JP2008056994A - Plasma ion metal deposition apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma ion metal deposition apparatus which can form plasma with high density even using a wide and shallow hollow cathode, and can stably deposit a metal film. <P>SOLUTION: The plasma ion metal deposition apparatus is equipped with: an anode 2 and a hollow cathode 3 confronted within a vacuum chamber 1 held to a thin gas atmosphere; a voltage application circuit 18 for applying voltage for plasma discharge to the anode 2 and the hollow cathode 3; a material gas feeding chamber 10 for feeding a material gas into the vacuum chamber 1; and a sample stand 4 for mounting a sample 7 to be formed with a metal film in the hollow cathode 3. An annular shielding wall 3a bulging from the upper edge of the cathode circumferential wall 3b in the hollow cathode 3 to the inside of the hollow cathode 3 is provided, and the material gas for film deposition is introduced into the hollow cathode 3. Concretely, the material gas for film deposition is introduced from the side of the cathode circumferential wall 3b in the hollow cathode 3 into a plasma region on the sample stand 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention forms a conductive film on the surface of a defective conductor sample in a scanning electron microscope as a pretreatment of the sample when using a scanning electron microscope, and eliminates the charging phenomenon that occurs during observation of a scanning electron microscope image. In addition, the present invention relates to a plasma ion metal deposition apparatus as a pretreatment apparatus for metal deposition that promotes the generation efficiency of secondary electrons.

  The observation with a scanning electron microscope (SEM) requires that the surface of the sample is a good electrical conductor. For this reason, a defective electrical conductor sample such as a biological sample or an inorganic compound is observed after a thin metal film or carbon film of several tens of nm is formed on the surface.

  Conductive film deposition on the SEM sample is performed by depositing gold, platinum, or an alloy thereof using a vacuum deposition apparatus or an ion sputtering metal deposition apparatus. Since the metal particles to be deposited need to be a continuous film, a certain thickness is required. For this reason, the fine structure of the sample surface is concealed, and the deposited metal is crystallized to become coarse particles, which are confused with the structure of the sample surface and prevent accurate judgment.

  Carbon deposition is also used for antistatic, but carbon is used only when the generation efficiency of secondary electrons is low and X-ray analysis is mainly used. Sometimes it is also used as auxiliary means to compensate for the lack of electrical conductivity of the metal. However, since a thickness of 10 nm or more is necessary for a sample having a complicated shape, the entire deposited film becomes thick and the fine structure is buried and cannot be observed.

In order to solve this problem, it is necessary to form a thin conductive film that does not lose the fine structure of the sample surface, and that the thin film has sufficient secondary electron emission efficiency for scanning electron microscope image formation. It is.
Pt or Pt—Pd particles deposited to a thickness of about 1 nm by ion sputtering have a secondary electron emission capability of less than 1 nm, and have sufficient potential for observing the fine structure of the sample surface. . However, it is impossible to form a continuous film for a sample having a complicated shape, which is insufficient for preventing charging.

  As one of means for forming a conductive film of a sample for a scanning electron microscope, there is a means for depositing metal osmium (Os) by plasma ion deposition using osmium tetroxide gas as a raw material. The plasma deposited Os film forms a continuous film even with a thin film of 1 nm or less, and exhibits an antistatic effect even on a sample surface having a complicated shape.

  In the case of a flat cathode in which a sample is placed on the cathode and discharged in an atmosphere of dilute osmium tetroxide gas of about 5 to 6 Pa in the deposition of Os by plasma ion deposition, the discharge voltage is about 1000 to 1500V. At such a high voltage, the sample is damaged by the impact of high-energy osmium ions.

  As a countermeasure, the cathode is a hollow cathode, and the sample is insulated and installed in the cathode, so that the discharge voltage in the osmium gas atmosphere is less than half that of the planar electrode. Thereby, the impact force of the ion with respect to a sample becomes 1/4 or less, and sample damage can be reduced. For example, Patent Document 1 and Patent Document 2 described below describe a film forming apparatus using such a hollow cathode.

  In the formation of a metal film by plasma ion deposition using such hollow cathode discharge, for example, when a microcircuit pattern of a semiconductor wafer is observed and inspected by SEM, a plurality of samples having a large area are simultaneously formed. There is an increasing demand for processing. However, in order to process a plurality of samples having a large area at the same time, a sample table having a large area exceeding the diameter of 250 mm is required. For this purpose, it is necessary to increase the area of the hollow cathode.

