JP4466019B2 - Diamond element and method for manufacturing diamond element - Google Patents

Description

  The present invention relates to a diamond element applicable to an electron-emitting device, an atom probe, a near-field optical probe, and the like, and a method for manufacturing the same.

3A to 3C are diagrams showing a conventional diamond element and a manufacturing process thereof. As shown in FIGS. 3A to 3C, a method of forming a pyramid 35 having a sharp apex by forming a microcylinder 33 on a diamond single crystal substrate 31 and epitaxially growing a diamond crystal on the microcylinder 33. was there.
Yoshiki Nishibayashi et al., "Various Field Emitters of Single Crystal Diamond", New Diamond and Frontier Carbon Technology, Vol. 13, No. 1 2003, p. 19-30 Yutaka Ando et al., "Fabrication of Diamond Emitter Tips by Reactive Ion Etching", New Diamond and Frontier Carbon Technology, Vol. 12, No. 3 2002, p. 137-140

  The diamond element manufactured by the above conventional example has a problem that the height uniformity of the protrusion is poor.

  The present invention has been made in view of the above problems, and an object thereof is to provide a diamond element having excellent height uniformity.

The diamond element of the present invention has a substrate whose surface is substantially parallel to a specific crystal plane of a diamond crystal, and a second crystal plane that is provided on the substrate and is different from the specific crystal plane. A substantially pyramidal body, and a columnar body projecting from the tip of the substantially pyramid and having a sharpened tip, the specific crystal plane being a (100) plane, and the second crystal plane being ( 111) plane.

  The diamond element manufacturing method of the present invention includes a first step of forming a structure in which a columnar body protrudes from a substrate whose surface is a plane substantially parallel to a specific crystal plane of a diamond crystal, and the first step. By exposing the obtained substrate to a plasma of a gas containing hydrogen as a main component, a diamond crystal having an exposed second crystal plane different from the crystal plane is grown from the base of the columnar body, A second step of sharpening the tip of the columnar body, and the diamond crystal growing from the base of the columnar body ends the second step before reaching the tip of the columnar body, A structure in which the columnar body protrudes from a tip portion of a substantially pyramidal body having the substrate as a bottom surface and the second crystal plane as a side surface is formed.

  By plasma-treating the tip of the columnar body, the tip of the columnar body can be sharpened without greatly changing the height of the columnar body. In particular, since the substantially pyramidal body that reinforces the physical strength of the columnar body is provided, the columnar body can be made extremely thin, and the tip of the columnar body is sharpened by a short plasma treatment. Therefore, the variation in the height of the plurality of columnar bodies with sharpened tips is reduced.

  In the diamond element of the present invention, it is preferable that the maximum diameter of a cross section perpendicular to the length direction of the columnar body is 300 nm or less.

  When the maximum diameter of the cross section of the columnar body is 300 nm or less, suitable height uniformity (variation is 100 nm or less) can be easily achieved.

  In the diamond element of the present invention, it is preferable that the boundary between the side surface of the columnar body and the side surface of the substantially pyramidal body is a boundary where different crystal planes are in contact.

  Before the side surface of the columnar body and the side surface of the substantially pyramidal body become a continuous crystal plane, that is, the substantially pyramidal body grows to the vicinity of the tip of the columnar body, and the growth of the substantially pyramidal body reaches the height of the columnar body. By stopping the plasma treatment before the influence is exerted, the height variation of the columnar body can be further reduced.

  In the diamond element of the present invention, it is preferable that a length of a portion protruding from the substantially pyramid in the columnar body is less than a half of a height of the columnar body.

  When more than half of the columnar body is covered with the substantially pyramidal body, the columnar body is not easily broken, and the heat dissipation effect and the light guiding effect of the substantially pyramidal body are enhanced.

  A diamond element excellent in height uniformity can be provided without being affected by the grain boundary between crystals.

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

(First embodiment)
The structure of the diamond element 1 of the first embodiment will be described. FIG. 1C shows a longitudinal sectional view of the diamond element 1 of the first embodiment. 1A and 1B show a process in which a diamond crystal grows in the (111) direction from the base of a columnar body to reach a substantially pyramidal body. However, in these drawings, only one columnar body is shown for simplification.

  The diamond element 1 includes a diamond single crystal substrate 11 having a (100) plane as a surface 11a. A plurality of quadrangular columns 13 (columnar bodies) protrude perpendicularly from the surface 11a from the substrate 11 at regular intervals. The quadrangular column 13 is composed of a diamond single crystal that is continuous with the diamond single crystal constituting the substrate 11. The diameter of the cross section of the quadrangular column 13 is 300 nm or less.

