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WO1997018912A1 - Lames de couteaux a tranchant ultra-effile et procede de fabrication - Google Patents

Lames de couteaux a tranchant ultra-effile et procede de fabrication Download PDF

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Publication number
WO1997018912A1
WO1997018912A1 PCT/US1995/015690 US9515690W WO9718912A1 WO 1997018912 A1 WO1997018912 A1 WO 1997018912A1 US 9515690 W US9515690 W US 9515690W WO 9718912 A1 WO9718912 A1 WO 9718912A1
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WIPO (PCT)
Prior art keywords
ridge
edge
substrate
forming
blade
Prior art date
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Ceased
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PCT/US1995/015690
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English (en)
Inventor
Robert B. Marcus
William S. Trimmer
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Individual
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Individual
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Priority to AU44142/96A priority Critical patent/AU4414296A/en
Priority to PCT/US1995/015690 priority patent/WO1997018912A1/fr
Publication of WO1997018912A1 publication Critical patent/WO1997018912A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B26—HAND CUTTING TOOLS; CUTTING; SEVERING
    • B26B—HAND-HELD CUTTING TOOLS NOT OTHERWISE PROVIDED FOR
    • B26B9/00—Blades for hand knives
    • B26B9/02—Blades for hand knives characterised by the shape of the cutting edge, e.g. wavy

Definitions

  • This invention relates to implements, particularly knife blades, having ultra sharp cutting edges formed from semiconductor materials, preferably monocrystalline silicon.
  • ultra-sharp is meant that the radius of curvature of the cutting edge ⁇ can be a ⁇ small as O.Snm while extending up to lOOnr ⁇ .
  • the edges can be " atomically” sharp. Often, however, for reasons of strength and durability, somewhat less sharp edge ⁇ are preferred.
  • the invention resides, in part, in the recognition that the technology shown in the above cited patents is useful in the fabrication of implements having cutting edges, and disclosed hereinafter are various novel and inventive variations and applications of technology for fabricating cutting and/or slicing instruments having edges of exceptional sharpness.
  • an elongated ridge having a v-ery_sharp_ apex is formed extending along a surface of a block of silicon.
  • the silicon block is part of a wafer of silicon having a flat surface, and a plurality of ridges are provided on the flat surface.
  • one side wall of each ridge preferably rises from a wafer fir ⁇ t flat surface while the opposite side wall rises from a wafer second flat surface vertically spaced from the first surface; the height of the ridges thus varying from side to side thereof with respect to the adjoining wafer surfaces.
  • Pairs of trenches are disposed adjacent and parallel to opposite sides of each of the elongated ridges, with at least one trench of each pair so close to the ridge that a side wall of the one trench effectively forms an extension of an adjoining side wall of the ridge.
  • Small, generally rectangular blocks of silicon, each containing a single extending ridge, are then separated from the wafer.
  • Each block comprises a knife blade having a cutting edge disposed at the intersection of two block side surfaces.
  • One surface comprises the wafer flat surface adjoining one side of the ridge, and the other surface is the side wall of the one trench adjoining the opposite side of the ridge.
  • a silicon block having oppositely disposed first and second surfaces is etched entirely—thr. ⁇ ugh_irom the first to the second surface.
  • the etched surface is caused to intercept the second surface at a highly acute angle for forming what is to be a blade edge disposed between the etched surface and the second surface. Additionally, the shape of the etched surface is controlled for providing blades having various desirable side surface configurations.
  • the blade edges can be sharpened to practically “atomic sharpness".
  • the blade edges and/or edge adjoining surfaces are coated with a protective coating, e.g., silicon dioxide, silicon nitride and/or various smooth and hard materials commonly used to coat knife blades.
  • a protective coating e.g., silicon dioxide, silicon nitride and/or various smooth and hard materials commonly used to coat knife blades.
  • Such coatings if used, reduce the sharpness of the edge ⁇ , but exceptionally sharp edges are still provided.
  • FIGURE S 1, 2, 4, 5, 8-13, 15, 17, 21 and 22 are a series of cross-sectional views of a semiconductor workpiece illustrating a sequence of processing steps in accordance with one aspect of the invention for forming a knife blade;
  • FIGURES 3 and 6 are plan views of the workpiece shown in Figs. 2 and 5, respectively;
  • FIGURE 7 i- ⁇ -a-v-iew_ similar to Fig. 6 but showing a variation therefrom;
  • FIGURE 14 is a plan views of a portion of a semiconductor workpiece illustrating a processing step performed after the step illustrated in FIGURE 13;
  • FIGURE 15 is a cross-section of the blade workpiece taken along line 16-16 of Figure 14;
  • FIGURE 16 is similar to Figure 14 but showing a variation theref om
  • FIGURE 18 is a perspective view of a knife blade according to the invention.
