JP6420706B2 - Passivation film forming method for solar cell and passivation film forming apparatus for solar cell - Google Patents

Description

  The present invention relates to a solar cell passivation film forming method and a solar cell passivation film forming apparatus for producing a highly efficient solar cell.

As a technique for improving the photoelectric conversion efficiency of crystalline silicon solar cells, so-called back contact type solar cells in which the electrode on the light receiving surface is eliminated to eliminate optical loss due to the shadow of the electrode have been widely studied in recent years. . FIG. 12 is a diagram illustrating an example of a basic structure of the back contact solar cell 10. A p ⁺ region 12 in which an additive imparting p-type conductivity is diffused at a high concentration and an n ⁺ region in which an additive imparting n-type conductivity is diffused at a high concentration on the non-light-receiving surface of the crystalline silicon substrate 11 13 are alternately formed. In order to reduce loss due to recombination of photoexcited carriers, the surface of the p ⁺ region 12 and the surface of the n ⁺ region 13 are respectively covered with passivation films 14a and 14b, and the surface of the light receiving surface of the substrate 101 and the passivation film 14a, The surface of 14b is covered with protective films 15a and 15b, respectively. Electrodes 16 are formed in the p ⁺ region 12 and the n ⁺ region 13 respectively. Further, a texture for confining light having irregularities of several microns is formed on the light receiving surface of the crystalline silicon substrate 11 (not shown).

In general, it is effective to apply aluminum oxide having a negative charge to the passivation film 14a that covers the surface of the p ⁺ region 12 that is p-type silicon, and the passivation film that covers the surface of the n ⁺ region 13 that is n-type silicon. It is known that it is effective to apply silicon nitride having a positive charge to the film 14b. A film made of aluminum oxide or silicon nitride is generally formed by a method such as plasma CVD or atomic layer deposition. Therefore, when forming on the non-light-receiving surface of the back contact solar cell, patterning according to the shape of the p ⁺ region 12 and the n ⁺ region 13 is necessary after the film is formed. As a patterning method, a region to be left is patterned with a resist and a substrate is etched in an acid solution to remove a region to be removed, or an etching paste is applied to a region to be removed as in Patent Document 1 and the region is removed. And the like.

JP 2008-010746 A

  When a passivation film made of aluminum oxide or silicon nitride is formed by a method such as plasma CVD or atomic layer deposition, it is necessary to perform patterning in accordance with the shape of the high concentration region. Therefore, in the case of using a resist, for example, in addition to using a large amount of resist at the time of resist coating after film formation, it is necessary to go through a plurality of steps such as pattern exposure, development, etching, and resist removal. There was a problem of becoming.

  An object of the present invention is to provide a solar cell passivation film forming method and a solar cell passivation film forming apparatus capable of forming a passivation film at low cost with a small amount of material and with a simple process.

(1) The solar cell passivation film forming method of the present invention has a p ⁺ type p ⁺ region having a carrier concentration higher than that of a crystalline silicon substrate having p type or n type conductivity and an n type conductivity type. And forming a passivation film on the one surface of the crystalline silicon substrate having an n ⁺ region formed on one surface, wherein a precursor gas containing an organic metal is selectively applied to the surface of the p ⁺ region A precursor layer forming step of forming a precursor layer by spraying on the substrate, and an oxidation step of forming a metal oxide film by oxidizing at least the precursor layer by exposure to an oxidizing gas. This enables selective deposition of the metal oxide film is a passivation film for the p ⁺ region in the p ⁺ region. Therefore, since it is not necessary to form a metal oxide film on the entire surface of the substrate, the film forming material can be saved and the process is simple, so that the metal oxide film can be formed at low cost.

  (2) In the precursor layer forming step, the relative position of the precursor gas discharge port for discharging the precursor gas with respect to the crystalline silicon substrate may be changed in a direction parallel to the surface of the crystalline silicon substrate. In this way, a precursor layer can be formed in accordance with a pattern that moves relatively along the surface of the crystalline silicon substrate.

(3) In the oxidation step, the relative position of the oxidizing gas outlet for discharging the oxidizing gas with respect to the crystalline silicon substrate may be changed in a direction perpendicular to the oxidizing gas outlet and parallel to the crystalline silicon substrate. . In this way, by changing the relative positional relationship between the oxidizing gas discharge port and the crystalline silicon substrate, by oxidizing the surface of the p ⁺ region where the precursor layer is formed by oxidizing the oxidizing gas, it is possible to easily oxidize the metal. A film can be formed.

(4) A plurality of precursor gas discharge ports are provided along the arrangement direction, and in the precursor layer forming step, the relative positions of the plurality of precursor gas discharge ports with respect to the crystalline silicon substrate are perpendicular to the arrangement direction and the crystalline silicon It may be changed in a direction parallel to the substrate. Thus, by discharging the precursor gas from each precursor gas discharge port while changing the relative positional relationship between the precursor gas discharge port and the crystalline silicon substrate, p ⁺ formed in a stripe or matrix form on the substrate surface A precursor layer can be easily formed on the surface of the region.

  (5) In the oxidation step, the precursor gas discharge port is set so that the relative position of the linear oxidizing gas discharge port for discharging the oxidizing gas with respect to the crystalline silicon substrate is perpendicular to the arrangement direction and parallel to the crystalline silicon substrate. It is good to change following. In this way, the precursor layer continuously formed while the precursor gas discharge part moves can be oxidized while the oxidizing gas discharge part 220 also moves, so that a metal oxide film can be continuously formed. “Following” means that the oxidizing gas discharge port moves to a region on the surface of the crystalline silicon substrate that faces the precursor gas discharge port so as to face the surface later.

