Etching apparatus that oscillate wafers during etching
Oscillating silicon wafers during etching using rollers with grooves and oscillating motion addresses non-uniform etching rates, ensuring uniform etching and shape preservation.
Patent Information
- Application Number
- PCT/US2025/036493
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2024-07-10
- Filing Date
- 2025-07-03
- Publication Date
- 2026-01-15
AI Technical Summary
Existing etching processes for silicon wafers result in non-uniform etching rates due to non-uniform hydrodynamics, leading to uneven removal of silicon, particularly at the wafer edge, which affects the shape and uniformity of the machined surface.
The method involves oscillating silicon wafers during etching by using rollers with grooves and oscillating motion to manipulate the hydrodynamic boundary layer, ensuring uniform etching across the wafer surface.
This approach achieves a more uniform etching process by reducing the boundary layer thickness, allowing for consistent etching across the wafer surface, thereby preserving the intended shape and improving process efficiency.
Smart Images
Figure US2025036493_15012026_PF_FP_ABST
Abstract
Description
ETCHING APPARATUS THAT OSCILLATE WAFERS DURING ETCHINGCROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 669,677, filed July 10, 2024, which is incorporated herein by reference in its entirety.FIELD OF THE DISCLOSURE
[0002] The field of the disclosure relates to etching apparatus for etching a plurality of silicon wafers to remove silicon from a surface of each silicon wafer and to methods for etching a plurality of silicon wafers to remove silicon from a surface of the silicon wafers.BACKGROUND
[0003] After surface machining processes for a wafer, the mechanical damage may be removed by a wet etching procedure. Normally, more than one wafer at a time is etched in a parallel arrangement, using rotation to maintain even exposure to the etching solution. Unfortunately, a higher etching rate occurs near the wafer edge due to the laminar flow passing upwards through the wafers. The solution flow through the parallel wafers will generate a boundary layer for diffusing products and reactants at the entrance region and in the fully development region. A thinner, lower boundary layer thickness will increase the etching rate. The removal rate of etching process is not uniform due to the effect of non-uniform hydrodynamics on the diffusion of products reactants. Therefore, the shape of the machined wafer is not fully preserved, most notably at the edge.
[0004] A need exists for methods to change the boundary layer thickness near the wafer edge, which will locally modify the etching rate.
[0005] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the disclosure, which are described and / orclaimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.SUMMARY
[0006] One aspect of the present disclosure is directed to a method for etching a plurality of silicon wafers to remove silicon from a surface of each silicon wafer. Each wafer has a central axis, front and back surfaces that are generally perpendicular to the central axis, and a peripheral edge. The plurality of silicon wafers is immersed in a pool of etchant. The pool of etchant is disposed within an etching apparatus housing. The housing has an inlet and an outlet configured such that etchant flows across the front and back surfaces of the plurality of wafers. The plurality of silicon wafers are in contact with a plurality of rollers. The plurality of rollers is rotated to cause the plurality of silicon wafers to rotate. Each roller has an axis of rotation. At least one roller of the plurality of rollers is oscillated along the axis of rotation of the roller as etchant flows from the inlet to the outlet.
[0007] Another aspect of the present disclosure is directed to a method for etching a plurality of silicon wafers to remove silicon from a surface of each silicon wafer. Each wafer has a central axis, front and back surfaces that are generally perpendicular to the central axis, and a peripheral edge. The plurality of silicon wafers is immersed in a pool of etchant. The pool of etchant is disposed within an etching apparatus housing. The housing has an inlet and an outlet configured such that etchant flows across the front and back surfaces of the plurality of wafers. The plurality of silicon wafers are in contact with a plurality of rollers. Each roller has an axis of rotation. The plurality of rollers is rotated to cause the plurality of silicon wafers to rotate. Each roller includes a plurality of annular grooves for securing the plurality of silicon wafers. At least one roller includes one or more grooves having axial undulations for moving the silicon wafer along the axis of rotation of the roller.
[0008] Yet another aspect of the present disclosure is directed to an etching apparatus for etching a plurality of silicon wafers to remove silicon from a surface of each silicon wafer. The etching apparatus includes an etching apparatus housing for holding a pool of etchant. The housing has an inlet and an outlet for circulating etchant. The etching apparatus includes a plurality of rollers disposed within the etching apparatus housing. Each roller has an axis of rotation. The etching apparatus includes a driver connected to at least one roller of the plurality of rollers. The driver causes the at least one roller to oscillate along the axis of rotation of the roller.
