阅读说明：本技术 超薄含氧氮硅薄膜的制备方法及其在钝化接触电池中的应用 (Preparation method of ultrathin oxygen-containing nitrogen-silicon film and application of ultrathin oxygen-containing nitrogen-silicon film in passivation of contact battery ) 是由 叶继春 曾俞衡 闫宝杰 郑晶茗 廖明墩 黄丹丹 于 2020-03-20 设计创作，主要内容包括：本发明公开了超薄含氧氮硅薄膜的制备方法,方法是1)将硅片表面清洗干净；2)在PECVD中,通入NH<Sub>3</Sub>或N<Sub>2</Sub>或其他含氮源但是不含氧源的气氛,并打开等离子体,解离通入的气氛,并使硅片表面氮化；通过调节温度、等离子体功率、压力、气体流量等参数调节表面氮的浓度和含氮层的深度；3)将表面已氮化的硅片进行氧化处理,从而形成氧氮硅层材料；4)接着,对表面氧氮硅层再进行一次PECVD表面氮化处理,形成氮氧氮硅层,氮氧氮硅层的厚度在5nm以下；5)在表面制备p型硅薄膜层。采用本发明的方法可使氮元素尽量富集于表面位置和近硅片界面位置,从而使氮氧氮硅界面材料层用于p型隧穿氧化硅钝化接触结构,可以减少硼对界面的破坏,提升钝化效果；该材料用于n型同样有效,可以减少磷对界面层的破坏。(The invention discloses a preparation method of an ultrathin oxygen-containing nitrogen-silicon film, which comprises the following steps of 1) cleaning the surface of a silicon wafer; 2) in PECVD, NH is introduced 3 Or N 2 Or other nitrogen-containing but oxygen-free atmosphere, and openedPlasma, dissociating the introduced atmosphere and nitriding the surface of the silicon wafer; adjusting the concentration of nitrogen on the surface and the depth of the nitrogen-containing layer by adjusting parameters such as temperature, plasma power, pressure, gas flow and the like; 3) carrying out oxidation treatment on the silicon wafer with the nitrided surface so as to form a silicon oxynitride layer material; 4) then, carrying out PECVD surface nitridation treatment on the surface oxynitride-silicon layer again to form an oxynitride-silicon layer, wherein the thickness of the oxynitride-silicon layer is less than 5 nm; 5) and preparing a p-type silicon film layer on the surface. By adopting the method, nitrogen elements can be enriched at the surface position and the position close to the silicon wafer interface as much as possible, so that the nitrogen-oxygen-silicon interface material layer is used for the p-type tunneling silicon oxide passivation contact structure, the damage of boron to the interface can be reduced, and the passivation effect is improved; the material is also effective for n-type, and can reduce the damage of phosphorus to the interface layer.)

1. The preparation method of the ultrathin nitrogen oxide nitrogen silicon film is characterized by comprising the following steps:

1) cleaning the surface of the silicon wafer; 2) in PECVD, NH is introduced₃Or N₂Or other atmosphere containing nitrogen source but no oxygen source, and opening the plasma to dissociate the introduced atmosphere and nitridize the surface of the silicon wafer; adjusting the concentration of nitrogen on the surface and the depth of the nitrogen-containing layer by adjusting the parameters of temperature, plasma power, pressure and gas flow; 3) carrying out oxidation treatment on the silicon wafer with the nitrided surface so as to form a silicon oxynitride layer material; 4) then, carrying out PECVD surface nitridation treatment on the surface oxynitride-silicon layer again to form an oxynitride-silicon layer, wherein the thickness of the oxynitride-silicon layer is less than 5 nm; 5) and preparing a p-type silicon film layer on the surface.

2. The method for preparing an ultrathin oxynitride-nitride-silicon thin film according to claim 1, wherein step 4) is omitted, and the oxynitride thin film is prepared in the steps of 1), 2), 3) and 5) in sequence, and has a thickness of 5nm or less; or omitting the step 2), and sequentially performing the steps 1), 3), 4) and 5) to prepare the oxynitride film with the thickness of less than 5 nm.

3. The method for preparing an ultra-thin SiON thin film as claimed in claim 1 or claim 2, wherein the oxidation treatment in step 3) comprises at least one of: the method comprises the steps of carrying out high-temperature thermal oxidation treatment by adopting oxygen or nitrogen/oxygen mixed gas or laughing gas, carrying out ozone oxidation by adopting laughing gas and carbon dioxide for plasma-assisted oxidation, and carrying out wet chemical oxidation by adopting hot nitric acid and hot nitric sulfuric acid mixed acid.

4. The method for preparing an ultra-thin SiON-Si film as claimed in claim 1 or 2, wherein the oxidation treatment in step 3) is carried out by high temperature thermal oxidation treatment using laughing gas as a shielding gas, and the annealing temperature is 400 ℃ to 900 ℃.

5. The method for preparing an ultra-thin SiON-Si film according to claim 1, wherein the thickness of the SiON-Si layer in step 4) is 1.5nm to 3.5 nm.

