JP2010173904A - Glass composition and conductive paste using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass composition containing substantially no PbO nor SiO<SB>2</SB>and fluidizing quickly at firing temperature. <P>SOLUTION: The glass composition does not substantially include PbO and SiO<SB>2</SB>, and contains, by mass% in terms of oxides: 79%≤Bi<SB>2</SB>O<SB>3</SB><99.9%; 0.1%≤B<SB>2</SB>O<SB>3</SB>≤5.2%; 0%<ZnO≤11%; 0-10% at least one of BaO, MgO, CaO and SrO; 0-10% Al<SB>2</SB>O<SB>3</SB>; 0-5% at least one of CeO<SB>2</SB>, CuO and Fe<SB>2</SB>O<SB>3</SB>; and 0-2% at least one of Li<SB>2</SB>O, Na<SB>2</SB>O and K<SB>2</SB>O, and further satisfies 0.007<B<SB>2</SB>O<SB>3</SB>/Bi<SB>2</SB>O<SB>3</SB><0.375 in the scaling ratio of mol%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a lead-free glass composition that is substantially free of PbO and SiO ₂ and is contained in a conductive paste that forms an electrode for a semiconductor device. In particular, a glass composition contained in a conductive paste for forming an electrode on an n-type or p-type Si semiconductor substrate of a crystalline Si solar cell, a conductive paste produced using this glass composition, and a paste formed using this paste The present invention relates to a solar cell including the prepared electrode.

  In recent years, from the viewpoint of global warming and the use of clean energy, the demand for solar cells for home use or industrial use has increased remarkably. In particular, many solar cells using a crystalline Si semiconductor substrate are currently used.

  The structure of the crystalline Si solar cell is as follows. An n-type layer is provided on the surface of a p-type Si semiconductor substrate to form a pn junction, and a light-receiving surface electrode is provided on the n-type layer side serving as a light-receiving surface. A form having a back electrode is widely adopted on the p-type layer side. The light receiving surface is covered with an antireflection film in order to capture more incident light.

  In this crystalline Si solar cell, the above-mentioned light receiving surface electrode and back electrode are made of a conductive paste obtained by kneading a metal powder (specifically, Ag powder) having an electrical conductivity and an organic vehicle on a crystalline Si semiconductor substrate. After being applied by a printing method such as a screen printing method, it is fired in a firing furnace to be formed as a sintered body of metal powder. This printing method is known as a method for forming an electrode of an electronic device because automation is easy and productivity improvement is desired.

  In addition, in order to increase the adhesive strength between the electrode and the crystalline Si semiconductor substrate, the glass powder is dispersed in the sintered electrode by sintering a conductive paste to which glass powder is added. It is desirable that According to Non-Patent Document 1, it is disclosed to use a glass composition containing PbO in a conductive paste.

Furthermore, glass compositions containing substantially no lead and containing Bi ₂ O ₃ , B ₂ O ₃ and ZnO as main components are also used in flat displays. The glass composition used for this flat display was a low melting glass, a glass that crystallized at a temperature of 550 ° C. or higher, and a glass that did not crystallize at 450 to 550 ° C. (Patent Document 1).

JP 2006-137737 A

P, Fath et al., 19th European Photovoltaic Solar Energy Conference, 7-11, 2004.

  Non-Patent Document 1 discloses that in the baking process, the conductive paste reacts with the antireflection film (mainly made of silicon nitride) on the crystalline Si semiconductor substrate, thereby electrically connecting the n-type layer formed on the light receiving surface. It is described that it can contact. It is also shown that the glass composition added to the conductive paste plays the role during this reaction.

  However, the firing profile in the firing step for forming the electrodes used for the applications of this crystalline Si solar cell is the start of heating in the firing temperature range (generally 700 to 800 ° C. regardless of the type of electrode material). The time from heating to the end of heating is as short as several minutes. For this reason, it is required to have good fluidity in this short time. A glass composition containing PbO as disclosed in Non-Patent Document 1 has been used as a material having this good fluidity, but in recent years, there is concern about lead compounds contained in electronic components from the viewpoint of environmental protection. In this application, the necessity of lead-free has been screamed.

