DE2049945A1 - Stripping solution and its use - Google Patents

Description

Priorities: October 15, 1960 in USA Serial No. 8 ^ 6 036 and September 25, 1970 in USA Serial I: o.

In chemistry was the removal of organic deposits, Layers or films of silicon or silicon dioxide surfaces have always been a problem of great concern. Although different acidic mixtures containing chromium were used, there was still room for improvements in efficiency in terms of both speed and temperature for the Distance. Although also the cleaning of industrial and laboratory stands can be named as an area of application for such compositions, it is particularly important to point out that in recent years a more important utility in the manufacture of semiconductors for electronic

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BATH ORIGINAL

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Purposes. In the manufacture of leakage conductors, it is common practice in certain operations to develop a desired circuit pattern on the silicon body or a silicon dioxide layer thereon during the many stages of processing. These circuit diagrams are usually etched into the silicon body or the silicon dioxide layer by selective etching using an etching base applied in the desired circuit diagram. This is usually done by coating the semiconductor with a polymeric photoelectric cover (either of the positive or negative acting type which is exposed to visible or ultraviolet light or some other source of energy such as an electron beam through a window with the circuit diagram on it) The part of the photoelectric cover film exposed to the energy source in the case of positive wake-up agents or the part of the photoelectric cover film not exposed to the energy source in the case of negative cover media is dissolved and removed by a developer solvent. The remaining photoelectric cover film is then usually dried and removed Burned in and leaves the desired circuit diagram on a polymeric: etching base that is not attacked by the chemicals if the areas on the caustic conductor that are not protected by the polymeric etching base are etched or otherwise treated in the desired manner If the work is to be carried out, it is necessary to remove the remaining polymeric etching base. Sulfuric acid and sulfuric acid solutions or slurries with one; The content of odorous acids was found to be at ⁰ O to 100 C or higher.

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ven 'e: r :: nraturon as rirksar: for the ^r - "ntf ernurr; this remaining nolyi.'eren." tκf round. Various OIV;!. Ani "che readings that include ■ '■ sutr-.si.dttel and phenolisehe materials ₅ are also in.rksaine stripper, ^t they -'enn OO to 100 ° C or used it vrorden.

The subject of the problem is thus a well of solutions and their use. The solutions are, ^ eeifjiiet for the above-driven equipment deployment operations. The stripping solutions after the discovery do not cause any scratching, drilling or other visible decomposition of silicon objects or silicon dioxide films : e: \ -: .. on oiliciuriye ^ enutändan even after 5 or 10 cycles of "■" • e.'ichichtunr and removal of the Xtnp; ruiides, and they do not affect the electrical '.-' io only and the ^ iliciobjects. "The solutions are also virl-isar. lir'chen to Lntfernurr other Polyrerer and "of similar organic deposits of other inorganic ^ v: ie Zieselsäure _a RIAS, etc., and of organic FlS - Chen, ^r -NLE polyethylene, polytetrafluoroethylene, and ^{acrylonitrile.:.} -utadien-Styrolterpolyrj -eren. The Losunren according to the invention ur cups "ch ^T -? efelsc.ure, sufficient nitric acid (Q..5 " · to 80 5 '1 "TO-), and the solubility of chromium trioxide (CrO ^) significantly increases increase, and 0.3 "■ CrO ^ up to its .v": ttirun; ~ skonzentration in the Liösunr; at 3 ^ ° C. The ^T V- ^ ii ^and ^ - - ^ - ^ from poor! after at least 75 "'of the solution, and the amount of water present can be from et'-rc 2 '' to about 20 % _9, preferably from about 2 ^ to about, ^T a V '. vary, "./it borrowed ';;larger!' water proportions lead to a considerably lower stripping efficiency.

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^ The stripping capacity of the readings after the discovery increases as the OrO ^ -balt rises, and the preferred solutions are those which contain relatively high proportions of the CrO ₇ . contain. The solutions according to the invention: which contain more than 2 "'CrO ^, have in this respect a certain advantage in comparison with known stripping solutions of sulfuric acid and CrO ₇ .. Even with solutions according to the invention which are less than 2"' of the trioxide, one obtains an effective stripping of coatings at room temperature (10 to 40 ° C), while such 'iberzüge with known stripping agents could only be stripped or removed effectively at temperatures of 90 to 100 ° C or above.

CrO ₇ can be added to the present systems in any convenient form. Such a form is available from Fandel in the crystalline state as chromic anhydride. CrO ₇ can also be added to the systems in the form of salts. Examples are the chromate salts such as Ma ₂ CrO ^ .101 ^ 0, K ^ CrO _i} and (TIH ^) ₂ CrO ₁₁ and the dichromate salts such as MapCr-jO ,,. 2H ₂ O ₅ K ₂ Cr ₃ O ₇ and (WK ₁ J) ₂ Cr ₂ O ₇ .

