JP6060611B2 - Composition - Google Patents

Description

  The present invention relates to a composition used for removing an inorganic thin film made of silicon nitride (SiN) or the like.

Inorganic thin films such as silicon oxide (SiO ₂ ) and SiN are used in various semiconductor elements, solar cells, and the like as interlayer insulating films, passivation films, antireflection films, and the like.
For example, in some solar cells, an antireflection film made of a SiN film is formed on the light receiving surface side and a passivation film is formed on the surface opposite to the light receiving surface in order to improve conversion efficiency.

In the manufacture of a crystalline silicon solar battery cell that is generally used as a solar battery, a phosphorus diffusion layer that becomes an n + layer is formed on the surface layer of a p-type silicon wafer, and a pn junction is formed between the lower p layer. Thereafter, after forming an antireflection film on the n + layer, electrodes are formed on the light receiving surface side and the back surface side, and a passivation film is formed as necessary.
In the manufacture of solar cells, electrodes are often connected to the n + layer after the formation of an antireflection film or a passivation film, and thus it is necessary to provide openings in these inorganic thin films.

One method for providing an opening in an inorganic thin film is an etching method. As an etching method, a method using a photoresist is generally used. However, each step of resist film formation, exposure, development, etching, and resist removal is necessary, and since many materials are used, it is not efficient.
There is also a method of forming an opening with a laser. However, since the processing position control is complicated and requires processing time, productivity is not sufficient. In addition, there is a possibility that the n + layer, the wafer, and the like below are damaged by the laser.
In addition, conventionally, the most common manufacturing method is to apply a conductive paste containing a compound that constitutes glass, such as a metal serving as an electrode and silicon oxide, to cause fire through (fired penetration) by heating, and inorganic There is a method of forming an opening in a thin film and simultaneously connecting an electrode and an n + layer. However, since this method requires high-temperature treatment at 250 ° C. or higher, the n + layer and the wafer may be damaged and power generation efficiency may be reduced.
In addition, although the method of forming an inorganic thin film in the pattern form from the beginning is considered, it is not efficient because the process is complicated, and it is not sufficient in terms of the accuracy of pattern formation.

On the other hand, a method has been proposed in which an etching paste is printed to form a pattern or the like on an inorganic thin film, and then heated to form an opening below the etching paste.
As a component (etching component) for removing the inorganic thin film, for example, Patent Document 1 describes an etching medium containing phosphoric acid or phosphate. However, since the optimum etching temperature is as high as 250 ° C. or higher, the n + layer, the wafer, and the like may be damaged.

  In addition, as an etching component, at least one fluorine selected from the group consisting of ammonium, alkali metal and antimony fluorides, ammonium, alkali metal and calcium acid fluorides, alkylated ammonium, and potassium tetrafluoroborate A method using a compound and, optionally, an etching medium containing a predetermined inorganic mineral acid and organic acid is described (see Patent Document 2). However, an etching medium in which a fluorine compound and an acid are mixed has a problem of extremely high toxicity.

JP 2005-506705 gazette Special table 2008-527698

  An object of the present invention is to provide a novel composition that can be used as an etching paste and can sufficiently remove an inorganic thin film (such as a SiN layer) even at a low temperature (250 ° C. or lower).

According to the present invention, the following compositions and the like are provided.
1. A composition containing the following components (A) and (B).
(A) Boron trifluoride monoethylamine complex (B) 1-butyl-3-methylimidazolium hexafluorophosphoric acid Furthermore, the composition of 1 containing a solvent.
3. The composition of 1 or 2 whose total content rate of the said component (A) and (B) is 30-80 mass% of the whole.
4. The composition according to 2 or 3, comprising a solvent having a vapor pressure at 25 ° C. of less than 1.34 × 10 ³ Pa.
5. A method for removing a silicon nitride (SiN) film using the composition according to any one of 1 to 4 above.
6). 6. The method according to 5, comprising a step of forming the composition on the SiN film by a printing method and a step of removing the SiN film by heating.
7). A substrate obtained by removing the SiN film using the method described in 5 or 6 above.

  According to the present invention, a composition containing a novel etching component can be provided. By using the composition of the present invention, the inorganic thin film can be removed at a lower temperature than before.

It is the electron micrograph of the surface of the silicon wafer which printed the etching paste in the 200-micrometer-width linear form, and was etched. It is a cross-sectional photograph before the etching process of a silicon wafer. It is a cross-sectional photograph after the etching process of a silicon wafer.

