Laminated film, substrate with laminated film, electro-optical device using same, and method for manufacturing substrate with laminated film

Abstract

To provide a substrate with a laminated film.SOLUTION: The ferroelectric thin film includes a buffer layer (210) made of an oxide containing La as a main component, and a ferroelectric layer (220) formed on the buffer layer (210) and made of PZT or PLZT, wherein an intensity ratio (= IB / IA) is 0.33 or more, where IA [counts·degree] is an integrated intensity of a peak of the buffer layer appearing within a range of a diffraction angle (2 θ) of 12.90 ° or more and 13.95 ° or less, and IB [counts·degree] is an integrated intensity of a peak of the buffer layer appearing within a range of a diffraction angle (2 θ) of 38.50 ° or more and 40.20 ° or less, in an X-ray diffraction result with a scan axis of 2 θ / θ and using a CuK α ray.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminated film, a substrate with the laminated film, an electro-optical device using the same, and a method for producing a substrate with the laminated film. [Background technology]

[0002] Non-Patent Document 1 discloses a method for forming a buffer layer on a substrate that highly orients a thin film made of lead zirconate titanate (hereinafter referred to as PZT). This buffer layer is formed by first applying a solution of polyvinylpyrrolidone (hereinafter referred to as PVP) to the substrate, then dissolving lanthanum nitrate hexahydrate in a solvent, spin-coating the solution onto the PVP, and then heat-treating the substrate to form a buffer layer on the substrate.

[0003] Patent Document 1 discloses a functional element using PZT, and Non-Patent Document 2 discloses the use of PZT in an optical module, in which a buffer layer containing lanthanum is provided between a silicon substrate and PZT. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Jong-Jin Choi and 3 others, "Growth of highly (100) oriented lead zirconate titanate films on silicon and glass substrates using lanthanum nitrate as a buffer layer," Applied Physics Letters, Vol. 85, 2004, pp. 4621-4623 [Non-patent document 2] J.P. George and 7 others, "Lanthanide-Assisted Deposition of Strongly Electro-optic PZT Thin Films on Silicon: Toward Integrated Active Nanophotonic Devices," Applied Materials Interfaces, Vol. 7, 2015, pp. 13350-13359 [Patent documents]

[0005] [Patent Document 1] International Publication No. 2004 / 079059 Summary of the Invention [Problem to be solved by the invention]

[0006] When a ferroelectric layer of PZT or lanthanum-doped lead zirconate titanate (hereinafter referred to as PLZT) is formed on a substrate, it is not sufficiently oriented, and if sufficient orientation is not obtained, it becomes difficult to use it in, for example, an optical modulator.

[0007] In view of the above problems, an object of the present invention is to obtain a laminated film having a highly oriented ferroelectric layer. [Means for solving the problem]

[0008] The laminated film of the present invention comprises a buffer layer made of an oxide containing La as a main component, and a ferroelectric layer made of PZT or PLZT formed on the buffer layer, and the integrated intensity of the peak of the buffer layer appearing within a diffraction angle (2θ) range of 12.90° to 13.95° in X-ray diffraction results using CuKα rays with a scan axis of 2θ / θ is expressed as I A[Counts·degree], and the integrated intensity of the peak of the buffer layer appearing within the range of the diffraction angle (2θ) of 38.50° to 40.20° is defined as I B In terms of [Counts·degree], the intensity ratio of the following formula (1) is 0.33 or more.

[0009]

number

[0010] X-ray diffraction (XRD) results show that I A / I B is an index showing the phase state of the buffer layer, and when the intensity ratio is 0.33 or more, the buffer layer is in a state where a phase transition from a crystalline phase with a peak appearing in the diffraction angle range of 12.90° to 13.95° to a crystalline phase with a peak appearing in the diffraction angle range of 38.50° to 40.20° has progressed sufficiently. The progress of this phase transition to a crystalline phase with a peak appearing in the diffraction angle range of 38.50° to 40.20° can make the ferroelectric layer on this buffer layer highly oriented.

[0011] In this case, the I that appears in the diffraction angle range of 12.90° to 13.95° in the X-ray diffraction results A [Counts·degree] is the integrated intensity of the La(NO3)3(100) peak in the buffer layer, and is the I peak that appears in the diffraction angle range of 38.50° to 40.20° in the X-ray diffraction results. B [Counts·degree] may be the integrated intensity of the peak of LaONO3(004) or La2O2(CO3)(060) in the buffer layer.

[0012] The intensity ratio is an index showing the phase state of the buffer layer, and when the intensity ratio is 0.33 or more, the buffer layer is in a state where the phase transition from La(NO3)3 to LaONO3 or La2O2(CO3) has progressed sufficiently. The LaONO3 or La2O2(CO3) in this buffer layer has an effect on the orientation of the ferroelectric layer.

[0013] In the laminated film of the present invention, the scan axis is set to 2θ / θ, and CuKα radiation is used to perform X-ray diffraction analysis at each of arbitrary nine points in the plane measured from the ferroelectric layer side. The integrated intensity of the peak of PZT(100) or PLZT(100) appearing within the range of diffraction angle (2θ) of 21.60° or more and 22.10° or less is defined as I XY [Counts·degree], the integrated intensity I XY The ratio of the standard deviation to the maximum value is 0.13 or less.

[0014]

number

[0015] I XY is the integrated intensity of the PLZT(100) or PZT(100) peak appearing between 21.60° and 22.10° in the X-ray diffraction results. The standard deviation is the integrated intensity I obtained from nine measurement points. XY The maximum value is the degree of variation of the nine integrated intensities I XY is the maximum integrated intensity [Counts·degree] among the

[0016] The ratio of Equation (2) (= standard deviation / maximum value) is the integrated intensity I of the ferroelectric layer in the plane of the laminated film. XY When the θ is 0.13 or less, the ferroelectric layer has high uniformity of orientation at multiple locations within the surface. This allows a uniformly oriented film made of PLZT or PZT to be obtained even when applied to a large wafer, such as a 4-inch wafer.

[0017] The laminated film-coated substrate of the present invention comprises a substrate body and the laminated film provided on the substrate body directly or via an intermediate layer. The substrate body can be, for example, a Si substrate without an oxide film, a Si substrate with an oxide film, a glass substrate, a sapphire substrate, or the like.

