JP2010141178A - Etching method and method of manufacturing semiconductor device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an etching method which forms a tapered via hole in a semiconductor substrate by using a metal mask and through a simple method. <P>SOLUTION: The etching method includes: a step to form a metal conductive layer on the semiconductor substrate; a step to form a first plated layer having a first opening on the metal conductive layer; a step to form a second plated layer having a second opening smaller in width than the first opening on the sidewall of the first plated layer; a step to etch the semiconductor substrate by performing first dry etching using the second plated layer as a mask; a step to etch the second plated layer by selective wet etching to leave the first plated layer after the first dry etching; and a step to perform second dry etching using the first plated layer as a mask after etching the second plated layer and to further etching the semiconductor substrate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an etching method for etching a semiconductor substrate using a metal mask and a method for manufacturing a semiconductor device using the etching method.

  Wiring in the semiconductor substrate is manufactured by a method called a damascene method in which wiring connection holes (via holes) and wiring grooves (trench) are formed by etching the semiconductor substrate and Cu is embedded therein, for example. There are many cases. Control of the shape of via holes and trenches formed in a semiconductor substrate is an important element for forming a material to be a wiring with good embedding and obtaining a desired wiring resistance and wiring capacitance.

  In order to form a via hole or a trench (hereinafter simply referred to as a via hole) in a semiconductor substrate, it is common to perform dry etching with a mask formed in a desired pattern on the semiconductor substrate. It is. A resist layer or an insulating film may be used as the above-described mask, but the mask made of these materials may be significantly reduced by ion bombardment during dry etching. That is, the selectivity with respect to the semiconductor substrate to be etched is poor. Therefore, a metal mask that can perform highly selective etching on a semiconductor substrate is often used. In particular, when the semiconductor substrate is a difficult-to-etch material, reactive ion etching that accelerates ions with a high self-bias and bombards the semiconductor substrate is often used. When such highly ionic etching is performed, etching with improved selectivity is performed using a metal mask as a mask.

  For example, Patent Document 1 discloses a configuration in which an object to be etched is Ti, an upper layer formed by an electrolytic plating method, and a patterned Au layer is provided as a metal mask. In Patent Document 1, a resist mask is used for patterning the Au layer.

Japanese Patent Laid-Open No. 01-140629 JP 2005-322811 A JP 2001-156170 A JP 2008-074016 A JP 2007-234761 A JP 2003-298167 A Japanese Patent Laid-Open No. 08-115655

  Along with the progress of miniaturization of semiconductor elements, it may be necessary to form a film with a high fillability in a via hole having a high aspect ratio. The shape of the via hole is important in order to form a film with good fillability in a via hole having a high aspect ratio. That is, the via hole is preferably uniform in shape from the top of the hole to the bottom of the hole and has a shape in which the width decreases from the top of the via hole to the bottom of the hole in order to obtain good embedding.

  Here, the width of the via hole is preferable for improving the embedding property regardless of whether the width is gradually decreased from the top of the hole toward the bottom of the hole or is decreased stepwise. A via hole in which the width of the via hole gradually decreases from the top of the hole toward the bottom of the hole or decreases stepwise is referred to as a “tapered via hole”.

  Regardless of the method such as the dual damascene method, in order to form the aforementioned tapered via hole, for example, it is conceivable to form a metal mask in a tapered shape and perform dry etching of the semiconductor substrate. However, when the metal mask is formed by vapor deposition or sputtering, there is a problem that it is difficult to make the side wall of the metal mask tapered. Furthermore, in order to form a metal mask having a desired pattern by using a vapor deposition method or a sputtering method, it is necessary to use a resist mask or lift-off, which causes a problem that the process becomes complicated.

  Here, it is conceivable to employ a plating method as a method for forming the metal mask. However, for example, when a metal mask (Au layer 5 formed by electrolytic plating in Patent Document 1) is formed by the plating method described in Patent Document 1 and the semiconductor substrate is etched, the via holes have a uniform width. There was a problem that a tapered via hole could not be obtained.

  The present invention has been made to solve the above-described problems. An etching method for forming a tapered via hole in a semiconductor substrate by a simple method using a metal mask and a semiconductor device using the etching method are disclosed. An object is to provide a manufacturing method.

