JP2004287248A - Method for layering refractive index film and patterned layered body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for layering a refractive index film that can easily and readily be implemented and a patterned layered body manufactured by the same. <P>SOLUTION: A different refractive index film is layered by (a) depositing an energy-sensitive insulating film on a substrate, (b) depositing a film having a 1st refractive index which is patterned by irradiation with patterning energy, and (c) depositing a film having a 2nd refractive index on the film having the 1st refractive index. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for laminating films having different refractive indexes and a laminate that can be formed by the method. More specifically, the present invention provides a refractive index film that combines the patterning of an energy-sensitive insulating film by irradiation with patterning energy and the stack of another film having a different refractive index from the patterned film. The present invention relates to a method for laminating (another film having a different refractive index may have a pattern) and a laminate that can be formed by the method.
[0002]
[Prior art]
The present invention can be applied to a general laminate in which different refractive index films are laminated, but for convenience of explanation, first, prior art relating to a typical laminate (photonic crystal) having an alternating structure of different refractive index films will be described first. .
[0003]
With the development of social and economic activities, the importance of optoelectronics that enables large-capacity communication in the field of information communication and information processing is increasing more and more. On the other hand, due to the recent increase in capacity and speed of information to be transmitted, the limit of information communication and information processing using only existing optical technologies is approaching its limit. In recent years, a photonic crystal capable of freely controlling a light path has been spotlighted as one of the technologies having a possibility of overcoming such limitations. This photonic crystal is a material in which substances having different refractive indices are periodically combined at an interval of the same level as the wavelength of light.
[0004]
Light incident on such a photonic crystal is entangled with reflection, refraction, interference, and the like, and has a unique optical phenomenon (for example, characteristic light propagation such as “dispersion”, “anisotropic”, and “photonic bandcap”). not only cause based on characteristics), when a photonic crystal is improved propagation characteristics of 10 ³ times more light than the conventional optical materials are expected. For this reason, photonic crystals are expected to be applied to various optical application fields as optical filters, optical waveguides, band filters, display devices, and the like. Furthermore, photonic crystal, an area ratio of 10 ^one-third less and ultra-small optical circuit, superprism, zero threshold lasers; and radiation field, the optical functional device capable of controlling the propagation characteristics (e.g., sudden bending angle of Optical waveguides, ultra-small optical resonators, optical modulators, wavelength demultiplexers, ultra-low threshold laser arrays, etc.).
[0005]
As described above, a photonic crystal is a new optical material having a periodically changing refractive index and functions as a base medium for future ultra-small and large-scale photonic integrated circuits (PICs) (Non-Patent Documents 1 and 2). It is believed that. In order to realize high-performance PICs, a three-dimensional photonic crystal having a complete photonic band gap is required (Non-Patent Documents 3 and 4). Functional devices such as nano-amp laser arrays and optical waveguides with sharp bends can be integrated using, for example, three-dimensional photonic crystals in PICs (Non-Patent Document 5).
[0006]
However, on the other hand, it is naturally extremely difficult to form a two-dimensional or three-dimensional periodic structure with a size close to the wavelength of light, and therefore, a technology that can easily produce a three-dimensional photonic crystal. In particular, there is a strong demand for a technique for manufacturing a three-dimensional photonic crystal whose structure can be easily controlled.
There are a few reports on such three-dimensional photonic crystal manufacturing techniques. However, the reported methods for producing three-dimensional photonic crystals are either quite complex (Non-Patent Documents 6, 7 and 8) or have little freedom in structural design (Non-Patent Documents). 9 and 10).
[0007]
Further, it is considered that realization of a low-cost optoelectronic integrated circuit (OEIC) is practically difficult unless a Si-based material is used for manufacturing the three-dimensional photonic crystal (Non-Patent Documents 8 to 10). ).
