JP2771076B2 - Method for removing metal impurities from resist components - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to one method for removing metal impurities from resist components. More specifically, the present invention removes metal impurities (including sodium, iron, calcium, chromium, copper, nickel, zinc, etc.) from a solution of a resist component or a resist composition, and therefore, converts the solution to a quaternary ammonium salt solution. And contacting the pre-washed cation exchange resin with the cation exchange resin.

[0002]

BACKGROUND OF THE INVENTION Photoresist compositions are used in microlithographic processes for the fabrication of miniaturized electronic components, such as in the manufacture of integrated circuits and printed circuit boards. Generally, in these methods, a thin coating or film of a photoresist composition is first applied to a silicon wafer used to make integrated circuits, or a substrate material such as aluminum or copper plates for printed wiring boards. The coated substrate is then baked to evaporate the solvent in the photoresist composition and fix the coating on the substrate.

[0003] The coated surface of the baked substrate is then subjected to image-wise radiation exposure. This radiation exposure causes a chemical conversion in the exposed areas of the coating surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energies are types of radiation currently commonly used in microlithographic processes. After this imagewise exposure, the coated substrate is treated with a developer to dissolve and remove either the radiation-exposed or unexposed areas of the substrate-coated surface.

[0004] There are two types of photoresist compositions, negative working and positive working. Both negative-acting and positive-acting compositions are generally made from a film-forming resin and a photoactive compound dissolved in a suitable coating solvent. Additives for specific functions can be added. When the negative-acting photoresist composition is imagewise exposed to radiation, the areas of the resist composition that have been exposed to radiation become less soluble in the developer (eg, a crosslinking reaction occurs) while the photoresist is exposed to radiation. The unexposed areas of the coating remain relatively soluble in the developer. Thus, treatment of the exposed negative working resist with a developer will remove the unexposed areas of the resist coating and produce a negative image in the resist coating; The desired portion of the side substrate surface is removed.

On the other hand, when the positive working photoresist composition is imagewise exposed to radiation, the areas of the resist composition that have been exposed to radiation become more soluble in the developer (eg, where an intramolecular transfer reaction occurs). And, areas that were not simultaneously exposed remain relatively insoluble in the developer. Thus, treatment of the exposed positive working resist with a developer will remove the exposed areas of the resist coating, producing a positive image in the photoresist coating. The coating of the desired portion of the underlying substrate surface is stripped.

[0006] After this development step, the now partially unprotected substrate is treated with a substrate etchant, a plasma gas or the like. The etchant or plasma gas etches the portion of the substrate where the photoresist coating was removed during development. Areas of the substrate where the photoresist coating still remains are protected, and the etched pattern thus forms in the substrate material, corresponding to the photomask used for imagewise exposure to radiation. The remaining areas of the photoresist coating are then removed by a stripping process, leaving a clean etched substrate surface. In some cases, it may be desirable to heat treat the remaining resist layer after the development step and before the etching step to increase adhesion to the underlying substrate and resistance to the etchant.

[0007] Positive-acting photoresist compositions are currently preferred because they generally have better resolution and pattern transfer characteristics than negative-acting ones. Preferred positive working photoresists generally comprise a novolak resin and an O-quinonediazide photoactive compound dissolved in a suitable solvent.

[0008] Impurity levels in photoresist compositions have become of increasing concern. Contamination by photoresist impurities, especially metals, causes degradation of semiconductor devices made with the photoresist and shortens the life of these devices.

The level of impurities in the photoresist composition is determined by (1) selecting a material for the photoresist composition that meets strict impurity level specifications, and (2) preventing the introduction of impurities into the photoresist composition. And has been and is being controlled by careful management of process parameters.
As photoresist applications have further advanced, more stringent impurity standards have to be created.

When a novolak resin material is used to make a positive photoresist, such a novolak resin is subjected to a distillation or recrystallization purification step to remove impurities, especially metals. However, such a process has disadvantages. For one thing, this is time consuming and costly. More importantly, they cannot now remove the required impurities down to very low levels (ie, as low as ppb at the highest levels) due to advanced applications.

