JP5988644B2 - Processing method of optical device wafer - Google Patents

Description

  In the present invention, an optical device layer composed of an n-type semiconductor layer and a p-type semiconductor layer is stacked on a surface of an epitaxial substrate such as a sapphire substrate or silicon carbide, and is partitioned by a plurality of streets formed in a lattice shape. The present invention also relates to a method of processing an optical device wafer in which an optical device layer in an optical device wafer in which optical devices such as light emitting diodes and laser diodes are formed in a plurality of regions is transferred to a transfer substrate.

  In the optical device manufacturing process, an optical device layer composed of an n-type semiconductor layer and a p-type semiconductor layer is laminated on the surface of a substantially disk-shaped epitaxial substrate such as a sapphire substrate or silicon carbide in a lattice shape via a buffer layer. An optical device wafer is configured by forming optical devices such as light-emitting diodes and laser diodes in a plurality of regions partitioned by a plurality of formed streets. Each optical device is manufactured by dividing the optical device wafer along the street. (For example, refer to Patent Document 1.)

  In addition, as a technology for improving the brightness of optical devices, light consisting of an n-type semiconductor layer and a p-type semiconductor layer stacked on the surface of an epitaxial substrate such as a sapphire substrate or silicon carbide constituting an optical device wafer via a buffer layer Device layer is molybdenum (Mo), copper (Cu), silicon (Si), etc.Transfer substrate is gold (Au), platinum (Pt), chromium (Cr), indium (In), palladium (Pd), etc. Patent Document 2 discloses a manufacturing method called lift-off, in which bonding is performed through layers, the epitaxy substrate is peeled off by irradiating the buffer layer with a laser beam from the back side of the epitaxy substrate, and the optical device layer is transferred to the transfer substrate. Has been.

JP-A-10-305420 JP 2005-516415 gazette

  Thus, the energy distribution of the laser beam condensed by a condenser having a condenser lens that is generally used has a Gaussian distribution in which the central portion becomes stronger and becomes weaker toward the outside. Accordingly, when the buffer layer is destroyed by irradiating the buffer layer with a laser beam in a laser processing apparatus, there is a problem that the buffer layer is unevenly caused to deteriorate the quality. Also, if the surface of the sapphire substrate is formed to promote the growth of the optical device layer and the buffer layer, the pulse laser beam is blocked by the unevenness and the buffer layer is not destroyed uniformly, and the epitaxy substrate is peeled off. There is a problem that becomes difficult.

  The present invention has been made in view of the above-mentioned facts, and its main technical problem is to provide an optical device wafer processing method capable of uniformly breaking the buffer layer and reliably peeling the epitaxy substrate. is there.

In order to solve the above main technical problem, according to the present invention, an optical device layer of an optical device wafer in which an optical device layer is laminated on a surface of an epitaxy substrate via a buffer layer is bonded to a transfer substrate via a bonding metal layer. An optical device wafer processing method for transferring an optical device layer of an optical device wafer to a transfer substrate,
A diffusion treatment step for performing a diffusion treatment for forming a rough surface for diffusing a laser beam on the back surface of the epitaxy substrate;
The buffer layer is irradiated with a pulsed laser beam having a wavelength that is transparent to the epitaxy substrate and absorbs the buffer layer from the back side of the epitaxy substrate subjected to the diffusion treatment, and destroys the buffer layer. A buffer layer destruction process;
An optical device layer transfer step of separating the epitaxy substrate from the optical device layer and transferring the optical device layer to the transfer substrate after performing the buffer layer destruction step;
An optical device wafer processing method is provided.

In the diffusion treatment step, a rough surface having a surface roughness Ra of 0.01 to 1 μm is applied to the back surface of the epitaxy substrate.
Moreover, the said diffusion process process coat | covers the back surface of an epitaxy board | substrate with the member which permeate | transmits the pulse laser beam which gave the rough surface of surface roughness Ra: 0.01-1 micrometer.
In the diffusion process, a rough surface is formed by grinding diamond abrasive grains having a particle size of 1 to 10 μm with a grindstone hardened with a bonding agent.
The pulse laser beam irradiated in the buffer layer destruction step has a wavelength of 160 to 300 nm and an average output of 0.05 to 0.1 W.

