Thiourea-And Cyanide-free Bath and Process for Electrolytic Etching of Gold

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Hu et ai.(10) Pub. No.:US 2005/0061683 Al(43) Pub. Date: Mar. 24, 2005

(54) THIOUREA-AND CYANIDE-FREE BATHAND PROCESS FOR ELECTROLYTICETCHING OF GOLD

(75) Inventors: Zhongmin Hu, Kalispell, MT (US);Erik J. Young, Dallas, TX (US)

Correspondence Address:CHRISTENSEN, O'CONNOR, JOHNSON,KINDNESS, PLLC1420 FIFTH AVENUESUITE 2800SEATTLE, WA 98101-2347 (US)

(73)(21) Appl. No.:

Assignee: Semitool, Inc.10/667,795

30~

(22) Filed: Sep. 22, 2003Publication Classification

(51) Int. CI? B23H 3/00(52) U.S. CI. 205/674(57) ABSTRACTAn aqueous thiourea-free gold etching bath for electrolyti-cally etching gold from a microelectronic workpiece. Oneembodiment of the aqueous thiourea-free bath contains: (a)about 0.5-1.5 M iodide; (b) about 0.1-0.3 M sulfite; and (c)about 1.0-3.0 g/L wetting agent. The bath is useful in aprocess for electrolytically etching gold from a microelec-tronic workpiece. A tool system in which the baths andprocesses of the present invention may be used is alsodescribed.



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THIOUREA-AND CYANIDE-FREE BATH ANDPROCESS FOR ELECTROLYTIC ETCHING OF

GOLDFIELD OF THE INVENTION

[0001] The invention is in the field of electrolytical etch-ing of gold (symbol Au) from a microelectronic workpiecein an etching bath. More particularly, the invention relates toelectrolytically etching gold from a microelectronic work-piece in an etching bath that is free of the suspectedcarcinogen, thiourea.

BACKGROUND OF THE INVENTION[0002] In the semiconductor industry, particularly in thesegment of the semiconductor industry focused on commu-nication applicat ions, gold is widely used as a conductivematerial. When gold is used to form conductive features, athin layer of gold is frequently deposited and employed as aseed layer. Subsequently, for example, after electrolyticdeposition, certain portions of the gold seed layer are nolonger desired and thus need to be removed from thesemiconductor workpiece.[0003] Both wet-etching and electrolytic etching can beused to remove a gold seed layer from semiconductorworkpieces. One wet-etching process is disclosed in U.S.Pat. No. 5,221,421 to Leibovitz et al. One disadvantageassociated with a wet-etch process is that it can producelevels of surface roughness on the gold features that areconsidered undesirable by manufacturers of semiconductordevices. Another disadvantage of a wet-etch process is thatit results in undercutting around the base of the gold fea-tures. Undercutting of the gold features is undesirablebecause it compromises the mechanical strength and elec-trical properties of the features. In addition, the wet-etchingprocess conditions need to be strictly controlled. Forexample, small variations in temperature and/or reagentconcentration significantly affect the amount of goldremoved. This problem may result in over-removal andover-undercutting.[0004] To this end, an electrolytic process is easier tocontrol and is advantageous over a wet-etching process.Both thiourea and cyanide have been used in commercialbaths and processes for electrolytically etching gold from asemiconductor workpiece. The problem associated with theprocess using thiourea is that thiourea is a suspected humancarcinogen. Cyanide is a very poisonous chemical exposureto which harms the brain and heart. Thiourea and cyanidepose potential health and safety risks in the workplace.Moreover, disposal of a thiourea-containing and cyanide-containing bath presents an environmental hazard.[0005] Accordingly, the primary advantage of the presentinvention is that it electrolytically removes gold without theuse of thiourea or cyanide.

