KR101736520B1

KR101736520B1 - Method and device for crystallizing an amorphous semiconductor layer with a laser beam

Info

Publication number: KR101736520B1
Application number: KR1020127011597A
Authority: KR
Inventors: 카이 슈미트; 클라우스 피펏; 스테판 비네케; 볼프강 비올
Original assignee: 코히런트 게엠바하; 호흐슐레 퍼 안게반테 비센샤프트 운드 쿤스트 파흐호흐슐레 힐데스하임/홀츠민덴/괴팅겐; 레이저 라보라토리움 괴팅겐 이.브이. (엘엘쥐)
Priority date: 2009-10-26
Filing date: 2010-10-22
Publication date: 2017-05-29
Also published as: WO2011054454A1; KR20120086303A; DE102009050680A1; DE102009050680B4

Abstract

The present invention relates to a method and apparatus for crystallizing an amorphous semiconductor layer with a laser beam, wherein a uniformly illuminated beam cross-section of the laser beam is uniformly projected onto at least the surface area of the semiconductor layer. The present invention is characterized in that at least a surface of at least a semiconductor layer illuminated by a laser beam while a laser beam is projected onto a semiconductor layer is provided with a static pressure plasma in the form of an ionized gas, Lt; / RTI > and / or the laser beam.

Description

[0001] The present invention relates to a method and an apparatus for crystallizing an amorphous semiconductor layer with a laser beam,

The present invention relates to a method and apparatus for crystallizing an amorphous semiconductor layer by means of a laser beam projecting a uniformly illuminated cross-section at least in the surface area of the semiconductor layer.

At least a part of the radiant energy is absorbed by the semiconductor material and converted into heat by illuminating the amorphous semiconductor layer with laser radiation of appropriate wavelength and emission power, and the semiconductor material is locally melted by the heat. Since the radiation inflow into the surface region of the locally confined semiconductor layer is generally in the form of a pulse, a crystallization process occurs upon re-cooling of the molten semiconductor material, and the crystallization process transforms the original amorphous semiconductor structure into a polycrystalline semiconductor structure. The thermal induction crystallization process, also referred to as an annealing process, is applied to the fabrication of polycrystalline silicon-based technology assemblies, such as TFT-thin film transistors and the like.

Thin film transistors are preferably used in flat screen areas of PCs, TVs or other devices, especially in consumer electronics. In general, a thin amorphous silicon layer provided on a glass or plastic flat substrate with a layer thickness of about 50 nm is melted in a short time by being exposed to laser radiation by a so-called LTPS process (Low Temperature Polysilicon Technology), solidified into a polycrystalline layer upon cooling , The polycrystalline layer is particularly suitable for the production of active-matrix (LCD) and active-matrix (OLED). The manufacture of high resolution displays, especially with high pixel density per ppi (ppi) density, requires the use of polycrystalline silicon-based thin film transistors.

To produce the display as efficiently and inexpensively as possible in industry standards, it is necessary to implement as little total energy input as possible and at the same time with the minimum energy input into the glass or plastic plate, the crystallization process of the amorphous silicon as wide as possible. For this reason, an excimer laser is preferably used for melting the amorphous layer. These lasers provide the high pulse energy required for an efficient process in addition to the required wavelength and excellent efficiency in the UV spectrum. In addition to the use of UV lasers, lasers of other wavelengths, e.g. 527.532 nm, are also used in the development stage.

Basically, when an excimer laser is used, an integrated processing method is formed, and by this processing method, the amorphous silicon can be modified so as to ensure a high current mobility of the free charge carrier. The uniformity of the layer properties distributed over the plate in addition to the current mobility is an important characteristic of high quality displays.

In a so-called Eximer Laser Annealing, for example as described in US 2006/0035103 A1, a linearly formed laser beam is directed onto a substrate coated with amorphous silicon with a pulse of 600 Hz. The laser beam is absorbed at the surface of the thin amorphous silicon layer of 50 to 100 nm, at which time the substrate is not heated and damaged. In the ELA method, the nearly rectangular beam profile of the excimer laser is transformed into a fixed uniform line having a length of 465 mm and a width of 0.4 mm. The energy density for this process is from 350 mJ / cm 2 to 400 mJ / cm 2. However, in this method, the amorphous silicon layer is not completely melted. Crystal growth starts at the upper boundary of the fixed lower silicon layer and proceeds in the direction of the molten upper silicon layer.

