JP2004160518A - Method for laser beam machining - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for laser beam machining, which improves a throughput of laser beam machining. <P>SOLUTION: A work 26 to be machined is irradiated with a laser beam through a stencil mask 24 equipped with through-holes of a prescribed pattern. A thin-film material on the work 26 to be machined is directly machined and patterned by the laser beam passing through the through-holes of the prescribed pattern. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser processing method such as a liquid crystal display (hereinafter referred to as “low temperature p-Si TFT-LCD”) using a polycrystalline silicon thin film transistor by a low temperature process method, for example.
[0002]
[Prior art]
As a necessity in the multimedia information age, thin displays are used in many products such as mobile phones, personal digital assistants (PDAs, etc.), notebook PCs, and camera-integrated VTRs. Examples of the display include a liquid crystal display using a polycrystalline silicon thin film transistor by a low temperature process method (low temperature p-Si TFT-LCD), an active matrix driving type organic EL (electroluminescence) display (hereinafter referred to as “organic EL”), and the like. Is used. TFTs (thin film transistors) are used to drive these displays, which enables high definition and low power consumption, and it is expected that applications can be expanded by integrating various circuits in the future. Yes. Further, for example, when mass-producing high-definition liquid crystal panels for liquid crystal displays, demands for higher reliability at lower cost are increasing.
[0003]
For example, a low-temperature p-Si TFT-LCD or organic EL, which is a typical thin display device, has a configuration in which a liquid crystal layer and a light emitting layer are sandwiched between a TFT array substrate and a counter substrate (color filter substrate in the case of color display). A transparent conductive film for conducting is formed on the counter substrate. The transparent conductive film is formed on the entire surface in the manufacturing process, and then a desired pattern is formed by etching through photolithography. The photolithography process includes processes such as resist coating, baking, exposure, development, and post baking, and requires a large coater developer and an etching apparatus, which has been a factor in hindering cost reduction.
[0004]
In order to avoid such a complicated process, a technique has been proposed in which a resist that has been required in photolithography is unnecessary and a thin film material such as the above-described transparent conductive film is directly processed with a laser beam. For example, a known laser irradiation device is used to irradiate an object to be processed with laser light, and the beam size of the laser light is adjusted by a lens through a photomask in which a light shielding film such as Cr (chromium) is formed on a glass substrate. The scale is reduced to 1 to several tenths, and the thin film on the substrate that is the object to be processed is irradiated (for example, see Patent Document 1).
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-142094
[Problems to be solved by the invention]
However, the above-described photomask assumes that the energy density of the irradiated laser beam is relatively weak for exposure. Therefore, when the energy density of the laser beam on the mask surface increases, the light-shielding film is made of the laser beam. Absorbing energy may generate heat and damage the light-shielding film. In addition, when a short wavelength laser is used as the laser to be irradiated, the glass substrate absorbs the laser light, and the transmittance is lowered at the transmission portion without the light shielding film, so that the function as a mask is lowered. The damage to the light-shielding film varies depending on the melting point of the light-shielding film material and the wavelength of the irradiation laser, and generally has a disadvantage that the light-shielding film tends to be damaged in the case of a material having a low melting point or a short wavelength laser.
[0007]
If the energy applied to the photomask is limited to avoid damage to the photomask, the energy required to process the thin film on the glass substrate may be insufficient. As one of means for obtaining sufficient processing energy, there is a method of condensing laser light and increasing the energy density. An optical system uses a condensing lens to condense laser light. The energy density (fluence) Em on the mask, the lens reduction ratio M, and the fluence Es on the processing stage can be expressed by the following equations. (The reduction ratio M is obtained by the laser beam size on the mask / the laser beam size on the processing stage).
Es = Em × M ²
[0008]
The energy density on the processing stage is the product of the energy on the mask and the square of the reduction rate. To increase the energy density on the processing stage, it can be realized by increasing the reduction rate (condensing the laser beam). . However, by increasing the reduction ratio, there is a problem that the area of one-time laser beam irradiation on the workpiece 26 is reduced and throughput is lowered. In order to improve the throughput, there is a conflicting problem in the present situation that the fluence of the laser beam on the mask surface is increased and the reduction ratio is decreased.
