WO2015160065A1 - Conductive paste composition and semiconductor device comprising the same - Google Patents

Conductive paste composition and semiconductor device comprising the same Download PDF

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Publication number
WO2015160065A1
WO2015160065A1 PCT/KR2014/012355 KR2014012355W WO2015160065A1 WO 2015160065 A1 WO2015160065 A1 WO 2015160065A1 KR 2014012355 W KR2014012355 W KR 2014012355W WO 2015160065 A1 WO2015160065 A1 WO 2015160065A1
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WO
WIPO (PCT)
Prior art keywords
powder
metal
conductive paste
metal oxide
paste composition
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PCT/KR2014/012355
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French (fr)
Inventor
Won Il Son
Sang Jin Oh
Jae Hyung Song
Seung Ki Cho
Cheol Hee Kim
Jung Geun Park
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Duksan Hi-Metal Co., Ltd.
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Publication of WO2015160065A1 publication Critical patent/WO2015160065A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/20—Conductive material dispersed in non-conductive organic material
    • H01B1/22—Conductive material dispersed in non-conductive organic material the conductive material comprising metals or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/14—Conductive material dispersed in non-conductive inorganic material
    • H01B1/16—Conductive material dispersed in non-conductive inorganic material the conductive material comprising metals or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/02—Details
    • H01L31/0224—Electrodes
    • H01L31/022408—Electrodes for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/022425—Electrodes for devices characterised by at least one potential jump barrier or surface barrier for solar cells

Definitions

  • the present invention relates to a conductive paste composition, and more particularly, to a conductive paste composition for forming a thin film pattern such as an electrode or wiring to connect electrical signals of semiconductor devices.
  • the present invention relates to a semiconductor device, especially a solar cell, having an electrode or wiring formed of the conductive paste composition.
  • a conductive paste (or ink) is applied on a substrate to form a pattern for transferring an electrical signal.
  • a conductive paste typically includes a conductive powder, a glass frit, and an organic medium.
  • a conductive paste is printed in the form of a linear pattern or other patterns on a substrate and then fired.
  • a conductive paste should be printed in a pattern having a desired line width via a desired printing process, and also, enables the resulting electrode to be attached onto a substrate while possessing durability, so as to exhibit high adhesion and low resistance.
  • desired printability research has to be ongoing into compositions adapted for fine line widths and properties for printing processes corresponding thereto. To this end, the size of a conductive powder or the properties of an organic medium is regarded as important.
  • desired adhesiveness research has to be carried out into stably attaching the conductive paste composition to a substrate for a long period of time. To this end, the composition of a glass frit is regarded as important.
  • electrical conductivity requires studies for ohmic contact and line resistance due to a reduction in line width. To this end, the composition of a conductive powder and a frit is regarded as important.
  • a conductive paste composition has to be individually characterized with regard to printability, adhesiveness and electrical conductivity depending on the end use.
  • an anti-reflective film made of silicon nitride, titanium oxide or silicon oxide is formed on a semiconductor substrate to promote absorption of solar light and may thus may function as an insulator, undesirably damaging the flow of electrons to the substrate (or from the substrate).
  • a conductive paste for heat generation should infiltrate the anti-reflective film during firing in order to achieve efficient electrical contact with the substrate, and also should be specifically characterized so as to form strong bonding to the substrate.
  • a conductive paste for use in a flexible substrate should be developed to have a composition able to maintain adhesiveness despite flexibility of the substrate.
  • a conductive powder, a glass frit and an organic medium which are technical elements for use in ensuring printability, adhesiveness and electrical conductivity of the conductive paste composition, have antagonistic influences on each other, and thus development of balanced technology for individual technical elements is required.
  • Cited reference 1 Korean Patent Application Publication No. 2005-243500 discloses a conductive paste including an organic binder, a solvent, a glass frit, a conductive powder and at least one metal selected from the group consisting of Ti, Bi, Zn, Y, In and Mo or a metal compound thereof, wherein the average particle size of metal or metal compound is 0.001 to less than 0.1 ⁇ m.
  • the conductive paste including ultrafine metal or a metal compound is fired, thereby forming a front electrode having stability, high electrical conductivity and superior adhesion between the conductive paste and the semiconductor through the anti-reflective layer.
  • the coating film may shrink, thus increasing contact resistance.
  • thermal shrinkage behavior coefficient of linear expansion
  • microcracks may be created on the surface of the semiconductor substrate.
  • an increase in the contact resistance may undesirably result in lowered FF and thus deteriorated conversion efficiency.
  • the present invention is intended to provide a conductive paste composition having enhanced printability and electrical conductivity by improving a conductive powder.
  • the present invention is intended to provide a semiconductor device having increased efficiency and good durability while reducing a line width.
  • An aspect of the present invention provides a conductive paste composition, comprising: a conductive powder including a first metal powder having an average diameter (D50) of 1 ⁇ 3 ⁇ m, and a metal nanopowder agglomerate having a size of 0.5 ⁇ 10 ⁇ m obtained by agglomerating a metal nanopowder having an average diameter (D50) of 100 ⁇ 200 nm; a metal oxide powder; an organic medium; and an additive.
  • a conductive paste composition comprising: a conductive powder including a first metal powder having an average diameter (D50) of 1 ⁇ 3 ⁇ m, and a metal nanopowder agglomerate having a size of 0.5 ⁇ 10 ⁇ m obtained by agglomerating a metal nanopowder having an average diameter (D50) of 100 ⁇ 200 nm; a metal oxide powder; an organic medium; and an additive.
  • the conductive powder may further include a second metal powder having an average diameter (D50) of 0.5 ⁇ 1 ⁇ m.
  • the first metal powder, the second metal powder, and the metal nanopowder agglomerate may comprise at least one metal selected from the group consisting of Cu, Ag, Au, Ni, Al, W and Zn.
  • the metal nanopowder agglomerate may be used in an amount of 0.1 ⁇ 10 parts by weight based on 100 parts by weight of the first metal powder, and the second metal powder may be used in an amount of 10 ⁇ 40 parts by weight based on 100 parts by weight of the first metal powder.
  • the first metal powder may be configured such that the outer surface thereof has projections so as to be irregular, and the highest point of the projections may be higher by 0.1 ⁇ 0.6 ⁇ m than a portion having no projection.
  • the metal oxide powder may comprise X1-X2-...-Xn-O (wherein Xn is a metal selected from the group consisting of Pb, Te, Bi, W, Mo, Zn, Al, Si, B, Fe, Co, Cr, Cu, Ni, V, Li, P and Mn, and essentially contains Pb, Te and Bi, and n is an integer of 3 or more), and in the metal oxide powder, an amount of Pb, a wt%, an amount of Te, b wt% and an amount of Bi, c wt% may satisfy both of [Relation 1] and [Relation 2] below.
  • the metal oxide powder may include a first metal oxide powder having a first glass transition temperature of a°C and a second metal oxide powder having a second glass transition temperature of b°C, and the first glass transition temperature of the first metal oxide powder may fall in the range of 170 ⁇ a ⁇ 310, and the second glass transition temperature of the second metal oxide powder may fall in the range of 230 ⁇ b ⁇ 320, with satisfying 10 ⁇ b-a ⁇ 60.
  • the additive may be used in an amount of 1 ⁇ 5 parts by weight based on 100 parts by weight of the conductive powder, and may comprise Te-X-O, Te-Y or Te-Y-Z (wherein X is at least one metal selected from the group consisting of alkali metals and alkaline earth metals, and Y and Z are at least one metal selected from the group consisting of Zn, Ag, Na, Mg and Al, Y ⁇ Z).
  • the conductive paste composition according to the present invention may comprise 70 ⁇ 90 wt% of the conductive powder, 0.7 ⁇ 9 wt% of the metal oxide powder, 3.5 ⁇ 18 wt% of the organic medium, and 0.7 ⁇ 4.5 wt% of the inorganic additive, based on the total weight of the conductive paste composition.
  • a silicon solar cell comprising: a silicon semiconductor substrate; an emitter layer formed on the substrate; an anti-reflective film formed on the emitter layer; a front electrode connected to the emitter layer through the anti-reflective film; and a rear electrode connected to a rear side of the substrate, wherein the front electrode is formed by applying the conductive paste composition as above in a predetermined pattern on the anti-reflective film and then performing firing.
  • a conductive paste composition includes a conductive powder comprising a metal nanopowder agglomerate, thus enhancing electrical conductivity and printability.
  • the conductive paste composition includes a metal powder having projections on the outer surface thereof, thus enhancing electrical conductivity and printability.
