JP2005354036A - Forming method of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid the use of an expensive process by using an inexpensive material, and to provide a large amount of semiconductor devices of high performance. <P>SOLUTION: The semiconductor device is formed by a forming method comprising a process for forming a gate electrode 2 on at least a flexible insulating substrate 1, a process for covering a surface of the gate electrode with a flattening material 3, a process for polishing a part of the flattening material and the gate electrode, a process for forming a gate insulating film 4 on a surface of the polished flattening material, a process for forming source/drain electrodes 5 on the gate insulating film, and a process for forming a semiconductor layer 6 between the source/drain electrodes. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor device used for an IC card, electronic paper, an RFID tag and the like and a method for forming the same.

In recent years, IC cards, electronic paper, RFID tags, and the like have attracted attention. For these, semiconductor devices are used. Semiconductor devices are becoming more and more multifunctional year by year, but conversely, they are becoming thinner and lighter, and in order to realize them, integration in a limited space and thinner elements are required.
In addition, if the substrate used in the semiconductor device is thinned to reduce the thickness, the element is easily broken. For example, IC cards are stored and carried in card holders and wallets, but they are often bent and twisted by external force in pockets and bags, and are strongly demanded to be flexible and difficult to break. It has been. In addition, since it is necessary to perform wiring by wire bonding or the like, there is a problem that the reliability is remarkably lowered, for example, the element itself or wiring is broken by bending or twisting.
Moreover, current semiconductor manufacturing processes require high temperature processes that cannot be tolerated by plastic films.
For this reason, in order to supply a large amount of semiconductor devices at low cost and to form a semiconductor device on a flexible base material, a semiconductor device formed using a printing method has also appeared (for example, see Patent Document 1). ).

  The printing method is attracting attention for the following reasons. That is, (1) it is possible to use a flexible resin film as a base material because it can be processed at a low temperature. -It is possible to achieve high-speed production by a roll process, and (3) printing solution is easy because a solution-like semiconductor can be used. For these reasons, a large amount of semiconductor devices formed on a flexible base material can be provided at low cost.

As a method of forming a semiconductor device using a printing method, for example, a method of applying a resist ink or a light-shielding ink using an offset printing method to form a semiconductor pattern or a circuit board (for example, see Patent Document 2), or A method of forming a wiring pattern using a conductive polymer solution by an inkjet printing method (for example, see Patent Document 3) is known.
Republished patent WO98-29261 JP-A-7-240523 Japanese Patent Laid-Open No. 2003-123047

As a material to which the printing method can actually be applied, a polymer thick film paste for forming a conductive pattern is widely used as an electrode material, and nano-sized metal particles such as gold and silver are processed into ink. Things are commercially available.
Examples of semiconductor materials include polythiophene, polyallylamine derivatives, and pentacene precursors. Further, not only organic substances but also fine particles such as cadmium selenide, silicon, germanium, or these metal organic compounds can be used as long as they can be prepared as a solution.
In addition, oxide semiconductors such as InGaZnO-based, InGaO-based, ZnGaO-based, InZnO-based, ZnO, and SnO ₂ can be used as semiconductor materials that can be formed at temperatures at which plastic films can be used.
In addition, polymer materials such as polyvinylphenol and polymethylmethacrylate can be used as the insulating film material, and high dielectrics such as barium titanate used for capacitors can be used as a resin with an appropriate viscosity at a predetermined ratio. Paste can be used.
By using these materials, semiconductor devices based on the printing method have become real, and many research reports have been published.
Here, the semiconductor device by the printing method is not limited to the case where all of the electrodes, the insulating film, and the semiconductor, which are the components of the semiconductor, are formed by the printing method, but when some of these elements are formed by the printing method. Shall also be included.

