JP2010170937A - Discharge electrode for ionizer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge electrode for an ionizer, capable of preventing a fine metal particle from being scattered, and capable of enhancing stability of ion generation. <P>SOLUTION: Surface layer metal 2 is laminated on a tip part surface of base material metal 1 constituting a needle electrode. metal having 100 W/mK or more of thermal conductivity is preferably used as the base material metal 1, and metal having a work function larger than a work function of the base material metal 1, and having 1,000&deg;C or more of melting point, is preferably used as the surface layer metal 2. For example, tungsten (W) and a tungsten alloy (Th-W alloy, La-W alloy) are used preferably as the base material metal 1, nickel (Ni) is most preferably used as the surface layer metal 2, and platinum (Pt), gold (Au), palladium (Pd) and the like are preferably used as the surface layer metal 2. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a discharge electrode of an ionizer used for removing static electricity generated in a clean room or the like.

  In a clean room for semiconductor manufacturing, the relative humidity is a low-humidity environment where the generation of static electricity is about 40%, and plastic containers with high electrical resistance are frequently used to transport wafers and semiconductor elements. Static electricity is easily generated. This static electricity causes dust to adhere to the wafer surface and destroys ICs and semiconductor elements on the wafer, thus reducing the product yield. In addition, with the recent increase in the density of semiconductor elements, it is desired to have a clean room with an ultra-high cleanliness, and the static resistance of semiconductor elements has also decreased. Yes.

  Therefore, conventionally, an ionizer has been used as a countermeasure for removing static electricity in the clean room as described above. In this ionizer, a high voltage is applied to an electrode provided on the ionizer to cause corona discharge, and the charge generated on the charged body is neutralized by ions generated at that time to perform static elimination.

However, in the corona discharge ionizer as described above, there has been a problem that the needle-shaped electrode is worn and fine metal particles are scattered. Therefore, the present applicant previously proposed an ionizer for a clean room provided with a needle-like ion generating electrode having a laminated structure in which the surface of a tungsten electrode is covered with nickel as shown in Patent Document 1.
Japanese Patent No. 3321187

  As a result of further studies on the mechanism of dust generation from the discharge electrode of the clean room ionizer as described above, the present inventors have obtained the following knowledge. That is, the present inventors examined the wear prevention effect of the conventional discharge electrode (thorium-tungsten alloy (Th-W) electrode), and the result shown in FIG. 4 was obtained. The test conditions were that the above discharge electrode was ultrasonically cleaned using a DC pulse type ionizer having an applied voltage of 15 kV, a discharge current of 3 μA, and a pair of positive and negative electrodes for about 100 hours. 4A to 4C are images of the tip of the electrode taken with a scanning electron microscope (JSM-840, manufactured by JEOL Ltd., magnification: 175 times).

  As shown in FIGS. 4B and 4C, it was found that the positive electrode was obviously significantly worn compared to the negative electrode. This is presumably because chemical sputtering with corrosion is dominant in the positive electrode. That is, since the positive electrode is sputtered with oxygen ions, a fragile oxide film (corrosion layer) is formed on the surface layer portion, which is sputtered again, so that it is considered that sputtering proceeds faster.

  On the other hand, as shown in FIG. 4C, since the negative electrode is not worn much, it is considered that physical sputtering is dominant in the negative electrode. Moreover, it is considered that the tip shape of the electrode becomes round as shown in FIG. 4B due to wear of the electrode, so that stable discharge is difficult and ion generation becomes unstable.

  Therefore, the present inventors, based on the knowledge that the scattering of the electrode itself due to ion sputtering (electrode wear) is one of the causes of dust generation from the electrode, Research has been conducted on a discharge electrode that can prevent the scattering of fine metal particles by preventing it and can improve the stability of ion generation by stable discharge.

  The present invention has been proposed to solve the above-described problems of the prior art, and its purpose is to prevent the scattering of fine metal particles by preventing the wear of the needle-like electrode. Another object of the present invention is to provide a discharge electrode of an ionizer that can improve the stability of ion generation by stable discharge.

  In order to achieve the above object, the discharge electrode of the ionizer according to claim 1 is configured such that a needle-like electrode is formed using a metal having a thermal conductivity of 100 W / mK or more as a base metal, and a work function thereof is that of the base metal. A metal having a work function and a melting point of 1000 ° C. or higher is laminated on the surface of the tip of the needle electrode as a surface layer metal.

  According to the invention described in claim 1 having the above-described configuration, the needle electrode is configured using a metal having a high thermal conductivity as a base material, and the work function of the base metal is the surface of the tip portion. By laminating a metal larger than the work function and having a melting point of 1000 ° C. or higher, the surface of the electrode is less likely to be oxidized, and the disadvantage of the surface layer metal that tends to accumulate heat can be covered by the base metal. Wear of the needle electrode can be prevented.

According to a second aspect of the present invention, in the discharge electrode of the ionizer according to the first aspect, the tip of the needle-like electrode has a truncated cone shape.
According to the second aspect of the invention having the above-described configuration, it is possible to prevent electric field concentration from occurring at the tip portion of the needle-like electrode, so that ion sputtering does not concentrate at one point. As a result, wear of the electrode tip can be more effectively prevented.

The invention according to claim 3 is the discharge electrode of the ionizer according to claim 1 or 2, wherein the base metal is tungsten or a tungsten alloy, and the surface metal is nickel, platinum, gold, palladium. It is either of these.
The invention according to claim 3 specifically defines the base metal and the surface metal, and by using these metals to form the discharge electrode, it is possible to prevent wear of the needle electrode. it can.

  According to the present invention, a discharge electrode of an ionizer that can prevent the scattering of fine metal particles by preventing the wear of the needle-shaped electrode and can improve the stability of ion generation by stable discharge. Can be provided.