  • FIGURE 19 is similar to Fig. 18 but showing a variation of the blade cutting edge resulting from using the etchant mask shown in Fig. 7;
  • FIGURE 20 is side view of the blade shown in Fig. 18 in use a ⁇ a microtome
  • FIGURE 22 is a view similar to Fig. 21 but showing a variation therefrom;
  • FIGURE 23 is a plan view of a portion of a semiconductor workpiece for forming a knife blade in accordance with a second aspect of thi ⁇ invention;
  • FIGURE 24 is a cross-section of the blade workpiece taken along line 24-24 of Fig. 23;
  • FIGURE 25 is a view similar to Fig. 23 but showing a variation therefrom;
  • FIGURES 26 and 27 are cross-sectional views illustrating successive processing . s eps performed on the workpiece shown in Figs. 23 and 24 (Fig. 26 also being a section taken along line 26- 26 of Fig. 28);
  • FIGURE 28 is a view similar to Fig. 23 but at a still later stage in the fabrication process
  • FIGURE 29 is a cross-section taken along line 29-29 of Fig. 28;
  • FIGURES 30, 31 and 33 are views similar to Fig. 29 but at later stages in the fabrication process;
  • FIGURE 32 is a view similar to Fig. 26 but at a later fabrication stage
  • FIGURE 34 is a perspective view of a first blade embodiment made according to the second aspect of this invention.
  • FIGURE 35 is a view similar to Fig. 34 but showing the blade variation following from use of the etchant mask shown in Fig. 25;
  • FIGURES 36, 39 and 42 are cross-sectional views illustrating the formation of a second blade embodiment according to the second aspect of this invention
  • FIGURES 37 and 40 are plan views of a blade workpiece but at successive fabrication steps following that shown in Fig. 36;
  • FIGURES 38 and 41 are cross-sections taken along lines 38-38 and 41-41, of Figs. 37 and 40, respectively;
  • FIGURE 43 is a view similar to Fig. 42 but on an enlarged scale and illustrating a use of the blade;
  • FIGURES 44 and 45 are plan views each showing a portion of a wafer of the type used in the semiconductor device industry and used according to the present invention for the ⁇ imultaneous fabrication of identical blade ⁇ .
  • FIGURES 46 and 53 are perspective views of knife blades for illustrating uses thereof.
  • FIGURES 46-53 are various sectional views and Fig. 54 is a perspective view illustrating variations from processing step ⁇ illustrated in previously described figures.
  • the starting workpiece (Fig. 1 herein) comprises a monocrystalline silicon substrate 10, referred to as a "wafer", having a surface 12 lying in a ⁇ 110 ⁇ crystalline plane.
  • a wafer a monocrystalline silicon substrate 10
  • a relatively large wafer is used and a plurality of identical devices are simultaneously fabricated on the wafer.
  • the individual devices are separated from one another.
  • the fabrication of but one device.of many on the wafer is described.
  • the wafer surface 12 is covered with an etchant masking layer 14 (Fig. 1) of silicon dioxide (or silicon nitride and silicon dioxide) which is photolithographically patterned (by means of a photomask and a photoresist layer, not illustrated) to provide (Figs. 2 and 3) an etch mask 14 with a side edge 14a.
  • the silicon surface is then etched downwardly and isotropically around the mask 14 to provide a surface 12a shown in profile in Fig. 4.
  • the depth of the etch can be varied, and typically is in the range of 20 - 300 microns.
  • the etched surface 12a (for each device being made on the wafer) is present along only the one edge 14a of the mask 14.
  • a plurality of devices are preferably simultaneously fabricated.
  • Figs. 44 and 45 show examples of identical devices formed on a common wafer.
  • the etch mask 14 is then removed and replaced with another masking layer which is photolithographically patterned to provide (Figs. 5 and 6) a narrow, elongated rectangular etch mask 15 having side edges 16a-d, with the side edge l ⁇ a approximately coinciding with the vertical edge 12b of the etched surface 12a, and the side edges 16b-d overlying the original surface 12.
  • the etch mask 14 is not removed, but repatterned to provide the new mask 15.
  • the dimensions of the mask 15 are a function of the blade being made, but typical dimensions are: length 5-30 millimeters, width 2-10 micrometers and a thickness or height of 0.2-1.5 micrometers. In Fig.
  • the side edges 16a and 16b of the mask are straightand extend parallel to the ⁇ 112> direction on the block surfaces 12 and 12a and the mask side edges 16c and 16d are perpendicular to the mask edges 16a and 16b.
  • a variation of the mask is shown in Fig. 7. In Fig. 7, the mask edges 16a and 16b, while still extending generally parallel to the ⁇ 112> direction, are provided with a saw-tooth or undulating shape. The effect of this variation is described hereinafter.
  • the surfaces 12 and 12a adjoining the mask 15 are then etched to form (Fig. 9) an extending ridge 18 directly beneath the mask.
  • a two-step etching process is used, the first being a known anisotropic etching [such as Reactive Ion Etching (RIE) or KOH Solution] for forming (Fig. 8) an etched surface 12c adjoining the edges 16b-d of the mask 15.
  • RIE Reactive Ion Etching
  • KOH Solution KOH Solution
  • the amount of anisotropic etching (corresponding to the height of the vertical wall 17 formed directly .. beneath the mask edge ⁇ 16b-d) is typically between 1-10 micrometers. Because the surface 12a (Fig. 5) is also etched during the anisotropic etching, the reference numeral 12d is used in Fig. 8 for the etched surface adjoining the edge l ⁇ a of the mask 15.
  • the side walls of the ridge 18 converge inwardly towards the step of the ridge.
