Abstract:
It is an object to improve a yield of a step of cutting off a substrate. A substrate is cut off by using an ablation process. An ablation process uses a phenomenon in which a molecular bond in a portion irradiated with a laser beam, that is, a portion which absorbs the laser beam is cut off, photodegraded, and evaporated. In other words, a substrate is irradiated with a laser beam, a molecular bond in a portion of the substrate is cut off, photodegraded, and evaporated; accordingly, a groove is formed in the substrate. A method for cutting the substrate has steps of selectively emitting a laser beam and forming a groove in the substrate, and selectively emitting a laser beam to the groove and cutting off the substrate. Methods for manufacturing a groove in a substrate and cutting off a substrate are used for manufacturing a semiconductor device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for manufacturing a groove of a substrate and a method for cutting off a substrate. In addition, the present invention relates to a method for manufacturing a semiconductor device. The semiconductor device corresponds to a device including a transistor. 
     2. Description of the Related Art 
     In recent years, development of a semiconductor device including a transistor has been advanced. A semiconductor device is formed by forming a transistor over a substrate, and then cutting off the substrate. 
     In many cases, a substrate is cut off as follows. First, a groove (also referred to as a scribe line) is formed at the surface of the substrate by using a scribing device. Then, the substrate is forcibly cut off along the groove by using a cutting device. In addition, a substrate is cut off by using a laser beam (hereinafter, a laser beam is included in laser light) as follows. First, the substrate is selectively irradiated with a laser beam to locally heat the substrate. Then, the surface of the substrate which is heated is locally cooled by a cooling medium. Subsequently, a crack is formed by utilizing thermal stress which is generated in the substrate, and accordingly, the substrate is cut off (for example, see Patent Document 1) 
     [Patent Document 1] Japanese Patent Laid-Open No. 2001-64029 
     When a substrate is cut off by using a scribing device, there is a case where a groove is not formed in a desired shape due to a layer which is provided over the surface of the substrate. As a result, the substrate cannot be cut off in a desired shape, which results in reduction in a yield. In addition, the substrate is cut off by using press power; therefore, a crack is easily generated from the groove and the cutting surface is adversely affected (see a photograph showing a cutting surface of a glass substrate of  FIG. 6D ). Also, a burr may arise when that the substrate is plastic. “Burr” is called a state that a corner of the substrate is unprocessed smoothly. The state is often beard-form. As described above, cutting off a substrate by using a scribing device has been a factor of generating an exterior problem of a cutting surface and reducing a yield. In addition, it has been difficult to form a scribe line in a polygonal shape or a rounded shape in cutting off a substrate by using a scribing device. 
     In addition, a cutter is used for a scribing device, and such a cutter becomes worn after using multiple times; therefore, it is necessary that the cutter is replaced. Since a cutter is expensive, it has been difficult to reduce manufacturing cost in using a cutter. 
     Moreover, when a substrate is cut off by using a laser beam, there are cases where the substrate is transformed due to heating and a crack is generated in the substrate due to stress which remains inside the substrate. 
     SUMMARY OF THE INVENTION 
     The present invention is made in view of the above problems. It is an object of the resent invention to provide a method for manufacturing a groove of a substrate, a method for cutting off a substrate, and a method for manufacturing a semiconductor device, each of which can improve a yield. 
     A method for manufacturing a groove of a substrate of the present invention includes steps of selectively emitting a laser beam to form the groove in the substrate. One feature of the present invention is that an ablation process is used. The ablation process utilizes a phenomenon in which a molecular bond in a portion irradiated with a laser beam, that is, the portion absorbing the laser beam is cut off, photodegraded, and evaporated is used. In other words, the method for manufacturing a groove of a substrate of the present invention is as follows. A substrate is irradiated with a laser beam, and then a molecular bond in a portion of the substrate is cut off, photodegraded, and evaporated; accordingly, the groove is formed. 
     A method for manufacturing a groove of a substrate of the present invention includes steps of selectively emitting a laser beam to form the groove in the substrate and selectively emitting a laser beam to the groove to cut off the substrate. An ablation process is used in the present invention, and a substrate is irradiated with a laser beam, a molecular bond in a portion of the substrate is cut off, photodegraded, and evaporated; accordingly, the substrate is cut off. 
     In addition, in the present invention, a substrate may be thinned by performing one or both of grinding and polishing to the substrate by using one or both of a grinding device and a polishing device. More specifically, the substrate may be thinned to be 100 μm or less by using one or both of the grinding device and the polishing device. By thinning the substrate, formation of a groove in the substrate and cutting off the substrate can be performed easily at short times. 
