Patent Application
20060060796
This invention pertains generally to the field of surface treatment and particularly to surface treatment by ion implantation techniques.
Ion implantation offers great commercial promise for the improvement of the surface characteristics of a variety of materials, including metals, ceramic and plastics. In the conventional ion implantation process ions are formed into a beam and accelerated to high energy before being directed into the surface of a solid target. Such ion implantation allows production of materials with new surface properties. In particular, implantation can be used to improve greatly the friction, wear and corrosion resistance properties of the surfaces of both metals and non-metals. For example, the surface properties of metals, ceramic components and ceramic cutting tools can be improved by ion implantation of nitrogen. For a general discussion of the techniques and potential advantages of ion implantation, see generally S. Picraux, et al., “Ion Nitriding and Ion Implantation: A Comparison,” Metal Progress, August 1985, pp. 18-21; V. M. Cassidy, “Ion Implantation Process Toughness Metalworking Tools,” Modern Metals, September 1984, pp. 65-67.
Conventional techniques as described by Conrad in U.S. Pat. No. 4,764,394 describes a unique technique to directly implant metal surfaces with ions from the surrounding plasma, however if the metal surface has sharp features then it causes premature breakdowns in the plasma thus limiting the performance of the device.
While commercially viable applications of conventional ion implantation techniques have been demonstrated, the relatively high cost of the process has limited its use thus far to high unit cost items having special applications, especially for ceramic substrates. A significant problem associated with nonmetallic targets is caused by the charge that quickly builds up around the target as the ions embed on the surface. Such a surface charge prevents further implantation. Furthermore, to get the ions to embed on the surface, an electrode has to be inserted into the target for pulsing. The need to manipulate a three-dimensional target to allow all sides of the target to be implanted adds cost and complexity, constrains the maximum size of the target which can be implanted, and increases the total time required to obtain satisfactory implantation of all target surfaces for any sized targets. Another problem associated with such an ion implantation technique is that depending on the electrode shape ions do not arrive perpendicular to the surface. Normal incidence of ions to the surface is preferred since as the angle of incidence with respect to the normal decreases, sputtering increases and the net retained dose in the target decreases. Hence a new technique is proposed in the present invention to overcome the above limitations and extend the applicability of Plasma source ion implantation technique to various purposes that include the treatment of surfaces of the metal objects with sharp edges, and non-metallic surfaces.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.
The present invention provides significantly improved production efficiencies in ion implantation of three-dimensional materials by achieving implantation of the target from all sides of the target simultaneously. Consequently, the production efficiency for implantation of three-dimensional objects is greatly increased over conventional ion implantation techniques. Since an electrode need not be inserted inside the target, and complicated target manipulation is not required.
In accordance with the present invention, which may be denoted plasma source ion implantation for nonmetals, the target to be implanted is surrounded by a substantially transparent enclosure (hereafter referred to as ‘enclosure’) specifically manufactured for a given target within an evacuated chamber. Such enclosures can be manufactured using any of the already available techniques such as rapid-prototyping. The plasma is generated within the chamber through any of the available techniques such as capacitively or inductively coupled plasma generator, magnetron ionization source, microwave ionization source, electromagnetic ionization source (e.g., Ultraviolet rays, X-rays etc.) and through electron impact ionization. For instance, the electrons for the impact ionization may be generated using filament electron sources. A high negative potential pulse is then applied to the enclosure relative to the walls of the chamber to accelerate ions from the plasma across the plasma sheath towards the enclosure in directions substantially normal to the surfaces of the wire mesh (used in the construction of the enclosures) at the points where the ions impinge upon the surface of the wire mesh. Since the enclosure is transparent (typically 85% or higher), most ions continue to move towards the target and get embedded on its surface. A positive charge builds up on the surface of the target quickly and hence a positive pulse is then applied to the enclosure to accelerate electrons from the plasma towards the target that neutralizes the positive charge on the surface of the target. Repeated application of positive and negative pulses to the enclosure will result in implantation of ions on the surface of the target in sufficient quantities until the desired concentration of implanted ions within the target object is achieved.
