JP2013131670A - Semiconductor substrate surface etching apparatus, semiconductor substrate surface etching method for forming asperities on surface using the same, and gas nozzle unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor substrate surface etching apparatus which is adaptable to mass production while ClF3, XeF2, BrF3, and BrF5 gases are used; a semiconductor substrate surface etching method for forming asperities on a surface of the substrate by use of the apparatus; and a gas nozzle unit.SOLUTION: The semiconductor substrate surface etching apparatus comprises: a reaction chamber arranged so that the pressure inside it can be reduced to an atmospheric pressure or below; a moving stage to put a semiconductor substrate on, which can be moved in the reaction chamber; a nozzle for blowing an etching gas against a surface of the semiconductor substrate put on the moving stage, provided that the etching gas contains at least one kind of gas selected from the group consisting of ClF3, XeF2, BrF3, and BrF5; and a nozzle for blowing a cooling gas containing a nitrogen gas or an inert gas against the semiconductor substrate put on the moving stage.

Description

  The present invention relates to a surface etching apparatus for a semiconductor substrate, a method for etching a surface of a semiconductor substrate using the surface etching method, and a gas nozzle unit.

  In silicon solar cells (photoelectric conversion elements), etc., an uneven shape called texture is provided on the light receiving surface of the silicon substrate to suppress reflection of incident light and prevent leakage of light taken into the silicon substrate to the outside. Yes.

  Texture formation on the surface of a silicon substrate is generally performed by a wet process using an alkaline (KOH) aqueous solution as an etchant. Texture formation by a wet process requires a cleaning process using hydrogen fluoride, a heat treatment process, and the like as post-processing. For this reason, there is a risk of contaminating the surface of the silicon substrate, and there is a disadvantage in terms of cost.

  On the other hand, a method for forming a texture on the surface of a silicon substrate by a dry process has also been proposed. For example, 1) a method using a method called reactive ion etching using plasma, and 2) a gas of ClF3, XeF2, BrF3, or BrF5 is introduced into a reaction chamber under an atmospheric pressure atmosphere with a silicon substrate. A method of etching the surface of a silicon substrate by introducing it has been proposed (see Patent Document 1).

JP-A-10-313128

  When reactive ion etching using plasma is used, the surface of the silicon substrate is easily damaged by plasma, which may adversely affect the performance as a device (for example, a solar cell). In addition, since a plasma generator or the like is required, there is a problem that the cost of the apparatus increases.

  On the other hand, the silicon substrate surface can be etched by using ClF3, XeF2, BrF3 and BrF5 gases as described in Patent Document 1, but the etching reaction is an exothermic reaction, and the temperature of the silicon substrate is If it rises above a certain level, the desired etching cannot be performed. If the reacted gas stays, the desired etching cannot be performed.

  Therefore, the surface of the silicon substrate has to be etched while repeating the etching process and the cooling process, and there is a surface that is not a method suitable for mass production. Accordingly, an object of the present invention is to provide an apparatus for etching a semiconductor substrate surface that can be used for mass production while using a gas that causes an exothermic reaction with a semiconductor substrate as an etching gas, and using a fresh etching gas at all times. Further, when ClF3, XeF2, BrF3 and BrF5 gases are used as etching gases, a certain etching shape can be obtained, but a texture structure suitable for a silicon substrate of a solar cell cannot always be obtained.

  Therefore, the present invention provides an apparatus for forming an appropriate texture structure for a silicon substrate of a solar cell without damaging the silicon substrate by optimizing an etching gas composition containing ClF3, XeF2, BrF3, and BrF5. This is the issue.

  That is, the first of the present invention relates to the following surface etching apparatus.

