US20010046722A1 - Electrode for optical waveguide element - Google Patents
Electrode for optical waveguide element Download PDFInfo
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- US20010046722A1 US20010046722A1 US09/527,468 US52746800A US2001046722A1 US 20010046722 A1 US20010046722 A1 US 20010046722A1 US 52746800 A US52746800 A US 52746800A US 2001046722 A1 US2001046722 A1 US 2001046722A1
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
- G02F1/035—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect in an optical waveguide structure
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- This invention relates to an electrode for applying an electric voltage to an optical channel waveguide of an optical waveguide element in which the optical channel waveguide is formed by proton exchange, and a method of forming the electrode.
- optical waveguide elements having an optical channel waveguide formed on a substrate.
- a method of forming the optical channel waveguide there has been known a proton exchange process.
- metal film is first formed on a surface of a substrate, an opening is formed in the metal film by etching and proton exchange is carried out on the surface of the substrate using the metal film as a mask.
- an electric voltage is applied to the optical channel waveguide through electrodes disposed near or just above the optical channel waveguide.
- Metal film 2 such as of Cr is first formed on a substrate 1 as shown in FIG. 9A.
- a resist layer 3 is formed on the metal film 2 in a predetermined pattern by photolithography as shown in FIG. 9B.
- the metal film 2 is etched to form openings 4 in a predetermined pattern in the metal film 2 using the resist layer 3 as a mask, and the resist layer 3 is removed as shown in FIG. 9C.
- the metal film 2 is then removed by etching as shown in FIG. 9E and the substrate 1 is annealed as required.
- a conductive film 7 such as of aluminum is formed over the surface of the substrate 1 as shown in FIG. 9F.
- a resist layer 8 is formed over the conductive film 7 with portions opposed to the optical channel waveguides 5 exposed by photolithography as shown in FIG. 9G.
- the conductive film 7 is removed at the portions opposed to the optical channel waveguides 5 by etching using the resist 8 as a mask as shown in FIG. 9H.
- each optical channel waveguide 5 When the resist 8 is thereafter removed, the conductive films 7 are left on opposite sides of each optical channel waveguide 5 .
- the conductive films 7 on opposite sides of each optical channel waveguide 5 can be used as electrodes for applying an electric voltage to the optical channel waveguide 5 .
- the metal film which is used as a mask for setting the pattern of the optical waveguide upon proton exchange is left there and used as the electrodes. That is, metal film is formed on a surface of a substrate, openings of predetermined shapes are formed in the metal film, proton exchange is carried out on the surface of the substrate with the metal film used as a mask, thereby forming optical channel waveguides, and the metal film is removed with at least a part of the edges of the openings left there.
- the metal film fractions are used as the electrodes.
- the openings of predetermined shapes are formed in the metal film generally by etching though liftoff may be used.
- the thickness of the metal film should be several hundred namometers (nm) at most.
- the resistance of the electrodes becomes high and accordingly optical waveguide elements provided with such electrodes are hard to operate at high speed (e.g., high speed modulation at several hundred MHz or higher).
- the primary object of the present invention is to provide an electrode for an optical waveguide element which is formed with its one edge precisely aligned with one edge of the optical channel waveguide and at the same time makes it feasible to operate the optical waveguide element at high speed.
- Another object of the present invention is to provide a method of forming such electrodes for an optical waveguide element.
- the metal film used as a mask in the proton exchange is first processed into metal film fractions of predetermined shapes corresponding to the shapes of electrodes to be formed, each metal film fraction including at least a part of an edge portion defining one of the openings, and then the metal film fractions are plated with plating metal and used as the electrodes for applying an electric voltage to the optical channel waveguides.
- an electrode for an optical waveguide element which is formed on a substrate, on which an optical channel waveguide is formed by proton exchange, with its one edge aligned with one edge of the optical channel waveguide and is for applying an electric voltage to the optical channel waveguide
- the improvement comprises that the electrode comprises a metal film fraction which is a part of metal film used as a mask when the optical channel waveguide is formed by the proton exchange and a plating metal layer formed on the metal film fraction by plating.
- a buffer layer is formed between the substrate and the metal film.
- the metal film used as a mask for setting the pattern of the optical channel waveguide upon proton exchange naturally has an edge aligned with an edge of the optical channel waveguide. Accordingly when an electrode is formed by plating the metal film including at least a part of an edge portion defining one of the openings, the edge of the electrode can be precisely aligned with the edge of the optical channel waveguide.
- the thickness of the electrode increases and the resistance of the electrode lowers as compared with when the metal film is used as an electrode as it is. Accordingly the optical waveguide element in which an electric voltage is applied to the optical channel waveguide through the electrode can be operated at high speed.
- the finished electrode cannot have an edge aligned with the edge of the optical channel waveguide even if the metal film on which the plating metal is plated has an edge aligned with the edge of the optical channel waveguide, which results in the same problem as that described above in conjunction with FIG. 10.
- the method in accordance with the third aspect of the present invention can overcome this problem. That is, when the negative photo-resist applied to the substrate after the proton exchange is exposed to light from the back side of the substrate using the metal film as a mask, the exposed part of the photo-resist has an edge precisely aligned with the edge of the optical channel waveguide. Accordingly, by removing the negative photo-resist with the exposed part left there and effecting the plating using the exposed part of the photo-resist as a mask, the plating metal cannot hang out over the optical channel waveguide and the edge of the electrode plated with the plating metal can be precisely aligned with the edge of the optical channel waveguide.
- FIGS. 1A to 1 H are views for illustrating the procedure of forming the electrodes of an optical waveguide element by a method in accordance with a first embodiment of the present invention
- FIGS. 2A to 2 F are plan views showing the state of the substrate at different steps shown in FIGS. 1A to 1 H,
- FIGS. 3A to 3 H are views for illustrating the procedure of forming the electrodes of an optical waveguide element by a method in accordance with a second embodiment of the present invention
- FIGS. 4A to 4 H are plan views showing the state of the substrate at different steps shown in FIGS. 3A to 3 H,
- FIGS. 5A to 5 E are views for illustrating the procedure of forming the electrodes of an optical waveguide element by a method in accordance with a third embodiment of the present invention.
