremely high charge mobility, an on/off ratio of 6 digits or more can be ensured. Therefore, an active matrix liquid crystal device having extremely high-speed signal response can be obtained. Further, by utilizing the high mobility characteristics of the silicon single crystal thin film, it becomes possible to simultaneously form the peripheral driver circuits 21 and 22 in the same silicon single crystal thin film layer. In addition, the pixel electrode 3 can be formed by patterning the silicon single crystal thin film layer 2 itself into a predetermined shape. As a result, unlike the conventional method, the single crystal thin film semiconductor device for a light valve substrate according to the present invention can be manufactured using a semiconductor process consistently up to the final step.

Finally, referring to Figures 6(A) to 6(F),
A method for manufacturing the single crystal thin film semiconductor device for a light valve substrate shown in the figure will be described in detail. First, in the step shown in FIG. 6(A), a quartz glass substrate 31 and a silicon single crystal substrate 32 are prepared. It is preferable to use a high-quality silicon wafer used for LSI manufacturing as the silicon single crystal substrate 32, whose crystal orientation has uniformity in the range of <100>0.0±1.0, and whose single crystal lattice is uniform. The defect density is 500/C- or less. First, the surface of the prepared quartz glass substrate 31 and the back surface of the silicon single crystal substrate 32 are precisely smoothed.

Subsequently, both substrates are thermocompression bonded by overlapping and heating the smoothed surfaces. Through this thermocompression bonding process, both substrates 31 and 32 are firmly pressed together.

Subsequently, in the step shown in FIG. 6(B), the surface of the silicon single crystal substrate 32 is polished. As a result, a silicon single crystal thin film layer 33 polished to a desired thickness is formed on the surface of the quartz glass substrate 31. Incidentally, in order to reduce the thickness of the silicon single crystal substrate 32, an etching process may be used instead of the polishing process. The silicon single-crystal thin film layer 33 obtained in this manner has a thickness so thin as to be optically transparent, and the quality of the silicon wafer 32 is substantially preserved, so that the uniformity of crystal orientation and lattice are maintained. A substrate material with extremely high defect density can be obtained.

By the way, various types of semiconductor laminated substrates having a two-layer structure consisting of an insulating carrier layer and a silicon single crystal thin film layer are conventionally known. This is a so-called SOI substrate. For example, a Sol substrate is made by depositing a polycrystalline silicon thin film layer on the surface of an insulating carrier layer using a chemical vapor deposition method, etc., and then performing a heat treatment such as laser beam irradiation to recrystallize the polycrystalline film to form a single layer. It was obtained by converting it into a crystal structure. However, in general, single crystals obtained by recrystallization of polycrystals do not necessarily have --like crystal orientation and have a large lattice defect density.

For these reasons, SO produced by conventional methods
It has been difficult to directly apply SOI manufacturing technology to I substrates in the same way as silicon wafers.

On the other hand, according to the present invention, fine and high-resolution optical Made it possible to manufacture valve devices.

Next, in a step shown in FIG. 6(C), a pixel electrode 34 is formed by patterning the silicon single crystal thin film layer 33 along a predetermined shape. At the same time, an element region 35 is also formed in connection with the pixel electrode 34. The pixel electrode 34 and the element region 35 are composed of a common silicon single crystal thin film layer 33. Subsequently, the surface of the silicon single crystal thin film layer 33 patterned into a predetermined shape is thermally oxidized to form a silicon oxide film 36 on the entire surface. Furthermore, a gate electrode 37 having a predetermined shape is deposited in the element region 35 with a silicon oxide film 36 interposed therebetween.

Subsequently, in the step shown in FIG. 6(D), the gate electrode 3
Impurity ions are implanted through the silicon oxide film 36 using 7 as a mask. As a result, impurities are selectively introduced into the silicon single crystal thin film layer 33, and the gate electrode 3
A source region 38 and a drain region 39 are formed on both sides of 7. Pixel electrode 3 connected to drain region 39 at the same time
Impurities are also introduced into 4. As a result, the conductivity of the pixel electrode 34 can be lowered to a practical level. Through the above steps, a single crystal thin film insulated gate field effect transistor is formed in the element region 35, and its drain region 39 is directly electrically connected to the pixel electrode 34. In this way, unlike the conventional method, the pixel electrode 34 can also be processed using a complete semiconductor process. In addition,
Since the switch element and the pixel electrode are formed at the same time, unlike the conventional method, there is no adverse effect of irregularities on the surface of the substrate caused by the formation of the switch element.

Furthermore, in the step shown in FIG. 6(E), the switch element is covered with an interlayer insulating film 40. This interlayer insulating film 4
After forming a contact hole communicating with the source region 38, an aluminum batten 41 is deposited. As a result, external conduction to the switch element can be established.

Finally, in the step shown in FIG. 6(F), the switch element is covered with a protective film 42. In addition, when the thus completed single crystal thin film semiconductor device for a light valve substrate is used for assembling a liquid crystal panel, the substrate surface is coated with an alignment film 43.

〔Effect of the invention〕

As described above, according to the present invention, pixel electrode groups and switch element groups are integrally formed using LSI manufacturing technology on a high quality semiconductor single crystal thin film layer formed on an insulating substrate. There is. Therefore, it is possible to obtain a single crystal thin film semiconductor device for a light valve substrate having extremely high pixel density and switch element integration density. In particular, by forming not only the switch element but also the pixel electrode in a semiconductor single crystal thin film layer, electrical continuity between the switch element and the corresponding pixel electrode is automatically established, thereby simplifying the structure. Furthermore, unlike the conventional method, the semiconductor process can be carried out consistently up to the final step, so it is possible to obtain a single-crystal thin film semiconductor device for a light valve substrate of high quality and with few defects.

[Brief explanation of the drawing]

FIG. 1 is a schematic partial sectional view showing an embodiment of a single crystal thin film semiconductor device for a light valve substrate, FIG. 2 is a schematic partial sectional view showing a modification thereof, and FIG. 3 is a schematic partial sectional view showing another modification thereof. FIG. 4 is a schematic partial cross-sectional view showing an example, FIG. 4 is a schematic partial cross-sectional view showing another modification, and FIG. 5 is an active matrix constructed using a single-crystal N film semiconductor device for a light valve substrate. A schematic exploded perspective view showing a type of liquid crystal device, and FIG.
) to FIG. 6(P) are process diagrams showing a method of manufacturing a single crystal thin film semiconductor device for a light valve substrate.

Claims (1)

[Claims] 1. An electrically insulating substrate, a semiconductor single-crystal thin film layer disposed on the surface of the substrate, and a group of pixel electrodes made of the semiconductor single-crystal thin film layer patterned into a predetermined shape; It is composed of a plurality of single crystal thin film elements integrated into a semiconductor single crystal thin film layer, and each single crystal thin film element selectively supplies power directly to the corresponding pixel electrode through the semiconductor single crystal thin film layer. A semiconductor device for a light valve board comprising a group of connected switch elements. 2. Each single crystal thin film element comprises an insulated gate field effect transistor having a gate electrode and a pair of impurity diffusion regions, one of the impurity diffusion regions being continuous with the corresponding pixel electrode. Semiconductor device for light valve substrate. 3. The semiconductor device for a light valve substrate according to claim 1, wherein the semiconductor single crystal thin film layer is a polished semiconductor single crystal thin film layer adhered to the surface of the substrate. 4. The light valve substrate according to claim 1, wherein the thickness of the semiconductor single crystal thin film layer in the portion constituting the pixel electrode is smaller than the layer thickness of the semiconductor single crystal thin film layer in the portion where the corresponding thin film element is integrated. Semiconductor equipment.