Abstract:
The present invention provides a laser processing apparatus having a laser oscillator for outputting a pulsed laser beam; deflection unit for deflecting the pulsed laser beam to irradiate a object to be processed with the deflected pulsed laser beam; a mounting base on which the object is placed and which is movable in an axial direction or two-axial directions perpendicular to each other; and local shielding unit for controlling an atmosphere around the surface of the object to be processed which is irradiated with the laser beam. When a thin semiconductor film with a thickness of 1 μm or less is formed over the surface, minute convex portions are formed, which causes a problem that characteristics of TFTs vary among elements. Minute particles generated and adhered to a main surface of a substrate through a laser processing, which is difficult to remove in general surface cleaning, become preventable by the invention.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a laser processing apparatus, and more particularly to a laser marking apparatus used for marking on a substrate and the like. 
     2. Description of the Related Art 
     In a manufacturing process of a semiconductor device, marking of characters and numeric characters is directly performed on a substrate using a laser in order to manage the substrates which flow through a manufacturing line. 
     As to an example of a laser processing apparatus used for this kind of application, a CO 2  gas laser oscillator is used, and a laser beams is oscillated by a polygon mirror and directed to a predetermined place of a glass substrate, whereby marking of characters, symbols, and the like is performed. Then, in some cases, a gas nozzle for spraying N 2  gas is provided for a place to be marked with the purpose of avoiding cracks and with the purpose of cooling the place (for example, refer to JP 11-005181A(pp. 3-4, FIG. 1)). 
     A problem of a conventional laser processing apparatus used for marking resides in that minute particles or dusts, which are generated secondarily, contaminate a surface of a glass substrate in a process of forming a large number of concave parts in the surface of the substrate by laser ablation. 
     The inventor has found that: when minute particles, each of which is generated through a process of laser marking and has a diameter of approximately from 0.1 μm to 1 μm, adhere to a main surface of a glass substrate, it is difficult to remove the particles in general surface cleaning; when a thin semiconductor film with a thickness of 1 μm or less is formed on the surface, minute convex portions are formed; and as a result, characteristics of thin film transistors (TFTs) vary among elements. Further, the inventor has found that, when thermal processing such as laser annealing is performed to the semiconductor film, a part of the semiconductor film, to which the processing has been performed, bursts out and flies, as a result, a minute hole with a diameter of approximately from 0.2 μm to 2 μm is formed. This causes dispersion in the characteristics of TFTs among elements. Further, abnormal shapes such as the above-described convex portions and holes cause heat generation due to a concentration of the electric field at the portions, which leads to characteristic abnormality and decrease in reliability in the TFT. 
     Of course, it is considered that marking is performed to a rear surface (opposite surface to the main surface over which a film such as a semiconductor film is formed) of a glass substrate. However, a marking portion comes to have unevenness through ablation, and therefore, a problem arises, when the glass substrate is placed on a flat surface, the flat surface is not in parallel with the main surface of the substrate, which poses an obstacle in a manufacturing process of a semiconductor device. For example, when a substrate is to be fixed over a mounting base of an exposure apparatus, a glass substrate is warped, which leads to a defect that accurate patterns are not exposed. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above problem, and therefore has an object to provide a laser processing apparatus that enables possibly inexpensive and satisfactory marking. 
     A laser processing apparatus according to the present invention comprises: a laser oscillator for outputting a pulsed laser beam; deflection unit for deflecting the pulsed laser beam to irradiate a object to be processed; a mounting base on which the object to be processed is placed and which is movable in an axial direction or two-axial directions perpendicular to each other; in irradiation of the object to be processed with the pulsed laser beam; and local shielding unit for controlling an atmosphere around the surface of the object to be processed which is irradiated with the laser beam when the pulsed laser beam is irradiated thereto. 
     The local shielding unit is provided with an entrance window for receiving and transmitting pulsed laser beam at an upper surface of the unit. Further, the local shielding unit is provided with an exhaust port at a side surface of an upper portion inside the local shielding unit. The exhaust port forcibly exhausts atmospheric gas around the surface of the object to be processed, which is irradiated with the laser beam. 
     Further, as to another structure of the local shielding unit, the unit is provided with a window for receiving and transmitting pulsed laser beams at an upper surface of the unit; the unit is provided with an opening portion for jetting nitrogen gas or inert gas from an outer circumferential portion thereof; and is provided with an exhaust port for forcibly exhausting gas, which is at a side surface of the upper portion inside the unit. The shielding unit filled with the gas is above the surface of the object to be processed, which is irradiated with the laser beam, and the gas is forcibly exhausted through the exhaust port. 
