WO2015183634A1

WO2015183634A1 - Methods of removing silicon from silicon-eutectic alloy compositions, and products made by such methods

Info

Publication number: WO2015183634A1
Application number: PCT/US2015/031552
Authority: WO
Inventors: Vasgen Shamamian; Edward NYUTU
Original assignee: Dow Corning Corporation
Priority date: 2014-05-27
Filing date: 2015-05-19
Publication date: 2015-12-03

Abstract

New methods for selectively etching silicon-silicide materials, and products made therefrom are disclosed. A method may include contacting surfaces of a silicon-silicide product with a caustic etchant. Concomitant to the contacting step, at least some of the silicon may be removed from the silicon-silicide product via the caustic etchant, wherein the average amount of silicon removed during the removing step is a silicon removal rate (Si-RR). Also concomitant to the contacting step (b), a majority of the silicides of the silicon-silicide product may be retained, wherein the average rate of silicides removal during the retaining step is a silicide removal rate (MSi_x-RR). The ratio of the silicide removal rate to the silicon removal rate may be at least 5.0 (Si-RR / MSi_x-RR ≥ 5.0). A substance may be deposited into pores created due to the etching of the silicon to create tailored products.

Description

METHODS OF REMOVING SILICON FROM SILICON-EUTECTIC ALLOY COMPOSITIONS, AND PRODUCTS MADE BY SUCH METHODS

BACKGROUND

[001] Silicon (Si) eutectic alloys can be fabricated by melting and casting processes (see, e.g., WO 2011/022058). Such silicon eutectic alloys of WO2011/022058 may realize improved fracture toughness.

SUMMARY OF THE DISCLOSURE

[002] Broadly, the present patent application relates to methods of removing silicon from a silicon-silicide product, while retaining a majority of the silicide(s) of the silicon- silicide product.

[003] Referring now to FIG. 1, the methods may involve contacting (100) surfaces of a silicon-silicide product with one or more caustic etchants. For instance, the caustic etchant may be a metal (e.g., a group I metal) hydroxide, such a potassium or sodium hydroxide, and similar hydroxide etchants, such as tetra methyl ammonium hydroxide (TMAH), among others. The silicon-silicide product may include a first phase comprising silicon and a second phase comprising at least one silicide. During the contacting, the caustic etchant may contact both (A) at least some of the first phase comprising the silicon and (B) at least some of the second phase comprising the silicides. Concomitant to the contacting step, at least some of the silicon may be removed (120) from the silicon-silicide product via the caustic etchant. The average amount of silicon removed during the removing step is referred to herein as the "silicon removal rate" or "Si-RR". Also concomitant to the contacting step, a majority of the silicides of the silicon-silicide product may be retained (140), i.e., a relatively small amount of silicides (or no silicides) are removed. The average rate of silicides removal is referred to herein as the "silicides removal rate" or "MSi_x-RR". Thus, the caustic etchant may "selectively etch" the silicon of the silicon-silicide product, thereby enabling recovery (200) of a selectively-etched silicon-silicide product. In one embodiment, the selective etch achieves a ratio of silicon removal rate to silicides removal rate of at least 5.0 (i.e., "Si-RR" divided by "MSi_x-RR" is > 5.0), i.e., the rate at which silicon is removed from the silicon- silicide product is at least 5 times faster than the rate at which silicides are removed from the silicon-silicide product ("the selective etch ratio").

[004] The silicon-silicide product may be any product having both silicon and at least one silicide ("silicide(s)"). The silicide(s) may be proximal to, or adjacent to (in contact with), the silicon. Some examples of silicon-silicide products that may be selectively etched are described in further detail below.

[005] The silicon of the silicon-silicide product may be any silicon susceptible of removal by a caustic etchant, such as any of monocrystalline silicon, polycrystalline silicon, amorphous silicon, and combinations thereof. In one embodiment, the silicon-silicide product comprises monocrystalline silicon. In another embodiment, the silicon-silicide product comprises polycrystalline silicon. In yet another embodiment, the silicon-silicide product comprises both monocrystalline and polycrystalline silicon. In another embodiment, the silicon of the silicon-silicide product consists essentially of monocrystalline silicon. In yet another embodiment, the silicon of the silicon-silicide product consists essentially of polycrystalline silicon.

[006] As noted above, the silicon of the silicon-silicide product may be removed via a caustic etchant (e.g., a caustic etchant solution). In one approach, the caustic etchant is a liquid consisting essentially of a metal hydroxide in water. In one embodiment, the liquid comprises KOH. In one embodiment, the KOH concentration is from 10 wt. % to 30 wt. %. In one embodiment, the caustic etchant solution temperature is from 20° to 90° C during the etching step.

[007] The silicide(s) of the silicon-silicide product may be any silicide(s) resistant to removal by the caustic etchant. In one embodiment, the silicide(s) comprise a disilicide. In another embodiment, the silicide(s) comprise a monosilicide. In yet another embodiment, the silicide(s) comprise both some monosilicide and some disilicide. Higher order silicides may also potentially be removed. As used herein, "silicide" means a compound comprising at least one metal bonded to silicon.

[008] The silicon-silicide product is contacted by the caustic etchant to remove at least some of the silicon of the silicon-silicide product. The contacting step may be achieved via any suitable apparatus and methodology, including spraying, immersion, and sonication, among others. Notably, the contacting step may occur in the absence of an applied electrical current (i.e., is not an electrochemical etch).

