JP5152715B2 - Three-dimensional fine processing method and three-dimensional fine structure - Google Patents

Description

  The present invention 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 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 the device limitations (complexity, enlargement, and cost) 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 non-damaged and non-polluted, 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 the balance between them is important. Since the electron beam has a shorter wavelength than that of light, it is being developed as exceeding the resolution limit of photolithography.

  In electron beam lithography, generally, an organic resist has been conventionally used in the same manner as optical lithography from the viewpoint of throughput, and an inorganic resist having excellent resolution has not been generally used because of its low sensitivity. PMMA is generally used as an organic resist having relatively low sensitivity but excellent resolution. Making the sensitivity of an inorganic resist with excellent resolution equal to or surpassing that of PMMA is one target for the development of inorganic resists.

  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 GaAs natural oxide film used as a mask in one embodiment of the present invention as a resist.

  Another problem in electron beam lithography is the effect of secondary electron scattering from within the resist and substrate as well as the incident electrons (referred to as the proximity effect). Due to this influence, a region considerably larger than the beam diameter of the incident electron beam becomes a reaction region for the resist. This effect determines the resolution between adjacent drawing lines. Many efforts have been made to reduce the proximity effect, and one example is the reduction of the effective beam diameter using the refractive index control of the intrusion electron beam in the substrate by a multilayer resist. However, at present, the proximity effect (resist reaction region larger than the beam diameter) is a major limitation on miniaturization.

  In general, resists can be classified into two types according to sensitivity characteristics. One is a digital resist that causes a sharp reaction at a certain critical value depending on the energy dose of the electron beam, and the other is for a certain energy dose range. It is an analog type resist that reacts continuously. Of these two types, a digital type that can easily obtain a spatial resolution has been advantageous for miniaturization in the submicron region. The resulting “hard” reaction region has been used as a mask and has provided a selective function for subsequent etching and 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. In order to produce an arbitrary three-dimensional microstructure, it was necessary to develop an analog type resist having excellent spatial resolution and excellent height difference control, and development of a post-process.

  Conventionally, as a selective growth process after mask pattern formation, a growth method (CVD, GSMBE, CBE, etc.) using a gas species having a long surface diffusion length has been used. This is because the mask width (that is, the region width that should be selectively suppressed) is extremely large because the mask pattern formed before the growth is generally produced by photolithography, which causes selective growth to a non-mask region. This is because the growth source atoms irradiated on the mask must be eliminated by diffusion. Selective growth using this technique is applied to all compound semiconductors including GaN and Si processes, and has been established as a technique for controlling a three-dimensional structure.

  However, there is a problem that an extremely fine mask region is buried due to the large surface diffusion length of the gas species for the smaller three-dimensional structure control including the submicron region. A small mask region requires a combination with a corresponding process with a short surface diffusion length (greater than the mask width).

For example, there is one disclosed in Patent Document 1 as using the CVD method. In Patent Document 1, 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.
Japanese Patent Laid-Open No. 8-172053

  However, since the thing of patent document 1 uses the MOCVD method, the diffusion length of a surface atom becomes long, and the selective growth of the III-V group compound semiconductor on the substrate of a high-density arrangement cannot fully be performed, It is difficult to increase the density of the substrate. Moreover, it is impossible to make the growth crystal film thicknesses in the crystal growth direction constant in the nano order.

  The present invention has been made in view of the above circumstances, and the purpose thereof is to easily increase the density of the substrate, and the crystal film thickness in the crystal growth direction is made uniform in the nano order. The object is to provide a three-dimensional microfabrication method and a high-density three-dimensional microstructure capable of forming a pattern in situ.

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 a first aspect of the present invention, there is provided a method for performing the following steps in a three-dimensional microfabrication method for forming a fine structure on the surface of a III-V compound layer formed on the surface of a substrate. That is, in the first step, the surface of the III-V compound layer is irradiated with an electron beam in a vacuum, thereby replacing the natural oxide film on the surface of the III-V compound layer with a group III oxide, Modified mask portions are periodically formed on the III-V compound layer . In the second step, the temperature of the substrate is raised in a vacuum, so that the natural oxide film in portions other than the modified mask portion is desorbed to expose the surface of the III-V group compound layer . In the third step, the substrate is heated at a predetermined temperature in an environment in which a group V raw material is supplied to a vacuum, so that the group III atoms are preferentially separated from the exposed portion of the surface of the group III-V compound layer. A dent is formed in the exposed portion by hopping the modified mask portion. In the fourth step, a group III-V compound crystal is selectively grown in the depression by performing a molecular beam epitaxial growth method using a solid growth raw material. The acceleration voltage of the electron beam in the first step is 1 kV or more and 50 kV or less, the range of the line dose is 10 nC / cm or more and 1 μC / cm or less, and the electron beam irradiation is performed in a single line mode. In the first step, the electron beam is irradiated so as to draw a line that coincides with any one of the crystal orientations [100], [110], and [−110] of the III-V compound layer. In the second step, the substrate is heated to a temperature of 300 ° C. or higher and 650 ° C. or lower. In the third step, the substrate is heated to a temperature of 300 ° C. or more and 650 ° C. or less, and the depth of the recess formed in the III-V group compound layer is determined by the modified mask portion and the adjacent one. When the opening on the surface of the III-V group compound layer formed between the modified mask portion is smaller than when it is large, the depth of the depression is increased when the size of the opening is 1000 nm or more. The depth is 1/100 or less of the size of the opening. When the size of the opening is 300 nm or less, the depth of the recess is 1/4 or more of the size of the opening. By crossing a plurality of electron beam drawing lines in the first step, a group III-V compound crystal is selectively grown in the area surrounded by the drawing lines in the fourth step.

