技术领域technical field
本发明涉及太阳能电池的制造方法，特别涉及光电变换效率的提高。The present invention relates to a method of manufacturing a solar cell, and in particular to improvement of photoelectric conversion efficiency.
背景技术Background technique
以往，在太阳能电池中，作为一个例子，如专利文献1所示公开了一种方法，在该方法中，作为向作为光入射面的受光面、或者作为与受光面相向的面的背面的杂质扩散方法而使用CVD(Chemical Vapor Deposition，化学气相沉积)法等，使扩散源成膜之后，在氮气环境中对基板和成为扩散源的膜进行加热，使杂质向基板内扩散。Conventionally, in solar cells, as an example, as shown in Patent Document 1, a method is disclosed, in which the impurity The diffusion method uses CVD (Chemical Vapor Deposition, chemical vapor deposition) method, etc., after forming a diffusion source film, the substrate and the diffusion source film are heated in a nitrogen atmosphere to diffuse impurities into the substrate.
现有技术文献prior art literature
专利文献patent documents
专利文献1：日本特开2004-247364号公报Patent Document 1: Japanese Patent Laid-Open No. 2004-247364
发明内容Contents of the invention
然而，在上述专利文献1所述的太阳能电池的制造方法中，在基板上形成磷硅酸盐玻璃(PSG：Phosphorus Silicate Glass)膜、或者硼硅酸盐玻璃(BSG：Boron SilicateGlass)膜之后，在氮气环境中进行用于杂质扩散的热处理。因此，在成膜时，磷或者硼等杂质蔓延到基板背面，从附着的生成物还同时产生向背面的杂质扩散，所以有时发生意想之外的向背面的杂质混入。杂质的混入导致太阳能电池的载流子寿命降低。另外，存在上述成膜物由于膜厚厚等理由而难以加工、再加上上述杂质的混入而易于成为电气的短路的原因的问题。However, in the solar cell manufacturing method described in Patent Document 1 above, after forming a phospho-silicate glass (PSG: Phosphorus Silicate Glass) film or a boron silicate glass (BSG: Boron Silicate Glass) film on a substrate, Heat treatment for impurity diffusion is performed in a nitrogen atmosphere. Therefore, during film formation, impurities such as phosphorus and boron spread to the back surface of the substrate, and impurities diffuse to the back surface from the adhered products at the same time, so that unexpected impurities may be mixed into the back surface. The incorporation of impurities leads to a decrease in the carrier lifetime of the solar cell. In addition, there is a problem that the above-mentioned film-formed product is difficult to process due to reasons such as a thick film, and the contamination of the above-mentioned impurities tends to cause an electrical short circuit.
本发明是鉴于上述完成的，其目的在于在使固相扩散源成膜之后接着通过热处理进行杂质扩散时，抑制杂质混入到背面，并且排除成膜物所致的加工阻碍，改善电气性绝缘，得到载流子寿命长的太阳能电池。The present invention is accomplished in view of the above, and its object is to prevent impurities from being mixed into the back surface when the impurity is diffused by heat treatment after forming a solid-phase diffusion source into a film, and to improve electrical insulation by eliminating the processing hindrance caused by the film-formed product. A solar cell with a long carrier lifetime is obtained.
本发明为了解决上述课题并达成目的，提供一种太阳能电池的制造方法，其特征在于，包括：使固相扩散源成膜于具有相对置的第1主面和第2主面的第1导电类型的半导体基板的第1主面的工序；去除在成膜的工序中形成于第2主面的生成物的工序；对被去除生成物的半导体基板进行加热，从固相扩散源在第1主面侧形成第2导电类型的第1扩散层的工序；在半导体基板的第2主面形成具有第1导电类型的第2扩散层的工序；去除固相扩散源的工序；以及将第2扩散层和第1扩散层电气地分离的工序。在将第2扩散层和第1扩散层电气地分离的工序之前实施去除固相扩散源的工序。In order to solve the above-mentioned problems and achieve the purpose, the present invention provides a method of manufacturing a solar cell, which is characterized in that it includes: forming a solid phase diffusion source on a first conductive surface having opposing first and second main surfaces. The process of the first main surface of the type semiconductor substrate; the process of removing the product formed on the second main surface in the process of film formation; heating the semiconductor substrate from which the product is removed, from the solid phase diffusion source in the first The process of forming the first diffusion layer of the second conductivity type on the main surface side; the process of forming the second diffusion layer having the first conductivity type on the second main surface of the semiconductor substrate; the process of removing the solid phase diffusion source; The process of electrically separating the diffusion layer from the first diffusion layer. Before the step of electrically separating the second diffusion layer and the first diffusion layer, the step of removing the solid phase diffusion source is performed.
根据本发明，起到如下效果：在使固相扩散源成膜之后接着通过热处理进行杂质扩散时，抑制杂质混入到作为背面的第2主面，并且排除成膜物所致的加工阻碍，改善电气性绝缘，能够得到载流子寿命长的太阳能电池。According to the present invention, there is an effect that when impurity diffusion is performed by heat treatment after the solid-phase diffusion source is formed into a film, impurities are suppressed from being mixed into the second main surface as the back surface, and processing hindrance caused by film-formed substances is eliminated, improving It is electrically insulating, and a solar cell with a long carrier life can be obtained.
附图说明Description of drawings
图1是示出实施方式1的太阳能电池的制造方法的流程图。FIG. 1 is a flowchart illustrating a method of manufacturing a solar cell according to Embodiment 1. As shown in FIG.
图2(a)至(d)是示出实施方式1的太阳能电池的制造方法的工序剖面图。2( a ) to ( d ) are process cross-sectional views showing the method of manufacturing the solar cell according to the first embodiment.
图3(a)至(d)是示出实施方式1的太阳能电池的制造方法的工序剖面图。3( a ) to ( d ) are process cross-sectional views showing the method of manufacturing the solar cell according to the first embodiment.
图4是示出实施方式1的太阳能电池的制造工序中的热处理工序的关于炉内温度和环境状态的时序图的说明图。FIG. 4 is an explanatory diagram showing a time chart of the temperature in the furnace and the environmental state in the heat treatment process in the solar cell manufacturing process according to Embodiment 1. FIG.
图5是示出实施方式1的太阳能电池的制造工序的主要部分的说明图。FIG. 5 is an explanatory view showing main parts of the manufacturing process of the solar cell according to Embodiment 1. FIG.
图6是示出实施方式2的太阳能电池的制造方法的流程图。FIG. 6 is a flowchart illustrating a method of manufacturing a solar cell according to Embodiment 2. FIG.
图7是示出实施方式2的太阳能电池的制造工序的主要部分的工序剖面图。7 is a process sectional view showing main parts of the manufacturing process of the solar cell according to Embodiment 2. FIG.
图8是示出实施方式3的太阳能电池的制造方法的流程图。FIG. 8 is a flowchart illustrating a method of manufacturing a solar cell according to Embodiment 3. FIG.
图9是示出实施方式3的太阳能电池的制造工序的主要部分的工序剖面图。9 is a process sectional view showing main parts of the manufacturing process of the solar cell according to Embodiment 3. FIG.
(符号说明)(Symbol Description)
1：n型单晶硅基板；1A：受光面；1B：背面；2：BSG膜；3：硅氧化膜；4：含硼的生成物；5：含氧化硅的生成物；7：p型扩散层；8：硅氧化膜；14：n型扩散层；15a：受光面反射防止膜；15b：背面绝缘膜；16：电极；16a：受光面电极；16b：背面电极；17：扩散源；18：n型扩散层；20：低浓度的n型扩散层。1: n-type monocrystalline silicon substrate; 1A: light-receiving surface; 1B: back surface; 2: BSG film; 3: silicon oxide film; 4: product containing boron; 5: product containing silicon oxide; 7: p-type Diffusion layer; 8: silicon oxide film; 14: n-type diffusion layer; 15a: anti-reflection film on light-receiving surface; 15b: back insulating film; 16: electrode; 16a: light-receiving surface electrode; 16b: back electrode; 17: diffusion source; 18: n-type diffusion layer; 20: low-concentration n-type diffusion layer.