[009] As disclosed above, during the contacting step (100) at least some of the silicon is removed from the silicon-silicide product while at least a majority of the silicide(s) are retained. In one approach, at least 0.5 wt. % of the silicon is removed from the silicon- silicide product. Correspondingly, in this approach, less than 0.1 wt. % of the silicide(s) are removed due to the selective etch ratio being at least 5.0 (i.e., "Si-R " divided by "MSi_x-RR" is > 5.0). In one embodiment, at least 1 wt. % of silicon is removed. In another embodiment, at least 5 wt. % of silicon is removed. In yet another embodiment, at least 10 wt. % of silicon is removed. In another embodiment, at least 15 wt. % of silicon is removed. In yet another embodiment, at least 25 wt. % of silicon is removed. In another embodiment, at least 50 wt. % of silicon is removed. In yet another embodiment, at least 75 wt. % of silicon is removed. In another embodiment, at least 90 wt. % of silicon is removed. In yet another embodiment, at least 95 wt. % of silicon is removed. In another embodiment, at least 99 wt. % of silicon is removed. In yet another embodiment, essentially all of the silicon is removed (e.g., when the silicides form an interconnected network).

[0010] As disclosed above, the selective etch ratio is at least 5.0 (i.e., "Si-RR" divided by "MSi_x-RR" is > 5.0). In one embodiment, the selective etch ratio is at least 10. In another embodiment, the selective etch ratio is at least 50. In yet another embodiment, the selective etch ratio is at least 100. In another embodiment, the selective etch ratio is at least 500. In yet another embodiment, the selective etch ratio is at least 1000. In another embodiment, the selective etch ratio is at least 5000. For purposes of determining the selective etch ratio, when no detectable level of silicide(s) are removed due to the contacting step, "MSi_x-RR" is 100 angstroms per minute.

[0011] As disclosed above, the disclosed methods may be useful in removing at least some silicon of a silicon-silicide product. The silicon-silicide product may be any silicon product having silicide(s) therein, such as silicon-eutectic alloys, semiconductor devices, and microelectro-mechanical systems, to name a few.

[0012] In one embodiment, the silicon-silicide product is a silicon eutectic alloy. As used herein, a "silicon-eutectic alloy" is a material predominately composed of silicon (at least 50.1 at. % Si) and having an aggregation of a first phase comprising one of (A) eutectic silicon and (B) eutectic silicide(s), and a second phase dispersed within the first phase. The second phase may comprise, for example, a silicide(s) phase or solid solution (which phases may be in stable, metastable, or unstable phase). A silicon-eutectic alloy does not have to be "perfectly eutectic", i.e., a silicon-eutectic alloy does not need to have a composition that is located perfectly on the eutectic point of its corresponding phase diagram. For example, a Si- CrSi₂ eutetic alloy has one eutectic point at about 24 wt. % Cr and 76 wt. % Si. However, compositions outside of this point may produce acceptable silicon-eutectic alloys having a defined aggregation of a first phase and a second phase dispersed within the first phase. Third or more distinct phases may also be present. WO2011/022058 to Schuh et al. and U.S. Patent No. 4,724,223 to Ditchek et al, each of which is incorporated herein by reference in its entirety, disclose methods of producing silicon eutectic alloy products.

[0013] In one embodiment, the first phase of the aggregation is an elemental silicon phase, i.e., the first phase comprises silicon in the form of crystalline silicon and/or amorphous silicon. In another embodiment, the first phase includes silicon and one or more metallic element(s) M in silicide form. In one embodiment, one of the first and second phases of the aggregation comprises one or more colonies of aligned high aspect ratio structures (e.g., 2: 1, or larger). In one embodiment, a silicon eutectic alloy body is symmetric about a longitudinal axis, and one of the first and second phases of the eutectic aggregation comprises high aspect ratio structures oriented along a radial direction with respect to the longitudinal axis.

[0014] The solid phases that form upon cooling through a eutectic temperature at a eutectic composition may define a eutectic aggregation having a morphology that depends on the solidification process. For instance, the silicide portion of the silicon eutectic alloy may be in the form of lamella, rods, globes (globular), acicular (needle-like), disks, flakes, dendrites, interpenetrated / percolated, Chinese script and combinations thereof. The phases may be regular (normal) or irregular (anomalous). Examples of normal: regular spacing (e.g., regular lamella spacing, regular rod spacing). Examples of anomalous: no apparent orientation relationship between the silicon and the silicide in the silicon-silicide material (e.g., irregular spacing, broken lamella, fibrous silicides, interconnected-percolated silicides, Chinese script silicides). The form of the silicide(s) may be controlled by, for example, the type of metal(s) used in the silicon-eutectic alloy, and solidification conditions, and/or eutectic phase growth rates, to name a few.

[0015] In one embodiment, a second phase (silicide phase) may comprise discrete eutectic structures, whereas a matrix phase, or first phase, (silicon) may be substantially continuous. For example, the eutectic aggregation may include a reinforcement (second) phase of rod-like, plate-like (lamella), acicular and/or globular structures, or others of the above -noted silicide phases, dispersed in a substantially continuous matrix phase. Such eutectic structures may be referred to as "reinforcement phase structures."

