阅读说明：本技术 p型多晶硅薄膜制备方法及其在钝化接触太阳电池中的应用 (preparation method of p-type polycrystalline silicon thin film and application of p-type polycrystalline silicon thin film in passivation contact solar cell ) 是由 廖明墩 叶继春 曾俞衡 闫宝杰 智雨燕 黄丹丹 卢琳娜 郑晶茗 于 2020-03-20 设计创作，主要内容包括：本发明公开了p型多晶硅薄膜制备方法,主要是在硅片上依次制备氧化硅层-非晶硅或多晶硅层-金属铝层,形成多叠层结构薄膜,然后对根据工艺需要进行400-1100℃高温退火,使铝在硅薄膜层中形成激活的杂质。本发明首先利用金属铝作为插入层,将其沉积于硼掺杂非晶硅或本征多晶硅表面,然后利用退火处理使铝在沉积层中扩散,特别是当形成多层叠层结构时,铝处于非晶硅或多晶硅夹层中,能够使扩散更加均匀,形成较好的掺杂,提供空穴,可以显著增加薄膜的载流子浓度,减低薄膜方阻,降低钝化介质/多晶硅与硅片之间的接触电阻率；此外,部分铝还可以扩散进入硅片,从而增强硅衬底的电阻率。由于铝的激活温度低、扩散速率高,可以减低处理温度和处理时间,显著降低工艺时间,节省成本。(The invention discloses a preparation method of a p-type polycrystalline silicon film, which is mainly characterized by sequentially preparing a silicon oxide layer-amorphous silicon or a polycrystalline silicon layer-metal aluminum layer on a silicon wafer to form a multi-lamination structure film, and then carrying out high-temperature annealing at the temperature of 400-1100 ℃ according to the process requirements to enable aluminum to form activated impurities in the silicon film layer. The method comprises the steps of firstly utilizing metal aluminum as an insertion layer, depositing the metal aluminum on the surface of boron-doped amorphous silicon or intrinsic polycrystalline silicon, and then utilizing annealing treatment to diffuse the aluminum in the deposition layer, wherein particularly when a multilayer laminated structure is formed, the aluminum is positioned in an amorphous silicon or polycrystalline silicon interlayer, so that the diffusion is more uniform, better doping is formed, a hole is provided, the carrier concentration of a film can be obviously increased, the sheet resistance of the film is reduced, and the contact resistivity between a passivation medium/polycrystalline silicon and a silicon wafer is reduced; in addition, part of the aluminum can also diffuse into the silicon wafer, thereby enhancing the resistivity of the silicon substrate. Because the activation temperature of the aluminum is low and the diffusion rate is high, the treatment temperature and the treatment time can be reduced, the process time is obviously reduced, and the cost is saved.)

The preparation method of the p-type polycrystalline silicon film is characterized by comprising the following steps:

1) firstly, preparing a dielectric layer on a silicon wafer; 2) depositing a layer of boron-doped amorphous silicon or intrinsic polycrystalline silicon on the surface of the dielectric layer; 3) depositing a layer of metal aluminum on the surface of the boron-doped amorphous silicon or the intrinsic polycrystalline silicon by adopting a physical vapor phase method; 4) repeating the steps 2) and 3) according to requirements, namely repeatedly depositing boron-doped amorphous silicon or intrinsic amorphous silicon and depositing a metal aluminum layer by physical vapor deposition to form a multi-layer-structure film; 5) and (3) performing 400-1100 ℃ high-temperature annealing according to the process requirement, wherein the annealing time is 1-180min, so that the aluminum forms activated impurities in the silicon thin film layer.

2. The method according to claim 1, wherein the dielectric layer in step 1) is a silicon oxide layer, a silicon oxynitride layer, a silicon nitride layer or other silicide dielectric layer.

3. The method for preparing a p-type polycrystalline silicon thin film according to claim 1, wherein the method for depositing the boron-doped amorphous silicon or the intrinsic polycrystalline silicon in the step 2) adopts one of PECVD, L PCVD, APCVD, magnetron sputtering and electron beam evaporation.

4. The method for preparing the p-type polycrystalline silicon thin film according to claim 1, wherein the physical vapor phase method in the step 3) is one of thermal evaporation, magnetron sputtering and electron beam evaporation.

