TW201326475A - Polycrystalline silicon ingot, process for producing same, and uses thereof - Google Patents

Abstract

A process for producing a polycrystalline silicon ingot by unidirectionally solidifying molten silicon in a crucible upward from the bottom of the crucible, wherein the molten silicon is unidirectionally solidified under such conditions that when the temperature measured at a position in the vicinity of the center of the undersurface of the crucible falls from (Tm-20) DEG C to (Tm-60) DEG C, where Tm is the temperature measured at the position when the silicon temperature is the melting point of the silicon, then there is a period during which that temperature falls at a rate of 1-10 DEG C/hr, thereby obtaining the polycrystalline silicon ingot.

Description

Polycrystalline germanium ingot and its manufacturing method and use thereof

The present invention relates to a polycrystalline germanium ingot, a method of making the same, and uses thereof.

The use of natural energy has attracted attention by replacing oil that has various problems with the global environment. Among them, the solar cell does not require a large device, and does not generate noise during operation, and is therefore particularly actively used in Japan or Europe.

Solar cells using compound semiconductors such as cadmium telluride have also been put into practical use, but solar cells using crystalline germanium substrates have a large share in terms of the safety of the materials themselves or their current performance or cost efficiency. Among them, a solar cell (polycrystalline silicon solar cell) using a polycrystalline germanium substrate has a large occupation rate.

A polycrystalline silicon wafer which is generally widely used as a substrate of a polycrystalline silicon solar cell is used for cutting an ingot which is produced by a method called a casting method in which a molten crucible is unidirectionally solidified in a crucible to obtain a large polycrystalline ingot, and Wafer by slicing.

The polycrystalline silicon wafer fabricated by the casting method generally has a distribution in the power characteristics of the solar cell as shown in FIG. 5 depending on the position of the height direction in the ingot or the block.

The reason for the distribution of the characteristics of Fig. 5 is usually as explained below.

First, in the initial region I for unidirectional solidification, the characteristics are degraded due to the influence of impurities diffused by the ruthenium. In the region II on the upper side thereof, impurities or impurities in the raw material are incorporated into the crystal due to segregation. Produced less, so the characteristics are the best in the block. Further, in the region III on the upper side, the amount of impurities incorporated into the crystal gradually increases, and the generation of crystal defects increases, and the characteristics are lowered as compared with the region II. Further, in the region IV on the upper side, as in the region III, the generation of impurities or crystal defects incorporated in the crystal is further increased, and the ingot is solidified until the end, and thereafter the impurities generated from the uppermost surface portion are The high concentration portion causes the reverse diffusion of impurities, which in turn increases the amount of impurities, so that the characteristic is more remarkable than that of the region III.

In the above description, the influence of the impurities in the raw material or the impurities eluted from the ruthenium is considered, but even in the case where it is assumed that there is no such influence, in the regions III and IV, as the upper portion becomes the minority carrier capture The crystal defects are also gradually increased, and thus the characteristics of the solar cell tend to decrease.

It is considered that the cause of the crystal defect is the stress due to the temperature distribution in the ingot, and the following two methods have been proposed from the viewpoint of suppressing the stress.

For example, Japanese Laid-Open Patent Publication No. 2005-152985 (Patent Document 1) proposes a mold holder which is disposed on the lower portion of the crucible during unidirectional solidification (casting), and the heat flow rate at the center portion is larger than that of the periphery. method.

In the second, for example, International Publication No. 2005/092791 (Patent Document 2) proposes a method of performing heat flow control on the way of ingot growth by changing the structure of the heat (heat exchange) area.

Further, as a measure for improving the quality of the polycrystalline iridium ingot different from the above method, a method for increasing the particle size has been proposed.

For example, in the Japanese Patent No. 4,203,603 (Patent Document 3) and the Japanese Patent Laid-Open Publication No. 2005-132671 (Patent Document 4) Method: By crystallizing the bottom of the crucible, dendrites are generated as crystal nucleuses at the bottom of the ingot (in the initial stage of solidification) to coarsen the crystal grains.

In Japanese Patent No. 4,054,873 (Patent Document 5), there is proposed a method of obtaining a quasi-single crystal by growing a crystal piece (melting residue) remaining in a melting step of a niobium raw material to grow a crystal grain.

Further, Japanese Patent No. 4569957 (Patent Document 6) proposes a method in which a seed crystal such as SiC disposed at the bottom of the crucible is uniformly grown from a crystal orientation to obtain a quasi-single crystal.