  [1] A reaction chamber capable of reducing pressure, a moving stage capable of transporting a semiconductor substrate in the reaction chamber, and a nozzle unit for injecting or exhausting gas toward the surface of the semiconductor substrate placed on the moving stage. The nozzle unit includes a first nozzle that injects an etching gas toward the surface of the semiconductor substrate placed on the moving stage, and a cooling gas that is injected toward the semiconductor substrate placed on the moving stage A second nozzle, an outer side of the first and second nozzles, a gas exhaust port for exhausting the etching gas and the cooling gas, an outer side of the gas exhaust port, and the moving stage. A semiconductor substrate surface etching apparatus comprising a gas supply port for injecting a gas that does not react exothermically with the material of the semiconductor substrate.

  [2] The surface etching apparatus according to [1], wherein the etching gas includes one or more gases selected from the group consisting of ClF3, XeF2, BrF3, and BrF5.

  [3] The surface etching apparatus according to [1] or [2], wherein the cooling gas includes nitrogen gas or inert gas.

  [4] The surface etching apparatus according to any one of [1] to [3], wherein the gas exhaust port is disposed on both outer sides via the etching gas nozzle and the cooling gas nozzle.

  [5] The surface etching apparatus according to any one of [1] to [4], wherein the gas supply port includes nitrogen gas or inert gas disposed on both outer sides of the exhaust port.

  [6] The surface etching apparatus according to any one of [1] to [5], wherein the pressure in the reaction chamber can be adjusted in a range of 1 KPa to atmospheric pressure.

  The second of the present invention relates to a method for producing a semiconductor substrate having a concavo-convex shape formed on the surface shown below.

  [7] A method of manufacturing a semiconductor substrate having a concavo-convex shape formed on the surface using the surface etching apparatus of [1], wherein the semiconductor substrate placed on the movable stage in the reaction chamber is decompressed. A step of preparing, a step of spraying an etching gas from a nozzle for injecting an etching gas onto the semiconductor substrate while moving the moving stage, and a nozzle for injecting a cooling gas to the semiconductor substrate while moving the moving stage. A semiconductor comprising: a step of spraying a cooling gas; a step of exhausting the etching gas and the cooling gas; and a step of injecting a gas curtain toward the moving stage up to the etching gas, the cooling gas, and the exhaust port Substrate surface etching method.

  [8] The method for etching a surface of a semiconductor substrate according to [7], wherein the temperature of the semiconductor substrate is maintained at 130 ° C. or lower.

  [9] The surface etching method for a semiconductor substrate according to [7], wherein the semiconductor substrate is vibrated while moving the moving stage.

  [10] The surface etching method for a semiconductor substrate according to [7], wherein the semiconductor substrate is a silicon substrate having a substrate surface orientation (111).

  The third of the present invention relates to the gas nozzle unit shown below.

  [11] A first nozzle that injects an etching gas, a second nozzle that injects a cooling gas, and a gas that is disposed outside the first and second nozzles and exhausts the etching gas and the cooling gas. A gas nozzle unit comprising: an exhaust port; and a gas supply port that is disposed outside the gas exhaust port and injects a gas that does not react exothermically with the material of the semiconductor substrate.

  According to the surface etching apparatus of the present invention, the surface of the semiconductor substrate can be efficiently dry etched. In addition, since the temperature rise of the semiconductor substrate during the process can be controlled, it can cope with mass production.