  Each quadrangular column 13 is covered with a substantially quadrangular pyramid 15 (substantially pyramid) having a truncated quadrangular pyramid, and a tip end portion 13 a protrudes from the tip end portion of the substantially quadrangular pyramid 15. The substantially quadrangular pyramid 15 is a diamond single crystal having a surface 11a ((100) plane) of the substrate 11 as a bottom surface and a (111) plane as a side surface 15a (exposed surface). As shown in FIGS. 1A and 1B, the substantially quadrangular pyramid 15 is formed by growing a diamond single crystal on the substrate 11 in the (111) direction from the root of the quadrangular column 13. The growth of the substantially quadrangular pyramid 15 is stopped before the substantially quadrangular pyramid 15 covers the distal end portion 13 a of the quadrangular column 13.

  The distal end portion 13a of the quadrangular column 13 is sharpened. Although there are some variations in the height of the plurality of quadrangular prisms 13, the difference between the lowest and the highest is within 100 nm.

  The substrate used in the diamond element of the present invention may be a substrate obtained by heteroepitaxial growth of a diamond single crystal. Further, the surface layer portion and the columnar body of the substrate used in the diamond element of the present invention may be highly oriented polycrystalline diamond.

(Second Embodiment)
The structure of the diamond element 2 of the second embodiment will be described. FIG. 2C shows a longitudinal sectional view of the diamond element 2 of the second embodiment. 2A and 2B show a process in which a diamond crystal grows in the (111) direction from the base of a columnar body to reach a pyramidal body. However, in these drawings, only one columnar body is shown for simplification.

  The diamond element 2 includes a diamond single crystal substrate 21 having a surface 21a substantially parallel to the (100) plane. There is a predetermined off angle between the (100) plane and the surface 21a.

  A plurality of square pillars 23 (columnar bodies) protrude perpendicularly to the surface 21a from the substrate 21 at regular intervals. The square pillar 23 is composed of a diamond single crystal continuous with the diamond single crystal constituting the substrate 21. The diameter of the cross section of the square pillar 23 is 300 nm or less.

  Each square column 23 is covered with a quadrangular pyramid 25, and the tip 23 a protrudes from a side surface 25 a near the apex of the quadrangular pyramid 25. The quadrangular pyramid 25 is a diamond single crystal having a (100) plane of the diamond single crystal constituting the substrate 21 as a bottom surface and a (111) plane as a side surface 25a. As described above, since there is a predetermined off-angle between the (100 face) and the surface 21a, the quadrangular pyramid 25 is inclined by the off-angle with respect to the surface 21a. Therefore, the apex of the quadrangular pyramid 25 is located outside the quadrangular prism 23 extending perpendicularly from the surface 21a.

  As shown in FIGS. 2A and 2B, the quadrangular pyramid 25 is formed by growing a diamond single crystal on the substrate 21 in the (111) direction from the root of the quadrangular prism 23. The growth of the quadrangular pyramid 25 is stopped before the quadrangular pyramid 25 covers the tip 23a of the quadrangular column 23.

  FIG. 2D is a diagram illustrating a shape of a boundary portion between adjacent side surfaces 25 a in the quadrangular pyramid 25. The sides of both side surfaces 25a are recessed such that the recessed portion 25b is parallel to the boundary.

  The front end portion 23a of the square pillar 23 is sharpened. There is some variation in the height of the plurality of square pillars 23, but the difference between the lowest and the highest is within 100 nm.

(Production method)
An embodiment of the diamond element manufacturing method of the present invention will be described. First, a (100) single crystal diamond substrate produced by a high-pressure synthesis method is flattened to a height difference of 25 nm or less by polishing. Preferably, planarization is performed so that the height difference is 10 nm or less. At this time, the planarized surface of the substrate is made parallel to the (100) plane. Instead of the (100) single crystal diamond substrate, a substrate in which a diamond single crystal film is heteroepitaxially grown in the surface layer portion or a substrate in which a highly oriented diamond polycrystal film is grown in the surface layer portion may be used.

  Al dots having a diameter of 200 nm or less are formed in a predetermined arrangement on the planarized substrate surface. Since it is processed into fine dots having a diameter of 200 nm or less, electron lithography is suitable as a pattern forming means. It is also conceivable that the second resist formed on the Al film is formed into a large dot pattern by photolithography, and the Al film is overetched to form a fine dot pattern having a diameter of 200 nm or less. In this case, the Al micro dots vary in size, but variations up to 25 nm are acceptable.