- FIGS. 6A to 6 D are plan views showing the state of the substrate at different steps shown in FIGS. 5A to 5 E,
- FIGS. 7A to 7 E are views for illustrating the procedure of forming the electrodes of an optical waveguide element by a method in accordance with a fourth embodiment of the present invention.
- FIGS. 8A to 8 C are plan views showing the state of the substrate at different steps shown in FIGS. 7A to 7 E,
- FIGS. 9A to 9 H are views for illustrating the procedure of forming the electrodes of an optical waveguide element by a conventional method
- FIG. 10 is a view for illustrating alignment error of the electrodes formed by the conventional method.
- the finished optical waveguide element comprises a substrate 10 which may comprise an x-plate of, for instance, a LiNbO 3 crystal.
- a pair of optical channel waveguides 11 which form a directional photocoupler, are formed on a surface of the substrate 10 to extend in Y-direction, and three electrodes 12 , 13 and 14 are formed on the surface of the substrate 10 on opposite sides of the portions of the optical channel waveguides 11 where they extend in parallel to each other close to each other and between the portions.
- the electrodes 12 and 14 are connected to a drive circuit (not shown) and the electrode 13 is connected to the drive circuit by way pad electrodes 16 .
- a predetermined electric voltage is applied to each of the optical channel waveguides 11 through the electrodes 12 , 13 and 14 .
- Each of the edges of the electrodes 12 , 13 and 14 adjacent to the optical channel waveguides 11 should be precisely aligned with the corresponding edge of the optical channel waveguides 11 . Otherwise it becomes difficult to precisely apply the predetermined voltage to each optical channel waveguide 11 .
- FIGS. 1A to 1 H are cross-sectional views taken along line A-A in FIG. 2A.
- Resist layers 20 are first formed by known lithography on the surface of a substrate 10 in the shape of optical channel waveguides 11 to be formed as shown in FIGS. 1A and 2A.
- a Ta layer 21 , an Au layer 22 and a Ta layer 23 are formed by sputtering in this order on the surface of the substrate 10 over the resist layers 20 as shown in FIG. 1B.
- the layers 21 , 22 and 23 are, for instance, 15 nm, 10 nm and 15 nm respectively in thickness.
- the substrate 10 carrying thereon the resist layers 20 and the metal layers 21 , 22 and 23 is then dipped in acetone and subjected to ultrasonic cleaning, and the resist layers 20 and the Ta layer 21 , the Au layer 22 and the Ta layer 23 on the resist layers 20 are removed from the substrate 10 by liftoff as shown in FIGS. 1C and 2B.
- the substrate 10 is dipped in pyrophosphoric acid heated to 150° C. to 200° C. for a predetermined time, whereby the exposed part of the substrate 10 is subjected to proton exchange and optical channel waveguides 11 are formed on the surface of the substrate 10 as shown in FIG. 1D. Since the fractions of the metal film comprising the Ta layer 21 , the Au layer 22 and the Ta layer 23 left on the substrate 10 function as a mask upon proton exchange, the optical channel waveguides 11 formed are in the shape of the resist layers 20 .
- the resulting substrate 10 carrying thereon the optical channel waveguides 11 and the fractions of the metal layer are cleaned and subjected to heat treatment at 340° C. to 400° C. for a predetermined time. Then the upper Ta layer 23 is removed by etching with fluoronitric acid (1:2) as shown in FIG. 1E.
- a resist pattern having openings in portions where the wirings are to be formed is formed by lithography. Then Au/Cr is deposited on the substrate 10 by low resistance heating vacuum deposition and the resist pattern is removed by liftoff, leaving wirings 25 of Au/Cr as shown in FIG. 2C.
- negative photo-resist 26 is applied to the substrate 10 , and light is projected onto the surface of the substrate with the photo-resist 26 covered with a photo-mask having openings respectively corresponding to the electrodes 12 , 13 and 14 and the pad electrodes 16 , thereby exposing the portion of the photo-resist 26 not covered with the photo-mask. Then light is projected onto the backside of the substrate 10 so that the portions of the photo-resist 26 just above the optical channel waveguides 11 are exposed with the Ta layer 21 and the Au layer 22 functioning as a mask.
- Au layer 27 of, for instance, 1 to 4 ⁇ m is formed on the substrate 10 by electrolytic plating with the pattern of the photo-resist 26 used as a mask as shown in FIG. 1G.
- the resist layer 26 is removed by a plasma asher or resist release solution as shown in FIG. 2E, and the Au layer 22 and the Ta layer 21 are removed by etching using the Au layer 27 formed by the plating as a mask as shown in FIG. 1H.
- the electrodes 12 , 13 and 14 and the pad electrodes 16 consisting of the Ta layer 21 , the Au layer 22 and the plated Au layer 27 are formed as shown in FIG. 1H and 2F.
- the wirings 25 are plated with Au 27 and have an increased thickness.
- the electrodes 12 , 13 and 14 are formed by leaving the edges of the Ta layer 21 and the Au layer 22 which define the optical channel waveguides 11 and at the same time the Au layer 27 on the Ta layer 21 and the Au layer 22 is formed using the photo-resist pattern 26 , which precisely conforms to the shape of the optical channel waveguides 11 , as a mask so that the Au layer 27 cannot hang out over the optical channel waveguides 11 , the edges of the electrodes 12 , 13 and 14 facing the optical channel waveguides 11 are precisely in alignment with the edges of the optical channel waveguides 11 .
- the electrodes 12 , 13 and 14 and the pad electrodes 16 consist of the Ta layer 21 and the Au layer 22 plated with a thick Au layer 27 , they are low in electric resistance and can apply an electric voltage at a high frequency not lower than several hundred MHz, whereby high speed drive of the optical waveguide element can be realized.
