Etching method

Abstract

To provide an etching method capable of reducing processing defects.SOLUTION: According to an embodiment, an etching method is provided. The etching method includes forming a layer 4 containing a first metal catalyst on a surface 1a containing a semiconductor, a first etching for etching with the first metal catalyst, forming a layer 8 containing a second metal catalyst with a larger diffusion coefficient than the first metal catalyst in the layer 4 containing the first metal catalyst, and a second etching for etching with the second metal catalyst.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to an etching method. [Background technology]

[0002] Etching is known as a method for forming holes and grooves in substrates such as semiconductor wafers. For example, there is a metal-assisted etching method (also called MacEtch (Metal-Assisted Chemical Etching)). One example of the metal-assisted etching (MacEtch) method is an etching method that uses a precious metal as a catalyst. When a high aspect ratio trench is processed in a substrate containing Si by this method, processing defects such as porous Si occur near the upper end of the trench. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-147699 [Patent Document 2] U.S. Patent Publication US2010 / 0248449A1 [Non-patent literature]

[0004] [Non-Patent Document 1] Proposal of a new diffusion equation in relation to solid-state reactions by Goro Yamaguchi et al., Journal of the Ceramic Association 78[9] 1970, pp. 293-298 Summary of the Invention [Problem to be solved by the invention]

[0005] An etching method capable of reducing processing defects is provided. [Means for solving the problem]

[0006] According to an embodiment, an etching method is provided, which includes forming a layer including a first metal catalyst on a surface including a semiconductor, performing a first etching step using the first metal catalyst, and forming a layer including a second metal catalyst having a larger diffusion coefficient than the first metal catalyst on the layer including the first metal catalyst, and performing a second etching step using the second metal catalyst. [Brief description of the drawings]

[0007] [Figure 1] 1 is a flowchart showing a flow of steps included in an etching method according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing a schematic structure obtained by forming a first metal catalyst in the method according to the embodiment. [Diagram 3] FIG. 4 is a cross-sectional view illustrating a structure obtained by a first etching in the method according to the embodiment. [Figure 4] FIG. 3 is a cross-sectional view showing a schematic structure obtained by forming a second metal catalyst in the method according to the embodiment. [Diagram 5] FIG. 4 is a cross-sectional view illustrating a structure obtained by a second etching in the method according to the embodiment. [Figure 6] FIG. 4 is a cross-sectional view showing a schematic diagram of a structure obtained by forming a first Au catalyst layer in a method of a comparative example. [Figure 7] FIG. 4 is a cross-sectional view showing a schematic structure obtained by etching using a first Au catalyst in a method of a comparative example. [Figure 8] FIG. 4 is a cross-sectional view showing a schematic structure obtained by forming a second Au catalyst layer in a method of a comparative example. [Figure 9] FIG. 13 is a cross-sectional view showing a schematic structure obtained by etching using a second Au catalyst in the method of the comparative example. [Figure 10] 11 is an electron microscope photograph showing the vicinity of the upper end of a trench processed by a method of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiments will be described in detail with reference to the drawings. Note that components that perform the same or similar functions are given the same reference numerals throughout the drawings, and duplicated descriptions will be omitted.

[0009] FIG. 1 is a flow chart showing the flow of steps in an etching method according to an embodiment. As shown in FIG. 1, the etching method according to an embodiment includes 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). Each step will be described below with reference to FIG. 2 to FIG. 5. Each figure shows a processing surface to be etched as being parallel to a plane defined by the x-axis direction and the y-axis direction. The processing surface may be, for example, a main surface of a substrate. Processing by etching proceeds in a direction 100 along the z-axis direction from the processing surface. The x-axis, y-axis, and z-axis intersect perpendicularly to each other. (Process S1) A first metal catalyst is formed on a surface comprising a semiconductor.

[0010] The semiconductor may be selected from, for example, silicon (Si); germanium (Ge); semiconductors made of compounds of group III and group V elements, such as gallium arsenide (GaAs) and gallium nitride (GaN); and silicon carbide (SiC). According to one example, the surface comprising a semiconductor is a surface comprising silicon. Note that the term "group" as used herein refers to the "group" of the short periodic table.

