Patent Number: 044619545
Section: description

SPECIFIC DESCRIPTION Referring to the drawing, a slender tube 1 is positioned to bring its open end into spaced juxtaposition with a workpiece 2 across a small gap. The slender tube 1, which has an inner diameter ranging preferably between 0.1 and 5 mm, is furnished with an ionizable gas from a source 3. The flow of the gas into the slender tube 1 through an inlet conduit is controlled by a valve 4 arranged between the source 3 and the inlet conduit. A coil 5 is wound around the slender tube 1 and energized by a high-frequency power supply 6 to ionize the gas therein. DC output terminals 7 are connected to the slender tube 1 and the workpiece 2 to apply an ion accelerating voltage thereacross to energize the ions within the tube 1. The workpiece 2 and the tube 1 are shown as connected with negative and positive poles of the DC supply 7, respectively. When the tube 1 is composed of an insulating material such as glass, the conductor leading from the positive pole of the ower supply 7 is arranged to pass through the body of the tube 1 and to terminate on the inner wall thereof. A further electromagnetic coil 8 is provided surrounding the slender tube 1 and energized by a power supply (not shown) to focus a beam of the energized ions onto a limited area of the surface of the workpiece 2. A lower portion of the slender tube 1 and the workpiece 2 which is securely mounted on a table 9 are accommodated in a vacuum chamber 10 which is evacuated by a vacuum pump 11. The space within the chamber 10 is hermatically sealed by insulating bellows 12 and 13. The slender tube 1 is movable vertically along a Z-axis by means of a motor 14 and guided movably into the chamber 10 via the bellows 12. The table 9 is arranged so as to be movable horizontally by means of a pair of motors 15 and 16. The motor 15 is arranged to displace the workpiece 1 along an X-axis and the motor 16 is arranged to displace the workpiece 1 along a Y-axis orthogonal to the X-axis in the horizontal plane. A drive controller 17, constituted by a numerical-control (NC) unit, is provided to furnish the motors 15 and 16 with drive signals to allow the lower end of the slender tube 1 to effectively move in a scanning manner over a desired area or path on the workpiece 2. The gap distance between the lower end of the tube 1 and the workpiece 2 is controlled by a control circuit 18 which responds to a voltage drop sensed at a detecting resistor 19 across the tube 1 and the workpiece 2 to act on the Z-axis motor 14. In this manner, the gap is held at a distance ranging between 10 and 1000 .mu.m, preferably not greater than 100 .mu.m and more preferably not greater than 50 .mu.m. The vacuum within the chamber 10 is maintained at a level depending on the types of processing the workpiece 2, e.g., at a pressure of 10.sup.-4 to 10.sup.-1 Torr when the workpiece 2 is to be ion-etched and at a pressure of 10.sup.-6 to 10.sup.-4 Torr when the workpiece 2 is to be ion-implanted. The ionizable gas (which term includes a mixture of gases) introduced into the slender tube 1 may be at least one of the following gases argon (Ar), nitrogen (N2), oxygen (O2) and hydrogen (H2, H), or may be one of Freon (trade name) gases or chloride gas. The latter gases are employed when their chemical reactive actions with the workpiece material is to be added to the mechanical action by their ions impinging on the workpiece with an elevated kinetic energy. The control valve 4 is adjusted to regulate the flow of the ionizable gas into the tube 1 while the chamber 10 is evacuated to maintain the pressure therein at an adequate level and to expel impurities in the working region between the tube 1 and the workpiece 2. The gaseous particles introduced into the tube 1 are subjected to energization by the high-frequency coil 5 and thereby ionized at least in most part or partially while flowing through the tube 1. A high-gradient electrical field in the range between 1 and 10 kV is established by the terminals 7 to energize and accelerate the ionized particles which are also focused by the action of the electromagnetic coil 8. As a result, a narrow beam of energetic ions is provided and ejected through the end opening of the tube 1 to impinge on the surface of the workpiece 2 for a desired ion processing purpose. For a machining operation, for example, the workpiece 2 may be displaced to expose its successive areas to the beam of energetic ions. A path of displacement determined by a desired contour or cavity to be machined in the workpiece 2 is preprogrammed in the NC unit 17 and reproduced in the form of drive pulses furnished to the motors 15 and 16. As the workpiece 2 is displaced along a prescribed path or a