Conventionally, there is known an atmospheric pressure plasma generating device which makes an inert gas into a plasma in the vicinity of atmospheric pressures (in a range of 500 to 1500 mmHg in terms of pressure) and makes a reactive gas into a plasma by the generated radicals of the inert gas to carry out a plasma processing such as surface reforming, etching, and deposition. In such an atmospheric pressure plasma generating device, the inert gas and the reactive gas mixed at a predetermined ratio in advance are provided to one end of a cylindrical reaction vessel. Applying a high-frequency electric field to the reaction vessel makes the mixed gas into a plasma and the generated plasma ejected from the other end of the reaction vessel is subjected to a processed object to carry out the processing.
With reference to FIG. 21, the principle of plasma generation will be described in the case of using argon serving as the inert gas and oxygen serving as the reactive gas. Applying the high-frequency electric field, an Ar atom (Ar) in a reaction space in which a discharge plasma is generated is excited or ionized by an electron (e) in the discharge plasma and becomes an argon radical (Ar*), an argon ion (Ar+), or an electron (e). The argon radical (Ar*) being in a metastable state with high energy reacts with the same or different kind of atom in the vicinity thereof in order to return to a stable state by making that atom excited or ionized, so that that reaction occurs with an avalanche multiplication. If there is the oxygen in the vicinity thereof at that time, an oxygen atom (O) is excited or ionized and becomes an oxygen radical (O*), an oxygen ion (O+), or an electron (e). The oxygen radical (O*) reacts with a material in the surface of a processed object and carries out a plasma processing such as surface reforming and removing organic matter by reacting with the organic matter in the surface. The radical of the inert gas maintains the metastable state for a longer time in comparison with the radical of the reactive gas, and hence the inert gas is used for generating the plasma in general. Using a gas for deposition as the reactive gas can achieve deposition. Using hydrogen can expect reduction operation.
A conventional example 1 according to an atmospheric pressure plasma generating device, as shown in FIG. 22, includes a reaction vessel 101 for forming a reaction space, a pair of electrodes 103a and 103b disposed in the outside periphery of the reaction vessel 101 with an interval in an axial direction, and a high-frequency power supply 104 for applying alternating or pulse-shaped high-frequency voltages between the pair of electrodes 103a and 103b. A mixed gas 102 into which the inert gas and the reactive gas are mixed at a predetermined ratio is supplied from one end of the reaction vessel 101, and the alternating or pulse-shaped high-frequency voltage is applied between the pair of electrodes 103a and 103b. Thus, a plasma is generated in the reaction space and the generated plasma 105 is ejected from the other end of the reaction vessel 101. Applying the plasma 105 on the surface of a processed object 106 can carry out a plasma processing (refer to Japanese Patent Laid-Open Publication No. 2002-1253).
In the structure shown in FIG. 22, it needs dozens of times of input power to excite the mixed gas into which the inert gas and the reactive gas are mixed and make the reactive gas into a plasma as compared with a case of exciting only the inert gas, so that there is the problem in which a device becomes large. As the principle of plasma generation solving such a problem, as shown in FIG. 23, it is proposed that only an inert gas (Ar in the drawing) 113 is supplied to a reaction vessel 111 to which a high-frequency power supply 112 applies a high-frequency electric field and a reactive gas (O2 gas in the drawing) 116 is supplied from a reactive gas supply pipe 115 to the plasma 114 ejected from the reaction vessel 111. In a conventional example 2 embodying the principle of plasma generation, as shown in FIG. 24, the plasma 114 ejected from the reaction vessel 111 is sprayed from one side of a processed object 117 and the reactive gas 116 is sprayed from the other side of the processed object 117 through the reactive gas supply pipe 115 (refer to Japanese Patent Laid-Open Publication No. Hei 9-59777).
