JP5462737B2 - Substrate on which graphene film is grown and electronic / optical integrated circuit device using the same - Google Patents

Description

  The present invention relates to the use of graphene as an electronic / optical device, and more particularly to a substrate on which a graphene film is grown and an electronic / optical integrated circuit device using the same.

Graphene (also referred to as graphene sheet) is a six-membered ring sheet in which benzene rings are spread on a two-dimensional plane, and does not constitute a closed curved surface. A carbon nanotube is formed by rounding graphene into a cylindrical shape to form a closed curved surface, and graphite is formed by stacking a large number of graphenes. Each carbon atom of graphene forms sp ² hybrid orbitals, and delocalized electrons exist above and below the sheet.

The physical properties of graphene are as follows: (1) The carrier mobility is about 200,000 cm ² / Vs, an order of magnitude higher than that of silicon (Si) crystals, which exceeds that of metals and carbon nanotubes. (2) Nanodevices It has been reported that peculiar 1 / f noise can be greatly reduced, (3) exhibiting a negative refractive index, and (4) electrons on graphene behave as if the mass is zero. From these features, graphene is regarded as a promising new material for “Post-Si”.

In order to realize an electronic / optical device using graphene, a substrate on which graphene is formed is necessary. As a technique for forming graphene on the surface of a substrate, Non-Patent Document 1 reports a method of peeling a graphene film from a highly oriented graphite crystal using an adhesive tape and rubbing (transferring) the substrate. Non-Patent Document 2 reports a method of forming a nanographite layer on a platinum substrate by chemical vapor deposition using a custom-made ultrahigh vacuum apparatus. In Non-Patent Document 3, a (111) _SiC face-oriented cubic silicon carbide (3C-SiC) thin film (thickness 80 nm) is grown on a silicon (110) _Si face substrate. A method of thermal reforming in a high vacuum has been reported.

K. S. NOVOSELOV, A. K. GEIM, S. V. MOROZOV, D. JIANG, M. I. KATSNELSON, I. V. GRIGORIEVA, S. V. DUBONOS, and A. A. FIRSOV: “Two-dimensional gas of massless Dirac fermions in graphene”, Nature 438, 197 (2005) Shiro ENTANI, Susumu IKEDA, Manabu KIGUCHI, Koichiro SAIKI, Genki YOSHIKAWA, Ikuyo NAKAI, Hiroshi KONDOH, and Toshiaki OHTA: “Growth of nanographite on Pt (111) and its edge state”, Appl. Phys. Lett. 88, 153126 ( 2006). Yu Miyamoto, Yuki Suematsu, Hiroyuki Handa, Atsushi Imano: Graphene and graphite formation by thermal modification of 3C-SiC thin film on Si substrate, Proceedings of the 69th Japan Society of Applied Physics (2008 Autumn Chubu University), p. .808.

  However, although the forming method described in Non-Patent Document 1 seems to be simple as an experimental method, it is difficult to increase the area and is not a method that can be adopted industrially. The formation method described in Non-Patent Document 2 has an advantage that a film can be formed at a relatively low temperature (room temperature to 850 K), but has a problem of manufacturing cost because a special ultrahigh vacuum apparatus is used. The formation method described in Non-Patent Document 3 is an excellent method in that a film can be formed on a Si substrate, but it requires high-temperature heat treatment (about 1350 ° C.) in an ultra-high vacuum. There are material limitations and manufacturing cost disadvantages.

  Further, in order to use a graphene film as a circuit conductor in an electro-optical device, a combination of a technique for growing a continuous graphene film with secured electrical continuity and a technique for forming a circuit pattern using a graphene film, or At least a technique for selectively growing a continuous graphene film at a desired position (for example, a circuit pattern) for forming a device is required.

  Accordingly, an object of the present invention is to provide a substrate on which a graphene film is selectively grown at a desired position and an electronic / optical integrated circuit device using the same, in order to meet the above-mentioned problems / requirements.

One aspect of the present invention has the following features in order to achieve the above object.
(1) The present invention is a substrate on which a graphene film composed of a single layer or a plurality of layers is grown,
An aluminum oxide film is present on the surface of the substrate facing the graphene film, the composition of the aluminum oxide film is Al _2-x O _{3 + x} (x ≧ 0), and the graphene film is the aluminum oxide film The graphene film has an electrical conductivity of 1 × 10 ⁴ S / cm when the electrical conductivity is measured under the condition that the distance between the voltage terminals is 0.2 mm. A substrate on which a graphene film is grown is provided.

