Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Reexamination Certificate
2000-12-26
2003-07-22
Utech, Benjamin L. (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
C117S922000
Reexamination Certificate
active
06596075
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to methods of and apparatus for use in producing a crystal sheet from a melt of semiconductor or metal, and in particular to methods of and apparatus for use in producing a sheet of silicon to be used as the substrate of a solar cell.
2. Description of the Background Art
Conventionally, a substrate of crystallized silicon is produced by producing an ingot in the Czochralski method or casting a source material to produce an ingot and then slicing the ingot for example with a wire saw. However, the slicing step is costly and cutting a portion results in a loss of the source material of silicon. As such, in the area of solar cell, to address an important issue, i.e., cost reduction, silicon ribbon methods are being increasingly developed. In this method, a sheet of silicon is extracted directly from a melt of silicon to eliminate the necessity of providing a slicing step.
Of such silicon ribbon methods, a method of growing a crystal having a large solidification interface is disclosed for example in Japanese Patent Laying-Open No. 61-275119.
FIG. 49
schematically shows a method of producing silicon in the silicon ribbon method disclosed in the document. With reference to
FIG. 49
, a rotative cooling element
902
in the form of a cylinder has a side surface partially immersed into melted silicon
903
, and rotative cooling element
902
is rotated and a silicon ribbon
901
solidified on a cylindrical surface of cooling element
902
is successively extracted. Note that melted silicon
903
is held in a container
904
.
Japanese Patent Laying-Open No. 10-29895 also discloses a silicon-ribbon production apparatus.
FIG. 50
is a schematic view of the silicon-ribbon production apparatus disclosed in the above publication. As shown in the figure, this apparatus is configured of a rotative cooling element
931
in the form of a cylinder, a container
934
holding melted silicon
932
therein, and a roller
935
guiding a silicon ribbon
933
.
Rotative cooling element
931
has an cylindrical side surface partially immersed into melted silicon
932
. As rotative cooling element
931
is rotated silicon ribbon
933
solidified and grown on the cylindrical surface of the cooling element is extracted successively.
Furthermore, a crystal sheet can be produced directly from a melt in an EFG (Edge-defined Film-fed Growth) method, in which a die having an opening in the form of a slit is used to raise a melt through capillarity and at an upper end of the melt a seed crystal is used to extract a silicon ribbon. A crystal sheet can also be produced in the Dendrite Web method, in which a melt has a surface supercooled to produce a crystal sheet.
In methods using a rotative cooling element in the form of a cylinder, however, silicon solidifies and grows to cover an exterior of the cylinder and silicon that is grown thus has a curvature along the cylinder and thus curves. Such silicon is inconvenient if it is used as a substrate of a solar cell as the substrate is required to be flat in a process step such as screen-printing an electrode, laminating, vacuum-chucking and the like. Furthermore, a conventional substrate tray provided to be suitable for a flat substrate, cannot be used. Furthermore, when grown silicon removed from a rotative cooling element is extracted successively in a predetermined direction it needs to be pulled in the direction with tensile strength precisely controlled. Furthermore, the sheet of grown, crystallized silicon warping in geometry is hardly pulled successively in one direction.
Furthermore, in the EFG method and the Dendrite Web method, a crystal sheet is grown at a rate significantly affected by heat of solidification generated and heat transfer determined by a temperature profile in a vicinity of a solid-liquid interface between the crystal sheet and the melt. As such, successively and reliably producing a crystal sheet entails precisely controlling the temperature of the solid-liquid interface and the temperature profile in the vicinity thereof. Current temperature controlling systems, however, would not satisfactorily respond in proportion to crystal-growth rate in general. Furthermore, in the above methods a crystal sheet that is being grown is cooled by annealing or through natural heat liberation. As a result, the crystal sheet is disadvantageously required to grow at a reduced rate.
Furthermore, when a silicon ribbon is removed from the rotative cooling element the exact silicon ribbon pulls and thus removes the subsequent silicon ribbon from the rotative cooling element. As such, an enormous load is imposed on the silicon ribbon and thus tends to damage the silicon ribbon. Furthermore, if a silicon ribbon is damaged extracting it can not immediately be resumed and it can thus hardly be reliably successively extracted.
Furthermore, in the conventional methods, it is difficult to control an in-plane temperature profile of a crystal sheet and it is thus necessary to consider thermal conductivity and the like in selecting a material for a substrate and a member therearound and also to optimize a heating portion such as a heater or a cooling portion in arrangement and geometry. In selecting a member, however, not only its thermal conductivity but its wettability and removability with respect to a crystal sheet, coefficient of thermal expansion matched, refractoriness and durability as well as cost need to be considered. As such, the temperature profile can hardly be optimized. Furthermore, it is often difficult technically as well as mechanically to optimize the heating portion and the cooling portion for both of the quality of the crystal of the crystal sheet and the removability thereof. In particular, removability is a parameter significantly depending on the material(s) of the substrate and precise control can thus hardly be achieved. As such, it is difficult to produce a crystal sheet of high quality successively and reliably.
SUMMARY OF THE INVENTION
The present invention has been made to overcome such disadvantages as described above. The present invention contemplates a method of manufacturing a crystal sheet capable of reliably, successively extracting a crystal sheet, an apparatus for use in manufacturing the same, and a solar cell employing the crystal sheet.
The present invention also contemplates a method capable of producing a crystal sheet of high quality, an apparatus for use in manufacturing the same, and a solar cell employing the crystal sheet.
The present invention provides an apparatus for use in producing a crystal sheet including: a plate having a main surface on which a crystal sheet is to be formed; a container holding a melt therein; a movable member holding the plate to bring the main surface of the plate into contact with the melt and then move the plate away from the melt; and cooling means for cooling the movable member.
In the apparatus thus configured a crystal sheet is formed on a main surface of a plate held by a movable member cooled by a cooling means. As such, the crystal sheet formed on the main surface of the plate can be cooled via the movable member with an optimal rate to provide a crystal sheet of high quality. Furthermore, the crystal sheet formed on the main surface of the plate can be free of warpage and it can thus be produced with high quality.
Furthermore, preferably, the apparatus for use in producing a crystal sheet further includes a removal means removing a crystal sheet from the main surface of the plate transported from the movable member. The plate is provided with a throughhole and the removal means has a first protrusion fit into the throughhole.
As such, the first protrusion of the removal means can be fit into the throughhole of the plate to remove the crystal sheet from the plate.
Furthermore, preferably, the movable member has a second protrusion fit into the throughhole of the plate. As such, if a crystal sheet is grown on the main surface with the throughhole receiving the second protrusion, any crystal
Igarashi Kazuto
Mitsuyasu Hidemi
Nunoi Tohru
Taniguchi Hiroshi
Tsukuda Yoshihiro
Anderson Matthew A.
Sharp Kabushiki Kaisha
Utech Benjamin L.
LandOfFree
Method of producing a crystal sheet, apparatus for use in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of producing a crystal sheet, apparatus for use in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing a crystal sheet, apparatus for use in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3060157