I 1111111111111111 11111 111111111111111 IIIII IIIII IIIII IIIII 111111111111111111
`US007456140B2
`
`c12) United States Patent
`Small et al.
`
`(IO) Patent No.:
`(45) Date of Patent:
`
`US 7,456,140 B2
`*Nov. 25, 2008
`
`(54) COMPOSITIONS FOR CLEANING ORGANIC
`AND PLASMA ETCHED RESIDUES FOR
`SEMICONDUCTOR DEVICES
`
`(75)
`
`Inventors: Robert J. Small, Dublin, CA (US);
`Bakul P. Patel, Pleasanton, CA (US);
`Wai Mun Lee, Fremont, CA (US);
`Douglas Holmes, San Ramon, CA (US);
`Jerome Daviot, Antony (FR); Chris
`Reid, Glasgow (GB)
`(73) Assignee: EKC Technology, Inc., Hayward, CA
`(US)
`
`( *) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 326 days.
`
`EP
`WO
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,592,773 A
`4,395,479 A
`4,401,747 A
`4,403,029 A
`4,428,871 A
`
`7/1971 Muller
`7/1983 Ward et al.
`8/1983 Ward, Jr. et al.
`9/1983 Ward, Jr. et al.
`1/1984 Ward et al.
`
`(Continued)
`
`FOREIGN PATENT DOCUMENTS
`
`0 662 705
`98/36045
`
`8/2000
`8/1998
`
`OTHER PUBLICATIONS
`
`This patent is subject to a terminal dis(cid:173)
`claimer.
`
`(21) Appl. No.: 10/920,494
`
`(22)
`
`Filed:
`
`Aug. 17, 2004
`
`(65)
`
`Prior Publication Data
`
`US 2005/0202987 Al
`
`Sep. 15, 2005
`
`Related U.S. Application Data
`
`(63) Continuation-in-part of application No. 09/903,064,
`filed on Jul. 10, 2001, now Pat. No. 6,777,380.
`
`(60) Provisional application No. 60/217,650, filed on Jul.
`10, 2000.
`
`(51)
`
`Int. Cl.
`CllD 7150
`(2006.01)
`(52) U.S. Cl. ......................... 510/175; 510/176; 134/1.3
`(58) Field of Classification Search ................. 510/175,
`510/176; 134/1.3
`See application file for complete search history.
`
`P.J. Ireland, "High Aspect Ratio Contacts: A Review of the Current
`Tungsten Plug Process," Thin Solid Films 304 (1997), pp. 1-12.
`
`(Continued)
`
`Primary Examiner-Gregory E Webb
`(74) Attorney, Agent, or Firm-Morgan Lewis & Bockius
`LLP
`
`(57)
`
`ABSTRACT
`
`A composition for the stripping of photoresist and the clean(cid:173)
`ing of residues from substrates, and for silicon oxide etch,
`comprising from about 0.01 percent by weight to about 10
`percent by weight of one or more fluoride compounds, from
`about 10 percent by weight to about 95% by weight of a
`sulfoxide or sulfone solvent, and from about 20 percent by
`weight to about 50 percent by weight water. The composition
`may contain corrosion inhibitors, chelating agents, co-sol(cid:173)
`vents, basic amine compounds, surfactants, acids and bases.
`
`7 Claims, 7 Drawing Sheets
`
`TOK Ex. 1023
`PGR Petition
`
`

`

`US 7,456,140 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`4/1985
`4,508,591 A
`5/1988
`4,744,834 A
`9/1988
`4,770,713 A
`5,129,955 A
`7/1992
`1/1993
`5,181,985 A
`5,560,857 A
`10/1996
`10/1996
`5,563,119 A
`5,571,447 A * 11/1996
`5,603,849 A
`2/1997
`5,630,904 A
`5/1997
`5,645,737 A
`7/1997
`5,672,577 A
`9/1997
`5,705,089 A
`1/1998
`5,709,756 A
`1/1998
`5,792,274 A
`8/1998
`5,885,477 A
`3/1999
`5,905,063 A
`5/1999
`5,928,430 A
`7/1999
`5,962,385 A
`10/1999
`5,972,862 A
`10/1999
`5,981,454 A
`11/1999
`6,048,406 A
`4/2000
`6,235,693 Bl
`5/2001
`6,248,704 Bl *
`6/2001
`6,261,745 Bl*
`7/2001
`6,492,311 B2 * 12/2002
`6,638,899 Bl* 10/2003
`
`Bartlett et al.
