JP6967239B2 - Electron beam transmission membrane and electronic device - Google Patents

Description

The present invention relates to an electron beam transmitting membrane and an electronic device.

Electron beam transmission membranes are used for various purposes. For example, it is used to elucidate the operation of electronic devices at the atomic level. Electronic devices are generally formed on a substrate, but if the thickness of the substrate is too thick, electron beams cannot pass through. Therefore, by thinly processing a part of the substrate to form an electron beam transmitting film, it is possible to measure the operation of the electronic device using a transmission electron microscope.

The electron beam permeable membrane is also used to elucidate the reaction mechanism of biomolecules and viruses. Biomolecules and viruses can die under high vacuum. Therefore, the reaction mechanism of these reactions has been elucidated by irradiating biomolecules and viruses with electron beams generated in a high vacuum region via an electron beam permeable membrane.

Various electron beam transmission films are known. When measuring the operation of an electronic device, the substrate is processed to produce an electron beam transmitting film. As a method for processing a substrate, focused ion beam (FIB) processing (Non-Patent Document 1), wet etching processing using a photolithography method (Patent Document 1), and the like are known. In addition, the membrane is also used as an electron beam transmitting membrane (Patent Document 2).

Japanese Unexamined Patent Publication No. 2010-61812 Japanese Unexamined Patent Publication No. 2006-219314

L. A Giannuzzi, and F. A. Stevie, A review of focused ion beam milling techniques for TEM specimen preparation, Micron 30 (1999) 197-204.

However, all of the above methods have a problem that the processing time for producing the electron beam transmitting film is long. In addition, both methods require large-scale equipment for processing and require capital investment. The method using the photolithography method has many processing processes and is complicated, and there is a possibility of contamination by a resist or the like used as a mask.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an electron beam transmitting membrane that can be easily manufactured and is inexpensive.

As a result of diligent studies, the present inventors have found that an electron beam transmitting film can be obtained easily and at low cost by using a local plasma etching technique. It was also found that the structure prepared by using the local plasma etching technique can be used as an electron beam transmitting film.
The present invention provides the following means for solving the above problems.

(1) The electron beam transmitting film according to the first aspect has a recess formed from the first surface of the base substrate toward the facing second surface, the recess has a curved surface, and the recess has a curved surface. The thickness of the bottom portion and the second surface is equal to or less than the thickness through which the electron beam can pass.

(2) In the electron beam transmitting film according to the above aspect, the thickness of the bottommost portion of the recess and the second surface may be 200 nm or less.

(3) In the electron beam transmitting film according to the above aspect, the substrate may be a semiconductor substrate having an insulator layer on the second surface side.

(4) In the electron beam transmission film according to the above embodiment, the insulator layer may be silicon oxide or silicon nitride, and the semiconductor substrate may be a silicon substrate.

(5) The electronic device according to the second aspect includes the electron beam transmitting film according to the above aspect and an element portion provided on the second surface on which the recess of the electron beam transmitting film is not formed.

The electron beam permeable membrane according to the above aspect can be easily produced and is low in cost.

It is sectional drawing of the electron beam transmission membrane which concerns on this embodiment. It is a figure which showed schematically the manufacturing process of the electron beam transmission film which concerns on this embodiment. It is sectional drawing of the electron beam transmission film which has the recess made by wet etching using the photolithography method. It is sectional drawing of the electronic device which concerns on this embodiment. It is a photograph of the electron beam transmission film produced in Example 1. It is a figure which observed the metal wiring M through an electron beam transmission film in Example 1. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

"Electron beam transmission membrane"
FIG. 1 is a schematic cross-sectional view of an electron beam transmitting membrane according to the present embodiment. The electron beam transmitting film 10 shown in FIG. 1 is a substrate 1 on which a recess 4 is formed. The recess 4 is formed from the first surface 1a of the substrate 1 toward the facing second surface 1b. The recess 4 has a bowl-shaped curved surface 4a. In FIG. 1, the substrate 1 is composed of a semiconductor substrate 2 and an insulator layer 3. The insulator layer 3 is provided on the second surface 1b side of the substrate 1.

The electron beam transmission film 10 according to the present embodiment is manufactured by a local plasma etching technique. The curved surface 4a of the recess 4 has a structure peculiar to that manufactured by the local plasma etching technique.

The local plasma etching technique is a technique that can perform local processing with a submillimeter diameter by using plasma without leaving a residue on the sample. This method also has an advantage that the temperature rise of the object to be processed can be suppressed and damage can be reduced.