[0008]
[Non-patent document 1]
E. FIG. Yablonovitch, Phys. Rev .. Lett. 58 (1987) 2059.
[Non-patent document 2]
S. John, Phys. Rev .. Lett. 58 (1987) 2486.
[Non-Patent Document 3]
E. FIG. Yablonovitch, T.W. Gmitter, and K .; Leung, Phys. Rev .. Lett. 67 (1991) 2295.
[Non-patent document 4]
J. D. Joannopoulos, P .; R. Villeneuve, and S.M. Fan, Nature 386 (1997) 143.
[Non-Patent Document 5]
S. John, Physics Today. 44 (1991) 32.
[Non-Patent Document 6]
S. Noda, N .; Yamamoto, and A. Sasaki, Jpn J .; Appl. Phys. 35 (1996) L909.
[Non-Patent Document 7]
S. Noda, N .; Yamamoto, H .; Kobayashi, M .; Okano, and K.K. Tomoda, Appl. Phys. Lett. 75 (1999) 905.
[Non-Patent Document 8]
J. G. FIG. Fleming and S.M. -Y. Lin, Opt. Lett. 24 (1999) 49.
[Non-Patent Document 9]
M. Notomi, T .; Tamamura, T .; Kawashima, and S.M. Kawakami, Appl. Phys. Lett. 77 (2000) 4256.
[Non-Patent Document 10]
M. Notomi, A .; Shinya, E .; Kuramochi, I .; Yokohama, C .; Takahashi, K .; Yamada, J .; Takahashi, T .; Kawashima, and S.M. Kawakami, IEICE Trans. Electron. E85-C (2002) 1025.
[0009]
[Problems to be solved by the invention]
An object of the present invention is to provide a method of laminating a refractive index film and a patterned laminate, which can solve the above-mentioned drawbacks of the prior art.
[0010]
Another object of the present invention is to provide a method of laminating a refractive index film which is simple and easy to carry out, and a patterned laminate produced by the method.
[0011]
[Means for Solving the Problems]
As a result of earnest research, the present inventor has performed patterning with an energy-sensitive insulating film using patterning energy instead of performing fine processing using a photoresist as in the conventional processing method, and then performing other processing. It has been found that stacking a refractive index film is extremely effective for achieving the above object.
[0012]
The method of laminating a refractive index film of the present invention is based on the above findings, and more specifically,
(A) forming an energy-sensitive insulating film on a substrate,
(B) patterning the energy-sensitive insulating film by irradiation with patterning energy to form a patterned film having a first refractive index;
(C) forming a film having a second refractive index different from the first refractive index on the film having the first refractive index.
[0013]
According to the present invention, further, a substrate; a first refractive index film having a predetermined pattern disposed on the substrate; a first refractive index disposed on the first refractive index film A laminate is provided that includes at least a film and a second refractive index film having a different refractive index.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described more specifically with reference to the drawings as necessary. In the following description, “parts” and “%” representing the quantitative ratios are (as a rule) based on mass unless otherwise specified.
[0015]
(Layer of refractive index film)
FIG. 1 is a schematic cross-sectional view showing one basic embodiment of the laminate of the present invention. Referring to FIG. 1, in the laminate of this embodiment, a patterned first refractive index film 3 made of MSQ based on MSZ (for example, having a refractive index of about 1.45) is formed on a substrate 2 made of Si or the like. Further, a second refractive index film 4 made of SOG (spin-on-glass; having a refractive index of, for example, about 1.38) is disposed on the first refractive index film 3. In FIG. 1, the first refractive index film 3 is patterned, but if necessary, the second refractive index film 4 may be patterned (instead of the first refractive index film), Further, both the first and second refractive index films may be patterned.
[0016]
FIG. 2 is a schematic sectional view showing another embodiment of the laminate of the present invention. Referring to FIG. 2, in a laminated body 1 a of this embodiment, a patterned first refractive index film 3 a is further disposed on laminated body 1 having the configuration shown in FIG. 1. By making the alignment as shown in FIG. 2, for example, it is easy to make the laminate of the present invention into the form of a photonic crystal.
[0017]
(Production method of laminate)
The laminate can be suitably manufactured by, for example, the following manufacturing method.
[0018]
FIG. 3 is a schematic cross-sectional view showing one basic mode of the lamination method of the present invention. Referring to FIG. 3, photosensitive MSZ (methylsilazane) (refractive index: 1.55) is spin-coated on substrate 2 such as a Si wafer to form an MSZ film having a thickness of 150 nm on the Si wafer. (FIG. 3 (a)). After prebaking at 90 ° C. for 1 minute, the photosensitive MSZ film is left in a clean room atmosphere at 25 ° C. and 50% humidity for 10 minutes to absorb H ₂ O. Next, in order to manufacture a basic two-dimensional structure, EB lithography is performed using an EB (electron beam) stepper (for example, Hitachi HL-700 EB stepper) (FIG. 1B).
