JP2018170379A - Semiconductor device, solar cell, and manufacturing method of solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device having an insulating film in which carbon is introduced to have a negative fixed charge.SOLUTION: Carbon 22 is ion-implanted on the upper surface of a silicon substrate 11 by an ion implantation apparatus as indicated by 21. Next, wet oxidation is performed on the silicon substrate 11 after carbon ion implantation to form a wet oxide film 23 containing carbon on the surface of the silicon substrate 1. As a result, an insulating film of the wet oxide film 23 having a negative fixed charge density higher than that of the wet oxide film not containing carbon is formed on the surface of the silicon substrate 11. Since the wet oxide film 23 has a negative fixed charge density due to the effect of carbon, good passivation characteristics can be obtained.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a semiconductor device, a solar cell, and a method for manufacturing the solar cell, and more particularly, a semiconductor device having at least an insulating film formed on a silicon substrate, a solar cell using the insulating film of the semiconductor device as a passivation film, and the solar cell It relates to the manufacturing method.

  Renewable energy can be used repeatedly without depleting energy resources, and does not emit carbon dioxide, which causes global warming during power generation. Therefore, it is attracting attention as a clean energy alternative to fossil fuels such as oil, coal, and natural gas. Has been. One type of renewable energy is sunlight, and a power generation method that directly converts sunlight into electric power using a solar cell is called solar power generation. A solar cell is a photoelectric conversion element that absorbs light energy and converts it into electricity, and is formed on a semiconductor substrate such as a silicon substrate.

  There are various types of solar cells. For example, crystalline silicon having a structure in which a diffusion layer having a conductivity type different from that of a silicon substrate is formed on the surface of a silicon substrate, and an insulating film and an antireflection film are stacked thereon. Solar cells are known. In order to increase the efficiency of such a solar cell, it is important to passivate (passivate) the insulating film and suppress recombination of carriers generated in the silicon substrate.

According to the extended Shockley lead holes (Shockly-Read-Hall) model, the semiconductor and the carrier recombination rate S of the interface between the insulating film interface defect density D _it and the carrier density at the interface (electron density n _s, The hole density is called p _s ). In order to reduce the recombination rate S, _it is necessary to lower the interface defect density _Dit or increase the carrier density at the interface. The interface defect density and carrier density will be described by taking silicon dioxide, which is a typical insulating film (passivation film), as an example. Since interface defects are mainly caused by dangling bonds, the density of interface defects is reduced by terminating the dangling bonds. It is known that heat treatment in a hydrogen atmosphere is effective as a method for terminating dangling bonds. On the other hand, as a technique for increasing the electron density n _s and the hole density p _s , a technique for bending a band near the interface and moving minority carriers away from the interface is known. This is called a field effect passivation effect. This effect can be derived by introducing a fixed charge in the insulating film at the interface with the diffusion layer.

  Negative fixed charge is effective for passivation of p-type diffusion layers formed by trivalent dopants such as boron, and positive fixed charge is effective for passivation of n-type diffusion layers formed by pentavalent dopants such as phosphorus. It is known that As the insulating film, a silicon dioxide film, a silicon nitride film, or an aluminum oxide film is given. The silicon dioxide film has a feature that the interface defect density is lower than that of the silicon nitride film or the aluminum oxide film. The silicon nitride film is characterized in that the polarity of the fixed charge changes to positive or negative depending on the composition of silicon and nitrogen. Furthermore, the aluminum oxide film is characterized by having a high density of negative fixed charges (see Non-Patent Documents 1 and 2 and Patent Document 1).

JP 2006-253520 A

Junsuke Miyajima, “Interface deactivation film in crystalline silicon solar cells”, Journal of Plasma Fusion Research, vol.85, No.12 (2009) 820-824 V.V.Afanas’ev et al., “Positive charging of thermal SiO2 / (100) Si interface by hydrogen annealing”, Applied Physics Letters 72 (1) 79 (1998)

  However, when a silicon dioxide film is used as an insulating film, although it has a low interface defect density, it has a positive fixed charge and its fixed charge density is lower than that of a silicon nitride film, thus realizing a highly efficient solar cell. Therefore, it is not suitable for an insulating film formed on a p-type diffusion layer which is indispensable for the purpose.