FIG. 2 is a diagram schematically showing the manufacturing process of the electron beam transmitting film 10 according to the present embodiment. Local plasma etching technology has a process of preparing a capillary having an electrode that can apply high frequency, a process of bringing one end of this capillary close to the processing target, and a process of introducing etching gas into the capillary and applying high frequency to plasma. It has a step of generating it. Hereinafter, a specific description will be given.

First, as shown in FIG. 2, a capillary 12 having a cylindrical electrode 11 connected to a power source 13 to which alternating current can be applied is prepared. Alumina or the like can be used for the capillary 12.

Next, the first end 12a of the capillary is brought close to the first surface 1a of the substrate 1 to be processed. Etching gas is introduced into the capillary 12 and sucked into the second end 12b side of the capillary 12. That is, the etching gas produces a gas flow from the first end 12a of the capillary 12 toward the second end 12b. In FIG. 2, the flow of the gas flow is shown as an arrow.

When a current is applied to the electrode 11 by the power supply 13, a high frequency is generated. The etching gas in the capillary 12 to which a high frequency is applied is turned into plasma. A part of the generated plasma P seeps out from the first end 12a of the capillary 12 against the gas flow, and locally etches the first surface 1a of the substrate 1.

The local etching proceeds so as to strip the atoms one layer at a time from the first surface 1a of the substrate 1. Therefore, the corners formed in the etching process gradually disappear, and a bowl-shaped curved surface 4a is formed. The progress of etching is confirmed by the camera 14. Etching ends when the camera detects light of a specific wavelength among the light generated by plasma emission. The light generated by plasma emission is detected by the camera in order from the long wavelength light. Therefore, the depth of the recess 4 can be freely set by setting which wavelength is detected when the etching is stopped.

When the local etching method is used, a Si substrate having a thickness of about 500 μm can be penetrated in about 20 minutes, and the recess 4 can be formed extremely easily and quickly. The formation speed of the recess 4 can be freely designed by adjusting the etching gas type, the etching gas supply speed, the intensity of the applied high frequency, the degree of vacuum in the processing environment, and the like.

FIG. 3 is a cross-sectional view of an electron beam transmitting film having recesses produced by wet etching using a photolithography method. The point that the electron beam transmission film 20 shown in FIG. 3 has a recess 24 formed from the first surface 21a to the second surface 21b of the substrate 21 including the semiconductor substrate 22 and the insulator layer 23 is shown in FIG. It is the same as the electron beam transmission membrane 10 which concerns on this embodiment shown. On the other hand, the cross-sectional view shape of the recess 24 is trapezoidal, and the difference is that the surface 24a forming the recess 24 is not a curved surface.

In the photolithography method, a protective film such as a resist is provided at a place other than the portion where the recess 24 is desired to be opened, and the etching process is performed. The etching rate in the opening of the resist is substantially constant except in the vicinity of the resist. Therefore, when the photolithography method is used, the shape of the recess 24 is in principle trapezoidal, and the curved surface 4a of the recess 4 shown in FIG. 1 is not formed.

The photolithography method requires various steps such as coating, exposure, development, and resist peeling. Therefore, a long time is required to form the recess 24, which is high cost.

As described above, the recess 4 of the electron beam transmitting film 10 according to the present embodiment has a curved surface 4a peculiar to the manufacturing method. In other words, the fact that the electron beam transmitting film 10 has a curved surface 4a means that the thinnest portion of the electron beam transmitting film 10 is supported by the arch-shaped substrate 1. As seen in the shape of the pier, the arch shape is the structure that can most efficiently support the load from above to below, and can suppress the deflection of the thinnest part. When the deflection of the thinnest part is suppressed, the area of the thinnest part can be increased. The thinnest part is the most important as the electron beam transmitting film 10, and it is extremely important in the electron beam transmitting film that the area of the thinnest part can be widened.

Further, the electron beam passes between the recess 4 of the electron beam transmitting film 10 and the second surface 2b. Therefore, as shown in FIG. 1, the thickness d between the bottommost portion 4b of the recess 4 and the second surface 2b of the substrate 1 is equal to or less than the thickness through which the electron beam can pass. The thickness through which the electron beam can pass varies depending on the intensity of the irradiated electron beam and the like.

Specifically, the thickness d between the bottommost portion 4b of the recess 4 and the second surface 2b of the substrate 1 is preferably 200 nm or less, more preferably 150 nm or less, and further preferably 120 nm or less. preferable. Further, if the thickness d is too thin, the strength of the electron beam transmitting film 10 is lowered, so that the thickness d is preferably 10 nm or more, more preferably 30 nm or more, still more preferably 50 nm or more.

