Patent Application
20080015280
A radiation-sensitive composition for forming waveguides comprises (A) a (meth)acrylate having an adamantyl group, (B) other photopolymerizable compounds added optionally, and (C) a photopolymerization initiator. Each of the components will now be described in detail.
(A) A (meth)acrylate having an adamantyl group used in the present invention has no limitations on the type thereof, and has only to be a (meth)acrylate having an adamantyl group in the molecule thereof.
Examples of the (meth)acrylate having an adamantyl group include a compound represented by the general formula (1)
(in the formula, R1 is a hydrogen atom or a methyl group; R2 is —CH2CH2—, —CH2CH(CH3)—, or —CH2CH(OH)CH2—; n is an integer from 0 to 10), and a compound represented by the general formula (2)
(in the formula, R1 is a hydrogen atom or a methyl group; R2 is —CH2CH2—, —CH2CH(CH3)—, or —CH2CH (OH) CH2—; R3 is a hydrogen atom, a methyl group, or an ethyl group; n is an integer from 0 to 10).
The (meth)acrylate having an adamantyl group represented by the general formula (1) or (2), in which n is 0, is an ester of an alcohol having an adamantyl group and (meth) acrylic acid. Here, examples of the alcohol having an adamantyl group include 1-adamantanol, 2-adamantanol, 2-methyl-2-adamantanol, 2-ethyl-2-adamantanol.
In the general formulae (1) and (2), n is preferably in the range of 0 to 5, more preferably in the range of 0 to 3. When n is in the preferred range, it is possible to keep good transmission loss even after storage in heat and humidity for a long period of time.
By using the (meth)acrylate having an adamantyl group as a constituent component of a radiation-sensitive composition, the radiation-sensitive composition can exhibit improved heat resistance (i.e. increased glass-transition temperature), increased adhesion to a substrate such as a silicon wafer and the like (i.e. decreased curing shrinkage ratio), improved long-term reliability (i.e. long-term retention of low transmission loss under severe conditions such as low temperature, high temperature and high humidity, drastic temperature change, etc.), and the like.
The radiation-sensitive composition of the present invention includes (A) a (meth)acrylate having an adamantyl group in an amount of preferably from 5 to 50 mass percent, more preferably from 10 to 40 mass percent, most preferably from 15 to 30 mass percent. When the amount is less than 5 mass percent, problems such as an increase in the transmission loss, and an occurrence of a large curing shrinkage that is followed by a separation depending on use conditions, can occur after storage in heat and humidity, and other problems can also occur. When the amount exceeds 50 mass percent, it may be difficult to obtain an intended refractive index, and other problems can also occur.
Examples of (B) other photopolymerizable compounds usable in the present invention include a (meth)acrylate other than component (A), a compound having a vinyl group, and the like.
Component (B) has only to have one or more ethylenically unsaturated groups in the molecule thereof, and any of a monomer, a reactive oligomer, or a reactive polymer (i.e. macropolymer) can be used.
Examples of a (meth) acrylate having one (meth) acryloyl group in the molecule thereof include a macromonomer having a number average molecular weight of 3,000 to 10,000, and other (meth)acrylates.
Examples of the macromonomer include a poly(methyl methacrylate) having a methacryloyl group (i.e. methacryloyl group-containing PMMA), a polystyrene having a methacryloyl group, and the like.
