MODIFIED TUNNEL OXIDE LAYER AND PREPARATION METHOD, TOPCON STRUCTURE AND PREPARATION METHOD, AND SOLAR CELL

Abstract

A modified tunnel oxide layer and a preparation method, a TOPCon structure and a preparation method, and a solar cell are provided. The modified tunnel oxide layer is SiO.sub.x subjected to plasma surface treatment, and a Si.sup.4+ content in the SiO.sub.x is greater than or equal to above 18%. The density of the interface state subjected to plasma surface treatment decreases, and compared with the silicon oxide layer prepared in the prior arts, boron has a low diffusion rate in the modified silicon oxide layer and hence the damaging effect of the boron on the tunnel oxide layer is reduced effectively, thereby improving the integrity of the silicon oxide layer and maintaining chemical passivation effect. The modified tunnel oxide layer significantly increases the performance indexes of the TOPCon structure.

Claims

1. A modified tunnel oxide layer, wherein the modified tunnel oxide layer is SiO.sub.x subjected to plasma surface treatment, and a Si.sup.4+ content in the SiO.sub.x is greater than or equal to above 18%.

2. The modified tunnel oxide layer of claim 1, wherein the modified tunnel oxide layer has a thickness of 1 nm to 4 nm.

3. A preparation method of the modified tunnel oxide layer of claim 1, comprising: step S1: by an ion-free bombardment oxidation method, forming a SiO.sub.x layer on a surface of a semiconductor substrate to obtain a SiO.sub.x surface; and step S2: with hydrogen and an oxygen-containing gas as a treatment atmosphere, performing treatment on the SiO.sub.x surface by plasma to obtain the modified tunnel oxide layer.

4. The preparation method of claim 3, wherein the ion-free bombardment oxidation method in the step S1 is selected from any one of the followings: oxidizing gas oxidation method, low-temperature oxidation method and chemical reagent oxidation method.

5. The preparation method of claim 3, wherein the step S2 is carried out in a plasma enhanced chemical vapor deposition (PECVD) apparatus.

6. The preparation method of claim 5, wherein a plasma treatment method in the step S2 is a continuous plasma treatment or pulsed plasma treatment.

7. The preparation method of claim 3, wherein the oxygen-containing gas is selected from any one of the followings: N.sub.2O, CO.sub.2 and O.sub.2.

8. A TOPCon structure, comprising the modified tunnel oxide layer of claim 1.

9. A preparation method of a TOPCon structure, comprising: cleaning a semiconductor substrate; preparing a modified tunnel oxide layer; preparing a doped amorphous silicon layer; and annealing; wherein the modified tunnel oxide layer is prepared by the preparation method of claim 3.

10. A solar cell, comprising the TOPCon structure of claim 8.

11. The preparation method of claim 3, wherein the modified tunnel oxide layer has a thickness of 1 nm to 4 nm.

12. The TOPCon structure of claim 8, wherein the modified tunnel oxide layer has a thickness of 1 nm to 4 nm.

13. The preparation method of claim 9, wherein in the preparation method of the modified tunnel oxide layer, the ion-free bombardment oxidation method in the step S1 is selected from any one of the followings: oxidizing gas oxidation method, low-temperature oxidation method and chemical reagent oxidation method.

14. The preparation method of claim 9, wherein in the preparation method of the modified tunnel oxide layer, the step S2 is carried out in a PECVD apparatus.

15. The preparation method of claim 14, wherein in the preparation method of the modified tunnel oxide layer, a plasma treatment method in the step S2 is a continuous plasma treatment or pulsed plasma treatment.

16. The preparation method of claim 9, wherein in the preparation method of the modified tunnel oxide layer, the oxygen-containing gas is selected from any one of the followings: N.sub.2O, CO.sub.2 and O.sub.2.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0028] FIG. 1 is a micro-structural diagram illustrating a modified tunnel oxide layer according to an embodiment 1 of the present disclosure.

[0029] FIG. 2 is a micro-structural diagram illustrating a modified tunnel oxide layer according to an embodiment 2 of the present disclosure.