  Moreover, since the low melting glass described in Patent Document 1 is a glass that crystallizes at a temperature exceeding 550 ° C., good fluidity cannot be obtained at 700 to 800 ° C.

Accordingly, in order to solve the above-mentioned problems, the present invention is a glass composition that substantially does not contain PbO and SiO ₂ , and is a glass composition that flows well even when the heating time in the firing temperature range is short. The purpose is to provide goods.

Therefore, in order to solve the above-mentioned problems, the invention corresponding to claim 1 is a glass composition that substantially does not contain PbO and SiO _2. 79% ≦ Bi _{2 in} terms of oxide in mass%. O ₃ <99.9%, 0.1% ≦ B ₂ O ₃ ≦ 5.2%, 0% <ZnO ≦ 11%, and 0.007 <B ₂ O ₃ / Bi in terms of mol% ₂ O ₃ <0.375 was satisfied. By setting it as such a composition range, Bi system crystal | crystallization precipitates in the temperature rising process to the baking temperature for sintering an electrode, and removes the organic component in a paste (debinder) temperature (500 degreeC) vicinity The glass can be prevented from flowing. Further, since this Bi-based crystal is considered to have a melting point lower than the above firing temperature, it melts in the temperature rising process, and therefore has excellent fluidity at 700 to 800 ° C.

The invention corresponding to claim 2 contains 0 to 10% by mass of at least one of BaO, MgO, CaO and SrO and 0 to 10% by mass of Al ₂ O ₃ in the glass composition of the invention corresponding to claim 1. To do.

The invention corresponding to claim 3 contains 0 to 5% by mass of at least one of CeO ₂ , CuO and Fe ₂ O ₃ in the glass composition of the invention corresponding to claim 1 or 2.

The invention corresponding to claim 4 is the glass composition according to any one of claims 1 to 3, wherein at least one of Li ₂ O, Na ₂ O and K ₂ O is 0 to 2.0 mass. % Content.

The invention corresponding to claim 5 mixes the metal powder, the organic vehicle, and the glass powder formed from the glass composition according to any one of claims 1 to 4 in the conductive paste. It was supposed to be. In the present invention, the metal powder includes not only powdered materials but also flaky materials. Further, as the metal powder, Ag powder, Cu powder, Pd powder, Au powder and Pt powder can be considered, and Ag powder is preferable. However, the Cu powder is preferably handled in a reducing atmosphere (mainly N ₂ ) due to the characteristics of the material.

  The invention corresponding to claim 6 is a method for producing an electrode formed on a semiconductor substrate, wherein the glass powder formed from the glass composition according to any one of claims 1 to 4 and a metal powder A step of mixing an organic vehicle to form a paste, a step of applying the paste onto a semiconductor substrate to produce a coated substrate, and a step of firing the coated substrate to form an electrode on the semiconductor substrate. It was. As the semiconductor substrate, a crystalline semiconductor substrate (crystalline Si or crystalline Ge), preferably crystalline Si is used.

  An invention corresponding to claim 7 is a solar cell in which an antireflection film is formed on a light receiving surface on a semiconductor substrate, and includes an electrode formed using the conductive paste according to the invention corresponding to claim 5. did.

According to the present invention, a glass composition substantially free of PbO and SiO ₂ can be crystallized once at a temperature lower than the firing temperature, and then the crystals can melt and rapidly flow at the firing temperature. Therefore, when added to a conductive paste applied to a semiconductor substrate on which an antireflection film is formed, it reacts well with the antireflection film and enables good electrical bonding between the electrode and the semiconductor substrate. Can be expected.