具体实施方式Detailed ways
以下，根据附图详细地说明本发明的太阳能电池的制造方法以及太阳能电池的实施方式。此外，本发明不限定于该实施方式，能够在不脱离其要旨的范围内适宜地变更。另外，在以下所示的附图中，为了易于理解，各层或者各部件的比例尺有时与现实不同，在各附图之间也是同样的。Hereinafter, embodiments of the method for manufacturing a solar cell and the solar cell of the present invention will be described in detail with reference to the drawings. In addition, this invention is not limited to this embodiment, It can change suitably in the range which does not deviate from the summary. In addition, in the drawings shown below, the scale of each layer or each member may be different from the actual scale for easy understanding, and the same is true between the drawings.
实施方式1.Implementation mode 1.
图1是示出本发明的太阳能电池的制造方法的实施方式1的制造工序的流程图，图2(a)至(d)以及图3(a)至(d)是示出实施方式1的太阳能电池的制造方法的工序剖面图。图2(a)至(d)是示出实施方式1的太阳能电池的制造方法中的、在图1中所示的炉内的连续处理中的太阳能电池基板变化的剖面图。图3(a)至(d)是示出实施方式1的制造工序中的、接着图2(a)至(d)所示的热处理的工序中的太阳能电池的剖面变化的示意图。图4是关于炉内的温度和环境状态的时序图。FIG. 1 is a flow chart showing the manufacturing steps of Embodiment 1 of the method for manufacturing a solar cell according to the present invention, and FIGS. 2(a) to (d) and FIGS. A cross-sectional view of a process of a solar cell manufacturing method. 2( a ) to ( d ) are cross-sectional views showing changes in solar cell substrates during continuous processing in the furnace shown in FIG. 1 in the solar cell manufacturing method according to Embodiment 1. FIG. 3( a ) to ( d ) are schematic diagrams showing cross-sectional changes of the solar cell in the manufacturing process of Embodiment 1 following the heat treatment shown in FIGS. 2( a ) to ( d ). Fig. 4 is a timing chart regarding the temperature and environmental state in the furnace.
在实施方式1的太阳能电池的制造方法中，在将第1扩散层和第2扩散层电气地分离的pn分离工序之前，使固相扩散源成膜并加热来形成第1扩散层，去除固相扩散源。进而，在用于形成第1扩散层的热处理工序之前，去除被成膜在第2主面的固相扩散源。In the solar cell manufacturing method of Embodiment 1, before the pn separation step of electrically separating the first diffusion layer and the second diffusion layer, the solid phase diffusion source is formed into a film and heated to form the first diffusion layer, and the solid phase diffusion source is removed. source of phase diffusion. Furthermore, before the heat treatment step for forming the first diffusion layer, the solid phase diffusion source formed on the second main surface is removed.
在实施方式1的太阳能电池的制造方法中，在使固相扩散源成膜以及进行加热来形成扩散层之后，去除固相扩散源，进行电气分离，所以进行加工后的部位的绝缘性能提高。进而另外，在通过加热工序从固相扩散源进行杂质扩散的工序之前，包括去除被成膜在第2主面的固相扩散源的工序，所以虽然固相扩散材料蔓延附着到半导体基板的与使固相扩散源成膜的面相反一侧的面，但通过在去除固相扩散源后进行热处理，避免来自附着物的杂质扩散到基板。In the method of manufacturing a solar cell according to Embodiment 1, after the solid phase diffusion source is formed into a film and heated to form a diffusion layer, the solid phase diffusion source is removed and electrical isolation is performed, so the insulating performance of the processed portion is improved. Furthermore, before the step of impurity diffusion from the solid-phase diffusion source by the heating step, the step of removing the solid-phase diffusion source film-formed on the second main surface is included, so although the solid-phase diffusion material spreads and adheres to the semiconductor substrate and The surface opposite to the surface on which the solid-phase diffusion source is formed into a film, but heat treatment is performed after the solid-phase diffusion source is removed, prevents impurities from attached matter from diffusing to the substrate.
在实施方式1的太阳能电池中，使用n型单晶硅基板1作为具有成为受光面1A的第1主面和成为背面1B的第2主面的第1导电类型的半导体基板。使用图1、图2(a)至(d)、图3(a)至(d)以及图4来说明制造方法。首先，在损伤层去除步骤S101中，去除在表面的晶片切片时产生的污染或者损伤。将n型单晶硅基板1浸渍到例如溶解了大于等于1wt％且小于10wt％的氢氧化钠而得到的碱性溶液，进行切片污染以及损伤去除。之后，对于n型单晶硅基板1的受光面1A，浸渍到例如将异丙醇或者辛酸等添加剂添加到大于等于0.1wt％且小于10wt％的碱性溶液而得到的溶液从而形成作为用于得到反射防止构造的凹凸的纹理。此外，切片污染以及损伤的去除、和纹理的形成既可以同时进行或者也可以单独地进行。关于纹理的形成，不仅形成于受光面1A而且也可以还形成于背面1B。在图2以及图3中，为了易于理解，未图示出纹理，与受光面1A、背面1B一起表示为平坦面。In the solar cell according to Embodiment 1, n-type single crystal silicon substrate 1 is used as a semiconductor substrate of the first conductivity type having a first main surface serving as light receiving surface 1A and a second main surface serving as rear surface 1B. The manufacturing method will be described using FIG. 1 , FIGS. 2( a ) to ( d ), FIGS. 3 ( a ) to ( d ), and FIG. 4 . First, in the damaged layer removal step S101, contamination or damage generated during wafer slicing on the surface is removed. The n-type single crystal silicon substrate 1 is immersed in an alkaline solution in which, for example, 1 wt % to less than 10 wt % of sodium hydroxide is dissolved to remove chip contamination and damage. After that, for the light-receiving surface 1A of the n-type single crystal silicon substrate 1, for example, a solution obtained by adding additives such as isopropanol or octanoic acid to an alkaline solution of 0.1 wt% or more and less than 10 wt% is formed to form a I get the uneven texture of the anti-reflection structure. In addition, removal of contamination and damage of the slice, and formation of texture may be performed simultaneously or independently. The texture may be formed not only on the light receiving surface 1A but also on the back surface 1B. In FIGS. 2 and 3 , the texture is not shown for easy understanding, and the light-receiving surface 1A and the back surface 1B are shown as flat surfaces.
接下来，在成膜前清洗步骤S102中，对n型单晶硅基板1的表面进行清洗。在该清洗工序中，例如使用被称为RCA清洗的、组合硫酸和过氧化氢的混合溶液、氢氟酸水溶液、氨和过氧化氢的混合溶液、盐酸和过氧化氢的混合溶液的去除有机物、金属、以及氧化膜的工序，或者，例如根据纹理形成方法而仅采用氢氟酸水溶液的氧化膜去除工序。另外，关于清洗液，也可以从包含如下内容的溶液来选择：清洗液的种类内的一种或者多种、或者、氢氟酸和过氧化氢水的混合溶液、或者含有臭氧的水。Next, in the cleaning step S102 before film formation, the surface of the n-type single crystal silicon substrate 1 is cleaned. In this cleaning process, for example, the removal of organic substances using a mixed solution of sulfuric acid and hydrogen peroxide, an aqueous solution of hydrofluoric acid, a mixed solution of ammonia and hydrogen peroxide, or a mixed solution of hydrochloric acid and hydrogen peroxide, which is called RCA cleaning , metal, and oxide film, or, for example, an oxide film removal process using only hydrofluoric acid aqueous solution depending on the texture forming method. In addition, the cleaning solution can also be selected from solutions containing one or more types of cleaning solutions, or a mixed solution of hydrofluoric acid and hydrogen peroxide water, or water containing ozone.
此外，为了防止各个处理液自身对其他造成污染、或者成为意想之外的反应的原因、并且为了确保取出到装置外后的安全，在各个工序之间或者干燥前的阶段等中，利用纯水等进行水洗。In addition, in order to prevent each treatment liquid itself from contaminating others or causing an unexpected reaction, and to ensure safety after taking it out of the device, pure water is used between each process or in the stage before drying. Wait for washing.