(6) In the oxidation step, the surface of the n ⁺ region may also be exposed to the oxidizing gas. Even if a protective film containing positive charges is simply formed on the surface of the n-type silicon, the passivation effect on the n-type silicon surface can be obtained by the electric field effect. However, when a protective film is directly formed on the surface of n-type silicon in this way, the defect density at the interface with silicon tends to increase. Therefore, in the present invention, prior to the formation of the protective film, the surface of the n ⁺ region is exposed to an oxidizing gas atmosphere to form a very thin silicon oxide film in the n ⁺ region. As a result, the defect density at the interface between the silicon oxide film and silicon can be lowered, and a higher passivation effect can be obtained compared with the case where the protective film is formed directly on the n-type silicon surface, thereby improving the conversion efficiency. Can do.

  (7) A sufficient passivation effect can be obtained by repeating the precursor layer formation step and the oxidation step until a predetermined metal oxide film thickness is obtained.

  (8) As precursor gas used for formation of a precursor layer, the mixed gas containing an inert gas is suitable. Accordingly, the inert gas functions as a carrier gas, and the gas containing the organic metal can be smoothly discharged. (9) As the organic metal contained in the precursor gas, an alkylaluminum that can be expected to have high reactivity is suitable.

(10) As the oxidizing gas used for oxidizing the precursor layer, oxygen, ozone, water, or a combination thereof is suitable. Thereby, it is possible to obtain a higher oxidation reaction including not only the precursor layer but also the surface of the n ⁺ region. (11) It is particularly preferable to use water or a mixed gas of ozone and inert gas as the oxidizing gas. Thereby, the inert gas functions as a carrier gas, and the oxidizing gas can be discharged smoothly.

(12) The solar cell passivation film forming apparatus of the present invention has ap ⁺ region having a p-type conductivity and an n-type conductivity, having a carrier concentration higher than that of a crystalline silicon substrate having a p-type or n-type conductivity. An apparatus for forming a passivation film on the one surface of the crystalline silicon substrate having an n ⁺ region formed on one surface, and discharging a precursor gas containing an organic metal toward the p ⁺ region A precursor gas discharge section comprising: a plurality of precursor gas discharge ports arranged in a straight line; and a precursor gas discharge port that sucks and exhausts an excess of precursor gas through the adjacent precursor gas discharge ports; an oxidant gas discharge section having a linear oxidant gas discharge port for discharging the oxidant gas toward the p ⁺ region. When spraying the precursor gases in the p ⁺ regions, for sucking the excess discharging the precursor gas from the outlet exhaust can be selectively film a metal oxide film is a passivation film for the p ⁺ region in the p ⁺ region. Therefore, since it is not necessary to form a metal oxide film on the entire surface of the substrate, the film forming material can be saved and the process is simple, so that the metal oxide film can be formed at low cost.

(13) The precursor gas discharge section includes the same number of precursor gas discharge ports as the p ⁺ region along the arrangement direction, and the relative position with respect to the crystal silicon substrate is perpendicular to the arrangement direction and with respect to the crystal silicon substrate. It is preferable to move relative to the crystalline silicon substrate so as to change in a parallel direction. The surface of the p ⁺ region formed in a stripe or matrix on the substrate surface by discharging the precursor gas from each precursor gas discharge port while changing the relative positional relationship between the precursor gas discharge port and the crystalline silicon substrate. A precursor layer can be easily formed.

(14) With respect to the relationship between the opening width of each of the precursor gas discharge ports in the arrangement direction and the width of each p ⁺ region to which the precursor gas discharged from each discharge port is sprayed, the opening width of each discharge port is It is desirable that the width be smaller than the width of each p ⁺ region corresponding to. Since the precursor gas is inevitably diffused to a certain extent by being discharged, by setting the opening width of the discharge port to be narrow in consideration of diffusion, the spray range of the precursor gas is set in the p ⁺ region. Can be controlled within range.

  (15) The oxidizing gas discharge unit may be arranged in series with the precursor discharge unit in a direction in which the relative position to the crystalline silicon substrate changes. In this way, the precursor layer continuously formed while the precursor gas discharge part moves can be oxidized while the oxidizing gas discharge part 220 also moves, so that a metal oxide film can be continuously formed.

  (16) The oxidizing gas discharge port is opened with an opening width equal to or larger than the width of the crystalline silicon substrate in a direction perpendicular to the direction in which the relative position with respect to the crystalline silicon substrate is changed, so that the entire crystalline silicon substrate is more reliably It can be exposed to an oxidizing gas atmosphere.

  (17) The oxidizing gas discharge section may further include an oxidizing gas exhaust port that is adjacent to the oxidizing gas discharge port in parallel and that sucks and exhausts excess oxidizing gas. When the surplus oxidizing gas diffuses and reaches the adjacent precursor gas discharge section, the organic metal contained in the precursor gas is oxidized in situ, and the metal oxide adheres to the precursor gas discharge section. Therefore, by providing an oxidizing gas exhaust port to prevent the excessive oxidizing gas from diffusing, it is possible to prevent the metal oxide from adhering to the precursor gas discharge portion.

