WO2011116660A1 - 提纯硅的方法 - Google Patents

提纯硅的方法 Download PDF

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Publication number
WO2011116660A1
WO2011116660A1 PCT/CN2011/071772 CN2011071772W WO2011116660A1 WO 2011116660 A1 WO2011116660 A1 WO 2011116660A1 CN 2011071772 W CN2011071772 W CN 2011071772W WO 2011116660 A1 WO2011116660 A1 WO 2011116660A1
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silicon
temperature
impurities
purified
grains
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PCT/CN2011/071772
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English (en)
French (fr)
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姜学昭
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北京中和辰旭科技发展有限公司
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Application filed by 北京中和辰旭科技发展有限公司 filed Critical 北京中和辰旭科技发展有限公司
Priority to US13/636,312 priority Critical patent/US20130011320A1/en
Priority to CA2793788A priority patent/CA2793788A1/en
Priority to JP2013500315A priority patent/JP2013522161A/ja
Priority to EP11758770A priority patent/EP2551238A1/en
Publication of WO2011116660A1 publication Critical patent/WO2011116660A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C01B33/037—Purification

Definitions

  • the present invention relates to a method of producing high purity silicon for use in a solar cell. Background technique
  • Photovoltaic power generation is a technique that uses the photovoltaic effect of a semiconductor interface to convert light energy directly into electrical energy.
  • the key component of this technology is solar cells, and one of the key steps in the preparation of solar cells is to produce high purity silicon.
  • the current metallurgical process (physical method), which has yielded some results, is generally a combination of two types of purification methods.
  • the first type is a directional solidification and a zone melting method that removes most of the impurities in the silicon and improves the overall purity of the silicon. This is the basic method in physics.
  • the second type is a special purification method for boron and phosphorus, which are electroactive impurities in silicon, which are difficult to remove by the first type of method.
  • Complementary addition of the two types of methods has produced high purity silicon capable of producing solar cells.
  • the solar cell produced has the defects of insufficient photoelectric conversion efficiency and rapid decay, which indicates that the impurity content in the high-purity silicon prepared by the prior art is not stable, and the purity of silicon is also required. Further improve. Therefore, the current metallurgical method cannot meet the needs of solar cells.
  • the principle of de-purification by directional solidification and zone melting is based on the segregation effect of impurities in the solid-liquid two-phase equilibrium of silicon.
  • the so-called segregation effect is that the concentration of impurities in the solid phase is not the same as the concentration in the liquid phase.
  • C solid indicates the concentration of impurities in the silicon solid phase;
  • C liquid indicates the concentration of impurities in the liquid phase;
  • the thermodynamic characteristics of impurities and silicon determine a physical phenomenon that is ubiquitous in nature.
  • the directional solidification and zone melting techniques use the decoagulation effect of impurities to make the ingots to be purified, so that the ingots are melted (integral or one section), and the solid-liquid interface is controlled to move from the ingot to the ingot. Since the K value of most impurities in silicon is less than 1, the concentration of impurities in the solid phase is much lower than that in the liquid phase, so the impurities in silicon are redistributed during the movement from the head to the tail at the solid-liquid interface. The impurities continuously discharged from the solidified solid phase to the liquid phase are brought to the post-solidified by the unsolidified liquid phase silicon. Part, until the end is reached. Finally, the purified high-purity silicon is obtained by cutting off the tail of the impurity enrichment. In addition to silicon, directional solidification and zone melting techniques are widely used in the purification of more materials and become one of the basic methods of purification.
  • the solid-liquid interface acting on the segregation of impurities is invariably equal to the cross-sectional area of the ingot.
  • the effect of increasing the segregation effect can only reduce the speed of the interface movement. It can be seen from Fig. 1 that after one directional solidification operation, the ingot concentration below the original concentration Q) is less than half the length of the entire ingot.
  • a primary object of the present invention is to provide a novel method for purifying silicon which can significantly improve purification efficiency compared to directional solidification and zone melting, and to increase the purity of industrial silicon to meet the requirements of solar cells.
  • the present invention adopts the following technical solutions:
  • a method of purifying silicon the steps of which are as follows:
  • the acid-etched silicon grains are separated from the acid solution, soaked with water, washed with water until neutral, filtered, and dried to obtain a high-purity silicon product.