[0009] Yet a further aspect of the present disclosure is directed to an etching apparatus for etching a plurality of silicon wafers to remove silicon from a surface of each silicon wafer. The etching apparatus includes an etching apparatus housing for holding a pool of etchant. The housing has an inlet and an outlet for circulating etchant. The etching apparatus includes a plurality of rollers disposed within the etching apparatus housing. Each roller has an axis of rotation. Each roller includes a plurality of annular grooves for securing the plurality of silicon wafers. At least one roller includes one or more grooves having axial undulations for moving the silicon wafer along the axis of rotation of the roller.
[0010] Various refinements exist of the features noted in relation to the above-mentioned aspects of the present disclosure. Further features may also be incorporated in the above-mentioned aspects of the present disclosure as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments of the present disclosure may be incorporated into any of the abovedescribed aspects of the present disclosure, alone or in any combination.BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a perspective of a wafer that may be treated by the method of the present disclosure;
[0012] FIG. 2 is a side view of an embodiment of an etching apparatus;
[0013] FIG. 3 is a top view of the etching apparatus without wafers loaded therein;
[0014] FIG. 4 is a top view of the etching apparatus with wafers loaded therein;
[0015] FIG. 5 is a top view of a roller of the etching apparatus;
[0016] FIG. 6 is a perspective view of the rollers of the etching apparatus having at least one oscillating roller;
[0017] FIG. 7 is a perspective view of the rollers of another embodiment of the etching apparatus having at least one roller having grooves with axial undulations;
[0018] FIG. 8 is a partial top view of a roller of the etching apparatus ofFIG. 7;
[0019] FIG. 9 shows the boundary layer thickness when wafers are not oscillated;
[0020] FIG. 10 shows the simulated velocity contour at wafer oscillation rate of 0.48 seconds;
[0021] FIG. 11 shows the simulated velocity contour at wafer oscillation rate of 0.54 seconds;
[0022] FIG. 12 shows the simulated velocity contour at wafer oscillation rate of 0.60 seconds;
[0023] FIG. 13 shows the simulated velocity contour at wafer oscillation rage of 0.66 seconds;
[0024] FIG. 14 shows the simulated velocity contour at wafer oscillation rate of 0.72 seconds; and
[0025] FIG. 15 shows the leveling thickness when wafers are oscillated and when they are not oscillated in the process of record (POR).
[0026] Corresponding reference characters indicate corresponding parts throughout the drawings.DETAILED DESCRIPTION
[0027] The present disclosure provides a method for treating a silicon wafer with an etchant such as to remove surface damage during wafering of the silicon wafer. Provisions of the present disclosure provide an oscillating function (e.g., reciprocating function) to a rotation device to oscillate wafers in and out of the plane defined by the axes of the rollers. Without being bound to any particular theory, such oscillation may manipulate the thickness of the hydrodynamic boundary layer near the edge of the wafers by mechanically oscillating them in and out of alignment of the normal direction of the fluid flow, such that the boundary layer at the edge is on average matching the boundary layer thickness over the surface of the wafers.
[0028] The methods of embodiments of the present disclosure may generally etch any starting material such as a silicon wafer that has been sliced from a single crystal silicon ingot and further processed (e.g., after grinding). The wafer may be sliced from the ingot using any means known to persons skilled in the art, such as, for example, an internal diameter slicing apparatus or a wiresaw slicing apparatus.
[0029] Regardless of the precise combination of prior processing, the silicon wafer starting material may have any conductivity type, resistivity, diameter, crystal orientation and target thickness appropriate for the intended semiconductor application. For example, the wafer diameter is generally at least about 100 mm and may be about 150 mm, about 200 mm, about 300 mm, about 450 mm or greater, and the thickness of the wafer may be from about 475 pm to about 900 pm or greater.
[0030] Referring now to FIG. 1, silicon wafers 1 treated by methods of the present disclosure generally include a central axis X, a front surface 3 and a back surface 5 that are generally perpendicular to the central axis, and a radius (R) extending from the central axis to a point on the peripheral edge 7 of the wafer 1. The wafers may also include one or more flats or orientation notches 9 at the peripheral edge 7 of the wafer 1. Generally, the methods of embodiments of the presentdisclosure comprise etching the front and back surface and the peripheral edge of a silicon wafer by removing silicon from the front and back surface and the peripheral edge to provide smoothed surfaces.
