US20030201586A1

US20030201586A1 - Apparatus and method for supplying cesium using injector

Info

Publication number: US20030201586A1
Application number: US10/147,851
Authority: US
Inventors: Daesig Kim
Original assignee: Filteray Fiber Optics Inc
Current assignee: Filteray Fiber Optics Inc
Priority date: 2002-04-29
Filing date: 2002-05-20
Publication date: 2003-10-30
Also published as: KR20030085198A

Abstract

An apparatus and method for supplying cesium by using an injector is disclosed in the present invention, which increases vaporization efficiency and stably supplies cesium gas for a long period of time. The apparatus includes a mass flow controller controlling an amount of an externally introduced inert gas, a pre-heater pre-heating the inert gas introduced through a first gas flow tube from the mass flow controller, a cesium storage unit emitting cesium by using a pressure gas supplied through a pressure gas supplying tube, an injector emitting the cesium supplied from the cesium storage unit, and a cesium vaporizer vaporizing the cesium emitted from the injector and emitting the inert gas introduced from the pre-heater through a second gas flow tube along with the cesium gas through a third gas flow tube. It is emphasized that this abstract is provided to comply with the rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description

This application claims the benefit of the Korean Application No. P2002-23379 filed on Apr. 29, 2002, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method for supplying cesium (Cs), and more particularly, to an apparatus and method for supplying cesium using an injector, which increases vaporization efficiency of cesium and enables a continuous supply of cesium gas for a long period of time.

2. Discussion of the Related Art

Generally, an ion source is used in ion injection, sputter deposition, ion beam deposition, and ion spectroscopy. More specifically, when sufficient amount of cesium ions exists on the surface of the substrate to be processed, the cesium ions decrease the work function of the surface of the substrate. This is because cesium has a low electron affinity. Therefore, the cesium existing on the surface of the substrate increases an amount of the negative ion emission.

Under the atmospheric pressure, cesium has a liquid point of 28° C. and a boiling point of 690° C. At 100° C., cesium has a vapor pressure of 10E−4 Torr.

However, cesium is easily oxidized when it is exposed to oxygen. Moreover, cesium explodes when it is brought into contact with humidity. Therefore, vapor pressure of cesium cannot be controlled easily, which results in many limitations in the application of cesium.

A related art apparatus for supplying cesium will be described with reference to the accompanying drawings.

FIG. 1 illustrates a schematic view of the related art apparatus for supplying cesium using solid electrolyte, which is disclosed in U.S. Pat. No. 5,521,389.

As shown in FIG. 1, the related art apparatus for supplying cesium using solid electrolyte includes an

ion pellet

11 having a cesium compound in the form of an oxide sealed therein, an ion emitter 12 emitting cesium ions from the cesium compound inside the ion pellet 11 when brought into contact with metal, and a heater 13 heating the ion pellet 11 so that cesium ions can be emitted through the ion emitter 12.

The related art apparatus for supplying cesium also includes a heat cutoff layer (not shown), which is made of one of molybdenum and tantalum and formed on an outer surface of the

heater

13 in order to prevent heat produced from the heater 13 to be radiated to the outside. An anode electrode (not shown) for an electrical connection of the ion pellet 11 and a metal tube (not shown) preventing the cesium compound from flowing out of the ion pellet 11 are also included in the apparatus.

Herein, the

ion emitter

12 is a porous electrode coated with tungsten on a side surface of the ion pellet 11. Also, the heater 13 formed on the circumference of the ion pellet is made of a filament coated with alumina.

As described above, in the related art apparatus for supplying cesium using solid electrolyte, the solid electrolyte including cesium emits cesium ions at an elevated temperature ranging from 900 to 1000° C. For an effective emission of the electrodes, the temperature should be maintained at least at 1000° C.

Due to a limited amount of solid electrolyte sealed within the

ion pellet

11, this type of cesium source is not desirable for a long-term use. Particularly, ion beam flux is limited. Therefore, it is difficult to carry out a deposition process on a wide surface.

In addition, when the

ion pellet

11 is used under an oxygen environment for a long period of time, an oxide layer is formed on the porous ion emitter 12 due to oxidation of cesium, which results in an instability in the discharged amount of cesium ions. Therefore, in order to accurately control the discharged amount of cesium ions, an apparatus that can control the heating of the ion pellet 11 by measuring the discharged amount is required. When using the apparatus for supplying cesium in a physical vapor deposition process, cesium produced by a high temperature heating process is only diffused by a thermal kinetic movement of gas within a vacuum. Therefore, the flux cannot be controlled.