[0018] The electro-optical device of the present invention is characterized by comprising the above-described laminated film-coated substrate, and examples of the electro-optical device include an optical modulator, an optical switch, and a phase shifter.

[0019] The method for manufacturing a laminated film-coated substrate of the present invention comprises a first film formation step of forming a buffer layer made of an oxide mainly composed of La directly on a substrate body or via an intermediate layer, and a second film formation step of forming a ferroelectric layer on the buffer layer, wherein the first film formation step sets the firing temperature for firing lanthanum nitrate at 450°C or higher and 650°C or lower, and further sets the heating time t1 from room temperature to the firing temperature at 200 seconds or longer.

[0020] By increasing the temperature rise time t1 in the first film formation process, the phase transition from La(NO3)3 to LaONO3 or La2O2(CO3) can be promoted. LaONO3 or La2O2(CO3) has an effect on the orientation of the ferroelectric layer. If the temperature rise time t1 is less than 200 seconds, the phase transition to LaONO3 or La2O2(CO3) cannot be sufficiently carried out, resulting in poor orientation of the ferroelectric layer. [Effects of the Invention]

[0021] According to the present invention, a ferroelectric layer can be highly oriented, and can be suitably used in electro-optical devices such as optical modulators. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a cross-sectional view of a substrate with a laminate film according to an embodiment of the present invention. [Figure 2] 2 is a graph showing XRD intensity in X-ray diffraction measurement of the laminated film-coated substrate of FIG. [Figure 3] 3 is a graph showing the XRD intensity of FIG. 2 at an enlarged scale. [Figure 4] 1 is a graph showing XRD intensity in X-ray diffraction measurement of a substrate with a laminate film of a comparative example. [Figure 5] 5 is a graph showing the XRD intensity of FIG. 4 at an enlarged scale. [Figure 6]FIG. 2 is a cross-sectional view of an optical modulator using the laminated film-coated substrate of FIG. [Figure 7] 1A to 1C are diagrams for explaining a manufacturing method of an optical modulator according to an embodiment. [Figure 8] FIG. 1 is a diagram showing an evaluation system for evaluating the characteristics of an optical modulator according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0024] The laminated film-coated substrate 1 shown in FIG. 1 includes a substrate body 10 and a laminated film 20 formed on the substrate body 10.

[0025] The substrate body 10 is not particularly limited, and may be, for example, a Si substrate without an oxide film, a Si substrate with an oxide film, a glass substrate, a sapphire substrate, etc. The size of the substrate body 10 is also not limited, and may be formed as, for example, a circular wafer with a diameter of 10 mm or more and 350 mm or less, or a rectangular wafer with one side of 10 mm or more and 350 mm or less.

[0026] The laminated film 20 includes a buffer layer 210 and a ferroelectric layer 220 formed on the buffer layer 210. In the illustrated example, the buffer layer 210 is directly laminated on the substrate body 10, but an intermediate layer made of SiO2, Al2O3, ZrO2, HfO2, Pt, Au, or the like may be interposed between the substrate body 10 and the buffer layer 210. For example, the buffer layer 210 may be formed on the first surface 11 of the substrate body 10, or the buffer layer 210 may be formed on an intermediate layer formed on the first surface 11.

[0027] The buffer layer 210 is made of an oxide containing La as a main component. Examples of the oxide constituting the buffer layer 210 include La(NO3)3, LaONO3, and La2O2CO3. FIG. 2 shows the results of X-ray diffraction (XRD) measurement of the buffer layer 210 using CuKα radiation with a scan axis of 2θ / θ. For the measurement, the buffer layer 210 and the ferroelectric layer 220 thereon are deposited on a substrate, and the measurement is performed from the surface side of the ferroelectric layer 220. In this embodiment, the buffer layer 210 and the ferroelectric layer 220 thereon are deposited on a Si substrate with a thermal oxide film (SiO2 film), and the measurement is performed from the surface side of the ferroelectric layer 220 on which the ferroelectric layer 220 is deposited. The integrated intensity of the peaks of the buffer layer appearing within a diffraction angle (2θ) range of 12.90° to 13.95° shown in FIG. 2 is defined as I A [Counts·degree], the integrated intensity of the peaks of the buffer layer appearing within the diffraction angle (2θ) range of 38.50° to 40.20° is defined as I B In terms of [Counts·degree], the intensity ratio of the following formula (1) is 0.33 or more. Note that the diffraction angle is the angle between the incident X-ray and the scattered X-ray in XRD measurement, and is twice the scattering angle θ.

[0028]

number

[0029] The intensity ratio shown in formula (1) is an index showing the phase state of the buffer layer 210, and a higher intensity ratio indicates that a phase effective in orienting PLZT is formed in the buffer layer. In this embodiment, the peak of La(NO3)3(100) appears at an angle between 12.90° and 13.95°, and the peak of LaONO3(004) or La2O2(CO3)(060) appears at an angle between 38.50° and 40.20°.

[0030] In the X-ray diffraction results of the buffer layer 210, the integrated intensity of the La(NO3)3(100) peak appearing at angles between 12.90° and 13.95° is I A[Counts·degree], and the integrated intensity of the peak of LaONO3(004) or La2O2(CO3)(060) appearing between 38.50° and 40.20° is I B [Counts·degree].

[0031] In this X-ray diffraction result, phases can be identified using the patterns disclosed in the PDF (Powder Diffraction File) card number (PDF-2 2025) in the International Centre for Diffraction Data (ICDD) database. The PDF card numbers of each crystalline phase and the peak assignments of interest are as follows: ·La(NO3)3:No.00-052-1103 The peaks between 12.90° and 13.95° are attributed to triclinic La(NO3)3(100). LaONO3:No.00-047-0890 The peaks around 38.50° to 40.20° are attributed to tetragonal LaONO3(004). La2O2(CO3): No.00-048-1113 The peaks around 38.50° to 40.20° are attributed to monoclinic La2O2(CO3)(060).