  • the workpiece shown in Fig. 8 is isotropically etched (Fig. 9) using a "dry” proces ⁇ (RIE) or a “wet” process (KOH Solution) for both extending the height of the ridge 18 and for undercutting the edges l ⁇ a and 16b of the ridge for providing the desired convergence of the ridge side walls at the ridge top.
  • the isotropic etching is terminated before the ridge side walls intersect because a ridge apex formed by such intersecting sides is relatively rounded and blunt.
  • a ridge having a flat top 20 (Fig. 8) having a width of 2-10 micrometers ( corresponding to the width of the mask 15)
  • the width of the ridge top 20 ( Fig. 9) is reduced, during isotropic etching, to around 0.1-1.0 micrometers.
  • the mask 15 is then stripped (Fig. 10) from the ridge 18 and the ridge top 20 is sharpened using an oxide forming and oxide stripping processing sequence such as that described in US patent 5,201,892.
  • the workpiece is heated in dry oxygen at a temperature around 950° C to form an oxide layer 22 -Fi ⁇ 1_U_ covering all exposed silicon surfaces including the ridge, and the oxide layer is then etched away in concentrated hydrofluoric acid solution.
  • the oxide forming-oxide stripping sequence can be performed a number of times. Each oxidation brings the two sides of the ridge closer together with increasingly smaller angle until they meet at an "atomically sharp" edge. Additional oxidation has no effect on the final edge configuration.
  • Fig. 12 shows a pointed ridge 18 resulting after the oxide layer 22 formed in a final oxidizing-sharpening process (Fig. 11) has been removed.
  • a uniquely shaped structure comprising an elongated ridge having an atomically sharp edge, but wherein the height of the ridge with respect to adjoining surfaces varies from side to side of the ridge.
  • the height HI between the apex 19 of the ridge and the adjoining flat surface can be, for example, in the range of 20 to 300 micrometers; the height H2 can be, for example, in the range of 5-50 micrometers. The reason for this unique structure is described hereinafter.
  • an etchant masking layer is reapplied to the workpiece.
  • Fig. 14 is a plan view of a single blade workpiece but additionally shows a surrounding portion of the wafer surface which is patterned by the masking layers 23, 24 into a grid-like frame of intersecting strips R (rows) and C (columns).
  • Fig. 15 i ⁇ a cross- section taken along line 15-15 of Fig. 14 and shows the workpiece shown in Fig. 13 after the patterning of the masking layers 23, 24.
  • the edges 26 and 28 of the mask 23, 24 extend parallel to the ridge 18, with the mask edge 26 being disposed quite close to the ridge 18 and the edge 28 being disposed some convenient, larger distance from the ridge.
  • the spacings of the mask edges 26 and 28 from a vertical mid-plane of the ridge 18 are about 2 micrometers and between 1-10 millimeters, respectively.
  • the small spacing of the edge 26 from the ridge is important, while the larger spacing oj;_ the edge 28 is les ⁇ important and dependent upon how the blade is to be used.
  • both the ridge 18 and the mask edges 26 and 28 extend parallel to the same ⁇ 112> direction.
  • the mask edges 29 (Fig. 14) and rows R extend parallel to a ⁇ 112> direction of the wafer surface and make an angle of 109.5 degrees with mask edges 26 and 18.
  • Fig. 16 shows a variation of the masking layer pattern shown in Fig. 14.
  • the mask "horizontal" edges are normally perpendicular to the mask “vertical” edges, but are not straight, as in Fig. 14, but have a sawtooth shape, i.e., the edges comprise a series of side by side triangular wedges with the sides 29a of the wedges being parallel to two different directions of the type ⁇ 112>, i.e., each wedge side 29a corresponds to the intersection of a vertical ⁇ 111 ⁇ plane with the wafer surface.
  • the overall shape of the microtome knife (as seen from the top) can be kept nominally rectangular, with vertical walls etched through the wafer both at mask edges 26 and 29.
  • the silicon wafer is then anisotropically etched entirely through the thickness of the wafer using known anisotropic etches such as aqueous potassium hydroxide, ethylenediamine or tetramethylammonium hydroxide.
  • FIG. 1 _or_J.6_ A plan view of the resulting workpiece appears exactly as shown in Fig. 1 _or_J.6_ except that ⁇ ub ⁇ tantially all of the wafer surface portions identified by numerals 12e and 12f have been etched away. The only portion ⁇ remaining of the original wafer are those portions underlying the patterned masking layers 23, 24.
  • the workpiece is now (see, also, Fig. 44) a filigree of spaced apart blade workpieces connected only by short tabs T to a grid-like frame R,C.
  • the tabs T for example, have a width of 10-100 micrometers.
  • the frame row and column strips have a width of 0.1 to 1.0 mm.
  • the various edges 26, 28 and 29 of the blade workpieces are spaced from the frame strips by between 0.5-1.0 mm.
  • FIG. 17 A cross-section of the blade workpiece appears as shown in Fig. 17 (See also Fig. 18). Owing to the described alignments of the mask edges 26, 28 and 29 with the crystal directions, anisotropic etching results in a generally rectangular block 10a having pairs of flat parallel surfaces 32,33 and 34,35 perpendicular to the top (as illustrated) surfaces 12e and 12f and the bottom surface 36. The top and bottom surfaces are not actually rectangles, but rhomboids with the side surface 34 forming an angle of 109.5 degrees with the side surface 32, as shown in Fig. 14.