Prior technical literature

Patent literature

Patent Document 1: Japanese Patent Laid-Open Publication No. 2005-152985

Patent Document 2: International Publication No. 2005/092791

Patent Document 3: Japanese Patent No. 4203603

Patent Document 4: Japanese Patent Laid-Open Publication No. 2005-132671

Patent Document 5: Japanese Patent No. 4054883

Patent Document 6: Japanese Patent No. 4569957

In the method of Patent Document 1, there is a problem that, particularly in the case where the heater is located beside the crucible, the shape of the solid-liquid interface is further deteriorated, and effects such as reduction in crystal defect density and crack prevention cannot be obtained.

In the method of Patent Document 2, there is a problem that although the controllability of cooling from the side wall of the crucible can be improved, the device configuration is extremely complicated, and the temperature is high. There are more movable parts, and the cost of the device increases or the fault increases.

In the methods of Patent Documents 3 to 5, there is an advantage that the deterioration of the grain boundary can be suppressed by the coarsening of the crystal grains, especially when the ingot size is small, the stress due to the temperature distribution is relatively small. The crystal defects introduced on the top side of the ingot are also suppressed to some extent. However, since the size of the ingot is increased and the crystal defects on the top side are increased, the improvement in the characteristics of the bottom side can be observed, but the problem that the characteristics of the solar cell fabricated on the top side is reduced remains.

In the method of Patent Document 6, it is considered that the ruthenium crystal grown from the adjacent SiC or the like forms a defect at the boundary portion where the collision occurs, and even if the ingot looks macroscopically as a single crystal, there are a large number of defects in electrical properties. Further, regarding the top side, the size of the ingot is increased and the density of the crystal defects on the top side is increased, and the problem of the characteristics of the solar cell fabricated on the top side remains.

On the other hand, the larger the size of the polycrystalline germanium ingot, the more the price per wafer of the polycrystalline silicon wafer can be suppressed, and the size of the ingot tends to increase.

Therefore, in order to achieve high performance and low cost of the final polycrystalline silicon solar cell module, it is required to easily and inexpensively perform a method of reducing the crystal defect density or preventing cracking in the production of a large-sized polycrystalline silicon ingot.

An object of the present invention is to provide a method for producing a polycrystalline germanium ingot which can reduce the crystal defect density and prevent cracking at a simple and low cost, and a polycrystalline germanium ingot obtained therefrom and use thereof.

The inventors of the present invention repeatedly conducted intensive studies and found that it was produced by unidirectional solidification in the upper portion of the crucible from the bottom of the crucible. In the case of a crystal ingot, the temperature at the bottom of the crucible at the start of solidification (crystal growth) is controlled to promote the generation of a crystal nucleus, and the above problems can be solved, and the present invention has been completed.

Thus, according to the present invention, there is provided a method for producing a polycrystalline ruthenium ingot which is obtained by unidirectional solidification of a molten yttrium in a crucible from the bottom of the crucible to produce a polycrystalline bismuth ingot, and the enthalpy temperature is the melting point of cerium The detection temperature in the vicinity of the center of the lower surface is set to Tm, and the temperature is lowered by the temperature change rate of 1 to 10 ° C / hour while the detection temperature is lowered from (Tm - 20) ° C to (Tm - 60) ° C. Under the conditions, the molten ruthenium is unidirectionally solidified to obtain a polycrystalline ruthenium ingot.

Moreover, according to the present invention, there is provided a method for producing a polycrystalline ruthenium in which a ruthenium in a crucible is unidirectionally solidified from a bottom portion of the crucible to produce a polycrystalline bismuth ingot, and the crucible temperature is a melting point of bismuth. The detection temperature at the lower 20 mm position near the center of the lower surface is set to Tm', and the detection temperature is lowered from (Tm'-20) °C to (Tm'-60) °C, and there is 1 to 10 ° C / hour. The rate of temperature change causes the temperature to decrease. Under the conditions, the molten enthalpy is unidirectionally solidified to obtain a polycrystalline bismuth ingot.

Moreover, according to the present invention, there is provided a polycrystalline germanium ingot produced by the above polycrystalline ingot manufacturing method, a polycrystalline germanium obtained by processing the polycrystalline germanium ingot, a polycrystalline germanium wafer obtained by processing the polycrystalline germanium block, and a polycrystalline germanium obtained by using the polycrystalline germanium. Wafer-made polycrystalline solar cells.

In the present invention, the term "solar battery" means a "solar battery unit" constituting a minimum unit and electrically connecting a plurality of solar battery units. Into the "solar battery module."