SUMMARY OF THE INVENTION[0006] The present invention provides a bath and processfor electrolytically etching gold in a safe and effectivemanner using materials not generally considered to behazardous. In one embodiment, the bath includes iodide,sulfite, a wetting agent, and water, and is free of thiourea andcyanide. In another embodiment, the bath includes chlo-

Mar. 24, 20051

rides, a wett ing agent, and water, and is also free of thioureaand cyanide. The baths are useful in a process for electro-lytically etching gold in the absence of the suspected car-cinogen thiourea or the poisonous chemical cyanide. Theprocess is effective at removing gold from a substrate, insome embodiments, leaving no residual gold at the micro-scopic level . In addit ion, the present invention etches goldwith lit tle undercutt ing of the features that remain after theetching and without producing an undesirable amount ofsurface roughness on the remaining gold features.[0007] One embodiment of the present invention is anaqueous thiourea-free electrolytic etching bath that includes(a) about 0.1-3.0 M iodide; (b) about 0.01-1.0 M sulfi te; and(c) about o . 1-5.0 g/L wetting agent.[0008] In another embodiment of the present invention,the aqueous thiourea-free electrolytic etching bath includesabout 1 to 6 M chloride and about 0.1-5.0 gIL wett ing agent.[0009] In another embodiment, the invention is a processfor electrolytically etching gold from a microelectronicworkpiece, the process including steps of (a) providing anaqueous electrolytic etching bath free of thiourea and cya-nide; (b) providing a microelectronic workpiece havingsome amount of gold thereon; (c) contacting the gold withthe etching bath; and (d) providing an electric current flowbetween the gold and a cathode disposed in electrical contactwith the bath, whereby at least a portion of the gold isremoved from the microelectronic workpiece. Examples ofgold etching baths free of thiourea and cyanide are describedabove.[0010] In another embodiment of the present invention,the invention is a tool system for electrolytically etchinggold from a microelectronic workpiece. The tool systemincludes one or more stations for carrying out the followingfunctions (a) receiving a microelectronic workpiece havingsome amount of gold thereon; (b) providing an etching bathfree of thiourea and cyanide for electrolytically etching gold;(c) contacting the gold with the etching bath; (d) providingelectric current flow between the gold feature and a cathodedisposed in electrical contact with the etching bath; (e)removing at least a port ion of the gold from the microelec-tronic workpiece; (f) rinsing residual chemistry from themicroelectronic workpiece; and (g) drying the microelec-tronic workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS[0011] The foregoing aspects and many of the attendantadvantages of this invention will become more readilyappreciated as the same become better understood by ref-erence to the following detai led description, when taken inconjunction with the accompanying figures.[0012] FIGS. lA-IF schematically illustrate a process forforming a gold feature employing the gold etching bath andprocess of the present invention.[0013] FIG. 2 is schematic plan view of a tool useful forcarrying out the process described with reference to FIG. 1.

DETAILED DESCRIPTION OF THEPREFERRED EMBODIMENTS

[0014] As used throughout the specification, the followingabbreviations and symbols have the following meanings,



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unless the context clearly indicates otherwise: GaAs=gal-lium arsenide; A=angstrom; Nmin=angstroms per minute;,um=micrometer; Memolariry; g/Legrams per liter; andml/Lernilliliters per liter.[0015] The term "etching" refers to the electrolyticremoval of gold, unless the context clearly indicates other-wise. Electrochemical deposition refers to both electrolyticdeposition and electroless deposition. "Anode" refers to theelectrode at which electrolytic oxidation occurs. "Cathode"refers to the electrode at which electrolytic reduction occurs.The term "undercutting" refers to the undesirable resultwhere gold is etched away along the base of a feature,thereby creating a notch or undercut along the base of thefeature. The term "wetting agent" refers to an organiccompound that reduces the surface tension of the bath andthat serves as a wetting agent. The term "PEG" refers topolyethylene glycol.[0016] As used herein, the term "microelectronic work-piece" or "workpiece" is not limited to semiconductorwafers, but rather refers to workpieces having generallyparallel planar first and second surfaces, that are relat ivelythin, including semiconductor wafers, ceramic workpieces,and other workpieces upon which microelectronic circuits orcomponents including submicron features, data storage ele-ments or layers, and/or micromechanical elements areformed.[0017] As discussed above, the present invention relates toa thiourea-free gold etching bath, free of suspected carcino-gens and processes using such baths that are effective to etchgold from the surface of microelectronic workpieces. In anapplicat ion where gold seed layers are to be etched using thebaths and processes of the present invention, in someembodiments the baths and processes of the present inven-tion are able to remove the gold seed layers completely, suchthat when specimens are observed under a scanning electronmicroscope (SEM), no residual gold is observable on areaswhere the gold seed layer was removed. Etching of the goldseed layers in accordance with the present invention can beachieved without imparting undesirable amounts of surfaceroughness (e.g., R, greater than 150 angstroms) to featuresthat remain after the etching process. In addition to theabove, etching gold seed layers using the baths and pro-cesses of the present invention can be carried out withoutundercutting gold features that are intended to remain on thesurface of the microelectronic workpiece after the gold seedlayer has been removed. Exemplary baths and processes aredescribed below.

