The present invention relates to a structure. In particular, the present invention relates to a structure for an X-ray phase contrast imaging apparatus.
A grating made from a structure having a periodic structure is used as a spectral element for various apparatuses. In particular, a grating formed from a structure made from a metal having a high X-ray absorbance characteristic is used in the fields of the nondestructive inspection of objects and medical care.
One purpose of the structure made from a metal having a high X-ray absorbance characteristic is a shield grating of an imaging apparatus to pick up an image by using X-ray Talbot interferometry. The imaging method by using the X-ray Talbot interferometry (X-ray Talbot interference method) is one of imaging methods (X-ray phase imaging methods) taking advantage of X-ray phase contrast.
The X-ray Talbot interference method will be described briefly. In general imaging apparatus to execute the X-ray Talbot interference method, X-rays, which can interfere spatially, pass through an object and a diffraction grating to diffract the X-rays, so as to form an interference pattern. A shield grating to periodically screen out the X-rays is disposed at the position at which the interference pattern is formed, so as to form a moire. The resulting moire is detected with a detector and a pickup image is obtained by using the detection result.
A general shield grating for the X-ray Talbot interference method will be described. In the shield grating, X-ray screening portions (hereafter simply referred to as screening portions) and X-ray transmission portions (hereafter simply referred to as transmission portions) are arranged at a pitch of about 2 to 8 micrometers depending on the resolution required of the imaging. The screening portion has an aspect ratio, that is, the ratio of the height to the width (width in the direction of arrangement of the screening portions and the transmission portions), of about 30 or more and is made from a material, e.g., gold, having high X-ray absorbance. In a favorable method for producing a shield grating having a screening portion made from gold, a mold is produced from silicon having excellent mechanical strength and exhibiting relative easiness in working at a high aspect ratio, and gold is filled therein with plating. However, in production of a mold having a high aspect ratio, it is known that in a drying step after a wet treatment, e.g., Wet cleaning or development, arrangement may be disturbed by mutual sticking of convex portions (or portions sandwiched between a recessed portion) of the mold due to the surface tension of the droplet. If the arrangement of the mold is disturbed, the arrangement of a metal structure obtained by filling the metal is disturbed. In PTL 1, the surface tension during drying is reduced by using supercritical CO2 and, thereby, mutual sticking of convex portions (or portions sandwiched between the recessed portion) of the mold having a high aspect ratio.
The mutual sticking of convex portions (or portions sandwiched between the recessed portion) of the mold due to the surface tension of the droplet can be reduced by using the method described in PTL 1. However, the present inventors found a new problem in that sticking sometimes occurred because of another factor depending on the aspect ratio of a portion to be filled with a metal of the mold. It was found that an oxide film on the silicon surface of the mold having a high aspect ratio was charged because of friction and the like against a medium during supercritical drying, and sometimes mutual sticking of convex portions (or portions sandwiched between the recessed portion) of the mold occurred because of this charge. Likewise, it was found that sometimes mutual sticking of convex portions (or portions sandwiched between the recessed portion) of the mold occurred because of charges in the steps of, for example, plasma cleaning, drying after Wet cleaning, and conveying other than the supercritical drying step.
The present invention provides a silicon mold in which disturbances in arrangement of convex portions (or portions sandwiched between the recessed portion) of the mold are reduced than ever by reducing mutual sticking of convex portions (or portions sandwiched between a recessed portion) of the mold due to charges than ever, a method for manufacturing a structure by using the silicon mold, and a high-aspect ratio structure in which disturbances in arrangement are reduced.
A method for manufacturing a structure, according to an aspect of the present invention, includes the steps of forming a recessed portion in a silicon substrate, cleaning, drying, or conveying a silicon substrate while charges of a plurality of portions sandwiched between the recessed portion are removed, and filling a metal into the recessed portion of the silicon substrate subjected to the cleaning, drying, or conveying.
Other aspects of the present invention will be made clear by the embodiments described below.
A silicon mold in which disturbances in arrangement due to charges are reduced, a method for manufacturing a structure by using the silicon mold, and a high-aspect ratio silicon mold and a structure, in which disturbances in arrangement are reduced, can be provided.
