TW201334054A - The method of single-side smooth etching of a silicon substrate - Google Patents

Abstract

Method for smoothing a silicon substrate (50) by etching (16) on one side, wherein a protective layer (54; 56) is formed (12; 24) at least on a first side of the silicon substrate, then a second side of the silicon substrate (50) is smoothed by etching (16) by means of an alkaline etching solution having a temperature in the range of between 50 DEG C and 90 DEG C, and, during this process of smoothing by etching (16), those regions of the silicon substrate (50) on which the protective layer (54; 56) has been formed are protected against action of the etching solution by means of the protective layer (54; 56).

Description

Single-sided planarization etching method of germanium substrate

The present invention relates to a one-sided planarization etching method for a tantalum substrate.

In particular, the manufacture of various solar cells today requires a smooth back surface which is one of the substrates used as a solar cell substrate. The back side is understood to be the surface of the solar cell substrate or the large area of the substrate, and is designed to be remote from the incident light when the solar cell is in operation. The smoothed back side reduces the recombination of charge carriers generated on the tantalum substrate or the back side of the solar cell substrate. The passivated surface condition of the back side can increase the efficiency by up to 1% compared to a solar cell having a non-smooth back side. In particular, the back side of the solar cell substrate that has been textured and flattened can produce significant performance improvements.

Up to now, the back side of the substrate has been planarized by an acid polishing etch liquid. However, various solar cell manufacturing methods have empirically shown that the use of an acidic polishing etchant can cause undesirable or unnecessary side effects. In particular, the back side may be invaded by an etching process of an acid polishing etchant. Other ranges of etched solar cell substrates. Experience has shown that the range of emitter doping can be severely impaired. Therefore, the acid polishing etchant can only be used in many cases before forming the emitter doping. It is not suitable for all solar cell processes.

In view of the above, in order to overcome various problems of the above-described conventional techniques, the main object of the present invention is to provide a single-sided planarization etching method for a tantalum substrate which can be elastically applied.

The object of the present invention can be achieved by the claims and features as set forth in claim 1 of the present invention.

The more preferred embodiments are the subject matter of the respective patent applications of the present invention.

A single-sided planarization etching method for a germanium substrate according to the present invention includes forming at least one protective layer on a first side of a germanium substrate. Then, one of the second faces of the ruthenium substrate is planarized by an alkaline etch solution having a temperature between 50 ° C and 90 ° C. In the planarization etching process, the protective layer is protected by the protective layer in the range in which the protective layer has been formed.

The planarization etching according to the present invention means that at least a portion of the surface of the germanium substrate is planarized. In other words, the planarization etch refers to at least a portion of the surface of the germanium substrate being flat.

Thus, the higher temperature of the alkaline etchant can achieve an isotropic etch characteristic of the alkaline etchant, which enables the second of the etched ruthenium substrate to be planarized. surface. The first side of the ruthenium substrate can be protected from the action of a low cost alkaline etchant, for example by a bismuth silicate glass layer or a tantalum nitride layer. Furthermore, it has been empirically shown that planarizing the second side by etching by the method of the present invention is less costly than using an acidic etchant. The advantages of the above alkaline etching solution come from low chemical cost and long service life with respect to the acid polishing etchant.

As for the alkaline etching solution, an aqueous solution of sodium hydroxide (NaOH) or an aqueous solution of potassium hydroxide (KOH) has been experimentally confirmed to be suitable.

Preferably, the first side is located opposite the second side. More preferably, the first side of the solar cell substrate refers to a front side and the second side of the solar cell substrate refers to a back side. The back surface of the solar cell substrate refers to a surface that is disposed away from incident light when the solar cell is in operation. Conversely, the front side of the solar cell substrate refers to the surface on which the incident light is placed when the solar cell is in operation.

In order to achieve planarization etching of the back surface of the germanium substrate, the germanium substrate is partially or completely immersed in the etching liquid. In particular, the planarization etching can be achieved by single-sided etching, for example, the back surface of the germanium substrate is arranged to be infiltrated by the etching liquid, and the front surface of the germanium substrate is higher than the water level of the etching liquid. Most germanium substrates can be planarly or continuously planarized. Therefore, the method can be compatible not only with stacked work equipment but also with automated production lines.