By this method, without removing the natural oxide film naturally formed on the surface of the substrate, this natural oxide film is irradiated with an electron beam to replace it with a chemically stable group III oxide. A modified mask portion can be formed. Then, by periodically forming the modified mask portion and then preferentially peeling the exposed surface of the substrate, a negative pattern can be accurately produced. In addition, if the drawing interval of the electron beam is widened, the preferential peeling portion becomes shallow, and if the drawing interval is narrowed, it is deeply peeled off. A three-dimensional microstructure having a shape can be formed. Even for a high-density pattern, selective growth of a III-V group compound crystal can be easily performed by controlling the growth conditions of the MBE method to control 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. Further, since the negative pattern can be formed with higher accuracy, the fine structure can be accurately and reproducibly, and a negative three-dimensional fine structure can be formed with high accuracy. Furthermore, it is possible to easily form a three-dimensional fine structure in which fine structure units are arranged vertically and horizontally.

  In the three-dimensional microfabrication method, it is preferable to perform dry etching with bromide before or after the third step or simultaneously with the third step.

  By this method, the degree of freedom in controlling the depth of the depression formed can be increased, and a three-dimensional microstructure having a more complicated shape can be formed.

  In the three-dimensional microfabrication method, it is preferable to perform the first to third steps in a single ultra-high vacuum environment.

  By this method, the cost of microfabrication on the substrate surface can be greatly reduced, and the throughput can be improved.

In the three-dimensional microfabrication method, in the fourth 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, the crystal growth rate is 0.01 ML / sec or more and 2 ML / sec or less, and the thickness of the crystal growth layer is between the modified mask portion and the adjacent modified mask portion. It is preferable to be inversely proportional to the size of the opening formed in the.

  By this method, a positive three-dimensional microstructure can be formed with high accuracy.

  In the three-dimensional microfabrication method, in the fourth step, by using the electron diffraction method, in-situ observation of the substrate surface during the growth of the group III-V compound crystal by the molecular beam epitaxial growth method, It is preferable that the growth of the III-V compound crystal can be controlled.

  By this method, the growth of the III-V group compound crystal can be controlled with high accuracy, so that a three-dimensional microstructure can be manufactured with high accuracy and its reproducibility is also good.

  In the three-dimensional microfabrication method, it is preferable that the first process to the fourth process are collectively performed in a single ultra-high vacuum environment.

  By this method, the cost of microfabrication on the substrate surface can be greatly reduced, and the throughput can be improved.

  In the three-dimensional microfabrication method, the width of the group III oxide after the natural oxide film is detached in the second step is preferably smaller than the irradiated electron beam diameter.

  By this method, it is possible to control the structure smaller than the region of the natural oxide film to be modified, and it is possible to realize further high precision and high density of the fine structure.

  In the three-dimensional fine processing method, it is preferable to form a three-dimensional fine structure having a plurality of types of three-dimensional shapes by changing the irradiation interval of the electron beam.

  By this method, a three-dimensional microstructure having complicated and various shapes can be easily formed.

  Next, embodiments of the invention will be described. In FIG. 2, each step of the three-dimensional microfabrication method of this embodiment is shown in order from (a) to (d). FIG. 3 is a graph showing an example of the temperature transition of each step in the three-dimensional microfabrication method of the present embodiment, and the symbols (a) to (d) shown in the graph are shown in FIGS. 2 (d) respectively.

  FIG. 2A shows a GaAs substrate (III-V compound substrate) 1 as an object of microfabrication of the present embodiment. A natural oxide film 2 having a thickness of about 3 nm to 6 nm is formed on the surface of the GaAs substrate 1.

In the microfabrication method of this embodiment, first, as shown in FIG. 2A, the natural oxide film 2 is irradiated with an electron beam in a vacuum. Then, the natural oxide film 2 in the electron beam irradiated portion is replaced with a chemically stable oxide Ga ₂ O ₃ (Group III oxide). At this time, when a periodic pattern such as parallel lines is drawn on the surface of the GaAs substrate 1 by the electron beam, a depression due to preferential peeling can be formed on the surface of the GaAs substrate 1 by a process described later. Note that, from the viewpoint of forming a highly accurate pattern, it is preferable that the electron beam is irradiated with an acceleration voltage of 1 kV to 50 kV and a line dose range of 10 nC / cm to 1 μC / cm. Further, it is preferable that the electron beam irradiation be performed in a single line mode.