  • the side surfaces 32 and 33 extend parallel to the ridge 18, and all the side surfaces 32-35 lie in the ⁇ 111 ⁇ set of planes.
  • the masking layers 23 and 24 are then removed and the workpiece appears as shown in Fig. 18 with the tabs not shown for clarity.
  • the workpiece includes a ridge 18 extending upwardly from one surface 12e of the block and closely adjacent to a block—surface 32 intersecting the surface 12f.
  • the apex 40 of the ridge is exceptionally sharp. This is further discussed hereinafter.
  • the block 10a has a length L of between 5 - 30 mm, a thickness T of 0.5 mm and a width W of 2.0 mm.
  • the width W f (Fig.
  • Fig. 18 shows a straight cutting edge 40.
  • an etchant mask 15a (Fig. 7) is used having undulating ⁇ ide edges 16a
  • the resulting cutting edge 40a (Fig. 19) is serrated. This occurs because of variations in the thickness of the ridge resulting from the undulating mask edges.
  • the thickness of the ridge 18 (Fig. 11) is progressively reduced until the side walls along the full length of the ridge intersect to form a sharp apex. Such intersection occurs first where the ridge top surface 20 is most narrow.
  • the ridge apex is lowered.
  • the amount of reduction of height is a function of the mask width from point to point along the mask, i.e., upon the pattern of undulations of the mask side edges.
  • the present invention makes use of known technology, including a known process of providing an extending ridge having an .exceptionally sharp apex.
  • the structures described in the afore-cited US patents are not described as having utility as knife blades and, indeed, an element of the present invention is the recognition that certain novel structures, relatively easily made using known semiconductor processing techniques, have utility a ⁇ knife blades.
  • Elongated, ultra-sharp blades are required.
  • Typical microtome blades e.g., of glass, diamond, sapphire or stainless steel, have typical cutting ⁇ urfaces, e.g. oppositely disposed flat surfaces tapering smoothly inwardly to a sharp edge, i.e., a wedge.
  • Such a blade has utility in, for example, microtome instruments.
  • the blade 10a In use in a microtome, the blade 10a is mounted in a suitable holder and used, as shown in Fig. 20, for cutting a thin layer 42 from a tissue body 44. Owing to the thinness, e.g., 10-100 nm, of the tissue layer 42, and its attendant flexibility, the layer 42 flows smoothly along the surface 12e without rupture. Accordingly, a useful blade is provided.
  • a common practice in the use of microtome blades is the provision of a thin film of water on one side of a blade cutting surface on which the freshly cut thin layer floats for easy removal.
  • a film of water is present on t e—-surface 12e, and for providing space for an adequately thick film of water, the height HI of the ridge above the surface 12e is preferably in excess of 20 microns. This is a relatively large height, and well in excess of the height of the cones and ridges provided as disclosed in the afore-cited patents. Such large height is obtained by the processes hereinbefore described resulting (e.g., Fig. 12) in a ridge 18 having different heights with respect to its adjoining surfaces.
  • a ridge 18 having a large height is provided while still having a relatively large thickness owing to the presence of the surface 12f slightly below the cutting edge (see, also, Fig. 21). Such enlarged thickness adds strength to the cutting wedge.
  • the blade shape shown in Fig. 18 provides, in some uses, a special advantage. Some surgical (non-microtome) operations, for example, require a scalpel structure permitting the knife blade to be inserted to a chosen depth but not beyond.
  • the height HI of the ridge 18 (Fig. 20) above the block surface 12e is selected and varied from blade to blade, depending upon the desired depth of cut. In use, the ridge 18 is pressed into a body being cut until the surface 12e impacts against the body, the depth of the cut thus automatically corresponding to the height HI.
  • Blades made according to the present invention can have cutting edges significantly sharper than heretofore available.
  • Photomicrographs of stainless steel blade edges show the blade edges with a radius of curvature of approximately 100 nm.
  • the edges of blades made as herein disclosed appear with a radius of curvature of 0.5 nm.
  • the surfaces adjacent to the cutting edge appear rough on both stainless steel and glass knive ⁇ at low magnification (5,000x)
  • the corre ⁇ ponding surfaces of the inventive blades are much smoother even at high magnifications (100,000x).
  • exceptionally sharp blade edges are made possible according to the invention.
  • a semiconductor processing step such as the isotropic etch for forming ridge 18 (Fig. 9) is not uniform across a wafer, and that the width of the ridge may vary from blade to blade along the wafer surface.
  • the parts of the wafer with the narrower ridges will necessarily form ato ically-sharp edges before other parts of the wafer with wider ridges.
  • all parts of the wafer will eventually form atomically sharp edges; and while the heights HI and H2 (Fig.
  • the exceptionally sharp blade edges made pos ⁇ ible according to the invention are obviously relatively fragile. Therefore, in many applications, it_is preferable to at least slightly dull the edges (or to make them less than maximally sharp) and, depending upon the knife application, strengthening the edges by the addition of one or more protective layers.