  Furthermore, by optimizing the composition of the etching gas, it is possible to form a texture structure with fine irregularities that has not been realized so far on the surface of the semiconductor substrate. Furthermore, since the gas once blown can react with the substrate without stagnation of the reaction gas, the gas can be quickly exhausted, so that the reaction can always be performed with a fresh gas. Furthermore, a semiconductor substrate suitable as a solar cell can be preferably provided, and the photoelectric conversion rate of the solar cell can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the outline | summary of the 1st example of the surface etching apparatus of this invention, FIG.1 (a) is a perspective view when an apparatus is seen from the side; FIG.1 (b) has seen the apparatus from the upper surface Perspective view of when The figure which shows the outline | summary of the 2nd example of the surface etching apparatus of this invention It is an electron micrograph which shows the state of the silicon substrate surface etched with the surface etching apparatus of this invention, Fig.3 (a) is a silicon substrate surface of the substrate orientation surface (100) etched with the surface etching apparatus of this invention. FIG. 3B and FIG. 3C are electron micrographs showing the state of the silicon substrate surface of the substrate orientation plane (111) etched by the surface etching apparatus of the present invention; FIG. (D) is a figure which shows the electron micrograph which shows the state of the silicon substrate surface of a substrate orientation surface (100) etched using alkali (KOH) aqueous solution. The figure which shows the lifetime value of the silicon substrate of Examples 1-2 and comparative example (1) The light reflectance of the silicon substrate on the substrate orientation surface (111) in the unprocessed state, and the silicon substrate on the substrate orientation surface (111) etched with the surface etching apparatus of the present invention (Example 2, FIGS. 3B and 3). The figure which shows the light reflectivity of (c). The figure which shows the nozzle unit in the surface etching apparatus of this invention The figure which shows the electron micrograph which shows the state (bird's eye view) of the silicon substrate surface etched with the surface etching apparatus of this invention The figure which shows the electron micrograph which shows the state (upper surface) of the silicon substrate surface etched with the surface etching apparatus of this invention

(About etching equipment)
The surface etching apparatus of the present invention includes a reaction chamber, a movable stage capable of transporting a semiconductor substrate, a nozzle for injecting etching gas, a nozzle for injecting cooling gas, an exhaust port for exhausting them, and an exhaust port outside A nozzle for injecting a gas curtain.

  The inside of the reaction chamber of the surface etching apparatus of the present invention can be in a reduced pressure state, and the etching process can be performed under reduced pressure conditions. The internal pressure of the reaction chamber during the etching process is adjusted to a range of 1 KPa to atmospheric pressure, and is usually controlled to 10 KPa to atmospheric pressure, preferably 30 KPa to 90 KPa.

  A moving stage for transferring the semiconductor substrate is disposed in the reaction chamber. It is preferable that the moving stage can transport the semiconductor substrate in the reaction chamber, and can adjust the relative positional relationship between a nozzle (a nozzle for injecting an etching gas and a nozzle for injecting a cooling gas), which will be described later, and the semiconductor substrate. . Thereby, the gas from a nozzle is sprayed on the desired position of the semiconductor substrate surface.

  The surface etching apparatus of the present invention has a nozzle for injecting an etching gas. The etching gas is appropriately selected depending on the material of the semiconductor substrate, etc .; typically, it contains at least one gas of ClF3, XeF2, BrF3, and BrF5. These gas molecules are physically adsorbed on the surface of the semiconductor substrate and move to the etching site. Gas molecules that have reached the etching site are decomposed and react with a semiconductor material (typically silicon) to produce a volatile fluorine compound. As a result, the surface of the semiconductor substrate is etched to form an uneven shape.

  The etching gas preferably contains a gas containing oxygen atoms in the molecule. The gas containing oxygen atoms is typically oxygen gas (O2), but may be carbon dioxide (CO2) or the like. The concentration (volume concentration) of the oxygen atom-containing gas in the etching gas is preferably at least twice the total concentration of ClF3, XeF2, BrF3, and BrF5 gases.

  By including an oxygen atom-containing gas in the etching gas, it is possible to form an uneven shape suitable for the texture structure of the solar cell on the surface of the semiconductor substrate. The reason is not necessarily clear, but for example, when ClF 3 gas is physically adsorbed on the silicon surface, it reacts with silicon and becomes SiF 4 and gasifies. At this time, oxygen atoms are terminated in the dangling bonds of the silicon network structure, so that Si—O bonds are partially configured. Thereby, a region (Si—Si) that is easily etched and a region (Si—O) that is difficult to etch are formed. It is considered that the chemical reaction is promoted by the difference in the etching rate and the shape can be controlled.

