Claims
- 1. A device for the reflection of a beam of low-energy ions, comprising:
- an elongated electrode array extending generally in a direction of travel of a beam of low-energy ions incident upon said array, said array consisting essentially of a multiplicity of electrode elements elongated transversely to said direction, closely spaced in said direction and provided with mutually parallel long sides, the long sides of successive electrode elements along said array being juxtaposed with one another, the center-to-center spacing .lambda./2 of successive electrode elements, where .lambda. is a periodicity of said electrodes in said direction, being a minimum consistent with maintenance of electrical potentials on said elements, and
- means for applying electrical potentials (.+-.AV) of opposite sign to the successive electrode elements and of a magnitude sufficient to effect reflection of incident ions of said beam moving in said direction from said array as said ions approach respective electrode elements of said array.
- 2. The device defined in claim 1 wherein said elements are arranged so as to define a guide laterally surrounding said beam of ions.
- 3. The device defined in claim 2 wherein said elements are rings.
- 4. The device defined in claim 2 wherein said elements are rectangular frames.
- 5. The device defined in claim 2 wherein said elements are respective turns of a multicoil helix.
- 6. The device defined in claim 5 wherein said multicoil helix is a double helix.
- 7. The device defined in claim 2 wherein said guide is curved with a radius of curvature R defined by the relationship: ##EQU2## where: g is a geometry factor depending upon the ratio between a gap spacing b between said elements and said periodicity .lambda.;
- D is the minimum diameter of the ion guide;
- .+-..DELTA.V is the electrical potential applied to said electrode elements in volts; and
- U is an electrical potential in volts corresponding to the kinetic energy eU of the ions, where e is the unit charge of an electron.
- 8. The device defined in claim 2 wherein said elements are bars defining a planar array
- 9. The device defined in claim 2 wherein said elements are parallel bars defining a curved array.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 3734423 |
Oct 1987 |
DEX |
|
CROSS REFERENCE TO RELATED APPLICATION
This application is related to the commonly assigned, concurrently filed copending application Ser. No. 257,103 based upon open German application P37 34 442.0 of Oct. 12, 1987, and naming Jakob SCHELTEN, one of the present applicants, as the inventor.
My present application relates to a device for the reflection of low energy ions.
While a variety of electromagnetic techniques have been used heretofore for the deflection of ion beams and such earlier proposals have involved various deflecting plate arrangements and the use of electrically energized coils, by and large it has not been possible heretofore in a simple and economical manner to provide an efficient device for the relatively precise reflection of a low-energy ion beam.
It is, therefore, the principal object of the present invention to provide an improved device by means of which low-energy ions can be reflected.
Another object of the invention is to provide an improved ion-beam reflector which can not only serve as a so-called ion mirror, but also can confine the ion beam in an ion guide.
These objects and others which become apparent hereinafter are attained, in accordance with the present invention by providing a multiplicity of elongated electrode elements, with the closest possible spacing, having their longitudinal sides parallel to one another and arranged in an array in which neighboring electrode elements are energized with electrical potential of opposite signs so that the signs of the electrical potentials along the array in the direction of travel of the ion beam alternating from electrode element to electrode element.
When we refer here to the minimum possible distance between adjacent electrodes, we mean the smallest distance which can be established between these electrodes without electrical arcing or discharge or breakdown therebetween.
The array and the entire guide formed by the array of electrode elements can be disposed in a high-vacuum chamber or space.
The reflector can be used wherever ion beam reflection and guidance is desired and, for example, in a device for irradiating large surfaces as described in the aforementioned copending application.
The reflection of the ions is effected at a small-thickness or boundary zone of the guide adjacent the electrodes of the array and formed in the vacuum space containing the ion beam.
According to a feature of the invention, the electrode elements laterally surround the ion beam and define an ion guide for the latter.
The individual electrode elements can be formed as rings which can be insulated from one another and collectively surround the ion beam.
According to a feature of the invention, the electrode elements laterally surround the ion beam and define an ion guide for the latter.