[0016] The reinforcement phase structures in the eutectic aggregation may further be referred to as high aspect ratio structures when at least one dimension (e.g., length) exceeds another dimension (e.g., width, thickness, diameter) by a factor of 2 or more. Aspect ratios of reinforcement phase structures may be determined by, for instance, optical or electron microscopy using standard measurement and image analysis software. If useful, the solidification process may be controlled to form and align high aspect ratio structures in the matrix phase. For example, when the eutectic alloy is produced by a directional solidification process, it is possible to align a plurality of the high aspect ratio structures along the direction of solidification.

[0017] The eutectic alloys described herein may be composed entirely or in part of the eutectic aggregation of silicon-containing and silicide(s). Depending on the concentration ratio of the silicon and the metallic element(s) M, at least about 70 vol.%, or at least about 80 vol.%, or at least about 90 vol.% of the eutectic alloy may comprise the eutectic aggregation. In one embodiment, a eutectic alloy body may include at least about 50.1 at. % Si. In another embodiment, the alloy may include at least about 60 at.% Si. In yet another embodiment, the alloy may include at least about 70 at.% Si. In another embodiment, the alloy may include at least about 80 at.% Si. In yet another embodiment, the alloy may include at least about 90 at.% Si.

[0018] The metal (M) of the silicide(s) may be any metal that can form a silicide, which silicide is resistant to being etched by the caustic etchant. Examples of some metals that may be used include Li, Na, K, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ba, La, Hf, Ta, Re, Os, Ir, W, Pt, Bi, U, rare earth elements, and mixtures thereof. In one embodiment, the metal comprises chromium. In one embodiment, the metal is titanium. In one embodiment, the metal is cobalt. In one embodiment, the metal is vanadium. In one embodiment, the metal comprises at least one of Cr, Ti, Co, V, & combinations thereof.

[0019] Referring now to FIG. 2, one embodiment of a method for producing selectively- etched silicon-silicide products having preselected characteristics is shown. In the illustrated embodiment, the method includes preselecting one or more silicon-silicide characteristics (70), producing the silicon-silicide product, wherein the silicon-silicide product realizes the one or more preselected silicon-silicide product characteristics (72), and then completing (74) the contacting (100), removing (not shown), and retaining (not shown) steps. Thus, selectively-etched silicon-silicide products having preselected characteristics may be recovered (200).

[0020] In one approach, a preselected silicon-silicide characteristic is a pre-etch silicon characteristic. In one embodiment, a pre-etch silicon characteristic comprises one of a silicon type and a silicon grain size (if any). In one embodiment, the preselected silicon type is one of monocrystalline and polycrystalline silicon. In one embodiment, the preselected silicon type is polycrystalline silicon. In these embodiments, a preselected silicon characteristic may include a preselected silicon grain size.

[0021] In one approach, a preselected silicon-silicide characteristic is a preselected pre- etch silicide characteristic. In one embodiment, a preselected silicide characteristic may be a pre-etch silicide dimension characteristic and/or a pre-etch silicide type characteristic.

[0022] In one embodiment, a preselected pre-etch silicide characteristic is a pre-etch silicide dimension characteristic. The preselected pre-etch silicide dimension characteristic may be, for instance, one or more of a preselected silicide volume, silicide spacing, silicide characteristic length, and silicide aspect ratio. A preselected silicide volume may be achieved by selection of appropriate metal(s) of the silicide(s). A preselected silicide spacing and/or silicide characteristic length and/or silicide aspect ratio may be achieved by controlling the silicon eutectic alloy manufacturing process. Examples of silicide characteristic lengths and silicide aspect ratios are illustrated in FIGS. 9a-9f.

[0023] As used herein, "silicide volume" refers to the volume of silicides in a silicon- silicide product. For silicon eutectic alloys, the silicide volume may be from, for example, 0.5 to 57 vol. % (prior to the contacting step).

[0024] As used herein, "silicide spacing" refers to the average characteristic spacing of the silicides of a eutectic silicon-silicide product. Silicide spacing may be from, for example, 0.1 to 50 microns in a silicon eutectic alloy body. Silicide spacing may be controlled by controlling the cooling rate during the silicon eutectic alloy production process. A higher cooling / solidification rate, in general, results in smaller (closer) silicide spacing and/or smaller silicide grain sizes.

[0025] In one embodiment, a preselected silicide characteristic is a silicide type characteristic. The predetermined silicide type characteristic may be, for instance, a predetermined type and/or amount of monosilicides, a predetermined type and/or amount of disilicides, and combinations thereof.

[0026] Referring now to FIG. 3, another embodiment of a method for producing selectively-etched silicon-silicide products having preselected characteristics is shown. In the illustrated embodiment, the method includes selecting one or more selectively-etched product characteristics (80), and then completing (84) the contacting (100), removing (not shown), and retaining (not shown) steps. Thus, selectively-etched silicon-silicide products having preselected characteristics may be recovered (200).