     According to one feature of the present invention, a method for manufacturing a semiconductor device uses the above method for manufacturing a groove of a substrate and the above method for cutting off a substrate. The method for manufacturing a semiconductor device of the present invention includes steps of forming a layer including a transistor over a substrate; forming a first insulating layer over the layer including the transistor; forming a conductive layer which is connected to a source region or a drain region of the transistor through an opening provided in the first insulating layer; forming a second insulating layer which covers the conductive layer; and cutting off the first insulating layer, the insulating layer which is provided in the layer including the transistor, the second insulating layer, and the substrate by selectively emitting a laser beam. 
     A method for manufacturing a semiconductor device of the present invention includes steps of forming a layer including a transistor over a substrate; forming a first insulating layer over the layer including the transistor; forming a conductive layer which is connected to a source region or a drain region of the transistor through an opening provided in the first insulating layer; forming a second insulating layer which covers the conductive layer; forming a groove in one or more of the first insulating layer, the insulating layer which is provided in the layer including the transistor, the second insulating layer, and the substrate by selectively emitting a laser beam; and cutting off the first insulating layer, the insulating layer which is provided in the layer including the transistor, the second insulating layer, and the substrate by selectively emitting a laser beam. 
     A method for manufacturing a semiconductor device of the present invention includes steps of forming a layer including a transistor over one of surfaces of a substrate; forming a first insulating layer over the layer including the transistor; forming a conductive layer which is connected to a source region or a drain region of the transistor through an opening provided in the first insulating layer; forming a second insulating layer which covers the conductive layer; polishing the other surface of the substrate; and cutting off the first insulating layer, the insulating layer which is provided in the layer including the transistor, the second insulating layer, and the substrate by selectively emitting a laser beam. 
     Note that a solid laser which can oscillate a laser beam having a wavelength of 1 to 380 nm which is a visible light region may be used for a laser. More preferably, an Nd:YVO 4  laser having a wavelength of an ultraviolet region may be used. It is because compared with other laser beams at a longer wavelength side, the Nd:YVO 4  laser beam having a wavelength of an ultraviolet region is more easily absorbed in a substrate and an ablation process can be performed. 
     Note that a glass substrate may be used for a substrate. It is because a glass substrate easily absorbs a laser beam of an ultraviolet region, and therefore, an ablation process is easily performed. 
     A method for cutting off the substrate or forming the groove in the substrate in the present invention can be applied to methods of fabricating a liquid crystal display device and an EL (OLED) display device or the like. Moreover, a method of cutting off the substrate or forming the groove in the substrate in the present invention can be applied to not only an active matrix type display device but also a passive matrix type display device. Note that the liquid crystal and the EL (OLED) display devices and the active matrix type and passive matrix type display devices also have insulating layers. 
     The present invention uses an ablation process; accordingly, forming a groove in an insulating layer which is provided in a substrate and over the substrate and cutting off the insulating layer which is provided in the substrate and over the substrate can be performed easily at short times, and a yield can be improved. Moreover, the present invention uses a laser beam; therefore, a process of such a desired shape as not only a simple square shape but also a polygonal shape or a rounded shape can be easily performed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIGS. 1A and 1B  are views each explaining a semiconductor device of the present invention; 
         FIGS. 2A and 2B  are views each explaining a semiconductor device of the present invention; 
         FIGS. 3A and 3B  are views each explaining a semiconductor device of the present invention; 
         FIGS. 4A and 4B  are views each explaining a semiconductor device of the present invention; 
         FIGS. 5A to 5D  are views each explaining a semiconductor device of the present invention; 
         FIGS. 6A to 6D  are photographs (SEM images) each showing a cutting surface of a glass substrate; 
         FIG. 7  is a view explaining a semiconductor device of the present invention; 
         FIGS. 8A to 8F  are views each explaining a semiconductor device of the present invention; 
         FIGS. 9A to 9D  are views each explaining a semiconductor device of the present invention; 
         FIGS. 10A to 10C  are views each explaining a semiconductor device of the present invention; and 
         FIGS. 11A and 11B  are views each explaining a semiconductor device of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Best Mode for Carrying Out the Invention 
     Embodiment Mode of the present invention will be explained in detail using the accompanying drawings. However, the present invention is not limited to the description below, and it is easily understood by those skilled in the art that modes and details thereof can be modified in various ways without departing from the purpose and the scope of the present invention. Therefore, the present invention is not understood as being limited to the description in Embodiment Mode. Note that in the structure of the present invention which is hereinafter described, the reference numerals denoting the same portions are used in common in different drawings. 