[0011] The surface including a semiconductor may be, for example, a semiconductor substrate. The semiconductor substrate may be, for example, a semiconductor wafer. The semiconductor wafer may be doped with impurities, and may have semiconductor elements such as transistors and diodes formed thereon. The main surface of the semiconductor wafer may be parallel to any crystal plane of the semiconductor. The semiconductor wafer may be, for example, a silicon wafer whose main surface is a (100) plane, or a silicon wafer whose main surface is a (110) plane.

[0012] FIG. 2 shows an example of a structure obtained by step S1. A mask layer 2 is provided on at least a part of the surface of a semiconductor-containing substrate 1, for example, one of the main surfaces 1a of the substrate 1. The main surface 1a of the substrate 1 is, for example, a surface parallel to a plane defined by the x-axis direction and the y-axis direction. The semiconductor includes, for example, Si. The substrate 1 may have any shape. Here, as an example, the substrate 1 is a single crystal silicon wafer. The surface orientation of the single crystal silicon wafer is not particularly important. In FIG. 2, a silicon wafer having one main surface 1a that is a (100) plane is used as the substrate 1. A silicon wafer having one main surface that is a (110) plane can also be used as the substrate 1.

[0013] The mask layer 2 has one or more openings 3. The shape of the openings 3 is not particularly limited. The openings 3 have, for example, a groove shape extending in the y-axis direction and penetrating in the z-axis direction. The number of openings 3 is also not limited, and can be one or more. The mask layer 2 can prevent the metal catalyst from coming into contact with the area of ​​the surface of the substrate 1 that is covered by the mask layer 2. The mask layer 2 can be, for example, a resist.

[0014] Examples of materials for the mask layer 2 include organic materials such as polyimide, fluororesin, phenolic resin, acrylic resin, and novolac resin, and inorganic materials such as silicon oxide and silicon nitride.

[0015] The mask layer 2 can be formed, for example, by an existing semiconductor process. The mask layer 2 made of an organic material can be formed, for example, by photolithography. The mask layer 2 made of an inorganic material can be formed, for example, by forming an inorganic material layer by a vapor deposition method, forming a mask by photolithography, and patterning the inorganic material layer by etching. Alternatively, the mask layer 2 made of an inorganic material can be formed by oxidizing or nitriding the surface region of the substrate 1, forming a mask by photolithography, and patterning the oxide or nitride layer by etching. The mask layer 2 can be omitted.

[0016] A layer 4 containing a first metal catalyst (hereinafter referred to as first metal catalyst layer 4) is provided on a portion of the main surface 1a of the substrate 1 that is exposed to the openings 3 of the mask layer 2. After providing the mask layer 2 on the main surface 1a of the substrate 1, the first metal catalyst layer 4 can be formed on the portion of the main surface 1a exposed to the openings 3 of the mask layer 2 by, for example, electroless plating or sputtering.

[0017] The first metal catalyst layer 4 includes, for example, first metal catalyst particles 4a. An example of the first metal catalyst layer 4 including the first metal catalyst particles 4a is a layer structure formed by accumulating the first metal catalyst particles 4a. The first metal catalyst layer 4 is not limited to one including the first metal catalyst particles 4a. For example, the first metal catalyst layer 4 may include one in which the first metal catalyst is formed in a film shape. In this case, the first metal catalyst layer 4 can be formed by, for example, a sputtering method.

[0018] The first metal catalyst layer 4 including the first metal catalyst particles 4a can be formed by, for example, displacement plating, which is an example of electroless plating. The displacement plating solution is, for example, a mixture of a salt of the first metal catalyst and hydrofluoric acid. Hydrofluoric acid can remove the natural oxide film on the surface of the substrate. By adjusting the concentration of the first metal catalyst salt or the concentration of hydrofluoric acid in the displacement plating solution, the size of the first metal catalyst particles and the density of the first metal catalyst layer can be set within a predetermined range. For example, by lowering the concentration of the first metal catalyst salt or the concentration of hydrofluoric acid, it is possible to form first metal catalyst particles of nanometer size and obtain a catalyst layer in which the first metal catalyst particles are distributed at a high number density. In addition, by increasing the concentration of the first metal catalyst salt or the concentration of hydrofluoric acid, the first metal catalyst particles are bonded together, and a catalyst layer in which large first metal catalyst particles are distributed at a low number density can be obtained.