[0027] In one approach, a preselected selectively-etched characteristic is a post-etch silicide characteristic. In one embodiment, the post-etch silicide characteristic is a silicide exposure characteristic. The silicide exposure characteristic relates to the exposed amount of surface area amount of the silicide(s) in the final selectively-etched product. For example, the silicide exposure characteristic may be a preselected amount of exposed silicide(s) surface area in the final selectively-etched product. In one embodiment, the preselected silicide exposure characteristic relates to a "full etch" where all of the silicon is removed, thereby exposing nearly all the surface area of the silicide(s) of the silicon-silicide product. In another embodiment, the etch is a "light etch" where only a small portion of silicon is removed, thereby exposing a small portion of the surface area of the silicide(s). Accordingly, the contacting step (100) may be conducted to achieve the preselected silicide exposure characteristic (e.g., by controlling duration, concentration and/or temperature parameters of the contacting step, among others). In one embodiment, at least 5% of the surface area of at least one silicide is exposed after the etch. In another embodiment, at least 10% of the surface area of at least one silicide is exposed after the etch. In yet another embodiment, at least 20% of the surface area of at least one silicide is exposed after the etch. In another embodiment, at least 30% of the surface area of at least one silicide is exposed after the etch. In yet another embodiment, at least 40% of the surface area of at least one silicide is exposed after the etch. In another embodiment, at least 50% of the surface area of at least one silicide is exposed after the etch. In yet another embodiment, at least 60% of the surface area of at least one silicide is exposed after the etch. In another embodiment, at least 70% of the surface area of at least one silicide is exposed after the etch. In yet another embodiment, at least 80% of the surface area of at least one silicide is exposed after the etch. In another embodiment, at least 90% of the surface area of at least one silicide is exposed after the etch. Even higher amounts of surface area may be exposed.

[0028] As one example, and referring now to FIG. 4a, prior to the etching, a silicon- silicide product may be a monolithic body having silicon (10) and silicides (20). Due to the etching, and referring now to FIG. 4b, some of the silicon (10) is removed, thereby exposing at least some of the silicides (20).

[0029] In another embodiment, masking (or other suitable methods / apparatus) may be used during the contacting step to produce tailored products. For instance, a mask (40) may be used to cover at least a portion of the silicon during a contacting step (100). The mask (40) may be inert and/or impermeable to the etching fluid, such as a mask made of silica (Si0₂) or silicon nitride (e.g., for KOH and/or NaOH type caustic etchants), for instance.

[0030] In one aspect, and referring now to FIG. 5, a method may include depositing (300) a substance (e.g., a third phase) onto at least a portion of the selectively-etched product, thereby at least partially covering a surface of the silicon-silicide product with the substance. In one embodiment, the substance covers at least a portion of a silicide. In one embodiment, the substance covers at least a portion of the silicon. In one embodiment, the substance covers at least a portion of the silicon and at least one silicide. In one embodiment, the substance covers at least a portion of at least one silicide, but the substance is absent from the silicon. In one embodiment, the substance covers at least a portion of the silicon, but the substance is absent from the silicide(s).

[0031] In one embodiment, the substance covers at least 25% of the outer surface of the silicon-silicide product, which coverage may be relative to the silicon, the silicide(s), and combinations thereof. In one embodiment, the substance covers at least 50% of the outer surface of the silicon-silicide product, which coverage may be relative to the silicon, the silicide(s), and combinations thereof. In one embodiment, the substance covers at least 75% of the outer surface of the silicon-silicide product, which coverage may be relative to the silicon, the silicide(s), and combinations thereof. In one embodiment, the substance covers at least 90%) of the outer surface of the silicon-silicide product, which coverage may be relative to the silicon, the silicide(s), and combinations thereof. In one embodiment, the substance covers at least 95% of the outer surface of the silicon-silicide product, which coverage may be relative to the silicon, the silicide(s), and combinations thereof. In one embodiment, the substance covers substantially all of the outer surface of the silicon-silicide product, which coverage may be relative to the silicon, the silicide(s), and combinations thereof.

[0032] In one approach, the depositing step (300) comprising forming (310) a film. For instance, and with reference now to FIGS. 5 and 10a, due to the contacting (100), recovering (200) and depositing (300) steps, a functionalized, selectively-etched product (la) may be produced. As described above, the product (la) may include a first phase (10) comprising silicon, and a second phase (30). The second phase (30) is dispersed within the first phase (10), and the second phase (30) includes at least one silicide. At least one pore (20a) is dispersed within the first phase (10), and adjacent to a portion of the second phase (30). The at least one pore (20a) may comprise a terminal closed end, the terminal closed end being defined by an end (12) of the first phase (10). Due to the depositing step (300), the product (la) further includes a film (50) that at least partially covers a surface of the at least one pore (20a).

[0033] For instance, the film (50) may comprise a first portion (50a) located at partially on an end (12) of the second phase (10), which end (12) defines the terminal lower end of the pore (20a). The film 50 may comprise a second portion (50b) located at least partially on an inner sidewall of the second phase (30), which inner sidewall defines sides/sidewalls of the pore (20a). Thus, a functionalized, selectively-etched product (la) may be produced, which functionalization can be tailored based on the composition of the film (50) and/or the type of silicide of the second phase (30).

[0034] In the illustrated embodiment of FIG. 10a, the film (50) substantially coats all surfaces of the at least one pore (20a). In the illustrated embodiment of FIG. 10a, the film (50) also includes a third portion (50c) located on outer surfaces of the product (la). However, the film (50) may only include the first portion (50a) and/or the second portion (50b). Furthermore, the first portion (50a) may coat the entire end (12) or may only coat a portion of the end (12). The second portion (50b) may coat the entire inner sidewall or may only coat a portion of the inner sidewall.

[0035] The depositing step (300) may be completed one or more times to provide multiple film layers. For instance, and with reference now to FIG. 10b, a product (lb) may include a first film (50) and a second film (52) at least partially located on the first film. The first film (50) may comprise a first substance and the second film (52) may comprise a second substance. The first substance may be the same as or different than the second substance. In one embodiment, the first substance is a different material than the second substance. Any number of film layers can be used / deposited, and which films may be deposited onto one another and/or onto surface(s) of the first phase (10) and/or the second phase (30) of the product (lb).