     In the above-described structure according to the present invention, the exhaust port is provided inside the local shielding unit, and the gas in the local shielding unit is forcibly exhausted. As a result, a flow current is generated from an outer circumferential portion to the inner side surface of the upper portion at which the exhaust port is provided. Therefore, the minute particles, each of which is generated through laser marking and has a diameter of approximately from 0.1 μm to 1 μm, can be prevented from scattering to the periphery to the object to be processed and adhering to the main surface thereof. 
     Note that, as to a convenient unit, a local shield may be formed of a transparent material with respect to a wavelength of the pulsed laser beam to thereby cover a processing region. 
     A laser processing apparatus according to the present invention comprises: a laser oscillator for outputting a pulsed laser beam; deflection unit for deflecting the pulsed laser beam to irradiate a substrate; a mounting base on which the substrate is placed and which is movable in an axial direction or two-axial directions perpendicular to each other; and application unit for forming a protective film over a surface of the substrate when the pulsed laser beam is irradiated thereto. 
     It is sufficient that the protective film is temporarily formed at the time of laser processing, and the film is not necessarily adhered to the substrate surface. As the protective film in the form of liquid, there may be adopted one obtained by thinly applying liquid such as water or alcohol onto the substrate surface. In this case, the protective film may be formed by performing spin coating with an applicable solution or spraying the solution in the form of mist. The protective film provides an effect of preventing minute particles from scattering at the time of laser processing. Therefore, even if the minute particles each of which has a diameter of approximately from 0.1 μm to 1 μm scatter, they can be prevented from adhering to the main surface of the substrate. Thereafter, the protective film in the form of liquid can be easily removed by being dried after laser processing. 
     The laser processing apparatus according to the present invention can be used particularly as a laser marking apparatus for marking the substrate with a laser beam. 
     In the laser processing apparatus according to the present invention, the local shielding unit is provided for the irradiation area of the laser beam, and the gas in the local shielding unit is forcibly exhausted. Thus, the flow current is generated from the outer circumferential portion to the side surface of the upper portion inside the local shielding unit where the exhaust port is provided. As a result, the minute particles each of which is generated through the laser marking and which has a diameter of approximately from 0.1 μm to 1 μm can be prevented from scattering to the periphery of the object to be processed and adhering to the main surface of the object. 
     Further, as other embodiment mode of the laser processing apparatus, an application unit is provided therein, and a protective film in the form of liquid is formed by thinly applying liquid such as water or alcohol onto the substrate surface. Therefore, the minute particles can be prevented from scattering in laser processing. Even if the minute particles each of which has a diameter of approximately from 0.1 μm to 1 μm scatter, they can be prevented from adhering to the main surface of the substrate. 
     The present invention provides the effect of preventing the particles, which scatter in processing, from adhering to the surface of the glass substrate to which laser processing is performed and keeping the surface of the glass substrate clean. Of course, the present invention is not limited to the glass substrate, and can be applied to a quartz substrate, a semiconductor substrate, a plastic substrate, and the like. 
     In addition, when an object to be processed such as a substrate is processed by using the laser beam, the object can be prevented from being contaminated due to droplets of processed powder or being scratched. Therefore, the laser processing apparatus can be employed for various materials such as glass, metal, and ceramic. 
     Laser processing is a widely used technique in various fields of industrial application such as cutting, drilling and welding. And the present invention can be applied not only to marking on a semiconductor film but also to the removal of minute articles created during laser processing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a diagram showing the structure of the laser marking apparatus according to Embodiment Mode 1; 
         FIG. 2  is a diagram showing the local shielding unit of the laser marking apparatus according to the present invention; 
         FIG. 3  is a diagram showing the structure of the laser marking apparatus according to Embodiment Mode 2; 
         FIG. 4  is a diagram showing the structure of the laser marking apparatus according to Embodiment Mode 3; and 
         FIG. 5  is a diagram showing the structure of the laser marking apparatus according to Embodiment Mode 4. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Description will be made of forms of a laser processing apparatus according to the present invention with reference to the accompanying drawings. Note that the present invention can be implemented in various forms, and it is understood easily by those skilled in the art that embodiment modes and details of the invention can be variously changed without departing from the spirit and scope of the invention. Therefore, the present invention is not construed with a limitation put on the contents of the embodiment modes. 