In a first embodiment, a method for manufacturing a two-dimensional structure will be described. The two-dimensional structure produced according to the present embodiment can be used as a two-dimensional shield grating in an X-ray Talbot interference method.
Next, a method for manufacturing a structure in the present embodiment will be described with reference to
The method for manufacturing a structure according to the present embodiment is provided with a step to form a mold with a silicon substrate 1 and a step to fill a metal 8 into the mold. In the step to form the mold with the silicon substrate, initially, a step to form a plurality of convex portions is performed by forming a recessed portion through etching of a first surface 9 of the silicon substrate 1. The plurality of convex portions are portions sandwiched between the recessed portion and are the portions left through etching. Thereafter, a step to clean the silicon substrate, a step to dry the silicon substrate, a step to form an insulating film on the silicon substrate, and a step to remove the insulating film on the bottom between the plurality of convex portions of the silicon substrate and form a seed layer are performed and, thereby, a mold is formed. Subsequently, a step to fill a metal 8 into the resulting mold is performed, so that a structure usable as a shield grating of an imaging apparatus to execute an X-ray Talbot interference method is produced.
When this manufacturing method is executed, at least part of the steps performed after the step to form the plurality of convex portions on the silicon substrate before the step to fill the metal into the mold are performed while charges of the plurality of convex portions are removed. In the present embodiment, part of the silicon substrate is the electrically conductive opening and charges of the plurality of convex portions are removed by connecting the electrically conductive opening to a ground electrode. For this purpose, a step to form an electrically conductive opening in part of the silicon substrate is performed in the step to form the mold with the silicon substrate. In this regard, a portion electrically connected to a plurality of convex portions of the silicon substrate can be used as the electrically conductive opening and, therefore, in the case where at least part of an electrically conductive surface of the silicon substrate is exposed, the exposed portion can be used as the electrically conductive opening. That is, the step to form the electrically conductive opening may be omitted insofar as at least part of the electrically conductive surface of the silicon substrate is exposed.
By the way, in the present specification, the term “charges of the plurality of convex portions are removed” also includes that charges of the plurality of convex portions are not removed completely, but the amount of charge is reduced. Furthermore, the term “the steps performed after the step to form the plurality of convex portions before the step to fill the metal into the mold” includes conveying steps as well. Examples of the conveying steps include a step to convey from the step to form the plurality of convex portions to the step to clean the silicon substrate and a step to convey from the step to form the mold to the step to fill a metal into the mold.
The method for manufacturing a structure according to the present embodiment will be described below in detail.
Initially, in order to form a mold with a silicon substrate 1, a step to form a plurality of convex portions 10 is performed by forming a recessed portion through etching of a first surface 9 of the silicon substrate. In the present embodiment, the step to form the plurality of convex portions 10 on the first surface 9 of the silicon substrate is performed while a step to form an electrically conductive opening 3 for connecting the plurality of convex portions 10 to a ground electrode 4 on the silicon substrate 1 is performed. According to this, the step to convey from the step to form the plurality of convex portions to the step to clean the silicon substrate 1 can be performed while the electrically conductive opening 3 is electrically connected to the ground electrode 4. In the present specification, a step to make preparations for etching is specified to be also included in the step to form a plurality of convex portions 10.
The silicon substrate 1 is prepared. A single crystal silicon wafer and a SOI wafer can be used for the silicon substrate 1 because high-precision working by a semiconductor process or a MEMS process becomes possible and the mechanical strength is high. The first surface 9 of the silicon substrate 1 prepared is a polished surface. In the case where the silicon substrate 1 has a size equal to a 4-inch wafer, the thickness is preferably 300 micrometers to 525 micrometers in consideration of the production process and the easiness in conveyance.
As shown in
As shown in
A photoresist is applied to the mask 2 formed on the first surface 9 of the silicon substrate, and an optional pattern is formed through lithography. The method for selecting the pattern depends on the shape required of the plurality of convex portions 10 formed on the silicon substrate, described later. The mask 2 is patterned by etching the mask 2 while the photoresist serves as a mask.
