Patent Application
20060071182
1. Field of the Invention
The present invention relates to a method of processing a semiconductor apparatus and an apparatus for processing the semiconductor apparatus which are employed for cutting a conductor in an interlayer insulation film in the semiconductor apparatus such as a semiconductor chip.
2. Description of the Related Art
When a conductor in a semiconductor apparatus is conventionally cut by means of the Focused Ion Beam (FIB) (hereinafter, such a process is referred to as FIB process), assist gas chemically reacting with a conductor material is used. In the case of cutting an aluminum wiring, for example, assist gas made of chlorine or bromine is used. As another example, a method of insulating the conductor material using oxygen as the assist gas, which is recited in No. 04-98747 of the Publication of the Unexamined Japanese Patent Applications, is available.
In recent years, copper having a relatively low resistance is used as the conductor in order to cope with an increasingly higher performance of the semiconductor apparatus. However, copper is characterized in that fragments generated from the conductor cut in the FIB process (hereinafter, referred to as conductive residue) are easily dispersed around. The dispersed conductive residue, which is attached to a cut section of the conductor and a side surface of a cut hole, becomes an obstacle in electrically isolating the conductor.
For example,
When aluminum is used as the conductor, chlorine gas or bromine gas chemically reacting with the aluminum is used as the assist gas, the dispersion of the conductive residue can be controlled. However, there does not exist any assist gas capable of satisfactorily preventing the dispersion in the case of using the copper as the conductor.
Therefore, a main object of the present invention is to provide a method of and an apparatus for processing a semiconductor apparatus capable of precisely achieving an electrical isolation after a cutting process.
A method of processing a semiconductor apparatus according to the present invention is a semiconductor apparatus processing method wherein a processing beam is irradiated on a semiconductor apparatus comprising an insulation film and a conductor embedded in the insulation film while the insulation film is scanned from a surface side thereof so that the insulation film and the conductor are burned and cut. The processing method according to the present invention comprises a scanning region setting step for setting a scanning region of the processing beam to a region where a scanning column direction thereof traverses a cut section of the conductor and a processing beam scanning step for irradiating the processing beam for the scan along the set scanning region.
In the beam scanning step, the processing beam used for scanning a final scanning column is supplied with a dosage capable of eliminating a conductive residue generated by the irradiation of the processing beam on the conductor and attached to a cut end surface facing the final scanning column in the beam scanning step.
An apparatus for processing the semiconductor apparatus corresponding to the semiconductor processing method comprises a scanning region setting device for setting the scanning region of the processing beam to the region where the scanning column direction thereof traverses the cut section of the conductor and a processing beam scanning device for irradiating the processing beam for scanning along the set scanning region.
The beam scanning device supplies the dosage capable of eliminating the conductive residue generated by the irradiation of the processing beam on the conductor and attached to the cut end surface facing the final scanning column to the processing beam used for scanning the final scanning column.
Thereby, the conductor can be cut in the unfailingly electrically isolated state without any conductive residue attached to the cut end surface.
In the beam scanning step, the scanning region is beam-scanned a plurality of times, and the processing beam irradiated on each of the final scanning columns beam-scanned the plurality of times may be supplied with the dosage capable of eliminating the conductive residue generated by the irradiation of the processing beam on the conductor and attached to the cut end surface facing the final scanning column, wherein the aforementioned effect can be exerted in the same manner.
The beam scanning step preferably includes an insulation film eliminating step in which the processing beam is irradiated on the insulation film covering the cut section of the conductive film so that a cut hole for exposing the cut section of the conductive film is formed in the insulation film and a conductive film cutting step in which the conductive film exposed out of a bottom section of the cut hole is cut. In this constitution, the processing beam used for scanning the final scanning column is supplied with the dosage capable of eliminating the conductive residue generated by the irradiation of the processing beam on the conductor and attached to the cut end surface facing the final scanning column in the conductive cutting step.
It is preferable that the scanning region setting step be implemented after the insulation film eliminating step, and the scanning region be set to a region where the final scanning column falls on a side surface of the cut hole or a region where the final scanning column is disposed slightly closer to the inside of the insulation film than the side surface of the cut hole in the scanning region setting step.
