ENGRAVING PROCESS

Abstract

According to one embodiment, the invention relates to an etching process. The etching process comprises: the formation of a layer (4) containing a first metal catalyst on a surface (1a) containing a semiconductor; a first etch using the first metal catalyst; the formation of a layer (8) containing a second metal catalyst having a higher diffusion coefficient than that of the first metal catalyst on the layer (4) containing the first metal catalyst; and a second etch using the second metal catalyst. Figure 1

Description

Title of the invention: ENGRAVING PROCESS

[0001] DOMAIN

[0002] The embodiments described herein generally relate to an etching process.

[0003] CONTEXT

[0004] Etching is known as a method for forming a hole or groove in a substrate such as a semiconductor wafer. Examples of etching include a metal-assisted etching method (also called metal-assisted chemical etching (MacEtch)). The metal-assisted etching (MacEtch) method is, for example, an etching method using a noble metal or the like as a catalyst. In the case where a trench having a high aspect ratio is processed in a substrate containing Si by this method, a processing defect such as porous Si appears near an upper end portion of the sidewall defining the trench. Brief description of the drawings

[0005] [Fig.l] [Fig.l] is a flowchart illustrating a flow of steps included in an etching method according to one embodiment.

[0006] [Fig.2] [Fig.2] is a sectional view schematically illustrating a structure obtained by the formation of a first metal catalyst in the method of the embodiment.

[0007] [Fig.3] [Fig.3] is a sectional view schematically illustrating a structure obtained by a first etching in the method of the embodiment.

[0008] [Fig.4] [Fig.4] is a sectional view schematically illustrating a structure obtained by the formation of a second metal catalyst in the method of the embodiment.

[0009] [Fig.5] [Fig.5] is a sectional view schematically illustrating a structure obtained by a second etching in the method of the embodiment.

[0010] [Fig.6] [Fig.6] is a sectional view schematically illustrating a structure obtained by the formation of a first layer of Au catalyst in a method of a comparative example.

[0011] [Fig.7] [Fig.7] is a sectional view schematically illustrating a structure obtained by etching using a first Au catalyst in the method of the comparative example.

[0012] [Fig.8] [Fig.8] is a sectional view schematically illustrating a structure obtained by etching using a second Au catalyst in the process of the comparative example.

[0013] [Fig.9] [Fig.9] is a sectional view schematically illustrating a structure obtained by the formation of a second layer of Au catalyst in the method of the comparative example.

[0014] [Fig. 10] [Fig. 10] is an electron micrograph illustrating the region of an upper end of a trench treated by the method of the comparative example. DETAILED DESCRIPTION

[0015] Generally, according to one embodiment, an etching method is described. The etching method comprises: forming a layer containing a first metal catalyst at a surface containing a semiconductor; a first etching using the first metal catalyst; forming a layer containing a second metal catalyst having a higher diffusion coefficient than that of the first metal catalyst at the layer containing the first metal catalyst; and a second etching using the second metal catalyst.

[0016] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Components which perform the same or similar functions are designated by the same reference numerals in the drawings, and repetitive descriptions will be omitted.

[0017] [Fig. 1] is a flowchart illustrating a flow of steps in an etching method according to one embodiment. As described in [Fig. 1], the etching method of the embodiment comprises forming a first metal catalyst (step S1), a first etching (step S2), forming a second metal catalyst (step S3), and a second etching (step S4). Hereinafter, the respective steps will be described with reference to Figures 2 to 5. Each of the figures is illustrated assuming that a surface to be etched is parallel to a plane defined by an x-axis direction and a y-axis direction. The surface to be treated may be, for example, a main surface of a substrate. It is assumed that the etching process progresses in a 100° direction along a z-axis direction from the surface to be treated. The x-axis, the y-axis, and the z-axis intersect perpendicularly.

[0018] (Step SI)

[0019] A first metal catalyst is formed at a surface containing a semiconductor.

[0020] The semiconductor is for example silicon (Si); germanium (Ge); a semiconductor formed from a compound containing a group III element and a group V element, such as gallium arsenide (GaAs) or gallium nitride (GaN); and silicon carbide (SiC). In one example, the surface containing a semiconductor is a surface containing silicon. The term "group" used here is a "group" in the abbreviated periodic table.