  • an excessively sharp edge e.g., having a radius of curvature of around 0.5nm
  • it is po ⁇ sible to slightly dull the edge e.g., to a radius of curvature of l-50nm
  • etching e.g., briefly immersing the workpiece in an etchant bath, or by controlled oxidation at a temperature above 1,100°C.
  • the ridge 18, and the surfaces 12e, 12f and 32 adjoining the ridge can be coated with a thin layer 46 of hard material (hardness greater than 1500 kg/ram 2 ) which not only increases the radius of curvature of the edge 40 (depending upon the thickness of the layer 46), but serves to strengthen and protect the ridge 18 and the cutting edge 40.
  • the layer 46 can be deposited only on one surface of the ridge 18 as shown in Fig. 22.
  • Such partial coating maintains a smaller radius of curvature at the edge than would be obtained with complete coverage (as shown in Fig. 21), and maintains sharpness for a longer time than is the case with no coverage. Sharpness is maintained because the less hard surface at the knife edge (silicon) wears away preferentially, maintaining the sharpness of the edge provided by the harder remaining material.
  • the layer 46 can comprise a thin (e.g., 2-50nm) film of silicon dioxide thermally grown (e.g., in dry oxygen at a temperature- in—excess—of- -1-075° C)-on the workpiece, or a layer (either directly on the silicon surfaces or overlying a previously applied layer of silicon dioxide) of a hard, smooth material such as silicon nitride, titanium diboride, diamond-like carbon or ⁇ ilicon carbide. Such material ⁇ can be deposited by known processes, e.g., by RF sputtering, and with thicknesses in the range of 2-100nm.
  • a thin film of silicon dioxide thermally grown e.g., in dry oxygen at a temperature- in—excess—of- -1-075° C
  • a layer either directly on the silicon surfaces or overlying a previously applied layer of silicon dioxide
  • a hard, smooth material such as silicon nitride, titanium diboride, diamond-like carbon or ⁇ ili
  • the ridge 18 (terminating in the cutting edge 40) projects perpendicularly from an adjoining surface 12e (i.e., "vertically” from the flat surface 12e of the wafer) .
  • Processes are now described resulting in blades where the blade edge is located at the intersection of generally parallel but gradually inwardly tapering side surfaces (i.e., a blade edge extending generally "horizontally” in the plane of a wafer flat surface).
  • One advantage of the "horizontal" blades is that curved blade edges can be readily made.
  • the ⁇ tarting workpiece (Fig ⁇ . 23 and 24) is a silicon wafer 50 having a pair of oppositely dispo ⁇ ed, parallel top and bottom ⁇ urfaces 52 and 54. An etched surface is to be cut entirely through the wafer and, to this end, an etchant masking layer, preferably of silicon carbide or boron nitride of 100-200nm thickness, is grown on the top surface 52 and then patterned to provide an 56 " of predetermined shape (e.g., a semicircular portion 57 having a peripheral edge 58 joined to a rectangular portion 59 having a peripheral edge 59a) .
  • Fig. 25 shows a mask 56a having an undulating mask edge 58a. This results in a blade, described hereinafter, having a serrated edge.)
  • the etchant mask 56 Because the etchant mask 56 is to be used during etching entirely through the thickness of the wafer, as hereinafter described, the etchant mask 56 also defines a grid-like frame (Fig. 23) including column ⁇ trips C, row ⁇ trip ⁇ R and tabs T.
  • the workpiece is then oxidized in known manner, e.g., in dry oxygen at 1,050° C for 3 hours, for growing a layer 60 (Fig. 26) of silicon dioxide on the top surface 52 where it is not covered by the masking layer 56 and a silicon dioxide layer 62 completely covering the bottom surface 54.
  • the oxide layers 60 and 62 preferably have a thickness of less than about 1 micron.
  • a second layer 68 (Fig. 27) of silicon carbide or boron nitride is grown over the masking layer 56 and the top oxide layer 60 and, simultaneously, a third layer 68a of the carbide or nitride is grown over the bottom oxide layer 62.
  • the layer 68, but not the layer 68a, is then preferably covered with a "stiffening" layer 69, e.g., a polymer such as polyimide having a thickness around 5-10 mocrometers .
  • the two upper layers 68 and 69 are then patterned (Figs.
  • a capping mask 70 overlying only the semicircular portion 57 of the underlying fir ⁇ t etchant mask 56 but with a peripheral edge 72 extending beyond (e.g., 0.5 mm) and parallel to the edge 58 of the semicircular portion 57 of the etchant mask 56—and—di-reefcly contacting the oxide layer 60.
  • the capping mask 70 does not extend onto the rectangular portion 59 of the first etchant mask 56, nor onto the grid-like frame (R,C) also defined by the first etchant mask 56, hence sections taken through the workpiece shown in Fig. 28 along lines 26-26 still appear as shown in Fig. 26.
  • a silicon oxide etchant e.g., HF
  • HF silicon oxide etchant
  • a ledge 76 (Fig. 30) of silicon carbide or boron nitride covered with the stiffening layer 69 is left extending over and spaced from a newly exposed surface 78 of the silicon wafer.
  • the ledge 76 terminates in a semicircular edge 72.
  • a plan view of the workpiece still appears as shown in Fig. 28.
  • the etched surface 78 curves upwardly to join the original wafer surface 52 along a line 80 spaced inwardly from and parallel to the outer edge 72 of the ledge 76.
