JP7053839B2 - Cassette and washing tub set - Google Patents

Description

The techniques disclosed herein relate to a cassette that is immersed in a treatment solution in a cleaning bath while holding at least one semiconductor substrate, and a cleaning bath set comprising this cassette.

Conventionally, it has been known to hold a semiconductor substrate in a cassette in order to immerse the semiconductor substrate in a treatment liquid of a cleaning bath and perform ultrasonic treatment. For example, in Patent Document 1, a substrate (in Patent Document 1, a transparent substrate of a liquid crystal display element) is held in a cassette, and the substrate held in this cassette is immersed together with a cassette in a treatment liquid of a washing bath. The substrate is ultrasonically treated.

Japanese Unexamined Patent Publication No. 6-1384437

By the way, when the patterning of the thin film formed on the silicon wafer is performed by the lift-off method, the patterning step includes a thin film peeling step. When ultrasonic treatment is introduced in this peeling process, the yield of the process is dramatically improved.

However, when performing ultrasonic treatment, standing waves may occur in the treatment liquid in the washing bath depending on the shape of the cassette and the washing bath. In this case, the non-uniformity of the sound pressure due to the standing wave causes uneven cleaning, and the semiconductor substrate having a particularly thin thickness (for example, the semiconductor substrate for a solar cell) has a high sound pressure at the antinode part of the standing wave. It is easily damaged by being pressed by the part).

The technology disclosed here has been made in view of these points, and the purpose thereof is to provide a cassette and a cleaning bathtub set that can perform ultrasonic treatment of a semiconductor substrate satisfactorily regardless of the shape of the cleaning bathtub. To provide.

To achieve the above objectives, the following cassettes and wash tub sets are provided.

The cassette is a cassette that is immersed in the treatment liquid while holding the at least one semiconductor substrate in order to immerse the at least one semiconductor substrate in the treatment liquid in the cleaning bath for ultrasonic treatment. The cassette is composed of a cylindrical body, and includes an outer peripheral surface exposed to the outside of the tubular body and a holding portion for holding the at least one semiconductor substrate on the inner peripheral surface of the tubular body. In a cross section orthogonal to the cylindrical axis direction of the cylindrical body, a part of the peripheral surface in the circumferential direction is a curved line, and the rest is a straight line.

The cleaning bath set is composed of a cylindrical body that is immersed in the treatment liquid while holding the at least one semiconductor substrate in order to immerse the at least one semiconductor substrate in the treatment liquid for ultrasonic treatment. The cassette is provided with a washing bath which is arranged inside the cylindrical body so that the cylindrical axis direction is in the vertical direction and can be immersed in a storage liquid. The cassette is the cassette. It has an outer peripheral surface exposed to the outside of the cylindrical body and a holding portion for holding the at least one semiconductor substrate on the inner peripheral surface of the tubular body, and is orthogonal to the cylindrical axial direction of the tubular body. A part of the outer peripheral surface in the circumferential direction is a curved line, and the rest is a straight line.

According to the cassette and the washing tub set, the ultrasonic treatment of the semiconductor substrate is satisfactorily performed regardless of the shape of the washing tub and the position where the cassette is installed, and a thin semiconductor substrate (for example, a semiconductor substrate for a solar cell) is used. Even if ultrasonic treatment is performed, the semiconductor substrate will not be damaged.

FIG. 5 is a plan view showing a washing bath in which a cassette according to an exemplary embodiment is arranged so as to be immersed in a stored treatment liquid together with the cassette. It is sectional drawing which cut the washing tub along the plane (horizontal plane) orthogonal to the cylinder axis direction. It is sectional drawing which cut along the line III-III of FIG. It is sectional drawing which shows the cylindrical body of the cassette which held the semiconductor substrate, and cut along the plane orthogonal to the cylindrical axis direction of the tubular body. It is a schematic sectional view partially showing a solar cell. It is a bottom view which shows the back side main surface of the crystal substrate which constitutes a solar cell. It is a figure corresponding to FIG. 5 which shows one process of the manufacturing method of a solar cell. It is a figure corresponding to FIG. 5 which shows one process of the manufacturing method of a solar cell. It is a figure corresponding to FIG. 5 which shows one process of the manufacturing method of a solar cell. It is a figure corresponding to FIG. 5 which shows one process of the manufacturing method of a solar cell. It is a figure corresponding to FIG. 5 which shows one process of the manufacturing method of a solar cell. It is a figure corresponding to FIG. 5 which shows one process of the manufacturing method of a solar cell. It is a figure corresponding to FIG. 5 which shows one process of the manufacturing method of a solar cell. It is a figure corresponding to FIG. 4 which shows another shape of the tubular body of a cassette. FIG. 4 is a view corresponding to FIG. 4, showing still another shape of the tubular body of the cassette. FIG. 4 is a view corresponding to FIG. 4, showing still another shape of the tubular body of the cassette. FIG. 4 is a view corresponding to FIG. 4, showing still another shape of the tubular body of the cassette. FIG. 4 is a view corresponding to FIG. 4, showing still another shape of the tubular body of the cassette. FIG. 4 is a view corresponding to FIG. 4, showing still another shape of the tubular body of the cassette.

Hereinafter, exemplary embodiments will be described in detail with reference to the drawings.

1 to 3 show a washing bath 21 in which a cassette 51 according to an exemplary embodiment is arranged so as to be immersed in a stored treatment liquid. As shown in FIG. 4, the cassette 51 has at least one (plurality) in order to immerse at least one (multiple in this embodiment) semiconductor substrate 57 in the treatment liquid in the cleaning bath 21 for ultrasonic treatment. ) Is immersed in the treatment liquid while holding the semiconductor substrate 57. In the present embodiment, the semiconductor substrate 57 is a semiconductor substrate for the solar cell 10. In FIG. 3, the description of the semiconductor substrate 57 is omitted.

