WO2001055789A2

WO2001055789A2 - Chemically amplified short wavelength resist

Info

Publication number: WO2001055789A2
Application number: PCT/EP2001/000824
Authority: WO
Inventors: Wolf-Dieter Domke; Stefan Hien; Ernst Richter; Michael Sebald
Original assignee: Infineon Technologies Ag
Priority date: 2000-01-25
Filing date: 2001-01-25
Publication date: 2001-08-02
Also published as: WO2001055789A3

Abstract

A resist capable of imaging by exposure to radiation having a wave length of about 157 nm includes an imagewise convertible film-forming polymer substituted with at least one chemical functional deblocking group cleavable under acid-catalyzed baking conditions to form polar groups imparting solubility of the deblocked polymer in aqueous alkaline developer. At least one photo acid generator compound releases an acid upon exposure to radiation and catalyzes the cleavage of the deblocking groups. An effective amount of at least one radical scavenger compound is used to minimize reactions decreasing the solubility of the deblocked polymer in aqueous alkaline developer. At least one solvent is also provided.

Description

CHEMICALLY AMPLIFIED SHORT WAVELENGTH RESIST

Background of the Invention:

Field of the Invention:

This invention relates to chemically amplified resists

suitable for imaging by exposure to radiation of very short

wave lengths about 157 nm.

Chemical amplified resists (chemical amplification resists;

CAR) are being investigated worldwide and used in different

lithographic technologies. They are described, for example, in a survey by H. Ito, Solid State Technology, July 1996, p.

164 ff . The principle of chemical amplification is used with wet developable single layer resists, and also with

completely or partly dry developable bilayer resist systems.

A specific group of these resists work according to the

principle of acid-catalytic deblocking. In a positive working

resist, a non-polar chemical group in the film forming polymer

(e. g. a carboxylic acid tert-butylester group) is converted

into a polar carboxylic acid by a baking step at elevated

temperatures in the presence of a photolytically generated

acid catalyst. Additional examples of "blocking" groups are tert-butoxycarbonyloxy (t-BOC) or acetal groups. The

resulting changes in polarity are used in a subsequent

development step with an alkaline aqueous based developer to

selectively dissolve the exposed (polar) areas of the resist.

Chemical amplified positive resists are well known and have

been frequently described in publications (e. g. W.M. Moreau,

Semiconductor Lithography, Plenum Press 1988) .

As the trend in optical lithography for the patterning of

semiconductors goes to shorter wavelengths in order to resolve

even smaller structures (and so afford an increase in

information density) , the 157nm lithography technology (R.R.

Kunz, T.M. Bloomstein, D.E. Bloomstein, D.E. Hardy, D.K.

Downs, J.E. Curtin, J. Photopolym. Sci. Technol., 10(5), 561-

570,1999) becomes increasingly important (M. Sasago, J.

Photopolym. Sci. Technol., 10(5), 585-590,1999).

One obstacle to the widespread utilization of 157 nm imaging

technology is that when a chemically amplified positive resist

is exposed with increasing doses of radiation at a wavelength

of 157nm, a complex non-linear dose-response behavior is

observed: first there is an increase in solubility of the

resist film in alkaline aqueous based developers according to the increasing exposure dose (as would be expected for a

positive resist) , but with further increase in exposure dose,

this behavior is reversed and a decrease in solubilty is

obtained. This can be shown in a simple photo-sensitivity

analysis as is described for example in "Technologie

hochintegrierter Schaltungen" , 2. Auflage, Springer-Verlag,

Berlin, 106, 1996. This phenomenon can be explained by the

fact, that with increasing exposure doses increasing amounts

of radicals (J. Falbe, M. Regitz, "Rόmpp Chemie

Lexikon" ,Thieme, Stuttgart, vol. 5 (1995), page 3758) are

formed in the resist film, which initiate an unwanted cross-

linking reaction (radical polymerization) (ibid. ) and thus

decrease the solubility in the developer. Especially in a

vacuum or in an inert atmosphere environment one can expect an

intensified radical reaction, because oxygen, which would

react as a radical scavenger, is absent.

