Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With decomposition of a precursor
Reexamination Certificate
1996-08-01
2004-12-14
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With decomposition of a precursor
C117S095000, C117S097000, C117S923000, C117S939000
Reexamination Certificate
active
06830617
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of Industrial Use
The present invention disclosed in this specification relates to a method for manufacturing a crystalline silicon thin film, further relates to a method for manufacturing a semiconductor device using this crystalline silicon thin film.
2. Prior Art
Conventionally, the following technique is known. That is, an amorphous silicon film formed on a glass substrate, or a quartz substrate is crystallized to fabricate a crystalline silicon film, and a thin film transistor is formed by using this crystalline silicon film.
As for methods for forming this crystalline silicon film, they are classified into the following methods substantially. That is, laser light is irradiated to an amorphous silicon film formed by a plasma CVD method and the like to convert this amorphous silicon film into a crystalline silicon film, and a heat treatment is carried out to an amorphous silicon film formed by a plasma CVD method and the like, so that this amorphous silicon film is converted into a crystalline silicon film.
As a method for forming such a crystalline silicon film, a technique disclosed in Japanese Laid-open Patent Application No. 06-232059 is known. This technique is used to crystallize the amorphous silicon film at a lower temperature by using the metal elements that promote the crystallization of silicon.
PROBLEMS TO BE SOLVED BY THE INVENTION
According to the research made by present applicant, when a metal element that promotes the crystallization of silicon is used to obtain the crystalline silicon film, and further the thin-film transistor is manufactured by using this crystalline silicon film, the characteristic of this thin-film transistors tends to differ.
An object of the invention disclosed in this specification is, for the technique to form a crystalline silicon film by using a metal element that promotes the crystallization of silicon, to provide a technique which prevents the metal element from locally concentrating in this crystalline silicon film.
MEANS TO SOLVE THESE PROBLEMS
As a result of extensive study to solve the above problem that the concentration of metal element occurs in the crystalline silicon film, the below-mentioned matters were recognized.
FIG. 2
represents an observation result of a lump of a nickel element in a crystalline silicon film of 1 &mgr;m square, which is crystallized by using the nickel element.
A description will now be made of a method for manufacturing the crystalline silicon film from which the data indicated in
FIG. 2
could be obtained. First, an amorphous silicon film having a thickness of 500 Å is formed on a glass substrate by a plasma CVD method. Then, a nickel acetate solution is coated on the surface of the amorphous silicon film. Under this state, it is realized that the nickel element is in contact with the surface of the amorphous silicon film. Then, the heat treatment is carried out for 4 hours at a heating temperature (indicated as SPC temperature in the figure) described in FIG.
2
. As a result, a crystalline silicon film formed on a glass substrate can be obtained.
The differences between the samples to obtain three sorts of data shown in
FIG. 2
are the heating temperatures to obtain the crystalline silicon film.
The method for observing the lump of nickel element indicated in
FIG. 2
is performed in accordance with the following manner. That is, the obtained crystalline silicon film is etched by FPM (mixture solution of hydrogen peroxide and fluorine compound) to remove the region where nickel is lumped (this region is nickel silicide). Then, the total number of the holes which the lump of nickel is removed is counted by using an electron microscope.
In
FIG. 3
, there are shown conditions of the holes which indicate the region where nickel is lumped. That is,
FIG. 3
shows photographs taken by an electron microscope, showing the state after the surface of this crystalline silicon film has been etched by FPM.
Although this observation method could not measure the absolute value of the number of the lumps of nickel element, but evaluate the relative number.
As indicated in
FIG. 2
, the higher the temperature of the heating process is increased, the smaller the number of the detected lumps of nickel elements become. However, when the number of the lumps of nickel element is measured by SIMS (secondary ion mass spectroscopy), the concentrations of the nickel elements are substantially equal to each other, irrelevant to the differences in the temperatures at the heat treatment (during SPC). As a consequence, it is assumed that as to segregation of the nickel element, the higher the temperature at the heat treatment is increased, the larger each of these lumps becomes.
Also, it is found that the higher the temperature at the heating process is increased, the longer the diffusion distance of the nickel element becomes. This diffusion distance “D” may be expressed by approximately D
0
texp(&Dgr;E/kT). In this formula, “D
0
” indicates a properly selected constant, “t” denotes a heating time, “&Dgr;E” denotes a properly selected constant, “k” is a Boltzmann constant, “T” represents the heating temperature (SPC temperature). The trend expressed by this formula may be applied not only to the nickel element, but also to other metal elements.
As apparent from the above-described formula, when the heating temperature is increased, the diffusion distance of the nickel element is increased exponentially. On the other hand, the higher the heating temperature is increased, the larger the lumps of nickel element becomes.
Also, as a result of the research made by the Applicant, it could be recognized that the nickel element tends to concentrate into the region where the stress distortion is concentrated.
The present invention disclosed in this specification has been accomplished based upon the above mentioned matter. One aspect of the present invention disclosed in this specification is characterized by comprising the steps of:
forming an amorphous silicon film on a substrate having an insulating surface;
patterning said amorphous silicon film to form a predetermined pattern;
holding a metal element that promotes a crystallization of silicon in contact with said amorphous silicon film;
performing a heat treatment to crystallize said amorphous silicon film, thereby being converted into a crystalline silicon film; and
etching a peripheral portion of the pattern of said crystalline silicon film.
Further, another aspect of the present invention is characterized by comprising the steps of:
forming a region into which a defect and/or stress is concentrated in a preselected region of an amorphous silicon film;
holding a metal element that promotes the crystallization of silicon in contact with said amorphous silicon film;
performing a heat treatment so as to crystallize said amorphous silicon film; and
etching said preselected region.
The further aspect of the present invention is characterized by comprising the steps of:
forming a region into which a defect and/or stress is concentrated in a preselected region of an amorphous silicon film;
holding a metal element that promotes the crystallization of silicon in contact with said amorphous silicon film;
performing a heat treatment so as to crystallize said amorphous silicon film and, at the same time, segregating said metal element into said preselected region; and
etching said preselected region.
In each of the above described invention, generally speaking, when a glass substrate is utilized, the temperature of the heat treatment is preferably selected to be 450 to 750° C.
When a quartz substrate is used as the substrate, the temperature of the heat treatment is preferably selected to be 800 to 1100° C. In particular, selecting such a high temperature is preferable to obtain the high crystallinity.
In accordance with the present invention disclosed in this specification, as for a metal element that promotes the crystallization of silicon, one or plural sorts of metal elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt,
Miyanaga Akiharu
Ohtani Hisashi
Teramoto Satoshi
Yamazaki Shunpei
Fish & Richardson P.C.
Kunemund Robert
Semiconductor Energy Laboratory Co,. Ltd.
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