(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`9
`
`1
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`
`",~::~:~0~":',';!, o,....n;wtion •
`
`(l
`
`1111111111111111 IIIIII IIIII 11111111111111111111111111111111111111111111111111111111111111111
`
`(43) International Publication Date
`13 April 2006 (13.04.2006)
`
`PCT
`
`(10) International Publication Number
`WO 2006/039090 A2
`
`(51) International Patent Classification:
`CIID 7132 (2006.01)
`C23G 1/00 (2006.01)
`
`(21) International Application Number:
`PCT/US2005/032411
`
`(22) International Filing Date:
`13 September 2005 (13.09.2005)
`
`(25) Filing Language:
`
`(26) Publication Language:
`
`English
`
`English
`
`(30) Priority Data:
`10/955,810
`
`30 September 2004 (30.09.2004) US
`
`(71) Applicant (for all designated States except US): LAM
`RESEARCH CORPORATION [US/US]; 4650 Cushing
`Parkway, Fremont, CA 94537 (US).
`
`(72) Inventors; and
`(75) Inventors/Applicants (for US only): LEONTE, Oana
`[US/US]; 2730 Markham Court, Hayward, CA 95452
`(US). CHEBI, Robert [US/US]; 199 Exeter Avenue, San
`Carlos, California 94070 (US).
`
`(74) Agent: BRADIN, David, S.; Womble Carlyle Sandridge
`& Rice, PLLC, P.O. Box 7037, Atlanta, GA 30357-0037
`(US).
`
`(81) Designated States (unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`AT, AU, AZ, BA, BB, BG, BR, BW, BY, BZ, CA, CH, CN,
`CO, CR, CU, CZ, DE, DK, DM, DZ, EC, EE, EG, ES, Fl,
`GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE,
`KG, KM, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA,
`MD, MG, MK, MN, MW, MX, MZ, NA, NG, NI, NO, NZ,
`OM, PG, PH, PL, PT, RO, RU, SC, SD, SE, SG, SK, SL,
`SM, SY, TJ, TM, TN, TR, TT, TZ, UA, UG, US, UZ, VC,
`VN, YU, ZA, ZM, ZW.
`
`(84) Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM,
`ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM),
`European (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, Fl,
`FR, GB, GR, HU, IE, IS, IT, LT, LU, LV, MC, NL, PL, PT,
`RO, SE, SI, SK, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA,
`GN, GQ, GW, ML, MR, NE, SN, TD, TG).
`
`[Continued on next page}
`
`-iiiiiiii
`iiiiiiii -
`
`!!!!!!!! (54) Title: SOLUTIONS FOR CLEANING SILICON SEMICONDUCTORS OR SILICON OXIDES
`
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`
`(57) Abstract: A solution for cleaning silicon semiconductors or silicon oxides, and methods
`for cleaning silicon semiconductors or silicon oxides using the solution, is disclosed. The solu(cid:173)
`tion includes hydrogen peroxide, ammonium hydroxide, an alkanolamine, and at least one of a
`tetraalkylammonium hydroxide, an alkanolamide, an amido-betaine, an c ca dihydroxyphenol, a
`carboxylic acid, a phosphonic acid, a chelating agent or a surfactant. The weight ratio of am(cid:173)
`monium hydroxide to peroxide to water is between about 1:1:5 and 1:1-4:50, the weight ratio of
`ammonium hydroxide to water is between 1:5 and 1:50, and the molar ratio of component A to
`ammonium hydroxide is between 1: 10 and 1:5000 is disclosed. The solution can achieve the ef(cid:173)
`ficiency equivalent to that of the conventional RCA two-step cleaning solution within a shorter
`time by one step preserving the silicon and silicon oxide substrate integrity and effectively remove
`contaminants such as organics, particles and metals from the surfaces of silicon semiconductors
`and silicon oxides without using strong acids such as HCI and sulfuric acid.
`
`TOK Ex. 1020
`PGR Petition
`
`- i
`
`iiiiiii
`
`!!!!!!!! -
`iiiiiiii ----
`
`!!!!!!!!
`iiiiiiii
`
`

`

`WO 2006/039090 A2
`
`1111111111111111 IIIIII IIIII 11111111111111111111111111111111111 lllll lllll llll 1111111111111111111
`
`Declarations under Rule 4.17:
`as to applicant's entitlement to apply for and be granted a
`patent (Rule 4.17(ii))
`as to the applicant's entitlement to claim the priority of the
`earlier application (Rule 4.17(iii))
`Published:
`without international search report and to be republished
`upon receipt of that report
`
`For two-letter codes and other abbreviations, refer to the "Guid(cid:173)
`ance Notes on Codes and Abbreviations" appearing at the begin(cid:173)
`ning of each regular issue of the PCT Gazette.
