Gold or Gold Alloy Etching Liquid Composition and Etching Method

Abstract

To provide: a gold or gold alloy etchant which is superior in the wettability to a substrate having a gold film and a gold alloy film and in the fine processability, and which does not contain N-methyl-2-pyrrolidinone (NMP) having a long liquid life; and an etching method.SOLUTION: A gold or gold alloy etchant comprises an iodine, an iodide, an organic solvent and water. The organic solvent is one or more kinds of a group consisting of 3-methoxy-N,N-dimethyl propanamide, 3-butoxy-N,N-dimethyl propanamide, ethylene glycol, propylene glycol, diethylene glycol, 1,2-ethanediol, 1,4-butanediol and 2,3-butanediol.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an etching solution and an etching method for gold or a gold alloy formed on a substrate such as a semiconductor wafer.

Background Art

[0002] Currently, a gold film is used as a conductor in integrated circuits, printed circuit boards, etc. The gold film has high conductivity, is easy to form a film, and is chemically stable, but it is difficult to etch. The etching method of the gold film is performed by wet etching. Usually, there are a dip method in which an etching solution is stored in an etching tank made of quartz, Teflon (registered trademark), etc., and a wafer is immersed therein, and a spin method in which the wafer is vacuum-sucked or mechanically chucked to a support base and the etching solution is sprayed while rotating to perform etching.

[0003] Examples of the etching solution for the gold film include "cyanide-based", "aqua regia-based", and "iodine-based". The "cyanide-based" contains sodium hydroxide and sodium cyanide as components. Since gold easily forms a complex with cyanide ions, etching is easy. However, it has disadvantages such as being strongly alkaline, difficult to handle, highly irritating, and toxic. Therefore, in the applications of the electronics industry, there are few usage examples other than an example used for complete removal of the lead pattern after electroplating (Patent Document 1). The "aqua regia-based" is a mixed acid of hydrochloric acid and nitric acid, and is often used in the treatment of gold films on semiconductor substrates. However, it has disadvantages such as a slow etching rate and being difficult to handle due to its strong acidity (Patent Document 2). On the other hand, the "iodine-based" consists of potassium iodide and iodine, and has a neutral liquid property and is easy to handle. Therefore, it has been widely used as an etching solution for gold films on semiconductor substrates (Patent Documents 3 and 4).

[0004] In addition, it is known to contain an organic solvent in order to improve the wettability, fine processability, and solution life of an "iodine-based" etching solution with respect to a substrate. Among these, it is known that N-methyl-pyrrolidinone (NMP) is useful (Patent Documents 5 and 6).

[0005] However, in recent years, from the perspective of having an adverse effect on human health, regulations on NMP have become stricter, and due to the situation where it has become difficult to use an etching solution containing NMP, the demand for a gold or gold alloy etching solution that does not contain NMP is increasing.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0007] Accordingly, an object of the present invention is to provide a gold or gold alloy etching solution and an etching method that do not contain NMP, are excellent in wettability and fine processability with respect to a substrate having a gold film and a gold alloy film, and have a long solution life.

Means for Solving the Problems

[0008] In the process of earnestly studying a gold or gold alloy etching solution and an etching method that are excellent in wettability and fine processability with respect to a substrate having a gold film and a gold alloy film, have a long liquid life, and do not contain NMP, it has been found that an iodine-based etching solution containing a specific organic solvent is excellent in wettability and fine processability with respect to a substrate having a gold film and a gold alloy film and has a long liquid life even when it does not contain NMP, and the present invention has been completed.

[0009] That is, the present invention relates to the following. [1] An etching solution for gold or gold alloy, characterized by containing iodine, iodide, an organic solvent, and water, wherein the organic solvent is one or more selected from the group consisting of 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, ethylene glycol, propylene glycol, diethylene glycol, 1,2-ethanediol, 1,4-butanediol, and 2,3-butanediol. The present invention relates to the etching solution.

[0010] [2] The etching solution according to [1], characterized in that the organic solvent is 3-methoxy-N,N-dimethylpropanamide.

[0011] [3] The etching solution according to [1] or [2], which does not contain N-methyl-2-pyrrolidinone.

[0012] [4] The etching solution according to any one of [1] to [3], characterized in that the iodide is potassium iodide.

[0013] [1] to [4], and a method for etching a gold film formed on a substrate, characterized by immersing the substrate in the etching solution according to any one of [1] to [4].

Effects of the Invention

[0014] According to the present invention, in a gold or gold alloy etching solution, even when a high-precision microfabrication technique is required without changing its composition and performance, it is possible to fully cope without using NMP.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described in detail.

[0017] The gold or gold alloy etching solution of the present invention is an etching solution composed of iodine, iodide, an organic solvent and water.