  The etching method according to the present invention includes a step of forming a metal conductive layer having an opening on a semiconductor substrate, and an electrolytic plating method or an electroless plating method using the metal conductive layer as a power feeding layer. A step of forming a first plating layer having one opening, and an electroplating method or an electroless plating method using the first plating layer as a power feeding layer, so that the side wall of the first plating layer is wider than the first opening. Forming a second plating layer having a narrow second opening. Then, a first dry etching is performed using the second plating layer as a mask to etch the semiconductor substrate, and a selective wet etching is performed to leave the first plating layer after the first dry etching. And a step of etching the plating layer and a step of etching the semiconductor substrate by performing a second dry etching using the first plating layer as a mask after etching the second plating layer.

  The etching method according to the present invention includes a step of forming a metal conductive layer on a semiconductor substrate, and an opening formed on the metal conductive layer by an electrolytic plating method or an electroless plating method using the metal conductive layer as a power feeding layer. A step of forming one plating layer, a step of forming a resist layer in the opening so as to have a predetermined gap from the side wall of the first plating layer, and an electrolytic plating method using the first plating layer as a power feeding layer, or Forming a second plating layer so as to fill the predetermined gap in the side wall of the first plating layer by an electroless plating method. A step of removing the resist layer; a step of removing the resist layer and then performing a first dry etching using the second plating layer as a mask; and etching the semiconductor substrate; and a step after the first dry etching. Performing a selective wet etching to leave the first plating layer and etching the second plating layer; and after etching the second plating layer, performing a second dry etching using the first plating layer as a mask; And a step of further etching the semiconductor substrate.

  The etching method according to the present invention includes a step of forming a metal conductive layer on a semiconductor substrate, and an opening formed on the metal conductive layer by an electrolytic plating method or an electroless plating method using the metal conductive layer as a power feeding layer. Forming a plating layer; forming a resist layer in the opening and on the first plating layer in the vicinity of the opening; and forming the resist layer and supplying the first plating layer to the power feeding layer And a step of forming a second plating layer in contact with the resist layer on the first plating layer on which the resist layer is not formed by an electrolytic plating method or an electroless plating method. And removing the resist layer to expose the first plating layer in the vicinity of the opening; and after removing the resist layer, performing a first dry etching using the first plating layer as a mask to etch the semiconductor substrate And etching the first plating layer in the vicinity of the opening and the metal conductive layer below the first plating layer, and performing a second dry etching using the second plating layer as a mask after the first dry etching, And a step of further etching the semiconductor substrate.

  According to the present invention, a tapered via hole can be formed in a semiconductor substrate by a simple method.

Embodiment 1
The present embodiment relates to an etching method for forming a tapered via hole. This etching method is used as a method for manufacturing a semiconductor device. The present embodiment will be described with reference to FIGS. In some cases, the same material or the same and corresponding components are denoted by the same reference numerals and the description thereof is omitted.

  FIG. 1 is a flowchart for explaining the etching method of this embodiment. Hereinafter, description will be made along this flowchart. First, a metal conductive layer having an opening is formed on a semiconductor substrate (step 10). In this embodiment, the semiconductor substrate is GaN or SiN. Further, the metal conductive layer has a multilayer structure including a Ti layer in contact with the semiconductor substrate and an Au layer in contact with the first plating layer.

  When step 10 is completed, the process proceeds to step 12. In step 12, a first plating layer having a first opening is formed on the metal conductive layer by an electrolytic plating method or an electroless plating method using the metal conductive layer as a power feeding layer. FIG. 2 is a diagram illustrating step 12 and is a cross-sectional view of the semiconductor substrate. As shown in FIG. 2, a first plating layer 34 is formed on the metal conductive layer 32 formed on the semiconductor substrate 30. In the present embodiment, the first plating layer 34 is Ni. The width of the first opening of the first plating layer 34 is represented by W1 in the figure.

  When step 12 is finished, the process proceeds to step 14. In step 14, a second plating layer 36 having a second opening on the side wall of the first plating layer 34 is formed by an electrolytic plating method or an electroless plating method using the first plating layer 34 as a power feeding layer. FIG. 3 is a diagram illustrating step 14. As shown in FIG. 3, the second plating layer 36 is formed so as to cover the side wall and the upper surface of the first plating layer 34. In the present embodiment, the second plating layer 36 is Cu. The width of the second opening of the second plating layer 36 is represented by W2 in FIG.

