JP4152738B2 - Method for manufacturing semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The invention disclosed in this specification relates to a method for manufacturing a thin film transistor or another semiconductor device using a laser beam.
[0002]
[Prior art]
In recent years, a technique for manufacturing an active matrix liquid crystal display device using a thin film transistor formed on a glass substrate is known. In general, when a glass substrate is used, due to the problem of heat resistance of the glass substrate (generally about 600 degrees), heat treatment at a high temperature cannot be performed, and a thin film having the required crystallinity cannot be obtained. There is a problem that a temperature necessary for activation of the drain region cannot be given.
[0003]
As means for solving the above problems, there are a method of crystallizing an amorphous silicon film using a laser beam and a method of recrystallizing and activating a source / drain region. However, there is a problem that there are many variations in characteristics.
[0004]
[Problems to be solved by the invention]
The problem that the characteristics of thin film transistors manufactured through various annealing processes by laser light irradiation vary widely is considered to be due to the pulse interval of a pulsed excimer laser used as laser light. Normally, the pulse oscillation width is about 50 ns. In such a case, the surface of the silicon film is in a molten state in a time of several tens of ns or less, and crystallization from the liquid phase proceeds in the short time. At this time, since the crystallization time is very short, the crystallinity and the film quality after irradiation with laser light are largely changed by a slight difference in film quality and a difference in surface flatness.
[0005]
[Means for Solving the Problems]
The gist of the invention disclosed in this specification is to maintain the molten state of the surface for as long as possible when irradiating the silicon film with pulsed laser light and to enhance the effect of the laser light irradiation.
[0006]
The main configuration of the present invention is as follows.
A pulse laser beam having a pulse width of 1 μs to 100 ms is irradiated to an amorphous silicon film or an amorphous silicon film.
[0007]
The main purpose of the above structure is to crystallize an amorphous silicon film by irradiating an amorphous silicon film or an amorphous silicon film with a pulse laser beam having a pulse width of 1 μs to 100 ms. It is what.
In the above structure, when the silicon film contains a metal element that promotes crystallization, the effect can be further enhanced.
[0008]
In the above configuration,
The silicon film contains one or more elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, and Au, which are metal elements that promote crystallization. If so, the effect can be further enhanced.
[0009]
In the above structure, when an impurity imparting one conductivity type is added to the silicon film, the effect can be further increased.
[0010]
As the metal element for promoting the crystallization, an entry type atom with respect to silicon such as Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, or An can be used. These elements diffuse into the silicon film in the heat treatment step. Then, the crystallization of silicon proceeds simultaneously with the diffusion of the above-mentioned interstitial elements. In other words, the ingress metal promotes the crystallization of the amorphous silicon film with a catalytic action in advance of diffusion.
[0011]
Further, since the above-mentioned entry type element diffuses quickly into the silicon film, the amount of introduction (addition amount) is important. That is, if the amount introduced is small, the effect of promoting crystallization is small and good crystallinity cannot be obtained. Moreover, when there are too many the introduction amounts, the semiconductor characteristic of silicon will be impaired.
[0012]
Therefore, there exists an optimum amount of the metal element introduced into the amorphous silicon film. For example, when Ni is used as the metal element that promotes crystallization, the effect of promoting crystallization can be obtained if the concentration in the crystallized silicon film is 1 × 10 ¹⁵ cm ⁻³ or more. It has also been found that if the concentration in the crystallized silicon film is 1 × 10 ¹⁹ cm ⁻³ or less, the semiconductor characteristics are not hindered. The concentration here is defined by the minimum value obtained by SIMS (secondary ion analysis). Moreover, the effect can be acquired also about metal elements other than Ni enumerated above in the same concentration range as Ni.
[0013]
Even when Al or Sn is used in addition to the metal elements listed above, crystallization of the amorphous silicon film can be promoted. However, Al and Sn form an alloy with silicon and do not diffuse into the silicon film. Crystallization proceeds in such a manner that a portion where silicon and an alloy are formed becomes a crystal nucleus, and crystal growth is performed from that portion. In this case, since Al and Sn do not diffuse into the silicon film, crystallization proceeds from this crystal nucleus portion. When Al or Sn is used in this way, crystal growth is performed only from a portion where Al or Sn is introduced (that is, an alloy layer of these elements and silicon). There is a problem that the crystallinity is generally poor as compared with the case where is used. For example, there is a problem that it is difficult to obtain a uniformly crystallized crystalline silicon film.
