Source: http://www.google.com/patents/US20070137254?dq=5343970
Timestamp: 2017-12-11 03:23:15
Document Index: 298352926

Matched Legal Cases: ['art 150', 'art 150', 'art 150', 'art 150', 'art 150', 'art 180', 'art 180', 'art 150', 'art 150', 'art 150', 'art 150', 'arts 150', 'arts 150', 'art 960', 'art 950', 'art 960', 'art 950', 'art 960']

Patent US20070137254 - Optical transmission substrate, method for manufacturing optical ... - Google Patents
Provided is an optical transmission substrate including: a first substrate; an optical waveguide which has clad covering a core and a periphery of the core and extends on an upper surface of the first substrate; a second substrate provided parallel to the first substrate so that a lower surface thereof...http://www.google.com/patents/US20070137254?utm_source=gb-gplus-sharePatent US20070137254 - Optical transmission substrate, method for manufacturing optical transmission substrate and optoelectronic integrated circuit
Publication number US20070137254 A1
Application number US 11/679,460
Also published as US7212713, US7421858, US20050117833
Publication number 11679460, 679460, US 2007/0137254 A1, US 2007/137254 A1, US 20070137254 A1, US 20070137254A1, US 2007137254 A1, US 2007137254A1, US-A1-20070137254, US-A1-2007137254, US2007/0137254A1, US2007/137254A1, US20070137254 A1, US20070137254A1, US2007137254 A1, US2007137254A1
Inventors Tadashi Fukuzawa, Masaki Hasegawa
Original Assignee Tadashi Fukuzawa, Masaki Hasegawa
US 20070137254 A1
This application is a division of U.S. application Ser. No. 10/977,170, filed on Oct. 29, 2004.
(Nonpatent Document 1)B. J. Offrein et. al., “Tunable WDM Add/Drop Components in Silicon Oxynitride Waveguide Technology”, 49th Electronic Components & Technology Conference 1999 Proceedings, p. 19-25
(Nonpatent Document 4)Maruno, “Polymer Optical Waveguide Device”, IEICE (Institute of Electronics, Information and Communication Engineers) Transactions C Vol. J84-C, p. 1-6, 2001
According to a first aspect of the present invention, provided is an optical transmission substrate including: a first substrate; an optical waveguide ,which consists of a core and a clad covering periphery of the core, extends on an upper surface of the first substrate; a second substrate provided parallel to the first substrate so that a lower surface thereof contacts an upper surface of the optical waveguide; a reflection surface which is provided on a cross section of the core at an end of the optical waveguide and reflects light, which travels through the core of the optical waveguide, toward the second substrate; and a light guide which is provided in the second substrate and guides the light, which is reflected toward the second substrate, toward an upper surface of the second substrate from a position closer to the core than an upper surface of the clad.
FIGS. 2(a)-2(c) are first views showing a method for manufacturing the optical transmission substrate 10 according to this embodiment. FIG. 2 (a) shows a lower clad layer formation step and FIGS. 2 (b) and (c) show a side and an upper surface of the optical transmission substrate 10, respectively, in a reflection part formation step.
FIGS. 3(a)-3(c) are second views showing the method for manufacturing the optical transmission substrate 10 according to this embodiment. FIG. 3 (a) shows a state where a photoresist is formed in the reflection part formation step, FIG. 3 (b) shows a state where an evaporated metal film 310 is evaporated and FIG. 3 (c) shows a state where the evaporated metal film 310 is lifted off.
FIGS. 4(a)-4(c) are third views showing the method for manufacturing the optical transmission substrate 10 according to this embodiment. FIGS. 4 (a) and 4 (b) show the side and the upper surface of the optical transmission substrate 10, respectively, in a core formation step and FIG. 4 (c) shows a metal film formation step.
FIGS. 5(a)-5(c) are fourth views showing the method for manufacturing the optical transmission substrate 10 according to this embodiment. FIG. 5 (a) shows an upper clad layer formation step, FIG. 5 (b) shows a substrate lamination step and FIG. 5 (c) shows an opening formation step.
FIGS. 6(a)-6(b) are fifth views showing the method for manufacturing the optical transmission substrate 10 according to this embodiment. FIG. 6 (a) shows a metal film removal step and FIG. 6 (b) shows a light guide installation step.
