JP2010237539A - Three-dimensional microfabrication method and three-dimensional microstructure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a three-dimensional microfabrication method to fabricate a micro mask precisely by reducing regions modified by electronic beams and to fabricate a precise three-dimensional micro structure using the mask. <P>SOLUTION: A three-layer inorganic resist oxidation film 10 including an As thin film 2, a Ga<SB>2</SB>O<SB>3</SB>thin film 4 and an As thin film 5 on the surface of a GaAs substrate 1. In the processes shown in (f) to (g) in selected figures, the Ga<SB>2</SB>O<SB>3</SB>thin film 4 and part of the GaAs substrate 1 are closely fixed by the electronic beams irradiated onto the surface of the three-layer inorganic resist oxidation film 10 in vacuum, thus to form a heat-resistant modified mask portion 17. In the process shown in (h), the As thin film 2 is sublimated, and the Ga<SB>2</SB>O<SB>3</SB>thin film 4 other than the modified mask portion 17 is separated to make the surface of the GaAs substrate 1 expose. In the process shown in (i), the three-dimensional microfabrication structure is fabricated on which a dent is formed by performing etching and by detaching Ga preferably from the exposed portion of the GaAs substrate 1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention mainly relates to a three-dimensional microfabrication method for forming a microstructure on the surface of a group III-V compound layer formed on the surface of a substrate or on the surface of a group III-V compound substrate.

  The current semiconductor microfabrication centering on optical lithography has reached the technological limit, and in order for the semiconductor-related industry to continue to be the main driver of the economic and industrial field, it is urgent to develop a methodology based on a new paradigm. is there. One of them is nanotechnology, which is expected to release from the device limitations (complexity, enlargement, and cost increase) of optical lithography technology.

  The technical issue that should be targeted is the development of 3D nano-miniaturization technology that enables small-lot, multi-product production (easy design change and low cost). In particular, from the viewpoint of the development of “optical / electronic devices”, the required process functions are assumed to be no damage and no contamination, and “collective devices” and “in-situ control” are required.

  There are two conditions required for lithography: throughput (resist sensitivity enhancement) and resolution (resist resolution), and a balance between them is important. Since the electron beam has a shorter wavelength than that of light, the electron beam lithography using the electron beam is being developed as exceeding the resolution limit of the optical lithography.

  In electron beam lithography, a high-acceleration electron beam drawing apparatus (for example, an acceleration voltage that can be set to 50 kV or more) that can obtain a minute electron beam diameter of 10 nm or less has been conventionally used. Since it is deep, a decrease in resist sensitivity is a problem. As a resist used in electron beam lithography, an organic resist is generally used in the same manner as optical lithography from the viewpoint of throughput. For example, PMMA is often used because it has a relatively low sensitivity among organic resists but is excellent in resolution. However, in recent years, there has been a strong demand for further improvement in resolution even for such a relatively good resolution PMMA.

  On the other hand, it is a general recognition that inorganic resists are superior in resolution to organic resists and are suitable for electron beam lithography in this respect, but are difficult to use due to low sensitivity. Accordingly, one of the targets for inorganic resist development is to make the sensitivity of the inorganic resist equal to or exceed that of PMMA. FIG. 1 shows the relationship between resist sensitivity and resolution for typical organic resists and inorganic resists. FIG. 1 also shows the positioning of a multilayer inorganic resist oxide film used as an inorganic material mask in one embodiment of the present invention.

  In addition, the electron beam lithography has a problem that the reaction region of the resist becomes larger than the beam diameter due to the influence (proximity effect) of secondary electron scattering from not only the incident electrons but also the resist and the substrate. If the reaction area of the resist is increased, the resolution between adjacent drawing lines of the electron beam is affected, and the three-dimensional microstructure produced in the subsequent process is affected. Many efforts have been made to reduce the expansion of the reaction region of the resist, and one example is the reduction of the effective beam diameter using the refractive index control of the electron beam entering the substrate by the multilayer resist. However, with the current technology, the proximity effect is a major limitation, which has been an obstacle to improving the resolution. For the progress of miniaturization, further suppression of the proximity effect in the resist film is desired. For example, it is preferable that the extent of the modified region due to the proximity effect is smaller than the range of the electron beam diameter.

  Therefore, in recent years, electron beam lithography using a low acceleration voltage of 5 kV or less has attracted attention as means for realizing suppression of the proximity effect and improvement of resist sensitivity by concentration of incident electrons near the substrate surface.

  Non-patent document 1, for example, discloses a method of forming a pattern using this type of electron beam. In Non-Patent Document 1, a random drawing method by Drouin et al. Is reported as an example of an approach method for the charging effect. Random drawing is a method of charging the substrate itself by low-acceleration electron beam lithography by patterning design rules on the order of several micrometers on the substrate surface by drawing randomly instead of sequentially drawing adjacent designs. It is a technique to alleviate

  Non-Patent Documents 2 and 3 and Patent Documents 1, 2 and 3 disclose three-dimensional microfabrication methods using the low-acceleration electron beam direct writing method. These documents describe a three-dimensional microfabrication method in which silicide is formed by irradiating an electron beam to a dissimilar metal material such as Ni or Cu sputter-deposited on a Si substrate and used as an etching mask. Is disclosed. In general, the electron beam has the highest electron density at the center of the beam and decreases as it moves away from the center (the electron density can be predicted with a Gaussian distribution), so only the scattering center region of the electron beam (region below the beam diameter) is selective. As a result, the silicide is formed.

  In general, resists can be classified into two types based on sensitivity characteristics. One is a digital resist that depends on the energy irradiation amount of an electron beam and causes a steep reaction at a critical value. The other is an analog resist in which the reaction proceeds continuously according to the amount of energy irradiation. Of these two types, a digital type that easily obtains spatial resolution has been advantageous for miniaturization in the submicron region. That is, in the case of using a digital resist, the formed “hard” reaction region is used as a mask, and has provided a selective function with respect to subsequent etching or growth (called regrowth). On the other hand, an analog resist has a limit in spatial resolution, but functions as a “soft” mask for a subsequent process, and thus has been used to fabricate a structure with a controlled height difference. From the viewpoint of producing arbitrary (various shapes) three-dimensional microstructures, it was necessary to develop an analog resist having excellent spatial resolution and excellent height difference control, and a process development of a post process.

  As a selective growth process after forming a mask pattern, a growth method (CVD, GSMBE, CBE, etc.) using a gas species having a long surface diffusion length is conventionally known. Selective growth using this technique is applied to all compound semiconductors including GaN and Si processes, and has been established as one of three-dimensional structure control techniques. For example, there is one disclosed in Patent Document 4 as using the CVD method. In Patent Document 4, a group III-V compound semiconductor is selectively grown using a metal organic chemical vapor deposition method (hereinafter referred to as MOCVD method) among CVD methods.

US Pat. No. 5,918,143 US Pat. No. 6,261,938 US Patent Application Publication No. 2005/0106861 Japanese Patent Laid-Open No. 8-172053

D. Drouin et al, Microsc. Microanal. 10 (2004) 804 D. Drouin et al, Jpn. J. et al. Appl. Phys. 41 (2002) 4122 D. Drouin et al, J. MoI. Vac. Sci. Technol. A 18 (2000) 681

  When performing electron beam lithography using a low acceleration voltage, since the penetration depth of an electron beam is very shallow (1 kV: depth <10 nm), a thin film resist having a thickness of several nm or less is required. However, since conventionally used organic resists are formed by spin coating, it has been difficult to uniformly coat organic materials on the entire surface of the substrate with a thickness of about 10 nm.

  In addition, in electron beam lithography using a low acceleration voltage, electrons repel each other and the beam diameter may spread when reaching the resist film. In addition, charges may accumulate on the substrate surface, which may hinder the drawing of the electron beam and cause distortion of the transferred pattern shape. Therefore, the electron beam lithography using the low acceleration voltage has problems of suppressing the expansion of the modified region (reduction of the line width transferred to the resist) and correcting the distortion of the transfer pattern shape caused by charging. .

  In this regard, Non-Patent Document 1 demonstrates the suppression of the charging effect by the random drawing method by performing electron beam lithography on the metal surface. However, when an easily charged oxide film or the like is used as a resist, The effect of the effect was not surely eliminated. Further, there is room for improvement from the viewpoint of reducing the modified region by the electron beam.

  In addition, the low-acceleration electron beam direct writing method disclosed in Non-Patent Documents 2 and 3 and Patent Documents 1 to 3 may cause non-uniformity or defects in the substrate / metal interface due to forced metal deposition. there were. Therefore, there has been a demand for a thin film forming method that can provide a uniform interface in place of forced metal deposition. In addition, since the formation of silicide requires generation of high heat (750 ° C.), there has been a limit toward higher sensitivity.

  In addition, the growth method using a gas species with a long surface diffusion length has a problem in that an extremely fine mask region is buried due to a large surface diffusion length for further small three-dimensional structure control including a submicron region. There is. In this respect, also in Patent Document 4, since the MOCVD method is used, the diffusion length of the surface atoms becomes long, and the selective growth of the group III-V compound semiconductor on the high-density array substrate cannot be sufficiently performed. It was difficult to increase the density of the substrate. In addition, the thickness of each growth crystal in the crystal growth direction on the nano order could not be made uniform. Therefore, it was necessary to combine with a process having a short surface diffusion length corresponding to a small mask region.

  In recent years, as the device structure becomes nanoscale, accurate processing accuracy at the molecular level is also required for electron beam lithography. However, in the conventional dry etching method using plasma ions, the etching accuracy depends on the scanning accuracy of electron beam drawing, and thus it is difficult to require the sub-nano-order orientation accuracy. Therefore, a new process for correcting the deviation in the scanning direction of the electron beam with sub-nanometer accuracy is required.

  For example, it is possible to transfer a precise pattern by changing the shape of the electron beam, but ultimately it depends on the scanning accuracy of the electron beam. It was difficult to reproduce. That is, a method for correcting the pattern shape with high accuracy other than scanning with an electron beam is required.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to make it possible to precisely form a fine mask by reducing the modified region by the electron beam, and to make precise use of the mask. The object is to provide a three-dimensional microfabrication method capable of producing a three-dimensional microstructure.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

  According to the first aspect of the present invention, a negative three-dimensional microfabrication method for forming a microstructure on the surface of a group III-V compound layer formed on the surface of the substrate or on the surface of a group III-V compound substrate A method comprising the following steps is provided: That is, in the first step, a V group film composed of V group atoms is formed on the surface of the substrate, and a III-V compound film is further formed on the surface of the V group film. In the second step, the group III-V compound film formed in the first step is modified with a superheated steam to a group III oxide film, and a group V film is formed on the surface of the group III oxide film. A layer inorganic resist oxide film is formed. In the third step, the electron beam irradiated on the surface of the three-layer inorganic resist oxide film in vacuum passes through the group V film formed in the second step and acts on a part of the group III oxide film. Thus, excess oxygen molecules can be separated from the group III oxide film. A part of the surface of the substrate is oxidized while a part of the group V film formed on the surface of the substrate in the first step is heated and sublimated to generate a group III oxide. Thereby, a part of the surface of the group III oxide film and the substrate is in close contact, and a modified mask portion having heat resistance is formed in a shape corresponding to the irradiated portion of the electron beam. In the fourth step, by raising the temperature of the substrate in a vacuum, the group V film formed on the surface of the substrate is sublimated, and the group III oxide film other than the modified mask portion is detached. Thus, the surface of the substrate is exposed. In the fifth step, the substrate is heated at a predetermined temperature in an environment in which a group V raw material is supplied to a vacuum, and an etching process is performed to preferentially remove the group III atoms from the exposed portion of the substrate. Create the original microstructure.

