FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patents Rules  2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

1. APPARATUS FOR PRODUCING MULTICRYSTALLINE SILICON INGOTS BY
INDUCTION METHOD

2.

1. (A) PILLAR LTD.
(B) Ukraine
(C) 1  Magnitogorska Str.  office 404  Kiev  02660 Ukraine

2. (A) TESYS LIMITED
(B) Ukraine
(C) 3  Pivnichno-Syretska Str. Kiev  04136 Ukraine

3. (A) SILICIO SOLAR  S.A.U.
(B) Spain
(C) Poligono Industrial "LA NAVA I" Avenida Roma 1 E-13500 Puertollano
(Ciudad Real) Spain

The following specification particularly describes the invention and the manner in which it is to be performed.

Technical Field
This invention relates to apparatus for producing multicrystalline silicon ingots by the induction method and can be used in the manufacture of solar cells from multicrystalline silicon.
Background Art
Solar cells that produce electricity from the sun""s rays are built of crystalline silicon  both monocrystalline and multicrystalline  i.e.  polycrystalline silicon consisting of large crystals.
Interest to multicrystalline silicon has been ever growing because multicrystalline silicon solar cells efficiency is close to that of monocrystalline silicon solar cells  while the multicrystalline silicon growing equipment productivity is several times as high as that of monocrystalline silicon growing equipment. Also  multicrystalline silicon growing is simpler than monocrystalline silicon growing.
Known in the art is an apparatus for producing multicrystalline silicon ingots by the induction method  which apparatus comprising a chamber wherein installed is a cooled crucible enveloped by an inductor and having a movable bottom and four walls consisting of sections spaced apart by vertically extending slots. There is also a set of heating means for controlled cooling of the ingot (EP No. 1754806  published 21.02.2007  cl. S30B 11/00) [I]. Also  the apparatus is equipped with a separate partition means capable of being installed on the crystallized ingot in the melting space of the cooled crucible and further heating the lump silicon charge  melting and casting above the top level of the partition device.
A disadvantage of the known apparatus resides in the multicrystalline silicon low productivity and non sufficient quality of obtained multicrystalline silicon. Multicrystalline silicon has a large number of defects in the crystal structure.
An apparatus for producing multicrystalline silicon ingots by the induction method bearing closely on the invention comprises an enclosure  which includes means for start-up heating of silicon  a cooled crucible
enveloped by an inductor and having a movable bottom and four walls consisting of sections spaced apart by vertically extending slots  means for moving the movable bottom  and a controlled cooling compartment arranged under the cooled crucible wherein the inside face thereof defines a melting chamber of a rectangular or square cross-section and the walls of the cooled crucible extend outwards at least from the inductor toward the lowest portion of the cooled crucible to thereby expand the melting chamber  (EP 0349904 published 10.01.1990  cl. B22D 11/10) [2]. The angle of expanding the melting chamber is from 0.4 to 2°.
A disadvantage of the known apparatus resides in a decreased quality of multicrystalline silicon ingot and a decrease in productivity of the manufacture of multicrystalline silicon ingots due to frequent silicon melt spills.
Disclosure of Invention
The present invention aims at providing an improved apparatus for producing multicrystalline silicon ingots by the induction method  in which""  by proposed structural changes  the silicon melt spilling is reduced to thus obtain multicrystalline silicon of better quality and to enhance multicrystalline silicon productivity.
This objective is achieved by providing an apparatus for producing multicrystalline silicon ingots by the induction method  comprising an enclosure  which includes means for start-up heating of silicon  a cooled crucible enveloped by an inductor and having a movable bottom and four walls consisting of sections spaced apart by vertically extending slots  means for moving the movable bottom  and a controlled cooling compartment arranged under the cooled crucible wherein the inside face thereof defines a melting chamber of a rectangular or square cross-section and the walls of the cooled crucible extend outwards at least from the inductor toward the lowest portion of the cooled crucible to thereby expand the melting chamber. According to the invention  each wall of the cooled crucible has a central section providing the absence of a vertically extending slot at the middle of a side of the melting chamber  and the angle ß of expanding the melting chamber is defined by the equation
ß = arctg [2¦ (?r - 1.35• 10 3• f> ) / d] 
where
d is the dimension of the smaller side of the rectangle or of the side of the square of the cross-section of the melting chamber at the inducer level  6 is the dimension of the adjoining side of the cross-section of the melting chamber at the inducer level 
k is an empirical coefficient  which is 1.5 to 2.
Coefficient k has the biggest values where the perimeter of the ingot being grown is long.
The width of the central section of each wall of the cooling crucible is from 1/6 to 1 of the dimension of the melting chamber side.
In the process of silicon melting and casting by induction melting in the cooled crucible bottom with moving walls designed as water-cooled vertical sections of electro- and heat conductive material  meniscus formed by part of the melt is outpressed by electromagnetic forces from the crucible inner surface and gets balanced by its hydrostatic pressure. With a continuous supply of the raw material  the balance is broken and the lower level of the meniscus is periodically poured towards the inner surface of the cooled crucible where the melt crystallizes and the wall accretion forms on the perimeter of the cooled crucible to hold the silicon melt and prevent its contact with the crucible.
As the melting process proceeds and the ingot moves downwards  the wall accretion becomes thicker. The temperature of the outer surface of the wall accretion bearing on the crucible is lower than the silicon melting point and depends on its thermal conductivity and heat transfer to the walls of the crucible  while the inner surface of the wall accretion has a temperature equal to the melting point of silicon. The wall accretion thus formed has a temperature gradient both in the cross section and in the height of the melt bath.
In the production of multicrystalline silicon ingots by induction melting  the melt spills into the gap between the wall accretion and the cooled crucible are due to several factors.
One of the factors is associated with the transverse gradient of temperature across the wall accretion.
Due to the temperature gradient there occurs thermal shrinkage of the wall accretion. Also  at temperatures from 9000C to 10500C  which are higher than the silicon flow temperature  the wall accretion undergoes plastic deformation. The magnitude of thermal shrinkage of the wall accretion depends on the temperature gradient and size and shape of the melting chamber formed by the cooled crucible. Any excess of heat shrinkage over the permitted value leads to inadequate wall accretion cooling  its overheating  melting and spills into the gap between the wall accretion and the inner wall of the cooled crucible.
Another factor that leads to silicon spills into the gap between the wall accretion and the inner wall of the cooled crucible is in the breaking of the wall accretion when it catches on the cooled crucible inner walls. Liquid silicon does not wet the inside of the cooled crucible walls and does not stick to the walls when there are no defects on their surface. The main defects on the surface of the cooled crucible inner walls are vertical slots between the wall sections  which slots are necessary for the inductor electromagnetic field to penetrate into the silicon melt and to heat it.
