JP2008047815A - Photoelectric conversion apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric conversion apparatus which exhibits effect of reinforcing a wafer in a manufacturing process, is excellent in handlability, exhibits stable mounting characteristics in mounting process and exhibits high reliability when it is actually used. <P>SOLUTION: A unit module can be obtained from a wafer in which a polyimide film having a tensile elastic modulus of not less than 4 GPa and a linear expansion coefficient of not more than 12 ppm is laminated on at least one surface via a thermally fused layer made of a thermoplastic polyimde resin. This unit module is formed into a panel to form the photoelectric conversion apparatus. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion device having a photoelectric conversion element formed on at least one surface, and more particularly to a thin photoelectric conversion device (preferably having a wafer thickness of 500 μm or less).

  In recent years, photoelectric energy conversion devices such as solar cells have been made thinner, smaller and lighter, and semiconductor wafers for such photoelectric conversion devices have been made thinner due to cost reduction requirements.

A semiconductor wafer is generally obtained by cutting a single crystal or polycrystal ingot into a thin plate with a wire saw or the like, and grinding and polishing the surface. Although it has become possible to obtain very thin wafers due to recent technological innovations, semiconductor wafers are generally brittle and very susceptible to cracking due to bending loads. A technique is widely known in which a wafer is prevented from cracking during handling and processing of a general semiconductor wafer, and at the same time, an adhesive tape is attached to the wafer so as to facilitate handling. The pressure-sensitive adhesive tape used in such a process is called a carrier tape, a dicing tape, or the like, which is attached only during the processing and is peeled off before moving to the mounting process. Such process technology can be found in, for example, Patent Documents 1 to 3.
JP 2006-156638 A JP 2005-290091 A JP 05-129431 A

On the other hand, a die attach film used for the purpose of fixing a semiconductor element to a support such as a substrate is known. These are made of a heat-resistant material, inserted between the back surface of the semiconductor chip and the substrate, used for the purpose of bonding the two, and do not reinforce the semiconductor element itself.
JP 2004-186296 A

On the other hand, it seems to be meaningful to attach a film or the like for the purpose of reinforcement not only during the processing step but also at the stage of the photoelectric conversion device that is diced and finally becomes a product. Patent Documents 5 to 7 disclose die attach films that can be used in both the wafer processing step and the semiconductor element bonding step in order to simplify the process and reduce costs.
JP 2002-294177 A JP 2003-109916 A JP 2003-129025 A

  As described above, it is well known that the handling property is improved by attaching a film to a semiconductor wafer being processed, and the wafer processing is completed for the film attached during the semiconductor wafer processing. It is a well-known idea that it is not peeled off later and used in the mounting process. However, in the conventional technology, particularly in terms of long-term durability when the process film is left in the mounting process and whether it can withstand various wide requirements in the mounting process, particularly strong heat stress and repeated heat There was no sufficient resistance to stress, and in particular, it was not fully satisfactory for the requirement of ensuring practical durability of photoelectric conversion devices such as solar cells.

  As described above, it is well known that the handling property is improved by attaching a film to a semiconductor wafer being processed, and the wafer processing is completed for the film attached during the semiconductor wafer processing. It is a well-known idea that it is not peeled off later and used in the mounting process. However, in the conventional technology, especially in terms of long-term durability when the process film is left in the mounting process and whether it can withstand various wide requirements in the mounting process, particularly strong heat stress and repeated heat There was not enough resistance to stress, and it was not enough to meet the requirements. These problems have been a major problem particularly in a photoelectric conversion device such as a solar cell which is a semiconductor element having a large area, but the problem of the present invention is that sufficient durability is obtained during processing and in actual use. That is.

As a result of continuing intensive studies in view of such circumstances, the present inventors have reached the next invention. That is, the present invention
1. A polyimide film having a tensile elastic modulus of 4 GPa or more and a linear expansion coefficient of 12 ppm or less is laminated on at least one side of a semiconductor wafer having a photoelectric conversion element formed on at least one side through a heat-fusible layer. Photoelectric conversion device,
2. 2. The photoelectric conversion device according to 1 above, wherein the glass transition temperature of the heat-fusible layer is 180 ° C. or higher.
3. The photoelectric conversion device according to 1 or 2, wherein the heat-fusible layer is a thermoplastic polyimide,
4). The photoelectric conversion device according to any one of 1 to 3, wherein the semiconductor wafer is single crystal silicon,
5. The photoelectric conversion device according to any one of 1 to 4, wherein the semiconductor wafer is polycrystalline silicon,
6). The photoelectric conversion device according to any one of 1 to 5, wherein the semiconductor wafer is a compound semiconductor,
It is.

  In the present invention, a polyimide film having a thermal characteristic equivalent to that of a semiconductor wafer and having excellent heat resistance is attached to the wafer, thereby protecting the wafer from vibration and impact during the semiconductor processing process and improving handling properties. In addition, it is difficult to cut and divide the wafer into a photoelectric conversion element shape, and the element itself can be reinforced in the mounting process and in actual use. A conversion device can be obtained.