`Haq
`Ward
`Tanaka
`Lampert et al.
`Sakon et al.
`Ward
`Ward et al. .................. 510/206
`Li
`Aoyamaetal.
`Robinson et al.
`Lee
`Sugihara et al.
`Ward et al.
`Tanabe et al.
`Rasmussen et al.
`Tanabe et al.
`Ward et al.
`Maruyama et al.
`Torii et al.
`Small
`Misra et al.
`Cheng
`Small et al. ................. 510/176
`Tanabe et al. ............... 430/331
`Lee et al ..................... 510/176
`Wakiya et al.
`. ............. 510/176
`
`8/2004 Small eta!. ................. 510/176
`6,777,380 B2 *
`OTHER PUBLICATIONS
`C. Lee and S.C. Lee, "Effects of Plasma Treatments on the Erosion of
`TEOS-BPSG Films by Chemical Etchants," Solid State Electronics,
`vol. 41, No. 6, pp. 921-923 (1997).
`M.R. Baklanov, et al., "Applicability of HF Solutions for Contact
`Hole Cleaning on Top ofTiSi2," Electrochemical Society Proceed(cid:173)
`ings, vol. 97-35, pp. 602-609 (1998).
`C. Rafols, et al., "Ionic Equilibria in Aqueous Organic Solvent Mix(cid:173)
`tures: The Equilibria of HF in an Ethanol + Water Mixture Used for
`Cleaning Up Semiconductors," J. Electroanalytical Chem. 433, pp.
`77-83 (1997).
`K. Ueno, et al., "Cleaning ofCHF3 Plasma-Etched SiO2/SiN/Cu Via
`Structures with Dilute Hydrofluoric Acid Solutions," J. Electrochem.
`Soc., vol. 144, No. 7, pp. 2565-2572 (Jul. 1997).
`T. Kujime, et al., "The Cleaning of Particles From Si Water Surface
`by Fluorine Solution Excited by Megasonic," Proceedings of the
`1996 Semi. Pure Water and Chemicals, pp. 245-256 (1996).
`P. Singer, "Wafer Cleaning: Making the Transition to Surface Engi(cid:173)
`neering," Semiconductor Int'!, p. 88-92 (Oct. 1995).
`M. Liehr and S.R. Kasi, "HF and UV-Ozone Integrated Wafer
`Preclean: Chemistry and Effects on Thermal Gate Oxide," 1991 Int'!
`Conf. on Solid State Devices and Materials, Yokohama, pp. 484-486
`(1991).
`L.O. Ohman and Sjoberg, "Equilibrium and Structural Studies of
`Silicon(IV) and Aluminum(III) in Aqueous Solution. Part 9. A
`Potentiometric Study of Mono- and Poly-nuclear Aluminum(III)
`Citrates," J. Chem. Soc. Dalton Trans., pp. 2513-2517 (1983).
`* cited by examiner
`
`

`

`U.S. Patent
`
`Nov.25,2008
`
`Sheet 1 of 7
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`US 7,456,140 B2
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`Page i
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`U.S. Patent
`
`Nov. 25, 2008
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`Sheet 2 of 7
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`U.S. Patent
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`U.S. Patent
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`Nov. 25, 2008
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`Sheet 4 of 7
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`US 7,456,140 B2
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`U.S. Patent
`
`Nov.25,2008
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`Sheet 5 of 7
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`US 7,456,140 B2
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`U.S. Patent
`
`Nov. 25, 2008
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`Sheet 6 of 7
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`U.S. Patent
`
`Nov. 25, 2008
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`Sheet 7 of 7
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`

`

`US 7,456,140 B2
`
`1
`COMPOSITIONS FOR CLEANING ORGANIC
`AND PLASMA ETCHED RESIDUES FOR
`SEMICONDUCTOR DEVICES
`
`CLAIM OF PRIORITY
`
`This application is a continuation-in-part of U.S. applica(cid:173)
`tion Ser. No. 09/903,064, filed Jul. 10, 2001, now U.S. Pat.