An optical device wafer processing method according to the present invention includes a diffusion processing step for performing a diffusion processing for forming a rough surface for diffusing a laser beam on the back surface of an epitaxy substrate, and then performing the diffusion processing on the epitaxial substrate subjected to the diffusion processing. The buffer layer is destroyed by irradiating the buffer layer from the back side with a pulsed laser beam having a wavelength that is transparent to the epitaxy substrate and absorbing the buffer layer, and destroys the buffer layer. The laser beam is appropriately diffused by the rough surface provided on the back surface of the epitaxy substrate, and the energy distribution of the pulse laser beam at the condensing point is made uniform and the buffer layer is evenly destroyed. Further, since the pulse laser beam is diffused, even when the surface of the epitaxy substrate is uneven, the buffer layer is uniformly broken without being interrupted by the uneven wall. Therefore, the epitaxy substrate can be easily and reliably peeled from the optical device layer, and the optical device layer can be transferred to the transfer substrate.

1 is a perspective view of an optical device wafer processed by the optical device wafer processing method according to the present invention and a cross-sectional view showing an enlarged main part. Explanatory drawing of the transfer board | substrate joining process which joins a transfer board | substrate to the surface of the optical device layer of the optical device wafer shown in FIG. The perspective view of the grinding device for implementing the diffusion process process in the processing method of the optical device wafer by this invention. Explanatory drawing which shows one Embodiment of the diffusion process process in the processing method of the optical device wafer by this invention. Explanatory drawing which shows other embodiment of the diffusion process process in the processing method of the optical device wafer by this invention. The perspective view of the laser processing apparatus for implementing the buffer layer destruction process in the processing method of the optical device wafer by this invention. Explanatory drawing which shows the buffer layer destruction process in the processing method of the optical device wafer by this invention. Explanatory drawing which shows the optical device layer transfer process in the processing method of the optical device wafer by this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a method for processing an optical device wafer according to the present invention will be described in detail with reference to the accompanying drawings.

FIGS. 1A and 1B are a perspective view and an enlarged sectional view of a main part of an optical device wafer processed by the optical device wafer processing method according to the present invention.
An optical device wafer 2 shown in FIGS. 1A and 1B includes an n-type gallium nitride semiconductor layer 221 and a surface 21a of an epitaxy substrate 21 made of a sapphire substrate having a disk shape with a diameter of 50 mm and a thickness of 600 μm. An optical device layer 22 made of a p-type gallium nitride semiconductor layer 222 is formed by an epitaxial growth method. When the optical device layer 22 including the n-type gallium nitride semiconductor layer 221 and the p-type gallium nitride semiconductor layer 222 is stacked on the surface of the epitaxy substrate 21 by the epitaxial growth method, the surface 21a of the epitaxy substrate 21 and the optical device layer 22 are formed. Between the n-type gallium nitride semiconductor layer 221 to be formed, a buffer layer 23 made of gallium nitride (GaN) and having a thickness of, for example, 1 μm is formed. In the optical device wafer 2 configured in this manner, the thickness of the optical device layer 22 is, for example, 10 μm in the illustrated embodiment. In the optical device layer 22, as shown in FIG. 1A, optical devices 224 are formed in a plurality of regions partitioned by a plurality of streets 223 formed in a lattice shape.

  As described above, in order to peel the epitaxy substrate 21 in the optical device wafer 2 from the optical device layer 22 and transfer it to the transfer substrate, a transfer substrate bonding step of bonding the transfer substrate to the surface 22a of the optical device layer 22 is performed. . That is, as shown in FIGS. 2 (a), (b) and (c), the surface 22a of the optical device layer 22 formed on the surface 21a of the epitaxy substrate 21 constituting the optical device wafer 2 has a thickness of 1 mm. The transfer substrate 3 made of the copper substrate is joined via the joining metal layer 4 made of gold tin. The transfer substrate 3 can be made of molybdenum (Mo), silicon (Si) or the like, and the bonding metal forming the bonding metal layer 4 can be gold (Au), platinum (Pt), or chromium (Cr). Indium (In), palladium (Pd), or the like can be used. In the transfer substrate bonding step, the bonding metal is deposited on the surface 22a of the optical device layer 22 formed on the surface 21a of the epitaxy substrate 21 or the surface 3a of the transfer substrate 3 to form the bonding metal layer 4 having a thickness of about 3 μm. Then, the bonding metal layer 4 and the surface 3a of the transfer substrate 3 or the surface 22a of the optical device layer 22 are faced to each other and bonded to the surface 22a of the optical device layer 22 constituting the optical device wafer 2 by pressing. The composite substrate 200 is formed by bonding the surfaces 3a of the two through the bonding metal layer 4.

