Method for crystallizing amorphous layer

Details Method for crystallizing amorphous layer Method for crystallizing amorphous layer

1998-05-22

2001-06-05

Kunemund, Robert (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Processes of growth from solid or gel state

Using heat

C117S003000, C438S162000, C438S166000, C438S186000

Reexamination Certificate

active

06241817

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method for crystallizing amorphous layer. More particularly, the present invention relates to a method for crystallizing amorphous layer wherein the amorphous layer is coated with a nickel-containing solution and heated afterwards.
2. Discussion of Related Art
Polysilicon layer has been employed for the active layer of a thin film transistor in semiconductor devices, notably liquid crystal display devices. This is because the polysilicon layer has a high carrier mobility relative to amorphous silicon layer. Such polysilicon is normally grown at high temperatures. However, there have been recently developed techniques for fabrication of polysilicon thin film transistors at low temperatures.
This low-temperature polysilicon involves some advantages in that it can be processed at low temperatures, can form large areas and can perform comparably to high formation-temperature polysilicon.
Many techniques are known for crystallization of amorphous silicon layer, such as SPC (Solid Phase Crystallization), laser crystallization and so forth. Laser crystallization is a technique wherein amorphous silicon layer is subjected to a heat treatment making use of a laser for crystallization at low temperatures, i.e. less than 400° C. (see Hiroyaki Kuriyama et al., Jpn, J. Phys. 31, 4550 (1992)). Laser crystallization, however, is not useful for the purpose of formation of polysilicon layer on a substrate which is large in area, because the polysilicon layer in this case is not formed uniformly and costs a great deal due to the use of expensive equipment for which the yields are low.
In the SPC technique, amorphous silicon layer is heated in the 550° to 700° C. range of temperature for about 1-24 hours. This has the advantage that the amorphous silicon layer crystallizes uniformly with inexpensive equipment. However, it is inapplicable to a glass substrate since the layer crystallizes at relatively high temperatures only after a long time, plus the yields are low.
Metal-induced crystallization is another example of a method for crystallizing amorphous silicon at low temperatures (See S. Haquc et al., Appl. Phys. 79, 7529 (1996)). In metal-induced crystallization, amorphous silicon is brought into contact with a specified kind of metal in order to lower the crystallization temperature. For example, in a nickel-induced crystallization, the final nickel silicide phase, NiSi
2
acts as a crystal seed that promotes polycrystalline silicon growth (see C. Hayzelden et al., J. Appl. Phys. 73, 8279 (1993)). Nickel silicide NiSi
2
has a silicon-like structure with a lattice constant of 5.405 Å, approximate to that of silicon (5.340 Å), and accelerates the change of amorphous silicon into poly silicon (See C. Hayzelden et al., Appl. Phys. Lett. 60, 225 (1992)). When metal-induced crystallization is applied to a prior art, metal solid layer having a certain thickness is deposited on amorphous silicon layer by sputtering technique. And then, the amorphous silicon layer having metal solid layer thereon is subjected to a heat treatment.
The period of time and temperature of the heat treatment as well as the amount of metal used can affect metal-induced crystallization. For example, crystallization temperature becomes lowered with an increase in the amount of metal. For the metal-induced crystallization described above, amorphous layer crystallizes at low temperatures with growth efficiency increasing in proportion to the amount of metal. Metal functions as catalyst for crystallizing the amorphous layer.
However, an example of the problem with such a metal-induced crystallization of amorphous silicon lies in the change of inherent properties of the silicon layer that results from contaminant metals entering the polysilicon layer. Furthermore, heat treatment takes a long time i.e. 10 hours or more, and the growth temperature is relatively high.
Despite the metal-induced crystallization being attainable at low temperatures, the natural properties of silicon layer may be changed by the presence of contaminating metals. An increase in the amount of metal substantially increases the efficiency of metal-induced crystallization, but also raises the problem of metal-contamination. It is therefore desirable to reduce metal-contamination of silicon layer due to the metal-induced crystallization as well as to lower the crystallization temperature.
SUMMARY OF THE INVENTION
Accordingly, the objectives of the present invention are to solve the problem described above and create a method for crystallizing an amorphous layer into a polycrystalline layer which is adapted to a metal-induced crystallization that decreases metallic contamination by coating the amorphous silicon layer with a nickel-containing solution and subsequently carrying out a heat treatment.
The nickel-containing solution may include another metal such as Au or Pd, which results in the further reduction of crystallization temperature. The present invention in this case is especially applicable to the crystallization of an amorphous layer of silicon such as amorphous silicon.
In the crystallization of an amorphous layer through a metal-induced crystallization, the amorphous layer is coated with a nickel-containing solution (such as a nickel solution or a mixed solution prepared by adding another metal to the nickel solution) and subjected to a heat treatment in order to lower the crystallization temperature and prevent the layer from being contaminated with metal.
The present invention provides a method for crystallizing an amorphous layer into a polycrystalline layer, the method for comprising the steps of: providing an amorphous layer and a nickel-containing seed film on a substrate structure; said nickel-containing seed film being formed by coating a surface of said amorphous layer or said substrate with a nickel-containing solution; and heating said amorphous layer and said nickel-containing seed film to convert said amorphous layer into a polycrystalline layer at a lower temperature than if said seed film were not present.
In more detail, the present invention provides a method for crystallizing an amorphous layer including the steps of: forming an amorphous layer on an insulating substrate such as quartz, glass or oxide layer; coating the amorphous layer with a nickel-containing solution by a spin coating or dipping technique; and carrying out a heat treatment in the 3000 to 8000° C. range of temperature in vacuum or under the nitrogen atmosphere.
The nickel-containing solution may be a nickel solution prepared by dissolving nickel in a specified solvent, or a mixed solution prepared by adding another metal to the nickel solution dissolved in a specified solvent or by mixing the nickel solution with the metal solution where another metal is dissolved.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, and are intended to provide further explanation of the invention as claimed.


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Yoon, Soo Young, et al., “Low temperature metal induced crystallization of amorphous silicon using a Ni solution”, J. Applied Physics vol. 82 No. 11:5865-67, Dec. 1997.*
H. Kuriyama et al., “Improving the Uniformity of Poly-Si Films Using a New Excimer Laser Annealing Method for Giant-Microelectronics” Jpn. J. Appl. Phys vol. 31, pp. 4550-4554, Dec. 1992.
M.S. Haque et al., “Aluminum-induced crystallization and counter-doping of phosphorous doped hydrogenated amorphous silicon at low temperature”, J. Appl. Phys. 79(10), pp. 7529-7536, May 15, 1996.
C. Hayzelden, et al. “Silicide formation and silicide-mediated crystallization of nickel-implanted amorphous silicon thin films”, J. Appl. Phys. 73(12), pp. 8279-8289, Jun. 15, 1993.
C. Hayzelden, et al. “In situ transmission electron microscopy

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