Abstract:
The present invention relates to components in ion implanters having surfaces adjacent to the path of the ion beam through the ion implanter. Such surfaces will be prone to deposition and the present invention addresses problems associated with delamination of deposited material. An ion implanter component is provided that has a surface defining at least in part an ion beam path through the ion implanter, wherein at least a portion of the surface has been roughened. The portion of the surface may be roughened to provide surface features defined at least in part by sharp changes in orientation of adjacent parts of the surface.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to components in ion implanters having surfaces adjacent to the path of the ion beam through the ion implanter. Such surfaces will be prone to deposition and the present invention addresses problems associated with delamination of deposited material. 
       BACKGROUND OF THE INVENTION 
       [0002]    Ion implanters are used in the manufacture of semi-conductor devices and other materials. In such ion implanters, semiconductor wafers or other substrates are modified by implanting atoms of a desired species into the body of the wafer, for example to form regions of varying conductivity. 
         [0003]    Ion implanters are well known and generally conform to a common design as follows. An ion source generally comprises an arc chamber in which a hot plasma is generated. The plasma will contain ions of a desired species to be implanted. 
         [0004]    An extraction lens assembly produces an electric field that extracts ions from the ion source and forms a mixed beam of ions. Only ions of a particular species are usually required for implantation in a wafer or other substrate, for example a particular dopant for implantation in a semi-conductor wafer. The required ions are selected from the mixed ion beam that emerges from the ion source by using a mass analysing magnet in association with a mass resulting slit. By setting appropriate operational parameters on the mass analysing magnet and the ion optics associated therewith, an ion beam containing almost exclusively the required ion species emerges from the mass resolving slit. 
         [0005]    This ion beam is transported to a process chamber where the ion beam is incident on a substrate held in place in the ion beam path by a substrate holder. Accordingly, ions are produced in an ion source and transported to a process chamber along an ion beam path. 
         [0006]    In addition to the above-described operations, further procedures may be performed. For example, it is common to perform low-energy implants, but this has an associated problem in that a slow moving ion beam is susceptible to space charge blow-up. Accordingly, ions are often accelerated as they are extracted from the ion source to travel along the ion beam path at high energy. The ion beams then pass through a deceleration lens assembly prior to implantation in the wafer. In addition, other ion optics may be included along the ion beam path to steer and shape the ion beam and to prevent loss of current from the ion beam. Other components such as a plasma flood system may be placed along the ion beam path. 
         [0007]    The various parts of the ion implanter are operated under the management of a controller, typically a suitably trained person, a programmed computer or the like. A more detailed description of an ion implanter of this general type can be found in U.S. Pat. No. 4,754,200. 
         [0008]    During normal operation of an ion implanter, material is produced that gets deposited on various components within the ion implanter. This material arises from a number of sources. For example, some material may be lost from the ion beam, such as the species to be implanted or contaminants entrained within the ion beam. Another major source of deposition material is the photo-resist cover that is provided on semiconductor wafers to be implanted. The heat generated by the ion beam striking the wafer causes outgassing of carbon, hydrogen and hydrocarbons that may then deposit on surfaces. Another source of contaminants is material from ion implanter components that surround the ion beam path. If the ion beam strikes such components, material may be sputtered from that surface only to adhere to another surface within the ion implanter. As the surfaces surrounding the ion beam path are typically made from graphite, graphite is a major component in the deposited material. 
         [0009]    Clearly, surfaces adjacent to the ion beam are most prone to receiving deposits. As the amount of material deposited accumulates, the chances of the deposits delaminating to form flakes or particles increases. These flakes or particles frequently detach from their host surface and may become entrained in the ion beam. Consequently, the flakes or particles may reach the wafer where they represent a contaminant and may damage the semiconductor material. 
       SUMMARY OF THE INVENTION 
       [0010]    Against this background, and from a first aspect, the present invention resides in an ion implanter component having a surface defining at least in part an ion beam path through the ion implanter, wherein at least a portion of the surface has been roughened. 