接着上述清洗工序，在固相扩散源向受光面1A侧成膜的成膜步骤S103中，如图2(a)所示，使固相扩散源向n型单晶硅基板1的受光面1A成膜、例如形成作为含有硼的氧化膜的BSG(Boron Silicate Glass：硼硅酸盐玻璃)膜2。在进行成膜时，使用例如减压CVD、常压CVD。此外，在上述成膜工序时，由于成膜气体的蔓延，含硼的生成物4附着到n型单晶硅基板1的背面1B。接着，在BSG膜2的上部形成在热处理时成为罩即保护膜的膜、例如硅氧化膜3。从工序的连续性角度来看，优选与BSG膜2同样地利用减压CVD、常压CVD等成膜工序形成硅氧化膜3。在形成硅氧化膜3时，也与形成BSG膜2时同样地，成膜气体蔓延到背面1B而附着含氧化硅的生成物5。Following the above-mentioned cleaning process, in the film forming step S103 in which the solid-phase diffusion source is formed on the light-receiving surface 1A side, as shown in FIG. For film formation, for example, a BSG (Boron Silicate Glass: borosilicate glass) film 2 which is an oxide film containing boron is formed. For film formation, for example, reduced-pressure CVD and normal-pressure CVD are used. In addition, during the above-mentioned film forming process, boron-containing product 4 adheres to rear surface 1B of n-type single crystal silicon substrate 1 due to diffusion of film forming gas. Next, a film serving as a cover or protective film during heat treatment, for example, a silicon oxide film 3 is formed on the upper portion of the BSG film 2 . From the viewpoint of process continuity, it is preferable to form the silicon oxide film 3 by a film-forming process such as reduced-pressure CVD or normal-pressure CVD similarly to the BSG film 2 . When forming the silicon oxide film 3 , as in the case of forming the BSG film 2 , the film forming gas spreads to the rear surface 1B, and the product 5 containing silicon oxide adheres thereto.
在背面的生成物去除步骤S104中，如图2(b)所示，去除被形成在背面1B侧的生成物。在此，去除被形成在n型单晶硅基板1的背面1B侧的生成物。即，在形成BSG膜2和硅氧化膜3之后，去除背面1B侧的含硼的生成物4以及含氧化硅的生成物5。通过例如使用氟酸水溶液的溶解进行去除，但由于含硼的生成物4是与BSG膜2本质上同样的物质，含氧化硅的生成物5是与硅氧化膜3本质上同样的物质，所以最好使用例如单面蚀刻装置，仅使背面1B侧接触到氟酸水溶液来去除含硼的生成物4以及含氧化硅的生成物5。作为单面蚀刻装置的一个例子，能够通过使用使蚀刻面朝下并从下侧喷吹蚀刻液的装置、或者、具有仅将单面浸渍到蚀刻液的构造的蚀刻装置等从而实现单面蚀刻。In the rear surface product removal step S104, as shown in FIG. 2(b), the product formed on the rear surface 1B side is removed. Here, the product formed on the rear surface 1B side of the n-type single crystal silicon substrate 1 is removed. That is, after the BSG film 2 and the silicon oxide film 3 are formed, the boron-containing product 4 and the silicon oxide-containing product 5 on the rear surface 1B side are removed. For example, the removal is carried out by dissolution using an aqueous hydrofluoric acid solution, but since the boron-containing product 4 is substantially the same substance as the BSG film 2, and the silicon oxide-containing product 5 is substantially the same substance as the silicon oxide film 3, It is preferable to remove the boron-containing product 4 and the silicon oxide-containing product 5 by exposing only the rear surface 1B side to the hydrofluoric acid aqueous solution using, for example, a single-side etching device. As an example of a single-sided etching device, one-sided etching can be realized by using a device that makes the etching surface face down and sprays the etching solution from the lower side, or an etching device that has a structure in which only one side is immersed in the etching solution. .
接下来，在进行热处理的步骤S105中，对n型单晶硅基板1连续地实施加热处理。该加热处理使用热处理炉。首先，使热处理炉预热，如图2(c)所示，为了形成扩散层，在惰性气体环境下进行热处理。通过热处理，硼从BSG膜2扩散，形成p型扩散层7。Next, in step S105 of performing heat treatment, heat treatment is continuously performed on n-type single crystal silicon substrate 1 . For this heat treatment, a heat treatment furnace is used. First, the heat treatment furnace is preheated, and heat treatment is performed in an inert gas atmosphere in order to form a diffusion layer as shown in FIG. 2( c ). By heat treatment, boron diffuses from BSG film 2 to form p-type diffusion layer 7 .
在接下来连续地在包含氧O2的气体环境下进行热处理的步骤中，一边供给氧O2一边进行热处理。在该热处理中，一边切换温度和成膜气体环境，一边进行升温、加热、降温。加热过程中的气体环境被分成例如包含氮、氩等惰性气体的气体环境、和包含氧的气体环境中。虽然都在从800℃至1100℃的温度段加热任意的时间，但在包含氧的气体环境下，实施1分钟至20分钟以下的时间的加热。In the subsequent step of continuously performing heat treatment in an atmosphere containing oxygen O2 , the heat treatment is performed while supplying oxygen O2 . In this heat treatment, temperature rise, heating, and temperature drop are performed while switching the temperature and film-forming gas atmosphere. The gas atmosphere during heating is divided into, for example, a gas atmosphere containing an inert gas such as nitrogen or argon, and a gas atmosphere containing oxygen. In all cases, the heating is carried out for an arbitrary time in the temperature range from 800° C. to 1100° C., but the heating is performed for 1 minute to 20 minutes or less in an oxygen-containing gas atmosphere.
首先，在例如包含氮、氩等惰性气体的气体环境下，使得达到如从BSG膜2进行杂质扩散的温度T、例如800℃至1100℃，形成期望的p型扩散层7。在p型扩散层7的形成结束之后使氧流入，从而如图2(d)所示，在形成有p型扩散层7的n型单晶硅基板1的表面整体形成硅氧化膜8。First, the desired p-type diffusion layer 7 is formed in a gas atmosphere containing an inert gas such as nitrogen or argon to a temperature T such as 800° C. to 1100° C. for impurity diffusion from the BSG film 2 . Oxygen flows in after the formation of p-type diffusion layer 7 is completed, and silicon oxide film 8 is formed on the entire surface of n-type single crystal silicon substrate 1 on which p-type diffusion layer 7 is formed, as shown in FIG.
在图4中，用曲线a表示该热处理的温度分布图。在炉内用氮进行置换并使炉预热，在成为氮气体环境并且温度T＝900℃时，在时刻t01向热处理炉放入n型单晶硅基板1，直至时刻t02为止维持时间t1期间，t1的范围是1分钟至30分钟。在时刻t02，对热处理炉供给氧。在供给氧的同时，在上述温度T下直至时刻t03为止维持时间t2期间，t2的范围是1分钟至20分钟。在上述氧化工序中，放入到热处理炉内的n型单晶硅基板1由于在气体环境中包含的氧而表面被氧化。关于该氧化，由于受光面1A侧被BSG膜2和硅氧化膜3覆盖，所以在未被膜覆盖的背面1B侧选择性地发展，但在p型扩散层7的表面中也发生一部分氧化，如图2(d)所示，形成硅氧化膜8。在时刻t03停止氧的供给，供给氮气而进行氮置换。硅氧化膜8在后述的n型扩散层的形成时，作为防止n型杂质进入的屏障的一部分发挥功能。其厚度最好为5nm以上10nm以下。在小于5nm时，在后面的工序中作为屏障的功能弱化，在10nm以上时屏障功能变大而起到相反作用，无法良好地形成背面侧的n型扩散层的危险性增大。In FIG. 4, the temperature profile of this heat treatment is shown by curve a. The furnace is replaced with nitrogen and the furnace is preheated. When it becomes a nitrogen gas atmosphere and the temperature T=900°C, put the n-type single crystal silicon substrate 1 into the heat treatment furnace at timet01 , and maintain the time until timet02 . During t1,t1 ranges from1 minute to 30 minutes. At time t02 , oxygen is supplied to the heat treatment furnace. While supplying oxygen, the above-mentioned temperature T is maintained for a period of timet2 until timet03 , andt2 ranges from 1 minute to 20 minutes. In the above oxidation step, the surface of the n-type single crystal silicon substrate 1 placed in the heat treatment furnace is oxidized by oxygen contained in the gas atmosphere. Regarding this oxidation, since the light-receiving surface 1A side is covered with the BSG film 2 and the silicon oxide film 3, it selectively progresses on the back surface 1B side not covered with the film, but a part of the oxidation also occurs in the surface of the p-type diffusion layer 7, as As shown in FIG. 2(d), silicon oxide film 8 is formed. At timet03 , the supply of oxygen is stopped, and nitrogen gas is supplied to perform nitrogen replacement. The silicon oxide film 8 functions as a part of a barrier that prevents entry of n-type impurities during the formation of the n-type diffusion layer described later. Its thickness is preferably not less than 5 nm and not more than 10 nm. If the thickness is less than 5 nm, the function as a barrier will be weakened in the subsequent process, and if the thickness is more than 10 nm, the barrier function will be increased to the contrary, and the risk that the n-type diffusion layer on the back side cannot be formed satisfactorily increases.