Preferably, the ion source plasma surrounding the target object is formed by introducing the ion source material in the gas or vapor form into the highly evacuated space within the confining chamber. The gaseous material may then be ionized by directing ionizing radiation, such as a diffuse beam of electrons, through the source gas in a conventional manner. Consequently, a plasma of ions is formed which completely surrounds the target object and the enclosure so that ions may be implanted into the target from all sides, if desired. Multiple targets with dedicated enclosures, properly spaced within the plasma, may be implanted simultaneously in accordance with the invention. Another technique to generate plasma around the target is to use either a single or multiple number of grids to which the radio frequency (RF) signal is applied. Such grids may be either spherical or is shaped such that the enclosure is substantially similar to the object being implanted. This kind of enclosure shaping will surround the target object predominantly uniformly.
Utilizing the ion implantation process and apparatus of the present invention, ion implantations may be performed on complex, three-dimensional objects formed of a great variety of materials, including pure metals, alloys, semi-conductors, ceramics, and organic polymers. Significant increases in surface hardness are obtained with ion implantation of a variety of source materials, including gases such as nitrogen, into metal and ceramic surfaces. Ion implantation of organic plastic materials can produce desirable surface characteristic modifications including a change in the optical properties and the electrical conductivity of the polymer. Ion implantation is also found to be particularly beneficial when used in conjunction with conventional heat treatment hardening techniques. Metal objects, which have been both ion implanted in accordance with the present invention, and heat-treated are found to exhibit significantly greater hardness and resistance to wear than objects which are only heat treated or ion implanted, but not both.
A significant advantage of the present technique over the other earlier techniques is the ability to work with surfaces that have sharp features. The enclosure protects the metallic target objects from the high voltage breakdown problems thus helping achieve the desired ion current densities and energies for ion implantation purposes.
The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which, like reference numerals identify like elements, and in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed.
This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8).
Illustrative embodiments of the invention are described below. It will course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. The present invention will now be described with reference to the attached figures. Additionally, the relative sizes of the various features and structures depicted in the drawings may be exaggerated or reduced as compared to the actual size of those features or structures. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present invention. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.
With reference to the drawings, an ion implantation apparatus in accordance with the present invention is shown generally at 10 in partial cross-section in
The target object illustratively shown at 20 as a three-dimensional block (for example a cone is shown in
It is a particular advantage of the present invention that target objects with a variety of complex shapes can be ion implanted, however each of the targets 20 would require preferably a dedicated enclosure, a single enclosure can be used multiple number of times with similar targets. The need for a complex manipulation of either an ion beam or the target as required in conventional line of sight ion implantation is not required, thereby eliminating the need for the conventional ion accelerator stage, raster scan apparatus and target manipulator. Also, no electrode is inserted into the target (for target biasing) and hence complex target manipulations are not required. The arm 22 holds the enclosure 23a in a fixed position by a conductive clamp (not shown) on the stage 21.
The arm may be covered with electrical insulation, if desired, or even shielded so that ions are not attracted to the arm. In addition, the support arms 22 and 22a may also be formed so that a coolant fluid is circulated through it to allow thermodynamic cooling of the target 20 during the ion implantation process to maintain the target in substantial thermal equilibrium. Cooling of the target during implantation is desirable to minimize the thermal diffusion of ions away from the target surface. The conductive support arm 22 is electrically isolated, by an insulator 23, from the cylindrical wall 12 of the chamber through which it passes, and the insulator 23 is also formed to provide an air-tight seal to the wall 12 of the chamber. The nonconductive arm 22b is connected to a motor 22b through an airtight seal to the wall 12. A high voltage, pulse power supply 24 is used to provide the high voltage through a supply line 25 to the conductive support arm 22. The supply 24 provides repetitive pulses of high voltage, e.g., in the 5 kV to 3 MV range, of duration selected as described below. For example, the high voltage supply may be of the pulse line-pulse transformer type providing pulse lengths in the range of a few microseconds, or the supply may be chosen from various types of high voltage tube modulated pulses capable of providing relatively long pulse lengths at least in the milliseconds range.