A semiconductor device generally used in an IC card or the like is a so-called TFT (Thin Film Transistor) type semiconductor device in which a gate electrode, a gate insulating film, source / drain electrodes, and a semiconductor film are stacked. In this semiconductor device, the thinner the gate electrode, the higher the cutoff frequency, which is a measure of high speed, and the smaller the element size, the smaller the parasitic capacitance and circuit resistance. ing.
In order to form such a semiconductor device, (1) the relative positions of the gate electrode and the source / drain electrodes are accurately determined, and (2) the distance (channel length) between the source / drain electrodes is accurately determined. There are two issues.
In a conventional method for forming a semiconductor device using a photo process, each layer is superposed by optical position reading, and exposure is performed by mechanically aligning a photo mask.
Although the optical alignment is accurate, the apparatus is expensive, and the productivity is low, so an increase in product cost is inevitable.

  In order to reduce the cost of semiconductor devices, it is effective to avoid the use of a vacuum process and to use a copper-clad substrate or thick film paste for the gate electrode. Similarly expensive equipment is required. For this reason, it is desirable that alignment can be performed in a self-aligning manner.

  The present invention has been made to solve the above problems, and aims to provide a large amount of high-performance semiconductor devices at low cost by using inexpensive materials and avoiding the use of expensive processes. .

In order to solve the above problems, the present invention includes at least a step of forming a gate electrode on a flexible insulating substrate, a step of covering the surface of the gate electrode with a planarizing material, and one of the planarizing material and the gate electrode. A step of polishing a portion, a step of forming a gate insulating film on the surface of the polished planarizing material, a step of forming source / drain electrodes on the gate insulating film, and a semiconductor layer between the source / drain electrodes A method for forming a semiconductor device including a step of forming the semiconductor device is employed.
By adopting such a method, a large area can be flattened, so that the gate electrode can be formed thinly and accurately, and the position of the gate electrode and the source / drain electrode can be accurately defined using an inexpensive material. In addition, it is possible to provide a large number of semiconductor devices with high performance at a low cost with a constant channel length.

In the present invention, the gate electrode can be formed by a screen printing method. Alternatively, the gate electrode can be formed by etching a copper-clad substrate.
If the Kate electrode is formed by such a method, an inexpensive material can be used, so that the cost can be reduced.
In the present invention, the gate insulating film can be formed by spin coating or die coating.
Since the surface including the planarizing material is mirror-finished, it can be formed in a large area at a stretch by a spin coating method, and there is an advantage that the forming speed can be increased and the processing can be efficiently performed.
Furthermore, the step of polishing and removing a part of the planarizing material can be performed using a wet polishing method.
In addition, the semiconductor layer can be formed by dropping an organic semiconductor solution by inkjet and then drying by heating.
A means in which the semiconductor layer is an oxide semiconductor can be adopted.
Furthermore, it is preferable to use a polyester resin or a polyimide resin as the flexible insulating substrate.

  According to the present invention, it is possible to provide a large amount of high-performance semiconductor devices at low cost by using an inexpensive material and avoiding an expensive process.

FIG. 1 shows a cross-sectional structure of a semiconductor device formed according to the present invention.
In a semiconductor device 10 formed according to the present invention, a gate electrode 2 is formed on a substrate 1 made of a flexible insulator, and the periphery of the gate electrode 2 is filled with a planarizing material 3. The surface of the planarizing material 3 including the gate electrode 2 is covered with a gate insulating film 4.
On the gate insulating film 4, a source electrode 5-1 and a drain electrode 5-2 are formed at a position sandwiching the gate electrode 2 with a certain distance, thereby constituting a channel. A semiconductor layer 6 is provided between the source electrode 5-1 and the drain electrode 5-2 so as to be connected to each end. The bonding pad 7 is provided on the source electrode 5-1 and the drain electrode 5-2 on the surface of the substrate thus configured, and the other part is covered with the protective film 8 to form the semiconductor device 10.