Thiourea and Cyanide-Free Electrolytic EtchingBaths

[0018] One embodiment of an electrolytic etching bath ofthe present invention is an aqueous bath including iodide(n, sulfite (S032-), and a wetting agent.[0019] In this bath, iodide functions as a complexingagent. Sulfite is present as a sacrificial stabilizer and pHbuffering species. The wetting agent promotes wetting of thesurface of the workpiece that functions as the anode.Through normal operation of the bath, sulfite will be oxi-dized requiring regular replenishment to ensure the stabilityof the bath. Replenishment of sulfite should be based onregular analysis results. In addition to maintaining the sulfiteconcentration, the pH of the solution must be monitored and

Mar. 24, 20052

maintained to ensure proper operation and stability of thebath. Baths of the preferred concentration range describedbelow have lives on the order of greater than 15 amp-miniliter , e.g. , 20 amp-min/liter to 35 amp-minlliter .

Iodide[0020] The source of iodide is a water-soluble salt thatdissociates in water to produce 1-. Examples of such water-soluble salts are: l ithium iodide (LiI); lithium iodide trihy-drate (LiI.3H20); sodium iodide (NaI); sodium iodide dihy-drate. (NaI.2H20); ammonium iodide (NH4I); andpotassium iodide (KI). Suitable gold etching results havebeen achieved using KI. The concentrat ion of iodide may bea molarity of about 0.1-3.0. A narrower molarity range isabout 0.5-1.5. Suitable gold etching results have beenachieved with a molarity of about 1.0.

Sulfite[0021] The source of sulfite is a water-soluble salt thatdissociates in water to produce sulfite (S032-) and/orbisulfite (HS03 -), depending on the pH of the solution.Examples of such water-soluble salts are: lithium sulfitemonohydrate (Li2S03.H20); sodium sulfite (Na2S03);sodium sulfite hepta-hydrate (Na2S03.7H20); sodiumbisulfite (NaHS03); potassium sulfite (K2S03); and potas-sium sulfite dihydrate (~S03.2H20). Suitable gold etchinghas been achieved using Na2S03. The concentration ofsulfite may be a molarity of about 0.01-1.0. A narrowermolarity range is about 0.1-0.3. Suitable gold etching hasbeen achieved with a molarity of about 0.2.[0022] Around pH 7.2, both S032- and HS0331 are presentin solution. The relat ive concentrat ion of these two speciesis determined by the solution pH. The use of sodium bisulfite(or sodium hydrogensulfite), together with sodium hydrox-ide, is equivalent to the use of sodium sulfite.

Wetting Agent[0023] A wetting agent is employed in the etching bath. Awide variety of known nonionic and ionic wetting agentsmay be employed. One example is commercially availablepolyethylene glycol polymers. Suitable gold etching hasbeen achieved using polyethylene glycol polymers havingan average molecular weight ranging between about 2,000and about 35,000. The concentration of wetting agent maybe about 0.01-5.0 giL, depending on the species used. Anarrower range of wetting agent concentration is about1.0-3.0 gIL. Suitable etching has been achieved with aconcentrat ion of about 3.0 g/L.[0024] One particular etching bath of the invention ISshown in the following Table 1.

TABLE 1Concentration

Component giL MKI 166Na2S03 25 0.2Wetting agent 3Water Balance



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[0025] In another embodiment, an electrolytic etchingbath of the present invention is an aqueous bath containingchloride (Cn and a wetting agent.[0026] One primary source of chloride is hydrochloricacid. Chloride-containing salt such as sodium chloride andammonium chloride can also serve as a source of chloride;however, the solution of the salts must first be acidified byadding acids such as sulfuric acid. Useful wetting agentsinclude those described above in the context of the iodideand sulfite-containing baths. Sodium dodecylsulfate is alsoa useful wett ing agent. The concentration of sodium dode-cylsulfate in the bath can vary from about 0.01 g/liter toabout 1 g/liter. The concentration of chloride in the bathsmay be a molarity of about 1 to about 6.[0027] The chloride-containing gold etching baths are notas effective as the iodide/sulfite-containing baths in remov-ing gold from a substrate down to a microscopic level. Thechloride-containing bath nonetheless is useful in applica-tions where removal of gold down to the microscopic levelis unnecessary.[0028] Effective etching of gold is achieved by contactingthe gold features with the chloride-containing gold etchingbath under the conditions described below with respect to anelectrolytic gold etching process. For the chloride-contain-ing etching bath, the pH is maintained acidic in order toachieve effective etching of the gold.

