JP2008310299A - Method of manufacturing 3-d photonic crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing 3-D photonic crystal capable of 3-D periodic structure precisely and inexpensively. <P>SOLUTION: The method of manufacturing the 3-D photonic crystal comprises: a deposition process for forming a dielectric thin film; an ion injection process for forming a mask on the dielectric thin film by selectively injecting the ion into the dielectric thin film by the focused ion beam; a pattern formation process for forming a pattern by selectively removing the exposed dielectric thin film except the masked part formed on the dielectric thin film; a sacrificial layer forming process for forming the sacrificial layer on the dielectric thin film on which the pattern has formed; and a process for flatening the sacrificial layer formed on the dielectric film layer till the pattern is exposed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a three-dimensional photonic crystal.

The photonic crystal is a structure in which the refractive index of the constituent material is periodically distributed, and is an artificial material that can realize a novel function only by the structure design.
The greatest feature of the photonic crystal is that a region where a specific electromagnetic wave cannot propagate, that is, a so-called photonic band gap is formed by the difference in refractive index of the constituent material and the periodicity of the structure. By introducing an appropriate defect into the refractive index distribution in the photonic crystal, an energy level (defect level) due to this defect is formed in the photonic band gap.
As a result, the photonic crystal can freely control the electromagnetic wave. Moreover, the size of devices using photonic crystals can be much smaller than conventional devices.
In addition, the three-dimensional photonic crystal has a feature that the refractive index distribution of the constituent material has a three-dimensional period, and the electromagnetic wave existing at the defect position is difficult to leak to the outside.
That is, the three-dimensional photonic crystal is most suitable for electromagnetic wave propagation control.

In such a three-dimensional photonic crystal, a wood pile structure (or rod pile structure) disclosed in Patent Document 1 is known as one of typical structures. The woodpile structure in this three-dimensional photonic crystal has a structure as shown in FIG.
In FIG. 2, reference numeral 70 denotes a three-dimensional periodic structure, which includes a plurality of stripe layers in which a plurality of rods 40 are arranged in parallel and periodically with a predetermined in-plane period, and these are sequentially stacked. .
Specifically, the three-dimensional periodic structure 70 is
A first stripe layer in which a plurality of rods are arranged in parallel and periodically with a predetermined in-plane period;
A second stripe layer laminated on the first stripe layer so as to be orthogonal to each rod belonging to the first stripe layer;
A third stripe layer laminated on the second stripe layer so as to be parallel to each rod belonging to the first stripe layer and shifted by a half of the in-plane period;
Four stripes comprising: a fourth stripe layer laminated on the third stripe layer so as to be parallel to each rod belonging to the second stripe layer and shifted by a half of the in-plane period. Has a layer.
Then, a three-dimensional periodic structure 70 is configured by sequentially laminating a plurality of sets of these four stripe layers.
The period of the structure of the photonic crystal is about half of the wavelength of the electromagnetic wave to be controlled.
However, the three-dimensional photonic crystal is expected to have ideal device characteristics, but generally has a complicated structure, is complicated to manufacture, and requires many steps.

Conventionally, as a method for manufacturing a three-dimensional photonic crystal having a woodpile structure, Patent Document 2 proposes a method for thermally bonding different members by the following lamination technique.
In this thermal bonding method, first, a rod array arranged in parallel with a stripe layer provided on a substrate and arranged at a predetermined in-plane cycle is formed.
Then, the stripe layers are bonded together by aligning the layers by thermal bonding, and then the substrate of one stripe layer is removed.
By repeating such a process, a woodpile structure having a number of layers equal to the number of times of joining can be obtained.
With the above stacking technique, it is possible to manufacture a three-dimensional photonic crystal having a relatively complicated structure.

As a method for producing a three-dimensional photonic crystal, Patent Document 3 discloses the following lamination technique.
In this lamination technique, a sacrificial layer is formed after thin film formation and thin film processing. Then, the sacrificial layer is polished by a chemical mechanical polishing (CMP) technique, and the sacrificial layer is planarized until the processed thin film is exposed.
By repeating the above process, a three-dimensional photonic crystal can be manufactured with higher processing accuracy than a lamination method that does not use a sacrificial layer.