Next, a method for forming a semiconductor device of the present invention will be described with reference to the drawings. In the following drawings, the scale is not necessarily drawn accurately for easy understanding.
2 and 3 are process cross-sectional views illustrating a method for forming a semiconductor device of the present invention.
First, as shown in FIG. 2A, a gate electrode 2 is formed on a substrate 1 made of a flexible insulator.
As the substrate 1, it is preferable to use a polyester resin film or a polyimide resin film in order to form a semiconductor element thin and small and to have flexibility to bend and bend. Of course, an inorganic insulating substrate such as glass or alumina can also be used depending on the application.
The gate electrode 2 may be formed by, for example, printing a conductive thick film paste at a predetermined position using screen printing or the like, followed by baking, or using a copper-clad substrate with a copper foil attached. Alternatively, it may be formed by patterning into a predetermined shape. The thick film paste is not particularly limited as long as it has high electrical conductivity, has an appropriate viscosity, and can be applied without unevenness when printed. For example, silver (Ag) and carbon (C) fine particles dispersed in an organic polymer and adjusted to an appropriate viscosity can be used. The thickness of the gate electrode 2 is preferably as thin as possible within the range of 10 to 20 μm.
The gate electrode 2 formed by screen printing the thick film paste is as thick as several tens of μm, and the surface has irregularities. Even if the source / drain electrodes are formed on the gate insulating film via the gate insulating film, It is difficult to form source / drain electrodes having accurate dimensions and shapes.
In addition, since the gate electrode formed by patterning into a predetermined shape using a copper-clad substrate is too thick, a high-performance semiconductor device cannot be obtained.

  Therefore, as shown in FIG. 2B, the planarizing material 3 is applied to the surface of the substrate including the gate electrode 2 to cover the gate electrode 2. As the planarizing material, a paste obtained by dispersing a solder resist or barium titanate in an organic solvent in addition to a polymer material such as polyvinyl phenol or polymethyl acrylate can be used. The method for applying the planarizing material is not particularly limited, and a known printing method, that is, a plate printing method such as screen printing, an ink jet printing method, a plateless printing method such as electrostatic printing, and the like can be used. .

Next, as shown in FIG. 2C, a part of the planarizing material 3 including the gate electrode 2 is polished and removed to finish a mirror surface.
There is no restriction | limiting in particular in the grinding | polishing method, A well-known method can be utilized. For example, chemical mechanical polishing (CMP) widely used in the semiconductor field can be used for polishing by buffing with an abrasive and an etching agent. In order to efficiently polish at high speed, it is preferable to employ a buffing method after using water-resistant abrasive paper. As the abrasive grain size of the abrasive paper, for example, after polishing with # 500, # 1200, # 2400, # 4000, polishing with a buff and alumina suspension polishing liquid or silica suspension polishing liquid, Can be polished. Polishing is performed so that the thickness after polishing is 10 to 20 μm.

  Next, as shown in FIG. 3D, a gate insulating film 4 is applied to the surfaces of the mirror-polished gate electrode 2 and the planarizing material 3. As the gate insulating film, in addition to a polymer material such as polyvinylphenol or polymethyl acrylate, a paste obtained by dispersing solder resist or barium titanate in an organic solvent can be used. The coating method is not particularly limited, and a known roll coating method, gravure coating method, die coating method, spin coating method, or the like can be used. The thickness of the gate insulating film 4 is suitably 1 μm or less.

Next, as shown in FIG. 3 (e), source / drain electrodes 5 are formed on the upper surface of the gate insulating film 4 with a predetermined interval between the gate electrodes 2.
The source / drain electrodes 5 are formed by printing a conductive thick film paste using screen printing or the like and then baking it. An appropriate thickness of the source / drain electrode 5 is about 10 to 20 μm.

Next, as shown in FIG. 3 (f), the semiconductor layer 6 is formed by connecting the source / drain electrodes 5. The semiconductor layer 6 is a known organic semiconductor such as a polythiophene derivative, a polyphenylene vinylene derivative, a polythienylene vinylene derivative, a polyallylamine derivative, a polyacetylene derivative, an acene derivative, an oligothiophene derivative, an InGaZnO series, an InGaO series, a ZnGaO series, an InZnO series An oxide semiconductor such as ZnO or SnO ₂ can be used.
Finally, a bonding pad is provided on the source / drain electrode 5 including the semiconductor layer 6, and the entire surface of the substrate excluding the bonding pad is covered with a protective film to obtain a semiconductor device.

