Patent Publication Number: US-7909967-B2

Title: Electro-chemical processor

Description:
BACKGROUND 
     Silicon is the basic building block material of most microelectronic devices. Other micro-scale devices such as microelectro-mechanical devices (MEMs), and micro-optic devices, are also generally made of silicon. These devices are used in virtually all modern electronic products. The raw silicon material used in making these types of microscopic devices is ordinarily provided in the form of thin flat polished wafers. 
     Porous silicon is a form of silicon having tiny openings or pores. These pores can absorb and emit light. This allows porous silicon devices to interact with light and electronic devices in many useful ways. Porous silicon also has a very large surface area and acts as a strong adsorbent. These properties make porous silicon useful in mass spectrometry, micro-fluidic devices, sensors, fuel cell electrodes, optical, chemical and mechanical filters, biochips and biosensors, fuses for airbags, and various other products. 
     The porous silicon material itself may also be used as a porous and/or solvable substrate, for example in diagnostic or therapeutic products. Accordingly, porous silicon is increasingly becoming an important material in a wide range of products and technologies. 
     Porous silicon is generally manufactured in an electro-chemical etching process. A silicon wafer is typically exposed to an electrolyte including concentrated hydrofluoric acid (HF). The electrolyte on one side of the wafer is sealed off from the electrolyte on the other side of the wafer. Electrical current is passed through the electrolyte on each side, making one side the cathode and the other side the anode. The silicon wafer may optionally be exposed to light during this process. The process etches pores in the wafer. The pores are microscopic. A 150 mm diameter wafer may have more than 1 billion pores after electro-chemical processing. 
     Although various types of porous silicon machines or processors have been used, disadvantages remain in performance, reliability, speed, and other design parameters. HF is highly corrosive and toxic. Accordingly, it must be carefully contained within the processor. Since HF will react with virtually all metals, metals cannot effectively be used in areas of the processor that may come into contact with HF. Moreover, even the smallest of amount of interaction between the HF in the electrolyte and metal can contaminate the wafer. The uniform processing required to consistently produce high quality porous silicon also requires uniform electrical current flow through the electrolyte. Achieving uniform current flow is affected by the design of the processor and may be challenging to achieve. Existing processors have offered only varying results in the face of these engineering design challenges. In view of these factors, improved methods, processors and systems for making porous silicon are needed. 
     SUMMARY 
     A novel processor has now been invented providing various improvements in making porous silicon or in similar electro-chemical processing. This new processor provides highly uniform processing. Potential for contamination of wafers before, during, and after processing is significantly reduced. Potential for corrosion of processor components is similarly largely avoided, offering long term reliability and performance, and reduced maintenance requirements. The processor is also adaptable for use in an automated processing system, providing relatively rapid processing. These advantages are achieved via a new processor having a first seal in housing, and a first electrode in the housing associated with the first seal. A second seal in the housing may be moved relative to the first seal. A second electrode is associated with the second seal. The housing may be set up to pivot from a horizontal position to a vertical position. This allows a wafer to be loaded and unloaded in a horizontal position, and processed in a substantially vertical position. 
     The invention resides as well in methods for electro-chemical processing, and in sub-combinations of the elements and steps described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, wherein the same reference number indicates the same element, in each of the views: 
         FIG. 1  is a top and front perspective view of a porous silicon processor. 
         FIG. 2  is a bottom and back perspective view of the processor shown in  FIG. 1  with the mounting plates omitted for purpose of illustration. 
         FIG. 3  is an exploded top and front perspective view of the processor shown in  FIGS. 1 and 2 . 
         FIG. 4  is a plan view of the processor shown in  FIGS. 1-3 . 
         FIG. 5  is a partial section view taken along line  5 - 5  of  FIG. 4 . 
         FIG. 6  is a partial section view taken along line  6 - 6  of  FIG. 4 . 
         FIG. 7  is a partial section view taken along line  7 - 7  of  FIG. 4 . 
         FIG. 8  is a partial section view taken along line  8 - 8  of  FIG. 4 . 
         FIG. 9  is a section view taken along line  9 - 9  of  FIG. 4  and showing the head of  FIGS. 1-8  alone. 
         FIG. 10  is a top and front perspective view of the head shown in  FIG. 9  with the head cover removed. 
         FIG. 11  is a top and front perspective view of the base shown in  FIGS. 1-8 , with  FIG. 11  showing the base separated from the head. 
         FIG. 12  is a plan view of the base shown in  FIG. 11 . 
         FIG. 13  is a section view taken along line  13 - 13  of  FIG. 12 . 
         FIG. 14  is a section view taken along line  7 - 7  of  FIG. 4  and showing the processor in a closed or processing position, with  FIGS. 5-8  showing the processor in an open position, for loading and unloading a wafer. 
