WO2013044210A2

WO2013044210A2 - Stripping compositions having mixtures of alkylamides

Info

Publication number: WO2013044210A2
Application number: PCT/US2012/056872
Authority: WO
Inventors: Hao-Chun Lee; Taishih Maw; Fu-Chi Wu; Kai-Chien CHANG; Hsu-Chiang FANG
Original assignee: E. I. Du Pont De Nemours And Company
Priority date: 2011-09-23
Filing date: 2012-09-24
Publication date: 2013-03-28
Also published as: WO2013044210A3; CN103019049B; TWI567510B; KR20140071445A; TW201317721A; CN103019049A

Abstract

The present invention discloses stripping compositions having mixtures of alkylamides. The stripping compositions comprise 50-70% by weight of N-methylformamide, 30 50% by weight of N,N-dimethylacetamide, and the remainder being water. The stripping compositions have the advantages of being water miscible, being non-corrosive to copper or copper alloy, and having low toxicity to humans and the environment. Due to the stripping composition comprising two main components, the used stripping solution can be easily recovered by fractional distillation and reconstituted to the original formulation, and recycled in the manufacturing process to provide benefits including cost reduction and environmental protection. Also disclosed in the present invention are methods for removing photoresist using the stripping compositions.

Description

STRIPPING COMPOSITIONS HAVING MIXTURES OF ALKYLAMIDES

Field of the Invention

This invention relates to a stripping composition containing mixtures of alkylamides, particularly to an alkylamide stripping

composition applied to photoresist removal or to cleaning or removal of the aligning film.

Description of the Prior Art

The science and technology industry develops and progresses continuously, and this includes thin-film transistor liquid crystal display (TFT-LCD) technology. Because it has evolved with the advantages of small capacity without taking up space, low power consumption, low radiation, and product durability, thin-film transistor liquid crystal displays have gradually replaced cathode-ray tube displays. With an increasing demand for displays in general, the output of thin-film transistor liquid crystal displays in particular rises gradually, in turn driving the evolution of the technology. With fifth, sixth, seventh, and even eighth generation plants constantly being built, the amount invested in thin-film transistor liquid crystal displays is also growing. Therefore, it can be expected that future technological progress and economies of scale will be alarming. However, with the continuous evolution of the technology, the glass substrates for thin-film transistor liquid crystal displays have also been constantly enlarged, and consumption of various chemicals has likewise increased continuously. In addition to consuming large amounts of money and resources, the manufacturing process of thin-film transistor liquid crystal displays produces chemical substances that have become a considerable burden on the environment and violate the spirit of environmental protection. Therefore, to recover chemical substances after reaction during the manufacturing process not only can reduce the cost of production, but it can also enhance market competitiveness and furthermore contribute significantly to environmental protection.

l During the manufacturing process of thin-film transistor liquid crystal displays, the amount of stripping agent (stripper) used is quite considerable. Therefore, if the stripper can be recovered and recycled, it would help

significantly in terms of both economic return and environmental protection. Chemical substances generated during the photoresist removal process mainly include water, remaining stripper, and substances generated after the photoresist and other reactions. However, to recover the stripper, the recovery system used in existing thin-film transistor liquid crystal display plants involves recovering various substances in light of their characteristics of different boiling points and using the technology of distillation; also said stripper needs to be recombined in accordance with its original percentages after recovery.

However, the known composition of the stripper is pretty complicated, and it may consist of 4-6 kinds of chemical substances and therefore be very difficult to recover, and the stripper after recovery is required to undergo a very complicated reduction process before it can be recombined. Therefore, through recovery of known strippers in actual application it is difficult to attain reasonable economic returns, thus reducing the plant's intention to use the stripper recovery system. In this way, not only is the opportunity to reduce costs lost, but it will result in a considerable burden on the environment.

In addition, the components of many known strippers are highly volatile and are likely to cause an excessive evaporation speed, thus restricting the bath life of these strippers. So in storing and using these strippers, it is necessary to take special preventive measures for human and environmental safety.

However, because of the simple composition of strippers available so far they cannot remove the photoresist entirely from various substrates. It usually requires a very long retention time or repeated coatings before it can be removed.

Therefore, high expectations have arisen for a high-performance stripper that is capable of removing the photoresist entirely, that is not corrosive, that has a low evaporation rate and low viscosity, and that is miscible with water, so that no other additional solvents are required to remove said stripper, that is not toxic to the human body and environmentally friendly, and that is easy to recover.

