CA2017338A1

CA2017338A1 - Method of using selected photoactive compounds in high resolution acid hardening photoresists with near ultraviolet radiation

Info

Publication number: CA2017338A1
Application number: CA002017338A
Authority: CA
Inventors: Wayne Edmund Feely
Original assignee: Rohm and Haas Co
Current assignee: Rohm and Haas Co
Priority date: 1989-06-20
Filing date: 1990-05-23
Publication date: 1990-12-20
Also published as: BR9002906A; AU5764390A; JPH0387748A; ZA904704B; IL94799A; NO902666D0; CN1048931A; IL94799A0; IE902217L; KR910001455A; EP0404499A2; EP0404499A3; KR0155990B1; IE902217A1; JP3026503B2; FI903096A0; NO902666L; US5391465A

Abstract

-i-PATENT APPLICATION OF
Wayne Edmund Feely for METHOD OF USING SELECTED PHOTOACTIVE
COMPOUNDS IN HIGH RESOLUTION, ACID HARDENING
PHOTORESISTS WITH NEAR ULTRAVIOLET RADIATION
DN87-07 BWS/skm ABSTRACT OF DISCLOSURE
A method is provided for using selected photoactive compounds in acid hardening photoresists to produce thermally stable, high resolution images with near ultraviolet exposing radiation. These photoactive compounds can be used as photosensitizers for halogen-containing photoacid generators which by themselves do not otherwisegenerate sufficient acid upon exposure to near ultraviolet radiation to catalyze the crosslinking of acid hardening resins. The photoactive compounds are selected from the group consisting of phenothiazine, derivatives of phenothiazine, and phenoxazine.
EXPRESS MAIL LABEL NO. B13944782

Description

2 ~ ~1 l 3 ~ ~

BA~KGROWND OF THE II~VE~TIQ~
This invention relates to a method of using selected photoactive compounds with acid hardening resins to pro~uce thermally stable, submicron images using near ultraviolet radiation.

Workers in the field of photolithography desire photoresists capable of producing images with submicron resolution. My prior application SN 616,518 is dir~cted to a dual acting aqueous developable polymer coating composition containing an acid hardening resin system and a photoacid ~enerator which produces carboxylic acid upon exposure to actinic radiation s~ch as, for example near ultraviolet radiation, leading to images having a resolution as low as about 0.7 microns. My prior application SN 818,430 disclosad an acid hardening negative acting photoresist composition capable of producing even higher resolution, down to about 100 nanometers, utilizing short wavelength actinic radiation such as, for example; deep uitraviolet, x-ray and electron beam radiation. The halogen-containing photoacid generators used in that invention are useful with short wavelength radiations but do not produce sufficient acid upon ~xposure to near ultraviolet radiation to catalyze the crosslinking ot the acid hardening photoresist. Accordingly, the photoresists containin~ thcse photoacid ~enerators can not be employed for use with near ultraviolet radiation to produce submicron images.

Recently a nurnb0r of photolithographic imaging equipment manufacturers have ~ ~ ~ y~
announced advances in lenses and imaging systems capable of focusin~ near ultraviolet radiation to submicron dimensions.

Since conventional near ultraviolet photoresists are not capable of providing thermally stable high resolution submicron imag6s (U.S. 3,692,560; 3,697,274;

3,890,152; and 4,404,~72), these photoresists cannot be utilized with such advanced lens0s and imaging systems to produce thermally stable, submicron images.

U.S. Patent 3,042,515 discloses printout compositions which produce a color change upon sxposure to ultraviolet light. The composition contains one or more aryl amines and on~ or mor~ halogenated compounds. The use of diphanylamine, triphenylamine and N-phenyl-1-naphthyl-amine along with iodoform, carbon tetrachloride and carbon tetrabromide is disclosed.

U.S. Patent 4,634,657 discloses photoimaging compositions which produce improved color comprising substituted 1,2-dibromoethane compounds, a leuco dye, optional monomeric csmpound and a photoinitiator. Among extensive lists of useful leuco dyes, aminopheno~hiazine and aminophenoxazine are included. There is no teachin~ or suggestion in ~his disclosure of the production of photoresists.

Oblec~s of th~ Invention It is therefore an object of the present invention to provide photoactive compounds which can be smployed with acid hardening resin systems to produce negative thermally stable, highly resolved submicron images utilizing near ultraviolet radiation.

Another object of the invention is to provide a resist that is stable upon axposure to radiation in the visible range. Another object of the invention is the production of a thick resist, on tha order of 2~0 microns having straight wall profiles.

Still another object of ths invention is a method of producing images tha~
become detached from the substrate on which they are produced during the development stap.

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SUMMARY OF THE INVENTION

A method is provided for using selected photoactive compounds and acid hardening resin syst~ms to produce photoresist compositions which preduce thermally stable, high resolution submicron images when exposed to near ultraviolet radiation.

In one embodiment, the presan~ invention relates to negative resists ~ha~ contain an acid hardening resin system, a photoacid gener~tor that does not otherwise ~enerate acid upon exposure ta near ultraviolet radiation at wavelengths of ~rom about 365 nm to about 406nm and a sensitizer which promotas the production of acid by the photoacid generator whon exposed to radiation at these wavelengths and its use in preparing both ~hin and thick images.

The sensitizers of the presen~ invention ar~ selected frnm phenothiazine and derivatives thereof, and phenoxazine. Preferred phenothiæine derivatives are 10-methylphenothiazine, 2-trifluoromethylphenothiazirle and 2-chlorophenothiæine.

