WO1996012214A1

WO1996012214A1 - Low metal ion photoactive compounds and photoresists compositions produced therefrom

Info

Publication number: WO1996012214A1
Application number: PCT/US1995/012720
Authority: WO
Inventors: M. Dalil Rahman; Ralph R. Dammel; Owen B. Evans
Original assignee: Hoechst Celanese Corporation
Priority date: 1994-10-12
Filing date: 1995-10-12
Publication date: 1996-04-25

Abstract

A process for producing a photoactive compound having a very low level of metal ions comprising: a) washing an acidic ion exchange resin with water, followed by washing with a mineral acid solution and washing the resin with deionized water, and thereby reducing the level of sodium and iron ions in the ion exchange resin to less than 100 ppb each; b) washing the ion exchange resin with a solvent which is the same as, or at least compatible with, the solvent to be used to provide a solution of the photoactive compound to remove substantially all of the water; c) providing a solution of 5 to 40 weight percent of a photoactive compound in a suitable solvent; d) passing the photoactive compound solution through the ion exchange resin and reducing the level of sodium and iron ions in the solution to less than 100 ppb each. A photoresist composition can then be formulated by providing an admixture of: (i) the treated photoactive compound; (ii) a suitable alkali soluble novolak resin; and (iii) a suitable photoresist solvent.

Description

DESCRIPTION

LOW METAL ION PHOTOACTIVE COMPOUNDS AND

PHOTORESISTS COMPOSITIONS PRODUCED THEREFROM

BACKGROUND OF THE INVENTION The present invention relates to a process for producing photosensitizers

(photoactive compounds) for photoresists, which sensitizers have a very low level of metal ions, especially sodium and iron, and to a process for using such sensitizers in photoresist compositions used to produce semiconductor devices. Further, the present invention also relates to a process for making light-sensitive compositions useful in positive-working liquid photoresist compositions for g-line/i-line lithography.

Photoresist compositions are used in microlithography processes for making miniaturized electronic components such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of a film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate the solvent in the photoresist composition and to fix the coating onto the substrate. The baked, coated surface of the substrate is next subjected to an image-wise exposure to radiation. This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the photoresist.

Metal contamination has been a problem for a long time in the fabrication of high density integrated circuits and computer chips, often leading to increased defects, yield losses, degradation and decreased performance. In plasma processes, metals such as sodium and iron, when they are present in the photoresist or in a coating on the photoresist can cause contamination especially during plasma stripping. However, these problems have been overcome to a substantial extent during the fabrication process, for example, by utilizing HCL gathering of the contaminants during a high temperature anneal cycle.

As semiconductor devices have become more sophisticated, these problems have become much more difficult to overcome. When silicon wafers are coated with a liquid positive photoresist and subsequently stripped off, such as with oxygen microwave plasma, the performance and stability of the semiconductor device is often seen to decrease.

As the plasma stripping process is repeated, more degradation of the device frequently occurs. A primary cause of such problems can be the metal contamination in the photoresist, particularly sodium and iron ions. Metal levels of less than 1.0 ppm can adversely affect the properties of such semiconductor devices.

There are two types of photoresist compositions, negative- working and positive- working. When negative-working photoresist compositions are exposed image-wise to radiation, the areas of the resist composition exposed to the radiation become less soluble to a developer solution (e.g. a cross-linking reaction occurs) while the unexposed areas of the photoresist coating remain relatively soluble to such a solution. Thus, treatment of an exposed negative- working resist with a developer causes removal of the non-exposed areas of the photoresist coating and the creation of a negative image in the coating. Thereby uncovering a desired portion of the underlying substrate surface on which the photoresist composition was deposited.

On the other hand, when positive-working photoresist compositions are exposed image-wise to radiation, those areas of the photoresist composition exposed to the radiation become more soluble in the developer solution (e.g. a rearrangement reaction occurs) while those areas not exposed remain relatively insoluble in the developer solution. Thus, treatment of an exposed positive- working photoresist with the developer causes removal of the exposed areas of the coating and the creation of a positive image in the photoresist coating. Again, a desired portion of the underlying substrate surface is uncovered.