[0021] The surface containing a semiconductor may be, for example, a semiconductor substrate. The semiconductor substrate is, for example, a semiconductor wafer. The semiconductor wafer may be doped with an impurity and may be formed with a semiconductor element such as a transistor or a diode. Furthermore, a major surface of the semiconductor wafer may be parallel to any crystal plane of the semiconductor. A usable semiconductor wafer is, for example, a silicon wafer whose major surface is a (100) plane or a silicon wafer whose major surface is a (110) plane.

[0022] An example of a structure obtained in step S1 is illustrated in [Fig. 2]. A mask layer 2 is provided on at least a portion of a surface of a substrate 1 containing a semiconductor, for example, a main surface 1a of the substrate 1. The main surface 1a of the substrate 1 is, for example, a surface parallel to a plane defined by an x-axis direction and a y-axis direction. The semiconductor comprises, for example, Si. The substrate 1 may have any shape. Presently, as an example, the substrate 1 is a single-crystal silicon wafer. A plane orientation of the single-crystal silicon wafer is not particularly limited. In [Fig. 2], a silicon wafer of which the main surface 1a is a (100) plane is used as the substrate 1. As the substrate 1, a silicon wafer of which the main surface is a (110) plane may also be used.

[0023] The mask layer 2 has one or more openings 3. The shape of the opening 3 is not particularly limited. The opening 3 has, for example, a groove shape extending in the y-axis direction and penetrating in the z-axis direction. In addition, the number of openings 3 is not limited and may be one or more. The mask layer 2 may prevent contact of a metal catalyst with a region of the surface of the substrate 1 covered by the mask layer 2. The mask layer 2 may be, for example, a resist.

[0024] Examples of the material of the mask layer 2 include organic materials such as a polyimide, a fluororesin, a phenolic resin, an acrylic resin and a novolac resin, and inorganic materials such as silicon oxide and silicon nitride.

[0025] The mask layer 2 may be formed, for example, by an existing semiconductor method. The mask layer 2 made of an organic material may be formed, for example, by photolithography. The mask layer 2 made of an inorganic material may be formed, for example, by forming a layer of inorganic material by a vapor deposition method, forming a mask by photolithography and structuring of the inorganic material layer by etching.

[0026] Alternatively, the mask layer 2 made of an inorganic material may be formed by oxidation or nitration of the surface region of the substrate 1, formation of a mask by photolithography and structuring of an oxide or nitride layer by etching. The mask layer 2 may be omitted.

[0027] A layer 4 containing the first metal catalyst (hereinafter referred to as the first metal catalyst layer 4) is disposed on a portion of the main surface 1a of the substrate 1 in the position of the opening 3 of the mask layer 2. In other words, the first metal catalyst layer 4 is disposed on the portion of the main surface 1a of the substrate 1 not covered by the mask layer 2. After the mask layer 2 is disposed on the main surface 1a of the substrate 1, the first metal catalyst layer 4 may be formed on a portion of the main surface 1a positioned in the opening 3 of the mask layer 2, for example, by an electroless plating method or a sputtering method.

[0028] The first metal catalyst layer 4 contains, for example, first metal catalyst particles 4a. As an example of the first metal catalyst layer 4 containing the first metal catalyst particles 4a, a layer structure formed by deposition of the first metal catalyst particles 4a may be indicated. The first metal catalyst layer 4 is not limited to those containing the first metal catalyst particles 4a. For example, the first metal catalyst layer 4 may comprise a first metal catalyst formed in the form of a film. In this case, the first metal catalyst layer 4 may be formed, for example, by a sputtering method.

[0029] The first metal catalyst layer 4 containing the first metal catalyst particles 4a may be formed, for example, by displacement deposition, which is an example of electroless deposition. A displacement deposition solution is, for example, a mixed solution of a salt of the first metal catalyst and hydrofluoric acid. The hydrofluoric acid can remove a native oxide film on the surface of the substrate. By adjusting a concentration of a salt of the first metal catalyst or a concentration of hydrofluoric acid in the displacement deposition solution, a size of the first metal catalyst particles and a density of the first metal catalyst layer can be adjusted within predetermined ranges.For example, if the concentration of the first metal catalyst salt or the concentration of hydrofluoric acid is decreased, first metal catalyst particles having a nanometer size can . be formed, and a catalyst layer in which the first metal catalyst particles are distributed at a high number density can be obtained. In addition, if the concentration of the first metal catalyst salt or the concentration of hydrofluoric acid is increased, the first metal catalyst particles are bound, so that a catalyst layer in which the large first metal catalyst particles are distributed at a high number density can be obtained.