Next, as shown in FIG. 2B, the GaAs substrate 1 in which a part of the surface natural oxide film 2 is replaced with Ga ₂ O ₃ is placed in an environment in which As ₄ (group V material) is supplied in a vacuum. Then, the temperature is raised to a predetermined temperature of 580 ° C. or higher and 630 ° C. or lower. Note that FIG. 3 shows an example of temperature control when the fine processing of FIG. 2 is performed. In the example of FIG. 3, the temperature is linearly increased to 630.degree. Then, when the temperature reaches around 580 ° C., as shown in FIG. 2B, the natural oxide film 2 other than the portion replaced with Ga ₂ O ₃ is thermally desorbed and removed.

Here, the natural oxide film region modified by the electron beam method is generally determined by an incident electron beam (primary electron) and scattered electrons (secondary electrons) in the thin film. However, according to the method of the present embodiment, not only the natural oxide film 2 other than the portion replaced with Ga ₂ O ₃ , but also the modification by the low energy secondary electrons in the portion replaced with Ga ₂ O _3. The region is also thermally desorbed. That is, in the present embodiment, the mask formed by drawing an electron beam on the natural oxide film exhibits selectivity only for the high energy region of the primary electrons. Therefore, the width of Ga ₂ O ₃ (modified portion 3) after the natural oxide film is detached can be made smaller than the beam diameter of the irradiated electron beam. Thereby, it is possible to control the structure below the natural oxide film region to be modified.

Next, heating the GaAs substrate 1 at a predetermined temperature of 580 ° C. or more and 630 ° C. or less (610 ° C. in the example of FIG. 3) is continued in an environment where As ₄ is supplied in a vacuum. Then, Ga molecules on the surface of the GaAs substrate 1 in which Ga ₂ O ₃ is not present are peeled off and diffused preferentially from the surface, move to the edge of the periodic pattern drawing region of the electron beam, and are deposited. As a result, as shown in FIG. 2C, a recess 4 is formed on the surface of the GaAs substrate 1, and a negative three-dimensional microstructure is produced. The depth of the recess 4 obtained in this way is almost inversely proportional to the size of the opening formed between the modified portion 3 which is a portion modified with Ga ₂ O ₃ and the modified portion 3 adjacent thereto. To do. Specifically, when the size (opening diameter) of the opening is 1000 nm or more, the depth of the recess 4 can be set to 1/100 or less of the opening diameter. Moreover, when the size (opening diameter) of the opening is 300 nm or less, the depth of the recess 4 can be set to 1/4 or more of the opening diameter.

Next, GaAs is selectively grown by a molecular beam epitaxy method (MBE method) in the recess 4 formed on the surface of the substrate. In this MBE method, the growth direction of GaAs is aligned with the plane orientation (100) of the GaAs substrate 1, the crystal growth temperature is set to a predetermined temperature of 450 ° C. to 600 ° C. (580 ° C. in the example of FIG. 3), and As ₄ molecules And the Ga atom flux ratio (F _As / F _Ga ) is in the range of 1 to 100, and the GaAs crystal growth rate is 0.01 ML / sec to 2 ML / sec (molecular layer / second: growth rate for a two-dimensional thin film). Conversion). The thickness of the GaAs growth layer obtained in this way is almost inversely proportional to the size of the opening formed between the modified portion 3 and the adjacent modified portion 3.

  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, as shown in FIG. 2D, the GaAs growth crystal 5 is formed on the surface of the GaAs substrate 1, and a positive three-dimensional microstructure can be produced. This makes it possible to produce a substrate with a high density and a constant thickness of each GaAs growth crystal.

  FIG. 4 shows a case where the line spacing of the electron beam with respect to the substrate surface is increased and the three-dimensional microfabrication method described in FIG. 2 is performed in the same manner. In this specification, the line interval of the electron beam refers to a distance (distance between center lines in the width direction of the electron beam) in which the electron beam is irradiated in a single line mode and then translated to the next irradiation line.

  Here, as shown in FIG. 4C and FIG. 2C, in the microfabrication method of the present embodiment, when the electron beam drawing interval is widened, the depth of the depression formed by the preferential peeling is reduced. When the drawing interval is narrowed, the depth of the depression due to the priority peeling is increased.