  Hereinafter, specific embodiments (hereinafter referred to as embodiments) of discharge electrodes of an ionizer according to the present invention will be described with reference to the drawings.

(1) First Embodiment (1-1) Configuration (1-1-1) Base Metal and Surface Metal As shown in FIG. 1, the discharge electrode of the present embodiment is a base metal constituting a needle electrode. The surface layer metal 2 is laminated on the surface of the tip of 1. As the base metal 1, it is preferable to use a metal having a thermal conductivity of 100 W / mK or more, and as the surface metal 2, the work function indicating the corrosiveness of the metal is chemically stable of about 5 eV or more. It is preferable to use a metal having a melting point of 1000 ° C. or higher, which is a strong metal (a metal that is not easily oxidized).

Next, the metal used in this embodiment will be described more specifically. That is, in the physical property values of various metals shown in Table 1, as the base metal 1, a metal having a thermal conductivity of 100 W / mK or more and a melting point much higher than that of the surface metal 2 is used. It is preferable. For example, as shown in Table 1, it is preferable to use tungsten (W) or a tungsten alloy (Th—W alloy, La—W alloy) as the base metal 1.

  On the other hand, the surface metal 2 is a metal whose work function is higher than that of the base metal 1, in other words, a metal that is less susceptible to corrosion than the base metal 1 and has a melting point of 1000 ° C. or higher. It is preferable to use a metal. For example, as shown in Table 1, as the surface metal 2, nickel (Ni) is most preferable, and platinum (Pt), gold (Au), palladium (Pd), and the like are preferable.

  Thus, the significance of laminating the surface metal 2 on the tip of the base metal 1 is as follows. For example, nickel (Ni), which has a high work function, is difficult to oxidize, but because the thermal conductivity is small, heat tends to be trapped at the tip of the electrode. This is because, by using a large tungsten (W) as a base material and laminating Ni thereon, the base material W can cover the shortcomings of Ni, where heat is easily trapped, and wear can be prevented.

(1-1-2) Manufacturing Method of Discharge Electrode Subsequently, a manufacturing method of the discharge electrode of the present embodiment will be described. That is, in this embodiment, after surface metal 2 having a melting point lower than that of base metal 1 is plated on the surface of base metal 1 to a thickness of 3 to 6 μm, it is heated in a gas containing no oxygen ( The surface metal 2 and the base metal 1 are brought into close contact with each other by reducing the temperature stepwise.

(1-2) Actions / Effects About the discharge electrode (surface metal: Ni, base metal: La—W alloy) of the present embodiment and the conventional discharge electrode (Th—W) produced by the manufacturing method as described above. When the anti-wear effect was examined, the results shown in FIG. 2 were obtained. The test conditions were as follows: the above discharge electrode was used in a DC pulse type ionizer having an applied voltage of 15 kV, a discharge current of 3 μA, and a pair of positive and negative electrodes, and the conventional discharge electrode was used for 100 hours. The form of discharge electrode was used for one year. As can be seen from FIG. 2, the discharge electrode of the present embodiment is significantly less worn than the conventional discharge electrode.

  As described above, according to this embodiment, a metal having a high thermal conductivity is used as a base material, and a metal having a work function larger than that of the base metal and having a melting point of 1000 ° C. or higher is laminated thereon. As a result, the surface of the electrode is less likely to be oxidized, and the disadvantage of the surface metal that is likely to accumulate heat can be covered by the base metal, so that the wear of the needle electrode can be prevented.

(2) Second Embodiment As shown in FIG. 3, the discharge electrode of the present embodiment is a modification of the first embodiment, and in order to avoid the concentration of one point of the electric field, the tip of the electrode of the laminated structure is a cone. It is characterized by a trapezoidal shape. This is because the pointed electrode is subject to electric field concentration at the tip, and ion sputtering is concentrated at one point, so that the electrode tip is easily worn.

  According to the discharge electrode of the present embodiment having the above-described configuration, it is possible to prevent electric field concentration from occurring at the tip by making the tip of the electrode a truncated cone, so that ion sputtering is concentrated at one point. There is nothing. As a result, wear of the electrode tip can be more effectively prevented.

Sectional drawing which shows the structure of 1st Embodiment of the discharge electrode of the ionizer which concerns on this invention. It is the photograph which shows the result which investigated the wear prevention effect about the discharge electrode (surface layer metal: Ni, base metal: La-W alloy) of this embodiment, and the conventional discharge electrode (Th-W), (A ) Is a conventional discharge electrode, and (B) is a discharge electrode of this embodiment. Sectional drawing which shows the structure of 2nd Embodiment of the discharge electrode of the ionizer which concerns on this invention. It is the photograph which shows the result of having investigated the wear prevention effect about the conventional discharge electrode (Thorium tungsten alloy (Th-W) electrode), (A) is an unused electrode, (B) is a positive electrode after ultrasonic cleaning. , (C) is a negative electrode after ultrasonic cleaning.

1 ... Base metal 2 ... Surface metal

Claims (3)

The needle electrode is composed of a metal having a thermal conductivity of 100 W / mK or more as a base metal,
A discharge electrode of an ionizer, characterized in that a metal having a work function larger than the work function of the base metal and a melting point of 1000 ° C. or more is laminated as a surface metal on the tip end surface of the needle electrode. .   The discharge electrode of the ionizer according to claim 1, wherein a tip portion of the needle-like electrode has a truncated cone shape.   The discharge electrode of the ionizer according to claim 1 or 2, wherein the base metal is tungsten or a tungsten alloy, and the surface layer metal is any one of nickel, platinum, gold, and palladium.