Preferably, a tantalate glass layer or a tantalum nitride layer is formed as a protective layer. In this way, the protective layer can be realized by existing solar cell manufacturing techniques. In particular, it has been experimentally confirmed that a phosphonate glass layer and a borosilicate glass layer can be used as a protective layer.

According to a variant of the invention, the solar cell substrate is single-sided polished and etched, and a dopant-containing tellurite glass layer is formed as a protective layer during the diffusion of the emitter. In this way, the protective layer can be manufactured at low cost during an emitter diffusion step that is indispensable for solar cell fabrication. In particular, it has been experimentally proven that a monophosphoric acid glass layer or a borosilicate glass layer can be used as a dopant-containing tellurite glass layer.

The emitter diffusion can be substantially achieved by any existing means, where a single-sided or multi-sided emitter diffusion method can be used. In particular, a tube diffusion has been experimentally proven to be effective. In the process of emitter diffusion, for example, if a dopant-containing tellurite glass layer is formed on the second side of the germanium substrate by diffusion of the tube, the dopant-containing tellurite glass layer is preferably It is removed before planarization etching. In this case, for example, it can be achieved by a conventional one-sided etching method, in particular using a low-concentration hydrofluoric acid solution. Preferably, the dopant-containing tellurite glass layer on the second side of the germanium substrate is removed during the edge separation step. With this method including edge separation, an additional edge separation step is not required with respect to the solar cell manufacturing method. A process step is generally referred to as an edge separation step in which the surface on the second side of the germanium substrate is electrically insulated from the emitter doping. For this purpose, for example, the emitter doping of the second side of the germanium substrate is etched away so that the dopant-containing tellurite glass layer can be removed from the second side of the germanium substrate at low cost during etching. .

Preferably, the dopant-containing tellurite glass layer formed during the diffusion of the emitter is removed by wet chemical etching of the second side of the germanium substrate. More preferably, for this purpose, one of the first types of citrate glass etchants, including water, 10 g/l to 50/l hydrofluoric acid, 200 g/l To 1000 g/l of sulfuric acid and/or 250 g/l to 500 g/l of nitric acid. In this way, the emitter doping of the second side of the germanium substrate can be simultaneously removed by the first type of tellurite glass etching solution if necessary. It is also possible here that a combination of the removal of the dopant-containing tellurite glass layer on the second side of the substrate can also be achieved by edge separation.

Preferably, after the planarization etching on the second side of the germanium substrate, the dopant-containing tellurite glass layer formed on the first side of the germanium substrate can be made of a second type of tellurite glass. The etchant is removed and the second side of the germanium substrate is overetched by a second type of tellurite glass etchant. In this manner, after planarization etching, the structure that may remain on the second surface of the germanium substrate is further planarized. The residual edges can be smoothed. It has been experimentally confirmed that an aqueous solution containing hydrofluoric acid and nitric acid can be used as the second type of tellurite glass etching solution.

According to another aspect of the present invention, a solar cell substrate is planarized by single-sided etching, and a tantalum nitride layer is formed on the first surface of the tantalum substrate as a protective layer. The tantalum nitride layer is further retained as an antireflection layer on the tantalum substrate. Such a variation provides another option for forming a protective layer at a lower cost because the formation of a tantalum nitride layer on a plurality of solar cell processes is provided as an anti-reflective layer.

The fabrication of a solar cell includes the formation of an emitter. Preferably, before the formation of the tantalum nitride layer, an emitter diffusion is performed and a dopant-containing tellurite glass layer is formed on the germanium substrate. The dopant-containing tellurite glass layer is completely removed prior to forming the tantalum nitride layer. In this way, the tantalum nitride layer as a protective layer is left on the germanium substrate as an anti-reverse Shot layer. The dopant-containing tellurite glass layer is preferably wet chemically removed, such as by a second type of tellurite glass etchant. One possible edge separation, such as edge separation using the first type of tellurite glass etchant described above, is preferably also performed prior to the formation of the tantalum nitride layer.

A variation provides that the germanium substrate has at least a portion of a surface texture prior to forming the protective layer. In this way, in the example of a solar cell substrate, for example, light can be coupled into the solar cell substrate, thereby increasing the efficiency of the processed solar cell. The surface texture is preferably formed on the first side and the second side of the tantalum substrate. The component formed by the surface texture on the second side of the ruthenium substrate is then planarized by the subsequent planarization etch. The surface texture is preferably formed by wet chemical texturing.

