KR101505618B1 - Composition for the formation of a protective thin film having high heat resistance and chemical resistance, and method for preparing a protective thin film using same - Google Patents

Abstract

The present invention relates to a protective thin film composition having high heat resistance and high chemical resistance including a coupling compound and a method for producing a protective thin film using the same, wherein the protective thin film obtained from the protective thin film composition according to the present invention has heat Can maintain its shape without deformation and exhibits excellent chemical resistance to an acid, a base or an organic solvent, and can maintain the shape of the exposed interface even in the plasma treatment, so that it can perform an excellent function as a protective film against the underlying material .

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protective thin film composition having high heat resistance and high internal chemical resistance and a method for producing a protective thin film using the same. BACKGROUND ART [0002]

The present invention relates to a protective film composition having high heat resistance and high chemical resistance including a coupling compound and a method for producing a protective film using the same.

Conventionally, organic or imide-based compositions used for a flattening film, an insulating material, or a protective thin film for a display device or a semiconductor device occupy the majority of the composition. The acrylic composition is easy to synthesize, and has excellent processability and coating performance when applied to a device, but its properties such as heat resistance and chemical resistance are limited to a certain extent. The imide-based composition has excellent properties such as heat resistance and chemical resistance, There are limitations in that solvents are restricted due to this difficult and low solubility.

Thus, the present inventors have found a coupling compound which is easy to synthesize and exhibits excellent heat resistance, solubility and chemical resistance, and using this, a curable resin composition used for forming a flattening film, an insulating material or a protective thin film of a display device or a semiconductor device The present invention has been completed.

Accordingly, an object of the present invention is to provide a protective thin film composition which exhibits excellent heat resistance, solubility and chemical resistance.

Another object of the present invention is to provide a method for producing a protective thin film using the protective thin film composition.

It is still another object of the present invention to provide a protective thin film produced according to the above method.

It is still another object of the present invention to provide a semiconductor device comprising the protective thin film composition.

It is still another object of the present invention to provide a method of manufacturing the semiconductor device.

In order to accomplish the above object, the present invention provides a protective thin film composition comprising an aromatic compound having a repeating unit represented by the following formula (1):

[Chemical Formula 1]

In this formula,

A is

, ≪ / RTI >

Wherein R ₁ is hydroxy or -OR (wherein R is C _{1 -10} alkyl group or a C _{6 -10} aryl group),

R ₂ is hydrogen, a hydroxy group, -OR (wherein R is a C _1-10 alkyl group or a C _6-10 aryl group), a C _1-5 alkyl group, a C _6-10 aryl group, a nitro group (-NO ₂ ) -NR'R " wherein R 'and R " are each independently hydrogen or a C _1-5 alkyl group.

In order to accomplish the above other objects, the present invention provides a method for manufacturing a protective thin film, comprising coating the protective thin film composition on a substrate and then performing heat treatment.

According to another aspect of the present invention, there is provided a protective thin film produced according to the above method.

According to another aspect of the present invention, there is provided a semiconductor device including an insulating film including a protective thin film composition comprising an aromatic compound having a repeating unit represented by the general formula (1).

According to another aspect of the present invention,

Forming an etching target layer on a semiconductor substrate;

Forming a mask pattern on the etch target layer; And

And patterning the etching target layer using the mask pattern,

Wherein the mask pattern comprises an aromatic compound having a repeating unit represented by the formula (1).

The protective thin film obtained from the protective thin film composition according to the present invention maintains its shape without thermal deformation even at a high temperature of 300 ° C or higher and exhibits excellent chemical resistance to an acid, a base or an organic solvent. In addition, It is possible to perform an excellent function as a protective thin film against the underlying material.

1 shows a cross-sectional view of a semiconductor device comprising a protective thin film composition prepared according to one embodiment.
2 to 7 are cross-sectional views of semiconductor devices manufactured according to one embodiment of the present invention.
<Description of Symbols>
100: semiconductor substrate
200:
310: a first interlayer insulating film
320: a second interlayer insulating film
330: a third interlayer insulating film
410: first wiring layer
420: second wiring layer
500: desired device pattern
501: etch target layer
600: mask pattern
601: mask layer
700: photoresist pattern

The present invention relates to a composition for forming a protective thin film at high temperature or exposure to a compound, and the protective thin film composition of the present invention is intended for surface protection of a lower material and selective chemical treatment.

