JP2011144418A - Plasma deposition method for conductive thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma deposition method for a conductive thin film, which is highly excellent in deposition workability, is capable of stably depositing the conductive thin film with a film thickness of several nm order avoiding instant flow of excessive current when applying a direct current at high voltage between an anode and a cathode, is excellent in reproducibility and is capable of depositing the conductive thin film with a film thickness of several nm by extending application time of the direct current at high voltage. <P>SOLUTION: The plasma deposition method of the conductive thin film includes steps of: (1) introducing a trace amount of a raw material gas when pressure inside a reaction vessel reaches a prescribed vacuum pressure and applying the direct current at high voltage to both electrodes; (2) depositing a conductive metal the same onto a sample surface, when the introduction of the trace amount of the raw material gas results in a low concentration of the raw material gas inside the reaction vessel so as to enable conduction of a low electric current between both electrodes, by inducing glow discharge between both electrodes so as to convert conductive metal molecules into plasma while controlling the amount of the raw material gas introduced so as to maintain the low current state; and (3) maintaining the low concentration of the raw material gas and the low current state for a prescribed period of time so as to deposit the conductive metal molecules onto the sample surface and forming the conductive thin film with a thickness of nm order. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a plasma film forming method for a conductive thin film in which a surface of a sample to be examined with an electron microscope, particularly a scanning electron microscope (SEM), is formed with a conductive thin film.

  For example, when the sample to be examined by SEM is an insulator, it is necessary to form a conductive film on the sample surface in order to enable emission of secondary electrons by the irradiated electron beam. As a technique for forming a conductive film on the surface of a sample, for example, a film forming method using a plasma film forming apparatus disclosed in Patent Document 1 is known.

  That is, in the plasma film forming apparatus of Patent Document 1, the positive electrode and the negative electrode on which the sample is placed are vacuum-sucked to form a predetermined degree of vacuum in a reaction vessel in which the positive electrode and the negative electrode are placed at a predetermined interval. In the state where a metal compound gas is introduced into the reaction vessel and a predetermined degree of vacuum is applied, a direct current high voltage is applied between the positive electrode and the negative electrode to generate a glow discharge on the surface of the sample on the negative electrode. A conductive film is formed by depositing conductive metal molecules.

  Specifically, after vacuuming the inside of the reaction vessel to form 0.9 Pa, a sublimation gas such as osmium tetroxide is introduced to form the inside of the reaction vessel at 9 pa between the positive electrode and the negative electrode. An osmium film having a thickness of about 10 nm is formed by applying a direct current high voltage to generate glow discharge with a current of 2 to 4 mA to convert osmium molecules into plasma and depositing it on the surface of the sample.

  However, when observing a sample by SEM, the formed osmium film is also magnified at the same time, and therefore, when observing or analyzing only the sample, a thick osmium film is used. Is an obstacle. In order to avoid this obstacle, it is necessary to form an osmium film formed on the surface of the sample with a film thickness of several nanometers, but the osmium film with a film thickness of several nanometers by the conventional film formation method described above. When the film is formed, the following problems occur.

First, when a high DC voltage is applied between the positive electrode and the negative electrode while introducing a sublimation gas into the reaction vessel and increasing the concentration, an excessive current may flow instantaneously, resulting in poor film quality. The conductive thin film could not be stably formed with a film thickness on the order of several nm, and the reproducibility was poor.

  Second, in order to control the DC high voltage application time to form a conductive thin film with a film thickness on the order of several nanometers, the DC high voltage application time must be controlled in a very short time of several seconds. In order to form a conductive thin film with a film thickness on the order of several nm, workability was poor.

JP 2002-4056 A

The problem to be solved is that when a high DC voltage is applied between the positive electrode and the negative electrode in a state where a sublimation gas is introduced into the reaction vessel and the concentration is increased, an excessive current instantaneously flows and the film quality is reduced. The conductive thin film cannot be stably formed with a film thickness on the order of several nm, and the reproducibility is poor. In addition, in order to form a conductive thin film with a thickness on the order of several nanometers, it is necessary to control the DC high voltage application time in an extremely short time of several seconds, and the conductive thin film can be stably formed. However, the workability is bad.

