Correlation of the chemical and electrical properties of AZ1350J photoresist solutionTapan Kumar Gupta Citation: Journal of Applied Physics 56, 1145 (1984); doi: 10.1063/1.334089 View online: http://dx.doi.org/10.1063/1.334089 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/56/4?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Correlation of chemical composition and electrical properties of rf sputtered alumina films J. Vac. Sci. Technol. A 27, 234 (2009); 10.1116/1.3065978 Mechanical properties and pattern collapse of chemically amplified photoresists J. Vac. Sci. Technol. B 18, 3450 (2000); 10.1116/1.1319833 Electrical properties of a new polymer/photoresist composite J. Appl. Phys. 80, 2279 (1996); 10.1063/1.363056 Implanted boron depth profiles in the AZ111 photoresist J. Appl. Phys. 63, 2083 (1988); 10.1063/1.341112 Correlation of chemical and electrical properties of plasmadeposited tetramethylsilane films J. Appl. Phys. 52, 903 (1981); 10.1063/1.328774

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

137.149.200.5 On: Sat, 29 Nov 2014 20:17:20

Correlation of the chemical and electrical properties of AZ1350J photoresist solution

Tapan Kumar GuptaB)

Department of Physics, Indian Institute of Technology, Kharagpur 721302, India

(Received 8 April 1983; accepted for publication 6 February 1984)

The dielectric properties of the photoresist AZ1350J in diethyloxalate solution have been measured by a capacitance technique. Measurements of permittivity (E,) at different dilutions are seen to obey the logarithmic law of mixing, while the temperature dependence curve predicts a change in phase of the resist at approximately 66°C. Polarization measurement of the mixtures shows a relaxation type of orientational polarization and a decreasing value of polarization on UV light irradiation, confirming the structural change in the photoresist.

I. INTRODUCTION

The study of electrical and other properties of dielec­trics 1-4 in relation to their chemical composition and to var­ious external factors (temperature,5.6 frequency,7 humidity,S and radiation effect9

) has developed into an important field of science.

The distribution of chains with dipolar groups in orient­ed polymers 1~12 has been studied by many investigators and different models have been proposed by them from time to time. According to Debye and Bueche9 comparison of the dipole moment of a polymeric molecule with that of one of its structural units can yield information about the material. After a dielectric is energized (or deenergized) the process of establishing dipole polarization requires a long time com­pared to that of almost inertialless phenomena of deforma­tion polarization. The time will be longer if the absolute vis­cosity of the material is high.

The present paper considers techniques for measuring the polarizability and dipole moment of photoresist AZ 1350, a diazoquinon resist, for the purpose of studying its structural behavior. This material has been investigated pre­viously by other methods. 13--16 In the present work, a corre­lation between the dielectric properties of the resist solution and its chemical behavior is derived from the experimental observations.

II. MATHEMATICAL BACKGROUND

Assuming the solution is a physical mixture, the molec­ular weight MI2 of the solution is given by

M12 =MIFI + M~2 = WI + Wz, (1) WI W2 -+-MI M2

where M I , M 2, WI' and F I , F2 represent the molecular weights, weights in grams, and mole fraction of the solvent and solute, respectively.

If Co is the capacitance of a pair of parallel plates in vacuum and ..jC12 is the difference in the capacitive values in air and in the polymer solution, then KI2 the dielectric con-

-I Present address: Department of Physics, Boston College, Chestnut Hi11, Massachusetts 02617.

stant of the mixture is given by

K 1 ..dC12 12= +--,

Co (2)

and PI2 the polarization density or dipole moment per unit volume of the mixture is given by

P _ K12 - 1 MI2 1"- , - KI2 + 1 DI2

where DI2 is the density of the mixture.

III. MEASUREMENT TECHNIQUE

A. Material

(3)

The polymeric material 13 was a Shipley AZ1350J pos­itive photoresist. Dilution was done by adding diethyloxa­late. In order to avoid cross linking, experimental observa­tions were taken in the absence of blue light in a class-IOO conditioned yellow housing room.

B. Experimental apparatus

Since the dielectric constant K is related to the capaci­tance fEqs. (2) and (3)], the experimental procedure consisted of measuring the capacitances of a parallel plate condenser in air, in the photoresist solution, and in the solvent.

The parallel plates used in this method were copper, rectangular in shape, having areas nearly equal to (3.8 X4.15) X 10-4 cm2

, withagap of 0.60 X 10-2 m. Two thick copper wires were fused to the plates for making external connections and were secured in ebonite. The two copper plates with the copper wires were mounted inside a glass beaker. External connections were made by means of coaxial cables (Fig. 1).