DETAILED DESCRIPTIONS OF THE EMBODIMENTS

[0030] In order to make the above objects, features and advantages of the present disclosure clearer and more intelligible, the specific embodiments of the present disclosure will be detailed below with the drawings. It should be noted that the following embodiments are used only to illustrate the implementation methods and typical parameters of the present disclosure rather than to limit the parameter range of the present disclosure. Therefore, any reasonable changes derived herefrom shall be within the scope of protection of the claims of the present disclosure.

[0031] It should be noted that the endpoints of the ranges and any values disclosed herein are not limited to such precise ranges or values. These ranges and values shall be understood as including values approaching these ranges or values. For any numerical ranges, combination may be performed between the endpoint values of each range, between the endpoint value of each range and an individual point value and between the individual endpoint values to produce one or more new numerical ranges. These numerical ranges shall be considered as disclosed herein.

[0032] As mentioned in the background, the current preparation methods for the tunnel oxide layer in the TOPCon include nitric acid oxidation method, N.sub.2O plasma oxidation method, thermal oxidation method and ozone oxidation method. In these methods, reagents or gases or the like with strong oxidizing property are used to oxidize silicon wafer surface to form an ultrathin layer of SiO.sub.2 as tunnel oxide layer. But, after these oxide layers grow P-Poly, there may be excessively large contact resistivity or many defect states due to excessively compact oxide layer, leading to poor passivation effect.

[0033] In view of the above, a specific embodiment of the present disclosure provides a preparation method of a TOPCon structure, which includes the following steps: cleaning of a semiconductor substrate, preparation of a modified tunnel oxide layer, preparation of a doped amorphous silicon layer, and annealing.

[0034] The preparation method of the modified tunnel oxide layer includes the following steps: at step S1, by ion-free bombardment oxidation method, a SiOx layer is formed on a surface of the semiconductor substrate; at step S2, with hydrogen and oxygen-containing gas as treatment atmosphere, SiOx surface is treated with plasma to obtain a modified tunnel oxide layer.

[0035] The ion-free bombardment oxidation method in the step S1 may be an oxidizing gas oxidation method, a low-temperature oxidation method (100 to 600 C.) or a chemical reagent oxidation method, and the typical method is an ozone oxidation method, a nitric acid oxidation method or the like. In this step, one silicon oxide layer without bombardment damage is prepared. By this method, the ion bombardment damage in the subsequent second step can be significantly reduced, thereby obviously increasing the passivation quality.

[0036] The plasma treatment method in the step S2 is a continuous plasma treatment or pulsed plasma treatment. This step is carried out in a PECVD apparatus. In a specific embodiment, a plasma treatment power is 5 to 10 w, with a treatment time of 50 to 150 S. A flow ratio of the hydrogen and the oxygen-containing gas is 2:1 to 8:1. In this method, surface modification treatment is performed on SiO.sub.x layer by the hydrogen and the oxygen-containing gas, and hydrogen plasma has a heating effect on the surface, increasing the energy of the atoms such as oxygen and nitrogen and enhancing the bonding quality. Hydrogen plasma can etch weak bonds of the SiO.sub.x surface to enable the valence bond in the silicon oxide to be more stable. These two effects enable SiO.sub.x to retain more stable SiOs, thereby increasing the performance.

[0037] The oxygen-containing gas is N.sub.2O or CO.sub.2, and preferably, N.sub.2O. The combination of N atoms and silicon oxide can significantly lower the concentration of the boron on the silicon surface, thereby reducing the boron defects. The N atoms also have a capturing effect on the H atoms, which can effectively reduce H spillover in a sintering process, enabling iVoc to remain at a high level in the subsequent sintering process.

[0038] The modified tunnel oxide layer prepared in the above method has a thickness of 1 to 4 nm, the Si.sup.4+ content in SiO.sub.x reaches over 18%, and the density of the interface state is lower than 0.510.sup.12 eV.sup.1 cm.sup.2. Compared with the silicon oxide layer prepared in the prior arts, the boron has a low diffusion rate in the modified silicon oxide layer, effectively reducing the damaging effect of the boron on the tunnel oxide layer, improving the integrity of the silicon oxide layer and maintaining the chemical passivation effect.

