JP2005354035A - 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 inexpensively 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 forming a gate insulating film 4 on the gate electrode 2; a process for forming source/drain electrodes 5 on the gate insulating film; a process for polishing and removing a part of the source/drain electrodes 5 and the gate insulating film 4, and forming a channel between the source/drain electrodes; and a process for forming a semiconductor layer 6 between the channels. <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 thinning of 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, wallets, etc., but they are often required to be bent and twisted by external force in pockets and bags, and are strongly required to be flexible and not easily broken. . 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) Since processing at low temperature is possible, it is possible to use a flexible resin film as a base material. (2) For this reason, a roll-shaped resin film is used so-called roll-to-roll. The reason is that high-speed production can be performed by the process, and (3) since a solution-like semiconductor can be used, printing processing is easy. For these reasons, a large amount of semiconductor devices formed on a flexible base material can be provided at low cost.

As a method for forming a semiconductor device using a printing method, for example, a method of forming a semiconductor pattern or a circuit board by applying a resist ink or a light-shielding ink using an offset printing method (see, for example, Patent Document 2), or the like. 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 SnO2 can also 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 forming a gate insulating film on the gate electrode, and a source / drain on the gate insulating film. A semiconductor including a step of forming an electrode, a step of polishing and removing part of the source / drain electrode and the gate insulating film to form a channel between the source / drain electrode, and a step of forming a semiconductor layer between the channel The device forming method was adopted.
If such a method is adopted, the position of the gate electrode and the source / drain electrode can be accurately defined by using an inexpensive material, and a large number of semiconductor devices having good performance with a constant channel length can be provided at low cost. It becomes possible to do.

In the present invention, the gate insulating film can be formed by a screen printing method.
The gate electrode can be formed by a screen printing method.
The gate electrode can be formed by etching a copper-clad substrate.
Furthermore, the step of polishing and removing a part of the source / drain electrodes and the gate insulating film may 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.
The semiconductor layer may be an oxide semiconductor.
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 surface of the substrate 1 including the gate electrode 2 is covered with a gate insulating film 4. . On the gate insulating film 4, a channel is formed with a certain distance between the source electrode 5-1 and the drain electrode 5-2, with a portion raised by the gate electrode 2 interposed therebetween. A semiconductor layer 6 is provided on the source electrode 5-1 and the drain electrode 5-2. The bonding pad 7 is provided on the source electrode 5-1 and the drain electrode 5-2 on the surface of the substrate configured as described above, 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.

  Next, as shown in FIG. 2B, a gate insulating film 4 is formed on the surface of the substrate including the gate electrode 2. At this time, since the gate electrode 2 is raised, a normal spin coating method is not preferable because it is difficult to obtain a uniform film. For forming the gate insulating film, it is preferable to use a printing method such as a screen printing method. As a material of the gate insulating film 4 that can be formed by a printing method, a paste obtained by dispersing solder resist or barium titanate in an organic solvent can be used. The thickness of the gate insulating film 4 is suitably 10 to 30 μm.

  Next, as shown in FIG. 2C, a conductive thick film paste is printed on the entire surface of the gate insulating film 4 using screen printing or the like and then baked to form the conductive film 5. The same thick paste as that used when forming the gate electrode can be used. The thickness of the conductive film 5 is suitably about 10 to 20 μm.

Next, as shown in FIG. 3D, the raised portion of the previous conductive film 5 at the gate electrode is polished and flattened. At this time, part of the flat part of the conductive film 5 and part of the raised part of the gate insulating film 4 are also polished.
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.

Next, as shown in FIG. 3E, a semiconductor layer 6 is formed between the source / drain electrodes 5 with the gate electrode 2 interposed therebetween.
As the semiconductor layer 6, known organic semiconductors such as polythiophene derivatives, polyphenylene vinylene derivatives, polythienylene vinylene derivatives, polyallylamine derivatives, polyacetylene derivatives, acene derivatives, oligothiophene derivatives, InGaZnO-based, InGaO-based, ZnGaO-based, InZnO An oxide semiconductor such as ZnO or SnO ₂ can be used. The semiconductor layer 6 is formed slightly larger than the size L of the gate electrode 2.
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 barium titanate paste was screen-printed on the surface and heated and cured at 150 ° C. to form a gate insulating film having a thickness of 10 μm.

Thereafter, the same polymer thick film paste as that used for forming the gate electrode was screen-printed on the gate insulating film, and this was heat-cured at 150 ° C. for 30 minutes to obtain a conductive film having a thickness of 15 μm.
As a result, the gate insulating film and the conductive film were laminated following the thickness of the gate electrode formed first, so that the height was increased only on the gate electrode.

  Thereafter, the surface was polished by a wet polishing apparatus. Polishing was performed using # 500, # 1200, # 2400, # 4000 water-resistant abrasive paper, and then mirror-polished with buff, alumina suspension and silica suspension to flatten the surface. As a result, most of the conductive film and the gate insulating film located on the gate electrode were removed to form a channel. As a result, the thickness of the gate insulating film on the gate electrode was 1 μm, and the source / drain electrodes were formed separated into two portions.