     A method for manufacturing a semiconductor device of the present invention will be explained with reference to  FIGS. 1A and 1B ,  FIGS. 2A and 2B ,  FIGS. 3A and 3B ,  FIGS. 4A and 4B ,  FIGS. 5A to 5D , and  FIGS. 6A to 6D . Note that a case where six thin film integrated circuits are manufactured over a substrate  11  will be explained hereinafter. Further, a region where one thin film integrated circuit is provided in each of  FIG. 1A ,  FIG. 2A , and  FIG. 3A  corresponds to a region  26  surrounded by a dashed line.  FIG. 1B ,  FIG. 2B , and  FIG. 3B  correspond to cross-sectional views of point A to point B of  FIG. 1A ,  FIG. 2A , and  FIG. 3A , respectively. 
     First, an insulating layer  12  is formed over one of the surfaces of the substrate  11  (see  FIG. 1B ). Next, a layer including a plurality of transistors  13  is formed over the insulating layer  12 , and then, insulating layers  15  and  16  are formed over the layer including the plurality of transistors  13 . Next, conductive layers  17  to  24  are formed, each of which is connected to a source region or a drain region of each of the plurality of transistors  13  through openings provided in the insulating layers  15  and  16 . Subsequently, an insulating layer  25  is formed so as to cover the conductive layers  17  to  24 . 
     The substrate  11  corresponds to a glass substrate, a plastic substrate, a silicon substrate, a quartz substrate, and the like. A glass substrate or a plastic substrate is preferably used as the substrate  11 . A glass substrate or a plastic substrate having 1 meter or longer on a side is easily manufactured, and a desired shaped glass substrate or plastic substrate is also easily manufactured. Therefore, when a large-sized square glass substrate or plastic substrate having 1 meter or longer on a side is used, for example, productivity can be considerably improved. Such merits are great advantages as compared with a case of using a circular silicon substrate. 
     The insulating layer  12  functions to prevent intrusion of an impurity from the substrate  11 . The insulating layer  12  is formed by a single layer or a stacked layer of a layer containing oxide of silicon or nitride of silicon by a sputtering method, a plasma CVD method, or the like. A material for the oxide of silicon is a substance containing silicon (Si) and oxygen (O), and silicon oxide, silicon oxide containing nitrogen, or the like corresponds thereto. A material for the nitride of silicon is a substance containing silicon and nitrogen (N), and silicon nitride, silicon nitride containing oxygen, or the like corresponds thereto. Note that the insulating layer  12  may not necessarily be formed when it is not necessary to be formed. 
     Each of the plurality of transistors  13  has a semiconductor layer  27 , an insulating layer  14 , and a conductive layer  29  which is a gate electrode. The semiconductor layer  27  has an impurity region  30  functioning as a source region or a drain region, and a channel formation region  31 . An impurity element imparting N-type or P-type is added to the impurity region  30 . Specifically, an impurity element imparting N-type (an element belonging to Group 15 of the periodic table, for example phosphorus (P) or arsenic (As)) or an impurity element imparting P-type (for example boron (B)) is added. The insulating layer  14  corresponds to a gate insulating layer. 
     Note that although only the plurality of transistors  13  are formed in the structure shown in the drawing, the present invention is not limited thereto. An element which is provided over the substrate  11  may be appropriately adjusted in accordance with an application of the semiconductor device. In a case of forming a semiconductor device having a function to transmit and receive electromagnetic waves, for example, only a plurality of transistors may be formed, or alternatively, a plurality of transistors and a conductive layer functioning as an antenna may be formed over the substrate  11 . Note that the conductive layer functioning as an antenna may not necessarily be formed by one layer but a multilayer. In addition, in a case of forming a semiconductor device having a function to store data, a plurality of transistors and a memory element (such as a transistor or a memory transistor) may also be formed over the substrate  11 . Also, in a case of forming a semiconductor device (such as a CPU or a signal generating circuit) having a function to control a circuit, generate a signal, or the like, a transistor may be formed over the substrate  11 . Moreover, other elements such as a resistor element and a capacitor element may be formed in addition to the above elements, if necessary. Note that in a case of forming a semiconductor device having a function to transmit and receive electromagnetic waves, only a plurality of transistors may be formed over the substrate  11 . 
     The insulating layers  15  and  16  are formed by a single layer or a stacked layer by an inorganic material or an organic material by using an SOG (spin on glass) method, a droplet discharging method, a screen printing method, or the like. For example, nitride of silicon containing oxygen may be formed as the insulating layer  15 , and oxide of silicon containing nitrogen may be formed as the insulating layer  16 . 
     Next, a laser beam is selectively emitted, that is, to a predetermined position, and grooves  32  are formed in one or more of the insulating layers  14 ,  15 ,  16 , and  25  that are provided in the layer including the substrate  11 , the insulating layer  12 , and the plurality of transistors  13  (see  FIGS. 2A and 2B ). In the structure shown in the drawing, the insulating layers  12 ,  14 ,  15 , and  16  are cut off by a laser beam, and the grooves  32  are formed in the substrate  11 . 