[0019] The first metal catalyst has a smaller diffusion coefficient than the second metal catalyst. Therefore, the first metal catalyst is less likely to diffuse into the substrate 1 than the second metal catalyst. This makes it possible to prevent the formation of a metal catalyst diffusion layer 5 in a portion of the substrate located near the first metal catalyst layer 4.

[0020] The diffusion coefficient can be the diffusion coefficient into the semiconductor component (e.g., Si) that constitutes the substrate. The diffusion coefficient can be calculated using Fick's second law. An example of the calculation method is described in Non-Patent Document 1.

[0021] The first metal catalyst may include 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 into Si is 3.8×10 at 1400 K. -13 (m 2 / s) or more 4.6×10 -9 (m 2 / s) or less. The diffusion coefficient of Pt into Si is, for example, 7.7×10 at 1400K. -15 (m 2 / s) or more 1.8×10 -10 (m 2 / s) or less. The diffusion coefficient of Pd into Si is, for example, 4.8×10 at 1400K. -9 (m 2 / s). The diffusion coefficient of each element is referenced to the diffusion database (Kakusan DICE) by the National Institute for Materials Science (nims.go.). The value of the diffusion coefficient can vary depending on the conditions of the Si wafer (e.g., resistivity, whether it is n-type or p-type, crystal orientation, etc.), so there can be a range. The resistivity of a Si wafer, which is an example of a substrate, is, for example, 1 to 5 Ω·cm. The first etching is performed, for example, at around room temperature. In this case, the diffusion coefficient of Ag into Si is 3.8×10 at 1400K. -13 (m 2 / s) can be used. The diffusion coefficient of Pt into Si is 7.7×10 at 1400K. -15 (m 2 / s) can be used. (Process S2) In the first etching, etching is performed using a first metal catalyst. The etching is performed, for example, by a metal-assisted etching method (also called MacEtch (Metal-Assisted Chemical Etching)). According to the metal-assisted etching using the first metal catalyst, etching progresses toward (directly below) the first metal catalyst, and a recess having a depth in the z-axis direction can be formed.

[0022] An example of step S2 will be described with reference to FIG.

[0023] The substrate 1 provided with the first metal catalyst is etched with an etching agent. For example, the substrate 1 is immersed in a liquid etching agent to bring the etching agent into contact with the substrate 1. Details of the etching agent (hereinafter referred to as the first etching agent) will be described next.

[0024] The first etching agent contains an oxidizing agent and hydrogen fluoride (hydrogen hydrofluoric acid). A specific example of the first etching agent is an aqueous solution containing an oxidizing agent and hydrogen fluoride.

[0025] The oxidizing agent may be selected from, for example, hydrogen peroxide, nitric acid, AgNO3, KAuCl4, HAuCl4, K2PtCl6, H2PtCl6, Fe(NO3)3, Ni(NO3)2, Mg(NO3)2, Na2S2O8, K2S2O8, KMnO4, and K2Cr2O7. Hydrogen peroxide is preferred as the oxidizing agent since it does not produce harmful by-products.

[0026] The concentration of hydrogen fluoride (hydrogen hydrofluoric acid) in the first etching agent can be 3.5 mol / L or more and 4.5 mol / L or less. The concentration of hydrogen peroxide in the first etching agent can be 0.3 mol / L or more and 0.8 mol / L or less. By setting at least one of the concentration of hydrogen fluoride (hydrogen hydrofluoric acid) and the concentration of hydrogen peroxide within the above range, the speed of the first etching can be slowed down, making it easier to obtain a recess shape that reflects the distribution of the first metal catalyst. For example, since etching hardly progresses in a portion where the first metal catalyst is small or not present, a needle-like convex portion can be partially provided on the inner surface of the recess. By setting both the concentration of hydrogen fluoride (hydrogen hydrofluoric acid) and the concentration of hydrogen peroxide within the above range, it becomes easier to partially provide a needle-like convex portion on the inner surface of the recess.