  In FIGS. 5A to 5F, the drawing line interval is changed in six steps from 6 μm to 1.4 μm and drawn in a lattice shape with an electron beam, and the natural oxide film is detached and preferentially peeled off. FIG. 2 shows a surface AFM photograph of a negative three-dimensional microstructure subjected to the above-described process. 6 (a) to 6 (f) schematically show the formation depths of the recesses for the negative three-dimensional microstructure shown in FIGS. 5 (a) to 5 (f). . Although the irradiation electron beam diameters are equal, the mask width d2 in the case of FIG. 6F irradiated with the drawing line interval of the minimum 1.4 μm is the same as that of FIG. ) Is clearly recognized (d2 <d1), and the knowledge that the mask width after the formation of the depression is inversely proportional to the depth of the preferential peeling is obtained.

  7A to 7C, the drawing line interval is changed in three steps from 1.4 μm to 3.0 μm and drawn in a lattice shape with an electron beam. The surface AFM photograph and the cross-sectional AFM photograph of the negative type three-dimensional microstructure which performed priority peeling are shown. FIG. 7 also shows that a shallow depression is formed when the drawing line interval is wide, and a depression becomes deep when the drawing line interval is narrow.

When the electron beam writing interval is increased in this way, the non-irradiated region is shallowly peeled because the diffusion length (mu free path) of the surface diffusion atoms of Ga atoms becomes smaller than the drawing line interval. This is considered to be because it becomes difficult to move like a hopping motion on the surface of Ga ₂ O ₃ as a mask and difficult to be carried out of the processing region.

  On the other hand, in the case of conventional etching (for example, dry etching using bromide), when the mask interval is wide, the etching can be deep, and when the mask interval is narrow, the etching is shallow. Therefore, the three-dimensional microfabrication method of the present invention has characteristics opposite to those of conventional etching, and enables the production of three-dimensional micro structures having complicated and various shapes that could not be produced conventionally. To do.

  FIG. 8A is a surface AFM photograph showing a state in which a negative three-dimensional microstructure is formed by the above-described preferential peeling. FIG. 8B is a surface AFM photograph showing a state in which a positive three-dimensional microstructure is formed by MBE after a three-dimensional microstructure similar to that in FIG. 8A is fabricated. 9A is a cross-sectional model diagram showing the depth of the recess having the shape of FIG. 8A, and FIG. 9B shows the crystal growth height of the shape of FIG. 8B. It is a section model figure. In this way, by selectively growing a III-V compound crystal by MBE method in a depression of a negative type three-dimensional fine structure, a fine structure with a high density and a uniform crystal film thickness in the crystal growth direction can be obtained. Can be formed.

  FIGS. 10A to 10D are a surface SEM photograph and a cross-sectional SEM photograph showing a state in which a positive three-dimensional microstructure is formed by MBE after forming a negative three-dimensional microstructure by preferential peeling. It is. 10A and 10B show the case where a GaAs crystal is selectively grown on a GaAs substrate, and FIGS. 10C and 10D show the case where an InAs crystal is selectively grown on a GaAs substrate. Is the case.

  As described above, in the positive three-dimensional microstructure manufactured by the method of the present embodiment, a depression is once formed, and a III-V group compound crystal is selectively grown therefrom by the MBE method. Therefore, for example, as shown in FIGS. 10B and 10C, the rise of the wall is very good at the base of the grown crystal, and a highly accurate fine structure can be formed.

In addition, as shown in FIGS. 5, 7, 8, and 10, priority peeling is performed depending on the geometrical arrangement (drawing line interval and parallel lines or intersecting lines) at the time of electron beam irradiation on the substrate surface. By changing the growth conditions of the MBE method, each pattern formed on the surface of the GaAs substrate functions as a negative mask for growth, and selective preferential peeling is performed in the non-irradiated region of the electron beam. It can be seen that a three-dimensional structure has been grown. One three-dimensional structural unit is composed of stable crystal facets and is flat at the atomic level. In addition, by trimming the penumbra part of the modified region to Ga ₂ O ₃ by electron beam beam drawing with priority peeling, the effective size of drawing is reduced to a negligible amount relative to the electron beam diameter. I understand. Thereby, a high-density fine structure, for example, a fine structure in which the interval between adjacent unit structures is submicron or less can be easily produced.

As described above, according to the three-dimensional microfabrication method of this embodiment, the natural oxide film 2 is irradiated with an electron beam without removing the natural oxide film 2 naturally formed on the surface of the GaAs substrate 1. This makes it possible to form chemically stable Ga ₂ O ₃ (modified portion 3). And even if the circuit pattern is a high-density array, a negative circuit pattern by preferential peeling can be accurately produced, and a GaAs crystal is grown only on this negative circuit pattern portion. At the same time, the circuit shape can be accurately formed. In addition, the fabrication cost can be reduced while being a nano-order high-density circuit.

  Further, when the natural oxide film modified by electron beam writing in this embodiment is considered as a kind of inorganic resist, the resist sensitivity with respect to the preferential peeling process and the MBE process performed later is generally used as high resolution lithography. It has the same sensitivity as PMMA, which is an organic resist, and has the highest sensitivity and excellent resolution among inorganic resists (see FIG. 1). Therefore, the throughput, which is a problem when using an inorganic resist, can be greatly improved.