Examples of other (meth) acrylates having one (meth) acryloyl group in the molecule thereof include a (meth)acrylate having a phenoxy group such as phenoxyethyl (meth)acrylate, phenoxy-2-methylethyl (meth)acrylate, phenoxyethoxyethyl (meth)acrylate, 3-phenoxy-2-hydroxypropyl (meth)acrylate, 2-phenylphenoxyethyl (meth)acrylate, 4-phenylphenoxyethyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, (meth)acrylate of ethylene oxide modified p-cumylphenol, 2-bromophenoxyethyl (meth)acrylate, 4-bromophenoxyethyl (meth)acrylate, 2,4-dibromophenoxyethyl (meth)acrylate, 2,6-dibromophenoxyethyl (meth)acrylate, 2,4,6-tribromophenoxyethyl (meth)acrylate, and the like; isobornyl (meth)acrylate, bornyl (meth)acrylate, tricyclodecanyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, 4-butylcyclohexyl (meth)acrylate, acryloylmorpholine, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, amyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, butoxyethyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, methoxyethylene glycol (meth) acrylate, ethoxyethyl (meth) acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, diacetone (meth)acrylamide, isobutoxymethyl (meth)acrylamide, N,N-dimethyl (meth)acrylamide, t-octyl (meth)acrylamide, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, 7-amino-3,7-dimethyloctyl (meth)acrylate, and the like.
Examples of a (meth)acrylate having two (meth)acryloyl groups in the molecule thereof include a bisphenol-containing di(meth)acrylate, an alkyl diol diacrylate, and other (meth)acrylates.
Examples of a bisphenol-containing di (meth) acrylate include di(meth)acrylate of ethylene oxide adduct of bisphenol A, di (meth) acrylate of ethylene oxide adduct of tetrabromobisphenol A, di(meth)acrylate of propylene oxide adduct of bisphenol A, di (meth) acrylate of propylene oxide adduct of tetrabromobisphenol A, bisphenol A epoxy di(meth)acrylate which is obtained by epoxy ring-opening reaction of bisphenol A diglycidyl ether with (meth) acrylic acid, tetrabromobisphenol A epoxy di (meth) acrylate which is obtained by epoxy ring-opening reaction of tetrabromobisphenol A diglycidyl ether with (meth) acrylic acid, bisphenol F epoxy di(meth)acrylate which is obtained by epoxy ring-opening reaction of bisphenol F diglycidyl ether with (meth) acrylic acid, tetrabromobisphenol F epoxy di (meth) acrylate which is obtained by epoxy ring-opening reaction of tetrabromobisphenol F diglycidyl ether with (meth) acrylic acid, and the like.
Examples of an alkyl diol diacrylate include 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, and the like.
Examples of other (meth) acrylates having two (meth) acryloyl groups in the molecule thereof include a polyalkylene glycol diacrylate such as ethylene glycol di(meth)acrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, and the like; neopentyl glycol di(meth)acrylate, tricyclodecane dimethanol diacrylate, and the like.
Examples of a (meth)acrylate having three (meth)acryloyl groups in the molecule thereof include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropanetrioxyethyl (meth)acrylate, tris(2-acryloyloxyethyl)isocyanurate, pentaerythritol polyacrylate, and the like.
Examples of a compound having a vinyl group include N-vinylpyrrolidone, N-vinylcaprolactam, vinylimidazole, vinylpyridine, and the like.
From a viewpoint of improving heat resistance of a cured product or the like, it is preferable that the whole or a part of component (B) is composed of a (meth)acrylate having two or more (meth)acryloyl groups in the molecule thereof.
As component (B), one compound may be used alone, or two or more compounds may be used in combination. The type and the amount to be added of component (B) may be determined as appropriate considering the intended refractive index and the like of the cured radiation-sensitive composition.
The radiation-sensitive composition of the present invention includes (B) other photopolymerizable compounds in an amount of preferably from 40 to 94.99 mass percent, more preferably from 53 to 89.9 mass percent, most preferably from 65 to 84.5 mass percent. When the amount is less than 40 mass percent, it may be difficult to obtain the intended refractive index, and other problems can also occur. When the amount exceeds 94.99 mass percent, it becomes difficult to satisfy all the characteristics required for the optical waveguide, such as long-term reliability, heat resistance (i.e. glass-transition temperature; Tg), adhesion of the waveguide to the substrate, and the like.