FIG. 2 illustrates a schematic view of an apparatus for supplying cesium using a refractory metal ribbon, which is disclosed in U.S. Pat. No. 5,466,941. This structure resolves the problems caused in the apparatus for supplying cesium using solid electrolyte.

As shown in FIG. 2, the apparatus for supplying cesium using a refractory metal ribbon includes an

extraction electrode pair

21, a refractory metal ribbon 22 ionizing the cesium discharged from the extraction electrode 21, and an electrode for forming a beam (not shown) formed on the upper and lower portions of the refractory metal ribbon 22 in order to form the positively charged and ionized cesium ions into a beam.

A heater (not shown) controlling vapor pressure used for discharging non-ionized cesium to the

refractory metal ribbon

22 is also included in the apparatus. Herein, the refractory metal ribbon is formed of tungsten.

However, in the apparatus for supplying cesium using a refractory metal ribbon with the above structure, the

extraction electrode

21 must be heated at an elevated temperature ranging from 300 to 400° C. in order to discharge non-ionized cesium. Furthermore, the refractory metal ribbon 22 must be heated at an elevated temperature of 1200° C. in order to positively charge the discharged cesium.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an apparatus and method for supplying cesium using an injector that substantially obviates one or more of problems due to limitations and disadvantages of the related art.

Another object of the present invention is to provide an apparatus and method for supplying cesium using an injector whereby cesium vaporization efficiency is increased in order to provide a larger amount of cesium gas.

Another object of the present invention is to provide an apparatus and method for supplying cesium using an injector, which prevents the cesium from being oxidized or deteriorated, thereby allowing a stable supply of cesium for a long period of time.

A further object of the present invention is to provide an apparatus and method for supplying cesium using an injector, which can control the supplied amount of cesium with precision.

Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an apparatus for supplying cesium by using an injector includes a mass flow controller controlling an amount of an externally introduced inert gas, a pre-heater pre-heating the inert gas introduced through a first gas flow tube from the mass flow controller, a cesium storage unit emitting cesium by using a pressure gas supplied through a pressure gas supplying tube, an injector emitting the cesium supplied from the cesium storage unit, and a cesium vaporizer vaporizing the cesium emitted from the injector and emitting the inert gas introduced from the pre-heater through a second gas flow tube along with the cesium gas through a third gas flow tube.

Herein, externally applied pulse signals allow the injector to emit liquid cesium on a regular basis. The injector also controls the size of a cesium particle, the amount of cesium, and the level of spray.

In another aspect of the present invention, a method of supplying cesium by using an injector includes controlling an amount of an externally introduced inert gas, pre-heating the inert gas, emitting and vaporizing cesium supplied by a pressure gas, and emitting the vaporized cesium along with the pre-heated inert gas.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention. [0029]
In the drawings: [0030]
FIG. 1 illustrates a schematic view of a related art apparatus for supplying cesium using solid electrolyte; [0031]
FIG. 2 illustrates a schematic view of a related art apparatus for supplying cesium using a refractory metal ribbon; and [0032]
FIG. 3 illustrates a schematic view of an apparatus for supplying cesium according to the present invention.[0033]

