Patent Number: 044619545
Section: summary

FIELD OF THE INVENTION The present invention relates in general to ion-processing techniques such as machining (material removal), etching, implantation, plating and cleaning by energetic ions. More particularly, the invention is concerned with an improved method of and apparatus for processing a workpiece with a beam of energetic ions whereby the mean free path of energetic ions with which the workpiece is bombarded is regulated. BACKGROUND OF THE INVENTION Conventional ion-processing apparatus is characterized by massive and complicated equipments including separately an ion chamber, an acceleration chamber, a focusing section and a workpiece mounting chamber. Since the chambers are massive, they cannot easily be evacuated. In addition, difficulties have been encountered in assuring an adequate localization of ions impinging on a desired area and a uniformity of the density of the impinging ions on a localized area. Also, the processing rate has generally been limited to an unsatisfactory level. Thus, the conventional ion-processing art has left much to be desired not only as regards equipment but also as regard to the processing precision and efficiency. OBJECTS OF THE INVENTION It is, accordingly, an important object of the present invention to provide an improved ion-processing method capable of achieving the machining, etching, implantation, plating and cleaning of a workpiece surface with an energetic beam of ions with increased efficiency and precision. A further important object of the invention is to provide an improved ion-processing apparatus which is adapted to carry out the improved method and is relatively simple in structure and organization and relatively compact. SUMMARY OF THE INVENTION In accordance with the present invention there is provided, in a first aspect thereof, a method of processing a workpiece with a beam of energetic ions, which method comprises the steps of: positioning a slender tubular member to bring its open end into spaced juxtaposition with the workpiece across a small gap of a size ranging between 10 and 1000 .mu.m in an evacuated space; supplying the tubular member with an ionizable material in the form of gas or vapor (hereinafter: ionizable gas) for feeding it into the small gap through the open end; energizing the supplied gas to form ions thereof and applying an electrical potential to the formed ions to propel them in a beam across the small gap to impinge onto a limited area of the surface of the workpiece juxtaposed with the open end of the slender tubular member; and maintaining the pressure within the small gap in excess of the pressure of the space surrounding the small gap. The small gap defined between the open end of the slender tubular member and the workpiece is preferably of a size not greater than 100 .mu.m and more preferably not in excess of 50 .mu.m. In addition, the pressures of the space and within the small gap are maintained preferably in the range between 10.sup.-6 and 10.sup.-4 Torr and in the range of 10.sup.-4 and 10.sup.-1 Torr, respectively. The pressure within the small gap is maintained desirably at least by one order of magnitude in Torr greater than the pressure of the space. The gas forming ions may be argon, nitrogen, hydrogen and/or oxygen. The gas may also be of a substance selected from the group which consists of polyhalogenated hydrocarbons containing fluorine and chlorine (marketed as "Freons"), fluorides and chlorides. These gases are chemically reactive with the workpiece material and thus can provided the action of chemical reaction in addition to the mechanical action of energetic ions impinging upon the workpiece. The invention also provides, in a second aspect thereof, an apparatus for processing a workpiece with a beam of ions, which apparatus comprises: a slender tubular member having an open end and communicating with an inlet conduit; means for positioning the slender tubular member to bring the open end into spaced juxtaposition with the workpiece across a small gap of a size range between 10 and 1000 .mu.m in an evacuated space; means for supplying an ionizable gas into the slender tubular member through the inlet conduit and feeding the gas into the small gap through the open end; means for energizing the supplied gas to form ions of the thereof and applying an electrical potential to the formed ions to propel them in a beam across the small gap to impinge on a limited area of the surface of the workpiece juxtaposed with the open end of the slender tubular member; and means for maintaining the pressure within the small gap in excess of the pressure of the space surrounding the small gap. Specifically, the last-mentioned means includes a receptacle for receiving the workpiece and at least a portion of the open end of the slender tubular member and vacuum pump means for maintaining the pressure of the space within the receptacle in range between 10.sup.-6 and 10.sup.-4 Torr. The supply means includes valve means constituting a portion of the pressure-maintaining means and arranged between the inlet conduit and a source of the gas. The valve means is adjustable to maintain the pressure within the small gap in a range between 10.sup.-4 and 10.sup.-1 Torr. Preferably, means is provided which is responsive to a change in the pressure within the small gap for controlling at least one of the vacuum pump means and the valve means. In addition, means is provided which is responsive to a change in the gap size for relatively displacing the slender tubular member and the workpiece so as to maintain the gap size substantially at a predetermined value. Means is also provided for relatively displacing the workpiece and the slender tubular member in a plane substantially orthogonal to the longitudinal axis of the slender tubular member along a prescribed path to successively process the workpiece surface in a scanning manner over a preselected area thereof. It is desirable that the tubular member be composed at least in part of an electrically conductive material to constitute one of a pair of electrodes with respect to the workpiece constituting the other electrode for establishing the said electrical potential therebetween. Preferably, the slender tubular member is composed at least at a portion of the open end of such electrically conductive material. The tubular member may have an inner diameter ranging between 0.1 and 5 mm. Preferably, means is further provided for applying a magnetic field to the beam of energetic ions in the region of the small gap to controlledly facilitate dispersion of the ions in the beam impinging on the workpiece. The magnetic field should preferably be of a flux density not less than 500 Gauss.