  • an electronic device can be enhanced in printability and durability of an electrode or wiring formed with the conductive paste composition, thus increasing efficiency of a semiconductor device.
  • FIG. 1 is an electron microscope image illustrating a conductive powder having projections with a size of 0.4 ⁇ 0.6 ⁇ m according to an embodiment of the present invention
  • FIG. 2 is an electron microscope image illustrating a conductive powder having projections with a size of 0.1 ⁇ 0.2 ⁇ mm according to an embodiment of the present invention
  • FIG. 3 is an electron microscope image (MAG 2.50kx) illustrating a metal nanopowder agglomerate according to an embodiment of the present invention.
  • FIG. 4 is an electron microscope image (MAG 40.0kx) illustrating a metal nanopowder agglomerate according to an embodiment of the present invention.
  • a conductive paste composition comprises a conductive powder, a metal oxide powder, an organic medium and an additive.
  • a conductive powder is a powder comprising a first metal powder and a metal nanopowder agglomerate.
  • average diameter (D50) refers to a powder diameter at 50% in the cumulative powder diameter distribution.
  • a first metal powder is a metal powder having an average diameter (D50) of 1 ⁇ 3 ⁇ m.
  • the shape of the metal powder is not limited but a spherical powder having projections on the outer surface thereof is preferable.
  • the powder may function to improve sintering properties based on a principle of an increase in the specific surface area.
  • the average diameter is a size including projections, and the projections mean that the highest point of the projections is higher by 0.1 ⁇ 0.6 ⁇ m than a portion having no projection without limitation of shape or size so long as they enable the outer surface of the powder to be irregular.
  • FIGS. 1 and 2 illustrate the electron microscope images of the metal powders having projections.
  • the metal nanopowder agglomerate is obtained by agglomerating a metal nanopowder having an average diameter (D50) of 100 ⁇ 200 nm, and the average diameter (D50) of the metal nanopowder agglomerate is preferably 0.5 ⁇ 10 ⁇ m.
  • the metal nanopowder having a size of 100 ⁇ 200 nm plays a role in enhancing adhesion between the substrate and the electrode, it may increase line resistance due to sintering shrinkage of the electrode and may cause physical defects such as cracking after firing to thus decrease the sintering density, undesirably resulting in poor long-term reliability.
  • such an agglomerate is effective at increasing sintering density and ensuring long-term reliability without cracking.
  • the metal nanopowder agglomerate may be used in an amount of 0.1 ⁇ 10 parts by weight based on 100 parts by weight of the first metal powder.
  • the conductive powder may further include a second metal powder having an average diameter (D50) of 0.5 ⁇ 1 ⁇ m.
  • the average diameter of the second metal powder is smaller than that of the first metal powder.
  • the use of the second metal powder is considered to improve a function of reducing line resistance based on a principle of an increase in the packing density.
  • the second metal powder may be contained in an amount of 10 ⁇ 40 parts by weight based on 100 parts by weight of the first metal powder.
  • a metal such as Cu, Ag, Au, Ni, Al, W or Zn may be used.
  • a metal such as Cu, Ag, Au, Ni, Al, W or Zn may be used.
  • Ag is preferably useful.
  • the specific surface area of the conductive powder may be 0.05 ⁇ 5 m 2 /g. If the specific surface area thereof is less than 0.05 m 2 /g, it is impossible to form a fine line (70 ⁇ m or less) due to the large particle size. In contrast, if the specific surface area thereof exceeds 5 m 2 /g, poor workability such as a need for a large amount of solvent to adjust viscosity may result.
  • the conductive powder is used in an amount of 60 ⁇ 90 wt% based on the total weight of the conductive paste composition. If the amount of the conductive powder exceeds 90 wt%, viscosity may increase, making it difficult to form a composition in a paste phase. In contrast, if the amount thereof is less than 70 wt%, the amount of the conductive powder may be lowered, and thus electrical conductivity of the resulting front electrode and the aspect ratio of the printed pattern may decrease.
  • a metal oxide powder is an X1-X2- ... -Xn-O oxide powder, wherein Xn is selected from the group consisting of Pb, Si, Sn, Li, Ti, Ag, Na, K, Rb, Cs, Ge, Ga, Te, In, Ni, Zn, Ca, Mg, Sr, Ba, Se, Mo, W, Y, As, La, Nd, Co, Pr, Gd, Sm, Dy, Eu, Ho, Yb, Lu, Bi, Ta, V, Fe, Hf, Cr, Cd, Sb, Bi, F, Zr, Mn, P, Cu, Ce, Fe and Nb, and n is an integer of 2 or more.
  • X1-X2- ... -Xn-O may be at least partially crystalline.
  • the metal oxide powder has a desired powder size by mixing X1, X2, ... , and Xn oxides, followed by melting, cooling, grinding and screening.
  • the average particle size (D50) of the metal oxide powder may be 0.1 ⁇ 3.0 ⁇ m.
  • the metal oxide powder preferably has a melting temperature of 250 ⁇ 900°C.
  • the metal oxide powder has a softening temperature of 300 ⁇ 550°C so that the conductive paste may be sintered at 600 ⁇ 950°C, appropriately wet or properly adhered to the substrate. If the softening temperature is lower than 300°C, sintering may proceed, making it impossible to sufficiently obtain the effects of the invention. In contrast, if the softening temperature is higher than 550°C, sufficient melt fluidity is not caused during firing, and thus desired adhesive strength cannot be exhibited. In some cases, liquid sintering of Ag cannot be promoted. As such, "softening temperature” refers to a softening temperature based on a fiber elongation method according to ASTM C338-57.
  • the chemical composition of the metal oxide powder is not limited in the present invention, and a typical material may be used.
  • the metal oxide powder may comprise a single kind of metal oxide powder, or two or more kinds of metal oxide powder having different glass transition temperatures.
  • Xn may include at least two metals selected from the group consisting of Pb, Te, W, Mo, Zn, Al, Bi, Si, B, Fe, Co, Cr, Cu, Ni, V, Li, P and Mn.
  • the metal oxide powder essentially contains Pb, Te and Bi.
  • Pb calculated in terms of oxide, PbO
  • the amount of Pb is a wt% based on the total weight of the metal oxide powder, it preferably falls in the range of 0.1 ⁇ a ⁇ 20, and more preferably 1 ⁇ a ⁇ 15. Given the amount range, pn bonding reliability may be ensured under various sheet resistance values and solar cell efficiency may increase.
  • the amount of Te (calculated in terms of oxide, TeO 2 ) is b wt% based on the total weight of the metal oxide powder, it preferably falls in the range of 50 ⁇ b ⁇ 80 and more preferably 60 ⁇ b ⁇ 75. If the amount of TeO 2 is less than 50 wt%, Ag solidity by TeO 2 may decrease and thus contact resistance may increase. In contrast, if the amount of TeO 2 exceeds 80 wt%, reactivity with the Si interface may become weak due to excessive addition of TeO 2 , and thus contact resistance may increase.
  • a, b and c preferably satisfy both of [Relation 1] and [Relation 2] below.
  • the metal oxide powder may further include Zn.
  • Zn When the amount of Zn in the metal oxide powder is d wt%, it may satisfy [Relation 3] below.
  • An example of the metal oxide powder may be Pb-Te-Bi-Si-B-Zn-Al-O.
  • the amounts of respective metals are set in terms of oxides, including 0.5 ⁇ 15 wt% of PbO, 50 ⁇ 75 wt% of TeO 2 , 10 ⁇ 20 wt% of Bi 2 O 3 , 0.1 ⁇ 10 wt% of SiO 2 , 0.1 ⁇ 10 wt% of B 2 O 3 , 1 ⁇ 8 wt% of ZnO and 0.1 ⁇ 3 wt% of Al 2 O 3 .
  • the metal oxide powder may be Pb-Te-W-Mo-Zn-Bi-Al-O.
  • the amounts of respective metals are set in terms of oxides, including 0.5 ⁇ 15 wt% of PbO, 60 ⁇ 75 wt% of TeO 2 , 0.5 ⁇ 15 wt% of ZnO, 10 ⁇ 20 wt% of Bi 2 O 3 and 0.1 ⁇ 12 wt% of Al 2 O 3 .
  • the sum of WO 3 and MoO 3 is 5 ⁇ 30 wt%.
  • the metal oxide powder when two kinds of metal oxide powder are used, the metal oxide powder may include both of a first metal oxide powder having a first glass transition temperature of a°C and a second metal oxide powder having a second glass transition temperature of b°C.
  • the first metal oxide powder preferably has a first glass transition temperature of 170 ⁇ a ⁇ 310
  • the second metal oxide powder may have a second glass transition temperature of 230 ⁇ b ⁇ 320.