In the case where a film of Cr is disposed as the mask 2 on SiO2, initially, Cr is patterned through reactive ion etching with an etching solution of Cr or a chlorine gas. Thereafter, SiO2 is patterned through reactive ion etching with a fluorine based gas, e.g., a CHF3 gas, so that the mask 2 is patterned.
As shown in
The electrically conductive opening 3 will be described.
The electrically conductive opening 3 is connected to the ground electrode 4 directly or indirectly and, thereby, has a function of reducing an influence of charges exerted on the plurality of convex portions 10 of the silicon substrate. The ground electrode is a ground potential and may be a chuck, e.g., an electrostatic chuck, in the case of a plasma process.
It is desirable that the step in which the plurality of convex portions 10 of the silicon substrate may be charged is performed while the electrically conductive opening 3 is connected to the ground electrode 4.
The steps in which the convex portions 10 are charged easily include a drying step after Wet cleaning, conveying steps between the steps, and the step by using plasma (plasma process).
In the case where these steps, in which the convex portions 10 are charged easily, are performed, mutual sticking of the convex portions due to charges of the convex portions can be reduced by connecting the electrically conductive opening 3 to the ground electrode 4. Needless to say, mutual sticking of the convex portions becomes a cause of disturbances in pitch of the plurality of convex portions 10, so that an influence is exerted on the pitch of a structure obtained by filling a metal in the downstream step. In the case where the surfaces of the convex portions 10 are covered with a native oxide as well, the convex portions 10 may be charged. Therefore, it is better to perform the above-described steps while the electrically conductive opening 3 is connected to the ground electrode 4.
In the present embodiment, as shown in
In order to perform the above-described steps, in which the convex portions are charged easily, while the electrically conductive opening 3 is connected to the ground electrode 4, the step to form the electrically conductive opening is specified to be the step performed prior to the step to fill a metal serving as an X-ray absorber. In the case where the step to form the electrically conductive opening 3 is performed prior to the step to etch the first surface 9 of the silicon substrate, charges of the plurality of convex portions 10 can be reduced in a conveying step from the step to form the plurality of convex portions 10 of the silicon substrate to the step to clean the silicon substrate 1 as well.
It is desirable that the area of the insulator in the surface of the silicon substrate is minimized from the viewpoint of reduction in charge of the silicon substrate. Therefore, it is desirable that the whole second surface 11, which ensures a large area easily, of the silicon substrate serves as the electrically conductive opening 3. In this regard, the second surface 11 of the silicon substrate refers to the surface opposite to the first surface 9 of the silicon substrate. Meanwhile, in the case where the second surface 11 of the silicon substrate serves as the electrically conductive opening 3, electrical connection to the silicon substrate is ensured easily in the plasma process by using the electrostatic chuck. In the case where it is difficult to form the electrically conductive opening 3 on the second surface 11 of the silicon substrate or in the case where a SOI substrate is used as the silicon substrate, part of or an entirety of the outside of the region provided with the plurality of convex portions 10 of the first surface 9 of the silicon substrate may serve as the electrically conductive opening 3.
In the present embodiment, in order to form the electrically conductive opening 3, a film of SiO2 formed on the second surface 11 is etched with dilute hydrofluoric acid while the first surface 9 is protected by application of a photoresist to the first surface 9. In the case where a film of Cr serving as a mask is disposed as an upper layer of SiO2, etching of SiO2 may be performed after the Cr film is etched by, for example, using an etching solution of Cr. The photoresist applied to protect the first surface 9 is removed.
As shown in
The cross-sectional shapes and the arrangement pattern of the plurality of convex portions 10 may be selected on the basis of the imaging system of X-ray phase imaging, the mechanical strength of the mold and the structure produced by using the mold, and the easiness in production of the structure. In the case where the two-dimensional structure, such as, the structure produced in the present embodiment, is used as the shield grating in an imaging apparatus of the X-ray Talbot interference method, the imaging system becomes a two-dimensional Talbot interference system, in which the two-dimensional information can be obtained by one time of imaging. When the structure in which the cross-sectional shapes of the plurality of convex portions are circular is compared with the structure in which the cross-sectional shapes are quadrangular, the structure in which the cross-sectional shapes are circular is easy to form the plurality of convex portions through reactive ion etching described later. On the other hand, the structure in which the cross-sectional shapes are quadrangular has high mechanical strength and can screen out X-rays ideally and selectively with respect to pixels of the detector.