[0030] The first metal catalyst has a lower diffusion coefficient than a second metal catalyst. Therefore, the first metal catalyst is less likely to diffuse into the substrate 1 than the second metal catalyst. Therefore, it is possible to suppress the diffusion of the first metal catalyst into the substrate 1, thereby suppressing the generation of a metal catalyst diffusion layer 5 in a substrate portion located near the first metal catalyst layer 4.

[0031] As the diffusion coefficient, a diffusion coefficient in a semiconductor component (e.g., Si) constituting the substrate can be used. The diffusion coefficient can be calculated by means of an equation of Fick's second law. An example of a method for calculating the diffusion coefficient is described in Proposai of a New Diffusion Equation Related to Solid State Reaction by Goro Yamaguchi et al., Journal of the Ceramic Association, Japan 78 [9] 1970, pages 293-298.

[0032] The first metal catalyst may contain at least one selected from the group consisting of Ag, Pt and Pd. A preferred first metal catalyst is at least one of Pt and Pd. According to one example, -the diffusion coefficient of Ag in Si is 3.8 x 10-13 (m2 / s) or more and 4.6 x 10-9 (m2 / s) or less at 1400 K. According to one example, the diffusion coefficient of Pt in Si is 7.7 x 10-15 (m2 / s) or more and 1.8 x 10-10 (m2 / s) or less at 1400 K. According to one example, the diffusion coefficient of Pd in ​​Si is 4.8 x 10-9 (m2 / s) at 1400 K. For the diffusion coefficient of each of the elements, reference is made to the diffusion database (Kakusan) DICE of the National Institute for Materials Science (nims.go.). A diffusion coefficient value may vary depending on the conditions of a Si wafer (e.g., resistivity, difference between n-type and p-type, crystal orientation, and the like), and thus may have a certain range.The resistivity of the Si wafer, as an example of the substrate, is 1 to 5 Q-cm as an example. In addition, the first etching is carried out, for example, at a temperature close to normal. In this case, as the diffusion coefficient of Ag in Si, 3.8 x 10-13 (m2 / s) at 1400 K can be used. In addition, as the diffusion coefficient of Pt in Si, 7.7 x 10-15 (m2 / s) at 1400 K can be used.

[0033] (Step S2)

[0034] In the first etching, the etching is performed by means of the first metal catalyst. The etching is performed, for example, by a metal-assisted etching method (also called metal-assisted chemical etching (MacEtch)). According to the metal-assisted etching using the first metal catalyst, the etching occurs toward a lower side or directly below the first metal catalyst, and a recess having a depth in the z-axis direction may be formed.

[0035] An example of step S2 is described below with reference to [Fig.3].

[0036] The substrate 1 provided with the first metal catalyst is etched with an etchant. For example, the substrate 1 is immersed in the liquid etchant to bring the liquid etchant into contact with the substrate 1. The details of the etchant (hereinafter referred to as the first etchant) are described below.

[0037] The first etchant contains an oxidant and hydrogen fluoride (hydrofluoric acid). A specific example of the first etchant is an aqueous solution containing an oxidant and hydrogen fluoride.

[0038] The oxidant may be selected from, for example, hydrogen peroxide, nitric acid, AgNO3, KAuC14, HAuC14, K2PtC16, H2PtC16, Fe(NO3)3, Ni(NO3)2, Mg(NO3)2, Na2S2O8, K2S2O8, KMnO4 and K2Cr2O7. Hydrogen peroxide is preferred as the oxidant because it does not produce a harmful by-product.