`
`

`

`WO 2006/039090
`
`PCT /0S2005/032411
`
`SOLUTIONS FOR CLEANING SILICON
`
`SEMICONDUCTORS OR SILICON OXIDES
`
`Field of the Invention
`
`[0001] The present invention pertains to solutions for cleaning silicon
`
`semiconductors or silicon oxides. More specifically, the present invention provides
`
`solutions which can remove contaminants such as organics, particles and metals from
`
`the surfaces of silicon semiconductors and silicon oxides by one step.
`
`Background of the Invention
`
`[0002) The fabrication of devices beyond current scaling imposes alternative
`
`cleaning solutions to the traditional RCA cleaning to comply with the specs for
`
`particles, metals, organic and material (silicon and silicon oxide) loss, as published by
`
`ITRS surface preparation road map as requirements at 65nm-technology node and
`
`beyond.
`
`[0003) There are continuous efforts in the art of production of silicon
`
`semiconductors and micro-circuits to meet the requirements associated with the new
`
`leading edge devices. The cleaning steps are responsible for surface preparation and for
`
`controlling surface contamination, which is critical for device performance, reliability
`
`and cost. The increased fragility of the scaled and new device structures is limiting the
`
`aggressiveness of the cleaning processes that may be employed.
`
`[0004) In 1970, RCA (Radio Corporation of America) developed an effective
`
`cleaning system for removing contaminants from surfaces of silicon semiconductors
`
`and silicon oxides. The system comprises two cleaning steps. An aqueous solution
`
`comprising hydrogen peroxide and ammonium hydroxide is used in the first step to
`
`remove organic contaminants. Since the solution may inevitably cause contamination
`
`with heavy metals such as Fe, Zn and Al which are trace metal contaminants in the
`
`solution, a solution containing HCl must be used in the second step to remove the metal
`
`contaminants. According to the RCA system, an effective cleaning operation comprises
`
`using a solution comprising 5: 1: 1 to 7:2: 1 by volume of water/30% hydrogen peroxide
`
`/27% ammonium hydroxide in the first step for 10 to 20 minutes and using a solution
`
`

`

`WO 2006/039090
`
`PCT /0S2005/032411
`
`comprising 6:1:1 to 8:2:1 by volume ofwater/30% hydrogen peroxide /37% HCl in the
`
`second step for 10 to 20 minutes. The Standard Clean-I, SC-1 (RCA-1) function is to
`
`remove the organic and particle contaminants, while the Standard Clean-2, SC-2 (RCA-
`
`2) function is to remove the metallic contaminants. In other words, RCA system must
`
`use strong acid chemicals such HCl, involves two steps and needs at least 20 minutes
`
`for cleaning.
`
`[0005) Though RCA system can effectively remove heavy metal contaminants
`
`from the surfaces of wafers, particles contained in the acidic cleaning solution which
`
`comprises HCl will stick to and contaminate the surfaces. Further, RCA system
`
`involves two separate steps and this is an inconvenient operation. Persons in
`
`semiconductor device and silicon wafer in particle sries continuously search for new
`
`formulations to replace RCA system to provide an easier, more effective and more
`
`economical cleaning system.
`
`[0006) Various approaches have been developed to replace the RCA system
`
`and most of them are directed to the cleaning solution of the second step. Japanese
`
`Patent KOK.AI (Laid-Open) No. Sho 58-30135 discloses the use of an acidic aqueous
`
`solution containing HF, sulfuric acid and hydrogen peroxide. Japanese Patent KOK.AI
`
`(Laid-Open) No. Hei 2-100320 discloses the use of a combination of a mixture of
`
`ammonium hydroxide and hydrogen peroxide in water and a mixture of HCI and
`
`hydrogen peroxide in water. A solution of strong acid and a very small amount of a
`
`compound containing fluorine is disclosed in Japanese Patent KOK.AI (Laid-Open) No.