The composition of the present invention contains the following components (A) and (B) as essential components.
(A) Boron trifluoride monoethylamine complex (B) 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM] -PF ₆ )

The component (A) is an etching component and is liquefied by heating to dissolve and remove the inorganic thin film, particularly the SiN film. The component (B) is an ionic liquid. In the present invention, by using the above components (A) and (B) in combination, the etching rate is improved and the heating temperature during etching can be lowered as compared with the case where the component (A) is used alone.
Component (A) is solid at room temperature and becomes liquid at the removal temperature of the inorganic thin film (etching temperature, 250 ° C. or lower in the present application).

The component (A) preferably has a particle size before mixing of 100 μm or less in order to improve printability.
In addition, the particle size here is a number average particle size, and is obtained as an average value of 100 randomly selected without overlapping in the SEM observation image. Specifically, a carbon adhesive tape is affixed on the SEM sample stage, and the component (A) is sprinkled thereon. Among the components (A) on the sample stage, those that are not adhered are blown off with an air gun. Using a vacuum sputtering apparatus (for example, ION SPUTTER, manufactured by Hitachi High-Tech), Pt is sputtered to a thickness of 10 to 20 nm on the SEM sample stage to which the component (A) is adhered to obtain a sample for SEM. The sample for SEM is observed with an SEM apparatus (for example, ESEM XL30, manufactured by Philips) at an overload voltage of 10 kV. The magnification is selected so that the average conductive particle diameter occupies about 10% of the field of view. 100 particles randomly selected from the observed particle images, excluding the etching components whose outline cannot be confirmed, and selected to be the maximum distance among the parallel straight lines circumscribing each etching component image Measure the distance between two straight lines. An average value is obtained for these 100 values and is defined as the number average particle diameter. When 100 particles cannot be selected from one field of view, measurement is performed from a plurality of fields.

Further, the particle diameter (dispersed particle diameter) of the component (A) after dispersion is preferably 100 μm or less from the viewpoint of screen printing accuracy, and preferably 0.01 μm or more from the viewpoint of viscosity characteristics.
The dispersed particle diameter is obtained as a volume average particle diameter using a laser scattering particle size distribution analyzer. Specifically, using a laser scattering particle size distribution measurement device (for example, LS13 320, manufactured by Beckman Coulter) equipped with a universal liquid module, the main body is turned on for 30 minutes to stabilize the light source, and then the liquid module is used. Only the solvent used in the composition is introduced from the measurement program by the Rinse command, and De-bubble, Measurement Offset, Align, and Measurement Background are performed from the measurement program. Subsequently, using Measurement Loading of the measurement program, the composition is added to the liquid module until the measurement program is changed from the sample amount Low to OK. Thereafter, Measurement is performed from the measurement program to obtain a particle size distribution. As settings of the laser scattering method particle size distribution measuring apparatus, Pump Speed: 70%, Include PIDS data: ON, and Run Length: 90 seconds are used. The refractive index of the component (A) and the solvent is used as the refractive index of the dispersion medium and the dispersoid, respectively.

What is necessary is just to adjust the content rate of a component (A) suitably in consideration of the property of the composition at the time of use. Although it is preferable that the content of the etching component is high, in consideration of applying the composition by a printing method, it is important to adjust the viscosity and paste properties of the composition. The content of component (A) is preferably 30 to 80% by mass, particularly preferably 50 to 70% by mass, based on the entire composition.
It is preferable that the content rate of a component (B) is 3.0-64.0 mass% with respect to the whole composition, and it is especially preferable that it is 5.0-56.0 mass% especially.