The CrO, solubility peaks at equivalent sulfuric acid concentrations of about B5 "" ·, and the preferred high CrO ^ compositions of the invention have an equivalent sulfuric acid concentration of at least 75 1 or an F'TO-. Content of at least ^ 0 t and an equivalent sulfuric acid concentration of at least 67%. equivalent sulfuric acid concentration means:

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20A9945

Here "inarrsnendzatzung after dsr ^T rf irr ^ un"'cannii.c'i small "' another component ·.;: Unfold.;, So la; r; e this dio be.-i ^v · ■ · .. sichtifte use nods r ^ t-'ren ^r 'lnor, ^ hlor Alk li ^r:?.? - - tr] Io odo ~ ^ raalkplvnetalle, "crate, Pbbsohate or other materials that the Siliciuragerenstünde or niliciundio :: Iäfilri may not be available in active concentrations. Depending on the application and the size:; iellen ^ rO ₇ . -Concentration in the Ausstreiflj3unp; en after the '"' rfinclunr. /Ilkaliii'.otalle or other cations that are introduced in the Ι'Όη.ι of Calsen, tolerated, -; if they are not in an active concentration The r'estinmun ';: the concentration at which a starred cation or ba.:ti: rite cations are active can easily be carried out by routine experiments If the '..' economy and quality are desirable ₅ a '. ^T atriuF.rjal2 of chromic acid to the toe ■ ranzpunkt. The kest at HrO ₇ , which may be required, could then be in the Torr .: Eosi ^ cäureanhydrida or a p> Galzes be added in'de;. · the 'ation is not objectionable, such as an ammonium salt beis ^ iel'iv.'eirse hydrogen (V) is of course not objectionable ^p cation ÜR!.. some Z ^{T., r} blocks, it is preferred that solutions vresentlichen completely free of cations uie 'Ia ^+, K ⁺ and! .TIj, and in this,! '' All the CrO _{7 is provided} in a form other than an "alaform. By being essentially complete; is free of cations, it is intended to have only traces of ^y ation impurities that initiate the } '^ "Ί _} . and MHO-, can be introduced, for example on the order of 10 ppi ·; Or less.

BATH ORIGINAL

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i.e. the weight ^{- "GrC 1} - ,," as they are mentioned here, concern; len CrO -.-- remainder and not the compound which is the source of the dhromat-ions. Thus, a ^m eil Dichromatsälz r.it 2 Chror.iato ■ men have a higher CrO -, -. "Nuivalenz air, part of a OhroimtfjEilzes

'j

with only one .; Chromium atom.

In the manufacture of semiconductors from silicon dioxide-coated Siliciumgegünst "Persons' often ./erden metallic aluminum · - movies with the Siliciumdioxidf-Ilmen united, so daP in diener: must the harmless to f \ as used PiJ.Ilen stripper. 3 are aluminum, for example the Ιι, 3 ^Λ .- · Ρα-tentschrift 3 ^ 26 l \? 2 _f ev / iooen. Decü ^ lich the corrosive V. ^r ir!: Ung auf Aluminum ei ", ^r The strippers according to the invention can be found to be equivalent or better than those known stripping agents which have been used for these purposes , if they are used in the case of unwinding temperatures.

Γ3 no special procedure is required for setting the solutions according to the present invention ;. Fs can V'aser and then sulfuric acid to nitric acid under: in.hren and cool k zUf ^ efieb, and then OrO-, with further stirring and Cooling can be added. Part of the '.' 'Aster or the fesante V / ater could be present as a pesta.ndte.il one or both of the acids used, or it may be a nitric acid, which is more as the desired '! en ^ e to V'asser contains, used v / earth, and instead of all or part of the sulfuric acid, oleum can also be used.

The solutions can be used in the usual ',.' Iron to remove the coatings, Deposits, etc. are used. So the area to be cleaned can

1 0 9 8 1 7/1 A k 6 & ad original

20A9945

.-; on3t '\ γ.γ ^! by immersing in a flowing ctror: or under "your in the V" surr '"-evaschen - / earth, or c-.her inde ¹ " r.an one d ^ r "'b:> t3 ^o ahl au" den Ge.:en;"tand judges, the .V'sunken have the ".'ichti. ^ En advantage, since" they are not only at, ^ -. "" Harsh ^r> c - ur: .tenrr _: · - i'nturen "- ^T ir ''. na ^v: " ind. but da ° never also] r- er'öbten \ ' ^r -y ^ ': ■■ -. · - doors v.'ir ^ san r: ind and with such Cer.vor.?türen 'it increased viii "un o ~ e3chv ^r indi;':] ': cit einfeoetzt *. ^: e ^ den] '"ηηεη. ror ^ .t err'ibt i.hv ^ "'? r ^T - * ': ndun'- at ten ^ eraturon of 1 ^ 0 ^r od-l. an extremely fast Znt.fernunp from. '"- it2; -; round, -.'ie" orr. ¹ '- "" etpll -'- tz ^ around ₃ der; · or "hrilic'- ¹ referred to as """' v ^ ' ^T "ird and a" rodulrt the Eo.nt

Me fol ^; en ^ en ^ eisniele serve the ^ elucidation of the finding. Example 1 illustrates the preparation of the solutions.