In patternwise 157nm exposures i. e. exposure of the resist

film through a mask, this results in an insoluble scum between

the resist structures and in rounded resist profiles with non-

vertical sidewalls. Such structures are not suitable for any

subsequent processes in semiconductor production (e. g.

substrate etch, etc.). In summary the problem is that conventional chemically

amplified photo resists result in a poor resolution capability

because of the above described phenomenon.

As yet, no solution to this problem has been offered in the

art.

Summary Of The Invention

It is accordingly an object of the invention to provide a

short wave length chemically amplified resist that overcomes

the above mentioned disadvantages of the prior art resists and methods of this general type and affords reliable increase in

solubilization in aqueous alkaline developer with increasing exposure to radiation having a wave length of about 157 nm.

With the foregoing and other objects in view there is

provided, according to this invention, a resist capable of

imaging by exposure to radiation having a wave length of about

157 nm comprising:

• an imagewise convertible film-forming polymer

substituted with at least one chemical functional deblocking

group cleavable under acid-catalyzed baking conditions to

form polar groups imparting solubility of the deblocked

polymer in aqueous alkaline developer, • at least one photo acid generator compound that releases

an acid upon exposure to radiation and catalyzes the cleavage

of said deblocking groups,

• an effective amount of at least one radical scavenger

compound to minimize reactions decreasing the solubility of

said deblocked polymer in aqueous alkaline developer, and

• at least one solvent.

If desired, additional components and additives can be

included in the resist of the invention to improve for

example film forming properties, shelf life stability, dose sensitivity, delay time stability etc.

The resist according to the invention is applied to a

pattemable substrate and dried in a subsequent baking step

(60 - 160°C) , during which the solvent is evaporated.

Patternwise exposure generates acid in the exposed parts of

the solid resist film by photolysis of the photo acid

generator. The exposure can be done optically with radiation

of the appropriate wavelength (e. g. ultra-violet light, X-

ray) through a photomask or by direct exposure with focused

electrons or ions . In a subsequent bake step (Post Exposure Bake, PEB) , one or

more of the functional deblocking groups of the polymer are

cleaved by catalytic reaction with the acid generated in the

patternwise exposure, thus generating polar solubilizing

groups such as carboxyl or phenolic hydroxyl. In the exposed

areas, the resist film thus becomes soluble in an alkaline

aqueous based developer. In the final development step - done

for example with a 2.38% solution of tetramethylammonium

hydroxide (TMAH) in water - the exposed areas are dissolved

and thus a positive relief structure is generated in the

resist film. This means, the substrate is uncovered in the

exposed areas, whereas the unexposed areas are still covered

by the solid resist film.

It is a particular advantage of the invention that by

including an effective amount of a radical scavenger in the

resist unwanted crosslinking of the polymer chain by radicals

which are generated through exposure, is effectively

suppressed and thus scumming- and residue- free development of

the exposed areas of the resist film is achieved.

While the invention is illustrated and described herein as

embodied in a resist as defined above, it is nevertheless not

intended to be limited to the details shown, since various modifications and structural changes can be made therein

without departing from the spirit of the invention and within

the scope and range of equivalents of the claims .

The construction and method of operation of the invention,

together with additional objects and advantages thereof will

be best understood from the following description of specific

embodiments .

Description of Preferred Embodiments

The imagewise convertible film-forming polymer is a polymer

having acid-labile deblocking groups with low alkaline

solubility in the main chain and/or in a side-chain which can

be converted in an exposed region by catalytic reaction with

acid under baking conditions into alkaline soluble groups .

The acid-labile groups deblocking groups can include ester

groups, ether groups and acetal groups, for example tert-

alkylester, tert-butylester-, tert-butoxycarbonyloxy- ,

tetrahydrofuranylester- , tetrahydropyranylester- , tert-

alkylether-, tert-butylether- , tert-butoxycarbonyloxy-,

tetrahydrofuranylether- , tetrahydropyranylether- , or

corresponding acetal groups . Acid-labile deblocking groups which allow for increased

transparency of the polymers (and thus the resist film) for

light of very short wavelengths (e. g. 157 nm) are

particularly preferred, as for example 1,1,1,3,3,3, -

hexafluoro-2-hydroxy-isopropyl, where the hydroxyl function is

blocked by tert-alkyl-, tert-butoxycarbonyl- ,

tetrahydrofuranyl-, tetrahydropyranyl- , acetal- or other

groups capable of acid-catalyzed deblocking. Besides those

acid-labile groups additional groups to improve the

lithographic properties of the resist or its etch resistance,

such as carboxyl, and hydroxyl, and carboxylic acid anhydride

groups, can be included in the polymer. Further reactive groups e. g. succinic anhydride groups can be present in the

polymer to guarantee a subsequent chemical treatment of the

resist structures.

