Etching solution and etching method for gold or gold alloy

Abstract

It is known that when etching gold films using etching solutions containing iodine and iodide, N-methyl-2-pyrrolidinone (NMP) is added to improve the etching solution's wettability, microfabrication property, and solution life. However, in recent years, the use of NMP has been regulated due to its adverse effects on human health. The present invention provides an etching solution and etching method for gold film that improves wettability, microfabrication property, and solution life without containing NMP. In order to address the problem of the prior art, the present invention provides etching solutions and etching methods for gold films that improve wettability, microfabrication property, and liquid life without NMP, characterized by the inclusion of a specific organic solvent in the etching solution containing iodine and iodide. [No Figure]

Description

[0001] The present invention relates to an etching method and an etchingsolution for gold or gold alloy formed on a substrate such as a semiconductorwafer.BACKGROUND OF THE INVENTION

[0002] Nowadays, gold films are used as electrical conductors in integratedcircuits and printed circuit boards. Gold films not only have high conductivity butalso are easy to deposit and are chemically stable, but they are challenging to etch.The etching method of gold films is performed by using wet etching, which usuallyincludes a dipping method and a spin method. In the dipping method, the etchingsolution is stored in an etching tank made of materials such as quartz or Teflon®and the wafer is immersed in it. In the spin method, the wafer is vacuum sucked ormechanical chucked onto a support stage and sprayed with the etching solutionwhile it is rotated.

[0003] Examples of etching solutions for gold films include “cyanide-based”,“aqua regia-based” and “iodine-based” solutions. For “cyanide-based” solution,which consists of sodium hydroxide and sodium cyanide, the “cyanide-based”solution is easy to etch because gold easily forms a complex with cyanide ions, butthe “cyanide-based” solution is with drawbacks of difficult handle due to it is withstrong, basicity, and strong irritation and toxicity. Therefore, in the electronicindustry, there are only very few usage examples of the cyanide-based solution,except for an example that lead pattern is complete removed after electroplating(prior art document 1). The “aqua regia-based” solution is a mixture ofhydrochloric acid and nitric acid, and it is commonly used in the treatment of goldfilms on semiconductor substrates, but it has the drawbacks of slow etching speedand being difficult to handle due to its strong acidity (prior art document 2). Incontrast, the “iodine-based” solution, composed of potassium iodide and iodine,has been widely used as an etching solution for gold films on semiconductorsubstrates because it is neutral pH and is easy to handle (prior art document 3 andprior art document 4).

[0004] It is also known that organic solvents are included in the iodine-basedetching solution to improve wettability, microfabrication property, and lifetime ofthe solution on the substrate, wherein N-methyl-pyrrolidinone (NMP) isparticularly useful (patent document 5, patent document 6).

[0005] However, in recent years, due to concerns about the detrimental effects ofN-methyl-2-pyrrolidone (NMP) on human health, regulations on NMP havebecome stricter, and the use of etching solutions containing NMP has becomechallenging, leading to an increasing demand for NMP-free gold or gold alloyetching solutions.

[0006] PRIOR ART DOCUMENTSPatent Document 1: JPH-08148810Patent Document 2: JPH-05136152Patent Document 3: JPH05251425Patent Document 4: US5221421Patent Document 5: JP2004-211142APatent Document 6: JP2006-291341ASUMMARY OF THE INVENTION

[0007] Therefore, the purpose of the present invention is to provide a gold orgold alloy etching solution and etching method that does not contain NMP, but iswith excellent wettability and microfabrication property on substrates with goldand gold alloy films, and with a long solution life.

[0008] During the diligent investigation of gold or gold alloy etching solutionsand etching methods without NMP and with excellent wettability, microfabricationproperties and a long solution life for substrates having gold and gold alloy films,we found that iodine etchant containing a specific organic solvent has excellentwettability and microfabrication properties for substrates having gold and goldalloy films and a long solution life even when it does not contain NMP, and thusachieved the present invention.

[0009] That is, the present invention relates to:An etching solution for gold or gold alloy, comprising: iodine, iodide, organicsolvent and water, wherein the organic solvent is one or more selected from thegroup consisting of 3-methoxy-N,N-dimethylpropanamide,3-butoxy-N,N-dimethylpropanamide, ethylene glycol, propylene glycol, diethyleneglycol, 1,2-ethanediol, 1,4-butanediol and 2,3-butanediol.

[0010] The etching solution as described above, wherein the organic solvent is3-methoxy N,N-dimethylpropanamide.

[0011] The etching solution as described above, wherein the etching solution isfree of N-methyl-2-pyrrolidinone.