In another embodimen~ the invention relates to the use of 2-~hlorophenothiazine as a photoacid generator in an acid hardaning resist.

!n another embodiment the invention relates to the application of a thin coatingof ~water soluble polymer to the surface of the substrate on which the acid hardenin~
photoresist is to be subssquently applied and imaged. By first producing a crosslinked ~ ~ ~L ~
image ~he image will be freed from ~he substrate upon aqueaous development from which the images can be recovered by filtration or centrifuging or similar means.

Detailed Description of the Invelltion N~ar ultraviolet or near UV radiation as used her~in is defined to mean radiatlon having a wavelength in tha range of from greater than about 350 nanom~ters to about 450 nanometers. Mercury vapor lamps are a common source of ultraviolet radiationand produce near UV radiation having three peak wavelengths at about 365 nanometers, 406 nanometers and 436 nanomaters. These peak wavelengths are refcrred to by the industry as 1, H and G lines respectively. The photosensitizers of the present invention respond to near ultraviolet light from 365 nanometers to about 406 nanometers (I and H lines).

Before describing th~ selected photoactive compounds used in the proc~ss of the invention it is necessary to describe what is meant by acid hardening resin systems.

Asid Hardlening ~esins System~

Acid hardening resin systems are mixtures of polymers which cure, crosslink or harden by the catalytic action of acids upon heating. In order for an acid hardening rasin system to be useful in this invention, it must, in the uncured state, be soluble in a non-reacting solvent or solvant mixture and must bs capable of forming a S~ 3 !~ $

homogeneous, uniform, non-tacky, adherent film, fr~e of cracks, crazing and other defects, on the substrate surface onto which it is applied. Acid hardening resinsystems are well known and can be prepared from a wide variety of aminoplast or phenoplast polymers alone or in combination with compounds or low mol~cular weight polymers containing a plurality of hydroxyl, carboxyl, amide or imide groups. The acid hard0ning resin system comprises either a mix$ure of aminoplas~ resin and a reactive hydrogen containin~ compound or a phenoplas~ resin. The phe~oplast resin can be either a resol resin or a mixture of novolac and a latent formaldehyde generating compound. The selection of the acid hardening resin system suitable for use in the photoresist of the invention may be made by ona of ordinary skill in the ar~ depending on the choice of solvent amployed and is not asserted to be eritical to the present invention .
Aminoplast r0sins suitable for use in the acid hardening system include urea-formaldehyde, melamine-formaldehyds, benzoguanamine-formaldehyde, glycoluril-formaldehyde resins and cornbinations thereof. Polymeric aminoplasts may be prepared by the reaction of acrylamide or methacrylamide copolymers with formaldehyde in an alcohol-containing solution, or alternatively by the copolymerization of N-alkoxymethyl acrylamide or methacrylamide with other suitable monomers. Examples of some suitable aminoplasts include the melamine resins manufactured by American Cyanarnid Company such as Cymel~ 300, 301, 303, 350, 370, 380, 1116 and 1130; benzoglJanamine resins such as Cymel@) 1123 and 1125;
glyooluril rasin Cyrnel@~ 11701171, 1172; and urea-based resins Bee~le~ 60, 65 and c~ :~ J
80. A large number of similar aminoplasts ara presently commercially available from various suppliers.

As indicated above the aminoplasts are used in combination wi~h reacRve hydrogen-containing compounds in th~ acid hardening r~sin system. These reactive hydrogen-containing compounds includs: novolac r0sins; poiyvinylphenols; and copolymers of these with styrene, a-methylstyrene, acrylic resins, etc. polyglutarimides; polyacrylic acid or polymethacrylic acid copolymers; alkali-soluble polyacrylamides and polymethacrylamide copolymers; copolymers containing 2-hydroxyethyl(meth)acrylate and 2-hydroxypropyl(meth)acrylate; and polyvinyl alcohols such as those preparedfrom partially hydrolyzed polyvinyl acetates; alkali-soluble styrene-allyl alcohol copolymsrs; and mix~ures thereof. Novolac resins containing hydroxyl groups and sites for the electrophilic substitution of aromatic rings at positions ortho or para relative to the hydroxyl group are preferred. Novolac resins that are useful in conjunction with aminoplasts in the acid hardening resin system are alkali-soluble film forming phenolic resins having a molecular weight (weight average) ranging from about 300 to about 100,000 and preferably from about 1000 to 20,000. Th~se novolac resins may be prQpared by the condensation reaction of a phenol, a naphthol or a substituted phenol, such as; cresol, xylenol, ethylphenol, butylphenol, isopropyl methoxyphenol, chloroph0nol, bromophenol, r~sorcinol, naphthol, chloronaph~hol, bromonaphthol or hydroquinone with formaldehyde, acataldehyde, benzaldehyde, furfural acrolein or the like. Blends of suitable novolac resins may also be used in order to adjus~ the dissolution rate of ~h~ exposed coatin~ in aqueous base solutions as well as for adjusting the viscosity, hardness and other physical properties of the eoating. Suitable novolac resins are disclosed in numerous patsnts including U.S.
3,148,983; 4,404,3~7; 4,1 15,128; 4,377,~31; 4,423,138; and 4,424,315, the disclosure of which are incorporated by ref0r~nce herein.