^T c is "iel 1

In. a r; l "serne round-bottom flask advise a cooling bath. , Führer. Thermo ^v : eter and ^r -'rocl \ enrohr -mrden TO '" parts 7 ^η ₃ ί'ί. "' - i ^r ; er.? al ? eters "u · - re -ireben. Then 7 ° 2 parts of distilled water and ~ -'l ⁿ parts ? ^R ;, 5 ^r - "'-i ^ er" chv / efels ^ .ure one after the other and allr.i'.hlicb under Hübren and Cool to. ^ Eset ^ t. The temperature was kept at 20 ° C. Tachdera the Sclivrefelsfurezucabe under EiI-dun- ;. of the solvent ended v; ar, ^T .; the temperature was lowered to 0 to 5 ° 0 because at this temperature CrO ₇ is more soluble in it. "u 1,000 parts of Lösunpei-iittelr» ;; ere now Co, 5 parts CRO, (as crystals of Ghror; ^3:.: .ureanh / drid). sugereben parts are here "euichtsteile.

· ". '; ■ the ^",' vm ^ .en after the Lrfindunp "with regard to their Yerv; endun'_; at dr.r! Ierct ^ llun ¹ ; of semiconductors au bov'orten,% 'urde the fol-

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test carried out. Silicon wafers coated with silicon dioxide film (8,000 Angstroms thick, vapor-grown films) commercially by methods commonly used in the semiconductor industry were used as test samples. Its base solution, which is commercially available for this purpose, was applied evenly to the film using known centrifugal casting techniques. The composition used is a xylene solution of a polyisoprene type prepolymer and a sensitizer or developer for promoting hardening and insolubilization. The composition is available from the Eastman Kodak Company under the trade designation "KMER". The prepolymer is capable of penetrating light rays at or near the visible to ultraviolet limit, ie with wavelengths of about 315 to 430 microns and particularly near the. ^r! itte this range, cured to v, ground ^r. this is converted into a xylene insoluble protective coating. Oie üb exogeneη platelets were for about 30 minutes heated wefjzudampfen to a temperature of about 100 0 to the solvent. Fie then vrurden masked with an opaque stencil to cover parts of the coating, and then exposed to light rays from a 600 VJatt VJestinghouse lamp "Oxy" ovie Flood ^{: r} from a distance of about 22 cm for about 1/2 minute in order to clear the surface; to make hard and insoluble. The platelets were then immersed and washed in iriETi solvent (xylene) to remove the uncured portions of the coating. The flakes were then baked at 160 ° C (or 200 ° C where indicated) for 30 minutes to further cure the polymer. Every tile

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now had a silicon dioxide film on one surface which was partly exposed and partly from a hardened organic Polymer was protected.

To the stiffening effects dfer different stripping solutions test, a plate was immersed in the streak solution to be tested at 27 to 28 ° C, unless otherwise stated,

for

namely the time given in the following table. The platelet was then washed by immersion in water and then placed in a stream of distilled water. The washed Platelets were examined visually and microscopically (at 20X) to determine the extent of removal of the Polymers and the constitution of the silicon dioxide layer to be determined.

1098 17/1 US

Tabel

Equivalents
TT O f *% Of
n _o ÖUh, IO Concentration as ENT, % Solvent CrO Minutes for
the runaway
fencing (2) 1.0 at
game 85.5 H ₂ SO, j
5.0 H ₀ O j
6.85 0.5 to 1 94.1 81.2 38.7 13.8 3.1 1.5- 4.0 2 (1) 73.5 57.7 40.0 3.6 0.93 1.5 to 4.0 Previous year 73.5 44.1 40.0 15.9 0.5 1.5 to , 5- 4th 79.5 44.1 40.0 15.9 3.33 1.0+: 1 VJl 94.3 47.7 10.8 12.3 2.04 1.5- , 0- 6 (1) 85.5 84.0 1.0 5.2 6.42 1.5+; 4th (3) 7th 85.5 84.6 1.0 14.4 6.42 0.08 4.0 8th 85.5 84.6 1.0 14.4 0.5 1.5 to , Ο 9 94.5 84.6 1.0 14.4 2.22 1.5+; 4th 10 71.5 93.6 72.0 5.4 2.83 1.5- 11 97.5 20.0 10.0 8.0 4.32 0.5 12th 97.5 87.75 1.0 2.25 0.46 1.5- 13th 85.5 96.5 0.5 2.5 5.61 1.5- 14th 94.5 85.1 4o, o 14.4 9.25 1.5- ΙΟ 15th 79.5 56.7 10.0 3.3 1.86 4.0 to 16 71.5 18.5

(1) The coating was then baked at 200 ° C. for 30 minutes .