The present invention provides a protective thin film composition comprising an aromatic compound having a repeating unit represented by the following formula (1):

In this formula,

A is

, &Lt; / RTI &gt;

Wherein R ₁ is a hydroxy group or -OR, wherein R is a C _1-10 alkyl group or a C _6-10 aryl group,

R ₂ is hydrogen, a hydroxy group, -OR (wherein R is a C _1-10 alkyl group or a C _6-10 aryl group), a C _1-5 alkyl group, a C _6-10 aryl group, a nitro group (-NO ₂ ) -NR'R &quot; wherein R 'and R &quot; are each independently hydrogen or a C _1-5 alkyl group.

로 이루어진 군에서 선택되고, R₁은 히드록시기 또는 -OCH₃이고, R₂는 히드록시기, -NH₂ 또는 -OCH₃이다.
Preferably, A is

, R ₁ is a hydroxy group or -OCH ₃ , and R ₂ is a hydroxy group, -NH ₂ or -OCH ₃ .

The aromatic compound may be prepared by coupling reaction of the compound represented by the formula A with 1,3,5-trioxane under an ordinary reaction condition in an organic solvent, preferably an acid such as toluenesulfonic acid ) Can be added.

The aromatic compound has a weight average molecular weight of 1,000 to 20,000, for example, 1,000 to 10,000.

The aromatic compounds exhibit a residual content (wt%) of not less than 93% at a high temperature of 350 ° C or higher, and exhibit excellent heat resistance and excellent solubility, which are completely dissolved in various organic solvents at room temperature (Experimental Examples 1 and 2).

The protective thin film composition of the present invention may contain, in addition to the above aromatic compounds, cyclohexanone, propylene glycol monomethyl ether acetate (PGMEA),? -Butyrolactone (GBL) A solvent selected from the group consisting of 2-pyrrolidone (NMP), chloroform, toluene, and mixtures thereof.

The composition of the present invention may comprise from 0.1 to 30% by weight of the aromatic compound, and from 70 to 99.9% by weight of the solvent, based on the total weight.

The present invention also provides a method for producing a protective thin film, comprising coating the protective thin film composition on a substrate and then heat-treating the substrate.

The coating method may be used without limitations as long as it is well known in the art, and may be a coating method such as spin-on-coating, slit coating, bar coating or spray coating.

The thickness of the protective thin film composition and the heat treatment conditions are not particularly limited, but the protective thin film composition may be applied on the substrate to a thickness of 10 nm to 5 탆, and the protective thin film composition may be applied at 200 to 600 캜, preferably 240 to 400 캜 Treated for 1 to 5 minutes to be cured to form a protective thin film. The protective film thus prepared may have a final thickness of 10 nm to 5,000 nm, preferably 50 nm to 500 nm.

According to one embodiment of the present invention, the protective thin film composition of the present invention can be heat-treated at 350 ° C for 2 minutes by coating with a spin coating method to form a protective thin film having a thickness of about 350 nm.

The protective thin film of the present invention thus fabricated can be applied to a surface treatment of metal mechanical parts, a packaging material for electrical parts, a protective film for displays or semiconductor processes, and more particularly to a flat panel display device, a planarizing film, Insulating material, a mask for selective treatment of the underlying film, and the like.

The present invention also provides a semiconductor device comprising a protective thin film produced by the above method. Specifically, the present invention provides a semiconductor device comprising an insulating film comprising a protective thin film composition comprising an aromatic compound having a repeating unit represented by the general formula (1).

1, a semiconductor device according to an embodiment includes a semiconductor substrate 100, an element portion 200, interlayer insulating films 310, 320, and 330, and wiring layers 410, 420, and 430 .

The semiconductor substrate 100 may be a silicon substrate. The semiconductor substrate 100 may include an insulating layer such as a silicon oxide layer.

The element portion 200 is formed on the semiconductor substrate 100. The element portion may be a transistor, an image sensor, or a capacitor.

The interlayer insulating films 310, 320, and 330 are formed on the semiconductor substrate 100. For example, a first interlayer insulating film 310 is formed on the semiconductor substrate 100. The first interlayer insulating film 310 covers the element portion 200.

Also, a second interlayer insulating film 320 is formed on the first interlayer insulating film 310. The second interlayer insulating film 320 covers the first wiring layer 410.