[0039] The above modified tunnel oxide layer may be applied to a P-type TOPCon cell or N-type TOPCon cell and can significantly increase the performance indexes of the TOPCon structure. iVoc in the passivation index of the P-type TOPCon can reach above 730 mV, and the corresponding single-side saturation current density (J.sub.0) is lowered to below 7 fA/cm.sup.2, and the contact resistivity is lowered to 5 mcm.sup.2.

[0040] The present disclosure will be detailed below with specific embodiments. In the following embodiments and control embodiments, the semiconductor substrate is an n-type monocrystalline silicon wafer with a thickness of 160 m, with two sides chemically polished and the resistivity being 0.8 .Math.cm.

Embodiment 1

[0041] A double-sided p-type tunnel silicon oxide passivated structure is provided, and its preparation method includes the following steps.

[0042] 1) A silicon wafer was cut into a size of 4 cm4 cm and subjected to standard RCA cleaning.

[0043] 2) The silicon wafer was placed in an ozone generator to grow a SiO.sub.2 film.

[0044] 3) The sample was placed into a PECVD apparatus and continuous plasma treatment was performed with N.sub.2O and H.sub.2 as treatment atmosphere and the flow ratio of 4:1 for a time of 100 S under the power of 5 W.

[0045] 4) Next, a boron-doped amorphous silicon film was deposited on both sides of the silicon wafer by using the PECVD apparatus.

[0046] 5) The sample was placed into a tubular annealing furnace for annealing under an annealing temperature of 800 to 920 C. for a time of 30 minutes.

[0047] Observation is made to the modified tunnel oxide layer of the p-type tunnel silicon oxide passivated structure. As shown in FIG. 1, the modified tunnel oxide layer has a thickness of 1.7 nm.

Embodiment 2

[0048] A double-sided p-type tunnel silicon oxide passivated structure is provided, and its preparation method includes the following steps.

[0049] 1) A silicon wafer was subjected to standard RCA cleaning.

[0050] 2) The silicon wafer was placed into an ozone generator to grow a SiO.sub.2 film.

[0051] 3) The sample was placed into a PECVD apparatus and continuous plasma treatment was performed with N.sub.2O and H.sub.2 as treatment atmosphere and the flow ratio of 2:1 for a time of 100 S under the power of 5 W.

[0052] 4) Next, a boron-doped amorphous silicon film was deposited on both sides of the silicon wafer by using the PECVD apparatus.

[0053] 5) The sample was placed into a tubular annealing furnace for annealing under an annealing temperature of 800 to 920 C. for a time of 30 minutes.

[0054] Observation is made to the modified tunnel oxide layer of the p-type tunnel silicon oxide passivated structure. As shown in FIG. 2, the modified tunnel oxide layer has a thickness of 1.6 nm.

Embodiment 3

[0055] A double-sided p-type tunnel silicon oxide passivated structure is provided, and its preparation method includes the following steps.

[0056] 1) A silicon wafer was subjected to standard RCA cleaning.

[0057] 2) The silicon wafer was placed into an ozone generator to grow a SiO.sub.2 film of about 1.5 nm.

[0058] 3) The sample was placed into a PECVD apparatus and continuous plasma treatment was performed with N.sub.2O and H.sub.2 as treatment atmosphere and the flow ratio of 8:1 for a time of 100 S under the power of 5 W.

[0059] 4) Next, a boron-doped amorphous silicon film was deposited on both sides of the silicon wafer by using the PECVD apparatus.

[0060] 5) The sample was placed into a tubular annealing furnace for annealing under an annealing temperature of 800 to 920 C. for a time of 30 minutes.

Embodiment 4

[0061] A double-sided p-type tunnel silicon oxide passivated structure is provided, and its preparation method includes the following steps.

[0062] 1) A silicon wafer was subjected to standard RCA cleaning.

[0063] 2) The silicon wafer was placed into an annealing furnace to receive low-temperature oxidation treatment under the oxidation temperatures of 200 C., 300 C. and 400 C. and grow a SiO.sub.2 film of about 1.5 nm.

[0064] 3) The sample was placed into a PECVD apparatus and continuous plasma treatment was performed with N.sub.2O and H.sub.2 as treatment atmosphere and the flow ratio of 2:1 for a time of 100 S under the power of 5 W.