- the resist layers 20 and the Ta layer 21 , the Au layer 22 and the Ta layer 23 on the resist layers 20 are removed from the substrate 10 by liftoff in the step shown in FIG. 1C, the Au layer 22 is not exposed. Accordingly, the problem of short circuit due to adhesion of particles of Au to the surface of Au layer and/or deterioration in bonding due to stain of the surface can be avoided.
- the dimensional accuracy of the openings can be higher than by forming the same by etching, which results in a higher dimensional accuracy of the optical channel waveguides 11 .
- the Ta layer 23 which is apt to be stained, is removed after the proton exchange, a clean surface of the Au layer 22 is exposed, whereby the contact resistance between the Au layers 22 and the wirings 25 can be reduced and at the same time, a uniform Au layer 27 can be obtained since the Au layer 22 wets well with plating solution.
- the width of the wirings 25 which extend across the optical channel waveguides 11 as measured in the direction in which an optical wave is guided is preferably not larger than 50 ⁇ m, whereby light propagation loss due to the wirings 25 can be reduced to about 5%.
- the Ta layer 23 which is relatively hard, cannot be damaged and accordingly the pattern of the optical channel waveguides 11 cannot be adversely affected.
- FIGS. 4A to 4 H are cross-sectional views taken along line B-B in FIG. 3A.
- Resist layers 20 are first formed by known lithography on the surface of a substrate 10 in the shape of optical channel waveguides 11 to be formed as shown in FIGS. 3A and 4A.
- a Ta layer 21 , an Au layer 22 and a Ta layer 23 are formed by sputtering in this order on the surface of the substrate 10 over the resist layers 20 as shown in FIG. 3B.
- the layers 21 , 22 and 23 are, for instance, 15 nm, 100 nm and 15 nm respectively in thickness.
- the substrate 10 carrying thereon the resist layers 20 and the metal layers 21 , 22 and 23 is then dipped in acetone and subjected to ultrasonic cleaning, and the resist layers 20 and the Ta layer 21 , the Au layer 22 and the Ta layer 23 on the resist layers 20 are removed from the substrate 10 by liftoff as shown in FIGS. 3C and 4B.
- the substrate 10 is dipped in pyrophosphoric acid heated to 150° C. to 200° C. for a predetermined time, whereby the exposed part of the substrate 10 is subjected to proton exchange and optical channel waveguides 11 are formed on the surface of the substrate 10 as shown in FIG. 3D. Since the fractions of the metal film comprising the Ta layer 21 , the Au layer 22 and the Ta layer 23 left on the substrate 10 function as a mask upon proton exchange, the optical channel waveguides 11 formed are in the shape of the resist layers 20 .
- the resulting substrate 10 carrying thereon the optical channel waveguides 11 and the fractions of the metal layer are cleaned and subjected to heat treatment at 340° C. to 400° C. for a predetermined time. Then the upper Ta layer 23 is removed by etching with fluoronitric acid (1:2) as shown in FIG. 3E.
- a resist pattern 30 for defining the shapes of the electrodes is formed on the substrate 10 as shown in FIG. 4C and the Ta layer 21 and the Au layer 22 are etched as shown in FIG. 4D using the resist pattern as a mask.
- a resist pattern having openings in portions where the wirings are to be formed is formed by lithography. Then Au/Cr is deposited on the substrate 10 by low resistance heating vacuum deposition and the resist pattern is removed by liftoff, leaving wirings 25 of Au/Cr as shown in FIG. 4E.
- Au layer 27 of, for instance, 1 to 4 ⁇ m is formed on the substrate 10 by electrolytic plating with the pattern of the photo-resist 26 used as a mask as shown in FIG. 3G.
- the resist layer 26 is removed by a plasma asher or resist release solution as shown in FIG. 4G. Then the substrate 10 is cut along the chained lines shown in FIG. 4 G. Thus the electrodes 12 , 13 and 14 and the pad electrodes 16 consisting of the Ta layer 21 , the Au layer 22 and the plated Au layer 27 are formed as shown in FIGS. 3H and 4H.
- FIGS. 5A to 5 E are cross-sectional views taken along line C-C in FIG. 6A.
- a substrate 10 carrying thereon the optical channel waveguides 11 and the fractions of the metal layers 21 and 22 as shown in FIGS. 5A and 6A is obtained in the same manner as in the first embodiment.
- photo-resist 40 is applied to the substrate and a photo-mask 41 shown in FIG. 6C is disposed on the backside of the substrate, and light is projected onto the backside of the substrate through the photo-mask 41 , thereby exposing the photo-resist 40 to light through the mask 41 .
- a pattern of the photo-resist 40 having one opening just above each of the optical channel waveguides 11 is formed as shown in FIGS. 5B and 6B.
- buffer layers 42 of SiO 2 are formed in a thickness of 100 nm to 500 nm, for instance, by sputtering using the resist pattern 40 as a mask as shown in FIG. 5C.
- Wirings 25 of Cr/Au are formed on the buffer layers 42 as shown in FIGS. 5E and 6E.
- electrodes for applying an electric voltage to the optical channel waveguides 11 are formed, for instance, in the manner described above in conjunction with the first embodiment.
- buffer layers 42 of SiO 2 between the optical channel waveguides 11 and the wirings 25 extending across the optical channel waveguides 11 , light propagation loss due to the wirings 25 can be reduced.
- FIGS. 7A to 7 E are cross-sectional views taken along line D-D in FIG. 8A.
- a substrate 10 carrying thereon the optical channel waveguides 11 and the fractions of the metal layers 21 and 22 as shown in FIGS. 7A and 8A is obtained in the same manner as in the first embodiment.
- photo-resist 40 is applied to the substrate and a photo-mask 41 shown in FIG. 8C is disposed on the backside of the substrate, and light is projected onto the backside of the substrate through the photo-mask 41 , thereby exposing the photo-resist 40 to light through the mask 41 .