It has been experimentally established that wall sections spaced apart by vertical slots and arranged on the perimeter of a rectangular or square shape to form four walls  each having a central section  which provides no vertical slot in the middle of the corresponding cooled crucible wall  and the size of the melting chamber formed by the walls of the cooled crucible being taken into account while expanding the melting chamber  stabilizes the formation of the gap as a result of the thermal shrinkage of the wall accretion in silicon induction melting  which provides for a decrease in silicon melt spills.
Moreover  the arrangement outlined provides for elimination of the wall accretion catching on the cooled crucible walls surface  including areas with the smallest gap between the wall accretion and cooled crucible wall surface  and allows for taking into account the thermal shrinkage and transverse dimensions of the multicrystalline silicon ingots obtained. As a result  silicon melt spills are significantly decreased and silicon crystallizes under stable conditions at a constant rate.
The enhancement of stability of the melting and crystallization process results in formation of large crystallites that produce multicrystalline silicon. Moreover  the stability of the crystallization process eliminates defects in the crystal structure to provide for quality products obtained therefrom  namely  solar cells.
Thus  the proposed design of the apparatus for producing multicrystalline silicon ingots provides for higher output of multicrystalline silicon suitable for solar cell production.
Brief Description of Drawings
The invention is further described with reference to  though not limited by  the following drawings  in which:
fig. 1 is a longitudinal sectional view of an apparatus for producing multicrystalline silicon ingots by induction melting;
in fig. 2 is a longitudinal sectional view of a cooled crucible containing a melt;
in fig. 3 is a cross sectional view of the cooled crucible illustrating the melting chamber.
Best Mode for Carrying Out the Invention
An apparatus for producing multicrystalline silicon ingots by induction melting (Fig. 1) includes an enclosure 1 communicating with a charging hopper 2. In the enclosure 1 there are means 3 for start-up heating of silicon  a cooled crucible 4 enclosed by an inductor 5  and a controlled cooling compartment 6 arranged below the cooled crucible 4. The cooled crucible 4 is defined by a movable bottom 7 and sections 8 and central sections 9 (Fig. 3) spaced apart by vertical slots 10. The movable bottom 7 associated with means 11 for moving the same vertically within the controlled cooling compartment 6. The sections 8 and central sections 9 spaced apart by vertical slots 10 form four mutually perpendicular walls 12  13  14  and 15. The inner surface of the cooled crucible 4 defines a melting chamber 16 of square or rectangular cross section  into which silicon lump material 17 is charged. The central section 9 of each wall 12  13  14  and
15 of the cooled crucible 4 provides no vertical slot in the middle of the side of the melting chamber 16. The sections 8 and central sections 9 of the walls 12  13  14  and 15 of the cooled crucible 4 (Fig.2)  by sloping outwards  expand the melting chamber 16 at least from the inductor 5 toward the lowest portion  or the bottom  of the cooled crucible 4  and the angle ß of expanding the melting chamber is defined by the equation:
ß = arctg [2 - (k - 1 35¦ 10"3• b ) / d] 
where
d is the dimension of the smaller side of the rectangle or of the side of the square of the cross-section of the melting chamber 16 at the level of the inducer 5 
b is the dimension of the adjoining side of the cross-section of the melting chamber 16 at the level of the inducer level 5 
k is an empirical coefficient  which is 1.5 to 2.
The central section 9 of each wall 12  13  14 and 15 of the cooled crucible 4 (Fig. 3) has a width of from 1/6 to 1 of the dimension of the side of the melting chamber 16.
The walls 12  13  14  and 15 of the cooled crucible 4 are detachably connected to a manifold 18. The manifold 18 provides supply  distribution and dispensing of a cooled liquid (water).
The walls 12  13  14  and 15 of the cooled crucible 4 are made of copper or an alloy based on copper  the means 3 for start-up heating of silicon and the movable bottom 7 are made of an electroconductive material such as graphite.
The apparatus of the invention operates as follows.
In the enclosure 1  a controlled atmosphere is created. The movable bottom 7 is moved to the top of the cooled crucible 4 to limit the melting space 16 from below. To the melting chamber 16  a silicon lump material 17 is added from the charging hopper 2 and the means 3 for start-up heating of silicon is brought in. The high-frequency electromagnetic field is created by the inductor 5. The movable bottom 7 and the means 3 for start-up heating of silicon are heated in the electromagnetic field of the inductor 5 and the silicon lump material 17 is heated due to heat transfer within the melting chamber 16. When the temperature reaches 700-800 0C  the charge undergoes induction heating and melting.
The means 3 for start-up heating of silicon is moved from the electromagnetic field of the inductor 5  and a silicon melt bath is formed in the melting chamber 16 in accordance with the form of its cross-section (Fig. 2  fig. 3). As a result of the heat transfer  the silicon melt crystallizes and a wall accretion 19 is formed on the periphery of the melt bath near the walls of the cooled crucible 4. It keeps the melt from spilling from the melting space 16 and prevents the interaction of molten silicon with the walls 12  13  14  and 15 of the cooled crucible 4. Due to the electromagnetic field of the inductor 5 the upper melt bath is squeezed from the walls 12  13  14  and 15 of the cooled crucible 4 and a meniscus is formed  and the silicon lump material 17 is continuously fed from the charging hopper 2 onto the meniscus surface. The silicon lump material 17 is melted to increase the hydrostatic pressure of the meniscus. Periodically  when pressure equilibrium is upset  the melt is spilled over the upper end of the wall accretion toward the walls 12  13  14 and  15 of the cooled crucible 4  the outer layer of the melt crystallizes  and the wall accretion 19 continuously grows. The movable bottom 7 is moved down from the inductor 5 zone  and the silicon melt continuously crystallizes at the lower portion thereof to form a multicrystalline ingot 20 as the melting process and ingot downward movement proceed. The multicrystalline ingot 20 continuously moves down to the controlled cooling compartment 6. The multicrystalline ingot 20 is withdrawn at such a rate that the melt bath remains relatively constant at the level of the inductor 5 and the cooled crucible 4 and the melt continuously crystallizes in the bottom portion of the bath to form the ingot. In the controlled cooling compartment 6  the ingot is cooled under controlled conditions and thermal stresses are removed.
Multicrystalline ingots that were obtained in the apparatus of the invention had cross-sectional sizes of 340 x 340 mm2 and 340 x 530 mm2.
Ingots of the cross-sectional size of 340 x 340 mm2 were obtained in the in the melting chamber of a square cross-section with the side dimension of 342 mm at the level of the inductor. The width of the central section of the cooled crucible was 60 mm  so there was a vertical slot absent in the middle of the melting chamber side. The angle ß of expanding the melting chamber was:
ß = arctg [2¦ (1 5 - 1 35¦ 10"3• 342) / 342] = 0 35°.
In the multicrystalline silicon ingot production  the melt spills fall far short of the prior art figures. The spilling that took place  stopped at short distances. As a result  multicrystalline silicon ingots thus produced had large areas of zero-defect monocrystalline silicon. The multicrystalline silicon production capacity increased by 12%.