According to the present invention, it is possible to provide a method for producing a polycrystalline germanium ingot which can reduce the crystal defect density or crack prevention at a simple and low cost, and a polycrystalline germanium ingot obtained therefrom and use thereof.

That is, according to the present invention, high-quality polycrystalline germanium ingots, blocks, and wafers can be manufactured at low cost, and a polycrystalline solar cell having high cost and high power can be supplied to the market.

The method for producing a polycrystalline germanium ingot according to the present invention is the case where the temperature change rate is 2 to 7 ° C / hour, and when the temperature is decreased by 20% or more at the temperature change rate of 1 to 10 ° C / hour, In particular, the above effects are exerted.

The method for producing a polycrystalline ruthenium ingot according to the present invention is characterized in that a ruthenium in a crucible is unidirectionally solidified from a bottom portion of the crucible to produce a polycrystalline bismuth ingot, and the enthalpy temperature becomes a enthalpy of enthalpy. The detection temperature in the vicinity of the center of the surface is set to Tm, and the temperature is lowered by a temperature change rate of 1 to 10 ° C / hour while the detection temperature is lowered from (Tm - 20) ° C to (Tm - 60) ° C. Under the conditions, the molten ruthenium is unidirectionally solidified to obtain a polycrystalline ruthenium ingot.

The detection temperature "Tm" can be determined so that when the raw material solid is melted in the crucible, the temperature of the melt is the melting point of the crucible and the fixed value is obtained before the end of the melting of the crucible, and the detection temperature near the center of the lower surface of the crucible It also becomes the detection temperature at a substantially fixed time. In this state, the temperature of the crucible melt becomes the melting point of the crucible, and Tm is near the center of the lower surface of the crucible at this time. Detect temperature. It is believed that since the platform is always cooled, the Tm is a few °C lower than the melting point of the crucible. The measured absolute value of Tm has a slight deviation in the display due to the calibration method of the thermocouple or the degree of deterioration, individual difference, deviation of the setting of the device, etc., and the error of the measured absolute value is large. However, by correcting the detection temperature in the vicinity of the center of the lower surface of the crucible based on Tm, the cause of the above deviation can be eliminated, and the reproducibility of the crystal growth condition can be ensured. It can also be observed that the absolute value of the measured value of Tm in the present embodiment is higher than the melting point of the crucible for the above reasons, and is in the range of 1407 ° C to 1418 ° C.

In the case of a polycrystalline germanium ingot manufacturing apparatus or the like in which a cerium melt is injected into a crucible, for example, the temperature of the molten metal is measured by a radiation thermometer, and the relationship with the detected temperature in the vicinity of the center of the underarm surface is obtained, thereby determining the above-mentioned " Tm".

Moreover, the method for producing a polycrystalline germanium ingot according to the present invention is characterized in that a molten crucible in a crucible is unidirectionally solidified from the bottom of the crucible to form a polycrystalline ingot, and the crucible temperature is the melting point of the crucible. The detection temperature at the lower 20 mm position near the center of the lower surface is set to Tm', and the detection temperature is lowered from (Tm'-20) °C to (Tm'-60) °C, and there is 1 to 10 ° C / hour. The rate of temperature change causes the temperature to decrease. Under the conditions, the molten enthalpy is unidirectionally solidified to obtain a polycrystalline bismuth ingot.

The above-described detected temperature "Tm'" is different only in the temperature measurement point, and can be determined in the same manner as the above "Tm". Here, as the temperature measurement point, the position 20 mm below the vicinity of the lower surface of the crucible is selected. However, if it is electrically connected to the crucible, as long as it is a region that can be correlated with the temperature of the crucible in the crucible, it can become a temperature measurement point. .

The inventors of the present invention conducted evaluation, analysis, and investigation of crystal defects on a plurality of polycrystalline bismuth ingots, and as a result, found that the method of reducing the density of crystal defects on the top side of the ingot is considered to be more effective than before and by suppressing the usual use. In addition to the method of temperature distribution and stress reduction, there are other methods.

Specifically, the inventors of the present invention have conceived the idea that the technique described in Patent Documents 3 to 6 which suppresses the deterioration of the grain boundary by the coarsening of crystal grains is completely opposite, and found a polycrystalline ingot having a small crystal grain size. The stress is stronger than that of the larger crystal grain size, and it is difficult to cause crystal defects.