Here, the configuration of the solar cell 10 will be described with reference to FIGS. 5 and 6. The solar cell 10 uses a crystal substrate 11 made of silicon (Si). The crystal substrate 11 has two main surfaces 11S (11SU, 11SB) facing each other. Here, the main surface on which light is incident is referred to as the front main surface 11SU, and the main surface on the opposite side is referred to as the back main surface 11SB. The front side main surface 11SU is a side that positively receives light from the back side main surface 11SB and is a light receiving side, and the back side main surface 11SB is a side that is not positively received light and is a non-light receiving side.

The solar cell 10 is a so-called heterojunction crystalline silicon solar cell, which is a back contact type (back surface electrode type) solar cell in which an electrode layer is arranged on a back side main surface 11SB.

The solar cell 10 includes a crystal substrate 11, an intrinsic semiconductor layer 12 (12U, 12p, 12n), a conductive semiconductor layer 13 (p-type semiconductor layer 13p, n-type semiconductor layer 13n), a low reflection layer 14, and an electrode layer 15 ( A transparent electrode layer 17 and a metal electrode layer 18) are included.

In the following, for convenience, the members individually corresponding to the p-type semiconductor layer 13p or the n-type semiconductor layer 13n may be suffixed with "p" or "n".

The crystal substrate 11 may be a semiconductor substrate formed of single crystal silicon, or may be a semiconductor substrate (single crystal silicon substrate) formed of polycrystalline silicon. Hereinafter, a single crystal silicon substrate will be described as an example.

The conductive type of the crystal substrate 11 may be an n-type single crystal silicon substrate into which an impurity that introduces an electron into a silicon atom (for example, a phosphorus (P) atom) is introduced, and a hole is introduced to the silicon atom. It may be a p-type single crystal silicon substrate into which an impurity (for example, a boron (B) atom) is introduced. Hereinafter, an n-type single crystal substrate, which is said to have a long carrier life, will be described as an example.

As shown in FIG. 7, the crystal substrate 11 has a texture structure TX (convex) and valleys (concave) formed on the surfaces of the two main surfaces 11S from the viewpoint of confining the received light. It may have a first texture structure). The texture structure TX (concavo-convex surface) is, for example, by anisotropic etching applying the difference between the etching rate of the (100) plane in the plane orientation and the etching rate of the (111) plane in the plane orientation of the crystal substrate 11. Can be formed.

The size of the unevenness in the texture structure TX can be defined by, for example, the number of vertices (mountains). In the present embodiment, from the viewpoint of light uptake and productivity, the range is preferably 50,000 pieces / mm ² or more and 100,000 pieces / mm ² or less, and particularly 70,000 pieces / mm ² or more and 85,000 pieces / mm ² or less. It is preferably in the range of.

The thickness of the crystal substrate 11 may be 250 μm or less. When measuring the thickness of the crystal substrate 11, the measurement direction is the direction perpendicular to the average plane of the crystal substrate 11 (the average plane means the plane of the entire substrate that does not depend on the texture structure TX). Therefore, hereinafter, this vertical direction, that is, the direction in which the thickness is measured is referred to as the thickness direction (also the thickness direction of the semiconductor substrate 57).

If the thickness of the crystal substrate 11 is excessively small, the mechanical strength is lowered, external light (sunlight) is not sufficiently absorbed, and the short-circuit current density is reduced. Therefore, the thickness of the crystal substrate 11 is preferably 50 μm or more, more preferably 70 μm or more. Here, when the texture structure TX is formed on both main surfaces 11S (11SU, 11SB) of the crystal substrate 11, the thickness of the crystal substrate 11 is the unevenness of each of the front side main surface 11SU and the back side main surface 11SB. It is represented by the distance between straight lines connecting convex vertices (vertices facing each other in the thickness direction) in the structure.

The intrinsic semiconductor layer 12 (12U, 12p, 12n) covers both main surfaces 11S (11SU, 11SB) of the crystal substrate 11 to perform surface passivation while suppressing the diffusion of impurities to the crystal substrate 11. The term "intrinsic (i-type)" is not limited to perfect authenticity that does not contain conductive impurities, and is "weak" that contains trace amounts of n-type impurities or p-type impurities within the range in which the silicon-based layer can function as an intrinsic layer. It also includes layers that are substantially true of "n-type" or "weak p-type".

The intrinsic semiconductor layer 12 (12U, 12p, 12n) is not essential and may be appropriately formed as needed.

The material of the intrinsic semiconductor layer 12 is not particularly limited, but may be an amorphous silicon-based material, and may be a hydrided amorphous silicon-based thin film (a—Si: H thin film) containing silicon and hydrogen as a thin film. There may be. The term "amorphous" as used herein is a structure having a long period and no order, that is, not only a completely disordered structure but also a structure having a short period and no order is included.

The thickness of the intrinsic semiconductor layer 12 is not particularly limited, but may be 2 nm or more and 20 nm or less. This is because when the thickness is 2 nm or more, the effect as a passivation layer for the crystal substrate 11 is enhanced, and when the thickness is 20 nm or less, the deterioration of the conversion characteristics caused by the high resistance can be suppressed.

The method for forming the intrinsic semiconductor layer 12 is not particularly limited, but a plasma CVD (Plasma enhanced Chemical Vapor Deposition) method is used. According to this method, the passivation of the substrate surface can be effectively performed while suppressing the diffusion of impurities into the single crystal silicon. Further, in the plasma CVD method, by changing the hydrogen concentration in the layer of the intrinsic semiconductor layer 12 in the thickness direction, it is possible to form an energy gap profile effective for recovering carriers.

The conditions for forming a thin film by the plasma CVD method are, for example, a substrate temperature of 100 ° C. or higher and 300 ° C. or lower, a pressure of 20 Pa or higher and 2600 Pa or lower, and a high frequency power density of 0.003 W / cm ² or higher and 0.5 W /. It may be cm ² or less.

In the case of the intrinsic semiconductor layer 12, the raw material gas used for forming the thin film includes silicon-containing gas such as monosilane (SiH ₄ ) and disilane (Si ₂ H ₆ ), or their gas and hydrogen (H ₂ ). May be a mixed gas.

In addition, a gas containing a different element such as methane (CH ₄ ), ammonia (NH ₃ ), or monogerman (GeH ₄ ) is added to the above gas to form silicon carbide (SiC) or silicon nitride (SiN). The energy gap of the thin film may be appropriately changed by forming a silicon compound such as _x ) or silicon germanium (SIGe).