[0014]
[Action]
By irradiating the amorphous silicon film with laser light having a pulse width of 1 μs or more, the molten state of the amorphous silicon film surface can be lengthened and the crystal growth time can be lengthened. it can. By extending the crystal growth time, the crystal growth process is less affected by the film quality and surface flatness. Therefore, it is possible to always obtain a certain effect without being affected by subtle differences in film quality and subtle differences in surface flatness. That is, a crystalline silicon film having always constant crystallinity and electrical characteristics can be obtained.
[0015]
In addition, when a metal element for promoting crystallinity is introduced into the silicon film irradiated with laser light, crystallization by laser light irradiation further proceeds. In this case as well, an annealing effect by laser light irradiation can be obtained without being greatly affected by subtle differences such as the flatness of the film-quality surface.
[0016]
【Example】
Examples using the invention disclosed in this specification will be described below. In the following embodiments, an example of a thin film transistor disposed in each pixel of an active matrix type liquid crystal display device is shown. However, such a thin film transistor can be used for a peripheral circuit region of a liquid crystal display device, an image sensor, and various thin film integrated circuits.
[0017]
[Example 1]
First, a silicon oxide film 102 is formed as a base film on a glass substrate 101 (for example, Corning 7059) to a thickness of 2000 mm by sputtering. Next, an amorphous silicon film 103 is formed to a thickness of 1000 mm by plasma CVD or low pressure thermal CVD. Next, nickel which promotes crystallization is introduced onto the amorphous silicon film. Here, nickel element is introduced into the amorphous silicon film by applying a nickel acetate solution onto the amorphous silicon film by spin coating.
[0018]
Next, the amorphous silicon film 103 is crystallized by performing heat treatment at 550 degrees for 4 hours. This heat treatment can be performed at a temperature of 450 ° C. or higher, but thermal damage to the glass substrate becomes a problem at 550 ° C. or higher, and is preferably performed at 550 ° C. or lower.
[0019]
After completion of the heat treatment, the crystallinity of the crystalline silicon film is further improved by irradiating laser light. The crystalline silicon film given crystallinity by heating by the action of the metal element that promotes crystallization as described above contains many amorphous components. Therefore, by irradiation with laser light, the amorphous component can be crystallized and the crystallinity can be improved. The laser beam irradiation performed here is performed with a pulse width of 100 μs and an irradiation energy density of 250 mJ / cm ² .
[0020]
Next, by patterning the obtained crystalline silicon film, an active layer of the thin film transistor is obtained. Then, a silicon oxide film 104 functioning as a gate insulating film is formed to a thickness of 100 mm by plasma CVD. Further, a gate electrode 105 is formed by forming a film containing aluminum as a main component to a thickness of 5000 mm and performing patterning. Then, the oxide layer 106 is formed by performing anodization in the electrolytic solution using the gate electrode as an anode.
[0021]
Then, the source region 107 and the drain region 111 are formed by implanting ions into the impurity imparting one conductivity type. At this time, the offset gate region 108 and the channel formation region 109 are formed simultaneously. Here, P (phosphorus) ions are implanted in order to manufacture an N-channel thin film transistor. (Fig. 1 (B))
[0022]
Then, the source / drain regions are activated by irradiating with laser light. In this step, recrystallization of the source / drain regions made amorphous in the previous impurity ion implantation step and activation of the implanted impurities are performed. The laser beam irradiation here uses XeCl laser beam having a wavelength of 308 nm, the pulse width is 100 μs, and the irradiation energy density is 250 mJ / cm ² .
[0023]
Then, an interlayer insulating film 112, a silicon oxide film 113 which is a pixel electrode, a source electrode 114, and a drain electrode 115 are formed, thereby completing a thin film transistor.
[0024]
FIG. 2 shows the relationship between the variation (relative value) of the threshold value (V _th ) of a completed thin film transistor in which the pulse width is varied from 50 ns to 100 μs in the manufacturing process shown in this example. is there.