[0027] The first etchant may further include a buffering agent, such as at least one of ammonium fluoride and ammonia. In one embodiment, the buffering agent is ammonium fluoride. In another embodiment, the buffering agent is a mixture of ammonium fluoride and ammonia. The first etchant may further include other components, such as water.

[0028] As described above, according to MacEtch using the first metal catalyst, the material of the substrate 1, silicon in this case, is oxidized only in the region of the substrate 1 adjacent to the first metal catalyst particles 4a. The oxide thus generated is dissolved and removed by hydrofluoric acid. Therefore, only the portion adjacent to the first metal catalyst particles 4a is selectively etched.

[0029] As etching progresses, layer 4 containing first metal catalyst particles 4a moves toward the other main surface (hereinafter referred to as the second surface) of substrate 1, where etching similar to that described above occurs. As a result, as shown in Fig. 3, etching progresses from main surface 1a (first surface) toward the second surface in a direction perpendicular to main surface 1a (first surface), forming recesses 6.

[0030] However, since the layer 4 containing the first metal catalyst particles 4a has gaps between the first metal catalyst particles 4a, etching hardly progresses at the positions corresponding to these gaps. As a result, as shown in FIG. 3, needle-shaped protrusions 7 each extending in the depth direction of the recess 6 along a direction intersecting the main surface 1a (first surface), for example, the z-axis direction, are generated on the inner surface of the bottom of the recess 6 as etching residues. It is not necessary to provide the needle-shaped protrusions 7. In this case, the first metal catalyst layer 4 may be formed by a sputtering method.

[0031] When a recess 6 is formed by the first etching, the first metal catalyst remains near the opening edge of the recess 6. However, since the remaining first metal catalyst is unlikely to diffuse into the substrate portion near the opening edge of the recess 6, the formation of a metal catalyst diffusion layer 5 can be suppressed.

[0032] In this manner, a substrate is obtained which has a surface including a semiconductor and on which a recess is provided.

[0033] After the first etching, the substrate is separated from the first etching agent, for example by being pulled up from the first etching agent. Thereafter, the substrate may be washed with water.

[0034] 3 illustrates a method for forming needle-shaped protrusions 7, but protrusions 7 may have other shapes. For example, protrusions 7 may each have a flat plate shape and be arranged apart from each other in the thickness direction. (Process S3) A layer containing a first metal catalyst (hereinafter referred to as a first metal catalyst layer) is formed with a layer containing a second metal catalyst having a larger diffusion coefficient than the first metal catalyst (hereinafter referred to as a second metal catalyst layer).

[0035] The second metal catalyst layer may be deposited (e.g., precipitated) on the entire first metal catalyst layer, or may be deposited (e.g., precipitated) on a portion of the first metal catalyst layer. Also, the second metal catalyst layer is preferably deposited on the first metal catalyst layer, but may be formed directly on a portion of the surface including the semiconductor.

[0036] The layer containing the second metal catalyst is formed by, for example, an electroless plating method or a sputtering method.

[0037] The second metal catalyst has a larger diffusion coefficient than the first metal catalyst. As with the first metal catalyst, the diffusion coefficient can be the diffusion coefficient into the semiconductor component (e.g., Si) that constitutes the substrate. The diffusion coefficient can be calculated in the same manner as described for the first metal catalyst.

[0038] The second metal catalyst may contain Au. The second etching is performed, for example, at room temperature. The diffusion coefficient of Au into Si is, for example, 3.0×10 -12 (m 2 / s) or more 2.0×10 -7 (m 2 / s). This value is taken from the diffusion database (Kakusan DICE) by the National Institute for Materials Science (nims.go.). For example, if a silicon wafer with a resistivity of 1 to 5 Ω cm is used as the substrate, the diffusion coefficient of Au into silicon is 3.0×10 at 1400 K. -12 (m 2 / s) can be used.