Basically, this method has proven to be optimal for the production of a polysilicon layer for a screen. In particular, the manufacturing process of AM-OLED is possible only in the LTPS flat panel according to the prior art. Additional cost optimization of the fabrication and fabrication process of LTPS screens with screen diagonal larger than 42 inches requires an expanded beam cross-section on the substrate. The fabrication of 50 inch TV substrates requires, for example, 650 mm to 750 mm lines.

In order to be able to carry out the annealing process in the same way by the extended rectangular beam profile as in the case of the above-mentioned beam profile having a length of 465 mm, the line width of the beam profile is suitably reduced . However, this assumes a much more complex and costly imaging optical system than the optical system used. Another way to extend the beam cross-section in a line form without reducing the energy density required for an effective annealing process is to increase the cost of purchasing and operating the annealing device, such as the use of a more complex optical system, when using a more powerful laser light source .

In US 2006/0024442 A1 (particularly paragraphs [0039 to 0045]) with the implementation of a crystallization process using a laser, the size of the crystal grains formed during crystallization depends on the controlled inflow of radiant energy and, in this regard, Lt; RTI ID = 0.0 > temperature < / RTI > In order to support the highest possible current mobility of the free charge carriers in the region of the polycrystalline semiconductor layer to be formed, the process parameters in the annealing process must be selected so as to form as large a particle size as possible uniformly distributed throughout the plate during crystallization. However, a defect position in the form of crystal grooves or unsaturated crystal bonds, so-called "dangling bonds " is formed in the crystal structure, and the mobility of the free charge carrier is lowered by the defect position. A hydrogen plasma is used to remove or minimize defects and the hydrogen plasma interacts with the illuminated semiconductor layer surface during the annealing process or following the annealing process and exhibits passive action on the defect location being formed. The generated hydrogen plasma includes free radicals and non-covalent electrons that bind to unsaturated crystals at defect positions in the crystal structure.

DE 693 27 559 T2 proposes a two-step process for the production of films consisting of polysilicon. In the first step an amorphous silicon film is provided on the substrate surface by polishing or PVD- or CVD deposition of the silicon powder. For crystallization, the amorphous silicon film is tempered by a laser gun, in which case silicon seed crystals having a particle diameter corresponding to the silicon film thickness are formed. The silicon crystal grains are exposed to the etching process in the presence of hydrogen radicals to control the density and size distribution of the formed silicon crystal grains. The hydrogen radicals are directed to the surface of the silicon layer which is formed by an ECR (Electron Cyclotron Resonance) -plasma device and which is to be processed in the form of a current composed of hydrogen radicals.

JP 2004-031511 A describes a positive pressure chamber in which a plasma processing apparatus and a laser emission apparatus are disposed. The substrate to be processed passes through the plasma processing apparatus first by the transfer system and then through the laser radiation apparatus. By this sequential treatment the further purification step can be omitted.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a semiconductor laser device having a laser beam projecting a beam cross section uniformly illuminated in at least a surface area of a semiconductor layer so as to improve the effect of locally heating and melting the semiconductor material, Lt; RTI ID = 0.0 > crystallization < / RTI > Particularly, it is important to find a way to convert the radiant energy of the laser beam into thermal energy more efficiently in the semiconductor layer to be processed, and therefore, it is possible to provide a large- Can be processed. In addition, the annealing equipment already in use must be able to be overcome by measures that are cheap and fairly simple to handle.

The above problem is solved by claim 1. The object of claim 12 is an apparatus for crystallization of an amorphous semiconductor. The dependent claims and the detailed description are described with particular reference to embodiments as features which advantageously improve upon the spirit of the invention.

According to the present invention, a significant efficiency increase in the conversion of the radiant energy of the laser beam into the thermal energy in the illuminated semiconductor layer is caused by the laser beam at least in the surface region of the semiconductor layer illuminated by the laser beam during laser beam projection into the semiconductor layer Or by providing a constant pressure plasma in the form of an ionized gas that interacts with the illuminated semiconductor layer and / or the laser beam.

By various experiments, the static plasma or air plasma interacting with the semiconductor surface in addition to the laser beam action on the surface of the semiconductor layer to be processed is subjected to a radiation energy coupling and thermal The efficiency of the conversion of the radiant energy into the energy can be remarkably increased. The gradation phenomenon can be caused, for example, in the form of an etching process in the semiconductor layer by the static pressure plasma interacting with the laser radiation and the semiconductor layer, or at least only slightly, because the static pressure plasma is mostly ionized Gas components. Therefore, the static pressure plasma is used only as a means for enhancing the optical coupling into the amorphous semiconductor layer, in which case the macroscopic structure of the semiconductor layer is not damaged in relation to the layer thickness and surface morphology.

