J. R. Conrad

Plasma source ion‐implantation technique for surface modification of materials

Plasma source ion‐implantation (PSII) is a new ion‐implantation technique which has been optimized for surface modification of materials such as metals, plastics, and ceramics. PSII departs radically from conventional implantationtechnology by circumventing the line‐of‐sight restriction inherent in conventional ion implantation. In PSII, targets to be implanted are placed directly in a plasma source and then pulse biased to a high negative potential. A plasma sheath forms around the target and ions bombard the entire target simultaneously. Preliminary experiments have demonstrated that PSII: (1) efficiently implants ions to concentrations and depths required for surface modification, (2) produces material with improved microhardness and wear properties, and (3) dramatically improves the life of manufacturing tools in actual industrial applications. For example, the tool life of M‐2 pierce punches used to produce holes in mild steel plate has been increased by a factor of 80.

Sheath thickness and potential profiles of ion‐matrix sheaths for cylindrical and spherical electrodes

Analytic expressions have been obtained for the potential profile and sheath thickness of the transient ion‐matrix sheath which forms when a large negative step potential is applied to planar, cylindrical, and spherical electrodes immersed in a plasma.

Model of plasma source ion implantation in planar, cylindrical, and spherical geometries

A model has been developed that describes the propagation of the transient sheath during a pulse of high negative voltage applied to a conductor immersed in a plasma such as that present in plasma source ion implantation. This model assumes that the transient sheath obeys the Child–Langmuir law for space‐charge‐limited emission at each instant during the propagation of the sheath. Expressions are obtained for the sheath‐edge position as a function of time. The model predicts the final sheath extent and average ion current to the target during each pulse for planar, cylindrical, and spherical geometries.

Measurement of electron emission due to energetic ion bombardment in plasma source ion implantation

An experimental procedure has been developed to measure electron emission due to energetic ion bombardment during plasma source ion implantation. Spherical targets (radius=2 cm) of copper, stainless steel, graphite, titanium alloy (Ti‐6Al‐4V) and aluminum alloy (6061) were biased negatively to 20, 30, and 40 kV in argon and nitrogen plasmas. A Langmuir probe was used to detect the propagating sheath edge and a Rogowski transformer was used to measure the current to the target. The measurements of electron emission coefficients compare well with those measured under similar conditions [B. Szapiro and J. J. Rocca, J. Appl. Phys. 65, 3713 (1989)].

Plasma source ion implantation: A new, cost-effective, non-line-of-sight technique for ion implantation of materials☆

Abstract Surface modification by ion bombardment is a well-established technique for improving the hardness, friction, wear resistance and corrosion resistance of materials. Surface modification of materials by conventional ion implantation is a line-of-sight process in which a directed beam of energetic ions is rastered across a target. If the target is three dimensional, the process generally requires target manipulation to achieve uniform implantation over the entire surface of the object. This target manipulation requirement can seriously limit the cost effectiveness of ion implantation relative to more conventional surface treatments, especially for large and/or heavy targets. We are developing a new technique, plasma source ion implantation (PSII), which circumvents the line-of-sight restriction of conventional ion implantation. In PSII, targets to be implanted are placed directly in a plasma source chamber and are then pulse biased to high negative voltage (10 – 100 kV in our experiments). A thick, ion matrix sheath forms around the target, and ions accelerate through the sheath drop and bombard the target from all sides simultaneously without the necessity of target manipulation. Although the PSII process bears a superficial resemblance to existing techniques such as “ion plating”, “ion coating” or “plasma nitriding”, PSII produces a deposition profile characteristic of high energy ion implantation. Our experiments have demonstrated that PSII (1) efficiently implants ions to the concentrations and depths required for surface modification, (2) produces material with improved microhardness and wear properties and (3) dramatically improves the life of manufacturing tools in actual industrial applications. For example, in recent industrial field tests the tool life of M-2 pierce punches used to produce holes in mild steel plate has been increased by a factor of 70 – 80. In this paper we describe (1) the latest results from a series of ongoing field tests, (2) extensions of the PSII process to ion beam mixing and ion beam enhanced deposition modes of operation, and implantation of molecular ions, and (3) the comparative economics of surface modification by PSII relative to conventional ion implantation.