     Embodiment Mode 1 
     A laser processing apparatus in this embodiment mode has a structure in which local shielding unit is provided in order to prevent minute particles, which scatter in processing, from adhering to a substrate surface. The laser processing apparatus shown in  FIG. 1  is provided with a laser oscillator  10 , a beam shaping optical system  11 , a deflection unit  12 , a condensing optical system  13 , local shielding unit  14 , and a mounting base  15 . The mounting base  15  is operated in an axial direction or two-axial directions in conjunction with the laser oscillator  10  by means of a control unit  20 , and desired processing can be performed at an arbitrary position of a glass substrate  21  on the mounting base  15 . As for a deflection unit, any deflector which can change the direction of a laser beam may be used, for example, a mirror which reflects a laser beam. For example, Galvano mirror or polygon mirror may be applied to the deflecting unit of the present invention. 
     Gas supply unit  16  supplies inert gas such as nitrogen gas or rare gas to the cylindrical local shielding unit  14 . The inert gas is jetted from an opening portion  17 , which is in a lower part of the local shielding unit  14  and faces the glass substrate  21  and is provided in an outer circumferential portion of the unit, whereby the atmosphere in the periphery of the area irradiated with a laser beam is exchanged to attain shielding against air. An exhaust port  18  which forcibly exhausts the inert gas is provided inside the local shielding unit  14 , and the local shielding unit  14  is filled with the inert gas that is jetted from the opening portion  17  and is forcibly exhausted by means of exhaust unit  19 . 
       FIG. 2  is a diagram showing details of the local shielding unit  14 . The laser beam is irradiated to the glass substrate through a condensing lens, for example, a convex lens as a condensing optical system  13  (hereinafter written as the condensing optical system  13 ), and the local shielding unit  14  is substantially located coaxially with an irradiation position being the center. The local shielding unit  14  may be adhered to the glass substrate  21 , however, the local shielding unit  14  is preferably arranged so as to have a void with a length of approximately from 1 mm to 10 mm with respect to the glass substrate  21 . It is preferable that the opening portion  17  for jetting the inert gas have its inward opening surface such that a flow current is generated in an inner cylinder of the local shielding unit  14 . The local shielding unit  14  is filled with the inert gas which is jetted from the opening portion  17 , and the inert gas is exhausted forcibly. In this case, the flow current is generated from the outer circumferential portion to the inner side surface of the upper portion where the exhaust port is provided; and the flow current exhausts minute particles, each of which is generated through laser processing and has a diameter of approximately from 0.1 μm to 1 μm. Thus, the particles are prevented from scattering to the peripheral portion of the local shielding unit  14  and contaminating the glass substrate  21 . Further, the inert gas has a function of cooling the glass substrate, and also has an effect of avoiding cracks and the like during marking processing. 
     In laser marking processing, characters, numeric characters, symbols, and the like are marked through dot drawing by using a pulsed laser beam. In this case, a C 0   2  laser (at a wavelength of 10.6 μm), a CO laser (at a wavelength of 5.5 μm), or the like is used as the laser oscillator, and a polygon mirror may be incorporated in the deflection unit  12  and combined with the laser oscillator. 
     A glass substrate to which laser processing is performed comprises commercial no alkali glass such as aluminosilicate glass or barium borosilicate glass, as typified by a substrate used for a liquid crystal panel. The glass substrate is in the state of bare glass before film formation. Even in case of using the glass substrate over which a thin film with a thickness of several hundred nm such as a silicon oxide film or an amorphous silicon film is formed, application of the laser processing apparatus in this embodiment mode enables laser processing with a clean state kept because scattering materials are not diffused to the surrounding area of the substrate. 
     Embodiment Mode 2 
     As to a convenient local shielding unit for preventing minute particles that scatter in processing from adhering to a substrate surface, a cover may be formed of a transparent material with respect to a wavelength of the pulsed laser beam to cover a processed region. 
       FIG. 3  is a diagram for explaining the mode, and a local shielding unit  22  is provided between the condensing optical system  13  and the glass substrate  21  so as to cover a processed portion of the glass substrate  21 . In  FIG. 3 , like components are denoted by like numerals as of  FIG. 1  and  FIG. 2 . The local shielding unit  22  may be formed of a transparent material with respect to a wavelength of a laser beam used for processing, and synthetic quartz or glass such as barium borosilicate glass or aluminosilicate glass is adopted. ZnSe may be used in case that the wavelength of the laser beam is from 1 μm to 10 μm. 