According to the appropriate measures according to the present invention, the laser output entering per unit area can be reduced as much as possible without continuously interfering with the crystallization process. The measures according to the present invention can enlarge the beam cross section toward the amorphous semiconductor layer in a desired manner or reduce the energy density required for crystallization without further modification of the annealing apparatus used so far. Thus, the use of a constant pressure plasma in accordance with the present invention in connection with an annealing process enables the extension of the line beam cross-section of the laser beam illuminating the amorphous semiconductor layer, in which case the output need not use a stronger laser beam source and a complex optical system . Thus, efficiency and throughput in the annealing apparatus can be increased at low cost.

The action according to the present invention makes it possible to carry out the known annealing process under atmospheric pressure conditions, so that the process technology can be omitted from the complex and cost-intensive vacuuming measures.

A plasma generator known as a plasma source is used and a static plasma or an air plasma can be formed at each position of the surface of the semiconductor layer illuminated with the laser beam under atmospheric pressure condition by the plasma generator.

A preferred embodiment for forming a static pressure plasma provides at least one electrode arrangement that results in a high pressure, and the electrode is preferably disposed opposite the semiconductor layer at the ground potential. An electric field is formed between the electrode and the semiconductor layer due to a prescribed electric potential difference, and an air plasma is generated in the region of the surface of the semiconductor layer where the atmospheric electric discharge and the laser beam act on the electric field. The electrode causing high pressure is preferably formed in the form of a blade, i.e. the high pressure has an electrode edge that narrows towards the peak, the electrode edge is formed in the form of a sharp blade, and has a radius of several micrometers down.

It is particularly preferred to use at least two electrodes arranged as close to the surface as possible to the surface of the semiconductor layer, with a voltage selected to the appropriate size being set to initiate the atmospheric electrical discharge. In all cases, it is desirable to coat the electrode surface with a dielectric layer to prevent a very uneven discharge between the electrodes or between at least one electrode and the surface of the semiconductor layer.

For example, it is suitable to use a so-called plasma nozzle as described in DE 195 32 412 A1, in which a kind of plasma film flow can be formed by the plasma nozzle, and the plasma film flow is generated by the surface region of the semiconductor layer illuminated by the laser beam Lt; / RTI >

Regardless of how the constant-pressure plasma is formed, it has proved desirable to form a constant-pressure plasma as thin as possible over the surface area illuminated by the laser beam, in order to keep the optical interaction associated with the loss between the laser beam and the plasma as small as possible . Because the laser beam penetrates the region of the static pressure plasma generally perpendicular to the surface of the semiconductor layer along the thickness of the plasma layer, the plasma layer thickness is such that the light energy loss of the laser beam is reduced by a factor of 1 due to the interaction between the laser beam and the constant- %.

The electrode density formed inside the static pressure plasma is much smaller than the so-called cut-off density of the used laser wavelength, preferably smaller than half, particularly preferably smaller than at least a certain size, 10 < / RTI > Also, since the maximum plasma layer thickness through which the laser beam will pass must be properly selected in consideration of the possible absorption of the laser radiation in the plasma by the reverse braking radiation, the absorption of the laser radiation caused by the reverse braking radiation in the plasma is less than 1% . A static pressure plasma with a maximum plasma layer thickness of 5 mm is suitable, as shown in other details with reference to specific examples.

The present invention will now be described with reference to the drawings without limiting the scope of the invention in general.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows an annealing apparatus comprising a plasma generator in the form of a plasma nozzle.
Figure 2 shows an annealing device comprising an electrode for forming a static pressure plasma.
Figure 3 shows an annealing device with electrode pairs for static pressure plasma formation.

Fig. 1 shows the main components of an annealing apparatus, and an amorphous semiconductor layer 3, preferably a thin amorphous silicon layer, provided on the substrate 4 by the annealing apparatus is crystallized into a laser beam L. To this end, an excimer laser is preferably provided as the laser beam source 1, and the excimer laser can be preferably provided with laser radiation having a wavelength of 248.308 or 351 nm. It is also possible and possible to use a solid plasma which preferably emits a wavelength of 527 to 532 nm. Direct use of a high power laser diode with a radiation wavelength of 800 nm or more can also be considered.