The hollow cathode has a cylindrical peripheral wall erected around the disk electrode. The plasma density at the hollow cathode increases as the depth of the cylindrical peripheral wall increases with respect to the cathode diameter, and a stable plasma can be obtained. However, in order to increase the diameter of the hollow cathode and obtain a depth corresponding to the diameter, it is necessary to make the depth of the hollow cathode considerably large, and there is a problem that the apparatus becomes large.
JP 2000-65702 A JP 2000-266653 A

  In view of the problems in the conventional plasma ion metal deposition apparatus using plasma ion deposition utilizing hollow cathode discharge, the present invention can form a high-density plasma stably even with a wide and shallow hollow cathode. It is an object of the present invention to provide a plasma ion metal deposition apparatus capable of forming a metal film.

  In the present invention, in order to achieve the above object, an annular shielding wall 3a projecting inward from a cylindrical cathode peripheral wall 3b of a hollow cathode 3 provided with a sample stage 4 on which a sample 7 on which a metal film is to be formed is provided. A source gas for film formation is introduced into the hollow cathode 3 from the cathode peripheral wall 3b side, and the plasma region in the hollow cathode 3 is limited by the shielding wall 3a to generate high-density plasma. I tried to make it.

  That is, the plasma ion metal deposition apparatus according to the present invention has an anode 2 and a hollow cathode 3 facing each other in a vacuum chamber 1 maintained in a rare gas atmosphere, and a voltage for plasma discharge is applied to the anode 2 and the hollow cathode 3. A voltage application circuit 18 to be applied, a source gas supply chamber 10 for supplying source gas into the vacuum chamber 1, and a sample stage 4 on which a sample 7 for forming a metal film in the hollow cathode 3 is placed. An annular shielding wall 3 a projecting from the upper edge of the cathode peripheral wall 3 b of the hollow cathode 3 to the inside of the hollow cathode 3 is provided, and a raw material gas for forming a film is introduced into the hollow cathode 3. Specifically, the raw material gas for film formation is introduced into the plasma region on the sample table 4 from the cathode peripheral wall 3 b side of the hollow cathode 3.

  Since the plasma ion metal deposition apparatus according to the present invention is provided with an annular shielding wall 3a protruding from the cylindrical cathode peripheral wall 3b of the hollow cathode 3 to the inside thereof, the plasma region in the hollow cathode 3 is the shielding wall. Limited by 3a. Then, by introducing the source gas into the hollow cathode 3, the source gas is ionized in a limited plasma region in the hollow cathode 3 to generate plasma. Thereby, even if it is the wide and shallow hollow cathode 3, a high plasma density is obtained.

  In particular, when the raw material gas for forming the film is introduced into the hollow cathode 3 from the cathode peripheral wall 3b side, the annular shielding wall 3a protruding from the cylindrical wall 1c of the hollow cathode 3 to the inside of the hollow cathode 3 enters the plasma region. Has a function to guide. Thereby, a high plasma density can be obtained efficiently and stably.

  As described above, according to the present invention, even if the hollow cathode 3 is wide and shallow, a high plasma density can be obtained efficiently and stably, so that it is not necessary to deepen the wide hollow cathode 3. Thereby, the plasma ion metal deposition apparatus provided with the comparatively wide sample stand 4 can be comprised small.

  The plasma density due to the discharge of the hollow cathode increases as the depth of the cathode peripheral wall increases with respect to the diameter of the cathode peripheral wall. When the diameter of the sample stage increases, the sample installation area in the hollow cathode increases. However, it is difficult to deepen the hollow cathode in proportion to this because of the problem of increasing the size of the apparatus. In the present invention, in order to compensate for this, a shielding wall is projected inwardly from the upper edge of the cathode side wall of the hollow cathode, thereby making it possible to increase the plasma density.

A plasma ion metal deposition apparatus using a hollow cathode according to an embodiment of the present invention is shown in FIG.
The vacuum chamber 1 has a top plate 1a and a bottom plate 1d facing each other in parallel, and a peripheral wall 1c made of a cylindrical glass plate is hermetically sandwiched between the outer peripheral sides thereof. The inner surface, that is, the lower surface of the top plate 1a of the vacuum chamber 1 is covered with a contamination prevention plate 1b.