The glass composition of the present invention is typically used as the glass powder in the 1~2μm about triturated with D _50. When this glass powder, metal powder (specifically, Ag powder) and organic vehicle are kneaded and used as a conductive paste, it is fired at 700 to 800 ° C. to form an electrode of a sintered body. . Next, the mass% of each component of the glass composition will be described by simply indicating%.

Bi ₂ O ₃ is an essential component for increasing the softening fluidity of the glass and joining the semiconductor substrate and the electrode. If Bi ₂ O ₃ is less than 79%, the softening point of the glass composition becomes high and the glass may flow during debinding. Preferably it is 83% or more, More preferably, it is 85% or more. On the other hand, if it is 99.9% or more, vitrification becomes extremely difficult. Preferably it is 97% or less, More preferably, it is 95% or less. It is also an essential component for precipitating crystals that crystallize and melt at a temperature lower than the firing temperature range.

B ₂ O ₃ is a glass network former and is an essential component. Vitrification becomes difficult when B ₂ O ₃ is less than 0.1%. Preferably it is 1% or more, More preferably, it is 2.5% or more. On the other hand, if it exceeds 5.2%, it becomes a glass with low water resistance, not only reducing the durability of the electrode, but also the softening point becomes high, the glass flows at the time of debinding, and the crystals are within the firing temperature range. It may precipitate and reduce the fluidity. Preferably it is 5.1% or less, More preferably, it is 4.8% or less.

  ZnO is an essential component for adjusting glass stabilization, improving adhesion to a semiconductor substrate, adjusting the glass softening point, and the like. If ZnO is not contained, it becomes difficult to precipitate crystals at the time of debinding, and 2% or more is preferable for stabilizing the glass. On the other hand, if it exceeds 11%, the fluidity of the glass may be reduced. Preferably it is 9% or less.

  MgO, CaO, SrO and BaO are optional components, and may be contained in a total amount of up to 10% in order to improve the adhesive strength with the semiconductor substrate and to stabilize the glass. However, if it exceeds 10%, the fluidity of the glass may decrease, or the glass may become unstable. Preferably they are 1.3% or more and 8% or less. More preferably, it is 1.5% or more and 6% or less.

Al ₂ O ₃ is an optional component, but has an effect of improving glass stability. However, if it exceeds 10%, the glass fluidity is lowered. Preferably it is 8% or less, More preferably, it is 6% or less.

CeO ₂ , CuO and Fe ₂ O ₃ are optional components, but have the effect of reducing the corrosion of the melting tank by maintaining the production stability during glass production, particularly when the glass is melted, and the atmosphere is acidic. Therefore, when producing using refractories, such as platinum, industrially, it is good to contain at least one sort. The total content is preferably 0 to 3% (excluding 0%).

Li ₂ O, Na ₂ O and K ₂ O may not be contained, but may be contained as long as the upper limit is 2%. Preferably it is 1% or less, More preferably, it is 0.5% or less. When the above-mentioned alkali metal oxide is contained, for example, when the glass of the present invention is used for an electrode member of a solar cell, alkali metal ions that are easily thermally diffused diffuse into the semiconductor substrate, and the electrode performance as a solar cell is significantly deteriorated. There is a risk of causing.

Further, the ratio of the content of B ₂ O _{3 and} the content of Bi ₂ O ₃ is an important condition for precipitating the desired crystal at the time of debinding, and when the content is converted into a mole, It is necessary to satisfy the relationship 0.007 <B ₂ O ₃ / Bi ₂ O ₃ <0.375. The lower limit is preferably 0.150, more preferably 0.250. The upper limit is preferably 0.350, more preferably 0.340. The desired crystal is a state in which the crystal is contained at around 500 ° C. and the fluidity of the glass is suppressed, and the recrystallization of the precipitated crystal starts from around 550 to 650 ° C. and flows well at 700 to 800 ° C. It will melt.