According to the invention, the structure of the main chain of

the imagewise convertible polymer is not critical. Thus

exclusively carbon-containing main chains formed for example

by (co) polymerization of unsaturated monomers (e. g.

styrenes, acrylates, methacrylates , etc.) or cyclic monomers

are as eligible as polysiloxanes, polyethers and polyesters.

Preferably, the polymer can contain partially or completely

fluorinated building blocks to improve the transparency at 157 m. The weight average molecular weight of the polymer can

range from 1000 to 100000, preferably from 5000 to 20000.

Thus, the imagewise convertible polymer is preferably a

copolymer having polymer units with acid-labile groups and

different polymer units . Particularly preferred are imagewise

convertible polymers comprising 10-35 mol% of at least one

polymer unit (I) having acid-labile groups and 65-90 mol% of

at least one polymer unit selected from the group consisting

of adhesion-promoting polymer units (II) , thermally stable

polymer units (III), reactive polymer units (IV), and polymer

units modifying thermal properties (V) , provided that the mol%

of polymer units sum to 100%.

The polymer units are defined according to the monomer from

which they can be derived, even though the carbon-carbon

double bond in the monomer is consumed in forming the

copolymer. Thus, a ter -butyl methacrylate polymer unit, for

example, has the structure -CH--C (CH₃) (C00C₄H_g-t) -

The acid-labile polymer units (I) are polymer units

substituted with one or more acid-labile carboxylic acid ester

groups . These groups decompose under the catalytic influence

of the photoactively generated combination of sulfonic acids according to this invention at 80°C and higher to afford

carboxylic acid groups which assist in the aqueous alkaline

development of the resist. The acid-labile polymer units (I)

make up 10-35 mol% of the total polymer units taken as 100

mol% .

The adhesion-promoting polymer units (II) are polymer units

substituted with polar groups such as carboxylic acid groups

-C0₂H, or cyano groups -CN. The adhesion-promoting polymer

units (II) make up 0-10 mol% of the total polymer units taken

as 100 mol%.

The thermally stable polymer units (III) are polymer units substituted with aromatic, cycloaliphatic, aliphatic or

alkylsilane groups and resist carbon-carbon bond cleavage to

at least 230°C. The thermally stable polymer units (III) make

up 0-70 mol% of the total polymer units taken as 100%.

The reactive polymer units (IV) are polymer units substituted

with reactive groups such as carboxylic acid anhydride groups,

epoxide groups, and isocyanate groups permitting controlled

crosslinking by addition reactions with suitable di- and

polyfunctional agents such as diamines, and

bis (aminoalkyl) silanes . Reactive polymer units (IV) can also be substituted with radical scavenging groups such as

sterically hindered phenol groups, sterically hindered amine

groups, and thioether groups. The reactive polymer units (IV)

make up 0 to 50% of the total polymer units taken as 100%.

The polymer units (V) modifying thermal properties are polymer

units substituted with hydrocarbon groups or carboxylic ester

groups and serve to adjust such properties as glass transition

temperatures, heat distortion temperatures and low temperature

flexibility. The polymer units (V) modifying thermal

properties make up 0-10% of the total polymer units taken as

100%.

The photo acid generator according to this invention is a

compound which releases an acid upon exposure. The photo acid

generator compound can be ionic or covalent, and is typically

a salt of an acid with a base that is decomposed upon

exposure, illustrated by benzenediazonium fluoborate, thus

liberating the acid. The acid preferably has a pK_a in the range

from -20 to 3. It is sometimes of advantage to combine salts

of two different acids differing in pK_a by at least one unit. A

preferred group of photo acid generator compounds includes

onium compounds comprising sulfonium salts R₃S^*X^" and iodonium

salts R,I^*X^~. The radicals R are identical or different, and each denote an aliphatic, aromatic or aryl-carbonyl-alkylene

radical or two radicals R together form an alkylene radical.