On the other hand, in the conventional thin film processing method, Patent Document 4 discloses the following pattern forming method and semiconductor device manufacturing method.
Here, in thin film processing, thin film processing is made possible by the following ion beam implantation step and a step of dry etching the material to be etched.
That is, in the ion beam implantation step, ion implantation is performed by changing the implantation position of the ion beam focused on the material to be etched and changing at least one of acceleration voltage, ion atomic species, and ion valence. An ion concentration peak region is formed in the depth direction.
In the dry etching step, the material to be etched is dry-etched with an etching gas that forms ions and an etching suppression region in the ion concentration peak region of the material to be etched. Through these steps, thin film processing is performed.
US Pat. No. 5,335,240 JP 2004-219688 A US Pat. No. 5,998,298 US Pat. No. 5,236,457

However, in the conventional lamination method using the thermal bonding method as described in Patent Document 2, the manufacturing method is complicated, the number of steps increases in proportion to the number of layers of the photonic crystal, and the technical difficulty increases. Productivity is poor and cost is high.
Further, every time the layers are stacked, heating and pressing processes are required, and the stress in the structure increases as the number of layers increases, resulting in deformation of the structure.
Such structural disturbance reduces the processing accuracy of the photonic crystal.

Moreover, the laminating method using the sacrificial layer as in Patent Document 3 in the conventional example can reduce the problems of the laminating method using the thermal bonding, but the following problems remain.
That is, in the second and subsequent thin film processing steps, a portion of the thin film layer formed in the previous step may be exposed and may be damaged.
In order to reduce such damage, it is conceivable to form an etch stop layer in the thin film portion to be protected.
However, when the etch stop layer is completely removed after processing, a gap is formed between the structures, which may affect the characteristics of the photonic crystal.
In addition, when the etch stop layer is partially removed, the characteristics of the structure may be affected because the material of the remaining etch stop layer is different from the dielectric constituting the photonic crystal.
For these reasons, conventionally, there has been a problem in adopting a method of providing an etch stop layer.

On the other hand, in the conventional thin film processing method found in Patent Document 4, processing in the depth direction is possible with respect to the material to be etched. However, since a technique such as a sacrificial layer is not used, Only processing is possible.
It has not been solved to enable the production of a three-dimensional photonic crystal having a complex multilayer structure such as a woodpile using these techniques.

  In view of the above problems, an object of the present invention is to provide a method for manufacturing a three-dimensional photonic crystal that can manufacture a three-dimensional periodic structure with high accuracy and low cost.

In order to solve the above problems, the present invention provides a method for producing a three-dimensional photonic crystal configured as follows.
The manufacturing method of the three-dimensional photonic crystal of the present invention is as follows:
A film forming process for forming a dielectric thin film;
An ion implantation step of selectively implanting ions by a focused ion beam into the dielectric thin film to form a mask on the dielectric thin film;
A pattern forming step of selectively removing a portion where the dielectric thin film other than the mask portion formed on the dielectric thin film is exposed, and forming a pattern;
A sacrificial layer forming step of forming a sacrificial layer on the dielectric thin film on which the pattern is formed;
And a planarization step of planarizing the sacrificial layer formed on the dielectric thin film until the pattern is exposed.
The method for producing a three-dimensional photonic crystal according to the present invention is characterized in that the dielectric thin film is formed of Si or a Si compound containing a Si oxide or nitride.
In the method for producing a three-dimensional photonic crystal according to the present invention, in the film formation step, any one of sputtering, vacuum evaporation, chemical vapor deposition, or epitaxial growth is used to form the dielectric thin film. It is characterized by.
The method for producing a three-dimensional photonic crystal according to the present invention is characterized in that Ga ions are used as ions of the focused ion beam in the ion implantation step.
The method for producing a three-dimensional photonic crystal according to the present invention is characterized in that reactive ion etching with a fluorine-based gas is used for selective removal of the exposed portion of the dielectric thin film in the pattern forming step. To do.
In the method for producing a three-dimensional photonic crystal according to the present invention, the sacrificial layer in the sacrificial layer forming step is selected from materials that can be easily flattened in the flattening step.
In the method for producing a three-dimensional photonic crystal according to the present invention, any one of sputtering, vacuum evaporation, chemical vapor deposition, or epitaxial growth is used for forming the sacrificial layer in the sacrificial layer forming step. And
The method for producing a three-dimensional photonic crystal of the present invention is characterized in that either mechanical polishing or chemical mechanical polishing is used for planarization in the planarization step.
In addition, the method for producing the three-dimensional photonic crystal of the present invention includes
A first step of manufacturing a structure in which a plurality of pattern forming layers including a sacrificial layer in which a plurality of rod-shaped portions are arranged in parallel and periodically with a predetermined in-plane period are stacked;
A second step of manufacturing a three-dimensional periodic structure by collectively removing the sacrificial layer with a liquid etchant in a structure in which a plurality of pattern forming layers containing the sacrificial layer are stacked,
The first step includes
A film forming process for forming a dielectric thin film;
An ion implantation step of selectively implanting ions by a focused ion beam into the dielectric thin film to form a mask on the dielectric thin film;
A pattern forming step of selectively removing a portion where the dielectric thin film other than the mask portion formed on the dielectric thin film is exposed, and forming a pattern;
A sacrificial layer forming step of forming a sacrificial layer on the dielectric thin film on which the pattern is formed;
A step of repeating the flattening step of flattening the sacrificial layer formed on the dielectric thin film until the pattern is exposed, four or more times in this order;
It is characterized by including.
The method for producing a three-dimensional photonic crystal according to the present invention is characterized in that the liquid etching agent is a liquid etching agent containing iron chloride.
Moreover, the manufacturing method of the three-dimensional photonic crystal of the present invention uses the three-dimensional photonic crystal manufactured by the above-described manufacturing method of the three-dimensional photonic crystal as a manufacturing mold,
After embedding a material for forming a three-dimensional photonic crystal in the production mold, the production mold is removed,
A three-dimensional periodic structure made of the embedded material having an inverted shape of the manufacturing mold is manufactured.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the three-dimensional photonic crystal which can manufacture a three-dimensional periodic structure with sufficient precision and low cost is realizable.