[0031] Embodiments of methods of the present disclosure are generally conducted by immersing one or more wafers in a bath, or pool of etchant. The method may be a single-step operation that may be incorporated into the overall silicon wafer processing operation. It is to be further noted that the present process provides a further benefit with respect to process efficiency since it is amenable to concurrent treatment of a plurality of wafers. More particularly, the present process may be easily adapted to etching of at least 2, at least 4, at least 5, at least 6, at least 8, at least 10, or more wafers. For example, the present process may be adapted to treat at least 10 wafers, at least 20 wafers, at least 30 wafers, at least 40 wafers, or at least 50 wafers.
[0032] FIGS. 2-4 illustrate an embodiment of an etching apparatus 20 suitable for use in the methods of the present disclosure. As shown in FIG. 2, the etching apparatus 20 generally includes an etching apparatus housing 25 (or more simply “housing 25”). Within the etching apparatus housing 25 are bottom rollers 35 that may support and / or secure a number of wafers 1. It is to be understood that rollers 35 may be located in various other arrangements besides that shown in FIGS. 2-4. For example, the etching apparatus 20 may include more, or less, rollers bottom rollers 35 than depicted in FIGS. 2-4.
[0033] The apparatus 20 may also include top rollers 46 within the housing 25. The top rollers 46 help the wafer 1 to more precisely rotate about its axis. For purposes of the present disclosure, “top rollers” includes rollers positioned to engage wafers at a point on the uppermost 180 degrees of the wafer circumference and “bottom rollers” includes rollers positioned to engage wafers at a point on the lowermost 180 degrees of the wafer circumference (or at the mid-point).
[0034] The apparatus 20 may have any number of rollers 35, 46 that allow the apparatus to operate as described herein. For example, the apparatus 20 may include 3, 4, 5, 6 or more rollers.
[0035] As shown in FIG. 5, each of the rollers 35, 46 include grooves 40 that are generally in alignment with the grooves 40 of the other rollers 35, 46. In this manner, multiple wafers in generally parallel alignment may be secured by the rollers. Each roller 35, 46 includes a central axis X and includes a plurality of annular grooves 40 about the axis X.
[0036] The top rollers 46 may adjustably move up and down relative to the housing 25 such that the top rollers “float” above the wafers 1. Weights or biasing elements may be attached to the top rollers 46 to assist the rollers in engaging and securing the wafers 1.
[0037] The etching apparatus 20 may include an inlet 50 (FIG. 3) and an outlet 55 formed in the housing 25. A valve (not shown) may be disposed within the inlet 50 to regulate the flow of etchant into and out of the housing 25. The outlet 55 may be an overflow weir (see FIG. 2 wherein the outlet 55 is shown on both sides) that maintains the height of the pool of etchant in the etching apparatus. The inlet 50 and outlet 55 are configured such that etchant flows across the front and back surfaces of the plurality of wafers 1. As shown in FIGS. 3-4, the outlet 55 is disposed above the inlet 50 relative to a vertical axis A (FIG. 2) of the housing 25 such that etchant flows upward through the wafers 1. In other embodiments, the outlet 55 is disposed below the inlet 50 relative to the vertical axis A such that etchant flows downward through the wafers.
[0038] In embodiments of the present disclosure, wafers are added to the etching apparatus 20 such that the wafers are pinched between the grooves 40 of the rollers 35, 46. The pitch between the wafers may be, for example, between 5 mm and 7 mm. A lid 60 (FIG. 2) is closed after the wafers are positioned in the apparatus. To immerse the wafers 1 with the etchant, etchant is caused to enter the etching apparatus through the inlet 50 (FIGS. 2-3).
[0039] The depth of the reservoir of etchant in the etching apparatus 20 is determined by the height of the outlet 55. In some embodiments, etchant that exits the overflow outlet 55 may be returned back to the apparatus 20.
[0040] Once the etching apparatus 20 is filled with etchant, the rollers 35, 46 are driven by rotation drive to rotate the wafers in the pool of etchant. The rate of rotation may be from about 10 rpm to about 40 rpm. Etchant generally flows from the inlet 50, through the wafers 1, thereby contacting the front and back surfaces of the wafers, and through outlet 55.
