KR101518122B1 - Polarizing phase difference plate and laser processing machine - Google Patents

Abstract

Provided is a transmission type polarizing retarder which is easy to fabricate and has a small loss of transmitted light amount of primary external light, and a laser processor using the same.
A polarizing retardation plate 100 is formed on at least one main surface of a substrate 102 with a diffraction grating having the same material as the substrate 102 and a constant period P in which a plurality of convex portions 103 are aligned, Structural birefringence is used. The period P of the diffraction grating satisfies P < / n by using the wavelength? Of the incident light and the refractive index n of the substrate material. The cross-sectional shape of the convex portion 103 is formed into a tapered shape 106 from the bottom portion to the tip portion. ZnS is used as the substrate material.

Description

TECHNICAL FIELD [0001] The present invention relates to a polarization phase difference plate and a laser processing apparatus,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a polarizing retarder for original external light using a structure birefringence generated from a fine periodic structure. The present invention also relates to a laser processing machine using the polarized light retarder.

BACKGROUND OF THE INVENTION [0002] It is known that a conventional laser machining apparatus that performs machining such as hole drilling on a workpiece such as a print substrate has the following configuration. One laser beam is split into two laser beams by a first polarizing beam splitter, one laser beam is passed through a mirror and the other laser beam is irradiated by a first galvanometer scanner. Axis direction to guide the two laser beams to the second polarizing beam splitter, and then the second galvanometer scanner scans the workpiece in the XY-2-axis direction to process the workpiece on the XY stage have. Here, the laser light transmitted through the first polarizing beam splitter is reflected by the second polarizing beam splitter, while the laser light reflected by the first polarizing beam splitter constitutes an optical path passing through the second polarizing beam splitter. This laser processing machine can perform two machining operations at the same time by scanning two laser beams separately (see, for example, Patent Document 1). On the other hand, the light source of such a laser processing machine is mainly made of a carbon dioxide gas laser.

However, in the above-described conventional laser processing machine, since the two laser beams irradiated to the workpiece are linearly polarized light whose polarization direction is 90 ° different from each other, depending on the material of the workpiece, There is a problem that this becomes an ellipse. Further, there is a problem that the major axis direction of the elliptical machining hole differs depending on which laser beam has been machined. The phenomenon that the machining holes become elliptic is remarkable when the workpiece is a copper foil.

In order to cope with such a problem, it is conceivable to insert a commercially available reflection type retardation plate into the optical path between the second polarizing beam splitter and the galvanometer to circularly polarize the light. However, The galvanometer scanner is spaced apart, so that the range in which the first galvanometer scanner can be scanned is narrowed, and the lens aberration becomes large, and the processing quality is deteriorated.

For this reason, it is required to make linearly polarized laser light circularly polarized or elliptically polarized by providing a transmission type polarizing retarder. As a polarizing retarder, it is known to use a structure birefringence generated from a fine periodic structure (for example, Patent Documents 2 to 4, etc.). Particularly, in Patent Documents 2 and 3, the convex portion is formed into a taper shape to suppress Fresnel reflection. In Patent Document 4, zinc selenide (ZnSe) capable of transmitting primary external light is used as a substrate material, and Fresnel reflection is reduced by using YF ₃ on the surface.

In the case of producing a polarizing retarder using birefringence characteristics of a material, cadmium sulfide (CdS) can be exemplified as a material capable of transmitting primary external light.

International Publication No. 2003/082510 Japanese Patent Laid-Open No. 2007-178793 Japanese Patent Application Laid-Open No. 2005-044429 Japanese Patent Application Laid-Open No. 2011-232551 Japanese Patent Application Laid-Open No. 2006-258914 Japanese Patent Application Laid-Open No. 2008-096892 Japanese Patent Application Laid-Open No. 2008-279597 Japanese Patent Application Laid-Open No. 2006-323059 Japanese Patent Application Laid-Open No. 2005-177788

However, since cadmium sulfide generates toxic hydrogen sulfide by the incorporation of acid, it is difficult to handle from the viewpoint of environmental measures at the place of production and place of use.