After this development operation, the now partially unprotected substrate may be treated with a substrate-etchant solution or plasma gases and the like. The etchant solution or plasma gases etches that portion of the substrate where the photoresist coating was removed during development. The areas of the substrate where the photoresist coating still remains are protected and, thus, an etched pattern is created in the substrate material which corresponds to the photomask used for the image-wise exposure of the radiation. Later, the remaining areas of the photoresist coating may be removed during a stripping operation, leaving a clean etched substrate surface. In some instances, it is desirable to heat treat the remaining photoresist layer, after the development step and before the etching step, to increase its adhesion to the underlying substrate and its resistance to etching solutions.

Positive working photoresist compositions are currently favored over negative working resists because the former generally have better resolution capabilities and pattern transfer characteristics. Photoresist resolution is defined as the smallest feature which the resist composition can transfer from the photomask to the substrate with a high degree of image edge acuity after exposure and development. In many manufacturing applications today, resist resolution on the order of less then one micron are necessary. In addition, it is almost always desirable that the developed photoresist wall profiles be near vertical relative to the substrate. Such demarcations between developed and undeveloped areas of the resist coating translate into accurate pattern transfer of the mask image onto the substrate.

SUMMARY OF THE INVENTION The present invention relates to a process for producing a photosensitizer containing very low levels of metal ions, especially sodium and iron. The invention further relates to a process for producing photoresists and for producing semiconductor devices using such photoresists.

The sensitizers obtained have very low levels of metal ions such as iron, sodium, potassium, calcium, magnesium, copper and zinc. Sodium and iron are the most common metal ion contaminants and among the easiest to detect. The level of these metal ions serves as an indicator of the level of other metal ions. The level of sodium and iron ions, are each respectively, less than 100 ppb, preferably less than 50 ppb, more preferably less than 20 ppb and most preferably less than 10 ppb. The present invention provides a process for producing a photoactive compound having a very low level of metal ions, particularly sodium and iron. In the preferred embodiment, the process utilizes an acidic ion exchange resin to purify photoactive compounds The subject process comprises: a) washing an acidic ion exchange resin with water, preferably deionized (DI) water, followed by washing with a mineral acid solution (e.g. a 5-98% solution of sulfuric, nitric or hydrochloric acid) and washing the resin with DI water, and thereby reducing the level of sodium and iron ions in the ion exchange resin to less than 100 ppb each, preferably less than 80 ppb and most preferably no more than 50 ppb; b) washing the ion exchange resin with a solvent which is the same as, or at least compatible with, the solvent to be used to provide a solution of the photoactive compound to remove substantially all of the water; c) providing a solution of 5 to 40 weight percent of a photoactive compound in a suitable solvent; d) passing the photoactive compound solution through the ion exchange resin and reducing the level of sodium and iron ions in the solution to less than 50 ppb each, preferably less than 20 ppb and most preferably less than 10 ppb;

A photoresist composition can then be formulated by providing an admixture of: (i) the treated photoactive compound;

(ii) a suitable alkali soluble novolak resin; and (iii) a suitable photoresist solvent.

An acidic ion exchange resin, such as a styrene/divinylbenzene cation exchange resin, is utilized in the present process. Such ion exchange resins are available from Rohm and Haas Company, e.g. AMBERLYST® 15 resin. These resins typically contain as much as 80,000 to 200,000 ppb of sodium and iron. Before being utilized in the process of the invention, the ion exchange resin must be treated with water and then a mineral acid solution to reduce the metal ion level. Preferably the ion exchange resin is initially rinsed with DI water, followed by a mineral acid solution, such as a 10 percent sulfuric acid solution, rinsed again with deionized water, treated again with the mineral acid solution and once more rinsed with deionized water. Before purifying the photoresist composition solution, it is critical that the ion exchange resin is first rinsed with a solvent which is the same as, or at least compatible with, the solvent for the photoactive compound..