One Particular Bath Makeup Procedure[0029] One particular non-limiting bath makeup proce-dure to achieve the concentrations in the above Table 1 is asfollows. For each liter of bath, weigh out 25 g sodium sulfi teand dissolve it in about 0.7 L water, adjust the pH to 7.0-7.4with acids such as sulfurous acid and/or sulfuric acid.[0030] The next step is to add 166 g of KI and 3 gpolyethylene glycol (PEG with an average molecular weightof about 20,000) to the above solution.[0031] The next step is to stir to dissolve the KI and thenadd water to make a final volume of 1 liter.[0032] Finally, transfer the bath to an opaque containerand keep it airtight for storage and transportation. If ayellowish color develops after long-term storage, sodiumsulfite (e.g., 20 gIL) should be added and the bath pHadjusted to 7.0-7.4 prior to use.

Electrolytic Gold Etching Processes[0033] In the process aspect of the present invention, anelectrolytic etching bath (as described above) free of thio-urea and cyanide for etching gold from a semiconductorworkpiece is used. In one embodiment of a process of thepresent invention, the microelectronic workpiece is a GaAswafer or a silicon wafer, which has been processed to havethereon gold features, a gold seed layer, and an underlyingconductive layer of barrier materials such as titanium/titanium nitride, tantalum/tantalum nitride, and titanium/tungsten. The anode is the electrically-conductive surface ofthe workpiece. The cathode is preferably an inert cathode.An exemplary inert cathode is a platinized titanium cathode.The process can be carried out in a plating reactor of

Mar. 24, 20053

conventional design operated in etching mode. Specificprocess parameters and ranges of process parameters are setforth in Table 2 below.

TABLE 2Parameter Specific RangeTemperaturepHCurrent densi ty (mA/cm2)CurrentNitrogen purge and blanketQuiescence (no flow and purge)when reactor idl es

25 C. 20-30 C.7.2 6.4--81.5 0.1-10

DCPreferredPreferred

[0034] A wide pH range outside 6.4-8.0 is operable. How-ever, a pH close to 7.2 is preferred. The complexing abili tyof iodide is not affected by pH over a wide pH range;however, the stability of iodide itself, and thus the consump-tion of sulfite, is dependent on pH. At a pH approachingneutral, the bath is significantly more stable than at an acidicpH. In addition, at a pH approaching pH 7.2, the solution pHis buffered by the HS03 -/S03 2- couple. The pH of thesolution should be monitored on a daily basis using astandard pH electrode at room temperature.[0035] A current density from 0.1 m.Azcm" to 10 rrtA'cm"is operable. A current density from 1 mNcm2 to 3 mNcm2is preferred. A current density of 3 m.Azcm" may be used toetch a thicker gold seed layer (e.g., a gold seed layer of about1500 A thickness). A current density of 1.5mNcm2 has beenfound to be a judicious choice for etching thinner features,e.g., a 500 A gold seed layer. At such a current density, theetching of a 500 A gold seed layer is completed in about 70seconds.[0036] An exemplary power supply for the process pro-vides up to 10 volts at an average current of 5 amps orhigher.[0037] Etching endpoint detection can be used during thegold etching process. The etching endpoint is determined bymonitoring the current/voltage characteristics of the electro-chemical cell.[0038] As indicated in Table 1 above, a nitrogen purge anda nitrogen blanket are preferred in order to reduce theconsumption of sulfite and prolong the bath life. Quiescence(no flow and no purge) when the reactor is idle is preferredin order to reduce the consumption of sulfite and prolong thebath life.[0039] An exemplary mode of etching is to rotate theworkpiece in an etching reactor at a speed of about 10-100revolutions per minute with an etching bath as describedabove impinging against the workpiece at a flow rate ofabout 1-6 gallons per minute. For 100-mm wafers, anexemplary flow rate is about 3.5 gallons per minute. For125-mm wafers, an exemplary flow rate is about 4 gallonsper minute. For 150-mm and 200-mm wafers, an exemplaryflow rate is about 5.5 gallons per minute. Other modes mayalso be used.[0040] Comparative testing has been conducted betweenthe prior thiourea -containing bath and a bath of the presentinvention. The tests measured the line resistance of a goldfeature and the current leakage between adjacent gold fea-