The composition of the present invention preferably contains a solvent. By using a solvent, the viscosity and printability of the composition can be improved. The solvent is not particularly limited as long as the component (A) described above can be dispersed. When the composition of the present invention is printed using screen printing, if the viscosity changes due to volatilization of the solvent during printing, the printability changes, so the vapor pressure at 25 ° C. is 1.34 × 10. ^It is less than ³ Pa, preferably less than 1.0 × 10 ³ Pa · s.
Solvents include aliphatic hydrocarbon solvents such as nonane, decane, dodecane, and tetradecane; aromatic hydrocarbon solvents such as ethylbenzene, anisole, mesitylene, naphthalene, cyclohexylbenzene, diethylbenzene, phenylacetonitrile, phenylcyclohexane, benzonitrile, and mesitylene Solvent; ester solvent such as isobutyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, glycol sulfite, ethyl lactate, ethyl lactate; alcohol solvent such as 1-butanol, cyclohexanol, glycerin; terpineol, Terpineol C, dihydroterpineol, dihydroterpinyl acetate, dihydroxyterpinyloxyethanol, terpinyl methyl ether, dihydroterpinyl methyl ether Terpene solvents such as Tersolve DTO-210, Tersolve THA-90, Tersolve THA-70, Tersolve TOE-100, and Tersolve MTPH (manufactured by Nippon Terpene Chemical Co., Ltd.); cyclohexanone, 2-hexanone, 2-heptanone, 2-octanone Ketone solvents such as 1,3-dioxolan-2-one and 1,5,5-trimethylcyclohexen-3-one; diethylene glycol ethyl ether, diethylene glycol diethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol Monopropyl ether, propylene glycol monobutyl ether, propylene glycol monomethyl ether acetate, diethylene glycol ethyl ether acetate, di Ethylene glycol propyl ether acetate, diethylene glycol isopropyl ether acetate, diethylene glycol butyl ether acetate, diethylene glycol-t-butyl ether acetate, triethylene glycol methyl ether acetate, triethylene glycol ethyl ether acetate, triethylene glycol propyl ether acetate, triethylene glycol isopropyl ether acetate, Alkylene glycol solvents such as triethylene glycol butyl ether acetate, triethylene glycol-t-butyl ether acetate, dipropylene glycol dimethyl ether, dipropylene glycol monobutyl ether; dihexyl ether, butyl phenyl ether, pentyl fe Ether solvents such as ether, methoxytoluene and benzyl ethyl ether; carbonate solvents such as propylene carbonate and ethylene carbonate; amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide and N-methylpyrrolidone, malononitrile And nitrile solvents such as
Of these, terpineol, γ-butyrolactone, N-methylpyrrolidone, glycol sulfite, and propylene carbonate are preferable.
These solvents can be used alone or in combination of two or more.

The content of the solvent may be appropriately adjusted in consideration of the properties of the composition at the time of use. Usually, it is preferable that it is 15-65 mass% with respect to the whole composition, and it is especially preferable that it is 25-50 mass%.
Moreover, it is preferable that the total content rate of the component (A) and (B) mentioned above is 30-80 mass% with respect to the whole composition.

  The composition of the present invention, in addition to the above-described components, optionally prevents thixotropic properties, a substrate wettability adjuster, a particle dispersant, a defoaming agent, cocoon skin, etc. Additives such as an external appearance improver (leveling agent), additives for promoting uniform drying, viscosity adjusting materials (fine particles, solvents, additives), doping agents, pH adjusting agents, and the like can be added.

  For example, depending on the printing method, it is preferable to impart thixotropy for fine line drawing. Examples of the method for imparting thixotropy include a method using a thixotropic agent and a method for dispersing fine particles. These methods may be used in combination.

Examples of the thixotropic agent include ethyl cellulose (Dow Chemical Co., Etocel (registered trademark)), BYK-405, 410, 411, 415, 420, 425, 420, 430, 431, etc. (Bic Chemie Co., Ltd.), Disparlon thixo Commercially available products such as the series of tropic agents (Enomoto Kasei) are listed. The thixotropic agent is not particularly limited as long as the solvent to be used and the desired thixotropy can be obtained.
In addition, polysiloxane, polyacryl, polyamide, polyvinyl alcohol, alkyl-modified cellulose, peptide, polypeptide, and a copolymer having two or more of these structures are also preferable.

  Examples of the fine particles include organic fine particles and inorganic fine particles such as metal oxide particles. By adding fine particles, viscosity and thixotropy can be appropriately adjusted, and printability (for example, fine line drawing property and shape retention) and etching property can be controlled. Further, when heated to the etching temperature of the inorganic thin film, the etching component becomes liquid, but the fluidity is suppressed by the particles and the shape of the printed SiN liquid composition is prevented from being deformed.

Examples of the organic fine particles include polystyrene beads, polyethylene particles, acrylic particles, polysiloxane resin particles, isoprene rubber particles, and polyamide particles.
Examples of the inorganic fine particles include metal oxide particles such as copper oxide, copper hydroxide, iron oxide, alumina, zinc oxide, lead oxide, magnesia, tin oxide, calcium carbonate, carbon, silica, mica, and smectite. .
Further, if the surface is an electrically attracting particle, a similar effect can be expected because a pseudo-aggregation is formed in the composition.