Alternatively, ion exchange resins have been used for novolak impurities. One common method is to pass an impure novolak resin solution through a cation exchange resin (e.g., AMBERLYST styrene sulfonic acid-divinylbenzene cation exchange resin). However, such a process has several problems associated with it, including the following:

1. Treatment of the novolak with a cation exchange resin reduces the pH value of the novolak-containing solution and will likely result in significant corrosion of the metal container for storing the purified novolak-containing solution.

2. Purified novolaks may have a reduced dissolution rate during the photoresist development process, which is caused by unwanted adsorption of low molecular weight portions of the novolak resin onto the cation exchange resin. There will be.

3. Alkali metals such as sodium and potassium are easily removed by common cation exchange resins. However, divalent or trivalent metal cations (eg Cu ⁺² , Ni ⁺² , Zn ⁺² , Fe ⁺² , Fe ^+2
+3 , Ca ^{+ 2} , or Cr ^{+ 3} ions) have a low affinity for common cation exchange resins. Iron and other metals that are easily oxidized cannot be completely removed because they can become colloidal metal oxides or hydroxides. Such colloids are not significantly removed by cation exchange resin treatment.

Ion exchange resins, especially cation exchange resins of the strong acid type, decompose resist components or solvents containing hydrolyzable groups such as esters. For example, ethyl lactate is decomposed by Amberlyst A-15 to form polylactites, which impair the lithographic performance of the photoresist. As used herein, "polylactide" refers to a cyclic dimer of lactic acid (lactic acid), a polymer or oligomer product of lactide, and the like, generated by hydrolysis of ethyl lactate.

In addition to the standard cation exchange resin treatment of novolak resins, complete photoresist compositions (eg, novolak resins, photosensitizers, and solvents) are known to undergo both cation and anion exchange resin treatments. Have been. For example, Japanese Patent Publication No. 57-74370
In the above publication, a method for reducing impurities in a resist by using a cation exchange resin and an anion exchange resin separately and sequentially is disclosed. In Japanese Patent Laid-Open Publication No. Hei 1-228,560 issued September 12, 1989, the content of metal impurities in a photosensitive resin solution or a photoresist composition is reduced by a mixture of a cation and an anion exchange resin. Indicates that it can be done. However, both of these methods have the disadvantage that divalent and trivalent metal impurities cannot be removed and that they may decompose resist components or solvents contained in the resist composition.

Usually, such cation and anion exchange resins are washed with deionized water or a similar solvent in which the resist components are dissolved. However, other acidic contaminants, as well as metal ions such as sodium or potassium, are strongly bound to the anionically charged groups of the cation exchange resin, so washing with such water or solvents may cause metal impurities. Cannot clean the resin that has already adhered.

Accordingly, there remains a need in the photoresist art for improved methods of removing metallic impurities from novolak resins and other materials used as photoresist components. The present invention is one answer to this need.

[0019]

SUMMARY OF THE INVENTION Accordingly, one embodiment of the present invention is to remove metal impurities from the resist component: (a) dissolving the resist component in a solvent; (b) cation exchange resin with a quaternary ammonium compound solution. (C) contacting the pre-washed cation exchange resin with a resist component solution to remove metal impurities from the resist component solution; and (d) supporting metal impurities from the resist component solution. And a method for removing metal impurities comprising the steps of separating the cation exchange resin.

[0020]

DETAILED DESCRIPTION As used herein and in the claims, the term "resist component" includes alkali-soluble resins such as novolak resins and polyvinylphenol resins, photoactive compounds and their precursors, and photoresists. Each additive (eg, a sensitivity enhancer, a dye, etc.) commonly used in the composition is included. The term also includes precursor compounds for making each such component. Examples of such precursor compounds are bone nucleus compounds for making photoactive compounds, as well as photoactive ester compound precursors (eg, naphthoquinonediazidosulfonyl chloride).

The term "novolak resin" used herein is:
It refers to any novolak resin that is completely dissolved in an alkaline developer commonly used for positive-acting photoresist compositions. Suitable novolak resins include phenol-formaldehyde novolak resin, cresol-formaldehyde novolak resin, xylenol-formaldehyde novolak resin, cresol-xylenol-formaldehyde novolak resin, preferably about 500 to about 40,000, more preferably about 800 to Those having a molecular weight of about 20,000 are included.