[0009]
In addition, in the process of manufacturing a TFT array substrate on which a TFT which is a drive circuit for driving a low-temperature p-Si TFT-LCD, an organic EL, or the like is formed, the formed amorphous silicon (hereinafter also referred to as “a-Si”) is used. There is a laser annealing step in which the thin film is irradiated with laser light to crystallize it. Hereinafter, the case of laser annealing of amorphous silicon will be described. However, the object of laser annealing is not limited to silicon. Here, in order to explain laser annealing of an amorphous silicon thin film, a procedure for producing a low temperature p-Si thin film semiconductor device having a bottom gate TFT structure will be described as an example.
[0010]
FIG. 5 is a schematic cross-sectional view showing the layer structure from the glass substrate to the reflective layer of the TFT array substrate. A gate electrode 8 is formed by sputtering Mo (molybdenum) or the like on a substrate 7 such as glass. Subsequently, a first gate insulating film 9 made of silicon nitride is formed by, for example, plasma CVD (chemical vapor deposition) so as to cover the gate electrode 8, and then a second gate insulating film 10 made of silicon oxide is formed. An insulating film is formed by forming a film. Next, as the thin film semiconductor layer 11, for example, amorphous silicon is similarly formed by plasma CVD. After film formation, annealing is performed to remove hydrogen contained in the amorphous silicon. Subsequently, excimer laser is irradiated to convert amorphous silicon into polycrystalline silicon (p-Si). This process is called laser annealing.
[0011]
The polycrystalline silicon film is patterned. Thereafter, a silicon oxide film is formed by the CVD method, and this silicon oxide is patterned by self-alignment using the gate electrode 8 as a mask, so that the stopper layer 12 covers the portion of the polycrystalline silicon film located on the gate electrode 8. Form. For example, an impurity P (phosphorus) is implanted using the stopper layer 12 as a mask to form an LDD (Lightly Doped Drain) structure. After the stopper layer 12 and its periphery are masked with a photoresist, an impurity P (phosphorus) is implanted to form an n-channel region. Then, the impurity is activated by lamp annealing. Similarly, the p channel is created by masking unnecessary regions with a photoresist, and then implanting, for example, B (boron) to form a p channel region and performing an annealing process.
[0012]
Thereafter, as an interlayer insulating film, silicon oxide 13 and silicon nitride 14 are sequentially stacked by, for example, plasma CVD to form an insulating film having a two-layer structure.
[0013]
Next, a diffusion plate (scattering layer) 15 for diffusing reflected light to obtain uniform brightness is formed, and a planarizing layer 16 is further formed thereon. A transparent conductive film 17 such as ITO (indium tin oxides) is formed thereon to form a pixel electrode film in the transmissive portion. Further, a conductive film 18 made of, for example, Al or Ag is formed as a pixel electrode film in the reflective portion. Through the above steps, a thin film semiconductor device used for a drive circuit substrate of an active matrix display device is completed.
[0014]
In the laser annealing of amorphous silicon, an opening pattern is formed with a resist on amorphous silicon formed on the entire surface, and the resist is used as a blocking mask. For example, a line beam with a striped laser beam shape is used. Is a laser irradiation method that scans almost the entire surface. There was a problem in throughput because the irradiation area was wide over the entire substrate.
[0015]
In view of such a point, the present invention provides a laser processing method capable of improving the throughput of laser processing.
[0016]
[Means for Solving the Problems]
In the laser processing method of the present invention, a workpiece is irradiated with laser light through a stencil mask having holes of a predetermined pattern, and the thin film material on the workpiece is directly processed by the laser light passing through the holes of the predetermined pattern. Patterning is performed.
For example, this laser processing includes patterning processing of a thin film material by laser ablation, laser annealing processing, and the like.