Aminoplasts may also b~ us0d in conjunction with polyglutarimides, prepared according to lJ.S. 4,246,374, having a wei~ht avarage molecular weight ranging from about 1000 to about 100,0û0, which arc solubl~ in aqueous base and contain at least 40 weight percsnt of the nitrogen atoms in the NH or animonia form. When polyglutarimides are used in conjunction with aminoplast resins, the aminoplast is present at a concentration of from about 20 to about 80 percent by weigh~ based on the weight of the polyglutarimide.
Alkali soluble polyvinylphenols having a weigh~ average molecular weight rangingfrorn about 2000 to about 100,000 can also be employed with aminoplasts to form useful acid hardening resin systsms. These coatings yield thermally stable images capable of withstanding hea~ing for about 30 minutes at ternperatures ranging from about 400 to about ~;00C.

An alkali-soluble (meth)acrylic acid-styrene copoiym~r containing at least 15 weight percent, and pr~f~rably 30 wei~ht perccnt, (meth)acrylic acid and havin~ a weight average moleeular weight of about 12,000 can also be used in combination wi~h aminoplasts to form an acid hardening resin system useful in ~he practice of theinvention.

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Acid har~ening rasin systems useful in the photosensitive coatings of the invsntion can also be prepared from phenoplasts by combining a compound that is a latent source of formaldehyds in an acidic media with a novolac resin.

The acid hardening phenoplast-containing resin system can also be formulated with alkali-soluble poiyvinylph~nols, havin~ weight average molecular wei~ht ranging from about 2000 to about 50,000 and preferable about 2000 to about 20,00û, in place of the novolac resins. The useful concen~ration of the latent formaldehyde generator or phenoplast in the acid hardening resin system has been found to be from about 3 to about 30 percsnt by weight based on the weight of the novolac or polyvinylphenol r0sin.

eb~ll~

The photosensitizers and photoacid generators selected are compatible with the acid hardening resin systems and solvent systems such that uniform, adherent fiims of high quality can ba formed therefrom on substrate surfaces. The photosensitizers are also preferably selected such that they do not produce a sufficient amount of acid to cause the acid-hardening r~sin to reac~ in respons~ to li~ht at wavelengths longer than the near UV and do not sensitize the other photoacid generator compounds presen~ in the photoresis~ to the effects of such li~ht. The pho~osensitizers are also selected such that they are stable in photor~sist mixtures for up to one year at ambient temperature ~ ~ L . ~ 3 ~
st, Is not to change in lithographically impor~ant parameters such as viscosity, photospeed, devslopment charactenstics and the like.

The selected photoactive compounds cmployed in the present invention are not novel compounds and are known to possass photoactivity. Thay are not known, however, to be useful as photosensitizers in photoresists containing acid hardening resin systems.

"Photosensi~izers'' as used har~in rafers to the ability of the photoactive compound to ac~ivate, or sensitize, a photoacid generator, such as for exampla, those disclosed in my copending application S.h~. 818,430, which are h~reby incorporated by reference herein, to produce acid for the catalysis of the acid hardening resin. "Photoacid generator" as used herein refers to a compound or polymer which generates an acid for the catalysis of the acid hardening resin system upon expo~ure to actinic radiation.

These photoactive compounds have the common ability, however, to sensitize or activate photoacid generators which by themselves do not ~enerate acid upon axposure to near UV radia~ion having wavelengths of from about 365 to about 406nm.
Although tho exact mechanism of the sensitizing reaction is unknown in the present case, it is believed that the photoactive compound acts as a photosensitizer when i~
absorbs the exposing n0ar UV radiation. This causes the compound to go to an excited electronic state from which it may then participate in one of sevaral different kinds of processes to transfer ~ha absorbed energy to the photoacid generator and ~ ~' !! '3 J ~ ~ ~
cause it to produce acid, such as for exarnple, such as for example by: transfer of a photoelectron; disscciation into one or more free radicals which can enter into reactions; dissociation into one or more ions which can enter into reactions; or through excitation transfer involving the forrnation of an exiplex complex between the halogen compound and the sensitizer.
The phenoxazine and phenothiazine derivativè sensitizers can be represented by the formula:

~ N ~R ~

where X is suHur, or oxygen, R can be hydro~en or C~-C6 alkyl, and R1 can be hydrogen, halogen, C~-C~ alkyl, substituted or unsubstituted. Examples include phenoxazine, phenothiazine, and halo, alkyl or haloalkyl substituted phenothiazines such as 2-chlorophenothiazine and 10-methylphenothiazine. Amino-substituted alkyl substituents, such as in chlorpromazine ara to be avoided; a test resist containing chlorpromæine could not bei developed after exposure.
These photosensitizers can be used in combination with one or more of the halogenated photoacid generators disclosed in my copending application S.N.
818,430 for use with short wavelength actinic radiation. These photoacid generators include~ bis [p-chlorophenyl]-2,2,2-trichloroethane (DDT); 1,1-bis [p-methoxyphenyl]-2,2,2-trichloroethane(Methoxychlor ~); 1,2,5i6,9,10-!L i t~
hexabromocyclododecane; 1,1 0-dibromodecane; 1,1 -bis[p-chlorophenyl]-2,2-dichloroethane; 414'-dichloro-2-(trichloromethyl)benzhydrol or 1,1-bis(chlorophenyl)2-2,2-trichloroethanol (Kelthane~); hexachlorodimethylsul~one; 2-chloro-6-(trichloromethyl)pyridine; O,O-diethyl-C)-(3,5,6-triohloro-2-pyridyl)phosphorothioate (I:)ursban~); 1 ,2,3,4,5,6-hexachlorocyclohexan~; N(1 ,1-bis [p-chlorophenyi]-2,2,2-trichoroethylacetamide, tris~2,3-dibromopropyl]isocyanurate; 2,2-bis [p~chlorophenyl]-1,1-dichloroethylene; and their isomers, analogs, homologs and residual compounds.