  Furthermore, the etching gas may contain nitrogen gas or inert gas. If the concentrations of ClF3, XeF2, BrF3 and BrF5 in the etching gas are too high, etching may proceed isotropically and a desired uneven shape may not be obtained on the surface of the semiconductor substrate. Therefore, nitrogen gas or inert gas may be mixed as a dilution gas.

  The surface etching apparatus of the present invention has a nozzle for injecting a cooling gas. The cooling gas may be any gas that does not exothermically react with the material of the semiconductor substrate, and examples thereof include nitrogen gas and inert gas (such as helium gas and argon gas).

  As described above, ClF3, XeF2, BrF3, and BrF5 react with the semiconductor, but since the reaction is an exothermic reaction, the semiconductor substrate temperature rises. When the temperature of the semiconductor substrate rises, etching is likely to proceed isotropically, and a desired uneven shape cannot be obtained on the surface of the semiconductor substrate. Therefore, the semiconductor substrate is cooled by spraying a cooling gas on the semiconductor substrate that has generated heat by the etching reaction.

  The temperature of the semiconductor substrate is preferably maintained at 130 ° C. or lower, more preferably 100 ° C. or lower, and further preferably 80 ° C. or lower. On the other hand, the temperature of the semiconductor substrate should just be hold | maintained more than the boiling point of the etching gas injected. For example, since the boiling point of ClF 3 is about 12 ° C., the temperature of the semiconductor substrate is kept at 12 ° C. or higher when using ClF 3.

  The surface etching apparatus of the present invention may have two or more nozzles for injecting an etching gas, or may have two or more nozzles for injecting a cooling gas. The arrangement of the nozzles is not particularly limited, but is preferably arranged along the transport direction (the relative movement direction of the semiconductor substrate, more specifically, the movement direction of the moving stage). It is preferable that the nozzle for injecting the etching gas and the nozzle for injecting the cooling gas are regularly arranged.

  For example, nozzles for injecting etching gas and nozzles for injecting cooling gas may be alternately arranged along the transport direction. Or the nozzle which injects etching gas and the nozzle which injects several cooling gas may be arrange | positioned repeatedly along the conveyance direction. However, it is usually preferable that the nozzles for injecting two etching gases are not arranged in succession.

  Further, the shape of each nozzle is not particularly limited, but it may be preferable that the nozzle is widened toward the nozzle outlet so that gas can be blown over a large area of the surface of the semiconductor substrate.

  The surface etching apparatus of the present invention has gas exhaust ports on both outer sides so as to sandwich a nozzle for injecting an etching gas and a nozzle for injecting a cooling gas. Since the gas once blown onto the semiconductor substrate can be quickly exhausted without retaining the reaction gas after reacting with the substrate, it can always be reacted with a fresh gas (a surface etching apparatus of this form The nozzle unit will be described in detail later in “Regarding the nozzle unit”). The gas exhaust port may be exhausted by a pump or exhausted by a fan.

  Further, the shape of each exhaust port is not particularly limited.

  The surface etching apparatus of the present invention includes a nozzle for injecting an etching gas, a nozzle for injecting a cooling gas, a gas exhaust port for exhausting the gas injected on both sides of the nozzle, and gas curtains on both sides of the gas exhaust port. A gas supply port. The etching gas nozzle, the cooling gas nozzle, the gas exhaust port, and the gas supply port (gas curtain) may be one gas nozzle unit, and a plurality of similar gas nozzle units may be provided. This gas supply port (gas curtain) has a role of preventing the leakage of the ejected gas to the outside of the gas nozzle unit.

  The gas supply port (gas curtain) may be any gas that does not exothermically react with the material of the semiconductor substrate, and examples thereof include nitrogen gas and inert gas (such as helium gas and argon gas).

  The surface etching apparatus of the present invention may have a nozzle for injecting a mask forming gas. The mask forming gas is preferably a fluorocarbon gas, and examples of the fluorocarbon gas include tetrafluoromethane (CF4) and hexafluoroethane (C2F6). When the molecules of the mask forming gas are adsorbed on the surface of the semiconductor substrate, the adsorbed portion becomes difficult to be etched. Therefore, the surface of the semiconductor substrate can be selectively etched, and a desired uneven shape may be easily obtained.