The semiconductor wafer in the present invention is a single crystal composed of a single element such as diamond, silicon, germanium, polycrystal, single crystal of group IV such as silicon carbide, polycrystal, gallium arsenide, gallium nitride, gallium phosphide, indium. III-V group compound semiconductors such as phosphorus, II-VI group compound semiconductors such as cadmium telluride and zinc selenide, polycrystals, aluminum gallium arsenide, aluminum, gallium, indium phosphide, copper indium selenium, copper A single crystal or multi-crystal ingot of a multi-component compound semiconductor such as indium gallium selenium, which is cut into a thin plate shape.
A photoelectric conversion element described below is formed on the surface of these wafers through processing by a so-called semiconductor process.
In the present invention, the thickness of the wafer is preferably 800 μm or less, more preferably 450 μm or less, still more preferably 250 μm. Even more preferably 150 μm or less. When the wafer thickness g is thicker than this, the reinforcing effect due to the film attachment is not recognized significantly. The lower limit of the thickness of the wafer in the present invention is 8 μm or more, preferably 15 μm or more, more preferably 25 μm or more, and still more preferably 45 μm or more. If the lower limit is less than this range, it becomes difficult to handle the film until it is pasted, and it becomes difficult to obtain a predetermined effect.

  The photoelectric conversion element in the present invention mainly refers to an element that performs light-to-electrical conversion, such as a solar cell or an optical sensor. In addition, electric-to-light conversion elements such as light-emitting diodes and semiconductor lasers are also included in the category. These manufacturing processes are based on publicly known methods.

  In the present invention, it is essential that a polyimide film having a tensile modulus of elasticity modulus of 4 GPa or more and a linear expansion coefficient of 12 ppm or less is bonded to at least one surface of the wafer via an adhesive.

Although the polyimide film in this invention is not specifically limited, The combination of the following aromatic diamine and aromatic tetracarboxylic acid (anhydride) is mentioned as a preferable example.
A. A combination of an aromatic diamine having a benzoxazole structure and an aromatic tetracarboxylic acid.
B. A combination of an aromatic diamine having a diaminodiphenyl ether skeleton and an aromatic tetracarboxylic acid having a pyromellitic acid skeleton.
C. A combination of an aromatic diamine having a phenylenediamine skeleton and an aromatic tetracarboxylic acid having a biphenyltetracarboxylic acid skeleton.
D. A combination of one or more of the above ABCs.
Used in a polyimide benzoxazole film mainly composed of polyimide benzoxazole obtained by reacting an aromatic diamine having a benzoxazole structure that can be particularly preferably used in the present invention and an aromatic tetracarboxylic acid anhydride, Examples of aromatic diamines having a benzoxazole structure include the following compounds.

Among these, amino (aminophenyl) benzoxazole isomers are preferable from the viewpoint of ease of synthesis. Here, “each isomer” refers to each isomer in which two amino groups of amino (aminophenyl) benzoxazole are determined according to the coordination position (eg, the above “formula 1” to “formula 4”). Each compound described in the above. These diamines may be used alone or in combination of two or more.
In the present invention, it is preferable to use 70 mol% or more of the aromatic diamine having the benzoxazole structure.

The present invention is not limited to the above items, and the following aromatic diamines may be used. Preferably, the diamines do not have the benzoxazole structure exemplified below as long as the total aromatic diamine is less than 30 mol%. Is a polyimide film using one or two or more in combination.
Examples of such diamines include 4,4′-bis (3-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) phenyl] ketone, and bis [4- (3-aminophenoxy) phenyl]. Sulfide, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine,

3,3′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl sulfide, 3,3′-diaminodiphenyl sulfoxide, 3,4′-diaminodiphenyl sulfoxide 4,4′-diaminodiphenyl sulfoxide, 3,3′-diaminodiphenyl sulfone, 3,4′-diaminodiphenyl sulfone, 4,4′-diaminodiphenyl sulfone, 3,3′-diaminobenzophenone, 3,4′- Diaminobenzophenone, 4,4′-diaminobenzophenone, 3,3′-diaminodiphenylmethane, 3,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, bis [4- (4-aminophenoxy) phenyl] methane, 1 , 1-Bi [4- (4-aminophenoxy) phenyl] ethane, 1,2-bis [4- (4-aminophenoxy) phenyl] ethane, 1,1-bis [4- (4-aminophenoxy) phenyl] propane, 1 , 2-bis [4- (4-aminophenoxy) phenyl] propane, 1,3-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl ]propane,