Patent Document 2 uses a thermoplastic resin as a substrate material, and Patent Document 3 uses glass as a substrate material, so that any material absorbs the original external light.

In Patent Document 4, since ZnSe is used, toxic gas is generated at the time of processing. Because of this, special disposal facilities are needed and can not be easily processed. Further, since YF ₃ deposited on the surface has a high water absorption rate, when a high energy laser beam is transmitted, a thermal lens is generated due to a temperature rise due to absorption. A thermal lens is a phenomenon in which a temperature distribution is generated in the optical element due to a temperature rise due to absorption, and a lens effect is generated. In the case of a laser processing machine, if a thermal lens is generated, the light converging point of the beam is spaced from the surface of the workpiece, resulting in a poor quality of the workpiece.

An object of the present invention is to provide a transmission type polarizing retarder which is easy to fabricate and has a small loss of transmitted light quantity of primary external light.

It is also an object of the present invention to provide a laser processing machine capable of forming a machining hole of a garden shape in a system in which one laser beam is split into two laser beams to perform simultaneous processing at two locations.

According to one aspect of the present invention, there is provided a diffraction grating having a constant period P in which at least one principal surface of a substrate is made of the same material as a substrate and in which a plurality of convex portions are aligned, As a polarizing retarder using structured birefringence,

The period P of the diffraction grating satisfies P < / n by using the wavelength? Of the incident light and the refractive index n of the substrate material,

Sectional shape of the convex portion is formed in a tapered shape from the bottom portion to the tip portion,

And ZnS is used as a substrate material.

In the present invention, it is preferable that a flat portion parallel to the main surface of the substrate is formed on the protruding portion of the convex portion.

In the present invention, it is preferable that the diffraction grating is formed on both surfaces of the substrate.

In the present invention, it is preferable that a plurality of the polarizing retarder are stacked.

In the present invention, it is preferable that the polarized light retardation plate is laminated so that convex portions of the diffraction grating face each other.

In the present invention, it is preferable that the convex portion of the diffraction grating is processed by dry etching.

In another aspect of the present invention, the laser beam emitted from one laser oscillator is split into two linearly polarized laser beams by a first polarizing beam splitter, the two linearly polarized laser beams are collected by a second polarizing beam splitter, A laser processing machine for making a laser beam incident on a mirror of a meter scanner and irradiating the laser beam onto a workpiece by scanning with a galvanometer scanner to perform hole drilling at a predetermined position of the workpiece,

And the polarizing retarder is provided between the second polarizing beam splitter and the galvanometer scanner.

According to the present invention, it is possible to obtain a transmissive polarizing retarder having a small loss of transmitted light amount of primary external light. In addition, with the laser processing machine using such a polarizing retarder, high quality laser processing can be realized.

1 is a perspective view showing a polarizing retarder according to Embodiment 1 of the present invention,
Fig. 2 is a cross-sectional view showing a processing procedure of a polarization retarder;
3 is a sectional view showing a polarized light retarder according to Embodiment 2 of the present invention,
4 is a cross-sectional view showing a polarization retarder according to Embodiment 3 of the present invention,
5 is a configuration diagram showing an example of a laser processing machine equipped with a polarizing retarder according to the present invention.

(Example 1)

1 is a perspective view showing a polarization retarder according to a first embodiment of the present invention. The polarization retardation film 100 has a substrate 102 and a diffraction grating formed on at least one main surface of the substrate 102 and formed of the same material as the substrate 102 and made of a single material. The diffraction grating is constituted by arranging a plurality of convex portions 103 extending in a straight line parallel to the x direction with a constant period P along the y direction.

