JP2013177264A - METHOD FOR FORMING THIN FILM LAYER BY Si FINE PARTICLE, SEMICONDUCTOR DEVICE AND METHOD OF MANUFACTURING SEMICONDUCTOR DEVICE, AND SOLAR CELL AND METHOD OF MANUFACTURING SOLAR CELL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form silicon (Si) fine particles having high surface stability and a particle size of at least several hundreds nm or less from the so-called chips of a silicon substrate, and to create a solar cell by using the same.SOLUTION: Si fine particles having a particle size of at least several hundreds nm or less, and obtained by being pulverized by a bead mill method after being pulverized from chips of a silicon substrate are treated with hydrofluoric acid, dispersed into ethanol, dropped and applied onto a substrate to obtain a thin film layer. Then, the thin film layer is subjected to a nitric acid oxidation treatment to remove surface impurities, and simultaneously a tunnel junction layer between Si fine particles by a silicon oxide film formed on the Si fine particle is achieved, and a solar cell is created by using it, to thereby obtain stable and effective photoelectric conversion characteristics.

Description

The present invention can be used as a low-cost printable electronic material from a silicon wafer material, and has a particle size as a Si fine particle suitable for forming a thin-film solar cell or a silicon (hereinafter referred to as Si) semiconductor device. A method of obtaining Si fine particles of several hundred nanometers (nm) or less, in which case impurities near the surface can be removed, and Si fine particles are formed in a thin film layer by tunnel junction through an oxide film, The present invention relates to a semiconductor device, a semiconductor device manufacturing method, a solar cell, and a solar cell manufacturing method.

Conventionally, when obtaining this kind of Si fine particles, for example, Si particles having a particle size of 50 to 1000 microns (μm) are treated with a mixed acid of hydrofluoric acid (hereinafter referred to as hydrofluoric acid) and nitric acid, It is known to produce Si fine particles and to simultaneously use hydrofluoric acid and nitric acid in the acid treatment step (see JP-A-6-148822). However, in this acid etching step, the porous surface is formed by etching the Si surface, which is unsuitable for obtaining fine particles having a particle size of several hundred nm or less.

On the other hand, although fine particles of Si are attracting attention as printable electronic materials, particles having a particle size of several hundred nanomicrons (nm) or less are desirable for use as thin film electronic materials. Such particles are produced mainly by a laser ablation method, a CVD method or a high-frequency sputtering method, but the production equipment is expensive and the productivity and the low cost are disadvantageous, such as lack of mass productivity. .

Further, when Si fine particles having a particle size of several hundred nm or less are used, the surface area ratio with respect to the particle size is remarkably large. Therefore, it is difficult to control the particle size in the above-described conventional acid etching process, which is not practical for industrial use.

Japanese Unexamined Patent Publication No. 6-148822

The object of the present invention is to further reduce the size of Si fine particles that can be used as a printable electronic material, and to remove impurities in the vicinity of the surface of the Si fine particles together with a technique for realizing Si particles having a particle size of several hundred nm or less. In addition, a semiconductor device manufacturing method including forming a thin film layer by a tunnel junction through an oxide film, and a high-performance solar cell or semiconductor device thereby.

The present invention provides a process of forming a thin film layer of Si fine particles on a predetermined substrate surface by supplying Si fine particles with a solution that has been surface-treated with hydrofluoric acid in advance and dispersed in a solvent such as ethanol. Si fine particles having a process of forming a tunnel junction between the Si fine particles in the thin film layer by supplying nitric acid onto the thin film layer by the fine particles and oxidizing the surface of the Si fine particles The thin film layer forming method, the semiconductor device, the semiconductor device manufacturing method, the solar cell, and the solar cell manufacturing method.

The gist of the present invention is to supply Si fine particles obtained by finely pulverizing Si chips, in a solution dispersed in a solvent such as ethanol, to form a thin film layer of the Si fine particles on a predetermined substrate surface, Further, nitric acid is supplied onto the Si thin film layer to oxidize the surface of the Si fine particles, thereby integrating the Si fine particles in the Si thin film layer with a tunnel junction.

The present invention provides, for example, a Si thin particle having a particle size of several hundred nm or less dispersed in a solvent such as ethanol to form a Si thin film layer of the Si fine particle on a predetermined substrate surface. Nitric acid is supplied onto the layer to oxidize the surface of the Si fine particles, thereby forming a process of forming the inside of the Si thin film layer as a tunnel junction layer between Si particles.