Preferably, the pulsed laser beam L is coupled into the optical system 2 for beam forming and guidance, and beamforming is performed, in particular for beam homogenization of the laser beam and for line beam cross-section formation in the optical system. The laser beam L is projected on the surface of the amorphous semiconductor layer 3 while forming a line illumination area having a line length of preferably 650 mm and a line width of about 0.4 mm after being emitted from the optical module 2. [

The pulse-operated laser 1 forms a laser pulse L, which is projected laterally offset with respect to the amorphous semiconductor layer 3 in accordance with each pulse. This can be done by deflecting the laser beam L against the placed substrate 4 or by deflecting the substrate 4 placed on the X / Y-adjustment table against the fixed laser beam. It is also guaranteed that the entire possible surface of the amorphous silicon layer 3 is illuminated by the laser beam L in the raster technique, since it is contemplated to combine the two degrees of freedom described above together. Alternatively, it is possible to use a laser which operates continuously. In this case, the movement speed of the X / Y-adjustment table should be correspondingly high in order to keep the operation time per unit area small and to prevent substrate damage.

A static pressure plasma 6 is formed according to the present invention at the position of the laser beam L projected onto the amorphous semiconductor substrate 3, and the plasma contains an ionized gas component of air. It is assumed in Fig. 1 that a plasma nozzle device 5 is used for the formation of the static pressure plasma 6, and that the nozzle device can form a plasma film flow in longitudinal contact with the surface area of the semiconductor layer. In order to prevent hand performance interaction between the laser beam (L) and the static pressure plasma, the layer thickness (d) of the plasma film flow should not be greater than 5 mm.

2 shows an annealing device consisting of the parts 1 to 4 described above. Unlike the above-described embodiment, the plasma 6 is formed toward the substrate 4 and the semiconductor layer 3 placed thereon at a ground potential during direct discharge into the air. In this case, the electrode 7, which is preferably surrounded by the dielectric (D), is slightly spaced from the surface of the semiconductor layer 3, preferably at a distance of up to 7 mm, and the electrode is connected to a high voltage source not shown.

Another alternative embodiment for forming the static pressure plasma 6 is shown in Fig. In this case, the two electrodes 7 are arranged close to the surface toward the surface of the semiconductor layer 3. In this case, although not necessarily, the substrate 4 and the semiconductor layer 3 placed thereon must be grounded. Since the individual electrodes 7 are each surrounded by the dielectric layer D, the electrodes 7 are also disposed directly on the surface of the semiconductor layer 3 for easier handling, thereby causing the static plasma 6 It can be formed as close to the surface as possible and as a thin layer. In the case of FIG. 3, the laser beam L passes through the static pressure plasma 6 between the two electrodes 7.

The method according to the invention can basically be used independently of the crystallization instructions in the semiconductor layer 3. [ An annealing method in which the substrate is only partially melted, as in the case of the ELA method described above, may also be used. However, it is also possible to use the so-called Line-Scan-SLS method (Sequential Lateral Solidification) in which the laser beam can melt the entire depth of the amorphous semiconductor layer and the solidification of each side of the side- .

In many crystallization guidelines, it is desirable to use a so-called long laser pulse, i.e. a laser pulse with a pulse duration greater than 50 ns, to extend the duration of time during which the semiconductor material melts, thereby simultaneously creating a tendency to form larger crystallized particles . Even in this case, the combination of the laser radiation and the static pressure plasma positively affects the reduction of the laser pulse energy required for the crystallization process or the proper expansion of the surface to be processed of the semiconductor layer surface to be illuminated.

1 laser
2 Optical system for beam formation and guidance
3 semiconductor layer
4 substrate
5 Plasma nozzle device
6 Hydrostatic Plasma
7 electrode
d Plasma layer thickness
D dielectric

Claims

A method for crystallizing an amorphous semiconductor layer (3) with a laser beam (L) projecting a beam cross section uniformly illuminated in a surface region of at least a semiconductor layer (3)
A static pressure plasma 6 in the form of an ionized gas is provided in a surface region of the semiconductor layer 3 illuminated by at least the laser beam L while projecting at least the laser beam into the semiconductor layer 3, The plasma interacts with the semiconductor layer 3 and / or the laser beam L illuminated by the laser beam L,
Characterized in that the static pressure plasma (6) is formed by a plasma nozzle arrangement (5), which forms a plasma film flow in longitudinal contact with the surface area of the semiconductor layer (3) &Lt; / RTI >

A method for crystallizing an amorphous semiconductor layer with a laser beam according to claim 1, wherein the air plasma as the static pressure plasma is formed by a plasma generator under atmospheric pressure and atmospheric pressure.