  Since the second plating layer 36 is formed on the side wall of the first plating layer 34, the second opening width W2 is smaller than the aforementioned W1.

  When step 14 is completed, the process proceeds to step 16. In step 16, the semiconductor substrate 30 is etched by performing the first dry etching using the second plating layer 36 as a mask. FIG. 4 is a diagram illustrating step 16. A hole having a width W2 is formed in the semiconductor substrate 30 by the first dry etching.

  When step 16 ends, the process proceeds to step 18. In step 18, selective wet etching is performed to leave the first plating layer 34, and the second plating layer 36 is etched. FIG. 5 is a diagram illustrating step 18. Hydrochloric acid or the like is used for wet etching of the second plating layer 36, and the second plating layer 36 made of Cu can be selectively etched with respect to the first plating layer 34. By step 18, the first plating layer 34 appears on the surface.

  When step 18 is completed, the process proceeds to step 20. In step 20, the semiconductor substrate 30 is further etched by performing second dry etching using the first plating layer 34 as a mask. FIG. 6 is a diagram illustrating step 20. Since the second dry etching uses the first plating layer 34 as a mask, the semiconductor substrate 30 is etched with the width W1.

  When step 20 is completed, the process proceeds to step 22. In step 22, the first plating layer 34 is etched by wet etching. For wet etching of the first plating layer 34, a mixed solution of sulfuric acid and nitric acid is used, and the first plating layer 34 made of Ni is etched.

  After the step 22 is finished, the metal conductive layer 32 is appropriately removed to obtain a semiconductor substrate 30 having a tapered via hole as shown in FIG. The etching method of this embodiment includes the above-described processing.

  According to the etching method of this embodiment, a tapered via hole can be easily formed in a semiconductor substrate. Therefore, it is possible to form a wiring with good embedding even when a via hole having a high aspect ratio is formed. In particular, when the semiconductor substrate on which the via hole is formed is, for example, a difficult-to-etch material, highly ionic etching in which ions are accelerated with high energy is performed. In such a case, if a metal mask is used as a mask as in this embodiment, the semiconductor substrate can be dry etched with high selectivity while leaving the metal mask.

  Further, in the etching method of this embodiment, a metal mask having a two-layer structure composed of the first plating layer 34 and the second plating layer 36 is used. Then, a narrow (W2) hole is formed in the semiconductor substrate 30 by the first dry etching using the second plating layer 36 as a mask, the second plating layer 36 is removed by wet etching, and the second dry etching is performed. A wide (W1) hole is formed in the semiconductor substrate 30 by etching. The tapered via hole can be formed in such a simple process because the materials of the first plating layer 34 and the second plating layer 36 are different and the respective solutions (etchants) are different. This is because selective etching is easy.

  For example, when the resist mask or the insulating film mask has a two-layer structure similarly to this, wet etching can be performed with an organic solvent and hydrofluoric acid, respectively, but it is difficult to selectively etch one layer. Therefore, a tapered via hole in which the width of a via hole is controlled cannot be formed by etching a semiconductor substrate using a resist mask or an insulating film mask.

  As described above, it is a feature of this embodiment that a tapered via hole in which the width of the via hole is controlled can be formed using a metal mask having a two-layer structure made of a material that can selectively wet-etch only one of the layers. .

  In the present embodiment, the materials of the first plating layer 34 and the second plating layer 36 are Ni and Cu, respectively, but are not limited to these as long as wet etching with high selectivity can be performed as described above. Good. For example, when the first plating layer is Ni and the second plating layer is Au, only Au can be selectively etched with an iodine-based etching solution, so that the effect of this embodiment can be obtained. Similarly, the first plating layer 34 and the second plating layer 36 may be formed of different materials selected from Ni, Cr, Pt, Au, Cu, and W. That is, the effect of the present invention can be obtained as long as the first plating layer and the second plating layer can be selectively wet etched.