  • the "stiffening" layer 69 is used for adding physical strength to the cantilevered ledge 76. While not always essential, depending upon the particular blade being made, the “stiffening" layer 69 is generally desirable for increasing the reliability, i.e., the yield during manufacture of the process.
  • the original silicon surface 78 underlying the ledge 76 along with all other silicon surface ⁇ exposed through the etchant mask 56 is then isotropically etched entirely through the wafer.
  • the profile (slope from point to point in a vertical plane) of the various surfaces etched through the wafer is a function of the configuration of the overlying etchant mask.
  • an etched surface 86 (Fig. 31) is produced which has a relatively continuous slope and is essentially a flat surface.
  • Fig. 45 which shows a plurality of completed blades still attached by tabs T to the grid-like frame R,C, the etched surface 86 forms a semicircular (or C-shaped) cutting surface terminating in a cutting edge 90.
  • the cutting edge 90 is shown at the intersection of the etched surface 86 and the wafer bottom surface 54.
  • Fig. 32 shows an etched surface 87 formed beneath the edge 59a (Fig. 28) of the rectangular portion 59 of the first etchant mask 56.
  • the surface 87 has a generally circularly curved profile, including a surface portion 87a which is essentially perpendicular to the wafer surface 52.
  • the circular etched surface results from the fact that, during isotropic etching, the etching proceeds at an equal rate, both laterally and downwardly. The equal lateral and downward etching occurs because the etchant fluid has access to the vertical wall formed directly beneath the mask as the horizontal surface adjoining the mask edge is etched downwardly.
  • the etching process begins with a cantilevered ledge 76 (Fig. 30) already in place, the restricted space beneath the mask ledge tends to retard circulation and replacement of spent etchant fluid within the restricted space. Accordingly, beneath the ledge 76, the rate of etching is slowed and the rate of slowing is a function of the length of the ledge. The greater the beginning ⁇ . length of the cantilevered ledge, the more gradual is the taper of the etched silicon surface 86.
  • both etched surfaces 86 and 87 intersect the wafer bottom surface 54 at highly acute angles along lines 90 and 91, respectively. While the edges formed by both lines 90 and 91 are relatively sharp, they are not atomically sharp because they have been produced solely by etching and not sharpened by an oxidizing-oxide stripping process.
  • Fig. 33 shows a cross-section at the edge of the semicircular portion 57 (Fig. 28) of the blade.
  • the edge 90, as well as the edge 91 (Fig. 32), are now atomically sharp.
  • FIG. 34 shows a completed blade having a serrated or undulating circular edge 90a resulting from use of a mask 58a as shown in Fig. 25.
  • Fig. 45 shows a completed blade connected by tabs T to a grid-like frame. The blades are removed by breaking the tabs.
  • the ⁇ tarting- orkpiece (Fig. 36) comprises a silicon wafer 100 having a patterned masking layer 102 on a top surface 104 thereof and a continuous masking layer 106 on a lower surface 108.
  • the masking layers 102 and 106 are of silicon carbide, boron nitride, platinum or palladium of around 120nm thickness.
  • a thin (20nm) titanium layer 109 is preferably thermally grown on the silicon surfaces 104 and 108 prior to the deposition of the metal layers.
  • the surfaces 104 and 108 can be parallel to any silicon crystal planes.
  • the composite edge 110 of the masking layers 102, 109 is shaped (e.g., similarly as the edges 58 and 59a shown in Fig. 23) in accordance with the desired shape of the cutting edge in the completed blade. Then (Fig ⁇ . 37 and 38), the wafer is isotropically etched to provide a first etched surface 112. The etching depth is generally in the range 50-300 microns, depending on the desired final shape of the surface of the cutting edge.
  • the etched surface 112 (Fig. 38) comprises a horizontal portion 114 joined to a circularly curved portion 116 which intercepts the original surface 102 along an edge 119. If the etching step illustrated in Fig.
  • the resulting etched surface would appear as shown in Fig. 39. While a sharp edge 120 at the intercept of the etched surface 118 with the silicon lower surface 108 would be present, the etched portion 118 would include a wall portion 122 rela-tively closely spaced to the edge 120 and extending substantially perpendicular to the lower surface 108. While a blade having such a surface 118 adjoining the cutting edge 120 has utility, e.g., similarly as the blade illustrated in Fig. 20, a generally preferred blade shape is, as previously mentioned, a blade where the surface ⁇ adjoining the cutting edge extend rearwardly thereof with relatively gradual tapers.
  • the composite masking layer 102, 109 (Fig. 38) is further patterned to provide a composite edge 128 (Figs. 40 and 41) extending along the periphery of the semicircular portion 57 of the blade workpiece and parallel to and spaced (e.g., 10-500 microns) from the intersection 119 of the previously etched surface 112 (Fig. 38) with the upper surface 104.
  • the further patterning i.e., the cutting back of the original edge 110 of the ma ⁇ king layer 102, 109 occurs only around the semicircular portion 57 of the mask and not along the rectangular portion 59.
  • a further isotropic etching proces ⁇ is performed (Fig. 42) for providing an etched surface 132 underlying the masking edge.
