Semiconductor device manufacturing: process – Gettering of substrate – By layers which are coated – contacted – or diffused
Reexamination Certificate
1999-10-12
2003-09-23
Zarabian, Amir (Department: 2822)
Semiconductor device manufacturing: process
Gettering of substrate
By layers which are coated, contacted, or diffused
C438S471000, C438S473000, C438S474000, C438S514000
Reexamination Certificate
active
06624049
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photoelectric conversion device using a semiconductor substrate, and more particularly to a solar battery. The structure of the solar battery is applicable to the solar batteries of various types using a bulk semiconductor such as a known mono-crystal wafer or polycrystal wafer.
Also, the present invention relates to a photoelectric conversion device using a thin film semiconductor formed on an insulating or conductive substrate for a photoelectric conversion layer, and the solar battery using the thin film semiconductor is applicable to the solar batteries of various types.
The present invention is applicable to a junction type solar battery based on a p-n junction, a non-junction type solar battery having a Schottky barrier, a MIS structure or the like, a multi-layer junction type solar battery, a hetero junction type solar battery and so on.
2. Description of the Related Art
The solar batteries can be manufactured using a variety of semiconductor material or organic compound material, however, from the industrial viewpoint, silicon which is semiconductor is mainly used for the solar batteries. The solar batteries using silicon can be roughly classified into a bulk type solar battery using a wafer of mono-crystal silicon, polycrystal silicon or the like and a thin film solar battery having a silicon film formed on a substrate.
Also, the reduction of the manufacture costs has been required for the spread of the solar batteries, and in particular, the thin film solar battery has been expected to provide the effects of the reduced costs because the raw material used for the thin film solar battery is reduced in comparison with the bulk type solar battery.
At present, in the field of the thin film solar battery, an amorphous silicon solar battery has been put to practical use. However, because the amorphous silicon solar battery is lower in conversion efficiency than the solar batteries using mono-crystal silicon or polycrystal silicon, and also suffers from problems such as light deterioration, its use is limited. For that reason, as another means, the thin film solar battery using a crystalline silicon film has also been developed.
As mentioned above, although the high conversion efficiency and the reduction of the manufacture costs are required at the same time for the solar battery, both are substantially contrary to each other. For example, in the case of pursuing the conversion efficiency, it can be relatively readily achieved by using the mono-crystal wafer of a high grade (defects and the like are remarkably reduced) although the manufacture costs are increased as much.
On the contrary, under existing circumstances, even though the costs can be reduced by using the mono-crystal wafer of a low grade (so-called solar battery grade, etc.), the conversion efficiency is slightly lowered unavoidably. In particular, the polycrystal wafer, the thin film solar battery and so on have been developed for primarily reducing the costs, so that the conversion efficiency is subordinate to the reduction of the costs.
Also, in view of the low costs, attention has been paid particularly to the thin film solar battery using the crystalline silicon thin film. However, since the crystalline silicon thin film, for example, the mono-crystal silicon thin film is small in absorption coefficient, the thin film solar battery suffers from such a problem that it does not sufficiently function as the photoelectric conversion device without thickening the film.
Since a grain boundary always exists in the polycrystal silicon thin film generally obtained, the grain boundary forms an electronic state having an energy corresponding to a forbidden band, to thereby shorten the lifetime of carriers. In other words, when the film is thickened, the carriers are recombined before they reach an electrode, thereby making it difficult to ensure a sufficient photoelectric conversion efficiency.
SUMMARY OF THE INVENTION
As described above, importance has been brought into the development of the solar battery to which attention has been paid as a new energy source in recent years, and a large problem on how to manufacture a solar battery high in conversion efficiency while restraining the manufacture costs arises toward the development of an energy in the future.
The present invention has been made to solve the above problem, and therefore an object of the present invention is to provide a technique by which a crystalline silicon substrate of a low grade (for example, a solar battery grade, etc.) frequently used in a bulk type solar battery is changed into a silicon substrate having a crystalline property of a high grade (for example, a semiconductor grade, etc.).
Then, the first object of the present invention is to provide a bulk type solar battery that can achieve a high conversion efficiency and the low costs together by manufacturing the solar battery using the crystalline silicon substrate having the high crystalline property.
A second object of the present invention is to provide a technique by which a crystalline silicon thin film that forms a photoelectric conversion region is formed of a crystalline silicon thin film which is reduced in defects and has a high crystalline property, etc., more than those of the conventional crystalline silicon thin film.
Then, the second object of the present invention is to provide a bulk type solar battery that can achieve a high conversion efficiency and the low costs together by manufacturing the solar battery using the crystalline silicon thin film having the high crystalline property.
In order to solve the above problems, according to the present invention, in a photoelectric conversion device using a semiconductor substrate having crystalline property, catalytic elements are segregated in defects inside of the semiconductor substrate. Thereafter, while the catalytic elements within the semiconductor substrate are gettered by halogen elements or the elements of group XV, the defects inside of the semiconductor substrate are removed.
The above semiconductor substrate may be a substrate using Si material, GaAs material or CdS material. More particularly, as a general example, it may be a mono-crystal silicon wafer or a polycrystal silicon wafer. At present, there have been known a variety of means for forming the solar battery on the silicon wafer.
For example, it is generally structured such that a layer having a weak reverse conductive type (an n-type layer) is formed, for example, on a surface of a p-type silicon wafer, to form a p-n junction, carriers collected on the n-type layer are drawn out to obtain a current. Also, apart from the p-n junction, there is a case in which a junction form such as a p-i-n junction (in case of crystalline silicon, it is substantially directed to a p
+
-p-n junction, p
+
-p
−
-n junction, etc.) is applicable.
Also, according to the present invention, a semiconductor substrate having a crystalline property and a layer containing catalytic elements which is in close contact with an upper surface of the semiconductor substrate are subjected to a heat treatment, and thereafter while the catalytic elements inside of the crystalline semiconductor thin film are segregated by halogen elements or the elements of group XV, the defects inside of the semiconductor thin film are removed.
In the above structure, the substrate material may be, for example, ceramic, stainless steel, metal silicon, tungsten, quartz, sapphire, etc. Also, although a variety of means for manufacturing the thin film solar battery have been reported, the present invention is applicable not only to the structure and manufacture method of the solar battery but also to wide fields.
For example, there is a method in which impurities such as P(phosphorus) which give a reverse conductive type are added to a crystalline silicon thin film having a substantially intrinsic i-type (or weak p-type) in the vicinity of a main surface thereof (a side to which a solar light is made incid
Fish & Richardson P.C.
Guerrero Maria
Semiconductor Energy Laboratory Co,. Ltd.
Zarabian Amir
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