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tures onwafers processed using the thiourea-containing bathand using a thiourea and cyanide-free bath of the presentinvention. The test results in Table 3 below show that thethiourea-free bath of the present invention is equal orsuperior to the prior thiourea -containing bath.

TABLE 3Leakagecurrent

Lineresistance

Solution (bath) Average Std. dev. Average Std. dev.Thiourea-containing bath 7.0SE-07 2.0E-07 100.6 1.4Thiourea-free bath 1.4SE-07 1.lE-07 99.3 2.2

[0041] In order to control the pH of the bath, 5% (v/v)sodium hydroxide solution can be used to raise bath pH and5% (v/v) sulfurous acid or 5% (w/v) sodium bisulfite solu-tion to lower pH. 5% (v/v) sulfuric acid may be used as analternative to sulfurous acid and sodium bisulfite solutions.[0042] Sulfite concentration in the bath can be determinedby iodimetry and should be properly controlled within theconcentration ranges described above.[0043] An example of an application of the gold etchingbaths and the gold etching processes of the present inventioninclude formation of gold features on semiconductor wafers.Referring to FIG. lA, a semiconductor substrate 10 isprovided with an adhesion/barrier layer 12, e.g., titanium/tungsten. Overlying barrier layer 12 is a conductive seedlayer 14, e.g., gold. In accordance with conventional pro-cesses, a photoresist 16 is deposited onto conductive seedlayer 14 and patterned to expose portions of conductive seedlayer 14. In FIG. rc, gold feature 18 is electrochemicallydeposited onto the exposed portion of seed layer 14. There-after, as illustrated in FIG. 1D, photoresist 16 is removed.The gold etching bath and processes of the present inventioncan then be used to etch away the exposed portion ofconductive seed layer 14 when such layer is comprised ofgold as illustrated in FIG. IE. Subsequent to the removal ofthe gold seed layer 14, that isnot covered by gold feature 18,the exposed portions of barrier layer 12 are removed asillustrated in FIG. IF.

Tool System[0044] The foregoing process for forming gold featuresmay be suitably carried out in commercially available appa-ratus, which are arranged and have controllers that are thenmodified to be programmed to carry out pre-depositiontreatments, deposition, etching, and post-etching treatments.One suitable tool system for implementing the presentinvention is the LT21O tool system available from Semi-tool, Inc. of Kalispell, Mont., and as further described inU.S. Pat. No. 6,203,582 to Berner et al. assigned to Semi-tool, Inc., the disclosure of which is hereby expresslyincorporated by reference. Other commercially availabletool systems such as the Equinox or Paragon model toolsavailable from Semitool, Inc. are also suitable for use inpracticing the present invention as well as systems offeredby other manufacturers.[0045] In general, the tool system includes a plurality ofworkstations for carrying out different operations. The vari-ous workstations are controlled by a controller.