According to the findings of the inventors of the present invention, (1) even in the closely adjacent portion of the polycrystalline iridium ingot, the density of crystal defects introduced into the interior according to the larger crystal grain size and the smaller particle are greatly different ( 2) There is a correlation between the crystal grain size of the ingot and the crystal defect density on the top side, and (3) the exception is that the smaller the crystal grain size, the lower the crystal defect density on the top side of the ingot. It is not easy to think of the adjacent part in the ingot, and there is a large difference in the thermal stress that the ingot grows. Therefore, it is considered that the portion having a smaller crystal grain size is subjected to the stress relaxation in the crystal grain by sliding of the grain boundary portion or the like. As a result, crystal defects can be suppressed from being introduced into the crystal grains.

Therefore, when the polycrystalline ruthenium ingot is solidified by unidirectional solidification in the crucible, the characteristic of the top side of the polycrystalline iridium ingot can be alleviated by promoting the generation of the crystal nucleus at the bottom of the crucible and reducing the crystal grain size.

In order to reduce the crystal defects on the top side of the polycrystalline ingot, it has been considered that it is necessary to reduce the thermal stress applied to the ingot by flattening the solid-liquid interface. In contrast, in the present invention, only the crystal grain size of the reduced crystal grain size is performed. It Control can reduce the crystal defects on the top side of the polycrystalline germanium ingot.

The apparatus for producing a polycrystalline germanium ingot which can be used in the method for producing a polycrystalline germanium ingot of the present invention is not particularly limited, and can be carried out using a known manufacturing apparatus.

As an example, for example, it can be implemented by a manufacturing apparatus or the like that cools the bottom surface of the crucible by a cooling mechanism such as a refrigerant circulation provided on the base side of the crucible, and moves the crucible away by the lifting drive mechanism. The heating mechanism gradually solidifies the molten crucible in the crucible from the molten crucible near the bottom of the crucible by using the above two conditions in combination. At this time, the temperature of the heater is controlled by a known method, specifically, by a thermocouple or a radiation thermometer, and the temperature change rate of melting, solidification, and cooling of the crucible is monitored.

(Manufacturing method of polycrystalline germanium ingot)

Hereinafter, a method of producing the polycrystalline germanium ingot of the present invention will be described based on the drawings, but the present invention is not limited to the embodiment.

The method for producing a polycrystalline semiconductor ingot of the present invention can also be carried out using a known device as shown in FIG.

Fig. 4 is a schematic cross-sectional view showing an example of a device used in the method for producing a polycrystalline semiconductor ingot of the present invention.

The apparatus is generally used to manufacture a polycrystalline germanium ingot and includes a chamber (closed container) 7 constituting a resistance heating furnace.

Inside the chamber 7, a crucible 1 made of graphite, quartz (SiO ₂ ) or the like is disposed, and the internal environment of the chamber 7 can be maintained in a sealed state.

A crucible 3 made of graphite supporting the crucible 1 is disposed in the chamber 7 of the housing 1 . The stern 3 can be raised and lowered by the elevation drive mechanism 12 to circulate the refrigerant (cooling water) in the cooling tank 11 therein.

In the upper part of the platform 3, a crucible 2 such as graphite is disposed, and a crucible 1 is disposed therein. It is also possible to arrange an outer cover such as graphite which surrounds the crucible 1 instead of the outer crucible 2.

The electric resistance heating body 10 such as a graphite heater is disposed so as to surround the outer crucible 2, and the heat insulating material 8 is disposed so as to cover it from above.

The electric resistance heating body 10 is heated from the periphery of the crucible 1 to melt the raw material crucible 4 in the crucible 1.

The shape of the heating means such as the heating element can be controlled by heating by the electric resistance heating body 10, cooling by the cooling tank 11 from the lower side of the crucible 1 and lifting and lowering of the crucible 1 by the lifting/lowering mechanism 12. Or the configuration is not particularly limited.

In order to detect the temperature of the bottom surface of the crucible 1, the underarm thermocouple 5 is disposed near the center of the lower surface of the crucible 1, and the outer submerged thermocouple 6 is disposed near the center of the lower surface of the crucible, and the output of the crucible is input to the control device 9 And the heating state of the electric heating body 10 is controlled by the electric resistance. In addition to the above thermocouples, thermocouples or radiation thermometers for detecting temperature can also be configured.

The chamber 7 can keep the inside of the chamber in a sealed state to prevent the inflow of oxygen, nitrogen, or the like from the outside, usually after the introduction of the raw material such as polycrystalline germanium and before the melting, the chamber 7 is evacuated, and then an inert gas such as argon is introduced. Gas while remaining in an inert environment.