Hereinafter, as described above, the epitaxy substrate 21 of the optical device wafer 2 in the composite substrate 200 in which the surface 3a of the transfer substrate 3 is bonded to the surface 22a of the optical device layer 22 constituting the optical device wafer 2 via the bonding metal layer 4 is used. A processing method for peeling the optical device layer 22 from the optical device layer 22 and transferring the optical device layer 22 to the transfer substrate 3 will be described.
First, a diffusion treatment process is performed in which a diffusion treatment for diffusing a laser beam is performed on the back surface of the epitaxy substrate 21. In the illustrated embodiment, this diffusion treatment step is performed using a grinding apparatus 5 shown in FIG. A grinding apparatus 5 shown in FIG. 3 includes a chuck table 51 that holds a workpiece, and a grinding unit 52 that grinds the workpiece held on the chuck table 51. The chuck table 51 is configured to suck and hold the workpiece on the upper surface, and is rotated in a direction indicated by an arrow 51a in FIG. 3 by a rotation driving mechanism (not shown). The grinding means 52 includes a spindle housing 521, a rotating spindle 522 that is rotatably supported by the spindle housing 521 and rotated by a rotation driving mechanism (not shown), a mounter 523 attached to the lower end of the rotating spindle 522, and the mounter And a grinding wheel 524 attached to the lower surface of 523. The grinding wheel 524 includes an annular base 525 and a grinding wheel 526 that is annularly mounted on the lower surface of the base 525, and the base 525 is attached to the lower surface of the mounter 523 with fastening bolts 527. ing. The grinding wheel 526 is preferably a grindstone in which diamond abrasive grains having a particle size of 1 to 10 μm are hardened with a bonding agent.

  In order to perform the diffusion process using the grinding apparatus 5 described above, the transfer substrate 3 side of the composite substrate 200 is placed on the upper surface (holding surface) of the chuck table 51 as shown in FIG. The composite substrate 200 is sucked and held on the chuck table 51 by a suction means (not shown) (wafer holding step). Accordingly, in the composite substrate 200 held on the chuck table 51, the back surface 21b of the epitaxy substrate 21 constituting the optical device wafer 2 is on the upper side. When the composite substrate 200 is sucked and held on the chuck table 51 in this way, the grinding wheel 524 of the grinding means 52 is moved in the direction indicated by the arrow in FIG. 3 while the chuck table 51 is rotated in the direction indicated by the arrow 51a in FIG. For example, the grinding wheel 526 is rotated in the direction indicated by 524a at 500 rpm to bring the grinding wheel 526 into contact with the back surface 21b of the epitaxy substrate 21, which is the surface to be processed, as shown in FIG. In (a), as shown by an arrow 524b, a predetermined amount is ground and fed downward (in a direction perpendicular to the holding surface of the chuck table 51) at a grinding feed rate of 0.1 μm / second, for example. As a result, as shown in FIG. 4B, the back surface 21b of the epitaxy substrate 21 constituting the optical device wafer 2 is ground, and the back surface 21b of the epitaxy substrate 21 is formed into a rough surface. The back surface 21b of the epitaxy substrate 21 thus formed on the rough surface is preferably applied to a rough surface with a surface roughness Ra of 0.01 to 1 μm. As described above, this can be achieved by using a grindstone in which diamond abrasive grains having a particle diameter of 1 to 10 μm are hardened with a bonding agent such as vitrified bond.

Next, another embodiment of the diffusion treatment process will be described with reference to FIG.
In the embodiment shown in FIGS. 5A and 5B, the back surface 21b of the epitaxy substrate 21 constituting the optical device wafer 2 is transmitted with a pulsed laser beam having a rough surface with a surface roughness Ra of 0.01 to 1 μm. It coat | covers with the member 6 to do. The member 6 that transmits the pulsed laser beam may be, for example, a sapphire substrate, and the rough surface 6a can be implemented by the grinding apparatus 5 in the same manner as the diffusion treatment process shown in FIGS. In this way, the member 6 having the rough surface with the surface roughness Ra of 0.01 to 1 μm is coated on the back surface 21b of the epitaxy substrate 21 as shown in FIG. In order to avoid an air gap between the back surface 21b of the epitaxy substrate 21 and the member 6, it is desirable to interpose a liquid such as water between them.