FIGS. 7(a)-7(c) are first views showing a method for manufacturing an optical transmission substrate 10 according to a first modified example of this embodiment. FIG. 7 (a) shows a step of providing a reflection part 150 in the reflection part formation step and FIGS. 7 (b) and 7 (c) show a step of forming a tilted portion 155.
FIGS. 8(a)-8(d) are second views showing the method for manufacturing the optical transmission substrate 10 according to the first modified example of this embodiment. FIG. 8 (a) shows a step of forming a reflection surface 160, FIG. 8 (b) shows a step of removing a part of the reflection part 150, FIG. 8 (c) shows a step of forming an optical waveguide 130 and FIG. 8 (d) shows the metal film formation step and the substrate lamination step.
FIGS. 9(a)-9(d) are third views showing the method for manufacturing the optical transmission substrate 10 according to the first modified example of this embodiment. FIG. 9 (a) shows the substrate lamination step, FIG. 9 (b) shows the opening formation step, FIG. 9 (c) shows the metal film removal step and FIG. 9 (d) shows the light guide installation step.
Instead of the one described above, the optical fiber 170 maybe a GRIN lens (Graded Index Lens) through which light travels while being condensed in a center portion thereof or may also be a hollow-core optical fiber. Here, in the case of realizing the optical fiber 170 by use of the graded index optical fiber, the GRIN lens or the like, a length of the optical fiber 170 is determined so as to converge light on a light receiving element provided in an upper end of the optical fiber 170. Moreover, in the case of realizing the optical fiber 170 by use of the hollow-core optical fiber, as disclosed in nonpatent document 5, a hole having such a size and a period as to be a forbidden band for light propagated through the optical fiber 170 is provided around a core to be a photonic crystal.
First, the first substrate 100 is prepared. Next, as shown in FIG. 2 (a), in a lower clad layer formation step, the lower clad layer of the optical waveguide 130 is formed on the upper surface of the first substrate 100. This lower clad layer is a layer to be the clad 120 a in the optical waveguide 130 of FIG. 1. More specifically, polysilane A to be the clad 120 a of the optical waveguide 130 is applied onto the first substrate 100 by spin coating or curtain coating, pre-baked at 120 □ and calcined at 250 □. Thus, the lower clad layer is formed.
Next, FIGS. 2 (b) and 2 (c) show the side and the upper surface of the optical transmission substrate 10. As shown in FIGS. 2 (b) and 2 (c), in a reflection part formation step, the reflection part 150 is formed on an upper surface of the lower clad layer. Specifically, the reflection part 150 has a tilted portion 155 for providing the reflection surface 160 reflecting light, which travels through the core 110 of the optical waveguide 130, toward the second substrate 140. In this embodiment, a cross section of the reflection part 150 is a 50×50 μm square, which is the same thickness as that of the core 110 of the optical waveguide 130.
Next, as shown in FIG. 3 (a), in a photoresist formation step in the reflection part formation step, a photoresist 300 is formed in such a manner that the tilted portion 155 is exposed to the upper surface side of the optical transmission substrate 10 and the other portions are covered with the photoresist 300. Next, as shown in FIG. 3 (b), in a vapor deposition step in the reflection part formation step, aluminum or silver is evaporated onto the upper surface of the optical transmission substrate 10. Thus, an evaporated metal film 310 is formed on upper surfaces of the photoresist 300 and the tilted portion 155. Next, as shown in FIG. 3 (c), in a lift-off step in the reflection part formation step, the photoresist 300 is lifted off to remove the photoresist 300 and aluminum or silver which is evaporated onto the upper surface of the photoresist 300. As a result, aluminum or silver is evaporated onto the tilted portion 155 and the reflection surface 160 can be formed.