1,1-bis [4- (4-aminophenoxy) phenyl] butane, 1,3-bis [4- (4-aminophenoxy) phenyl] butane, 1,4-bis [4- (4-aminophenoxy) Phenyl] butane, 2,2-bis [4- (4-aminophenoxy) phenyl] butane, 2,3-bis [4- (4-aminophenoxy) phenyl] butane, 2- [4- (4-aminophenoxy) Phenyl] -2- [4- (4-aminophenoxy) -3-methylphenyl] propane, 2,2-bis [4- (4-aminophenoxy) -3-methylphenyl] propane, 2- [4- ( 4-aminophenoxy) phenyl] -2- [4- (4-aminophenoxy) -3,5-dimethylphenyl] propane, 2,2-bis [4- (4-aminophenoxy) -3,5-dimethylphen Le] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane,

1,4-bis (3-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) benzene, 4,4′-bis (4-aminophenoxy) ) Biphenyl, bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl] sulfoxide, bis [4- ( 4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl] ether, 1,3-bis [4- (4-aminophenoxy) ) Benzoyl] benzene, 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,4-bis [4- (3 Aminophenoxy) benzoyl] benzene, 4,4′-bis [(3-aminophenoxy) benzoyl] benzene, 1,1-bis [4- (3-aminophenoxy) phenyl] propane, 1,3-bis [4- (3-aminophenoxy) phenyl] propane, 3,4'-diaminodiphenyl sulfide,

2,2-bis [3- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, bis [4- (3-aminophenoxy) phenyl] methane, 1,1 -Bis [4- (3-aminophenoxy) phenyl] ethane, 1,2-bis [4- (3-aminophenoxy) phenyl] ethane, bis [4- (3-aminophenoxy) phenyl] sulfoxide, 4,4 '-Bis [3- (4-aminophenoxy) benzoyl] diphenyl ether, 4,4'-bis [3- (3-aminophenoxy) benzoyl] diphenyl ether, 4,4'-bis [4- (4-amino-α) , Α-dimethylbenzyl) phenoxy] benzophenone, 4,4′-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] diphenylsulfone, bis 4- {4- (4-aminophenoxy) phenoxy} phenyl] sulfone, 1,4-bis [4- (4-aminophenoxy) phenoxy-α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-aminophenoxy) phenoxy-α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-amino-6-trifluoromethylphenoxy) -α, α-dimethylbenzyl] benzene, 1,3 -Bis [4- (4-amino-6-fluorophenoxy) -α, α-dimethylbenzyl] benzene, 1,3-bis [4- (4-amino-6-methylphenoxy) -α, α-dimethylbenzyl Benzene, 1,3-bis [4- (4-amino-6-cyanophenoxy) -α, α-dimethylbenzyl] benzene,

3,3′-diamino-4,4′-diphenoxybenzophenone, 4,4′-diamino-5,5′-diphenoxybenzophenone, 3,4′-diamino-4,5′-diphenoxybenzophenone, 3, 3'-diamino-4-phenoxybenzophenone, 4,4'-diamino-5-phenoxybenzophenone, 3,4'-diamino-4-phenoxybenzophenone, 3,4'-diamino-5'-phenoxybenzophenone, 3,3 '-Diamino-4,4'-dibiphenoxybenzophenone, 4,4'-diamino-5,5'-dibiphenoxybenzophenone, 3,4'-diamino-4,5'-dibiphenoxybenzophenone, 3,3'- Diamino-4-biphenoxybenzophenone, 4,4′-diamino-5-biphenoxybenzophenone, 3,4 -Diamino-4-biphenoxybenzophenone, 3,4'-diamino-5'-biphenoxybenzophenone, 1,3-bis (3-amino-4-phenoxybenzoyl) benzene, 1,4-bis (3-amino- 4-phenoxybenzoyl) benzene, 1,3-bis (4-amino-5-phenoxybenzoyl) benzene, 1,4-bis (4-amino-5-phenoxybenzoyl) benzene, 1,3-bis (3-amino) -4-biphenoxybenzoyl) benzene, 1,4-bis (3-amino-4-biphenoxybenzoyl) benzene, 1,3-bis (4-amino-5-biphenoxybenzoyl) benzene, 1,4-bis (4-Amino-5-biphenoxybenzoyl) benzene, 2,6-bis [4- (4-amino-α, α-dimethylbenzyl) pheno Si] A part or all of the hydrogen atoms on the aromatic ring in the benzonitrile and the aromatic diamine are halogen atoms, alkyl groups having 1 to 3 carbon atoms or alkoxyl groups, cyano groups, or alkyl groups or alkoxyl group hydrogen atoms. Examples thereof include aromatic diamines substituted with a halogenated alkyl group having 1 to 3 carbon atoms, partially or entirely substituted with halogen atoms, or alkoxyl groups.

  The aromatic tetracarboxylic acids used in the present invention are, for example, aromatic tetracarboxylic anhydrides. Specific examples of the aromatic tetracarboxylic acid anhydrides include the following.

