JP7199677B2 - Local plasma device - Google Patents

Description

The present invention relates to local plasma devices.

Electron beam permeable films are used in various applications. For example, it is used to elucidate the behavior of electronic devices at the atomic level. Electronic devices are generally formed on a substrate, and electron beams cannot pass through the substrate if the substrate is too thick. Therefore, by thinning a part of the substrate and forming an electron beam transparent film, it becomes possible to measure the operation of the electronic device using a transmission electron microscope.

Electron beam permeable membranes are also used to elucidate reaction mechanisms of biomolecules and viruses. Biomolecules and viruses may die under high vacuum. Therefore, elucidation of these reaction mechanisms is being carried out by irradiating biomolecules and viruses with electron beams generated in a high-vacuum region through 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 transmissive film. As a substrate processing method, focused ion beam (FIB) processing (Non-Patent Document 1), wet etching processing using photolithography (Patent Document 1), and the like are known. In addition, the use of a membrane as an electron beam transmission film has also been carried out (Patent Document 2).

Japanese Patent Application Laid-Open No. 2010-61812 JP 2006-219314 A

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 the problem that the processing time for producing the electron beam transmissive film is long. In addition, both methods require large-scale equipment for processing, and require capital investment. The method using photolithography involves many complicated processing steps, and there is a possibility of contamination due to the resist used as a mask.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electron beam permeable film that can be easily manufactured at a low cost.

As a result of intensive studies, the inventors have found that an electron beam transmitting film can be obtained simply and at low cost by using local plasma etching technology. In addition, the inventors have found that a structure fabricated using a localized plasma etching technique can be used as an electron beam transmitting film.
In order to solve the above problems, the present invention provides the following means.

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

(2) In the electron beam transmissive film according to the aspect described above, the thickness between 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 aspect described above, the substrate may be a semiconductor substrate having an insulator layer on the second surface side.

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

(5) An electronic device according to a second aspect includes the electron beam permeable film according to the above aspect, and an element section provided on the second surface of the electron beam permeable film where the concave portion is not formed.

The electron beam permeable film according to the above aspect can be easily produced at a low cost.

It is a cross-sectional schematic diagram of the electron beam permeable film concerning this embodiment. It is the figure which showed typically the manufacturing process of the electron beam permeable film concerning this embodiment. FIG. 4 is a cross-sectional view of an electron beam transmitting film having recesses produced by wet etching using a photolithographic method; It is a cross-sectional schematic diagram of the electronic device concerning this embodiment. 1 is a photograph of an electron beam transparent film produced in Example 1. FIG. 4 is a view of metal wiring M observed through an electron beam transparent film in Example 1. FIG.

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

"Electron beam transparent membrane"
FIG. 1 is a schematic cross-sectional view of an electron beam transparent film according to this embodiment. The electron beam transmissive film 10 shown in FIG. 1 is the substrate 1 in which the concave portion 4 is formed. The concave portion 4 is formed from the first surface 1a of the substrate 1 toward the opposing second surface 1b. The recess 4 has a bowl-shaped curved surface 4a. In FIG. 1, a substrate 1 consists 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 transmissive film 10 according to this embodiment is produced by local plasma etching technology. The curved surface 4a of the concave portion 4 has a structure unique to those manufactured by the local plasma etching technique.

Local plasma etching technology is a technology that enables local processing with a submillimeter diameter without leaving residue on the sample using plasma. This method also has the advantage of suppressing the temperature rise of the object to be processed and reducing the damage.

FIG. 2 is a diagram schematically showing the manufacturing process of the electron beam transmissive film 10 according to this embodiment. The local plasma etching technique involves the steps of preparing a capillary having an electrode capable of applying high frequency waves, bringing one end of this capillary close to the object to be processed, introducing an etching gas into the capillary, and applying high frequency waves to generate plasma. and generating. A specific description will be given below.

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

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

When a current is applied to the electrode 11 by the power source 13, a high frequency is generated. The etching gas in the capillary 12 to which the high frequency is applied is turned into plasma. Part of the generated plasma P oozes 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 atoms from the first surface 1a of the substrate 1 layer by layer. Therefore, the corners formed in the etching process are gradually eliminated, and a bowl-shaped curved surface 4a is formed. The progress of etching is confirmed by the camera 14 . Etching is terminated when the camera detects light of a specific wavelength out of the light generated by the plasma emission. Light generated by plasma emission is detected by a camera in order from light with a longer wavelength. Therefore, the depth of the concave portion 4 can be freely set by setting which wavelength is detected to stop the etching.