`No. 6,777,380, which claims the benefit of U.S. Provisional
`Patent Application No. 60/217,650, filed Jul. 10, 2000, both
`of which are incorporated herein by reference in their entirety.
`
`FIELD OF THE INVENTION
`
`This invention relates to semi-aqueous stripping and clean(cid:173)
`ing compositions that are particularly useful for stripping
`photoresists and cleaning organic and inorganic compounds,
`including post etch and post ash residues, from a semicon(cid:173)
`ductor substrate. The invention is also useful as a silicon
`oxide etchant.
`
`BACKGROUND
`
`Fluoride containing chemistries have been used for many
`years with prime silicon wafers (wafers that have not yet
`undergone ion implantation or device construction) in the
`semiconductor industry. Normally the fluoride chemistry
`(usually dilute hydrofluoric acid) is used as the last process
`step in the sequence called "RCA rinses". The substrate is
`often contaminated from previous process steps with mono(cid:173)
`layer amounts of metal, anions and/or organic contaminants
`or surface residues (particles). These contaminants have been
`shown to have a significant impact on the electrical integrity
`of simple test device structures and these structures need to be
`cleaned efficiently without impairing their integrity. Such
`cleaning methods could include techniques discussed in the
`technical literature, for example, mt. Conf. On Solid State
`Devices and Materials, 1991, pp. 484-486 or Kujime, T. et al.,
`Proc. of the 1996 Semi. Pure Water and Chemicals, pp. 245-
`256 and Singer, P., Semi. International, p. 88, Oct. 1995.
`Patents that teach methods for cleaning prime wafers with
`low pH solutions include U.S. Pat. Nos. 5,560,857 and 5,645,
`737; 5,181,985; 5,603,849; 5,705,089.
`Using fluoride chemistries (usually HF) as a final RCA
`cleaning step will cause the silicon wafer surface to be in a
`hydrophobic state (the surface is covered with Si-H groups)
`which will repel water. During this step a certain proportion
`of the wafer surface is dissolved (removed). Unless the con(cid:173)
`ditions are carefully monitored (time, temperature, solution
`composition) the substrates can be damaged, as reported by
`Rafols, C. et al., J. Electroanalytic Chem. 433. pp. 77-83,
`1997. Numerous compositions combine water and organic
`solvents. The water concentration in these solutions is very
`critical. Silica oxide has an etch rate of21 A/min (@25° C.)
`in HF/water, but in isobutanol the rate was reduced to 2.14
`A/min and even lower in acetone (an aprotic solvent) the rate
`was only 0.12 A/min, as reported at NSF/SRC Eng. Res.
`Center, Environmentally Benign Semiconductor Manufac(cid:173)
`turing, Aug. 5-7, 1998, Stanford University.
`After the Front End of Line (FEOL) cleaning process the
`wafer proceeds to the typical Back End of Line (BEOL)
`manufacturing process for semiconductor devices, in which
`the devices might be dynamic random access memories
`(DRAMs), static random access memories (SRAMs), logic,
`electrically programmable read only memories (EPROMs),
`complementary metal on silicon (CMOS), and the like. Etch(cid:173)
`ing fabrication technology using chemical reactions (liquid or
`
`5
`
`2
`plasma) has been used as a method of forming a wiring
`structure on such semiconductor substrates.
`A photoresist film is deposited on the wafer to form a mask,
`then a substrate design is imaged on the film layer, baked, and
`the undeveloped image is removed with a developer. The
`remaining image is then transferred to the underlying mate(cid:173)
`rial through etching ( either a dielectric or metal) with reactive
`etching gases promoted with plasma energy.
`The etchant gases selectively attack the unprotected area of
`10 the substrate. Liquid or wet etching chemistries have been
`used extensively over the years to etch metals, oxides and
`dielectrics. These chemistries can be very aggressive and can
`result in isotropic etching ( etching equally in all directions).
`Increasingly, plasma etching, reactive ion etching or ion
`15 milling are used, and such etching processes produce unde(cid:173)
`sirable by-products from the interaction of the plasma gases,
`reacted species and the photoresist. The composition of such
`by-products is generally made up of the etched substrates,
`underlying substrate, photoresist and etching gases. The for-
`20 mation of such by-products is influenced by the type of etch(cid:173)
`ing equipment, process conditions and substrates utilized.