  The semiconductor substrate having a concavo-convex shape formed on the surface by the surface etching apparatus of the present invention is typically a silicon substrate, but may be a germanium substrate, silicon carbide, or the like. Furthermore, the substrate whose surface is etched may be a sapphire substrate other than the semiconductor substrate. The silicon substrate is usually single crystal silicon, but may be polycrystalline silicon or amorphous silicon.

  The single crystal silicon substrate may be a silicon substrate having a substrate surface orientation (100), a silicon substrate having a substrate surface orientation (111), or a silicon substrate having another substrate surface orientation. Good. When a silicon substrate having a substrate surface orientation (111) is etched by a conventional wet process using an alkaline aqueous solution, the uneven surface cannot be formed on the substrate surface, and the surface is simply isotropically etched. However, according to the surface etching apparatus of the present invention, the silicon substrate having the substrate surface orientation (111) can also be formed with uneven shapes on the substrate surface.

  The semiconductor substrate may be a semiconductor wafer or a semiconductor thin film formed on another substrate.

(About the nozzle unit)
The nozzle unit 100 of the present invention is as shown in FIG. That is, the nozzle unit 100 of the present invention includes the following constituent members.

  (1) An etching gas supply nozzle 60 that supplies an etching gas containing ClF3, XeF2, BrF3, and BrF5.

  (2) A cooling gas supply nozzle 70 that is disposed outside the etching gas supply nozzle 60 and supplies a cooling gas containing nitrogen gas or inert gas.

  (3) A gas exhaust port 80 for exhausting the gas supplied from the etching gas supply nozzle 60 and the cooling gas supply nozzle 70 so as not to spread outward.

  (4) A gas supply port 90 that is arranged outside the gas exhaust port 80 and gas curtains so that no gas flows from the gas exhaust port 80 to the outside.

  Note that the etching gas supply nozzle 60 and the cooling gas supply nozzle 70 may be a single nozzle. In this case, the etching gas and the cooling gas may be mixed and supplied to the nozzle.

  As described above, by forming the nozzle unit, a desired uneven shape can be formed on the semiconductor substrate 1 with high accuracy.

(About etching method)
A semiconductor substrate having a concavo-convex shape formed on the surface can be manufactured using the surface etching apparatus of the present invention. Specifically, a semiconductor substrate is set in the surface etching apparatus of the present invention, and the pressure in the reaction chamber is reduced. Thereafter, the semiconductor substrate set on the moving stage is moved relative to the nozzle. While relatively moving the semiconductor substrate, an etching gas is sprayed from a nozzle for injecting an etching gas to the surface of the semiconductor substrate, and a cooling gas is sprayed from a nozzle for injecting a cooling gas.

  By blowing the cooling gas, the temperature of the semiconductor substrate is maintained at 130 ° C. or lower, preferably 100 ° C. or lower, more preferably 80 ° C. or lower.

  The semiconductor substrate may be vibrated while the semiconductor substrate is moved by the moving stage, or the nozzle may be vibrated. Thereby, a finer uneven shape can be formed on the surface of the semiconductor substrate. Further, the relative movement of the semiconductor substrate does not have to be in one direction, and may move in a two-dimensional direction or may move in a three-dimensional direction. Furthermore, the moving stage may reciprocate.

  FIG. 1A and FIG. 1B show an outline of a first example of the surface etching apparatus of the present invention. FIG. 1 (a) is a perspective view when the device is viewed from the side; FIG. 1 (b) is a perspective view when the device is viewed from the top.

  The surface etching apparatus shown in FIGS. 1A and 1B includes a load lock chamber 10, a reaction chamber 20, and an unload lock chamber 30. The interiors of the load lock chamber 10, the reaction chamber 20, and the unload lock chamber 30 can all be decompressed. That is, the load lock chamber 10 is provided with a dry pump 12, a valve 13, and a gate valve 14; the unload lock chamber is provided with a dry pump 32, a valve 33, and a gate valve 34.

