Abstract:
An example provides a method including sputtering a metal catalyst onto a substrate, exposing the substrate to a solution that reacts with the metal catalyst to form a plurality of pores in the substrate, and etching the substrate to remove the plurality of pores to form a recess in the substrate.

Description:
BACKGROUND 
       [0001]    A number of devices may be implemented with recesses or voids (such as, e.g., a chamber or channel) in a substrate. Micro-electrical-mechanical systems (MEMS) devices, for example, may include air chambers to house components and/or to provide functionality to the devices. Printheads, which sometimes may be MEMS-based, may include firing chambers, ink feed slots, or ink channels. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0002]    The detailed description section references the drawings, wherein: 
           [0003]      FIG. 1  is a flow diagram of an example method for etching a substrate; 
           [0004]      FIGS. 2-5  illustrate sectional views of a substrate at various stages of another example method for etching the substrate; 
           [0005]      FIGS. 6 and 7  illustrate sectional views of a substrate at various stages of another example method for etching the substrate; 
           [0006]      FIGS. 8 a  and 8 b    illustrate sectional views of a substrate at various stages of another example method for etching the substrate; 
           [0007]      FIGS. 9 a  and 9 b    illustrate sectional views of a substrate at various stages of another example method for etching the substrate; and 
           [0008]      FIGS. 10 a  and 10 b    are block diagrams of an example apparatus for etching a substrate; all in which various examples may be implemented. 
       
    
    
       [0009]    Certain examples are shown in the above-identified figures and described in detail below. The figures are not necessarily to scale, and various features and views of the figures may be shown exaggerated in scale or in schematic for clarity and/or conciseness. 
       DETAILED DESCRIPTION OF EMBODIMENTS 
       [0010]    Many devices are fabricated to include recesses or other openings (e.g., chambers, channels, voids, etc.). Micro-electrical-mechanical systems (MEMS) devices, for example, may include chambers to house components and/or to provide functionality to the devices. Printheads may include firing chambers, ink feed slots, or ink channels, and sometimes may be fabricated using MEMS technology. In some cases, recesses or voids may be formed in a layer and the layer may be bonded with at least one other layer to form a device. 
         [0011]    Bulk micromachining of substrates may be performed using dry or wet etching processes. Bulk dry etch processes, however, may be lengthy as these processes are commonly performed on a one-wafer-run basis. In some wet etch operations, trenches with sloped, rather than vertical, sidewalls may be formed. 
         [0012]    Described herein are implementations of methods for etching a substrate. In some examples, a method for etching a substrate may include contacting a substrate with a probe comprising metal and etching the substrate using a solution that reacts with the metal to form an opening in the substrate. In various implementations, the probe may be electrically biased to facilitate the etching. Etching the substrate using the probe may facilitate forming, at least in part, a device, such as, for example, a MEMS device, a printhead, or another device, or may facilitate die singulation or other substrate cutting. In various implementations, the probe may be moved relative to the substrate, or the substrate moved relative to the probe, or vice versa. In some of these implementations, an angle of the probe relative to the substrate may be modified during etching, or an angle of the substrate relative to the probe may be modified during etching. In some implementations, both the probe and the substrate may be moved relative to each other during etching. After etching, the probe may be separated from the substrate and may be used to etch another substrate or another location of the same substrate. 
         [0013]    An example method  100  for etching a substrate is illustrated in  FIG. 1 . Processing for the method  100  may begin or proceed with contacting a substrate with a probe comprising metal, at block  102 . The substrate may comprise one layer or multiple layers. For example, the substrate may comprise at least one layer of silicon, silicon germanium, a nitride, an oxide, a polymer, a ceramic, a metal, a group III-V material, a combination thereof, etc. In at least some implementations, the substrate may comprise silicon or silicon with at least one other layer thereon. In various implementations, the substrate may comprise any material suitable for forming a device, such as, for example, a MEMS device, a printhead, or another device. Various other substrate materials may be possible within the scope of the present disclosure. 
         [0014]    It is noted that although various drawings referenced herein may depict the substrate as a single unitary layer, it should be understood that the substrate may in fact comprise multiple substrate layers and that any reference to a surface of the substrate may mean a surface of a substrate that comprises multiple layers. In some implementations, the substrate may comprise multiple substrates bonded together, and the multiple substrates may comprise the same crystal orientations or different crystal orientations. 