[0039] A concentration of hydrogen fluoride (hydrofluoric acid) in the first etchant may be 3.5 mol / l or more and 4.5 mol / l or less. A concentration of hydrogen peroxide in the first etchant may be 0.3 mol / l or more and 0.8 mol / l or less. At least one of the concentration of hydrogen fluoride (hydrofluoric acid) or the concentration of hydrogen peroxide is adjusted within the above range, so that the speed of the first etching can be slowed down. Therefore, it is easy to obtain a recess shape reflecting the distribution of the first metal catalyst. For example, etching hardly occurs in a portion where the first metal catalyst is little present or not present and thus, a needle-shaped protrusion can be partially provided at an inner surface of the recess.The concentration of hydrogen fluoride (hydrofluoric acid) and the concentration of hydrogen peroxide are adjusted within the above ranges, so that it is easier to partially arrange the needle-like protrusion at the inner surface of the recess.

[0040] The first etchant may further contain a buffer. The buffer contains, for example, at least one of ammonium fluoride or ammonia. According to a For example, the buffer is ammonium fluoride. In another example, the buffer is a mixture of ammonium fluoride and ammonia.

[0041] The first etching agent may further contain any other component such as water.

[0042] As described above, according to MacEtch using the first metal catalyst, the material of the substrate 1, here silicon, is oxidized only in a region of the substrate 1 close to the first metal catalyst particles 4a. The resulting oxide is dissolved and removed by hydrofluoric acid. Therefore, only the portion close to the first metal catalyst particles 4a is selectively etched.

[0043] The layer 4 containing the first metal catalyst particles 4a moves toward the other main surface (hereinafter referred to as the second surface) of the substrate 1 during the progress of the etching, where an etching similar to that above is performed. Accordingly, as illustrated in [Fig. 3], the etching occurs in a direction perpendicular to the main surface 1a (first surface) from the main surface 1a (first surface) toward the second surface, so that a recess 6 is formed.

[0044] However, since the layer 4 containing the first metal catalyst particles 4a has gaps between some of the first metal catalyst particles 4a, etching practically does not occur at the positions corresponding to these gaps. Accordingly, as illustrated in [Fig. 3], needle-shaped projections 7 each extending in a direction intersecting the main surface 1a (first surface), for example, a depth direction of the recess 6 along the z-axis direction are generated as etching residues on the inner surface of a bottom portion of the recess 6. It should be noted that the needle-shaped projections 7 may not be provided. In this case, the first metal catalyst layer 4 may be formed by a sputtering method.

[0045] In the case where the recess 6 is formed by the first etching, the first metal catalyst remains near an opening end of the recess 6. The remaining first metal catalyst is practically not diffused into the substrate portion near the opening end of the recess 6, so that the generation of the metal catalyst diffusion layer 5 can be suppressed.

[0046] As described above, a substrate having a surface containing a semiconductor and provided with a recess on the surface is obtained.

[0047] The substrate after the first etching is separated from the first etchant, for example by pulling it upwards from the first etchant. Then, the substrate can be washed with water.

[0048] In [Fig. 3], a method of forming the needle-shaped projections 7 is illustrated, but the projections 7 may have another shape. For example, the projections 7 each have a flat plate shape and may be arranged in the thickness direction so as to be separated from each other.

[0049] (Step S3)

[0050] A layer containing a second metal catalyst having a higher diffusion coefficient than that of the first metal catalyst (hereinafter referred to as the second metal catalyst layer) is formed at a layer containing the first metal catalyst (hereinafter referred to as the first metal catalyst layer.

[0051] The second metal catalyst layer may be deposited (e.g., precipitated) over the entire first metal catalyst layer, or may be deposited (e.g., precipitated) over a portion of the first metal catalyst layer. Further, the second metal catalyst layer is preferably deposited over the first metal catalyst layer, but may be formed directly over a portion of the semiconductor-containing surface.

[0052] The layer containing the second metal catalyst is formed, for example, by an autocatalytic deposition process or a cathodic sputtering process.

[0053] The second metal catalyst has a higher diffusion coefficient than the first metal catalyst. As the diffusion coefficient, a diffusion coefficient in a semiconductor component (e.g., Si) constituting the substrate may be used, similarly to the first metal catalyst. As a method for calculating the diffusion coefficient, a method similar to that described for the first metal catalyst may be used.