  Thus, by using superheated steam, the III-V compound film can be modified with high efficiency into a chemically stable group III oxide, and an inorganic resist oxide film can be formed on the surface of the substrate in situ. it can. Further, since the energy of the electron beam is concentrated on the group V film formed on the surface of the group III oxide film, the inorganic resist oxide film can be modified with high efficiency by effectively utilizing the energy of the electron beam. At the same time, the proximity effect can be suppressed. Therefore, the modified region of the inorganic resist oxide film by the electron beam in the third step can be narrowed, and three-dimensional microfabrication using the negative inorganic resist oxide film can be performed more precisely.

  In the three-dimensional microfabrication method, the following conditions are preferably satisfied. That is, the thickness of the group V film formed on the surface of the substrate in the first step is 1 nm to 5 nm, and the thickness of the group III-V compound film formed on the surface of the group V film is 1 nm to 5 nm. It is as follows. The thickness of the group V film formed on the surface of the group III oxide film in the second step is 1 nm or more and 10 nm or less.

  As a result, the inorganic resist oxide film can be modified using an electron beam using a low acceleration voltage with a penetration depth of about several nanometers. In an electron beam using a low acceleration voltage, incident electrons concentrate near the surface of the substrate, so that the resist sensitivity can be improved efficiently.

  According to the second aspect of the present invention, a negative three-dimensional microfabrication method for forming a fine structure on the surface of a group III-V compound layer formed on the surface of a substrate or on the surface of a group III-V compound substrate A method comprising the following steps is provided: That is, in the first step, a group V film composed of group V atoms is formed on the surface of the substrate, and a group III-V compound film is further formed on the surface of the group V film. In the second step, the group III-V compound film formed in the first step is modified to a group III oxide film with superheated steam to form a two-layer inorganic resist oxide film. In the third step, surplus oxygen molecules can be separated from the group III oxide film by irradiating the surface of the two-layer inorganic resist oxide film with an electron beam in a vacuum. Then, while a part of the group V film formed on the surface of the substrate in the first step is heated and sublimated, a part of the surface of the substrate is oxidized at the sublimated part to generate a group III oxide. The Thereby, a part of the surface of the group III oxide film and the substrate is in close contact, and a modified mask portion having heat resistance is formed in a shape corresponding to the irradiated portion of the electron beam. In the fourth step, by raising the temperature of the substrate in a vacuum, the group V film formed on the surface of the substrate is sublimated, and the group III oxide film other than the modified mask portion is detached. The surface of the substrate is exposed. In the fifth step, the substrate is heated at a predetermined temperature in an environment in which a group V raw material is supplied to a vacuum, and an etching process is performed to preferentially remove the group III atoms from the exposed portion of the substrate. Create the original microstructure.

  Thus, by using superheated steam, the III-V group compound film is highly efficiently modified into a chemically stable group III oxide, and an inorganic resist oxide film is formed in situ on the surface of the substrate. Can do. Further, since the energy of the electron beam is concentrated not on the inside of the substrate but on the group V film formed on the surface of the substrate, the inorganic resist oxide film can be modified with high efficiency by effectively utilizing the energy of the electron beam. it can. In addition, the modified region can be narrowed by the amount of energy concentrated on the group V film. Therefore, three-dimensional microfabrication using a negative inorganic resist oxide film can be performed with high efficiency.

  In the three-dimensional microfabrication method, the thickness of the group V film formed on the surface of the substrate in the first step is 1 nm or more and 5 nm or less, and the group III-V formed on the surface of the group V film. The thickness of the compound film is preferably 1 nm or more and 5 nm or less.

  As a result, the inorganic resist oxide film can be modified by an electron beam using a low acceleration voltage with a penetration depth of several nanometers. In an electron beam using a low acceleration voltage, incident electrons concentrate near the surface of the substrate, so that the resist sensitivity can be improved efficiently.

In the three-dimensional microfabrication method, the III-V group compound layer or the III-V group compound substrate is formed of Al _x Ga _y In _1-xy As _z P _1-z (0 ≦ x <1, 0 ≦ y, z ≦ 1) is preferable.

  Thereby, according to the pattern to produce, a three-dimensional fine structure can be produced efficiently by selecting the material of a III-V group compound layer or a III-V group compound substrate suitably.

In the three-dimensional microfabrication method, the group III oxide film formed in the second step is preferably an Al ₂ O ₃ thin film or an In ₂ O ₃ thin film.

  Thereby, a three-dimensional fine structure can be formed with high accuracy.

  In the three-dimensional microfabrication method, Si or SiC is preferably used as the substrate.

  Thereby, a three-dimensional fine structure can be manufactured at low cost.

In the three-dimensional microfabrication method of the acceleration voltage of the electron beam in the third step is not more than 20kV than 0.5 kV, the range of the surface dose is at 50 nC / cm ² or more 16μC / cm ² or less, The electron beam irradiation is preferably performed in a single line mode.

  Thereby, since the modified mask portion can be formed with high accuracy, the accuracy and reproducibility of the fine structure can be improved.

  In the three-dimensional microfabrication method, it is preferable that a plurality of electron beam drawing lines intersect each other in the third step.

  Thereby, it is possible to easily form a three-dimensional fine structure in which fine structural units formed in a depression shape are arranged vertically and horizontally.

  In the three-dimensional microfabrication method, it is preferable that the drawing line intersects with another drawing line at a midway portion in the longitudinal direction.

  Thereby, the shape of a plurality of depressions formed on the surface of the substrate can be made uniform.

  The three-dimensional microfabrication method preferably includes the following steps. That is, in the third step, the electron beam is irradiated with crystal orientations [100], [010], [011], [01-1], [110] [−110], [111], [−1] of the substrate. -1-1] is irradiated so as to draw a line that matches any of the above. In the fourth step, the substrate is heated to a temperature of 300 ° C. or higher and 650 ° C. or lower. In the fifth step, the substrate is heated to a temperature of 300 ° C. or higher and 650 ° C. or lower, and an etching rate is 0.3 ML / sec or lower.

  As a result, a three-dimensional microstructure is formed along the crystal orientation by self-organization, so that precise processing at the molecular level becomes possible.

  In the three-dimensional microfabrication method, it is preferable that in the third step, multiple scanning is performed by repeatedly irradiating the same place with an electron beam.

  As a result, charging on the surface of the substrate, which hinders drawing and causes distortion of the transfer pattern, can be suppressed, and the reproducibility of the drawing pattern can be effectively improved.

  In the above three-dimensional microfabrication method, when the same position is irradiated with an electron beam, the multiple scanning is 10 times of the time required to scan 1 mm with the electron beam since the previous scanning of the place. It is preferable to irradiate the electron beam after a time more than double has elapsed.

  Thereby, the charging effect can be effectively suppressed.

  In the three-dimensional microfabrication method, in the third step, it is preferable that the electron beam is converged and irradiated by passing the electron beam through a donut-shaped limiting aperture.

  Thereby, the electron beam diameter can be reduced and finer three-dimensional microfabrication can be performed.

  In the three-dimensional microfabrication method, a sixth step of selectively growing a group III-V compound crystal in a portion etched in the fifth step by performing a molecular beam epitaxial growth method using a solid growth raw material. It is preferable that it is further included.

  Thereby, even if it is a high-density pattern, the selective growth of a III-V group compound crystal can be easily performed by controlling the growth conditions of MBE method and controlling the surface atom diffusion length. It is also easy to make the crystal film thickness in the crystal growth direction uniform. Furthermore, the growth crystal of the III-V group compound has a good wall rise at the base portion, and can form a highly accurate fine structure.

In the three-dimensional microfabrication method, it is preferable that the following conditions are satisfied in the sixth step. That is, the substrate is heated to a temperature of 300 ° C. or higher and 650 ° C. or lower. Further, the flux ratio F _V / F _III of the group V and group III of the solid growth raw material is 1 or more and 100 or less. Further, the crystal growth rate is 0.01 ML / sec or more and 2 ML / sec or less.

  Thereby, a three-dimensional fine structure can be formed with high accuracy.

  In the above-described three-dimensional microfabrication method, it is preferable that a three-dimensional microstructure is produced in multiple stages by combining a step of producing a positive three-dimensional microstructure and a step of producing a negative three-dimensional microstructure.

  Thereby, a complicated-shaped three-dimensional microstructure can be formed.

  In the three-dimensional microfabrication method, a modified mask portion of a group III oxide film is formed on the surface of a positive three-dimensional microstructure or on the surface of a negative three-dimensional microstructure, and is etched. It is preferable to further form a new three-dimensional microstructure.

  Thereby, a three-dimensional fine structure can be produced more precisely and complicatedly.

  According to a third aspect of the present invention, a three-dimensional microstructure manufactured by the three-dimensional microfabrication method is provided.

  In the three-dimensional microstructure described above, the interval between adjacent unit structures is preferably submicron or less.

  Thereby, a high-density microstructure that can be suitably applied to the three-dimensional nano-miniaturization technology can be provided.

The graph which shows the comparison of the resist sensitivity and average molecular weight (resolution) of typical organic resist and inorganic resist. Explanatory drawing which showed the process of forming a three-layer inorganic resist oxide film in a GaAs substrate in steps from (a) to (e). From (f) to (j), a three-dimensional structure is formed using a three-layer inorganic resist oxide film, and crystals are selectively grown on the three-dimensional structure by molecular beam epitaxy (MBE) using a solid growth raw material. Explanatory drawing shown in steps of the order. The graph which shows an example of the temperature transition of each process in the three-dimensional microfabrication method of this embodiment. Explanatory drawing which showed typically the mode of the expansion of the electron beam inside a board | substrate when irradiated with an electron beam. Explanatory drawing which showed the simulation result of the electron energy distribution inside a board | substrate when irradiated with an electron beam. Explanatory drawing which showed suppression of the proximity effect at the time of using a 3 layer inorganic resist oxide film. Explanatory drawing which showed reduction of the modification | reformation area | region at the time of using a donut shape for the aperture of an electron beam. Explanatory drawing which showed reduction of the mask width by etching in steps. The graph which shows the change of the photosensitive sensitivity with respect to the acceleration voltage in a 3 layer inorganic resist oxide film, a 2 layer inorganic resist oxide film, and a natural oxide film. Explanatory drawing which showed typically the difference of the mask width at the time of using a 3 layer inorganic resist oxide film, and the mask width at the time of using a 2 layer inorganic resist oxide film. The microscope picture which shows the difference between the mask width at the time of using a 3 layer inorganic resist oxide film, and the mask width at the time of using a 2 layer inorganic resist oxide film. Explanatory drawing which showed typically the three-dimensional structure produced without adding an AlAs layer and the three-dimensional structure produced by adding an AlAs layer to a board | substrate. The microscope picture which showed the mode of the three-dimensional structure produced without adding an AlAs layer and the three-dimensional structure produced by adding an AlAs layer to a board | substrate. In explanatory view schematically showing a three-layer inorganic resist oxide film is the state of the GaAs substrate formed on the surface including the ₂ O _3. In micrograph showing the state of the three-dimensional structure manufactured using the three-layer inorganic resist oxide film containing ₂ O _3. Explanatory drawing which showed typically the mode of the reduction | decrease of the mask width accompanying progress of etching time. A photomicrograph showing step by step how the mask width is reduced over time. The schematic diagram which showed the drawing pattern of the electron beam. The photomicrograph which showed the three-dimensional structure formed in the shape according to the drawing pattern of an electron beam. Explanatory drawing which showed typically the mode of a part of crystal | crystallization at the time of irradiating an electron beam along the line inclined 10 degree | times with respect to the crystal orientation of a board | substrate. The microscope picture which showed the mode of the three-dimensional structure produced by irradiating an electron beam along the line inclined 10 degree | times with respect to the crystal orientation of a board | substrate. A photomicrograph showing the state of a three-dimensional structure produced by multiple scanning of electron beams. A photomicrograph showing the surface of a GaAs substrate on which a GaAs growth crystal is selectively grown by MBE on a three-dimensional microstructure produced by multiple scanning of electron beams. Explanatory drawing which showed typically a mode that an InAs crystal was made to grow by negative type | mold microfabrication on a negative type three-dimensional structure. The microscope picture which shows the mode of the three-dimensional structure which grew the InAs crystal | crystallization by the positive microfabrication on the negative three-dimensional structure. Micrograph showing an embodiment of forming a three-dimensional structure using a mixed oxide film and al ₂ O ₃ and Ga ₂ O ₃ was mixed with the inorganic resist oxide film. Al ₂ O ₃ and Ga ₂ O ₃ and is a state in which the formation of the GaAs growth crystal Si substrate using a mixed oxide film obtained by mixing the inorganic resist oxide film shown schematically illustration. A photomicrograph showing the growth of GaAs crystals formed on a Si substrate.

