Patent Application
20100043964
The present invention relates to a bonding method and bonding apparatus which improve the application of an adhesive onto a substrate before bonding, in order to manufacture a recording medium in which a pair of substrates are bonded together by means of an adhesive.
Currently, in the field of optically readable recording media such as optical disks or magneto-optical disks, disks having a wide variety of different specifications are used, for instance, there are read-only media and media which enable rewriting of the recorded information. An optical disk such as a DVD, for example, is basically manufactured by providing information recording regions on one side or both sides of two substrates, and bonding the substrates together by means of an adhesive. The adhesive layer for bonding the substrates together is required to have an extremely accurate thickness in order that information can be read and written accurately by laser.
One example of a procedure for manufacturing a bonded disk of this kind is described now with reference to
As shown in
The chuck E holding one substrate P is closed inside the space that has been reduced to vacuum pressure, and the substrates P are lowered, in addition to which a pressing section T is lowered and caused to apply pressure by a drive source, such as a cylinder, thereby bonding the one substrate P to the other substrate P. A vacuum pressure is created during bonding in order to eliminate as far as possible any gas molecules present between the surfaces that are to be bonded.
Thereupon, as shown in
In a disk which is manufactured by bonding together substrates onto which an adhesive has been applied as described above, when laser light used for reading and writing information is irradiated onto the disk, then it is necessary for the disk to be a flat disk which is free of warping or distortion, in such a manner that stable spots are formed. Consequently, in a disk of this kind, it is desirable that the film thickness of the adhesive layer during bonding should be as uniform as possible.
However, if adhesive is applied by spin coating as described above, then the adhesive on the rotating substrate is caused to spread due to centrifugal force. Therefore, the thickness of the film in the outer circumferential portion becomes thicker compared to the inner circumferential portion of the substrate (for example, approximately 10 μm), and hence it is difficult to achieve a uniform film thickness over the whole of the substrate.
One technology which has been proposed in order to resolve this by applying resin uniformly by spin coating is a method in which ultraviolet light is irradiated onto the resin on the disk thereby changing the viscosity of all of the resin, during spin coating and before halting the rotation of the disk, whereby the flowing movement of the resin toward the outer circumferential portion is restricted (see Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-open No. 2002-319192
It is known that the variation (fluctuation) of the film thickness of the adhesive layer in the circumferential direction (in-circumference variation) becomes greater from the inner circumference of the disk toward the outer circumference. However, with increase in the recording density in recent years, as in the case of HD (High Definition DVD) and BD (Blu-ray Disc), the uniformity of the adhesive layer required in the final disk has become subject to extremely strict requirements. For example, in a conventional DVD, the range of variation is approximately 30 μm, but in HD or BD disks, greater accuracy of approximately 10 μm is necessary. Consequently, the requirement for suppressing in-circumference variation becomes even greater.
Such in-circumference variation is particularly liable to occur when the adhesive layer is required to be formed thickly, but if the viscosity is changed by irradiating ultraviolet light onto the resin during spin coating as described in Patent Document 1, then it is difficult to control the thickness of the applied film at the same time as suppressing in-circumference variation.
Furthermore, there are cases where a method is used in which the substrates are left at atmospheric pressure after bonding, in order to squeeze out air bubbles generated during the bonding process by pressurization at atmospheric pressure. However, when the substrates are left at atmospheric pressure in this way, there is an increase in the in-circumference variation of the adhesive layer. This is thought to be because the time from the deposition of the adhesive until its curing becomes long and hence there is increased chance of the adhesive flowing during the curing process. For example,
Moreover, when adhesive is applied by spin coating, the surplus adhesive is scattered, as described above. The adhesive scattered in this way is recycled and reused. However, if ultraviolet light is irradiated onto the whole surface of the substrates during rotation as in Patent Document 1, then the scattered adhesive will include adhesive which has been irradiated with ultraviolet light and has started to be cured. In this case, in order to reuse the adhesive, it is necessary to separate the adhesive which has started to be cured from the adhesive which has not yet been cured, but this is extremely difficult.