Preferably, the second side of the ruthenium substrate is planarized by an aqueous solution of potassium hydroxide. It has been experimentally confirmed that, in particular, an aqueous potassium hydroxide solution having a potassium hydroxide concentration of 10 to 30% by weight.

Preferably, the second side of the germanium substrate is planarized by an alkaline etching solution having a temperature between 70 ° C and 85 ° C. The stated temperature range has proven to be particularly effective.

Further, it has been experimentally confirmed that the second side can be planarized and etched at 10 to 300 seconds, preferably 30 seconds to 300 seconds.

The results show that the method of the invention can be applied to the production of solar cells with passivated backside or solar cells with passivated emitters and passivated backside, so-called PERC (Passivated Emitter and Rear Cell) type batteries. Emitter system to understand the range of emitters There is an electrically inactive surface state inside, and the passivated back side refers to a surface state having a passivation on the back side of the solar cell.

In order to enable a further understanding and understanding of the present invention, the embodiments are described in detail with reference to the accompanying drawings, wherein the same elements are designated by the same reference numerals. However, the invention may be embodied in a variety of different embodiments and is not limited to the embodiments shown and described. The description so far and the following illustrations have a majority of the features included in the subsidiary claims section. However, these features, as well as all of the features described above and in the following description, are those of ordinary skill in the art that can be individually referenced and further combined. In particular, these features can be achieved separately or in combination with the methods described in the dependent items.

10‧‧‧Texture etched solar cell 矽 substrate

12‧‧‧ Tube emitter diffusion with the formation of a tantalum-containing glass layer containing dopants

14‧‧‧Remove the doped tellurite glass layer on the back side

16‧‧‧ planarizing the back side in a potassium hydroxide solution having a temperature between 70 ° C and 85 ° C

18‧‧‧Remove residual material from the doped tellurite glass layer and overetch the back

20‧‧‧ Wet chemical edge separation

22‧‧‧ Complete removal of the doped tellurite glass layer

24‧‧‧ deposited tantalum nitride layer on the front side

50‧‧‧Solid battery substrate

51‧‧‧ surface texture

52‧‧‧ emitter doping

54‧‧‧Doped tellurite glass layer

56‧‧‧layer of tantalum nitride

Figure 1 is a schematic view showing a first embodiment of the method of the present invention

Figure 2 is a schematic view showing a second embodiment of the method of the present invention

FIG. 3 is a schematic view showing various process steps of the solar cell substrate of the method shown in FIG. 1 of the present invention;

4 is a schematic view showing various process steps of the solar cell substrate of the method shown in FIG. 2 of the present invention;

1 and 3 illustrate a first embodiment of the method of the present invention Schematic diagram. In the present embodiment, first, a solar cell 矽 substrate 50 is textured etched 10. Here, as shown in FIG. 3, the front surface of one of the solar cell stack substrates 50 facing upward has the surface texture 51 of the back surface of one of the solar cell stack substrates 50 facing downward as shown in FIG. In addition, the remaining surface area of the solar cell 矽 substrate also has a surface texture 51. For the sake of clarity, the schematic illustration of the surface texture 51 is avoided at the edge of the solar cell raft substrate 50 in the schematic views of FIGS. 3 and 4. The texturing etch 10 of the solar cell raft substrate 50 is preferably carried out by a wet chemical texture etchant.

Next, tube emitter diffusion 12 is performed. By this is meant a tube diffusion to form an emitter doping 52, which is schematically represented by a dashed line as shown in FIG. A dopant-containing tellurite glass layer 54 is formed during the diffusion of the emitter of the tube. Here, a phosphonate glass layer or a borosilicate glass layer is preferred.

In a subsequent method step, the dopant-containing tellurite glass layer 54 on the back side of the solar cell germanium substrate 50 is removed 14. For example, it can be carried out by using a bismuth silicate glass etching solution of the second type. The dopant-containing tellurite glass layer 54 in the remaining regions remains on the solar cell germanium substrate 50 and acts as a protective layer against the subsequent planarization etch 16.