  Next, embodiments of the invention will be described. In the following description, the “three-layer inorganic resist oxide film” means a V group film, a Group III oxide film adjacent to the Group V film, a Group V film adjacent to the Group III oxide film, The inorganic resist layer comprised from these three layers is meant. The “two-layer inorganic resist oxide film” means an inorganic resist layer composed of two layers of a group V film and a group III oxide film adjacent to the group V film.

  First, referring to FIG. 2, FIG. 3 and FIG. 4, a process of forming a three-dimensional microstructure by forming a three-layer inorganic resist oxide film on a III-V group compound substrate, A step of producing a three-dimensional microstructure by generating a growth crystal of a group V compound will be described. FIG. 2 is an explanatory diagram showing the steps of forming the three-layer inorganic resist oxide film 10 on the GaAs substrate 1 in order from (a) to (e). FIG. 3 shows how a crystal is selectively grown on a three-dimensional structure formed using a three-layer inorganic resist oxide film 10 by molecular beam epitaxy (MBE) using a solid growth raw material from (f) to (j). It is explanatory drawing shown in order step by step. FIG. 4 is a graph showing an example of the temperature transition of each step in the three-dimensional microfabrication method of the present embodiment, and (a) to (i) shown in the graph are shown in FIG. This corresponds to e) and FIGS. 3 (f) to 3 (i), respectively.

  First, the process of forming the three-layer inorganic resist oxide film 10 on the surface of the GaAs substrate 1 will be described. FIG. 2A shows a GaAs substrate (III-V compound substrate) 1 as an example of an object to be finely processed. As shown in FIG. 2B, an As thin film 2 is formed on the surface of the GaAs substrate 1 by depositing As by molecular beam epitaxial growth in an ultra-high vacuum environment. The As thin film 2 preferably has a thickness of 1 nm to 5 nm.

Next, as shown in FIG. 2C, GaAs is deposited on the surface of the As thin film 2 to form a GaAs thin film (III-V group compound film) 3. The thickness of the GaAs thin film 3 is preferably 1 nm or more and 5 nm or less. Next, as shown in FIG. 2 (d), superheated steam treatment is performed to cause an oxidation reaction in the GaAs thin film 3, and the GaAs thin film 3 is oxidized into an oxide Ga ₂ O ₃ thin film 4 (group III oxide). To do. The chemical formula in which superheated steam modifies GaAs to Ga ₂ O ₃ is shown below.
2GaAs + 3H ₂ O → Ga ₂ O ₃ + As ₂ + 3H ₂
Or
2GaAs + 3H ₂ O → Ga ₂ O ₃ + 2AsH ₃
This oxidation treatment is performed using superheated steam at 300 ° C. in a heating environment at 150 ° C. to 250 ° C., and the treatment time is preferably 1 minute or more and 15 minutes or less.

Next, as shown in FIG. 2 (e), by depositing As the surface of the Ga ₂ O ₃ thin film 4 to form the As thin film 5. The As thin film 5 preferably has a thickness of 1 nm to 10 nm. In this state, three layers of thin films are formed on the surface of the GaAs substrate 1 in order of the As thin film 2, the Ga ₂ O ₃ thin film 4, and the As thin film 5 from the GaAs substrate 1 side. As a result, a three-layer inorganic resist oxide film 10 is formed on the surface of the GaAs substrate 1.

  As described above, the production (deposition) of the three-layer inorganic resist oxide film is preferably performed by a molecular beam epitaxial (MBE) method using a solid material. Using the MBE method has the following advantages. First, in the formation of a thin film by the MBE method, damage to the substrate surface that induces defects at the interface between the thin film and the substrate, which is a problem in the sputtering method that deposits the inorganic material of the thin film, is caused. There is no risk. Secondly, the MBE method does not require chemical decomposition of gas species like the metal organic chemical vapor deposition (MOCVD) method and the chemical vapor deposition (CVD) method, and therefore, under a low temperature environment below room temperature, the vapor pressure High metal As can be deposited on the surface of the semiconductor substrate. Third, the MBE method enables precise thin film control in molecular layer units by in-situ observation using a reflection high-energy electron diffraction apparatus (RHEED).

  Next, a process of forming a mask on the surface of the GaAs substrate 1 using the three-layer inorganic resist oxide film 10 as a negative inorganic resist layer and forming a three-dimensional microstructure using the mask will be described.

First, as shown in FIG. 3F, a GaAs substrate 1 on which a three-layer inorganic resist oxide film is formed is prepared. Next, as shown in FIG. 3G, the three-layer inorganic resist oxide film 10 is irradiated with an electron beam whose electron beam diameter, current density, and the like are set to predetermined values in a vacuum. The irradiated electron beam passes through the As thin film 5 on the uppermost layer of the three-layer inorganic resist oxide film 10 and acts on the Ga ₂ O ₃ thin film 4 underlying the As thin film 5. Oxygen molecules from part of the Ga ₂ O ₃ thin film 4 by the action of the electron beam is separated. The surface of the GaAs substrate 1 is oxidized chemically by oxygen molecules separated from the Ga ₂ O ₃ thin film 4 while a part of the As thin film 2 that is the base of the Ga ₂ O ₃ thin film 4 is heated and sublimated with high efficiency. Stable Ga ₂ O ₃ is produced. A part of the surface of the GaAs substrate 1 and the Ga ₂ O ₃ thin film 4 are brought into close contact with each other by forming Ga ₂ O ₃ in a part where the part of the As thin film 2 is heated and sublimated. (Formation of modified mask portion 17). A part of the Ga ₂ O ₃ thin film 4 (modified mask portion 17) that is in close contact with the substrate functions as a mask in a process described later. The modified mask portion 17 is in close contact with a part of the surface of the GaAs substrate 1 to improve heat resistance. As described herein, in the case of the three-layer inorganic resist oxide film 10 including the Ga ₂ O ₃ thin film 4, the modified mask portion 17 has a heat resistance of 580 ° C. or higher.

  The modified mask portion 17 is formed in a shape corresponding to the electron beam drawing pattern. Next, electron beam irradiation will be described.

  By drawing a periodic pattern that intersects multiple electron beam drawing lines, it is composed of low index planes that are self-organized accurately in crystal orientation by preferential separation (sublimation) of the surface of the GaAs substrate 1 by a process described later. Will be formed. In addition, it is preferable that the said drawing line cross | intersects other drawing lines in the middle part of a longitudinal direction from a viewpoint of making the shape of a hollow uniform.

From the viewpoint of forming a highly accurate pattern, it is preferable that the electron beam irradiation has an acceleration voltage in the range of 0.5 kV to 20 kV and an acceleration voltage of 0.5 to 5 kV as the core. The range of the surface dose is 50 μC / cm ² or more and 16 mC / cm ² or less, and the electron beam irradiation is preferably performed in a single line mode.

  Further, the electron beam is emitted from the crystal orientation [100], [010], [011], [01-1], [110] [−110], [111], [−1-1-1] of the GaAs substrate 1. It is preferable that the drawing is performed almost in line with a line that matches any of the above. As a result, the shape of the recess formed by the process described later must completely match the lines of crystal orientation [100], [010], [011], [01-1], [110] [−110]. Because it becomes.

  Furthermore, it is preferable that the electron beam is irradiated not by irradiating the substrate surface with a necessary electron dose at a time but by performing multiple scanning for drawing a low electron dose in a plurality of times. Thereby, the charging effect on the surface of the GaAs substrate 1 is suppressed, and the reproducibility of the drawing pattern can be effectively improved by removing the cause of the hindrance to the drawing and the distortion of the transfer pattern. In addition, since the blur near the end of the modified mask portion 17 (corresponding to the tail portion of the electron beam Gaussian distribution) can be minimized, the heat resistance near the end of the modified mask portion 17 is improved.

  Further, in the multiple scanning, when the electron beam is irradiated to the same place, the irradiation is set so that a predetermined time has passed. From the viewpoint of reliably removing the charging effect on the surface of the GaAs substrate 1, it is preferable to irradiate the electron beam after 10 times or more of the time necessary for scanning 1 mm with the electron beam has elapsed.

Next, a process of detaching the Ga ₂ O ₃ thin film 4 other than the modified mask portion 17 will be described. In the step shown in FIG. 3H, heating is performed at a predetermined temperature of 300 ° C. or more and 650 ° C. or less in an environment where As ₄ is supplied in a vacuum, and Ga ₂ O ₃ other than the As thin film 2 and the modified mask portion 17 is used. The thin film 4 and the uppermost As thin film 5 are removed from the GaAs substrate 1. At this time, it is preferable to heat the GaAs substrate 1 at 580 ° C. or higher as shown in the graph of FIG. 4 because the Ga ₂ O ₃ thin film 4 other than the modified mask portion 17 can be removed satisfactorily. As a result, a Ga ₂ O ₃ inorganic material mask 6 that functions as a mask in a process described later is formed on the surface of the GaAs substrate 1. As described above, the Ga ₂ O ₃ inorganic material mask 6 becomes periodic by drawing a periodic pattern with an electron beam.

This desorption of the oxide film (Ga ₂ O ₃ thin film 4) can be explained by the following phenomenon. That is, as the As thin film 2 is heated and sublimated, Ga atoms can be separated from the surface of the GaAs substrate 1. As a result, the Ga ₂ O ₃ thin film 4 other than the modified mask portion 17 reacts with the Ga atoms separated from the surface of the GaAs substrate 1 to generate highly volatile Ga ₂ O. By this reaction, the Ga ₂ O ₃ thin film 4 is detached. However, it can be considered that the Ga ₂ O ₃ thin film 4 is removed from the GaAs substrate 1 by being lifted off together with the As thin film 2.

Next, the etching process will be described. In the step shown in FIG. 3I, heating of the GaAs substrate 1 is continued at a predetermined temperature (650 ° C. in the example of FIG. 4) in an environment in which As (V group raw material) is supplied in a vacuum. In the present embodiment, the predetermined temperature is preferably 580 ° C. or higher and 650 ° C. or lower. Then, Ga atoms are peeled off preferentially from the exposed portion of the GaAs substrate 1 that is not covered by the Ga ₂ O ₃ inorganic material mask 6 and diffused and sublimated. When the electron beam drawing is performed in a periodic pattern, a part of the diffused Ga atoms moves to the edge of the drawing region and accumulates. As a result, a three-dimensional microstructure is formed in which the recesses 18 formed of self-organized low index surfaces are periodically formed in the exposed portion of the GaAs substrate 1. Note that the etching rate is preferably 0.3 ML / sec or less. Furthermore, it is preferable that the etching depth of the GaAs substrate 1 be about the single-line electron beam irradiation region.

  In the formation of the three-dimensional structure by self-organization, the edge of the modified mask portion (tail portion of the electron beam Gaussian distribution) is detached due to sublimation occurring in the GaAs substrate 1, so that the width of the modified portion is increased. Can be made smaller than the electron beam diameter.

Next, a process of selectively growing GaAs in the recess 18 by molecular beam epitaxy (MBE) will be described. This MBE method is carried out so that the growth direction of GaAs matches the plane orientation (001) of the GaAs substrate 1 and satisfies the following conditions. That is, the crystal growth temperature of 450 ° C. or higher 600 ° C. below the predetermined temperature (580 ° C. in the example of FIG. 4), the flux ratio of As ₄ molecular and Ga atoms (F _As / F _Ga) in the range of 1 to 100, inclusive And Then, the GaAs crystal growth rate is set to 0.01 ML / sec or more and 2 ML / sec or less (molecular layer / second: growth rate conversion for a two-dimensional thin film).