[0032] In the laminate film 20 or the laminate film-coated substrate 1 of this embodiment, the intensity ratio is 0.33 or more to control the phase transition from La(NO3)3(100) to LaONO3(004) or La2O2(CO3)(060) to be sufficiently advanced during the calcination treatment of lanthanum nitrate in the manufacturing method described below. The intensity ratio of the buffer layer 210 of this embodiment may be 0.35 or more, more preferably 0.39 or more, and even more preferably 0.49 or more. Theoretically, this intensity ratio can be quite large if the La(NO3)3(100) peak becomes undetectable, but in practice it rarely exceeds 1.0, with 1.0 being the upper limit.

[0033] Since the buffer layer 210 has an intensity ratio of 0.33 or more, when a ferroelectric layer 220 is formed on the buffer layer 210, the orientation of the ferroelectric layer 220 becomes high. When the substrate 1 with the laminated film is subjected to X-ray diffraction measurement, for example, when the ferroelectric layer is made of PLZT, a high peak of oriented PLZT(100) appears as shown in FIG. 3.

[0034] On the other hand, if the phase transition from La(NO3)3 to LaONO3 or La2O2(CO3) is insufficient during the calcination of lanthanum nitrate, the peak of LaONO3(004) or La2O2(CO3)(060) does not appear prominently between 38.50° and 40.20°, as shown in FIG. 4. When a ferroelectric layer is formed on the buffer layer 210 in which the phase transition to LaONO3 or La2O2(CO3) is insufficient and X-ray diffraction measurement is performed, the peak appears low due to insufficient PLZT(100) orientation, as shown in FIG. 5. Thus, if the intensity ratio is less than 0.33, the ferroelectric layer 220 cannot be formed on the buffer layer 210 with high orientation.

[0035] The thickness of the buffer layer 210 is not limited, but is, for example, 4 nm to 50 nm, and preferably 8 nm to 25 nm. If the thickness is less than 4 nm, it is difficult to form a uniform film, and if it exceeds 50 nm, when a ferroelectric layer is formed on the buffer layer 210 to fabricate a photoelectric element, there is a concern that light confinement in the ferroelectric layer will be insufficient, preventing efficient photoelectric conversion.

[0036] The ferroelectric layer 220 is made of PZT (lead zirconate titanate: Pb(Zr,Ti)O3) or PLZT (lanthanum-doped lead zirconate titanate: [(Pb,La)(Zr,Ti)O3]).

[0037] Furthermore, when the XRD intensity of the ferroelectric layer was confirmed by X-ray diffraction measurement using CuKα radiation with a scan axis of 2θ / θ and targeting arbitrary nine points within the surface of the ferroelectric layer side of the laminated film-coated substrate 1, the in-plane integrated intensity I XY The ratio of the standard deviation to the maximum value of the integrated intensity I XY The integrated intensity I XY The buffer layer 210 and the ferroelectric layer 220 thereon are formed on a Si substrate with a thermal oxide film (SiO2 film), and measurements are taken at nine points from the surface of the ferroelectric layer 220 on the side where the ferroelectric layer 220 is formed. From the X-ray diffraction results obtained at each measurement point, the integrated intensity of the PLZT(100) or PZT(100) peak appearing in the range of diffraction angles (2θ) of 21.60° to 22.10° is shown. The standard deviation is the integrated intensity I of the nine points. XY The maximum value is the integrated intensity I XY Hereinafter, the ratio of formula (2) may be referred to as standard deviation / maximum value.

[0038]

number

[0039] In the laminated film 20 or laminated film-coated substrate 1 of this embodiment, the standard deviation / maximum value is 0.13 or less to increase the uniformity of the orientation of the ferroelectric layer 220 at multiple locations within the plane. This makes it possible to sufficiently increase the uniformity of the characteristics of multiple optical modulators formed using, for example, the laminated film-coated substrate 1. On the other hand, if the standard deviation / maximum value exceeds 0.13, the yield of multiple optical modulators formed using the laminated film-coated substrate decreases. Note that the standard deviation / maximum value in this embodiment may be 0.10 or less. The lower limit of this ratio is 0, which is the theoretical case where there is no variation (standard deviation is 0).

[0040] 6 is a cross-sectional view showing an example of an optical modulator 100 fabricated using the laminated film-coated substrate 1 shown in FIG. 1, and this optical modulator 100 has a general-purpose Mach-Zehnder interference waveguide structure. In the illustrated example, a ferroelectric layer 220 is dry-etched to have two waveguides 221 separated by a branch (not shown). Reference numeral 40 denotes an electrode, and reference numeral 50 denotes a cladding layer. In this optical modulator 100, the core layer is formed from a highly oriented ferroelectric layer 220, thereby favorably exhibiting an electro-optic effect.

[0041] (Method of manufacturing the laminated film-coated substrate 1) The manufacturing method of the laminated film-coated substrate 1 includes a first film formation process of forming a buffer layer 210 on the substrate body 10 (hereinafter sometimes referred to as the substrate), and a second film formation process of forming a ferroelectric layer 220 on the buffer layer 210.

[0042] [First Film Formation Step: Buffer Layer 210] The first film formation process includes a first coating process of coating the surface of the substrate with polyvinylpyrrolidone (hereinafter referred to as PVP), a second coating process of coating the PVP with lanthanum nitrate, a pre-baking process of pre-baking the lanthanum nitrate on the substrate, and a baking process of baking the lanthanum nitrate on the substrate.

[0043] The first coating step includes a step of applying a PVP solution to a substrate and a step of volatilizing the solvent.

[0044] The PVP solution consists of PVP and a solvent, with the PVP concentration ranging from 0.05 wt% to 0.5 wt%. Examples of the solvent include 2-methoxyethanol, 1-propanol, methanol, and ethanol. The PVP solution was dropped onto the substrate and spin-coated. Alternatively, dip coating may be used instead of spin coating. After applying the PVP solution, the substrate is placed on a heating unit heated to, for example, 150°C to volatilize the solvent. This forms a PVP film, which acts as a surfactant and helps to uniformly deposit lanthanum nitrate.

[0045] The second coating step includes applying a lanthanum nitrate solution onto the PVP and evaporating the solvent.