  Claim 1 of the present invention contains conductive metal molecules while forming a high vacuum state by evacuating the air in the reaction vessel in which the positive electrode and the negative electrode are arranged to face each other at a predetermined interval. Plasma that forms a conductive thin film by supplying glowing source gas and generating glow discharge by direct current high voltage applied between both electrodes to turn conductive metal molecules into plasma and deposit it on the sample surface on the negative electrode In the film forming method, (1). A high DC voltage is applied between both electrodes while a small amount of raw material gas is introduced when the pressure in the reaction vessel reaches a predetermined vacuum pressure (2). When the raw material gas concentration in the reaction vessel becomes a low concentration state where both electrodes are connected at a low current value due to a small amount of raw material gas inflow, the minute inflow amount of the raw material gas is reduced so as to maintain the low current state. (3). Conductive metal molecules are turned into plasma by glow discharge generated between both electrodes while being controlled, and are deposited on the sample surface. The conductive thin film is formed on the order of nm by conductive metal molecules deposited on the sample surface while maintaining the low concentration state and low current state of the source gas according to (2) for a predetermined time, (1) It is characterized by comprising the steps of (3) to (3).

According to a fourth aspect of the present invention, a raw material gas containing conductive metal molecules is formed in a high vacuum state by exhausting air in a reaction vessel having a positive electrode and a negative electrode facing each other at a predetermined interval by a vacuum exhaust means. Film formation method of forming a conductive thin film by generating glow discharge by a direct current high voltage applied between both electrodes and converting conductive metal molecules into plasma and depositing on the sample surface on the negative electrode (1). Flowing a source gas diluted with an inert gas when the pressure in the reaction vessel reaches a predetermined vacuum pressure (2). When the pressure in the reaction vessel rises due to the inflow of diluted source gas and the source gas concentration reaches the required low concentration state, a DC high voltage is applied between both electrodes, and a low current is applied between both electrodes. Conduct by value (3). Conductive metal molecules are converted into plasma by glow discharge generated at a low current value between both electrodes while controlling the inflow of the source gas diluted so as to maintain the low current value state, and deposited on the sample surface ( 4). The conductive thin film is formed in nm order with conductive metal molecules deposited on the surface of the sample while maintaining the low concentration state and the low current state of the source gas according to the above (3) for a predetermined time. It is characterized by comprising the steps (4) to (4).

  In the present invention, when a direct current high voltage is applied between the positive electrode and the negative electrode, an excessive current is prevented from flowing instantaneously, and a conductive thin film is stably formed with a film thickness on the order of several nm. Excellent reproducibility can be achieved. In addition, it is possible to stably form a conductive thin film with a film thickness on the order of several nanometers by extending the DC high voltage application time, which is excellent in workability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional explanatory view showing an outline of a plasma film forming apparatus used when carrying out a method of the present invention according to Example 1. FIG. 6 is a cross-sectional explanatory view showing an outline of a plasma film forming apparatus used when carrying out the method of the present invention according to Example 2.

  The present invention is to form a conductive thin film on the order of nm with conductive metal molecules deposited on a sample surface while maintaining a low concentration state and a low current state of a source gas in a reaction vessel for a predetermined time. The best form.

The present invention will be described below with reference to the drawings showing examples.
First, the plasma film forming apparatus 1 used when carrying out the method of the present invention corresponding to claim 1 will be described. As shown in FIG. 1, the reaction vessel 3 of the plasma film forming apparatus 1 is made of pressure-resistant glass and has an upper portion. The top plate portion 5 and the substrate portion 7 are detachably attached to the lower portion, and are attached in an airtight manner. A positive electrode 9 is attached to the lower surface of the central portion of the top plate 5 in an electrically insulated state, and a sublimation chamber 11 is provided on the lower surface of the top plate 5 located around the positive electrode 9. The top plate part 5 is provided with a source gas introduction part 13 for introducing a source gas into the sublimation chamber 11. The sublimation chamber 11 is provided with a source gas outlet 15 for introducing source gas into the reaction vessel 3.

An organic or inorganic metal compound crystal powder is housed in an airtight manner in the hollow portion of the raw material gas introducing portion 13, and the raw material gas sublimated in the hollow portion is introduced into the sublimation chamber 11. Examples of the metal of the metal compound include Group I (Au, Ag, Cu), Group II (Mg, Zn, Cd), Group III (B, Al, Ga, In, Y), and Group IV (Ti , Si, Ge, Sn, Pb), Group V (V, Nb, Ta, As, Sb, Bi), Group VI (Cr, Mo, W, Se), Group VII (Mn), Group VIII (Os, Ir Pt, Pd, Rh, Co, Ni, Fe) and the like. Since osmium tetroxide (OsO ₄ ) is suitable as the source gas of the present embodiment, the following description will be made using osmium sublimation gas.

The source gas outlet 15 has a structure in which the opening degree of the sublimation chamber 11 with respect to the reaction vessel 3 can be adjusted by a flow rate variable member 17 such as a needle valve, and is introduced into the reaction vessel 3 by rotating the flow rate variable member 17. The concentration of the osmium sublimation gas and thus the pressure in the reaction vessel 3 can be adjusted.