By using the local etching method, a Si substrate having a thickness of about 500 μm can be penetrated in about 20 minutes, and the concave portion 4 can be formed very simply and quickly. The formation speed of the recesses 4 can be freely designed by adjusting the type of etching gas, the supply speed of the etching gas, the intensity of the applied high frequency, the degree of vacuum of the processing environment, and the like.

FIG. 3 is a cross-sectional view of an electron beam transmissive film having recesses produced by wet etching using a photolithography method. The electron beam transmitting film 20 shown in FIG. 3 has a concave portion 24 formed from the first surface 21a toward the second surface 21b of the substrate 21 including the semiconductor substrate 22 and the insulator layer 23, as shown in FIG. It is the same as the electron beam transparent film 10 according to the present embodiment shown. On the other hand, the cross-sectional 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 on a portion other than the portion where the concave portion 24 is to be opened, and an etching process is performed. The etching rate inside the opening of the resist is substantially constant except for the vicinity of the resist. Therefore, when the photolithographic method is used, the shape of the recess 24 is basically trapezoidal, and the curved surface 4a of the recess 4 shown in FIG. 1 is not formed.

Photolithography requires various steps such as resist coating, exposure, development, and resist stripping. Therefore, it takes a long time to form the concave portion 24, resulting in high cost.

As described above, the concave portion 4 of the electron beam transparent film 10 according to this embodiment has the curved surface 4a unique to the manufacturing method. In other words, the fact that the electron beam transparent film 10 has the curved surface 4 a means that the thinnest part of the electron beam transparent film 10 is supported by the arch-shaped substrate 1 . As can be seen in the shape of the bridge piers, the arch shape is the structure that can most efficiently support the load from above to below, and it is possible to suppress the deflection of the thinnest part. If the deflection of the thinnest portion is suppressed, the area of the thinnest portion can be increased. The thinnest portion of the electron beam transmitting film 10 is most important, and it is extremely important for the electron beam transmitting film to be able to increase the area of the thinnest portion.

Further, the electron beam is transmitted between the concave portion 4 of the electron beam permeable film 10 and the second surface 1b . Therefore, as shown in FIG. 1, the thickness d between the bottommost portion 4b of the recess 4 and the second surface 1b of the substrate 1 is less than or equal to 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 electron beam to be irradiated.

Specifically, the thickness d between the bottommost portion 4b of the recess 4 and the second surface 1b of the substrate 1 is preferably 200 nm or less, more preferably 150 nm or less, and 120 nm or less. More preferred. If the thickness d is too thin, the strength of the electron beam transmitting film 10 is lowered.

The thickness d between the bottommost portion 4b of the recess 4 and the second surface 1b of the substrate 1 can be measured using a laser microscope. Observation of the concave portion 4 using a laser microscope reveals an optical interference film. The light interference film is produced by interference between the light reflected by the curved surface 4 a of the concave portion 4 and the light reflected by the second surface 1 b 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 number of diffraction times is m, the thickness d _L in the light ring portion is obtained by d _L =(m+1/2)×λ/2n. The thickness d _D in is obtained by d _D =m×λ/2n.

Also, the thickness d between the bottommost portion 4b of the concave portion 4 and the second surface 1b of the substrate 1 may be obtained from the intensity of transmitted light incident on the camera 14 during fabrication. The relationship between the intensity of transmitted light and the thickness d can be obtained by measuring the transmittance for each wavelength in advance. In general, where I is the intensity of transmitted light, I ₀ is the intensity of incident light, α is the absorption coefficient of the substrate 1, and d is the film thickness, the relationship I=I ₀ e ^-αd holds.

The position of the bottom 4b of the recess 4 can be set arbitrarily. It is preferable that the lowest portion 4b of the concave portion 4 reaches the insulator layer 3 from the viewpoint of ease of electron beam transmission. This is because the electron beam is refracted at the interface when the electron beam passes through substances having different refractive indices. On the other hand, from the viewpoint of increasing the strength of the electron beam transmissive film 10, it is preferable that the bottommost portion 4b of the concave portion 4 does not reach the insulator layer 3. FIG. When the semiconductor substrate 2 is removed, the compressive stress of the remaining insulator layer 3 is released and may buckle.