Embodiments of the present invention will be described below with reference to the drawings.
In the following drawings, the same symbols are used for the same elements. However, materials, structures, shapes, numerical values, and the like in the present invention are not limited to those listed here.
FIG. 1 is a diagram illustrating a method for manufacturing a three-dimensional photonic crystal in the present embodiment.
In FIG. 1, 10 is a substrate, 20 is a dielectric thin film, 30 is an ion implantation part, and 60 is a sacrificial layer.
In the present embodiment, the steps shown in FIGS. 1A to 1J can be used to form the three-dimensional photonic crystal shown in FIG.
Here, for ease of explanation, an example in which a woodpile structure is configured as the structure of a three-dimensional photonic crystal will be described.

First, in a film forming process for forming a dielectric thin film, a dielectric thin film 20 as a main material constituting a photonic crystal is formed on a substrate 10 as shown in FIG.
Examples of the material 20 include single crystal or amorphous Si, or a Si compound containing Si oxide or nitride.
As the film forming method, sputtering, vacuum evaporation, chemical vapor deposition, or epitaxial growth is suitable.
The thickness of the dielectric thin film 20 is preferably several tens of nm to several tens of μm. The substrate 10 has a flat film formation surface, and has an adhesive property with the dielectric thin film 20 to be formed.
For example, quartz, sapphire, glass, acrylic, Si, GaN, GaAs, InP, InGaAs, TiO ₂ , ZnO, or other materials having these thin films.
If necessary, an adhesion layer for improving adhesion may be formed at the interface contacting the substrate 10 and the first dielectric thin film 20.

Next, in an ion implantation step, ions by a focused ion beam are selectively implanted into the dielectric thin film, and a mask by ion implantation is formed on the dielectric thin film.
Here, as shown in FIG. 1B, ions are implanted into the dielectric thin film 20 to form a mask pattern 30.
Therefore, for example, accelerated Ga ions are selectively implanted into the mask pattern 30 portion of the dielectric thin film 20 while scanning with a focused ion beam (FIB).
In addition to Ga, In may be used as the kind of ions that can be implanted.
The size of the mask pattern 30 may be determined as necessary. For example, the width is several tens of nm to several μm, the in-plane period is several hundred nm to several μm, and the length is about 5 μm to 1000 μm.
The distribution of Ga ions in the depth direction is controlled by FIB acceleration voltage, its in-plane distribution (that is, pattern shape) is FIB in-plane scanning, and its density is controlled by FIB current and implantation time.
If the material of the dielectric thin film 20 and the type of ions (for example, Ga, In) are determined, the acceleration voltage, current, and implantation time necessary to obtain a predetermined depth and density can be obtained by simple simulation. The mask pattern 30 can be formed easily and with high accuracy.
The focused ion beam is preferably a single bundle beam or a multi-bundle beam as required.
In the case of a multi-bundle beam, it is possible to further improve the efficiency of the ion arrangement process by making the acceleration voltage, current, beam diameter, and scanning of each beam independent.
Here, the ion implantation may be stopped only near the surface of the dielectric thin film 20. Therefore, the acceleration voltage of FIB is preferably between 0.5 kV and 120 kV, and the optimum value is 1 kV to 30 kV.
The ion density is practically between 1 × 10 ^{18 and} 1 × 10 ²³ cm ⁻³ , and the order of 5 × 10 ²⁰ cm ⁻³ is most preferable.