Examples of the conductive semiconductor layer 13 include a p-type semiconductor layer 13p and an n-type semiconductor layer 13n. As shown in FIG. 5, the p-type semiconductor layer 13p is formed on a part of the back side main surface 11SB of the crystal substrate 11 via the intrinsic semiconductor layer 12p. The n-type semiconductor layer 13n is formed on the other part of the back side main surface of the crystal substrate 11 via the intrinsic semiconductor layer 12n. That is, the intrinsic semiconductor layer 12 is interposed between the p-type semiconductor layer 13p and the crystal substrate 11 and between the n-type semiconductor layer 13n and the crystal substrate 11 as intermediate layers that play a passivation role, respectively.

The thickness of each of the p-type semiconductor layer 13p and the n-type semiconductor layer 13n is not particularly limited, but may be 2 nm or more and 20 nm or less. This is because when the thickness is 2 nm or more, the effect as a passivation layer for the crystal substrate 11 is enhanced, and when the thickness is 20 nm or less, the deterioration of the conversion characteristics caused by the high resistance can be suppressed.

The p-type semiconductor layer 13p and the n-type semiconductor layer 13n are arranged so that the p-type semiconductor layer 13p and the n-type semiconductor layer 13n are electrically separated from each other on the back side main surface 11SB of the crystal substrate 11. The width of the conductive semiconductor layer 13 may be 50 μm or more and 3000 μm or less, and may be 80 μm or more and 800 μm or less (note that the width of the semiconductor layer and the width of the electrode layer described later are patterns unless otherwise specified. The length of a portion of each layer that has been made, by patterning, for example, intended to be the length perpendicular to the extension direction of the linearized portion).

When the photoexciters (carriers) generated in the crystal substrate 11 are taken out via the conductive semiconductor layer 13, the holes have a larger effective mass than the electrons. Therefore, from the viewpoint of reducing the transportation loss, the width of the p-type semiconductor layer 13p may be narrower than that of the n-type semiconductor layer 13n. For example, the width of the p-type semiconductor layer 13p may be 0.5 times or more and 0.9 times or less the width of the n-type semiconductor layer 13n, and may be 0.6 times or more and 0.8 times or less. May be good.

The p-type semiconductor layer 13p is a silicon layer to which a p-type dopant (boron or the like) is added, and may be formed of amorphous silicon from the viewpoint of suppressing impurity diffusion or suppressing series resistance. On the other hand, the n-type semiconductor layer 13n is a silicon layer to which an n-type dopant (phosphorus or the like) is added, and may be formed of an amorphous silicon layer in the same manner as the p-type semiconductor layer 13p.

As the raw material gas of the conductive semiconductor layer 13, a silicon-containing gas such as monosilane (SiH ₄ ) or disilane (Si ₂ H ₆ ), or a mixed gas of a silicon-based gas and hydrogen (H ₂ ) may be used. As the dopant gas, diborane (B ₂ H ₆ ) or the like can be used for forming the p-type semiconductor layer 13p, and phosphine (PH ₃ ) or the like can be used for forming the n-type semiconductor layer. Further, since the amount of impurities such as boron (B) and phosphorus (P) added may be very small, a mixed gas obtained by diluting the dopant gas with the raw material gas may be used.

Further, in order to adjust the energy gap of the p-type semiconductor layer 13p or the n-type semiconductor layer 13n, different types such as methane (CH ₄ ), carbon dioxide (CO ₂ ), ammonia (NH ₃ ) or monogerman (GeH ₄ ) are used. The p-type semiconductor layer 13p or the n-type semiconductor layer 13n may be compounded by adding a gas containing the element of.

The low reflection layer 14 is a layer that suppresses the reflection of light received by the solar cell 10. The material of the low reflection layer 14 is not particularly limited as long as it is a translucent material that transmits light, and is, for example, silicon oxide (SiO _x ), silicon nitride (SiN _x ), zinc oxide (ZnO), or oxidation. Titanium (TIO _x ) can be mentioned. Further, as a method for forming the low reflection layer 14, for example, a resin material in which nanoparticles of an oxide such as zinc oxide or titanium oxide are dispersed may be applied.

The electrode layer 15 is formed so as to cover the p-type semiconductor layer 13p or the n-type semiconductor layer 13n, respectively, and is electrically connected to each conductive semiconductor layer 13. As a result, the electrode layer 15 functions as a transport layer for guiding carriers generated in the p-type semiconductor layer 13p or the n-type semiconductor layer 13n.

The electrode layer 15 may be formed only of a metal having high conductivity. Further, it is transparent from the viewpoint of electrical bonding with the p-type semiconductor layer 13p and the n-type semiconductor layer 13n, or from the viewpoint of suppressing the diffusion of atoms with respect to both the semiconductor layers 13p and 13n of the metal as the electrode material. The electrode layer 15 made of a conductive oxide may be provided between the metal electrode layer and the p-type semiconductor layer 13p and between the metal electrode layer and the n-type semiconductor layer 13n, respectively.

In the present embodiment, the electrode layer 15 formed of the transparent conductive oxide is referred to as a transparent electrode layer 17, and the metal electrode layer 15 is referred to as a metal electrode layer 18. Further, as shown in the bottom view of the back side main surface 11SB of the crystal substrate 11 shown in FIG. 6, the electrode layer formed on the back of the comb in the p-type semiconductor layer 13p and the n-type semiconductor layer 13n having a comb tooth shape, respectively. Is referred to as a bus bar portion, and the electrode layer formed on the comb tooth portion may be referred to as a finger portion.

The transparent electrode layer 17 is not particularly limited as a material, but is, for example, zinc oxide (ZnO) or indium oxide (InO _x ), or various metal oxides such as titanium oxide (TIO _x ) and tin oxide (Tino x) in indium oxide. Examples thereof include transparent conductive oxides to which SnO), tungsten oxide (WO _x ), molybdenum oxide (MoO _x ) and the like are added at a concentration of 1% by weight or more and 10% by weight or less.