         FIG. 15  is an enlarged section view of the seals and ejector tab shown in  FIG. 5 . 
         FIG. 16  is a perspective view of the lower seal retainer shown in  FIGS. 13-15 . 
         FIG. 17  is a perspective view of the upper seal retainer shown in  FIGS. 14-15 . 
         FIG. 18  is a section view taken along line  18 - 18  of  FIG. 17 . 
         FIG. 19  is a perspective view of an automated processing system including the processor shown in  FIGS. 1-15 . 
         FIG. 20  is a top view of the system shown in  FIG. 19 . 
         FIG. 21  is a front view of the system shown in  FIG. 19 . 
         FIG. 22  is a side view of the system shown in  FIG. 19 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Turning now in detail to the drawings, as shown in  FIGS. 1-3 , a first processor assembly or head  34  is attached to a second processor assembly or base  32 , to form an electro-chemical processor  30 . A motor or other actuator, such as a rotate motor  38 , can move the processor  30  from the horizontal position shown in  FIGS. 1-3 , one-quarter turn, into a vertical position. 
     A retainer generally designated  48  is provided on the head and/or the base for holding them together. Various forms of retainer  48  may be used. In a basic form, the retainer  48  may simply be bolts or other fasteners holding the head onto the base.  FIGS. 1-4  show another form of retainer  48  having four spaced apart cam handles  50  pivotably attached to the base  32  via pivot bolts  54 , and with a cam latch  52  pivotably attached onto each cam handle  50 . When engaged or locked, the cam handles  50  securely seal the head  34  to the base  32 , as shown in  FIG. 1 . The cam handles  50  may be quickly released (by pulling radially outwardly), to allow the head  34  to be separated from the base  32 , for system set up, inspection, or maintenance. 
     Turning in addition now to  FIG. 5 , when secured together, the head  34  and the base  32  may form a containment chamber  60 , with process chambers  146  and  240  within the containment chamber. Referring momentarily again to  FIGS. 1-3 , a load/unload workpiece opening or slot  56  extends through the base  32 , to allow a wafer to be moved through the containment chamber  60  to the process chambers. A containment drain or opening and gas/vapor exhaust  58  may be provided in the base  32 , generally opposite from the load slot  56 . A frame  62  may surround the load slot  56  at the front of the processor  30 . 
     For electro-chemical processing, the processor  30  is provided with two electrodes and two process chamber seals. At least one process chamber seal is moveable. An electrode may move with the moveable process seal. The moveable seal may be in the head  34  or in the base  32 . The other electrode and process chamber seal, may be fixed or moving, and typically are fixed in place within the processor  30 . The drawings show an example of the processor  30  where the moving electrode and seal is in a head, and a fixed electrode and seal is in a base, positioned vertically on top of the base. However, these positions may be reversed, as they are not essential to the invention. Except for the two electrodes and the two process chamber seals, the other specific components described below, including those forming the containment chamber  60 , are not necessarily essential and may be omitted, or substituted out in place of an equivalent functional element. 
     The specific mechanism or force selected to move the moveable seal is also not essential. This movement may be provided by hydraulic, pneumatic, electric, gas or steam pressure, or mechanical forces. In the design shown, hydraulic force is used, with water as the hydraulic fluid. In this example of a hydraulically driven processor, as shown in  FIG. 5 , a piston cap  78  is attached to the head cover  70 . A piston  74  is fixed in position relative to the cover  70  by a piston nut  76  and a piston plate  80 . A cylinder  82  is supported around the piston  74 , with the lower end of the piston  74  sealed against the interior cylinder walls by a piston seal  94 . A piston ring  88  is attached to the upper end of the cylinder  82 . An inner piston ring seal  90  seals the piston ring  88  against the piston  74 . An outer piston ring seal  92  seals the piston ring  88  against the cylinder  82 . For clarity of illustration, fluid and electrical lines and cables are generally omitted from the drawings. 
     A cylinder ring  86  is attached to an annular flange  84  of the cylinder  82 . An upper or first electrode ring  106  is in turn attached to an annular flange of the cylinder ring  86  via cap screws  112 . An upper or first electrode  96  (in this case, the cathode) is held in place between the electrode ring  106  and the cylinder ring  86 . The electrode  96  is sealed against the electrode ring  106  by first and second seals  110  and  108  at the front surface and cylindrical side of the electrode  96 . A third seal  104  and a fourth seal  105  seal the back surface of the electrode  96  against the cylinder ring  86 . An annular groove  102  is positioned between the third seal  104  and the fourth seal  105  for improved leak detection, as described below. An electrode lead or wire  95  runs through a electrical fitting  155  on the upper fittings plate  180  and through a fitting  160  on the cylinder ring  86  and is attached to a buss plate  98  via a cap screw  100 . Metal cap screws may be used to secure the buss plate onto the back surface of the electrode  96 . Typically, multiple cap screws are used to secure the buss plate to the electrode, in a geometric pattern, since the number and location of the screws may affect the uniformity of current flow through the electrode, and ultimately affect current uniformity at the wafer. 