In accordance with this invention, ionized plasma is generated which surrounds the enclosure 23a within the chamber 11 so that ions may be accelerated into the target from all sides. To generate the surrounding plasma, where a gas is to be used as the material to be implanted, a gas source 28 is connected by a line 29 to leak the gas at a low, controlled rate into the chamber 11 as it is being evacuated by the vacuum pump 16. Prior to ionization, there thus will be a low pressure atmosphere of the gas from the gas source 28 within the chamber 11 mixed with very low levels of other impurity gases such as oxygen, etc. For purposes of illustration, the following description will assume that a source of nitrogen gas is provided from the gas source 28, although it will be apparent that many other sources of ionizing ambient may be provided by the vaporization of liquids and solids to form the ambient gas. The neutral gas within the chamber may be ionized in various ways. One method illustrated in
Similarly other ionization sources such as a magnetron, electron cyclotron resonance heating system, microwave horn antennas etc., and any combination thereof may be used for ionizing the ambient gases within the chamber 11. Utilizing a multi-dipole filament discharge electron source 31 at an operating pressure in the range of approximately 10−6 to 10−3 Torr, satisfactory plasmas are formed having a density of 106 to 1011 ions per cubic centimeter with an electron temperature of a few electron volts and an ion temperature of less than one electron volt. In one embodiment of the invention sources of ionizing electromagnetic radiation (e.g., ultraviolet light, X-rays etc.,) may be utilized to ionize the gas within the chamber 11 to form plasma, which surrounds the target object.
In one embodiment of the invention the ionization of the ambient gas within the chamber 11 is produced by RF power applied to another electrically isolated enclosure (not shown in the figures) placed around the enclosure 23a with respect to ground. Provisions have to be made to electrically connect such a source with the RF power supply placed outside the chamber, while simultaneously isolating it from the rest of the apparatus 10.
In another embodiment of the invention the ionization is provided by applying the RF power to a coil that is placed either substantially outside the chamber surrounding it or inside the chamber surrounding the target. In either case such an electric coil would have to be isolated from the rest of the apparatus 10.
In another embodiment of this invention, the enclosure is placed inside an object and the plasma is generated inside the enclosure and the ions are accelerated outwards. These ions implant on the inner surfaces of the object. One way to generate the plasma for such applications would be to use another enclosure like material but of smaller dimensions and subsequently applying RF power to it. In another embodiment of this invention an electron gun is used to generate plasma within the enclosure.
In another embodiment of the invention minute (e.g., nanoparticles) particles are dropped into the chamber with plasma in it and/or are subsequently ionized using the electrons from the filament electron source. These charged particles are then accelerated by the enclosure on to the target's outer and/or inner surfaces.
A great variety of materials can be used as the target objects 20 for ion implantation in this manner, including pure metals and alloy metals such as steel, semiconductors, ceramics, organic polymers etc. Any type of the various plasma sources for ion implantation may be utilized as the source of the ions to be implanted, with these ions being introduced into the chamber 11 to form plasma, which substantially surrounds the target object. These include gases such as nitrogen, oxygen, hydrogen, noble gases, fluorocarbons, hydrocarbons, vapors of solids, vapors of fluids and any mixture combination thereof. For example, evaporation of boron and/or carbon layers on to a substrate such as Al2O3 followed by implantation with nitrogen ions.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
Hence, it is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims. For example, the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention
The presently claimed invention claims priority based on provisional applications Ser. Nos. 60/607,271 filed on Sep. 7, 2004 and 60/607,039 filed Sep. 3, 2004.
| Number | Date | Country | |
|---|---|---|---|
| 60607271 | Sep 2004 | US | |
| 60607039 | Sep 2004 | US |