The thickness of the transparent electrode layer 17 may be 20 nm or more and 200 nm or less. The method for forming the transparent electrode layer suitable for this thickness is, for example, a physical vapor deposition (PVD) method such as a sputtering method, or a metalorganic organic substance using a reaction between an organometallic compound and oxygen or water. Examples thereof include a chemical vapor deposition method (MOCVD: Metal-Organic Chemical Vapor Deposition).

The material of the metal electrode layer 18 is not particularly limited, and examples thereof include silver (Ag), copper (Cu), aluminum (Al), nickel (Ni), and the like.

The thickness of the metal electrode layer 18 may be 1 μm or more and 80 μm or less. Examples of the method for forming the metal electrode layer 18 suitable for this thickness include a printing method in which the material paste is printed by inkjet or screen printing, or a plating method. However, the present invention is not limited to this, and when a vacuum process is adopted, a vapor deposition or sputtering method may be adopted.

The width of the comb tooth portion in the p-type semiconductor layer 13p and the n-type semiconductor layer 13n and the width of the metal electrode layer 18 formed on the comb tooth portion may be about the same. However, the width of the metal electrode layer 18 may be narrower than the width of the comb tooth portion. Further, the width of the metal electrode layer 18 may be wider than the width of the comb tooth portion as long as the leakage current between the metal electrode layers 18 is prevented.

In the present embodiment, the intrinsic semiconductor layer 12, the conductive semiconductor layer 13, the low reflection layer 14, and the electrode layer 15 are laminated on the back side main surface 11SB of the crystal substrate 11, and the passivation and conductivity of each joint surface are laminated. A predetermined annealing treatment is performed for the purpose of suppressing the generation of defect levels at the type semiconductor layer 13 and its interface and crystallization of the transparent conductive oxide in the transparent electrode layer 17.

Examples of the annealing treatment according to the present embodiment include an annealing treatment in which the crystal substrate 11 on which each of the above layers is formed is placed in an oven heated to 150 ° C. or higher and 200 ° C. or lower. In this case, the atmosphere in the oven may be the atmosphere, and further, if hydrogen or nitrogen is used as the atmosphere, more effective annealing treatment can be performed. Further, this annealing treatment may be an RTA (Rapid Thermal Annealing) treatment in which the crystal substrate 11 on which each layer is formed is irradiated with infrared rays by an infrared heater.

Hereinafter, a method for manufacturing the solar cell 10 will be described with reference to FIGS. 7 to 13.

First, as shown in FIG. 7, a crystal substrate 11 having a texture structure TX on each of the front side main surface 11SU and the back side main surface 11SB is prepared.

Next, as shown in FIG. 8, for example, an intrinsic semiconductor layer 12U is formed on the front main surface 11SU of the crystal substrate 11. Subsequently, the antireflection layer 14 is formed on the formed intrinsic semiconductor layer 12U. For the antireflection layer 14, silicon nitride (SiN _x ) or silicon oxide (SiO _x ) having an appropriate light absorption coefficient and refractive index is used from the viewpoint of the light confinement effect of confining the incident light.

Next, as shown in FIG. 9, an intrinsic semiconductor layer 12p using, for example, i-type amorphous silicon is formed on the back side main surface 11SB of the crystal substrate 11. Subsequently, the p-type semiconductor layer 13p is formed on the formed intrinsic semiconductor layer 12p. As a result, the p-type semiconductor layer 13p having the intrinsic semiconductor layer 12p interposed therebetween is formed on the back side main surface 11SB, which is one of the main surfaces of the crystal substrate 11.

After that, a plurality of lift-off layer LFs (first lift-off layer LF1 and second lift-off layer LF2) are formed on the formed p-type semiconductor layer 13p. Specifically, the first lift-off layer LF1 and the second lift-off layer LF2 containing silicon-based thin film materials having different densities are sequentially laminated on the p-type semiconductor layer 13p. As a result, the first lift-off layer LF1 is formed on the p-type semiconductor layer 13p, and the second lift-off layer LF2 is formed on the first lift-off layer LF1.

Next, as shown in FIG. 10, the second lift-off layer LF2, the first lift-off layer LF1 and the p-type semiconductor layer 13p are patterned on the back side main surface 11SB of the crystal substrate 11. As a result, the p-type semiconductor layer 13p is selectively removed, and a non-formed region NA in which the p-type semiconductor layer 13p is not formed is generated. On the other hand, at least the second lift-off layer LF2, the first lift-off layer LF1 and the p-type semiconductor layer 13p remain in the region not etched on the back side main surface 11SB of the crystal substrate 11.

Such a patterning step is realized by a photolithography method, for example, by forming a resist film (not shown) having a predetermined pattern on the second lift-off layer LF2 and etching a region masked by the formed resist film. do. In the case shown in FIG. 10, by patterning each layer of the intrinsic semiconductor layer 12p, the p-type semiconductor layer 13p, the first lift-off layer LF1 and the second lift-off layer LF2, a part of the back side main surface 11SB of the crystal substrate 11 is formed. A non-formed region NA, that is, an exposed region of the back side main surface 11SB is generated in the region.

As the etching solution used in the step shown in FIG. 10, for example, a mixed solution of hydrofluoric acid and an oxidizing solution (for example, hydrofluoric acid) or a solution in which ozone is dissolved in hydrofluoric acid (hereinafter, ozone / foot). Acid solution). The etching agent that contributes to the etching of the lift-off layer LF is hydrogen fluoride. The patterning here is not limited to wet etching using an etching solution. The patterning may be, for example, dry etching or pattern printing using an etching paste or the like.

Next, as shown in FIG. 11, the intrinsic semiconductor layer including the second lift-off layer LF2, the first lift-off layer LF1, the p-type semiconductor layer 13p, and the intrinsic semiconductor layer 12p is placed on the back side main surface 11SB of the crystal substrate 11 on the intrinsic semiconductor layer. The 12n and n-type semiconductor layers 13n are sequentially formed. As a result, the laminated film of the intrinsic semiconductor layer 12n and the n-type semiconductor layer 13n is formed on the non-formed region NA, on the surface and side surface (end surface) of the second lift-off layer LF2, and on the first lift-off layer LF1 and p-type semiconductor. It is formed on the side surface (end face) of the layer 13p and the intrinsic semiconductor layer 12p.