  In addition, as a method of giving a rough surface to the member 6 that covers the back surface 21b of the epitaxy substrate 21 and the back surface 21b of the epitaxy substrate 21, a sandblasting process or an etching process can be used in addition to the grinding process described above.

  If the above-described diffusion treatment step is performed, a pulsed laser beam having a wavelength that is transparent to the epitaxy substrate 21 from the back surface 21b side of the epitaxy substrate 21 and absorbs the buffer layer 23. , And a buffer layer destruction step of destroying the buffer layer 23 is performed. This buffer layer destruction step is performed using a laser processing apparatus 7 shown in FIG. A laser processing apparatus 7 shown in FIG. 6 includes a chuck table 71 that holds a workpiece, and a laser beam irradiation unit 72 that irradiates a workpiece held on the chuck table 71 with a laser beam. The chuck table 71 is configured to suck and hold the workpiece. The chuck table 71 is moved in a processing feed direction indicated by an arrow X in FIG. 6 by a processing feed means (not shown), and in FIG. 6 by an index feed means (not shown). It can be moved in the index feed direction indicated by the arrow Y.

  The laser beam application means 72 includes a cylindrical casing 721 arranged substantially horizontally. In the casing 721, pulse laser beam oscillating means including a pulse laser beam oscillator and repetition frequency setting means (not shown) are arranged. A condenser 722 equipped with a condenser lens 722 a for condensing the pulse laser beam oscillated from the pulse laser beam oscillation means is attached to the tip of the casing 721. The laser beam irradiating unit 72 includes a condensing point position adjusting unit (not shown) for adjusting the condensing point position of the pulse laser beam collected by the condenser 722.

  In order to perform the buffer layer destruction step using the laser processing apparatus 7, the transfer substrate 3 side of the composite substrate 200 is placed on the upper surface (holding surface) of the chuck table 71 as shown in FIG. Then, the composite substrate 200 is sucked and held on the chuck table 71 by a suction means (not shown) (wafer holding step). Accordingly, in the composite substrate 200 held on the chuck table 71, the back surface 21b of the epitaxy substrate 21 constituting the optical device wafer 2 is on the upper side. If the composite substrate 200 is sucked and held on the chuck table 71 in this way, the machining feed means (not shown) is operated to move the chuck table 71 to the laser beam irradiation region where the condenser 722 of the laser beam irradiation means 72 is located, The buffer layer 23 is irradiated from the back surface 21b (upper surface) side of the epitaxy substrate 21 with a laser beam having a wavelength that is transparent to sapphire and absorbable to gallium nitride (GaN). The laser beam irradiation process to destroy is implemented. In this laser beam irradiation step, the chuck table 71 is moved to a laser beam irradiation region where the condenser 722 of the laser beam irradiation means 72 is positioned as shown in FIG. 7A, and one end (the left end in FIG. 7A). Is positioned immediately below the condenser 722 of the laser beam irradiation means 72. Next, as shown in FIG. 7B, the spot diameter of the spot S on the upper surface of the buffer layer 23 of the pulse laser beam irradiated from the condenser 722 is set to 400 μm. This spot diameter may be a condensing spot diameter or a spot diameter by defocusing. Then, the chuck table 71 is moved at a predetermined processing feed speed in the direction indicated by the arrow X1 in FIG. 7A while irradiating the pulsed laser beam from the condenser 722 by operating the laser beam irradiation means 72. Then, as shown in FIG. 7C, when the other end of the epitaxy substrate 21 (the right end in FIG. 7C) reaches the irradiation position of the condenser 722 of the laser beam irradiation means 72, the pulse laser beam is irradiated. While stopping, the movement of the chuck table 71 is stopped (laser beam irradiation step). This laser beam irradiation step is performed on a region corresponding to the entire surface of the buffer layer 23. As a result, the buffer layer 23 is destroyed, and the bonding function between the epitaxy substrate 21 and the optical device layer 22 by the buffer layer 23 is lost. In the above-described buffer layer destruction step, the back surface 21b of the epitaxy substrate 21 is formed to have a rough surface with a surface roughness Ra of 0.01 to 1 μm, so that the epitaxy substrate is formed on the buffer layer 23 from the back surface 21b side of the epitaxy substrate 21. When a pulsed laser beam having a wavelength that is transmissive to 21 and absorbs to the buffer layer 23 is irradiated, the pulsed laser beam is appropriately diffused, and the energy distribution of the pulsed laser beam at the focal point becomes uniform. The buffer layer 23 is evenly destroyed. Further, since the pulse laser beam is diffused, even if the surface of the epitaxy substrate 21 is uneven, the buffer layer 23 is uniformly broken without the pulse laser beam being blocked by the uneven wall.