Next, FIGS. 4 (a) and 4 (b) show the side and the upper surface of the optical transmission substrate 10. As shown in FIGS. 4 (a) and 4 (b), in a core formation step, the core 110 of the optical waveguide 130 is formed in such a manner that the cross section of the core 110 contacts the reflection surface 160 at the end of the optical waveguide 130. More specifically, as in the case of the lower clad layer formation step, polysilane B is applied onto the first substrate 100, on which the lower clad layer is formed, by spin coating or curtain coating and is pre-baked. Thus, a layer having a thickness of 50 micrometers is formed. Accordingly, a photomask pattern having an opening in a portion to be the core 110 of the optical waveguide 130 is formed on the layer of polysilane B and irradiated with ultraviolet rays to increase a refractive index of the portion to be the core 110 in the layer of polysilane B. Thus, the core 110 is formed. Here, the polysilane A and the polysilane B may be polysilane of the same material. Alternatively, the polysilane A may be polysilane into which a material more suitable for the clad is mixed and the polysilane B may be polysilane into which a material more suitable for the core is mixed.
Next, as shown in FIG. 4 (c), in a metal film formation step, a metal film 400 is formed on the upper surface of the core 110 at the end of the optical waveguide 130. This metal film 400 serves as a stopper for forming an opening by making a hole down to immediately above the core 110 from the upper surface of the second substrate 140 in order to insert the optical fiber 170 from the upper surface of the second substrate 140 and allow the core part 180 of the optical fiber 170 and the core 110 of the optical waveguide 130 to directly contact each other.
Next, as shown in FIG. 5 (a), in an upper clad layer formation step, an upper clad layer is formed on and above the core 110 in the optical waveguide 130 in a state where the metal film 400 is formed. This upper clad layer is a layer to be the clad 120 b in the optical waveguide 130 of FIG. 1. In this embodiment, in order for the clad 120 b to have a sufficient thickness, the upper clad layer is also formed on the metal film 400 in addition to on the core 110 in the optical waveguide 130. More specifically, as in the case of the lower clad layer formation step, the same polysilane A as that of the lower clad layer is applied to cover the polysilane B layer. Thus, the structure of the optical waveguide is formed.
Next, as shown in FIG. 5 (b), in a substrate lamination step, the second substrate 140 is laminated on an upper surface of the upper clad layer. Thus, the first substrate 100 and the second substrate 140 are attached to each other so as to put the optical waveguide 130 therebetween. Accordingly, a piece of board is obtained. The structure of FIG. 5 (b) is the same as that of a board used in a normal SLC manufacturing process except that the optical waveguide 130 is provided in the center thereof. Therefore, an electric interconnect portion can be completed by using a SLC process generally used to perform pattern formation of electric interconnect, via hole production by use of a carbon dioxide laser, a plating process and the like. Here, if it is required to produce a via for the electric interconnect directly above or directly below the optical waveguide 130, in the step of forming the first substrate 100, in which the hole is produced, or the second substrate 140, a copper pattern for protecting the optical waveguide 130 is formed beforehand in the first substrate 100 or the second substrate 140. This process can be performed as a part of usual pattern formation of a printed circuit board.
Next, as shown in FIG. 5 (c), in an opening formation step, the second substrate 140 and the clad 120 b, which are laminated on the metal film 400, are selectively removed to form an opening extending to the upper surface of the metal film 400 from the upper surface of the second substrate 140. More specifically, a position corresponding to the metal film 400 in the upper surface of the second substrate 140 is irradiated with a laser having a first wavelength. Thus, resin and glass epoxy, which are materials of the second substrate 140, are selectively removed to form the opening in the second substrate 140. Here, copper reflects the carbon dioxide laser. Thus, by using the carbon dioxide laser as the laser having the first wavelength, the hole production is stopped in a pattern portion of the metal film 400 and the core 110 of the optical waveguide 130 is not damaged.
Next, as shown in FIG. 6 (a), in a metal film removal step, the metal film 400 is selectively removed. More specifically, the metal film 400 made of copper is irradiated with a laser having a second wavelength, which is different from the first wavelength. Thus, the metal film 400 is removed. Here, second harmonic of a YAG laser has a wavelength of 530 nm and is absorbed by copper. However, the second harmonic is not absorbed by polysilane or glass. Thus, by using the second harmonic YAG laser as the laser having the second wavelength, the metal film 400 can be selectively removed. Furthermore, in this step, a guide hole, into which a guide pin is inserted, is also produced, the guide pin being used for alignment in mounting an optical element or the optical fiber 170.