Measurements of spatial and temporal sheath evolution for spherical and cylindrical geometries in plasma source ion implantation

A comparison of experimental measurements and numerical calculations of temporal and spatial sheath evolution is presented. Spherical targets of copper and stainless steel (radius=2 cm) and a cylindrical target (radius=0.95 cm, height=18 cm) were immersed in an argon plasma with plasma densities of 2×108–8×109 cm−3 and biased negatively (20–50 kV). A Langmuir probe was used to detect the propagating sheath edge. Experimental measurements of sheath edge position were in good agreement with those determined by numerical calculations.

Ion beam assisted coating and surface modification with plasma source ion implantation

Plasma source ion implantation (PSII) is a non‐line‐of‐sight technique which is being developed as an alternative to beamline accelerator technology for ion implantation. The initial development phase of PSII concentrated on implantation of ion species which are gaseous at room temperature (primarily nitrogen ions) and employed a cylindrical vacuum chamber 16 in. high and 14 in. in diameter. A second generation PSII system is being constructed to extend the PSII process to ion beam mixing and ion beam assisted coating modes of operation. The new, larger system (with dimensions 36×36×36 in.) will feature multiple‐array sources for sputter deposition concurrent with ion bombardment.

Development of an energetic ion assisted mixing and deposition process for TiNx and diamondlike carbon films, using a co-axial geometry in plasma source ion implantation

Plasma source ion implantation (PSII) is a relatively simple technique for the ion implantation/deposition of materials. In PSII a substrate is immersed in a plasma, and high negative voltage pulses are applied to accelerate ions into the substrate resulting in modification of the properties of the material in the near surface region. A technique was developed to produce uniform diamondlike carbon coatings and TiNx films inside and outside a hollow cylinder (substrate). A description of apparatus, experimental methods for this type of deposition process, and preliminary results are presented in this article.Plasma source ion implantation (PSII) is a relatively simple technique for the ion implantation/deposition of materials. In PSII a substrate is immersed in a plasma, and high negative voltage pulses are applied to accelerate ions into the substrate resulting in modification of the properties of the material in the near surface region. A technique was developed to produce uniform diamondlike carbon coatings and TiNx films inside and outside a hollow cylinder (substrate). A description of apparatus, experimental methods for this type of deposition process, and preliminary results are presented in this article.

Plasma source ion implantation dose uniformity of a 2×2 array of spherical targets

We have employed Rutherford backscattering spectroscopy and secondary ion mass spectrometry to characterize the ion implantation dose uniformity which can be achieved with plasma source ion implantation (PSII), a non‐line‐of‐sight technique for ion implantation of nonplanar targets in nonsemiconductor applications. In order to characterize the dose uniformity achievable with PSII, four spherical Ti‐6Al‐4V targets were PSII implanted simultaneously as a 2×2 square array in a nitrogen plasma with density 3×109 cm−3 at an energy of 50 keV to a nominal dose of 3×1017 atoms/cm2. The measured root‐mean‐square variation of both the retained dose and the mean range was found to be less than 15%, which is well within the acceptable tolerance range for nonsemiconductor applications of ion implantation. Our results demonstrate that PSII can achieve acceptable dose uniformity on nonplanar targets without target manipulation, and that such uniformity can be achieved in a batch processing mode.

Plasma source ion implantation: A new approach to ion beam modification of materials

Abstract Plasma source ion implantation (PSII) is a nonline-of-sight technique for surface modification of materials which is optimized for ion implantation of non-planar targets in non-semiconductor applications. In PSII, targets to be implanted are placed directly in a plasma source chamber and are then pulse biased to high negative voltage (10–100 kV in our experiments). A thick ion matrix sheath forms around the target, and ions accelerate through the sheath drop and bombard the target from all sides simultaneously without the necessity of target manipulation. Compared with conventional ion implantation, PSII minimizes the problems of shadowing and excessive sputtering of the target material, which can severely limit the retained dose of the implanted ion species. PSII has demonstrated (1) efficient implantation of ions to the concentrations and depths required for surface modification, (2) dramatic improvement in the life of manufacturing tools in actual industrial applications, (3) acceptable dose uniformity on non-planar targets without target manipulation and (4) that such uniformity can be achieved in a batch-processing mode. An examination of the comparative economics of surface modification by PSII relative to conventional ion implantation indicates substantial reductions in operating costs, by virtue of the greater throughput possible with PSII.