We Claim:

Claim 1. An apparatus for producing multicrystalline silicon ingots by the induction method  comprising an enclosure  which includes means for startup heating of silicon  a cooled crucible enveloped by an inductor and having a movable bottom and four walls consisting of sections spaced apart by vertically extending slots  means for moving the movable bottom  and a controlled cooling compartment arranged under the cooled crucible wherein the inside face thereof defines a melting chamber of a rectangular or square cross-section and the walls of the cooled crucible extend outwards at least from the inductor toward the lowest portion of the cooled crucible to thereby expand the melting chamber  characterized in that each wall of the cooled crucible has a central section providing the absence of a vertically extending slot at the middle of a side of the melting chamber  and the angle ß of expanding the melting chamber is defined by the equation
ß = arctg [2• (k - 1.35¦ IO 3¦ b ) / «/]  where
d is the dimension of the smaller side of the rectangle or of the side of the square of the cross-section of the melting chamber at the inducer level  b is the dimension of the adjoining side of the cross-section of the melting chamber at the inducer level 
k is an empirical coefficient  which is 1.5 to 2.
Claim 2. The apparatus according to Claim 1  characterized in that the central section of each wall of the cooled crucible has a width of from 1/6 to 1 of the dimension of the side of the melting chamber.

Dated this 17th Day of February  2012.