`These by-products are generally referred to as "sidewall poly(cid:173)
`mer," "veil" or "fences" and cannot be removed completely
`by either oxygen plasma or conventional solvents. Examples
`25 of alkaline/solvent mixture types of photoresist strippers
`which are known for use in stripping applications include
`dimethylacetamide or dimethylformamide and alkanola(cid:173)
`mines as described in U.S. Pat. Nos. 4,770,713 and 4,403,
`029; 2-pyrrolidone, dialkylsulfone and alkanolamines as
`30 described in U.S. Pat. Nos. 4,428,871, 4,401,747, and 4,395,
`479; and 2-pyrrolidone and tetramethylammonium hydrox(cid:173)
`ide as described in U.S. Pat. No. 4,744,834. Such stripping
`compositions, however, have only proven successful in clean(cid:173)
`ing "sidewall polymer" from the contact openings and metal
`35 line etching in simple microcircuit manufacturing involving a
`single layer of metal process when the metal structure
`involves mainly Al-Si or Al-Si--Cu and the "sidewall
`polymer" residue contains only an organometallic compound
`with aluminum.
`If etching residue is not removed from the substrate, the
`residue can interfere with subsequent processes involving the
`substrate. The need to effectively remove etching residue and
`photoresist from a substrate becomes more critical as the
`industry progresses into submicron processing techniques.
`45 The requirement for cleaning solutions that remove all types
`of residue generated as a result of plasma etching of various
`types of metals, such as aluminum, aluminum/silicon/copper,
`titanium, titanium nitride, titanium/tungsten, tungsten, sili(cid:173)
`con oxide, polysilicon crystal, etc., while not corroding the
`50 underlying metal presents a need for more effective chemistry
`in the processing area. The effect of poor cleaning results in
`low device yield, low device reliability, and low device per(cid:173)
`formance.
`Also, if the components in these residues are not removed
`55 or neutralized in some manner then the residues will absorb
`moisture and form acidic species that can corrode the metal
`structures. The resultant acid corrodes wiring materials to
`bring about an adverse effect such as an increase in electrical
`resistance and wire disconnection. Such problems frequently
`60 occur, in particular in aluminum and aluminum alloys gener(cid:173)
`ally used as wiring material. The wafer substrate in contact
`with acidic materials, if not controlled, can destroy the metal
`structures. Following completion of the etching operation it is
`necessary that the post-etch resist mask be removed from the
`65 protective surface to permit finishing operations.
`It is desirable to develop an improved cleaning composi(cid:173)
`tion to remove the organic polymeric substance from a coated
`
`40
`
`

`

`US 7,456,140 B2
`
`4
`3
`inorganic substrate without corroding, dissolving or dulling
`Other methods for cleaning metal and metal oxide residues
`the metal circuitry or chemically altering the wafer substrate.
`on wafers include spraying water vapor into the plasma ash(cid:173)
`ing chamber followed by introducing fluorine containing
`Sidewall residues have been removed with either acidic
`gases (hydrofluoric acid) (U.S. Pat. No. 5,181,985) or a liquid
`organic solvents or alkaline organic solvents. The acidic sol(cid:173)
`5 containing hydrofluoric acid, ammonium fluoride and water
`vents are generally composed of phenolic compounds or
`with a pH between 1.5 to less than 7.
`chloro-solvent and/or an aromatic hydrocarbon and/or alky(cid:173)
`Some chemistries have also included chelating agents to
`lbenzenesulfonic acids. These formulations generally need to
`help remove ionic and anionic contamination from the wafer
`be used at temperatures up to and beyond 100° C. These
`surface (PCT US98/02794) but chelating agents such as citric
`chemistries normally need to be rinsed with isopropanol.
`10 acid, gallic acid, and catechol among others, can be aggres(cid:173)
`In addition, stripping compositions used for removing pho(cid:173)
`sive toward the aluminum oxide that covers the Al metal lines.
`toresist coatings and cleaning compositions for removing
`Studies by Ohman and Sjoberg show that the strong complex(cid:173)
`post-etch residue have for the most part been highly flam(cid:173)
`ing ability of citric ions can increase the aluminum oxide
`mable, generally hazardous to both humans and the environ(cid:173)
`solubility and thereby expose the metal to further corrosion,
`ment, and comprise reactive solvent mixtures exhibiting an
`15 by factors of 166 and 468 at pH 5 and 6 (see Ohman et al., J.