  • the surface 132 extends entirely through the silicon wafer 100 and intersects the wafer lower surface 108 along a line 134 parallel to the original edge 110 (Fig. 36) of the masking layer 102, 109. Beneath the original edge 110 of the masking layer 102, 109 adjoining the rectangular portion 59 (Fig. 37) of the masking layer, the etched surface (118) is as shown in Fig. 39.
  • the basic configuration of the blade is established.
  • Further processing steps e.g., reducing the curvature of the blade edge 134 and providing one or more protective coating layers, either on one side only or on both sides of the blade surfaces, can be performed as previously described.
  • Fig. 42 show ⁇ the etched surface 132 including a horizontal portion 135 interconnecting two curved portions 136 and 138.
  • the curved portion 138 curves sharpwardly upwardly, the vertical height of the portion 138 can be made relatively small (particularly in comparison with the height of the sharply rising wall 118 shown in Fig. 39), and the curved portion 138 is positioned relatively far from the cutting edge 134. Accordingly, in spite of the relatively sharp rise of the surface portion 138, the overall shape of the surface 132 adjoining the blade cutting edge corresponds, particularly in function, to a surface having a continuous and gradual rearward taper.
  • curved portion 136 of the etched surface 132 immediately adjoining the edge 134 is shown on an enlarged scale in Fig. 43, where the blade is shown in use for cutting through a piece of material.
  • th surface 136 is generally concave until becoming convex along surface portion 140 intersecting the horizontal portion 135 of th etched surface 132.
  • concave blade surface 136 (corresponding generally, to a "hollow ground” blade surface), terminating in convex surface "bump” 140, is a desirable feature in that the bum 140 serves to add a tensile force, indicated by the arrows 142 i Fig. 43, to the material being cut.
  • Such force decreases the loca bond strength of the- material in advance of the blade edge 134 an improves the cutting action of the blade.
  • the position an dimensions of the bump 140 are a function of the shape of th etched surface 132 (Fig. 42), which is a function of the relativ placement of the mask edges 110 and 128 (Figs. 36 and 41, respectively), and the length of time of the two etchin treatments. Accordingly, different configuration ⁇ are obtainable.
  • Fig. 44 shows an array of formed blades 150 disposed on common silicon wafer 152.
  • Each blade 150 is formed as previousl described in connection with Figs. 1-18, but all the blades are simultaneously fabricated.
  • tabs T joining each blade to a supporting grid work of the wafer 152 are broken for separating all the blades from the wafer and from one another.
  • Fig. 45 is a view similar to that of Fig. 44 but wherein blades of the type ⁇ hown in Fig. 34 are being made.
  • the method of fabricating arrays of knives and removing the knives from the silicon wafers as shown in Figs. 44 and 45 achieve ⁇ the simultaneous fabrication of large numbers of knives at one time. This economical means of fabrication is a significant advantage provided by the invention.
  • type II There are methods for automatically indicating a preselected depth of blade cut for two types of blade cutting motions.
  • One type of cutting action (called type I) is where the blade moves in a direction normal (Fig. 46) to its cutting edge.
  • type II is where the blade moves in a direction that .has...a large component of motion parallel to the cutting edge.
  • a second method for automatically indicating a preselected depth of blade cut for type I action is used in connection with the blade shown in Fig. 41 and involves adjustment of the relative positions of the mask edge 128 and the etched edge 119, and adjustment of the duration of the corresponding isotropic etches.
  • the etch time used for forming surface 112 (Fig. 38) is short so that the vertical distance between surface 114 and the original surface 104 i ⁇ small; see Fig. 47 in comparison with Fig. 48.
  • the subsequently formed mask edge 128 is positioned close to the edge 119.
  • the edge 128 is coincident with edge 119
  • the edge 128 is set back a short distance (say 30 microns) from edge 119.
  • Figs. 50 and 51 respectively.
  • Wall 138 is steep in both cases because of the shor etch time used to form surface 114 (Figs. 47,48,49), and intersect the upper surface in a nearly perpendicular direction. In use, such perpendicular step offers some resistance to furthe penetration of the blade. The depth at which this resistance is encountered is preselected by adjustment of the position of the mask edge 128 with respect to the edge 119, and adjustment of the duration of the corresponding isotropic etches.
  • a third method for automatically indicating a preselected depth of blade cut for type I action replaces the first of two isotropic etches with an anisotropic etch.
  • An anisotropic etch produces a vertical wall 150 (Fig. 52) instead of a curved surface 116 (Fig. 38).
  • the anisotropic etching is made by applying known methods of Reactive Ion Etching (RIE) or wet chemical etching; the former is used where curved knife edges are needed, and the latter is used on ⁇ 110 ⁇ oriented wafers only for straight edges since the vertical wall 150 made by wet anisotropic etching necessarily lies on a ⁇ 111 ⁇ plane as described earlier.
  • Blade structures Fig.
  • the method for automatically indicating a preselected depth of blade cut for type II action is to adjust the position of mask edge 128 (Fig. 41) with respect to edge 119 differently for different parts of the knife.
  • type II cutting action is assumed to be used with the knife shown in Fig. 54 in the direction shown to the depth X X.
  • the edge 128 is set back from the edge 119 as ⁇ hown in Fig. 41, giving a final profile as shown in Fig. 42.