[0025]
As can be seen from FIG. 2, it can be seen that the variation (relative value) of the threshold value (V _th ) of the completed thin film transistor can be greatly reduced by setting the pulse width to 1 μs or more.
[0026]
The upper limit of the pulse width is suitably 100 ms or less. This is determined by the problem that it is difficult to oscillate a pulse width longer than this, and the problem that the problem of thermal damage to the glass substrate becomes obvious.
[0027]
[Example 2]
FIG. 2 shows a block diagram in the case where an active matrix circuit configured using thin film transistors (TFTs), a driver circuit thereof, and other circuits are formed over a substrate 504. The TFTs 126 and 127 shown in this embodiment are used for logic circuits of the X / Y decoder / driver, CPU, and various memories. On the other hand, the TFT 128 is used as a pixel switching TFT 501 of an active matrix circuit, a sampling TFT of a driver circuit, and matrix elements of various memories. The capacitor 129 is used as an auxiliary capacitor 503 of the pixel cell 502 of the active matrix circuit or a storage element of various memory circuits. When various circuits required on a glass substrate as shown in FIG. 2 are configured, it is useful to use a configuration in which a difference in laser irradiation effect is small between manufacturing steps as disclosed in this specification.
[0028]
【The invention's effect】
By setting the oscillation frequency of the pulse laser light to 1 μs or more, the annealing effect on the semiconductor using the pulse laser light can be made constant. Thus, a thin film transistor with small variation in characteristics can be produced. It goes without saying that the invention disclosed in this specification can be used for manufacturing various semiconductors.
[Brief description of the drawings]
FIG. 1 shows a manufacturing process of a thin film transistor of an example.
FIG. 2 shows a relationship between variation in threshold value of a manufactured thin film transistor and a pulse width of irradiated laser light.
FIG. 3 shows an outline of an electro-optical device using a thin film transistor.
[Explanation of symbols]
101 glass substrate 102 base film (silicon oxide film)
103 Amorphous silicon film 104 Gate insulating film (silicon oxide film)
105 Gate electrode 106 Oxide layer 107 Source region 108 Offset gate region 109 Channel forming region 110 Offset gate region 111 Drain region 112 Interlayer insulating film 113 Pixel electrode (ITO) electrode 114 Source electrode 115 Drain electrode

Claims (5)

Form a base film on the glass substrate,
Forming an amorphous silicon film on the base film;
Crystallization is performed by irradiating the amorphous silicon film with pulsed laser light having a pulse width of 1 μs to 100 ms,
An active layer of a thin film transistor is formed by patterning the crystallized silicon film,
Forming a gate insulating film on the active layer;
Forming a gate electrode on the gate insulating film;
A source region and a drain region are formed by adding an impurity imparting one conductivity type to the active layer ,
A method for manufacturing a semiconductor device, wherein the impurity added to the source region and the drain region is activated by irradiating the active layer with pulsed laser light having a pulse width of 1 μs to 100 ms. Form a base film on the glass substrate,
Forming an amorphous silicon film on the base film;
Introducing a metal element that promotes crystallization of silicon into the amorphous silicon film;
The amorphous silicon film introduced with the metal element is crystallized by heat treatment,
By irradiating the crystallized silicon film with pulsed laser light having a pulse width of 1 μs to 100 ms, the crystallinity of the crystallized silicon film is improved,
By patterning the silicon film with improved crystallinity , an active layer of the thin film transistor is formed,
Forming a gate insulating film on the active layer;
Forming a gate electrode on the gate insulating film;
A source region and a drain region are formed by adding an impurity imparting one conductivity type to the active layer ,
A method for manufacturing a semiconductor device, wherein the impurity added to the source region and the drain region is activated by irradiating the active layer with pulsed laser light having a pulse width of 1 μs to 100 ms.   3. The metal element according to claim 2, wherein the metal element includes one or more elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, and Au. A method for manufacturing a semiconductor device. 4. The method for manufacturing a semiconductor device according to claim 2, wherein the concentration of the metal element in the silicon film is 1 × 10 ¹⁵ to 1 × 10 ¹⁹ cm ⁻³ .   5. The method for manufacturing a semiconductor device according to claim 2, wherein the temperature of the heat treatment is in a range of 450 to 550 degrees.

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