[0039] An example of forming the second metal catalyst by displacement plating, which is an example of electroless plating, will be described with reference to FIG. 4. A recess 6 having a depth in the z-axis direction is formed in the substrate 1 after the first etching. A first metal catalyst layer 4 including first metal catalyst particles 4a is present on the bottom inner surface and side walls of the recess 6. In the first metal catalyst layer 4, gaps exist in some areas between the first metal catalyst particles 4a. At least one needle-shaped protrusion 7 (multiple in the case of FIG. 4) is formed at a location corresponding to the gap between the first metal catalyst particles 4a on the bottom inner surface of the recess 6. When the second metal catalyst is formed by displacement plating, since the protrusion 7 is needle-shaped, displacement plating proceeds over almost the entirety of the protrusion 7. Therefore, the second metal catalyst can be precipitated in the form of particles extending in a direction intersecting with the main surface (first surface) in accordance with the shape of the protrusion 7. That is, by this displacement plating, a second metal catalyst layer 8 including second metal catalyst particles 8a having a shape extending in the depth direction along the z-axis direction of the recess 6 is obtained. The second metal catalyst layer 8 also contains granular second metal catalyst particles 8b. The second metal catalyst layer 8 is in contact with the protrusions 7. Since there are gaps between the first metal catalyst particles 4a of the first metal catalyst layer 4, a part 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 prevents the second metal catalyst layer 8 from being formed on the side wall of the recess 6. Therefore, it is possible to suppress the second metal catalyst layer 8 from adhering to the side wall defining the recess 6, particularly to the vicinity of the upper end of the side wall.

[0040] The displacement plating solution used in displacement plating is, for example, a mixture of an aqueous solution of tetrachloroauric acid (III), an aqueous solution of gold sulfite, or an aqueous solution of potassium cyanide gold (I) and hydrofluoric acid. Hydrofluoric acid can remove the native oxide film on the surface of the substrate.

[0041] The second metal catalyst particles may all have a shape extending in the depth direction of the recess, but may also include particles having this shape and particles having a granular shape. The second metal catalyst layer may also include a film-like second metal catalyst. In this case, the second metal catalyst layer is formed, for example, by a sputtering method. (Process S4) A second etch is performed using a second metal catalyst.

[0042] The etching is performed, for example, by a metal-assisted etching (MacEtch) method. By metal-assisted etching using a second metal catalyst, etching proceeds toward (directly below) the second metal catalyst, and a recess having a depth in the z-axis direction can be formed.

[0043] An example of step S4 will be described with reference to FIG.

[0044] The substrate 1 provided with the second metal catalyst is etched with an etching agent. For example, the substrate 1 is immersed in a liquid etching agent to bring the etching agent into contact with the substrate 1. Details of the etching agent (hereinafter, referred to as the second etching agent) will be described next.

[0045] The second etching agent contains an oxidizing agent and hydrogen fluoride (hydrogen hydrofluoric acid). A specific example of the second etching agent is an aqueous solution containing an oxidizing agent and hydrogen fluoride.

[0046] Examples of the oxidizing agent include those described for the first etching agent. Hydrogen peroxide is preferred as the oxidizing agent because it does not produce harmful by-products.

[0047] The concentration of hydrogen fluoride (hydrogen hydrofluoric acid) in the second etching agent is desirably higher than the concentration of hydrogen fluoride (hydrogen hydrofluoric acid) in the first etching agent. Specifically, it can be 6.5 mol / L or more and 8.0 mol / L or less. The concentration of hydrogen peroxide in the second etching agent is desirably higher than the concentration of hydrogen peroxide in the first etching agent. Specifically, it can be 1.5 mol / L or more and 2.5 mol / L or less. By setting at least one of the concentration of hydrogen fluoride (hydrogen hydrofluoric acid) and the concentration of hydrogen peroxide within the above range, the speed of the second etching can be increased, and therefore recesses having a high aspect ratio can be processed with good productivity.

