ULTRATHIN SILICON OXYNITRIDE INTERFACE MATERIAL, TUNNEL OXIDE PASSIVATED STRUCTURE AND PREPARATION METHODS AND APPLICATIONS THEREOF

Abstract

An ultrathin silicon oxynitride interface material, a tunnel oxide passivated structure and preparation methods and applications thereof are provided. The ultrathin silicon oxynitride interface material is an SiON film with a thickness of 1 nm to 4 nm, and the percentage content of N atoms is 1% to 40%. Compared with silicon oxide, the diffusion rate of boron in the SiON film of the present disclosure is low, which effectively reduces the damaging effect of boron, improves the integrity of the SiON film and maintains the chemical passivation effect. The SiON film with high nitrogen concentration can noticeably lower the concentration of boron on the silicon surface so as to lessen the boron-induced defects. Furthermore, the SiON film has an energy band structure approximate to silicon nitride, which increases the hole transport efficiency and hole selectivity, and further improves the passivation quality and reduces the contact resistivity.

Claims

1. An ultrathin silicon oxynitride interface material, wherein the ultrathin silicon oxynitride interface material is an SiON film with a thickness of 1 nm to 4 nm, and a percentage content of N atoms in the SiON film ranges from 1% to 40%.

2. A preparation method of the ultrathin silicon oxynitride interface material according to claim 1, comprising the following steps: step S1, growing a layer of an SiO.sub.2 film on a silicon wafer by an ion-free bombardment oxidation method; step S2, performing a surface nitriding treatment on the SiO.sub.2 film in a plasma enhanced chemical vapor deposition (PECVD) with a nitrogen-containing gas and an oxygen-containing gas filled treatment atmosphere to generate the SiON film.

3. The preparation method of the ultrathin silicon oxynitride interface material according to claim 2, wherein in the step S2, the nitrogen-containing gas is NH.sub.3, and the oxygen-containing gas is N.sub.2O.

4. The preparation method of the ultrathin silicon oxynitride interface material according to claim 2, wherein in the step 2, a flow ratio of the nitrogen-containing gas to the oxygen-containing gas ranges from 2:1 to 8:1.

5. The preparation method of the ultrathin silicon oxynitride interface material according to claim 2, wherein in the step S1, the ion-free bombardment oxidation method is an ozone oxidation method or a nitric acid oxidation method.

6. A tunnel oxide passivated structure, comprising a silicon wafer, a passivation tunneling layer, and a doped polycrystalline silicon layer, wherein a material of the passivation tunneling layer is the ultrathin silicon oxynitride interface material according to claim 1, and the passivation tunneling layer is located between the silicon wafer and the doped polycrystalline silicon layer.

7. The tunnel oxide passivated structure according to claim 6, wherein a material of the doped polycrystalline silicon layer is a boron-doped amorphous silicon film.

8. A preparation method of the tunnel oxide passivated structure according to claim 6, comprising the following steps: step S1, growing a layer of an SiO.sub.2 film on the silicon wafer by an ion-free bombardment oxidation method; step S2, performing a surface nitriding treatment on the SiO.sub.2 film in a PECVD method with a nitrogen-containing gas and an oxygen-containing gas filled treatment atmosphere to generate the SiON film; step S3, depositing a boron-doped amorphous silicon film on the SiON film by the PECVD method; step S4, performing an annealing treatment to obtain the tunnel oxide passivated structure.

9. The preparation method of the tunnel oxide passivated structure according to claim 8, wherein in the step S4, an annealing temperature ranges from 820 C. to 1100 C.

10. The tunnel oxide passivated structure according to claim 6, wherein the tunnel oxide passivated structure is applied to N-type or P-type tunnel oxide passivated contact solar cells.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0029] FIG. 1 is a structural diagram of a tunnel oxide passivated contact solar cell.

[0030] FIG. 2 is a micro-structure of an SiON film in embodiment 1.

DETAILED DESCRIPTIONS OF THE EMBODIMENTS

[0031] 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 further detailed below in combination with drawings. It should be noted that the embodiments below are used only to describe the implementation methods and typical parameters of the present disclosure rather than to limit the parameter scope of the present disclosure. Any reasonable changes derived herefrom can still fall within the scope of protection of the claims of the present disclosure.

[0032] It is noted that the endpoints and any values of the ranges disclosed herein are not limited to the accurate ranges or values. These ranges and values should be understood as including values approximate to these ranges and values. For numerical ranges, combination can be performed between endpoint values of each range, between an endpoint value and an individual point value of each range or between individual point values to obtain one or more new numerical ranges. These numerical ranges should be regarded as specifically disclosed herein.