The planarization etch 16 is carried out in an aqueous solution of potassium monoxide at a temperature between 70 ° C and 85 ° C. For the purpose of planarizing the etch 16, the solar cell ruthenium substrate 50 can be completely immersed in an aqueous potassium hydroxide solution. During the planarization etching 16, the surface texture 51 on the back surface of the solar cell substrate 50 can be planarized by etching action via the potassium hydroxide solution or the like at a given temperature. Except for the back side of the solar cell 矽 substrate 50, too The solar cell crucible substrate 50 is instead protected by the action of the potassium hydroxide solution containing dopants against the action of the potassium hydroxide solution, so that the surface texture 51 can be retained.

Next, the remaining portion of the dopant-containing tellurite glass layer 54 is removed 18. This can be done, for example, using a second type of phosphonium phosphate etching solution. Further, the back surface 50 of the solar cell ruthenium substrate is over-etched, whereby if it has a surface that is not completely planarized on the back surface of the solar cell ruthenium substrate 50, it can be further planarized.

Thus, a solar cell substrate 50 having one emitter doping 52 is left with a surface texture 51 on the front side and a back surface flattened thereon. The solar cell crucible substrate 50 can be processed into a solar cell by the prior art. In particular, it is possible to manufacture a solar cell having a passivated back surface, such as a PERC type (Passivated Emitter and Rear Cell)-solar cell.

2 and 4 illustrate another embodiment of the method of the present invention. Similarly, first, the solar cell 矽 substrate 50 is textured etched 10. This is followed by the formation of a tube oxide diffusion layer 12 with a dopant-containing tellurite glass layer 54. The embodiment shown in FIG. 3 differs from the embodiment shown in FIG. 3 in that wet chemical edge separation 20 is further implemented to remove dopant-containing defects on the back side of the solar cell substrate 50 in a relatively low cost manner. The acid salt glass layer 54 and the emitter doping 52. This can be achieved, for example, by a first type of tellurite glass etching solution. In the embodiment shown in Figures 1 and 3, the removal of the dopant-containing tellurite glass layer on the back side can be separated by wet chemical edge separation in the embodiment shown in Figures 2 and 4 Come to generation. Another way of producing the method of the invention is produced in this manner.

In the embodiment shown in Figures 2 and 4, the complete removal 22 of the dopant-containing tellurite glass layer 54 is followed by wet chemical edge separation 20. This can be achieved using a second type of tellurite glass etchant.

Next, a tantalum nitride layer 56 is deposited on the front side 24 of the solar cell substrate 50. This can be achieved by a conventional chemical vapor deposition method (CVD method). Since the dopant-containing tellurite glass layer 54 needs to be completely removed 22 before the deposition of the tantalum nitride layer 56, the tantalum nitride layer 56 can remain on the solar cell germanium substrate 50 as an anti-reflective layer. When the dopant-containing tellurite glass layer 54 was not completely removed before, as long as the removal of the dopant-containing tellurite glass layer 54 in the current solar cell processing process is unnecessary, nitrogen The ruthenium layer 56 can obviously also remain as an anti-reflection layer.

Further, the back surface of the solar cell ruthenium substrate 50 is planarized and etched 16 in a potassium hydroxide solution having a temperature of 70 ° C to 85 ° C. For this purpose, for example, the solar cell crucible substrate 50 can be completely immersed in a potassium hydroxide solution. Under such planarization etching 16, the back surface of the solar cell germanium substrate 50 is planarized, and in the process, the tantalum nitride layer 56 serves as a protective layer in the remaining regions and protects the solar cell germanium substrate 50 against the influence of the potassium hydroxide solution. .

Therefore, the obtained solar cell crucible substrate 50 has a surface texture 51 on the front surface, and an emitter doping 52 and a tantalum nitride layer 56 as an antireflection layer, and has a flattened back surface. The solar cell crucible substrate 50 can be further processed into a solar cell by the prior art. The metal-contact energy of the emitter doping on the front surface of the solar cell 矽 substrate 50 is The tantalum nitride layer is sintered by conventional prior art techniques for this purpose. The flattened back side of this solar cell 矽 substrate 50 provides the ideal prerequisite for fabricating a solar cell having a passivated back surface. Since one passivation treatment of the emitter can also be achieved by the tantalum nitride layer 56, it is also possible to manufacture a solar cell having a passivated emitter and a passivated back surface.