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[0046] FIG. 2 is a schematic representation of a suitabletool system 30 for forming gold features on the surface of amicroelectronic workpiece, such as a semiconductor wafer.The tool system 30 may include a plurality of workstations50, 60, 70, 80, and 90. Workpieces are initially prepared forprocessing at one or more pre-treatment stations 50 whichperform, for example, cleaning, prewetting, and rinsingsteps. The workpiece is then passed to a station 60, inwhichthe electrochemical deposition of gold is carried out. Fol-lowing the electrochemical deposition of the gold featureand removal of the photoresist, for example, in workstation70, the workpiece is delivered to workstation 80 where thegold etching process of the present invention is carried outusing a gold etching bath formed in accordance with thepresent invention. After the gold etching process, the work-piece can be delivered to workstation 90where post-etchingprocessing occurs such as cleaning, rinsing, and drying theworkpiece.[0047] Electric power is supplied to the various worksta-tions by a power supply. This power supply connects elec-trically between the surface of the microelectronic work-piece (which functions as the anode during etching) and thecathode that is located within the workstation and that is incontact with the gold etching bath. The power supply iscapable of selectively supplying either a forward platingpower or a reverse etching power, with both forward andreverse voltage and current control capabilities, althoughthis is not required for electrolytic etching using a directcurrent power source.[0048] The supply of reverse etching power is preferablyautomatically controlled by a programmable controller,which includes a central processing unit that operates inaccordance with program code to cause the power supply tosupply reverse power, at desired levels and for desired timeperiods in accordance with the present invention. Alterna-tively, the etching power can be provided by reversing theconnections between the power supply and the reactor.[0049] The controller may include a data input device (notshown), such as a keypad, touch screen, other user interface,or a floppy or CD disk drive. The tool may also includefurther workstations (not shown) for additional processingsteps, as dictated by the workpiece being processed.[0050] Unless indicated otherwise, in stating a numericalrange for a compound or a temperature or a time or otherprocess matter or property, such a range is intended tospecifically designate and disclose the minimum and themaximum for the range and each number, including eachfraction and/or decimal, between the stated minimum andmaximum for the range. For example, a range of 1 to 10discloses 1.0, 1.1, 1.2 ... 2.0, 2.1, 2.2, ... and so on, up to10.0. Similarly, a range of 500 to 1000 discloses 500, 501,502, ... and so on, up to 1000, including every number andfraction or decimal therewithin. "Up to x" means "x" andevery number less than "x", for example, "up to 5" discloses0.1, 0.2, 0.3, ... , and so on up to 5.0.[0051] While the preferred embodiments of the inventionhave been illustrated and described, it will be appreciatedthat various changes can be made therein without departingfrom the spirit and scope of the invention.



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The embodiments of the invention in which an exclusiveproperty or privilege is claimed are defined as follows:1. An aqueous, thiourea-free bath for electrolytical ly

etching gold from a microelectronic workpiece, said bathcomprising:(a) iodide;(b) sulfite; and(c) a wetting agent.2. An aqueous, thiourea-free bath for electrolytically

etching gold from a microelectronic workpiece, said bathcomprising:(a) about 0.1-3.0 Mof iodide;(b) about 0.01-1.0 Mof sulfi te; and(c) about 0.01-5.0 gIL of wetting agent.3. The bath of claim 2, wherein a source of iodide is

selected from the group consisting of LiI, LiI.3H20, NaI,NaI.2H20, and KI.4. The bath of claim 2, wherein a source of iodide is KI.5. The bath of claim 2, wherein the concentration of

iodide is about 0.5-1.5 M.6. The bath of claim 2, wherein a source of sulfite is

selected from the group consisting of Li2S03.H20, Na2S03,Na2S03.7H20, and K2S03.2H20.7. The bath of claim 2, wherein a source of sulfite is

Na2S038. The bath of claim 2, wherein the concentration of sulfiteis about 0.1-0.3 M.9. The bath of claim 2, wherein the wetting agent is a

polyethylene glycol.10. The bath of claim 2, wherein the wetting agent is a

polyethylene glycol having an average molecular weightranging from about 2,000 to about 35,000.11. The bath of claim 9, wherein the concentration of the

wetting agent is about 1.0-3.0 giL.12. The bath of claim 2, wherein the pH of said bath isabout 6.4-8.0.13. An aqueous, thiourea-free bath for electrolytical ly

etching gold from a microelectronic workpiece, said bathcomprising:(a) about 0.5-1.5 Mof iodide wherein the source of iodideis selected from the group consist ing of LiI, LiI.3H20,NaI, NaI.2H20, and KI;

(b) about 0.1-0.3 Mof sulfite wherein the source of sulfiteis selected from the group consisting of Li2S03.H20,Na2S03, Na2S03.7H20, and ~S03.2H20; and

(c) about 1.0-3.0 g/L of a polyethylene glycol.14. An aqueous, thiourea-free bath for electrolytical ly

etching gold from a microelectronic workpiece, said bathcomprising:(a) about 1.0 Mof iodide, wherein the source of iodide isKI;

(b) about 0.2 Mof sulfite, wherein the source of sulfite isNa2S03;

(c) about 3.0 gIL polyethylene glycol having an averagemolecular weight ranging from about 2,000 to about35,000.