As a photopolymerization initiator used in the present invention, it is preferable to use a compound capable of generating activated radical species by being irradiated with activated energy ray such as ultraviolet light (i.e. a photo-radical polymerization initiator).
Examples of the photopolymerization initiator include acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone, 4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether, benzoin ethyl ether, benzyl dimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one, 2-hydroxy-2-methyl-1-phenylpropane-1-one, thioxanthone, diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propane-1-one, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and the like.
When any polymerization initiator other than the photopolymerization initiator is used, and polymerization is performed not by irradiation but by heat, etc., it requires long-term heating to cure thoroughly. Accordingly, polymerization by heat is not preferred from a view point of productivity. In addition, if a silicon wafer is used as the substrate, the optical waveguide is likely to separate from the substrate when placed back to room temperature after cured by heat due to a difference in heat shrinkage ratio between the optical waveguide and the substrate.
In the present invention, the radiation-sensitive composition includes (C) a photopolymerization initiator in an amount of preferably from 0.01 to 10 mass percent, more preferably from 0.1 to 7 mass percent, most preferably from 0.5 to 5 mass percent. When the amount is less than 0.01 mass percent, problems such as a decrease in patterning properties, a decrease in curing speed, and the like, can occur. When the amount exceeds 10 mass percent, problems such as a decrease in patterning properties, a deterioration in transmission characteristics, and the like, can occur.
The radiation-sensitive composition of the present invention can further contain a solvent, photosensitizer, antioxidant, UV absorber, light stabilizer, silane coupling agent, coating surface improver, thermal polymerization inhibitor, leveling agent, surfactant, colorant, storage stabilizer, plasticizer, lubricant, filler, aging resistor, wetting agent, mold release agent, and the like as appropriate.
The radiation-sensitive composition of the present invention can be manufactured by mixing the above components in the usual manner.
The radiation-sensitive composition of the present invention has a viscosity of generally from 100 to 20,000 cp at 25 degree C., preferably from 200 to 10,000 cp at 25 degree C, more preferably from 300 to 5,000 cp at 25 degree C. When the viscosity is too high, an unevenness or swell sometimes occurs when the radiation-sensitive composition is applied onto the substrate. When the viscosity is too low, it is sometimes difficult to obtain an intended film thickness. The viscosity can be adjusted by determining the type and the amount to be added of the monomers or the solvent as appropriate.
The cured product of the radiation-sensitive composition of the present invention, which is obtained by irradiating the radiation-sensitive composition with radiation such as ultraviolet light to cure, preferably has the following characteristics.
When the radiation-sensitive composition of the present invention is used as material for a core portion of an optical waveguide, the cured product of the radiation-sensitive composition has a refractive index nD25 preferably of 1.54 or more, more preferably of 1.55 or more. When the refractive index is less than 1.54, good transmission characteristics (i.e. low waveguide loss) sometimes cannot be obtained.
When the radiation-sensitive composition of the present invention is used as material for a clad layer of an optical waveguide, the cured product of the radiation-sensitive composition has a refractive index nD25 preferably at least 0.01 lower than the refractive index nD25 of the core portion, more preferably at least 0.03 lower than the refractive index nD25 of the core portion. When the difference in the refractive indexes is not less than 0.01, it is possible to obtain lower waveguide loss.
Here, the term “refractive index nD25” means the refractive index when an emission ray of Na at 589 nm is passed through at 25 degree C.
The cured product of the radiation-sensitive composition of the present invention has a glass-transition temperature (Tg) preferably of 80 degree C. or higher, more preferably of 100 degree C. or higher, most preferably of 110 degree C. or higher. When the glass-transition temperature is less than 80 degree C., the optical waveguide sometimes has insufficient heat resistance.
Here, the term “glass-transition temperature” means the temperature where a loss tangent shows a maximum value, which is measured using a sympathetic vibration dynamic viscoelasticity measuring apparatus with a vibrational frequency of 10 Hz.
