JPS639978A - Manufacture of thin-film transistor - Google Patents

Abstract

PURPOSE:To conduct the annealing of electrode layers, the high-degree movement of a channel section and the activation of source-drain regions simultaneously by the one-time irradiation of an ultraviolet laser by forming a gate or source-drain electrodes for a thin-film transistor by a transparent metal. CONSTITUTION:A gate insulating film 3 and a gate electrode 9 consisting of a transparent metal are patterned on an amorphous hydride semiconductor thin-film 2 on a glass substrate 1 first. P<+> or B<+> ions 11 are implanted in approximately 10<16>/cm through an ion implantation method and source-drain regions are each shaped in a self-alignment manner, and ultraviolet pulse laser-beams 10 are projected from the transparent electrode 9 side. Accordingly, the transparent electrode 9 is annealed first, and a change into a polycrystal and the high- degree movement of a channel region and the activation of carriers in the source-drain regions are performed simultaneously.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a thin film transistor.

[Prior art and problems to be solved by the invention]

Conventionally, most thin film transistors used in liquid crystal displays, contact image sensors, and the like are formed on amorphous silicon or polycrystalline silicon substrates. In particular, amorphous silicon is suitable for integrating transistor elements over a large area because it can be formed uniformly over a large area and at low temperatures. However, the electron mobility of amorphous silicon is at most 1 cm 2 /V −S
It is about 100 times smaller than bulk silicon, so a transistor using this is sufficient for matrix switching, but cannot be manufactured at sufficient speed if peripheral driving circuits are included at the same time. . In addition, if polycrystalline silicon is used, a considerably high mobility can be obtained and it is possible to renormalize the drive circuit, but since the manufacturing process involves a relatively high temperature process, there are material limitations on the insulating substrates etc. that can be used. receive. That is, only expensive glass substrates can be used. This poses a major cost problem when using a large-area insulating substrate.

Therefore, a technique using ultraviolet laser light irradiation has been proposed as a means of locally heating and melting only the surface portion of an amorphous semiconductor film while keeping the glass substrate at a low temperature to obtain a polycrystalline thin film with high mobility. (For example, Proceedings of the 16th
3rd Solid State Element Materials Conference, C-3-8, p12
>. This is based on the idea that the absorption depth of light with a wavelength of 400 nm or less into a semiconductor layer is about several hundred amps, and that only the surface of the semiconductor layer can be heated.

4(a) to 5(d) and FIG. 5 show a manufacturing process diagram of a conventional thin film transistor using ultraviolet laser light. According to the manufacturing method shown in FIG. 4, the amorphous semiconductor film 2 on the glass substrate 1 is exposed to ultraviolet pulsed laser
．． J. Terumosa n Polycrystalline, high mobility 1st first (a)
This is done as shown in the figure. After a gate portion consisting of a gate insulating film 3 and a gate electrode 4 is formed by film formation and patterning, ions 11 are further implanted by a self-alignment technique to form source and drain regions, respectively. [See Figure 4(b)].

After this, the ultraviolet laser 10 is irradiated again to activate the ion-implanted layer, and then a source electrode 6 and a drain electrode 7 are provided, respectively, resulting in a completed product! [See Figures 4(c) and (d)]. Therefore, this manufacturing method includes two heat treatment steps using ultraviolet laser light.

Further, FIG. 5 shows a method of manufacturing a thin film transistor having a so-called staggered structure, and in this case, ultraviolet laser light 10 is irradiated from above and below at once. According to this method, only one heat treatment step is required, but the interface between the semiconductor film 2 and the glass substrate 1 is heated, so there is a drawback that there are restrictions on the materials that can be used as the glass substrate.

In view of the above-mentioned circumstances, an object of the present invention is to form at least the gate electrode with a transparent metal, thereby annealing the electrode layer, increasing the mobility of the channel portion, and increasing the mobility of the source through a single ultraviolet laser irradiation from the transparent electrode. Another object of the present invention is to provide a method for manufacturing a thin film transistor in which the drain region can be activated at the same time.

[Means for solving problems]

According to the present invention, a method for manufacturing a thin film transistor includes a heat treatment step for a semiconductor crystal film in which an amorphous semiconductor film on an insulating substrate is polycrystallized by irradiation with ultraviolet laser light and annealed. an ultraviolet laser beam irradiation step in which the gate and/or source and drain electrodes are each made of a transparent metal, and the amorphous semiconductor film in the channel and/or source and train regions is heat-treated through the transmitted light of the gate and/or source and drain electrodes; including having

Here, an indium tin oxide alloy can be used as the transparent metal, and its film thickness is set in a range of 800 to 1000 Å.