According to the present invention, Si fine particles are supplied in a solution dispersed in a predetermined solvent to form a Si thin film layer of Si fine particles on a predetermined substrate surface, and then nitric acid is supplied onto the Si thin film layer. Then, by forming an oxide film on the surface of the Si fine particles, a predetermined semiconductor functional layer in which the Si fine particles in the Si thin film layer are integrated by a tunnel junction is formed, and a desired semiconductor utilizing the semiconductor functional layer is formed. The device can be easily realized.

According to the present invention, Si fine particles are supplied in a solution dispersed in a solvent such as ethanol, a thin film layer is formed by the Si fine particles on a predetermined substrate surface, and nitric acid is further supplied onto the Si thin film layer. By forming an oxide film on the surface of the Si fine particles and integrating the Si fine particles in the Si thin film layer with a tunnel junction, the Si thin film layer becomes a semiconductor layer that is easy to transfer electric charge, A high-performance semiconductor device can be realized.

According to the present invention, at least Si particles having a particle size of several hundred nm or less are supplied in a solution dispersed in a solvent such as ethanol to form a thin film layer of the Si fine particles on a predetermined substrate surface, and further, the Si Nitric acid is supplied onto the thin film layer, an oxide film is formed on the surface of the Si fine particles, and the Si fine particles in the Si thin film layer are integrated by a tunnel junction between particles, thereby easily transferring the semiconductor layer. Thus, for example, when the same layer is used as a photoelectric conversion layer in a solar cell structure, a solar cell with high conversion efficiency can be realized even with a thin film layer having a thickness of 0.01 to several tens of μm.

In the present invention, chips (chips) generated in large quantities when a Si wafer is sliced from an ingot are used, and with the recent thinning of Si wafers, the generation ratio of the chips increases. Since a 180 nm-thick Si wafer generates the same amount of chips as the weight of the wafer, it can be used to create low-cost and useful semiconductor devices and solar cells.

In addition, according to the present invention, it is possible to contribute to the creation of a high-efficiency solar cell having a band gap controlled by the particle size and controlled by the quantum size effect.

It is an observation figure by the transmission electron microscope (TEM) of the thin film layer by Si fine particle obtained by implementation of this invention. FIG. 4 is a current-voltage characteristic diagram of a pn junction formed by an n-type semiconductor substrate obtained by the practice of the present invention and a thin film layer made of Si fine particles. It is a photovoltaic-photocurrent characteristic figure of the solar cell obtained in the Example of this invention.

Next, the present invention will be described in detail by way of examples which are embodiments with reference to the drawings.

Chips produced by a fixed abrasive cutting method from a p-type crystal Si ingot are pulverized in ethanol by a bead mill method using ZrO ₂ beads having a diameter of 0.5 mm, and then centrifuged with ethanol and Si. The fine particles were separated, and the Si fine particles were immersed in 50% hydrofluoric acid at room temperature for about 20 minutes to remove the oxide film formed on the surface, and then rinsed with ultrapure water. . At this time, the concentration of hydrogen fluoride (HF) in the hydrofluoric acid chemical solution is not limited in action, but since the effect was small at 5% in practice, preferably more than 30 wt% to 99 wt% hydrofluoric acid is used. It was appropriate to select and use as appropriate, especially when a hydrofluoric acid chemical solution having a concentration of more than 50 wt% to 99 wt% was used. The chips used here are not limited to p-type, but may be i-type and / or n-type, and the conductivity can be arbitrarily selected.

Next, the Si fine particles are dropped and supplied onto the entire surface of a 2.5 cm square n-type single crystal Si wafer with a solution dispersed in high-concentration ethanol, and dried in a room-temperature reduced-pressure atmosphere. A thin film layer having a thickness was formed. Thereafter, nitric acid having a concentration of 70% was dropped onto the thin film layer, and heat treatment was performed on a hot plate at 150 ° C. for 1 minute. As a result, the thin film layer became a thin film layer of a p-type semiconductor tunneled by a thin silicon oxide film formed by nitric acid oxidation on the surface of the Si fine particles. Further, as a result of XPS measurement performed after the nitric acid treatment, it was clear that impurities from the Si fine particles progressed in the course of the nitric acid treatment, and in particular, carbon was reliably removed. Note that the supply of Si fine particles to the entire surface of a 2.5 cm square n-type single crystal Si wafer was dropped by a solution dispersed in high-concentration ethanol, but other supply methods such as coating supply are also possible. is there. Further, by using microwaves for the nitric acid heat treatment, the treatment time can be shortened and the annealing effect of Si fine particles can be improved.