- a pattern of the photo-resist 40 having one opening just above each of the optical channel waveguides 11 is formed as shown in FIGS. 7B and 8B.
- buffer layers 42 of SiO 2 and Cr/Au layers 45 are formed in this order, for instance, by sputtering using the resist pattern 40 as a mask as shown in FIG. 7C.
- the substrate is plated with Au 27 except the portions just above the optical channel waveguides 11 .
- Au 27 is formed on the Ta layer 21 and the Au layer 22 which form the electrodes for applying an electric voltage to the optical channel waveguides 11 and on the Cr/Au layer 45 forming the wirings as shown in FIG. 7E.
- the composite metal layer comprising the Au layer 27 , the Au layer 22 and the Ta layer 21 is processed to predetermined shapes of the electrodes, for instance, by etching.
- electrodes and wirings having increased thicknesses can be formed.
Abstract
Description
- 1. Field of the Invention
- This invention relates to an electrode for applying an electric voltage to an optical channel waveguide of an optical waveguide element in which the optical channel waveguide is formed by proton exchange, and a method of forming the electrode.
- 2. Description of the Related Art
- There have been provided various optical waveguide elements having an optical channel waveguide formed on a substrate. As a method of forming the optical channel waveguide, there has been known a proton exchange process.
- In the proton exchange process, metal film is first formed on a surface of a substrate, an opening is formed in the metal film by etching and proton exchange is carried out on the surface of the substrate using the metal film as a mask.
- Generally an electric voltage is applied to the optical channel waveguide through electrodes disposed near or just above the optical channel waveguide.
- A conventional method of forming the electrodes for applying an electric voltage to the optical channel waveguide will be described with reference to FIGS. 9A to9H, hereinbelow.
-
Metal film 2 such as of Cr is first formed on asubstrate 1 as shown in FIG. 9A. - A resist layer3 is formed on the
metal film 2 in a predetermined pattern by photolithography as shown in FIG. 9B. - Then the
metal film 2 is etched to formopenings 4 in a predetermined pattern in themetal film 2 using the resist layer 3 as a mask, and the resist layer 3 is removed as shown in FIG. 9C. - Thereafter proton exchange is carried out using the
metal film 2 with theopenings 4 as a mask, thereby formingoptical channel waveguides 5 on the surface of thesubstrate 1 as show in FIG. 9D. - The
metal film 2 is then removed by etching as shown in FIG. 9E and thesubstrate 1 is annealed as required. - Thereafter a
conductive film 7 such as of aluminum is formed over the surface of thesubstrate 1 as shown in FIG. 9F. - A
resist layer 8 is formed over theconductive film 7 with portions opposed to theoptical channel waveguides 5 exposed by photolithography as shown in FIG. 9G. - Then the
conductive film 7 is removed at the portions opposed to theoptical channel waveguides 5 by etching using theresist 8 as a mask as shown in FIG. 9H. - When the
resist 8 is thereafter removed, theconductive films 7 are left on opposite sides of eachoptical channel waveguide 5. Theconductive films 7 on opposite sides of eachoptical channel waveguide 5 can be used as electrodes for applying an electric voltage to theoptical channel waveguide 5. - However this method is disadvantageous in the following point. That is, when the
resist mask 8 is formed over theconductive film 7 with the portions opposed to theoptical channel waveguides 5 exposed, the edge of theresist mask 8 circumscribing theoptical channel waveguide 5 cannot be precisely aligned with the edge of theoptical channel waveguide 5 due to fluctuation in skill of the operator and/or in precision of the exposure device. Accordingly, the edges of the electrodes (conductive film) hang over the optical channel waveguide or are positioned away from the edge of theoptical channel waveguide 5 as shown in FIG. 10 in an enlarged scale, which results in fluctuation in performance of the optical waveguide element or deterioration in yield. In FIG. 10, L denotes the alignment error. - In Japanese Unexamined Patent Publication No. 7(1995)-146457, there is disclosed a method of forming the electrodes for a optical waveguide element which can overcome such a problem. In the method, the metal film which is used as a mask for setting the pattern of the optical waveguide upon proton exchange is left there and used as the electrodes. That is, metal film is formed on a surface of a substrate, openings of predetermined shapes are formed in the metal film, proton exchange is carried out on the surface of the substrate with the metal film used as a mask, thereby forming optical channel waveguides, and the metal film is removed with at least a part of the edges of the openings left there. The metal film fractions are used as the electrodes.
- In the method the openings of predetermined shapes are formed in the metal film generally by etching though liftoff may be used.
- When metal film is processed by etching or liftoff, the thickness of the metal film should be several hundred namometers (nm) at most. When such thin metal film is used as an electrode, the resistance of the electrodes becomes high and accordingly optical waveguide elements provided with such electrodes are hard to operate at high speed (e.g., high speed modulation at several hundred MHz or higher).
- In view of the foregoing observations and description, the primary object of the present invention is to provide an electrode for an optical waveguide element which is formed with its one edge precisely aligned with one edge of the optical channel waveguide and at the same time makes it feasible to operate the optical waveguide element at high speed.
- Another object of the present invention is to provide a method of forming such electrodes for an optical waveguide element.
- In the method of the present invention, a part of the metal film which is used as a mask for setting the pattern of the optical waveguide upon proton exchange is left there as in the above identified Japanese patent publication (Japanese Unexamined Patent Publication No. 7(1995)-146457), then the metal film is plated and used as the electrodes.
- That is, in accordance with a first aspect of the present invention, there is provided a method of forming electrodes for an optical waveguide element comprising the steps of
- forming a metal film on a surface of a substrate,
- forming openings of predetermined shapes in the metal film,
- carrying out proton exchange on the surface of the substrate with the metal film used as a mask, thereby forming optical channel waveguides,
- leaving at least a part of edge portions of the metal film defining the openings,
- plating the metal film with plating metal, and
- processing the metal film plated with the plating metal into electrodes of predetermined shapes for applying an electric voltage to the optical channel waveguides.