[0054] The second metal catalyst may contain Au. In addition, the second etching is carried out, for example, at a temperature close to normal. According to one example, the diffusion coefficient of Au in Si is 3.0 x 10-12 (m2 / s) or more and 2.0 x 10-7 (m2 / s) or less at 1400 K. For this value, reference is made to the diffusion database (Kakusan) DICE of the National Institute for Materials Science (nhns.go.). For example, in the case where a Si wafer having a resistivity of 1 to 5 Ω-cm is used as a substrate, 3.0 x 10-12 (m2 / s) at 1400 K can be used as the diffusion coefficient of Au in Si.

[0055] An example in which the second metal catalyst is formed by displacement deposition as an example of electroless deposition is described below with reference to [Fig. 4]. The recess 6 having a depth in the z-axis direction is formed in the substrate 1 after the first etching. The first metal catalyst layer 4 containing the first metal catalyst particles 4a is present on a lower inner surface and a side wall of the recess 6. In the first metal catalyst layer 4, gaps are present between some of the first metal catalyst particles 4a. One or more (in the case of [Fig. 4], a plurality of needle-shaped protrusions 7 are formed at locations corresponding to the gaps between the first metal catalyst particles 4a at the lower inner surface of the recess 6. In the case where the second metal catalyst is formed by displacement deposition, displacement deposition occurs almost completely since the protrusions 7 have a needle shape. Therefore, in correspondence with the shape of the protrusions 7, the second metal catalyst can be precipitated in a particulate form extending in a direction intersecting the main surface (first surface).That is, this displacement deposition produces a second metal catalyst layer 8 containing second metal catalyst particles 8a having a shape extending in the depth direction along the z-axis direction of the recess 6. The second metal catalyst layer 8 further contains granular second metal catalyst particles 8b. The second metal catalyst layer 8 is in contact with the protrusions 7. In addition, since gaps are present between the first metal catalyst particles 4a of the first metal catalyst layer 4, a portion of the second metal catalyst layer 8 can be in direct contact with the inner surface of the recess 6.As a result, the second metal catalyst of the second metal catalyst layer 8 diffuses into the substrate 1 through the inner surface of the recess 6 to increase the diffusion layer 5 of the metal catalyst. On the other hand, the first metal catalyst layer 4 provided on the side wall of the recess 6 inhibits the formation of the second metal catalyst layer 8 on the side wall of the recess 6. Therefore, it is possible to suppress the adhesion of the second metal catalyst layer 8 to the side wall defining the recess 6, particularly near the upper end of the side wall.

[0056] The displacement deposition solution used in the displacement deposition is, for example, a mixed solution of hydrofluoric acid and one of an aqueous tetrachloroauric (III) acid solution, an aqueous gold sulfite solution, or an aqueous potassium cyanide-gold (I) solution. Hydrofluoric acid can remove a native oxide film on the surface of the substrate.

[0057] All of the second metal catalyst particles may have a shape extending in the direction of the depth of the recess, but the second metal catalyst particles may include particles having this shape and particles having a granular shape. The second metal catalyst layer may contain a second metal catalyst in film form. In In this case, the second layer of metal catalyst can be formed, for example, by a sputtering process.

[0058] (Step S4)

[0059] A second etching using a second metal catalyst is carried out.

[0060] The etching is carried out, for example, by a metal-assisted etching (MacEtch) method. According to the metal-assisted etching using the second metal catalyst, the etching occurs toward a lower side or directly below the second metal catalyst, and a recess having a depth in the z-axis direction can be formed.

[0061] An example of step S4 is described below with reference to [Fig.5].

[0062] The substrate 1 provided with the second metal catalyst is etched with an etchant. For example, the substrate 1 is immersed in the liquid etchant to bring the liquid etchant into contact with the substrate 1. The details of the etchant (hereinafter referred to as the second etchant) are described below.

[0063] The second etchant contains an oxidant and hydrogen fluoride (hydrofluoric acid). A specific example of the second etchant is an aqueous solution containing an oxidant and hydrogen fluoride.

[0064] Examples of oxidant include the same as those described for the first etchant. Hydrogen peroxide is preferred as the oxidant because it does not produce a harmful by-product.