  (18) An inert gas discharge port for discharging an inert gas from an opening having a width equal to or larger than the opening width of the oxidizing gas discharge port may be further provided between the precursor gas discharge unit and the oxidizing gas discharge unit. As a result, the separation between the precursor gas and the oxidizing gas becomes better, and the metal oxide particles in the formed metal oxide film even when the precursor gas discharging portion and the oxidizing gas discharging portion are close to each other. Generation can be suppressed.

  (19) Between the precursor gas discharge portion and the inert gas discharge port, an excess width having an opening width greater than or equal to a width in a direction in which the plurality of precursor gas discharge ports of the precursor gas discharge portion are linearly arranged An inert gas exhaust port that sucks and exhausts the inert gas may be further provided. As a result, it is possible to prevent the precursor gas from being mixed into the inert gas and degrading the separation between the precursor gas and the oxidizing gas.

  (20) An inert gas exhaust port that has an opening width equal to or greater than the opening width of the oxidizing gas discharge port between the oxidizing gas discharge unit and the inert gas discharge port, and sucks and exhausts the excess inert gas. You may prepare. Thereby, it is possible to prevent the oxidizing gas from being mixed into the inert gas and degrading the separation between the precursor gas and the oxidizing gas.

(21) An alignment mechanism for aligning the crystalline silicon substrate and the precursor gas discharge port may be further provided. Thereby, the position of each p ⁺ region formed in the crystalline silicon substrate can be accurately matched with the position at which each discharge port of the precursor gas discharge unit sprays the precursor gas.

It is a figure explaining the preparation process of the passivation film by this invention. It is a manufacturing flow figure of the passivation film by this invention. It is a figure which shows the positional relationship of the passivation film formation apparatus for solar cells of this invention, and a crystalline silicon substrate. It is sectional drawing which shows the state which discharges precursor gas to a board | substrate from a precursor gas discharge part. It is a figure which shows the structural example of a precursor gas discharge part. It is a figure which shows the positional relationship of the passivation film formation apparatus for solar cells of this invention, and the typical formation pattern of the p ⁺ area | region of a back contact type solar cell. It is a figure which shows the structural example of an oxidizing gas discharge part. It is a figure which shows the structural example of the passivation film formation apparatus for solar cells which concerns on this invention. It is a figure which shows the positional relationship of a precursor gas discharge part, an oxidizing gas discharge part, and an inert gas discharge part. It is a figure which shows the structural example of an inert gas discharge part. It is another figure which shows the positional relationship of a precursor gas discharge part, an oxidizing gas discharge part, and an inert gas discharge part. It is a figure which shows an example of the structure of the solar cell by a prior art.

  A fabrication process of a passivation film according to the present invention will be described with reference to FIG. Note that the manufacturing process described here can be appropriately changed within the scope of the technical idea expressed in the present invention, and such modified or improved embodiments are also included in the technical scope of the present invention. It is.

FIG. 1A shows that a p ⁺ region 102 and an n ⁺ region 103 are formed adjacent to each other on the non-light-receiving surface side, which is one surface of a crystalline silicon substrate 101, which is an object for forming a passivation film by the method of the present invention. It shows the state that has been done. The concentration of the added impurity on the surface of the p ⁺ region 202 is preferably 1 × 10 ¹⁹ or more and less than 3 × 10 ²⁰ atoms / cm ³ , more preferably 5 × 10 ¹⁹ or more and 1 × 10 ²⁰ atoms / cm ³ . Is good. If it is less than 1 × 10 ¹⁹ atoms / cm ³ , the contact resistance between the substrate and the electrode increases, and if it exceeds 3 × 10 ²⁰ atoms / cm ³ , charge carriers are regenerated due to defects in the p ⁺ region and Auger recombination. Coupling becomes significant and the output of the solar cell is reduced. On the other hand, the concentration of added impurities on the surface of the n ⁺ region 103 is preferably 1 × 10 ¹⁹ or more and 1 × 10 ²¹ atoms / cm ³ or less, more preferably, in order to obtain good electrical contact between the substrate and the electrode. Is preferably about 5 × 10 ¹⁹ or more and about 1 × 10 ²¹ atoms / cm ³ . If it is less than 1 × 10 ¹⁹ atoms / cm ³ , the contact resistance between the substrate and the electrode increases, and the output of the solar cell decreases. The upper limit of 1 × 10 ²¹ atoms / cm ³ is the solid solubility limit of phosphorus in silicon.

Although not applied in this example, in order to increase sensitivity to short-wavelength light, a low concentration diffusion region having the same conductivity type as the substrate and having a surface concentration of 1 × 10 ¹⁷ to 1 × 10 ¹⁹ atoms / cm ³ is used as the light receiving surface In some cases, it is provided.

  A method for forming a passivation film on the crystalline silicon substrate having the high concentration region shown in FIG. FIG. 2 shows a production flow diagram.

First, as shown in FIG. 1 (b), the p ⁺ region 102 organic metal to the surface, for example by spraying the precursor gas containing the alkyl aluminum selectively, to form a precursor layer 104 over the p ⁺ region 102 (S1 ). Since the precursor requires high reactivity, trimethylaluminum is particularly preferably used. Further, it is preferable to use an inert gas such as nitrogen or argon as a carrier gas and to mix with trimethylaluminum heated to 40 to 60 ° C. and gasified. The concentration of trimethylaluminum is preferably 0.1 mg / L or more. If it is less than 0.1 mg / L, the precursor layer formation may be insufficient. The upper limit of the concentration is not particularly limited, but is preferably about 50 mg / L or less from the viewpoint of cost.