6. The method for preparing the ultrathin nitrogen oxygen nitrogen silicon film as claimed in claim 1 or 2, wherein the preparation method of the p-type polycrystalline silicon layer in the step 5) is that L PCVD method or PECVD method or different physical vapor deposition methods are used for directly preparing doped polycrystalline silicon or doped amorphous silicon layer, or intrinsic polycrystalline silicon or amorphous silicon is firstly deposited, and then the preparation of doped polycrystalline silicon is realized by combining high-temperature diffusion, ion implantation and high-temperature annealing, wherein the annealing temperature is required to be more than 800 ℃.

7. The method as claimed in claim 6, wherein the annealing temperature is 880-1100 ℃ in combination with the high temperature annealing.

8. Use of the preparation process according to claim 1 or 2 for the preparation of passivated contact structures in passivated contact cells.

Technical Field

The invention relates to a solar cell manufacturing technology, in particular to a preparation method of a passivation contact structure.

Background

The german freundhoff institute proposed in 2013 a crystalline silicon solar cell with a typical structure of an n-type cell as shown in fig. 1, which is called poly-Si passivated contact technology. The core of the structure is to passivate the surface of a silicon wafer by adopting an ultrathin silicon oxide layer and a doped polycrystalline silicon laminated structure.

The passivation mechanism of the tunneling silicon oxide passivation contact structure mainly comes from two aspects: the chemical passivation effect of the interface silicon oxide layer is the first one, and the field passivation effect of the doping atoms is the second one. Improving the integrity of the interface silicon oxide is beneficial to improving the chemical passivation effect of the surface.

For the tunneling silicon oxide passivation contact technology, an n-type phosphorus-doped polycrystalline silicon film is adopted for electron collection, and a p-type boron-doped polycrystalline silicon film is adopted for hole collection. The n-type passivation contact technology has good effect, so the method is widely accepted as the next-generation industrial high-efficiency crystalline silicon battery technology.

Currently, the bottleneck of Poly-Si passivation contact technology is mainly p-type. The technical index of the p-type passivation contact technology is poor, as shown in the tableThe passivation quality is now poor. In general, J_0s>20fA/cm²，iV_oc<680mV (n-type silicon wafer substrate). It is generally believed that the main reasons for the poor p-type passivation contact technology are two: firstly, the concentration of boron in the polycrystalline silicon is low, and secondly, the interface silicon oxide is easily damaged by the diffusion of boron.

In contrast, the n-type Poly-Si passivation contact technology has much more reliable quality, has high technical index and shows good passivation quality, and can easily realize single-side saturated dark current J on different equipment_0s<8fA/cm²Corresponding implicit open circuit voltage iV_oc>An excellent index of 730mV (n-type silicon wafer substrate); low simultaneous contact resistivity rho_c<10mΩcm². The mass production verification stage is started.

Therefore, improving the passivation quality of p-type Poly-Si passivation contact technology is an important issue that needs to be overcome currently. The passivation quality of the p-type Poly-Si passivation contact technology is improved, and the further development of the technology is promoted. Wherein, the improvement of the integrity of the interface silicon oxide is very beneficial to the improvement of the interface passivation effect.

Disclosure of Invention

Aiming at improving the integrity of interface silicon oxide in a p-type Poly-Si passivation contact structure, the invention provides an oxygen-nitrogen-silicon material for replacing silicon dioxide, and provides a preparation method capable of preparing the oxygen-nitrogen-silicon layer in situ, wherein the method is suitable for mass production type Plasma Enhanced Chemical Vapor Deposition (PECVD) equipment.

The technical scheme of the invention is to provide a preparation method of an ultrathin nitrogen-oxygen-nitrogen-silicon film, which comprises the following steps of 1) cleaning the surface of a silicon wafer; 2) in PECVD, ammonia (NH) gas is introduced₃) Or nitrogen (N)₂) Or other atmosphere containing nitrogen source but no oxygen source, opening the plasma, dissociating the introduced atmosphere, and nitriding the surface of the silicon wafer; the concentration of nitrogen on the surface and the depth of the nitrogen-containing layer can be adjusted by adjusting parameters such as temperature, plasma power, pressure, gas flow and the like; 3) carrying out oxidation treatment on the silicon wafer with the nitrided surface so as to form a silicon oxynitride layer material; 4) then, the surface silicon oxynitride layer is subjected to PECVD surface nitridation treatment again to form the silicon oxynitrideA layer, the silicon oxynitride layer having a thickness of 5nm or less; 5) and preparing a p-type silicon thin film layer (the silicon thin film layer can be amorphous silicon or polysilicon) on the surface.

On the other hand, according to the requirements of process procedures or device performance, the step 4) can be omitted, namely, the steps 1), 2), 3) and 5) are sequentially carried out, and the oxygen-nitrogen thin film is prepared and has the thickness of less than 5 nm; or omitting the step 2), namely sequentially performing the steps 1), 3), 4) and 5) to prepare the oxynitride film with the thickness of less than 5 nm.