- In the method of forming electrodes for an optical waveguide element in accordance with a second aspect of the present invention, the metal film used as a mask in the proton exchange is first processed into metal film fractions of predetermined shapes corresponding to the shapes of electrodes to be formed, each metal film fraction including at least a part of an edge portion defining one of the openings, and then the metal film fractions are plated with plating metal and used as the electrodes for applying an electric voltage to the optical channel waveguides.
- In the method of forming electrodes for an optical waveguide element in accordance with a third aspect of the present invention, in the method of the first or second aspect of the present invention, negative photo-resist is applied to the substrate after said proton exchange and before said plating, then the photo-resist is exposed to light from the back side of the substrate using the metal film as a photo-mask, the photo-resist is subsequently removed with the part of the photo-resist which is on the optical channel waveguides and accordingly exposed to light left there, and then the plating is effected using as a mask the part of the photo-resist left on the substrate.
- In accordance with a fourth aspect of the present invention, there is provided an electrode for an optical waveguide element which is formed on a substrate, on which an optical channel waveguide is formed by proton exchange, with its one edge aligned with one edge of the optical channel waveguide and is for applying an electric voltage to the optical channel waveguide, wherein the improvement comprises that the electrode comprises a metal film fraction which is a part of metal film used as a mask when the optical channel waveguide is formed by the proton exchange and a plating metal layer formed on the metal film fraction by plating.
- Preferably a buffer layer is formed between the substrate and the metal film.
- The metal film used as a mask for setting the pattern of the optical channel waveguide upon proton exchange naturally has an edge aligned with an edge of the optical channel waveguide. Accordingly when an electrode is formed by plating the metal film including at least a part of an edge portion defining one of the openings, the edge of the electrode can be precisely aligned with the edge of the optical channel waveguide.
- When the metal film plated with metal is used as an electrode, the thickness of the electrode increases and the resistance of the electrode lowers as compared with when the metal film is used as an electrode as it is. Accordingly the optical waveguide element in which an electric voltage is applied to the optical channel waveguide through the electrode can be operated at high speed.
- When the plating metal layer comes to hang out over the optical channel waveguide from the edge of the metal film, the finished electrode cannot have an edge aligned with the edge of the optical channel waveguide even if the metal film on which the plating metal is plated has an edge aligned with the edge of the optical channel waveguide, which results in the same problem as that described above in conjunction with FIG. 10.
- The method in accordance with the third aspect of the present invention can overcome this problem. That is, when the negative photo-resist applied to the substrate after the proton exchange is exposed to light from the back side of the substrate using the metal film as a mask, the exposed part of the photo-resist has an edge precisely aligned with the edge of the optical channel waveguide. Accordingly, by removing the negative photo-resist with the exposed part left there and effecting the plating using the exposed part of the photo-resist as a mask, the plating metal cannot hang out over the optical channel waveguide and the edge of the electrode plated with the plating metal can be precisely aligned with the edge of the optical channel waveguide.
- When a buffer layer is formed between the substrate and the metal film, light propagation loss due to the electrode can be reduced.
- FIGS. 1A to1H are views for illustrating the procedure of forming the electrodes of an optical waveguide element by a method in accordance with a first embodiment of the present invention,
- FIGS. 2A to2F are plan views showing the state of the substrate at different steps shown in FIGS. 1A to 1H,
- FIGS. 3A to3H are views for illustrating the procedure of forming the electrodes of an optical waveguide element by a method in accordance with a second embodiment of the present invention,
- FIGS. 4A to4H are plan views showing the state of the substrate at different steps shown in FIGS. 3A to 3H,
- FIGS. 5A to5E are views for illustrating the procedure of forming the electrodes of an optical waveguide element by a method in accordance with a third embodiment of the present invention,
- FIGS. 6A to6D are plan views showing the state of the substrate at different steps shown in FIGS. 5A to 5E,
- FIGS. 7A to7E are views for illustrating the procedure of forming the electrodes of an optical waveguide element by a method in accordance with a fourth embodiment of the present invention,
- FIGS. 8A to8C are plan views showing the state of the substrate at different steps shown in FIGS. 7A to 7E,
- FIGS. 9A to9H are views for illustrating the procedure of forming the electrodes of an optical waveguide element by a conventional method, and
- FIG. 10 is a view for illustrating alignment error of the electrodes formed by the conventional method.