C. Measurement ot capacitance

The dielectric properties of the AZ1350J photoresist solution (PRJ were studied by observing its behavior as a dielectric in the capacity measuring apparatus shown in Fig. l. The beat frequency17 technique was employed using a crystal controlled oscillator at 2467 kHz ((0) as the reference frequency. This signal was mixed with that ofa variable fre­quency oscillator and the zero beat condition observed by means of an earphone [Fig. l(b)]. The frequency of the vari-

1145 J. Appl. Phys. 56 (4),15 August 1984 0021-8979/84/161145-04$02.40 @ 1984 American Institute of Physics 1145

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

137.149.200.5 On: Sat, 29 Nov 2014 20:17:20

x X r---- -----,

(a)

E

P, .I? = Copper plate

E = Ebonite plate

(b)

C1 = Variable preclSlOO capacitodG.R.Mass. U.S.A) C2 = Capacitor formed with copper plate P" ~ .

FIG. I. (a) Shows the schematic representa­tion of the experimental apparatus used to measure the capacitance of a parallel plate condenser. (b) Represents the circuit dia­gram of the oscillator circuit including the fixed frequency crystal oscillator. (c) Repre­sents the block diagram of the beat frequen­cy oscillator. A = Mixed Amplifier. E = Earphone.

B = Crystal (freq. 2467 KHzl L, L = Inductance.

(c)

able frequency oscillator is dependent on the values of the components of the tank circuit C1, C2, andL2• The value of L2 was kept fixed so that the values of C1 and C2 actually determined the circuit frequency fo. Capacitor C1 Was a vari­able precision capacitor (General Radio Model 722-D). The zero beat condition was established by adjustments of C1,

permitting determination of changes in C2 as the properties of the PR solution were altered.

D. Measurement of molecular weight (Mu)

The method adopted was measurement of the angular distribution of scattered light based on a design of Bosworth et al. 18 and Freeman et al. 19 The measurements were made at room temperature (30 "q, over the angular range from 30-90 deg for several concentrations. The molecular weight MI2

was calculated from an extrapolation to zero angle and con­centration on a Zimm plott; the standard deviation in the mol.ecular weight was estimated from a least squares fit to the zero angle line.

E. Effect of temperature

The investigation of the effect of temperature on the permittivity of the PR solution was carried out using the same apparatus as described above (Fig. 1). The changes of capacitance values with the change in temperature were re­corded (Fig. 3) using a copper-constantan thermocouple. The capacitance values were measured at discrete tempera­tures starting at 30 ·C, increasing in steps to l00·C and de­creasing in identica1 steps back to 30 .c.

1146 J. Appl. Phys., Vol. 56, NO.4, 15 August 1984

F. Irradiation effect

Changes in the dielectric properties of the PR solution upon irradiation were studied again using the apparatus of Fig. 1. The irradiation source was a high pressure Hg lamp [H4 AB 100 W, GE] filtered to remove wavel.engths shorter than 3700 A. Exposure of the solution produced measurable changes in the dielectric constant up to an irradiation time of from 4 to 5 min, after which no further change was observed.

IV. RESULTS AND DISCUSSION

Experimental values of ..de12 and the value of KJ2 for the PR mixture when fitted to Eq. (2) gives a value of Co of 2.53 ± 0.3 pF, while the calculated value base on the area (A ) of the capacitor plates (3.8 X 4.5 X to- 4m 2

) and their separa­tion (d) (0.6 X 1.0- 2 m) yields 2.32 pF. Since the experimental values are susceptible to several instrumental errors, the two values agree wen within experimental error.

The relation between the permittivity E, of a two polar liquid dielectric system-a mixture of photoresist, AZ1350J, and a diluent, dielethyloxalate-and the volume percent of the photoresist is shown in Fig. 2. The data are seen to obey a logarithmic law of mixing, fitting wen into the equation:

;=m

log E, = L Y; log Eo ;= I

where m is the mixture of the components. The present mod­el disagrees with those proposed by Landau and Lifshitz and by Beer,4 for the case of chaotic mixtures. It does, however, agree with the results of Langton and Mathews4 for the case

Tapan Kumar Gupta 1146

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

137.149.200.5 On: Sat, 29 Nov 2014 20:17:20

~ 20 c Q

:; 16 ~

'0

.~ 8 > -§ 4 & t 00~~~~~~~~ 20 40 60 80 %

8 - Volume content of AZ

1350J(8) in diethyl oxalate (Al.