These novolak resins are preferably made by addition-condensation polymerization of a phenolic monomer or monomers (eg, phenol, cresol, xylenol or mixtures thereof) with an aldehyde source such as formaldehyde, and It is stable and has properties such as water insolubility, alkali solubility, and film forming property. One preferred novolak resin is a polycondensation between a mixture of meta- and para-cresols with formaldehyde, about 1,0
It has a molecular weight of from about 00 to about 10,000. Representative methods for producing novolak resins are all shown in U.S. Patent Nos. 4,377,631; 4,529,682; and 4,587,196 issued to Medhat Toukhy. Have been.

Another preferred novolak resin is 199
PCT Gazette WO 91/0 published March 21, 2001
No. 3769.

As used herein and in the claims, the term "photoactive compound" includes any of the common photoactive compounds commonly used in photoresist compositions. While quinonediazide compounds as a generic concept are one preferred class of compounds, one of the preferred classes is naphthoquinonediazide compounds. As mentioned previously, photoactive compound precursors can also be treated according to the present invention. One of the photoactive compound precursors handled by this method is 2,6-bis (2,3,4-trihydroxyphenyl) methylene-4.
-Methylphenol, which is also known as 7-PyOL, which is disclosed in U.S. Pat. No. 4,992,35.
No. 6 in Example 3.

Photoresist additives can be handled according to the present invention. Such additives include sensitivity enhancers, dyes, and the like. A preferred sensitivity enhancer is 1-[(1'-methyl-1 '-(4'-hydroxyphenyl) -ethyl)] 4- [1', 1'-bis- (4-hydroxyphenyl) ethyl] benzene. Things are also TR
ISP-PA).

In the first step of the method of the present invention, the resist component is dissolved in a solvent or solvent mixture to facilitate contact of the resist component with the cation exchange resin. Examples of suitable solvents include acetone, methoxyacetoxypropane, ethyl cellosolve acetate, n-butyl acetate, ethyl lactate, ethyl-3-ethoxypropionate, propylene glycol, alkyl ether acetate, or mixtures thereof, and the like. included. Co-solvents such as xylene or n-butyl acetate can also be used. One preferred solvent is a mixture of ethyl lactate and ethyl-3-ethoxypropionate, wherein the weight ratio of ethyl lactate: ethyl-3-ethoxypropionate is from about 30:70 to about 8%.
0:20.

The solids content of the resulting resist component solution is not critical. Preferably, the amount of solvent or solvent mixture is from about 50% to about 500% or more by weight; more preferably from about 75% to about 400% by weight based on the weight of the resist components.

Although it is preferred to use a single resist component as the material processed by the method of the present invention, it is contemplated that combinations of resist components may be used within the purposes of the present invention. For example, according to the present invention, fully positive working photoresist formulations (eg, novolak resin or resins, photoactive compounds such as quinonediazide sensitizers, and solvents or mixed solvents, as well as dyes, sensitivity enhancers, interfaces) It may be desirable to use a combination of conventional optional minor ingredients such as active agents, etc.).

The metal impurities in the solution of the resist component will be present in the form of monovalent metal cations such as alkali metals (ie, Na ⁺ and K ⁺ ). This metallic impurity may come from the chemical precursors for the resist components (ie, in the case of novolak resins, this is the phenolic monomer and aldehyde source) and the solvent used to make the solution. These impurities may also come from the solvent used to make the resist components, or the equipment used to synthesize or store them.

In general, the amount of metal impurities in the resist components, such as novolak resins, is 500 parts by weight for metals such as sodium and iron prior to applying the method of the present invention.
In the range of ~ 5,000 ppb or more. Sodium impurities are generally in the form of monovalent ions (Na ⁺ ). Iron may be present, in part, in divalent (Fe ⁺² ) or trivalent (Fe ⁺³ ) form, and sometimes in the form of hydroxides or colloids of oxides.

The solution of the resist component is prepared by the usual method of mixing the solvent and the resist component. Generally, it is preferable to add the resist component to a sufficient amount of the solvent and dissolve the resist component in the solvent. This step is facilitated by stirring or other conventional mixing means.

The next step in the method of the present invention is to contact the solution of the resist component with at least one cation exchange resin.