  As a result, the GaAs growth crystal 7 is formed in the depression 18 as shown in FIG. The thickness of the GaAs growth layer film thus obtained is almost inversely proportional to the size of the opening formed between the modified mask portion 17 and the modified mask portion 17. Further, it is preferable that the GaAs growth layer film has an interval for drawing an electron beam (for example, an interval between adjacent parallel lines).

  Here, the GaAs crystal growth rate is preferably adjusted using a reflection high-energy electron diffraction apparatus (hereinafter referred to as RHEED) for in situ observation of the surface state of the sample thin film or the substrate. If the GaAs crystal growth rate is determined, the film thickness of the grown crystal can be controlled by adjusting the GaAs crystal growth time.

  As described above, the GaAs growth crystal 7 is formed on the surface of the GaAs substrate 1, and a positive three-dimensional microstructure can be produced (FIG. 3 (j)).

In the above embodiment, the As thin film 5 is further formed on the surface of the Ga ₂ O ₃ thin film 4 in the step of FIG. 2E, but this step may be omitted. In this case, the modified Ga ₂ O ₃ thin film 4 from the GaAs thin film 3 is directly irradiated with an electron beam. Even when the vapor deposition step of the As thin film 5 is omitted, the other steps can be performed in exactly the same manner as described above.

  Next, with reference to FIG. 5 and FIG. 6, the sensitivity enhancement of the resist using the multilayer inorganic resist oxide film will be described using the GaAs substrate (III-V compound substrate) 1 as an example.

  First, with reference to FIG. 5, how the electron beam spreads inside the substrate when the two-layer inorganic resist oxide film 20 is used as the resist layer will be described. FIG. 5 is an explanatory view schematically showing how the electron beam spreads inside the GaAs substrate 1 when the electron beam is irradiated.

FIG. 5A shows a GaAs substrate 1 on which a two-layer inorganic resist oxide film 20 is formed. The two-layer inorganic resist oxide film 20 is composed of an As thin film 2 formed on the GaAs substrate 1 and a Ga ₂ O ₃ thin film 4 formed on the As thin film 2. FIG. 5B shows a GaAs substrate 1 on which a GaAs natural oxide film 51 is formed. The composition of the vicinity of the surface of the GaAs native oxide film 51 is formed as a main component similarly Ga ₂ O ₃ has a two-layer inorganic resist oxide film 20, the vicinity of the interface between the GaAs substrate 1, a metal As52 is not Precipitates in a uniform state.

  When the surface of the two-layer inorganic resist oxide film 20 is irradiated with an electron beam using a low acceleration voltage of 5 kV or less, the center 50 of the spread of the internal scattering of the electron beam is as shown in FIG. Alternatively, it is located near the surface of the GaAs substrate 1. On the other hand, when the surface of the GaAs natural oxide film 51 is irradiated with the electron beam under the same conditions as described above, the center 50 of the spread of the internal scattering of the electron beam is the surface in the GaAs substrate 1 as shown in FIG. It is located on the back side (lower side of the drawing). Comparing FIG. 5A and FIG. 5B, in the two-layer inorganic resist oxide film 20, the center 50 of the electron beam internal scattering spread is located on the As thin film 2 or GaAs substrate 1 surface side. I understand. Therefore, when the electron beam is irradiated under the same conditions, the electron beam internal scattering center 50 is located on the resist layer side formed on the substrate surface when the two-layer inorganic resist oxide film 20 is used. Can be modified with high efficiency.

  Next, the simulation result of the energy distribution of the electron beam inside the GaAs substrate 1 will be described with reference to FIG. FIG. 6 is an explanatory diagram showing a simulation result of electron energy distribution in the GaAs substrate 1 when irradiated with an electron beam. In the simulation shown below, the calculation was performed assuming that the acceleration voltage of the electron beam was 1 kV, the electron beam diameter was 500 nm, and the number of electrons was 100,000.

On the left side of FIG. 6A, a schematic diagram of the GaAs substrate 1 on which the two-layer inorganic resist oxide film 20 is formed is shown. In the two-layer inorganic resist oxide film 20, the thickness of the As thin film 2 formed on the GaAs substrate 1 is 1.5 nm, and the thickness of the Ga ₂ O ₃ thin film 4 formed on the As thin film 2 is 1. Each is set to 5 nm. 6A shows the simulation result of the electron beam energy distribution in the GaAs substrate 1 when the surface of the two-layer inorganic resist oxide film 20 is irradiated with the electron beam under the irradiation conditions. Has been.

The thickness of the Ga ₂ O ₃ thin film 34 formed on the surface of the GaAs substrate 1 shown on the left side of FIG. 6B is set to 3.0 nm. On the right side of FIG. 6B, the electron beam energy distribution in the GaAs substrate 1 when the Ga ₂ O ₃ thin film 34 formed on the surface of the GaAs substrate 1 is irradiated with the electron beam under the irradiation conditions. The simulation results are shown.

  Comparing the simulation results shown in FIGS. 6A and 6B, the energy density of the beam near the surface of the GaAs substrate 1 is higher when the two-layer inorganic resist oxide film 20 is used. I understand that. This indicates that when the two-layer inorganic resist oxide film 20 is irradiated with an electron beam, the energy of the electron beam is concentrated on the As thin film 2 formed on the surface of the GaAs substrate 1.

  Thus, since the energy of the electron beam is concentrated not on the GaAs substrate 1 but on the As thin film 2 formed on the surface of the GaAs substrate 1, the inorganic resist oxide film is efficiently utilized by effectively utilizing the electron beam energy. Can be modified. In addition, since the energy of the electron beam is concentrated on the As thin film 2, the modified region can be narrowed.

  Next, suppression of the proximity effect when the three-layer inorganic resist oxide film 10 is used will be described with reference to FIG. FIG. 7 is an explanatory diagram showing suppression of the proximity effect by electron beam irradiation when the three-layer inorganic resist oxide film 10 is used.

  FIG. 7A shows the state of electron beam internal scattering spreading in the substrate when the surface of the three-layer inorganic resist oxide film 10 is irradiated with an electron beam. FIG. 7B shows the state of the internal scattering of the electron beam in the substrate when the surface of the two-layer inorganic resist oxide film 20 is irradiated with the electron beam. In both cases shown in FIGS. 7A and 7B, an electron beam using a low acceleration voltage of 5 kV or less is used.

As shown in FIG. 7A, when the three-layer inorganic resist oxide film 10 is used, the energy 50 of the electron beam is concentrated on the As thin film 5 formed on the uppermost layer. It is located in the uppermost As thin film 5. Further, the spread of the internal scattering of the electron beam spread by the As thin film 5 is small in the Ga ₂ O ₃ thin film 4 which is the base. In the As thin film 2 formed on the GaAs substrate 1, the spread of scattering in the electron beam is larger than that in the Ga ₂ O ₃ thin film 4, although it is smaller than the spread in the As thin film 5. Thus, it can be seen that the spread of internal scattering of the electron beam in the Ga ₂ O ₃ thin film 4 is smaller than that of the As thin film sandwiched between the upper and lower sides. This means that the region where the Ga ₂ O ₃ thin film 4 is modified by the electron beam is small.

In addition, since the metal layer formed of the As thin film 5 exists in the uppermost layer irradiated with the electron beam, the modified region may be thinner than the half-value width of the electron beam diameter. Non-Patent Document 1 shows that when a low-acceleration electron beam is directly drawn on the resist film surface on which the metal layer is present, the modified region width becomes narrower than the half-value width (electron beam diameter) of the energy distribution of the electron beam. This is because it has been reported. In this embodiment, since Ni or the like is not used as the metal layer, it is not necessary to perform sputter deposition that induces the generation of defects at the interface between the substrate and the metal layer. In addition, unlike the method disclosed in Non-Patent Document 1, it is not necessary to set the threshold electron dose required for reforming to a very high value (about 19 mC / cm ² ). Thus, by applying the present invention, it is possible to efficiently reduce the electron beam modification region.

On the other hand, in FIG. 7B, since the As thin film is not formed in the uppermost layer, the center of the electron beam internal scattering spread is near the interface between the As thin film 2 formed on the substrate and the surface of the GaAs substrate 1. Is located. Ga ₂ O ₃ directly irradiated electron beam to the thin film 4 is made larger scattering in Ga ₂ O ₃ thin film 4 from inside As thin film 2.

  When comparing FIG. 7A and FIG. 7B, the electron beam internal scattering spreads more when the three-layer inorganic resist oxide film 10 is formed on the GaAs substrate 1 than the two-layer inorganic resist oxide film 20. The center of is located on the top side. The difference in the position of the center 50 of the internal scattering of the electron beam is due to the concentration of the electron beam energy in the As thin film as already described with reference to FIGS. More specifically, the electron energy for the GaAs substrate 1 depends on whether the electron energy is concentrated on the As thin film 5 formed on the uppermost layer or the As thin film 2 formed on the surface of the GaAs substrate 1. The center position of will change.

Thus, by using the three-layer inorganic resist oxide film 10, the proximity effect in the Ga ₂ O ₃ thin film 4 can be obtained more than when the GaAs natural oxide film 51 (see FIG. 5B) is used as the inorganic resist. Can be suppressed. Therefore, the modified region can be made narrower, and a high-density fine structure, for example, a fine structure in which the interval between adjacent unit structures is sub-micron or less can be easily produced.

As described above, the three-dimensional microstructure of this embodiment is manufactured through the following steps. That is, in the steps shown in FIGS. 2A to 2C, the As thin film 2 is formed on the surface of the GaAs substrate 1 and the GaAs thin film 3 is formed on the surface of the As thin film 2. In the steps shown in FIGS. 2D to 2E, the GaAs thin film 3 is modified to a Ga ₂ O ₃ thin film 4 by superheated steam, and an As thin film 5 is formed on the surface of the Ga ₂ O ₃ thin film 4. A three-layer inorganic resist oxide film 10 is formed. In the steps shown in FIGS. 3F to 3G, the electron beam irradiated on the surface of the three-layer inorganic resist oxide film 10 in vacuum passes through the As thin film 5 and a part of the Ga ₂ O ₃ thin film 4. By acting on, the excess oxygen molecules can be separated from the Ga ₂ O ₃ thin film 4. Then, while a part of the As thin film 2 is heated and sublimated, a part of the surface of the GaAs substrate 1 is oxidized to generate Ga ₂ O ₃ . As a result, the Ga ₂ O ₃ thin film 4 and a part of the surface of the GaAs substrate 1 are in close contact with each other, and the modified mask portion 17 having a heat resistance of 580 ° C. or higher is formed in a shape corresponding to the irradiated portion of the electron beam. In the step shown in FIG. 3 (h), by raising the temperature of the GaAs substrate 1 in a vacuum, the As thin film 2 formed on the surface of the GaAs substrate 1 is sublimated, and a portion of the Ga other than the modified mask portion 17 is Ga. _{The 2} O ₃ thin film 4 is detached and the surface of the GaAs substrate 1 is exposed. In the step shown in FIG. 3I, the GaAs substrate 1 is heated at a predetermined temperature in an environment where As ₄ is supplied to a vacuum, thereby performing an etching process for preferentially peeling Ga from the exposed portion of the GaAs substrate 1. This creates a three-dimensional microstructure.

Thus, by using superheated steam, the GaAs thin film 3 is highly efficiently modified to a chemically stable Ga ₂ O ₃ thin film 4 and an inorganic resist oxide film is formed on the surface of the GaAs substrate 1 in situ. Can do. Further, since the energy of the electron beam is concentrated on the As thin film 5 formed on the surface of the Ga ₂ O ₃ thin film 4, it is possible to modify the inorganic resist oxide film with high efficiency by effectively utilizing the energy of the electron beam. In addition, the proximity effect can be suppressed. Therefore, the modified region of the inorganic resist oxide film by the electron beam can be narrowed, and three-dimensional microfabrication using the negative inorganic resist oxide film can be performed more precisely.