10‧‧‧Texture etched solar cell 矽 substrate

12‧‧‧ Tube emitter diffusion with the formation of a tantalum-containing glass layer containing dopants

14‧‧‧Remove the doped tellurite glass layer on the back side

16‧‧‧ planarizing the back side in a potassium hydroxide solution having a temperature between 70 ° C and 85 ° C

18‧‧‧Remove residual material from the doped tellurite glass layer and overetch the back

Claims (14)

A single-sided planarization etching method (16) for a germanium substrate (50), wherein - at least (12; 24) a protective layer (54; 56) is formed on a first side of the germanium substrate; An alkaline etching solution planarizes etching (16) a second side of the germanium substrate (50), the alkaline etching liquid having a temperature between 50 ° C and 90 ° C; - the planarization etching (16) In the process, the protective layer (54; 56) is formed on the germanium substrate (50) by the protective layer (54; 56) to protect against the action of the etching liquid; wherein the tantalate glass A layer (54) or a tantalum nitride layer (56) is formed (12; 24) as a protective layer (54; 56). The method of claim 1, wherein the monophosphoric acid phosphate layer or the borosilicate glass layer is formed as a protective layer (54). A method according to any one of the preceding claims, wherein the solar cell substrate (50) is a single-sided planarization etch (16). The method of claim 3, wherein the method of claim 3, wherein. During the process of emitter diffusion (12), a dopant-containing tellurite glass layer (54) is formed as (12) as a protective layer (54), preferably a phosphonate glass layer or a boronic acid. Salt glass layer. The method of claim 4, wherein the dopant-containing tellurite glass layer (54) formed during the emitter diffusion (12) is attached to the germanium substrate (50) The planarization etch (16) of the second side is removed (14). The method of claim 5, wherein the dopant-containing tellurite glass layer (54) formed during the emitter diffusion (12) is by the second of the germanium substrate The surface is wet chemically etched (14) and removed (14), preferably by a first type of bismuth silicate glass etchant, including water, 10 g/l to 50/l hydrofluoric acid , from 200 g/l to 1000 g/l of sulfuric acid and/or from 250 g/l to 500 g/l of nitric acid. The method of any one of claims 4 to 6, wherein after the planarization etching (16) of the second surface of the germanium substrate (50), the germanium substrate (50) The dopant-containing tellurite glass layer (54) formed on the first side is removed (18) by one of the second type of bismuth glass etching solution and the second side of the germanium substrate is second The bismuth glass etchant of the type is over-etched (18). The method of claim 3, wherein a tantalum nitride layer (56) is formed on the first surface of the germanium substrate (50) as a protective layer (56) and is retained (in the The substrate serves as an anti-reflection layer (24). The method of claim 8, wherein - before the formation of the tantalum nitride layer (56), an emitter diffusion (12) is performed and is applied to the substrate (50). Forming (12) a dopant-containing tellurite glass layer (54); and - prior to forming the tantalum nitride layer (56) (24), the dopant-containing tellurite glass layer (54) ) is completely removed (22). The method of any of the preceding claims, wherein the ruthenium substrate (50) is at least partially before the formation of the protective layer (54; 56) The portion has a surface texture (51) whereby the surface texture (51) is preferably formed (10) on the first side and the second side of the base substrate (50). The method of any of the preceding claims, wherein the second side of the ruthenium substrate (50) is planarized (16) by an aqueous potassium hydroxide solution, preferably by having potassium hydroxide. A concentration of 10 to 30% by weight of an aqueous potassium hydroxide solution. The method of any one of the preceding claims, wherein the second side of the germanium substrate (50) is planarized by the alkaline etching liquid (16), and the etching liquid has a ratio of 70 One temperature (16) from °C to 85 °C. The method of any of the preceding claims, wherein the second side 16) is planarized and etched during a period of from 10 seconds to 300 seconds, preferably from 30 seconds to 300 seconds. The method of any one of claims 3 to 13, wherein the solar cell substrate (50) is fabricated with a passivated backside solar cell, preferably with a passivated emitter and passivated One of the solar cells on the back.