`
`Hei 4-234118. A solution containing 0.50% HF and 0.1 to 1 % hydrogen peroxide is
`
`disclosed in "TRYBOROZIST" Vol. 37, No. 3, (1992) pp. 218-224 and the cleaning is
`
`conducted at room temperature. U.S. Pat. No. 5,560,857 discloses the use of an aqueous
`
`acidic solution containing 0.005% to 0.05% by weight HF and 0.3% to 20.0% by
`
`weight hydrogen peroxide and having a pH in the range from 1 to 5. In other words,
`
`most modifications on RCA system are directed to the substitution of the solution used
`
`in the second cleaning step.
`
`[0007) However, as mentioned above, in addition to the shortcoming of particle
`
`contamination, RCA system further has the disadvantages of an inconvenient operation
`
`(involving two steps and requiring at least 20 minutes) and the use of strong acid
`
`chemicals. All the aforementioned known approaches cannot avoid these disadvantages.
`
`There is a necessity in the art of an effective cleaning system to simplify the RCA
`
`2
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`WO 2006/039090
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`PCT /0S2005/032411
`
`system, avoid the use of strong acid chemicals and meet the simple, effective and
`
`economical requirements.
`
`Summary of the Invention
`
`[0008] Cleaning solutions that can significantly reduce the cleaning time,
`
`simplify the cleaning procedures and avoid using strong acid chemicals are disclosed,
`
`as well as methods for using the compositions to clean silicon semiconductors or silicon
`
`oxides are disclosed. The silicon semiconductors are present, for example, in
`
`semiconductor integrated circuit devices.
`
`Integrated circuit elements with good key
`
`device electrical performance and charge to breakdown and breakdown field properties
`
`that are superior to those cleaned by RCA systems are also disclosed.
`
`[0009] The solutions include hydrogen peroxide, ammonium hydroxide, an
`
`alkanolamine, and at least one of a component A selected from a tetraalkylammonium
`
`hydroxide, an alkanolamide or amido-betaine, an a,a-dihydroxyphenol, a carboxylic
`
`acid or a phosphonic acid or their salts, a chelating agent and a surfactant.
`
`[0010] The weight ratio of ammonium hydroxide to peroxide to water is
`
`typically between about 1: 1 :5 and about 1: 1: 100, and the molar ratio of component A to
`
`ammonium hydroxide is between 1:10 and 1:1000. The alkanolamine is typically
`
`present in a ratio of about 0.1 to about 10 percent by weight, more typically in a range
`
`of about 0.1 to about 5 weight percent.
`
`[0011] In one embodiment, the solution includes substantially no fluoride ions,
`
`and in this embodiment, the amount of surface etching of the substrate to be cleaned is
`
`minimized. In this embodiment, the amount of etching/material loss by etching is less
`
`than about two angstroms, whereas a comparable solution with the same components,
`
`to which fluoride is added, typically results in a material loss of more than twenty
`
`angstroms.
`
`[0012] The methods of cleaning involve contacting the substrate to be cleaned
`
`with the solutions described herein for a sufficient amount of time to remove
`
`contaminants, such as organics, particles and metals from the surfaces of the substrates.
`
`In one embodiment, the methods further involve mechanical cleaning steps, although
`
`these often result in additional material loss.
`
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`3
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`

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`WO 2006/039090
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`PCT /0S2005/032411
`
`[0013) The cleaning solutions and methods can replace the solutions used in
`
`the first and second steps of RCA system and can provide the efficiency of RCA
`
`cleaning system in a single step.
`
`Brief Description of the Drawings
`
`[0014) FIG. 1 shows a conventional procedure for preparing capacitor elements
`
`of integrated circuit, wherein:
`
`10 represents a chip;
`
`20 represents an oxide layer;
`
`30 represents a photoresist layer;
`
`40 represents a gate oxide layer;
`
`50 represents a polysilicon layer;
`
`60 represents an aluminum layer;
`
`70 represents a photoresist layer; and
`
`80 represents an aluminum layer.
`
`Detailed Description of the Invention
`
`[0015) The present invention provides solutions which can provide the cleaning
`
`efficiency equivalent to that provided by RCA system in one step and can be used for
`
`cleaning the surfaces of silicon semiconductors and silicon oxides, and methods for
`
`cleaning these surfaces using the solutions. Specifically, the present invention provides
`
`solutions for removing contaminants such as organics, particles and metals from the
`
`surfaces of silicon semiconductors and silicon oxides at controlled etch rates of silicon
`
`and silicon oxide with the preservation of substrate integrity.