It is particularly preferred that R represents C _ to C₁₂.alkyl,

(C_6- to C₁₄.aryl) -CO-CH₂_ or C₆_ to C₁₂.aryl, where the aryl

radicals can include N, 0 or S atoms, or two radicals R

together denote tetramethylene -(CH₂)₄-. The aromatic radicals

R can also be monosubstituted or polysubstituted by OH, N0₂,

halogen or alkoxy groups, in particular with C_x_ to C₄.alkyl

radicals. Furthermore, the aromatic radicals R can be

substituted by aliphatic or further aromatic radicals, in particular by C_:_ to C₁₂.alkyl or C_s_ to C₁₄.aryl.

The anion X^" of the onium salt can be:

- a monohalogenated, polyhalogenated or perhalogenated

aliphatic sulfonate group, in particular a C_x_ to C₁₂.

alkylsulfonate group, for example a trifluoromethanesulfonate or nonafluorobutanesulfonate group;

- an aromatic sulfonate group, in particular a c_s_ to C₁₄.

arylsulfonate group, for example a benzenesulfonate or

naphthalenesulfonate group;

- a monohalogenated, polyhalogenated or perhalogenated

aromatic sulfonate group, in particular a fluorinated C_s_ to

C₁₄.arylsulfonate group, for example a

pentafluorobenzenesulfonate group ; - an aromatic sulfonate group monosubstituted or

polysubstituted by an electron acceptor, in particular a C_s_ to

C_14-arylsulfonate group substituted by N0₂, CN or halogen, for

example a dinitrobenzenesulfonate group;

- a mono- or polyalkyl-substituted aromatic sulfonate group,

in particular a C_s_ to C_14-arylsulfonate group substituted by C^

to C₄.alkyl, for example a toluenesulfonate group.

The anion X^" can also have the following meaning:

- a linear or branched aliphatic or cyclic sulfonate group, in

particular a C_x. to C₁₆.alkyl- or -cycloalkylsulfonate group, for example a hexadecylsulfonate, cyclohexanesulfonate or

camphorsulfonate group (C₁₀H_lsO-SO₃-) ;

- an aromatic sulfonate group, in particular a C₆_ to C₁₄.

arylsulfonate group, for example a benzenesulfonate or

naphthalenesulfonate group;

- a mono- or polyalkyl-substituted aromatic sulfonate

group, in particular a C_s_ to C₁₄.arylsulfonate group

substituted by C_x_ to C₄.alkyl, for example a toluenesulfonate

group .

Particularly preferred sulfonic acids include p-

toluenesulfonic acid (pK_a = -7) , hexadecanesulfonic acid (pK_a =

- 2 ) , cyclohexanesulfonic acid (pK_a = 2.4) and camphorsulfonic acid (p _j = -1) , and partly fluorinated or perfluorinated

alkanesulfonic acids, such as trifluoromethanesulfonic acid

(pK_a = -20) .

The quantity of photoacid generator used in the resist is no

more than needed to catalyze the elimination of protective

groups from the acid-labile polymer unit during post exposure

bake (PEB) , preferably from 0.1 to 10% by weight of the

polymer constituent of the resist. Particularly preferred use

levels of photoacid generator are in the range from 1% to 6%

by weight of the polymer constituent of the resist. The

quantity of photoactive onium compound (A) is greater than the quantity of photoactive onium compound (B) . A weight ratio of

the quantity of photoactive onium compound (A) to the quantity

of photoactive onium compound (B) is preferably in the range

from 20:1 to 5:1 and most preferably approximately 10:1.

The radical scavenger according to this invention can be

monomeric or polymeric; when polymeric, it can have a

molecular weight ranging from 500 to 10000, preferably 2000 to

6000. The radical scavenger can also be provided as an

additive to the resist and, when polymeric, as a polymer unit

included in the film forming polymer of the invention. All

solid and liquid radical scavengers can be used, provided that they are soluble in the solvent of the resist. The radical

scavenger absorbs crosslinking-inducing radicals formed during

exposure of the resist and thus efficiently suppresses the

crosslinking of polymer chains in the exposed areas of the

resist film.