[0033] An embodiment of the present disclosure provides a tunnel oxide passivated structure, which includes a silicon wafer, a passivation tunneling layer and a doped polycrystalline silicon layer, and a material of the passivation tunneling layer is an ultrathin SiON interface material, and the passivation tunneling layer is located between the silicon wafer and the doped polycrystalline silicon layer. The ultrathin SiON interface material is an SiON film with a thickness of 1 nm to 4 nm, and the percentage content of N atoms in the SiON film ranges from 1% to 40%.

[0034] The tunnel oxide passivated structure may be applied to N-type or P-type tunnel oxide passivated contact solar cells. When it is applied to the p-TOPCon, the material of the doped polycrystalline silicon layer is a boron-doped amorphous silicon film. The SiON interface material with high nitrogen content helps increase the passivation quality of the p-TOPCon based on the principle: 1) compared with silicon oxide, the diffusion rate of the boron in the SiON film is low, which effectively reduces the damaging effect of the boron on the SiON film, improves the integrity of the SiON film and maintains the chemical passivation effect; 2) the SiON film with high nitrogen concentration can noticeably lower the concentration of boron on the silicon surface so as to lessen the boron-induced defects; 3) the SiON film has an energy band structure approximate to silicon nitride and has a small valence band offset, which helps hole transport, increases the hole transport efficiency and hole selectivity, and further improves the passivation quality and reduces the contact resistivity. The iVoc of the P-type TOPCon can reach above 720 mV, with the contact resistivity less than 5 mcm.sup.2.

[0035] An embodiment of the present disclosure further provides a preparation method of the above tunnel oxide passivated structure, which includes the following steps: [0036] at step S1, growing a layer of SiO.sub.2 film on a silicon wafer by ion-free bombardment oxidation method; [0037] at step S2, performing surface nitriding treatment on the SiO.sub.2 film in the plasma enhanced chemical vapor deposition (PECVD) with a nitrogen-containing gas and an oxygen-containing gas filled treatment atmosphere to generate an SiON film; [0038] at step S3, depositing a boron-doped amorphous silicon film on the SiON film by PECVD method; [0039] at step S4, performing annealing treatment to obtain the tunnel oxide passivated structure.

[0040] In a specific embodiment of the present disclosure, in the step S1, the ion-free bombardment oxidation method is an ozone oxidation method or a nitric acid oxidation method, and preferably the ozone oxidation method; in the step S2, the nitrogen-containing gas is NH.sub.3 and the oxygen-containing gas is N.sub.2O; a flow ratio of the nitrogen-containing gas to the oxygen-containing gas ranges from 2:1 to 8:1; in the step S3, an annealing temperature ranges from 820 C. to 1100 C.

[0041] The present disclosure will be detailed below by way of specific embodiments. In the following embodiments and comparative embodiments, the silicon wafer is an N-type monocrystalline silicon wafer of 160 m, which is chemically polished on both sides, with the resistivity being 0.852 cm. The passivated structure adopted by the following embodiments and comparative embodiments is a double-sided p-type tunnel silicon oxide passivated structure.

Embodiment 1

[0042] In this embodiment, a tunnel oxide passivated structure is prepared, which includes the following steps: [0043] (1) a silicon wafer was cut into a size of 4 cm4 cm and subjected to standard RCA cleaning; [0044] (2) the silicon wafer was placed in an ozone generator to grow a layer of SiO.sub.2 film of about 1.5 nm; [0045] (3) a sample was placed into PECVD and treated in a treatment atmosphere of N.sub.2O and NH.sub.3 to generate an SiON film, and the flow ratio of N.sub.2O to NH.sub.3 was 4:1, the power was 5 W, the treatment time was 300 s; the thickness of the SiON film was 1.7 nm, with its microstructure shown in FIG. 2; [0046] (4) a boron-doped amorphous silicon film was respectively deposited on both sides of the silicon wafer by PECVD; [0047] (5) the sample was placed into a tubular annealing furnace for annealing of 30 min at an annealing temperature of 880 C. to 1000 C.

Embodiment 2

[0048] In this embodiment, a tunnel oxide passivated structure is prepared, which includes the following steps: [0049] (1) a silicon wafer was cut into a size of 4 cm4 cm and subjected to standard RCA cleaning; [0050] (2) the silicon wafer was placed in an ozone generator to grow a layer of SiO.sub.2 film of about 1.5 nm; [0051] (3) a sample was placed into PECVD and treated in a treatment atmosphere of N.sub.2O and NH.sub.3 to generate an SiON film, and the flow ratio of N.sub.2O to NH.sub.3 was 2:1, the power was 5 W, the treatment time was 300 s; [0052] (4) a boron-doped amorphous silicon film was respectively deposited on both sides of the silicon wafer by PECVD; [0053] (5) the sample was placed into a tubular annealing furnace for annealing of 30 min at an annealing temperature of 880 C. to 1000 C.