  • the edge 128 is made coincident with edge 119 giving a final profile as shown in Fig. 39.
  • a new resistance to motion is added when the knife penetrates to the distance X X and the knife profile changes from that shown in Fig. 42 to that shown in Fig. 39.

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  • Life Sciences & Earth Sciences (AREA)
  • Forests & Forestry (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Micromachines (AREA)

Abstract

La présente invention concerne des lames de couteaux présentant des tranchants (19) exceptionnellement effilés réalisés à partir de tranche de silicium monocristallin en employant une technique connue de traitement de semi-conducteurs. Selon une réalisation, une arête (18) de forme allongée, et dont le dessus est plat (20) et recouvert d'un masque (15) pour réactif d'attaque, subit une attaque chimique en contre-dépouille du masque (15) jusqu'à ce que la paroi latérale de l'arête (17) prenne une forme convergeant vers la pointe (19) de l'arête. Après suppression du masque (15), on forme sur l'arête un sommet (19) en angle aigu par une série d'opérations de formation d'oxyde et d'élimination de l'oxyde. Ce procédé permet de mettre en forme, en partant d'une tranche de silicium (10), différentes lames de couteau en silicium, chaque lame comportant une arrête en tranchant (19) effilé. Selon une autre réalisation, la tranche de silicium (50) est soumise à attaque chimique dans sa totalité comprise depuis la face supérieure (52) jusqu'à la face inférieure (54) de façon à constituer par attaque chimique une paroi biseautée (87) venant en intersection avec la paroi du fond (54) et formant un tranchant (91) très effilé. Le tranchant (91) est aiguisé par une série d'opérations de formation d'oxyde et d'élimination de l'oxyde, jusqu'à réalisation du tranchant (91) de lame complète. Pour les deux réalisations, on a recours à différents masques d'attaque chimique et différents procédés d'attaque chimique pour obtenir des lames de diverses formes.
PCT/US1995/015690 1995-11-22 1995-11-22 Lames de couteaux a tranchant ultra-effile et procede de fabrication Ceased WO1997018912A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU44142/96A AU4414296A (en) 1995-11-22 1995-11-22 Knifes blades having ultra-sharp cutting edges and methods of fabrication
PCT/US1995/015690 WO1997018912A1 (fr) 1995-11-22 1995-11-22 Lames de couteaux a tranchant ultra-effile et procede de fabrication

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US1995/015690 WO1997018912A1 (fr) 1995-11-22 1995-11-22 Lames de couteaux a tranchant ultra-effile et procede de fabrication

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WO1997018912A1 true WO1997018912A1 (fr) 1997-05-29

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013138597A1 (fr) * 2012-03-14 2013-09-19 Jennings Drake Carlisle Couteau destiné à la transformation du bois et procédés permettant de plaquer et de traiter la surface d'un couteau destiné à la transformation du bois

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US358234A (en) * 1887-02-22 Painter s hacking-knife
NL45742C (fr) * 1900-01-01
US3469488A (en) * 1968-07-22 1969-09-30 Anthony M Gaspari Stencilling die
US3728980A (en) * 1971-02-10 1973-04-24 Fraze Ermal C Scoring die
US3802078A (en) * 1971-06-07 1974-04-09 P Denes Cutting device and method for making same
US3975891A (en) * 1974-02-22 1976-08-24 Roland Eric Gunther Mower blades
US3977061A (en) * 1973-09-17 1976-08-31 Sandvik Aktiebolag Cutting insert and method of making the same
US4980021A (en) * 1989-04-03 1990-12-25 Shin-Etsu Chemical Co. Ltd. Method for preparation of edged medical tool
US4991481A (en) * 1989-06-23 1991-02-12 Gerber Garment Technology, Inc. Blade for cutting sheet material and related cutting method

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US358234A (en) * 1887-02-22 Painter s hacking-knife
NL45742C (fr) * 1900-01-01
US3469488A (en) * 1968-07-22 1969-09-30 Anthony M Gaspari Stencilling die
US3728980A (en) * 1971-02-10 1973-04-24 Fraze Ermal C Scoring die
US3802078A (en) * 1971-06-07 1974-04-09 P Denes Cutting device and method for making same
US3977061A (en) * 1973-09-17 1976-08-31 Sandvik Aktiebolag Cutting insert and method of making the same
US3975891A (en) * 1974-02-22 1976-08-24 Roland Eric Gunther Mower blades
US4980021A (en) * 1989-04-03 1990-12-25 Shin-Etsu Chemical Co. Ltd. Method for preparation of edged medical tool
US4991481A (en) * 1989-06-23 1991-02-12 Gerber Garment Technology, Inc. Blade for cutting sheet material and related cutting method

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013138597A1 (fr) * 2012-03-14 2013-09-19 Jennings Drake Carlisle Couteau destiné à la transformation du bois et procédés permettant de plaquer et de traiter la surface d'un couteau destiné à la transformation du bois
US8894770B2 (en) 2012-03-14 2014-11-25 Andritz Iggesund Tools Inc. Process and apparatus to treat metal surfaces
US9068260B2 (en) 2012-03-14 2015-06-30 Andritz Iggesund Tools Inc. Knife for wood processing and methods for plating and surface treating a knife for wood processing

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