Aqueous antireflective coatings for photoresist compositions

The present invention relates to a novel aqueous antireflective coating solution and a process for its use in photolithography. The antireflective coating solution comprises a novel polymer and water, where the novel polymer of the antireflective coating comprises at least one unit containing a dye that absorbs from about 180 nm to about 450 nm, at least one unit containing a crosslinking group and at least one unit derived from a hydrophilic vinyl monomer or a vinyl monomer capable of becoming hydrophilic.

EXAMPLE 1 
Synthesis of N-(3-Hydroxyphenylmethacrylamide) 
A suspension of 3-aminophenol (47 g, 0.43 mol) in acetone (100 ml) was 
chilled to 0.degree. C. To this, a solution of methacrylic anhydride (66.2 
g, 0.43 mol) in acetone (150 ml) was added dropwise. A white precipitate 
formed and the reaction mixture was stirred for 1 hour. The resultant 
precipitate was poured into crushed ice and the solid product collected by 
filtration, and recrystallized (1:1 EtOH (ethanol):H.sub.2 O). The melting 
point was 172.degree.-173.degree. C. and the yield was 86.6%. 
EXAMPLE 2 
A solution of N-(3-hydroxyphenylmethacrylamide) (5.32 g, 0.03 mol) from 
Example 1, in .gamma. butyrolactone (40 ml), was prepared by heating the 
mixture to 65.degree. C. while stirring. On complete dissolution, the 
solution was degassed by vigorously bubbling argon, via an inlet needle in 
a sealed rubber septum, through the solution for up to 2 hours. Previously 
degassed diethylene glycol monovinyl ether was then injected into the 
reaction mixture. After an additional 20 minutes, an aliquot from a 
solution of AIBN (azo-bis-isobutyro-nitrile) (49 mg, 1 mol % total 
monomers) in .gamma. butyrolactone (1 ml) was also injected. In total, 2 
aliquots were added at intervals of 6 hours. Both inlet and outlet needles 
were then removed and the sealed vessel was allowed to stir at 65.degree. 
C. for 18 hours. The resultant solution was then precipitated into ethyl 
acetate (300 ml) as nonsolvent, and the solid collected by filtration, 
redissolved in ethanol (50 ml) and reprecipitated into ethyl acetate. 
Purification was further carried out by successive reprecipitations of 
polymer solution until no monomer was observed by TLC. The polymer formed 
as a white powder and was dried under reduced pressure overnight. 
EXAMPLE 3 
The diazonium salt of sulfanilic acid was prepared as follows. To a 
solution of tetramethyl ammonium hydroxide in water (25% solids) (3.6 ml, 
0.01 mol) was added sulfanilic acid (1.73 g, 0.01 mol), followed by 
isobutyl nitrite (1.5 ml. 0.012 mol) and the resultant suspension 
temperature maintained below 10.degree. C. A solution of HCl (37.8 wt % in 
water) (1.62 ml, 0.02 mol) was added to water (5 ml) and the solution 
slowly added to the reaction mixture, forming the diazonium salt. 
EXAMPLE 4 
The copolymer from Example 2 (3.09 g, 0.01 mol equiv. phenylacrylamide) was 
dissolved in ethanol (30 ml), then on addition of tetramethyl ammonium 
hydroxide in water (25 wt % solids) (7.2 ml, 0.02 mol), the immediate 
precipitate that formed was gradually redissolved. Additional water (5 ml) 
and ethanol (10 ml) were then added and the solution chilled to 5.degree. 
C. The diazonium salt prepared from Example 3 was then added dropwise to 
the polymer solution, which immediately formed a suspension. Additional 
water was added throughout the course of the addition (20 ml total) and 
the mixture allowed to stir. Gradually the suspension was converted to an 
orange solution (4 hours) which was filtered and the subsequent solution 
precipitated into 2-propanol (700 ml) as nonsolvent. The product was 
collected by filtration and purified by reprecipitation. 
EXAMPLE 5 
11.96 g (0.0675 mol) of N-(3-hydroxyphenylmethacrylamide) from Example 1 
was dissolved in .gamma. butyrolactone (75 ml) and DMF (dimethylformamide) 
(75 ml), The mixture was heated to 65.degree. C. while stirring. The 
solution was degassed by vigorously bubbling argon, via an inlet needle in 
sealed rubber septum, through the solution for 1 hour. 4.41 ml (0.0225 
mol) of N-(hydroxymethyl)acrylamide and 6.48 ml (0.06 mol) methyl 
methacrylate were injected into the solution. The solution was degassed 
for 0.5 hour. An aliquot from a solution of AIBN (0.251 g, 1.5 mmol, 1 mol 
% total monomer) in .gamma. butyrolactone (2 ml) was injected and degassed 
for 0.5 hour. In total, 2 aliquots were added at intervals of 4 hours. 
Both the inlet and outlet needles were removed and the sealed vessel was 
stirred at 65.degree. C. for 19 hours. 