[0017]
According to the present invention, since a thin film material such as a transparent conductive film is directly processed by a laser using a stencil mask provided with a predetermined pattern of holes, the portion in which the predetermined pattern of holes is provided is provided. Since there is no absorption of laser light, the influence of heat due to absorption of laser light on the laser irradiation surface of the mask can be suppressed as compared with a photomask.
[0018]
Further, in the laser processing method of the present invention, the stencil mask is formed by forming a light shielding film of a metal material or a dielectric material on a substrate, and an opening in which a pattern is formed is provided with holes of a predetermined pattern. It is made of a light shielding film.
[0019]
In the laser processing method of the present invention, the stencil mask is formed by forming an intermediate layer between the substrate and the light shielding film.
[0020]
According to the present invention, when an intermediate layer is provided between the substrate and the light-shielding film, an improvement in function and adhesion as an etching stopper can be expected.
[0021]
In the laser processing method of the present invention, the stencil mask is formed by forming an intermediate layer on a substrate and forming a light shielding film of a metal material or a dielectric material on the intermediate layer. After the substrate is thinned to a predetermined thickness, holes having the same predetermined pattern are formed through the substrate, the intermediate layer, and the light shielding film.
[0022]
In the laser processing method of the present invention, a material having a high thermal conductivity and a low linear expansion coefficient is used as the material of each film constituting the stencil mask.
[0023]
According to the present invention, the effect of diffusing heat generated by the absorption of laser light and the deformation of the mask pattern can be prevented, and high-precision laser processing can be performed.
[0024]
Further, in the laser processing method of the present invention, irregularities are provided on the surface of the stencil mask where the laser beam is irradiated.
[0025]
According to the present invention, the surface area of the laser light irradiation surface is increased, the temperature rise due to the laser light in the temperature-controlled space can be prevented, and the mask pattern deformation and displacement due to the influence of heat can be suppressed. .
[0026]
Further, in the laser processing method of the present invention, a metal film having a high reflectivity selectively with respect to the wavelength of the laser is formed on the opening portion of the stencil mask provided with the holes of the predetermined pattern or the entire surface of the mask substrate. It is what you do.
[0027]
According to the present invention, the influence of heat due to the absorption of the laser beam can be suppressed by reflecting the laser beam irradiated by forming a highly reflective metal film on the laser beam irradiation surface of the mask.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the laser processing method of the present invention will be described below with reference to the drawings.
[0029]
FIG. 1 shows a configuration diagram of an example of a laser irradiation apparatus used for laser processing of this example. This example is characterized in that a stencil mask (perforated mask) is used for laser processing, and the stencil mask itself is characterized. The configuration of the laser irradiation apparatus is the same as that generally used, but is not limited thereto.
[0030]
For example, in the figure, 19 is a laser oscillator, 20 is a variable attenuator, 21 is a mirror, 21a and 21a are mirrors, 22 is an optical system, 24 is a stencil mask with a predetermined pattern of holes, 25 is a projection lens, and 26 is The workpiece 27 has a function of fixing the workpiece 26 such as a vacuum chuck, and is movable in the XY direction and the θ direction to perform appropriate scanning of the laser light irradiation surface of the workpiece 26. It is a stage. It is a stage that enables alignment. A two-dot chain line in the figure represents an optical path of laser light emitted from the laser oscillator 19.
[0031]
As the laser medium and wavelength used in this example, for example, Nd: YAG (wavelengths: 1064, 532, 355, 266 nm), or excimer laser KrF (wavelength: 248 nm), ArF (wavelength: 193 nm) or the like is desirable. . Hereinafter, in this example, it is considered that an excimer laser generally used in laser annealing or the like is suitable for large-area irradiation, and KrF is most suitable in consideration of the wavelength. A laser beam having a predetermined pulse width is irradiated a predetermined number of times by a KrF laser to perform desired processing in a short time.