The resist material is not limited to Al, and SiO ₂ or TiN can also be used. It is also conceivable to process a material such as Au that is difficult to perform lithography into a predetermined pattern by lift-off.

  The substrate on which the Al micro dots are formed is etched in the direction perpendicular to the surface by RIE to form a cylinder. The height of the cylinder is preferably at least twice the diameter. By increasing the height of the cylinder, it is possible to maintain the state in which the tip of the cylinder protrudes from the substantially pyramid state even when the substantially pyramidal body is greatly grown in a later process. After the etching, the Al film is removed with an acid.

By the above process, a structure in which a plurality of cylinders protrude vertically from the surface of the substrate which is the (100) plane is obtained. Next, the substrate is exposed to a microwave plasma of a gas mainly containing hydrogen. This gas is composed entirely of hydrogen, or hydrogen gas containing a small amount of gas containing oxygen atoms such as O ₂ , CO, CO ₂ (eg, 0.1% CO ₂ is mixed in H ₂₎ Gas).

  A hydrogen-containing gas is excited by microwaves in the vicinity of the minimum energy at which the diamond crystal is etched. Excitation with microwaves is preferred, but excitation with RF or DC is also possible. The substrate temperature is 700 to 900 ° C., and the gas pressure is 2.5 to 6.7 kPa.

  By exposing to such a plasma gas, the substrate with the microcylinder is gently etched, and a diamond crystal grows in the (111) direction on the substrate with the microcylinder. As a result, the shape of the substrate with the minute cylinders changes as follows.

  The cylinder is reconfigured into a quadrangular prism with the (100) plane as the side surface. Furthermore, the tip of the quadrangular column is sharpened. At the same time, a diamond crystal grows in the (111) direction from the base of the quadrangular prism. Diamond crystals grow in the (100) direction, but the growth in the (111) direction is about 20 times faster.

  A substantially quadrangular pyramid grows with the surface of the substrate as the bottom, the (111) plane as the side, and the central axis overlapping the quadrangular prism. On the other hand, the tip of the quadrangular column is sharpened but hardly grows in the direction perpendicular to the substrate surface. The plasma processing is stopped in a state where the substantially quadrangular pyramid covers more than half of the quadrangular column and the tip of the quadrangular column is exposed. In particular, in order to reduce the variation in the height of a plurality of quadrangular prisms, there is a boundary that distinguishes the side surfaces of the substantially quadrangular pyramid and the side surface of the quadrangular prism, that is, the crystal planes that constitute the side surface of the substantially quadrangular pyramid. It is preferable to stop the plasma treatment while there is a boundary line that discontinuously changes with the crystal plane constituting the side surface of the quadrangular prism. As a result of the above process, the diamond element of the present invention is obtained.

  In the above process, a microcylinder having a cross-sectional diameter of 200 nm or less is formed, and the microcylinder is reconfigured into a microsquare column. Since the minute square column is very thin, the tip of the minute square column is sharpened by a short plasma treatment. Therefore, before the tip of the substantially quadrangular pyramid catches up with the tip of the minute quadrangular prism, the tip of the minute quadrangular prism is sharpened.

  Further, since the ratio of the (111) direction growth rate to the (100) direction growth rate is large, the height of the minute square column is the same as that at the start of the plasma treatment even when the substantially quadrangular pyramid grows to the vicinity of the tip of the minute square column. It has not changed greatly. For this reason, the variation in the height of the plurality of small quadrangular prisms after the plasma treatment does not increase. In particular, by reducing the maximum diameter (diagonal length) of the cross section of the small quadrangular column to 300 nm or less and shortening the time required for sharpening, variation in the height of the small quadrangular column when the diamond element of the present invention is completed is achieved. It can be 100 nm or less. There is a large possibility of achieving a suitable structure (the tip of the small quadrangular column is sharpened and the height variation of the small quadrangular prism is 100 nm) when the maximum diameter of the cross section of the small quadrangular column is around 300 to 400 nm. change.

  In the above manufacturing method, the substrate is polished so that the surface is parallel to the (100) plane, but the substrate may be polished so that a predetermined off angle is generated between the surface and the (100) plane. In that case, a quadrangular pyramid with the (100) plane as the bottom grows with an inclination to the surface of the substrate. As described above, the structure in which the quadrangular pyramid is inclined with respect to the quadrangular prism is suitable for applying the diamond element to the near-field optical probe or the atomic probe.