The individual electrode elements can be formed as rings which can be insulated from one another and collectively surround the ion beam.
In another embodiment of the invention, the electrode elements can be formed as rectangular frames along with one another and insulated from one another so that they will define an ion guide of rectangular cross section. It has been advantageous, further, to form the elements, rather than as discrete spaced-apart elements, as elements of a continuous coil so that the array can be constituted by a multicoil helix, preferably a double helix with the elements being respective turns of the coils. In this case, the turns of the two coils interdigitate with one another to provide electrode elements of alternating electrical potential sign (or polarity) along the beam path.
The ion guide formed by the array of electrode elements of the invention can be analogized to a light guide such as an optical fiber, formed from two materials with different indices of refraction and with which a light beam can be reflected at the boundary surface where the angle of incidence is less than the angle of incidence for total reflection.
Such light guides are used for wide-band low-loss piping of light, have flexible delivery of light, and enable distribution of light from one source to a plurality of sources in signal transmission and for a variety of other purposes. As in a light Pipe, thee is a reflection of an ion beam in accordance with the invention in a zone proximal to the boundary of the ion guide in the case in which the angle of incidence of the ion beam is less than a critical limiting angle. The ion guide of the invention likewise can be used for broad-beam, low-loss transmission of ion beams if desired in a flexible manner and in a nonstraight path.
The electrical field strength, which is greatest along the boundary of the ion guide, decays exponentially in accordance with the characteristic 1/e length in accordance with the relation
The reflection of the ion beam in the device of the invention is a reflection with the characteristic that the angle of incidence is equal to the angle of reflection when the incident angle .alpha. of the ion beam is less than a critical maximum angle .alpha..sub.c determined by the relationship
The angles .alpha. and .alpha..sub.c are measured with respect to the axis of the ion guide path at any particular location.
In the foregoing relationship g is a geometry factor which depends upon the ratio between a width b of the spacing between two neighboring electrodes and twice the distance between two electrodes measured on a center to center basis, i.e. periodicity .lambda.. For a first approximation,
In this latter relationship, moreover, .+-..DELTA.V is the potential applied to the electrode elements while U is the electrical potential in volts which corresponds to the kinetic energy eU of the ions where e is the elementary charge.
The limiting angle .alpha..sub.c for reflection does not depend on the periodicity .lambda..
The characteristic that the reflection has equal incident and reflection angles is independent of the energy of the ions, i.e. the deflection is not dispersive. The construction of the ion guide, however, must take into consideration the maximum field strength since that is dependent upon the periodicity. The maximum field strength E.sub.max is related to the potential .+-..DELTA.V applied to the electrode elements and the periodicity .lambda. in accordance with the relationship:
With a curved ion guide, the radius of curvature R will be determined by the relationship: ##EQU1## where: R is the radius of curvature of the ion guide (preferably in mm);
Ion guides in accordance with the invention can be used for ions with low energy and ion beams of relatively large diameters. The relationship between the ion beam energy and the diameter has an upper limit defined by the relationship
As noted, ion guides in accordance with the invention can be utilized in apparatus for large-surface irradiation. It can be used to generate ion mixtures, utilizing an ion gain for vaporizing materials which are to be vapor deposited. It may also be used for reactive ion beam etching, e.g. of semiconductor substrates, whereby ions with energies of less than 1 KeV can be delivered from an ion source.
According to another feature of the invention, the electrode elements can be bars arranged in a planar array, or in a curved array to form planar or curved mirrors for the dispersion-free reflection of ion beams.
The device for the reflection of a beam of low-energy ions generically thus comprises:
US Referenced Citations (1)
| Number |
Name |
Date |
Kind |
| 4079285 |
Little |
Mar 1978 |
|
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 1223215 |
Feb 1971 |
GBX |
Non-Patent Literature Citations (1)
| Entry |
| Andrew, Journal of Physics E, vol. 7, No. 1, Jan. 1974, pp. 61-64. |
Patent Grant
4866279