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

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

As described above, the electron beam transmissive film 10 according to this embodiment can be easily manufactured using the local plasma etching technique and is inexpensive. Further, since the concave portion 4 of the electron beam transparent film 10 has the curved surface 4a, the bending of the thinnest portion can be suppressed.

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

The element section 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 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, dynamic changes in the semiconductor region 33 can be observed from the first surface 1a side of the electron beam transmissive film 10 using a transmission electron microscope. In an electron microscope, an electron beam is applied to an object to be observed. The electron beam transmissive film 10 has the concave portion 4 so that the electron beam can pass therethrough. Therefore, the electron beam can observe dynamic changes in the semiconductor region 33 even with the electron beam permeable film 10 .

In the case of the electronic device 100 shown in FIG. 4, the insulator layer 3 is preferably provided on the second surface 1b of the substrate 1 in order to avoid external influences on the semiconductor region 33. As shown in FIG.

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

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to specific embodiments, and various can be transformed or changed.

For example, the element section 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.

Further, when the electron beam permeable film 10 is used as a partition for clarifying the reaction mechanism of biomolecules and viruses, the electron beam permeable film 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 _SiO2 film is produced by thermal oxidation.

Also, as shown in FIG. 2, an alumina capillary 12 having a first end 12a constricted to an inner diameter of 1 mm is prepared. The capillary 12 is provided with a cylindrical electrode 11 connected to a power supply 13 capable of applying alternating current. Then, the first end 12a of the capillary 12 is placed at a position about 0.1 mm away from the prepared Si substrate.

An etching gas is supplied into the chamber using a mass flow controller. Carbon fluoride was used as an etching gas. Carbon fluoride may be mixed and diluted with a rare gas such as Ar, but here it is used without being diluted. The capillary 12 is evacuated from the second end 12b side, and a gas flow is formed from the first end 12a toward the second end 12b.

Then, 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 in a range about the inner diameter of the first end 12a, and localized etching proceeds.

The progress of etching was monitored with a camera 14 through a short-pass filter on the _SiO2 surface. Etching was stopped when only the wavelength of 440 nm or less of the plasma emission was transmitted with a constant intensity. The time required for the etching process was about 20 minutes.

FIG. 5 is a photograph of the electron beam transparent film produced in Example 1. FIG. FIG. 5(a) is an overall image of the concave portion photographed from an oblique direction, and FIG. 5(b) is an image of the cross section of the electron beam transmissive film photographed with a scanning electron microscope (SEM). The recess had an opening diameter of 1.2 mm and a depth of about 380 μm.

Also, the thickness between the bottommost portion of the recess and the non-processed surface of the substrate was determined from the optical interference film observed with a laser microscope. The thickness between the bottom of the recess and the unprocessed surface of the substrate, determined from the clearly recognizable light and dark rings, was 69 nm to 120 nm.

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

Then, the prepared electron beam transparent film was placed on the substrate on which the metal wiring was prepared, and observed with a scanning electron microscope. FIG. 6(a) is a view of the substrate on which the metal wiring M is formed through the electron beam transparent film, observed with visible light, and FIG. 6(b) is a diagram showing the metal wiring M formed through the electron beam transparent film. It is the SEM figure which observed the board|substrate which carried out with the electron beam.

Since the Si substrate can transmit visible light, the metal wiring M can be confirmed anywhere as shown in FIG. 6(a). On the other hand, for 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 electron beams in the recesses and can be used as an electron beam transmitting film.

DESCRIPTION OF SYMBOLS 1, 21... Substrate 1a, 21a... First surface 1b, 21b... Second surface 2, 22... Semiconductor substrate 3, 23... Insulator layer 4, 24... Concave part 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 region, 34... Gate electrode, P... Plasma, M... Metal wiring

Claims (3)

a plasma generator capable of introducing an etching gas into the interior thereof and converting the etching gas into plasma;
a camera for observing the state of the workpiece processed by the plasma generator ,
The local plasma apparatus , wherein the camera is arranged on the side of the second surface facing the first surface to be processed of the workpiece . 2. The local plasma apparatus according to claim 1, wherein said plasma generator stops plasmatification of said etching gas when said camera detects light of a specific wavelength among the light generated by said plasmatization. 2. The local plasma apparatus according to claim 1, wherein said plasma generator stops turning said etching gas into plasma when the intensity of incident light incident on said camera reaches a predetermined value.

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