According to the apparatus of such a configuration, the polycrystalline germanium ingot is basically produced by filling the crucible 1 with the crucible raw material 4, performing gas exchange in the chamber 7 by degassing (vacuumization) and introduction of an inert gas, The crucible raw material 4 is melted by melting, confirmed by melting, and maintained, temperature controlled, and lifted and driven by the mechanism 12 Start of solidification by operation, confirmation of completion of curing, annealing, and ingot removal.

In the production method of the present invention, the detection temperature in the vicinity of the center of the lower surface of the crucible when the crucible temperature reaches the melting point of 矽 is set to Tm, and the detection temperature is lowered from (Tm-20) °C to (Tm-60). During the period of °C, there is a time when the temperature is lowered by a temperature change rate of 1 to 10 ° C / hour.

Further, in the production method of the present invention, the detection temperature at a position of 20 mm below the center of the lower surface of the crucible when the crucible temperature reaches the melting point of 矽 is set to Tm', and the temperature is detected from (Tm'- 20) While °C is lowered to (Tm'-60) °C, there is a time when the temperature is lowered by a temperature change rate of 1 to 10 °C / hour.

The inventors of the present invention have confirmed the following.

In the case where the crucible material is melted in the crucible, the temperature at the vicinity of the center of the lower surface of the crucible and the position of 20 mm below the center of the lower surface of the crucible before the end of the melting show a substantially constant value. By setting the fixed value as the reference temperature (Tm, Tm', respectively), as described above, for example, even when the thermocouple is replaced, the individual difference (deviation) can be excluded, and the temperature condition can be stabilized. At the same time as the completion of the melting, as the liquid temperature rises, the temperature of the underarm also rises, but since it usually enters the process of unidirectional solidification, the temperature is gradually lowered.

The temperature measurement point is not necessarily 20 mm below the center of the crotch surface or near the center of the crotch surface, as long as it is in a relationship with the temperature near the center of the crotch surface in the temperature range in which the nucleus is generated at the bottom surface of the crucible, A position that is convenient for thermocouple setting can be appropriately selected. However, it is preferred that the temperature of the temperature measurement point thus selected is The temperature in the vicinity of the center of the lower surface maintains a substantially constant difference in state. For example, if it is in the sill, it is preferably as far as possible above the sill, and if it is in-plane, it is preferably not susceptible to change in heater power. The central part of the influence.

For example, in the apparatus of FIG. 4, when the temperature detected by the thermocouple disposed near the center of the lower surface of the outer crucible 2 and the detection temperature near the center of the lower surface of the crucible 1 always have a fixed temperature difference, the crucible is about to be melted. When the enthalpy temperature is fixed (the melting point of enthalpy), the detection temperature near the center of the lower surface of 坩埚2 is set to Tm", so that the detection temperature near the center of the lower surface of the outer raft is lowered from (Tm"-20) °C to (Tm" -60) The temperature during the period from °C to the vicinity of the center of the underarm surface is equivalent to a period from (Tm-20) °C to (Tm - 60) °C, and temperature control is possible.

Specifically, as described in the embodiment, the detection temperature of the thermocouple disposed near the center of the lower surface of the outer crucible 2 (20 mm below) and the detection temperature near the center of the lower surface of the crucible 1 always have a temperature difference of -10 ° C. The temperature control in the production method of the present invention can be carried out during the period from (Tm'-20) °C to (Tm'-60) °C.

According to the findings of the inventors of the present invention, it is considered that in the above temperature range, a crystal nucleus is generated from the melting enthalpy at the bottom of the crucible, and the crystal grain size depends on the probability of occurrence of the crystal nucleus at the bottom of the crucible and the growth rate of the crystal nucleus.

Further, by the time of cooling at the temperature change rate described above, the growth rate in the horizontal direction of the crystal nucleus at the bottom of the crucible is suppressed, and as a result, the density of the crystal nucleus can be increased, and the crystal grain size can be controlled to be small, and can be lowered. The crystal defects on the top side of the polycrystalline germanium ingot can alleviate the deterioration of its characteristics.