  In this embodiment, the metal conductive layer 32 has a multilayer structure in which a Ti layer is provided in contact with the semiconductor substrate 30 and an Au layer is provided in contact with the first plating layer 34. There are two purposes for forming such a metal conductive layer 32. The first is to promote catalyst activation when the first plating layer 34 is formed by electrolysis or electroless plating. Secondly, the first plating layer 34 is prevented from peeling off after the first plating layer 34 is formed. In particular, a typical via hole has a depth of several tens of μm, and the first plating layer is peeled off when the first plating layer, which is a metal mask, must also be formed with a film thickness of several μm to several tens of μm. There is a concern that the yield will decrease. Therefore, having a metal conductive layer made of Ti and Au as in the present embodiment is preferable from the viewpoint of yield because the adhesion of the first plating layer can be improved. Here, the thickness of the metal conductive layer is not particularly limited. For example, for a 10 μm plated layer, even if the Ti and Au layers constituting the metal conductive layer are each about 30 nm, there is an effect of preventing the peeling of the plated layer. . The Ti layer mainly contributes to improving the adhesion between the layers, and the Au layer mainly contributes to preventing oxidation of the Ti surface.

  In the present embodiment, the semiconductor substrate 30 is GaN or SiN, but is not limited thereto. In the present embodiment, the reason why the metal mask is used for etching the semiconductor substrate is that the semiconductor substrate is a difficult-to-etch material and requires high ionic etching, so that it is not suitable for a resist mask or an insulating film mask. However, even when the semiconductor substrate is not a difficult-to-etch material, when the tapered via hole is formed using a metal mask as a mask, the above-described etching method can be widely applied.

  In the present embodiment, the metal mask employs a two-layer structure of the first plating layer 34 and the second plating layer 36. However, when the metal mask has a three-layer structure, for example, a tapered via hole with a lower step can be formed. That is, when a metal mask having a three-layer structure capable of selectively wet-etching one layer is used, a via hole shape in which the width of the via hole gradually decreases toward the bottom can be obtained. Therefore, as long as wet etching can be selectively performed as described above, the metal mask may have a plurality of layers.

Embodiment 2
The present embodiment relates to an etching method for forming a tapered via hole, and in particular, an etching method capable of controlling the via hole shape with high accuracy, and the width of the via hole gradually decreases from the top of the hole toward the bottom of the hole. The present invention relates to an etching method for forming a tapered via hole. The etching method of the present embodiment is also used as a method for manufacturing a semiconductor device as in the first embodiment. This embodiment will be described with reference to FIGS. In addition, it is the same as that of Embodiment 1 about the point which attaches | subjects the same code | symbol to the same material or the same, and the corresponding component, and abbreviate | omits description multiple times.

  FIG. 8 is a flowchart for explaining the etching method of this embodiment. Hereinafter, description will be made along this flowchart. First, a metal conductive layer is formed on a semiconductor substrate (step 50). In this embodiment, the semiconductor substrate is GaN or SiN. Further, the metal conductive layer has a multilayer structure including a Ti layer in contact with the semiconductor substrate and an Au layer in contact with the first plating layer.

  When step 50 is completed, the process proceeds to step 52. In step 52, a first plating layer having an opening on the metal conductive layer is formed by an electrolytic plating method or an electroless plating method using the metal conductive layer as a power feeding layer. FIG. 9 is a diagram for explaining step 52, which is a sectional view of a semiconductor substrate. As shown in FIG. 9, the first plating layer 74 of the present embodiment is formed on the metal conductive layer 72 formed on the semiconductor substrate 30. In order to pattern the first plating layer 74 as shown in FIG. 9, a resist layer is appropriately formed. As in the first embodiment, the first plating layer 74 is made of Ni and has a first opening having a width W1.

  When step 52 is completed, the process proceeds to step 54. FIG. 10 is a diagram for explaining step 54. In step 54, a resist layer 76 is formed in the first opening described above so as to have a predetermined gap from the side wall of the first plating layer 74. The width of the resist layer 76 is W2, which is narrower than W1. In the present embodiment, the resist layer 76 is formed on the metal conductive layer 72.

  When step 54 is completed, the process proceeds to step 56. FIG. 11 is a diagram for explaining step 56. In step 56, a second plating layer 78 is formed on the side wall of the first plating layer 74 by an electrolytic plating method or an electroless plating method using the first plating layer 74 as a power feeding layer. The second plating layer 78 fills the aforementioned predetermined gap. The second plating layer 78 is made of Cu as in the first embodiment.