  • a difference between the second glass transition temperature b of the second metal oxide powder and the first glass transition temperature a of the first metal oxide powder may satisfy 10 ⁇ b-a ⁇ 60. If the temperature difference is less than 10°C, an effect of widening the firing temperature range may become insignificant. In contrast, if the temperature difference exceeds 60°C, either the first or the second metal oxide powder cannot function as the metal oxide powder during the firing.
  • the first metal oxide powder preferably contains Te, and may further include at least one metal selected from the group consisting of Bi, Zn, B, Al, Ba, Si, W and Fe.
  • the second metal oxide powder preferably contains Pb, and may further include at least one metal selected from the group consisting of Li, Na, Ti, Cu, Ni, V, P, K and Sn.
  • the amount of the first metal oxide powder may be set to 80 ⁇ 90 wt%, and the amount of the second metal oxide powder may be set to 0.5 ⁇ 20 wt%.
  • the amount of the metal oxide powder is not particularly limited so long as the purposes of the present invention are achieved, it may be set to 1 ⁇ 10 parts by weight based on 100 parts by weight of the conductive powder. If the amount of the metal oxide powder is less than 1 part by weight, adhesive strength may become poor. In contrast, if the amount thereof exceeds 10 parts by weight, it is difficult to perform the subsequent soldering process attributed to glass floating or the like.
  • organic medium refers to incorporation of a binder and a solvent, wherein a binder may include a solvent.
  • a viscosity modifier may be further added as the additive, as necessary.
  • examples of the binder may include, but are not limited to, cellulose derivatives, such as methyl cellulose, ethyl cellulose or ethyl hydroxyethyl cellulose, wood rosin, ethyl cellulose-phenol resin mixture, polymethacrylate of lower alcohol and monobutyl ether of ethyleneglycol monoacetate, acrylic resin, alkyd resin, polypropylene-based resin, polyvinylchloride-based resin, polyurethane-based resin, rosin-based resin, terpene-based resin, phenol-based resin, aliphatic petroleum resin, acrylic acid ester-based resin, xylene-based resin, Coumarone-Indene-based resin, styrene-based resin, dicyclopentadiene-based resin, polybutene-based resin, polyether-based resin, urea-based resin, melamine-based resin, vinylacetate-based resin, and polyisobutyl-based resin.
  • cellulose derivatives such
  • the solvent may include, but are not limited to, hexane, toluene, ester alcohol, terpene such as ⁇ - or ⁇ -terpineol, kerosene, dibutyl phthalate, butyl carbitol, butyl carbitol acetate, hexylene glycol, benzyl alcohol, alcohol ester, diethyleneglycol diethylether, diacetonealcohol terpineol methylethylketone, ethylcellosove, cyclohexanone, butylcellosolve, and butylcellosolve acetate.
  • any one or a mixture of two or more selected from the group consisting of bis(2-(2-butoxyethoxy)ethyl)adipate, dibasic ester, octyl epoxytallate, isotetradecanol and pentaerythritol ester of hydrogenated rosin may be used instead of or together with the solvent as above.
  • dibasic ester may include any one or a mixture of two or more selected from the group consisting of dimethylester of adipic acid, dimethylester of glutaric acid, and dimethylester of succinic acid.
  • the amount of the organic medium may be 5 ⁇ 20 parts by weight based on 100 parts by weight of the conductive powder. If the amount of the organic medium exceeds 20 parts by weight, the resulting front electrode may have lowered electrical conductivity. In contrast, if the amount of the organic medium is less than 5 parts by weight, bondability with the substrate may deteriorate.
  • the conductive paste according to an embodiment of the present invention may include inorganic and organic additives.
  • An inorganic additive may include any metal selected from the group consisting of Li, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Pb, Cu, Zn, Ag, Te, Zn, Na, Mg, Al, W and Fe, metal oxides, and alloys or alloy oxides thereof. Examples thereof may include PbO, CuO, ZnO, MgO and WO 3 .
  • the inorganic additive may include a metal alloy or metal alloy oxide, containing Te, and preferable examples thereof include Te-X-O, Te-Y and Te-Y-Z, wherein X is at least one metal selected from the group consisting of alkali metals or alkaline earth metals, and Y and Z are at least one metal selected from the group consisting of Zn, Ag, Na, Mg and Al, provided that Y and Z are not the same metal.
  • Te-X-O is exemplified by Li 2 TeO 3 , Na 2 TeO 3 , SrTeO 3 , BeTeO 3 or MgTeO 3 , and Te-Y or Te-Y-Z may be Ag-Te, Li-Te-Zn, Te-Zn-K, or Te-Zn-Na.
  • the inorganic additive according to the present invention includes a metal able to promote a solid-phase reaction via reaction with the metal contained in the conductive powder, and thus may accelerate grain growth of the metal powder, which is the conductive powder, even at low temperature. Thereby, the firing temperature range of the paste composition may become wide, thus increasing electrical conductivity.
  • the particle size of the additive according to the present invention is not particularly limited.
  • the average particle size may be smaller than 10 mm.
  • the average particle size is 0.01 ⁇ 5 ⁇ m, and is more preferably 50 ⁇ 200 nm.
  • the amount of the inorganic additive is 1 ⁇ 10 parts by weight, and preferably 1 ⁇ 5 parts by weight, based on 100 parts by weight of the conductive powder. If the amount of the inorganic additive exceeds 5 parts by weight based on 100 parts by weight of the conductive powder, the amount of the conductive powder may decrease and thus the resistance of the front electrode formed of the corresponding paste composition may increase, thereby deteriorating solar cell efficiency. In contrast, if the amount of the inorganic additive is less than 1 part by weight based on 100 parts by weight of the conductive powder, it is difficult to sufficiently exhibit the effects by the additive.
  • the organic additive may include, but is not limited, to a dispersant, an antioxidant, a UV absorber, a defoaming agent, a thickener, a stabilizer, and a viscosity modifier, which may be used alone or in combination of two or more and may be mixed within a range that does not impair the effects of the present invention.
  • the dispersant such as stearic acid, palmitic acid, myristic acid, oleic acid or lauric acid, may be mixed with the conductive paste.
  • the dispersant is not limited to organic acid so long as it is typically useful.
  • the conductive paste is prepared by mixing a conductive powder, a metal oxide powder, an organic medium, and an additive using a 3-roll kneader.
  • the conductive paste according to the present invention is preferably applied on a desired portion of an electronic device via screen printing. When it is applied using such a printing process, it may have a predetermined viscosity.
  • the viscosity of the conductive paste according to the present invention may be 50 ⁇ 300 PaS as measured using #14 spindle with a Brookfield HBT viscometer and using a utility cup at 10 rpm and 25°C.
  • the conductive paste according to the present invention is applied via screen printing on a substrate of a semiconductor device to be manufactured, and then dried.
  • the substrate coated with the conductive paste is fired at about 700 ⁇ 950°C, thus forming a conductive paste pattern.
  • a conductive powder was prepared by mixing a first Ag powder having an average diameter of 2 ⁇ m, and an Ag nanopowder agglomerate having a size of 10 ⁇ m (formed by agglomerating 200 nm sized Ag nanopowder).
  • a metal oxide powder was composed of 6.5 g of MO1 having an average diameter of 2 ⁇ m (based on the total weight of the metal oxide powder, 78.0 wt% of PbO, 11.5 wt% of SiO 2 , 7.5 wt% of B 2 O 3 , 0.5 wt% of Al 2 O 3 , 1.0 wt% of ZnO, 0.5 wt% of Fe 2 O 3 , 0.5 wt% of Cr 2 O 3 , 0.1 wt% of Co 2 O 3 , and 0.4 wt% of MnO 2 ).
  • a conductive paste composition was prepared by mixing, based on 100 g of the paste composition, 70.0 g of the first Ag powder, 11.0 g of the Ag nanopowder agglomerate, 6.5 g of the metal oxide powder, 10.2 g of a terpineol solution containing 20 wt% of ethylcellulose as an organic solvent, and 2.3 g of an inorganic additive ZnO.
  • a conductive paste composition was prepared in the same manner as in Example 1, with the exception that the amount of the conductive powder was changed as shown in Table 1 below.
  • Conductive paste compositions were prepared in the same manner as in Example 1, with the exception that the conductive powder and the metal oxide powder were changed as shown in Table 1 below.
  • the second Ag powder of the conductive powder was a powder having an average diameter of 0.7 ⁇ m.
  • Conductive paste compositions were prepared in the same manner as in Example 1, with the exception that the conductive powder and the metal oxide powder were changed as shown in Table 1 below.