The third interlayer insulating film 330 is formed on the second interlayer insulating film 320. The third interlayer insulating film 330 covers the second wiring layer 420.

The first interconnection layer 410 is disposed on the first interlayer insulating film 310. The first wiring layer 410 is connected to the device unit 200.

The second interconnection layer 420 is disposed on the second interlayer insulating film 320. The second wiring layer 420 is connected to the device unit 200 and / or the first wiring layer 410.

The first interlayer insulating film 310, the second interlayer insulating film 320, and the third interlayer insulating film 330 may include the protective thin film composition according to the embodiments described above or the embodiments described later.

More specifically, in order to form the first interlayer insulating film 310, after the element portion 200 is formed on the semiconductor substrate 100, the protective thin film composition according to the present embodiments is coated. The protective thin film composition may be coated by a coating method such as spin-on-coating, slit coating, bar coating or spray coating.

Thereafter, the coated protective thin film composition is cured by a heat curing process or the like, and the first interlayer insulating film 310 may be formed.

In the same manner, the second interlayer insulating film 320 and the third interlayer insulating film 330 may be formed.

The present invention also provides a method of manufacturing a semiconductor device, comprising: forming an etching target layer on a semiconductor substrate; Forming a mask pattern on the etch target layer; And a step of patterning the etching target layer using the mask pattern, wherein the mask pattern comprises a protective film composition comprising an aromatic compound having a repeating unit represented by the formula (1) .

As shown in FIGS. 2 to 7, a semiconductor device can be manufactured using the protective thin film composition according to the present embodiments.

Referring to FIG. 2, an etching target layer 501 is formed on a semiconductor substrate 100. The etch target layer 501 may be a metal layer or a silicon layer.

Referring to FIG. 3, a mask layer 601 is formed on the etch target layer 501. The mask layer 601 may include a protective thin film composition according to the present embodiments. More specifically, the protective thin film composition is coated on the etching target layer 501. Thereafter, the coated protective thin film composition is cured, and the mask layer 601 is formed.

Referring to FIG. 4, a photoresist layer is formed on the mask layer 601, and the photoresist layer is subjected to an exposure process and a development process. Accordingly, a photoresist pattern 700 is formed on the mask layer 601.

Referring to FIG. 5, the mask layer 601 is patterned through the photoresist pattern 700. Accordingly, the mask pattern 600 is formed.

Referring to FIG. 6, the etching target layer 501 is etched through the mask pattern 600, and a desired device pattern 500 may be formed on the semiconductor substrate 100.

Referring to FIG. 7, the mask pattern 600 and the photoresist pattern 700 are removed. Thereafter, an additional layer is formed on the device pattern 500, and a semiconductor device can be formed.

Thus, the protective thin film composition according to the present embodiment can be used to form the mask pattern, and the semiconductor device can be formed through the mask pattern.

According to one embodiment of the present invention, the protective film formed using the composition of the present invention has a good overall shape. In addition, even when exposed to acids, bases and organic solvents, there is no change in thin film and thickness and excellent chemical resistance is exhibited. In addition, the plasma etching process (even when exposed to plasma) slows down the thin film consumption rate, Peeling and the like are not shown, so that they can be effectively used as protective films and masks of lower film quality (see Examples 3 to 5).

[Example]

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Example 1 Preparation of Protective Thin Film Aromatic Compounds

A 500 ml three-necked round flask was equipped with a thermometer, condenser, dropping funnel, and then immersed in an oil bath at 120 ° C. The thermostat was placed on a hot plate, and stirring was performed using a stirring magnet. At this time, the cooling water temperature of the condenser was fixed at 10 ° C.

To the three-necked flask, 63.0 g of 0.22 mol of binaphthol (1,1'-Bi-2-Naphthol), 25.8 g of 0.286 mol of trioxane (1,3,5-trioxane) and 212 g of cyclohexanone Cyclohexanone) was added and the mixture was dissolved. Then, 2.1 g of p-toluenesulfonic acid monohydrate (11 mmol) was added, followed by stirring for 12 hours. At this time , the temperature of the reactor was maintained at 120 캜.

During the reaction, a sample was taken from the reaction mixture and the weight average molecular weight of the sample was measured. When the desired weight average molecular weight was reached, the reaction time was determined as the completion time, and the reaction was gradually cooled at room temperature to terminate the reaction.