Cation exchange resins useful for the present invention include those that can remove metals from the resist component and are compatible with the resist component and the solvent used (co
mpatible) All cation exchange resins are included.
Suitable cation exchange resins include phenol sulfonate-
Formaldehyde condensate, phenol-benzaldehyde sulfonate condensate, styrenesulfonic acid-divinylbenzene copolymer, acrylic acid-divinylbenzene copolymer, methacrylic acid-divinylbenzene copolymer, and other types of polymers containing sulfonic or carboxylic acid groups, etc. Is included. One preferred particulate cation exchange resin is Amberlyst 15, available from Rohm and Haas. This is a styrene sulfonic acid-divinylbenzene copolymer.

The relative amount of the cation exchange resin used in the method of the present invention is preferably from about 1% to about 10% by weight based on the solution of the resist component. More preferably, the relative amount is from about 2 to about 4% by weight based on the amount of the solution.

A critical feature of the present invention is that the cation exchange resin is pre-treated or pre-washed with a quaternary ammonium salt solution. This quaternary ammonium cation was found to enhance the ion exchange reaction between the pre-washed cation exchange resin and the resist component without undesirably lowering the pH of the resist component being treated.

The anions, especially hydroxyl groups, in the quaternary ammonium salt compound can extract a cationic counter ion (ie, H ⁺ or Na ⁺ ) of the cation exchange resin, so that the bulky quaternary ammonium cation It is thought to be a counter ion on the exchange resin. The replacement of the H ⁺ or Na ⁺ cation counter ion by the bulky quaternary ammonium cation counter ion results in high efficiency of reducing metal ions and suppression of hydrolysis of the resist component or the solvent containing the resist component. Spawn.

The quaternary ammonium salt compounds include tetramethylammonium hydroxide (TMAH), but other classes of quaternary ammonium salts as well as other tetra-alkylammonium hydroxides are suitable for the process of the present invention. Will. Other quaternary ammonium cations may include tetraethylammonium, methyltriethanolammonium, dimethyldiethanolammonium, trimethylethanolammonium and benzylmethyldiethanolammonium.

The most preferred quaternary ammonium salt compounds are polymeric quaternary ammonium compounds.
These include hexadimethrin bromide (hexadim)
ethlinebromide), poly (vinylbenzyltrimethylammonium) chloride, polyimidazoline, and quaternized poly (vinylpyridine).

The polymeric quaternary ammonium compound is preferable because its cation is stronger than the monomeric quaternary ammonium cation for the anionic groups of the cation exchange resin.

The quaternary ammonium salt is contacted with the ion exchange resin in the form of a solution, most preferably in an aqueous solution. The amount of ammonium salt in the solution generally ranges from about 1 to about 5
0% by weight.

The amount of quaternary ammonium salt compound used should be in excess with respect to the weight of the cation exchange resin being treated. Generally, the amount of quaternary ammonium salt used will range from about 150 to 1,000 of the cation exchange resin.
% By weight or more.

The pre-cleaning method may be any method conventionally used for cleaning a cation exchange resin with water or an organic solvent. One preferred method is to add the resin to a large excess of an aqueous solution containing 2 to 30% by weight of the quaternary ammonium salt, stir the resulting suspension at ambient temperature for 20 to 60 minutes, and then add The quaternary ammonium salt solution is decanted. This stirring and decanting are repeated three to five times. In this way, the washed resin can be further washed with the same solvent liquid, which will be used in the contacting step (c) to pre-swell the cation exchange resin.

The contact between the cation exchange resin and the resist component solution can be performed by a column system or a batch system. In the column system, the cation exchange resin is packed in an ion exchange column, and a solution of the resist component is passed through the column. Preferably, the solution of the resist component is passed at a constant temperature and at a constant speed to maximize the adsorption of metal impurities on the cation exchange resin.

In a batch system, a pre-washed cation exchange resin is mixed into a solution of a resist component to form a suspension. After a sufficient contact time, the cation exchange resin is removed from the resist component solution, preferably by filtration. Preferably, it is advantageous if the cation exchange resin is dispersed in a solvent before it is mixed with the resist component solution. Furthermore, this type of contact is preferably performed at a constant temperature to maximize adsorption on the cation exchange resin.

In each case, the time of each contact is such that at least a part (preferably at least a large part... At least 50% by weight... More preferably at least 90% by weight) of metal impurities present in the resist component solution is adsorbed. Should be sufficient.

