JP5274768B2 - Film forming apparatus and method for preventing abnormal discharge from occurring at cylindrical cathode used in film forming apparatus - Google Patents

Description

  The present invention relates to a film forming apparatus for forming a carbon film as a field emission cold cathode material, and a method for preventing abnormal discharge from occurring in a cylindrical cathode used in the film forming apparatus.

  Field emission is a phenomenon in which electrons are radiated to a vacuum due to electric field concentration. For example, carbon nanotubes (CNT) have recently attracted attention as a field emission type cold cathode (hereinafter, cold cathode) material that emits electrons by this field emission. Development is ongoing. CNTs are extremely thin and have a high aspect ratio, and when used as a cold cathode material, it is said that a cold cathode having excellent field emission characteristics can be obtained.

  The field emission characteristic (current / voltage (IV) characteristic) is a voltage V and a field emission current (emission current) I when a voltage V is applied between the anode and the cold cathode and electric field is emitted from the cold cathode. It is a characteristic indicated by a curve indicating the relationship, and is characterized by a voltage (threshold value) at which field emission is started, and the slope and shape of the curve.

  Such a cold cathode is placed opposite to the anode with the phosphor, a voltage is applied between the cold cathode and the anode, and electrons are emitted from the cold cathode by field emission, and the emitted electrons collide with the phosphor for acceleration. There is a cold-cathode fluorescent lamp that causes a phosphor to be excited to emit light.

  A predetermined amount of electron emission is required for light emission of the phosphor. A current-voltage (IV) characteristic curve showing the emission current indicating the electron emission amount on the vertical axis and the voltage between the positive and negative electrodes on the horizontal axis indicates the electron emission performance of the cold cathode. In the case of CNT, the slope of the IV characteristic curve rises gently. For this reason, in CNT, the voltage V required for obtaining an emission current for the phosphor to start light emission becomes high.

  Therefore, it is desired to realize a carbon film for a cold cathode that provides an IV characteristic capable of starting emission of a phosphor with a lower applied voltage V.

  The present applicant has developed a technique for forming a carbon film for a cold cathode, which has better IV characteristics than CNTs, on a substrate surface such as a conductive wire. The film forming apparatus described below has been developed by the present applicant.

  Hereinafter, with reference to FIG. 4, the film forming apparatus 1 includes a vacuum film forming chamber 6 having a gas introduction system 2 and a vacuum exhaust system 4, and a cylindrical shape disposed inside the vacuum film forming chamber 6. And a cathode 8. The peripheral wall of the cylindrical cathode 8 has a spiral shape (coil shape). A conductive wire 10 is disposed in the internal space of the cylindrical cathode 8 as a substrate to be deposited. The cylindrical cathode 8 generates plasma in a confined state in its internal space. In this sense, the cylindrical cathode 8 can be referred to as a plasma confined cathode.

  The cylindrical cathode 8 is connected to the negative electrode of the DC power source 12. The positive electrode of the DC power supply 12 is grounded. The conductive wire 10 is energized and heated by an AC power supply 14 and a DC bias is applied by a DC power supply 16.

  In the film forming apparatus 1 having the above-described configuration, the vacuum film forming chamber 6 is depressurized by the vacuum exhaust system 4 and the carbon film forming gas is introduced from the gas introducing system 2, and the direct current negative voltage from the direct current power source 12 is obtained. Is applied to the cylindrical cathode 8, plasma 18 is generated in a confined state in the internal space of the cylindrical cathode 8. Thereby, the carbon film forming gas introduced into the cylindrical cathode 8 is decomposed, and the decomposed carbon component is formed on the surface of the conductive wire 10 disposed in the cylindrical cathode 8. It was.

  However, the vacuum pressure in the vacuum film forming chamber 6 was limited to a range of 1000 to 2000 Pa. This limitation is that when the vacuum pressure exceeds 2000 Pa, abnormal discharge occurs from the cylindrical cathode 8, and the carbon film is not formed on the surface of the conductive wire 10, or the film quality is deteriorated even if it is formed. Because it was.