The thickness d between the bottommost portion 4b of the recess 4 and the second surface 2b of the substrate 1 can be measured using a laser microscope. When the concave portion 4 is observed using a laser microscope, an optical interference film can be seen. The optical interference film is generated by the interference between the light reflected by the curved surface 4a of the recess 4 and the light reflected by the second surface 1b of the substrate 1. Assuming that the wavelength of the incident light is λ, the refractive index of the substrate 1 is n, and the diffraction time is m, the thickness d _L in the bright ring portion is obtained by d _L = (m + 1/2) × λ / 2n, and the dark ring portion is obtained. The thickness d _{D in} is _{obtained by d D} = m × λ / 2n.

Further, the thickness d between the bottommost portion 4b of the recess 4 and the second surface 2b of the substrate 1 may be obtained from the intensity of the transmitted light incident on the camera 14 at the time of fabrication. The relationship between the intensity of the transmitted light and the thickness d is obtained by measuring the transmittance for each wavelength in advance. Generally, if the intensity of transmitted light is I, the intensity of incident light is I ₀ , the absorption coefficient of substrate 1 is α, and the film thickness is d, the relationship of _{I = I 0} e − ^{αd holds.}

The position of the bottommost portion 4b of the recess 4 can be arbitrarily set. From the viewpoint of ease of electron beam transmission, it is preferable that the bottommost portion 4b of the recess 4 reaches the insulator layer 3. This is because when an electron beam is transmitted through a substance having a different refractive index, the electron beam is refracted at the interface. On the other hand, from the viewpoint of increasing the strength of the electron beam transmitting film 10, it is preferable that the bottommost portion 4b of the recess 4 does not reach the insulator layer 3. When the semiconductor substrate 2 is removed, the compressive stress of the remaining insulator layer 3 is released, and buckling may occur.

The substrate 1 is not limited to the semiconductor substrate 2 shown in FIG. 1 and the insulator layer 3. For example, it may be a single-layer substrate or a multi-layer substrate having two or more layers. Further, the present invention is not limited to semiconductors and insulators, and may have a metal layer. On the other hand, from the viewpoint of suppressing the scattering of electron beams, it is preferable not to include the metal layer.

As shown in FIG. 1, when the substrate 1 has the semiconductor substrate 2 and the insulator layer 3, the electron beam transmission film 10 can be easily incorporated into the electronic device. As the semiconductor substrate 2, a known semiconductor such as a Si substrate can be used. When the substrate is silicon, silicon oxide (SiO ₂ ), silicon nitride (SiN), or the like can be used for the insulator layer 3.

As described above, the electron beam transmission film 10 according to the present embodiment can be easily manufactured by using a local plasma etching technique, and is low in cost. Further, since the concave portion 4 of the electron beam transmitting film 10 has the curved surface 4a, the deflection of the thinnest portion can be suppressed.

"Electronic device"
FIG. 4 is a schematic cross-sectional view of the electronic device according to the present embodiment. The electronic device 100 shown in FIG. 4 includes an electron beam transmitting film 10 shown in FIG. 1 and an element portion 30 provided on a second surface 1b in which a recess 4 of the electron beam transmitting film 10 is not formed.

The element unit 30 shown in FIG. 4 is a transistor including a source electrode 31, a drain electrode 32, a semiconductor region 33, and a gate electrode 34. The gate electrode 34 controls the electrons flowing in the semiconductor region 33 between the source electrode 31 and the drain electrode 32.

In the electronic device 100 shown in FIG. 4, the dynamic change of the semiconductor region 33 can be observed from the first surface 1a side of the electron beam transmitting film 10 by using a transmission type electron beam microscope. In an electron microscope, an electron beam is applied to the observation target. Since the electron beam transmitting film 10 has the recess 4, the electron beam can be transmitted through the electron beam transmitting film 10. Therefore, even if the electron beam has the electron beam transmitting film 10, the dynamic change of the semiconductor region 33 can be observed.

In the case of the electronic device 100 shown in FIG. 4, it is preferable to provide the insulator layer 3 on the second surface 2b of the substrate 1 in order to avoid the influence from the outside on the semiconductor region 33.

As described above, since the electronic device 100 according to the present embodiment has the electron beam transmitting film 10, the state of the element unit 30 can be observed via the electron beam transmitting film 10.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments and varies within the scope of the gist of the present invention described in the claims. Can be transformed / changed.

For example, the element unit 30 is not limited to the transistor shown in FIG. 4, and any element can be used. For example, MEMS, sensors, batteries, actuators, micropumps, biochips, microchannels, micropower generation, vibration power generation elements, memories, analysis electrodes and the like can be used.

When the electron beam permeable membrane 10 is used as a partition wall for elucidating the reaction mechanism of a biomolecule or a virus, the electron beam permeable membrane 10 may be used alone.

"Example 1"
First, a 380 μm-thick Si substrate having a 280 nm-thick SiO _{2 film on the surface is prepared.} The SiO ₂ film is produced by thermal oxidation.