The subject process also comprises: a) washing an acidic ion exchange resin with water, preferably deionized water, followed by washing with a mineral acid solution (e.g. a 5-98% solution of sulfuric, nitric or hydrochloric acid) and washing the resin with DI water, and thereby reducing the level of sodium and iron ions in the ion exchange resin to less than 100 ppb each, preferably less than 80 ppb and most preferably no more than 50 ppb; b) washing a basic ion exchange resin with water, preferably deionized water, followed by washing with a base solution (e.g. 1-18% ammonium hydroxide solution and washing the resin with DI water, and thereby reducing the level of sodium and iron ions in the ion exchange resin to less than 100 ppb each, preferably less than 80 ppb and most preferably no more than 50 ppb; c) mixing the prewashed acidic ion exchange resin and prewashed basic ion exchange resin in the ratio of from 5 to 95 or 95 to 5 by weight, most preferably about 50 to 50 by weight, and washing the mixture with DI water; d) washing the ion exchange resin mixture with a solvent which is the same as, or at least compatible with the solvent to be used to provide a solution of the photoactive compound to remove substantially all of the water; e) providing a solution of 5 to 40 weight percent of a photoactive compound in a suitable solvent; f) passing the photoactive compound solution through the ion exchange resin mixture and reducing the level of sodium and iron ions in the solution to less than

50 ppb each, preferably less than 20 ppb and most preferably less than 10 ppb; g) formulating a photoresist composition by providing an admixture of: (i) the treated photoactive compound; (ii) a suitable alkali soluble novolak resin; and (iii) a suitable photoresist solvent. If the photoactive compounds or any of its components contains one or more constituents which will react chemically with either the acidic or the basic ion exchange resin, the photoactive compound or component should be initially formulated without such constituents This will provide a photoactive compound or component substantially free of any constituents which will react with either the acidic or the basic ion exchange resin. The solution of the photoactive compound or component, e.g. a solution of from about 5 to 40 weight percent in a suitable solvent, is passed through the ion exchange resin. Such solutions may typically contain from 500 to 20,000 ppb each of sodium and iron ions. During the process of the present invention, these levels are each reduced to as low as 100 ppb, or lower, each.

Suitable photoresist solvents (which are preferably deionized) for the photoactive compound and the photoresist composition include diglyme, propylene glycol monoethyl either acetate (PGMEA), ethyl lactate, ethyl-3-ethoxypropionate, mixtures of ethyl lactate and ethyl-3-ethoxy proprionate, 2-heptanone, xylene, butyl acetate, ethylene glycol monoethyl ether acetate and mixtures of two or more of these solvents.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Photoresist coatings are particularly suitable for application to thermally grown silicon/silicon dioxide-coated wafers, such as are utilized in the production of microprocessors and other miniaturized integrated circuit components. Aluminum aluminum oxide or gallium arsenide wafers can also be used. The substrate may also comprise various polymeric resins, especially transparent polymers such as polyesters. The substrate may have an adhesion promoted layer of a suitable composition, such as one containing hexa-alkyl disilazane. The photoresist is coated onto the substrate composition, and the substrate is treated at a temperature from about 70°C to about 110°C for from about 30 seconds to about 180 seconds on a hot plate or for from about 15 to about 90 minutes in a convection oven. This temperature treatment is selected in order to reduce the concentration of residual solvents in the photoresist, while not causing substantial thermal degradation of the photosensitizer. In general, one desires to minimize the concentration of solvents and this first temperature treatment is conducted until substantially all of the solvents have evaporated and a thin coating of photoresist composition, on the order of one micron in thickness, remains on the substrate.

