Method for manufacturing a semiconductor device

Abstract

Method for manufacturing a semiconductor device, comprising: a manufacturing step for producing an etching solution (29) by dissolving titanium in an ammonia-hydrogen peroxide solution (22) in advance prior to using the ammonia-hydrogen peroxide solution (22) for etching; a flow step for the flow of the etching solution (29) after the manufacturing step, such that a concentration of the etching solution (29) in a treatment bath (20) becomes constant; and a treatment step for etching a metal layer (14, 42) onto a semiconductor wafer (10) with the etching solution (29) by placing the semiconductor wafer (10), which has a photoresist layer (16) and the metal layer (14, 42), into the treatment bath (20) after the flow step has been started.

Description

Area

[0001] The present invention relates to a method for manufacturing a semiconductor device. background

[0002] Various techniques for preventing changes in etching speed are known with respect to wet etching on a metal layer, as described in Patent Literatures 1 and 2 shown below. Literature listPatent literature [PTL 1] JP 2002 - 241 968 A [PTL 2] JP 2009 - 267 115 A [PTL 3] US 2002 / 0 001 967 A1 [PTL 4] CN 1 706 986 A [PTL 5] JP 2014 - 11 342 A SummaryTechnical problem

[0003] In a semiconductor manufacturing process, wet etching is performed on a titanium layer using an ammonia-hydrogen peroxide solution. A technique for circulating an etching solution to homogenize the concentration or stabilize the temperature is also known. However, circulating the ammonia-hydrogen peroxide solution promotes the decomposition of hydrogen peroxide, and therefore, the hydrogen peroxide concentration decreases over time. The etching rate is greatly influenced by the hydrogen peroxide concentration. Therefore, the etching rate decreases as time passes after the preparation of the ammonia-hydrogen peroxide solution, and the etching rate cannot be maintained at a constant level.

[0004] The present invention has been conceived to solve the problem described above, and an object of the present invention is to provide a semiconductor device manufacturing method capable of maintaining the etching speed for a long period of time. Solution to the problem

[0005] A method for manufacturing a semiconductor device according to the present invention comprises: a preparation step of preparing an etching solution by dissolving titanium in an ammonia-hydrogen peroxide solution in advance before using the ammonia-hydrogen peroxide solution for etching; a flowing step of flowing the etching solution after the preparation step so that a concentration of the etching solution in a treatment bath becomes constant; and a treatment step of etching a metal layer on a semiconductor wafer with the etching solution by placing the semiconductor wafer having a photoresist layer and the metal layer in the treatment bath after the flowing step is started. Advantageous effect of the invention

[0006] According to the present invention, the etching rate can be kept constant for a long period of time by preventing the decomposition of hydrogen peroxide in an ammonia-hydrogen peroxide solution. Brief description of the drawings Fig. 1 shows a flowchart illustrating a method of manufacturing a semiconductor device according to an embodiment of the present invention. Fig. 2 is a diagram illustrating a wet etching apparatus according to the embodiment of the present invention. Fig. 3 is a diagram illustrating a wet etching apparatus according to the embodiment of the present invention. Fig. 4 is a diagram illustrating a step of preparing the etching solution according to the embodiment of the present invention. Fig. 5 is a diagram illustrating a step of preparing the etching solution according to the embodiment of the present invention. Fig. 6 is a diagram illustrating an etching step according to the embodiment of the present invention. Fig. 7 shows a diagram illustrating the results of an experiment on a comparative example compared to the embodiment. Fig. Fig. 8 is a diagram illustrating the results of experiments on the embodiment of the present invention. Fig. 9 is a diagram illustrating the results of experiments on the embodiment of the present invention. Description of the embodiment

[0007] Fig. 1 shows a flowchart illustrating a method of manufacturing a semiconductor device according to an embodiment of the present invention. Fig. 2 and Fig. 3 are diagrams illustrating a wet etching apparatus 50 according to the embodiment of the present invention. In the present embodiment, a flowchart of Fig. 1 using the wet etching device 50 for etching a titanium layer 14 onto a Fig. 6 shown silicon carbide (SiC) wafer 10.