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to the illustrated embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. [0034]
FIG. 3 illustrates a schematic view of an apparatus for supplying cesium according to the present invention. [0035]
As shown in FIG. 3, the apparatus for supplying cesium by using an injector includes a mass flow controller (MFC) [0036] 31 controlling an amount of an externally introduced inert gas, a pre-heater 34 pre-heating the inert gas introduced through a first gas flow tube 32 from the mass flow controller (MFC) 31 and emitting the pre-heated inert gas through a second gas flow tube 33, a cesium storage unit 36 emitting cesium by using a pressure gas supplied through a pressure gas supplying tube 35, an injector 37 emitting the cesium supplied from the cesium storage unit 36, and a cesium vaporizer 39 vaporizing the cesium emitted from the injector 37 and emitting the inert gas introduced from the pre-heater 34 through the second gas flow tube 33 along with the cesium gas through a third gas flow tube 38.
In addition, the apparatus for supplying cesium by using an injector according to the present invention further includes a [0037] heater 40 heating the pre-heater 34, the cesium storage unit 36, and the cesium vaporizer 39, a plurality of heating wires heating the first, second, and third gas flow tubes 32, 33, and 38, a first cutoff valve 41 installed within the second gas flow tube 33 and supplying and cutting off the inert gas introduced to the cesium vaporizer, 39 from the pre-heater 34, and a second cutoff valve 42 installed within the third gas flow tube 38 and supplying and cutting off the cesium gas supplied to a deposition device 43 from the cesium vaporizer 39, and a pressure gas regulator (not shown) installed within the pressure gas supplying tube 35 and controlling the amount of pressure gas introduced to the cesium storage unit 36.
Herein, a two-stage pressure regulator is used as the pressure gas regulator. A [0038] tube 44 connects the cesium storage unit 36 and the injector 37. A heating wire may also be formed on the circumference of the tube 44 in a similar manner as the first, second, and third gas flow tubes 32, 33, and 38.
In addition to argon (Ar), nitrogen (N[0039] ₂) and helium (He) may also be used as an inert gas. The inert gas may also be used as a pressure gas supplied to the cesium storage unit 36. The cesium storage unit 36, which is filled with liquid cesium, may be maintained at a temperature of at least 29° C. in order to maintain the cesium in a liquid phase.
The [0040] injector 37 is controlled by pulse signals applied by an external controlling device, wherein an emitter within the injector 37 repeatedly opens and closes so as to emit liquid cesium on a regular basis.
The apparatus for supplying cesium is not only applicable to a physical vapor deposition system, but also to any vapor deposition system using ion beam, a chemical mechanical vapor deposition system, a display device of an electronic tube a camera tube, an electronic microscope, and a photoelectron generator. [0041]
The operation of the above-described apparatus for supplying cesium of the present invention will now be explained. [0042]
The [0043] mass flow controller 31 controls the amount of the externally introduced inert gas. The heater 40 installed on the circumference of the pre-heater 34 pre-heats the inert gas introduced to the pre-heater 34 through the first gas flow tube 32.
A pressure gas is supplied to the [0044] cesium storage unit 36, which is filled with liquid cesium. At this point, the pressure gas supplied through the pressure gas supplying tube 35 emits the liquid cesium with the cesium storage unit 36 to the outside. More specifically, pressure within the cesium storage unit 36 increases as the pressure gas is introduced therein. The liquid cesium is then sent to the injector 37 through a tube 44.
Herein, the amount of liquid cesium sent to the [0045] injector 37 from the cesium storage unit 36 may vary according to the amount of pressure gas, which is regulated by the pressure gas regulator.
The [0046] injector 37 receiving cesium from the cesium storage unit 36 periodically emits cesium into the cesium vaporizer 39 in accordance with pulse signals generated from an external power supply. Herein, the shape and size of the emitter within the injector determine the size of a cesium particle, the amount of cesium, and the area of cesium spray. Therefore, in order to obtain a desired amount of cesium and area of cesium spray, an adequate size and shape should be selected for the emitter in the injector.
When the fine particles of cesium are emitted from the [0047] injector 37 reach the inner surface of the heated cesium vaporizer 39, the cesium is vaporized by an instantaneous heating process. Due to the instantaneous vaporization of cesium, the pressure within the cesium vaporizer 39 increases instantaneously as well. The degree of cesium vaporization increases in accordance with the small size of the emitted cesium particles and the large area of spray.
The vaporized cesium is then discharged through the third [0048] gas flow tube 38 along with the pre-heated inert gas introduced from the pre-heater 34, and finally supplied to the deposition device 43.
Herein, the [0049] heater 40 heats the cesium vaporizer 39 to a temperature ranging from about 200 to 300° C. and vaporizes the cesium. The heating wires maintain the first, second, and third gas flow tubes 32, 33, and 38 at about the same temperature as the cesium vaporizer 39.
The above-described apparatus for supplying cesium according to the present invention uses the pressure gas regulator to regulate the amount of cesium supplied to the [0050] injector 37, thereby regulating with precision the amount of cesium gas supplied to the deposition device 43. Additionally, by vaporizing the fine particles of the liquid cesium emitted from the injector 37, vaporization efficiency of cesium may be enhanced.
More specifically, the emitted amount of cesium gas depends highly on the amount of supplied cesium gas, more specifically, the pressure of the pressure gas, the viscosity of cesium, and the pulse signals of the injector, and the degree of cesium vaporization. The degree of cesium vaporization relies on the size of liquid cesium particles, the area of spray, and the heating temperature. [0051]
In addition, the first, second, and third [0052] gas flow tubes 32, 33, and 38 are maintained at a high temperature, thereby preventing clogging of the tubes caused by an oxidation of cesium. Thus, high quality cesium gas may be supplied to a vacuum system (i.e., a deposition device 43), thereby facilitating the production of negatively charged ions on to a substrate to be treated.
Furthermore, cesium gas is supplied to the deposition device along with the inert gas, which prevents the counter flow of oxygen or other oxidizing substances therein. Thus, cesium can be used stably for a long period of time without being deteriorated. [0053]
More specifically, in comparison with the related art, when vaporizing cesium by using the apparatus for supplying cesium according to the present invention, a larger amount of cesium gas may be stably and continuously supplied for a long period of time. [0054]
The above-described apparatus for supplying cesium according to the present invention has the following advantages. [0055]
An injector emitting liquid cesium is installed within the apparatus for supplying cesium in order to vaporize the fine cesium particles, thereby increasing vaporization efficiency. Accordingly, a large amount of cesium gas can be supplied to the deposition device. [0056]
A pressure gas regulator regulates the amount of pressure gas supplied to the cesium storage unit, which allows the regulation of the amount of liquid cesium supplied to the injector. The pulse signals control the degree of opening and closing of the injector. As a result, the amount of cesium gas supplied to the deposition device can be regulated. [0057]
A heater or a plurality of heating wires are installed, so that the temperature of the entire system including a pre-heater, a cesium vaporizer, and gas flow tubes is readily controlled and maintained. Also, an inert gas is supplied to a deposition device along with cesium gas, which prevents the cesium from being oxidized. Thus, cesium gas may be stably supplied for a long period of time without being deteriorated. [0058]
It will be apparent to those skilled in the art that various modifications and variations can be made in the apparatus and method for supplying cesium by using an injector of the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. [0059]