     Referring to  FIGS. 5 and 15 , a head seal  128  is attached to the bottom surface of the electrode ring  106  via an upper seal clamp ring  132 . The cylindrical open space shown in  FIG. 5  as CC between the electrode  96  and the plane of the head seal forms an upper process chamber  146  when the seal  128  is in contact with a wafer. The upper end of a bellows  120  is attached to the underside of an annular cam ring  72  on the cover  70  by an upper bellows retainer ring  122 . The lower end of the bellows  120  is attached to a lip on the electrode ring  106  via a lower bellows retainer ring  124 . As a result, upon actuation of the cylinder  82 , the entire moveable electrode assembly  152 , including the piston ring  88 , cylinder  82 , cylinder ring  86 , electrode  96 , electrode ring  106 , and the seal  128  can move vertically relative to the cover  70 , as well as to the base  32 , with the bellows  120  maintaining a seal between the electrode assembly  152  and the base  32 . 
     Referring now also to  FIGS. 7 and 10 , an electrolyte liquid port or outlet  148  connects from an outlet or recirculation fitting  150  to a duct  148  in the electrode ring  106  that opens into the chamber  146 . An electrolyte liquid inlet  142 , which may be located opposite from the outlet  148 , leads to an electrolyte recirculation or inlet fitting  140 , with an connection line  153 , shown in dotted lines in  FIG. 10 , connecting the fitting  140  to a fitting  154  on the upper fitting bracket  180 . A diffuser plate  126  having multiple small openings is positioned over the inlet  148  in the upper process chamber  146 . Windows or openings  71  and  73  are provided in the side walls of the cover  70 , to provide clearance for the up and down vertical movement of the fluid and electrical fittings, e.g., the electrical connector  160  and the liquid process chemical recirculation or outlet fitting  150 , as the electrode assembly  152  moves up and down. Referring still to  FIG. 7 , an optical liquid detector  170  extends through a clamp nut  172  and seal  174  in the cylinder ring  86 , with the tip of the detector  170  positioned within the groove  102 . The detector  170  can be connected to a processor controller (such as the controller  304  described below) via fiber optic lines passing through a strain relief feature on the head. The fluid and electrical or optical lines connecting to the head may be made through adapters on connectors on the upper fitting bracket to provide strain relief as the processor  30  moves between horizontal and vertical positions. 
     As also shown in  FIG. 7 , an upper seal vent  116  is provided between the second seal  108  and the third seal  104 . The vent  116  is designed to reduce wicking of electrolyte inwardly between the back surface of the electrode  96  and the bottom surface of the cylinder ring  86 . Similarly, a lower seal vent  118  is located to reduce wicking of electrolyte between the back surface of the lower or second electrode  208  and the electrode cover  206 , in the event of a leak of electrolyte past the first seal  110  and the second seal  108 . 
     Turning to  FIG. 8 , an optical flag plate  168  extends up from the cylinder ring  86 . Upper and lower optical sensors  162  and  164  attached to the cover  70 , and are also connected via the fiber optic leads  163  and  165  to the processor controller. Strain relief fittings such as the clamp plate  169  shown in  FIG. 5 , are typically provided on these leads, so that they may better accommodate the movement of the processor. The sensors  162  and  164  detect the position of the flag plate  168 , which corresponds to the position of the moveable electrode assembly  152  relative to the base  32 . Also as shown in  FIG. 8 , the electrode ring  106  includes bores  114 . Guide pins  214  in the base  32  extend into the bores  114 , to maintain the moveable electrode assembly  152  in alignment with the base  32 . 
       FIG. 9  shows the head  34  separated from the base  32 . With the head retainer  48  released, in this case by pulling the cam handles  50  outwardly, the head  34  may be separated from the base  32 . The electrical and fluid lines connecting to the head may be flexible, so that the head may be removed from the base without the need to break these connections. 
       FIG. 10  shows the head  34  separated from the base  32 , and with the head cover  70  removed, for purpose of illustration. As shown in  FIG. 10 , the upper fitting bracket  180  and the optical flag plate  168  are attached to the cylinder ring  86 . The cap screws  79  which ordinarily attach the piston cap  78  and the piston plate  80  to the cover  70  are shown in their assembled positions, but without the cover  70  in place. The upper optical sensor  162  and the lower optical sensor  164  are attached to the side wall of the cover  70 . However, they are shown in  FIG. 10  for purpose of illustration only. An alignment pin  182  in the electrode ring  106  may extend into a vertical slot on an inside surface of the head cover  70 , to keep the head cover angularly aligned with the movable electrode assembly  152 . As shown in  FIGS. 1 ,  2  and  9 , cylinder water supply and return lines extend from fittings  176  and  178  on the upper fittings bracket  180  to upper and lower cylinder ports  156  and  158  extending through the walls of the cylinder  82 . Alternately supplying water under pressure through the upper and lower cylinder ports  156  and  158  hydraulically moves the moveable electrode assembly  152  between up or open and down or closed positions. 