Disclosed in KR2010033653 is an anhydrous stripper that comprises 70- 99 wt% of a mixture of N-methylformaldehyde (NMF) and N, N- dimethylacetamide (DMAC) and 0.1 -10 wt% tetraethylene glycol. And the weight ratio of N-methylformaldehyde to N, N-dimethylacetamide is

1 : 1 to 2 (i.e., less than or equal to 1 ).

Summary of the Invention

Provided in the present invention is a stripper containing a mixture of alkylamides, wherein N-methylformaldehyde (NMF), N, N-dimethylacetamide (DMAC), and water are mixed to serve as a photoresist stripper, aligning film cleaner, or aligning film stripper.

Provided in the present invention is an alkylamide stripper. As an alkylamide stripper made with N-methylformaldehyde and N, N- dimethylacetamide as the two primary components, it can easily strip a photoresist without damaging the copper film or copper alloy film exposed below the photoresist, therefore, the alkylamide stripper has the advantage of being applicable to the manufacturing process of copper.

Provided in the present invention is a stripper containing a mixture of alkylamides, and as the alkylamide stripper consists only of two primary components with a difference in boiling point under atmospheric pressure greater than 30°C, it can be easily recovered through the technology of fractional distillation, and the alkylamide stripper recovered can be recombined and reduced and recycled, thus attaining the effects of reduction of production cost and environmental protection.

To attain the effects mentioned above, the present invention provides an alkylamide stripper that comprises N-methylformaldehyde, which accounts for 50- 70% of the total weight; N, N-dimethylacetamide, which accounts for 30-50% of the total weight; and water, which accounts for the remainder of the total weight.

By means of implementation of this invention, at a minimum the following effects can be attained:

I. As the alkylamide stripper is not corrosive to copper or copper alloy, therefore, it is well suited to the manufacturing process of copper.

II. As the alkylamide stripper is simple in composition, has a low evaporation rate and low viscosity, and is miscible with water, so that no other additional solvents are required to remove said stripper, therefore, the used alkylamide stripper can be easily recovered, to attain the effects of reduction of production cost and environmental protection.

In order that any technical personnel in this field can understand the technical content of the present invention and implement it accordingly, the content, range of claims, and attached drawings disclosed in this specification will be described in the preferred embodiment.

Brief Description of the Drawings

Figure 1 to Figure 3 are schematic diagrams of examples illustrating the flow process of the application of an alkylamide stripper of the present invention to the removal of a photoresist.

Figure 4 is an optical microscope diagram of Example 1 .

Figure 5 is a scanning electron microscope diagram of Example 1.

The symbols for the primary components in the drawings are as follows: 10 substrate; 20 copper metal film; 30 photoresist.

Detailed Description of the Preferred Embodiment

The stripper of the present invention is an alkylamide stripper that comprises N-methylformaldehyde, N, N-dimethylacetamide, and water; the alkylamide stripper in the examples of the present invention can be expressed using the following formula:

Wherein R" is methyl; R and R' are the same, being hydrogen or methyl. When R and R' are both hydrogen, it is N-dimethylformaldehyde (CAS No.: 123- 39-7); whereas when R and R' are both methyl, it is N, N-dimethylacetamide (CAS No.: 127-19-5). Besides, the chemical formula of the alkylamide stripper of the present invention also can respectively be expressed as C₂H₅NO (HC(=0)NHCH₃; N-methylformaldehyde) and C₄H₉NO (CH₃C(=0)N(CH₃)₂; N, N-dimethylacetamide).

A specific example of the present invention is that the alkylamide stripper of the present invention does not contain tetraethylene glycol. Another specific example of the present invention is that the alkylamide stripper of the present invention primarily comprises N-methylformaldehyde, which accounts for 50-70% of the total weight; N, N-dimethylacetamide, which accounts for 30-50% of the total weight; and water, which accounts for the remainder of the total weight.

Generally speaking, N-methylformaldehyde in the alkylamide stripper of the present invention accounts for 50-70% of the total weight, preferably 55-65%, and more preferably 58-62%. And N, N-dimethylacetamide in the alkylamide stripper of the present invention accounts for 30-50% of the total weight, preferably 35-45%, and more preferably 38-42%. Water in the alkylamide stripper of the present invention accounts for the remainder of the total weight, usually less than 5%, preferably less than 3%, more preferably less than 1 %, and most preferably less than 0.1 %.