Moreover, in the three-dimensional microfabrication method of this embodiment, the following conditions are satisfied. The thickness of the As thin film 2 formed on the surface of the GaAs substrate 1 is 1 nm or more and 5 nm or less. In the step of FIG. 2C, the thickness of the GaAs thin film 3 formed on the surface of the As thin film 2 is 1 nm or more and 5 nm or less. The thickness of the As thin film 5 formed on the surface of the Ga ₂ O ₃ thin film 4 is 1 nm or more and 10 nm or less.

  As a result, the inorganic resist oxide film can be modified using an electron beam using a low acceleration voltage with a penetration depth of about several nanometers. In the electron beam using the low acceleration voltage, incident electrons concentrate near the surface of the GaAs substrate 1, so that the resist sensitivity can be improved efficiently.

  In the three-dimensional microfabrication method of this embodiment, the GaAs growth crystal 7 is selectively grown in the depression 18 formed by performing the etching process by performing the MBE method using the solid growth raw material. It further includes the step shown in (j).

  Thereby, even if it is a high-density pattern, the selective growth of the GaAs growth crystal 7 can be easily performed by controlling the growth conditions of the MBE method and controlling the surface atom diffusion length. It is also easy to make the crystal film thickness in the crystal growth direction uniform. Further, the growth crystal of the GaAs growth crystal 7 has a good wall rise at the base portion, and can form a highly accurate fine structure.

  In the above embodiment, the electron beam is irradiated by a normal point beam, but the form of electron beam irradiation can be changed. Next, with reference to FIG. 8, irradiation of an electron beam when a donut-shaped ring aperture is used will be described. FIG. 8A shows a case where an electron beam is passed through a donut-shaped limiting aperture to GaAs substrate 1 on which a two-layer inorganic resist oxide film 20 is formed, thereby converging the electron beam diameter. The electron beam energy distribution and the modified region are schematically shown. FIG. 8B schematically shows the electron beam energy distribution and the modified region when the GaAs substrate 1 on which the two-layer inorganic resist oxide film 20 is formed is irradiated with an electron beam using a normal point beam. Has been.

  As shown in FIG. 8A, the beam diameter of the electron beam when a donut-shaped ring aperture is used is reduced. Thereby, compared with the case where a normal point beam is used, the modification area | region width | variety can be made smaller. Therefore, by combining with the three-layer inorganic resist oxide film 10 and the two-layer inorganic resist oxide film 20, a more precise three-dimensional microstructure can be produced.

Referring now to FIG. 9 will be described Ga ₂ O ₃ reduction of inorganic material mask 6 the width occurring during sublimation etching of the GaAs substrate 1. FIG. 9 is an explanatory view showing stepwise reduction of the width of the Ga ₂ O ₃ inorganic material mask 6 by etching.

As shown in FIG. 9A, the two-layer inorganic resist oxide film 20 is modified by irradiating the two-layer inorganic resist oxide film 20 formed on the surface of the GaAs substrate 1 with an electron beam under a predetermined condition. The Next, the GaAs substrate 1 is heat-treated in a vacuum. By this heat treatment, the GaAs substrate 1 is decomposed, and Ga atoms are melted from the surface of the GaAs substrate 1. Most of the molten Ga atoms are subjected to sublimation etching in a vacuum, and a three-dimensional structure composed of crystal planes on the surface of the GaAs substrate 1 is self-organized. However, some of the molten Ga atoms migrate on the surface of the GaAs substrate 1, so that the migrated Ga atoms react with the Ga ₂ O ₃ inorganic material mask 6. High Ga ₂ O volatile by this reaction is generated, so that the width of the Ga ₂ O ₃ inorganic material mask 6 is gradually reduced.

  Hereinafter, the present invention will be described more specifically with reference to examples. In each example, the crystal growth rate in the MBE method was measured and controlled using RHEED.

  First, with reference to FIG. 10, the improvement of the photosensitivity when a multilayer inorganic resist oxide film is used will be described. FIG. 10 is a graph showing changes in photosensitive sensitivity with respect to the electron beam acceleration voltage in the three-layer inorganic resist oxide film 10, the two-layer inorganic resist oxide film 20, and the natural oxide film.

  As shown in FIG. 10, the absolute value of the photosensitivity of each inorganic resist oxide film decreases (higher sensitivity) as the acceleration voltage decreases. On the other hand, paying attention to the difference in the photosensitivity of each inorganic resist oxide film, the two-layer inorganic resist oxide film 20 and the three-layer inorganic resist oxide film 10 have higher photosensitivity than the natural oxide film. I understand. In addition, although the photosensitivity changes in accordance with the change in acceleration voltage, the relative relationship of the photosensitivity between the natural oxide film, the two-layer inorganic resist oxide film 20 and the three-layer inorganic resist oxide film 10 is There is almost no change. That is, the natural oxide film, the two-layer inorganic resist oxide film 20 and the three-layer inorganic resist oxide film 10 each exhibit a behavior in which the absolute value of the photosensitivity increases as the acceleration voltage increases at a substantially constant ratio. . This result shows that the deterioration of the photosensitivity in each inorganic resist oxide film with the increase in acceleration voltage depends only on the number of electrons that react in the surface oxide film. This means that the mechanism for modifying the oxide film by the electron beam is the same.

Next, referring to FIGS. 11 and 12, the width of the Ga ₂ O ₃ inorganic material mask 6 when the three-layer inorganic resist oxide film 10 is used and the Ga when the two-layer inorganic resist oxide film 20 is used. The difference between the width of the ₂ O ₃ inorganic material mask 26 will be described. FIG. 11A schematically shows the state of the Ga ₂ O ₃ inorganic material mask 6 when the three-layer inorganic resist oxide film 10 is used, and FIG. 11B shows the two-layer inorganic resist oxide film 20. A state of the Ga ₂ O ₃ inorganic material mask 26 when used is schematically shown. 12A shows a state of the Ga ₂ O ₃ inorganic material mask 6 in the case of using the three-layer inorganic resist oxide film 10 by a micrograph, and FIG. 12B shows the two-layer inorganic resist oxide film 20. The state of the Ga ₂ O ₃ inorganic material mask 26 when used is shown by a micrograph.

In both cases of using the three-layer inorganic resist oxide film 10 and the two-layer inorganic resist oxide film 20, the acceleration voltage is 1 kV and the surface dose is 500 μC / cm as the electron beam drawing conditions. It is set to be ² . The electron beam drawing pattern is set so that a plurality of parallel lines matching the [110] direction of the GaAs substrate 1 and a plurality of parallel lines matching the [−110] direction intersect perpendicularly. Yes. The plurality of parallel lines were drawn so that the line spacing was 2.4 μm. Here, the line interval in this specification refers to a distance (distance between center lines in the width direction of the electron beam) that is irradiated with an electron beam in a single line mode and then translated to the next irradiated line.

Hereinafter, a case where the three-layer inorganic resist oxide film 10 is used will be described. That is, the As thin film 2 was deposited to a thickness of 1.5 nm on the (001) plane of the GaAs substrate 1 from which the natural oxide film was removed in an ultrahigh vacuum (molecular beam epitaxial growth) environment. Further, GaAs was deposited on the As thin film 2 by 1.5 nm. Thereafter, superheated steam oxidation treatment was performed to form a Ga ₂ O ₃ thin film 4 on the surface of the GaAs substrate 1. This oxidation treatment was performed for 5 minutes using superheated steam at 300 ° C. in a heating environment at 200 ° C. Then, an As thin film 5 was again deposited on the Ga ₂ O ₃ thin film 4 by 5 nm. By irradiating the three-layer inorganic resist oxide film 10 thus produced with the electron beam under the above conditions, the GaAs substrate 1 and the Ga ₂ O ₃ thin film 4 are selected as shown in the upper side of FIG. In close contact (in a form corresponding to the shape of the drawing pattern).

Next, the GaAs substrate 1 was heated to 580 ° C. or higher in a vacuum, and the portion of the Ga ₂ O ₃ thin film 4 that was not modified by the electron beam was peeled off. Thereafter, the GaAs substrate was heated at 650 ° C. for 3 hours under the supply of 0.7 ML / sec As ₄ molecules. This promotes GaAs sublimation at the surface portion of the GaAs substrate 1 that is not masked by the Ga ₂ O ₃ inorganic material mask 6, and as shown in the lower side of FIG. A three-dimensional structure was formed.

Even when the two-layer inorganic resist oxide film 20 was used, a three-dimensional structure was formed on the surface of the GaAs substrate 1 under the same conditions. In this case, as a method of forming the three-dimensional structure, the above-described three-layer inorganic resist oxide film 10 is used except that the step of depositing an As thin film 5 on the Ga ₂ O ₃ thin film 4 is omitted. It is the same.

As a result, as shown in FIG. 12, in any case of the three-layer inorganic resist oxide film 10 and the two-layer inorganic resist oxide film 20, the three-dimensional structure having the Ga ₂ O ₃ inorganic material mask 6 formed on the surface. Were self-assembled to form openings aligned vertically and horizontally on the GaAs substrate 1. This three-dimensional structure is composed of a (110) plane and a (111) A plane. Comparing FIG. 12A and FIG. 12B, the case where the three-layer inorganic resist oxide film 10 is used is more Ga ₂ O ₃ inorganic than the case where the two-layer inorganic resist oxide film 20 is used. It can be seen that the material mask width is narrowed. This is because the energy of the electron beam concentrates on the As thin film 5 deposited on the Ga ₂ O ₃ thin film 4, thereby spreading the electron beam at the interface between the GaAs substrate 1 and the three-layer inorganic resist oxide film 10 (proximity effect). ) Proved to be effectively suppressed.

  Next, with reference to FIGS. 13 and 14, an embodiment in which a three-dimensional structure is produced by forming an AlAs layer 11 on a GaAs substrate 1 will be described. FIG. 13A schematically shows a three-dimensional structure produced when an AlAs layer 11 is added to the GaAs substrate 1. FIG. 13B schematically shows the state of the three-dimensional structure produced when the AlAs layer 11 is not added. FIG. 14A shows a state of the three-dimensional structure produced by adding the AlAs layer 11 with a micrograph, and FIG. 14B shows the three-dimensional structure produced without adding the AlAs layer 11. The state of the body is shown by a photomicrograph.

First, an AlAs layer having a thickness of 10 nm was deposited on the (001) plane of the GaAs substrate 1 from which the natural oxide film was removed. The conditions at this time were a growth temperature of 580 ° C., an Al supply rate of 0.5 ML / sec, and an As ₄ supply rate of 2.0 ML / sec.

  Then, a GaAs layer 15 having a thickness of 100 nm was further deposited on the surface of the AlAs layer 11. The conditions at this time were a growth temperature of 580 ° C., a Ga supply rate of 0.5 ML / sec, and an As supply rate of 2.0 ML / sec.

Next, superheated steam oxidation treatment was performed to oxidize the surface portion of the GaAs layer 15, and the surface was modified to a Ga ₂ O ₃ thin film. In this example, a Ga ₂ O ₃ thin film was formed on the GaAs layer 15 by performing this oxidation treatment for 5 minutes using 300 ° C. superheated steam in a 200 ° C. heating environment.

Next, a modified mask portion having a heat resistance of 580 ° C. or higher was selectively formed on the surface of the GaAs substrate 1 by irradiating the Ga ₂ O ₃ thin film formed on the GaAs layer 15 with an electron beam. This electron beam irradiation was performed by setting the acceleration voltage to 5 kV and the surface dose to 8 mC / cm ² . Further, the drawing pattern of the electron beam was set such that a plurality of parallel lines matching the [110] direction of the GaAs substrate 1 and a plurality of parallel lines matching the [−110] direction intersect perpendicularly. . The plurality of parallel lines were drawn so that the line spacing was 2.4 μm.