  In the present invention, the “graphene film consisting of a plurality of layers” is defined as a graphene film consisting of 20 or less graphene sheets. This is because when the number of layers exceeds 20, various physical properties (for example, electron mobility) are almost the same as those of bulk graphite, and the characteristics as graphene become dilute. More preferably, the graphene film has 10 layers or less. The term “parallel to the surface of the aluminum oxide film” as used in the present invention means to be parallel to the surface when viewed from a macro viewpoint (for example, on the order of 1 μm or more). In other words, it means parallel to the surface assuming that the unevenness at the microscopic viewpoint (order of less than 1 μm, for example, 10 nm order or less) is averaged. In addition, “fluctuation from parallel” caused by fine unevenness at the atomic level on the substrate surface is allowed.

In order to achieve the above object, the present invention can add the following improvements and changes to the substrate on which the graphene film according to the invention of (1) is grown.
(I) The graphene film is composed of a plurality of graphene domains, and the average size of the graphene domains is 25 nm or more.
(Ii) The interlayer distance between the atomic layer of the graphene film adjacent to the aluminum oxide film and the atomic layer of the aluminum oxide film adjacent to the graphene film is 0.34 nm or less. In the present invention, the “atom” includes a case where the element is an ion.
(Iii) The arithmetic average surface roughness Ra of the aluminum oxide film is 1 nm or less. In the present invention, the “surface” of “arithmetic average surface roughness” means the surface of the aluminum oxide film before the graphene film is grown. For a substrate on which the graphene film is grown, the “graphene film” ”And“ aluminum oxide film ”.
(Iv) The maximum surface height Rz of the aluminum oxide film is 10 nm or less. As used in the above (iv), the “surface” of the “maximum surface height” in the present invention means the surface of the aluminum oxide film before the graphene film is grown, and the substrate on which the graphene film is grown In this case, it means the interface between the “graphene film” and the “aluminum oxide film”.
(V) The average thickness of the aluminum oxide film is 10 nm or more and 500 nm or less.
(Vi) The substrate is a silicon single crystal substrate on which a silicon oxide film is formed.
(Vii) A circuit pattern is formed on the aluminum oxide film, and a minimum dimension of the circuit pattern is less than 1 μm.
(Viii) The circuit pattern is formed by reactive ion etching.
(Ix) The area of the substrate is 20 cm ² or more. In addition, the area of a board | substrate shall mean the area of one main surface.
(X) An electronic / optical integrated circuit device using a substrate on which the graphene film is grown.
(Xi) The electronic / optical integrated circuit device uses the graphene as a channel of a field effect transistor, a light emitting device, a light receiving device, and a circuit wiring.

Another aspect of the present invention has the following characteristics in order to achieve the above object.
(2) The present invention is a method for manufacturing a substrate in which a graphene film composed of a single layer or a plurality of layers is grown in parallel to the surface of the substrate,
A silicon single crystal substrate having a silicon oxide film formed on the surface is used as the substrate, and an aluminum oxide film having a composition of Al _2-x O _{3 + x} (x ≧ 0) serving as a base of the graphene film is provided at least on the substrate. The “underlayer forming step” formed on one outermost surface, the “circuit patterning step” for processing the aluminum oxide film into a desired circuit pattern, and the graphene film by the chemical vapor deposition method using a carbon-containing compound as a raw material There is provided a method for manufacturing a substrate on which a graphene film is grown, characterized by comprising a “graphene film forming step” for forming a film only on a circuit pattern.

In order to achieve the above object, the present invention can add the following improvements and changes to the method for manufacturing a substrate on which the graphene film according to the invention of (2) is grown.
(Xii) The “circuit patterning step” is reactive ion etching using CHF ₃ gas.
(Xiii) Before the “graphene film forming step”, the method further includes a “surface flattening step” for processing the arithmetic average surface roughness Ra of the aluminum oxide film to be 1 nm or less.
(Xiv) The chemical vapor deposition method of the “graphene film forming step” is a method in which acetylene, propylene, or methane is used as the raw material and is grown in a non-oxidizing atmosphere at a temperature of 750 to 1000 ° C. for 0.1 to 10 minutes. . Note that the non-oxidizing atmosphere means an atmosphere inert to oxidation (for example, an atmosphere substantially free of oxygen such as vacuum, nitrogen, argon, or the like).

  According to the present invention, it is possible to realize a substrate at a low cost by selectively growing a continuous graphene film in which electrical continuity is ensured at a desired position on the substrate. In addition, an electronic / optical integrated circuit device using a substrate on which the graphene film is grown can be provided.