  • the method for purifying silicon as described above characterized in that the covering agent is wheat straw or rice straw, and the amount is added to completely cover the surface of the silicon to be purified.
  • a silicon purification method utilizing a grain boundary polyhesive effect characterized in that a molten silicon to be purified is introduced into a temperature control crystallizer to regulate the number of silicon crystal nuclei and grain growth speed during solidification, utilizing grain surface and melting
  • the impurity segregation effect at the bulk interface causes the impurities discharged from the grains to collect at the final solidified grain boundaries, and then the silicon grains surrounded by the impurities are released to obtain purified silicon.
  • the regulation of the number of silicon nuclei during solidification means that a large number of crystal nuclei are simultaneously formed in an instant, and the solid-liquid interface is increased.
  • the release of the silicon grains surrounded by the impurities means that the high-purity silicon crystal grains encapsulated by the impurities are released when the grain boundary impurities are dissolved by the acid solution.
  • Impurities concentrated at the grain boundaries will precipitate from the grain boundaries during the cooling process to form a separate impurity phase.
  • the temperature control crystallizer is composed of an outer temperature control table and a crystallizer body disposed in the temperature control table, and the temperature control table controls the temperature of the silicon melt in the crystallization process by a built-in heating element, the crystallizer
  • the body has a temperature-controlled thermocouple connected to the program temperature controller.
  • the invention proposes a novel method for purifying by utilizing the impurity segregation effect, which is hereinafter referred to as a grain boundary polytype method.
  • the process is: introducing molten industrial silicon into a special, temperature-controlled crystallizer.
  • the macroscopic means is used to regulate the number of silicon nucleus and the grain growth rate during solidification, so that the effect of impurity segregation on the surface of the crystal grain and the melt interface is fully exerted, and the impurities discharged from the crystal grains are concentrated to the finally solidified grains.
  • the boundary Thereafter, an effective means is applied to release the pure silicon crystal grains encapsulated by the impurities. Higher purity silicon.
  • the advantages are:
  • the separation efficiency of impurities during solidification is greatly improved, thereby improving the efficiency and effect of purification.
  • the purification method of the present invention is to simultaneously form a large number of crystal nuclei in an instant, and the resulting solid-liquid interface is very large. As the silicon grain grows, the increase in the solid-liquid interface area is proportional to the square of the grain radius size, and the effect of the separation and purification will also change significantly.
  • the crystallization process is carried out with 10kg of silicon: the average grain size of industrial silicon after solidification in the crystallizer is 1m, if the time from crystallization to full solidification is 30 minutes, then the growth rate of the crystal grains (the advancing speed of the solid-liquid interface) is 1 mm / h; then, 10 kg of silicon is cast into a square ingot with a section of 9 cm x 9 cm, the ingot is 53 cm long, and the direction is solidified at this speed. 530 hours
  • the grain boundary poly-method is initiated by a large number of crystal nuclei. Each crystal grain extends 1 metre into the surrounding space to accumulate, and the impurity is transported to the grain boundary, which takes only 30 minutes.
  • Figure 1 is a plot of impurity concentration versus solidified portion during directional solidification.
  • Figure 2 shows the step cooling curve of the industrial silicon melt cooling process.
  • Figure 3 is a front elevational view showing the appearance of a temperature controllable crystallizer for carrying out the purification method of the present invention.
  • Figure 4 is a left side view showing the appearance of a temperature controllable crystallizer for carrying out the purification method of the present invention.
  • Figure 5 is a right side elevational view of a temperature controllable crystallizer for carrying out the purification process of the present invention.
  • Figure 6 is a cross-sectional view taken along line A-A of Figure 4.
  • Fig. 7 is a cross-sectional view taken along line BB of Fig. 3; detailed description
  • the temperature control crystallizer consists of an outer temperature control table and a crystallizer body placed in the temperature control stage.
  • the crystallizer body has a two-layer structure including a casing 1 made of a heat resistant metal and a liner 2 made of a refractory material.
  • a casing 1 made of a heat resistant metal
  • a liner 2 made of a refractory material.
  • five high temperature resistant alloy tubes 3 are placed, two of which are on one side and the other three on the other side.