A negative electrode 19 is attached to the upper surface of the central portion of the substrate portion 7 in an electrically insulated state. A sample stage 21 is provided on the upper surface of the negative electrode 19, and the sample 23 placed on the sample stage 21 is positioned in a region of a negative glow layer (about 1 to 6 mm from the upper surface of the negative electrode) described later. .

The substrate section 7 is provided with an exhaust pipe 25 connected to a vacuum suction device (not shown) so as to communicate with the inside of the reaction vessel 3, and the inside of the reaction vessel 3 is driven to a predetermined vacuum pressure by driving the vacuum suction device. A vacuum is formed at (0.9 Pa). The positive electrode 9 is connected to the (+) electrode of a DC power supply device (not shown), and the negative electrode 19 is connected to the (−) electrode of the DC power supply device. A DC glow discharge is generated by applying a DC high voltage of 3 kV.

A vacuum pressure sensor (not shown) is provided in the reaction vessel 3 or between the exhausts 25 to detect the vacuum pressure in the reaction vessel 3.

Next, a method for forming a conductive thin film using the plasma film forming apparatus 1 will be described. The inside of the reaction vessel 3 is hermetically sealed with a sample 23 for SEM microscopy set on a sample stage 21 and four. The source gas introduction part 13 in which the osmium oxide crystal is accommodated is set, and the osmium tetroxide crystal is sublimated in the sublimation chamber 11 to generate osmium sublimation gas.

In the above state, the vacuum evacuation device is driven to form a vacuum in the reaction vessel 3 at, for example, 0.9 Pa, and then the DC power supply device is turned on while the evacuation state is continued, so A high DC voltage is applied, and the flow rate variable member 17 is finely operated to allow the osmium sublimation gas in the sublimation chamber 11 to flow into the reaction vessel 3 in a small amount. At this time, in a state where the osmium sublimation gas is not flowing into the reaction vessel 3, the space between the positive electrode 9 and the negative electrode 19 is kept in an electrically insulated state by a vacuum, and no current flows between the two electrodes.

When the osmium sublimation gas flowing into the reaction vessel 3 has a predetermined concentration, and therefore the pressure in the reaction vessel 3 reaches a predetermined pressure (about 3 Pa), an electric current flows due to the presence of osmium molecules between both electrodes, and both electrodes A direct current glow discharge is generated between them. At this time, since the concentration of the osmium sublimation gas in the reaction vessel 3 is low, the current flowing between both electrodes also becomes a low current, and a minute amount of osmium molecules is converted into plasma and deposited on the surface of the sample 23.

Then, the glow discharge state is maintained for a predetermined time while controlling the inflow amount of the osmium sublimation gas flowing into the reaction vessel 3 by operating the flow rate variable member 17 so that the current value between both electrodes maintains the low current state. Then, an osmium thin film having a thickness of the order of several nm is formed on the surface of the sample 23.

That is, in this embodiment, the amount of osmium sublimation gas flowing into the reaction vessel 3 and the concentration thereof are controlled so that the current value between the electrodes becomes a low current value, thereby controlling the osmium molecule relative to the sample 23. Osmium thin film with a film thickness of several nm order can be formed by depositing a small amount of osmium, and excessive current can be prevented from flowing transiently between both electrodes, and osmium film with a film thickness of several nm order. A thin film is formed uniformly.

Specific examples of forming an osmium thin film having a thickness of 1 nm by the method of this embodiment are shown in Table 1, and specific examples of forming an osmium thin film having a thickness of 2 nm are shown in Table 2.

The film thickness of the osmium thin film shown in Tables 1 and 2 above is not the actual measurement of the film thickness of the formed osmium thin film, but the time for forming a film thickness of 1 nm with a conventional plasma film forming apparatus.・ The value converted from the current product.

The “flow rate variable member rotational speed” in the above Tables 1 and 2 represents the opening degree of the flow rate variable member 17 with respect to the inside of the reaction vessel 3, and when “0” is closed, the opening degree increases with the rotational speed. Indicates that the flow rate increases as the volume increases.

The current values “0 to 1 intermittent” in Tables 1 and 2 indicate that the current value between both electrodes is intermittent between 0 mA and 1 mA, and the glow discharge state flashes.

The current values “0 to 1” in Tables 1 and 2 indicate that the start of glow discharge between both electrodes is 0 nA and the final value is 1 mA.