It is preferable that a step of forming a insulation thin film for covering the exposed conductive film at the bottom section of the cut hole be included prior to the conductive film cutting step, or the insulation thin film for covering the conductive film remain at the bottom section of the cut hole in the insulation film eliminating step. In the presence of the insulation film on the exposed conductive film, the cut section of the conductor is not limited to a close proximity of the cut hole of the interlayer insulation film. Thereby, a cutting depth with respect to the interlayer insulation film under the conductor can be easily controlled, which prevents a possible damage on the conductor as the under layer.
A method of processing the semiconductor apparatus according to the present invention comprises a conductor cutting step in which a processing beam is irradiated on a semiconductor apparatus comprising an insulation film and a conductor embedded in the insulation film from a surface side of the insulation film so that the insulation film and the conductor are burned and cut, a cleaning scanning region setting step in which a scanning region of a cleaning beam is set to a region where a scanning column direction thereof traverses a cut section of the conductor and a final scanning column thereof falls on a cut end surface of the conductor or the final scanning column is disposed slightly closer to an inner side of the insulation film than a side surface of the cut hole, and a cleaning beam scanning step for irradiating the cleaning beam for scanning along the set scanning region.
In the cleaning beam scanning step, the cleaning beam used for scanning the final scanning column is supplied with the dosage capable of eliminating the conductive residue generated by the irradiation of the processing beam on the conductor and attached to the cut end surface facing the final scanning column.
An apparatus for processing the semiconductor apparatus corresponding to the foregoing method of processing the semiconductor apparatus comprises a conductor cutting device for irradiating the processing beam on the semiconductor apparatus comprising the insulation film and the conductor embedded in the insulation film from the surface side thereof so that the insulation film and the conductor are burned and cut, a cleaning scanning region setting device for setting the scanning region of the cleaning beam to the region where the scanning column direction thereof traverses the cut section of the conductor and the final scanning column thereof falls on the cut end surface of the conductor or the region where the final scanning column is disposed slightly closer to the inside of the insulation film than the side surface of the cut hole, and a cleaning beam scanning device for irradiating the cleaning beam for scanning along the set scanning region.
The cleaning beam scanning device supplies the cleaning beam used for scanning the final scanning column with the dosage capable of eliminating the conductive residue generated by the irradiation of the processing beam on the conductor and attached to the cut end surface facing the final scanning column.
In the foregoing constitution, the interlayer insulation film under the conductor layer can also be cut when the conductor is burned and cut, which assures a larger cutting region in the conductor. However, there is often an energy shortage in the processing beam, which makes it easy for the conductive residue to be attached. Therefore, the beam scanning is used for cleaning so as to eliminate the conductive residue. As a result, the conductor can be cut in the unfailingly electrically isolated sate.
The conductive film cutting step preferably includes an insulation film eliminating step in which the processing beam is irradiated on the insulation film covering the cut section of the conductive film so that the cut hole for exposing the cut section of the conductive film is formed in the insulation film, a step of forming an insulation thin film for covering the exposed conductive film at the bottom section of the cut hole and a conductive film cutting step for cutting the conductive film exposed out of the bottom section of the cut hole.
The conductive film cutting step preferably includes an insulation film eliminating step for irradiating the processing beam on the insulation film covering the cut section of the conductive film so that the cut hole for exposing the cut section of the conductive film is formed in the insulation film and a conductive film cutting step for cutting the conductive film exposed out of the bottom section of the cut hole, wherein an insulation thin film for covering the conductive film remains at the bottom section of the cut hole in the insulation film eliminating step. In the presence of the insulation film on the exposed conductive film, the cut section of the conductor is not limited to the close proximity of the cut hole of the interlayer insulation film. Thereby, the cutting depth with respect to the interlayer insulation film under the conductor can be easily controlled, which prevents a possible damage on the conductor as the under layer.
The conductor cutting step preferably includes a processing beam scanning region setting step for setting the scanning region of the processing beam to the region where the scanning column direction thereof traverses a cut section of the conductor and a processing beam scanning step for irradiating the processing beam for scanning along the set scanning region, wherein the scanning region of the processing beam is shifted so as to set the scanning region of the cleaning beam in the cleaning scanning region setting step, and the cleaning beam is used for the scan along the scanning region of the cleaning beam set by shifting the scanning region of the processing beam in the cleaning beam scanning step. Thereby, the cleaning beam scanning step results in executing a beam shift processing in which the processing beam is merely shifted, which alleviates an influence from the cutting process on the interlayer insulation film under the conductor. As a result, the cutting depth with respect to the interlayer insulation film under the conductor can be easily controlled, which prevents a possible damage on any conductor as the under layer.