     A laser medium, an excitation source, and a resonator are included in a laser. Any type of laser may be used in the present invention although a laser is classified into a gas laser, a liquid laser, and a solid laser according to a medium, and classified into a free electron laser, a semiconductor layer, and an X-ray laser according to the type of oscillation. Note that a gas laser or a solid laser is preferably used, and a solid laser is more preferably used. 
     A gas laser includes a helium-neon laser, a carbon dioxide laser, an excimer laser, and an argon ion laser. An excimer laser includes a rare gas excimer laser and a rare gas halide excimer laser. A rare gas excimer laser oscillates by three kinds of excite molecules: argon, krypton, and xenon. An argon iron laser includes a rare gas ion laser and a metal vapor ion laser. 
     A liquid laser includes an inorganic liquid laser, an organic chelate laser, and a pigment laser. In an inorganic liquid laser and an organic chelate laser, rare earth ions such as neodymium, which are utilized for a solid laser, are used as a laser medium. 
     A laser medium used in a solid laser is a solid base doped with active species functioning as a laser. The solid base is crystal or glass. The crystal is YAG (yttrium aluminum garnet crystal), YLF, YVO 4 , YAlO 3 , sapphire, ruby, or alexandrite. In addition, the active species functioning as a laser are, for example, trivalent irons (such as Cr 3+ , Nd 3+ , Yb 3+ , Tm 3+ , Ho 3+ , Er 3+ , and Ti 3+ ). 
     As a laser used in the present invention, a continuous wave laser or a pulse oscillation laser can be used. The irradiation condition of a laser beam (for example, frequency, power density, energy density, beam profile, or the like) are appropriately controlled in consideration of a thickness of the substrate  11 , the insulating layers  12 ,  14 , and  15 , and a material thereof. 
     As a laser used when the substrate  11  is the glass substrate, a solid laser having a wavelength of 1 nm or more to 380 nm or less, which is an ultraviolet region, is preferably used. More preferably, an Nd:YVO 4  laser having a wavelength of 1 nm or more to 380 nm or less, which is an ultraviolet region, is used. It is because light is more easily absorbed in a substrate (especially a glass substrate) by using a laser having a wavelength of an ultraviolet region compared with other laser at a longer wavelength side, and an ablation process is easily performed. Moreover, it is because an ablation process is easily performed especially by using an Nd:YVO 4  laser. Also, a laser beam having a wavelength in a range of 1 nm or more to 350 nm or less may be used in case of a plastic substrate (for example, a substrate comprising polyethylene terephthalate). In this case, preferably an Nd:YVO 4  laser is also used. 
     Note that a laser irradiation device for emitting the above laser beam has a moving table, a substrate, a head portion, and a control portion. The moving table is provided with an adsorption hole. The substrate is held by the adsorption hole over the moving table. The head portion emits a laser beam which is emitted from a laser oscillation device through a laser head. The control portion positions the laser head at a random place over the surface of the substrate by moving one or both of the moving table and the head portion, and accordingly, a laser beam is emitted. Note that the control portion recognizes and determines a portion to be processed from a relative position on the basis of a mark for positioning over a substrate which is taken by a CCD camera. 
     Next, a laser beam is selectively emitted to cut off the substrate  11 , the insulating layers  12 ,  14 ,  15 ,  16 , and  25  (see  FIGS. 3A and 3B ). Or, these may dynamically be cut with a formed groove. Through the above process, a laminated body  33  including the substrate  11  and the plurality of transistors  13  can be obtained. 
     Subsequently, the laminated body  33  including the substrate  11  and the plurality of transistors  13  is sealed using films  34  and  35  if necessary (see  FIG. 4A ). The films  34  and  35  are made of a material such as polyethylene, polycarbonate, polypropylene, polyester, vinyl, polyvinyl fluoride, vinyl chloride, ethylene vinyl acetate, urethane, or polyethylene terephthalate, or a fiber material (for example, paper). Each of the films may be a single layer or a stacked layer of a plurality of films. In addition, an adhesion layer may also be provided over the surface thereof. The adhesion layer corresponds to a layer containing an adhesive such as a polyester or polyolefin thermal flexible resin, a thermal curing resin, an ultraviolet curing resin, a vinyl acetate resin adhesive, a vinyl copolymer resin adhesive, an epoxy resin adhesive, a urethane resin adhesive, a rubber adhesive, or an acrylic resin adhesive. 