       FIGS. 11 ,  12 , and  13  show the base  32  separated from the head  34 . Referring to  FIGS. 11 ,  12 , and  8 , three guide pins  214  project upwardly from a base electrode ring  204  into the bores  114  in the head electrode ring  106 . A pin seal  215  seals the base of the pin against the base electrode ring  204 , although in ordinary use, the guide pins  214  are not extensively exposed to the corrosive electrolyte liquid. 
     As shown in  FIGS. 11 and 12 , the two front guide pins  214 , closest to the load slot  56 , are spaced apart by a dimension DD which is nominally larger than the wafer diameter. The third guide pin  214  is located towards the back of the processor  30 , closer to the containment drain  58 . Referring to  FIGS. 8 and 12 , the guide pins  214  are located on a diameter concentric with and slightly greater than, the diameter of the seal  128 . The lower section of each guide pin  214  has a shoulder  218  which may act as a hard stop to set the spacing between the seals when the processor is closed, thereby also setting a predefined amount of seal compression on the wafer. 
     Referring to  FIG. 13 , the base  32  has a base ring  200 . A seal seat  202  at the upper end of the base ring  200  holds a containment seal  36 , which is shown in  FIG. 3 . The containment seal  36  seals the head to the base to form the containment chamber. Similar to the head  34 , the lower or second electrode  208  (in this case the anode) is secured in place in the base by a base electrode ring  204  and a base electrode cover  206 . As in the head  34 , the electrode  208  is sealed against the base electrode ring  204  by first and second seals  110  and  108 . The base electrode ring  204  is similarly sealed against the electrode  208  by third and fourth seals  104  and  105  positioned on opposite sides of a groove  102 . As in the head  34 , an optical liquid detector  170  extends through the base electrode cover  206  to the groove  102 . A buss plate  98  is similarly attached to the electrode  208 , as described above with reference to the head  34  in  FIG. 5 . Referring to  FIGS. 13 and 15 , a base seal  210  is attached to the base electrode ring  204  by a base seal retainer  212  attached to the base electrode ring  204 . 
     Wafer guides or protrusions  213  extend up slightly from the base seal retainer  212  as shown in  FIGS. 5-8  and  16  and help with wafer alignment or positioning, when a wafer is placed onto the base seal  210 , as described below. The upper or head seal  128  is generally the same diameter as the base seal  210 . Indeed, the head and base seals may be the same. As shown in  FIG. 3 , the processor  30  may have seals  128  and  210  and other components adapted for processing a wafer having a flat edge. In this case the seals, seal retainers, and the electrodes may be generally D-shaped. For round wafers, these components may be round. 
     Referring to  FIGS. 15 ,  17  and  18 , the upper seal clamp ring  132  has resilient ejector tabs  130  that press down slightly on the outer edge of the wafer, when the head seal  128  is engaged against the wafer  250 .  FIG. 15  shows in dotted lines the nominal position where the ejector tabs  130  would be with no wafer present. The seal  128  and the upper seal clamp ring  132  are dimensioned so that as the movable electrode assembly  152  moves up away from the wafer  250 , the seal  128  separates from the wafer first, while the ejector tabs  130  continue to hold the wafer down onto the base seal  210 . This prevents any potential for having a wafer stick to the head seal  128  as the seal is lifted away from the wafer after processing. 
     As shown in  FIG. 13 , an electrolyte inlet fitting  220  leads into an inlet  224  in the base electrode ring  204 . As in the head  34 , a diffuser plate or similar liquid diffusing element  126  may be attached to the base electrode ring  204  over the inlet  224 . With the base seal  210  in contact with a wafer, a base or lower process chamber  240  is formed between the electrode  208  and the wafer, with the lower process chamber  240  surrounded by the base electrode ring  204 . An electrolyte outlet  226  runs from the lower process chamber  240  to an electrolyte outlet fitting  222 . A diffuser plate  126  may also be provided over the electrolyte outlet  226 . 
     Referring back to  FIG. 5 , a lower fitting bracket  228  is attached to the base electrode cover  206 . The optical liquid detector  170  in the base  32  connects to a fitting  232  on the bracket  228 , along with the electrolyte line connections, to provide strain relief. A lower electrode wire  234  extends through an electrical feed through fitting  230  in the electrode cover  206  and connects to the buss plate  98  on the electrode  208 . 