These tetracarboxylic dianhydrides may be used alone or in combination of two or more.
In the present invention, one or two or more non-aromatic tetracarboxylic dianhydrides exemplified below may be used in combination as long as they are less than 30 mol% of the total tetracarboxylic dianhydrides. Examples of such tetracarboxylic acid anhydrides include butane-1,2,3,4-tetracarboxylic dianhydride, pentane-1,2,4,5-tetracarboxylic dianhydride, and cyclobutanetetracarboxylic acid. Acid dianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, cyclohexane-1,2,4,5-tetracarboxylic dianhydride, cyclohex-1-ene-2,3 5,6-tetracarboxylic dianhydride, 3-ethylcyclohex-1-ene-3- (1,2), 5,6-tetracarboxylic dianhydride, 1-methyl-3-ethylcyclohexane-3 -(1,2), 5,6-tetracarboxylic dianhydride, 1-methyl-3-ethylcyclohex-1-ene-3- (1,2), 5,6-tetracarboxylic dianhydride 1-ethylcyclohexane -(1,2), 3,4-tetracarboxylic dianhydride, 1-propylcyclohexane-1- (2,3), 3,4-tetracarboxylic dianhydride, 1,3-dipropylcyclohexane- 1- (2,3), 3- (2,3) -tetracarboxylic dianhydride, dicyclohexyl-3,4,3 ′, 4′-tetracarboxylic dianhydride,

Bicyclo [2.2.1] heptane-2,3,5,6-tetracarboxylic dianhydride, 1-propylcyclohexane-1- (2,3), 3,4-tetracarboxylic dianhydride, 1 , 3-Dipropylcyclohexane-1- (2,3), 3- (2,3) -tetracarboxylic dianhydride, dicyclohexyl-3,4,3 ′, 4′-tetracarboxylic dianhydride, bicyclo [2.2.1] Heptane-2,3,5,6-tetracarboxylic dianhydride, bicyclo [2.2.2] octane-2,3,5,6-tetracarboxylic dianhydride, bicyclo [2.2.2] Oct-7-ene-2,3,5,6-tetracarboxylic dianhydride and the like. These tetracarboxylic dianhydrides may be used alone or in combination of two or more.

  The solvent used for polycondensation (polymerization) of the aromatic diamines and aromatic tetracarboxylic acids (anhydrides) to obtain a polyamic acid dissolves both the raw material monomer and the polyamic acid produced. Although it will not specifically limit if it carries out, A polar organic solvent is preferable, for example, N-methyl-2-pyrrolidone, N-acetyl-2-pyrrolidone, N, N-dimethylformamide, N, N-diethylformamide, N, Examples thereof include N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoric amide, ethyl cellosolve acetate, diethylene glycol dimethyl ether, sulfolane, and halogenated phenols. These solvents can be used alone or in combination. The amount of the solvent used may be an amount sufficient to dissolve the monomer as a raw material. As a specific amount used, the mass of the monomer in the solution in which the monomer is dissolved is usually 5 to 40% by mass, The amount is preferably 10 to 30% by mass.

Conventionally known conditions may be applied for the polymerization reaction for obtaining the polyamic acid (hereinafter also simply referred to as “polymerization reaction”). As a specific example, in a temperature range of 0 to 80 ° C., 10 Stirring and / or mixing continuously for 30 minutes. If necessary, the polymerization reaction may be divided or the temperature may be increased or decreased. In this case, the order of adding both monomers is not particularly limited, but it is preferable to add aromatic tetracarboxylic acid anhydrides to the solution of aromatic diamines. The mass of the polyamic acid in the polyamic acid solution obtained by the polymerization reaction is preferably 5 to 40% by mass, more preferably 10 to 30% by mass, and the viscosity of the solution is measured with a Brookfield viscometer (25 ° C.). From the viewpoint of the stability of liquid feeding, it is preferably 10 to 2000 Pa · s, and more preferably 100 to 1000 Pa · s.
The reduced viscosity (ηsp / C) of the polyamic acid in the present invention is not particularly limited, but is preferably 3.0 dl / g or more, and more preferably 4.0 dl / g or more.
By setting it as these reduced viscosities, the control which the curl degree in 300 degreeC of the polyimide benzoxazole obtained becomes 10% or less becomes easy.

  Vacuum defoaming during the polymerization reaction is effective for producing a high-quality polyamic acid organic solvent solution. Moreover, you may perform superposition | polymerization by adding a small amount of terminal blockers to aromatic diamines before a polymerization reaction. Examples of the end capping agent include compounds having a carbon-carbon double bond such as maleic anhydride. The amount of maleic anhydride used is preferably 0.001 to 1.0 mol per mol of aromatic diamine.

  As an imidization method by high-temperature treatment, a conventionally known imidation reaction can be appropriately used. For example, using a polyamic acid solution that does not contain a ring-closing catalyst or a dehydrating agent, the imidization reaction proceeds by subjecting it to a heat treatment (so-called thermal ring-closing method), or a polycyclic acid solution containing a ring-closing catalyst and a dehydrating agent. In particular, a chemical ring closing method in which an imidization reaction is performed by the action of the above ring closing catalyst and a dehydrating agent can be given.