[0065] 4) Next, a boron-doped amorphous silicon film was deposited on both sides of the silicon wafer by using the PECVD apparatus.

[0066] 5) The sample was placed into a tubular annealing furnace for annealing under an annealing temperature of 800 to 920 C. for a time of 30 minutes.

Embodiment 5

[0067] A double-sided p-type tunnel silicon oxide passivated structure is provided, and its preparation method includes the following steps.

[0068] 1) A silicon wafer was subjected to standard RCA cleaning.

[0069] 2) The silicon wafer was placed into nitric acid to grow a SiO.sub.2 film of about 1.5 nm.

[0070] 3) The sample was placed into a PECVD apparatus and pulsed plasma treatment was performed with N.sub.2O and H.sub.2 as treatment atmosphere and the flow ratio of 2:1 for a time of 10 sec under the power of 6 W. Then, the plasma was shut off and nitrogen gas was introduced to blow for 10 s. The above was one cycle. Then ten cycles were repeated continuously.

[0071] 4) Next, a boron-doped amorphous silicon film was deposited on both sides of the silicon wafer by using the PECVD apparatus.

[0072] 5) The sample was placed into a tubular annealing furnace for annealing under an annealing temperature of 800 to 920 C. for a time of 30 minutes.

Control Embodiment 1

[0073] A double-sided p-type tunnel silicon oxide passivated structure is provided, and its preparation method includes the following steps.

[0074] 1) A silicon wafer was cut into a size of 4 cm4 cm and subjected to standard RCA cleaning.

[0075] 2) The silicon wafer was placed into nitric acid to form a surface oxide layer.

[0076] 3) After the silicon wafer was cleaned and blown dry, a boron-doped amorphous silicon film was deposited on both sides of the silicon wafer by using the PECVD apparatus.

[0077] 4) The sample was placed into a tubular annealing furnace for annealing under an annealing temperature of 800 to 920 C. for a time of 30 minutes.

Control Embodiment 2

[0078] A double-sided p-type tunnel silicon oxide passivated structure is provided, and its preparation method includes the following steps.

[0079] 1) A silicon wafer was cut into a size of 4 cm4 cm and subjected to standard RCA cleaning.

[0080] 2) The silicon wafer was placed into a PECVD apparatus, and plasma treatment was performed on both sides with N.sub.2O as treatment atmosphere for a time of 100 S under the power of 10 W.

[0081] 3) Next, a boron-doped amorphous silicon film was deposited on both sides of the silicon wafer by using the PECVD apparatus.

[0082] 4) The sample was placed into a tubular annealing furnace for annealing under an annealing temperature of 800 to 920 C. for a time of 30 minutes.

[0083] The passivation performance and contact performance of the embodiments 1 to 5 are analyzed and tested, and the passivation performance of the control embodiments 1 and 2 is analyzed and tested. The test results are shown in Table 1 for comparison.

TABLE-US-00001 TABLE 1 passivation performances of the samples in the embodiments and control embodiments Control Control Annealing Passivation Embodiment Embodiment Embodiment Embodiment Embodiment embodiment embodiment temperature effect 1 2 3 4 5 1 2 800 C. iVoc 717 718 710 730 733 705 662 (mV) Contact 12 12 10 18 16 14 15 resistivity (mcm.sup.2) 860 C. iVoc (mV) 731 726 713 733 735 696 703 Contact 5 4 7 6 3 4 3 resistivity (mcm.sup.2) 920 C. iVoc (mV) 720 719 708 736 738 653 696 Contact 1 0.8 1.5 1.5 2 0.8 0.7 resistivity (m .Math. cm.sup.2)

[0084] From the data comparison, it can be known that the p-type tunnel silicon oxide passivated structure in the embodiments 1 to 5 have the modified tunnel oxide layer and has much better passivation performance than in the control embodiments 1 and 2. The back junction cells prepared by the process in the embodiment 1 have an efficiency of up to 23.17%.

[0085] Although the descriptions are made as above, the present disclosure is not limited hereto. Any persons skilled in the arts can make various modifications and variations without departing from the spirit and scope of the present disclosure. Therefore, the scope of protection of the present disclosure shall be defined by the appended claims.