  When the off-angle is provided on the substrate surface, if the microcylinder formed before plasma processing is thickened and the plasma processing time is shortened, the quadrangular pyramid has a shape in which the boundary between adjacent side surfaces is cut off. Prone. As shown in FIG. 2D, the structure in which the recessed portions are doubled, that is, the structure in which the recessed portions are formed so as to be parallel to the boundary on the sides of the both side surfaces improves the uniformity of the height of the minute quadrangular prism. It is preferable in terms of maintenance.

(Example 1 of manufacturing method)
The surface of the (100) single crystal diamond substrate was polished and flattened to a height difference of several nm. An Al film is deposited on the surface of the substrate. Further, a second resist (wet etching resist) is applied on the Al film. The second resist was formed into a pattern in which dots having a diameter of 0.8 μm were arranged by photolithography.

  This substrate was over-etched by wet etching, and the second resist was removed to form a pattern in which Al dots having a diameter of 0.2 to 0.5 μm were arranged.

By performing RIE in a gas of CF ₄ / O ₂ = 1%, this substrate was processed into a structure in which a plurality of cylinders protruded vertically from the surface. Under some Al dots, the cylinder disappeared due to excessive side etching. However, under much Al, a cylinder having a cross-sectional diameter of 0.2 to 0.3 μm was formed. FIG. 4 is an imaging diagram of a (100) single crystal diamond substrate on which a cylinder is formed in Example 1.

  The substrate was exposed to microwave plasma of 100% hydrogen gas using an MPCVD apparatus. The processing conditions were a hydrogen gas flow rate of 100 to 300 sccm, a gas pressure of 3.3 to 5.3 kPa, a substrate stage temperature of 750 ° C., and a microwave output of 1300 W. The processing time was 15 to 360 minutes.

  When the above plasma treatment was started, the cylinder became thinner and was reconstructed into a square column having a diameter of 50 to 200 nm. At the same time, a pyramid-shaped growth hill grew from the base of the quadrangular prism. FIG. 5A is an imaging diagram showing the growth of the growth hill, and FIG. 5B is a partially enlarged view thereof.

  When the plasma treatment was continued, the growth hill grew and the tip of the quadrangular column sharpened. The growth rate of the growth hill was much larger than the growth rate of the surface of the square column. Even when the tip of the growth hill approached the tip of the quadrangular column, there was little change in the height of the quadrangular column. Before the tip of the growth hill overtakes the tip of the square column, the tip of the square column was sharpened sufficiently. 6A to 6C are imaging diagrams illustrating a process in which the growth hill grows from the base of the quadrangular column and the tip of the quadrangular column sharpens at the same time.

  FIG. 7A is a diagram showing the shape of the boundary between the side surfaces of the growth hill. As shown in FIG. 7A, the boundary portion between the side surfaces (region a shown in FIGS. 6A and 7A) was shaped to be cut so that the recessed portion became a plane parallel to the boundary line.

  FIG. 7B is an enlarged view of the front end portion of the quadrangular prism in the initial stage of the plasma processing shown in FIG. 6A. FIG. 7C is an enlarged view of the front end portion of the quadrangular prism in the final stage of the plasma processing shown in FIG. 6C. The tip shown in FIG. 7B has a rounded tip. The tip shown in FIG. 7C is thicker than the tip shown in FIG. 7B, but has a sharp point.

  The plasma treatment was stopped when the tip of the quadrangular column was sufficiently sharpened. The standard height of the square prism of the diamond element completed by the above process was 3 μm, and the variation from the standard height was within 1%.

(Example 2 of manufacturing method)
The manufacturing method of Example 2 differs from the manufacturing method of Example 1 in the following points. The Al film deposited on the surface of the (100) diamond single crystal substrate was formed into a pattern in which Al dots having a diameter of 0.3 μm were arranged by electron beam lithography and etching. By performing RIE in a gas of CF ₄ / O ₂ = 1%, a cylinder having a cross-sectional diameter of 0.2 μm was formed.

  When this cylindrical substrate was subjected to plasma treatment, a square pillar with a sharpened tip and a diameter of 80 to 100 nm and a growth hill having the same shape as in Example 1 were obtained. The standard height of the square prism of this diamond element was 3 μm, and the variation from the standard height was within 1%.

(Comparative example of manufacturing method)
The manufacturing method of the comparative example differs from the manufacturing method of Example 1 in the following points. The cross-sectional diameter of the cylinder before the plasma treatment was set to 0.8 μm.

  When this cylindrical substrate was plasma treated, the tip of the growth hill caught up with the tip of the quadrangular column before the tip was sharp. At this time, the standard height of the quadrangular prism was 6 μm, and the variation from the standard height was within 5%.

