JP2007079465A - Optical control element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical control element with high productivity and its manufacturing method by preventing a thin plate and an electrode on the thin plate from being broken in a polishing process for a substrate, a wafer heating process, and further a substrate cutting process etc., when the optical control element using the substrate which is made thin is manufactured. <P>SOLUTION: The manufacturing method for the optical control element which has a thin plate 1 of ≤50 μm in thickness formed of the substrate having electrooptical effect, an optical waveguide formed on the thin plate, and electrodes 3 and 4 for control which modulates an optical wave propagated in the optical waveguide is characterized in that when the electrodes for control are formed on the substrate, a protection electrode 12 is formed of the same material with the electrode for control on a substrate surface except the electrodes for control. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light control element and a method for manufacturing the same, and particularly relates to a light control element using a thin plate having a thickness of 50 μm or less formed of a substrate having an electro-optic effect.

Conventionally, in the optical communication field and the optical measurement field, a light control element such as a waveguide type light modulator in which an optical waveguide or a modulation electrode is formed on a substrate having an electro-optic effect is widely used.
In order to realize a wider optical modulation frequency, it is important to match the speed of the modulation signal microwave and the light wave, and various methods have been devised so far. Specific examples include thicker buffer layers, higher aspect ratios of electrodes, and ridge structures.

In Patent Document 1 or 2 below, an optical waveguide and a modulation electrode are incorporated in an extremely thin substrate (hereinafter referred to as “first substrate”) having a thickness of 30 μm or less, and the dielectric constant is lower than that of the first substrate. Other substrates are bonded to reduce the effective refractive index with respect to the microwave, thereby achieving speed matching between the microwave and the light wave.
JP-A 64-18121 JP 2003-215519 A

By using the thinned first substrate like this, the design flexibility of the light control element is dramatically increased. For example, an optical modulator having a wide band and a low driving voltage can be manufactured without using a buffer layer. It becomes possible. Furthermore, from the viewpoint of reducing the propagation speed of microwaves, it is synonymous with the use of a material having a low dielectric constant for the substrate. Specifically, the first substrate is specifically set to 150 μm or less, and particularly in the region of 26 GHz or more The following non-patent document 1 discloses that the influence of the dielectric loss (tan δ) of the wave itself can be reduced, and is applied to widening the bandwidth of the optical modulator.
Y. Yamane et.al., “Investigation of sandblast machining techniques for broadband LN modulators”, Sumitomo Osaka Cement Technical report 2002, pp49-54 (2003)

  On the other hand, as shown in FIG. 1, in an optical control element such as an optical modulator, an optical waveguide 2 is formed on a substrate 1 having an electro-optic effect, and control for modulating a light wave propagating through the optical waveguide is performed. An electrode is formed. As shown in FIG. 1, the control electrode is made up of the signal electrode 3, the ground electrode 4, and the like, and the substrate surface or the buffer layer formed on the substrate surface is exposed in a region that does not contribute to light modulation. .

  In the light control element as shown in FIG. 1, usually, a plurality of light control elements are formed in one wafer (a substrate of several inches φ having an electro-optic effect), and finally the wafer is cut. Thus, individual light control elements are manufactured. Further, in the light control element having the thin substrate as described above, the back surface of the substrate is polished in a wafer state to reduce the thickness. Further, a wafer heating process is also performed, such as doping impurities on the thinned substrate or heating the substrate at a predetermined temperature to remove distortion of the substrate.

  In the polishing step, as shown in FIG. 2, after the control electrodes 3 and 4 are formed on the wafer-like substrate 1, the substrate 1 is fixed to the polishing dummy substrate 11 with an adhesive 10 such as wax. The back side is polished. However, since the control electrodes 3 and 4 are only discretely arranged at the time of the polishing process, the stress at the time of polishing applied to the joint portion between the substrate 1 and the adhesive 10 is a portion indicated by A or B in FIG. Such as a part of the control electrode is peeled off from the substrate 1.

  Further, in the wafer heating process and the substrate cutting process for the thinned substrate, the thermal stress and mechanical strength are different between the portion where the control electrode is formed and the portion where these are not formed, and the substrate 1 can be easily formed. It was causing problems such as damage.

  The problem to be solved by the present invention is to solve the above-mentioned problems, in the production of a light control element using a thinned substrate, in the polishing process of the substrate, the wafer heating process, and further in the substrate cutting process. An object of the present invention is to provide a light control element with high productivity and a method for manufacturing the same, by preventing the thin plate and the electrode on the thin plate from being damaged.