The thickness of the ion implantation layer may be optimized depending on the material of the dielectric thin film, the etching depth, and the ion species to be etched.
For example, when the dielectric thin film is Si, the etching depth is 10 μm, and the ions are Ga ions, the thickness of the ion implantation layer is expressed in the projection standard deviation, and about 100 nm is optimal in the range of 50 nm to 500 nm.
If the material of the dielectric thin film and the ion type are determined, this thickness is almost determined by the accelerating voltage of ions, and can be roughly predicted by a known theoretical calculation method.
Further, it is desirable that the peak position in the ion depth distribution is in the vicinity of the surface layer of the dielectric thin film in consideration of the controllability of etching.
The peak position is theoretically determined by the ion acceleration voltage if the material of the dielectric thin film and the ion species are determined, and can be roughly predicted by a known theoretical calculation method.
For example, a part of ion implantation may be performed at a low acceleration voltage in the process of mask formation.
The lower the acceleration voltage, the shallower the ion implantation depth, so that the peak position can be brought near the surface layer of the dielectric thin film (for example, within 0 nm to 50 nm from the outermost surface).
In addition to using a low acceleration voltage, there are the following methods.
By adjusting the mask formation conditions when forming the mask by FIB, that is, acceleration voltage, current density, ion beam narrowing method, beam scanning method and irradiation time, etc., the surface layer of the dielectric thin film can be formed while implanting ions. Can be sharpened.
By doing so, it is possible to bring the peak position to the outermost surface of the dielectric thin film (for example, within 0 nm to 50 nm from the outermost surface).
The cutting depth can be continuously adjusted from approximately 0 nm depending on the mask forming conditions, and is preferably 1/10 or less of the thickness of the dielectric thin film.

Next, in the pattern forming step, using a mask by ion implantation formed on the dielectric thin film, the dielectric thin film portion other than the ion implanted portion is selectively removed to form a pattern.
That is, a portion where the dielectric thin film is exposed other than the mask portion formed on the dielectric thin film is selectively removed.
Here, as shown in FIG. 1C, the dielectric thin film 20 is etched to partially remove the portion indicated by 50.
For such selective removal of the dielectric thin film portion, for example, reactive ion etching (RIE) using a fluorine-based gas is used.
In particular, when the thickness of the dielectric thin film is thicker than 1 μm, the RIE method that alternately performs etching and pattern side wall protection is desirable.
For example, when the dielectric thin film is Si, during RIE, SF ₆ and C ₄ F ₈ gases are alternately introduced and etching is performed for a desired time. When SF ₆ gas is introduced, etching proceeds mainly.
When C ₄ F ₈ gas is introduced, side wall protection mainly proceeds. Thus, the etching resistance of the mask is further improved, and the amount of Ga in the Ga mask and the mask thickness can be reduced.
Moreover, it becomes possible to obtain a pattern with good perpendicularity by this etching. Furthermore, in the RIE using the Ga mask, the inclination angle, flatness, or shape of the side wall can be controlled by adjusting the processing conditions.
Adjusting the processing conditions means that when performing the two actions of etching and pattern side wall protection alternately, the time, pressure in the apparatus, processing power, and the flow rate of SF ₆ and C ₄ F ₈ are adjusted according to the purpose. Means optimal adjustment.