The present invention was devised in order to resolve the aforementioned problems of the prior art, an object thereof being to provide a bonding method and a bonding apparatus whereby uniformity of the adhesive layer during application can be ensured, while suppressing variation in the adhesive layer during manufacture.
In order to achieve the object described above, the present invention is a bonding method for bonding a first substrate and a second substrate by means of an adhesive which undergoes curing by irradiation of electromagnetic radiation, characterized in comprising: applying the adhesive, at respectively different thicknesses, to one surface of the first substrate and one surface of the second surface; irradiating electromagnetic radiation onto the thinner of the adhesive applied to the first substrate and the adhesive applied to the second substrate; bonding together the surface of the first substrate to which the adhesive has been applied and the surface of the second substrate to which the adhesive has been applied; and irradiating electromagnetic radiation onto the adhesive between the first substrate and the second substrate.
Another mode of the present invention is a bonding apparatus for bonding together a first substrate and a second substrate by means of an adhesive which undergoes curing by irradiation of electromagnetic radiation, characterized in comprising: at least one application unit for applying the adhesive, at respectively different thicknesses, to one surface of the first substrate and one surface of the second substrate; a pre-irradiation unit for irradiating electromagnetic radiation onto the thinner of the adhesive applied to the first substrate and the adhesive applied to the second substrate; a bonding unit for bonding together the surface of the first substrate to which the adhesive has been applied and the surface of the second substrate to which the adhesive has been applied; and a post-irradiation unit for irradiating electromagnetic radiation onto the adhesive between the first substrate and the second substrate.
In the invention described above, since the thicknesses of the adhesive applied to the substrates that are to be bonded together are made different and electromagnetic radiation is irradiated onto the thinner of the adhesives before bonding, then the adhesive is cured, flowing movement is prevented, and in-circumference variation can be suppressed. Furthermore, the occurrence of exhaust gas is suppressed by the curing, and the amount of residual air bubbles can be reduced.
According to a further mode of the invention, after bonding together the surface of the first substrate to which the adhesive has been applied and the surface of the second substrate to which the adhesive has been applied, the substrates are left in an air atmosphere before irradiating electromagnetic radiation.
A further mode of the invention also comprises a resting unit for, after bonding together the surface of the first substrate to which the adhesive has been applied and the surface of the second substrate to which the adhesive has been applied, leaving the substrates at rest for a prescribed period of time in an air atmosphere, and before irradiating electromagnetic radiation
In modes such as those described above, since a resting time in an air atmosphere is allowed after bonding together the first substrate and the second substrate and before curing the adhesive, then it is possible to reduce the occurrence of air bubbles.
In a further mode of the invention, the application unit has at least one spin coating device for spreading the adhesive by causing the first substrate and the second substrate to rotate, control means being further provided for controlling the spin coating device such that the conditions of rotation are respectively different for the first substrate and the second substrate.
In modes such as those described above, it is possible to control the application thickness of the adhesive by changing the conditions of rotation, such as the rotational speed.
In a further mode of the invention, the application unit comprises at least one spin coating device for spreading the adhesive by rotating the first substrate and the second substrate, control means further provided for controlling the spin coating device such that the number of spreading operations is respectively different for the first substrate and the second substrate is also provided.
In modes such as those described above, the application thickness of the adhesive is controlled on the basis of the number of superimposed application operations performed, by changing the number of adhesive spreading operations, and therefore uniformity can be ensured readily even if the adhesive is formed thickly.
As described above, according to the present invention, it is possible to provide a bonding method and a bonding apparatus whereby the uniformity of an adhesive layer during application can be ensured and variation in the adhesive layer during manufacture can be suppressed.
Next, a preferred embodiment of the present invention (hereinafter, called “embodiment”) will be described with reference to the drawings. In the present embodiment, adhesive is applied to different thicknesses on a pair of substrates, and the adhesive is provisionally cured, whereupon the substrates are bonded together, and by this means in-circumference variation of the adhesive is suppressed.