  • the length of the alloy tube in the middle is 1/2 of that of the other four alloy tubes, and the alloy tube forms a blind end at the inner wall of the outer casing 1 near the center of the crystallizer, and the other end
  • an opening is formed that communicates with the outside.
  • Both ends of the remaining four alloy tubes pass through the crystallizer body, and an opening communicating with the outside is formed on the outer wall of the outer casing 1.
  • an upper cover 4 having a refractory heat insulating material is disposed above the main body of the crystallizer, and a reserved hole 5 is formed therein.
  • the temperature control table also has a two-layer structure including an outer casing 6 made of a heat resistant metal and an inner liner 7 made of a heat insulating material.
  • a plurality of heating elements 8 are provided in the lining 7.
  • the metal plate 6 and the inner liner 7 are provided with a plurality of through holes 9, which are in communication with the openings of the alloy tube 3 of the crystallizer body on the outer casing 1.
  • the crystallizer body is placed in the inner liner 7 of the temperature control table, and the thermocouple is inserted into the five alloy tubes 3 through the through holes 9 on the temperature control table, wherein the shorter alloy tubes are used to insert the temperature control thermocouples.
  • the temperature-controlled thermocouple is fixed to the portion near the center of the crystallizer by its blind end.
  • the upper cover thermocouple is inserted into the inside of the crystallizer body through the reserved hole 5 of the upper cover 4.
  • the temperature of each thermocouple output is monitored, and the temperature control thermocouple is connected to a program temperature controller (not shown) to regulate the heating element 8 in the temperature control stage, thereby controlling the temperature of the silicon melt during crystallization. .
  • the thermocouples in the other four alloy tubes can be moved to monitor the temperature uniformity during crystallization inside the mold.