  The glass composition of the present invention contains the above components, but may contain other components as long as the object of the present invention is not impaired. In that case, the total content of such components is preferably 10% or less, more preferably 8% or less, and even more preferably 5% or less.

Further, in the present invention, PbO and SiO ₂ is not substantially contained. In a high bismuth-containing glass, if SiO ₂ is positively contained as an essential component, precipitation of crystals containing Si is promoted at the firing temperature described above, and thus there is a concern that the fluidity during firing will be significantly deteriorated. . It is not preferable that PbO is contained from the environmental aspect as described above. Even if both oxides are contained, they are at an impurity level.

  The conductive paste for solar cell using the glass of the present invention is prepared by mixing glass powder and organic vehicle for imparting printability and metal powder (specifically, Ag powder) as an electrode material. Is done. The organic vehicle is, for example, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, oxyethyl cellulose, benzyl cellulose, propyl cellulose, nitrocellulose or the like dissolved in a solvent such as α-terpineol, butyl carbitol acetate, ethyl carbitol acetate, Acrylic resins such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-hydroxyethyl methacrylate and the like such as methyl ethyl ketone, α-terpineol, butyl carbitol acetate, ethyl carbitol acetate, etc. The thing melt | dissolved in the solvent is mentioned.

  The prepared conductive paste is applied to a crystalline Si semiconductor substrate on which an antireflection film is formed by screen printing using 200 to 325 mesh, and is baked by an infrared lamp heating device (baking furnace). In firing, the glass powder in the conductive paste and the antireflection film react with each other, so that the Ag electrode and the n-type layer or the p-type layer on the crystalline Si semiconductor substrate can be electrically connected.

  The firing is performed at 700 to 800 ° C. In the intermetallic reaction between the crystalline Si semiconductor substrate and the Ag electrode, the glass composition contained in the conductive paste serves as a binder. In the process of firing, if it flows too much at about 500 ° C., the decomposition of the organic components in the paste is hindered, and the risk of carbon remaining in the electrode increases. As described above, when carbon remains in the electrode, the paste foams and the appearance of the surface is impaired, and the installation portion on the substrate is lowered, which may reduce the reactivity in electrode formation. In addition, the glass that crystallizes around 700 ° C. does not flow, the reaction between the antireflection film and the glass is less likely to occur, the electrical connection becomes insufficient, and the contact resistance of the electrode is remarkably increased. There is a risk of reduction in luminous efficiency. Therefore, it is considered that good adhesion can be obtained without disturbing between the crystalline Si semiconductor substrate and the Ag electrode by causing the glass composition to flow well around 700 ° C., which is the firing temperature.

(Method for manufacturing solar cell)
The manufacturing method of the solar cell of this invention is demonstrated in detail. In the following description, a p-type crystalline Si semiconductor substrate sliced to a thickness of 250 μm or less will be described, but an n-type crystalline Si semiconductor substrate may be used.

  First, in order to clean the sliced surface of the substrate, the surface is etched by a trace amount with NaOH or hydrofluoric acid.

  Thereafter, a concavo-convex structure for reducing light reflectance is formed on the surface of the crystalline Si semiconductor substrate on the light receiving surface side by using a dry etching method or a wet etching method. However, the formation of the concavo-convex structure can be omitted. In order to obtain a highly efficient one, it is desirable to form a concavo-convex structure.

Next, an n-type layer is formed by diffusion. P (phosphorus) is preferably used as the n-type doping element, which is formed on the light receiving surface of the semiconductor substrate. For example, a gas phase thermal diffusion method using POCl ₃ (phosphorus oxychloride) in a gas state as a diffusion source can be used. This n-type layer is formed to a thickness of about 0.2 to 0.5 μm. In this process, when a diffusion region is formed in an undesired portion, an unnecessary portion may be removed by an etching process in a later step.