  When the present applicant researched about generation | occurrence | production of abnormal discharge, the carbon substance decomposed | disassembled by plasma generation becomes easy to adhere not only to the electroconductive wire 10 but the cylindrical cathode 8 surface. Since the carbon material adhering to the cylindrical cathode 8 is an amorphous carbon material, the charge is likely to be charged up, and the discharge is caused when the charge charge amount exceeds a certain value. Conceivable.

Therefore, the vacuum pressure must be limited to 2000 Pa or less in order to prevent the occurrence of the abnormal discharge according to the place where the present applicant experimented. When the vacuum pressure is lowered, film formation conditions are restricted on the surface of the conductive wire 10 and a carbon film suitable for a cold cathode material having excellent IV characteristics cannot be formed.
JP-A-10-223128

  Therefore, the problem to be solved by the present invention is that when the range of carbon film formation conditions is expanded so that abnormal discharge does not occur even when the vacuum pressure is increased, and the carbon film is used as a cold cathode material, IV It is an object of the present invention to provide a film forming apparatus capable of providing a cold cathode having improved characteristics and a method for preventing an abnormal discharge from occurring in a cylindrical cathode used in the film forming apparatus.

  A film forming apparatus according to the present invention is a carbon film forming gas introduced into a vacuum film forming chamber by applying a DC negative voltage to a cylindrical cathode disposed in a vacuum film forming chamber and generating plasma in a confined state inside the tube. Is a film forming apparatus for forming a carbon film on the surface of the substrate disposed inside the cylindrical cathode by decomposing the gas, and the gas is decomposed by the plasma generated by applying the DC negative voltage. In the process, the pulsed positive voltage is repeatedly applied to the cylindrical cathode to neutralize the charge charged on the carbon material adhering to the cylindrical cathode, thereby preventing the occurrence of abnormal discharge due to the charge charging up. It is possible to prevent it.

  Although the shape of the said cylindrical cathode is not specifically limited, If either one of both ends is opening, a surrounding wall may be closed, Preferably it has an opening in a part of surrounding wall. The shape (pattern) of the peripheral wall includes a spiral shape, a mesh shape, a fence shape, a lattice shape, and the like as a shape having a large number of openings in the peripheral wall. These shapes are preferable for uniformly forming a carbon film on the surface of the substrate disposed inside the cylindrical cathode.

 The carbon material is a carbon material having a high resistance value and low conductivity.

  The cylindrical cathode includes a cylindrical body having both ends opened and one end opened and the other end closed. The cross-sectional shape of the cylindrical cathode is not particularly limited, but when the substrate shape is a wire shape, a circular shape is preferable.

  Although the shape of a board | substrate is not specifically limited, A planar shape or wire shape can be illustrated. For example, when a wire-like cold cathode is formed by forming a carbon film on a wire-like substrate, a cold-cathode fluorescent lamp in which this wire-like cold cathode is arranged inside a glass tube having an anode with a phosphor on the inner surface is constructed. Can do.

  The purpose of repeatedly applying the pulsed positive voltage to the cylindrical cathode is not limited to periodic repetition, but also includes irregular repetition.

  In the above case, it is preferable that the pulsed positive voltage is periodically and repeatedly applied so that the application period of the pulsed positive voltage within one period is shorter than the application period of the DC negative voltage. By this application, the occurrence of abnormal discharge due to charge up can be effectively prevented without affecting the carbon film formation on the substrate surface.

  In the above case, the duty period of the pulsed positive voltage application period is controlled to the period during which the charged charge can be neutralized by the application of the pulsed positive voltage with respect to the DC negative voltage application period within each cycle at a predetermined frequency. It is preferable.

  The duty control may be performed by controlling the frequency, or may be performed by changing the application period of the pulsed positive voltage when the frequency is the same. In this case, the shape of the pulsed positive voltage can be included in the duty control.

  It is preferable that the predetermined frequency is 1 kHz to 20 kHz, and one application period of the pulsed positive voltage within one cycle at the predetermined frequency is 5 μs to 200 μs.