It is preferable that an insulator depositing gas be supplied to the cut section of the conductor after the cleaning beam scanning step is implemented so that an insulator is deposited in the cut section through a reaction generated by the insulator depositing gas with respect to the cleaning beam. Thereby, the insulator depositing gas is made to react with the cleaning beam in the cut hole so that the cut hole is filled with the insulator. As a result, the electrical insulation of the conductor can be further ensured, and an efficiency of processing can be increased.
It is preferable that the insulator depositing gas be supplied to the cut section of the conductor after the beam scanning step is implemented so that the insulator is deposited in the cut section through the reaction generated by the insulator depositing gas with respect to the processing beam. Thereby, the insulator depositing gas is made to react with the processing beam in the cut hole so that the cut hole is filled with the insulator. As a result, the electrical insulation of the conductor can be further ensured, and the processing efficiency can be increased.
It is preferable that a tilting generated in the cut end surface by the focused beam be cancelled in the beam scanning step and the cleaning beam scanning step and the semiconductor apparatus be tilted instead in such manner that the cut end surface is vertical to the surface of the insulation film.
It is preferable that a direction of the beam irradiation be set to such a direction that the cut end surface is vertical to the surface of the insulation film in the beam scanning step or the cleaning beam scanning step. Thereby, the side surface of the cut hole is orthogonal to the surface of the conductor so that the attachment of the conductive residue to the side surface can be controlled and the electrical insulation can be further ensured.
According to the present invention, the short cut resulting from the dispersion of the conductive residue can be prevented, and the electrical insulation can be realized by cutting the copper wiring. Further, it becomes unnecessary to use the assist gas in the cutting process. Other than the foregoing effects, the conductor can be electrically insulated while the side etching generated from the interlayer insulation film formed from a material having a low dielectric constant is prevented. Even a plurality of conductors stacked on one another can be cut without generating the short circuit among the conductors.
The cutting process can be successfully carried out in any conductor material other than copper.
As described, the present invention relates to a technology for cutting the conductor using the beam and thereby electrically insulating the conductor, and is particularly effective for the semiconductor apparatus in which copper is used increasingly often as the conductor material. The present invention can also be applied when a conductor in a circuit substrate is cut.
These and other objects as well as advantages of the invention will become clear by the following description of preferred embodiments and explicit in the appended claims of the invention. Many other benefits of the invention not described in this specification will come to the attention of those skilled in the art upon implementing the present invention.
Hereinafter, preferred embodiments of a semiconductor processing method and an apparatus for implementing the method according to the present invention are described referring to the drawings.
A semiconductor processing method (apparatus) according to an embodiment 1 of the present invention is described referring to
First, a case of implementing the zigzag scan using the processing beam 3 once using the processing bema 3 is described referring to
The processing beam 3 is pulse-irradiated on the interlayer insulation film 1 at sufficiently short time intervals. In the drawings, a reference symbol 3a denotes an irradiation region of each pulse intermittently irradiated and constituting the processing beam 3. The irradiation region is referred to as a spot 3a. The processing beam 3 is focused so that the spots 3a are sufficiently smaller than the processing box 4 in terms of area. The processing beam 3 is intermittently pulse-irradiated so that the spots 3a that are temporally adjacent overlap one another.
When a burning/cutting step using the processing beam 3 is implemented, a trace of the processing beam 3, which is positioned at a final scanning column of all of scanning columns of the processing beam 3, forms a final cut surface 4a of the processing box 4. As shown in
The processing box 4 is disposed so that the final cut surfaced 4a faces the conductor 2, and more specifically, in a direction where a scanning column direction traverses a cut section of the conductor 2. Thereby, a region 2c of the conductor 2 in contact with the final cut surface 4a is electrically isolated from a region 4d not in contact therewith and other wiring structures. In
A reference symbol 1b denotes a side surface of the cut hole 1a and has a shape tilted slightly inward relative to the irradiation direction as a result of a characteristic of the processing beam 3 irradiated in the focused manner. In the example shown in
During a period when the irradiation of the processing beam 3 is commenced until it is terminated, the processing beam 3 is irradiated on the interlayer insulation film 1 and the conductor 2 so that the interlayer insulation film 1 and the conductor 2 are cut. At that time, a cut depth is increased as the number of the spots 3a subjected to the irradiation in a superposing manner is increased. The processing beam 3 is irradiated on the spots 3a in the state where they partially overlap with one another. Because of that, the cutting depth at a point at which the cutting process is terminated (positioned on the final-cut-surface-4a side) is larger than the cutting depth a point at which the cutting process is commenced (positioned on another cut-surface side other than the final-cut-surface-4a side). Therefore, when the cut surface is observed, a bottom section thereof has a shape tilted from the cutting commencing point toward the cutting terminating point (final cut surface 4a).