  The semiconductor substrate 1 is supplied from the substrate supply unit 5 to the load lock chamber 10. The semiconductor substrate 1 is placed on a moving stage and supplied to the load lock chamber 10. For example, it may be stored in a container such as a tray and supplied to the load lock chamber 10. About 100 semiconductor substrates 1 may be accommodated in one container.

  From the load lock chamber 10 to the unload lock chamber 30 through the reaction chamber 20, a roller transport machine 50 serving as a transport mechanism is provided. The semiconductor substrate 1 set in the roller transfer device 50 can be transferred from the load lock chamber 10 to the unload lock chamber 30 through the reaction chamber 20.

  In the reaction chamber 20, an etching gas supply nozzle 60 and a cooling gas supply nozzle 70 are provided; gas can be blown onto the surface of the semiconductor substrate 1 transported inside the reaction chamber 20. The etching gas supply nozzle 60 and the cooling gas supply nozzle 70 are provided alternately along the transport direction. Further, the reaction chamber 20 is provided with a dry pump 22 and a valve 23, and the gas generated by the etching reaction can be exhausted.

  The roller transporter 50 may transport the semiconductor substrate 1 in one direction from the load lock chamber 10 to the unload lock chamber 30, but may transport it while reciprocating (moving left and right in the drawing). .

  The semiconductor substrate 1 ′ transferred to the unload lock chamber 30 is discharged to the substrate discharge unit 35 and collected. A desired uneven shape is formed on the surface of the semiconductor substrate 1 ′ facing the nozzles (the etching gas supply nozzle 60 and the cooling gas supply nozzle 70). At the same time, the reacted gas and excess gas are discharged. Thereafter, the semiconductor substrate 1 ′ may be subjected to a treatment for removing the fluorine component remaining in the hydrogen gas atmosphere as necessary. For example, high-temperature annealing is performed or plasma treatment is performed.

  FIG. 2 shows an outline of a second example of the surface etching apparatus of the present invention. FIG. 2 shows only the outline inside the reaction chamber of the surface etching apparatus. A plurality of semiconductor substrates 1 are placed on a disk-shaped moving stage 3 that serves as a transport mechanism. The stage 3 can move the semiconductor substrate by rotating (see the arrow direction). Etching gas supply nozzles 60 and cooling gas supply nozzles 70 are arranged radially from the rotation center of the rotation direction of the stage 3. Etching gas and cooling gas can be sprayed onto the surface of the semiconductor substrate 1 while rotating the stage 3. When a desired concavo-convex shape is formed on the surface of the semiconductor substrate 1, a treatment for removing the fluorine component remaining in the hydrogen gas atmosphere may be performed as necessary.

[Example 1]
Using the surface etching apparatus of the present invention, an uneven shape was formed on the silicon substrate surface of the substrate orientation surface (100). First, a silicon substrate was set in the reaction chamber, and the internal pressure of the reaction chamber was maintained at 30 to 90 Kpa. An etching gas containing ClF3 gas 500 cc, O2 gas 2000 cc, and N2 gas 5000 cc is sprayed on the surface of the silicon substrate set in the reaction chamber for 1 minute, and then N2 gas 5000 cc is applied to the silicon substrate surface over 1 minute. Sprayed to cool. This cycle was repeated three times. The silicon substrate to which the ClF 3 gas is sprayed tends to generate heat suddenly and rise in temperature when the substrate temperature exceeds 60 ° C. Therefore, processing was performed in a cycle of 1 minute so that the substrate temperature did not reach its displacement temperature (about 60 ° C.). As a result, an optical micrograph of the obtained silicon substrate surface is shown in FIG. As shown in FIG. 3A, it can be seen that a quadrangular pyramidal hole is formed on the substrate surface.