`
`I. Cleaning Solutions
`
`[0016) The solutions of the present invention include hydrogen peroxide,
`
`ammonium hydroxide, alkanolamines, and at least one component A selected from the
`
`group
`
`consisting of
`
`tetraalkylammonium
`
`hydroxides,
`
`alkanolamides,
`
`a,a(cid:173)
`
`dihydroxyphenols, carboxylic acids,
`
`phosphonic acids, chelating agents and
`
`surfactants.
`
`[0017) As used herein, the alkyl groups in the various components described
`
`herein generally include between 1 and 6 carbon atoms. The alkyl groups can be
`
`straight chained, branched or cyclic having generally 1-6 carbon atoms, specifically, for
`
`w
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`4
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`WO 2006/039090
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`PCT /0S2005/032411
`
`example, a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a
`
`cyclopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl
`
`group, a n-pentyl group, an isopentyl group, a tert-pentyl group, a 1-methylpentyl
`
`group, a cyclopentyl group, a n-hexyl group, an isohexyl group and a cyclohexyl group.
`
`Alkanolamines
`
`[0018] Examples of suitable alkanolamines include, but are not limited to,
`
`monoethanolamine, diethanolamine,
`
`triethanolamine, 2-methylaminoethanol, 2-
`
`ethylaminoethanol,
`
`N-methyldiethanolamine,
`
`dimethylaminoethanol,
`
`2-(2-
`
`aminoethoxy)ethanol, 1-amino-2-propanol, monopropanolamine, and dibutanolamine,
`
`4-(2-hydroxyethyl)morpholine, and 4-(3-aminopropyl)morpholine.
`
`Tetraalkylammonium Hydroxides
`
`[0019] Examples of suitable tetraalkylammonium hydroxides that can be used
`
`m
`
`the cleaning solutions described herein
`
`include, but are not
`
`limited
`
`to,
`
`tetraalkylammonium hydroxides having methyl, ethyl, propyl, butyl, and hydroxyethyl
`
`groups, and combinations thereof (e.g., tetramethylammonium hydroxide (hereinafter
`
`referred
`
`to
`
`as
`
`TMAH),
`
`tetraethylammonium
`
`hydroxide,
`
`trimethyl
`
`hydroxyethylammonium hydroxide, methyl tri (hydroxyethyl) ammonium hydroxide,
`
`tetra (hydroxyethyl) ammonium hydroxide, benzyl trimethylammonium hydroxide and
`
`the like).
`
`Alkanolamides /Amido-Betaines
`
`[0020] An alkanolamide is a compound that includes a alkyl hydroxy group and
`
`an amide group. An amido-betaine is a compound that includes an amide group and a
`
`betaine group. Examples of suitable alkanolamides are those derived from fatty acids.
`
`A preferred alkanolamide is cocodiethanolamide. Other suitable alkanolamides include
`
`lauric/myristic monoethanolamide, coconut monoethanolamide, lauric diethanolamide,
`
`unmodified coconut diethanolamide, and other modified fatty alkanolamides or amido(cid:173)
`
`betaines as also cocoamidopropyl betaine.
`
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`WO 2006/039090
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`PCT /0S2005/032411
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`Dihydroxypheno ls
`
`[0021] Dihydroxyphenols are phenols that include at least two hydroxy groups,
`
`and optionally include other functional groups, such as alkyl, halo, carboxylic acid,
`
`amine, and the like. Examples of suitable dihydroxyphenols include, but are not limited
`
`to, o-dihydroxyphenol, m-dihydroxyphenol, p-dihydroxyphenol, gallic acid, catechol,
`
`alkyl resorcinols such as 2-methyl resorcinol and 5-methyl resorcinol, and 3,4-
`
`dihydroxyphenylalanine.
`
`Carboxylic Acids/Chelating Agents/Surfactants
`
`[0022] A chelate, sometimes referred to as a sequestrant, a complex ion, and/or
`
`a coordination compound, is an organic compound that combines with a metal ion to
`
`form a complex in which the donor atoms are connected to each other as well as to the
`
`metal. Ethylenediaminetetraacetic acid (EDTA) is one of the best known examples of a
`
`chelating agent. EDTA has two amine donor groups and four carboxyl donor groups. It
`
`can thus supply the complete requirements for the coordination sphere of many metals
`
`with a single molecule where it might take three molecules of ethylenediamine to meet
`
`the same-requirements. A chelating agent that supplies two donor electrons to the metal
`
`is said to be bidentate. Similarly ter-, quadri, quinqui-, and sexadentate donors, bind the
`
`metal in 3, 4, 5, and 6 positions,. respectively. Hence, EDTA is sexadentate and
`
`ethylenediamine is bidentate, for example.