  • Conductive paste compositions were prepared in the same manner as in Examples 3 and 4, with the exception that the conductive powder, the metal oxide powder and the inorganic additive were changed as shown in Table 1 below.
  • Conductive paste compositions were prepared in the same manner as in Example 9, with the exception that the kinds of metal oxide powder and inorganic additive were changed as shown in Table 1 below.
  • Conductive paste compositions were prepared in the same manner as in Examples 2, 4, 6 and 8, with the exception that the Ag nanopowder was not provided in the form of an agglomerate as shown in Table 1 below.
  • a conductive paste composition was prepared in the same manner as in Comparative Example 4, with the exception that the kind of metal oxide powder was changed as shown in Table 1 below.
  • the conductive paste compositions of the above examples and comparative examples were pre-mixed using a universal mixer, and kneaded using a 3-roll kneader, thus obtaining individual conductive pastes.
  • the amounts (g) of materials used and the features thereof are shown in Table 1 below.
  • the composition proportions (wt%) of the metal oxide powders MO1 ⁇ MO6 are shown in Table 2 below, and the composition proportions of MO7 ⁇ MO10 are shown in Table 3 below.
  • a solar cell was manufactured using the conductive paste of each of Examples 1 to 12 and Comparative Examples 1 to 5. Specifically, a silicon substrate was prepared, and a conductive paste (Ag paste) for solder connection was applied on the rear side thereof using screen printing and then dried. Subsequently, an Al paste (PV333 made by E.I. du Pont de Nemours and Company) for a rear electrode was applied via screen printing so as to partially overlap the dried Ag paste, and then dried.
  • a conductive paste Al paste for solder connection
  • each paste was set to 120°C.
  • the film thickness of each electrode of the rear side which is a dried film thickness
  • the Al paste and the Ag paste were applied to 35 ⁇ m and 20 ⁇ m, respectively.
  • the paste of the invention was applied on a light-receiving side (front side) via screen printing and then dried.
  • a 1.5 inch pattern for evaluation comprising a finger line having a width of 100 ⁇ m and a bus bar having a width of 2 mm was employed, and the film thickness was 13 ⁇ m after firing.
  • the paste applied on the substrate was co-fired in an IR firing furnace under conditions of a peak temperature of about 730°C and an IN-OUT time of about 5 min, thus obtaining a desired solar cell.
  • the solar cell obtained using the conductive paste according to the present invention was configured such that the Ag electrode was formed on the light-receiving side (front side) and the Al electrode (first electrode) composed mainly of Al and the Ag electrode (second electrode) composed mainly of Ag were formed on the rear side.
  • the electric properties (I-V properties) of the obtained solar cell substrate were evaluated by a cell tester. Using a system (NCT-M-150AA) made by NPC as a cell tester, Eff (Conversion Efficiency) (%) and FF (Fill Factor) were measured. The results are shown in Table 4 below.
  • the adhesion of the obtained solar cell was measured as follows. Specifically, the surface of the front electrode formed using an electrode forming process was heated to 200°C and a SnPbAg-based solder ribbon (line width: 2 mm, indium corporation, SUNTABTM) was attached to a length of 10 cm thereto. Then, while one end of the attached portion was pulled in a 180° direction with a universal tensile tester (QC-508E, COMETECH), a force (N, newton) until the electrode and the solder ribbon were peeled from each other was measured.
  • the evaluation results based on the following criteria are shown in adhesion (N) in Table 4 below.

Abstract

Disclosed is a conductive paste composition, including: a conductive powder including a first metal powder having an average diameter (D50) of 1 ~ 3 μm, and a metal nanopowder agglomerate having a size of 0.5 ~ 2 μm obtained by agglomerating a metal nanopowder having an average diameter (D50) of 100 ~ 200 nm; a metal oxide powder; and an organic medium.

Description

CONDUCTIVE PASTE COMPOSITION AND SEMICONDUCTOR DEVICE COMPRISING THE SAME
The present invention relates to a conductive paste composition, and more particularly, to a conductive paste composition for forming a thin film pattern such as an electrode or wiring to connect electrical signals of semiconductor devices. In addition, the present invention relates to a semiconductor device, especially a solar cell, having an electrode or wiring formed of the conductive paste composition.
A conductive paste (or ink) is applied on a substrate to form a pattern for transferring an electrical signal. A conductive paste typically includes a conductive powder, a glass frit, and an organic medium. In order to form a pattern for transferring an electrical signal on a substrate, a conductive paste is printed in the form of a linear pattern or other patterns on a substrate and then fired.
Requirements of a conductive paste include printability, adhesiveness and electrical conductivity. Specifically, a conductive paste should be printed in a pattern having a desired line width via a desired printing process, and also, enables the resulting electrode to be attached onto a substrate while possessing durability, so as to exhibit high adhesion and low resistance. For desired printability, research has to be ongoing into compositions adapted for fine line widths and properties for printing processes corresponding thereto. To this end, the size of a conductive powder or the properties of an organic medium is regarded as important. For desired adhesiveness, research has to be carried out into stably attaching the conductive paste composition to a substrate for a long period of time. To this end, the composition of a glass frit is regarded as important. Also, electrical conductivity requires studies for ohmic contact and line resistance due to a reduction in line width. To this end, the composition of a conductive powder and a frit is regarded as important.
Meanwhile, a conductive paste composition has to be individually characterized with regard to printability, adhesiveness and electrical conductivity depending on the end use. For example, when it is used for an electrode for a crystalline silicon solar cell, an anti-reflective film made of silicon nitride, titanium oxide or silicon oxide is formed on a semiconductor substrate to promote absorption of solar light and may thus may function as an insulator, undesirably damaging the flow of electrons to the substrate (or from the substrate). Hence, a conductive paste for heat generation should infiltrate the anti-reflective film during firing in order to achieve efficient electrical contact with the substrate, and also should be specifically characterized so as to form strong bonding to the substrate. Furthermore, a conductive paste for use in a flexible substrate should be developed to have a composition able to maintain adhesiveness despite flexibility of the substrate.
As such, a conductive powder, a glass frit and an organic medium, which are technical elements for use in ensuring printability, adhesiveness and electrical conductivity of the conductive paste composition, have antagonistic influences on each other, and thus development of balanced technology for individual technical elements is required.
Since the conversion efficiency of a solar cell is obtained by multiplying open voltage, short current density and fill factor (FF), it may be lowered in proportion to a decrease in FF. However, the characteristics of electrodes are considered important to increase power generation in solar cells. For instance, as the resistance value of the electrode is lower, the power generation efficiency may increase. In this regard, Cited reference 1 (Korean Patent Application Publication No. 2005-243500) discloses a conductive paste including an organic binder, a solvent, a glass frit, a conductive powder and at least one metal selected from the group consisting of Ti, Bi, Zn, Y, In and Mo or a metal compound thereof, wherein the average particle size of metal or metal compound is 0.001 to less than 0.1 μm. In Cited reference 1, the conductive paste including ultrafine metal or a metal compound is fired, thereby forming a front electrode having stability, high electrical conductivity and superior adhesion between the conductive paste and the semiconductor through the anti-reflective layer. However, when the composition of the conductive paste including the ultrafine metal or the metal compound as disclosed in Cited reference 1 is printed, dried and then fired on the surface of the semiconductor substrate, the coating film (paste film) may shrink, thus increasing contact resistance. In some cases, due to a difference in thermal shrinkage behavior (coefficient of linear expansion) between the paste film and the semiconductor substrate, microcracks may be created on the surface of the semiconductor substrate. Moreover, an increase in the contact resistance may undesirably result in lowered FF and thus deteriorated conversion efficiency.
Accordingly, the present invention is intended to provide a conductive paste composition having enhanced printability and electrical conductivity by improving a conductive powder.
In addition, the present invention is intended to provide a semiconductor device having increased efficiency and good durability while reducing a line width.
An aspect of the present invention provides a conductive paste composition, comprising: a conductive powder including a first metal powder having an average diameter (D50) of 1 ~ 3 μm, and a metal nanopowder agglomerate having a size of 0.5 ~ 10 μm obtained by agglomerating a metal nanopowder having an average diameter (D50) of 100 ~ 200 nm; a metal oxide powder; an organic medium; and an additive.
In the conductive paste composition according to the present invention, the conductive powder may further include a second metal powder having an average diameter (D50) of 0.5 ~ 1 μm.
In the conductive powder according to the present invention, the first metal powder, the second metal powder, and the metal nanopowder agglomerate may comprise at least one metal selected from the group consisting of Cu, Ag, Au, Ni, Al, W and Zn.
