Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Recrystallized semiconductor material
Reexamination Certificate
2001-02-09
2004-08-17
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Recrystallized semiconductor material
C257S458000
Reexamination Certificate
active
06777714
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a crystalline silicon semiconductor device and its method for fabrication, and particularly relates to a crystalline silicon semiconductor device having a polycrystalline silicon layer oriented entirely in an uniformed manner and a method for fabricating it or a crystalline silicon semiconductor device and its method for fabrication in which the polycrystalline silicon layers can be efficiently formed.
2. Description of the Related Art
A semiconductor device in which a polycrystalline silicon is grown on a substrate such as of glass or the like is known for a material of an electric cell preferable for a solar cell. Since this semiconductor device is not required for a large area and high quality of a silicon substrate, it allows for a large amount of cost down, however, in order to presently obtain a semiconductor device of good quality, a quartz plate of thermal resistance must be used as a substrate, therefore, it is difficult to secure a costly advantage because the quartz plate is expensive.
As a method for solving this problem, a method in which a thin film of an amorphous silicon formed on a substrate is melted and crystallized by laser annealing and a polycrystalline silicon layer is formed on it has been proposed. This method has been disclosed in K. Yamamoto et al., IEEE First World Conference on Photovoltaic Energy Conversion (1994, in Hawaii), pp. 1575-1578, and according to this, since the rise of a substrate temperature is suppressed, the description indicates that the use of a lower cost substrate is possible.
However, according to this method, since it takes a lot of time for forming a bedding crystal film and a polycrystalline silicon layer, especially the growth rate of a polycrystalline silicon layer is slow, thereby resulting in costing large expenses and at the same time, furthermore, there is a large amount of economic expenses caused by higher use loss ratio of silicon raw materials, that has to be a costly as a whole.
As another method of advantageously growing a polycrystalline silicon layer, a method of amorphous silicon being polycrystallized by making amorphous silicon contact with metallic catalyst and heating it has been proposed by R. C. Cammarata et al., J. Mater. Res., Vol. 5, No. 10 (1990) p. 2133-2138.
It is indicated, according to this method, that forming a film of polycrystalline silicon can be performed at low temperature and high rate. Especially crystallization at lower temperature can be achieved, for example, by introducing a trace quantity of Ni metal and heating it.
Then, according to this method, in the case where a thin film just like a TFT element in the order of 100 nm thickness is a subject, it is ascertained by L. K. Lam et al., Appl. Pys. Lett., Vol. 74, No. 13 (1999) pp. 1866-1868 that crystallization proceeds a few &mgr;m in the inplane direction, therefore, a crystal of high quality which is oriented quite well in the inplane direction can be obtained. Moreover, as a method of applying this orientation growth, a method in which amorphous silicon is crystallized by a metallic catalyst being selectively arranged nearby the position of a TFT element and by performing heating process to it and high performance is contemplated by forming an element with a grain of the crystal has been also proposed in Japanese Patent Application Laid-Open Publication No. 6-244104.
However, according to conventional methods shown here, since any one of them has a limitation involving with an area being crystallized, it is difficult to apply these methods to the production of a semiconductor device for a solar cell.
In a semiconductor device for use in a solar cell, although the thickness of a silicon film is required around 1 &mgr;m since a sufficient optical absorption is required within a film, when such a thick film is a subject, an area where crystallization can be performed by conventional methods is only in the order of 100 &mgr;m
2
. Even if a metallic catalyst is formed on the entire surface of an amorphous silicon layer of an area suitable for a solar cell and heating process is performed to it, a silicon layer thus obtained represents only an arborescent growth which is branched and heterogeneous, it is impossible to obtain a good silicon layer which is crystallized in uniformity.
SUMMARY OF THE INVENTION
Accordingly, the first object of the present invention is to provide a crystalline silicon semiconductor device having a polycrystalline silicon layer which is oriented in a uniformed manner on the whole area suitable for a solar cell in a semiconductor device in which a polycrystalline silicon layer is grown by using a metallic catalyst, and a method for fabricating it.
Moreover, the second object of the present invention is to provide a crystalline silicon semiconductor device at an advantageous cost in which a polycrystalline silicon layer having a predetermined thickness can be efficiently formed on a cheap substrate and its method for fabrication.
In order to achieve the above-described first object, the present invention provides a crystalline silicon semiconductor device characterized in that it comprises a substrate and a polycrystalline silicon layer formed by amorphous silicon layer provided on the substrate and heat-treated in the presence of a metallic catalyst, the polycrystalline silicon layer is consisted of a polycrystalline silicon layer which is grown by heat-treating the amorphous silicon layer in the presence of the metallic catalyst dispersed in a dotted shape at lower portion or upper portion of the amorphous silicon layer.
Moreover, in order to achieve the above-described first object, in a method of a crystalline silicon semiconductor device forming a polycrystalline silicon layer of a predetermined thickness on a substrate, the present invention provides a method of a crystalline silicon semiconductor device characterized in that an amorphous silicon layer of a predetermined thickness is formed on a metallic catalyst dispersed in a dotted shape on the substrate and the amorphous silicon layer of the predetermined thickness is crystallized into a polycrystalline silicon layer by heat-treating the amorphous silicon layer of the predetermined thickness.
Furthermore, in order to achieve the above-described first object, in a method for fabrication of a crystalline silicon semiconductor forming a polycrystalline silicon layer of a predetermined thickness on a substrate, the present invention provides a method for fabrication of a crystalline silicon semiconductor device characterized in that a metallic catalyst is dispersed in a dotted shape on an amorphous silicon layer of the predetermined thickness formed on the substrate and the amorphous silicon layer of the predetermined thickness is crystallized into a polycrystalline silicon layer by heat-treating the amorphous silicon layer of the predetermined thickness.
The above-described amorphous silicon layer, in most cases, is consisted of an intrinsic (i type) silicon, and polycrystal layer which is grown by this is also consisted of a substantially intrinsic silicon. Moreover, on both surfaces of this polycrystalline silicon layer, amorphous silicon layers of n-type and p-type which are different electrically conductive types are commonly formed. It is desirable that a polycrystalline silicon layer is formed in a thickness of more than 0.6 &mgr;m in order to secure the optical absorption characteristic.
In the above-described method for fabrication, as means for dispersing a metallic catalyst in a dotted shape on a substrate, a method of providing a concave portion on the surface of the substrate and making the metallic catalyst positioned in this concave portion is easy to be performed. Concretely, a method in which salt solution of the metallic catalyst is applied and dried on the surface of the substrate providing a concave portion thereby leaving the metallic catalyst in a thick film state within the concave portion remained is secured one. As a concave portion, it is prefe
Minagawa Yasushi
Muramatsu Shin-ichi
Oka Fumihito
Takahashi Susumu
Yazawa Yoshiaki
Antonelli Terry Stout & Kraus LLP
Crane Sara
Hitachi Cable Ltd.
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