In a preferred embodiment the temperature is from about 85°C to about 95°C. The treatment is conducted until the rate of change of solvent removal becomes relatively insignificant. The temperature and time selection depends on the photoresist properties desired by the user, as well as the equipment used and commercially desired coating times. The coating substrate can then be exposed to actinic radiation, e.g., ultraviolet radiation, at a wavelength of from about 300 nm to about 450 nm, x-ray, electron beam, ion beam or laser radiation, in any desired pattern, produced by use of suitable masks, negatives, stencils, templates, etc.

The substrate is then optionally subjected to a post exposure second baking or heat treatment either before or after development. The heating temperatures may range from about 90°C to about 120°C, more preferably from about 100°C to about 110°C. The heating may be conducted for from about 30 seconds to about 2 minutes, more preferably from about 60 seconds to about 90 seconds on a hot plate or about 30 to about 45 minutes by convection oven.

The exposed photoresist-coated substrates are developed to remove the image- wise exposed areas by immersion in an alkaline developing solution or developed by spray development process. The solution is preferably agitated, for example, by nitrogen burst agitation. The substrates are allowed to remain in the developer until all, or substantially all, of the photoresist coating has dissolved from the exposed areas. Developers may include aqueous solutions of ammonium or alkali metal hydroxides. One preferred hydroxide is tetramethyl ammonium hydroxide. After removal of the coated wafers from the developing solution, one may conduct an optional post- development heat treatment or bake to increase the coating's adhesion and chemical resistance to etching solutions and other substances. The post-development heat treatment can comprise the oven baking of the coating and substrate below the coating's softening point. In industrial applications, particularly in the manufacture of microcircuitry units on silicon/silicon dioxide-type substrates, the developed substrates may be treated with a buffered, hydrofluoric acid base etching solution. The following specific examples will provide detailed illustrations of the methods of producing and utilizing compositions of the present invention. These examples are not intended, however, to limit or restrict the scope of the invention in any way and should not be construed as providing conditions, parameters or values which must be utilized exclusively in order to practice the present invention.

Example 1 50 grams of wet acidic ion exchange resin (AG® 50WX12, from Biol Rad) was placed in a conical flask and deionized water was added so that all of the resin beads were under water. The slurry of ion exchange resin was poured into a glass column. The resin was allowed to settle to the bottom and the column was back flushed with deionized water for 25 minutes. The resin was again allowed to settle to the bottom. A 10 percent sulfuric acid solution was passed down through the resin bed at a flow rate such that the residence time was 14 minutes. Six bed volumes of the acid solution were passed through the resin bed. Deionized water was passed down through the resin bed at the same flow rate until the measured pH of the effluent water matched the pH of 6 for fresh deionized water. Two bed volumes of electronic grade acetone were passed down through the column, followed by two bed volumes of PGMEA, at the same flow rate as before. A 20 percent solution of tricyclodecanedimethylol-2,l,5-diester (TDQ) in PGMEA containing 660 ppb sodium and 560 ppb iron was passed down through the column at a flow rate such that the residence time was 14 minutes. The materials obtained by this purification contained less than 10 ppb sodium and 90 ppb iron.

Example 2 Example 1 was repeated with Amberlyst® 15 acidic cationic exchange resin (from Rohm & Haas). The final solvent in the column was diglyme instead of PGMEA. A solution of 20 percent solution of tricyclodecanedimethylol-2, 1 ,5-diester (TDQ) in diglyme was passed through the column at a flow rate such that the residence time was 14 minutes. The untreated solution had 80 ppb sodium and 100 ppb iron. The cationic exchange resin treated solution had less than 20 ppb sodium and 10 ppb iron. Example 3 Example 1 was repeated with 5% of the 2,1,4-diazonaphthoquinone sulfonic acid ester of 2,3,4,4'-tetrahydroxybenzophenone (91-92% esterification) (RI 191 made by Hoechst Celanese Corporation) in PGMEA containing 270 ppb sodium and 270 ppb iron and the materials obtained by this purification process contained less than 10 ppb sodium and 90 ppb iron.