In the conductive powder according to the present invention, the metal nanopowder agglomerate may be used in an amount of 0.1 ~ 10 parts by weight based on 100 parts by weight of the first metal powder, and the second metal powder may be used in an amount of 10 ~ 40 parts by weight based on 100 parts by weight of the first metal powder.
In the conductive powder according to the present invention, the first metal powder may be configured such that the outer surface thereof has projections so as to be irregular, and the highest point of the projections may be higher by 0.1 ~ 0.6 μm than a portion having no projection.
In the conductive paste composition according to the present invention, the metal oxide powder may comprise X1-X2-…-Xn-O (wherein Xn is a metal selected from the group consisting of Pb, Te, Bi, W, Mo, Zn, Al, Si, B, Fe, Co, Cr, Cu, Ni, V, Li, P and Mn, and essentially contains Pb, Te and Bi, and n is an integer of 3 or more), and in the metal oxide powder, an amount of Pb, a wt%, an amount of Te, b wt% and an amount of Bi, c wt% may satisfy both of [Relation 1] and [Relation 2] below.
[Relation 1]
70≤a+b+c≤90 (1≤a≤15, 60≤b≤75)
[Relation 2]
2.5≤b/c≤7.5 (60≤b≤75)
In the conductive paste composition according to the present invention, the metal oxide powder may include a first metal oxide powder having a first glass transition temperature of a℃ and a second metal oxide powder having a second glass transition temperature of b℃, and the first glass transition temperature of the first metal oxide powder may fall in the range of 170≤a≤310, and the second glass transition temperature of the second metal oxide powder may fall in the range of 230≤b≤320, with satisfying 10≤b-a≤60.
In the conductive paste composition according to the present invention, the additive may be used in an amount of 1 ~ 5 parts by weight based on 100 parts by weight of the conductive powder, and may comprise Te-X-O, Te-Y or Te-Y-Z (wherein X is at least one metal selected from the group consisting of alkali metals and alkaline earth metals, and Y and Z are at least one metal selected from the group consisting of Zn, Ag, Na, Mg and Al, Y≠Z).
The conductive paste composition according to the present invention may comprise 70 ~ 90 wt% of the conductive powder, 0.7 ~ 9 wt% of the metal oxide powder, 3.5 ~ 18 wt% of the organic medium, and 0.7 ~ 4.5 wt% of the inorganic additive, based on the total weight of the conductive paste composition.
Another aspect of the present invention provides a silicon solar cell, comprising: a silicon semiconductor substrate; an emitter layer formed on the substrate; an anti-reflective film formed on the emitter layer; a front electrode connected to the emitter layer through the anti-reflective film; and a rear electrode connected to a rear side of the substrate, wherein the front electrode is formed by applying the conductive paste composition as above in a predetermined pattern on the anti-reflective film and then performing firing.
According to the present invention, a conductive paste composition includes a conductive powder comprising a metal nanopowder agglomerate, thus enhancing electrical conductivity and printability.
Also, the conductive paste composition includes a metal powder having projections on the outer surface thereof, thus enhancing electrical conductivity and printability.
According to the present invention, an electronic device can be enhanced in printability and durability of an electrode or wiring formed with the conductive paste composition, thus increasing efficiency of a semiconductor device.
The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is an electron microscope image illustrating a conductive powder having projections with a size of 0.4 ~ 0.6 μm according to an embodiment of the present invention;
FIG. 2 is an electron microscope image illustrating a conductive powder having projections with a size of 0.1 ~ 0.2μmm according to an embodiment of the present invention;
FIG. 3 is an electron microscope image (MAG 2.50kx) illustrating a metal nanopowder agglomerate according to an embodiment of the present invention; and
FIG. 4 is an electron microscope image (MAG 40.0kx) illustrating a metal nanopowder agglomerate according to an embodiment of the present invention.
In the following description of the present invention, the terms used herein are merely intended to describe specific embodiments and are not construed as limiting the scope of the present invention by the appended claims. Unless otherwise defined, all of technical or scientific terms used herein have the same meanings as those typically understood by persons having ordinary knowledge in the art to which the present invention belongs.
Unless otherwise stated, the terms "comprise", "comprises" and "comprising" are used to designate the presence of an object, a step or groups of objects and steps described in the specification and claims, and should be understood so as not to exclude presence or additional probability of any other objects, steps or groups of objects or steps.
Unless otherwise noted, various embodiments of the present invention may be combined with any other embodiments. In particular, any feature which is mentioned preferably or favorably may be combined with any other features which may be mentioned preferably or favorably.
Conductive paste composition
According to an embodiment of the present invention, a conductive paste composition comprises a conductive powder, a metal oxide powder, an organic medium and an additive.
1. Conductive powder
A conductive powder is a powder comprising a first metal powder and a metal nanopowder agglomerate. As used herein, "average diameter (D50)" refers to a powder diameter at 50% in the cumulative powder diameter distribution.
A first metal powder is a metal powder having an average diameter (D50) of 1 ~ 3 μm. As such, the shape of the metal powder is not limited but a spherical powder having projections on the outer surface thereof is preferable. When the powder has projections on the outer surface thereof, it may function to improve sintering properties based on a principle of an increase in the specific surface area. As such, the average diameter is a size including projections, and the projections mean that the highest point of the projections is higher by 0.1 ~ 0.6 μm than a portion having no projection without limitation of shape or size so long as they enable the outer surface of the powder to be irregular. FIGS. 1 and 2 illustrate the electron microscope images of the metal powders having projections.
The metal nanopowder agglomerate is obtained by agglomerating a metal nanopowder having an average diameter (D50) of 100 ~ 200 nm, and the average diameter (D50) of the metal nanopowder agglomerate is preferably 0.5 ~ 10 μm. Although the metal nanopowder having a size of 100 ~ 200 nm plays a role in enhancing adhesion between the substrate and the electrode, it may increase line resistance due to sintering shrinkage of the electrode and may cause physical defects such as cracking after firing to thus decrease the sintering density, undesirably resulting in poor long-term reliability. However, when the metal nanopowder is made into an agglomerate, such an agglomerate is effective at increasing sintering density and ensuring long-term reliability without cracking.
The metal nanopowder agglomerate may be used in an amount of 0.1 ~ 10 parts by weight based on 100 parts by weight of the first metal powder.
In an embodiment of the present invention, the conductive powder may further include a second metal powder having an average diameter (D50) of 0.5 ~ 1 μm. The average diameter of the second metal powder is smaller than that of the first metal powder. The use of the second metal powder is considered to improve a function of reducing line resistance based on a principle of an increase in the packing density.
The second metal powder may be contained in an amount of 10 ~ 40 parts by weight based on 100 parts by weight of the first metal powder.
For the metal powder or metal nanopowder, a metal such as Cu, Ag, Au, Ni, Al, W or Zn may be used. Preferably useful is Ag.
The specific surface area of the conductive powder may be 0.05 ~ 5 m2/g. If the specific surface area thereof is less than 0.05 m2/g, it is impossible to form a fine line (70 μm or less) due to the large particle size. In contrast, if the specific surface area thereof exceeds 5 m2/g, poor workability such as a need for a large amount of solvent to adjust viscosity may result.
The conductive powder is used in an amount of 60 ~ 90 wt% based on the total weight of the conductive paste composition. If the amount of the conductive powder exceeds 90 wt%, viscosity may increase, making it difficult to form a composition in a paste phase. In contrast, if the amount thereof is less than 70 wt%, the amount of the conductive powder may be lowered, and thus electrical conductivity of the resulting front electrode and the aspect ratio of the printed pattern may decrease.
2. Metal oxide powder (X1-X2-…- Xn -O powder)
A metal oxide powder is an X1-X2-…-Xn-O oxide powder, wherein Xn is selected from the group consisting of Pb, Si, Sn, Li, Ti, Ag, Na, K, Rb, Cs, Ge, Ga, Te, In, Ni, Zn, Ca, Mg, Sr, Ba, Se, Mo, W, Y, As, La, Nd, Co, Pr, Gd, Sm, Dy, Eu, Ho, Yb, Lu, Bi, Ta, V, Fe, Hf, Cr, Cd, Sb, Bi, F, Zr, Mn, P, Cu, Ce, Fe and Nb, and n is an integer of 2 or more. In the metal oxide powder, X1-X2-…-Xn-O may be at least partially crystalline.
The metal oxide powder has a desired powder size by mixing X1, X2, …, and Xn oxides, followed by melting, cooling, grinding and screening.
The average particle size (D50) of the metal oxide powder may be 0.1 ~ 3.0 μm. As such, the metal oxide powder preferably has a melting temperature of 250 ~ 900℃.