Furthermore, as shown in FIG. 25, the following configuration is known as a conventional example 3. A reactive gas supply space 121 is disposed in the middle and a pair of reaction spaces 122 and 123 to which an inert gas is supplied and a high-frequency power supply 124 applies a high-frequency electric field is disposed on both sides thereof. The reactive gas passes through the excited inert gas to mix it with the inert gas, and the reactive gas made into a plasma carries out a plasma processing on a processed object 125 (refer to Japanese Patent Laid-Open Publication No. 2003-49272).
Also the following is known as a device which carries out a plasma processing by an atmospheric pressure plasma. The device is provided with a plasma head which generates an atmospheric pressure plasma and ejects a plasma jet from an outlet and moving means which relatively moves a processed object and the plasma head so as to face the plasma head to a particular processed portion of the processed object. A plasma processing is carried out by spraying the plasma jet on the particular processed portion of the processed object (refer to Japanese Patent Laid-Open Publication No. Hei 11-251304).
A device shown in FIGS. 26A and 26B is known as a conventional example 4 related to a method and device for mounting a component on a substrate. The conventional example 4 uses a plasma head 131 which is provided with a cylindrical reaction space 132 and a pair of electrodes 133 and 134 disposed inside and outside of the reaction space 132. The plasma head 131 applies a high-frequency voltage between the electrodes 133 and 134 while supplying an inert gas 135 from an upper end of the reaction space 132, so that a plasma is generated in the reaction space 132 and a plasma jet 136 is ejected from a lower end 132a of the reaction space 132. The plasma head 131 is relatively moved to a table 138 on which a panel 137 for a flat panel display is fixed as an arrow ‘a’ in order to carry out a plasma processing on a connection electrode component 139 which is composed of transparent electrodes 139a formed in parallel at a side end of the panel 137 (refer to Japanese Patent Laid-Open Publication No. 2002-28597).
It is also known to carry out a plasma processing in a like manner by using a plasma head having the structure shown in FIG. 22 (refer to Japanese Patent Laid-Open Publication No. 2003-167526). A compact micro plasma jet generating device for generating a micro inductively coupled plasma jet under an atmospheric pressure is also proposed (refer to the description of Japanese Patent No. 3616088).
However, the structure shown in FIG. 22 has the problem that large input power is necessary to generate a plasma as described above and the device become large. In addition to this, the lifetime of the reactive gas which is made into a plasma is short and the plasma 105 disappears immediately after being ejected from the other end of the reaction vessel 101. Thus, the reactive gas made into a plasma does not work effectively unless the distance L between the other end of the reaction vessel 101 and the processed object 106 is short, and hence there is the problem that the distance range of the plasma processing is limited to small.
In the structure shown in FIG. 24, since the excited reactive gas having a short lifetime disappears immediately after going out of the reaction vessel 111, it is impossible to make the reactive gas 116 into a plasma except in the vicinity of the outlet of the reaction vessel 111. Thus, there is the problem that the reactive gas 116 is not sufficiently made into a plasma. In the structure shown in FIG. 25, the reactive gas is easily mixed with the inert gas in comparison with the structure shown in FIG. 24 because the reactive gas is passed through the excited inert gas for mixture, and hence there is an advantage that a range in which the reactive gas is made into plasma becomes uniform. However, the lifetime of the inert gas is still short, and there is the problem that a distance range of the plasma processing is limited to small.
In the plasma processing method disclosed in the above Japanese Patent Laid-Open Publication No. Hei 11-251304, it is necessary to successively generate the plasma jet by keeping on supplying the mixed gas of the inert gas and the reactive gas or at least the inert gas not only during applying the plasma jet to the processed portion of the processed object but also during moving between the processed portions. This is because if the generation of the plasma jet is stopped once, it takes time to ignite a plasma again and generate a stable plasma jet and hence productivity is significantly reduced. Also a gas supplied until the plasma jet comes to be stable is wasted without contributing the plasma processing. Therefore, the amount of consumed gas is significantly increased in comparison with the case of vacuum plasma processing to an extent such as several liters per minute to several hundreds liters per minute. Also an expensive gas of high purity is necessary because a plasma becomes unstable if a gas of low purity is used for the atmospheric pressure plasma. As a result, there is the problem that running costs of the plasma processing become extremely high.