[0036] Referring now to FIGS. 5 and 10c, in another approach, the depositing step (300) comprising forming (320) a mass within at least one pore of the selectively-etched product, thereby at least partially covering a surface of the at least one pore of the silicon-silicide product with the substance. As shown in FIG. 10c, the product (lc) may include a first phase (10) comprising silicon, and a second phase (30). The second phase (30) is dispersed within the first phase (10), and the second phase (30) includes at least one silicide. At least one pore (20a) is dispersed within the first phase (10). The at least one pore (20a) may comprise a terminal closed end located within the first phase (10), the terminal closed end being defined by an end (12) of the first phase (10). Due to the depositing step (300), the product (lc) further includes a mass (60) that at least partially covers a surface of the at least one pore (20a). The mass (60) may be in the form of a plug. For instance, and as illustrated, the mass (60) may cover an end (12) of the first phase (10). The mass (60) may also partially cover inner sidewalls of the second phase (30). In one embodiment, the mass (60) occupies at least 10% of the pore volume of the at least one pore (20a). In another embodiment, the mass (60) occupies at least 25% of the pore volume of the at least one pore (20a). In yet another embodiment, the mass (60) occupies at least 50%> of the pore volume of the at least one pore (20a). In another embodiment, the mass (60) occupies at least 75% of the pore volume of the at least one pore (20a). In yet another embodiment, the mass (60) occupies at least 95% of the pore volume of the at least one pore (20a). In another embodiment, the mass (60) occupies substantially the entire pore volume, occupying 99% or more of the pore volume of the at least one pore (20a).

[0037] The depositing step (300) may be completed one or more times to provide multiple mass layers. For instance, and with reference now to FIG. lOd, a product (Id) may include a multi-layer mass, which multi-layer mass includes a first mass (60) and a second mass (62) at least partially located on the first mass (60). The first mass (60) may comprise a first substance and the second mass (62) may comprise a second substance. The first substance may be the same as or different than the second substance. In one embodiment, the first substance is a different material than the second substance. Any number of mass layers can be used / deposited, and which mass layers may be deposited onto one another and/or surface of the first phase (10) and/or the second phase (30) of the product (Id).

[0038] In another approach (not illustrated), a deposit comprises both a film and a mass. In one embodiment, the film is deposited first, the mass is deposited second, and the mass is at least partially located on the film. In another embodiment, the mass is deposited first, the film is deposited second, and the film is at least partially located on the mass.

[0039] In another approach (not illustrated), a substance is deposited on at least a portion of an outer surface of the product, but the substance is not deposited into any pores. In this regard, masking and the like may be used to mask the pores during the depositing step.

[0040] In another approach (not illustrated), a first substance may be deposited into a first pore of the product, and a second substance may be deposited into a second pore of the product. The first pore may be free of the second substance. Likewise, the second pore may be free of the first substance. In this regard, masking and the like may be used to mask appropriate ones of the pores during the various depositing steps.

[0041] Referring now to FIG. 6, the depositing step (300) may comprise incorporating (350) a precursor into at least a portion of the at least one pore, and converting (360) the precursor into the substance. During the incorporating step (350), the precursor may be a fluid (351), such as a gas (352) and/or a liquid (353), or the precursor may be a solid (354). The converting step (360) generally converts the precursor into a solid (362). Thus, the substance is usually of a solid form.

[0042] In one embodiment, the depositing step (300) comprises one or more of chemical vapor deposition (CVD), chemical vapor infiltration, spaying, immersion, sputtering, electrochemical deposition, electroless deposition, melt infiltration, spin coating, and evaporation, among others. When used, the CVD process may be one or more of atmospheric pressure CVD (APCVD), low-pressure CVD (LPCVD), ultrahigh vacuum CVD (UHVCVD), aerosol assisted CVD (AACVD), direct liquid injection CVD, microwave plasma-assisted CVD (MPCVD), plasma-enhanced CVD (PECVD), remote plasma-enhanced CVD (RPECVD), atomic-layer CVD (ALCVD), combustion CVD (CCVD), hot-wire CVD (HWCVD) or hot filament CVD (HFCVD), hybrid physical-chemical vapor deposition (HPCVD), metalorganic chemical vapor deposition (MOCVD), rapid thermal CVD, vapor- phase epitaxy (VPE) and photo-initiated CVD (PICVD).

[0043] The substance may be any material useful on a surface of the selectively-etched product. In one embodiment, the substance is electrically conductive. For instance, the substance may include metal(s) (e.g., Al, Cu, Ag, Au, W and combinations thereof), conductive metal oxide(s) (e.g. InO), conductive nitride(s) (e.g., tungsten nitride, titanium nitride), conductive silicide(s) (e.g., titanium disilicide, titanium silicide, tantalum disilicide), conductive polymer(s) (e.g., polyacetylene, polythiophene), graphite, and combinations thereof.

[0044] In another embodiment, the substance is a dielectric (i.e., an insulator). For instance, the substance may include ceramic(s) (e.g., insulative oxide(s) (e.g., alumina, silica), titanate(s), apatite(s), carbide(s), boride(s), nitride(s) (e.g., silicon nitride), and combinations thereof), polymer(s) (e.g., PTFE, PET), organosilicon compounds (e.g. PDMS), carbon-based material(s) (e.g., diamond / diamond-like carbon, organics), and combinations thereof. [0045] In another embodiment, the substance is semiconductive. For instance, the substance may include silicon, germanium, phosphide(s), semiconductive silicide(s) (e.g., chromium disilicide, iron disilicide, ruthenium silicide and combinations thereof), silicon carbide, and combinations thereof.