In the present invention, the metal oxide powder has a softening temperature of 300 ~ 550℃ so that the conductive paste may be sintered at 600 ~ 950℃, appropriately wet or properly adhered to the substrate. If the softening temperature is lower than 300℃, sintering may proceed, making it impossible to sufficiently obtain the effects of the invention. In contrast, if the softening temperature is higher than 550℃, sufficient melt fluidity is not caused during firing, and thus desired adhesive strength cannot be exhibited. In some cases, liquid sintering of Ag cannot be promoted. As such, "softening temperature" refers to a softening temperature based on a fiber elongation method according to ASTM C338-57.
The chemical composition of the metal oxide powder is not limited in the present invention, and a typical material may be used. The metal oxide powder may comprise a single kind of metal oxide powder, or two or more kinds of metal oxide powder having different glass transition temperatures.
When a single kind of metal oxide powder is used, Xn may include at least two metals selected from the group consisting of Pb, Te, W, Mo, Zn, Al, Bi, Si, B, Fe, Co, Cr, Cu, Ni, V, Li, P and Mn. In the present invention, the metal oxide powder essentially contains Pb, Te and Bi. When the amount of Pb (calculated in terms of oxide, PbO) is a wt% based on the total weight of the metal oxide powder, it preferably falls in the range of 0.1≤a≤20, and more preferably 1≤a≤15. Given the amount range, pn bonding reliability may be ensured under various sheet resistance values and solar cell efficiency may increase. Also, when the amount of Te (calculated in terms of oxide, TeO2) is b wt% based on the total weight of the metal oxide powder, it preferably falls in the range of 50≤b≤80 and more preferably 60≤b≤75. If the amount of TeO2 is less than 50 wt%, Ag solidity by TeO2 may decrease and thus contact resistance may increase. In contrast, if the amount of TeO2 exceeds 80 wt%, reactivity with the Si interface may become weak due to excessive addition of TeO2, and thus contact resistance may increase.
In the metal oxide powder essentially containing Pb, Te and Bi according to the present invention, when the amounts of Pb, Te and Bi are a wt%, b wt% and c wt%, respectively, a, b and c preferably satisfy both of [Relation 1] and [Relation 2] below.
[Relation 1]
70≤a+b+c≤90 (1≤a≤15, 60≤b≤75)
[Relation 2]
2.5≤b/c≤7.5 (60≤b≤75)
The metal oxide powder may further include Zn. When the amount of Zn in the metal oxide powder is d wt%, it may satisfy [Relation 3] below.
[Relation 3]
0.5≤d/a≤3.5 (1≤a≤15)
An example of the metal oxide powder may be Pb-Te-Bi-Si-B-Zn-Al-O. As such, the amounts of respective metals are set in terms of oxides, including 0.5 ~ 15 wt% of PbO, 50 ~ 75 wt% of TeO2, 10 ~ 20 wt% of Bi2O3, 0.1 ~ 10 wt% of SiO2, 0.1 ~ 10 wt% of B2O3, 1 ~ 8 wt% of ZnO and 0.1 ~ 3 wt% of Al2O3.
Another example of the metal oxide powder may be Pb-Te-W-Mo-Zn-Bi-Al-O. As such, the amounts of respective metals are set in terms of oxides, including 0.5 ~ 15 wt% of PbO, 60 ~ 75 wt% of TeO2, 0.5 ~ 15 wt% of ZnO, 10 ~ 20 wt% of Bi2O3 and 0.1 ~ 12 wt% of Al2O3. The sum of WO3 and MoO3 is 5 ~ 30 wt%.
In the present invention, when two kinds of metal oxide powder are used, the metal oxide powder may include both of a first metal oxide powder having a first glass transition temperature of a℃ and a second metal oxide powder having a second glass transition temperature of b℃. The first metal oxide powder preferably has a first glass transition temperature of 170≤a≤310, and the second metal oxide powder may have a second glass transition temperature of 230≤b≤320. A difference between the second glass transition temperature b of the second metal oxide powder and the first glass transition temperature a of the first metal oxide powder may satisfy 10≤b-a≤60. If the temperature difference is less than 10℃, an effect of widening the firing temperature range may become insignificant. In contrast, if the temperature difference exceeds 60℃, either the first or the second metal oxide powder cannot function as the metal oxide powder during the firing.
The first metal oxide powder preferably contains Te, and may further include at least one metal selected from the group consisting of Bi, Zn, B, Al, Ba, Si, W and Fe. The second metal oxide powder preferably contains Pb, and may further include at least one metal selected from the group consisting of Li, Na, Ti, Cu, Ni, V, P, K and Sn.
Based on the total weight of the metal oxide powder, the amount of the first metal oxide powder may be set to 80 ~ 90 wt%, and the amount of the second metal oxide powder may be set to 0.5 ~ 20 wt%.
Although the amount of the metal oxide powder is not particularly limited so long as the purposes of the present invention are achieved, it may be set to 1 ~ 10 parts by weight based on 100 parts by weight of the conductive powder. If the amount of the metal oxide powder is less than 1 part by weight, adhesive strength may become poor. In contrast, if the amount thereof exceeds 10 parts by weight, it is difficult to perform the subsequent soldering process attributed to glass floating or the like.
3. Organic medium
As used herein, "organic medium" refers to incorporation of a binder and a solvent, wherein a binder may include a solvent. In the present invention, when the organic medium is very viscous, a viscosity modifier may be further added as the additive, as necessary.
In the present invention, examples of the binder may include, but are not limited to, cellulose derivatives, such as methyl cellulose, ethyl cellulose or ethyl hydroxyethyl cellulose, wood rosin, ethyl cellulose-phenol resin mixture, polymethacrylate of lower alcohol and monobutyl ether of ethyleneglycol monoacetate, acrylic resin, alkyd resin, polypropylene-based resin, polyvinylchloride-based resin, polyurethane-based resin, rosin-based resin, terpene-based resin, phenol-based resin, aliphatic petroleum resin, acrylic acid ester-based resin, xylene-based resin, Coumarone-Indene-based resin, styrene-based resin, dicyclopentadiene-based resin, polybutene-based resin, polyether-based resin, urea-based resin, melamine-based resin, vinylacetate-based resin, and polyisobutyl-based resin.
Examples of the solvent may include, but are not limited to, hexane, toluene, ester alcohol, terpene such as α－ or β－terpineol, kerosene, dibutyl phthalate, butyl carbitol, butyl carbitol acetate, hexylene glycol, benzyl alcohol, alcohol ester, diethyleneglycol diethylether, diacetonealcohol terpineol methylethylketone, ethylcellosove, cyclohexanone, butylcellosolve, and butylcellosolve acetate.
In particular, any one or a mixture of two or more selected from the group consisting of bis(2-(2-butoxyethoxy)ethyl)adipate, dibasic ester, octyl epoxytallate, isotetradecanol and pentaerythritol ester of hydrogenated rosin may be used instead of or together with the solvent as above. Herein, dibasic ester may include any one or a mixture of two or more selected from the group consisting of dimethylester of adipic acid, dimethylester of glutaric acid, and dimethylester of succinic acid.
The amount of the organic medium may be 5 ~ 20 parts by weight based on 100 parts by weight of the conductive powder. If the amount of the organic medium exceeds 20 parts by weight, the resulting front electrode may have lowered electrical conductivity. In contrast, if the amount of the organic medium is less than 5 parts by weight, bondability with the substrate may deteriorate.
4. Additive
The conductive paste according to an embodiment of the present invention may include inorganic and organic additives.
An inorganic additive may include any metal selected from the group consisting of Li, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Pb, Cu, Zn, Ag, Te, Zn, Na, Mg, Al, W and Fe, metal oxides, and alloys or alloy oxides thereof. Examples thereof may include PbO, CuO, ZnO, MgO and WO3.
In the present invention, the inorganic additive may include a metal alloy or metal alloy oxide, containing Te, and preferable examples thereof include Te-X-O, Te-Y and Te-Y-Z, wherein X is at least one metal selected from the group consisting of alkali metals or alkaline earth metals, and Y and Z are at least one metal selected from the group consisting of Zn, Ag, Na, Mg and Al, provided that Y and Z are not the same metal.
Most preferable Te-X-O is exemplified by Li2TeO3, Na2TeO3, SrTeO3, BeTeO3 or MgTeO3, and Te-Y or Te-Y-Z may be Ag-Te, Li-Te-Zn, Te-Zn-K, or Te-Zn-Na. The inorganic additive according to the present invention includes a metal able to promote a solid-phase reaction via reaction with the metal contained in the conductive powder, and thus may accelerate grain growth of the metal powder, which is the conductive powder, even at low temperature. Thereby, the firing temperature range of the paste composition may become wide, thus increasing electrical conductivity.