  In the three-dimensional microfabrication method of this embodiment, as described above, the peeling effect is reduced when the drawing interval of the electron beam is increased. In order to solve this, it is conceivable that bromide is introduced in the preferential peeling step of FIG. 3C to use preferential peeling and dry etching in units of one atomic layer. This dry etching may be performed simultaneously with the preferential peeling process, or may be performed before or after the preferential peeling process.

  In dry etching with bromide, the surface of the GaAs substrate 1 where the electron beam writing interval is large can be etched deeply, while the portion where the writing interval is narrow becomes shallow. Therefore, by performing both this dry etching and preferential peeling, the degree of freedom of shape depth control can be increased, and a circuit pattern having a more complicated shape can be formed. Furthermore, even when the MBE method is subsequently used, a free shape pattern can be easily formed by changing the MBE growth conditions.

  The above three-dimensional microfabrication method is preferably carried out in a single ultra-high vacuum environment (in a series of steps) because the manufacturing cost can be reduced. Further, as described above, when a plurality of electron beam drawing lines are crossed in a lattice pattern on the substrate and a GaAs crystal is selectively grown in a minute area on the substrate surrounded by the drawing lines, the fine structure unit is vertically and horizontally. A three-dimensional microstructure can be formed. In this case, the GaAs growth crystal depends on the area of the area, the crystal orientation of the substrate, and the crystal growth film thickness.

Hereinafter, the present invention will be described more specifically with reference to examples. In each of the following examples, the surface of the GaAs substrate is processed, and an electron beam whose electron beam diameter is reduced to 0.5 μm is applied to a natural oxide film (As ₂ O ₃ or the like) on the surface. In particular, irradiation was performed under the conditions of an acceleration voltage of 5 kV, a current amount of 1.0 × 10 ⁻⁹ A, and a line dose amount of 0.2 μC / cm. In each example, the crystal growth rate in the MBE method was measured and controlled using RHEED.

Example 1
In this example, the surface of the GaAs substrate with the plane orientation (100) was irradiated with an electron beam, and the natural oxide film was selectively replaced with Ga ₂ O ₃ . The electron beam was irradiated so as to draw a plurality of parallel lines, and the directions of the drawing lines were matched with the [−110] direction and the [110] direction of the GaAs substrate 1. The interval between drawing lines of the electron beam was 1.4 μm, and irradiation was performed so that a plurality of parallel lines alternately intersected vertically. Next, the substrate was heated to 630 ° C. in a vacuum, and the natural oxide film other than the portion replaced with Ga ₂ O ₃ was peeled off. Next, the substrate was heated at 610 ° C. for 20 minutes to preferentially peel the surface of the portion of the GaAs substrate 1 where the natural oxide film was peeled off. As a result, negative microfabrication was performed, and a three-dimensional microstructure having a groove width of 300 nm and a depth of 70 nm was formed as shown in FIG.

Next, a GaAs crystal was grown by the MBE method. The crystal growth temperature is 580 ° C., the flux ratio of As ₄ molecules and Ga atoms (F _As / F _Ga ) is 4, and the GaAs crystal growth rate is 0.5 ML / sec (molecular layer / second: growth on a two-dimensional thin film. The crystal growth time was 20 min. As a result, positive microfabrication was performed, and a substrate having a surface structure as shown in FIG. 10A was obtained.

(Example 2)
In this example, the surface of the GaAs substrate with the plane orientation (100) was irradiated with an electron beam, and the natural oxide film was selectively replaced with Ga ₂ O ₃ . The electron beam was irradiated so as to draw a plurality of parallel lines, and the direction of the drawing lines was matched with the [−110] direction of the GaAs substrate. The interval between the electron beam drawing lines was 0.6 μm. Next, the substrate was heated to 630 ° C. in a vacuum, and the natural oxide film other than the portion replaced with Ga ₂ O ₃ was peeled off. Next, the substrate was heated at 610 ° C. for 20 minutes to preferentially peel the surface of the portion of the GaAs substrate where the natural oxide film was peeled off.

Next, a GaAs crystal was grown by the MBE method. The crystal growth temperature is 520 ° C., the flux ratio of As ₄ molecules and Ga atoms (F _As / F _Ga ) is 100, and the GaAs crystal growth rate is 0.02 ML / sec (molecular layer / second: growth on a two-dimensional thin film. The crystal growth time was 300 min. As a result, positive microfabrication was performed, and a substrate having a surface structure as shown in FIG. 10B was obtained. The surface-grown GaAs grown crystal had a width of 500 nm at the root and a height of 500 nm.