Another specific example of the present invention is that the alkylamide stripper of the present invention basically does not contain water.

Another specific example of the present invention is that the weight ratio of N-methylformaldehyde to N, N-dimethylacetamide is greater than 1 .

The stripper of the present invention can be easily prepared through mixing various components at room temperature.

As shown in Figure 1 to Figure 3, the specific flow process of application of the alkylamide stripper of the present invention to stripping the residual photoresist 30 in the manufacturing process of copper is described.

As shown in Figure 1 , in the manufacturing process of copper, a copper metal film 20, such as a copper film or copper alloy film, is set on a substrate 10, and the copper metal film 20 is coated with a photoresist 30, and the photoresist 30 is patterned, so that the photoresist 30 can be used as a shield. Then as shown in Figure 2, the copper metal film 20 not covered by the photoresist 30 is etched and removed through an etching process, thus making a copper circuit.

Finally, as shown in Figure 3, the residual photoresist 30 on the copper metal film 20 can be removed using the alkylamide stripper of the present invention, so that the alkylamide stripper of the present invention can serve as a photoresist stripper for the photoresist 30, and as the alkylamide stripper is not corrosive to copper or copper alloy, therefore, it can protect the copper circuit from damage when the residual photoresist 30 is removed, thus reducing the resistance and capacitance delay (RC-Delay) effect of the electronic

components.

The stripper of the present invention can be used to make electronic components with copper or copper alloy as the circuit material. Here, copper alloy with copper as the primary component refers to copper alloy containing greater than or equivalent to 90% in mass, and copper alloy containing other elements such as Sn, Ag, Mg, Ni, Co, Cr, Ti, Mo, Si or Al, etc.

A specific example of the present invention is the alkylamide stripper of the present invention, and it is a photoresist stripper for removing the photoresist on the surface of the electronic component. The metal circuit of said electronic component as mentioned above is composed of copper or copper alloy.

The implementation of the alkylamide stripper of the present invention puts the photoresist and/or the side wall polymer (SWP) in contact with the stripper of the present invention. Actual status, such as temperature, time, etc., is to be determined by the properties and thickness of the photoresist material and/or the side wall polymer to be removed, and other factors such as familiarity by technical personnel in this field. Generally speaking, photoresist stripping is a process wherein at a temperature in the range of 25-90°C the electronic component with the photoresist on the surface contacts (such as by means of spraying and dipping) the stripping composition of the present invention for a certain period of time (5-30 minutes), is washed with water, and the electronic component described is dried with an inert gas.

The photoresist materials in the examples are organic polymer materials, including the electron beam photoresist, X-ray photoresist, ion beam photoresist, etc. Actual examples of special organic polymer materials include n-photoresist containing phenol formaldehyde resin or poly (p-vinyl phenol), photoresist containing polymethyl methacrylate, etc.

Examples of the residues (side wall polymers) after etching, ion beam bombardment or plasma treatment in particular include: metal organic compounds and/or inorganic salts, oxides, hydroxides or residue that can be combined alone with the organic polymer resin of the photoresist to form a film or composition. Traditional substrates that technical personnel in this field are familiar with include but are not limited to silicon, silicon dioxide, aluminum, aluminum alloy, copper, copper alloy, etc., and the photoresist material and/or the side wall polymer can be removed from said substrate using the stripper of the present invention.

In addition, provided in the present invention is a method to remove the photoresist from the surface of the electronic component. Said method consists of the following steps: at a temperature in the range of 25-90°C, the electronic component with the photoresist on the surface contacts the alkylamide stripper of the present invention for 5-30 minutes, to remove said photoresist. In the method described above, the metal circuit of said electronic component is composed of copper or copper alloy.

A specific example of the method of the present invention is one wherein the alkylamide stripper composed of N-methylformaldehyde, which accounts for 50-70% of the total weight, N, N-dimethylacetamide, which accounts for 30-50% of the total weight, and water, which accounts for the remainder of the total weight, contacts the photoresist-containing electronic component at a

temperature in the range of 50-90°C for 5-30 minutes, thus removing the photoresist.