Subsequently, as shown in FIG. 1C, the precursor layer 104 is oxidized to form a metal oxide film, which is a passivation film, here an aluminum oxide film 105 (S2). Here, if only the aluminum oxide film 105 is formed, only the precursor layer 104 may be exposed to the oxidizing gas. However, the entire non-light-receiving surface is exposed to the oxidizing gas, so that the precursor layer non-forming region n is formed. ^A very thin silicon oxide film 106 having a thickness of several atomic layers to 1 nm is formed on the surface of the ⁺ region 103, thereby terminating defects on the silicon surface and obtaining a good passivation effect. Oxygen, ozone or water can be used as the oxidizing gas. The advantage of using oxygen is that the apparatus is simplified. However, by adding ozone to oxygen or using water, a higher oxidation reaction including not only the precursor layer 104 but also the surface of the n ⁺ region 103 can be achieved. can get. When ozone is used, a good oxidation reaction is usually obtained by using an oxygen concentration of 10 vol% or higher. In addition, an inert gas such as nitrogen or argon may be mixed and used as a carrier gas to ozone of higher concentration. When water is used, an inert gas such as nitrogen or argon is preferably mixed as a carrier gas and used at a concentration of about 5 to 100 mg / L.

  In this method, only one molecular layer of metal oxide film is formed in one cycle of precursor layer formation and oxidation. Therefore, in general, it is necessary to repeat the step of forming the precursor layer 104 (S1) and the step of oxidizing the precursor layer 104 to form the aluminum oxide film 105 (S2) until a predetermined metal oxide film thickness is obtained. is there. Although the film thickness of aluminum oxide for sufficiently obtaining the passivation effect varies depending on the film forming conditions, it is generally about 1 nm to 20 nm, but the number of repetitive cycles at this time is about 10 to 250 times.

  Thereafter, the substrate is preferably heat-treated in an inert gas atmosphere at 350 to 600 ° C. for about 5 to 30 minutes. By this step, the negative charge density of the aluminum oxide film is increased and a high passivation effect is obtained.

  Subsequently, a protective film 107 is formed on the non-light-receiving surface of the crystalline silicon substrate 101 as shown in FIG. As the protective film 107, a silicon nitride film or a silicon oxide film is often formed by plasma CVD from the viewpoint of productivity.

In general, since a protective film made of silicon nitride, silicon oxide, or the like often contains a positive charge, a passivation effect is exhibited on the n-type silicon surface by the electric field effect. However, the defect density at the interface with silicon tends to be relatively high. On the other hand, in the present invention, as described above, the surface of the n ⁺ region is oxidized in the step of FIG. 1C, and an extremely thin silicon oxide film is formed thermochemically. As is generally known, the thermochemically formed silicon oxide film-silicon interface is deposited by plasma CVD because the defect density is relatively low due to the defect termination effect on the silicon surface by the silicon oxide film. A high passivation effect can be obtained as compared with the method of directly forming the protective film on the silicon surface. Therefore, conversion efficiency can be improved.

  The protective film 108 is formed in the same manner as the protective film 107. In addition to a silicon nitride film and silicon oxide, silicon carbide, amorphous silicon, titanium oxide, tin oxide, zinc oxide, or the like may be used as a single layer or a combination thereof.

Finally, as shown in FIG. 1E, electrodes 109 are formed in the p ⁺ region 102 and the n ⁺ region 103. In view of cost, a method of screen printing a silver paste in which silver powder and glass frit are mixed with an organic binder is generally used. After printing and drying the silver paste, a heat treatment at 700 to 860 ° C. is performed for about 1 second to 5 minutes, thereby forming a laminated body of the protective film 107 and the aluminum oxide film 105 and a laminated body of the protective film 107 and the silicon oxide film 106. The silver powder is penetrated to make the electrode and silicon conductive.

  Further, without using screen printing, an opening is formed by laser ablation or the like in the laminate of the protective film 107 and the aluminum oxide film 105 and the laminate of the protective film 107 and the silicon oxide film 106, and electrodes are formed by plating or the like. Also good.

  The step of forming the precursor layer (S1, FIG. 1B) and the step of oxidizing the precursor layer to form a metal oxide film (S2, FIG. 1C) will be described in further detail.

The step of forming the precursor layer and the step of oxidizing the precursor layer to form the metal oxide film can be performed using the solar cell passivation film forming apparatus 200 of the present invention. The solar cell passivation film forming apparatus 200 includes a precursor gas discharge unit 210 and an oxidizing gas discharge unit 220. The precursor gas discharge unit 210 discharges a precursor gas containing an organic metal toward the p ⁺ region, and a plurality of linearly arranged precursor gas discharge ports 211 and a precursor gas discharge port adjacent to each other are separated from each other. And a precursor gas exhaust port 212 for sucking and exhausting the precursor gas. The oxidizing gas discharge unit 220 includes an oxidizing gas discharge port 221 that discharges an oxidizing gas toward at least the p ⁺ region. FIG. 3 shows the positional relationship between the crystalline silicon substrate 101 on which the p ⁺ region 102 and the n ⁺ region 103, which are objects forming a passivation film, are formed, and the precursor gas discharge unit 210 and the oxidizing gas discharge unit 220. It is shown. The precursor gas discharge port 211, the precursor gas discharge port 212, and the oxidizing gas discharge port 221 are opposed to the crystalline silicon substrate 101. From the viewpoint of looking down at the crystalline silicon substrate 101 as shown in FIG. And provided on the back side of the oxidizing gas discharge part 220. With such a configuration, the solar cell passivation film forming apparatus 200 allows the precursor gas discharge unit 210 and the oxidizing gas discharge unit 220 to be parallel to the surface of the crystalline silicon substrate 101 and have a predetermined gap, for example, in the Y-axis direction. A passivation film is formed by sequentially spraying a precursor gas and an oxidizing gas onto a predetermined portion of the surface of the crystalline silicon substrate 101 while sliding.