         [0015]    The probe may comprise any metal that reacts with the solutions described herein to etch the substrate via metal-assisted chemical etching. For example, in various implementations, the metal may comprise a metal catalyst that reacts with a solution of hydrofluoric acid, hydrogen peroxide, or nitric acid, or a combination thereof to etch the substrate. Examples of suitable metals may include, but are not limited to, gold, silver, platinum, ruthenium, platinum, palladium, molybdenum, chromium, copper, tantalum, titanium, tungsten, and alloys thereof. In various implementations, the probe may be solid metal or may be plated or otherwise have a surface covered, at least in part, with the metal. 
         [0016]    In various implementations, the probe may be disposed on a mount or other platform to facilitate handling of the probe. The mount may include one probe or may include a plurality of probes of the same or different shapes, depending on the pattern to be etched into the substrate. The probe, whether disposed on the mount or not, may be rigid or flexible, and may have a thickness and shape suitable for the particular etching operation. For example, the probe may comprise a wire or other raised feature that has a metal surface for contacting the substrate. Raised features may be formed, for example, by patterning a metal layer, laminating a metal pattern, etc. 
         [0017]    The method may proceed to block  104  by etching the substrate using a solution that reacts with the metal of the probe to form an opening in the substrate. In various implementations, the solution may comprise hydrogen peroxide and/or nitric acid with hydrofluoric acid and water, and the etching operation may comprise a metal-assisted chemical etch process in which the metal is a catalyst, and the substrate surface acts as an anode and the metal acts as the cathode. The metal may catalyze the reduction of hydrogen peroxide or nitric acid, which may result in a flow of electrons from the anode to the cathode and the “sinking” of the metal probe into the substrate to anisotropically etch the substrate. In various implementations, an etch rate using the solution and the metal catalyst may be 5 μm per minute or greater. In various implementations, nitric acid added to a solution of hydrogen peroxide, hydrofluoric acid, and water may add isotrophy to the etch to dissolve the porous substrate as it is created. In some of these implementations, the amount of the nitric acid may control, at least in part, lateral etching of areas near the surface of the substrate while the ratio of the nitric acid to the hydrogen peroxide may control, at least in part, the sidewall profile. 
         [0018]    Etching of the substrate by the solution may be performed at ambient temperature or another suitable temperature. Increasing temperature may, in some cases, increase or otherwise impact the etch rate. In some implementations, the etching of the substrate by the solution may be performed under agitation or in a still bath. The solution may be formulated by any concentration to provide a particular etch rate. Likewise, the ratio of hydrogen peroxide to hydrofluoric acid to water or nitric acid to hydrofluoric acid to water may depend on the particular etch rate, and may vary during the etch operation. In various implementations, the etching may be performed under illumination with UV or optical wavelengths, which may increase or other increase efficiency of the etch. 
         [0019]    In various implementations, the probe may be moved relative to the substrate or the substrate moved relative to the probe, or both. For example, the angle of the probe relative to the substrate or the substrate relative to the probe, or both, may be modified during etching of the substrate. By moving the probe/substrate during etching, more complex devices may be formed or may be formed with fewer separate operations than by keeping the probe stationary. 
         [0020]    In various implementations, the probe may be electrically biased to facilitate the etching of the substrate. Positively biasing the probe, for example, may allow the solution to be formulated devoid of hydrogen peroxide, and in at least some implementations in which the probe is positively biased, the solution may comprise hydrofluoric acid, nitric acid, and water, and is substantially devoid of hydrogen peroxide. 
         [0021]    In various implementations, the probe may be separated from the substrate after the etching. The probe may be re-used to etch another substrate or another location of the same substrate. 
         [0022]    Understanding of the various methods for etching a substrate as described herein may be facilitated with reference to  FIGS. 2-9   a / 9   b,  which describe various operations for etching a substrate by way of sectional views of the substrate at various stages of various example methods. It should be noted that various operations discussed and/or illustrated may be generally referred to as multiple discrete operations in turn to help in understanding various implementations. The order of description should not be construed to imply that these operations are order dependent, unless explicitly stated. Moreover, some implementations may include more or fewer operations than may be described. 