         [0011]    This is in contrast to the established wisdom of utilising smooth surfaces within the ion implanter. In particular, components carrying voltages are smooth to ensure good electrical field characteristics and to minimise the chance of arcing where the voltage is large. Other components will generally be formed without any subsequent treatment to roughen their surfaces and usually a smoothing process is applied to those as well. However, roughening the surfaces has been found to be advantageous in respect of deposited material. While roughening the surface does not prevent deposition of material, the absence of large continuous surfaces prevents accumulations of deposits large enough to allow delamination and flake formation. In addition, roughening may even aid in trapping deposits and resisting detachment of material from the surface. 
         [0012]    Some components are likely to benefit more from surface roughening than others. For example, some components are regularly clipped by the ion beam. The parts of these components regularly clipped by the ion beam do not tend to see large accumulations of deposits. This is most probably because the ion beam serves to clean those surfaces, either by sputtering off deposits as they form or by thermal cycling. However, other components that either never receive direct ion beam strike or only occasionally see ion beam strike will benefit more from surface roughening. In addition, areas of a component regularly clipped by an ion beam, but away from the area where the ion beam strikes the component may also benefit from roughening. 
         [0013]    The surface may be roughened to provide a pattern of surface features, for example a regular pattern of surface features. Preferably, the surface features are defined at least in part by sharp changes in orientation of adjacent portions of the surface. In particular, the surface features may be defined at least in part by adjacent faces that meet at a sharp edge. 
         [0014]    A variety of surface features or surface patterning may be formed. For example, the surface may be roughened by forming a series of grooves. Preferred ranges of depths of the grooves are: 0.1 mm to 10 mm, 0.25 mm to 7.5 mm, and 0.5 mm to 5 mm. Optionally, the surface may be provided with a series of side-by-side grooves. The side-by-side grooves may be regularly spaced. Preferred ranges for the pitch of these grooves are: 0.1 mm to 10 mm, 0.25 mm to 7.5 mm, and 0.5 mm to 5 mm. 
         [0015]    Where grooves are formed in the surface, they may take a variety of shapes, both in the plane of the surface and in cross-section. For example, the grooves may be linear or they may be curved or kinked. In terms of cross-section, v-shaped, u-shaped, saw tooth grooves, and box-like trenches are all currently contemplated. 
         [0016]    Optionally, the surface may be roughened by forming two or more series of intersecting grooves. Preferably, first and second series of grooves may be formed with the first and second series orthogonal. The grooves may be v-shaped, thereby forming an array of tetrahedra. 
         [0017]    From a second aspect, the present invention resides in an ion implanter component having a surface defining at least in part an ion beam path through the ion implanter, wherein the surface is faceted to provide a plurality of faces separated by edges. 
         [0018]    From a third aspect, the present invention resides in an ion implanter component having a surface defining at least in part an ion beam path through the ion implanter, wherein at least a portion of the surface is textured with a pattern comprising surface features with a depth in the range of 0.5 mm to 5 mm and a pitch in the range of 0.5 mm to 5 mm. 
         [0019]    The present invention also resides in an ion implanter including any of the components described above. 
         [0020]    From a fourth aspect, the present invention resides in a method of making an ion implanter component having a surface intended to define at least in part an ion beam path through the ion implanter, the method comprising roughening at least a portion of the surface. The roughening may be performed to produce any of the components described above. 