[0046] Other properties may be tailored. For example, the material may have magnetic, optical, and/or structural (e.g., scratch resistance) properties. Further, multiple different materials can be used as the substance. For instance, any combination of the electrical conductors, dielectrics, and semiconductors described above may be used.

[0047] In one embodiment, the substance is a caustic-resistance substance, such as silica and/or silicon nitride and/or silicon carbide. Products having a caustic-resistance substance as a coating may facilitate use of the product in a caustic environment. Such products may also realize improved wear properties. The substance may also be resistant to swelling (e.g., hybrid composites (e.g., organic-inorganic, PDMS/CrSi₂), due to the rigid ceramic (CrSi₂) framework). Moreover, such composites may have improved mechanical properties.

[0048] In one embodiment, the methods described herein are utilized in combination with those disclosed in commonly owned U.S. Provisional Patent Application No. 61/948,267, entitled "METHODS OF REMOVING SILICIDES FROM SILICON COMPOSITIONS, AND PRODUCTS MADE BY SUCH METHODS" to selectively etch both silicon and silicides, thereby providing a selectively etched silicon-silicide product, which has had both at least some silicon and at least some silicides purposefully etched.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 is a flow chart illustrating one embodiment of a method for producing selectively-etched silicon-silicide products.

[0050] FIG. 2 is a flow chart illustrating another embodiment of a method for producing selectively-etched silicon-silicide products.

[0051] FIG. 3 is a flow chart illustrating another embodiment of a method for producing selectively-etched silicon-silicide products.

[0052] FIG. 4a is a perspective, schematic view of one embodiment of a partially-etched product.

[0053] FIG. 4b is a cross-sectional, schematic view of an etched version of the product of FIG. 4a. [0054] FIG. 5 is a flow chart illustrating one embodiment of a method for producing selectively-etched silicon- silicide products having a substance deposited in at least one pore.

[0055] FIG. 6 is a flow chart illustrating a related embodiment of a method for producing selectively-etched silicon- silicide products having a substance deposited in at least one pore.

[0056] FIGS. 7a-7b are SEM photos of selectively etched products from Example 1.

[0057] FIGS. 8a-8b are SEM photos of selectively etched products from Example 2.

[0058] FIGS. 9a-9f illustrate various examples of silicide characteristic lengths and silicide aspect ratios.

[0059] FIG. 10a is a schematic, close-up, cut-away view of a pore of a silicon-silicide product incorporating a deposit in the form of a film.

[0060] FIG. 10b is a schematic, close-up, cut-away view of a pore of a silicon-silicide product incorporating a deposit in the form of a multi-layer film.

[0061] FIG. 10c is a schematic, close-up, cut-away view of a pore of a silicon-silicide product incorporating a deposit in the form of a mass.

[0062] FIG. lOd is a schematic, close-up, cut-away view of a pore of a silicon-silicide product incorporating a deposit in the form of a multi-layer mass.

DETAILED DESCRIPTION

Example 1 - Selective etch (removal) of silicon in a directionally solidified binary Si-Cr eutectic alloy product, followed by deposition of SiC

[0063] A binary Si-Cr eutectic alloy product was made by directional solidification in the form of Czochralski-growth processing. After casting, the Si-Cr eutectic alloy product had a first eutectic phase comprised of polysilicon (Si) and a second eutectic phase comprised of CrSi₂. The second eutectic phase was in the form of rods having an average rod diameter of about 2.0 micrometers, an average inter-rod spacing of about 4.0 microns, and occupying about 32 vol. % of the binary Si-Cr eutectic alloy product. From this product, several test coupons were obtained. The coupons size was 20 mm in diameter x 3 mm thickness.

[0064] Next, the test coupons were immersed in an aqueous solution having about 30 wt. % KOH at about 80°C to partially etch the silicon. The etch depth was controlled by immersion duration. The test coupons were then rinsed in deionized water and methanol and then conventionally dried.

[0065] The etched coupons were then submerged in a pre-ceramic polymer solution of allylhydridopolycarbosilane (AHPCS) for several hours at room temperature, after which a vacuum is created so as to facilitate infiltration of the pores with the AHPCS solution. The allylhydridopolycarbosilane (SMP-10) was purchased from Starfire LLC. The coupons were then removed from the AHPCS solution, after which the coupons were then pyrolyzed in a furnace under an argon atmosphere by heating to 400°C (holding for 1 hour), and then to 950°C (holding for 1-2 hours), thereby producing SiC (silicon carbide). In order to completely fill replace the etched silicon, several of the above infiltration and pyrolysis (PIP) cycles were executed. FIGS. 7a- 7b are SEMs showing a top view (surface view) and a cross- section view, respectively, of the materials. The materials generally include a base of silicon (first phase), various chromium disilicide rods (second phase) and SiC (third phase) covering various surface of the silicon and the chromium disilicide rods. EDS analysis confirmed the presence of SiC. Fewer cycles could be used to only partially cover the silicon and/or silicide materials.