5. The method for preparing p-type polysilicon film according to claim 1, wherein the cumulative thickness of the deposited metallic aluminum layer in step 3) is less than 50 nm.

6. The method for preparing p-type polysilicon film according to claim 1, wherein the cumulative thickness of the deposited metal aluminum layer in step 3) is less than 10 nm.

7. The method for preparing a p-type polycrystalline silicon thin film according to claim 1, wherein the thin film having a laminated structure is formed in the step 4), and the number of laminated layers is 1 to 3.

8. The method for preparing a p-type polycrystalline silicon thin film according to claim 1, wherein the thin film having a laminated structure is formed in the step 4), and the number of laminated layers is 1-2.

9. The method of claim 1, wherein the thickness of the dielectric layer in step 1) is less than 5 nm.

10. The method of claim 1, wherein the thickness of the dielectric layer in step 1) is 1.4-2.4 nm.

11. The use of the p-type polycrystalline silicon thin film prepared by the preparation method according to claim 1 for passivating a contact structure.

Technical Field

The invention relates to preparation of solar cell components, in particular to preparation of a p-type polycrystalline silicon film.

Background

The german freundhoff institute proposed a crystalline silicon solar cell in 2013, the typical structure of which is shown in fig. 1, and which is often referred to as a tunnel silicon oxide passivated contact solar cell (TOPCon). 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 electron collection adopts an n-type phosphorus-doped polycrystalline silicon film, and the hole collection adopts a p-type boron-doped polycrystalline silicon film. Generally, the sheet resistance of an n-type TOPCon structure prepared by adopting an n-type phosphorus-doped polycrystalline silicon thin film with the thickness of more than 100nm can be reduced to be less than 60 omega/sq, and the requirement of battery preparation is met. On the contrary, the p-type TOPCon structure prepared by the p-type boron-doped polysilicon has large sheet resistance and cannot meet the requirement of preparing a high-efficiency battery. For example, even when the thickness of the boron-doped polysilicon is increased to 200nm, the overall sheet resistance is still higher than 300 Ω/sq, and the requirement for manufacturing a high-efficiency battery cannot be satisfied.

The problems of the boron-doped polysilicon and the p-type TOPCon structure thereof at present are mainly as follows:

the method comprises the steps of (1) as the boron activation concentration in boron-doped polycrystalline silicon is low and the hole mobility is low, the sheet resistance of a boron-doped p-type polycrystalline silicon film is obviously higher than that of a phosphorus-doped n-type polycrystalline silicon film, (2) as the boron concentration in the boron-doped polycrystalline silicon film is low and the contact resistivity of a p-type TOPCon structure and silicon is high even if the thickness of the boron-doped polycrystalline silicon is increased to 200nm, the requirement for preparing a high-efficiency battery cannot be met, (3) as the boron concentration in the boron-doped polycrystalline silicon film is low and the contact resistivity of the p-type TOPCon structure and silicon is high in a metallization sintering process, the contact performance of a metal electrode is poor, (4) as the boron concentration in the boron-doped polycrystalline silicon is low, the field passivation effect of the p-type TOPCon structure is reduced, (5) as the existing solar battery adopts a method for preparing intrinsic polycrystalline silicon with L PCVD and then preparing the boron-doped polycrystalline silicon film, the boron-doped polycrystalline silicon film has the problem that the preparation rate is very slow, the yield is at least 3, the yield is seriously influenced by adopting PCVD 2-3, and the subsequent high-diffusion process for preparing the polycrystalline silicon film is not less than 2).

Disclosure of Invention

In order to solve the technical problems, reduce the sheet resistance of the p-type boron-doped polycrystalline silicon and simultaneously reduce the overall sheet resistance of a p-type TOPCon structure, the invention provides a method for preparing a p-type aluminum-doped boron-doped polycrystalline silicon film, and the film can be used for the p-type TOPCon technology.