         [0021]    From a fifth aspect, the present invention resides in a method of preventing delamination of deposits accumulated on surfaces defining an ion beam path through an ion implanter, the method comprising providing the ion implanter with any of the components described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0022]    In order that the present invention may be better understood, a preferred embodiment will now be described with reference to the accompanying drawings, in which: 
           [0023]      FIG. 1  is a schematic representation of an ion implanter; 
           [0024]      FIG. 2   a  is a perspective view of a roughened surface of a component in accordance with a first embodiment of the present invention such that the surface is provided with v-shaped grooves; 
           [0025]      FIG. 2   b  is a section showing the v-shaped grooves of  FIG. 2   a ; 
           [0026]      FIG. 2   c  is a plan view of the surface shown in  FIG. 2   a;    
           [0027]      FIG. 3   a  is a perspective view of a roughened surface of a component in accordance with a second embodiment of the present invention such that the surface is provided with saw-tooth shaped grooves; 
           [0028]      FIG. 3   b  is a section showing the saw-tooth shaped grooves of  FIG. 3   a;    
           [0029]      FIG. 3   c  is a plan view of the surface shown in  FIG. 3   a;    
           [0030]      FIG. 4   a  is a perspective view of a roughened surface of a component in accordance with a third embodiment of the present invention such that the surface is provided with trenches; 
           [0031]      FIG. 4   b  is a section showing the trenches of  FIG. 4   a;    
           [0032]      FIG. 4   c  is a plan view of the surface shown in  FIG. 4   a;    
           [0033]      FIG. 5   a  is a perspective view of a roughened surface of a component in accordance with a fourth embodiment of the present invention such that the surface is provided with fluted channels; 
           [0034]      FIG. 5   b  is a section showing the fluted channels of  FIG. 5   a;    
           [0035]      FIG. 6   c  is a plan view of the surface shown in  FIG. 5   a;    
           [0036]      FIG. 6   a  is a perspective view of a roughened surface of a component in accordance with a fifth embodiment of the present invention such that the surface is provided with intersecting v-shaped grooves thereby to form tetrahedra; 
           [0037]      FIG. 6   b  is a section showing the intersecting v-shaped grooves of  FIG. 6   a;  and 
           [0038]      FIG. 6   c  is a plan view of the surface shown in  FIG. 6   a.    
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    In order to provide a context for the present invention, an exemplary application is shown in  FIG. 1 , although it will be appreciated this is merely an example of the application of the present invention and is in no way limiting. 
         [0040]      FIG. 1  shows an ion implanter  10  for implanting ions in semiconductor wafers  12  that may be used in accordance with the present invention. The ion implanter  10  comprises a vacuum chamber  15  pumped through valve  24 . Ions are generated by ion source  14  and are extracted by an extraction lens assembly  26  to form an ion beam  34 . In this embodiment this ion beam  34  is steered and shaped through the ion implanter  10  such that the ion beam  34  passes through a mass analysis stage  30 . Ions of a desired mass are selected to pass through a mass resolving slit  32  and then conveyed onward along an ion beam path  34  towards the semiconductor wafer  12 . Before reaching the semiconductor wafer  12 , the ions are decelerated by deceleration lens assembly  48  and pass through a plasma flood system  49  that acts to neutralise the ion beam  34 . 
         [0041]    The ion source  14  generates an ion beam of a desired species. The ion source  14  generally comprises an arc chamber  16  containing a cathode  20  located one end thereof. The ion source  14  may be operated such that an anode is provided by the walls  18  of the arc chamber  16 . The cathode  20  is heated sufficiently to generate thermal electrons. Thermal electrons emitted by the cathode  20  are attracted to the anode, the adjacent chamber walls  18  in this case. The thermal electrons ionise gas molecules as they traverse the arc chamber  16 , thereby forming a plasma and generating the desired ions. 
         [0042]    The path followed by the thermal electrons may be controlled to prevent the electrons merely following the shortest path to the chamber walls  18 . A magnet assembly  46  provides a magnetic field extending through the arc chamber  16  such that thermal electrons follow a spiral path along the length of the arc chamber  16  towards counter cathode  44  located at the opposite end of the arc chamber  16 . 
         [0043]    A gas feed  22  supplies the arc chamber  16  with either the species to be implanted or a precursor gas species. The arc chamber  16  is held at a reduced pressure within the vacuum chamber  15 . Thermal electrons travelling through the arc chamber  16  ionise the gas molecules present in the arc chamber  16  and may also crack molecules. The ions created in the plasma will also contain trace amounts of contaminant ions, e.g. those generated from the material of the chamber walls that is usually graphite. 
         [0044]    Ions from within the arc chamber  16  are extracted through an exit aperture  28  provided on a front plate  27  of the arc chamber  16  using a negatively biased (relative to ground) extraction electrode  26 . A potential difference is created between the ion source  14  and the following mass analysis stage  30  by a power supply  21  such that the extracted ions are accelerated, the ion source  14  and mass analysis stage  30  being electrically isolated from each other by an insulator (not shown). 