  100-500 degreeC is illustrated as a heating maximum temperature of a thermal ring closure method, Preferably it is 200-480 degreeC. When the maximum heating temperature is lower than this range, it is difficult to close the ring sufficiently. When the maximum heating temperature is higher than this range, deterioration proceeds and the composite tends to become brittle. A more preferable embodiment includes a two-stage heat treatment in which treatment is performed at 150 to 250 ° C. for 3 to 20 minutes and then treatment is performed at 350 to 500 ° C. for 3 to 20 minutes.

In the chemical ring closure method, imidization can be completely performed by heating after forming a precursor complex having self-supporting property by partially proceeding imidization reaction of the polyamic acid solution.
In this case, the condition for partially proceeding with the imidization reaction is preferably a heat treatment for 3 to 20 minutes at 100 to 200 ° C., and the condition for allowing the imidization reaction to be completely performed is preferably 200 to 400 ° C. For 3 to 20 minutes.

The timing for adding the ring-closing catalyst to the polyamic acid solution is not particularly limited, and may be added in advance before the polymerization reaction for obtaining the polyamic acid. Specific examples of the ring-closing catalyst include aliphatic tertiary amines such as trimethylamine and triethylamine, and heterocyclic tertiary amines such as isoquinoline, pyridine, and betapicoline. Among them, heterocyclic tertiary amines are mentioned. At least one amine selected from is preferred. Although the usage-amount of a ring-closing catalyst with respect to 1 mol of polyamic acids does not have limitation in particular, Preferably it is 0.5-8 mol.
The timing of adding the dehydrating agent to the polyamic acid solution is not particularly limited, and may be added in advance before the polymerization reaction for obtaining the polyamic acid. Specific examples of the dehydrating agent include aliphatic carboxylic acid anhydrides such as acetic anhydride, propionic anhydride, butyric anhydride, and aromatic carboxylic acid anhydrides such as benzoic anhydride. Among them, acetic anhydride, benzoic anhydride, etc. Acids or mixtures thereof are preferred. Moreover, the usage-amount of the dehydrating agent with respect to 1 mol of polyamic acids is not particularly limited, but is preferably 0.1 to 4 mol. When a dehydrating agent is used, a gelation retarder such as acetylacetone may be used in combination.

Although the thickness of the polyimide film of this invention is not specifically limited, Usually, it is 1-150 micrometers, Preferably it is 9-50 micrometers. This thickness can be easily controlled by the coating amount when a film raw material solution such as a polyamic acid solution is applied to the support and the raw material concentration in the film raw material solution such as a polyamic acid solution.
In the (polyimide) film of the present invention, it is preferable to add a lubricant to the (polyimide) film to give fine irregularities on the film surface to improve the slipping property of the film.
As the lubricant, inorganic or organic fine particles having an average particle diameter of about 0.03 μm to 3 μm can be used. Specific examples include titanium oxide, alumina, silica, calcium carbonate, calcium phosphate, calcium hydrogen phosphate, calcium pyrophosphate, Examples include magnesium oxide, calcium oxide, and clay minerals.
The (polyimide) film of the present invention may be a non-stretched film or a stretched film. Here, the non-stretched film is mechanical in the surface expansion direction of the film by tenter stretching, roll stretching, inflation stretching, or the like. A film that can be obtained without intentionally applying a large external force.

  The tensile elastic modulus of the polyimide film in the present invention is essential to be 4 GPa or more, preferably 4.8 GPa or more, and more preferably 6.5 GPa or more. If the tensile modulus is below this range, the effect of reinforcing the wafer is reduced. Although the upper limit of the tensile modulus of the polyimide film in the present invention is not particularly defined, it is generally 30 GPa or less, preferably 23 GPa or less, and more preferably 15 GPa or less. If the tensile elastic modulus is too high, an unexpected strain stress may be generated on the wafer due to strain at the time of bonding or the like.

  The linear expansion coefficient of the polyimide film in the present invention is essential to be 12 ppm or less, preferably 9 ppm or less, and more preferably 6 ppm or more. If the linear expansion coefficient exceeds this range, distortion stress may be generated in the wafer due to temperature change, which may cause damage such as cracking. The lower limit of the linear expansion coefficient of the polyimide film in the present invention is preferably −12 ppm or more, more preferably −7 ppm or more, still more preferably −2 ppm or more, and still more preferably 1 ppm or more. Even when the linear expansion coefficient is lower than the value of the child, distortion stress may be generated in the wafer due to temperature change, which may cause breakage or the like.