[0008] As in Fig. As shown in Figure 2, the wet etching apparatus 50 is provided with a treatment bath 20, a first piping 30, a circulation pump 32, a temperature controller 34, a second piping 36, and a concentration meter 38. An etching solution 29 is stored in the treatment bath 20. One end and the other end of the first piping 30 are connected to the treatment bath 20 to circulate the etching solution 29 therein. The circulation pump 32 and the temperature controller 34 are provided at intermediate positions in the first piping 30. The etching solution 29 can be circulated through the first piping 30 by operating the circulation pump 32. The temperature controller 34 is provided at an intermediate position in the first piping 30. The etching solution 29 is caused to flow through the temperature controller 34 to enable control of the temperature of the etching solution 29.One end of the second pipeline 36 is connected to an outlet of the circulation pump 32, while the other end of the second pipeline 36 is positioned above the treatment bath 20. Droplets 39 of the etching solution 29 can be supplied from the other end of the second pipeline 36. The concentration measuring device 38 is provided at an intermediate position in the second pipeline 36. From a value measured by the concentration measuring device 38, the concentration of the circulating etching solution 29 can be detected. The flow rate in the first pipeline 30 can be set, for example, to several liters per minute, and the flow rate in the second pipeline 36 can be set to several cubic centimeters per minute.

[0009] As a concrete structure of the treatment bath 20, a treatment bath with a plurality of baths, such as in Fig. 3 shown. Fig. 3 shows a sectional view of a processing bath 20. The processing bath 20 comprises an inner bath 201, into which the SiC wafer 10 is to be placed, and an outer bath 202, which is provided to enclose the inner bath 201. The etching solution 29 overflowing from the inner bath 201 flows into the outer bath 202. The circulation pump 32 draws the etching solution 29 in the outer bath 202 from one end of the first pipe 30, which is connected to a bottom surface of the outer bath 202. The circulation pump 32 supplies the etching solution 29 to the inner bath 201 via the other end of the first pipe 30, which is connected to a bottom surface of the inner bath 201. The etching solution 29 is thereby circulated in the processing bath 20. The present invention is not limited to the processing bath 20 having the Fig. 3. A single-bath structure may be sufficient for the present invention. The etching solution 29 in the treatment bath may be stirred using known means, in addition to the means for circulating it using the first conduit 30.

[0010] In the flow chart of Fig. The steps illustrated in Figure 1 are described below. First, in steps S100 and S102, the etching solution 29 is prepared. Specifically, the etching solution 29 is prepared by dissolving titanium in an ammonia-hydrogen peroxide solution 22 prior to etching. (Step S100)

[0011] In step S100, the ammonia-hydrogen peroxide solution 22 is first mixed. Fig. 4 is a diagram illustrating a step of preparing the etching solution 29 according to the embodiment of the present invention. Ammonia water 24 in which no titanium is dissolved, a hydrogen peroxide solution 26, and pure water 28 are successively added to the treatment bath 20, thereby preparing the ammonia-hydrogen peroxide solution 22. It is advantageous to add each liquid at the time of preparing the solution because the concentration changes when the solution is mixed in advance. The ammonia-hydrogen peroxide solution 22 is in a state used before etching, that is, an unused state, and therefore does not contain any metal such as titanium. (Step S102)

[0012] The process then proceeds to a step S102 and titanium is dissolved in the ammonia-hydrogen peroxide solution 22. Fig. Fig. 5 is a diagram illustrating the step of preparing the etching solution 29 according to the embodiment of the present invention. With reference to Fig. 5, the titanium layer 42 is dissolved in the ammonia-hydrogen peroxide solution 22, for example, by placing a semiconductor wafer 44, which has a titanium layer 42 formed on a semiconductor substrate 40, such as a silicon (Si) substrate, into the treatment bath 20. The semiconductor wafer 44 serves to previously dissolve titanium in the ammonia-hydrogen peroxide solution 22. Therefore, unlike the wafer to be etched, the semiconductor wafer 44 does not have a photoresist layer provided for patterning the titanium layer 42. The present invention is not limited to the embodiment using the semiconductor wafer 44. For example, fine titanium particles can be introduced into the treatment bath 20. The etching solution 29 is completed by step S102. (Step S104)

[0013] Subsequently, in a step S104, the circulation pump 32 is switched on in the Fig. 2 is actuated for circulating the etching solution 29. In a preferred mode according to the present embodiment, the etching solution 29 is circulated in the treatment bath 20 using the circulation pump 32 to make the concentration and temperature of the etching solution in the treatment bath 20 constant. Etching uniformity is improved by circulating the etching solution 29. That is, the concentration of the etching solution 29 in the treatment bath 20 can be maintained constant by circulating the etching solution 29 in the treatment bath 20 by means of the circulation pump 32. Since the temperature control device 34 is attached to the treatment bath 20, and since the etching solution 29 is circulated so that the temperature of the etching solution 29 is constant, changes in the etching rate with temperature changes can also be prevented.