Firstly, the composition of the bonding apparatus according to the present embodiment (hereinafter, called the “present apparatus”) will be described with reference to
The present apparatus comprises a first spin coating device 1, a second spin coating device 2, a pre-irradiation unit 4 constituted by a turntable 3, a bonding unit 5, a post-irradiation unit 6, and the like. The first spin coating device 1 is a device which coats an ultraviolet-curable adhesive B1 by spin coating onto one substrate P1 that is to be bonded. This first spin coating device 1 comprises a turntable 11 on which a substrate P1 is mounted and a drive source 12 which causes the turntable 11 to rotate, and it serves to cause adhesive B1 that has been dripped onto the substrate by an adhesive supply unit (not illustrated) to spread due to the rotation of the substrate P1.
The second spin coating device 2 is a device which coats an ultraviolet-curable adhesive by spin coating onto another substrate P2 that is to be bonded, as shown in
Furthermore, as shown in
The turntable 3 has a first introduction position 31, corresponding to the pre-irradiation unit 4, where the substrate P1 is introduced, a second introduction position 32 where the substrate P2 is introduced after being inverted by an inverting device (not illustrated) in such a manner that the bonding surfaces are facing each other, a bonding position 33 which corresponds to the bonding unit 5, an ultraviolet light irradiation position 34 which corresponds to the post-irradiation unit 6, and an output position 35 where the completed disk D is output to the next stage. This turntable 3 is composed so as to turn intermittently in accordance with the respective positions described above, by means of a drive mechanism (not illustrated).
The pre-irradiation unit 4 is a device which performs provisional curing by irradiating ultraviolet light in an air atmosphere onto the adhesive B1 which has been applied to the substrate P1. Here, “in an air atmosphere” means in an environment which inhibits curing, for example, an oxygen-containing gas atmosphere. In general, it is easiest to use normal air, but any environment which contains oxygen or which inhibits curing would be suitable.
The bonding unit 5 is a device which bonds together the substrates P1 and P2 in a vacuum. The bonding unit 5 has a vacuum chamber which is operated by an elevator mechanism, a vacuum source which reduces the interior of the vacuum chamber to a vacuum, and a pressing unit which is operated by an elevator mechanism and applies pressure to the substrates P1 and P2, but since this involves commonly known technology, it is not described further here.
The post-irradiation unit 6 is a device which irradiates ultraviolet light in a vacuum onto the bonded substrates P1 and P2, by means of a UV irradiation device, and thereby fully cures the adhesives B1 and B2 between the substrates P1 and P2. The post-irradiation unit 6 also comprises a vacuum chamber which is operated by an elevator mechanism and a vacuum source which reduces the interior of the vacuum chamber to a vacuum pressure, and the like, but since this involves commonly known technology, it is not described further here.
Irradiation is carried out in a vacuum in order to remove any factors which may inhibit curing, such as the presence of oxygen, or the like, but it is not absolutely necessary to carry out irradiation in an environment which is free of oxygen. This is because the adhesive bonding surfaces of the substrates P1 and P2 after they have been bonded together form a substantially unified body, which is cured regardless of the atmosphere. If bonding is carried out in an air atmosphere, then the end face on the outer circumference comes into contact with the air, but this portion reaches full curing in the course of storage (over several days) on the manufacturing line. If irradiation is carried out in a vacuum as described above, then a merit is obtained in that the end face on the outer circumference can be cured more reliably. A similar beneficial effect can be obtained by removing (purging) oxygen with an inert gas (N2).
The supply volume of adhesive from the adhesive supply unit, the rotation of the turntable and speed of rotation of same, the emission of light by the irradiation devices, and the operation of the heating device, the elevator mechanism and the vacuum source, and the like, are controlled by means of a control device. This control device may be realized, for example, by a dedicated electronic circuit or a computer which is operated by a prescribed program. Therefore, one mode of the present invention is a computer program for controlling the operation of the present apparatus according to the sequence described below, or a recording medium which stores such a computer program.