在以上的加热工序之后，在供给氮的同时使温度下降，在时刻t04，从加热处理炉取出n型单晶硅基板1，根据需要，去除背面1B侧的硅氧化膜8。在去除硅氧化膜8之后，背面1B露出。此外，在被形成于背面1B的硅氧化膜8薄的情况下也可以不进行去除，接着向背面1B实施杂质扩散。After the above heating step, the temperature is lowered while supplying nitrogen, and at time t04 , n-type single crystal silicon substrate 1 is taken out from the heat treatment furnace, and silicon oxide film 8 on the rear surface 1B side is removed as necessary. After silicon oxide film 8 is removed, rear surface 1B is exposed. In addition, when the silicon oxide film 8 formed on the back surface 1B is thin, it does not need to be removed, and impurity diffusion is then performed on the back surface 1B.
之后，在步骤S106中，向背面1B实施杂质扩散。在此，作为例子，说明使用用于形成n型扩散层的利用POCl3气体的磷扩散工序的情况。在该工序中，针对n型单晶硅基板1的整个面，POCl3气体热分解而首先形成磷硅酸盐玻璃(PSG)膜，将其作为扩散源，在之后接着的加热工序中向内部浸透即扩散。这样，在POCl3气体环境下进行背面扩散的步骤S106中，磷扩散用的POCl3气体中的磷迅速地扩散到露出的背面1B，形成有p型扩散层7的受光面1A侧形成有成为扩散屏障的硅氧化膜8、BSG膜2、硅氧化膜3，所以能防止磷的混入。此时，关于背面1B侧，由于每2张进行重叠而被配置成直接暴露于炉的气体环境中，PSG膜被形成为期望的厚度。After that, in step S106, impurity is diffused to the rear surface 1B. Here, as an example, a case where a phosphorus diffusion process using POCl3 gas for forming an n-type diffusion layer is used will be described. In this step, POCl3 gas is thermally decomposed on the entire surface of the n-type single crystal silicon substrate 1 to form a phosphosilicate glass (PSG) film first, and this is used as a diffusion source, and in the subsequent heating step Soaking means spreading. In this way, in the step S106 of backside diffusion in thePOCl3 gas atmosphere, phosphorus in thePOCl3 gas for phosphorus diffusion rapidly diffuses to the exposed backside 1B, and the p-type diffusion layer 7 is formed on the side of the light-receiving surface 1A. The silicon oxide film 8, the BSG film 2, and the silicon oxide film 3 of the diffusion barrier can prevent the incorporation of phosphorus. At this time, since the rear surface 1B side is stacked every two sheets and placed so as to be directly exposed to the gas atmosphere of the furnace, the PSG film is formed to a desired thickness.
另一方面，关于受光面1A侧，由于每2张进行重叠而被配置成不直接暴露于炉的气体环境中，磷玻璃的成膜被大幅限制。进而，在其表面形成硅氧化膜8、BSG膜2、硅氧化膜3，他们作为扩散屏障发挥功能，所以防止磷混入到硅内部。即，在背面1B选择性地实施磷的扩散而在背面形成n型扩散层14。On the other hand, since the side of the light-receiving surface 1A is stacked every two and placed so as not to be directly exposed to the gas atmosphere of the furnace, film formation of phosphorous glass is greatly restricted. Furthermore, silicon oxide film 8, BSG film 2, and silicon oxide film 3 are formed on the surface, and they function as diffusion barriers, so that phosphorus is prevented from being mixed into silicon. That is, phosphorus is selectively diffused on the back surface 1B to form the n-type diffusion layer 14 on the back surface.
即，如图3(a)所示，在背面1B选择性地实施磷的扩散，在背面1B形成n型扩散层14。That is, as shown in FIG. 3( a ), phosphorus is selectively diffused on the back surface 1B, and an n-type diffusion layer 14 is formed on the back surface 1B.
在形成n型扩散层14之后，在固相扩散源去除步骤S107中，如图3(b)所示，去除作为固相扩散源的BSG膜2。例如，使用5％至25％的氢氟酸水溶液来去除BSG膜2和硅氧化膜3以及作为屏障发挥功能的硅氧化膜8。此时，也可以将利用水洗得到的氧化膜、一般被称为自然氧化膜的膜用作后述的钝化层或者该钝化层的一部分。或者，也可以以相同的目的，使用通过以包含臭氧的水进行清洗而得到的氧化膜。After forming the n-type diffusion layer 14, in the solid phase diffusion source removal step S107, as shown in FIG. 3(b), the BSG film 2 as the solid phase diffusion source is removed. For example, 5% to 25% hydrofluoric acid aqueous solution is used to remove BSG film 2 and silicon oxide film 3 and silicon oxide film 8 functioning as a barrier. In this case, an oxide film obtained by washing with water, or a film generally called a natural oxide film may be used as a passivation layer described later or a part of the passivation layer. Alternatively, an oxide film obtained by washing with ozone-containing water may also be used for the same purpose.
接着，在pn结分离步骤S108中，去除基板侧面部的p型扩散层7，将p型扩散层7和n型扩散层14分离。具体而言，将例如经过此前的工序的n型单晶硅基板1如图5所示层叠几十至几百张，夹入到保持器H之间，通过等离子放电，生成等离子激励气体PG，执行对基板侧面进行蚀刻处理的端面蚀刻。作为等离子激励气体PG，使用对稳定且毒性低、蚀刻速度高的CF4气体进行等离子化而得到的氟等离子气体。或者，也可以使用对基板表面或背面的侧端部附近或者基板侧面照射激光的激光分离。例如，去除构成基板侧面部的基板侧面、基板表面的侧端部附近、基板背面的侧端部附近中的任意部位的p型扩散层7即可。图5是示出作为实施方式1的太阳能电池的制造工序的主要部分的端面蚀刻工序的说明图。Next, in the pn junction separation step S108, the p-type diffusion layer 7 on the side surface of the substrate is removed, and the p-type diffusion layer 7 and the n-type diffusion layer 14 are separated. Specifically, for example, n-type single crystal silicon substrates 1 that have passed through the previous process are stacked in tens to hundreds of sheets as shown in FIG. End face etching is performed to etch the side surface of the substrate. As the plasma excitation gas PG, a fluorine plasma gas obtained by plasmating a stable CF4 gas with low toxicity and a high etching rate is used. Alternatively, laser separation may be used in which laser light is irradiated to the vicinity of side end portions on the front or rear surface of the substrate or to the side surface of the substrate. For example, the p-type diffusion layer 7 may be removed from any of the side surfaces of the substrate constituting the side surface of the substrate, the vicinity of the side ends of the substrate surface, and the vicinity of the side ends of the back surface of the substrate. 5 is an explanatory view showing an end face etching step which is a main part of the manufacturing process of the solar cell according to Embodiment 1. FIG.
使导致电气短路的部分、区域绝缘是电气分离的本质。具体而言，是指通过去除或者加工在硅基板内p型扩散层和n型扩散层接触或者接近的部位而使导电性大幅降低而电气性绝缘。即，只要是包括将形成在第1主面侧的第1扩散层、和半导体基板的第2主面侧的逆导电类型区域电气地分离的工序的工艺即可。例如，也可以在将半导体基板的第2主面侧和第1扩散层电气地分离的工序之前，实施去除半导体基板的基板侧面部的第1扩散层的工序。It is the essence of electrical separation to insulate the part, the area, which causes the electrical short circuit. Specifically, it refers to electrical insulation by removing or processing the portion where the p-type diffusion layer and the n-type diffusion layer are in contact with or close to each other in the silicon substrate, so that the conductivity is greatly reduced. That is, any process may be used as long as it includes a step of electrically isolating the first diffusion layer formed on the first main surface side and the reverse conductivity type region on the second main surface side of the semiconductor substrate. For example, before the step of electrically separating the second main surface side of the semiconductor substrate from the first diffusion layer, the step of removing the first diffusion layer on the substrate side portion of the semiconductor substrate may be performed.