     Each surface of the films  34  and  35  may be coated with powder of silicon dioxide (silica). A waterproof property can be maintained even under a high temperature environment or a high humidity environment by coating. In other words, a function of humidity resistance can be obtained. In addition, the surface thereof may also be coated with a conductive material such as indium tin oxide. The material which is used for coating charges static electricity, and accordingly, the plurality of transistors  13  can be protected from static electricity. That is, a function of preventing static electricity can be obtained. Moreover, the surface thereof may also be coated with a material containing carbon as its main component (for example, diamond like carbon or carbon containing nitrogen). The strength is increased by coating, and accordingly, a semiconductor device can be prevented from deteriorating and being destroyed. In addition, the films  34  and  35  may also be formed from a material in which a material for a base material (such as a resin) and a material containing silicon oxide, a conductive material, or carbon as its main component are mixed. Moreover, the films  34  and  35  can obtain a function of preventing static electricity by applying a surface active agent over the surface, or alternatively, by directly adding the surface active agent into the films. 
     Each surface layer of the films  34  and  35  or each surface adhesion layer of the films  34  and  35  is melted by heat treatment, and accordingly, the plurality of transistors  13  are sealed with the films  34  and  35 . In addition, adhesion is performed by pressure treatment. 
     According to one feature of the present invention, a laminated body including the substrate  11  and the plurality of transistors  13  is provided between the films  34  and  35 . By the above feature, intrusion of harmful gas, water, or an impurity element can be suppressed. Therefore, deterioration or destruction of the plurality of transistors  13  is suppressed, and accordingly, the reliability can be improved. 
     Note that a conductive layer functioning as an antenna may be provided at one or both of the films  34  and  35 . When the laminated body  33  including the plurality of transistors  13  is sealed with the films  34  and  35 , the conductive layer over the films  34  and  35  and the plurality of transistors  13  may be electrically connected to each other. At this time, it is preferable to provide an exposed conductive layer for connection in the laminated body including the plurality of transistors  13 . Then, sealing is performed so that the conductive layer for connection and the conductive layer over the films  34  and  35  are in contact with each other. Accordingly, a semiconductor device capable of transmitting and receiving electromagnetic waves can be provided. 
     Note that the substrate  11  may be thinned by performing one or both of grinding and polishing to the other surface of the substrate  11  by using one or both of a grinding device (for example, a grinding machine) and a polishing device (for example, a grinding stone). Thereafter, a laser beam is selectively emitted to cut off the insulating layers  12 ,  14 ,  15 , and  16 , and the thinned substrate  11 . Subsequently, the laminated body  33  including the substrate  11  and the plurality of transistors  13  is sealed by using the films  34  and  35  (see  FIG. 4B ). Note that one or both of grinding and polishing may be performed to the substrate  11  so that the thickness of the substrate  11  is 100 μm, preferably 50 μm or less, and more preferably 5 μm or less. 
     Note that when one or both of grinding and polishing is/are performed, a film aimed at protection may be provided over the insulating layer  25  to be fixed, and thereafter, one or both of grinding and polishing is/are performed to the other surface of the substrate  11 . Note that the film which is provided over the insulating layer  25  may be a film having a surface provided with an UV curing adhesive. In addition, after one or both of grinding and polishing is/are performed, the film provided over the insulating layer  25  may be left or removed. 
     As described above, by thinning the substrate  11 , the insulating layers  12 ,  14 ,  15 , and  16 , and the substrate  11  can be easily cut off at short times using a laser beam. In addition, by thinning the substrate, a semiconductor device having flexibility can be provided. By making a semiconductor device have flexibility, design can be improved, and the semiconductor device can be easily mounted on an object with a flexible shape; accordingly, the semiconductor device can be utilized in various fields. 
     In addition, although a shape of the cut substrate  11  is a simple square shape in the above process, the present invention is not limited thereto. For example, a hexagonal groove  32  may be formed in the laminated body including the substrate  11  by scanning and emitting a laser beam (see  FIG. 5A ), and subsequently, the laser beam is emitted to cut off the laminated body including the substrate  11  (see  FIG. 5B ). Accordingly, a hexagonal laminated body including the substrate  11  can be formed. Moreover, a circular groove  32  may be formed in the laminated body including the substrate  11  by emitting a laser beam (see  FIG. 5C ), and the laser beam may be emitted to cut off the laminated body including the substrate  11  (see  FIG. 5D ). Accordingly, a circular laminated body including the substrate  11  can be formed. 
     An interior angle of the top shape of the laminated body including the substrate  11  is set to be 90 degrees or more (for example, a polygonal shape such as hexagon), or eliminating corner of the laminated body including the substrate  11  (for example, a circular shape or an ellipse shape) by devising the shape as described above; accordingly, the semiconductor device can be easily treated in carrying. In addition, generation of a defect, a crack or a burr at the time of mounting on a product can be prevented. 