  • the industrial silicon melt is poured into a mold that can be temperature controlled.
  • the point A is the temperature of the silicon melt when entering the crystallizer, and the temperature gradually decreases as the melt dissipates.
  • point B many nuclei in the melt form and begin to grow, and the silicon melt begins to be in the solid-liquid two-phase equilibrium phase. Due to the release of latent heat from the solid phase, the temperature of the silicon melt remains constant during the two-phase equilibrium phase, constant at about 1410 °C.
  • impurities are segregated.
  • the silicon grains grow freely in the volume of the crystallizer, and the surface of the grains is a two-phase equilibrium solid-liquid interface. As the grain grows, the interface area expands in proportion to the square of the grain radius size.
  • the impurities are discharged into the molten silicon that has not yet solidified, and finally aggregated to the grain boundaries of the grains.
  • the impurities (K ⁇ 1 impurity) of the crystal grains are enriched in the molten silicon at the grain boundary.
  • the solidified silicon in the crystallizer was taken out, appropriately crushed, placed in an acid bath, and soaked for about 12 hours with a mixed acid solution.
  • the acid solution is immersed along the grain boundary, and the grain boundary is broken after the impurities are dissolved, and the purified silicon crystal grains are released.
  • the silicon crystal grains are separated from the acid liquid and then washed with pure water to neutrality, and after drying, a high-purity silicon finished product is obtained.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Silicon Compounds (AREA)

Abstract

本发明涉及一种提纯硅的方法，该方法步骤为：向熔融态的待提纯硅加入占待提纯硅的重量百分比10%的熔融态Na2CO3，搅拌10min后，在混合物熔体的表面加覆盖剂后密闭；开始监控并记录待提纯硅的温度；当温度降至1490-1510℃时，减小降温速率；当温度降至硅的熔点时，恒定加热功率；当硅开始降温时，停止加热；自然冷却到室温，取出固态硅；室温下将硅击碎后加入混酸溶液，置通风橱中静置12小时；将已被浸蚀碎裂的硅晶粒与酸液分离后加水浸泡，水洗至中性，过滤、烘干得到高纯硅成品。与传统的定向凝固和区熔相比，极大地提高了凝固过程中杂质的分凝效率，极大地缩短了提纯过程，并提高了纯材料的实收率。