In order to solve the above-mentioned problem, in the invention according to claim 1, a thin plate having a thickness of 50 μm or less formed of a substrate having an electro-optic effect, an optical waveguide formed on the thin plate, and propagating through the optical waveguide In the manufacturing method of the light control element having the control electrode for modulating the light wave, when forming the control electrode on the substrate, the protective electrode is made of the same material as the control electrode on the substrate surface other than the control electrode It is characterized by forming.
`` Protective electrode '' in the present invention is not an electrode related to the drive or operation of the light control element, but when manufacturing the light control element, the thermal stress and mechanical stress applied to the thinned substrate are relaxed, It means an electrode that functions to increase the mechanical strength of the substrate.

  The invention according to claim 2 is characterized in that, in the method for manufacturing a light control element according to claim 1, a groove is formed in the protective electrode.

  According to a third aspect of the present invention, in the method for manufacturing a light control element according to the first or second aspect, after the formation of the protective electrode, any one of a polishing process of the back surface of the substrate, a wafer heating process, or a substrate cutting process. It is characterized by performing.

  In the invention according to claim 4, a thin plate formed of a substrate having an electro-optic effect and having a thickness of 50 μm or less, an optical waveguide formed on the thin plate, and a control for modulating a light wave propagating through the optical waveguide A light control element having a control electrode has a protective electrode formed of the same material as the control electrode on a substrate surface other than the control electrode.

  The invention according to claim 5 is the light control element according to claim 4, wherein the protective electrode is electrically connected to a ground electrode constituting the control electrode.

  According to the first aspect of the invention, when the control electrode is formed on the substrate, the protective electrode is formed of the same material as the control electrode on the surface of the substrate other than the control electrode, thereby increasing the mechanical strength of the substrate. Even when thermal stress or mechanical stress is applied to the substrate, the protective electrode has the same mechanical and thermal characteristics as the control electrode, so that the substrate does not break down. Moreover, since the protective electrode can be formed by the same formation method as the control electrode, the manufacturing process is not complicated.

  According to the second aspect of the present invention, since the protective electrode has a groove, the adhesive enters the groove when the substrate is bonded to the polishing dummy substrate with an adhesive during polishing of the substrate, and the entire substrate In addition, the adhesive spreads efficiently and the bonding strength at the time of bonding can be further increased. Further, when thermal stress or mechanical stress is applied to the substrate, it is possible to effectively prevent the substrate from being damaged by preventing the stress from being transmitted by the groove.

  According to the third aspect of the present invention, after forming the protective electrode, any one of the polishing process on the back surface of the substrate, the wafer heating process, or the substrate cutting process is performed. In the process or the substrate cutting process, the substrate can be effectively protected.

  According to the invention of claim 4, since the light control element has a protective electrode formed of the same material as the control electrode on the substrate surface other than the control electrode, the substrate is damaged at the time of manufacturing the light control element. This makes it possible to eliminate problems such as In addition, even after the light control element is completed, the mechanical strength of the thin plate constituting the light control element is increased, and the thin plate is also resistant to thermal stress distortion due to temperature changes and mechanical stress distortion due to mechanical shock and pressurization. It is possible to effectively suppress the breakage and local deformation.

  According to the fifth aspect of the present invention, since the protective electrode is electrically connected to the ground electrode constituting the control electrode, the protective electrode does not operate as a floating electrode and has an electrically stable structure.

Hereinafter, the present invention will be described in detail using preferred examples.
The present invention includes a thin plate having a thickness of 50 μm or less formed of a substrate having an electro-optic effect, an optical waveguide formed on the thin plate, and a control electrode for modulating a light wave propagating through the optical waveguide. In the method for manufacturing a light control element, a protective electrode is formed of the same material as the control electrode on the substrate surface other than the control electrode when the control electrode is formed on the substrate.

  As the substrate having an electro-optic effect, for example, lithium niobate, lithium tantalate, PLZT (lead lanthanum zirconate titanate), quartz-based materials, and combinations thereof can be used. In particular, lithium niobate (LN) or lithium tantalate (LT) crystals having a high electro-optic effect are preferably used.

  The optical waveguide is formed by thermally diffusing impurities such as Ti on the substrate. In order to form the control electrode, an underlayer such as Ti or Au is formed by a vapor deposition method, a predetermined electrode pattern is left by a photolithography method, the underlayer is masked, and an Au electrode is formed by an electrolytic plating method. To do. Thereafter, the photoresist film and a part of the base layer are removed by wet etching.

  A feature of the light control element according to the present invention is that it has a protective electrode 12 in addition to the control electrodes 3 and 4 formed on the substrate 1 as shown in FIG. Such a protective electrode is formed by the same method as the control electrode, and is preferably formed simultaneously with the control electrode from the viewpoint of productivity.

The protective electrode 12 is formed on the substrate 1 as much as possible within the range where the control electrode signal electrode and the gap between the signal electrode and the ground electrode are not deformed or eliminated in the region where the control electrode is not formed. It is formed so as to cover the surface. Further, when a buffer layer (not shown) made of SiO ₂ or the like is not formed between the substrate 1 and the control electrode, the optical waveguide formed on the surface of the substrate 1 and the protective electrode are not in direct contact with each other. Furthermore, it is preferable to determine the shape of the protective electrode.