         [0045]    The mixture of extracted ions are then passed through the mass analysis stage  30  so that the mixture passes around a curved path under the influence of a magnetic field. The radius of curvature travelled by any ion is determined by its mass, charge state and energy. The magnetic field is controlled so that, for a set beam energy, only those ions with a desired mass-to-charge ratio energy exit along a path coincident with the mass resolving slit  32 . The ion beam  34  is then transported to the target, i.e. the substrate wafer  12  to be implanted or a beamstop  38  when there is no wafer  12  in the target position. Before arriving at the wafer  12  or beamstop  38 , the ions are decelerated using a deceleration lens assembly  48  positioned between the mass analysis stage  30  and upstream of the target position. The deceleration lens assembly  48  is followed by a plasma flood system  49  that operates to produce a flood of electrons that are available to the semiconductor wafer  12  to neutralise the effect of the incident positive ions. 
         [0046]    A semiconductor wafer  12  will be mounted on a wafer holder  36 , wafers  12  being successively transferred to and from the wafer holder  36  for serial implantation. Alternatively, parallel processing may be used where many wafers  12  are positioned on a carousel  36  that rotates to present the wafers to the instant ion beam in turn. 
         [0047]    A controller is shown at  50  that comprises a suitably programmed computer. The controller  50  is provided with software for managing operation of the ion implanter  10 . 
         [0048]    In general, the ion implanter  10  will be susceptible to deposition from materials such as graphite and photo-resist. In particular, the surfaces that are close to the ion beam path  34  will particularly see deposition of material and material that later breaks free from those surfaces is more likely to become entrained in the ion beam. As mentioned above, excessive accumulation of deposited material leads to delamination such that flakes detach and become entrained in the ion beam. These flakes may be of varying sizes and may be further broken up to result in a large amount of very small particles (sub-micrometer). These particles may deposit and stick to the semiconductor wafers  12 . In order to alleviate this problem, certain surfaces may be adapted to prevent the accumulation of particulates. As will be appreciated, to prevent deposition of material is difficult to achieve, but action may be taken to prevent the formation of large areas of material that may later be prone to delamination. 
         [0049]    In particular, components within the ion implanter  10  may be provided with roughened surfaces. Such surfaces may be roughened to interrupt the otherwise large surface area and so prevent large flakes of material accumulating. Electrically passive surfaces are particularly suitable to such treatment. Surfaces that are electrically active, and in particular those that carry high voltages, are less susceptible to such treatment as the roughening may have adverse effects on their electrical properties. For example, roughening of the surface carrying a high voltage may lead to an increased risk of arcing. 
         [0050]    Surfaces that are considered particularly suitable for roughening include those provided in the flight tube, those provided the back side of aperture plates, the mass analyser  30  including the mass resolving slit  32 , the plasma flood system  49 , and electrodes of the deceleration lens electrode assembly  48  that do not carry high voltages. 
         [0051]    Many forms of surface roughening may be used to prevent flake formation and there follows a description of some preferred embodiments. 
         [0052]      FIGS. 2   a  to  2   c  show a surface patterning that may be used in accordance with a first embodiment of the invention. A portion of a component  200  within the ion implanter  10  is shown in  FIGS. 2   a  to  2   c  that is provided with a roughened surface  202 . The surface  202  bears a series of abutting, linear v-shaped grooves  204  arranged side-by-side so as to form successive sharp ridges  206  and sharp troughs  208 . The size of the grooves  204  may be characterised by the dimensions A and B that correspond to depth and pitch respectively, as indicated on  FIG. 2   b.  These dimensions may take various values, and need not all be the same. Typical values for A or B may be in the range 0.5 mm to 5 mm. 