In the interlayer insulation film 1 and the conductor 2 thus subject to the cutting process, a conductive residue 2b generated by cutting the conductor 2 is attached to the side surfaces 1b of the cut hole 1a as shown in
The irradiation of the processing beam 3 is characterized in the following conflicting functions, which are: generate the conductive residue 2b from the conductor 2; and vaporize/eliminate the conductive residue 2b attached to the cut surface. A performance of eliminating the conductive residue 2b depends on the dosage of the processing beam 3 in the same manner as the amount of the generated conductive residue 2b. The performance of eliminating the conductive residue 2b is improved as the dosage is increased. Provided that a predetermined cutting depth is obtained, the irradiation time of the processing beam 3 on the respective spots 3a is extended as the number of the repeated scans using the processing beam 3 in the processing box 4 is lessened, as a result of which the dosage supplied to the spots 3a is increased. Thereby, the conductive residue 2b attached to the cut end surface 2a can be more efficiently eliminated by the processing beam 3. More specifically, the cut end surface 2a is more refined as the scan using the processing beam 3 is repeated at a reduced frequency, and the cut end surface 2a can be even more refined when the scan is implemented once.
Because the scan (zigzag scan) is implemented once in the case of the example shown in
However, in the case of securing the dosage in a large number of irradiations, the cleaning effect is weakened, which increases the possibility that the generated conductive residue 2b is attached. Therefore, in the constitution shown in
Next, a case of implementing the zigzag scan using the processing beam 3 a plurality of times is described referring to
In the foregoing description, the scan using the processing beam 3 follows the zigzag path. In place of that, the scan may be performed in a same direction, for example, as shown in a plan view of
In the embodiment 1, there is not need to use the assist gas, which naturally eliminates the need to provide a device of ejecting the assist gas. Accordingly, the apparatus constituted in a simplified manner can be conveniently used in comparison to the method in which the assist gas is used.
In recent years, an interlayer insulation film formed from a material having a low dielectric constant is sometimes used, and it has been pointed out that side etching generated from the assist gas becomes more remarkable when the assist gas is used when the interlayer insulation film formed from the aforementioned material is beam-processed. More specifically, the interlayer insulation film 1 formed from the material having the low dielectric constant generates a larger reaction with the assist gas, which advances the side etching in the horizontal direction more rapidly than the advancement of the processing beam. The side etching is such an unnecessary etching phenomenon in the horizontal direction. The semiconductor processing method according to the embodiment 1, on the contrary, does not at all undergo such an inconvenience (side etching) because the assist gas is not used.
A method (apparatus) of processing the semiconductor apparatus according to an embodiment 2 of the present invention is described referring to
When the conductor 2 is exposed, settings of conditions for the beam irradiation, such as the adjustment of an energy of the irradiated beam and the adjustment of a beam scanning speed, are adjusted so that the exposed surface of the conductor 2 becomes flat. Next, the processing box 4 is disposed on an upper side of the exposed conductor 2. When the processing box 4 is set, the final cut surface 4a of the processing box 4 is arranged to fall on the side surface 1b (cut end surface) of the cut hole 1a or partially overlap the inner side of the side surface 1b (inner side of the interlayer insulation film 1). The state in which the processing box 4 is disposed is shown in a sectional view of
The conductor 2 is cut as a result of the beam irradiation thereon by means of the scanning method described in the embodiment 1 referring to
In order to ensure the electrical isolation of the conductor 2, it is important to electrically isolate the region 2c disposed on the cut-end-surface-2a side of the conductor 2 and a conductive residue 2b1 disposed thereabove (on the surface of the interlayer insulation film 1) from each other. Therefore, in the embodiment 2, the cut end surface 2a is disposed on the side surface 1b of the cut hole 1a. Thereby, the side surface 1b of the cut surface 1a, to which the conductive residue 2b is hardly attached, is interposed between the region 2c and the conductive residue 2b. Therefore, when a height of the side surface 1b (depth of the cut hole 1a) has a sufficiently large value, the region 2c and the conductive residue 2b1 can be reliably electrically isolated from each other.