At this time, using the mask pattern 30 formed in the ion implantation step shown in FIG. 1B as an etching mask, the dielectric thin film portion 50 other than the ion implanted portion that is visible from a direction substantially perpendicular to the upper surface of the dielectric thin film 20 is formed. Selectively remove.
By this etching, a pattern of the first layer of the photonic crystal is formed.
In this pattern forming process, the etching resistance differs greatly between the ion implanted portion 30 and the non-ion implanted portion.
Thereby, even if the ion non-implanted portion is completely removed, the ion implanted portion 30 is hardly etched.
For example, when about 5 × 10 ²⁰ cm ^{−3 of} Ga ions are implanted from the surface layer of Si to a depth of 20 nm, the etching resistance of the Ga ion implanted portion is 500 times or more that of the non-ion implanted portion in the RIE process using SF _6. It is.

Next, in a sacrificial layer forming step, a sacrificial layer is formed on the dielectric thin film on which the pattern is formed.
Here, as shown in FIG. 1D, the sacrificial layer thin film 60 is formed on the dielectric thin film including the structure of the first layer.
The sacrificial layer thin film 60 is selected from materials that can be easily planarized with respect to the dielectric thin film 20 and the ion implantation part 30 in a subsequent planarization step. For example, a thin film of copper (Cu) is suitable.
The thickness of the copper thin film depends on the pattern of the dielectric thin film, but is preferably 0.1 to 5 μm. The copper thin film can be formed by sputtering, vacuum evaporation, chemical vapor deposition, or epitaxial growth. Hereinafter, this is referred to as a sacrificial layer forming step.

Next, in the planarization step, the sacrificial layer formed on the dielectric thin film is planarized until the pattern is exposed.
Here, as shown in FIG. 1E, the sacrificial layer thin film is planarized.
This flattening process is performed so that the underlying dielectric thin film pattern, that is, the ion implanted portion 30 is exposed, and the height of the copper thin film 60 is substantially the same as 30.
The planarization process uses, for example, mechanical polishing or chemical mechanical polishing (CMP).

Next, as shown in FIGS. 1F to 1I, the film formation process, the ion implantation process, the pattern formation process, the sacrificial layer formation process, and the planarization process are repeated a predetermined number of times. A structure containing a sacrificial layer as shown in FIG.
That is, by repeating the above process four times, a plurality of pattern forming layers in which a plurality of rod-shaped portions are arranged in parallel and periodically with a predetermined in-plane period to obtain a one-cycle woodpile structure are laminated. Structure can be obtained.

Specifically, a structure in which a pattern forming layer containing a sacrificial layer as shown in FIG. 1 (i) is laminated by the following process using each step of the above-described method for producing a three-dimensional photonic crystal. Manufacturing.
That is, the film formation step, the ion implantation step, the pattern formation step, the sacrificial layer formation step, and the planarization step are repeated four or more times in this order,
A structure containing the sacrificial layer in which a pattern forming layer in which a plurality of rod-shaped portions are arranged in parallel and periodically with a predetermined in-plane period is laminated is manufactured.
At that time, in the first process, a plurality of rod-shaped portions are arranged in parallel and periodically with a predetermined in-plane period by the film formation step, the ion implantation step, the pattern formation step, and the sacrificial layer formation step. A first pattern forming layer disposed on the substrate is formed.
Next, in the second process, the film formation step, the ion implantation step, the pattern formation step, the sacrificial layer formation step,
A second pattern forming layer having a rod-shaped portion extending in a direction orthogonal to each rod-shaped portion is formed on each rod-shaped portion in the first pattern-forming layer.
Next, in the third process, on the second pattern formation layer, the rod shape portion located parallel to the rod shape portion in the first pattern formation layer and shifted by ½ of the in-plane period Forming a third pattern forming layer having
Next, in the fourth process, on the third pattern formation layer, the rod shape positioned parallel to each rod shape portion in the second pattern formation layer and shifted by ½ of the in-plane period A fourth stripe layer having a portion is formed.
By the above process, a structure for obtaining the above-described one-cycle woodpile structure can be obtained.

However, when the uppermost dielectric thin film pattern is formed, there is no problem even if the sacrifice layer forming step and the planarization step are omitted.
Here, in order to perform pattern alignment between layers with high accuracy, the pattern arrangement of each layer may be determined with reference to an alignment mark (not shown) formed in advance on a substrate or a dielectric thin film.
Examples of the method for forming the alignment mark include photolithography and the lift-off method. Examples of the material for the alignment mark include Au / Cr.