Next, as shown in FIG. 6 (b), in a light guide installation step, the optical fiber 170 guiding light, which is received from a light emitting part, to the core 110 at a first end of the optical waveguide 130 and the optical fiber 170 guiding light, which travels through the core 110 and is reflected toward the second substrate 140 at a second end of the optical waveguide 130, toward the upper surface of the second substrate 140 from the position where the metal film 400 is removed are provided in the respective openings. More specifically, a multimode optical fiber having a core diameter of 50 micrometers, which is cut so as to have the same height as the surface of the optical transmission substrate 10, is inserted into the opening and an optical device is mounted thereon. Here, in the light guide installation step according to this embodiment, a light guide which contacts the core 110 at the end of the optical waveguide 130 is installed. In this event, it is preferable that the coupling efficiency is further improved in such a manner that the core 110 at the end of the optical waveguide 130 and the light guide are bonded to each other by use of an optical adhesive and a difference in the refractive index between the core 110 and the core part 180 is reduced.
Before the metal film 400 is formed and after the core 110 of the optical waveguide 130 is formed, that is, in the state of FIG. 4 (c), a core upper clad layer formation step of forming a core upper clad layer on the upper surface of the core 110 of the optical waveguide 130 is provided. Accordingly, in the metal film formation step, the metal film 400 is formed on an upper surface of the core upper clad layer at the end of the optical waveguide 130. Thus, the metal film 400 is formed on the core 110. Next, in the upper clad layer formation step, the upper clad layer is formed on the upper surface of the core upper clad layer in the optical waveguide 130 in the state where the metal film 400 is formed. As a result, the core upper clad layer, the metal film 400 and the upper clad layer are laminated directly above the core 110.
First, as shown in FIG. 7 (a), in the mirror support formation step in the reflection part formation step, on the first substrate 100, polysilane having a thickness of 150 μm, which is equivalent to the thickness of the three layers including the clad 120 a, the core 110 and the clad 120 b, is applied and pre-baked at 120 □. Next, as shown in FIGS. 7 (b) and 7 (c), by use of a blade 20 having a tilt angle of 45 degrees, the reflection part 150 at an end of a polymer waveguide (PWG) to be the optical waveguide 130 is diced. Thus, tilted portions 155 are formed at two spots including an incidence side and an exit side.
Next, as shown in FIG. 8 (a), in the vapor deposition step in the reflection part formation step, aluminum or silver is laminated by vapor deposition or sputtering and reflection surfaces 160 are formed. Here, when the reflection surfaces 160 are formed of silver, it is preferable that palladium of about 2.5 weight % and copper of about 2.5 weight % are added to silver to improve heat resistance of the reflection surfaces 160.
Next, as shown in FIG. 8 (b), in an optical waveguide region removal step, a center portion of the reflection part 150 except for the portions where the reflection surfaces 160 are provided is subjected to mask exposure and development. Thus, the center portion of the reflection part 150 is removed while leaving both ends where the reflection surfaces 160 are provided.
Next, as shown in FIG. 8 (c), in the lower clad layer formation step, the lower clad layer made of polysilane is applied again onto the center portion where polysilanae is removed and is calcined. Next, in the core formation step, a core material of polysilane is applied onto the lower clad layer and the mask exposure is performed. Thus, the core 110 is formed by photobleach and calcined. Thereafter, in the upper clad layer formation step, the upper clad layer is applied onto the core 110 and calcined. By performing the processes described above, an optical waveguide 130 having the reflection surfaces 160 provided at its both ends can be prepared, the reflection surfaces facing upward at 45 degrees. Here, the three layers are also formed of the clad material and the core material between the reflection surfaces 160 and the ends of the light guide. However, the clad 120 b at the second substrate 140 side is formed to be sufficiently thin so as to have about the same thickness as the diameter of the core 110. Thus, loss of light attributable to this layer can be reduced.
Next, as shown in FIG. 8 (d), in the metal film formation step, the metal films 400 are formed at the ends of the core 110 in the optical waveguide 130. Thereafter, in the substrate lamination step, the second substrate 140 is laminated on the upper surfaces of the upper clad layer and the reflection part 150. The above-described operations shown in FIG. 7 (a) to FIG. 8 (d) are repeated and the optical waveguides 130 are provided, respectively, in a plurality of layers of the reflection parts 150 provided in the optical transmission substrate 10. Thus, a multilayer structure for performing multilayer optical interconnect can be formed. In this case, the ends of the optical waveguides 130, which are positioned, respectively, in the plurality of layers of the reflection parts 150 provided in the optical transmission substrate 10, are provided in different positions from each other in the plane of the optical transmission substrate 10. In addition, the ends thereof are arranged so as not to overlap with each other when viewed from the upper surface or the lower surface of the optical transmission substrate 10. Here, as shown in FIG. 9 (a), a third substrate 900 and a fourth substrate 910, such as SLC built-up substrates, may be laminated on the lower surface of the first substrate 100 and the upper surface of the second substrate 140, respectively.