- A finished optical waveguide element will be first described with reference to FIG. 2F for the purpose of simplicity of understanding. As shown in FIG. 2F, the finished optical waveguide element comprises a
substrate 10 which may comprise an x-plate of, for instance, a LiNbO3 crystal. A pair ofoptical channel waveguides 11, which form a directional photocoupler, are formed on a surface of thesubstrate 10 to extend in Y-direction, and threeelectrodes substrate 10 on opposite sides of the portions of theoptical channel waveguides 11 where they extend in parallel to each other close to each other and between the portions. Theelectrodes electrode 13 is connected to the drive circuit byway pad electrodes 16. A predetermined electric voltage is applied to each of theoptical channel waveguides 11 through theelectrodes - Each of the edges of the
electrodes optical channel waveguides 11 should be precisely aligned with the corresponding edge of theoptical channel waveguides 11. Otherwise it becomes difficult to precisely apply the predetermined voltage to eachoptical channel waveguide 11. - A method in accordance with a first embodiment of the present invention which makes it feasible to form the
electrodes - Resist
layers 20 are first formed by known lithography on the surface of asubstrate 10 in the shape ofoptical channel waveguides 11 to be formed as shown in FIGS. 1A and 2A. - Then a
Ta layer 21, anAu layer 22 and aTa layer 23 are formed by sputtering in this order on the surface of thesubstrate 10 over the resistlayers 20 as shown in FIG. 1B. Thelayers - The
substrate 10 carrying thereon the resistlayers 20 and the metal layers 21, 22 and 23 is then dipped in acetone and subjected to ultrasonic cleaning, and the resistlayers 20 and theTa layer 21, theAu layer 22 and theTa layer 23 on the resistlayers 20 are removed from thesubstrate 10 by liftoff as shown in FIGS. 1C and 2B. - The
substrate 10 is dipped in pyrophosphoric acid heated to 150° C. to 200° C. for a predetermined time, whereby the exposed part of thesubstrate 10 is subjected to proton exchange andoptical channel waveguides 11 are formed on the surface of thesubstrate 10 as shown in FIG. 1D. Since the fractions of the metal film comprising theTa layer 21, theAu layer 22 and theTa layer 23 left on thesubstrate 10 function as a mask upon proton exchange, theoptical channel waveguides 11 formed are in the shape of the resist layers 20. - The resulting
substrate 10 carrying thereon theoptical channel waveguides 11 and the fractions of the metal layer are cleaned and subjected to heat treatment at 340° C. to 400° C. for a predetermined time. Then theupper Ta layer 23 is removed by etching with fluoronitric acid (1:2) as shown in FIG. 1E. - In order to form wirings for connecting the
central electrode 13 and the pad electrodes 16 (FIG. 2F), a resist pattern having openings in portions where the wirings are to be formed is formed by lithography. Then Au/Cr is deposited on thesubstrate 10 by low resistance heating vacuum deposition and the resist pattern is removed by liftoff, leavingwirings 25 of Au/Cr as shown in FIG. 2C. - Thereafter negative photo-resist26 is applied to the
substrate 10, and light is projected onto the surface of the substrate with the photo-resist 26 covered with a photo-mask having openings respectively corresponding to theelectrodes pad electrodes 16, thereby exposing the portion of the photo-resist 26 not covered with the photo-mask. Then light is projected onto the backside of thesubstrate 10 so that the portions of the photo-resist 26 just above theoptical channel waveguides 11 are exposed with theTa layer 21 and theAu layer 22 functioning as a mask. (The portions corresponding to thewiring 25 are not exposed.) When the photo-resist is developed, only the exposed portions of the photo-resist 26 are left on thesubstrate 10 as shown in FIGS. 1F and 2D. The order of the exposure from the front side of the substrate and the exposure from the backside of the substrate may be reversed. - Then
Au layer 27 of, for instance, 1 to 4 μm is formed on thesubstrate 10 by electrolytic plating with the pattern of the photo-resist 26 used as a mask as shown in FIG. 1G. - The resist
layer 26 is removed by a plasma asher or resist release solution as shown in FIG. 2E, and theAu layer 22 and theTa layer 21 are removed by etching using theAu layer 27 formed by the plating as a mask as shown in FIG. 1H. Thus theelectrodes pad electrodes 16 consisting of theTa layer 21, theAu layer 22 and the platedAu layer 27 are formed as shown in FIG. 1H and 2F. Also thewirings 25 are plated withAu 27 and have an increased thickness. - Since the
electrodes Ta layer 21 and theAu layer 22 which define theoptical channel waveguides 11 and at the same time theAu layer 27 on theTa layer 21 and theAu layer 22 is formed using the photo-resistpattern 26, which precisely conforms to the shape of theoptical channel waveguides 11, as a mask so that theAu layer 27 cannot hang out over theoptical channel waveguides 11, the edges of theelectrodes optical channel waveguides 11 are precisely in alignment with the edges of theoptical channel waveguides 11. - Since the
electrodes pad electrodes 16 consist of theTa layer 21 and theAu layer 22 plated with athick Au layer 27, they are low in electric resistance and can apply an electric voltage at a high frequency not lower than several hundred MHz, whereby high speed drive of the optical waveguide element can be realized. - Further when the resist
layers 20 and theTa layer 21, theAu layer 22 and theTa layer 23 on the resistlayers 20 are removed from thesubstrate 10 by liftoff in the step shown in FIG. 1C, theAu layer 22 is not exposed. Accordingly, the problem of short circuit due to adhesion of particles of Au to the surface of Au layer and/or deterioration in bonding due to stain of the surface can be avoided. - By forming the openings for defining the shape of the
optical channel waveguides 11 by liftoff of the resistlayers 20 and theTa layer 21, theAu layer 22 and theTa layer 23 on the resistlayers 20, the dimensional accuracy of the openings can be higher than by forming the same by etching, which results in a higher dimensional accuracy of theoptical channel waveguides 11. - When the
Ta layer 23, which is apt to be stained, is removed after the proton exchange, a clean surface of theAu layer 22 is exposed, whereby the contact resistance between the Au layers 22 and thewirings 25 can be reduced and at the same time, auniform Au layer 27 can be obtained since theAu layer 22 wets well with plating solution. - The width of the
wirings 25 which extend across theoptical channel waveguides 11 as measured in the direction in which an optical wave is guided is preferably not larger than 50 μm, whereby light propagation loss due to thewirings 25 can be reduced to about 5%. - Further even when fine dust on the surface of the substrate is removed by a mechanical process, for instance, by brush scrape before the proton exchange, the
Ta layer 23, which is relatively hard, cannot be damaged and accordingly the pattern of theoptical channel waveguides 11 cannot be adversely affected. - Though, in the first embodiment, the