Anisotropic etching can be used for etching the first surface 9. In order to perform etching at a high aspect ratio and a narrow pitch in the reactive ion etching, as in the present embodiment, a Bosch process is suitable, where etching with a SF6 gas and deposition of a side surface protective film with a C4F8 gas are performed alternately. Furthermore, a wet process with an alkali solution taking advantage of the crystal orientation of the silicon substrate 1 can also be used. X-ray lithography is suitable for photolithography. The heights of the plurality of convex portions 10 are determined on the basis of the height required of a metal 8, described later, to be filled. The heights of the convex portions 10 are specified to be about 10% higher than the height required of the metal 8 and, thereby, when the metal is filled in between the plurality of convex portions, overflow of the metal from between the convex portions 10 on the basis of the filling rate difference of the metal can be prevented.
The filling height of the metal 8 changes depending on the energy of X-rays used for the X-ray imaging apparatus and the material for the metal structure. It is desirable that the metal 8 filled in between the plurality of convex portions 10 can screen out about 80% or more of the incident X-rays. For example, in the case where the energy of the X-ray is 22 key and the metal 8 is Au, it is enough that the filling height of the metal 8 is about 50 micrometers and it is desirable that the depth of the plurality of convex portions 10 is 55 micrometers or more. After the plurality of convex portions 10 are formed, the convex portions 10 are in the state of mutually sticking easily because SiO2 and SiN of the mask formed on the top surfaces 12 of the plurality of convex portions 10 or native oxides on the surfaces of the convex portions 10 are charged. Consequently, conveyance from the step to form the plurality of convex portions 10 to the next step can be performed while the electrically conductive opening 3 is in contact with the ground electrode 4. When charges are brought close to the plurality of convex portions 10, the insulating film (SiO2 or SiN) formed on the top surfaces of the convex portions is charged. However, charges reverse to the charge of the insulating film are collected in the vicinity of the interface between the insulating film and the convex portions 10 and, thereby, forces of the convex portions 10 to pull at each other are weakened, so that sticking can be reduced.
In the case where the pitch between the plurality of convex portions 10 is 4 micrometers or less and the aspect ratio of each of the plurality of convex portions is 20 or more, mutual sticking of the convex portions due to charges occurs significantly and easily, so that the effect of connecting the electrically conductive opening 3 to the ground electrode 4 is exerted significantly and easily.
The insulating film (SiO2 or SiN) formed on the top surfaces 12 of the convex portions is left because a function as a mask is exerted in a downstream step.
As shown in
In the case where the plurality of convex portions 10 are formed by the Bosch process, a fluorocarbon based protective film remains on the side surfaces of the plurality of convex portions 10, so that the silicon substrate is cleaned. In the case where the insulating film is disposed on the first surface of the convex portions, it is desirable that the silicon substrate is cleaned by a cleaning method, wherein the insulating film is not dissolved.
As shown in
In the drying step after the Wet cleaning is performed, mutual sticking of the convex portions due to the surface tension of droplet can be prevented by employing supercritical drying. In a chamber 17, CO2 21 is introduced into the state in which the silicon substrate is immersed in isopropyl alcohol (IPA) 18 and the temperature is raised and the pressure is increased until the critical point of CO2, that is, 31 degrees centigrade and 7.4 MPa, is exceeded. Isopropyl alcohol and CO2 21 are discharged while CO2 21 is further introduced. After isopropyl alcohol runs out of the chamber 17, the pressure is decreased to return supercritical CO2 to gas phase CO2.
The supercritical drying has a high effect of preventing mutual sticking of the convex portions due to the surface tension of droplet. However, the insulating film on the convex portion surface is charged because of friction with CO2 during drying, so that mutual sticking of the convex portions due to charges may occur. Therefore, it is better to perform supercritical drying while the electrically conductive opening 3 is connected to the ground electrode 4, so as to reduce charges of the convex portion surfaces.