  When step 56 is finished, the process proceeds to step 58. FIG. 12 is a diagram for explaining step 58. In step 58, the resist layer 76 is stripped. For removing the resist layer 76, a known method such as ashing is used. Then, as shown in FIG. 12, when the resist layer 76 is peeled off, a second opening having an opening width corresponding to the width W2 of the resist layer 76 is obtained. In step 58, the portion of the metal conductive layer 72 directly under the resist layer 76 is also etched by wet etching or the like, and a part of the semiconductor substrate 30 is exposed on the surface.

  When step 58 is completed, the process proceeds to step 60. FIG. 13 is a diagram for explaining step 60. In step 60, the semiconductor substrate 30 is etched by performing first dry etching using the second plating layer 78 as a mask.

  When step 60 is completed, the process proceeds to step 62. FIG. 14 is a diagram for explaining step 62. In step 62, selective wet etching is performed to leave the first plating layer 74 and the second plating layer 78 is etched. Details of the selective etching are the same as those in the first embodiment. When step 62 is completed, a first opening having a width W1 by the first plating layer 74 appears.

  When step 62 is finished, the process proceeds to step 64. FIG. 15 is a diagram for explaining step 64. In step 64, the semiconductor substrate 30 is further etched by performing second dry etching using the first plating layer 74 as a mask. When step 64 is completed, a tapered via hole is obtained as shown in FIG.

  When step 64 is completed, the process proceeds to step 66. FIG. 16 is a diagram for explaining step 66. In step 66, the first plating layer 74 made of Ni is wet-etched with a mixed solution of sulfuric acid and nitric acid. Thereafter, the metal conductive layer 72 is appropriately removed to obtain a semiconductor substrate 30 having a tapered via hole as shown in FIG. 16, and the processing is completed. The etching method of this embodiment includes the above-described processing.

  This embodiment can obtain the same effect as that of the first embodiment by using a metal mask having a two-layer structure. Further, as described in step 56, the second plating layer 78 is formed so as to fill a predetermined gap formed by the first plating layer 74 and the resist layer 76. Therefore, since the opening of the second plating layer 78 matches the width W2 of the resist layer 76, W2 can be controlled with high accuracy.

  The resist layer 76 of this embodiment is formed on the metal conductive layer 72. As already described, the metal conductive layer 72 has an effect of preventing peeling of the upper layer film, so that the resist layer can be prevented from falling down. Forming a resist layer on the metal conductive layer 72 in this way is particularly effective when the opening of the first plating layer (first opening) is narrow and the resist layer is likely to collapse. On the other hand, if there is no risk of the resist layer falling, the resist layer may be formed directly on the substrate 30 instead of on the metal conductive layer 72. Therefore, in this embodiment, the resist layer is disposed in contact with the metal conductive layer. It is not an essential requirement.

  In the tapered via hole formed in the semiconductor substrate in the present embodiment, the width of the via hole is reduced stepwise from the top of the hole toward the bottom of the hole. However, if the via hole has a tapered shape, the via hole filling property may be improved. When the etching method of this embodiment is applied, for example, by forming the resist layer 80 in a reverse taper shape as shown in FIG. 17, it is possible to form a tapered via hole having a tapered via hole shape.

  This will be described with reference to FIGS. The flow of the etching method described with reference to FIGS. 17 to 23 basically follows the flowchart of FIG. 8 except that the resist layer 80 is formed in a reverse taper shape rather than perpendicular to the metal conductive layer 72. In general, the sidewall shape of the resist layer can be controlled by performing chemical treatment on the resist layer surface so that the solubility in the developer varies depending on the location, or adjusting the exposure conditions, even if the resist layer is the same. . The resist layer shape can be changed to a reverse taper shape (overhang shape) by the above-described method or the like. FIG. 17 is a view showing a resist layer 80 having a reverse taper shape. The flow after the formation of the resist layer is as already described in this embodiment, but will be briefly described with reference to FIGS.

  When the resist layer 80 is formed, the second plating layer 82 is formed (FIG. 18). Next, the resist layer 80 is peeled off (FIG. 19). Since the resist layer 80 has a reverse taper shape, the second plating layer 82 has a taper shape with respect to the metal conductive layer 72 and the semiconductor substrate 30. Next, first dry etching is performed (FIG. 20), and the second plating layer 82 is etched by selective wet etching (FIG. 21). Next, second dry etching is performed to further etch the semiconductor substrate 30 (FIG. 22). Next, the metal conductive layer 72 and the like are appropriately removed, and a tapered via hole having a tapered shape can be formed as shown in FIG.