[0046] The lanthanum nitrate solution consists of lanthanum nitrate hexahydrate and a solvent, with the concentration of lanthanum nitrate hexahydrate being between 0.5 wt% and 3 wt%. Examples of the solvent include 2-methoxyethanol, 1-propanol, methanol, and ethanol. The lanthanum nitrate solution was dropped onto the PVP and spin-coated. Note that dip coating may also be used instead of spin coating. After applying the lanthanum nitrate solution, the substrate is heated to between 150°C and 250°C to volatilize the solvent.

[0047] In the pre-baking process, the substrate is heated to 300°C to 400°C to pre-baked the lanthanum nitrate. After heating to the pre-baking temperature, the substrate is placed on a heating unit whose temperature is lower than the pre-baking temperature and gradually cooled, and then removed from the heating unit and allowed to cool in the air.

[0048] In the firing step, the substrate is fired to crystallize the lanthanum nitrate. The firing temperature is 450°C or higher and 650°C or lower, preferably 480°C or higher and 650°C or lower, and more preferably 500°C or higher and 600°C or lower. The holding time at the firing temperature is 1 second or higher and 1000 seconds or lower, and preferably 30 seconds or higher and 180 seconds or lower. Furthermore, in the firing process, the temperature rise time t1 from room temperature to the firing temperature is 200 seconds or higher and 1000 seconds or lower, preferably 240 seconds or higher and 1000 seconds or lower, and more preferably 240 seconds or higher and 750 seconds or lower. The temperature rise time t1 may be 240 seconds or higher and 720 seconds or lower.

[0049] The temperature rise time t1 is adjusted to control the lanthanum nitrate after firing to a phase state suitable for forming the ferroelectric layer 220. If the temperature rise time t1 is less than 200 seconds, the phase transition of lanthanum nitrate to LaONO3 or La2O2(CO3) is insufficient, and the ferroelectric layer 220 cannot be formed with high orientation on the buffer layer 210. If the temperature rise time t1 exceeds 1000 seconds, there is a risk of contamination with phases other than LaONO3 or La2O2(CO3).

[0050] The rate of temperature rise v1 from room temperature to the firing temperature is 0.5°C / sec to 10°C / sec, preferably 0.70°C / sec to 2.5°C / sec. If the rate of temperature rise v1 is less than 0.5°C / sec, there is a risk of contamination with phases other than LaONO3 or La2O2(CO3), while if the rate of temperature rise v1 exceeds 10°C / sec, the phase transition to LaONO3 or La2O2(CO3) will be insufficient.

[0051] The thickness of the buffer layer 210 can be increased by repeating the first coating step of applying PVP, the second coating step, and the baking step.

[0052] [Second Film Forming Step: Ferroelectric Layer 220] The second film formation process includes a step of applying a film formation solution for PLZT or PZT onto the buffer layer 210, a step of volatilizing the solvent, a pre-baking step of pre-baking the film formation material, and a baking step of baking the film formation material.

[0053] In the coating process, the film-forming solution is dropped onto the substrate on which the buffer layer 210 has already been formed, and spin-coated. Note that dip coating or the like may be used instead of spin-coating. After coating the film-forming solution, the solvent is evaporated. For example, the substrate on which the film-forming solution has been coated is placed on a heating unit heated to 150°C.

[0054] In the pre-baking process, the substrate is heated to 300°C or higher and 450°C or lower to pre-baked the film-forming material. After heating to the pre-baking temperature, the substrate is placed on a heating unit whose temperature is lower than the pre-baking temperature and gradually cooled, and then removed from the heating unit and allowed to cool in the air.

[0055] In the baking process, the substrate is baked to crystallize the film-forming material. The baking temperature is 500°C to 750°C, preferably 550°C to 650°C. The baking temperature is maintained for 1 second to 500 seconds, preferably 30 seconds to 90 seconds. The temperature rise time t2 from room temperature to the baking temperature is 30 seconds to 1000 seconds, preferably 240 seconds to 720 seconds. The temperature rise rate from room temperature to the baking temperature is 0.65°C / second to 10°C / second, preferably 0.90°C / second to 2.5°C / second. The thickness of the ferroelectric layer 220 can be increased by repeating the process from applying the film-forming solution to the baking process of baking the film-forming material, for example. After the baking process, the laminated film-coated substrate 1 is completed.

[0056] In the laminated film-coated substrate 1 of this embodiment, the phase state of the buffer layer 210 is controlled by heat treatment during manufacturing, and thus the ferroelectric layer 220 is formed in an oriented state. Furthermore, in the laminated film-coated substrate 1, the ferroelectric layer 220 has uniform orientation throughout the surface. Therefore, the uniformity of the characteristics of the optical modulator formed using the laminated film-coated substrate 1 can be sufficiently improved.

[0057] The present invention can be practiced without being limited to the above-described and illustrated examples.

[0058] The laminated film-coated substrate 1 of the present invention can be used not only for optical modulators but also for optical switches, phase shifters, etc. The method for forming the ferroelectric layer on the buffer layer is not limited to the above description, and other methods such as chemical solution deposition, chemical vapor deposition, sputtering, and evaporation may also be used. [Example]

[0059] The samples were substrates with laminated films, each consisting of a buffer layer formed on a Si substrate with different film thicknesses and firing conditions, and a ferroelectric layer of PLZT or PZT formed on this buffer layer.The films of each sample were analyzed, and the characteristics of the optical modulators fabricated using the samples were confirmed.

[0060] The Si substrate used was a Si wafer with a thermal oxide film (film thickness: 3 μm). The Si substrate was 4 inches and 0.525 mm thick.

[0061] The method for manufacturing a substrate with a laminated film includes a cleaning step for cleaning a Si substrate, a first film formation step for forming a buffer layer on the cleaned Si substrate, and a second film formation step for forming a ferroelectric layer made of PLZT or PZT on the buffer layer.

[0062] [Cleaning process] The washing steps were carried out in the following order from the first wash to the third wash. In the first cleaning, the Si substrate was immersed in acetone and subjected to ultrasonic cleaning for 2 minutes. In the second cleaning, the Si substrate was immersed in pure water and subjected to ultrasonic cleaning for 2 minutes. For the third cleaning, the solution was heated to 75°C, and the Si substrate was immersed in it for 20 minutes (RCA SC1 cleaning). The solution consisted of pure water, hydrogen peroxide (35 wt%), and ammonia water (29 wt%), with a volume ratio of pure water:hydrogen peroxide (35 wt%):ammonia water (29 wt%) = 3:1:1. After the second cleaning and before the third cleaning, the Si substrate may be heat-treated at a temperature between 500°C and 800°C.