     In the processor  30  shown in  FIGS. 1-8 , the electrode  96  in the head  34  is typically made the cathode, while the electrode  208  in the base  32  is typically made the anode, by selecting the polarity of the current source attached to each electrode. The electrodes  96  and  208  may otherwise be the same. Although various materials may be used, the design shown uses electrodes made from boron-doped silicon. Each electrode is about 25 mm thick. The diameter of the electrodes may be substantially the same as the diameter of the wafer. The diameter of the head and base seals  128  and  210  is typically 2-10 mm less than the wafer diameter, providing, for example, an edge exclusion zone (the outer annular area of the wafer protruding beyond the seal) from about 1-5 mm. The electrode surface may be diamond coated. If used, the diamond coating is doped to make it electrically conductive. 
     As the electrolyte generally will include concentrated hydrofluoric acid, the components of the processor  30  coming in contact with the electrolyte are made of materials, such as Teflon (fluorine resins) or PVDF, which are resistant to corrosion by HF or other reactive electrolyte chemicals. The cap screws or other fasteners in the processor  30  generally may be made of similar plastic or non-metal materials. Referring to  FIG. 5 , the buss plates  98 , electrode wire leads, and wire lead attaching screws are metal, as these components require high electrical conductivity. However, these may be the only metal components in the processor  30  (excluding the motor  38  or other external components). In addition, these metal components are sealed off from the electrolyte introduced into the process chambers  146  and  240  by the first seal  110 , second seal  108 , third seal  104 , and the fourth seal  105 . 
     In the event of any leakage around the electrode, electrolyte would first collect in the groove  102 , and be detected by the optical liquid detector  170 . In addition, the seal vents  116  and  118  will tend to divert any leaking electrolyte away from the back of the electrode. Upon detection of a leak, the controller shuts down the processor  30 , before any electrolyte can move past the fourth seal  105 . In this way, the electrolyte is entirely isolated from any metal in the processor  30 . Metal contamination of the electrolyte or wafer, or inadvertent release of electrolyte into the head or base, is accordingly avoided. 
     The processor  30  provides highly uniform current flow through the process chambers  146  and  240 , yet within a relatively small space. The clearance space around the processor  30 , to allow it to rotate between horizontal and vertical positions, is also relatively small. Referring again to  FIG. 5 , the electrodes shown have a diameter of about 150 mm and a thickness of about 25 mm. For this type of design, an electrode (or wafer) diameter to electrode thickness ratio of about 4-10:1 may be used. The height of the chambers (dimension CC in  FIG. 5 ) is also generally about the same as the electrode thickness in this example, with ratios of chamber height to electrode thickness ranging from about 2.5 to 1 to about 1 to 1 may be useful. 
     The height of the chambers, and/or the electrode thickness, can of course also exceed these ranges, although this may tend to make the entire processor larger, with no improvement in current uniformity. The diameter and height of the containment chamber  60  are not critical and may be selected to accommodate the size and/or shape of other internal processor components, within a compact space. While the drawings show the chambers  146  and  240  as having substantially the same height, one chamber may have a larger height than the other. The chambers  128  and  240  as described above have minimal diameter and height. In addition to providing for a compact processor, this also speeds up processing, since process liquids can be quickly filled and drained from the chambers. Typically, the containment chamber  60  may have a diameter of about 1.1 to 2 or 1.1 to 3 times the diameter of the seals  128  or  210  or the workpiece. The height of the containment chamber  60  may be from about %5-%50 of the diameter of the seals  128  or  210 . 
     In use, the processor  30  is initially loaded with a wafer  250 . For loading (and unloading a wafer), the processor  30  is in the horizontal position as shown in  FIG. 1 . The moveable electrode assembly  152  in the head  34  is in the up position, as shown in  FIGS. 5-9 . A wafer is moved into the processor  30  through the load slot  56 , typically by a robot. As the wafer moves into the processor, the edges of the wafer may contact the wafer guides  213  which protrude up from the base seal retainer  212 . This properly centers and locates the wafer  250  relative to the seals  128  and  210 . The wafer  250  is then released, with the wafer resting on the lower or base seal  210 . The robot (or other wafer mover used) is withdrawn. 
     The controller opens valves causing water to be supplied under pressure to the lower cylinder port  158 . This drives the cylinder  82  and the entire moveable electrode assembly  152  downwardly. Referring to  FIGS. 9 and 14 , water within the cylinder  82  above the piston seal  94  flows out of the cylinder via the upper cylinder port  156  and out the processor  30  via a return line. The water is used only as a hydraulic fluid and does not come into contact with the electrolyte or wafer  250 . Accordingly, water purity is not critical, so that standard tap water, under standard plumbing pressures, may be used. The moveable electrode assembly  152  continues to move down towards the wafer until it bottoms out on the hard stop provided by the shoulders  218  of guide pins  214 . The lower position sensor  164  provides a signal to the controller confirming that the moveable electrode assembly is in the process position. The water pressure provided to the cylinder may optionally be regulated, although regulation is not necessary. The upper or head seal  128  is pressed into sealing contact with the top surface of the wafer  250 . The base seal  210  is also in sealing contact with the wafer  250 . The processor  30  is then in a closed position, as shown in  FIG. 14 . Water pressure may be maintained during processing. 