As shown in
It is desirable that the film thickness of the insulating film 7 formed on the side surfaces of the convex portions is 10 nm or more. However, even when the insulating film is not formed on the side surfaces of the convex portions, deposition of the metal on the side surfaces of the convex portions can be neglected depending on the resistance of the silicon substrate, the current applied in the electroplating, or the pattern of the convex portions. In the case where an insulating film is formed on the second surface, it is desirable that the film thickness of the insulating film 7 is 10 nm or more. However, even when the insulating film is not formed on the second surface, precipitation of the plating on the second surface can be prevented by performing electroplating in such a way that the second surface does not come into contact with the plating solution. In the case where, for example, the silicon substrate is subjected to thermal oxidation, an insulating film may also be formed on the electrically conductive opening 3, and the insulating film may be etched again to form the electrically conductive opening 3 which is used for removing charges of the convex portions.
As shown in
Initially, highly anisotropic reactive ion etching is performed and, thereby, the insulating film between the plurality of convex portions is removed (
Subsequent to removal of the insulating film on the bottom between the convex portions, a feeding point 5 used in the electroplating step described later is formed (
Then, a seed layer 6 is formed on the bottom 19 between the plurality of convex portions (
According to the above-described steps, a silicon mold can be formed. However, the method for forming the silicon mold is not limited to that described above insofar as in the method, at least part of the steps after the step to form the plurality of convex portions on the silicon substrate to the step to fill the metal into the silicon mold are performed while charges of the plurality of convex portions are removed. For example, the step to form the insulating film shown in
As shown in
Electroplating is employed as the method for filling the metal favorably. The power is supplied from the bottom between the plurality of convex portions 10 through the seed layer 6 and the metal 8 is filled, so that filling with reduced voids can be performed. Chemical vapor deposition (CVD), vacuum sputtering, vacuum evaporation, and the like may also be employed as the method for filling the metal. Gold, copper, nickel, iron, alloys thereof, and the like may be used as the metal to be filled. In the case where the structure is used as the shield grating, gold having a large X-ray absorption coefficient can be used.
In a second embodiment, a method for manufacturing a one-dimensional structure will be described. The one-dimensional structure produced according to the present embodiment can be used as a one-dimensional shield grating in the X-ray Talbot interference method.
The present embodiment is different from the first embodiment in that the pattern of the patterning of the mask is in the shape of a line, and the other steps are basically the same as the steps of the first embodiment. In this regard, in the one-dimensional structure, slit-shaped metal structures, which function as screen portions, are periodically arranged. Therefore, the present embodiment is different from the first embodiment in that a plurality of recessed portions are formed by etching the first surface of the silicon substrate, so as to form a mold, and a structure is produced by filling the metal into the plurality of recessed portions of the mold. Meanwhile, even when a recessed portion in which the end portions of a plurality of recessed portions are coupled is formed, regions other than the coupled regions may be used as a one-dimensional shield grating.
In a third embodiment, the mold and the structure produced according to the first embodiment will be described with reference to
In this regard, the incidence of sticking refers to the incidence of convex portions in contact with other convex portions among the convex portions. For example, in the case where there are 50 convex portions and sticking occurs at one place, when 2 convex portions are in contact at the one place, the incidence of sticking is 2/50*100=4%, and when 3 convex portions are in contact, the incidence of sticking is 3/50*100=6%.
As is described in PTL 1, in the case where the supercritical drying is employed, the incidence of sticking of the mold or the structure is about 5% and in the case where the silicon substrate is cleaned with alcohol and is air-dried without employing the supercritical drying, the incidence of sticking is about 70%.
The resulting structure can be used as a shield grating, in which disturbances in arrangement are reduced, in the X-ray Talbot interference method.
In a fourth embodiment, the structure produced in the case where an insulating film is formed on the top surfaces and side surfaces of the convex portions and the second surface in the first embodiment will be described with reference to
In the structure produced according to the present embodiment, the plurality of convex portions 10 having an aspect ratio of 20 or more and 200 or less are disposed on the first surface 9 of the silicon substrate 1. The insulating film 7 is disposed on the top surfaces 12 of the plurality of convex portions 10, the side surfaces of the plurality of convex portions 10, and the second surface 11 opposite to the first surface 9. On the bottom between the plurality of convex portions, a seed layer is disposed on the surface of the silicon substrate. This silicon mold is used, the metal is filled while the seed layer serves as a seed and, thereby, a structure can be produced having the plurality of convex portions formed on the first surface of the silicon substrate and a metal body disposed in at least part of the portion between the plurality of convex portions. The aspect ratios of the plurality of convex portions are 20 or more and 200 or less and the incidence of sticking of the plurality of convex portions is 0% or more and 3% or less.