  By forming the metal mask in a tapered shape in this way, the via hole can be etched into the tapered shape. Further, since the side wall of the tapered via hole is inclined in a tapered shape, discontinuity (step breakage) of the filler due to the step in the via hole can be prevented when the via hole is filled with metal. Therefore, the embedding property can be further improved. Here, the case where the second plating layer has a tapered shape is illustrated, but the above-described effect can be obtained if any plating layer of the metal mask having a multilayer structure is formed in a tapered shape.

  Also in the present embodiment, modifications similar to those in the first embodiment can be made without departing from the scope of the present invention, for example, the material of the semiconductor substrate is not particularly limited.

Embodiment 3
The present embodiment relates to an etching method for forming a tapered via hole by a simpler process. This embodiment will be described with reference to FIGS. The etching method of the present embodiment is also used as a method for manufacturing a semiconductor device as in the first embodiment. In addition, it is the same as that of Embodiment 1, 2 about the point which attaches | subjects the same code | symbol to the same material or the same, and corresponding component, and abbreviate | omits description multiple times.

  FIG. 24 is a flowchart for explaining the etching method of this embodiment. Hereinafter, description will be made along this flowchart. First, a metal conductive layer is formed on a semiconductor substrate (step 100). Next, a first plating layer 124 made of Cu is formed on the metal conductive layer by an electrolytic plating method or an electroless plating method using the metal conductive layer as a power feeding layer (step 102). FIG. 25 is a diagram for explaining step 102. As shown in FIG. 25, the first plating layer 124 has a first opening which is an opening having a width W1. The thickness of the first plating layer 124 is formed to be 1/10 or less of the depth of the via hole to be formed in the semiconductor substrate 30.

  Note that the semiconductor substrate 30 of the present embodiment is SiC. Further, since the material and the formation method of the metal conductive layer 122 are the same as those in the first embodiment, description thereof is omitted.

  When step 102 is completed, the process proceeds to step 104. In step 104, a resist layer is formed. FIG. 26 is a diagram for explaining step 104. In step 104, a resist layer 126 is formed on the first plating layer 124 in the first opening and in the vicinity of the first opening. As shown in FIG. 26, the resist layer 126 is formed so as to fill the first opening and further cover the portion of the first plating layer 124 near the first opening. The width of the resist layer 126 is W1 as described above in the portion filling the first opening. The portion on the first plating layer 124 is W2, which is wider than W1.

  When step 104 is completed, the process proceeds to step 106. FIG. 27 is a diagram for explaining step 106. In step 106, the second plating layer 128 is formed on the first plating layer 124 on which the resist layer 126 is not formed by an electrolytic plating method or an electroless plating method using the first plating layer 124 as a power feeding layer. The second plating layer 128 is formed in contact with the resist layer 126. In the present embodiment, the second plating layer 128 is made of Ni.

  When step 106 is completed, the process proceeds to step 108. FIG. 28 is a diagram for explaining step 108. In step 108, the resist layer 126 is removed. When the resist layer 126 is peeled off by a well-known method, the second opening represented by the opening width W2 appears by the second plating layer 128, and the first opening represented by the opening width W1 by the first plating layer 124. Also appears.

  As described in the second embodiment, when the metal conductive layer 122 is disposed immediately below the resist layer 126, it may be removed by selective wet etching or the like in step 108.

  When step 108 is completed, the process proceeds to step 110. FIG. 29 is a diagram for explaining step 110. In step 110, first dry etching is performed using the first plating layer 124 as a mask. In the first dry etching, the semiconductor substrate 30 is etched, and the first plating layer 124 in the vicinity of the first opening and the metal conductive layer 122 thereunder are etched.

  Here, the first dry etching is performed using a mixed gas of sulfur fluoride and oxygen. Under this condition, the first dry etching cannot selectively etch the semiconductor substrate 30 with respect to the first plating layer 124 and the metal conductive layer 122. That is, the selectivity is poor, and the first plating layer 124 and the metal conductive layer 122 immediately below it are also etched in the first dry etching. On the other hand, since the second plating layer 128 is made of Ni, it can be etched with high selectivity with respect to the semiconductor substrate 30 and the film reduction is slight.