[0012] The etching solution as described above, wherein the iodide is potassiumiodide.

[0013] A method for etching a gold film formed on a substrate, comprisingimmersing the substrate in the etching solution as described above.

[0014] With the present invention, an etching solution for gold or gold alloywithout using NMP can fully deal with the situation that the composition andperformance of the etching solution is required to remain unchanged and even thesituation that a highly precise microfabrication technique is required.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG.1 is a graph showing the etching rate of gold film in an etching solutioncontaining NMP or 3-methoxy-N,N-dimethylpropanamide.FIG.2 is a graph showing the contact angle on a bare silicon substrate for a solutioncontaining NMP or 3-methoxy-N,N-dimethylpropanamide.FIG.3 is a graph showing the surface condition of gold bumps when immersed inan etching solution containing NMP or 3-methoxy-N,N-dimethylpropanamide.FIG.4 is a graph showing the appearance of gold bumps when immersed in anetching solution containing 3-methoxy-N,N-dimethylpropanamide, 1,4-butanediol,or diethylene glycol.DETAILED DESCRIPTION OF THE PREFERRED EXAMPLES

[0016] The following is a detail description of the present invention.

[0017] An etching solution for gold or gold alloy of the present inventioncomprises iodine, iodide, organic solvent and water.

[0018] The iodides are not particularly limited and include, for example,potassium iodide, sodium iodide, ammonium iodide, rubidium iodide, cesiumiodide, magnesium iodide, calcium iodide, strontium iodide, zinc iodide, cadmiumiodide, mercury(II) iodide, and lead(II) iodide, and one or more of these can beused. Potassium iodide, sodium iodide, and ammonium iodide are especiallypreferred as iodides in terms of water solubility, price, ease of handling, andtoxicity.

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

[0020] The organic solvent used in the present invention are capable ofsuppressing the etching rate of gold or gold alloy films, have excellent wettability,have gold surface smoothing ability, are effective in suppressing the amount of sideetching, and suppress the volatilization of iodine. Specifically,3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide,ethylene glycol, propylene glycol, diethylene glycol, 1,2-ethanediol, 1,4-butanedioland 2,3-butanediol; preferably 1,4-butanediol, ethylene glycol,3-methoxy-N,N-dimethylpropanamide, and more preferably 3-methoxy-N,Ndimethylpropanamide.

[0021] The content of organic solvents in the etching solution is not limited, andit is preferable to adjust the amount used according to the type of organic solventused. Generally, a range of 1 to 99% by volume can be used, preferably 5 to 50%by volume, and more preferably 10 to 40% by volume. For example, if the additiveis N,N-dimethylpropanamide, the amount used is preferably 10-30% by volume,more preferably 15-25% by volume.

[0022] The etching solution also contains water. The content of water in theetching solution is not limited and can be, for example, the residual portion ofother components. For example, the water content can be 1 to 99% by volume,preferably 60 to 90% by volume.

[0023] The etching solution described above is used to etch gold and gold alloys.Gold alloys include, for example, gold alloys with palladium, magnesium,aluminum, titanium, manganese, iron, cobalt, nickel, molybdenum, tungsten,platinum, silver, copper, etc. The etching solution is applicable to a combination ofone or more of these. In the gold alloy, it is preferable that the gold content is 60%or more by weight and it is more preferable that the gold content be 80% or moreby weight.

[0024] Etching conditions using the etching solution of the present invention arenot limited, and can be performed, for example, according to the conditions ofknown etching methods.As a method for contacting the etching target with the etching solution, there is adipping method in which a container is filled with an iodine-based etching solutionand the etching target is immersed. At that time, it is preferable to oscillate theetching object or forcefully circulate the iodine etching solution in the container.This allows the etching solution to be etched uniformly. The spray method, inwhich iodine etching solution is sprayed onto the etched object, or the spin method,in which iodine etching solution is discharged from a nozzle onto the spinningetched object, may also be used. These may also be used in combination with thedip method. The etching time is not limited, and can be from 1 to 60 minutes. Also,the etching temperature (iodine etching solution temperature for the dip method, oriodine etching solution temperature or etching object temperature for the spray andspin methods) is not limited, and may be, for example, 20 to 50°C. In this example,the temperature of the iodine etching solution, etching object, etc. may be adjustedby heating means such as a heater or cooling means, if necessary.

[0025] The present invention also relates to a method for etching a gold film orgold alloy film using the etching solution described above, and a method formanufacturing semiconductor materials formed by said method. Semiconductormaterials formed by the above-mentioned method include wiring materials, bumps,and the like. The present invention has been described in detail based on suitableexamples.