The separation step (d) of the present invention necessarily occurs immediately after the contact step (c) when using a column system. In a batch system, separation step (d) requires additional work by the operator.

After the contacting and separating steps, the resist component system thus treated has a metal content reduced to less than about 100 ppb by weight. For example, the amount by weight of sodium impurities can be as little as 100 ppb to
It is in the range of 0 ppb or less.

It may be preferable to contact the solution of the resist component with any other optional material besides the pre-washed cation exchange resin. One of the preferred optional materials is an anion exchange resin. Such a resin can be used when the efficiency of nonmetal removal is poor. Suitable anion exchange resins include quaternary ammonium group-containing phenolic resins, quaternary ammonium group-containing styrene-divinylbenzene copolymers, aromatic polyamines, polyethylene imines, and the like. One preferred anion exchange resin is a quaternary ammonium styrene-divinylbenzene resin called Amberlyst A-27, manufactured by Rohm and Haas. Another preferred anion exchange resin is an aliphatic amino group containing styrene-divinylbenzene resin called Amberlyst A-21, which is also made by Rohm and Haas.

If the untreated resist component solution contains a significant amount of insoluble colloidal hydroxides or oxides, the resist component solution is added to the solution before contacting with the cation exchange resin. It can be passed through a micro-porous membrane having a pore size of 1-0.5 μm. This purification step will remove at least some of the insoluble colloid and will make the contacting step (c) more efficient.

The following examples and comparative examples are provided to further illustrate the present invention. All parts and percentages are by weight unless otherwise indicated.

Example 1 A granular cation exchange resin (Amberlyst 15 manufactured by Rohm and Haas Co., Ltd., which is a styrene sulfonic acid-divinylbenzene sulfonate copolymer) was mixed with 25% by weight of tetramethyl Ammonium hydroxide (TMA
H) and washed with an aqueous solution of cation exchange resin (10 g) and TMAH (10 g).
0g) were mixed in a plastic bottle. The bottle was rolled in a bottle rotator for 30-40 minutes at ambient temperature. Next, the cation exchange resin particles were decanted by TMAH.
Separated from aqueous solution. The separated resin particles were again mixed with the same amount of fresh TMAH aqueous solution, spun for 30-40 minutes, and decanted two more times for a total of three washes.

A meta / para mixed cresol novolak resin was made by reacting a 40 mole% m-cresol / 60 mole% p-cresol mixture with formaldehyde. The molecular weight of this novolak resin was 6,500 as measured by GPC. This novolak (63 g) was dissolved in a mixed solvent of ethyl lactate (EL, 96 g) and ethyl-3-ethoxypropionate (EEP, 41 g). The solution was placed in a plastic bottle and the cation exchange resin (8.0 g) washed three times was added to the bottle.

The resulting suspension was rotated in a bottle rotator for 24 hours. Cation exchange resin particles were then removed from the suspension by filtering the suspension through a membrane filter having a pore size of 0.2 μm.

The content of sodium impurities and the pH of the novolak solution were measured before adding the cation exchange resin and after removing it by filtration. The content of sodium impurities was measured by graphite furnace atomic absorption spectroscopy.
In addition, the decomposition of ethyl lactate during the resin treatment was measured by gas chromatography to measure how much polylactide was produced during the resin treatment. The results of these measurements are shown in Table 1 below.

Example 2 The same granular cation exchange resin used in Example 1 was replaced with poly (vinylbenzyltrimethylammonium) chloride (PBTM) 12.5.
Aqueous methanol containing 50% by weight (water / methanol = 50 /
The solution was washed by the following method: a cation exchange resin (10 g) and a PBTM solution (100 g) were placed in a plastic bottle. This bottle is 3 ambient temperature
Rolled in bottle rotator for 0-40 minutes. The cation exchange resin particles were then separated from the PBTM solution by decantation. The separated resin particles are again mixed with the same amount of new PBTM.
Mixing with the solution, spinning for 30-40 minutes and decanting were performed two more times, for a total of three washes.

The same novolak resin solution (20
0 g) and the cation exchange resin particles (8.0 g) washed with the PBTM were added to a plastic bottle.