  The hygroscopic expansion coefficient of the polyimide film in the present invention is preferably 30 ppm or less, more preferably 26 ppm or less, further preferably 22 ppm or more, and still more preferably 17 ppm or less. Although the contribution of the hygroscopic expansion coefficient is smaller than the linear expansion coefficient, similarly, if the hygroscopic expansion coefficient exceeds this range, distortion stress occurs in the wafer due to changes in the humidity under the environment, leading to photoelectric conversion element failures and wafer damage. There is a case. The lower limit of the hygroscopic expansion coefficient is not particularly defined, but is preferably 0 ppm. Here, the hygroscopic expansion coefficient is determined by leaving a film with two or more marks for measurement (interval of 50 mm or more) at a relatively low humidity (10 to 40% RH, temperature is 15 to 40 ° C.) for 24 hours. The difference between the measured mark interval and the mark interval measured after leaving the film at a relatively high humidity (70 to 100%, temperature is 20 to 60 ° C.) for 24 hours is standardized by dividing the difference by the humidity difference. Can be obtained.

  In order to keep the tensile modulus, linear expansion coefficient, and hygroscopic expansion coefficient of the polyimide film within a predetermined range, 45% or more of each of tetracarboxylic acid anhydrides and diamines is an aromatic compound, and further tetracarboxylic acid anhydrides. This can be realized by setting the amount of the compound having an ether bond to 40 mol% or less, preferably 30 mol% or less, and more preferably 20 mol% or less in both or any one of the diamines and diamines.

  In the present invention, the heat-sealing layer refers to a layer made of a heat-resistant polymer exhibiting thermoplasticity. Examples of the heat-sealing layer include fluororesins, pre-aromatic polyesters, polyether imides, polyacrylimides, polyamide imides, etc. Although it will not specifically limit if it is a thing which shows favorable adhesiveness to both of the selected semiconductor wafers, Preferably, it is polyetherimide.

  The glass transition temperature of the heat sealing layer of the present invention is preferably 180 ° C. or higher, more preferably 200 ° C. or higher, still more preferably 220 ° C. or higher, and still more preferably 235 ° C. or higher. If the glass transition temperature is less than this range, heat resistance may be insufficient when a chip cut from a wafer is mounted, leading to troubles such as film peeling or blistering. The upper limit of the glass transition temperature is not particularly limited.

The storage rate of the heat-sealing layer of the present invention is preferably in the range of 0.5 to 10 GPa. The lower limit of the storage elastic modulus is preferably 0.8 GPa or more, more preferably 1.2 GPa or more, and still more preferably 1.5 GPa or more. On the other hand, the upper limit is 7 GPa or less, more preferably 5 GPa or less. If the storage elastic modulus of the adhesive is less than this range, the effect of reinforcing the wafer by the film is difficult to obtain. If the storage elastic modulus of the adhesive exceeds this range, an unexpected strain stress may be generated on the wafer due to distortion during bonding.
Here, the storage elastic modulus of the adhesive means the storage elastic modulus of a cured product thin film obtained by curing the adhesive on a film having a thickness of about 2 to 200 μm.

In such a combination of photoelectric conversion element and film attachment, the photoelectric conversion element is formed on at least one side of the wafer, and the film is attached on at least one side. Usually, a mode in which a photoelectric conversion element is attached to one side and a polyimide film is attached to the opposite side is preferred, but the invention is not particularly limited to this combination. In some cases, it may be useful to attach a polyimide film to the surface on which the photoelectric conversion element is formed.
The photoelectric conversion elements may be formed on both sides of the wafer. Also in this case, the surface on which the polyimide film is attached may be one side or both sides. Such photoelectric conversion elements are electrically connected by a method such as ordinary wire bonding, bump bonding, and automatic tape bonding. Also, the front and back of the wafer can be connected by a through electrode.

There is no particular limitation on the timing of attaching the polyimide film to the wafer. In the case of a configuration in which a photoelectric conversion element is pasted on one side and a polyimide film is pasted on the opposite side, it is preferable that the handling is facilitated by sticking before entering the wafer processing process or at a relatively early stage of the process. A general laminator or press may be used for pasting.
Careful attention must be paid to the selection of a cushioning agent in order to attach the wafer so as not to damage it.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In addition, the acquisition property in an Example was measured with the following method.
1. Reduced viscosity of polyamic acid (ηsp / C)
A solution dissolved in N-methyl-2-pyrrolidone so that the polymer concentration was 0.2 g / dl was measured at 30 ° C. using an Ubbelohde type viscosity tube.
2. The thickness of the polyimide film The thickness was measured using a micrometer (Millitron 1254D manufactured by Fine Reef).
3. Tensile modulus of polyimide film A polyimide film to be measured was cut into strips of 100 mm × 10 mm in the flow direction (MD direction) and the width direction (TD direction), respectively, as test pieces. Using a tensile tester (manufactured by Shimadzu Corporation, Autograph (trade name), model name AG-5000A) under the conditions of a tensile speed of 50 mm / min and a distance between chucks of 40 mm, the tensile modulus of elasticity in each of the MD direction and TD direction, Tensile rupture strength and tensile rupture elongation were measured.