[0041] Generally, any etchant that results in etching of the surfaces of the wafers 1 may be used. For example, the etchant may be an acidic etchant in the form of an aqueous solution comprising a source of hydrogen ions. Alternatively, the etchant may be a caustic etchant in the form of an aqueous solution comprising a source of hydroxide ions.
[0042] Acidic etchants suitable for etching in accordance with the present disclosure include those generally known in the art including, for example, those described in U.S. Patent Nos. 3,964,957; 5,340,437; 5,211,794; 4,388,140; 5,236,548; 5,246,528; 4,971,645; 4,251,317; 4,849,701; 6,294,469; 5,233,218; 6,482,749; 6,046,117, the entire contents of which are incorporated herein by reference for all relevant purposes. The source of hydrogen ions may be selected from the group consisting of hydrofluoric acid, nitric acid, phosphoric acid, acetic acid, sulfuric acid, hydrochloric acid, citric acid, oxalic acid, propionic acid, permanganic acid, and combinations thereof. Typically, the source of hydrogen ions is present in the etchant at a concentration of at least about 40 wt%, more typically at least about 50 wt%, still more typically at least about 60 wt% and, even more typically, at least about 70 wt%.
[0043] In various embodiments, the acidic etchant consists essentially of water and the source of hydrogen ions. In various other embodiments, the acidic etchant comprises one or more additives along with the source of hydrogen ions. For example, the acidic etchant may comprise a surfactant selected from the group consisting of ammonium fluoroalkylsulfonate (e.g., Novec™ 4300), potassium perfluorooctanesulfonate, dodecylbenzene sulfonic acid, alkyl aryl sulfonic acid, and combinations thereof. In various embodiments the acidic etchant may comprise a fluorochemical surfactant (e.g., Fluorad® FC-95). Whether a surfactant is the lone additive, or other additives are included in the etchant, the volumetric ratio of additiveto source of hydrogen ions is generally at least about 0.001 :1, typically at least about 0.002: 1 and, more typically, at least about 0.003:1. For example, in various embodiments the volumetric ratio of additive to source of hydrogen ions is from about 0.001 to about 1 : 1, from about 0.002:1 to about 0.5: 1, or from about 0.003: 1 to about 0.25:1.
[0044] Caustic etchants suitable for etching in accordance with the present disclosure include those generally known in the art including, for example, those described in U.S. Patent Nos. 7,323,421; 6,110,839; 6,383,060; and 6,503,363, the entire contents of which are incorporated herein by reference for all relevant purposes. Generally, the caustic etchant is in the form of an aqueous solution comprising a source of hydroxide ions. The source of hydroxide ions generally comprises an alkali metal hydroxide selected from the group consisting of sodium hydroxide, potassium hydroxide, tetramethyl ammonium hydroxide, and combinations thereof.
[0045] The time for which the wafers 1 is immersed in the etchant may be selected in view of, for example, the starting surface roughness and / or the desired finished surface features. Regardless of the particular circumstances, the wafers 1 are generally immersed in the etchant for at least about 30 seconds, at least about 1 minute, at least about 2 minutes, at least about 3 minutes, at least about 4 minutes, or at least about 5 minutes (e.g., for a time of from about 1 minute to about 20 minutes, from about 1 minute to about 15 minutes, or from about 2 minutes to about 10 minutes).
[0046] In some embodiments, the direction of rotation of the wafers 1 may be reversed such that the wafers are rotated in both clockwise and counter-clockwise directions while contacting etchant.
[0047] After etching, the pool of etchant may be drained such as by reverse flow through the inlet 50. The valve in the inlet 50 may be opened to cause etchant to exit or be expelled from the housing 25. The lid 60 is opened and the wafers 1 may be removed from the etching apparatus 20.
[0048] In accordance with provisions of the present disclosure and with reference to FIG. 6, one or more of the rollers 35, 46 are oscillated along its axis of rotation X (FIG. 5) as etchant flows from the inlet 50 (FIG. 3) to the outlet 55 of the etching apparatus 20. By oscillating one of the rollers 35, 46, the thickness of the boundary layer near the edge of the wafers 1 may be reduced which allows more etchant to flow across the wafer surfaces and allows for more uniform etching across the wafer.