  However, the magnitude of the pulsed positive voltage is not particularly limited as long as it can neutralize the charged electric charge, but is preferably +100 V to +300 V, more preferably +100 V to +250 V, and optimally. Is about 200V. Of course, even if the magnitude of the pulsed positive voltage is +100 V or less and +250 V or more, the present invention includes the present invention as long as it has a magnitude capable of neutralizing the charged charge.

  In this case, the shape of the pulsed positive voltage is not particularly limited. However, if the apex angle is not a rectangular waveform but an acute triangular shape of, for example, several degrees as a shape expression, the voltage rises from zero V in the positive direction and reaches the maximum value. Since the voltage falls in the negative direction after that, the application period is, for example, about 5 μs in the vicinity of zero V, and is, for example, about 1 to 2 μs in the vicinity of the optimum maximum height of 200 V.

  Therefore, if the shape of the pulsed positive voltage is the acute triangular shape, the application period of the pulsed positive voltage is 5 μs to 200 μs, and 5 μs, which is the shortest application period, is an application period in the vicinity of a voltage of zero V.

  If the shape of the pulsed positive voltage is a substantially perfect rectangular shape, the application period is a period corresponding to the pulse width from the rising edge to the falling edge.

  Since the pulsed positive voltage need only be neutralized by the pulsed positive voltage, the pulsed positive voltage can be set very short compared to the DC negative voltage application period. The direct current plasma film formation can be performed by applying.

  As described above, according to the film forming apparatus of the present invention, the cylindrical cathode is applied to the DC negative voltage application period within each cycle at a predetermined frequency in the process in which the gas is decomposed by DC plasma and the film is formed. Since a pulsed positive voltage is applied in a short application period, a carbon material with high resistance and low conductivity adheres to the cylindrical cathode during the film formation process by plasma without affecting the film formation on the substrate. Even if the attached carbon substance is charged up, the charge can be neutralized with a pulsed positive voltage, and as a result, control can be performed so that abnormal discharge due to charge charge up does not occur. Therefore, in the film forming apparatus of the present invention, it becomes possible to form a carbon film on the substrate surface by controlling the vacuum film forming chamber to a high vacuum pressure, and the formed carbon film is used as a cold cathode material. It is possible to improve the IV characteristics of the cold cathode.

  According to the present invention, a method for preventing abnormal discharge from occurring in a cylindrical cathode for a film-forming apparatus applies a negative DC voltage to a cylindrical cathode disposed in a vacuum film-forming chamber, generates plasma in a confined state therein, and creates a vacuum. In the process of forming the carbon film on the surface of the substrate disposed inside the cylindrical cathode by decomposing the gas for forming the carbon film introduced into the deposition chamber, a pulsed positive voltage is repeatedly applied to the cylindrical cathode, Preferably, by applying a periodic charge to neutralize the electric charge charged to the carbon material having a lower conductivity and a higher resistance than the carbon film attached to the cylindrical cathode, the occurrence of abnormal discharge due to the charge up of the electric charge is prevented. It is characterized by preventing.

  According to the present invention, a carbon film can be formed without causing abnormal discharge from the cylindrical cathode even if the film forming pressure range is increased. As a result, the present invention can provide a cold cathode having improved IV characteristics when the carbon film is formed at a higher deposition pressure range and the formed carbon film is used as a cold cathode material. become able to.

  Hereinafter, a film forming apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a film forming apparatus according to an embodiment. In FIG. 1, the same parts as those in FIG. 4 are denoted by the same reference numerals, and description of the parts related to the same reference numerals will be simplified.

  In the embodiment, a pulse voltage generation unit 20 is provided instead of the DC power supply 12. As shown in FIG. 2, the pulse voltage generator 20 applies the DC negative voltage V1 to the cylindrical cathode 8 in the first application period T1 and the pulsed positive voltage V2 to the second within each period T in a predetermined frequency range. Application period T2 is applied.

  The pulse voltage generation unit 20 can be configured by a pulse power supply, but is not limited thereto. It is only necessary to be able to control the output of the DC negative voltage V1 and the pulsed positive voltage V2. Further, the pulse voltage generator 20 can variably control the period T at the frequency and the application periods T1 and T2.

  As the cylindrical cathode 8, a cylindrical cathode having a spiral shape as an example is used. The cylindrical cathode 8 is one having both ends opened as an example.