When the light enters the diffraction grating along the z direction, the effective refractive index of the polarization component in the x direction (TE polarized light) and the effective refractive index of the polarization component in the y direction (TM polarized light) are different from each other, Birefringence occurs. As a result, a propagation velocity difference occurs between TE polarized light and TM polarized light, and elliptically polarized light is generated in accordance with a retardation (retardation) corresponding to the propagation velocity difference. When the phase difference is set to? / 2, the diffraction grating has a function equivalent to a quarter wave plate for converting linearly polarized light into circularly polarized light or converting circularly polarized light into linearly polarized light. When the phase difference is set to?, The diffraction grating has the same function as a half-wave plate that converts TE polarized light into TM polarized light or converts TM polarized light into TE polarized light.

It is known that the accurate retardation and transmittance of such a diffraction grating can be calculated almost accurately by the RCWA method (rigorous coupled-wave analysis method), which is one of the strict electromagnetic analysis methods.

In such a fine periodic structure, a condition in which incident light does not diffract and is transmitted as it is with '0-order light' is a case in which the period P satisfies the following formula (1).

Where? Is the wavelength of the light used and? Is the angle of incidence of the light to the polarizing retarder. Further, n is the refractive index of the base material constituting the polarizing retarder, and n _i is the refractive index of the medium (air) on the incident side. It can be seen from Equation (1) that by satisfying P < lambda / n, loss of the higher order diffracted light can be prevented even in the normal incident light with phi = 0 DEG.

The cross-sectional shape of the convex portion 103 is formed in a tapered shape 106 having an angle? From the bottom portion to the tip portion. On the other hand, when θ = 0 °, a taperless lamellar shape is obtained. An upper flat portion 104, which is parallel to the main surface of the substrate 102, is formed at the base of the convex portion 103. A bottom flat portion 105 parallel to the main surface of the substrate 102 is formed at the bottom of the convex portion 103 so as to be interposed between the convex portion 103 and the adjacent convex portion 103.

Next, the substrate material will be described. Germanium (Ge, refractive index n = 4.004) is a typical material that transmits original external light and is relatively easy to handle, which does not generate toxic substances even when processed. Table 1 below shows an example of design data when Ge is used as a substrate material. The RCWA method (rigorous coupled wave analysis method) was used for the calculation method. The wavelength of use was 9.29 占 퐉 for a carbon dioxide gas laser, and the refractive index of air was 1.

The cross-sectional shape of the convex portion 103 is a tapered shape 106 having a tilt angle? The depth H shown in Fig. 1 is in the range of 0 to 15 [mu m], the filling factor f is in the range of 0 to 1, the taper angle of the taper portion is in the range of 0 [deg.] To 90 [ And the dimension Lt of the upper flat portion 104 of the convex portion 103 is not less than 0.3 mm and the dimension of the bottom flat portion 105 is not less than 0.3 mm, Table 1 shows the results of searching for a condition in which the ratio of Te reflectance and Tm reflectance becomes the smallest among the conditions satisfying the condition that Lb is 0 mm or more.

The filling factor f is the ratio of the width W of the convex portion 103 to the period P at the position H / 2 which is half the height H of the convex portion 103, that is, f = W / P. The period P was set to 2.31 탆 as a value close to? / N in the range of P <? / N.

(Table 1), it can be seen that when Ge is used as the substrate material, the Te reflectance is much higher than 5% when the retardation is? / 2,? / 4,? / 8. It can be seen that the Tm reflectance increases when the retardation is? / 8.

It is known that the reflectance is reduced by providing the inclined portion in the convex portion 103, but it can be understood that the reflectance can not be sufficiently reduced in the original external light. Particularly, in the case of a low retardation such as? / 8, which is relatively easy to manufacture due to its small aspect ratio, the Te reflectance is 20% or more, which is not suitable for actual use.

The raw external material has a high refractive index, a large Fresnel reflection, and a low energy utilization rate as compared with a material for visible light (with a refractive index of about 1.5). Particularly, since the grating depth H becomes smaller as the phase difference plate is small in phase difference, the change in the refractive index in the thickness direction becomes abrupt and the reflectance increases, and the influence is large.