  Then, as shown in FIG. 30, in the first dry etching, the portion of the first plating layer 124 (the first plating layer in the vicinity of the first opening) where the second plating layer 128 is not formed on the upper layer and the metal conductive immediately below the portion. Continue until layer 122 is etched.

  When step 110 is completed, the process proceeds to step 112. FIG. 31 is a diagram for explaining step 112. In step 112, second dry etching is performed using the second plating layer 128 as a mask. Since the second opening formed by the second plating layer 128 is wider than the first opening, the second dry etching is performed so that the via hole is wider.

  Thereafter, the metal conductive layer 122, the first plating layer 124 and the second plating layer 128 immediately below the second plating layer 128 are appropriately removed, and the semiconductor substrate 30 having the tapered via holes as shown in FIG. 30 is obtained. To end the process. The etching method of this embodiment includes the above-described processing.

  In the first and second embodiments, in order to etch a specific layer of a metal mask having a multilayer structure, a wet etching step for widening the opening width of the metal mask is performed between the first dry etching and the second dry etching. It was essential. However, in the present embodiment, in the first dry etching, not only the semiconductor substrate but also the first plating layer 124 near the first opening and the metal conductive layer 122 immediately below the first plating layer are etched. Therefore, the opening width can be widened from W1 to W2 simply by continuing dry etching without wet etching. Therefore, according to the etching method of the present embodiment, the tapered via hole can be formed by a simple process.

  The features of this embodiment are as described above. Therefore, in the first dry etching, material selection is performed so that the selection ratio between the first plating layer and the metal conductive layer immediately below the semiconductor substrate is low as well as the semiconductor substrate is etched. Here, it is preferable that the selection ratio of the semiconductor substrate to the first plating layer and the underlying metal conductive layer is less than 5. Further, it is preferable that the second plating layer is formed to be sufficiently thick so that the second plating layer does not disappear and disappear in the first dry etching, and the selection ratio between the second plating layer and the semiconductor substrate is preferably greater than 10. . However, the limitation of the selection ratio is not limited to these because it is appropriately determined according to the environment in which the first dry etching is performed. In this embodiment, the semiconductor substrate is made of SiC, the metal conductive layer is made of Ti and Au, the first plating layer is Cu, the second plating layer is Ni, and the first dry etching is made of sulfur fluoride and oxygen. Although an example using a mixed gas has been described, other materials can be adopted as long as the effects of the present invention can be obtained, and the present invention is not limited thereto.

  In the present embodiment, the first dry etching and the second dry etching have been described as separate steps, but these are essentially the same steps that do not involve a change in gas type. In other words, in the present embodiment, in order to explain that the opening width of the metal mask changes from the first opening to the second opening, it is only formally divided into two dry etching steps.

  In the present embodiment, the film thickness of the first plating layer 124 is 1/10 or less of the depth of the via hole to be formed in the semiconductor substrate. This is because a part of the first plating layer can be etched by the first dry etching. Therefore, the thickness of the first plating layer 124 is not limited to the thickness of the present embodiment because it is appropriately determined in consideration of the above-described selection ratio.

  In addition, various modifications can be made without departing from the scope of the present invention.

2 is a flowchart of an etching method according to the first embodiment. It is a figure explaining the 1st plating layer. It is a figure explaining a 2nd plating layer. FIG. 5 is a diagram for explaining first dry etching. It is a figure explaining the process of etching a 2nd plating layer by selective wet etching. It is a figure explaining 2nd dry etching. It is a figure explaining the taper-shaped via hole formed by the etching method of Embodiment 1. 6 is a flowchart of an etching method according to a second embodiment. It is a figure explaining the 1st plating layer. It is a figure explaining a resist layer. It is a figure explaining a 2nd plating layer. It is a figure explaining resist layer peeling. FIG. 5 is a diagram for explaining first dry etching. It is a figure explaining the process of etching a 2nd plating layer by selective wet etching. It is a figure explaining 2nd dry etching. It is a figure explaining the taper-shaped via hole formed by the etching method of Embodiment 2. It is a figure explaining the resist layer of a reverse taper shape. It is a figure explaining a 2nd plating layer. It is a figure explaining resist layer peeling. FIG. 5 is a diagram for explaining first dry etching. It is a figure explaining the process of etching a 2nd plating layer by selective wet etching. It is a figure explaining 2nd dry etching. It is a figure explaining a taper-shaped taper-shaped via hole. 6 is a flowchart of an etching method according to a second embodiment. It is a figure explaining the 1st plating layer. It is a figure explaining a resist layer. It is a figure explaining a 2nd plating layer. It is a figure explaining resist layer peeling. FIG. 5 is a diagram for explaining first dry etching. FIG. 6 is a diagram for explaining a first plating layer and the like at the end of the first dry etching. It is a figure explaining 2nd dry etching. It is a figure explaining the taper-shaped via hole formed by the etching method of Embodiment 3.