EXAMPLE 6 
4.68 g (0.03375 mol) of 4-aminobenzoic acid were dissolved in 6.68 ml 
(0.084375 mol) of concentrated hydrochloric acid and 70 ml of water, 
contained in a 250 ml three-neck round-bottom flask. A thermometer was 
placed in the solution and the flask immersed in a bath of crushed ice, 
cooled until the temperature of the solution fell below 2.degree. C. The 
solution contained a white suspension. Diazotization was done by the 
addition of 4.19 ml (0.0338 mol) tert-butyl nitrite. The diazonium 
solution was stirred in ice-water for about 1 hour. The suspension changed 
to a yellow solution. 
EXAMPLE 7 
80 ml (0.075 mol) of the polymer solution from Example 5 was placed in a 
500 ml round bottomed flask. To this was added 320 ml of DMF and a 
solution of (25% in water) 42.52 ml (0.1185 mol) tetramethylammonium 
hydroxide while stirring. The solution was cooled in an ice-water bath to 
10.degree. C. and the cold diazonium salt solution was added. The solution 
changed to orange color. The mixture was allowed to stir about 3 hours and 
warmed to room temperature. The resultant solution was precipitated into 
excess isopropanol, and the polymer collected by filtration and vacuum 
dried. 
EXAMPLE 8 (COMATIVE) 
Several 4" wafers were coated with AZ.RTM. 7805 (available from Hoechst 
Celanese Corporation, 70 Meister Ave., Somerville, N.J. 08876) and baked 
using a temperature of 90.degree. C. for 90 seconds to give thickness from 
0.5 .mu.m (micrometers) to 0.9 .mu.m (micrometers). These wafers were 
imagewise exposed with a NIKON.RTM. 0.54 NA i-line stepper using a clear 
quartz as the reticle and a program that directed the stepper to print a 
11.times.11 exposure matrix with dose increments of 2 mJ/cm.sup.2. The 
exposed wafers were baked at 110.degree. C. for 60 seconds and puddle 
developed with AZ.RTM. 300 MIF developer (available from Hoechst Celanese 
Corporation, 70 Meister Ave., Somerville, N.J. 08876) for 35 seconds. The 
minimum dose required to clear the film was plotted as a function of the 
corresponding resist thickness, a sinusoidal curve was obtained, called 
the swing curve. The % Swing ratio was calculated empirically by the 
following equation: 
EQU % Swing Ratio=(Emax-Emin)/((Emax+Emin)/2).times.100 
where Emax and Emin corresponding to the dose-to-clear the resist film 
thickness at the maximum and minimum energy on a swing curve. The smaller 
the value of % Swing Ratio the lower is the impact of reflectivity and the 
better is linewidth control over reflective substrate or topography. 
The % Swing Ratio for AZ.RTM. 7805 was 34.8%. 
EXAMPLE 9 
The polymer from Example 4 was dissolved in water to give a 5 weight % 
solution. The polymer solution was spin coated on several 4" silicon 
wafers, and baked on a hot plate at 220.degree. C. for 60 seconds to give 
a thickness of 0.121 micron. The wafers were then coated with with AZ.RTM. 
7805 (available from Hoechst Celanese Corporation, 70 Meister Ave., 
Somerville, N.J. 08876) and baked using a temperature of 90.degree. C. for 
90 seconds to give thickness from 0.5 .mu.m (micrometers) to 0.9 .mu.m 
(micrometers). These wafers were imagewise exposed with a NIKON.RTM. 0.54 
NA i-line stepper using a clear quartz as the reticle and a program that 
directed the stepper to print a 11.times.11 exposure matrix with dose 
increments of 2 mJ/cm.sup.2. The exposed wafers were baked at 110.degree. 
C. for 60 seconds and puddle developed with AZ.RTM. 300 MIF developer for 
35 seconds. The minimum dose required to clear the film was plotted as a 
function of the corresponding resist thickness, and a sinusoidal curve was 
obtained, called the swing curve. The % Swing Ratio was calculated as in 
Example 8. 
The % Swing Ratio for AZ.RTM. 7805 with antireflective polymer coating of 
this Example was 22%, showing a reduction in the % Swing Ratio from the 
resist without the antireflective coating. 
EXAMPLE 10 
The polymer from Example 7 was dissolved in water to give a 5 weight % 
solution. The polymer solution was spin coated on several 4" silicon 
wafer, and baked on a hot plate at 220.degree. C. for 60 seconds to give a 
thickness of 0.198 micron. The wafers were then coated with with AZ.RTM. 
7805 (available from Hoechst Celanese Corporation, 70 Meister Ave., 
Somerville, N.J. 08876) and baked using a temperature of 90.degree. C for 
90 seconds to give thickness from 0.5 .mu.m (micrometers) to 0.9 .mu.m 
(micrometers). These wafers were imagewise exposed with a NIKON.RTM. 0.54 
NA i-line stepper using a clear quartz as the reticle and a program that 
directed the stepper to print a 11.times.11 exposure matrix with dose 
increments of 2 mJ/cm.sup.2. The exposed wafers were baked at 110.degree. 
C. for 60 seconds and puddle developed with AZ.RTM. 300 MIF developer for 
35 seconds. The minimum dose required to clear the film was plotted as a 
function of corresponding resist thickness, and a sinusoidal curve was 
obtained, called the swing curve. The % Swing Ratio was calculated as in 
Example 8. 
The % Swing Ratio for AZ.RTM. 7805 with antireflective polymer coating of 
this Example was 2.1%, showing a significant reduction in the % Swing 
Ratio from the resist without the antireflective coating.