Ta layer 21 and theAu layer 22 are processed to a predetermined shape after plated withAu 27, theTa layer 21 and theAu layer 22 are processed to a predetermined shape before plated withAu 27 in a second embodiment described hereinbelow with reference to FIGS. 3A to 3H and 4A to 4H. FIGS. 4A to 4H are cross-sectional views taken along line B-B in FIG. 3A. - Resist
layers 20 are first formed by known lithography on the surface of asubstrate 10 in the shape ofoptical channel waveguides 11 to be formed as shown in FIGS. 3A and 4A. - Then a
Ta layer 21, anAu layer 22 and aTa layer 23 are formed by sputtering in this order on the surface of thesubstrate 10 over the resistlayers 20 as shown in FIG. 3B. Thelayers - The
substrate 10 carrying thereon the resistlayers 20 and the metal layers 21, 22 and 23 is then dipped in acetone and subjected to ultrasonic cleaning, and the resistlayers 20 and theTa layer 21, theAu layer 22 and theTa layer 23 on the resistlayers 20 are removed from thesubstrate 10 by liftoff as shown in FIGS. 3C and 4B. - The
substrate 10 is dipped in pyrophosphoric acid heated to 150° C. to 200° C. for a predetermined time, whereby the exposed part of thesubstrate 10 is subjected to proton exchange andoptical channel waveguides 11 are formed on the surface of thesubstrate 10 as shown in FIG. 3D. Since the fractions of the metal film comprising theTa layer 21, theAu layer 22 and theTa layer 23 left on thesubstrate 10 function as a mask upon proton exchange, theoptical channel waveguides 11 formed are in the shape of the resist layers 20. - The resulting
substrate 10 carrying thereon theoptical channel waveguides 11 and the fractions of the metal layer are cleaned and subjected to heat treatment at 340° C. to 400° C. for a predetermined time. Then theupper Ta layer 23 is removed by etching with fluoronitric acid (1:2) as shown in FIG. 3E. - Thereafter, a resist
pattern 30 for defining the shapes of the electrodes is formed on thesubstrate 10 as shown in FIG. 4C and theTa layer 21 and theAu layer 22 are etched as shown in FIG. 4D using the resist pattern as a mask. - In order to form wirings for connecting the
central electrode 13 and the pad electrodes 16 (FIG. 3F), a resist pattern having openings in portions where the wirings are to be formed is formed by lithography. Then Au/Cr is deposited on thesubstrate 10 by low resistance heating vacuum deposition and the resist pattern is removed by liftoff, leavingwirings 25 of Au/Cr as shown in FIG. 4E. - Thereafter negative photo-resist26 is applied to the
substrate 10, and light is projected onto the backside of thesubstrate 10 so that the portions of the photo-resist 26 just above theoptical channel waveguides 11 are exposed with theTa layer 21 and theAu layer 22 functioning as a mask. (The portions corresponding to thewirings 25 are not exposed.) When the photo-resist is developed, only the exposed portions of the photo-resist 26 are left on thesubstrate 10 as shown in FIGS. 3F and 4F. - Then
Au layer 27 of, for instance, 1 to 4 μm is formed on thesubstrate 10 by electrolytic plating with the pattern of the photo-resist 26 used as a mask as shown in FIG. 3G. - The resist
layer 26 is removed by a plasma asher or resist release solution as shown in FIG. 4G. Then thesubstrate 10 is cut along the chained lines shown in FIG. 4G. Thus theelectrodes pad electrodes 16 consisting of theTa layer 21, theAu layer 22 and the platedAu layer 27 are formed as shown in FIGS. 3H and 4H. - The advantage of the second embodiment is basically the same as that of the first embodiment.
- A third embodiment of the present invention will be described hereinbelow with reference to FIGS. 5A to5E and 6A to 6E. FIGS. 5A to 5E are cross-sectional views taken along line C-C in FIG. 6A.
- A
substrate 10 carrying thereon theoptical channel waveguides 11 and the fractions of the metal layers 21 and 22 as shown in FIGS. 5A and 6A is obtained in the same manner as in the first embodiment. - Thereafter, positive photo-resist40 is applied to the substrate and a photo-
mask 41 shown in FIG. 6C is disposed on the backside of the substrate, and light is projected onto the backside of the substrate through the photo-mask 41, thereby exposing the photo-resist 40 to light through themask 41. When the photo-resist 40 is subsequently developed, a pattern of the photo-resist 40 having one opening just above each of theoptical channel waveguides 11 is formed as shown in FIGS. 5B and 6B. - Then buffer layers42 of SiO2 are formed in a thickness of 100 nm to 500 nm, for instance, by sputtering using the resist
pattern 40 as a mask as shown in FIG. 5C. - Thereafter the photo-resist40 is removed by liftoff. In this manner a
buffer layer 42 of SiO2 is formed on each of theoptical channel waveguides 11 as shown in FIGS. 5D and 6D. - Wirings25 of Cr/Au are formed on the buffer layers 42 as shown in FIGS. 5E and 6E.
- Thereafter electrodes for applying an electric voltage to the
optical channel waveguides 11 are formed, for instance, in the manner described above in conjunction with the first embodiment. - By thus forming buffer layers42 of SiO2 between the
optical channel waveguides 11 and thewirings 25 extending across theoptical channel waveguides 11, light propagation loss due to thewirings 25 can be reduced. - A fourth embodiment of the present invention will be described hereinbelow with reference to FIGS. 7A to7E and 8A to 8D. FIGS. 7A to 7E are cross-sectional views taken along line D-D in FIG. 8A.
- A
substrate 10 carrying thereon theoptical channel waveguides 11 and the fractions of the metal layers 21 and 22 as shown in FIGS. 7A and 8A is obtained in the same manner as in the first embodiment. - Thereafter, positive photo-resist40 is applied to the substrate and a photo-
mask 41 shown in FIG. 8C is disposed on the backside of the substrate, and light is projected onto the backside of the substrate through the photo-mask 41, thereby exposing the photo-resist 40 to light through themask 41. When the photo-resist 40 is subsequently developed, a pattern of the photo-resist 40 having one opening just above each of theoptical channel waveguides 11 is formed as shown in FIGS. 7B and 8B. - Then buffer layers42 of SiO2 and Cr/Au layers 45 are formed in this order, for instance, by sputtering using the resist
pattern 40 as a mask as shown in FIG. 7C. - Thereafter the photo-resist40 is removed by liftoff. In this manner, a
buffer layer 42 of SiO2 and a wiring of Cr/Au layer 45 are formed on each of theoptical channel waveguides 11 as shown in FIGS. 7D and 8D. - Then the substrate is plated with
Au 27 except the portions just above theoptical channel waveguides 11. Thus athick Au layer 27 is formed on theTa layer 21 and theAu layer 22 which form the electrodes for applying an electric voltage to theoptical channel waveguides 11 and on the Cr/Au layer 45 forming the wirings as shown in FIG. 7E. - Thereafter the composite metal layer comprising the
Au layer 27, theAu layer 22 and theTa layer 21 is processed to predetermined shapes of the electrodes, for instance, by etching. Thus electrodes and wirings having increased thicknesses can be formed.