因此，对于n型单晶硅基板，虽然以涉及去除或者加工为前提条件，但本案所涉及的BSG膜2以及硅氧化膜3由于针对等离子放电加工的耐性强、并且与其它扩散手法的扩散源相比厚度也大，所以当在保留它们的状态下进行端面蚀刻时，加工不充分而无法进行良好的分离。Therefore, for the n-type single crystal silicon substrate, although it involves removal or processing as a prerequisite, the BSG film 2 and silicon oxide film 3 involved in this case have strong resistance to plasma discharge processing and are compatible with diffusion sources of other diffusion methods. Since they are also large in comparison to the thickness, when the end faces are etched while leaving them, the processing is insufficient and good separation cannot be performed.
因此，通过在去除BSG膜2以及硅氧化膜3之后，进行端面蚀刻，能够利用端面蚀刻进行充分的分离。Therefore, by performing end face etching after removing the BSG film 2 and the silicon oxide film 3 , sufficient separation can be achieved by the end face etching.
另外，关于BSG膜2以及硅氧化膜3的去除，需要在作为后续工序的反射防止膜或者背面绝缘膜的形成前去除，所以在端面蚀刻之前去除BSG膜2以及硅氧化膜3整体的方法最简便，对生产率提高或者制造成本降低也有效。In addition, the removal of the BSG film 2 and the silicon oxide film 3 needs to be removed before the formation of the antireflection film or the back insulating film as a subsequent process, so it is best to remove the entire BSG film 2 and the silicon oxide film 3 before etching the end faces. It is simple and effective for improving productivity or reducing manufacturing costs.
如以上所述，进行基板端面的裁切或者蚀刻，如图3(c)所示，形成在受光面1A侧具备p型扩散层7、在背面1B侧具备n型扩散层14的太阳能电池基板。As described above, the end face of the substrate is cut or etched, and as shown in FIG. .
此外，根据分离的状况即泄漏电流的大小或者成为最终的发电产品的模块内的单元排列，也能够省略其分离工序。In addition, depending on the state of separation, that is, the magnitude of the leakage current, or the arrangement of cells in the module to be the final power generation product, the separation step can also be omitted.
之后，在反射防止膜形成以及背面绝缘膜形成步骤S109中，在背面1B使用例如等离子CVD形成包含氮化硅膜的背面绝缘膜15b。此外，也可以在氮化硅膜与n型扩散层之间形成钝化层。在该情况下，钝化层最好为硅氧化膜，除了使用通过一般的热氧化得到的氧化膜以外，也可以如上所述使用通过水洗或者含臭氧的水的清洗得到的氧化膜。Thereafter, in step S109 of forming an antireflection film and forming a back insulating film, a back insulating film 15b including a silicon nitride film is formed on the back surface 1B by, for example, plasma CVD. In addition, a passivation layer may be formed between the silicon nitride film and the n-type diffusion layer. In this case, the passivation layer is preferably a silicon oxide film. In addition to using an oxide film obtained by general thermal oxidation, an oxide film obtained by washing with water or washing with ozone-containing water may also be used as described above.
接下来，在受光面1A侧，也同样地通过使用了例如等离子CVD的氮化硅膜来形成受光面反射防止膜15a。此外，也可以在构成受光面反射防止膜15a的氮化硅膜与n型扩散层14之间形成钝化层。Next, also on the light receiving surface 1A side, a light receiving surface antireflection film 15 a is formed by using, for example, a silicon nitride film by plasma CVD in the same manner. In addition, a passivation layer may be formed between the silicon nitride film constituting the anti-reflection film 15 a on the light receiving surface and the n-type diffusion layer 14 .
在该情况下，钝化层最好成为硅氧化膜、氧化铝膜中的某一个或者双方的层叠体。在钝化层使用硅氧化膜的情况下，除了一般的热氧化以外，也可以如上所述使用通过水洗或者含臭氧的水的清洗得到的氧化膜。另外，在使用氧化铝膜的情况下，利用例如等离子CVD或者ALD(AtomicLayerDeposition；原子堆积法)来形成。在该情况下，在成膜时内包的固定电荷具有提高钝化能力的效果，所以更优选。In this case, the passivation layer is preferably a silicon oxide film or an aluminum oxide film, or a laminate of both. When a silicon oxide film is used for the passivation layer, besides general thermal oxidation, an oxide film obtained by washing with water or washing with ozone-containing water may be used as described above. In addition, when an aluminum oxide film is used, it is formed by, for example, plasma CVD or ALD (Atomic Layer Deposition; atomic deposition method). In this case, the contained fixed charge has the effect of improving the passivation ability at the time of film formation, so it is more preferable.
特别地，当在BSG膜2以及硅氧化膜3的去除工序中的氢氟酸水溶液处理之后实施端面蚀刻工序的情况下，由于在端面蚀刻处理时层叠利用氢氟酸水溶液处理而清洁后的基板表面，所以基板表面彼此接触、以及由于使用氟等离子气体，所以表面状态变得不稳定，通过在接下来的工序中形成钝化层所起到的钝化效果有时降低。In particular, when the end surface etching process is performed after the hydrofluoric acid aqueous solution treatment in the removal process of the BSG film 2 and the silicon oxide film 3, since the substrate after cleaning by the hydrofluoric acid aqueous solution treatment is stacked during the end surface etching treatment, Surfaces, so the substrate surfaces are in contact with each other, and the surface state becomes unstable due to the use of fluorine plasma gas, and the passivation effect by forming a passivation layer in the next process sometimes decreases.
特别地，在蚀刻中使用CF4等氟系蚀刻液、用氟等离子气体蚀刻的情况下，氟离子有时在蚀刻后吸附到硅基板表面而残留。在该基板表面用等离子CVD形成氮化硅膜时，从氟离子之上形成氮化硅膜，氟原子在硅基板与氮化硅膜之间残留，所以表面钝化效果降低。In particular, when a fluorine-based etchant such as CF4 is used for etching, and fluorine plasma gas is used for etching, fluorine ions may be adsorbed to the surface of the silicon substrate after etching and remain. When a silicon nitride film is formed on the surface of the substrate by plasma CVD, the silicon nitride film is formed from above the fluorine ions, and fluorine atoms remain between the silicon substrate and the silicon nitride film, so that the surface passivation effect is reduced.
另一方面，ALD是通过将水的导入、氮N2净化、TMA(三甲基铝)导入、N2净化作为1个循环反复多个循环从而在硅基板表面形成氧化铝膜的方法。在ALD中，包含N2净化的循环被反复，所以在N2净化时，吸附到基板表面的氟被排出，能够形成清洁的表面状态。On the other hand, ALD is a method of forming an aluminum oxide film on the surface of a silicon substrate by repeating multiple cycles of water introduction, nitrogenN2 purge, TMA (trimethylaluminum) introduction, andN2 purge as one cycle. In ALD, a cycle includingN2 purge is repeated, so fluorine adsorbed on the substrate surface is discharged duringN2 purge, and a clean surface state can be formed.
因此，通过在钝化层形成时使用ALD，即使在氢氟酸水溶液处理之后实施氟等离子气体处理的情况下，也能够得到充分的钝化效果。Therefore, by using ALD at the time of passivation layer formation, even when performing a fluorine plasma gas process after a hydrofluoric-acid aqueous solution process, sufficient passivation effect can be acquired.
此外，关于受光面反射防止膜15a和背面绝缘膜15b以及双方的钝化层的形成顺序，未必仅限定于上述顺序，也可以适当地选择上述以外的顺序来形成。In addition, the formation order of the light-receiving surface antireflection film 15a, the back surface insulating film 15b, and both passivation layers is not necessarily limited to the above-mentioned order, and may be formed by appropriately selecting an order other than the above-mentioned ones.