The primary particle shape of the fine particles can be selected from a substantially spherical shape, a needle shape, a plate shape, a rice grain shape, and the like. In particular, for the purpose of imparting thixotropy, a needle shape, a plate shape, a rice grain shape, or a bead shape is preferable.
For dispersion of the fine particles, a dispersion aid or a dispersion stabilizer can be added as long as the target function is not impaired.
The major axis (long side) of the fine particles is preferably 10 nm to 10 μm.
The major axis (long side) of the fine particles can be obtained by a method similar to the method for obtaining the particle size of the etching component from the SEM observation image.

  The content of the thixotropic agent is preferably 0.1 to 5.0% by mass with respect to the entire composition. If it is less than 0.1% by mass, a sufficient effect for expression of thixotropy may not be obtained. On the other hand, if it exceeds 5.0 mass%, the viscosity may become too high. The content of the thixotropic agent is particularly preferably 1.0 to 4.0% by mass.

The composition of this invention can be manufactured by mixing the component (A) and (B) mentioned above, the solvent mix | blended as needed, the said additive, etc.
In order to improve the uniformity of the composition, propeller agitation, ultrasonic dispersing device (eg, Nippon Seiki Seisakusho, ultrasonic homogenizer), revolving mixer (eg, Shinky, Foaming Rentaro), high-speed emulsification / dispersion It is preferable to mix using a disperser such as a machine (eg, TK homomixer series manufactured by PRIMIX Co., Ltd.), a rake machine, a three-roll mill, a bead mill, a sand mill, or a pot mill. In addition, dispersion | distribution can implement these apparatuses individually or in combination.

  When air bubbles are generated in the mixed composition after dispersion, the air bubbles in the composition can be removed by standing under reduced pressure, stirring and degassing under reduced pressure, or the like.

The composition of the present invention can be suitably used as an etching paste for an inorganic thin film, particularly an SiN film.
The composition of the present invention can be applied to, for example, plate printing, screen printing, flexographic printing, microcontact printing, etc., and plateless printing, inkjet printing, slit printing, dispenser printing, and the like.
In particular, a printing method capable of patterning without contact is preferable because damage to the substrate due to application of a printing pressure can be avoided.

Since the viscosity of the composition depends on the printing method and the printing apparatus, it is not particularly limited and can be prepared so as to be suitable for each printing method.
For example, in screen printing, the viscosity at 25 ° C. is preferably 100 mPa · s or more, and particularly preferably 1 Pa · s or more.
In inkjet printing, 3 to 20 mPa · s is generally a preferred range.

The method of removing the SiN film using the composition includes a step of forming the composition (etching material) of the present invention on the SiN film by a printing method (printing step) and a step of removing the SiN film by heating. (Etching step).
The SiN film is used as an interlayer insulating film of a semiconductor element such as a CMOS, a passivation film, an antireflection film of a solar cell, or the like. The SiN film is formed by a known method such as chemical vapor deposition (CVD). “SiN” does not mean that the stoichiometric ratio (Si: N) is 1: 1.

In the printing process, a desired pattern on the SiN film is formed using the etching material by the known printing method described above. The SiN film located under the pattern is finally removed (etched).
After printing, if necessary, the solvent of the etching material is volatilized and removed by heating or decompression. The removal of the solvent may be combined with the heating in the etching step, but is appropriately selected because each temperature condition may be different.

  In an etching process, it heats at 100-250 degreeC, More preferably, 100-200 degreeC for 1 to 60 minutes. When the temperature exceeds 250 ° C., for example, in the case of a solar cell, the dopant doped in the n + layer or the like diffuses, and an interdiffusion layer is formed at the P-type / N-type interface, which may deteriorate the characteristics of the solar cell. is there.

If there is a residue after the etching process, a cleaning process is provided to remove the residue.
Examples of the cleaning step include ultrasonic cleaning using pure water, brush cleaning, spray cleaning, running water cleaning, and the like.

  The method for removing a SiN film of the present invention can be applied to a substrate having a SiN film. Examples of the substrate include glass (quartz, window glass, borosilicate glass, non-alkali glass), silicon wafer, and the like when Si is the main component. Depending on the purpose of use, it may contain impurities or may be oxidized. Moreover, the shape of the surface is not ask | required.

  The substrate obtained by removing the SiN film using the method of the present invention becomes an intermediate processed product of various semiconductor devices and solar cells. For example, in the case of a solar cell, a solar cell can be produced by forming a power supply wiring (electrode) using a metal paste or the like after removing the SiN film. The n + portion may be formed by doping an exposed silicon surface with a dopant such as phosphorus.