In a fifth embodiment, a method for manufacturing a structure produced from the structure which is produced in the above-described embodiment and which includes a metal body and a silicon substrate, will be described with reference to
In the case where the resin layer is formed while the metal body is deformed into an R-shape, the directions of the plurality of holes disposed in the metal body in the depth direction become the directions reflecting the R-shape. Meanwhile, in the case where the resin layer is formed while the metal body is deformed into a spherical R-shape, the directions of the plurality of holes of the metal body in the depth direction can be made directions concentrated on one point on an extension of the plurality of holes. Here, the R-shape refers to a shape of a circular cylinder cut in the depth direction, and the spherical R-shape refers to a continuous curved surface in the shape of a sphere.
For example, a method in which the metal body is brought into contact with a mold directly or indirectly, so as to be deformed, can be employed as the method for deforming the metal body.
According to the present embodiment, as shown in
Meanwhile, if the metal bodies are coupled to each other in the one-dimensional structure shown in the second embodiment, it is possible that the metal bodies are taken out by the above-described method, and the resin layer is formed after deformation.
In the present embodiment, the holes 23 formed in the metal body are through holes, although the holes 23 may not penetrate the metal body 8. For example, when the metal is filled through electroplating, if the top surface of the metal exceeds the top surfaces of the convex portions, the holes become not through holes. The present embodiment can also be applied to such a structure.
In Example 1, the method for manufacturing the structure according to the first embodiment will be described in more detail.
As in the first embodiment, the present example will be described with reference to
In the step shown in
As shown in
As shown in
In the step shown in
In the step shown in
Supercritical drying of the silicon substrate 1 is performed in the step shown in
The supercritical drying is performed while the electrically conductive opening 3 is connected to the ground electrode 4, so that charges of the convex portions are reduced.
The insulating film is formed on the surface of the silicon substrate 1 in the step shown in
The insulating film formed on the bottom 19 between the convex portions is etched to expose Si in the step shown in
Part of the insulating film 7 formed in the step shown in
The seed layer 6 is formed on the bottom 19 between the convex portions in the step shown in
The seed layer is also formed on the top surfaces of the convex portions because of adhesion of Cr and Cu through the electron beam evaporation. However, in the case where the film is formed perpendicularly to the silicon substrate 1 through directional electron beam evaporation, there is no continuity between the seed layer on the top surfaces of the convex portions and the seed layer 6 on the bottom between the convex portions.
In the step shown in
In Example 2, an example, which is different from Example 1, of the method for manufacturing the structure according to the first embodiment will be described with reference to
The present example is different from Example 1 in that CVD is employed for formation of the insulating film, and an insulating film is not formed on the second surface.
In the step shown in
In the step shown in
In the step shown in
In the step shown in
In the step shown in
In the step shown in
In the step shown in
In the step shown in
In Example 3, another concrete example of the structure according to the first embodiment will be described. The present example is different from Example 1 in that the step to form the insulating film shown in
In the present example, a silicon substrate 1 having a thickness of 525 micrometers and a diameter of 100 mm is used. Etching is performed in such a way that convex portions 10 having a diameter of 2 micrometers are formed while being arranged at a pitch of 4 micrometers in a region 50 mm square on the first surface 9 of this silicon substrate. The heights of the convex portions 10 is 70 micrometers, a SiO2 layer having a thickness of 0.5 micrometers and serving as an insulating film 7 made from an inorganic compound is formed on the top surfaces 12 of the convex portions 10, and the aspect ratios are about 35. An electrically conductive surface of the silicon substrate is exposed at the second surface 11 opposite to the first surface 9. Charges of the convex portions 10 can be removed efficiently by connecting the electrically conductive surface of the second surface 11 serving as the electrically conductive opening to the ground electrode. After etching, the silicon substrate is subjected to O2 plasma cleaning. The O2 plasma cleaning is performed at 1,400 W, a pressure of 0.6 Torr, and an oxygen flow rate of 300 sccm for 600 seconds. Charges generated by collision of plasma with the convex portions 10 are removed from the electrically conductive opening of the second surface 11. Consequently, mutual sticking of adjacent convex portions 10 due to static electricity can be suppressed and disturbance in arrangement of the convex portions 10 can be suppressed. Connection of the electrically conductive opening to the ground electrode in drying of the silicon substrate after the Wet cleaning exerts a charge removing effect with respect to charges, which occur in drying, of the convex portions. For example, instead of the O2 plasma cleaning, the silicon substrate may be subjected to cleaning with a mixed solution of sulfuric acid and hydrogen peroxide, rinsing with pure water, immersion in isopropyl alcohol, and supercritical drying by using CO2.