Next, an antireflection film is formed. As a material of the antireflection film, SiNx (silicon nitride, Si ₃ N ₄ is the center, and the composition ratio (x) has a width) is mainly used. The thickness is selected according to the semiconductor material so that non-reflection conditions can be realized with respect to appropriate incident light. In the case of a Si semiconductor substrate, the refractive index may be about 2.2 and the thickness may be about 70 nm. As its manufacturing method, a plasma CVD method, a sputtering method, or the like is used.

  Next, the front surface electrode and the back surface electrode are formed on the front surface side and the back surface side of the semiconductor substrate. These electrodes apply | coat the electrically conductive paste for solar cell electrodes containing the glass powder of this invention to the surface of a semiconductor substrate using well-known coating methods, such as a screen printing method. Further, an Al paste for solar cell electrodes and an Ag paste for soldering are applied to the back surface. Thereafter, firing is performed at a peak temperature of about 700 to 800 ° C. for several tens of seconds to several minutes to form an electrode.

  The solar cell is manufactured as described above. In particular, since a lead-free glass powder is used in the present invention, a preferable solar cell can be manufactured from the viewpoint of environmental protection.

  The raw materials are prepared and mixed so as to have the composition shown in mass% in the columns of each component in Tables 1 to 4, and melted for 1 hour in a 1000 to 1250 ° C. electric furnace using a platinum crucible. After forming into a glass powder, it was pulverized with a ball mill, and then coarse particles were removed with a 325 mesh sieve to obtain a glass powder. Examples 1 to 20 are examples, and examples 21 to 27 are comparative examples.

  The transition point: Tg (unit: ° C) and the crystallization point: Tc (unit: ° C) of each glass powder were measured using a differential thermal analyzer (DTA).

  The fluidity of each glass powder was evaluated as follows. A sample (flow button) in which a glass powder with a constant volume measured in each sample is press-molded with a mold having a diameter of 12.7 mm (1/2 inch) is prepared, and this is performed under three conditions from 500 to 700 ° C. The fluidity was evaluated by heating and flowing in a batch firing furnace. Samples having a diameter of 30 mm or more after the temperature rise are indicated as H in the table as having good fluidity, those having a diameter of 15 mm or less are L, and those exceeding 15 mm and less than 30 mm show the values. The glass powder used for the conductive paste is required to have a fluidity at 500 ° C. of L (in this example, the sample does not crystallize and flow) and a fluidity at 700 ° C. of H.

  The glass composition of the present invention can be used not only for electrodes of solar cells but also for members of micromachines (MEMS), low-temperature co-fired substrates (LTCC), and plasma display panels.

Claims (7)

Substantially free of PbO and SiO ₂ , 79% ≦ Bi ₂ O ₃ <99.9%, 0.1% ≦ B ₂ O ₃ ≦ 5.2%, 0% < A glass composition characterized by containing ZnO ≦ 11% and satisfying 0.007 <B ₂ O ₃ / Bi ₂ O ₃ <0.375 in terms of mol%. The glass composition according to claim 1, comprising 0 to 10% by mass of BaO, MgO, CaO and SrO and 0 to 10% by mass of Al ₂ O ₃ . CeO _2, CuO, at least one of the containing 0-5 wt% claim 1 or 2 glass composition according to the _Fe 2 _{O 3.} Li _{2 O,} Na 2 O, the glass composition according to claim 1, at least one of _{K 2} O containing 0 to 2.0 wt%.   The electrically conductive paste produced by mixing metal powder, an organic vehicle, and the glass powder formed from the glass composition in any one of Claims 1-4.   A step of mixing a glass powder formed from the glass composition according to claim 1, a metal powder, and an organic vehicle into a paste, and a step of applying the paste on a semiconductor substrate to produce a coated substrate And a method of manufacturing the electrode, comprising firing the coated substrate and forming an electrode on the semiconductor substrate.   A solar cell in which an antireflection film is formed on a light receiving surface on a semiconductor substrate, the solar cell comprising an electrode formed using the conductive paste according to claim 5.