[0049] In some embodiments, at least one of the rollers 35, 46 oscillates while one of the other rollers 35, 46 does not oscillate during flow of etchant. This causes the wafers to pivot back and forth about its contact point with the stationary roller.
[0050] As noted above, at least one of the rollers 35, 46 oscillates along its axis X. In some embodiments, at least two of the rollers 35, 46 oscillate. In some embodiments, each of the rollers 35, 46 oscillates along its axis of rotation X as etchant flows from the inlet 50 to the outlet 55. In this regard, the entire assembly of FIG. 6 may be oscillated together to cause the wafers to oscillate and disturb the boundary layer (e.g., as in a barrel-like enclosure in which the entire assembly moves back and forth in and out of the dominant plane of liquid flow).
[0051] As shown in FIG. 6, a driver 70 is connected to the one or more rollers 35, 46 to cause the roller to oscillate along the axis of rotation of the roller. While the driver 70 is shown as connected to the lower rollers 35, it should be understood that the driver may be connected to any or all of the rollers that oscillate along its axis (e.g., at least two, three or all rollers). For example, the driver 70 may be a worm gear, cam or motor.
[0052] The one or more rollers that oscillate may oscillate at a rate of at least 25 oscillations per minute or at least 50, at least 75, or at least 100 oscillations per minute (e.g., 25 to 500, 25 to 250 or 25 to 150 oscillations per minute). The oscillation frequency maybe set by the density, viscosity and bubble fraction of the liquid according to the function:co=F(p, ,x) eq. 1 where p is the fluid density, q is the fluid viscosity, and x is the volume fraction of gas bubbles.
[0053] The etching apparatus 20 may include a second driver for rotating the plurality of rollers. The second driver may include a gear that rotates to drive each of the rollers 35, 46 of the etching apparatus. The gear may be driven by, for example, an electric motor.
[0054] In the apparatus 20 illustrated in FIG. 6, the annular grooves 40 (FIG. 5) are uniform (i.e., not undulating). As shown in FIG. 5, each groove 40 is circumferentially uniform along the width of the groove 40. As discussed more fully below, in other embodiments (FIG. 7), the grooves may be non-uniform along their width (e.g., undulating).
[0055] Referring now to FIG. 7, another embodiment of the etching apparatus 20 is shown. One or more of the rollers 35, 46 includes one or more grooves 40 that have axial undulations 65 (FIG. 8) (i.e., the groove weaves back and forth relative to the roller axis). As the roller 35, 46 rotates, the undulations rotate and move the silicon wafer along the axis of rotation X (Fig. 5) of the roller 35, 46. In this regard, the roller 35, 46 may include some grooves that are uniform along its width (i.e., do not include undulations). In other embodiments, each of the grooves 40 of the roller 35, 46 may include axial undulations that move each semiconductor wafer along the axis of rotation X of the roller 35, 46.
[0056] More than one of the rollers 35, 46 may include grooves 40 with undulations. For example, two, three or each of the rollers may include such undulations.
[0057] Compared to conventional methods for etching, the methods of the present disclosure have several advantages. The methods of the present disclosure may oscillate wafers in the normal direction of the etchant flow path. The oscillating wafer induces normal direction flow to interfere with the etchant flow path over thewafer surface and reduces the thickness of the boundary layer. Reducing the thickness of the boundary layer allows more etchant to flow across the wafer surfaces and provides a more uniform etch.EXAMPLES
[0058] The processes of the present disclosure are further illustrated by the following Examples. These Examples should not be viewed in a limiting sense.Example 1: Effect of Wafer Oscillation on Boundary Laver Thickness
[0059] When the wafers do not oscillate during the etching process, the etchant flows from the wafer lower position to the upper position with the boundary layer thickness is shown being shown in the dark line in FIG. 9.
[0060] In various simulations, the wafers oscillated + / - 0.5 mm with a wafer to wafer pitch of 6.35 mm. The wafer rotation rate was 20 rpm and the wafers moved 0.5 mm for 0.24 seconds. The velocity contour of the simulation with the wafer oscillating at 0.48 seconds is shown in FIG. 10, at 0.54 seconds is shown in FIG. 11, at 0.60 seconds is shown in FIG. 12, at 0.66 seconds is shown in FIG. 13, and at 0.72 seconds is shown in FIG. 14.