Next, as shown in FIG. 12, the n-type semiconductor layer 13n deposited on the second lift-off layer LF2 by removing the laminated first lift-off layer LF1 and the second lift-off layer LF2 using an etching solution. And the intrinsic semiconductor layer 12n is removed from the crystal substrate 11 (this step is referred to as a lift-off step). Examples of the etching solution used in this lift-off step include a solution containing hydrofluoric acid as a main component.

Then, a rinsing solution is used to remove the etching solution adhering to the crystal substrate 11 (this step is referred to as a rinsing step). In the rinsing step, the n-type semiconductor layer 13n and the intrinsic semiconductor layer 12n covering the lift-off layer LF, which could not be completely removed in the lift-off step, are removed. As the rinsing liquid, for example, a pure water base to which a liquid adjusting agent for adjusting the surface tension is added is used as described later.

The surface tension of the etching solution and the rinsing solution used in the lift-off step and the rinsing step is preferably 25 mN / m or more and 70 mN / m or less, and particularly preferably 30 mN / m or more and 60 mN / m or less. By keeping the surface tension within this range, the lift-off process proceeds smoothly due to the high wettability to the p-type semiconductor layer 13p and the lift-off layer LF, and the n-type semiconductor layer 13n and the intrinsicity peeled off in the lift-off step and the rinsing process. The semiconductor layer 12n tends to aggregate in the etching solution and the rinsing solution. As a result, the particles aggregate and become large, so that the reattachment of the n-type semiconductor layer 13n and the intrinsic semiconductor layer 12n to the crystal substrate 11 is suppressed. Further, when the etching solution or the rinsing solution is circulated, the particles can be easily removed by filtering. In this way, fine exfoliation and suspended matter do not convection in the liquid for a long time, so that both productivity and yield are improved.

Next, as shown in FIG. 13, the separation groove is formed on the back side main surface 11SB of the crystal substrate 11, that is, on each of the p-type semiconductor layer 13p and the n-type semiconductor layer 13n by, for example, a sputtering method using a mask. The transparent electrode layer 17 (17p, 17n) is formed so as to give rise to 25. The transparent electrode layer 17 (17p, 17n) may be formed as follows instead of the sputtering method. For example, a transparent conductive oxide film is formed on the entire surface of the back surface main surface 11SB without using a mask, and then transparent conductivity is formed on the p-type semiconductor layer 13p and the n-type semiconductor layer 13n by a photolithography method. It may be formed by etching to leave a sex oxide film. Here, by forming the separation groove 25 that separates and insulates the p-type semiconductor layer 13p and the n-type semiconductor layer 13n from each other, leakage current is less likely to occur.

Then, a linear metal electrode layer 18 (18p, 18n) is formed on the transparent electrode layer 17 by using, for example, a mesh screen (not shown) having an opening.

In this way, the back surface bonded type solar cell 10 is formed. In the lift-off step and / or the rinsing step in the forming process of the solar cell 10, ultrasonic treatment is performed using the washing bath 21 in which the treatment liquid is stored, whereby the n-type semiconductor layer 13n and the intrinsic semiconductor layer 12n are subjected to ultrasonic treatment. The peeling becomes more reliable. The treatment liquid in the washing bath 21 is an etching solution used in the lift-off step in the lift-off step, and a rinsing liquid in the rinsing step. In the present embodiment, the semiconductor substrate 57 held in the cassette 51 is a semiconductor substrate in the state of FIG. 11 or 12 (on the crystal substrate 11, the intrinsic semiconductor layer 12p, the p-type semiconductor layer 13p, the intrinsic semiconductor layer 12n, n). A type semiconductor layer 13n or the like is laminated). In the present embodiment, the semiconductor substrate 57 has a substantially rectangular shape when viewed from the thickness direction thereof.

As shown in FIGS. 3 and 4, in the present embodiment, the cassette 51 is composed of a resin tubular body 52, and the washing bathtub is formed so that the tubular body 52 is in the vertical direction. It is immersed in the treatment liquid in 21. The tubular body 52 is not limited to the resin, and may be made of metal, for example. Hereinafter, the cassette 51 (cylindrical body 52) will be described as being in a posture (a posture of being immersed in the treatment liquid) arranged in the washing bath 21.

The tubular body 52 has an outer peripheral surface 52a exposed to the outside of the tubular body 52 and an inner peripheral surface 52b forming a space inside the tubular body 52. In the cross section of the tubular body 52 orthogonal to the tubular axis direction (cross section cut along the horizontal direction), a part of the outer peripheral surface 52a in the circumferential direction is curved and the rest is straight. In the present embodiment, as shown in FIG. 4, in a cross section orthogonal to the cylindrical axis direction of the tubular body 52, the outer peripheral surface 52a has two straight lines 52c parallel to each other, one ends of the two straight lines 52c, and the like. The shape includes an arc-shaped curve 52d whose center of curvature is located inside the tubular body 52 (hereinafter referred to as a stadium shape) that connects the ends. In the present embodiment, the inner peripheral surface 52b also has basically the same shape as the outer peripheral surface 52a. That is, the inner peripheral surface 52b is provided with a holding protrusion 52e and a substrate support portion 52f as described later. Instead of the arc-shaped curve 52d, a bow-shaped curve may be used.