  A vacuum exhaust device 13 such as a rotary pump is connected to the vacuum chamber 1 via an open / close valve 14 such as an electromagnetic valve. When a highly corrosive gas such as osmium tetroxide, which will be described later, is introduced into the vacuum chamber 1, fluorine-based vacuum oil that is not violated by osmium gas is used for the vacuum exhaust device 13, and the pump exhaust side is used. An active gas absorption device such as activated carbon or zeolite is provided. The degree of vacuum in the vacuum chamber 1 is measured by a vacuum gauge 15 provided on the exhaust pipe.

An insulating bush 8a passes through the center of the upper plate 1a of the vacuum chamber 1, and a disc-shaped anode 2 is provided below the upper plate 1a of the vacuum chamber 1 while being insulated by the insulating bush 8a. It has been.
Further, the vacuum chamber 1 is provided with an air leak valve 17 for introducing air into the vacuum chamber 1 on the upper plate 1a.

  On the other hand, an insulating bush 8b passes through the center of the bottom plate 1d of the vacuum chamber 1, and a hollow cathode 3 is provided on the bottom plate 1d of the vacuum chamber 1 while being insulated by the insulating bush 8b. . The anode 2 and the hollow cathode 3 face each other vertically in the vacuum chamber 1.

  The hollow cathode 3 includes a disc-shaped cathode bottom plate 3c disposed on the bottom plate 1d of the vacuum chamber 1, a cylindrical cathode peripheral wall 3b rising from the outer periphery of the cathode bottom plate 3c, and an upper edge of the cathode peripheral wall 3b. And an annular shielding wall 3 a projecting from the portion to the inside of the hollow cathode 3. For example, the diameters of the cathode bottom plate 3c and the cathode peripheral wall 3b are about 250 mm, and the inner diameter of the shielding wall 3a is preferably 80% or less. The shielding wall 3a is detachably attached to the cathode peripheral wall 3b.

  A sample stage 4 is provided on the cathode bottom plate 3c of the hollow or sword 3 while being fitted to the insulating bush 8b. The sample table 4 and the hollow or sword 3 are insulated by the insulating bush 8b. The sample stage 4 has a diameter slightly smaller than the inner diameter of the cathode peripheral wall 3 b of the hollow or sword 3. A gap is provided between the sample table 4 and the cathode bottom plate 3c and the cathode peripheral wall 3b. A sample 7 whose surface is coated with a film is placed on the sample table 4.

A disc-shaped electrostatic shield plate 5 is provided between the cathode bottom plate 3 c of the hollow cathode 3 and the bottom plate 1 d of the vacuum chamber 1 while being fitted to the insulating bush 8 b. The electrostatic shield plate 5 is insulated from the hollow or sword 3 by the insulating bush 8b.
A passage is provided along the central axis of the insulating bush 8b, whereby a source gas introduction passage 9 is formed. The insulating bush 8b is provided with a plurality of radial passages 9a communicating with the source gas introduction passage 9. The passage 9a communicates with a gap between the sample table 4 and the cathode bottom plate 3c on the outer peripheral side of the insulating bush 8b.

A raw material gas supply chamber 10 is connected to the raw material gas introduction path 9 via a flow rate adjusting valve 11 including an open / close valve 12 such as an electromagnetic valve and a needle valve.
Separately, an atmospheric gas adjusting valve (Ev-Gas) 16 is connected to the vacuum chamber 1 at the bottom plate 1d. The atmosphere gas adjustment valve 16 is composed of a needle valve or the like, and introduces a plasma forming gas such as air, N ₂ , or Ar into the vacuum chamber 1 while adjusting it, thereby adjusting the atmosphere in the vacuum chamber 1. .

A high voltage is applied between the anode 2 and the hollow cathode 3 by a voltage application device 18. This voltage application device 18 is connected to a power source by a switch 20, is adjusted in voltage by a voltage regulator 19, is rectified to a direct current, and is applied to the anode 2 and the hollow cathode 3.
In such a plasma ion metal deposition apparatus, the operation of coating a sample with a metal film will be described below.