It is a cross-sectional schematic diagram which shows the example of a manufacture procedure of the board | substrate with which the graphene film which concerns on embodiment of this invention was grown. It is a graph which shows an example of the light transmission spectrum of the grown graphene film. It is a map which shows an example of the in-plane distribution measurement result (100 nm angle | corner) of the electrical conduction of the board | substrate with which the graphene film was grown. It is an example of the graph which shows the relationship between the growth time in the growth temperature of 800 degreeC, and the average number of layers of a graphene film. It is an example of the graph which shows the relationship between the growth time in the growth temperature of 900 degreeC, and the average number of layers of a graphene film. It is the graph which showed the relationship between the average domain size of a graphene film, and the composition ( _{x in} Al2 _{-xO3 +} x) of an aluminum oxide film. It is a graph which shows the relationship between the average domain size of a graphene film, and electrical conductivity and electrical resistivity. It is a graph which shows one example of the relationship between the etching time by the reactive ion etching of the aluminum oxide film and silicon thermal oxide film which concerns on this invention, and an etching depth. 1 is a schematic perspective view showing an example of an electronic / optical integrated circuit device using a substrate on which a graphene film according to the present invention is grown.

  Hereinafter, embodiments according to the present invention will be described in accordance with manufacturing procedures with reference to the drawings. However, the present invention is not limited to the embodiments taken up here, and may be improved or combined as appropriate without departing from the scope of the invention. In addition, the same code | symbol is attached | subjected to the part which is synonymous in drawing, and the overlapping description is abbreviate | omitted.

  FIG. 1 is a schematic cross-sectional view showing an example of a manufacturing procedure of a substrate on which a graphene film according to an embodiment of the present invention is grown. First, as the substrate 100, a silicon single crystal substrate 101 (for example, 2 inch diameter, thickness 500 to 600 μm) on which a silicon oxide film 102 (for example, a thermal oxide film having a thickness of 20 to 300 nm) is formed is prepared. To do. Next, an aluminum oxide film 103 having a corundum structure is formed on the surface of the substrate 100 (the surface of the silicon oxide film 102) by a vapor phase growth method such as sputtering, ion beam, or laser evaporation. This is referred to as a “base formation process”.

Here, in forming the aluminum oxide film 103, it is desirable to control the composition thereof to be Al _2-x O _{3 + x} (x ≧ 0), and Al _2-x O _{3 + x} (x> 0). It is more desirable to control so that it becomes. The composition can be controlled, for example, by controlling the oxygen partial pressure during vapor phase growth. By forming the aluminum oxide film 103 having an oxygen-rich composition equal to or higher than the stoichiometric composition, a graphene domain having a large average size can be grown (details will be described later).

  The arithmetic average surface roughness Ra of the aluminum oxide film 103 is desirably 1 nm or less. More desirably, it is 0.3 nm or less. When the arithmetic average surface roughness Ra is greater than 1 nm, the graphene film is difficult to grow parallel to the surface of the aluminum oxide film 103. This is probably because there is some correlation between the nucleation of graphene film growth and the arithmetic average surface roughness Ra. Furthermore, the maximum surface height Rz of the aluminum oxide film 103 is preferably 10 nm or less. More desirably, it is 3 nm or less.

  When the arithmetic average surface roughness Ra of the formed aluminum oxide film 103 is larger than 1 nm, it is processed to be 1 nm or less by polishing (for example, chemical mechanical polishing) or the like. This is called a “surface flattening step”. It is to be noted that the “surface planarization step” includes processing the silicon single crystal substrate 101 or the silicon oxide film 102 to have an arithmetic average surface roughness Ra of 1 nm or less before forming the aluminum oxide film 103 in advance. Shall be. The arithmetic average surface roughness Ra and the maximum surface height Rz shall conform to JIS B 0601.

  The average thickness of the aluminum oxide film 103 to be formed is preferably 10 nm or more and 500 nm or less. When the average thickness of the polycrystalline aluminum oxide film 103 is less than 10 nm, the number of contact points between the crystal grains decreases and the coverage in the in-plane direction decreases (for example, the aluminum oxide film 103 has an island shape). Therefore, the surface flatness is deteriorated as a result. On the other hand, if it is thicker than 500 nm, cracks and the like due to thermal strain and the like in the subsequent process are likely to occur, and as a result, surface flatness (for example, arithmetic average surface roughness Ra) is deteriorated.

  There is no particular limitation on the method for forming the aluminum oxide film 103. As a result, a method other than the vapor phase growth method may be used as long as the composition and the average film thickness can be controlled within a desired range. For example, a method may be used in which a metal aluminum film is formed on the surface of the substrate 100 (on the surface of the silicon oxide layer 102), and then the aluminum oxide film 103 is formed by oxygen plasma treatment or the like. Note that the substrate 100 on which the aluminum oxide film 103 is formed is not limited to the silicon single crystal substrate 101 on which the above-described silicon oxide film 102 is formed, and heat resistance against thermal history in a later process and It can be appropriately selected in consideration of the use of the substrate on which the graphene film is grown (for example, an electronic / optical integrated circuit device). For example, various semiconductor substrates having various types of insulating films formed on the surface, various insulating substrates, and the like can be used.