[0014] When the ammonia-hydrogen peroxide solution is circulated, the decomposition of hydrogen peroxide is promoted, and therefore, the concentration of hydrogen peroxide decreases over time. The etching rate is greatly influenced by the concentration of hydrogen peroxide. Therefore, the etching rate decreases as time passes after the preparation of the ammonia-hydrogen peroxide solution 22, and the etching rate cannot be maintained constantly. The decomposition of hydrogen peroxide tends to be promoted when the ammonia-hydrogen peroxide solution 22 is circulated, particularly for two reasons described below. The first reason is that in the case where the treatment bath 20 is provided with two baths, as in Fig. 3, the contact area between the ammonia-hydrogen peroxide solution 22 and the atmospheric air is increased because the structure is such that the ammonia-hydrogen peroxide solution 22 overflows from the inner bath 201 into the outer bath 202 when the ammonia-hydrogen peroxide solution 22 is circulated. The second reason is that oxygen dissolved in the ammonia-hydrogen peroxide solution 22 escapes from the solution through a cavitation effect due to pressure changes in the circulating pump 32.

[0015] The inventor of the present invention has conducted serious studies and found that the decomposition of hydrogen peroxide in the ammonia-hydrogen peroxide solution can be prevented by dissolving titanium beforehand. This allows the etching rate to be maintained constant over a long period of time. The reason why the decomposition of hydrogen peroxide can be prevented by dissolving titanium immediately after preparing the ammonia-hydrogen peroxide solution is described below. A reaction of hydrogen peroxide represented by Formula 1 below occurs in an alkaline solution to generate a hydroperoxy radical, i.e., OOH. H2O2 + OH ⇔ H2O + OOH (Formula 1)

[0016] The hydroperoxy radical is believed to be effective in promoting the decomposition of hydrogen peroxide by reacting with hydrogen peroxide in an alkaline solution.

[0017] It is assumed that the reaction shown in formula 2 below occurs and the decomposition of H2O2 proceeds at an increasingly faster rate. H2O2 + OOH → O2 + H2O + OH (Formula 2)

[0018] By dissolving titanium in the ammonia-hydrogen peroxide solution, a reaction is caused which is represented by the following formula 3. TiOOH + NH3 = NH2OH / TiOH (Formula 3) The hydroperoxy radical is primarily consumed to produce hydroxylamine. Hydroxylamine, i.e., NH2OH, is a titanium salt. Since the reaction represented by Formula 3 is caused, the reaction of the hydroperoxy radical, which causes the decomposition of hydrogen peroxide represented by Formula 2, can be prevented. The amount of titanium to be dissolved in the ammonia-hydrogen peroxide solution 22 can be determined experimentally so that the reaction represented by Formula 2 above is sufficiently prevented.

[0019] Subsequently, in a step S106, the SiC wafer 10 is placed in the treatment bath 20 and immersed in the etching solution 29. Fig. 6 shows a diagram illustrating an etching step according to the embodiment of the present invention. The SiC wafer 10 to be etched includes a titanium layer 14 deposited on a SiC substrate 12 and a photoresist layer 16 deposited on the titanium layer 14, and includes the photoresist layer patterned in the desired shape. Fig. 6 shows a state in which an etched groove 15 is formed in the titanium layer 14.

[0020] In the present embodiment, the titanium layer 14 is etched onto the SiC wafer in step S106. However, the present invention is not limited to this. A layer of a metal other than titanium can be etched using the etching solution 29. For example, a nickel layer can be deposited on the SiC wafer 10 instead of the titanium layer 14 and etched in step S106. However, from the standpoint of preventing contamination, it is advantageous that the previously dissolved metal and the metal to be etched are the same. The manufacturing method according to the present embodiment is therefore suitable for etching on the titanium layer 14. Since both titanium and nickel are bonded to the silicon carbide by means of a Schottky junction, the etching method according to the present embodiment is preferably used to form a Schottky barrier electrode on the SiC substrate 12.