"Residual"eompounds are intended to include closely related impurities or-other modifications of the above halo~enated organic cornpounds which result during their synthesis and which may b~ present in minor amounts in commercial products containing a major amount of the above compounds. Residual compounds include those known in the art such as for example those described in U.S. 2,812,280.

Ths preferred deep UV photoacid generators are: DDT, Methoxychlor, Kelthane, tris(2,3-dibromopropyl)-isocyanurate, and 2,2,2-tribromoethansl.

I have found ~hat certain of tha selected photoactive compounds are preferred. For example, 2-chlorophenothiazine is a preferred photoacid generator at 406 and 36~
nanometers. In addition, the combination of phenothiazine as a photosensitizer with 2 chlorophenothiazine as photoacid generator is a preferred combination at 406 and 365 nanometers.

r~

(:)ther photoacid generators that are us0ful in the near UV can be used with acid hardening rasins including dichloroac~tophenorle derivatives, substituted and unsubsti~uted N-me~hylquinolinium salts, such as for exampls para-toluene sulfonate, and N-alkoxypyridinium salts such as are described in U.S. Patent 2,971,002.

The concentration of the photoactivc compound required to be used with an acid hardening resin system depends on whether ~he photoactive compound is baing ~mploy~d as a photosensitizer or photoacid genarator. In the case wh~re tha photoactive compound is employed as a pho~osensitizer it can be used at a concentration of ~rom about 0.5 to about 25 percent by weight on total solids (including acid hardening resin and photoacid gen0rator). In the case whsre the photoactivecompound is being used as a photsacid generator its concentration ran~es from about 0.5 to about 25 percent by weight on total solids.

Accordingly, the overall composition of a near UV photoresist employing the photoactive compounds of the present invention is from about 99 to about 75 wt% acid hardening resin, 1 to about 25 wt% photoactive photosansitizer or photoacid gencrator.

The near UV pho~or~sist may be formulated by admixing tha photoactiva compound and other photoacid generator with the acid hardening resin in solvent. Tha mixture is stirred untii a homogeneous solution is obtained.

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The solvcnt systems used to formulat0 the photoactive compound or rnixture thereof with photoacid generator and acid hardening resin includes typically non-reacting solvents which have been found to be useful with the acid hardening resins and photoacid generators of the photosensitive coating composition of the invantion includes: glycol ethers, such as ethylene glycol monomethyl ether, ethylene glycol monoethyi ~ther, ethylens glycol dimethyl ether, Proposol@~ B and P and the like;
Cellosolve~ estars, such as methyJ Cellosolve acetate, athyl C~llosolve acetate and the acetates of Proposol~ 8 and P, and the like; aromatic hydrooarbons; such as toulene, xylene and the lika; k0tones, such as acetone, methylethylketone, cyclopentanone, cyclohexanone and the like; esters, such as 0thylacetate, butyl acetate, isobutyl isobu~yrate, butyrolac~one and the like; amides, such as a dimethyl acetamide (DMAC), N-rnethyl pyrrolidone (NMP), dimethyl forrnamide (DMF) and the like; chlorinated hydrocarbons, such as methylene chloride, ethy.lane dichloride, 1,1,1-trichloroethane, chlorobenzene, ortho-dichlorobenzene and the liks; nitrobenzene;
dimethylsulfoxide; and mixtur~s of ths above. Mixtures of these compounds, optionally containing minor amounts of other suitable compounds, are also useful as solvents. The photosensitive coating soiution contains at least ~0 percen~ by weight solvent and preferably from about 65 to 95 percent by weight solvent. The solvent system used must not react adversely with the other components in the coating solution and the coating formad ~herefrorn must b~ of a homogeneous nature free from sediment, crystallized components, particulates and dirt.

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The photoresist may then be applied to a substrate surface as by spinning, dipping or other conv0ntional coating t~chniques.

Fot exampls, when spin coating is utilized, the solids content of the coating solution can be adjustad to provide the filrn with tha thicknass desirsd based on tha ~ype of spinning eqLJipment utilized, the viscosity of the solution, the RPM of the spinner and the amount of time allowed for the spinning process.

When the photosensitive coating composition of the invention are used as photoresists, spin coating of the solution coating is particularly suitable for depositing an adherent, uni~orm film on the surface of a substrate, such as, for example, the surfacc of silicon or silicon dixoide coated wafers used in the production of microprocessors and other miniaturized integrated circuit components. Aluminum-aluminum oxide and silicon nitride coated wafers can also be coated with the photcsensitive coatings of the invention and the resulting films show excellent adhesion tc the substrates.

Electroetic d~vices, such as silicon wafers containing complete electronic circuits, can be coated with the photosensitive coating composition of the invention using the above techniques to provide protection and insulation for the electronic components.
These protectiva coatings reducs the sffects of dirt, electrical con~aminan~s, moisture, alpha particles and handling dama~e, whil~ at the time time permitting certain areas of ~ v ~ 7 ~J~ 3 ~3 the coating to be removed for the purpose of attaching alectrical con~acts. Areas of the surface that arc d~sired to be cleared of the coating in order to subsequently make electrical connections can be accomplished by ~xposing these areas using a photomask and proceedin~ by the other steps of the process of the invention while leaving a ~hsrmally stable protective coating. In addition, thsse coatings may serve as useful dielec~ric and insulating layers for electronic devices.