  In FIG. 2, T, T1, and T2 are shown based on a voltage of zero V for convenience of explanation.

  The pulsed positive voltage V2 is applied to the cylindrical cathode 8 by repeating the duty with respect to the DC negative voltage V1 at each period T at the above frequency and periodically repeating. By setting the pulse width of the pulsed positive voltage V2 within this period T to the order of μs, the DC negative voltage V1 is applied to the surface of the conductive wire 10 so that a substantially conductive carbon film is continuously formed. .

  The predetermined frequency is preferably in the frequency range of 1 kHz to 20 kHz, more preferably 1 kHz to 3 kHz, and optimally about 2 kHz.

  The second application period T2 is preferably 5 μs to 200 μs, more preferably 10 μs to 30 μs, and most preferably about 20 μs.

  The DC negative voltage is preferably −550 V to −700 V, more preferably −550 V to 650 V, and most preferably about 600 V.

  The pulsed positive voltage is preferably +100 V to +300 V, more preferably +100 V to +250 V, and most preferably about 200 V.

  A process of forming a carbon film on the surface of the conductive wire 10 under the condition of applying a voltage to the cylindrical cathode 8 will be described. First, the inside of the vacuum film forming chamber 6 is depressurized, and CH4 (methane gas) and H2 (hydrogen gas) are introduced from the gas introduction system 2 as an example of the carbon film forming gas, and a pulse voltage generator is applied to the cylindrical cathode 8. Twenty generation voltages are applied.

  This generated voltage is the voltage shown in FIG. Among the voltages shown in FIG. 2, the plasma 18 is generated inside the cylindrical cathode 8 by the DC negative voltage V <b> 1 applied in the first application period T <b> 1. The introduced gas is decomposed by the plasma 18, and a carbon film is formed on the surface of the conductive wire 10 disposed inside the cylindrical cathode 8.

  This carbon film includes carbon nanowalls, carbon nanotubes, carbon nanofibers, acicular carbon films, and the like. The carbon film deposition conditions include a carbon film deposition gas, for example, a flow rate of a carbon-based gas, a flow rate of a carrier gas, a temperature of the conductive wire 10, a pressure in the vacuum deposition chamber 6, and the like. By defining these variously, a target carbon film can be formed.

  On the other hand, when a carbon material decomposed by plasma and having a high resistance is deposited on the outer peripheral surface of the cylindrical cathode 8 during the film formation process in the first application period T1, the carbon material is negatively affected. Charges are charged up.

  In the second application period T2 subsequent to the first application period T1, the pulsed positive voltage V2 is applied to the cylindrical cathode 8, so that the carbon material adhering to the outer peripheral surface of the cylindrical cathode 8 is charged up. The negative charges are neutralized by the pulsed positive voltage V2. As a result, abnormal discharge does not occur from the cylindrical cathode 8 due to the charge-up charge as in the prior art.

  As described above, in this embodiment, the gas is decomposed by the DC plasma 18 and the carbon film is formed on the surface of the conductive wire 10. Since the voltage V2 is applied, even if a high-resistance carbon material adheres to the cylindrical cathode 8 in the process of forming the carbon film by the plasma 18 and the charged carbon material is charged up, the pulsed positive voltage V2 As a result of neutralizing the charge and eliminating the charge-up, abnormal discharge due to the charge charge-up does not occur.

  Therefore, in this embodiment, the inside of the vacuum film formation chamber 6 can be controlled to a high vacuum pressure, and the IV characteristics of the cold cathode using the formed carbon film as a cold cathode material can be improved. it can.

  In FIG. 3, the carbon film is formed on the surface of the conductive wire 10 by controlling the pressure in the vacuum film forming chamber 6 at 1500 Pa (x in the figure), 2000 Pa (Δ in the figure), and 8000 Pa (□ in the figure). The IV characteristic curves A, B, and C when the conductive wire 10 is used as a cold cathode and opposed to the anode are shown.

 In the IV characteristic curves A and B, −600 V is applied to the cylindrical cathode 8 as the DC negative voltage V1, and the pulsed positive voltage V2 is not applied.