Example 2 - Selective etch (removal) of silicon in a directionally solidified binary Si-Cr eutectic alloy product, followed by deposition of Si_YN_y/SiC

[0066] A binary Si-Cr eutectic alloy product was made by directional solidification in the form of Czochralski-growth processing, and in a manner similar to that of Example 1. Several coupons of the product were obtained. Next, the test coupons (30mm x 20mm x 3mm) were immersed in an aqueous solution having about 20 wt. % KOH at about 90°C to partially etch the silicon. The etch depth was controlled by immersion duration. The test coupons were then rinsed in deionized water and methanol and then conventionally dried.

[0067] Selective complete or partial etching of Si phase in Si-CrSi₂ eutectic composites to form porous chromium disilicide surface or freestanding disilicide monoliths and subsequent infiltration and pyrolysis with polysilazane pre-ceramic polymer to make Si_xN_y/CrSi₂ materials on the surface of the Si-CrSi₂ eutectic alloy in the case of partial etching of the silicon phase or freestanding SiC/CrSi₂ materials in the case of complete leaching of the Si phase.

[0068] The porous monoliths were then vacuum infiltrated with Ceraset Polysilazane 20 (PSZ) obtained from KiON Technologies, after which the samples were pyrolyzed in a nitrogen atmosphere at 1000°C for 1 hour. Several cycles were completed. After three cycles, approximately 44% weight gain was reached. FIGS. 8a-8b are SEM cross-section micrographs of the final product, at different resolutions, likely showing silicon oxynitride/silicon carbide material in places previously occupied by silicon, based on the composition chemistry. Example 3 - Selective etch (removal) of silicon in a directionally solidified binary Si-Cr eutectic alloy product, followed by deposition of hydroxyapatite

[0069] A binary Si-Cr eutectic alloy product was made by directional solidification in the form of vacuum melt processing, and in a manner similar to that of Example 1. Several coupons of the product were obtained. Next, the test coupons (30mm x 20mm x 3mm) were immersed in an aqueous solution having about 20 wt. % KOH at about 90°C to partially etch the silicon (to an etch depth of about 50 microns). The etch depth was controlled by immersion duration. The test coupons were then rinsed in deionized water and methanol and then conventionally dried.

[0070] The pores of the etched test coupons were then infiltrated with 20 wt. % hydroxyapatite nanoparticles (< 200 nm, Aldrich 677418) suspended in a polycarbosilane solution (SMP-10). The test coupons were then calcined in air in order to convert the infiltrated material into a silica matrix with hydroxyapatite particles. After conversion, the test coupons included surface films of silica that contained calcium and phosphorous.

Example 4 - Selective etch (removal) of silicon in a directionally solidified binary Si-Cr eutectic alloy product, followed by deposition of polydimethylsiloxane

[0071] A binary Si-Cr eutectic alloy product was made by directional solidification in the form of vacuum melt processing, and in a manner similar to that of Example 1. Several wafer of the product were obtained. Next, the test wafers (15 mm diameter x 1000 μιη thick) were immersed in an aqueous solution having about 30 wt. % KOH at about 90°C to etch (partially or fully etch) the silicon (to an etch depth of about 50 -1000 microns). The etch depth was controlled by immersion duration. The test wafers were then rinsed in deionized water and methanol and then conventionally dried.

[0072] The pores of the etched test wafers were then vacuum infiltrated with Dow Corning thermosetting elastomer, Slygard 184 (poly(dimethyl)siloxane,PDMS) and then cured at about 145°C for about 30 minutes to form organic-inorganic composite materials (PDMS/CrSi₂) on the surface of the Si-CrSi₂ eutectic alloy in the case of partial etching of the silicon phase, or freestanding PDMS/CrSi₂ hybrid materials in the case of complete leaching of the Si phase. After infiltration and curing, the test wafers included surface films that contained silicon, carbon, and oxygen.

[0073] While various embodiments of the present disclosure have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present disclosure.

Claims

CLAIMS What is claimed is:

1. A method comprising:

(a) contacting surfaces of a silicon-silicide product with a caustic etchant;

(i) wherein the silicon-silicide product comprises a first phase comprising silicon and a second phase comprising at least one silicide;

(ii) wherein, during the contacting, the caustic etchant contacts both (A) at least some of the first phase comprising the silicon and (B) at least some of the second phase comprising the at least one silicide;

(b) concomitant to the contacting step (a), removing at least some of the silicon of the first phase from the silicon-silicide product via the caustic etchant, wherein the average amount of silicon removed during the removing step is a silicon removal rate (Si-R );

(c) concomitant to the contacting step (b), retaining a majority of the at least one silicide of the second phase of the silicon-silicide product, wherein the average rate of silicide removal during the retaining step is a silicide removal rate (MSi_x-RR);

wherein the ratio of the silicon removal rate to the silicide removal rate is at least 5.0 (Si-RR / MSi_x-RR > 5.0);

wherein, due to steps (a)-(c) the silicon-silicide product contains pores;

(d) depositing a substance into at least one pore of the silicon-silicide product, thereby at least partially covering a surface of the at least one pore of the silicon-silicide product with the substance.

2. The method of claim 1, wherein the silicon-silicide product is a silicon-eutectic alloy, wherein the second phase comprising the at least one silicide is dispersed within the first phase, wherein the first phase comprises silicon eutectic.

3. The method of claim 2, wherein, prior to the contacting step, the silicides are in the form of lamella, rods, globes, acicular, disks, flakes, dendrites, interpenetrated, Chinese script and combinations thereof.

