Semiconductor device manufacturing: process – Bonding of plural semiconductor substrates – Subsequent separation into plural bodies
Reexamination Certificate
2000-09-07
2004-01-27
Diamond, Alan (Department: 1753)
Semiconductor device manufacturing: process
Bonding of plural semiconductor substrates
Subsequent separation into plural bodies
C438S455000, C438S409000, C438S405000, C438S960000, C438S977000, C438S064000, C438S067000, C438S080000, C136S261000, C136S251000, C136S244000
Reexamination Certificate
active
06682990
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a separation method of a semiconductor layer, and a production method of a solar cell using the semiconductor layer separated by the above separation method.
2. Related Background Art
The greenhouse effect gases, e.g., carbon dioxide and nitrogen oxides resulting from burning oil at thermal power plants and gasoline by vehicles, are polluting the global environments. Therefore, power generation by solar cells has been increasingly attracting attention, viewed from the above environmental concerns and anticipated depletion of crude oil.
The solar cell of thin-film crystal silicon (Si) has various advantages; it can be produced at low cost, because of its thin power generation layer which decreases required quantity of a Si raw material, the power generating layer of crystal Si can exhibit a higher conversion efficiency and durability than the other types of solar cells, e.g., that using amorphous Si, and it can be bent to some extent, which makes it applicable to curved surfaces, e.g., car bodies, home electric appliances and roofs.
Japanese Patent Application Laid-Open No. 8-213645 discloses a method of separating thin-film single-crystal Si using an epitaxial layer grown on a porous Si layer, in order to realize a solar cell of thin-film crystal Si.
FIG. 23
shows a schematic section explaining the method of producing the solar cell of thin-film Si, disclosed by Japanese Patent Application Laid-open No. 8-213645, where
101
: Si wafer,
102
: porous Si layer,
103
: p
+
type single-crystal Si layer,
104
: p
−
type single-crystal Si layer,
105
: n
+
type single-crystal Si layer,
106
: protective layer,
109
and
111
: adhesives, and
110
and
112
: jigs. In the method of producing solar cell, shown in
FIG. 23
, the porous Si layer
102
is formed on the surface of the Si wafer
101
by anodization. Then, the p
+
type single-crystal Si layer
103
is epitaxially grown on the porous Si layer
102
, and then the p
−
type single-crystal Si layer
104
and n
+
type single-crystal Si layer
105
are grown thereon, in this order. The protective layer
106
is further formed thereon. The protective layer
106
and Si wafer
101
are adhered to the jigs
112
and
110
, respectively, by adhesives
111
and
109
. A tensile force P is applied to the jigs
112
and
109
, to separate the Si wafer
101
from the single-crystal Si layers
103
,
104
and
105
as epitaxial layers at the porous Si layer
102
. These single-crystal Si layers
103
,
104
and
105
are used to produce a solar cell. The used Si wafer
101
can be recycled to reduce the production cost.
One of the methods of forming single-crystal or a polycrystalline Si is a liquid-phase growth method. This method can produce at a low cost a thick Si layer needed as the power generation layer for solar cells, in comparison with the other methods including a chemical vapor deposition (CVD) method. U.S. Pat. No. 4,778,478 discloses a concrete example of the method of liquid-phase growth.
FIG. 21
shows a schematic section of the slide type apparatus for liquid-phase growth, disclosed by U.S. Pat. No. 4,778,478, where
50
: slide board of a refractory material, e.g., graphite,
54
and
56
: solvent reservoirs,
58
: movable slide of metallic substrate,
60
: cavity at the boat bottom,
63
: barrier layer,
68
and
70
: solvents,
72
: portion to which a transparent electroconductive electrode is attached,
75
: nozzle for forming an antireflection layer,
74
: chamber for containing the nozzle
75
,
76
: wheel, and
78
: nozzle for forming the barrier layer
63
. This apparatus first unwinds the movable slide
58
wound like a roll on the wheel
76
, and forms the barrier layer
63
by the nozzle
78
. It then forms the semiconductor layer as the power generating layer, grown in liquid phase from the solvents
68
and
70
in the reservoirs
54
and
56
; the transparent electrode at the portion to which the transparent electrode is attached; and the antireflection layer by the nozzle
75
, to produce the solar cell. This method efficiently effects the slide type liquid phase growth, and is advantageous for mass production of solar cells.
U.S. Pat. No. 5,544,616 discloses a dipping type apparatus for liquid-phase growth.
FIG. 22
shows the schematic section of this apparatus, where
201
: outlet,
202
: quartz crucible,
203
: boat of graphite,
204
: heater,
205
: nozzle from which argon gas is injected,
206
: thermocouples,
208
: lid,
209
: insulated region, and
210
: supporting table of graphite. This apparatus grows a semiconductor layer on a substrate by dipping the substrate in the solvent held in the quartz crucible
202
.
Japanese Patent Application Laid-Open No. 8-46018 discloses a method, in which a wafer is supported by adsorbing its back side on a table via an ice layer. In this method, since the wafer was diced with a low-elasticity dicing tape attached to its back side, strain was generated in the wafer during the dicing step, thereby leading to chipping and cracking of the wafer. Therefore, this application discloses that use of a high-elasticity ice layer for the support of the wafer prevents the above problem and dispenses with a dicing tape, thereby improving dicing efficiency.
Japanese Patent Application Laid-Open No. 8-213645 discloses a method of separating a single-crystal Si layer from an Si wafer, in which the single-crystal Si layer adhered to a jig
112
by an adhesive
111
via a protective layer
106
is separated from the Si wafer
101
whose back side is adhered to a jig
110
by an adhesive
109
by pulling the jigs
112
and
110
in the opposite directions to mechanically destroy a porous Si layer as the separation layer. This publication also discloses that the jig
110
is removed from the Si wafer
101
to which the jig is adhered by an adhesive
109
, and the Si wafer
101
is reclaimed for recycle. However, it is necessary for the adhesive
109
to fast adhere the Si wafer
101
to the jig
110
, in order to transfer a high tensile force to the porous Si layer
102
in a separation step, which makes it difficult to later remove the jig
110
from the Si wafer
101
. In other words, it is difficult to completely remove the adhesive
109
from the Si wafer
101
, and the Si wafer may be damaged during the removal step.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a separation method of semiconductor layer which fast supports the layers during the separation step, allows them to be easily separated from the jigs after the separation step, and brings about advantages, e.g., prevention of damages of the substrate, to facilitate the subsequent steps. It is another object of the present invention to provide a production method of a solar cell using the above separation method.
The inventors of the present invention have intensively studied in order to solve the above problems and accomplished the following inventions. The first separation method of a semiconductor layer according to the present invention is a method for separating a semiconductor layer and a semiconductor substrate which supports the semiconductor layer from each other at a separation layer formed between them, wherein a face of the substrate at a side opposite to a separation layer is held by utilizing an ice layer. The second separation method of a semiconductor layer according to the present invention is a method for separating a semiconductor layer and a semiconductor substrate which supports the semiconductor layer from each other at a separation layer formed between them, wherein a face of the semiconductor layer at a side opposite to a separation layer is held by utilizing an ice layer. These two inventions may be effected simultaneously. The production method of a solar cell according to the present invention comprises using the semiconductor layer separated by the above-mentioned separation method as a photoactive layer for solar cells.
The separation method
Iwakami Makoto
Iwane Masaaki
Iwasaki Yukiko
Mizutani Masaki
Nakagawa Katsumi
Canon Kabushiki Kaisha
Diamond Alan
Fitzpatrick ,Cella, Harper & Scinto
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