 The IV characteristic curve C is a curve when the frequency is 2 kHz, −600 V is applied as the DC negative voltage V1 in the first application period T1, and the second application period T2 is 20 μs and +200 V is applied as the pulsed positive voltage V2.

  As shown by these IV characteristic curves A, B, and C, the IV characteristic when the cold cathode is composed of a carbon film formed at a pressure of 1500 Pa (marked in the drawing) is a voltage of 2.2 V and the IV characteristic curve A is When the cold cathode is made up of a carbon film formed at a pressure of 2000 Pa (Δ in the figure), the IV characteristic curve B rises at a voltage of 1.8 V and the film is formed at a pressure of 8000 Pa (□ in the figure). When the cold cathode is formed of the carbon film, the IV characteristic curve C rises at a voltage of 1.4V.

  That is, by applying the pulsed positive voltage V2 periodically, abnormal discharge does not occur from the cylindrical cathode 8 even if the pressure in the vacuum film forming chamber 6 is controlled to be high. It is possible to form a carbon film excellent in IV characteristics by controlling the temperature high.

  As described above, in the embodiment, in the process in which the gas introduced into the vacuum film forming chamber 6 is decomposed by the plasma generated in the cylindrical cathode 8 and the carbon film is formed on the surface of the conductive wire 10, By periodically applying a pulsed positive voltage V2 to the cathode 8, it becomes possible to control the pressure in the vacuum film forming chamber 6 to be high without causing abnormal discharge from the cylindrical cathode 8 side. As described above, a carbon film having excellent IV characteristics can be formed.

FIG. 1 is a diagram showing a schematic configuration of a film forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a waveform of a voltage applied to the cylindrical cathode. FIG. 3 is a diagram showing a comparison of IV characteristics of cold cathodes using a carbon film formed as a cold cathode material when a carbon film is formed by controlling the pressure in the cylindrical cathode at a high or low level. FIG. 4 is a diagram showing a schematic configuration of a conventional film forming apparatus.

Explanation of symbols

2 Gas introduction system 4 Vacuum exhaust system 6 Vacuum deposition chamber 8 Cylindrical cathode 10 Conductive wire (substrate, deposition target)
20 Pulse voltage generator

Claims (5)

By applying a DC negative voltage to the cylindrical cathode disposed in the vacuum film forming chamber, generating plasma in a confined state therein, and decomposing the carbon film forming gas introduced into the vacuum film forming chamber, A film forming apparatus for forming a carbon film on a substrate surface disposed inside the cylindrical cathode,
In the process in which the gas is decomposed by the plasma generated by applying the DC negative voltage and the film formation is performed, a pulsed positive voltage is repeatedly applied to the cylindrical cathode to the carbon material attached to the cylindrical cathode. A film forming apparatus characterized by neutralizing a charge to be charged, thereby preventing occurrence of abnormal discharge due to charge-up of the charge.   2. The film formation according to claim 1, wherein the pulsed positive voltage is periodically and repeatedly applied with the pulsed positive voltage application period within one cycle being shorter than the DC negative voltage application period. apparatus.  Duty control of the application period of the pulsed positive voltage with respect to the application period of the DC negative voltage within each cycle at a predetermined frequency to a period in which the charged charge can be neutralized by application of the pulsed positive voltage. The film forming apparatus according to claim 1, wherein:   4. The film formation according to claim 3, wherein the predetermined frequency is 1 kHz to 20 kHz, and one application period of the pulsed positive voltage is 5 μs to 200 μs within one period at the predetermined frequency. apparatus.  By applying a DC negative voltage to the cylindrical cathode disposed in the vacuum film forming chamber, generating plasma in a confined state therein, and decomposing the carbon film forming gas introduced into the vacuum film forming chamber, In the process of forming a carbon film on the surface of the substrate disposed inside the cylindrical cathode, a pulsed positive voltage is repeatedly applied to the cylindrical cathode to neutralize the charge charged on the carbon material attached to the cylindrical cathode. Thus, an abnormal discharge is prevented from occurring in the cylindrical cathode for a film forming apparatus, wherein the occurrence of abnormal discharge due to charge-up is prevented.

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