         [0023]    Turning now to  FIG. 2 , a method for etching a substrate  206  may begin or proceed with contacting a surface  208  of the substrate  206  with a probe  210  of a template  212 . The probe  210  may comprise metal, as discussed herein. As shown, the template  212  includes a plurality of probes  210 , with various shapes and sizes. In various implementations, the template  212  may include a mount  214  on which the probes  210  may be disposed. In other implementations, the probes  210  may be free-standing or individually controlled. In various implementations, the probes  210  may comprise a wire or a raised feature on the mount  214 , or a combination thereof. 
         [0024]    The method may proceed with etching the substrate  206  using a solution that reacts with the metal of the probes  210 , as shown in  FIG. 3 , to form openings  216  in the substrate  206  corresponding to the locations of the probes  210 , as shown in  FIG. 4 . The probe  210  may be separated from the substrate  206  after the etching, and re-used to etch another substrate or another location of the same substrate  206 . 
         [0025]    The openings  214  may comprise trenches, blind holes, or through-holes. To form through-holes, the etching may continue until a probe  210  reaches a second surface  218 , opposite the first surface  208 , of the substrate  206  so that the opening  216  extends through an entire thickness of the substrate  206 . The substrate  206  including the openings  216  may form, at least in part, a MEMS device, a printhead, or another device. In various ones of these implementations, a printhead may be formed with the MEMS device. 
         [0026]    In some implementations, after etching the substrate  206  to form the openings  216 , the substrate  206  may be etched to remove at least some of the openings  216  to form at least one recess  220  in the substrate  206 , as shown in  FIG. 5 . In various implementations, all or fewer than all of the plurality of openings  216  may be etched. As shown, for example, some of the openings  216  may not be etched while other openings  216  are etched to form the recess  220 . The substrate  206  may be etched to remove the openings  216  using a wet etch with an etchant such as, but not limited to, tetra-methyl ammonium hydroxide or potassium hydroxide. In other implementations, the substrate  206  may be etched to remove the openings  216  using a dry etch. In various implementations, the recess or recesses  220  may further form, at least in part, a MEMS device, a printhead, or another device. 
         [0027]    In various implementations, a substrate may be etched on opposite surfaces for forming a device. As shown in  FIG. 6 , a method for etching a substrate may include contacting opposite surfaces of a substrate  606  with probes  610   a,    610   b  of templates  612   a,    612   b,  and etching the substrate  606  using a solution that reacts with the metal of the probes  610   a,    610   b  to form openings  616  in the substrate  606  corresponding to the locations of the probes  610   a,    610   b,  as shown in  FIG. 7 . The substrate  606  including the openings  616  may form, at least in part, a MEMS device, a printhead, or another device. In various ones of these implementations, a printhead may be formed with the MEMS device. 
         [0028]    In various implementations, moving a probe and/or a substrate relative to each other may facilitate forming more complex patterns in a substrate.  FIGS. 8 a  and 8 b    show an example of etching a substrate  806  in which a probe  810  is moved laterally relative to the substrate  806  during etching. As shown in  FIG. 8 a   , the method may begin or proceed with etching the substrate  806  using a solution that reacts with the metal of the probe  810 , as shown in  FIG. 8 a   . The probe  810  may be moved laterally relative to the substrate  806 , as shown in  FIG. 8 b   , which may form an opening  814  in the substrate  806 . In various implementations, moving the probe  810  during the etch may allow an opening  814  larger than the probe  810  to be formed in the substrate  806 . For example, in various implementations, moving the probe  810  may be used to form a line or to cut the substrate  806  (such as, e.g., to singulate die, etc.). Although not shown here, in various implementations, the probe  810  may be moved in multiple directions during the etch to form other patterns in the substrate  806 . For example, the probe  810  may be moved laterally (such as, e.g., movement along an x-axis or a y-axis, or a combination thereof, where the x-axis and y-axis are parallel with the surface of the substrate  806 ) or up/down (such as, e.g., movement along a z-axis), or both, during an etch. In other implementations, the substrate  806  may be moved laterally relative to the probe  810  instead of or in addition to moving the probe  810  laterally relative to the substrate  806  during etching. 
         [0029]      FIGS. 9 a  and 9 b    show an example of etching a substrate  906  in which an angle of a probe  910  is modified during etching of the substrate  906 . The method may begin or proceed with etching the substrate  906  using a solution that reacts with the metal of the probe  910 , as shown in  FIG. 9 a   . The probe  910  may be angled during the etch, as shown in  FIG. 9 b   , which may form an opening  914  in the substrate  906 . In other implementations, the angle of the substrate  906  relative to the probe  910  may be modified during etch instead of or in addition to modifying the angle of the probe  910  relative to the substrate  906 . 