[0021] The results of experiments on the embodiment of the present invention are described below with reference to Fig. 7 to 9 described. Fig. Figure 7 shows a diagram illustrating the results of an experiment on a comparative example compared to the embodiment. Fig. 8 and Fig. 9 are diagrams illustrating the results of experiments on the embodiment of the present invention. Fig. 7 and Fig. 9, the NH3 concentration is shown with a diamond; the H2O2 concentration is shown with a square; and the amount of removed titanium is shown with a triangle in a case where the SiC wafer 10 is immersed in the etching solution 29 for 4 minutes. Fig. 7 and Fig. 9, the scale on the left indicates the concentration [%], while the scale on the right indicates the amount of removed titanium layer [nm].

[0022] Fig. Figure 7 is a graph illustrating the results of an experiment using an ammonia-hydrogen peroxide solution in which no titanium is dissolved as a comparison example. The results show concentration changes with respect to elapsed time and an amount of titanium removed. The elapsed time is a time elapsed after the preparation of the ammonia-hydrogen peroxide solution. In a range where the elapsed time was 0 to about 10 hours immediately after the start of the experiment, the H2O2 concentration rapidly decreased to 10% or less. When the elapsed time became about 100 hours, the H2O2 concentration decreased to about 1 to 0%. The amount of titanium removed was measured at a stage where the elapsed time was 100 hours and found to be substantially zero nm.

[0023] Fig. Figure 8 shows the relationship between the H2O2 concentration and the titanium etching rate. The amount of removed titanium in the case where the SiC wafer 10 was immersed in the etching solution 29 for 4 minutes was plotted in relation to the changed H2O2 concentration. As the H2O2 concentration decreases, the titanium etching rate decreases, as shown in Fig. 8 is shown.

[0024] Fig. Fig. 9 shows the results of an experiment using the etching solution 29 according to the present embodiment. In contrast to the results shown in Fig.According to the results shown in Figure 7, the H2O2 concentration was extremely low even when the elapsed time was 100 hours or more. The reduction in the H2O2 concentration was stable at approximately 12%. Etching of the titanium layer 14 was performed at a stage where the elapsed time was approximately 160 hours in the experiment of the present embodiment. The removal amount by this etching was approximately 300 nm. Thus, in the present embodiment, the etching rate can be kept constant for a long period of time by preventing the decomposition of hydrogen peroxide in the ammonia-hydrogen peroxide solution. List of reference symbols 10 SiC wafers 12 SiC substrate 14, 42 titanium layer 15 etched groove 16 photoresist layer 20 treatment baths 22 Ammonia-hydrogen peroxide solution 24 Ammonia water 26 Hydrogen peroxide solution 28 pure water 29 Etching solution 30 first pipeline 32 Circulation pump 34 Temperature control device 36 second pipeline 38 Concentration meter 39 droplets 40 semiconductor substrate 44 semiconductor wafers 50 wet etching device 201 inner bath 202 outer bath

Claims

[1] A method of manufacturing a semiconductor device, comprising: a preparation step of preparing an etching solution (29) by dissolving titanium in an ammonia-hydrogen peroxide solution (22) in advance before using the ammonia-hydrogen peroxide solution (22) for etching; a flow step for flowing the etching solution (29) after the manufacturing step so that a concentration of the etching solution (29) in a treatment bath (20) becomes constant; and a treatment step for etching a metal layer (14, 42) on a semiconductor wafer (10) with the etching solution (29) by placing the semiconductor wafer (10), which has a photoresist layer (16) and the metal layer (14, 42), in the treatment bath (20) after the flow step has been started. [2] A method of manufacturing a semiconductor device according to claim 1, wherein the metal layer (14, 42) is formed of titanium. [3] A method for manufacturing a semiconductor device according to claim 1 or 2, wherein a temperature of the etching solution (29) is adjusted by flowing the etching solution (29) by flowing the etching solution (29) via a temperature control device (34). [4] A method for manufacturing a semiconductor device according to any one of claims 1 to 3, wherein the treatment bath (20) comprises a first bath (201) in which the etching solution (29) is stored, a second bath (202) into which the etching solution (29) overflowing from the first bath (201) flows, and a flow channel (30) connecting the first bath (201) and the second bath (202), and wherein in the flow step, the etching solution (29) is circulated from the second bath (202) to the first bath (201) through the flow channel (30). [5] A method of manufacturing a semiconductor device according to any one of claims 1 to 4, wherein the semiconductor wafer (10) is a SiC wafer and the metal layer (14, 42) is connected to the SiC wafer by means of a Schottky junction.

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