`
`[0023] Generally, chelating compounds that are useful in the cleaning solutions
`
`described herein include, but are not limited to, sugars, amino acids, organic diacids,
`
`diamines, alpha ketoacids, alphahydroxyacids, aminodiacids, amino triacids, amino
`
`tetraacids, and organic polyacids and their sodium, potassium, and ammonium salts.
`
`Specific examples of these chelating compounds include, but are not limited to the
`
`sugars, acids and salts of maleic acid, malonic acid, tartaric acid, citric acid, ascorbic
`
`acid, glycine,
`
`lactic acid, malic acid, succinic acid, oxalic acid, dextrose,
`
`ethylenediaminetetraacetic acid (EDTA), tris(hydroxymethyl)aminomethane, lactose,
`
`mannitol, glutaric acid, malic acid, succinic acid, glycerol, humic acid, fulvic acid,
`
`sorbic acid, sorbose, ethylene diamine, 1,2 diaminocyclohexane, trimethylenediamine,
`
`tetramethylenediamine, 1,2 diaminopropane, diethylenetriamine, triethylenetetramine,
`
`triaminodiethylamine, N-hydroxyethylethylenediamine,
`
`sodium
`
`polyphosphate,
`
`6
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`WO 2006/039090
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`PCT /0S2005/032411
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`potassium polyphosphate, ammonium polyphosphate, sodium hexametaphosphate and
`
`mixtures thereof.
`
`[0024]
`
`In one embodiment, the chelating agent is at least one compound
`
`selected from the group consisting of ethylenediaminetetraacetic acid, oxalic acid,
`
`ammonium oxalate, 1-hydroxyethylidenediphosphonic acid, citric acid, ammonium
`
`citrate, catechol, ethylenediaminediorthohydroxyphenylacetic acid
`
`[EDDHA], 8-
`
`quinolinol, and tropolone.
`
`[0025] The chelating agent used in the present cleaning solutions can be 100%
`
`of any particular chelator, or a combination of chelator in any ratio. A combination or
`
`mixture of chelating compounds may dissolve faster than a single compound. However,
`
`100% oxalic acid, 100% citric acid, 100% EDTA, and combinations of these three can
`
`be preferred.
`
`[0026] Examples of carboxylic acids and carboxylic acid-containing chelating
`
`agents that can be used in the cleaning solutions include, but are not limited to, fatty
`
`acid and alkyl ether carboxylic acid and their corresponding salts and esters (for
`
`example, C 1•20 esters). Carboxylic acids with between 1 and 20 carbon atoms can also
`be used, as can compounds with two or more carboxylic acid groups. Examples of
`
`carboxylic acids, and chelating agents including carboxylic acid groups, include
`
`malonic acid, succinic acid, stearic acid, maleic acid, lactic acid, glycolic acid,
`
`hydroxycaboxylic acids such as citric acid and tartaric acid, and aminopolycarboxylic
`
`acids such as ethylenediamine tetraacetate (EDTA), trans-1,2-diaminocyclohexane(cid:173)
`
`N,N,N'-
`
`,N'-tetraacetate
`
`(CyDTA), diaminopropanol
`
`tetraacetate
`
`(DPTA-OH),
`
`ethylenediamine diacetate (EDDA), ethylenediamine dipropionic acid dichloride
`
`(EDDP), hydroxyethylethylenediamine
`
`triacetate (EDTA-OH), glycoletherdiamine
`
`tetraacetate (GEDTA), 1,6-hexamethylenediamine-N,N,N',- N'-tetraacetate (HDTA)
`
`and diaminopropane tetraacetate (Methyl-EDTA).
`
`[0027] Other suitable chelating agents include quinaldines such as quinaldic
`
`acid, aromatic diamines such as diaminobenzene and diaminonaphthalene, ureas such
`
`as urea and uric acid, thioureas such as thiourea and thiosemicarbazide.
`
`[0028]
`
`Polyamines such as diethylenetriamine, dipropylenetriamine and
`
`triethylenetetraamine, aminopolycarboxylic acids
`
`such as
`
`triethylenetetramine
`
`hexaacetate (TTHA) and diethylenetriamine-N,N,N',N",- N"-pentaacetate (DTPA), can
`
`also be used.