Explanation of symbols

30 Semiconductor substrate, 32 Metal conductive layer, 34 First plating layer, 36 Second plating layer

Claims (10)

Forming a metal conductive layer having an opening on a semiconductor substrate;
Forming a first plating layer having a first opening on the metal conductive layer by an electrolytic plating method or an electroless plating method using the metal conductive layer as a power feeding layer;
Forming a second plating layer having a second opening narrower than the first opening on a side wall of the first plating layer by an electrolytic plating method or an electroless plating method using the first plating layer as a power feeding layer; When,
Etching the semiconductor substrate by performing a first dry etching using the second plating layer as a mask;
Performing selective wet etching to leave the first plating layer after the first dry etching to etch the second plating layer;
And a second dry etching process using the first plating layer as a mask after the second plating layer is etched to further etch the semiconductor substrate. Forming a metal conductive layer on a semiconductor substrate;
Forming a first plating layer having an opening on the metal conductive layer by an electrolytic plating method or an electroless plating method using the metal conductive layer as a power feeding layer;
Forming a resist layer in the opening so as to have a predetermined gap from a side wall of the first plating layer;
Forming a second plating layer so as to fill the predetermined gap in a side wall of the first plating layer by an electrolytic plating method or an electroless plating method using the first plating layer as a power feeding layer;
Peeling the resist layer;
Etching the semiconductor substrate by performing a first dry etching using the second plating layer as a mask after removing the resist layer;
Etching the second plating layer by performing selective wet etching to leave the first plating layer after the first dry etching;
And a second dry etching process using the first plating layer as a mask after the second plating layer is etched to further etch the semiconductor substrate.   The etching method according to claim 2, wherein the resist layer is formed in a reverse taper shape. The first plating layer is Ni;
The second plating layer is Cu;
The etching method according to claim 1, wherein hydrochloric acid is used in the wet etching. The first plating layer is Ni;
The second plating layer is Au;
The etching method according to claim 1, wherein an iodine-based etching solution is used in the wet etching.   The first plating layer and the second plating layer are formed of different materials selected from Ni, Cr, Pt, Au, Cu, and W, respectively. The etching method according to one item. Forming a metal conductive layer on a semiconductor substrate;
Forming a first plating layer having an opening on the metal conductive layer by an electrolytic plating method or an electroless plating method using the metal conductive layer as a power feeding layer;
Forming a resist layer in the opening and on the first plating layer in the vicinity of the opening;
After the resist layer is formed, the second plating layer is in contact with the resist layer on the first plating layer on which the resist layer is not formed by an electrolytic plating method or an electroless plating method using the first plating layer as a power feeding layer. Forming a plating layer;
Peeling the resist layer and exposing the first plating layer in the vicinity of the opening;
After the resist layer is peeled off, a first dry etching is performed using the first plating layer as a mask to etch the semiconductor substrate, and the first plating layer in the vicinity of the opening and the metal conductive layer below it are etched. When,
And a step of performing a second dry etching using the second plating layer as a mask after the first dry etching, and further etching the semiconductor substrate.   The metal conductive layer has a multilayer structure including a Ti layer in contact with the semiconductor substrate and an Au layer in contact with the first plating layer. Etching method.   The etching method according to claim 1, wherein the semiconductor substrate is a GaN substrate or a SiC substrate.   The manufacturing method of the semiconductor device using the etching method as described in any one of Claims 1-9.

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