[0063] [First film formation process: buffer layer] The first film formation process includes a first coating process in which the surface of the cleaned Si substrate is coated with polyvinylpyrrolidone (hereinafter referred to as PVP), a second coating process in which the PVP is coated with lanthanum nitrate, a pre-baking process in which the lanthanum nitrate on the substrate is pre-baked, and a baking process in which the lanthanum nitrate on the substrate is baked.

[0064] The first coating step includes a step of applying a PVP solution to a Si substrate that has been subjected to substrate cleaning, and a step of volatilizing the solvent.

[0065] The PVP solution was prepared by weighing 0.05 g of polyvinylpyrrolidone (k = 15, average molecular weight 10,000) into a glass container, adding 19.7 g of 2-methoxyethanol (purity > 99.0%), and stirring for 30 minutes. While PVP with k = 30 (average molecular weight 40,000) or k = 90 (average molecular weight 360,000) can also be used, using a lower molecular weight PVP allows for easier dissolution in the solvent. The PVP solution was stirred before dripping, and after complete dissolution, 1 mL of the PVP solution was dripped onto a Si substrate and spin-coated using a spin coater. Spin coating was performed at 500 rpm for 5 seconds, followed by 4000 rpm for 30 seconds.

[0066] After the spin coating, the Si substrate coated with the PVP solution was placed on a hot plate heated to 150° C. for 1 minute to volatilize the solvent.

[0067] The second coating step includes applying a lanthanum nitrate solution onto the PVP and evaporating the solvent.

[0068] Lanthanum nitrate solution was prepared by weighing 0.311 g of lanthanum nitrate hexahydrate (purity >99.0%) into a glass container, adding 2-methoxyethanol, and stirring for 30 minutes. Lanthanum nitrate hexahydrate may be heated up to 200 °C to remove the water of hydration before adding the 2-methoxyethanol.

[0069] The lanthanum nitrate solution was stirred before dripping, and after completely dissolving, 1 mL of the lanthanum nitrate solution was dripped onto the PVP and spin-coated using a spin coater. The spin coating was performed at 500 rpm for 5 seconds, followed by 4000 rpm for 30 seconds. After spin coating, the Si substrate coated with the lanthanum nitrate solution was placed on a hot plate heated to 150°C for 1 minute to volatilize the solvent.

[0070] In the pre-baking process, the Si substrate was placed on a hot plate heated to 300°C for 5 minutes, then placed on a hot plate heated to 150°C for 30 seconds to gradually lower the temperature of the Si substrate, and then removed from the hot plate and allowed to cool in the air.

[0071] In the firing process, the Si substrates were fired in a firing apparatus at a firing temperature of 590°C, a temperature hold time of 60 seconds, and in air. For each sample, the heating time t1 from room temperature to 590°C was varied between 59 and 720 seconds. This corresponds to a heating rate of between 0.82°C / s and 10.00°C / s. A Rapid Thermal Annealing apparatus (RTA-8000) manufactured by Advance Riko Co., Ltd. was used for the firing process (hereafter referred to as the RTA apparatus). Lanthanum nitrate was crystallized by the firing process. The thickness of the buffer layer could be increased by repeating the first coating process (applying PVP), the second coating process, and the firing process. For each sample, the number of layers underlying the ferroelectric layer was two (11 nm thick) and four (22 nm thick). Table 1 shows the temperature rise time t1 and film thickness of each sample.

[0072] [Second film formation process: ferroelectric layer] The second film-forming process includes the steps of applying a sol-gel solution for PLZT or PZT onto the buffer layer, volatilizing the solvent, pre-firing the PLZT or PZT, and firing the PLZT or PZT. For samples 1 to 8, Mitsubishi Materials Corporation's film-forming E1 solution (concentration 15%, composition ratio: Pb:La:Zr:Ti = 115:8:65:35) was used as the PLZT sol-gel solution (samples 1 to 8). Samples were also fabricated with varying Pb:La:Zr:Ti composition ratios, as shown in Table 1. Specifically, samples were prepared using solutions with a fixed Zr:Ti ratio of 65:35 and a Pb:La ratio of 106:6 (sample 9), 108:4 (sample 10), 110:2 (sample 11), and 110:4 (samples 12 and 13), as well as samples (sample 15) where the Zr:Ti ratio was varied and a Pb:La:Zr:Ti ratio of 111:4:52:48 was used.

[0073] The same process was carried out when forming a PZT layer, and the PZT sol-gel liquid was E1 liquid for film formation manufactured by Mitsubishi Materials Corporation (concentration 15%, composition ratio: Pb:Zr:Ti=112:65:35) (Sample 14).

[0074] The coating process involved dropping 1 mL of the sol-gel solution onto a Si substrate with a buffer layer already formed, and spin-coating using a spin coater. The spin coating was performed at 500 rpm for 5 seconds, followed by 4000 rpm for 30 seconds. After spin-coating, the Si substrate with the sol-gel solution was placed on a hot plate heated to 150°C for 1 minute to volatilize the solvent.

[0075] In the pre-baking process, the Si substrate was placed on a hot plate heated to 300°C for 5 minutes, then placed on a hot plate heated to 150°C for 30 seconds to gradually lower the temperature of the Si substrate, and then removed from the hot plate and allowed to cool in the air.

[0076] In the firing process, the Si substrate was fired in the RTA device at a firing temperature of 640°C, a temperature holding time of 60 seconds, and an O2 firing atmosphere. In the firing process for each sample, the temperature rise time t2 from room temperature to the firing temperature of 640°C was varied within a range of 64 to 720 seconds. The firing process crystallized the PLZT or PZT.

[0077] The ferroelectric layer was formed by repeating the sol-gel solution application process and the baking process. Ellipsometry measurements were performed to calculate the film thickness of the ferroelectric layer of the sample. A spectroscopic ellipsometer (JA Woollam M-2000) was used for the measurements, and measurements were performed in reflection mode at three angles of incidence / reflection: 60°, 70°, and 80°. The Cauchy optical model was applied to the obtained results and fitting was performed to evaluate the film thickness.