If the temperature change rate of cooling exceeds 0 ° C / hour and does not reach 1 ° C / hour, the crystal grain size is controlled to be small, but the crystal growth is too time consuming, and as a result, the metal impurities are promoted. The enthalpy diffuses (dissolves) into the enthalpy or solidified enthalpy, so that the advantages are offset. Further, when the temperature change rate of cooling exceeds 10 ° C /hr, the growth rate of the crystal nucleus generated in the bottom of the crucible cannot be suppressed in the horizontal direction, and as a result, the density of the crystal nucleus cannot be increased. Therefore, the temperature change rate of cooling is preferably from 1 to 10 ° C / hour. A better temperature change rate is 2 to 7 ° C / hour.

In the production method of the present invention, the ratio of the time at which the temperature is lowered by the temperature change rate of 1 to 10 ° C / hour during the temperature decrease period is preferably higher, for example, preferably 20% or more, more preferably 40. %the above. By making the ratio higher, the density of generation of the crystal nucleus at the bottom of the crucible is increased, and the ratio of the region where the crystal grain size is controlled to be small increases.

(polycrystalline germanium ingot)

The polycrystalline germanium ingot of the present invention is produced by the method for producing a polycrystalline germanium ingot of the present invention.

(polycrystalline block)

The polycrystalline germanium block of the present invention is obtained by processing the polycrystalline germanium ingot of the present invention.

The polycrystalline germanium block can be obtained by cutting a surface portion of the polycrystalline tantalum ingot of the present invention in which the impurities such as a tantalum material are diffused by using a known device such as a band saw.

Further, the surface of the polycrystalline crucible may be polished as needed.

(polycrystalline silicon wafer)

The polycrystalline germanium wafer of the present invention is obtained by processing the polycrystalline germanium block of the present invention.

The polycrystalline silicon wafer can be obtained by processing a polycrystalline germanium block of the present invention into a desired thickness by using a known device such as a multi-wire cutting machine. In the current situation, the thickness is usually about 170 to 200 μm, but there is a tendency to reduce the thickness in order to reduce the cost.

Further, the surface of the polycrystalline silicon wafer may be polished as needed.

(polycrystalline solar cells)

The polycrystalline germanium solar cell of the present invention is produced using the crystalline germanium wafer of the present invention.

The polycrystalline germanium solar cell can be fabricated using, for example, a crystalline germanium wafer of the present invention and by a known solar cell process. That is, when a known material is used and a p-type impurity-doped germanium wafer is doped by a known method, an n-type impurity is doped to form an n-type layer to form a pn junction, thereby forming a surface electrode and a back surface electrode. A polycrystalline silicon solar cell unit is obtained.

Similarly, in the case of a germanium wafer doped with an n-type impurity, a p-type impurity is doped to form a p-type layer to form a pn junction, and a surface electrode and a back electrode are formed to obtain a polycrystalline silicon solar cell. Or a MIS (Metal Insulator Semiconductor) type solar cell in which a thin insulating layer is deposited by vapor deposition of a metal, etc., in addition to the pn junction of the ruthenium, and the like, for example, a conductive type and a conductive type are formed. A thin film such as an amorphous material having a crystal wafer opposite to that of a p-type or n-type germanium having a different structure may be used. Moreover, a plurality of polycrystalline germanium solar cells are electrically connected to obtain a polycrystalline solar cell module.

As described above, in the present specification, the concept of "solar battery unit" and "solar battery module" is simply referred to as "solar battery". Therefore, for example, if it is described as "polycrystalline solar cell", it means "polycrystalline silicon solar cell" and "polycrystalline solar cell module".

Example

Hereinafter, the present invention will be specifically described by way of Test Examples, but the present invention is not limited by such Test Examples.

(Test Example 1) Study on the dependence of temperature change rate

A graphite outer raft 2 is provided on a graphite ram 3 (880 mm × 880 mm × thickness 200 mm) in the polycrystalline iridium ingot manufacturing apparatus shown in Fig. 4 (internal size: 900 mm × 900 mm × height 460 mm, bottom plate) Thickness and side thickness 20 mm), with quartz 坩埚1 (internal size: 830 mm × 830 mm × 420 mm, bottom plate thickness and side thickness 22 mm). Further, the thermocouple for temperature measurement was placed at two locations near the center of the lower surface of the crucible 1 and near the center of the lower surface of the outer crucible 2.

Next, 420 kg of the raw material 矽4 which adjusted the boron dopant concentration so that the specific resistance of the ingot became about 1.5 Ωcm was added to 坩埚1, and the inside of the apparatus was evacuated and replaced with argon gas. Thereafter, the crucible raw material was melted by using a heating mechanism (graphite heater 10) disposed next to the crucible as a heating means of the apparatus, and after melting of all the raw materials was confirmed, the crucible was solidified unidirectionally under the following conditions, and annealed at 1200 ° C for 2 hours. The temperature was lowered at a cooling rate of 100 ° C / hour, and then the polycrystalline germanium ingot was taken out from the apparatus.