Another specific example of the method of the present invention is one wherein the alkylamide stripper composed of N-methylformaldehyde, which accounts for 55-65% of the total weight, N, N-dimethylacetamide, which accounts for 35-45% of the total weight, and water, which accounts for the remainder of the total weight, contacts the photoresist-containing electronic component at a temperature in the range of 55-85°C for 5-30 minutes, thus also removing the photoresist.

Yet another specific example of the method of the present invention is one wherein the alkylamide stripper composed of N-methylformaldehyde, which accounts for 58-62% of the total weight, N, N-dimethylacetamide, which accounts for 38-42% of the total weight, and water, which accounts for the remainder of the total weight, contacts the photoresist-containing electronic component at a temperature in the range of 60-80°C for 5-30 minutes, thus also removing the photoresist. The alkylamide stripper of the present invention can serve not only as a photoresist stripper for electronic components, but it is also applicable to stripping or cleaning aligning films having polyimide as the primary component.

A specific example of the present invention is the alkylamide stripper of the present invention, which serves as an aligning film stripper or an aligning film cleaner, wherein said aligning film is composed of polyimide.

The alkylamide stripper of the present invention not only is applicable to the manufacturing process of LCD or semi-conductor components, but as the alkylamide stripper is not corrosive to copper or copper alloy, it is also particularly applicable to the manufacturing process of copper to remove the photoresist or to stripping or cleaning the aligning film.

Besides, as the alkylamide stripper consists only of two primary components, which are N-methylformaldehyde and N, N-dimethylacetamide, with the difference in their boiling points under atmospheric pressure greater than 30°C, therefore, when the manufacturing process is over the alkylamide stripper can be easily separated from the liquid waste from the reaction and recovered through the technology of fractional distillation, and said alkylamide stripper can be easily recombined and reduced in accordance with the original percentage after the recovery, so as to recycle the alkylamide striper recovered, thus attaining the effects of reduction of production cost and environmental protection.

The alkylamide stripper of the present invention is particularly useful and advantageous, for multiple reasons as described below. The stripper of the present invention is miscible with water, not corrosive, and basically nontoxic to human body and the environment. As its evaporation rate is slower than known strippers, it can be recycled many times, and without having to take complicated safety precautions. Meanwhile, as the waste of the coat stripped can be removed at any time, it is convenient for collection and treatment. At the same working temperature, the stripper of the present invention has even better stripping effects. Besides, the stripper of the present invention is simple in composition and easy to prepare, and all that is needed is to mix its primary components at room temperature, without having to take any special safety precautions for humans or the environment. The following is an even more detailed description of the present invention with examples that are absolutely not intended to restrict the applications of the present invention.

Examples

A. Test of strippability and corrosiveness on copper foil

A piece of copper foil of proper size (about 6 cm 26 cm, about 2.2 g) is cut off, and the surface of the copper foil is cleaned using a micro etching agent, to remove the oxides on the surface. After it is washed clean with deionized water and baked dry, the weight (initial weight) of the copper foil is accurately measured. The copper foil is placed in a flask containing 400 g of the stripper (the components are listed in Table 1 ), to test its corrosiveness for copper, and after it is heated at 80°C for 8 h, the weight of the copper foil is accurately measured. The weight loss of the copper foil is measured and its corrosion rate is calculated (See Table 2).

Table 1

Table 2

B. Test of film-stripping effects

The copper foil substrate is of the standard specifications of an LCD panel, the photoresist width is about 3 μηη, and the thickness is 1 -1 .5 μηη.

Strippers of different formulas are heated to 80°C, the substrate to be tested is placed in the stripper for 5 seconds and taken out, then it is dipped in water for 3 seconds, before the water stain is blown dry using an air dryer. The residue of the photoresist before the stripping and after the stripping is observed using an optical microscope and scanning electron microscope, as shown in Figure 4 and Figure 5, and results of the assessment are listed on Table 3.

Photoresist stripping effects:

: With extremely little photoresist residue, and also very little back stain of the photoresist.

o: With a small amount of photoresist residue, and also a small amount of back stain of the photoresist.

·: With some photoresist circuit pattern afterimage, and some back stain of the photoresist. Table 3

It can be observed in the photo of the optical microscope that

Comparative Example 1 (pure NMF) and Comparative Example 2 (pure DMAC) are the worst in terms of the film-stripping effects, as there is some photoresist circuit pattern afterimage, and some back stain of the photoresist; Comparative Example 4 is slightly better than Comparative Example 1 and Comparative Example 2, as there is a small amount of photoresist residue, and also a small amount of back stain of the photoresist; and the other formulas can all effectively strip the photoresist, and the back stain of the photoresist is very little.