[Action/Principle]

Amorphous silicon and polycrystalline silicon typically have significantly lower electron mobilities than bulk silicon. This is said to be mainly due to the barrier effect of carriers trapped in dangling bonds caused by dangling bonds in amorphous silicon, and in polycrystalline silicon, which exist in large numbers at grain boundary interfaces in crystals. Therefore, amorphous silicon is not pure amorphous silicon, but hydrogenated silicon is generally used. This hydrogen inactivates the dangling bonds present in the film and lowers the barrier potential, making the film usable for practical use. Even in polycrystalline silicon, considerably high mobility can be expected if the barrier at the grain boundaries can be lowered by hydrogenating and inactivating the down-ring ponds at the grain boundaries. However, it is difficult to deposit hydrogenated polycrystalline silicon using conventional methods. Therefore, by first forming a film of hydrogenated amorphous silicon and then subjecting it to short-time pulsed laser annealing, it becomes polycrystalline as soon as the hydrogen is released, so the film can be formed as a hydrogenated polycrystalline film with hydrogen remaining in the film. It can be membraned. According to this method, it is possible to form a polycrystalline film without lowering the substrate temperature, and since it is hydrogenated, a film with higher mobility than conventional polycrystalline films can be obtained.

Therefore, the conventional thin film transistor (FET) according to the present invention
In the manufacturing process, a hydrogenated amorphous semiconductor thin film, a gate insulating film, and a transparent metal for a gate electrode are first formed on a glass insulating substrate at a substrate temperature of 300° C. or lower.

This transparent metal is formed into a film with a thickness of about 1000A using a sputtering method at a substrate temperature of about 100℃. It is determined by the balance between the thickness of the mask required for ion implantation. Therefore, the thickness of the transparent metal is an important factor in this manufacturing method. Next, a gate electrode is formed by patterning this film, and further, using this gate electrode, ion implantation is performed by self-alignment to form source and drain regions, respectively. Thereafter, the entire surface is irradiated with ultraviolet pulsed laser light, and the channel portion is optically annealed through a transparent gate electrode and its mobility is increased. The ion implantation layers in the source and train regions are also activated at the same time. Process simplification and reproducibility are therefore significantly improved. Of course, not only the gate electrode but also the source and train electrodes may be made of transparent metal. In this case, the ultraviolet pulsed laser beam used for optical annealing may be, for example, a XeCl excimer laser with a wavelength of 30 nm.
There is 8 nm.

For example, if an indium tin oxide alloy (ITO) is used as a transparent metal, the transmittance of this metal is 30.
%, but this transmittance improves as the heat treatment progresses. Therefore, both the photo-annealing of the gate electrode portion and the annealing of the semiconductor film can be efficiently performed. in this case,
The transmittance of indium tin oxide alloy (ITO) worsens as the wavelength becomes shorter, so wavelengths shorter than this are not very suitable.If the gate electrode is made of an opaque normal metal such as Cr as in the past, it will not be able to withstand ultraviolet light. Because the absorption coefficient is so large, if the ultraviolet laser is applied strongly, the gate electrode may evaporate, or the difference in thermal expansion coefficient between the electrode layer and the insulating film may damage not only the electrode layer but also the semiconductor film. A phenomenon such as evaporative scattering occurs.Therefore, the semiconductor film cannot be sufficiently heat-treated with a laser power that does not cause such a phenomenon.In other words, the present invention overcomes the conventional technology including these problems. The following problems will be solved at once.The present invention will be described in detail below with reference to the drawings.

〔Example〕

FIGS. 1(a) to 1(c) are process diagrams showing one embodiment of the present invention. According to this embodiment, only the gate electrode is made of transparent metal (
For example, it is made of an indium tin oxide alloy). That is, as shown in FIG. 1 (a), a gate insulating film 3 and a gate electrode 9 made of transparent metal are first patterned on the hydrogenated amorphous semiconductor thin film 2 of the glass substrate 1. At this time, the hydrogenated amorphous semiconductor thin film 2 is patterned. The semiconductor thin film 2 is formed by a plasma CVD method, and the gate insulating film is formed from silicon dioxide or silicon nitride, which is also formed by a plasma method.

The substrate temperature at this time is approximately 300°C.

In addition, indium tin oxide alloy (ITO) is used as a transparent metal.
) is used, and the film is formed to a thickness of about 1000 Å at a substrate temperature of about 100° C. by the Suba-Tsuta method. This thickness is determined by the tradeoff between ease of patterning the indium tin oxide alloy film and resistivity as an electrode.