In the solidification step, the following conditions are set: by controlling the heater temperature and the descending speed of the crucible, the detection temperature is near the center of the lower surface of the crucible. The temperature change rate of the thermocouple during the period from Tm-20 °C to Tm-60 °C is 0.5 ° C / hour, 1 ° C / hour, 2 ° C / hour, 5 ° C / hour, 7 ° C / hour, 10 ° C / hour. At 15 ° C / hour and 20 ° C / hour, it is roughly fixed. The "temperature change rate" indicates a negative tendency at the time of cooling. In this test, the measured value of Tm is in the range of 1410 ° C to 1418 ° C.

The temperature conditions other than the temperature change rate of the thermocouple are set to be substantially the same, and in particular, the influence of the occurrence of the nucleus at the bottom of the ingot can be evaluated.

The relationship between the detection temperature of the vicinity of the center of the lower surface of the crucible 1 and the vicinity of the center of the lower surface of the outer crucible 2 (the position of 20 mm below the center of the lower surface of the crucible) was confirmed. As a result, it was confirmed that the state of the difference was approximately 10 ° C. The detection temperature in the vicinity of the center of the lower surface from Tm-20 ° C to Tm - 60 ° C corresponds to the detection temperature in the vicinity of the center of the lower surface of the outer crucible 2 from Tm '-20 ° C to Tm '-60 ° C.

The obtained polycrystalline germanium ingot was processed into a block (156 mm × 156 mm × 200 mm) using a band saw, and then it was sliced using a wire saw to obtain a polycrystalline germanium wafer (156 mm × 156 mm × thickness 0.18 mm) of about 12,000 pieces. .

The obtained polycrystalline silicon wafer was put into a normal solar cell process, and 12,000 solar cells (shape 156 mm × 156 mm × thickness 0.18 mm) were produced for each ingot, and the power (W) was measured.

It is understood that most of the reason why the power of the solar cell is lowered is that the crystal defects on the top side of the ingot, especially when the crystal growth time is extremely long, that is, when the production time of the ingot is extremely long, the impurity on the bottom side of the ingot is diffused.

Therefore, it is known whether the ingot is good or not by evaluating the power distribution of the solar cell.

For the power of each solar cell, the lower limit power of level 1 is normalized to 100, and the high power side is classified into levels 1 to 3, and the existence ratio (%) is calculated for each ingot.

Level 1: Power is above 100

Level 2: Power is above 93 and not up to 100

Level 3: Power is less than 93

The results obtained are shown in Table 1 and Figure 2.

As is clear from the results of Table 1 and Figure 2, when the temperature change rate is 1 to 10 ° C / hour, especially 2 to 7 ° C / hour or less, the production rate of high grade products is high. The ingots are of good quality.

On the other hand, it is understood that when the temperature change rate is less than 1 ° C / hour and when it exceeds 10 ° C / hour, the production rate of the low grade product is high and the quality of the ingot is poor.

Further, the crystal grain size of the obtained polycrystalline ingot was visually observed, and as a result, it was found that the larger the temperature change rate, the larger the crystal grain size.

(Test Example 2) Study on the occupancy rate of temperature change rate

In the solidification step, the temperature change rate of the thermocouple is changed to 1 to 10 ° C / small by controlling the heater temperature and the helium falling speed. In the same manner as in Test Example 1, a polycrystalline germanium ingot was produced in the same manner as in Test Example 1 except that the ratio (occupancy ratio) of the time was 0%, 20%, 40%, 60%, 80%, and 100%, respectively. Battery and evaluate its power distribution. In addition, the temperature change rate was changed to 25 ° C / hour, except that the temperature change rate was in the range of 1 to 10 ° C / hour.

In this test, the measured value of Tm is in the range of 1407 ° C to 1415 ° C.

Fig. 1 shows the relationship between the elapsed time (hour) when the occupancy rate is 60% and the detected temperature (°C) near the center of the underarm surface. In the figure, TG1, TG10, and TG25 indicate lines of temperature change rates of 1 ° C / hour, 10 ° C / hour, and 25 ° C / hour, respectively.

That is, in Test Example 2, similarly to Test Example 1, in particular, the influence of the occurrence of the nucleus at the bottom of the ingot was evaluated.

