Patent Grant
11791160
This application is a 371 National Phase Application of International Patent Application PCT/JP2020/046746, filed Dec. 15, 2020, which claims priority to Japanese Patent Application No. 2020-002754, filed Jan. 10, 2020, the entire contents of which are incorporated herein by reference and priority is claimed to each.
The present invention relates to a polycrystalline film, a method for forming polycrystalline film, a laser crystallization device, and a semiconductor device.
Thin semiconductor films or thin metal films are processed for semiconductor devices. Examples of thin semiconductor films are thin silicon films and thin amorphous silicon films and thin polycrystalline films. Examples of thin metal films are thin aluminum films and thin copper films.
Flat panel displays (FPD: Flat Panel Display), such as liquid crystal panels or organic EL (Electro-Luminescence) panels, use a vast number of thin film transistors (hereinafter referred to as TFTs) as switching elements. TFTs use thin silicon films, such as thin amorphous silicon films and thin polycrystalline silicon films, for their active layers. Thin amorphous silicon films are processed for thin polycrystalline silicon films using various laser processes including laser annealing to initiate phase transitions from laser induced melting to solidification to obtain microstructures.
Methods and processes are known for forming thin polycrystalline silicon films. Patent literature 1 (i.e., JP 5534402 B2) and patent literature 2 (i.e., JP 2007-281465 A) describe such methods and processes. Patent literature 1 describes a method that uses a first laser annealing and a second or subsequent laser annealing. With a mask having a pattern in which an opaque region is surrounded on its outer boundary by a transparent region, a thin amorphous silicon film is irradiated with a laser beam in the first laser annealing step. In the second or subsequent laser annealing step, without the mask, the amorphous silicon film is irradiated with a laser beamlet having sufficient energy to effect complete melt of only the amorphous silicon without effecting melt of the polycrystalline silicon. According to this known method, lateral crystal growth is initiated when irradiated regions are fully melted and solidification is initiated at the solidus-liquidus interface between masked and unmasked regions, so that a crystal grows in radial outward directions using the associated one masked region as a seeding site. This results in creation of a thin polycrystalline silicon film composed of uniform crystal grains.
Patent literature 2 describes a method of forming a thin polycrystalline silicon film using a mask having a pattern in which an opaque region is less, in area, than the resolution limit and a transparent region is greater, in area, than the resolution limit.
As mentioned before, examples of thin metal films for semiconductor devices are thin copper films and thin aluminum films. The electrical resistivity or specific resistivity of copper (Cu) is low, so the threshold current density increases. The electrical resistivity of aluminum (Al) is low next to that of silver (Ag) and that of copper (Cu).
Patent literature 1: JP 5534402 B2
Patent literature 2: JP 2007-281465 A
In accordance with the methods described in patent literatures 1 and 2, neighboring grains grown from seed crystals form a grain interface where they meet. As they grow, the stress concentration at the confluence of three or four grain boundaries at a triple or quadruple point forms pronounced mounts. Such surface protrusions of a polycrystalline silicon film cause a problem that breakdown voltage for TFT decreases.
With increasingly shrinking interconnect stripe widths, metallization may have the following problems. For example, if thin aluminum film formed by sputtering is used as material for wiring, interconnect resistance rises and electromigration shortens device lifetime because of migration of aluminum atoms. High-temperature treatment is proved to be effective in extending lifetime for aluminum (Al) wiring because aluminum grains line up in a bamboo structure. However, high-temperature heat treatment is not applicable to fabrication of flat panel displays (FPDs), such as liquid crystal display devices because the glass substrate has melting point ranging from 400 to 500° C. There are more challenges to overcome when applying high-temperature heat treatment to Al wire connection on resin substrate because the resin substrate is lower, in melting point, than the glass substrate.
Further, conventional film deposition, such as chemical vapor deposition (CVD) and sputtering deposition, does not suffice to apply copper (Cu) to a sufficient thickness for wire connection. Moreover, the thin copper film is extremely difficult to be processed by etching. To address the problems, damascene patterning process, in which electroplating is used to grow copper (Cu) in grooves formed beforehand, is being widely used.
As is known, columnar structures and sparse grain boundaries, which are not observed in bulk material, are generated during electroplating for growing thin copper film. Such thin copper film has factors, such as, raised resistance and intergranular disconnection, which lower the reliability of wire connection. Improving the crystal quality by subjecting the thin copper film to heat treatment is a measure to prevent rapid disconnection of wire connection. However, residual high tensile stress remains in wiring covered by or stayed connected with other material immediately after heat treatment, causing stress dependent migration to occur, decreasing reliability of wiring.