According to the invention it is advantageous to use a radical

scavenger from the following chemical classes:

Sterically hindered phenols and hydroquinones e. g. 2,6-di-

tert-butylphenol; 2, 2 ' -methylenbis- (4-methyl-6-tert-

butylphenol) ; 2, 6-di-tert-butyl-4-methylphenol; 1,3,5-

trimethyl-2,4, 6-tris (3 '5' -di-tert-butyl-4-

hydroxybenzyl) benzene; tetrakis (methylene (3 , 5-di-tert-butyl-4-

hydroxyhydrocinnamate) ) methane; n-octadecyl 3 , 5-di-tert-butyl-

4-hydroxyhydrocinnamate; bis- (4-hydroxy-2-methyl-5-tert . -

butylphenyl) -sulfide; hydroquinone ; tert-butylhydroquinone;

bis- (2-hydroxy-5-methyl-3-tert-butyl-phenyl) -methane; 4,4'-

dihydroxy-biphenyl; 2 , 5-dihydroxy-l-tert-butylbenzene; 2,5-

dihydroxy-1, -di-tert-butylbenzene ;

Aromatic amines e. g. aniline-acetone-condensation products;

p-phenylendiamine and diphenylamine derivatives; n,n'-di-sec-

butyl-p-phenylendiamine; n, n-diphenyl-p-phenylendiamine; 4,4 ' - bis (dimethylbenzyl) diphenylamine,- dihydroquinoline;

polymerized 2, 2,4-trimethyl-l, 2-dihydroquinoline; n-phenyl-n' -

(p-toluolsulfonyl) -p-phenylendiamine,- and aromatic amine

monomers for use in copolymers : n-(4-

anilinophenyDmethacrylamide; 1, 4-bis (2-butylamino) -benzene;

1, 4-dianilino-benzene; 1-anilino-naphthalene, 2-anilino-

naphthalene;

Organic sulfur compounds e. g. thioethers; zinc-di(4-

methylpentyl) -dithiophosphate; n-dodecylthiol; dialkyl esters

of thiopropionic acid; dilaurylthiodiproplonate; bis- (2-

dodecyloxycarbonyi-ethyl) -sulfide; and bis- (dimethylamino-

thiocarbonyl) -disulfide;

Phosphorus compounds e. g. phosphonite;

tris (nonylphenyl) phosphite; tris (2 , 4-di-tert-

butylphenyl) phosphite; tetrakis (2, 4-di tert-butylphenyl) 4, 4 ' -

biphenylendiphosphonite; bis (2, 4 -di-tert-

butylphenyl) pentaerythritol diphosphite; phosphorous acid

tris- (2-octylmercapto-ethylester) ; and phosphoric acid tris-

(dimethylamide) ;

Sterically hindered amines e. g. 2,2,6,6,-

tetramethylpiperidine and derivatives; bis (2, 2,6,6- tetrapiperidin-4-yl) sebacate; and tetrakis (2,2,6,6-

tetrapiperidin-4-yl) butane-1, 2,3, 4-tetracarboxylate

Nitroso compounds e. g. nitrosobenzene, 2-methyl-2-nitroso-

propane ; benzaldehyde-tert . -butyl-nitrone;

Heterocyclic aromatic compounds e. g. 10, 10-dimethyl-9 , 10-

dihydro-acridine,- benzimidazole; 2-mercapto-benzimidazole;

phenothiazine .

The listed radical scavengers are only an exemplary choice of

the radical scavengers according to the invention. Frequently,

it is of advantage to use a combination of two or more radical

scavengers, for example a sterically hindered phenol with an

organic sulfur compound and a phosphite ester with a

sterically hindered amine.

The solvent according to the invention can be any of the known

photoresist solvents or mixtures thereof, which are suitable

to dissolve the resist components according to the invention

to afford a clear, particle-free and shelf-life stable

solution and assure a good film quality after the coating of

the substrate, preferred solvents are methoxypropylacetate, cyclopentanone, cyclohexanone, y-butyrolactone, ethyl lactate

and mixtures thereof .