[0032]
Next, the stencil mask used in this example uses, for example, synthetic quartz, calcium fluoride, or Si for the mask substrate 4, and the light shielding film 6 is made of a metal material such as Cr, Cu, Al, or a dielectric material (LiF, Fluorides such as MgF ₂ and oxides such as SiO ₂ and Al ₂ O ₃ are applicable. As shown in the cross-sectional views of FIGS. 2 and 3, depending on the combination of the light shielding film 6 of the stencil mask 24 and the mask base material 4, for example, SiO ₂ , calcium fluoride or the like for the purpose of improving the etching stopper or adhesion. An intermediate layer 5 may be provided.
[0033]
For example, in the stencil mask shown in FIG. 2, an intermediate layer 5 is formed on a mask base 4 having a certain thickness and a necessary strength, and a light shielding film 6 is formed thereon to form a mask base. 4 and the intermediate layer 5 are etched to leave the light-shielding film 3 and to form holes having a predetermined pattern shape in order to enhance the heat radiation of the laser light irradiation surface of the intermediate layer 5. Laser light is transmitted through the hole of a predetermined pattern of the light shielding film 6 to the workpiece 26. Naturally, the thickness of the light-shielding film 6 is set to a film thickness having an appropriate strength so as not to be loosened or swung. Moreover, the damage of the mask base material 4 can be suppressed by making the edge of the mask base material 4 and the intermediate layer 5 of the opening 3 a little distance from the laser light irradiation portion.
[0034]
In the stencil mask shown in FIG. 3, after the intermediate layer 5 is formed on the mask base material 4 and the light shielding film 6 is formed thereon, the mask base material 4 in the opening 3 is left by a predetermined thickness. Etching is performed, and holes having the same predetermined pattern shape are formed through the mask base material 4, the intermediate layer 5, and the light shielding film 6. By comprising in this way, the intensity | strength of the opening part 3 can further be improved from the thing of FIG.
[0035]
The stencil mask 24 opens a predetermined pattern, and the repeated pattern is determined by the opening shape. For example, when the beam size of the laser beam is larger than the pattern size on the stencil mask 24, the stage 27 repeats moving and stopping at a predetermined distance corresponding to the pattern size, and processing is performed by step-and-repeat patterning during the stop. This is a method of irradiating the object 26. In addition, when the beam size is smaller than the pattern size, a synchronous scan method in which the stage 27 and the stencil mask 24 move and irradiate synchronously is used.
[0036]
In the laser irradiation apparatus having the above-described configuration, an optical system 22 that emits laser light from the laser oscillator 1, passes through a variable attenuator 20 that controls energy density, and makes the laser beam rectangular and makes irradiation energy uniform. Then, after passing through the stencil mask 24, a reduction ratio is set as necessary through the projection lens 25, and a laser beam having an energy density of 100 to 1000 mJ / cm ² is applied to the workpiece 26 on the stage 27 in this example. The patterning of the transparent conductive film 17 and the like of the low-temperature p-Si TFT array substrate shown in FIG. 5 can be realized.
[0037]
In addition, it is preferable to use a material having the highest thermal conductivity and the lowest coefficient of linear expansion as the material of each film of the stencil mask 24. In combination with the effect of diffusing the heat generated by the absorption of the laser beam, for example, a pattern is formed. Prevents deformation of the mask pattern, such as the size of the hole to be changed, enables high-accuracy pattern processing, and extends the life of the mask as compared to conventional photomasks by suppressing deterioration in shape change be able to.
[0038]
Further, the laser beam irradiation surface of the stencil mask of FIG. 3 described above is surface-treated with a chemical solution such as hydrofluoric acid (HF) to form irregularities. In this way, the laser irradiation surface of the stencil mask is roughened to provide unevenness and increase the surface area, thereby improving the heat dissipation effect and preventing the temperature rise due to the laser light in the temperature-controlled space, and the mask pattern due to thermal effects High-accuracy patterning with reduced deformation and displacement is possible.
[0039]
Furthermore, in order to prevent light imaged as noise on the workpiece 26 called stray light, for example, a low reflection film such as chromium oxide is provided on either the light shielding film 6 side of the mask substrate 4 or the laser irradiation surface of FIG. It is preferable to coat (AR film).