600 g of an 80:20 weight ratio n-hexane: ethanol mixed solution was prepared, and then the reactant obtained above was added dropwise with stirring. The supernatant obtained at this time was removed and only the aggregated polymer was obtained on the bottom of the flask. The residue was then dried in a vacuum oven at 80 DEG C for 24 hours to remove residual solvent and impurities to yield an aromatic compound.

The obtained compound was measured by gel permeation chromatography (GPC). As a result, the weight average molecular weight of the compound was 3,500 and the degree of dispersion was 1.9.

Example 2: Preparation of a protective thin film aromatic compound

Example 1 was repeated except that 63.0 g of 0.22 mol of binaphthol was added to the reactor in Example 1 instead of 63.0 g of 0.2 mol of dimethoxy-1,1-Binaphthalene. Compounds were prepared in the same manner.

The obtained compound was measured by GPC under THF. As a result, the compound had a weight average molecular weight of 2,200 and a dispersion degree of 2.1.

Example 3: Preparation of a protective thin film aromatic compound

Except that 62.8 g of 0.22 mol of 2-Amino-2'-Hydoxy-1,1'-Binaphthyl was added to the reactor instead of 63.0 g of 0.22 mol of binaphthol in Example 1 , The compound was prepared in the same manner as in Example 1.

The obtained compound was measured by GPC under THF, and as a result, the weight average molecular weight of the compound was 1,900 and the degree of dispersion was 2.2.

Example 4 Preparation of a Protective Thin Film Aromatic Compound

A 500 ml three-necked round flask was equipped with a thermometer, a condenser and a dropping funnel, and then immersed in an oil bath at 140 ° C. The thermostat was placed on a hot plate, and stirring was performed using a stirring magnet. At this time, the cooling water temperature of the condenser was fixed at 10 ° C.

To the three-necked flask, 65.7 g of 0.17 mol of dihydroxy-1,1'-bianthracene, 19.9 g of 0.22 mol of trioxane and 207 g of cyclohexanone as a solvent were added, . Then, 3.23 g of 17 mmol of paratoluenesulfonic acid was added and the reaction was carried out by stirring for 24 hours. At this time, the temperature of the reactor was maintained at 140 占 폚.

During the reaction, a sample was taken from the reaction mixture and the weight average molecular weight of the sample was measured. When the desired weight average molecular weight was reached, the reaction time was determined as the completion time, and the reaction was gradually cooled at room temperature to terminate the reaction.

600 g of an 80:20 weight ratio n-hexane: ethanol mixed solution was prepared, and the reaction product was added dropwise with stirring. The supernatant obtained at this time was removed and only the aggregated polymer was obtained on the bottom of the flask. The residue was then dried in a vacuum oven at 80 DEG C for 24 hours to remove residual solvent and impurities to yield a protective thin film aromatic compound.

The obtained compound was measured by GPC under THF. As a result, the compound had a weight average molecular weight of 1,700 and a dispersion degree of 2.4.

Comparative Example 1

A protective thin film composition was prepared according to the method described in Korean Patent Laid-Open Publication No. 2009-0130309.

Specifically, in a sealed reaction vessel equipped with a sufficiently dried stirrer, 3 mmol of 3,4-oxydianiline was dissolved in 7.3 ml of dehydrated N-methyl-1,2-pyrrolidone (NMP) And 3 mmol of p-toluenesulfonic acid-2-anhydride powder. The mixture was stirred at room temperature for 3 hours to obtain a clear, homogeneous, and tangent, linear polyimide precursor solution. This linear polyimide precursor solution was appropriately diluted to about 10 to 20 wt%, 10 mL of a dehydrating cyclization reagent (acetic anhydride / pyridine = volume ratio 7/3) was added dropwise, and the mixture was stirred at room temperature for 12 hours to imidize. The polyimide solution thus obtained was dropped into a large amount of methanol, and the precipitated polyimide was collected and dried to obtain a polyimide powder.

Comparative Example  2

In Comparative Example 1, 2,2-bis (4- (4-aminophenoxy) phenyl) propane (BAPP) and 4,4-oxydianiline -ODA) was used in combination (copolymerization composition = BAPP: 4,4-ODA = 70:30 (mol ratio)), a polyimide powder was obtained in the same manner as in Comparative Example 1.