Example 1
(1) Preparation of composition (etching paste) Boron trifluoride monoethylamine complex (melting point 88 ° C.) (Wako Pure Chemical Industries, Ltd.) 25 g was ground in an automatic mortar for 9 hours and passed through a 100 μm sieve. A fine powder of an ethylamine complex was obtained.
1.0 g of fine powder of boron trifluoride monoethylamine complex, 3.5 g of 1-butyl-3-methylimidazolium hexafluorophosphoric acid (manufactured by Wako Pure Chemical Industries, Ltd.) which is an ionic liquid, long particles (particle diameter 200 nm) Etching paste was obtained by mixing 4.5 g of copper oxide nanoparticles (in-house synthesized product) having an aspect ratio of 3) and 1.0 g of terpineol isomer mixture (manufactured by Wako Pure Chemical Industries, Ltd.) in an agate mortar.

(2) Printing of SiN etching paste and etching of SiN film P-type silicon wafer (1-50Ω) (Mito Seiko Co., Ltd.) with 150 nm of SiO ₂ and 90 nm of SiN laminated on the mirror surface by PE-CVD with SiN Used as a silicon substrate.
A 5 cm × 5 cm square and a straight line having a width of 200 μm were printed on the SiN film by screen printing of the SiN etching paste.
The printed silicon substrate with the SiN film was heat-treated on a hot plate heated to 160 ° C. for 30 minutes, then allowed to cool and ultrasonically cleaned in ultrapure water.
In the SiN-attached silicon substrate after the etching process, the SiN film at the lower part of the printing part has been removed.
FIG. 1 shows an electron micrograph of the surface of a silicon wafer obtained by printing an etching paste in a straight line having a width of 200 μm and performing an etching process. Moreover, the cross-sectional photograph before the etching process of the silicon wafer is shown in FIG. 2, and the cross-sectional photograph after the etching process is shown in FIG.
It can be confirmed that the SiN film is removed by etching.

Comparative Example 1
Etching by mixing 4.5 g of fine powder of boron trifluoride monoethylamine complex obtained in Example 1 (1), 4.5 g of long granular copper oxide nanoparticles, and 1.0 g of terpineol isomer mixture in an agate mortar. A paste was obtained.
In the same manner as in Example 1, screen printing was performed on a silicon substrate with a silicon nitride film, and heating was performed at 160 ° C. for 30 minutes to perform ultrasonic cleaning.
As a result, a part of the SiN film where the etching paste was printed in a square of 5 cm × 5 cm was etched, but the SiN film was not removed from the part printed in a straight line having a width of 200 μm.

Comparative Example 2
Etching paste was obtained by mixing 4.5 g of 1-butyl-3-methylimidazolium hexafluorophosphoric acid, 4.5 g of long granular copper oxide nanoparticles, and 1.0 g of terpineol isomer mixture in an agate mortar.
In the same manner as in Example 1, screen printing was performed on a silicon substrate with a silicon nitride film, and heating was performed at 160 ° C. for 30 minutes to perform ultrasonic cleaning.
As a result, the silicon nitride film in the portion where the etching paste was printed was not removed.

Comparative Example 3
Instead of 3.5 g of 1-butyl-3-methylimidazolium hexafluorophosphoric acid, 3.5 g of 1-butyl-3-methylimidazolium iodide (manufactured by Wako Pure Chemical Industries, Ltd.) as an ionic liquid was used. Except for the above, an etching paste was prepared and etched in the same manner as in Example 1.
As a result, the silicon nitride film in the portion where the etching paste was printed was not removed.

  From the results of Example 1 and Comparative Examples 1 to 3, it can be seen that the composition of the present invention can easily etch the inorganic thin film at a relatively low temperature without damaging the substrate.

The composition of the present invention is suitable for removing an inorganic thin film made of silicon nitride (SiN) or the like.
The method of removing the SiN film of the present invention can be used for manufacturing processes of various semiconductor elements and solar cells.

Claims (6)

A composition containing the following components (A) and (B).
(A) Boron trifluoride monoethylamine complex (B) 1-butyl-3-methylimidazolium hexafluorophosphoric acid   Furthermore, the composition of Claim 1 containing a solvent.   The composition according to claim 1 or 2, wherein a total content of the components (A) and (B) is 30 to 80% by mass. The composition of Claim 2 or 3 containing the solvent whose vapor pressure in 25 degreeC is less than 1.34 * 10 < ³ > Pa.   A method for removing a silicon nitride (SiN) film using the composition according to claim 1. Forming the composition on the SiN film by a printing method;
And removing the SiN film by heating.