之后，如图3(d)所示，在受光面1A和背面1B分别形成受光面反射防止膜15a和背面绝缘膜15b之后，在电极形成步骤S110中，在受光面1A侧和背面1B侧分别形成受光面电极16a和背面电极16b。作为电极材料，使用例如铜、银、铝或者它们的混合物等。例如，通过利用例如网板印刷将把铜、银、铝或者它们的混合物的金属粉体与玻璃、陶瓷成分的粉体以及有机溶剂混合并成为膏状而成的材料形成为期望形状的图案并干燥以及烧结而形成。这样，太阳能电池完成。After that, as shown in FIG. 3( d), after the light-receiving surface anti-reflection film 15a and the back insulating film 15b are respectively formed on the light-receiving surface 1A and the back surface 1B, in the electrode forming step S110, the light-receiving surface 1A side and the back surface 1B side are respectively A light-receiving surface electrode 16a and a rear surface electrode 16b are formed. As the electrode material, for example, copper, silver, aluminum, or a mixture thereof is used. For example, by using, for example, screen printing, a material obtained by mixing metal powder of copper, silver, aluminum, or a mixture thereof with glass, powder of ceramic components, and an organic solvent into a paste form is formed into a pattern of a desired shape and formed by drying and sintering. In this way, the solar cell is completed.
如以上说明，根据实施方式1的太阳能电池的制造方法，在对固相扩散源进行成膜以及加热而形成扩散层并去除固相扩散源之后，进行电气分离，所以进行了加工的部位的绝缘性能提高，能够减少太阳能电池的泄漏电流。另外，抑制向受光面和背面混入作为目标的杂质以外的、形成相反导电类型的杂质或者污染物质，实现载流子寿命长且光电变换效率高的太阳能电池。As described above, according to the solar cell manufacturing method of Embodiment 1, the solid-phase diffusion source is formed into a film and heated to form a diffusion layer, and the solid-phase diffusion source is removed. After that, electrical separation is performed, so the insulation of the processed part is performed. The performance is improved, and the leakage current of the solar cell can be reduced. In addition, the mixing of impurities or pollutants of opposite conductivity types other than the targeted impurities into the light-receiving surface and the back surface is suppressed, and a solar cell with long carrier life and high photoelectric conversion efficiency is realized.
另外，即使在固相扩散源的BSG膜2和硅氧化膜3的形成时蔓延到背面1B而形成含硼的生成物，由于在为了扩散进行加热之前去除，所以通过之后的加热也能够防止向背面的杂质扩散。In addition, even if a boron-containing product is formed by spreading to the back surface 1B during the formation of the BSG film 2 and the silicon oxide film 3 of the solid-phase diffusion source, since it is removed before heating for diffusion, it can be prevented by subsequent heating. Impurities on the backside diffuse.
因此，抑制向受光面和背面混入作为目标的杂质以外的、形成相反导电类型的杂质或者污染物质，能够得到载流子寿命长且光电变换效率高的太阳能电池。Therefore, it is possible to obtain a solar cell having a long carrier life and high photoelectric conversion efficiency by suppressing contamination of the light-receiving surface and the rear surface with impurities or pollutants having an opposite conductivity type other than the target impurities.
此外，切片损伤的去除工序、纹理的形成工序、以及清洗处理工序是为了说明实施方式1的工序而采用的例子，不限定于此，可以使用任意的工序，不限制为上述工序。同样地，关于背面的n型扩散层14的形成工序、pn结的分离工序、受光面反射防止膜15a和背面绝缘膜15b的形成工序、以及受光面电极16a和背面电极16b的形成工序，也可以使用任意的工序，不限制为上述工序。另外，关于从n型扩散层14的形成工序至电极16的形成工序，只要作为太阳能电池发挥功能，则也可以适当地调换顺序，不限制为记载的顺序。Note that the slice damage removal step, texture formation step, and cleaning treatment step are examples used to describe the steps of Embodiment 1, and are not limited thereto. Any steps may be used, and are not limited to the above steps. Similarly, regarding the formation process of the n-type diffusion layer 14 on the back surface, the separation process of the pn junction, the formation process of the light-receiving surface antireflection film 15a and the back surface insulating film 15b, and the formation process of the light-receiving surface electrode 16a and the back surface electrode 16b, Arbitrary procedures may be used and are not limited to the above-mentioned procedures. In addition, the order from the formation process of the n-type diffused layer 14 to the formation process of the electrode 16 may be appropriately switched as long as it functions as a solar cell, and is not limited to the described order.
另外，为了说明，使用n型单晶硅基板1，固相扩散源使用BSG膜2，对背面1B使用基于磷扩散的n型扩散层14，但不限制为上述结构。只要作为太阳能电池发挥功能，则关于基板，也可以使用多晶硅基板、碳化硅等其他硅系晶体基板，关于导电类型，也可以使用p型的基板。进而，固相扩散源也可以使用如PSG膜那样的包含形成n型扩散层的杂质的例子。也可以在与固相扩散源相反的面的扩散时，使用如硼那样的形成p型扩散层的杂质。如以上所述，关于基板、关于形成于受光面和背面的扩散层，也能够适当地选择形成p型、n型中的某一个、以及形成扩散层的杂质元素。In addition, for the sake of explanation, an n-type single crystal silicon substrate 1 is used, a BSG film 2 is used as a solid-phase diffusion source, and an n-type diffusion layer 14 by phosphorus diffusion is used for the back surface 1B, but the above configuration is not limited. As long as it functions as a solar cell, other silicon-based crystal substrates such as polycrystalline silicon substrates and silicon carbide may be used as the substrate, and p-type substrates may be used as the conductivity type. Furthermore, as the solid phase diffusion source, an example containing impurities forming an n-type diffusion layer such as a PSG film can also be used. An impurity that forms a p-type diffusion layer such as boron may be used for diffusion on the surface opposite to the solid-phase diffusion source. As described above, with regard to the substrate and the diffusion layers formed on the light receiving surface and the rear surface, either p-type or n-type impurity elements and the impurity elements forming the diffusion layers can be appropriately selected.
实施方式2.Implementation mode 2.
实施方式2的太阳能电池的制造方法相比于实施方式1所示的太阳能电池的制造方法，在受光面侧、背面侧的某一方或者两方形成局部的高浓度扩散层。除了背面侧的氧化膜去除工序和磷扩散工序以外都相同，所以参照实施方式1而省略详细的说明。Compared with the solar cell manufacturing method described in Embodiment 1, the method of manufacturing a solar cell according to the second embodiment forms a local high-concentration diffusion layer on one or both of the light-receiving side and the back side. Except for the process of removing the oxide film on the rear side and the process of diffusing phosphorus, the process is the same, so referring to Embodiment 1, detailed description is omitted.
图6是关于实施方式2的太阳能电池的制造方法，是示出从热处理到pn结的分离工序的流程图。图7(a)以及图7(b)是示出n型的杂质扩散工序中的n型单晶硅基板1的剖面变化的示意图。以下，使用图6以及图7来说明。FIG. 6 is a flowchart showing steps from heat treatment to pn junction separation in the method of manufacturing a solar cell according to Embodiment 2. FIG. 7( a ) and FIG. 7( b ) are schematic diagrams showing cross-sectional changes of the n-type single crystal silicon substrate 1 in the n-type impurity diffusion step. Hereinafter, it demonstrates using FIG.6 and FIG.7.
在实施方式2的太阳能电池的制造方法中，在实施作为用于形成p型扩散层7的热处理工序的步骤S105之后，连续地如图7(a)所示实施固相扩散源向背面侧的成膜步骤S106a、作为热处理工序的背面扩散步骤S106b。在此，在背面1B的硅氧化膜8上形成高浓度地包含呈现n型导电类型的杂质、例如包含1×1020个/cm3以上的磷的扩散源17。之后，在形成扩散源17之后，在上述背面扩散步骤S106b中，与实施方式1的背面扩散步骤S106同样地，对n型单晶硅基板1在POCl3气体环境中实施热处理。例如，在800℃至1000℃的温度下，实施来自扩散源17的杂质扩散。In the method of manufacturing a solar cell according to Embodiment 2, after step S105 is performed as a heat treatment step for forming the p-type diffusion layer 7, the solid-phase diffusion source toward the back side is continuously performed as shown in FIG. 7( a ). The film forming step S106a, and the backside diffusion step S106b as a heat treatment process. Here, on silicon oxide film 8 on rear surface 1B, diffusion sources 17 containing impurities exhibiting n-type conductivity at a high concentration, for example, phosphorus containing 1×1020 particles/cm3 or more, are formed. Thereafter, after the diffusion source 17 is formed, in the above-mentioned backside diffusion step S106b, heat treatment is performed on the n-type single crystal silicon substrate 1 in a POCl3 gas atmosphere in the same manner as the backside diffusion step S106 of Embodiment 1. For example, impurity diffusion from diffusion source 17 is performed at a temperature of 800°C to 1000°C.