  When a silicon nitride film is used as the insulating film, the silicon nitride film can change the polarity of the fixed charge to positive or negative depending on the composition of silicon and nitrogen, but the refractive index also changes depending on the composition of silicon and nitrogen. Therefore, when considering not only an insulating film but also a function as an antireflection film, it is limited to n-type passivation effective for positive fixed charges. Therefore, in order to solve this problem, proposals have been made to use a hierarchical structure of a plurality of silicon nitride films having different compositions of silicon and nitrogen as an insulating film (see, for example, JP-A-2006-128258). However, this insulating film has a problem that the manufacturing process becomes complicated.

  On the other hand, various cell structures have been proposed for increasing the efficiency of solar cells. For example, a back electrode type solar cell called a back contact cell has a structure in which a plurality of p-type regions and n-type regions are alternately provided on the back surface of the substrate, and electrodes are separately connected to the p-type region and the n-type region, High efficiency is achieved by concentrating the electrodes on the back side of the substrate and eliminating the electrodes on the light receiving surface on the surface of the substrate so that light is efficiently taken in. The back electrode type solar cell is only an example. In solar cells, it is desired to develop an insulating film (passivation film) that has a low interface defect density and can control a fixed charge density.

  The present invention has been made in view of the above points, and a method for manufacturing a semiconductor device having an insulating film in which carbon is introduced to have a negative fixed charge, a solar cell using the insulating film, and a solar cell using the insulating film An object is to provide a manufacturing method.

  In order to achieve the above object, a method of manufacturing a semiconductor device according to the present invention includes an ion implantation step of ion-implanting carbon into a surface of a silicon substrate to contain carbon in the silicon substrate, and the carbon being ion-implanted. Forming a wet oxide film as an insulating film on the surface of the silicon substrate containing carbon by wet-oxidizing the silicon substrate.

  In order to achieve the above object, a method for manufacturing a solar cell according to the present invention is a method for manufacturing a solar cell in which a diffusion layer, a passivation film, and a surface electrode are at least laminated on the surface of a texture structure of a silicon substrate. A diffusion layer forming step for forming a diffusion layer on the surface of the texture structure of the silicon substrate; and an insulating film containing carbon on the surface of the diffusion layer by ion implantation of carbon from above the diffusion layer as the passivation film And an insulating film forming step to be formed.

  Moreover, in order to achieve said objective, the solar cell which concerns on this invention was manufactured by the manufacturing method of the solar cell of this invention, It is characterized by the above-mentioned.

  According to the present invention, a negative fixed charge density can be given to the insulating film due to the effect of carbon, so that good passivation characteristics can be obtained.

It is sectional drawing of an example of the semiconductor device manufactured by the manufacturing method of the semiconductor device which concerns on this invention. It is element sectional drawing of each manufacturing process of 1st Embodiment of the manufacturing method of the semiconductor device which concerns on this invention. It is element sectional drawing of each manufacturing process of 2nd Embodiment of the manufacturing method of the semiconductor device which concerns on this invention. It is element sectional drawing of each manufacturing process of 3rd Embodiment of the manufacturing method of the semiconductor device which concerns on this invention. It is sectional drawing of one Embodiment of the solar cell which concerns on this invention. It is a flowchart for process description of one Embodiment of the manufacturing method of the solar cell which concerns on this invention. 5 is a flowchart for explaining a method for evaluating a fixed charge of a silicon dioxide film formed by wet oxidation of a silicon substrate into which carbon ions are implanted. It is a characteristic view which shows a CV measurement result.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of an example of a semiconductor device manufactured by the method for manufacturing a semiconductor device according to the present invention. In the figure, the semiconductor device 10 has a structure in which a silicon dioxide film 13 is formed on the surface of a silicon substrate 11 as an insulating film by ion implantation of carbon 12. Here, the surface shape of the silicon substrate 11 on which the silicon dioxide film 13 is formed will be described. Generally, a light receiving surface of a solar battery cell is formed with a pyramid structure (or uneven structure) called a texture in order to efficiently take light into a substrate. When the diffusion layer is formed on the light receiving surface side, a passivation film, that is, a silicon dioxide film is formed on the texture surface.