First, the process for forming the precursor layer will be described. FIG. 4 is a schematic view showing a cross section of the state in which the precursor gas discharge unit 210 discharges the precursor gas 213 from the precursor gas discharge port 211 to the substrate 101. Precursor gas discharge ports 211 adjacent to each other are separated by a precursor gas exhaust port 212. A part of the precursor gas 213 discharged from the precursor gas discharge port 211 adheres to the p ⁺ region 102 and the rest is sucked and discharged to the precursor gas exhaust port 212. Thus, the precursor layer 104 is selectively formed only in the p ⁺ region 102 without being formed in the n ⁺ region 103.

  When the gap d between the crystalline silicon substrate 101 and the precursor gas discharge portion 210 or between the crystalline silicon substrate 101 and the precursor gas discharge port 211 is made as narrow as possible, the pattern accuracy for forming the precursor layer increases. Is preferably about 30 to 300 μm in order to achieve both accuracy and process stability.

  FIG. 5 is a view of an example of the precursor gas discharge unit 210 as viewed from the precursor gas discharge port 211 side. The precursor gas exhaust port 212 is formed not only to separate the precursor gas discharge ports 211 but also to completely surround the precursor gas discharge ports 211. Thereby, the spray destination of the precursor gas 213 can be controlled more accurately. The shape of the precursor gas discharge port 211 is preferably circular or square.

6 (a) and 6 (b) show two typical examples of the p ⁺ region pattern of the back contact solar cell, and the p ⁺ region is formed on the non-light-receiving surface of the crystalline silicon substrate 101 in each pattern. In this case, the precursor gas discharge unit 210 and the oxidizing gas discharge unit 220 are set. Here, the X axis and the Y axis constitute a plane parallel to the surface of the crystalline silicon substrate 101.

First, the case of the crystalline silicon substrate 101 in which the p ⁺ region 102 and the n ⁺ region 103 are formed in a stripe shape (FIG. 6A) will be described. The crystalline silicon substrate 101 and the precursor gas discharge unit 210 continuously form the precursor layer 104 while changing the relative position. In order to realize such a forming method, according to the present invention, the relative position of the precursor gas discharge portions 210 with respect to the crystalline silicon substrate 101 of the straight lines formed by the same number of precursor gas discharge ports 211 as the p ⁺ region is set with respect to the straight lines. It is moved relative to the crystalline silicon substrate 101 so as to change in a direction perpendicular to and parallel to the crystalline silicon substrate 101. Since the movement of the precursor gas discharge unit 210 is a relative movement, the precursor gas discharge unit 210 may move in parallel in the upper space of the crystal silicon substrate 101 while the crystalline silicon substrate 101 is stationary, or the precursor gas discharge unit. The crystal silicon substrate 101 may move while 210 is stationary in the upper space of the crystal silicon substrate 101. For example, in FIG. 6A, even if the precursor gas discharge unit 210 moves in the positive direction of the Y axis or the crystalline silicon substrate 101 moves in the negative direction of the Y axis, the crystalline silicon of the precursor gas discharge unit 210 The relative position with respect to the substrate 101 similarly changes in the positive direction of the Y axis.

When the direction in which the relative position of the precursor gas discharge unit 210 changes is the positive direction of the Y axis, the plurality of precursor gas discharge ports 211 are arranged in a direction parallel to the crystalline silicon substrate 101 and perpendicular to the Y axis, that is, Provided linearly in the X-axis direction. At this time, the precursor gas 213 is continuously sprayed from the precursor gas discharge ports 211 to the surface of the crystal silicon substrate 101 while changing the relative position of the precursor gas discharge unit 210 in the positive direction of the Y-axis. On the surface of 101, a precursor layer 104 extending in the Y-axis direction is formed in stripes by the number of the precursor gas discharge ports 211. Therefore, the precursor gas discharge ports 211 are provided in the number corresponding to the number of the p ⁺ regions 102, and the p ⁺ regions 102 are formed in advance on the surface portion of the crystalline silicon substrate 101 where each of the precursor gas discharge ports 211 forms the precursor layer 104 in a stripe shape. By doing so, the precursor layer 104 can be selectively formed in the p ⁺ region 102.

Opening width W1 in the X-axis direction of each precursor gas discharge port 211, the need to selectively film forming the p ⁺ region 102 must be less than the width W2 of at least X-axis direction of each p ⁺ region 102 However (see FIG. 4), in a general back contact type solar cell, it is preferable that it is approximately 0.1 to 0.8 times W2. If it is larger than 0.8 times, the precursor layer 104 may be formed beyond the p ⁺ region due to the spread of the discharged precursor gas 213, and if it is 0.05 times or less, a sufficient gas flow rate cannot be obtained. There are many cases.