4. The method of claim 1, wherein the silicides are chromium silicides of the formula Cr_aSi_b, wherein b is 1 or 2.

5. The method of claim 1, wherein the depositing comprises:

depositing a precursor into at least a portion of the at least one pore; and

converting the precursor into the substance.

6. The method of claim 5, wherein, after the depositing, the substance is in the form of a film, and wherein the film is located on a surface of the at least one pore.

7. The method of claim 6, wherein, after the depositing step, the film substantially coats all surfaces of the at least one pore.

8. The method of claim 1, wherein, after the depositing, the substance in the form of a mass.

9. The method of claim 8, wherein the at least one pore comprises a pore volume, and wherein, after the depositing step, the mass occupies at least 10% of the pore volume of the at least one pore.

10. The method of claim 9, wherein the mass occupies at least 25% of the pore volume of the at least one pore.

11. The method of claim 9, wherein the mass occupies at least 50% of the pore volume of the at least one pore.

12. The method of claim 9, wherein the mass occupies at least 75% of the pore volume of the at least one pore.

13. The method of claim 9, wherein the mass occupies at least 95% of the pore volume of the at least one pore.

14. The method of claim 9, wherein the mass occupies at least 99% of the pore volume of the at least one pore.

15. The method of claim 1, wherein, after the depositing, the substance at least partially covers outer surfaces of the silicon-silicide product.

16. The method of claim 1, wherein the depositing is a first depositing, wherein the substance is a first substance, and wherein the method comprises:

after the first depositing, second depositing a second substance into the at least one pore of the silicon-silicide product, thereby at least partially covering at least one (a) a surface of the at least one pore of the silicon-silicide product, and (b) the first substance, with the second substance.

17. The method of claim 16, wherein the first substance is a different material than the second substance.

18. The method of claim 16, wherein the first substance is the same material as the second substance.

19. The method of claim 16, wherein the first substance is in the form of a film or a mass, and wherein the second substance is in the form of a film or a mass, wherein the second substance is at least partially located on the first substance.

20. The method of claim 19, wherein the first substance is in the form of a first mass, and wherein the second substance is in the form of a second mass, wherein the second mass is at least partially located on the first mass.

21. The method of claim 19, wherein the first substance is in the form of a first film, and wherein the second substance is in the form of a second film, wherein the second film is at least partially located on the first film.

22. The method of claim 19, wherein one of the first substance and the second substance is in the form of a mass, and wherein the other of the first substance the second substance is in the form of a film.

23. The method of claim 1, wherein the depositing is a first depositing, wherein the substance is a first substance, wherein the at least one pore comprises at least a first pore, and wherein the method comprises:

after the first depositing, second depositing a second substance into a second pore of the silicon-silicide product, thereby at least partially covering a surface of the second pore of the silicon-silicide product with the second substance, wherein the second pore is a different pore than the first pore, and wherein the second pore is free of the first substance.

24. A product comprising:

a first phase comprising silicon;

a plurality of etched pores dispersed within the first phase;

wherein the plurality of etched pores comprise a proximal end located at a surface of the product;

wherein the plurality of etched pores comprise a terminal closed end located within the first phase;

a second phase dispersed within the silicon, wherein the second phase comprises a silicide, and wherein at least some of the second phase is adjacent at least some of the plurality of etched pores;

a third phase located within at least some of the plurality of etched pores, wherein the third phase is a different material than the first phase and second phase.

25. The product of claim 24, wherein the third phase is in the form of a film, and wherein the film is located on surfaces of at least some of the plurality of etched pores.

26. The product of claim 24, wherein the third phase is in the form of a film, and wherein the film substantially coats all surfaces of at least one pore of the plurality of etched pores.

27. The product of claim 24, wherein the third phase is in the form of a mass, and wherein the mass occupies at least 10% of a volume of at least one pore of the plurality of etched pores.

28. The product of claim 27, wherein the mass occupies at least 25% of the volume of at least one pore of the plurality of etched pores.

29. The product of claim 27, wherein the mass occupies at least 50% of the volume of at least one pore of the plurality of etched pores.

30. The product of claim 27, wherein the mass occupies at least 75% of the volume of at least one pore of the plurality of etched pores.

31. The product of claim 27, wherein the mass occupies at least 95% of the volume of at least one pore of the plurality of etched pores.

32. The product of claim 27, wherein the mass occupies at least 99% of the volume of at least one pore of the plurality of etched pores.

33. The product of claim 24, wherein the third phase comprises carbon.

34. The product of claim 24, wherein the third phase consists essentially of carbon.

35. The product of claim 24, wherein the third phase comprises silicon carbide, silicon nitride or mixtures thereof.

36. The product of claim 24, wherein the third phase consists essentially of silicon carbide, silicon nitride, or mixtures thereof.

37. The product of claim 24, wherein the third phase comprises an electrically conductive material.

38. The product of claim 37, wherein the electrically conductive material is a material selected from the group consisting of metals, conductive metal oxides, conductive nitrides, conductive silicides, conductive polymers, graphite, and combinations thereof.

39. The product of claim 24, wherein the third phase comprises a dielectric.

40. The product of claim 39, wherein the dielectric is selected from the group consisting of ceramics, titanates, apatites, carbides, borides, nitrides, polymers, carbon-based materials, and combinations thereof.

41. The product of claim 24, wherein the third phase comprises a semiconductor.

42. The product of claim 41, wherein the semiconductor is a material selected from the group consisting of silicon, germanium, phosphides, semiconductive silicides, silicon carbide, and combinations thereof.