在扩散源正下方存在形成于背面1B的硅氧化膜8，其厚度薄到5nm至10nm、并且扩散源17的杂质浓度是高浓度，所以不会对n型扩散层的形成带来影响。该部分的扩散源17由通过POCl3气体的热分解形成的磷硅酸盐玻璃(PSG)膜形成，在与扩散源17接触的n型单晶硅基板1内杂质发生扩散，形成高浓度的n型扩散层18。在未被扩散源17覆盖的区域形成浓度比n型扩散层18低的n型扩散层20。Immediately below the diffusion source is the silicon oxide film 8 formed on the back surface 1B, which is as thin as 5 nm to 10 nm, and the impurity concentration of the diffusion source 17 is high, so it does not affect the formation of the n-type diffusion layer. The diffusion source 17 in this part is formed by the phosphosilicate glass (PSG) film formed by the thermal decomposition ofPOCl3 gas, and the impurities in the n-type single crystal silicon substrate 1 in contact with the diffusion source 17 diffuse to form a high-concentration n-type diffusion layer 18 . An n-type diffusion layer 20 having a concentration lower than that of the n-type diffusion layer 18 is formed in a region not covered by the diffusion source 17 .
然后，经由pn结分离步骤S108，实施图1所示的反射防止膜以及背面绝缘膜形成步骤S109、电极形成步骤S110。Then, through the pn junction separation step S108, the antireflection film and back insulating film forming step S109 and the electrode forming step S110 shown in FIG. 1 are carried out.
另一方面，扩散源17正下方以外的区域的n型单晶硅基板1附着从扩散源17向气体环境脱离的杂质，但相比于扩散源17自身的杂质浓度，其浓度或者总量低，无法通过被形成于n型单晶硅基板1的表面的氧化膜。On the other hand, the n-type single crystal silicon substrate 1 in the region other than directly under the diffusion source 17 adheres to the impurities detached from the diffusion source 17 to the gas environment, but the concentration or total amount is lower than the impurity concentration of the diffusion source 17 itself. , cannot pass through the oxide film formed on the surface of the n-type single crystal silicon substrate 1 .
因此，根据实施方式2，能够在扩散层形成具有两个级别的浓度的构造。在适当地选取两者的分配时，扩散源17正下方以外的区域能够抑制为更低的浓度，所以实现更高效的太阳能电池。Therefore, according to Embodiment 2, a structure having two levels of concentration can be formed in the diffusion layer. When the distribution of the two is appropriately selected, the concentration in the region other than directly below the diffusion source 17 can be suppressed to be lower, so that a more efficient solar cell can be realized.
如以上所述，形成固相扩散源的工序是如下工序：向作为第2主面的背面1B选择性地形成，通过来自作为该扩散源17的PSG膜的扩散，形成作为第1导电类型的n型扩散层20。As described above, the process of forming the solid phase diffusion source is a process of selectively forming the solid phase diffusion source on the back surface 1B as the second main surface, and forming a layer of the first conductivity type by diffusion from the PSG film as the diffusion source 17. n-type diffusion layer 20 .
根据实施方式2，能够从制造方法去掉背面1B的氧化膜去除工序，不会对形成于n型单晶硅基板1的硅氧化膜8造成影响而能够结束至n型杂质的扩散工序为止的工序。According to Embodiment 2, the oxide film removal step of the rear surface 1B can be eliminated from the manufacturing method, and the steps up to the n-type impurity diffusion step can be completed without affecting the silicon oxide film 8 formed on the n-type single crystal silicon substrate 1 .
此外，形成作为第1导电类型的扩散层的n型扩散层的工序是在作为n型单晶硅基板1的第2主面的背面1B形成包含1×1020个/cm3以上的杂质的扩散源的工序。通过该方法，即使在扩散源接触的部位存在硅氧化膜，也能够形成杂质扩散层，能够省略去除n型单晶硅基板1的背面1B的硅氧化膜8的工序。另外，保持将作为太阳能电池基板的n型单晶硅基板1的表面整个区域用硅氧化膜8覆盖的状态而实施来自扩散源的扩散，所以即使从扩散源释放到气体环境中的杂质附着到n型单晶硅基板1，也不会扩散到基板内部。In addition, in the step of forming the n-type diffusion layer as the diffusion layer of the first conductivity type, an impurity containing 1×1020 impurities/cm3 or more is formed on the rear surface 1B, which is the second main surface of the n-type single crystal silicon substrate 1 . Diffusion source process. With this method, an impurity diffusion layer can be formed even if a silicon oxide film is present at the site where the diffusion source contacts, and the step of removing silicon oxide film 8 on rear surface 1B of n-type single crystal silicon substrate 1 can be omitted. In addition, since the diffusion from the diffusion source is carried out while the entire surface of the n-type single crystal silicon substrate 1 as the solar cell substrate is covered with the silicon oxide film 8, even impurities released into the gas atmosphere from the diffusion source adhere to the substrate. The n-type single crystal silicon substrate 1 also does not diffuse into the substrate.
如以上所述，根据实施方式2的太阳能电池的制造方法，由于不需要背面的氧化膜去除工序，所以防止形成p型和n型的杂质邻接的泄漏通道，实现二极管特性优良的太阳能电池。As described above, according to the solar cell manufacturing method of Embodiment 2, since the oxide film removal process on the back surface is unnecessary, the formation of leakage channels adjacent to p-type and n-type impurities is prevented, and a solar cell with excellent diode characteristics is realized.
实施方式3.Implementation mode 3.
关于BSG膜2以及硅氧化膜3的去除，也可以并非完全去除，而仅将端面以及其极邻近的部分作为对象而去除BSG膜2以及硅氧化膜3。图8是示出实施方式3的太阳能电池的制造方法的流程图、图9(a)至图9(d)是示出实施方式3的太阳能电池的制造工序的主要部分的工序剖面图。Regarding the removal of the BSG film 2 and the silicon oxide film 3 , the BSG film 2 and the silicon oxide film 3 may not be completely removed, but only the end faces and their very adjacent portions may be removed. 8 is a flowchart showing a method of manufacturing a solar cell according to Embodiment 3, and FIGS. 9( a ) to 9 ( d ) are process sectional views showing main parts of the manufacturing process of a solar cell according to Embodiment 3. FIG.
关于BSG膜2以及硅氧化膜3的去除，由于需要在作为后续工序的反射防止膜或者背面绝缘膜的形成前去除，所以如实施方式1所示，在分离加工前去除BSG膜2以及硅氧化膜3整体的方法最简便，易于对生产率提高或者制造成本降低作出贡献。然而，分离加工前的重要去除的地方只是成为加工对象的部位，具体而言端面以及其极邻近的部分成为对象。受光面1A以及背面1B的大半部分无需在分离加工前去除。With regard to the removal of the BSG film 2 and the silicon oxide film 3, since it needs to be removed before the formation of the antireflection film or the back insulating film as a subsequent process, as shown in Embodiment 1, the BSG film 2 and the silicon oxide film 3 are removed before the separation process. The method in which the film 3 is integrated is the most convenient, and it is easy to contribute to an improvement in productivity or a reduction in manufacturing cost. However, the important removal before the separation process is only the part to be processed, specifically, the end face and its very adjacent parts are the target. Most of the light-receiving surface 1A and the back surface 1B do not need to be removed before the separation process.
因此，在实施方式3中，通过边旋转边滴下蚀刻液的方法，仅将端面以及其极邻近的部分作为对象，去除BSG膜2以及硅氧化膜3。关于其他工序，与实施方式1相同。Therefore, in the third embodiment, the BSG film 2 and the silicon oxide film 3 are removed only on the end face and its very adjacent portion by dropping the etchant while rotating. About other steps, it is the same as Embodiment 1.
直至在POCl3气体环境下进行背面扩散的背面扩散步骤S106为止的步骤，与实施方式1同样地进行，如图9(a)所示，形成背面的n型扩散层14。图9(a)与实施方式1的图2(d)相当。The steps up to the backside diffusion step S106 in which the backside is diffused in a POCl3 gas atmosphere are performed in the same manner as in Embodiment 1, and the n-type diffusion layer 14 on the backside is formed as shown in FIG. 9( a ). FIG. 9( a ) corresponds to FIG. 2( d ) of the first embodiment.