[0065] It is desirable that a concentration of hydrogen fluoride (hydrofluoric acid) in the second etchant is higher than the concentration of hydrogen fluoride (hydrofluoric acid) in the first etchant. More specifically, the concentration of hydrogen fluoride in the second etchant may be 6.5 mol / l or more and 8.0 mol / l or less. It is desirable that a concentration of hydrogen peroxide in the second etchant is higher than the concentration of hydrogen peroxide in the first etchant. More specifically, the concentration of hydrogen peroxide in the second etchant may be 1.5 mol / l or more and 2.5 mol / l or less. At least one of the concentration of hydrogen fluoride (hydrofluoric acid) or the concentration of hydrogen peroxide is adjusted within the above range, so that the speed of the second etching can be increased.Therefore, a recess with a high aspect ratio can be processed with high productivity.

[0066] The second etchant may further contain a buffer. Examples of buffer include the same as those described for the first etchant.

[0067] The second etching agent may further contain any other component such as water.

[0068] According to MacEtch using the second metal catalyst described above, the material of the substrate 1, here silicon, is oxidized only in a region of the recess 6 in the substrate 1 close to the second metal catalyst particles 8a and 8b. The resulting oxide is dissolved and removed by hydrofluoric acid. Therefore, only the portion close to the second metal catalyst particles 8a and 8b is selectively etched. Since the second metal catalyst particles 8a have a shape extending in the depth direction of the recess 6, a substrate portion located immediately below the second metal catalyst layer 8 can be selectively etched. Therefore, it is possible to form a recess 6 with a high aspect ratio having a depth direction in a direction intersecting (e.g. perpendicularly) the main surface 1a of the substrate 1.

[0069] In addition, since the first metal catalyst layer 4 is present near the upper end of the side wall defining the recess 6, the attachment of the second metal catalyst layer 8 is suppressed. Therefore, the metal catalyst diffused into the portion of the substrate near the upper end of the side wall is mainly the first metal catalyst. Since the first metal catalyst has a lower diffusion coefficient than the second metal catalyst, it is possible to suppress the dissolution of a semiconductor (e.g., Si) near the upper end of the side wall. Accordingly, it is possible to reduce processing defects in which the vicinity of the upper end of the side wall defining the recess 6 becomes porous.Therefore, a recess with a high aspect ratio can be processed with high productivity.

[0070] The substrate after the second etching is separated from the second etchant, for example by pulling it upwards from the second etchant. The substrate can then be washed. The mask layer can also be removed if necessary.

[0071] Figures 2 to 5 illustrate a simplified structure for easy understanding. In fact, during the plating process to generate the first metal catalyst particles 4a or the second metal catalyst particles 8a and 8b, the catalyst particles may be bonded to each other. Therefore, the first metal catalyst layer 4 and the second metal catalyst layer 8 do not necessarily have a structure in which the two layers can be clearly distinguished from each other as illustrated in the drawings.

[0072] <exemples>

[0073] Examples are described below.

[0074] <Exemple 1>

[0075] Firstly, a silicon wafer whose main surface is a (100) plane is prepared. Then, a mask layer having an opening is formed on the main surface of this silicon wafer. The mask layer is formed by photolithography using a photosensitive resin.

[0076] Next, an aqueous solution of silver nitrate and hydrofluoric acid is mixed to prepare a displacement deposition solution. This displacement deposition solution has a silver nitrate concentration of 0.001 mol / l and a hydrogen fluoride concentration of 1 mol / l.

[0077] The temperature of the displacement deposition solution is adjusted to 20°C and the silicon wafer formed with the mask layer is immersed therein for 180 seconds. As described above, a first metal catalyst layer containing silver particles as the first metal catalyst is formed on the silicon wafer in the position of the opening of the mask layer.

[0078] Next, hydrofluoric acid and hydrogen peroxide are mixed to prepare a first etchant. The first etchant is an aqueous solution having a hydrogen fluoride concentration of 3.8 mol / l and a hydrogen peroxide concentration of 0.5 mol / l. The temperature of the first etchant is adjusted to 20°C, and the substrate formed with the mask layer and the first metal catalyst layer is immersed for 30 seconds for etching (first etching). As a result, a trench is formed and needle-shaped Si is formed in the trench. The needle-shaped Si is present mainly on the lower inner surface of the trench. In addition, the first metal catalyst layer is present from the lower inner surface of the trench to the vicinity of the upper end of the trench wall surface.