[0026] [EXAMPLES]The present invention will be explained more specifically with reference to theexamples and comparative examples below.

[0027] [COMPARATIVE EXAMPLE 1 to 6 AND EXAMPLE 1 to 7]An aqueous solution of 0.079M iodine and 0.60M potassium iodide was used asthe standard solution, and an etching solution was prepared by adding organicsolvent to this standard solution. Next, a 2 x 2 cm Ni specimen was electrolyticallyplated with 3 μm thick gold, and immersed in the aforementioned etching solutionat a solution temperature of 30°C stirred at approximately 200 rpm for 1 minute toetch. The specimen was rinsed with ultrapure water, dried with nitrogen gas, andthe etching rate was calculated by the gravimetric method. The results are shown intable 1 and FIG. 1.

[0028] (Table 1)[Table 1] Etching rate of gold filmOrganicPotassiumIodine Solvent Etchingiodide Organic Solventsconcentration Content rate(nm / min.)concentration(vol%)comparativenone 0 440example 1comparative10 420example 2comparative20 385example 3comparativeNMP 30 346example 4comparative40 275example 5comparative50 155example 6example 1 0.079M 0.60M 1,4-butandiol 20 323example 2 diethylene glycol 20 310example 3 3-methoxy-N,N- 10 424example 4 20 328example 5 dimethylpropanamide 30 290example 6 40 237example 7 50 141From the results in table 1 and FIG. 1, it is observed that the etching rate can becontrolled by 1,4-butanediol, diethylene glycol, and3-methoxy-N,N-dimethylpropanamide without the use of NMP, and that theseorganic solvents have better etching control properties compared to NMP.

[0029] [COMPARATIVE EXAMPLE 7 to 12 AND EXAMPLE 8 to 14]An aqueous solution of 0.079 M iodine and 0.60 M potassium iodide was used asthe standard solution, and a solution was prepared by adding organic solvent to thisstandard solution. Bare silicon substrate were treated with 1% dilute hydrofluoricacid solution for 1 minute, rinsed with ultrapure water, and dried with nitrogen gas.The contact angle of 1 μl of the above solution on the bare silicon substrate wasmeasured using a contact angle meter (Model CA-X150 manufactured by KyowaSurface Science Co.). The results are shown in table 2 and FIG. 2.

[0030] (Table 2)[Table 2] Contact angleOrganicPotassiumIodine Solvent Contactiodide Organic Solventsconcentration Content angle(°)concentration(vol%)comparativenone 0 58.9example7comparative10 32.2example8comparative20 33.2example9comparativeNMP 30 34.1example10comparative40 34.8example11comparative 0.079M 0.60M 50 34.8example12example8 1,4-butangiol 20 40.5example9 diethylene glycol 20 44.4example10 10 36.5example11 20 38.73-methoxy-N,N-dimethylpropanamideexample12 30 36.9example13 40 38.7example14 50 37From the results in Table 2 and FIG. 2, it was observed that contact angles below50°C can be achieved by 1,4-butanediol, diethylene glycol and3-methoxy-N,N-dimethylpropanamide without the use of NMP, i.e., excellentwettability.

[0031] [COMPARATIVE EXAMPLE 13 to 18 AND EXAMPLE 15 to 21]An aqueous solution of 0.079M iodine and 0.60M potassium iodide was used asthe standard solution, and an etching solution was prepared by adding organicsolvent to this standard solution. Then, a 1 x 1 cm gold bump substrate (gold bump(15 μm) / gold sputter layer (210 nm) / TiW layer / Si layer) was immersed in theabove etching solution at a liquid temperature of 30°C stirred at about 200 rpm forthe just etching time of gold sputter layer. The gold bump substrate was washedwith ultrapure water, dried with nitrogen gas, and the surface smoothing ability andappearance of gold bumps were observed using a scanning electron microscope(SEM) (Hitachi High-Tech Corporation SU8200series). The results are shown intable 3 and FIG. 3 and 4. The gold bump appearance in FIG. 4 was obtained byimmersing the gold bump substrate in the etching solution of comparison examples13 and example 15, 16, and 18 at a liquid temperature of 25°C stirred at about 350rpm for the just etching time of the gold sputter layer.