(2) The minus sign in this column indicates a complete removal in less than the specified time. The plus sign means that in the specified time everything was removed except for a trace.

(3) Test at the ordinary stripping temperature of 90 to 100 ° C.

No etching, peeling, or other visible degradation of the silicon flakes was observed. Besides, the electric one stayed Resistance of the platelets unchanged.

10981 7 / 1U6

Compositions in the numbers 1, 6, 7, 10, 12 and 1 ^L \ , which are at least ΠΟ? H ₂ SO ₁ J, at least 2 3 CrO ,, at least 2 £ water and at least 0.5% but not more than 14 % 11110-, have a valuable combination of properties that they can be used as a stripping agent in the fcesonde.rs Making semiconductors makes. They have a quick wiping effect, a high wiping capacity, do not smoke at all and are particularly less corrosive than aluminum reed,

Prior to the present invention, compositions containing nitric acid, chromic acid and sulfuric acid were described for other purposes, such as metalworking, but these compositions differ fundamentally from those of the present invention in that they have much higher water contents and are generally an essential ingredient, which increases the activity of the composition. Such compositions are disclosed in US Patents 2,172,171, 2 ^ ° 7905, 2 QoI: - l \ k and 3,050,071, which show Chrowasserstoffsäure, phosphoric acid, boric acid and hydrofluoric acid as essential components. The compositions of these patents are completely unsuitable for the purpose of the present invention.

All proportions and proportions expressed in numbers are here in the description on the basis of weight, based on the entire solution, unless otherwise stated.

Of course, modifications can be made within the scope of the invention. For example, it is for the It is clear to those skilled in the art that various additives are added to the stripping solutions can be added according to the invention ^ without the

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basic properties of the stripping solutions are changed. Examples are thickeners such as colloidal silica.

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Claims (10)

Claims 1.j stripping solution, characterized in that it comprises sulfuric acid, at least 0.3 5S chromium trioxide, 0.5 to 80 % HNO, and 2 to 20 % water, the sulfuric acid and nitric acid together making up at least 75 % of the solution and the Solution is free of active amounts of fluorine, chlorine, alkali and alkaline earth metals. 2. stripping solution according to claim 1, characterized in that it is essentially completely free of cations other than hydrogen ions. 3. stripping solution according to claim 2, characterized by a chromium trioxide content of at least 2% and a sulfuric acid equivalent concentration of at least 75% or a chromium trioxide content of at least 2% and a ΗΝΟ concentration of at least HO% and a sulfuric acid equivalent concentration of at least 67 2. 4. Stripping solution according to claim 1, characterized in that it contains sulfuric acid, at least 2 % chromium trioxide, 0.5 to 80 % HNO, and 2 to 16 % water, the sulfuric acid and nitric acid making up at least 75% of the solution, the sulfuric acid equivalent concentration at least 67 % of the solutions with a content of at least 40 % HNO and at least 75 % of the solutions with a content of less than 40 % HNO. 5. stripping solution according to claim 1, characterized in that it contains sulfuric acid, 0.3 to ¹ I% chromium trioxide, 0.5 to 80 % HNO, and 109817 / U46 20A9945 Contains 12 to 20 % water, with sulfuric acid and nitric acid together making up at least 75 t of the solution and the sulfuric acid equivalent concentration in at least 67 % of the solutions with a content of at least 40 % HMO, and at least 75 % in solutions with a content of less than ¹ JO % ENT ₃ lies. 6. stripping solution according to claim 1 for removing organic deposits from silicon or silicon dioxide surfaces, characterized in that it has a chromium trioxide content of at least 2%> a water content of at least 2 %, an ILjSOjj content of at least 80 % and an HMO content of has at least 0.5 % and not more than Ik% . 7. stripping solution according to claim 4 to 6, characterized in that that they are essentially free of cations other than hydrogen ions is. 8. Use of a stripping solution according to claim 1 to 7 for removal organic deposits from inorganic surfaces F by washing these surfaces with the streak solution. Use according to claim 8 for removing etch base polymer from a silicon dioxide film or a silicon article for the manufacture of a semiconductor. 10. Use according to claim 9 by washing with the stripping solution at a temperature of 10 to HO ⁰ C. 109817 / 1U6