Then heated GaAs substrate 1 over 580 ° C. in a vacuum environment, peeling the Ga ₂ O ₃ of the portion not modified by electron beam (part which is not modified in thermostable Ga ₂ O ₃₎ I let you. As a result, a Ga ₂ O ₃ inorganic material mask 16 is formed on the surface of the GaAs layer 15 formed on the AlAs layer 11. Then, by heating the GaAs substrate 1 at 650 ° C. for 5 hours, GaAs sublimation was promoted from the surface of the GaAs layer 15 not covered with the Ga ₂ O ₃ inorganic material mask 16. As a result, as shown in FIGS. 13A and 14A, a three-dimensional structure having an opening formed in a portion not covered with the Ga ₂ O ₃ inorganic material mask 16 could be obtained. .

  As shown in FIG. 13A, the three-dimensional structure obtained by the above method was formed with a (1-10) plane extending in a direction perpendicular to the (100) plane of the GaAs substrate 1. The etching depth was 100 nm. This is because the thickness of the GaAs layer 15 deposited on the AlAs layer 11 reaches the AlAs layer 11 and etching in the depth direction stops.

  On the other hand, even when the AlAs layer 11 shown in FIGS. 13B and 14B was not added, a three-dimensional microstructure was produced under the same conditions. As a result, as shown in FIGS. 13B and 14B, the three-dimensional structure composed of the (111) A plane and the (110) plane is self-organized.

  As described above, by adding AlAs to the III-V group compound layer, a three-dimensional structure composed of a (1-10) plane extending in a direction perpendicular to the (100) plane of the GaAs substrate 1 is obtained. I was able to get it.

Next, with reference to FIGS. 15 and 16, an embodiment in which a three-dimensional structure is formed using a three-layer inorganic resist oxide film 30 containing In ₂ O ₃ will be described. FIG. 15 is an explanatory view schematically showing the state of the GaAs substrate 1 on which the three-layer inorganic resist oxide film 30 containing In ₂ O ₃ is formed. FIG. 16 is a photomicrograph showing the three-dimensional structure produced using the three-layer inorganic resist oxide film 30 containing In ₂ O ₃ .

First, an As thin film 2 is deposited to a thickness of 1.5 nm on the (001) plane of the GaAs substrate 1 from which the natural oxide film has been removed using an MBE method in an ultrahigh vacuum environment. A thin film was deposited at 1.5 nm. Next, in an environment of 200 ° C., a superheated steam oxidation treatment was performed for 5 minutes to oxidize the In thin film, and the In ₂ O ₃ thin film 8 was modified. An As thin film 5 was further deposited on the In ₂ O ₃ thin film 8 thus formed.

The three-layer inorganic resist oxide film 30 formed as described above was irradiated with an electron beam to form a modified mask portion having a heat resistance of 580 ° C. or more as a part of the In ₂ O ₃ thin film 8. This electron beam irradiation was performed with an acceleration voltage of 1 kV and a surface dose of 200 μC / cm ² . Further, the drawing pattern of the electron beam was set so that a plurality of parallel lines matching the [110] direction of the GaAs substrate 1 intersect a plurality of parallel lines matching the [−110] direction. The plurality of parallel lines were drawn so that the line spacing was 2.0 μm.

Then, the GaAs substrate 1 is heated to above 580 ° C. in vacuo, stripped of In ₂ O ₃ of the portion not modified by electron beam (part which is not modified in heat-stable In ₂ O ₃₎ It was. As a result, an In ₂ O ₃ inorganic material mask is formed on the GaAs substrate 1. Next, the GaAs substrate 1 was heated at 650 ° C. for 4 hours to promote sublimation of GaAs from the surface of the GaAs substrate 1 not covered with the In ₂ O ₃ inorganic material mask, and an etching process was performed. As a result, as shown in FIG. 16, a three-dimensional structure having an opening formed on the substrate could be obtained. Thus, even when In ₂ O ₃ is used for the three-layer inorganic resist oxide film 30, a three-dimensional microstructure can be formed with high accuracy.

By the way, as already described with reference to FIG. 5B, the GaAs natural oxide film is composed mainly of Ga ₂ O ₃ , and a metal is present in the vicinity of the interface between the natural oxide film and the GaAs substrate 1. As is precipitated. Further, as described in the description with reference to FIG. 10, it can be said that the oxide film modification mechanism by the electron beam in the inorganic resist oxide film is the same as that in the case of using the natural oxide film.

  That is, the modification of the oxide film by the electron beam of the three-layer inorganic resist oxide film 10 or the two-layer inorganic resist oxide film 20 described in the above embodiment is the same as the modification of the oxide film by the electron beam of the natural oxide film. Although there are differences in quality areas, it is essentially the same. Next, an etching and electron beam drawing method will be described using an embodiment using a natural oxide film as an inorganic resist oxide film. In addition, the Example shown below is applicable even when the 3 layer inorganic resist oxide film 10 and the 2 layer inorganic resist oxide film 20 are used as an inorganic resist.

  First, with reference to FIG. 17, an embodiment relating to the reduction of the width of the modified region as the etching time elapses will be described. FIG. 17 is an explanatory view schematically showing how the mask width is reduced as the etching time elapses. FIG. 18 is a photomicrograph showing the state of the reduction of the mask width as the etching time elapses.

By drawing an electron beam on the surface of the natural oxide film formed on the (001) surface of the GaAs substrate 1, the natural oxide film irradiated with the electron beam becomes a chemically stable oxide Ga ₂ O ₃ (III Group oxide). This Ga ₂ O ₃ functions as an inorganic material mask having high heat resistance (580 ° C. or higher). This electron beam irradiation was performed by setting the acceleration voltage to 5 kV and the surface dose to 8 mC / cm ² . Further, the drawing pattern of the electron beam was set so that a plurality of parallel lines matching the [110] direction of the GaAs substrate 1 intersect a plurality of parallel lines matching the [−110] direction. Further, the diameter of the electron beam is set to 500 nm, whereby the width of the mask formed by electron beam irradiation is 1 μm or more.

Next, the GaAs substrate 1 was heated to 580 ° C. or higher in a vacuum environment, and the natural oxide film other than the portion replaced with Ga ₂ O ₃ was removed by thermal desorption. Thereafter, the GaAs substrate is heated to 650 ° C. under supply of As ₄ molecules at 0.7 ML / sec, thereby promoting GaAs sublimation on the surface of the GaAs substrate 1 where the oxide film of the GaAs substrate is peeled off, and self-organized tertiary. An original structure was produced.

  As shown in FIG. 17, this sublimation etching resulted in the self-organization of a three-dimensional structure composed of {001} plane, {110} plane, and {111} A plane. Further, the mask width, which was 1 μm or more in the initial stage of etching, was reduced as the etching time became longer. More specifically, as shown in FIG. 18, the mask width is 600 nm in 3 hours etching, 400 nm in 5 hours etching, and reduced to about 50 nm in 10 hours etching. became.

  Next, a periodic pattern in which a plurality of electron beam drawing lines intersect will be described with reference to FIGS. 19 and 20. FIG. 19 is a schematic diagram showing an electron beam drawing pattern. FIG. 20 is a photomicrograph showing a three-dimensional structure formed in a shape corresponding to an electron beam drawing pattern.

  In both FIG. 19A and FIG. 19B, a plurality of parallel lines matching the [110] direction of the GaAs substrate 1 and a plurality of parallel lines matching the [−110] direction intersect perpendicularly. This is a drawing pattern. The drawing pattern in FIG. 19A is in a state in which one end portion (lower end portion in the drawing) of a plurality of parallel lines is in contact with parallel lines extending in different directions. On the other hand, as shown in FIG. 19A, the drawing pattern of FIG. 19B intersects so that the end of one side of the parallel line overruns parallel lines extending in different directions.

  The electron beam is irradiated according to the drawing pattern shown in 19 (a) or 19 (b), and the three-dimensional structure shown in the micrograph of FIG. 20 (a) or FIG. I was able to get it. As shown in FIG. 20, the electron beam is drawn along a plurality of parallel lines in two directions, so that openings are periodically formed on the GaAs substrate.

  Comparing FIG. 20A and FIG. 20B, the drawing pattern shown in FIG. 20A shows the opening formed in the vicinity of the lower end of the parallel line (the range surrounded by the dotted line). The shape was different from the shape of the opening formed in the central portion, and the shape of the opening became non-uniform. On the other hand, as shown in FIG. 20B, the drawing pattern to be overrun has no difference in shape between the opening near the end on the lower side of the parallel line and the opening arranged in the center, and the whole A uniform opening was formed through. This result means that the surface diffusion in the entire drawing pattern (including the end portion) is made uniform by drawing the electron beam so as to overrun the end of the drawing pattern.

This example was performed based on the following conditions. That is, the surface of the natural oxide film formed on the (001) surface of the GaAs substrate 1 is irradiated with an electron beam. Under this irradiation condition, the acceleration voltage is 5 kV and the surface dose is 8 mC / cm ^2. Set. After irradiation with the electron beam, the GaAs substrate 1 was heated to 580 ° C. or higher in a vacuum environment, and the natural oxide film other than the portion replaced with Ga ₂ O ₃ was removed by thermal desorption. Then, by heating the GaAs substrate at 650 ° C. for 3 hours under the supply of 0.7 ML / sec As ₄ molecules, it promotes GaAs sublimation on the surface where the oxide film of the GaAs substrate peeled off, and self-organized three-dimensional A structure was formed.

  Next, with reference to FIG. 21 and FIG. 22, a three-dimensional structure when the electron beam is irradiated in a direction inclined by a predetermined angle with respect to the crystal orientation will be described. FIG. 21 is an explanatory view schematically showing a part of the crystal when the drawing line is inclined by 10 degrees with respect to the crystal orientation of the GaAs substrate 1 and the electron beam is irradiated. FIG. 22A is a photomicrograph showing a three-dimensional structure produced by irradiating an electron beam with an inclination of 10 degrees with respect to the crystal orientation of the GaAs substrate 1. FIG. 22B is a photomicrograph showing a three-dimensional structure produced by irradiating an electron beam without tilting the drawing line with respect to the crystal orientation of the GaAs substrate.

In this embodiment, an electron beam is drawn on the surface of the natural oxide film formed on the (001) plane of the GaAs substrate 1. The electron beam irradiation in this example was performed with the acceleration voltage set to 5 kV and the surface dose amount set to 8 mC / cm ² .

  First, as shown in FIG. 21, a case where the direction of the drawing line of the electron beam is inclined by a predetermined angle from the direction of the crystal orientation will be described. In this embodiment, the electron beam is drawn so that a plurality of parallel lines that coincide with the [010] direction of the GaAs substrate 1 and a plurality of parallel lines that coincide with a direction inclined by 10 degrees from the [100] direction intersect. A pattern was set and electron beam irradiation was performed. The micrograph shown in FIG. 22A is obtained by performing electron beam irradiation according to this drawing pattern and then performing GaAs sublimation etching.

  As shown in FIG. 22A, a three-dimensional structure corresponding to a drawing pattern of an electron beam is formed on a GaAs substrate, and a plurality of openings are formed vertically and horizontally. When focusing on the [010] direction in FIG. 22A, the openings are arranged so as to be linearly aligned along the [010] direction. On the other hand, focusing on the [100] direction, the openings adjacent in the [100] direction are in a positional relationship slightly offset in the [010] direction. In addition, the outline of each opening part has a part which corresponds with respect to each of [010] direction and [100] direction.

  Further, under the same conditions, a plurality of parallel lines whose electron beam drawing direction matches the [010] direction of the GaAs substrate 1 and a plurality of parallel lines that match the [100] direction intersect at right angles. What is drawn is the photomicrograph of FIG. As shown in FIG. 22B, it can be seen that when the electron beam is drawn along the line along the crystal orientation, the offset between the adjacent openings as described above does not occur, and the lines are neatly arranged vertically and horizontally. Further, the contour of each opening is formed so as to follow both the [010] direction and the [100] direction.