[0018] The iodide is not particularly limited. For example, potassium iodide, sodium iodide, ammonium iodide, rubidium iodide, cesium iodide, magnesium iodide, calcium iodide, strontium iodide, zinc iodide, cadmium iodide, mercury(II) iodide, lead(II) iodide, etc. may be mentioned, and one or more of these can be used. In particular, from the viewpoints of solubility in water, price, ease of handling, toxicity, etc., potassium iodide, sodium iodide, and ammonium iodide are preferable as the iodide.

[0019] The content of iodine in the iodine-based etching solution is not particularly limited, but for example, it can be 1 to 1000 mM. Preferably, it is 10 to 200 mM. The content of the iodide in the iodine-based etching solution is not particularly limited, but for example, it can be 1 to 3000 mM. Preferably, it is 150 to 1500 mM. Also, the ratio of the contents of iodine and iodide (molar concentration ratio, iodine:iodide) is not particularly limited, but preferably it is 1:3 to 1:10, and more preferably it is 1:5 to 1:10.

[0020] The organic solvent used in the present invention can suppress the etching rate of the gold or gold alloy film, has excellent wettability, has the ability to smooth the gold surface, has an effect of suppressing the side etching amount, and suppresses the volatilization of iodine. Specifically, they are 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, ethylene glycol, propylene glycol, diethylene glycol, 1,2-ethanediol, 1,4-butanediol, and 2,3-butanediol. Among them, 1,4-butanediol, ethylene glycol, and 3-methoxy-N,N-dimethylpropanamide are preferable, and 3-methoxy-N,N-dimethylpropanamide is more preferable.

[0021] The content of the organic solvent in the etching solution is not particularly limited, and it is preferable to appropriately adjust the amount used according to the type of organic solvent used. Generally, it can be used in the range of 1 to 99% by volume, preferably 5 to 50% by volume, more preferably 10 to 40% by volume. For example, when the additive is N,N-dimethylpropanamide, the amount used is preferably 10 to 30% by volume, more preferably 15 to 25% by volume.

[0022] In addition, the etching solution contains water. The content of water in the etching solution is not particularly limited. For example, it can be the remaining part of other components. For example, the water content can be 1 to 99% by volume, preferably 60 to 90% by volume.

[0023] The etching solution of the present invention described above is used for etching gold and gold alloys. Examples of the gold alloy include gold alloys with palladium, magnesium, aluminum, titanium, manganese, iron, cobalt, nickel, molybdenum, tungsten, platinum, silver, copper, etc. The etching solution can be applied to those combined with one or more of these. In the gold alloy, the gold content is preferably 60% by weight or more, more preferably 80% by weight or more.

[0024] The etching conditions using the etching solution of the present invention are not particularly limited. For example, they can be carried out according to the conditions of known etching methods. Examples of the contact method between the object to be etched and the etching solution include the dip method of filling a container with an iodine-based etching solution and immersing the object to be etched. At that time, it is preferable to swing the object to be etched or forcibly circulate the iodine-based etching solution in the container. Thereby, the object to be etched is etched uniformly. Alternatively, a spray method in which an iodine-based etching solution is attached to an object to be etched by spraying, a spin method in which an iodine-based etching solution is discharged from a nozzle onto a rotating object to be etched, or the like may be used. Further, these methods may be used in combination with the dip method. The etching time is not particularly limited, and for example, it can be set to 1 to 60 minutes. Further, the etching temperature (in the dip method, the temperature of the iodine-based etching solution; in the spray method and the spin method, the temperature of the iodine-based etching solution or the temperature of the object to be etched) is not particularly limited, and for example, it can be set to 20 to 50°C. At this time, if necessary, the temperature of the iodine-based etching solution, the object to be etched, etc. may be adjusted by heating means such as a heater or a cooling means.

[0025] The present invention also relates to a method for etching a gold film or a gold alloy film using the above-described etching solution, and a method for manufacturing a semiconductor material formed by the method. Examples of the semiconductor material formed by the method include wiring materials and bumps. As described above, the present invention has been described in detail based on preferred embodiments, but the present invention is not limited thereto, and each component can be replaced with any component that can exhibit the same function, or any component can be added.

Examples

[0026] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited by these examples.

[0027] [Comparative Examples 1 to 6 and Examples 1 to 7] An aqueous solution of 0.079 M iodine and 0.60 M potassium iodide was used as a standard solution, and an etching solution obtained by adding an organic solvent to this standard solution was prepared. Next, a 2×2 cm Ni specimen was electroplated with electrolytic gold to a thickness of 3 μm, and immersed in the etching solution at a liquid temperature of 30°C stirred at about 200 rpm for 1 minute for etching. The test piece was washed with ultrapure water, dried with nitrogen gas, and the etching rate was calculated by the gravimetric method. The results are shown in Table 1 and Figure 1.

[0028] (Table 1) [Table 1] Etching Rate of Gold Film TIFF0007711874000001.tif122166 From the results of Table 1 and Figure 1, it was confirmed that the etching rate can be controlled by 1,4-butanediol, diethylene glycol, and 3-methoxy-N,N-dimethylpropanamide without using NMP, and further, these organic solvents have excellent etching controllability compared to NMP.