  Next, the lifetime of the silicon substrate shown in FIG. The measurement was performed after the surface of the semiconductor substrate was subjected to iodine passivation (iodine / ethanol method). The lifetime refers to the time until excess carriers (electrons or holes) generated on and inside the semiconductor substrate disappear due to recombination and decrease to a predetermined value. The lifetime was measured by the μ-PCD method (microwave photoconductivity decay method). As a measuring apparatus, LTA-1510 (KOBELCO Kaken) was used. The specific measurement conditions were a microwave probe frequency of 10 GHz and a laser wavelength of 904 nm. There were two types of irradiated laser light, level 2 (injection amount: 1E14 / cm2) and level 3 (injection amount: 1E15 / cm2). The measurement result of the lifetime is shown in FIG.

[Example 2]
Using the surface etching apparatus of the present invention, an uneven shape was formed on the silicon substrate surface of the substrate orientation plane (111). The processing conditions are the same as in Example 1, and after spraying an etching gas containing 500 cc of ClF3 gas, 2000 cc of O2 gas, and 5000 cc of N2 gas over the surface of the silicon substrate set in the reaction chamber, N2 gas 5000 cc was sprayed on the silicon substrate surface for 1 minute to cool. This cycle was repeated three times. Optical micrographs of the surface are shown in FIGS. 3 (b) and 3 (c).

  FIG. 3 (b) is an optical micrograph showing the substrate surface obliquely from above; FIG. 3 (c) is a cross-sectional optical micrograph. As shown in FIGS. 3B and 3C, it can be seen that convex portions on the triangular pyramid are formed on the substrate surface. The lifetime of the silicon substrate shown in FIG. 3B was measured by the same method as described above. The result is shown in FIG.

  Further, the light reflectance of the silicon substrate shown in FIGS. 3B and 3C and the light reflectance of the silicon (111) substrate before etching (untreated) were measured. The result is shown in FIG. As shown in FIG. 5, it can be seen that the light reflectance of the silicon substrate shown in FIGS. 3B and 3C is reduced in all wavelength regions, making it easier to capture light. In particular, in the wavelength range of 500 nm to 1000 nm, the reflectance of the silicon substrate before etching is about 35% or more, whereas the light reflectance of the silicon substrate shown in FIGS. 3B and 3C is It turns out that it has reduced to about 14%.

[Example 3]
Using the surface etching apparatus of the present invention, an uneven shape was formed on the silicon substrate surface of the substrate orientation plane (111). First, a silicon substrate was set in the reaction chamber, and the internal pressure of the reaction chamber was maintained at 30 to 90 Kpa. An etching gas containing 300 cc of ClF3 gas, 300 cc of O2 gas, and 10000 cc of N2 gas is blown over the surface of the silicon substrate set in the reaction chamber over 3 minutes, and exhausted from both sides at the same time. Since the reaction gas after reacting with the substrate can be quickly exhausted without retaining the reaction gas, the reaction was always performed with a fresh gas.

  As a result, optical microscope photographs of the obtained silicon substrate surface are shown in FIGS. As shown in FIGS. 7 and 8, it can be seen that triangular pyramidal holes and pyramid-shaped recesses are formed on the substrate surface.

  This clearly shows the characteristic of being etched from a surface orientation that is relatively easy to be etched such as 100, 101, etc. other than the surface orientation 111.

[Comparative Example (1)]
A concavo-convex shape was formed on the silicon substrate surface of the substrate orientation surface (100) by a general wet etching method using a conventional aqueous solution of alkali (KOH). That is, it is formed through a wet process such as HF cleaning, an alkali (KOH) solution, or hydrofluoric acid. An optical micrograph of the surface is shown in FIG. As shown in FIG. 3D, it can be seen that pyramidal protrusions are formed on the substrate surface. The lifetime of the silicon substrate shown in FIG. 3D was measured by the same method as described above. The result is shown in FIG.