     Embodiment 1 
     Results of an experiment using the present invention will be explained with reference to  FIGS. 6A to 6D . Each of  FIGS. 6A to 6C  shows a cutting surface of a glass substrate. 
     As a first experiment, it was attempted to selectively emit a laser beam to a glass substrate, form a groove in the glass substrate, and cut off the glass substrate dynamically. Note that the size of the glass substrate which was used was 126.6 mm×126.6 mm×thickness of 0.7 mm. An Nd:YVO 4  laser having a wavelength of 266 nm was used for a laser. The irradiation condition of the laser beam was as follows: output power of 2.0 W, frequency of 15 kHz, and feeding speed of 20 mm/sec. 
     As a result of selectively emitting a laser beam to the glass substrate, a V-shaped groove was formed in the glass substrate (see  FIG. 6A ). Then, as a result of emitting a laser beam to the glass substrate again, a deeper groove was formed in a depth direction (see  FIG. 6B ). Next, the feeding speed of 20 mm/sec was changed to 5 mm/sec, and a laser beam is emitted to the glass substrate again; accordingly, a deeper groove was formed in the depth direction (see  FIG. 6C ). Subsequently, when it was attempted to dynamically cut off the glass substrate where the above groove was formed, the glass substrate could be easily cut off. In this case, the position of the groove to which the laser beam was emitted became the cutting surface. 
     As a second experiment, it was attempted to cut off the glass substrate only by selectively emitting a laser beam to the glass substrate. The laser beam was emitted 6 times. Note that the size of the glass substrate which was used was 126.6 mm×126.6 mm×thickness of 0.7 mm. An Nd:YVO 4  laser having a wavelength of 266 nm was used for a laser. The irradiation condition of the laser was as follows: output power of 2.0 W, frequency of 15 kHz, and feeding speed of 5 mm/sec. As a result of the experiment, the glass substrate could be easily cut off without generating a crack and the like. 
     As a third experiment, the glass substrate was polished to be 100 μm thick or less by using a polishing device. Then, it was attempted to cut off the glass substrate only by selectively emitting a laser beam to the glass substrate which was polished. Note that the size of the glass substrate which was used was 126.6 mm×126.6 mm×thickness of 0.7 mm. An Nd:YVO 4  laser having a wavelength of 266 nm was used for a laser. The irradiation condition of the laser was as follows: output power of 2.0 W, frequency of 15 kHz, and feeding speed of 30 mm/sec. As a result of the experiment, the glass substrate could be easily cut off without generating a crack and the like. 
     According to these results, it is found that it is necessary to control a thickness of a glass substrate and to appropriately adjust irradiation condition of a laser such as output power, feeding speed, and the number of irradiation in a case of emitting a laser beam to a glass substrate to form a groove in the glass substrate, and also, in a case of emitting a laser beam to a glass substrate to cut off the glass substrate. 
     In addition, when a laser beam is emitted to a glass substrate to form a groove in the glass substrate, a cutting surface of the groove is rounded (see  FIGS. 6B and 6C ). In a case where the cutting surface is rounded as described above, a defect of a corner of the cutting surface or a crack can be prevented from being generated as compared with a case where there is a corner at a cutting surface. According to such an advantage, a glass substrate can be easily handled mainly when the glass substrate is carried using a robot or the like. Moreover, also in being mounted on a product, generation of a defect or a crack can be suppressed, and generation of a damage or destruction of a substrate can be suppressed. 
     Embodiment 2 
     A structure of a semiconductor device of the present invention will be explained with reference to  FIG. 7 . A semiconductor device  100  of the present invention has an arithmetic processing circuit  101 , a memory circuit  103 , an antenna  104 , a power source circuit  109 , a demodulation circuit  110 , and a modulation circuit  111 . The antenna  104  and the power source circuit  109  are essential component parts of the semiconductor device  100 , and the other parts are appropriately provided in accordance with an application of the semiconductor device  100 . 
     The arithmetic processing circuit  101  analyzes an order, controls the memory circuit  103 , and outputs data which is transmitted to an exterior portion to the modulation circuit  111  on the basis of a signal which is inputted from the demodulation circuit  110 . 