(Example 3)
In this example, the surface of the GaAs substrate with the plane orientation (100) was irradiated with an electron beam, and the natural oxide film was selectively replaced with Ga ₂ O ₃ . The electron beam was irradiated so as to draw a plurality of parallel lines, and the direction of the drawing lines was matched with the [−110] direction of the GaAs substrate. The interval between the electron beam drawing lines was 1.8 μm. Next, the substrate was heated to 630 ° C. in a vacuum, and the natural oxide film other than the portion replaced with Ga ₂ O ₃ was peeled off. Next, the substrate was heated at 610 ° C. for 20 minutes to preferentially peel the surface of the portion of the GaAs substrate where the natural oxide film was peeled off. As a result, a negative three-dimensional microstructure having a groove width of 540 nm and a depth of 35 nm was formed.

Next, an InAs crystal was grown by the MBE method. The crystal growth temperature is 500 ° C., the flux ratio of As ₄ molecules and In atoms (F _As / F _In ) is 7, and the InAs crystal growth rate is 0.3 ML / sec (molecular layer / second: growth on a two-dimensional thin film. The crystal growth time was 40 min. As a result, positive microfabrication was performed, and a substrate having a surface structure as shown in FIG. 10C was obtained. The InAs grown crystal having this surface structure had a width of 500 nm and a height of 600 nm at the root.

As described above, chemically stable Ga ₂ O ₃ can be formed by injecting an electron beam into the natural oxide film formed on the surface of the GaAs substrate. Then, preferential peeling is performed using this Ga ₂ O ₃ as a mask (with bromide dry etching if necessary), and further crystal growth by MBE is performed, so that the surface of the GaAs substrate has a high degree of freedom. The shape pattern can be processed. Further, by changing the growth conditions of the MBE method, the shape pattern can be controlled and processed in nano-order units. In addition, the above-described electron beam injection, preferential peeling, and MBE process can be performed by a series of steps in the same apparatus, and the manufacturing cost can be greatly reduced.

  As described above, the present invention can easily process an arbitrary circuit pattern on a substrate with good reproducibility. As a result, not only semiconductor devices, but also useful elements utilizing various quantum device characteristics, such as wavelength discrimination devices, photonic crystals, quantum wires, quantum boxes, diffraction gratings, semiconductor laser structures, micromachines, microcomponents, etc. Is also possible.

  Next, advantages of the present embodiment by comparison with a conventionally used thick oxide mask will be described with reference to the prior art of FIG. 11 and FIG. 2 as appropriate. FIG. 11 is a schematic view showing each step of a conventional three-dimensional microfabrication method in which an oxide mask is formed after peeling a natural oxide film on a substrate surface and a crystal is grown thereon by MBE.

  That is, as described above, in this embodiment, the natural oxide film 2 is drawn with an electron beam, so that a hard and stable oxide mask (modified portion) is formed as shown in FIGS. 2 (a) and 2 (b). 3) can be created. On the other hand, in the prior art, as shown in FIG. 11A, the natural oxide film on the substrate is peeled off and removed, and then the oxide mask 13 is newly formed by a method such as CVD as shown in FIG. To form. Therefore, in the prior art, the thickness of the mask is increased and the affinity with the substrate is poor, and the boundary area with the mask becomes non-uniform at the atomic level, resulting in blurring at the boundary and unclear outlines.

Further, in this embodiment, the natural oxide film is peeled off by vacuum heating with As ₄ supplied, and Ga atoms on the surface of the GaAs substrate without the natural oxide film are peeled off from the substrate to perform a hopping motion on the periodic mask. Then, it moves to the end of the substrate (end of the periodic mask formation region). Due to the collective movement effect of the surface Ga atoms, as shown in FIG. 2C, a depression can be formed in a region where the substrate surface is exposed between the oxide masks. It is important for the formation of the recess that etching by thermal sublimation of surface atoms is not a dominant factor. On the other hand, in the conventional technique, when the surface of the substrate 1 is heated under vacuum while supplying As ₄ , Ga atoms on the surface of the GaAs substrate are peeled off from the substrate, but the oxide mask is thick and the boundary of the mask is blurred. Since the outline is unclear, the movement of the surface Ga atoms is prevented and the hopping motion cannot be performed. For this reason, as shown in FIG.11 (c), a hollow cannot be formed in the area | region where the board | substrate surface between masks was exposed.

Furthermore, in this embodiment, when GaAs growth is performed by MBE method by vacuum heating under the supply of Ga and As _4, GaAs grows in the depression 4 on the substrate surface as shown in FIG. The three-dimensional structure of the GaAs growth crystal 5 reflecting the structural features of the above is accurately laminated. On the other hand, in the related art, GaAs grows on the substrate surface where the oxide mask 13 does not exist by performing the same MBE method, but the outline is unclear with the edge of the oxide mask 13 blurred. It is difficult to accurately stack GaAs on the substrate.