Further, the oxidation treatment may be performed in various ways, including: high temperature thermal oxidation process (oxygen (O)₂) Nitrogen/oxygen (N)₂/O₂) Mixed gas, laughing gas (N)₂O)), ozone (O)₃) Oxidation, plasma-assisted oxidation (N)₂O、CO₂) Wet chemical oxidation (hot nitric acid, hot nitric sulfuric acid mixed acid), and the like.

Preferably, laughing gas (N) is used₂O) is used as protective gas to carry out high-temperature thermal oxidation treatment, and the annealing temperature is 400-900 ℃.

Further, the thickness of the nitrogen-oxygen-nitrogen-silicon layer in the step 4) is 1.5nm-3.5 nm;

further, the preparation method of the p-type polysilicon in the step 5) covers various conventional preparation methods, such as L PCVD method or PECVD method or various Physical Vapor Deposition (PVD) methods for directly preparing doped polysilicon or doped amorphous silicon layer and performing crystallization treatment, or depositing intrinsic polysilicon or amorphous silicon first and then preparing doped polysilicon by combining high temperature diffusion, ion implantation and high temperature annealing, wherein the annealing temperature needs to be above 800 ℃, and preferably is 880-1100 ℃.

The invention has the advantages and beneficial effects that: 1) the nitrogen-silicon interface material layer is used for a p-type tunneling silicon oxide passivation contact structure, so that the passivation effect can be improved; the material is also effective for n-type, and can reduce the damage of phosphorus to the interface layer. 2) The invention shall naturally cover the preparation method of the silicon oxynitride layer.

Drawings

Fig. 1 is a schematic diagram of a typical structure of a current n-type battery.

Detailed Description

The specific operation and principles of the present invention are further described below in conjunction with specific embodiments.

The invention provides a method for preparing an ultrathin oxygen-nitrogen-silicon film in situ, taking the preparation of a nitrogen-oxygen-nitrogen film as an example, the adoption of a nitrogen-oxygen-silicon interface material is beneficial to improving the passivation quality of p-type Poly-Si passivation contact, and the basic principle is as follows: 1) compared with silicon oxide, the silicon nitride oxide/silicon nitride/silicon; 2) the energy band structure of the nitrogen-oxygen-nitrogen silicon layer is close to that of silicon nitride, the valence band order of the nitrogen-oxygen-nitrogen silicon layer is small, hole transmission is facilitated, hole transmission efficiency and hole selectivity are improved, and passivation quality is improved; and simultaneously, the contact resistivity is also favorably reduced. Therefore, the silicon oxide is replaced by the silicon oxynitride, the damage effect of boron on the interface tunneling layer is inhibited, the integrity of the interface tunneling layer is improved, and compared with the conventional silicon oxide layer interface layer, the passivation quality is improved by adopting the p-type Poly-Si passivation contact technology of the silicon oxynitride interface layer; secondly, nitrogen, oxygen, nitrogen and silicon are used as an interface layer, so that the contact resistivity of the p-type Poly-Si passivation contact structure can be reduced; the silicon oxynitride is denser than silicon oxide, has higher thickness and can bear higher annealing treatment; finally, the nitrogen-oxygen-nitrogen-silicon material has reliable performance and simple preparation method, is suitable for in-situ preparation of PECVD equipment, has good industrial application prospect, is not only suitable for p-type Poly-Si passivation contact technology, but also can be used for n-type Poly-Si passivation contact technology.

In the preparation process, the key is to form the nitrogen oxide nitrogen silicon film material with the gradient distribution of components. The nitrogen-oxygen-nitrogen-silicon material comprises the following components in distribution: the nitrogen is mainly enriched at the interface between the near-surface layer and the near-silicon, and the concentration distribution of main elements of the film material shows a nitrogen-oxygen-nitrogen rule from the surface to the silicon substrate. Therefore, the invention firstly uses PECVD to carry out nitridation treatment on the surface of the silicon wafer; surface oxidation treatment is needed after surface nitridation to form silicon oxynitride; and finally, repeatedly carrying out surface nitridation treatment to form the nitrogen-oxygen-nitrogen silicon layer. The treatment has the advantage that nitrogen elements are enriched as much as possible at the surface position and the position close to the silicon wafer interface. Nitrogen is enriched at the two positions as much as possible, namely the nitrogen-oxygen-nitrogen-silicon film has the following composition characteristics: from nitrogen oxygen nitrogen silicon to silicon direction, the nitrogen concentration is in high-low-high distribution, namely the nitrogen impurity concentration near the silicon surface layer and the film surface is high, the middle is lower, the nitrogen content of the high concentration area is not less than 30 at%, and the nitrogen content of the low concentration area is not less than 8 at%; in addition, nitrogen permeates into one side of the nitrogen-oxygen-nitrogen film/silicon interface, the depth is usually not more than 5nm, the concentration is gradually reduced from the interface to the interior of the silicon wafer, and the concentration near the surface is not less than 1 at%, so that the barrier effect of the material on boron is favorably improved.

The substrates used in the following examples were all n-type single crystal silicon wafers 170 μm thick, both sides were chemically polished, the resistivity was 3 Ω · cm, and the passivation structure used was a double-sided p-type tunnel oxide passivation structure.