The technical scheme of the invention is to provide a preparation method of a p-type polycrystalline silicon film, which comprises the following steps:

1) firstly, preparing a dielectric layer on a silicon wafer; 2) depositing a layer of boron-doped amorphous silicon or intrinsic polycrystalline silicon on the surface of the dielectric layer; 3) depositing a layer of metal aluminum on the surface of the boron-doped amorphous silicon or the intrinsic polycrystalline silicon by adopting a physical vapor phase method; 4) repeating the steps 2) and 3) according to requirements, namely repeatedly depositing boron-doped amorphous silicon or intrinsic amorphous silicon and depositing a metal aluminum layer by physical vapor deposition to form a multi-layer-structure film; 5) and (3) performing 400-1100 ℃ high-temperature annealing according to the process requirement, wherein the annealing time is 1-180min, so that the aluminum forms activated impurities in the silicon thin film layer.

Further, the dielectric layer in step 1) is a silicon oxide layer, a silicon oxynitride layer, a silicon nitride layer or other silicide dielectric layers.

Further, the method for depositing the boron-doped amorphous silicon or the intrinsic polycrystalline silicon in the step 2) adopts one of PECVD, L PCVD, APCVD, magnetron sputtering and electron beam evaporation.

Further, the physical vapor phase method in step 3) may be one of thermal evaporation, magnetron sputtering and electron beam evaporation.

Further, the accumulated thickness of the deposited metal aluminum layer in the step 3) is less than 50 nm.

Preferably, the cumulative thickness of the layer of metallic aluminum deposited in step 3) is less than 10 nm.

Further, the film having a 1-3-layer structure may be formed in the step 4), preferably 1-2 layers.

Further, the thickness of the dielectric layer in step 1) is less than 5nm, preferably 1.4-2.0nm, and when the thickness of the dielectric layer is greater than 2.4nm, the filling factor of the device is affected, and in order to enable electrons to tunnel through the dielectric layer serving as the passivation tunneling layer, the dielectric layer needs to be made very thin, and is usually controlled to be less than 2.4 nm.

The invention has the advantages and beneficial effects that:

according to the invention, firstly, metal aluminum is used as an insertion layer and is deposited on the surface of boron-doped amorphous silicon or intrinsic polycrystalline silicon, then, the aluminum is diffused in the deposition layer by annealing treatment, and particularly, when a multilayer laminated structure is formed, the aluminum is positioned in an amorphous silicon or polycrystalline silicon interlayer, so that the diffusion is more uniform, better doping is formed, a hole is provided, the carrier concentration of a film can be obviously increased, and the sheet resistance of the film is reduced; in addition, part of the aluminum can also diffuse into the silicon wafer, thereby enhancing the resistivity of the silicon substrate. Because the activation temperature of the aluminum is low and the diffusion rate is high, the treatment temperature and the treatment time can be reduced, the process time is obviously reduced, and the cost is saved.

Drawings

Fig. 1 is a schematic structural diagram of an n-type TOPCon silicon solar cell.

Fig. 2 is a schematic structural diagram of the p-type polysilicon thin film structure of the present invention before (a) and after (b) annealing.

FIG. 3 is a graph showing the results of the ECV analysis in example 1 of the present invention.

Detailed Description

The present invention will be further described with reference to the following embodiments.