  On the other hand, when a diffusion layer is formed on the back surface as in the back electrode type, since it is not necessary to form a texture, a passivation film, that is, a silicon dioxide film is formed on a flat surface. In FIG. 1, for the sake of simplicity, a silicon dioxide film 13 is formed on a flat surface of a silicon substrate 11. However, in the case of a texture structure as well, fixed charges with a low interface defect density are obtained by carbon 12 introduced by ion implantation. A silicon dioxide film whose density is controlled to have a negative fixed charge density is formed.

Next, embodiments of the semiconductor device manufacturing method according to the present invention will be described.
FIG. 2 is an element cross-sectional view of each manufacturing process of the first embodiment of the method for manufacturing a semiconductor device according to the present invention. First, a silicon substrate 11 shown in FIG. 2A is prepared, and as shown in FIG. 2B, carbon 22 is ion-implanted into the upper surface of the silicon substrate 11 as shown by 21 by an ion implantation apparatus. Subsequently, as shown in FIG. 2C, wet oxidation is performed on the silicon substrate 11 after the carbon ion implantation to form a wet oxide film 23 containing carbon on the surface of the silicon substrate 1. As a result, an insulating film made of the wet oxide film 23 having a higher negative fixed charge density than the wet oxide film not containing carbon is formed on the surface of the silicon substrate 11. Since the wet oxide film 23 has a negative fixed charge density due to the effect of carbon, good passivation characteristics can be obtained.

  Here, the wet oxidation will be further described. Silicon carbide substrates are mainly used in power devices. Also in a field effect transistor using a silicon carbide substrate, a silicon dioxide film is used as an insulating film. There is a wet oxidation method as a method for forming a silicon dioxide film on a silicon carbide substrate. A silicon dioxide film on a silicon carbide substrate produced by wet oxidation has a negative fixed charge, which is a problem because it deteriorates the characteristics of a field effect transistor (for example, see Reference 1: R Palmieri et al., “ Trapping of majority carriers in SiO2 / 4H-SiC sirucctures ”, JOURNAL OF PHYSICS D: APPLIED PHYSICS 42 (2009) 125301)).

  Further, when silicon carbide is oxidized to silicon dioxide, excess carbon atoms are released to the silicon dioxide side. Hydrogen atoms contained in water vapor used in wet oxidation break silicon-oxygen bonds among silicon-carbon-oxygen bonds, and carbon and oxygen react. Furthermore, when carbon and oxygen form carbonate ions, they have a negative charge. Reference 2 (Yasuhiro Ebihara) indicates that the negative fixed charge of the silicon dioxide film formed when wet-oxidizing a silicon carbide substrate having a silicon-carbon composition ratio of 1: 1 is a carbonate ion caused by hydrogen atoms. et al., “Intrinsic origin of negative fixed charge in wet oxidation for silicon carbide”, Applied Physics Letters 100 (2012) 212110).

  Therefore, in view of the above points, the present inventors have come to the idea that when a silicon substrate containing carbon is wet oxidized, carbonate ions having a negative fixed charge are formed, and the silicon substrate containing carbon is wet. The inventors have created a novel invention that has never been seen before, in which a silicon dioxide film having a negative fixed charge is formed on the silicon substrate by oxidation.