  Next, similarly to the conventional semiconductor process technology, the aluminum oxide film 103 formed on the substrate 100 is processed to have a desired circuit pattern. This is referred to as a “circuit patterning step”. At this time, the aluminum oxide film 103 is left only in the portion 104 that becomes the circuit wiring portion, and the aluminum oxide film 103 in other portions is completely removed. The silicon oxide film 102 is preferably left as an insulating layer. The “surface planarization step” may be performed after the “circuit patterning step”.

  There is no particular limitation on the patterning method, and it is sufficient that a desired circuit pattern can be formed as a result. For example, circuit patterning can be performed by using a process of photolithography and wet etching. A resist mask is formed on the aluminum oxide film 103 by photolithography, and the portion of the aluminum oxide film 103 not covered with the resist mask 103 is etched and removed with a buffer hydrofluoric acid solution to form a circuit wiring portion 104 (circuit pattern). ). The method using photolithography and wet etching can be suitably used when the minimum dimension of the circuit pattern is 1 μm or more.

  In wet etching, it is difficult to ensure dimensional accuracy of less than 1 μm due to the nature of the technique. Therefore, when the minimum dimension of the circuit pattern is less than 1 μm, the circuit patterning can be performed by, for example, a process of photolithography and lift-off. In the case of this process, patterning by photolithography (a resist mask is formed on a portion to be removed) is performed before the aluminum oxide film 103 is formed.

In addition to the above process, circuit patterning can also be performed by using a process of photolithography and dry etching. Here, according to conventional technical common sense, aluminum oxide has higher hardness than silicon oxide, and the dry etching rate of aluminum oxide is much smaller than that of silicon oxide. It was expected that it would be difficult to form the circuit pattern by dry etching. However, it has been found that a circuit pattern can be processed by reactive ion etching using CHF ₃ gas as an etching gas on a substrate on which a graphene film according to the present invention is grown (details will be described later). As a result, circuit patterning can be performed with high dimensional accuracy (at least less than 1 μm and 500 nm or less is possible) as in the conventional semiconductor process technology.

  Next, a graphene film 105 is formed on the portion 104 (aluminum oxide film 103) to be a circuit wiring portion by chemical vapor deposition (CVD) using a carbon-containing compound as a raw material. "I do. Thereby, the circuit wiring part 106 is formed, and the substrate 200 on which the graphene film is grown is manufactured. As an example of film formation conditions, propylene is used as the source gas, argon gas is used as the carrier gas, and a mixed gas with an average source concentration of 0.15 to 3% by volume is averaged at a flow rate of 15 to 50 cm / min (standard at the average flow rate on the substrate). And is grown at a growth temperature of 450 to 1000 ° C. (preferably 750 to 1000 ° C.) for 0.1 to 60 minutes (preferably 0.1 to 10 minutes). In addition to propylene, other carbon-containing compounds such as acetylene, methane, propane, and ethylene can be used as the raw material.

[Measurement of the average number of layers of grown graphene]
In the present invention, the average number of layers constituting the grown graphene film was determined by measuring light transmittance of the grown graphene film. The light transmittance T of one layer of graphene is given by physical constants (e: electron charge, c: speed of light, h bar: converted Planck constant) as shown in the following formula (1). It is theoretically expected to converge to a constant light transmittance Tc without depending on the wavelength.

  In Non-Patent Document 4, it is reported that the light transmittance of the graphene 1 layer converges at 97.7%. Therefore, in the present invention, assuming that Tc = 97.7%, the average number of layers Lg constituting the graphene film grown using the following formula (2) was calculated.

R. R. Nair, P. Blake, A. N. Grigorenko, K. S. Novoselov, T. J. Booth, T. Stauber, N. M. R. Peres, and A. K. Geim: “Fine Structure Constant Defines Visual Transparency of Graphene”, SCIENCE 320, 1308 (2008).

  On the aluminum oxide (α-alumina) single crystal substrate, the following growth conditions (raw material gas: propylene, carrier gas: argon, average raw material concentration: 1.2% by volume, standard state converted average flow velocity: 41 cm / min, growth temperature: A graphene film was formed at 800 ° C. and a growth time of 2.5 minutes, and a measurement sample was manufactured. The result of light transmittance measurement using the measurement sample is shown in FIG. FIG. 2 is a graph showing an example of a light transmission spectrum of a grown graphene film. Note that light transmittance was measured using an aluminum oxide single crystal substrate on which no graphene film was formed as a reference sample, and the measurement result of the graphene film was corrected.

  As shown in FIG. 2, the measured light transmittance gradually increased from the short wavelength side (400 nm) and converged to a constant value Tc on the long wavelength side (about 2000 nm or more). Fluctuations at 1800-1900 nm and above 2200 nm were considered to be due to moisture in the atmosphere. From the obtained Tc, the average number of layers was calculated using the above-mentioned formula (2), and it was calculated as Lg = 0.7.