After patterning the gate electrode portion, P- and B' ions 11 are implanted at a thickness of about 10 cm by ion implantation to form source and drain regions in a self-aligned manner. Next, as shown in FIG. 1(b), an ultraviolet pulsed laser beam 10 is irradiated from the transparent electrode 9 side, and this heat treatment first anneals the transparent electrode 9, then polycrystallizes the channel region, increases the mobility, and transforms the source and train regions. Activation of carriers in is performed at the same time. In this heat treatment process, a XeC1 excimer laser having a wavelength of 308 nm was used as the ultraviolet pulsed laser beam 10.

This is used as ultraviolet light because at wavelengths shorter than this, the transmittance to the transparent gate electrode 9 decreases, and at wavelengths longer than this, it penetrates deeply into the semiconductor film 2, making local heating impossible. This is because relatively strong power can be obtained in this wavelength range.

In this wavelength range, the absorption depth of the semiconductor film 2 is approximately 200 degrees, and only the surface portion is heated. After that, silicon dioxide or silicon nitride is formed as a passivation film 8, holes are made in the necessary parts, and a source electrode 6 and a drain electrode 7 are formed using ordinary electrode materials, as shown in FIG. 1(c). A thin film transistor like this is obtained. For this electrode material, a resistance heating vapor deposited film or a sputtered film of C' can be used.

In the above process, except for the ultraviolet light annealing process, the temperature of all the ponds is below 300'C, and the ultraviolet light irradiation only needs to be done once.

FIGS. 2(a) to 2(b) are process diagrams showing an embodiment of the pond of the present invention. According to this embodiment, the gate electrode, source electrode, and drain electrode are all formed of transparent electrodes. According to this embodiment, as shown in FIG. 2(a), after ion implantation by self-alignment, a passivation film 8 is deposited,
By opening a window, a source electrode 12 and a drain electrode 13 made of transparent metal are formed, respectively, before a photo-annealing process. Therefore, the annealing step using the ultraviolet laser beam 10 is performed from the transparent electrode side of the completed device as shown in FIG. 2(b). According to this embodiment, the semiconductor film 2 to be heat-treated is not exposed to the atmosphere and is free from problems such as contamination, so that a highly reliable thin film transistor can be manufactured.

FIG. 3 is a partial process diagram showing an embodiment of the present invention. According to this embodiment, a thin film transistor having a star-so-guard structure can be manufactured by only one irradiation with ultraviolet laser light.

That is, after each of the source and train 12 and 13 is formed of transparent metal, the semiconductor film 2 is formed, and the source and drain regions are again formed in a self-aligned manner via the transparent gate electrode 9. Thereafter, heat treatment is performed using ultraviolet pulsed light 10 to complete the process. As described above, according to this embodiment, a staggered elliptical thin film transistor can also be manufactured through a simpler process.

〔Effect of the invention〕

As described in detail above, according to the present invention, the method for manufacturing a thin film transistor using ultraviolet laser light is improved by forming the gate electrode or all electrodes from a transparent metal, while keeping the glass substrate at a low temperature, and by forming the gate electrode or all the electrodes from a transparent metal. The process can be improved to a simpler one. That is, not only can the production efficiency of thin film transistors be significantly improved, but also the reliability thereof can be significantly improved.

[Brief explanation of drawings]

FIGS. 1(a) to (c) are process diagrams showing one embodiment of the present invention, FIGS. 2(a) to (b) are process diagrams showing another embodiment of the present invention, and FIG. Partial process diagrams showing an embodiment of the invention, FIGS. 4(a) to 4(d) and FIG. 5 are manufacturing process diagrams of a conventional thin film transistor using ultraviolet laser light.

Claims (3)

[Claims] (1) A method for manufacturing a thin film transistor including a heat treatment step for a semiconductor crystal film in which an amorphous semiconductor film on an insulating substrate is polycrystallized by irradiation with ultraviolet laser light and annealed,
The gate and/or source and drain electrodes of the thin film transistor are each made of a transparent metal, and an ultraviolet laser beam heat-treats the amorphous semiconductor film in the channel and/or source and drain regions through transmitted light of the gate and/or source and drain electrodes. A method for manufacturing a thin film transistor, comprising an irradiation step. (2) The transparent metal is an indium tin oxide alloy (IT
O) The method for manufacturing a thin film transistor according to claim (1). (3) The film thickness of the electrode made of the transparent metal is 800 to 10
The method for manufacturing a thin film transistor according to claim (1), wherein each of the thin film transistors is set in a range of 00 Å.