As is clear from Tables 1 and 2 above, the degree of vacuum in the reaction vessel 3 is kept substantially constant (3 Pa) at the start and end of glow discharge, and the inflow amount of osmium sublimation gas is gradually increased. The value of current flowing between both electrodes gradually increases and the film formation time is shortened.

In the above description, a DC high voltage was applied between the electrodes while the inside of the reaction vessel 3 was vacuum-formed at a high degree of vacuum (0.9 Pa). However, the present invention applies osmium sublimation gas to the reaction vessel 3. A DC high voltage may be applied between the two electrodes when the high vacuum state, for example, 1 Pa, is reached after the inflow and before the glow discharge starts.

The application time of the DC high voltage applied between the electrodes is programmed according to the relationship between the degree of vacuum in the reaction vessel 3 and the flow rate of the osmium sublimation gas into the reaction vessel 3, and thus the opening degree by the flow rate variable member 17. A method of automatically forming an osmium thin film having a film thickness on the order of several nm by controlling the application time by the program may be used.

  A plasma film forming apparatus 51 used for carrying out the method of the present invention corresponding to claim 2 has the following configuration added to the plasma film forming apparatus 1 described in the first embodiment.

That is, as shown in FIG. 2, an inert gas introduction pipe 53 is provided in part of the substrate portion 7 of the plasma film forming apparatus 51 so as to communicate with the inside of the reaction vessel 3. The inert gas introduction pipe 53 is connected to a supply source 59 such as a gas cylinder filled with an inert gas such as nitrogen gas, argon gas, or helium gas via an opening / closing valve 55 such as a solenoid valve and a flow rate regulator 57. The inert gas whose flow rate has been adjusted by the flow rate regulator 57 as the on-off valve 55 is opened and closed is introduced into the reaction vessel 3.

As a result, the inert gas whose flow rate is controlled with respect to the osmium sublimation gas that has been adjusted in flow rate by the flow rate variable member 17 and has flowed into the reaction vessel 3 is introduced and diluted at a desired ratio.

Since other configurations are the same as those of the plasma film forming apparatus 1 of the first embodiment, the same members are denoted by the same reference numerals as those of the first embodiment and detailed description thereof is omitted.

Next, a method for forming a conductive thin film by the method of this embodiment using the plasma film forming apparatus 51 will be described. Inside the reaction vessel 3 with the sample 23 for the SEM speculum set on the sample stage 21. The source gas introduction part 13 that is hermetically sealed and contains osmium tetroxide crystals is set, and the osmium tetroxide crystals are sublimated in the sublimation chamber 11 to generate osmium sublimation gas.

The vacuum evacuation apparatus is driven in the above state to form a vacuum in the reaction vessel 3 at, for example, 0.9 Pa, and then the flow variable member 17 is operated while maintaining the vacuum evacuation state so that the osmium sublimation gas in the sublimation chamber 11 is maintained. Is introduced into the reaction vessel 3, the opening / closing valve 55 is opened and closed to introduce the inert gas whose flow rate is adjusted into the reaction vessel 3, and the osmium sublimation gas flowing into the reaction vessel 3 is introduced into the reaction vessel 3. Dilute in proportions according to volume.

In addition, the dilution ratio of the osmium sublimation gas with the inert gas in the reaction vessel 3 is determined based on a current value between both electrodes, which will be described later, and a film formation time. That is, in order to lengthen the film formation time while keeping the current value flowing between both electrodes constant, the dilution ratio of the osmium sublimation gas is increased. On the other hand, when the film formation time is shortened, the dilution ratio is decreased.

Then, when the vacuum pressure in the reaction vessel 3 reaches, for example, the same vacuum pressure (9 Pa) as in the conventional film forming method described above, a DC high voltage is applied between the positive electrode 9 and the negative electrode 19. At this time, since the osmium sublimation gas in the reaction vessel 3 is diluted with an inert gas and the concentration of the osmium sublimation gas is lower than that of the conventional film formation method, a relatively low current (0 to 1 mA) is present between both electrodes. ) Only flows.

For this reason, in the reaction vessel 3, glow discharge is performed at a low current in the same manner as in Example 1, and osmium molecules are turned into plasma and deposited on the surface of the sample 23. Then, the state in which the low concentration osmium sublimation gas is glow-discharged at a low current is continued for a predetermined time to form an osmium thin film on the surface of the sample 23 on the order of several nm.

In Examples 1 and 2 described above, a method of forming an osmium thin film on the surface of the sample 23 on the surface of the sample 23 using the osmium sublimation gas as the source gas was used. May be sublimated or gasified by heating.