(Measurement of interlayer distance and domain size of grown graphene from substrate surface)
A scanning tunneling microscope was used to measure the interlayer distance and domain size of the grown graphene from the substrate surface. As the measurement sample, a graphene film grown on an aluminum oxide single crystal substrate so as to have an average number of layers Lg <1.0 was used as in the sample used for light transmittance measurement. This is because, in a graphene film having an average number of layers Lg <1.0, the above-described measurement is facilitated because a portion where single-layer graphene grows on the substrate and a portion where graphene itself does not grow. It is.

  Using a measurement sample with an average number of layers Lg <1.0, the distance between the single-layer graphene and the substrate surface (interlayer distance between the atomic layer of the graphene film adjacent to the substrate surface and the atomic layer on the substrate surface) was measured. , Measured from 0.30 to 0.34 nm. Since this value is almost equal to the interlayer distance in the multi-layer graphene film, the graphene film formed on the substrate is not “attached” but “grown” and grown parallel to the substrate surface. This is a strong suggestion.

  On the other hand, in the measurement of the domain size of the grown graphene, it was found that when the domain size exceeds 10 nm, it is difficult to obtain the domain size from a normal scanning tunneling microscope image. Therefore, in the present invention, the in-plane distribution measurement of the electrical conductivity of the substrate on which graphene has been grown was performed using a scanning tunneling microscope to determine the domain size. That is, the domain size of graphene was measured by utilizing the difference in electric conduction characteristics between the portion where single-layer graphene was grown and the portion where graphene itself was not grown.

  The in-plane distribution of electrical conduction was measured as follows. At a measurement point of 100 x 100 in a 100 nm square area (1 nm pitch), the measurement point where a current of 20 pA or more flowed at an applied voltage of 2.5 V was determined as the "graphene growing part" and the applied voltage The measurement point that was less than 20 pA at 2.5 V was determined as “the part where graphene was not grown”. In addition, the electrical conductivity characteristics with and without graphene are measured separately. A current of 100 pA or more flows at an applied voltage of 2.5 V in a portion where single-layer graphene is grown, and a current hardly flows in a portion where no graphene is present. (Less than 5 pA at an applied voltage of 2.5 V) was confirmed.

  FIG. 3 is a map showing an example of an in-plane distribution measurement result (100 nm square) of electrical conduction of a substrate on which a graphene film is grown. In FIG. 3, the measured sample is a substrate (aluminum oxide single crystal substrate, source gas: propylene, carrier gas: argon, average source concentration: 1.2 vol%, standard state) with a graphene film having an average number of layers of 0.7 The converted average flow velocity is 41 cm / min, the growth temperature is 800 ° C, the growth time is 2.5 minutes, and the measurement point determined as “the part where graphene is growing” is indicated by white dots. Measurement points that were judged as “not part” were indicated by black dots.

  As shown in FIG. 3, since the black dot band is considered to be the outer edge of the graphene domain, the interval between the black dot bands was measured as the graphene domain size (for example, a double-headed arrow in the figure). The average size of the graphene domain was calculated by averaging the measured values of a total of 30 points, 3 points in each region in 10 different 100 nm square regions on the substrate on which the graphene film was grown.

[Effects of growth conditions on graphene film growth]
The effect of growth conditions on the growth of graphene films was investigated. An aluminum oxide single crystal substrate was used as the substrate. First, the relationship between the growth temperature and growth time and the average number of graphene layers was investigated. At this time, the flow rate of propylene as a raw material gas was fixed and the flow rate of argon as a carrier gas was changed, and two conditions with different average raw material concentrations and standard state converted average flow rates were examined.

FIG. 4 is an example of a graph showing the relationship between the growth time at a growth temperature of 800 ° C. and the average number of graphene films, and FIG. 5 shows the relationship between the growth time at a growth temperature of 900 ° C. and the average number of graphene films. It is an example of the graph which shows a relationship. 4, as shown in FIG. 5, the average number of layers grown graphene films result that is proportional to the growth time is proportional to the average raw density is obtained. As can be seen from this result, the average number of graphene films can be controlled mainly by controlling the growth time.

  Next, samples in which the average number of graphene films grown at each growth temperature was less than 1.0 were prepared, and the average domain size of graphene was investigated. As a result, when the growth temperature is 800 ° C, the average domain size is about 29 nm, and when the growth temperature is 900 ° C, the average domain size is about 31 nm. The influence of the growth temperature on the average domain size is not so large (average domain size) It was not the main factor affecting size).

  In addition, a sample in which a graphene film with an average number of layers of 0.5 to 1.0 was grown by changing only the growth time under the growth conditions of the graphene film, and the average domain size of each sample was compared. It was within about 10%. This suggests that growth time does not significantly affect the average domain size (it is not the main factor affecting the average domain size).