Planarizing films or layers up to about 10 micrometers in thickness can also be deposited using the above-techniques on surFaces, so as to planarize microelectronic devices and aluminum relief structures present on the wafer surface.
The r0sist sxhibits low absorbance at th~ exposing wavelength of 365 nanometers. Unlike high absorbing resists, a low absorbance resist allows the exposin~ radiation to pass through the resist to the substrata even at low exposure doses. When a low absorbance resist is fully sxposed and heated the walls of theresist have a straight veretical profile. High absorbanca resists typically have undercut sides, which are undesired.

It has been found ~hat because the photos~nsitive coating composition can be applied as an adherent, uniform film of desired thickness on a surface, the coating is particularly useful in forming thermally stable planarizing layers on surfaces.
Accordingly, the coating can be appliad to surfaces of non-uniform topography as a protective coating or photoresist of ~hickness sufficient to uniformly protect all the surface irregularities.

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In addition, since the imaged photoresist is crosslinked and insoluble in spinning solvent and capable of submicron imag~ resolution, multiple thermally stable ima~es can be built, one on top of the other, so as to form a three dimensional grid matrix. A
matrix of sets of parallel lines may thus be formad, ~ach set intersecting the previous set of lines at an~les relative to the previous set varying from a right angle to nearly parallel, with subsequsnt sets optionally being parallel to other sets so long as they intersect at least one previous set. in this manner, a thermally stable screen or filter can be formed on the surface. In addition, as a result of the thermal stability and high image resolution achievable with the photosansitive coating composition of the invention, two dimensional fiiters can also bc prepared according to the process of the invention. After the solution coating has been applied to the substrate surface, the substrate is baked to remove residual solvent, forming a film or coating. It is important for achieving reproducible results durin~ the subsequent exposure and development steps that the residual solvent level be accurately controlled. Baking the substrate containin~ the solution coating at about 90C to about 1 00C for about 30 minutes has been found to satisfactorily dry ~he film. Alternative methods such as hot-plate heating with controlled times and temperatures can also give suitable results.

The dri~d fllm, which is substantially free of solvent, should be touch-tack free (TTF) so that dust and dirt will not accurnulate by adhesion to tho film. TTF formation is also important to prevent adhesion of the coated substrate to a photomask during conlact 5. ~

expssure. To deterrnine it a l~F fim has besn formed, after drying, conon tibers of a small cotton ball must not cling to the film when touchad thereto.

When ths photosensitive coating composition is used as a photoresist to form thermally stable ima~es on silicon wafers, it is preferred to pretreat the wafers with a silylamina derivative, such as hexamethyldisilazane or chloromethylsilane or the like.

After the photosensitive film is deposit0d on a surface and exposed by conventional techniques to actinic radiation as through a photomask, and then baked the film can be deveioped to form a ne~ative image.

To prepar0 a ~hermally stable negative image, the latent image in the exposed photosensitive film areas, which contains acid released by the photosensitive compounds is heated to from 70C to about 120C to form a thermoset or hardened image and tha unexposed portions of the fllm are dissolved away using ~he aqueous base developer solution. The remaining thermoset image can be heated (hard baked) to temperatures from about 100 to about 125C to form a hi~h quality thermally stable negative image.

In the practice of the process o~ the invention the developer can b~ an aqueous solution of inorganio alkali suoh as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium silicate, sodium metasilicate, aqueous ammonia or th~ like or aquaous solutions of an organio alkali such as choline base iL ~ ~ f ~1 ~`3 and tetra-methyl, -ethyl. -hydroxyethyl, -propyl, -butyl, ammonium hydroxid~ solutions in water, primary amines; for example ~thylamine, n-propylamine and tha lik~;
secondary amines, ~or example disthylamine, di-n-propyl amine and the like, ~ertia~
amines, for exarnple triethylamine, methyldiethylamine and the like; alcohol amines, fQr exampl~ dimethylethanolamine, triethanol-ammonium hydroxide and the like; cyclic amines for sxample pyrrole, piperidine, 1-alpha-diæabicyclo (5,4,0)-7-undecane (DBU), 1,5-diazabicyclo (4,3,0)-5-nonan0 (DBN) and the like can be utilized. In addition, minor amounts of from about 0.1 to about 20 weight per~ent of th~ developer solution of water soluble organic solvents, such as for example, methanol, ethanol, isopropanol, n-propanol, Cellosolve~ or the like, or a surfactant such as Triton@~ X-100, may be added to the aqueous base developer. Other developers suitable for use in the practice of the proc~ss of the invention are disclosed in US patents 3,110,596;
3,173,788; 3,586,504 and 4,423,138.

Af~er a thermally stable crosslinked image has been formed on the substrat~
surface, a second photosensitive film may be applied directly over the first image and onto the remaining portions of the substrats and processed again for example to form a planarizing layers or a second layer of new images on top of the first set.