In view of the above-mentioned issues, an object of the present invention is to provide polycrystalline films, such as thin polycrystalline silicon films, thin aluminum films, and thin copper films, which are free from surface protrusions, electrically homogeneous and stable, and mechanically stable, a method for creating the polycrystalline films, a laser crystallization device for use in manufacture of the polycrystalline films, and semiconductor devices including the polycrystalline films and having good electrical property and increased breakdown voltage.
In view of above, there is provided a polycrystalline film, including: evenly distributed crystal grains lining up in parallel lines extending along the surface of the film, and a no-lateral-growth region left at each of locations exposed to both ends of a grain interface, which serves as a partition between the neighboring two crystal grains, in a pattern that exposes the laterally crystallized film after lateral crystal growth, where: one of the both ends of the grain interface is separated from the other in a direction along the surface of the film.
It is preferable that the film surface portions of the crystal grains are flush with the film surface portions of the no-lateral-growth regions to make a flat and even surface.
It is preferable that each of the crystal grains is in the shape of a column having a height from the lower surface to the upper surface of the film, and the crystal grain includes a crystal core in the middle inside its limits within the surface of the film, the crystal core being in the shape of a column having a height from the lower surface to the upper surface of the film.
It is preferable that the distance, within the surface of the film, from the crystal core of each of the neighboring two crystal grains to the no-lateral-growth region is not shorter than the maximal lateral crystal growth length of the crystal grains.
It is preferable that the crystal grains and the no-lateral-growth regions are made of a material selected from semiconductor materials and metals.
In another aspect of the present invention, there is provided a method for forming a polycrystalline film by directing laser through a mask to irradiate an amorphous film to leave a large number of evenly distributed crystal grains lining up in parallel lines extending along the surface of the film, the method including: providing a mask configured to modulate that portion of the laser which is directed therethrough to evenly distributed seed crystal generating regions set beforehand on an amorphous film to have an attenuated intensity; allowing the amorphous film to crystalize using the seed crystal generating regions as seed crystals, and leaving a no-lateral-growth region left at each of locations exposed to both ends of a grain interface, which serves as a partition between the neighboring two crystal grains, in a pattern that exposes the laterally crystallized film after lateral crystal growth, where: one of the both ends of the grain interface is separated from the other in a direction along the surface of the film.
It is preferable that the distance between the seed crystal generating region for one of the neighboring two crystal grains with the grain interface therebetween and that for the other is shorter than two times the maximal crystal growth length of the crystal grains, and the distance between the seed crystal generating regions for the neighboring two crystal grains with the no-lateral-growth region therebetween is longer than two times the maximal crystal growth length of the crystal grains.
It is preferable that the amorphous film is made of a material selected from semiconductor materials and metals.
In other aspect of the present invention, there is provided a laser crystallization device, including: a laser source for generating laser; and a mask configured to modulate the laser directed therethrough to the surface of an amorphous film, wherein the mask is configured to modulate that portion of the laser which is directed therethrough to evenly distributed seed crystal generating regions set beforehand on an amorphous film to have an attenuated intensity; the laser with which a portion of the amorphous film adjacent to at least one of the seed crystal generation regions is irradiated has an intensity that is sufficient to melt through the entire thickness of the irradiated portion; the irradiated portion of the amorphous film laterally crystalizes using the seed crystal generating regions as seed crystals upon cooling, and the mask is configured to leave a no-lateral-growth region left at each of locations exposed to both ends of a grain interface, which serves as a partition between the neighboring two crystal grains, in a pattern that exposes the laterally crystallized film after lateral crystal growth, where: one of the both ends of the grain interface is separated from the other in a direction along the surface of the film.
It is preferable that the mask includes an opaque array pattern which allows that the distance between the seed crystal generating region for one of the neighboring two crystal grains with the grain interface therebetween and that for the other is shorter than two times the maximal crystal growth length of the crystal grains, and that the distance between the seed crystal generating regions for the neighboring two crystal grains with the no-lateral-growth region therebetween is longer than two times the maximal crystal growth length of the crystal grain.
It is preferable that the amorphous film is made of a material selected from semiconductor materials and metals.
In other aspect of the present invention, there is provided a semiconductor device including: a polycrystalline film including evenly distributed crystal grains lining up in parallel lines extending along the surface of the film, and a no-lateral crystal growth region left at each of locations exposed to both ends of a grain interface, which serves as a partition between the neighboring two crystal grains, in a pattern that exposes the laterally crystallized film after lateral crystal growth, one of the both ends of the grain interface being separated from the other in a direction along the surface of the film.