[Relationship between composition Al _2-x O _{3 + x} and graphene domain size of aluminum oxide film]
The relationship between the composition Al _2-x O _{3 + x of the} aluminum oxide film as the underlayer and the domain size of graphene was investigated. As described above, when the aluminum oxide film 103 is formed by a vapor phase growth method such as a sputtering method, an ion beam method, or a laser evaporation method, the oxygen partial pressure in the growth atmosphere is controlled by controlling the oxygen partial pressure in the growth atmosphere. It is possible to control the amount of oxygen. Therefore, as an example, when an aluminum oxide film is formed by sputtering, an aluminum oxide film (Al _{2- x} O _{3 + x} , film thickness 150 nm) was formed on the substrate. As the substrate, a silicon single crystal substrate with a thermal oxide film (outer diameter 2 inches, substrate thickness 525 μm, thermal oxide film thickness 200 nm) was used.

When the composition of the aluminum oxide film (Al _2-x O _{3 + x} ) formed using XPS (X-ray photoelectron spectroscopy, manufactured by Shimadzu Corporation) was measured, the oxidation was different from x = -0.3 to 0.32. It was confirmed that the film was an aluminum film. After confirming that the arithmetic average surface roughness Ra of the deposited aluminum oxide film (Al _2-x O _{3 + x} ) is 1 nm or less, on the aluminum oxide film (Al _2-x O _{3 + x} ) In addition, a graphene film having an average number of layers of 0.7 was formed (raw material gas: propylene, carrier gas: argon, average raw material concentration: 1.2 vol%, standard state conversion average flow velocity: 41 cm / min, growth temperature: 800 ° C., Growth time: 2.5 minutes). The average domain size of the grown graphene was measured by the above-described in-plane distribution measurement of electrical conduction.

FIG. 6 is a graph showing the relationship between the average domain size of the graphene film and the composition of the aluminum oxide film ( _{x in} Al _2-x O _{3 +} x). As shown in FIG. 6, the average domain size of graphene varies greatly with _x in Al _2-x O _{3 + x} , and aluminum oxide film having an oxygen-rich composition of x ≧ 0, that is, a stoichiometric composition or more. It became clear that the average domain size of graphene grown can be increased by using as a base film. Further, it can be said that x> 0 is more preferable.

[Relationship between average domain size and electrical conductivity in graphene films]
In order to use graphene as a circuit conductor of an electro-optical device, it is desirable to form a continuous graphene film that secures electrical continuity between graphene domains and has good electrical conductivity. Therefore, the electrical conductivity of the grown graphene film was investigated.

The sample for investigation was produced according to the procedure shown in FIG. An aluminum oxide film having a corundum structure was formed by sputtering on the surface of a silicon single crystal substrate on which a thermal oxide film was formed. At this time, aluminum oxide films (Al _2−x O _{3 + x} ) having different oxygen contents were formed by controlling the atmospheric oxygen partial pressure during sputtering. After confirming that the arithmetic average surface roughness Ra of each aluminum oxide film is 1 nm or less, a plurality of aluminum oxide film strip lines (width 2 μm, length 1 mm) are formed by photolithography and lift-off processes. Then, a substrate from which the aluminum oxide film in other portions was removed was prepared. Next, a graphene film is formed on each substrate under the condition that the average number of layers is about 1.0 (source gas: propylene, carrier gas: argon, growth temperature: 800 ° C.), and graphene films having different average domain sizes are formed. Grown up.

  Each sample on which the graphene film was formed was observed with a scanning tunneling microscope. As a result, in each sample, the graphene film grew only on the strip line of the aluminum oxide film, and on the thermal oxide film from which the aluminum oxide film was removed. The graphene film was not grown. In other words, it was confirmed that the graphene film was selectively grown on the strip line of the aluminum oxide film. From this result, it was suggested that the nucleation mechanism and the growth mechanism of the graphene film differ between the aluminum oxide film and the thermal oxide film (silicon oxide film).

Next, the electrical conductivity and electrical resistivity of the graphene film on the stripline were measured by the four probe method. The distance between the voltage terminals in the measurement was 0.2 mm. FIG. 7 is a graph showing the relationship between the average domain size of the graphene film and the electrical conductivity / electric resistivity. In FIG. 7, the left side vertical axis of the graph represents electrical conductivity, and the right side vertical axis represents electrical resistivity. As shown in FIG. 7, as the average domain size increases, the electrical conductivity increases dramatically. By increasing the average domain size from about 10 nm to about 30 nm, the electrical conductivity of the graphene film is about 1 The figure improved to 1 × 10 ⁴ S / cm or more. Further, in order to obtain an electric conductivity of 1 × 10 ⁴ S / cm or more, an average domain size of about 25 nm or more was considered preferable. From this result, it was proved that the substrate on which the graphene film according to the present invention was grown had a continuous graphene film having good electrical conductivity while ensuring electrical continuity between the graphene domains. .