Description

提纯硅的方法
技术领域
本发明涉及一种制取高纯硅的方法， 所制高纯硅用于太阳能电池。 背景技术
光伏发电是利用半导体界面的光生伏特效应而将光能直接转变为电 能的一种技术。 这种技术的关键元件是太阳能电池， 而制备太阳能电池的 关键环节之一制备高纯硅。
避开现有技术中高成本、 高能耗、 环保负担重的改良西门子法， 寻求 用于太阳能电池的低成本、低能耗、环境友好型的制取高纯硅的新提纯方法， 是降低光伏发电成本， 促进光伏发电向主体能源转化的一项战略举措。
已略见成效的现行的冶金法 （物理法） 大体上是两类提纯方法的组合。 第一类是可以除去硅中绝大多数杂质， 提高硅整体纯度的定向凝固和区域 熔化法。 这是物理法中的基础方法。 第二类是针对第一类方法难以除掉的 硅中电活性杂质硼、 磷的专项提纯方法。 两类方法互补加合已制备出能制 造出太阳能电池的高纯硅。 从实际效果看， 所制出的太阳能电池存在光电 转换效率不够高和出现快衰退现象的缺陷， 这表明现有技术制得的高纯硅 中的杂质含量尚不稳定， 硅的纯度也还需进一步提高。 因此， 现行的冶金 法尚不能满足太阳能电池的需要。
采用定向凝固和区域熔化法进行除杂提纯的原理是基于杂质在硅处 在固-液两相平衡时的分凝效应。所谓分凝效应就是杂质在固相中的浓度与 液相中的浓度不相同。 C固表示杂质在硅固相中的浓度； C液表示杂质在液 相中的浓度； K表征杂质的分凝效应， 则 K=C 固 /C 液， 这是由固-液两相 平衡时杂质和硅的热力学特征确定的， 是普遍存在于自然界的一种物理现 象。
定向凝固和区域熔化技术便是借用杂质的分凝效应将待提纯的硅制 成锭条， 让锭条熔化 （整锭或一段）， 控制固 -液界面从锭首移向锭尾。 由 于硅中绝大多数杂质的 K值均小于 1， 杂质在固相中的浓度远低于在液相 中的浓度， 因此在固 -液界面从头向尾的移动过程中， 硅中杂质重新分配， 从凝固的固相中不断排出到液相的杂质被未凝固的液相硅带到后凝固的 部分， 直到到达尾部。 最后， 切去杂质富集的尾部即得到被提纯后的高纯 硅。 除硅外， 定向凝固和区域熔化技术还广泛地应用于更多材料的提纯， 成为提纯的基本方法之一。
定向凝固后杂质沿锭长分布的情况参见图 1。 对于 K<1的杂质， 随着 固 -液界面从锭首向锭尾移动过程，被固相排出的杂质累积在固 -液界面上， 致使界面液相侧浓度升高， 导致结晶时固相中杂质浓度也随之升高。 图 1 中， 曲线 a显示的便是在固 -液界面累积的杂质要靠浓差扩散向熔体硅中转 移的结果。 曲线 b显示的是固相排出的杂质迅即扩散至液相中， 使杂质浓 度呈均匀状态的极限状态 （理想状态）。 采取减慢界面移动速度和加快杂 质扩散速度的措施后， 凝固后杂质沿锭长的分布介于 a， b两条曲线之间。
在定向凝固和区域熔化技术中，对杂质分凝起作用的固-液交界面是一 成不变的等于锭条的横截面积。 这种情况下要提高分凝效果只能降低界面 移动速度。从图 1看出， 一次定向凝固操作后， 杂质浓度降至原始浓度 Q) 以下的锭长不足整个锭长的一半。
在分析了定向凝固和区域熔化法的提纯过程后发现， 在利用杂质分凝 效应进行除杂提纯中存在着低效、 耗时、 耗能、 耗材的严重不足。 这种传 统的分凝模式用于杂质含量较高的粗金属工业硅的提纯更是不适宜的。 发明内容
本发明的主要目的是提供一种新的提纯硅的方法， 相比于定向凝固和 区域熔化法可以显著提高提纯效率， 将工业硅的纯度提高到可以满足太阳 能电池的要求。
为实现上述目的， 本发明采用以下技术方案：
一种提纯硅的方法， 其步骤如下：
( 1 ) 向熔融态的待提纯硅加入占待提纯硅的重量百分比 10%的熔融 态 Na2CO3， 搅拌 lOmin后， 在混合物熔体的表面加覆盖剂后密闭；
(2) 开始监控并记录待提纯硅的温度；
(3 ) 当温度降至 1490〜1510°C (即高于硅熔点 80〜100°C ) 时， 减 小降温速率；
(4) 当温度降至硅的熔点时， 恒定加热功率；
(5 ) 当硅开始降温时， 停止加热； (6) 将硅自然冷却到室温， 取出结晶的固态硅；
(7 ) 室温下将结晶的硅击碎后浸没于混酸溶液中， 置通风橱中静置
12小时；
(8 ) 将经过酸浸蚀的硅晶粒与酸液分离后加水浸泡， 水洗至中性， 过滤、 烘干得到高纯硅成品。
如上所述的提纯硅的方法， 其特征在于， 所述覆盖剂为麦秸或稻秸， 加入量以将待提纯硅的表面完全覆盖为准。
如上所述的提纯硅的方法， 其中， 所述混酸溶液为重量百分比 19%的 HC1、 重量百分比 49%的 HNO3、 重量百分比 49%的 H2SO4中的一种、 或 它们之中任意两种或多种的等重量的混合溶液。 利用晶界聚杂效应的硅提纯方法， 其特征在于， 将熔融态的待提纯硅 导入可控温结晶器中， 调控凝固时硅晶核数量、 晶粒长大速度， 利用晶粒 表面和熔体界面上的杂质分凝效应使晶粒排出的杂质聚集到最终凝固的 晶粒间界处， 然后将被杂质包裹的硅晶粒解脱即得提纯硅。