The particle size of the additive according to the present invention is not particularly limited. In an embodiment, the average particle size may be smaller than 10 mm. Preferably, the average particle size is 0.01 ~ 5 μm, and is more preferably 50 ~ 200 nm.
The amount of the inorganic additive is 1 ~ 10 parts by weight, and preferably 1 ~ 5 parts by weight, based on 100 parts by weight of the conductive powder. If the amount of the inorganic additive exceeds 5 parts by weight based on 100 parts by weight of the conductive powder, the amount of the conductive powder may decrease and thus the resistance of the front electrode formed of the corresponding paste composition may increase, thereby deteriorating solar cell efficiency. In contrast, if the amount of the inorganic additive is less than 1 part by weight based on 100 parts by weight of the conductive powder, it is difficult to sufficiently exhibit the effects by the additive.
The organic additive may include, but is not limited, to a dispersant, an antioxidant, a UV absorber, a defoaming agent, a thickener, a stabilizer, and a viscosity modifier, which may be used alone or in combination of two or more and may be mixed within a range that does not impair the effects of the present invention.
In particular, the dispersant, such as stearic acid, palmitic acid, myristic acid, oleic acid or lauric acid, may be mixed with the conductive paste. Furthermore, the dispersant is not limited to organic acid so long as it is typically useful.
Preparation of conductive paste composition
According to the present invention, the conductive paste is prepared by mixing a conductive powder, a metal oxide powder, an organic medium, and an additive using a 3-roll kneader. The conductive paste according to the present invention is preferably applied on a desired portion of an electronic device via screen printing. When it is applied using such a printing process, it may have a predetermined viscosity. The viscosity of the conductive paste according to the present invention may be 50 ~ 300 PaS as measured using #14 spindle with a Brookfield HBT viscometer and using a utility cup at 10 rpm and 25℃.
Manufacture of semiconductor device using conductive paste composition
The conductive paste according to the present invention is applied via screen printing on a substrate of a semiconductor device to be manufactured, and then dried. The substrate coated with the conductive paste is fired at about 700 ~ 950℃, thus forming a conductive paste pattern.
Examples
<Preparation of conductive paste composition>
Example 1
A conductive powder was prepared by mixing a first Ag powder having an average diameter of 2 μm, and an Ag nanopowder agglomerate having a size of 10 μm (formed by agglomerating 200 nm sized Ag nanopowder).
A metal oxide powder was composed of 6.5 g of MO1 having an average diameter of 2 μm (based on the total weight of the metal oxide powder, 78.0 wt% of PbO, 11.5 wt% of SiO2, 7.5 wt% of B2O3, 0.5 wt% of Al2O3, 1.0 wt% of ZnO, 0.5 wt% of Fe2O3, 0.5 wt% of Cr2O3, 0.1 wt% of Co2O3, and 0.4 wt% of MnO2).
A conductive paste composition was prepared by mixing, based on 100 g of the paste composition, 70.0 g of the first Ag powder, 11.0 g of the Ag nanopowder agglomerate, 6.5 g of the metal oxide powder, 10.2 g of a terpineol solution containing 20 wt% of ethylcellulose as an organic solvent, and 2.3 g of an inorganic additive ZnO.
Example 2
A conductive paste composition was prepared in the same manner as in Example 1, with the exception that the amount of the conductive powder was changed as shown in Table 1 below.
Examples 3 and 4
Conductive paste compositions were prepared in the same manner as in Example 1, with the exception that the conductive powder and the metal oxide powder were changed as shown in Table 1 below. The second Ag powder of the conductive powder was a powder having an average diameter of 0.7 μm.
Examples 5 and 6
Conductive paste compositions were prepared in the same manner as in Example 1, with the exception that the conductive powder and the metal oxide powder were changed as shown in Table 1 below.
Examples 7 to 9
Conductive paste compositions were prepared in the same manner as in Examples 3 and 4, with the exception that the conductive powder, the metal oxide powder and the inorganic additive were changed as shown in Table 1 below.
Examples 10 to 12
Conductive paste compositions were prepared in the same manner as in Example 9, with the exception that the kinds of metal oxide powder and inorganic additive were changed as shown in Table 1 below.
Comparative Examples 1 to 4
Conductive paste compositions were prepared in the same manner as in Examples 2, 4, 6 and 8, with the exception that the Ag nanopowder was not provided in the form of an agglomerate as shown in Table 1 below.
Comparative Example 5
A conductive paste composition was prepared in the same manner as in Comparative Example 4, with the exception that the kind of metal oxide powder was changed as shown in Table 1 below.
The conductive paste compositions of the above examples and comparative examples were pre-mixed using a universal mixer, and kneaded using a 3-roll kneader, thus obtaining individual conductive pastes. The amounts (g) of materials used and the features thereof are shown in Table 1 below. The composition proportions (wt%) of the metal oxide powders MO1 ~ MO6 are shown in Table 2 below, and the composition proportions of MO7 ~ MO10 are shown in Table 3 below.
Table 1
Composition Conductive powder Metal oxide Organic medium Inorganicadditive
1st Ag powder Ag nanopowder 2nd Ag powder 1st metal oxide 2nd metal oxide
Ex. 1 70.0 Projection X 11.0 Agglomerate - 6.5 MO1 - 10.2 2.3 ZnO
2 75.0 ProjectionX 6.0 Agglomerate - 6.5 MO1 - 10.2 2.3 ZnO
3 54.3 ProjectionX 4.3 Agglomerate 22.4 6.5 MO3 - 10.2 2.3 ZnO
4 63.5 ProjectionX 5.0 Agglomerate 12.5 6.5 MO2 - 10.2 2.3 ZnO
5 70.0 ProjectionO 11.0 Agglomerate - 6.5 MO4 - 10.2 2.3 ZnO
6 75.0 ProjectionO 6.0 Agglomerate - 6.5 MO1 - 10.2 2.3 ZnO
7 54.3 ProjectionO 4.3 Agglomerate 22.4 6.5 MO5 - 10.2 2.3 Te-Zn-Na
8 63.5 ProjectionO 5.0 Agglomerate 12.5 6.5 MO2 - 10.2 2.3 ZnO
9 63.5 ProjectionO 5.0 Agglomerate 12.5 6.5 MO6 - 10.2 2.3 Na2TeO3
10 63.5 Projection O 5.0 Agglomerate 12.5 5.5 MO7 1.0 MO7 10.2 2.3 ZnO
11 63.5 Projection O 5.0 Agglomerate 12.5 5.5 MO8 1.0 MO8 10.2 2.3 Ag-Te
12 63.5 Projection O 5.0 Agglomerate 12.5 5.5 MO9 1.0 MO9 10.2 2.3 Na2TeO3
C.Ex. 1 75.0 Projection X 6.0 Agglomerate X - 6.5 MO1 - 10.2 2.3 ZnO
2 63.5 Projection X 5.0 Agglomerate X 12.5 6.5 MO2 - 10.2 2.3 ZnO
3 75.0 Projection O 6.0 Agglomerate X - 6.5 MO1 - 10.2 2.3 ZnO
4 63.5 Projection O 5.0 Agglomerate X 12.5 6.5 MO2 - 10.2 2.3 ZnO
5 63.5 Projection O 5.0 Agglomerate X 12.5 5.5 MO10 1.0 MO10 10.2 2.3 ZnO
Table 2
Metal oxide powder (wt% based on the total metal oxide powder) Tg (℃)
Composition PbO TeO2 Bi2O3 SiO2 B2O3 Al2O3 ZnO Fe2O3 Cr2O3 Co2O3 MnO2 CuO2 Li2O
MO1 78.0 - - 11.5 7.5 0.5 1.0 0.5 0.5 0.1 0.4 - - 186
MO2 33.8 41.1 20.6 - - - 3.3 1.2 - - - - 420
MO3 4.1 72.6 15.9 - 0.7 - 4.8 - 0.5 - 0.4 0.7 0.3 286
MO4 2.6 69.0 19.8 0.5 - - 6.0 0.4 - - - 0.7 1.0 275
MO5 1.8 69.5 14.3 3.2 4.1 1.8 5.3 - - - - - - 312
MO6 9.2 68.0 11.8 - - 2.8 4.3 1.9 - - - 0.8 1.2 283
Table 3
1st Metal oxide powder 2nd Metal oxide powder
Composition (wt%) TeO2 Bi2O3 ZnO WO3 Fe2O3 Tg(℃) PbO Li2O Ni2O3 CuO2 V2O5 P2O5 Tg(℃)
MO7 77.2 17.0 5.4 - 0.4 263 74.6 14.9 - 10.5 - - 288
MO8 79.8 14.4 5.0 0.8 - 226 54.4 14.3 7.3 16.8 5.4 1.8 300
MO9 67.5 24.4 6.7 1.4 - 287 48.4 30.3 2.1 11.7 4.6 2.9 312
MO10 30.2 39.4 12.6 9.2 8.6 413 36.2 31.2 12.8 - 11.4 8.4 464
Test Example
<Manufacture of solar cell>
A solar cell was manufactured using the conductive paste of each of Examples 1 to 12 and Comparative Examples 1 to 5. Specifically, a silicon substrate was prepared, and a conductive paste (Ag paste) for solder connection was applied on the rear side thereof using screen printing and then dried. Subsequently, an Al paste (PV333 made by E.I. du Pont de Nemours and Company) for a rear electrode was applied via screen printing so as to partially overlap the dried Ag paste, and then dried.