A plurality of holding protrusions 52e for holding the semiconductor substrate 57 are provided on the inner peripheral surface 52b of the tubular body 52 at a portion corresponding to the two straight lines 52c of the stadium shape so as to be arranged in the direction in which the straight lines 52c extend. ing. In the portion of each straight line 52c, the distance between the holding protrusions 52e adjacent to each other in the direction in which the straight line 52c extends is exaggerated for the thickness of the semiconductor substrate 57 (in FIG. 4, for the sake of clarity). ), While the semiconductor substrate 57 is held in an upright posture extending in the vertical direction. Further, a substrate support portion 52f (see FIG. 3) is provided at the lower end portion between the holding protrusions 52e adjacent to each other on each surface so that the lower surface of the semiconductor substrate 57 abuts to support the semiconductor substrate 57. The holding protrusions 52e and the substrate support portion 52f correspond to the holding portions that hold the semiconductor substrate 57. The configuration for holding the semiconductor substrate 57 is an example, and other configurations may be adopted. Further, the posture of the semiconductor substrate 57 held by the cassette 51 may be any posture, for example, a posture inclined with respect to the vertical direction. Further, the surface of the semiconductor substrate 57 may face in any direction.

The washing bathtub 21 includes a bottom wall portion 22 extending in the horizontal direction and a cylindrical side wall portion 23 rising upward from the peripheral edge portion of the bottom wall portion 22 and storing the treatment liquid inside, and the upper side is opened. It is formed in the shape of a bottomed cylinder. That is, the tubular side wall portion 23 is formed so as to stand up in a direction intersecting the in-plane direction of the bottom wall portion 22. The tubular axial direction of the tubular side wall portion 23 coincides with the vertical direction (that is, in the present embodiment, it can be said that the crossing direction of the bottom wall portion 22 with respect to the in-plane direction is the vertical direction). The washing bath 21 is also made of resin like the tubular body 52. The washing bath 21 is not limited to the resin, and may be made of, for example, metal.

In the present embodiment, in the cross section of the tubular side wall portion 23 orthogonal to the tubular axial direction (cross section cut along the horizontal direction), the tubular side wall portion 23 is formed in a substantially rectangular shape. Regarding the washing bath 21, the direction in which the long side of the rectangle of the cross section of the tubular side wall portion 23 extends is referred to as the longitudinal direction, and the direction in which the short side of the rectangle extends is referred to as the lateral direction. The cross-sectional shape of the tubular side wall portion 23 is not limited to a substantially rectangular shape, and may be any shape. Further, the size of the washing tub 21 is such that the cassette 51 is arranged inside the washing tub 21 so that the axial direction of the tubular body 52 is in the vertical direction, and the cassette 51 is immersed in the treatment liquid in the washing tub 21. Can be of any size as long as it is possible.

The washing tub 21 has a vertical direction (in-plane direction of the bottom wall portion 22) and a lateral direction (in-plane direction of the bottom wall portion 22) of the cassette 51 immersed in the treatment liquid. ) May be further provided with a restraining unit 30 for restraining the movement to). In the present embodiment, the restraint portion 30 is an example having a first restraint portion 31 for restraining the lateral movement of the cassette 51 and a second restraint portion 41 for restraining the vertical movement of the cassette 51. Will be described using. If the first restraint portion 31 can also restrain the movement of the cassette 51 in the vertical direction, the restraint portion 30 may have only the first restraint portion 31. Similarly, if the second restraint portion 41 can also restrain the lateral movement of the cassette 51, the restraint portion 30 may have only the second restraint portion 41. Further, it is possible to eliminate the restraining portion 30 itself, and the cassette 51 may be simply placed on the bottom wall portion 22.

In the present embodiment, as shown in FIG. 2, a plurality of first restraining portions 31 are provided so as to be arranged in the circumferential direction around the outer side of the cassette 51 (cylindrical body 52) immersed in the treatment liquid. In the embodiment, the first restraint piece 32 of 4) is included. The four first restraining pieces 32 are provided on the bottom wall portion 22 of the washing bathtub 21 and are located on a virtual line 35 corresponding to the outer line of the lower end surface of the tubular body 52. The four first restraining pieces 32 have a mating surface 32a that matches the outer peripheral surface 52a of the tubular body 52, and a receiving surface 32b that receives the lower end surface of the tubular body 52. The mating surface 32a of the two first restraint pieces 32 (hereinafter, also referred to as the first restraint piece 32A) out of the four first restraint pieces 32 is a flat surface, and is on the outer peripheral surface 52a of the tubular body 52. It matches the portion corresponding to the straight line 52c. On the other hand, the mating surface 32a of the remaining two first restraint pieces 32 (hereinafter, also referred to as the first restraint piece 32B) is a concave curved surface and corresponds to the curve 52d on the outer peripheral surface 52a of the tubular body 52. Match the part.

When the lower end surface of the tubular body 52 is in contact with the receiving surface 32b, the height position of the upper end surface of the tubular body 52 is lower than the height position of the liquid surface of the treatment liquid. The receiving surface 32b has a role of forming a gap between the lower end surface of the tubular body 52 and the bottom wall portion 22 of the cleaning bathtub 21 to promote the inflow and outflow of the treatment liquid to the inside of the tubular body 52. Even if the lower end surface of the tubular body 52 is in direct contact with the bottom wall portion 22 without the receiving surface 32b, a slight gap is actually formed between them, and the lower end surface of the tubular body 52 is in direct contact with the inside of the tubular body 52. The treatment liquid flows in and out. However, when the tubular body 52 is pressed by the second restraining portion 41, if the tubular body 52 is used for a long period of time, the gap may be eliminated due to the deformation of the tubular body 52, so that the receiving surface 32b It is preferable to provide.

The four first restraining pieces 32 are moved by a moving mechanism 36 (see FIG. 3) such as a motor that moves the first stopping piece 32 so as to be detachable from the cassette 51 immersed in the treatment liquid. Be done. In the present embodiment, the moving mechanism 36 is provided on the lower surface of the bottom wall portion 22, and for example, the cleaning bathtub 21 is provided on the bottom wall portion 22 so that the two first restraining pieces 32A are separated from each other. The two first restraining pieces 32B are moved in the longitudinal direction of the washing tub 21 on the bottom wall portion 22 so as to be separated from each other. The detailed configuration of the moving mechanism 36 will be omitted.