If the crosslinked image is desired to be remov~d from the substrate surface, the image may be stripped using oxygen plasma treatment or by the us~ of a strippingsolution at ~levated temperatures on the order of 75C to about 1 80C. Suitablestripping solutions include N-methylpyrolidone (NMP), dimethy! sulfoxide, dimethyl formamida or NMP and thc monom~thyl ether of ~thylene glycol and the lik~ as disclosed in U.S. 4,428,871. It may also be flood exposed with 1-5 j/cm2 of 254 nanometer light to photodegrade it so that it becomes soluble in organic solvants such as acetone, MEK, MDC, etc.
Resists according to the invention exhibit low absorbance to the exposing wavelengths. When a low absorbanco r~sist is under0xpssed, a low concentration of acid is produced through th~ depth of the resis~. When an underexposcd low absorbance r~sist is heated it produces a matrix of lightly crosslinked resin. The uncrosslinked resin fraction is extracted during development and the image shrinks in height, producing an image that is less than the full thickness of the resist. If images of this type are observed using low absorbance r~sist either the exposure dose or the concentration of photos~nsitve ~ompound may need to be increased.
It is envisioned that a mask could be prepared to produce multiple images of an enantiomorphic structure that is nst superimposable with its mirror image using resist according to the invention. If these images were prepared near the dimensions of a wavelength of light and metal plated to make them conductive, it is believed that a beam of plane polarized light would be rotated by the structures. Multiple copies of the structure could be arrayed on a surface and used to polarize ordinary li~ht by reflection or transmission, or a suspension of free-floating enantiomorphic struc~ures could be used.

The following examples are presented to further illustrate tha invention and are not intended to limi~ the br~adth of the invention.

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The followin~ abbreviations appear in the data rsported and have the indicated meanin~:

CPTZ = 2-chlorophenothiazin~
Cl~CCI 3 DDT = (Cl~CH CCl 3 ER-8 = (Cl~c~ Cl3 DC:PP = Tris (2,3-dichloropropyl) phospha~e ~ OH
Kelth = Kelthane = (Cl~C--CCl 3 T = tris (2,3-dibromopropyl) isocyanurate TBE = 2,2,2-tribromoethanol o~ X ~7 -2TCMQ = 2-trichloromethyl-4-(3H)-quinazolinone AHR - Acid hardening resin AR - Amino resin PAG = Photoacid ~enerator SEN = Photosensitiz0r C303 = Gymel~ 303, similarly a "C" preceeding other numbers in the data tables indicate different Cymel resins.
DOSE = Unl0ss other wise st~ted the dose set ~orth in ~he examples and tables is expressed as mJ/cm2 E~mQ~

Resist solutions were prepared by mixing the following ingredients:

~olution Solids a) Novolac resin 30% solids 10.00g (3.û0g) + } = (AHR) 3.60 b) Cymel303 (Methylolated melamine resin) 0.60g (0.609) ]

c) PhotoacidGenerator-tris(2,3 û.36g (0-369) = (PAG) dibromopropyl)isocyanurate d) Photosensitizer Candidate (1 %) 0.036y (0.0369) = (SEN) 's~

Acid Hardening Resin (AHR) was prspared by mixing novolac and arninoplast r~sin (Cymel 303) in proportions such that the amount of aminoplast was 20% of the novolac resin solids by weight. In the followin~ tables the amount of photoacid generator (PAG) and photosensitizer (SEN) are reported as percentages by weight based on tho acid hardening resin. The amount of acid hardaning resin is the which is the sum of novolac and amino rasin solids. For axampl0, in the formulation described above the amount of PAG is 10 % by weight calculated on AHR and th~ amount of Photosensitizer (SEN) is 1% by weight calculated on AHR.

The photoresists were prepared under yellow safe lights. They were spin coated at 3-4000 RP Vl on silicon wafers with a thin silicon dioxide surface layer (70um), which were first primed wi~h hexamethyldisilazane (HMDS).

The coated wafers were prebaked at 90C for 30 min. to remove solvent and ~hen cooled to ambient temperature. The coating thickness was then measured with a Dektak Mod~l 30-30 profilometer. Wafers were then imaged by-contact printing using an Optilina s~ep wedge mask in a Hybrid Technology Group Model L84-5X contact printer. An exposure of 150 mj/cm2 at 365 nm was used in the initial screening. In early experiments, exposures were to broad band radiation using only the dichroic mirrors of the printer for wavel~ngth dofinition. In experim~nts where the exposure ~ ~L 7 ~ ~ 3 ~3 dose is identitied with an asterisk, a narrow + 1 Onm bandpass filter was used for a more precise measure of sensiti\lity.

After axposure, the wafers were postbaked at 90C for 30 minutes to crosslink via reaction between the amino resln and novolac. Aft~r cooling, the wafers were doveloped using Shipley Microposd 351 developor generally diluted 1 part developcr to 2-3 parts water. At times, the dilution was changed with other resin forrnulations so that an unexposed composition would ba rernoved from the wafer in 1-2 minutes.
The exposed wafers were developed until unexposed areas were clear of photoresist, and then washed wlth cold water ~ollowed by air drying ~or about 30minutes at room temperature. The thickness of the photoresist in an area that received 100% exposure was then measured and the percentage rasist retained was calculated based upon the initial thickness.

Table I below illustrates the surprising effectiveness of phenothiazine as a sensiti~er for tris-(2,3-dibromopropyl)isocyanurate photoacid generator in an acid hardenin~ resin systam. The effectiveness of the resist is measured as percantage o~
the thichness of resist that is rl~tained as a nogabve imago a~er development.

~L~
~,~
L~nlh~a Example 1 Phenothiazine 1 10 92%
Diphenylamine 1 10 9%
Triphsnylamins 1 10 44%
N-phenyl-1-naphthyl-amine 1 10 67%
Malachite Gr~en Base 1 10 0%
Acridine 1 10 0%
No sensitizer 0 10 0%

The tabl~ demonstrates that phenothiæine is surprisingly ~ffective as a sensitizer for tris-(2,3-dibromopropyl) isooyanurata, a photoacid generator that otherwise does not respond to near ultraviobt radiation at 365 nm.