Experimental Example 1: Evaluation of heat resistance

The compounds prepared in Examples 1 to 4 and Comparative Examples 1 and 2 were weighed in amounts of 20 mg each, and thermal stability was confirmed using a thermogravimetric analyzer. The thermogravimetric analyzer used was TF-DTA2000 from Bruker AXS, and the mass reduction was measured at a rate of 10 ° C / min under nitrogen. The results are shown in Table 1 below.

As shown in Table 1, the residual weight of the compounds of Examples 1 to 4 was 93% or more at a high temperature of 350 占 폚 or more, indicating excellent heat resistance.

Sample name Residual weight% (350 캜, wt%) Example 1 96.5% Example 2 95.3% Example 3 93.2% Example 4 97.7% Comparative Example 1 97.6% Comparative Example 2 95.8%

Experimental Example  2: Solubility evaluation

0.5 g of the compound powder prepared in Examples 1 to 4 and Comparative Examples 1 and 2 was added to 5 g of various solvents and the solubility was confirmed at room temperature. As the solvent, a mixed solution of γ-butyrolactone (GBL), tetrahydrofuran, cyclohexanone (CH), CP mixture (cyclohexanone: PGMEA 50:50 wt%) and propylene glycol monomethyl ether acetate (PGMEA) Was used. The results are shown in Table 2.

As shown in Table 2, it was confirmed that the compounds of Examples 1 to 4 exhibited excellent solubility in most of the solvents.

GBL THF C.H CP mixed liquid PGMEA Example 1 ◎ ◎ ◎ ◎ ◎ Example 2 ◎ ◎ ◎ ◎ ○ Example 3 ◎ ◎ ◎ ◎ ◎ Example 4 ◎ ◎ ◎ △ X Comparative Example 1 △ X X X X Comparative Example 2 ◎ X X X X ?: Completely dissolved at room temperature,
○: Completely dissolved at partial melting at room temperature or heating
DELTA: Partial melting at the time of heating,
X: Insoluble

Experimental Example  3: Thin film formation

0.5 g of the compound prepared in Examples 1 to 4 was dissolved in 4.5 g of cyclohexanone to prepare a sample solution (protective film composition). Each of the sample solutions prepared above was coated on an 8 inch silicon wafer by spin coating and baked at 350 ° C for 2 minutes to form a thin film having a thickness of 300 nm.

Further, the compound powders prepared in Comparative Examples 1 and 2 were formed into thin films in the same manner as described above, except that the compound powders were dissolved in NMP instead of cyclohexanone. The results of the thin film formation are shown in Table 3.

As shown in Table 3, only the thin films prepared using the compounds of Examples 1 to 4 according to the present invention had good thin film shapes.

Sample name Thin film shape Example 1 Good overall thin film shape (mirror surface, good edge) Example 2 Homology Example 3 Homology Example 4 Homology Comparative Example 1 The center of the thin film was good, the edge part shrinkage Comparative Example 2 The center of the thin film was good, the edge part shrinkage

Experimental Example  4: Chemical resistance evaluation of thin films

The thin film specimens of Examples 1 to 4 and Comparative Examples 1 and 2 prepared in Experimental Example 3 were immersed in a HCl aqueous solution (HCl: water = 15: 85 wt%) and NaOH aqueous solution (NaOH: water = 15: 85 wt %), Cyclohexanone and propylene glycol monomethyl ether acetate for 2 minutes, respectively, and the chemical resistance was confirmed by observing the state of the thin film and the change in thickness. The results are shown in Table 4 below.

As shown in Table 4, the thin film samples prepared using the compounds of Examples 1 to 4 showed no change in the film thickness, and showed no change in thickness before and after the evaluation, indicating good chemical resistance.

HCl aqueous solution NaOH aqueous solution Cyclohexanone PGMEA Example 1 ○ ○ ○ ○ Example 2 ○ ○ ○ ○ Example 3 ○ ○ ○ ○ Example 4 ○ ○ ○ ○ Comparative Example 1 ○ ○ ○ ○ Comparative Example 2 ○ ○ ○ ○ ○: No change of the thin film in the naked eye, and no change in thickness before and after evaluation
?: There is a slight change in the naked eye, and the thickness change before and after evaluation is 1 nm or less
X: Sharp change with naked eye

Experimental Example  5: Evaluation of thin film shape after etching of thin film

The thin film samples of Examples 1 to 4 and Comparative Examples 1 and 2 prepared in Experimental Example 3 were subjected to plasma etching using a mixed gas of CH ₂ F ₂ / CF _{4, and} the consumption rate of the thin film was measured. Further, the change of the thin film shape after the plasma etching was evaluated. The results are shown in Table 5 below.