[0029] [Comparative Examples 7 - 12 and Examples 8 - 14] An aqueous solution of 0.079 M iodine and 0.60 M potassium iodide was used as a standard solution, and a solution obtained by adding an organic solvent to this standard solution was prepared. Also, a bare silicon substrate that was treated with a 1% dilute hydrofluoric acid solution for 1 minute, washed with ultrapure water, and dried with nitrogen gas was prepared. Next, the contact angle of 1 μl of the above solution on the bare silicon substrate was measured using a contact angle meter (CA-X150 type manufactured by Kyowa Interface Science Co., Ltd.). The results are shown in Table 2 and Figure 2.

[0030] (Table 2) [Table 2] Contact Angle TIFF0007711874000002.tif102166 From the results of Table 2 and Figure 2, it was confirmed that without using NMP, 1,4-butanediol, diethylene glycol, and 3-methoxy-N,N-dimethylpropanamide can achieve a contact angle of 50°C or less, that is, they have excellent wettability.

[0031] [Comparative Examples 13 - 18 and Examples 15 - 21] An aqueous solution of 0.079 M iodine and 0.60 M potassium iodide was used as a standard solution, and an etching solution obtained by adding an organic solvent to this standard solution was prepared. Next, a 1×1 cm gold bump substrate (gold bump (15 μm) / gold sputter layer (210 nm) / TiW layer / Si layer) was immersed in the etching solution at a liquid temperature of 30°C stirred at approximately 200 rpm for just the etching time of the gold sputter layer for etching. The gold bump substrate was washed with ultrapure water and dried with nitrogen gas, and the surface smoothing ability and appearance of the gold bumps were observed using a scanning electron microscope (SEM) (Hitachi High-Tech Corporation SU8200 series). The results are shown in Table 3, Figures 3 and 4. Note that the appearance of the gold bumps in Figure 4 was obtained by immersing the gold bump substrate in the etching solutions of Comparative Example 13 and Examples 15, 16, and 18 at a liquid temperature of 25°C stirred at approximately 350 rpm for just the etching time of the gold sputter layer.

[0032] (Table 3) [Table 3] Surface smoothing ability TIFF0007711874000003.tif116163 From the results in Table 3 and Figure 3, it was confirmed that without using NMP, 1,4-butanediol, diethylene glycol, and 3-methoxy-N,N-dimethylpropanamide have the same gold bump surface smoothing ability as NMP.

[0033] [Comparative Examples 19 - 21 and Examples 22 - 26] An aqueous solution of iodine 0.027 M and potassium iodide 0.11 M was used as a standard solution, and an etching solution with an organic solvent added to this standard solution was prepared. Next, a 2×1 cm sputtered gold substrate (resist / gold sputter layer (50 nm) / Ti layer / Si layer) was immersed in the etching solution at a liquid temperature of 25°C stirred at approximately 200 rpm for 1.5 times the just etching time of the gold sputter layer for etching. The sputtered gold substrate was washed with ultrapure water and dried with nitrogen gas, and the side etching amount was observed using a scanning electron microscope (SEM) (Hitachi High-Tech Corporation SU8200 series). The results are shown in Table 4.

[0034] (Table 4) [Table 4] Side etching amount TIFF0007711874000004.tif65163 From the results in Table 4, it was confirmed that without using NMP, 1,4-butanediol, diethylene glycol, and 3-methoxy-N,N-dimethylpropanamide exhibited an effect of suppressing the amount of side etching.

[0035] [Comparative Examples 22 to 23 and Examples 27 to 28] An aqueous solution of 0.079 M iodine and 0.60 M potassium iodide was used as a standard solution. A solution was prepared by adding an organic solvent to this standard solution, and the iodine volatilization inhibitory ability was evaluated by redox titration using a sodium thiosulfate solution at regular time intervals. The results are shown in Table 5.

[0036] (Table 5) [Table 5] Iodine Volatilization Inhibitory Ability TIFF0007711874000005.tif59163 From the results in Table 5 and Figure 5, it was confirmed that without using NMP, 1,4-butanediol, diethylene glycol, and 3-methoxy-N,N-dimethylpropanamide exhibited an effect of suppressing iodine volatilization.

Claims

1. An etchant for gold or a gold alloy, characterized by containing iodine, iodide, an organic solvent and water, wherein the organic solvent is 3-methoxy-N,N-dimethylpropanamide.

2. The etchant according to Claim 1, which does not contain N-methyl-2-pyrrolidinone.

3. The etchant according to any one of Claims 1 or 2, wherein the iodide is potassium iodide.

4. A method for etching a gold film formed on a substrate, characterized by immersing the substrate in the etchant according to any one of Claims 1 to 3.

Images