[0040]
Furthermore, a metal material having a high reflectivity with respect to the wavelength of the laser, such as aluminum, is vapor-deposited as a reflective film on the mask base 4 in the opening of the stencil mask of FIG. To do. By adopting such a configuration, the reflection film reflects the laser beam, so that the absorption of the laser beam on the irradiated surface can be limited and damage to the stencil mask can be prevented.
[0041]
By adopting the stencil mask configuration described above or by combining them, it is possible to obtain a stencil mask with less pattern shape deterioration and damage due to the influence of irradiation laser light absorption.
[0042]
By adopting the configuration as described above, it is possible to suppress the thermal influence due to the laser light absorption on the laser irradiation surface of the stencil mask as compared with the conventional photomask. This is particularly effective when the laser wavelength is short because the mask substrate of the photomask generally has absorption for short wavelength lasers.
[0043]
In addition, since it is possible to increase the energy of the laser beam irradiated to the irradiation surface of the stencil mask, the irradiation area can be increased by reducing the reduction rate of the irradiation laser beam, and the laser processing throughput can be improved. Can do.
[0044]
Then, by deleting the conventional photolithography process and etching process, the process can be shortened, and the cost of manufacturing equipment and materials used can be greatly reduced. At the same time, chemicals and waste liquids are reduced, which can contribute to the environment.
[0045]
Next, another example of the embodiment of the laser processing method of the present invention will be described. As a laser irradiation apparatus for performing laser annealing, a laser beam is reduced and projected onto a stencil mask 24 in which holes having a predetermined pattern are formed as shown in FIG. 1, and a stencil mask is used as shown in FIG. Application is conceivable in any case where 24 and the workpiece 26 are close to each other and irradiated at the same magnification. 4, parts corresponding to those in FIG. 1 are given the same reference numerals, and are the same as those in FIG. 1 except that the stencil mask 24 on the laser optical path is brought close to the workpiece 26. It is the composition.
[0046]
In laser annealing, for example, laser light emitted from a laser oscillator 19 passes through an optical system, and passes through a stencil mask 24 in which holes having a predetermined pattern are formed, and then is applied to a workpiece 26 in a predetermined pattern shape by, for example, a step-and-repeat method. Irradiated. At this time, the stencil mask 24 having the same structure as that used for patterning the transparent conductive film 17 as shown in FIG. 2 or 3 can be applied. For example, the semiconductor thin film 11 such as amorphous silicon irradiated with the laser beam absorbs the energy of the laser beam having the same beam size and is crystallized by heat, so that it is converted from amorphous silicon to polycrystalline silicon. Laser annealing can be realized. The thin film to which the laser annealing of this example is applied is not limited to this example.
[0047]
According to the present example, it is possible to adopt, for example, a step-and-repeat irradiation method by using the stencil mask 24 instead of the conventional method in which the laser beam irradiation is performed on the entire surface of the substrate, and the throughput of laser processing. Can be improved.
[0048]
In addition, it can be easily understood that the same effects as the above-described example can be obtained.
[0049]
It should be noted that the present invention is not limited to the above-described embodiments, and various other configurations can be taken without departing from the gist of the present invention.
[0050]
【The invention's effect】
According to the present invention, a conventional photolithography process and an etching process can be eliminated by directly laser processing a thin film material using a stencil mask provided with holes of a predetermined pattern, and manufacturing equipment and materials used There is an advantage that the cost can be significantly reduced. At the same time, chemicals and waste liquids are reduced, and there is a benefit that can contribute to the environment.
[0051]
Further, according to the present invention, since a thin film material such as a transparent conductive film is directly processed by a laser using a stencil mask provided with a predetermined pattern of holes, the opening at the opening provided with the predetermined pattern of holes is provided. Since there is no absorption of laser light, the influence of heat due to absorption of laser light on the laser irradiation surface of the mask can be suppressed as compared with a photomask.
[0052]
Further, according to the present invention, by using a stencil mask as a mask for laser annealing, it is possible to partially irradiate the laser beam on the entire surface of the substrate, which improves the throughput of laser processing. There is.