The processing conditions of the laser beam irradiation process in the buffer layer destruction process are set as follows, for example.
Light source: Excimer laser Wavelength: 248nm
Repetition frequency: 50Hz
Average output: 0.08W
Pulse width: 10 ns
Spot diameter: φ400μm
Processing feed rate: 20 mm / sec

The pulse laser beam irradiated in the buffer layer destruction step has a wavelength of 160 to 300 nm and an average output of 0.05 to 0.1 W. That is, since the absorption edge of sapphire is 150 nm and the absorption edge of the buffer layer made of gallium nitride (GaN) is 310 nm, the wavelength having transparency to sapphire and absorbing to the buffer layer is It is desirable that it is 160-300 nm.
The laser beam irradiation step for breaking the buffer layer 23 is performed by positioning the condenser 722 on the outermost periphery of the epitaxy substrate 21 and moving the condenser table 722 toward the center while rotating the chuck table 71. The entire surface of 23 may be irradiated with a laser beam to destroy the buffer layer 23 and to lose the bonding function between the epitaxy substrate 21 and the optical device layer 22 by the buffer layer 23.

  If the buffer layer destruction process described above is performed, an optical device layer transfer process is performed in which the epitaxy substrate 21 is peeled from the optical device layer 22 and the optical device layer 22 is transferred to the transfer substrate 3. This optical device layer transfer step is carried out using a transfer device 8 shown in FIGS. 8A and 8B, the transfer apparatus 8 includes a first holding means 81 for holding the transfer board 3 of the composite substrate 200, and the transfer board 3 is bonded on the first holding means 81. The second holding means 82 for holding the epitaxial substrate 21 side of the optical device wafer 2 is provided. The first holding means 81 is configured to suck and hold the composite substrate 200 via the transfer substrate 3 on the holding surface which is the upper surface. Further, the first holding means 81 is adapted to be rotated by a rotation drive mechanism (not shown). The second holding means 82 includes a suction holding pad 83 and a support shaft portion 84 that supports the suction holding pad 83. The suction holding pad 83 includes a disk-shaped base 831 and a pad 832. The base 831 is made of an appropriate metal material, and a support shaft portion 84 projects from the center of the upper surface. The base 831 constituting the suction holding pad 83 is provided with a circular recess 831a whose lower part is opened. A pad 832 formed in a disk shape by a porous ceramic member is fitted in the recess 831a. In this way, the holding surface that is the lower surface of the pad 832 fitted in the recess 831 a of the base 831 is disposed so as to face the holding surface that is the upper surface of the first holding means 81. A circular recess 831 a formed in the base 831 constituting the suction holding pad 83 is communicated with a suction means (not shown) through a suction passage 84 a provided in the support shaft portion 84. Accordingly, when a suction means (not shown) is operated, negative pressure is applied to the holding surface, which is the lower surface of the pad 832, via the suction passage 84 a and the recess 831 a of the base 831, and the holding surface, which is the lower surface of the pad 832, is described later. Thus, the epitaxy substrate 21 constituting the optical device wafer 2 can be sucked and held.

  The second holding means 82 configured as described above is connected to the separating means 85 movable in the vertical direction in FIGS. 8A and 8B. In the illustrated embodiment, the separating means 85 is composed of an air cylinder mechanism, and the piston rod 851 is connected to a support shaft portion 84 constituting the second holding means 82. The separating means 85 configured in this way positions the second holding means 82 on the upper side of the first holding means 81, and lowers and rises, whereby the second holding means 82, the first holding means 81, Is moved in the direction of approaching and separating relatively.