Further, as shown in FIG. 2, an alumina capillary 12 having a first end 12a narrowed to an inner diameter of 1 mm is prepared. The capillary 12 is provided with a cylindrical electrode 11 connected to a power source 13 to which alternating current can be applied. Then, the first end 12a of the capillary 12 is installed at a position close to the prepared Si substrate by about 0.1 mm.

Etching gas is supplied into the chamber using a mass flow controller. Fluorocarbon was used as the etching gas. Fluorocarbon may be mixed and diluted with a rare gas such as Ar, but here, it is used without dilution. The capillary 12 is exhausted from the second end 12b side, and a gas flow from the first end 12a to the second end 12b is formed.

Next, a high frequency of 13.56 MHz was applied to the electrode 11 to turn the etching gas into plasma. The plasma is localized between the first end 12a of the capillary and the prepared Si substrate within a range of about the inner diameter of the first end 12a, and the localized etching proceeds.

The progress of etching was monitored by the camera 14 on the _{two sides of the SiO through a short pass filter.} Then, when only the wavelength of 440 nm or less of the plasma emission was transmitted with a constant intensity, the etching was stopped. The time required for the etching process was about 20 minutes.

FIG. 5 is a photograph of the electron beam transmitting membrane produced in Example 1. FIG. 5A is an overall image of the recess taken from an oblique direction, and FIG. 5B is an image of a cross section of the electron beam transmitting film taken with a scanning electron microscope (SEM). The opening diameter of the recess was 1.2 mm, and the depth was about 380 μm.

Further, the thickness between the bottom of the recess and the unprocessed surface of the substrate was determined from the optical interference film observed with a laser microscope. The thickness between the bottom of the recesses, which can be clearly recognized from the bright and dark rings, and the unprocessed surface of the substrate was 69 nm to 120 nm.

Elemental analysis in the vicinity of the recess was also performed using a Raman microscope (excitation wavelength 488 nm) and an energy dispersive X-ray (EDX) analyzer. As a result, the presence of _{SiO 2} was confirmed within the range of 50 μm in diameter. The fact that SiO ₂ is confirmed indicates that the Si substrate has been removed. That is, this result is consistent with the result of the depth of the recess and the thickness between the bottom of the recess and the unprocessed surface of the substrate.

Then, the prepared electron beam transmission film was placed on the substrate on which the metal wiring was made, and observed with a scanning electron microscope. FIG. 6A is a view of observing a substrate on which a metal wiring M is manufactured via an electron beam transmitting film with visible light, and FIG. 6B is a diagram in which a metal wiring M is manufactured via an electron beam transmitting film. It is an SEM diagram which observed the substrate with an electron beam.

Since the Si substrate can transmit visible light, the metal wiring M can be confirmed at any place as shown in FIG. 6A. On the other hand, in the electron beam, the metal wiring M can be confirmed in the portion where the recess is provided. In other words, the structure produced in Example 1 can transmit an electron beam in the recess and can be used as an electron beam transmitting film.

1,21 ... Substrate, 1a, 21a ... First surface, 1b, 21b ... Second surface, 2,22 ... Semiconductor substrate, 3,23 ... Insulator layer, 4,24 ... Recessed, 4a ... Curved surface, 24a ... Surface, 4b ... bottom, 11 ... electrode, 12 ... capillary, 12a ... first end, 12b ... second end, 13 ... power supply, 14 ... camera, 30 ... element part, 31 ... source electrode, 32 ... drain electrode, 33 ... semiconductor area, 34 ... gate electrode, P ... plasma, M ... metal wiring

Claims (4)

It has a substrate with a semiconductor substrate and an insulator layer,
The substrate has a recess formed from the first surface of the substrate toward the facing second surface.
The recess has a curved surface and has a curved surface.
The curved surface is formed from the semiconductor substrate to the insulator layer.
An electron beam transmitting film in which the thickness of the bottommost portion of the recess and the second surface is equal to or less than the thickness through which an electron beam can pass. The electron beam transmitting film according to claim 1, wherein the thickness of the bottommost portion of the recess and the second surface is 200 nm or less. The electron beam transmission film according to claim 2, wherein the insulator layer is silicon oxide or silicon nitride, and the semiconductor substrate is a silicon substrate. And electron-ray transparent film,
The element portion provided on the second surface on which the concave portion of the electron beam transmitting film is not formed is provided .
The electron beam transmitting film has a recess formed from the first surface of the substrate toward the facing second surface.
The recess has a curved surface and has a curved surface.
An electronic device in which the thickness of the bottommost portion of the recess and the second surface is equal to or less than the thickness through which an electron beam can pass.

Images