  By forming such a protective electrode 12, even when the substrate 1 is bonded to the polishing dummy substrate 11 via the adhesive 10 and polished, the control electrodes 3 and 4 are prevented from being damaged and extremely stable. Thus, the light control element can be manufactured.

FIG. 4 is a view showing a state in which a plurality of light control elements are formed on the wafer substrate 20.
Each light control element has a signal electrode 3 that is a part of the control electrode. In FIG. 4, the ground electrode and the protective electrode in each element are not shown. A protective electrode 21 is also formed in a shaded area on the wafer substrate other than the light control element. Preferably, as shown in FIG. 4, a plurality of grooves 22 and 23 are formed in the protective electrode at a depth of about 10 to 30 μm.

  As shown in FIG. 4, since the protective electrode 21 is formed on the entire wafer, the mechanical strength can be increased even when the wafer substrate 20 is thinned. In addition, in the wafer heating process and the substrate cutting process, Even if thermal stress or mechanical stress is applied to the wafer substrate 20, there are few areas where stress distortion occurs, and the substrate itself is prevented from being damaged.

When the substrate is bonded to the polishing dummy substrate with an adhesive when the substrate is polished by the grooves 22 and 23 formed in the protective electrode, the adhesive enters the groove and rotates the wafer substrate 20 by spin coating or the like. However, the adhesive spreads efficiently over the entire substrate. In addition, the bonding strength at the time of bonding can be further increased by the adhesive that has entered the groove.
Further, when thermal stress or mechanical stress is applied to the wafer substrate 20 as in the wafer heating process or the substrate cutting process, the groove prevents the stress from being transmitted to the entire substrate by the groove. Can be effectively suppressed.

FIG. 5 is a diagram showing another example in which a protective electrode is formed on each light control element.
The protective electrode on the substrate can be formed integrally with the ground electrode 4 of the control electrode. As shown in FIG. 5, it is possible to cover all the substrates as shown by the region C except for the signal electrode 3 and the gap between the signal electrode 3 and the ground electrode 4. It is necessary to form a buffer layer between the protective electrode and the substrate so that the light wave propagating through the waveguide 2 is not absorbed by the protective electrode.
On the other hand, as indicated by the region D, the protective electrode can be formed so as to exclude the portion of the optical waveguide 2.

The present invention can be suitably used particularly for a light control element using a substrate having a thickness of 50 μm or less, but is not limited thereto, and the present invention is applied to a substrate having a thickness of 50 μm or more. Even so, it is possible to achieve a certain effect.
When a substrate (thin plate) having a thickness of 50 μm or less is used, an adhesive or a direct bonding method is used on the back surface of the thin plate to further increase the mechanical strength as the light control element. Join.

  According to the light control element and the method of manufacturing the same according to the present invention, a thin plate or a thin plate can be used in a substrate polishing process, a wafer heating process, or a substrate cutting process when manufacturing a light control element using a thinned substrate. It is possible to prevent the upper electrode from being damaged and to provide a light control element with high productivity and a method for manufacturing the same.

The schematic of the conventional light control element is shown. It is a figure which shows the mode at the time of board | substrate grinding | polishing of the conventional light control element. It is a figure which shows the mode at the time of board | substrate grinding | polishing of the light control element based on this invention. It is a figure which shows the state which formed the protective electrode in the wafer substrate. It is a figure which shows the state which formed the protective electrode in the light control element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Optical waveguide 3 Signal electrode 4 Ground electrode 10 Adhesive 11 Polishing dummy substrate 12, 21 Protective electrode 20 Wafer substrate 22, 23 Groove

Claims (5)

An optical control element formed of a substrate having an electro-optic effect and having a thickness of 50 μm or less, an optical waveguide formed on the thin plate, and a control electrode for modulating a light wave propagating through the optical waveguide In the manufacturing method of
A method for producing a light control element, comprising: forming a control electrode on a substrate surface other than the control electrode by using the same material as the control electrode when forming the control electrode on the substrate.   2. The method of manufacturing a light control element according to claim 1, wherein a groove is formed in the protective electrode.   3. The light control element manufacturing method according to claim 1, wherein after the protective electrode is formed, any one of a polishing process of a back surface of the substrate, a wafer heating process, and a substrate cutting process is performed. A method for manufacturing a control element. An optical control element formed of a substrate having an electro-optic effect and having a thickness of 50 μm or less, an optical waveguide formed on the thin plate, and a control electrode for modulating a light wave propagating through the optical waveguide In
A light control element comprising a protective electrode formed of the same material as the control electrode on a substrate surface other than the control electrode. 5. The light control element according to claim 4, wherein the protective electrode is electrically connected to a ground electrode constituting the control electrode.

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