The substrate bonding procedure carried out by the present apparatus described above will now be explained with reference to
For the substrate P1, in the first spin coating device 1, as shown in
Thereafter, as shown in
With a general ultraviolet-curable resin (adhesive), if ultraviolet light is irradiated onto the whole surface in an air atmosphere, then full curing does not occur at a normal irradiation intensity. This is because the presence of air in the vicinity of the surface of the resin inhibits the curing process. In other words, when ultraviolet light is irradiated in an air atmosphere, it is possible to perform provisional curing while maintaining the adhesive on the surface. For example, it has been demonstrated that full curing is not carried out even under conditions of 1000 mW at 1 to 2 seconds. However, the irradiation conditions during provisional curing are not limited to those described above.
Adhesive is applied to the other substrate P2 by the second spin coating device 2. For instance, the application pressure is 0.2 MPa, the application time is 0.15 sec, and the adhesive is distributed for 1 sec by high-speed spinning at 10,000 rpm (step 304). As shown in
Next, an ultraviolet-curable adhesive is applied dripwise again on top of the adhesive of the substrate P2 on which the cured portion has been formed, and by rotating the turntable 11 at high speed, the adhesive is caused to spread (step 306). For instance, using the same adhesive as that used in the first application, the application pressure is 0.2 MPa, the application time is 0.6 sec, and the adhesive is spread for 1 sec by high-speed spinning at 4000 rpm. In this case, the adhesive is spread by applying heat locally using the heating device 24. For instance, a spot heater is used as the heat source, the wavelength is 700 to 3000 nm, the output setting is 350 W, the heating range is 40 mm to 60 mm in the radial direction of the substrate P2, and the heating time is 1 sec.
The adhesive which is warmed, thereby reducing the viscosity of the adhesive, is distributed and spread readily to the outer circumference as a result of the centrifugal force created by the rotation of the substrate P2. Alternatively, the adhesive receives thermal energy, and the volatilization volume is raised. Therefore, the adhesive remaining at the outer circumference becomes thinner, thus suppressing increase in the thickness of the adhesive, and therefore it is possible to achieve a uniform thickness throughout the substrate. It is also possible to apply a heated air flow to the outer circumference simultaneously, so as to supplement the heating of the adhesive.
As described above, the adhesive B2 on the substrate P2 is made thicker and the adhesive B1 on the substrate P1 is made thinner, in accordance with the rotating conditions set for spin coating and the number of application operations. Thereupon, the substrate P2 is inverted by the inverting device (step 307), and introduced over the substrate P1 in such a manner that the application surface of the adhesive B2 is facing downwards (step 308).
Thereupon, the two substrates P1 and P2 are conveyed to the bonding unit 5, and bonding is carried out in a vacuum similarly to the prior art (step 309). The substrates P1 and P2 which have been bonded together are conveyed to the post-irradiation unit 6, and ultraviolet light is irradiated onto the whole surface in a vacuum, thereby fully curing the adhesives B1 and B2 (step 310). In this case, ultraviolet light is irradiated from the side of the substrate P1 on which the semi-transparent metal film has been sputtered. The disk D which is completed by curing of the adhesive is output from the output position 35 (step 311).
According to the present embodiment described above, by making the adhesive B1 which is applied to the substrate P1 that is to be bonded thinner than the adhesive B2 which is applied to the substrate P2, and provisionally curing the adhesive B1, it is possible to enhance the effect in suppressing flowing movement of the adhesive B1, as well as being able to suppress in-circumference variation in the thickness of the adhesive layer after the substrates P1 and P2 have been bonded together.