     Referring momentarily to  FIGS. 1-4 , the controller actuates the rotate motor  38 , pivoting the entire processor  30  about 90 degrees, so that the wafer  250  is moved into a vertical orientation, with the slot  56  facing up and with the drain  58  facing down. The rotate motor  38 , or an equivalent driving element, may be supported on a deck  42  or other supporting surface. The processor  30  can be supported on a pair of pivot blocks  332  attached to the base  32 . In  FIG. 4 , the pivot blocks  332  are attached to flange bearings  40  with the rotate motor attached to the right side pivot block  332 , optionally through a gear drive reducer  39 . 
     The controller then opens valves supplying electrolyte to the processor  30 . Electrolyte flows into the upper and lower process chambers  146  and  240  through the inlets  148  and  224 , and through the diffuser plates  126 , as shown in  FIGS. 7 and 14 . The process chambers are filled from the bottom up. Valves controlling flow through the return lines  142  and  226  may be opened to allow the chambers to vent while filling with electrolyte, or during other times, or at all times during the processing. 
     Electrical current is applied to the electrodes  96  and  208 . Current flows from the cathode or first electrode, through the electrolyte in the chamber  240 , through the wafer, and through the electrolyte in the chamber  146  to the anode, or other electrode. The wafer is sufficiently conductive to provide a bi-polar electrode function. Electrolyte may be continuously provided at a low flow rate, so that the electrolyte in the chambers  146  and  240  is constantly refreshed, although without substantial fluid turbulence. 
     During processing, the chambers  146  and  240  are virtually entirely filled with electrolyte to provide more uniform processing. Gasses generated during processing may be carried off via the circulation of electrolyte through the chambers  146  and  240 . Alternatively, separate gas exhaust ports may optionally be used in the chambers  146  and  240 . The motor  38  may be controlled to oscillate the processor  30  about a near vertical position, to assist with gas removal, either while the chamber is being filled with electrolyte, or during processing, or both. The process described produces amorphous porous silicon. 
     The electrolyte parameters, such as chemical composition, temperature, pressure, flow rate, concentration, etc., may be varied to achieve desired process results. Current flow may also be selected as desired. The current may be increased to a high enough level to transition from a porous silicon process to a wafer polishing process. The processor  30  may therefore be used for wafer polishing. The electrolyte may include water, relatively concentrated HF, and an alcohol, such as isopropyl alcohol. Processing continues, for example, for about 2-10 minutes, until the wafer surface  250  is sufficiently etched and becomes porous silicon. Electrical current is turned off. The electrolyte is drained from the chambers. The chambers and workpiece may then be rinsed by filling the chambers with a rinse liquid, such as de-ionized water, and then draining the rinse liquid. The rotate motor  38  is actuated in the reverse direction, to pivot the processor  30  back into the horizontal position shown in  FIG. 1 . 
     The controller then supplies water pressure to the cylinder  82  in the reverse direction, to lift the moveable electrode assembly  152  up and away from the wafer  250 . As shown in  FIG. 15 , the ejector tabs  130  on the upper seal clamp ring  132  hold the wafer  250  down onto the base seal  210  until the head seal  128  is separated from the wafer  250 . This prevents the wafer  250  from inadvertently sticking to the head seal  128 . The wafer is then removed from the processor  30 , again, typically via a robot grasping the edges of the wafer  250  from above, and withdrawing the wafer out of the processor  30  through the load slot  56 . The processor  30  is then ready to process a subsequent wafer  250 . The rotate motor  38  may optionally gently or even rapidly rock or oscillate the chamber  30  at various times, to help to agitate the electrolyte, displace gas bubbles, provide mixing of other chemicals that may be used, or to help distribute rinsing liquid. A gas, such as heated nitrogen, may also optionally be provided into the processor for drying the wafer. 
