Radiant energy – Ion generation – Field ionization type
Reexamination Certificate
2001-12-31
2004-10-12
Lee, Wilson (Department: 2821)
Radiant energy
Ion generation
Field ionization type
C204S192150
Reexamination Certificate
active
06803585
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to ion-beam technology, in particular, to electron-cyclotron resonance type ion beam sources for use in ion implanters. Implanters of this kind find application for ion implantation in the manufacture of electronic devices such as LSI and VLSI semiconductor circuits.
BACKGROUND OF THE INVENTION
An ion implanter is a device, which is used for material processing in industrial manufacture. Major application of them is concentrated on semiconductor device fabrication, especially on modifying electrical properties of semiconductor materials by ion implantation, and in particular for implantation of boron and phosphorus ions into silicon. An ion source constitutes an important part of the aforementioned implanter, and its operation determines the efficiency, reliability, and performance characteristics of the implanter. The ion-beam source used in the implanter ionizes neutral molecules and accelerates the obtained ions from hundreds of eV to the required energy level of several hundred KeV. The ions are then formed into a uniform beam of a given shape and extension.
Until recently, however, the majority of ion-beam sources used in implanters for semiconductor industry were based on cumbersome, complicated, and expensive ion acceleration techniques. Examples of such technique are described, e.g., by V. V. Simonov, et al. in “
Oborudovanie Ionnoi Implantatsii
” (Ion Implantation Equipment), Moscow, “Radio I Svyaz” Publishers, 1988, pp. 35-38.
In 80's, ion-beam sources using large plasma volumes with simplified methods for the formation of ion beams, e.g., with the use of ion-plasma optics, came into use. Almost all of them consisted of two main functional units, i.e., a gas-discharge chamber for generating plasma used as an ion emitter and an ion-optical system for extracting ions from the plasma, accelerating the extracted ion, and forming a directional ion beam. The working medium used as a material for implantation was a gaseous substance supplied to the discharge chamber or a solid substance, e.g., a solid material sputterable into the plasma volume.
Since requirements of operation conditions vary from one application to another in a very wide range, it is difficult to create a universal ion source that could satisfy all these conditions at the same time. The plasma-type ion sources have found wide application in ion implanters due to high reliability and operation performance. Depending on methods of plasma generation, these ion sources can be roughly classified as high-frequency and microwave ion sources, cold-cathode type ion sources, plasma sources with hot cathodes, Penning-discharge type ion sources with hot cathodes, quasi-magnetron sources, low-pressure ion sources with arc discharge, etc. Given below is a short description of the aforementioned ion sources which find practical application.
High-frequency and microwave ion sources are based on the use of high-frequency or microwave energy for generating plasma. Of this group of ion sources, so called electron cyclotron resonance sources (hereinafter referred to as ECR sources) have found a very wide practical application. In these sources, a phenomenon of electron cyclotron resonance (ECR) is used for increasing effective concentration of electrons in plasma and thus makes it possible to generate plasma of high density. ECR is resonance of electrons in a magnetic field on a predetermined frequency, such as 2.45 GHz for the magnetic field of 0.0875 T intensity. ECR sources can be used as ion emitters with extraction of ions from both the end faces and sides of the gas-discharge chamber. Since the present invention pertains to implanters with ECR sources, they will be described later in more detail.
Cold-cathode type ion sources are sources with cold cathodes, which generate plasma in a glow discharge due to emission of electrons into a working gas from the surfaces of cathodes, resulting in ionization of the working gas molecules. The ions formed in the working gas are accelerated toward the cathode and bombard the cathode surface causing the surface to emit secondary electrons. The plasma is formed as a result of multiple repetitions of the above process. Implanters with cold-cathode ion sources are used mainly for small and ultra-small doses of implantation. Their advantage is simplicity of construction and a relatively long service life. Disadvantages are low beam currents (not exceeding 100 &mgr;A), significant fluctuations in the beam, and the limitation of using only gaseous working media.
Hot-cathode type ion sources generate an arc discharge, which is maintained by electrons emitted from the surface of a hot cathode and possessing energy exceeding the level of energy required for ionization of a gaseous working medium. Discharge occurs in a magnetic field, which is oriented parallel to the electron acceleration direction or perpendicular thereto. In the latter case the source is known as a magnetron type source. Although ion implanters utilizing such ion sources are advantageous in that they are simple in construction, are capable of generating high ion beam currents, and have a relatively stable discharge, they do not possess features required for controlling distribution of current in the resulting ion beam.
In hot-cathode ion sources with the use of a Penning discharge phenomenon for increasing concentration of electrons in plasma, extraction of ions normally occurs through a round opening in an anti-cathode (axial extraction). Ion sources of such type are known as Nilson ion sources and are used in implanters of Veeco Co. (USA) and Balzers Co. (Liechtenstein). These ion sources make it possible to utilize both gaseous and solid working media. However, with standard ion extraction energy of 30 kV, currents extracted from the Nilson-type ion sources do not exceed several hundred microamperes. Thus the implanters containing such sources inherit their disadvantages.
Quazi-magnetron ion sources, also known as Freeman ion sources, have a direct incandescence-type cathode arranged parallel to the axis of a cylindrical anode. In contrast to conventional magnetron sources, the sources of this type used for implantation have the incandescence filament offset toward the ion-emitting slit in the side surface of the cylindrical anode. Advantages of these sources, as compared to conventional hot-cathode sources, are relatively low intensity of the magnetic field (below 1 T) and weak dependence of the ion beam parameters to the parameters of discharge. The main disadvantage of quazi-magnetron ion sources is a short service life (no more than 20 hours), which is unacceptable for industrial use.
Given below is a more detailed description of ECR ion sources, which are used in ion implanters and to which the device and method of the invention pertain.
U.S. Pat. No. 5,625,195 issued to Andre Grouillet in 1997 discloses a high-energy implantation process using an ion implanter of the low-or medium-current type with an ECR ion source. In order to increase the implantation energy, this ion implanter incorporates a microwave generator with a traveling-wave tube generating an electromagnetic field with a frequency greater than or equal to 6 GHz. The initial ion source of the implanter is replaced by an electron cyclotron resonance multiply-charged ion source, including a waveguide-forming plasma cavity, whose characteristic dimension in the transverse plane of the cavity is of the same order of magnitude as the wavelength of the electromagnetic field. The microwave generator of this implanter and the plasma cavity of the multiple-charged ion source are electromagnetically coupled. A complex gaseous medium, compatible with the beam of ions desired, is admitted into the plasma cavity. The inlet flow rate of the gaseous medium is adjusted so as to maintain a residual vacuum in the plasma cavity, which is less than the pressure threshold compatible with production of multiply-charged ions. The focusing of the ion beam extracted from the plasma cavity is adjusted onto the focal poi
Lee Wilson
Tran Chuc
LandOfFree
Electron-cyclotron resonance type ion beam source for ion... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electron-cyclotron resonance type ion beam source for ion..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electron-cyclotron resonance type ion beam source for ion... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3275127