What should be noted here is the exposure of the underlying pattern in the pattern formation process for the second and subsequent layers (FIG. 1 (h)).
For example, in FIG. 1 (h), when the pattern processing of the second layer proceeds to below the second dielectric thin film, a part of the first layer pattern (for example, a portion indicated by 35) as a base Is exposed.
Usually, pattern processing often performs end point control over time, and it is difficult to stop the processing without exposing the pattern exposed portion 35 to the etching atmosphere at all. Conventionally, it is difficult to provide an etch stop layer, and the pattern exposed portion 35 is inevitably damaged.
This lowers the processing accuracy of the photonic crystal structure and affects the element characteristics.
On the other hand, in the present invention, Ga ions are implanted into the pattern exposed portion 35 to bring high etching resistance to the portion.
That is, the etching mask is embedded in the dielectric thin film by ion implantation. Since this built-in mask does not interfere with the structure formation of the second and subsequent layers, it is not necessary to remove it after thin film processing.
This mask can protect the structure of the thin film as an etch stop layer even in the processing of the next and subsequent layers. Thereby, processing damage can be reduced and higher processing accuracy can be obtained.

Subsequently, in the sacrificial layer removal step, the sacrificial layer in the sacrificial layer-containing photonic crystal structure of FIG. 1 (i) is collectively removed with a liquid etchant in order to obtain the three-dimensional periodic structure shown in FIG. 1 (j). To do. Thereby, a desired photonic crystal is obtained.
As the liquid etching agent, for example, when the sacrificial layer is Cu, an etching solution containing iron chloride can be used.
Through the above lamination process, a three-dimensional photonic crystal structure made of a dielectric thin film, in particular, Si or a Si compound containing a Si oxide or nitride is produced.

As described above, the dielectric thin film processing mask according to the present embodiment is embedded in the thin film by ion implantation and does not obstruct the formation of the structure after the next layer, and therefore does not need to be removed after the thin film processing.
This mask can protect the structure of the thin film as an etch stop layer even in the processing of the next and subsequent layers.
Thereby, processing damage can be reduced and higher processing accuracy can be obtained.
In addition, since the method for producing a three-dimensional photonic crystal according to the present invention is simpler than the prior art, the production cost can be reduced.

  In the above description, only the three-dimensional woodpile structure has been described as the three-dimensional photonic crystal, but the present invention is not limited to this. Other three-dimensional structures can be easily formed by the method of the present invention.

Examples of the present invention will be described below, but the present invention is not limited to these examples.
[Example 1]
Since this embodiment is based on basically the same process as the manufacturing method of the three-dimensional photonic crystal described in the embodiment of the present invention, it will be described here with reference to FIG.
The description of the drawings overlapping with the description in the embodiment of the present invention is omitted.
In this example, a woodpile type three-dimensional photonic crystal structure shown in FIG.
First, the film forming process shown in FIG. In this step, the dielectric thin film 20 which is a main material constituting the photonic crystal is formed on the substrate 10.
Quartz was used as the substrate 10. As the dielectric thin film 20, a Si thin film having a thickness of about 100 nm was formed by a sputtering method.

Next, the ion implantation process shown in FIG. In this step, Ga ions are selectively implanted into the portion 30 while scanning with a focused ion beam (hereinafter referred to as FIB).
The pattern 30 has a width of about 100 nm, a length of 100 μm, and an in-plane period of about 300 nm. The area of the entire pattern is about 100 μm square.
The acceleration voltage of FIB is set to about 5 kV to 30 kV, and Ga ions are implanted almost uniformly from the outermost surface of the Si thin film to a depth of about 30 nm.
The beam diameter of the FIB is reduced to about 10 nm, the beam current and the scanning speed are adjusted, and the maximum density of Ga ions is set to about 5 × 10 ²⁰ cm ⁻³ .

Next, the pattern forming process shown in FIG. In this step, the Si thin film 20 is etched with a fluorine-based gas RIE, and a portion indicated by 50 is partially removed.
At this time, using the pattern 30 formed in the ion implantation step shown in FIG. 1B as an etching mask, the Ga ion non-implanted portion 50 that is visible from a direction substantially perpendicular to the upper surface of the Si thin film 20 is selectively removed.
By this etching, a pattern of the first layer of the photonic crystal is formed.
For example, the RIE method in which SF ₆ and C ₄ F ₈ gases are alternately introduced is used for the RIE here.
When SF ₆ gas is introduced, etching proceeds mainly. When C ₄ F ₈ gas is introduced, side wall protection mainly proceeds. Thus, the etching resistance of the mask is further improved, and the amount of Ga in the Ga mask and the mask thickness can be reduced.
In this pattern formation step, the etching resistance of the Ga ion implanted portion 30 can be obtained that is 500 times that of the Ga ion non-implanted portion 50 or more.