The invention aims to solve the technical problems of reducing the sheet resistance of the p-type boron-doped polycrystalline silicon and reducing the overall sheet resistance of the p-type TOPCon structure, and the method for preparing the p-type boron-doped polycrystalline silicon film can obviously reduce the sheet resistance of the film, reduce the contact resistance rate and meet the requirement of low sheet resistance on the back of a battery. The underlying physical principle behind this is: under high-temperature annealing, aluminum in the amorphous silicon interlayer can diffuse to form doping atoms to provide holes, so that the carrier concentration of the film can be obviously increased, and the sheet resistance of the film is reduced; meanwhile, aluminum-silicon alloy or metal aluminum particles in the polycrystalline silicon film are beneficial to enhancing the resistivity of the film; because the diffusion rate of the aluminum is fast, the temperature for forming the aluminum-silicon alloy is low, better doping can be formed by annealing treatment at low temperature, and the annealing temperature is reduced; meanwhile, the diffusion rate of the aluminum is high, and part of the aluminum can also diffuse into the silicon wafer, so that the resistivity of the silicon substrate is enhanced; because the activation temperature of the aluminum is low and the diffusion rate is high, the treatment temperature and the treatment time can be reduced, the process time is obviously reduced, and the cost is saved. In addition, the thickness of the aluminum insertion layer prepared by the invention is low, generally less than 10nm, and after high-temperature treatment, aluminum can be diffused and doped in the polycrystalline silicon film, and the shape of the metal layer can not be maintained, so that the optical property of the film can not be influenced. Meanwhile, aluminum in the polycrystalline silicon film is distributed in silicon as a doping agent, and obvious aluminum crystal phase separation and silicon crystal phase separation are avoided, so that the method is obviously different from aluminum-induced crystallization of polycrystalline silicon. The concentration distribution of aluminum is reduced from the position of the aluminum layer to the surfaces of the silicon wafer and the polycrystalline silicon film in sequence, and the highest activation concentration on the surface of the silicon wafer is not more than 5 x 10¹⁹cm^-3Common activation concentrations are 1-3 x 10¹⁹cm^-3(ii) a The diffusion depth of aluminum in silicon is not more than 1 micron, the typical diffusion depth is 50-200nm, the activation concentration and the diffusion depth of aluminum have important influence on the performance of the final p-type polycrystalline silicon film, the aluminum is quickly activated at the annealing process temperature of the invention, the aluminum in the amorphous silicon interlayer diffuses to form doping atoms distributed in the silicon and provide holesThe carrier concentration of the film can be obviously increased, and the sheet resistance of the film is reduced; however, too high a temperature or too long a time may cause a decrease in the field passivation effect due to a decrease in the fixed negative charge density in the passivation film, and may also cause a deterioration in the overall passivation effect. Therefore, the activation concentration and the diffusion concentration of the aluminum are regulated and controlled to reach the optimal level of the material by reasonably controlling the temperature and the time.

In conclusion, the method can obviously reduce the sheet resistance of the p-type silicon film and the p-type TOPCon structure thereof, and meanwhile, the p-type polycrystalline silicon film still has good light transmittance, thereby meeting the requirement of battery preparation. It should be noted that the invention adopts different principles and prepares different structures to solve different technical problems compared with the conventional aluminum-induced preparation of the polycrystalline silicon thin film. The conventional aluminum-induced crystallization amorphous silicon film can reduce the activation energy of silicon crystallization by means of Al element so as to crystallize the amorphous silicon film at a lower temperature, and Al and Si can form a eutectic when the aluminum-induced crystallization is carried out. Al, like a catalyst in crystallization, can weaken the strength of Si — Si bonds and promote nucleation of Si. Since the chemical potential of each atom in amorphous silicon is higher than that of crystalline silicon, the phenomenon that Si atoms are supersaturated in an Al layer occurs, and when the saturation concentration on an Al/Si phase diagram is exceeded, crystal nuclei are precipitated and crystal grains are grown.

Based on the principle, the invention firstly prepares a p-type precursor film, and the basic structure of the precursor film is as follows: silicon thin film (a)/aluminum (B)/silicon thin film (a), i.e., ABA structure. Any combination of ABABAB … structures may be used as required.

The preparation methods of the silicon film and the aluminum film comprise various corresponding film preparation methods, such as different methods of PECVD, L PCVD, APCVD, magnetron sputtering, electron beam evaporation and the like, wherein the PECVD method is preferably adopted to deposit the boron-doped amorphous silicon or the intrinsic polysilicon, so that the problems of long time consumption, poor film deposition uniformity and the like in the silicon film preparation process can be avoided.

The cumulative thickness of the single or multiple aluminum films is typically less than 10nm, and may be increased to 20nm, typically not more than 50nm, as desired.

The novel p-type polycrystalline silicon thin film structure prepared by the invention is mainly used for a passivation contact structure and is applied to a silicon solar cell. The basic structure is 'novel p-type polycrystalline silicon film/dielectric layer/crystalline silicon substrate', it is noted that polycrystalline silicon must be used together with a dielectric layer, which is a silicon oxide layer, a silicon oxynitride layer or a silicon nitride layer, and the effect is poor when the polycrystalline silicon is used alone. The thickness of the dielectric layer is less than 5nm, the preferable thickness is usually 1.4-2.4nm, and when the thickness is preferable, the influence of the thickness of the dielectric layer on the filling factor of the device can be better avoided, so that electrons can tunnel through the dielectric layer serving as a passivation tunneling layer.