The drying temperature of each paste was set to 120℃. As for the film thickness of each electrode of the rear side, which is a dried film thickness, the Al paste and the Ag paste were applied to 35 μm and 20 μm, respectively.
Also, the paste of the invention was applied on a light-receiving side (front side) via screen printing and then dried. A printer made by Price Co., and a stainless wire 250-mesh mask with an 8 inch × 10 inch frame, were used. A 1.5 inch pattern for evaluation comprising a finger line having a width of 100 μm and a bus bar having a width of 2 mm was employed, and the film thickness was 13 μm after firing. Subsequently, the paste applied on the substrate was co-fired in an IR firing furnace under conditions of a peak temperature of about 730℃ and an IN-OUT time of about 5 min, thus obtaining a desired solar cell. The solar cell obtained using the conductive paste according to the present invention was configured such that the Ag electrode was formed on the light-receiving side (front side) and the Al electrode (first electrode) composed mainly of Al and the Ag electrode (second electrode) composed mainly of Ag were formed on the rear side.
1. Measurement of light conversion efficiency and fill factor
The electric properties (I-V properties) of the obtained solar cell substrate were evaluated by a cell tester. Using a system (NCT-M-150AA) made by NPC as a cell tester, Eff (Conversion Efficiency) (%) and FF (Fill Factor) were measured. The results are shown in Table 4 below.
2. Measurement of adhesion
The adhesion of the obtained solar cell was measured as follows. Specifically, the surface of the front electrode formed using an electrode forming process was heated to 200℃ and a SnPbAg-based solder ribbon (line width: 2 mm, indium corporation, SUNTABTM) was attached to a length of 10 cm thereto. Then, while one end of the attached portion was pulled in a 180° direction with a universal tensile tester (QC-508E, COMETECH), a force (N, newton) until the electrode and the solder ribbon were peeled from each other was measured. The evaluation results based on the following criteria are shown in adhesion (N) in Table 4 below.
<Evaluation criteria>
Excellent: 3N or more
Good: 2N or more
Bad: 1N or less
The numeral values of electrical properties in Table 4 were obtained by averaging the measurement values of five solar cell samples.
Table 4
Eff (%) FF Adhesion
Ex. 1 18.51 76.1 Good
2 18.62 76.8 Good
3 18.92 77.9 Excellent
4 18.96 77.8 Good
5 18.71 76.8 Excellent
6 19.25 78.1 Good
7 19.21 78.4 Excellent
8 19.34 78.5 Good
9 19.36 78.7 Excellent
10 19.41 79.4 Excellent
11 19.54 80.1 Excellent
12 19.43 79.6 Excellent
C.Ex. 1 15.54 70.2 Good
2 15.91 70.8 Good
3 15.72 70.2 Good
4 16.24 70.4 Good
5 14.82 69.2 bad
The features, structures, effects and so on illustrated in individual exemplary embodiments as above may be combined or modified with the other exemplary embodiments by those skilled in the art. Therefore, the contents related to such combinations or modifications should be understood to fall within the scope of the present invention.

Claims (11)

  1. A conductive paste composition, comprising:
    a conductive powder including a first metal powder having an average diameter (D50) of 1 ~ 3 μm, and a metal nanopowder agglomerate having an average diameter (D50) of 0.5 ~ 10 μm obtained by agglomerating a metal nanopowder having an average diameter (D50) of 100 ~ 200 nm;
    a metal oxide powder;
    an organic medium; and
    an additive.
  2. The conductive paste composition of claim 1, wherein the conductive powder further includes a second metal powder having an average diameter (D50) of 0.5 ~ 1 μm.
  3. The conductive paste composition of claim 2, wherein the first metal powder, the second metal powder, and the metal nanopowder agglomerate comprise at least one metal selected from the group consisting of Cu, Ag, Au, Ni, Al, W and Zn.
  4. The conductive paste composition of claim 3, wherein the metal nanopowder agglomerate is used in an amount of 0.1 ~ 10 parts by weight based on 100 parts by weight of the first metal powder.
  5. The conductive paste composition of claim 4, wherein the second metal powder is used in an amount of 10 ~ 40 parts by weight based on 100 parts by weight of the first metal powder.
  6. The conductive paste composition of claim 5, wherein the first metal powder is configured such that an outer surface thereof has projections so as to be irregular, and a highest point of the projections is higher by 0.1 ~ 0.6 μm than a portion having no projection.
  7. The conductive paste composition of claim 1, wherein the metal oxide powder comprises X1-X2-…-Xn-O (wherein Xn is a metal selected from the group consisting of Pb, Te, Bi, W, Mo, Zn, Al, Si, B, Fe, Co, Cr, Cu, Ni, V, Li, P and Mn, and essentially contains Pb, Te and Bi, and n is an integer of 3 or more), and
    in the metal oxide powder, an amount of Pb, a wt%, an amount of Te, b wt% and an amount of Bi, c wt% satisfy [Relation 1] and [Relation 2] below:
    [Relation 1]
    70≤a+b+c≤90 (1≤a≤15, 60≤b≤75); and
    [Relation 2]
    2.5≤b/c≤7.5 (60≤b≤75).
  8. The conductive paste composition of claim 1, wherein the metal oxide powder includes a first metal oxide powder having a first glass transition temperature of a℃ and a second metal oxide powder having a second glass transition temperature of b℃, and
    the first glass transition temperature of the first metal oxide powder is 170≤a≤310, and the second glass transition temperature of the second metal oxide powder is 230≤b≤320, with satisfying 10≤b-a≤60.
  9. The conductive paste composition of claim 1, wherein the additive is used in an amount of 1 ~ 5 parts by weight based on 100 parts by weight of the conductive powder, and comprises Te-X-O, Te-Y or Te-Y-Z (wherein X is at least one metal selected from the group consisting of alkali metals and alkaline earth metals, and Y and Z are at least one metal selected from the group consisting of Zn, Ag, Na, Mg and Al, Y≠Z).
  10. The conductive paste composition of claim 1, comprising:
    70 ~ 90 wt% of the conductive powder;
    0.7 ~ 9 wt% of the metal oxide powder;
    3.5 ~ 18 wt% of the organic medium; and
    0.7 ~ 4.5 wt% of the additive.
  11. A silicon solar cell, comprising:
    a silicon semiconductor substrate;
    an emitter layer formed on the substrate;
    an anti-reflective film formed on the emitter layer;
    a front electrode connected to the emitter layer through the anti-reflective film; and
    a rear electrode connected to a rear side of the substrate,
    wherein the front electrode is formed by applying the conductive paste composition of any one of claims 1 to 10 in a predetermined pattern on the anti-reflective film and then performing firing.
PCT/KR2014/012355 2014-04-15 2014-12-15 Conductive paste composition and semiconductor device comprising the same WO2015160065A1 (en)

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WO2018206950A1 (en) * 2017-05-12 2018-11-15 Johnson Matthey Public Limited Company Conductive paste, electrode and solar cell
CN116102951A (en) * 2022-12-26 2023-05-12 苏州微介面材料科技有限公司 Antistatic nonflammable water-based epoxy coating

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JP6967845B2 (en) * 2016-09-27 2021-11-17 株式会社ノリタケカンパニーリミテド Silver paste and electronic elements

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WO2018206950A1 (en) * 2017-05-12 2018-11-15 Johnson Matthey Public Limited Company Conductive paste, electrode and solar cell
CN116102951A (en) * 2022-12-26 2023-05-12 苏州微介面材料科技有限公司 Antistatic nonflammable water-based epoxy coating

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