  In order to perform the optical device layer transfer step using the transfer device 8 described above, the transfer substrate 3 of the composite substrate 200 described above is placed on the first holding means 81 of the transfer device 8 as shown in FIG. The composite substrate 200 is sucked and held on the first holding means 81 by placing the side and operating a suction means (not shown) (wafer holding step). Accordingly, in the composite substrate 200 held on the first holding means 81, the back surface 21b of the epitaxy substrate 21 constituting the optical device wafer 2 is on the upper side. Next, the separation means 85 comprising an air cylinder mechanism is actuated to lower the second holding means 82, and the holding surface which is the lower surface of the pad 832 constituting the suction holding pad 83 as shown in FIG. Is brought into contact with the upper surface which is the back surface 21b of the epitaxial substrate 21 constituting the optical device wafer 2 of the composite substrate 200 sucked and held by the first holding means 81. Then, by operating a suction means (not shown), the upper surface, which is the back surface 21b of the epitaxy substrate 21, is sucked and held on the holding surface which is the lower surface of the pad 832 constituting the suction holding pad 83. Accordingly, the transfer substrate 3 is sucked and held by the first holding means 81, and the epitaxy substrate 21 is sucked and held by the second holding means 82. Next, as shown in FIG. 8 (a), a rotation driving mechanism (not shown) that rotates the first holding means 81 is operated to rotate the first holding means 81 by a predetermined angle in the direction indicated by the arrow 81a. . At this time, since the buffer layer 23 is uniformly destroyed in the buffer layer destruction step, it is easily destroyed completely. If the buffer layer 23 is destroyed in this way, as shown in FIG. 8B, the separating means 85 including an air cylinder mechanism is operated to raise the second holding means 82. As a result, the epitaxy substrate 21 is peeled from the optical device layer 22 while being sucked and held on the lower surface of the pad 832 constituting the suction holding pad 83 of the second holding means 82, and the optical device layer 22 is transferred to the transfer substrate 3. (Optical device layer transfer step).

2: Optical device wafer 21: Epitaxy substrate 22: Optical device layer 23: Buffer layer 3: Transfer substrate 4: Bonding metal layer 200: Composite substrate 5: Grinding device 51: Chuck table of grinding device 52: Grinding means 524: Grinding wheel 526: Grinding wheel 7: Laser processing device 71: Chuck table of laser processing device 72: Laser beam irradiation means 722: Condenser 8: Transfer device 81: First holding means 82: Second holding means 83: Suction holding pad 85: Separation means

Claims (5)

The optical device layer of the optical device wafer in which the optical device layer of the optical device wafer in which the optical device layer is laminated on the surface of the epitaxy substrate through the buffer layer is bonded to the transfer substrate through the bonding metal layer is transferred to the transfer substrate. An optical device wafer processing method comprising:
A diffusion treatment step for performing a diffusion treatment for forming a rough surface for diffusing a laser beam on the back surface of the epitaxy substrate;
The buffer layer is irradiated with a pulsed laser beam having a wavelength that is transparent to the epitaxy substrate and absorbs the buffer layer from the back side of the epitaxy substrate subjected to the diffusion treatment, and destroys the buffer layer. A buffer layer destruction process;
An optical device layer transfer step of separating the epitaxy substrate from the optical device layer and transferring the optical device layer to the transfer substrate after performing the buffer layer destruction step;
An optical device wafer processing method characterized by the above.   The optical device wafer processing method according to claim 1, wherein in the diffusion treatment step, a rough surface having a surface roughness Ra of 0.01 to 1 μm is applied to the back surface of the epitaxy substrate.   2. The method of processing an optical device wafer according to claim 1, wherein in the diffusion treatment step, the back surface of the epitaxy substrate is coated with a member that transmits a pulsed laser beam having a rough surface with a surface roughness Ra of 0.01 to 1 [mu] m.   4. The method of processing an optical device wafer according to claim 2, wherein the diffusion treatment step is performed by grinding a diamond abrasive grain having a particle diameter of 1 to 10 [mu] m with a grindstone hardened with a bonding agent to give a rough surface.   5. The processing of an optical device wafer according to claim 1, wherein the pulse laser beam irradiated in the buffer layer destruction step has a wavelength of 160 to 300 nm and an average output of 0.05 to 0.1 W. Method.

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