  For example, electron guns, electron tubes, vacuum tubes, electron emission elements in FED (Field Emission Display), STM (Scanning Tunneling Microscope), AFM (Atomic Force Microscope), atomic probes and near-field light in SNOM (Scanning Near-field Optical Microscope) Applicable to probes.

FIG. 1C shows a longitudinal sectional view of the diamond element 1 of the first embodiment. 1A and 1B show a process in which a diamond crystal grows in the (111) direction from the base of a columnar body to reach a substantially pyramidal body. FIG. 2C shows a longitudinal sectional view of the diamond element 2 of the second embodiment. 2A and 2B show a process in which a diamond crystal grows in the (111) direction from the base of a columnar body to reach a pyramidal body. FIG. 2D shows the shape of the boundary portion between adjacent side surfaces 25 a in the quadrangular pyramid 25. 3A to 3C are diagrams showing a conventional diamond element and a manufacturing method thereof. FIG. 4 is an imaging diagram of a (100) single crystal diamond substrate on which a cylinder is formed in Example 1. FIG. 5A is an imaging diagram showing the growth of the growth hill, and FIG. 5B is a partially enlarged view thereof. 6A to 6C are imaging diagrams illustrating a process in which the growth hill grows from the base of the quadrangular column and the tip of the quadrangular column sharpens at the same time. FIG. 7A is a diagram showing the shape of the boundary between the side surfaces of the growth hill. FIG. 7B is an enlarged view of the front end portion of the quadrangular prism in the initial stage of the plasma processing shown in FIG. 6A. FIG. 7C is an enlarged view of the front end portion of the quadrangular prism in the final stage of the plasma processing shown in FIG. 6C.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Diamond element, 11 ... Diamond single-crystal board | substrate, 11a ... Surface, 13 ... Square pillar, 13a ... Tip part, 15 ... About square pyramid, 15a ... Side surface DESCRIPTION OF SYMBOLS 2 ... Diamond element, 21 ... Diamond single crystal substrate, 21a ... Surface, 23 ... Square pillar, 23a ... Tip part, 25 ... Square pyramid, 25a ... Side surface, 31 ... Diamond single crystal substrate, 33 ... Micro cylindrical body, 35 ... Pyramidal body.

Claims (11)

A substrate whose surface is a plane substantially parallel to a specific crystal plane of the diamond crystal;
A substantially pyramidal body provided on the substrate and having a second crystal plane different from the specific crystal plane as a side surface;
A columnar body that protrudes from the tip of the substantially pyramidal body and has a sharpened tip.
The specific crystal plane is a (100) plane;
The diamond element, wherein the second crystal plane is a (111) plane . The diamond element according to claim 1, wherein the maximum diameter of a cross section perpendicular to the length direction of the columnar body is 300 nm or less. 2. The diamond element according to claim 1, wherein a difference between a height of one of the columnar bodies and a height of the other columnar body is 100 nm or less. 2. The diamond element according to claim 1, wherein a boundary between a side surface of the columnar body and a side surface of the substantially pyramidal body is a boundary where different crystal planes are in contact with each other. The diamond element according to claim 1, wherein a boundary between adjacent side surfaces of the substantially pyramid is a ridge line including a concave angle. The diamond element according to claim 1, wherein a central axis of the substantially pyramid is inclined with respect to a central axis of the columnar body. The diamond element according to claim 5 or 6 , wherein there is a predetermined off angle between the surface of the substrate and the specific crystal plane. 2. The diamond element according to claim 1, wherein a length of a portion of the columnar body protruding from the substantially pyramidal body is less than a half of a height of the columnar body. A first step of forming a structure in which a columnar body protrudes from a substrate whose surface is a plane substantially parallel to a specific crystal plane of a diamond crystal;
By exposing the substrate obtained in the first step to plasma of a gas containing hydrogen as a main component, a diamond crystal having a second crystal face different from the crystal face from the base of the columnar body as an exposed face. And a second step of sharpening the tip of the columnar body,
By completing the second step before the diamond crystal growing from the base of the columnar body reaches the tip of the columnar body, a substantially pyramid having the substrate as a bottom surface and the second crystal surface as a side surface. Forming a structure in which the columnar body protrudes from the tip of the body. The diamond element manufacturing method according to claim 9 , wherein the specific crystal plane is a (100) plane. The method for manufacturing a diamond element according to claim 10 , wherein the second crystal plane is a (111) plane.

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