In the four first restraining pieces 32, the matching surface 32a abuts on the outer peripheral surface 52a of the cylindrical body 52 in close proximity to the cassette 51 by the moving mechanism 36, and presses the tubular body 52 inward. As a result, the lateral movement of the cassette 51 is stopped. Depending on the pressing force of the four first restraint pieces 32 on the tubular body 52, the four first restraint pieces 32 can also restrain the movement of the cassette 51 in the vertical direction. On the other hand, when the cassette 51 is taken in and out of the washing bath 21, the four first restraining pieces 32 are separated from the cassette 51 by the moving mechanism 36. At this time, each of the first restraint pieces 32 moves by an amount so that the receiving surface 32b does not come off from the lower end surface of the tubular body 52. This makes it easy to put the cassette 51 in and out of the washing tub 21.

The first restraining piece 32 does not necessarily have to be configured to be movable, and may be fixed to the bottom wall portion 22. In this case, the first restraining piece 32 is provided at a position where the matching surface 32a substantially abuts on the outer peripheral surface 52a of the tubular body 52 in a state where the lower end surface of the tubular body 52 is in contact with the receiving surface 32b. Be done. Further, only a part of the first restraint pieces 32 among the plurality of first restraint pieces 32 may be configured to be movable.

Further, the first restraining piece 32 may be provided on the cylindrical side wall portion 23 via a support member instead of being provided on the bottom wall portion 22. In this case, the first restraint piece 32 may be configured to be detachable from the cassette 51 immersed in the treatment liquid via the support member thereof.

The number of the first restraint pieces 32, the number of the first restraint pieces 32 configured to be detachable from the cassette 51, and the moving direction when the first restraint piece 32 is configured to be movable are as follows. It depends on the cross-sectional shape of the tubular body 52, and is appropriately set so as to prevent the cassette 51 from moving in the lateral direction.

The position of the cassette 51 (the position of the first restraining piece 32) with respect to the washing tub 21 as viewed from above is usually the central portion of the washing tub 21, but may be anywhere in the washing tub 21.

The washing bathtub 21 further includes a top surface portion 24 rotatably attached to the tubular side wall portion 23 via a rotation mechanism 25. The top surface portion 24 is divided into two divided portions 24a in the lateral direction of the washing bath 21. A hinge shaft 24b is provided at the end on the long side of each of the divided portions 24a so as to penetrate in the longitudinal direction of the washing bath 21. The hinge shaft 24b is fixed to the split portion 24a and is rotatably supported by the hinge shaft support portion 23a provided at the portion corresponding to the long side at the upper end of the tubular side wall portion 23. The two split portions 24a rotate by the rotation of the respective hinge shafts 24b, like a double door, to open and close the opening at the upper end of the washing bath 21. Although the detailed configuration is omitted, the rotation mechanism 25 has, for example, one motor connected to the hinge shaft 24b of the two division portions 24a via a reduction mechanism, and two motors are rotated by the rotation of the motor. The hinge shaft 24b of the split portion 24a rotates in opposite directions, and the two split portions 24a rotate. In the present embodiment, the two divided portions 24a do not cover all the parts of the opening at the upper end of the washing bath 21, but it is also possible to cover all the parts of the opening.

The second restraint portion 41 includes a second restraint piece 42 provided so as to face the bottom wall portion 22 and change the distance from the bottom wall portion 22. Specifically, as shown in FIGS. 1 and 3, two second restraining pieces 42 are provided at the tips of the two divided portions 24a on the top surface portion 24 (the ends opposite to the hinge shaft 24b). They are provided one by one (four in total), and are configured so that the distance between the two divided portions 24a and the bottom wall portion 22 changes as the two divided portions 24a rotate via the rotating mechanism 25.

When the two dividing portions 24a close the opening at the upper end of the washing tub 21 by the rotating mechanism 25, the four second restraining pieces 41 hit the portion corresponding to the curve 52d on the upper end surface of the tubular body 52. In contact with it, the tubular body 52 is pressed downward. As a result, the movement of the cassette 51 in the vertical direction is stopped. Depending on the pressing force of the four second restraining pieces 42 against the tubular body 52, the second restraining piece 42 can also restrain the lateral movement of the cassette 51. Each second restraint piece 42 may be made of an elastic member such as rubber. The portion where the second restraining piece 41 presses the tubular body 52 may be anywhere on the upper end surface of the tubular body 52.

An ultrasonic transmitter 61 that transmits ultrasonic waves to the treatment liquid stored in the cleaning bath 21 is attached to the outer surface of the tubular side wall portion 23 of the cleaning bath 21. The mounting position of the ultrasonic transmitter 61 may be any position in the circumferential direction on the outer surface of the tubular side wall portion 23, but is a flat surface portion on the outer surface of the tubular side wall portion 23 in consideration of ease of mounting. Is preferable. In the present embodiment, the axial direction of the ultrasonic wave transmitted from the ultrasonic wave transmitter 61 is the horizontal direction.

The ultrasonic waves transmitted from the ultrasonic transmitter 61 are reflected by the inner side surface of the tubular side wall portion 23 of the washing bath 21 and the outer peripheral surface 52a of the tubular body 52. No matter how many times this reflection is repeated, the ultrasonic waves transmitted from the ultrasonic transmitter 61 due to the stadium shape of the outer peripheral surface 52a of the tubular body 52 are the same as when the transmission was started at the position where the transmission was started. It never returns to an angle. That is, the ultrasonic orbit is not a periodic orbit, but a so-called chaotic orbit. This holds true regardless of the shape of the washing bath 21. As a result, no standing wave is generated in the treatment liquid, and a uniform sound field is formed in the treatment liquid. The semiconductor substrate 57 is ultrasonically processed by the processing liquid in which such a uniform sound field is formed.

Therefore, in the present embodiment, the movement of the cassette 51 in the vertical direction and the lateral direction is stopped by the first restraint piece 32 and the second restraint piece 42, and the outer peripheral surface 52a of the cassette 51 is in the processing liquid. Since the stadium shape is such that standing waves do not occur in the semiconductor substrate 57, the semiconductor substrate 57 is sonicated well. Further, since a standing wave is not generated in the processing liquid, even if the semiconductor substrate 57 for the solar cell 10 having a thin thickness is ultrasonically treated, the semiconductor substrate 57 is not damaged. As a result, deterioration of the performance of the solar cell 10 due to the dangling bond of silicon is suppressed.