[0079] A displacement deposition solution for forming the second metal catalyst layer is prepared by mixing an aqueous solution of tetrachloroauric(III) acid and hydrofluoric acid. This displacement deposition solution has a tetrachloroauric(III) acid concentration of 0.003 mmol / l and a hydrogen fluoride concentration of 1 mol / l. A second metal catalyst layer is formed by adjusting the temperature of the displacement deposition solution to 20°C and immersing the substrate formed with the mask layer, the first metal catalyst layer, and the needle-shaped Si in the displacement deposition solution for 3 minutes. The second metal catalyst layer contains gold particles as the second metal catalyst. Some gold particles have a columnar shape and extended in the trench depth direction. Some of the other gold particles are granular.

[0080] Next, hydrofluoric acid and hydrogen peroxide are mixed to prepare a second etchant. The second etchant is a aqueous solution having a hydrogen fluoride concentration of 3.8 mol / l and a hydrogen peroxide concentration of 0.5 mol / l. The temperature of the second etchant is adjusted to 20°C, and the substrate formed with the mask layer, the second metal catalyst layer, and the needle-shaped Si is immersed for 70 seconds for etching (second etching). As a result, a trench having a predetermined depth and a predetermined aspect ratio is formed without generating a porous region near the upper end of the trench wall surface. [0081 ]<Exemple 2>

[0082] A trench having a predetermined depth and a predetermined aspect ratio is formed without generating a porous region in the vicinity of the upper end of the trench wall surface in the same manner as in Example 1, except that the first metal catalyst layer is formed by the following method.

[0083] A solution of hexachloroplatinic (IV) acid and hydrofluoric acid is mixed to prepare a displacement deposition solution. This displacement deposition solution has a hexachloroplatinic (IV) acid concentration of 0.0005 mol / l and a hydrogen fluoride concentration of 1 mol / l.

[0084] The temperature of the displacement deposition solution is adjusted to 20°C and the silicon wafer formed with the mask layer is immersed therein for 120 seconds. As described above, a first metal catalyst layer containing platinum particles as the first metal catalyst was formed on the silicon wafer in the position of the opening of the mask layer.

[0085] <Exemple 3>

[0086] A trench having a predetermined depth and a predetermined aspect ratio is formed without generating a porous region in the vicinity of the upper end of the trench wall surface in the same manner as in Example 1, except that the first metal catalyst layer is formed by the following method.

[0087] An aqueous solution of palladium(II) nitrate and hydrofluoric acid is mixed to prepare a displacement deposition solution. This displacement deposition solution has a palladium(II) nitrate concentration of 0.0005 mol / l and a hydrogen fluoride concentration of 1 mol / l.

[0088] The temperature of the displacement deposition solution is adjusted to 20°C and the silicon wafer formed with the mask layer is immersed therein for 180 seconds. As described above, a first metal catalyst layer containing palladium particles as the first metal catalyst is formed on the silicon wafer in the position of the mask layer opening.

[0089]

[0090] <Exemple comparatif>

[0091] A comparative example is described below with reference to Figures 6 to 10.

[0092] Firstly, a silicon wafer 11 whose main surface 11a is a plane (100) is prepared. Then, a mask layer 12 having an opening 13 is formed on the main surface 11a of this silicon wafer. The mask layer 12 is formed by photolithography using a photosensitive resin.

[0093] An aqueous solution of tetrachloroauric(III) acid and hydrofluoric acid is mixed to prepare a displacement deposition solution. This displacement deposition solution has a tetrachloroauric(III) acid concentration of 0.0005 mmol / l and a hydrogen fluoride concentration of 1 mol / l. A first Au 14 catalyst layer containing the first Au 14a particles is formed by adjusting the temperature of the displacement deposition solution to 20°C and immersing a substrate 11 formed with the mask layer 12 for 90 seconds. A structure formed by this displacement deposition is shown in [Fig.6]. As described in [Fig.6], an Au 15 diffusion layer is formed in a substrate portion located near the first Au 14a particles.