It is unnecessary to use the assist gas in the embodiment 2 as in the embodiment earlier, which naturally eliminates the need to use the assist gas ejecting device. As a result, the apparatus constituted in a simplified manner in comparison to the method not requiring the assist gas can be used. In the semiconductor processing method (apparatus) according to the embodiment 2, wherein the assist gas is not used, the inconvenience mentioned earlier (side etching) is not at all generated.
In the semiconductor processing method (apparatus) according to the embodiment 2, it is important to prevent the conductive residue 2b from attaching to a conductor 2A provided underneath the conductor 2 to be cut in order to avoid the short circuit or any damage with respect to the conductor 2A. In order to do so, a cutting amount B in the vertical direction is controlled. Parameters for controlling the cutting amount B in the vertical direction include the dosage, a spot irradiation time of the processing beam 3 (a length of time when the processing beam is retained on the respective spots 3a), an interval between the adjacent spots 3a, and a processing-box length A, which should be set to optimum values. For example, there is no problem when the dosage: 1 nC/μm2 retaining time on the spots 3a: 10 μsec, interval between the adjacent beam spots 3a: 0.01 μm, and processing-box length A: 0.5 μm because the cutting depth B can be controlled to be approximately 1.0 μm.
In the embodiment 2, the side surface 1b of the cut hole 1a formed in the interlayer insulation film 1 was used in order to electrically isolate the conductor 2 from the conductive residue 2b. In such a constitution, the electrical isolation is not insufficient resulting in the short circuit unless the sufficient depth of the cut hole 1a (height of the side surface 1b) can be ensured. Further, it becomes necessary to positionally adjust the side surface 1a and the final cut surface 4a of the processing box 4 with a high accuracy, which requires an additional labor. In contrast to the embodiment 2, the conductor 2 can be electrically isolated from the conductive residue 2b regardless of the depth of the cut hole 1a and without accurately positionally adjusting the side surface 1a and the final cut surface 4a in an embodiment 3 of the present invention. Below is described a method (apparatus) of processing the semiconductor apparatus according to the embodiment 3.
As shown in
When the conductor 2 is exposed, the settings of the conditions for the beam irradiation, such as the adjustment of the beam irradiation energy and the adjustment of the beam scanning speed, are adjusted so that the exposed surface of the conductor 2 becomes flat. As shown in
Then, the conductor 2 is cut from an upper part of the insulation thin film 5 using the processing beam 3 as shown in
In the method according to the embodiment 3, the exposed surface of the conductor 2 is covered with the insulation thin film 5. Therefore, though the final cut surface 4a is separated from the side surface 1b and disposed at the center of the bottom section of the cut hole 1a, the presence of the insulation thin film 5 between the region (region on the final-cut-surface-4a side) 2c of the conductor 2 and the conductive residue 2b1 thereabove enables the region 2c and the conductive residue 2b1 to be reliably electrically isolated from each other. Thereby, the depth of the cut hole 1a is irrelevant to the improvement of the electrical isolation between the conductor 2 and the conductive residue 2b1, which alleviates the requirement of the cutting amount B in the vertical direction and threby facilitates the process. Further, an energy level of the processing beam 3 can be reduced because it is not necessary to increase the depth of the cut hole 1a.
As shown in
An embodiment 4 of the present invention relates to a method (apparatus) of processing the semiconductor apparatus wherein the cut surface of the conductor is cleaned and then electrically isolated. A sectional view of
Therefore, the processing box 4 is reset after the conductor is cut as shown in
After the processing box 4 is set, a cleaning beam 3′ is irradiated again on the cut end surface 2a so that the conductive residue 2b on the cut end surface 2a is eliminated. The cleaning beam 3′ is irradiated in the same manner as the processing beam 3 in the embodiments 1 and 2. In such a manner, the conductive residue 2b on at least the cut end surface 2a can be eliminated, and the region 2c of the conductor 2 can be thereby electrically isolated from the region 2d and other wiring structures without fail. When the cleaning process is carried out, the cutting depth in the vertical direction is controlled by adjusting conditions for irradiating the cleaning beam 3′ so that the conductor 2A underneath the layer to be cut can be protected from any damage.