In the resist according to the invention the described

components can be applied in the following ratios by weight:

Imagewise convertible film forming polymer: 1 - 50 %,

preferably 2 - 20 %

Photoacid generator: 0.005 - 10 % preferably 0.02 - 1%

Radical scavenger: 0.0001 - 5%, preferably 0.002 - 0.5 %

Solvent: 50 - 99 %, most probable 88 - 98 %.

The important step according to the invention is the

application of a radical scavenger in a chemically amplified

photoresist formulation to avoid unwanted crosslinking

reactions in the exposed areas of a resist film. With that,

for the first time high-quality, high resolution and residue-

free structures can be obtained by 157nm exposures .

Claims

We claim :

1. A resist capable of imaging by exposure to radiation having a wave length of about 157 nm or less than 157 nm comprising: an imagewise convertible film-forming polymer substituted with at least one chemical functional deblocking group cleavable under acid-catalyzed baking conditions to form at least one polar group imparting enhanced solubility of the deblocked polymer in aqueous alkaline developer, at least one photo acid generator compound that releases an acid upon exposure to radiation and catalyzes the cleavage of said deblocking groups, an effective amount of at least one radical scavenger compound to minimize reactions decreasing the solubility of said deblocked polymer in aqueous alkaline developer, and at least one solvent.

2. The resist according to claim 1, in which at least one deblocking group of said polymer is a tert-alkyl-, tert-butyl-, tetrahydrofuranyl-, or tetrahydropyranyl carboxylate ester group.

3. The resist according to claim 1, in which at least one deblocking group of said polymer is a tert-alkyl-, tert-butyl-, tetrahydrofuranyl-, or tetrahydropyranyl ether or -acetal group.

4. The resist according to one of claims 1 to 3, in which said polymer contains 1, 1, 1, 3, 3, 3, -hexafluoro-2-hydroxy-isopropyl- groups where the OH-groups blocked by tert-alkyl-, tert-butyl-, tetrahydrofuranyl-, tetrahydropyranyl-tert-butoxycarbonyloxy-, or acetal-groups in at least one deblocking group.

5. The resist according to one of claims 1 to 4, in which said polymer includes carboxylic acid anhydride structures.

6. The resist according to claim 5, in which said polymer includes succinic anhydride structures.

7. The resist according to one of claims 1 to 6, in which said polymer includes 10-35 mol% of at least one polymer unit (I) having acid-labile groups and 65-90 mol% of at least one polymer unit selected from the group consisting of adhesion-promoting polymer units (II), thermally stable polymer units (III), reactive polymer units (IV) , and polymer units modifying thermal properties (V) , provided that the mol% of polymer units sum to 100%.

8. The resist according to one of claims 1 to 7, in which said photo acid generator is an onium compound.

9. The resist according to one of claims 1 to 8, in which the photo acid generator is a covalent compound.

10. The resist according to one of claims 1 to 9, in which the radical scavenger is an aromatic heterocyclic compound.

11. The resist according to one of claims 1 to 9, in which the radical scavenger is a nitroso compound.

12. The resist according to one of claims 1 to 9, in which the radical scavenger is a sterically hindered amine.

13. The resist according to one of claims 1 to 9, in which the radical scavenger is a phosphorus-containing compound.

14. The resist according to one of claims 1 to 9, in which the radical scavenger is an organic sulfur compound.

15. The resist according to one of claims 1 to 9, in which the radical scavenger is an aromatic amine.

16. The resist according to one of claims 1 to 9, in which the radical scavenger is a sterically hindered phenol.

17. The resist according to one of claims 1 to 16, additionally containing at least one additive to improve resist properties including shelf life stability, delay time stability, film forming properties, adjustment of absorption wavelengths, and adjustment of exposure dose.

18. The resist according to one of claims 1 to 17, in which at least one solvent is l-methoxy-2-propylacetate, cyclohexanone, gamma-butyroxactone, or ethyl lactate.

19. Method for producing a relief structure in a resist film for lithographically patterning a semiconductor wherein a resist according to one of claims 1 to 18 is applied to a pattemable substrate, the solvent is evaporated in a subsequent baking step to afford a solid resist film, the solid resist film is patternwise exposed to a radiation of wavelength of about 157 nm or less than 157 nm the exposed resist film is heated in a Post Exposure Bake Step, and said exposed areas are dissolved in an aqueous alkaline developer whereby a positive relief structure is obtained.