(Example 1)
On a polyester film having a thickness of 100 μm, a polymer thick film paste made of silver and carbon as a conductor was printed by screen printing, and this was heat-cured at 150 ° C. for 30 minutes in a drying oven to obtain a gate electrode having a thickness of 20 μm. did.
Thereafter, a solder resist was screen printed as a planarizing layer on the surface of the film including the gate electrode and cured by heating at 150 ° C. The thickness of the flattened layer after curing was 30 μm.

  Thereafter, the surface of the planarizing layer was polished with a wet polishing apparatus. Polishing was performed using # 500, # 1200, # 2400, and # 4000 water-resistant polishing paper, and then the surface was flattened by mirror polishing with a buff, an alumina suspension and a silica suspension. As a result, the thickness of the planarization layer including the gate electrode was 12 μm.

Next, a negative photoresist was spin-coated on the surface of the planarization layer, and then cured by irradiation with ultraviolet rays to form a gate insulating film. The thickness of the gate insulating film was 1 μm.
Next, a polymer thick film paste using silver and carbon as conductors was screen-printed at predetermined positions on the gate insulating film to form source / drain electrodes.
Furthermore, the source / drain electrodes were connected, and an anisole solution of a polythiophene derivative was dropped from the nozzle of an ink jet apparatus and dried by heating at 150 ° C. in the atmosphere to form a semiconductor layer.

Finally, bonding pads were provided on the source / drain electrodes, and the entire surface of the substrate except the bonding pads was covered with a protective film to complete the semiconductor device.
FIG. 4 shows the result of measuring the relationship between the drain voltage V and the drain current I (VI characteristic) of this semiconductor device. In the figure, curve (a) to curve (i) correspond to the case where the gate voltage is changed every 10V, such as 0V, 10V, 20V, 30V, 40V, 50V, 60V, 70V, 80V, 90V. . As shown in FIG. 4, when the gate voltage is 0 (zero) V (curve a), the drain current hardly flows, and the drain current flows as the gate voltage increases.

(Example 2)
Using a copper-clad substrate obtained by laminating a 18 μm thick copper foil on a polyimide film, the copper foil was etched by a known method to form a gate electrode.
Thereafter, a solder resist was screen printed on the surface and cured by heating at 150 ° C. to form a flattened layer having a thickness of 30 μm.

  Thereafter, the surface of the planarizing layer was polished with a wet polishing apparatus. Polishing was performed using # 500, # 1200, # 2400, and # 4000 water-resistant polishing paper, and then the surface was flattened by mirror polishing with a buff, an alumina suspension and a silica suspension. As a result, the thickness of the planarized layer after polishing was 12 μm.

  Thereafter, a negative photoresist was spin-coated on the planarizing layer surface to form a film, and then cured by irradiation with ultraviolet rays to form a gate insulating film. The thickness of the gate insulating film was 1 μm.

Next, a polymer thick film paste using silver and carbon as conductors was screen-printed at predetermined positions on the gate insulating film to form source / drain electrodes.
Furthermore, the source / drain electrodes were connected, and an anisole solution of a polythiophene derivative was dropped from the nozzle of an ink jet apparatus and dried by heating at 150 ° C. in the atmosphere to form a semiconductor layer.
Finally, bonding pads were provided on the source / drain electrodes, and the entire surface of the substrate except the bonding pads was covered with a protective film to complete the semiconductor device.

(Example 3)
As in Example 1, a polymer thick film paste using silver and carbon as conductors was printed on a 100 μm thick polyester film by screen printing, and this was heat-cured at 150 ° C. for 30 minutes in a drying oven. The gate electrode was 20 μm thick.
Thereafter, a solder resist was screen printed as a planarizing layer on the surface of the film including the gate electrode and cured by heating at 150 ° C. The thickness of the flattened layer after curing was 30 μm.

  Thereafter, the surface of the planarizing layer was polished with a wet polishing apparatus. Polishing was performed using # 500, # 1200, # 2400, and # 4000 water-resistant polishing paper, and then the surface was flattened by mirror polishing with a buff, an alumina suspension and a silica suspension. As a result, the thickness of the planarization layer including the gate electrode was 12 μm.