  Comparing FIG. 22 (a) and FIG. 22 (b), the directions of the individual openings (dents) are the same, and they are self-organized along both the [010] direction and the [100] direction. In common. From this, it can be seen that by drawing parallel lines along the crystal orientation, the orientation of the opening is self-organized so as to follow the crystal orientation. As a result, it is possible to produce an accurate three-dimensional microstructure at the molecular level exceeding the limit of scanning accuracy of the electron beam. When the electron beam was drawn with a drawing interval of 3 μm or more, the opening was tilted when compared with the state of FIG. 22 without being along the [100] direction. Therefore, from the viewpoint of self-organization along the crystal orientation, the line spacing is preferably less than 3 μm.

  Next, with reference to FIG. 23, an example of a three-dimensional structure manufactured by multiple scanning of electron beams will be described. FIG. 23 is a photomicrograph showing a three-dimensional structure produced by multiple scanning of electron beams.

Also in this embodiment, an electron beam is drawn on the surface of the natural oxide film formed on the (001) surface of the GaAs substrate 1, and the drawing condition is that the acceleration voltage is 5 kV and the surface dose of one scan. The amount was set to 0.04 μC / cm ² . The electron beam was subjected to 200 multiple scans in the [−110] direction at intervals of 3 seconds. In addition, by repeating the scanning 200 times, the total amount of electron dose irradiated to the substrate was 8 mC / cm ² .

Next, the GaAs substrate 1 was heated to 580 ° C. or higher in a vacuum environment, and the natural oxide film other than the portion replaced with Ga ₂ O ₃ was removed by thermal desorption. Then, by heating the GaAs substrate at 650 ° C. for 5 hours under the supply of 0.7 ML / sec As ₄ molecules, it promotes GaAs sublimation on the surface where the oxide film of the GaAs substrate peeled off, and self-organized three-dimensional A structure was formed. The three-dimensional structure thus obtained is shown in the micrograph of FIG.

For comparison, a three-dimensional structure was also produced for a sample that was irradiated with an electron beam once with the surface dose of the electron beam set to 8 mC / cm ² . A three-dimensional structure as a comparative example is shown in the micrograph of FIG.

  Comparing FIG. 23 (a) and FIG. 23 (b), the mask of the inorganic material obtained by multiple scanning is larger than the mask width of the inorganic material obtained by single scanning as shown in FIG. 23 (b). It can be seen that the width is thicker. This result shows that the thermal resistance near the edge of the mask portion (corresponding to the tail portion of the electron beam Gaussian distribution) is improved by the multiple scanning.

  Next, referring to FIG. 24, an embodiment in which the separation characteristics of individual three-dimensional structures are improved in selective growth by MBE growth by performing the multiple scanning when irradiating an electron beam will be described. FIG. 24 is a photomicrograph showing the state of the surface of a GaAs substrate on which a GaAs growth crystal is selectively grown by the MBE method on a three-dimensional microstructure produced by multiple scanning of electron beams.

Also in this example, an electron beam was drawn on the surface of the natural oxide film formed on the (001) plane of the GaAs substrate 1 to produce a modified mask portion. The electron beam irradiation was performed by setting the acceleration voltage to 5 kV and the surface dose to 0.04 μC / cm ² . Further, the drawing pattern of the electron beam was set so that a plurality of parallel lines matching the [110] direction of the GaAs substrate 1 and a plurality of parallel lines matching the [−110] direction intersect perpendicularly. The plurality of parallel lines were drawn so that the line spacing was 2.0 μm. In this example, multiple scans were performed 200 times in the [−110] direction (the total electron dose was 8 mC / cm ² ).

Next, the GaAs substrate 1 was heated and held at 610 ° C. for 20 minutes in a vacuum environment. As a result, the natural oxide film other than the portion replaced with Ga ₂ O ₃ is thermally desorbed and removed, and an inorganic material mask is formed on the surface of the GaAs substrate 1. Thereafter, an MBE method using Ga atoms and As ₄ molecules as solid raw materials was performed on the GaAs substrate on which the inorganic material mask was formed. As conditions for this MBE method, the growth temperature was 580 ° C., the Ga supply rate was 0.5 ML / sec, the As supply rate was 2.0 ML / sec, and GaAs was deposited for 35 minutes under these conditions. The micrograph of FIG. 24A shows the three-dimensional structure thus obtained.

For comparison, GaAs is crystal-grown under the same conditions as in the case of the multiple scanning except that the electron dose of the electron beam is set to 8 mC / cm ² and the electron beam scanning is performed only once. A three-dimensional structure was produced. The three-dimensional structure of this comparative example is shown in the micrograph of FIG.

  Comparing FIG. 24A and FIG. 24B, when multiple scanning is performed, as shown in FIG. 24A, GaAs crystals formed between the masks are adjacent to each other with the mask interposed therebetween. Each is separated in an independent state without being integrated with the grown crystal. On the other hand, in the case of the one-time scanning shown in FIG. 24B, adjacent GaAs crystals are connected to each other and are mixed together. From this result, it can be seen that, by performing multiple scanning, the separation characteristics of individual three-dimensional structures are improved in selective growth by MBE growth. This is because the influence of charging is reduced by multiple scanning.

  Next, with reference to FIGS. 25 and 26, an embodiment in which the epitaxy selective growth is accurately arranged in the crystal orientation will be described. FIG. 25 is an explanatory view schematically showing a state in which an InAs crystal 40 is grown on a negative three-dimensional structure by positive microfabrication. FIG. 26 is a photomicrograph showing the state of a three-dimensional structure in which an InAs crystal is grown on a negative three-dimensional structure by positive microfabrication.

Also in this embodiment, an electron beam is drawn on the surface of the natural oxide film formed on the (001) surface of the GaAs substrate 1, and the irradiation conditions include an acceleration voltage of 5 kV and a surface dose of 8.0 μC. / Cm ² is set. Further, the drawing pattern of the electron beam was set so that a plurality of parallel lines matching the [110] direction of the GaAs substrate 1 intersect a plurality of parallel lines matching the [−110] direction. The plurality of parallel lines were set so that the line interval was 1.8 μm.

Next, the GaAs substrate 1 was heated to 580 ° C. or higher in a vacuum environment, and the natural oxide film other than the portion replaced with Ga ₂ O ₃ was removed by thermal desorption. As a result, the Ga ₂ O ₃ inorganic material mask 36 is formed on the GaAs substrate 1. As shown in FIG. 25A, by heating the GaAs substrate at 650 ° C. for 5 hours under the supply of 0.7 ML / sec As ₄ molecules, the GaAs on the surface of the GaAs substrate 1 where the oxide film is peeled is removed. A self-organized three-dimensional structure was produced by encouraging sublimation. The three-dimensional structure thus obtained is shown as a micrograph on the left side of FIG.

  In addition, a three-dimensional structure obtained under the same conditions except that the interval between the parallel lines is changed from 1.8 μm to 3.0 μm is shown on the right side of FIG. By performing negative microfabrication in this way, a three-dimensional structure composed of the (110) plane and the (111) A plane is obtained.

Furthermore, as shown in FIG. 26B, an InAs crystal 40 was grown on the three-dimensional structure formed in this way by the MBE method. The crystal growth temperature at this time is 580 ° C., the flux ratio (F _As / F _Ga ) between As ₄ molecules and Ga atoms is 7, and the InAs crystal growth rate is 0.3 ML / sec (molecular layer / second; two-dimensional The crystal growth time was 20 minutes. As a result, positive microfabrication was performed, and a substrate having a surface structure as shown in FIG. 26B was obtained.

  Although the embodiments and examples of the present invention have been described above, the above configuration can be further modified as follows.

In the above-described embodiment and examples, the Ga ₂ O ₃ thin film 4 and the In ₂ O ₃ thin film 8 are used as the inorganic resist oxide film, but the present invention is not limited to this configuration. , For example, Al ₂ O ₃ thin film or the Al ₂ O ₃ and Ga ₂ O ₃ are mixed and oxide film, it is possible to use a three-layered inorganic resist oxide film 10 and the two-layer inorganic resist oxide film 20. In this case, an As thin film 2 is formed on the surface of the GaAs substrate 1, a mixed oxide film in which Al ₂ O ₃ and Ga ₂ O ₃ are mixed is formed on the As thin film 2, and further above the mixed oxide film. For example, a method of forming an As thin film 5 to form a three-layer inorganic resist oxide film can be considered.

Hereinafter, an embodiment in which an oxide film in which Al ₂ O ₃ and Ga ₂ O ₃ are mixed is used as an inorganic resist oxide film will be described. In the following embodiments, a three-dimensional structure is formed by using only a mixed oxide film in which Al ₂ O ₃ and Ga ₂ O ₃ are mixed as an inorganic resist oxide film without forming a group V film such as the As thin film 2. I am making it. FIG. 27A shows an electron beam drawn using a two-layer inorganic resist oxide film containing an oxide film in which Al ₂ O ₃ and Ga ₂ O ₃ are mixed, and then heated at 610 ° C. for 20 minutes. It is an AFM image which shows the mode of the GaAs substrate 1 surface. FIG. 27B is a cross-sectional SEM image showing a state of a GaAs growth crystal selectively grown on the surface of the GaAs substrate 1.

In this example, first, an AlGaAs thin film having a thickness of 1 nm was deposited on the (001) plane of the GaAs substrate 1 from which the natural oxide film was removed. The conditions at this time are a substrate temperature of 580 ° C., an Al supply rate of 0.1 ML / sec, a Ga supply rate of 0.4 ML / sec, and an As supply rate of 2.0 ML / sec. For 2 seconds. Then, a mixed oxide film in which Al ₂ O ₃ and Ga ₂ O ₃ are mixed is formed on the surface of the GaAs substrate by performing superheated steam oxidation for one minute using 300 ° C superheated steam in a 200 ° C heating environment. did.

Next, by irradiating the mixed oxide film of Al ₂ O ₃ and Ga ₂ O ₃ formed as described above with an electron beam, a modified mask portion having a heat resistance of 580 ° C. or higher is selectively used. Formed. This electron beam irradiation was performed by setting the acceleration voltage to 5 kV and the surface dose to 5 mC / cm ² . Further, the electron beam was drawn with a plurality of parallel lines coinciding with the [110] direction of the GaAs substrate 1 so that the line interval was 1.6 μm.

Next, in a vacuum environment, the GaAs substrate 1 was heated and held at 610 ° C. for 20 minutes to peel off the portion that was not modified by the electron beam. As a result, an inorganic material mask region is formed on the GaAs substrate 1 as shown in FIG. MBE growth using Ga atoms and As ₄ molecules as solid raw materials was performed on the GaAs substrate 1 on which the mask region was formed. The conditions at this time were a growth temperature of 580 ° C., a Ga supply rate of 0.5 ML / sec, and an As supply rate of 2.0 ML / sec. Under these conditions, GaAs was deposited for 35 minutes. As a result, GaAs was selectively grown on the surface of the portion where the oxide film was peeled off.

From this result, it was possible to obtain a GaAs growth crystal as shown in FIG. In this GaAs growth crystal, an opening of a three-dimensional structure composed of a {1-10} plane, a (111) B plane, and a (001) plane extending in a direction perpendicular to the (001) plane is [110]. The result was arranged along the direction. This is because an oxide film material in which Al ₂ O ₃ and Ga ₂ O ₃ are mixed has a heat resistance of 580 ° C. or more by electron beam writing, and functions as a mask for selective growth using the MBE method. Means that

Next, referring to FIG. 28 and FIG. 29, the three-dimensional structure is formed on the surface of the Si substrate 41 using a two-layer inorganic resist oxide film including an oxide film in which Al ₂ O ₃ and Ga ₂ O ₃ are mixed. Examples formed in the following will be described. FIG. 28 is an explanatory view schematically showing a state in which a GaAs growth crystal is formed on a Si substrate using a two-layer inorganic resist oxide film including an oxide film in which Al ₂ O ₃ and Ga ₂ O ₃ are mixed. . FIG. 29 is a photomicrograph showing the appearance of the GaAs growth crystal 47 formed on the Si substrate 41. FIG. 29 shows the GaAs growth crystal 47 formed on the substrate with the (001) plane of the Si substrate tilted by 45 degrees.