     In some applications, the processor may operate with the chambers filled with electrolyte or other process liquid, but with no electrical current flowing. Since the processor is well designed to operate with highly reactive or corrosive electrolyte, it can also operate with other reactive or corrosive process liquids, including HF, without use of electricity. This provides a purely chemical process, rather than an electro-chemical process. Since the chambers  128  and  240  are sealed off from each other, different process liquids may be provided into each chamber, simultaneously or sequentially. Consequently, the front or device side of the wafer and the back side of the wafer may simultaneously be processed using different process liquids and/or gases. With this type of processing, the process liquids may optionally be introduced into the chambers  128  and  240  with the wafer in a horizontal orientation, or in a vertical orientation. If the processor  30  is intended for non-electrical processing, the electrodes may be removed and the electrode rings simply replaced with plates to form the upper and lower process chambers. In addition, the seals  128  and  210  may be designed to seal directly against each other, without contacting the wafer at all, and with the wafer supported within, rather than on, the lower seal  210 . 
     Some wafers may be provided with a mask to determine which areas of the wafer are made porous. After electro-chemical processing, electrical current may be turned off, additional chemical processing steps may be performed, with or without changes to the electrolyte, to etch off the mask, or another layer or film on the wafer. 
     Referring to  FIGS. 5 ,  6 , and  7 , during processing the electrolyte is sealed within the upper and lower process chambers  146  and  240 . These process chambers are surrounded by the containment chamber  60 , which is open at one side at the load slot  56 , and at the opposite side at the containment drain  58 . However, there is no other fluid pathway out of the containment chamber  60 . The bellows  120  seals the upper electrode ring  106  to the cover  70 . Accordingly, a rinse liquid, such as water, may be provided into the containment chamber  60  via the load slot  56 , to rinse all exposed surfaces within the containment chamber  60 . The containment chamber itself may also be provided with rinse nozzles  252  connected to a rinse liquid source as shown in  FIG. 5 , for rinsing the chamber. 
     The rinse liquid may be provided between wafer processing, while the processor is open and the seals  128  and  210  are completely exposed. This allows virtually all surfaces of the seals to be rinsed, removing any trapped or adhering electrolyte. Rinsing can advantageously be performed with the processor  30  once again rotated into the vertical orientation, with the rinse liquid flowing via gravity through the containment chamber  60  and draining out of the containment drain  58 . Rinsing with the chamber open allows the processor to maintain uniform process start up conditions, since a complete rinse of all surfaces contacted by electrolyte (or other process chemicals) may be achieved between each process cycle. 
     The substantially non-conductive rinse liquid may also optionally be flowed through the containment chamber  60  while the processor is closed, during actual processing of a wafer. Since the electrolyte is sealed within the process chambers  146  and  240 , the rinse liquid does not come into contact with the electrolyte, and the rinse liquid only contacts the outer seal surfaces and the annular edge of the wafer extending radially outwardly beyond the seals  128  and  210  (typically by about 2-6 mm). Since the electrolyte is an electrical conductor, any leaking electrolyte may alter the otherwise uniform conduction path provided by the processor  30 . This can cause non-uniform processing. Running rinse liquid through the containment chamber during processing will remove any leaking electrolyte, thereby maintaining the uniform conduction path necessary for providing high quality porous silicon. 
     The rinse liquid may also be provided into or through the containment chamber upon detection of an electrolyte leak or other fault condition, to carry away any leaking or exposed electrolyte. One example of a containment chamber rinse system is described below in connection with an automated processing system. 
     As shown in  FIGS. 19-22 , the processor  30  may be used in an automated processing system  300 . Various types of automated systems may be used, including varying numbers of processors  30 , arranged in whichever way (e.g., linear array, arcuate array, vertically stacked, etc.) may be preferred. In the automated system  300  shown in  FIGS. 19-22 , two processors  30  and two spin rinse dryers  322  are provided within an enclosure  302 . A load window  308  is provided at a load/unload station  306 , at the front of the enclosure  302 . Air inlets  310  are located on the top of the enclosure  302 . A robot  316  moves along a lateral rail, to transfer wafers  250  from the load station  306  into or out of the processors  30  or spin rinse dryers  320 . An isolation wall  318  may be provided between the processors  30  and the robot  316 , to reduce exposure of the robot  316  to process chemicals used in the processors  30 . An opening is provided in the isolation wall  318 , to allow an end effector of the robot  316  to reach into the processors  30 . A wafer transfer zone or area  340  may be provided between the isolation wall  318  and the processors  30 . When a wafer is moved between processors  30  and  320 , the wafer may remain within the transfer zone  340  as the robot  316  carries the wafer parallel to the isolation wall  318 . Any residual process liquids that may be on the wafer may therefore come into contact only with the end effector, but not with the rest of the robot  316 . A controller  304  controls movement and operation of the robot  316 , processors  30 , spin rinse dryers  320 , as well as various other components within the system  300  (e.g., pumps, valves, actuators, displays, interlocks, communications, etc.), as is well known in the semiconductor field. The deck  324 , isolation wall  318 , enclosure  302 , and other components of the system  300  may advantageously be made of plastic materials, to better avoid contamination and corrosion. 