4). Linear expansion coefficient (CTE) of polyimide film
About the polyimide film to be measured, the stretch rate in the MD direction and the TD direction is measured under the following conditions, and the stretch rate / temperature at intervals of 30 ° C. to 45 ° C., 45 ° C. to 60 ° C.,. This was measured up to 300 ° C., and the average value of all measured values was calculated as CTE. The meanings of the MD direction and the TD direction are the same as in the measurement of “3.” above.
Device name: TMA4000S manufactured by MAC Science
Sample length: 20mm
Sample width: 2 mm
Temperature rise start temperature: 25 ° C
Temperature rise end temperature: 400 ° C
Temperature increase rate: 5 ° C / min
Atmosphere: Argon

5. Storage elastic modulus of heat-sealing layer The storage elastic modulus E ′ in the present invention is measured as follows.
Measurement method: A solid viscoelastic device RSA-II (manufactured by Rheometrics) was used.
Tensile mode: (auto tension)
Measurement temperature: 30 ° C
Frequency: 10Hz

6). Glass transition temperature (Tg) of heat-sealing layer
Measuring method: Using a solid viscoelastic device RSA-II (manufactured by Rheometric),
Tensile mode: (auto tension)
Measurement temperature: 15 ° C. to 300 ° C./temperature increase rate 5 ° C./min Frequency: 10 Hz
It calculated | required from the inflection point of the storage elastic modulus E 'of the chart obtained by measuring by.

Abbreviations of compounds used in Examples and the like are described below.
PMDA: pyromellitic dianhydride ODA: 4,4'-diaminodiphenyl ether PDA: paraphenylenediamine

[Examples 1 to 6, Comparative Example 1]
(Preparation of polyamic acid solution, preparation of polyimide film)
1.22 parts by mass of spherical particles of amorphous silica Seahoster KE-P10 (manufactured by Nippon Shokubai Co., Ltd.), 420 parts by mass of N-methyl-2-pyrrolidone, the wetted part of the container, and the piping for infusion are austenitic stainless steel The mixture was placed in a container of SUS316L and stirred with a homogenizer T-25 basic (manufactured by IKA Labortechnik) at a rotation speed of 1000 rpm for 1 minute to obtain a preliminary dispersion. The average particle size in the preliminary dispersion was 0.11 μm.
A nitrogen inlet tube, a thermometer, a liquid contact part of a container equipped with a stirring rod, and an infusion pipe were replaced with nitrogen in the reaction container made of austenitic stainless steel SUS316L, and then 223 parts by mass of 5-amino-2- ( p-Aminophenyl) benzoxazole was added. Next, 4000 parts by mass of N-methyl-2-pyrrolidone was added and completely dissolved, and then the preliminary dispersion obtained above was added with 420 parts by mass and 217 parts by mass of pyromellitic dianhydride. When the mixture was stirred at ° C. for 24 hours, a brown viscous polyamic acid solution A was obtained. The reduced viscosity (ηsp / C) was 3.8 dl / g.

The polyamic acid solution A obtained in the polymerization example was coated on the non-lubricant surface of polyethylene terephthalate film A-4100 (manufactured by Toyobo Co., Ltd.) using a comma coater (gap: 650 μm, coating width: 1240 mm). It passed on the continuous drying furnace which has four drying zones, and it dried on the following predetermined conditions.
First zone: Upper temperature 105 ° C, lower temperature 110 ° C
Air volume 20 cubic m / min for both top and bottom Second zone: Upper temperature 110 ° C, lower temperature 110 ° C
Air volume 30 cubic m / min for both top and bottom Third zone: Upper temperature 110 ° C, lower temperature 110 ° C
Air volume 20 cubic m / min for both top and bottom Zone 4: Upper temperature 110 ° C, lower temperature 110 ° C
Upper air flow 15 cubic m / min, lower air flow 20 cubic m / min The length of each zone is the same, and the total drying time is 15 minutes.
The air volume is the sum of the air volumes from the outlets for each zone.
The polyamic acid film (also referred to as green film) that became self-supporting after drying was peeled from the polyester film, and both ends were cut to obtain respective green films having a thickness of 65 μm and a width of 700 mm.
The obtained green film was passed through a continuous heat treatment furnace purged with nitrogen while holding both ends with a pin tenter, and the first stage was heated at 180 ° C. for 5 minutes and at a heating rate of 4 ° C./second. As the second stage, two stages of heating were performed at 400 ° C. for 5 minutes to advance the imidization reaction. Then, it cooled to room temperature in 5 minutes, and the 38-micrometer-thick polyimide film which exhibits brown was obtained. The properties of the obtained film are shown in Table 1.

  Similarly, a polyimide film was obtained using tetracarboxylic dianhydride and diamine shown in Table 1. The properties of the obtained polyimide film are shown in Table 1. When two types of monomers were used for acid anhydride or diamine, the molar ratio was adjusted to 1: 1.