The seed layer 6 is formed on the bottom 19 between the convex portions 10 of the structure. The seed layer 6 is produced by forming films of Cr of 10 nm and Cu of 120 nm in that order through directional electron beam evaporation. This is used as a silicon mold, and nickel is filled through electroplating. Energization for the electroplating is performed from the silicon surface of the second surface exposed at the plating solution. A nickel sulfamate plating solution is used as the plating solution. In the structure of the present example, the metal is filled into the silicon mold produced by suppressing mutual sticking of adjacent convex portions due to static electricity and, therefore, disturbance in arrangement of the metal body can also be suppressed.
In Example 4, the structure according to the fourth embodiment will be described more concretely with reference to
The method for manufacturing the structure of the present example up to the supercritical drying of the silicon substrate is the same as that in Example 3. As in Example 3, the silicon substrate after etching is subjected to O2 plasma cleaning and cleaning with a mixed aqueous solution of sulfuric acid and aqueous hydrogen peroxide, rinsing with pure water, immersion in isopropyl alcohol, and supercritical drying by using CO2. Subsequently, the whole surface of the silicon substrate is subjected to thermal oxidation by being put into a thermal oxidation furnace. The thickness of a thermally grown oxide film formed at this time is about 10 nm. Consequently, the thermally grown oxide film serving as an insulating film can be formed on both a recessed portion and the second surface 11 at the same time. The insulating film 7 is formed on the second surface 11 as well and, thereby, deposition of the plating on the second surface 11 is suppressed in plating in a downstream step.
The insulating film formed on the bottom between the convex portions is removed through anisotropic etching, and the seed layer 6 is formed. In the formation of the seed layer 6, films of Cr of 5 nm and Au of 100 nm are formed in that order through directional electron beam evaporation. Silicon of part of the second surface 11 exposed at the plating solution is exposed and energization is performed. A weak alkaline cyan-free Au plating solution is used as the plating solution. In this manner, Au plating grows from the seed layer 6, and a metal body made from gold can be formed by filling gold in between the convex portions. The insulating film 7 having a sufficient thickness is disposed on the side surfaces of the convex portions and the second surface 11, so that even when the insulating film 7 is dissolved into the weak alkaline plating solution to some extent, the side surfaces of the convex portions and the surface of silicon of the second surface 11 are not exposed. Therefore, precipitation of the plating on the side surfaces of the convex portions and the second surface can be suppressed until the Au plating is finished. Consequently, a two-dimensional structure can be produced while disturbances in arrangement of the convex portions 10 caused by sticking due to charges of the convex portions and poor plating in filling of the metal in between the convex portions are suppressed.
In Example 5, the method for manufacturing the structure according to the fifth embodiment will be described more concretely with reference to
In Example 6, the method for manufacturing the structure according to the fifth embodiment will be described more concretely with reference to
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2011-192816, filed Sep. 5, 2011 and No. 2012-155512, filed Jul. 11, 2012, which are hereby incorporated by reference herein in their entirety.
Number | Date | Country | Kind |
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2011-192816 | Sep 2011 | JP | national |
2012-155512 | Jul 2012 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2012/005008 | 8/7/2012 | WO | 00 | 3/4/2014 |