Embodiment 3

[0054] In this embodiment, a tunnel oxide passivated structure is prepared, which includes the following steps: [0055] (1) a silicon wafer was cut into a size of 4 cm4 cm and subjected to standard RCA cleaning; [0056] (2) the silicon wafer was placed in an ozone generator to grow a layer of SiO.sub.2 film of about 1.5 nm; [0057] (3) a sample was placed into PECVD and treated in a treatment atmosphere of N.sub.2O and NH.sub.3 to generate an SiON film, and the flow ratio of N.sub.2O to NH.sub.3 was 8:1, the power was 5 W, the treatment time was 300 s; [0058] (4) a boron-doped amorphous silicon film was respectively deposited on both sides of the silicon wafer by PECVD; [0059] (5) the sample was placed into a tubular annealing furnace for annealing of 30 min at an annealing temperature of 880 C. to 1000 C.

Comparative Embodiment 1

[0060] In this comparative embodiment, a tunnel oxide passivated structure is prepared, which includes the following steps: [0061] (1) a silicon wafer was cut into a size of 4 cm4 cm and subjected to standard RCA cleaning; [0062] (2) the silicon wafer was placed in nitric acid to form an SiO.sub.2 film; [0063] (3) after the silicon wafer is cleaned and dried, a boron-doped amorphous silicon film was deposited respectively on both sides of the silicon wafer by PECVD; [0064] (4) the sample was placed into a tubular annealing furnace for annealing of 30 min at an annealing temperature of 880 C. to 1000 C.

Comparative Embodiment 2

[0065] In this comparative embodiment, a tunnel oxide passivated structure is prepared, which includes the following steps: [0066] (1) a silicon wafer was cut into a size of 4 cm4 cm and subjected to standard RCA cleaning; [0067] (2) the silicon wafer was placed into PECVD and treated in a treatment atmosphere of N.sub.2O and NH.sub.3 to generate an SiON film, and the flow ratio of N.sub.2O to NH.sub.3 was 2:1, the power was 5 W, the treatment time was 300 s; [0068] (3) after the silicon wafer is cleaned and dried, a boron-doped amorphous silicon film was deposited respectively on both sides of the silicon wafer by PECVD; [0069] (4) the sample was placed into a tubular annealing furnace for annealing of 30 min at an annealing temperature of 880 C. to 1000 C.

[0070] By using the X-ray photoelectron spectroscopy, the composition of the passivation tunneling layer in the tunnel oxide passivated structure in the embodiment and comparative embodiment is analyzed, with an analysis result shown in Table 1 below:

TABLE-US-00001 TABLE 1 Contents of Si, O and N in the passivated tunneling layer Content Content Content percentage percentage percentage Composition of Si atoms of O atoms of N atoms Embodiment 1 50.74 43.59 5.67 Embodiment 2 50.68 38.94 10.38 Embodiment 3 49.67 47.59 2.74 Comparative 51.65 48.25 0.1 Embodiment 1 Comparative 50.31 48.93 0.76 Embodiment 2

[0071] The tunnel oxide passivated structure for testing passivation performance in the embodiments and comparative embodiments has the following passivation performance results shown in Table 2 below:

TABLE-US-00002 TABLE 2 Passivation performance of the tunnel oxide passivated structure Annealing Embodiment Embodiment Embodiment Comparative Comparative temperature 1 2 3 Embodiment 1 Embodiment 2 880 C. 717 mV 713 mV 710 mV 678 mV 612 mV 920 C. 720 mV 715 mV 713 mV 694 mV 664 mV 980 C. 726 mV 722 mV 708 mV 653 mV 698 mV 1000 C. 696 mV 687 mV 623 mV 612 mV 662 mV

[0072] From the test result, it can be known that the passivation performance of the tunnel oxide passivated structure prepared in the embodiments 1 to 3 is superior to those of the comparative embodiments 1 to 2. With the proper annealing temperature, the passivation effect of the embodiments 1 to 3 can enable the iVoc to be above 720 mV. The back contact cells prepared by the process of the embodiment 1 can have the efficiency of up to 22.04%.

[0073] Although the present disclosure is made as above, the present disclosure is not limited hereto. Any persons of skill in the arts can make various changes and modifications without departing from the spirit and scope of the present disclosure, and thus the scope of protection of the present disclosure shall be referred to the scope defined in the claims.