FIG. 1 is a transmission electron microscope (TEM) view of a thin film layer formed of Si fine particles immediately after nitric acid heat treatment. Si fine particles having a size of about 5 nm to about 10 nm were confirmed as indicated by a circle in the center of the figure. Further, from the TEM image of FIG. 1, it was confirmed that the Si fine particles had crystallinity.

FIG. 1 is a cross-sectional view of a thin film layer formed of Si fine particles. Actually, however, Si fine particles having a particle diameter of several nanometers to several tens of nanometers are distributed and exist three-dimensionally. Is a Si thin film layer connected by a tunnel junction between Si oxide films. And as a result of measuring this Si thin film layer by XPS, it was confirmed that the film thickness of the formed silicon oxide film is about 2.6 nm.

The wafer is then heat treated at 900 ° C. in nitrogen.
Further, the surface electrode is formed by vapor-depositing a 0.2 μm-thick aluminum layer and annealing at a temperature of 650 ° C. for a short time, and the back electrode is formed by depositing a 0.2 μm-thick aluminum layer, A solar cell structure was prepared without annealing.

FIG. 2 is a voltage-current characteristic diagram obtained by measuring electrical characteristics between pn junctions of a solar cell formed on an n-type single crystal Si wafer. The solid line curve with and without nitric acid oxidation treatment of this example and This is shown in comparison with a dotted curve. From this result, when the structural interface between the p-type Si fine particle thin film layer and the n-type single crystal Si substrate surface according to this example is expressed by an ideal coefficient n (maximum value n = 1) indicating good rectification, a solid line In the case of the curve, the n value is 1.7, which is a good rectifying property, and it has been found that a significantly superior pn junction is formed compared to the n value of 4.5 in the case of the dotted curve.

FIG. 3 shows a current-voltage curve observed by irradiating light to a thin film layer of p-type Si fine particles applied and formed on an n-type single crystal Si wafer, that is, a relationship characteristic diagram between photovoltaic power and photocurrent. The solid line curve with nitric acid oxidation treatment of this example is shown in comparison with the dotted line curve without nitric acid oxidation treatment. The solar cell structure in this example generates sufficient photovoltaic power and photocurrent upon irradiation with sunlight, functions as a photoelectric conversion layer, and has a conversion efficiency of 0. Even when compared with 1.8 × 10 ⁻⁴ % without nitric acid oxidation in the dotted curve, it shows that the nitric acid oxidation treatment has a very effective effect on the solar cell.

The processing by the bead mill method involves re-grinding Si particles in a container together with appropriate bead spheres, and by appropriately selecting the bead sphere size and oscillating time, reproduction processing to the desired fine particle state Is possible.

In addition, the formation of Si particles is not limited to those obtained by pulverizing p-type crystalline Si chips produced by the fixed abrasive cutting method into ultrafine particles, but also single-crystal or polycrystalline Si substrates (ingots) When forming a thin substrate (wafer) from a material, so-called chips are used as a raw material, and this can be re-miniaturized by the ball mill method, bead mill method, shock wave method or jet mill method. . The chips generated in this case are usually as inexpensive as the objects to be discarded, and if this is used, extremely low-cost Si fine particles can be produced.

Since the silicon oxide film on the surface of the Si particles obtained in this embodiment is extremely thin and stable, the movement of electric charges between adjacent Si particles in the thin film layer can be moved by a tunnel effect, such as a solar cell. There is almost no hindrance to the movement of carriers (charges) generated by the photoelectric effect in Therefore, a pin-type thin film semiconductor layer is formed with this kind of Si fine particles, for example, by printing technology, etc., and semiconductor devices such as solar cells, p-type and n-type TFTs, and CMOS-TFTs using them are created. This is a preferred embodiment of the present invention.

According to this embodiment, an etching process in which Si fine particles obtained to a particle size of at least several hundred nm or less are dispersed in hydrofluoric acid having a hydrogen fluoride concentration of 20% or more and a chemical oxidation process with nitric acid are performed. By the processing method or manufacturing method of the Si fine particles included, the surface stability can be realized extremely high, and the Si fine particle thin film layer can be created at a low cost, and the significance for industrial use is really great. Further, it is possible to produce a more effective Si ink material by blending an appropriate binder material or dispersion material with the Si fine particles.