Next, a sacrificial layer forming step shown in FIG.
In this step, a copper thin film 60 is formed as a sacrificial layer thin film on the Si thin film including the structure of the first layer. The copper thin film is deposited by sputtering, but has a thickness of about 0.3 μm.

  Next, the planarization process shown in FIG. In this step, the copper thin film 60 is polished by a well-known CMP method, but the underlying Si thin film pattern 30 is exposed, and the polishing is advanced so that the height of the copper thin film 60 is substantially the same as 30.

Next, as shown in FIGS. 1F to 1I, the film formation process, the ion implantation process, the pattern formation process, the sacrificial layer formation process, and the planarization process are repeated, and FIG. A sacrificial layer-containing photonic crystal structure as shown in FIG.
In order to perform pattern alignment between layers with high accuracy, alignment marks (not shown) are formed on the substrate 10 in advance. The pattern arrangement of each layer is determined based on the alignment mark.
Electron beam lithography and the lift-off method are used to form the alignment mark. The material of the alignment mark is Au (thickness 100 nm) / Cr (thickness 10 nm).

In the pattern formation step of FIG. 1 (h), when the pattern processing of the second layer proceeds below the Si thin film of the second layer, a part of the pattern of the first layer (for example, a part indicated by 35) as a base ) Is exposed.
Normally, the end point of the pattern processing is often controlled by time, and it is difficult to stop the processing without exposing the pattern exposed portion 35 to the etching atmosphere at all.
Conventionally, it is difficult to provide an etch stop layer, and the pattern exposed portion 35 is inevitably damaged. This lowers the processing accuracy of the photonic crystal structure and affects the element characteristics.
On the other hand, in this embodiment, Ga ions are implanted into a portion where pattern formation is desired, and this portion (the portions 30 and 35) has high etching resistance.
That is, the etching mask is embedded in the Si thin film by ion implantation.
Since this built-in mask does not interfere with the structure formation of the second and subsequent layers, it is not necessary to remove it after thin film processing. This mask can protect the structure of the thin film as an etch stop layer even in the processing of the next and subsequent layers.
In FIG. 1 (h), the portion 35 is exposed, but since this portion has high etching resistance, the processing damage received is low.
Therefore, higher processing accuracy can be obtained than a conventional processing method without an etch stop layer.

Subsequently, in order to obtain the three-dimensional structure shown in FIG. In this step, the sacrificial layer in the structure of FIG. 1 (i) is collectively removed with an iron chloride-containing etching solution to obtain a desired woodpile type three-dimensional photonic crystal.
FIG. 1 (j) shows a one-cycle (four-layer) woodpile photonic crystal.
By the above stacking process, a three-dimensional structure typified by a three-dimensional photonic crystal can be manufactured with higher processing accuracy and lower cost.

[Example 2]
In Example 2, a method of manufacturing a three-dimensional periodic structure using the three-dimensional photonic crystal manufactured by the above-described three-dimensional photonic crystal manufacturing method as a manufacturing mold will be described.
In this example, a new photonic crystal structure is produced using the photonic crystal 70 formed in Example 1 as a manufacturing mold.
As a manufacturing method, first, the atmosphere part 50 between the rods 40 of the photonic crystal 70 is embedded with another material by a chemical vapor deposition (CVD) method or an atomic layer deposition (ALD) method.
The material is, for example, titanium oxide (TiO ₂ ). By optimizing the embedding conditions, the atmosphere part 50 can be densely embedded without a gap.

Then, the outermost rod 40 is partially exposed by polishing or dry etching. Then, the rod 40 (Si) is completely removed by dry etching or solution etching.
As a dry etching method, there is a method using XeF ₂ gas. The solution that can be used for the solution etching may be any solution that dissolves Si but does not etch TiO ₂ and the quartz substrate.
For example, a TMAH (tetramethylammonium hydroxide) aqueous solution is suitable. By the above process, a three-dimensional photonic crystal made of TiO ₂ is formed. There are also materials such as GaN, SiO ₂ and ZnO instead of TiO ₂ . It is clear that each material is possible, although the process of embedding is slightly different.
Further, although the substrate 10 is made of quartz, there is no problem even if it is changed as necessary.