It is preferable that the film surface portions of the crystal grains are flush with the film surface portions of the no-lateral-growth regions to make a flat and even surface.
It is preferable that each of the crystal grains is in the shape of a column having a height from the lower surface to the upper surface of the film, and the crystal grain includes a crystal core in the middle inside its limits within the surface of the film, the crystal core being in the shape of a column having a height from the lower surface to the upper surface of the film.
It is preferable that the distance, within the surface of the film, from the seed crystal forming region for each of the neighboring two crystal grains to one of the no-lateral-growth regions is not shorter than the maximal lateral crystal growth length of the crystal grains.
It is preferable that the crystal grains and the no-lateral-growth regions are made of a material selected from semiconductor materials and metals.
It is preferable that the polycrystalline film is a polycrystalline silicon film, and the polycrystalline silicon film is an active semiconductor layer forming a channel region of a thin film transistor.
It is preferable that the thin film transistor is a bottom gate thin film transistor.
It is preferable that the thin film transistor is a top gate thin film transistor.
It is preferable that the polycrystalline film is made of aluminum (Al) and the crystal grains line up in a bamboo structure after patterning.
It is preferable that the polycrystalline film is made of copper (Cu).
Embodiments according to the present invention provide: polycrystalline films, such as thin polycrystalline silicon films, thin aluminum films, and thin copper films, which are free from surface protrusions, electrically homogeneous and stable, and mechanically stable; a method for forming the polycrystalline films; a laser crystallization device for use in manufacture of the polycrystalline films, and semiconductor devices using the polycrystalline films and having good electrical property and increased breakdown voltage.
Referring to the accompanying drawings, the following description provides specific details in order to provide a thorough description of embodiments of the present invention, which pertain to a polycrystalline film, a method for forming the polycrystalline film, a laser crystallization device, and a semiconductor device. Note, any drawings accompanying the application are for illustrative purposes only, and are thus not drawn to scale.
Referring, now, to
As depicted in
The mask 12-1 modulates the laser beam L oscillated from the laser source 11. The modulated laser beam L passes through the lens system 14 and strikes the surface of the thin amorphous silicon film 20. The mask 12-1 reduces the optical energy striking the surface of the thin amorphous silicon film 20 at evenly distributed unirradiated regions (see
In this laser crystallization device 10, using irradiation with laser beam L passed through the mask 12-1, the thin amorphous silicon film 20 within each of irradiated regions, which are adjacent to unirradiated regions each including a microcrystalline region 31A, is fully melted. As a result, the peripheral portion of each of the unirradiated regions is heated by heat conduction and melted, leaving the center of the unirradiated region as the microcrystalline region 31A. Lateral crystal growth is initiated upon cooling after irradiated regions are fully melted, commencing solidification using microcrystalline regions 31A as seed crystal forming regions to grow crystal grains 31 as shown in
As schematically depicted in
In detail, the distance between each and the neighboring one of central microcrystalline regions 31A, which serve as seeding sites for lateral crystal growth, in each of rows and columns on selected area of the surface of the thin amorphous silicon film 20 is shorter than twice the maximal lateral crystal growth length (i.e., 1.5 μm) of the crystal grains 31. Thus, as depicted in
Further, the distance between any two neighboring of the microcrystalline regions 31A which are diagonally opposite to each other on the selected area of the thin amorphous silicon film 20 is longer than twice the maximal lateral crystal growth length of the crystal grains 31. As depicted in
In such a laser crystallization device 10 and a method for forming a polycrystalline film using the same, laser annealing using the mask 12-1 configured as described above initiates lateral crystal growth using the microcrystalline regions 31A as seeding sites in a polycrystalline silicon film 30 as shown in
Further, in the polycrystalline silicon film 30 according to the present embodiment, the surface portions of crystal grains 31 are flush with the surface portions of no-lateral-growth regions 33. This is because the lateral crystal growth does not extend beyond the maximal lateral crystal growth length into the no-lateral-growth regions 33 which are left after lateral crystal growth, so the stress concentration otherwise created among the neighboring crystal grains 31 is avoided. Thus, the no-lateral-growth regions 33 serve as sites for mitigating the stress concentration derived from lateral crystal growth.