`undesirable degree of toxicity. Moreover, these compositions
`Chem. Soc., Dalton Trans. (1983), p. 2513).
`are not only toxic, but their disposal is costly since they might
`Other resist-remover chemistries, such as those in U.S. Pat.
`have to be disposed of as a hazardous waste. In addition, these
`No. 5,792,274, have included a salt of hydrogen fluoride
`compositions generally have severely limited bath life and,
`combined with a water-soluble organic solvent and water at a
`for the most part, are not recyclable or reusable.
`20 pH of 5 to 8. However, no mention is made of the use of
`The photoresist around the contact hole of common inter(cid:173)
`ammonium hydrogen fluoride (also known as animonium
`layer dielectrics, TEOS (tetraethylorthosilicate) and boron
`bifluoride ), which provides greater stability than animonium
`phosphosilicate glass (BPSG), which are commonly used in
`fluoride, or the use of a synergistic mixture of co-solvents or
`ultra large scale integration (ULSI) structures for better con(cid:173)
`basic amine compounds with DMSO and a fluorinated com-
`formity of step coverage, is usually removed with HF solu(cid:173)
`25 pound.
`tions. It is not uncommon for the HF to also attack the dielec(cid:173)
`U.S. Pat. No. 6,048,406 issued Apr. 11, 2000 to Misra et al.
`tric material. Such attack is not desirable ( see Lee, C. and Lee,
`entitled "Benign Method for Etching Silicon Dioxide"
`S. C., Solid State Electronics, 41, pp. 921-923 (1997)).
`teaches using an aqueous solution of ammonium hydrogen
`Accordingly, a need exists for a more environmentally
`fluoride ((NH4 )HF 2 ) as an alternative to hydrofluoric acid
`friendly stripping and cleaning formulation.
`30 because it is more benign for wet etching silicon oxide. How(cid:173)
`Dilute hydrofluoric acid solutions can under certain con(cid:173)
`ever, there is no teaching of the use of a formulation that can
`ditions remove the sidewall polymers by aggressively attack(cid:173)
`remove photoresist or an etching residue. Also, there is no
`ing the via sidewall of the dielectric and therefore changing
`teaching of adding a synergistic mixture of co-solvents or
`the dimensions of the device, as taught by Ireland, P., Thin
`basic amine compounds.
`Solid Films, 304, pp. 1-12 (1997), and possibly the dielectric 35
`U.S. Pat. No. 5,885,477 issued Mar. 23, 1999to Rasmussen
`constant. Previous chemistries that contain HF, nitric acid,
`et al. entitled "Silicon Dioxide Etch Process Which Protects
`water and hydroxylamine are aggressive enough to etch sili(cid:173)
`Metal" teaches using an aqueous solution of ammonium fluo(cid:173)
`con, as taught by U.S. Pat. No. 3,592,773 issued to A. Muller.
`ride and hydrofluoric acid with a salt to etch silicon oxide
`Recent information also indicates that the dilute HF solutions
`while minimizing corrosion. However, there is no teaching of
`can be ineffective for cleaning the newer CF x etch residues, as
`40 the use of animonium hydrogen fluoride, co-solvents or basic
`taught by K. Ueno et al., "Cleaning ofCHF 3 Plasma-Etched
`amine compounds.
`SiO2/SiN/Cu Via Structures with Dilute Hydrofluoric Acid
`U.S. Pat. No. 4,508,591 issuedApr. 2, 1985 to Bartlett et al.
`Solutions," J. Electrochem. Soc., vol. 144, (7) 1997. Contact
`entitled "Polymethyl Methacrylate Compatible Silicon Diox(cid:173)
`holes opened on to the TiSi 2 have also been difficult to clean
`ide Complexing Agent" teaches using ammonium fluoride
`with HF solutions since there appears to be an attack of the
`45 and citric acid to etch silicon dioxide. However, as with Ras(cid:173)
`underlying TiSi 2 layer. There may also be difficulty with mass
`mussen et al., there is no teaching of the use of animonium
`transport of the chemicals in the narrow hydrophilic contact
`hydrogen fluoride, co-solvents or basic amine compounds.