[0078] Table 1 shows the film thickness of the ferroelectric layer of each sample and the temperature rise time t2 during the firing process of PLZT or PZT.

[0079] [Membrane evaluation] The crystal phase of the buffer layer formed on the Si substrate and the orientation of the ferroelectric layer were analyzed by X-ray diffraction (XRD). The X-ray diffractometer used was a fully automated multipurpose X-ray diffractometer (SmartLab) manufactured by Rigaku Corporation. A Cu tube was used to generate X-rays, and Kα rays were used for diffraction.

[0080] A. Crystalline phase of the buffer layer The scan axis was 2θ / θ, and the angle range was from 10° to 60°. The sampling step was 0.01°, the scan speed was 10° / min, IS = 0.300 mm, RS1 = 5 mm, and RS2 = 5 mm. Measurements were performed on the center of a 4-inch wafer placed on the measurement stage. The measurement was performed with a 5° incident-side Soller slit, a 10 mm incident-length limiting slit (IS length), a 0.5° parallel slit analyzer (PSA), and a 5° incident-side Soller slit. A scintillation counter (Rigaku, SC-70) was used as the detector.

[0081] The obtained XRD intensity data was subjected to a peak search using integrated powder X-ray analysis software (PDXL2 Version 2.8.4.0, Rigaku), and the integrated intensity I of the La(NO3)3(100) peak appearing between 12.90° and 13.95° was calculated. A Calculate the integral intensity I (Counts·degree) of the peak of LaO(NO3)(004) or La2O2(CO3)(060) appearing between 38.50° and 40.20°. B [Counts·degree] was calculated. At this time, the peak search was performed automatically with "Refine background" turned on. The peak shape was a divided pseudo-Voigt function. In this case, Kβ rays and filter edges were not removed, and the α cut value for the peak search was set to 3.00, with the α cut range from a minimum of 0.50 to a maximum of 20.00. Amorphous peaks were excluded from detection. Peak optimization was performed only once after the measurement file was opened. The intensity ratio (formula (1) above) was then calculated.

[0082] The evaluation of the crystalline phase was based on the following: an intensity ratio of 0.33 or more was considered to indicate that the phase transition from La(NO3)3 to LaO(NO3) or La2O2(CO3) had progressed sufficiently and the phase state of the buffer layer was good; an intensity ratio of less than 0.33 was considered to indicate that the phase state of the buffer layer was poor. Integrated intensity of each sample I A and the integrated intensity I B The intensity ratios are shown in Table 1.

[0083] B. Orientation of ferroelectrics Mapping measurements were performed at nine points on the ferroelectric layer using CuKα radiation with a scan axis of 2θ / θ to confirm the in-plane distribution of the XRD intensity. The integrated intensity was measured with the orientation flat of the Si substrate (wafer) placed in front of the stage, with the center coordinate set at (0mm, 0mm), and measurements were taken at (-40mm, 0mm), (-20mm, 0mm), (0mm, 0mm), (20mm, 0mm), (40mm, 0mm), (0mm, 40mm), (0mm, 20mm), (0mm, -20mm), and (0mm, -40mm). The entrance longitudinal limiting slit (IS longitudinal) was set to 2mm.

[0084] The XRD intensity data obtained at each measurement point was subjected to a peak search under the above conditions using integrated powder X-ray analysis software (PDXL2, Rigaku), and the integrated intensity I of the PLZT(100) or PZT(100) peak appearing between 21.60° and 22.10° was calculated. XY The integral intensity I XY The standard deviation [Counts·degree] of the 9-point integrated intensity I XY The maximum value [Counts·degree] was identified, and the ratio of the standard deviation and the maximum value in the above formula (2) was calculated.

[0085] The orientation of the ferroelectric layer was evaluated as follows: a standard deviation / maximum value of 0.13 or less was considered to be good, with high uniformity of PLZT or PZT orientation across the surface of the Si substrate (wafer); a standard deviation / maximum value of more than 0.13 was considered to be poor, with large variations in the degree of PLZT or PZT orientation across the surface. The standard deviation / maximum values ​​for each sample are shown in Table 1.

[0086] [Light modulation characteristics] A. Fabrication of optical modulator The waveguide pattern and electrodes were fabricated using electron beam lithography and etching processes. First, a 20 mm x 20 mm plate was cut out from the sample (Fig. 7(a)), and this plate was washed with acetone. In Fig. 7(a), reference numeral 10A denotes the substrate body, reference numeral 210A denotes a buffer layer formed on the first surface 11A of the substrate body 10A, and reference numeral 220A denotes a ferroelectric layer. Then, a resist 60A was spin-coated onto the surface of the ferroelectric layer 220A (Fig. 7(b)). The spin-coating was performed at 2000 rpm for 30 seconds, and the resist was dried on a hot plate at 120°C for 2 minutes. After irradiating with an electron beam using an electron beam lithography system, the resist was developed and a waveguide pattern 70A was transferred to the resist 60A (Fig. 7(c)).

[0087] Then, the ferroelectric layer 220A was subjected to reactive ion etching using a reactive ion etching apparatus to fabricate a Mach-Zehnder interference waveguide 221A (FIG. 7(d)). This etching was performed using a mixed gas of CHF3 and Ar, with a process pressure of 1.8 Pa and an RF power of 150 W. The etching depth of the ferroelectric layer 220A was approximately 100 nm, and was controlled by adjusting the etching time.

[0088] Next, we fabricated an electrode 40A that applies a voltage to the waveguide 221A during phase modulation. To fabricate the electrode 40A, we first coated a resist on the ferroelectric layer 220A of the plate, then irradiated it with an electron beam using an electron beam lithography system, and developed it to transfer the electrode structure onto the resist. Next, we used a vacuum deposition system to deposit Cr (approximately 10 nm) and Al (approximately 400 nm) to complete the electrode 40A (Figure 7(e)).

[0089] Furthermore, a cladding layer 50A was formed on the waveguide 221A using polymethyl methacrylate resin (PMMA), completing the optical modulator 100A (FIG. 7(f)). The electrode spacing was 6 μm, and the electrode length was 4 mm.