As shown in Table 5, the thin film samples prepared using the compounds of Examples 1 to 4 showed slower consumption rates of the thin films than the samples of Comparative Examples 1 and 2, and even after the etching, And exhibited a good thin film shape without development. Based on the above results, it can be seen that the composition prepared using the compound of the present invention is suitable for use as a protective thin film or mask of a lower material in a plasma using process.

Sample name Etching rate (nm / s) Thin film shape after etching Example 1 3.6 Good Example 2 4.0 Good Example 3 4.3 Good Example 4 3.3 Good Comparative Example 1 4.9 Good Comparative Example 2 5.3 Good

Claims (12)

1. A protective thin film composition comprising an aromatic compound having a repeating unit represented by the following formula
[Chemical Formula 1]

In this formula,
A is

, &Lt; / RTI &gt;
Wherein R ₁ is a hydroxy group or -OR, wherein R is a C _1-10 alkyl group or a C _6-10 aryl group,
R ₂ is hydrogen, hydroxyl, -OR (wherein R is C _1-10 alkyl or C _6-10 aryl group), C _1-5 alkyl, C _{6 -10} aryl group, a nitro group (-NO _2), or -NR'R &quot; wherein R 'and R &quot; are each independently hydrogen or a C _{1 -5} alkyl group. The method according to claim 1,
A is

&Lt; / RTI &gt;
R ₁ is a hydroxy group or -OCH ₃ ;
R ₂ is a hydroxy group, -NH ₂ or -OCH ₃ . The method according to claim 1,
Wherein the aromatic compound has a weight average molecular weight of 1,000 to 20,000. The method according to claim 1,
Wherein the composition is selected from the group consisting of cyclohexanone, propylene glycol monomethyl ether acetate (PGMEA),? -Butyrolactone (GBL), N-methyl-1,2-pyrrolidone (NMP) , Chloroform, toluene, and a mixture thereof. 5. The method of claim 4,
Wherein the composition comprises from 0.1 to 30% by weight of the aromatic compound and from 70 to 99.9% by weight of the solvent based on the total weight of the composition. A method for producing a protective thin film comprising coating a protective thin film composition according to any one of claims 1 to 5 on a substrate followed by heat treatment. The method according to claim 6,
Wherein the coating is performed by a spin-on-coating, a slit coating, a bar coating or a spray coating method. The method according to claim 6,
Wherein the heat treatment is performed at 200 to 600 ° C. A protective film produced by the manufacturing method according to claim 6. 10. The method of claim 9,
Wherein the protective thin film has a thickness of 10 nm to 5,000 nm. 1. A semiconductor device comprising an insulating film comprising a protective thin film composition comprising an aromatic compound having a repeating unit represented by the following formula
[Chemical Formula 1]

In this formula,
A is

, &Lt; / RTI &gt;
Wherein R ₁ is a hydroxy group or -OR, wherein R is a C _1-10 alkyl group or a C _6-10 aryl group,
R ₂ is hydrogen, a hydroxy group, -OR (wherein R is a C _1-10 alkyl group or a C _6-10 aryl group), a C _1-5 alkyl group, a C _6-10 aryl group, a nitro group (-NO ₂ ) -NR'R &quot; wherein R 'and R &quot; are each independently hydrogen or a C _1-5 alkyl group. Forming an etching target layer on a semiconductor substrate;
Forming a mask pattern on the etch target layer; And
And patterning the etching target layer using the mask pattern,
Wherein the mask pattern comprises an aromatic compound having a repeating unit represented by the following Chemical Formula 1:
[Chemical Formula 1]

In this formula,
A is

, &Lt; / RTI &gt;
Wherein R ₁ is hydroxy or -OR (wherein R is C _{1 -10} alkyl group or a C _{6 -10} aryl group),
R ₂ is hydrogen, hydroxyl, -OR (wherein R is C _{1 -10} alkyl or C _{6 -10} aryl group), C _1-5 alkyl, C _{6 -10} aryl group, a nitro group (-NO _2), or -NR'R &quot; wherein R 'and R &quot; are each independently hydrogen or a C _{1 -5} alkyl group.

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