所述调控凝固时硅晶核数量是指， 在瞬间同时形成数量众多的晶核， 增大固-液界面。
所述将被杂质包裹的硅晶粒解脱是指， 当用酸液浸蚀溶解晶界杂质 时， 被杂质包裹的高纯硅晶粒就被解脱出来。
浓集在晶粒间界处的杂质在降温过程中将从晶粒间界处析出， 形成独 立的杂质相。
所述可控温结晶器由外层的控温台和置于控温台内的结晶器本体组 成， 所述控温台通过内置加热元件控制结晶过程中硅熔体的温度， 所述结 晶器本体内具有控温热偶与程序控温仪相连。 本发明的有益效果为：
本发明提出一种全新的利用杂质分凝效应进行提纯的方法， 以下简称 做晶界聚杂法。其过程是： 将熔融态工业硅导入特制、可控温的结晶器中。 用宏观手段调控凝固时硅晶核数量、 晶粒长大速度， 使晶粒表面和熔体界 面上的杂质分凝效应得到充分发挥， 从晶粒排出的杂质被聚集到最终凝固 的晶粒间界处。 此后再施以有效手段将被杂质包裹的纯硅晶粒解脱后获得 更高纯度的硅。 与传统的定向凝固和区熔相比， 其优势在于：
1 . 极大地提高了凝固过程中杂质的分凝效率， 从而提高了提纯的效 率和效果。 本发明的提纯法是在瞬间同时形成数量众多的晶核， 产生的固 -液界面非常大。 随着硅晶粒长大， 固-液界面面积的增长与晶粒半径尺寸 的二次方成正比， 随之分凝提纯的效果也会有明显的变化。
2. 极大地缩短了提纯过程。 以 10kg工业硅采用晶界聚杂法的结晶过 程与 10kg硅进行定向凝固相比： 工业硅在结晶器中凝固后平均晶粒尺寸 以 1亳米计， 如果从结晶开始到全部凝固的时间是 30分钟， 那么晶粒的 生长速度 （固-液界面的推进速度） 是 1亳米 /小时； 那么， 将 10kg硅铸成 断面 9cmX 9cm的方锭， 锭长 53cm， 按此速度进行定向凝固， 需 530小时
(22天）才能完成。 而晶界聚杂法是由数目巨大的晶核共同启动， 每颗晶 粒向四周空间中延伸 1亳米便相聚， 把杂质赶到了晶粒间界处， 其耗时只 需 30分钟。
3. 提高了纯材料的实收率。 众多晶粒同时在立体空间生长最终交连 成一体， 硅中杂质由于高效的分凝效应被聚集到最终凝固的晶粒交界处。 浓集在晶粒间界处的杂质在降温过程中将从间界处的硅中析出， 形成独立 的杂质相。 当用酸液浸蚀溶解晶界杂质时， 被杂质包裹的高纯硅晶粒就被 解脱出来。 如此收集得到的提纯硅的损耗很小， 与定向凝固数次切除的不 纯尾部相比， 大大提高了实收率。
由于晶界聚杂法的除杂原理与定向凝固和区域熔化相同， 分凝效果却 异常显著， 提纯后硅的纯度品质将会得到有效提高。 再经去硼、 磷处理后 可以很好地满足太阳能电池对高纯硅的技术要求。 附图说明
图 1为定向凝固过程中杂质浓度对凝固部分的曲线。
图 2为工业硅熔体冷却过程的步冷曲线。
图 3为进行本发明提纯方法的可控温结晶器的外观主视图。
图 4为进行本发明提纯方法的可控温结晶器的外观左视图。
图 5为进行本发明提纯方法的可控温结晶器的外观右视图。
图 6为图 4的 A-A剖视图。
图 7为图 3的 B-B剖视图。 具体实施方式
进行本发明晶界聚杂法的典型的可控温结晶器的外观及结构如图 3- 图 7所示。
该可控温结晶器由外层的控温台和置于控温台内的结晶器本体组成。 该结晶器本体具有双层结构， 包括由耐热金属制成的外壳 1和由耐火材料 制成的内衬 2。 在外壳 1 的内壁上悍有五根耐高温合金管 3， 其中两根位 于一侧， 另外三根位于另一侧。 在三根同侧的合金管之中， 位于中间的合 金管的长度为其他四根合金管的 1/2， 该合金管在外壳 1 的内壁接近结晶 器中心的部位形成一盲端， 另一端则穿过结晶器本体， 形成与外部连通的 开口。 其余四根合金管的两端均穿过结晶器本体， 在外壳 1的外壁上形成 与外部连通的开口。 为防止散热， 于结晶器主体上方设有耐火绝热材料的 上盖 4， 其上设有一预留孔 5。
该控温台也具有双层结构， 包括由耐热金属制成的外壳 6和由保温材 料制成的内衬 7。 该内衬 7内设有多个加热元件 8。 该金属板 6和内衬 7 上设有多个通孔 9， 该通孔 9与结晶器本体的合金管 3在外壳 1上的开口 对应连通。
将结晶器本体置于控温台的内衬 7之中， 通过控温台上的通孔 9将热 偶插入五根合金管 3中， 其中， 较短的合金管用以插入控温热偶， 并通过 其盲端将该控温热偶固定于接近结晶器中心的部位。 将上盖热偶通过上盖 4的预留孔 5插入结晶器本体的内部。 对各热偶输出的温度进行监控， 并 将控温热偶与程序控温仪 （图中未示出） 相连， 进而调控控温台中的加热 元件 8， 从而控制结晶过程中硅熔体的温度。 其他四根合金管中的热偶可 以进行移动， 以监测结晶器内部结晶过程中温度的均匀性。