The results obtained are shown in Table 2 and Figure 3.

As is clear from the results of Table 2 and FIG. 3, when the occupancy rate of the specific temperature change rate is 20% or more, especially in the case of 40% or more, the generation rate of the low-grade product is lowered, and good results are obtained. Quality ingots.

1‧‧‧坩埚

2‧‧‧ Appearance

3‧‧‧坩埚台

4‧‧‧ Raw materials矽

5‧‧‧坩埚下热 thermocouple

6‧‧‧ External thermocouple (20 mm thermocouple under the armpit)

7‧‧‧ chamber

8‧‧‧Insulation materials

9‧‧‧Control device

10‧‧‧Resistive heating body (graphite heater)

11‧‧‧Cooling trough

12‧‧‧ Lifting drive mechanism

TG1‧‧‧The rate of temperature change is 1 °C / hour

TG10‧‧‧The rate of temperature change is 10 °C / hour

TG25‧‧‧The rate of temperature change is 25 °C / hour

Fig. 1 is a graph showing the temperature change in the vicinity of the center of the underarm surface at the time of production of a polycrystalline germanium ingot (Test Example 2).

Fig. 2 is a graph showing the relationship between the power of the solar cell and the temperature change rate at the time of production of the polycrystalline germanium ingot (Test Example 1).

Fig. 3 is a graph showing the relationship between the power of the solar cell and the occupancy rate of the temperature change rate at the time of production of the polycrystalline germanium ingot (Test Example 2).

Fig. 4 is a schematic cross-sectional view showing an example of a device used in the method for producing a polycrystalline semiconductor ingot of the present invention.

Fig. 5 is a conceptual diagram showing the relationship between the position of the usual polycrystalline germanium in the height direction and the power of the fabricated solar cell.

TG1‧‧‧The rate of temperature change is 1 °C / hour

TG10‧‧‧The rate of temperature change is 10 °C / hour

TG25‧‧‧The rate of temperature change is 25 °C / hour

Claims (14)

A method for producing a polycrystalline bismuth ingot, which is a method for producing a polycrystalline bismuth ingot by unidirectional solidification of a molten cerium in a crucible from a bottom of the crucible, and detecting temperature near a center of a lower surface of the crucible when a crucible temperature reaches a melting point of cerium When Tm is set, the temperature is lowered by a temperature change rate of 1 to 10 ° C / hr during the period from the decrease of (Tm - 20) ° C to (Tm - 60) ° C. The molten crucible is unidirectionally solidified to obtain a polycrystalline ingot. The method for producing a polycrystalline germanium ingot according to claim 1, wherein the temperature change rate is 2 to 7 ° C / hour. The method for producing a polycrystalline germanium ingot according to claim 1, wherein the temperature is decreased by 20% or more at the temperature change rate of 1 to 10 ° C / hour. A polycrystalline germanium ingot manufactured by the method for producing a polycrystalline germanium ingot of claim 1. A polycrystalline germanium block obtained by processing a polycrystalline germanium ingot of claim 4. A polycrystalline germanium wafer obtained by processing a polycrystalline germanium block as claimed in claim 5. A polycrystalline germanium solar cell fabricated using the polysilicon wafer of claim 6. A method for producing a polycrystalline bismuth ingot, which is a method for producing a polycrystalline bismuth ingot by unidirectional solidification of a molten yttrium in a crucible from a bottom portion of the crucible, and lowering the vicinity of the center of the lower surface of the crucible when the crucible temperature reaches the melting point of the crucible The detection temperature of the mm position is set to Tm' at the above detection temperature. During the period from (Tm'-20) °C to (Tm'-60) °C, there is a time for the temperature to decrease at a temperature change rate of 1 to 10 ° C / hour. Under the conditions, the molten enthalpy is unidirectionally solidified. A polycrystalline germanium ingot is obtained. The method for producing a polycrystalline germanium ingot according to claim 8, wherein the temperature change rate is 2 to 7 ° C / hour. The method for producing a polycrystalline germanium ingot according to claim 8, wherein the temperature is decreased by 20% or more at the temperature change rate of 1 to 10 ° C / hour. A polycrystalline germanium ingot manufactured by the method for producing a polycrystalline germanium ingot of claim 8. A polycrystalline germanium block obtained by processing a polycrystalline germanium ingot of claim 11. A polycrystalline germanium wafer obtained by processing a polycrystalline germanium block of claim 12. A polycrystalline germanium solar cell fabricated using a polysilicon wafer as claimed in claim 13.