  FIG. 12 shows a comparison of the features of the mask used in the present invention and the prior art. As shown in the table of FIG. 12, the present invention uses a modified mask of a natural oxide film that has high adhesion and affinity with the substrate and can be formed extremely thin, so that the diffusion length of Ga atoms on the mask is increased. And a hopping motion as shown in FIG. 2C can be realized.

  FIG. 13 shows a comparison of shapes depending on the pitch between the drawing masks for the preferential peeling and selective growth based on the three-dimensional microfabrication method disclosed in this embodiment. As shown in the upper side of the table of FIG. 13, in the case of preferential separation by hopping, Ga atoms hop more frequently when the mask pitch is smaller than when the pitch between masks is large. Become. As described above, the present invention makes it possible to control the depth of negative three-dimensional microfabrication by using the property that the depth of preferential peeling depends on the size of the opening region between the masks.

  Further, as shown in the lower side of the table of FIG. 13, in the case of selective growth by the MBE method, the growth height of the crystal depends on the height hc depending on the incident material flux and the pitch between masks (size of the opening region). The heights h1 and h2 depending on are added. Among these, the portion depending on the inter-mask pitch is larger when the inter-mask pitch is smaller than when the inter-mask pitch is large (h1 <h2). As described above, the present invention makes it possible to control the height of positive three-dimensional microfabrication using the property that the crystal growth height depends on the size of the opening region between the masks.

  Although the preferred embodiment of the present invention has been described above, the above configuration can be changed as follows, for example.

Although the GaAs substrate has been described in the above embodiment, the substrate can be changed to use a substrate made of a III-V group compound other than GaAs. For example, it is conceivable to use a substrate made of Al _x Ga _y In _1-xy As _z P _1-z (0 ≦ x <1, 0 ≦ y, z ≦ 1). Further, a thin film of III-V compound (III-V compound layer) may be formed on the surface of an appropriate substrate by an appropriate method, and then the above-described three-dimensional microfabrication method may be implemented. it can. This thin film may be a thin film made of, for example, Al _x Ga _y In _1-xy As _z P _1-z (0 ≦ x <1, 0 ≦ y, z ≦ 1).

In the above embodiment, the case where GaAs or InAs is crystal-grown by the MBE method has been described, but various other III-V group compounds (for example, InP) can be crystal-grown. For example, the irradiation direction of the electron beam is made to coincide with any of the crystal orientations [100], [110], and [−110] of the substrate, and the growth temperature of the group III-V compound crystal is set to 300 ° C. or more and 650 ° C. or less. The flux ratio (F _V / F _III ) between group V atoms and group III atoms of the solid growth raw material is 1 or more and 100 or less, and the crystal growth rate is 0.01 ML / sec or more and 2 ML / sec or less (molecular layer / second: 2 III-V group compound in which the thickness of the crystal growth layer is inversely proportional to the size of the opening formed between the modified mask portion and the adjacent modified mask portion. Crystals can be selectively grown.

  In the above embodiment, the case where negative three-dimensional microfabrication by preferential peeling and positive three-dimensional micromachining by MBE are combined has been described. By changing the processing conditions of the process, Only one of the positive molds can be finely processed.

The graph which shows the comparison of the resist sensitivity and average molecular weight (resolution) of typical organic resist and inorganic resist. Schematic which shows each process of the three-dimensional microfabrication method which concerns on one Embodiment of this invention. FIG. 2A shows a first step of irradiating a natural oxide film on the surface of the substrate with an electron beam, and FIG. 2B shows a second step of detaching the natural oxide film in the non-irradiated region of the electron beam by heating the substrate. FIG. 2 (c) shows a third step of forming a negative three-dimensional microstructure by preferentially peeling the desorbed portion of the natural oxide film by heating the substrate, and FIG. 2 (d) shows solid growth. A fourth step of selectively growing a crystal by molecular beam epitaxy (MBE) using a raw material will be described. The graph which shows an example of the temperature transition of each process in the three-dimensional microfabrication method of this embodiment. Schematic which shows the case where the drawing interval of an electron beam is made larger than the case of FIG. 2, and the process similar to FIG. 2 (a)-FIG.2 (d) is performed. Surface AFM photographs of negative three-dimensional microstructures formed with various electron beam writing intervals. Sectional model figure which shows the formation depth of a hollow part about the negative type three-dimensional fine structure shown to Fig.5 (a)-FIG.5 (f). FIG. 6 is a surface AFM photograph and a cross-sectional AFM photograph of a negative three-dimensional microstructure formed with various electron beam drawing intervals. FIG. FIG. 8A is a surface AFM photograph showing a negative three-dimensional microstructure formed by preferential peeling. FIG. 8B is a surface AFM photograph showing a state in which a positive-type high-density three-dimensional microstructure is formed by MBE after a three-dimensional microstructure similar to that shown in FIG. Sectional model figure which shows the formation depth or crystal growth height of a hollow part about the three-dimensional fine structure shown to Fig.8 (a) and FIG.8 (b). The surface SEM photograph and cross-sectional SEM photograph which show a mode that the III-V group compound semiconductor crystal was selectively grown by MBE method while changing various conditions, and the positive type high-density three-dimensional fine structure was formed. The schematic diagram which shows each process of the three-dimensional microfabrication method of the prior art which forms an oxide mask after peeling the natural oxide film of the board | substrate surface, and grows a crystal | crystallization by MBE method on it. The figure which compared the characteristic of the mask of a prior art, and the mask of this invention. The figure which shows the comparison of the shape change by the magnitude of the pitch between masks at the time of the priority peeling and selective growth which are performed by this embodiment.