  FIG. 3 is an element cross-sectional view of each manufacturing process of the second embodiment of the method for manufacturing a semiconductor device according to the present invention. First, carbon 22 is ion-implanted into the upper surface of the silicon substrate 11 shown in FIG. Subsequently, as shown in FIG. 3B, the silicon substrate 11 after the carbon ion implantation is oxidized to form a silicon dioxide film 25 containing carbon on the surface of the silicon substrate 1. As a result, an insulating film made of the silicon dioxide film 25 having a higher negative fixed charge density than the silicon dioxide film containing no carbon is formed on the surface of the silicon substrate 11. The characteristics of the passivation depend on the defect density and fixed charge density at the interface between the silicon dioxide film 25 and the silicon substrate 11, but the interface defect in the silicon dioxide film 25 is lower in density than the aluminum oxide film, and carbon Since the silicon dioxide film 25 has a negative fixed charge density due to the above effect, the semiconductor device manufactured in this embodiment can obtain good passivation characteristics.

FIG. 4 is an element cross-sectional view of each manufacturing process of the third embodiment of the method for manufacturing a semiconductor device according to the present invention. First, carbon 22 is ion-implanted into the upper surface of the silicon substrate 11 shown in FIG. Subsequently, as shown in FIG. 4B, the silicon substrate 11 after the ion implantation is annealed to recover the damage during the ion implantation. Finally, as shown in FIG. 4C, the element is oxidized. As a result, a silicon dioxide film 27 having a low interface defect density and a negative fixed charge density is formed as an insulating film. Since the silicon dioxide film 27 has a negative fixed charge density in the semiconductor device of the present embodiment as well as the semi-consensus device manufactured by the manufacturing method of the first and second embodiments, the manufactured semiconductor device is good. Passivation characteristics are obtained.
The purpose of the annealing process in FIG. 4B is to recover damage by ion implantation. However, if the damage by ion implantation can be recovered by the oxidation process in FIG. 4C, the annealing process can be omitted.

  Next, the solar cell according to the present invention will be described. FIG. 5 shows a cross-sectional view of one embodiment of a solar cell according to the present invention. In the figure, a solar cell 100 has a diffusion layer 102, an insulating film (passivation film) 103, and an antireflection film 104 laminated on the surface of a silicon substrate 101 that is a semiconductor substrate, and further an interval on the antireflection film 104. The surface electrode 105 is formed and a BSF (Back Surface Field) layer 106 and a back electrode 107 are laminated on the back surface of the silicon substrate 101. Although the basic structure itself of such a solar battery cell is known, the solar battery cell 100 of the present embodiment has an insulating film (passivation film) 103 manufactured by the method for manufacturing a semiconductor device according to the present invention. This is a unique feature.

  The diffusion layer 102 has a conductivity type different from that of the silicon substrate 101 and forms a pn junction with the silicon substrate 101. The insulating film (passivation film) 103 is provided to suppress recombination of carriers generated in the silicon substrate 101 when light is incident, and is an insulating film having a conductivity type different from that of the silicon substrate 101. The antireflection film 104 suppresses reflection of sunlight on the substrate surface. The BSF 106 is a high concentration diffusion layer for suppressing the recombination of carriers generated in the silicon substrate 101.

Next, an embodiment of a method for manufacturing a solar cell according to the present invention will be described.
FIG. 6: shows the flowchart for process description of one Embodiment of the manufacturing method of the solar cell which concerns on this invention. The manufacturing method of this embodiment shall manufacture the crystalline silicon solar cell shown in FIG. First, a texture structure is formed on the surface side that becomes the light receiving surface of an n-type silicon substrate 101 doped in n-type (step S1). Subsequently, the p-type diffusion layer 102 is formed in the texture structure (step S2). Subsequently, the BSF 106 is formed on the back surface of the silicon substrate 101 (step S3).