The cured product of the radiation-sensitive composition of the present invention has a curing shrinkage ratio preferably of 10% or less, more preferably of 8% or less. When the curing shrinkage ratio exceeds 10%, adhesion to the substrate such as a silicon wafer and the like decreases, resulting in that the separation from the substrate depending on use conditions is likely to cause.
The radiation-sensitive composition of the present invention can be used as the materials of both or any one of the core portion and the clad layers, wherein the core portion and the clad layers constitute the optical waveguide. The radiation-sensitive composition of the present invention can be preferably used as at least the material for the lower clad layer due to excellent adhesion to the substrate.
In
An example of a method for manufacturing the optical waveguide 1 is as follows.
First, the radiation-sensitive composition of the present invention is applied onto the substrate 2 using a spin coater, and then irradiated with ultraviolet light to be cured, thus forming the lower clad layer 3. Next, another radiation-sensitive composition for forming the core portion is applied onto the lower clad layer 3, and irradiated with ultraviolet light from the upper side, via a photo-mask having a prescribed line pattern. By this irradiation, only the irradiated parts are cured, and the other parts, that is the uncured parts, are then removed using a developer. In this way, the core portion 5 can be obtained.
Next, the radiation-sensitive composition of the present invention is applied onto the upper surfaces of the lower clad layer 3 and the core portion 5, and then irradiated with ultraviolet light to be cured and form the upper clad layer 4, thus accomplishing the optical waveguide 1.
The present invention will now be described based on the following Examples.
Components listed in Table 1 were put into a flask, and stirred to become a transparent liquid while maintaining the liquid temperature at 60 degree C., thus obtaining a liquid radiation-sensitive composition (“Composition 1” to “Composition 5” in Table 1).
Characteristics of the obtained radiation-sensitive compositions were evaluated as follows.
(a) Refractive Index
The refractive index was measured using an Abbe refractive index detector, wherein an emission line of Na at 589 nm was passed through.
(b) Glass-Transition Temperature
The radiation-sensitive composition was applied onto a glass substrate to be 120 μm thick using an applicator to form a composition layer, and then, the composition layer was irradiated with ultraviolet light at 1.0 J/cm2 in a nitrogen atmosphere using a conveyor UV irradiation device, thus obtaining a cured film. Next, a temperature dependence of a loss tangent was measured for the cured film at a vibrational frequency of 10 Hz using a sympathetic vibration dynamic viscoelasticity measuring apparatus. The temperature where the obtained loss tangent reached a maximum was taken as the glass-transition temperature.
(c) Curing Shrinkage Ratio
The liquid density (D1) of the radiation-sensitive composition was measured at 23 degree C. using a pycnometer. Next, a cured film having a thickness of 120 μm was manufactured by the same method as the above “(b) Glass-transition temperature”, and the film was left for 24 hours in a thermo-hygrostat of 23 degree C and 50% humidity. A sample of 40 millimeter cube was then obtained by being cut out, and weighed (W1). The sample also weighed in distilled water at 25 degree C. (W2). The film density (D2) was calculated using the following expression.
Film density=[W1/(W1-W2)]×0.9971
By using the values of D1 and D2, the curing shrinkage ratio was calculated using the following expression.
Curing shrinkage ratio=[1−(D1/D2)]×100
(d) Separation Resistance
The radiation-sensitive composition was applied onto a surface-treated quartz substrate using an applicator, to be a coating film having a thickness of 50 μm. Next, the coating film of the radiation-sensitive composition was irradiated with ultraviolet light at a radiation dose of 500 mJ/cm2 using a conveyor UV irradiation device equipped with a metal halide lamp having a maximum light intensity of 250 mW/cm2, to be cured. The adhesion was evaluated by a cross-cut peeling test using sellotape in accordance with JIS K5600-5-6. When 100 squares in the grid were observed, the case that 80 or more squares remained without peeled off were taken as “o”, the case that not less than 50 but less than 80 squares were remained without peeled off was taken as “▴”, and the case that less than 50 squares remained were taken as “x”.