(Preparation of heat-fusible polyimide: polymerization of polyamic acid comprising 4,4′-oxydiphthalic anhydride)
The inside of the reaction vessel equipped with a nitrogen introduction tube, a thermometer, and a stirring rod was replaced with nitrogen, and then 930 parts by mass of 1,3-bis (4-aminophenoxy) benzene was introduced, and 15000 parts by mass of N, N-dimethylacetamide was introduced. After stirring well so as to be uniform, 40.5 parts by mass of Snowtex (trade name) DMAC-Zl (manufactured by Nissan Chemical Industries, Ltd.) obtained by dispersing colloidal silica in dimethylacetamide (8.1% silica) The solution was cooled to 0 ° C., 990 parts by mass of 4,4′-oxydiphthalic anhydride was added, and the mixture was stirred for 17 hours. A pale yellow and viscous polyamic acid solution X was obtained. The solution obtained had a ηsp / C of 3.1 dl / g. The glass transition temperature of the polyimide film obtained from this polyamic acid was 240 degreeC.
Plasma treatment is performed on one side of the polyimide film having a thickness of 38 μm obtained above, then the polyamic acid solution X is applied and dried to a dry thickness of 5 μm, and heat treatment is similarly performed to obtain the polyamic acid solution X on one side. A two-layer polyimide film containing the obtained heat-fusible polyimide was obtained.

(Lamination of wafer and film)
The heat-bonded surface of the obtained double-layer polyimide film and the wafer are overlapped and temporarily attached, charged into a press machine and heated from room temperature to 280 ° C. at a heating rate of about 5 ° C./min. Until cooled.
As the wafer, a single crystal silicon wafer having a diameter of about 100 mm and a thickness of 0.25 mm and a single crystal GaAs wafer having a diameter of 50 mm and a thickness of 0.4 mm were used.

(Handling evaluation)
The obtained film-reinforced wafer is divided into single wafers. A single crystal silicon wafer is placed in a carrier for 100 mm wafers manufactured by Dainichi Shoji Co., Ltd., and a GaAs wafer is placed in a carrier for 50 mm wafers. After applying vibration for 5 hours, the damage condition of the wafer was confirmed, and the handling property was evaluated. The results are shown in Table 3.

(Solar cell processing process)
A solar cell having a pin junction was formed on the surface where the film of the single crystal silicon wafer was not attached by a general method. A solar cell was also formed on one side of the GaAs wafer.
(Laser cut property evaluation)
The wafer surface of the obtained film-reinforced wafer was divided into 20 mm × 20 mm rectangular chips with a dicing saw, and the film surface was cut with a laser cutter. All of the reinforced wafers showed good cutting properties.

(Solder heat resistance evaluation)
A 20 mm x 20 mm chip divided from a film-reinforced wafer is placed on an alumina substrate wafer and subjected to a heat treatment at 240 ° C for 3 minutes using a reflow soldering device to check for chip abnormalities, especially the appearance of the film attachment surface. Went. The results are shown in Table 3.

(PCT resistance evaluation)
A square unit module inscribed from a round wafer reinforced with a film is cut out, placed in a stainless mesh cage, and used for 96 hours in a saturated vapor pressure of 121 ° C. × 2 atm using a PCT device PC242-III manufactured by Hirayama Seisakusho. A pressure heating test was conducted. Abnormality of the module after the test, especially the appearance inspection of the film attachment surface was performed. The results are shown in Table 3.

(Evaluation of heat cycle resistance)
The unit module is placed in a stainless mesh cage and immersed in a methanol bath at -50 ° C and a silicone oil bath at + 120 ° C for 10 minutes alternately for 10 minutes each time. Appearance inspection of the surface was performed. The results are shown in Table 3.

  As described above, the photoelectric conversion device obtained from the film-reinforced wafer according to the configuration of the present invention exhibits good handling properties, solder heat resistance, PCT resistance, heat cycle resistance, and vibration and impact during the processing process. This product is useful as a photoelectric conversion device that is expected to have sufficient durability even during mounting processes such as modularization and paneling, and during actual use after mounting processes, and that requires high reliability. is there.

Claims (6)

  A polyimide film having a tensile elastic modulus of 4 GPa or more and a linear expansion coefficient of 12 ppm or less is laminated on at least one side of a semiconductor wafer having a photoelectric conversion element formed on at least one side through a heat-fusible layer. Photoelectric conversion device.   The photoelectric conversion device according to claim 1, wherein the heat-fusible layer has a glass transition temperature of 180 ° C. or higher.   The photoelectric conversion device according to claim 1, wherein the heat-fusible layer is a thermoplastic polyimide.   The photoelectric conversion device according to claim 1, wherein the semiconductor wafer is single crystal silicon.   The photoelectric conversion device according to claim 1, wherein the semiconductor wafer is polycrystalline silicon.   The photoelectric conversion device according to claim 1, wherein the semiconductor wafer is a compound semiconductor.