[0019]
The film is developed in an aqueous solution of tetramethyl ammonium hydroxide (TMAH) for 1 minute and rinsed with deionized water for 2 minutes. After curing in air at 420 ° C. for 30 minutes, the energy sensitive MSZ film is converted to a methylsilsesquioxane (MSQ) film (refractive index of 1.45) (from such MSZ to MSQ) For details of the conversion, see, for example, S. Mukaigawa, T. Aoki, Y. Shimizu, and T. Kikkawa, Jpn. J. Appl. Phys. 39 (2000) 2189).
[0020]
In these processes, both the EB-resist and the dry etching processes are removed in patterning, forming the desired pattern of the MSQ film.
[0021]
Next, a spin-on-glass (SOG; refractive index of 1.38) film is spin-coated at 2000 rpm to form a 200-nm-thick film on a flat film (FIG. 1C). After baking, an SOG film having a flat top surface is formed.
[0022]
By repeating the above process, a three-dimensional photonic crystal (FIG. 1D) having a periodically changing refractive index can be easily manufactured. Such a process of the present invention reduces the number of process steps in the method of the present invention by about one-half as compared to the conventional manufacturing process described below (FIG. 3), and thus the desired properties It is extremely easy to form a photonic crystal having
In the present invention, a photosensitive insulating film having a different refractive index may be used for both the first and second refractive index films. Further, in the present invention, when a photonic crystal is manufactured with a plurality of stacked structures, a defect may be introduced at an arbitrary position in an arbitrary layer to realize light waveguide or light confinement. Good.
[0023]
(Conventional resist process)
On the other hand, in the conventional manufacturing method shown in the schematic cross-sectional view of FIG. 4, compared to the above-described embodiment of the present invention (FIG. 3), a film of a photonic crystal material having a refractive index different from that of SOG is formed (FIG. 4 (a)) Formation of a resist coating (FIG. 4B), dry etching of a resist mask material (FIG. 4D), and removal of the resist mask (FIG. 4E) are added.
[0024]
In addition, additional films of material for the dry etch stop, such as silicon nitride, may be required between the SOG and photonic crystal materials (JG Fleming and S.-Y. Lin, Opt. Lett. 24 (1999) 49).
[0025]
(Each material etc.)
Materials and the like that can be used in the method of laminating a refractive index film (for example, a photonic crystal) having the above-described configuration and a patterned laminate according to the present invention are described below.
[0026]
(substrate)
There is no particular limitation as long as an energy-sensitive insulating film can be formed thereon. Examples of the material of the substrate that can be used in the present invention include a Si substrate, a glass substrate compound semiconductor substrate, and a metal substrate.
[0027]
Among them, a semiconductor material, particularly silicon, can be suitably used from the viewpoint of easiness of processing and / or easiness of combination with another device.
[0028]
(Energy-sensitive insulating film)
On the substrate, based on the irradiation of patterning energy (for example, electron beam and / or ultraviolet light) that can be used for manufacturing a patterned laminate, as long as it is an energy-sensitive insulating material capable of forming a predetermined pattern, There is no particular limitation. From the viewpoint of compatibility with the LSI fabrication technology, it is particularly preferable to use a photosensitive insulating film material such as photosensitive MSZ (methylsilazane) (for other usable materials, see, for example, the Journal of Photopolymer Science). and Technology Vol.10 No.4 1997 (ISSN 0914-9244) Published by The Technical Association of Photopolymers).
[0029]
(Patterned energy)
In the present invention, the patterning energy to be used for patterning the energy-sensitive insulating film is not particularly limited, but is preferably an energy ray or an electromagnetic wave from the viewpoint of compatibility with LSI fabrication technology. From the viewpoint of the energy level, among the above-mentioned energy rays, an electron beam can be suitably used because it has a good spatial resolution and a fine pattern can be formed, and as the electromagnetic wave, ultraviolet rays are suitable for forming a fine pattern. It is suitable for use.
[0030]
(Second refractive index film)
The material constituting the second refractive index film (assuming that the refractive index is b) to be disposed on the first refractive index film based on the above-mentioned energy-sensitive insulating film is not particularly limited. From the viewpoint of providing a suitable refractive index difference or ratio with the first refractive index film (the refractive index = a), the absolute value | ab− of these refractive index differences is 0.05 or more. And more preferably 0.07 or more.
[0031]
The material constituting the second refractive index film is preferably an inorganic material, and more preferably SOG (spin-on-glass), from the viewpoint of compatibility with LSI fabrication technology.