The shape of the outer peripheral surface 52a of the cassette 51 is not limited to the stadium shape. A part of the peripheral surface 52a in the circumferential direction is curved in the cross section orthogonal to the cylindrical axial direction of the tubular body 52 so that the trajectory of the ultrasonic wave becomes a chaotic trajectory regardless of the shape of the washing bath 21. Moreover, the balance may be a straight line. In this case, in the cross section orthogonal to the tubular axial direction of the tubular body 52, the curve on the outer peripheral surface 52a is preferably singular or plural, and is preferably an arc-shaped or arch-shaped curve. The center of curvature of at least one arc-shaped or bow-shaped curve may be located inside the cylindrical body 52 or may be located outside the tubular body 52. Alternatively, the center of curvature of some of the plurality of arcuate or arcuate curves is located inside the cylindrical body 52, and the center of curvature of the remaining curves is located outside the tubular body 52. May be.

Specifically, as shown in FIG. 14, the outer peripheral surface 52a of the tubular body 52 may be formed in a substantially D shape in a cross section orthogonal to the cylindrical axial direction of the tubular body 52. In this case, the curve of the outer peripheral surface 52a of the tubular body 52 is an arc-shaped or arch-shaped curve whose center of curvature is located inside the tubular body 52. In FIG. 14, in order to illustrate the position of the first restraint piece 32 with respect to the tubular body 52, the first restraint piece 32 (the receiving surface 32b is omitted) is shown by a two-dot chain line (FIG. 15). The same applies to FIG. 19).

Alternatively, the outer peripheral surface 52a of the tubular body 52 may be formed in any one of FIGS. 15 to 19 in a cross section orthogonal to the cylindrical axis direction of the tubular body 52. In the shape of FIG. 16, in the central portion of the inner space of the tubular body 52, a rod-shaped holding member 55 (corresponding to the holding portion) that holds the semiconductor substrate 57 together with the holding protrusion 52e provided on the inner peripheral surface 52b is provided. It is provided so as to extend in the direction of the cylinder axis. The outer peripheral surface of the holding member 55 is also provided with a holding protrusion 55a similar to the holding protrusion 52e. The holding member 55 is supported by support members 56 (only the lower support member 56 can be seen in FIG. 16) fixed at two upper and lower positions in the tubular axial direction on the inner peripheral surface 52b. Further, in the shape of FIG. 17, there are two curves of the outer peripheral surface 52a of the tubular body 52, which are arched, and the center of curvature of the one arched curve is located inside the tubular body 52. On the other hand, the center of curvature of another arch-shaped curve is located outside the cylindrical body 52. In this shape, as shown in FIG. 17, a holding protrusion 52e may be provided at a portion of the inner peripheral surface 52b of the tubular body 52 corresponding to the bow-shaped curve.

The present invention is not limited to the above-described embodiment, and can be substituted within a range that does not deviate from the gist of the claims.

For example, in the above embodiment, the semiconductor substrate 57 for the solar cell 10 is held in the cassette 51 and ultrasonically processed, but the present invention is not limited to this, and the semiconductor substrate for applications other than the solar cell is also ultrasonically treated. , Cassette 51 can be used.

The above embodiments are merely examples, and the scope of the present invention should not be construed in a limited manner. The scope of the present invention is defined by the scope of the claims, and all modifications and modifications belonging to the equivalent scope of the claims are within the scope of the present invention.

21 Cleaning bathtub 51 Cassette 52 Cylindrical body 52a Outer peripheral surface 52b Inner peripheral surface 52e Holding protrusion (holding part)
52f Board support part (holding part)
55 Holding member (holding part)
57 Semiconductor substrate

Claims (7)

A cassette that is immersed in the treatment liquid while holding the at least one semiconductor substrate in order to immerse the at least one semiconductor substrate in the treatment liquid in the cleaning bathtub for ultrasonic treatment.
The cassette is composed of a tubular body and has a tubular body.
The outer peripheral surface exposed to the outside of the tubular body and
A holding portion for holding the at least one semiconductor substrate is provided on the inner peripheral surface of the tubular body.
A cassette in which a part of the peripheral surface in the circumferential direction is curved and the rest is straight in a cross section orthogonal to the cylindrical axis direction of the tubular body. The cassette according to claim 1, wherein in a cross section orthogonal to the tubular axial direction of the tubular body, the curve on the outer peripheral surface is singular or plural, and is an arc-shaped or arch-shaped curve. The cassette according to claim 2, wherein the center of curvature of at least one arc-shaped or bow-shaped curve is located inside the cylindrical body. The cassette according to claim 2, wherein the center of curvature of at least one arc-shaped or bow-shaped curve is located outside the tubular body. A plurality of arc-shaped or bow-shaped curves are provided, and the arc-shaped or bow-shaped curves are provided.
The center of curvature of some of the plurality of arc-shaped or bow-shaped curves is located inside the cylindrical body.
The cassette according to claim 2, wherein the center of curvature of the remaining curve is located outside the tubular body. In a cross section orthogonal to the cylindrical axis direction of the tubular body, the outer peripheral surface has two straight lines parallel to each other and the one end portion and the other end portion of the two straight lines are connected to each other, and the center of curvature is the tubular shape. The cassette according to claim 2 or 3, which is formed in a shape including an arc-shaped or bow-shaped curve located inside the body or in a substantially D-shape. It ’s a washing tub set,
A cassette made of a tubular body, which is immersed in the treatment liquid while holding the at least one semiconductor substrate in order to immerse the at least one semiconductor substrate in the treatment liquid for ultrasonic treatment.
The cassette is provided with a washing bath that is arranged inside so that the cylindrical body is vertically oriented in the cylindrical axis direction and can be immersed in the stored treatment liquid.
The cassette has an outer peripheral surface exposed to the outside of the cylindrical body and a holding portion for holding the at least one semiconductor substrate on the inner peripheral surface of the tubular body.
A washing bathtub set in which a part of the peripheral surface in the circumferential direction is curved and the rest is straight in a cross section orthogonal to the tubular axial direction of the tubular body.

Images