         [0030]      FIGS. 10 a  and 10 b    are block diagrams of an example apparatus  1000  for etching a substrate. The apparatus  1000  may include probes  1010  comprising metal and a platform  1022  configured to hold a substrate. In various implementations, the probes  1010  may be disposed on a mount  1014 . In various implementations, the mount  1014  may be configured to electrically bias the probes  1010  when the probes  1010  are in contact with a substrate on the platform  1022 . 
         [0031]    The apparatus  1000  may include an actuator assembly  1024  configured to bring the probes  1010  and the platform  1022  into proximity to cause the probes  1010  to contact a substrate disposed on the platform  1022 . In various implementations, the actuator assembly  1024  may be configured to move the probes  1010  or modify an angle of the probes  1010 , or both, relative to a substrate on the platform  1022  when the probes are in contact with the substrate. In some implementations, the platform  1022  may be configured to move the substrate or modify an angle of the substrate, or both, relative to the probes  1010  instead of or in addition to moving the actuator assembly  1024  during etching. In some of these implementations, the platform  1022  may be configured to bring the substrate toward the probes  1010  instead of in addition to the actuator assembly  1024  bringing the probes  1010  into proximity with the platform  1022 . 
         [0032]    A fluid unit  1026  may provide a solution to a substrate when the probes  1010  are in contact with the substrate, the solution to react with the metal to form an opening in the substrate. The fluid unit  1026  may comprise a bath tank, a sprayer module, or other application module for providing the solution to a substrate mounted on the platform  1022 . 
         [0033]    The apparatus  1000  may include a controller  1028  to control at least one aspect of the apparatus  1000 . In various implementations, the controller  1028  may cause the actuator assembly  1024  to bring the probes  1010  and the platform  1022  into proximity to cause the probes  1010  to contact a substrate (such as, e.g., moving the probes  1010  toward the platform  1022  or the platform  1022  toward the probes  1010 , or both), to move the probes  1010  relative to the substrate when the probes  1010  are in contact with the substrate, or to modify an angle of the probes  1010  relative to the substrate when the probes  1010  are in contact with the substrate, or some combination thereof. In various implementations, the controller  1028  may electrically bias the probes  1010  when the probes  1010  are in contact with a substrate on the platform  1022 . In various implementations, the controller  1028  may control the fluid unit  1026  to cause the solution to be provided to the substrate. 
         [0034]    Various aspects of the illustrative embodiments are described herein using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. It will be apparent to those skilled in the art that alternate embodiments may be practiced with only some of the described aspects. For purposes of explanation, specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the illustrative embodiments. It will be apparent to one skilled in the art that alternate embodiments may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative embodiments. 
         [0035]    Flow diagrams are provided to describe various methods for etching a substrate, in accordance with various implementations. While the flow diagrams illustrate various operations in a particular order, the drawings are not intended to limit the present disclosure to any particular order. Additionally, the drawings are not intended to imply that all operations are required for all implementations. 
         [0036]    The phrases “in an example,” “in various examples,” “in some examples,” “in various embodiments,” and “in some embodiments” are used repeatedly. The phrases generally do not refer to the same embodiments; however, they may. The terms “comprising,” “having,” and “including’ are synonymous, unless the context dictates otherwise. The phrase “A and/or B” means (A), (B), or (A and B). The phrase “A/B” means (A), (B), or (A and B), similar to the phrase “A and/or B”. The phrase “at least one of A, B, and C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C). The phrase “(A) B” means (B) or (A and B), that is, A is optional. Usage of terms like “top”, “bottom”, and “side” are to assist in understanding, and they are not to be construed to be limiting on the disclosure. 
         [0037]    Although certain embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent embodiments or implementations calculated to achieve the same purposes may be substituted for the embodiments shown and described without departing from the scope of this disclosure. Those with skill in the art will readily appreciate that embodiments may be implemented in a wide variety of ways. This application is intended to cover any adaptations or variations of the embodiments discussed herein. It is manifestly intended, therefore, that embodiments be limited only by the claims and the equivalents thereof.