`
`7
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`PCT /0S2005/032411
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`[0029] Examples of carboxylic acids derivatives functioning as surfactants are
`
`PEG-150 stearate, glycolic acid ethoxylate ethers, e.g. laureth carboxylic acids, sorbitan
`
`laureate sulfate, PEG-80 sorbitan laureate, ammonium lauryl sulfate, others.
`
`Phosphonic Acids/Chelating Agents
`
`[0030] Examples of chelating compounds having phosphonic acid groups
`
`include,
`
`for
`
`example,
`
`ethylenediaminetetramethylenephosphonic
`
`acid,
`
`ethylenediaminedimethylenephosphonic acid, nitrilotrismethylenephosphonic acid, 1-
`
`hydroxyethylidenediphosphonic
`
`acid,
`
`aminopolyphosphonic acids such as ethylenediaminetetrakis (methylenephosphonic
`
`acid) (EDTPO), ethylenediamine-N,N'-bis (methylenephosphonic acid) (EDDPO)
`
`isopropyldiaminetetrakis (methylenephosphonic acid) and aminopolyphosphonic acids
`
`such as diethylenetriamine-N ,N ,N' ,N" ,N"-penta ( methylenephosphonic acid). Among
`
`them, 1-hydroxyethylidenediphosphonic acid is preferred.
`
`Weight/Mole Ratios of Individual Components
`
`[0031] The weight ratio of ammonium hydroxide to peroxide to water is
`
`typically between about 1: 1 :5 and about 1: 1-4: 100, and the molar ratio of component A
`
`to ammonium hydroxide is between 1:10 and 1:1000. The amount of alkanolamine is
`
`typically between about 0.1 and about 10 weight percent, more typically between about
`
`0.1 and 5 weight percent.
`
`[0032] The cleaning solutions described herein include specific amounts of
`
`hydrogen peroxide, ammonium hydroxide and at least one component A, wherein the
`
`weight ratio of hydrogen peroxide to water is between 1: 5 and 1: 100, preferably
`
`between 1: 10 and 1 :40 and most preferably between 1 :20 and 1 :40; the weight ratio of
`
`ammonium hydroxide to water is between 1:5 and 1:100; preferably between 1:10 and
`
`1 :50 and most preferably between 1 :20 and 1 :40; and the molar ratio of component A to
`
`ammonium hydroxide is between 1: 10 and 1 :5000, preferably between 1: 10 and 1: 1000,
`
`most preferably between 1 :50 and 1 :500, especially between 1: 100 and 1 :500.
`
`[0033] The cleaning solutions described herein can replace the two-step RCA
`
`system and can provide the efficiency of RCA system within a shorter time by one step
`
`and effectively remove the contaminants such as organics, particles and metals from
`
`surfaces of silicon semiconductors and silicon oxides.
`
`8
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`WO 2006/039090
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`PCT /0S2005/032411
`
`[0034] In one embodiment, the cleaning solution is used prior to the formation
`
`of gate oxide on surfaces of silicon semiconductors or silicon oxides to remove
`
`contaminants including organics, particles and metals from the surfaces. The cleaning
`
`solution can achieve cleaning efficiency in one step and within a time shorter than that
`
`of two-step RCA system without using strong acids such as HCl and sulfuric acid.
`
`[0035] The cleaning solutions are generally in the form of aqueous solutions,
`
`and can be prepared by adding and dissolving the above-listed components in the
`
`above-described weight/mole ratios in water.
`
`[0036] The components can be separately dissolved in water and then mixed to
`
`form the cleaning solutions, or solid or liquid compounds can be added directly to
`
`water, followed by dissolving and stirring, or the like. The cleaning solutions are
`
`preferably filtered before use, and it is also preferred that the water used to prepare the
`
`cleaning solutions is purified by distillation, ion exchange or the like, and is ideally in
`
`the form of "ultrapure water" as this term is known in the art.
`
`[0037] The cleaning solutions are preferably weakly acidic to alkaline,
`
`generally with a pH in the range of 4-13, preferably between about pH 5 and 12, more
`
`preferably, between about 6 and 9. In such pH range, silicon dioxide interlayer
`
`dielectrics have less risk of being etched. Further, the cleaning effect for particles and
`
`copper oxide
`
`is
`
`improved due
`
`to enhanced electric repulsion between
`
`the
`
`semiconductor surface and the particles.
`
`II. Cleaning Methods
`
`[0038] The semiconductors can be cleaned using any conventional method of
`
`cleaning semiconductors using cleaning solutions, including dipping and spraying
`
`techniques.