Example 4 Into a glass column was poured a slurry of cleaned Amberlyst® 15 cationic exchange resin treated according to the procedure of Example 1 and DI water, on top of it a slurry of Modified Deionizing Resin Blue BB (MDR Blue B) from Hoechst Celanese

Corporation, lab sample) and DI water was added. This mix bed was washed initially with DI water and then with distilled acetone. A reaction mixture of RI 292 in acetone (RI 292 is a mixed ester of trishydroxyphenylethane and 2,1,4- and 2,1,5- diazonaphthoquinone sulfonylchloride made by Hoechst Celanese Corporation) was passed through the above mixed bed column under nitrogen pressure (68.94 kilopaschals/10 psi). The untreated solution had a metal ion content as follows: 20 ppb sodium, 1700 ppb iron. The treated samples had a very low level of metal ions 20 ppb sodium and 40 ppb iron.

Claims

WHAT IS CLAIMED

1. A process for producing a photoactive compound having a very low level of metal ions comprising^* a) washing an acidic ion exchange resin with water, followed by washing with a mineral acid solution and washing the resin with deionized water, thereby reducing the level of sodium and iron ions in the ion exchange resin to less than 100 ppb each, b) washing the ion exchange resin with a solvent which is the same as, or at least compatible with, the solvent to be used to provide a solution of the photoactive compound to remove substantially all of the water, c) providing a solution of 5 to 40 weight percent of a photoactive compound in a suitable solvent, d) passing the photoactive compound solution through the ion exchange resin and reducing the level of sodium and iron ions in the solution to less than 100 ppb each

2 A process for producing a photoresist composition comprising providing an admixture of. a) a photoactive compound produced by the process of claim 1 , b) a suitable alkali soluble novolak resin; and c) a suitable photoresist solvent

3 The method of claim 1 wherein said ion exchange resin is washed to reduce the level of sodium and iron ions to less than 80ppb each

4 The method of claim 1 wherein said ion exchange resin is washed to reduce the level of sodium and iron ions to less than 50 ppb each

5 The method of claim 1 wherein said photoresist solvent is selected from the group consisting of propylene glycol methyl ether acetate, ethyl lactate and ethyl-3 - ethoxyproprionate

6. A process for producing a photoactive compound having a very low level of metal ions comprising: a) washing an acidic ion exchange resin with water followed by washing with a mineral acid solution and washing the resin with deionized water, and thereby reducing the level of sodium and iron ions in the ion exchange resin to less than 100 ppb each; b) washing a basic ion exchange resin with water followed by washing with a base solution and washing the resin with deionized water, and thereby reducing the level of sodium and iron ions in the ion exchange resin to less than 100 ppb each; c) mixing the prewashed acidic ion exchange resin and prewashed basic ion exchange resin in the ratio of from 5 to 95 or 95 to 5 by weight and washing the mixture with deionized water; d) washing the ion exchange resin mixture with a solvent which is the same as, or at least compatible with the solvent to be used to provide a solution of the photoactive compound to remove substantially all of the water; e) providing a solution of 5 to 40 weight percent of a photoactive compound in a suitable solvent; f) passing the photoactive compound solution through the ion exchange resin mixture and reducing the level of sodium and iron ions in the solution to less than 100 ppb each.

7. A process for producing a photoresist composition by providing an admixture of: a) a suitable photoactive compound produced by the process of claim 6; b) a suitable alkali soluble novolak resin; and c) a suitable photoresist solvent.

8. The method of claim 6 wherein said ion exchange resin is washed to reduce the level of sodium and iron ions to less than 80 ppb each.

9. The method of claim 6 wherein said ion exchange resin is washed to reduce the level of sodium and iron ions to less than 50 ppb each.

10. The method of claim 6 wherein said photoresist solvent is selected from the group consisting of propylene glycol methyl ether acetate, ethyl lactate and ethyl-3 - ethoxypropionate .