A plasma processing apparatus according to claim 1 or 2, wherein the static pressure plasma (6) is provided in the form of a plasma layer extending perpendicularly to the surface region of the semiconductor layer (3) and completely covering the periphery of at least the surface region, Characterized in that the plasma layer has a maximum layer thickness (d) in which the optical energy loss of the laser beam (L) is less than 1% due to the interaction between the laser beam (L) and the static pressure plasma (6) A method for crystallizing an amorphous semiconductor layer with a laser beam.

A plasma processing apparatus according to claim 1 or 2, wherein the static pressure plasma (6) is provided in the form of a plasma layer extending perpendicularly to the surface region of the semiconductor layer (3) and completely covering the periphery of at least the surface region, Wherein the plasma layer has an electrode density that is less than the blocking density for the laser wavelength.

A plasma processing apparatus according to claim 1 or 2, wherein the static pressure plasma (6) is provided in the form of a plasma layer extending perpendicularly to the surface region of the semiconductor layer (3) and completely covering the periphery of at least the surface region, Wherein the plasma layer has a maximum plasma layer thickness with an absorption of laser radiation in the plasma by reverse braking radiation being less than 1%. &Lt; Desc / Clms Page number 19 >

4. A method according to claim 3, wherein a maximum plasma layer thickness of 5 mm is selected.

3. The semiconductor laser according to claim 1 or 2, characterized in that the laser beam (L) is operated in a pulsed manner and is offset laterally with respect to the semiconductor layer (3) with respect to the semiconductor layer surface after at least one laser pulse A method for crystallizing an amorphous semiconductor layer with a laser beam.

3. A method according to claim 1 or 2, characterized in that amorphous silicon is used as the semiconductor layer (3), and said silicon is illuminated with a laser beam (L) whose radiation cross section is made uniform. Way.

The laser beam according to claim 1 or 2, wherein the laser beam (L) having a uniform cross-section has a wavelength in the UV spectrum range, a wavelength in the visible spectrum range, or a wavelength in the IR- &Lt; / RTI >

A method for crystallizing an amorphous semiconductor layer with a laser beam according to claim 1 or 2, characterized in that the static pressure plasma (6) is formed by an electrode device provided close to the surface of the semiconductor layer (3) .

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CLAIMS 1. An apparatus for crystallizing an amorphous semiconductor layer (3), comprising: a laser (1) forming a laser beam (L), said laser beam comprising a beam deflector having at least one unit for smoothing said laser beam An apparatus capable of being projected at least on the surface region of the amorphous semiconductor layer (3) by a unit (2)
The apparatus comprises a unit for providing a static pressure plasma (6) near the surface, wherein the unit is in the form of a plasma layer which completely covers the periphery of at least the laser irradiated surface area of the amorphous semiconductor layer (3) To provide a constant-pressure plasma (6)
A unit for providing the static pressure plasma is a plasma nozzle device (5), which comprises an amorphous semiconductor layer (3) so as to form a plasma flow in longitudinal contact with the surface region of the amorphous semiconductor layer (3) Wherein the amorphous semiconductor layer (3) is arranged to face the amorphous semiconductor layer (3).

13. A device according to claim 12, characterized in that the unit for providing the static pressure plasma (6) comprises at least one electrode (7), the electrodes being arranged at an interval of at most 7 mm with respect to the surface area of the amorphous semiconductor layer And wherein the amorphous semiconductor layer is disposed on the substrate.

The device for crystallizing an amorphous semiconductor layer according to claim 12, characterized in that the two electrodes (7) are arranged at intervals of at most 7 mm with respect to the surface area of the amorphous semiconductor layer (3).

The device for crystallizing an amorphous semiconductor layer according to claim 13 or 14, characterized in that the electrode (7) is formed in the form of a blade.

The device for crystallizing an amorphous semiconductor layer according to claim 13 or 14, characterized in that the electrode (7) is insulated by a dielectric.

The device for crystallizing an amorphous semiconductor layer according to claim 13 or 14, characterized in that the laser beam (L) is coupled between the electrodes (7).

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The semiconductor device according to any one of claims 12 to 14, wherein the amorphous semiconductor layer (3) is disposed on a substrate (4), and the substrate is placed on an xy- Is movable relative to a fixed unit providing a fixed laser beam (L) and said static plasma (6). &Lt; Desc / Clms Page number 13 >

15. The apparatus for crystallizing an amorphous semiconductor layer according to any one of claims 12 to 14, wherein the laser beam and / or the plasma are formed in a line shape.