A process of forming the GaAs growth crystal 47 on the Si substrate 41 will be described. First, an AlGaAs thin film having a thickness of 3 nm was deposited on the (001) plane of the Si substrate 41 from which the natural oxide film was removed. The conditions at this time were room temperature, Al supply rate was 0.005 ML / sec, Ga supply rate was 0.1 ML / sec, As supply rate was 2.0 ML / sec, and AlGaAs was deposited for 101 seconds. . As a result, the AlGaAs thin film was formed on the surface of the Si substrate 41. Then, a two-layer inorganic resist containing a mixed oxide film in which Al ₂ O ₃ and Ga ₂ O ₃ are mixed by performing a superheated steam oxidation process using a 300 ° C superheated steam in a 200 ° C heating environment for 5 minutes. An oxide film was formed on the surface of the Si substrate 41.

Then, a mixed oxide film of Al ₂ O ₃ and Ga ₂ O ₃ formed as described above by irradiating the electron beam, and selectively forming the modified mask portion having a 580 ° C. or more heat resistant . The electron beam irradiation was performed by setting the acceleration voltage to 5 kV and the surface dose to 8 mC / cm ² . The drawing pattern of the electron beam was set such that a plurality of parallel lines matching the [110] direction of the Si substrate 41 and a plurality of parallel lines matching the [−110] direction intersect perpendicularly. The plurality of parallel lines were drawn so that the line spacing was 1.8 μm.

Next, the Si substrate 41 was heated and held at 610 ° C. for 20 minutes in a vacuum environment, and then the temperature was lowered to 580 ° C. to perform MBE growth using Ga atoms as solid raw materials and As ₄ molecules. As conditions for this MBE growth, the growth temperature was 580 ° C., the Ga supply rate was 0.1 ML / sec, and the As supply rate was 2.0 ML / sec. Under these conditions, GaAs was deposited for 59 minutes by the MBE method. As a result, a GaAs growth crystal 47 as shown in FIG. 28 was obtained. Further, as shown in FIG. 29 as a photomicrograph, a mixed inorganic material mask 46 is periodically arranged on the surface of the Si substrate 41 (according to the drawing pattern of the electron beam), and the surface of the Si substrate 41 is made of GaAs. As a result, the grown crystal 47 was selectively formed.

From this result, it can be seen that the mixed oxide film in which Al ₂ O ₃ and Ga ₂ O ₃ are mixed functions as an inorganic resist oxide film. That is, a part of the mixed oxide film in which Al ₂ O ₃ and Ga ₂ O ₃ are mixed is modified into a modified mask portion having a heat resistance function of 580 ° C. or more by irradiation with an electron beam. Next, the mixed oxide film that has not been modified by the electron beam is removed by an etching process, whereby a portion irradiated with the electron beam is formed on the surface of the Si substrate 41, and is used for selective growth using the MBE method. It acted as a mask.

From the above examples, it was shown that the mixed oxide film in which Al ₂ O ₃ and Ga ₂ O ₃ are mixed functions as an inorganic resist oxide film. Therefore, it is also possible to produce a three-dimensional microstructure using these inorganic resist oxide films as a three-layer inorganic resist oxide film and a two-layer inorganic resist oxide film.

  In addition, Si or SiC can be selected as a material for a substrate when a three-dimensional microstructure is formed using the three-layer inorganic resist oxide film 10 and the two-layer inorganic resist oxide film 20 shown in the above embodiment. For example, a configuration in which a GaAs layer is formed on the surface of a substrate made of Si or SiC, and the three-layer inorganic resist oxide film 10 or the two-layer inorganic resist oxide film 20 is formed on the GaAs layer can be changed.

  As described above, in the three-dimensional microfabrication method using the present invention, the three-dimensional microfabrication is performed by arbitrarily combining the steps of producing a positive three-dimensional microstructure and a negative three-dimensional microstructure. The structure can be made in multiple stages. For example, a modified mask portion of a group III oxide film is formed on the surface of a positive three-dimensional microstructure or on the surface of a negative three-dimensional microstructure, and a new three-dimensional microstructure is further formed by etching treatment. Forms to form are also possible. Also, various conditions such as the setting of the electron beam and temperature are not limited to the above-described embodiment, and can be appropriately changed according to circumstances.

1 GaAs substrate (III-V group compound substrate)
2 As thin film (Group V film)
3 GaAs thin film (III-V compound film)
4 Ga ₂ O ₃ thin film (Group III oxide film)
5 As thin film (Group V film)
7 GaAs growth crystal (III-V group compound crystal)
10 Three-layer inorganic resist oxide film 20 Two-layer inorganic resist oxide film

Claims (20)

In the three-dimensional microfabrication method for forming a microstructure on the surface of the III-V compound layer formed on the surface of the substrate or the surface of the III-V compound substrate,
Forming a group V film composed of group V atoms on the surface of the substrate, and further forming a group III-V compound film on the surface of the group V film;
The group III-V compound film formed in the first step is modified to a group III oxide film with superheated steam, and a group V film is formed on the surface of the group III oxide film, thereby forming a three-layer inorganic resist oxide film. A second step of forming
The electron beam irradiated on the surface of the three-layer inorganic resist oxide film in a vacuum passes through the group V film formed in the second step and acts on a part of the group III oxide film, so that the III Excess oxygen molecules can be separated from the group oxide film, and a part of the surface of the substrate is oxidized while a part of the group V film formed on the surface of the substrate in the first step is heated and sublimated to form a group III. When the oxide is generated, a part of the surface of the group III oxide film and the substrate is in close contact, and a modified mask portion having heat resistance is formed in a shape corresponding to the irradiated portion of the electron beam. Process,
By raising the temperature of the substrate in a vacuum, the group V film formed on the surface of the substrate is sublimated, and the group III oxide film in a portion other than the modified mask portion is detached, and the surface of the substrate A fourth step in which is exposed;
A negative three-dimensional microstructure is produced by heating the substrate at a predetermined temperature in an environment where a Group V raw material is supplied to a vacuum and performing an etching process that preferentially removes Group III atoms from the exposed portion of the substrate. And a fifth step to
A three-dimensional micromachining method comprising: The three-dimensional microfabrication method according to claim 1,
The thickness of the group V film formed on the surface of the substrate in the first step is 1 nm to 5 nm, and the thickness of the group III-V compound film formed on the surface of the group V film is 1 nm to 5 nm. Yes,
A three-dimensional microfabrication method, wherein the thickness of the group V film formed on the surface of the group III oxide film in the second step is 1 nm or more and 10 nm or less. In the three-dimensional microfabrication method for forming a microstructure on the surface of the III-V compound layer formed on the surface of the substrate or the surface of the III-V compound substrate,
Forming a group V film composed of group V atoms on the surface of the substrate, and further forming a group III-V compound film on the surface of the group V film;
A second step of forming a two-layer inorganic resist oxide film by modifying the III-V compound film formed in the first step into a group III oxide film with superheated steam;
By irradiating the surface of the two-layer inorganic resist oxide film in vacuum with an electron beam, excess oxygen molecules can be separated from the group III oxide film, and the group V film formed on the surface of the substrate in the first step While a part of the substrate is heated and sublimated, a part of the surface of the substrate is oxidized at the sublimated part to generate a group III oxide, whereby the group III oxide film and a part of the surface of the substrate Is a third step in which the modified mask portion having heat resistance is formed in a shape corresponding to the irradiated portion of the electron beam,
By raising the temperature of the substrate in a vacuum, the group V film formed on the surface of the substrate is sublimated, and the group III oxide film in portions other than the modified mask portion is desorbed, so that the surface of the substrate becomes A fourth step to be exposed;
A negative three-dimensional microstructure is produced by heating the substrate at a predetermined temperature in an environment where a Group V raw material is supplied to a vacuum and performing an etching process that preferentially removes Group III atoms from the exposed portion of the substrate. And a fifth step to
A three-dimensional micromachining method comprising: The three-dimensional microfabrication method according to claim 3,
The thickness of the group V film formed on the surface of the substrate in the first step is 1 nm to 5 nm, and the thickness of the group III-V compound film formed on the surface of the group V film is 1 nm to 5 nm. A three-dimensional microfabrication method characterized by being. A three-dimensional microfabrication method according to any one of claims 1 to 4,
The III-V group compound layer or the III-V group compound substrate is composed of AlxGayIn _1-xy As _z P _1-z (0 ≦ x <1, 0 ≦ y, z ≦ 1). A characteristic three-dimensional micromachining method. A three-dimensional microfabrication method according to any one of claims 1 to 5,
The group III oxide film formed in the second step is an Al ₂ O ₃ thin film or an In ₂ O ₃ thin film. A three-dimensional micromachining method according to any one of claims 1 to 6,
A three-dimensional microfabrication method characterized by using Si or SiC as a substrate. A three-dimensional microfabrication method according to any one of claims 1 to 7,
The accelerating voltage of the electron beam in the third step is not more than 20kV than 0.5 kV, the range of the surface dose is at 50 nC / cm ² or more 16μC / cm ² or less, the irradiation of the electron beam is the single-line mode A three-dimensional microfabrication method characterized in that A three-dimensional microfabrication method according to any one of claims 1 to 8,
A three-dimensional microfabrication method characterized by crossing a plurality of electron beam drawing lines in the third step. The three-dimensional microfabrication method according to claim 9,
3. The three-dimensional microfabrication method according to claim 1, wherein the drawing line intersects with another drawing line at a middle portion in the longitudinal direction. A three-dimensional microfabrication method according to any one of claims 1 to 10,
In the third step, the electron beam is irradiated with crystal orientations [100], [010], [011], [01-1], [110] [−110], [111], [-1-1] of the substrate. -1] is irradiated so as to draw a line that matches any one of
In the fourth step, the substrate is heated to a temperature of 300 ° C. or higher and 650 ° C. or lower,
In the fifth step, the substrate is heated to a temperature of 300 ° C. or more and 650 ° C. or less, and an etching rate is 0.3 ML / sec or less. A three-dimensional microfabrication method according to any one of claims 1 to 11,
In the third step, multiple scanning is performed by repeatedly irradiating an electron beam to the same place. The three-dimensional microfabrication method according to claim 12,
In the multiple scanning, when irradiating an electron beam to the same place, the electron beam is scanned after a time more than 10 times the time required for scanning 1 mm by the electron beam has elapsed since the last time the place was scanned. A three-dimensional microfabrication method characterized by irradiating a beam. A three-dimensional microfabrication method according to any one of claims 1 to 13,
In the third step, the electron beam is irradiated with a converged electron beam diameter by passing the electron beam through a donut-shaped limiting aperture. A three-dimensional microfabrication method according to any one of claims 1 to 14,
A three-dimensional process further comprising a sixth step of selectively growing a group III-V compound crystal in a portion etched by the fifth step by performing a molecular beam epitaxial growth method using a solid growth source. Fine processing method. The three-dimensional microfabrication method according to claim 15,
In the sixth step, the substrate is heated to a temperature of 300 ° C. or more and 650 ° C. or less, and the solid growth raw material group V and group III flux ratio F _V / F _III is 1 or more and 100 or less. A three-dimensional microfabrication method characterized in that the growth rate is 0.01 ML / sec or more and 2 ML / sec or less. A three-dimensional microfabrication method according to any one of claims 1 to 16,
A three-dimensional microfabrication method characterized in that a three-dimensional microstructure is produced in multiple stages by combining a step of producing a positive three-dimensional microstructure and a step of producing a negative three-dimensional microstructure. The three-dimensional microfabrication method according to claim 17,
A modified mask portion of a group III oxide film is formed on the surface of a positive three-dimensional microstructure or on the surface of a negative three-dimensional microstructure, and a new three-dimensional microstructure is further formed by etching treatment. A three-dimensional microfabrication method characterized by that.   A three-dimensional microstructure produced by the three-dimensional microfabrication method according to any one of claims 1 to 18.   The three-dimensional microstructure according to claim 19, wherein the interval between adjacent unit structures is equal to or less than submicron.