[0048] The second etching agent may further include a buffering agent. Examples of the buffering agent include those similar to those described for the first etching agent.

[0049] The second etchant may further include other components, such as water.

[0050] According to the MacEtch using the second metal catalyst described above, the material of the substrate 1, here silicon, is oxidized only in the region of the recess 6 of the substrate 1 adjacent to the second metal catalyst particles 8a, 8b. The oxide thus generated is dissolved and removed by hydrofluoric acid. Therefore, only the portion adjacent to the second metal catalyst particles 8a, 8b is selectively etched. Since the second metal catalyst particles 8a have a shape extending in the depth direction of the recess 6, the substrate portion located directly below the second metal catalyst layer 8 can be selectively etched. Therefore, the recess 6 having a high aspect ratio and having a depth direction in a direction intersecting (for example, perpendicular to) the main surface 1a of the substrate 1 can be formed.

[0051] Furthermore, the first metal catalyst layer 4 is present near the upper end of the sidewall defining the recess 6, suppressing adhesion of the second metal catalyst layer 8. Therefore, the metal catalyst diffusing into the substrate portion near the upper end of the sidewall is mainly the first metal catalyst. The first metal catalyst has a smaller diffusion coefficient than the second metal catalyst, and therefore can suppress dissolution of the semiconductor (e.g., Si) near the upper end of the sidewall. As a result, processing defects in which the upper end of the sidewall defining the recess 6 becomes porous can be reduced. Therefore, recesses with a high aspect ratio can be processed with good productivity.

[0052] After the second etching, the substrate is separated from the second etching agent, for example by being lifted from the second etching agent. The substrate may then be washed. If necessary, the mask layer may also be removed.

[0053] 2 to 5 show simplified structures for ease of understanding. In reality, the catalyst particles may be connected to each other during plating to produce the first metal catalyst particles 4a or the second metal catalyst particles 8a, 8b. Therefore, the first metal catalyst layer 4 and the second metal catalyst layer 8 do not necessarily have structures that allow the two layers to be clearly distinguished from each other as shown in the drawings. EXAMPLES

[0054] Examples will be described below. <Example 1> First, a silicon wafer with one main surface being a (100) plane was prepared. Next, a mask layer having an opening was formed on the main surface of the silicon wafer. The mask layer was formed by photolithography using a photoresist.

[0055] Next, the aqueous silver nitrate solution and hydrofluoric acid were mixed to prepare a displacement plating solution, which had a silver nitrate concentration of 0.001 mol / L and a hydrogen fluoride concentration of 1 mol / L.

[0056] The temperature of this displacement plating solution was adjusted to 20° C., and the silicon wafer with the mask layer formed thereon was immersed in it for 180 seconds. In this manner, a first metal catalyst layer containing silver particles as the first metal catalyst was formed on the silicon wafer exposed through the openings in the mask layer.

[0057] Next, hydrofluoric acid and hydrogen peroxide were mixed to prepare a first etching agent. The first etching agent was an aqueous solution with a hydrogen fluoride concentration of 3.8 mol / L and a hydrogen peroxide concentration of 0.5 mol / L. The temperature of this first etching agent was adjusted to 20°C, and the substrate on which the mask layer and the first metal catalyst layer were formed was immersed in the first etching agent for 30 seconds to perform etching (first etching). As a result, a trench was formed and needle-like Si was formed in the trench. The needle-like Si was mainly present on the bottom inner surface of the trench. The first metal catalyst layer was also present from the bottom inner surface of the trench to near the top end of the wall surface.

[0058] The displacement plating solution for forming the second metal catalyst layer was prepared by mixing an aqueous solution of tetrachloroauric (III) acid and hydrofluoric acid. The displacement plating solution had a tetrachloroauric (III) acid concentration of 0.003 mmol / L and a hydrogen fluoride concentration of 1 mol / L. The second metal catalyst layer was formed by adjusting the temperature of the displacement plating solution to 20°C and immersing the substrate on which the mask layer, the first metal catalyst layer, and the needle-like Si were formed in the displacement plating solution for 3 minutes. The second metal catalyst layer contained gold particles as the second metal catalyst. Some of the gold particles had a columnar shape and extended in the depth direction of the trench. Other gold particles were granular.