FIG. 2. Represents the permittivity E, ofa mixture of two polar liquids­diethyloxalate and AZ 1350J photoresist vs the volume content of AZ 13501 photoresist, in the mixture.

of cyclohexanol C6H))CH and ethyl acetate C2HsCOOCH3. The dependence of the permittivity of AZ 1350J on tem­

perature is given in Fig. 3. Above room temperature, the orientation of dipoles fa­

cilitatated an increase in the permittivity, and at still higher temperatures, chaotic thermal oscillations of the molecules are intensified and the degree of order in their orientation is diminished, causing a sudden increase in the permittivity value. This behavior is comparable with that observed in nitrobenzene by Smyth and Hitchock.20

In an earlier report,13 it was shown that a AZ1350J resist containing O-benzaquinone diazide decomposes at about 66·C. Thus, this jump in permittivity may also be attributed to a change of phase as has been observed in the case of solid dielectrics.

The relation between dilution of the photoresist and the molecular weight is illustrated in Fig. 4. The upper portion of the curve in the region of low concentration of diethyl oxalate the relationship is approximately linear. Assuming the mixture is of a physical nature given by the molecular

--_. Temperature in·C

FIG. 3. Represents permittivity E, vs temperature curve for AZ1350J pho­toresist.

1147 J. Appl. Phys., Vol. 56, No.4, 15 August 1984

~ ::> x E ~ :::

15

740

640

\\ \

\ \

\ \

\ \

Theory • Experiment

\ \

\ \

\ \

\ \

- Volume content of diethyl oxalate (A).

FIG. 4. Represents molecular weight M\2 vs volume content of diethyloxa­late in AZ1350J.

composition with mass content X; of the components in a mixture and not with the volume content Y; the upper por­tion of the curve can be represented by the arithmetic law of mixing:

;=m

D* = L x;D;. ;=)

where D * and D; are the densities of the mixture and compo­nents, respectively; the strong nonlinearity in the lower por­tion of the curve, assumed to be due to rapid loss in weight of the solvent and consequent change in density of the resist solution, does not fit the model well. Rather, it is seen to fit

--_a Volume content of diethyl oxalate (A).

FIG. 5. Represents polarization PJ2 in cc vs volume content of diethyloxa­late in AZ13501 photoresist.

Tapan Kumar Gupta 1147

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

137.149.200.5 On: Sat, 29 Nov 2014 20:17:20

the equation

(Mdv2 = (Mdvi exp[ - C(VI - v2)],

where (Md, (M12 ) are the molecular weights and VI' V2 the volumes of the PR solution and the solvent, respectively.

The variation of polarization of the mixture (Pd with dilution is given in Fig. 5. The plot shows that the rate of change of polarization is not uniform throughout the entire region of the curve. This may be attributed to the fact that orientational polarization belongs to a slow relaxation type of process. In this, oriented polar molecules behave as spheres rotating in a viscous medium, overcoming viscosity and the coefficient of internal friction, both of which are affected by the changes in concentration. According to De­bye9 the relaxation times are functions of the dynamic vis­cosity of the solution and the volume of the molecules.

The electromechanical relaxation in orientational poly­mers in the presence of an electric field has been studied by Strathdee et 01.10 They found the effect to be associated with the rotation of the dipolar elements. Also, the shift of the dipole orientation was found to be linear in the presence of a microscopic electric field.

Experimental observation shows that the dipole mo­ment per unit volume [the polarization (Pd of 1:1 AX1350J PR solution in diethy loxalate], upon irradiation with UV light, changes from 290 to nearly 90 cc, the value of the polarization of the solvent itself. Early reports 13.2 I show that, due to cross linking of the resist in UV light, changes occur in the molecular weight and the structural formula of the starting material.