     The memory circuit  103  has a circuit including a memory element and a control circuit which writes and reads data. At least an identification number of the semiconductor device itself is stored in the memory circuit  103 . The identification number is used to distinguish from other semiconductor devices. In addition, the memory circuit  103  has one or more kinds selected from an organic memory, a DRAM (Dynamic Random Access Memory), a SRAM (Static Random Access Memory), an FeRAM (Ferroelectric Random Access Memory), a mask ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Electrically Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory), and a flash memory. The organic memory has a structure in which a layer containing an organic compound is interposed between a pair of electrodes, and the structure is simple; therefore, the organic memory has at least two advantages. One advantage is that a manufacturing process can be simplified and cost can be reduced. The other advantage is that an area of a laminated body can be easily reduced and an organic memory with high capacity can be easily realized. Moreover, since an organic memory is a nonvolatile memory, a battery may be incorporated or may not necessarily be incorporated. Therefore, it is preferable to use an organic memory as the memory circuit  103 . 
     The antenna  104  converts a carrier wave which is supplied from a reader/writer  112  into an AC electrical signal. Also, load modulation is added by the modulation circuit  111 . The power source circuit  109  generates a power source voltage by using the AC electrical signal which is converted by the antenna  104  to provide a power source voltage for each circuit. 
     The demodulation circuit  110  demodulates the AC electrical signal which is converted by the antenna  104  and supplies the demodulated signal to the arithmetic processing circuit  101 . The modulation circuit  111  adds load modulation to the antenna  104  on the basis of a signal which is supplied from the arithmetic processing circuit  101 . 
     The reader/writer  112  receives the load modulation which is added to the antenna  104  as a carrier wave. Also, the reader/writer  112  transmits the carrier wave to the semiconductor device  100 . Note that the carrier wave is an electromagnetic wave transmitted and received by the reader/writer  112 , and the reader/writer  112  receives a carrier wave which is modulated by the modulation circuit  111 . 
     As described above, the semiconductor device of the present invention having a function to transmit and receive an electromagnetic wave wirelessly is referred to as an RFID (Radio Frequency Identification), an RF chip, an RF tag, an IC tag, an IC label, a wireless chip, a wireless tag, an electronic chip, an electronic tag, a wireless processor, or a wireless memory. This embodiment can be freely combined with other embodiment modes. 
     Embodiment 3 
     The semiconductor device  100  to which the present invention is applied can be used for various goods and various systems by utilizing a function to transmit and receive an electromagnetic wave. The goods are, for example, keys (see  FIG. 8A ), bills, coins, securities, bearer bonds, certificates (such as a driver&#39;s license and a residence certificate; see  FIG. 8B ), documents, containers (such as a petri dish; see  FIG. 8C ), packing containers (such as wrapping paper and a bottle; see  FIGS. 8E and 8F ), a recording medium (such as a disk and a video tape), vehicles (such as a bicycle), accessories (such as a bag and glasses; see  FIG. 8D ), foods, clothes, livingwares, electronic devices (such as a liquid crystal display device, an EL display device, a television device, and a portable terminal), and the like. The semiconductor device of the present invention is attached or mounted on surfaces of the above described goods having various shapes to be fixed. Also, a system indicates a goods management system, an authentication function system, a distribution system, or the like, and high functionality, multi functionality, and high added value of the system can be attempted. This embodiment can be freely combined with other embodiment modes and embodiments. 
     Embodiment 4 
     In this embodiment, a method for manufacturing a transistor will be explained with reference to  FIGS. 9A to 9D ,  FIGS. 10A to 10C , and  FIGS. 11A and 11B . 
     First, an insulating layer  552  is formed over a substrate  551  (see  FIG. 9A ). Then, an insulating layer  553  is formed over the insulating layer  552 . Next, a semiconductor layer  554  is formed over the insulating layer  553 . Subsequently, a gate insulating layer  555  is formed over the semiconductor layer  554 . 
     The insulating layers  552  and  553 , the semiconductor layer  554 , the gate insulating layer  555 , and the like may be formed by using plasma treatment. It is preferable that plasma treatment herein used is performed with electron density of 1×10 11  cm −3  or more and electron temperature of plasma of 1.5 eV or less. More specifically, it is preferable that the plasma treatment is performed with electron density of 1×10 11  cm −3  or more and 1×10 13  cm −3  or less and an electron temperature of plasma of 0.5 eV or more and 1.5 eV or less. 
     When the electron density of plasma is high and the electron temperature near a substance to be processed (for example, the insulating layers  552  and  553 , the semiconductor layer  554 , the gate insulating layer  555 , or the like) is low, a damage due to plasma to the substance to be processed can be prevented. Also, since electron density of plasma is 1×10 11  cm −3  or more, which is high, oxide or nitride which is formed by oxidizing or nitriding a substance to be irradiated by using plasma treatment can be formed as a film which is excellent in uniformity of thickness or the like and is also fine, compared with a thin film which is formed by a CVD method, a sputtering method, or the like. Moreover, since electron temperature of plasma is 1.5 eV or less, which is low, the oxidizing or nitriding treatment can be performed at lower temperature compared with conventional plasma treatment or thermal oxidation method. For example, the oxidizing or nitriding treatment can be sufficiently performed even when the plasma treatment is performed at lower temperature by at least 100° C. than a strain point of a glass substrate. 