In the case of the crystalline silicon substrate 101 in which the p ⁺ region is formed in a matrix (FIG. 6B), the processing can be basically performed in the same manner as in the case of FIG. 6A, but each precursor gas 213 is discharged by p. ^The difference is that the precursor layer 104 is intermittently formed in synchronization with the location of the ⁺ region 102.

  The relative speed of the crystalline silicon substrate 101 with respect to the precursor gas discharge unit 210 is preferably about 0.5 to 1.5 m / s from the viewpoint of productivity and film quality. 6 (a) and 6 (b) are arranged such that the film-forming surface of the substrate faces upward, and conversely, the film-forming surface faces downward and the film is formed. Arrangement is also acceptable.

The step of forming the metal oxide film by oxidizing the precursor layer is preferably performed in the same manner as the step of forming the precursor layer. FIG. 7 is a view of an example of the oxidizing gas discharge unit 220 suitable for this purpose as viewed from the gas discharge port side. The oxidizing gas discharge unit 220 includes at least an oxidizing gas discharge port 221. The oxidizing gas discharge port 221 preferably has an opening width that is equal to or larger than the width of the crystalline silicon substrate 101 in a direction perpendicular to the direction in which the relative position with respect to the crystalline silicon substrate 101 changes. As a result, the n ⁺ region 103 is also exposed to the oxidizing gas, and an extremely thin silicon oxide film is formed thermochemically, so that the passivation effect when forming the protective film can be enhanced. At this time, the oxidizing gas discharge unit 220 is preferably arranged in series with the precursor gas discharge unit 210 in a direction in which the relative position with respect to the crystalline silicon substrate 101 changes. “In series” means that the oxidizing gas outlet follows the precursor gas outlet so that the oxidizing gas outlet faces the area on the surface of the crystalline silicon substrate that faces the precursor gas outlet first. Means. That is, the oxidizing gas discharge unit 220 moves relative to the crystalline silicon substrate 101 following the precursor gas discharge unit 210. As a result, the precursor layer continuously formed while the precursor gas discharge unit 210 moves can be oxidized while the oxidizing gas discharge unit 220 moves, so that a metal oxide film can be continuously formed.

  An oxidant gas exhaust port 222 that adjoins the oxidant gas discharge port 221 in parallel with the oxidant gas discharge port 221 and sucks and exhausts excess oxidant gas may be further provided. At this time, the opening width in the longitudinal direction of the oxidizing gas exhaust port 222 is preferably equal to or larger than the opening width in the longitudinal direction of the oxidizing gas discharge port 221. As a result, the surplus oxidizing gas is recovered without being scattered around, so that it is possible to prevent aluminum oxide from adhering to the precursor gas discharge unit 210.

  FIG. 8 shows a configuration of a solar cell passivation film forming apparatus 300, which is an example of a more specific implementation form of the solar cell passivation film forming apparatus 200. The solar cell passivation film forming apparatus 300 includes an alignment part (i) for adjusting the position of the crystalline silicon substrate 101 and the precursor gas discharge port 211 and a film forming part (ii) for forming an aluminum oxide film. The The alignment unit (i) includes a substrate detection unit 301 and a position adjustment mechanism 302. In the film forming part (ii) for forming the aluminum oxide film, a precursor gas discharge unit 210 and an oxidation gas discharge unit 220 are arranged in this order in the Y direction, and further includes a transfer device 303 for moving the crystalline silicon substrate 101. The position adjustment mechanism 302 and the transfer device 303 may further include a mechanism (not shown) for heating the crystalline silicon substrate 101. Heating may be performed by giving the conveyor 303 a temperature adjustment function, or may be performed by remotely heating with a heater.

  The crystalline silicon substrate 101 is set in the position adjustment mechanism 302 with the non-light-receiving surface facing upward, and the position adjustment mechanism 302 specifies the deviation between the current position of the substrate detected by the substrate detection unit 301 and the appropriate position. Adjust to the proper position. After the position of the crystalline silicon substrate 101 is adjusted, the crystalline silicon substrate 101 is fixed to the transfer machine 303. The crystalline silicon substrate 101 is conveyed from the left side of FIG. 8 and passes under the precursor gas discharge unit 210 while receiving the discharge of the precursor gas 213. In order to sufficiently form the precursor layer 104, the discharge amount of the precursor gas 213 is preferably about 0.5 L / min or more. The upper limit of the discharge amount is not particularly limited, but is preferably 50 L / min or less from the viewpoint of cost. As a result, a precursor layer 104 is formed on the surface of the crystalline silicon substrate 101. The crystalline silicon substrate 101 passes under the oxidizing gas discharge part 220 while receiving the discharge of the oxidizing gas. In order to obtain a sufficient oxidation reaction, the discharge amount of the oxidizing gas is preferably 1 to 2 times the discharge amount of the precursor gas. Thereby, the precursor layer 104 is oxidized and an aluminum oxide film 105 which is a metal oxide film is formed.

  As described above, since the film thickness obtained in one cycle of precursor layer formation and oxidation is about one molecular layer, it is necessary to repeat the formation and oxidation cycles of the precursor layer 104 in order to obtain a predetermined film thickness of aluminum oxide. . Therefore, the crystalline silicon substrate 101 is once exposed to the precursor gas 213 while being oxidized in the reverse direction in the Y direction after being once oxidized on the entire surface of the substrate. After the precursor layer 104 is formed again, the crystalline silicon substrate 101 is exposed to an oxidizing gas while being transported again in the Y direction, and an aluminum oxide film is grown.