..,, r 3 ~.3 ~L~

Resist solutions were prepare~ and processed as described in Exampla 1 using phenothiazine as the sansitizar in each case and varying the photoacid ~enerator as shown.

~ ~ ~1~ ~ ~ .~eD PAG
A 92/100 Phanothiazine T C303 1 10 B 95/150 Phsnothiazine DDT C303 1 10 41 /20~
C 87/20~ 40/150 Phenothiazine DDT C303 5 10 D 9fl/150 Ph~nothiazine K01th C303 1 10 E 93/150 Phenothiæine M~thox C303 1 10 F 151/0~ Ph~nothiazine DCE C303 1 10 G 93/150 Ph~nothiazine TBE C303 1 10 25/20~
H 84/150 Phanothiazine TBF C303 1 10 49/50^
94/150 Phenothiazine 2TC:Ma C303 1 10 69/1 20~
J 25/150 Phenothiazine DCPP C303 1 10 K 37t150 Phsnothiazine DC:PP C303 1 10 - Thi~ ~xposure was conductecl through a bandpass tilter whk:h alhwed passa~e of l~ht a1 th~ indicat~d wavebr.~gth ~/- 1 onm.

~7 t ~f~

/Q Rased U~c Wei~ht of AHR
Sl~e~ ~_ Sen PMi L 56/150 Phenothiazine DCPP C303 4 10 M 82/1~0 Phanothiazine DCPP C303 10 10 N 80/150 Phenothiazine DCPP ~'-303 10 39/40^
0 52/150 Phenothiazina DCPP C:303 10 P 94/50- Phenothiazine ER-8 C303 5 10 69l5^
Q 89/50^ Phenothiazine ER-8 C1123 5 10 ~ 00/20-80/25^
R 48/50' Phenothiazine EP~-8 C1171 5 10 57/20^
S 97/50^ Phenothiazine ER-8 Be60 5 10 T 93/50^ Phenothiazine ER-8 C1158 5 10 ~L~

itizer PA~ ~ ~P.n PAG_ U 92120- 74t150 Phenothiazine CP~ C303 5 10 V 94/20~ 73/150~ 10-Methylpheno CPlZ C303 5 10 thiazine W 78/20~ 60/150 Phenothiazine CH13 C303 5 lO
.

Th0 data dernonstrates that phenothiazine s~nsitkes various photoacid generators to near UV radiation at 365 nm. Note that the phenothiazine sensitized acid hardening resin resist exhibited good retention upon davelopment, often exceeding 90% of the original thickness.

~9 Resists were prepared and processed as des0cribed as in Exarnple 1. Phenothiazine derivatives and phenoxazine were used as the sensitizers as shown.

~ S~
_ ~_ 406~ en PAG
X 80/50~ 1 0-Methylpheno- DDT C303 5 10 thiazine Y 54/1505/150~ 2TrHloromethyl- T C303 1 10 8/40^ phano~hiazina 5/20~
Z 94/15018/150~ 2-Chloropheno- T C303 1 10 57/40^ thiazine 33/20~
815a AA 17/20^ 0/150~ 10-Methyipheno- T C303 5 10 thiazine AB 73/20^ 85/150^ Phenoxazine CHI3 C303 1 10 ~ ~ ~. S e~ ~ f~
Resists were prepared using ~hloropher~thiazine as the photoacid generator. The data demonstra~es the surprising effec~iveness of 2~hlorophenothiazine as a photoacid generator at 365 nm and 406 nm.

AG
AC 99/150 8~/150~ 2-Chloropheno- C303 1 û
92/40^ 26/50^ thiazine 98/1 0^
55t5^
AD 92/2û^ 92/150 2-Chloropheno- C303 10 thiazine AE 9~/20~ 92/150~ 2-5hloropheno- C303 15 thiæine AF 87/20~ 2 Chloropheno C303 20 thiazine AG 100/20^ 2-Chloropheno . C303 25 thiazine la~
Resists were prepared as described in Example 1 except that the amount of sensitizer and photoacid generator was varied as shown.

/~sed Upon Weight of AHR
~ ~6 &r~-nizer P~G AR ~5i_ AH 30/15û Phenothiazine T C303 1 5/20a Al 81/150 Phenothiazine T C303 4 37/40^
AJ 98/150 Phenothiazine T C303 4 10 90t40~
55/20^
AK 91/50 Phenothiazine T C303 10 72/20~
AL 90/40~ Phenothiazine T C303 10 5 78~20-28l5-AM 94140- Phenothiazine T C303 10 10 4915a T~BL~ ~ b~ G ~ ? ~ ~ ~

~ s~s~
365 .4~........ n~i~zqr PA9 _ A~ ~ierL PA~
AN 93/40^ Phenothiazine T C303 10 15 ~6/20^
595~
AO 87/40^ Phenothiazin~ T l'303 15 AP 91/40~ Phenothiazine T C303 15 5 52l5~
AQ 100/49^ Phenothiazin~ T C303 15 10 66lS~
AR 0/40- Phenothiazin~ None C303 15 0 AS 0/40 Phenothiazine T C303 0 15 AT 100/40~ Phenothiazine T C303 20 5 48l5^
AU 81/40~ Phenothiazine T C303 5 10 3~3 73~
~LE~

, ~, /O~ased U~n V\~ei~ht o~R
~. 406 ~ensR~c PAQ~ en PAG
AV 33/40~ Phenothiazine T C303 5 10 AW 81/40~ Phenothiazine T C303 5 10 AX 52/10~ Pharlothiazin~ TBE C303 5 10 AY ~2/20~ 25/150~ Ph~nothiazins T C303 5 10 ~ ~..?L ~
I~L~ Vl Resists were prepared using diHerent Acid hardening resins as shown. The data demonstra~es that resists containing various acid hardening r~sins can be prepared according to the invention.