The laser crystallization device and the method for forming a polycrystalline film according to the present embodiment generates a polycrystalline silicon film 30, as depicted in
First, in the second embodiment, the thin aluminum film 40A is formed on a glass substrate (not shown). In order to deposit the aluminum film 40A on a glass substrate, aluminum atoms are ejected toward the substrate by sputtering. As depicted in
Referring, next, to
Referring to
Further, in the present embodiment, appropriately setting the irradiation condition of the laser beam suppresses the occurrence of thermal damage to the glass substrate on which the aluminum film 40C is deposited.
(Semiconductor Device)
In this thin film transistor 50, a gate electrode 52 is formed on a glass substrate 51 in a predetermined pattern, a gate insulating film 53 is formed on the gate electrode 52, and a polycrystalline silicon film 30 is formed on the gate insulating film 53 as an active semiconductor layer forming a channel region. A source electrode 54S and a drain electrode 54D are formed on the polycrystalline silicon film 30.
The thin film transistor 50 reduces variation in contact resistance because of the smooth planar surface of the polycrystalline silicon film 30. Moreover, the thin film transistor 50 has no or little drop in breakdown voltage because surface protrusions near the last place in the crystal to solidify are avoided due to a reduction in stress concentration even on the lower side of the polycrystalline silicon film 30.
The thin aluminum or copper film with a bamboo structure which is created during execution of the step of forming a polycrystalline metal film according to the embodiment of the present invention may be used for wiring among a gate electrode 52, a source electrode 54S, and a drain electrode 54D in such thin film transistor 50. In this case, the thin film transistor 50 achieves a high breakdown voltage because the thin aluminum or copper film has no or little surface protrusions on its lower side overlying that area of a gate insulating film 53 which overlies the gate electrode 52.
In this thin film transistor 60, an insulating film 62 is formed on a glass substrate 61, and a source electrode 63S and a drain electrode 63D are formed on the insulating film 62. A polycrystalline silicon film 30 is formed on the source electrode 63S and the drain electrode 63D. A gate insulating film 64 is formed on the polycrystalline silicon film 30, and a gate electrode 65 is formed on the gate insulating film 64 in a predetermined pattern.
This thin film transistor 60 achieves a high breakdown voltage because the surface of the polycrystalline silicon film 30 has no or little protrusions.
The thin aluminum or copper film with a bamboo structure which is created during execution of the step of forming a polycrystalline metal film according to the embodiment of the present invention may be used for wiring among a gate electrode 65, a source electrode 63S, and a drain electrode 63D in the thin film transistor 60. In this case, the thin film transistor 60 achieves a high breakdown voltage because the thin aluminum or copper film has no or little surface protrusions on its lower side overlying that area of a gate insulating film 64 which overlies the gate electrode 65.
Although the embodiments of the present invention have been described above, it should be understood that the description and drawings illustrating the embodiments are exemplary only, and should not be taken as limiting the scope of the present invention. It will be apparent to those of ordinary skill in the art that the following description reveals various alternative embodiments, examples, and operational techniques.
Although the first and second embodiments use the mask 12-1 depicted in
In the first and second embodiments, the mask 12-1 in which the opaque region 12B is arranged on the glass substrate 12A is used, but phase-shift masks may be used.
In the forgoing description about the embodiments, silicon (Si) is used as the semiconductor material to make up the crystal grains and the no-lateral-growth regions, but other semiconductor materials may be used. Although, in the foregoing description, examples in which aluminum and copper are used as the metal to make up the crystal grains and the no-lateral-growth regions are presented, but it is of course possible to apply other metals that crystallize in a film.
As depicted in
Compared to the comparative example, the laser crystallization device according to the embodiment depicted in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-002754 | Jan 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/046746 | 12/15/2020 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2021/140849 | 7/15/2021 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20070238270 | Kim | Oct 2007 | A1 |
| 20120220140 | Kajiyama et al. | Aug 2012 | A1 |
| Number | Date | Country |
|---|---|---|
| 63-060517 | Mar 1988 | JP |
| 63060517 | Mar 1988 | JP |
| 05-190449 | Jul 1993 | JP |
| 2007-281465 | Oct 2007 | JP |
| 2012-019231 | Jan 2012 | JP |
| 5534402 | Jul 2014 | JP |
| Entry |
|---|
| International Search Report for corresponding International Patent Application No. PCT/JP2020/046746 dated Mar. 2, 2021, with English Translation (5 pp.). |
| Written Opinion for corresponding International Patent Application No. PCT/JP2020/046746 dated Mar. 2, 2021, (4 pp.). |
| Number | Date | Country | |
|---|---|---|---|
| 20230027404 A1 | Jan 2023 | US |