  Next, a silicon dioxide film 103 which is an insulating film containing carbon, which is a feature of the present embodiment, is formed on the diffusion layer 102 (step S4). That is, in step S4, carbon is first ion-implanted from above the diffusion layer 102 having a depth of about 0.5 to 1.0 μm. Since the ion implantation depth is on the order of 10 nm, the silicon dioxide film 103 containing carbon is formed in the extreme surface layer of the diffusion layer 102. Thereafter, the entire element is subjected to thermal annealing. In step S4, as in the method described with reference to FIG. 3, after the silicon dioxide film 103 containing carbon is formed on the extreme surface layer of the diffusion layer 102 by ion implantation, the entire element may be oxidized. 4, after the silicon dioxide film 103 containing carbon is formed on the extreme surface layer of the diffusion layer 102 by ion implantation, the entire element may be annealed and then oxidized.

  Subsequent to the process of step S4, an antireflection film 104 is formed on the silicon dioxide film 103 containing carbon that functions as a passivation film (step S5). Subsequently, a plurality of surface electrodes 105 having a constant width are formed on the antireflection film 104 in parallel with each other by firing through (step S6). Then, a back electrode 107 is formed on the BSF 106 (step S7). The front electrode 105 is, for example, silver (Ag), and the back electrode 107 is, for example, aluminum (Al). Thus, according to the manufacturing method of this embodiment, since the silicon dioxide film (insulating film) 103 that functions as a passivation film contains carbon, it has a negative fixed charge density and good passivation characteristics.

Next, evaluation of the fixed charge of a silicon dioxide film formed by wet oxidation of a silicon substrate into which carbon ions are implanted will be described with reference to the flowchart of FIG. First, a p-type 7 Ω · cm silicon substrate was prepared (step S11), and a silicon dioxide film having a thickness of 30 nm was formed on the surface of the silicon substrate using a thermal oxidation method (step S12). Subsequently, carbon was implanted from above the silicon dioxide film by applying an ion implantation method to the surface of the silicon dioxide film formed on the silicon substrate (step S13). The ion implantation conditions are an acceleration energy of 10 keV and a dose of 1 × 10 ¹⁵ / cm ³ .

  Subsequently, the entire device was immersed in an aqueous hydrofluoric acid solution to remove the 30 nm-thick silicon dioxide film (step S14). According to TRIM (the Transport of Ions in Matter), which is a Monte Carlo simulation of ion implantation, the average projected range when carbon is ion-implanted under this condition is 34 nm. The reason why the silicon dioxide film having a thickness of 30 nm is attached before the carbon ion implantation is to increase the carbon concentration of the surface layer of the silicon substrate in consideration of the average projected range. Thereafter, the silicon substrate containing carbon from which the silicon dioxide film used at the time of ion implantation was removed was wet oxidized at 900 ° C. to newly form a silicon dioxide film on the surface (step S15). Next, electrodes were formed on each of the surface of the silicon substrate containing carbon having the silicon dioxide film formed on the surface by wet oxidation and the back surface of the silicon substrate, thereby forming a metal oxide semiconductor (MOS) capacitor (step S16). . This capacitor is the semiconductor device of this embodiment in which a silicon dioxide film, which is an insulating film formed on the surface of a silicon substrate containing carbon, has a negative fixed charge. And the CV measurement of this capacitor was performed (step S17).

FIG. 8 is a characteristic diagram showing the CV measurement results. In the figure, a solid line I indicates a CV curve which is a result of CV measurement performed on the semiconductor device of this embodiment in step S17 in the flowchart of FIG. In FIG. 8, a dotted line II indicates a CV curve showing a CV measurement result of a semiconductor device in which a silicon dioxide film is formed on the surface of a silicon substrate into which carbon ions are not implanted. When a fixed charge exists in the oxide film (in the film and at the interface), the CV curve shifts in the bias voltage direction without changing its shape. This shift is shifted by the bias voltage derived when the fixed charge amount C in the oxide film or at each interface is divided by the oxide film capacitance C ₀ .

