Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Total dielectric isolation
Reexamination Certificate
1998-03-25
2001-04-03
Bowers, Jr., Charles (Department: 2813)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Total dielectric isolation
C438S482000, C257S052000, C257S064000
Reexamination Certificate
active
06211038
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device, and a method for manufacturing such a device. More particularly, the invention relates to a semiconductor device, such as a high-performance thin-film crystalline solar cell using a thin-film crystal which can be formed on a low-cost substrate, and to a method for manufacturing such a device.
2. Description of the Related Art
Solar cells (solar cell devices) are widely being studied as energy sources for driving various kinds of apparatuses or as electric power supplies subjected to system interconnection with commercial electric power. It is desirable for a solar cell device to be formed on a low-cost substrate in order to reduce production cost. Silicon is generally used as a semiconductor constituting a solar cell. Particularly, single-crystal silicon is superior from the viewpoint of efficiency in converting optical energy into electric power, i.e., the photoelectric conversion efficiency. On the other hand, amorphous silicon is advantageous from the viewpoint of providing a large area and a low cost. Recently, polycrystalline silicon has come to be used in order to obtain a cost as low as amorphous silicon and an energy conversion efficiency as high as single-crystal silicon.
In methods for manufacturing semiconductor devices using single-crystal or polycrystalline silicon, it is difficult to reduce the device's thickness to a value less than 0.3 mm because a plate-shaped substrate is provided by slicing a bulk crystal. A substrate obtained by slicing a bulk crystal has generally a thickness greater than a thickness necessary for absorbing incident light (20 &mgr;m-50 &mgr;m), so the material is not efficiently utilized in the direction of the thickness. Recently, a method for forming a silicon sheet according to a spinning method in which a fused silicon liquid is poured into a mold has been proposed. Nevertheless, the minimum thickness obtained in this method is about 0.1 mm-0.2 mm. Accordingly, there is still room for further decreasing the thickness of silicon to reduce the amount of silicon and realize a low cost. If the thickness of crystalline silicon is reduced, it is possible to reduce the weight of a semiconductor device, such as a solar cell or the like, to provide a flexible device if necessary, and to widen the range of application. Particularly when using silicon for a solar cell, a thin crystal is more resistant to shock from the outside, such as hail or the like, than a thick crystal, and is therefore preferable from the viewpoint of increasing reliability in practical application.
As described above, a technique for providing a high-quality thin crystal, particularly a single crystal, which allows the manufacture of a semiconductor device, such as a solar cell or the like, having a high performance with a low cost is desired.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above-described circumstances.
It is an object of the present invention to provide a method for manufacturing a high-quality and thinner semiconductor device.
It is another object of the present invention to provide a method for manufacturing a semiconductor device having a thin semiconductor layer with a lower cost.
It is still another object of the present invention to provide a method for manufacturing a semiconductor device, such as a solar cell or the like, with a lower cost by effectively utilizing a crystalline substrate by utilizing a material obtained by slicing the crystalline substrate to a necessary thickness for forming a flat layer, serving as a thin crystalline layer.
It is yet another object of the present invention to provide a high-performance (for example, high-efficiency in the case of a solar cell) semiconductor device having a thin crystalline semiconductor layer on an inexpensive flexible substrate which can be applied to various applications.
According to one aspect, the present invention which achieves these objectives relates to a method for manufacturing a semiconductor device including the steps of (a) forming a porous layer including a large number of fine pores in a surface portion of a crystalline substrate to a predetermined thickness, (b) transforming a part of the porous layer including the surface thereof into a crystalline smooth layer which does not substantially include fine pores, and (c) peeling the smooth layer from the crystalline substrate at a portion of the porous layer which has not been transformed into the smooth layer.
The method preferably includes the step of forming a semiconductor junction within the smooth layer before peeling the smooth layer from the crystalline substrate. It is also preferable to include the step of forming a semiconductor junction by forming a crystalline layer having a conductivity type different from the conductivity type of the smooth layer on the surface of the smooth layer before the peeling step. The step of forming the semiconductor junction preferably includes thermal diffusion of a dopant from the surface of the smooth layer. The formation of the crystalline layer having the conductivity type different from the conductivity type of the smooth layer includes a liquid-phase growth method.
It is also preferable that the step of transforming the porous layer into the smooth layer includes heat treatment in a hydrogen atmosphere or changes the sizes of the fine pores from the crystalline substrate toward the surface of the porous layer or includes energy radiation from the surface of the porous layer. The energy radiation preferably includes an electromagnetic wave having a wavelength equal to or less than 600 nm or an electron beam. The semiconductor device may be a solar cell.
In addition to the above-described steps (a)-(c), the method may also include the step of (d) bonding grid wires on the semiconductor of the smooth layer peeled from the crystalline substrate and laminating an anti-reflection layer and a lamination layer on the grid wires, and further the step of (e) bonding a metallic plate on the back of the peeled smooth layer. The crystalline substrate from which the smooth layer has been peeled may be again utilized as the crystalline substrate in the above-described step (a).
The foregoing and other objects, advantages and features of the present invention will become more apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.
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Iwasaki Yukiko
Nakagawa Katsumi
Nishida Shoji
Sakaguchi Kiyofumi
Yonehara Takao
Blum David S
Bowers, Jr. Charles
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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