It can be observed in the photo taken by the scanning electron microscope that all photoresist circuit patterns are invisible, indicating that the photoresist has been stripped, whereas there is still a small amount of photoresist residue visible in photos of Comparative Example 1 and Comparative Example 2, and it is not visible in other formulas, indicating that these formulas are all well capable of stripping film.

The results listed in Table 3 indicate that compared with individual alkylamide components (Comparative Example 1 and Comparative Example 2), the combination of two alkylamides from the stripper of the present invention provides a better synergistic stripping effect. C. Test of the loss of stripper

The strippers of Comparative Example 3 (DMAC 60% + NMF 40%) and Example 2 (DMAC 40% + NMF 60%), 50 g of each, are placed in a 100 mL flask, heated to 80°C, heated continuously and changes in its overall weight are tracked.

Table 4

Analysis and comparison of the data listed in Table 4 shows that due to high volatility of DMAC, during heating, there is a relatively large weight loss of the stripper, as after heating for 10 hours the remaining stripper in Comparative Example 3 is 63.2% of the original whereas the remaining stripper in Example 2 is 75.8% of the original, the former having a greater loss by 12.6%. As the stripper is used mostly in a heated status (50°C-90°C), to reduce the loss of the stripper in the process of heating is helpful for both environmental protection and enhancement of the working time.

With the stripper of the present invention, due to a higher content of NMF (accounting for 50-70wt% of the total weight), the overall vapor loss speed is relatively slow, so that said stripper has an even longer continuous working time, and less stripper enters wastewater and waste gas in the form of vapor. D. Flash point test

The stripper needs to be heated to within a certain temperature range (60°C-90°C) before attaining the required stripping effect. However, at this operating temperature, safety becomes an important consideration. The flash point of DMAC is 63°C, while the flash point of NMF is 1 19°C. The flash point is tested using the closed cup ASTM D93 method, and the flash point of

Comparative Example 3 is 80.5 °C, while that of Example 2 is 88.5 °C. The flash point of the stripper of the present invention is higher than that of known strippers (Comparative Example 3), and this helps with enhancing the safety of the factory operation.

The examples mentioned above are for describing the characteristics of the present invention, with the aim of helping technical personnel of this field to understand the content of the present invention and implement it accordingly, instead of restricting the coverage of the claims of the present invention;

therefore, all other equivalent modifications or changes completed without deviating from the spirit disclosed in the present invention should still be covered by the claims attached.

Claims

Claims What is claimed is:

1. An alkylamide stripping composition comprising 50-70% by weight of N methylformamide, 30-50% by weight of Ν,Ν-dimethylacetamide and the remainder being water, wherein the percents are relative to the total weight of the composition.

2. The alkylamide stripping composition of Claim 1 is essentially free of tetraethylene glycol.

3. The alkylamide stripping composition of Claim 1 , wherein the weight ratio of N methylformamide to Ν,Ν-dimethylacetamide is greater than 1 .

4. The alkylamide stripping composition of Claim 1 comprising 55-65% by weight of N-methylformamide, 35-45% by weight of Ν,Ν-dimethylacetamide and less than 5% by weight of water, wherein the percents are relative to the total weight of the composition.

5. The alkylamide stripping composition of Claim 1 comprising 58-62% by weight of N-methylformamide, 38-42% by weight of Ν,Ν-dimethylacetamide and less than 3% by weight of water, wherein the percents are relative to the total weight of the composition.

6. The alkylamide stripping composition of Claim 1 is a photoresist stripper for removing photoresist from a surface of an electronic component.

7. The alkylamide stripping composition of Claim 6, wherein the electronic component has a metal wire system composed of copper or copper alloy.

8. The alkylamide stripping composition of Claim 1 is a stripper or a cleaner for an aligning film composed of polyimide.

9. A method for removing photoresist from a surface of an electronic component comprising: contacting the photoresist of the electronic component with the alkylamide stripping composition of Claim 1 at a temperature in the range of 25-90°C for 5 seconds to 30 minutes to remove the photoresist.

10. The method of Claim 9, wherein the electronic component has a metal wire system composed of copper or copper alloy.