Also there is the problem that it is difficult to stably apply the plasma jet to the processed portion of the processed object and not to apply the plasma jet to a position except for the processed portion because the plasma jet is successively ejected. In other words, it is necessary to intricately control the relative movement between the plasma head and the processed object in order to get the stable application of the plasma jet to the processed portion and not to apply it at all to the position except for the processed portion. Accordingly, there is the problem that equipment and the structure of a control mechanism become sophisticated.
Furthermore, since the lifetime of the reactive gas made into a plasma is short within the plasma generated as described above, the plasma jet disappears immediately after being ejected from the outlet of the plasma head. Accordingly, the reactive gas made into a plasma does not effectively work without shortening the distance between the outlet of the plasma head and the processed object, so that there are the problems that the efficiency of the plasma processing deteriorates and movement control during the processing becomes complicated because the distance range of the plasma processing is limited to small.
In the plasma generating methods disclosed in the foregoing Japanese Patent Laid-Open Publications No. Hei 11-251304, No. 2002-28597, and No. 2003-167526, a capacitively coupled plasma (non-equilibrium plasma) is generated with the use of a pair of electrodes conforming to parallel plates, and the plasma density of the generated plasma is 1011 to 1012/cm3 at the maximum. Since it takes much time to carry out the plasma processing on a component to-be-bonded portion of a substrate using such capacitively coupled plasma with low plasma density, it is impossible to adjust the plasma processing to the tact of the other processes of a component mounting process. Thus, it is necessary to carry out the plasma processing in a separate process from the component mounting process, and hence there is the problem that the productivity of component mounting is seriously reduced. When the plasma processing is carried out in the separate process, there is the problem that the plasma-processed portion is contaminated again during carrying the substrate from the plasma processing process to the component mounting process. Furthermore, it becomes impossible to incorporate the plasma processing into a component mounting line in actual fact since the size of the flat panel display is upsized and exceeds forty inches in recent years, though this is still possible in a case that the size of the flat panel display is a few inches. The plasma temperature of the capacitively coupled plasma is approximately several hundreds degrees centigrade and hence there is little fear of damaging the flat panel display by heat.
On the other hand, an inductively coupled plasma (thermal plasma) disclosed in the description of Japanese Patent No. 3616088 have a plasma density of 1016 to 1017/cm3 and the density is approximately 105 times higher than that of the capacitively coupled plasma. Thus, the inductively coupled plasma has high reactivity and high processing ability. However, the plasma temperature of the thermal plasma is several to ten thousands degrees centigrade, so that there is the problem that the thermal plasma damages a substrate by heat when the substrate to which the plasma is applied has a heat-sensitive portion. For example, in a liquid crystal panel manufacturing process in recent years, a substrate on which a polarizing plate has been already attached is supplied to a component mounting line to mount electronic components for driving liquid crystal. If a plasma processing process is incorporated into the mounting line, the plasma with high temperature affects and damages the polarizing plate, so that it is impossible to do so.
In light of the foregoing conventional problems, an object of the present invention is to provide a method and device for generating an atmospheric pressure plasma which generates an atmospheric pressure plasma with small input power. The use of the atmospheric pressure plasma achieves a plasma processing in a wide range in a perspective direction with respect to a reaction space in which the plasma is generated and in a planar direction.
Another object of the invention is to provide a method and device for plasma processing which stably and efficiently processes only a processed portion of a processed object with high productivity by simple structure and control at low costs.
Still another object of the invention is to provide a method and device for mounting a component on a substrate which efficiently carries out a plasma processing on a component to-be-bonded portion of a substrate without damaging it by heat and incorporates the plasma processing into a component mounting process.