     Embodiment Mode 3 
     A laser processing apparatus in this embodiment mode is provided with an application unit that forms a protective film over a substrate surface in order to prevent minute particles that scatter in processing from adhering to the substrate surface. In  FIG. 4 , like components are denoted by like numerals as of  FIG. 1 . The laser processing apparatus shown in  FIG. 4  is provided with the laser oscillator  10 , the beam shaping optical system  11 , deflecting unit  12 , the condensing optical system  13 , an application unit  50 , a mounting base  52  that chucks the glass substrate  21  and rotates simultaneously, and a rotational speed sensor  53 . The mounting base  52  is operated in conjunction with the laser oscillator  10  by means of the control unit  20 , and processing can be performed at an arbitrary position of the glass substrate  21  fixed onto the mounting base  52 . 
     The application unit  50  that forms a protective film rotates the glass substrate  21 , and supplies liquid such as water (pure water) or alcohol to the surface simultaneously. Then, a liquid film  55  is formed on the surface of the glass substrate  21 , and processing is performed in this state. Since the liquid film  55  is formed on the entire surface of the glass substrate, even if minute particles, each of which has a diameter of approximately from 0.1 μm to 1 μm, scatter, the minute particles can be prevented from adhering to the main surface of the substrate. The liquid film  55  is not required after processing; accordingly, spin drying is performed while the mounting base  52  is being rotated. Therefore, the liquid supplied from the application unit  50  is preferably a material such as alcohol that has relatively high volatility. The minute particles generated in processing are contained in a solution, and are released outside of the glass substrate together with the solution due to a centrifugal force. Thus, the particles do not adhere to the surface of the glass substrate again. Even if the minute particles each of which has a diameter of approximately from 0.1 μm to 1 μm scatter into a gas phase, the particles can be prevented from adhering to the main surface of the substrate. 
     Since processing is performed while the glass substrate  21  is being rotated, the rotational speed sensor  53  optically detects the rotational speed of the substrate and the position of a marker  54  attached onto the mounting base  52 , and oscillates a laser pulse at predetermined timing in conjunction with the laser oscillator  10  by means of the control unit  20 . Further, the mounting base  52  shall be movable in an axial direction or two-axial directions perpendicular to each other, and is operated in conjunction with the rotation of the glass substrate. 
     In laser marking processing, characters, numeric characters, symbols, and the like are marked through dot drawing with the use of a pulsed laser beam. In this case, a CO 2  laser (at a wavelength of 10.6 μm), a CO laser (at a wavelength of 5.5 μm), or the like is used as the laser oscillator, and a polygon mirror may be incorporated in the deflecting unit  12  and combined with the laser oscillator. 
     A glass substrate to which laser processing is performed is made of commercial no alkali glass such as aluminosilicate glass or barium borosilicate glass, as typified by a substrate used for a liquid crystal panel. The glass substrate is in the state of bare glass before film formation. Application of the laser processing apparatus in this embodiment mode enables laser processing with a clean state kept because scattering materials are not diffused to the surrounding area of the substrate. Further, when a system being capable of supplying plural chemical solutions to the application unit  50  is provided, a function of performing spin cleaning can be additionally provided. 
     Embodiment Mode 4 
     A mounting base  60 , which holds the substrate  21  sloped, may be provided as shown in  FIG. 5  instead of the mounting base that chucks the glass substrate and rotates in Embodiment Mode 3. 
     In  FIG. 5 , like components are denoted by like numerals as of  FIG. 1  and  FIG. 4 . Liquid such as water (pure water) or alcohol is supplied to the surface of the glass substrate  21  from an upper portion of the sloped glass substrate  21  by means of the application unit  50 . The liquid may be supplied in the form of mist. Consequently, the liquid flows from an upper end portion to a lower portion of the substrate held sloped, whereby a liquid film  55  is formed. The condensing optical system  13  is arranged in the normal direction of the glass substrate  21 , and performs irradiation with a laser beam. In laser marking processing, characters, numeric characters, symbols, and the like are marked through dot drawing by using a pulsed laser beam. In this case, a CO 2  laser (at a wavelength of 10.6 μm), a CO laser (at a wavelength of 5.5 μm), or the like is used as the laser oscillator, and a polygon mirror may be incorporated in the beam shaping optical system  11  and combined with the laser oscillator. 
     The above-described embodiment mode can attain the same effect as that in Embodiment 3. In this embodiment mode, a rotational mechanism is not required, and the structure of the laser processing apparatus can be simplified accordingly.