  When the precursor gas discharge unit 210 and the oxidizing gas discharge unit 220 are close to each other, an inert gas discharge unit is further provided between the precursor gas discharge unit 210 and the oxidizing gas discharge unit 220 as shown in FIG. 230 may be provided. As shown in FIG. 10, the inert gas discharge unit 230 includes, for example, a slit-like inert gas discharge port 231 and an inert gas exhaust port 232, but the precursor gas discharge unit 210 and the oxidizing gas discharge unit 220 are provided. When an exhaust port is provided, only the inert gas discharge port 231 may be configured. The opening width of the inert gas discharge port 231 in the direction in which the plurality of precursor gas discharge ports are arranged in a straight line is preferably equal to or larger than the opening width of the oxidizing gas discharge port. Thereby, the separation of the precursor gas and the oxidizing gas becomes better, and the generation of aluminum oxide particles in the film forming section can be suppressed.

For the combination of each gas discharge section, for example, a plurality of oxidizing gas discharge sections 220 may be provided as shown in FIG. 11 (a), or a plurality of precursor gas discharge sections 210 may be provided as shown in FIG. 11 (b). However, since it is preferable that the process ends with the oxidation process, the oxidizing gas discharge unit 220 may be provided on the substrate discharge direction side.
〔Example〕

A phosphor-doped n-type silicon substrate in which linear p ⁺ regions (width 1.5 mm) and n ⁺ regions (width 0.2 mm) are formed in parallel and alternately on a non-light receiving surface, and a position adjustment stage with backlight After alignment with the CCD camera, the precursor gas discharge port and the precursor gas discharge port having a p ⁺ region width ratio W1 / W2 of 0.8 to the p ⁺ region at a TMA concentration of 1 mg / L into the p ⁺ region at 7 L / min. A precursor layer is formed by spraying, and then an oxidizing gas having a H ₂ O concentration of 30 mg / L is sprayed at 50 L / min over the entire non-light-receiving surface of the substrate from an oxidizing gas outlet having a linear opening. ^{+ The} surface of the region was oxidized. Precursor layer formation and oxidation were repeated to form an aluminum oxide film with a thickness of 20 nm. The relative velocity between each gas discharge port and the substrate is 1.5 m / s. Thereafter, the substrate was heat-treated in a nitrogen atmosphere at 450 ° C. for 30 minutes, and subsequently, a silicon nitride film having a refractive index of 2.0 and a thickness of 100 nm was formed on both surfaces of the substrate by plasma CVD. Further, a silver paste was applied by screen printing on the p ⁺ region and the n ⁺ region, and after drying, an electrode was formed by a heat treatment at 820 ° C. in a belt furnace to obtain a solar battery cell.
[Comparative example]

A substrate similar to the example was used, and an aluminum oxide film having a thickness of 20 nm was formed on the entire surface of the non-light-receiving surface by atomic layer deposition. Next, a resist was formed only on the p ⁺ region by photolithography, and the substrate was immersed in an HF aqueous solution having a concentration of 1% to remove the aluminum oxide film on the n ⁺ region. Thereafter, the photoresist was washed with an organic solvent, a mixture of concentrated sulfuric acid at 80 ° C. and hydrogen peroxide solution. Thereafter, the substrate was heat-treated in a nitrogen atmosphere at 450 ° C. for 30 minutes, and subsequently, a silicon nitride film having a refractive index of 2.0 and a thickness of 100 nm was formed on both surfaces of the substrate by plasma CVD. Further, a silver paste was applied by screen printing on the p ⁺ region and the n ⁺ region, and after drying, an electrode was formed by a heat treatment at 820 ° C. in a belt furnace to obtain a solar battery cell.

  Table 1 shows the results of measuring the solar cell characteristics of the solar cells of Example 1 and Comparative Example 1 using a current-voltage measuring device using artificial sunlight having an air mass of 1.5. From this result, it can be seen that in the embodiment according to the present invention, a higher release voltage is obtained compared to the comparative example, and the conversion efficiency is improved.

DESCRIPTION OF SYMBOLS 101 Crystal silicon substrate 102 p ⁺ area | region 103 n ⁺ area | region 104 Precursor layer 105 Aluminum oxide film 106 Silicon oxide film 107,108 Protective film 200,300 Passivation film formation apparatus for solar cells 210 Precursor gas discharge part 211 Precursor gas discharge port 212 Precursor Gas outlet 220 Oxidizing gas outlet 221 Oxidizing gas outlet 222 Oxidizing gas outlet 230 Inert gas outlet 231 Inactive gas outlet 232 Inert gas outlet 301 Substrate detector 302 Position adjustment mechanism 303 Conveyor

Claims (21)