Next, a case where a material having a refractive index n of 2.2 or less such as zinc sulfide (ZnS) is used as a substrate material. (Table 2) shows the result of searching for the condition that the reflectance becomes the smallest with respect to ZnS, by using the same method as in the case of Ge in Table 1 (Table 1). At this time, the dimension Lt of the upper flat portion 104 of the convex portion 103 was 0.3 mm or more. The period P is set to 4.22 탆 as a value close to? / N in the range of P <? / N.

(Table 2), when ZnS was used as the substrate material, the Te reflectance and the Tm reflectance were all 1.4% or less when the retardations were? / 2,? / 4 and? / 8, , It can be seen that it is possible to obtain a phase difference plate for a raw external light having a good energy utilization efficiency. In particular, in the case of a low retardation such as lambda / 8, which is relatively easy to manufacture due to its relatively small aspect ratio, the Te reflectance is 1.4% and a phase difference plate suitable for actual use can be obtained.

In this way, when the raw external light is transmitted through the phase difference plate using the structural birefringence, the refractive index of the material is high, and therefore, the choice of the refractive index is important to suppress the Fresnel reflection.

Also in the period P, when the ZnS having a refractive index of 2.2 or less is used from the relationship of P < lambda / n, the period P can be made as large as about 4.22 mu m so that it can be processed by grinding machining or by an i line stepper It is possible to obtain an advantage that it can be relatively easily processed by using photolithography and etching.

Since ZnS does not generate toxic gas even when processed, special waste treatment facilities are unnecessary, and facility investment is suppressed.

In addition, when ZnS is used, since a layer of YF ₃ or the like is unnecessary on the lattice surface as in Patent Document 4, the cost is reduced. Since the absorption coefficient of YF ₃ is as high as about 10 [1 / cm], while the absorption coefficient of ZnS is 10 ^-5 [1 / cm 2], the YF ₃ layer is not used, The generation of the thermal lens can be prevented. As a result, since the reflectance is high, high-quality processing can be realized even in the copper foil processing in which high energy laser light is required.

Next, a method for manufacturing the polarizing plate 100 will be described. Here, a case in which the substrate is processed by using an etching process is illustrated in order to obtain a structure in which the flat portion 104 is provided at the base of the convex portion 103. [ If the flat portion 104 is provided on the protruding portion of the convex portion 103, the Fresnel reflection may increase because the refractive index change at the interface suddenly becomes discontinuous. In the case of ZnS, however, The reflectance is as small as 1.4% or less even if the dimension Lt of the flat portion 104 is about 0.3 占 퐉, so that it can be seen from the above analysis results that the reflectance is sufficiently suitable for use.

2 (a), a photoresist pattern is formed on the surface of the substrate 102 made of ZnS by lithography to form a flat shape of the flat portion 104 And a mask 110 corresponding to the mask pattern. Then, as shown in Fig. 2 (b), the substrate 102 is etched using the mask 110, and finally the mask 110 is removed.

When dry etching is used, the problem is to process the angle of the taper to a desired value with high precision. This time, the angle of incidence of the ion beam to the substrate was adjusted by using an ion milling apparatus which is almost isotropic dry etching so that the taper angle was adjusted to a desired value. It has been experimentally confirmed that this method can be processed into a sectional shape of a lambda / 8 phase difference lattice of (Table 2).

Alternatively, instead of ion milling, anisotropic dry etching such as reactive ion etching (RIE) may be used. The etching conditions may be such that the etching is performed in the lateral direction, that is, isotropic etching is performed, and the tapered shape is formed so that the width becomes narrower toward the upper part. Specifically, by changing the flow rate and pressure of the etching gas, it is possible to select from the anisotropic etching conditions to the isotropic etching conditions having a large undercut, whereby the taper angle? Is determined.

On the other hand, in the case where the convex portion 103 has a flat portion without a flat portion, it is necessary to grind the tapered portion 106. However, since the optical element of the laser processing machine has a diameter of about 50 mm, . On the other hand, the etching process is advantageous because the etching time can be shortened because the etching process can be performed on a large surface at a time.