prescribed set of successive paths, the beam of energetic ions continuously projected from the slender tube 2 progressively removes material in a scanning manner from the workpiece so that the desired contour or cavity is eventually generated in the workpiece 2. In this manner, for example, a rectangular cavity can be formed by causing the ion beam to repetitively traverse a raster scan pattern between the preprogrammed x-y limits and removing additional material during each scan pattern until it arrives at the specified depth. Likewise, a nonrectangular contour cavity may be generated by causing the ion beam to scan single lines of varying length which form a pattern which is repeated at progressively greater depths until the specified depth is reached. In an ion-etching operation, a chemically reactive gas such as a gas of CnFm family is supplied from the source 3 into the slender tube 1 where it is ionized. The chemically reactive ions are thus provided so as to bombard the workpiece 2 therewith. Etching is effected by a combination of ion impingement mechanical action and ion reaction with the workpiece material, which assures an enhanced processing efficiency and rate. The reactive gases for use may also include halogen gases such as Cl, F, I and Br and halide gases. Since the guide tube 1 is used, is slender and is juxtaposed with the workpiece 2 across a small gap distance, the highly effective supply of ions and their selective ejection onto a limited area of the workpiece surface are achieved, thus enhancing both ion processing efficiency and precision. The principles of the invention are applicable to ion-plating, ion-implantation and ion-cleaning as well. An ionizable gas supplied into the slender tube 1 may also be ionized by applying a high voltage across the tube 1 and the workpiece 2, by subjecting the gas to a high energy beam of energetic particles such as electrons or of laser, and/or by subjecting the gas to an electrical discharge which is preferably pulsed. The volume of the gas supplied into the tube 1 is preferably controlled in response to the gap voltage across the tube 1 and the workpiece 2. The gap voltage is generally detectable in proportion to the gap distance. The vacuum pump 1 may also be regulated to control the vacuum pressure within the chamber 10 in conjunction with the volume of the gap supply and/or the gap distance. It has been found to be critical in the arrangement described to regulate the mean free path of energetic ions for impingement onto the workpiece surface. To this end, the small gap size described needs to be maintained. In addition, the vacuum pressure needs to be controlled locally. It has been found that the pressure within the small gap should be maintained in the range between 10.sup.-4 and 10.sup.-1 Torr while the pressure of the space surrounding the small gap within the chamber 10 should be maintained in the range between 10.sup.-6 and 10.sup.-4 Torr. A predetermined pressure difference of at least one order in Torr between the small gap and the atmosphere has been found to be desirable. The pressure within the small gap may be maintained by continuously replenishing the gas into the slender tube 1 from the source 3. The valve 4 is adjusted to establish a desired volume flow of the gas and hence pressure within the gap. A change in the pressure in the gap may be detected at the sensing resistor 19 and a control circuit 20 provided to respond to the detected pressure change to control the valve 4. Likewise, the pressure of the space surrounding the small gap within the chamber 10 is regulated by the vacuum pump 11. A control circuit 21 associated with the vacuum pump 11 may also be provided to responds to the signal detected at the sensing resistor 19. The slender tubular member 1 is preferably composed of an electrically conductive material such as tungsten or copper. In this case, the power supply 7 is used to energize the gas supplied from the source 3 and conducted through the tube 1 to form ions of the gas and to apply an acceleration potential to propel the formed ions in a beam across the small gap and to impinge on the workpiece. The coil 5 and the power supply 6 may then be dispensed with. The coil 8 may, as energized by an external power supply, be used to apply a magnetic field to the energetic ions in the region of the small gap. It has been found that the magnetic field of a flux density in excess of 500 Gauss is particularly effective to controlledly facilitate dispersion of ions and electrons in a beam and thus the energetic ions impinging on the workpiece in the small gap. In this manner, the precision of processing the workpiece surface with an energetic ion beam has been found to be markedly increased.