In the embodiment 4, the processing box 4 for the cleaning process is additionally set. In a method (apparatus) of processing the semiconductor apparatus according to an embodiment 5 of the present invention described below, the labor of additionally setting the processing box 4 is saved by using the processing box 4 set for the cutting process also as the processing box 4 for the cleaning process. In order to use the processing box 4 for the additional purpose, the processing box 4 is provided with a shift function set therein, which enables the processing box 4 to be shifted with a shape thereof being maintained. In the embodiment 5, the shift function of the processing box 4 (shift function of the processing beam 3) is used so as to clean the cut end surface 2a.
A sectional view of
Next, as shown in
In order to deal with the possibility, as shown in
The processing box 4 set for the cutting process is arranged to have a width larger than a box width of the conductor 2 (width of the final cut surface 4a) to be suitably used for the cleaning, which realizes the reliable cleaning.
Thereby, the spots 3a of the cleaning beam 3′ are gradually moved toward the final cut surface 2a. Then, when the processing beam is irradiated on the spots 3a once in the final cut surface 4a and the cut end surface 2a is thereby cleaned, the shift of the processing box 4 and the beam irradiation on the spots 3a are terminated. A horizontal arrow in
The conductive residue 2b on the cut end surface 2a of the conductor 2 is eliminated in the cleaning process thus implemented, and the region 2c of the conductor 2 is thereby electrically isolated from the region 2d and other wiring structures. A reference symbol C denotes a cleaning surface.
In the case of the present embodiment, the shift function of the processing box 4 is utilized, and the removal of the conductor and the cleaning process are basically implemented through the consecutive irradiations of the processing beam 3 and the cleaning beam 3′. Therefore, any damage generated on the conductor and the like by the irradiations of the processing beam 3 and the cleaning beam 3′ can be limited to a minor level. As a result, any possible damage on the conductor 2A beneath the conductor to be cut can be reduced without tightening the beam conditions for controlling the depth.
In a method (apparatus) of processing the semiconductor apparatus according to an embodiment 6 of the present invention, the present invention is implemented to the formation of a through hole at the central part in the width direction of the conductor 2 in place of the cutting process of the conductor 2 having the large width. Here is described an example in which a cut hole 1a′ having a through-hole shape is formed in two conductors having a large width. A section view of
Next, as shown in
Next, as shown in
An apparatus for processing the semiconductor apparatus according to an embodiment 7 of the present invention relates to an insulator deposit subsequent to the cutting process of the conductor.
Next, as shown in
As described, according to the present embodiment, the cutting process of the conductor 2 and the deposit of the insulator 9 are carried out in a sequence of processing processes. When the cutting process and the deposit of the insulation are thus serially carried out, any burden in the operation and the processing time can be reduced.
In some cases, two kinds of gasses are used when the insulator 9 is deposited. A first gas is supplied in advance so that the conductive residue 2b is ejected from the cut hole 1a. Around the time when the cutting process of the conductor 2 is completed, a second gas is supplied so that the insulator is deposited at the cut section, and the insulation is completed. As the first gas is used, for example, oxygen. As the second gas is used, for example, TMCTS (Tetra Methyl Cyclo Tetra Siloxane).
In an apparatus for processing the semiconductor apparatus according to an embodiment 8 of the present invention, a stage 10 of the processing apparatus is tilted so that the sectional surface is finally orthogonally formed. Generally, the processing beam 3, which is focused, has a conical beam shape. The processing beam 3 having the beam shape is used for the cutting process, as shown in
Therefore, according to the present embodiment, the stage 10 is tilted so that the cut end surface 2a′ formed by the processing beam is orthogonal to the surface of the conductor 2 as shown in
In an embodiment 9 of the present invention, the processing beam 3 of the processing apparatus is tilted so that the cut surface is finally orthogonally formed. As described in the embodiment 8, the processing beam 3 has the conical beam shape, which is shown in
While there has been described what is at present considered to be preferred embodiments of this invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of this invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-291305 | Oct 2004 | JP | national |