     In use, wafers  250  are delivered to the load station  306 , typically within a cassette, box, or carrier  314 . The load window  308  opens. The robot  316  picks up a wafer  250  at the load station  306  and moves the wafer  250  into one of the processors  30 . The wafer may optionally be first moved into a pre-aligner  312 , or other chamber for a pre-processing step. The wafer  250  is processed within the processor  30 , as described above. In the interim, the robot  316  may return to the load station  306  to repeat the load sequence and load another wafer into the second processor  30 . Upon completion of processing, each wafer  250  may be moved by the robot  316  into one of the spin rinse dryers  320 . The spin rinse dryers  320  shown have lift/rotate apparatus  322  used to lift and rotate the head of the spin rinse dryer  322  into a load/unload position. Various types of spin rinse dryers (or other types of additional chambers or processors, e.g., metrology, anneal, etc.), with or without lift/rotate apparatus, may be equivalently used. After each wafer  250  is rinsed and dried, the robot  316  moves the wafer back to the load station  306 , where the wafer is typically placed back into the same cassette  314 , or into a different cassette. 
     The processor  30  itself may also perform rinsing and drying, as a stand alone unit or within a processing system. After an optional line purging step, rinsing may be performed by flowing a rinse liquid, such as de-ionized water, through the process chambers  146  and  240 , typically with the wafer and the chamber in the vertical position. The rinse liquid may then be relatively slowly drained out, to perform a slow extraction type of drying process. In many applications, this process will leave the wafer sufficiently dry for subsequent handling or processing, even if some droplets of rinse liquid remain on the wafer. In an alternative drying process, a surface tension/meniscus drying step may be used after rinsing the wafer. In this alternative process, a drying fluid, such as isopropyl alcohol, can be provided into the process chambers during the drying step. 
     Referring to  FIG. 21 , the system  300  may optionally include an isolation chamber rinse system  190 . If used, the rinse system  190  may include a rinse water channel or array of spray nozzles  192  aligned with and adjacent to the load slot frame  62  of the processor  30 , when the processor is rotated into the vertical position. Similarly, an isolation drain collection pipe  194  may be provided in the system  300 , adjacent to and aligned with the isolation drain  58 , when the processor  30  is in the vertical position. Adequate clearance is provided between the processor  30  and the channel  192  and collection pipe  194 , so that the processor  30  can freely pivot between the vertical and horizontal positions. The isolation drain  58  may optionally be connected to a drain/exhaust line, such as the collection pipe  194 , via a flexible tube  334  shown in  FIG. 14 , which can accommodate the vertical to horizontal movement of the processor  30 , to help insure that no liquid or vapors draining from the processor  30  are released into the system  300 . 
     The isolation chamber which is generally shown at  60  in  FIGS. 5 ,  6  and  14 , may be rinsed by moving the processor  30  into the vertical position, and then providing rinse water from the overhead array of spray nozzles  192  through the load slot  56  into the processor  30 . The rinse water drains out of the processor  30  through the isolation drain  58 , and into the collection pipe  194 . The collection pipe  194  connects to a system or facility drain. The isolation chamber rinse system  190  may be used to provide routine rinsing of the isolation chamber  60 , during wafer processing, between wafer processing, or periodically, after processing a preselected number of wafers. The isolation chamber rinse system  190  may also be used if a fault condition is detected indicating a potential leak of electrolyte. In this condition, the isolation chamber  60  can be rapidly flooded with rinse water, to reduce any leakage of electrolyte (liquid or vapors) into the system  300 . The processor may optionally be made and used without any isolation chamber  60 . The processor  30  may also be used as a chemical process chamber, rather than as an electro-chemical processor, by not providing any current to the electrodes, or by omitting the electrodes entirely, e.g., by replacing the rings  106  and  204  with plates with a solid and continuous center section. In this design, the various chemical process liquids may be used, instead of electrolyte. 
     Although wafer loading/unloading with the wafer in a horizontal position is more commonly used in many types of existing wafer handling equipment, the processor  30 , or the automated system  300 , may also be adapted to operate with wafer loading/unloading in a vertical orientation. Terms used here, including in the claims, such as upper and lower, above and below, etc. are intended for explanation and not requirements that one element be above or below another element. Indeed, the processor  30  may be operated upside down. While porous silicon has been described above, the processor  30  may also be used for processing similar materials, including gallium compounds. The terms vertical and horizontal here include positions within 5, 10 or 15 degrees of vertical or horizontal, respectively. The processor  30  may also be used in a fixed position. For example, the processor  30  may be used without any rotate motor  38  and mounting plates  330 . In this design, the processor  30  may be supported in a fixed horizontal position, or in a fixed vertical position, or at an angle between horizontal and vertical. 
     Various changes and substitutions may of course be made without departing from the spirit and scope of the invention. The invention, therefore, should not be limited, except by the following claims and their equivalents.