The sample 7 is processed according to a predetermined procedure, and a sample in a dry state is placed on the sample table 4. First, the inside of the vacuum chamber 1 is exhausted to a pressure of about 2 Pa by the vacuum exhaust device 13. Thereafter, a gas such as air, N ₂ , or Ar is introduced into the vacuum chamber 1 by the atmospheric gas adjustment valve 16, and the inside of the vacuum chamber 1 is maintained at a pressure of about 8 to 10 Pa suitable for plasma discharge. In this state, a high voltage is applied between the anode 2 and the hollow cathode 3.

In the internal space of the hollow cathode 3 surrounded by the cylindrical cathode peripheral wall 3b and the annular shielding wall 3a, gas molecules such as air, N ₂ , and Ar maintained at several Pa are positively charged ions by discharge. And negatively charged electrons, and plasma is formed. Further, undecomposed gas molecules are ionized by collision with electrons, and plasma formation is promoted. Then, the electrons separated in the internal space of the hollow cathode 3 have a longer time to stagnate in the closed space, and accordingly, the chance of collision with undecomposed gas molecules increases, so that plasmaization is promoted. The plasma density in the internal space of the hollow cathode 3 increases. On the other hand, in the space outside the hollow cathode 3, the separated electrons diffuse into a wide space in the vacuum chamber 1 and travel toward the anode, so that the probability of collision with undecomposed gas molecules is low, and thus the plasma density is low. Become.

With the plasma discharge in the interior space of the hollow cathode 3, a source gas of osmium tetroxide (OsO ₄ ) is introduced from the source gas supply chamber 10 into the interior space of the hollow cathode 3. The crystal of osmium tetroxide is usually stored in an ampule-shaped container 6, but this container 6 is opened and stored in the source gas supply chamber 10. The osmium tetroxide crystal is sublimable. When the opening / closing valve 12 and the flow rate adjusting valve 11 of the source gas supply chamber 10 are opened, the osmium tetroxide gas sublimated from the osmium tetroxide crystal passes through the source gas introduction passage 9 to form a vacuum chamber. 1 is introduced.

  The osmium tetroxide gas from the source gas introduction path 9 toward the vacuum chamber 1 is guided to the gap between the cathode bottom plate 3 c of the hollow cathode 3 and the sample stage 4 through the radial passage 9 a of the source gas introduction path 9. . Further, the osmium tetroxide gas flows from the gap between the cathode bottom plate 3 c and the sample table 4 toward the cathode peripheral wall 3 b, and flows through the gap between the cathode peripheral wall 3 b and the sample table 4. The osmium tetroxide gas rises along the cathode peripheral wall 3 b and diffuses on the sample stage 4.

  When the anode 2 and the hollow cathode 3 are in a discharge state, the internal space of the hollow cathode 3 is a high-density plasma. Therefore, the osmium tetroxide gas is decomposed by the plasma energy here, and the metal osmium The (Os) particles separate and adhere to the surface of the sample 7. In particular, in the internal space of the hollow cathode 3 facing the anode 2, the plasma density is high and the energy of the plasma is strong, so that the decomposition power of the osmium tetroxide gas is large. Thereby, even if the depth is shallow compared with the diameter of the hollow cathode 3, a plasma density can be raised. That is, the surface coating of the sample 7 can be performed even at a lower discharge voltage than that without the shielding wall 3a.

It is a vertical side view which shows one Example of the plasma ion metal deposition apparatus by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Anode 3 Hollow cathode 3a Shielding wall 3b Cathode surrounding wall 4 Sample stand 7 Sample

Claims (2)

The anode (2) and hollow cathode (3) facing each other in the vacuum chamber (1) maintained in a rare gas atmosphere, and a voltage for applying a voltage for plasma discharge to the anode (2) and the hollow cathode (3) A sample stage (18) on which an application circuit (18), a source gas supply chamber (10) for supplying source gas into the vacuum chamber (1), and a sample (7) for forming a metal film in the hollow cathode (3) are mounted. 4) is provided with an annular shielding wall (3a) projecting from the upper edge of the cathode peripheral wall (3b) of the hollow cathode (3) to the inside thereof, and this hollow cathode (3 A plasma ion metal deposition apparatus characterized by introducing a raw material gas for forming a film into the film. 2. The plasma ion metal coating according to claim 1, wherein the raw material gas for film formation is introduced into the plasma region on the sample stage (4) from the cathode peripheral wall (3 b) side of the hollow cathode (3). Landing gear.

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