If the adhesive B1 is provisionally cured, then since a portion of the region is cured previously, the occurrence of expelled gas when the substrates P1 and P2 are bonded together in a vacuum is suppressed, and the occurrence of remaining air bubbles can be reduced. Moreover, the irradiation of ultraviolet light in order to achieve provisional curing is carried out when spin coating has finished and there is no scattering of the adhesive B1, and consequently, the recovered adhesive can be used without problem since none of the adhesive scattered during spin coating will have started to cure. Performing irradiation at a separate location to spin coating also provides similar beneficial effects. Since the spot irradiation which is carried out during rotation of the substrate P2 only involves irradiation onto a limited partial region, then there is no problem in recovering the adhesive.
Furthermore, the thickness of application can be adjusted easily by altering the application amount of the adhesive, the conditions of rotation, and the number of spreading operations. In particular, if it is wished to increase the application thickness, then a uniform thickness can be ensured by forming a cured portion and then applying adhesive in a superimposed fashion while heating, as described above, and consequently the beneficial effects in suppressing in-circumference variation can be enhanced.
The present invention is not limited to the embodiments described above. For example, the extent of curing of the one adhesive prior to bonding is not limited to that specified above. Consequently, even if the thinner adhesive which has been applied to one substrate is fully cured rather than provisionally cured, by means of various techniques such as irradiating in a vacuum, irradiating after purging with an inert gas, increasing the irradiation intensity, increasing the irradiation time, or the like, it is still possible to obtain beneficial effects in suppressing in-circumference variation after bonding. In this case, adhesiveness during bonding is ensured by the other adhesive which has not been cured.
Since in-circumference variation can be suppressed by provisional curing, then it is possible further to suppress the occurrence of air bubbles by ensuring a rest time after bonding. For instance, as shown in
Adhesive which is applied thinly becomes less liable to flow, the smaller its thickness. For instance, if adhesive is applied in an extremely thin layer (of the order of several microns; a thickness whereby a cured portion is formed by spot irradiation), then flowing movement is suppressed and a beneficial effect in suppressing in-circumference variation after bonding is obtained. Provisional curing is performed in order to enhance this effect of suppressing in-circumference variation, but if an adhesive is applied extremely thinly, then there are cases where it is possible to suppress in-circumference variation in a similar manner to that described above, even if provisional curing is not carried out.
Furthermore, the adhesive used is not limited to an ultraviolet-curable resin, and it is also possible to use various adhesives, such as resins which are used by other sources of electromagnetic radiation (including laser light), or thermally curable resins, or the like. Consequently, various different types of electromagnetic radiation can be irradiated, such as ultraviolet light, infrared light (including heat), laser light of a prescribed wavelength, or the like, depending on the type of resin used. In the embodiment described above, in order to apply the adhesive to a large thickness, a cured portion is formed and adhesive is then applied again in a superimposed fashion, but it is also possible to achieve a large thickness by simple superimposed application, or by a single application operation in which the dropped volume of adhesive is increased. It is also possible to omit heating for spreading the adhesive. Furthermore, bonding does not necessarily have to be carried out in a vacuum.
There may be one or a plurality of application units for applying adhesive. For example, it is possible to use a common spin coating device for the first substrate and the second substrate. Superimposed application may be carried out using a plurality of spin coating devices. The application unit is not limited to a spin coating device and includes any current or future device which can be used to apply an adhesive.
Furthermore, the pre-irradiation unit may be situated at any position, provided that it is after the spin coating step and before the bonding step. For example, it may be disposed in the spin coating device, or in the conveyance path from the spin coating device to the turntable. It may be provided for either one of the substrates P1 and P2 on the turntable, or for both of the substrates.
The size, shape and material, and the like, of the substrate can be chosen freely, and the present invention can be applied to any substrate which may be used in the future. Consequently, as well as being applicable to disks for recording media of any format, it may of course also be applied to write-once read-many type recording media and rewriteable recording media. Furthermore, in addition to disks for recording media, the present invention can also be applied to any substrates which are bonded together by means of adhesive. In other words, reference to “substrate” in the claims is not limited to a circular disk-shaped substrate, or the like, but rather is a broad concept which includes flat plane-shaped products.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-263943 | Sep 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/001024 | 9/20/2007 | WO | 00 | 3/27/2009 |