Mar. 24, 2005515. A process for electrolytically etching gold from a

microelectronic workpiece, said process comprising stepsof:(a) providing a thiourea-free etching bath;(b) providing a microelectronic workpiece having thereonat least some amount of gold;

(c) contacting said gold with said etching bath; and(d) providing electric current flow between said gold anda cathode disposed in electrical contact with said bath,whereby at least a port ion of said gold is removed fromsaid microelectronic workpiece.

16. A process for electrolytically etching gold from amicroelectronic workpiece, said process comprising stepsof:(a) providing an aqueous thiourea-free etching bath com-prising:(1) about 0.5-1.5 Mof iodide;(2) about 0.1-0.3 Mof sulfi te; and(3) about 1.0-3.0 gIL of wetting agent;

(b) providing a microelectronic workpiece having at leastsome amount of gold thereon;

(c) contacting the gold with the etching bath; and(d) providing an electric current flow between the goldand a cathode disposed in electrical contact with thebath, whereby at least a port ion of the gold is removedfrom the microelectronic workpiece.

17. The process of claim 16, wherein a source of saidiodide in said bath is selected from the group consisting ofLiI, LiI.3H20, NaI, NaI.2H20, and KI.18. The process of claim 16, wherein a source of saidiodide in said bath is KI.19. The process of claim 16, wherein the concentrat ion of

said iodide in said bath is about 0.9-1.1 M.20. The process of claim 16, wherein a source of said

sulfite in said bath is selected from the group consisting ofLi2S03H20, Na2S03, Na2S03.7H20, and ~S03.2H20.

21. The process of claim 16, wherein a source of saidsulfite in said bath is Na2S03.22. The process of claim 16, wherein the concentrat ion ofsaid sulfite in said bath is about 0.18-0.22 M.23. The process of claim 16, wherein the wetting agent in

said bath is a polyethylene glycol .24. The process of claim 16, wherein the wetting agent in

said bath is a polyethylene glycol having an average molecu-lar weight ranging from about 2,000 to about 35,000.25. The process of claim 23, wherein the concentrat ion of

the wetting agent in said bath is about 2.7-3.3 gIL.26. The process of claim 16, wherein the pH of said bathis about 6.4-8.0.27. A process for electrolytically etching gold from a

microelectronic workpiece, said process comprising stepsof:(a) providing an thiourea-free etching bath having atemperature of about 20-30 c., said bath comprising:(1) about 0.9-1.1 M of iodide, wherein the source ofiodide is selected from the group consisting of LiI,LiI.3H20, NaI, NaI.2H20, and KI;


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(2) about 0.18-0.22 M of sulfite, wherein the source ofsulfite is selected from the group consisting ofLi2S03.H20, Na2S03, Na2S03.7H20, and~S032H20;

(3) about 2.7-3.3 gIL of a polyethylene glycol; and(4) the balance is water;

(b) providing a microelectronic workpiece having at leastsome amount of gold thereon;

(c) contacting the gold with the etching bath;(d) providing electric current flow between the gold and

a cathode disposed in electrical contact with the bath;and

(e) removing at least a portion of the gold from saidmicroelectronic workpiece.

28. The process of claim 27, wherein the pH of said bathis about 6.4-8.0.

29. A tool for electrolytically etching gold from a micro-electronic workpiece, said tool comprising one or morestations for carrying out the following functions:

(a) receiving a surface of a microelectronic workpiecehaving at least some amount of gold thereon;

(b) providing an aqueous thiourea-free gold etching bathfor electrolytically etching gold;

Mar. 24, 20056

(c) contacting the gold with the etching bath;(d) providing electric current flow between the gold and

a cathode disposed in electrical contact with the etchingbath, whereby at least a portion of the gold is removedfrom said microelectronic workpiece; and

(e) rinsing residual chemistry from the microelectronicworkpiece.

30. The tool of claim 29, further comprising a supply ofthe aqueous thiourea-free gold etching bath.

31. An aqueous, thiourea-free bath for electrolyticallyetching gold from a microelectronic workpiece, said bathcomprising:

(a) chloride; and(b) a wetting agent.32. The bath of claim 31, wherein the chloride is present

in an amount of about 1 to 6 M.33. The bath of claim 32, wherein a source of the chlorideis hydrochloric acid.

34. The bath of claim 31, wherein the wetting agent ispolyethylene glycol.

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Thiourea-And Cyanide-free Bath and Process for Electrolytic Etching of Gold

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