[0059] Next, hydrofluoric acid and hydrogen peroxide were mixed to prepare a second etching agent. The second etching agent was an aqueous solution with a hydrogen fluoride concentration of 3.8 mol / L and a hydrogen peroxide concentration of 0.5 mol / L. The temperature of this second etching agent was adjusted to 20°C, and the substrate on which the mask layer, the second metal catalyst layer, and the needle-like Si were formed was immersed in this for 70 minutes for etching (second etching). As a result, a trench of a specified depth (aspect ratio) was formed without generating pores near the top end of the wall surface of the trench. <Example 2> A trench of a predetermined depth (aspect ratio) was formed without generating pores near the upper end of the wall surface of the trench in the same manner as in Example 1, except that a first metal catalyst layer was formed by the following method.

[0060] A displacement plating solution was prepared by mixing a hexachloroplatinic (IV) acid solution and hydrofluoric acid. This displacement plating solution had a hexachloroplatinic (IV) acid concentration of 0.0005 mol / L and a hydrogen fluoride concentration of 1 mol / L.

[0061] The temperature of this displacement plating solution was adjusted to 20° C., and the silicon wafer with the mask layer formed thereon was immersed in it for 120 seconds. In this manner, a first metal catalyst layer containing platinum particles as the first metal catalyst was formed on the silicon wafer exposed in the openings of the mask layer. <Example 3> A trench of a predetermined depth (aspect ratio) was formed without generating pores near the upper end of the wall surface of the trench in the same manner as in Example 1, except that a first metal catalyst layer was formed by the following method.

[0062] A displacement plating solution was prepared by mixing an aqueous solution of palladium (II) nitrate and hydrofluoric acid. This displacement plating solution had a palladium (II) nitrate concentration of 0.0005 mol / L and a hydrogen fluoride concentration of 1 mol / L.

[0063] The temperature of this displacement plating solution was adjusted to 20° C., and the silicon wafer with the mask layer formed thereon was immersed in it for 180 seconds. In this manner, a first metal catalyst layer containing palladium particles as the first metal catalyst was formed on the silicon wafer exposed through the openings in the mask layer. <Comparative Example> A comparative example will be described with reference to FIGS.

[0064] First, a silicon wafer 11 having a main surface 11a of a (100) plane was prepared. Next, a mask layer 12 having an opening 13 was formed on the main surface 11a of the silicon wafer. The mask layer 12 was formed by photolithography using a photoresist.

[0065] Next, a displacement plating solution was prepared by mixing an aqueous solution of tetrachloroauric (III) acid and hydrofluoric acid. The displacement plating solution had a tetrachloroauric (III) acid concentration of 0.0005 mmol / L and a hydrogen fluoride concentration of 1 mol / L. The first Au catalyst layer 14 containing the first Au particles 14a was formed by adjusting the temperature of the displacement plating solution to 20° C. and immersing the substrate 11 on which the mask layer 12 was formed in the displacement plating solution for 90 seconds. The structure formed by this displacement plating is shown in FIG. 6. As shown in FIG. 6, an Au diffusion layer 15 was formed in the substrate portion located near the first Au particles 14a.

[0066] Next, hydrofluoric acid and hydrogen peroxide were mixed to prepare an etching agent. This etching agent had a hydrogen fluoride concentration of 3.8 mol / L and a hydrogen peroxide concentration of 0.5 mol / L. The temperature of this etching agent was adjusted to 20°C, and the substrate 11 on which the mask layer 12 and the first Au catalyst layer 14 were formed was immersed in the etching agent for 75 seconds to perform etching. As a result, a trench 16 was formed as shown in FIG. 7, and a needle-like Si 17 was formed on the inner surface of the bottom of the trench 16. The Au diffusion layer 15 was present on the entire inner surface of the trench 16.