     Subsequently, a conductive layer  501  and a conductive layer  503  are stacked over the gate insulating layer  555 . Each of the conductive layer  501  and the conductive layer  503  is formed by using metal such as tungsten, chromium, tantalum, tantalum nitride, molybdenum, alloy or a compound containing the above metal as its main component. Note that the conductive layer  501  and the conductive layer  503  are formed by using different materials from each other. Specifically, in an etching process which is performed afterward, a material which generates difference in etching rate is used. 
     Next, a mask  506  made of a resist is formed over the conductive layer  503 . The mask  506  is formed by using an exposure mask including a light-shielding film and a translucent film. A specific structure of the mask will be explained hereinafter. 
     Then, the conductive layer  503  is etched using the mask  506  to form a mask  507  and a conductive layer  504  (see  FIG. 9B ). The mask  507  is sputtered by ion which is accelerated in an electric field, divided into two patterns, and placed separately. Next, the conductive layer  501  is etched using the mask  507  and the conductive layer  504  to form a conductive layer  502  (see  FIG. 9C ). 
     Subsequently, the mask  507  and the conductive layer  504  are selectively etched to form a mask  508  and a conductive layer  505  (see  FIG. 9D ). The mask  508  is sputtered by ion which is accelerated in an electric field and the size is reduced. In this process, a bias voltage which is applied to the substrate side is adjusted so that the conductive layer  502  is prevented from being etched. 
     Then, an impurity element imparting one conductivity type is added to the semiconductor layer  554  to form first concentration impurity regions  509 ,  516 , and  517  (see  FIG. 10A ). At this time, an impurity element is added to the semiconductor layer  554  in a self-aligned manner by using the conductive layers  502  and  505 . 
     Next, an impurity element imparting one conductivity type is added to the semiconductor layer  554  to form second concentration impurity regions  510  and  511  (see  FIG. 10B ). The second concentration is made to be higher than the first concentration. Note that an impurity element imparting one conductivity type is not added to the semiconductor layer  554  which is overlapped with the conductive layer  505 . Therefore, the semiconductor layer  554  which is overlapped with the conductive layer  505  functions as a channel formation region. Through the above process, a thin film transistor  520  is completed. 
     Next, insulating layers  512  and  513  are formed so as to cover the thin film transistor  520  (see  FIG. 10C ). Then, conductive layers  514  and  515  connected to the second concentration impurity regions  510  and  511  are formed through openings provided in the insulating layers  512  and  513 . 
     According to one feature of the above process, the conductive layers  501  and  503  are etched using the mask  506  having a different thickness and a complicated shape. The masks  507  that are placed separately can be formed by using the mask  506 . Then, a distance between two channel formation regions can be shortened. Specifically, the distance between two channel formation regions can be set to be less than 2 μm. Therefore, in a case of forming a multigate thin film transistor having two or more of gate electrodes, the occupation area thereof can be reduced. Therefore, high integration can be realized and a high definition semiconductor device can be provided. 
     Next, a method for forming the mask  506  will be explained with reference to  FIGS. 11A and 11B .  FIG. 11A  is a plan view in which part of an exposure mask is enlarged. Also,  FIG. 11B  is a cross-sectional view of part of the exposure mask corresponding to  FIG. 11A  and a cross-sectional view of the laminated body including the substrate  551 . 
     The exposure mask has a light-transmitting substrate  560 , light-shielding films  561  and  562 , and a translucent film  563 . The light-shielding films  561  and  562  are made of a metal film such as chromium, tantalum, or CrNx (x is a positive integer). It is necessary that a material for the translucent film  563  is appropriately selected with respect to an exposure wavelength, and for example, TaSixOy (x and y are positive integers), CrOxNy (x and y are positive integers), CrFxOy (x and y are positive integers), MoSixNy (x and y are positive integers), and MoSixOy (x and y are positive integers) may be used. The translucent film  563  functions as an assist pattern. 
     When a resist mask is exposed by using the exposure mask having the above structure, the resist mask is classified broadly into a region which is not exposed  521  and a region which is exposed  522 . When a development process is performed in this state, the resist of the region which is exposed  522  is removed, and part of the resist of a portion corresponding to the translucent film  563  in the exposure mask in the region which is not exposed  521  is removed. A mask having a shape as shown in  FIG. 9A  is formed. 
     This application is based on Japanese Patent Application serial No. 2005-156583 filed in Japan Patent Office on May 30 in 2005, the entire contents of which are hereby incorporated by reference.