By the above method, after the material for forming the three-dimensional photonic crystal is embedded in the manufacturing mold, the manufacturing mold side is removed, and a three-dimensional periodic structure is manufactured by using the embedded material with the inverted shape of the manufacturing mold. can do.
As a result, it is possible to form a photonic crystal made of a material completely different from the Si photonic crystal formed in the stacking process shown in the first embodiment.

The figure explaining the manufacturing method of the three-dimensional periodic structure in embodiment and Example 1 of this invention. The schematic diagram explaining the three-dimensional photonic crystal which has the woodpile structure in a prior art example.

Explanation of symbols

10: Substrate 20: Dielectric thin film 30: Mask pattern 35 by ion implantation: Pattern exposed portion 40: Photonic crystal rod 50: Atmosphere portion 60: Sacrificial layer 70: Photonic crystal

Claims (11)

A method for producing a three-dimensional photonic crystal,
A film forming process for forming a dielectric thin film;
An ion implantation step of selectively implanting ions by a focused ion beam into the dielectric thin film to form a mask on the dielectric thin film;
A pattern forming step of selectively removing a portion where the dielectric thin film other than the mask portion formed on the dielectric thin film is exposed, and forming a pattern;
A sacrificial layer forming step of forming a sacrificial layer on the dielectric thin film on which the pattern is formed, and a flattening step of flattening the sacrificial layer formed on the dielectric thin film until the pattern is exposed;
A method for producing a three-dimensional photonic crystal, comprising:   2. The method of manufacturing a three-dimensional photonic crystal according to claim 1, wherein the dielectric thin film is formed of Si or a Si compound containing an oxide or nitride of Si. 3.   3. The method according to claim 1, wherein in the film formation step, any one of sputtering, vacuum evaporation, chemical vapor deposition, or epitaxial growth is used to form the dielectric thin film. A method for producing a two-dimensional photonic crystal.   The method of manufacturing a three-dimensional photonic crystal according to any one of claims 1 to 3, wherein Ga ions are used as ions of the focused ion beam in the ion implantation step.   5. The reactive ion etching using a fluorine-based gas is used for selective removal of the exposed portion of the dielectric thin film in the pattern forming step. A method for producing a two-dimensional photonic crystal.   6. The three-dimensional photonic crystal according to claim 1, wherein the sacrificial layer in the sacrificial layer forming step is selected from materials that can be easily flattened in the flattening step. Method.   7. The method according to claim 1, wherein sputtering, vacuum evaporation, chemical vapor deposition, or epitaxial growth is used for forming the sacrificial layer in the sacrificial layer forming step. A method for producing a three-dimensional photonic crystal.   8. The method of manufacturing a three-dimensional photonic crystal according to claim 1, wherein either mechanical polishing or chemical mechanical polishing is used for the flattening in the flattening step. A method of manufacturing a three-dimensional photonic crystal, wherein a plurality of pattern forming layers including a sacrificial layer in which a plurality of rod-shaped portions are arranged in parallel and periodically with a predetermined in-plane period are stacked. 1 process,
A second step of manufacturing a three-dimensional periodic structure by collectively removing the sacrificial layer with a liquid etchant in a structure in which a plurality of pattern forming layers containing the sacrificial layer are stacked,
The first step includes
A film forming process for forming a dielectric thin film;
An ion implantation step of selectively implanting ions by a focused ion beam into the dielectric thin film to form a mask on the dielectric thin film;
A pattern forming step of selectively removing a portion where the dielectric thin film other than the mask portion formed on the dielectric thin film is exposed, and forming a pattern;
A sacrificial layer forming step of forming a sacrificial layer on the dielectric thin film on which the pattern is formed;
A step of repeating the flattening step of flattening the sacrificial layer formed on the dielectric thin film until the pattern is exposed, four or more times in this order;
A method for producing a three-dimensional photonic crystal, comprising:   The method for producing a three-dimensional photonic crystal according to claim 9, wherein the liquid etching agent is a liquid etching agent containing iron chloride. A three-dimensional photonic crystal produced by the method for producing a three-dimensional photonic crystal according to claim 9 is used as a production mold.
After embedding a material for forming a three-dimensional photonic crystal in the production mold, the production mold is removed,
A method for producing a three-dimensional photonic crystal, comprising producing a three-dimensional periodic structure with the embedded material having an inverted shape of the production mold.

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