Next, a silicon dioxide film having a thickness of 0.1 μm was formed on the surface of the planarizing layer using a sputtering method to form a gate insulating film.
Next, a source / drain electrode made of a gold thin film is formed at a predetermined position on the gate insulating film by vapor deposition. Further, the source / drain electrode is connected, and a pentacene precursor is dropped from the nozzle of the ink jet apparatus, and is then atmospherically discharged. A semiconductor layer was formed by heating and drying at 150 ° C.
Finally, bonding pads were provided on the source / drain electrodes, and the entire surface of the substrate except the bonding pads was covered with a protective film to complete the semiconductor device.

(Example 4)
As in Example 1, a polymer thick film paste using silver and carbon as conductors was printed on a 100 μm thick polyester film by screen printing, and this was heat-cured at 150 ° C. for 30 minutes in a drying oven. The gate electrode was 20 μm thick.
Thereafter, a solder resist was screen printed as a planarizing layer on the surface of the film including the gate electrode and cured by heating at 150 ° C. The thickness of the flattened layer after curing was 30 μm.

  Thereafter, the surface of the planarizing layer was polished with a wet polishing apparatus. Polishing was performed using # 500, # 1200, # 2400, and # 4000 water-resistant polishing paper, and then the surface was flattened by mirror polishing with a buff, an alumina suspension and a silica suspension. As a result, the thickness of the planarization layer including the gate electrode was 12 μm.

Next, a silicon dioxide film having a thickness of 0.1 μm was formed on the surface of the planarizing layer using a sputtering method to form a gate insulating film.
Next, a source / drain electrode made of a gold thin film is formed at a predetermined position on the gate insulating film by vapor deposition. Further, the source / drain electrode is connected, and a mixed gas of Ar + O ₂ is used as a semiconductor layer by RF magnetron sputtering. InGaZnO ₄ was deposited at room temperature to form a semiconductor layer. Here, the semiconductor layer was patterned using a shadow mask during film formation.
Finally, bonding pads were provided on the source / drain electrodes, and the entire surface of the substrate except the bonding pads was covered with a protective film to complete the semiconductor device.

It is a figure which shows the cross-section of the semiconductor device formed by this invention. It is sectional process drawing explaining the manufacturing process of the semiconductor device of this invention. FIG. 3 is a sectional process diagram subsequent to FIG. 2; It is a figure which shows a VI characteristic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Gate electrode, 3 ... Planarizing material, 4 ... Gate insulating film, 5 ... Source / drain electrode, 6. .... Semiconductor layer, 7 ... Bonding pad, 8 ... Protective film, 10 ... Semiconductor device

Claims (8)

  At least a step of forming a gate electrode on a flexible insulating substrate, a step of covering the surface of the gate electrode with a planarizing material, a step of polishing the planarizing material and a part of the gate electrode, and the polishing A step of forming a gate insulating film on the surface of the planarizing material; a step of forming a source / drain electrode on the gate insulating film; and a step of forming a semiconductor layer between the source / drain electrodes. A method for forming a semiconductor device.   The method for forming a semiconductor device according to claim 1, wherein the gate electrode is formed by a screen printing method.   The method for forming a semiconductor device according to claim 1, wherein the gate electrode is formed by etching a copper-clad substrate.   4. The method for forming a semiconductor device according to claim 1, wherein the gate insulating film is formed by a spin coating method.   The method for forming a semiconductor device according to claim 1, wherein the step of polishing and removing a part of the planarizing material is performed using wet polishing.   The method for forming a semiconductor device according to claim 1, wherein the semiconductor layer is formed by applying an organic semiconductor solution by ink-jet dropping and then drying by heating.   The method for forming a semiconductor device according to claim 1, wherein the semiconductor layer is an oxide semiconductor. The method for forming a semiconductor device according to claim 1, wherein the flexible insulating substrate is made of a polyester resin or a polyimide resin.

Images