/cRela~ % Bas~d Upon We~htQf AHR
~ SensReer. _ . . e~ M Sen AZ 41/150 Ph~nothiazine T C380 5 10 BA 48/150 Phenothiazine T C1168 5 10 BB 39/150 Phenothiazine T C1170 5 10 BC 32/150 Phenothiazine T C1171 5 10 BD 70/150 Phenothiazine T C1123 5 10 BE 28/160 Ph~nothiazins T C1134 5 10 ~ .

A resist solution was pr~par~d by mixing 100 grams of 30% solids novolac resin, 6.00 grams of Cymel 303, 3.6 grams of tris-(~,3-dibromopropyl)isocyanurat~ and 1.80 grams of phenothiazine. A wafsr was ccated with a thick layer of the resist solution using an airbrush, and baked. Tha wafer was exposed at 365 nanometers through a photomask of th~ type described in Serial No. 818,571, baked to crosslink and washed with developer. Three dimensional ima~es were produced that were 250 microns thick with straight side wall profilss, in the fully exposed areas of the mask and with thinner surface r01ief areas where the light was attenuatsd by the mask.

A wafer was coatecl with a 10% aqueous selution of a 2000 rnol0cular weight polyvinyl alcohol (Aldrich Chemical Company) by spin coating at 3000-4000 RPM toproduce a 0.1 micrometer thick dry fiim and baked for 30 minutes at 90 degreesC. The wafer was then coated with a 1-3 rnicrometar layer cf resist prepared by mixing 100 grams of 30% solids novolac resin, 6.û0 grams of cyme! 303, 3.6 grams of tris-(2,3-dibromopropyl)isocyanurate and 1.80 grams of phenothi~zine. The resist was baked for 30 rninutes at 90 degreesC, and exposed at 3~5 nanometers by contact printing using a mask that contained clear areas that described the shape of symbols on a 10 micrometer scale. After baking for 30 minutes at 90 degrees C to crosslink the images the wafer was washed with dilute aqueous developer. The images of symbols were collected by centrifugation, washed with water and then with dilute acetic acid and dried.
If made in distinctly recegr1izeable shapes, these free-floating irnages may be used as identification markers for exampl~ in solid or liquid products or in paper such as currency, bonds, etc. to prevent counterfeiting. The images may carry the identifying information in the form of symbols or characters that are directly observable using magnification equipment or may be made in distinctly identifying shapes that are paired with identifying information in an index. The markers could also be tagged to ease detection for example using fiuorascent dyes, magnetic fillers and the like.

Claims

1. A method of producing high resolution negative photoresist images comprising: pattern wise exposing a photoresist composition to near ultraviolet radiation, said photoresist comprising a phenothiazine derivative, a deep UV photoacid generator and an acid hardening resin system, then heating said resist and developing the image by removing unexposed areas with a developer.

2. A method of producing high resolution negative photoresist images comprising:

exposing portions of a layer of photo resist composition to an effective amount of near ultraviolet radiation in a pattern, said photoresist comprising: from about 50 to about 98 percent acid hardening resin;

from about 0.5 to about 25 percent of a deep UV photoacid generator that does not generate an effective amount of acid in response to near ultraviolet radiation and from about 0.5 to about 25 percent of a sensitizer of the formula:

where X is sulfur, or oxygen, R can be hydrogen or C1-C6 alkyl, and R1 can be hydrogen, halogen or C1-C6 alkyl, substituted or unsubstituted;

which renders said photoacid generator sensitive to near ultraviolet radiation;

then heating said photoresist to selectively cause the reaction in the exposed areas; and developing the image by selectively removing the unexposed portions of the photoresist.

3. A method of producing high resolution negative photoresist comprising exposing a photoresist composition to near ultraviolet radiation, said photoresist comprising acid hardening resin system and 2-chlorophenothiazine as a photoacid generator.

4. A negative photoresist composition for use with exposing tools that operate using near UV radiation comprising an acid hardening resin system, a deep UV photoacid generator that does not generate sufficient acid in response to near UV and a sensitizer of the formula:

where X is sulfur, or oxygen, R is hydrogen or C1-C6 alkyl, and R1 is hydrogen, halogen or C1-C6 alkyl, substituted or unsubstituted, which upon exposure to near UV radiation causes the deep UV photoacid generator to generate acid.

5. A negative photoresist composition for use with exposing tools that operate using near UV radiation comprising an acid hardening resin system and 2-chlorophenothiazine.

6. A negative photoresist composition for producing relief images which include submicron features and have straight side wall profiles using near UV radiation which comprises the photoresist of claim 4.

7. The photoresist of claim 6 wherein the images include features having a depth greater than 100 microns.

8. The photoresist of claim 7 wherein the images include features having a depth greater than 200 microns.

9. The photoresist of claim 7 wherein the image has more than one surface elevation produced by exposing the resist using a mask that includes opaque, clear and partial light transmitting areas.

10. A product identification marker comprising a microscopically detectable free-floating image of a distinctly recognizable shape produced according to the method of claim 2.