[0061] Oscillation was used to etch the wafer and was compared with the process of record (POR) in FIG. 15. As shown in FIG. 15, the wafer edge thickness may be smoothed to obtain a uniform thickness profile.
[0062] As used herein, the terms “about,” “substantially,” “essentially” and “approximately” when used in conjunction with ranges of dimensions, concentrations, temperatures or other physical or chemical properties or characteristics is meant to cover variations that may exist in the upper and / or lower limits of the ranges of the properties or characteristics, including, for example, variations resulting from rounding, measurement methodology or other statistical variation.
[0063] When introducing elements of the present disclosure or the embodiment(s) thereof, the articles "a," "an," "the," and "said" are intended to meanthat there are one or more of the elements. The terms "comprising," "including," “containing,” and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of terms indicating a particular orientation (e.g., "top," "bottom," "side," etc.) is for convenience of description and does not require any particular orientation of the item described.
[0064] As various changes could be made in the above constructions and methods without departing from the scope of the disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawing[s] shall be interpreted as illustrative and not in a limiting sense.
Claims
WHAT IS CLAIMED IS:
1. A method for etching a plurality of silicon wafers to remove silicon from a surface of each silicon wafer, each wafer comprising a central axis, front and back surfaces that are generally perpendicular to the central axis, and a peripheral edge, the method comprising: immersing the plurality of silicon wafers in a pool of etchant, the pool of etchant being disposed within an etching apparatus housing, the housing having an inlet and an outlet configured such that etchant flows across the front and back surfaces of the plurality of wafers, wherein the plurality of silicon wafers are in contact with a plurality of rollers; rotating the plurality of rollers to cause the plurality of silicon wafers to rotate, each roller having an axis of rotation; and oscillating at least one roller of the plurality of rollers along the axis of rotation of the roller as etchant flows from the inlet to the outlet.
2. The method as set forth in claim 1 wherein at least one roller of the plurality of rollers does not oscillate along the axis of rotation of the roller as etchant flows from the inlet to the outlet.
3. The method as set forth in claim 1 or claim 2 wherein at least two rollers of the plurality of rollers oscillates along the axis of rotation of the roller as etchant flows from the inlet to the outlet.
4. The method as set forth in claim 1 wherein each roller of the plurality or rollers oscillates along the axis of rotation of the roller as etchant flows from the inlet to the outlet.
5. The method as set forth in any one of claims 1 to 4 wherein the outlet is disposed above the inlet relative to a vertical axis of the housing.
6. The method as set forth in any one of claims 1 to 4 wherein the outlet is disposed below the inlet relative to a vertical axis of the housing.
7. The method as set forth in any one of claims 1 to 6 wherein each roller includes a plurality of annular grooves for securing the plurality of silicon wafers, each groove of the plurality of grooves being circumferentially uniform along the width of the groove.
8. The method as set forth in any one of claims 1 to 7 wherein the plurality of rollers comprises at least 3 rollers.
9. The method as set forth in any one of claims 1 to 7 wherein the plurality of rollers comprises at least 4 rollers.
10. The method as set forth in any one of claims 1 to 7 wherein the plurality of rollers comprises at least 5 rollers.
11. The method as set forth in any one of claims 1 to 10 wherein the etchant is an acidic etchant in the form of an aqueous solution comprising a source of hydrogen ions.
12. The method as set forth in any one of claims 1 to 10 wherein the etchant is a caustic etchant in the form of an aqueous solution comprising a source of hydroxide ions.
13. A method for etching a plurality of silicon wafers to remove silicon from a surface of each silicon wafer, each wafer comprising a central axis, front and back surfaces that are generally perpendicular to the central axis, and a peripheral edge, the method comprising: immersing the plurality of silicon wafers in a pool of etchant, the pool of etchant being disposed within an etching apparatus housing, the housing having an inlet and an outlet configured such that etchant flows across the front and back surfaces of the plurality of wafers, wherein the plurality of silicon wafers are in contact with a plurality of rollers, each roller having an axis of rotation; and rotating the plurality of rollers to cause the plurality of silicon wafers to rotate, each roller including a plurality of annular grooves for securing the pluralityof silicon wafers, wherein at least one roller includes one or more grooves having axial undulations for moving the silicon wafer along the axis of rotation of the roller.