Experimental evidence indicates22,23 that the presence of nitrogen increases the value of the dipole moment. Then this nearly zero value of P12 of the PR solution after UV irradiation may be taken to be a result of the flatness of the molecular structure, because, according to Halverson and Hirt,24 diazo compounds have a transition moment perpen­dicular to the plane of the ring, giving rise to an essentially parallel type of rotation bands for totally symmetric vibra­tion. In this case the bond angle may have a value approach­ing 90° giving rise to a zero dipole moment. Owing to Steric hinderances, the polymer chain cannot take aU configura­tions allowed by free rotation about the chain bonds. In the case of an AZ 1350J PR it is assumed that, after exposure, the simple chain of N units is completely stiff and the fixed di­poles on the stiff chain are so oriented that the dipoles ~mcel each other.9 The photochemical reactions after UV exposure are thought to give 3-indene carboxilic acid with the forma­tion of Ketene intermediate. This is in accordance with the reaction proposed by Sus.2S But according to Levine26 the end product should be

R

R

1148 J. Appl. Phys., Vol. 56, No.4, 15 August 1984

The present measurement of dipole moments does not sup­port Levine, because, if the final material contains C = 0 bonds then, according to Coop and Sutton,27 this will yield a highly flexible polar bond which will give rise to high atom polarization in presence of the field. The present investiga­tion suggests, however, that the end material cannot have a C = 0 bond but rather a COOH bond, as suggested by Sus.

V. CONCLUSION

Many investigators in the past have utilized electron beam, IR, and carbon 13 nuclear magnetic resonance spec­troscopic techniques for the investigation of the structure and photochemistry of photoresists. This is the first time that a direct correlation between chemical and electrical properties of photoresists has been made by the dipole mea­surement method. The new investigation of dipole measure­ment may not be considered sufficient for establishing the structural formula and this further study of the material is indicated.

ACKNOWLEDGMENTS

The author is grateful to Professor George Goldsmith for his valuable suggestions and Professor R. A. Uritam, Chairperson, Department of Physics, Boston College, for taking interest in the work. He is also thankful to the Re­viewers whose comments and suggestions helped recast the presentation.

IV. E. Bottom, J. App!. Phys. 43, 1493 (1972). 2A. J. Slobodnik, Jr. and J. e. Sethares, J. App!. Phys. 43, 247 (1972). 'A. H. Fabmyand E. L. Adler, J. App\. Phys. 44, 3949 (1973). 'Cited in B. Tareev, Physics of Dielectric Materials, translation by A. Troitsky (Mir, Moscow, 1975). ~R. T. Smith and F. S. Welsh, J. App!. Phys. 42, 2219 (1971). 6R. e. Neville, B. Itoeneisen, and C. A. Mead, J. App\. Phys. 43, 2127 (1972).

7A. S. Nowick and B. S. Berry, An Elastic Relaxation in Crystalline Solids (AlP, New York, 1972).

SR. S. Lakes, R. A. Harper, and 1. L. Katz, J. App\. Phys. 48, 808 (1977). "P. Debye and F. Bueche, J. Chern. Phys. 19, 589 (1951). IOJ. Strathdee and W. H. Robinson, J. App\. Phys. 53, 3184 (1976). "M. Oshiki and E. Fukuda, Jpn. J. App\. Phys. 15,43 (1976). 12T. Furukawa, J. Aiba. and E. Fukuda, J. App\. Phys. SO, 3615 (1979). IJ-y'apan Kumar Gupta, Eur. Polym. J. 17, 1129 (1981). I·Dietrich Meyerhofer,lEEE Trans. Electron. Devices ED-27, 921 (1980). 16D. F.l1ten and R. J. Sutton, Electrochern. Soc. 119, 539 (1972). I7E. E. Terman and J. M. Pettit, Electronic Measurements, 2nd ed.

(McGraw-Hill, Tokyo, 1952). ISp. C. Bosworth, R. C. Mason, H. W. Melville, and F. W. Peaker, J. Polym.

Sci. 9, 565 (1952). 1~. Freeman and P. P. Manning. J. Polym. Sci. A 2,2017 (1964). zoe. P. Smyth and C. S. Hitchock, 1. Am. Chern. Soc. 55, 1830 (1933). 21D. I. e. Ke\1s and J. E. Gui\1et, J. Polym. Sci. 7, 1895 (1969). 22A. L. Mcce\1an, Tables of Experimental Dipole Moments (Freeman, San

Francisco, 1963). 2'G. Brinbaum, S. J. Kryder, and Harold Lyons., J. Appl. Phys. 22,95

(1951). uF. Halverson and R. C. Hirt, J. Chern. Phys. 19, 712 (1951). 2~O. Siis, Justus Liebigs Ann. Chern. 556, 65 (1944). 26H. A. Levine, Polym. Prepr., Am. Chern. Soc., Div. Polym Chern. 19, 377

(1969). 271. E. Coop and L. E. Sutton, J. Chern. Soc., London, Part 11,1269(1938).

Tapan Kumar Gupta 1148 [This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

137.149.200.5 On: Sat, 29 Nov 2014 20:17:20