  FIG. 4 shows lifetime values of the silicon substrates of Examples 1 and 2 and Comparative Example (1). The left bar graph is the value at level 2; the right bar graph is the value at level 3. As shown in FIG. 4, it can be seen that the lifetime value of the silicon substrate of Example 1 is almost comparable to the lifetime value of the silicon substrate of Comparative Example (1). On the other hand, it can be seen that the lifetime value of the silicon substrate of Example 2 is significantly higher than that of Comparative Example (1).

  According to the surface etching apparatus of the present invention, the surface of the semiconductor substrate can be efficiently dry etched. In addition, since the temperature rise of the semiconductor substrate during the process can be suppressed, it can cope with mass production. Furthermore, by optimizing the composition of the etching gas, it is possible to form a fine uneven texture structure on the surface of the semiconductor substrate that has not been realized; the light reflectance can be reduced and the lifetime can be improved. . Therefore, it can be particularly suitably applied to a solar cell manufacturing process.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 60 Etching gas supply nozzle 70 Cooling gas supply nozzle 80 Gas exhaust port 90 Gas supply port 100 Nozzle unit

Claims (11)

A reaction chamber capable of depressurization;
A moving stage capable of transporting a semiconductor substrate inside the reaction chamber;
A nozzle unit that injects or exhausts gas toward the surface of the semiconductor substrate placed on the moving stage;
The nozzle unit is
A first nozzle for injecting an etching gas toward a semiconductor substrate surface mounted on the moving stage;
A second nozzle for injecting a cooling gas toward the semiconductor substrate placed on the moving stage;
A gas exhaust port disposed outside the first and second nozzles for exhausting the gas;
A gas supply port that is disposed outside the gas exhaust port and injects a gas that does not generate an exothermic reaction with the material of the semiconductor substrate toward the moving stage;
An apparatus for etching a surface of a semiconductor substrate.   The surface etching apparatus according to claim 1, wherein the etching gas includes one or more gases selected from the group consisting of ClF 3, XeF 2, BrF 3, and BrF 5.   The surface etching apparatus according to claim 1, wherein the cooling gas includes nitrogen gas or inert gas.   The said gas exhaust port is a surface etching apparatus as described in any one of Claims 1-3 arrange | positioned at the outer both sides of the said etching gas and the said cooling gas.   The surface etching apparatus according to any one of claims 1 to 4, wherein the gas supply port includes nitrogen gas or inert gas disposed on both outer sides of the exhaust port.   The surface etching apparatus according to any one of claims 1 to 5, wherein a pressure inside the reaction chamber can be adjusted in a range of atmospheric pressure to 100 KPa. A method for etching a surface of a semiconductor substrate, wherein the surface etching apparatus according to claim 1 is used to form an uneven shape on the surface.
Preparing a semiconductor substrate placed on a moving stage inside the reaction chamber that has been decompressed;
Spraying an etching gas from a nozzle for injecting an etching gas onto the semiconductor substrate while moving the moving stage; and
Spraying cooling gas from a nozzle that injects cooling gas onto the semiconductor substrate while moving the moving stage;
Exhausting the etching gas and the cooling gas;
Spraying a gas curtain toward the moving stage up to the etching gas, the cooling gas, and the exhaust port.   The method for etching a surface of a semiconductor substrate according to claim 7, wherein the temperature of the semiconductor substrate is maintained at 130 ° C. or lower.   The method for etching a surface of a semiconductor substrate according to claim 7, wherein the semiconductor substrate is vibrated while moving the moving stage.   The surface etching apparatus according to claim 7, wherein the semiconductor substrate is a silicon substrate having a substrate surface orientation (111). A first nozzle for injecting an etching gas;
A second nozzle for injecting cooling gas;
A gas exhaust port disposed outside the first and second nozzles for exhausting the gas;
A gas supply port that is disposed outside the gas exhaust port and injects a gas that does not exothermically react with the material of the semiconductor substrate;
A gas nozzle unit.

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