之后，实施端面的固相扩散源去除步骤S107S，通过边使基板旋转边滴下蚀刻液的方法等，如图9(b)所示，仅将端面以及其极邻近的部分作为对象，去除BSG膜2以及硅氧化膜3。Afterwards, the end surface solid phase diffusion source removal step S107S is carried out, and the BSG film is removed only on the end surface and its very adjacent parts as shown in FIG. 2 and silicon oxide film 3.
接下来，实施pn结分离步骤S108，在受光面以及背面这两面的大半部分，将残存的BSG膜2以及硅氧化膜3作为保护膜进行端面蚀刻，如图9(c)所示，去除基板端面的p型扩散层7。Next, the pn junction separation step S108 is implemented, and the remaining BSG film 2 and silicon oxide film 3 are used as protective films on most of the light-receiving surface and the back surface, and the end faces are etched. As shown in FIG. 9(c), the substrate is removed. The p-type diffusion layer 7 on the end face.
然后，实施残存的固相扩散源去除步骤S107SS，如图9(d)所示，去除残存的BSG膜2以及硅氧化膜3。此时，也去除表面以及背面的硅氧化膜8。其与实施方式1中的图3(c)相当，与实施方式1同样地，形成反射防止膜15a、保护膜15b、受光面电极16a、背面电极16b，完成太阳能电池。Then, the remaining solid-phase diffusion source removal step S107SS is performed, and as shown in FIG. 9( d ), the remaining BSG film 2 and silicon oxide film 3 are removed. At this time, the silicon oxide film 8 on the front surface and the back surface is also removed. This corresponds to FIG. 3(c) in Embodiment 1, and the antireflection film 15a, protective film 15b, light-receiving surface electrode 16a, and back electrode 16b are formed similarly to Embodiment 1 to complete a solar cell.
通过上述结构，残存在受光面以及背面这两面的大半部分的BSG膜2以及硅氧化膜3能够作为分离加工时的保护膜而有效利用。由此，还能够进一步改善太阳能电池的特性。另外，能够抑制泄漏电流。With the above structure, the BSG film 2 and the silicon oxide film 3 remaining on most of both the light receiving surface and the rear surface can be effectively used as a protective film during separation processing. Thereby, the characteristics of the solar cell can be further improved. In addition, leakage current can be suppressed.
在实施方式1至3中，在热处理工序之后，在形成与形成的扩散层不同的导电类型扩散层的工序中，去除作为保护膜的硅氧化膜的一部分。因此，能够使用利用简单的气体实现的杂质扩散，由于除了氧化膜去除部以外的膜残存，所以能够防止杂质混入而形成泄漏通道。In Embodiments 1 to 3, after the heat treatment step, in the step of forming a diffusion layer of a conductivity type different from that of the formed diffusion layer, a part of the silicon oxide film as a protective film is removed. Therefore, impurity diffusion using a simple gas can be used, and since the film other than the oxide film removal portion remains, it is possible to prevent impurities from being mixed and form a leak path.
如以上说明，在实施方式1至3中，示出用于通过在形成成为固相扩散源的包含杂质的膜之后进行去除背面侧的扩散源的后热处理从而防止来自背面的生成物的杂质扩散的制造工序。具体而言，在热处理时，在通常的热处理中使用氮、氩等惰性气体来实施处理时，在中途在使氧流入的气体环境中实施热处理，实施2段热处理。在使杂质从固相扩散源的膜扩散的不含氧的气体环境的热处理之后，实施氧的供给。即，利用在放入到炉之后接触的氧，在基板背面的生成物和基板界面形成作为扩散屏障的氧化膜，在终止氧的供给的过程中，从成膜物实施杂质扩散，杂质仅扩散到成膜面。然后，利用在热处理工序的最后流入的氧，在固相扩散源的成膜面也形成氧化膜，附加作为针对接着实施的其他种类的扩散的屏障的功能。能够通过该方法使杂质仅扩散到成膜面。As described above, in Embodiments 1 to 3, it is shown that the impurity diffusion of the product from the back surface is prevented by performing post-heat treatment to remove the diffusion source on the back side after forming a film containing impurities to be a solid-phase diffusion source. manufacturing process. Specifically, when heat treatment is performed using an inert gas such as nitrogen or argon in normal heat treatment, heat treatment is performed in a gas atmosphere in which oxygen flows in the middle, and two-stage heat treatment is performed. Oxygen supply is performed after heat treatment in an oxygen-free gas atmosphere to diffuse impurities from the film of the solid-phase diffusion source. That is, an oxide film as a diffusion barrier is formed on the product on the rear surface of the substrate and the interface of the substrate by the oxygen that comes into contact with the furnace after being placed in the furnace. During the process of stopping the supply of oxygen, the impurity is diffused from the film-formed product, and the impurity only diffuses to the film-forming surface. Then, an oxide film is also formed on the film-forming surface of the solid-phase diffusion source by oxygen flowing in at the end of the heat treatment process, and functions as a barrier against other types of diffusion to be carried out next. By this method, impurities can be diffused only to the film formation surface.
此外，关于扩散工序后的氧化工序，既可以如在实施方式1中使用图4说明，通过将氧导入用于扩散的热处理工序的最后的必要时间来实施，也可以在热处理工序后的降温工序中，将氧导入必要时间。另外，也可以在使扩散炉的温度暂时下降至常温之后，实施氧化热处理工序。In addition, the oxidation step after the diffusion step may be implemented by introducing oxygen into the last necessary time of the heat treatment step for diffusion as described in Embodiment 1 using FIG. In, oxygen is introduced for the necessary time. In addition, the oxidation heat treatment step may be performed after temporarily lowering the temperature of the diffusion furnace to normal temperature.
另外，在实施方式1至3中，用于进行杂质扩散的热处理工序中的温度由应扩散的杂质的种类来决定，可适当地变更。另外，关于扩散气体环境，为了通过杂质的种类控制扩散速度，还能够设为氢气体环境等还原性气体环境，可适当地调整。In Embodiments 1 to 3, the temperature in the heat treatment step for impurity diffusion is determined according to the type of impurity to be diffused, and can be changed as appropriate. In addition, the diffusion gas atmosphere can also be set to a reducing gas atmosphere such as a hydrogen gas atmosphere in order to control the diffusion rate according to the type of impurity, and can be appropriately adjusted.
另外，在实施方式1至3中，说明了在半导体基板的第2主面即背面侧也形成具有与半导体基板相同的导电类型的第2扩散层的例子，但也可以不形成第2扩散层。在该情况下，在半导体基板和第1扩散层的pn分离之前，去除固相扩散源。另外，使用n型单晶硅基板作为半导体基板，但当然还能够应用以p型单晶硅基板为首的p型以及n型多晶硅基板等其他晶系硅基板、或者当然还能够应用于使用以碳化硅等硅化合物为首的化合物半导体的扩散层的形成。另外，与半导体基板的导电类型对应地，第1以及第2导电类型的杂质也分别确定，但关于杂质的种类，除了作为n型的杂质的磷、砷、作为p型的杂质的硼、镓以外，当然还能够应用通常的杂质。In addition, in Embodiments 1 to 3, an example was described in which the second diffusion layer having the same conductivity type as that of the semiconductor substrate was also formed on the back side, which is the second main surface of the semiconductor substrate, but the second diffusion layer may not be formed. . In this case, the solid phase diffusion source is removed before pn separation between the semiconductor substrate and the first diffusion layer. In addition, although an n-type single crystal silicon substrate is used as a semiconductor substrate, it is of course also possible to apply other crystalline silicon substrates such as p-type and n-type polycrystalline silicon substrates including p-type single crystal silicon substrates, or of course also applicable to the use of carbonized silicon substrates. Formation of diffusion layers of compound semiconductors including silicon compounds such as silicon. In addition, impurities of the first and second conductivity types are also determined according to the conductivity type of the semiconductor substrate. However, the types of impurities include phosphorus and arsenic as n-type impurities, and boron and gallium as p-type impurities. Besides, usual impurities can of course also be used.
虽然说明了本发明的几个实施方式，但这些实施方式仅为例示，并不意图限定发明的范围。这些新的实施方式能够以其他各种方式来实施，能够在不脱离发明的要旨的范围内，进行各种省略、置换、变更。这些实施方式及其变形包含于发明的范围，并且包含于权利要求书记载的发明和其等同的范围。Although some embodiments of the present invention have been described, these embodiments are merely examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in other various forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope of the invention, and are included in the invention described in the claims and the equivalent scope thereof.
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