In the description of Examples 1 and 2, the source gas introduction unit 13 is set on the top plate unit 5 and the osmium sublimation gas is generated in the sublimation chamber 11, but the concentration of the generated osmium sublimation gas is as follows. The temperature in the sublimation chamber and the amount of osmium tetroxide crystals accommodated in the raw material gas inlet 13 tend to be largely unstable and not stable. In the present invention, in order to stabilize the concentration of the osmium sublimation gas in the reaction vessel 3, a gas introduction pipe is provided in the top plate part 5 or the substrate part 7 without using the sublimation chamber 11, and the gas introduction is performed. The pipe may be connected to a gas cylinder filled with osmium through an on-off valve such as a solenoid valve, and the osmium gas at a constant concentration supplied from the gas cylinder may be flow-regulated by the on-off valve to flow into the reaction vessel 3. .
When the source gas is introduced into the reaction vessel 3 from the gas cylinder as described above, the gas connected to the gas cylinder with respect to one introduction pipe communicating with the inside of the reaction vessel 3 to the top plate portion or the substrate portion. The inert gas introduction pipe connected to the introduction pipe and the gas supply source may be connected in parallel so that the diluted raw material gas diluted with the inert gas at a desired ratio is introduced into the reaction vessel 3. .

DESCRIPTION OF SYMBOLS 1 Plasma film-forming apparatus 3 Reaction container 5 Top plate part 7 Substrate part 9 Positive electrode 11 Sublimation chamber 13 Raw material gas introduction part 15 Raw material gas outlet part 17 Flow variable member 19 Negative electrode 21 Sample stand 23 Sample 25 Exhaust pipe 51 Plasma film formation Device 53 Pipe for introducing inert gas 55 On-off valve 57 Flow regulator 59 Supply source

Claims (7)

A source gas containing conductive metal molecules is supplied while the inside of the reaction vessel in which the positive electrode and the negative electrode are opposed to each other at a predetermined interval is exhausted by a vacuum exhaust means to form a high vacuum state. In a plasma film forming method for forming a conductive thin film by generating a glow discharge by a direct current high voltage applied between electrodes to make conductive metal molecules into plasma and depositing on a sample surface on a negative electrode,
(1). When a pressure in the reaction vessel reaches a predetermined vacuum pressure, a DC high voltage is applied between both electrodes while flowing a small amount of raw material gas.
(2). When the raw material gas concentration in the reaction vessel becomes a low concentration state where both electrodes are connected at a low current value due to a small amount of raw material gas inflow, the minute inflow amount of the raw material gas is reduced so as to maintain the low current state. Conductive metal molecules are turned into plasma by glow discharge generated between both electrodes while being controlled, and deposited on the sample surface.
(3). A conductive thin film is formed on the order of nm by conductive metal molecules deposited on the sample surface while maintaining the low concentration state and low current state of the source gas according to (2) for a predetermined time.
A plasma film forming method for a conductive thin film comprising the steps (1) to (3). The method for forming a conductive thin film according to claim 1, wherein the source gas is an osmium sublimation gas. 2. The method of claim 1, wherein the source gas is an osmium gas having a constant concentration supplied from a gas cylinder. A source gas containing conductive metal molecules is supplied while the inside of the reaction vessel in which the positive electrode and the negative electrode are opposed to each other at a predetermined interval is exhausted by a vacuum exhaust means to form a high vacuum state. In a plasma film forming method for forming a conductive thin film by generating a glow discharge by a direct current high voltage applied between electrodes to make conductive metal molecules into plasma and depositing on a sample surface on a negative electrode,
(1). When the pressure in the reaction vessel reaches a predetermined vacuum pressure, a source gas diluted with an inert gas is allowed to flow in,
(2). When the pressure in the reaction vessel rises due to the inflow of diluted source gas and the source gas concentration reaches the required low concentration state, a DC high voltage is applied between both electrodes, and a low current is applied between both electrodes. Conducting by value,
(3). Conductive metal molecules are plasmatized and deposited on the sample surface by glow discharge generated at a low current value between both electrodes while controlling the inflow of the source gas diluted so as to maintain the low current value state.
(4). A conductive thin film is formed on the order of nm with conductive metal molecules deposited on the sample surface while maintaining the low concentration state and low current state of the source gas according to (3) for a predetermined time.
A plasma film forming method for a conductive thin film comprising the steps (1) to (4). 5. The method for forming a conductive thin film according to claim 4, wherein the source gas is osmium sublimation gas. 5. The plasma deposition method for a conductive thin film according to claim 4, wherein the source gas is an osmium gas having a constant concentration supplied from a gas cylinder. 5. The plasma deposition method for a conductive thin film according to claim 4, wherein the inert gas is at least one of nitrogen gas, argon gas, and helium gas.

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