[0090] In fabricating the optical modulator, an electron beam resist (RP6200) manufactured by Allresist GmbH was used as the resist, an electron beam lithography system (G100) manufactured by Elionix Corporation was used for electron beam lithography, and a reactive ion etching system (RIE-10NR) manufactured by Samco Corporation was used for etching.

[0091] To induce the electro-optical effect of PLZT or PZT, an electric field orientation process was performed. A DC voltage was applied using electrode 40A fabricated on ferroelectric layer 220A on a hot plate at 90°C. The polarity of the electric field was the same for both phase modulation sections. The DC field strength was preferably 25 V / μm to 60 V / μm, and the holding time was preferably 30 minutes to 200 minutes, but can be set arbitrarily within this range. Specifically, the power supply was adjusted so that the DC field strength was 30 V / μm. After holding the voltage for 30 minutes, the temperature was lowered to room temperature, completing the electric field orientation process.

[0092] B. Evaluation of optical modulation characteristics 5 is a diagram showing an evaluation system 300 for evaluating the optical modulation characteristics of an optical modulator 100A, in which the width of a phase modulation waveguide 221A in a ferroelectric layer 220A of the optical modulator 100A is 1.4 μm. The Mach-Zehnder interference waveguide is equipped with multi-mode circuits (hereinafter referred to as MMI) 80A and 80B on the input and output sides, and the light intensity is divided into 50% each by the input side MMI 80A and branched into the two phase modulation waveguides 221A, and the light is combined again by the output side MMI 80B.

[0093] Laser light with a wavelength of 1550 nm was incident on this optical modulator 100A from a laser light source 310 via an optical fiber 320, and a modulation voltage (triangular wave) was input to the electrodes by a function generator 330. One of the electrodes was used as a ground electrode. The modulated output light was sent to a photodetector 350 via an optical fiber 340, and the signal from the photodetector 350 was analyzed by an oscilloscope 360. The half-wave voltage (the voltage when the phase of the light is shifted by 90°) of the optical modulator 100A using each sample was then determined. The polarization of the laser light incident on the optical modulator 100A was TE mode.

[0094] The optical modulation characteristics were evaluated such that a half-wave voltage of less than 7.0 V was considered good, and a half-wave voltage of 7.0 V or more was considered poor. The half-wave voltage of the optical modulator using each sample and the evaluation of its optical modulation characteristics are shown in Table 1. The evaluation was graded as A or B as pass, C as fail, with A being better than B.

[0095] [Table 1]

[0096] A. Samples 1 to 4 Samples 1 to 4 have in common that they were manufactured with a buffer layer thickness of 22 nm, a ferroelectric layer (PLZT layer) thickness of 300 nm, and the temperature rise time t2 during the PLZT firing process fixed at 64 seconds. However, Samples 1 to 4 differ in that the temperature rise time t1 during the lanthanum nitrate firing process was varied.

[0097] Among samples 1 to 4, samples 3 and 4 in which the temperature rise time t1 was set to 240 seconds or more had a half-wave voltage of less than 7 V. In addition, the buffer layers of samples 3 and 4 had an intensity ratio I B / I A The values ​​were 0.49 and 0.40, indicating that the phase transition from La(NO3)3 to LaONO3 or La2O2(CO3) was progressing. Thus, by heating lanthanum nitrate at a slow rate (heating rate: 0.70°C / sec or more and 2.5°C / sec or less), the phase transition to LaONO3 or La2O2(CO3) was promoted, enabling the formation of highly oriented PLZT. This resulted in a low half-wave voltage and good optical modulation characteristics.

[0098] Samples 1 and 2 are comparative examples. The temperature rise time t1 was set to 59 seconds or 120 seconds, and the lanthanum nitrate was heated at a high speed. The buffer layer had an intensity ratio I B / I AThe values ​​were 0.26 and 0.25, respectively, and the phase transition from La(NO3)3 to LaONO3 or La2O2(CO3) was insufficient. In samples 1 and 2, the PLZT could not be formed with a high orientation, and the half-wave voltage was high and the optical modulation characteristics were poor.

[0099] In addition, for samples 1 to 4, the longer the heating time t1 of lanthanum nitrate, the smaller the standard deviation / maximum value of the PLZT layer, and the smaller the integrated intensity I XY It was confirmed that the uniformity of

[0100] B. Samples 4 and 5 Samples 4 and 5 have in common the fact that they were manufactured with a buffer layer thickness of 22 nm, a PLZT layer thickness of 300 nm, and the heating time t1 during the lanthanum nitrate firing process fixed at 720 seconds, which is the time that facilitates the phase transition. However, they differ in that the heating time t2 during the PLZT firing process was changed to either 64 seconds or 640 seconds.

[0101] For both samples 4 and 5, the intensity ratio I obtained from X-ray diffraction measurements of the buffer layer B / I A The value was 0.39 or more, indicating that the phase transition from La(NO3)3 to LaONO3 or La2O2(CO3) was progressing, and the half-wave voltage was 5.3 V or less, indicating good optical modulation characteristics.

[0102] In samples 4 and 5, the standard deviation / maximum value increased when the heating time t2 during the PLZT firing process was long. This indicates that shortening the heating time t2 during the PLZT firing process for a buffer layer in which the phase transition from La(NO3)3 to LaONO3 or La2O2(CO3) has progressed sufficiently is effective in reducing the integrated intensity I XY The variation in the integrated intensity I in the plane of the PLZT layer is reduced. XY It was confirmed that the uniformity of

[0103] C. Samples 6 to 8 Samples 6 to 8 have in common the fact that they were manufactured with a buffer layer thickness of 11 nm and a PLZT layer thickness of 300 nm, but differ in that the temperature rise time t1 during the lanthanum nitrate firing treatment was changed to 59 seconds or 720 seconds, and the temperature rise time t2 during the PLZT firing treatment was changed to 64 seconds or 640 seconds. Sample 6 is a comparative example.