The obtained suspension was rotated in a bottle rotating machine for 24 hours. The cation exchange resin particles are 0.2
The suspension was separated from the suspension by filtration through a septum filter with a pore size of μm.

The sodium content, pH and polylactide formation of the resin solution were measured in the same manner as described in Example 1. The results are shown in Table 1.

Comparative Example 1 The same granular cation exchange resin used in Examples 1 and 2 was washed with ethyl lactate in the following manner: a cation exchange resin (10 g) and ethyl lactate (100 g) were plastic bottled. Was added. The bottle was rolled in a bottle rotator for 30-40 minutes at ambient temperature. The cation exchange resin particles were then separated from the ethyl lactate by decantation. The separated cation exchange resin particles were mixed with the same amount of fresh ethyl lactate solution, spun for 30-40 minutes and decanted two more times for a total of three washes.

Both the same novolak resin solution (200 g) used in Examples 1 and 2 and cation exchange resin particles (8.0 g) washed with ethyl lactate were added to a plastic bottle.

The obtained suspension was rotated in a bottle rotating machine for 24 hours. The cation exchange resin particles are 0.2
The suspension was separated from the suspension by filtration through a septum filter with a pore size of μm.

The sodium impurity content, pH and polylactide formation of the resin solution were measured in the same manner as in Examples 1 and 2. These results are shown in Table 1.

[0063]

[Table 1]

The gas chromatographic test for polylactide involves the following procedure: (a) Add 4% by weight of cation exchange resin to ethyl lactate and spin the resulting suspension at ambient temperature for 24 hours. (B) The resin is removed from the solvent by filtration. (C) Heat the solvent to 70-80 ° C under reduced pressure to evaporate. (D) The obtained viscous residue is weighed, and the weight% of the residue with respect to the charged solvent is calculated. The weight% values are shown in Table 1. This residue was confirmed to be polylactide by infrared spectroscopy using a real polylactide sample.

The results shown in Table 1 demonstrate the following advantages of pre-washing with a solution of a quaternary ammonium salt, especially a polymeric salt: The pH change of the novolak solution before and after treatment with the resin pre-washed with the quaternary ammonium salt is significantly smaller than that of the control (C-1). This drop in pH causes the lithographic properties of the photoresist to deteriorate. 2. The extent of decomposition of ethyl lactate (formation of polylactide) by the resin pre-washed with the quaternary ammonium salt is significantly lower than that of the control (C-1). The formation of polylactide results in a deterioration of the lithographic properties of the photoresist. 3. The efficiency of metal reduction by the resin pre-washed with the quaternary ammonium salt is almost the same as that of the control (C-1). 4. In addition to the above, the polymeric salt pre-wash system has the additional advantage of lower quaternary ammonium cation release for novolak solutions than the corresponding monomeric system; quaternary ammonium Contamination by cations causes deterioration of the lithographic properties of the photoresist.

While the present invention has been described above with reference to specific embodiments thereof, it is evident that many changes, modifications and variations may be made without departing from the inventive concepts disclosed herein. . It is therefore intended to cover all such changes, modifications and variations within the spirit and broad scope of the appended claims.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-234878 (JP, A) JP-A-63-126502 (JP, A) JP-A-59-176303 (JP, A) JP-A-49- 28687 (JP, A) JP-A-64-56148 (JP, A) JP-A-56-24042 (JP, A) JP-A-4-298507 (JP, A) JP-A-2-5011367 (JP, A) Dictionary of Chemistry (October 20, 1989), Michinori Oki, 3 editors, Tokyo Kagaku Dojin, pp. 154-156 (58) Fields investigated (Int. Cl. ⁶ , DB name) G03F 7/004 G03F 7/38 501 C08F 6/06 H01L 21/027

Claims (3)

(57) [Claims] (A) dissolving the resist component in a solvent; (b) washing the cation exchange resin with a quaternary ammonium compound solution; and (c) combining the pre-washed cation exchange resin with the resist component solution. Contacting to remove metal impurities from the resist component solution; and (d) separating the cation exchange resin carrying the metal impurities from the resist component solution. A method for removing impurities. 2. The method according to claim 1, wherein said quaternary ammonium salt compound is a polymeric ammonium salt compound. 3. The method of claim 2, wherein said polymeric ammonium salt compound is poly (vinylbenzyltrimethylammonium) chloride.