Explanation of symbols

1 GaAs substrate (III-V group compound substrate)
2 Natural oxide film 3 Modified part 4 Dimple 5 GaAs crystal (III-V compound crystal)

Claims (8)

In the three-dimensional microfabrication method of forming a fine structure on the surface of the III-V compound layer formed on the surface of the substrate,
By irradiating the surface of the III-V group compound layer with an electron beam in a vacuum, the natural oxide film on the surface of the III-V group compound layer is replaced with a group III oxide, and the III-V group compound layer A first step of periodically forming a modified mask portion thereon;
A second step in which the surface of the III-V group compound layer is exposed by desorbing the natural oxide film in a portion other than the modified mask portion by raising the temperature of the substrate in a vacuum;
By heating the substrate at a predetermined temperature in an environment in which a group V raw material is supplied to a vacuum, group III atoms are preferentially separated from the exposed portion of the surface of the group III-V compound layer, so that the modified mask portion is exposed. A third step of forming a depression in the exposed portion by hopping
A fourth step of selectively growing a group III-V compound crystal in the depression by performing a molecular beam epitaxial growth method using a solid growth raw material;
Only including,
The acceleration voltage of the electron beam in the first step is 1 kV or more and 50 kV or less, the range of the line dose is 10 nC / cm or more and 1 μC / cm or less, and the electron beam irradiation is performed in a single line mode,
In the first step, the electron beam is irradiated so as to draw a line that coincides with any of the crystal orientations [100], [110], and [−110] of the III-V compound layer,
In the second step, the substrate is heated to a temperature of 300 ° C. or higher and 650 ° C. or lower,
In the third step, the substrate is heated to a temperature of 300 ° C. or more and 650 ° C. or less, and the depth of the recess formed in the III-V group compound layer is determined by the modified mask portion and the adjacent one. When the opening on the surface of the III-V group compound layer formed between the modified mask portion is smaller than when it is large, the depth of the depression is increased when the size of the opening is 1000 nm or more. The depth is 1/100 or less of the size of the opening, and when the size of the opening is 300 nm or less, the depth of the recess is 1/4 or more of the size of the opening,
A three-dimensional III-V compound crystal is selectively grown in an area surrounded by the drawing lines in the fourth step by crossing a plurality of electron beam drawing lines in the first step. Fine processing method. The three-dimensional microfabrication method according to claim 1 ,
A three-dimensional microfabrication method comprising performing dry etching with a bromide before or after the third step or simultaneously with the third step. The three-dimensional microfabrication method according to claim 1 or 2 ,
A three-dimensional micromachining method, wherein the first to third steps are performed in a single ultra-high vacuum environment. A three-dimensional microfabrication method according to any one of claims 1 to 3 ,
In the fourth step, the substrate is heated to a temperature of 300 ° C. or more and 650 ° C. or less, and a solid growth raw material group _V / III group flux ratio F _V / F _III is 1 or more and 100 or less. The growth rate is 0.01 ML / sec or more and 2 ML / sec or less, and the film thickness of the crystal growth layer is larger than that when the opening formed between the modified mask portion and the adjacent modified mask portion is large. A three-dimensional microfabrication method characterized in that the smaller is smaller, the larger . A three-dimensional microfabrication method according to any one of claims 1 to 4 ,
In the fourth step, the group III-V group is observed by in-situ observation of the surface of the group III-V compound layer during the growth of the group III-V compound crystal by molecular beam epitaxy using an electron diffraction method. A three-dimensional microfabrication method characterized in that the growth of a compound crystal can be controlled. A three-dimensional microfabrication method according to any one of claims 1 to 5 ,
A three-dimensional microfabrication method comprising performing the first step to the fourth step in a single ultra-high vacuum environment. A three-dimensional micromachining method according to any one of claims 1 to 6 ,
A three-dimensional microfabrication method, wherein the width of the group III oxide after the natural oxide film is detached in the second step is smaller than the irradiated electron beam diameter. A three-dimensional microfabrication method according to any one of claims 1 to 7 ,
A three-dimensional microfabrication method, wherein a three-dimensional microstructure having a plurality of types of three-dimensional shapes is formed by changing an irradiation interval of the electron beam.