A p ⁺ region having a p-type conductivity and an n ⁺ region having an n-type conductivity are formed on one surface having a carrier concentration higher than that of a crystalline silicon substrate having a p-type or n-type conductivity. A method for forming a passivation film for a solar cell, comprising forming a passivation film on the one surface of the crystalline silicon substrate,
A precursor layer forming step of selectively spraying a precursor gas containing an organic metal on the surface of the p ⁺ region to form a precursor layer;
An oxidation step in which at least the precursor layer is oxidized by exposing it to an oxidizing gas to form a metal oxide film;
A method for forming a passivation film for a solar cell.   2. The precursor layer forming step, wherein a relative position of a precursor gas discharge port for discharging the precursor gas with respect to the crystalline silicon substrate is changed in a direction parallel to the surface of the crystalline silicon substrate. A method for forming a passivation film for a solar cell as described.   The said oxidation step WHEREIN: The relative position with respect to the said crystalline silicon substrate of the oxidizing gas discharge port which discharges the said oxidizing gas is changed in the direction parallel to the said crystalline silicon substrate. Of forming a passivation film for solar cell. A plurality of the precursor gas discharge ports are provided along the arrangement direction,
In the precursor layer forming step, the relative positions of the plurality of precursor gas discharge ports with respect to the crystalline silicon substrate are changed in a direction perpendicular to the arrangement direction and parallel to the crystalline silicon substrate. The method for forming a passivation film for a solar cell according to claim 2.   In the oxidation step, a relative position of a linear oxidizing gas discharge port for discharging the oxidizing gas with respect to the crystalline silicon substrate is set to be perpendicular to the arrangement direction and parallel to the crystalline silicon substrate. The method for forming a passivation film for a solar cell according to claim 4, wherein the method changes following the gas discharge port. 6. The method for forming a passivation film for a solar cell according to claim 1, wherein in the oxidation step, the surface of the n ⁺ region is also exposed to an oxidizing gas. 6.   The method for forming a passivation film for a solar cell according to any one of claims 1 to 6, wherein the precursor layer forming step and the oxidation step are repeated until a predetermined metal oxide film thickness is obtained.   The method for forming a passivation film for a solar cell according to any one of claims 1 to 7, wherein the precursor gas is a mixed gas containing an inert gas.   The method for forming a passivation film for a solar cell according to any one of claims 1 to 8, wherein the organic metal is alkylaluminum.   10. The method for forming a passivation film for a solar cell according to claim 1, wherein the oxidizing gas includes any one or a combination of oxygen, ozone, and water.   11. The method for forming a passivation film for a solar cell according to claim 1, wherein the oxidizing gas is a mixed gas of water or ozone and an inert gas. 11. A p ⁺ region having a p-type conductivity and an n ⁺ region having an n-type conductivity are formed on one surface having a carrier concentration higher than that of a crystalline silicon substrate having a p-type or n-type conductivity. A passivation film forming apparatus for a solar cell that forms a passivation film on the one surface of a crystalline silicon substrate,
Excess precursor gas is sucked through a plurality of linearly arranged precursor gas discharge ports for discharging a precursor gas containing an organic metal toward the p ⁺ region and the precursor gas discharge ports adjacent to each other. A precursor gas discharge section comprising a precursor gas exhaust port for exhausting;
An oxidant gas discharge section comprising a linear oxidant gas discharge port for discharging oxidant gas toward at least the p ⁺ region;
A passivation film forming apparatus for solar cells. The precursor gas discharge unit includes the same number of the precursor gas discharge ports as the p ⁺ regions along the arrangement direction, and the relative position with respect to the crystal silicon substrate is perpendicular to the arrangement direction and to the crystal silicon substrate. The apparatus for forming a passivation film for a solar cell according to claim 12, wherein the apparatus moves relative to the crystalline silicon substrate so as to change in a parallel direction. The opening width in the arrangement direction of each of the precursor gas discharge ports is equal to or less than the width in the arrangement direction of each of the plurality of p ⁺ regions to which the precursor gas is sprayed from each of the precursor gas discharge ports. The passivation film forming apparatus for solar cell according to claim 13, characterized in that it is characterized in that: The passivation film for a solar cell according to claim 13 or 14, wherein the oxidizing gas discharge part is arranged in series with the precursor gas discharge part in a direction in which a relative position with respect to the crystalline silicon substrate changes. Forming equipment.   16. The oxidant gas discharge port is opened with an opening width equal to or greater than the width of the crystalline silicon substrate in a direction perpendicular to a direction in which a relative position with respect to the crystalline silicon substrate changes. The passivation film forming apparatus for solar cells described.   The solar cell according to claim 13 or 14, wherein the oxidizing gas discharge unit further includes an oxidizing gas exhaust port that is adjacent to and parallel to the oxidizing gas discharge port and sucks and exhausts excess oxidizing gas. Passivation film forming device. And wherein the precursor gas discharge portion between said oxidizing gas discharging unit further comprises an inert gas discharge port for discharging the inert gas from the opening of the apertures wider than the width of the oxidizing gas discharge port the passivation film forms forming device for a solar cell according to any one of claims 15 to 17.   Between the precursor gas discharge portion and the inert gas discharge port, the excess gas has an opening width equal to or larger than a width in a direction in which the plurality of precursor gas discharge ports are arranged in a straight line. The passivation film forming apparatus for a solar cell according to claim 18, further comprising an inert gas exhaust port for sucking and exhausting the inert gas. Between the oxidizing gas discharging part and the inert gas discharge port, with apertures wider than the opening width of the oxidizing gas discharge port, an inert gas outlet for aspirating the excess of the inert gas exhaust The apparatus for forming a passivation film for a solar cell according to claim 18 or 19, further comprising:   21. The solar cell passivation film forming apparatus according to claim 12, further comprising an alignment mechanism that aligns the crystalline silicon substrate and the precursor gas discharge port.

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