In addition, according to the present embodiment, it is used as a printable material for applying and forming a thin film for a solar cell, and the photoelectric conversion layer is a very thin film layer having a thickness of 0.01 to several tens of μm, and has high conversion efficiency A functional element of performance, or a crystalline Si substrate, a polycrystalline Si substrate, a non-crystalline Si substrate, a glass substrate, or a plastic substrate is formed on the first photoelectric conversion layer by the present Si fine particles and formed by coating with Si fine particles. It can be applied to a solar cell having a multilayer structure in which the second thin film photoelectric conversion layer is sequentially formed, and a high-performance solar cell with further improved photoelectric conversion efficiency can be realized.

In the present invention, nitric acid oxidation treatment is performed on Si fine particles obtained by pulverization of Si crystal chips, for example, Si fine particles having a particle size of several hundred nm or less, and impurities near the surface can be removed. The present invention can be applied to a method for forming a thin film layer by tunnel junction through an oxide film, a semiconductor device, a method for manufacturing a semiconductor device, a solar cell, and a method for manufacturing a solar cell, and its industrial application effects are extremely large. The obtained Si fine particles are highly usable as a printable material for forming a thin film, and the Si paste produced using these Si fine particles is a thin film suitable for semiconductor devices, liquid crystal TFTs, etc. in addition to solar cells. Contributes to being able to be used as a forming material. Therefore, according to the present invention, highly stable and reliable Si fine particles can be obtained at low cost, and solar cells and semiconductor devices using thin film layers using these Si fine particles can be easily realized industrially. it can.

Claims (10)

A method for forming a thin film layer from Si fine particles, comprising a step of surface-treating Si fine particles produced from ingot as cut chips and finely pulverized with a pulverizer with nitric acid. 2. The method for forming a thin film layer using Si fine particles according to claim 1, wherein the silicon fine pulverization method is formed by any one of a bead mill, a ball mill, a jet mill, a shock wave pulverization method, or a combination thereof. A process of forming Si thin film layers by dispersing Si fine particles in a solvent and supplying them on a predetermined substrate surface, and supplying nitric acid onto the Si thin film layers to form an oxide film on the surface of the Si fine particles. A method of manufacturing a semiconductor device comprising a step of forming a thin film semiconductor layer of a tunnel junction. The step of dispersing Si fine particles in hydrofluoric acid in advance and surface-treating, the step of dispersing the Si fine particles in a solvent and supplying them onto a predetermined substrate surface to form a Si thin film layer, and adding nitric acid on the Si thin film layer A method of manufacturing a semiconductor device, comprising: supplying and forming an oxide film on the surface of the Si fine particles. Si fine particles obtained by finely pulverizing Si chips are pre-dispersed in hydrofluoric acid and surface-treated, and then the Si fine particles are dispersed in a solvent and supplied onto a predetermined substrate surface. Forming a Si thin film layer, further supplying nitric acid onto the Si thin film layer to form an oxide film on the surface of the Si fine particles, and tunnel bonding by the oxide film between the Si fine particles in the Si thin film layer A method for manufacturing a semiconductor device integrated in a semiconductor. A semiconductor device having a Si thin film layer in which Si fine particles are tunnel-bonded between particles through an oxide film. A semiconductor device comprising an interparticle junction semiconductor layer including an oxide film made of Si ultrafine particles, obtained by the method for producing Si fine particles according to claim 1. A solar cell comprising a photoelectric conversion layer made of a semiconductor layer in which the Si fine particles according to claim 1 are covered with an oxide film and tunnel-bonded between the particles. A step of dispersing Si fine particles in hydrofluoric acid in advance, a step of dispersing the Si fine particles in a solvent and supplying the solution onto a predetermined substrate surface, forming a Si thin film layer with the Si fine particles, nitric acid on the thin film layer And a step of forming an oxide film on the surface of the Si fine particles to form a tunnel junction between the Si fine particles. A solar cell provided with a photoelectric conversion layer comprising an interparticle junction including an oxide film of Si ultrafine particles, obtained by the method for producing Si fine particles according to any one of claims 1 to 4.