`
`[0039]
`
`In one embodiment, a mechanical cleaning step is also performed,
`
`before, during or after the chemical cleaning step. Examples of suitable mechanical
`
`cleaning steps for these materials are described, for example, in U.S. Patent No.
`
`6,780,773, the contents of which are hereby incorporated by reference.
`
`[0040] Physical cleaning includes, for example, brush-scrub cleaning to clean
`
`the surface of a semiconductor with a high-speed rotation brush made of
`
`polyvinylalcohol, and megasonic cleaning using high frequency.
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`WO 2006/039090
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`PCT /0S2005/032411
`
`[0041] The physical cleaning can be done in various ways: after providing a
`
`cleaning solution on the surface of a semiconductor by dipping the semiconductor in the
`
`cleaning solution and then taking it out of the cleaning solution; while a semiconductor
`
`is dipped in a cleaning solution; or as the surface of the semiconductor is sprayed or
`
`showered in the cleaning agent.
`
`[0042] Figure 1 shows a conventional procedure for prepanng capacitor
`
`elements of integrated circuits. Chip 10 is cleaned by using a cleaning solution and
`
`oxide layer 20 is formed above chip 10 by wet oxidation. A photoresist layer is then
`
`formed above layer 20 and a mask is used to expose the desired region so as to obtain
`
`photoresist layer 30. Thereafter, the uncovered oxide region is removed by an etching
`
`agent and photoresist layer 30 is removed. Chip 10 which is covered by oxide layer 20
`
`is. cleaned by a cleaning solution and then gate oxide layer 40 is formed by dry
`
`oxidation. Polysilicon layer 50 is formed on chip 10 and optional dopants can be used
`
`to dope polysilicon layer 50 into the desired type. Aluminum layer 60 is formed on
`
`polysilicon layer 50. A photoresist layer is formed on aluminum layer 60 and a mask is
`
`used to expose the desired region so as to obtain photoresist layer 70. An etching agent
`
`is used to remove the regions of aluminum and polysilicon layers uncovered by
`
`photoresist layer and any possible oxides formed on the back side of chip 10.
`
`Aluminum layer 80 is formed on the back side of chip 10 and photoresist layer 70 is
`
`moved. Chip 10 is put in an annealing furnace for annealing to obtain the desired
`
`integrated circuit element.
`
`Assessment of Cleaning Efficiency
`
`[0043] The semiconductor thickness can be measured (before and after
`
`cleaning, if desired) using spectroscopic ellipsometry. This can be used, for example,
`
`to provide a measure of how much wafer thickness was lost as a result of cleaning. The
`
`presence of residual metal or organic contaminants can be measured by various mass
`
`spectrometry techniques as are known in the art.
`
`[0044] The electrical properties of cleaned semiconductors can be tested by
`
`determining the statistical distributions of charge to breakdown and breakdown field of
`
`the semiconductors. The charge to breakdown and breakdown field can be tested, for
`example, at a current density of 50 mA/cm2
`
`• The efficiency of the cleaning solution
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`10
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`WO 2006/039090
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`PCT /0S2005/032411
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`described herein can be evaluated by comparing the electrical properties of cleaned
`
`semiconductors with those provided by an RCA system. In
`
`[0045] The foregoing is illustrative of the present invention and is not to be
`
`construed as limiting thereof. The invention is defined by the following claims, with
`
`equivalents of the claims to be included therein.
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`WO 2006/039090
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`Claims:
`
`PCT /0S2005/032411
`
`1. An aqueous solution for cleaning surfaces of silicon semiconductors or
`
`silicon oxides comprising hydrogen peroxide, ammonium hydroxide, an alkanolamine,
`
`and at
`
`least one component A selected
`
`from
`
`the group consisting of a
`
`tetraalkylammonium hydroxide, an alkanolamide, an amido-betaine, an a,a(cid:173)
`
`dihydroxyphenol, a carboxylic acid, a phosphonic acid, a chelating agent and a
`
`surfactant, where the alkyl groups in the above groups include between 1 and 6 carbon
`
`atoms,
`
`wherein the weight ratio of ammonium hydroxide to peroxide to water is
`
`between about 1:1:5 and about 1:1-4:100, and the molar ratio of component A to
`
`ammonium hydroxide is between 1: 10 and 1: 1000, and the amount of alkanolamine is
`
`between 0.1 and 10 weight percent of the solution.