[Dry etching rate of aluminum oxide film according to the present invention]
A silicon single crystal substrate 101 having a silicon oxide film 102 (thermal oxide film) having a thickness of 300 nm is prepared, and aluminum oxide having a thickness of 300 nm is formed on the substrate with Al _2-x O _{3 + x} (x> 0). A film 103 was formed by a process of photolithography and lift-off, and a sample for investigating the dry etching rate was produced. The sample was subjected to reactive ion etching (etching gas: CHF ₃ gas, gas pressure: 1.0 Pa, etching power: 100 W). FIG. 8 is a graph showing an example of the relationship between etching time and etching depth by reactive ion etching of an aluminum oxide film and a silicon thermal oxide film according to the present invention.

As shown in FIG. 8, the etching depth of the aluminum oxide film and the silicon thermal oxide film according to the present invention monotonously increased in proportion to the etching time. From these inclinations, the aluminum oxide film according to the present invention has a dry etching rate of about 45 nm / min, which is about 9 times the dry etching rate (about 5 nm / min) of the silicon thermal oxide film. It was found to have a selectivity. The same result was obtained when the composition of the aluminum oxide film 103 was Al _2-x O _{3 + x} (x = 0). This sufficiently high etching selectivity enables circuit patterning with high dimensional accuracy.

As an example, an aluminum oxide film (thickness) having a composition of Al _2-x O _{3 + x} (x> 0) on a silicon single crystal substrate 101 having a silicon oxide film 102 (thermal oxide film) having a thickness of 100 nm. 30 nm) by reactive ion etching with the above etching conditions (etching gas: CHF ₃ gas, gas pressure: 1.0 Pa, etching power: 100 W, etching time: 1 minute) on the aluminum oxide film Circuit patterning was performed. As a result, it was demonstrated that a fine pattern of 30 nm × 100 nm can be formed in plan view. These dry etching selection ratios and circuit patterning results were surprising results that could not be predicted from conventional technical common sense.

The detailed mechanism for obtaining the results as described above is not yet elucidated, but as one of the factors, the aluminum oxide film 103 according to the present invention has an oxygen-rich composition higher than the stoichiometric composition. It is possible that Further, even in the case of Al _2-x O _{3 + x} (x = 0) having a stoichiometric composition, the method for forming the aluminum oxide film 103 according to the present invention controls the oxygen partial pressure during vapor phase growth. Therefore, even if the average composition is a stoichiometric composition, it is considered that a local (microscopic) oxygen-rich composition region and an oxygen-poor composition region are mixed, It is considered that the oxygen-rich composition region contributed to a high dry etching rate.

[Electronic / Optical Integrated Circuit Device Using Substrate Grown with Graphene Film]
FIG. 9 is a schematic perspective view showing an example of an electronic / optical integrated circuit device using a substrate on which a graphene film according to the present invention is grown. An electronic / optical integrated circuit device 300 according to the present invention uses, for example, the substrate 200 on which the graphene film described above is grown, and a part of the circuit wiring portion 106 on which the graphene film is formed is replaced with a graphene channel 301 of a field effect transistor, respectively. This is used as the graphene light-receiving / emitting layer 302 of the graphene light-emitting element. A gate electrode 305 is formed in the graphene channel 301 of the field effect transistor through a source electrode 303, a drain electrode 304, and a gate insulating film 306.

  Further, a positive electrode 307 and a negative electrode 308 are formed on the graphene light emitting / receiving layer 302. Note that a graphene light-emitting element refers to an element that emits light by direct transition into graphene having a band gap by injecting electrons from one electrode and holes from the other electrode. On the other hand, a graphene light-receiving element is an element that detects light by applying a voltage between two electrodes connected to graphene having a band gap and detecting electrons and holes generated by light irradiation.

  As described above, since the method for manufacturing a substrate on which a graphene film according to the present invention is grown does not use an ultra-high vacuum process or a special manufacturing apparatus, the cost of the manufacturing apparatus can be kept low. Furthermore, since the growth temperature of the graphene film is relatively low, an inexpensive and large-area substrate that has been widely used in electronic devices can be used. That is, it can be said that it is an invention that greatly contributes to cost reduction of manufacturing and is suitable for industrialization. In addition, by using a substrate on which a graphene film according to the present invention is grown and combining a field effect transistor, a light emitting / receiving element, and a wiring using the graphene film, a next-generation electronic / optical integrated circuit device is realized. Is possible.