[0032]
(Patterned laminate)
In the present invention, the patterned laminate having at least the substrate, the patterned first refractive index film, and the second refractive index film preferably has the following film thickness.
[0033]
Thickness of first refractive index film: preferably 50 nm to 50 μm (more preferably 50 nm to 2 μm)
Thickness of second refractive index film: preferably 50 nm to 50 μm (more preferably 50 nm to 2 μm)
[0034]
(Photonic crystal)
In the present invention, at least on the above-mentioned substrate, a photonic crystal having a repeating structure of a patterned first refractive index film and a second refractive index film (that is, one embodiment of a patterned laminate) It is preferable to have the following size or characteristics.
[0035]
Number of repetitions of the first refractive index film and the second refractive index film: 2 or more, further 2 to 40 times (particularly 3 to 10 times)
Suitable optical properties of the photonic crystal:
Formation of a complete photonic band
In the above embodiment, SOG (refractive index is about 1.4) and MSQ (refractive index is about 1.5) are used, but the difference in refractive index between these materials is, for example, that other chemical materials are SOG or It can be varied by changing the refractive index of at least one of these by incorporating it into the energy sensitive MSZ.
[0037]
Hereinafter, the present invention will be described more specifically with reference to examples.
[0038]
【Example】
Example 1
(Formation of patterned laminate)
Referring to FIG. 3, a photosensitive MSZ (methylsilazane) (refractive index: 1.55; Clariant, trade name: PS-Signblow (trade name)) is formed on a substrate 2 made of a Si wafer (diameter 2 inches, manufactured by Shin-Etsu Semiconductor). (Trademark)) was spin-coated at 2,000 rpm using a spin coater (trade name, manufactured by Tatsumo Corporation) to form an MSZ film having a thickness of 150 nm on the Si wafer (FIG. 3A).
[0039]
After pre-baking the MSZ film at 90 ° C. for 1 minute, the photosensitive MSZ film was left in a clean room atmosphere at 25 ° C. and 50% humidity for 10 minutes to absorb H ₂ O. Next, in order to produce a basic two-dimensional structure, EB lithography was performed using an EB stepper (for example, Hitachi HL-700) to form a patterned MSZ film (FIG. 3B).
[0040]
The EB lithography conditions used at this time were as follows.
<EB lithography conditions>
Formed MSZ film pattern: line and space pattern having a width of 300 nm and a length of 4 mm The MSZ film patterned as described above was placed in a 2.38% aqueous solution of tetramethylammonium hydroxide (TMAH) at 23 ° C. for 1 minute. Develop and rinse with deionized water for 2 minutes.
[0041]
The rinsed MSZ film was cured in air at 420 ° C. for 30 minutes to convert the energy-sensitive MSZ film to an MSQ (methylsilsesquioxane) film (refractive index of 1.45). The formation of such an MSQ film was confirmed by infrared absorption analysis. In these processes, both the EB-resist and the dry etching process were removed in the pattern formation, and it was found by SEM analysis that the desired pattern of the MSQ film was formed.
[0042]
Next, a spin-on-glass liquid (SOG liquid; refractive index of 1.38; OCD T-7, manufactured by Tokyo Ohka Kogyo Co., Ltd.) was spin-coated on the patterned MSQ film. A 200 nm-thick SOG film was formed on a flat film by spin coating at 2000 rpm (manufactured by Tatsumo) (FIG. 3C). After baking in air (80 ° C. for 3 minutes; 150 ° C. for 3 minutes; 200 ° C. for 3 minutes), an SOG film having a flat top surface was formed.
[0043]
Example 2
(SEM observation)
A sample for scanning electron microscope (SEM) observation was produced by cleaving the patterned laminate obtained in Example 1. Using this sample, SEM observation was performed under the following conditions.
<SEM observation conditions>
SEM device: manufactured by Hitachi, trade name: S4700
FIG. 5 shows an image observed by the SEM. As can be seen in FIG. 5 (a), it was found that the basic two-dimensional structure of the MSZ film with the stripe pattern was actually formed and covered by the SOG film having a flat top surface. Note that when the film was cured with MSZ, it was relatively difficult to obtain a sharp cross section for SEM observation. Therefore, in this SEM observation, MSZ was not cured (therefore, in FIG. 5, The stripe pattern is composed of MSZ). The lines and spaces in the stripe pattern are 300 nm, which is suitable for photonic crystals in the optical wavelength range (500-1600 nm). Due to the flatness of the top SOG surface, a periodic two-dimensional structure of MSZ could be repeatedly laminated (FIG. 5 (b)).