  Thereafter, an anisole solution of a polythiophene derivative was dropped from a nozzle of an ink jet device on the source / drain electrodes and dried at 100 ° 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 (VI characteristic) between the drain voltage V and the drain current I 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, almost no drain current flows when the gate voltage is 0 (zero) V, 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 printed on the surface by screen printing and heated and cured at 150 ° C. to form a gate insulating film having a thickness of 10 μm.

Thereafter, a polymer thick film paste using silver and carbon as conductors was screen-printed on the gate insulating film, and this was heat-cured at 150 ° C. for 30 minutes to obtain a conductive film having a thickness of 15 μm.
As a result, the gate insulating film and the conductive film were laminated following the thickness of the gate electrode formed first, so that the height was increased only on the gate electrode.

  Thereafter, the surface was polished by a wet polishing apparatus. Polishing was performed using # 500, # 1200, # 2400, # 4000 water-resistant abrasive paper, and then mirror-polished with buff, alumina suspension and silica suspension to flatten the surface. As a result, most of the conductive film and the gate insulating film located on the gate electrode were removed to form a channel. As a result, the thickness of the gate insulating film on the gate electrode was 1 μm, and the source / drain electrodes were formed separated into two portions.

  Thereafter, an anisole solution of a polythiophene derivative was dropped from a nozzle of an ink jet device on the source / drain electrodes and dried at 100 ° 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)
Similarly to Example 2, a gate electrode having a thickness of 18 μm was formed using a copper-clad substrate.
Thereafter, a solder resist was printed on the surface by screen printing and heated and cured at 150 ° C. to form a gate insulating film having a thickness of 10 μm.

Thereafter, a polymer thick film paste using silver and carbon as conductors was screen-printed on the gate insulating film, and this was heat-cured at 150 ° C. for 30 minutes to obtain a conductive film having a thickness of 15 μm.
As a result, the gate insulating film and the conductive film were laminated following the thickness of the gate electrode formed first, so that the height was increased only on the gate electrode.

  Thereafter, the surface was polished by a wet polishing apparatus. Polishing was performed using # 500, # 1200, # 2400, # 4000 water-resistant abrasive paper, and then mirror-polished with buff, alumina suspension and silica suspension to flatten the surface. As a result, most of the conductive film and the gate insulating film located on the gate electrode were removed to form a channel. As a result, the thickness of the gate insulating film on the gate electrode was 1 μm, and the source / drain electrodes were formed separated into two portions.

Then, the pentacene precursor was dripped from the nozzle of the inkjet device on the source / drain electrodes, and dried at 100 ° 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 4
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 printed on the surface by screen printing and heated and cured at 150 ° C. to form a gate insulating film having a thickness of 10 μm.

Thereafter, a polymer thick film paste using silver and carbon as conductors was screen-printed on the gate insulating film, and this was heat-cured at 150 ° C. for 30 minutes to obtain a conductive film having a thickness of 15 μm.
As a result, the gate insulating film and the conductive film were laminated following the thickness of the gate electrode formed first, so that the height was increased only on the gate electrode.

  Thereafter, the surface was polished by a wet polishing apparatus. Polishing was performed using # 500, # 1200, # 2400, # 4000 water-resistant abrasive paper, and then mirror-polished with buff, alumina suspension and silica suspension to flatten the surface. As a result, most of the conductive film and the gate insulating film located on the gate electrode were removed to form a channel. As a result, the thickness of the gate insulating film on the gate electrode was 1 μm, and the source / drain electrodes were formed separated into two portions.

A source / drain electrode was connected, and a semiconductor layer was formed as a semiconductor layer by depositing InGaZnO ₄ at room temperature using a mixed gas of Ar + O ₂ by RF magnetron sputtering. 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

1 ... substrate, 2 ... gate electrode, 4 ... gate insulating film, 5 ...
Source / drain electrodes, 6 ... semiconductor layer, 7 ... bonding pad, 8
... Protective film, 10 ... Semiconductor device

Claims (8)

  Forming at least a gate electrode on a flexible insulating substrate; forming a gate insulating film on the gate electrode; forming a source / drain electrode on the gate insulating film; and A method for forming a semiconductor device, comprising: a step of polishing and removing part of a drain electrode and a gate insulating film to form a channel between the source and drain electrodes; and a step of forming a semiconductor layer between the channel.   2. The method of forming a semiconductor device according to claim 1, wherein the gate insulating film 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 a screen printing method.   The method of forming a semiconductor device according to claim 1, wherein the gate electrode is formed by etching a copper-clad substrate.   5. The method of forming a semiconductor device according to claim 1, wherein the step of polishing and removing a part of the source / drain electrodes and the gate insulating film is performed by 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.

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