`holes, as taught by Baklanov, M. R. et al., Proc. Electrochem.
`Nor is there any teaching to use such a formulation for remov-
`Soc., 1998, 97-35, pp. 602-609.
`ing etch residue or photoresist.
`Recently, fluoride-based chemistries have been used in 50
`Accordingly, there exists a need to develop improved sili-
`limited cases to remove post etch residues. Many of these
`con dioxide etchant and photoresist and post-etch residue
`compositions contain fluoride components, specifically
`remover for a variety of unwanted materials from a wide
`hydrogen fluoride. In addition, these compositions might
`variety of substrates. Particularly in the field of integrated
`contain strong caustic chemicals (choline-derivatives, tet(cid:173)
`circuit fabrication, it should be recognized that the demands
`raalkyl animonium hydroxide, ammonium hydroxide) such 55 for improved removal performance with avoidance of attack
`as disclosed in U.S. Pat. No. 5,129,955; U.S. Pat. No. 5,563,
`on the substrates are constantly increasing. This means that
`compositions that were suitable for less sophisticated inte(cid:173)
`119; or U.S. Pat. No. 5,571,447, or might use a two-phase
`grated circuit substrates may not be able to produce satisfac(cid:173)
`solvent system, which contains one phase with hydrofluoric
`tory results with substrates containing more advanced inte-
`acid and water while a second phase contains a nonpolar
`60 grated circuits
`in
`the process of fabrication. These
`organic solvent (ketones, ethers, alkanes or alkenes) (U.S.
`Pat. No. 5,603,849). Other formulations include hydroxy(cid:173)
`compositions should also be economical, environmental
`lamine and ammonium fluoride (U.S. Pat. No. 5,709,756,
`friendly and easy to use.
`issued to Ward). Additional examples include quaternary
`The discussion of the background to the invention herein is
`ammonium salt and fluoride based compositions, as disclosed
`included to explain the context of the invention. This is not to
`in published European Application 0662705, and organocar(cid:173)
`65 be taken as an admission that any of the material referred to
`boxylic ammonium salt or amine carboxylate and fluoride
`was published, known, or part of the common general knowl(cid:173)
`based compositions, as disclosed in U.S. Pat. No. 5,630,904.
`edge as at the priority date of any of the claims.
`
`

`

`US 7,456,140 B2
`
`5
`Tbroughout the description and claims of the specification
`the word "comprise" and variations thereof, such as "com(cid:173)
`prising" and "comprises", is not intended to exclude other
`additives, components, integers or steps.
`
`SUMMARY OF THE INVENTION
`
`Accordingly, the present invention teaches a new and
`improved stripping and cleaning composition and a process
`for its use. The present invention also includes silicon oxide
`etching compositions and their use. This composition is aque(cid:173)
`ous, dissolves both organic and inorganic substances, and,
`when used in the process, is able to strip and clean a variety of
`substrates.
`The novel stripping, cleaning and etching compositions of 15
`the invention exhibit synergistically enhanced capabilities
`that are not possible from the use of the individual compo(cid:173)
`nents, or the components in combination with other compo(cid:173)
`nents.
`It is one objective of the invention to provide etch residue 20
`removing compositions that: effectively clean post-etch resi(cid:173)
`dues from substrates, inhibit redeposition of metal ions, and
`are corrosion resistant.
`It is a further objective of the invention to provide effective
`photoresist stripping compositions.
`Anotherobjective is to provide effective silicon oxide etch(cid:173)
`ing compositions.
`These and related objectives are attained through the use of
`the composition and process disclosed herein.
`A composition in accordance with this invention is for
`photoresist stripping and comprises from about 0.01 percent
`by weight to about 10 percent by weight of one or more
`fluoride compounds, an effective amount of up to about 95
`percent by weight of one or more solvents that are sulfoxides
`or sulfones, and at least about 20 percent by weight water.
`Additionally, the composition may optionally contain basic
`amines, co-solvents, corrosion inhibitors, chelating agents,
`surfactants, acids and bases. A preferred embodiment con(cid:173)
`tains ammonium hydrogen fluoride, DMSO, and water.