         [0053]      FIGS. 3   a  to  3   c  show a second embodiment of the present invention. Again, a portion of a component  300  within an ion implanter  10  is shown that is provided with a roughened surface  302 . Once more, the surface  302  comprises a series of grooves  304 . To illustrate that the sides of the grooves  304  need not adopt the same angle as per the embodiment of  FIGS. 2   a  to  2   c,  the grooves  304  of  FIGS. 3   a  to  3   c  have one upright side and one sloping side. This arrangement results in a saw-tooth profile as is most evident from the side view of  FIG. 3   b.  The grooves  304  may be characterised by the dimensions A and B corresponding to depth and pitch. As for the embodiment of  FIGS. 2   a  to  2   c,  typical sizes of 0.5 mm to 5 mm would be suitable. 
         [0054]    While the embodiments shown in  FIGS. 2   a  to  2   c  and  FIGS. 3   a  to  3   c  have grooves  204  and  304  that abut to form sharp ridges  206  and  306 , the grooves may instead be separated. This will result in flat sections between adjacent grooves  204 ,  304 . These flat sections should have small width, for example between 0.5 mm and 5 mm, to prevent flake formation. An example of a roughened surface  402  having grooves  404  separated by flat sections  404  is shown in  FIGS. 4   a  to  4   c.  In these Figures, the component  400  is provided with grooves  404  in the form of a series of parallel trenches  404 . The trenches  404  have flat bottoms  408  and vertical sides  410 . Typical depths A are 0.5 mm to 5 mm and typical widths B for the flat tops  406  and flat bottoms  408  are also 0.5 mm to 5 mm. 
         [0055]      FIGS. 5   a  to  5   c  show a fourth embodiment of the present invention where a component  500  is provided with a roughened surface  502  that comprises a series of fluted channels  504 . As is best seen in  FIG. 5   b,  the generally u-shaped channels  504  are separated by flat sections  506 . As will clear from the above, the fluted channels  504  may abut so as to form sharp ridges  506 . The angle subtended by each fluted channel  504  may be less than the 180° shown in  FIGS. 5   a  and  5   b.    
         [0056]    The embodiments of  FIGS. 2 to 5  all show side-by-side grooves  204 ,  304 ,  404  and  504 . However, intersecting arrays of grooves may also be used to roughen the surfaces  202 ,  302 ,  402  and  502 . For example, two arrays of side-by-side grooves  204 ,  304 ,  404 ,  504  may be formed at an angle to one another so as to intersect.  FIGS. 6   a  to  6   c  show such an arrangement where a surface  602  has been roughened by forming first and second series of v-shaped grooves  604 . Each series of grooves  604  comprise parallel, abutting grooves  604  that form a series of troughs  608 . The two series are arranged to be orthogonal such that the intersecting troughs  608  cut through what would be the ridges  606  to form a regular array of tetrahedra  612 . 
         [0057]    The ridged patterns formed on the surfaces  202 ,  302 ,  402 ,  502  and  602  means that there are no extensive flat areas on which depositions may accumulate to a sufficient size to delaminate and form flakes. Accordingly, while deposition will continue, large flakes do not result that may later detach from the surfaces  202 ,  302 ,  402 ,  502  and  602 . In fact, the patterned surfaces  202 ,  302 ,  402 ,  502  and  602  perform far better in retaining deposited material that might otherwise detach, for example due to incidence of the ion beam  34  or through thermal cycling. 
         [0058]    The surfaces  202 ,  302 ,  402 ,  502  and  602  may be roughened in any number of ways. How the pattern is formed may be dependent upon the material of the surface  202 ,  302 ,  402 ,  502  and  602  itself. For example, metal surfaces may be machined to form a required pattern or they may be pressed to form the pattern. Machining may include sanding or grinding. For other materials such as graphite, other techniques such as ablation, sputtering or etching may be used (graphite parts are usually also machined similarly to metal parts). 
         [0059]    As will be appreciated by the person skilled in the art, variations may be made to the above embodiment without departing from the scope of the invention defined by the claims. 
         [0060]    For example, all of the above embodiments show a series of linear grooves formed in a surface. However, the grooves need not be linear. For example, the grooves may be curved or kinked. Moreover, the grooves need not all be the same shape or all the same size.