14. The method as set forth in claim 13 wherein each groove of the least one roller has axial undulations for moving each silicon wafer along the axis of rotation of the roller.
15. The method as set forth in claim 13 or claim 14 wherein at least two rollers have grooves having axial undulations for moving the silicon wafer along the axis of rotation of the roller.
16. The method as set forth in any one of claims 13 to 15 wherein at least one roller of the plurality of rollers does not include grooves having axial undulations for moving the silicon wafer along the axis of rotation of the roller.
17. The method as set forth in any one of claims 13 to 16 wherein the outlet is disposed above the inlet relative to a vertical axis of the housing.
18. The method as set forth in any one of claims 13 to 16 wherein the outlet is disposed below the inlet relative to a vertical axis of the housing.
19. The method as set forth in any one of claims 13 to 18 wherein the plurality of rollers comprises at least 3 rollers.
20. The method as set forth in any one of claims 13 to 18 wherein the plurality of rollers comprises at least 4 rollers.
21. The method as set forth in any one of claims 13 to 18 wherein the plurality of rollers comprises at least 5 rollers.
22. The method as set forth in any one of claims 13 to 21 wherein the etchant is an acidic etchant in the form of an aqueous solution comprising a source of hydrogen ions.
23. The method as set forth in any one of claims 13 to 21 wherein the etchant is a caustic etchant in the form of an aqueous solution comprising a source of hydroxide ions.
24. An etching apparatus for etching a plurality of silicon wafers to remove silicon from a surface of each silicon wafer, the etching apparatus comprising: an etching apparatus housing for holding a pool of etchant, the housing having an inlet and an outlet for circulating etchant; a plurality of rollers disposed within the etching apparatus housing, each roller having an axis of rotation; and a driver connected to at least one roller of the plurality of rollers, wherein the driver causes the at least one roller to oscillate along the axis of rotation of the roller.
25. The etching apparatus as set forth in claim 24 wherein the driver is connected to at least two rollers of the plurality of rollers and causes the at least two rollers to oscillate along the axis of rotation of the roller.
26. The etching apparatus as set forth in claim 24 or claim 25 wherein the driver is a first driver, the etching apparatus comprising a second driver for rotating the plurality of rollers.
27. The etching apparatus as set forth in any one of claims 24 to 26 wherein at least one roller of the plurality of rollers is configured to not oscillate along the axis of rotation of the roller as etchant flows from the inlet to the outlet.
28. The etching apparatus as set forth in any one of claims 24 to 27 wherein the outlet is disposed above the inlet relative to a vertical axis of the housing.
29. The etching apparatus as set forth in any one of claims 24 to 28 wherein the plurality of rollers comprises at least 3 rollers.
30. The etching apparatus as set forth in any one of claims 24 to 28 wherein the plurality of rollers comprises at least 4 rollers.
31. An etching apparatus for etching a plurality of silicon wafers to remove silicon from a surface of each silicon wafer, the etching apparatus comprising: an etching apparatus housing for holding a pool of etchant, the housing having an inlet and an outlet for circulating etchant; and a plurality of rollers disposed within the etching apparatus housing, each roller having an axis of rotation, each roller including a plurality of annular grooves for securing the plurality of silicon wafers, wherein at least one roller includes one or more grooves having axial undulations for moving the silicon wafer along the axis of rotation of the roller.
32. The etching apparatus as set forth in claim 31 wherein each groove of the least one roller has axial undulations for moving each silicon wafer along the axis of rotation of the roller.
33. The etching apparatus as set forth in claim 32 wherein at least two rollers have grooves having axial undulations for moving the silicon wafer along the axis of rotation of the roller.
34. The etching apparatus as set forth in any one of claims 31 to 33 wherein at least one roller of the plurality of rollers does not include grooves having axial undulations for moving the silicon wafer along the axis of rotation of the roller.
35. The etching apparatus as set forth in any one of claims 31 to 34 wherein the outlet is disposed above the inlet relative to a vertical axis of the housing.
36. The etching apparatus as set forth in any one of claims 31 to 35 wherein the plurality of rollers comprises at least 3 rollers.
37. The etching apparatus as set forth in any one of claims 31 to 35 wherein the plurality of rollers comprises at least 4 rollers.