将工业硅熔体浇入可程序控温的结晶器中。 根据图 2所示的工业硅熔 体冷却过程步冷曲线可知， A点是进入结晶器时硅熔体的温度， 随着熔体 散热， 温度逐渐下降。 到达 B点时熔体内的众多晶核形成并开始生长， 硅 熔体开始处在固 -液两相平衡阶段。 由于固相潜热的释放， 硅熔体的温度在 两相平衡阶段保持不变， 恒定在约 1410°C。 在晶核长大的过程中， 杂质发 生分凝。 硅晶粒在结晶器容积空间内自由生长， 而晶粒表面即两相平衡的 固-液界面。随着晶粒长大，界面面积与晶粒半径尺寸的二次方成正比扩展， 而杂质被排到尚未凝固的熔融硅中， 最后聚集到众晶粒的晶粒间界处。 在 晶界处的熔融硅中富集了晶粒排出的杂质 （K<1 的杂质）。 当硅熔体全部 凝固时到达曲线 C点， 不再有固相潜热释放， 此后温度继续下降， 杂质陆 续在晶界处析出。 将结晶器中凝固的硅取出， 适当破碎后置于酸槽中， 用 混酸溶液浸泡约 12 小时。 酸液沿晶界浸入， 溶解杂质后晶界破裂， 提纯 后的硅晶粒被解脱出来。 将硅晶粒与酸液分离后用纯净水清洗至中性， 干 燥后即得到高纯硅成品。
实施例 1
( 1 ) 将熔融硅浇进已置于控温台内的结晶器中， 向其中加入占待提 纯硅的重量百分比 10%的熔融态 Na2CO3， 搅拌 lOmin后， 在其表面加覆 盖剂麦秸， 盖上上盖 4。
(2) 在上盖的预留孔 5中插入上盖热偶， 开启温度记录仪。
(3 ) 当温度降至约 1500°C时， 启动控温台内的加热元件 8以减小降 温速率。
(4) 当温度降至硅的熔点时， 拔出上盖热偶并封闭预留孔 5。 此时恒 定控温台加热功率。 记下中管处的固定控温热偶温度指示值及其与上盖热 偶的差值， 此后便以固定控温热偶显示的温度值判断结晶过程， 由温度记 录仪连续打印温度。
(5 ) 当温度曲线呈现拐点， 显示开始降温时， 表示结晶过程完结， 停止加热。
(6) 自然冷却到室温， 取出结晶器倒出固态硅。
(7) 室温下将硅击碎后放入酸浸槽， 加入重量百分比 49%的 HNO3 和重量百分比 49%的 H2SO4的 1： 1 (重量比）混合溶液， 将硅块浸没， 置 通风橱中静置 12小时。
(8 ) 将已被浸蚀碎裂的硅晶粒与酸液分离后加水浸泡， 水洗至中性， 过滤、 烘干得到高纯硅成品。

Claims

权利要求书
1. 一种提纯硅的方法， 其特征在于， 步骤如下：
( 1 ) 向熔融态的待提纯硅加入占待提纯硅的重量百分比 10%的熔融 态 Na2CO3， 搅拌 lOmin后， 在混合物熔体的表面加覆盖剂后密闭；
(2) 开始监控并记录待提纯硅的温度；
(3 ) 当温度降至 1490〜1510°C时， 减小降温速率；
(4) 当温度降至硅的熔点时， 恒定加热功率；
(5 ) 当硅开始降温时， 停止加热；
(6) 将硅自然冷却到室温， 取出结晶的固态硅；
(7 ) 室温下将结晶的硅击碎后浸没于混酸溶液中， 置通风橱中静置 12小时；
(8 ) 将经过酸浸蚀的硅晶粒与酸液分离后加水浸泡， 水洗至中性， 过滤、 烘干得到高纯硅成品。
2. 如权利要求 1所述的提纯硅的方法， 其特征在于， 所述覆盖剂为 麦秸或稻秸。
3. 如权利要求 1所述的提纯硅的方法， 其特征在于， 所述混酸溶液 为重量百分比 19%的 HC1、 重量百分比 49%的 HNO3、 重量百分比 49%的 H2SO4中的一种、 或其中任意两种或多种的等重量的混合溶液。
4.利用晶界聚杂效应的硅提纯方法， 其特征在于包括， 将熔融态的待 提纯硅导入可控温结晶器中， 调控凝固时硅晶核数量、 晶粒长大速度， 利 用晶粒表面和熔体界面上的杂质分凝效应使晶粒排出的杂质聚集到最终 凝固的晶粒间界处， 然后将被杂质包裹的硅晶粒解脱即得提纯硅。
5.如权利要求 4所述的利用晶界聚杂效应的硅提纯方法，其特征在于， 所述调控凝固时硅晶核数量是指， 在瞬间同时形成数量众多的晶核， 增大 固-液界面。
6.如权利要求 4所述的利用晶界聚杂效应的硅提纯方法，其特征在于， 所述将被杂质包裹的硅晶粒解脱是指， 当用酸液浸蚀溶解晶界杂质时， 被 杂质包裹的高纯硅晶粒就被解脱出来。
7.如权利要求 4所述的利用晶界聚杂效应的硅提纯方法，其特征在于， 浓集在晶粒间界处的杂质在降温过程中将从晶粒间界处析出， 形成独立的 杂质相。
8.如权利要求 4所述的利用晶界聚杂效应的硅提纯方法，其特征在于， 所述可控温结晶器由外层的控温台和置于控温台内的结晶器本体组成， 所 述控温台通过内置加热元件控制结晶过程中硅熔体的温度， 所述结晶器本 体内具有控温热偶与程序控温仪相连。
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