[0104] For both samples 7 and 8, the temperature rise time t1 during the calcination treatment of lanthanum nitrate was set to 720 seconds, and the temperature was raised at a slow rate (temperature rise rate: 0.82 ° C / sec). B / I A The values ​​of the half-wave voltages were as high as 0.57 or 0.95, and the phase transition to LaONO3 or La2O2(CO3) was promoted, resulting in a half-wave voltage of less than 7 V, and the optical modulation characteristics were excellent. Among them, sample 8 exhibited a half-wave voltage of 6 V or less (5.8 V), which was particularly excellent. Furthermore, sample 8 had a small standard deviation / maximum value, and the integrated intensity I XY On the other hand, in sample 7, the standard deviation / maximum value increased, and the integrated intensity I XY There was variation and uniformity could not be achieved.

[0105] In this way, for samples 7 and 8, the longer the heating time t2 during the firing process of PLZT, the smaller the standard deviation / maximum value, and the larger the integrated intensity I XY The uniformity of the integrated intensity I of sample 7 was high. XY The reason for the low uniformity of the thin buffer layer is that the crystal uniformity is poor to begin with. For samples 1, 2, 3, and 7, the PLZT layers were deposited under conditions where the buffer layer was 11 or 22 nm thick, the heating time t2 during the PLZT firing process was 64 seconds, and the PLZT layer was 300 nm thick. The standard deviation / maximum value for the 11 nm buffer layer was greater than the standard deviation / maximum value for the 22 nm buffer layer. On the other hand, for sample 8, where the heating time t2 during the PLZT firing process was longer, the PLZT was exposed to a higher temperature for a longer period, which is thought to have resulted in a more uniform crystalline state.

[0106] For samples 7 and 8, the buffer layer intensity ratio I B / I A When t2 is large and the thickness of the buffer layer is thin, it is found that the temperature rise time t2 of the PLZT is important for the orientation at various points within the plane of the PLZT layer, and the standard deviation / maximum value can be reduced.

[0107] In sample 6, the temperature rise time t1 during the lanthanum nitrate firing treatment was set to a short time of 59 seconds, and in the X-ray diffraction measurement of the buffer layer of sample 6, no peak between 38.50° and 40.20° was confirmed, the orientation of the PLZT layer was low, and the half-wave voltage exceeded 7 V, resulting in poor optical modulation characteristics.

[0108] D. Sample 14 In sample 14, the ferroelectric layer was a PZT layer, the buffer layer was 11 nm thick, and the PZT layer was 300 nm thick. The temperature rise time t1 during the sintering process of lanthanum nitrate was set to 720 seconds, which facilitates the phase transition, and the temperature rise time t2 during the sintering process of PZT was set to 640 seconds. As with the PLZT in sample 5, the intensity ratio I B / I A A highly oriented PZT was obtained with a value of 0.69, and the standard deviation / maximum value was less than 0.10, resulting in high uniformity.

[0109] E. Samples 9-13 and 15 In samples 9 to 13 and 15, the composition ratio of the sol-gel solution: Pb:La:Zr:Ti was varied, the thickness of the buffer layer was set to 11 nm, and the thickness of the ferroelectric layer was set to 300 nm or 600 nm (sample 13). The temperature rise time t1 during the sintering treatment of lanthanum nitrate was set to 720 seconds, and the temperature rise time t2 during the sintering treatment of PLZT was set to 640 seconds. These samples were obtained by measuring the intensity ratio I B / I A is 0.33 or more, the orientation of PLZT is high, and I XY The standard deviation / maximum value was 0.06 or less, which means high uniformity was obtained, and the half-wave voltage was low at 4.3 V or less, which means good optical modulation characteristics.

[0110] From the results of D and E above (the results of samples 9 to 15), the intensity ratio IB / I A is 0.33 or more, I XY It can be seen that by making the standard deviation / maximum value of 0.06 or less, a uniform ferroelectric layer with high orientation can be obtained regardless of the composition of the ferroelectric layer, PLZT or PZT. [Explanation of symbols]

[0111] 1. Substrate with laminated film 10,10A board body 20 Laminated Film 210,210A buffer layer 220 Ferroelectric layer 220A PLZT layer 231,231A waveguide 40,40A electrode 50,50A cladding layer 100,100A Optical Modulator 300 Rating System

Claims

1. a buffer layer made of an oxide containing La as a main component, and a ferroelectric layer made of PZT or PLZT formed on the buffer layer, The scan axis is 2θ / θ, and the integrated intensity of the peak of the buffer layer appearing within the range of diffraction angle (2θ) of 12.90° to 13.95° in the X-ray diffraction results using CuKα rays is defined as I Ａ [Counts·degree], and the integrated intensity of the peak of the buffer layer appearing within the range of the diffraction angle (2θ) of 38.50° to 40.20° is defined as I Ｂ A laminated film characterized in that the intensity ratio of the following formula (1), expressed in [Counts·degree], is 0.33 or more. [Equation 1]

2. I Ａ [Counts·degree] is the La(NO ３ ) ３ is the integrated intensity of the (100) peak, Ｂ [Counts·degree] is the LaONO buffer layer ３ (004) or La ２ O ２ (CO ３ 2. The laminated film according to claim 1, wherein the integrated intensity of the peak of (060) is

3. The scan axis is 2θ / θ, and the integrated intensity of the peaks appearing within the range of diffraction angle (2θ) of 21.60° to 22.10° in the X-ray diffraction results measured at nine points in the plane from the ferroelectric layer side using CuKα radiation is defined as I ＸＹ [Counts·degree], the integrated intensity I in the plane of the following formula (2) is ＸＹ 2. The laminated film according to claim 1, wherein the ratio of the standard deviation to the maximum value is 0.13 or less. [Equation 2]

4. A substrate with a laminated film, comprising: a substrate body; and the laminated film according to any one of claims 1 to 3, provided on the substrate body directly or via an intermediate layer.

5. An electro-optical device including a substrate with a laminated film, An electro-optical device, characterized in that the substrate with the laminated film comprises a substrate body and the laminated film according to any one of claims 1 to 3 provided on the substrate body directly or via an intermediate layer.

6. a first film formation step of forming a buffer layer made of an oxide mainly composed of La on a substrate body directly or via an intermediate layer, and a second film formation step of forming a ferroelectric layer on the buffer layer, A method for manufacturing a substrate with a laminated film, characterized in that the first film formation step is characterized in that the firing temperature for firing lanthanum nitrate is 450°C or higher and 650°C or lower, and further, the temperature rise time t1 from room temperature to the firing temperature is 240 seconds or longer.

Images