`
`2. The solution of claim 1, wherein the molar ratio of component A to
`
`ammonium hydroxide is between 1: 100 and 1 :500
`
`3. The solution of claim 1, wherein the weight ratio of animonium hydroxide to
`
`water is between 1: 10 and 1 :40.
`
`4. The solution of claim 1, wherein the weight ratio of hydrogen peroxide to
`
`water is between 1: 10 and 1 :40.
`
`5. The solution of claim 1, wherein the alkanolamine is selected from the group
`
`consisting
`
`of monoethanolamine,
`
`methyldiethanolamine,
`
`diethanolamine,
`
`triethanolamine,
`
`2-methylaminoethanol,
`
`2-ethylaminoethanol,
`
`N-
`
`methyldiethanolamine, dimethylaminoethanol, 2-(2-aminoethoxy)ethanol, l-amino-2-
`
`propanol, monopropanolamine,
`
`N,N-dimethyl-2-(2-aminoethoxy)ethanol,
`
`and
`
`dibutanolamine.
`
`6. The solution of claim 1, wherein the tetraalkylammonium hydroxide is
`
`selected
`
`from
`
`the
`
`group
`
`consisting of
`
`tetramethylammonium
`
`hydroxide,
`
`tetraethylammonium
`
`hydroxide,
`
`tetrabutylammonium
`
`hydroxide,
`
`trimethyl
`
`hydroxyethylammonium hydroxide, methyl tri (hydroxyethyl) ammonium hydroxide,
`
`tetra (hydroxyethyl) ammonium hydroxide, and benzyl trimethylammonium hydroxide.
`
`7. The solution of claim 1, wherein the alkanolamide or amido-betaine is
`
`selected
`
`from
`
`the group consisting of cocodiethanolamide,
`
`lauric/myristic
`
`monoethanolamide,
`
`coconut
`
`monoethanolamide,
`
`la uric
`
`diethanolamide,
`
`cocoamidopropyl betaine and modified or unmodified coconut diethanolamide.
`
`12
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`WO 2006/039090
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`PCT /0S2005/032411
`
`8. The solution of claim 1, wherein the a,a-dihydroxyphenol is selected from
`
`the group consisting of o-dihydroxyphenol, m-dihydroxyphenol, p-dihydroxyphenol,
`
`gallic acid, catechol, alkyl resorcinols, and 3,4-dihydroxyphenylalanine.
`
`9. The solution of claim 1, wherein the carboxylic acid is selected from the
`
`group consisting of fatty acids, C 1_20 alkyl ether carboxylic acids, C 140 carboxylic acids
`with one or two carboxylic acid groups, and salts or esters thereof.
`
`10. The solution of claim 1, wherein the chelating agent is selected from the
`
`group
`
`consisting
`
`of
`
`ethylenediamine
`
`tetraacetate
`
`(EDTA),
`
`trans-1,2-
`
`diaminocyclohexane-N,N,N'- ,N'-tetraacetate (CyDTA), diaminopropanol tetraacetate
`
`(DPTA-OH), ethylenediamine diacetate (EDDA), ethylenediamine dipropionic acid
`
`dichloride
`
`(EDDP),
`
`hydroxyethylethylenediamine
`
`triacetate
`
`(EDTA-OH),
`
`glycoletherdiamine tetraacetate (GEDTA), 1,6-hexamethylenediamine-N,N,N',- N'(cid:173)
`
`tetraacetate (HDTA), diaminopropane tetraacetate (methyl-EDTA), ascorbic acid,
`
`oxalic acid, ammonium oxalate, 1-hydroxyethylidenediphosphonic acid, citric acid,
`
`ammonmm
`
`citrate,
`
`catechol,
`
`ethylenediaminediorthohydroxyphenylacetic
`
`acid
`
`[EDDHA], 8-quinolinol, and tropolone.
`
`11. A method for cleaning surfaces of silicon semiconductors or silicon oxides
`
`in a single step comprising applying a solution according to claim 1 to the surfaces of
`
`the silicon semiconductors or silicon oxides.
`
`12. The method of claim 11, further comprising a mechanical cleaning step.
`
`13
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`

`

`WO 2006/039090
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`PCT /0S2005/032411
`
`Figurel/1
`
`I
`f:=-~i
`-1-
`r : r= . ~ . ====-=mn::t.E~g
`.J. .
`EL--·._· _5_T~20 ~10
`
`10
`
`