  As shown in FIG. 8, the CV curve I of the semiconductor device of this embodiment in which a silicon dioxide film is formed on the surface of a silicon substrate containing p-type carbon shows that the silicon dioxide on the surface of the silicon substrate not containing carbon. Compared to the CV curve II of the semiconductor device on which the film is formed, it is clearly shifted to the positive voltage side. This means that negative fixed charges are formed on the silicon dioxide film on the surface of the silicon substrate containing ion-implanted carbon.

  Note that the flow chart of the solar cell 100 having the cross-sectional structure shown in FIG. 5 and the manufacturing method shown in FIG. 6 is one embodiment, and the present invention is not limited to this, and various other types of solar cells. The present invention can be applied to an insulating film having a battery passivation function.

DESCRIPTION OF SYMBOLS 10 Semiconductor device 11, 101 Silicon substrate 12 Carbon 13, 25, 27 Silicon dioxide film 21 Ion implantation 22 Carbon 23 Wet oxide film 100 Solar cell 102 Diffusion layer 103 Insulating film (silicon dioxide film; passivation film)
104 Antireflection film 105 Surface electrode 106 BSF
107 Back electrode

Claims (8)

An ion implantation step of ion-implanting carbon into the surface of the silicon substrate to contain carbon in the silicon substrate;
Forming a wet oxide film as an insulating film on the surface of the silicon substrate containing carbon by wet-oxidizing the silicon substrate into which the carbon has been ion-implanted;
A method for manufacturing a semiconductor device, comprising: An ion implantation step of ion-implanting carbon into the surface of the silicon substrate to contain carbon in the silicon substrate;
A step of forming a silicon dioxide film as an insulating film on the surface of the silicon substrate containing carbon by oxidizing the silicon substrate into which the carbon has been ion-implanted after being annealed or without being annealed;
A method for manufacturing a semiconductor device, comprising: A method for producing a solar cell in which at least a diffusion layer, a passivation film and a surface electrode are laminated on the surface of a texture structure of a silicon substrate,
A diffusion layer forming step of forming a diffusion layer on the surface of the texture structure of the silicon substrate;
An insulating film forming step of ion-implanting carbon from above the diffusion layer to form an insulating film containing carbon on the surface of the diffusion layer as the passivation film;
The manufacturing method of the solar cell characterized by including. The insulating film forming step includes
An ion implantation step of ion-implanting carbon from above the diffusion layer to form a silicon dioxide film containing carbon on the surface of the diffusion layer;
4. The method includes wet-oxidizing an element including the silicon dioxide film and the diffusion layer to form a wet oxide film containing carbon on the surface of the diffusion layer as the insulating film. The manufacturing method of the solar cell of description. The insulating film forming step includes
An ion implantation step of ion-implanting carbon from above the diffusion layer to form a silicon dioxide film containing carbon on the surface of the diffusion layer;
A step of forming an oxide film containing carbon on the surface of the diffusion layer as the insulating film by oxidizing the element including the silicon dioxide film and the diffusion layer after annealing or oxidizing without annealing. The manufacturing method of the solar cell of Claim 3 characterized by the above-mentioned.   It has the said insulating film manufactured by the manufacturing method of the solar cell as described in any one of Claims 3 thru | or 4 as a passivation film, The solar cell characterized by the above-mentioned. An oxide film forming step of forming an oxide film on the surface of the silicon substrate;
An ion implantation step of ion-implanting carbon into the silicon substrate from above the oxide film to contain carbon in the silicon substrate;
A removal step of removing the oxide film;
Forming a new silicon dioxide film as an insulating film on the surface of the silicon substrate containing carbon by wet-oxidizing the silicon substrate from which the oxide film has been removed;
A method for manufacturing a semiconductor device, comprising:   8. The semiconductor according to claim 7, wherein the oxide film forming step forms the oxide film having a thickness smaller than an average projected range when the carbon is ion-implanted in the ion implantation step. Device manufacturing method.

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