`A composition in accordance with this invention is for 40
`post-etch residue cleaning and comprises from about 0.01
`percent by weight to about 10 percent by weight of one or
`more fluoride compounds, an effective amount of from about
`10 to about 95 percent by weight of one or more certain
`solvents, and at least about 20 percent by weight water. A 45
`preferred embodiment consists of ammonium hydrogen fluo(cid:173)
`ride, DMSO, and water.
`Additionally, the composition may optionally contain
`basic amines, co-solvents, corrosion inhibitors, chelating
`agents, surfactants, acids and bases.
`Another preferred composition for cleaning and stripping
`consists ofanm10niumhydrogenfluoride, DMSO, water, and
`a co-solvent selected from the group consisting of acetic acid,
`methyl acetate, methyl lactate, ethyl acetate, ethylene glycol
`diacetate, ethyl lactate, propylene glycol, propylene carbon- 55
`ate, N-methyl pyrrolidone, glycol ethers such as methoxy(cid:173)
`ethoxyethanol, butoxyethoxyethanol, and the like, and poly(cid:173)
`ethylene glycol monolaurate.
`Another preferred composition for cleaning and stripping
`consists ofanm10niumhydrogenfluoride, DMSO, water, and 60
`a basic amine selected from the group consisting ofhydroxy(cid:173)
`lamine, hydrazine, 2-amino-2-ethoxy ethanol, monoethano(cid:173)
`lamine, diethylhydroxylamine, choline, tetramethylammo(cid:173)
`nium formate, monoisopropanolamine, diethanolamine, and
`triethanolamine.
`If said composition in accordance with this invention is
`used for metal and oxide etching, the content of the fluoride
`
`5
`
`6
`compound is elevated. For example, for use as a silicon
`etchant, it is preferred to have about 20% of a 40% aqueous
`ammonium fluoride solution.
`A process for photoresist stripping in accordance with this
`invention comprises contacting the substrate with a compo(cid:173)
`sition comprising one or more fluoride compounds, water and
`sulfoxide solvent at a temperature and for a time sufficient to
`strip the photoresist.
`A process for cleaning residue from a substrate in accor-
`10 dance with this invention comprises contacting the substrate
`with a composition comprising one or more fluoride com(cid:173)
`pounds, water and sulfoxide solvent at a temperature and for
`a time sufficient to clean the substrate.
`A process for metal or oxide etch in accordance with this
`invention comprises contacting the metal or oxide with a
`composition comprising one or more fluoride compounds,
`water and sulfoxide or sulfone solvent at a temperature and
`for a time sufficient to etch the metal or oxide.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is an SEM of a via effectively cleaned using a
`formulation containing a co-solvent.
`FIG. 2 shows the effect of choline on the etch rate of
`25 fluoride containing compounds.
`FIG. 3 shows the inverse relationship of corrosion rate v.
`the etch rate of HF 2 - .
`FIGS. 4A, 4B and 4C show the results of cleaning with
`hydrofluoric acid, ammonium hydrogen fluoride and ammo-
`30 nium fluoride respectively.
`FIGS. SA, SB and SC show the cleaning results when using
`different additional compounds, propylene glycol, acetyl
`acetone and 2-amino-2-ethoxy ethanol, respectively.
`FIGS. 6A and 6B show results of cleaning vias using ester
`35 co-solvents.
`FIG. 7 shows the results with a 1:1.5:1 ratio of dimethyl(cid:173)
`sulfoxide/ethyl laurate/water.
`
`DETAILED DESCRIPTION
`
`This invention relates to semi-aqueous stripping and clean(cid:173)
`ing compositions that are particularly useful for stripping
`photoresists and cleaning organic and inorganic compounds,
`including post etch and post ash residues, from a semicon(cid:173)
`ductor substrate. The invention is also useful as a silicon
`oxide etchant. As used herein, the term "semi aqueous" refers
`to a mixture of water and organic solvent. The invention also
`includes methods of using this composition to strip photore(cid:173)
`sists, clean organic and inorganic compounds from semicon-
`50 ductor substrates, and etch silicon oxide. More particularly,
`the invention describes semi aqueous stripping, cleaning and
`etching compositions and processes for the use thereof. The
`solutions contain fluoride compounds, sulfoxide or sulfone
`solvents, water and may contain other solvents, corrosion
`inhibitors, chelating agents, basic amine compounds, surfac(cid:173)
`tants, acids and bases.