Claims (11)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US09/527,468 US6355496B2 (en) | 1996-10-28 | 2000-03-17 | Electrode for optical waveguide element |
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP28480096A JP3827780B2 (en) | 1996-10-28 | 1996-10-28 | Electrode for optical waveguide device and method for forming the same |
JP284800/1996 | 1996-10-28 | ||
JP8-284800 | 1996-10-28 | ||
US08/958,581 US6060334A (en) | 1996-10-28 | 1997-10-28 | Electrode for optical waveguide element and method of forming the same |
US09/527,468 US6355496B2 (en) | 1996-10-28 | 2000-03-17 | Electrode for optical waveguide element |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US08/958,581 Division US6060334A (en) | 1996-10-28 | 1997-10-28 | Electrode for optical waveguide element and method of forming the same |
Publications (2)
Publication Number | Publication Date |
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US20010046722A1 true US20010046722A1 (en) | 2001-11-29 |
US6355496B2 US6355496B2 (en) | 2002-03-12 |
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US08/958,581 Expired - Lifetime US6060334A (en) | 1996-10-28 | 1997-10-28 | Electrode for optical waveguide element and method of forming the same |
US09/527,468 Expired - Fee Related US6355496B2 (en) | 1996-10-28 | 2000-03-17 | Electrode for optical waveguide element |
Family Applications Before (1)
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US08/958,581 Expired - Lifetime US6060334A (en) | 1996-10-28 | 1997-10-28 | Electrode for optical waveguide element and method of forming the same |
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US (2) | US6060334A (en) |
JP (1) | JP3827780B2 (en) |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2005121842A1 (en) | 2004-06-09 | 2005-12-22 | Schott Ag | Building up diffractive optics by structured glass coating |
US10185165B2 (en) | 2015-03-31 | 2019-01-22 | Sumitomo Osaka Cement Co., Ltd. | Optical waveguide device |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
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US6596557B1 (en) * | 2000-03-02 | 2003-07-22 | Orchid Lightwave Communications, Inc. | Integrated optical devices and methods of making such devices |
JP2014165337A (en) * | 2013-02-25 | 2014-09-08 | Rohm Co Ltd | Light-emitting element, light-emitting element package, and method of manufacturing light-emitting element |
CN112764245B (en) * | 2021-01-26 | 2022-05-17 | 济南晶正电子科技有限公司 | Electro-optic crystal film, preparation method and electronic component |
CN115110050B (en) * | 2022-07-01 | 2023-12-05 | 复旦大学 | Method for preparing ultrathin coplanar waveguide with front and back communicated surfaces on diamond surface |
Family Cites Families (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3616282A (en) * | 1968-11-14 | 1971-10-26 | Hewlett Packard Co | Method of producing thin-film circuit elements |
FR2606554A1 (en) * | 1986-11-10 | 1988-05-13 | Schweizer Pascal | Method of manufacturing integrated electro-optical components requiring just a single masking operation and the components arising from the said method |
JPH0792574B2 (en) * | 1988-12-21 | 1995-10-09 | インターナショナル・ビジネス・マシーンズ・コーポレーション | Liquid crystal display device and manufacturing method thereof |
JPH077135B2 (en) * | 1989-02-09 | 1995-01-30 | 松下電器産業株式会社 | Optical waveguide, optical wavelength conversion element, and method for manufacturing short wavelength laser light source |
JPH0830767B2 (en) * | 1992-10-30 | 1996-03-27 | 日本電気株式会社 | Hologram element |
JP3317313B2 (en) * | 1993-11-25 | 2002-08-26 | 富士写真フイルム株式会社 | Method for forming electrode of optical waveguide element |
JP2674535B2 (en) * | 1994-12-15 | 1997-11-12 | 日本電気株式会社 | Light control device |
US5834055A (en) * | 1995-08-30 | 1998-11-10 | Ramar Corporation | Guided wave device and method of fabrication thereof |
US5895742A (en) * | 1996-07-19 | 1999-04-20 | Uniphase Telecommunications Products, Inc. | Velocity-matched traveling-wave electro-optical modulator using a benzocyclobutene buffer layer |
JP3791630B2 (en) * | 1996-09-20 | 2006-06-28 | 富士写真フイルム株式会社 | Optical wavelength conversion element |
-
1996
- 1996-10-28 JP JP28480096A patent/JP3827780B2/en not_active Expired - Fee Related
-
1997
- 1997-10-28 US US08/958,581 patent/US6060334A/en not_active Expired - Lifetime
-
2000
- 2000-03-17 US US09/527,468 patent/US6355496B2/en not_active Expired - Fee Related
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2005121842A1 (en) | 2004-06-09 | 2005-12-22 | Schott Ag | Building up diffractive optics by structured glass coating |
US20080248267A1 (en) * | 2004-06-09 | 2008-10-09 | Schott Ag | Building Up Diffractive Optics by Structured Glass Coating |
US8741550B2 (en) | 2004-06-09 | 2014-06-03 | Schott Ag | Building up diffractive optics by structured glass coating |
US10185165B2 (en) | 2015-03-31 | 2019-01-22 | Sumitomo Osaka Cement Co., Ltd. | Optical waveguide device |
Also Published As
Publication number | Publication date |
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JP3827780B2 (en) | 2006-09-27 |
US6355496B2 (en) | 2002-03-12 |
US6060334A (en) | 2000-05-09 |
JPH10133237A (en) | 1998-05-22 |
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