[0032] (Table 3)[Table 3] Surface smoothing energyPotassium Organic Gold BumpIodineiodide Solvent surfaceconcentratio Organic Solventsconcentratio Content Smoothingnn (vol%) energycomparativenone 0 ×example 13comparative10 ◎example 14comparative20 ◎example 15comparativeNMP 30 ◎example 16comparative40 ◎example 17comparative 0.079M 0.60M50 ◎example 18example 15 1,4-butangiol 20 ○example 16 diethylene glycol 20 ○example 17 10 ◎example 18 20 ◎3-methoxy-N,N-dimethylpropanamiexample 19 30 ◎deexample 20 40 ◎example 21 50 ◎◎:Nearly no roughness on gold bump surface○:Slightly improved gold bump surface roughness×: Rough gold bump surfaceThe results in table 3 and FIG. 3 confirm that 1,4-butanediol, diethylene glycol,and 3-methoxy-N,N-dimethylpropanamide have the same gold bump surfacesmoothing ability as NMP without the use of NMP.

[0033] [COMPARATIVE EXAMPLE 19 to 21 AND EXAMPLE 22 to 26]An aqueous solution of 0.027M iodine and 0.11M potassium iodide was used asthe standard solution, and an etching solution was prepared by adding organicsolvent to this standard solution. Then, a 2 x 1 cm sputter gold substrate (resist / gold sputter layer (50 nm) / Ti layer / Si layer) was etched by immersing it in theabove etching solution at a liquid temperature of 25°C stirred at about 200 rpm for1.5 times the just etching time of the gold sputter layer. The sputtered goldsubstrate was washed with ultrapure water, dried with nitrogen gas, and the amountof side etching was observed using a scanning electron microscope (SEM) (HitachiHigh-Tech Corporation SU8200series). The results are shown in table 4.

[0034] (Table 4)[Table 4] Side etching amountOrganicPotassiumIodine Solvent Side etchingiodide Organic Solventsconcentration Content amount (nm)concentration(vol%)comparativenone 0 449example 19comparative10 484example 20NMPcomparative20 198example 21example 22 0.027M 0.11M 1,4-butangiol 20 520example 23 diethylene glycol 20 480example 24 10 411example 25 3-methoxy-N,N-dimethylpropanamide 20 225example 26 25 90The results in Table 4 confirm that 1,4-butanediol, diethylene glycol, and3-methoxy-N,N-dimethylpropanamide can suppress the side etching amountwithout the use of NMP.

[0035] [COMPARATIVE EXAMPLE 22 to 23 AND EXAMPLE 27 to 28]A solution of 0.079 M iodine and 0.60 M potassium iodide was used as a standardsolution and a solution was prepared by adding organic solvent to this standardsolution, and the iodine volatilization inhibition ability was evaluated by redoxtitration using sodium thiosulfate solution at regular time intervals. The results areshown in Table 5.

[0036] (Table 5)[Table 5] Iodine volatilization inhibition abilityPotassium Organic IodineIodineiodide Solvent volatilizationconcentratio Organic Solventsconcentratio Content inhibitingnn (vol%) abilitycomparativenone 0 ×example 22comparativeexample 23 0.079M 0.60MNMP 20 ○example 27 3-methoxy-N,N-dimethylpropanami 20 ○example 28 de 25 ○○:Iodine content change rate of 5% or less after 24 hours.△: Iodine content change rate after 24 hours: 5% or more but less than 20%.×: Iodine content change rate of 20% or more after 24 hours.The results in table 5 and FIG. 5 confirm that 1,4-butanediol, diethylene glycol,and 3-methoxy-N,N-dimethylpropanamide can inhibit iodine volatilization withoutthe use of NMP.

Claims

1. An etching solution for gold or gold alloy, characterised in that the etchingsolution comprising:iodine, iodide, organic solvent and water,wherein the organic solvent is one or more selected from a group consisting of:3-methoxy-N,N-dimethylpropanamide and3-butoxy-N,N-dimethylpropanamide.

2. The etching solution as claimed in claim 1, wherein the organic solvent is3-methoxy N,N-dimethylpropanamide.

3. The etching solution as claimed in claim 1 or 2, wherein the etching solutiondoes not comprise N-methyl-2-pyrrolidinone.

4. The etching solution as claimed in claim 1 to 3, wherein the iodide is potassiumiodide.

5. The etching solution as claimed in claim 1, wherein the organic solvent furthercomprises one or more selected from a group consisting of: ethylene glycol,propylene glycol, diethylene glycol, 1,2-ethanediol, 1,4-butanediol and2,3-butanediol.

6. A method for etching the gold film formed on a substrate, characterised in thatthe method comprising immersing the substrate in the etching solution accordingto any one of claims 1 to 5.

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