[0053]
According to the present invention, the temperature of a stencil mask can be controlled by using a material having a high thermal conductivity and a low linear expansion coefficient, so that temperature rise can be prevented and distortion of the pattern due to heat can be avoided. By providing unevenness on the irradiated surface, the heat dissipation effect can be enhanced. Furthermore, when a highly reflective metal film is formed on the laser light irradiation surface of the stencil mask, the influence of heat due to the absorption of the laser light can be suppressed by reflecting the laser light. By adopting or combining these configurations, it is possible to obtain a stencil mask with little pattern shape deterioration and damage due to the influence of laser light, and there is an advantage that high-precision laser processing can be performed.
[0054]
By obtaining a stainless steel mask as described above, it is possible to increase the energy density of the laser light irradiated onto this stencil mask, and the irradiation area can be increased by reducing the reduction rate of the irradiated laser light. There is a benefit of improving throughput.
[0055]
Further, according to the present invention, by using a stencil mask as a mask for laser annealing, there is no peeling of a photosensitive resin (photoresist etc.) thin film conventionally used for the mask, so that the lower layer generated at the time of peeling. There is an advantage that the film quality can be maintained without any damage.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an example of a laser irradiation apparatus.
FIG. 2 is a cross-sectional view showing an example of a stencil mask.
FIG. 3 is a cross-sectional view showing an example of a stencil mask.
FIG. 4 is a schematic configuration diagram showing an example of a laser annealing apparatus.
FIG. 5 is a cross-sectional view showing a layer structure of a low-temperature p-Si TFT-LCD.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Transparent substrate, 2 ... Resin layer, 3 ... Transparent conductive film, 4 ... Mask base material, 5 ... Intermediate layer, 6 ... Shading film, 7 ... substrate, 8 ... gate electrode, 9 ... first gate insulating film, 10 ... second gate insulating film, 11 ... silicon, 12 ... stopper Layer, 13... First interlayer insulating film, 14... Second interlayer insulating film, 15... Diffusion plate, 16. 18... Conductive film, 19... Laser oscillator, 24 ... Stencil mask, 26 ... Workpiece, 27 ... XY stage

Claims (9)

The workpiece is irradiated with laser light through a stencil mask provided with holes of a predetermined pattern, and the thin film material on the workpiece is directly processed by the laser light passing through the holes of the predetermined pattern. Laser processing method. The laser processing method according to claim 1,
A laser processing method, wherein the laser processing is a patterning process of a thin film material by laser ablation. The laser processing method according to claim 1,
The laser processing method, wherein the laser processing is laser annealing. In the laser processing method of Claim 1 or 2 or 3,
The stencil mask is formed by forming a light shielding film of a metal material or a dielectric material on a substrate,
The laser processing method, wherein an opening in which a pattern is formed is formed of the light shielding film provided with a hole of a predetermined pattern. In the laser processing method of Claim 4,
A laser processing method comprising: forming an intermediate layer between the substrate of the stencil mask and the light shielding film. In the laser processing method of Claim 1 or 2 or 3,
The stencil mask is formed by forming an intermediate layer on a substrate and forming a light shielding film of a metal material or a dielectric material on the intermediate layer,
The laser processing method, wherein the opening in which the pattern is formed is formed by forming holes of the same predetermined pattern through the substrate, the intermediate layer, and the light shielding film after the substrate is thinned to a predetermined film thickness. The laser processing method according to claim 4, 5 or 6,
A laser processing method, wherein a material having a high thermal conductivity and a low linear expansion coefficient is used as a material of each film constituting the stencil mask. The laser processing method according to claim 4, 5 or 6,
Irradiation is provided on the surface of the stencil mask where the laser beam is irradiated. In the laser processing method of Claim 6,
A metal film having a high reflectance is selectively formed with respect to the wavelength of the laser, which is used on the opening portion of the stencil mask provided with the holes of the predetermined pattern or on the entire surface of the mask substrate. A laser processing method.

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