(Example 2)

3 is a cross-sectional view showing a polarizing retarder according to Embodiment 2 of the present invention. The polarized light retardation plate 100 is formed on both surfaces of the substrate 102 in the same manner as the substrate 102 and has a diffraction grating formed on one surface of the substrate 102. In this embodiment, And a diffraction grating formed of a single material.

The diffraction grating on the upper surface of the substrate 102 and the diffraction grating on the lower surface of the substrate 102 are vertically symmetrical so that the position, period and taper shape of the convex portion 103 coincide with each other. By the two-sided installation of such a diffraction grating, the retardation of the polarization retardation plate 100 can be doubled as compared with that on one side.

In addition, by using zinc sulfide (ZnS) as a substrate material, a transmission type polarizing retarder having a small reflectance and a small loss in transmitted light can be obtained as in the case of Example 1.

Regarding the production method, dry etching such as ion milling and reactive ion etching can be used in the same manner as in the first embodiment.

(Example 3)

4 is a cross-sectional view showing a polarizing retarder according to Embodiment 3 of the present invention. In the present embodiment, two polarizing retardation plates 100 according to the first embodiment are used so that the convex portions 103 are opposed to each other to constitute a laminated polarizing retardation plate. The bonding method may be bonding, fusion bonding, mechanical pressure bonding, or the like.

Since the convex portion is exposed to the outside air in the polarizing plate 100 of Embodiment 1, foreign substances floating in the air may adhere to the convex portion and the valley portion of the convex portion. Once foreign matter is attached, it is difficult to remove. When a high-energy laser beam is passed in a state in which a foreign matter is adhered, foreign matter absorbs light, and a temperature distribution is generated in the optical element, thereby generating a thermal lens.

In this embodiment, since the two polarizing retarder plates 100 are superimposed so that the convex portions 103 face each other, the convex portions 103 do not touch the outside air, so that foreign matter such as trash floating in the air, Can be prevented from being attached to the base. As a result, even when high-energy laser light passes through, it is possible to prevent generation of a thermal lens, and high-quality processing can be realized in laser processing.

Further, when the laser beam passes through the laminated polarized light retarder, it passes twice through the same diffraction grating, and the retardation of the polarized light retarder 100 can be doubled. Conversely, when retardation such as the use of one polarizing retarder is obtained, half of the retardation of one diffraction grating is sufficient. (Table 2), the smaller the retardation, the smaller the aspect ratio of the convex portions, and hence the manufacture of the diffraction grating becomes easier.

As described above, an example in which two polarizing retardation plates of the one-sided diffraction grating are laminated has been described. However, in the configuration in which three or more polarizing retardation plates (Fig. 1) of one side diffraction grating are laminated, A configuration in which two or more polarization phase difference plates (FIG. 3) are laminated, a configuration in which a polarization phase difference plate (FIG. 1) of one side diffraction grating and a polarization phase difference plate (FIG. 3) of both side diffraction gratings are combined can be used as well.

(Example 4)

5 is a configuration diagram showing an example of a laser processing machine equipped with a polarizing retarder according to the present invention. As in Patent Document 1, a laser machining apparatus divides a single laser beam into two laser beams and performs simultaneous machining at two places in order to perform machining such as hole drilling in a workpiece such as a printed board .

The linearly polarized laser light 2 outputted from the CO ₂ laser oscillator 1 is converted into circularly polarized light by the retarder 3 and passed through the mirror 5 and then transmitted through the first polarizing beam splitter 6 to the two laser beams. One laser beam 7 passes through the mirror 5 and the other laser beam 8 is scanned by the first galvanometer scanner 11 in the YZ 2 -axis direction. The two laser beams 7 and 8 are introduced into the second polarization beam splitter 9 and joined together and are scanned in the XY 2 axis direction by the second galvanometer scanner 12, And the workpiece 13 on the XY stage 14 is processed.