Next, as shown in FIG. 9 (b), in the opening formation step, the fourth substrate 910 and the second substrate 140, which are laminated on the metal films 400, are selectively removed by use of the carbon dioxide laser. Accordingly, openings extending to the upper surfaces of the metal films 400 from the upper surface of the second substrate 140 are formed. Next, as shown in FIG. 9 (c), in the metal film removal step, the metal films 400 are selectively removed. Thereafter, as shown in FIG. 9 (d), in the light guide installation step, a multimode optical fiber, which is cut in a length to reach a surface of the fourth substrate 910, or a GRIN lens, of which focal length is optimized so as to focus light on a light receiving part 960, is inserted into each of the openings. Subsequently, a light emitting part 950 is provided above the light guide on the light emitting side and the light receiving part 960 is provided above the light guide on the light receiving side. Thus, optical signals can be transmitted from the light emitting part 950 to the light receiving part 960.
FIG. 10 shows a relationship between a wavelength of a laser and absorptance of the laser for each material. As shown in FIG. 10, resin and glass have high absorptance of the carbon dioxide laser and are evaporated by being irradiated with the carbon dioxide laser. Meanwhile, copper has low absorptance of the carbon dioxide laser. Thus, even if copper is irradiated with the carbon dioxide laser, copper reflects the laser and is not affected thereby. In this embodiment, the property described above is utilized and the fourth substrate 910, the second substrate 140 and/or the clad 120 b can be selectively removed by use of the carbon dioxide laser in the opening formation step shown in FIG. 5 (c) and FIG. 9 (b).
Moreover, as shown in FIG. 10, resin and copper have high absorptance of the second harmonic of the YAG laser and are evaporated by being irradiated with the second harmonic of the YAG laser. Meanwhile, glass has low absorptance of the second harmonic of the YAG laser. Thus, even if glass is irradiated with the second harmonic of the YAG laser, glass is not affected thereby. In this embodiment, the property described above is utilized and the metal films 400 can be selectively removed by use of the second harmonic of the YAG laser in the metal film removal step shown in FIG. 6 (a) and FIG. 9 (c).
Next, by use of a photoresist mask in which the tilted portion 155 is exposed, aluminum or silver is evaporated to form the reflection surface 160. On the clad layer on one side of the optical waveguide 130 and the first substrate 100 on which the reflection surface 160 is formed, polysilane B to be the core 110 of the optical waveguide 130 is applied. Accordingly, a hole made in the polysilane B to form the reflection surface 160 is closed. Thus, the surface of the first substrate 100 becomes a state of being covered with a smooth film of polysilane B. Next, a pattern of the core 110 is formed by use of a positive optical resist and a portion other than the core 110 is exposed to ultraviolet rays. Since the refractive index is lowered in the portion irradiated with light, the light can be kept in a portion in the vicinity of the core 110 of the optical waveguide 130. By performing the processes described above, the optical transmission substrate 10 becomes a state similar to that shown in FIGS. 4 (a) and 4 (b), in which the core 110 of the optical waveguide 130 and the clad 120 have the same height and the reflection surface 160 also has the same height. Therefore, by use of the method shown in FIG. 4 (c) and the subsequent drawings, the optical transmission substrate 10 including the optical waveguide 130 can be manufactured.
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U.S. Classification 65/386
International Classification G02B6/122, G02B6/13, C03B37/022, G02B6/42, G02B6/43, H05K1/02, G02B6/30, G02B6/12, G02B6/125
Cooperative Classification H05K1/0274, G02B2006/12104, H05K1/144, G02B6/4214, G02B6/43, G02B6/125, G02B6/30
European Classification G02B6/125, G02B6/43, G02B6/42C3R, G02B6/30