[0044]
FIG. 6 is an SEM image (bird's-eye view) of a woodpile structure formed using the process of the present invention. For clear SEM observation, this sample was immersed in an HF solution (concentration: about 1% by volume) for a short time (about 4 minutes) to increase the contrast between SOG and MSZ. It was observed that the etching rate was different between the SOG in the blanket portion and the SOG in the trench portion. According to the findings of the present inventors, this difference was considered to be caused by a difference in stress.
[0045]
In FIG. 6, it can be seen that the stacked MSZ stripe pattern is layered by crossover with the underlying pattern.
[0046]
Example 3
(Formation of photonic crystal)
An MSQ film patterned under the same conditions as in Example 1 was further formed on the patterned laminate (FIG. 3C) formed in Example 1 (FIG. 3D). However, in the second formation of the patterned MSQ film, the pattern of the patterned MSQ film formed in the first time and the pattern of the patterned MSQ film formed in the second time are shifted by a half cycle. As such, these pattern formations were aligned.
[0047]
An SOG film was further formed on the patterned second MSQ film under the same conditions as in Example 1 (FIG. 3C).
[0048]
FIG. 7 is an SEM image of a two-dimensional structure having a Y-branch waveguide manufactured as described above. Thus, using the method of the present invention, a basic two-dimensional structure could be easily incorporated into a three-dimensional photonic crystal for a functional device.
[0049]
【The invention's effect】
As described above, according to the present invention, a method of laminating a refractive index film that can be simply and easily performed by directly combining a patterning technique, and a patterned laminate manufactured by the method are provided.
[0050]
Furthermore, a three-dimensional photonic crystal can be easily formed by applying the present invention. A basic structure having a stacked stripe pattern, a woodpile structure, and a two-dimensional Y-shaped waveguide can be realized by the present invention. Using this process, the number of process steps can be reduced to about one-half that using conventional resist. According to the present invention, a low-cost OEIC can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an example of a basic embodiment of a patterned laminate that can be formed according to the present invention.
FIG. 2 is a schematic cross-sectional view showing another example of the basic aspect of the patterned laminate that can be formed according to the present invention.
FIG. 3 is a schematic cross-sectional view showing an example of a basic mode of a method for laminating a refractive index film of the present invention.
FIG. 4 is a schematic cross-sectional view showing an embodiment of a process using a conventional resist.
FIG. 5 is an SEM photograph showing a patterned laminate (stripe structure) obtained in an example.
FIG. 6 is an SEM photograph showing a patterned laminate (wood pile structure) obtained in an example.
FIG. 7 is an SEM photograph showing a patterned laminate (Y-type waveguide) obtained in an example.

Claims (9)

(A) forming an energy-sensitive insulating film on a substrate,
(B) patterning the energy-sensitive insulating film by irradiation with patterning energy to form a patterned film having a first refractive index;
(C) a method of laminating different refractive index films, comprising a step of forming a film having a second refractive index different from the first refractive index on the film having the first refractive index. 2. The method according to claim 1, wherein the patterning energy is an electron beam or an ultraviolet ray. 3. The method according to claim 1, wherein the energy-sensitive insulating film is a photosensitive MSZ (methylsilazane) film. (A1) forming an energy-sensitive insulating film on the film having the second refractive index;
(B1) patterning the energy-sensitive insulating film by irradiation with patterning energy to form a patterned film having a first refractive index;
(C1) The method according to claim 3, wherein a film having a second refractive index different from the first refractive index is formed on the film having the first refractive index. 5. The method according to claim 4, wherein the steps (a1) to (c1) are repeated a plurality of times to form a photonic crystal. The method according to claim 1, wherein the substrate is a silicon substrate. Board and
A first refractive index film having a predetermined pattern, disposed on the substrate,
A laminate comprising at least a second refractive index film having a different refractive index from the first refractive index film, the second refractive index film being disposed on the first refractive index film. The laminate according to claim 7, wherein the first refractive index films and the second refractive index films are alternately arranged. 9. The laminate according to claim 8, wherein a plurality of the first refractive index films and a plurality of the second refractive index films are alternately arranged to form a photonic crystal.

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