[0067] The displacement plating solution for forming the second Au catalyst layer 18 including the second Au particles 18a and 18b was prepared by mixing an aqueous solution of tetrachloroauric (III) acid and hydrofluoric acid. The displacement plating solution had a tetrachloroauric (III) acid concentration of 0.003 mmol / L and a hydrogen fluoride concentration of 1 mol / L. The second Au catalyst layer 18 was formed by adjusting the temperature of the displacement plating solution to 20° C. and immersing the substrate on which the mask layer, the first metal catalyst layer, and the needle-like Si were formed in the displacement plating solution for 3 minutes. The structure obtained by this displacement plating is shown in FIG. 8. As shown in FIG. 8, the second Au particles 18a had a columnar shape extending in the depth direction of the trench 16. The second Au particles 18b had a granular shape. The Au diffusion layer 15 was present on the entire inner surface of the trench 16.

[0068] Next, an etching agent was prepared by mixing hydrofluoric acid and hydrogen peroxide. This etching agent had a hydrogen fluoride concentration of 7.5 mol / L and a hydrogen peroxide concentration of 2 mol / L. The temperature of this etching agent was adjusted to 20°C, and the substrate on which the mask layer 12, the second Au catalyst layer 18, and the needle-like Si 17 were formed was immersed in the etching agent for 70 minutes to perform etching. As shown in FIG. 9, the obtained trench 16 had a porous shape 19 near the upper end of the wall surface. FIG. 10 shows an enlarged view of a scanning electron microscope (SEM) photograph of the upper end of the wall surface of the trench 16 obtained by the method of the comparative example. As shown in FIG. 10, although the trench 16 had a predetermined aspect ratio, a counterbored (dented) was formed near the upper end of the wall surface of the trench 16. It is presumed that this is because the Si was dissolved by the action of the Au diffusion layer 15 present near the upper end of the wall surface of the trench 16.

[0069] According to at least one of the above-described embodiments or examples of the etching method, the method includes forming a layer containing a first metal catalyst on a surface containing a semiconductor, performing a first etching step using the first metal catalyst, forming a layer containing a second metal catalyst having a larger diffusion coefficient than the first metal catalyst on the layer containing the first metal catalyst, and performing a second etching step using the second metal catalyst. This method can prevent processing defects from occurring on the wall surface that defines the recess, for example, near the upper end of the wall surface. This makes it easy to process a recess with a high aspect ratio.

[0070] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0071] Reference Signs List 1...substrate, 1a...main surface, 2...mask layer, 3...opening, 4...first metal catalyst layer, 4a...first metal catalyst particle, 5...metal catalyst diffusion layer, 6...recess, 7...protrusion, 8...second metal catalyst layer, 8a, 8b...second metal catalyst particle, 11...substrate, 11a...main surface, 12...mask layer, 13...opening, 14...first Au catalyst layer, 14a...first Au particle, 15...Au diffusion layer, 16...trench, 17...acicular Si, 18...second Au catalyst layer, 18a, 18b...second Au particle, 19...porous shape, 100...direction, S1...formation of first metal catalyst, S2...first etching, S3...formation of second metal catalyst, S4...second etching.

Claims

1. forming a layer comprising a first metal catalyst on a surface comprising a semiconductor; a first etching step of etching using the first metal catalyst; forming a layer including a second metal catalyst having a diffusion coefficient larger than that of the first metal catalyst on the layer including the first metal catalyst; a second etching step of etching using the second metal catalyst; An etching method comprising:

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

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

4. The etching method according to claim 1 , wherein the second metal catalyst contains Au.

5. 3. The etching method according to claim 1, wherein the first metal catalyst contains at least one selected from the group consisting of Ag, Pt, and Pd, and the second metal catalyst contains Au.

6. 3. The etching method according to claim 1, wherein at least one of the layer containing the first metal catalyst and the layer containing the second metal catalyst is formed by electroless plating or sputtering.

7. The etching method according to claim 1 , wherein the semiconductor includes Si.

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