A radiation-sensitive composition for a clad layer shown in Table 2 was applied onto a substrate composed of a silicon wafer (thickness: 0.5 mm) using a spin coater, and then, irradiated with ultraviolet light having a wavelength of 365 nm and a light intensity of 35 mW/cm2 for 30 seconds using a mask aligner to be cured, thus forming a lower clad layer (thickness: 40 μm).
A radiation-sensitive composition for a core portion shown in Table 2 was applied onto the lower clad layer using a spin coater, and then, exposure was carried out by irradiating ultraviolet light having a wavelength of 365 nm and a light intensity of 35 mW/cm2 for 10 seconds, via a photo-mask having a 50 μm-width waveguide pattern. The substrate after the exposure was soaked into acetone, so that the unexposed parts were resolved. Heating was then carried out for 10 minutes at 100 degree C., thus forming a core portion (thickness: 50 μm).
Furthermore, the same radiation-sensitive composition as that for the lower clad layer was applied onto the upper surfaces of the lower clad layer and the core portion using a spin coater, and then, irradiated with ultraviolet light having a wavelength of 365 nm and a light intensity of 35 mW/cm2 for 30 seconds to be cured, thus forming an upper clad layer (thickness from the upper surface of the core portion: 40 μm).
Thus, an optical waveguide comprising the core portion and the clad layers was completed.
The obtained optical waveguides were evaluated as follows. (a) Waveguide loss The waveguide loss was measured using a cutback method, wherein the end face of the optical waveguide was cut by cleavage, and light having a wavelength of 850 nm was then inserted through a multimode fiber (50 μm in diameter). The cutback was carried out such that the measurement was carried out at five points at 1 cm interval from the end of the waveguide having a length of 5 cm. The obtained light intensity was plotted against the waveguide length, and the value of the loss was obtained by the gradient. The case that the obtained value of the loss was 0.5 dB/cm or less was taken as “o”, and the case that the obtained value of the loss was more than 0.5 dB/cm was taken as “x”.
(b) Temperature Characteristics
The following (1) to (3) were evaluated. (1) Change in optical characteristics at low temperature A linear waveguide having a waveguide length of 20 mm was prepared and the initial insertion loss was measured. After that, the linear waveguide was left for 500 hours at −40 degree C. and again the insertion loss was measured. The degree of change in the insertion loss between before and after the low-temperature treatment was calculated. The case that the degree of change in the insertion loss (i.e. the degree of increase from the initial insertion loss) exceeded 1.0 dB was taken as “x”, and the case that the amount of change in the insertion loss was 1.0 dB or less was taken as “o”.
By the same method as above, the initial insertion loss was measured, and then, the waveguide was left for 1,000 hours at high temperature and high humidity (temperature: 85 degree C., relative humidity: 85%). After that, the insertion loss was measured again. The degree of change in the insertion loss between before and after the high-temperature and high-humidity treatment was calculated. The case that the degree of change in the insertion loss (i.e. the degree of increase from the initial insertion loss) exceeded 1.0 dB was taken as “x”, and the case that the degree of change in the insertion loss was 1.0; dB or less was taken as “o”.
After the initial insertion loss was measured by the same method as that described above, a heat cycle, in which the waveguide was left at a temperature of −40 degree C. for 30 minutes, and then, left at a temperature of 85 degree C. for 30 minutes, was repeated; 500 times. After that, the insertion loss was measured again. The degree of change in the insertion loss between before and after the heat cycle treatment was calculated. The case that the degree of change in the insertion loss (i.e. the degree of increase from the initial insertion loss) exceeded 1.0 dB was taken as “x”, and the case that the degree of change in the insertion loss was 1.0 dB or less was taken as “o”.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-068734 | Mar 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/03433 | 2/23/2005 | WO | 00 | 3/26/2007 |