100 ... substrate, 101 ... silicon single crystal substrate, 102 ... silicon oxide film,
103 ... Aluminum oxide film, 104 ... Part that becomes circuit wiring part,
105 ... graphene film, 106 ... circuit wiring part, 200 ... substrate on which the graphene film is grown,
300 ... electronic / optical integrated circuit device, 301 ... graphene channel, 302 ... graphene light emitting / receiving layer,
303 ... Source electrode, 304 ... Drain electrode, 305 ... Gate electrode, 306 ... Gate insulating film,
307 ... Positive electrode, 308 ... Negative electrode.

Claims (16)

A substrate on which a graphene film consisting of a single layer or multiple layers is grown,
An aluminum oxide film is present on the surface of the substrate, and the composition of the aluminum oxide film is Al _2-x O _{3 + x} (x > 0),
The graphene film is parallel to the surface of the aluminum oxide film and grows only on the surface,
A substrate on which a graphene film is grown, wherein the electrical conductivity of the graphene film is 1 × 10 ⁴ S / cm or more when the electrical conductivity is measured under the condition of a distance between voltage terminals of 0.2 mm. In the substrate on which the graphene film according to claim 1 is grown,
The graphene film is composed of a plurality of graphene domains, and an average size of the graphene domains is 25 nm or more. A substrate on which a graphene film is grown. In the substrate on which the graphene film according to claim 1 or 2 is grown,
A substrate on which a graphene film is grown, wherein an interlayer distance between an atomic layer of the graphene film adjacent to the aluminum oxide film and an atomic layer of the aluminum oxide film adjacent to the graphene film is 0.34 nm or less. In the substrate on which the graphene film according to claim 1 is grown,
A substrate on which a graphene film is grown, wherein the aluminum oxide film has an arithmetic average surface roughness Ra of 1 nm or less. In the substrate on which the graphene film according to claim 1 is grown,
A substrate on which a graphene film is grown, wherein the maximum surface height Rz of the aluminum oxide film is 10 nm or less. In the substrate on which the graphene film according to claim 1 is grown,
A substrate on which a graphene film is grown, wherein an average thickness of the aluminum oxide film is 10 nm or more and 500 nm or less. In the substrate on which the graphene film according to claim 1 is grown,
The substrate on which a graphene film is grown, wherein the substrate is a silicon single crystal substrate having a silicon oxide film formed on a surface thereof. In the substrate on which the graphene film according to claim 7 is grown,
A substrate on which a graphene film is grown, wherein a circuit pattern is formed on the aluminum oxide film, and a minimum dimension of the circuit pattern is less than 1 μm. In the substrate on which the graphene film according to claim 8 is grown,
A substrate on which a graphene film is grown, wherein the circuit pattern is formed by reactive ion etching. In the substrate on which the graphene film according to claim 1 is grown,
A substrate on which a graphene film is grown, wherein the area of the substrate is 20 cm ² or more.   11. An electronic / optical integrated circuit device using a substrate on which the graphene film according to claim 1 is grown. The electronic / optical integrated circuit device according to claim 11,
An electronic / optical integrated circuit device, wherein the graphene is used as a channel of a field effect transistor, a light emitting device, a light receiving device, and a circuit wiring. A method of manufacturing a substrate in which a graphene film composed of a single layer or a plurality of layers is grown in parallel to the surface of the substrate,
A silicon single crystal substrate having a silicon oxide film formed on the surface is used as the substrate, and an aluminum oxide film having a composition of Al _2-x O _{3 + x} (x > 0) serving as a base of the graphene film is provided at least on the substrate. "Base formation process" to be formed on one outermost surface,
A "circuit patterning step" for processing the aluminum oxide film into a desired circuit pattern;
It possesses a "graphene film forming step" of forming the graphene layer only on the circuit pattern by chemical vapor deposition of carbon-containing compound as a starting material,
The “base formation step” is performed by a vapor phase growth method, and a partial pressure of oxygen during growth is controlled . A method of manufacturing a substrate on which a graphene film is grown. In the manufacturing method of the substrate by which the graphene film according to claim 13 was grown,
The method of manufacturing a substrate on which a graphene film is grown, wherein the “circuit patterning step” is reactive ion etching using CHF ₃ gas. In the manufacturing method of the substrate by which the graphene film according to claim 13 or 14 was grown,
Prior to the “graphene film forming step”, the graphene film further includes a “surface flattening step” for processing the arithmetic average surface roughness Ra of the aluminum oxide film to be 1 nm or less. A method of manufacturing a substrate on which a substrate is grown. In the manufacturing method of the substrate by which the graphene film according to any one of claims 13 to 15 was grown,
The chemical vapor deposition method of the “graphene film forming step” is a method in which acetylene, propylene or methane is used as the raw material and is grown at a temperature of 750 to 1000 ° C. for 0.1 to 10 minutes in a non-oxidizing atmosphere. A method for manufacturing a substrate on which a graphene film is grown.

Images