Claims

What is claimed is:

1. An apparatus for supplying cesium by using an injector, comprising:

a mass flow controller controlling an amount of an externally introduced inert gas;

a pre-heater pre-heating the inert gas introduced through a first gas flow tube from the mass flow controller;

a cesium storage unit emitting cesium by using a pressure gas supplied through a pressure gas supplying tube;

an injector emitting the cesium supplied from the cesium storage unit; and

a cesium vaporizer vaporizing the cesium emitted from the injector and emitting the inert gas introduced from the pre-heater through a second gas flow tube along with the cesium gas through a third gas flow tube.

2. The apparatus according to claim 1, wherein the injector is controlled by externally applied pulse signals.

3. The apparatus according to claim 1, wherein the injector regulates a size of a cesium particle, an amount of cesium, and an area of cesium spray.

4. The apparatus according to claim 1, wherein the inert gas includes one of argon, nitrogen, and helium.

5. The apparatus according to claim 1, wherein the cesium storage unit is filled with liquid cesium.

6. The apparatus according to claim 1, wherein an inside of the cesium storage unit is maintained at a temperature of at least 29° C.

7. The apparatus according to claim 1, wherein the cesium vaporizer is maintained at a temperature ranging from about 200 to 300° C.

8. The apparatus according to claim 1, wherein the pressure gas is formed of an inert gas.

9. The apparatus according to claim 8, wherein the inert gas is formed of nitrogen.

10. The apparatus according to claim 1, further comprising a heater heating the pre-heater, the cesium storage unit, and the cesium vaporizer.

11. The apparatus according to claim 1, further including a plurality of heating wires heating the first, second, and third gas flow tubes.

12. The apparatus according to claim 1, further including a valve installed within both the second and third gas flow tubes in order to control an amount of cesium flowing therein.

13. The apparatus according to claim 1, further including a pressure gas regulator regulating an amount of pressure gas introduced to the cesium storage unit.

14. The method for supplying cesium by using an injector, comprising:

controlling an amount of an externally introduced inert gas;

pre-heating the inert gas;

emitting and vaporizing cesium supplied by a pressure gas; and

emitting the vaporized cesium along with the pre-heated inert gas.

15. The method according to claim 14, wherein the cesium in the emitting and vaporizing cesium supplied by a pressure gas is emitted on a regular basis.

16. The method according to claim 14, wherein an amount of the pressure gas in the emitting and vaporizing cesium supplied by a pressure gas is controlled in order to regulate an amount of cesium to be emitted.