[0094] Next, hydrofluoric acid and hydrogen peroxide are mixed to prepare an etchant. The etchant has a hydrogen fluoride concentration of 3.8 mol / l and a hydrogen peroxide concentration of 0.5 mol / l. The temperature of the etchant is adjusted to 20°C, and the substrate 11 formed with the mask layer 12 and the first Au catalyst layer 14 is immersed for 75 seconds for etching. Accordingly, as depicted in [Fig. 7], a trench 16 is formed, and needle-shaped Si 17 is formed at the lower inner surface of the trench 16. The Au diffusion layer 15 is present on the entire inner surface of the trench 16.

[0095] A displacement deposition solution for forming the second Au 18 catalyst layer containing the second Au 18a and 18b particles is prepared by mixing an aqueous solution of tetrachloroauric(III) acid and hydrofluoric acid. This displacement deposition solution has a tetrachloroauric(III) acid concentration of 0.003 mmol / l and a hydrogen fluoride concentration of 1 mol / l. The second Au 18 catalyst layer is formed by adjusting the temperature of the displacement deposition solution to 20°C and immersing the substrate formed with the mask layer, the first metal catalyst layer and the needle-shaped Si in the displacement deposition solution for 3 minutes. A structure obtained by this displacement deposition is illustrated in [Fig.8]. As described in [Fig.8], the second Au 18a particles have a columnar shape extending in the depth direction of trench 16. The second Au 18b particles have a granular shape. The Au 15 diffusion layer is present on the entire inner surface of trench 16.

[0096] Next, hydrofluoric acid and hydrogen peroxide are mixed to prepare an etchant. The etchant has a hydrogen fluoride concentration of 7.5 mol / l and a hydrogen peroxide concentration of 2 mol / l. The temperature of the etchant is adjusted to 20°C, and the substrate formed with the mask layer 12, the second Au catalyst layer 18, and the needle-shaped Si 17 is immersed for 70 seconds for etching. As depicted in [Fig. 9], the obtained trench 16 has a porous shape 19 near the upper end of the wall surface. [Fig. 10] shows an enlarged view of a scanning electron micrograph (SEM photograph) of the vicinity of the upper end of the wall surface of the trench 16 obtained by the method of the comparative example. As depicted in [Fig.10], the trench 16 has a predetermined aspect ratio, but a depression or a small pore is generated near the upper end of the surface of the wall of the trench 16. It is presumed that Si has been dissolved by the action of the Au 15 diffusion layer present near the upper end of the surface of the wall of the trench 16. .

[0097] The etching method of at least one embodiment or example described above comprises: forming a layer containing a first metal catalyst at a surface containing a semiconductor; first etching using the first metal catalyst; forming a layer containing a second metal catalyst having a higher diffusion coefficient than that of the first metal catalyst at the layer containing the first metal catalyst; and second etching using the second metal catalyst. This method can suppress the occurrence of a processing defect at a wall surface defining a recess, for example, near an upper end of a wall surface. Therefore, it is easy to process a recess having a high aspect ratio.

[0098] Although certain embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in various other forms; further, various omissions, substitutions, and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The appended claims and their equivalents are intended to cover forms or modifications which would be within the scope and spirit of the inventions.< / exemples>

Claims

Claims

1. An etching method comprising: forming (S1) a layer (4) comprising a first metal catalyst at a surface (1a) comprising a semiconductor; first etching (S2) using the first metal catalyst; forming (S3) a layer (8) comprising a second metal catalyst having a higher diffusion coefficient than that of the first metal catalyst at the layer (4) comprising the first metal catalyst; and second etching (S4) using the second metal catalyst.

2. The etching method of claim 1, wherein the first etching and the second etching are metal-assisted etching.

3. The etching method of claim 1 or 2, wherein the first metal catalyst comprises at least one catalyst selected from the group consisting of Ag, Pt and Pd.

4. An etching method according to any one of claims 1 to 3, wherein the second metal catalyst comprises Au.

5. The etching method of claim 1 or 2, wherein the first metal catalyst comprises at least one catalyst selected from the group consisting of Ag, Pt and Pd, and the second metal catalyst comprises Au.

6. An etching method according to any one of claims 1 to 5, wherein at least one of the layer (4) comprising the first metal catalyst or the layer (8) comprising the second metal catalyst is formed by an electroless deposition method or a sputtering method.

7. An etching method according to any one of claims 1 to 6, wherein the semiconductor comprises Si.

Images