`The manufacture of electronic devices typically involves
`the use of photoresist removers, etch residue removers and
`silicon oxide etchants at particular times in the manufacturing
`process. Fluoride containing formulations have been used to
`some extent for these purposes. However, some formulations
`with fluoride containing compounds such as anm10nium fluo(cid:173)
`ride have given inconsistent silicon oxide etch rates due to the
`evaporation of anmionia from the liquid phase. When the
`65 ammonia evolves from the solution, the concentration of the
`active species of HF2 - and HF increases and more aggres(cid:173)
`sively attacks the silicon dioxide. In addition, it has been
`
`

`

`US 7,456,140 B2
`
`8
`preferred fluoride compounds are anmionium fluoride and
`ammonium hydrogen fluoride. The most preferred fluoride
`compound is anmionium hydrogen fluoride. For removing
`residues and photoresists, the fluoride compounds are desir-
`5 ably present in an amount of from about 0.01 percent by
`weight to about 10 weight percent. In general, the lower the
`concentration of the fluoride compound in the composition,
`the higher the temperature of use needs to be.
`The silicon oxide etch compositions of the present inven(cid:173)
`tion also contain one or more fluoride compounds but the
`compounds are preferably present in an amount from about 7
`weight percent to about 10 weight percent.
`The second component include sulfoxide solvents and sul(cid:173)
`fone solvents or mixtures thereof which correspond to the
`following:
`
`7
`found that the use of aqueous formulations of fluoride com(cid:173)
`pounds, such as ammonium fluoride and hydrofluoric acid,
`and solvents, such as dimethylsulfoxide, fail to provide
`adequate resist and residue removal without significant cor(cid:173)
`rosion of the underlying metal unless additional compounds
`are added to the formulation.
`The present invention discloses novel formulations which
`provide consistent silicon oxide etch rates and effectively
`remove photoresist and etch residues while inhibiting the
`corrosion of the underlying metal. In one embodiment, the 10
`present invention applies the use of aqueous fluoride formu(cid:173)
`lations that use anmionium hydrogen fluoride, which is a
`more stable fluoride compound and does not result in the
`same problems experienced by ammonium fluoride and
`hydrogen fluoride regarding either inconsistent silicon oxide 15
`rates or excessive corrosion.
`In another embodiment, the invention applies the use of
`aqueous fluoride formulations with sulfoxide and sulfone
`solvents and co-solvents including esters such as methyl
`acetate, ethyl acetate, butyl acetate, methyl lactate, and ethyl 20
`lactate, glycols such as propylene glycol, ethylene glycol
`diacetate, polyethylene clycol monolaurate, lactams such as
`N-methyl pyrrolidone and the like, and other suitable solvents
`such as propylene carbonate, glycol ethers such as 2-(2-meth(cid:173)
`oxyethoxy)ethanol, and 2-(2-butoxyethoxy)ethanol (also
`known as diethylene glycol monobutyl ether), and the like,
`which aid in the cleaning effectiveness of the fluoride formu(cid:173)
`lation.
`It is to be understood that the glycol ether co-solvents for
`use with the present invention are preferably lower alkyl 30
`glycol ethers such as diethylene glycol ethers, and the alkoxy
`substituent groups are also preferably lower alkyl groups with
`from 1 to 5 carbon atoms. Such glycol ether co-solvents are
`expressed by the following formula:
`
`where R 1 and R2 are an H, OH or alkyl group, and at least one
`25 is an alkyl group, and
`
`35
`
`In this formula, R is a lower alkyl, with preferably 1 to 5
`carbon atoms and may be straight chain or branched. Even
`more preferably, Risa butyl group. In other embodiments, R
`may have from 6 to 10 carbon atoms and may be straight chain
`or branched. The integers m and n are also preferably in the
`range 1 to 5, but may also lie in the range 1 to 10. Even more
`preferably, m=2 and n=2. Although represented as chains, the 50
`(CH2)m and (CH2)n groups may also admit to branching.
`In another embodiment, the invention applies the use of
`aqueous fluoride formulations with sulfoxide and sulfone
`solvents and basic amine compounds such as 2-amino-2-
`ethoxy ethanol, monoethanolamine, monoisopropanolamine 55
`and the like which assist in cleaning effectiveness and inhibit
`corros10n.
`These embodiments can be used separately or combined.
`The first component of the composi