The laser light 7 transmitted through the first polarizing beam splitter 6 is reflected by the second polarizing beam splitter while the laser light 8 reflected by the first polarizing beam splitter 6 is reflected by the second polarizing beam splitter 6. [ (9). This laser processing machine can perform two machining operations at the same time by scanning two laser beams separately.

In this laser processing machine, the polarization directions 7a and 8a of the laser beam passing between the second polarization beam splitter 9 and the second galvanometer scanner 12 are orthogonal to each other. Here, in Examples 1 to 3 And the longitudinal direction 111 of the convex portion 103 (x direction in FIG. 1) of the two laser beams 7 and 8, which are incident thereon, And is positioned so as to form an angle of 45 DEG with respect to the polarization directions 7a and 8a.

The 1/4 wavelength polarized light retardation plate 100 converts the linearly polarized laser beams 7 and 8 emitted from the second polarization beam splitter 9 into circularly polarized laser beams. As a result, two circularly polarized laser beams 7 and 8 can be irradiated to the work 13 to form a hole of a garden shape.

In this embodiment, since the transmission type polarization retarder 100 is used, it is not necessary to extend the optical path between the second polarizing beam splitter 9 and the second galvanometer scanner 12, There is no degradation in quality.

On the other hand, when the linearly polarized light is converted into the circularly polarized light by using the polarizing light retarder 100, although the phase difference of? / 4 is ideal, even if the circularly polarized light deviates from the? / 4 wavelength and the circularly polarized light becomes about 30% It has been experimentally proved that it is possible to drill a hole in the shape of a garden, so that it is not limited to the vicinity of? / 4. Of course, two retardation plates of? / 8 may be used to function as a quarter-wave plate. As shown in Fig. 3, a diffraction grating of? / 8 is provided on both surfaces of the substrate, And may function as a plate.

In the present embodiment, the case where the laser beam incident on the first polarization beam splitter 6 is circularly polarized light is described. However, linearly polarized light whose polarization direction is inclined at 45 with respect to the Y-axis is incident on the first polarizing beam splitter 6 .

1: laser oscillator 2: laser light
3: Retarder 5: Mirror
6: first polarizing beam splitter 7, 8: laser beam
9: second polarizing beam splitter 10: f? Lens
11: First galvanometer scanner 12: Second galvanometer scanner
13: workpiece 14: XY stage
100: polarized light retardation plate 102:
103: convex portion 104: upper flat portion
105: bottom flat portion 106: tapered shape
110: mask 111: length direction of the convex portion

Claims (7)

Wherein at least one main surface of the substrate is provided with a diffraction grating having a constant period P in which a plurality of convex portions are arranged and which is the same as the substrate and is made of a single material and the polarization birefringence As the retarder,
The period P of the diffraction grating satisfies P < / n by using the wavelength? Of the incident light and the refractive index n of the substrate material,
Sectional shape of the convex portion is formed in a tapered shape from the bottom portion to the tip portion,
As a substrate material, ZnS
Polarized light.
The method according to claim 1,
Wherein a flat portion parallel to the main surface of the substrate is formed on the peak portion of the convex portion.
3. The method according to claim 1 or 2,
Wherein the diffraction grating is formed on both surfaces of the substrate.
A polarizing retarder laminate characterized in that a plurality of polarized light retardation plates according to claim 1 or 2 are laminated.
5. The method of claim 4,
And the convex portions of the diffraction grating are laminated so as to face each other.
3. The method according to claim 1 or 2,
Wherein the convex portion of the diffraction grating is processed by dry etching.
The laser beam emitted from one laser oscillator is split into two linearly polarized laser beams by a first polarizing beam splitter and the two linearly polarized laser beams are collected by a second polarizing beam splitter and incident on a mirror of a galvanometer scanner , A laser beam machine for scanning a workpiece with a galvanometer scanner to perform a hole drilling process at a predetermined position of the workpiece,
And a polarizing retarder according to claim 1 or 2 is provided between the second polarizing beam splitter and the galvanometer scanner
Wherein the laser beam is a laser beam.

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